Antenna, method for manufacturing antenna, and method for using antenna

Abstract

To provide an antenna having excellent relative radiation efficiency in a specific frequency band, and to provide a method of manufacturing the antenna and a method of using the antenna.SOLUTION: The antenna is an antenna for a radar used in a frequency band of 70GHz or more and 90GHz or less, and a relative radiant efficiency measured at a frequency of 82. 5GHz is 17. 5dB or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] TECHNICAL FIELD The present disclosure relates to antennas, methods of making antennas, and methods of using antennas. [Background technology]

[0002] There is a demand for planar antennas suitable for millimeter wave communications. As such planar antennas, planar antennas having a dielectric substrate are known (Patent Document 1). It is known to use a resin substrate as such a substrate. For example, Patent Document 2 proposes a printed wiring board having a dielectric layer made of fluororesin. Patent Document 3 proposes a resin substrate containing a polymer having an arylene group. Patent Document 4 proposes a printed circuit board having a resin layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-320356 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-8260 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-32098 [Patent Document 4] International Publication No. 2020 / 059606 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide an antenna with good relative radiation efficiency in a specific frequency band, a method for manufacturing the same, and a method for using the same. [Means for solving the problem]

[0005] The present disclosure relates to an antenna for radar used in the frequency band of 70 GHz or more and 90 GHz or less, which has a relative radiation efficiency of 17.5 dB or more measured at a frequency of 82.5 GHz.

[0006] The antenna is preferably a patch array antenna. It is preferable that the antenna has a plurality of antenna elements, and the plurality of antenna elements are configured into 8 to 16 antenna element rows, each row having 16 to 64 antenna elements arranged in a straight line, and the 8 to 16 antenna element rows are arranged parallel to each other.

[0007] The antenna has a dielectric layer, and the dielectric layer is a fluororesin sheet containing a fluororesin and silica particles, and it is preferable that the oxygen element ratio on one or both sides of the fluororesin sheet is 3.0 atomic% or more when measured by X-ray photoelectron spectroscopy (XPS), and the coefficient of linear expansion (CTE) of the fluororesin sheet is 100 ppm / °C or less. The fluororesin is preferably polytetrafluoroethylene. Furthermore, it is preferable that the nitrogen element ratio on the surface of the fluororesin sheet is 1.35 atomic % or more when measured by X-ray photoelectron spectroscopy (XPS). Furthermore, it is preferable that the silicon element ratio on the surface of the fluororesin sheet is 0.5 atomic % or more when measured by X-ray photoelectron spectroscopy (XPS). Furthermore, it is preferable that the static contact angle of water measured one second after a 2 μL droplet of water is deposited on the same surface of the fluororesin sheet is 105° or less.

[0008] The silica particles are preferably spherical silica. As the silica particles, it is preferable to use silica particles treated with a silane coupling agent. The silica particles preferably have an average particle size of 10 μm or less. It is preferable that the fluororesin sheet does not contain glass fibers. The content of the silica particles is preferably 30% by mass or more based on the total amount of the fluororesin sheet. The content of the silica particles is preferably 50% by mass or more based on the total amount of the fluororesin sheet. The content of the silica particles is preferably 50% by mass or more and 65% by mass or less with respect to the total amount of the fluororesin sheet.

[0009] The fluororesin sheet preferably has a dielectric loss tangent value of 0.0015 or less at 10 GHz. The thickness of the fluororesin sheet is preferably 5 to 250 μm.

[0010] The antenna is preferably formed from a metal clad laminate having a metal foil and the dielectric layer as essential layers. The metal foil is preferably a copper foil. The surface roughness (Rz) of the copper foil is preferably 1.0 μm or less. The copper foil preferably has a surface roughness (Rq) of 0.01 to 0.15 μm. It is preferable that the copper foil and the dielectric layer are directly laminated together, and the peel strength of the interface between the copper foil and the dielectric layer is 0.5 kN / m or more. The antenna is preferably a millimeter wave antenna for mobility applications. Preferably, the relative radiation efficiency measured at a frequency of 82.5 GHz is 18.0 dB or more and 20.0 dB or less, the antenna has a dielectric layer, the dielectric layer is a fluororesin sheet containing a fluororesin and silica particles, the fluororesin is polytetrafluoroethylene, the silica particles are spherical silica, the content of the silica particles is 50 mass% or more and 65 mass% or less with respect to the total amount of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both sides of the fluororesin sheet is 3.0 atomic% or more and 25.0 atomic% or less, the silicon element ratio measured by X-ray photoelectron spectroscopy (XPS) on the same side of the fluororesin sheet is 0.5 atomic% or more and 10.0 atomic% or less, and the coefficient of linear expansion (CTE) of the fluororesin sheet is 31 ppm / °C or more and 70 ppm / °C or less.

[0011] The present disclosure also relates to a method for manufacturing an antenna, which includes a dielectric layer formation step of forming a dielectric layer, in which fluororesin particles and silica particles are mixed to form a film, and then a surface treatment is performed.

[0012] In the dielectric layer forming step, it is preferable to form a film using a composition substantially consisting of the fluororesin particles and filler particles containing at least the silica particles, and then perform a surface treatment. It is preferable that the method further includes a metal clad laminate forming step of forming a metal clad laminate, and in the metal clad laminate forming step, the dielectric layer and a metal foil are laminated, heated at 180 to 390°C, and press-molded at a pressure of 0.5 to 5 MPa under vacuum or in an inert gas atmosphere. It is preferable that the method further includes an etching step of etching the metal clad laminate.

[0013] The present disclosure also provides a method of using the antenna, the method including using the antenna in a frequency band of 70 GHz or more and 90 GHz or less. [Effects of the Invention]

[0014] The antenna of the present disclosure and the antenna manufactured by the manufacturing method of the present disclosure have good relative radiation efficiency in a specific frequency band, and the method of using the antenna of the present disclosure can achieve good relative radiation efficiency in a specific frequency band. DETAILED DESCRIPTION OF THE INVENTION

[0015] [antenna] The antenna of the present disclosure will be described below. The antenna of the present disclosure is an antenna for radar used in a frequency band of 70 GHz or more and 90 GHz or less. The antenna of the present disclosure is preferably an antenna for radar used in a frequency band of 75 GHz or more and 85 GHz or less. Hereinafter, the "frequency band of 70 GHz or more and 90 GHz or less" may be referred to as a "predetermined frequency band." The antenna of the present disclosure transmits and receives radio waves in the predetermined frequency band.

[0016] The antenna of the present disclosure is used in a predetermined frequency band, and therefore is suitably used as an antenna for millimeter-wave radar that transmits and receives radio waves in the millimeter wave band (particularly the predetermined frequency band). Because radio waves in the millimeter wave band (particularly the predetermined frequency band) have a high degree of linearity, the antenna of the present disclosure is particularly suitably used as a millimeter-wave antenna for mobility purposes, such as collision prevention.

[0017] In this disclosure, mobility refers to all means of movement and transportation, including automobiles in general, such as private cars, buses, taxis, and trucks, two-wheeled vehicles such as motorcycles, bicycles, and mopeds, as well as trains, senior cars, compact one-seater personal mobility vehicles, etc. Furthermore, mobility is not necessarily limited to vehicles that move on land, but may also be vehicles that move in the air or underwater, such as aircraft, drones, and ships.

[0018] The relative radiation efficiency of the antenna of the present disclosure measured at a frequency of 82.5 GHz is 17.5 dB or more. Hereinafter, the "relative radiation efficiency measured at a frequency of 82.5 GHz" may be referred to as the "predetermined relative radiation efficiency."

[0019] Here, the higher the predetermined relative radiation efficiency of the antenna, the more the antenna can be made smaller and more energy-efficient. In one example, when the antenna's energy usage is the same, increasing the predetermined relative radiation efficiency of the antenna by about 1.8 dB tends to reduce the antenna's board size by about 33%. In another example, when the antenna's board size is the same, increasing the predetermined relative radiation efficiency of the antenna by about 1.8 dB tends to reduce the antenna's energy usage by about 30%. The predetermined relative radiation efficiency of the antenna disclosed herein is 17.5 dB or higher, which is higher than that of conventional products (for example, see Comparative Example 1 described below), and therefore the antenna can be made smaller and more energy-efficient.

[0020] From the viewpoint of increasing the predetermined relative radiation efficiency and promoting antenna miniaturization and energy saving, the predetermined relative radiation efficiency of the antenna is preferably 18.0 dB or more, more preferably 18.5 dB or more, even more preferably 19.0 dB or more, and even more preferably 19.1 dB or more. There is no particular restriction on the upper limit of the predetermined relative radiation efficiency, but from the viewpoint of productivity, etc., it is preferably 30.0 dB or less, more preferably 20.0 dB or less, and even more preferably 19.5 dB or less.

[0021] In this disclosure, the predetermined relative radiation efficiency of an antenna is measured by performing planar scanning near-field measurement using a vector network analyzer ("MS46522B" manufactured by Anritsu Corporation) under the following conditions: a measurement range in the XY-axis direction on the XY plane of ±150 mm, a movement step of 1 mm, a distance between the receiving probe and the antenna under test of 50 mm, and a measurement frequency of 82.5 GHz.

[0022] The antenna of the present disclosure has, for example, a substrate, an antenna element, and a transmission line. Hereinafter, a "substrate having an antenna element and a transmission line" may be referred to as an "antenna circuit board." The structure of the antenna of the present disclosure is not particularly limited and can be appropriately selected from known structures.

[0023] The antenna of the present disclosure is preferably a patch antenna. A patch antenna is a type of antenna used in high frequency bands above microwaves. A patch antenna is also called a microstrip antenna. A patch antenna is a general term for antennas formed using conductors printed on a dielectric substrate (a substrate having a dielectric layer). A patch antenna has the advantage of low manufacturing costs.

[0024] The antenna of the present disclosure is preferably a patch array antenna. A patch array antenna is a patch antenna that creates high directivity by arranging multiple antenna elements on a plane. A patch array antenna can change its directivity by applying signals with different phases and amplitudes to each antenna element. For this reason, patch array antennas have been widely used in recent years as antennas for automotive radars, etc. One method for controlling the directivity of a patch array antenna is, for example, to connect a phase shifter or a variable attenuator to each antenna element of the patch array antenna and control them.

[0025] When the antenna of the present disclosure is a patch array antenna, the patch array antenna includes a substrate and a plurality of antenna elements provided on the substrate, the plurality of antenna elements being arranged in an array on the substrate.

