Method for manufacturing electromagnetic wave noise suppression sheet

Abstract

An electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity is provided. The electromagnetic noise suppression sheet (100) of the present invention comprises a first layer (10) substantially composed of carbon nanotubes and carboxymethyl cellulose, wherein the mass ratio of carboxymethyl cellulose to carbon nanotubes in the first layer (10) is more than 1 / 5 and less than 3.

Description

Technical Field

[0001] This invention relates to electromagnetic noise suppression sheets and their manufacturing methods. Background Technology

[0002] Carbon nanotubes have a structure similar to rolling a uniform planar graphene sheet into a tube. Due to this unique structure, carbon nanotubes possess a wide variety of properties and hold promise for applications in a wide range of fields.

[0003] For example, Patent Document 1 describes a ratio of 1 g / cm³ relative to the substrate. 2 The electromagnetic wave suppression sheet is made by coating multi-walled carbon nanotubes using the above method.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-174833 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] Such electromagnetic wave suppression sheets are used, for example, by attaching them to electronic devices. Electronic devices are prone to heat accumulation. Therefore, high electromagnetic noise suppression performance and high thermal conductivity are required. High thermal conductivity allows the electronic device to dissipate heat efficiently.

[0009] One objective of several aspects of the present invention is to provide an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity. Another objective of several aspects of the present invention is to provide a method for manufacturing an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity.

[0010] Solution for solving the problem

[0011] One embodiment of the electromagnetic noise suppression sheet of the present invention is as follows:

[0012] It contains a first layer that is essentially composed of carbon nanotubes and sodium carboxymethyl cellulose.

[0013] In the first layer, the mass ratio of sodium carboxymethyl cellulose to the mass of the carbon nanotube is more than 1 / 5 and less than 3.

[0014] In one embodiment of the electromagnetic noise suppression sheet, it could also be that...

[0015] The ratio is less than 1.

[0016] In any of the embodiments of the electromagnetic noise suppression sheet, it can also be that...

[0017] The ratio is 1 / 3 or more.

[0018] In any of the embodiments of the electromagnetic noise suppression sheet, it can also be that...

[0019] The surface resistivity of the first layer is less than 60 Ω / □.

[0020] In any of the embodiments of the electromagnetic noise suppression sheet, it can also be that...

[0021] The thickness of the first layer is 2 μm or more.

[0022] In any of the embodiments of the electromagnetic noise suppression sheet, it can also be that...

[0023] The carbon nanotubes are multi-walled carbon nanotubes.

[0024] In any of the embodiments of the electromagnetic noise suppression sheet, it can also be that...

[0025] It includes a second layer that has the first layer.

[0026] One embodiment of the method for manufacturing the electromagnetic noise suppression sheet of the present invention includes:

[0027] The process of preparing a dispersion containing carbon nanotubes, sodium carboxymethyl cellulose, and water; and

[0028] The process of drying the dispersion to form the first layer

[0029] In the process of preparing the dispersion, only sodium carboxymethyl cellulose is used as a dispersant.

[0030] In the dispersion, the mass ratio of sodium carboxymethyl cellulose to the mass of the carbon nanotubes is more than 1 / 5 and less than 3.

[0031] In one embodiment of the method for manufacturing the electromagnetic noise suppression sheet, it could also be that...

[0032] The ratio is less than 1.

[0033] In any embodiment of the method for manufacturing the electromagnetic noise suppression sheet, it may also be that...

[0034] The ratio is 1 / 3 or more.

[0035] In any embodiment of the method for manufacturing the electromagnetic noise suppression sheet, it may also be that...

[0036] The process includes, prior to the process of forming the first layer, a process of coating the dispersion onto the second layer.

[0037] Invention Effects

[0038] The electromagnetic noise suppression sheet of the present invention comprises a first layer substantially composed of carbon nanotubes and sodium carboxymethyl cellulose. In the first layer, the mass ratio of sodium carboxymethyl cellulose to the mass of carbon nanotubes is more than 1 / 5 and less than 3. Therefore, it has high electromagnetic noise suppression performance and high thermal conductivity. Attached Figure Description

[0039] Figure 1 This is a schematic cross-sectional view of the electromagnetic noise suppression sheet of this embodiment.

[0040] Figure 2 This is a schematic cross-sectional view of the electromagnetic noise suppression sheet of this embodiment.

[0041] Figure 3 This is a schematic cross-sectional view of the electromagnetic noise suppression sheet of this embodiment.

[0042] Figure 4 This is a flowchart illustrating the manufacturing method of the electromagnetic noise suppression sheet of this embodiment.

[0043] Figure 5 This is a flowchart illustrating the manufacturing method of the electromagnetic noise suppression sheet of this embodiment.

[0044] Figure 6 This is a table showing the transmission attenuation rate of coated paper when the mass ratio of carbon nanotubes to sodium carboxymethyl cellulose is changed.

[0045] Figure 7 This is a graph showing the transmission attenuation rate of coated paper relative to frequency when the mass ratio of carbon nanotubes to sodium carboxymethyl cellulose is changed.

[0046] Figure 8 This is a table showing the transmission attenuation rate relative to frequency when the thickness of the coated paper is changed.

[0047] Figure 9 This is a graph showing the transmission attenuation rate of the coated paper relative to frequency when the thickness of the coated paper is changed.

[0048] Figure 10 This is a table showing the transmission attenuation rate of coated paper under varying pass-through rates.

