Electromagnetic wave shielding film

Abstract

To provide an electromagnetic wave shielding film which can sufficiently exhibit characteristics as an electromagnetic wave shielding material while suppressing the thickness of a carbon nanotube nonwoven fabric, is easy to handle, and covers electronic components and wiring mounted inside an electronic apparatus.SOLUTION: An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a specific resistance of 0.00005 to 0.05 Ω·cm and a thickness of 1 to 500 μ m, and a resin, wherein the electromagnetic wave shielding film comprises a laminated film in which two or more layers of the carbon nanotube nonwoven fabric are laminated and having a total thickness of 5 to 1,500 μ m, an adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on an adhesive surface of the adhesive layer.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave shielding film that covers electronic components, wiring, etc. mounted inside an electronic device to shield against electromagnetic waves. [Background technology]

[0002] In recent years, high-speed communications such as 5G and 6G, which use millimeter and terahertz electromagnetic waves, have been under consideration for future practical use. Wireless devices that use electromagnetic waves for communication are on the rise, and the amount of electromagnetic waves in the air continues to increase. As a result, electronic devices may malfunction due to interference from surrounding electromagnetic waves, or may leak information due to electromagnetic waves emitted by the devices themselves. Furthermore, to promote autonomous driving of automobiles and other vehicles, it is necessary to properly transmit and receive a variety of electromagnetic waves, from low to high frequencies.

[0003] To avoid such interference caused by electromagnetic waves, electromagnetic wave shielding measures have become an important technological challenge. Against this background, there is a demand for electromagnetic wave shielding materials with excellent electromagnetic wave shielding performance in the microwave, millimeter wave, and terahertz wave bands. As the use of electromagnetic waves becomes more sophisticated, there is also a growing need for new functionality in electromagnetic wave shielding materials, such as thinner films, lighter weight, and larger areas.

[0004] Many electromagnetic wave shielding technologies have been proposed using metallic materials as well as carbon black, graphene, carbon nanotubes, conductive polymers, etc. Among these, carbon nanotubes made from carbon are attracting attention as a promising electromagnetic wave shielding material.

[0005] Electromagnetic wave shielding materials using carbon nanotubes include a paste material in which carbon nanotubes are dispersed in a resin (Patent Document 1) and a water-based paint in which carbon nanotubes are dispersed in an aqueous solution (Patent Document 2). However, both are difficult to handle, and the carbon nanotubes used are in the form of fine fibers with a large specific surface area, making them difficult to disperse in large quantities, resulting in insufficient conductivity and making them unsuitable for practical use.

[0006] Additionally, an electromagnetic wave shielding material has been disclosed in which a protonating agent such as hydronium ions or hydrochloric acid is added to a carbon nanotube sheet, and further ferromagnetic materials such as iron or cobalt are added to improve conductivity (Patent Document 3). However, because the conductivity is lower and the reflection loss is smaller than that of metal foils such as aluminum or copper, in order to achieve shielding performance equivalent to that of metals, the sheet film thickness must be increased, resulting in increased attenuation loss, which poses a challenge when mounting on devices that are becoming increasingly miniaturized.

[0007] Recently, carbon nanotube agglomerate sheets have been attracting attention as electromagnetic wave shielding materials, but the agglomerate sheets have lower electrical conductivity than metal foils such as aluminum and copper foils, and their properties are not being fully utilized. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-144000 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-174833 [Patent Document 3] Japanese Patent Application Laid-Open No. 2015-187077 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above circumstances, and provides an electromagnetic wave shielding film that can fully exhibit its properties as an electromagnetic wave shielding material while reducing the thickness of a carbon nanotube nonwoven fabric, and is easy to handle, and that covers electronic components and wiring mounted inside electronic devices. [Means for solving the problem]

[0010] As a result of extensive research into achieving the above object, the present inventors have found that the following electromagnetic wave shielding film achieves the above object, and have thus completed the present invention.

[0011] Therefore, the present invention provides the following electromagnetic wave shielding film. 1. An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω·cm and a thickness of 1 to 500 μm, and a resin, An electromagnetic wave shielding film comprising a laminated film having two or more layers of the carbon nanotube nonwoven fabric laminated together and having a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. 2. The electromagnetic wave shielding film according to 1, wherein the laminated film is a resin laminated film in which a carbon nanotube nonwoven fabric and a resin film are laminated together. 3. The electromagnetic wave shielding film according to 2, wherein the resin film is a thermoplastic resin film, and the softening point of the thermoplastic resin is 400°C or lower. 4. The electromagnetic wave shielding film according to 3, wherein the thermoplastic resin constituting the thermoplastic resin film comprises at least one selected from polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate and polyimide. 5. The electromagnetic wave shielding film according to 2, wherein the resin film is a thermosetting resin film, and the thermosetting resin is one or more selected from epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins and acrylic resins. 6. The electromagnetic wave shielding film according to 1, wherein the laminated film is an impregnated laminated film in which two or more layers of impregnated films in which carbon nanotube nonwoven fabric is impregnated with resin are laminated together. 7. The electromagnetic wave shielding film according to 1, wherein the laminated film is an impregnated film in which a carbon nanotube nonwoven fabric is impregnated with a resin, and a nonwoven fabric impregnated laminated film in which the carbon nanotube nonwoven fabric is laminated on the impregnated film. 8. The electromagnetic wave shielding film according to 6 or 7, wherein the resin comprises one or more thermoplastic resins selected from polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, and polyimide. 9. An electromagnetic wave shielding film according to 6 or 7, wherein the resin comprises one or more thermosetting resins selected from epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins and acrylic resins. 10. The electromagnetic wave shielding film according to any one of 1 to 9, wherein the carbon nanotubes constituting the carbon nanotube nonwoven fabric are single-walled carbon nanotubes, multi-walled carbon nanotubes or a mixture thereof. [Effects of the Invention]

[0012] An electromagnetic wave shielding film formed by laminating two or more layers of the thin carbon nanotube nonwoven fabric of the present invention exhibits electromagnetic wave shielding properties equivalent to those obtained when using only one layer of thick carbon nanotube nonwoven fabric, and can fully demonstrate the properties of an electromagnetic wave shielding material made of carbon nanotubes. [Brief explanation of the drawings]

