Radar radome

Abstract

This radome is for a radar that transmits and / or receives a radio wave having a high frequency. The radome for a radar is characterized by being a laminate comprising three layers of a skin layer including a resin, a heater, and a heat-insulating layer in the stated order.

Description

Technical Field

[0001] The present invention relates to a radome for a radar.

Background Art

[0002] In recent years, in order to mainly mount an automatic driving function and a collision prevention function for automobiles, a system for detecting obstacles and the like by a radar using high-frequency radio waves has been developed. However, generally, since high-frequency radio waves are greatly attenuated by water, for example, it is known that when water, snow, or the like adheres to the radome of a millimeter-wave radar, the performance of the radar deteriorates significantly. In order to cope with such a situation, for example, Patent Documents 1 to 3 describe that a heater is installed in a radome for an in-vehicle radar device to impart a snow melting and water removing function.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the above prior art, especially when melting snow and removing water using a heater while the vehicle is running, the heat generated by the heater cannot be efficiently utilized for heating the radome, and an increase in the power consumption of the heater has been a problem. In addition, since the power consumption of the heater required for removing water, snow, etc. differs significantly between when the vehicle is stopped and when it is running, it has been known that the radome may be damaged by heat when the vehicle suddenly stops from a running state (Patent Document 1). Furthermore, there are a portion directly heated by the heater and a portion that is not efficiently heated due to its distance from the heater, and it has been known that this can pose a problem in controlling the heater (Patent Document 3).

[0005] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a radome for a radar in which the power consumption of a heater is suppressed and temperature unevenness on the surface is reduced.

Means for Solving the Problems

[0006] The present invention is as follows. [1] A radome for transmitting and / or receiving high-frequency radio waves, which is a laminate composed of N layers (N is an integer of 3 or more) including an outer skin layer containing resin, a heater, and a heat insulating layer in this order, Regarding each layer existing between the back surface of the heater and the back surface of the redome, "the thermal resistance R of each layer (m·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)". 各層 (m 2 The thermal resistance R of each layer calculated by adding up all the thermal resistances R of each layer 各層 The thermal resistance R of the entire layer existing between the back surface of the heater and the back surface of the redome obtained by adding them all up is 0.01 to 1.0 m 2 ·K / W, The back surface of the heater is the surface on the side opposite to the skin layer side in the lamination direction, and the back surface of the redome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the redome. The minimum value of the value of Λ obtained by the following formula (B) is 0 .20 or less characterized by a radome.

Equation

[0007] According to the present invention, it is possible to provide a radome for a radar in which the power consumption of the heater is suppressed and the temperature unevenness on the surface is reduced. [Brief Description of the Drawings]

[0008]

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MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, embodiments for carrying out the present invention (hereinafter also referred to as "the present embodiments") will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made and implemented within the scope of the gist thereof.

[0010] [Radome] The radome of the present embodiment is a radome for a radar that transmits and / or receives high-frequency radio waves, and is a laminate including an outer skin layer containing resin, a heater, and a heat insulation layer in this order.

[0011] The radome of the present embodiment is used to protect a radar that transmits and / or receives high-frequency radio waves. By being protected by the radome of the present embodiment, the communication quality of the radar is stabilized, and a wide communication range can be realized. Examples of the radar that transmits and / or receives high-frequency radio waves include millimeter-wave radars and the like.

[0012] The shape and size of the radome are not particularly limited, and may be appropriately determined according to the shape and size of the radar for which the radome is used. However, from the viewpoint of having sufficient mechanical strength and high radio wave transmissivity, the thickness is preferably 1 mm or more, more preferably 3 mm or more, and preferably 30 mm or less, more preferably 10 mm or less, and still more preferably 7 mm or less.

[0013] The radome of the present embodiment may include other layers in addition to the three layers of the outer skin layer, the heater, and the heat insulation layer. The total number of layers including the three layers of the outer skin layer, the heater, and the heat insulation layer is not particularly limited, but is preferably 10 layers or less because it is easy to increase radio wave transmissivity and easy to manufacture. Further, the radome may include other layers between the skin layer and the heater as long as the effects of the present invention are not impaired. However, from the viewpoints of efficiently heating the skin layer by the heater, enhancing the radio wave transmissivity of the radome, and reducing costs, it is preferable not to include other layers therebetween. Further, other layers may be included between the heater and the heat insulating layer. However, from the viewpoints of enhancing the heat insulation property of the radome, enhancing the radio wave transmissivity of the radome, and reducing costs, it is preferable not to include other layers therebetween. The radome of the present embodiment particularly preferably consists only of the skin layer, the heater, and the heat insulating layer. Also, the layers constituting the radome may or may not be in close contact with each other. However, from the viewpoints of making it difficult for moisture, dust, etc. to enter between the layers, improving the mechanical strength (bending strength, bending rigidity, etc.) of the entire radome, and facilitating the construction of radio wave transmissivity, it is preferable that at least a part of each layer is in close contact with an adjacent layer by an adhesive or heat welding. When using an adhesive, since the adhesive itself affects the radio wave transmissivity as described later, it may be applied to a portion that does not affect the radio waves transmitted and received by the radar (for example, the outer peripheral portion of the radome).

[0014] When radio waves pass through the radome, interface reflection occurs at the interfaces between adjacent layers in the radome and at the interface between the radome and the air layer (the surface of the radome). When interference occurs due to the reflected waves and they reinforce each other, the influence of the reflection becomes large and the transmittance of the radio waves becomes small. Further, the interface reflection tends to increase as the difference in the magnitudes of the complex refractive indices of the incident-side layer and the outgoing-side layer at the interface increases. For example, for radio waves mainly incident from the front direction (radio waves incident at an incident angle of 0°), in one layer, when the thickness of the layer is close to an integer multiple of half the wavelength of the radio waves passing through the layer, the reflected waves generated at each interface (each surface of the layer) cancel each other out, and the reflectance can be reduced. By the reflected waves at each interface weakening each other as a whole, the interference due to reflection is reduced. However, generally, the difference in the magnitude of the complex refractive index is most likely to be large at the interface between the radome and the air layer (the surface of the radome), and the interface reflection tends to increase. Therefore, it is particularly preferable to adopt a configuration in which the reflected waves generated in the skin layer weaken each other. Therefore, when the radome of the present embodiment is a laminate composed of N layers (N is an integer of 3 or more) including an epidermal layer, a heater, and a heat insulating layer, it is preferable that the minimum value of the value of Λ obtained by the following formula (B) is 0.20 or less, more preferably 0.15 or less, still more preferably 0.12 or less, and even more preferably 0.10 or less.

Number

[0015] Generally, when a layer composed of an adhesive or bonding agent with a large magnitude of complex refractive index (large relative permittivity and dielectric loss tangent) is included (the layers are laminated by being bonded through an adhesive or bonding agent, etc.), the attenuation, refraction of radio waves, and interface reflection generated by the difference in the magnitude of the complex refractive index between adjacent layers tend to increase. Therefore, when the radome includes a layer composed of an adhesive or bonding agent, it is preferable that the thickness of the layer is thinner, and it is more preferable that the layer is not included in the range where the radio wave enters and exits (each layer is laminated directly in contact with each other without an adhesive or bonding agent). Examples of the above adhesives and bonding agents include pressure-sensitive adhesives, adhesives cured by heat, ultraviolet rays, etc., and adhesives applied in a molten state and solidified by cooling. Examples of the resin used in the above adhesives include acrylic resin, vinyl acetate resin, nitrile rubber resin, styrene-butadiene rubber, chloroprene rubber, starch, epoxy resin, cyanoacrylate resin, silicone rubber, etc.

[0016] Among the layers of the radome, especially for the thick layer with a thickness of 0.1 mm or more, the complex refractive index n i in terms of the magnitude N i is preferably 2.5 to 1.0, more preferably 2.0 to 1.0, and still more preferably 1.8 to 1.0. When the magnitude N i of the complex refractive index n i of each layer of the radome is within the above range, it is easy to reduce interface reflection, easy to improve the front transmittance, and easy to reduce the incident angle dependence of the radio wave transmittance. Also, the difference in the complex refractive index between adjacent interfaces tends to be small, and the change in the minimum value of Λ due to the increase or decrease in the thickness d i of each layer is small, so the design margin of the thickness of each layer can be increased, the manufacturing stability can be improved, and the incident angle dependence of the electromagnetic wave transmittance can be reduced. The maximum value of the difference in the magnitude of the complex refractive index between adjacent layers is preferably 1.2 or less, more preferably 1.0 or less, and still more preferably 0.8 or less. When the maximum value of the difference in the magnitude of the complex refractive index between adjacent layers is within the above range, the interface reflection at the interface between adjacent layers is reduced, so the radio wave transmittance is likely to be improved, and the incident angle dependence of the radio wave transmittance is reduced. Also, not only for the layers with the largest difference in the magnitude of the complex refractive index, but also for other layers, it is preferable that the difference in the magnitude of the complex refractive index is small. In this specification, "adjacent layers" means the layers adjacent to each other among the layers constituting the radome, and includes the air layer in contact with the surface of the radome. The complex refractive index of each layer of the radome (the complex refractive index n of the i-th layer i) can be measured by known methods and can be calculated from the relative permittivity and dielectric loss tangent according to the following formula. Also, the obtained complex refractive index n i from its magnitude N i can be calculated.

Equation

[0017] The radome of this embodiment preferably has a front transmittance (radio wave transmittance at an incident angle of 0°) of 80% or more, more preferably 90% or more, and even more preferably 95% or more at a specific radio wave frequency. In this specification, the "specific radio wave frequency" refers to any radio wave frequency transmitted and received by the radar. Generally, as the frequency increases, the straightness and attenuation of radio waves increase, and the incident angle dependence of the radio wave transmittance of the radome increases. Therefore, the radome of this embodiment is particularly suitable at frequencies of 1 to 100 GHz. The front transmittance can be controlled, for example, by adjusting the complex refractive index and / or thickness of each layer constituting the radome. Decreasing the minimum value of the Λ value increases the front transmittance.

