JP2022055763A - Laminated sheet for radar unit - Google Patents

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

The present invention relates to a laminated sheet having high electromagnetic wave shielding, millimeter wave selective cut property, and thin film formability, which can be suitably used for a radar unit that emits millimeter waves.

In recent years, information and communication technology using electromagnetic waves as a medium has expanded, and metric waves in the hundreds of MHz to several GHz band, quasi-millimeter waves in the band of several GHz to several tens of GHz, and millimeters in the band of several tens of GHz to several hundred GHz. Electromagnetic waves of various frequency bands represented by waves are flying in the atmosphere. The metric wave is mainly used for mobile phones and wireless communication, and the quasi-millimeter wave is mainly used for mobile communication such as 4G / 5G and wireless LAN (Wi-fi) communication.

Information using electromagnetic waves in a collision prevention system that detects obstacles and automatically applies brakes in the technical field of automobiles, and controls the speed and inter-vehicle distance of own vehicles by measuring the position and speed of surrounding vehicles. Communication technology is used. In order to achieve higher detection performance, this collision prevention system uses millimeter waves (76 to 79 GHz), which have stronger directivity and higher energy than conventional frequencies (24 GHz) and are easily reflected by the material surface. It is being advanced. It is important that the collision prevention system using millimeter-wave radar responds only to the electromagnetic waves emitted and reflected from the radar unit, causing malfunction due to unnecessary electromagnetic waves (noise) incident from the surroundings. Electromagnetic wave absorption technology may be used to cut unwanted noise. (Patent Documents 1 and 2) Specifically, it is used as a housing portion for protecting the antenna base of a radar unit and as a millimeter-wave sidelobes cut sheet that spreads in a direction different from the transmission direction of the radar.

As a technique for absorbing high-frequency electromagnetic waves, a magnetic electromagnetic wave absorber (Patent Document 3) containing a magnetic material capable of absorbing high-frequency electromagnetic waves such as ε-iron oxide, a resistance layer, a dielectric layer, and a conductive reflective layer that utilize resistance loss. A λ / 4 type electromagnetic wave laminated absorber (Patent Document 4) or the like in which the above is laminated is generally used. In the case of a magnetic electromagnetic wave absorber, since it is necessary to contain ε-iron oxide in a high concentration, there is a problem that the total weight of the electromagnetic wave absorber increases and a problem that the cost becomes high. Further, in the case of a λ / 4 type electromagnetic wave absorber using resistance loss, the thickness of the entire electromagnetic wave absorber is as thick as mm to cm, which is complicated because the loss is caused by canceling the interference with the electromagnetic wave reflected by the conductive reflective layer. There is a problem that it does not have molding followability to a radar unit housing having a large shape.

Japanese Unexamined Patent Publication No. 2004-31696 Japanese Unexamined Patent Publication No. 2018-63159 Japanese Unexamined Patent Publication No. 2019-075571 International Publication No. 2020-067145

In view of the above problems, it is an object of the present invention to provide a laminated sheet for a radar unit having high shielding properties of millimeter waves, thin film formability, and light weight.

In order to solve the above problems, the present invention has the following configurations. That is, it is a laminated sheet used for a radar unit having an antenna substrate that emits millimeter waves, and is characterized by having all of the following features (1) to (3).
(1) Includes a laminated unit in which five or more layers A and B having different compositions are alternately laminated.
(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 having a peak top having a reflection attenuation amount of 15 dB or more.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a laminated sheet for a radar unit, which is a thin film and has excellent frequency selectivity and shielding property of millimeter wave electromagnetic waves. Specifically, by increasing the difference in the dielectric constants of the alternately arranged layers having different dielectric constants and forming a configuration in which the number of laminated layers is large, the effect of dielectric polarization at each interface having different dielectric constants is enhanced and laminated. The dielectric constant of the entire 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 an additive having a lower content concentration than the conventional single film sheet / low number of laminated sheets.

This is an example of a cross-sectional view of a radar unit in which the laminated sheet of the present invention can be suitably used. It is a schematic diagram showing the electromagnetic wave component radiated from an antenna. Among the peaks obtained by measuring the reflection attenuation peak of the laminated sheet according to the embodiment of the present invention, the schematic diagram showing the half-value width of the reflection attenuation peak having the largest reflection attenuation at the peak top and the electromagnetic wave attenuation. Is. Among the peaks obtained by measuring the reflection attenuation peak of the laminated sheet according to the embodiment of the present invention, the schematic diagram showing the half-value width of the reflection attenuation peak having the largest reflection attenuation at the peak top and the electromagnetic wave attenuation. Is. Among the peaks obtained by measuring the reflection attenuation peak of the laminated sheet according to the embodiment of the present invention, the schematic diagram showing the half-value width of the reflection attenuation peak having the largest reflection attenuation at the peak top and the electromagnetic wave attenuation. Is. Among the peaks obtained by measuring the reflection attenuation peak of the laminated sheet according to the embodiment of the present invention, the schematic diagram showing the half-value width of the reflection attenuation peak having the largest reflection attenuation at the peak top and the electromagnetic wave attenuation. Is.

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

(1) Includes a laminated unit in which five or more layers A and B having different compositions are alternately laminated.

(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 having a peak top having a reflection attenuation of 15 dB or more.

First, a radar unit having an antenna substrate that emits millimeter waves, which can suitably use the laminated sheet of the present invention, will be described. The radar unit is not limited to the following configuration.

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 view showing an electromagnetic wave component emitted from an antenna. The radar unit shown in FIG. 1 has an antenna (3), an antenna chassis (6), and a radio frequency (RF) chassis (7) in a housing surrounded by a radome (1) and a case (2) in this order from the radome side. ), The RF module (4), and the control circuit board (5) are provided in this order.

The radome is a square cover made of resin. The radome has a function of transmitting radio waves transmitted from the antenna and radio waves reflected from the target and received by the antenna. The radome is formed by injection molding of resin or the like, and the entire surface including the side surface has radio wave transmission.

The main lobe (8) of the millimeter wave transmitted from the antenna has strong straightness, and most of the radio waves are transmitted in the vertical direction from the antenna surface, but the first radio wave transmitted from the front of some antennas in a direction other than vertical. One sidelobes (9) pass through the side surface of the radome, are reflected by peripheral members constituting or outside the vehicle in the vicinity, enter the radome again, and are received by the receiving antenna. May cause malfunction of. Therefore, it is preferable to provide an electromagnetic wave absorber on the side surface of the radome to prevent transmission of the sidelobes. The electromagnetic wave absorber provided in the radome may be provided inside the radome or outside the radome. The electromagnetic wave absorber may be attached to a resin constituting the radome, or may be integrally molded with the radome so that only the side surface portion has the electromagnetic wave absorption performance.

The case (2) has a box shape with an open front surface of a quadrangle to include an antenna, an RF module, and a control circuit board. Of the millimeter waves emitted from the antenna, the case has a millimeter wave frequency band emitted from the antenna on the case itself in order to prevent malfunction due to reflection of the sidelobes (9, 10) and back lobe (11). It is preferable to contain electromagnetic wave absorption. Further, it is preferable to form a recess having a certain depth on the surface corresponding to the back surface of the case in order to prevent malfunction due to radio waves emitted from the control circuit board. By forming this recess, the radio wave emitted from the control circuit board and the radio wave reflected by the recess and having the opposite phase interfere with each other and cancel each other out, thereby suppressing the radio wave leakage caused by the control circuit board to the outside. You can. As a result, it is possible to prevent the signal created by the control circuit board from transmitting an unintended radio wave signal to the receiving circuit, and it is possible to improve the reliability of the output signal of the high frequency module. The depth of the recess is required to be designed to have a length of λ / 4, where λ is the wavelength of the radio wave emitted from the transmission circuit. As a result, the phase difference of the wave of λ / 4 minutes is delayed from the entrance of the recess to the innermost part, and the phase of the wave of λ / 4 minutes is further delayed from the innermost part to the inlet. As a result, a so-called anti-phase state occurs in which a phase delay of half a wavelength occurs as a whole, and unnecessary radio waves can be canceled.

The antenna (3) transmits a transmitted wave in the millimeter wave band, and also receives a received wave including a reflected wave whose transmitted wave is reflected by a target. It is preferable that the antenna is composed of a planar antenna made of a printed circuit board having a microstrip line from the viewpoint of cost and high degree of free design, but a waveguide slot antenna method, an arch antenna method, and a triplate patch array method are used. Other antenna methods such as, etc. can also be used. As a method for forming the printed circuit board, a coplanar type, a grand coplanar type, a differential line type, or the like can be used in addition to the microstrip line. The antenna may have at least one transmitting port and at least one receiving port, and the number of ports is not particularly limited. Further, a shared port that can freely switch between a transmission port and a reception port may be provided.

A metal antenna chassis for supporting the antenna can be provided on the back surface of the antenna. The antenna chassis has a role of preventing noise propagation between the antenna and the RF module by being made of metal as well as supporting the antenna. Further, a through hole may be provided in the antenna chassis to provide a waveguide function for transmitting and receiving signals between the antenna and the RF module.

An RF chassis can be provided on the back surface of the antenna chassis between the antenna chassis and the RF module. The RF chassis has a similar role to the antenna chassis, and has the functions of suppressing noise propagation and transmitting and receiving signals by providing a waveguide through hole while supporting the RF module.

The RF module is provided with a millimeter wave transmission / reception unit and an analog circuit including a transmission control circuit and a reception circuit, and can be configured by a printed circuit board. The millimeter wave transmitter / receiver transmits the transmitted wave and receives the received wave to and from the antenna via a patch for transmitting / receiving the millimeter wave. The transmission control circuit in the analog circuit is a part that performs frequency modulation and generates a transmitted wave. The receiving circuit is a part that detects a signal from the received wave in the millimeter wave transmission / reception unit.

The control circuit board includes a digital signal processor and a microcomputer. In the digital signal processor, the transmission wave is created by controlling the frequency modulation of the transmission control circuit, and the Fourier transform analysis of the signal received from the reception circuit is performed to calculate the distance, angle, relative velocity, etc. It is responsible for detecting the position of. The microcomputer is responsible for the control function of the entire millimeter-wave radar.

As described above, in order to prevent the millimeter-wave radar unit from malfunctioning due to unwanted reflection of the sidelobes and back lobes transmitted from the antenna, the radome and the case corresponding to the housing are required to have electromagnetic wave absorption performance. Since these radomes and cases are molded into a specific box shape for the purpose of containing an antenna or a circuit, it is desirable to use a sheet material having moldability. The laminated sheet of the present invention, which can be preferably used as a radome of such a millimeter-wave radar and an electromagnetic wave absorber for a case and has millimeter-wave absorption performance and moldability, will be described in detail below.

The laminated sheet for a radar unit of the present invention needs to include a laminated unit in which five or more layers A and B having different compositions are alternately laminated.