[0013] [Figure 1A] 1 is a longitudinal cross-sectional view schematically showing an example of a first electromagnetic wave shielding film in which a carbon nanotube nonwoven fabric and a resin film are laminated together. FIG. [Figure 1B] FIG. 2 is a longitudinal cross-sectional view schematically showing an example of a second electromagnetic wave shielding film that is an impregnated laminate film. [Figure 1C] FIG. 10 is a longitudinal cross-sectional view schematically showing an example of a third electromagnetic wave shielding film in which an impregnated film and a carbon nanotube nonwoven fabric are laminated. [Figure 2] FIG. 2 is a perspective view schematically showing an example in which the first electromagnetic wave shielding film is wound into a roll like glass cloth. [Figure 3]FIG. 1 is a perspective view schematically showing an example of a state in which a roll-shaped electromagnetic wave shielding film is cut into tape shapes. [Figure 4A] 10 is a longitudinal cross-sectional view schematically showing an example in which the release film is peeled off from the first electromagnetic wave shielding film and the film is attached to the surface of an electronic component. FIG. [Figure 4B] FIG. 10 is a longitudinal cross-sectional view that schematically shows an example in which the release film is peeled off from the second electromagnetic wave shielding film and the film is attached to the surface of an electronic component. [Figure 4C] FIG. 10 is a longitudinal cross-sectional view schematically showing an example in which the release film is peeled off from the third electromagnetic wave shielding film and the film is attached to the surface of an electronic component. [Figure 5] FIG. 10 is a perspective view schematically showing an example in which the surface of a copper wiring is wrapped with an electromagnetic wave shielding film cut into a tape shape. [Figure 6] 1 is a longitudinal cross-sectional view schematically showing an example in which the entire circuit board is covered with an electromagnetic wave shielding film, with some of the cross sections not shaded. [Figure 7] FIG. 2 is a schematic diagram of a measurement system for electromagnetic wave shielding characteristics in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below. The electromagnetic wave shielding film of the present invention is an electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω·cm and a thickness of 1 to 500 μm, and a resin, The electromagnetic wave shielding film has a laminated film having two or more layers of the carbon nanotube nonwoven fabric laminated thereon and a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. As described above, there are no particular limitations on the type of laminated film as long as two or more layers having the specific carbon nanotube nonwoven fabric are laminated, but the number of layers having the carbon nanotube nonwoven fabric may be two or more, and specific examples include the following three embodiments. (1) The laminated film is a resin laminated film in which a carbon nanotube nonwoven fabric and a resin film are laminated together. (2) The laminated film is an impregnated laminated film in which two or more layers of impregnated films in which carbon nanotube nonwoven fabric is impregnated with resin are laminated together. (3) The laminated film is an impregnated film obtained by impregnating a carbon nanotube nonwoven fabric with a resin, and a nonwoven fabric impregnated laminated film obtained by laminating the carbon nanotube nonwoven fabric on the impregnated film. The electromagnetic wave shielding film has a pressure-sensitive adhesive layer laminated on one outermost surface of the laminate film, specifically, a laminate film selected from (1) a resin laminate film, (2) an impregnated laminate film, and (3) a nonwoven fabric impregnated laminate film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer.

[0015] Hereinafter, the electromagnetic wave shielding film having the (1) resin laminate film will be referred to as the first electromagnetic wave shielding film, the electromagnetic wave shielding film having the (2) impregnated laminate film will be referred to as the second electromagnetic wave shielding film, and the electromagnetic wave shielding film having the (3) nonwoven fabric impregnated laminate film will be referred to as the third electromagnetic wave shielding film. (1) An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω cm and a thickness of 1 to 500 μm, and a resin, wherein two or more layers each having the carbon nanotube nonwoven fabric are laminated together, and the laminated film is a resin laminated film in which the carbon nanotube nonwoven fabric and a resin film are laminated together, and the resin laminated film has a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. (2) An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω cm and a thickness of 1 to 500 μm, and a resin, wherein two or more layers each comprising the carbon nanotube nonwoven fabric are laminated together, and the laminated film comprises two or more layers of impregnated films in which the carbon nanotube nonwoven fabric is impregnated with a resin, the laminated film having a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. (3) An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω cm and a thickness of 1 to 500 μm, and a resin, wherein two or more layers each comprising the carbon nanotube nonwoven fabric are laminated together, and the laminated film comprises an impregnated film in which the carbon nanotube nonwoven fabric is impregnated with a resin, a nonwoven fabric impregnated laminated film in which the carbon nanotube nonwoven fabric is laminated on the impregnated film, and the total thickness of the laminated film is 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer.

[0016] In the present invention, it is essential that the laminate film has two or more layers of the carbon nanotube nonwoven fabric. The laminate film as a whole may have two or more layers of a specific carbon nanotube nonwoven fabric, and is not particularly limited as long as it has two or more layers, with two or three layers being preferred, and two layers being more preferred. If two or more layers of carbon nanotube nonwoven fabric are laminated, the first carbon nanotube nonwoven fabric, resin film, and resin laminate film can each be selected from one layer or two or more layers; in the second, the impregnated film can be selected from two or more layers; and in the third electromagnetic wave shielding film, the impregnated film, carbon nanotube nonwoven fabric, and nonwoven fabric-impregnated laminate film can each be selected from one or more layers.

[0017] <Carbon nanotube nonwoven fabric> The thickness of the carbon nanotube nonwoven fabric used in the present invention is 1 to 500 μm, preferably 1 to 300 μm. The carbon nanotube nonwoven fabric is made up of a plurality of carbon nanotubes entangled with one another. The carbon nanotubes constituting the carbon nanotube nonwoven fabric are preferably single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture thereof, and although their diameter and length are not particularly limited, they generally have a diameter of 50 nm or less and a length of 2 mm or less. The carbon nanotube nonwoven fabric used in the present invention is preferably made up of carbon nanotubes 10 to 500 μm in length entangled with one another.

[0018] Carbon nanotubes can be produced by reacting a carbon source such as methane with a catalyst such as ferrocene in the gas phase at temperatures between 1,000 and 1,500°C. To enhance the electrical conductivity of such nonwoven fabrics, highly conductive nonwoven fabrics with a resistivity of 0.000005 to 0.05 Ω·cm, preferably 0.0001 to 0.01 Ω·cm, and more preferably 0.0005 to 0.003 Ω·cm are used. Resistivity measurements are based on JIS K7194:1994, "Test Method for Resistivity of Conductive Plastics Using the Four-Probe Method."

[0019] The electromagnetic wave shielding film of the present invention may use a carbon nanotube nonwoven fabric having a silica layer on the surface of the carbon nanotube fibers. For example, the carbon nanotube nonwoven fabric may be treated with a polysilazane compound or the like to form a silica layer on the fiber surface of the carbon nanotube nonwoven fabric.

[0020] In the electromagnetic wave shielding film of the present invention, the fiber surface of the carbon nanotube nonwoven fabric can be surface treated with a sizing agent, i.e., a diluted solution of a thermosetting resin, in order to improve wettability with thermosetting resins such as epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins, and acrylic resins.

[0021] Furthermore, by treating the surface of the carbon nanotube nonwoven fabric with a coupling agent, the carbon nanotube nonwoven fabric and the resin adhere to each other, improving the durability of the electromagnetic wave shielding sheet. Examples of coupling agents include silane coupling agents and alkoxide compounds of titanium, aluminum, etc. Among these, silane coupling agents are preferred, and preferred silane coupling agents include organosilicon compounds represented by the following formula (1): Y-Si-X3(1) (In the formula, Y is an organic group having a reactive functional group, and X is a hydrolyzable group.)