[0018] In addition, for the radome of this embodiment, the oblique transmittance (TE-direction radio wave transmittance at an incident angle of 30°) at a specific radio wave frequency is preferably 50% or more, more preferably 70% or more, and still more preferably 80% or more. When the oblique transmittance at a specific radio wave frequency is within the above range, the dependence of the transmittance on the incident angle tends to be small, and it is easy to maintain a high transmittance over a wide range of angles. Further, even if the shape of the portion through which the radio wave of the radome passes has a structure having not only a plate shape but also a curved surface or a corner, since the dependence of the transmittance on the incident angle is small, it is less affected by the shape, and the degrees of freedom in the size, design, etc. of the radome and the radar are improved. Note that, in principle, the TE polarized wave has a higher dependence on the incident angle than the TM polarized wave with respect to the transmittance, and generally, the TE-direction radio wave transmittance tends to decrease as the incident angle increases. However, when the TE-direction radio wave transmittance at 30° is high, the decrease in the TE-direction radio wave transmittance accompanying the increase in the incident angle can be suppressed in the range of 0 to 30°. The oblique transmittance can be controlled, for example, by adjusting the complex refractive index and / or thickness of each layer constituting the radome. By reducing the complex refractive index, adjusting the layer structure, etc., the oblique transmittance increases.

[0019] The above-mentioned front transmittance and oblique transmittance can be obtained by measuring the radio wave attenuation amount of the radome by a known method, or by calculating from the information obtained by measuring the relative permittivity, dielectric characteristics, layer structure, thickness, etc. by a known method (for example, a method of calculating the reflection coefficient and transmission coefficient from the characteristic matrix and converting them into the transmittance and reflectance). Specifically, it can be measured by the method described in the examples below.

[0020] For the radome of this embodiment, from the viewpoint of enhancing radio wave permeability and from the viewpoint that the transmission / reception accuracy of the radar is likely to decrease due to the influence of the reflected wave, the front reflectance (radio wave reflectance at an incident angle of 0°) at a specific radio wave frequency is preferably 10% or less, more preferably 5% or less, and still more preferably 3% or less. Similarly, from the perspective of enhancing radio wave transparency, the perspective that the radar's transmission / reception accuracy is likely to decrease due to the influence of reflected waves, and the perspective of enhancing radio wave transparency for radio waves with a wide range of incident angles, the oblique reflectivity (TE-direction radio wave reflectivity at an incident angle of 30°) at a specific radio wave frequency is preferably 50% or less, more preferably 30% or less, and even more preferably 20% or less.

[0021] The above-mentioned front reflectivity and oblique reflectivity can be obtained by measuring the reflection attenuation amount of the radome by a known method, or by calculating from the information obtained by measuring the relative permittivity, dielectric properties, layer structure, thickness, etc. by a known method (for example, a method of calculating the reflection coefficient and transmission coefficient from the characteristic matrix and converting them into the transmittance and reflectivity).

[0022] The radome preferably has a thermal resistance R on the back side of the heater of 0.01 to 1.0 m 2 ·K / W, more preferably 0.01 to 0.90 m 2 ·K / W, and even more preferably 0.05 to 0.50 m 2 ·K / W. The higher the thermal resistance R on the back side of the heater, the higher the utilization efficiency of the heater can be, and the heating value and power consumption of the heater required to keep the outer surface of the radome at a constant appropriate temperature tend to be suppressed. However, the lower the thermal resistance R, the easier it is to reduce the thickness of the radome, so the radio wave absorption rate becomes smaller and the radio wave transparency tends to be excellent. Note that the thermal resistance R on the back side of the heater is calculated by adding up the thermal resistance R 各層 (m 2 ·K / W) of each layer existing between the back surface of the heater and the back surface of the radome (in other words, between the heater and the module), where "the thermal resistance R of each layer 各層 (m Note that the "back surface of the heater" is the surface on the main surface of the heater that is opposite to the surface on the epidermal layer side in the lamination direction, and the "back surface of the radome" is the surface perpendicular to the lamination direction among the surfaces that come into contact with the module when the module (radar module) is installed on the radome.

[0023] [[Epidermal layer]] The epidermal layer constituting the radome of this embodiment is the layer that constitutes the outer surface of the radome. The epidermal layer is not particularly limited as long as it is a layer containing resin, but it is preferably a resin plate made of resin.

[0024] Examples of the resin constituting the epidermal layer include the same ones as the thermoplastic resin and thermosetting resin contained in the heat insulation layer described later. From the viewpoints of mechanical strength and radio wave transmissivity, polyamide resin, polyester resin, polypropylene resin, polystyrene resin, polycarbonate resin, modified polyphenylene ether resin, etc. are suitable. The epidermal layer may optionally further contain additives such as flame retardants, glass fibers, carbon fibers, etc. However, since the relative permittivity and dielectric tangent generally tend to increase, from the viewpoints of improving radio wave transmissivity and reducing scattering and refraction, it is preferable that the above additives, glass fibers, carbon fibers, etc. are not contained or the content is small.

[0025] The manufacturing method of the epidermal layer is not particularly limited. For example, injection molding, extrusion sheet molding, sheet molding using a hot roll, or a known hot press method can be used.

[0026] The shape and size of the skin layer are not particularly limited and may be appropriately determined according to the shape and size of the dome, etc. However, from the perspective of having both sufficient mechanical strength and high radio wave permeability, the thickness is preferably 1 to 10 mm, more preferably 1 to 8 mm, and even more preferably 1 to 5 mm. In particular, from the perspective of increasing the front transmittance and improving the radio wave permeability, the thickness of the skin layer is preferably closer to λ / 2×L (where λ is the wavelength of the radio wave in the skin layer and L is a positive integer), and specifically, the minimum value of Λ (skin layer) represented by the following formula (A) is preferably 0.15 or less, more preferably 0.10 or less, and even more preferably 0.05 or less. In calculating Λ (skin layer), layers substantially integrated with the skin layer (such as a coating layer, a hard coat layer, etc.) are also included in the calculation. Among the values close to λ / 2×L for the thickness of the skin layer, from the perspective of good radio wave permeability in the front and diagonal directions and the perspective of being able to reduce the total thickness, the smaller the value of L (the smaller the thickness), the better.

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[0027] In the radome of this embodiment, in order to enhance the radio wave transmissivity of the skin layer, even if the thickness of the skin layer is made thinner than that of a conventional radome composed only of the skin layer, the overall thickness of the radome can be made sufficient by adjusting the thickness of the heat-insulating layer, thereby enabling the radome as a whole to maintain sufficient mechanical strength. Further, in particular, by using a foam or the like with high radio wave transmissivity for the heat-insulating layer, even if the overall thickness of the radome is increased to maintain sufficient mechanical strength, high radio wave transmissivity can be achieved for the radome as a whole. Thus, from the viewpoint of having both sufficient mechanical strength and high radio wave transmissivity as a radome, it is particularly preferable that the thickness of the skin layer of the radome of this embodiment is a value close to an integral multiple of λ / 2 (λ: wavelength of the electromagnetic wave passing through the skin layer), and the thickness of the radome is 3 mm or more.

[0028] The density of the skin layer is preferably 3 2.0 g / cm or less, more preferably 3 1.5 g / cm or less, and even more preferably 3 1.1 g / cm or less. When the density of the skin layer is within the above range, the magnitude of the complex refractive index becomes smaller, interface reflection can be reduced, and the incident angle dependence of the radio wave transmissivity is reduced. Also, from the viewpoint of mechanical strength, the density of the skin layer is preferably 3 0.1 g / cm or more, more preferably 3 0.3 g / cm or more, and even more preferably 3 0.5 g / cm or more. Note that the density of the skin layer can be obtained in the same manner as the method for measuring the density of the heat-insulating layer described in the examples below.

[0029] [[Heater]] The radome of this embodiment includes a heater for imparting a snow melting and water removing function to the radome. Generally, when water or ice is contained in or attached to a radome that transmits high-frequency radio waves, the radio wave transmissivity tends to deteriorate significantly. However, the radome of this embodiment includes a heater, so that water and ice can be removed, and deterioration of the radio wave transmissivity can be suppressed. The heater is not particularly limited, and a linear heater such as a heater wire, a planar heater such as a film heater (including a heater in which a linear heater is carried or laminated on a film containing a resin), etc. can be used. Since the heater is generally made of metal, its radio wave permeability is low. Therefore, from the viewpoint of reducing the influence on radio wave permeability, the thickness of the heater is preferably 0.1 mm or less, more preferably 0.05 mm or less, and even more preferably 0.3 mm or less. In the case of a linear heater or a heater including a linear heater, the line width of the metal heater wire is preferably 1 / 10 or less, more preferably 1 / 15 or less, and even more preferably 1 / 20 or less with respect to the wavelength used. Also, the ratio of the area occupied by the metal part of the linear heater or the heater including the linear heater to the area of the portion where radio waves enter and exit is preferably 10% or less, more preferably 5% or less. When the line width of the linear heater and the ratio of the area occupied by the metal part are within the above ranges, the influence of the linear heater on the radio wave permeability of the radome can be made sufficiently small.

[0030] Preferably, at least a part of the surface of the heater excluding the surface on the epidermis layer side is covered by a heat insulating layer. The "surface on the epidermis layer side" means the surface facing the epidermis layer, including not only the surface perpendicular to the lamination direction but also all the surfaces that can be visually recognized when the heater is taken out and viewed (hypothetically) from the epidermis layer side in the lamination direction. Also, "at least a part of the surface of the heater excluding the surface on the epidermis layer side is covered by the heat insulation layer" means that when paying attention to the surface of the heater excluding the surface on the epidermis layer side, all or a part of it is covered by the heat insulation layer, and it does not exclude the form in which a part of the surface on the epidermis layer side of the heater is also covered by the heat insulation layer. Moreover, not only the mode in which the heater is directly covered by the heat insulation layer but also the mode in which there is a gap (air) between the heat insulation layer and the heater and there is a part where the heat insulation layer covers the heater in a surrounding manner (for example, the heater wire is embedded in the groove provided in the heat insulation layer and there is a gap between the groove and the heater wire, etc.) shall be included. From the viewpoint of enhancing the heat insulation property of the radome and improving the utilization efficiency of the heater, it is preferable that 10% or more of the surface of the heater excluding the surface on the epidermis layer side is covered by the heat insulation layer, more preferably 50% or more, still more preferably 80% or more, and particularly preferably 100%. Also, from the same viewpoint, it is preferable that the heater is directly covered by the heat insulation layer.

