Electromagnetic wave absorber and method for manufacturing the same

Abstract

To provide an electromagnetic wave absorber capable of improving adhesion between an electromagnetic wave absorption layer and a resin layer.SOLUTION: An electromagnetic wave absorber 100 according to the present invention comprises an electromagnetic wave absorption layer 10 comprising carbon nanotubes, and a resin layer 50 provided on the electromagnetic wave absorption layer 10 and formed by curing a resin composition comprising urethane (meth)acrylate, thiol, and a photopolymerization initiator, wherein the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 3 or more, and a content ratio of thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave absorber and a method for manufacturing the same.

Background Art

[0002] A carbon nanotube has a structure in which a uniform planar graphene sheet is wound into a cylindrical shape. Because of such a unique structure, a carbon nanotube has various properties and is expected to be applied in a wide range of fields.

[0003] For example, Patent Document 1 describes an electromagnetic wave noise suppression sheet including a coating layer containing carbon nanotubes and an overcoat layer provided on the coating layer to suppress scratches on the coating layer and impart dielectric breakdown strength.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the electromagnetic wave noise suppression sheet as described above, it is desired to improve the adhesion between the layer containing carbon nanotubes and the overcoat layer.

[0006] One of the objects according to some aspects of the present invention is to provide an electromagnetic wave absorber capable of improving the adhesion between the layer containing carbon nanotubes and the overcoat layer. Another object according to some aspects of the present invention is to provide a method for manufacturing an electromagnetic wave absorber capable of improving the adhesion between the layer containing carbon nanotubes and the overcoat layer.

Means for Solving the Problems

[0007] One aspect of the electromagnetic wave absorber according to the present invention is an electromagnetic wave absorption layer containing carbon nanotubes, a resin layer provided on the electromagnetic wave absorption layer and formed by curing a resin composition containing urethane (meth)acrylate, thiol, and a photopolymerization initiator, and includes the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 3 or more, the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

[0008] In one aspect of the electromagnetic wave absorber according to the present invention, the number of thiol groups per monomer in the thiol may be 3 or more.

[0009] In one aspect of the electromagnetic wave absorber according to the present invention, the content ratio of the thiol in the resin layer may be 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

[0010] In one aspect of the electromagnetic wave absorber according to the present invention, the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate may be 15 or less.

[0011] In one aspect of the electromagnetic wave absorber according to the present invention, the electromagnetic wave absorption layer may contain polyacrylic acid.

[0012] One aspect of the method for manufacturing an electromagnetic wave absorber according to the present invention is a step of forming an electromagnetic wave absorption layer containing carbon nanotubes, a step of applying a resin composition containing urethane (meth)acrylate, thiol, and a photopolymerization initiator to the electromagnetic wave absorption layer, a step of irradiating the applied resin composition with ultraviolet rays to cure it and form a resin layer including the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 3 or more, the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

[0013] In one aspect of the method for manufacturing an electromagnetic wave absorber according to the present invention, the number of thiol groups per monomer in the thiol may be 3 or more.

[0014] In one aspect of the method for manufacturing an electromagnetic wave absorber according to the present invention, the content ratio of the thiol in the resin layer may be 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

[0015] In one aspect of the method for manufacturing an electromagnetic wave absorber according to the present invention, the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate may be 15 or less.

[0016] In one aspect of the method for manufacturing an electromagnetic wave absorber according to the present invention, in the step of forming the electromagnetic wave absorption layer, a mixed solution containing the carbon nanotube, polyacrylic acid, and water may be prepared.

Advantages of the Invention

[0017] According to the electromagnetic wave absorber of the present invention, it includes an electromagnetic wave absorption layer containing carbon nanotubes, and a resin layer formed by curing a resin composition provided on the electromagnetic wave absorption layer and containing urethane (meth) acrylate, thiol, and a photopolymerization initiator. The number of (meth) acryloyl groups per monomer in the urethane (meth) acrylate is 3 or more, and the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth) acrylate. Therefore, according to the electromagnetic wave absorber of the present invention, the adhesion between the electromagnetic wave absorption layer and the resin layer can be improved.

[0018] According to the method for manufacturing an electromagnetic wave absorber of the present invention, it includes a step of forming an electromagnetic wave absorption layer containing carbon nanotubes, a step of applying a resin composition containing urethane (meth) acrylate, thiol, and a photopolymerization initiator to the electromagnetic wave absorption layer, and a step of irradiating ultraviolet rays to the applied resin composition to cure it and form a resin layer. The number of (meth) acryloyl groups per monomer in the urethane (meth) acrylate is 3 or more, and the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth) acrylate. Therefore, according to the method for manufacturing an electromagnetic wave absorber of the present invention, the adhesion between the electromagnetic wave absorption layer and the resin layer can be improved.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Best Mode for Carrying Out the Invention

[0020] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Also, not all of the configurations described below are essential constituent elements of the present invention.

[0021] 1. Electromagnetic wave absorber 1.1. Configuration First, the electromagnetic wave absorber according to the present embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the electromagnetic wave absorber according to the present embodiment.

[0022] The electromagnetic wave absorber 100 has a sheet shape in which the length in the in-plane direction (the direction orthogonal to the thickness direction) is sufficiently long with respect to the thickness direction. The electromagnetic wave absorber 100 can also be referred to as an electromagnetic wave absorption sheet. The planar shape of the electromagnetic wave absorber 100 is not particularly limited, and for example, it is rectangular.

[0023] The electromagnetic wave absorber 100 has electromagnetic wave absorption properties for absorbing electromagnetic waves. The electromagnetic wave absorption properties are evaluated, for example, by measuring the transmission attenuation rate Rtp (dB) by the microstrip line method. The larger the Rtp, the higher the electromagnetic wave absorption properties.

[0024] As shown in FIG. 1, the electromagnetic wave absorber 100 includes, for example, an electromagnetic wave absorption layer 10, a support layer 20, an adhesive layer 30, a release layer 40, and a resin layer 50. Hereinafter, each member will be described in order.

[0025] 1.1.1. Electromagnetic wave absorption layer The electromagnetic wave absorption layer 10 is provided on the support layer 20. The electromagnetic wave absorption layer 10 is provided between the support layer 20 and the resin layer 50. The thickness of the electromagnetic wave absorption layer 10 is, for example, 1 μm or more and 10 μm or less, preferably 3 μm or more and 5 μm or less. If the thickness of the electromagnetic wave absorption layer 10 is 1 μm or more, the electromagnetic waves can be sufficiently absorbed. If the thickness of the electromagnetic wave absorption layer 10 is 10 μm or less, the occurrence of cracks in the electromagnetic wave absorption layer 10 can be suppressed. The thickness of each layer such as the electromagnetic wave absorption layer 10 is measured by, for example, SEM (Scanning Electron Microscope). The electromagnetic wave absorption layer 10 contains, for example, carbon nanotubes (hereinafter also referred to as "CNT") and a dispersant. Hereinafter, each component of the electromagnetic wave absorption layer 10 will be described.

