Electromagnetic noise suppression sheet and method of manufacturing the same

Abstract

Provided is an electromagnetic wave noise suppressing sheet that has an electromagnetic wave noise suppressing function, exhibits high thermal conductivity, and is inexpensive.　An electromagnetic wave noise suppressing sheet 100 according to the present invention includes a first layer 10 that contains carbon nanotubes, an inorganic filler, and carboxymethyl cellulose, wherein the inorganic filler is at least one substance selected from the group consisting of graphite, carbon black, and inorganic pigments, and the ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is in the range of 1 / 4 to 2.

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. Due to 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] Furthermore, since the above-mentioned carbon nanotubes are expensive, if a part of the carbon nanotubes can be replaced with other inorganic materials while maintaining the electromagnetic wave noise suppression performance, costs can be reduced.

[0007] An object of some aspects of the present invention is to provide an electromagnetic noise suppression sheet that has high electromagnetic noise suppression performance and thermal conductivity, and is inexpensive.An object of some aspects of the present invention is to provide a method for producing an electromagnetic noise suppression sheet that has high electromagnetic noise suppression performance and thermal conductivity, and is inexpensive. [Means for solving the problem]

[0008] One aspect of the electromagnetic noise suppression sheet according to the present invention is Carbon nanotubes, inorganic filler, and carboxymethyl cellulose sodium and a first layer including: the inorganic filler is at least one selected from the group consisting of graphite, carbon black, and inorganic pigments; The ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is 1 / 4 or more and 2 or less.

[0009] In one embodiment of the electromagnetic noise suppression sheet, The inorganic filler may be the graphite.

[0010] In one embodiment of the electromagnetic noise suppression sheet, The inorganic filler may be the inorganic pigment.

[0011] In one embodiment of the electromagnetic noise suppression sheet, The inorganic pigment may be kaolin.

[0012] In any one of the above-described electromagnetic noise suppression sheets, The ratio may be less than or equal to 1.

[0013] In any one of the above-described electromagnetic noise suppression sheets, The ratio may be 1 or greater.

[0014] In any one of the above-described electromagnetic noise suppression sheets, The first layer may include a second layer disposed thereon.

[0015] One aspect of the method for producing an electromagnetic noise suppression sheet according to the present invention is to Carbon nanotubes, inorganic filler, and carboxymethyl cellulose sodium and water; drying the dispersion to form a first layer; Including, the inorganic filler is at least one selected from the group consisting of graphite, carbon black, and inorganic pigments; In the dispersion, the ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is 1 / 4 or more and 2 or less.

[0016] In one embodiment of the method for producing an electromagnetic noise suppression sheet, The inorganic filler may be the graphite.

[0017] In one embodiment of the method for producing an electromagnetic noise suppression sheet, The inorganic filler may be the inorganic pigment.

[0018] In one embodiment of the method for producing an electromagnetic noise suppression sheet, The inorganic pigment may be kaolin.

[0019] 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]

[0020] The electromagnetic noise suppression sheet according to the present invention comprises carbon nanotubes, an inorganic filler, and carboxymethyl cellulose. sodium and a first layer including the inorganic filler, wherein the inorganic filler is at least one selected from the group consisting of graphite, carbon black, and inorganic pigments. The ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is 1 / 4 or more and 2 or less, so that the electromagnetic noise suppression performance and thermal conductivity are high, and the cost is low. [Brief explanation of the drawings]

[0021] [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 carbon black or graphite is used as the inorganic filler. [Figure 7] FIG. 7 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 4:1. [Figure 8] FIG. 8 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 1:1. [Figure 9] FIG. 9 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 1:2. [Figure 10] FIG. 10 is a graph showing the transmission attenuation rate of coated paper versus frequency when the carbon nanotube:inorganic filler ratio is 1:4. [Figure 11] FIG. 11 is a table showing the transmission attenuation rate of coated paper when inorganic pigments are used as inorganic fillers. [Figure 12]FIG. 12 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 4:1. [Figure 13] FIG. 13 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 1:1. [Figure 14] FIG. 14 is a graph showing the transmission attenuation rate of coated paper versus frequency when the ratio of carbon nanotubes to inorganic filler is 1:2. [Figure 15] FIG. 15 is a graph showing the transmission attenuation rate of coated paper versus frequency when the carbon nanotube:inorganic filler ratio is 1:4. DETAILED DESCRIPTION OF THE INVENTION

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 the components will be described below in order.

