Coaxial Cable

Abstract

To provide a coaxial cable which has less constraints in a specification or a process while having high electric characteristics.SOLUTION: A coaxial cable includes a center conductor extending in a first direction, a first dielectric layer which contains a porous insulation material and is formed on the center conductor, a second dielectric layer which contains a solid insulation material and is formed on the first dielectric layer, an external conductor which contains a metallic foil and is formed on the second dielectric layer, and a jacket which contains an insulating resin material and is formed on the external conductor. In the coaxial cable, when in a cross section vertical in the first direction, an area of a region between an inner peripheral side interface of the second dielectric layer and an outer peripheral side interface of the internal conductor is stipulated as a first area, and an area of a region between the inner peripheral side interface of the second dielectric layer and an outer peripheral side interface of the second dielectric layer is stipulated as a second area, the second area is larger than the first area.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a coaxial cable having excellent electrical characteristics, and in particular to a coaxial cable capable of realizing high-speed transmission of 15 GHz or more with high quality. [Background technology]

[0002] PCT / JP2004 / 007117 discloses a foamed coaxial cable comprising an inner conductor, a foamed insulation layer formed on the outer periphery of the inner conductor, and an outer conductor formed on the outer periphery of the foamed insulation layer, characterized in that a skin layer having a substantially perfect circular shape is formed on the outer periphery of the foamed insulation layer. In this way, a skin layer is provided by extrusion molding on the outer periphery of the wound layer of a porous tape body, which improves the productivity of the insulator, improves the outer diameter precision, and increases the resistance to pressure. Furthermore, it is disclosed that in this coaxial cable, the inner conductor has an outer diameter accuracy of 4 / 1000 mm or less, the foamed insulation layer is formed by winding a porous tape body, and after the foamed insulation layer is formed, it has an approximately circular outer shape and an outer diameter accuracy of ±0.02 mm, and a skin layer is formed on the outer periphery of the foamed insulation layer, having an approximately circular outer shape and an outer diameter accuracy of ±0.02 mm, and the accuracy of the characteristic impedance value between the inner conductor and the outer conductor with the foamed insulation layer and the skin layer interposed is ±1 Ω. With this configuration, it is possible to provide a foamed coaxial cable that can increase the transmission speed, improve the accuracy of the characteristic impedance value, and increase the flexibility of the cable, and even if the cable is subjected to mechanical stress such as bending, twisting, pressing, sliding, etc., the stress can be reduced, thereby maintaining a specified mechanical strength and minimizing changes in the characteristic impedance value. Summary of the Invention [Problem to be solved by the invention]

[0003] The technology described in Prior Art Document 1 is expected to achieve excellent electrical characteristics because each element constituting the coaxial cable is formed with high precision, but the inner conductor, foamed insulation layer, and skin layer each require high precision formation on an elemental basis, which can impose restrictions on specifications or processes, and also leaves room for improvement in productivity. The present invention provides a coaxial cable that has high electrical properties and is subject to fewer constraints in terms of specifications or processes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] PCT / JP2004 / 007117 DISCLOSURE OF THEINVENTION [Means for solving the problem]

[0005] A coaxial cable according to the present invention is a coaxial cable comprising a central conductor extending in a first direction, a first dielectric layer containing a porous insulating material and formed on the central conductor, a second dielectric layer containing a solid insulating material and formed on the first dielectric layer, an outer conductor containing a metal foil and formed on the second dielectric layer, and an outer covering containing an insulating resin material and formed on the outer conductor, wherein, in a cross section perpendicular to the first direction, the coaxial cable is characterized in that, when an area of ​​a region between an inner interface of the second dielectric layer and an outer interface of the inner conductor is defined as a first area, and an area of ​​a region between an inner interface of the second dielectric layer and an outer interface of the second dielectric layer is defined as a second area, the second area is larger than the first area.

[0006] In addition, a coaxial cable according to the present invention is a coaxial cable comprising: a central conductor extending in a first direction; a first dielectric layer including a porous insulating material and formed on the central conductor; a second dielectric layer including a solid insulating material and formed on the first dielectric layer; an outer conductor including a metal foil and formed on the second dielectric layer; and an outer jacket including an insulating resin material and formed on the outer conductor, wherein, in a cross section perpendicular to the first direction, the first dielectric layer of the coaxial cable includes a first region of the first dielectric layer having a first radial thickness, the second dielectric layer of the coaxial cable includes a first region of the second dielectric layer having a second radial thickness, and the second radial thickness of the second dielectric layer is greater than the first radial thickness of the first dielectric layer. [Brief description of the drawings]

[0007] [Figure 1] 1 is a schematic cross-sectional view for explaining a basic structure of a coaxial cable according to the present invention. [Diagram 2] 1 is a cross-sectional view for explaining the technical idea of ​​a coaxial cable according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the coaxial cable according to the present invention will be described. Note that the embodiments described below do not limit the invention according to the claims, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention. Furthermore, the respective embodiments in each example may be freely combined within the scope that does not lose the technical significance of the present invention.