[0049] Figure 11 This is a graph showing the transmission attenuation rate of coated paper relative to frequency when the number of passes is changed. Detailed Implementation

[0050] The preferred embodiments of the present invention will now be described in detail using the accompanying drawings. Furthermore, the embodiments described below are not intended to unduly limit the scope of the invention as defined in the claims. Additionally, not all of the components described below are necessarily essential elements of the present invention.

[0051] 1. Electromagnetic wave noise suppression sheet

[0052] 1.1. Overall Composition

[0053] First, the electromagnetic noise suppression sheet of this embodiment will be described with reference to the accompanying drawings. Figure 1 This is a schematic cross-sectional view of the electromagnetic noise suppression sheet 100 of this embodiment.

[0054] The electromagnetic noise suppression sheet 100 has a sheet shape with a length in the in-plane direction (orthogonal to the thickness direction) that is sufficiently long relative to the thickness direction. The planar shape of the electromagnetic noise suppression sheet 100 is not particularly limited, for example, it is rectangular.

[0055] like Figure 1 As shown, the electromagnetic noise suppression sheet 100 includes, for example, a coating layer 10 as a first layer, a support layer 20 as a second layer, an adhesive layer 30, and a release layer 40. The components will be described in turn below.

[0056] 1.1.1. Coating layer

[0057] 1.1.1.1. Physical properties, etc.

[0058] The coating layer 10 is disposed on the support layer 20. The coating layer 10 is a layer coated on the support layer 20.

[0059] The surface resistivity of the coating layer 10 is, for example, 150 Ω / □ or less, preferably 60 Ω / □ or less, more preferably 50 Ω / □ or less, and even more preferably 40 Ω / □ or less. The surface resistivity of the coating layer 10 is correlated with the electromagnetic noise suppression performance of the electromagnetic noise suppression sheet 100, and tends to have higher electromagnetic noise suppression performance with lower surface resistivity. If the surface resistivity of the coating layer 10 is 150 Ω / □ or less, the electromagnetic noise suppression performance can be improved. The surface resistivity of the coating layer 10 can be measured according to "JIS K 7194".

[0060] The thickness of the coating layer 10 is, for example, 1.0 μm or more and 300 μm or less, preferably 2.0 μm or more and 250 μm or less, and more preferably 3.0 μm or more and 200 μm or less. If the thickness of the coating layer 10 is 1.0 μm or more, the surface resistivity of the coating layer 10 can be reduced. If the thickness of the coating layer 10 is 300 μm or less, the possibility of crack formation in the coating layer 10 can be reduced. The thickness of the coating layer 10 can be measured using SEM (Scanning Electron Microscope).

[0061] The in-plane thermal conductivity of the coating layer 10 is, for example, 0.90 W / m·K or higher, preferably 0.93 W / m·K or higher, more preferably 1.0 W / m·K or higher, and even more preferably 1.3 W / m·K or higher. The term "in-plane thermal conductivity of the coating layer 10" refers to the thermal conductivity in a direction orthogonal to the thickness direction of the coating layer 10 (the stacking direction of the coating layer 10 and the support layer 20). Hereinafter, "in-plane thermal conductivity of the coating layer 10" will also be simply referred to as "thermal conductivity of the coating layer 10". If the thermal conductivity of the coating layer 10 is 0.90 W / m·K or higher, the thermal conductivity of the electromagnetic noise suppression sheet 100 can be increased. When the thermal diffusivity is set to α, the specific heat is set to C, and the density is set to ρ, the thermal conductivity λ can be calculated using the following formula (1).

[0062] λ=α×C×ρ…(1)

[0063] 1.1.1.2. Materials

[0064] The coating layer 10 comprises carbon nanotubes (hereinafter also referred to as "CNTs") and sodium carboxymethyl cellulose (hereinafter also referred to as "CMC"). The coating layer 10 is substantially composed of CNTs and CMCs. The term "substantially composed of CNTs and CMCs" includes the case where it is composed of only CNTs and CMCs, as well as the case where it is composed of CNTs, CMCs, and other trace substances. The term "other trace substances" refers to substances other than CNTs and CMCs, whose mass is less than 0.5% by mass relative to the mass of the coating layer 10. "Other trace substances" can be additives intentionally added during the manufacture of the electromagnetic noise suppression sheet 100, or they can be impurities accidentally introduced.

[0065] (1) Carbon nanotubes (CNTs)

[0066] The CNTs included in coating layer 10 are either single-walled carbon nanotubes (SWCNTs) formed by rolling a single six-membered ring network (graphene sheet) made of carbon into a cylindrical shape, or multi-walled carbon nanotubes (MWCNTs) formed by rolling multiple graphene sheets into concentric circles. Coating layer 10 may contain only one of SWCNTs and MWCNTs, or both, but considering the dispersibility of CNTs, it is preferable to contain only MWCNTs. That is, the CNTs included in coating layer 10 are preferably MWCNTs. The two ends of the CNTs can be closed or open.

[0067] The CNTs described above can be fabricated to the preferred size using methods such as arc discharge, laser ablation, or CVD (Chemical Vapor Deposition). The CNTs contained in the coating layer 10 can be CNTs fabricated using any method.

[0068] The diameter of the CNTs 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 CNTs is 1 nm or more and 100 nm or less, a dispersion with good dispersibility of CNTs can be produced when forming the coating layer 10. The diameter of the CNTs can be measured by SEM.

