Manufacturing method for electromagnetic noise suppression sheet

Abstract

Provided is an electromagnetic wave noise suppressing sheet that has an electromagnetic wave noise suppressing function and exhibits high thermal conductivity.　An electromagnetic wave noise suppressing sheet 100 according to the present invention includes a first layer 10 substantially composed of carbon nanotubes and carboxymethyl cellulose, wherein the ratio of the mass of the carboxymethyl cellulose to the mass of the carbon nanotubes in the first layer 10 is in the range of 1 / 5 to 3.

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic noise suppression sheet and a method for producing the same. [Background technology]

[0002] Carbon nanotubes have a structure similar to a uniform, flat graphene sheet rolled into a cylindrical shape. Because of this unique structure, carbon nanotubes have a variety of properties and are expected to be applied in a wide range of fields.

[0003] For example, in Patent Document 1, multi-walled carbon nanotubes are distributed at a density of 1 g / cm relative to the substrate. 2 An electromagnetic wave suppression sheet coated as described above is described. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-174833 Summary of the Invention [Problem to be solved by the invention]

[0005] The electromagnetic wave suppression sheet described above is used by being attached to, for example, an electronic device. Electronic devices tend to trap heat. Therefore, high thermal conductivity is required in addition to electromagnetic wave noise suppression performance. High thermal conductivity allows the heat of the electronic device to be dissipated efficiently.

[0006] An object of some aspects of the present invention is to provide an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity, and a method for producing an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and high thermal conductivity. [Means for solving the problem]

[0007] One aspect of the electromagnetic noise suppression sheet according to the present invention is Carbon nanotubes and carboxymethyl cellulose sodium and a first layer consisting essentially of In the first layer, the ratio of the carboxymethyl cellulose to the mass of the carbon nanotubes sodium The mass ratio is between 1 / 5 and 3.

[0008] In one embodiment of the electromagnetic noise suppression sheet, The ratio may be less than or equal to 1.

[0009] In any one of the above-described electromagnetic noise suppression sheets, The ratio may be 1 / 3 or greater.

[0010] In any one of the above-described electromagnetic noise suppression sheets, The first layer may have a surface resistivity of 60 Ω / □ or less.

[0011] In any one of the above-described electromagnetic noise suppression sheets, The first layer may have a thickness of 2 μm or more.

[0012] In any one of the above-described electromagnetic noise suppression sheets, The carbon nanotubes may be multi-walled carbon nanotubes.

[0013] In any one of the above-described electromagnetic noise suppression sheets, The first layer may include a second layer disposed thereon.

[0014] One aspect of the method for producing an electromagnetic noise suppression sheet according to the present invention is to Carbon nanotubes and carboxymethyl cellulose sodium and water; drying the dispersion to form a first layer; Including, In the step of preparing the dispersion, the carboxymethyl cellulose is used as a dispersant. sodium Only using In the dispersion, the ratio of the carboxymethyl cellulose to the mass of the carbon nanotubes is sodium The mass ratio is between 1 / 5 and 3.

[0015] In one embodiment of the method for producing an electromagnetic noise suppression sheet, The ratio may be less than or equal to 1.

[0016] In any one of the above-described methods for producing an electromagnetic noise suppression sheet, The ratio may be 1 / 3 or greater.

[0017] In any one of the above-described methods for producing an electromagnetic noise suppression sheet, The method may include a step of applying the dispersion to a second layer before the step of forming the first layer. [Effects of the Invention]

[0018] The electromagnetic noise suppression sheet according to the present invention is made of carbon nanotubes and carboxymethyl cellulose. sodium and a first layer consisting essentially of carboxymethyl cellulose relative to the mass of the carbon nanotubes, sodium The mass ratio is between 1 / 5 and 3, so it has high electromagnetic noise suppression performance and thermal conductivity. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to this embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing the electromagnetic noise suppression sheet according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to this embodiment. [Figure 4]FIG. 4 is a flowchart illustrating a method for manufacturing an electromagnetic noise suppression sheet according to this embodiment. [Figure 5] FIG. 5 is a flowchart illustrating a method for manufacturing an electromagnetic noise suppression sheet according to this embodiment. [Figure 6] FIG. 6 is a table showing the transmission attenuation rate of coated paper when the mass ratio of carbon nanotubes to sodium carboxymethyl cellulose is changed. [Figure 7] FIG. 7 is a graph showing the transmission attenuation rate of coated paper versus frequency when the mass ratio of carbon nanotubes to sodium carboxymethyl cellulose is changed. [Figure 8] FIG. 8 is a table showing the transmission attenuation rate versus frequency when the thickness of coated paper is changed. [Figure 9] FIG. 9 is a graph showing the transmission attenuation rate of coated paper versus frequency when the thickness of the coated paper is changed. [Figure 10] FIG. 10 is a table showing the transmission attenuation rate of coated paper when the number of passes is changed. [Figure 11] FIG. 11 is a graph showing the transmission attenuation rate of coated paper versus frequency when the number of passes is changed. DETAILED DESCRIPTION OF THE INVENTION

[0020] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention as defined in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0021] 1. Electromagnetic noise suppression sheet 1.1. Overall structure First, the electromagnetic noise suppression sheet according to this embodiment will be described with reference to the drawings. Fig. 1 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet 100 according to this embodiment.

