2-core parallel coaxial cable

Abstract

To provide a two-core parallel coaxial cable that has low transmission loss, good skew properties and a small diameter.SOLUTION: A two-core parallel coaxial cable 10 has two insulation wires 3 arranged in parallel, each of which has a central conductor 1 and an insulator 2 provided around the central conductor 1. The two-core parallel coaxial cable further has: a film-like outer conductor 4 that covers the two insulation wires 3, 3; a cover conductor 5 that covers the film-like outer conductor 4; and an outer cover 6 that covers the cover conductor 5. The insulation wire side of the film-like outer conductor 4 is provided with an adhesive layer 4A that prevents a misalignment between each insulation wire 3 and the film-like outer conductor 4 during terminal processing. The adhesive strength between the film-like outer conductor 4 and two insulation wires 3, 3 is preferably 300 gf / 100 mm or more as a result of an adhesion measuring test.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a small diameter, two-core parallel coaxial cable having good transmission characteristics and skew characteristics. [Background technology]

[0002] Coaxial cables with an outer conductor are known as coaxial cables with excellent shielding characteristics. Excellent shielding characteristics are also required for two-core parallel coaxial cables, which have a coaxial structure in which two insulated wires, each with an insulator covering the outer periphery of a central conductor, are arranged in parallel, and are shown in, for example, Patent Documents 1 and 2.

[0003] Patent Document 1 proposes a two-core parallel coaxial cable in which two cores, each having an internal conductor coated with an insulator, are arranged in parallel, a first composite tape, which is a plastic tape with a metal vapor deposition layer formed on one or both sides, is attached longitudinally around the outer periphery of these two cores with the metal vapor deposition layer facing outward, a horizontally wound shield is attached around the outer periphery of the first composite tape, and a second composite tape, which is a plastic tape with a metal vapor deposition layer formed on one or both sides, is wound around the outer periphery of the horizontally wound shield with the metal vapor deposition layer facing inward, and the outer periphery of the second composite tape is covered with a jacket.

[0004] Patent Document 2 proposes a high-speed differential transmission cable in which an insulating coating layer with a longitudinally continuous void is provided around the outer periphery of a central conductor to form a signal line, two of these are arranged in parallel, and a drain wire is placed in the central valley between the two signal lines, and an outer conductor is formed by winding or longitudinally attaching metal laminate tape, metal vapor deposition tape, or metal tape while maintaining a four-core or three-core flat structure, and then covering the entire cable with a jacket. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-31046 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-103179 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a demand for further improvements in the transmission characteristics of such twin-core parallel coaxial cables, and there is a particular need for the development of twin-core parallel coaxial cables with lower transmission loss and better skew characteristics (small delay time difference in the transmission path) as differential cables for use in self-driving cars using 5G (fifth generation mobile communication systems). The goal for twin-core parallel coaxial cables is a low delay of 5PS (picoseconds) / m or less.

[0007] However, while conventional two-core parallel coaxial cables, which have a coaxial structure with individual insulated wires, have good skew characteristics, variations in the terminal processing when attaching the two-core parallel coaxial cable to a connector can cause the lengths of the two insulated wires to vary. These length differences cause skew, making it impossible to achieve low latency.

[0008] The present invention has been made to solve the above problems, and an object of the present invention is to provide a small-diameter, two-core parallel coaxial cable that has low transmission loss and good skew characteristics. [Means for solving the problem]

[0009] The two-core parallel coaxial cable of the present invention is a two-core parallel coaxial cable having two insulated wires arranged in parallel, each having a center conductor and an insulator arranged around the center conductor, a film-shaped outer conductor covering the two insulated wires, a cover conductor covering the film-shaped outer conductor, and an outer jacket covering the cover conductor, characterized in that an adhesive layer is provided on the surface of the film-shaped outer conductor facing the insulated wires, which prevents the insulated wires from shifting from the film-shaped outer conductor during terminal processing.

