TW202121446A - High-frequency coaxial cable - Google Patents

Abstract

This high-frequency coaxial cable comprises: a center conductor; an insulating coating layer which covers the outer circumference of the center conductor; a shield layer which covers the insulating coating layer; and a jacket layer which covers the shield layer, wherein the shield layer includes a resin sheet and a metal layer with which the resin sheet is coated, and the shield layer has a resistance value of at most 0.100 [Omega].cm2 in the thickness direction.

Description

Coaxial cable for high frequency

The present invention relates to a coaxial cable for high frequency.

Electronic equipment (personal computers, digital cameras, 8 cm cameras, mobile terminals, etc.), medical equipment, sensing networks, mesh networks, and communication equipment between the two workshops, etc., sometimes use coaxial cables for communication.

For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2015-8072) discloses a coaxial cable for high-frequency signal transmission, which is laminated with an insulating coating layer formed on the outer periphery of the center conductor, and has a shielding layer and a sheath on the outer side Layered coaxial cable, characterized in that the insulating coating layer has a predetermined porous insulating coating layer and a solid insulating coating layer made of fluororesin formed directly above the porous insulating coating layer, and the porous insulating coating layer The porosity of the layer is more than 70% and less than 80%, and the gaps are connected to each other. In addition, this document also describes that it is preferable to use a braided conductor as a shielding layer. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2015-8072

In order to achieve high-speed communication between the above-mentioned devices, high-frequency signals are required for communication. According to the findings of the inventor of the present case, as described in Patent Document 1, when a braided conductor is used as a shielding layer, the transmission loss tends to increase when a high-frequency signal is transmitted. In addition, communication equipment is also required to be smaller and thinner. Along with this, the diameter of the coaxial cable is also required to be reduced. However, the narrower diameter of the coaxial cable will cause transmission loss and band degradation of the transmission path, and the transmission quality will be degraded due to cross talk between transmission paths or external noise. Therefore, as the diameter of the coaxial cable is reduced, problems related to transmission loss when transmitting high-frequency signals have become more prominent. Therefore, it is desired to realize a coaxial cable with a narrow diameter and capable of suppressing transmission loss when transmitting high-frequency signals. That is, the subject of the present invention is to provide a coaxial cable with a narrow diameter and capable of suppressing transmission loss when transmitting high-frequency signals.

As a result of detailed research by the inventor of the present case, it was found that the above-mentioned problems can be solved by using a material of a predetermined composition as a shielding layer, and the present invention has been completed. That is, the present invention is realized by the following means. [1] A coaxial cable for high frequency, comprising: a linear central conductor; an insulating coating layer covering the central conductor; a shielding layer covering the insulating coating layer; and a sheath layer covering the shielding layer; the shielding layer having The resin sheet and the metal layer coated on the resin sheet, the shielding layer has a thickness direction resistance value of ^{0.100Ω･cm 2 or less.} [2] The coaxial cable as in [1] above, wherein the weight per unit area of the metal layer is 25 g/m ² or more. [3] The coaxial cable according to any one of [1] or [2] above, wherein the surface resistivity of the shielding layer is below 0.01Ω/□. [4] A coaxial cable for high frequency, comprising: a central conductor; an insulating coating layer covering the outer periphery of the central conductor; a shielding layer covering the insulating coating layer; and a sheath layer covering the shielding layer; the shielding layer provided with a resin sheet And a metal layer coated on the resin sheet; the metal layer forms a closed shape in the cross section of the coaxial cable. [5] The coaxial cable according to any one of [1] to [4] above, wherein the resin sheet is a sheet having higher heat resistance than the sheath layer. [6] The coaxial cable according to any one of [1] to [5] above, wherein the resin sheet is a polyaramide paper containing short polyaramide fibers and/or polyaramide fibrids. [7] The coaxial cable according to any one of [1] to [6] above, wherein the resin sheet contains a conductive filler. [8] The coaxial cable as in any one of [1] to [7] above, wherein the coaxial cable is overhand knotted and pulled at a strength of 1/2 of the tensile strength of the sheath layer When the coaxial cable is stretched, the outer diameter of the single junction part is less than 4 times the outer diameter of the coaxial cable. [9] The coaxial cable as in any one of [1] to [8] above, wherein in the range of 0.045～18GHz, the slope of frequency (GHz)-transmission attenuation (dB) is above -0.8 (dB/GHz) .

According to the present invention, there is provided a coaxial cable capable of suppressing transmission loss even when the frequency of the transmitted signal is high.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [First Implementation Type] (Coaxial cable)

FIG. 1 is a cross-sectional view schematically showing a high-frequency coaxial cable 10 according to the first embodiment of the present invention. The coaxial cable 10 of this embodiment, as shown in FIG. 1, has a central conductor 1, an insulating coating layer 2, a shielding layer 3, and a sheath layer 4. The center conductor 1 is linear. The insulating coating layer 2 covers the center conductor 1 full circle. The shielding layer 3 is covered with the insulating coating layer 2 for a full circle. The sheath layer 4 covers the shield layer 3 in a full circle. In order to strengthen the adhesion between the central conductor 1 and the insulating coating layer 2, the adhesion between the insulating coating layer 2 and the shielding layer 3, and the adhesion between the shielding layer 3 and the sheath layer 4, an adhesive layer may also be provided between each member.

