Laminated Sheet

Abstract

The present invention addresses the problem of providing a laminated sheet having an excellent electromagnetic wave shielding performance, and the main purpose of the present invention is to obtain a laminated sheet including an alternately laminated unit in which at least five layers of layer A and layer B are alternately laminated, wherein in a reflection attenuation amount chart for the laminated sheet, the electromagnetic wave attenuation amount at the peak top of the reflection attenuation peak having the greatest peak top attenuation amount is 5 dB or above.

Description

[Technical Field]

[0001] The present invention relates to a laminate sheet having excellent electromagnetic wave shielding properties. [Background technology]

[0002] With advances in communications technology, meter waves (in the hundreds of megahertz to several gigahertz band) are primarily used for mobile phones and other wireless communications, centimeter waves (in the several gigahertz to several tens of gigahertz band) are primarily used for mobile communications such as 4G and 5G and wireless LAN (Wi-Fi) communications, and millimeter waves (in the tens to hundreds of gigahertz band) are primarily used for automobile collision prevention radar. Thus, electromagnetic waves of various frequency bands circulate in the atmosphere. The appropriate frequency band for an electromagnetic wave is selected based on the information capacity, transmission distance, and application. However, because electromagnetic waves of similar frequency bands are used in various devices and applications, concerns have arisen about device malfunctions, communication disruptions, and information leaks. Furthermore, concerns have been raised about the effects of electromagnetic waves on the sensitive human body. To address these concerns and concerns, there is a growing need for electromagnetic wave shielding materials that can block electromagnetic waves. In particular, in recent years, the development of communication technologies that utilize electromagnetic waves in the gigahertz frequency band has accelerated to enable high-speed, high-capacity communications, creating a demand for electromagnetic wave shielding materials that can block electromagnetic waves in this frequency band.

[0003] Electromagnetic waves propagate through space as waves composed of two components: an electric field and a magnetic field. Electromagnetic shielding materials that block electromagnetic waves reflect electromagnetic waves on their surface or within the material, or absorb them internally, thereby dissipating or attenuating the energy of the electromagnetic waves. Combining reflection and absorption can enhance their effectiveness. For example, conductive reflection technology based on reflection on the material's surface can be enhanced by creating a difference in electrical resistance (impedance calculated based on the dielectric constant) between the air interface and the electromagnetic shielding material interface. Generally, applying or laminating a material with very low resistance, such as metal (copper), to the surface of a substrate can provide electromagnetic shielding across a wide frequency range (see Patent Document 1). Meanwhile, electromagnetic wave absorption technology based on absorption within the material involves incorporating conductive and / or magnetic materials into the material, converting electromagnetic waves that enter the material into induced currents, thereby dissipating the energy of the electromagnetic waves. Absorption performance is achieved by incorporating metal materials such as carbon or ferrite into dielectric polymers such as rubber. (Patent Documents 2 to 4) Furthermore, by overlapping layers with different impedances, electromagnetic waves reflected on the front and back of the electromagnetic wave shielding material can be interfered with and canceled out, resulting in loss (Patent Document 5). In particular, the electromagnetic wave shielding properties due to absorption vary depending on the combination of the dielectric (insulating) substrate and the conductive material contained therein, the substrate thickness, and the formulation of the conductive material (type of material, combination method, content), but the arrangement of the conductive material within the substrate is also an important factor, and there is knowledge known as the Maxwell-Wagner effect, which shows that the effectiveness of the entire shielding material can be increased by arranging the conductive materials in a certain direction and stacking them side by side to improve conductivity (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2011-502285 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-158395 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-118073 [Patent Document 4] Japanese Patent Application Publication No. 2019-057730 [Patent Document 5] Japanese Patent Application Publication No. 2019-102665 [Non-patent literature]

[0005] [Non-Patent Document 1] ZMDang,Prog.Matter.Sci.,2012,57,660-723 Summary of the Invention [Problem to be solved by the invention]

[0006] Electromagnetic shielding materials utilizing conductive reflection technology, such as those described in Patent Document 1, are developed using techniques such as metal sputtering, vacuum deposition, and coating the outermost layer with a paste material containing conductive and / or magnetic materials. However, these techniques can cause short circuits in electronic and communication devices due to peeling, and can also pose durability issues. Meanwhile, with regard to electromagnetic shielding materials utilizing magnetic or dielectric absorption, such as those described in Patent Documents 2 to 5, existing technologies incorporating conductive materials into the substrate require thickening the substrate or increasing the conductive material content in order to increase the absolute value of electromagnetic attenuation (to improve electromagnetic shielding performance). In other words, once a specific material is selected, the electromagnetic shielding performance is proportional to the product of the amount of conductive material contained per unit volume of the substrate and the thickness of the substrate (this relationship is known as the "volume law"). However, increasing the substrate thickness increases the stiffness of the electromagnetic shielding material, making it difficult to apply to applications requiring formability, such as wrapping around cables or assembling shielding materials around enclosures with complex, uneven shapes.

[0007] On the other hand, when considering the moldability and production efficiency of the shielding material, continuous sheeting by melt extrusion using thermoplastic resin is preferable to press-processed products using thermoplastic resin. However, when forming a sheet containing a high concentration of conductive material, the thickening effect (thixotropy) of the resin composition during extrusion becomes strong, which causes uneven discharge when extruding into a sheet, making it difficult to form a sheet of uniform thickness, and the sheet becomes brittle and prone to cracking. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following configuration: A laminated sheet including an alternating laminate unit in which two layers with different electrical conductivity, the layer with lower electrical conductivity being referred to as layer A and the layer with higher electrical conductivity being referred to as layer B, are alternately laminated in a total of five or more layers so that layer A is disposed as the outermost layer, and layer A is made of a thermoplastic resin alone. Becoming The layer B is a conductive material having a thermoplastic resin as a matrix resin. The matrix is ​​carbon black with a dibutyl phthalate (DBP) oil absorption of 150 mL / 100 g or more and 800 mL / 100 g or less. Conductive material dispersed in resin or with thermoplastic resin as matrix resin Carbon black with a dibutyl phthalate (DBP) oil absorption of 150 mL / 100 g or more and 800 mL / 100 g or less and other materials such as conductive materials and magnetic materials other than organic carbon materials. Matrix Dispersed in resin (However, the content of the conductive material is 1% by weight or more and less than 15% by weight of the total weight of the laminate sheet.) And then, The carbon black having a dibutyl phthalate (DBP) oil absorption of 150 [mL / 100 g] or more and 800 [mL / 100 g] or less is contained in an amount of 1% by weight or more and less than 15% by weight of the total weight of the laminate sheet, and When a frequency-return loss curve is obtained for the laminate sheet, with the vertical axis representing return loss and the horizontal axis representing frequency, the return loss at the peak top of the return loss peak with the largest return loss at the peak top (return loss RL) is 5.0 dB or more, the number of interfaces per unit thickness between layer A and layer B is 2 faces / 100 μm or more, the return loss peak with the largest return loss at the peak top exists in a frequency band of 1 to 100 GHz, and when the return loss at the peak top of the return loss peak with the largest return loss at the peak top is RL [dB], the frequency corresponding to the peak top is f [GHz], and the thickness of the laminate sheet is t [mm], RL / (t×f) is 0.2 or more and 15 or less, and the surface resistance of layer B is 7.0×10 4 A laminated sheet having a hardness of less than [Ω / □]. [Effects of the Invention]

[0009] The laminate sheet of the present invention exhibits high electromagnetic wave shielding properties. Therefore, it can be suitably used as an electromagnetic wave shielding material. In a more preferred embodiment, a laminate structure in which highly conductive layers and low conductive layers are alternately laminated provides steep and high electromagnetic wave shielding properties in a specific frequency band. Furthermore, even with a low content of conductive material and a thin film, it is possible to obtain electromagnetic wave shielding properties at a level equivalent to that of conventional technology. Therefore, it is expected that the sheet can be molded into applicable products and that stable production of the sheet can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic diagram illustrating the half-width of the return loss peak with the largest return loss at the peak top and the return loss at the peak top in a frequency-return loss curve of a laminate sheet according to one embodiment of the present invention. [Figure 2] 2 is a schematic diagram illustrating the half-value width of the return loss peak with the largest return loss at the peak top and the return loss at the peak top in a frequency-return loss curve of a laminated sheet of an embodiment different from that of FIG. 1. FIG. [Figure 3] 1 and 2. FIG. 4 is a schematic diagram illustrating the half-width of the return loss peak with the largest return loss at the peak top and the return loss at the peak top in a frequency-return loss curve of a laminate sheet of an embodiment different from those in FIGS. [Figure 4] FIG. 4 is a schematic diagram illustrating the half-width of the return loss peak with the largest return loss at the peak top and the return loss at the peak top in a frequency-return loss curve of a laminate sheet in an embodiment different from those in FIGS. DETAILED DESCRIPTION OF THE INVENTION

[0011] The laminate sheet of the present invention will be described in detail below.

[0012] The laminate sheet of the present invention is a laminate sheet including an alternating laminate unit in which A layers and B layers having different electrical conductivities are alternately laminated for a total of five or more layers, and when a frequency-return loss curve is obtained for the laminate sheet, where the vertical axis is return loss and the horizontal axis is frequency, the return loss at the peak top of the return loss peak with the largest peak top return loss (return loss RL) must be 5 dB or more. The frequency-return loss curve is obtained by the measurement method described below.

[0013] The laminate sheet of the present invention comprises two distinct layers, Layer A and Layer B, each with a different conductivity. The materials constituting Layer A and Layer B may be transparent / opaque, flexible / rigid, flat / non-flat, organic (polymeric) material / inorganic (metallic) material, and are not particularly limited. However, in consideration of processability, a substrate made of a flexible organic polymeric material is preferred. It is particularly desirable for the base material to be made primarily of a thermoplastic resin. Here, "mainly made" means that the layer is made solely of a thermoplastic resin, or that the thermoplastic resin is used as a matrix resin with other materials, such as conductive materials or magnetic materials, dispersed in the resin.

[0014] Furthermore, the laminate sheet of the present invention may also be coated with a hard coat using a thermosetting resin or a photocurable resin.

[0015] The A layer and the B layer in the laminate sheet of the present invention must have different electrical conductivities. For convenience, and in consideration of the preferred embodiment of the laminate sheet described below, the layer with lower electrical conductivities will be referred to as the A layer, and the layer with higher electrical conductivities will be referred to as the B layer. The difference in electrical conductivities between the A layer and the B layer means that the A layer and the B layer have different surface resistance values, which are indicators of electrical conductivities / insulation properties in the layer direction (plane direction of the sheet) of each layer. Specifically, the difference in electrical conductivities between the A layer and the B layer means that, when the higher surface resistance value of the A layer and the B layer is α [Ω / □] and the lower surface resistance value is β [Ω / □], the α / β is 1.1 or more. Preferably, the α / β is 10 2 More than 10, preferably 5 More preferably, 10 9The surface resistance, which is an indicator of electrical conductivity / insulation, is 1.0 × 10 5 When the surface resistance of the A layer is less than 1.0×10[Ω / □], it exhibits good electromagnetic wave shielding properties. 5 [Ω / □] or more, and the surface resistance of layer B is 1.0×10 5 It is more preferable that the surface resistance ratio is less than [Ω / □] and exhibits the above-mentioned ratio. There are no particular limitations on the method for making the A layer and the B layer different in conductivity. A simple material design for making the A layer and the B layer different in conductivity is to construct them from a composition containing a conductive material in a matrix. However, the conductivity can also be made different by using materials with different dielectric constants as the matrix material, or by varying the type and / or content of the conductive material contained. As will be described in detail later, in order to achieve high electromagnetic wave attenuation in a specific frequency band, it is important to control the relative dielectric constant within a specific range. In this case, in order to adjust the frequency of the reflection loss peak to the desired frequency band while maintaining electromagnetic wave attenuation, a configuration that allows fine adjustment of the conductivity of the A layer and the B layer is preferable. To make the A layer and the B layer different in dielectric constant, it is most preferable to incorporate a conductive material and / or a magnetic material into the A layer and / or the B layer. The relative dielectric constant referred to here is a dimensionless quantity that represents the magnitude of the dielectric constant when the dielectric constant (electric constant) in a vacuum is used as the reference. Hereinafter, the relative permittivity will be simply referred to as the dielectric constant.

[0016] The surface resistance is the resistance of a sample measured at its surface. It can be measured by peeling off the interface between the A and B layers to expose the interface, but it can also be measured more easily and reproducibly by slicing each layer to expose the surface of the sample.

[0017] In order for the laminate sheet of the present invention to exhibit a high value for the reflection loss peak attenuation, which has the largest peak-top attenuation, it is important to design the layer A and B constituting the alternating laminate unit that exhibits a high dielectric constant. Conventional single-layer sheet technologies typically achieve this by incorporating a high concentration of conductive and / or magnetic material into the resin to increase the dielectric constant, or by increasing the sheet thickness. However, with the laminate sheet of the present invention, by creating a dielectric constant difference between one layer with a high dielectric constant and the other with a low dielectric constant, the effect of dielectric polarization (generation of a dipole moment) occurring at the layer interface between the high- and low-dielectric-constant layers can be added, resulting in an increase in dielectric constant greater than the volume law, compared to single-layer sheets containing the same weight concentration of conductive and / or magnetic material. To strongly induce this dielectric polarization, which contributes to the increase in dielectric constant, one important design point is to maximize the difference in dielectric constant between the alternating A and B layers. As described above, methods for achieving different dielectric constants include the types of resins used in the A layer and the B layer, and the amounts of conductive material and / or magnetic material contained in the A layer and / or the B layer. A preferred embodiment is one in which only one of the A layer and the B layer contains a conductive material, while the other layer is composed of a single resin that does not contain a conductive material. A more preferred embodiment is one in which the layer that does not contain a conductive material is composed of a resin with a low dielectric constant, and the layer that contains a conductive material is composed of a resin that exhibits a high dielectric constant as a resin and also contains a high concentration of conductive material. Furthermore, as described below, increasing the number of layers is preferable because it increases the number of interfaces that cause dielectric polarization, and reducing the layer thickness is preferable because it increases the number of interfaces per unit thickness. That is, the number of interfaces between the A layer and the B layer per unit thickness of the alternate laminate unit is preferably 2 faces / 100 μm or more, more preferably 5 faces / 100 μm or more, and even more preferably 10 faces / 100 μm or more. There is no particular upper limit as long as the laminate can be manufactured stably, but from the viewpoint of productivity, it is generally 150 faces / 100 μm or less. In this case, the ratio of the surface resistance values ​​of the A layer and the B layer (A layer / B layer) is 1×10 10More than 1×10, preferably 12 It is best to do so.