[0022] The electromagnetic noise suppression sheet 100 has a sheet shape in which the length in the in-plane direction (the direction perpendicular to the thickness direction) is sufficiently longer than the thickness direction. The planar shape of the electromagnetic noise suppression sheet 100 is not particularly limited, but may be, for example, rectangular.

[0023] 1, 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. Each of these components will be described below in order.

[0024] 1.1.1. Coating layer 1.1.1.1. Physical properties, etc. The coating layer 10 is provided on the support layer 20. The coating layer 10 is a layer coated on the support layer 20.

[0025] 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 correlates with the electromagnetic noise suppression performance of the electromagnetic noise suppression sheet 100, and the lower the surface resistivity, the higher the electromagnetic noise suppression performance tends to be. 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 in accordance with "JIS K 7194."

[0026] 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 cracks occurring in the coating layer 10 can be reduced. The thickness of the coating layer 10 can be measured using a scanning electron microscope (SEM).

[0027] The thermal conductivity of the coating layer 10 in the in-plane direction is, for example, 0.90 W / m·K or more, preferably 0.93 W / m·K or more, more preferably 1.0 W / m·K or more, and even more preferably 1.3 W / m·K or more. The "thermal conductivity of the coating layer 10 in the in-plane direction" refers to the thermal conductivity in the direction perpendicular to the thickness direction of the coating layer 10 (the stacking direction of the coating layer 10 and the support layer 20). Hereinafter, the "thermal conductivity of the coating layer 10 in the in-plane direction" will also be simply referred to as the "thermal conductivity of the coating layer 10." A thermal conductivity of 0.90 W / m·K or more of the coating layer 10 can enhance the thermal conductivity of the electromagnetic noise suppression sheet 100. Thermal conductivity λ can be calculated using the following formula (1), where α is the thermal diffusivity, C is the specific heat, and ρ is the density.

[0028] λ=α×C×ρ (1)

[0029] 1.1.1.2. Materials The coating layer 10 is a mixture of carbon nanotubes (hereinafter also referred to as "CNT") and carboxymethyl cellulose. sodium (hereinafter also referred to as "CMC"). The coating layer 10 is substantially composed of CNT and CMC. "Substantially composed of CNT and CMC" includes a case where the coating layer 10 is composed of CNT and CMC (a case where the coating layer 10 is composed only of CNT and CMC) and a case where the coating layer 10 is composed of CNT, CMC, and other trace substances. "Other trace substances" are substances other than CNT and CMC, and the mass of such substances is 0.5 mass% or less of the mass of the coating layer 10. "Other trace substances" may be additives intentionally added during the production of the electromagnetic noise suppression sheet 100, or may be impurities unintentionally mixed in.

[0030] (1) Carbon nanotubes (CNTs) The CNTs contained in the coating layer 10 are single-walled carbon nanotubes (SWCNTs), in which a single six-membered ring network (graphene sheet) made of carbon is wound into a cylindrical shape, or multi-walled carbon nanotubes (MWCNTs), in which multiple graphene sheets are wound concentrically. The coating layer 10 may contain only SWCNTs or MWCNTs, or may contain both. However, considering the dispersibility of CNTs, it is preferable that the coating layer 10 contains only MWCNTs. That is, the CNTs contained in the coating layer 10 are preferably MWCNTs. Both ends of the CNTs may be closed or open.

[0031] The CNTs described above are produced to a desired size by, for example, an arc discharge method, a laser ablation method, a CVD (Chemical Vapor Deposition) method, etc. The CNTs contained in the coating layer 10 may be produced by any of these methods.

[0032] The diameter of the CNTs is, for example, 1 nm to 100 nm, preferably 5 nm to 50 nm, and more preferably 8 nm to 15 nm. When the diameter of the CNTs is 1 nm to 100 nm, a dispersion liquid with good CNT dispersibility can be prepared when forming the coating layer 10. The diameter of the CNTs can be measured using an SEM.

[0033] The fiber length of the CNT is, for example, 0.5 μm or more and 50 μm or less, and preferably 15 μm or more and 35 μm or less. If the fiber length of the CNT is 0.5 μm or more and 50 μm or less, a dispersion liquid with good CNT dispersibility can be prepared. The fiber length of the CNT can be measured using an SEM. Note that the "fiber length of the CNT" refers to the length of the CNT when it is bundled by van der Waals forces, and is the length of the CNT before it is dispersed in a solvent.

[0034] The BET specific surface area of ​​CNT is, for example, 50 m2 / g or more 500m 2 / g or less, preferably 100m 2 / g or more 300m 2 / g or less. The BET specific surface area of ​​the CNT is 50m 2 / g or more 500m 2 / g or less, a dispersion liquid with good CNT dispersibility can be prepared when forming the coating layer 10. The "BET specific surface area" refers to the specific surface area measured by the BET (Brunauer Emmett Teller) method, and can be measured using an automatic specific surface area measuring device.