[0026] 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.

[0027] The surface resistivity of the coating layer 10 is, for example, 400 Ω / □ or less, preferably 300 Ω / □ or less, and more preferably 200 Ω / □ or less. If the surface resistivity of the coating layer 10 is 400 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."

[0028] 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).

[0029] The thermal conductivity of the coating layer 10 in the in-plane direction is, for example, 1.10 W / m·K or more, preferably 1.20 W / m·K or more, and more preferably 1.50 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 1.10 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.

[0030] λ=α×C×ρ (1)

[0031] 1.1.1.2. Materials The coating layer 10 is made of a carbon nanotube (hereinafter also referred to as "CNT"), an inorganic filler, and carboxymethyl cellulose. sodium (hereinafter also referred to as "CMC"). The coating layer 10 may be composed of only CNTs, inorganic filler, and CMC. Each material will be explained below in turn.

[0032] (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 contain only MWCNTs. Both ends of the CNTs may be closed or open.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The BET specific surface area of ​​CNT is, for example, 50 m 2 / 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.

[0037] 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. When the CNT content is 0.1% by mass or more, the electromagnetic wave noise suppression performance can be improved. When the CNT content is 10.0 mass% If the content is below this, a dispersion liquid with good CNT dispersibility can be prepared when forming the coating layer 10.

[0038] (2) Inorganic filler The inorganic filler contained in the coating layer 10 is at least one selected from the group consisting of graphite, carbon black, and inorganic pigments. The inorganic filler may be one selected from this group, or may contain two or more selected from this group in any ratio.

[0039] The inorganic filler contained in the coating layer 10 may be graphite. When the inorganic filler is graphite, the thermal conductivity can be increased compared to when the inorganic filler is carbon black or an inorganic pigment. The BET specific surface area of ​​the graphite is not particularly limited, but is preferably 1 m 2 / g or more 100m 2 / g or less, and more preferably 5m 2 / g or more 20m 2 / g or less.

[0040] The inorganic filler contained in the coating layer 10 may be carbon black. Multiple carbon black particles are connected together to form a structure. The characteristics of carbon black are mainly determined by the particle size and the length of the structure. The amount of iodine adsorption depends on the particle size, and the larger the iodine adsorption, the smaller the particle size. The amount of DBP (Dibutyl Phthalate) absorption depends on the length of the structure, and the larger the DBP absorption, the longer the structure.

[0041] The iodine adsorption capacity of the carbon black contained in the coating layer 10 is, for example, 20 mg / g or more and 160 mg / g or less, preferably 120 mg / g or more. If the iodine adsorption capacity of the carbon black is 120 mg / g or more, the electromagnetic noise suppression performance can be improved compared to when the iodine adsorption capacity is less than 120 mg / g. The DBP absorption capacity of the carbon black is, for example, 20 ml / 100 g or more and 200 ml / 100 g or less, preferably 50 ml / 100 g or more. If the DBP adsorption capacity of the carbon black is 50 ml / 100 g or more, the electromagnetic noise suppression performance can be improved compared to when the DBP adsorption capacity is less than 50 ml / 100 g. The BET specific surface area of ​​the carbon black is, for example, 80 m 2 / g or more 160m 2 / g below is.

[0042] The iodine adsorption amount of carbon black can be determined in accordance with "JIS K 6217-1." The DBP absorption amount of carbon black can be determined in accordance with "JIS K 6217-4." The BET specific surface area of ​​carbon black can be determined in accordance with "JIS K 6217-2."