Here, "a laminated unit in which five or more layers A and B having different compositions are alternately laminated" (hereinafter, may be referred to as a laminated unit of A layer and B layer) means that the A layer and the B layer are used. It refers to a configuration in which there are five or more layers in total, which are alternately and continuously. That is, it refers to a state in which resins are laminated according to a regular arrangement of A (BA) n or B (AB) n (n is a natural number of 2 or more). For example, the configuration of A layer / B layer / A layer / B layer / A layer or the configuration of B layer / A layer / B layer / A layer / B layer corresponds to this, and a laminate having such a laminated unit. All the sheets correspond to the laminated unit of the A layer and the B layer regardless of the presence or absence of the layers other than the A layer and the B layer. In the laminated sheet of the present invention, as long as it has a laminated unit of A layer and B layer, the outermost layer may be any of layers A and B, and layers other than A layer and B layer, and the outermost layers on both sides are the outermost layers. It may be the same layer or different layers from each other. Further, the number of laminated units of the A layer and the B layer of the laminated sheet may be one or a plurality.

As a means for obtaining a laminated sheet having a laminated unit of A layer and B layer, as described later, a method of stepwise crimping and laminating layers having different compositions to each other, or laminating at once via a laminating device. And the like can be used. Further, a functional layer different from that of the laminated unit, such as another electromagnetic wave reflecting layer or an electromagnetic wave absorbing layer, may be formed on the laminated unit of the A layer and the B layer. In the case of having a plurality of laminated units of the A layer and the B layer, the plurality of laminated units can be directly laminated via the adhesive layer or by thermocompression bonding. Further, in the case of having a plurality of laminated units of the A layer and the B layer, the laminated units having peak tops in different frequency bands are used in an overlapping manner, and can be used as a material for simultaneously shielding a plurality of desired frequency bands. good.

The laminated sheet for a radar unit of the present invention has a laminated unit in which layers A and B are alternately laminated, thereby improving the electromagnetic wave shielding performance targeting a specific frequency band while suppressing the thickness of the entire laminated sheet. be able to. Normally, in order to improve the electromagnetic wave shielding performance by targeting a specific frequency band, it is necessary to improve the dielectric constant of the entire sheet. As a method for this, it is necessary to add an electromagnetic wave suppressing material at a high concentration and to increase the thickness of the sheet in the conventional single film or a sheet having a low number of layers.

On the other hand, in the case of a laminated sheet having a laminated unit of the A layer and the B layer of the present invention, by providing a dielectric constant difference between the A layer and the B layer, dielectric polarization occurs at the interface between layers having different dielectric constants, and the inside of the sheet. It becomes easier for the current to pass through. In addition, the alternating laminated structure allows the electromagnetic wave suppression material to be tightly confined in each layer, which increases the conductivity in the layer and is susceptible to loss due to the resistance of the conductive material added inside, which is a conventional product. Higher shielding performance can be achieved. As a result, it is possible to obtain an electromagnetic wave shielding material having excellent shielding performance even in an embodiment in which the thickness of the sheet is thinner than that of the conventional product and the content of the electromagnetic wave suppressing material is small. Here, the electromagnetic wave suppressing material is a general term for a conductive material having a property of imparting conductivity in response to an electric field when irradiated with an electromagnetic wave, and a magnetic material that absorbs a magnetic flux generated by a magnetic field. Details of the electromagnetic wave suppressing material that can be preferably used in the present invention will be described later.

Further, in such a laminated sheet, the layer thickness per layer is usually thin even if the sheet thickness is the same as that of the single film sheet, so that the packing density of the electromagnetic wave suppressing material in the layer becomes high and the distance between the electromagnetic wave suppressing materials increases. It narrows. As a result, the electron transfer efficiency between the electromagnetic wave suppressing materials is improved, and the electromagnetic wave suppressing performance of the entire laminated sheet is improved.

Further, in such a laminated sheet, especially when the laminated sheet is formed via the laminated device, the electromagnetic wave suppression material is easily arranged in the direction parallel to the laminated sheet surface according to the resin layer flow in the laminated device. By using a material that forms a high-order structure connected in a chain or an electromagnetic wave suppression material that exhibits a high aspect ratio, the conductivity in the plane direction is improved, and the incident electromagnetic wave resists the electromagnetic wave suppression material. In response, the electromagnetic wave shielding performance is improved. In order to realize such an aspect, it is preferable to use a slit type laminating device (feed block) as the laminating device. Due to the above mechanism, the laminated sheet contains a large amount of electromagnetic wave suppressing material in the single film sheet, or the value of the dielectric constant that could not be achieved unless the sheet thickness is increased, with a smaller amount of electromagnetic wave suppressing material and a thin film. It can also be realized with the sheet of.

The number of laminated units of the A layer and the B layer contained in the laminated sheet is preferably total because the more the layer interface between the layer showing a high dielectric constant and the layer showing a low dielectric constant, the easier it is to obtain the above effect. The number of layers is 13 or more, more preferably 31 layers or more in total, and more preferably 101 layers or more in total. The upper limit of the number of layers is preferably 1001 layers from the viewpoint of manufacturing cost, film forming property, and electromagnetic wave shielding performance. By setting the number of laminated units of the A layer and the B layer to 1001 layers or less, it is possible to suppress an increase in manufacturing cost due to an increase in the size of a device such as a feed block having fine slits. At the same time, depending on the dispersed state, shape, and size of the electromagnetic wave suppression material, the disturbance of the layer thickness due to the development of thixotropy, which is a problem due to the increase in the number of layers and the thinning of the thickness of each layer, is reduced, and the original shielding is achieved. It is also possible to maintain the steepness of performance and shielding. Suitable components constituting each of the layer exhibiting a low dielectric constant and the layer exhibiting a high dielectric constant, and their combinations are described below.

As long as the composition of the layer A and the layer B in the laminated sheet for a radar unit of the present invention is different, the constituents thereof are transparent / opaque, flexible / rigid, flat / non-flat, organic (polymer) material / inorganic. The (metal) material is not particularly limited. However, from the viewpoint of improving the processability of the obtained laminated sheet, it is preferable that the A layer and the B layer are mainly composed of an organic polymer material exhibiting flexibility. Further, a hard coat using a thermosetting resin or a photocurable resin can also be used. Here, the main component means that it contains more than 50% by mass and 100% by mass or less, preferably 70% by mass or more and 100% by mass or less, when all the components constituting the layer are 100% by mass. be.

The composition of the A layer and the B layer is different from each other because there is a component contained in only one of the A layer and the B layer, or the components of the A layer and the B layer are the same but their contents are different from each other. Say that. The A layer and the B layer in the laminated sheet of the present invention both contain an organic polymer material as a main component from the viewpoint of designability and electromagnetic wave shielding characteristics when the laminated sheet is used, and at least one of them is an organic material as an electromagnetic wave suppression material. It is preferable that the embodiment contains an inorganic material or an inorganic material.

The composition of the A layer and the B layer is not particularly limited as long as the compositions are different from each other. A possible composition is preferred. From this viewpoint, it is preferable that the organic polymer material in the A layer and the organic polymer material in the B layer have the same molecular skeleton. Here, the molecular skeleton means a repeating unit contained most in the molecular chain of the organic polymer material. For example, if the organic polymer material is polyethylene terephthalate, the ethylene terephthalate unit corresponds to the basic skeleton. As a specific example of the embodiment in which the organic polymer materials in the A layer and the B layer have the same molecular skeleton, the A layer contains a polyester resin as a main component, and the B layer also has the same basic skeleton as the polyester resin which is the main component of the A layer. An embodiment in which a polyester resin having a above-mentioned material is used as a main component can be mentioned.

A compatibility parameter can be used as an index showing the adhesion between the A layer and the B layer. The compatibility parameter can be estimated by a calculation method such as Hansen, Hoy, and Fedors, but the compatibility parameter of the thermoplastic resin, which is a component that can be suitably used as an organic polymer material, is a repetition of the molecular chain. A Fedors calculation method that can be calculated based on structural units is used. By using this method, the compatibility parameter of the thermoplastic resin containing the structural unit derived from the copolymerization component can be easily calculated according to the ratio of each structural unit. In the Fedors calculation method, the cohesive energy density of the molecule and the molar molecular volume, which depend on the type and number of substituents, determine the compatibility parameter, and the compatibility parameter is estimated according to the formula (1). Here, _Ecoh (cal / mol) represents the aggregation energy, and V represents the molar molecular volume (cm ³ / mol).

The compatibility parameter in the laminated sheet of the present invention is a value rounded off to the second decimal place of the estimated value calculated based on the Fedor formula. As compatibility parameters of typical thermoplastic resins, 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, Polymethylmethacrylate: 9.3 and the like.

The difference in the compatibility parameters between the A layer and the B layer for the A layer and the B layer of the laminated sheet for the radar unit of the present invention to show the interlayer adhesion even after being laminated is preferably 2.0 or less, which is more preferable. Is 1.0 or less. The A layer and the B layer may be made of exactly the same organic polymer material, and the lower limit is 0.0. However, when the compatibility parameter shows 0.0, in order to make the dielectric constants of the A layer and the B layer different, the type and content concentration of the electromagnetic wave suppressing material added to the A layer and the B layer shall be different. Is preferable. The dielectric constant is a numerical value indicating the response (degree of dielectric polarization) of a molecule when an electric field is applied from the outside, and is unique to a substance when the dielectric constant in vacuum (electric constant) is used as a reference. It is a dimensionless quantity of.

When the A layer or the B layer contains a plurality of organic polymer materials, the sum of the values of the compatibility parameters of each organic polymer material alone multiplied by the content ratio of the organic polymer materials is the phase of the layer. Use as a solubility parameter. For example, when the polyethylene terephthalate component (compatibility parameter: 10.7) and polymethyl methacrylate (compatibility parameter: 9.3) are contained in a ratio of 50:50, it corresponds to an intermediate value of both compatibility parameters. 10.0 is the compatibility parameter of the layer. When laminating layers containing different organic polymer materials as main components, add the organic polymer materials that are the main components of the other layer to one layer, and the numerical value of the compatibility parameter of both layers. It is also preferable to improve the adhesion between the two by bringing them closer to each other. The method of adding the organic polymer material which is the main component of the other layer may be a copolymerization method or a method of alloying the resin and kneading it in an extruder. Further, a method of adding a cross-linking type modifier having a basic skeleton of an organic polymer material which is a main component of the other layer can also be adopted.

