Laminated sheet for radar unit

Abstract

To provide a laminated sheet which is a thin film, has excellent frequency selectivity and high shielding of a millimeter electromagnetic wave, and can be suitably used for a millimeter electromagnetic wave radar unit.SOLUTION: The laminated sheet is used for a radar unit having an antenna substrate that emits a millimeter electromagnetic wave, and is characterized by having all of the following features (1) to (3). (1) The laminated sheet includes a laminated unit in which A layers and B layers having different compositions are alternately laminated in five or more layers. (2) At least one of the A layer and the B layer contains an electromagnetic wave suppressing material. (3) Within the frequency band of 20 to 100 GHz, there is a reflection attenuation peak with a peak top having a reflection attenuation amount RL of 15 dB or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated sheet that is suitable for use in radar units that emit millimeter waves, and which combines high electromagnetic wave shielding, millimeter wave selective cutting ability, and thin film moldability. [Background technology]

[0002] In recent years, information and communication technologies using electromagnetic waves have expanded, and electromagnetic waves of various frequency bands, such as meter waves in the hundreds of MHz to several GHz band, quasi-millimeter waves in the several GHz to tens of GHz band, and millimeter waves in the tens of GHz to hundreds of GHz band, are flying around in the atmosphere. Meter waves are mainly used in mobile phones and wireless communication, while quasi-millimeter waves are mainly used in mobile communications such as 4G and 5G, and wireless LAN (Wi-Fi) communications.

[0003] In the field of automotive technology, electromagnetic wave-based information and communication technology is used in collision avoidance systems that detect obstacles and automatically apply the brakes, or measure the position and speed of surrounding vehicles to control the vehicle's speed and distance. To achieve higher detection performance, these collision avoidance systems are increasingly using millimeter waves (76-79 GHz), which are more directional, have higher energy, and are more easily reflected by material surfaces than conventional frequencies (24 GHz). In collision avoidance systems using millimeter-wave radar, it is important that the system responds only to electromagnetic waves emitted from and reflected by the radar unit. To prevent malfunctions caused by unwanted electromagnetic waves (noise) incident from the surroundings, electromagnetic wave absorption technology is sometimes used to cut out unwanted noise. (Patent Documents 1, 2) Specifically, it is used in the housing portion to protect the antenna base of the radar unit, or as a side lobe cut sheet for millimeter waves that spread in a direction different from the direction of radar transmission.

[0004] As a technology for absorbing high-frequency electromagnetic waves, commonly used methods include magnetic electromagnetic wave absorbers containing magnetic materials capable of absorbing high-frequency electromagnetic waves, such as ε-iron oxide (Patent Document 3), and λ / 4 type laminated electromagnetic wave absorbers (Patent Document 4) which utilize resistive loss by laminating a resistive layer, a dielectric layer, and a conductive reflective layer. In the case of magnetic electromagnetic wave absorbers, it is necessary to include a high concentration of ε-iron oxide, which leads to problems such as an increase in the total weight of the electromagnetic wave absorber and high costs. In the case of λ / 4 type electromagnetic wave absorbers that utilize resistive loss, losses occur due to interference cancellation with electromagnetic waves reflected by the conductive reflective layer, resulting in a thick electromagnetic wave absorber with a thickness of mm to cm, which is problematic as it does not conform to the complex shape of radar unit housings. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2004-312696 [Patent Document 2] Japanese Patent Publication No. 2018-63159 [Patent Document 3] Japanese Patent Publication No. 2019-075571 [Patent Document 4] International Publication No. 2020-067145 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] In view of the above problems, the present invention aims to provide a laminated sheet for radar units that combines high millimeter-wave shielding, thin-film moldability, and lightweight properties. [Means for solving the problem]

[0007] To solve the above problems, the present invention has the following configuration. That is, a laminated sheet for use in a radar unit having an antenna substrate that emits millimeter waves, characterized in that it has all of the following features (1) to (3). It includes a laminated unit in which different A layers and B layers are alternately laminated in five or more layers. (2) At least one of the A layer and the B layer contains an electromagnetic wave suppression material. There is a reflection attenuation peak having a peak top with a reflection attenuation amount of 15 dB or more within a frequency band of 20 to 100 GHz.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a laminated sheet for a radar unit, which is a thin film and excellent in frequency selectivity and shielding property of millimeter-wave electromagnetic waves. Specifically, by increasing the difference in dielectric constants of the alternately arranged layers with different dielectric constants and adopting a configuration with a large number of laminated layers, the effect of dielectric polarization at each interface with different dielectric constants can be enhanced, and the dielectric constant of the entire laminated sheet can be increased. Therefore, it is possible to provide a laminated sheet for electromagnetic wave shielding, which has a thin film and molding followability with a low additive content concentration, compared with a conventional single film sheet or a sheet with a low number of laminated layers.

Brief Description of the Drawings

[0009] [Figure 1] It is an example of a cross-sectional view of a radar unit in which the laminated sheet of the present invention can be preferably used. [Figure 2] It is a schematic diagram showing an electromagnetic wave component irradiated from an antenna. [Figure 3] Among the peaks obtained by measuring the reflection attenuation peaks of the laminated sheet according to an embodiment of the present invention, it is a schematic diagram showing the half-value width and the electromagnetic wave attenuation amount of the reflection attenuation peak with the largest reflection attenuation amount at the peak top. [Figure 4] Among the peaks obtained by measuring the reflection attenuation peaks of the laminated sheet according to an embodiment of the present invention, it is a schematic diagram showing the half-value width and the electromagnetic wave attenuation amount of the reflection attenuation peak with the largest reflection attenuation amount at the peak top. [Figure 5] Among the peaks obtained by measuring the reflection attenuation peaks of the laminated sheet according to an embodiment of the present invention, it is a schematic diagram showing the half-value width and the electromagnetic wave attenuation amount of the reflection attenuation peak with the largest reflection attenuation amount at the peak top. [Figure 6] Of the peaks obtained by measuring the reflection attenuation amount peak of the laminated sheet according to one embodiment of the present invention, the half-value width of the reflection attenuation amount peak with the largest reflection attenuation amount at the peak top, and a schematic diagram showing the electromagnetic wave attenuation amount.

Mode for Carrying Out the Invention

[0010] The laminated sheet of the present invention is a laminated sheet used for a radar unit having an antenna substrate that transmits millimeter waves, and is characterized by having all of the following features (1) to (3). It is a laminated sheet for a radar unit.

[0011] (1) It includes a laminated unit in which five or more layers of different A layers and B layers are alternately laminated.

[0012] (2) At least one of the A layer and the B layer contains an electromagnetic wave suppression material.

[0013] (3) In the frequency band of 20 to 100 GHz, there is a reflection attenuation amount peak having a peak top with a reflection attenuation amount of 15 dB or more.

[0014] First, a radar unit having an antenna substrate that transmits millimeter waves, which can preferably use the laminated sheet of the present invention, will be described. Note that the radar unit is not to be construed as limited to the following configuration.

[0015] FIG. 1 shows a cross-sectional view of an example of a radar unit on which the laminated sheet of the present invention can be mounted, and FIG. 2 shows a schematic diagram representing the electromagnetic wave components irradiated from the antenna. The radar unit shown in FIG. 1 includes, in a housing surrounded by a radome (1) and a case (2), in order from the radome side, an antenna (3), an antenna chassis (6), a radio frequency (RF) chassis (7), an RF module (4), and a control circuit board (5).

[0016] A radome is a rectangular cover made of resin. Its function is to allow radio waves transmitted from the antenna and radio waves reflected from targets and received by the antenna to pass through. Radomes are formed by methods such as resin injection molding, and their entire surface, including the sides, is radio wave transparent.

[0017] The main lobe (8) of millimeter waves transmitted from the antenna has strong directivity, and most of the radio waves are emitted perpendicular to the antenna surface. However, some first side lobes (9) emitted from the front of the antenna in directions other than perpendicular pass through the side of the radome, are reflected by surrounding components of the vehicle or outside the vehicle, and re-enter the radome to be received by the receiving antenna, which can cause malfunctions in the radar system. Therefore, it is preferable to provide an electromagnetic wave absorber on the side of the radome to prevent the side lobes from passing through. The electromagnetic wave absorber provided on the radome may be provided on the inside of the radome or on the outside of the radome. The electromagnetic wave absorber may be bonded to the resin that makes up the radome, or it may be integrally molded with the radome so that only the side portion has electromagnetic wave absorption performance.

[0018] Case (2) has a box-like shape with an open front, as it encloses the antenna, RF module, and control circuit board. It is preferable that the case itself incorporates electromagnetic wave absorbing properties in the millimeter-wave frequency band emitted from the antenna, in order to prevent malfunctions caused by reflections of the side lobes (9, 10) and back lobe (11) of the millimeter waves emitted from the antenna. Furthermore, it is preferable to form a recess of a certain depth on the back surface of the case to prevent malfunctions caused by radio waves emitted from the control circuit board. This recess allows the radio waves emitted from the control circuit board and the radio waves reflected by the recess and in opposite phase to interfere and cancel each other out, suppressing radio wave leakage to the outside caused by the control circuit board. Consequently, it is possible to prevent signals generated by the control circuit board from transmitting unintended radio signals to the receiving circuit, thereby improving the reliability of the output signal of the high-frequency module. The depth of the recess should be designed to be λ / 4, where λ is the wavelength of the radio waves emitted from the transmitting circuit. As a result, the phase difference of the wave is delayed by λ / 4 as it travels from the entrance to the deepest part of the recess, and then further delayed by λ / 4 as it returns from the deepest part to the entrance. This creates a so-called inverse phase state, resulting in an overall phase delay of half a wavelength, which cancels out unwanted radio waves.

[0019] Antenna (3) transmits a millimeter-wave band transmission wave and receives a reception wave that includes a reflected wave from a target. While it is preferable for the antenna to be a planar antenna made of a printed circuit board with microstrip lines from the standpoint of cost and design flexibility, other antenna types such as waveguide slot antennas, arch antennas, and triplate patch arrays can also be used. In addition to microstrip lines, other methods for forming the printed circuit board include coplanar, ground coplanar, and differential line types. The antenna only needs to have at least one transmit port and one receive port; the number of ports is not particularly limited. Furthermore, it may have a shared port that allows for free switching between the transmit and receive ports.

[0020] A metal antenna chassis can be provided on the back of the antenna to support it. The antenna chassis, being made of metal, not only supports the antenna but also prevents noise propagation between the antenna and the RF module. Furthermore, through-holes can be provided within the antenna chassis to accommodate the function of a waveguide for transmitting and receiving signals between the antenna and the RF module.

