Electromagnetic wave shielding composition, method for producing substrate with electromagnetic wave shielding sheet, electromagnetic wave shielding sheet and printed wiring board

Abstract

To provide: an electromagnetic wave-shielding composition comprising powder of a tetrafluoroethylene-based polymer and a metallic magnetic filler; and a production method of a sheet with an electromagnetic wave-shielding sheet attached, which can be obtained from the composition, and to provide an electromagnetic wave-shielding sheet containing a tetrafluoroethylene-based polymer and a metallic magnetic filler; and a printed wiring board comprising the electromagnetic wave-shielding sheet.SOLUTION: An electromagnetic wave-shielding composition comprises: powder of a tetrafluoroethylene-based polymer of which the specific surface area is 25 m2 / g or less, the average grain size is 50 μm or less, and the melting temperature is 260°C or higher and 320°C or lower; and a metal magnetic material filler. The mass ratio of the metallic magnetic filler to the tetrafluoroethylene-based polymer is 0.1 or larger.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave shielding composition containing a tetrafluoroethylene-based polymer powder and a metal magnetic filler, and a method for producing a substrate with an electromagnetic wave shielding sheet obtained from the composition.The present invention also relates to an electromagnetic wave shielding sheet containing a tetrafluoroethylene-based polymer and a metal magnetic filler, and a printed wiring board provided with the electromagnetic wave shielding sheet. [Background technology]

[0002] Electromagnetic waves generated by printed wiring boards, electronic components, antennas, etc. interfere with each other, potentially affecting other electrical circuits and electronic components and causing malfunctions. Therefore, it is necessary to use electromagnetic wave shielding materials to block such electromagnetic noise and prevent malfunctions of various devices. High-frequency printed wiring boards are not only required to block electromagnetic noise, but also to adhere well to the substrate because non-adhesive materials such as fluororesins are used as substrate materials. Furthermore, because high-frequency printed wiring boards generate a large amount of heat, electromagnetic wave shielding materials are also required to have heat resistance and thermal conductivity.

[0003] Tetrafluoroethylene polymers have attracted attention as electromagnetic wave shielding materials due to their excellent physical properties such as electrical insulation, heat resistance, and thermal conductivity. For example, Patent Document 1 discloses an electromagnetic wave shielding material formed into a sheet by compounding polytetrafluoroethylene with carbon. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-323887 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electromagnetic wave shielding material described in Patent Document 1 has poor adhesion to high-frequency printed wiring substrates due to the non-stickiness of polytetrafluoroethylene.In addition, the dispersibility of carbon in polytetrafluoroethylene is still insufficient, so the electromagnetic wave shielding performance is also unsatisfactory. Therefore, there is a demand for an electromagnetic wave shielding material that has high electromagnetic wave shielding ability, excellent adhesion to printed wiring boards, and sufficient heat resistance and thermal conductivity.

[0006] The present inventors discovered that by using a powder of a specific tetrafluoroethylene-based polymer and a metal magnetic filler, an electromagnetic wave shielding material having high electromagnetic wave shielding ability and sufficient adhesiveness, heat resistance, and thermal conductivity can be obtained, and this discovery led to the completion of the present invention.

[0007] The present invention aims to provide an electromagnetic wave shielding composition containing a tetrafluoroethylene-based polymer powder and a metal magnetic filler, a method for producing a substrate with an electromagnetic wave shielding sheet obtained from the composition, an electromagnetic wave shielding sheet containing a tetrafluoroethylene-based polymer and a metal magnetic filler, and a printed wiring board equipped with the electromagnetic wave shielding sheet. [Means for solving the problem]

[0008] The present invention has the following aspects. <1> Specific surface area is 25m 2 Electromagnetic wave shielding composition comprising: a powder of a tetrafluoroethylene-based polymer having a molecular weight of 1000 ppm or less, an average particle size of 50 μm or less, and a melting temperature of 260°C or higher and 320°C or lower; and a metal magnetic filler, wherein the mass ratio of the metal magnetic filler to the tetrafluoroethylene-based polymer is 0.1 or higher. <2> The tetrafluoroethylene polymer has a main chain carbon number of 1×10 6 Each carbonyl-containing group has 10 to 5,000 carbonyl-containing groups. <1> Electromagnetic wave shielding composition. <3> The specific surface area of ​​the powder is 1m 2 / g or more 8m2 / g or less, <1> or <2> Electromagnetic wave shielding composition. <4> The average particle size of the powder is 1 μm or more and 8 μm or less. <1> from <3> Electromagnetic wave shielding composition according to any one of the above. <5> The metal magnetic filler is a filler containing at least one magnetic material selected from the group consisting of gold, silver, copper, iron, aluminum, titanium, cobalt, nickel, copper oxide, iron oxide, carbonyl iron, and ferrite. <1> from <4> Electromagnetic wave shielding composition according to any one of the above. <6> The metal magnetic filler is needle-shaped or wire-shaped and has an aspect ratio of 1000 or more. <1> from <5> Electromagnetic wave shielding composition according to any one of the above. <7> Also contains polytetrafluoroethylene powder, <1> from <6> Electromagnetic wave shielding composition according to any one of the above. <8> Further comprising a liquid dispersion medium, <1> from <7> Electromagnetic wave shielding composition according to any one of the above. <9> <1> from <7> a method for producing a substrate with an electromagnetic wave shielding sheet, the method comprising laminating an electromagnetic wave shielding sheet obtained by melt-extruding any one of the electromagnetic wave shielding compositions set forth above onto a substrate. <10> <8> The electromagnetic wave shielding composition according to claim 1, wherein the powder is sintered to form an electromagnetic wave shielding sheet. <11> An electromagnetic wave shielding sheet comprising a tetrafluoroethylene-based polymer having a melting temperature of 260°C or higher and 320°C or lower and a metal magnetic filler, wherein the mass ratio of the metal magnetic filler to the tetrafluoroethylene-based polymer is 0.1 or higher. <12> The fired product of the tetrafluoroethylene-based polymer powder and a metal magnetic filler are contained in the same layer. <11> Electromagnetic wave shielding sheet. <13> The thickness is 1 μm or more, <10> from <12> Electromagnetic wave shielding sheet. <14> <10> from <13> A printed wiring board provided with any one of the electromagnetic wave shielding sheets described above. <15> an electrical insulating layer of the printed wiring board containing a tetrafluoroethylene-based polymer, and at least a portion of the electromagnetic wave shielding sheet being in contact with the electrical insulating layer; <14> Printed wiring board. [Effects of the Invention]