[0069] The fiber length of CNTs 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 CNTs is 0.5 μm or more and 50 μm or less, a dispersion with good dispersibility of CNTs can be prepared. The fiber length of CNTs can be measured by SEM. Furthermore, the term "fiber length of CNTs" refers to the length of CNTs in their bundled state due to van der Waals forces, and is the length of CNTs before dispersion in the solvent.

[0070] The BET specific surface area of ​​CNT is, for example, 50m². 2 / g or more, 500m 2 / g or less, preferably 100m 2 / g or more, 300m 2 / g or less. If the BET specific surface area of ​​CNT is 50m² 2 / g or more, 500m 2When the concentration is below a certain value, a well-dispersible dispersion of CNTs can be produced when forming the coating layer 10. Furthermore, the so-called "BET specific surface area" is the specific surface area determined by the BET (Brunauer Emmett Teller) method, which can be measured using an automated specific surface area measuring device.

[0071] In the dispersion used to form the coating layer 10, the content of CNTs is, for example, 0.1% by mass or more and 10.0% by mass or less, preferably 0.5% by mass or more and 5.0% by mass or less, and more preferably 2.0% by mass or more and 4.0% by mass or less. If the content of CNTs is 0.1% by mass or more, the electromagnetic noise suppression performance can be improved. If the content of CNTs is 10.0% by mass or less, a dispersion with good CNT dispersibility can be produced when forming the coating layer 10.

[0072] (2) Sodium carboxymethyl cellulose (CMC)

[0073] CMC functions as a dispersant to disperse CNTs during the formation of coating layer 10. Only CMC is used as the dispersant for CNTs. A "dispersant" is an additive that helps prevent CNT aggregation and sedimentation when CNTs are dispersed in water. By using only CMC as the dispersant for CNTs, compared to adding anionic surfactants or other dispersants besides CMC, it is possible to prevent the incorporation of air bubbles.

[0074] The weight-average molecular weight of CMC is, for example, 5,000 or more and 100,000 or less, preferably 10,000 or more and 60,000 or less, and more preferably 10,000 or more and 35,000 or less. If the weight-average molecular weight of CMC is 5,000 or more, CMC is more likely to entangle with CNTs, thus improving the dispersibility of CNTs. However, if the weight-average molecular weight is too high, the dispersibility will deteriorate. Therefore, it is preferable that the molecular weight of CMC is 100,000 or less. Furthermore, "weight-average molecular weight" in this specification refers to the weight-average molecular weight converted from polystyrene as determined by gel permeation chromatography (GPC).

[0075] The degree of etherification of CMC is, for example, 0.6 or more and 1.2 or less, preferably 0.6 or more and 0.8 or less. If the degree of etherification of CMC is 0.6 or more and 1.2 or less, a dispersion with good dispersibility of CNT can be prepared.

[0076] In the dispersion used to form the coating layer 10, the content of CMC is, for example, 0.1% by mass or more and 10.0% by mass or less, preferably 0.5% by mass or more and 5.0% by mass or less, and more preferably 2.0% by mass or more and 4.0% by mass or less.

[0077] In coating layer 10, the mass M of CMC CMC relative to the mass M of CNT CNT The ratio of M CMC / M CNT The ratio is 1 / 5 or more and 3 or less (CNT:CMC = 5:1 to 1:3), preferably 1 / 3 or more and 1 or less (CNT:CMC = 3:1 to 1:1). If it is more than M CMC / M CNT If it is 1 / 5 or more, the thermal conductivity will be increased. If it is greater than M... CMC / M CNT A value below 3 can improve electromagnetic noise suppression performance. Compared to M... CMC / M CNT It can be determined by thermogravimetric analysis (TGA).

[0078] (3) Additives

[0079] The coating layer 10 may also contain various additives such as thickeners, preservatives, and pH adjusters as needed.

[0080] 1.1.2. Support layer

[0081] A support layer 20 is disposed on the adhesive layer 30. A coating layer 10 is disposed on the support layer 20. The support layer 20 supports the coating layer 10.

[0082] The support layer 20 may be, for example, a sheet containing pulp. The support layer 20 may also consist solely of pulp. Examples of pulp contained in the support layer 20 include: chemical pulps such as LBKP (bleached hardwood pulp) and NBKP (bleached softwood pulp); mechanical pulps such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (disc milling pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemimechanical pulp), and CGP (chemimechanical fine grinding pulp); wood pulps such as DIP (deinking pulp); or non-wood pulps such as kenaf, bagasse, bamboo, and cotton. The support layer 20 may contain only one of these pulps, or it may contain two or more in any proportion. Furthermore, the support layer 20 may also contain synthetic fibers without affecting quality.

[0083] The support layer 20 preferably contains LBKP. The content of LBKP in the support layer 20 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, the strain of the support layer 20 can be reduced.

[0084] The weight per square meter of the support layer 20 is 40g / m².2 In the following cases, the support layer 20 preferably contains NBKP. For example, the content of NBKP in the support layer 20 is 30% by mass or less. If the content of NBKP is 30% by mass or less, the smoothness and strength of the support layer 20 can be guaranteed.

[0085] The support layer 20 may also contain various additives as needed, such as fillers, paper strength enhancers, sizing agents, bulking agents, retention aids, water permeability improvers, aluminum sulfate, wet paper strength enhancers, coloring dyes, coloring pigments, fluorescent whitening agents, pitch control agents, thickeners, preservatives, and pH adjusters.