[0026] The arrangement of antenna elements in a patch array antenna is, for example, an m×n arrangement. m and n each represent the number of antenna elements and represent an integer of 2 or more. m is preferably an integer of 16 or more. m is preferably an integer of 64 or less. n is preferably an integer of 8 or more. n is preferably an integer of 16 or less. The number of antenna elements may be selected appropriately depending on the type, size, and performance of the antenna. A patch array antenna with an m×n arrangement of antennas has m×n antenna elements, and the m×n antenna elements form n antenna element rows in which m antenna elements are arranged in a straight line, and the n antenna element rows are arranged parallel to each other. In the antenna element row, the m antenna elements are arranged at a predetermined interval from each other. The n antenna element rows are arranged at a predetermined interval from each other. The m×n antenna elements are arranged, for example, in a triangular or rectangular array.

[0027] An example of an m×n arrangement of antenna elements in a patch array antenna is an arrangement of (an integer between 16 and 64 inclusive)×(an integer between 8 and 16 inclusive). A patch array antenna with an arrangement of (an integer between 16 and 64 inclusive)×(an integer between 8 and 16 inclusive) has multiple antenna elements, and the multiple antenna elements are arranged in 8 to 16 antenna element rows, each with 16 to 64 antenna elements arranged in a straight line, and the 8 to 16 antenna element rows are arranged in parallel to each other. In this arrangement, the multiple antenna elements are m×n (where m is an integer between 16 and 64 inclusive, and n is an integer between 8 and 16 inclusive) antenna elements.

[0028] More specifically, an m x n arrangement of antenna elements in a patch array antenna can be a 16 x 8 arrangement. A patch array antenna with a 16 x 8 arrangement has 128 antenna elements, and the 128 antenna elements are arranged in eight antenna element rows, each consisting of 16 antenna elements arranged in a straight line, and the eight antenna element rows are arranged parallel to each other.

[0029] The antenna element, transmission line, and substrate of the antenna of the present disclosure will be described below.

[0030] <Antenna element> The antenna elements transmit and receive radio waves in a predetermined frequency band. The antenna elements are provided, for example, on the surface (e.g., one or both sides) of a substrate. The antenna elements are not particularly limited as long as they can transmit and receive radio waves in the predetermined frequency band, but from the viewpoint of efficiently receiving radio waves, it is preferable to use a phased array antenna. A phased array antenna is an antenna in which multiple patch-shaped antenna elements are arranged in an array and the phase of each antenna element is controlled to enable transmission and reception in a desired direction. A phased array antenna can transmit and receive radio waves in a desired direction by electronically controlling the phase of each antenna element (beam steering) regardless of the antenna direction.

[0031] The antenna element may be any known antenna element, without any particular limitation. Examples of the antenna element include a loop antenna structure, a patch antenna structure, a stacked patch antenna structure, a patch antenna structure with a parasitic element, an inverted-F antenna structure, a slot antenna structure, a planar inverted-F antenna structure, a monopole, a dipole, a helical antenna structure, a Yagi (Yagi-Uda) antenna structure, a surface integrated waveguide structure, and an antenna element having a resonant element formed from a hybrid of these designs. Different types of antenna elements may be used for different combinations of frequency bands.

[0032] The material constituting the antenna element is not particularly limited as long as it is a conductor. Examples of materials constituting the antenna element include metals such as titanium, silicon, niobium, indium, zinc, tin, gold, silver, copper, aluminum, cobalt, chromium, nickel, lead, iron, palladium, platinum, tungsten, zirconium, tantalum, ruthenium, and hafnium; and metal oxides such as ITO (oxide of indium and tin), zinc oxide, and tin oxide. Furthermore, the material constituting the antenna element may contain two or more of these metals and metal oxides, or an alloy containing these metals as the main component. Among these, copper is preferred as the material constituting the antenna element from the viewpoint of conductivity. When the antenna element is made of a metal such as copper, the antenna element may be subjected to a blackening treatment by forming a film of the nitride, oxide, sulfide, or the like of the metal.

[0033] <Transmission line> Signals transmitted and received by the antenna element may be transferred to a transceiver circuit via a transmission line. When the antenna is provided with a transmission line, the transmission line may be provided, for example, on the surface (e.g., one or both sides) of a substrate or inside the substrate. Examples of the transmission line include a coaxial cable path, a microstrip transmission line, a stripline transmission line, an edge-coupled microstrip transmission line, an edge-coupled stripline transmission line, a waveguide structure for transmitting signals in a predetermined frequency band (e.g., a coplanar waveguide or a grounded coplanar waveguide), and a transmission line formed from a combination of these types of transmission lines. The material constituting the transmission line is not particularly limited, and the same material as the material constituting the antenna element can be used. The transmission line may also include a feed line for feeding power to the antenna.

[0034] Here, we will explain the loss of a power feeder line, which is an example of transmission loss. Power feeder line losses include conductor loss, dielectric loss, and radiation loss. Conductor loss is loss caused by current flowing on the surface of a line when a conductor is used for the line. Since current density is approximately inversely proportional to the height of the line, conductor loss also tends to be inversely proportional to the height of the line. Dielectric loss occurs due to the electric field within the line volume when a dielectric is used for the line. Dielectric loss tends to be constant with respect to the height of the line. In the case of open-system lines, radiation loss occurs due to discontinuities in the line, such as bends and branches. The higher the line, the greater the radiation loss tends to be. In the case of open-system lines such as microstrip lines, power feeder line loss is the sum of three types of loss: conductor loss, dielectric loss, and radiation loss.

[0035] As described above, the loss of a feed line is the sum of three losses: conductor loss, dielectric loss, and radiation loss. Therefore, if the dielectric loss is reduced, the loss of the feed line can be reduced. In order to reduce the dielectric loss, it is preferable to use a material with a small dielectric loss tangent for the dielectric layer for the following reasons. The dielectric layer and its dielectric loss tangent of the antenna of the present disclosure will be described later. The dielectric loss tangent tanδ is a parameter that represents the loss of a dielectric layer. The dielectric loss tangent tanδ is the ratio between the real part and the imaginary part of the complex relative permittivity, and is defined as in the following formula (1). When the dielectric loss tangent tanδ is sufficiently smaller than 1, the propagation constant γ of the line is approximated by the following formula (2). Therefore, the dielectric loss α d is expressed by the following formula (3). As can be seen from formula (3), the dielectric loss α d In order to reduce this, it is preferable to use a material with a small dielectric loss tangent tan δ for the dielectric layer.

[0036]

number

[0037] As described above, the loss of a feed line is the sum of three losses: conductor loss, dielectric loss, and radiation loss. Therefore, if the conductor loss is reduced, the loss of the feed line can be reduced. In order to reduce the conductor loss, it is preferable to control the conductivity of the conductor for the following reasons. Note that the metal clad laminate for forming the antenna of the present disclosure and its metal interface conductivity, which affect the conductivity of the conductor, will be described later. Conductivity σ is a parameter that represents the loss of a conductor. Since a conductor satisfies the formula "σ>>ωε", the surface impedance Z of the conductor S is approximated by the following equation (4). Therefore, the surface resistance R S is expressed by the following formula (5): where δ in formula (5) is the skin depth, which is expressed by formula (6): The skin depth δ is the depth at which the electromagnetic field strength is 1 / e (=-8.68 dB) of the value at the conductor surface, and is inversely proportional to the square roots of the frequency and the conductivity σ.

[0038]

number

[0039] <Substrate> Examples of materials constituting the substrate include plastic materials. Examples of such plastic materials include fluororesins, polyester-based resins (e.g., polyethylene terephthalate), (meth)acrylic resins (e.g., polymethyl methacrylate), polycarbonate, triacetyl cellulose, polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, and cyclic olefin-based polymers. These plastic materials may be used alone or in combination of two or more. From the viewpoint of improving the relative radiation efficiency of the antenna, fluororesins are preferred as materials constituting the substrate, and polytetrafluoroethylene (PTFE) is more preferred.

[0040] The thickness of the substrate is preferably 5 to 250 μm from the viewpoint of suppressing radiation loss of radio waves in a predetermined frequency band while mounting the antenna element. The substrate may be a single layer or multiple layers. The surface of the substrate may be subjected to a known surface treatment. Examples of known surface treatments include corona discharge treatment, plasma treatment, electron beam treatment, undercoat treatment, and coating treatment.

[0041] The substrate may be any of a rigid substrate, a flexible substrate, and a rigid-flexible substrate. The substrate may be any of a single-sided substrate, a double-sided substrate, and a multilayer substrate (e.g., a pulled-up substrate, etc.). In particular, it is suitable for use as a flexible substrate and a rigid substrate. When the fluororesin sheet does not contain glass fiber or cloth made of glass fiber, it is suitable for use as a flexible substrate. In particular, it is suitable for use as a high-frequency printed circuit board in a predetermined frequency band.

[0042] The substrate of the antenna of the present disclosure has, for example, a dielectric layer. The substrate may be composed of only the dielectric layer, or may further have layers other than the dielectric layer. Examples of materials that form the dielectric layer include the plastic materials described above. Among these, fluororesin is preferred as the material that forms the dielectric layer. Furthermore, the dielectric layer is preferably a fluororesin sheet. Below, a fluororesin sheet that can be suitably used as the dielectric layer of the antenna of the present disclosure will be described.

[0043] (Fluororesin sheet) A smooth interface between the metal foil and fluororesin sheet used to form the antenna element and circuits reduces transmission loss and improves antenna characteristics, so good adhesion between the fluororesin sheet and the metal foil with a smooth surface is required.

[0044] However, sheets made solely of fluororesin have a high linear expansion coefficient, which can cause substrate warpage and circuit defects. Furthermore, in particular, sheets made solely of PTFE resin are difficult to form functional groups containing oxygen, even after surface treatment, and sufficient adhesion to metal foils with smooth surfaces is not achieved, so further improvement is required. This problem arises because functional groups are difficult to generate on the surface of polytetrafluoroethylene resin, and the generated functional groups are prone to molecular motion, so the functional groups migrate from the surface to the interior of the resin and are difficult to expose on the surface, making it difficult to achieve the effects of surface treatment.

[0045] Therefore, the surface of a fluororesin sheet containing fluororesin and silica particles is subjected to a surface treatment such as plasma treatment to increase the oxygen element ratio on the surface of the fluororesin sheet, thereby improving the adhesion between the fluororesin sheet and a metal foil with a smooth surface of Rz 1.0 μm or less.