[0009] The present invention provides a composition that provides electromagnetic shielding performance with high electromagnetic wave shielding effect and sufficient adhesiveness, heat resistance, and thermal conductivity, and a method for producing a substrate with an electromagnetic wave shielding sheet obtained from the composition.The present invention also provides an electromagnetic wave shielding sheet that provides high electromagnetic wave shielding effect and sufficient adhesiveness, heat resistance, and thermal conductivity, and a printed wiring board that includes the electromagnetic wave shielding sheet. DETAILED DESCRIPTION OF THE INVENTION

[0010] The following terms have the following meanings: The term "tetrafluoroethylene-based polymer" refers to a polymer containing units (hereinafter also referred to as TFE units) based on tetrafluoroethylene (hereinafter also referred to as TFE). The "melting temperature of a polymer" is the temperature corresponding to the maximum value of the melting peak as measured by differential scanning calorimetry (DSC). The "glass transition temperature of a polymer" is a value measured by analyzing a polymer using dynamic mechanical analysis (DMA). The "average particle size of a powder" is the volume-based cumulative 50% diameter (hereinafter also referred to as "D50") of the particle size obtained by measuring the particle size of the powder using a laser diffraction / scattering method. In other words, the particle size distribution of the particles is measured using a laser diffraction / scattering method, and a cumulative curve is calculated with the total volume of the particle group as 100%. The "average particle size of a powder" is the particle size at the point on the cumulative curve where the cumulative volume is 50%. The "specific surface area of ​​the powder" is a value measured by the gas adsorption (constant volume method) BET multipoint method. The "viscosity" is a value measured for the dispersion using a Brookfield viscometer at room temperature (25°C) and a rotation speed of 30 rpm. The measurement is repeated three times, and the average value of the three measured values ​​is used. The "thixotropy ratio" is the value (η1 / η2) calculated by dividing the viscosity η1 obtained by measuring the liquid composition at a rotation speed of 30 rpm by the viscosity η2 obtained by measuring the liquid composition at a rotation speed of 60 rpm. The term "unit based on a monomer" refers to an atomic group based on the monomer formed by polymerization of the monomer. The unit may be a unit formed directly by the polymerization reaction, or may be a unit in which a part of the unit is converted into a different structure by treating the polymer. Hereinafter, a unit based on monomer a may also be simply referred to as a "monomer a unit."

[0011] The electromagnetic wave shielding composition of the present invention (hereinafter also referred to as "the composition") has a specific surface area of ​​25 m 2 The powder (hereinafter also referred to as "this powder") of a tetrafluoroethylene-based polymer (hereinafter also referred to as "F polymer") having a densitometric coefficient of 1 / g or less, an average particle size of 50 μm or less, and a melting temperature of 260°C or more and 320°C or less, and a metal magnetic filler (hereinafter also referred to as "magnetic filler"), and the mass ratio of the magnetic filler to the F polymer is 0.1 or more. From this composition, an electromagnetic wave shield (for example, an electromagnetic wave shielding sheet) can be obtained that has a high electromagnetic wave shielding effect and is sufficiently endowed with adhesiveness, heat resistance, and thermal conductivity.

[0012] Tetrafluoroethylene-based polymers are highly rigid polymers, so their surface energy is low and their powders tend to aggregate. Furthermore, as described in prior art documents (Patent Document 1), tetrafluoroethylene-based polymers have low affinity with magnetic fillers, so it was thought that it would be difficult to obtain a composition in which magnetic fillers are well dispersed in tetrafluoroethylene-based polymers. However, the present inventors have discovered that by using a powder of a specific tetrafluoroethylene-based polymer that has a predetermined thermal melting property and can be said to have a relatively high degree of freedom in molecular movement, and that the specific surface area and particle size of the powder are within a predetermined range, aggregation of the powder is suppressed, the interaction between the powder and the magnetic filler is relatively enhanced, and a composition in which the magnetic filler is well dispersed is more easily formed. The inventors have also found that such compositions are excellent in dispersion stability and fluidity, and that molded articles formed from them have sufficient electromagnetic wave shielding effect, adhesiveness, heat resistance, and thermal conductivity.

[0013] The F polymer is a heat-meltable polymer. The melting temperature of the F polymer is 260°C or higher and 320°C or lower, preferably 285°C or higher and 320°C or lower. In this case, the electromagnetic wave shield obtained from this composition tends to have excellent heat resistance and uniformity. The glass transition point of the F polymer is preferably 50° C. or higher, more preferably 75° C. or higher. The glass transition point of the F polymer is preferably 150° C. or lower, more preferably 125° C. or lower.

[0014] The fluorine content of the F polymer is preferably 70% by mass or more. Tetrafluoroethylene-based polymers with a high fluorine content have excellent physical properties such as electrical properties, but have low affinity with magnetic fillers, which further reduces their dispersibility. By using the present powder in this composition, even when the fluorine content is high, the dispersion of the magnetic filler is excellent, the physical properties of the F polymer are not impaired, and a composition with excellent dispersibility of the magnetic filler can be obtained. The fluorine content of the F polymer is preferably 76% by mass or less.

[0015] The F polymer is preferably a polymer containing TFE units and units based on perfluoro(alkyl vinyl ether) (hereinafter also referred to as PAVE) (hereinafter also referred to as PAVE units) (hereinafter also referred to as PFA) or a copolymer containing TFE and units based on hexafluoropropylene (hereinafter also referred to as FEP), more preferably PFA or FEP, and even more preferably PFA. These polymers may further contain units based on other comonomers.

[0016] As the PAVE, CF2=CFOCF3, CF2=CFOCF2CF3 or CF2=CFOCF2CF2CF3 (hereinafter also referred to as PPVE) is preferred, and PPVE is more preferred.

[0017] The F polymer preferably has a carbonyl group-containing group, which tends to improve the affinity between the powder and the magnetic filler. The carbonyl group-containing group may be contained in a monomer unit in the F polymer or in a terminal group of the main chain of the polymer. The latter embodiment includes an F polymer having the carbonyl group-containing group as a terminal group derived from a polymerization initiator, a chain transfer agent, etc.

