Communication cable

Abstract

A communication cable includes two insulated electric wires twisted together, each of the two insulated electric wires including a conductor and an insulator covering the conductor. Further, the communication cable includes a metal foil shield provided around the two insulated electric wires by lateral winding, and a sheath provided at an outer periphery of the metal foil shield. The insulator is a foamed body, and a foaming rate of the insulator is 39% or less. A concentricity of each of the two insulated electric wires is 94% or more and 100% or less.

Description

Technical Field

[0001] This invention relates to a communication cable. Background Technology

[0002] Communication cables installed in vehicles such as automobiles require advanced communication performance. As a signal transmission line for communication in the high-frequency band in the GHz range, patent document JP2015-185527A discloses a dual-core parallel shielded wire in which two parallel insulated wires are longitudinally covered by a metal foil resin tape and the resin tape is wound around its outside. Summary of the Invention

[0003] However, according to JP2015-185527A, in order to maintain the parallelism of two insulated wires with high precision, it is necessary to reduce the line speed, which may reduce the manufacturability of the communication cable. Furthermore, according to JP2015-185527A, when the concentricity of the signal transmission line varies along its length, a sharp signal attenuation (notch) may occur at certain frequencies, and communication performance may be degraded.

[0004] This invention was made in view of such problems in the prior art. Furthermore, the object of this invention is to provide a communication cable with improved manufacturability and communication stability.

[0005] The communication cable according to an aspect of the invention comprises: two insulated wires twisted together, each of the two insulated wires including a conductor and an insulator covering the conductor; a metal foil shield disposed around the two insulated wires by transverse winding; and a sheath disposed around the outer periphery of the metal foil shield. The insulator is a foamed material, and the foaming rate of the insulator is 39% or less. The concentricity of each of the two insulated wires is 94% or more and 100% or less.

[0006] According to the present invention, a communication cable with improved manufacturability and communication stability can be provided. Attached Figure Description

[0007] Figure 1 This is a side view showing an example of a communication cable according to an embodiment.

[0008] Figure 2 This is a cross-sectional view showing an example of a communication cable according to this embodiment.

[0009] Figure 3 This is a cross-sectional view showing an example of an insulated wire.

[0010] Figure 4 This is a cross-sectional view showing an example of an insulated wire.

[0011] Figure 5 This is a graph showing the relationship between frequency and insertion loss in Experiment 1.

[0012] Figure 6 This is a graph showing the relationship between frequency and insertion loss in Experiment 2.

[0013] Figure 7 This is a graph showing the relationship between frequency and insertion loss in Experiment 3.

[0014] Figure 8 This is a graph showing the relationship between frequency and insertion loss in Experiment 3.

[0015] Figure 9 This is a graph showing the relationship between frequency and insertion loss in Experiment 4.

[0016] Figure 10 This is a graph showing the relationship between frequency and insertion loss in Experiment 4.

[0017] Figure 11 This is a graph showing the relationship between frequency and insertion loss in Experiment 5. Detailed Implementation

[0018] Referring to the accompanying drawings, a communication cable according to an embodiment of the present invention will now be described in detail. Note that the dimensions in the drawings are exaggerated for ease of explanation and may differ from actual scale.

[0019] like Figure 1 As shown, the communication cable 1 is a two-core stranded shielded cable, comprising two insulated wires 10 twisted together, each of which includes a conductor 11 and an insulator 12 covering the conductor 11. Furthermore, the communication cable 1 includes a metal foil shield 20, which is laterally wound around the two insulated wires 10; and a sheath 40 disposed on the outer periphery of the metal foil shield 20. Additionally, the communication cable 1 may include a metal braid 30 disposed between the metal foil shield 20 and the sheath 40 to cover the outer periphery of the metal foil shield 20.

[0020] [Insulated wires]

[0021] The insulated wire 10 includes a conductor 11 and an insulator 12 covering the conductor 11. The conductor 11 can be formed from a single wire, and can be made from, for example... Figure 2The seven element wires shown can be formed by bundling multiple element wires together to form a stranded wire. Furthermore, conductor 11 can be formed from a single stranded wire, or it can be a composite stranded wire formed by bundling multiple stranded wires together. Additionally, conductor 11 can be a compressed conductor or an uncompressed conductor. The material forming conductor 11 is not particularly limited, but is preferably at least one conductive metal material selected from the group consisting of copper, copper alloys, aluminum, and aluminum alloys. Furthermore, soft copper wire, silver-plated soft copper wire, tin-plated soft copper wire, or tin-plated copper alloy can also be used as the material forming conductor 11, but it is preferred not to plating. When the material forming conductor 11 is not plating, communication performance can be maintained for a long time in the vehicle.