[0086] Furthermore, the support layer 20 only needs to be able to support the coating layer 10, and its material is not particularly limited. The support layer 20 can also be a film made of resin such as PET (polyethylene terephthalate) film, non-woven fabric, or synthetic paper made mainly of synthetic resin.

[0087] 1.1.3. Adhesive layer

[0088] An adhesive layer 30 is disposed on the release layer 40. The adhesive layer 30 has adhesive properties. The adhesive layer 30 only needs to have adhesive properties, and its material is not particularly limited. For example, it can be natural rubber, synthetic rubber, urethane resin, acrylic resin, vinyl acetate resin, vinyl acetate-acrylate copolymer resin, vinyl acetate-ethylene copolymer resin, etc.

[0089] 1.1.4. Peel-off layer

[0090] The release layer 40 is configured to be peelable relative to the adhesive layer 30. When attaching the electromagnetic noise suppression sheet 100 to an external device such as an electronic device, the electromagnetic noise suppression sheet 100 is attached to the external device by peeling the release layer 40 from the adhesive layer 30 and then bringing the adhesive layer 30 into contact with the external device.

[0091] The release layer 40 only needs to be peelable from the adhesive layer 30, and its material is not particularly limited. Examples include uncoated paper such as high-quality paper, ordinary coated paper, coated paper such as art paper, cellophane, films made of polyethylene, polyethylene terephthalate, etc., or film-laminated paper. Depending on the need, silicone resin, fluororesin, etc., can also be used as a release agent at a concentration of 0.1 g / m³. 2 ~3g / m 2 Apply and dry the coating to the desired dryness.

[0092] 1.2. Variations

[0093] like Figure 2As shown, the electromagnetic noise suppression sheet 100 may also include an outer coating layer 50. The outer coating layer 50 is disposed on the coating layer 10. The outer coating layer 50 is an insulating layer that suppresses damage to the coating layer 10 and imparts insulation breakdown strength.

[0094] The material of the outer coating 50 is not particularly limited, and examples include polyethylene terephthalate, polypropylene, vinyl chloride resin, fluororesin, silicone resin, styrene-acrylic resin, acrylic resin, urethane resin, epoxy resin, polyethylene wax, polycarbonate, polyphenylene ether, polysulfone, polyimide, thermoplastic polyester, phenolic resin, urea-formaldehyde resin, epoxy resin, melamine resin, diallyl phthalate resin, furan resin, and silicon-based inorganic compounds. The outer coating 50 may contain only one of these materials, or it may contain two or more in any proportion. The outer coating 50 preferably has heat resistance.

[0095] The thickness of the outer coating 50 is not particularly limited, for example, it can be 1 μm or more or less or 20 μm or less, preferably 2 μm or more or less or 10 μm or less. If the thickness of the outer coating 50 is 1 μm or more, scratches on the coating layer 10 can be suppressed, and electrical insulation and insulation breakdown strength can be imparted. If the thickness of the outer coating 50 is 20 μm or less, low cost can be achieved.

[0096] Furthermore, the electromagnetic noise suppression sheet 100 only needs to be as follows: Figure 3 As shown, it may include a coating layer 10 and a support layer 20, or it may not include an adhesive layer 30 and a release layer 40. The electromagnetic noise suppression sheet 100 may also consist only of a coating layer 10 and a support layer 20.

[0097] 1.3. Electromagnetic noise suppression performance

[0098] The electromagnetic noise suppression sheet 100 has electromagnetic noise suppression performance. The electromagnetic noise suppression performance is evaluated by measuring the transmission attenuation rate Rtp [dB] using the microstrip line method. The larger the Rtp, the higher the electromagnetic noise suppression performance.

[0099] 2. Manufacturing method of electromagnetic noise suppression sheet

[0100] 2.1. Overall Composition

[0101] Next, the manufacturing method of the electromagnetic noise suppression sheet 100 of this embodiment will be described with reference to the accompanying drawings. Figure 4 This is a flowchart illustrating the manufacturing method of the electromagnetic noise suppression sheet 100 of this embodiment.

[0102] For example, the manufacturing method of the electromagnetic noise suppression sheet 100 is as follows: Figure 4As shown, the process includes: a support layer forming step (step S11) to form a support layer 20; a release layer bonding step (step S12) to bond the release layer 40 to the support layer 20; a dispersion preparation step (step S13) to prepare a dispersion containing CNTs, CMCs, and water; a dispersion coating step (step S14) to coat the dispersion onto the support layer 20; and a coating layer forming step (step S15) to dry the dispersion to form a coating layer 10. Each step will be described sequentially below.

[0103] 2.2. Support layer formation process (step S11)

[0104] In the support layer formation process, for example, a support layer 20 is formed by forming pulp containing pulp but not CNTs using a paper machine. The pulp used to form the support layer 20 has a freeness (CSF) of, for example, 200 ml or more and 550 ml or less, preferably 250 ml or more and 500 ml or less. The CSF is determined by the method described in JIS P 8121-2. The paper forming method for the support layer 20 is not particularly limited; various devices can be used, such as a two-wire paper machine, a two-wire multilayer paper machine, a cylinder paper machine, a cylinder multilayer paper machine, a two-wire combined multilayer paper machine, or a double-wire paper machine. The paper forming method can be acidic or neutral.