[0031] [[Heat insulation layer]] The heat insulation layer constituting the radome of the present embodiment is disposed on the back side of the epidermis layer and the heater. Since the radome of the present embodiment has a heat insulation layer, it is superior in heat insulation property compared with those without a heat insulation layer, so the utilization efficiency of the heater can be improved, and the calorific value and power consumption of the heater required to keep the outer surface of the radome at an appropriate temperature constantly can be suppressed. Also, for example, when the radome is used for a millimeter-wave radar mounted on the front of a vehicle or the like, generally, during vehicle travel, the radome is cooled by the oncoming driving wind or the like, and heat is escaping from the radome. Usually, as the driving speed increases, the amount of heat escaping increases, so the amount of heat generated by the heater required to keep the outer surface of the radome at a constant appropriate temperature also becomes larger. Therefore, the amount of heat generated by the heater is controlled to be larger during driving than during parking. However, for example, when the vehicle makes an emergency stop and the control is delayed, the amount of heat generated by the heater becomes larger than the value required during parking, and the radome is overheated. In some cases, there is a risk that materials such as the resin constituting the radome will melt and catch fire. In the radome of this embodiment, as described above, since the amount of heat generated by the heater required can be suppressed compared to those without a heat insulation layer, the difference in the amount of heat generated by the heater between during parking and during driving can also be suppressed to be smaller. Even when the vehicle makes an emergency stop and the control is delayed, overheating of the radome, and thus the risk of failure and ignition of the radome and its peripheral components, can be reduced. Also, generally, in the skin layer of the radome, there are portions that are efficiently heated by the heater (such as directly above the heater wire and the central portion) and portions that are not efficiently heated by the heater (such as portions away from the heater wire), and a temperature difference occurs between them, that is, temperature unevenness may occur in the skin layer. When temperature unevenness occurs, water or ice may remain without being removed in the low-temperature portion. To prevent this, if the amount of heat generated by the heater is set according to the low-temperature portion, the other portions will have an excessive amount of heat generated, resulting in overheating, or the need to set the heater according to the low-temperature portion, which may increase power consumption. In the radome of this embodiment, as described above, since the utilization efficiency of the heater can be increased compared to those without a heat insulation layer, such temperature unevenness is reduced, and the possibility of water or ice remaining without being removed and the risk of overheated portions can be reduced.

[0032] The constituent material of the heat insulation layer is not particularly limited as long as it exhibits good radio wave permeability and excellent heat insulation properties inside the radome. However, it is preferably a foam and more preferably made of a foam because it is lightweight, has high heat insulation performance, has appropriate mechanical strength, and is easy to hold parts in the long term.

[0033] From the viewpoint of enhancing radio wave permeability and relaxing the requirements for thickness accuracy to improve manufacturability, the magnitude N2 of the complex refractive index of the heat insulation layer at a specific radio wave frequency is preferably 1.70 or less, more preferably 1.60 or less, and still more preferably 1.50 or less. The complex refractive index of the heat insulation layer can be measured by a known method and can be calculated from the relative permittivity and the dielectric loss tangent according to the following formula. Also, the magnitude N2 can be calculated from the obtained complex refractive index n2. [Number] (n2: complex refractive index of the heat insulation layer, j: imaginary unit, ε2: complex relative permittivity of the heat insulation layer, μ2: complex relative permeability of the heat insulation layer, tanδ: dielectric loss tangent, ε2’: relative permittivity, ε2’’: relative dielectric loss)

[0034] (Foam) The foam may be obtained by foaming a resin composition containing a base resin containing a thermoplastic resin or a thermosetting resin and optionally further containing additives such as a flame retardant. Examples of the foam include an extrusion foam, an injection foam, a bead foam (a foam made of foamed particles), a stretch foam, a solvent extraction foam, etc., and each refers to a foam produced by the extrusion foaming method, the injection foaming method, the bead foaming method, the stretch foaming method, or the solvent extraction foaming method described later. As the foam, there are a foam with an open-cell structure in which air or gas in the foam can flow in and out, and a foam with a closed-cell structure in which gas or air in the foam is retained by a resin wall or the like. However, from the viewpoints that the gas or air contained in the foam does not dissipate from the bubbles, and it is easy to effectively improve the heat insulation and mechanical strength, that the risk of occurrence of condensation or the like is small because the gas or air contained in the foam is retained in the bubbles, and that the water absorption is likely to be small, it is preferable that the foam is a foam with a closed-cell structure. Examples of the foam with a closed-cell structure include an injection foam and a bead foam. Among them, it has good formability, can omit the secondary processing of the foam by pre-forming, can prevent the cut surface from being exposed and reduce the generation of dust, etc., can reduce the entry of resin or the like into the cut surface of the foam when adhering to the resin plate layer, and can obtain good appearance, adhesion, and radio wave permeability. Since it has a closed-cell structure, it is easy to enhance the heat insulation and mechanical strength, and it is easy to control the cell diameter and distribution. Therefore, it is preferably a bead foam.

[0035] The content of the base resin is preferably 20% by mass or more, more preferably 40% by mass or more, still more preferably 60% by mass or more, particularly preferably 70% by mass or more, and preferably 100% or less, more preferably 95% or less, based on 100% by mass of the resin composition. In order to lower the dielectric constant and dielectric loss tangent, it is preferable that the base resin is made of a resin with low polarity. Also, from the same viewpoint, it is preferable that the resin has low water absorption.

[0036] Examples of the thermoplastic resin include polyphenylene ether-based resins, polystyrene-based resins, polyethylene-based resins, polyamide-based resins, polypropylene-based resins, ABS resins, vinyl chloride-based resins, acrylic resins, methyl methacrylate resins, nylon-based resins, fluorine-based resins, polycarbonate-based resins, polyurethane resins, polyester-based resins, etc. From the viewpoints of heat resistance, economy, and foamability, polyphenylene ether-based resins, polystyrene-based resins, polyethylene-based resins, polyamide-based resins, polypropylene-based resins, acrylic resins, and polycarbonate-based resins are preferable. These may be used alone or in combination of two or more kinds. As methods for reducing the relative permittivity and dielectric loss tangent of the base resin used for the foam, examples include selecting as the base resin those having a low density of the unfoamed resin, a low polarity of the unfoamed resin, few polar groups at the molecular chain ends, and the like. Particularly preferred resins from this viewpoint include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluorine resins, liquid crystal polymers, polyphenylene sulfide resins, and the like. Among them, considering the viewpoints of processability, cost, and flame retardancy, polyolefin resins, polystyrene resins, and polyphenylene ether resins are preferred.

[0037] The polyphenylene ether (PPE) - based resin may be a polymer represented by the following general formula (I). Here, in general formula (I), R 1 , R 2 , R 3 and R 4 each independently represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a phenyl group, or a haloalkyl group or haloalkoxy group having at least 2 carbon atoms between the halogen and the benzene ring in general formula (I) and not containing a 3α - carbon atom. Also, in general formula (I), n is an integer representing the degree of polymerization.

Chemical formula

[0038] Examples of polyphenylene ether resins include poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-diethyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,4-phenylene) ether, poly(2-methyl-6-propyl-1,4-phenylene) ether, poly(2,6-dipropyl-1,4-phenylene) ether, poly(2-ethyl-6-propyl-1,4-phenylene) ether, poly(2,6-dibutyl-1,4-phenylene) ether, poly(2,6-dilauryl-1,4-phenylene) ether, poly(2,6-diphenyl-1,4-diphenylene) ether, poly(2,6-dimethoxy-1,4-phenylene) ether, poly(2,6-diethoxy-1,4-phenylene) ether, poly(2-methoxy-6-ethoxy-1,4-phenylene) ether, poly(2-ethyl-6-stearyloxy-1,4-phenylene) ether, poly(2,6-dichloro-1,4-phenylene) ether, poly(2-methyl-6-phenyl-1,4-phenylene) ether, poly(2,6-dibenzyl-1,4-phenylene) ether, poly(2-ethoxy-1,4-phenylene) ether, poly(2-chloro-1,4-phenylene) ether, poly(2,6-dibromo-1,4-phenylene) ether, etc., but are not limited thereto. Among these, in particular, R 1 and R 2 are alkyl groups having 1 to 4 carbon atoms, and those in which R 3 and R 4 are hydrogen or alkyl groups having 1 to 4 carbon atoms are preferred. These may be used alone or in combination of two or more.

[0039] In this embodiment, the content of the polyphenylene ether resin is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and still more preferably 35 to 60% by mass with respect to 100% by mass of the base resin. When the content of the PPE resin is 20% by mass or more, it is easy to obtain excellent heat resistance and flame retardancy, and it is easy to reduce the dielectric constant and the dielectric loss tangent. Also, when the content of the PPE resin is 80% by mass or less, it is easy to obtain excellent processability.

[0040] The weight average molecular weight (Mw) of the polyphenylene ether-based resin is preferably from 20,000 to 60,000. The weight average molecular weight (Mw) is the weight average molecular weight determined by measuring the resin by gel permeation chromatography (GPC) and using a calibration curve (created using the peak molecular weight of commercially available standard polystyrene) obtained from the measurement of the molecular weight of the peaks in the chromatogram.

[0041] The polystyrene-based resin refers to a homopolymer of styrene and styrene derivatives, and a copolymer having styrene and styrene derivatives as the main component (a component contained in the polystyrene-based resin at 50% by mass or more). Examples of the styrene derivative include o-methylstyrene, m-methylstyrene, p-methylstyrene, t-butylstyrene, α-methylstyrene, β-methylstyrene, diphenylethylene, chlorostyrene, bromostyrene, and the like.

[0042] Examples of the homopolymer polystyrene-based resin include polystyrene, polyα-methylstyrene, polychlorostyrene, and the like. Examples of the polystyrene resin of the copolymer include binary copolymers such as styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, styrene-maleimide copolymer, styrene-N-phenylmaleimide copolymer, styrene-N-alkylmaleimide copolymer, styrene-N-alkyl-substituted phenylmaleimide copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-n-alkyl acrylate copolymer, styrene-n-alkyl methacrylate copolymer, ethyl vinyl benzene-divinyl benzene copolymer; ternary copolymers such as ABS, butadiene-acrylonitrile-α-methylbenzene copolymer; graft copolymers such as styrene graft polyethylene, styrene graft ethylene-vinyl acetate copolymer, (styrene-acrylic acid) graft polyethylene, styrene graft polyamide; and the like. These may be used alone or in combination of two or more.