The shielding layer 3 has a thickness direction resistance value of ^{0.100Ω･cm 2 or less.} The thickness direction resistance value of the shielding layer 3 is preferably 0.025Ω･cm ² or less. FIG. 2 is a schematic diagram showing an example of the structure of the shielding layer 3. In addition, the illustration of the constituent elements other than the shielding layer 3 is omitted in FIG. 2. The shielding layer 3 has a metal layer 3-1 and a resin sheet 3-2. The resin sheet 3-2 has an elongated shape with a width longer than the outer circumference of the insulating coating layer 2. The metal layer 3-1 is a layer coated on the resin sheet 3-2. The metal layer 3-1 is coated on both sides of the resin sheet 3-1. The side end surface (one end a, the other end b) of the resin sheet 3-2 is not provided with the metal layer 3-1. The shielding layer 3 has one end portion and the other end portion in the width direction overlapping in the radial direction of the cable 10, and is wound around the insulating coating layer 2 so as to cover the outer circumference of the insulating coating layer 2, that is, in a longitudinal reel.

According to the above configuration, since the shielding layer 3 has ^{a thickness direction resistance value of 0.100Ω·cm 2} or less, electromagnetic waves can be prevented from leaking from the inside to the outside of the shielding layer 3, and transmission loss can be suppressed. That is, even in the case of transmitting high-frequency signals, the transmission loss is not easy to increase. For example, according to this embodiment, a coaxial cable 10 with a frequency (GHz)-transmission attenuation (dB) slope above -0.8 (dB/GHz) in the range of 0.045 to 18 GHz can be obtained.

In addition, the resin sheet 3-2 coated with the metal layer 3-1 is excellent in processability. For example, if the shielding layer 3 formed of a single metal sheet is used for a small-diameter coaxial cable 10, the metal sheet may be broken and the shielding layer 3 may not be properly formed. In contrast, according to the present embodiment, even in the case of a coaxial cable 10 with a small diameter, the shielding layer 3 can be appropriately formed. Furthermore, according to the present embodiment, by using the resin sheet 3-2 coated with the metal layer 3-1 as the shielding layer 3, a flexible and lightweight coaxial cable 10 can be obtained. The soft and lightweight coaxial cable 10 can be used in various applications. For example, according to this embodiment, as shown in FIG. 3, the following coaxial cable 10 can be obtained: the coaxial cable 10 is single-knotted, and the coaxial cable 10 is stretched at a strength of 1/2 of the tensile strength of the sheath layer 4. In the case of the cable 10, the outer diameter of the single junction portion is 4 times or less the outer diameter of the coaxial cable 10.

In addition, the shielding layer 3 only needs to have the resin sheet 3-2 and the metal layer 3-1, and has ^{a thickness direction resistance value of 0.100 Ω·cm 2} or less, and it does not have to be rolled into the shape shown in FIG. 2. Moreover, it does not necessarily have to be wound in a longitudinal reel. For example, a belt-shaped resin sheet 3-2 coated with a metal layer 3-1 on the surface may be wound spirally on the insulating coating layer 2 without gaps. In the example shown in FIG. 2, the side end surface (one end a, the other end b) of the resin sheet 3-2 is not provided with the metal layer 3-1, but the metal layer 3-1 may be provided on the end surface. Furthermore, the metal layer 3-1 does not have to be formed on both sides of the resin sheet 3-1, as long as it is coated on at least one of the inner surface and the outer surface. Preferably, the metal layer 3-1 is formed on at least the inner surface of the resin sheet 3-1.

The components of the coaxial cable 10 will be described in detail below. (Central conductor)

The center conductor 1 is preferably a circular conductor (a conductor with a circular cross section). From the viewpoint of durability (bending resistance) against repeated bending and stranding, the central conductor 1 is preferably composed of a stranded conductor formed by twisting a plurality of conductor material wires. The diameter of the conductor material wire is preferably 0.05 mm or more from the viewpoint of reducing signal loss, and preferably 0.20 mm or less from the viewpoint of improving the bending resistance. In addition, the twist pitch of the stranded wire conductor is preferably 20 times or more and 50 times or less the diameter of the conductor material wire. If the stranding pitch is more than 20 times the diameter of the material wire, the length of the material wire will not become too long, resulting in an increase in resistance, and will not reduce the transmission attenuation characteristics. On the other hand, if the twisting pitch is less than 50 times the diameter of the material wire, the twisted shape will not easily collapse during repeated bending due to the loose twisting. The number of stranded wire conductors (the number of strands) is preferably 7 strands or 19 strands from the viewpoint of being close to a circular conductor. From the viewpoint of meeting the requirement of reducing the diameter of the coaxial cable 10, 7 strands are more preferable. The material constituting the center conductor 1 is not particularly limited as long as it is a conductive material, and copper, TA (Tin coated Annealed copper wires), and the like can be used. (Insulation coating)