[0009] The embodiment of the present invention may be any embodiment that satisfies the following conditions. (1) A coaxial cable comprising: a central conductor extending in a first direction; a first dielectric layer including a porous insulating material and formed on the central conductor; a second dielectric layer including a solid insulating material and formed on the first dielectric layer; an outer conductor including a metal foil and formed on the second dielectric layer; and an outer jacket including an insulating resin material and formed on the outer conductor, (2) A coaxial cable characterized in that, in a cross section perpendicular to a first direction, when an area of ​​a region between an inner interface of the second dielectric layer and an outer interface of the inner conductor is defined as a first area, and an area of ​​a region between the inner interface of the second dielectric layer and an outer interface of the second dielectric layer is defined as a second area, the second area is larger than the first area.

[0010] Next, the configuration of a coaxial cable according to an embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view for explaining the basic structure of a coaxial cable according to the present invention. As shown in the figure, the coaxial cable 10 extends in a longitudinal direction (a first direction), and includes a central conductor 21, a dielectric layer 22, an outer conductor 23, and an outer jacket 24.

[0011] [Center conductor] The central conductor 21 may be a thin copper or copper alloy wire having excellent strength and conductivity, or a single wire (single core) plated with a highly conductive metal, but may also be a twisted wire. For a coaxial cable compatible with a frequency band of 15 GHz or more, the central conductor 21 is preferably one having a diameter smaller than AWG27. In view of good conductor electrical resistance, the material is preferably tin-plated soft copper obtained by tin-plating soft copper, and more preferably silver-plated soft copper obtained by silver-plating soft copper. As described above, the central conductor 21 may be made of a single wire or a stranded wire made of multiple strands. When the coaxial cable 10 is used in a movable part, a stranded wire is preferable in terms of improving flexibility. In this case, it is preferable to strand 7 or 19 strands to form one stranded wire. Furthermore, when the coaxial cable 10 is used in a fixed portion, flexibility is not required, so it is preferable to construct it from a single wire in order to avoid suck-out caused by the periodicity of the twisting of the above-mentioned twisted wire.

[0012] [Dielectric layer] The material and thickness of the dielectric layer 22 shown in the figure are determined based on the following formula (1).

[0013] (Formula 1) TIFF0007641453000001.tif2142 Here, the symbols in equation (1) have the following meanings: fc = higher mode frequency [GHz] εɤ = relative permittivity of the dielectric layer De = outer diameter of dielectric layer [mm] de = outer diameter of the central conductor [mm] The dielectric layer 22 has a porous layer 22a formed on the central conductor 21 and a reinforcing layer 22b formed on the porous layer 22a.

[0014] The porous layer 22a may be any material as long as it is made of resin and has many pores. The pores refer to a number of micropores formed by foaming and stretching the resin. Although not limited to a specific resin, a fluororesin is preferably selected, specifically, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP), tetrafluoroethylene-perfluoroalkylvinylether copolymer resin (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkylvinylether copolymer resin (EPE), ethylene-tetrafluoroethylene copolymer resin (ETFE), ethylene-tetrafluoroethylene-hexafluoropropylene copolymer resin (THV), trifluorochloroethylene resin (PCTFE), ethylene-trifluorochloroethylene copolymer resin (ECTFE), vinylidene fluoride resin (PVdF), and vinyl fluoride resin (PVF) are selected. In addition, from the viewpoint of mechanical properties and chemical resistance, polyester resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), and polyarylate resins such as polyether ether ketone (PEEK) are also preferred. The porous structure of the stretched porous sheet that has been subjected to the stretching process is defined by the porosity and the pore size. In the present invention, the porosity is preferably 50% or more and 95% or less. More preferably, the porosity is 60% or more and 90% or less. The most preferable range is 65% or more and 85% or less. Furthermore, if the porosity is 95% or more, deformation is likely to occur when maintaining the shape during processing, making it difficult to maintain industrial quality. The above-mentioned porosity is calculated from the density. Moreover, for the foamed and extrusion coated product, the foaming ratio is preferably within the range of 50 to 90%. If it is below 50%, the decrease in dielectric constant is small and the strength is large, which hinders adhesion to the shield conductor and reduces the shielding effect. On the other hand, if the porosity exceeds 90%, the strength is significantly decreased, making it difficult to feed when forming a hollow compressed stranded wire around it and causing excessive deformation, so the porosity is limited to the range of 50 to 90%. The foam preferably has an average bubble diameter of 5 to 100 μm. In this specification, the expansion ratio means the rate of change in specific gravity before and after foaming, and is a value obtained by measuring the rate of change between the specific gravity inherent to the material constituting the foam and the apparent specific gravity of the foam by an underwater displacement method, and the average bubble diameter is a value calculated from a micrograph of the cross section.