[0010] According to this invention, an adhesive layer is provided on the surface of the film-shaped outer conductor facing the insulated wires to prevent misalignment between the insulated wires and the film-shaped outer conductor during termination, so the lengths of the two insulated wires do not change during termination when the connector is attached. As a result, skew that would otherwise occur due to changes in the lengths of the two insulated wires is eliminated, and low delay can be achieved.

[0011] In the twin-core parallel coaxial cable according to the present invention, the adhesive strength between the film-like outer conductor and the two insulated wires is 300 gf / 100 mm or more as a result of an adhesion measurement method. The adhesion measurement method, as will be described in the examples below, involves inserting only the two end-processed insulated wires into a jig having an elongated hole with the same outer shape as the two side-by-side insulated wires of the twin-core parallel coaxial cable, with the outer components including the film-like outer conductor hanging over the edge of the elongated hole, and measuring the tensile strength between the jig and the two insulated wires.

[0012] In the two-core parallel coaxial cable of the present invention, the insulator is made of fluororesin, the film-like outer conductor has a base film, a metal layer provided on one surface of the base film, and the adhesive layer provided on the other surface of the base film, the adhesive layer being formed to a thickness of 0.8 to 50 μm from a thermosetting resin containing any one of polyurethane resin, polyester resin, and polyesterimide resin, and the base film is a polyester film having a thickness of 2 to 20 μm.

[0013] In the two-core parallel coaxial cable according to the present invention, the insulator preferably has a foam structure or a hollow structure.

[0014] In the two-core parallel coaxial cable according to the present invention, the film-like outer conductor is wound longitudinally or crosswise around the two insulated wires arranged in parallel. [Effects of the Invention]

[0015] According to the present invention, a small-diameter two-core parallel coaxial cable with low transmission loss and good skew characteristics can be provided, which can be particularly preferably used as a differential cable for autonomous vehicles using 5G. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing an example of a two-core parallel coaxial cable according to the present invention. [Figure 2] FIG. 10 is a cross-sectional view showing an example in which the insulator constituting the insulated wire has a hollow structure. [Figure 3] FIG. 2 is a cross-sectional view showing an example of a film-shaped outer conductor. [Figure 4] 1A is a schematic diagram showing the shapes of insulated wires with the same length after terminal processing (A) and those with different lengths (B). FIG. [Figure 5] FIG. 2 is a schematic diagram showing an example of a method for measuring adhesive strength. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment of a two-core parallel coaxial cable according to the present invention will be described with reference to the drawings. Note that the present invention includes inventions with the same technical idea as the embodiments described below and the forms shown in the drawings, and the technical scope of the present invention is not limited to the description of the embodiments and the drawings.

[0018] [2-core parallel coaxial cable] 1, a two-core parallel coaxial cable 10 according to the present invention is a two-core parallel coaxial cable 10 including two parallel insulated wires 3, each having a central conductor 1 and an insulator 2 disposed around the central conductor 1, a film-like outer conductor 4 covering the two insulated wires 3, 3, a cover conductor 5 covering the film-like outer conductor 4, and an outer jacket 6 covering the cover conductor 5. The cable is characterized in that an adhesive layer 4A is provided on the surface of the film-like outer conductor 4 facing the insulated wires, which prevents misalignment between the insulated wires 3 and the film-like outer conductor 4 during terminal processing.

[0019] In this two-core parallel coaxial cable 10, an adhesive layer 4A is provided on the insulated wire side of the film-shaped outer conductor 4 to prevent misalignment between the insulated wires 3 and the film-shaped outer conductor 4 during terminal processing, so the lengths of the two insulated wires 3, 3 do not change due to terminal processing when attaching to the connector. As a result, skew that would occur due to changes in the lengths of the two insulated wires 3, 3 does not occur, and low delay can be achieved.

[0020] Each component will be described below.

[0021] <Insulated wire> The insulated wire 3 is an essential component of the twin-core parallel coaxial cable 10, and is composed of a central conductor 1 and an insulator 2 disposed around the central conductor 1. In the twin-core parallel coaxial cable 10 according to the present invention, two insulated wires 3 are arranged side by side in one direction, as shown in FIG. 1. "Arranged side by side" means arranged side by side, and although it is usually desirable that adjacent insulated wires 3, 3 are in contact with each other, they do not necessarily have to be in contact. An insulated wire 3 consisting of two wires is preferably used as a differential cable.