[0105] Alternatively, a sizing solution containing water-soluble polymers such as starch, polyvinyl alcohol, and polyacrylamide can be coated onto the surface of the support layer 20. By coating with this sizing solution, excessive penetration of the dispersion into the support layer 20 can be prevented when the dispersion is applied to the support layer 20. Furthermore, the surface strength of the support layer 20 can be improved. Examples of sizing solutions include styrene-based sizing agents, styrene-acrylate-based sizing agents, olefin-based sizing agents, alkyl ketene dimer sizing agents, and alkenyl succinic anhydride sizing agents. The sizing solution may also contain additives such as coloring pigments, coloring dyes, fluorescent dyes, and defoamers. Methods for applying the sizing solution include, for example, sizing presses, roller coaters, metal sizing machines, bar coaters, and rod coaters.

[0106] Alternatively, a coating containing pigments and binders can be applied to the surface of the support layer 20. By applying this coating, excessive penetration of the dispersion into the support layer 20 can be prevented when the dispersion is applied to the support layer 20. Examples of pigments used in the coating include inorganic pigments such as kaolin, light calcium carbonate, titanium dioxide, and plastic pigments, as well as organic pigments such as plastic pigments. Examples of binders used in the coating include various copolymer latexes such as styrene-butadiene, styrene-acrylic, vinyl acetate-acrylic, and butadiene-methyl methacrylate. Furthermore, the coating may also contain additives such as pH adjusters, defoamers, dispersants, lubricants, printability improvers, thickeners, water-retaining agents, fluorescent dyes, coloring pigments, and coloring dyes.

[0107] 2.3. Release layer bonding process (step S12)

[0108] In the release layer bonding process, the release layer 40, after being coated with adhesive layer 30 and dried, is bonded to one side of the support layer 20. The bonding between the release layer 40 and the support layer 20 is performed via adhesive layer 30.

[0109] 2.4. Dispersion preparation process (step S13)

[0110] 2.4.1. Preparation of the mixture

[0111] In the dispersion preparation process, CNTs, CMCs, and water are first mixed to create a mixture. The mixing of CNTs, CMCs, and water is performed, for example, using a homogenizer. Water is used as the solvent in the preparation of the mixture. Examples of water include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, as well as ultrapure water, which has had as many ionic impurities as possible removed. By using water as the solvent, an environmentally friendly mixture can be produced compared to using organic solvents. The mixture can also consist solely of CNTs, CMCs, and water.

[0112] In the mixture, the mass M of CMC CMC relative to the mass M of CNT CNT The ratio of M CMC / M CNT It is the ratio M in the above-mentioned coating layer 10 CMC / M CNT The same. Similarly, the ratio of M in the dispersion CMC / M CNT It is the ratio of M in coating layer 10 CMC / M CNT Same.

[0113] In the process of preparing the mixture, a thickener can also be further mixed in. That is, the mixture can also contain CNT, CMC, water, and a thickener. By including a thickener in the mixture, the viscosity of the dispersion can be adjusted.

[0114] The viscosity of the mixture is not particularly limited, but is preferably 100 mPa·s or higher and 4000 mPa·s or lower at 20°C. If the viscosity of the mixture is 100 mPa·s or higher, the dispersion is easily coated onto the support layer 20. If the viscosity of the mixture is 4000 mPa·s or lower, the mixture is easily ejected from the nozzle orifice of the wet microparticle device, as described later. The viscosity of the dispersion can be measured using a viscometer. When the mixture contains a thickener, the mass of the thickener relative to the mass of the mixture is, for example, 0.4% by mass or lower, preferably 0.1% by mass or lower, and more preferably 100 ppm (0.01% by mass) or lower.

[0115] Examples of thickeners include: celluloses such as methylcellulose and hydroxypropylcellulose, and their ammonium or alkali metal salts; poly(meth)acrylic acid, modified poly(meth)acrylic acid, and their alkali metal salts; polyvinyl alcohol-based (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; saponifications of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, and fumaric acid with vinyl esters; and water-soluble polymers such as polyacrylamide copolymers.

[0116] 2.4.2. Dispersion via underwater opposing collision method

[0117] Next, a dispersion is prepared by dispersing the CNTs contained in the prepared mixture using an underwater counter-collision method. In this dispersion preparation process, only CMC is used as the dispersant. By utilizing the underwater counter-collision method to disperse the CNTs contained in the mixture, even if the mixture contains only CMC as the dispersant, the CNTs can be dispersed well. Therefore, a well-dispersible CNT dispersion can be prepared.

[0118] In the underwater counter-collision method, a mixture containing CNTs is ejected at high pressure from a pair of oppositely arranged nozzle holes (a first nozzle hole and a second nozzle hole), causing the CNTs to disperse by collision between the mixture ejected from the first nozzle hole and the mixture ejected from the second nozzle hole. Preferably, in the underwater counter-collision method, the CNTs contained in the mixture ejected from the first nozzle hole are dispersed by collision between the CNTs contained in the mixture ejected from the second nozzle hole. In the underwater counter-collision method, it is sufficient that the central axes of the first nozzle hole and the second nozzle hole intersect each other; the two central axes can be on a straight line or inclined to each other. Alternatively, a method can be used to cause the mixture to collide with ceramic balls or the like from the nozzle holes.

[0119] In the underwater opposing collision method, for example, a mixture is ejected from a nozzle orifice with a diameter of 50 μm or more, 200 μm or less, preferably 80 μm or more, 120 μm or less, and more preferably 100 μm, causing the mixtures to collide with each other. If the diameter of the nozzle orifice is 50 μm or more, even mixtures with high viscosity can be ejected from the nozzle orifice. If the diameter of the nozzle orifice is 200 μm or less, the collision energy between the mixtures can be increased.