The insulating coating layer 2 is formed on the entire outer peripheral surface of the center conductor 1 so as to cover the center conductor 1. The material of the insulating coating layer 2 is not particularly limited as long as it is insulating. For example, polyethylene resins such as polyethylene, polypropylene, and polyvinyl chloride can be used; polytetrafluoroethylene (PTFE), tetrafluoroethylene and perfluoroalkane Fluorine-based resins such as vinyl ether copolymer (PFA), tetrafluoroethylene and hexafluoropropylene copolymer (FEP); and such foams. In order to realize a low capacitance cable, it is preferable to use a fluororesin having a lower dielectric constant. Specifically, polytetrafluoroethylene (PTFE), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), and tetrafluoroethylene/hexafluoropropylene copolymer (FEP) are desirable. The insulating coating layer 2 is preferably formed by tubular extrusion from the viewpoint of easy fixation of the central conductor 1. (Sheath layer)

The material of the sheath layer 4 is not particularly limited. For example, polyethylene resins such as polyethylene, polypropylene, and polyvinyl chloride can be used; polytetrafluoroethylene (PTFE), tetrafluoroethylene and perfluoroalkyl vinyl ether copolymer (PFA) and fluorine resins such as tetrafluoroethylene and hexafluoropropylene copolymer (FEP); and such foams. From the viewpoints of abrasion resistance, low friction, low temperature resistance, heat resistance, etc., polytetrafluoroethylene (PTFE), tetrafluoroethylene, perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene are ideal ･Fluorine resins such as hexafluoropropylene (FEP). (Shield)

The shielding layer 3 is provided between the insulating coating layer 2 and the sheath layer 4 as described above. The shielding layer 3 is composed of a resin sheet 3-2 coated with a metal layer 3-1. As mentioned above, the metal layer 3-1 is preferably coated on both sides of the resin sheet 3-2. However, the metal layer 3-1 may also be coated on the inner surface of the resin sheet 3-2. In addition, the metal layer 3-1 may be applied to the end surface of the resin sheet 3-2 in addition to the inner and outer surfaces of the resin sheet 3-2.

As the resin sheet 3-2, it is preferable to use a highly heat-resistant sheet. The "high heat-resistant sheet" is a sheet composed of a material having a higher melting point than the material constituting the sheath layer 4, or a sheet composed of a resin that does not substantially exhibit a stable melting point. It is preferable to coat such a resin sheet 3-2 with gold, silver, copper, zinc, nickel, tin, etc., or an alloy thereof to form the metal layer 3-1. Thereby, the shielding layer 3 excellent in conductivity can be formed. When the coaxial cable 10 is manufactured, the shielding layer 3 is arranged so as to cover the insulating coating layer 2. Next, the resin constituting the sheath layer 4 is placed in a molten state so as to cover the shield layer 3. Furthermore, the resin constituting the sheath layer 4 is cured. In the coaxial cable 10 manufactured in this way, the adhesion between the insulating coating layer 2, the shielding layer 3, and the sheath layer 4 becomes high. If the adhesion is high, transmission loss can be suppressed, and high-speed transmission can be performed.

The shielding layer 3 preferably has a surface resistivity of 0.01Ω/□ or less.

Ideally, the shielding layer 3 is preferably made of conductive polyaramide paper. The conductive polyaramide paper will be described in detail below. (Conductive polyaramide paper)

The conductive polyaramide paper uses polyaramide paper as the resin sheet 3-2, and the polyaramide paper is coated with a metal to form a metal layer 3-1. Conductive polyaramide paper, because (1) has conductivity, (2) has higher heat resistance than the resin constituting the sheath layer 4, (3) has high shape stability, and (4) has good processing Therefore, it is suitable as the resin sheet 3-2 for the coaxial cable of this embodiment.

The conductive polyaramide paper is cut into a rectangle extending in one direction, and the insulating coating layer 2 is arranged in a spirally wound or longitudinal roll shape on the outer periphery of the insulating coating layer 2 to form the shielding layer 3. From the viewpoint of productivity, it is preferable to form the shielding layer 3 in a longitudinal roll. After the shielding layer 3 is formed in a longitudinal roll, the molten material for the sheathing layer 4 is used, and the shielding layer 3 is fixed by tubular extrusion. This prevents gaps in the shielding layer 3. In addition, in the coaxial cable 10 formed by such a method, the adhesion between the insulating coating layer 2 and the shield layer 3 and the adhesion between the shield layer 3 and the sheath layer 4 are also improved. As mentioned above, by improving the adhesion, especially the transmission attenuation characteristics at high frequencies can be improved. Furthermore, in order to improve the transmission attenuation characteristics, a drain wire may also be arranged inside the sheath 4 within a range that does not hinder the flexibility of the cable. The material of the drain wire is preferably copper, TA, but not limited to these. In the case of spiral winding, it is preferable to wind the conductive polyarylene with a fixed ratio of 30% or more and less than 55% of the width of the conductive polyaramide paper overlapped between two adjacent turns. Amine paper, more preferably the overlap is more than 45% and less than 50%. If the overlap is 30% or more of the width of the conductive polyaramide paper, the difference between one piece and two pieces in the longitudinal direction of the conductive polyaramide paper can be completed. If the overlap is less than 55%, the conductive polyaramide paper will not overlap 3 or more parts in the longitudinal direction, and the variation in outer diameter or porosity can be suppressed, and the characteristic impedance of the entire coaxial cable 10 can be suppressed. Uneven. In order to obtain a stable characteristic impedance, it is preferable to configure the shielding layer 3 in the manner of a longitudinal roll.