[0046] By incorporating silica particles, when a fluororesin sheet is subjected to a surface treatment, the silica surface can also have functional groups derived from the surface treatment, thereby increasing the oxygen atomic ratio on the surface of the fluororesin sheet. This improves the adhesion between the fluororesin sheet and the metal foil, thereby improving the peel strength of the adhesive surface. Furthermore, by using a composite of fluororesin and silica particles, the linear expansion coefficient of the fluororesin sheet can be further reduced. Such a fluororesin sheet can achieve both a low linear expansion coefficient and good peel strength.

[0047] The fluororesin sheet is preferably a fluororesin sheet containing a fluororesin and silica particles, and has an oxygen element ratio of 3.0 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS) and a coefficient of linear expansion (CTE) of 100 ppm / °C or less. As described above, by using a fluororesin sheet containing a fluororesin and silica particles, the oxygen element ratio on the surface of the fluororesin sheet can be increased, thereby enabling good adhesion to metal foils with smooth surfaces. In addition, the coefficient of linear expansion (CTE) is low, which can sufficiently suppress substrate warpage and circuit defects.

[0048] The fluororesin sheet preferably has an oxygen element ratio of 3.0 atomic% or more on one or both sides thereof as measured by X-ray photoelectron spectroscopy (XPS). In particular, the oxygen element ratio of the sheet surface that adheres to the metal foil as measured by X-ray photoelectron spectroscopy (XPS) should be 3.0 atomic% or more. When the oxygen element ratio is 3.0 atomic% or more, bonding with the surface of the metal foil is achieved, improving the peel strength to the metal foil. The oxygen atomic ratio is preferably 3.0 atomic% or more, more preferably 5.0 atomic% or more, and even more preferably 10.0 atomic% or more. There is no particular upper limit, but in consideration of the effect on productivity and other physical properties, it is preferably 25.0 atomic% or less.

[0049] Specifically, the measurement by X-ray photoelectron spectroscopy (XPS) is carried out using a scanning X-ray photoelectron spectrometer (XPS / ESCA) PHI5000VersaProbeII (manufactured by ULVAC-PHI, Inc.).

[0050] In the surface of the fluororesin sheet having an oxygen element ratio of 3.0 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS), the nitrogen element ratio is preferably 1.35 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS). The nitrogen atomic ratio is more preferably 1.35 atomic % or more, even more preferably 2.5 atomic % or more, and most preferably 3.0 atomic % or more. By increasing the nitrogen element ratio on the surface of the fluororesin sheet, which contributes to adhesion, sufficient peel strength with the metal foil can be obtained without impairing the dielectric properties. There is no particular upper limit, but in consideration of the impact on productivity and other physical properties, it is preferably 25.0 atomic % or less.

[0051] In the surface of the fluororesin sheet having an oxygen element ratio of 3.0 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS), the silicon element ratio is preferably 0.5 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS). The silicon atomic ratio is more preferably 1.0 atomic % or more, even more preferably 1.5 atomic % or more, and most preferably 2.0 atomic % or more. Such a high silicon element ratio on the surface of the fluororesin sheet, which contributes to adhesion, exposes silica particles that can be surface-treated, thereby increasing the peel strength with the metal foil. While there is no particular upper limit, in consideration of the influence on other physical properties such as productivity and strength, it is preferably 10.0 atomic % or less.

[0052] On the surface of the fluororesin sheet having an oxygen element ratio of 3.0 atomic % or more as measured by X-ray photoelectron spectroscopy (XPS), the static contact angle of water measured 1 second after a 2 μL droplet landed is preferably 105° or less, more preferably 103° or less, and even more preferably 100° or less. By satisfying this range, new functional groups are generated in the fluororesin sheet, increasing the peel strength with the metal foil. Although there is no particular lower limit, in consideration of productivity, etc., the static contact angle of water is preferably 90° or more.

[0053] The static contact angle of water was measured using a contact angle meter ("DropMaster" manufactured by Kyowa Interface Science Co., Ltd.) at 23° C. with a droplet volume of 2 μL, one second after the droplet landed.

[0054] The fluororesin sheet preferably has a coefficient of linear expansion (CTE) of 100 ppm / °C or less. A coefficient within this range is preferable in that it results in a fluororesin sheet with low shrinkage and excellent dimensional stability. The coefficient of linear expansion (CTE) is more preferably 70 ppm / °C or less, even more preferably 50 ppm / °C or less, and even more preferably 40 ppm / °C or less. There is no particular lower limit, but in consideration of productivity, etc., the coefficient of linear expansion (CTE) is preferably 10 ppm / °C or more, more preferably 18 ppm / °C or more, and even more preferably 31 ppm / °C or more.

[0055] The linear expansion coefficient in this specification is determined by TMA measurement in a tensile mode using a TMA-7100 (manufactured by Hitachi High-Tech Science Corporation), using a fluororesin sheet cut into a length of 20 mm, a width of 5 mm, and a thickness of 150 μm as a sample piece, setting the distance between chucks at 10 mm, and applying a load of 49 mN at a heating rate of 2°C / min from 0 to 150°C, and measuring the displacement of the sample.

[0056] The fluororesin sheet preferably has a dielectric loss tangent of 0.0015 or less at 10 GHz. Setting the dielectric loss tangent within this range is preferable because it can minimize loss of electrical signals in the circuit. The dielectric loss tangent is more preferably 0.0012 or less, even more preferably 0.0011 or less, even more preferably 0.0010 or less, and particularly preferably 0.0009 or less. Meanwhile, the lower limit of the dielectric loss tangent is preferably 0.00001.

[0057] The fluororesin sheet preferably has a relative dielectric constant of 3.5 or less at 10 GHz. A dielectric constant within this range is preferable in that it results in low dielectric loss. The upper limit of the relative dielectric constant is more preferably 3.2, and even more preferably 3.1. Meanwhile, the lower limit of the relative dielectric constant is preferably 2.0, and more preferably 2.5.

[0058] The relative permittivity (Dk) and dielectric loss tangent (Df) at 10 GHz in this specification are values ​​obtained by measuring Dk and Df at 25°C and 10 GHz using a split cylinder type permittivity / dielectric loss tangent measuring device (manufactured by EM Lab).

[0059] The fluororesin sheet preferably has a thickness of 5 to 250 μm. The lower limit of the thickness is more preferably 15 μm or more, and even more preferably 30 μm or more. The upper limit of the thickness is more preferably 230 μm or less, and even more preferably 200 μm or less. The thickness can be selected in consideration of the balance between the electrical properties and linear expansion coefficient of the laminate.

[0060] As described above, the fluororesin sheet contains a fluororesin and silica particles. The fluororesin and silica particles will be described below.

[0061] (Fluorine resin) Fluorine resin has low dielectric properties and can therefore be suitably used in fluororesin sheets.

[0062] Fluororesins usable for the fluororesin sheet include, but are not limited to, PTFE, tetrafluoroethylene (TFE) / hexafluoropropylene (HFP) copolymer (FEP), TFE / alkyl vinyl ether copolymer (PFA), TFE / HFP / alkyl vinyl ether copolymer (EPA), TFE / chlorotrifluoroethylene (CTFE) copolymer, TFE / ethylene copolymer (ETFE), polyvinylidene fluoride (PVdF), and tetrafluoroethylene with a molecular weight of 300,000 or less (LMW-PTFE). These fluororesins may be used alone or in combination. Among these, PTFE is particularly preferred from the viewpoints of low dielectric constant and low linear expansion coefficient. PTFE with fibrillar properties is preferred. Fibrillar PTFE refers to PTFE that can be paste-extruded from unsintered polymer powder.

[0063] The PTFE may be modified polytetrafluoroethylene (hereinafter referred to as modified PTFE), homopolytetrafluoroethylene (hereinafter referred to as homoPTFE), or a mixture of modified PTFE and homoPTFE. From the viewpoint of maintaining good moldability of polytetrafluoroethylene, the content of modified PTFE in the polymeric PTFE is preferably 10% by mass or more and 98% by mass or less, and more preferably 50% by mass or more and 95% by mass or less.

[0064] The homo-PTFE is not particularly limited, and homo-PTFE disclosed in JP-A-53-60979, JP-A-57-135, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-63-137906, JP-A-2000-143727, JP-A-2002-201217, WO 2007 / 046345 pamphlet, WO 2007 / 119829 pamphlet, WO 2009 / 001894 pamphlet, WO 2010 / 113950 pamphlet, WO 2013 / 027850 pamphlet, etc. can be suitably used. Among these, homo-PTFE having high stretchability and disclosed in JP-A Nos. 57-135, 63-137906, 2000-143727, 2002-201217, WO 2007 / 046345, WO 2007 / 119829, WO 2010 / 113950, etc. is preferred.

[0065] The modified PTFE is composed of TFE and a monomer other than TFE (hereinafter referred to as a modified monomer). Modified PTFE includes, but is not limited to, PTFE uniformly modified with the modified monomer, PTFE modified at the beginning of the polymerization reaction, and PTFE modified at the end of the polymerization reaction. The modified PTFE is preferably a TFE copolymer obtained by polymerizing a small amount of a monomer other than TFE together with TFE within a range that does not significantly impair the properties of the TFE homopolymer.

[0066] Modified PTFEs that can be suitably used include those disclosed in, for example, JP-A-60-42446, JP-A-61-16907, JP-A-62-104816, JP-A-62-190206, JP-A-64-1711, JP-A-2-261810, JP-A-11-240917, JP-A-11-240918, WO 2003 / 033555 pamphlet, WO 2005 / 061567 pamphlet, WO 2007 / 005361 pamphlet, WO 2011 / 055824 pamphlet, WO 2013 / 027850 pamphlet, and the like. Among these, modified PTFEs having high stretchability and disclosed in JP-A Nos. 61-16907, 62-104816, 64-1711, 1999-240917, WO 2003 / 033555, WO 2005 / 061567, WO 2007 / 005361, WO 2011 / 055824, etc. are preferred.

[0067] The modified PTFE contains TFE units based on TFE and modified monomer units based on a modified monomer. The modified monomer units are a part of the molecular structure of the modified PTFE that is derived from the modified monomer. The modified PTFE preferably contains the modified monomer units in an amount of 0.001 to 0.500 mass% of the total monomer units, and more preferably 0.01 to 0.30 mass%. The total monomer units are the parts derived from all monomers in the molecular structure of the modified PTFE.

[0068] The modifying monomer is not particularly limited as long as it is copolymerizable with TFE, and examples thereof include perfluoroolefins such as hexafluoropropylene (HFP), chlorofluoroolefins such as chlorotrifluoroethylene (CTFE), hydrogen-containing fluoroolefins such as trifluoroethylene and vinylidene fluoride (VDF), perfluorovinyl ethers, perfluoroalkylethylenes (PFAE), ethylene, etc. The modifying monomer used may be one type or multiple types.