[0043] Examples of the polyethylene resin include resins such as high-density polyethylene, low-density polyethylene, linear low-density polyethylene, copolymer of ethylene and α-olefin, propylene-ethylene copolymer. These may be used alone or in combination of two or more. In addition, these polyethylene resins may have a crosslinked structure as appropriate with a crosslinking agent or the like.

[0044] Examples of the polyamide resin include polyamide, polyamide copolymer, and mixtures thereof. The polyamide resin may include polymers obtained by self-condensation of aminocarboxylic acid, ring-opening polymerization of lactam, and polycondensation of diamine and dicarboxylic acid. Examples of the polyamide include nylon 66, nylon 610, nylon 612, nylon 46, nylon 1212, etc. obtained by polycondensation of diamine and dicarboxylic acid, and nylon 6, nylon 12, etc. obtained by ring-opening polymerization of lactam. Examples of the polyamide copolymer include nylon 6 / 66, nylon 66 / 6, nylon 66 / 610, nylon 66 / 612, nylon 66 / 6T (where T represents a terephthalic acid component), nylon 66 / 6I (where I represents an isophthalic acid component), nylon 6T / 6I, and the like. Examples of these mixtures include a mixture of nylon 66 and nylon 6, a mixture of nylon 66 and nylon 612, a mixture of nylon 66 and nylon 610, a mixture of nylon 66 and nylon 6I, a mixture of nylon 66 and nylon 6T, and the like. These may be used alone or in combination of two or more.

[0045] In this embodiment, from the viewpoint of the processability of the foam, the content of the above thermoplastic resin other than the PPE-based resin is preferably 10 to 100% by mass, more preferably 20 to 80% by mass, based on 100% by mass of the base resin.

[0046] Examples of the thermosetting resin include phenolic resin, epoxy resin, unsaturated polyester resin, polyurethane, melamine resin, etc. Among them, phenolic resin and melamine resin are preferred. These may be used alone or in combination of two or more.

[0047] Examples of the additive include flame retardant, flame retardant aid, heat stabilizer, antioxidant, antistatic agent, inorganic filler, dripping inhibitor, ultraviolet absorber, light absorber, plasticizer, release agent, dye pigment, rubber component, resin other than the above base resin, etc., and can be added within a range that does not impair the effects of the present invention.

[0048] The content of the additive is preferably 0 to 40 parts by mass, more preferably 5 to 30 parts by mass, based on 100 parts by mass of the base resin.

[0049] Here, the flame retardant is not particularly limited, and examples include organic flame retardants and inorganic flame retardants. Examples of organic flame retardants include halogen-based compounds typified by bromine compounds, phosphorus-based compounds, and non-halogen-based compounds typified by silicone-based compounds. Examples of inorganic flame retardants include metal hydroxides typified by aluminum hydroxide and magnesium hydroxide, and antimony-based compounds typified by antimony trioxide and antimony pentoxide. These may be used alone or in combination of two or more.

[0050] Among the above flame retardants, from the viewpoint of environmental properties, non-halogen-based organic flame retardants are preferred, and phosphorus-based flame retardants and silicone-based flame retardants are more preferred.

[0051] As the phosphorus-based flame retardant, those containing phosphorus or a phosphorus compound can be used. Examples of phosphorus include red phosphorus. Examples of phosphorus compounds include phosphate esters and phosphazene compounds having a bond between a phosphorus atom and a nitrogen atom in the main chain. Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, tricyclohexyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyldiphenyl phosphate, dicresylphenyl phosphate, dimethylethyl phosphate, methyldibutyl phosphate, ethyldipropyl phosphate, hydroxyphenyldiphenyl phosphate, resorcinol bisdiphenyl phosphate, etc. Also included are phosphate ester compounds of these modified with various substituents and various condensed types of phosphate ester compounds. Among these, from the viewpoints of heat resistance, flame retardancy, and foaming properties, triphenyl phosphate and condensed type phosphate ester compounds are preferred. These may be used alone or in combination of two or more.

[0052] In addition, examples of silicone-based flame retardants include (mono- or poly-)organosiloxanes. Examples of (mono- or poly-)organosiloxanes include monoorganosiloxanes such as dimethylsiloxane and phenylmethylsiloxane; polydimethylsiloxane and polyphenylmethylsiloxane obtained by polymerizing these; and organopolysiloxanes such as copolymers thereof. In the case of organopolysiloxanes, the bonding groups of the main chain and branched side chains are hydrogen, an alkyl group, or a phenyl group, preferably a phenyl group, a methyl group, an ethyl group, or a propyl group, but are not limited thereto. The terminal bonding groups may be a hydroxyl group, an alkoxy group, an alkyl group, or a phenyl group. There are no particular restrictions on the shape of the silicones, and any shape such as oil, gum, varnish, powder, or pellet can be used. These may be used alone or in combination of two or more.

[0053] The content of the flame retardant may be within the range of the content of the additive. When the base resin is 100 parts by mass, it is preferably 0 to 30 parts by mass, more preferably 5 to 25 parts by mass. The more flame retardant added, the easier it is to obtain the effect of improving the flame retardancy of the foam. However, generally, adding a flame retardant tends to increase the dielectric constant and dielectric tangent.

[0054] Examples of the rubber component include, but are not limited to, butadiene, isoprene, 1,3-pentadiene, etc. It is preferable that these are dispersed in a particulate form in a continuous phase composed of a polystyrene-based resin. As a method of adding these rubber components, the rubber component itself may be added, or a resin such as a styrene-based elastomer and a styrene-butadiene copolymer may be used as a rubber component supply source. When adding a rubber component, the content of the rubber component may be within the range of the content of the additive. Assuming the base resin is 100 parts by mass, 0.3 to 15 parts by mass is preferred, 0.5 to 8 parts by mass is more preferred, and 1 to 5 parts by mass is even more preferred. When it is 0.3 parts by mass or more, the resin has excellent flexibility and elongation, the foam cell membrane is less likely to rupture during foaming, and a foam with excellent molding processability and mechanical strength can be easily obtained.

[0055] In this embodiment, in order to improve the flame retardancy of the redome, it is preferable to add more flame retardant to the resin composition. However, when the addition amount of the flame retardant increases, it has an adverse effect on the dielectric properties and foamability of the foam. In such a case, the rubber component is preferably used to impart foamability to the resin composition. In particular, in bead foaming in which the temperature is gradually increased from room temperature and the resin is foamed in a non-molten state, the above rubber component is important.

[0056] (Method for manufacturing a foam) The method for manufacturing the foam of this embodiment is not particularly limited, and examples include an extrusion foaming method, an injection foaming method, a bead foaming method (in-mold foaming method), a stretching foaming method, a solvent extraction foaming method, etc. The extrusion foaming method is a method of obtaining a plate-shaped, sheet-shaped, or columnar foam having a certain cross-sectional shape by injecting an organic or inorganic foaming agent into a molten resin using an extruder and releasing the pressure at the extruder outlet. The injection foaming method is a method of obtaining a foam having pores by injection molding a resin having foamability and foaming it in a mold. The bead foaming method (in-mold foaming method) is a method of obtaining a foam by filling foaming particles into a mold, heating them with steam or the like to expand the foaming particles, and simultaneously thermally fusing the foaming particles together. The stretching foaming method is a method of generating microvoids by stretching a resin in which additives such as fillers have been previously kneaded in the resin to produce a foam. The solvent extraction foaming method is a method of producing a foam by adding an additive that dissolves in a predetermined solvent to a resin, immersing a molded product in the predetermined solvent, and extracting the additive.

[0057] In the case of extrusion foaming, the resulting foam becomes plate-shaped, sheet-shaped, etc. To process this, a cutting step of cutting it into a desired shape, a heat bonding step of bonding the cut parts together, etc. are required. On the other hand, in the case of the bead foaming method, since a mold of a desired shape is created and filled with foaming particles for molding, it is easy to mold the foam into a finer shape or a complex shape. Even in the case of the injection foaming method, it is possible to mold the foam into a complex shape. However, in the case of bead foaming, it is easy to increase the foaming ratio of the foam, and in addition to heat insulation properties, flexibility is easily exhibited.

[0058] The blowing agent is not particularly limited, and generally used gases can be used. Examples include inorganic gases such as air, carbon dioxide, nitrogen gas, oxygen gas, ammonia gas, hydrogen gas, argon gas, helium gas, neon gas, etc.; fluorocarbons such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12), chlorodifluoromethane (R22), tetrachlorodifluoroethane (R112), dichlorofluoroethane (R141b), chlorodifluoroethane (R142b), difluoroethane (R152a), HFC-245fa, HFC-236ea, HFC-245ca, HFC-225ca, etc.; saturated hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, etc.; ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran, tetrahydropyran, etc.; ketones such as dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, ethyl n-butyl ketone, etc.; alcohols such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, t-butyl alcohol, etc.; carboxylic acid esters such as methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl propionate, ethyl propionate, etc.; chlorinated hydrocarbons such as methyl chloride, ethyl chloride, etc. These may be used alone or in combination of two or more.

[0059] From the viewpoint of flame retardancy, it is preferable that the foaming agent has no or little flammability and combustion-supporting properties. From the viewpoint of gas safety, an inorganic gas is more preferable. Further, inorganic gases are less soluble in resins than organic gases such as hydrocarbons, and gas is likely to escape from the resin after the foaming process or the molding process. Therefore, there is also an advantage that the dimensional stability of the foam over time after molding is more excellent. Furthermore, when an inorganic gas is used, plasticization of the resin due to residual gas is less likely to occur, and there is also an advantage that excellent heat resistance can be exhibited at an earlier stage without going through processes such as aging. Among inorganic gases, carbon dioxide gas is preferable from the viewpoints of solubility in resins and ease of handling. In addition, hydrocarbon-based organic gases generally have high flammability, and when they remain in the foam, the flame retardancy tends to deteriorate.

[0060] The foam of this embodiment is preferably manufactured by the above-described bead foaming method and preferably comprises foamed particles. By performing molding using the bead foaming method, the formability of the radome can be improved.