[0021] An RF chassis can be installed on the rear of the antenna chassis, between it and the RF module. The RF chassis has a similar function to the antenna chassis, supporting the RF module while also providing noise propagation suppression and signal transmission / reception functions through waveguide through-holes.

[0022] The RF module includes a millimeter-wave transceiver and an analog circuit comprising a transmit control circuit and a receive circuit, and can be constructed using a printed circuit board. The millimeter-wave transceiver transmits and receives signals to and from an antenna via a patch for transmitting and receiving millimeter waves. The transmit control circuit within the analog circuit is responsible for frequency modulation and generating the transmit wave. The receive circuit is responsible for detecting the signal from the wave received by the millimeter-wave transceiver.

[0023] The control circuit board includes a digital signal processor and a microcontroller. The digital signal processor is responsible for creating the transmitted wave by controlling the frequency modulation of the transmit circuit, and for performing Fourier transform analysis of the signal received from the receive circuit to calculate distance, angle, relative velocity, etc., and to detect the position of the target. The microcontroller is responsible for the overall control functions of the millimeter-wave radar.

[0024] As described above, in order to prevent malfunctions of the millimeter-wave radar unit due to undesirable reflections of side lobes and back lobes emitted from the antenna, electromagnetic wave absorption performance is required for the radome and case that constitute the housing. Since these radomes and cases are molded into a specific box shape for the purpose of enclosing the antenna and circuitry, it is desirable that they be made of a sheet material with moldability. The laminated sheet of the present invention, which can be preferably used as an electromagnetic wave absorber for such millimeter-wave radar radomes and cases and possesses millimeter-wave absorption performance and moldability, will be described in detail below.

[0025] The laminated sheet for radar units of the present invention must include a laminated unit in which five or more layers of A and B layers with different compositions are alternately laminated.

[0026] Here, "a laminated unit in which five or more layers of A and B layers with different compositions are stacked alternately" (hereinafter sometimes referred to as an A-layer and B-layer laminated unit) refers to a configuration in which A and B layers are stacked alternately in a continuous sequence, totaling five or more layers. In other words, it refers to a state in which resin is stacked according to a regular arrangement of A(BA)n or B(AB)n (where n is a natural number of 2 or more). For example, a configuration of A layer / B layer / A layer / B layer / A layer, or a configuration of B layer / A layer / B layer / A layer / B layer corresponds to this, and a laminated sheet having such a laminated unit is considered an A-layer and B-layer laminated unit regardless of the presence or absence of layers other than A and B layers. As long as the laminated sheet of the present invention has an A-layer and B-layer laminated unit, the outermost layer may be an A layer, a B layer, or a layer other than A and B layers, and the outermost layers on both sides may be the same layer or different layers. Furthermore, the number of A-layer and B-layer laminated units that the laminated sheet has may be one or more.

[0027] As a means of obtaining a laminated sheet having a laminated unit of layer A and layer B, as described later, methods such as laminating layers with different compositions in stages by pressing and bonding them together, or laminating them all at once via a lamination device can be used. In addition, a functional layer different from the laminated unit, such as another electromagnetic wave reflecting layer or an electromagnetic wave absorbing layer, may be formed on the laminated unit of layer A and layer B. When there are multiple laminated units of layer A and layer B, the multiple laminated units can be stacked together via an adhesive layer or directly by thermocompression. Furthermore, when there are multiple laminated units of layer A and layer B, laminated units having peak tops in different frequency bands may be stacked together to create a material that simultaneously shields multiple desired frequency bands.

[0028] The laminated sheet for radar units of the present invention has a laminated unit in which layers A and B are alternately stacked, thereby improving electromagnetic wave shielding performance targeting a specific frequency band while keeping the overall thickness of the laminated sheet down. Normally, improving electromagnetic wave shielding performance targeting a specific frequency band requires increasing the dielectric constant of the entire sheet. As a method to achieve this, conventional single-layer or low-layer sheets require adding electromagnetic wave suppression materials at high concentrations or increasing the thickness of the sheet.

[0029] In contrast, in the case of a laminated sheet having a laminated unit of layer A and layer B of the present invention, by providing a difference in dielectric constant between layer A and layer B, dielectric polarization occurs at the interface of layers with different dielectric constants, making it easier for current to pass through the inside of the sheet. Furthermore, because the alternating laminated structure allows the electromagnetic wave suppressing material to be densely confined within each layer, the conductivity within the layer is increased, and it is less susceptible to losses due to the resistance of the conductive material added inside, resulting in higher shielding performance compared to conventional products. As a result, even in embodiments where the sheet thickness is thinner and the content of electromagnetic wave suppressing material is lower than that of conventional products, an electromagnetic wave shielding material with excellent shielding performance can be obtained. Here, electromagnetic wave suppressing material refers collectively to conductive materials that have the property of imparting conductivity in response to an electric field when irradiated with electromagnetic waves, and magnetic materials that absorb magnetic flux emitted by a magnetic field. Details of electromagnetic wave suppressing materials that can be preferably used in the present invention will be described later.

[0030] Furthermore, in such laminated sheets, even with the same sheet thickness as a single-layer sheet, the thickness of each layer is typically thinner, resulting in a higher packing density of electromagnetic wave suppression material within each layer and a reduced distance between the electromagnetic wave suppression materials. As a result, the electron transfer efficiency between the electromagnetic wave suppression materials improves, and the overall electromagnetic wave suppression performance of the laminated sheet is enhanced.

[0031] Furthermore, in such laminated sheets, especially when the laminated sheet is formed via a lamination device, the electromagnetic wave suppression material tends to align in a direction parallel to the laminated sheet surface according to the resin laminar flow within the lamination device. Therefore, by using a material that forms a linearly linked higher-order structure or an electromagnetic wave suppression material exhibiting a high aspect ratio, conductivity in the planar direction is improved, and the electromagnetic wave shielding performance is improved as the incident electromagnetic waves receive resistance from the electromagnetic wave suppression material. To realize this embodiment, it is preferable to use a slit-type lamination device (feed block) as the lamination device. Due to the above mechanism, the laminated sheet can achieve dielectric constant values ​​that could not be achieved with single-film sheets without containing a large amount of electromagnetic wave suppression material or increasing the sheet thickness, with a smaller amount of electromagnetic wave suppression material and even with a thin-film sheet.

[0032] The number of laminated units of layer A and layer B contained within the laminated sheet is preferably 13 or more layers in total, more preferably 31 or more layers in total, and even more preferably 101 or more layers in total, because the above effect is more easily obtained when there are many layer interfaces between layers exhibiting high dielectric constant and layers exhibiting low dielectric constant. The upper limit of the number of layers is preferably 1001 layers from the viewpoint of manufacturing cost, film formation performance, and electromagnetic wave shielding performance. By limiting the number of laminated units of layer A and layer B to 1001 layers or less, the increase in manufacturing cost due to the enlargement of equipment such as feed blocks with fine slits can be suppressed. At the same time, depending on the dispersion state, shape, and size of the electromagnetic wave suppression material, the disturbance of layer thickness due to the emergence of thixotropy, which becomes a problem when the thickness of individual layers decreases as the number of layers increases, can be reduced, and the original shielding performance and steepness of shielding can be maintained. The following describes the suitable components that constitute each of the layers exhibiting low dielectric constant and the layers exhibiting high dielectric constant, as well as their combinations.

[0033] In the laminated sheet for radar units of the present invention, layers A and B are not particularly limited in terms of their constituent components, as long as their compositions differ, including transparent / opaque, flexible / rigid, flat / non-flat, and organic (polymer) / inorganic (metal) materials. However, from the viewpoint of improving the processability of the resulting laminated sheet, it is preferable that layers A and B are mainly composed of a flexible organic polymer material. Furthermore, hard coats using thermosetting resins or photocurable resins can also be used. Here, "main component" means that when the total components constituting the layer are considered as 100% by mass, it contains more than 50% by mass and up to 100% by mass, preferably 70% by mass or more and up to 100% by mass.

[0034] The composition of layer A and layer B being different from each other means that there is a component present in only one of layer A or layer B, or that the components of layer A and layer B are the same but their content differs from each other. In the laminated sheet of the present invention, from the viewpoint of processability and electromagnetic wave shielding characteristics when formed into a laminated sheet, it is preferable that both layers A and B are mainly composed of organic polymer materials, and at least one of them contains an organic or inorganic material as an electromagnetic wave suppression material.

[0035] The compositions of layer A and layer B are not particularly limited as long as their compositions are different, but in order to mitigate the reduction in effectiveness due to the separation of layer A and layer B, compositions that can reduce the separation of layer A and layer B are preferred. From this viewpoint, it is preferable that the organic polymer material in layer A and the organic polymer material in layer B have the same molecular skeleton. Here, the molecular skeleton refers to the repeating unit that is most abundant in the molecular chain of the organic polymer material. For example, if the organic polymer material is polyethylene terephthalate, then the ethylene terephthalate unit corresponds to the basic skeleton. A specific example of an embodiment in which the organic polymer materials in layer A and layer B have the same molecular skeleton is an embodiment in which layer A is mainly composed of polyester resin, and layer B is mainly composed of polyester resin having the same basic skeleton as the polyester resin that is the main component of layer A.

[0036] A compatibility parameter can be used as an indicator of the adhesion between layer A and layer B. The compatibility parameter can be estimated using calculation methods such as those of Hansen, Hoy, and Fedors. However, for thermoplastic resins, which are suitable components for use as organic polymer materials, Fedors' calculation method, which allows calculation based on the repeating structural units of the molecular chain, is used. Using this method, the compatibility parameter of thermoplastic resins containing structural units derived from copolymer components can be easily calculated according to the ratio of each structural unit. In Fedors' calculation method, the molecular cohesive energy density and molar molecular volume, which depend on the type and number of substituents, determine the compatibility parameter, and the compatibility parameter is estimated according to equation (1). Here, E coh (cal / mol) is the cohesive energy, and V is the molar molecular volume (cm³). 3 This represents ( / mol).

[0037]

number

[0038] The compatibility parameter in the laminated sheet of the present invention shall be a value obtained by rounding the estimated value calculated based on Fedor's formula to two decimal places. Typical compatibility parameters for thermoplastic resins include cellulose acetate: 11.0, cellulose: 15.6, polyacrylonitrile: 14.8, polyamide: 13.6, polyisobutylene: 7.7, polyethylene: 8.0, polyethylene terephthalate: 10.7, polyvinyl chloride: 10.1, polyvinyl acetate: 9.5, polycarbonate: 9.9, polystyrene: 9.4, polyvinyl alcohol: 12.6, polyphenylene sulfide: 12.5, polybutadiene: 8.3, polypropylene: 8.1, and polymethyl methacrylate: 9.3.