[0018] As the flexible organic polymer material that can be preferably used in the present invention, a thermoplastic resin is preferable, since it is particularly favorable from the viewpoint of sheet processability and film formability.Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, poly(1-butene), poly(4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly(α-methylstyrene), poly(p-methylstyrene), polynorbornene, and polycyclopentene; polyamide resins such as nylon 6, nylon 11, nylon 12, and nylon 66; vinyl monomer copolymer resins such as ethylene / propylene copolymer, ethylene / vinylcyclohexane copolymer, ethylene / vinylcyclohexene copolymer, ethylene / alkyl acrylate copolymer, ethylene / acrylic methacrylate copolymer, ethylene / norbornene copolymer, ethylene / vinyl acetate copolymer, propylene / butadiene copolymer, isobutylene / isoprene copolymer, and vinyl chloride / vinyl acetate copolymer; and acrylic resins such as polyacrylate, polymethacrylate, polymethyl methacrylate, polyacrylamide, and polyacrylonitrile. Polyester resins typified by polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, etc.; polyether resins typified by polyethylene oxide, polypropylene oxide, polyacrylene glycol, cellulose ester resins typified by diacetyl cellulose, triacetyl cellulose, propionyl cellulose, butyryl cellulose, acetylpropionyl cellulose, nitrocellulose; biodegradable polymers typified by polylactic acid, polybutyl succinate, etc.; and other polymers such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglycolic acid, polycarbonate, polyketone, polyether sulfone, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloroethylene resin, tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, etc.These thermoplastic resins can be used alone or as a polymer blend or alloy of two or more types. Blends and alloys can provide heat resistance, viscosity characteristics, and adhesion at interlayer interfaces that cannot be achieved with a single thermoplastic resin.

[0019] As mentioned above, the laminate sheet of the present invention includes an alternating laminate unit in which layers of different electrical conductivity are alternately laminated. This allows for dielectric polarization at the interface between the A and B layers, which have different electrical conductivity, thereby achieving enhanced electromagnetic wave shielding. Therefore, the dielectric constant of the thermoplastic resin constituting each layer is an important factor. Therefore, it is preferable that the resin constituting the A layer and the resin constituting the B layer have different dielectric constants. Specifically, a resin with a low dielectric constant of 3.0 or less is preferably selected. Considering versatility, processability, and lamination properties, it is preferable to select such a resin from thermoplastic resins such as polyolefin resins (dielectric constant: 2.0-2.3), polyester resins (dielectric constant: 2.8-3.0), polycarbonate (dielectric constant: 2.9-3.0), and polystyrene (dielectric constant: 2.4-2.6). These resins are particularly preferred for use in layers that do not contain conductive materials.

[0020] On the other hand, thermoplastic resins that can be preferably used in layers containing conductive materials preferably have a high dielectric constant, and are preferably selected from acrylic resins (dielectric constant: 3.0 to 4.5), nylon resins (dielectric constant: 3.5 to 5.0), cellulose-based resins (dielectric constant: 6.7 to 8.0), vinyl monomer copolymer resins (dielectric constant: 3.0 to 8.0), fluororesins (dielectric constant: 4.0 to 8.0), polyphenylene sulfide (dielectric constant: 3.5 to 4.0), etc.

[0021] Furthermore, while different dielectric constants for layers A and B can be achieved by using resins with different dielectric constants, this can also be achieved by using the same resin for layers A and B and adding a conductive material to impart conductivity to create a difference in dielectric constant. As described above and below, the laminate sheet of the present invention is characterized by alternately stacking layers A and B with different conductivities and creating a difference in dielectric constant between layers A and B, thereby improving electromagnetic wave shielding performance through dielectric polarization generated at the layer interface. While a greater difference in the dielectric constants between layers A and B is more effective in enhancing the dielectric polarization effect, in order to increase return loss, it is preferable for the layer with the higher dielectric constant (layer B) to be designed within a specific dielectric constant range described below. A configuration that facilitates material design to achieve the desired dielectric constant is preferred. Since fine adjustment of this dielectric constant is more easily achieved by adjusting the content of the conductive material added rather than the resin that constitutes the layer, a preferred laminate sheet embodiment that satisfies these requirements is one in which the layer with the lower dielectric constant (layer A) is composed of a layer that does not contain a conductive material, and the layer with the higher dielectric constant (layer B) is composed of a layer that contains a conductive material. More preferably, the resin constituting layer A is composed of a resin having a dielectric constant of 3.0 or less, and the resin constituting layer B is composed of a resin having a dielectric constant of 3.0 or more and contains a conductive material.

[0022] The laminate sheet of the present invention must include an alternating laminate unit in which five or more layers of A and B are alternately stacked. "Alternatingly stacked" refers to a state in which layers are stacked in a regular arrangement of A(BA)n or A(BA)nB (n is an integer of 2 or greater) when the A layer is the outermost layer. For example, laminate sheets having a layer A / B / A / B / A configuration or a layer B / A / B / A / B / A / B configuration, regardless of the presence or absence of layers other than the A and B layers, all fall under the category of a configuration containing an alternating laminate unit in which five or more layers of A and B are alternately stacked. As long as the laminate sheet of the present invention has an alternating laminate unit in which A and B layers are stacked, the outermost layer may be either an A layer, a B layer, or a layer other than the A and B layers. The outermost layers on both sides may be the same layer or different layers. Furthermore, the laminate sheet may contain one or more alternating laminate units. When there are multiple alternating laminate units, the individual alternating laminate units may have the same or different configurations. When multiple alternating laminated units are used, it is easy to achieve electromagnetic wave shielding corresponding to multiple wavelength ranges. That is, when multiple alternating laminated units are used in a stacked manner, it is easy to simultaneously shield multiple desired frequency bands by stacking alternating laminated units having peak tops in different frequency bands.

[0023] One method for alternately laminating elastomer resins such as rubber is to produce sheets by rolling and pressing two types of elastomer resins with different compositions, and then to obtain a laminated sheet by alternately stacking the different sheets and thermocompressing them.

[0024] On the other hand, methods for alternately laminating thermoplastic resins include, for example, preparing master pellets by distributing / dispersing the thermoplastic resins corresponding to each layer and appropriate additives, and then extruding the master pellets from different channels using two or more extruders. The master pellets are then laminated using known lamination devices such as multi-manifold feed blocks or static mixers. In particular, as described below, the laminate sheet of the present invention exhibits high electromagnetic wave attenuation performance at specific frequencies when it has a uniform thickness with little variance in layer thickness. Therefore, to achieve high-precision lamination, it is preferable to form the laminate sheet using a feed block with fine slits. Furthermore, using a slit-type feed block aligns and disperses the conductive and / or magnetic materials according to the laminar flow of the resin, making it easier to achieve a high dielectric constant for the laminate sheet. When forming a laminate using a slit-type feed block, the thickness and distribution of each layer can be achieved by adjusting the length and width of the slits to balance the pressure. Here, the slit length refers to the length of the comb teeth that form the channels through which layers A and B flow alternately within the slit plate.

[0025] When producing a laminated sheet using the latter thermoplastic resin, it is preferable that the melt viscosities of the two different thermoplastic resins (these thermoplastic resins will be referred to as resin A and resin B, respectively, for convenience) are at the same level. If the melt viscosities are significantly different, resin lamination disorder (flow marks) may occur at the lamination interface, making it impossible to produce a uniform sheet. This may result in uneven layer thicknesses of each layer and, therefore, uneven conductivity of each layer, which may cause variations in electromagnetic wave shielding properties depending on the position in the laminated sheet. In order to mold a uniform laminated sheet by melt extrusion, resin A or resin B must be extruded at a constant temperature (the melting point of either resin A or resin B, whichever has the higher melting point, +10°C) and a constant shear rate (100 sec -1In the above formula, the melt viscosity of the resin with the higher melt viscosity is X [poise] and the melt viscosity of the resin with the lower melt viscosity is Y [poise]. The ratio (X / Y) between these two is preferably 1.0≦X / Y≦5.0, more preferably 1.0≦X / Y≦2.0. Furthermore, when a conductive material is incorporated into a thermoplastic resin as a filler, the high concentration of the filler causes a shear rate-dependent change in melt viscosity (thixotropy), making flow marks more likely to occur during the resin lamination process. Even when using a thermoplastic resin alone, some types, such as olefin resins, exhibit shear-dependent melt viscosity, making them more likely to cause flow marks during lamination. Combining a resin prone to thixotropy with a filler further increases the occurrence of flow marks. Therefore, it is preferable to use a thermoplastic resin that is less likely to cause thixotropy. Specifically, considering the kneadability of the conductive material, it is preferable to select a thermoplastic resin from among olefin copolymer resins, nylon resins, polyester resins, etc. Alternatively, methods that make the shear dependency of the melt viscosity similar to that of the layer exhibiting high conductivity by adding a conductive material to the layer exhibiting low conductivity, such as adding particles other than the conductive material to the layer exhibiting low conductivity and not containing the conductive material, or using a resin material exhibiting non-Newtonian properties such as an olefin, are also effective in suppressing flow marks in the laminated sheet.

[0026] The laminated sheet of the present invention must have five or more layers. In any of the above-mentioned regular arrangements, a five-layer or greater configuration is required to include two or more high-dielectric-constant layers surrounded by low-dielectric-constant layers, thereby providing many interfaces where dielectric polarization occurs. Conventional single-layer or low-layer-count products could not achieve the desired electromagnetic wave shielding properties without adding a high concentration of conductive material or increasing the sheet thickness. However, alternating five or more layers makes it easier to obtain the effect of dielectric polarization at the interface between layers with different conductivities. In other words, dielectric polarization facilitates the flow of current within the sheet (especially in the region near the interface), and the resistance of the conductive material causes a loss of electromagnetic wave energy, resulting in an electromagnetic wave shielding material with high shielding properties. Furthermore, increasing the number of layers in a laminate sheet of a given thickness reduces the thickness of each layer of the laminate sheet, making it easier for the conductive and / or magnetic materials to disperse and align in a direction parallel to the surface, thereby increasing the conductivity and dielectric constant of the laminate sheet. This allows for the same conductivity and dielectric constant that could only be achieved with a single-layer product that contains a high concentration of conductive and / or magnetic materials to be achieved at a lower concentration. The total number of A and B layers in the alternating laminate unit contained in the laminate sheet is preferably 11 or more, more preferably 31 or more, and even more preferably 101 or more. In addition to the above effects, increasing the number of layers is preferable because, for a laminate sheet of the same thickness, increasing the packing density of the conductive material within the layer reduces the distance between the conductive materials, thereby increasing the electron transfer efficiency between the added conductive materials, thereby enhancing its effectiveness as an electromagnetic wave absorbing material. Furthermore, increasing the number of layers and reducing the thickness of each layer increases the number of layers contained per unit thickness, thereby enhancing the dielectric polarization effect and ultimately increasing the dielectric constant of the laminate sheet. There is no particular upper limit to the number of layers in the laminated sheet, but when a feed block having fine slits is used, an increase in the number of layers increases the size of the device, resulting in an increase in manufacturing costs.Furthermore, depending on the dispersion, shape, and size of the filler, if the number of layers increases and the thickness of each layer becomes thinner, the addition of particles can easily cause thixotropy, disrupting the resin flow and causing large variations in layer thickness, which can impair the inherent high shielding and steep electromagnetic wave shielding properties.For these reasons, the practical upper limit for the number of layers is 2000 layers or less.

[0027] The laminated sheet of the present invention may contain layers with different functions, such as an electromagnetic wave reflecting layer or an electromagnetic wave absorbing layer, in addition to the alternating laminate unit in which five or more layers of A layers and B layers with different electrical conductivities are alternately laminated.

[0028] The laminate sheet of the present invention is preferably an electromagnetic wave absorbing sheet containing a conductive material and / or a magnetic material. However, it can also be combined with an electromagnetic wave reflective layer that shields a wide frequency band to create a laminate sheet that can more strongly shield specific frequencies while broadly shielding electromagnetic waves. Alternatively, a new layer with a low dielectric constant can be provided on the top surface of the laminate sheet to further reduce electromagnetic wave reflection at the surface, resulting in a laminate sheet with enhanced electromagnetic wave absorption. In the latter case, the dielectric constant of the layer located on the top surface of the laminate sheet is preferably 4.0 or less, more preferably 3.0 or less. It is also preferable to provide a resistive layer that exhibits the same impedance as the air layer as a layer to suppress surface reflection. The impedance of air is 377 Ω, and known resistive layers that satisfy this resistance value include ITO.

