Electromagnetic wave shielding laminated sheet

Abstract

To provide a lightweight electromagnetic wave shielding laminated sheet capable of suppressing the transmission and reflection of electromagnetic waves.SOLUTION: An electromagnetic wave shielding laminated sheet (1) includes: an electromagnetic wave absorbing layer 10 that has a matrix and carbon nanotubes dispersed in the matrix, in which the bulk density is 997 kg / m3 or less; and a metal layer 30 overlapping the electromagnetic wave absorbing layer 10.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electromagnetic wave shielding laminate sheet, and more particularly to an electromagnetic wave shielding laminate sheet that is preferably used for shielding electromagnetic waves. [Background technology]

[0002] Patent Document 1 discloses an electromagnetic wave absorber having a laminated structure in which a first layer made of a dielectric, a second layer having conductivity, a third layer made of a dielectric, and a fourth layer having conductivity are laminated in this order, in which the sheet resistance of the second layer is 100 Ω / □ or more and 300 Ω / □ or less, and the fourth layer is an electromagnetic wave reflector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-102665 Summary of the Invention

[0004] An object of the present disclosure is to provide an electromagnetic wave shielding laminate sheet that is lightweight yet capable of suppressing the transmission and reflection of electromagnetic waves.

[0005] An electromagnetic wave shielding laminate sheet according to one embodiment of the present disclosure includes a matrix and carbon nanotubes dispersed in the matrix, and has a bulk density of 997 kg / m 3 and a metal layer overlying the electromagnetic wave absorbing layer. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic cross-sectional view of an electromagnetic wave shielding laminate sheet according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is an image of the electromagnetic wave absorbing layer in Example 2 taken with a scanning electron microscope. DETAILED DESCRIPTION OF THE INVENTION

[0007] The process by which the inventors have completed the present disclosure will now be outlined.

[0008] In the field of information and communications using electronic devices, weight reduction of carriers carrying electronic devices used in the aviation, space and terrestrial fields is an essential issue from the viewpoint of reducing fuel consumption.

[0009] In the above applications, shielding electromagnetic waves generated by electronic devices is important for preventing malfunction of the electronic devices due to noise, controlling the path of electromagnetic waves when communicating between electronic devices using electromagnetic waves, and so on, and in some cases it is necessary to suppress not only the transmission of electromagnetic waves but also the reflection of electromagnetic waves.

[0010] However, a practical material that is lightweight and yet can suppress both the transmission and reflection of electromagnetic waves at a high level has not yet been provided.

[0011] Therefore, the inventors have completed the present disclosure in order to provide an electromagnetic wave shielding laminate sheet that is lightweight yet capable of suppressing the transmission and reflection of electromagnetic waves.

[0012] An embodiment of the present disclosure will be described below. Note that the embodiment described below is merely one of various embodiments of the present disclosure. The following embodiment can be modified in various ways depending on the design as long as the object of the present disclosure can be achieved.

[0013] The electromagnetic wave shielding laminate sheet 1 according to this embodiment comprises a plurality of laminated layers. The plurality of layers includes at least an electromagnetic wave absorbing layer 10 and a metal layer 30. That is, the electromagnetic wave shielding laminate sheet 1 includes the electromagnetic wave absorbing layer 10 and the metal layer 30 that overlaps the electromagnetic wave absorbing layer 10. The electromagnetic wave absorbing layer 10 has a matrix and carbon nanotubes dispersed in the matrix, and has a bulk density of 997 kg / m 3 The following is the result.

[0014] According to this embodiment, the bulk density of the electromagnetic wave absorbing layer 10 is 997 kg / m 3 or less, a reduction in the weight of the electromagnetic wave shielding laminate sheet 1 is achieved. Furthermore, when electromagnetic waves are incident on the electromagnetic wave shielding laminate sheet 1 in a direction from the electromagnetic wave absorbing layer 10 side toward the metal layer 30 side, the electromagnetic waves are blocked by the metal layer 30 and are therefore less likely to transmit through the electromagnetic wave shielding laminate sheet 1. Furthermore, the electromagnetic waves reflected by the metal layer 30 are likely to be multiple-reflected between the metal layer 30 and the electromagnetic wave absorbing layer 10 within the electromagnetic wave shielding laminate sheet 1, and are therefore more likely to attenuate. For this reason, electromagnetic waves are less likely to be reflected from the electromagnetic wave shielding laminate sheet 1.

[0015] Therefore, in this embodiment, it is possible to realize an electromagnetic wave shielding laminated sheet 1 that is lightweight yet capable of suppressing the transmission and reflection of electromagnetic waves.

[0016] The configuration of the electromagnetic wave shielding laminated sheet 1 will now be described in more detail.

[0017] As described above, the electromagnetic wave shielding laminated sheet 1 includes a plurality of laminated layers, and the plurality of layers includes at least the electromagnetic wave absorbing layer 10 and the metal layer 30. The plurality of layers may include only the electromagnetic wave absorbing layer 10 and the metal layer 30, in which case the electromagnetic wave absorbing layer 10 and the metal layer 30 may be laminated so that they are in direct contact with each other. The plurality of layers may include, for example, an insulating layer 20, in which case the insulating layer 20 may be interposed between the electromagnetic wave absorbing layer 10 and the metal layer 30. That is, the electromagnetic wave absorbing layer 10, the insulating layer 20, and the metal layer 30 may be laminated in this order.