As the organic polymer material in the A layer and the B layer, it is preferable to use a thermoplastic resin which is an organic polymer material exhibiting flexibility from the viewpoint of processability and film forming property of the laminated sheet. Examples of the thermoplastic resin include polyethylene, polypropylene, poly (1-butene), poly (4-methylpentene), polyisobutylene, polyisoprene, polybutadiene, polyvinylcyclohexane, polystyrene, poly (α-methylstyrene), and poly (poly (α-methylstyrene)). P-methylstyrene), polynorbornene, polyolefin-based resins such as polycyclopentene, polyamide-based resins such as nylon 6, nylon 11, nylon 12, and nylon 66, ethylene / propylene copolymers, and ethylene / vinylcyclohexane copolymers. , Ethylene / vinyl cyclohexene copolymer, ethylene / alkyl acrylate copolymer, ethylene / acrylic methacrylate copolymer, ethylene / norbornen copolymer, ethylene / vinyl acetate copolymer, propylene / butadiene copolymer, isobutylene / isoprene copolymer, vinyl chloride / vinyl acetate copolymer, etc. Vinyl monomer copolymer resins, polyacrylates, polymethacrylates, polymethylmethacrylates, polyacrylamides, acrylic resins typified by polyacrylonitrile, polyethylene terephthalates, polypropylene terephthalates, polybutylene terephthalates, polyethylene-2,6-naphthalates, etc. Represented by polyester resin represented by, polyethylene oxide, polypropylene oxide, polyether resin represented by polyacrylene glycol, diacetyl cellulose, triacetyl cellulose, propionyl cellulose, butyryl cellulose, acetyl propionyl cellulose, nitro cellulose. Cellulose ester-based resins, polylactic acid, biodegradable polymers typified by polybutyl succinate, etc. In addition, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, polyacetal, polyglucoric acid, polycarbonate, polyketone, poly Ethersulphon, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyetherimide, polyimide, polysiloxane, tetrafluoroethylene resin, trifluoroethylene resin, trifluorochloride ethylene resin, tetrafluoroethylene-6 foot A propylene copolymer, polyvinylidene fluoride, or the like can be used. These thermoplastic resins may be used alone in each layer, or may be used as two or more kinds of polymer blends or polymer alloys. By performing blending and alloying, it is possible to obtain heat resistance, viscosity characteristics, adhesion at the interface between layers, etc., which cannot be obtained from one type of thermoplastic resin.

The laminated sheet for a radar unit of the present invention is based on a laminated sheet including a laminated unit in which layers having different compositions are alternately laminated. In the laminated sheet of such an embodiment, dielectric polarization is caused at the interface between the A layer and the B layer having different compositions, and the larger the number of laminated sheets and the larger the scale of polarization, the higher the complex dielectric constant of the entire laminated sheet can be. Specifically, among the A layer or the B layer constituting the laminated sheet, the dielectric constant of one layer is increased, the dielectric constant of the other layer is decreased, and a difference in the dielectric constant is provided to increase the dielectric constant. Due to the effect of dielectric polarization (generation of bipolar moment) generated at the layer interface between the high layer and the low dielectric constant layer, the volume rule is compared with the single film sheet containing the electromagnetic wave suppression material of the same weight concentration. The effect of improving the dielectric constant beyond the frame can be obtained. In order to strongly cause the dielectric polarization that contributes to the improvement of the dielectric constant, one of the important design points is how to increase the difference between the dielectric constants of the alternately arranged layers A and B. Examples of the method of increasing the difference in dielectric constant include a method of using resins having different dielectric constants in each layer and a method of providing a difference in the content of the electromagnetic wave suppressing material contained in the A layer and / or the B layer.

As the thermoplastic resin having a low dielectric constant, it is preferable to select a thermoplastic resin having a dielectric constant of 3.0 or less, and in consideration of versatility, processability, and stackability, a polyolefin resin (dielectric constant: 2.0). ~ 2.3), Polyester resin (dielectric constant: 2.8 to 3.0), Polycarbonate (dielectric constant: 2.9 to 3.0), Polystyrene (dielectric constant: 2.4 to 2.6), It is preferable to select from the thermoplastic resins such as. These resins are more preferably used for layers that do not contain conductive materials.

On the contrary, in order to achieve steep shielding performance in a narrower band, it is preferable that the material used as the organic polymer material has a high dielectric constant, acrylic resin (dielectric constant: 3.0 to 4.5), nylon. Resin (dielectric constant: 3.5 to 5.0), cellulose resin (dielectric constant: 6.7 to 8.0), vinyl monomer copolymer resin (dielectric constant: 3.0 to 8.0), fluorine It is preferable to select a resin (dielectric constant: 4.0 to 8.0), polyphenylene sulfide (dielectric constant: 3.5 to 4.0), or the like.

The laminated sheet of the present invention needs to contain an electromagnetic wave suppressing material in at least one of the A layer and the B layer. Since the laminated sheet of the present invention realizes electromagnetic wave shielding characteristics by losing the energy of the incident electromagnetic wave by receiving the resistance of the electromagnetic wave by the electromagnetic wave suppressing material having conductivity or magnetism, the inside thereof It is necessary to include electromagnetic wave suppression material. The electromagnetic wave suppressing material may be contained in one of the A layer and the B layer, or may be contained in both of them. Further, as the electromagnetic wave suppressing material, only one kind may be used, or a plurality of kinds of electromagnetic wave suppressing materials may be used in combination.

Further, considering that the difference in dielectric constant between the A layer and the B layer is increased, one layer of the A layer or the B layer does not contain an electromagnetic wave suppressing material in order to lower the dielectric constant, and the other layer. Is one of the preferred embodiments in which the composition contains an electromagnetic wave suppressing material in order to obtain a high dielectric constant. A more preferable embodiment is that the layer containing no electromagnetic wave suppressing material is made of a resin having a low dielectric constant, and the layer containing the electromagnetic wave suppressing material is made of a resin having a high dielectric constant as a resin.

The electromagnetic wave suppression material in the laminated sheet for a radar unit of the present invention is, for example, a carbon material (preferably an organic carbon-based carbon material) as a conductive material capable of mainly losing radio waves, and an inorganic material mainly as a magnetic material capable of losing magnetic waves. Metallic materials can be selected. Either one of the carbon material and the inorganic metal material can be used, or both can be used in combination. Further, the same layer may contain the conductive material and the magnetic material at the same time, or the A layer or the B layer may contain the conductive material and the magnetic material separately, respectively. However, from the viewpoint of the electromagnetic wave shielding performance of the laminated sheet for the radar unit, it is preferable that at least one of the electromagnetic wave suppressing materials is a carbon material.

It is preferable that the conductive material used for the laminated sheet for the radar unit of the present invention is appropriately selected from carbon materials having a small size of primary particles 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, single-layer nanotubes, multilayer nanotubes, and cup-stacked nanotubes. Carbon nanotubes, which are cylindrical carbons, flat carbons such as graphite, graphite, and graphene, spherical graphite, cylindrical graphite, carbon microcoils, fullerene, and carbon fibers (long fibers, short fibers) can be used. Above all, from the viewpoint of utilizing the effect of particle arrangement in the plane direction due to the laminated / thin film structure, it is preferable to use carbon black alone or in combination with other components, which tends to develop a primary structure (linear structure). .. In addition to the spherical carbon black that develops the structure in any direction, carbon nanotubes with a uniform structure and high aspect ratio are used to form a stronger conductive path in the layer direction without disturbing the laminated structure. It is also preferable to use flat carbon or the like in combination. By using conductive materials with different skeletons and structures together, the ratio of the content of each conductive material is distributed, and the real part ε'and the imaginary part ε of the complex permittivity are matched to the frequency band targeted for shielding. The numerical value of'' can be adjusted in various ways.

Examples of carbon black in which the primary structure is likely to develop include carbon black having a dibutyl phthalate (DBP) oil absorption (mL / 100 g) of 200 or more. The amount of DBP oil absorbed is an index showing the degree of development of the structure of carbon black. A material having a large numerical value means that carbon black particles are easily connected to each other in a straight line, which means that there are many voids between structures, so that a conductive path is easily formed even with a small content, which is included. It is preferable because conductivity can be easily imparted to the layer. From the above viewpoint, the amount of dibutyl phthalate (DBP) oil absorbed is more preferably 350 mL / 100 g or more.

When the carbon black structure develops and a conductive path is formed, when an electric field is generated by being irradiated by electromagnetic waves, the electromagnetic wave suppression material converts the electromagnetic wave energy into thermal energy more efficiently, resulting in high electromagnetic waves. Expected to have an inhibitory effect. The upper limit of the DBP oil absorption amount is not particularly limited, but considering that there is a concern that the structure may be destroyed when the conductive material is dispersed in the polymer material, 800 mL / 100 g is appropriate. be. The amount of DBP oil absorbed can be measured according to ASTM D 2414 (2019). As such a conductive spherical carbon, for example, those commercially available as acetylene black, furnace black, ketjen black and the like can be used.

Carbon black, which is a preferable electromagnetic wave suppressing 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 carbon nanotubes, which are cylindrical materials, and flat materials such as graphite, graphite, and graphene, as suitable carbon materials for increasing the real part of the dielectric constant ε'. With such an aspect, the dielectric constant is improved and the electromagnetic wave shielding performance can be obtained by dispersing the conductive material having a high aspect ratio in the thickness direction, which is known as the Maxwell-Wagner effect. .. Specifically, a thermoplastic resin exhibiting dielectric property (for example, a polyolefin resin, a polyester resin, an acrylic resin, a copolymer resin of a vinyl monomer, etc., which were exemplified above as a resin having a low dielectric constant) and a conductive material. A mode in which many micro-dielectric polarizations are formed at the interface between the two, and cylindrical and flat materials are aligned in parallel in the film thickness direction as conductive materials, and these polarizations are arranged in parallel like a parallel plate condenser and face each other. Therefore, when an electric field is applied by irradiating an electromagnetic wave, a large amount of electric charge is likely to be accumulated at the interface between the resin which is a low dielectric and the conductive material, and the conductivity in the laminated sheet can be enhanced.

Due to such an effect, when an electromagnetic wave is incident, it receives resistance from a conductive material, and the electromagnetic wave energy is easily converted into heat energy, and as a result, it can be expected that the electromagnetic wave shielding performance is improved. Based on this idea, in addition to forming the layer interface between the A layer and the B layer in this laminated sheet, the conductive materials are aligned in the plane direction of the laminated sheet and formed at the interface between the resin constituting the layer and the conductive material. It is preferable that the electric dipoles to be generated are parallel to each other in the plane direction of each layer of the laminated sheet. That is, the more the electromagnetic wave suppressing material has a structure having a high aspect ratio, the more likely it is that a laminated sheet having such an aspect can be obtained by undergoing a stretching step during film formation. It is preferable to use the same material in combination.