[0043] The inorganic filler contained in the coating layer 10 may be an inorganic pigment. An inorganic pigment is a chemically inorganic pigment made from an oxide obtained by a chemical reaction of natural ores or metals. If the inorganic filler is an inorganic pigment, costs can be reduced compared to when the inorganic filler is graphite or carbon black. Examples of inorganic pigments include kaolin, light calcium carbonate, and heavy calcium carbonate, and kaolin is preferred. If the inorganic pigment is kaolin, electromagnetic wave noise suppression performance can be improved compared to when the inorganic pigment is light calcium carbonate or heavy calcium carbonate.

[0044] In the coating layer 10, the mass M of the CNT CNT Mass of inorganic filler M F Ratio of M F / M CNT The ratio M is 1 / 4 or more and 2 or less (CNT:inorganic filler = 4:1 to 1:2). F / M CNT If the ratio M is 1 / 4 or more, the electromagnetic noise suppression performance and thermal conductivity can be improved. F / M CNT If the ratio M is 2 or less, costs can be reduced. F / M CNT can be measured by thermal gravimetric analysis (TGA).

[0045] When the inorganic filler contained in the coating layer 10 is graphite, the ratio M F / M CNT may be equal to or less than 1. F / M CNT If is less than or equal to 1, the ratio M F / MCNT The electromagnetic wave noise suppression performance for frequencies of 12 GHz or less can be improved compared to when the ratio M is greater than 1. When the inorganic filler contained in the coating layer 10 is graphite, F / M CNT may be equal to or greater than 1. F / M CNT If is greater than or equal to 1, the ratio M F / M CNT The thermal conductivity can be increased compared to when is smaller than 1. Furthermore, the electromagnetic noise suppression performance can be increased for frequencies of 14 GHz or higher.

[0046] When the inorganic filler contained in the coating layer 10 is kaolin, the ratio M F / M CNT may be equal to or less than 1. F / M CNT If is less than or equal to 1, the ratio M F / M CNT The electromagnetic noise suppression performance for frequencies of 7 GHz or less can be improved compared to when the ratio M is greater than 1. When the inorganic filler contained in the coating layer 10 is kaolin, the ratio M F / M CNT may be equal to or greater than 1. F / M CNT If is greater than or equal to 1, the ratio M F / M CNT The thermal conductivity can be increased compared to when R is smaller than 1. Furthermore, the electromagnetic noise suppression performance can be increased for frequencies of 9 GHz or higher.

[0047] (3) Carboxymethylcellulose sodium (CMC) CMC functions as a dispersant for dispersing CNTs when forming the coating layer 10. For example, only CMC is used as a dispersant for CNTs. The "dispersant" refers to an additive that disperses CNTs in water and contributes to preventing aggregation and sedimentation of CNTs. Dispersion of CNTs By using only CMC as a dispersant, it is possible to prevent the inclusion of air bubbles, etc., compared to, for example, when an anionic surfactant or the like is added as a dispersant in addition to CMC.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] In the coating layer 10, the total mass M of the CNTs and the inorganic filler SUM Mass M of CMC CMC Ratio of M CMC / M SUM is 1 / 5 or more and 3 or less, preferably 1 / 3 or more and 1 or less. CMC / M SUM If the ratio is 1 / 5 or more, the CNTs have good dispersibility. liquid The ratio M CMC / M SUM If the ratio M is 3 or less, the electromagnetic noise suppression performance can be improved. CMC / MSUM can be determined by thermogravimetric analysis.

[0052] (4) Additives The coating layer 10 may contain various additives such as a thickener, a preservative, and a pH adjuster, as needed.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] The basis weight of the support layer 20 is 40g / m 2In 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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 12The 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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 mixture that is more environmentally friendly than when an organic solvent is used as a solvent.

[0074] 2.4.2. Dispersion by underwater collision method Next, the CNTs contained in the prepared mixture are dispersed by underwater counter-impingement to prepare a dispersion. In the process of preparing the dispersion, for example, only CMC is used as the dispersant. By dispersing the CNTs contained in the mixture by underwater counter-impingement, the CNTs can be dispersed with good dispersibility even if the mixture contains only CMC as the dispersant. This makes it possible to prepare a dispersion with good CNT dispersibility.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 2.4.3. Mixing of inorganic fillers Next, an inorganic filler is mixed into the prepared dispersion to prepare a dispersion containing CNTs, an inorganic pigment, CMC, and water. The method for mixing the inorganic pigment is not particularly limited, but may be performed using a homogenizer, for example.