[0039] In the laminated radar unit of the present invention, the difference in compatibility parameters between layers A and B of the laminated sheet for the radar unit is preferably 2.0 or less, and more preferably 1.0 or less, so that the layers A and B maintain interlayer adhesion even after lamination. Layers A and B may be composed of exactly the same organic polymer material, with a lower limit of 0.0. However, if the compatibility parameter is 0.0, it is preferable to use different types and concentrations of electromagnetic wave suppression materials added to layers A and B in order to make the dielectric constants of layers A and B different. Note that dielectric constant is a numerical value that indicates the response of a molecule (degree of dielectric polarization) when an electric field is applied from the outside, and is a dimensionless quantity that is unique to the material and is based on the dielectric constant (electrical constant) in a vacuum.

[0040] If layer A or layer B contains multiple organic polymer materials, the compatibility parameter of the layer is calculated by multiplying the compatibility parameter of each individual organic polymer material by its content ratio and summing the results. For example, if polyethylene terephthalate (compatibility parameter: 10.7) and polymethyl methacrylate (compatibility parameter: 9.3) are contained in a 50:50 ratio, the compatibility parameter of the layer will be 10.0, which is the midpoint between the two compatibility parameters. When laminating layers that are mainly composed of different organic polymer materials, it is also preferable to improve the adhesion between the two layers by adding the main organic polymer material of the other layer to one layer to bring the compatibility parameters of both layers closer together. The method of adding the main organic polymer material of the other layer may be by copolymerization, or by alloying the resin and kneading it in an extruder. Alternatively, a method of adding a crosslinking type modifier having the basic skeleton of the main organic polymer material of the other layer can also be employed.

[0041] As for the organic polymer material in layers A and B, it is preferable to use a thermoplastic resin, which is a flexible organic polymer material, from the viewpoint of processability and film-forming properties of the laminated sheet.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 such as polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, and polyethylene-2,6-naphthalate; polyether resins such as polyethylene oxide, polypropylene oxide, and polyacrylate glycol; cellulose ester resins such as diacetylcellulose, triacetylcellulose, propionylcellulose, butyrylcellulose, acetylpropionylcellulose, and nitrocellulose; biodegradable polymers such as polylactic acid and polybutyl succinate; and other materials such as polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglycolic acid, polycarbonate, polyketone, polyethersulfone, polyetheretherketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloride resin, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride can be used.These thermoplastic resins may be used individually in each layer, or as a blend or alloy of two or more polymers. Blending or alloying allows for the acquisition of heat resistance, viscosity properties, and interlayer adhesion that cannot be obtained from a single thermoplastic resin.

[0042] The present invention provides a laminated sheet for radar units, which is based on a laminated sheet comprising a laminated unit in which layers of different compositions are alternately laminated. In such a laminated sheet, dielectric polarization is induced at the interface between layers A and B, which have different compositions, and the more layers there are and the larger the scale of polarization, the higher the complex dielectric constant of the entire laminated sheet can be. Specifically, by making one of the layers A or B constituting the laminated sheet have a high dielectric constant and the other layer have a low dielectric constant, a difference in dielectric constant is created. This is achieved by adding the effect of dielectric polarization (generation of a dipole moment) generated at the layer interface between the high-dielectric-constant and low-dielectric-constant layers, thereby achieving a dielectric constant improvement that exceeds the limits of the volume law compared to a single-film sheet containing the same weight concentration of electromagnetic wave suppression material. In order to strongly induce this dielectric polarization that contributes to the improvement of the dielectric constant, one of the important design points is how to increase the difference in dielectric constant between the alternately arranged A and B layers. Methods for increasing the difference in dielectric constant include using resins with different dielectric constants in each layer, and creating a difference in the amount of electromagnetic wave suppression material contained in the A and / or B layers.

[0043] For thermoplastic resins with a low dielectric constant, it is preferable to select a thermoplastic resin with a dielectric constant of 3.0 or less. Considering versatility, processability, and lamination properties, it is preferable to select 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 especially preferable to be used in layers that do not contain conductive materials.

[0044] Conversely, in order to achieve a narrower bandwidth and steeper shielding performance, it is preferable that the material used as the organic polymer material has a high dielectric constant, and it is preferable to select acrylic resin (dielectric constant: 3.0~4.5), nylon resin (dielectric constant: 3.5~5.0), cellulose resin (dielectric constant: 6.7~8.0), vinyl monomer copolymer resin (dielectric constant: 3.0~8.0), fluororesin (dielectric constant: 4.0~8.0), polyphenylene sulfide (dielectric constant: 3.5~4.0), etc.

[0045] The laminated sheet of the present invention requires that at least one of the A layer and the B layer contain an electromagnetic wave suppressing material. The laminated sheet of the present invention achieves electromagnetic wave shielding properties by causing the incident electromagnetic waves to lose energy due to resistance from the conductive or magnetic electromagnetic wave suppressing material; therefore, it is necessary to include an electromagnetic wave suppressing material inside. The electromagnetic wave suppressing material may be contained in one of the A layer and the B layer, or in both. Furthermore, only one type of electromagnetic wave suppressing material may be used, or multiple types of electromagnetic wave suppressing materials may be used in combination.

[0046] Furthermore, considering the need to increase the difference in dielectric constant between layer A and layer B, one preferred embodiment is one in which one of the layers, A or B, does not contain electromagnetic wave suppression material in order to lower its dielectric constant, while the other layer contains electromagnetic wave suppression material to obtain a high dielectric constant. A further preferred embodiment is one in which the layer without electromagnetic wave suppression material is made of a resin with a low dielectric constant, and the layer containing electromagnetic wave suppression material is made of a resin that exhibits a high dielectric constant.

[0047] In the laminated sheet for radar units of the present invention, the electromagnetic wave suppression material can be selected, for example, as a conductive material that can mainly lose radio waves, such as a carbon material (preferably an organic carbon-based carbon material), and as a magnetic material that can mainly lose magnetic waves, such as an inorganic metal material. Either the carbon material or the inorganic metal material can be used, or both can be used in combination. Furthermore, the conductive material and the magnetic material may be contained in the same layer simultaneously, or the conductive material and the magnetic material may be contained separately in layer A or layer B, respectively. However, from the viewpoint of the electromagnetic wave shielding performance of the laminated sheet for radar units, it is preferable that at least one of the electromagnetic wave suppression materials is a carbon material.

[0048] The conductive material used in the laminated sheet for the radar unit of the present invention is preferably selected from carbon materials with small primary particle sizes and suitable for melt extrusion. Examples of such carbon materials include carbon black (spherical carbon) such as acetylene black, channel black, lamp black, thermal black, Ketjen black, and furnace black; cylindrical carbon such as carbon nanotubes, such as single-walled nanotubes, multi-walled nanotubes, and cup-stacked nanotubes; flattened carbon such as graphite, graphite, and graphene; and other materials such as spherical graphite, cylindrical graphite, carbon microcoils, fullerenes, and carbon fibers (long fibers, short fibers). In particular, from the viewpoint of utilizing the effect of particle arrangement in the planar direction due to the laminated and thin-film structure, it is preferable to use carbon black alone or in combination with other components, as its primary structure (linear structure) develops easily. Furthermore, in order to more strongly form conductive paths in the layer direction without disrupting the laminated structure, it is also preferable to use in combination with spherical carbon black, which develops its structure in any direction, as well as carbon nanotubes or flattened carbon, which have a uniform structure and a high aspect ratio. By using conductive materials with different skeletons and structures in combination, the ratio of each conductive material's content can be adjusted to various values ​​for the real part ε' and the imaginary part ε'' of the complex dielectric constant, according to the target frequency band for shielding.

[0049] Carbon black that readily develops a primary structure is characterized by a dibutyl phthalate (DBP) oil absorption rate (mL / 100g) of 200 or more. DBP oil absorption is an indicator of the degree of structural development of carbon black. Materials with a high DBP value are preferable because the carbon black particles are more likely to connect to each other in a linear fashion, resulting in many voids between the structures. This makes it easier to form conductive paths even with a small amount of DBP, and thus easily impart conductivity to the layer containing it. From the above viewpoint, the dibutyl phthalate (DBP) oil absorption rate is more preferably 350 mL / 100g or more.

[0050] When the carbon black structure develops and conductive paths are formed, when an electric field is generated by irradiation with electromagnetic waves, the conversion of electromagnetic wave energy into thermal energy by the electromagnetic wave suppression material becomes more efficient, and a high electromagnetic wave suppression effect can be expected. There is no particular upper limit to the amount of DBP oil absorbed, but considering the concern that the structure may be destroyed when the conductive material is dispersed in the polymer material, 800 mL / 100 g is appropriate. The amount of DBP oil absorbed can be measured in accordance with ASTM D 2414 (2019). As such conductive spherical carbon, commercially available materials such as acetylene black, furnace black, and Ketjen black can be used.

[0051] Carbon black, a preferred electromagnetic wave suppression material, tends to have a low real part ε' (described later) of the dielectric constant, which is an important parameter in the laminated sheet of the present invention, among carbon materials. Therefore, it is preferable to use in combination cylindrical materials such as carbon nanotubes, or flattened materials such as graphite, graphite, and graphene, as suitable carbon materials to increase the real part ε' of the dielectric constant. By adopting this configuration, the dielectric constant is improved and the electromagnetic wave shielding performance is enhanced by dispersing a conductive material with a high aspect ratio in the thickness direction, known as the Maxwell-Wagner effect. Specifically, by forming many microscopic dielectric polarizations at the interface between a dielectric thermoplastic resin (for example, polyolefin resins, polyester resins, acrylic resins, vinyl monomer copolymer resins, etc., which were previously exemplified as resins with low dielectric constants) and a conductive material, and by aligning cylindrical or flat conductive materials parallel to the film thickness direction so that these polarizations are arranged in parallel and facing each other like a parallel plate capacitor, when electromagnetic waves are irradiated and an electric field is applied, a large amount of charge is more likely to accumulate at the interface between the low dielectric resin and the conductive material, thereby increasing the conductivity within the laminated sheet.