[0035] In the dispersion for forming the coating layer 10, the CNT content 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 CNT content is 10.0% or more, the electromagnetic noise suppression performance can be improved. mass% If the content is below this, a dispersion liquid with good CNT dispersibility can be prepared when forming the coating layer 10.

[0036] (2) Carboxymethylcellulose sodium (CMC) CMC functions as a dispersant for dispersing CNTs when forming the coating layer 10. Only CMC is used as a CNT dispersant. A "dispersant" is an additive that disperses CNTs in water and helps prevent the aggregation and sedimentation of CNTs. By using only CMC as a CNT dispersant, it is possible to prevent the inclusion of air bubbles, compared to, for example, when an anionic surfactant or other dispersant is added in addition to CMC.

[0037] The weight-average molecular weight of the CMC is, for example, 5,000 to 100,000, preferably 10,000 to 60,000, and more preferably 10,000 to 35,000. If the weight-average molecular weight of the CMC is 5,000 or more, the CMC easily becomes entangled with the CNTs, improving the dispersibility of the CNTs. However, if the weight-average molecular weight is too large, dispersibility will deteriorate, so the molecular weight of the CMC is preferably 100,000 or less. In this specification, the "weight-average molecular weight" refers to the weight-average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

[0038] The degree of etherification of CMC is, for example, from 0.6 to 1.2, and preferably from 0.6 to 0.8. If the degree of etherification of CMC is from 0.6 to 1.2, a dispersion liquid with good CNT dispersibility can be prepared.

[0039] In the dispersion for forming the coating layer 10, the CMC content is, for example, 0.1 mass% or more and 10.0 mass% or less, preferably 0.5 mass% or more and 5.0 mass% or less, and more preferably 2.0 mass% or more and 4.0 mass% or less.

[0040] In the coating layer 10, the mass M of the CNT CNT Mass M of CMC CMC Ratio of M CMC / M CNT The ratio M is 1 / 5 or more and 3 or less (CNT:CMC=5:1 to 1:3), and preferably 1 / 3 or more and 1 or less (CNT:CMC=3:1 to 1:1). CMC / M CNT If the ratio M is 1 / 5 or more, the thermal conductivity can be increased. CMC / M CNT If the ratio M is 3 or less, the electromagnetic noise suppression performance can be improved. CMC / M CNT can be measured by thermal gravimetric analysis (TGA).

[0041] (3) Additives The coating layer 10 may contain various additives such as a thickener, a preservative, and a pH adjuster, as needed.

[0042] 1.1.2. Supporter layer The support layer 20 is provided on the adhesive layer 30. The support layer 20 has the coating layer 10 provided thereon. The support layer 20 supports the coating layer 10.

[0043] The support layer 20 is, for example, a sheet containing pulp. The support layer 20 may be composed solely of pulp. Examples of pulp contained in the support layer 20 include chemical pulps such as LBKP (bleached hardwood kraft pulp) and NBKP (bleached softwood kraft pulp), mechanical pulps such as GP (groundwood pulp), PGW (pressurized groundwood pulp), RMP (refiner mechanical pulp), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), CMP (chemi-mechanical pulp), and CGP (chemi-ground pulp), wood pulps such as DIP (deinked pulp), and non-wood pulps such as kenaf, bagasse, bamboo, and cotton. The support layer 20 may contain only one type of pulp, or two or more types in any ratio. Furthermore, the support layer 20 may contain synthetic fibers to the extent that it does not impair quality.

[0044] The support layer 20 preferably contains LBKP. The LBKP content 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. When the LBKP content is 70% by mass or more, distortion of the support layer 20 can be reduced.

[0045] The basis weight of the support layer 20 is 40g / m 2 In the following cases, it is preferable that the support layer 20 contains NBKP. The content of NBKP in the support layer 20 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 support layer 20 can be maintained.

[0046] The support layer 20 may contain various additives, such as fillers, paper strength agents, sizing agents, bulking agents, retention aids, drainage aids, aluminum sulfate, wet paper strength agents, coloring dyes, coloring pigments, fluorescent whitening agents, pitch control agents, thickeners, preservatives, and pH adjusters, as needed.

[0047] The material of the support layer 20 is not particularly limited as long as it can support the coating layer 10. The support layer 20 may be a resin film such as a PET (polyethylene terephthalate) film, a nonwoven fabric, or a synthetic paper made primarily from synthetic resin.

[0048] 1.1.3. Adhesive layer The adhesive layer 30 is provided on the release layer 40. The adhesive layer 30 has adhesive properties. The material of the adhesive layer 30 is not particularly limited as long as it has adhesive properties, but examples thereof 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.

[0049] 1.1.4. Release layer The release layer 40 is provided so as to be releasable from the adhesive layer 30. When the electromagnetic noise suppression sheet 100 is to be attached to an external device such as an electronic device, the release layer 40 is peeled from the adhesive layer 30, and then the adhesive layer 30 is brought into contact with the external device, thereby attaching the electromagnetic noise suppression sheet 100 to the external device.