[0018] The metal layer 30 is, for example, a metal sheet. The material of the metal layer 30 is, for example, aluminum or copper, but is not limited to these. The metal layer 30 may be, for example, a thin film produced by a vapor deposition method or the like, or may be a metallic structural material.

[0019] The thickness of the metal layer 30 is adjusted as appropriate to obtain appropriate electromagnetic wave shielding ability, and is, for example, 1 nm or more. The thickness of the metal layer 30 is, for example, 100 mm or less, but may be greater than 100 mm.

[0020] As described above, the electromagnetic wave absorbing layer 10 has a bulk density of 997 kg / m 3 The weight of the electromagnetic wave shielding laminate sheet 1 can be reduced by satisfying the following. Furthermore, as described above, the electromagnetic wave absorbing layer 10 has a matrix and carbon nanotubes dispersed in the matrix, which can cause multiple reflection of electromagnetic waves between the metal layer 30 and the electromagnetic wave absorbing layer 10, thereby attenuating the electromagnetic waves. Note that the matrix refers to a matrix in the field of composite materials, and the matrix and carbon nanotubes are composited by dispersing the carbon nanotubes in the matrix.

[0021] The electromagnetic wave absorbing layer 10 preferably has a porous structure. In this case, the bulk density of the electromagnetic wave absorbing layer 10 is 997 kg / m 3 The following can be easily achieved. A porous structure is a structure having voids inside. An example of a porous structure is a structure in which long voids are arranged in a honeycomb pattern in the thickness direction of the electromagnetic wave absorbing layer 10. In this case, the electromagnetic wave absorbing layer 10 is porous but is less likely to break when a load is applied in the thickness direction. However, the porous structure of the electromagnetic wave absorbing layer 10 is not limited to this.

[0022] The matrix of the electromagnetic wave absorbing layer 10 preferably contains a water-soluble polymer. In this case, by producing the electromagnetic wave absorbing layer 10 by a freeze-drying method as described below, the weight of the electromagnetic wave absorbing layer 10 can be easily reduced, and the bulk density of the electromagnetic wave absorbing layer 10 can be reduced to 997 kg / m 3 The bulk density of the electromagnetic wave absorbing layer 10 is 500 kg / m or less. 3 More preferably, it is 100 kg / m or less. 3 It is more preferable that:

[0023] The solubility of the water-soluble polymer in water at 25°C is preferably 1 mg / 1 g-H2O or more. The water-soluble polymer may be any of natural polymers, semi-synthetic polymers, and synthetic polymers. The water-soluble polymer contains at least one selected from the group consisting of, for example, guar gum, carrageenan, sodium alginate, corn starch, xanthan gum, sodium chondrile sulfate, sodium hyaluronate, carboxymethylcellulose, sodium carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, cationized guar gum, carboxyvinyl polymer, polyacrylic acid, polyvinylpyrrolidone, and polyvinyl alcohol. The water-soluble polymer preferably contains at least one of carboxymethylcellulose and hydroxypropylmethylcellulose.

[0024] The matrix preferably further contains a cured product of a thermosetting resin. In this case, when the electromagnetic wave absorbing layer 10 comes into contact with water, the water-soluble polymer in the matrix is less likely to be eluted. The thermosetting resin preferably has the property of forming an aqueous emulsion when dispersed in water. In this case, when the electromagnetic wave absorbing layer 10 is produced by a freeze-drying method, the thermosetting resin can be easily dispersed in the matrix of the electromagnetic wave absorbing layer 10, which makes it even more difficult for the water-soluble polymer in the matrix to be eluted in water.

[0025] The thermosetting resin preferably contains an epoxy resin. When the thermosetting resin contains an epoxy resin, the thermosetting resin preferably further contains a curing agent for the epoxy resin, if necessary. In this case, the water-soluble polymer in the matrix is further prevented from leaching out when the electromagnetic wave absorbing layer 10 comes into contact with water. The epoxy resin, or the epoxy resin and curing agent, preferably have the property of forming an aqueous emulsion when dispersed in water. In this case, when the electromagnetic wave absorbing layer 10 is produced by a freeze-drying method, the epoxy resin can be easily dispersed in the matrix of the electromagnetic wave absorbing layer 10, thereby making it further difficult for the water-soluble polymer in the matrix to be leached out in water.

[0026] The compound contained in the epoxy resin is appropriately selected depending on the manufacturing method of the electromagnetic wave absorbing layer 10. For example, the epoxy resin contains an emulsion-type epoxy resin called a water-based epoxy resin, or an epoxy resin that is soluble in an organic solvent.

[0027] The emulsion-type epoxy resin preferably contains at least one selected from the group consisting of bisphenol A-type epoxy resins, bisphenol F-type epoxy resins, and the like.