[0026] 1.1.1.1. Carbon Nanotubes (CNT) Examples of CNTs include single-walled carbon nanotubes (SWNTs) in which a single six-membered ring network (graphene sheet) made of carbon is wound cylindrically, and multi-walled carbon nanotubes (MWNTs) in which a plurality of graphene sheets are wound concentrically. The CNT aqueous dispersion may contain only one of SWNTs and MWNTs, or may contain both. Both ends of the CNT may be closed or open.

[0027] CNTs are produced, for example, by an arc discharge method, a laser ablation method, a CVD (Chemical Vapor Deposition) method, or the like. CNTs are produced in a predetermined size by these methods.

[0028] The diameter of the CNT is, for example, 1 nm or more and 100 nm or less, preferably 5 nm or more and 50 nm or less, and more preferably 8 nm or more and 17 nm or less. If the diameter of the CNT is 1 nm or more and 100 nm or less, the dispersibility of the CNT can be improved.

[0029] The fiber length of the CNT is, for example, 0.5 μm or more and 50 μm or less, and preferably 15 μm or more and 35 μm or less. If the fiber length of the CNT is 0.5 μm or more and 50 μm or less, the dispersibility of the CNT can be improved. The diameter and fiber length of the CNT are measured using an SEM. Note that the "fiber length of the CNT" refers to the length of the CNT when it is bundled by van der Waals forces, and is the length of the CNT before it is dispersed in a solvent.

[0030] The BET specific surface area of CNT is, for example, 50 m 2 / g or more 500m 2 / g or less, preferably 100m 2 / g or more 300m 2 / g or less. The BET specific surface area of the CNT is 50m 2 / g or more 500m 2 / g or less, the dispersibility of CNTs can be improved. Note that "BET specific surface area" refers to the specific surface area measured by the BET (Brunauer Emmett Teller) method. The BET specific surface area is measured using an automatic specific surface area measuring device.

[0031] In the electromagnetic-wave absorbing layer 10, the CNT content is 1.0% by mass or more, preferably 2.0% by mass or more, and more preferably 3.0% by mass or more. If the CNT content is 1.0% by mass or more, it is possible to improve the performance specific to CNTs, such as electromagnetic wave absorption. In the electromagnetic-wave absorbing layer 10, the CNT content is, for example, 20.0% by mass or less, preferably 10.0% by mass or less, and more preferably 5.0% by mass or less. If the CNT content is 20.0% by mass or less, it is possible to improve the dispersibility of CNTs. The content of each component, such as CNT, is measured by thermal gravimetric analysis (TGA).

[0032] The volume-average particle diameter (median diameter) of the CNTs based on volume is, for example, 30.0 μm or less, preferably 15.0 μm or less, more preferably 10.0 μm or less, even more preferably 5.0 μm or less, and even more preferably 1.0 μm or less. If the median diameter of the CNTs is 30.0 μm or less, the dispersibility of the CNTs can be improved. The median diameter of the CNTs is, for example, 0.1 μm or more.

[0033] Note that the "median diameter of the CNTs" is the diameter at which, when the CNT particles are divided into two from a certain particle diameter, the larger side and the smaller side have equal amounts. The median diameter is also called "d50". The median diameter of the CNTs is measured by a laser diffraction / scattering particle size distribution measuring device (Partica LA-960V2: manufactured by Horiba, Ltd.).

[0034] 1.1.1.2. Dispersant The dispersant disperses the CNTs in water as the solvent. The dispersant may be a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. The dispersant may be a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group in an amount of 90% by mass or more, preferably 95% by mass or more.

[0035] The dispersant may be, for example, a polymer containing a repeating unit derived from acrylic acid and not containing a repeating unit derived from a monomer having a sulfonic acid group. The dispersant may be a polymer composed of a repeating unit derived from acrylic acid and may be a polymer composed of a repeating unit derived from acrylic acid. The dispersant may be polyacrylic acid.

[0036] The dispersant may be a polymer containing repeating units derived from monomers having a sulfonic acid group and not containing repeating units derived from acrylic acid. The dispersant may be a polymer composed of repeating units derived from monomers having a sulfonic acid group. Examples of the monomer having a sulfonic acid group include styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamido-2-methylpropane sulfonic acid, 2-hydroxy-3-acrylamidopropane sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, and the like. The dispersant may be polystyrene sulfonic acid.

[0037] The dispersant may be a polymer containing both repeating units derived from acrylic acid and repeating units derived from monomers having a sulfonic acid group. The dispersant may be a copolymer of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid, or a copolymer of acrylic acid and styrene sulfonic acid.

[0038] The dispersant may be carboxymethyl cellulose or a salt thereof. The dispersant may be sodium carboxymethyl cellulose. The dispersant may contain two or more components such as polyacrylic acid and sodium carboxymethyl cellulose.

[0039] The weight average molecular weight of the dispersant is, for example, 5000 or more and 1000000 or less, preferably 6000 or more and 800000 or less, and more preferably 7000 or more and 200000 or less. If the weight average molecular weight of the dispersant is 5000 or more, the dispersant can easily bind to CNTs and improve the dispersibility of CNTs. However, if the weight average molecular weight is too large, the dispersibility will conversely deteriorate. Therefore, the molecular weight of the dispersant is preferably 1000000 or less. The "weight average molecular weight" refers to the weight average molecular weight in terms of polystyrene measured by Gel Permeation Chromatography (GPC).

[0040] In the electromagnetic wave absorption layer 10, the content of the dispersant is, for example, 0.4% by mass or more and 10.0% by mass or less, preferably 0.5% by mass or more and 8.0% by mass or less, and more preferably 1.0% by mass or more and 6.0% by mass or less. If the content of the dispersant is 0.4% by mass or more and 10.0% by mass or less, the dispersibility of CNTs can be improved. The content of the dispersant is measured by thermogravimetric analysis.

[0041] In the electromagnetic wave absorption layer 10, the mass M of CNTs CNT to the mass M of the dispersant DISP of the ratio M DISP / M CNT is 1 / 10 or more and 5 or less (CNT:dispersant = 10:1 to 1:5), preferably 1 / 5 or more and 4 or less (CNT:dispersant = 5:1 to 1:4), more preferably 1 / 3 or more and 3 or less (CNT:dispersant = 3:1 to 1:3), and even more preferably 1 / 2 or more and 1 or less (CNT:dispersant = 2:1 to 1:1). If the ratio M DISP / M CNT is 1 / 10 or more, the performance specific to CNTs such as electromagnetic wave absorbability can be enhanced. If the ratio M DISP / M CNT is 5 or less, the dispersibility of CNTs can be improved.