[0084] In the dispersion, the mass of the CNTs, M CNT Mass of inorganic filler M F Ratio of M F / M CNT is the ratio M in the coating layer 10 described above. F / M CNT Similarly, in the dispersion, the total mass of the CNTs and the inorganic filler, M SUM Mass M of CMC CMC Ratio of M CMC / M SUM is the ratio M in the coating layer 10 described above. CMC / M SUM is the same as

[0085] The concentration and viscosity of the dispersion can be increased by adding an inorganic filler. To further increase the viscosity of the dispersion, a thickener may be added to the dispersion. 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 copolymers; 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.

[0086] The viscosity of the dispersion mixed with the inorganic filler 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 dispersion is 100 mPa·s or more, the dispersion can be easily applied to the support layer 20 using a roller as described above. If the viscosity of the dispersion is 4000 mPa·s or less, stagnation during the dispersion application process is suppressed, contamination is less likely, and the dispersion can be easily applied. The viscosity of the dispersion can be measured using a viscometer.

[0087] In the above, an example was described in which CNTs, CMC, and water are mixed to prepare a mixed liquid, the CNTs contained in the mixed liquid are dispersed by underwater head-on collision, and then an inorganic filler is mixed in. However, the dispersion preparation process is not limited to this example. For example, CNTs, an inorganic pigment, CMC, and water may be mixed to prepare a mixed liquid, and the mixed liquid may be subjected to underwater head-on collision to disperse the CNTs. Alternatively, for example, an inorganic pigment powder and a CMC powder may be added to a CNT-containing liquid that has been subjected to underwater head-on collision, and then mixed to prepare a dispersion in which CNTs are dispersed.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] Through the above steps, the electromagnetic noise suppression sheet 100 can be manufactured.

[0093] 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.

[0094] The material used for the overcoat solution is not particularly limited, but for example, polyethylene ethylene 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, phenolic 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.

[0095] 2.7. Variations FIG. 5 is a flowchart illustrating a method for manufacturing the electromagnetic noise suppression sheet 100 according to this embodiment.

[0096] 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).

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] 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 a degree of etherification of 0.7. Only CMC was used as the dispersant. No additives such as thickeners were added.

[0104] 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.

[0105] Next, carbon black or graphite was added as an inorganic filler to the dispersion and mixed to produce a dispersion containing the inorganic filler. This resulted in a dispersion containing CNTs, inorganic filler, CMC, and water. A homogenizer called "Biomixer BM-2" manufactured by Nippon Seiki Seisakusho Co., Ltd. was used for mixing. The mixing time was 5 minutes.

[0106] The carbon black used was "Asahi Thermal" and "SB720" manufactured by Asahi Carbon Co., Ltd. The graphite used was scaly graphite powder "J-CPB" manufactured by Nippon Graphite Industries Co., Ltd.

[0107] In the dispersion, the mass of the CNTs, M CNT and the mass of the inorganic filler M F Total of M SUM Mass of inorganic filler M F Ratio of M F / M CNT The mixture was shaken in the range of 1 / 4 to 4 (CNT:inorganic filler = 4:1 to 1:4).

[0108] In addition, in the dispersion, the total mass of the CNTs and the inorganic filler, M SUM Mass M of CMC CMC Ratio of M CMC / M SUM The dispersion was prepared so that the ratio of CNT to CMC was 1:1 ((CNT+inorganic filler):CMC=1:1). The dispersion was also prepared so that the total content of CNT, inorganic pigment, and CMC was 5% by mass.

[0109] 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.

[0110] In this manner, a coated paper was prepared as an electromagnetic noise suppression sheet.

[0111] 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.

[0112] Furthermore, the thickness of the coating layer of the above coated paper was measured by SEM.

[0113] 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.

[0114] Furthermore, the in-plane thermal conductivity was measured based on the above formula (1). Thermal conductivity measurements were performed on dry films because the CNT-containing layer needed to be thick. The dry films were prepared by placing the above dispersion containing CNT, inorganic filler, CMC, and water in an 8.5 cm diameter dish and drying it at 50°C for 12 hours to evaporate the water. 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.