[0028] The epoxy resin soluble in an organic solvent preferably contains an epoxy resin used in laminate applications, and specifically, it preferably contains at least one selected from the group consisting of bisphenol A epoxy resins, bisphenol F epoxy resins, brominated bisphenol A epoxy resins, naphthalene epoxy resins, biphenyl epoxy resins, and cresol novolac epoxy resins.

[0029] The curing agent may be a general curing agent for epoxy resins, and may contain at least one selected from the group consisting of a phenol-based curing agent, an amine-based curing agent, and an acid anhydride-based curing agent.

[0030] The ratio of the thermosetting resin to the electromagnetic wave absorbing layer 10 is preferably 5% by mass or more and 90% by mass or less. Furthermore, when the thermosetting resin contains an epoxy resin, or an epoxy resin and a curing agent, the ratio of the epoxy resin, or the epoxy resin and a curing agent, to the electromagnetic wave absorbing layer 10 is preferably 5% by mass or more and 90% by mass or less. When these ratios are 5% by mass or more, the water-soluble polymer in the matrix can be made even less likely to dissolve in water. Furthermore, when these ratios are 90% by mass or less, the thermosetting resin is less likely to hinder the weight reduction of the electromagnetic wave absorbing layer 10.

[0031] The carbon nanotubes in the electromagnetic wave absorbing layer 10 will now be described.

[0032] When the electromagnetic wave absorbing layer 10 contains carbon nanotubes, electromagnetic waves can be attenuated well within the electromagnetic wave shielding laminate sheet 1, and electromagnetic waves in the millimeter wave band and microwave band in particular can be attenuated efficiently.

[0033] Carbon nanotubes (hereinafter also referred to as CNTs) include, for example, at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0034] The G / D ratio in the Raman spectrum of CNTs is an index commonly used to evaluate the quality of CNTs. The Raman spectrum of CNTs measured by a Raman spectrometer contains the G band (1600 cm -1 around 1350 cm -1 A vibration mode called the G band (near the G band) is observed. The G band is a vibration mode derived from the hexagonal lattice structure of graphite, which is the cylindrical surface of the CNT, and the D band is a vibration mode derived from the amorphous portion. Therefore, the higher the peak intensity ratio of the G band to the D band (G / D ratio), the more crystalline the CNT can be evaluated. The higher the G / D ratio, the more conductive graphite structure the CNT has, and the higher its conductivity. Therefore, the electromagnetic wave absorption ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be improved with a smaller amount of CNT added, which is advantageous from a cost perspective. Furthermore, since a smaller amount of CNT is required, an electromagnetic wave shielding laminate sheet 1 with excellent formability can be obtained. The G / D ratio is preferably 3 or more.

[0035] Furthermore, the CNTs preferably include single-walled to five-walled carbon nanotubes, and more preferably single-walled carbon nanotubes. If the CNTs are single-walled carbon nanotubes, the electromagnetic wave absorption ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be improved with a smaller amount of addition compared to multi-walled carbon nanotubes.

[0036] The average diameter (Av) of the CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, and preferably 15 nm or less, and even more preferably 10 nm or less. If the average diameter (Av) of the CNTs is 0.5 nm or more, the electromagnetic wave absorption ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be further improved. Furthermore, if the average diameter (Av) of the CNTs is 15 nm or less, the electromagnetic wave shielding laminate sheet 1 is flexible, and therefore the electromagnetic wave absorption ability can be maintained even when it is bent.

[0037] The average diameter (Av) can be determined by measuring the CNTs using a transmission electron microscope. The average diameter (Av) can be adjusted by changing the CNT manufacturing method or manufacturing conditions, or by combining multiple types of CNTs obtained by different manufacturing methods.

[0038] The BET specific surface area of CNT is 600m 2 / g or more is preferable, and 2 / g or more is more preferable, and 2500m 2 / g or less, and 2 / g or less is more preferable. 2 / g or more, the electromagnetic wave absorbing ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be further improved. 2 If it is / g or less, the formability of the electromagnetic wave absorbing layer 10 can be improved.

[0039] In this specification, the term "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET method.

[0040] For example, according to the super-growth method described below, CNTs are obtained on a substrate having a catalyst layer for carbon nanotube growth on its surface as CNT aggregates (oriented aggregates) oriented in a direction substantially perpendicular to the substrate. In this case, the mass density of the oriented aggregate is 0.002 g / cm. 3 More than 0.2g / cm 3It is preferable that the mass density is 0.2 g / cm or less. 3 If the mass density is 0.002 g / cm or less, the CNTs can be dispersed uniformly, and the electromagnetic wave absorbing ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be further improved. 3 If the above conditions are met, the CNTs can be prevented from breaking apart, making them easier to handle.

[0041] It is preferable that the CNTs exhibit an upwardly convex t-plot obtained from the adsorption isotherm. In particular, it is more preferable that the CNTs are not subjected to an aperture treatment and exhibit an upwardly convex t-plot. In this case, the electromagnetic wave absorption ability of the electromagnetic wave shielding laminate sheet 1 in the high frequency range can be further improved.