[0022] Examples of Y include an amino group, an epoxy group, a hydroxyl group, a carboxyl group, a vinyl group, a methacryl group, and a mercapto group, and examples of X include an alkoxy group. Specific examples of the organosilicon compound represented by the above formula (1) include γ-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminobenzyltriethoxysilane, and γ-aminophenyltriethoxysilane. Silane compounds such as polysilazane can also be used.

[0023] In the electromagnetic wave shielding film of the present invention, an inorganic material may be added to the carbon nanotube nonwoven fabric. Examples of inorganic materials include conductive inorganic materials and insulating inorganic materials. By filling the gaps between the entangled fibers of the carbon nanotube nonwoven fabric with a conductive inorganic material, such as inorganic particles, inorganic fibers, or metal particles, it is possible to further increase electrical conductivity and improve electromagnetic wave shielding performance in the millimeter wave to terahertz frequency band. Among conductive inorganic materials, examples of inorganic particles include carbon black, carbon nanotubes, graphene, graphite, etc., examples of inorganic fibers include short carbon fibers, etc., and examples of metal particles include particles made of metals such as copper, iron, silver, and gold. Furthermore, resin particles surface-coated with these metals may also be used as the conductive inorganic material.

[0024] The use of inorganic particles or inorganic fibers as insulating inorganic materials with high thermal conductivity can further increase the thermal conductivity of the carbon nanotube nonwoven fabric, making it possible to achieve a thermal conductivity of 50 to 80 W / mK, for example. Among the insulating inorganic materials, examples of inorganic particles include silica, zinc oxide, alumina, boron nitride, and aluminum nitride. Examples of inorganic fibers include short alumina fibers, quartz fibers, and glass fibers.

[0025] The shape of the inorganic material is not particularly limited, but an average particle size of 0.5 to 30 μm is preferred from the viewpoint of heat dissipation and electrical conductivity. The average particle size of the inorganic material is measured by a laser diffraction method (cumulative average diameter D 50 (median diameter).

[0026] The inorganic material can be fixed by directly spraying it onto the carbon nanotube nonwoven fabric, and the inorganic material can be sprayed onto the carbon nanotube nonwoven fabric by any method, such as packing the inorganic material into the carbon nanotube nonwoven fabric using a press or laminator, dispersing the inorganic material in any solvent, spraying the dispersion onto the carbon nanotube nonwoven fabric with a sprayer, and then drying and removing the solvent, or a combination of these methods.

[0027] Any solvent can be used as the solvent for the dispersion, and highly volatile solvents are preferred, such as water, alcohols such as ethanol and isopropyl alcohol, acetone, toluene, hydrocarbon solvents, and silicone solvents. The concentration of the dispersion is preferably 0.1 to 100 parts by mass per 100 parts by mass of the inorganic material. When the inorganic material is fixed by spraying it onto the carbon nanotube nonwoven fabric, the amount of fixation is preferably 0.01 to 1,000 parts by mass per 100 parts by mass of the carbon nanotube nonwoven fabric. Furthermore, a metal foil such as copper or aluminum can be laminated onto the carbon nanotube nonwoven fabric.

[0028] <Resin film and protective layer of electromagnetic wave shielding film> The electromagnetic wave shielding film of the present invention comprises a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω·cm and a thickness of 1 to 500 μm, and a resin. The electromagnetic wave shielding film comprises a laminate film having two or more layers of the carbon nanotube nonwoven fabric and a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminate film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. Furthermore, the laminate film constituting the electromagnetic wave shielding film may have a protective layer disposed on the outermost surface opposite the pressure-sensitive adhesive layer. The protective layer will be described later.

[0029] <First electromagnetic wave shielding film resin film> The first electromagnetic wave shielding film is an electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω·cm and a thickness of 1 to 500 μm, and a resin, wherein two or more layers each comprising the carbon nanotube nonwoven fabric are laminated together, and the laminated film is a resin laminated film in which the carbon nanotube nonwoven fabric and a resin film are laminated together, and the electromagnetic wave shielding film comprises a resin laminated film having a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer.

[0030] Examples of the resin film and protective layer include a thermoplastic resin film and a thermosetting resin film. (thermoplastic resin film) From the viewpoints of film molding and electromagnetic wave shielding film processing, the softening point of the thermoplastic resin constituting the thermoplastic resin film is preferably 400°C or lower, more preferably 300°C or lower. The lower limit of the softening point is not particularly limited, but can be, for example, 70°C or higher. The softening point of the thermoplastic resin can be measured by the method described in JIS K7196-1991 "Test method for softening temperature by thermomechanical analysis of thermoplastic plastic films and sheets."

[0031] Examples of thermoplastic resins constituting the thermoplastic resin film include polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene ether, polyether ether ketone, polyether ketone, and polyethersulfone. These may be used alone or in combination of two or more. Among these, from the viewpoint of processability as an electromagnetic wave shielding film, those containing polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, and polyimide are preferred, and those containing polyethylene, polypropylene, polyethylene terephthalate, and polyethylene naphthalate are more preferred. Furthermore, when heat resistance is required, polyimide films are preferred, and when chemical resistance and solvent resistance are also required, fluororesin films are preferred. Note that other components, such as known additives, may be added to the thermoplastic resin within a range that does not impair the effects of the present invention.

[0032] The thickness of the thermoplastic resin film is preferably from 5 to 200 μm, more preferably from 10 to 100 μm.

[0033] <Thermosetting resin film of the first electromagnetic wave shielding film> In the first electromagnetic wave shielding film, examples of the thermosetting resin constituting the resin film include epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins, and acrylic resins. These may be used alone or in combination of two or more. Among these, silicone resins and bismaleimide resins are preferred from the viewpoints of heat resistance and flexibility.

[0034] The silicone resin used in the thermosetting resin film is not particularly limited as long as it is a thermosetting silicone resin composition, but preferred resins include addition-curable silicone resin compositions containing an alkenyl group-containing organopolysiloxane, an organohydrogenpolysiloxane, and a hydrosilylation catalyst, and condensation-curable silicone resin compositions containing an alkoxysilyl group- and / or hydroxysilyl group-containing organopolysiloxane and a condensation catalyst. Addition-curable silicone resin compositions are preferred from the viewpoint of various physical properties such as workability, storage stability, transparency, and electrical properties. Preferred addition-curable silicone resin compositions are addition-curable silicone resin compositions containing (A) an alkenyl group-containing organopolysiloxane having a resin structure, (B) an organohydrogenpolysiloxane having a resin structure, and (C) a platinum group metal catalyst.