[0029] The laminate sheet of the present invention must have a peak-top return loss of 5.0 dB or greater when a frequency-return loss curve is plotted with return loss on the vertical axis and frequency on the horizontal axis. The return loss is determined by measuring the intensity of the electromagnetic wave returning from the laminate sheet by irradiating the laminate sheet with an electromagnetic wave, placing a detector on the side where the electromagnetic wave is incident, and placing a material that totally reflects the electromagnetic wave back toward the incident side on the side opposite the side where the electromagnetic wave is incident. The return loss is calculated based on the relationship between the intensity of the incident electromagnetic wave and the intensity of the electromagnetic wave detected by the detector, as shown in Equation (1), and the ratio (T [%]) of the intensity of the returned electromagnetic wave to the intensity of the incident electromagnetic wave. The return loss Γ is expressed in decibels (dB). Measurement of return loss and identification of the peak top are performed using the method described below in "Return Loss Measurement." However, different equipment, procedures, and methods may be used as long as the same results are obtained. To briefly explain this method, we use the coaxial waveguide method or the free-space method to irradiate electromagnetic waves onto a laminated sheet with a metal reflector (e.g., aluminum) on the backside. The intensity of the electromagnetic waves returning from the laminated sheet is measured and calculated. The frequency is swept and the return loss is measured at each frequency. The frequency-return loss curve, plotted with return loss on the vertical axis and frequency on the horizontal axis, may show multiple peaks. Among these, we focus on the return loss peak with the largest peak intensity (attenuation). The "peak top" here refers to the point where the slope of the tangent to the return loss spectrum changes from positive to negative or negative to positive, i.e., the point where a line parallel to the x-axis touches the curve. When there is only one peak top, as shown in Figures 1 and 2, a baseline is drawn at the peak, and the return loss at the peak top frequency is expressed as the difference between the return loss at the peak top and the baseline. Hereinafter, the return loss at the peak top of the return loss peak is referred to as the return loss RL [dB]. Furthermore, even if a peak has a high amount of baseline attenuation as shown in FIG. 3, if it has a specific peak top, the difference in attenuation between the baseline of the peak top and the peak top is read.On the other hand, when a spectrum like that shown in Figure 4 is obtained, which has multiple peak tops including a shoulder peak, the frequency of the highest peak among the multiple peak tops is expressed as the difference between the attenuation corresponding to the peak top and the attenuation from the baseline of the entire peak including the multiple peak tops.

[0030]

number

[0031] The return loss RL at the return loss peak shown in this manner must be 5.0 dB or greater. A return loss RL of less than 5.0 dB means that when the baseline return loss is 0 dB, this is equivalent to the return loss Γ according to formula (1), and therefore indicates an electromagnetic wave transmittance of greater than 30%. Therefore, a laminate sheet with a return loss RL of less than 5.0 dB at the return loss peak cannot be said to have sufficient electromagnetic wave shielding properties. The return loss RL at the return loss peak where the return loss is greatest in the laminate sheet of the present invention is preferably 15.0 dB or greater, more preferably 20.0 dB or greater, and even more preferably 30.0 dB or greater. When the return loss RL at the peak top, where the return loss is greatest, is approximately 30.0 dB, this indicates that 99.9% of the incident electromagnetic waves are shielded compared to the electromagnetic wave shielding properties in the frequency bands around the peak, and it can be said to have very high electromagnetic wave shielding properties. The upper limit is not particularly limited, but is preferably 100 dB or less. The width of the frequency band where the return loss RL of the return loss peak with the largest peak-top return loss exceeds 5.0 dB is preferably as wide as possible while still exhibiting a steep and high electromagnetic wave shielding property, because this reduces frequency band fluctuations due to thickness variations in the laminate sheet. Specifically, the width of the frequency band where the return loss RL of the return loss peak with the largest peak-top return loss exceeds 5.0 dB is preferably 1.0 GHz or greater, more preferably 3.0 GHz or greater, and even more preferably 5.0 GHz or greater. The upper limit is preferably 20.0 GHz or less. A high return loss RL of the return loss peak with the largest peak-top return loss, 5.0 dB or greater, can be achieved by increasing the number of layers, minimizing thickness variations, and increasing the overall thickness of the laminate sheet from the viewpoint of the laminate sheet configuration. Furthermore, from the viewpoint of additives, conductive materials and / or additives exhibiting high conductivity / magnetism or by increasing the concentration of these additives.

[0032] The laminate sheet of the present invention preferably has a RL / (t × f) ratio of 0.2 to 15, where RL [dB] is the return loss at the return loss peak where the return loss at the return loss peak top is the largest, f [GHz] is the frequency at which this return loss is observed, and t [mm] is the total thickness of the laminate sheet. Compared to conventional techniques, the laminate sheet of the present invention is characterized by its alternating lamination of low-dielectric-constant and high-dielectric-constant layers, which allows for a thinner sheet thickness and improved formability compared to conventional single-layer or low-layer sheets. This feature is applicable to sheets targeting any frequency band. However, because thickness and frequency exhibit a trade-off relationship, the theoretical thickness of a laminate sheet with the same dielectric constant tends to be thinner when the frequency band is shifted to a higher frequency. For this reason, the thin-film effect of the laminate sheet of the present invention that exceeds the volume law cannot be explained solely by the relationship between return loss RL and thickness t (e.g., RL / t). It is important that the aforementioned relationship between the three elements—frequency f, laminate sheet thickness t, and return loss RL at the return loss peak—is superior to that of the prior art. RL / (t×f) is more preferably 0.45 to 12, and most preferably 0.75 to 10. When RL / (t×f) is less than 0.2, the return loss RL is low, and the electromagnetic shielding performance sufficient for use in electromagnetic shielding applications is insufficient. Alternatively, although the electromagnetic shielding performance is present, the thickness is too thick and the performance exceeding the volume law may not be sufficient. When RL / (t×f) is higher than 15, even if the return loss is high, the thickness may be too thin, resulting in poor lamination accuracy and film-forming properties of the laminate sheet due to the addition of high concentrations of conductive and / or magnetic materials. In order for RL / (t×f) to satisfy the preferred range, the effect is enhanced by combining the following elements: the number of laminated sheets is large, resulting in a state in which a lot of dielectric polarization is generated; there is little unevenness in layer thickness; the conductive material and / or exhibits high conductivity / magnetism; and, further, a configuration in which multiple types of conductive materials are used to allow for free design of the dielectric constant, and the real and imaginary parts of the dielectric constant of the layer exhibiting a high dielectric constant satisfy the dielectric constant relationship described below. The preferred conditions for each element are as explained in this specification.

[0033] The reflection attenuation peak of the laminate sheet of the present invention, which has the largest reflection attenuation, preferably exists in the 1 to 100 GHz frequency band. When the laminate sheet of the present invention is used for electromagnetic wave shielding in high-frequency applications that are difficult to target with conventional conductive reflection or magnetic absorption technologies, it is preferable that the maximum attenuation peak be in the GHz frequency band. To achieve this, it is most preferable to use a conductive material or a dielectric material, as described below, as the material contained in the laminate sheet to form a dielectric absorption type laminate sheet. Generally, to shield near-field frequencies below a few GHz, sheets containing a dielectric substrate containing a magnetic material, such as a metal such as silver or copper or a metal oxide such as ferrite, are used. However, when targeting high frequencies in the GHz band, a characteristic unique to magnetic materials, known as the Snoek limit, which prevents magnetic loss above a certain frequency, typically requires the inclusion of a high concentration of magnetic material to cover this. Conventional technologies using special materials such as ε-iron oxide exist, but these materials are expensive and require high concentrations, which can result in costs and film-forming properties that are inferior to those using conductive materials. When producing laminated sheets by melt extrusion, thixotropy is inevitable due to the inclusion of high concentrations of filler, and the added magnetic material may cause damage to the metal parts of the extruder. Therefore, when producing laminated sheets using the melt extrusion process with low filler concentrations, in order to achieve electromagnetic shielding properties in the GHz frequency range, it is preferable to add a conductive material or a conductive / magnetic composite material to achieve electromagnetic shielding properties in the high frequency range through electromagnetic wave absorption. When using a magnetic material in combination to target a frequency range of several GHz, it is preferable to use a metal material with a high aspect ratio, which allows for electromagnetic wave energy loss due to its high magnetic permeability. Adding a material with a high aspect ratio to a laminated sheet enables in-plane alignment of the material, which is difficult with conventional single-layer films, and can result in a material that exhibits shielding properties even in the GHz frequency range.The aspect ratio can be expressed as the ratio of the length in the thickness direction of the material to the length of the major axis in the planar direction, and if the former is t1 and the latter is t2, then t1 / t2 should preferably be between 0.001 and 0.95, and more preferably between 0.01 and 0.1. If the aspect ratio is less than 0.001, the magnetic material will be too thin, which can cause deformation or damage to the material during compounding or film formation, making it impossible to obtain the benefits of the magnetic material.

[0034] The laminated sheet of the present invention has a surface resistance value [Ω / □] of at least one of the outermost surfaces of 1.0×10 5 The above is preferable. When using a laminate sheet as an electromagnetic wave absorbing sheet, it is preferable to suppress the reflection of electromagnetic waves at the interface between an air layer and the outermost layer of the laminate sheet in order to efficiently propagate electromagnetic waves within the laminate sheet and lose the energy of the electromagnetic waves within the laminate sheet. When electromagnetic waves are perpendicularly incident, the reflectance R of the electromagnetic waves at the interface between two regions X and Y having different permittivity (ε) and magnetic permeability (μ) is expressed as shown in Equation (2). When focusing on the interfacial reflection between the air layer and the outermost surface of the laminate sheet, it is particularly affected by the difference in the ratio of the permittivity (ε) and magnetic permeability (μ) of the air layer and the outermost layer of the laminate sheet. Since the permittivity (ε) and magnetic permeability (μ) of the air layer are 1, it is effective to make the ratio of the permittivity (ε) and magnetic permeability μ of the outermost layer of the laminate sheet close to 1. Specifically, it is preferable to use a resin with low permittivity / low magnetic permeability so that the conductivity and magnetic permeability are close to those of the air layer, and to use a form that does not contain either conductive or magnetic materials. In the case of the laminated sheet of the present invention, it is difficult to use the dielectric constant / magnetic permeability as an index of insulation / conductivity, because it is difficult to measure each layer individually. Therefore, it is preferable to use the surface resistance value, which roughly shows a correlation, to express the insulation / conductivity of each layer. In the present invention, the values ​​are expressed as values ​​measured using a high resistivity meter and a low resistivity meter manufactured by Mitsubishi Chemical Corporation in accordance with the JIS standard. The surface resistance value [Ω / □], which is an index of conductivity that is less likely to cause surface reflection of electromagnetic waves, is 1.0 × 10 5 It is preferable that the resistance is 1.0×10 [Ω / □] or more, and more preferably 1.0×10 9 [Ω / □] or more, more preferably 1.0 × 1013 The surface resistance of the outermost surface is in the above range. There are no particular limitations on the method for achieving this range, but examples include reducing or eliminating the conductive / magnetic material or conductive polymer component contained in the layer having the outermost surface. 5 The layer having a surface resistance of 1.0×10 or more may be located on the side where electromagnetic waves are incident during mounting, and may be located on at least one side, but more preferably on the outermost surface of both sides. 5 In order to achieve a value of [Ω / □] or more, the layer located on the surface can be designed to contain a low concentration of conductive material and / or magnetic material, or to not contain conductive polymers or additives as a resin.

[0035]

number

[0036] In addition, μ X and ε X are the permittivity and permeability of region X, respectively, and μ Y and ε Y represent the permittivity and permeability of region Y, respectively.

[0037] The laminate sheet of the present invention preferably contains a conductive material in Layer A or Layer B. Only one type of conductive material may be contained, or multiple types of conductive materials may be used in combination.

[0038] The conductive material can be appropriately selected from organic carbon-based materials with small primary particle size suitable for melt extrusion. Of course, the conductive material is not limited to organic carbon-based materials and can also be used in combination with electromagnetic wave shielding materials or dielectric materials primarily composed of inorganic components other than organic carbon-based materials, as described below. When using an extruder to produce a laminated sheet using only inorganic component-based electromagnetic wave shielding materials or dielectric materials, high concentrations of the electromagnetic wave shielding material are required to achieve electromagnetic wave shielding performance due to conductivity / magnetism. This can lead to problems such as material pulverization and equipment damage due to friction between the metals of the equipment and the conductive material. Therefore, it is preferable that at least one of the conductive materials contains an organic carbon-based material primarily composed of carbon. "Mainly composed of carbon" means that the molar ratio of carbon in the conductive material is 50 mol% or more, preferably 80 mol% or more, more preferably 90 mol% or more, and particularly preferably 95 mol% or more.

[0039] Examples of organic carbon-based conductive materials include carbon black (spherical carbon) such as acetylene black, channel black, lamp black, thermal black, ketjen black, and furnace black; cylindrical carbon nanotubes such as single-walled nanotubes, multi-walled nanotubes, and cup-stacked nanotubes; flat carbon such as graphite, graphene, and other materials; and spherical graphite, cylindrical graphite, carbon microcoils, fullerenes, and carbon fibers (long and short fibers). Among these, conductive carbon black, which easily develops a primary structure (linear structure), is preferred for improving the conductivity of layers containing conductive materials by utilizing the effect of particle alignment in the plane direction due to the laminated structure. Furthermore, to form stronger conductive paths in the layer direction without disrupting the laminated structure, it is preferable to use carbon black, which develops a structure in any direction, in combination with carbon nanotubes or flat carbon, which have a uniform structure and a high aspect ratio. In particular, materials whose size and thickness are controlled at the nano level are preferred, and it is more preferred to use carbon black, carbon nanotubes, graphene, graphite, or the like.

[0040] This is known as the Maxwell-Wagner effect. A high-aspect-ratio conductive material (including the resulting higher-order structure) is aligned so that its longitudinal axis is substantially parallel to the surface of the laminate sheet. The material is then incorporated into a resin substrate (especially a thermoplastic resin substrate, such as polyolefin resin, polyester resin, acrylic resin, or vinyl monomer copolymer resin, as previously exemplified as a resin with a low dielectric constant). The resin substrate is sandwiched between layers of conductive material within the resin substrate containing the conductive material. This creates a significant amount of micro-dielectric polarization at the interface between the conductive material layer and the resin substrate layer, thereby enhancing electromagnetic wave shielding. Specifically, the conductive material contained in the dielectric resin substrate is aligned substantially parallel to the sheet plane through laminar flow and stretching during the lamination process, resulting in parallel, opposing polarizations like those of a parallel-plate capacitor. This facilitates the accumulation of a large amount of charge at the interface between the dielectric substrate and the conductive material when an electric field is applied by irradiating the laminate with electromagnetic waves, thereby enhancing the conductivity within the laminate sheet. As a result, when electromagnetic waves are incident, they are resisted by the conductive material, and the electromagnetic wave energy is more likely to be converted into thermal energy, resulting in improved shielding properties due to electromagnetic wave absorption.As conductive materials for achieving this aspect through lamination processes, stretching processes, etc., it is preferable to use, among the materials mentioned above, cylindrical or flat materials with high aspect ratios, carbon nanotubes, and carbon black with high DBP oil absorption.