[0042] 1.1.1.3. Other Additives The electromagnetic wave absorption layer 10 may further contain various additives such as preservatives, pH adjusters, colorants, and defoamers as required.

[0043] 1.1.2. Support Layer The support layer 20 is provided on the adhesive layer 30. The support layer 20 supports the electromagnetic wave absorption layer 10. The support layer 20 is provided between the electromagnetic wave absorption layer 10 and the adhesive layer 30. The thickness of the support layer 20 is, for example, 6 μm or more and 250 μm or less, preferably 12 μm or more and 125 μm or less.

[0044] ​The support layer 20 is, for example, a film made of resin such as polyethylene terephthalate (PET), polyimide (PI), polyamide (PA), polycarbonate (PC), etc. Note that as long as the support layer 20 can support the electromagnetic wave absorption layer 10, its material is not particularly limited, and it may be a metal foil such as aluminum foil or copper foil, a sheet containing pulp, a non-woven fabric, or a synthetic paper manufactured mainly from synthetic resin.

[0045] 1.1.3. Adhesive layer The adhesive layer 30 is provided on the release layer 40. The adhesive layer 30 is provided between the support layer 20 and the release layer 40. The adhesive layer 30 has adhesiveness. As long as the adhesive layer 30 has adhesiveness, its material is not particularly limited, and examples thereof include natural rubber-based, synthetic rubber-based, urethane-based resin, acrylic-based resin, vinyl acetate-based resin, vinyl acetate / acrylic ester copolymer resin, vinyl acetate / ethylene copolymer resin, etc.

[0046] 1.1.4. Release layer The release layer 40 is provided so as to be peelable from the adhesive layer 30. When attaching the electromagnetic wave absorber 100 to an external device such as an electronic device, after peeling the release layer 40 from the adhesive layer 30, the adhesive layer 30 is brought into contact with the external device to attach the electromagnetic wave absorber 100 to the external device.

[0047] As long as the release layer 40 is peelable from the adhesive layer 30, its material is not particularly limited, and examples thereof include uncoated paper such as high-quality paper, coated paper such as general coated paper and art paper, glassine paper, films using polyethylene, polyethylene terephthalate, etc., or film laminated paper. If necessary, as a release agent, silicone resin, fluororesin, etc. may be applied and dried in the range of 0.1 g / m 2 to 3.0 g / m 2 or less.

[0048] 1.1.5. Resin layer The resin layer 50 is provided on the electromagnetic wave absorption layer 10. The resin layer 50 is an overcoat layer that covers the electromagnetic wave absorption layer 10. The resin layer 50 is provided on the side opposite to the support layer 20 side of the electromagnetic wave absorption layer 10.

[0049] The thickness of the resin layer 50 is, for example, 2 μm or more and 10 μm or less, preferably 2.5 μm or more and 5 μm or less. If the thickness of the resin layer 50 is 2 μm or more, damage to the electromagnetic wave absorption layer 10 can be suppressed. If the thickness of the resin layer 50 is 10 μm or less, curling is less likely to occur in the resin layer 50.

[0050] The resin layer 50 has insulating properties. The surface resistivity of the resin layer 50 is, for example, 1×10 6 Ω / □ or more and 1×10 8 Ω / □ or less. If the surface resistivity of the resin layer 50 is 1×10 6 Ω / □ or more, leakage of the electromagnetic wave absorber 100 can be suppressed. The surface resistivity can be measured in accordance with "JIS K 7194". The resin layer 50 has low hydrophilicity. Therefore, moisture entering the electromagnetic wave absorption layer 10 can be reduced.

[0051] The resin layer 50 is formed by curing a resin composition containing urethane (meth)acrylate, thiol, and a photopolymerization initiator. Hereinafter, each component of the resin composition will be described.

[0052] 1.1.5.1. Urethane (meth)acrylate Urethane (meth)acrylate is a compound having a double bond of a (meth)acryloyl group and containing a urethane bond. Urethane (meth)acrylate cures and shrinks when irradiated with ultraviolet (UV) light.

[0053] Note that "(meth)acrylate" means acrylate or methacrylate having an alcohol residue equivalent thereto. "(Meth)acryloyl group" means acryloyl group or methacryloyl group having an alcohol residue equivalent thereto.

[0054] In the urethane (meth)acrylate in the resin composition, the number of (meth)acryloyl groups per monomer is 3 or more, preferably 15 or less. When the number of (meth)acryloyl groups per monomer is 3 or more, it has scratch resistance such that it is difficult to chip even when rubbed, and a resin layer 50 having high adhesion to the electromagnetic wave absorption layer 10 can be formed. When the number of (meth)acryloyl groups per monomer is 15 or less, when the urethane (meth)acrylate is irradiated with ultraviolet rays and cured and shrunk, it is possible to suppress the occurrence of curl in the resin layer 50 due to an excessively high curing shrinkage rate.

[0055] The urethane (meth)acrylate is obtained by reacting a (meth)acrylate having a hydroxyl group with a polyfunctional isocyanate. Examples of commercially available urethane (meth)acrylates include UN-2701, UN-2310, UN-3320HA, UN-3320HC, UN-3320HS, UN-904, UN-901T, UN-952, UN-954, UN-905, UN-906S (manufactured by Negami Kogyo Co., Ltd. as above), UA-1100H, U-15HA, UA-7100, U-6LPA, UA-33H, U-10HA, U-10PA (manufactured by Shin-Nakamura Chemical Co., Ltd. as above), and the like. The resin layer 50 may be formed by curing a resin composition containing a urethane acrylate, a thiol, and a photopolymerization initiator.

[0056] The content of the repeating unit derived from the urethane (meth)acrylate in the resin layer 50 is, for example, 50% by mass or more and 97% by mass or less, preferably 70% by mass or more and 95% by mass or less. When the content of the repeating unit derived from the urethane (meth)acrylate is 50% by mass or more, the adhesion between the resin layer 50 and the electromagnetic wave absorption layer 10 can be improved by the urethane bond of the urethane (meth)acrylate. When the content of the repeating unit derived from the urethane (meth)acrylate is 97% by mass or less, when the urethane (meth)acrylate is irradiated with ultraviolet rays and cured and shrunk, it is possible to suppress the occurrence of curl in the resin layer 50 due to an excessively high curing shrinkage rate.

[0057] The weight average molecular weight of the urethane (meth)acrylate is, for example, 300 or more and 100,000 or less, preferably 500 or more and 5,000 or less. If the weight average molecular weight of the urethane (meth)acrylate is 300 or more, the adhesion between the resin layer 50 and the electromagnetic wave absorption layer 10 can be improved. If the weight average molecular weight of the urethane (meth)acrylate is 100,000 or less, it is possible to suppress the viscosity of the solution containing the urethane (meth)acrylate from becoming too high and making handling difficult.