[0015] The reinforcing layer 22b may be configured in accordance with any one of the following conditions. (1) In a cross section perpendicular to the longitudinal direction (first direction), when the area of ​​a region between the inner circumferential interface of the reinforcing layer 22b and the outer circumferential interface of the central conductor 21 is defined as a first area, and the area of ​​a region between the inner circumferential interface of the reinforcing layer 22b and the outer circumferential interface of the reinforcing layer 22b is defined as a second area, the second area is larger than the first area. (2) In a cross section perpendicular to the longitudinal direction (first direction), the porous layer 22a of the coaxial cable 10 includes a first region of the porous layer 22a having a first radial thickness, and the reinforcing layer 22b of the coaxial cable 10 includes a first region of the reinforcing layer 22b having a second radial thickness, and the second radial thickness of the reinforcing layer 22b is greater than the first radial thickness of the first dielectric layer.

[0016] In a coaxial cable, it is very important that the distance between De (outer diameter of the dielectric layer) and de (outer diameter of the central conductor) is constant in order to obtain desired characteristics. First, the relationship between the thickness in the cross section of the coaxial cable 10 will be described with reference to FIG. 2. As shown in the figure, there are some parts in the cross section of the cable where the shape is not a perfect circle. Therefore, in the coaxial cable according to the present invention, the distance between the center of gravity CG of the central conductor 21 and the point where the interface of the outer periphery of the central conductor 21 intersects with the imaginary line VL passing through the center of gravity CG may be regarded as the radius de / 2 of the central conductor 21. Similarly, the distance between the center of gravity CG and the point where the interface of the inner periphery of the outer conductor 23 intersects with the imaginary line VL may be regarded as the radius De / 2 of the dielectric layer 22. The overall diameter of the coaxial cable may be calculated as the average of the diameters in four directions from the center of gravity on two imaginary straight lines VL that are perpendicular to each other. Furthermore, the radial thickness is defined by the intersection of a virtual straight line VL passing through the center of gravity CG with the interface of each layer. Specifically, as shown in Fig. 2, the radial thickness is the length of the line connecting the intersections of the virtual straight lines VL1 and VL2 passing through the center of gravity CG at the interface of each layer (Tp: thickness of the porous layer, Te: thickness of the reinforcing layer, Ts: thickness of the outer jacket). A porous dielectric layer with many air spaces formed therein can improve electrical characteristics due to its low dielectric constant, but its mechanical strength is relatively small compared to other constituent materials of the coaxial cable, and deformation of this layer can cause the De-de distance to become unstable. In response to this, the inventors of the present application have found that the De-de distance can be stabilized by making a specific layer have a predetermined configuration and actively utilizing it to stabilize the shape of the central conductor and the dielectric layer. Specifically, a solid insulating layer having a higher mechanical strength than the porous dielectric layer and a predetermined thickness is formed on the porous dielectric layer, and an outer conductor layer is formed on this solid insulating layer. The shape of the inner surface of the outer conductor that determines De is determined by this solid insulating layer having a high strength and a predetermined thickness, so that a coaxial cable with a stable De-de distance can be obtained even under stress such as external stress during use or manufacturing, and even when other constituent members such as the porous dielectric layer are not formed with special high precision.

[0017] [Outer conductor] The outer conductor 23 shown in the figure can be constructed by braiding or horizontally winding wires, winding a tape-like material, or laying it vertically. The wires and tape-like members are mainly made of metal, but any material with high shielding properties can be used. The tape-like member may be made of resin with metal vapor deposition, and if it is heat-resistant (e.g., 100°C or higher), it is more preferable that it is made of metal only.

[0018] [Outer cover] The jacket 24 shown in the figure is formed by covering the dielectric layer by extruding resin or by winding a resin tape.

[0019] A method for producing a coaxial cable according to the present invention will now be described. In the method of manufacturing a coaxial cable, first, a central conductor is prepared (S1: central conductor preparation step). As described above, a single wire or a stranded wire can be used for S1, and the rest can be produced by known manufacturing methods.

[0020] Next, a porous layer of the dielectric layer is formed on the central conductor (S2: porous layer forming step). In S2, the central conductor is covered by winding a porous tape around it or by extruding a foamed resin, and the rest can be produced by known manufacturing methods.