[0115] 3.1.3. Evaluation Results Figure 6 is a table showing the Rtp of coated paper with varying mass ratios of CNT and inorganic filler. Furthermore, Figure 6 shows the thickness of the coating layer, the surface resistivity of the coating layer, and the thermal conductivity of the dried film. Figures 7 to 10 are graphs showing the Rtp of coated paper versus frequency. Figure 7 is a graph for a CNT:inorganic filler ratio of 4:1. Figure 8 is a graph for a CNT:inorganic filler ratio of 1:1. Figure 9 is a graph for a CNT:inorganic filler ratio of 1:2. Figure 10 is a graph for a CNT:inorganic filler ratio of 1:4. The Rtp values ​​shown in Figure 6 were read from the graphs shown in Figures 7 to 10 at 6 GHz and 15 GHz.

[0116] As shown in Figures 6 to 10, regardless of the type of inorganic filler, coated paper with a CNT:inorganic filler ratio of 4:1 to 1:2 had a higher Rtp than coated paper with a CNT:inorganic filler ratio of 1:4. As shown in Figure 6, all samples exhibited high thermal conductivity, greater than 1.10. Coated paper with a CNT:inorganic filler ratio of 1:4 had a lower thermal conductivity than coated paper with a CNT:inorganic filler ratio of 1:2. We found that by keeping the CNT:CMC ratio in the range of 4:1 to 1:2, it is possible to improve both electromagnetic noise suppression performance and thermal conductivity, while also reducing costs.

[0117] As shown in Figure 6, the dried film using graphite had a higher thermal conductivity than the dried film using carbon black. This indicates that graphite is an inorganic filler that is more suitable than carbon black for achieving both electromagnetic noise suppression performance and thermal conductivity.

[0118] As shown in Figures 6 to 9, the coated papers with CNT:graphite ratios of 4:1 and 1:1 had higher electromagnetic noise suppression performance at frequencies below 12 GHz than the coated paper with CNT:graphite ratio of 1:2. On the other hand, at frequencies above 14 GHz, the coated papers with CNT:graphite ratios of 1:1 and 1:2 had higher electromagnetic noise suppression performance than the CNT:graphite ratio of 4:1. As shown in Figure 6, the dried films with CNT:graphite ratios of 1:1 and 1:2 had higher thermal conductivity than the dried film with CNT:graphite ratio of 4:1.

[0119] As shown in Figures 6 to 10, coated paper using "SB720" as an inorganic filler had a higher Rtp than coated paper using "Asahi Thermal." The iodine adsorption capacity of "SB720" was 138 mg / g, while that of "Asahi Thermal" was 27 mg / g. The DBP absorption capacity of "SB720" was 59 ml / 100 g, while that of "Asahi Thermal" was 28 ml / 100 g. Therefore, it was found that carbon black with higher iodine adsorption and DBP absorption capacity tends to have a higher Rtp.

[0120] 3.2. Second experimental example Second Real Experience In this example, an inorganic pigment was used as the inorganic filler instead of carbon black or graphite. Except for the use of an inorganic pigment, the preparation method and evaluation method were the same as those in the first experimental example.

[0121] The inorganic fillers used were kaolin, light calcium carbonate (hereinafter referred to as "light calcium carbonate"), and heavy calcium carbonate (hereinafter referred to as "heavy calcium carbonate"). The kaolin used was "Hydrogloss 90" manufactured by Imerys Minerals Japan Co., Ltd. The light calcium carbonate used was "Tama Pearl TP121" manufactured by Okutama Kogyo Co., Ltd. The heavy calcium carbonate used was "Softon 1500" manufactured by Bihoku Funka Kogyo Co., Ltd.