[0022] (center conductor) The central conductor 1 may be composed of a single wire extending in the longitudinal direction of the insulated wire 3, or may be composed of multiple stranded wires. The wire may be any type of wire as long as it is made of a highly conductive metal. Preferred examples of the wire include highly conductive metal conductors such as copper wire, copper alloy wire, aluminum wire, aluminum alloy wire, and copper-aluminum composite wire, as well as those with a plating layer applied to their surfaces. Copper wire and copper alloy wire are particularly preferred. Preferred plating layers include solder plating, tin plating, gold plating, silver plating, and nickel plating. The cross-sectional shape of the wire is also not particularly limited. Circular is preferred, but it may also be approximately circular or rectangular.

[0023] The cross-sectional shape of the central conductor 1 is not particularly limited. It may be circular (including elliptical) or rectangular, but is preferably circular. The outer diameter of the central conductor 1 is desirably as large as possible to reduce electrical resistance (AC resistance, conductor resistance). To reduce the outer diameter of the insulated wire 3, the outer diameter may be, for example, within a range of approximately 0.09 to 1 mm. An insulating coating (not shown) may be provided on the surface of the central conductor 1 as needed. The type and thickness of the insulating coating are not particularly limited, but a coating that decomposes easily during soldering is preferred, and a thermosetting polyurethane coating is a preferred example.

[0024] (insulator) The insulator 2 is a low-dielectric insulating layer continuously provided around the outer periphery of the central conductor 1 in the longitudinal direction. The material of the insulator 2 is not particularly limited and can be selected as desired depending on the required impedance characteristics. However, a low-dielectric-constant fluororesin with a dielectric constant of 2.0 to 2.5, such as PFA (ε2.1), FE (ε2.1), or ETFE (ε2.5), is preferred, with PFA resin being particularly preferred. The material of the insulator 2 may contain a colorant. The thickness of the insulator 2 is also not particularly limited and can be selected as desired depending on the required impedance characteristics. It is preferable that the thickness be within the range of approximately 0.15 to 1.5 mm. The method for forming the insulator 2 is not particularly limited. Solid, hollow, or foamed structures can all be easily formed by extrusion. In particular, the hollow structure and foam structure using low dielectric constant materials allow the thickness of the insulator 2 to be thin without degrading the transmission characteristics, so the outer diameter of the insulated wire 3 can be reduced, and as a result, the volume of the two-core parallel coaxial cable 10 can be reduced and the thickness of the two-core parallel coaxial cable 10 can be reduced.

[0025] FIG. 2 shows an example of a hollow insulator 2. This hollow structure has a void 2A within the structure, and can have a cross-sectional shape, for example, in which the void 2A is surrounded by an inner annular portion 2B, an outer annular portion 2C, and a connecting portion 2D. The void 2A is continuously provided within the insulator 2, and its shape is not particularly limited and may be round or rectangular. Such hollow insulators 2 are preferably adopted because they have excellent lateral pressure strength, are less likely to be crushed during the manufacturing process, and can achieve stable high-frequency characteristics. The hollow insulator 2 can be molded by resin extrusion around the outer periphery of a central conductor 1 traveling through an extrusion die. The thicknesses of the inner annular portion 2B, the outer annular portion 2C, and the connecting portion 2D are not particularly limited, but may be, for example, within a range of approximately 0.01 to 0.05 mm. The outer diameter of the formed hollow insulator 2 can be, for example, within a range of approximately 0.4 to 1.0 mm.

[0026] <Film-type outer conductor> As shown in Fig. 1, a film-like outer conductor 4 (hereinafter sometimes referred to as "outer conductor 4") is provided on the outer periphery of the two insulated wires 3, 3 so as to cover them. The film-like outer conductor 4 is not particularly limited as long as it is a film-like material that can be placed vertically or wrapped horizontally to cover the two insulated wires 3, 3. As shown in Fig. 3, the film-like outer conductor 4 is composed of a base film 4C, a metal layer 4B provided on one surface of the base film 4C directly or, if necessary, via an adhesive layer (not shown), and an adhesive layer 4A provided on the other surface of the base film 4C. This film-like outer conductor 4 is provided so as to cover the two insulated wires 3, 3 with the adhesive layer 4A side facing the insulated wires 3 and the metal layer 4B side facing the cover conductor 5.