[0052] Due to this effect, when electromagnetic waves are incident, they encounter resistance from the conductive material, making it easier for the electromagnetic wave energy to be converted into thermal energy. As a result, it is expected that the electromagnetic wave shielding performance will be enhanced. Based on this concept, in addition to the formation of the layer interface between layer A and layer B in this laminated sheet, it is preferable that the conductive material is aligned in the plane direction of the laminated sheet, and that the electric dipoles formed at the interface between the resin constituting the layer and the conductive material are generated in parallel in the plane direction of each layer of the laminated sheet. In other words, the higher the aspect ratio of the electromagnetic wave suppression material, the higher the possibility that it will become a laminated sheet of this type after undergoing a stretching process during film formation. Therefore, it is preferable to use cylindrical or flattened materials in combination.

[0053] Magnetic materials that can be used in the laminated sheet for the radar unit of the present invention include materials containing metallic components. For example, elemental metals such as silver, copper, iron, cobalt, nickel, chromium, aluminum, zinc, and tin, as well as their metal oxides, metal nitrides, metal carbides, metal borides, metal oxide nitrides, metal hydroxides, metal borides, organometallic complexes, and compounds and mixtures thereof can be used. Particularly preferred components include indium tin oxide (ITO) and indium zinc oxide (IZO), which are commonly used as transparent conductive metal oxides to increase magnetic permeability, as well as stainless steel materials and organometallic complexes such as carbonyl iron, hexacyano iron, and amino iron. It is preferable to use these inorganic metal materials in the form of rolled, flattened materials, as this makes it easier to disperse and arrange them in the planar direction in the laminated sheet of the present invention, thereby further improving electromagnetic wave shielding performance.

[0054] The electromagnetic wave suppression material used in the laminated sheet for the radar unit of the present invention can be appropriately selected from the conductive materials and magnetic materials mentioned above. However, if a large amount of magnetic material made of metal is included and the film is formed by melt extrusion, problems such as material pulverization and equipment damage may occur due to friction between the equipment and the magnetic material. Furthermore, due to the Snoek limit inherent to the material, magnetic materials tend not to be able to shield electromagnetic waves below a certain frequency (approximately 10 GHz) unless special materials such as ε-iron oxide are used, and may not be suitable as a shielding material for applications that utilize high-frequency electromagnetic waves such as 5G communication. For this reason, it is preferable to use at least one type of carbon material as the electromagnetic wave suppression material used in the present invention from the viewpoint of suppressing high-frequency electromagnetic waves. Furthermore, considering the effect of particle arrangement in the planar direction due to the laminated thin film structure mentioned above, carbon black, carbon nanotubes, graphite, and graphene are among the carbon materials, and among them, carbon black is the most preferable considering cost and other factors.

[0055] Furthermore, a dielectric material with excellent charge accumulation ability can be added as an electromagnetic wave suppression material used in the laminated sheet for the radar unit of the present invention. Dielectric materials are not materials that have the effect of directly causing loss by providing resistance to irradiated electromagnetic waves. However, as described later, in order to shield electromagnetic waves in a specific frequency band, it is preferable to control the real term ε' and the imaginary term ε'' of the dielectric constant of the laminated sheet to a specific range. In this case, by adding a dielectric material that can selectively improve the real term ε' of the dielectric constant, rather than just a conductive material in which both the real term ε' and the imaginary term ε'' of the dielectric constant tend to fluctuate, the numerical value of the dielectric constant can be controlled to a higher degree, and the electromagnetic wave shielding performance can be improved. 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, etc., which have a perovskite structure or a rutile-type structure, but titanium oxide, ferrite, and barium titanate are preferred because they are general-purpose and exhibit high dielectric constants.

[0056] In the laminated sheet for radar units of the present invention, from the viewpoint of achieving both electromagnetic wave shielding performance and the strength of the laminated sheet itself, it is preferable that the content of electromagnetic wave suppressing material is 1% by mass or more and 15% by mass or less when the total components constituting the laminated sheet are considered as 100% by mass. If the content of electromagnetic wave suppressing material exceeds 15% by mass, while it is easier to obtain high electromagnetic wave shielding performance, problems such as deterioration of lamination film formation due to thixotropy and weakening of the sheet may occur. In addition, if the difference in dielectric constant between the air and the outermost surface layer becomes large, electromagnetic waves may not reach the inside of the sheet due to surface reflection, and the desired dielectric polarization effect may not be obtained. On the other hand, if the content of electromagnetic wave suppressing material is less than 1% by mass, sufficient electromagnetic wave shielding performance cannot be obtained. From the above viewpoint, the content of electromagnetic wave suppressing material is more preferably 1.5% by mass or more and 5% by mass or less.

[0057] In addition, when the laminated sheet contains a plurality of types of electromagnetic wave suppression materials, the content of the electromagnetic wave suppression materials shall be calculated by summing up all the electromagnetic wave suppression materials. Further, in the laminated sheet of the present invention, if the content of the electromagnetic wave suppression materials is 1% by mass or more and 15% by mass or less based on 100% by mass of all the components constituting the laminated sheet, the content of the electromagnetic wave suppression materials in each layer (layer A, layer B) can be arbitrary.

[0058] It is important for the laminated sheet for a radar unit of the present invention to generate dielectric polarization utilizing the difference in dielectric constant between layer A and layer B. Therefore, even when the electromagnetic wave suppression material is contained in both layer A and layer B, in order to cause a difference in dielectric constant between the two layers, the content w A of the electromagnetic wave suppression material in layer A and the content w B of the electromagnetic wave suppression material in layer B are preferably different. More specifically, when the content of the electromagnetic wave suppression material in layer A is w A (% by mass) and the content of the electromagnetic wave suppression material in layer B is w B (% by mass), it is preferable to satisfy w B > w A . By adopting such an aspect, even if the components in layer A and layer B are the same, a difference in dielectric constant between the two layers can be caused.

[0059] Which of layer A and layer B has a higher content can be appropriately selected. However, in order to weaken the effect of surface reflection of electromagnetic waves and allow the electromagnetic waves to penetrate to the inside of the laminated sheet, and to realize a mode in which the incident electromagnetic waves receive resistance from the electromagnetic wave suppression material inside the sheet and are lost as thermal energy, layer A is located on the outermost surfaces on both sides, and it is preferable to satisfy the relational expression of w A < w B . Further, in order to increase the difference in dielectric constant between layer A and layer B, it is most preferable that layer A does not contain the electromagnetic wave suppression material and only layer B contains it.

[0060] The electromagnetic wave suppression material included in the laminated sheet for radar units of the present invention is preferably such that X / Y is 0.01 or more and 10.0 or less, and more preferably 0.01 or more and 6.0 or less, when X (nm) is the major axis of the higher-order structure formed by the most abundant component in the laminated sheet of the electromagnetic wave suppression material, and Y (nm) is the average layer thickness of the layer containing the most abundant component among layers A and B. Here, the higher-order structure of the electromagnetic wave suppression material refers to an aggregate formed by the interconnected electromagnetic wave suppression material. The component refers to the most abundant component in the sheet of the electromagnetic wave suppression material. X and Y can be measured by measuring the length of images captured with a differential interference microscope, and for measuring the length, for example, particle size analysis software "Macview" (manufactured by Mountec Co., Ltd.) can be used.

[0061] A high X / Y ratio means that the electromagnetic wave suppression material is more likely to be arranged parallel to the plane of the sheet within the layer. When X / Y is high, regions are more likely to be formed between the dielectric component such as resin and the electromagnetic wave suppression material, and dielectric polarization is more likely to occur at the interface between the electromagnetic wave suppression material and the dielectric component such as resin when electromagnetic waves are incident. As a result, the dielectric constant of the entire laminated sheet tends to improve. However, if X / Y becomes excessively high, clogging of the filter by the electromagnetic wave suppression material may occur during the film formation process, or the electromagnetic wave suppression material may not follow the flow of lamination and may break through the layer interface, causing lamination disorder.

[0062] More specifically, when X / Y is 0.01 or greater, it becomes easier to obtain a sufficient electromagnetic shielding effect while suppressing the amount of electromagnetic wave suppression material, and lamination disorder and defects in the film-forming sheet are also reduced. On the other hand, when X / Y is 10.0 or less, clogging of filters etc. by electromagnetic wave suppression material and lamination disorder caused by the electromagnetic wave suppression material not following the lamination flow can be reduced. From the above viewpoint, it is preferable that X / Y be between 0.1 and 10.0.

[0063] The X / Y ratio can be increased by making the electromagnetic wave suppression material flat, cylindrical, or a material that is easily linked in a linear chain as a higher-order structure to increase X, or by reducing the number of sheets stacked or the stacking ratio of layers containing the electromagnetic wave suppression material to reduce the thickness of each layer.

[0064] In addition to electromagnetic wave suppression materials, the laminated sheet of the present invention may optionally contain dispersants, surface modifiers, lubricants, crosslinking agents, vulcanization accelerators, antioxidants, nucleating agents, flame retardants, flow modifiers (plasticizers, thickeners), and antiblocking agents, to the extent that the inherent properties of the laminated sheet are not impaired. These components may be contained in layer A, layer B, or any layer other than layers A and B, as long as the inherent properties of the laminated sheet are not impaired.

[0065] The laminated sheet for radar units of the present invention requires that, in order to prevent malfunctions of peripheral devices due to transmitted high-energy millimeter waves emitted from the antenna, and the radar unit itself due to reflected waves, there exist a reflection loss peak with a peak top having a reflection loss RL of 15 dB or more within the frequency band of 20 to 100 GHz.

[0066] Return loss is a value that represents the amount of electromagnetic wave loss during its round trip within a laminated sheet, measured by measuring the intensity of the electromagnetic wave reflected back by the laminated sheet when an electromagnetic wave of a specific frequency is incident on the laminated sheet. It is expressed in decibels (dB). The measurement of return loss and the identification of the peak top can be performed using the method described in "Return Loss Measurement".

[0067] The return loss can be calculated using the coaxial waveguide method or the free-space method. This involves irradiating a laminated sheet, which has a metal such as aluminum deposited on its back surface or is a combination of existing reflectors, with electromagnetic waves from the side without the reflective layer. The intensity of the electromagnetic waves that travel back and forth within the laminated sheet after being reflected by the metal plate is then measured. During measurement, the return loss is measured by sweeping the frequency, and multiple peaks may be obtained in the return loss spectrum plotted with the vertical axis representing the return loss and the horizontal axis representing the frequency. The peak with the largest return loss is the one to focus on. The peak top, in this context, refers to the position where the sign (slope) of the tangent line in the return loss spectrum reverses from positive to negative, or from negative to positive.