[0022] The cross-sectional area of ​​conductor 11 is not particularly limited, but is preferably 0.22 sq or less. By setting the cross-sectional area of ​​conductor 11 to 0.22 sq or less, wiring of insulated wire 10 can be performed even in narrow, short paths. Figure 2 In this case, the cross-sectional area of ​​conductor 11 refers to the total cross-sectional area of ​​the seven inner wires. Furthermore, 0.22 sq refers to 0.22 ± 0.02 mm². By setting the cross-sectional area of ​​conductor 11 to 0.22 sq or less, the outer diameter of the inner wires will not increase excessively, and the insulated wire 10 is less likely to be flattened due to twisting within the range of twist pitch described later.

[0023] The insulator 12 is a foam. Furthermore, any electrically insulating resin can be used as the base resin forming the insulator 12 to ensure the electrical insulation of the conductor. Preferably, the base resin forming the insulator 12 includes at least one selected from the group consisting of foamed polyethylene, cross-linked foamed polyethylene, foamed polypropylene, cross-linked foamed polypropylene, and foamed polytetrafluoroethylene. These materials can be used alone or in combination of two or more.

[0024] From the perspective of heat resistance and manufacturing versatility, the base resin forming the insulator 12 is more preferably foamed polypropylene. Examples of polypropylene used as the base resin forming the insulator 12 include homopolymer polypropylene (homogeneous PP), atactic polypropylene (random PP), block polypropylene (block PP), and copolymers of other olefin components capable of copolymerizing with propylene. Examples of other olefins capable of copolymerizing with propylene include α-olefins such as ethylene, 1-butene, isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, and 3-methyl-1-hexene.

[0025] The characteristic impedance of the communication cable 1 used as a vehicle-mounted communication cable is preferably 100 ± 5 Ω. To set the characteristic impedance to 100 ± 5 Ω, the relative permittivity of the insulator 12 is preferably 1.55 or higher and 2.07 or lower. Vehicle-mounted communication cables require reduced weight and size. However, when the relative permittivity is high, the finished outer diameter of the insulated wire 10 needs to be increased. When the relative permittivity of the insulator 12 falls within the above range, this embodiment is even applicable to cross-sectional areas of 0.13 sq (mm²) as specified in ISO 21111-8. 2 The communication cable uses the smallest diameter conductor and its characteristic impedance can be controlled within the range of 100 ± 5 Ω. Note that the relative permittivity can be measured at a frequency of 10 GHz in an atmosphere at 30°C using the cavity resonator method.

[0026] The foaming rate of the insulator 12 is 39% or less, and preferably 15% or more and 39% or less. By setting the foaming rate of the insulator 12 to 39% or less, the characteristic impedance of the communication cable 1 can be controlled within the range of 100 ± 5 Ω. Furthermore, by setting the foaming rate of the foamed polypropylene to 39% or less, the flattening of the insulated wire 10 is less likely to occur, and notch filtering can be prevented. Note that the foaming rate can be confirmed by observing the cut surface obtained by cutting the insulated wire 10 in the cross-sectional or length direction using an electron microscope, taking the ratio of the area occupied by foam in the cross-sectional area of ​​the insulator 12 as the foaming rate, and calculating the average foaming rate in the cross-sectional and length directions. Alternatively, the foaming rate can also be confirmed by non-destructively observing the cut surface of the insulated wire 10 in the cross-sectional or length direction using an X-ray microscope (CT) and calculating the average foaming rate.

[0027] The insulator 12 can be manufactured using known molding methods such as foam extrusion molding. Furthermore, the insulator 12 is preferably formed by a physical foaming method involving the injection of an inert gas. By using a physical foaming method, the amount of foaming agent added can be reduced, and communication cables with excellent communication performance and reduced environmental impact can be manufactured.

[0028] The thickness of the insulator 12 is not particularly limited, but is preferably 0.15 mm or more, more preferably 0.18 mm or more. By setting the thickness of the insulator 12 as described above, the conductor 11 can be effectively protected. Furthermore, the thickness of the insulator 12 is not particularly limited, but is preferably 0.5 mm or less. By setting the thickness of the insulator 12 as described above, wiring of the insulated wire 10 can be performed even in narrow paths.