[0041] Carbon black suitable for use in the present invention includes carbon black having a dibutyl phthalate (DBP) oil absorption [mL / 100g] of 150 or more. DBP oil absorption [mL / 100g] is an index showing the degree of development of the carbon black structure. Materials with a high DBP oil absorption value indicate that carbon black particles are more likely to be connected in a linear chain, resulting in the presence of many voids within the structure. Therefore, even a small amount of carbon black is preferred because it can form conductive paths and provide conductivity. The DBP oil absorption [mL / 100g] of the carbon black is more preferably 250 or more, and even more preferably 350 or more. When the carbon black structure is developed and a conductive path is formed, when an electric field is generated by irradiation with electromagnetic waves, charge accumulates at the interface between the dielectric substrate and the conductive material. The electromagnetic wave energy is converted into thermal energy by the conductive material, which is an electromagnetic wave resistor, thereby exhibiting high shielding properties through electromagnetic wave absorption. Although there is no particular upper limit to the DBP oil absorption, considering that the structure may be destroyed when dispersed in the polymeric material that constitutes the conductive material, it is preferably 800 [mL / 100 g] or less. The DBP oil absorption can be measured in accordance with ASTM D 2414-79. Examples of such conductive spherical carbon that can be used include commercially available products such as acetylene black, furnace black, and ketjen black.

[0042] Examples of electromagnetic wave shielding materials that can be used in the laminate sheet of the present invention and are primarily inorganic components other than the conductive materials include metals such as silver, copper, iron, nickel, chromium, aluminum, zinc, and tin, as well as their oxides, nitrides, carbides, borides, oxynitrides, hydroxides, oxyborides, carbonyls, and organometallic complexes. Particularly preferred components include transparent conductive metal oxides such as indium tin oxide (ITO) and indium zinc oxide (IZO), stainless steel, and organometallic complexes such as iron carbonyl, iron hexacyano, and iron amino. Similar to the concept of the carbon material, these inorganic magnetic materials are preferably used in the form of flattened, extended materials, as this enhances the electromagnetic wave shielding properties of the laminate sheet of the present invention.

[0043] Furthermore, a dielectric material having excellent charge storage ability can be added as an additive to the laminate sheet of the present invention. The dielectric material does not have the effect of providing resistance to irradiated electromagnetic waves and directly causing the loss of energy of the electromagnetic waves. However, as will be described later, in order to shield electromagnetic waves in a specific frequency band, it is necessary to use the real term ε of the dielectric constant of the layer of the laminate sheet that exhibits a relatively high dielectric constant. h ' and the imaginary term ε h It is preferable to control the dielectric constant ε′′ to a specific range. h ' and the imaginary term ε h '' tend to vary numerically with the doping concentration, as well as the real term of the dielectric constant, ε h The use of a dielectric material that can selectively improve the complex dielectric constant is preferred because it allows for more precise control of the value of the complex dielectric constant. Dielectric materials that can be used here include magnesium oxide, titanium oxide, barium titanate, strontium titanate, calcium titanate, lead zirconate titanate, titanium oxide, iron oxide (ferrite), bismuth ferrite, and the like, which have a perovskite structure or a rutile structure, but titanium oxide, ferrite, barium titanate, and the like are preferred because they are versatile and exhibit a high dielectric constant.

[0044] The electromagnetic wave suppressing material used in the laminate sheet of the present invention preferably uses a combination of two or more of the organic carbon-based conductive material, the inorganic-based electromagnetic wave shielding material, and the dielectric material. This is because, when controlling the dielectric constant of the high-dielectric-constant layer described below to a preferred range that exhibits high electromagnetic wave attenuation, simply changing the concentration of a single material results in a linear relationship between the real and imaginary terms of the dielectric constant, making it difficult to control within a specific range. Therefore, by using a material that exhibits a linear relationship between the real and imaginary terms of the dielectric constant different from the above, it is possible to control the real and imaginary terms of the dielectric constant two-dimensionally on the dielectric constant plane, making it easier to design a laminate sheet with higher attenuation. In this case, different conductive materials may be used in combination, or a conductive material may be used in combination with an inorganic-based electromagnetic wave shielding material or dielectric material. In particular, iron oxide, barium titanate, titanium oxide, iron carbonyl, and the like, which have a high complex dielectric constant, can increase the real part of the complex dielectric constant without increasing the value of the imaginary part, and when used in combination with a carbon material, the dielectric constant can be adjusted more drastically, so they are preferably used as the second material.

[0045] From the perspective of achieving both electromagnetic wave shielding performance and the strength of the laminate sheet itself, the content of these electromagnetic wave shielding materials is preferably 1 wt% or more and less than 15 wt%, assuming that all components constituting the laminate sheet are 100 wt%. Generally, a high content of conductive material is necessary to achieve high conductivity. However, while a high content of conductive material achieves high conductivity, it can significantly impair film-forming and processability, potentially weakening the sheet itself. Conversely, if the content of conductive material is too low, sufficient electromagnetic wave shielding effect may not be achieved. Therefore, the content of conductive material is preferably 1 wt% or more and less than 15 wt%. More preferably, it is 1.5 wt% or more and less than 10 wt%, and even more preferably, it is 2 wt% or more and less than 5 wt%. When a laminate sheet contains multiple types of electromagnetic wave suppressing materials, the content of the electromagnetic wave suppressing materials is calculated by adding together the amounts of all the electromagnetic wave suppressing materials.

[0046] As mentioned above, the conductive material contained in the laminate sheet of the present invention may be contained in only one layer, either the A layer or the B layer, or in both the A layer and the B layer. However, if both the A layer and the B layer contain a conductive material, resulting in a highly conductive layer, the dielectric polarization effect at the interface between the layers of the laminate sheet may be insufficient. As a result, the laminate sheet as a whole may exhibit an effect similar to that of a single-film electromagnetic wave shielding material, and may not be able to achieve steep electromagnetic wave shielding properties at only the desired frequency. Furthermore, the increased conductivity and dielectric constant of the surface layer may cause surface reflection of electromagnetic waves, which may reduce the electromagnetic wave absorption effect of the conductive material compared to a laminate sheet containing the same concentration of conductive material as the entire laminate sheet but with a higher conductive material content in the B layer. Therefore, in a laminate sheet having an A(BA)n repeating unit, it is preferable that the amount of conductive material contained in the surface layer A be less than the amount of conductive material contained in the non-surface layer B. More specifically, it is preferred that the sum of the total contents of the conductive materials contained in Layer A is 1 wt% or less relative to the weight of the entire laminate sheet, and the sum of the contents of the conductive materials contained in Layer B is 1 wt% or more relative to the weight of the entire laminate sheet. Even more preferred is an embodiment in which the difference in the content of the conductive material between Layer A and Layer B is large, and in particular, Layer A does not contain a conductive material, and only Layer B contains a conductive material.

[0047] In addition to the conductive material, magnetic material, and dielectric material, the laminate sheet of the present invention may contain, as needed, dispersants, surface modifiers, lubricants, crosslinking agents, vulcanization accelerators, antioxidants, nucleating agents, flame retardants, light absorbers (ultraviolet absorbers, dyes, heat absorbers, etc.), flow modifiers (plasticizers, thickeners), antiblocking agents, etc., to the extent that the inherent properties of the laminate sheet are not impaired. Note that, as long as the inherent properties of the laminate sheet are not impaired, these components may be contained in layer A, layer B, or any layer other than layer A and layer B.

[0048] The laminate sheet of the present invention preferably has the layer A on at least one surface layer. By providing the layer A, which has low conductivity, on the surface layer, the reflection effect caused by the layer B, which has a high dielectric constant, can be suppressed, and electromagnetic waves irradiated onto the laminate sheet can be efficiently transmitted into the laminate sheet, allowing the laminate sheet to fully exhibit its effectiveness as an electromagnetic wave absorbing sheet. Whether the layer A is disposed on only one surface layer or on both surfaces can be appropriately selected in consideration of the practicality when using the laminate sheet as an electromagnetic wave absorbing material.

[0049] The electromagnetic wave shielding property and frequency band of the laminated sheet of the present invention are determined by the impedance Z shown in Equation (3) and Equation (4). in、 The return loss Γ can be calculated from the calculated return loss. in and Γ depend on the permittivity, magnetic permeability, and thickness of the entire sheet. Therefore, in order to achieve high electromagnetic wave shielding performance with a thin film, the product of the real part of the permittivity, ε', and the real part of the magnetic permeability, μ', must be a high value. In equations (3) and (4), Z0 is the characteristic impedance of the air, d is the thickness of the laminated sheet, λ is the wavelength, μ is the magnetic permeability of the entire laminated sheet, and ε is the permittivity of the entire laminated sheet, and the value of Z0 is 377 Ω.

[0050]

number

[0051]

number

[0052] The permittivity and permeability of the entire laminated sheet affect the design of the permittivity of layers A and B, which are alternately arranged to cause dielectric polarization. Specifically, the difference in permittivity between layers A and B is sufficiently large, and the real part of the permittivity of the layer that exhibits a relatively high permittivity, ε h ' and the imaginary part ε hControlling ε'' is extremely effective in adjusting the electromagnetic wave shielding properties. The region that exhibits high electromagnetic wave shielding properties for a specific frequency band at a specific sheet thickness can be calculated based on equations (3) and (4). Furthermore, in order for a laminated sheet to exhibit high electromagnetic wave shielding properties, the real part ε of the permittivity of the layer with a relatively high permittivity between layer A and layer B must be calculated. h ' and the imaginary part ε h It is preferable that "" satisfies the relational expression (A) or (B). (A) εh''≧1 and 0.17εh'+2.3≦εh''≦0.27εh'+3.3 (B) 5≧εh′′≧1, and 0.02εh′+1≦εh′′≦0.07εh′+1.9 The real part of the permittivity of the layer with a relatively high permittivity, ε h ' and the imaginary part ε h By controlling ''' within this range, it is possible to achieve high electromagnetic wave shielding properties at specific frequencies even when the sheet thickness is thin.

[0053] The real part ε' of the dielectric constant, the imaginary part ε'' described below, and the real part μ' of the magnetic permeability of the laminate sheet of the present invention can be measured by the method described in the "Dielectric Constant Measurement" section of the Examples. h ', ε h The dielectric constant ε′) can be measured by the above method and the method described in the “Calculation of the dielectric constant of each layer” section of the Examples. Briefly, a waveguide or lens antenna fixture is used according to the frequency to be measured, and the electromagnetic waves emitted from an electromagnetic wave generator are incident on a sample placed in the waveguide or between the lens antennas. The electromagnetic wave reflection and transmission characteristics are calculated in accordance with the known S-parameter method. The measurement device and calculation software are not particularly limited as long as they are capable of measurement and calculation. For example, the devices described in the Examples and the calculation software accompanying these devices can be used. In this case, the real term ε′ and imaginary term ε″ of the dielectric constant can be obtained by reading the values ​​automatically calculated by the calculation software.

[0054] The real part of the permittivity of the layer with a relatively high permittivity, εh ' and the imaginary part ε h The method of controlling the dielectric constant so that the relational expression (A) or (B) is satisfied is, for example, to improve the dielectric constant by using carbon black having a DBP oil absorption in the range described below as the conductive material, barium titanate, ferrite oxide, or titanium oxide as the dielectric material, carbonyl iron as the magnetic material, or graphite or graphene, which are conductive materials with a high aspect ratio. In particular, in order to satisfy the expression (A), the real part ε of the dielectric constant h ' and the imaginary part ε h Since it is required to increase both the dielectric constant and the dielectric constant, it is preferable to use carbon black. In order to satisfy the formula (B), the imaginary part of the dielectric constant, ε h Since a low .DELTA.' is required, this can be achieved by using at least one dielectric material, such as barium titanate, ferrite, or titanium oxide, or at least one conductive material with a high aspect ratio, such as graphite or graphene, either alone or in combination. Furthermore, this can also be achieved by using the stretching method described below to reduce the thickness of each layer, or by increasing the number of layers in a multilayer laminate sheet through a feed block with slits, thereby dispersing and orienting the conductive material and / or magnetic material in the plane direction of the sheet.

[0055] The laminate sheet of the present invention preferably has a ratio RL / fΔ of 5.0 or more, where fΔ [GHz] is the half-width of the reflection loss peak with the largest peak-top reflection loss and RL [dB] is the peak-top reflection loss of the reflection loss peak with the largest peak-top reflection loss. RL / fΔ is an index indicating the steepness of the reflection loss peak. By setting RL / fΔ in this range, the laminate sheet can be made into a material that shields only the desired electromagnetic wave range when mounted in electronic devices, communication devices, etc. RL / fΔ can be increased by reducing the layer thickness unevenness of Layer A and / or Layer B, increasing the dielectric constant difference between the high-conductivity layer and the low-conductivity layer by combining resins, using a conductive material with a high DBP oil absorption or a high aspect ratio, or increasing the number of layers. These ratios RL / fΔ are more preferably 10.0 or more, and even more preferably 20.0 or more. If the RL / fΔ at the maximum reflection loss peak is less than 5, it means that the material provides electromagnetic wave shielding across a wide frequency band, as with conventional products. However, if only specific frequencies of electromagnetic waves need to be attenuated, electromagnetic wave shielding in undesirable frequency bands may result. While there is no upper limit for the RL / fΔ at the maximum reflection loss peak, if the peak is very steep, slight changes in the thickness of the laminate sheet or the concentration of the conductive material may sensitively shift the peak top position, potentially preventing the desired electromagnetic wave shielding properties from being achieved. Therefore, it is preferable that the RL / fΔ at the maximum reflection loss peak is less than 200. The half-value width depends on the frequency of the reflection loss peak at which the peak top reflection loss is greatest. However, a smaller half-value width fΔ [GHz] is preferable for the laminate sheet of the present invention, as it can block only specific frequencies. Specifically, the half-value width fΔ [GHz] is preferably 10.0 or less, more preferably 5.0 or less, and even more preferably 2.0 or less.