[0058] 1.1.5.2. Thiol Thiol is an organic compound having hydrogenated sulfur at its terminal. Examples of the thiol contained in the resin composition include pentaerythritol tetrakis(3-mercaptobutyrate) (manufactured by Resonac Co., Ltd.: Karenz MT-PE1), 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione (manufactured by Resonac Co., Ltd.: Karenz MT-NR1), trimethylolpropane tris(3-mercaptobutyrate) (manufactured by Resonac Co., Ltd.: Karenz MT-TPMB), 2-ethyl-2-{[(3-sulfanylpropanoyl)oxy]methyl}propane- A mixture of 1,3-diyl bis(3-sulfanylpropanoate) (main component), 2-ethyl-2-[({3-[(3-sulfanylpropanoyl)sulfanyl]propanoyl}oxy)methyl]propane-1,3-diyl bis(3-sulfanylpropanoate), and 2-ethyl-2-(hydroxymethyl)propane-1,3-diyl bis(3-sulfanylpropanoate) (manufactured by SC Organic Chemical Co., Ltd.: TMMP), 2,2-bis[[(3-mercaptopropionyl)oxy]methyl]trimethylene bis[3-mercaptopropionate] (manufactured by SC Organic Chemical Co., Ltd.: PEMP), 3-mercaptopropionic acid ester of dipentaerythritol (manufactured by SC Organic Chemical Co., Ltd.: DPMP), 2-{2,4,6-trioxo-3,5-bis[2-(3-sulfanylpropanoyloxy)ethyl]-1,3,5-triazinane-1-yl}ethyl 3-sulfanylpropionate as the main component (75%), a mixture of 2-{2,4,6-trioxo-3-(2-hydroxyethyl)-5-[2-(3-sulfanylpropanoyloxy)ethyl]-1,3,5-triazinane-1-yl}ethyl 3-sulfanylpropionate and 2-{2,4,6-trioxo-3,5-bis[2-(3-sulfanylpropanoyloxy)ethyl]-1,3,5-triazinane-1-yl}ethyl 1-(3-sulfanylpropanoylthio)propionate (manufactured by SC Organic Chemical Co., Ltd.: TEMPIC), an alkali-treated product of the reaction product of pentaerythritol mainly composed of 3-(3-mercapto-propoxy)-2,2-bis-(3-mercapto-propoxymethyl)-propan-1-ol, the reaction product of pentaerythritol mainly composed of 3-allyloxy-2,2-bis(allyloxymethyl)propanol and 3-chloro-1-propene, and thioacetic acid (manufactured by SC Organic Chemical Co., Ltd.: Multhiol Y-3), an alkali-treated product of the reaction product of pentaerythritol mainly composed of 3-{3-(3-mercapto-propoxy)-2,2-bis[(3-mercaptopropoxy)methyl]propoxy}-1-propanethiol, the reaction product of pentaerythritol mainly composed of tetrakis[(allyloxy)methyl]methane and 3-chloro-1-propene, and S-thioacetic acid (manufactured by SC Organic Chemical Co., Ltd.: Multhiol Y-4) can be mentioned.

[0059] The thiol contained in the resin composition has a function of reducing the oxygen inhibition of urethane (meth)acrylate. FIG. 2 is a diagram for explaining the mechanism of reducing the oxygen inhibition of urethane (meth)acrylate by thiol.

[0060] As shown in FIG. 2, when urethane (meth)acrylate is irradiated with UV, it is excited from the ground state to the excited state, and radicals are generated. Urethane (meth)acrylate having radicals undergoes a polymerization reaction as the main reaction, such as reaction path R1.

[0061] Here, since oxygen molecules exist in the triplet state, they are in a place where the energy level is close to that of the generated radicals. Therefore, urethane (meth)acrylate having radicals reacts with oxygen molecules to generate peroxide radicals, as in reaction path R2. When peroxide radicals are generated, the polymerization of urethane (meth)acrylate stops.

[0062] On the other hand, thiol donates hydrogen to peroxide radicals to become thioyl radicals, as in reaction path R3. And urethane (meth)acrylate having thioyl radicals undergoes a polymerization reaction, as in reaction path R4. In this way, thiol can reduce the oxygen inhibition of urethane (meth)acrylate and restart the polymerization of urethane (meth)acrylate. When subjected to oxygen inhibition, the surface curability of the resin layer 50 is poor and the abrasion resistance deteriorates.

[0063] In this way, in the electromagnetic wave absorber 100, for example, even without polymerizing urethane (meth)acrylate in an inert gas atmosphere, a resin layer 50 with high surface curability and good abrasion resistance can be formed by thiol.

[0064] The thiol contained in the resin composition is preferably a polyfunctional thiol. The number of thiol groups per monomer in the thiol is, for example, 3 or more and 10 or less, preferably 4 or more and 6 or less. If the number of thiol groups per monomer in the thiol is 3 or more and 10 or less, oxygen inhibition of urethane (meth) acrylate can be reduced.

[0065] The thiol contained in the resin composition is preferably a secondary thiol or a tertiary thiol. Secondary thiols and tertiary thiols have a larger steric factor than primary thiols and can suppress the thermal addition reaction (gelation during storage) to the monomer.

[0066] The content ratio of thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less, preferably 5 parts by mass or more and 45 parts by mass or less, more preferably 5.3 parts by mass or more and 42.9 parts by mass or less, based on 100 parts by mass of urethane (meth) acrylate. If the content ratio of thiol is 3 parts by mass or more, a resin layer 50 having scratch resistance and high adhesion to the electromagnetic wave absorption layer 10 can be formed. If the content ratio of thiol is 50 parts by mass or less, it is possible to suppress the resin layer 50 from becoming too soft and conversely deteriorating in scratch resistance. Since thiol has an ether bond, if the content ratio is too large, it will become soft. The content of thiol in the resin layer 50 is, for example, 1% by mass or more and 40% by mass or less, preferably 3% by mass or more and 35% by mass or less.

[0067] 1.1.5.3. Photoinitiator The photoinitiator contained in the resin composition is not particularly limited as long as it generates radicals by the energy of ultraviolet rays and initiates the polymerization of the monomer. By using ultraviolet rays, excellent safety and cost reduction of the light source lamp can be achieved.

[0068] Examples of the photopolymerization initiator include, for example, aromatic ketones, acylphosphine oxide-based compounds, aromatic onium salt compounds, organic peroxides, thio compounds (such as thioxanthone-based compounds and thiophenyl group-containing compounds), hexaarylbiimidazole compounds, ketoxime ester compounds, borate compounds, azinium compounds, metallocene compounds, active ester compounds, compounds having a carbon-halogen bond, and alkylamine compounds.

[0069] Specific examples of the photopolymerization initiator include acetophenone, acetophenone benzyl ketal, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2-phenylacetophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diaminobenzophenone, Michler's ketone, benzoin propyl ether, benzoin ethyl ether, benzyldimethyl ketal, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-hydroxy-2-methyl-1-phenylpropan-1-one, thioxanthone, diethylthioxanthone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino-propan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,4-diethylthioxanthone, bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide.