[0021] Next, the dielectric layer is covered with a reinforcing layer (S3: Reinforcing layer covering step). In this step S3, a solid tape is wound around the inner layer, or a solid resin is extruded and passed through a forming die to form a predetermined outer diameter and a nearly perfect circle, thereby covering the porous portion. At this time, the thickness of the reinforcing layer is adjusted so that the thickness of each layer satisfies at least one of the following conditions. (1) In a cross section perpendicular to the longitudinal direction (first direction), when the area of ​​a region between the inner circumferential interface of the reinforcing layer 22b and the outer circumferential interface of the central conductor 21 is defined as a first area, and the area of ​​a region between the inner circumferential interface of the reinforcing layer 22b and the outer circumferential interface of the reinforcing layer 22b is defined as a second area, the second area is larger than the first area. (2) In a cross section perpendicular to the longitudinal direction (first direction), the porous layer 22a of the coaxial cable 10 includes a first region of the porous layer 22a having a first radial thickness, and the reinforcing layer 22b of the coaxial cable 10 includes a first region of the reinforcing layer 22b having a second radial thickness, and the second radial thickness of the reinforcing layer 22b is greater than the first radial thickness of the first dielectric layer.

[0022] Next, an outer conductor is formed (S4: outer conductor forming step). In S4, the outer conductor is formed by braiding or winding metal wires, or by attaching or winding a metal tape longitudinally, and the rest can be made by known manufacturing methods.

[0023] Next, the outer jacket is formed (S5: outer jacket forming step). In S5, the outer conductor is coated by extruding the resin or winding a resin tape around the outer conductor. In extrusion coating, a coating method can be selected from various coating methods such as pressure extrusion and tubing extrusion according to the viscosity of the resin.

[0024] In addition, the porous layer 22 of the coaxial cable 10 may further include a second region of the porous layer 22a having a third radial thickness, and the second radial thickness of the reinforcing layer 22b may be smaller than the third radial thickness of the porous layer 22a. If the reinforcing layer 22b is made excessively large, the difference in mechanical strength between the reinforcing layer 22b and the porous layer 22a becomes too large, and there is a risk that the reinforcing layer 22b will behave like a hollow tube when the coaxial cable 10 is bent. For example, if deformation occurs in which the curved region, including the internal space, is crushed flat, a wide region with a small De-De distance will be generated, making it impossible to obtain sufficient characteristics. In the coaxial cable 10 of this embodiment, the shape of the outer conductor 23 is supported mainly by the strength of the reinforcing layer 22b itself, so that a certain amount of unevenness in the thickness and surface shape of the porous layer 22a can be tolerated. However, by controlling the reinforcing layer 22b within the range of variation in the thickness of the porous layer 22a, it is possible to achieve a state in which the mechanical strength of the reinforcing layer 22b alone does not become exceptionally large.

[0025] 2, when the porous tape is wound, the porous layer 22a preferably has three or more overlapping layers in the longitudinal direction. This is because when the tape is wound, if there are two or less overlapping layers, a step occurs at the beginning of the overlap due to the thickness of the tape, and this step causes a void (e.g., GP1). The effect of this void can be reduced as the tape is wound more overlapping, making the electrical characteristics more stable.

Claims

1. A core conductor extending in a first direction; a first dielectric layer formed on the central conductor, the first dielectric layer including a porous insulating material; a second dielectric layer formed on the first dielectric layer and including a solid insulating material; an outer conductor including a metal foil formed on the second dielectric layer; A coaxial cable comprising: an outer sheath including an insulating resin material and formed on the outer conductor; In a cross section perpendicular to the first direction, the first dielectric layer of the coaxial cable includes a first dielectric layer first region having a first radial thickness, and the second dielectric layer of the coaxial cable includes a second dielectric layer first region having a second radial thickness; a second radial thickness of the second dielectric layer is greater than the first radial thickness of the first dielectric layer, and the first dielectric layer further includes a second region of the first dielectric layer having a third radial thickness; A coaxial cable, wherein a second radial thickness of the second dielectric layer is smaller than a third radial thickness of the first dielectric layer.

2. The coaxial cable has, in a cross section perpendicular to the first direction, 2. The coaxial cable according to claim 1, characterized in that when an area of ​​a region between an inner interface of the second dielectric layer and an outer interface of the central conductor is defined as a first area, and an area of ​​a region between the inner interface of the second dielectric layer and an outer interface of the second dielectric layer is defined as a second area, the second area is larger than the first area.

3. A coaxial cable as described in claim 1 or 2, characterized in that the central conductor of the coaxial cable is composed of only a single metal wire.

4. A coaxial cable as described in any one of claims 1 to 3, characterized in that the outer conductor includes an overlapping region in which metal foils overlap each other, and in the overlapping region, the metal foils are in direct contact with each other.

5. the jacket includes a jacket first region having a fourth radial thickness; The second radial thickness of the second dielectric layer is greater than a fourth radial thickness of the jacket.

5. The coaxial cable according to claim 1, wherein the coaxial cable is a

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