[0069] The perfluorovinyl ether is not particularly limited, and examples thereof include perfluorounsaturated compounds represented by the following general formula (A). CF2 = CF-ORf (A) (In the formula, Rf represents a perfluoroorganic group.)

[0070] In this specification, a perfluoroorganic group is an organic group in which all hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. The perfluoroorganic group may have an ether oxygen.

[0071] An example of perfluorovinyl ether is perfluoro(alkyl vinyl ether) (PAVE) in which Rf in the above general formula (A) is a perfluoroalkyl group having 1 to 10 carbon atoms. The number of carbon atoms in the perfluoroalkyl group is preferably 1 to 5. Examples of the perfluoroalkyl group in PAVE include perfluoromethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, and perfluorohexyl group. Preferred PAVEs are perfluoropropyl vinyl ether (PPVE) and perfluoromethyl vinyl ether (PMVE).

[0072] The perfluoroalkylethylene (PFAE) is not particularly limited, and examples thereof include perfluorobutylethylene (PFBE), perfluorohexylethylene (PFHE), and the like.

[0073] The modifying monomer in the modified PTFE is preferably at least one selected from the group consisting of HFP, CTFE, VDF, PAVE, PFAE, and ethylene.

[0074] The fluororesin is preferably non-melt-processable. Non-melt-processable means that the resin does not have sufficient fluidity even when heated above its melting point, and cannot be molded by melt molding techniques commonly used for resins. PTFE falls into this category.

[0075] It is preferable to use particles of such non-melt-processable fluororesin and form them into a fluororesin sheet by a molding method that fibrillates the particles, as will be described later.

[0076] The PTFE preferably has a standard specific gravity (SSG) of 2.0 to 2.3. The use of such PTFE facilitates the production of a PTFE membrane with high strength (cohesion and puncture strength per unit thickness). PTFE with a large molecular weight has long molecular chains, making it difficult to form a structure in which the molecular chains are regularly arranged. In this case, the length of the amorphous portion increases, and the degree of entanglement between molecules increases. It is believed that when the degree of entanglement between molecules is high, the PTFE membrane is less likely to deform under an applied load and exhibits excellent mechanical strength. Furthermore, the use of PTFE with a large molecular weight facilitates the production of a PTFE membrane with a small average pore size.

[0077] The lower limit of the SSG is more preferably 2.05, and even more preferably 2.1, and the upper limit of the SSG is more preferably 2.25, and even more preferably 2.2.

[0078] Standard specific gravity (SSG) was measured by preparing a sample in accordance with ASTM D-4895-89 and measuring the specific gravity of the obtained sample by the water displacement method.

[0079] In this embodiment, the molecular weight (number average molecular weight) of the PTFE constituting the PTFE particles is, for example, in the range of 2 million to 12 million. The lower limit of the molecular weight of the PTFE may be 3 million or 4 million. The upper limit of the molecular weight of the PTFE may be 10 million.

[0080] Methods for measuring the number average molecular weight of PTFE include a method of determining it from standard specific gravity and a method of measuring dynamic viscoelasticity in a melt. The method of determining it from standard specific gravity can be carried out by the water displacement method in accordance with ASTM D-792 using a sample molded in accordance with ASTM D-4895 98. The measurement method using dynamic viscoelasticity is explained, for example, by S. Wu in Polymer Engineering & Science, 1988, Vol. 28, 538 and the same document, 1989, Vol. 29, 273.

[0081] The refractive index of the PTFE is preferably in the range of 1.2 to 1.6. Having such a refractive index is preferable in terms of low dielectric constant. The refractive index can be adjusted to fall within the above range by, for example, adjusting the polarizability or the flexibility of the main chain. The lower limit of the refractive index is more preferably 1.25, more preferably 1.30, and most preferably 1.32. The upper limit of the refractive index is more preferably 1.55, more preferably 1.50, and most preferably 1.45.

[0082] The refractive index is a value measured using a refractometer (Abbemat 300).

[0083] The PTFE preferably has a maximum endothermic peak temperature (crystalline melting point) of 340±7°C.

[0084] The PTFE may be a low-melting-point PTFE having a maximum peak temperature of 338°C or lower on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter, or a high-melting-point PTFE having a maximum peak temperature of 342°C or higher on the endothermic curve on the crystalline melting curve measured by a differential scanning calorimeter.

[0085] The low-melting-point PTFE powder is a powder particle produced by emulsion polymerization, and has the maximum endothermic peak temperature (crystalline melting point) mentioned above, a dielectric constant (ε) of 2.08 to 2.2, and a dielectric dissipation factor (tan δ) of 1.9 × 10 -4~4.0×10 -4 Examples of commercially available products include Polyflon fine powders F201, F203, F205, F301, and F302 manufactured by Daikin Industries, Ltd., CD090 and CD076 manufactured by Asahi Glass Co., Ltd., and TF6C, TF62, and TF40 manufactured by DuPont.

[0086] High-melting-point PTFE powder is also a powder particle produced by emulsion polymerization, and has the above-mentioned maximum endothermic peak temperature (crystalline melting point), a dielectric constant (ε) of 2.0 to 2.1, and a dielectric dissipation factor (tanδ) of 1.6 × 10 -4 ~2.2×10 -4 Commercially available products include Polyflon fine powders F104 and F106 manufactured by Daikin Industries, Ltd., CD1, CD141, and CD123 manufactured by Asahi Glass Co., Ltd., and TF6 and TF65 manufactured by DuPont.

[0087] The powder formed by secondary aggregation of both PTFE polymer particles usually preferably has an average particle size of 250 to 2000 μm. In particular, granulated powder obtained by granulation using a solvent is preferred from the viewpoint of improving fluidity when filling a mold during preforming.

[0088] Powdered PTFE particles that satisfy the above-mentioned parameters can be obtained by a conventional manufacturing method, for example, following the manufacturing methods described in International Publication Nos. 2015-080291 and 2012-086710.

[0089] The powdered PTFE preferably has a primary particle diameter of 0.05 to 10 μm. The use of such a powder offers the advantages of excellent moldability and dispersibility. The primary particle diameter here is a value measured in accordance with ASTM D 4895.

[0090] The powdered PTFE preferably contains 50% by mass or more, more preferably 80% by mass or more, of polytetrafluoroethylene resin having a secondary particle diameter of 500 μm or more. The PTFE having a secondary particle diameter of 500 μm or more within this range has the advantage of being able to produce a fluororesin sheet with high strength. By using PTFE having a secondary particle diameter of 500 μm or more, a sheet with lower resistance and excellent toughness can be obtained.

[0091] The lower limit of the secondary particle diameter is more preferably 300 μm, and even more preferably 350 μm. The secondary particle diameter is more preferably 700 μm or less, and even more preferably 600 μm or less. The secondary particle diameter can be determined, for example, by a sieving method.

[0092] The powdered PTFE preferably has an average primary particle diameter of 50 nm or more, since this allows for the production of a sheet with higher strength and excellent homogeneity. It is more preferably 100 nm or more, even more preferably 150 nm or more, and particularly preferably 200 nm or more. The larger the average primary particle diameter of PTFE, the more effectively the increase in paste extrusion pressure can be suppressed when the powder is used for paste extrusion molding, resulting in excellent moldability. The upper limit of the average primary particle diameter is not particularly limited, but it may be 500 nm or less. From the viewpoint of productivity in the polymerization step, the average primary particle diameter is preferably 350 nm or less.

[0093] The average primary particle diameter can be determined by preparing a calibration curve of the transmittance of 550 nm projected light per unit length of an aqueous dispersion of PTFE obtained by polymerization, the polymer concentration of which is adjusted to 0.22% by mass, and the average primary particle diameter determined by measuring the unidirectional diameter in a transmission electron microscope photograph, and measuring the transmittance of the aqueous dispersion to be measured, and then using the calibration curve.

[0094] The PTFE particles used in the fluororesin sheet may have a core-shell structure. Examples of PTFE particles with a core-shell structure include modified polytetrafluoroethylene, which contains a core of high molecular weight polytetrafluoroethylene and a shell of lower molecular weight polytetrafluoroethylene or modified polytetrafluoroethylene. Examples of such modified polytetrafluoroethylene include the polytetrafluoroethylene described in JP-A-2005-527652.

[0095] (silica particles) The fluororesin sheet must contain silica particles. The shape of the silica particles is not particularly limited, but spherical particles are particularly preferred. Spherical particles are preferred because they are easy to process uniformly during drilling, have a small specific surface area, and have low transmission loss. In the fluororesin sheet, it is most preferred to use spherical silica.

[0096] The spherical silica refers to silica whose particle shape is close to a perfect sphere. Specifically, the sphericity is preferably 0.80 or more, more preferably 0.85 or more, even more preferably 0.90 or more, and most preferably 0.95 or more. The sphericity is calculated by taking a photograph with an SEM and calculating the value from the area and perimeter of the observed particle using the formula (sphericity) = {4π × (area) ÷ (perimeter)²}. The closer to 1, the closer to a perfect sphere. Specifically, the average value measured for 100 particles using an image processing device (Spectris Inc.: FPIA-3000) is used.

[0097] The spherical silica used in the fluororesin sheet preferably has a D90 / D10 of 2 or more (preferably 2.3 or more, or 2.5 or more) and a D50 of 10 μm or less, when calculated by volume from the smallest particle size. Furthermore, a D90 / D50 of 1.5 or more is preferable (even more preferably 1.6 or more). A D50 / D10 of 1.5 or more is preferable (even more preferably 1.6 or more). Furthermore, a D50 of 5 μm or less is even more preferable. Since small-particle-size spherical silica particles can fill the gaps between larger-particle-size spherical silica particles, excellent filling properties and high fluidity can be achieved. In particular, the particle size distribution preferably has a higher frequency on the small-particle-size side compared to a Gaussian curve. The particle size can be measured using a laser diffraction / scattering particle size distribution analyzer. Furthermore, because coarse particles make it difficult to form a thin sheet, it is preferable that coarse particles larger than a certain particle size have been removed using a filter or the like.

[0098] The water absorption of the spherical silica is preferably 1.0% or less, and more preferably 0.5% or less. The water absorption is based on the mass of the silica particles when dry. The water absorption is measured by leaving a dry sample at 40°C and 80% RH for 1 hour, and then measuring the water content generated by heating at 200°C using a Karl Fischer moisture content analyzer.