[0070] Examples of commercially available photoinitiators include, for example, Omnirad 651 (2,2-dimethoxy-1,2-diphenylethan-1-one), Omnirad 184 (1-hydroxy-cyclohexyl-phenyl-ketone), DAROCUR 1173 (2-hydroxy-2-methyl-1-phenyl-propan-1-one), Omnirad 2959 (1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-pro Pan-1-one), Omnirad 127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]phenyl}-2-methyl-propan-1-one), Omnirad 907 (2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one), Omnirad 369 (2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1), Omnirad 379 (2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl) phenyl]-1-butanone), DAROCUR TPO (2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide), Omnirad 819 (bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide), Omnirad TPO (2,4,6-trimethylbenzoyldiphenylphosphine oxide), Omnirad 784 (bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium), Omnirad OXE 01 (1,2-octanedione, 1-[4-(phenylthio)-, 2-(O-benzoyloxime)]), Omnirad OXE 02 (ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazole-3-yl]-, 1-(O-acetoxyoxime)), Omnirad 754 (a mixture of 2-[2-oxo-2-phenylacetoxyethoxy]ethyl ester of oxyphenylacetic acid and 2-(2-hydroxyethoxy)ethyl ester of oxyphenylacetic acid) (above, manufactured by BASF Japan Ltd.), KAYACURE DETX-S (2,4-diethylthioxanthone) (manufactured by Nippon Kayaku Co., Ltd.), Lucirin TPO, LR8893, LR8970 (above, manufactured by BASF Japan Ltd.), Ubecryl P36 (manufactured by UCB), etc.

[0071] The content ratio of the photoinitiator in the resin composition is, for example, 0.5 parts by mass or more and 10.0 parts by mass or less, preferably 1.0 parts by mass or more and 5.0 parts by mass or less, and more preferably 2.0 parts by mass or more and 4.0 parts by mass or less with respect to 100 parts by mass of urethane (meth) acrylate. If the content ratio of the photoinitiator is 0.5 parts by mass or more, the curability of the resin layer 50 can be improved. If the content ratio of the photoinitiator is 10.0 parts by mass or less, the remaining undissolved photoinitiator can be suppressed.

[0072] 1.1.5.4. Other Additives The resin composition constituting the resin layer 50 may contain various additives such as a curing accelerator, a tackifier, an antioxidant, a pigment, a dye, a plasticizer, a UV absorber, an antifoaming agent, a leveling agent, a filler, a flame retardant, a viscosity modifier, and an antiblocking agent as required.

[0073] 1.2. Effects In the electromagnetic wave absorber 100, it includes an electromagnetic wave absorption layer 10 containing CNT, and a resin layer 50 formed by curing a resin composition provided on the electromagnetic wave absorption layer 10 and containing urethane (meth) acrylate, thiol, and a photoinitiator. The number of (meth) acryloyl groups per monomer in urethane (meth) acrylate is 3 or more, and the content ratio of thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of urethane (meth) acrylate.

[0074] Therefore, in the electromagnetic wave absorber 100, as shown in "3. Examples and Comparative Examples" described later, the adhesion between the electromagnetic wave absorption layer 10 and the resin layer 50 can be improved.

[0075] Furthermore, the surface curability of the resin layer 50 can be improved, and the resin layer 50 can have scratch resistance such that it is not easily chipped even when rubbed. Furthermore, the resin layer 50 can have chemical resistance such that it is not easily dissolved even when exposed to a solvent. Thereby, damage to the electromagnetic wave absorption layer 10 can be suppressed. Furthermore, the resin layer 50 has bendability such that it is not easily cracked even when bent. Thereby Therefore, even if the electromagnetic wave absorption layer 10 is cracked, it can be prevented from scattering outside.

[0076] In the electromagnetic wave absorber 100, the number of thiol groups per monomer in the thiol may be 3 or more. If the number of thiol groups is 3 or more, the oxygen inhibition of urethane (meth) acrylate can be reduced.

[0077] In the electromagnetic wave absorber 100, the content ratio of thiol in the resin composition may be 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of urethane (meth) acrylate. If the content ratio of thiol is 5 parts by mass or more and 45 parts by mass or less, the scratch resistance and the adhesion between the resin layer 50 and the electromagnetic wave absorption layer 10 can be more reliably improved.

[0078] In the electromagnetic wave absorber 100, the number of (meth) acryloyl groups per monomer in urethane (meth) acrylate may be 15 or less. If the number of (meth) acryloyl groups is 15 or less, when urethane (meth) acrylate is irradiated with ultraviolet rays and cured and shrunk, it is possible to suppress the curing shrinkage rate from becoming too high and causing curl in the resin layer 50.

[0079] In the electromagnetic wave absorber 100, the electromagnetic wave absorption layer 10 may contain polyacrylic acid. If the electromagnetic wave absorption layer 10 contains polyacrylic acid, the scratch resistance and the adhesion between the resin layer 50 and the electromagnetic wave absorption layer 10 can be more reliably improved.

[0080] 2. Manufacturing method of electromagnetic wave absorber 2.1. Overall flow Next, a method for manufacturing the electromagnetic wave absorber 100 according to the present embodiment will be described with reference to the drawings. FIG. 3 is a flowchart for explaining the method for manufacturing the electromagnetic wave absorber 100 according to the present embodiment.

[0081] As shown in FIG. 3, for example, the method for manufacturing the electromagnetic wave absorber 100 includes a mixed liquid preparation step (step S1) of preparing a mixed liquid, a dispersion step (step S2) of dispersing CNTs contained in the mixed liquid to prepare a CNT aqueous dispersion, a dispersion liquid coating step (step S3) of coating the CNT aqueous dispersion on the support layer 20, a drying step (step S4) of drying the applied CNT aqueous dispersion to form the electromagnetic wave absorption layer 10, a resin composition coating step (step S5) of coating the electromagnetic wave absorption layer 10 with a resin composition, and an ultraviolet irradiation step (step S6) of irradiating the applied resin composition with ultraviolet rays to cure it and form the resin layer 50.

[0082] 2.2. Mixed Liquid Preparation Step (Step S1) In the mixed liquid preparation step, CNTs and a dispersant are added to water, and the CNTs, the dispersant, and water are mixed to prepare a mixed liquid. The mixing of the CNTs, the dispersant, and water is performed, for example, by a homogenizer. The homogenizer may be an ultrasonic type that generates cavitation with ultrasonic waves, a stirring type that stirs the mixed liquid, or a pressure type that applies pressure to the mixed liquid. By performing the treatment with the homogenizer, aggregates formed by the CNTs can be reduced. As a result, the subsequent dispersion step can be performed smoothly.