[0122] FIG. 11 is a table showing the Rtp of coated paper with varying mass ratios of CNT and inorganic filler. Furthermore, FIG. 11 shows the thickness of the coating layer, the surface resistivity of the coating layer, and the thermal conductivity of the dried film. FIGS. 12 to 15 are graphs showing the Rtp of coated paper versus frequency. FIG. 12 is a graph for a CNT:inorganic filler ratio of 4:1. FIG. 13 is a graph for a CNT:inorganic filler ratio of 1:1. FIG. 14 is a graph for a CNT:inorganic filler ratio of 1:2. FIG. 15 is a graph for a CNT:inorganic filler ratio of 1:4. The Rtp values ​​shown in FIG. 11 were obtained by reading the values ​​at 6 GHz and 15 GHz from the graphs shown in FIGS. 12 to 15.

[0123] As shown in Figures 11 to 15, regardless of the type of inorganic filler, coated paper with a CNT:inorganic filler ratio of 4:1 to 1:2 had a higher Rtp than coated paper with a CNT:inorganic filler ratio of 1:4. As shown in Figure 11, all samples exhibited high thermal conductivity, greater than 1.10. It was found that by keeping the CNT:CMC ratio in the range of 4:1 to 1:2, it is possible to improve both electromagnetic noise suppression performance and thermal conductivity, while also achieving cost reduction.

[0124] As shown in Figures 6 and 11, coated paper using inorganic pigments, which are non-conductive, showed almost no difference in Rtp compared to coated paper using conductive carbon black and graphite. Regarding thermal conductivity, the dried film using inorganic pigments did not reach the dried film using graphite, but it was comparable to the carbon black "SB720." This is because, although the thermal diffusivity of inorganic pigments is lower than that of carbon black, inorganic pigments have higher density and specific heat capacity than carbon black.

[0125] As shown in Figures 11 to 15, coated papers using kaolin tended to have a higher Rtp than coated papers using light calcium carbonate and heavy calcium carbonate. It was found that kaolin is an inorganic filler that is more suitable for achieving both electromagnetic noise suppression performance and thermal conductivity than light calcium carbonate and heavy calcium carbonate. Kaolin has a higher aspect ratio than light calcium carbonate and heavy calcium carbonate, and is more likely to become smooth. Therefore, kaolin has a surface resistivity of low and Rtp is large.

[0126] As shown in Figures 11 to 14, the coated papers with CNT:kaolin ratios of 4:1 and 1:1 had higher electromagnetic noise suppression performance at frequencies below 7 GHz than the coated paper with CNT:kaolin ratio of 1:2. On the other hand, at frequencies above 9 GHz, the coated papers with CNT:kaolin ratios of 1:1 and 1:2 had higher electromagnetic noise suppression performance than the coated paper with CNT:kaolin ratio of 4:1. As shown in Figure 11, the dried films with CNT:kaolin ratios of 1:1 and 1:2 had higher thermal conductivity than the dried film with CNT:kaolin ratio of 4:1.

[0127] 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.

[0128] 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]

[0129] 10...coating layer, 20...support layer, 30...adhesive layer, 40...peeling layer, 50...overcoat layer, 100...electromagnetic noise suppression sheet

Claims

1. a first layer including carbon nanotubes, an inorganic filler, and sodium carboxymethyl cellulose; the inorganic filler is graphite; a ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is 1 / 4 or more and 2 or less; The electromagnetic noise suppression sheet, wherein the first layer does not contain any of resin, rubber, oil, or organic solvent.

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

3. The electromagnetic noise suppression sheet according to claim 1 , wherein the ratio is 1 or greater.

4. The electromagnetic noise suppression sheet according to claim 1 , further comprising a second layer on which the first layer is provided.

5. A step of preparing a dispersion containing carbon nanotubes, an inorganic filler, sodium carboxymethyl cellulose, and water; drying the dispersion to form a first layer; Including, the inorganic filler is graphite; In the dispersion, the ratio of the mass of the inorganic filler to the mass of the carbon nanotubes is 1 / 4 or more and 2 or less, The method for producing an electromagnetic noise suppression sheet, wherein the dispersion does not contain any of resin, rubber, oil, and organic solvent.

6. The method for producing an electromagnetic noise suppression sheet according to claim 5 , further comprising the step of applying the dispersion to a second layer before the step of forming the first layer.

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