[0099] In addition, the above-mentioned parameters of the spherical silica can also be measured by heating the fluororesin sheet at 600°C for 30 minutes in an air atmosphere to burn off the fluororesin, removing the spherical silica particles, and then using the above-mentioned method.

[0100] The silica particles are preferably surface-treated. By previously subjecting the silica particles to surface treatment, interactions can be created between the silica particles, thereby reducing the linear expansion coefficient of the fluororesin sheet.

[0101] The surface treatment is not particularly limited, and any known treatment can be used. Specific examples include treatment with a silane coupling agent such as epoxysilane, aminosilane, isocyanatesilane, vinylsilane, acrylicsilane, hydrophobic alkylsilane, phenylsilane, or fluorinated alkylsilane, which has a reactive functional group; plasma treatment; and fluorination treatment. Among these, treatment with a silane coupling agent is preferred.

[0102] It is preferable to use silica particles treated with a silane coupling agent as the silica particles contained in the fluororesin sheet. Treating silica particles with a silane coupling agent can reduce the linear expansion coefficient, which is advantageous in that it improves adhesion to metal foil. In addition, by treating with a silane coupling agent, polar functional groups present on the silica particle surface react, reducing the amount of polar functional groups, resulting in excellent electrical properties. Furthermore, the functional groups contained in the silane coupling agent react with the metal foil surface, thereby increasing the peel strength with the metal foil.

[0103] Examples of the silane coupling agent include epoxy silanes such as γ-glycidoxypropyltriethoxysilane and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino silanes such as aminopropyltriethoxysilane and N-phenylaminopropyltrimethoxysilane, isocyanate silanes such as 3-isocyanatepropyltrimethoxysilane, vinyl silanes such as vinyltrimethoxysilane, and acrylic silanes such as acryloxytrimethoxysilane.

[0104] The average particle size of the silica particles is preferably 10 μm or less. An average particle size of 10 μm or less is preferable because the surface roughness of the sheet is low. The upper limit of the average particle size of the silica particles is more preferably 8 μm or less, and even more preferably 5 μm or less. The lower limit of the average particle size of the silica particles is not particularly limited, but is preferably 0.5 μm or more. An average particle size of 0.5 μm or more tends to favorably suppress filler aggregation. The average particle size here is the D50 value measured using a laser analysis particle size distribution analyzer.

[0105] The silica particles may be commercially available silica particles that satisfy the above-mentioned properties. Examples of commercially available silica particles include Denka fused silica FB grade (manufactured by Denka Company Ltd.), Denka fused silica SFP grade (manufactured by Denka Company Ltd.), Excelica (manufactured by Tokuyama Corporation), high-purity synthetic spherical silica particles Admafine (manufactured by Admatechs Co., Ltd.), Admanano (manufactured by Admatechs Co., Ltd.), and Admafuse (manufactured by Admatechs Co., Ltd.).

[0106] The content of the silica particles is preferably 30% by mass or more relative to the total amount of the fluororesin sheet. This content is preferable because it allows for a low linear expansion coefficient while maintaining a low dielectric constant and low loss. Furthermore, when PTFE is used as the fluororesin, oxygen and nitrogen functional groups are not easily formed on PTFE even when plasma treated. However, the presence of silica particles allows the silica surface to have functional groups derived from the surface treatment. As a result, the oxygen atomic ratio on the surface of the fluororesin sheet can be increased, improving the adhesion between the fluororesin sheet and the metal foil and improving the peel strength of the adhesive surface. The content of the silica particles is more preferably 35% by mass or more, even more preferably 50% by mass or more, and even more preferably 55% by mass or more relative to the total amount of the fluororesin sheet. While there is no particular upper limit for the content of silica particles, the content of silica particles is preferably 70% by mass or less, more preferably 68% by mass or less, and even more preferably 65% ​​by mass or less relative to the total amount of the fluororesin sheet.

[0107] (Other ingredients) The fluororesin sheet of the present disclosure may contain components other than the fluororesin and silica particles (hereinafter sometimes referred to as "other components"). The other components are not particularly limited, and examples thereof include fluorine-free thermosetting resins, fluorine-free thermoplastic resins, and fillers other than silica particles. It is preferable that the fluororesin sheet does not contain glass fibers. By not including glass fibers or cloth made of glass fibers, the fluororesin sheet can be made thinner and is more flexible, which has the advantage of making it easier to use in applications where it will be bent.

[0108] The filler other than silica particles is not particularly limited and examples thereof include organic fillers that are at least one selected from polyphenyl ester, polyphenylene sulfide, polyimide, polyether ether ketone, polyphenylene, polyamide, and wholly aromatic polyester resin, and inorganic fillers that are at least one selected from ceramics, talc, mica, aluminum oxide, zinc oxide, tin oxide, titanium oxide, calcium carbonate, calcium oxide, magnesium oxide, potassium titanate, calcium fluoride, boron nitride, barium sulfate, molybdenum disulfide, and potassium carbonate whiskers. Two or more of these may also be used in combination.

[0109] <Laminate> The above-mentioned dielectric layer (for example, a fluororesin sheet) can be used by being laminated with other substrates.

[0110] (Metal-clad laminate) The antenna of the present disclosure may be formed using a metal clad laminate in which a dielectric layer and a metal foil are laminated. Examples of the metal foil used in the present disclosure include metal foils made of the same material as the material constituting the antenna element, and preferred examples include copper foil, gold foil, silver foil, platinum foil, and ruthenium foil. Among these, copper foil is preferred because of its low conductor loss.

[0111] The antenna of the present disclosure may use a metal clad laminate in which a metal foil is bonded to one or both sides of a dielectric layer (more specifically, a fluororesin sheet). A metal clad laminate having a metal foil and a dielectric layer (more specifically, a fluororesin sheet) as essential layers is preferred. Fluororesin sheets containing fluororesin and silica particles have excellent adhesive properties. Therefore, a metal clad laminate in which a metal foil is directly laminated to the surface-treated surface of a dielectric layer (more specifically, a fluororesin sheet) is more preferred.

[0112] To obtain the above-described laminate configuration, the fluororesin sheet is used with metal foil adhered to one or both sides. As described above, the fluororesin sheet that can be used as the dielectric layer in the antenna of the present disclosure has excellent adhesiveness. Therefore, it also has excellent adhesion to metal foil with a high smoothness of Rz 1.0 μm or less.

[0113] Metal foils used to form antenna circuit boards have conventionally been given a certain degree of unevenness on their surfaces to ensure adhesion to fluororesin sheets. However, in high-frequency applications, the presence of unevenness on the surface of metal foils is undesirable because it causes loss of electrical signals. The above-mentioned laminate can achieve suitable adhesion even to highly smooth metal foils, and can be suitably used as an antenna circuit board.

[0114] The metal foil (preferably copper foil) preferably has a surface roughness (Rz) of 1.0 μm or less. A surface roughness (Rz) of 1.0 μm or less makes the interface between the metal foil and the fluororesin sheet smooth, increasing the metal interfacial conductivity and reducing transmission loss, which is preferable. It is sufficient for at least the surface of the metal foil that adheres to the fluororesin sheet to have an Rz of 1.0 μm or less, and the Rz of the other surface is not particularly limited. The fluororesin sheet has excellent adhesion to a highly smooth metal foil with an Rz of 1.0 μm or less, preferably an Rz of 0.9 μm or less, and even more preferably an Rz of 0.5 μm or less. There is no particular restriction on the lower limit of the Rz of the metal foil, but in consideration of productivity, etc., it is preferable that the Rz of the metal foil be 0.2 μm or more.

[0115] The Rz is the sum of the highest point (maximum peak height: Rp) and the deepest point (maximum valley depth: Rv). The Rz is the ten-point average roughness defined in JIS-B0601. In this specification, the Rz is a value measured using a surface roughness meter (product name: Surfcom 470A, manufactured by Tokyo Seiki Co., Ltd.) with a measurement length of 4 mm.

[0116] The metal foil (preferably copper foil) preferably has a surface roughness (Rq) of 0.01 to 0.15 μm. An Rq within the above range is preferable because it can increase the metal interface conductivity and effectively reduce transmission loss. It is sufficient for at least the surface of the metal foil that adheres to the fluororesin sheet to have an Rq of 0.01 to 0.15 μm, and the Rq of the other surface is not particularly limited. The Rq of the surface that adheres to the fluororesin sheet is more preferably 0.015 to 0.1 μm, and even more preferably 0.03 to 0.08 μm. The Rq is the root-mean-square height. In this specification, the Rq is a value measured using a stylus-type surface roughness tester (product name: SE600A, manufactured by Kosaka Laboratory Co., Ltd.) with a measurement length of 4 mm.

[0117] The thickness of the metal foil is not particularly limited, but is preferably 1 to 100 μm, more preferably 5 to 50 μm, and even more preferably 9 to 35 μm.

[0118] The metal foil is not particularly limited, and specific examples include rolled metal foil and electrolytic metal foil.

[0119] The metal foil having Rz of 1.0 μm or less and / or Rq of 0.01 to 0.15 μm is not particularly limited, and commercially available foils can be used. Examples of such commercially available metal foils include electrolytic copper foil CF-T9DA-SV-18 (thickness 18 μm / Rz 0.85 μm / Rq 0.05 μm) (manufactured by Fukuda Metal Foil & Powder Co., Ltd.).

[0120] The metal foil may be surface-treated to increase the peel strength between the metal foil and the fluororesin sheet.

[0121] The surface treatment of the metal foil is not particularly limited, but includes silane coupling treatment, plasma treatment, corona treatment, UV treatment, electron beam treatment, etc. The reactive functional group of the silane coupling agent is not particularly limited, but from the viewpoint of adhesion to resin substrates such as fluororesin sheets, it is preferable that the silane coupling agent has at least one terminal group selected from amino groups, (meth)acrylic groups, mercapto groups, and epoxy groups. Furthermore, the hydrolyzable group is not particularly limited, but examples thereof include alkoxy groups such as methoxy groups and ethoxy groups. The metal foil may have an anti-corrosion layer (such as an oxide film such as chromate), a heat-resistant layer, etc. formed thereon.

[0122] The surface-treated metal foil having a surface treatment layer of the above-mentioned silane compound on the surface of the metal foil can be produced by preparing a solution containing the silane compound and then surface treating the metal foil with this solution.

[0123] The metal foil may have a roughening treatment layer on its surface from the viewpoint of improving adhesion to a resin substrate, etc. If the roughening treatment is likely to deteriorate the performance required in the present disclosure, the amount of roughening particles electrodeposited on the metal foil surface may be reduced as necessary, or the metal foil may not be roughened at all.