[0027] The base film 4C is not particularly limited, but polyester films such as polyethylene terephthalate and polyethylene naphthalate are preferably used. The thickness of the base film 4C is selected arbitrarily, for example, from within a range of approximately 2 to 20 μm. The base film 4C made of such a material has a higher dielectric constant than the fluororesin that constitutes the insulator 2 described above. Therefore, if the base film 4C is thick, the overall dielectric constant will increase, resulting in reduced transmission characteristics. Therefore, the thickness of the base film 4C is preferably within a range of 2 to 10 μm, which does not make the overall dielectric constant too high.

[0028] The metal layer 4B is preferably a copper layer or an aluminum layer. The metal layer 4B is preferably a film formed on the base film 4C by vapor deposition or plating, or a metal foil attached via an optional adhesive layer (not shown, e.g., a polyester-based thermoplastic adhesive resin). The thickness of the metal layer 4B is not particularly limited and varies depending on the formation method. However, a film formed by vapor deposition or plating can have a thickness of approximately 2 to 8 μm, and a film formed by attaching a metal foil can have a thickness of approximately 6 to 16 μm. Even with such a thin metal layer 4B, the cover conductor 5 provided thereon stably holds the outer conductor 4 with the adhesive layer 4A side covering the insulated wire 3. The adhesive layer provided as needed to attach the metal layer 4B to the base film 4C is also not particularly limited, but is preferably a heat-bondable adhesive layer. Examples of suitable adhesives include urethane adhesives, epoxy adhesives, and acrylic adhesives. The metal layer 4B is arranged facing the cover conductor 5. Therefore, the metal layer 4B is electrically connected to the cover conductor 5, so that the shielding effect is stable and the transmission loss can be reduced.

[0029] The adhesive layer 4A is provided on one side of the base film 4C, opposite the side on which the metal layer 4B is provided. Examples of materials for the adhesive layer 4A include thermosetting resins such as polyurethane resin, polyester resin, and polyesterimide resin. The adhesive layer 4A is provided by applying the thermosetting resin to the base film 4C. The film-like outer conductor 4 is provided to cover the two insulated wires 3, 3, and then the cover conductor 5 and the outer jacket 6 are provided. The adhesive layer 4A is thermally cured at the extrusion temperature when the outer jacket 6 is provided, and the thermally cured adhesive layer 4A functions to bond the insulated wires 3 and the film-like outer conductor 4 together.

[0030] The thickness of the adhesive layer 4A is not particularly limited, but from the perspective of transmission characteristics, it is preferably within the range of 0.8 to 50 μm, and particularly preferably 0.8 to 5 μm. If the adhesive layer 4A's role is to bond the insulated wire 3 and the film-like outer conductor 4, the thickness can be set within a wider range. However, the dielectric constant of the resin material constituting the adhesive layer 4A is higher than that of the fluororesin. Therefore, if the adhesive layer 4A, which has a high dielectric constant, is made thick, the overall dielectric constant increases, resulting in a deterioration in transmission characteristics. Therefore, the thickness of the adhesive layer 4A is preferably set to a lower limit of 0.8 μm, which ensures adhesion between the insulated wire 3 and the film-like outer conductor 4, and to an upper limit of 50 μm, which does not increase the overall dielectric constant too much. To achieve particularly good transmission characteristics, the thickness of the adhesive layer 4A is preferably set to 0.8 to 5 μm. An adhesive layer 4A having a thickness of 0.8 to 5 μm is provided on a base film 4C having a thickness of 2 to 10 μm, and a film-like outer conductor 4 including such a thin resin structure (adhesive layer 4A and base film 4C) is provided on an insulated wire 3, thereby making it possible to make the transmission characteristics of the entire two-core parallel coaxial cable 10 particularly good, and the cable can be preferably used as a differential cable, etc., for use in self-driving automobiles that utilize 5G.