Examples of the magnetic material that can be used for the laminated sheet for the radar unit of the present invention include materials containing a metal component, and examples thereof include metals such as silver, copper, iron, cobalt, nickel, chromium, aluminum, zinc, and tin. Uses simple substances and these metal oxides, metal nitrides, metal carbides, metal boroides, metal oxide nitrides, metal hydroxides, metal oxide boroides, organic metal complexes, and their compounds and mixtures. can do. In particular, as a preferable component, indium tin oxide (ITO) and indium zinc oxide (IZO), which are generally used as transparent conductive metal oxides in order to increase magnetic permeability, as well as stainless steel materials and organic metal complexes. Carbonyl iron, hexacyano iron, amino iron and the like can be used. As for these inorganic metal materials, it is preferable to use a spread flat material because the laminated sheet of the present invention can be easily dispersed and arranged in the plane direction and the electromagnetic wave shielding performance can be further improved.

The electromagnetic wave suppression material used for the laminated sheet for the radar unit of the present invention can be appropriately selected from the above-mentioned conductive material and magnetic material, but is melt-extruded by containing a large amount of a magnetic material composed of metal. When the film is formed by the above method, problems such as material crushing and chipping of the device may occur due to friction between the device and the magnetic material. In addition, magnetic materials tend to be unable to shield electromagnetic waves of a certain frequency (about 10 GHz) or less unless a special material such as ε iron oxide is used due to the Snoke limit peculiar to the material, and electromagnetic waves in the high frequency band such as 5G communication tend to be blocked. It may not be suitable as a shielding material for the intended use. From this, it is preferable to use at least one carbon material as the electromagnetic wave suppression material used in the present invention from the viewpoint of electromagnetic wave suppression in the high frequency band. Furthermore, considering the point of utilizing the effect of particle arrangement in the plane direction due to the above-mentioned laminated / thin film structure, carbon black, carbon nanotubes, graphite, graphene as carbon materials, especially carbon black is included in consideration of cost. Is most preferable.

Further, as an electromagnetic wave suppressing material used for the laminated sheet for a radar unit of the present invention, a dielectric material having an excellent ability to store electric charges can be added. The dielectric material is not a material that has the effect of giving resistance to the irradiated electromagnetic wave and causing a direct loss. However, as will be 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, and at this time, the dielectric constant. By adding a dielectric material that can selectively improve the real term ε'of the permittivity, as well as the conductive material in which both the real term ε'and the imaginary term ε'' of the permittivity tend to fluctuate. , The numerical value of the permittivity can be controlled more highly, and the electromagnetic wave shielding property 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, and iron oxide (ferrite) that have a perovskite structure or a rutile structure. ), Bismus ferrite, etc., but titanium oxide, ferrite, barium titanate, etc. are preferable because they are versatile and exhibit a high dielectric constant.

From the viewpoint of achieving both the electromagnetic wave shielding performance and the strength of the laminated sheet itself, the laminated sheet for the radar unit of the present invention contains 1% by mass of the electromagnetic wave suppressing material when all the components constituting the laminated sheet are 100% by mass. It is preferably 15% by mass or less. When the content of the electromagnetic wave suppressing material exceeds 15% by mass, high electromagnetic wave shielding performance can be easily obtained, but problems such as deterioration of laminated film forming property due to thixotropy and weakening of the sheet occur. Further, when the difference between the dielectric constant in the air and the dielectric constant of the outermost surface layer becomes large, the electromagnetic wave does not reach the inside of the sheet due to surface reflection, and the desired effect of the dielectric polarization may not be obtained. On the other hand, if the content of the electromagnetic wave suppressing material is less than 1% by mass, the electromagnetic wave shielding performance cannot be sufficiently obtained. From the above viewpoint, the content of the electromagnetic wave suppressing material is more preferably 1.5% by mass or more and 5% by mass or less.

When the laminated sheet contains a plurality of types of electromagnetic wave suppressing materials, the content of the electromagnetic wave suppressing material shall be calculated by adding up all the electromagnetic wave suppressing materials. Further, in the laminated sheet of the present invention, if the content of the electromagnetic wave suppressing material is 1% by mass or more and 15% by mass or less when all the components constituting the laminated sheet are 100% by mass, each layer (A layer). , B layer), the content of the electromagnetic wave suppressing material can be arbitrary.

It is important that the laminated sheet for a radar unit of the present invention generates dielectric polarization using the difference in dielectric constant between the A layer and the B layer. Therefore, even when the electromagnetic wave suppressing material is contained in both the A layer and the B layer, in order to cause a dielectric constant difference between the two layers, the content of the electromagnetic wave suppressing material in the A layer w _A and the B layer. It is preferable that the content w _B of the electromagnetic wave suppressing material is different. More specifically, when the content of the electromagnetic wave suppressing material in the A layer is w _A (mass%) and the content of the electromagnetic wave suppressing material in the B layer is w _B (mass%), w _B > It is preferable to satisfy w _A. With such an embodiment, even if the components of the A layer and the B layer are the same, a difference in dielectric constant between the two layers can be generated.

Which of the A layer and the B layer has a higher content can be appropriately selected, but the effect of the surface reflection of the electromagnetic wave is weakened and the electromagnetic wave penetrates into the laminated sheet, and the incident electromagnetic wave is the resistance of the electromagnetic wave suppressing material inside the sheet. In order to realize the mode of losing heat energy in response to the above, it is preferable that the layer A is located on the outermost surfaces on both sides and the relational expression of w _A <w _B is satisfied. Further, in order to increase the dielectric constant difference between the A layer and the B layer, it is most preferable that the A layer does not contain the electromagnetic wave suppressing material and is contained only in the B layer.

The electromagnetic wave suppressing material contained in the laminated sheet for a radar unit of the present invention is contained most in the laminated sheet among the electromagnetic wave suppressing materials from the viewpoint of reducing the stacking disorder and improving the dielectric constant while suppressing the amount of the electromagnetic wave suppressing material. When the major axis of the higher-order structure formed by the components is X (nm) and the average thickness of the layers containing a large amount of the components among the A layer and the B layer is Y (nm), X / Y is 0. It is preferably 01 or more and 10.0 or less, and more preferably 0.01 or more and 6.0 or less. Here, the higher-order structure of the electromagnetic wave suppressing material means an aggregate formed by connecting the electromagnetic wave suppressing materials. Further, the said component means a component contained most in the sheet among the electromagnetic wave suppressing materials. Note that X and Y can be measured by measuring the length of an image taken by a differential interference microscope, and for the length measurement, for example, particle size analysis software "Macview" (manufactured by Mountech) can be used.

A high X / Y means that the electromagnetic wave suppressing materials are likely to be arranged in parallel to the plane direction of the sheet inside the layer. When the X / Y is high, a region sandwiched between the dielectric component such as resin and the electromagnetic wave suppressing material is likely to be formed, and when an electromagnetic wave is incident, the dielectric polarization is performed at the interface between the electromagnetic wave suppressing material and the dielectric component such as resin. Is more likely to occur. Therefore, the dielectric constant of the entire laminated sheet is likely to be improved. However, if the X / Y becomes excessively high, the filter may be clogged with the electromagnetic wave suppressing material in the film forming process, or the electromagnetic wave suppressing material may not follow the flow of the lamination and break through the layer interface, resulting in stacking disorder.

More specifically, when the X / Y is 0.01 or more, it becomes easy to obtain a sufficient electromagnetic wave shielding effect while suppressing the electromagnetic wave suppressing material, and the stacking disorder and the defect of the film-forming sheet are alleviated. On the other hand, when the X / Y is 10.0 or less, it is possible to reduce clogging of the filter or the like due to the electromagnetic wave suppressing material and stacking disorder caused by the electromagnetic wave suppressing material not following the flow of the stacking. From the above viewpoint, X / Y is preferably 0.1 or more and 10.0 or less.

For X / Y, the electromagnetic wave suppression material has a flat shape or a cylindrical shape, or X is made a material that can be easily connected linearly as a high-order structure to increase X, or the number of laminated sheets and the electromagnetic wave suppression material. It is possible to increase the thickness by reducing the stacking ratio of the layers containing the above and reducing the layer thickness per layer.

In addition to the electromagnetic wave suppressing material, the laminated sheet of the present invention contains, if necessary, a dispersant, a surface modifier, a lubricant, a cross-linking agent, a vulcanization accelerator, an antioxidant, a crystal nucleating agent, a flame retardant, and the like. A flow modifier (plasticizer, thickener), an anti-blocking agent, and the like may be contained within a range in which the original characteristics of the laminated sheet are not impaired. As long as the original characteristics of the laminated sheet are not impaired, these components may be contained in any of the layers other than the A layer, the B layer, the A layer and the B layer.

The laminated sheet for a radar unit of the present invention is 20 to 100 GHz from the viewpoint of suppressing malfunction of the peripheral device due to the transmitted wave of the millimeter wave having strong energy emitted from the antenna and the radar unit itself due to the reflected wave. It is necessary that there is a reflection attenuation peak having a peak top having a reflection attenuation amount RL of 15 dB or more in the frequency band.

The amount of reflection attenuation is the amount of electromagnetic wave loss when reciprocating in the laminated sheet when measuring the intensity of the electromagnetic wave reflected and returned by the laminated sheet with respect to the electromagnetic wave of a specific frequency incident on the laminated sheet. It is a expressed value and is expressed in units of decibels (dB). The reflection attenuation amount can be measured and the peak top can be specified by the method described in "Reflection attenuation amount measurement".

The amount of reflection attenuation uses the coaxial waveguide method or the free space method, and a metal such as aluminum is vapor-deposited on the back surface, or electromagnetic waves are applied to the laminated sheet combined with the existing reflection plate from the side without the reflection layer. , It is possible to measure and calculate the intensity of electromagnetic waves that reflect the metal plate and reciprocate in the laminated sheet. In the measurement, the frequency is swept to measure the reflection attenuation, and multiple peaks may be obtained in the reflection attenuation spectrum plotted with the vertical axis as the reflection attenuation and the horizontal axis as the frequency. Among them, the reflection attenuation is the most. Focus on peaks with large volumes. The peak top here refers to a position where the sign (slope) is inverted from positive to negative or negative to positive when considering the slope of the tangent line of the reflection attenuation spectrum.

Subsequently, the reflection attenuation amount of the reflection attenuation amount peak will be described with reference to the drawings with specific examples. FIGS. 3 to 6 show half-value width and electromagnetic wave attenuation of the reflection attenuation peak having the largest reflection attenuation at the peak top among the peaks obtained by measuring the reflection attenuation peak of the laminated sheet according to the embodiment of the present invention. A schematic diagram showing the amount is shown. In FIGS. 3 to 6, reference numerals 14 to 16 indicate, in order, the reflection attenuation spectrum, the peak top electromagnetic wave attenuation RL of the reflection attenuation peak with the largest peak top attenuation, and the largest peak top attenuation, respectively. The frequency fGHz of the reflection attenuation peak is shown.