[0035] The bismaleimide resin used in the thermosetting resin film is preferably a bismaleimide resin composition containing a bismaleimide resin having a dimer acid skeleton in the molecule and a reaction initiator. Other components such as known additives may be added to the thermosetting resin within a range that does not impair the effects of the present invention.

[0036] The thermosetting resin film that can be used is a thermosetting resin that has been preprocessed into a film having a thickness of preferably 5 to 200 μm, more preferably 10 to 100 μm.

[0037] <Resins used in the impregnated films of the second and third electromagnetic wave shielding films> In the second and third electromagnetic wave shielding films, the resin used for impregnation in the impregnated film may be a thermoplastic resin or a thermosetting resin. (thermoplastic resin) In the second and third electromagnetic wave shielding films, the thermoplastic resin used in the impregnated film can be used in liquid form when it is impregnated into the carbon nanotube nonwoven fabric, by dissolving it in a solvent or, in the case of a fluororesin, dispersing it in a dispersing solvent such as water to form a slurry resin. After the carbon nanotube nonwoven fabric is impregnated with the liquid thermoplastic resin in this way, the solvent or dispersing solvent is heated and dried to remove the solvent, thereby forming an impregnated film.

[0038] In the second and third electromagnetic wave shielding films, examples of the thermoplastic resin in the impregnated film include polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, polyimide, polyphenylene ether, polyether ether ketone, polyether ketone, and polyethersulfone. These may be used alone or in combination of two or more. Among these, those containing polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, and polyimide are preferred. Other components, such as known additives, may be added to the thermoplastic resin within a range that does not impair the effects of the present invention.

[0039] (thermosetting resin) In the second and third electromagnetic wave shielding films, examples of the thermosetting resin used in the impregnated film include epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins, and acrylic resins. These may be used alone or in combination of two or more. Among these, epoxy resins and bismaleimide resins are preferred.

[0040] Preferred examples of epoxy resins include epoxy resins having two or more glycidyl groups per molecule. Examples of epoxy resins used in the present invention include bisphenol-type epoxy resins such as bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, bisphenol AD-type epoxy resins, and bisphenol S-type epoxy resins; novolac-type epoxy resins such as epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, epoxy resins having a dicyclopentadiene skeleton, phenol novolac-type epoxy resins, and cresol novolac-type epoxy resins; and polyfunctional epoxy resins. These epoxy resins can be used alone or in combination of two or more.

[0041] As a curing agent for an epoxy resin, any curing agent that has a phenolic hydroxyl group or an amino group having active hydrogen and forms a crosslinked structure with the epoxy resin can be used. As a curing agent having a phenolic hydroxyl group, any phenolic resin with a phenolic hydroxyl group can be used. As a curing agent having an amino group, an aromatic amine curing agent that can produce an epoxy resin cured product with high heat resistance and high elastic modulus is preferred.

[0042] As the bismaleimide resin, a bismaleimide resin having a dimer acid skeleton in the molecule is preferably used because of its excellent heat resistance, low elasticity, toughness, and adhesiveness. Representative bismaleimide resins include the above-mentioned SLK-6895 (manufactured by Shin-Etsu Chemical Co., Ltd.) and SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.), as well as the SLK-2000 series (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0043] The amount of bismaleimide resin impregnated into the carbon nanotube nonwoven fabric is preferably 10 to 1,000 parts by mass per 100 parts by mass of the nonwoven fabric.

[0044] When a bismaleimide resin is used as the thermosetting resin, it is preferable to use a reaction initiator for the bismaleimide resin as a curing catalyst. The reaction initiator for the bismaleimide resin is not particularly limited as long as it promotes the crosslinking reaction, and examples thereof include ionic catalysts such as imidazoles, organic phosphorus compounds, tertiary amines, quaternary ammonium salts, boron trifluoride amine complexes, organophosphines, and organophosphonium salts; organic peroxides such as diallyl peroxide, dialkyl peroxide, peroxide carbonate, and hydroperoxide; and radical polymerization initiators such as azoisobutyronitrile.

[0045] Among these, organic peroxides are preferred, and examples of the organic peroxides include dicumyl peroxide, t-butyl peroxybenzoate, t-amyl peroxybenzoate, dibenzoyl peroxide, diuraloyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, di-t-butyl peroxide, and dibenzoyl peroxide.

[0046] The reaction initiator is preferably blended in an amount of 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the bismaleimide resin. The reaction initiator may be used alone or in combination of two or more.

[0047] In the second and third electromagnetic wave shielding films, other components such as known additives may be added to the thermosetting resin in the impregnated film within the range that does not impair the effects of the present invention.

[0048] The amount of resin impregnated into the carbon nanotube nonwoven fabric is preferably 100 to 1,000 parts by mass, more preferably 200 to 400 parts by mass, per 100 parts by mass of the nonwoven fabric.

[0049] <Additives added to resin in electromagnetic wave shielding film> The electromagnetic wave shielding film may contain other components, such as known additives, as long as the effects of the present invention are not impaired. Examples of other components include coupling agents and inorganic materials. The coupling agents and inorganic materials may be added to either the thermoplastic resin film or thermosetting resin film of the first electromagnetic wave shielding film, or to either the thermoplastic resin or thermosetting resin of the second electromagnetic wave shielding film. In particular, addition to the thermosetting resin composition, which is the raw material for the thermosetting resin film, is preferred.

[0050] A coupling agent can be used to improve the wetting and adhesive strength between the carbon nanotube nonwoven fabric and the resin. Specific examples of the coupling agent include those listed above as the agents to be added to the carbon nanotube nonwoven fabric, and the descriptions therein are incorporated herein by reference.

[0051] When such a coupling agent is added, the amount used is preferably 0.5 to 20 parts by mass per 100 parts by mass of the thermoplastic resin or thermosetting resin. The addition to the thermoplastic resin can be carried out, for example, by preparing a solution of the thermoplastic resin in a solvent and adding the coupling agent to the solution.

[0052] Examples of inorganic materials include conductive inorganic materials and insulating inorganic materials. Conductive inorganic materials can further increase electrical conductivity and can improve electromagnetic wave shielding performance in frequency bands from millimeter waves to terahertz. Insulating inorganic materials can further increase the thermal conductivity of the carbon nanotube nonwoven fabric. Specific examples of conductive inorganic materials and insulating inorganic materials include the examples mentioned above as materials to be added to the carbon nanotube nonwoven fabric, and reference is made to the descriptions thereof.

[0053] In the first electromagnetic wave shielding film, the inorganic material may be laminated as a thermoplastic resin film or a thermosetting resin film, and in the second electromagnetic wave shielding film, the inorganic material may be dispersed in a thermoplastic resin or a thermosetting resin, which is then impregnated into the carbon nanotube nonwoven fabric. When an inorganic material is added, the amount added is preferably 5 to 60 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the thermoplastic resin or thermosetting resin.