[0042] The "t-plot" can be obtained by converting the relative pressure measured by the nitrogen gas adsorption method into the average thickness "t" (nm) of the nitrogen gas adsorption layer. That is, the average thickness "t" of the nitrogen gas adsorption layer corresponding to the relative pressure is calculated from a known standard isotherm in which the average thickness "t" of the nitrogen gas adsorption layer is plotted against the relative pressure P / P0, and the above conversion is performed (the t-plot method by de Boer et al.).

[0043] In a material with pores on its surface, the growth of a nitrogen gas adsorption layer can be classified into the following three processes (1) to (3). The slope of the t-plot changes depending on the following processes (1) to (3). (1) The process of forming a monolayer of nitrogen molecules on the entire surface. (2) The formation of multi-layer adsorption and the accompanying capillary condensation filling process within the pores. (3) The process of multi-molecular adlayer formation on an apparently non-porous surface where the pores are filled with nitrogen.

[0044] In the case of a t-plot showing an upward convex shape, the plot is located on a straight line passing through the origin when the average thickness "t" of the nitrogen gas adsorption layer is small, but as "t" increases, the plot shifts downward from the straight line. A structure having such a t-plot shape has a large ratio of the internal specific surface area to the total specific surface area, indicating that many openings are formed in the CNTs.

[0045] The bending point of the t-plot for CNTs is preferably in the range of 0.2≦t(nm)≦1.5, more preferably in the range of 0.45≦t(nm)≦1.5, and even more preferably in the range of 0.55≦t(nm)≦1.0.

[0046] The "position of the bending point" is the intersection of the approximate straight line A in the process (1) and the approximate straight line B in the process (3).

[0047] The CNTs preferably have a ratio (S2 / S1) of the internal specific surface area S2 to the total specific surface area S1 obtained from a t-plot of 0.05 or more and 0.30 or less.

[0048] The total specific surface area S1 and the internal specific surface area S2 of the CNT are not particularly limited, but S1 is preferably 600 m 2 / g or more 1400m 2 / g or less, and 2 / g or more 1200m 2 / g or less is more preferable. 2 / g or more 540m 2 / g or less is preferable.

[0049] Here, the total specific surface area S1 and internal specific surface area S2 of the CNTs can be determined from the t-plot of the CNTs. Specifically, first, the total specific surface area S1 can be determined from the slope of the approximation line in step (1), and the external specific surface area S3 can be determined from the slope of the approximation line in step (3). Then, the internal specific surface area S2 can be calculated by subtracting the external specific surface area S3 from the total specific surface area S1.

[0050] Incidentally, the measurement of the adsorption isotherm of CNT, the creation of t-plots, and the calculation of the total specific surface area S1 and the internal specific surface area S2 based on the analysis of the t-plots can be performed using, for example, a commercially available measuring device, "BELSORP (registered trademark)-mini" (manufactured by BEL Japan Co., Ltd.).

[0051] CNTs having the above-described properties can be efficiently produced, for example, by a method (super-growth method; see International Publication No. 2006 / 011655) in which raw material compounds and a carrier gas are supplied to a substrate having a catalyst layer for carbon nanotube production on its surface to synthesize CNTs by chemical vapor deposition (CVD), and the catalytic activity of the catalyst layer is dramatically improved by the presence of a trace amount of oxidizing agent (catalytic activator) in the system. The catalyst layer is preferably formed on the substrate surface by a wet process. Hereinafter, carbon nanotubes obtained by the super-growth method may be referred to as "SGCNTs."

[0052] Note that CNTs produced by the super-growth method may be composed of only SGCNTs, or may be composed of SGCNTs and non-cylindrical carbon nanostructures. Specifically, the CNTs may include single-layer or multi-layer flat cylindrical carbon nanostructures (hereinafter sometimes referred to as "graphene nanotapes (GNTs)") that have tape-shaped portions along their entire length, with the inner walls being close to or bonded together.

[0053] In the present disclosure, "having a tape-shaped portion over the entire length" means "having a tape-shaped portion continuously or intermittently over 60% or more, preferably 80% or more, and more preferably 100% of the longitudinal length (total length)."

[0054] The fact that the GNTs have a flattened cylindrical shape and that tape-like portions in which the inner walls are close to or bonded together can be confirmed by, for example, sealing GNTs and fullerene (C60) in a quartz tube and heat-treating them under reduced pressure (fullerene insertion process) to obtain fullerene-intercalated GNTs, and observing them with a transmission electron microscope (TEM) reveals the presence of portions in the GNT where the fullerene is not inserted (tape-like portions).

[0055] The sheet resistance of the electromagnetic wave absorbing layer 10 is preferably 0.01 Ω / sq. or more and 100 Ω / sq. or less. In this case, electromagnetic waves are particularly likely to attenuate within the electromagnetic wave absorbing layer 10.