[0018] When the F polymer has a carbonyl group-containing group, the number of carbonyl group-containing groups in the F polymer is 1×10 6 Preferably, the number of carbonyl groups per particle is 10 to 5,000, more preferably 50 to 2,000. In this case, the affinity between the powder and the magnetic filler is easily improved. The number of carbonyl group-containing groups in the F polymer can be quantified by the polymer composition or the method described in WO 2020 / 145133.

[0019] The carbonyl group-containing group is preferably a carboxyl group, an alkoxycarbonyl group, an amide group, an isocyanate group, a carbamate group (-OC(O)NH), an acid anhydride residue (-C(O)OC(O)-), an imide residue (-C(O)NHC(O)-, etc.), or a carbonate group (-OC(O)O-), and more preferably an acid anhydride residue.

[0020] A preferred embodiment of the F polymer is a polymer containing TFE units and PAVE units and having a carbonyl group-containing group (hereinafter also referred to as a "carbonyl group-containing polymer"). This polymer has excellent dispersibility and forms microspherulites in molded articles obtained from the composition, which adhere well to the magnetic filler, thereby improving the properties of the resulting electromagnetic wave shielding material.

[0021] The carbonyl group-containing polymer is preferably a polymer containing TFE units, PAVE units, and units derived from a monomer having a carbonyl group-containing group.The carbonyl group-containing polymer preferably contains 90 mol% to 99 mol% of TFE units, 0.5 mol% to 9.97 mol% of PAVE units, and 0.01 mol% to 3 mol% of units derived from the monomer, based on the total units. The monomer is preferably itaconic anhydride, citraconic anhydride, or 5-norbornene-2,3-dicarboxylic anhydride (also known as himic acid anhydride; hereinafter also referred to as "NAH"). Specific examples of carbonyl group-containing polymers include the polymers described in WO 2018 / 16644.

[0022] The specific surface area of ​​this powder is 25m 2 / g or less, and 2 / g or less is preferable, and 5m 2 / g or less is more preferable. The specific surface area of ​​this powder is 1m 2 In this case, the aggregation of the powder is highly suppressed, and the interaction between the powder and the magnetic filler is particularly likely to be improved.

[0023] The average particle size (D50) of the present powder is 50 μm or less, preferably 20 μm or less, and more preferably 8 μm or less. The D50 of the present powder is preferably 1 μm or more, and more preferably 1.5 μm or more. In this case, the suppression of powder aggregation and the interaction between the present powder and the magnetic filler are highly balanced, which tends to particularly improve the dispersion stability of the present composition.

[0024] The powder may contain a resin or inorganic substance different from the F polymer. Specific examples of different resins include aromatic polyimides, aromatic maleimides, aromatic elastomers such as styrene elastomers, and aromatic polyamic acids. Specific examples of inorganic substances include metal oxides such as silicon oxide (silica), beryllium oxide, cerium oxide, alumina, soda alumina, magnesium oxide, zinc oxide, and titanium oxide, boron nitride, and magnesium metasilicate (steatite). It is preferable that at least a part of the surface of these inorganic substances is surface-treated. Examples of surface treatment agents used for the surface treatment include polyhydric alcohols such as trimethylolethane, pentaerythritol, and propylene glycol, saturated fatty acids such as stearic acid and lauric acid, and esters thereof, amines such as alkanolamines, trimethylamine, and triethylamine, paraffin wax, silane coupling agents, silicones, and polysiloxanes, with silane coupling agents being preferred.

[0025] The present powder containing a resin or inorganic material different from the F polymer preferably has a core-shell structure with the F polymer as the core and the resin or inorganic material as the shell, or a core-shell structure with the F polymer as the shell and the resin or inorganic material as the core. Such a present powder can be obtained, for example, by causing an F polymer powder and a resin or inorganic material powder to collide, aggregate, or coalesce to coalesce.

[0026] The magnetic filler used in the composition is a magnetic filler containing a metal, and is usually a ferromagnetic material. The metal in the magnetic filler may be a simple metal, an alloy, a metal oxide, a metal carbide, or a metal nitride. The magnetic filler may also be a ceramic filler. The metal magnetic filler is preferably a filler containing at least one magnetic material selected from the group consisting of gold, silver, copper, iron, aluminum, titanium, cobalt, nickel, copper oxide, iron oxide, carbonyl iron, and ferrite, more preferably a filler containing at least one magnetic material selected from the group consisting of nickel, copper oxide, iron oxide, carbonyl iron, and ferrite, and even more preferably nickel. Examples of ferrite include hexagonal ferrite and epsilon magnetic iron oxide, and strontium ferrite is preferred as the hexagonal ferrite.

[0027] The shape of the magnetic filler may be spherical, flake-like, leaf-like, dendritic, plate-like, needle-like, wire-like, or grape-like, with needle-like and wire-like shapes being preferred. The leaf-like shape refers to a shape in which the outer edge has at least one of a plurality of notches and branched leaves. The flake-like shape refers to a shape in which the outer edge does not have any notches or branched leaves. From the viewpoint of ease of handling and dispersibility, the average particle size of the magnetic filler is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 10 μm or less. The average particle size of the magnetic filler is preferably 10 nm or more, more preferably 100 nm or more, and even more preferably 1 μm or more. The average particle size is the D50 value, as with the present powder.

[0028] The ratio of the major axis to the minor axis of the magnetic filler (hereinafter also referred to as "aspect ratio") is preferably 5 or more, more preferably 100 or more, and even more preferably 200 or more. The aspect ratio is preferably 1,000,000 or less. When the aspect ratio of the magnetic filler is 5 or more, from the viewpoint of dispersibility, the average minor axis of the magnetic filler is preferably 50 nm or more. The average minor axis is preferably 500 nm or less, more preferably 300 nm or less. The average major axis is preferably 5 μm or more, more preferably 10 μm or more. The average major axis is preferably 40 μm or less, more preferably 30 μm or less. It is particularly preferable that the magnetic filler is needle-shaped or wire-shaped and has an aspect ratio of 100 or more. Even when such a magnetic filler is used, the present composition has excellent dispersibility, and the electromagnetic wave shield obtained therefrom has excellent electromagnetic wave shielding effect, adhesion, heat resistance, and thermal conductivity.

[0029] The magnetic filler may be used alone or in combination of two or more. When two or more types are used in combination, it is preferable that the average particle diameters of the different magnetic fillers are different. In this case, it is easy to highly fill the magnetic filler in the electromagnetic wave shield, and it is easy to obtain an electromagnetic wave shield with high electromagnetic wave shielding effect. The different types of magnetic fillers may contain the same magnetic material or different magnetic materials.