When a single peak top is provided as in the embodiments shown in FIGS. The amount of reflection attenuation at the top. Further, even if the peak has a high reflection attenuation of the baseline as in the embodiment of FIG. 5, if it has a specific peak top, the numerical difference between the baseline of the peak top and the dB of the peak top is read. Therefore, the amount of reflection attenuation at the peak top can be determined. On the other hand, when a spectrum as shown in FIG. 6 having a plurality of peak tops including a shoulder peak is obtained, it corresponds to the peak top with respect to the frequency of the peak top of the highest peak among the plurality of peak tops. The reflection attenuation at the peak top can be determined by the difference between the reflection attenuation and the reflection attenuation at the baseline of the entire peak including the plurality of peak tops.

The attenuation of the reflection attenuation peak thus shown needs to show a numerical value of 15 dB or more. The fact that the attenuation amount is less than 15 dB means that the electromagnetic wave shielding rate is less than 99% based on the relational expression of the attenuation amount RL and the shielding rate T described in the equation (2). In this case, the electromagnetic wave shielding amount is less than 99%. It cannot be said that it has enough sex. The attenuation of the reflection attenuation peak having the largest attenuation in the laminated sheet of the present invention is preferably 20 dB or more, more preferably 30 dB or more. When the attenuation of the peak top, which shows the maximum attenuation, is about 30 dB, it means that 99.9% of the incident electromagnetic waves are shielded compared to the electromagnetic wave shielding property of the frequency band before and after the peak. It can be said that it has a high electromagnetic wave shielding property. The upper limit is not particularly limited, but is preferably 100 dB or less. In order for the amount of attenuation of the reflection attenuation peak to show a high value of 15 dB or more, from the viewpoint of the configuration of the laminated film, the number of layers is large and the dielectric constant of the layer showing a relatively high dielectric constant is a relational expression described later. The composition is designed to satisfy the requirements, the electromagnetic wave suppression material exhibits high conductivity / magnetism from the viewpoint of additives, the content concentration of these materials is increased, and the dispersion orientation is performed in the laminating / stretching step. Can be achieved.

Further, the laminated sheet for the radar unit of the present invention has the attenuation amount of the reflection attenuation peak having the largest attenuation amount in the frequency band of 20 to 100 GHz in the frequency band of 20 to 100 GHz from the viewpoint of achieving both electromagnetic wave shielding property and moldability. When RLdB, the peak top frequency is fGHz, and the total thickness of the laminated sheet is tm, it is preferable that RL / (t × f) is 0.4 or more and 15 or less.

In contrast to the prior art, the laminated sheet of the present invention achieves dielectric polarization and dispersion / orientation of the electromagnetic wave suppressing material in the plane by alternately laminating layers having a low dielectric constant and layers having a high dielectric constant. However, there is one feature that the sheet thickness can be made thinner and formability can be imparted as compared with the conventional single film or sheet having a low number of laminated layers. This feature is applied to a sheet targeting any frequency band of 20 to 100 GHz, which is the frequency band used for the millimeter wave radar unit. However, in general, the thickness and the frequency band show a trade-off relationship, and when the frequency band is shifted to the high frequency band in a laminated sheet showing the same dielectric constant, the thickness tends to be theoretically thin. From this, it is the most important feature of the laminated sheet of the present invention that the relationship between the frequency f, the thickness t of the laminated sheet, and the attenuation amount RL of the reflection attenuation peak is superior to the prior art beyond the frame of the volume rule. Will be. From the above viewpoint, RL / (t × f) is more preferably 0.60 or more and 12 or less, and further preferably 0.8 or more and 10 or less.

When RL / (t × f) is lower than 0.4, the reflection attenuation amount RL is low, and sufficient electromagnetic wave shielding performance is not obtained enough to be used for electromagnetic wave shielding, or there is electromagnetic wave shielding property. However, it may be thick and may not show sufficient performance exceeding the volume rule. When RL / (t × f) is higher than 15, even if the amount of reflection attenuation is excellent, the thickness is too thin, and the lamination accuracy and film forming property of the laminated sheet deteriorate due to the high concentration of the electromagnetic wave suppressing material. May be done. In order to satisfy the preferable range of RL / (t × f), the number of laminated sheets is large and a large amount of dielectric polarization occurs, the layer thickness unevenness is small, and the electromagnetic wave suppressing material has excellent conductivity /. In addition to exhibiting magnetism, it is possible to freely design the permittivity by using multiple types of conductive materials, and the real and imaginary parts of the permittivity of the layer showing a high permittivity satisfy the dielectric constant relationship described later. It is effective, and the combination of these makes it more effective.

The electromagnetic wave shielding property and the frequency band of the laminated sheet for a radar unit of the present invention are determined by the impedance Z _in represented by the equations (3) and (4) and the reflection attenuation amount Γ calculated thereby. Also, as can be seen from the equation, Z _in and Γ depend on the dielectric constant, magnetic permeability and thickness of the entire sheet. Therefore, in order to achieve high electromagnetic wave shielding performance with a thin film, it is necessary to show a value in which the product of the real part ε'of the permittivity and the real part μ'of the magnetic permeability is high. In equations (3) and (4), Z ₀ is the characteristic impedance in the atmosphere, d is the thickness of the laminated sheet, λ is the wavelength, μ is the magnetic permeability of the entire laminated sheet, and ε is the dielectric constant of the entire laminated sheet. , And the value of Z ₀ is 377Ω.

The dielectric constant and magnetic permeability of the entire laminated sheet are influenced by the design of the dielectric constants of the A layer and the B layer which are alternately arranged to cause the dielectric polarization. Specifically, the real part ε _{h'and the imaginary part ε h '} ' of the dielectric constant of the layer showing a relatively high dielectric constant with a sufficiently large difference in the dielectric constant between the A layer and the B layer are controlled. Is extremely effective in adjusting the electromagnetic wave shielding property. The region showing high electromagnetic wave shielding property for a specific frequency band with a specific sheet thickness can be calculated based on the equation (3). Further, the laminated sheet of the present invention has a reflection attenuation peak in the band of 75 to 80 GHz, which is suitably used as a millimeter-wave radar for vehicles, and in order to exhibit high electromagnetic wave shielding property, the total thickness t of the laminated sheet, The real part ε _{h'and the imaginary part ε h '} ' of the dielectric constant of the layer having a relatively high dielectric constant among the A layer and the B layer satisfy the relational expression of (A) or (B). Is preferable.
(A) t≤0.75 and 0.17εh'+2.3≤εh''≤0.27εh'+3.37
(B) 0.75 <t≤1.5 and 0.02εh'+ 1≤εh''≤0.07εh'+1.9
By controlling the real part ε _{h'and the imaginary part ε h '} ' of the dielectric constant of a layer with a relatively high dielectric constant in this range at a predetermined laminated sheet thickness, a specific frequency is specified even when the sheet thickness is thin. It is possible to realize a high electromagnetic wave shielding property in the above.

The real part ε'of the dielectric constant of the laminated sheet of the present invention, the imaginary part ε'' described later, and the real part μ'of the magnetic permeability can be measured by the method described in the section "Measuring the Permittivity" of the examples. can. The real and imaginary parts (ε _h ', ε _h '') of the permittivity of each layer can be measured by the above method and the method described in "Calculation of the permittivity of each layer" in the above method. Briefly, using a waveguide or lens antenna jig according to the frequency you want to measure, the reflection of electromagnetic waves when the electromagnetic waves emitted from the electromagnetic wave generator are incident on the sample installed in the waveguide or between the lens antennas. -It can be obtained by calculating the transmission characteristics according to the known S parameter method. The measuring device and the calculation software are not particularly limited as long as they can measure and calculate, and for example, the device described in the embodiment or the calculation software attached to these devices can be used. In this case, the real number term ε'and the imaginary number term ε'' of the permittivity can be obtained by reading the values automatically calculated by the calculation software.

A method of controlling the real part ε _{h'and the imaginary part ε h '} ' of the dielectric constant of a layer having a relatively high dielectric constant so as to satisfy the relational expression of the above (A) or the above (B) is, for example, Use carbon black having the above-mentioned preferable DBP oil absorption as the conductive material, use graphite or graphene which is a conductive material having a high aspect ratio, or use barium titanate, ferrite oxide, or titanium oxide as the dielectric material. It is possible to improve the dielectric constant by using or using carbonyl iron as a magnetic material. In particular, in order to satisfy the equation (A), it is required to increase both the real part ε _{h'and the imaginary part ε h '} ' of the dielectric constant, so it is preferable to use carbon black, and the equation (B) is preferable. Since the imaginary part ε _h '' of the permittivity is required to be low in order to satisfy the above, dielectric materials such as barium titanate, ferrite, and titanium oxide, and conductivity with a high aspect ratio such as graphite and graphene. This can be achieved by using at least one type of sex material, alone or in combination. Further, by using the stretching method described later, the layer thickness per layer is reduced, the number of layers of the multilayer laminated sheet is increased via a feed block having slits, and the electromagnetic wave suppressing material is dispersed in the surface direction of the laminated sheet. It can also be achieved by using an oriented mode.

There are various methods for adjusting the total thickness of the laminated sheet, such as the total discharge amount from the extruder, the lip width of the die for forming the sheet, and the transport speed of the film forming apparatus. Above all, by uniformly doubling the speed of the film forming apparatus, the total thickness of the laminated sheet can be adjusted most easily and without affecting the laminated disorder. Further, in order to realize the in-plane orientation of the electromagnetic wave suppressing material and to make the thin film while increasing the dielectric constant of the layer having a high dielectric constant, in addition to adjusting the transport speed of the film forming apparatus, the laminated sheet is stretched as described later. This can be achieved by stretching in the longitudinal direction and the width direction.

Hereinafter, a preferable method of using the laminated sheet for a radar unit of the present invention will be specifically described based on the configuration of the radar unit described above. The laminated sheet for a radar unit of the present invention absorbs and loses unwanted side lobes and back lobes different from the main lobe transmitted from the antenna substrate of the radar unit, and therefore laterally viewed from the millimeter wave transmission direction of the radar unit. Alternatively, it is preferably provided at the rear.

As shown in FIG. 2, when the direction (12) perpendicular to the plane of the planar antenna is 0 °, the angle (13) formed with the direction is 15 ° or more. Refers to a three-dimensional range of 165 ° or less. Although the millimeter wave emitted from the antenna has directivity, it behaves as if it spreads radially. The main lobe is illuminated within a range of approximately 15 °, but the first side lobe (9), which is radiated to the front at a wider angle than that, causes diffuse reflection and bounces when it hits an object inside or outside the vehicle. The millimeter wave that has arrived may be received by the antenna or radiated to the control circuit board, which may cause the unit to malfunction. The place where the laminated sheet for millimeter wave radar of the present invention is installed in order to reduce the absorption loss of the first sidelobes is in the radome (1) which corresponds to the lid of the housing including the antenna substrate, in the place corresponding to the above angle range. It is preferably bonded or integrally molded with the radome.