As the polyaramide paper, those having polyaramide short fibers and/or polyaramide fibrids can be preferably used. More ideally, the polyaramide paper includes polyaramide staple fibers, polyaramide fibrids, and conductive fillers.

In the total weight of the polyaramide paper (the material before the metal layer 3-1 is coated), the content of the polyaramide staple fiber is preferably 5-60% by weight, more preferably 10-55% by weight, and It is preferably 20-50% by weight, but is not limited thereto. If the content of the polyaramide staple fiber is 5% by weight or more, the mechanical strength of the conductive polyaramide paper can be maintained. If the content of polyaramide staple fiber is less than 60% by weight, the content of polyaramide fibrids can be ensured and the mechanical strength can still be maintained.

In the total weight of the polyaramide paper, the content of the polyaramide fibrids is preferably 30 to 80% by weight, more preferably 35 to 70% by weight, still more preferably 40 to 65% by weight, but not Limited to this. Generally speaking, if the content of polyaramide fibrids is 30% by weight or more, the mechanical strength of the conductive polyaramide paper can be maintained, and if it is 80% by weight or less, it can be manufactured in a wet process (described later). ) The water filterability will not decrease, and the uniformity of conductive polyaramide paper can also be prevented. The content of the conductive filler in the total weight of the polyaramide paper is preferably 1-30% by weight, more preferably 3-30% by weight. If it is within such a range, the conductivity of the conductive polyaramide paper can be sufficiently ensured.

In order to reduce the thickness direction resistance value of the conductive polyaramide paper, the coating state of the metal layer 3-1 can also be emphasized. For example, when metal coating is applied, if it is also applied to the end surface of the conductive polyaramide paper, the resistance value in the thickness direction can be reduced. Specifically, the polyaramide paper is cut to the width when it is installed on the cable, and then metal coating is performed. Thereby, metal can also be coated on the end surface of polyaramide paper. As a result, the resistance value in the thickness direction can be reduced. Or during coating, the metal is continuously impregnated from one surface of the polyaramide paper to the other surface, and a polyaramide paper with a small thickness (for example, 50 μm or less, preferably 40 μm or less) is used. With this method, the resistance value in the thickness direction can also be reduced. By reducing the thickness direction resistance value in the shielding layer 3, electromagnetic waves can be prevented from leaking from the high-resistance portion of the shielding layer 3, and the transmission attenuation characteristics at high frequencies are particularly reduced.

As the metal material used in the metal layer 3-1, for example, gold, silver, copper, zinc, nickel, tin, etc., alloys of these, and the like can be cited. In consideration of conductivity and manufacturing cost, copper is preferred. However, it is not particularly limited as long as it is selected in consideration of electromagnetic wave shielding properties and durability. The content (weight per unit area) of the metal layer 3-1 formed on the conductive polyaramide paper preferably has an average value of 25 g/m ² or more. As long as the amount of the metal layer 3-1 is within this range, sufficient conductivity can be obtained. The weight per unit area of the metal layer 3-1 is more preferably 25-100 g/m ² .

Whether or not the metal layer 3-1 is properly formed in the conductive polyaramide paper can be confirmed by measuring the surface resistivity and the resistance value in the thickness direction. For example, if the surface resistivity measured with a resistance value meter is 0.01Ω/□ or less, and the thickness direction resistance value is 0.100Ω･cm ² or less, it can be said that the metal layer 3-1 can be properly formed. Specifically, the thickness direction resistance value can be obtained by multiplying the effective resistance value obtained in the resistance meter measurement by the contact area with the electrode as the thickness direction resistance value.

The thickness of the conductive polyaramide paper is not particularly limited, but preferably has a thickness in the range of 10 μm to 100 μm, and more preferably 20 to 80 μm. If it is 10 μm or more, the mechanical properties are lowered, and there is no problem in the operability such as transportation in the manufacturing process. On the other hand, as long as it is less than 100μm, when installed in the cable, there will be no gap between the insulating coating layer 2 and the shielding layer 3 and/or the shielding layer 3 and the sheath layer 4, and the high-frequency transmission attenuation characteristics Not easy to lower. The weight per unit area of the conductive polyaramide paper is preferably 35 to 110 g/m ² . (Polyaramide)

In the present invention, "polyaramide" refers to a linear polymer compound in which 60% or more of the amide bond is directly bonded to an aromatic ring. As such polyarylene amines, for example, poly(m-xylylenediamine) and its copolymers, poly(p-xylylenediamine) and its copolymers, copolymerized paraphenylene･3,4' -Diphenyl ether terephthalamide, etc. Such polyaramides are manufactured industrially by, for example, a solution polymerization method using a condensation reaction of an aromatic dichloride and an aromatic diamine, a two-stage interfacial polymerization method, etc., although they are commercially available For sale, but not limited to this. Among these polyaramides, from the viewpoint of having good molding processability, flame retardancy, heat resistance and other characteristics, it is preferable to use polymetaxylamide which does not show a stable melting point substantially. Phenylenediamine. (Polyaramide staple fiber)