[0031] (Vertical or horizontal wrapping) The film-like outer conductor 4 is wound around the two insulated wires 3, 3 either vertically or horizontally. "Vertical wrapping" refers to wrapping the film-like outer conductor 4 along the longitudinal direction of the two insulated wires 3. When the film-like outer conductor 4 is wound vertically, the adhesive layer 4A faces the insulated wire 3, and the metal layer 4B faces the cover conductor 5. This arrangement allows the adhesive layer 4A to bond the insulated wires 3 and the outer conductor 4, preventing misalignment between the insulated wires 3, 3 and the film-like outer conductor 4 during termination, and ensuring electrical continuity by contacting the metal layer 4B with the cover conductor 5. When wound vertically, the outer conductor is wound so that there is an overlapping portion 8, as shown in Figure 1.

[0032] Although not shown, "horizontal winding" refers to wrapping the film-like outer conductor 4 horizontally around the outer periphery of two insulated wires 3, 3. When the film-like outer conductor 4 is wound horizontally, as in the case of vertical wrapping, the adhesive layer 4A side faces the insulated wire 3 and the metal layer 4B side faces the cover conductor 5. In this way, the adhesive layer 4A bonds the insulated wire 3 and the outer conductor 4, preventing misalignment between the insulated wires 3, 3 and the film-like outer conductor 4 during terminal processing, and also brings the metal layer 4B into contact with the cover conductor 5 to provide electrical continuity. In horizontal winding, the wires are wound so that there is a partial overlap.

[0033] <Cover conductor> The cover conductor 5 is formed on the film-shaped outer conductor 4 in a braided structure of thin metal wires or a spirally wound shield structure of thin metal wires. The cover conductor 5 covers the film-shaped outer conductor 4 and prevents loosening or misalignment of the outer conductor 4, thereby contributing to maintaining stable transmission characteristics. In the case of a spirally wound shield structure, the spirally wound thin metal wires may be in a single layer or a multilayer, but are not particularly limited, and a single layer is preferred.

[0034] The thin metal wires constituting the cover conductor 5 are not particularly limited as long as they are thin metal wires with good electrical conductivity. For example, various thin metal wires, such as tin-plated copper wires, can be preferably used. The outer diameter of the thin metal wires can be, for example, within the range of about 0.04 to 0.1 mm. The number of thin metal wires can also be selected arbitrarily depending on whether a braided structure or a spirally wound shield structure is used, the size of the object to be covered, and other factors.

[0035] The cover conductor 5 prevents the film-shaped outer conductor 4 wrapped around the insulated wire 3 from shifting, so the distance between the film-shaped outer conductor 4 and the center conductor 1 is less likely to change even when the cable is bent or unbent. As a result, phase fluctuations are less likely to occur, and degradation of signal transmission characteristics (attenuation, skew) can be suppressed. In particular, in a two-core parallel coaxial cable 10 that transmits differential signals at high speed, changes in signal transmission speed between the two insulated wires 3, 3 can be suppressed, preventing degradation of transmission characteristics.

[0036] <Outer cover> The outer jacket 6 is provided on the outer periphery of the cover conductor 5, and its material is not particularly limited as long as it has insulating properties. It may be provided by spirally winding a resin tape with an adhesive layer on one side, but in the present invention, it is preferably provided by extruding a resin. In the case of resin extrusion, various resins that are commonly used as jackets for coaxial cables can be used as the constituent resin of the outer jacket 6. For example, it may be a fluorine-based resin such as PFA, FEP, or ETFE, a vinyl chloride resin, a polyolefin resin such as polyethylene, or a polyester resin such as polyethylene terephthalate. The thickness of the outer jacket 6 may be within a range of, for example, approximately 0.1 to 1 mm.