As a part of the millimeter wave emitted from the antenna, there is a second side back lobe (10) irradiated to the rear side when viewed from the irradiation direction of the millimeter wave. The term "rear side" as used herein means a three-dimensional range of more than 90 ° and less than 165 ° when the direction perpendicular to the plane of the planar antenna is 0 °. If this second sidelobes is diffusely reflected in the millimeter wave radar unit, it directly affects the control circuit board and may cause the unit to malfunction. As a place where the laminated sheet for millimeter wave radar of the present invention is installed in order to cause absorption loss of the second sidelobes, there is a case (2) corresponding to the main body of the housing including the antenna substrate of the millimeter wave radar unit. The laminated sheet of the present invention may be attached to the inner surface of the case, or the laminated sheet of the present invention may be integrally molded to form a case. In the case of the former bonding, since the weight of the case itself increases, the latter aspect of integral molding is more preferable in order to give the case itself electromagnetic wave absorption.

Some of the millimeter waves emitted from the antenna may be emitted behind the antenna, which is called the back lobe (11). The term "rear" as used herein means a three-dimensional range of 165 ° or more and 180 ° or less when the direction perpendicular to the plane of the planar antenna is 0 °. Since the RF module and the control circuit board, which are the heart of the radar unit, are located on the back surface of the antenna, they may be affected by malfunction due to the back lobe, so that they are desired to be shielded. In the radar unit configuration described above, since the metal antenna chassis and the RF chassis are interposed between the antenna and the control board, 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 heavy, the back lobe may penetrate the back surface and affect the RF module and the control circuit board. Therefore, it is preferable that the laminated sheet of the present invention is 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 in a form of being bonded to the surface of a support provided between the antenna and the RF module / control circuit board, and the laminated sheet itself may serve as a support.

In addition, the laminated sheet for the radar unit of the present invention can be used not as the radar unit itself but as a housing including the antenna substrate. Also, in order to prevent the radar unit from malfunctioning due to electromagnetic waves from the outside, it can be attached to a cover to protect the radar unit from external stimuli, around the emblem, the car body, etc., or as a part of the vehicle parts in the form of a molded product. You can also use it.

The laminated sheet for a radar unit of the present invention can also be combined with a reflector. By combining the reflector on the side opposite to the electromagnetic wave incident surface of the laminated sheet, the electromagnetic wave is reciprocated in the laminated sheet, so that the electromagnetic wave absorption efficiency can be further improved. On the other hand, when the reflector is arranged on the front surface, it is possible to reflect a certain amount of electromagnetic waves on the surface of the reflector and steeply shield a part of the transmitted electromagnetic waves in the laminated sheet. In order to fully utilize the electromagnetic wave shielding property due to the dielectric polarization of the laminated sheet of the present invention, the former configuration is more preferable.

The constituent material, shape, and thickness of the reflector are not particularly limited as long as they can reflect electromagnetic waves. Examples of the constituent material include metals such as aluminum, copper, iron and gold, alloys such as stainless steel, and carbon films. The shape is preferably matched to the material to be applied, and can be, for example, a plate shape such as a flat surface, a curved surface, or a hemisphere. Further, as a method of laminating the reflector with the laminated sheet of the present invention, for example, a method of laminating a ready-made reflector with an adhesive or the like, or a method of directly laminating the reflector on the surface of the laminated sheet by metal vapor deposition can be used.

Examples of reflectors include laminated type reflectors and polymer films in which a film made of metal, alloy, or carbon is formed on the surface of a plate reflector containing metal, alloy, or carbon, a polymer film, a sheet, or a plate. , Composite type reflectors in which metals, alloys and carbon are dispersed inside sheets and plates, and composite type reflectors containing a reticulated body made of metal and alloy inside polymer films, sheets and plates. Be done. Further, in the present invention, when the vehicle body, the support, the housing and the like contain metal, alloy, carbon and the like, they can be used as they are as a reflector.

As a preferred embodiment of the laminated sheet of the present invention, inside a housing such as a vehicle bumper by electromagnetic waves used in 5G communication, high-speed / large-capacity communication using higher frequency electromagnetic waves, collision prevention (ITS) radar, and the like. For the purpose of reducing unnecessary electromagnetic wave radiation from equipped electronic devices, semiconductors, and circuits, and preventing device malfunction due to radiation from external or adjacent devices, the above-mentioned electronic devices and communication devices having laminated sheets can be mentioned. can. In addition, any electronic device or communication device that uses frequencies in the GHz band can be used by mounting the laminated sheet of the present invention, not limited to the above. Among them, the laminated sheet of the present invention is used for millimeter-wave radar. Can be preferably used for.

Further, as a preferred embodiment of the laminated sheet of the present invention, a means of transportation such as a vehicle, an aircraft, or a ship having the above-mentioned laminated sheet, a wall surface of a structure such as a building, a tunnel or a guardrail, a highway, a bridge, or a steel tower, or a telegraph. , Communication facilities such as telephones, transportation routes such as pedestrian crossings and intersections, railway routes, roads, routes, and air routes. As a method of applying the laminated sheet of the present invention, it is attached to a structure such as a floor, a ceiling, a wall, a window, a pillar, etc. directly via an adhesive or the like, or via another sheet, a shielding plate, a panel, or the like. , It is possible to use a method such as integrally molding with the material of the application site. In addition, it can also be used as a wall material or window material for a shielded room to prevent the influence of electromagnetic wave jamming noise from the outside.

Next, a preferable method for producing the laminated sheet of the present invention will be described below by way of example, but the present invention is not construed as being limited to such examples.

First, a laminated sheet in the case of using rubber, a thermoplastic elastomer, or the like as a base polymer of a base material will be described as an example. First, a predetermined amount of the electromagnetic wave suppression material is mixed with the base polymer, and the mixture is kneaded and contained in a known device such as a kneader, a Banbury mixer, a mill mixer, a roll mill, a jet mill, or a ball mill to contain the electromagnetic wave suppression material-containing base polymer mixture. To get. The base polymer alone or the prepared base polymer containing an electromagnetic wave suppressing material is formed into a sheet having a desired thickness by rolling or melt extrusion by batch pressing, respectively. Then, the prepared sheet corresponding to the layer A and the sheet corresponding to the layer B (the compositions of both are different from each other) are alternately laminated in a total of 5 or more layers, and pressed or laminated to obtain a laminated sheet. The fusion temperature at this time is preferably 150 ° C. to 400 ° C., more preferably 250 to 380 ° C., although it depends on the type of resin used. However, it is generally difficult to make a thin film sheet by pressing, and the thickness of the sheet tends to be thickened by laminating by laminating. Therefore, the laminated sheet of the present invention is a method for making a laminated sheet using the following thermoplastic resin. It is preferable to use it.

Next, a method for producing a laminated sheet when a thermoplastic resin exhibiting flexibility, which is a preferable resin in the present invention, is used will be described as an example. First, the thermoplastic resin prepared in the form of pellets and a predetermined amount of electromagnetic wave suppression material are kneaded with a twin-screw extruder and extruded into a gut shape, which is cooled in a water tank and cut with a chip cutter. Form master pellets containing electromagnetic wave suppression material. At this time, the electromagnetic wave suppressing material may be dry-blended together with the resin and then weighed and fed from the hopper, or may be side-fed into the molten resin from an arbitrary position of the extruder using a side feeder. 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 to be used.

The respective thermoplastic resins or thermoplastic resin compositions constituting the A layer and the B layer have different compositions from each other. After drying these thermoplastic resins or thermoplastic resin compositions in hot air or under vacuum, they are supplied to separate extruders and heated and melted in the extruder to a temperature equal to or higher than the melting point of the thermoplastic resin. After that, the extrusion amount is made uniform by a gear pump or the like, the thermoplastic resin or the thermoplastic resin composition is discharged, and the foreign matter and the modified resin are removed by a filter or the like.

Subsequently, these thermoplastic resins or thermoplastic resin compositions are laminated by a multi-layer laminating device capable of laminating to a desired number of laminations, molded into a desired shape with a die, and discharged into a sheet shape. The sheet-like material discharged 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 exhibits conductivity, air is blown out from a slit-shaped, spot-shaped, or planar device to be brought into close contact with a cooling body such as a casting drum to be rapidly cooled and solidified. It is preferable to use a method of quenching and solidifying, or a method of applying a liquid on a cast drum and bringing the discharged sheet into close contact with the cast to obtain flatness. However, in the present invention, when a layer containing no electromagnetic wave suppressing material is arranged on the outermost surface layer, the SI cast method by applying electrostatic electricity can be used.

As the multi-layer stacking device, a multi-manifold die, a feed block, a static mixer, or the like can be used, but in particular, in order to efficiently obtain the multi-layer laminated body of the present invention, it is preferable to use a feed block having fine slits. .. When such a feed block is used, the device does not become extremely large, so that the amount of foreign matter generated due to thermal deterioration is small, and high-precision stacking is possible even when the number of stacks is extremely large. In addition, the stacking accuracy in the width direction is significantly improved as compared with the conventional technique. Furthermore, since the thickness of each layer can be adjusted by the shape of the slit (length, width) in this device, it is easy to achieve an arbitrary layer thickness, and particles are laminated by the effect of the resin flow during the laminating process. There is also an advantage that it is easy to orient the particles in the direction of the sheet surface. When the electromagnetic wave suppressing material is added, the flow of the resin flowing through the slit facilitates the dispersion arrangement of the electromagnetic wave suppressing material in the layer, which may help to improve the dielectric constant.

When a laminated sheet is produced using a slit type feed block, the thickness and distribution of each layer can be adjusted by changing the length and width of the slit to adjust the pressure balance. The length of the slit is the length of the comb tooth portion that forms a flow path for alternately flowing the A layer and the B layer in the slit plate. Further, a method of forming a laminated body with a feed block and then superimposing the layers so as to double the number of layers via a static mixer can also be preferably used.

The obtained cast sheet can be biaxially stretched in the longitudinal direction and the width direction, if necessary. When biaxial stretching is performed, biaxial stretching may be performed sequentially or biaxial stretching may be performed at the same time. Further, if necessary, re-stretching may be performed in the longitudinal direction and / or the width direction.

First, sequential biaxial stretching, which first stretches in the longitudinal direction and then stretches in the width direction, will be described. Here, the stretching in the longitudinal direction refers to uniaxial stretching for giving the sheet a molecular orientation in the longitudinal direction, and is usually performed by the difference in peripheral speed of the rolls. This stretching may be performed in one step or in multiple steps using a plurality of roll pairs. The draw 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. Further, 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 thus obtained is subjected to surface treatment such as corona treatment, frame treatment, plasma treatment, etc. as necessary, and then a primer layer for improving the adhesion with the film to be laminated on the upper part. Can also be formed. In the step of in-line coating, the primer layer may be applied to one side, or may be applied to both sides simultaneously or one side at a time.