[0056] In the laminate sheet of the present invention, the peak-top frequency of the return loss peak at which the peak-top return loss is greatest is determined by the permittivity / permeability of the conductive layer, and can therefore be controlled not only by the type and content of the conductive material but also by the thickness of the alternately laminated A and B layers with different conductivities. While frequencies that should and should not be attenuated vary depending on the application of electronic devices, communication devices, and transportation, the laminate sheet of the present invention can easily control the frequencies at which electromagnetic waves should be shielded, and therefore can be suitably used in electronic devices, communication devices, and transportation.

[0057] In the laminate sheet of the present invention, the coefficient of variation tBσ / tB, where tB [mm] is the average thickness of Layer B and tBσ [mm] is the standard deviation, is preferably 0.3 or less. As mentioned above, when Layer A is positioned as the surface layer and has a higher surface resistivity than Layer B, Layer B, which exhibits electrical conductivity, becomes the primary layer responsible for electromagnetic wave shielding through electromagnetic wave absorption. However, if the thicknesses of these layers vary, the dielectric constants of each layer will differ, resulting in variations in the frequency of the electromagnetic waves at which shielding is achieved. Uniforming the thickness of Layer B, which exhibits electrical conductivity, so that the coefficient of variation tBσ / tB falls within the above-mentioned range allows layers with a constant dielectric constant to overlap, resulting in a steeper electromagnetic wave shielding property and frequency selectivity with high electromagnetic wave attenuation, which is preferable. The coefficient of variation tBσ / tB, which indicates the variation in layer thickness, is preferably 0.2 or less, more preferably 0.1 or less. In the case of a laminate sheet made of a thermoplastic resin, the coefficient of variation can be reduced by using a slit-type feed block rather than using a mixer to increase the number of layers. Although there is no particular lower limit to the coefficient of variation tBσ / tB, in light of the productivity of the laminated sheet, it is practical to set it to 0.01 or more.

[0058] Furthermore, although there is no limitation on the thickness of Layer A of the laminate sheet of the present invention, if the layer is thinner than the distance of the conductive material contained in Layer B, the effect of macroscopic dielectric polarization between Layer A, which exhibits dielectric properties, and Layer B, which exhibits conductivity, may not be obtained, and electromagnetic wave loss may decrease. Therefore, when the average thickness of Layer A is tA [mm], it is preferable to design Layer A so that tA ≧ tB, since this ensures sufficient separation between adjacent Layer Bs.

[0059] A preferred embodiment of the present invention is an electromagnetic wave shield having the aforementioned laminate sheet and a reflector. The reflector is a plate-shaped material that has the function of reflecting electromagnetic waves. By combining it with the surface opposite to the electromagnetic wave incident surface of the laminate sheet, the electromagnetic waves are reflected back and forth within the laminate sheet, thereby improving the electromagnetic wave absorption efficiency. On the other hand, when the reflector is placed on the front surface, it is also possible to have a configuration in which a certain amount of electromagnetic waves are reflected by the surface of the reflector and the portion of the transmitted electromagnetic waves are sharply shielded within the laminate sheet. In order to fully utilize the electromagnetic wave absorption properties of the laminate sheet of the present invention, the former configuration is more preferable.

[0060] The reflector is not particularly limited in terms of its constituent material, as long as it can reflect electromagnetic waves. Examples of constituent materials include metals such as aluminum, copper, iron, and gold, alloys such as stainless steel, and carbon films. The shape and thickness of the reflector are not limited as long as it contains a metal or alloy, or carbon. The shape should be in accordance with the material to be used, but it can be a flat, curved, hemispherical, or other plate-like shape.

[0061] Examples of reflectors include plate reflectors containing metal, alloy, or carbon, laminated reflectors in which a film made of metal, alloy, or carbon is formed on the surface of a polymer film, sheet, plate, etc., composite reflectors in which metal, alloy, or carbon is dispersed inside a polymer film, sheet, plate, etc., and composite reflectors containing a mesh made of metal or alloy inside a polymer film, sheet, plate, etc. In addition, in the present invention, when a support, housing, etc. for each application contains a metal, alloy, carbon, etc., it can be used as a reflector as is.

[0062] A preferred embodiment of the present invention is an electronic device or communication device having the above-mentioned laminate sheet or the above-mentioned electromagnetic wave shield for the purpose of preventing false images caused by electromagnetic waves used in 4G / 5G communications, wireless LAN, collision prevention (ITS) radar, etc., reducing unnecessary electromagnetic wave radiation from electronic devices installed inside housings such as computers, mobile phones, radios, medical devices, and vehicle bumpers, preventing malfunctions of devices due to radiation from adjacent devices, etc. In addition, any electronic device or communication device that uses frequencies in the GHz band can be equipped with the laminate sheet of the present invention and used, without being limited to the above.

[0063] Furthermore, preferred embodiments of the present invention include transportation means such as vehicles, aircraft, and ships equipped with the laminate sheet or the electromagnetic wave shield described above, walls of structures such as buildings, tunnels, guardrails, highways, bridges, and steel towers, and communication facilities such as telegraph and telephone facilities. The laminate sheet of the present invention can be applied by attaching it directly to structures such as floors, ceilings, walls, and pillars using an adhesive or by attaching it to other sheets, shielding plates, panels, etc. It can also be used as a wall or window material for shielded rooms to protect against external electromagnetic jamming and noise.

[0064] Next, a preferred method for producing the alternately laminated unit of the laminated sheet of the present invention will be described below. Of course, the present invention is not limited to the examples described below.

[0065] An example of a method for producing an alternating laminate unit using rubber, thermoplastic elastomer, or the like as the base polymer of the substrate is described below. A predetermined amount of conductive material is blended with the base polymer and kneaded and incorporated using a known device such as a kneader, Banbury mixer, mill mixer, roll mill, jet mill, or ball mill to produce a conductive material-containing polymer. The base polymer alone or the prepared conductive material-containing polymer is rolled using a batch press or melt extruded to form a sheet of the desired thickness. The prepared sheet corresponding to layer A and the prepared sheet corresponding to layer B are then superimposed and pressed or laminated to obtain the desired layered alternating laminate unit. The fusion temperature, which depends on the resin used, is preferably in the range of 150°C to 400°C, more preferably 250°C to 380°C.

[0066] An example of a method for producing an alternating laminate unit when using a flexible thermoplastic resin, which is preferably used in the present invention, is described below. The thermoplastic resin prepared in pellet form and a predetermined amount of conductive material are kneaded using a twin-screw extruder, then extruded in the form of a gut, cooled in a water tank, and cut with a chip cutter to form master pellets containing the conductive material. The conductive material may be dry-blended with the resin and then metered and fed from a hopper, or it may be side-fed into the molten resin using a side feeder from any position in the extruder. The method can be selected appropriately depending on the specific gravity and shape of the conductive material used.

[0067] The thermoplastic resins constituting Layer A and Layer B are dried in hot air or under vacuum and then fed into separate extruders. Each resin is heated to or melted above its melting point in the extruder and discharged at a uniform extrusion rate using a gear pump or other device. Foreign matter and denatured resins are removed through a filter or other device. These resins are passed through a multi-layer lamination device capable of laminating the desired number of layers, molded into the desired shape using a die, and then discharged into a sheet. The sheet discharged from the die is extruded onto a cooling body such as a casting drum and cooled and solidified to obtain a cast sheet. Because the cast sheet itself is conductive, preferred methods include blowing air from a slit-shaped, spot-shaped, or planar device to bring the sheet into close contact with a cooling body such as a casting drum and rapidly solidifying it, or using a nip roll to bring the sheet into close contact with a cooling body and rapidly solidifying it.

[0068] As mentioned above, a multi-manifold die, a feed block, a static mixer, or the like can be used as a multi-layer lamination device. However, to efficiently obtain the multi-layer laminate structure of the present invention, it is particularly preferable to use a feed block with fine slits. The use of such a feed block prevents the device from becoming excessively large, reduces the amount of foreign matter generated due to thermal degradation, and enables high-precision lamination even when the number of layers is extremely large. Furthermore, the lamination accuracy in the width direction is significantly improved compared to conventional techniques. Furthermore, this device allows the thickness of each layer to be adjusted by the shape (length, width) of the slits, making it possible to achieve any desired layer thickness. Another suitable method is to form a laminate in the feed block and then stack the layers through a static mixer to double the number of layers, thereby increasing the number of layers. In this case, the layer thickness of each stacked laminate is exactly the same, which is consistent with the concept of the present invention, in which uniform layer thickness is preferred.

[0069] The resulting cast sheet can then be biaxially stretched in the longitudinal and transverse directions, if necessary. The stretching can be performed sequentially or simultaneously. Furthermore, the sheet can be further stretched again in the longitudinal and / or transverse directions.

[0070] First, we will explain the case of sequential biaxial stretching. Here, stretching in the longitudinal direction refers to stretching to impart molecular orientation to the sheet in the longitudinal direction, and is usually performed by varying the peripheral speed of rolls. It can be performed in one stage or in multiple stages using multiple pairs of rolls. The stretching ratio varies depending on the type of resin, but is usually preferably 1.1 to 15 times, with 1.5 to 4 times being particularly preferred. The stretching temperature is preferably set within the range of the glass transition temperature of the resin constituting the alternating laminate unit to the glass transition temperature + 100°C.

[0071] The thus obtained longitudinally stretched alternately laminated unit may be subjected to a surface treatment such as corona treatment, flame treatment, or plasma treatment as necessary, and then a primer layer may be formed to improve adhesion with the film to be laminated on top. In the in-line coating process, the primer layer may be applied to one side or to both sides simultaneously or one side at a time.

[0072] Width-direction stretching refers to stretching to impart width-direction orientation to a sheet. Typically, a tenter is used to convey the sheet while holding both ends with clips, stretching it widthwise. The stretching ratio varies depending on the type of resin, but typically 1.1 to 15 times is preferred, with 1.5 to 6 times being particularly preferred. The stretching temperature is preferably between the glass transition temperature of the resin constituting the alternating laminate unit and the glass transition temperature + 120°C. The biaxially stretched alternating laminate unit is then heat-treated in the tenter from the stretching temperature to the melting point, uniformly cooled slowly, and then cooled to room temperature and wound up. If necessary, relaxation treatments, such as a longitudinal and / or width-direction relaxation treatment, may be performed during the heat-treatment and slow cooling process to impart a low orientation angle and thermal dimensional stability to the sheet.

[0073] Next, simultaneous biaxial stretching will be described. In the case of simultaneous biaxial stretching, the obtained cast sheet may be subjected to a surface treatment such as corona treatment, flame treatment, or plasma treatment as necessary, and then functions such as easy slip, easy adhesion, and antistatic properties may be imparted by in-line coating. In the in-line coating process, the easy adhesion layer may be applied to one side of the alternating laminate unit, or may be applied to both sides of the alternating laminate unit simultaneously or one side at a time.

[0074] The cast sheet is then introduced into a simultaneous biaxial tenter, where it is conveyed while both ends of the sheet are held with clips and simultaneously stretched in the longitudinal and transverse directions. Simultaneous biaxial stretching machines include pantograph, screw, drive motor, and linear motor types. Drive motor or linear motor types are preferred, as they allow for arbitrary stretching ratios and relaxation treatment at any desired location. The stretching ratio varies depending on the type of resin, but an area ratio of 2 to 50 times is generally preferred, with an area ratio of 4 to 20 times being particularly preferred. The stretching speed may be the same or different in the longitudinal and transverse directions. The stretching temperature is preferably between the glass transition temperature of the resin constituting the alternating laminate unit and glass transition temperature + 120°C.

[0075] The thus simultaneously biaxially stretched alternating laminate unit is preferably subsequently heat-treated in a tenter at a temperature above the stretching temperature and below the melting point to impart flatness and dimensional stability. During this heat treatment, it is preferable to instantly relax the film in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone to suppress distribution of the main orientation axis in the width direction. After heat treatment in this manner, the film is uniformly and slowly cooled, then cooled to room temperature, and wound up. If necessary, relaxation treatment may also be performed in the longitudinal and / or width directions during the slow cooling from the heat treatment. The film is instantly relaxed in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone.

[0076] In order to obtain the desired electromagnetic wave shielding properties, the prepared alternating laminate units can be bonded together using an adhesive sheet, a pressure-sensitive adhesive sheet, double-sided tape, etc., either with the same alternating laminate units or with alternating laminate units having different thicknesses or compositions.

[0077] Furthermore, a layer with a different dielectric constant can be laminated on the outermost surface of the alternating laminate unit for the purpose of increasing electromagnetic wave transparency or causing electromagnetic wave reflection. In this case, a coating layer containing a material exhibiting suitable conductivity / magnetism may be applied, or different resin layers / mesh layers may be laminated via an adhesive sheet or the like. Resin / metal layers can also be laminated by film metal coating techniques such as sputtering (such as planar or rotary magnetron sputtering), evaporation (such as electron beam evaporation), chemical vapor deposition, metalorganic chemical vapor deposition, plasma-enhanced / assisted / activated chemical vapor deposition, and ion sputtering.

[0078] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Each property was measured by the following methods.

[0079] (Methods for measuring characteristics and evaluating effects) The methods for measuring the properties and evaluating the effects in the present invention are as follows.