[0061] The foamed particles used in the bead foaming method can be obtained by causing a foaming agent to be contained (impregnated) in a base resin to cause foaming. Specifically, for example, according to the method described in Example 1 of JP-A-4-372630, a base resin (in pellet form, bead form, etc.) is housed in a pressure-resistant container, the gas in the container is replaced with dry air, and then a foaming agent (gas) is press-fitted to impregnate the base resin with the foaming agent (gas). After that, the pressure is released, and the base resin pellets are transferred from the pressure container to a foaming furnace. A method of manufacturing foamed particles by heating and foaming the base resin pellets with pressurized steam while rotating a stirring blade in the foaming furnace can be mentioned. The conditions for impregnating the base resin with the foaming agent (gas) are not particularly limited. From the viewpoint of promoting the impregnation of the foaming agent (gas) into the base resin more efficiently, for example, the impregnation pressure is preferably 0.3 to 30 MPa, the impregnation temperature is preferably -20 to 100°C, and the impregnation time is preferably 10 minutes to 96 hours. Further, the maximum steam pressure of the pressurized steam in the foaming furnace is preferably 30 to 700 kPa·G from the viewpoints of easily obtaining a desired magnification and improving the appearance. In the method for producing the above expanded particles, the time from the completion of pressure release (release of impregnation pressure) in the pressure-resistant container to the start of heating with pressurized steam in the foaming furnace is preferably less than 600 seconds, more preferably within 300 seconds, still more preferably within 120 seconds, and particularly preferably within 60 seconds. When the time is within the above range, it is possible to suppress the non-uniform diffusion of the gas impregnated into the base resin, so that the cell diameter can be made uniform and the increase in the cell diameter can be prevented.

[0062] The method for forming a foam using the expanded particles is not particularly limited. For example, a method of filling the expanded particles into the cavity of a molding die, heating to cause expansion, and simultaneously heat-sealing the expanded particles together, and then solidifying the product by cooling to form a molded article can be mentioned. The method for filling the expanded particles is not particularly limited, and known methods can be used. Before filling the expanded particles into the cavity of the molding die, it is preferable to perform a pressurizing treatment on the expanded particles with a gas. By applying a certain gas pressure to the cells of the expanded particles, the expanded particles constituting the obtained foam can be firmly fused together, and the rigidity and appearance of the molded article can be improved. The gas used for the pressurizing treatment is not particularly limited, but air and inorganic gases are preferable from the viewpoints of ease of handling and economy. The method for the pressurizing treatment is not particularly limited, and examples include a method of filling the expanded particles into a pressurizing container, introducing a pressurizing gas, and increasing the pressure to a maximum pressure of 0.1 to 20 MPa over 10 minutes to 96 hours to supply the gas into the pressurizing container. The heating method when molding the expanded particles includes heating using a heat medium such as steam, heating with a heater such as an IR heater, heating using microwaves, and the like. When heating using a heat medium, a general-purpose heat medium is preferable, and steam is preferable from the viewpoint of efficiently heating the resin.

[0063] In this embodiment, the method for processing the foam into the target shape is not particularly limited, and examples include a method of filling foam particles or molten resin into a mold and molding, a method of cutting with a blade such as a saw blade or a die-cutting blade, a method of cutting with a mill, and a method of bonding a plurality of foams with heat or an adhesive.

[0064] From the viewpoint of reducing the magnitude of the complex refractive index by reducing the relative permittivity and dielectric loss tangent, thereby facilitating an increase in the radio wave transmittance and reducing the incidence angle dependence of the radio wave transmittance, the expansion ratio of the foam is preferably 1.2 (cm 3 / g) or more, more preferably 1.5 (cm 3 / g) or more, and still more preferably 1.7 (cm 3 / g) or more. Also, from the viewpoint of improving the mechanical strength, the expansion ratio of the foam is preferably 30 (cm 3 / g) or less, more preferably 15 (cm 3 / g) or less, and still more preferably 10 (cm 3 / g) or less.

[0065] The shape and size of the heat insulation layer are not particularly limited and may be appropriately determined according to the shape and size of the radome, etc. However, the thickness is preferably 1 to 30 mm, more preferably 1 to 10 mm, and still more preferably 1 to 5 mm, from the viewpoint of ensuring heat insulation and mechanical strength while enhancing radio wave permeability. Note that the expansion ratio of the foam can be specifically determined by the method described in the examples below.

[0066] The density of the heat insulation layer is preferably 0.01 to 1.2 g / cm 3 more preferably 0.02 to 1.0 g / cm 3 and still more preferably 0.05 to 0.5 g / cm 3 . When the density of the heat insulation layer is within the above range, excellent heat insulation can be exhibited, and it is easy to achieve both the rigidity and radio wave permeability of the radome. Note that the density of the heat insulation layer can be specifically measured by the method described in the examples.

[0067] When the heat insulation layer is a foam in particular, since it generally contains air, it is flammable. When it is used as a radome, in order to prevent it from spreading in case of ignition, flame retardancy is important. Therefore, the heat insulation layer preferably has a flame retardancy of V-2 or higher according to the UL94 standard, more preferably V-1 or higher, and still more preferably V-0. The flame retardancy can be varied by the type of resin and the type and content of the flame retardant used together with the resin during manufacturing. By providing the heat insulation layer with high flame retardancy, even if combustion occurs due to a short circuit or ignition in a radar or heater that transmits and receives radio waves, the spread of combustion can be suppressed. Note that the flame retardancy of the heat insulation layer according to the UL94 standard can be specifically measured by the method described in the examples.

[0068] Also, when it is close to a heat generating part such as a heater or a radar, in order to suppress the heat insulation property from deforming or deteriorating due to temperature, it is preferable that the heat insulation layer has high heat resistance. The heat resistance can be confirmed by referring to the dimensional stability at high temperature (Method B) described in JIS K6767 and checking the temperature at which the dimensional change exceeds 1%. The temperature at which the dimensional change exceeds 1% is preferably 70°C or higher, more preferably 80°C or higher, and still more preferably 100°C or higher.

[0069] From the viewpoint of enhancing the heat insulation property, the thermal conductivity of the heat insulation layer is preferably 1.0 W / K·m or less, more preferably 0.2 W / K·m or less, and still more preferably 0.1 W / K·m or less. Note that the thermal conductivity of the heat insulation layer can be specifically measured by the method described in the examples.

[0070] For each layer of the radome of this embodiment, the relative permittivity at a specific radio wave frequency is preferably 1.00 to 4.00, more preferably 1.00 to 3.00, and still more preferably 1.00 to 2.50. Further, for each layer of the radome of the present embodiment, the dielectric loss tangent tanδ at a specific radio wave frequency is preferably 0.05 or less, more preferably 0.01 or less, and even more preferably 0.005 or less. As a method for reducing the relative permittivity and dielectric loss tangent tanδ of the base resin used for each layer of the radome, examples include selecting as the base resin those with a low density of unfoamed resin, those with a low polarity of unfoamed resin, those with few polar groups at the molecular chain ends, and the like. From this perspective, particularly suitable resins include polyolefin resins, polystyrene resins, polyphenylene ether resins, polyimide resins, fluorine resins, liquid crystal polymers, polyphenylene sulfide resins, and the like. Among them, considering the viewpoints of processability, cost, and flame retardancy, polyolefin resins, polystyrene resins, and polyphenylene ether resins are preferred. Further, for the foam, in addition to the selection of the resin described above, the relative permittivity and dielectric loss tangent can be further reduced by increasing the expansion ratio (decreasing the density). Specifically, the relative permittivity and dielectric loss tangent tanδ of each layer can be measured by the method described in the examples below.

[0071] [Method for manufacturing radome] The manufacturing method of the radome of this embodiment is not particularly limited. For example, when the radome consists only of an outer skin layer, a heater, and a heat insulation layer, a recess (for example, when the heater is a heater wire, a groove for accommodating the heater wire) for installing (accommodating) the heater in the heat insulation layer is formed. After installing the heater in the recess, a method of arranging the outer skin layer (or the raw material resin of the outer skin layer) and the heat insulation layer with the heater installed in a mold and heat-fusing them; a method of heating and melting the adhesive surfaces of the outer skin layer and the heat insulation layer with the heater installed using a heat gun or the like and bonding them; a method of bonding at least two or more of the outer skin layer, the heater, and the heat insulation layer with an adhesive; particularly when the heat insulation layer is composed of a foam, when manufacturing the foam by an in-mold forming method such as the bead foaming method or the injection foaming method, the outer skin layer (or the raw material resin of the outer skin layer) and the heater are also arranged in the mold, and a method of heat-fusing each layer simultaneously with manufacturing the foam; a method of arranging the heater and the foam in the mold when manufacturing the outer skin layer by an in-mold forming method such as injection molding, and heat-fusing each layer simultaneously with forming the outer skin layer, etc. can be mentioned. Also, as described above, since the adhesive has a large complex refractive index and tends to increase the interfacial reflection, it is preferable that each layer is bonded without using the adhesive, or the adhesive is not included in the portion where radio waves enter and exit.

Example

[0072] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples at all.

[0073] The measurement and evaluation methods used in the examples and comparative examples will be described below.

[0074] [(1) Foaming ratio of the foam] Referring to the production method of each foam used as the heat insulation layer, a sample was produced with a size of 30 mm square and a thickness of 10 mm as a guide, the mass W [g] of the sample was measured, and the value (V / W) obtained by dividing the sample volume V [cm 3 by the mass W was taken as the foaming ratio (cm 3 / g).

[0075] [(2) Density of the heat insulation layer] With reference to the method for producing the heat insulation layer, samples were produced with a size of 30 mm square and a thickness of 10 mm as a guide. The mass W [g] of the samples was measured, and the density (g / cm 3 ) was calculated by dividing by the sample volume V [cm 3 .