[0050] The material of the release layer 40 is not particularly limited as long as it can be peeled from the adhesive layer 30, but examples thereof include uncoated paper such as fine paper, coated paper such as general coated paper or art paper, glassine paper, films using polyethylene, polyethylene terephthalate, or the like, or film-laminated paper. If necessary, a release agent such as silicone resin, fluororesin, or the like may be used in an amount of 0.1 g / m2 in terms of dry mass. 2 ~3g / m 2 It may be applied and dried.

[0051] 1.2. Variations 2, the electromagnetic noise suppression sheet 100 may include an overcoat layer 50. The overcoat layer 50 is provided on the coating layer 10. The overcoat layer 50 is an insulating layer that prevents scratches on the coating layer 10 and provides dielectric breakdown strength.

[0052] The material of the overcoat layer 50 is not particularly limited, but examples thereof include polyethylene terephthalate, polypropylene, vinyl chloride resin, fluororesin, silicone resin, styrene-acrylic resin, acrylic resin, urethane resin, epoxy resin, polyethylene wax, polycarbonate, polyphenylene oxide, polysulfone, polyimide, thermoplastic polyester, phenol resin, urea resin, epoxy resin, melamine resin, J Examples of the resin include allyl phthalate resin, furan resin, and silicon-based inorganic compounds. The overcoat layer 50 may contain only one of these resins, or may contain two or more of them in any ratio. The overcoat layer 50 preferably has heat resistance.

[0053] The thickness of the overcoat layer 50 is not particularly limited, but is, for example, 1 μm to 20 μm, preferably 2 μm to 10 μm. If the thickness of the overcoat layer 50 is 1 μm or more, scratches on the coating layer 10 can be suppressed and electrical insulation and dielectric breakdown strength can be imparted. If the thickness of the overcoat layer 50 is 20 μm or less, costs can be reduced.

[0054] 3, the electromagnetic noise suppression sheet 100 does not necessarily have to include the adhesive layer 30 and the release layer 40, as long as it includes the coating layer 10 and the support layer 20. The electromagnetic noise suppression sheet 100 may be composed of only the coating layer 10 and the support layer 20.

[0055] 1.3. Electromagnetic noise suppression performance The electromagnetic noise suppression sheet 100 has electromagnetic noise suppression performance, which 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 the Rtp, the higher the electromagnetic noise suppression performance.

[0056] 2. Manufacturing method for electromagnetic noise suppression sheets 2.1. Overall structure Next, a method for manufacturing the electromagnetic noise suppression sheet 100 according to this embodiment will be described with reference to the drawings. Fig. 4 is a flowchart illustrating the method for manufacturing the electromagnetic noise suppression sheet 100 according to this embodiment.

[0057] 4, the method for manufacturing the electromagnetic noise suppression sheet 100 includes, for example, a support layer forming step (step S11) of forming the support layer 20, a release layer bonding step (step S12) of bonding the release layer 40 to the support layer 20, a dispersion preparation step (step S13) of preparing a dispersion containing CNT, CMC, and water, a dispersion application step (step S14) of applying the dispersion to the support layer 20, and a coating layer formation step (step S15) of drying the dispersion to form the coating layer 10. Each step will be described in order below.

[0058] 2.2. Support layer formation step (step S11) In the support layer forming step, for example, a slurry containing pulp but not CNT is made into paper using a paper machine to form the support layer 20. The slurry for forming the support layer 20 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. The CSF is determined by the "JIS P 8 12 The method for making the support layer 20 is not particularly limited, and may be carried out using various machines such as a Fourdrinier paper machine, a multi-layer Fourdrinier paper machine, a cylinder paper machine, a multi-layer cylinder paper machine, a Fourdrinier cylinder combined multi-layer paper machine, or a twin-wire paper machine. The papermaking method may be acidic papermaking or neutral papermaking.

[0059] A sizing liquid containing a water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide may be applied to the surface of the support layer 20. Applying this sizing liquid can prevent the dispersion from excessively penetrating into the support layer 20 when coating the dispersion onto the support layer 20. Furthermore, the surface strength of the support layer 20 can be improved. The sizing liquid may include a surface sizing agent such as a styrene-based sizing agent, a styrene-acrylate-based sizing agent, an olefin-based sizing agent, an alkyl ketene dimer-based sizing agent, or an alkenyl succinic anhydride sizing agent. Furthermore, the sizing liquid may contain auxiliary agents such as color pigments, color dyes, fluorescent dyes, and antifoaming agents. The sizing liquid can be applied using, for example, a size press, a gate roll coater, a metaling sizer, a rod coater, or a bar coater.