[0056] The proportion of carbon nanotubes in the electromagnetic wave absorbing layer 10 is set appropriately taking into consideration the resistivity of the electromagnetic wave absorbing layer 10, and is, for example, 5% by mass or more and 60% by mass or less of the electromagnetic wave absorbing layer 10. This proportion is more preferably 10% by mass or more, and even more preferably 20% by mass or more. Furthermore, this proportion is more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0057] The electromagnetic-wave absorbing layer 10 may contain amorphous carbon such as carbon black or acetylene black. In this case, the amorphous carbon can adjust the sheet resistance of the electromagnetic-wave absorbing layer 10. The proportion of amorphous carbon in the electromagnetic-wave absorbing layer 10 is, for example, 10% by mass or more and 50% by mass or less.

[0058] The electromagnetic-wave absorbing layer 10 may contain cellulose nanofibers. In this case, the sheet resistance of the electromagnetic-wave absorbing layer 10 can be adjusted without impairing the structure or strength of the electromagnetic-wave absorbing layer 10. The proportion of cellulose nanofibers is 5% by mass or more and 60% by mass or less with respect to the electromagnetic-wave absorbing layer 10. If this proportion is 5% by mass or more, the sheet resistance of the electromagnetic-wave absorbing layer 10 can be adjusted, and if it is 60% by mass or less, it is unlikely to hinder the weight reduction of the electromagnetic-wave absorbing layer 10.

[0059] The thickness of the electromagnetic wave absorbing layer 10 is set appropriately depending on the wavelength of the electromagnetic waves that the electromagnetic wave shielding laminate sheet 1 is to shield. If the thickness of the electromagnetic wave absorbing layer 10 is about ¼ of the wavelength of the electromagnetic waves that the electromagnetic wave shielding laminate sheet 1 is to shield, the electromagnetic wave shielding laminate sheet 1 can efficiently shield the electromagnetic waves. Even if the thickness of the electromagnetic wave absorbing layer 10 is restricted in this way depending on the wavelength of the electromagnetic waves, the bulk density of the electromagnetic wave absorbing layer 10 can be set to 997 kg / m 3 or less, it is easy to achieve a reduction in the weight of the electromagnetic wave shielding laminate sheet 1. The thickness of the electromagnetic wave absorbing layer 10 is preferably 0.1 mm or more and 100 mm or less, more preferably 0.5 mm or more and 10 mm or less, and even more preferably 1 mm or more and 5 mm or less.

[0060] The electromagnetic wave absorbing layer 10 is produced, for example, by freeze-drying an aqueous dispersion containing the raw materials of the electromagnetic wave absorbing layer 10. In this case, it is easy to make the electromagnetic wave absorbing layer 10 porous and reduce the bulk density.

[0061] For example, the electromagnetic wave absorbing layer 10 is a freeze-dried body formed by freeze-drying an aqueous dispersion containing carbon nanotubes and a water-soluble polymer. The aqueous dispersion is prepared, for example, by mixing a water-soluble polymer, carbon nanofibers, and water. The proportion of water in the aqueous dispersion is appropriately set depending on the strength and bulk density required of the electromagnetic wave absorbing layer 10, and is, for example, 80% by weight or more and 99.9% by weight or less. The freeze-drying conditions are appropriately set, and the electromagnetic wave absorbing layer 10 can be produced, for example, by freezing the aqueous dispersion at a temperature of -80°C to -60°C and then drying it under conditions of a temperature of -50°C to -40°C and an absolute pressure of 5 Pa to 50 Pa.

[0062] When freezing the aqueous dispersion, the aqueous dispersion may be placed in a container and frozen with the sides and bottom of the container covered with insulating material. In this case, the aqueous dispersion in the container can be frozen sequentially from top to bottom. This makes it easier for the water-soluble resin molecules to be oriented in the vertical direction, and the electromagnetic wave absorbing layer 10 is more likely to have a porous structure in which long voids are arranged in a honeycomb pattern in the thickness direction.

[0063] When the matrix of the electromagnetic wave absorbing layer 10 contains a cured product of a thermosetting resin, the electromagnetic wave absorbing layer 10 is a freeze-dried body formed by freeze-drying an aqueous dispersion containing, for example, carbon nanotubes, a water-soluble polymer, and a thermosetting resin. The aqueous dispersion is prepared by mixing, for example, a water-soluble polymer, carbon nanofibers, an aqueous emulsion of a thermosetting resin, and water. The freeze-dried electromagnetic wave absorbing layer 10 can be produced by freeze-drying this aqueous dispersion in the same manner as above. In this method, when the thermosetting resin contains an epoxy resin, the epoxy resin preferably contains the emulsion-type epoxy resin referred to as the above-mentioned water-based epoxy resin.

[0064] When the matrix of the electromagnetic wave absorbing layer 10 contains a cured thermosetting resin, the electromagnetic wave absorbing layer 10 may be formed by, for example, freeze-drying an aqueous dispersion containing carbon nanotubes and a water-soluble polymer, impregnating the freeze-dried body with a thermosetting resin, and then curing the thermosetting resin. In this case, the freeze-dried body can be produced by the same method as when producing an electromagnetic wave absorbing layer 10 that does not contain a thermosetting resin. To impregnate the freeze-dried body with the thermosetting resin, for example, a varnish containing the thermosetting resin is prepared by impregnating the freeze-dried body with an organic solvent such as methyl ethyl ketone. The freeze-dried body can be impregnated with the thermosetting resin by impregnating the freeze-dried body with this varnish. The varnish-impregnated freeze-dried body is then dried to volatilize the organic solvent in the varnish. The freeze-dried body is then heated to cure the thermosetting resin. The heating conditions for the freeze-dried body are set to appropriate conditions that allow the curing reaction of the thermosetting resin to proceed, depending on the composition of the thermosetting resin. This makes it possible to produce the electromagnetic wave absorbing layer 10. In this method, when the thermosetting resin contains an epoxy resin, the epoxy resin preferably contains an epoxy resin that is soluble in the above-mentioned organic solvent.