[0076] [(3) Flame retardancy of the heat insulation layer] Regarding the heat insulation layer, a test was conducted in accordance with the UL-94 vertical method (20 mm vertical combustion test) of the US UL standard to evaluate the flame retardancy. The details of the measurement method are shown below. With reference to the method for producing the heat insulation layer, five test pieces with a length of 125 mm, a width of 13 mm, and a thickness of 5 mm were produced and used. The test pieces were vertically attached to the clamp, and indirect flame application with a 20 mm flame for 10 seconds was performed twice, and the combustion behavior was used to determine V-0, V-1, and V-2. V-0: For both the first and second times, the duration of flaming combustion is within 10 seconds. Furthermore, the total of the duration of flaming combustion and the duration of non-flaming combustion for the second time is within 30 seconds. Furthermore, the total of the flaming combustion times of the five test pieces is within 50 seconds, there is no sample that burns up to the position of the fixing clamp, and there is no cotton ignition due to combustion droppings. V-1: For both the first and second times, the duration of flaming combustion is within 30 seconds. Furthermore, the total of the duration of flaming combustion and the duration of non-flaming combustion for the second time is within 60 seconds. Furthermore, the total of the flaming combustion times of the five test pieces is within 250 seconds, there is no sample that burns up to the position of the fixing clamp, and there is no cotton ignition due to combustion droppings. V-2: For both the first and second times, the duration of flaming combustion is within 30 seconds. Furthermore, the total of the duration of flaming combustion and the duration of non-flaming combustion for the second time is within 60 seconds. Furthermore, the total of the flaming combustion times of the five test pieces is within 250 seconds, there is no sample that burns up to the position of the fixing clamp, and there is cotton ignition due to combustion droppings. In addition, those that do not fall under any of the above V-0, V-1, and V-2 were regarded as non-conforming (×).

[0077] [(4) Thermal conductivity of the heat insulation layer] The heat insulation layer was cut into a size of φ50mm×1mm thick, and the thermal conductivity (W / K·m) at a temperature of 23°C was measured in accordance with ASTM E1530 using a DTC-300 manufactured by TA Instruments.

[0078] [(5) Magnitude of the complex refractive index of the heat insulation layer] [[Relative permittivity and dielectric loss tangent tanδ of the heat insulation layer]] A sample with a size of 450mm×450mm×10mm thick was cut out from the heat insulation layer and prepared. Subsequently, the sample was set in the transmission attenuation measurement jig with a dielectric lens of the dielectric constant and dielectric loss tangent measuring device DPS10-02 manufactured by KEYCOM, and the transmission attenuation amount and phase change amount were measured under the conditions of room temperature (temperature 26°C, humidity 60%). Based on the obtained results and the thickness of the sample, fitting was performed between the calculated values and measured values of the transmission attenuation amount and phase change amount, and the relative permittivity and dielectric loss tangent when the fitting was the best were obtained and used as the measured values of the relative permittivity and dielectric loss tangent. [[Complex refractive index n2 of the heat insulation layer and its magnitude N2]] According to the following formula, the complex refractive index n2 of the heat insulation layer was calculated from the relative permittivity and dielectric loss tangent obtained from the [[relative permittivity and dielectric loss tangent tanδ of the heat insulation layer]]. Also, the magnitude N2 was calculated from the obtained complex refractive index n2.

Equation

[0079] [(6) Λ (skin layer) of the skin layer] The relative permittivity, dielectric loss tangent tanδ, complex refractive index n1, and magnitude N1 of the complex refractive index of the skin layer were obtained, and Λ (skin layer) of the skin layer was calculated by the following formula (A).

Equation

Equation

[0080] [(7) Λ of the radome] Relative permittivity, dielectric loss tangent tanδ, complex refractive index n of each layer of the radome i , Magnitude N of the complex refractive index i were obtained, and Λ of the radome was calculated by the following formula (B).

Equation

[0081] [(8) Power consumption and heat generation of the heater] Regarding the radome, the heater power consumption (W) when maintaining the surface layer surface at 10°C at an outside air temperature of -10°C was measured according to the following method. [[Model for calculating heater power consumption (W)]] The components of the radome model (skin layer 1, heater 2, insulation layer 3, module 4, and heat sink 5) for calculating the heater power consumption (W) are shown in Fig. 1. ​Also, the structures of the skin layer 1, heater 2, heat insulation layer 3, module 4, and heat sink 5 are shown in FIGS. 2 to 6 respectively. The values (dimension values) of each shape parameter are shown in Tables 1 and 2. As shown in FIG. 7, the model without the heat insulation layer for the comparative example is composed of the skin layer 1, heater 2, module 4, and heat sink 5. FIG. 8 shows the cross-section when the model without the heat insulation layer shown in FIG. 7 is cut by the plane along line A - A' in FIG. 7(b). The heater 2 is joined to the skin layer 1. A 10 - mm gap 6 is provided between the skin layer 1 and the module 4 as shown in FIG. 7(c). The heat sink 5 is joined to the module 4. The thickness 7 of the skin layer 1 is shown in FIG. 8. As shown in FIG. 9, the model with the heat insulation layer for the example is composed of the skin layer 1, heater 2, heat insulation layer 3, module 4, and heat sink 5. FIG. 10 shows the cross-section when the model with the heat insulation layer shown in FIG. 9 is cut by the plane along line A - A' in FIG. 9(b). The heater 2 is joined to the skin layer 1 and the heat insulation layer 3. The heat insulation layer 3 is joined to the module 4. The heat sink 5 is joined to the module 4. The thickness 7 of the skin layer 1 and the thickness 8 of the heat insulation layer 3 are shown in FIG. 10. [[Surface area to be considered]] FIG. 11 shows the region 9 that should be maintained at 10°C on the surface of the skin layer 1. The region 9 is the region obtained by projecting the region where the module 4 exists onto the surface of the skin layer 1.

[0082]

Table 1

[0083]

Table 2

[0084] [[Calculation method of heater power consumption (W)]] The mesh was cut and divided into elements for the above [model for calculating the heater power consumption (W)], and the temperature at each position when the heater 2 generates heat was calculated by a steady heat conduction analysis based on the finite element method. It is assumed that the amount of heat generated by the heater 2 is consistent with the heater power consumption (W). By repeatedly performing the finite element method calculation, the heater power consumption (W) was investigated such that the minimum temperature in the region 9 becomes 10 °C. [[Heat transfer analysis]] The steady heat conduction analysis was performed using the finite element method solver Abaqus manufactured by Dassault Systèmes. [[Heat generation condition]] It was assumed that the amount of heat (W) corresponding to the heater power consumption (W) is uniformly generated from the volume occupied by the heater 2. [[Boundary surface]] The boundary surfaces with boundary conditions set are shown in FIGS. 12 to 15. In FIGS. 12(a) to (c), the boundary conditions for the skin layer 1 and the heater 2 in the model without the heat insulation layer are shown. In FIGS. 13(a) and (b), the boundary conditions for the module 4 and the heat sink 5 in the model without the heat insulation layer are shown. In FIGS. 14(a) to (c), the boundary conditions for the skin layer 1 and the heater 2 in the model with the heat insulation layer are shown. And in FIGS. 15(a) to (c), the boundary conditions for the heat insulation layer 3, the module 4, and the heat sink 5 in the model with the heat insulation layer are shown. In the model without the heat insulation layer, as shown in FIGS. 12 and 13, as the boundary surfaces, the +Z plane 11 of the skin layer 1, the side surface 12 of the skin layer 1, the -Z plane 13 of the skin layer 1, the side surface 14 of the heater 2, the -Z plane 15 of the heater 2, the +Z plane 16 of the module 4, the side surface 17 of the module 4, the +Z plane 18 of the heat sink 5, the side surface 19 of the heat sink 5, the -Z plane 20 of the heat sink 5, and the rib surface 21 of the heat sink 5 were considered. In the model with the heat insulation layer, as shown in FIGS. 14 and 15, as the boundary surfaces, the +Z plane 31 of the skin layer 1, the side surface 32 of the skin layer 1, the -Z plane 33 of the skin layer 1, the side surface 34 of the heater 2, the +Z plane 35 of the heat insulation layer 3, the side surface 36 of the heat insulation layer 3, the -Z plane 37 of the heat insulation layer 3, the +Z plane 38 of the heat sink 5, the side surface 39 of the heat sink 5, the -Z plane 40 of the heat sink 5, the rib surface 41 of the heat sink 5, and the side surface 42 of the module were considered. At each interface, as shown below, the convective heat transfer boundary condition and the radiative heat transfer boundary condition were considered.

[0085] [[Convective heat transfer boundary condition]] As the convective heat transfer boundary condition, the heat flux Q shown in the following Equation 1 conv (W / m 2 ) was applied in the outward direction of the interface. [Number] In the equation, T is the temperature of the interface (K), T am is the ambient temperature (K), and h is the convective heat transfer coefficient (heat transfer rate) (W / m 2 K). The convective heat transfer coefficient (heat transfer rate) varies depending on the convective conditions. During parking, assuming that natural convection is occurring, the convective heat transfer coefficient (heat transfer rate) h n (W / mK 2 ) was calculated using the Churchill and Chu equations shown in the following Equations 2 to 4, which represent the natural convective heat transfer of a vertical flat plate. [Number] In the equation, Nu L is the Nusselt number, Ra L is the Rayleigh number, g is the gravitational acceleration (m / s 2 ), β is the coefficient of volume expansion (1 / K), L is the representative length (m) (here, the length in the vertical direction of the dome (Y-axis direction in FIGS. 7 and 9) was adopted), T is the temperature of the interface (K), T am is the ambient temperature (K), ν air is the kinematic viscosity of air (m 2 / s), Pr air is the Prandtl number of air, and λ air is the thermal conductivity of air (W / mK). When traveling at a speed of 100 km / h, it is assumed that forced convection occurs and air flows in a direction perpendicular to the surface of the skin layer 1. In this case, it is considered that the convection conditions are different depending on the relationship between the direction of convection and the direction of the boundary surface normal, and whether it is the front or the back with respect to the convection. Therefore, for the boundary surface where the direction of the normal is parallel to the direction of convection, the empirical formula of the convective heat transfer coefficient assuming a flat plate arranged perpendicular to the convection as shown in Fig. 16 was applied. L in Fig. 16 is the representative length (m). For the front surface where the normal is parallel to the direction of convection (corresponding to the left-right direction in Fig. 16) and the air directly hits, the convective heat transfer coefficient (heat transfer rate) h f (W / mK 2 ) was given. [Number] In the formula, Nu f is the Nusselt number, Re is the Reynolds number, and U0 is the convection velocity (m / s). For the surface where the normal is parallel to the direction of convection (corresponding to the left-right direction in Fig. 16) and the air does not directly hit, the convective heat transfer coefficient (heat transfer rate) h b (W / mK 2 ) was given. [Number] For the surface where the normal is perpendicular to the direction of convection (corresponding to the left-right direction in Fig. 16), the empirical formula of the convective heat transfer coefficient assuming a flat plate arranged parallel to the convection was applied. Specifically, the convective heat transfer coefficient (heat transfer rate) h s (W / mK 2 ) was given. [Number] In the formula, Nu S is the Nusselt number, Re is the Reynolds number, and S is the representative length (m) (here, the length of the flat plate in the convection direction is adopted).