[0060] Alternatively, a paint containing a pigment and an adhesive may be applied to the surface of the support layer 20. Applying such a paint can prevent the dispersion from excessively penetrating into the support layer 20 when the dispersion is applied to the support layer 20. Examples of pigments used in paints include inorganic pigments such as kaolin, precipitated calcium carbonate, titanium oxide, and plastic pigments, as well as 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 paint may contain auxiliary agents such as pH adjusters, antifoaming agents, dispersants, lubricants, printability improvers, thickeners, water retention agents, fluorescent dyes, coloring pigments, and coloring dyes.

[0061] 2.3. Peel layer bonding process (step S12) In the release layer bonding step, the release layer 40, which has been coated with and dried as an adhesive layer 30, is bonded to one surface of the support layer 20. The release layer 40 and the support layer 20 are bonded via the adhesive layer 30.

[0062] 2.4. Dispersion Preparation Step (Step S13) 2.4.1. Preparation of the mixture In the dispersion preparation process, first, CNT, CMC, and water are mixed to prepare a mixture. The CNT, CMC, and water are mixed, for example, using a homogenizer. In preparing the mixture, water is used as a solvent. Examples of water include pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, as well as water from which ionic impurities have been removed as much as possible, such as ultrapure water. Using water as a solvent allows for the preparation of a more environmentally friendly mixture than when an organic solvent is used as a solvent. The mixture may consist solely of CNT, CMC, and water.

[0063] In the mixture, the mass of CNTs, M CNT Mass M of CMC CMC Ratio of M CMC / M CNT is the ratio M in the coating layer 10 described above. CMC / M CNT Similarly, the ratio M CMC / M CNT is the ratio M in the coating layer 10 CMC / M CNT is the same as

[0064] In the step of preparing the mixture, a thickener may be further mixed to prepare the mixture. That is, the mixture may contain CNTs, CMC, water, and a thickener. By including a thickener in the mixture, the viscosity of the dispersion can be adjusted.

[0065] The viscosity of the mixture is not particularly limited, but is preferably 100 mPa·s or more and 4000 mPa·s or less at 20°C. If the viscosity of the mixture is 100 mPa·s or more, the dispersion can be easily applied to the support layer 20. If the viscosity of the mixture is 4000 mPa·s or less, the mixture can be easily discharged from the nozzle hole of a wet atomization device, as described below. The viscosity of the dispersion can be measured using a viscometer. When the mixture contains a thickener, the mass of the thickener is, for example, 0.4 mass% or less, preferably 0.1 mass% or less, and more preferably 100 ppm (0.01 mass%) or less, relative to the mass of the mixture.

[0066] Examples of thickeners include celluloses such as methyl cellulose and hydroxypropyl cellulose, and their ammonium salts or alkali metal salts; polycarboxylic acids such as poly(meth)acrylic acid and modified poly(meth)acrylic acid, and their alkali metal salts; polyvinyl alcohol (co)polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer; saponified 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.

[0067] 2.4.2. Dispersion by underwater collision method Next, the CNTs contained in the prepared mixture are dispersed using the underwater counter-impingement method to prepare a dispersion. In the process of preparing the dispersion, only CMC is used as the dispersant. By dispersing the CNTs contained in the mixture using the underwater counter-impingement method, it is possible to disperse the CNTs well, even if the mixture contains only CMC as a dispersant. This makes it possible to prepare a dispersion with good CNT dispersibility.

[0068] In the underwater counter collision method, a mixed liquid containing CNTs is discharged at high pressure from a pair of nozzle holes (first and second nozzle holes) arranged opposite each other, and the mixed liquid discharged from the first nozzle hole and the mixed liquid discharged from the second nozzle hole collide to disperse the CNTs. Preferably, in the underwater counter collision method, the CNTs contained in the mixed liquid discharged from the first nozzle hole collide with the CNTs contained in the mixed liquid discharged from the second nozzle hole to disperse the CNTs. In the underwater counter collision method, as long as the central axes of the first and second nozzle holes intersect with each other, the central axes may be aligned or may be tilted relative to each other. Alternatively, the mixed liquid may be discharged from the nozzle holes and collided with ceramic balls or the like.

[0069] In the underwater head-on collision method, the mixed liquid is ejected from a nozzle hole having a diameter of, for example, 50 μm to 200 μm, preferably 80 μm to 120 μm, and more preferably 100 μm, and the mixed liquid is caused to collide with itself. If the nozzle hole diameter is 50 μm or more, even a mixed liquid with high viscosity can be ejected from the nozzle hole. If the nozzle hole diameter is 200 μm or less, the collision energy between the mixed liquids can be increased.

[0070] In the underwater head-on 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, and more preferably 200 MPa, and the mixed liquids are caused to collide with each other. If the pressure is 150 MPa or more, the collision energy between the mixed liquids can be increased. If the pressure is 250 MPa or less, the collision energy is too high, which can prevent the CNT fibers from breaking and the viscosity of the dispersion from decreasing.

[0071] Specifically, the underwater head-on collision method is carried out using a wet atomization device "Starburst Lab" (model name: HJP-25005) manufactured by Sugino Machine Co., Ltd. This wet atomization device has a higher energy density than, for example, an ultrasonic homogenizer or a ball mill, and can produce a dispersion with good dispersibility in a short time. Furthermore, this wet atomization device can minimize the inclusion of impurities, making it possible to produce a dispersion with extremely little impurity inclusion.