[0068] Next, the return loss of the return loss peak will be explained with specific examples, referring to the drawings. Figures 3 to 6 show schematic diagrams showing the full width at half maximum and electromagnetic wave attenuation of the return loss peak with the largest peak top return loss among the peaks obtained by measuring the return loss peak of a laminated sheet according to one embodiment of the present invention. In Figures 3 to 6, reference numerals 14 to 16 indicate, respectively, the return loss spectrum, the electromagnetic wave attenuation RL at the peak top of the return loss peak with the largest peak top attenuation, and the frequency fGHz of the return loss peak with the largest peak top attenuation.

[0069] In the case of a single peak top as shown in Figures 3 and 4, the baseline of that peak is used as the reference, and the difference in the return loss between the peak top and the baseline at the frequency located at the peak top is defined as the return loss at the peak top. Furthermore, even if a peak has a high baseline return loss as shown in Figure 5, if it has a unique peak top, the return loss at the peak top can be determined by reading the difference in dB values ​​between the baseline and the peak top of that peak top. On the other hand, if a spectrum like Figure 6 is obtained that has multiple peak tops, including a shoulder peak, the return loss at the peak top can be determined by the difference between the return loss corresponding to the peak top of the highest peak among the multiple peak tops and the return loss at the baseline of the entire peak including the multiple peak tops.

[0070] The attenuation of the reflection attenuation peak shown in this manner must be 15 dB or greater. An attenuation of less than 15 dB means that, based on the relationship between the attenuation RL and shielding rate T described in equation (2), the shielding rate of electromagnetic waves is less than 99%, and in this case, it cannot be said that sufficient electromagnetic shielding is provided. The attenuation of the reflection attenuation peak with the greatest attenuation in the laminated sheet of the present invention is preferably 20 dB or greater, and more preferably 30 dB or greater. When the attenuation of the peak top showing the maximum attenuation is around 30 dB, it means that 99.9% of the incident electromagnetic waves are shielded compared to the electromagnetic shielding performance in the frequency band before and after the peak, and it can be said that it has very high electromagnetic shielding performance. There is no particular upper limit, but it is preferably 100 dB or less. In order for the attenuation of the reflection attenuation peak to show a high value of 15 dB or more, from the perspective of the structure of the laminated film, this can be achieved by having a large number of layers, designing the composition so that the dielectric constant of the layer showing a relatively high dielectric constant satisfies the relationship described later, and from the perspective of additives, by ensuring that the electromagnetic wave suppressing material exhibits high conductivity / magnetism, increasing the concentration of these materials, and dispersing and oriented them during the lamination and stretching process.

[0071]

number

[0072] Furthermore, from the viewpoint of achieving both electromagnetic wave shielding properties and moldability, it is preferable that the laminated sheet for radar units of the present invention exhibits a ratio of RL / (t×f) of 0.4 to 15 within the frequency band of 20 to 100 GHz, where RLdB is the attenuation of the reflection attenuation peak with the greatest attenuation at the peak top, fGHz is the frequency of the peak top, and tmm is the overall thickness of the laminated sheet.

[0073] Compared to conventional technologies, the laminated sheet of the present invention achieves dielectric polarization and in-plane dispersion and orientation of electromagnetic wave suppression materials by alternately laminating layers with low dielectric constants and layers with high dielectric constants. One feature of this invention is that it allows for a thinner sheet thickness and improved moldability compared to conventional single-layer or low-layer sheets. This feature is applicable to sheets targeting any frequency band of 20 to 100 GHz, which is used in millimeter-wave radar units. However, generally, there is a trade-off relationship between thickness and frequency band, and theoretically, the thickness tends to decrease when the frequency band is shifted to a higher frequency band for laminated sheets exhibiting the same dielectric constant. Therefore, the most notable feature of the laminated sheet of the present invention is that the relationship between frequency f, laminated sheet thickness t, and the attenuation amount RL of the reflection attenuation peak is superior to that of conventional technologies, exceeding the limits of the volume law. From the above viewpoint, RL / (t×f) is more preferably 0.60 to 12, and even more preferably 0.8 to 10.

[0074] If RL / (t×f) is lower than 0.4, the return loss RL is low, and sufficient electromagnetic shielding performance for use in electromagnetic shielding applications is not obtained, or although there is electromagnetic shielding, the thickness is too high and it does not exhibit sufficient performance beyond the volume law. If RL / (t×f) is higher than 15, even if the return loss is excellent, the thickness is too thin, which may worsen the lamination accuracy and film-forming properties of the laminated sheet due to the high concentration of electromagnetic suppression material. In order for RL / (t×f) to satisfy a desirable range, it is effective to have a large number of laminated sheets that generate a lot of dielectric polarization, to have little variation in layer thickness, for the electromagnetic suppression material to exhibit excellent conductivity / magnetism, and furthermore, to use a configuration in which multiple types of conductive materials are used and the dielectric constant can be freely designed, and for the real and imaginary parts of the dielectric constant of the layer showing a high dielectric constant to satisfy the dielectric constant relationship described later, and the effect is further enhanced when these are combined.

[0075] The electromagnetic shielding properties and frequency bandwidth of the laminated sheet for radar units of the present invention are given by the impedance Z shown in equations (3) and (4). in、 And it is determined by the return loss Γ calculated therefrom. Also, as can be seen from the formula, Z in Furthermore, Γ depends on the dielectric constant, permeability, and thickness of the entire sheet. Therefore, in order to achieve high electromagnetic shielding performance with a thin film, the product of the real part ε' of the dielectric constant and the real part μ' of the permeability must be a high value. In equations (3) and (4), Z0 is the characteristic impedance in air, d is the thickness of the laminated sheet, λ is the wavelength, μ is the permeability of the entire laminated sheet, and ε is the dielectric constant of the entire laminated sheet, with the value of Z0 being 377Ω.

[0076]

number

[0077]

number

[0078] The dielectric constant and permeability of the entire laminated sheet are influenced by the design of the dielectric constants of the A and B layers, which are arranged alternately to induce dielectric polarization. Specifically, the difference in dielectric constants between the A and B layers is sufficiently large, and the real part ε of the dielectric constant of the layer exhibiting a relatively high dielectric constant... h ' and the imaginary part ε h Controlling '' is extremely effective in adjusting electromagnetic shielding performance. The region in which high electromagnetic shielding performance is observed for a specific frequency band at a specific sheet thickness can be calculated based on equation (3). Furthermore, the laminated sheet of the present invention has a reflection attenuation peak in the 75-80 GHz band, which is suitably used as a millimeter-wave radar for vehicles, and exhibits high electromagnetic shielding performance. h ' and the imaginary part ε h It is preferable that '' satisfies either relation (A) or (B). (A) t ≤ 0.75, and 0.17εh' + 2.3 ≤ εh'' ≤ 0.27εh' + 3.37 (B) 0.75 <t≦1.5、かつ、0.02εh’+1≦εh’’≦0.07εh’+1.9 The real part ε of the dielectric constant of the layer with a relatively high dielectric constant at a given laminated sheet thickness. h ' and the imaginary part ε h By controlling the value within this range, it becomes possible to achieve high electromagnetic shielding performance at specific frequencies, even when the sheet thickness is thin.

[0079] The real part ε' of the dielectric constant, the imaginary part ε'' described later, and the real part μ' of the permeability of the laminated sheet of the present invention can be measured by the method described in the "Dielectric Constant Measurement" section of the Examples. Note that the real part and imaginary part (ε'' of the dielectric constant of each layer are described below. h ', ε hThe dielectric constant ε') can be measured by the method described above and the method described in "Calculation of Dielectric Constant of Each Layer" in the Examples. Briefly, it can be obtained by using a waveguide or lens antenna jig according to the frequency to be measured, and calculating the reflection and transmission characteristics of the electromagnetic waves when electromagnetic waves emitted from an electromagnetic wave generator are incident on a sample placed inside the waveguide or between lens antennas, 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 or the calculation software attached to these devices can be used. In this case, the real term ε' and the imaginary term ε'' of the dielectric constant can be obtained by reading the values ​​that are automatically calculated by the calculation software.

[0080] The real part of the dielectric constant of the layer with a relatively high dielectric constant ε h ' and the imaginary part ε h Methods for controlling '' to satisfy the above relation (A) or (B) include, for example, using carbon black with the preferred DBP oil absorption amount as a conductive material, using conductive materials with a high aspect ratio such as graphite or graphene, using barium titanate, ferrite oxide, or titanium oxide as a dielectric material, or using carbonyl iron as a magnetic material to improve the dielectric constant. In particular, in order to satisfy equation (A), the real part of the dielectric constant ε h ' and the imaginary part ε h Since it is required to increase both '', it is preferable to use carbon black, and in order to satisfy equation (B), the imaginary part of the dielectric constant ε h Since a low '' is required, this can be achieved by using at least one dielectric material such as barium titanate, ferrite, or titanium oxide, or a conductive material with a high aspect ratio such as graphite or graphene, either alone or in combination. Furthermore, it can also be achieved by using the stretching method described later to reduce the thickness of each layer, or by increasing the number of layers in the multilayer laminated sheet via a feed block with slits, thereby dispersing and oriented the electromagnetic wave suppression material in the plane direction of the laminated sheet.

[0081] There are various methods for adjusting the total thickness of a laminated sheet, including the total discharge volume from the extruder, the lip width of the die used for sheet formation, and the transport speed of the film-forming equipment. Among these, uniformly doubling the speed of the film-forming equipment is the simplest method that allows for adjustment of the total thickness of the laminated sheet without affecting lamination irregularities. Furthermore, in order to achieve in-plane orientation of the electromagnetic wave suppression material and to thin the film while increasing the dielectric constant of the high dielectric constant layer, this can be achieved by adjusting the transport speed of the film-forming equipment and stretching the laminated sheet in the longitudinal and width directions using the stretching method described later.

[0082] The following describes a preferred method of using the laminated sheet for radar units of the present invention, based on the radar unit configuration described above. The laminated sheet for radar units of the present invention is preferably provided to the side or rear of the radar unit when viewed from the millimeter-wave transmission direction, in order to absorb and reduce undesirable side lobes and back lobes that are different from the main lobes transmitted from the antenna substrate of the radar unit.

[0083] As viewed from the direction of millimeter wave transmission, the lateral direction refers to a three-dimensional range where the angle (13) with respect to the direction perpendicular to the plane of the planar antenna (12) is set to 0°, as shown in Figure 2, is between 15° and 165°. Although millimeter waves transmitted from the antenna are directional, they exhibit behavior that spreads radially. The main lobe is generally irradiated within a range of 15° or less, but the first side lobe (9), which is radiated forward at a wider angle than the main lobe, causes diffuse reflection when it hits objects inside or outside the vehicle, and the reflected millimeter waves may be received by the antenna or irradiated onto the control circuit board, potentially causing malfunction of the unit. In order to absorb the first side lobe, it is preferable to install the laminated sheet for millimeter wave radar of the present invention in a location within the aforementioned angle range on the radome (1), which is the lid of the housing enclosing the antenna substrate, or to have it integrally molded with the radome.