[0086] Table 3 and Table 4 show the physical properties of air at each temperature and the convective heat transfer coefficient (heat transfer rate) h at the time of stop using the same n and the convective heat transfer coefficient (heat transfer rate) h during driving at a speed of 100 km / h f h b and h s are shown. Also, h n h f h b h s Table 5 shows the types of convective heat transfer coefficients (heat transfer rates) applied at each boundary surface selected from among h

[0087]

Table 3

[0088]

Table 4-1

[0089]

Table 4-2

[0090]

Table 4-3

[0091]

Table 5

[0092] [[Radiative heat transfer boundary condition]] As the radiative heat transfer boundary condition between each boundary surface and the surroundings at temperature T am (K), the heat flux Q shown in the following formula 14 rad (W / m 2 ) was given.

Equation

Number

Number

[0093]

Table 6

[0094] [[Physical property values]] Table 7 shows the materials of each component used in the heat transfer analysis of the examples and comparative examples and the physical property values of each material. Regarding the specific heat, thermal conductivity, and emissivity of foamed PPE1 and foamed PPE2, the temperature dependencies as shown in Tables 8 to 10 were considered respectively. In the heat transfer analysis, the values of each physical property value at an arbitrary temperature were calculated by linearly interpolating using the values of each physical property value for the temperatures described in Tables 8 to 10. In addition, the difference (W) in the calorific value of the heater when traveling at a speed of 100 km / h and when stopped was obtained.

[0095] [Table 7]

[0096] [Table 8]

[0097] [Table 9]

[0098] [Table 10]

[0099] [(9) Temperature non-uniformity on the surface of the epidermal layer] When measuring the [power consumption and heat generation of the heater], the temperature non-uniformity on the surface of the epidermal layer when driving at a speed of 100 km / h was evaluated according to the following method. The temperature non-uniformity on the surface of the epidermal layer was evaluated as the difference (°C) between the maximum temperature and the minimum temperature in region 9 under the condition that the minimum temperature in region 9 is 10°C.

[0100] [(10) Radio wave transmittance of the radome, etc.] Regarding the radome, the front transmittance (radio wave transmittance at an incident angle of 0°), front reflectance (%), front absorptance (%), and oblique transmittance (TE-direction radio wave transmittance at an incident angle of 30°) at 79 GHz were measured according to the following method. First, samples with a size of 200 mm × 200 mm × each thickness were prepared with reference to the methods described in the examples and comparative examples. Subsequently, the samples were set in the transmission attenuation measurement jig with a dielectric lens of the frequency change method dielectric constant and dielectric loss tangent measuring device DPS10-02 manufactured by KEYCOM, and the transmission attenuation amount and reflection attenuation amount were measured under the conditions of room temperature (temperature 26°C, humidity 60%). The front transmittance (%) and front reflectance (%) were converted from the measurement results of the transmission attenuation amount (dB) and reflection attenuation amount (dB). Also, the front absorption rate (%) was calculated as 100 - (front transmittance + front reflectance) = front absorption rate. Regarding the oblique transmittance (%), after rotating and installing the sample so that the incident angle was 30°, the oblique transmission attenuation amount in the TE direction was measured in the same manner.

[0101] [(11) Load at 1 mm deflection of the radome] Regarding the radome, as one index for confirming the mechanical strength, the load (N) at 1 mm deflection was measured as follows. First, samples with a width of 10 mm × a length of 100 mm × each thickness were cut out from the radome. Subsequently, using an autograph (AG-X plus series AG-50kNPlus manufactured by Shimadzu Corporation), a three-point bending test was performed on the samples under the conditions of a span of 64 mm and a load speed of 10 mm / min. The load when the sample deflected 1 mm from the initial state was measured and used as the load at 1 mm deflection of the radome.

[0102] [(12) Thermal resistance R on the back side of the heater of the radome] Regarding the radome, the thermal resistance R (m 2 ·K / W) on the back side of the heater (the side of the main surface of the heater that is opposite to the surface layer side in the lamination direction) was calculated for each layer existing between the back side of the heater and the back side of the radome (between the heater and the module) as "thermal resistance R of each layer 各層 (m 2 ·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)". 各層It was calculated by adding them all together. When only one heat-insulating layer exists between the back surface of the heater and the back surface of the redome (for example, in the case of FIG. 10, the "single heat-insulating layer" corresponds to the portion with a thickness of 8 in the heat-insulating layer 3), it was obtained by "the thickness (m) of the heat-insulating layer existing between the back surface of the heater and the back surface of the redome ÷ the thermal conductivity (W / m·K) of the heat-insulating layer".

[0103] The materials and the like used in the examples and comparative examples are as follows.

[0104] [Epidermal layer] ·PC resin plate: Polycarbonate (Lexan EXL9330 manufactured by SABIC) was spread in a mold, and a resin plate (thickness 1.125 mm, 2.25 mm, or 4.5 mm) was produced by the hot pressing method at a temperature of 300 °C and a mold clamping force of 10 MPa. In addition, when the PC resin plate was used as the heat-insulating layer, it was produced by the same method.

[0105] [Heat-insulating layer] (1) Foamed PPE1 60% by mass of S201A (manufactured by Asahi Kasei Corporation) as polyphenylene ether (PPE), 15% by mass of bisphenol A-bis(diphenyl phosphate) (BBP) as a non-halogen-based flame retardant, 10% by mass of impact-resistant polystyrene resin (HIPS) with a rubber concentration of 6% by mass, and 15% by mass of GP685 (manufactured by PS Japan Corporation) as a general-purpose polystyrene resin (PS) were added, and after heating and melt-kneading in an extruder, it was extruded to produce base resin pellets. According to the method described in Example 1 of JP-A-4-372630, base resin pellets were placed in a pressure-resistant container, the gas in the container was replaced with dry air, and then carbon dioxide (gas) was injected as a foaming agent. After impregnating the base resin pellets with carbon dioxide over 3 hours under the conditions of a pressure of 3.0 MPa and a temperature of 10 °C, the pellets were taken out of the pressure vessel and immediately transferred. The base resin pellets were foamed with pressurized steam of up to 330 kPa·G while rotating the stirring blades in the foaming furnace at 77 rpm to obtain foamed particles. Also, the hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). Thereafter, these foamed particles were placed in a container, and a pressure treatment was performed by introducing pressurized air (raising the pressure to 0.4 MPa over 4 hours and then holding at 0.4 MPa for 16 hours). This was filled into an in-mold forming die having steam holes, heated with steam to expand and fuse the foamed particles to each other, then cooled, and taken out of the forming die to obtain a bead foam made of foamed particles (foaming ratio: 10 times, thickness: 3 mm, 10 mm, or 30 mm). (2) Foamed PPE2 A bead foam made of foamed particles (foaming ratio: 10 times, thickness: 3 mm) was obtained in the same manner as foamed PPE1, except that the method for producing the base resin pellets was as follows. 60 mass% of GP685 (manufactured by PS Japan Corporation) as a general-purpose polystyrene resin (PS) and 40 mass% of S201A (manufactured by Asahi Kasei Corporation) as a polyphenylene ether-based resin (PPE) were melt-kneaded by heating in an extruder and then extruded to produce base resin pellets. (3) Foamed PS 100 mass% of a general-purpose polystyrene resin (PS) (trade name "GP685", manufactured by PS Japan Corporation) was melt-kneaded by heating in an extruder and then extruded to produce base resin pellets. According to the method described in Example 1 of Japanese Patent Laid-Open No. 4-372630, the base resin pellets were placed in a pressure-resistant container, the gas in the container was replaced with dry air, and then carbon dioxide (gas) was injected as a foaming agent. After impregnating the base resin pellets with carbon dioxide over 3 hours under the conditions of a pressure of 3.0 MPa and a temperature of 10°C, the pellets were taken out of the pressure vessel and immediately transferred. The base resin pellets were foamed with pressurized steam up to a maximum of 70 kPa·G while rotating the stirring blades in the foaming furnace at 77 rpm to obtain foamed particles. Also, the hydrocarbon gas content of the foamed particles was measured by gas chromatography immediately after foaming, and it was below the detection limit (0.01 mass%). Thereafter, these foamed particles were placed in a container, and a pressure treatment was performed by introducing pressurized air (pressurizing up to 0.4 MPa over 4 hours and then maintaining at 0.4 MPa for 16 hours). This was filled into an in-mold forming die having steam holes, heated with steam to expand and fuse the foamed particles to each other, then cooled, and taken out from the forming die to obtain a bead foam (foaming ratio: 30 times, thickness: 3 mm) made of foamed particles.

[0106] [Heater] When calculating the power consumption, heat generation amount of the heater, and temperature unevenness on the surface of the skin layer as described above, calculations were performed assuming that a pure copper heater having the shape shown in FIG. 1 was used. When measuring the radio wave transmittance of the radome and the load at 1 mm deflection, since the heater wire had little influence on the radio wave transmittance and the load at 1 mm deflection and could be ignored, the measurement was performed using a laminate in which the skin layer and the heat insulation layer were laminated.

[0107] (Example 1) A radome was manufactured as follows using a PC resin plate as the skin layer, a heater, and foamed PPE1 (thickness: 3 mm) as the heat insulation layer. First, based on the production method described in the foamed PPE1, a foam having a groove for installing a heater was produced in the shape shown in FIG. 1. Subsequently, after installing the heater in accordance with the groove formed in the foam, the foam and the skin layer were heated with a heat gun and then quickly bonded to produce a radome laminated in the order of skin layer / heater / foam. Regarding the obtained radome, the measurement results of each physical property are shown in Table 11. When confirming the radio wave transmittance and the load at 1 mm deflection, a radome laminated in the order of skin layer / foam was produced and evaluated in the same manner as described above.