[0030] The mass ratio of the present powder to the magnetic filler in the present composition is such that the mass of the present powder is 1 and the mass of the magnetic filler is 0.1 or more, and from the viewpoint of electromagnetic wave shielding performance, it is preferably 0.2 or more, and more preferably 0.5 or more. From the viewpoint of the moldability of the composition, the mass ratio of the present powder to the magnetic filler in the composition is preferably 20 or less, and more preferably 10 or less, with the mass content of the present powder being 1. Even if the mass content of the magnetic filler is within this range and a large amount of magnetic filler is contained, the composition has excellent dispersibility, and the electromagnetic wave shield obtained from it has excellent electromagnetic wave shielding effect, adhesion, heat resistance, and thermal conductivity.

[0031] When the aspect ratio of the magnetic filler is 100 or more, the mass ratio of the present powder to the magnetic filler in the present composition is preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.3 or less, relative to the mass of the present powder, which is 1. The mass ratio of the present powder to the magnetic filler in the present composition is 0.1 or more, preferably 0.2 or more, relative to the mass of the present powder, which is 1. Magnetic fillers with an aspect ratio of 100 or more have excellent dispersibility and mixability with other materials, so the electromagnetic wave shield obtained from this composition has excellent electromagnetic wave shielding effect even when the content of magnetic filler is small.

[0032] The present composition may further contain polytetrafluoroethylene (hereinafter also referred to as "PTFE") powder (hereinafter also referred to as "PTFE powder"). PTFE may be a homopolymer of TFE or a copolymer of TFE and a trace amount of a comonomer such as PAVE, HFP, or fluoroalkylethylene, which is called a modified PTFE. The proportion of TFE units in PTFE is 99.5 mol % or more, preferably 99.9 mol % or more, of all units. PTFE is preferably non-thermofusible. A non-thermofusible polymer means a polymer that does not have a temperature at which the melt flow rate is 1 g or more and 1000 g or less per 10 minutes under a load of 49 N.

[0033] The average particle size of the PTFE powder is preferably 0.1 μm or more and 1 μm or less. When the present composition contains PTFE powder, the mass ratio of the present powder to the PTFE powder in the present composition is preferably 2 or more, and more preferably 3 or more, relative to the mass of the present powder, which is taken as 1. The mass ratio of the present powder to the PTFE powder in the present composition is preferably 0.01 or more, and more preferably 0.1 or more, relative to the mass of the present powder, which is taken as 1.

[0034] The composition may further contain other resins or inorganic fillers, if necessary. The other resin is a resin different from the F polymer and PTFE and is a polymer that does not contain a TFE unit. The other resin may be a thermosetting resin or a thermoplastic resin. Examples of the other resin include aromatic polyester, aromatic polyimide, aromatic polyamic acid, aromatic polyamideimide, epoxy resin, maleimide resin, urethane resin, thermoplastic elastomer, polyamideimide, polyphenylene ether, polyphenylene oxide, liquid crystal polyester, polysaccharide, nylon, acrylic resin, methacrylic resin, butyral, cyanate ester resin, ABR rubber, cellulose, PVA acrylic methacrylic, polyalkylene ether, polyoxyethylene alkyl ether, and fluoropolymers other than the F polymer and PTFE.

[0035] The inorganic filler is a filler different from a magnetic filler, and examples thereof include boron nitride filler, silica filler, and magnesium metasilicate filler, with silica filler being more preferred. These fillers may also be fired ceramic fillers. The inorganic filler is preferably a filler containing silicon oxide or magnesium metasilicate.

[0036] At least a part of the surface of the inorganic filler is preferably surface-treated. The inorganic filler is preferably an inorganic filler that has been surface-treated with a silane coupling agent, as such an inorganic filler has excellent affinity with the present powder and is likely to improve the dispersibility of the present composition. The silane coupling agent is preferably 3-aminopropyltriethoxysilane, vinyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, or 3-isocyanatopropyltriethoxysilane.

[0037] The present composition may be a liquid composition further comprising a liquid dispersion medium (hereinafter also referred to as "the present liquid composition"). The liquid dispersion medium is a liquid that has the function of dissolving, dispersing, or gelling the present powder or magnetic filler, and the present liquid composition is usually in the form of a slurry or gel. Liquid means that the viscosity at 25°C is 10 mPa·s or less.

[0038] The liquid dispersion medium is preferably degassed from the viewpoint of ensuring uniform distribution of the magnetic filler in the electromagnetic wave shielding sheet described below and suppressing voids.

[0039] The liquid dispersion medium may be water or a non-aqueous dispersion medium, and may be an aprotic dispersion medium or a protic dispersion medium. The liquid dispersion medium is preferably a non-aqueous dispersion medium, more preferably at least one selected from the group consisting of amides, ketones, esters, aromatic hydrocarbons, and glycols. Specific examples of the liquid dispersion medium include N-methyl-2-pyrrolidone, γ-butyrolactone, methyl ethyl ketone, cyclohexanone, cyclopentanone, toluene, xylene, ethylene glycol, propylene glycol, trimethylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, and tripropylene glycol, with N-methyl-2-pyrrolidone being preferred, and N-methyl-2-pyrrolidone being more preferred.

[0040] The liquid dispersion medium may be used alone or in combination of two or more. When two or more liquid dispersion media are used in combination, it is preferable that the different liquid dispersion media are compatible with each other. The boiling point of the liquid dispersion medium is preferably 125°C or higher and 250°C or lower.

[0041] The content of the powder in the liquid composition is preferably 30% by mass or more, more preferably 40% by mass or more. The content is preferably 60% by mass or less, more preferably 50% by mass or less. In this case, the liquid composition is likely to have excellent dispersion stability, and the resulting electromagnetic wave shielding sheet is likely to be dense and have excellent electrical properties and electromagnetic wave shielding ability.

[0042] The present liquid composition may further contain a nonionic surfactant from the viewpoint of further improving dispersion stability and handling properties. The hydrophilic portion of the surfactant preferably has an oxyalkylene group or an alcoholic hydroxyl group. The hydrophobic portion of the surfactant preferably has an acetylene group, a polysiloxane group, a perfluoroalkyl group, or a perfluoroalkenyl group. In other words, the surfactant is preferably an acetylene-based surfactant, a silicone-based surfactant, or a fluorine-based surfactant, and more preferably a silicone-based surfactant.