Examples of the "polyaramide staple fiber" include those obtained by cutting fibers using polyaramide as a raw material to a predetermined length. Examples of such fibers include "Teijinconex (registered) from Teijin Co., Ltd. "Trademark)", "Technora (registered trademark)", DuPont's "Nomex (registered trademark)", "Kevlar (registered trademark)", Teijin Aramid's "Twaron (registered trademark)" and other product names. But it is not limited to this. The polyaramide staple fiber may preferably have a fineness in the range of 0.05 dtex or more and less than 25 dtex. If it is a fiber with a fineness of 0.05 dtex or more, it does not become easy to aggregate in the production by the wet method (described later). Further, when a fiber is smaller than the fineness of 25dtex, a fiber diameter does not become too large, for example, even in a perfect circular shape manipulation density of 1.4g / cm ^3, in the case of more than 45μm diameter, the aspect ratio will not occur Defects such as deterioration, reduced mechanical reinforcement effect, and poor uniformity of polyaramide paper. If the uniformity of the conductive polyaramide paper is poor, and the conductivity of the conductive polyaramide paper is uneven, the electromagnetic wave shielding function obtained by the conductive polyaramide paper may not be sufficiently exhibited, which is not good. The length of the polyaramide staple fiber is preferably 1 mm or more and less than 25 mm. If the length of the short fiber is 1mm or more, the mechanical properties of the conductive polyaramide paper will not decrease. On the other hand, if the length is less than 25mm, it will be difficult to manufacture the conductive polyaramide paper by the wet method described later. The occurrence of "entanglement" and "bundling" are the causes of defects. (Polyaramid fibrids)

"Polyaramide fibrids" are thin film-like particles composed of polyaramides, also known as polyaramide slurries. Polyaramide fibrids can be produced by methods described in Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 37-5732, for example. Polyaramide fibrids are the same as general wood (cellulose) pulp and have papermaking properties. Therefore, they can be dispersed in water and then formed into sheets by a paper machine. In this case, for the purpose of maintaining quality suitable for papermaking, a so-called beating treatment can be performed. This beating treatment can be implemented by a dish-type refiner, a beating machine, and other paper-making raw material processing equipment that can achieve mechanical cutting. In this operation, the morphological change of the fibrids can be monitored by the degree of drainage (freeness) specified in JIS P8121. In the present invention, the drainage degree of the polyaramide fibrids after the beating treatment is preferably in the range of 10 to 300 cm ³ (Canadian standard freeness). If it is within this range, the strength of the subsequently formed sheet will not decrease. ^{If a water filtration degree of 10 cm 3} or more can be obtained, the utilization efficiency of the input mechanical power will not decrease, and the processing volume per unit time will not decrease. Furthermore, the miniaturization of fibrids will not decrease. It will overdo it without causing the so-called adhesive function to decrease. (Conductive filler)

Examples of "conductive fillers" include fibers with a wide range of conductivity ranging ^{from conductors with a volume resistance of about 10 -1} Ω･cm or less to semiconductors with a volume resistance of about 10 ^-1 to 10 ^{8 Ω･cm.} Shapes or particles (powder or sheet). Examples of such conductive fillers include materials with homogeneous conductivity such as metal fibers, carbon fibers, and carbon black, or metal-plated fibers, metal powder mixed fibers, carbon black mixed fibers, etc., conductive materials and non-conductive materials Materials etc. which are mixed to show conductivity as a whole, but are not limited to these. Among them, in this embodiment, it is preferable to use carbon fiber as the conductive filler. As the carbon fiber, it is preferable to carbonize fibrous organic matter by firing at a high temperature in an inactive environment. Generally speaking, carbon fibers are roughly classified into those made by firing polyacrylonitrile (PAN) fibers and those made by spinning pitch and firing. In addition, there are also those made by spinning resin such as rayon or phenol. Any one can be used if it is made by firing. Before firing, oxygen or the like can also be used for oxidative crosslinking treatment to prevent melting during firing. The fineness of the carbon fiber used in the present invention is preferably in the range of 0.5 to 10 dtex. In addition, the fiber length is preferably 1 mm to 20 mm. In the selection of the conductive filler, it is more preferable to use a material that has high conductivity and exhibits good dispersion in the wet papermaking method described later. In addition, in the case of selecting carbon fiber, it is more preferable to select one that has high strength and is not easy to be brittle. By selecting such a material, a conductive polyaramide paper that is a feature of the present embodiment, suitable for the conductivity of the shielding layer 3 and densified in a specific range by hot pressing, can be obtained. (Manufacturing method of conductive polyaramide paper)