[0054] In the present invention, the total thickness of the laminate film is 5 to 1,500 μm, preferably 5 to 1,000 μm, more preferably 10 to 500 μm, even more preferably 60 to 90 μm, and particularly preferably 34 to 90 μm. If the total thickness of the laminate film is within this range, the properties of the carbon nanotubes as an electromagnetic wave shielding material can be fully utilized. Note that the total thickness of the laminate film is the thickness of the part excluding the pressure-sensitive adhesive layer and the release film, and if a protective layer is present, the protective layer is also included in the total thickness of the laminate film.

[0055] <Laminated film of the first electromagnetic wave shielding film> In the first electromagnetic wave shielding film, the laminate film is a resin laminate film in which a carbon nanotube nonwoven fabric and a resin film are laminated. The total thickness of the laminate film (resin laminate film) is 5 to 1,500 μm, preferably 10 to 500 μm, and more preferably 34 to 90 μm. If the total thickness of the laminate film is within this range, the properties of the carbon nanotubes as an electromagnetic wave shielding material can be fully utilized. Furthermore, by configuring the laminate film to have a release film attached via an adhesive layer, handling is also easy.

[0056] The total thickness of the laminated film is the thickness when the laminated film is completed. If a thermoplastic resin film is laminated onto a carbon nanotube nonwoven fabric by heating and pressurizing, the total thickness after that. If the resin film is a thermosetting resin film that hardens after lamination, the total thickness after hardening.

[0057] <Laminated film of the second electromagnetic wave shielding film> In the second and third electromagnetic wave shielding films, the impregnated film is a carbon nanotube nonwoven fabric impregnated with a thermoplastic resin or a thermosetting resin, and the total thickness of the impregnated film is preferably 2.5 to 500 μm, more preferably 5 to 250 μm, and even more preferably 30 to 100 μm.

[0058] In the second electromagnetic wave shielding film, the laminate film is an impregnated laminate film formed by laminating two or more layers of impregnated films in which carbon nanotube nonwoven fabric is impregnated with resin. The total thickness of the laminate film (impregnated laminate film) is 5 to 1,500 μm, preferably 5 to 1,000 μm, more preferably 10 to 500 μm, and more preferably 60 to 90 μm. If the total thickness of the impregnated laminate film is within this range, the properties of the carbon nanotubes as an electromagnetic wave shielding material can be fully utilized.

[0059] <Third electromagnetic wave shielding film laminated film> In the third electromagnetic wave shielding film, the laminate film is an impregnated film in which a carbon nanotube nonwoven fabric is impregnated with a resin, or a laminated impregnated film in which two or more layers of such a film are laminated, and a nonwoven fabric impregnated laminate film in which the carbon nanotube nonwoven fabric is laminated on the impregnated film or the laminated impregnated film. The total thickness of the laminate film (nonwoven fabric impregnated laminate film) is 5 to 1,500 μm, preferably 10 to 500 μm, and more preferably 20 to 90 μm. If the total thickness is within this range, the properties of the carbon nanotubes as an electromagnetic wave shielding material can be fully utilized.

[0060] The total thickness of the laminated impregnated film or nonwoven fabric-impregnated laminated film is the thickness of the laminated impregnated film or nonwoven fabric-impregnated laminated film when it is completed. It is based on the thickness of the impregnated film obtained by impregnating the carbon nanotube nonwoven fabric with a thermoplastic resin solution and then heating and drying to remove the solvent, or, in the case where the thermosetting resin is hardened after impregnation into the carbon nanotube nonwoven fabric, it is based on the thickness after hardening.

[0061] The electromagnetic wave shielding film has a pressure-sensitive adhesive layer laminated on one outermost surface of the laminate film and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer. The outermost surface may be any outermost surface that can be adopted in each form, and in the second electromagnetic wave shielding film, it is one side of the impregnated laminate film, and in the third electromagnetic wave shielding film, it is one side of the nonwoven fabric impregnated laminate film.

[0062] <Adhesive layer> In the electromagnetic wave shielding film of the present invention, a pressure-sensitive adhesive is used to attach and fix the electromagnetic wave shielding film to the surface of an electronic component or a circuit board. Any available pressure-sensitive adhesive can be used, but acrylic resin pressure-sensitive adhesives and silicone resin pressure-sensitive adhesives are preferred, as they are available in a wide range of adhesive strengths.

[0063] Representative examples of silicone resin adhesives include KR100, KR130, KR3701, and KR3704 (all manufactured by Shin-Etsu Chemical Co., Ltd.). This type of adhesive is diluted with a solvent such as toluene, a catalyst is added, and then the adhesive is applied to one side of an electromagnetic wave shielding film. The adhesive layer is then formed by treating the film at a temperature of 100 to 150°C for several minutes to remove the solvent and heat-curing the film. The thickness of the adhesive layer can be adjusted by varying the dilution level of the solvent. Furthermore, the adhesive strength can be easily adjusted by mixing a light adhesive with a heavy adhesive. If the adhesive is to be attached to a heatable member, a thermosetting adhesive or adhesive may be used. The thickness of the adhesive layer is preferably 5 to 100 μm, and more preferably 10 to 70 μm.

[0064] <Release film> In the electromagnetic wave shielding film, the release film can be made of polypropylene, PET, polyethylene film, fluororesin film, etc. If the pressure-sensitive adhesive layer applied to the electromagnetic wave shielding film is difficult to peel from the release film, a release film treated with a release agent can be used.

[0065] The thickness of the release film is preferably 10 to 50 μm from the viewpoint of ease of use. A matte-finished film can also be used as the release film.

[0066] <Method of manufacturing electromagnetic wave shielding film> The first electromagnetic wave shielding film can be produced, for example, by a melt rolling method in which a resin film and a carbon nanotube nonwoven fabric are laminated and heated to reduce viscosity, and then laminated on the carbon nanotube nonwoven fabric, or by a transfer method in which a resin varnish is formed into a film using a coater or the like, and then transferred to the carbon nanotube nonwoven fabric using a press or laminator. As described above, the resin film can be a thermoplastic resin film or a thermosetting resin film, and the thermosetting resin film can be an uncured, semi-cured, or completely cured thermosetting resin film.

[0067] The melt rolling method is advantageous in various respects, such as not requiring solvent removal and a relatively favorable working environment. The melt rolling method involves expanding a carbon nanotube nonwoven fabric to the required width using a bar or the like, sandwiching a film of thermoplastic or thermosetting resin between release papers from above and below, and then peeling off the release papers and feeding the carbon nanotube nonwoven fabric between several pairs of heated metal rolls installed at approximately the same height in the direction of travel of the carbon nanotube nonwoven fabric. The carbon nanotube nonwoven fabric is then nipped to heat and pressurize the thermoplastic or thermosetting resin. In the melt rolling method, nip pressure is a linear pressure, so it is preferable to increase the number of nip rolls to achieve sufficient heating and pressurization. Alternatively, pressure molding may be performed using a molding press, such as a heatable multi-stage press, without using heated metal rolls.