[0083] Examples of the water for the mixed liquid include pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis permeate, and distilled water, and those with extremely low ionic impurities such as ultrapure water. It is also possible to use tap water. Since water is used as the solvent for the mixed liquid, it is more environmentally friendly than the case where an organic solvent is used as the solvent. The mixed liquid may contain only CNTs, a dispersant, and water. That is, the mixed liquid may be composed of only CNTs, a dispersant, and water. [[ID=II]]

[0084] 2.3. Dispersion Step (Step S2) In the dispersion step, the CNTs contained in the mixed liquid are dispersed. Specifically, in the dispersion step, a wet atomization device is used to disperse the CNTs contained in the mixed liquid. FIG. 4 is a cross-sectional view schematically showing the wet atomization device 200 used in the dispersion step.

[0085] As shown in FIG. 4, for example, the wet atomization device 200 includes a nozzle 210, a member 220 to be collided with, and a housing 230 that houses the nozzle 210 and the member 220 to be collided with.

[0086] The nozzle 210 is, for example, coated with DLC (Diamond-Like Carbon). Thereby, even if the mixed liquid is acidic, corrosion of the nozzle 210 can be suppressed. In particular, when the dispersant contained in the mixed liquid is polyacrylic acid, since the mixed liquid has strong acidity, it is preferable that the nozzle 210 is coated with DLC.

[0087] A nozzle hole 212 is formed in the nozzle 210. Only one nozzle hole 212 is formed in the nozzle 210. Only one nozzle 210 is provided. The nozzle 210 injects the mixed liquid produced in the mixed liquid production process from the nozzle hole 212.

[0088] The diameter of the nozzle hole 212 formed in the nozzle 210 is, for example, 0.10 mm or more and 0.60 mm or less, preferably 0.12 mm or more and 0.30 mm or less. If the diameter of the nozzle hole 212 is 0.10 mm or more, clogging of the nozzle hole 212 with the mixed liquid can be suppressed. If the diameter of the nozzle hole 212 is 0.60 mm or less, the collision energy of the mixed liquid can be increased.

[0089] The pressure applied to the mixed liquid ejected from the nozzle 210 is, for example, 100 MPa or more and 300 MPa or less, preferably 150 MPa or more and 250 MPa or less. If the pressure is 100 MPa or more, the collision energy of the mixed liquid can be increased. If the pressure is 300 MPa or less, it is possible to suppress the situation where the collision energy is too high and the CNT fibers are broken and the desired characteristics cannot be obtained.

[0090] The throughput of the mixed liquid sprayed from the nozzle 210 is, for example, 20 L / hr or more and 400 L / hr or less, preferably 25 L / hr or more and 100 L / hr or less. If the throughput is 20 L / hr or more, the processing time in the wet atomization device 200 can be shortened. If the throughput is 400 L / hr or less, clogging of the nozzle holes 212 with the mixed liquid can be suppressed.

[0091] The member to be collided with 220 is disposed opposite to the nozzle 210. The member to be collided with 220 is made of, for example, ceramic such as silicon nitride, or metal such as SUS (Steel Use Stainless). In the illustrated example, the member to be collided with 220 is a ceramic ball. The wet atomization device 200 has a ball collision chamber. The shape of the member to be collided with 220 is, for example, spherical. The member to be collided with 220 is, for example, eccentric with respect to the nozzle holes 212. Thereby, wear of the member to be collided with 220 can be reduced.

[0092] In the dispersion step, the mixed liquid is sprayed from the nozzle 210 and collided with the member to be collided with 220. CNTs contained in the mixed liquid are dispersed by the shearing force when passing through the nozzle holes 212, cavitation by in-liquid injection, and the impact force when the CNTs collide with the member to be collided with 220. The dispersed CNTs are discharged from the discharge holes 232 formed in the housing 230. Thereby, a CNT aqueous dispersion can be obtained.

[0093] The number of passes of the mixed liquid in the wet atomization device 200 is, for example, 1 or more and 10 or less, preferably 1 or more and 5 or less. If the number of passes is 10 or less, it is possible to suppress the fibers of CNTs from being cut by the collision of the mixed liquid and the desired characteristics not being obtained. Furthermore, the manufacturing time can be shortened. Furthermore, energy savings can be achieved.

[0094] Note that the "number of passes of the mixed liquid in the wet atomization device 200" refers to the number of times the mixed liquid circulates in the wet atomization device 200. For example, "the number of passes is 2 times" means that the mixed liquid is circulated twice so that the CNTs that have collided with the collided member 220 once collide with the collided member 220 again. In this way, the number of passes corresponds to the number of collisions of the mixed liquid ejected from the nozzle hole 212 against the collided member 220. The number of passes is proportional to the processing time in the wet atomization device 200. When the processing time in the wet atomization device 200 is long, the number of circulations of the mixed liquid increases.

[0095] Through the above steps, a CNT aqueous dispersion can be produced.

[0096] 2.4. Dispersion Coating Step (Step S3) In the dispersion coating step, the CNT aqueous dispersion produced in the dispersion step is coated on the support layer 20 on which the adhesive layer 30 and the release layer 40 are formed. Examples of the coating method include directly coating the support layer 20 using, for example, a wire bar coater, a knife coater, an air coater, a blade coater, a reverse roll coater, a die coater, a micro gravure coater, etc., and a method of attaching the CNT aqueous dispersion to a roller and transferring the CNT aqueous dispersion attached to the roller to the support layer 20, so-called roll coater, etc.

[0097] 2.5. Drying Step (Step S4) In the drying step, the CNT aqueous dispersion coated on the support layer 20 is dried. The drying method of the CNT aqueous dispersion is not particularly limited as long as the water contained in the CNT aqueous dispersion can be evaporated. Examples include hot air drying, infrared drying, and natural drying. The temperature of the drying furnace is, for example, 70°C or higher and 130°C or lower, preferably 80°C or higher and 120°C or lower, and more preferably 90°C or higher and 110°C or lower. If the temperature of the drying furnace is 70°C or higher, the water can be sufficiently evaporated. If the temperature of the drying furnace is 130°C or lower, the occurrence of cracks in the electromagnetic wave absorption layer 10 can be suppressed. The drying time is, for example, 0.5 minutes or more and 3 minutes or less.

[0098] Through the above steps, the electromagnetic wave absorption layer 10 can be formed on the support layer 20.

[0099] 2.6. Resin Composition Coating Step (Step S5) In the resin composition coating step, the resin composition is coated on the electromagnetic wave absorption layer 10. The resin composition contains urethane (meth)acrylate, thiol, and a photopolymerization initiator as described in the above-mentioned "1.1.5. Resin Layer". Further, the resin composition contains an organic solvent.

[0100] Specifically, the resin composition is prepared by adding urethane (meth)acrylate and thiol to an organic solvent, stirring, adding a photopolymerization initiator, and further stirring.