Conductive polyaramide paper, for example, can be produced by the following method: polyaramide staple fiber, polyaramide fibrid and conductive filler are mixed and then sheeted, and a pair of metal Hot pressing between the rollers, and then coating the metal. Specifically, for example, it can be applied: (i) After mixing polyaramide short fibers, polyaramide fibrids, and conductive fillers in a dry manner, forming a sheet by airflow, and performing it between a pair of metal rolls The method of forming the metal layer 3-1 after hot pressing, (ii) Disperse and mix polyaramide short fibers, polyaramide fibrids and conductive fillers in a liquid medium, and then spray them until the liquid is penetrable For example, a method of forming a sheet on a net or a belt, removing the liquid and drying, and forming the metal layer 3-1 after hot pressing between a pair of metal rolls. Among these, it is preferable to select a so-called wet papermaking method using water as a medium to form a sheet, and to apply a metal after hot pressing between a pair of metal rolls. In the wet papermaking method, at least a single or mixed aqueous slurry of polyaramide staple fibers, polyaramide fibrids, and conductive fillers is sent to a paper machine for dispersion, followed by dehydration, squeezing, and The drying operation, and the method of winding it as a sheet by this, is a general method. As the paper making machine, for example, a Fourdrinier paper making machine, a cylinder paper making machine, an inclined paper making machine, a composite paper making machine combining these, and the like can be used. In the case of manufacturing with a composite paper machine, a composite sheet composed of a plurality of paper layers can also be obtained by forming aqueous slurries with different blending ratios into sheets so as to integrate them into one. In wet papermaking, additives such as dispersibility enhancers, defoamers, and paper strength enhancers can also be used as required. When the conductive filler is a particulate material, it is possible to add an acrylic resin, a fixing agent, a polymer flocculant, and the like. In the conductive polyaramide paper, other fibrous components can also be added according to the needs, such as polyphenylene sulfide fiber, polyether ether ketone fiber, cellulose fiber, liquid crystal polyester fiber, polyimide fiber, poly Organic fibers such as amidoimide fibers, polyparaphenylene benzobisazole fibers, and inorganic fibers such as glass fibers, stone wool, and boron fibers. In addition, when the above-mentioned additives or other fibrous components are used, it is preferable to make it 20% by weight or less of the total weight of the conductive polyaramide paper before the metal layer is formed.

The thus-obtained sheet can be processed by hot pressing at high temperature and high pressure between a pair of flat plates or between metal rolls, thereby improving the mechanical strength. The conditions of the hot pressing process, for example, in the case of using a metal roll, are in the range of a temperature of 100 to 400°C and a linear pressure of 50 to 1000 kg/cm. In order to obtain the characteristics of conductive polyaramide paper, that is, high shielding properties, the roll temperature is preferably 330°C or higher, more preferably 330°C to 380°C. In addition, the linear pressure is preferably 50 to 500 kg/cm. This temperature is higher than the glass transition temperature of the meta-type polyaramide and is close to the crystallization temperature of the meta-type polyaramide. Therefore, the mechanical strength can be improved by performing hot pressing at this temperature. In addition, the materials constituting the conductive polyaramide paper can be firmly adhered to each other, and the resistance in the thickness direction can be reduced. The above-mentioned hot pressing process can also be performed multiple times. In addition, depending on the application, there are cases where excessive space saving is not required but the thickness must exceed 100 μm. In this case, the sheet-like objects obtained by the above method may be stacked in multiple sheets and subjected to hot press processing. As a method of coating a metal on the sheet obtained in this way, a vacuum vapor deposition method, a sputtering method, an electroless plating method, an electroplating method, etc. can be mentioned. From the viewpoint of the uniformity and productivity of the formed metal layer, it is particularly preferable to perform the electroplating method after the electroless plating method to increase the metal layer 3-1. [Second Implementation Type]

Next, the high-frequency coaxial cable 10 of the second embodiment will be described. In the first embodiment, an example in which the shielding layer 3 has a thickness direction resistance value of ^{0.100 Ω·cm 2 or less has been described.} In contrast, in this embodiment, the shielding layer 3 does not necessarily have a thickness direction resistance value of ^{0.100Ω･cm 2 or less.} Instead, in this embodiment, the structure of the shielding layer 3 is emphasized. Regarding other points, the same configuration as the first embodiment can be adopted.

In detail, in this embodiment, the metal layer 3-1 forms a closed shape in the cross section of the coaxial cable 10. FIG. 4A is a cross-sectional view schematically showing the shielding layer 3 of an example of this embodiment. As shown in FIG. 4A, in this embodiment, the metal layer 3-1 is coated on both sides of the resin sheet 3-2. In addition, the metal layer 3-1 is also applied to the end surface of the resin sheet 3-2. The shielding layer 3 is arranged to wind the insulating coating layer 2 in a longitudinal roll. The shielding layer 3 is wound so that one end part overlaps the other end part in the circumferential direction. According to the configuration shown in FIG. 4A, a metal layer 3-1 can also be provided on the end surface of the resin sheet 3-2. Therefore, in the cross section of the coaxial cable 10, a shape enclosed by the metal layer 3-1 is formed (that is, A shape in which the inside of the shielding layer 3 is completely covered by a sheet of metal layer 3-1). Therefore, a path for electromagnetic waves to leak from the inside of the shielding layer 3 to the outside is not formed. Therefore, even if the shielding layer 3 does not have ^{a thickness direction resistance value of 0.100 Ω·cm 2} or less, the increase in transmission loss can be suppressed. In addition, assuming that the metal layer 3-1 is not provided on the end face of the resin sheet 3-2 as shown in Fig. 2, if the shielding layer 3 does not have ^{a thickness direction resistance value of 0.100Ω･cm 2} or less, electromagnetic waves may be shielded from The inside of the layer 3 leaks to the outside through one end a, the resin sheet 3-2, and the other end b. That is, when the metal layer 3-1 does not form a closed shape in the cross section of the coaxial cable 10, in order to suppress the transmission loss, as described in the first embodiment, the shielding layer 3 must have a value of 0.100Ω･cm ² or less Resistance value in the thickness direction.