[0124] In order to improve various properties, one or more layers selected from the group consisting of a heat-resistant layer, a rust-proofing layer, and a chromate layer may be provided between the metal foil and the surface treatment layer. These layers may be a single layer or multiple layers.

[0125] When the metal clad laminate is formed by directly laminating the surface-treated surface of a dielectric layer (more specifically, a fluororesin sheet) and a metal foil (more specifically, a copper foil), the peel strength of the interface between the metal foil (more specifically, the copper foil) and the dielectric layer (more specifically, the fluororesin sheet) is preferably 0.5 kN / m or more. By using the above-described dielectric layer (more specifically, a fluororesin sheet), a peel strength of 0.5 kN / m or more can be achieved. By achieving a peel strength of 0.5 kN / m or more, the metal clad laminate can be suitably used. The peel strength is more preferably 0.7 kN / m or more. The upper limit of the peel strength is not particularly limited, but may be 3.0 kN / m or less, or may be 1.4 kN / m or less. The peel strength herein refers to the peel strength measured under the conditions described in the examples.

[0126] In addition, in the case of a laminate in which a metal foil is bonded to the surface-treated surface of a fluororesin sheet that has been surface-treated on only one side, a separate surface treatment may be applied to the untreated side of the fluororesin sheet in order to improve the adhesion between the laminate and other materials.

[0127] The metal clad laminate may further include a layer other than the metal foil and the fluororesin sheet, which is preferably a layer of at least one resin selected from the group consisting of polyimide, modified polyimide, liquid crystal polymer, polyphenylene sulfide, cycloolefin polymer, polystyrene, epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene.

[0128] The resin layer, which is a layer other than the metal foil and the fluororesin sheet, may contain reinforcing fibers. The reinforcing fibers are not particularly limited, but for example, glass cloth, particularly low dielectric type, is preferred.

[0129] The layers other than the metal foil and the fluororesin sheet are not particularly limited as long as they are made of the above-mentioned resins, and the layers other than the metal foil and the fluororesin sheet preferably have a thickness of 12.5 to 260 μm.

[0130] Metal clad laminates are used, for example, to form antenna circuit boards.

[0131] Since the metal clad laminate is used to form the antenna of the present disclosure, it is preferable that the metal interfacial conductivity is high. Preferably, it is 1.00 (1e7 S / m) or more, more preferably 3.00 (1e7 S / m) or more, and even more preferably 5.00 (1e7 S / m) or more. There is no particular upper limit, but it is preferably 6.00 (1e7 S / m) or less.

[0132] Since the metal clad laminate is also used to form an antenna circuit board, it is preferable that the transmission loss is close to 0. The transmission loss at a frequency of 67 GHz is preferably −4.20 dB / 100 mm or more, more preferably −4.00 dB / 100 mm or more, and even more preferably −3.30 dB / 100 mm or more.

[0133] The fluororesin sheet has good adhesion to unroughened metal foil, which has low transmission loss. When an antenna is obtained by processing a metal clad laminate including the fluororesin sheet and unroughened metal foil, the gain is improved. Therefore, the metal clad laminate including the fluororesin sheet and unroughened metal foil is particularly suitable for use in manufacturing the antenna of the present disclosure.

[0134] The laminate for forming the antenna circuit board may be formed by laminating a metal foil layer, the above-mentioned fluororesin sheet, and a substrate layer. The substrate layer is not particularly limited, but examples thereof include a fabric layer made of glass fiber and a resin film layer.

[0135] The resin film used as the substrate layer is preferably a heat-resistant resin film or a thermosetting resin film. Examples of heat-resistant resin films include polyimide, modified polyimide, liquid crystal polymer, and polyphenylene sulfide. Examples of thermosetting resins include those containing epoxy resin, bismaleimide, polyphenylene oxide, modified polyphenylene ether, polyphenylene ether, and polybutadiene. The heat-resistant resin film and the thermosetting resin film may contain reinforcing fibers. While the reinforcing fibers are not particularly limited, glass cloth, particularly low-dielectric type fibers, are preferred.

[0136] The dielectric properties, linear expansion coefficient, water absorption coefficient, and other properties of the heat-resistant resin film and thermosetting resin film are not particularly limited, but for example, the dielectric constant at 20 GHz is preferably 3.8 or less, more preferably 3.4 or less, and even more preferably 3.2 or less. The dielectric loss tangent at 20 GHz is preferably 0.0030 or less, more preferably 0.0025 or less, and even more preferably 0.0020 or less. The linear expansion coefficient is preferably 100 ppm / °C or less, more preferably 70 ppm / °C or less, and even more preferably 40 ppm / °C or less. The water absorption coefficient is preferably 1.0% or less, more preferably 0.5% or less, and even more preferably 0.1% or less.

[0137] When a metal clad laminate, which essentially contains a fluororesin sheet and a metal foil, is laminated with a substrate layer such as a resin film layer, the fluororesin sheet layer side of the metal clad laminate can be adhered to the substrate layer. In this case, the fluororesin sheet layer side of the metal clad laminate may be subjected to a surface treatment before lamination to improve adhesion performance. The surface treatment here is not particularly limited, and examples thereof include the above-mentioned plasma treatment.

[0138] In the laminate, the lamination order and manufacturing method of the metal foil layer, substrate, and fluororesin sheet described above are not particularly limited, and a layer configuration according to the purpose can be adopted. Specific examples of the lamination order include a substrate layer / fluororesin sheet / metal foil layer, a metal foil layer / fluororesin sheet / substrate layer / fluororesin sheet / metal foil layer, and a metal foil layer / substrate layer / fluororesin sheet / substrate layer / metal foil layer. Furthermore, other layers can also be included as necessary.

[0139] [Antenna manufacturing method] The method for manufacturing an antenna according to the present disclosure includes, for example, a dielectric layer forming step, a metal clad laminate forming step, and an etching step.

[0140] <Dielectric layer forming process> In the dielectric layer forming step, a dielectric layer is formed. Hereinafter, a case where a fluororesin sheet is formed as the dielectric layer will be described as an example. A fluororesin sheet, which is an example of a dielectric layer, can be obtained, for example, by mixing the above-mentioned fluororesin particles and silica particles, forming a film, and then surface treating the film. The method for forming the film is not limited, but can be paste extrusion molding, powder rolling molding, or the like.

[0141] As described above, it is preferable to use non-melt-processable fluororesin particles as the fluororesin particles used in the fluororesin sheet. When using such fluororesin particles, it is preferable to form them into a sheet by fibrillating powdered PTFE as a raw material.

[0142] The specific methods for the paste extrusion molding and powder rolling molding are not particularly limited, but the following general methods will be described.

[0143] (Film formation by paste extrusion molding) The method for producing the fluororesin sheet may include the steps of: (1a) mixing powdered fluororesin particles obtained using a hydrocarbon surfactant, silica particles, and an extrusion aid; (1b) paste-extrusion molding the resulting mixture; (1c) rolling the extrudate obtained by extrusion; (1d) drying the rolled sheet; and (1e) firing the dried sheet to obtain a molded product. The paste extrusion molding may also be performed by adding conventional additives such as pigments and fillers to the fluororesin particles and silica particles.

[0144] The extrusion aid is not particularly limited, and any commonly known extrusion aid can be used, such as hydrocarbon oil.

[0145] (Film formation by powder rolling) The fluororesin sheet can also be formed by powder rolling. Powder rolling is a method in which powdered fluororesin particles are fibrillated by applying shear force, thereby forming them into a sheet. This method may then include a step of calcining the mixture to obtain a molded product. More specifically, the fluororesin sheet can be obtained by a production method including the steps of: (1) applying shear force while mixing a raw material composition containing fluororesin particles and filler particles; (2) forming the mixture obtained in step (1) into a bulk form; and (3) rolling the bulk mixture obtained in step (2) into a sheet form. The method may further include a step (4) of calcining the sheet-like product obtained above at 200 to 400°C for 1 to 60 minutes. Step (2) may be omitted.

[0146] When a fluororesin sheet is produced by the powder rolling molding method, it is preferable to form a film using a composition that does not contain any liquid components and is essentially composed of fluororesin particles and filler particles containing at least silica particles. The phrase "essentially composed of fluororesin particles and filler particles containing at least silica particles" means that the content of components other than the fluororesin particles and the filler particles is 3 mass% or less based on the total amount of the composition. The filler particles contain at least silica particles, and other filler particles such as aluminum oxide, zinc oxide, titanium oxide, calcium carbonate, and magnesium oxide are preferred. Filler particles other than silica particles may be absent, one type may be used, or two or more types may be used in combination. The amount of filler particles other than silica particles is preferably 0.1 to 80 mass% of the total filler particles. It is particularly preferable to mix and mold only fluororesin particles and silica particles.

[0147] The fluororesin sheet obtained by the above-described method for producing a fluororesin sheet before surface treatment preferably has an oxygen element ratio of 1.5 atomic % or more, at least on the surface to be surface-treated, as measured by X-ray photoelectron spectroscopy (XPS). The presence of oxygen element on the surface of the fluororesin sheet before surface treatment enables good adhesion to a metal foil having a smooth surface. Furthermore, such a range is preferable in order to keep the oxygen element ratio of the fluororesin sheet after surface treatment within the above-described specific range as measured by X-ray photoelectron spectroscopy (XPS). The oxygen atomic ratio is preferably 1.65 atomic % or more, more preferably 1.7 atomic % or more, and even more preferably 1.8 atomic % or more. There is no particular upper limit, but in consideration of the influence on productivity and other physical properties, it is preferably 4.9 atomic % or less. There are no particular limitations on the method for adjusting the oxygen element ratio of the fluororesin sheet before surface treatment to the above-described range, and it may be controlled, for example, by adjusting the amount of silica particles added or the molding method.

[0148] The silicon element ratio of the fluororesin sheet before surface treatment is preferably 0.2 atomic % or more, as measured by X-ray photoelectron spectroscopy (XPS), at least on the surface to be surface-treated. The presence of silicon element on the surface of the fluororesin sheet before surface treatment enables good adhesion to metal foils with smooth surfaces. This range is also preferable in order to ensure that the silicon element ratio of the fluororesin sheet after surface treatment is preferably 0.5 atomic % or more, as measured by X-ray photoelectron spectroscopy (XPS). The silicon element ratio is preferably 0.3 atomic % or more, more preferably 0.5 atomic % or more, and even more preferably 0.7 atomic % or more. There is no particular upper limit, but in consideration of the influence on productivity and other physical properties, it is preferably 2.0 atomic % or less. The silicon element ratio of the fluororesin sheet before surface treatment can be set within the above range by, for example, adjusting the amount of silica particles added.