[0037] When a resin tape is used, fusing it to the cover conductor 5 can prevent the cover conductor 5 (especially in the case of a horizontally wound shield structure) from shifting in position. When a resin tape with a fusion layer is used, it is wound horizontally with the fusion layer side facing the cover conductor 5. Examples of materials for the resin tape include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyamide (PA), polyimide (PI), polyphenylene sulfide (PPS), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), fluorinated resin copolymer (perfluoroalkoxy fluororesin: PFA), polyether ether ketone (PEEK), etc. The thickness of the resin tape is not particularly limited as long as it is thick enough to ensure the required dielectric strength, but it can be approximately 0.004 to 0.01 mm. The fusion layer is provided on one side of the resin tape, and examples of its material include thermosetting resins such as polyurethane resin, polyester resin, and polyesterimide resin. The thickness of the fusion layer is not particularly limited, but can be about 0.001 mm.

[0038] <Adhesion strength between the film-shaped outer conductor and two insulated wires> The adhesive strength between the film-like outer conductor 4 and the two insulated wires 3, 3 of the obtained two-core parallel coaxial cable 10 is desirably 300 gf / 100 mm or more as a result of an adhesion measurement method. In this case, the adhesion measurement method is a method in which, as shown in Fig. 5, only the two end-processed insulated wires 3, 3 are inserted into a jig 20 having an elongated hole 21 that is the same as the outer shape of the two side-by-side insulated wires 3, 3 of the two-core parallel coaxial cable 10, so that the outer components including the film-like outer conductor 4 (the film-like outer conductor 4, the cover conductor 5, and the jacket 6) hang over the edge of the elongated hole 21, and the tensile strength between the jig 20 and the two insulated wires 3, 3 is measured.

[0039] The twin-core parallel coaxial cable 10 according to the present invention undergoes terminal processing for connection to a connector. This terminal processing includes a step of simultaneously stripping the insulators 2 constituting the insulated wires 3 from the center conductor 1. In this step, a force of approximately 250 to 300 gf / 100 mm is applied when stripping the insulators 2. In the present invention, by providing an adhesive layer 4A on the film-like outer conductor 4, the adhesive strength between the film-like outer conductor 4 and the two insulated wires 3, 3 is preferably 300 gf / 100 mm or more, more preferably 350 gf / 100 mm or more, as measured by the above-described adhesion measurement method. The upper limit of this value varies depending on the type of adhesive layer and the adhesion treatment (surface roughening, corona treatment, etc.) of the surface of the insulator 2 constituting the insulated wires 3, 3, but is not particularly limited. For example, it can be 800 gf / 100 mm. By achieving the above-described adhesive strength, the longitudinal misalignment at the terminals of the two insulated wires 3, 3 can be reduced to 5 PS / m or less, as described below.

[0040] When the twin-core parallel coaxial cable 10 according to the present invention is terminated without the adhesive layer 4A, the lengths of the two insulated wires 3, 3 will differ from each other, as shown in FIG. 4(B). This difference in length affects the skew characteristics. For example, to achieve a skew characteristic of 1 PS / m, the difference in length is 0.3 mm when the insulator 2 is a vacuum (theoretical value, dielectric constant 1.0), 0.21 mm when the insulator 2 is a hollow structure (foaming ratio 30%, dielectric constant 1.4), and 0.14 mm when the insulator 2 is a solid structure (fluororesin, dielectric constant 2.1). Therefore, to achieve a skew characteristic of 5 PS / m or less, the difference in length is 1.50 mm or less when the insulator 2 is a vacuum (theoretical value, dielectric constant 1.0), 1.05 mm or less when the insulator 2 is a hollow structure (foaming ratio 30%, dielectric constant 1.4), and 0.71 mm or less when the insulator 2 is a solid structure (fluororesin, dielectric constant 2.1).