FIG. 4B is a cross-sectional view schematically showing the shielding layer 3 of another example of this embodiment. In the shielding layer 3 shown in this example, only the inner surface of the resin sheet 3-2 is coated with the metal layer 3-1. In this example, the shielding layer 3 is also formed in a longitudinal roll. However, one end portion and the other end portion of the shielding layer 3 in the circumferential direction are wound on the insulating coating layer 2 in such a manner that the inner surfaces face each other, that is, the metal layers 3-1 are in contact with each other, thus forming a closed shape . Even in the case of such a configuration, as in the example shown in FIG. 4A, the cross section of the coaxial cable 10 is formed in a shape enclosed by the metal layer 3-1, so even if the shielding layer 3 does not have 0.100Ω･cm ² or less The thickness direction resistance value can also suppress transmission loss. In addition, in the case of the example described in FIG. 4B, the weight per unit area of the metal layer 3-1 can also be less than that of the first embodiment. For example, the weight per unit area of the metal layer 3-1 may be 10 g/m ² or more. Furthermore, in the example described in FIG. 4B, the upper limit of the surface resistivity measured on the side of the metal layer 3-1 can also be lower than that of the first embodiment. For example, the surface resistivity may be 0.02Ω/□ or less. [Example]

The following examples illustrate the present invention in more detail. In addition, these examples are only examples, and do not limit the content of the present invention in any way.

(Measurement method) (1) The basis weight, thickness, and density of the sheet are implemented in accordance with JIS C 2300-2, and the density is calculated by (basis weight/thickness). (2) The surface resistivity is implemented in accordance with JIS JISK 7194, and measured using Loresta-GP MCP-T610 ESP type (manufactured by Mitsubishi Chemical Corporation). (3) The thickness direction resistance value is sandwiched between a pair of electrodes. When the surface pressure applied to the sheet (including the weight of the electrodes) is 250g/cm ² , M-Ohm Hitester will be used. System) The measured resistance value is multiplied by the area of the electrode. (4) Transmission attenuation characteristics Prepare a coaxial cable with a sample length of 1m, and use a network analyzer (MS2028B Anritsu) to measure the attenuation characteristics in the high frequency band from 0.045GHz to 18GHz. (5) Flexibility A single knot of a coaxial cable with a sample length of 1 m is measured, and the outer diameter of the single knot shown in Figure 3 is measured when the coaxial cable is stretched at a strength of 1/2 of the tensile strength of the sheath layer 4. Since the tensile strength of polyvinyl chloride is 60 MPa, the cross-sectional area of the sheath layer 4 is calculated, and the strength obtained by multiplying it by 30 MPa is stretched by a tensile testing machine. (Raw material preparation)

The production device (wet precipitator) of slurry particles composed of a combination of a stator and a rotor described in Japanese Patent Application Laid-Open No. 52-15621 was used to produce fibrids of polymetaphenylene diamine. Treat it with a beating machine, and adjust the length weighted average fiber length to 0.9mm (water drainage 200cm ³ ). On the other hand, the meta-polyaramide fiber (Nomex (registered trademark), single yarn fineness 2.2dtex) manufactured by DuPont was cut into a length of 6mm (hereinafter referred to as "polyaramide staple fiber") and used as papermaking Use raw materials. (Example)

The meta-polyaramide fibrids, meta-polyaramide staple fibers and carbon fibers prepared as described above (manufactured by Toho Tenax Co., Ltd., fiber length 3mm, single fiber diameter 7μm, fineness 0.67dtex, volume resistivity 1.6×10-3Ω･cm) were dispersed in water to make a slurry. The slurry was mixed in such a way that meta-polyaramide fibrids, meta-aramid staple fibers and carbon fibers had the blending ratios shown in Table 1, and processed by a cylinder paper machine (width 30 cm) to produce Flakes. Next, with a pair of metal calender rolls, the obtained sheet was subjected to hot press processing at a temperature of 330° C. and a linear pressure of 150 kg/cm. The obtained sheet was cut into a width of 8 mm. Coating a metal (copper) layer on the cut sheet by electroless plating and electroplating to obtain conductive polyaramide paper. On the obtained conductive polyaramide paper, metal layers are arranged on both sides and end faces. The main characteristic values of the resulting conductive polyaramide paper are shown in Table 1.