[0065] The electromagnetic wave absorbing layer 10 and the metal layer 30 may be in direct contact with each other as described above, or an insulating layer 20 may be interposed between the electromagnetic wave absorbing layer 10 and the metal layer 30. The insulating layer 20 is a layer having electrical insulation properties.

[0066] When the electromagnetic wave shielding laminate sheet 1 has an insulating layer 20, the relative dielectric constant of the insulating layer 20 is preferably lower than the relative dielectric constant of the electromagnetic wave absorbing layer 10. In this case, multiple reflection of electromagnetic waves is particularly likely to occur within the electromagnetic wave shielding laminate sheet 1, and the electromagnetic waves are more likely to be attenuated within the electromagnetic wave shielding laminate sheet 1. This particularly suppresses reflection of electromagnetic waves by the electromagnetic wave shielding laminate sheet 1. The ratio of the relative dielectric constant of the electromagnetic wave absorbing layer 10 at 25°C to the relative dielectric constant of the insulating layer 20 at 25°C is preferably 1 or more and 50 or less.

[0067] The insulating layer 20 is made of, for example, an electrically insulating resin. The electrically insulating resin preferably contains a fluororesin such as polytetrafluoroethylene. In this case, the insulating layer 20 can easily have a low dielectric constant.

[0068] The insulating layer 20 may further contain a filler made of at least one of resin particles and ceramic particles. In this case, the filler can adjust the physical properties of the insulating layer 20, such as the hardness and linear expansion coefficient. In this case, the insulating layer 20 can be produced, for example, by kneading an electrically insulating resin with the filler and forming the resulting kneaded mixture into a sheet.

[0069] The insulating layer 20 may contain an adhesive such as an epoxy resin adhesive. In this case, the insulating layer 20 can bond the electromagnetic wave absorbing layer 10 and the metal layer 30 together.

[0070] The insulating layer 20 may contain silicone rubber. In this case, the insulating layer 20 is less likely to impair the flexibility of the electromagnetic wave shielding laminated sheet 1, and therefore the electromagnetic wave shielding laminated sheet 1 is less likely to break even when bent.

[0071] The material of the insulating layer 20 is not limited to the above, and the insulating layer 20 can contain an appropriate resin having electrical insulating properties, such as polycarbonate.

[0072] It is also preferable that the dielectric strength voltage of the insulating layer 20 is 5 V / μm or more. In this case, even when the electromagnetic wave shielding laminated sheet 1 is used in the vicinity of a 5G base station, for example, dielectric breakdown of the insulating layer 20 can be made less likely to occur.

[0073] The electromagnetic wave shielding laminate sheet 1 according to this embodiment, thanks to its configuration, is lightweight yet capable of suppressing the transmission and reflection of electromagnetic waves, particularly those in the microwave to millimeter wave bands. Therefore, the electromagnetic wave shielding laminate sheet 1 can be used to suppress the transmission and reflection of, for example, electromagnetic waves in the 3 GHz to 10 GHz range, which are the communication frequencies of ultra-wideband (UWB) wireless communications used within artificial satellites, as well as electromagnetic waves in the 28 GHz and 39 GHz bands, which are frequencies surrounding the communication frequencies of 5G communications. In these cases, the attenuation of electromagnetic waves transmitted through the electromagnetic wave shielding laminate sheet 1 and the attenuation of electromagnetic waves reflected by the electromagnetic wave shielding laminate sheet 1 can be reduced to -10 dB or less, and even -20 dB or less.

[0074] For example, the electromagnetic wave shielding laminated sheet 1 can be applied to artificial satellites to shield noise generated from coils for wireless power supply, or to control the transmission path of signal waves when communicating between electronic devices wirelessly rather than via wires to reduce weight. [Example]

[0075] Specific examples of this embodiment will be presented below, but this embodiment is not limited to the following examples.

[0076] 1. Preparation of electromagnetic wave absorbing layer (Examples 1 to 16) The materials shown in Tables 1 to 4 were added to distilled water, and ultrasonic waves were applied to the resulting mixture at 135 W output power using an ultrasonic horn. This was repeated three times for 3 minutes to prepare an aqueous dispersion with a solid content of 5% by mass. The aqueous dispersion was poured into a mold measuring 180 mm x 180 mm in plan view and 10 mm deep, and then frozen in a freezer at -80°C for 2 hours. The frozen aqueous dispersion (hereinafter referred to as "frozen product") was then freeze-dried using a freeze dryer. The absolute pressure of the atmosphere surrounding the frozen product was adjusted to a range of 10 Pa to 20 Pa, the temperature to -45°C to -50°C, and the cold trap temperature was set to -45°C. The frozen product was freeze-dried for 24 hours. In Examples 13 to 16, the frozen product was further heated at 80°C for 3 hours to cure the epoxy resin in Resin Composition A. This produced an electromagnetic-wave-absorbing layer. The electromagnetic-wave-absorbing layer was then removed from the mold.