[0041] Therefore, to achieve low latency of 5 PS / m or less in the twin-core parallel-axial coaxial cable 10, the difference in length between the two insulated wires 3, 3 that may occur during termination must be 1.05 mm or less for a hollow structure (foaming ratio 30%, dielectric constant 1.4) and 0.71 mm or less for a solid structure (fluororesin, dielectric constant 2.1). In the present invention, an adhesive layer 4A is provided on the insulated wire 3 side of the film-like outer conductor 4, and this adhesive layer 4A adheres to the two insulated wires 3, 3. This prevents or minimizes length changes of the two insulated wires 3, 3 during termination during connector installation, keeping them within the above-mentioned tolerance range. As a result, the skew caused by length changes between the two insulated wires 3, 3 can be suppressed to a low latency of 5 PS / m or less. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0043] [Example 1] The insulated wire 3 used a silver-plated annealed copper wire (AWG24) with an outer diameter of 0.501 mm as the central conductor 1. The insulator 2 was formed by extruding PFA resin (manufactured by DuPont) at 350°C using a die nipple for hollow structures to form a hollow structure with a cross-sectional shape in which a void 2A was surrounded by an inner annular portion 2B, an outer annular portion 2C, and a connecting portion 2D, as shown in Figure 2. In this hollow structure, the thickness of the inner annular portion 2B was 0.128 mm, the thickness of the outer annular portion 2C was 0.154 mm, and the thickness of the connecting portion 2D was 0.161 mm. The outer diameter D of the hollow structure (insulator 2) was 1.387 mm, and the porosity of the void 2A was 30% of the area of ​​the entire insulator (entire hollow structure). The dielectric constant ε was approximately 1.6. Thus, the insulated wire 3 was fabricated.

[0044] The two insulated wires 3, 3 were aligned so that they were in close contact with each other, and a film-like outer conductor 4 was placed longitudinally around the two insulated wires 3, 3, wrapping them. The film-like outer conductor 4 had an 8-μm-thick copper foil as a metal layer 4B on one side of a 4-μm-thick PET base film 4C via an adhesive layer (not shown in FIG. 3), and a 1-μm-thick adhesive layer 4A coated with a urethane adhesive resin on the other side of the PET base film 4C. The film-like outer conductor 4 had a width of 2.5 mm and a total thickness of 0.013 mm. This film-like outer conductor 4 was placed longitudinally with the adhesive layer 4A facing the insulated wire 3, with the overlapping portion 8 being 1.4 mm wide, as shown in FIG. 1.

[0045] A braided shield was then provided to cover the entire cable as the cover conductor 5. The cover conductor 5 with the braided shield structure was made of 80 silver-plated annealed copper wires with an outer diameter of 0.10 mm. Then, a PFA resin (manufactured by DuPont) layer was extruded at an extrusion temperature of about 380°C to form the outer jacket 6 with a thickness of 0.4 mm. In this way, a two-core parallel coaxial cable 10 with an outer diameter of 2.713 mm and a width of 4.1 mm was produced.

[0046] [Example 2] A film-like outer conductor 4 having a total thickness of 0.017 mm with an adhesive layer 4A having a thickness of 5 μm was used. Otherwise, in the same manner as in Example 1, a two-core parallel coaxial cable 10 having an outer diameter of 2.721 mm in thickness and 4.108 mm in width was produced.

[0047] [Example 3] A film-like outer conductor 4 was used with a total thickness of 0.019 mm, with the PET base film 4C being 10 μm thick. Otherwise, in the same manner as in Example 1, a two-core parallel coaxial cable 10 was produced with an outer diameter of 2.725 mm thick and 4.112 mm wide.

[0048] [Example 4] The film-like outer conductor 4 was wound horizontally with a 5.5 mm wrap (overlap width: 1 / 4 wrap). Otherwise, in the same manner as in Example 1, a two-core parallel coaxial cable 10 with an outer diameter of 2.725 mm thick and 4.112 mm wide was produced.

[0049] [Comparative Example 1] A film-like outer conductor 4 having a total thickness of 0.012 mm and no adhesive layer was used, and the metal layer side was attached vertically to the cover conductor 5 side in the same manner as in Example 1. Otherwise, in the same manner as in Example 1, a two-core parallel coaxial cable 10 having an outer diameter of 2.711 mm in thickness and 4.098 mm in width was produced.

[0050] Comparative Example 2 A film-like outer conductor 4 having a total thickness of 0.0125 mm, with the adhesive layer 4A having a thickness of 0.5 μm, was used. Otherwise, in the same manner as in Example 1, a two-core parallel coaxial cable 10 having an outer diameter of 2.712 mm in thickness and 4.099 mm in width was produced.