[Table 1] characteristic unit Example Raw material composition meta-polyaramide fibrid meta-polyaramide staple fiber carbon fiber weight% 50 45 5 The weight per unit area of the hot-pressed sheet g/m ² 39 Weight per unit area of conductive polyaramide paper g/m ² 79 thickness μm 67 density g/cm ³ 1.18 Surface resistivity Ω/□ 0.0068 Thickness direction resistivity Ω･cm ² 0.024 (Production of coaxial cable)

As the center conductor, seven copper wires with a diameter of 0.18 mm were twisted to make the outer diameter 0.53 mm. Right above it, an insulating coating layer of polyethylene with a thickness of 0.52 mm was formed by tubular extrusion to make an outer diameter of 1.59 mm. Directly above it, the conductive polyaramide paper of Table 1 was used as a shielding layer, and it was arranged in a longitudinal roll so that the outer diameter was 1.93 mm. Directly above it, by tubular extrusion, a polyvinyl chloride sheath 4 with a thickness of 0.4 mm was formed, and a coaxial cable with an outer diameter of 2.62 mm was produced as an example. The transmission attenuation characteristics of the coaxial cable of the embodiment are shown in FIG. 5. In the range of 0.045～18GHz, the slope of frequency (GHz)-transmission attenuation (dB) is -0.71 (dB/GHz). In addition, as a result of measuring flexibility, the outer diameter was 8 mm. The weight per unit length of the cable is 7.0 g/m. (Comparative example)

In the embodiment, the shielding layer is changed to a braided structure (density 93.1%) formed by braiding 16 copper wires with a diameter of 0.1 mm around 5, and the outer diameter is 2.04 mm. Directly above it, the sheath layer 4 of polyvinyl chloride with a thickness of 0.4 mm was formed by tubular extrusion to form a coaxial cable with an outer diameter of 2.95 mm, which was used as a coaxial cable of a comparative example. The transmission attenuation characteristics of the coaxial cable of the comparative example are shown in Fig. 5. In the range of 0.045～18GHz, the slope of frequency (GHz)-transmission attenuation (dB) is -2.5 (dB/GHz). Also, the flexibility was measured, and the result was an outer diameter of 13 mm. The weight per unit length of the cable is 11.6g/m.

As shown in FIG. 5, the coaxial cable of the embodiment exhibits excellent characteristics, especially regarding high-frequency transmission attenuation characteristics. On the other hand, in the coaxial cable of the comparative example, as shown in FIG. 5, the transmission loss increases rapidly at frequencies exceeding 10 GHz, which shows that it is not sufficient as a coaxial cable for high frequencies. In the comparative example, a braided structure is used as the shielding layer, and there are gaps between the metal fibers constituting the shielding layer. Because of this gap, the high-frequency characteristics are considered poor. In addition, the coaxial cable of the embodiment is softer and lighter than the comparative example. From this, it can be seen that the coaxial cable of the present invention can be usefully used as a coaxial cable for high-frequency power electronic equipment, such as electronic equipment in hybrid vehicles and electric vehicles.

1: Center conductor 2: Insulation coating 3: shielding layer 3-1: Metal layer 3-2: Resin sheet 4: Sheath layer 10: Coaxial cable for high frequency a: One end of the side end face of the resin sheet 3-2 b: The other end of the side end surface of the resin sheet 3-2

Fig. 1 is a cross-sectional view schematically showing a coaxial cable according to an embodiment of the present invention. Fig. 2 is a cross-sectional view schematically showing the shielding layer of the first embodiment. Figure 3 is a schematic diagram showing a coaxial cable with a single knot. FIG. 4A is a cross-sectional view schematically showing an example of the shielding layer of the second embodiment. 4B is a cross-sectional view schematically showing the shielding layer of another example of the second embodiment. Fig. 5 is a graph showing the transmission attenuation characteristics of the embodiment and the comparative example.

no

1: Center conductor

2: Insulation coating

3: shielding layer

4: Sheath layer

Claims (9)

A coaxial cable for high frequency, comprising: a central conductor; an insulating coating layer covering the outer periphery of the central conductor; a shielding layer covering the insulating coating layer; and a sheath layer covering the shielding layer; the shielding layer having a resin sheet and coating The metal layer on the resin sheet; The shielding layer has a thickness direction resistance value of ^{0.100Ω･cm 2 or less.} Such as the coaxial cable of claim 1, wherein the weight per unit area of the metal layer is more than ^{25g/m 2.} Such as the coaxial cable of claim 1 or 2, wherein the surface resistivity of the shielding layer is below 0.01Ω/□. A coaxial cable for high frequency, with: Center conductor Insulating coating, covering the outer periphery of the central conductor; Shielding layer, covering the insulating coating layer; and Sheath layer, covering the shielding layer; The shielding layer is provided with a resin sheet and a metal layer coated on the resin sheet; The metal layer forms a closed shape in the cross section of the coaxial cable. The coaxial cable according to any one of claims 1 to 4, wherein the resin sheet is a sheet with higher heat resistance than the sheath layer. The coaxial cable according to any one of claims 1 to 5, wherein the resin sheet is a polyaramide paper containing short polyaramide fibers and/or polyaramide fibrids. The coaxial cable according to any one of claims 1 to 6, wherein the resin sheet contains a conductive filler. Such as the coaxial cable of any one of claims 1 to 7, wherein when the coaxial cable is single-knotted, and the coaxial cable is stretched at a strength of 1/2 of the tensile strength of the sheath layer, the single-knot portion The outer diameter is less than 4 times the outer diameter of the coaxial cable. Such as the coaxial cable of any one of claims 1 to 8, wherein in the range of 0.045 to 18 GHz, the slope of frequency (GHz)-transmission attenuation (dB) is above -0.8 (dB/GHz).

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