[0084] Among the millimeter waves emitted from the antenna, there is a second side back lobe (10) that is emitted to the rear and side when viewed from the direction of millimeter wave irradiation. Here, "rear and side" refers to a three-dimensional range greater than 90° and less than 165°, where the direction perpendicular to the plane of the planar antenna is defined as 0°. If this second side lobe is diffusely reflected within the millimeter-wave radar unit, it can directly affect the control circuit board and cause the unit to malfunction. A location for installing the laminated sheet for millimeter-wave radar of the present invention to absorb the second side lobe is the case (2), which is the main body of the housing that encloses the antenna board of the millimeter-wave radar unit. The laminated sheet of the present invention may be bonded to the inner surface of the case, or the laminated sheet of the present invention may be integrally molded to form the case. In the former case, bonding would lead to an increase in the weight of the case itself, so the latter form of integral molding is more preferable in order to give the case itself electromagnetic wave absorbing properties.

[0085] Of the millimeter waves emitted from the antenna, some may be emitted to the rear of the antenna, and this is called the back lobe (11). Here, "rear" refers to a three-dimensional range of 165° to 180°, where 0° is the direction perpendicular to the plane of the planar antenna. Since the RF module and control circuit board, which are the heart of the radar unit, are located on the back of the antenna, they may be affected by malfunctions caused by the back lobe, and therefore shielding is desirable. In the radar unit configuration described above, a metal antenna chassis and RF chassis are interposed between the antenna and the control board, so the control circuit board can be protected from the back lobe by the reflection of the metal. However, if a metal substrate is not used to prevent the radar unit from becoming too heavy, the back lobe may penetrate the back and affect the RF module and control circuit board. For this reason, it is preferable that the laminated sheet of the present invention be provided in the space sandwiched between the antenna and the RF module / control circuit board. The laminated sheet of the present invention may be provided by being bonded to the surface of a support provided between the antenna and the RF module / control circuit board, or the laminated sheet itself may serve as the support.

[0086] Furthermore, the laminated sheet for radar units of the present invention can be used not only as the radar unit itself, but also as a housing that encloses the antenna substrate. In addition, to prevent malfunction of the radar unit due to external electromagnetic waves, it can be attached to covers, emblems, or the vehicle body to protect the radar unit from external stimuli, or used as part of a vehicle component in the form of a molded product.

[0087] The laminated sheet for radar units of the present invention can also be combined with a reflector. By combining the reflector on the side of the laminated sheet opposite to the electromagnetic wave incidence surface, the electromagnetic waves are made to reciprocate within the laminated sheet, thereby increasing the electromagnetic wave absorption efficiency. On the other hand, when the reflector is placed on the front side, it is possible to reflect a certain amount of electromagnetic waves at the surface of the reflector and then steeply shield some of the transmitted electromagnetic waves within the laminated sheet. To fully utilize the electromagnetic wave shielding characteristics due to dielectric polarization of the laminated sheet of the present invention, the former configuration is more preferable.

[0088] The reflector is not particularly limited in terms of its constituent material, shape, and thickness, 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 is preferably adapted to the material to which it is applied, and can be, for example, a flat, curved, or hemispherical plate. As for the method of laminating the reflector with the laminated sheet of the present invention, for example, a method of bonding a pre-existing reflector with an adhesive or a method of directly laminating it onto the surface of the laminated sheet by metal vapor deposition can be used.

[0089] 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, or plate; composite reflectors in which metal, alloy, or carbon is dispersed inside a polymer film, sheet, or plate; and composite reflectors in which a mesh made of metal or alloy is contained inside a polymer film, sheet, or plate. Furthermore, in the present invention, if the vehicle body, support, housing, etc., contains metal, alloy, or carbon, they can be used as reflectors as they are.

[0090] Preferred embodiments of the laminated sheet of the present invention include electronic devices and communication devices having the aforementioned laminated sheet, used for purposes such as reducing unwanted electromagnetic wave radiation from electronic devices, semiconductors, and circuits located inside the housing, such as vehicle bumpers, and preventing device malfunctions due to radiation from external or adjacent devices, in applications such as 5G communication, high-speed and high-capacity communication using higher frequency electromagnetic waves, and collision avoidance (ITS) radar. In addition, the laminated sheet of the present invention can be used with any electronic device or communication device that utilizes GHz band frequencies, but it is particularly suitable for use in millimeter-wave radar applications.

[0091] Furthermore, preferred embodiments of the laminated sheet of the present invention include means of transportation such as vehicles, aircraft, and ships having the aforementioned laminated sheet, walls of structures such as buildings, tunnels, guardrails, highways, bridges, and transmission towers, communication facilities such as telegraphs and telephones, and transportation routes such as pedestrian crossings, intersections, railway lines, roads, sea routes, and air routes. Methods for applying the laminated sheet of the present invention include attaching it directly to structures such as floors, ceilings, walls, windows, and columns via adhesives or other means, or via other sheets, shielding plates, panels, etc., or integrally molding it with the material of the application location. In addition, it can also be used as wall or window material for shielded rooms to prevent the effects of electromagnetic jamming noise from the outside.

[0092] Next, a preferred method for manufacturing the laminated sheet of the present invention will be described below with reference to an example, but the present invention is not to be construed as being limited to such example.

[0093] First, we will explain using a laminated sheet as an example when rubber or thermoplastic elastomer is used as the base polymer. First, a predetermined amount of electromagnetic wave suppression material is added to the base polymer and kneaded using known equipment such as a kneader, Banbury mixer, mill mixer, roll mill, jet mill, or ball mill to obtain an electromagnetic wave suppression material-containing base polymer mixture. Either the base polymer alone or the prepared electromagnetic wave suppression material-containing base polymer is molded into a sheet of the desired thickness by rolling or melt extrusion using a batch press. Then, the prepared sheets corresponding to layer A and layer B (the compositions of the two are different) are stacked alternately in a total of 5 or more layers and pressed or laminated to obtain a laminated sheet. The fusion temperature at this time depends on the type of resin used, but is preferably 150°C to 400°C, and more preferably 250°C to 380°C. However, it is generally difficult to create thin film sheets by pressing, and the thickness of the sheet tends to increase due to stacking by lamination, so it is preferable to use the following method for creating laminated sheets using thermoplastic resins for the laminated sheets of the present invention.

[0094] Next, a method for manufacturing a laminated sheet using a flexible thermoplastic resin, which is a preferred resin in the present invention, will be described as an example. First, the thermoplastic resin, prepared in pellet form, and a predetermined amount of electromagnetic wave suppressing material are mixed in a twin-screw extruder and extruded into a gut-like form. This is then cooled in a water tank and cut with a chip cutter to form a master pellet containing the electromagnetic wave suppressing material. At this time, the electromagnetic wave suppressing 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 feeding method is not limited to the above and can be appropriately selected according to the specific gravity and shape of the electromagnetic wave suppressing material used.

[0095] The thermoplastic resins or thermoplastic resin compositions that make up layer A and layer B have different compositions. These thermoplastic resins or thermoplastic resin compositions are dried in hot air or under vacuum and then supplied to separate extruders, where they are heated and melted to a temperature above the melting point of the thermoplastic resin. After that, the extrusion rate is made uniform using a gear pump or the like to discharge the thermoplastic resin or thermoplastic resin composition, and foreign matter and modified resin are removed using a filter or the like.

[0096] Next, these thermoplastic resins or thermoplastic resin compositions are laminated in a multilayer laminating apparatus capable of laminating to a desired number of layers, molded into the desired shape using a die, and extruded in sheet form. The sheet material extruded from the die is extruded onto a cooling body such as a casting drum and cooled and solidified to become a cast sheet. At this time, since the cast sheet itself is conductive, it is preferable to use a method in which air is blown from a slit-shaped, spot-shaped, or planar device to bring it into contact with a cooling body such as a casting drum and rapidly cool and solidify it, a method in which it is brought into contact with a cooling body using a nip roll and rapidly cool and solidify it, or a method in which a liquid is applied to the casting drum and the extruded sheet is brought into contact with the cast to obtain flatness. However, in the present invention, if a layer that does not contain electromagnetic wave suppression material is placed on the outermost layer, the SI casting method by electrostatic application can be used.

[0097] While multi-manifold dies, feed blocks, and static mixers can be used as multilayer lamination equipment, it is particularly preferable to use a feed block with fine slits to efficiently obtain the multilayer laminate of the present invention. Using such a feed block does not require an extremely large device, resulting in less foreign matter generation due to thermal degradation, and enabling 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 technology. In addition, this device has advantages such as the ability to easily achieve any desired layer thickness by adjusting the thickness of each layer with the shape (length, width) of the slits, and the ease with which particles can be oriented toward the laminated sheet surface by the effect of resin flow during the lamination process. When electromagnetic wave suppression materials are added, the flow of resin through the slits facilitates the dispersion and arrangement of the electromagnetic wave suppression materials within the layer, which may help improve the dielectric constant.

[0098] When manufacturing laminated sheets using a slit-type feed block, the thickness and distribution of each layer can be adjusted by changing the length and width of the slits to balance the pressure. The length of the slit refers to the length of the comb-like teeth that form the flow channels for alternating the flow of layer A and layer B within the slit plate. Alternatively, after forming the laminate with the feed block, a method of doubling the number of layers by stacking them via a static mixer can also be suitably used.

[0099] The resulting cast sheet can be biaxially stretched in the longitudinal and widthwise directions as needed. Biaxial stretching may be performed sequentially or simultaneously. Furthermore, further stretching in the longitudinal and / or widthwise directions may be performed as needed.

[0100] First, we will explain sequential biaxial stretching, which involves stretching the sheet longitudinally first and then in the widthwise direction. Here, longitudinal stretching refers to uniaxial stretching to impart a longitudinal molecular orientation to the sheet, and is usually performed by a difference in the peripheral speed of the rolls. This stretching may 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 7.0 times, and particularly preferably 1.5 to 4.0 times. Furthermore, the stretching temperature is preferably set within the range of the glass transition temperature of the resin constituting the sheet to the glass transition temperature + 100°C. The uniaxially stretched laminated sheet obtained in this way can be subjected to surface treatments such as corona treatment, flame treatment, or plasma treatment as needed, and then a primer layer can 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 it may be applied to both sides simultaneously or sequentially one side at a time.