[0068] In the transfer method, a base film is coated with a resin varnish, the solvent is dried to obtain a resin film, and then the carbon nanotube nonwoven fabric and the resin film are laminated and pressed together using a laminator or press to transfer the resin film to the carbon nanotube nonwoven fabric. Any film can be used as the base film, but resin films tend to peel easily, and PET film, PE film, PP film, Teflon (registered trademark) film, Aflex film, etc. are preferred.

[0069] If necessary, the surface of the substrate film can be subjected to various surface treatments such as corona treatment, plasma treatment, silicone treatment, etc. Any solvent can be used for the resin varnish, but highly volatile solvents are preferred, such as alcohols such as ethanol and IPA, acetone, toluene, xylene, anisole, hydrocarbon solvents, and silicone solvents.

[0070] The concentration of the resin varnish is preferably 0.1 to 200 parts by mass relative to 100 parts by mass of the resin. Any method can be used to coat the base film with the resin varnish, but a spin coater or bar coater is preferred because it is easy to use. The temperature at which the resin film on the base film is dried is preferably a temperature at which the thermosetting resin does not react, more preferably 30 to 120°C.

[0071] Furthermore, when the carbon nanotube nonwoven fabric and the resin film are laminated and pressed together using a laminator or press to transfer the resin film to the carbon nanotube nonwoven fabric, pressure or heat can be applied as necessary.

[0072] After laminating the resin film onto the carbon nanotube nonwoven fabric using the method described above, if necessary, the semi-cured thermosetting resin film is cured by applying heat and pressure to produce an electromagnetic wave shielding film. By selecting the chemical structures of the thermoplastic resin and thermosetting resin in the resin film and the curing method for the thermosetting resin, it is possible to produce laminate films ranging from hard and tough to flexible and conformable to different shapes.

[0073] The impregnated films constituting the second and third electromagnetic wave shielding films can be produced by, for example, a wet method in which a thermoplastic resin or a thermosetting resin is dissolved in a solvent or dispersed in a dispersion solvent to reduce viscosity, and then the resin is impregnated into a carbon nanotube nonwoven fabric.

[0074] In the wet method, a carbon nanotube nonwoven fabric is impregnated with a thermoplastic resin or a thermosetting resin, and then the volatile solvent or dispersion solvent is removed to produce a resin film impregnated with a thermoplastic resin or an impregnated film impregnated with an uncured thermosetting resin. If solvent remains in the impregnated film, it can have adverse effects during molding and cause problems such as a worsening of the working environment. For this reason, the amount of solvent remaining in the impregnated film is 1% by mass or less, preferably 0.5% by mass or less. The method for removing the solvent depends on the boiling point of the solvent used, but can easily be achieved by heat treatment at 80 to 150°C for about 10 minutes to 1 hour.

[0075] A laminated impregnated film can be produced by laminating two or more layers of impregnated films and applying heat and pressure. Alternatively, a laminated film of a thermosetting resin or a laminated film of a cured thermosetting resin can be produced by laminating an impregnated film or a laminated impregnated film with a carbon nanotube nonwoven fabric and applying heat and pressure.

[0076] Thereafter, a pressure-sensitive adhesive layer is laminated on the outermost surface of the laminate film, specifically, for example, on the outermost surface of the resin laminate film in the first electromagnetic wave shielding film, the outermost surface of the impregnated laminate film in the second electromagnetic wave shielding film, or the outermost surface of the nonwoven fabric impregnated laminate film in the third electromagnetic wave shielding film, and a release film is laminated on the adhesive surface of the pressure-sensitive adhesive layer, thereby obtaining the electromagnetic wave shielding film of the present invention. The outermost surface is not particularly limited in each embodiment, as long as it is a layer that can be taken.

[0077] The total thickness of the electromagnetic wave shielding film is preferably from 10 to 1,600 μm, more preferably from 10 to 1,500 μm, and even more preferably from 15 to 500 μm.

[0078] By processing using such a molding method, it is possible to supply a large-area electromagnetic wave shielding film of a desired thickness in sheet or roll form wound around a paper tube or the like.

[0079] The electromagnetic wave shielding film of the present invention processed in this manner is lightweight and has excellent electromagnetic wave shielding properties, processability, and ease of use, and is therefore suitable for use as surface coatings for electronic circuit boards equipped with a large number of electronic components, as storage containers for electromagnetic wave-generating devices such as automobile batteries, motor components, and DC / DC converter sealants, which require electromagnetic wave shielding properties. Furthermore, it can also be used as a component or storage container for communication equipment that uses high frequencies above millimeter waves and requires electromagnetic wave shielding and heat resistance.

[0080] 1A is a longitudinal cross-sectional view schematically showing an example of a first electromagnetic wave shielding film. This electromagnetic wave shielding film 1a is a six-layered electromagnetic wave shielding film having a four-layer laminate film formed by laminating a carbon nanotube nonwoven fabric 2, a resin film 3, and a protective layer 4, a pressure-sensitive adhesive layer 5 laminated on the carbon nanotube nonwoven fabric side of the laminate film, and a release film 6 laminated on the adhesive side of the pressure-sensitive adhesive layer 5.

[0081] This electromagnetic wave shielding film 1a can be processed by the molding method described above to produce a large-area electromagnetic wave shielding film with a predetermined thickness, and as shown in Figure 2, can be wound into a roll like glass cloth to form electromagnetic wave shielding film 8.The rolled electromagnetic wave shielding film 6 can then be cut into tape-like pieces as shown in Figure 3, and can be used as electromagnetic wave shielding film 9 cut into tape-like pieces.

[0082] The first electromagnetic wave shielding film 1a, which has a six-layer structure, can shield electromagnetic waves, for example, by peeling off the release film 6 and attaching it to the surface of an electronic component 11 provided on a printed wiring board 10, as shown in FIG. 4A. Similarly, the second electromagnetic wave shielding film 1b shown in Fig. 1B has a four-layer structure, i.e., an electromagnetic wave shielding film having an impregnated film 7 made by laminating a carbon nanotube nonwoven fabric with a resin, a pressure-sensitive adhesive layer 5 laminated on one side of the impregnated film 7, and a release film 6 laminated on the adhesive side of the pressure-sensitive adhesive layer 5. This electromagnetic wave shielding film can be shielded by, for example, peeling off the release film 6 and attaching the impregnated film 7 to the surface of an electronic component 11 provided on a printed wiring board 10 as shown in Fig. 4B. Fig. 3C is a longitudinal cross-sectional view schematically showing an example of a third electromagnetic wave shielding film in which an impregnated film and a carbon nanotube nonwoven fabric are laminated.