[0077] 2. Preparation of Electromagnetic Wave Absorbing Layer (Examples 17 to 20) A substrate having the same structure as the electromagnetic wave absorbing layer of Example 2 was produced under the same conditions as those for producing the electromagnetic wave absorbing layer of Example 2.

[0078] The substrate was immersed in a varnish obtained by diluting Resin Composition B with methyl ethyl ketone, thereby impregnating the substrate with the varnish. The varnish-impregnated substrate was then dried by heating at 100°C for 30 minutes, and then cured by heating at 180°C for 2 hours to produce an electromagnetic wave absorbing layer. The material ratios shown in Table 5 indicate the mass ratios of the substrate material and Resin Composition B used to produce the electromagnetic wave absorbing layer.

[0079] The details of the materials shown in the table are as follows: - Single-walled carbon nanotube 1: Zeon Nanotechnology Co., Ltd. Product name: ZEONANO (registered trademark) SG101. BET specific surface area: 1,050 m 2 / g. G / D ratio: 3.7. The average diameter (Av) of 3.3 nm was obtained by measuring the particle diameter of 100 randomly selected single-walled carbon nanotubes 1 using a transmission electron microscope. The t-plot obtained from the adsorption isotherm shows an upward convex shape. - Single-walled carbon nanotubes 2: Meijo Nano Carbon Co., Ltd., product number EC2.0. BET specific surface area 500m 2 / g. G / D ratio 37. The average diameter (Av) of 2.0 nm was obtained by measuring the particle diameter of 100 randomly selected single-walled carbon nanotubes 2 using a transmission electron microscope. -Cellulose nanofiber: manufactured by Daiichi Kogyo Seiyaku Co., Ltd., product name Leocrysta I-2SX. - Sodium carboxymethylcellulose: manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. - Acetylene black: manufactured by Denka Co., Ltd., product name Denka Black. Resin composition A: A mixture of Mitsubishi Chemical Corporation's water-based epoxy resin (product name 1155R55) and Mitsubishi Chemical Corporation's water-based epoxy curing agent (product name WD11M60) in a mass ratio of 100:53. Resin composition B: A mixture of brominated bisphenol A epoxy resin (product name 153-60M) manufactured by DIC Corporation dissolved in methyl ethyl ketone and epoxy hardener (product name dicyandiamide) manufactured by Nippon Carbide Industries Co., Ltd., in a mass ratio of 100:3.

[0080] The bulk density, volume resistivity in the thickness direction, sheet resistance and relative permittivity of the electromagnetic wave absorbing layer are shown in the table.

[0081] The bulk density was calculated from the measurement results of the outer dimensions of the electromagnetic wave absorbing layer and the measurement results of the mass of the electromagnetic wave absorbing layer.

[0082] When measuring the volume resistivity and sheet resistance in the thickness direction, the resistance of the electromagnetic wave absorbing layer was set to 10 4 Ω or more 10 13 When the resistance value of the electromagnetic wave absorbing layer was 10 Ω or less, the resistance value (Ω) at room temperature was measured using a high resistivity meter (manufactured by Mitsubishi Chemical Analytical Co., Ltd., "Hiresta (registered trademark) MCP-HT800", probe: URS probe) by the double ring method in accordance with JIS K 6911. -2 Ω or more 10 4When the resistance was less than Ω, the resistance value (Ω) at room temperature was measured according to JIS K 7194 using a four-point probe low resistivity meter (Mitsubishi Chemical Analytical Co., Ltd., "Loresta (registered trademark) MCP-610T", probe: ASP probe). Furthermore, for the measurement, three 100 mm × 100 mm square test pieces were cut out from the electromagnetic wave absorbing layer as measurement samples, and the probe was pressed against the center position of each measurement sample to measure the resistance value (Ω). The resistance values (Ω) of the three measurement samples were measured, and the average value was taken as the resistance value (Ω) of the electromagnetic wave absorbing material. From the obtained resistance value (Ω) and sample dimensions, the volume resistivity (Ω·cm) and sheet resistance (Ω / sq.) were calculated according to standard methods.

[0083] The relative dielectric constant was measured by the coaxial tube method.

[0084] 2. Preparation of laminated sheet for electromagnetic wave shielding Electromagnetic wave absorbing layers and metal layers, or electromagnetic wave absorbing layers, insulating layers and metal layers were laminated in the combinations shown in Tables 1 to 5 to prepare electromagnetic wave shielding laminate sheets.

[0085] The volume resistivity and sheet resistance in the thickness direction of each of the insulating layer and the metal layer, and the relative dielectric constant of the insulating layer were measured in the same manner as in the case of the electromagnetic wave absorbing layer.