Stretching in the width direction means stretching to give orientation in the width direction to the sheet, and is usually carried out by using a tenter while gripping both ends of the sheet 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 from the glass transition temperature of the resin constituting the sheet to the glass transition temperature + 120 ° C. The laminated sheet thus biaxially stretched is heat-treated in a tenter at a stretching temperature or higher and a melting point or lower, slowly cooled uniformly, cooled to room temperature, and wound up. Further, if necessary, a relaxation treatment or the like may be used in combination in the longitudinal direction and / or the width direction when slowly cooling from the heat treatment in order to impart a low orientation angle and thermal dimensional stability of the sheet.

Subsequently, the case of simultaneous biaxial stretching will be described. In the case of simultaneous biaxial stretching, the obtained cast sheet is subjected to surface treatment such as corona treatment, frame treatment, plasma treatment, etc. as necessary, and then slipperiness, adhesiveness, antistatic property, etc. are exhibited. The function may be imparted by in-line coating. In the step of in-line coating, the coat layer may be applied to one side of the sheet, or may be applied to both sides simultaneously or one side at a time.

Next, the cast sheet is guided to the simultaneous biaxial tenter, and the sheet is conveyed while gripping both ends of the sheet with clips, and is simultaneously and / or stepwise stretched in the longitudinal direction and the width direction. Simultaneous biaxial stretching machines (tenters) include pantograph type, screw type, drive motor type, linear motor type, etc., but the stretching ratio can be changed arbitrarily, and relaxation processing should be performed at any location. A drive motor system or a linear motor system that can be used is preferable. The stretching ratio varies depending on the type of resin, but usually, the area ratio is preferably 2.0 to 50 times, and more preferably 4.0 to 20 times. The stretching speed may be the same, or may be stretched in the longitudinal direction and the width direction at different speeds. The stretching temperature is preferably from the glass transition temperature to the glass transition temperature of the resin constituting the laminated unit + 120 ° C.

In order to impart flatness and dimensional stability to the sheet simultaneously biaxially stretched in this way, it is preferable to continuously heat-treat the sheet in the tenter to have a stretching temperature or higher and a melting point or lower. During this heat treatment, in order to suppress the distribution of the main orientation axis in the width direction, it is preferable to perform the relaxation treatment in the longitudinal direction instantly immediately before and / or immediately after entering the heat treatment zone. After being heat-treated in this manner, it is uniformly slowly cooled, cooled to room temperature, and wound up. Further, if necessary, a relaxation treatment may be performed in the longitudinal direction and / or the width direction when slowly cooling from the heat treatment. Immediately before and / or immediately after entering the heat treatment zone, the relaxation treatment can be performed in the longitudinal direction.

In the laminated sheet of the present invention thus obtained, in order to obtain the desired electromagnetic wave shielding performance, the laminated sheets having the same laminated sheets or different thicknesses and compositions are bonded to each other, such as an adhesive sheet, an adhesive sheet, and a double-sided tape. It can also be pasted together via.

Further, layers having different dielectric constants can be laminated on the outermost surface of the laminated sheet of the present invention for the purpose of enhancing electromagnetic wave transmission or causing electromagnetic wave reflection. At this time, a coating layer containing a material exhibiting suitable conductivity / magnetism may be applied, or different resin layers / mesh layers or the like may be laminated via an adhesive sheet or the like. In addition, sputtering (plane or rotary magnetron sputtering, etc.), evaporation (electron beam evaporation, etc.), chemical vapor deposition, organic metal chemical vapor deposition, plasma strengthening / support / activation chemical vapor deposition, ion sputtering, etc. used as sheet metal coating technology. The resin / metal layer can be appropriately laminated according to the required function.

Further, the laminated sheet of the present invention can be made into a laminated sheet that shields only a part of a specific frequency more strongly by combining an electromagnetic wave reflecting layer capable of shielding a wide frequency band. On the other hand, it is also possible to provide a new layer having a low dielectric constant for lowering the reflection of electromagnetic waves on the surface on the outermost surface of the laminated sheet to obtain a laminated sheet having a higher effect of absorbing electromagnetic waves. In order to increase the electromagnetic wave transmission, it is also preferable to provide a resistance layer having an impedance almost the same as the impedance of the air layer (377Ω). Examples of the known resistance layer include an ITO film and the like.
In addition to the latter, it is also preferable that the thickness of the layer showing a relatively high dielectric constant of the laminated sheet shows a layer thickness distribution in which the layer thickness continuously decreases from the surface to the inside of the sheet. The concentration of the electromagnetic wave suppression material added to the layer showing high dielectric constant is constant in all layers, but by continuously reducing the thickness of the layer showing high dielectric constant from the surface layer to the inner layer, the inner layer suppresses electromagnetic waves. The materials are tightly connected and the dielectric constant gradually increases. As a result, the electromagnetic wave can be taken into the inside of the laminated sheet without being inadvertently reflected by the layer near the surface, so that the effect of electromagnetic wave absorption can be enhanced.

Hereinafter, the present invention will be described with reference to Examples, but the present invention is not limited to these Examples. Each characteristic was measured by the following method.

(Characteristic measurement method and effect evaluation method)
The method for measuring the characteristics and the method for evaluating the effect in the present invention are as follows.

(1) Layer thickness, number of layers, layered structure, particle major axis The layer structure of the laminated sheet was determined by observing a sample obtained by cutting out a cross section parallel to the thickness direction using a microtome by differential interference microscope observation. More specifically, using a differential interference microscope "DMLBHC" manufactured by Leica, the cross section of the laminated sheet was observed under the condition of a magnification of 1000 times (eyepiece lens 10 times, objective lens 100 times), and a cross-sectional photograph was taken. The layer composition and the thickness of each layer were measured. The length was measured using the particle size analysis software "Macview" (manufactured by Mountech), and the layer thickness was measured by measuring the vertical distance between the layer interfaces where the contrast difference could be clearly discriminated. Data at 5 locations were randomly measured, and the average value of the thickness of each layer was used as actual measurement data. For the particle major axis, the longest distance of the high-order structure formed by the particles confirmed in the image was measured at a total of 100 points, and the averaged data was used.

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

(2-1) 1 GHz to 40 GHz frequency band A vector network analyzer (E8631A) manufactured by Agilent Technologies, Inc. was used. The frequency band of 0.5 GHz to 18 GHz is a donut-shaped coaxial waveguide with an outer diameter of φ7 mm and an inner diameter of φ3.04 mm, and the frequency band of 18 to 26.5 GHz is a rectangular lead of 4.32 mm × 10.67 mm. A wave guide was used, and a rectangular waveguide having an internal shape of 3.56 mm × 7.11 mm was used in the frequency band of 26.5 to 40 GHz. The laminated sheet sample was punched and inserted vertically into each of the waveguides for measurement. The measurement interval was set so that 200 points could be measured for each frequency band. The dielectric constant was analyzed using the analysis software N1500A-001 attached to the apparatus.

(2-2) A laminated sheet having a frequency band of 40 to 110 GHz and a size of 150 mm square was used. 33 to 50 GHz (WR-22), 50 to 75 GHz (WR-15), 75 using a lens antenna type relative permittivity / attenuation measuring device LAF-26.5A using the frequency change method manufactured by Keycom. The permittivity was measured for each frequency band of ~ 110 GHz (WR-10). Although the value of 33 to 40 GHz is also measured by the measurement method, the measurement data in (2-1) was used for the dielectric constant in the frequency band of 33 GHz or more and less than 40 GHz.

(3) Reflection attenuation measurement The measurement was carried out by changing the measurement unit and measurement method as follows according to the measurement frequency band.

(3-1) 1 GHz to 40 GHz frequency band A vector network analyzer (E8631A) manufactured by Agilent Technologies Co., Ltd. was used to measure the amount of reflection attenuation of the laminated sheet. The frequency band of 0.5 GHz to 18 GHz is a donut-shaped coaxial waveguide with an outer diameter of φ7 mm and an inner diameter of φ3.04 mm, and the frequency band of 18 to 26.5 GHz is a rectangular lead of 4.32 mm × 10.67 mm. The wave guide was measured using a rectangular waveguide having a frequency band of 26.5 to 40 GHz and an internal shape of 3.56 mm × 7.11 mm. The measurement interval was set so that 200 points could be measured for each frequency band. A 1 mm aluminum metal plate was installed on the back surface of the laminated sheet as a sample, and the incident electromagnetic wave was totally reflected when the laminated sheet did not absorb the electromagnetic wave. The reflection attenuation peak was analyzed using the S-parameter value of _S11 , which represents the intensity ratio of the reflected electromagnetic wave to the incident electromagnetic wave.

(3-2) An aluminum metal plate was attached to the back surface of a laminated sheet having a frequency band of 40 to 110 GHz and a frequency band of 150 mm square to prepare a measurement sample. Using Keycom's lens antenna type oblique incident type electromagnetic wave absorber (electromagnetic wave absorbing material) and reflection attenuation measuring device LAF-26.5B, in accordance with JIS R 1679 (2007), at oblique incident 15 ° Electromagnetic waves were irradiated, and the amount of reflection attenuation was measured for each frequency band of 33 to 50 GHz (WR-22), 50 to 75 GHz (WR-15), and 75 to 110 GHz (WR-10). Although the value of 33 to 40 GHz is also measured by the measurement method, the measurement data in (3-1) was used for the amount of reflection attenuation in the frequency band of 33 GHz or more and less than 40 GHz.

(4) Calculation of the dielectric constant of a layer showing a relatively high dielectric constant The impedance when the configuration of the laminated sheet is replaced with an equivalent electric circuit is the variable of the dielectric constant, magnetic permeability, and layer thickness of the A and B layers. We built and utilized macro software that can be calculated by substituting. By substituting the obtained impedance Z _in into the equation (4) based on the non-reflection condition equation and the reflection attenuation amount, the calculation for calculating the reflection attenuation amount Γ is continuously calculated over a certain frequency band. It was created. Then, the dielectric constant and the magnetic permeability of each layer are set so as to match the reflection attenuation spectrum measured by the method described in (3), and the dielectric constant and the magnetic permeability when the reflection attenuation spectrum is most similar are read. The permittivity and magnetic permeability of each layer were determined. When it is difficult to calculate the dielectric constant, a single-layer sheet is prepared with the same composition as the layer showing a relatively high dielectric constant in the example, and transmission is performed by the frequency change method using the vector network analyzer described above. Identify the frequency that indicates the minimum attenuation. Since this minimum value is an integral multiple of 1/2 of the execution wavelength transmitted through the sheet thickness, the dielectric constant was obtained. The same value can be confirmed with the attached software (SFW05) of the permittivity measurement system (Model No. DPS10) for free space measurement by the frequency change method of Keycom.