[0043] Specific examples of such surfactants include the "Ftergent" series (manufactured by Neos Corporation, Ftergent is a registered trademark), the "Surflon" series (manufactured by AGC Seimi Chemical Co., Ltd., Surflon is a registered trademark), the "Megafac" series (manufactured by DIC Corporation, Megafac is a registered trademark), the "Unidyne" series (manufactured by Daikin Industries, Ltd., Unidyne is a registered trademark), "BYK-347", "BYK-349", "BYK-378", "BYK-3450", "BYK-3451", "BYK-3455", "BYK-3456" (manufactured by BYK Japan KK), and "KF-6011" and "KF-6043" (manufactured by Shin-Etsu Chemical Co., Ltd.). When a surfactant is contained, the content of the surfactant in the liquid composition is preferably 1% by mass or more and 15% by mass or less, which increases the affinity between the components and tends to further improve the dispersion stability and handleability of the liquid composition.

[0044]

[0043] In addition to the other resins, inorganic fillers, liquid dispersion media, and surfactants, the present composition may further contain additives such as a thixotropy-imparting agent, a viscosity modifier, an antifoaming agent, a silane coupling agent, a dehydrating agent, a plasticizer, a weathering agent, an antioxidant, a heat stabilizer, a lubricant, an antistatic agent, a brightening agent, a colorant, a conductive agent, a release agent, a surface treatment agent, a flame retardant, and various fillers.

[0045] The viscosity of the liquid composition is preferably 10 mPa·s or more, more preferably 100 mPa·s or more. The viscosity of the liquid composition is preferably 10,000 mPa·s or less, more preferably 1,000 mPa·s or less. In this case, the liquid composition has excellent coatability, making it easy to form an electromagnetic wave shielding sheet of any desired thickness from the liquid composition. The thixotropy ratio of the present liquid composition is preferably at least 1. The thixotropy ratio of the present liquid composition is preferably at most 3, and more preferably at most 2. In this case, the present liquid composition not only has excellent coatability but also excellent homogeneity, making it easier to form a denser electromagnetic wave shielding sheet.

[0046] The dispersion layer ratio of the present liquid composition is preferably 60% or more, more preferably 70% or more. The upper limit of the dispersion layer ratio is 100%. The present composition has excellent dispersion stability, so it is easy to adjust the dispersion layer ratio to this level. The dispersion layer ratio is a value calculated by the following formula from the height of the entire composition in the screw tube and the height of the dispersion layer after leaving the composition standing at 25°C for 14 days, when 18 mL of the liquid composition is placed in a screw tube with an internal volume of 30 mL. If no dispersion layer is observed after leaving the composition standing and there is no change in the state, the overall height of the composition is considered to be unchanged, and the dispersion layer ratio is taken to be 100%. The higher the dispersion layer ratio, the more excellent the dispersion stability. Dispersion layer rate (%) = (height of dispersion layer) / (height of entire composition) × 100

[0047] From the viewpoint of improving the uniformity of the component distribution in the electromagnetic wave shielding sheet obtained from the liquid composition and obtaining a dense sheet, the foam volume ratio in the liquid composition is preferably less than 10%, more preferably less than 5%, and is preferably 0% or more. The foam volume ratio is calculated by dividing the volume of the liquid composition (V N ) and the combined volume of the bubbles when it is decompressed to 0.003 MPa (V V ) and the value is calculated using the following formula. Foam volume ratio [%] = 100 × (V V -V N ) / V N

[0048] The solid content of the liquid composition includes the powder and the magnetic filler, and if PTFE, other resins, or inorganic fillers are added, the solid content also includes the PTFE, other resins, or inorganic fillers. The solid content of the liquid composition refers to the total amount of substances that form the solid components in the electromagnetic shielding sheet formed from the liquid composition. The solid content concentration is preferably 40% by mass or more, more preferably 50% by mass or more, with the total mass of the liquid composition being 100%. From the viewpoint of dispersion stability of the liquid composition, the solid content concentration is preferably 90% by mass or less, more preferably 75% by mass or less.

[0049] From the viewpoint of dispersion stability of the present liquid composition, the content of the present powder is preferably 10% by mass or more, more preferably 20% by mass or more, based on 100% by mass of the solid content in the present liquid composition. The content of the present powder is preferably 70% by mass or less, more preferably 50% by mass or less, based on 100% by mass of the solid content. The content of the magnetic filler is preferably 5% by mass or more, more preferably 10% by mass or more, based on 100% by mass of the solid content. The content of the magnetic filler is preferably 95% by mass or less, more preferably 90% by mass or less.

[0050] The present composition can be obtained by mixing the present powder, a magnetic filler, and, if necessary, other components. The mixing method is not particularly limited as long as it is a method that can uniformly mix the present powder, the magnetic filler, and other components as necessary. The present composition may be obtained by mixing the present powder and the magnetic filler all at once, by adding either one in multiple batches and mixing, or by adding them continuously and mixing. Examples of mixers used for mixing include mixers with stirring blades, Henschel mixers, ribbon blenders, rocking mixers, and vibration mixers. The components of the present composition are preferably kneaded to obtain a uniform mixture, for example, by pre-mixing the components using a mixer such as a tumbler, a Henschel mixer, a planetary mixer, or the like, followed by further melt-kneading using a Banbury mixer, a roll, a Brabender mixer, a single-screw kneading extruder, a twin-screw kneading extruder, a kneader, or the like.

[0051] The present liquid composition may be obtained by adding the present powder and a magnetic filler to the liquid dispersion medium, by mixing the present powder with the liquid dispersion medium and then adding the magnetic filler thereto, or by mixing the magnetic filler with the liquid dispersion medium and then adding the present powder thereto. Mixing devices used to obtain the present liquid composition include agitators equipped with blades (Henschel mixers, pressure kneaders, Banbury mixers, planetary mixers, etc.), grinding devices equipped with media (ball mills, attritors, basket mills, sand mills, sand grinders, Dyno Mills, Dispermats, SC mills, spike mills, agitator mills, etc.), and dispersing devices equipped with other mechanisms (microfluidizers, nanomizers, ultimizers, ultrasonic homogenizers, dissolvers, dispersers, high-speed impellers, planetary mixers, colloid mills, thin film swirling high-speed mixers, etc.). When mixing the present powder, magnetic filler, and the liquid dispersion medium, they may be mixed while degassing. Alternatively, after mixing the present powder, magnetic filler, and the liquid dispersion medium, they may be left to stand for a while. In this case, the present liquid composition tends to have excellent dispersion stability. The addition may be carried out continuously or intermittently.