[0080] (1) Layer thickness, number of layers, and layer structure The layer structure of the laminate sheet was determined by observing cross sections of samples cut using a microtome according to the thickness of each layer constituting the laminate sheet using a differential interference microscope or a transmission electron microscope (TEM). Specifically, for the former, when the thickness of each layer constituting the laminate sheet was 1 μm or greater, the cross section of the laminate sheet was observed using a Leica DMLBHC differential interference microscope at 1000x magnification (10x eyepiece, 100x objective lens), and cross-sectional photographs were taken to measure the layer structure and thickness of each layer. Measurements were performed using the particle size analysis software Macview (Mountec Co., Ltd.), and layer thickness was measured by measuring the perpendicular distance between layer interfaces where contrast differences were clearly discernible. Data were measured at five random locations, and the average value of each layer thickness was used as the actual measurement data. The particle long diameter was determined by measuring the longest distance of the higher-order structure formed by the particles observed in the image at a total of 100 points and averaging the data. For the latter, transmission electron microscope (TEM) observations were performed using a transmission electron microscope (Hitachi, Ltd.) H-7100FA. Cross-sections of the laminated sheets were observed at an accelerating voltage of 75 kV. Cross-sectional photographs were taken, and the layer structure and thickness of each layer were measured. In some cases, staining techniques using RuO4 or OsO4 were used to achieve high contrast. Furthermore, observations were performed at a magnification of 100,000x for the thinnest layer (thin film layer) captured in a single image. For thin film layer thicknesses of less than 50 nm, 40,000x for those between 50 and 500 nm, and 10,000x for those 500 nm or greater. The layer thickness, number of layers, and layer structure were determined. The thickness of each layer in layer B in a specific cross-section of the obtained image was then measured, and the average layer thickness and standard deviation were calculated. The average thickness and standard deviation of the B layer at five different cross sections were calculated, and the average of the five calculated values ​​was used as the average value tB [mm] and the standard deviation tBσ [mm].

[0081] (2) Return loss measurement Measurements were performed by changing the measurement unit as follows according to the measurement frequency band. Based on the results obtained, a frequency-return loss curve was calculated, plotting return loss on the vertical axis and frequency on the horizontal axis.

[0082] (2-1) 1GHz to 40GHz frequency band The return loss of the laminated sheet was measured using an Agilent Technologies Vector Network Analyzer (E8361A). A donut-shaped coaxial waveguide with an outer diameter of 7 mm and an inner diameter of 3.04 mm was used for the 0.5 GHz to 18 GHz frequency band, a rectangular waveguide with a rectangular shape of 4.32 mm x 10.67 mm for the 18 to 26.5 GHz frequency band, and a rectangular waveguide with an internal shape of 3.56 mm x 7.11 mm for the 26.5 to 40 GHz frequency band. The frequency step size during measurement was set to allow measurement at 200 frequencies in each frequency band. A 3 mm aluminum metal plate was placed on the back of the laminated sheet sample, so that incident electromagnetic waves would be totally reflected when there was no electromagnetic wave absorption by the laminated sheet. S, which represents the intensity ratio of the reflected electromagnetic wave to the incident electromagnetic wave, is used. 11 The S-parameter values ​​were used to analyze the reflection loss peak.

[0083] (2-2) 40 to 110 GHz frequency band Measurement samples were prepared by laminating an aluminum metal plate to the back of a 150 mm square laminated sheet. Using a Keycom Corporation lens antenna type oblique incidence electromagnetic wave absorber (electromagnetic wave absorbing material) return loss measurement device LAF-26.5B, electromagnetic waves were irradiated at an oblique incidence angle of 15° in accordance with JIS R 1679, and return loss was measured in the frequency bands of 33 to 50 GHz (WR-22), 50 to 75 GHz (WR-15), and 75 to 110 GHz (WR-10). While this measurement method can also obtain values ​​for the 33 to 40 GHz frequency band, the return loss in the frequency band from 33 GHz to less than 40 GHz was measured using the measurement data in (2-1).

[0084] (3) Dielectric constant measurement The laminated sheet was analyzed by changing the measurement unit and measurement method for each measurement frequency as follows.

[0085] (3-1) 1GHz to 40GHz frequency band An Agilent Technologies Vector Network Analyzer (E8361A) was used. A donut-shaped coaxial waveguide with an outer diameter of 7 mm and an inner diameter of 3.04 mm was used for the 0.5 GHz to 18 GHz frequency band. A rectangular waveguide with a rectangular shape of 4.32 mm × 10.67 mm was used for the 18 to 26.5 GHz frequency band. A rectangular waveguide with an internal shape of 3.56 mm × 7.11 mm was used for the 26.5 to 40 GHz frequency band. A laminated sheet sample was punched and inserted vertically into each of the waveguides for measurement. The frequency step size during measurement was set to allow measurement at 200 frequencies in each frequency band. The complex permittivity was analyzed using the analysis software N1500A-001 provided with the instrument.

[0086] (3-2) 40 to 110 GHz frequency band A 150mm square laminated sheet was used. A Keycom LAF-26.5A lens antenna type dielectric constant and attenuation measuring device utilizing the frequency change method was used to measure the complex permittivity in the frequency bands of 33 to 50GHz (WR-22), 50 to 75GHz (WR-15), and 75 to 110GHz (WR-10). While this measurement method also measures values ​​from 33 to 40GHz, the complex permittivity in the frequency band from 33GHz to less than 40GHz was measured using the measurement data in (3-1).

[0087] (4) Surface resistance measurement (4-1) High resistance measurement High resistance region (1.0×10 6 ~1.0×10 13 The resistivity (Ω / □) was measured using a high resistivity meter, Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Corporation. A URS probe (MCP-HTP14) was pressed against the surface of a laminated sheet cut into a 10 cm square, and the resistance value was measured in accordance with JIS K 6911 (1995). Measurements were taken on five samples while changing the measurement position, and the arithmetic mean value of the five measured values ​​was used.

[0088] When measuring the surface resistance of the inner layer, the surface was polished with a polishing device to the thickness of the outermost layer confirmed with a transmission electron microscope, and then the surface resistance was measured by pressing a probe against the surface.

[0089] (4-2) Low resistance measurement Low resistance region (1.0×10 6 ~1.0×10 -1 The resistivity (Ω / □) was measured using a low resistivity meter Loresta-EP (MCP-T360) manufactured by Mitsubishi Chemical Corporation. An ASP probe (MCP-TP03P) was pressed against the surface of a laminated sheet cut into a 10 cm square, and the resistance value was measured in accordance with JIS K 7194. Measurements were taken on five samples while changing the measurement position, and the arithmetic mean value of the five measured values ​​was used.

[0090] (5)DBP oil absorption amount The laminated sheet was dissolved in a solvent that could dissolve the resin of the substrate, and the carbon-based conductive particles extracted and separated were measured using a Brabender Absorptometer C type in accordance with ASTM D2414-79. The carbon-based conductive particles were placed in a mixer at a rotation speed of 125 min -1 While kneading at 100°C, DBP was added dropwise at a rate of 4 mL / min, and the DBP oil absorption was analyzed based on the obtained viscosity curve.

[0091] (6) Calculation of the dielectric constant of each layer We created and used macro software that can calculate the impedance when the laminated sheet configuration is replaced with an equivalent electrical circuit by substituting the values ​​of the permittivity, permeability, and layer thickness of layers A and B. The obtained impedance Z inA macro was created to continuously calculate the return loss Γ over a certain frequency band by substituting Γ into equation (4), which is based on the non-reflection condition and return loss. The permittivity and permeability of each layer were then set to match the return loss spectrum measured using the method described in section (2). The permittivity and permeability values ​​for each layer were then read and determined based on the closest match. If it was difficult to calculate the permittivity, a single-layer sheet was prepared with the same composition as the layer exhibiting a relatively high permittivity in the example. The frequency variation method using the vector network analyzer described above was used to identify the frequency at which the minimum transmission loss was achieved. The permittivity was calculated based on the minimum value, which is an integer multiple of 1 / 2 the effective wavelength transmitted through the sheet thickness. This value can also be confirmed using the software (SFW05) included with Keycom's permittivity measurement system (Model No. DPS10) for free-space measurements using the frequency variation method. [Example]

[0092] ( Reference example 1 ) 100 parts by weight of ethylene-propylene terpolymer rubber manufactured by Mitsui Chemicals, Inc. was press-molded to produce Sheet A, 0.5 mm thick and 200 mm square. Meanwhile, 90 parts by weight of ethylene-propylene terpolymer rubber manufactured by Mitsui Chemicals, Inc. was blended with 10 parts by weight of conductive carbon black (spherical carbon) material with a primary particle diameter of 40 nm and a DBP oil absorption of 360, and the mixture was kneaded using a two-roll mill to prepare a rubber containing the conductive material. This conductive material-containing rubber was then pressed to produce Sheet B, 0.5 mm thick and 200 mm square. These molded rubber sheets were then thermocompressed at 250°C in the order of Sheet A, Sheet B, Sheet A, Sheet B, and Sheet A to form a five-layer laminated sheet with a thickness of 2.5 mm. When the return loss was measured using this laminated sheet, it was found to have a return loss peak with the largest attenuation at the peak top frequency of 30 GHz, with the return loss at the peak top being 12 dB and the half-value width being 2 GHz.

[0093] (Comparative Example 1) To 96 parts by weight of ethylene-propylene-terpolymer rubber manufactured by Mitsui Chemicals, Inc. , Reference example 1 Four parts by weight of the spherical carbon conductive material with a primary particle diameter of 39.5 nm and DBP oil absorption of 360 used in the above was compounded and kneaded using a two-roll mill to prepare a rubber containing the conductive material. The rubber containing the conductive material was then pressed and molded into a sheet of 2.5 mm thickness and 200 mm square to produce a single film sheet.

[0094] When the return loss was measured, Reference example 1 Compared to the above, the frequency band of the peak top of the reflection loss peak with the largest peak top attenuation is Reference example 1 However, the return loss at the top of the return loss peak was 7 dB, and the half-width was 5 GHz, so the bandwidth was wide and the return loss peak was weak.

[0095] ( Reference example 2 ) For 90 parts by weight of homo-polypropylene resin showing a melt flow rate of 30, Reference example 1 The spherical carbon-based conductive material used in the step 1 was added in an amount of 10 parts by weight, and the mixture was kneaded using a twin-screw extruder to which the conductive material was supplied by a side feed to prepare conductive master pellets.

[0096] A homopolypropylene resin with a melt flow rate of 30 was used for the A layer, and the conductive master pellets were used for the B layer. The prepared polypropylene resin and conductive master pellets were each fed into a twin-screw extruder and melt-mixed at 270°C. The mixing conditions for each twin-screw extruder were a screw rotation speed of 0.7 relative to the output rate. The extruded resins were then merged in nine multi-manifold feed blocks to form a 1mm-thick alternating laminate unit, with nine layers stacked alternately in the thickness direction at a layering ratio of 1.0. The resulting alternating laminate unit consisted of five A layers and four B layers containing conductive materials. Transmission electron microscopy confirmed that the layers were alternately stacked in the thickness direction. Furthermore, the layer thickness increased toward the center, with significant variation in thickness between each layer.

[0097] Two of the fabricated alternating laminated units were bonded together with a 25 μm thick adhesive sheet in between, resulting in a laminated sheet with a total of 19 layers, including the adhesive layer. Measurement of the return loss revealed that the peak with the largest return loss at 26 GHz had a return loss of 16 dB and a full width at half maximum of 2 GHz.

[0098] (Comparative Example 2) Reference example 2 For 95 parts by weight of homo-polypropylene resin with a melt flow rate of 30, Reference example 2 The conductive master pellets were prepared by adding 5 parts by weight of the spherical carbon conductive material used in the step 1., and the conductive master pellets were used as the resins for the A and B layers. Reference example 2 The mixture was then put into the twin-screw extruder used in Reference example 2Under the same conditions as above, an alternating laminate unit of layers A and B was fabricated, and a 1 mm thick pseudo-single film sheet (shown in the table as consisting of only layer A) was fabricated in which layers A and B were made of the same material. When the return loss was measured, it was found to have the largest return loss peak at a peak top frequency of 65 GHz, with a return loss of 11 dB and a half-value width of 10 GHz.

[0099] (Comparative Example 3) Two pseudo-single-layer sheets (shown in the table as consisting of only Layer A) prepared in Comparative Example 2 were laminated together with a 25 μm thick adhesive sheet in between to form a three-layer laminate sheet consisting of two pseudo-single-layer sheets and one adhesive layer. Measurement of the return loss showed that the peak with the largest attenuation, with a peak top frequency of 36 GHz, had a return loss of 13 dB and a half-value width of 5 GHz.

[0100] Example 3 Reference example 2 In the above, a feed block having 31 slits was used as the feed block, and 31 layers were alternately stacked in the thickness direction at a stacking ratio of 1.0. Reference example 2 In the same manner as above, an alternating laminate unit having a thickness of 1 mm was obtained. It was confirmed by a transmission electron microscope that the obtained alternating laminate unit was alternately laminated in the thickness direction so that there were 16 layers of A and 15 layers of B containing a conductive material. The laminate thickness was Reference example 2 Compared to when a multi-manifold type feed block was used, the coefficient of variation in the layer thickness of layer B was smaller, but due to the influence of the thixotropy of the resin, the alternating laminate unit had some layer disorder.

[0101] Two of the fabricated alternating laminated units were bonded together with a 25μm thick adhesive sheet in between, resulting in a laminated sheet with a total of 63 layers, including the adhesive layer. When the return loss was measured, it was found that due to the effect of increasing the number of layers, the return loss at the peak top of the return loss peak with the largest peak top attenuation was 20dB and the half-value width was 2.1GHz.

[0102] Example 4 An alternating laminate unit having a thickness of 1 mm was obtained in the same manner as in Example 3, except that the layers were joined in a feed block having a 31-layer slit, and then the number of layers was increased to 61 through one stage of a static mixer that doubled the number of layers in the thickness direction. Transmission electron microscopy confirmed that the resulting alternating laminate unit formed a unit in which 31 layers of A and 30 layers of B were alternately stacked in the thickness direction. At the portion where the 31-layer laminates joined, the thickness of the A layer was twice as thick. The coefficient of variation of the layer thickness of the B layer was similar to that of Example 3, but the resulting alternating laminate unit had stronger layer disorder than Example 3.

[0103] Two of the prepared alternating laminate units were bonded together with a 25 μm thick adhesive sheet interposed therebetween to obtain a laminate sheet with a total of 123 layers, including the adhesive layer. When the return loss was measured, the return loss at the peak top of the return loss peak, which had the largest peak top attenuation, was 24 dB, which was higher than that of Example 3.