[0083] Furthermore, as shown in Fig. 5, electromagnetic waves can be shielded by wrapping the surface of copper wiring 12 with electromagnetic wave shielding film 9 cut into tape. As shown in Fig. 6, a first electromagnetic wave shielding film 1a having a six-layer structure can shield electromagnetic waves by, for example, peeling off the release film 6 and applying it to the entire circuit board 13, including the surface of electronic components 11 provided on a printed wiring board 10, as shown in Fig. 6, to cover the circuit board. The same applies to second electromagnetic wave shielding films 1b and 1c. Note that in Fig. 4, the same hatched parts are made up of a single layer. In Fig. 6, some cross sections are not hatched. [Example]

[0084] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The materials used in the examples and comparative examples are shown below. The physical properties and characteristic values ​​in the present invention were measured by the following methods.

[0085] material (1) Carbon nanotube nonwoven fabric [Nonwoven fabric 1] A dispersion was prepared by mixing 100 parts water, 0.4 parts single-walled carbon nanotubes (EC1.5-P, Meijo Nano Carbon Co., Ltd.), and 0.4 parts ionic surfactant sodium deoxycholate (Fujifilm Wako Pure Chemical Industries, Ltd.) in a mixer (IFM-800DGM, Iwatani Corporation). The dispersion was applied to a release-treated PET film (E7006, Toyobo Co., Ltd.) using a doctor blade with a clearance of 1.5 mm, dried at 100 °C for 1 hour, and peeled off from the PET film to obtain a nonwoven fabric. This ionic surfactant-containing single-walled carbon nanotube nonwoven fabric had a thickness of 10 μm and a resistivity of 0.00075 (Ω·cm).

[0086] [Nonwoven fabric 2] MIRALON T01 (Huntsman) Thickness: 20 μm, resistivity: 0.0015 (Ω·cm)

[0087] [Nonwoven fabric 3] CNTM30 (Tortech) Thickness: 85 μm, resistivity: 0.0015 (Ω·cm)

[0088] (2)Thermoplastic resin, thermosetting resin [Thermosetting resin 1] 10 μm thick uncured addition-curing silicone resin film (LPS-AF500D, Shin-Etsu Chemical Co., Ltd.) [Thermosetting resin 2] Bismaleimide resin represented by the following formula (2) (SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight 5,200)

[0089] [ka] (where n≒5 (average value))

[0090] [Thermoplastic resin film 1] 25 μm thick polyethylene terephthalate film (E5100, manufactured by Toyobo Co., Ltd.) [Thermoplastic resin film 2] 50 μm thick polyethylene terephthalate film (E5100, manufactured by Toyobo Co., Ltd.)

[0091] (3) Adhesive 1 Silicone adhesive (product name: KR3704, manufactured by Shin-Etsu Chemical Co., Ltd.)

[0092] (4) Release film 1 Fluorocarbon resin film (50 μm thick) (product name: Aflex, manufactured by AGC Corporation)

[0093] [Measurement method] (1) Specific resistance The surface resistivity of the carbon nanotube nonwoven fabric was measured in accordance with "JIS K7194:1994 Resistivity test method for conductive plastics using the four-probe method." Specifically, it was measured using a Loresta-GX MCP-T700 (low-resistance resistivity meter, manufactured by Nitto Seiko Analytech Co., Ltd.). The measured value was used to calculate the resistivity. The resistivity was calculated using the following formula. Specific resistance (Ω cm) = Surface resistivity (Ω / cm 2 ) x thickness (cm) (2) Electromagnetic wave shielding properties To evaluate the electromagnetic shielding properties, we used a 12cm square cut of the electromagnetic shielding film to measure the transmission attenuation at 28 GHz and 77 GHz using a Keycom electromagnetic shielding measurement device. A schematic diagram of the measurement system is shown in Figure 7. The sample, an electromagnetic shielding film, was placed between two antennas on the y-axis connected to a vector network analyzer, with the surface perpendicular to the y-axis. Electromagnetic waves with an electric field oscillation in the z-axis direction were irradiated, and the electromagnetic waves transmitted through the sample were measured and the transmission attenuation (dB) was recorded. An Anritsu MS46122B vector network analyzer was used for the 28 GHz measurement, and an Anritsu MS46522B for the 77 GHz measurement.

[0094] [Example 1: (1)] Thermosetting resin film 1 and nonwoven fabric 1 were alternately laminated, heat-pressed at 80°C, and then cured in a dryer at 150°C for 4 hours to produce a four-layer laminated film (resin laminate film) with a total thickness of 32 μm. Pressure-sensitive adhesive 1 was applied to the nonwoven fabric 1 side of this four-layer film so that the adhesive layer would be 10 μm thick after curing. The film was then heated and cured at 100°C for 1 hour, and release film 1 was then laminated onto the adhesive layer to produce a six-layer electromagnetic wave shielding film. The transmission attenuation was measured using the method described above to determine the shielding properties of the resulting electromagnetic wave shielding film. The results are shown in Table 1. Furthermore, by peeling off the release film and applying it to an electronic circuit board equipped with semiconductor elements, a shielding film-coated circuit board that conformed to the unevenness of the circuit surface was produced (Figure 4A). The shielding film was easily peeled off from the shielding film-coated circuit board.

[0095] [Example 2: (1)] Nonwoven fabric 1 was laminated on both sides of thermoplastic resin film 1 and then heat-pressed at 240°C to produce a three-layer laminate film (resin laminate film). Furthermore, a film of thermosetting resin 1 was laminated as a protective layer on one side of this three-layer resin laminate film, and after heat-pressing at 80°C, it was cured in a dryer at 150°C for four hours to produce a four-layer resin laminate film with a total thickness of 51 μm. Pressure-sensitive adhesive 1 was applied to the nonwoven fabric 1 side of this four-layer film so that the pressure-sensitive adhesive layer would be 10 μm thick after curing, and the film was then heat-cured at 150°C for one hour. Release film 1 was then laminated on to produce a six-layer electromagnetic wave shielding film.

[0096] [Example 3: (1)] An electromagnetic wave shielding film was produced in the same manner as in Example 2, except that the thermoplastic resin film was changed to thermoplastic resin film 2. The total thickness of the laminated film (resin laminated film) was 76 μm.

[0097] [Example 4: (2)] A toluene solution containing 100 parts by mass of thermosetting resin 2, 1 part by mass of a curing catalyst (dicumyl peroxide (Percumyl D, manufactured by NOF Corporation)), and 200 parts by mass of toluene was prepared. Nonwoven fabric 2 was impregnated with this toluene solution and then heated at 100°C for 10 minutes to dry and remove the toluene, producing a semi-cured impregnated film with a thickness of 35 μm. Two of these impregnated films were laminated and pressure-cured at 180°C and 0.5 MPa for 1 hour to produce an impregnated laminated film with a total thickness of 76 μm. Pressure-sensitive adhesive 1 was applied to one side of the laminated film (impregnated laminated film) to a thickness of 10 μm after curing, and after heat-curing, release film 1 was laminated on top to produce a four-layer electromagnetic wave shielding film.