[0108] (Examples 2 to 11) A radome was obtained in the same manner as in Example 1, except that the material and thickness of each layer were changed as shown in Table 11. Regarding the obtained radome, the measurement and evaluation results of each physical property are shown in Table 11. When confirming the radio wave transmittance and the load at 1 mm deflection, a radome laminated in the order of skin layer / heat insulation layer was produced and evaluated in the same manner as described above.

[0109] (Comparative Examples 1 to 3) A radome was obtained in the same manner as in Example 1, except that the material and thickness of the skin layer were as shown in Table 11 and no heat insulation layer was provided (configured to consist only of the skin layer and the heater). Regarding the obtained radome, the measurement and evaluation results of each physical property are shown in Table 11. When confirming the radio wave transmittance and the load at 1 mm deflection, a radome consisting only of the skin layer was produced and evaluated in the same manner as described above.

[0110]

Table 11

Industrial Applicability

[0111] The radome of the present invention can be suitably used as a radome for a radar that transmits and / or receives high-frequency radio waves because it suppresses the power consumption of the heater and has little temperature unevenness on the surface.

Explanation of Signs

[0112] 1 Epidermal layer 2 Heater 3 Insulation layer 4 Module 5 Heat sink 6 Gap 7 Thickness of epidermal layer 1 8 Thickness of insulation layer 3 9 Region to be maintained at 10 °C on the surface of epidermal layer 1 11, 31 +Z plane of epidermal layer 1 12, 32 Side surface of epidermal layer 1 13, 33 -Z plane of epidermal layer 1 14, 34 Side surface of heater 2 15 -Z plane of heater 2 16 +Z of module 4 17, 42 Side surface of module 4 18, 38 +Z plane of heat sink 5 19, 39 Side surface of heat sink 5 20, 40 -Z plane of heat sink 5 21, 41 Rib surface of heat sink 5 35 +Z plane of insulation layer 3 36 Side surface of insulation layer 3 37 -Z plane of insulation layer 3 L Representative length U0 Convection velocity

Claims

1. A radome for transmitting and / or receiving high-frequency radio waves, which is a laminate composed of N layers (N is an integer of 3 or more) including an outer skin layer containing resin, a heater, and a heat insulation layer in this order, for each layer existing between the back surface of the heater and the back surface of the radome, the total thermal resistance R of the entire layer existing between the back surface of the heater and the back surface of the radome obtained by adding up all the thermal resistances R each layer of each layer calculated by "thermal resistance R each layer (m2·K / W) of each layer = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)" is 0.01 to 1.0 m2·K / W, the back surface of the heater is the surface on the side opposite to the outer skin layer side in the lamination direction, and the back surface of the radome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the radome, the minimum value of the value of Λ obtained by the following formula (B) is 0.20 or less A radome, characterized in that. 【Number 1】 (d ｉ : Thickness of the i-th layer [m], N ｉ : Complex refractive index n of the i-th layer obtained by the following formula group (C) ｉ of magnitude, λ ０ : Wavelength of electromagnetic wave in air [m], K: Any integer of 1 or more) 【Number 2】 (n ｉ : Complex refractive index of the i-th layer, j: Imaginary unit, ε ｒｉ : Complex relative permittivity of the i-th layer, μ ｒｉ : Complex relative permeability of the i-th layer, tanδ: Dielectric tangent, ε ｉ ’: Relative permittivity, ε ｉ ’’: Relative dielectric loss factor)

2. The radome according to claim 1, wherein the minimum value of Λ (outer skin layer) obtained by the following formula (A) for the outer skin layer is 0.15 or less. [Number 3] (d １ : Thickness of the epidermal layer [m], N １ : Magnitude of the complex refractive index n of the epidermal layer obtained by the following formula group (C1) １ , λ ０ : Wavelength of electromagnetic wave in air [m], K: Any integer of 1 or more) 【Number 4】 (n １ : Complex refractive index of the epidermis layer, j: Imaginary unit, ε １ : Complex relative permittivity of the epidermis layer, μ １ : Complex relative permeability of the epidermis layer, tanδ: Dielectric tangent, ε １ ’: Relative permittivity, ε １ ’’: Relative dielectric loss factor)

3. The radome according to claim 1 or 2, wherein at least a part of the surface of the heater excluding the surface on the outer skin layer side is covered by the heat insulation layer.

4. The radome according to claim 1 or 2, wherein the minimum value of Λ (outer skin layer) of the outer skin layer is 0.15 or less and the thickness of the radome is 3 mm or more.

5. The density of the heat insulation layer is 1.2 g / cm ３ The radome according to claim 1 or 2, wherein the density is 1.2 g / cm or less.

6. The magnitude N of the complex refractive index of the heat insulating layer ２ is 1.70 or less, The magnitude N of the complex refractive index of the heat insulation layer ２ is the magnitude of the complex refractive index n of the heat insulation layer obtained by the following formula group (C2), ２ and is The radome according to claim 1 or 2. 【Number 5】 (n ２ : Complex refractive index of the heat insulation layer, j: Imaginary unit, ε ２ : Complex relative permittivity of the heat insulation layer, μ ２ : Complex relative permeability of the heat insulation layer, tanδ: Dielectric loss tangent, ε ２ ’: Relative permittivity, ε ２ ’’: Relative dielectric loss factor)

7. For each layer existing between the back surface of the heater and the back surface of the redome, the thermal resistance R of each layer calculated by "thermal resistance R of each layer (m·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)" 各層 (m ２ ·K / W) is added together, and the thermal resistance R of the entire layer existing between the back surface of the heater and the back surface of the redome obtained thereby is 0.01 to 1.0 m 各層 ·K / W, and the magnitude N of the complex refractive index of the heat insulating layer ２ is 1.70 or less, ２ ​ The back surface of the heater is the surface on the side opposite to the outer skin layer side in the lamination direction, and the back surface of the radome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the radome, The magnitude N of the complex refractive index of the heat insulation layer ２ is the magnitude of the complex refractive index n of the heat insulation layer obtained by the following formula group (C2) ２ and is The radome according to claim 1 or 2. 【Number 6】 (n ２ : Complex refractive index of the heat insulation layer, j: Imaginary unit, ε ２ : Complex relative permittivity of the heat insulation layer, μ ２ : Complex relative permeability of the heat insulation layer, tanδ: Dielectric loss tangent, ε ２ ’: Relative permittivity, ε ２ ’’: Relative dielectric loss factor)

8. The radome according to claim 4, wherein the minimum value of Λ (outer skin layer) of the outer skin layer is 0.15 or less and the thickness of the radome is 3 mm or more.

9. Regarding each layer existing between the back surface of the heater and the back surface of the redome, the thermal resistance R of each layer calculated by " 各層 Thermal resistance R of each layer (m ２ ·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)" 各層 The total thermal resistance R of the entire layer existing between the back surface of the heater and the back surface of the redome obtained by adding all of them is 0.01 to 1.0 m ２ ·K / W, and The back surface of the heater is the surface on the side opposite to the outer skin layer side in the lamination direction, and the back surface of the radome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the radome, The radome according to claim 4.

10. The magnitude N of the complex refractive index of the heat insulating layer ２ is 1.70 or less, The magnitude N of the complex refractive index of the heat insulation layer ２ is the magnitude of the complex refractive index n of the heat insulation layer obtained by the following formula group (C2) ２ and is The radome according to claim 4. 【Number 7】 (n ２ : Complex refractive index of the heat insulation layer, j: Imaginary unit, ε ２ : Complex relative permittivity of the heat insulation layer, μ ２ : Complex relative permeability of the heat insulation layer, tanδ: Dielectric loss tangent, ε ２ ’: Relative permittivity, ε ２ ’’: Relative dielectric loss factor)

11. For each layer existing between the back surface of the heater and the back surface of the redome, the thermal resistance R of each layer calculated by "thermal resistance R of each layer 各層 (m ２ ·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)" 各層 The total thermal resistance R of the layers existing between the back surface of the heater and the back surface of the redome obtained by adding all of them is 0.01 to 1.0 m ２ ·K / W, and the magnitude N of the complex refractive index of the heat insulating layer ２ is 1.70 or less, The back surface of the heater is the surface opposite to the surface on the epidermis layer side in the lamination direction, and the back surface of the dome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the dome. The magnitude N of the complex refractive index of the heat insulating layer ２ is the magnitude of the complex refractive index n of the heat insulating layer obtained by the following formula group (C2) ２ and is The dome according to claim 4. 【Number 8】 (n ２ : Complex refractive index of the heat insulation layer, j: Imaginary unit, ε ２ : Complex relative permittivity of the heat insulation layer, μ ２ : Complex relative permeability of the heat insulation layer, tanδ: Dielectric loss tangent, ε ２ ’: Relative permittivity, ε ２ ’’: Relative dielectric loss factor)

12. For each layer existing between the back surface of the heater and the back surface of the redome, the thermal resistance R of each layer calculated by "thermal resistance R of each layer 各層 (m ２ ·K / W) = thickness of each layer (m) ÷ thermal conductivity of each layer (W / m·K)" 各層 The total thermal resistance R of the layers existing between the back surface of the heater and the back surface of the redome obtained by adding all of them is 0.01 to 1.0 m ２ ·K / W, and the magnitude N of the complex refractive index of the heat insulating layer ２ is 1.70 or less. The back surface of the heater is the surface opposite to the surface on the epidermis layer side in the lamination direction, and the back surface of the dome is the surface perpendicular to the lamination direction among the surfaces in contact with the module when the module is installed on the dome. The magnitude N of the complex refractive index of the heat insulating layer ２ is the magnitude of the complex refractive index n of the heat insulating layer obtained by the following formula group (C2) ２ and is The dome according to claim 8. 【Number 9】 (n ２ : Complex refractive index of the heat insulation layer, j: Imaginary unit, ε ２ : Complex relative permittivity of the heat insulation layer, μ ２ : Complex relative permeability of the heat insulation layer, tanδ: Dielectric tangent, ε ２ ’: Relative permittivity, ε ２ ’’: Relative dielectric loss factor)

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