[0104] Example 5 The resin constituting layer B is 90 parts by weight of polyethylene terephthalate resin with a melting point of 254°C and an intrinsic viscosity IV of 0.63. Reference example 1Ten parts by weight of the carbon-based conductive material used in Example 1 was blended and kneaded using a twin-screw extruder to which the conductive material was supplied via a side feed to produce conductive master pellets. A polyethylene terephthalate resin with a melting point of 254°C and an intrinsic viscosity IV of 0.8 was used as the resin constituting Layer A, and the conductive master pellets were used as the resin constituting Layer B. The prepared resins were each fed into a twin-screw extruder and melt-kneaded at 280°C in each twin-screw extruder. The extruded resins were then merged in a feed block with 31 slits and passed through one static mixer to form a 1mm-thick alternating laminate unit in which 61 layers were alternately stacked in the thickness direction at a lamination ratio of 1.0. Compared to Example 4, the use of a resin that is less thixotropic resulted in an alternating laminate unit with almost no layer disturbance.

[0105] Two of the fabricated alternating laminate units were bonded together with a 25 μm thick adhesive sheet interposed between them to obtain a laminate sheet with a total of 123 layers, including the adhesive layer. Measurement of the return loss revealed that the sheet had the largest return loss peak at a peak top frequency of 27 GHz, and that the peak top was steeper than in Example 4.

[0106] ( Reference example 7 ) In Example 5, a conductive master pellet prepared by blending 1 part by weight of the spherical carbon conductive material used in Example 1 with 99 parts by weight of polyethylene terephthalate resin having a melting point of 254°C and an intrinsic viscosity IV of 0.8 was used as the resin for Layer A, and a conductive master pellet prepared by blending 9 parts by weight of the spherical carbon conductive material with 91 parts by weight of polyethylene terephthalate resin having a melting point of 254°C and a viscosity IV of 0.63 was used as the resin for Layer B. A total of 123 layers of laminated sheets were obtained in the same manner as in Example 5. Measurement of return loss showed that, because the conductivity of Layer A was not particularly high, the return loss peak with the largest attenuation at its peak top frequency of 26 GHz was relatively steep.

[0107] ( Reference example 8 ) In Example 5, a conductive master pellet was used as the resin for Layer A, which was prepared by blending 90 parts by weight of polyethylene terephthalate resin having a melting point of 254°C and an intrinsic viscosity IV of 0.8 with 10 parts by weight of a spherical conductive carbon material having a primary particle size of 8 nm and a DBP oil absorption of 95 mL / 100 g. The same procedure as in Example 5 was repeated, except that a conductive master pellet was used as the resin for Layer B, which was prepared by blending 5 parts by weight of the spherical conductive carbon material used in Example 1 with 95 parts by weight of polyethylene terephthalate resin having a melting point of 254°C and a viscosity IV of 0.63. A total of 123 layers of laminated sheets were obtained. Measurement of return loss revealed a return loss peak with the largest attenuation at the peak top frequency of 25 GHz, and the peak had little steepness.

[0108] ( Reference example 3 ) In Example 5, a laminate sheet with a total of 123 layers was obtained using the same resin and manufacturing method as in Example 5, except that the content of the conductive material was 5 parts by weight. The low content reduced the conductivity, and the frequency band of the return loss peak with the largest peak-top attenuation shifted to a higher frequency band, but the laminate structure provided steep shielding properties. The laminate sheet had a return loss peak with the largest peak-top attenuation, with a peak-top frequency of 55 GHz, and the return loss at the peak-top of the return loss peak was 18 dB.

[0109] Example 9 In Example 5, a carbon-based conductive material with a primary particle diameter of 35 nm and a DBP oil absorption of 500 mL / 100 g was used as the conductive material, and a total of 123 layers of laminated sheets were obtained using the same resin and manufacturing method as in Example 5, except that the amount of conductive material was 5 parts by weight. By changing to a conductive material that forms a more structure, conductivity improved, but thixotropy became stronger and the layer thickness became more irregular. The laminated sheet had a reflection loss peak with the largest attenuation at the peak top, with a peak top frequency of 11 GHz, and the reflection loss of this reflection loss peak was 25 dB, showing a high attenuation peak.

[0110] Example 10 A total of 123 layers of laminated sheets were obtained using the same resins and manufacturing method as in Example 9, except that the amount of conductive material was changed to 3.6 parts by weight. By reducing the amount of conductive material, thixotropy did not occur, and no layer disorder occurred, resulting in a laminated sheet with a more uniform layer thickness. The resulting reflection attenuation peaks were as shown in Table 2.

[0111] Example 11 In Example 5, a carbon-based conductive material with a primary particle diameter of 44 nm and a DBP oil absorption of 220 mL / 100 g was used as the conductive material, and a total of 123 layers of laminated sheets were obtained using the same resin and manufacturing method as in Example 5, except that the amount of conductive material was 15 parts by weight. The conductive material was difficult to form a structure, and conductivity improved when incorporated at a high concentration. However, the increased particle concentration caused strong thixotropy, resulting in laminated sheet disorder. The laminated sheet had a reflection loss peak with the largest peak-top attenuation, with a peak-top frequency of 38 GHz. The reflection loss at the peak-top of this reflection loss peak was 23 dB, and the laminated sheet had a high, steep RL / fΔ.

[0112] Comparative Example 4 In Example 5, a spherical conductive carbon material with a primary particle diameter of 8 nm and a DBP oil absorption of 95 mL / 100 g was used as the conductive material, and a total of 123 layers of laminated sheets were obtained in the same manner as in Example 5, except that the amount of conductive material was 15 parts by weight. The conductive material was a carbon material used to achieve a jet-black color, and almost no conductivity was obtained within the layers. Furthermore, when the return loss was measured, the material had a return loss peak with the largest attenuation at the peak top frequency of 48 GHz, with a return loss of 4.5 dB and a half-width of 15 GHz. The return loss was small, and the material showed no steepness in the attenuation of electromagnetic waves.

[0113] ( Reference example 4 ) In Example 5, 5 parts by weight of the carbon-based conductive material used in Example 5 was blended as the conductive material, and 2 parts by weight of graphene powder material with an average particle size of 5 μm was further blended. These conductive materials were side-fed into a twin-screw extruder and kneaded to produce a conductive master pellet. A total of 123 layers of laminated sheets were obtained using the same resins and manufacturing method as in Example 5, except that the master pellet was used as the resin for Layer B. By incorporating the flat graphene powder, the laminated sheet exhibited significantly improved conductivity in the direction parallel to the sheet surface in the layers containing the graphene powder. The laminated sheet had a reflection loss peak with the largest peak-top attenuation, with a peak-top frequency of 8 GHz. The reflection loss at the peak-top of this reflection loss peak was 36 dB, resulting in a laminated sheet with a steep reflection loss peak with a large RL / fΔ.

[0114] Example 13 In Example 5, 5 parts by weight of the carbon-based conductive material used in Example 5 was blended as the conductive material, and 2 parts by weight of graphene powder material with an average particle size of 5 μm was further blended. These conductive materials were side-fed into a twin-screw extruder and kneaded to produce a conductive master pellet. A total of 123 layers of laminated sheets were obtained using the same resins and manufacturing method as in Example 5, except that the master pellet was used as the resin for Layer B. By incorporating the flat graphene powder, the laminated sheet exhibited significantly improved conductivity in the direction parallel to the sheet surface in the layers containing the graphene powder. The laminated sheet had a reflection loss peak with the largest peak-top attenuation, with a peak-top frequency of 8 GHz. The reflection loss at the peak-top of this reflection loss peak was 36 dB, resulting in a laminated sheet with a steep reflection loss peak with a large RL / fΔ.

[0115] Example 14 Five parts by weight of the carbon-based conductive material used in Example 5 was blended with 3 parts by weight of carbon nanotube material with an average diameter of 1.5 nm and an average length of 500 nm. These conductive materials were then side-fed into a twin-screw extruder to produce conductive master pellets. A total of 123 layers of laminated sheets were obtained using the same resins and manufacturing method as in Example 5, except that the master pellets were used as the resin for Layer B. By using a carbon nanotube material with a high aspect ratio, the laminated sheet exhibited improved conductivity in the direction parallel to the sheet surface in the carbon nanotube-containing layers. The laminated sheet had a reflection loss peak with the largest peak-top attenuation, with a peak-top frequency of 6 GHz. The reflection loss at the peak-top of this reflection loss peak was 26 dB, resulting in a steep reflection loss peak with a large RL / fΔ.

[0116] Example 15 In Example 13, the prepared alternating laminate unit was stretched 1.4 times in the longitudinal direction at 90°C and 1.5 times in the transverse direction at 100°C to obtain a laminate sheet with a thickness of 500 μm. Transmission electron microscope observation revealed a favorable tendency for the graphene powder to be more aligned in a direction parallel to the sheet surface compared to Example 13. Four of the obtained laminate sheets were bonded together with an adhesive to obtain the desired laminate sheet. Transmission electron microscope observation revealed a favorable tendency for both the spherical carbon and graphene powder to be more aligned in a direction parallel to the sheet surface. The design made it easier to induce dielectric polarization, resulting in a sheet with higher attenuation and steepness compared to Example 13.

[0117] Example 16 In Example 13, an alternating laminate unit was produced in the same manner as in Example 13, except that a feedblock with 101 slits, in which the pressure loss was adjusted by the slit length and width, was used as the lamination device, and the coefficient of variation of each layer thickness was set to 0.18. Two of the resulting laminated sheets were bonded together with an adhesive to produce the desired laminated sheet. A laminated sheet was obtained that had a steep return loss peak with a large RL / fΔ, with the largest peak-top attenuation at a frequency of 23 GHz, and the return loss at the peak-top of this return loss peak was 30 dB.

[0118] Example 17 An alternating laminate unit was produced in the same manner as in Example 13, except that a feed block with 201 slits, in which the pressure loss was adjusted by the slit length and width, was used as the lamination device. Two of the produced alternating laminate units were bonded together with a 25 μm thick adhesive sheet interposed therebetween, to obtain a laminate sheet with a total of 403 layers, including the adhesive layer. When the thickness of each layer was observed with a transmission electron microscope, it was confirmed that the coefficient of variation of each layer thickness was 0.12. The laminate sheet exhibited the properties listed in Table 2.

[0119] Example 18 An alternating laminate unit was produced in the same manner as in Example 13, except that a feed block with 501 slits, in which the pressure loss was adjusted by the slit length and width, was used as the lamination device. Two of the produced alternating laminate units were bonded together with a 25 μm thick adhesive sheet interposed therebetween, to obtain a laminate sheet with a total of 1003 layers, including the adhesive layer. When the thickness of each layer was observed with a transmission electron microscope, it was confirmed that the coefficient of variation of each layer thickness was 0.08. A laminate sheet exhibiting the properties listed in Table 2 was obtained.

[0120] ( Reference example 5 ) As the conductive material, 10 parts by weight of the graphene powder material with an average particle size of 5 μm used in Example 13 was blended, and these conductive materials were side-fed into a twin-screw extruder and kneaded to produce conductive master pellets. A laminate sheet with a total of 123 layers was obtained using the same resins and manufacturing method as in Example 13, except that the master pellets were used as the resin for Layer B. Due to the high conductivity of graphene, a steep peak top was observed at 800 MHz, indicating a high return loss.

[0121] ( Reference example 6 ) 95 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin with a melting point of 210°C was blended with 5 parts by weight of a carbon-based conductive material with a primary particle size of 40 nm and a DBP oil absorption of 400 mL / 100 g, and the conductive material was kneaded using a twin-screw extruder to which the conductive material was supplied via a side feed, to produce conductive master pellets.

[0122] The resin used for the A layer was a polyethylene terephthalate resin with a melting point of 254°C and an intrinsic viscosity of 0.8, while the conductive master pellets were used for the B layer. The prepared polyethylene terephthalate resin and conductive resin were each fed into a twin-screw extruder and melt-mixed at 270°C. The mixing conditions for each twin-screw extruder were a screw rotation speed of 0.7 relative to the output rate. The extruded resins were then merged in 11 multi-manifold feed blocks, and a molten sheet consisting of 11 layers stacked alternately in the thickness direction with a stacking ratio of 1.0 was extruded from the die. The extruded molten sheet was cooled and solidified on a casting drum, and a 1 mm-thick laminate sheet was obtained by adjusting the drum rotation speed. The resulting laminate sheet consisted of six A layers and five B layers containing conductive materials, and the alternating layers were confirmed by microscopic observation. The electromagnetic wave attenuation performance of the laminate sheet was as shown in Table 4.

[0123] (Comparative Example 5) 97.5 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin with a melting point of 210°C was blended with 2.5 parts by weight of conductive spherical carbon particles with a primary particle size of 40 nm and a DBP oil absorption of 400 mL / 100 g. The blend was then kneaded using a twin-screw extruder to which the conductive material was supplied via a side feed, producing conductive master pellets. The master pellets were extruded through a die into sheets, which were then cooled and solidified on a casting drum. A 1 mm-thick monolayer sheet was fabricated by adjusting the drum rotation speed. The performance of the resulting monolayer sheet is shown in Table 3. It did not exhibit exceptional electromagnetic wave shielding properties that exceeded the volume law.

[0124] (Comparative Example 6) In Comparative Example 5, the drum rotation speed was increased to obtain a 0.5 mm thick single-layer sheet. Two of these single-layer sheets were bonded together with a 0.05 mm thick acrylic adhesive sheet interposed between them to obtain a three-layer laminate sheet having a layer containing conductive particles as the outermost layer (in the table, this is indicated as consisting of only Layer A). The performance of the obtained single-layer sheet is shown in Table 3, and the three-layer laminate did not obtain sufficient electromagnetic wave shielding properties that exceeded the volume law.

[0125] Example 21 Reference example 6 In the above example, two types of resins were joined in a feed block having 51 slits, and a molten sheet in which 51 layers were alternately laminated in the thickness direction at a lamination ratio of 1.0 was extruded from a die. Reference example 6 A 1 mm thick laminated sheet was obtained in the same manner as described above. The resulting laminated sheet consisted of 26 A layers and 25 B layers containing conductive materials, and microscopic observation confirmed that the layers were alternately laminated in the thickness direction. As shown in Table 4, increasing the number of layers and using a slit-type feedblock resulted in an improvement in the return loss at the return loss peak.