[0149] (Surface treatment) The fluororesin sheet obtained by the above method can be surface-treated on one or both sides under appropriate conditions to obtain a fluororesin sheet that satisfies the above requirements. Fluororesins are generally difficult to adhere to metal foils. Therefore, it is preferable to perform a surface treatment on the fluororesin sheet to improve lamination properties. Such surface treatments are generally known to involve increasing the amount of oxygen atoms on the resin surface.

[0150] The specific method of the surface treatment is not particularly limited, and any known method can be used. The surface treatment of the fluororesin sheet can be a conventional discharge treatment such as plasma discharge treatment, corona discharge treatment, glow discharge treatment, or sputtering treatment. Among these, plasma treatment is preferred.

[0151] Plasma treatment is a process in which the fluororesin on the outer surface of a fluororesin sheet is etched by bringing the sheet into contact with plasma, thereby adding oxygen atoms, nitrogen atoms, etc. to the outer surface of the fluororesin sheet. For example, the surface free energy can be controlled by introducing oxygen gas, nitrogen gas, hydrogen gas, helium gas, argon gas, etc. into a discharge atmosphere.

[0152] Alternatively, the surface to be modified may be exposed to an atmosphere of an organic compound-containing inert gas, which is an inert gas containing an organic compound, and a high-frequency voltage is applied between electrodes to cause a discharge, thereby generating active species on the surface, and then the surface treatment may be performed by introducing a functional group of the organic compound or graft-polymerizing a polymerizable organic compound.

[0153] Examples of the organic compound in the organic compound-containing inert gas include polymerizable or non-polymerizable organic compounds containing oxygen atoms, such as vinyl esters such as vinyl acetate and vinyl formate; acrylic esters such as glycidyl methacrylate; ethers such as vinyl ethyl ether, vinyl methyl ether, and glycidyl methyl ether; carboxylic acids such as acetic acid and formic acid; alcohols such as methyl alcohol, ethyl alcohol, phenol, and ethylene glycol; ketones such as acetone and methyl ethyl ketone; carboxylic esters such as ethyl acetate and ethyl formate; and acrylic acids such as acrylic acid and methacrylic acid. Among these, vinyl esters, acrylic esters, and ketones are preferred, and vinyl acetate and glycidyl methacrylate are particularly preferred, in view of the fact that the modified surface is less likely to be deactivated, has a long life, and is easy to handle.

[0154] The concentration of the organic compound in the organic compound-containing inert gas varies depending on the type of organic compound, the type of fluororesin to be surface-treated, etc., but is usually 0.1 to 3.0% by volume, preferably 0.1 to 1.0% by volume, more preferably 0.15 to 1.0% by volume, and even more preferably 0.30 to 1.0% by volume. The discharge conditions may be appropriately selected depending on the desired degree of surface treatment, the type of fluororesin, the type and concentration of the organic compound, etc. Typically, the discharge rate is 50 W·min / m 2 More than 1500W min / m 2 Less than 70W·min / m 2 More than 1400W min / m 2 Discharge treatment is carried out within the following range. The treatment temperature can be any temperature within the range of 0°C to 100°C. A temperature of 80°C or less is preferable due to concerns about stretching and wrinkling of the fluororesin sheet.

[0155] <Metal clad laminate formation process> In the metal clad laminate forming step, a metal clad laminate is formed. In the metal clad laminate, the metal foil layer may be formed on one side or both sides of the rolled sheet. Methods for forming the metal foil layer include a method of laminating (adhering) a metal foil on the surface of the rolled sheet, a vapor deposition method, and a plating method. Methods for laminating the metal foil include a method using heat pressing. The heat pressing temperature may be from the melting point of the sheet −150° C. to the melting point of the sheet +40° C. The heat pressing time is, for example, 1 to 30 minutes.

[0156] For example, a suitable method is to produce a metal clad laminate by laminating a dielectric layer (more specifically, a fluororesin sheet) and a metal foil, heating the laminate at 180 to 390°C, and press-molding the laminate under a pressure of 0.5 to 5 MPa in a vacuum or in an inert gas atmosphere. Press-molding under such conditions prevents deterioration of the dielectric layer and also enables adhesion to the metal foil.

[0157] <Etching process> In the etching process, the metal clad laminate is etched. An antenna pattern is printed on the metal foil of the metal clad laminate by etching, forming an antenna circuit board, which is a printed circuit board. More specifically, based on antenna pattern data, the metal foil of the metal clad laminate is divided into a patterned region where the antenna pattern is formed and a non-patterned region where the antenna pattern is not formed. An etching solution is used to dissolve and remove the metal foil in the non-patterned region, leaving the metal foil in the patterned region, thereby forming an antenna pattern composed of metal foil on the substrate. The antenna pattern includes, for example, an antenna element and a transmission path. In this manner, an antenna is manufactured that includes an antenna circuit board having a substrate, an antenna element composed of metal foil, and a transmission path composed of metal foil. Examples of etching solutions include acid or alkali chemical solutions, more specifically, an aqueous solution of ferric chloride. After etching, the antenna circuit board may be washed and dried as needed. Instead of wet etching using an etching solution, dry etching using a gas may be performed. The specific etching method is not particularly limited, and any known method may be used.

[0158] [How to use the antenna] A method for using an antenna according to the present disclosure includes using the antenna in a predetermined frequency band. The antenna according to the present disclosure has a predetermined relative radiation efficiency as high as 17.5 dB or more, making it particularly suitable for use in the predetermined frequency band.

[0159] [Antenna use] The antenna of the present disclosure is suitable for use as an antenna for a radome, an antenna for a metasurface, or a reflector for a metasurface, which also require a low dielectric constant and low loss, making the present antenna suitable.

[0160] Although the embodiments of the present disclosure have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims. [Example]

[0161] The present disclosure will be specifically described below based on examples. However, the present disclosure is not limited to the following examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass," respectively.

[0162] Each of the obtained samples was evaluated based on the following criteria.

[0163] [Fluororesin sheet thickness] Measurements were taken using a micrometer.

[0164] [XPS measurement of fluororesin sheet surface] Measurements were performed using a scanning X-ray photoelectron spectrometer (XPS / ESCA) PHI5000VersaProbeII (ULVAC-PHI, Inc.).

[0165] Coefficient of Linear Expansion (CTE) TMA measurements were performed in tensile mode using a TMA-7100 (Hitachi High-Tech Science Corporation). A fluororesin sheet cut to a length of 20 mm, width of 5 mm, and thickness of 150 μm was used as a sample piece. The distance between the chucks was set to 10 mm, and the linear expansion coefficient was calculated from the displacement of the sample from 0 to 150°C at a heating rate of 2°C / min while applying a load of 49 mN.

[0166] [Dielectric constant and dielectric loss tangent of fluororesin sheet] The dielectric constant and dielectric loss tangent were measured at 25°C and 10 GHz using a split cylinder type dielectric constant and dielectric loss tangent measuring device (manufactured by EM Lab).

[0167] [Static contact angle of water] The static contact angle of water on the prepared fluororesin sheet was measured using a contact angle meter ("DropMaster" manufactured by Kyowa Interface Science Co., Ltd.) at 23°C, with a droplet volume of 2 μL, one second after the droplet landed.

[0168] [Peel Strength] After the surface treatment, copper foil (CF-T9DA-SV-18, manufactured by Fukuda Metal Foil Powder, Rz = 0.85 μm, Rq = 0.05 μm) was placed on top and bottom of the fluororesin sheet so that the treated side was in close contact with the fluororesin sheet, and the foil was then pressurized and heated in a vacuum heat press (360°C, 2.5 MPa, 300 s) to produce a sample. The resulting sample was cut into 10 mm wide strips, and the peel strength was measured using a Tensilon universal testing machine (manufactured by Shimadzu Corporation) by gripping the unbonded portion of the strip with the top and bottom chucks of the Tensilon and pulling at a rate of 50 mm per minute. The value obtained was taken as the peel strength.

[0169] [Specified relative radiation efficiency of antenna] The predetermined relative radiation efficiency of the antenna was measured in a millimeter-wave anechoic chamber. The right side of the millimeter-wave anechoic chamber was the transmitting side, and the left side was the receiving side. A transmitting device connected to the antenna under test (one of the antennas in Examples 1 to 10 and Comparative Example 1 described below) was installed on the right side of the millimeter-wave anechoic chamber. The reflection coefficient (S11) was measured using the transmitting device. A vector network analyzer ("MS46522B" manufactured by Anritsu Corporation) was used as the reflection coefficient measuring device that also served as the transmitting device. A receiving probe was installed on the left side of the millimeter-wave anechoic chamber. A WR12-sized separated waveguide was used as the receiving probe. Two linear stages were used to move the receiving probe on the XY plane, and planar scanning near-field measurements were performed. The measurement range in the XY-axis direction on the XY plane was ±150 mm, with a movement step of 1 mm. The distance between the receiving probe and the antenna under test was 50 mm. To measure the polarization characteristics, the receiving probe was rotated 0 degrees and 90 degrees around its longitudinal axis. The measurement frequency was 82.5 GHz. The relative radiation efficiency was calculated by converting the measured reflection coefficient (S11) using the planar scanning near-field far-field transformation (PNFFFT) method with the pattern integration method on the upper half plane. The specified relative radiation efficiency was rounded down to one decimal place to determine whether it was 17.5 dB or higher.

[0170] [Examples 1 to 10] <How to make sheets A to D> (Paste extrusion molding) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17) and silica particles shown in Table 1 were weighed out to the mass ratio shown in Table 1 and mixed in a mixer in the presence of dry ice. The temperature during mixing was -10°C or below. 18 to 23% oil (IP Solvent 2028) was added to the obtained mixed powder, mixed, and aged for about 5 hours. The aged composition was preformed under a pressure of 3 MPa, and the preformed compact was extruded at 40°C and 50 mm / min to obtain an extrusion sample. The extrusion sample was rolled using two rolls to obtain a sample with a thickness of 125 μm. The sample was passed through a drying roll at 200°C, dried for 2 hours, and baked at 360°C for 15 minutes to obtain a sheet. Furthermore, it was confirmed that a sample with a thickness of 30 μm could be produced by adjusting the gap and pressure of the two rolls.