[0052] When degassing, it is preferable to heat and reduce the pressure, and the heating temperature and reduced pressure are set appropriately depending on the liquid dispersion medium, and a pressure and temperature are selected that do not cause the liquid dispersion medium to boil. For example, the pressure is preferably about 0 Pa to 0.01 MPa, and the temperature is preferably 100°C to 250°C lower than the boiling point of the liquid dispersion medium. There is no particular limit to the degassing time, but since the degassing effect does not change significantly even if the degassing time is too long, it is usually from 10 minutes to 6 hours. During degassing, stirring or other procedures may be carried out to prevent bumping.

[0053] When the liquid composition is left standing, the temperature and pressure of the atmosphere are usually 10°C to 30°C and about 1 atmosphere, preferably at constant temperature and humidity. During the standing, the liquid composition may be left standing, or may be stirred to the extent that the present powder in the liquid composition does not aggregate or settle. The time for leaving it is preferably 24 hours or more, more preferably 48 hours or more, but is preferably 168 hours or less, since the effect obtained does not change significantly even if the time for leaving it is too long.

[0054] Alternatively, the present powder, magnetic filler, and liquid dispersion medium may be mixed in advance to form a paste, and the resulting paste may then be mixed with additional liquid dispersion medium to form the present liquid composition. The viscosity of the resulting paste is preferably 10,000 mPa·s or higher, more preferably 25,000 mPa·s or higher. The viscosity of the paste is preferably 100,000 mPa·s or lower, more preferably 80,000 mPa·s. In this case, agglomerations of the present powder and magnetic filler are easily broken down during mixing to obtain the paste, and the present liquid composition is likely to have excellent dispersion stability. The liquid dispersion medium used in the paste and the liquid dispersion medium added may be the same or different, but it is preferable that they are the same.

[0055] The electromagnetic wave shielding sheet of the present invention (hereinafter also referred to as "the sheet") comprises the F polymer and the magnetic filler, and the mass ratio of the magnetic filler to the F polymer is 0.1 or more. The present sheet may be a single layer or a laminated sheet of two or more layers, and it is sufficient that the entire sheet contains the F polymer and the magnetic filler, and that each layer contains the F polymer and magnetic filler so that the mass ratio of the magnetic filler to the F polymer is 0.1 or more. From the viewpoint of productivity, the present sheet is preferably a sheet that contains the F polymer and the magnetic filler in the same layer, and has a layer in which the mass ratio of the magnetic filler to the F polymer is 0.1 or more. The mass ratio of the magnetic filler to the F polymer in the sheet is preferably 0.2 or more, more preferably 0.5 or more, from the viewpoint of electromagnetic wave shielding performance, and is preferably 20 or less, more preferably 10 or less, from the viewpoint of strength of the sheet.

[0056] When the aspect ratio of the magnetic filler is 100 or more, the mass ratio of the magnetic filler to the F polymer in the sheet is preferably 1 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. The mass ratio of the magnetic filler to the F polymer in the sheet is 0.1 or more, more preferably 0.2 or more. Magnetic fillers with an aspect ratio of 100 or more have excellent dispersibility and are easily mixed with other materials, so even if the magnetic filler content is low, the sheet has excellent electromagnetic wave shielding effects. The present sheet may further contain PTFE, other resins, inorganic fillers, or additives as necessary. The definitions and ranges of the PTFE, other resins, inorganic fillers, and additives, including preferred embodiments thereof, are the same as those of the other resins, inorganic fillers, and additives in the present composition described above.

[0057] Methods for manufacturing this sheet, which is a laminated sheet of two or more layers, include, for example, a method in which a layer containing the F polymer and a layer containing the magnetic filler are created by melt extrusion or the like, and the two layers are laminated together by fusion, pressing, adhesive, or the like to form a sheet; and a method in which a liquid composition containing powder of the F polymer is applied to the surface of the layer containing the magnetic filler, and then heated to form a layer containing the F polymer. The layer containing the magnetic filler may contain a resin. The resin contained in the layer containing the magnetic filler may be a thermoplastic resin or a thermosetting resin, with a thermosetting resin being preferred. Examples of such resins include acrylic resins and methoxymethylated polyamide resins.

[0058] Examples of methods for producing the present single-layer sheet include a method in which the present composition is melt-extruded to form a sheet, and a method in which the present liquid composition is applied to a substrate, dried, and then peeled off from the substrate or the substrate is dissolved and etched to obtain a sheet. Such a method for producing the present single-layer sheet is preferable in that a sheet in which the magnetic filler is uniformly dispersed in the F polymer can be obtained.

[0059] When the present composition is melt-extruded into a sheet, the melt-extrusion is preferably carried out using an extruder having a T-die. The melt-extrusion may be carried out continuously after melt-kneading the present composition, or the composition may be melt-kneaded in the melt-extruder and then melt-extruded. The conditions for melt extrusion are appropriately set depending on the melt temperature of the composition, etc., but it is usually preferable to set the melt kneading temperature at least 20° C. higher than the melt temperature of the F polymer.

[0060] When applying the liquid composition to a substrate and drying it, peeling it off from the substrate or dissolving or etching the substrate to obtain a sheet, the liquid composition is applied to the surface of the substrate and heated to form a layer containing an F polymer and a magnetic filler (hereinafter also referred to as "F layer"), thereby producing a laminate having the substrate and the F layer. The sheet can be obtained by peeling the F layer from the laminate having the F layer. Alternatively, the sheet can be obtained by removing the substrate from the laminate having the F layer by dissolving or etching. The material of the substrate is not particularly limited as long as it is a material from which the present sheet can be easily peeled off or can be removed by etching or dissolution. The substrate preferably has a smooth surface.

[0061] The surface of the substrate may be surface-treated with a silane coupling agent, etc. When applying the liquid composition, any of the following coating methods can be used: spray coating, roll coating, spin coating, gravure coating, microgravure coating, gravure offset coating, knife coating, kiss coating, bar coating, die coating, fountain-meyer bar coating, and slot die coating.