[0126] Example 22 Reference example 6 In the above, two types of resins were joined in a feed block having 101 slits, and a molten sheet in which 101 layers were alternately laminated in the thickness direction at a lamination ratio of 1.0 was extruded from a die. Reference example 6 A 1 mm thick laminated sheet was obtained in the same manner as described above. The resulting laminated sheet consisted of 51 A layers and 50 B layers containing conductive materials, and microscopic observation confirmed that they were alternately laminated in the thickness direction. As shown in Table 4, by further increasing the number of layers, the return loss at the return loss peak was further improved.

[0127] Example 23 In Example 22, the drum rotation speed was increased to obtain a 0.33 mm thick layer-by-layer laminate unit. Three of these layer-by-layer laminate units were bonded together via 0.05 mm thick acrylic adhesive sheets to obtain a laminate sheet with a total of 305 layers and a thickness of approximately 1.0 mm. The performance of the obtained laminate sheet is shown in Table 4, and the effect of increasing the number of layers was observed.

[0128] Example 24 Reference example 6 In the above, two types of resins were joined in a feed block having 301 slits, and a molten sheet in which 301 layers were alternately laminated in the thickness direction at a lamination ratio of 1.0 was extruded from a die. Reference example 6 A 1 mm thick laminate sheet was obtained in the same manner as in Example 2. The obtained laminate sheet was composed of a total of 151 A layers and a total of 150 B layers containing conductive materials, and it was confirmed by microscopic observation that they were laminated alternately in the thickness direction. Compared to Example 23, by using a slit-type feed block with a larger number of layers, uneven layer thickness was reduced, and a laminate sheet was obtained that exhibited steeper electromagnetic wave shielding properties.

[0129] Example 25 In Example 22, the drum rotation speed was increased to obtain a laminate sheet with a thickness of 0.5 mm. By reducing the thickness, a laminate sheet was obtained in which the frequency band of the return loss peak, where the peak top attenuation was greatest, was shifted to a higher frequency while maintaining the magnitude of the return loss, as shown in Table 4, compared to the laminate sheet of Example 22.

[0130] Example 26 10 parts by weight of the carbon-based conductive material used in Example 11, which had a primary particle diameter of 44 nm and a DBP oil absorption of 220 mL / 100 g, was blended with 90 parts by weight of an isophthalic acid copolymerized polybutylene terephthalate resin having a melting point of 210°C, and the blend was kneaded using a twin-screw extruder to which the conductive material was supplied via a side feed, to produce conductive master pellets.

[0131] The resin used for the A layer was a polyethylene terephthalate resin with a melting point of 254°C and a viscosity IV of 0.8, and the resin used for the B layer was the conductive master pellet. The two resins were merged in a feed block with 101 slits, the same as in Example 22, and a molten sheet consisting of 101 layers laminated alternately in the thickness direction at a lamination ratio of 1.0 was extruded from the die. The extruded molten sheet was cooled and solidified on a casting drum, and a 1 mm thick laminated sheet was obtained by adjusting the drum rotation speed. A high concentration of low-conductivity material was added, and a laminated sheet exhibiting good electromagnetic wave blocking properties in the high-frequency band was obtained, as shown in Table 4.

[0132] Example 27 In Example 26, a dielectric material, barium titanate, was used as a dielectric constant adjuster for the conductive master pellets. Specifically, 80 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin with a melting point of 210°C was blended with 10 parts by weight of a carbon-based conductive material with a primary particle diameter of 44 nm and a DBP oil absorption of 220 mL / 100 g, and 20 parts by weight of barium titanate with an average particle diameter of 0.5 μm (manufactured by Sakai Chemical Industry Co., Ltd.) to produce a conductive master pellet. Otherwise, a 1 mm thick laminate sheet was obtained in the same manner as in Example 26. As shown in Table 4, by adjusting the dielectric constant, a laminate sheet with better electromagnetic wave shielding properties was obtained.

[0133] Example 28 5 parts by weight of the carbon-based conductive material used in Example 9, which had a primary particle diameter of 35 nm and a DBP oil absorption of 500 mL / 100 g, was blended with 95 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin having a melting point of 210°C, and the blend was kneaded using a twin-screw extruder to which the conductive material was supplied by a side feed, to produce conductive master pellets.

[0134] The resin used for the A layer was a polyethylene terephthalate resin with a melting point of 254°C and a viscosity IV of 0.8, and the resin used for the B layer was the conductive master pellet. The two resins were merged in a feed block with 101 slits, the same as in Example 22, and a molten sheet was extruded from the die, consisting of 101 layers stacked alternately in the thickness direction at a lamination ratio of 1.0. The extruded molten sheet was cooled and solidified on a casting drum, and a 1 mm thick laminate sheet was obtained by adjusting the drum rotation speed. As shown in Table 5, although the material had a high imaginary part of the dielectric constant, a laminate sheet exhibiting high electromagnetic wave shielding properties was obtained.

[0135] Example 29 In Example 28, a dielectric material, barium titanate, was used as a dielectric constant adjuster for the conductive master pellets. Specifically, 85 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin with a melting point of 210°C was blended with 5 parts by weight of a carbon-based conductive material with a primary particle diameter of 35 nm and a DBP oil absorption of 500 mL / 100 g, and 20 parts by weight of barium titanate with an average particle diameter of 0.5 μm (manufactured by Sakai Chemical Industry Co., Ltd.) to produce a conductive master pellet. Otherwise, a 1 mm thick laminate sheet was obtained in the same manner as in Example 28. As shown in Table 5, by adjusting the dielectric constant, a laminate sheet with excellent electromagnetic wave shielding properties was obtained.

[0136] Example 30 In Example 28, a graphene powder material with an average particle size of 5 μm used in Example 13 as a different carbon-based conductive material was used as a dielectric constant adjuster for the conductive master pellet. Specifically, 2 parts by weight of a carbon-based conductive material with a primary particle size of 35 nm and a DBP oil absorption of 500 mL / 100 g and 3 parts by weight of the graphene powder material with an average particle size of 5 μm were blended with 95 parts by weight of isophthalic acid copolymerized polybutylene terephthalate resin with a melting point of 210 °C to form a conductive master pellet. Otherwise, a 1 mm thick laminate sheet was obtained in the same manner as in Example 28. As shown in Table 5, by adjusting the dielectric constant, a laminate sheet exhibiting superior electromagnetic wave shielding properties compared to Example 28 was obtained.

[0137] Example 31 A 1 mm thick laminate sheet was obtained in the same manner as in Example 22, except that a 6-nylon resin with a melting point of 222°C was used as the resin for the A layer side. By using a resin with a high dielectric constant as the raw material for the A layer, the return loss decreased somewhat, as shown in Table 5. It is believed that the balance of the dielectric constants of the A layer and the B layer was not as good as in Example 22.

[0138] ( Reference example 9 ) In Example 22, a conductive master pellet was used as the resin used on the A layer side, which was a polyethylene terephthalate resin having a melting point of 254 ° C. and a viscosity IV of 0.65, and 2 parts by weight of the carbon-based conductive material used in Example 9 having a primary particle diameter of 35 nm and a DBP oil absorption of 500 mL / 100 g. A laminated sheet having a thickness of 1 mm was obtained in the same manner as in Example 22, except that example As in 31, the attenuation decreased, and the frequency band of the return loss peak, where the attenuation at the peak top was the largest, shifted to the higher frequency side.

[0139] Example 33 In Example 22, the obtained molten sheet was cooled and solidified in a cast drum, and then stretched twice in the sheet conveyance direction using a group of rolls adjusted to a temperature of 85°C by the difference in the peripheral speed of the rolls, to obtain a stretched laminate sheet with a thickness of 0.5 mm. The stretching process caused the carbon-based conductive material added to Layer B to be dispersed and oriented in the plane direction, thereby improving the dielectric constant, and a laminate sheet with the properties shown in Table 5 was obtained.

[0140] Example 34 In Example 22, the resulting molten sheet was cooled and solidified in a casting drum, and then stretched three times in the sheet conveyance direction using a group of rolls adjusted to a temperature of 85°C by the difference in the roll peripheral speed, followed by quenching. The sheet stretched in the conveyance direction was then continuously introduced into a tenter, and conveyed while holding both ends of the sheet with clips. It was then stretched 3.3 times in the width direction in a room controlled at 120°C, thereby obtaining an alternating laminate unit with a thickness of 0.166 mm. Three of the resulting alternating laminate units were bonded together using a 0.025 mm thick acrylic adhesive sheet to obtain a total of 305 layers of a laminate sheet with a thickness of approximately 0.5 mm. The properties of the resulting laminate sheet are as shown in Table 5, and a laminate sheet with excellent electromagnetic wave shielding properties that transcend the volume law was obtained.

[0141] Example 35 The molten sheet obtained in Example 30 was subjected to the stretching process described in Example 34 to obtain a 0.166 mm thick layer-by-layer laminate sheet. Three of the obtained layer-by-layer laminate units were bonded together via 0.025 mm thick acrylic adhesive sheets to obtain a total of 305 layers of a laminate sheet approximately 0.5 mm thick. Due to the effect of the in-plane dispersion and arrangement of the flat carbon, a laminate sheet with excellent electromagnetic wave shielding properties beyond the concept of the volume law, as in Example 34, was obtained.

[0142] [Table 1]

[0143] [Table 2]

[0144] [Table 3]

[0145] [Table 3]

[0146] [Table 2] [Industrial Applicability]

[0147] The laminated sheet of the present invention includes a unit in which layers of high conductivity and layers of low conductivity are alternately laminated. This allows it to achieve high electromagnetic wave attenuation despite being a thin film with a low concentration of conductive material, something that was difficult to achieve with conventional single-film or low-layer sheets. In a preferred embodiment, the laminated sheet can provide sharp and strong shielding against electromagnetic waves of a specific frequency, thereby preventing malfunctions of devices that use electromagnetic waves of a similar frequency band and preventing information leakage in high-volume data communications due to high-frequency electromagnetic waves. Specifically, the laminated sheet can be suitably used in electronic devices and communication devices that use communication technologies using electromagnetic waves in the GHz frequency band, as well as vehicles equipped with such devices and transportation systems, including all types of traffic control infrastructure. [Explanation of symbols]

[0148] 1: Reflection loss peak 2: The return loss at the peak where the attenuation at the peak top is the largest (return loss RL) 3: Half-width of the reflection attenuation peak with the largest peak-top attenuation

Claims

1. A laminate sheet including an alternating laminate unit in which two layers having different electrical conductivity, conveniently referred to as layer A and layer B having higher electrical conductivity, are alternately laminated for a total of five or more layers so that layer A is disposed as the outermost layer, wherein layer A is made of a thermoplastic resin alone, and layer B is made of a thermoplastic resin as a matrix resin in which carbon black, which is a conductive material, has a dibutyl phthalate (DBP) oil absorption of 150 [mL / 100g] or more and 800 [mL / 100g] or less is dispersed in the matrix resin, or a thermoplastic resin as a matrix resin in which carbon black, which is a conductive material, has a dibutyl phthalate (DBP) oil absorption of 150 [mL / 100g] or more and 800 [mL / 100g] or less and other materials such as a conductive material other than an organic carbon-based material and a magnetic material are dispersed in the matrix resin (however, the content of the conductive material is 1 wt% or more and less than 15 wt% with respect to the weight of the entire laminate sheet), and the laminate sheet contains 1 wt % or more and less than 15 wt % of carbon black having a DBP oil absorption of 150 [mL / 100 g] or more and 800 [mL / 100 g] or less, and when a frequency-return loss curve is obtained for the laminate sheet, plotting the return loss on the vertical axis and the frequency on the horizontal axis, the return loss at the peak top of the return loss peak with the largest return loss at the peak top (return loss RL) is 5.0 dB or more, the number of interfaces per unit thickness between layer A and layer B is 2 faces / 100 μm or more, the return loss peak with the largest return loss at the peak top exists in a frequency band of 1 to 100 GHz, and when the return loss at the peak top of the return loss peak with the largest return loss at the peak top is RL [dB], the frequency corresponding to the peak top is f [GHz], and the thickness of the laminate sheet is t [mm], RL / (t×f) is 0.2 or more and 15 or less, and the surface resistivity of layer B is 7.0×10 ４ A laminated sheet having a resistance of less than [Ω / □].

2. The surface resistance of at least one outermost surface of the laminated sheet is 1.0 × 10 ５ The laminate sheet according to claim 1, wherein the thickness is [Ω / □] or more.

3. 2. The laminate sheet according to claim 1, wherein the coefficient of variation tBσ / tB is 0.3 or less, where tB [mm] is the average thickness of the B layer and tBσ [mm] is the standard deviation.

4. The laminate sheet according to any one of claims 1 to 3, wherein a real part εh' [F / m] and an imaginary part εh'' [F / m] of the complex dielectric constant of the B layer satisfy the following formula (A) or (B): (A) εh″≧1, and 0.17εh′+2.3≦εh″≦0.27εh′+3.3 (B) 5≧εh″≧1, and 0.02εh′+1≦εh″≦0.07εh′+1.9

5. 5. The laminate sheet according to any one of claims 1 to 4, wherein a ratio RL / fΔ of a half-width fΔ [GHz] of the reflection attenuation peak having the largest electromagnetic wave attenuation amount at its peak top to a peak top electromagnetic wave attenuation (maximum attenuation) RL [dB] of the reflection attenuation peak having the largest electromagnetic wave attenuation amount at its peak top is 5.0 or more.

6. An electromagnetic wave shield comprising the laminate sheet according to any one of claims 1 to 5 and a reflector.

7. An electromagnetic wave-related device that corresponds to any one of electronic equipment, communication equipment, and equipment used in transportation, characterized in that the electromagnetic wave-related device comprises at least one of the laminate sheet according to any one of claims 1 to 5 and the electromagnetic wave shielding body according to claim 6.

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