[0101] Widthwise stretching refers to stretching to give the sheet a widthwise orientation, and is usually performed using a tenter, with the sheet being transported while gripping both ends with clips. The stretching ratio varies depending on the type of resin, but is usually preferably 1.1 to 7.0 times, and particularly preferably 1.5 to 5.0 times. The stretching temperature is preferably between the glass transition temperature of the resin constituting the sheet and the glass transition temperature + 120°C. The biaxially stretched laminated sheet is then subjected to heat treatment in the tenter, above the stretching temperature but below the melting point, and after uniform slow cooling, it is cooled to room temperature and wound up. If necessary, relaxation treatments in the longitudinal and / or widthwise directions may be used in combination with the slow cooling after heat treatment to impart a low orientation angle and thermal dimensional stability of the sheet.

[0102] Next, we will explain the case of simultaneous biaxial stretching. In the case of simultaneous biaxial stretching, the obtained cast sheet may be subjected to surface treatments such as corona treatment, flame treatment, or plasma treatment as needed, and then functions such as slipperiness, adhesion, and antistatic properties may be imparted by in-line coating. In the in-line coating process, the coating layer may be applied to one side of the sheet, or it may be applied to both sides simultaneously or sequentially to one side at a time.

[0103] Next, the cast sheet is guided to a simultaneous biaxial tenter, where it is transported while gripping both ends with clips, and stretched simultaneously and / or in stages in the longitudinal and width directions. Simultaneous biaxial stretchers (tenters) can be of the pantograph type, screw type, drive motor type, or linear motor type, but a drive motor type or linear motor type is preferred as it allows the stretching ratio to be changed arbitrarily and relaxation processing to be performed at any point. The stretching ratio varies depending on the type of resin, but is usually preferably 2.0 to 50 times as an area ratio, and more preferably 4.0 to 20 times. The stretching speed may be the same speed, or it may be stretched in the longitudinal and width directions at different speeds. The stretching temperature is preferably between the glass transition temperature of the resin constituting the laminated unit and the glass transition temperature + 120°C.

[0104] The sheet, thus simultaneously biaxially stretched, is preferably subjected to further heat treatment in a tenter, above the stretching temperature but below the melting point, in order to impart flatness and dimensional stability. During this heat treatment, it is preferable to instantly loosen the sheet in the longitudinal direction immediately before and / or immediately after entering the heat treatment zone in order to suppress the distribution of the main orientation axis in the width direction. After heat treatment in this manner, the sheet is uniformly cooled slowly and then cooled to room temperature before being wound up. If necessary, loosening may also be performed in the longitudinal and / or width directions during the slow cooling after heat treatment. Instantaneous loosening in the longitudinal direction can also be performed immediately before and / or immediately after entering the heat treatment zone.

[0105] The laminated sheets obtained in this manner can be bonded together using adhesive sheets, tack sheets, double-sided tape, etc., either identical laminated sheets or laminated sheets having different thicknesses and compositions, in order to obtain the desired electromagnetic wave shielding performance.

[0106] Furthermore, layers with different dielectric constants can be laminated on the outermost surface of the laminated sheet of the present invention for purposes such as increasing electromagnetic wave transmittance or causing electromagnetic wave reflection. At this time, a coating layer containing a suitable conductive / magnetic material may be applied, or different resin layers / mesh layers may be laminated via an adhesive sheet or the like. In addition, resin / metal layers can be appropriately laminated according to the required function using sheet metal coating technologies such as sputtering (planar or rotary magnetron sputtering, etc.), evaporation (electron beam evaporation, etc.), chemical vapor deposition, organometallic chemical vapor deposition, plasma-enhanced / assisted / activated chemical vapor deposition, and ion sputtering.

[0107] Furthermore, the laminated sheet of the present invention can be made to more strongly shield only certain specific frequencies by combining it with an electromagnetic wave reflective layer that can shield a wide frequency band. On the other hand, a new layer exhibiting a low dielectric constant can be provided on the outermost surface of the laminated sheet to further reduce the reflection of electromagnetic waves at the surface, thereby creating a laminated sheet with an enhanced electromagnetic wave absorption effect. To improve electromagnetic wave permeability, it is also preferable to provide a resistive layer that exhibits an impedance approximately the same as the impedance of the air layer (377Ω). Known resistive layers include ITO films. In addition to the latter, it is also preferable that the thickness of the layer exhibiting a relatively high dielectric constant in the laminated sheet exhibits a layer thickness distribution in which the layer thickness decreases continuously from the surface to the interior of the sheet. The concentration of the electromagnetic wave suppression material added to the layer exhibiting a high dielectric constant is constant in all layers, but by continuously decreasing the thickness of the layer exhibiting a high dielectric constant from the surface to the inner layers, the electromagnetic wave suppression material becomes more densely bonded in the inner layers, resulting in a gradual increase in dielectric constant. This makes it possible to incorporate electromagnetic waves into the laminated sheet without inadvertently reflecting them in the layers near the surface, thereby enhancing the effect of electromagnetic wave absorption. [Examples]

[0108] The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Each characteristic was measured by the following method. Examples 1 and 2 below are for reference only.

[0109] (Methods for measuring characteristics and evaluating effects) The method for measuring the characteristics and evaluating the effects in this invention is as follows.

[0110] (1) Layer thickness, number of layers, layer structure, particle length The layer structure of the laminated sheet was determined by differential interference microscopy (Differential Interference Microscopy) observation of samples obtained by cutting cross-sections parallel to the thickness direction using a microtome. More specifically, a Leica DMLBHC differential interference microscope was used to observe the cross-section of the laminated sheet at a magnification of 1000x (10x eyepiece, 100x objective lens), and cross-sectional photographs were taken to measure the layer structure and the thickness of each layer. For length measurement, the particle size analysis software "Macview" (Mountec) was used, and for layer thickness measurement, the vertical distance between layer interfaces where the contrast difference could be clearly distinguished was measured. Data was measured at five random locations, and the average value of the thickness of each layer was used as the measured data. For particle diameter, the longest distance of the higher-order structure formed by particles observed in the image was measured at a total of 100 points, and the average data was used.

[0111] (2) Dielectric constant measurement For the laminated sheets, the measurement unit and measurement method were changed as follows for each measurement frequency and analyzed.

[0112] (2-1) 1GHz to 40GHz frequency band An Agilent Technologies, Inc. vector network analyzer (E8361A) was used. For the 0.5GHz to 18GHz frequency band, a donut-shaped coaxial waveguide with an outer diameter of φ7mm and an inner diameter of φ3.04mm was used. For the 18 to 26.5GHz frequency band, a rectangular waveguide with dimensions of 4.32mm × 10.67mm was used. For the 26.5 to 40GHz frequency band, a rectangular waveguide with an internal shape of 3.56mm × 7.11mm was used. Laminated sheet samples were punched out and inserted vertically into the interior of each waveguide for measurement. The measurement interval was set to allow for 200 measurements for each frequency band. The dielectric constant was analyzed using the analysis software N1500A-001 included with the instrument.

[0113] (2-2) 40~110GHz frequency band A 150mm square laminated sheet was used. Using a lens antenna type dielectric constant / attenuation measurement device LAF-26.5A manufactured by Keycom Co., Ltd., which utilizes the frequency variation method, the dielectric constant was measured for each frequency band: 33-50GHz (WR-22), 50-75GHz (WR-15), and 75-110GHz (WR-10). Although this measurement method also measures values ​​for 33-40GHz, the dielectric constant for the frequency band between 33GHz and 40GHz was obtained using the measurement data from (2-1).

[0114] (3) Measurement of return loss The measurement unit and measurement method were changed as follows to match the measurement frequency band, and measurements were performed accordingly.

[0115] (3-1) 1GHz to 40GHz frequency band The return loss of a laminated sheet was measured using an Agilent Technologies, Inc. vector network analyzer (E8361A). A donut-shaped coaxial waveguide with an outer diameter of φ7 mm and an inner diameter of φ3.04 mm was used for the 0.5 GHz to 18 GHz frequency band, a rectangular waveguide with dimensions of 4.32 mm × 10.67 mm was used for the 18 to 26.5 GHz frequency band, and 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. Measurements were taken at intervals of 200 points for each frequency band. A 1 mm aluminum metal plate was placed on the back of the laminated sheet sample to simulate total internal reflection of incident electromagnetic waves without electromagnetic wave absorption by the laminated sheet. S (Saturation) is the intensity ratio of reflected electromagnetic waves to incident electromagnetic waves. 11 The reflection attenuation peak was analyzed using the S-parameter values.

[0116] (3-2) 40~110GHz frequency band A 150mm square laminated sheet was prepared as a measurement sample, with an aluminum metal plate attached to the back. Using a lens antenna type oblique incidence electromagnetic wave absorber (electromagnetic wave absorbing material) and return loss measurement device LAF-26.5B manufactured by Keycom Co., Ltd., electromagnetic waves were irradiated at an oblique incidence of 15° in accordance with JIS R 1679 (2007), and the return loss was measured for each frequency band: 33-50GHz (WR-22), 50-75GHz (WR-15), and 75-110GHz (WR-10). Although this measurement method also measures values ​​for 33-40GHz, the return loss in the frequency band between 33GHz and 40GHz was measured using the measurement data from (3-1).

[0117] (4) Calculation of the dielectric constant of a layer exhibiting a relatively high dielectric constant. We developed and utilized a macro that can calculate the impedance when the configuration of a laminated sheet is replaced with an equivalent electrical circuit by substituting the variables of dielectric constant, 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 the values ​​into equation (4), which is based on the non-reflection condition and the return loss. Then, the dielectric constant and permeability of each layer were set to match the return loss spectrum measured by the method described in section (3), and the dielectric constant and permeability at which the return loss spectrum most closely approximated were read to determine the dielectric constant and permeability of each layer. When it is difficult to calculate the dielectric constant, a single-layer sheet is created with the same composition as the layer showing a relatively high dielectric constant in the example, and the frequency showing the minimum value of the transmission loss is identified using the frequency variation method with the vector network analyzer described above. Since this minimum value is an integer multiple of 1 / 2 of the effective wavelength transmitted through the sheet thickness, the dielectric constant was determined. The same value can also be verified with the accompanying software (SFW05) of Keycom's free-space dielectric constant measurement system (Model No. DPS10) using the frequency variation method.

[0118] (5) DBP oil absorption The laminated sheet was dissolved in a solvent capable of dissolving the resin of the base material, and the extracted and separated carbon-based conductive particles were measured using a Brabender Type C absorbometer in accordance with ASTM D2414 (2019). The carbon-based conductive particles were introduced into a mixer at a rotation speed of 125 min[m]. -1 While mixing with [ ], DBP was added dropwise at a dropping rate of 4 [mL / min], and the amount of DBP absorbed was read based on the viscosity curve obtained.