[0062] The F layer is preferably formed by removing the liquid dispersion medium by heating, and then further heating to a high temperature to bake the polymer. The temperature for removing the liquid dispersion medium is preferably as low as possible, and is preferably 50 to 150°C lower than the boiling point of the liquid dispersion medium. For example, when N-methyl-2-pyrrolidone, which has a boiling point of approximately 200°C, is used, it is preferable to heat at 150°C or lower, preferably 100 to 120°C. It is preferable to blow air in the step of removing the liquid dispersion medium.

[0063] After removing the liquid dispersion medium, the substrate from which the liquid dispersion medium has been removed is preferably heated to a temperature range in which the F polymer is baked to form an F layer, and the F polymer is preferably baked, for example, in the range of 300° C. to 400° C. The F layer preferably contains a baked product of the F polymer. When the present sheet is formed by melt extrusion, the present sheet is further baked in a temperature range in which the F polymer is baked to form the present sheet containing the baked product of the F polymer. The present sheet is preferably produced from the present liquid composition. In particular, when the aspect ratio of the magnetic filler in the present liquid composition is high, it is easy to highly orient the magnetic filler in the present sheet while suppressing damage to the magnetic filler when forming the present sheet.

[0064] The sheet preferably has a shielding performance of 10 dB or more over the entire frequency range from 18.0 GHz to 26.5 GHz as measured by the Faraday cage method (hereinafter also referred to as the "FC method"). By dispersing the magnetic filler well in the sheet, the shielding performance over the entire frequency range from 18.0 GHz to 26.5 GHz as measured by the FC method can be kept within the above range. The thermal conductivity of the sheet is preferably 1 W / m·K or more, more preferably 3 W / m·K or more. The thermal conductivity is preferably 100 W / m·K or less.

[0065] The porosity of the present sheet is preferably 5% or less, more preferably 4% or less. The porosity is preferably 0.01% or more, more preferably 0.1% or more. The porosity is the percentage (%) of the area of ​​voids in the cross section of the molded product observed using a scanning electron microscope (SEM). When the present sheet is a laminated sheet of two or more layers, it is preferable that the porosity of at least one layer is within this range. In this case, the present sheet is likely to have excellent electromagnetic wave shielding performance.

[0066] The thickness of the sheet is preferably 1 μm or more, more preferably 5 μm or more, even more preferably 10 μm or more, and particularly preferably 50 μm or more. The thickness of the sheet is preferably 1000 μm or less, more preferably 500 μm or less, and even more preferably 200 μm or less. The thickness of the present sheet can be adjusted to fall within the above range by appropriately adjusting the clearance of the T-die, the take-up speed, the amount of the present liquid composition applied, the number of applications, and the like.

[0067] The sheet is molded onto a substrate or laminated with a substrate to obtain a substrate with an electromagnetic wave shielding sheet. Specifically, examples of such methods include a method in which the present liquid composition is applied to a substrate, dried, and then baked to form the present sheet on the substrate; a method in which the present composition is melt-extruded onto a substrate to form the present sheet on the substrate, and the present sheet is then laminated to the substrate; and a method in which the present sheet is laminated to the substrate by fusion, pressure bonding, adhesive, etc.

[0068] The shape of the substrate is not particularly limited and may be, for example, plate-like, box-like, rod-like, spherical, film-like, fibrous, etc., and the surface shape may be flat, curved, or uneven. The surface may be smooth or uneven, but a plate-like substrate (hereinafter also referred to as "substrate") is preferred because the present sheet is suitable for use in printed wiring boards. Examples of the material for the substrate include metal substrates such as metal foils of copper, nickel, aluminum, titanium, alloys thereof, etc.; resin films such as films of polyimide, polyarylate, polysulfone, polyarylsulfone, polyamide, polyetheramide, polyphenylene sulfide, polyaryletherketone, polyamideimide, liquid crystalline polyester, and liquid crystalline polyesteramide; and prepregs which are precursors of fiber-reinforced resin substrates. Specific examples of the electromagnetic wave shielded substrate include an electromagnetic wave shielded substrate having the present sheet and a metal substrate on at least one surface of the present sheet, an electromagnetic wave shielded substrate having the present sheet and an adhesive layer on at least one surface of the present sheet, and an electromagnetic wave shielded substrate having a metal substrate, the present sheet, and an adhesive layer in this order.

[0069] A specific example of an electromagnetic wave shielding substrate is a metal clad laminate having a metal foil and the present sheet on at least one surface of the metal foil. This has excellent physical properties such as electrical properties and is suitable as a printed wiring board material.

[0070] The peel strength between the sheet and the substrate is preferably 5 N / cm or more, more preferably 10 N / cm or more, and is preferably 100 N / cm or less.

[0071] A printed wiring board equipped with this sheet has excellent electromagnetic wave shielding performance. In particular, when a printed wiring board contains a tetrafluoroethylene-based polymer as an electrical insulating layer, the present sheet is suitable for use due to its excellent adhesiveness. It is more preferable that the present sheet and the electrical insulating layer are in at least partial contact. Examples of such tetrafluoroethylene-based polymers include the above-mentioned F polymer and non-thermofusible polytetrafluoroethylene.

[0072] The composition can provide an electromagnetic wave shielding sheet that has a high electromagnetic wave shielding effect and is sufficiently endowed with adhesiveness, heat resistance, and thermal conductivity, and is therefore suitable for use as an electromagnetic wave shielding layer for printed wiring boards and the like.