[0101] Examples of the organic solvent include alcohols such as methanol, ethanol, isopropanol, butanol, and octanol; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), and cyclohexanone; esters such as ethyl acetate, butyl acetate, ethyl lactate, γ-butyrolactone, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate (PGMEA); ethers such as ethylene glycol monomethyl ether and diethylene glycol monobutyl ether; aromatic hydrocarbons such as benzene, toluene, and xylene; and amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone.

[0102] The content of the organic solvent in the resin composition is, for example, 50% by mass or more and 80% by mass or less, preferably 55% by mass or more and 75% by mass or less, and more preferably 60% by mass or more and 70% by mass or less. If the content of the organic solvent is 50% by mass or more, the solute can be dissolved without residue. If the content of the organic solvent is 80% by mass or less, the organic solvent can be sufficiently evaporated after drying, and the density of the resin layer 50 formed by the resin composition can be improved.

[0103] The above resin composition is applied to the electromagnetic wave absorption layer 10. As the application method, for example, the method described in the above "2.4. Dispersion liquid application step (step S3)" can be used. Note that the resin composition may be applied by an inkjet method, a spray method, or the like.

[0104] 2.7. Ultraviolet irradiation step (step S6) In the ultraviolet irradiation step, the resin composition applied to the electromagnetic wave absorption layer 10 is dried to evaporate the organic solvent of the resin composition. Then, the dried resin composition is irradiated with ultraviolet rays to be cured. Through the above steps, the resin layer 50 can be formed on the electromagnetic wave absorption layer 10.

[0105] Examples of the drying method include infrared drying, hot air drying, natural drying, etc. The temperature of the drying furnace is, for example, 65°C or higher and 95°C or lower, preferably 70°C or higher and 90°C or lower, and more preferably 75°C or higher and 85°C or lower. If the temperature of the drying furnace is 65°C or higher, the organic solvent of the resin composition can be sufficiently evaporated. If the temperature of the drying furnace is 95°C or lower, curling of the resin layer 50 can be suppressed. The drying time is, for example, 0.5 minutes or more and 3 minutes or less.

[0106] The light amount of ultraviolet rays is, for example, 250 mJ / cm 2 or more and 550 mJ / cm 2 or less, preferably 300 mJ / cm 2 or more and 500 mJ / cm 2 or less, and more preferably 350 mJ / cm 2 or more and 450 mJ / cm 2 or less. If the light amount of ultraviolet rays is 250 mJ / cm 2 or more, the resin composition can be sufficiently cured. If the light amount of ultraviolet rays is 550 mJ / cm 2 or less, curling of the resin layer 50 can be suppressed.

[0107] Through the above steps, the electromagnetic wave absorber 100 can be manufactured.

[0108] Note that the formation order of the adhesive layer 30 and the release layer 40 is not particularly limited. The adhesive layer 30 and the release layer 40 may be formed before applying the CNT aqueous dispersion to the support layer 20 as described above, or may be formed after forming the resin layer 50. Further, the method for forming the adhesive layer 30 and the release layer 40 is not particularly limited.

[0109] 3. Examples and Comparative Examples Examples and comparative examples are shown below to more specifically explain the present invention. Note that the present invention is not limited in any way by the following examples and comparative examples.

[0110] 3.1. Preparation of Samples CNT, a dispersant, and water were mixed to prepare a mixed solution. For the mixing, a homogenizer "Bio Mixer BM-2" manufactured by Nippon Seiki Co., Ltd. was used. The mixing treatment time was set to 5 minutes.

[0111] As the CNT, "LUCAN BT1003M" manufactured by LG Chem was used. The CNT is MWCNT, with a diameter of 8 nm to 17 nm, a fiber length of 10 μm to 50 μm (bundle), and a BET specific surface area of 165 m 2 / g to 205 m 2 / g. The content of CNT in the mixed solution was set to 3.0 mass%.

[0112] As the dispersant, polyacrylic acid was used. Specifically, as the polyacrylic acid, "Aquaric HL-415" manufactured by Nippon Shokubai Co., Ltd. was used. The weight average molecular weight is 10,000. The concentration of the dispersant in the mixed solution was set to 3.0 mass%.

[0113] Next, for the above mixture, a wet atomization device having a ball collision chamber was used to disperse the CNTs contained in the mixture. As the wet atomization device, a wet atomization device "Starburst Turbo" (model name: HJP-25005) manufactured by Sugino Machine Limited was used. The diameter of the nozzle hole through which the mixture was sprayed was set to 0.17 mm, and the pressure applied to the mixture was set to 200 MPa. The throughput of the mixture was 47 L / hr. The mixture was made to collide with ceramic balls. The number of passes of the mixture through the wet atomization device was set to 3 times. Thus, a CNT aqueous dispersion containing CNTs, a dispersant, and water was prepared.

[0114] Next, the above CNT aqueous dispersion was applied onto a PET film with a thickness of 50 μm using a bar coater. As the PET film, "A4300" manufactured by Toyobo Co., Ltd. was used. Next, the PET film coated with the CNT aqueous dispersion was dried in a drying oven at 100°C for 2 minutes.

[0115] Thus, an electromagnetic wave absorption layer containing CNTs was formed on the PET film. The surface resistivity of the electromagnetic wave absorption layer was 60 Ω / sq. The surface resistivity was measured in accordance with "JIS K 7194" using "Loresta-AX MCP-T370" manufactured by Mitsubishi Chemical Analytech Co., Ltd. The thickness of the electromagnetic wave absorption layer was 3 μm.

[0116] Next, a resin composition was prepared. Specifically, a polyfunctional urethane acrylate, which is a photocurable compound, and a thiol, which is a photocuring aid, were added to toluene, which is an organic solvent, and stirred. Thereafter, a photopolymerization initiator was added and further stirred to prepare each resin composition.

[0117] Here, FIG. 5 is a table showing the production conditions and evaluation results of the samples of Examples 1 to 6 and Comparative Examples 1 to 4. As shown in FIG. 5, the number of functional groups of the polyfunctional urethane acrylate, that is, the number of acryloyl groups per monomer in the urethane acrylate, was varied from 2 to 15. Specifically, the following were used as each polyfunctional urethane acrylate.

[0118] <Examples 1 and 2> Trifunctional urethane acrylate, "SMT-001" manufactured by Negami Kogyo Co., Ltd. <Examples 3 and Comparative Examples 1 and 2> Hexafunctional urethane acrylate, "UA-1100H" manufactured by Shin-Nakamura Chemical Co., Ltd. <Example 4> Decafunctional urethane acrylate, "H-135" manufactured by Negami Kogyo Co., Ltd. <Examples 5 and 6> Pentadecafunctional urethane acrylate, "U-15HA" manufactured by Shin-Nakamura Chemical Co., Ltd. <Comparative Example 3> Bifunctional urethane acrylate, "UN-2701" manufactured by Negami Kogyo Co., Ltd.