[0072] The number of passes of the mixed solution in the wet atomization device is, for example, 1 to 40 times, preferably 1 to 10 times, and more preferably 1 time. If the number of passes is 40 times or less, it is possible to prevent the CNT fibers from being broken due to collisions between the mixed solutions, which would result in a decrease in the viscosity of the dispersion. If the number of passes is 1 or more, it is possible to disperse the CNTs with good uniformity. Furthermore, if the number of passes is 1 or more, no significant difference in the dispersibility of the CNTs is confirmed. Therefore, if the number of passes is 1, it is possible to shorten the processing time using the wet atomization device while maintaining good dispersibility.

[0073] Here, "the number of passes of the mixed liquid in the wet atomization device" refers to the number of times the mixed liquid is circulated in the wet atomization device. For example, "two passes" means that the mixed liquid is circulated twice so that CNTs that have collided once collide again. In this way, the number of passes corresponds to the number of collisions of CNTs contained in the mixed liquid. Furthermore, the number of passes is proportional to the processing time in the wet atomization device. If the processing time in the wet atomization device is long, the number of times the mixed liquid is circulated increases.

[0074] Note that, as long as a dispersion with good dispersibility can be prepared and an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and thermal conductivity can be produced, the device used in the underwater head-on collision method is not limited to the above-mentioned wet atomization device "Starburst Lab." Furthermore, as long as a dispersion with good dispersibility can be prepared and an electromagnetic noise suppression sheet with high electromagnetic noise suppression performance and thermal conductivity can be produced, it is not necessary to use the underwater head-on collision method.

[0075] Furthermore, before dispersing the CNTs by the underwater head-on collision method, it is preferable to treat the mixed solution with a homogenizer as a pretreatment. The homogenizer may be an ultrasonic type that generates cavitation using ultrasound, an agitation type that agitates the mixed solution, or a pressure type that applies pressure to the mixed solution. Treatment with a homogenizer can reduce CNT agglomerates, allowing for smooth dispersion.

[0076] The order of the dispersion preparation step and the support layer formation step is not particularly limited, and the support layer formation step may be performed after the dispersion preparation step, or the support layer formation step may be performed after the dispersion preparation step. Similarly, the order of the dispersion preparation step and the release layer adhesion step is not particularly limited.

[0077] 2.5. Dispersion Coating Process (Step S14) In the dispersion application step, the dispersion prepared in the dispersion preparation step is applied to the surface of the support layer 20 opposite to the release layer 40. The method for applying the dispersion is not particularly limited, but examples include methods of applying the dispersion to the support layer 20 using a die coater, gravure coater, wire bar coater, knife coater, air coater, blade coater, roll coater, reverse roll coater, etc.

[0078] 2.6. Coating layer formation process (step S15) In the coating layer formation step, the dispersion applied to the support layer 20 is dried to form the coating layer 10. The method for drying the dispersion is not particularly limited as long as it can evaporate the water contained in the dispersion, and examples thereof include hot air drying, infrared drying, and natural drying.

[0079] If the thickness of the support layer 20 is small, wrinkles may occur in the support layer 20 when the dispersion is dried. However, as shown in Fig. 4, by adhering a 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 possibility of wrinkles occurring in the support layer 20.

[0080] Through the above steps, the electromagnetic noise suppression sheet 100 can be manufactured.

[0081] As shown in Figure 2, when forming the overcoat layer 50, for example, the overcoat liquid that will become the overcoat layer 50 is applied to the coating layer 10 using the method listed as the method for applying a dispersion containing CNT to the support layer 20, and then the overcoat layer 50 is formed by hot air drying, infrared drying, or natural drying.

[0082] Materials used in the overcoat liquid are not particularly limited, but examples thereof include polyethylene terephthalate, polypropylene, vinyl chloride resin, fluororesin, silicone resin, styrene-acrylic resin, acrylic resin, urethane resin, epoxy resin, polyethylene wax, polycarbonate, polyphenylene oxide, polysulfone, polyimide, thermoplastic polyester, phenol resin, urea resin, epoxy resin, melamine resin, J Examples include allyl phthalate resin, furan resin, silicon-based inorganic compound, etc. The overcoat liquid may contain only one of these, or may contain two or more of them in any ratio.

[0083] 2.7. Variations FIG. 5 is a flowchart illustrating a method for manufacturing the electromagnetic noise suppression sheet 100 according to this embodiment.

[0084] In the example shown in FIG. 4, the release layer bonding step (step S12) was carried out before the dispersion liquid application step (step S14).

[0085] 5, the release layer bonding step (step S25) is performed after the dispersion coating step (step S23). If the support layer 20 has a large strength, such as a large thickness, performing the release layer bonding step (step S25) after the dispersion coating step (step S23) can reduce the possibility of wrinkles occurring in the support layer 20 when the dispersion dries.