[0120] In the water-based opposing collision method, the mixture is ejected at a pressure of 150 MPa or higher, 250 MPa or lower, preferably 180 MPa or higher, 220 MPa or lower, and more preferably 200 MPa, causing the mixture to collide with each other. If the pressure is 150 MPa or higher, the collision energy between the mixtures can be increased. If the pressure is 250 MPa or lower, the following situation can be prevented: the collision energy is too high and the CNT fibers break, resulting in a decrease in the viscosity of the dispersion.

[0121] Specifically, the underwater counter-collision method is performed using the "StarBurst Labo" wet micronization unit (model name: HJP-25005) manufactured by Sugino Machinery Co., Ltd. This wet micronization unit, for example, has a higher energy density than ultrasonic homogenizers and ball mills, enabling the production of well-dispersed dispersions in a short time. Furthermore, this wet micronization unit minimizes the introduction of impurities, producing dispersions with minimal impurity contamination.

[0122] The number of passes of the mixture in the wet micronization apparatus is, for example, 1 or more, 40 or less, preferably 1 or more, 10 or less, and more preferably 1. If the number of passes is 40 or less, it is possible to prevent the CNT fibers from breaking due to collisions with each other in the mixture, resulting in a decrease in the viscosity of the dispersion. If the number of passes is 1 or more, the CNTs can be dispersed uniformly and well. Moreover, if the number of passes is 1 or more, no significant difference in the dispersibility of the CNTs can be observed. Therefore, if the number of passes is 1, both good dispersibility and a reduction in the processing time of the wet micronization apparatus can be achieved.

[0123] Here, "the number of times the mixture passes through the wet microparticle unit" refers to the number of times the mixture circulates within the wet microparticle unit. For example, "two passes" means that if a CNT that has undergone one collision collides with another, the mixture circulates twice. Thus, the number of passes corresponds to the number of collisions of the CNTs contained in the mixture. Furthermore, the number of passes is proportional to the processing time of the wet microparticle unit. If the processing time of the wet microparticle unit is long, the number of times the mixture circulates increases.

[0124] Furthermore, the apparatus used in the underwater counter-collision method is only required to produce a well-dispersed dispersion and an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity; it is not limited to the aforementioned wet microparticle device "Star Burst Labo". Alternatively, the underwater counter-collision method can be omitted, as long as a well-dispersed dispersion and an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity can be manufactured.

[0125] Furthermore, it is preferable to pretreat the mixture using a homogenizer before dispersing CNTs via opposing collisions in water. The homogenizer can be an ultrasonic type that induces cavitation, a stirring type that agitates the mixture, or a pressure type that applies pressure to the mixture. Homogenization reduces CNT-induced agglomerates and facilitates smooth dispersion.

[0126] Furthermore, there is no particular restriction on the order of the dispersion preparation process and the support layer formation process; the support layer formation process can be performed after the dispersion preparation process or after the support layer formation process. Similarly, there is no particular restriction on the order of the dispersion preparation process and the release layer bonding process.

[0127] 2.5. Dispersion coating process (step S14)

[0128] In the dispersion coating process, the dispersion prepared in the dispersion preparation process is coated onto the side of the support layer 20 opposite to the release layer 40. There are no particular limitations on the method of coating the dispersion; for example, methods such as using a diecoater, gravure coater, wire bar coater, knife coater, air coater, blade coater, roll coater, and reverse roll coater can be used to coat the support layer 20.

[0129] 2.6. Coating layer formation process (step S15)

[0130] In the coating layer forming process, the dispersion applied to the support layer 20 is dried to form the coating layer 10. The drying method for the dispersion is not particularly limited as long as it can evaporate the water contained in the dispersion; for example, hot air drying, infrared drying, and natural drying are all acceptable methods.

[0131] If the thickness of the support layer 20 is small, wrinkles may occur in the support layer 20 during the drying of the dispersion, but if... Figure 4As shown, by bonding the release layer 40 to the support layer 20 before applying the dispersion to the support layer 20, the strength of the support layer 20 can be increased. This reduces the likelihood of wrinkles forming in the support layer 20.

[0132] Through the above processes, an electromagnetic noise suppression sheet 100 can be manufactured.

[0133] In addition, in such Figure 2 In the case where the outer coating 50 is formed as shown, for example, it is formed by applying the outer coating liquid that will become the outer coating 50 to the coating layer 10 using a method listed as a coating method for applying a dispersion containing CNTs to the support layer 20, and then performing hot air drying, infrared drying, and natural drying.

[0134] There are no particular limitations on the raw materials used in the external coating liquid. Examples include polyethylene terephthalate, polypropylene, vinyl chloride resin, fluoropolymer resin, silicone resin, styrene-acrylic resin, acrylic resin, urethane resin, epoxy resin, polyethylene wax, polycarbonate, polyphenylene ether, polysulfone, polyimide, thermoplastic polyester, phenolic resin, urea-formaldehyde resin, epoxy resin, melamine resin, diallyl phthalate resin, furan resin, and silicon-based inorganic compounds. The external coating liquid may contain only one of these materials or may contain two or more in any proportion.

[0135] 2.7. Variation Example

[0136] Figure 5 This is a flowchart illustrating the manufacturing method of the electromagnetic noise suppression sheet 100 of this embodiment.

[0137] In the above Figure 4 In the example shown, a release layer bonding process (step S12) was performed before the dispersion coating process (step S14).