[0086] 3.Evaluation Test (1) Density The measurement results of the density of the electromagnetic wave shielding laminate sheet are shown in the table.

[0087] (2)Flexibility The electromagnetic wave shielding laminate sheet was subjected to a 180° bending test using a cylindrical mandrel method using a mandrel with a radius of 10 mm. As a result, the electromagnetic wave shielding laminate sheet was rated as "good" if it could be wrapped around the mandrel and there was no damage to the electromagnetic wave shielding laminate sheet, and was rated as "poor" if it could be wrapped around the mandrel but was damaged, or if it could not be wrapped around the mandrel.

[0088] (3) Water resistance The electromagnetic wave shielding laminate sheet was immersed in purified water at 23°C ± 5°C for 30 minutes and then removed. As a result, if the electromagnetic wave shielding laminate sheet showed neither dissolution nor damage, it was evaluated as "good", and if at least one of dissolution and damage was observed, it was evaluated as "poor".

[0089] (4) Moisture resistance The electromagnetic wave shielding laminate sheet was placed in a flat-bottomed stainless steel container with the electromagnetic wave absorbing layer in contact with the bottom of the container. The container containing the electromagnetic wave shielding laminate sheet was left in a thermo-hygrostat maintained at 85°C and 85% RH for 500 hours. The container was then removed from the thermo-hygrostat, and the electromagnetic wave shielding laminate sheet was lifted from the bottom of the stainless steel container. If the electromagnetic wave shielding laminate sheet was not damaged, it was evaluated as "good," and if the electromagnetic wave shielding laminate sheet was damaged by sticking to the bottom of the container, it was evaluated as "poor."

[0090] (5) Attenuation characteristics of reflected waves A test specimen was prepared by fixing the electromagnetic wave shielding laminate sheet to an acrylic resin jig. A reference specimen was also prepared by fixing only the metal layer to the acrylic resin jig.

[0091] Using the free space method, the S (Scattering) parameter (S21) at two ports of the test piece for electromagnetic waves with frequencies of 1 to 18 GHz is measured. sample ) was measured. The measurement system used was a vector network analyzer (Agilent Technologies, "8720ES"), a transmitting antenna (SCHWARZBECK, "BBHA9120-B"), and a receiving antenna (SCHWARZBECK, "BBHA9120-B", same model number as the transmitting antenna). For the measurement, horizontally polarized electromagnetic waves emitted from the transmitting antenna were incident on the test piece at an incident angle of 45 degrees, and the reflected waves reflected at an angle of 90 degrees to the incident direction were received by the receiving antenna.

[0092] The S (Scattering) parameter (S21 reference ) was also measured in the same way.

[0093] The difference between the measurement value of the reference and the measurement value of the test piece was regarded as the reflection loss due to the electromagnetic wave shielding laminate sheet, and the attenuation (dB) of the reflected wave of the electromagnetic wave shielding laminate sheet was calculated according to the following formula (1).

[0094] Return loss (dB) = 20 log | S21 sample |-20log|S21 reference |···(1) The table shows the frequencies at which the reflected wave attenuation peaks in the frequency range of 1 to 18 GHz and the corresponding attenuation amounts.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] [Table 5]

Claims

1. A matrix and carbon nanotubes dispersed in the matrix, the bulk density of which is 997 kg / m ３ an electromagnetic wave absorbing layer, a metal layer overlying the electromagnetic wave absorbing layer; Laminated sheet for electromagnetic wave shielding.

2. The matrix contains a water-soluble polymer. The electromagnetic wave shielding laminate sheet according to claim 1.

3. further comprising an insulating layer between the electromagnetic wave absorbing layer and the metal layer; 3. The electromagnetic wave shielding laminate sheet according to claim 1 or 2.

4. the dielectric constant of the insulating layer is lower than the dielectric constant of the electromagnetic wave absorbing layer; The electromagnetic wave shielding laminate sheet according to claim 3.

5. The electromagnetic wave absorbing layer is porous. The electromagnetic wave shielding laminate sheet according to any one of claims 1 to 4.

6. the electromagnetic wave absorbing layer is a freeze-dried body formed by freeze-drying an aqueous dispersion containing the carbon nanotubes and a water-soluble polymer; The electromagnetic wave shielding laminate sheet according to any one of claims 1 to 5.

7. The matrix further contains a cured product of a thermosetting resin. The electromagnetic wave shielding laminate sheet according to any one of claims 1 to 5.

8. the electromagnetic wave absorbing layer is formed by freeze-drying an aqueous dispersion containing the carbon nanotubes, the water-soluble polymer, and the thermosetting resin, and curing the thermosetting resin in a freeze-dried body formed by freeze-drying the aqueous dispersion. The electromagnetic wave shielding laminate sheet according to claim 7.

9. The electromagnetic wave absorbing layer is formed by freeze-drying an aqueous dispersion containing the carbon nanotubes and a water-soluble polymer to form a freeze-dried product, impregnating the freeze-dried product with the thermosetting resin, and curing the thermosetting resin. The electromagnetic wave shielding laminate sheet according to claim 7.

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