[0119] Also, as shown in FIG. 5, the content ratio of urethane acrylate with respect to a total mass of 100 parts by mass of urethane acrylate and thiol was varied in the range of 60 to 100 parts by mass.

[0120] In Comparative Example 4, a hexafunctional acrylate monomer ("DPHA", dipentaerythritol hexaacrylate manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of urethane acrylate.

[0121] As the thiol, a tetrafunctional thiol, i.e., a thiol having 4 thiol groups per monomer in the thiol, was used. Specifically, "PE-1" manufactured by Resonac Co., Ltd. was used as the tetrafunctional thiol. Also, as shown in FIG. 5, the content ratio of thiol with respect to a total mass of 100 parts by mass of urethane acrylate and thiol was varied in the range of 0 to 40 parts by mass. The "content ratio (parts by mass)" shown in FIG. 5 is the parts by mass of thiol with respect to 100 parts by mass of urethane acrylate.

[0122] As the photopolymerization initiator, "Omnirad 184" manufactured by BASF Japan Ltd. was used. The content ratio of the photopolymerization initiator is 3 parts by mass with respect to 100 parts by mass of urethane acrylate.

[0123] Next, the above resin composition was applied onto the electromagnetic wave absorption layer using a bar coater. Next, the electromagnetic wave absorption layer coated with the resin composition was dried in a drying oven at 80°C for 1 minute, and then irradiated so that the integrated light quantity was 400 mJ / cm 2 to cure the resin composition. Thus, a resin layer was formed on the electromagnetic wave absorption layer. The thickness of the resin layer was 3 μm.

[0124] 3.2. Evaluation Method 3.2.1. Abrasion Resistance The above sample was rubbed 10 times with steel wool (manufactured by Nippon Steel Wool Co., Ltd., "Bonstar #0000") under a load of 200 g / cm 2 load, and the presence or absence of scratches was visually observed. The evaluation criteria are as follows.

[0125] A: No scratches B: Slight scratches C: Considerable scratches

[0126] 3.2.2. Curl A sample with a size of 100 mm × 100 mm was placed on a flat plate, and the distances of the four corners of the sample from the flat plate were measured. The evaluation criteria are as follows.

[0127] A: The average value of the four points is 5 mm or less B: The average value of the four points is more than 5 mm and 10 mm or less C: The average value of the four points is more than 10 mm

[0128] 3.2.3. Adhesion In accordance with the cross-cut method of JIS K 5600-5-6, a grid of 10 × 10 with a 1 mm interval was created on the surface of the resin layer, and an adhesive tape (manufactured by Nichiban Co., Ltd., "Cellophane Tape CT-24") was pasted thereon so that all the grids were covered. The pasted adhesive tape was pulled upward to peel it off from the surface of the resin layer. For all the 10 × 10 grids, the peeling situation of the resin layer from the electromagnetic wave absorption layer after peeling off the adhesive tape was visually confirmed and evaluated. The evaluation criteria are as follows.

[0129] A: None of the resin layers has peeled off. C: At least one of the resin layers has peeled off.

[0130] 3.3. Evaluation Results Fig. 5 shows the evaluation results regarding scratch resistance, curl, and adhesion between the resin layer and the electromagnetic wave absorption layer.

[0131] As shown in Fig. 5, Examples 1 to 6 all had an "A" evaluation in terms of scratch resistance, curl, and adhesion, indicating good results.

[0132] In Comparative Example 1, since it does not contain thiol, urethane acrylate was inhibited by oxygen, resulting in deteriorated scratch resistance and adhesion. In Comparative Example 2, although the adhesion had an "A" evaluation, the thiol content was too high, making the resin layer too soft and deteriorating the scratch resistance. In Comparative Example 3, since the functional group number of urethane acrylate was 2, urethane acrylate was inhibited by oxygen, and both the scratch resistance and adhesion deteriorated. In Comparative Example 4, since it does not contain urethane acrylate and thiol, the curl and adhesion deteriorated.

[0133] The above-described embodiments and modified examples are merely examples and are not limited thereto. For example, it is also possible to appropriately combine each embodiment and each modified example.

[0134] The present invention is not limited to the above-described embodiments, and various further modifications are possible. For example, the present invention includes a configuration that is substantially the same as the configuration described in the embodiments. Substantially the same configuration means, for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect. Further, the present invention includes a configuration in which a non-essential part of the configuration described in the embodiments is replaced. Also, the present invention includes a configuration having the same working effect as the configuration described in the embodiments or a configuration capable of achieving the same purpose. Additionally, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiments.

Explanation of Reference Numerals

[0135] 10…Electromagnetic wave absorption layer, 20…Support layer, 30…Adhesive layer, 40…Release layer, 50…Resin layer, 100…Electromagnetic wave absorber, 200…Wet atomization device, 210…Nozzle, 212…Nozzle hole, 220…Member to be collided, 230…Housing, 232…Discharge hole

Claims

1. An electromagnetic wave absorber comprising an electromagnetic wave absorption layer containing carbon nanotubes, a resin layer provided on the electromagnetic wave absorption layer and formed by curing a resin composition containing urethane (meth)acrylate, thiol, and a photopolymerization initiator, wherein the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 3 or more, the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

2. The electromagnetic wave absorber according to claim 1, wherein the number of thiol groups per monomer in the thiol is 3 or more.

3. The electromagnetic wave absorber according to claim 1 or 2, wherein the content ratio of the thiol in the resin composition is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

4. The electromagnetic wave absorber according to claim 1 or 2, wherein the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 15 or less.

5. The electromagnetic wave absorber according to claim 1 or 2, wherein the electromagnetic wave absorption layer contains polyacrylic acid.

6. A method for manufacturing an electromagnetic wave absorber, comprising: a step of forming an electromagnetic wave absorption layer containing carbon nanotubes; a step of applying a resin composition containing urethane (meth)acrylate, thiol, and a photopolymerization initiator to the electromagnetic wave absorption layer; a step of irradiating the applied resin composition with ultraviolet rays to cure it and form a resin layer, wherein the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 3 or more, the content ratio of the thiol in the resin composition is 3 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

7. The method for manufacturing an electromagnetic wave absorber according to claim 6, wherein the number of thiol groups per monomer in the thiol is 3 or more.

8. The method for manufacturing an electromagnetic wave absorber according to claim 6 or 7, wherein the content ratio of the thiol in the resin composition is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the urethane (meth)acrylate.

9. The method for manufacturing an electromagnetic wave absorber according to claim 6 or 7, wherein the number of (meth)acryloyl groups per monomer in the urethane (meth)acrylate is 15 or less.

10. The method for manufacturing an electromagnetic wave absorber according to claim 6 or 7, wherein in the step of forming the electromagnetic wave absorption layer, a mixed solution containing the carbon nanotube, polyacrylic acid, and water is prepared.

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