[0086] In the example shown in FIG. 5, the method for producing the electromagnetic noise suppression sheet 100 includes a dispersion preparation step (step S21) of preparing a dispersion containing CNT, CMC, and water, a support layer formation step (step S22) of forming the support layer 20, a dispersion application step (step S23) of applying the dispersion to the support layer 20, a coating layer formation step (step S24) of drying the dispersion to form the coating layer 10, and a release layer bonding step (step S25) of bonding the release layer 40 to the support layer 20.

[0087] The dispersion preparation step (step S21) is basically the same as the dispersion preparation step (step S13) described above. The support layer formation step (step S22) is basically the same as the support layer formation step (step S11) described above. The dispersion application step (step S23) is basically the same as the dispersion application step (step S14) described above. The coating layer formation step (step S24) is basically the same as the coating layer formation step (step S15) described above. The release layer bonding step (step S25) is basically the same as the release layer bonding step (step S12) described above.

[0088] 3. Experimental Example The present invention will be explained in more detail below by way of experimental examples, but the present invention is not limited to these examples.

[0089] 3.1. First experimental example 3.1.1. Fabrication of electromagnetic noise suppression sheet A mixed solution was prepared by mixing CNT, CMC, and water. A homogenizer "Biomixer BM-2" manufactured by Nippon Seiki Seisakusho Co., Ltd. was used for mixing. The mixing time was 5 minutes.

[0090] The CNTs used were "K-Nanos-100P" manufactured by Kumho Petrochemical Co., Ltd. The CNTs were 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.

[0091] The CMC used was "Cellogen 5A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. The CMC had a weight average molecular weight of 11,000 to 15,000 and an etherification degree of 0.7. Only CMC was used as a dispersant. In the mixed liquid, the mass M CNT Mass M of CMC CMC Ratio of M CMC / M CNT The mixture was shaken in the range of 1:9 to 9 (CNT:CMC = 9:1 to 1:9). No additives such as thickeners were added.

[0092] Next, the mixed solution was subjected to underwater head-on collision. The underwater head-on collision was performed using a wet atomization device "Starburst Lab" (model name: HJP-25005) manufactured by Sugino Machine Co., Ltd. The diameter of the nozzle hole from which the mixed solution was discharged was set to 100 μm, and the discharge pressure of the mixed solution was set to 200 MPa. The mixed solution was passed through the wet atomization device two times. In this way, a dispersion containing CNT, CMC, and water was produced.

[0093] The above dispersion was applied to a support layer (Hamayu (registered trademark) manufactured by Hokuetsu Corporation, basis weight 30 g / m) using a die coater. 2 ), and then dried at 60°C to 70°C to evaporate the water, producing coated paper consisting of a support layer and a coating layer.

[0094] In this manner, a coated paper was prepared as an electromagnetic noise suppression sheet.

[0095] Evaluation Method The electromagnetic noise suppression performance of the above 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 equipment used was a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ, connected to a test fixture "TF-18C" manufactured by KEYCOM. The measurement was performed in accordance with "IEC62333." The measurement frequency was 500 MHz to 18 GHz.

[0096] Furthermore, the thickness of the coating layer of the above coated paper was measured by SEM.

[0097] Furthermore, the surface resistivity of the coating layer of the coated paper was measured using a Loresta-AX MCP-T370 measuring instrument manufactured by Mitsubishi Chemical Analytech Co., Ltd. The measurement was carried out in accordance with JIS K 7194.

[0098] Furthermore, the in-plane thermal conductivity was measured based on the above formula (1). Thermal conductivity measurements were performed on the dry film, not the coated paper, because the CNT-containing layer needed to be thick. The dry film was prepared by placing the dispersion containing CNT, CMC, and water in an 8.5 cm diameter dish and drying it at 50°C for 12 hours to evaporate the water. Thermal conductivity measurements were performed because the CNT-containing layer needed to be thick. Thermal diffusivity was measured by the laser flash method using a NETZSCH LFA567 HyperFlash. Specific heat was measured using a TA Instruments Discovery DSC 25. Density was calculated from the volume and weight of the dry film.

[0099] 3.1.3. Evaluation Results Figure 6 shows the Rtp of coated papers with varying CNT to CMC mass ratios, as well as the coating thickness, surface resistivity, and thermal conductivity of the dried film.

[0100] As shown in Figure 6, it was found that when the CNT mass ratio is smaller than CNT:CMC = 1:3, the Rtp becomes extremely small. Furthermore, it was found that when the CNT mass ratio is larger than CNT:CMC = 5:1, the thermal conductivity becomes extremely poor. Therefore, it was found that by setting the CNT:CMC ratio in the range of 5:1 to 1:3, both the electromagnetic noise suppression performance and the thermal conductivity can be improved. Furthermore, it was found that by setting the CNT:CMC ratio in the range of 3:1 to 1:1, both the electromagnetic noise suppression performance and the thermal conductivity can be further improved.

[0101] It was found that there is a correlation between Rtp and surface resistivity, and that the higher the surface resistivity, the larger the Rtp tends to be.