[0119] <Resins and electromagnetic wave suppression materials> To obtain the sheets for each example and each comparative example, the following components were used as resin, rubber, and electromagnetic wave suppression material.

[0120] <Resin> • Homo-polypropylene: Homo-polypropylene resin exhibiting a melt flow rate of 30 (manufactured by Prime Polymer Co., Ltd.) • Isophthalic acid copolymerized polyethylene terephthalate (isophthalic acid copolymerized PET): Polyethylene terephthalate copolymerized with 24 mol% isophthalic acid. • Polyethylene terephthalate (PET): Polyethylene terephthalate with a melting point of 254°C and a viscosity of IV0.8.

[0121] <Electromagnetic wave suppression material> • Carbon Black A: Carbon black with a primary particle size of 50 nm and a DBP oil absorption capacity of 220 mL / 100 g. • Carbon Black B: Carbon black with a primary particle size of 40 nm and a DBP oil absorption capacity of 360 mL / 100 g. Carbon Black C: DBP carbon black with an oil absorption capacity of 500 mL / 100 g. • Graphene: Graphene powder with an average particle size (D50) of 5.8 μm. Barium titanate: Barium titanate powder with an average particle size (D50) of 0.1 μm. This example shows the creation of an electromagnetic wave absorber capable of shielding the millimeter-wave frequency band of 75-80 GHz and 24 GHz, but similar designs and effects can be obtained for other frequency bands as well.

[0122] (Example 1) Master pellets were prepared by mixing 96% by mass of homo-polypropylene with 4% by mass of carbon black C, and then using a twin-screw extruder with an electromagnetic wave suppression material as a side feed. Subsequently, homo-polypropylene pellets (raw material for layer A) and the master pellets (raw material for layer B) were fed into separate twin-screw extruders and both were melted and mixed at 270°C. At this time, the mixing conditions were set to a screw rotation speed of 0.7 relative to the discharge volume. Next, these were combined in a multi-manifold type feed block with five flow paths, and the raw materials for layer A and layer B were alternately laminated in the thickness direction in five layers with a lamination ratio of 1.0 so that the outermost layers on both sides would be layer A, thereby obtaining an alternating laminate. After supplying this alternating laminate to a T-die and forming it into a sheet, it was pressed onto a casting drum maintained at a surface temperature of 25°C using a nip-casting method and rapidly cooled and solidified to obtain a laminated sheet with a thickness of 0.5 mm. The evaluation results are shown in Table 1.

[0123] (Example 2) Master pellets were prepared by mixing 96% by mass of isophthalic acid copolymer PET resin with 4% by mass of carbon black C, and then using a twin-screw extruder with an electromagnetic wave suppression material as a side feed. Subsequently, polyethylene terephthalate pellets (raw material for layer A) and the master pellets (raw material for layer B) were fed into separate twin-screw extruders and both were melted and mixed at 280°C. At this time, the mixing conditions were set to a screw rotation speed of 0.7 relative to the discharge volume. These were then combined in a multi-manifold type feed block with five flow channels, and a laminated sheet with a thickness of 0.5 mm was formed in the same manner as in Example 1. The evaluation results are shown in Table 1.

[0124] (Example 3) A laminated sheet with a thickness of 0.5 mm was obtained in the same manner as in Example 2, except that the amount of carbon black C used, the lamination equipment, and the number of layers were as shown in Table 1. The evaluation results are shown in Table 1.

[0125] (Examples 4-11) A laminated sheet with a thickness of 0.5 mm was obtained in the same manner as in Example 2, except that the composition of the raw materials constituting each layer, the lamination apparatus, and the number of layers were as shown in Table 1, a slit-type feed block was used as the lamination apparatus, each raw material was passed through seven FSS-type leaf disc filters before supply, and each raw material was discharged while being weighed using a gear pump. The evaluation results are shown in Tables 1 and 2.

[0126] (Example 12) In Example 5, the carbon black C content in the isophthalic acid copolymer PET resin was set to 2.5% by mass, and a laminated sheet was obtained in the same manner as in Example 5. The obtained laminated sheet was heated in a roll group set to 90°C, and then stretched 3.0 times in the longitudinal direction while rapidly heating both sides of the film with a radiation heater over a stretching section length of 100 mm, and then cooled. This uniaxially oriented laminated sheet was led to a tenter, preheated with hot air at 90°C, and then stretched 3.3 times in the width direction at a temperature of 140°C to obtain a thin film laminated sheet with a thickness of 0.10 mm. Three thin film laminated sheets were bonded together via a 25 μm acrylic optical adhesive sheet to obtain a laminated sheet with a total of 305 layers, including the adhesive sheet layer. The evaluation results are shown in Table 2.

[0127] (Example 13) In Example 12, a 305-layer laminated sheet was obtained using the same method as in Example 12, except that the composition of the raw materials constituting each layer was as shown in Table 2. The evaluation results are shown in Table 2.

[0128] (Examples 14, 15) In Example 5, the composition of the raw materials constituting each layer was as shown in Table 2, and the thickness of the laminated sheet was adjusted to 1.5 mm by adjusting the rotation speed of the cast drum. Otherwise, a 101-layer laminated sheet was obtained in the same manner as in Example 5. The evaluation results are shown in Table 2. Due to the thickness of the sheet, it was not suitable for integral molding with radomes or cases, but it exhibited characteristics as an electromagnetic wave absorber suitable for use in bonded applications.

[0129] (Examples 16, 17) In Example 5, the composition of the raw materials constituting each layer was as shown in Table 2, and the thickness of the laminated sheet was adjusted to 1.5 mm by adjusting the rotation speed of the cast drum. Otherwise, a 101-layer laminated sheet was obtained in the same manner as in Example 5. By setting the sheet thickness to 1.0 mm, a laminated sheet suitable as an electromagnetic wave absorber for both integral molding and lamination was obtained.

[0130] (Comparative Examples 1-3) The composition of the raw materials for layer B was as shown in Table 2, and a Pinol apparatus capable of placing layer A on both surfaces of layer B was used as the lamination apparatus to form a 0.5 mm thick A / B / A 2-type 3-layer laminated sheet. The dielectric polarization effect was small, and although a high concentration of electromagnetic wave suppression material was added to create a material that absorbs millimeter waves (77 GHz), a laminated sheet with sufficient electromagnetic wave shielding performance could not be obtained.

[0131] [Table 1]

[0132] In the table, a "-" next to DBP oil absorption (carbon black) indicates that the material is an electromagnetic wave suppression material other than carbon black, and therefore there is no value.

[0133] [Table 2]

[0134] The laminated sheets of Examples 12 and 13 deviated slightly from the values ​​listed in the table due to deformation of the adhesive sheet during bonding, but the difference was so small that it was considered to be the same as the values ​​listed in the table. [Industrial applicability]

[0135] The laminated sheet of the present invention includes units in which layers with low dielectric constants and layers with high dielectric constants are alternately laminated, thereby achieving high electromagnetic wave attenuation with a low concentration of electromagnetic wave suppression material, which was difficult to achieve with conventional single-layer or low-layer sheets. Furthermore, in a preferred embodiment, by controlling the numerical values ​​of the complex dielectric constants of both layers to a specific range, it is possible to sharply and strongly shield only electromagnetic waves of a specific frequency, thereby effectively preventing malfunctions in devices using electromagnetic waves in similar frequency bands and preventing information leakage in high-capacity information communication using high-frequency electromagnetic waves. In particular, in millimeter-wave designs, since it also has thin-film formability, it can be suitably used for the frequency band of radar units that have millimeter waves. In addition, it can be suitably used in electronic devices, communication equipment, vehicles used as means of transport that carry them, and transportation systems including all infrastructure for traffic control that use communication technologies using electromagnetic waves in the GHz frequency band. [Explanation of Symbols]

[0136] 1: Radome 2: Case 3: Antenna 4: RF Module 5: Control circuit board 6: Antenna Chassis 7: RF Chassis 8: Main Robe 9: First side robe 10: Second side robe 11: Back robe 12: Direction perpendicular to the plane of the planar antenna 13: The angle between the plane of the planar antenna and the direction perpendicular to it. 14: Reflection loss spectrum 15: Electromagnetic wave attenuation at the peak of the reflection loss peak with the largest peak attenuation I 16: The frequency of the reflection loss peak with the largest peak attenuation.

Claims

1. A laminated sheet for use in a radar unit having an antenna substrate that emits millimeter waves, characterized in that it has all of the following features (1) to (5). (1) Includes a laminated unit in which 13 or more layers of A and B layers with different compositions are stacked alternately. (2) At least one of layer A and layer B contains an electromagnetic wave suppression material, and at least one of the electromagnetic wave suppression materials is a carbon material. (3) Within the frequency band of 20 to 100 GHz, there exists a return loss peak with a peak top where the return loss RL is 15 dB or more. (4) At least one of the outermost layers is layer A, and when the amounts of electromagnetic wave suppression material contained in layer A and layer B are wA and wB, respectively, the condition wA < wB is met. (5) When the major axis of the higher-order structure formed by the carbon material, which is the most abundant component in the laminated sheet of the electromagnetic wave suppression material, is X nm, and the average layer thickness of the layer containing the carbon material among the A layer and the B layer is Y nm, then X / Y is 0.01 or more and 10.0 or less.

2. The laminated sheet for a radar unit according to claim 1, characterized in that, within a frequency band of 20 to 100 GHz, when the attenuation of the reflection attenuation peak with the greatest attenuation at the top of the reflection attenuation peak is RL dB, the frequency is f GHz, and the total thickness of the laminated sheet is t mm, RL / (t × f) is 0.4 or more and 15 or less.

3. The laminated sheet for a radar unit according to claim 1 or 2, wherein at least one of the carbon materials is carbon black.

4. A laminated sheet for a radar unit according to any one of claims 1 to 3, wherein the total content of the electromagnetic wave suppression material is 1% by mass or more and 15% by mass or less, when the total components constituting the laminated sheet are taken as 100% by mass.

5. A laminated sheet for a radar unit according to any one of claims 1 to 4, which is provided to the side or rear of the radar unit when viewed from the direction of millimeter wave transmission.

6. A laminated sheet for a radar unit according to any one of claims 1 to 5, used as a housing that encloses the antenna substrate.

7. A radar unit comprising a laminated sheet for a radar unit according to any one of claims 1 to 6.

8. A transportation device equipped with a laminated sheet for a radar unit according to any one of claims 1 to 6.

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