[0138] In contrast, Figure 5 In the example shown, the release layer bonding process (step S25) is performed after the dispersion coating process (step S23). When the support layer 20 has a large thickness and high strength, even if the release layer bonding process (step S25) is performed after the dispersion coating process (step S23), the possibility of wrinkles forming in the support layer 20 during the drying of the dispersion can be reduced.

[0139] exist Figure 5In the example shown, the manufacturing method of the electromagnetic noise suppression sheet 100 includes: a dispersion preparation step (step S21) for preparing a dispersion containing CNT, CMC and water; a support layer formation step (step S22) for forming a support layer 20; a dispersion coating step (step S23) for coating the dispersion onto the support layer 20; a coating layer formation step (step S24) for drying the dispersion to form a coating layer 10; and a release layer bonding step (step S25) for bonding the release layer 40 to the support layer 20.

[0140] The dispersion preparation process (step S21) is basically the same as the dispersion preparation process (step S13) described above. The support layer formation process (step S22) is basically the same as the support layer formation process (step S11) described above. The dispersion coating process (step S23) is basically the same as the dispersion coating process (step S14) described above. The coating layer formation process (step S24) is basically the same as the coating layer formation process (step S15) described above. The release layer bonding process (step S25) is basically the same as the release layer bonding process (step S12) described above.

[0141] 3. Experimental Example

[0142] The following experimental examples illustrate the invention in more detail. However, the invention is not limited to the following experimental examples.

[0143] 3.1. Experimental Example 1

[0144] 3.1.1. Fabrication of Electromagnetic Noise Suppression Sheet

[0145] A mixture was prepared by mixing CNTs, CMCs, and water. A homogenizer, "Biomixer BM-2," manufactured by Nippon Seiki Co., Ltd., was used for mixing. The mixing time was set to 5 minutes.

[0146] The CNTs used are "K-Nanos-100P" manufactured by KUMHO PETROCHEMICAL. These CNTs are MWCNTs with a diameter of 8nm–15nm, a fiber length of 27μm (bundle), and a BET specific surface area of ​​220m². 2 / g.

[0147] The CMC used was "Cellogen 5A" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd. This CMC has a weight-average molecular weight of 11,000–15,000 and a degree of etherification of 0.7. Only CMC was used as a dispersant. In the mixture, the mass M of CMC was... CMC relative to the mass M of CNT CNT The ratio of M CMC / M CNTIt varies within the range of 1 / 9 to 9 (CNT:CMC = 9:1 to 1:9). No thickeners or other additives are added.

[0148] Next, the above mixture was subjected to an underwater counter-collision method. This method was performed using a wet microparticle atomization device, "Star Burst Labo" (model name: HJP-25005), manufactured by Sugino Machinery Co., Ltd. The diameter of the nozzle orifice expelling the mixture was set to 100 μm, and the expulsion pressure was set to 200 MPa. The mixture passed through the wet microparticle atomization device twice. This produced a dispersion containing CNTs, CMC, and water.

[0149] The above dispersion was applied to the support layer ("Hamayu" manufactured by Hokuetsu Co., Ltd., a registered trademark) using a die coater, with a basis weight of 30 g / m³. 2 After that, it is dried at 60℃~70℃ to evaporate the moisture, producing coated paper including a support layer and a coating layer.

[0150] In this way, coated paper that serves as an electromagnetic noise suppression sheet is produced.

[0151] 3.1.2. Evaluation Methods

[0152] The electromagnetic noise suppression performance of the aforementioned coated paper was evaluated. The electromagnetic noise suppression performance was evaluated by measuring the transmission attenuation rate Rtp [dB] using the microstrip line method. The measuring instrument used was a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ connected to a test fixture "TF-18C" manufactured by KEYCOM. The measurements were performed in accordance with "IEC 62333". The measurement frequency was set to 500MHz to 18GHz.

[0153] Furthermore, the thickness of the coating layer on the coated paper was measured using SEM.

[0154] Furthermore, the surface resistivity of the coating layer of the aforementioned coated paper was measured. The measuring instrument used was a "Loresta-AX MCP-T370" manufactured by Mitsubishi Chemical Analytech Co., Ltd. The measurements were performed in accordance with "JIS K 7194".

[0155] Furthermore, the in-plane thermal conductivity was determined based on Equation (1) above. Since the thermal conductivity measurement required thickening the CNT-containing layer, it was performed on a dried film instead of the coated paper. The dried film was prepared by placing the aforementioned dispersion containing CNTs, CMC, and water into a petri dish with a diameter of 8.5 cm and drying it at 50°C for 12 hours to evaporate the moisture. This is because the thermal conductivity measurement requires thickening the CNT-containing layer. The thermal diffusivity was measured using a NETZSCH LFA567 HyperFlash laser by laser flash method. The specific heat was measured using a TA Instruments Discovery DSC 25 laser. The density was calculated from the volume and weight of the dried film.

[0156] 3.1.3. Evaluation Results

[0157] Figure 6 This is a table showing the RTP of coated paper with varying CNT to CMC mass ratios. Furthermore, in Figure 6 The figure shows the thickness of the coating layer, the surface resistivity of the coating layer, and the thermal conductivity of the dried film.

[0158] like Figure 6 As shown, when the mass ratio of CNTs is less than CNT:CMC = 1:3, Rtp becomes extremely small. Furthermore, when the mass ratio of CNTs is greater than CNT:CMC = 5:1, the thermal conductivity becomes extremely poor. Therefore, it can be seen that by setting the CNT:CMC ratio to a range of 5:1 to 1:3, both electromagnetic noise suppression performance and thermal conductivity can be improved. Moreover, it can be seen that by setting the CNT:CMC ratio to a range of 3:1 to 1:1, both electromagnetic noise suppression performance and thermal conductivity can be further improved.