[0171] <How to make Sheet AP> (Powder rolling molding) PTFE powder (average particle size: 500 μm, apparent density: 460 g / L, standard specific gravity: 2.17) and silica particles shown in Table 1 were weighed out to obtain the mass ratio shown in Table 1, and stirred twice for 30 seconds at room temperature with a Wonder Crusher at 6. The resulting mixture was rolled with two rolls (roll gap: set to 100 μm, roll temperature: 100°C) to obtain a sample with a film thickness of 130 μm, which was then baked at 360°C for 15 minutes to obtain a sheet.

[0172] The silica used in producing Sheets A, AP, B, and C was spherical silica SC6500-SQ (average particle size 2.1 μm) manufactured by Admatechs Co., Ltd., which was surface-treated with 3-aminopropyltriethoxysilane (a treatment amount of 0.5% by mass or 1% by mass relative to the mass of the silica particles), as shown in Table 1. The silica used in producing Sheet D was spherical silica SC6500-SQ (average particle size 2.1 μm) manufactured by Admatechs Co., Ltd., which was used without surface treatment, as shown in Table 1.

[0173] [Table 1]

[0174] <Surface treatment of fluororesin sheet> A fluororesin sheet (each of the prepared sheets A to D and AP) was placed between the upper and lower electrodes in a treatment chamber (direct-type plasma surface treatment device, manufactured by Air Water Inc.), and the treatment chamber was filled with the treatment atmosphere of the following mixed gas, after which the surface of the fluororesin sheet was subjected to discharge plasma treatment for the treatment time shown in Table 2. The elemental composition of the surface-treated fluororesin sheet was measured by XPS. (treatment atmosphere) GA: A mixture of argon, helium, and oxygen GB: Argon, helium, nitrogen and oxygen mixture

[0175] <Preparation of double-sided copper-clad laminate> Copper foil (CF-T9DA-SV-18, manufactured by Fukuda Metal Foil Powder, Rz=0.85μm, Rq=0.05μm) was placed on top and bottom of the surface-treated fluororesin sheet so that the treated side was in close contact with the sheet, and the sheet was inserted into a vacuum heat press. The temperature was raised from room temperature to 360°C under vacuum, and then the sheet was pressed at 360°C with a pressure of 3MPa to produce a double-sided copper-clad laminate.

[0176] <Etching process> The copper foil of the double-sided copper-clad laminate was etched with an aqueous solution of ferric chloride to form a patch antenna pattern. The etched double-sided copper-clad laminate was washed with running clean water for 2 to 5 minutes, then washed with distilled water, and dried in a thermostatic oven at 80±3°C for approximately 60 minutes. In this way, the antennas of Examples 1 to 10, which are patterned patch array antennas, were obtained.

[0177] The substrate size of the fabricated antenna was 61.5 mm long and 24.5 mm wide. The patch antenna pattern fabricated by etching was as follows: The patch antenna pattern was a 16x8 arrangement, and the antenna elements were rectangular, 1.15 mm long and 1.30 mm wide. The antenna element array was arranged parallel to the length of the substrate. In the antenna element array, the 16 antenna elements were spaced apart by 2.20 mm (center-to-center distance between the antenna elements). The 8-row antenna element array was spaced apart by 1.90 mm (center-to-center distance between the antenna elements). The antenna elements were arranged in a rectangular array.

[0178] [Comparative Example 1] The antenna of Comparative Example 1 was fabricated in the same manner as in Examples 1 to 10, except that RO3003 (manufactured by Rogers) was used instead of the double-sided copper-clad laminate. RO3003 is a double-sided roughened copper-clad laminate of a composite sheet of fluororesin and filler. Analysis of RO3003 confirmed the presence of non-spherical inorganic fillers.

[0179] The results of Examples 1 to 10 and Comparative Example 1 are shown in Table 2.

[0180] [Table 2]

[0181] In addition to the measurements whose results are shown in Table 2, the following measurements were also performed.

[0182] [Metal interface conductivity measurement] From the double-sided copper-clad laminates thus prepared, circular dielectric samples (no copper on both sides) and circular dielectric samples (with circular copper foil patterning on one side) were prepared, and the metal layer interface conductivity (1e7 S / m) was measured in the frequency range of 14.5 GHz to 111.5 GHz using a balanced disk resonator method. The average metal layer interface conductivity of the double-sided copper-clad laminates used to prepare the antenna of Example 6 was 5.66 (1e7 S / m), a result equivalent to that of the reference copper disk.

[0183] Similarly, the average metal layer interface conductivity was measured using a commercially available double-sided copper-clad laminate (manufactured by Rogers) made of a composite sheet of fluororesin and filler, and was found to be 0.56 (1e7 S / m). This demonstrates that the double-sided copper-clad laminate used in fabricating the antenna of Example 6 has a higher metal interface conductivity than commercially available double-sided copper-clad laminates.

[0184] From the above experimental results, it is clear that the predetermined relative radiation efficiency of the antennas of Examples 1 to 10 is 1.67 dB or more better than that of the antenna of Comparative Example 1, and that the relative radiation efficiency in the predetermined frequency band is good. [Industrial Applicability]

[0185] The antenna of the present disclosure can be suitably used as an antenna for a millimeter wave radar for mobility purposes such as collision prevention.

Claims

1. An antenna for radar used in a frequency band of 70 GHz or more and 90 GHz or less, An antenna having a relative radiation efficiency of 17.5 dB or greater measured at a frequency of 82.5 GHz.

2. The antenna of claim 1 , wherein the antenna is a patch array antenna.

3. the antenna has a plurality of antenna elements; The plurality of antenna elements are configured to form 8 to 16 antenna element rows, each row having 16 to 64 antenna elements arranged in a straight line, 3. The antenna according to claim 1, wherein the 8 to 16 antenna element rows are arranged parallel to one another.

4. the antenna has a dielectric layer; the dielectric layer is a fluororesin sheet containing a fluororesin and silica particles, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) is 3.0 atomic% or more on one or both sides of the fluororesin sheet; 3. The antenna according to claim 1, wherein the fluororesin sheet has a coefficient of linear expansion (CTE) of 100 ppm / °C or less.

5. 5. The antenna according to claim 4, wherein the fluororesin is polytetrafluoroethylene.

6. 5. The antenna according to claim 4, wherein the nitrogen element ratio on said surface of said fluororesin sheet is 1.35 atomic % or more when measured by X-ray photoelectron spectroscopy (XPS).

7. 5. The antenna according to claim 4, wherein the silicon element ratio on said surface of said fluororesin sheet is 0.5 atomic % or more when measured by X-ray photoelectron spectroscopy (XPS).

8. 5. The antenna according to claim 4, wherein a static contact angle of water measured on said surface of said fluororesin sheet after one second from the arrival of a 2 μL droplet is 105° or less.

9. 5. The antenna of claim 4, wherein the silica particles are spherical silica.

10. 5. The antenna according to claim 4, wherein the silica particles are silica particles treated with a silane coupling agent.

11. 5. The antenna according to claim 4, wherein the silica particles have an average particle size of 10 μm or less.

12. The antenna according to claim 4 , wherein the fluororesin sheet does not contain glass fibers.

13. 5. The antenna according to claim 4, wherein the content of the silica particles is 30% by mass or more with respect to the total amount of the fluororesin sheet.

14. 5. The antenna according to claim 4, wherein the content of the silica particles is 50% by mass or more with respect to the total amount of the fluororesin sheet.

15. 5. The antenna according to claim 4, wherein the content of the silica particles is 50% by mass or more and 65% by mass or less with respect to the total amount of the fluororesin sheet.

16. 5. The antenna according to claim 4, wherein the fluororesin sheet has a dielectric loss tangent of 0.0015 or less at 10 GHz.

17. 5. The antenna according to claim 4, wherein the thickness of the fluororesin sheet is 5 to 250 μm.

18. The antenna according to claim 4 , wherein the antenna is formed from a metal clad laminate having a metal foil and the dielectric layer as essential layers.

19. 20. The antenna of claim 18, wherein the metal foil is a copper foil.

20. 20. The antenna according to claim 19, wherein the copper foil has a surface roughness (Rz) of 1.0 μm or less.

21. The antenna according to claim 19, wherein the surface roughness (Rq) of the copper foil is 0.01 to 0.15 μm.

22. 20. The antenna according to claim 19, wherein the copper foil and the dielectric layer are directly laminated together, and the peel strength of the interface between the copper foil and the dielectric layer is 0.5 kN / m or more.

23. 3. The antenna according to claim 1, which is a millimeter wave antenna for mobility.

24. The relative radiation efficiency measured at a frequency of 82.5 GHz is 18.0 dB or more and 20.0 dB or less, the antenna has a dielectric layer; the dielectric layer is a fluororesin sheet containing a fluororesin and silica particles, the fluororesin is polytetrafluoroethylene, The silica particles are spherical silica, The content of the silica particles is 50% by mass or more and 65% by mass or less with respect to the total amount of the fluororesin sheet, the oxygen element ratio measured by X-ray photoelectron spectroscopy (XPS) on one or both surfaces of the fluororesin sheet is 3.0 atomic % or more and 25.0 atomic % or less; the silicon element ratio on the surface of the fluororesin sheet is 0.5 atomic % or more and 10.0 atomic % or less when measured by X-ray photoelectron spectroscopy (XPS); 3. The antenna according to claim 1, wherein the fluororesin sheet has a coefficient of linear expansion (CTE) of 31 ppm / °C or more and 70 ppm / °C or less.

25. A method for manufacturing the antenna according to claim 1 or 2, comprising the steps of: a dielectric layer forming step of forming a dielectric layer, In the dielectric layer forming step, a film is formed by mixing fluororesin particles and silica particles, and the film is then surface-treated.

26. 26. The method for manufacturing an antenna according to claim 25, wherein in the dielectric layer forming step, a film is formed using a composition substantially consisting of the fluororesin particles and filler particles containing at least the silica particles, and a surface treatment is performed.

27. The method further includes a metal clad laminate forming step of forming a metal clad laminate, 26. The antenna manufacturing method according to claim 25, wherein in the metal clad laminate forming step, the dielectric layer and the metal foil are laminated, heated at 180 to 390°C, and press-molded at a pressure of 0.5 to 5 MPa under vacuum or in an inert gas atmosphere.

28. The method for manufacturing an antenna according to claim 27, further comprising an etching step of etching the metal clad laminate.

29. A method of using the antenna according to claim 1 or 2, comprising: A method of using an antenna, comprising using the antenna in a frequency band of 70 GHz or more and 90 GHz or less.

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