[0073] The composition, the method for producing a substrate with an electromagnetic wave shielding sheet, the electromagnetic wave shielding sheet, and the printed wiring board provided with the electromagnetic wave shielding sheet have been described above, but the present invention is not limited to the configurations of the above-described embodiments. For example, the composition, the electromagnetic wave shielding sheet, and the printed wiring board provided with the electromagnetic wave shielding sheet may have any other optional components added to the configurations of the above-described embodiments, or may be replaced with any other components that exhibit the same function. Furthermore, the method for producing a substrate with an electromagnetic wave shielding sheet may have any other optional step added to the configurations of the above-described embodiments, or may be replaced with any other step that produces the same effect. [Example]

[0074] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1. Preparation of each ingredient [powder] Powder 1: Contains 97.9 mol%, 0.1 mol%, and 2.0 mol% of TFE units, NAH units, and PPVE units, in that order; has a fluorine content of 76 mass%; and has a carbonyl group-containing group with a main chain carbon number of 1×10 6 Powder consisting of a polymer with 1000 particles per particle (D50: 2.0 μm, specific surface area: 3 m 2 / g) [Metallic magnetic filler] Magnetic filler 1: Nickel nanowire (average diameter: 90 nm, average length: 25 μm, aspect ratio: 278)

[0075] 2. Manufacturing example A mixture containing 20 parts by mass of Powder 1 and 30 parts by mass of NMP was mixed with a mixture containing 10 parts by mass of Magnetic Filler 1 and 40 parts by mass of NMP and sheared to obtain Liquid Composition 1 containing 20 parts by mass of Powder 1, 10 parts by mass of Magnetic Filler 1, and 70 parts by mass of NMP and having a viscosity of 400 mPa s. The dispersion layer ratio of Liquid Composition 1 was 70% or more. Liquid composition 1 was applied to the surface of a long copper foil with a thickness of 18 μm using a bar coater to form a wet film. Next, the metal foil on which this wet film had been formed was passed through a drying oven at 120°C for 5 minutes and dried by heating to obtain a dry film. The dry film was then heated at 380°C for 3 minutes in a nitrogen oven. This produced a substrate 1 with an electromagnetic shielding sheet, which had a metal foil and, on its surface, a molten and fired product of powder 1 and magnetic filler 1, and a 25 μm-thick electromagnetic shielding sheet layer as a molded product.

[0076] The copper foil of the substrate 1 with the electromagnetic wave shielding sheet was removed by etching with an aqueous solution of ferric chloride, to prepare a standalone electromagnetic wave shielding sheet 1. The electromagnetic wave shielding performance of the electromagnetic wave shielding sheet 1 was measured by the FC method, and the shielding performance was found to be 10 dB or more. The thermal conductivity of the electromagnetic wave shielding sheet 1 was measured and found to be 3 W / m·K or higher in the in-plane direction (W / m·K). After the electromagnetic wave shielding sheet 1 was kept at 200° C. for 30 minutes, it was visually inspected and found to have no visible warping or distortion, demonstrating that the electromagnetic wave shielding sheet 1 had excellent heat resistance.

[0077] The electromagnetic wave shielding sheet 1 was laminated with a 100 μm-thick glass cloth sheet impregnated with non-thermofusible polytetrafluoroethylene, a material used for insulating layers in high-frequency printed circuit boards, and the laminate was hot-pressed to obtain a laminate 1 having an electromagnetic wave shielding sheet layer and a glass cloth sheet layer. A rectangular test piece 100 mm long and 10 mm wide was cut out from the laminate 1, and the test piece was fixed at a position 50 mm from one end in the longitudinal direction. The electromagnetic wave shielding sheet layer and the glass cloth sheet layer were peeled off from one end in the longitudinal direction at a 90° angle to the test piece at a pulling rate of 50 mm / min. The maximum load applied during this process was 5 N / cm or more, and the laminate 1 demonstrated excellent interlayer adhesion. [Industrial Applicability]

[0078] As is clear from the above results, the electromagnetic shielding sheet obtained from this composition, which contains an F polymer and a magnetic filler, has a high electromagnetic shielding effect and is sufficiently equipped with adhesiveness, heat resistance, and thermal conductivity. Therefore, the electromagnetic shielding sheet and substrate with the electromagnetic shielding sheet obtained from the electromagnetic shielding composition of the present invention, and the electromagnetic shielding sheet containing an F polymer and a magnetic filler, have a high electromagnetic shielding effect and are sufficiently equipped with adhesiveness, heat resistance, and thermal conductivity, and can be suitably used as an electromagnetic shielding layer for printed wiring boards.

Claims

1. Specific surface area is 25m ２ Electromagnetic wave shielding composition comprising: a powder of a tetrafluoroethylene-based polymer having a molecular weight of 1000 or less, an average particle size of 50 μm or less, and a melting temperature of 260°C or more and 320°C or less; a metal magnetic filler having a needle or wire shape and an aspect ratio of 100 or more; and a liquid dispersion medium, wherein the mass ratio of the metal magnetic filler to the tetrafluoroethylene-based polymer is 0.1 or more.

2. The tetrafluoroethylene-based polymer has a main chain carbon number of 1×10 ６ 2. The electromagnetic wave shielding composition according to claim 1, wherein each of the carbonyl-containing groups has 10 to 5,000 carbonyl-containing groups.

3. The specific surface area of ​​the powder is 1 m ２ / g or more 8m ２ The electromagnetic wave shielding composition according to claim 1 or 2, wherein the tensile strength is 1 / g or less.

4. 4. The electromagnetic wave shielding composition according to claim 1, wherein the powder has an average particle size of 1 μm or more and 8 μm or less.

5. 5. The electromagnetic shielding composition according to claim 1, wherein the metal magnetic filler is a filler containing at least one magnetic material selected from the group consisting of gold, silver, copper, iron, aluminum, titanium, cobalt, nickel, copper oxide, iron oxide, carbonyl iron, and ferrite.

6. The electromagnetic wave shielding composition according to claim 1 , further comprising a polytetrafluoroethylene powder.

7. A method for producing a substrate with an electromagnetic wave shielding sheet, comprising applying the electromagnetic wave shielding composition according to claim 1 to a substrate, and firing the powder to form an electromagnetic wave shielding sheet.

8. An electromagnetic wave shielding sheet comprising a tetrafluoroethylene-based polymer having a melting temperature of 260°C or higher and 320°C or lower and a metal magnetic filler that is needle-shaped or wire-shaped and has an aspect ratio of 100 or higher, wherein the mass ratio of the metal magnetic filler to the tetrafluoroethylene-based polymer is 0.1 or higher.

9. 9. The electromagnetic wave shielding sheet according to claim 8, wherein the fired product of the tetrafluoroethylene-based polymer powder and the metallic magnetic filler are contained in the same layer.

10. 10. The electromagnetic wave shielding sheet according to claim 8, having a thickness of 1 μm or more.

11. A printed wiring board comprising the electromagnetic wave shielding sheet according to any one of claims 8 to 10.

12. 12. The printed wiring board according to claim 11, wherein an electrical insulating layer of the printed wiring board contains a tetrafluoroethylene-based polymer, and at least a portion of the electromagnetic wave shielding sheet is in contact with the electrical insulating layer.