[0159] It can be seen that Rtp is correlated with surface resistivity, and there is a tendency that the higher the surface resistivity, the larger the Rtp.

[0160] Thermal conductivity is highest when the CNT:CMC ratio is 1:1. When the mass ratio of CMC is greater than 1:1, the thermal diffusivity decreases, and therefore the thermal conductivity decreases. When the mass ratio of CNT is greater than 1:1, the thermal diffusivity increases, but the density decreases, and therefore the thermal conductivity decreases.

[0161] Figure 7 This is a graph showing the Rtp of the coated paper relative to frequency when the mass ratio of CNT to CMC is varied. Figure 6 The Rtp shown is from Figure 7 The coordinate graph shown was obtained by reading values ​​at 6 GHz and 15 GHz. Figure 7In addition, samples with only a support layer and no coating were also evaluated.

[0162] like Figure 7 As shown, in No. 4 to No. 10 (CNT:CMC = 9:1 to 1:1), the trend is roughly the same relative to frequency. However, in No. 4 to No. 10, within the frequency range of 3GHz to 5GHz, there is a tendency that the larger the CNT mass ratio, the smaller the Rtp. On the other hand, at higher frequencies above 8GHz, there is a tendency that the larger the CNT mass ratio, the larger the Rtp.

[0163] 3.2. Experimental Example 2

[0164] In Experiment 2, with a CNT:CMC ratio of 1:1, the Rtp of the coated paper with varying coating thickness was measured. The preparation and evaluation methods for the coated paper were the same as in Experiment 1.

[0165] Figure 8 This is a table showing the Rtp of coated paper when the thickness of the coating layer is varied. Figure 9 This is a graph showing the Rtp of the coated paper relative to frequency when the thickness of the coating layer is varied. Figure 8 The Rtp shown is from Figure 9 The coordinate graph shown was obtained by reading the values ​​at 6 GHz and 15 GHz.

[0166] like Figure 8 and Figure 9 As shown, in the frequency range of 2 GHz to 7 GHz, coated papers B and C with low surface resistivity have a larger Rtp compared to coated paper A. On the other hand, at higher frequencies than 12 GHz, coated paper A with high surface resistivity has a larger Rtp compared to coated papers B and C.

[0167] 3.3. Experimental Example 3

[0168] In Experiment 3, with a CNT:CMC ratio of 1:1, the Rtp of the coated paper was measured by changing the number of passes of the mixture through the wet micronization device. Except for the change in the number of passes, the preparation and evaluation methods of the coated paper were the same as in Experiment 1.

[0169] Figure 10 This is a table showing the Rtp of coated paper when the number of passes is varied. Figure 11 This is a graph showing the Rtp of the coated paper relative to the frequency when the number of passes is varied. Figure 10 The Rtp shown is from Figure 11 The coordinate graph shown was obtained by reading the values ​​at 6 GHz and 15 GHz.

[0170] Except for "untreated" coated paper that has been passed through the wet micronization device zero times, the same trend is observed. Compared to untreated coated paper, coated paper that has been passed through the wet micronization device more than once has a larger Rtp in the range of 500MHz to 9GHz.

[0171] The above-described embodiments and modifications are examples and are not limited to these. For example, the various embodiments and modifications can also be appropriately combined.

[0172] This invention is not limited to the embodiments described above and can be further modified in various ways. For example, this invention includes configurations that are substantially the same as those described in the embodiments. A substantially similar configuration refers to a configuration with the same function, method, and result, or a configuration with the same purpose and effect. Furthermore, this invention includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. Additionally, this invention includes configurations that have the same effect or purpose as those described in the embodiments. Furthermore, this invention includes configurations in which known techniques are added to the configurations described in the embodiments.

[0173] Explanation of reference numerals in the attached figures

[0174] 10…coating layer, 20…support layer, 30…adhesive layer, 40…release layer, 50…outer coating layer, 100…electromagnetic noise suppression sheet.

Claims

1. A method for manufacturing an electromagnetic noise suppression sheet, characterized in that, Include: The process of preparing a dispersion containing carbon nanotubes, sodium carboxymethyl cellulose, and water; and The process of drying the dispersion to form the first layer In the process of preparing the dispersion, only sodium carboxymethyl cellulose is used as a dispersant. In the dispersion, the mass ratio of sodium carboxymethyl cellulose to the mass of carbon nanotubes is more than 1 / 5 and less than 3. In the process of preparing the dispersion, the carbon nanotubes, sodium carboxymethyl cellulose, and water are mixed to form a mixture. The mixture is then sprayed out in water at a pressure of 150 MPa to 250 MPa to disperse the carbon nanotubes. The carbon nanotubes in the mixture have a fiber length of 15 μm or more and 35 μm or less.

2. The method for manufacturing the electromagnetic noise suppression sheet according to claim 1, wherein, The ratio is less than 1.

3. The method for manufacturing the electromagnetic noise suppression sheet according to claim 1 or 2, wherein, The ratio is 1 / 3 or more.

4. The method for manufacturing the electromagnetic noise suppression sheet according to claim 1 or 2, wherein, The process of coating the dispersion onto the second layer is included prior to the process of forming the first layer.

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