[0051] [evaluation] The adhesive strength between the film-like outer conductor 4 and the two insulated wires 3, 3 was measured for the two-core parallel coaxial cables 10 of Examples 1 to 4 and Comparative Examples 1 and 2. As shown in FIG. 5 , the measurement was performed by inserting only the two end-processed insulated wires 3, 3 into a jig 20 having an elongated hole 21 identical in outer shape to the two aligned insulated wires 3, 3 of the two-core parallel coaxial cable 10, with the outer components including the film-like outer conductor 4 (the film-like outer conductor 4, the cover conductor 5, and the jacket 6) hanging over the edge of the elongated hole 21, and measuring the tensile strength between the jig 20 and the two insulated wires 3, 3 using a tensile tester. The measurement conditions were a measurement length of 100 mm, a pulling speed of 200 mm / min, and a measurement range of 1 kgf (full range). The adhesive strength was evaluated as the force (gf) required to peel the two insulated wires 3, 3 from the adhesive layer 4A and move.

[0052] The force required for the two insulated wires 3, 3 to peel and move from the adhesive layer 4A was 150 gf in Comparative Example 1 and 250 gf in Comparative Example 2. On the other hand, it was 360 gf in Example 1 and 400 gf in Example 2. During terminal processing, the stripping force required to peel the insulator 2 constituting the insulated wire 3 from the center conductor is approximately 200 to 300 gf, which was greater in Examples 1 and 2. Therefore, in Examples 1 and 2, the lengths of the two insulated wires 3, 3 did not change or were less likely to change even during terminal processing during connector attachment. As a result, the skew caused by changes in the lengths of the two insulated wires 3, 3 was able to be suppressed to a low delay of 5 PS / m or less.

[0053] In Example 3, the thickness of the PET base film 4C was set to 10 μm, and in Example 4, the film-like outer conductor 4 was wound horizontally with a 5.5 mm wrap (overlap width: 1 / 4 wrap). In both cases, the effect of the adhesive layer 4A was maintained similar to that of Examples 1 and 2, and no significant deterioration in transmission characteristics was observed. [Explanation of symbols]

[0054] 1. Center conductor 2. Insulator 2A void area 2B Inner ring 2C Outer ring section 2D connections 3 insulated wire 4 Film-type outer conductor (metallic resin tape) 4A adhesive layer 4B Metal layer 4C base film 5 Cover conductor (braided shield or spiral wound shield) 6 Envelope 8 Overlap 10 2-core parallel coaxial cable 20 Adhesion force measurement jig 21 slotted hole

Claims

1. A two-core parallel coaxial cable having two insulated wires arranged in parallel, each wire having a central conductor and an insulator disposed around the central conductor, a film-shaped outer conductor covering the two insulated wires, a cover conductor covering the film-shaped outer conductor, and an outer jacket covering the cover conductor, an adhesive layer is provided on a surface of the film-shaped outer conductor facing the insulated wires, the adhesive layer preventing displacement between the insulated wires and the film-shaped outer conductor during terminal processing; The insulator is made of a fluororesin, a two-core parallel coaxial cable, characterized in that the film-like outer conductor has a base film, a metal layer provided on one surface of the base film, and the adhesive layer provided on the other surface of the base film, the adhesive layer being formed to a thickness of 0.8 to 5 μm from a thermosetting resin containing any one of polyurethane resin, polyester resin, and polyesterimide resin, and the base film being a polyester film having a thickness of 2 to 10 μm.

2. 2. The two-core parallel coaxial cable according to claim 1, wherein the adhesive strength between the film-like outer conductor and the two insulated wires is 300 gf / 100 mm or more as a result of an adhesion measurement method.

3. 3. The twin-core parallel coaxial cable according to claim 1, wherein the insulator has a foam structure or a hollow structure.

4. 4. The two-core parallel coaxial cable according to claim 1, wherein the film-like outer conductor is wound longitudinally or horizontally around the two insulated wires arranged in parallel.

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