[0102] The thermal conductivity was highest at a CNT:CMC ratio of 1:1. When the mass ratio of CMC was greater than CNT:CMC=1:1, the thermal diffusivity decreased, resulting in a lower thermal conductivity. When the mass ratio of CNT was greater than CNT:CMC=1:1, the thermal diffusivity increased, but the density decreased, resulting in a lower thermal conductivity.

[0103] Figure 7 is a graph showing the Rtp of coated paper versus frequency when the mass ratio of CNT to CMC is varied. The Rtp values ​​shown in Figure 6 were read from the graph in Figure 7 at 6 GHz and 15 GHz. Figure 7 also evaluates samples with only the support layer, which is not coated with a coating layer.

[0104] As shown in Figure 7, Nos. 4 to 10 (CNT:CMC = 9:1 to 1:1) showed roughly the same tendency with respect to frequency. However, for Nos. 4 to 10, in the frequency range of 3 GHz to 5 GHz, the Rtp tended to decrease as the CNT mass ratio increased. On the other hand, at frequencies higher than 8 GHz, the Rtp tended to increase as the CNT mass ratio increased.

[0105] 3.2. Second experimental example In the second experimental example, the Rtp of coated paper was measured with a CNT:CMC ratio of 1:1 and the coating layer thickness was varied. The method for producing and evaluating the coated paper was the same as in the first experimental example.

[0106] Figure 8 is a table showing the RTP of coated paper when the coating thickness is varied. Figure 9 is a graph showing the RTP of coated paper versus frequency when the coating thickness is varied. The RTP values ​​shown in Figure 8 were taken from the graph in Figure 9 at 6 GHz and 15 GHz.

[0107] As shown in Figures 8 and 9, at frequencies between 2 GHz and 7 GHz, coated papers B and C, which have low surface resistivity, had a higher Rtp than coated paper A. On the other hand, at frequencies higher than 12 GHz, coated paper A, which has a high surface resistivity, had a higher Rtp than coated papers B and C.

[0108] 3.3. Third Experimental Example In the third experimental example, the Rtp of coated paper was measured with a CNT:CMC ratio of 1:1 and the number of passes of the mixed solution through the wet atomization device was changed. Other than changing the number of passes, the method of producing and evaluating the coated paper was the same as in the first experimental example.

[0109] Figure 10 is a table showing the Rtp of coated paper when the number of passes is varied. Figure 11 is a graph showing the Rtp of coated paper versus frequency when the number of passes is varied. The Rtp values ​​shown in Figure 10 were read from the graph in Figure 11 at 6 GHz and 15 GHz.

[0110] The trends were similar for all coated papers except for the "untreated" coated paper with zero passes, i.e., no treatment with the wet atomizer. Coated papers with one or more passes (treated) had a higher Rtp than untreated coated papers in the range of 500 MHz to 9 GHz.

[0111] The above-described embodiment and modifications are merely examples, and the present invention is not limited to these. For example, the embodiments and modifications can be combined as appropriate.

[0112] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, the present invention includes configurations that are substantially identical to the configurations described in the embodiments. A substantially identical configuration means, for example, a configuration that has the same function, method, and result, or a configuration that has the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configurations described in the embodiments are replaced. The present invention also includes configurations that achieve the same effects or purposes as the configurations described in the embodiments. The present invention also includes configurations in which publicly known technology is added to the configurations described in the embodiments. [Explanation of symbols]

[0113] 10...coating layer, 20...support layer, 30...adhesive layer, 40...peeling layer, 50...overcoat layer, 100...electromagnetic noise suppression sheet

Claims

1. preparing a dispersion containing carbon nanotubes, sodium carboxymethyl cellulose, and water; drying the dispersion to form a first layer; Including, In the step of preparing the dispersion, only the sodium carboxymethyl cellulose is used as a dispersant, In the dispersion, the ratio of the mass of the sodium carboxymethyl cellulose to the mass of the carbon nanotubes is 1 / 5 or more and 3 or less, In the step of preparing the dispersion, the carbon nanotubes, the sodium carboxymethyl cellulose, and the water are mixed to prepare a mixture, and the mixture is discharged by an underwater head-on collision method at a pressure of 150 MPa or more and 250 MPa or less to disperse the carbon nanotubes; In the method for producing an electromagnetic noise suppression sheet, the fiber length of the carbon nanotubes in the mixed liquid is 15 μm or more and 35 μm or less.

2. The method for producing an electromagnetic noise suppression sheet according to claim 1 , wherein the ratio is 1 or less.

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

4. The method for producing an electromagnetic noise suppression sheet according to claim 1 , further comprising the step of applying the dispersion to a second layer before the step of forming the first layer.

5. The method for producing an electromagnetic noise suppression sheet according to claim 1 , wherein the carbon nanotubes have a diameter of 8 nm to 15 nm.

6. The weight average molecular weight of the sodium carboxymethyl cellulose is 11,000 or more and 15,000 or less.

6. The method for producing an electromagnetic noise suppression sheet according to claim 1, wherein the average molecular weight of the electromagnetic noise suppression sheet is 1,000 or less.

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