[0098] [Example 5: (2)] An electromagnetic wave shielding film was produced in the same manner as in Example 2, except that the carbon nanotube nonwoven fabric was changed to nonwoven fabric 2. The total thickness of the laminated film (impregnated laminated film) was 71 μm.

[0099] [Example 6: (3)] A toluene solution containing 100 parts by mass of thermosetting resin 2, 1 part by mass of a curing catalyst (dicumyl peroxide (Percumyl D, manufactured by NOF Corporation)), and 200 parts by mass of toluene was prepared. Nonwoven fabric 2 was impregnated with this toluene solution and then heated at 100°C for 10 minutes to dry and remove the toluene, producing a semi-cured impregnated film with a thickness of 40 μm. This impregnated film was laminated with nonwoven fabric 1 and pressure-cured at 180°C and 0.5 MPa for 1 hour to produce a laminated film (nonwoven fabric-impregnated laminated film) with a total thickness of 48 μm. Pressure-sensitive adhesive 1 was applied to the surface of nonwoven fabric 1 of the laminated film (nonwoven fabric-impregnated laminated film) to a thickness of 10 μm after curing, and after heat-curing, release film 1 was laminated on top to produce a four-layer electromagnetic wave shielding film.

[0100] [Comparative Example 1] A thermosetting resin film 1 was laminated onto nonwoven fabric 1 as a protective layer, followed by heat pressing at 80°C and curing in a dryer at 150°C for 4 hours to produce a two-layer laminated film with a total thickness of 16 μm. Pressure-sensitive adhesive 1 was applied to the nonwoven fabric 1 side of this two-layer film to a thickness of 10 μm after curing. The film was then heated and cured at 150°C for 1 hour, after which release film 1 was laminated to produce a four-layer electromagnetic wave shielding film. The shielding properties of the produced electromagnetic wave shielding film were measured using the above-mentioned measurement method after peeling off the release film. The results are shown in Table 1. Furthermore, by peeling off the release film and applying it to an electronic circuit board equipped with semiconductor elements, a shielding film-coated circuit board that conformed to the unevenness of the circuit surface was produced. The shielding film was easily peeled off from the shielding film-coated circuit board.

[0101] Comparative Example 2 An electromagnetic wave shielding film was produced in the same manner as in Comparative Example 1, except that the carbon nanotube nonwoven fabric was changed to Nonwoven fabric 2. The total thickness of the laminated film was 34 μm.

[0102] Comparative Example 3 An electromagnetic wave shielding film was produced in the same manner as in Comparative Example 1, except that the carbon nanotube nonwoven fabric was changed to Nonwoven fabric 3. The total thickness of the laminated film was 91 μm.

[0103] [Table 1]

[0104] [Table 2] In the table: Laminated film includes laminated film, laminated impregnated film, and laminated nonwoven fabric impregnated film.

[0105] Comparisons between Example 1 and Comparative Example 2, and Examples 2 to 6 and Comparative Example 3 show that an electromagnetic wave shielding film laminated with two or more layers of thin carbon nanotube nonwoven fabric exhibits electromagnetic wave shielding properties equivalent to that of a film using only one layer of thick carbon nanotube nonwoven fabric, and furthermore, it is possible to reduce the total thickness of the electromagnetic wave shielding film. [Industrial Applicability]

[0106] According to the present invention, it is easy to provide electromagnetic shielding to electronic components and wiring mounted inside electronic devices, and the electronic devices become compatible with high-speed communications such as 5G and 6G, and therefore have extremely high industrial value and applicability. [Explanation of symbols]

[0107] 1a: Six-layer first electromagnetic wave shielding film 1b: The second electromagnetic wave shielding film, which is four layers 2. Carbon nanotube nonwoven fabric 3 Resin film 4 protective layer 5. Adhesive layer 6 Release film 7 Impregnated film 8. Electromagnetic wave shielding film rolled up 9 Electromagnetic wave shielding film cut into tape 10 Printed wiring board 11 Electronic Components 12 Copper wiring 13 Circuit Board 14 Measurement sample 15 Antenna 16 Incident wave 17 Transmitted wave

Claims

1. An electromagnetic wave shielding film comprising a carbon nanotube nonwoven fabric having a resistivity of 0.00005 to 0.05 Ω cm and a thickness of 1 to 500 μm, and a resin, An electromagnetic wave shielding film comprising a laminated film having two or more layers of the carbon nanotube nonwoven fabric laminated thereon and having a total thickness of 5 to 1,500 μm, a pressure-sensitive adhesive layer laminated on one outermost surface of the laminated film, and a release film laminated on the adhesive surface of the pressure-sensitive adhesive layer.

2. 2. The electromagnetic wave shielding film according to claim 1, wherein the laminated film is a resin laminated film in which a carbon nanotube nonwoven fabric and a resin film are laminated.

3. 3. The electromagnetic wave shielding film according to claim 2, wherein the resin film is a thermoplastic resin film, and the softening point of the thermoplastic resin is 400° C. or lower.

4. 4. The electromagnetic wave shielding film according to claim 3, wherein the thermoplastic resin constituting the thermoplastic resin film comprises at least one selected from the group consisting of polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, and polyimide.

5. 3. The electromagnetic wave shielding film according to claim 2, wherein the resin film is a thermosetting resin film, and the thermosetting resin is at least one selected from the group consisting of epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins, and acrylic resins.

6. 2. The electromagnetic wave shielding film according to claim 1, wherein the laminated film is an impregnated laminated film in which two or more layers of impregnated films each having a carbon nanotube nonwoven fabric impregnated with a resin are laminated together.

7. 2. The electromagnetic wave shielding film according to claim 1, wherein the laminated film is an impregnated film obtained by impregnating a carbon nanotube nonwoven fabric with a resin, and a nonwoven fabric impregnated laminated film obtained by laminating the carbon nanotube nonwoven fabric on the impregnated film.

8. 8. The electromagnetic wave shielding film according to claim 6, wherein the resin comprises one or more thermoplastic resins selected from the group consisting of polyethylene, polypropylene, fluororesin, polyethylene terephthalate, polyethylene naphthalate, and polyimide.

9. 8. The electromagnetic wave shielding film according to claim 6, wherein the resin comprises one or more thermosetting resins selected from the group consisting of epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, phenolic resins, polyimide resins, polyamide resins, bismaleimide resins, maleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, polyester resins, silicone resins, and acrylic resins.

10. 8. The electromagnetic wave shielding film according to claim 1, wherein the carbon nanotubes constituting the carbon nanotube nonwoven fabric are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture thereof.

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