(5) DBP Oil Absorption Amount The laminated sheet is dissolved in a solvent that can dissolve the resin of the base material, and the extracted and separated carbon-based conductive particles are treated with ASTM D2414 (Absorbometer C type manufactured by Brabender). It was measured according to (2019). While kneading the carbon-based conductive particles charged in the mixer at a rotation speed of 125 [min ^-1 ], DBP was dropped at a dropping rate of 4 [mL / min], and the analysis was performed based on the obtained viscosity curve. The amount of DBP oil absorbed was read.

<Resin and electromagnetic wave suppression material>
In order to obtain the sheets of each example and each comparative example, the following components were used as a resin, rubber, and an electromagnetic wave suppressing material.

<Resin>
Homo-polypropylene: Homo-polypropylene resin showing melt flow rate 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 having a melting point of 254 ° C. and a viscosity of IV0.8.

<Electromagnetic wave suppression material>
-Carbon black A: Carbon black with a primary particle size of 50 nm and DBP oil absorption of 220 mL / 100 g-Carbon black B: Carbon black with a primary particle size of 40 nm and DBP oil absorption of 360 mL / 100 g-Carbon black C: DBP oil absorption of 500 mL / 100 g of carbon black graphene: graphene powder having an average particle size (D50) of 5.8 μm.
Barium titanate: Barium titanate powder having an average particle size (D50) of 0.1 μm.
In this embodiment, an example of creating an electromagnetic wave absorber capable of shielding a millimeter wave frequency band of 75 to 80 GHz and 24 GHz is shown, but the same design and effect can be obtained for other frequency bands.

(Example 1)
A master pellet was prepared by blending 4% by mass of carbon black C with 96% by mass of homopolypropylene and kneading with a twin-screw extruder in which an electromagnetic wave suppressing material was side-fed. Subsequently, the homopolypropylene pellets (raw material for layer A) and the master pellets (raw material for layer B) were charged into separate twin-screw extruders, and both were melted at 270 ° C. and kneaded. At this time, the kneading condition was set to 0.7 for the screw rotation speed with respect to the discharge amount. Next, these are merged by a multi-manifold type feed block having five flow paths, and the raw materials for the A layer and the raw materials for the B layer are laminated at a stacking ratio of 1.0 so that the resurface layers on both sides are the A layer. Five layers were alternately laminated in the thickness direction to obtain an alternating laminated body. The alternating laminated body was supplied to a T-die to form a sheet, and then pressed against a casting drum whose surface temperature was maintained at 25 ° C. by a nip cast method to quench and solidify the laminated sheet to a thickness of 0.5 mm. .. The results of each evaluation are shown in Table 1.

(Example 2)
A master pellet was prepared by blending 4% by mass of carbon black C with 96% by mass of an isophthalic acid copolymerized PET resin and kneading with a twin-screw extruder in which an electromagnetic wave suppressing material was side-fed. Subsequently, the polyethylene terephthalate pellets (raw material for layer A) and the master pellets (raw material for layer B) were put into separate twin-screw extruders, and both were melted at 280 ° C. and kneaded. At this time, the kneading condition was set to 0.7 for the screw rotation speed with respect to the discharge amount. Next, these were merged by a multi-manifold type feed block having five flow paths to obtain a laminated sheet having a thickness of 0.5 mm by the same method as in Example 1. The results of each evaluation are shown in Table 1.

(Example 3)
A laminated sheet having a thickness of 0.5 mm was obtained in the same manner as in Example 2 except that the blending amount of carbon black C, the laminating device, and the number of laminating were as shown in Table 1. The results of each evaluation are shown in Table 1.

(Examples 4 to 11)
The composition of the raw materials constituting each layer, the laminating device, and the number of laminating are as shown in Table 1. A slit type feed block is used as the laminating device, and each raw material is passed through seven FSS type leaf disk filters before supply. A laminated sheet having a thickness of 0.5 mm was obtained in the same manner as in Example 2 except that each raw material was discharged while measuring with a gear pump. The evaluation results are shown in Tables 1 and 2.

(Example 12)
In Example 5, the concentration of carbon black C contained in the isophthalic acid copolymerized PET resin was set to 2.5% by mass, and a laminated sheet was obtained in the same manner as in Example 5. The laminated sheet obtained here was heated in a roll group set at 90 ° C., and then stretched 3.0 times in the longitudinal direction while being rapidly heated from both sides of the film by a radiation heater between the stretched section lengths of 100 mm. After that, it was once cooled. This uniaxially stretched laminated sheet was guided 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 having a thickness of 0.10 mm. By laminating three thin-film laminated sheets via an acrylic 25 μm optical adhesive sheet, a total of 305 laminated sheets including the adhesive sheet layer were obtained. The evaluation results are shown in Table 2.

(Example 13)
In Example 12, 305 layers of laminated sheets were obtained in the same manner as in Example 12 except that the compositions of the raw materials constituting each layer were as shown in Table 2. The evaluation results are shown in Table 2.

(Examples 14 and 15)
In Example 5, the composition of the raw materials constituting each layer is as shown in Table 2, and the rotation speed of the cast drum is adjusted so that the thickness of the laminated sheet is 1.5 mm, which is the same as in Example 5. A 101-layer laminated sheet was obtained by the above method. The evaluation results are shown in Table 2. Since the sheet is thick, it was not suitable for integral moldability with radomes, cases, etc., but it had the characteristics of an electromagnetic wave absorber suitable for use by laminating.

(Examples 16 and 17)
In Example 5, the composition of the raw materials constituting each layer is as shown in Table 2, and the rotation speed of the cast drum is adjusted so that the thickness of the laminated sheet is 1.5 mm, which is the same as in Example 5. A 101-layer laminated sheet was obtained by the above method. By setting the sheet thickness to 1.0 mm, a laminated sheet as an electromagnetic wave absorber suitable for both integral molding and use by laminating was obtained.

(Comparative Examples 1 to 3)
The composition of the raw material for the B layer is as shown in Table 2, and a pinole device capable of arranging the A layer on both surface layers of the B layer is used as a laminating device, and the A layer / B layer / A having a thickness of 0.5 mm is used. A two-kind, three-layer laminated sheet of two layers was formed. Although the effect of dielectric polarization is small and an electromagnetic wave suppression material is added at a high concentration to make it a material that absorbs millimeter waves (77 GHz), a laminated sheet having sufficient electromagnetic wave shielding performance could not be obtained.

In the table, "-" in the DBP oil absorption amount (carbon black) means that there is no value because it is an electromagnetic wave suppressing material other than carbon black.

The laminated sheets of Examples 12 and 13 were slightly deviated from the values shown in the table due to the deformation of the adhesive sheet due to the bonding, but the difference was considered to be the values shown in the table because of a slight difference.

The laminated sheet of the present invention contains a unit in which layers having a low dielectric constant and layers having a high dielectric constant are alternately laminated, so that a low electromagnetic wave suppressing material, which has been difficult to achieve with a conventional single film or a sheet having a low number of laminated sheets, is low. A high electromagnetic wave attenuation can be achieved by containing the concentration. Further, as a preferred embodiment, by controlling the numerical values of the complex permittivity of both to a specific range, it is possible to steeply and strongly shield only the electromagnetic wave of a specific frequency, so that an apparatus using electromagnetic waves of a similar frequency band is used. It is possible to effectively prevent malfunctions and information leakage in large-capacity information communication due to high-frequency electromagnetic waves. In particular, in the design of millimeter waves, since it also has thin film formability, it can be suitably used for the frequency band of a radar unit having millimeter waves. In addition, it can be suitably used for electronic devices and communication devices that use communication technology that uses electromagnetic waves in the GHz frequency band, vehicles that are equipped with them as a means of transportation, or transportation facilities that include all infrastructure for traffic control. can.

1: Radome 2: Case 3: Antenna 4: RF module 5: Control circuit board 6: Antenna chassis 7: RF chassis 8: Main lobe 9: First side lobe 10: Second side lobe 11: Back lobe 12: Flat antenna 13: Angle formed by the direction perpendicular to the plane of the plane antenna 14: Reflection attenuation spectrum 15: Electromagnetic wave attenuation at the peak of the reflection attenuation peak with the largest attenuation at the peak top Quantity I
16: Frequency of reflection attenuation peak with the largest attenuation at the peak top

Claims (12)

A laminated sheet for a radar unit, which is a laminated sheet used for a radar unit having an antenna substrate that emits millimeter waves, and is characterized by having all of the following features (1) to (3).
(1) Includes a laminated unit in which five or more layers A and B having different compositions are alternately laminated.
(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 having a peak top having a reflection attenuation amount RL of 15 dB or more. In the frequency band of 20 to 100 GHz, when the attenuation of the reflection attenuation peak with the largest attenuation of the reflection attenuation peak top is RLdB, the frequency is fGHz, and the total thickness of the laminated sheet is tmm, RL / (t × f). The laminated sheet for a radar unit according to claim 1, wherein the frequency is 0.4 or more and 15 or less. The invention according to claim 1 or 2, wherein at least one outermost layer is the A layer, and wA <wB is satisfied when the contents of the electromagnetic wave suppressing materials contained in the A layer and the B layer are wA and wB, respectively. Laminated sheet for radar unit. The laminated sheet for a radar unit according to any one of claims 1 to 3, wherein at least one of the electromagnetic wave suppression materials is a carbon material. The laminated sheet for a radar unit according to claim 4, wherein at least one of the carbon materials is carbon black. The major axis of the higher-order structure formed by the component contained most in the laminated sheet among the electromagnetic wave suppressing materials was defined as X nm, and the average layer thickness of the layers containing the component most among the A layer and the B layer was defined as Y nm. The laminated sheet for a radar unit according to any one of claims 1 to 5, wherein the X / Y is sometimes 0.01 or more and 10.0 or less. The layering for a radar unit according to any one of claims 1 to 6, wherein the total content of the electromagnetic wave suppressing material is 1% by mass or more and 15% by mass or less when all the components constituting the laminated sheet are 100% by mass. Sheet. The thickness of the laminated unit is tmm, and the real part εh'F / m and the imaginary part εh of the complex permittivity of the layer having a relatively high complex permittivity among the A layer and the B layer constituting the laminated unit. '' The laminated sheet for a radar unit according to any one of claims 1 to 7, which satisfies the following relational expression (A) or (B) when F / m is set.
(A) t≤0.75 and 0.17εh'+2.3≤εh''≤0.27εh'+3.37
(B) 0.75 <t≤1.5 and 0.02εh'+ 1≤εh''≤0.07εh'+1.9 The laminated sheet for a radar unit according to any one of claims 1 to 8, which is provided laterally or rearward when viewed from the millimeter wave transmission direction of the radar unit. The laminated sheet for a radar unit according to any one of claims 1 to 9, which is used as a housing including the antenna substrate. A radar unit comprising the laminated sheet for the radar unit according to any one of claims 1 to 10. A transportation system equipped with the laminated sheet for a radar unit according to any one of claims 1 to 10.

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