[0029] The D-hardness of the insulator 12 is 60 or higher and 70 or lower, and preferably 62 or higher and 67 or lower. By setting the D-hardness of the insulator 12 to 60 or higher, it is less likely that the insulated wire 10 will be flattened due to twisting and foil winding, and it is possible to prevent notch waves. Furthermore, by setting the D-hardness of the insulator 12 to 70 or lower, deformation during twisting can be suppressed, and the stranded wire is less likely to unravel. Note that the D-hardness can be measured according to Japanese Industrial Standard JIS K 7215 (Test Method for Indicative Hardness of Plastics).

[0030] As additives added to the base resin forming the insulator 12, various additives can be appropriately mixed within a range that does not impair the effects of this embodiment. Examples of such additives include antioxidants, copper inhibitors, flame retardants, inorganic fillers, flame retardant aids, processing aids, crosslinking agents, metal deactivators, anti-aging agents, fillers, reinforcing agents, ultraviolet absorbers, stabilizers, plasticizers, pigments, dyes, colorants, antistatic agents, and foaming agents.

[0031] As a method for mixing the above-mentioned additives into the base resin forming the insulator 12, known means can be used. For example, the resin composition forming the insulator 12 can be obtained by mixing using known mixing machines, such as a Banbury mixer, kneader, tumbler, twin-screw extruder, and single-screw extruder.

[0032] In the insulated wire 10 of this embodiment, the conductor 11 can also be covered with the insulator 12 using known methods, and for example, it can be manufactured by a general extrusion molding method. Specifically, the insulator 12 can be formed by extruding the material of the insulator 12 and covering it on the outer surface of the conductor 11 formed by one or more inner wires. As the extruder used in the extrusion molding method, for example, a single-screw extruder or a twin-screw extruder including a screw, a perforated plate, a crosshead, a distributor, a nozzle, and a die can be used.

[0033] [Stranded wire]

[0034] Stranded wire is obtained by twisting two insulated wires 10 together, each insulated wire 10 including a conductor 11 and an insulator 12 covering the outer periphery of the conductor 11. For example... Figure 1 As shown, the appearance of stranded wire is that it is formed by twisting two insulated wires 10 together. Furthermore, Figure 2 The cross-sections of two adjacent insulated wires 10 are shown.

[0035] The two insulated wires 10 forming the stranded wire have identical construction. In the stranded wire, currents of opposite phase flow through the two insulated wires. Therefore, the stranded wire is configured to transmit signals based on the potential difference between the two insulated wires 10. However, when the concentricity of the two insulated wires 10 deviates along their length, notch filtering may occur at a specific frequency. Therefore, the concentricity of each of the two insulated wires 10 is 94% or more and 100% or less. By setting the concentricity of the two insulated wires 10 to 94% or more and 100% or less, notch filtering can be prevented, and impedance variations can be reduced, as described later. Note that the method of adjusting the concentricity is not particularly limited, but it can be adjusted, for example, when the conductor 11 is covered by the insulator 12.

[0036] The concentricity of two insulated wires 10 is measured using the following method. Figure 3 A cross-sectional view is shown when the center of conductor 11 coincides with the center of insulated wire 10. First, straight lines L1, L2, and L3 are drawn to divide the insulated wire 10 into six equal parts circumferentially. Next, straight lines M1, M2, and M3 are drawn to divide the conductor 11 into six equal parts circumferentially. Note that in Figure 3 In the insulated wire 10, the center of conductor 11 coincides with the center of conductor 11, and therefore lines L1 and M1, lines L2 and M2, and lines L3 and M3 are completely aligned with each other. Furthermore, on line L1 (M1), the thickness of the insulator 12 on one side outside conductor 11 is defined as a1, and the thickness on the other side is defined as b1. Similarly, on line L2 (M2), the thickness of the insulator 12 on one side outside conductor 11 is defined as a2, and the thickness on the other side is defined as b2. On line L3 (M3), the thickness of the insulator 12 on one side outside conductor 11 is defined as a3, and the thickness on the other side is defined as b3. Furthermore, the concentricity of the insulated wire 10 can be calculated using the following formula (1).

[0037] [Mathematical Expression 1]

[0038]

[0039] In equation (1) above, C represents the concentricity (%). In other words, the thickness ratio of the insulator 12 is calculated on each of the lines L1 (M1), L2 (M2), and L3 (M3), and the average of the three points is considered the concentricity at that location. Furthermore, the average of the concentricities measured at ten locations every 1 m along the length of the insulated wire 10 is defined as the concentricity of the insulated wire 10. Note that in Figure 3 In the case where a1=b1, a2=b2 and a3=b3 respectively, the concentricity C of the insulated wire 10 is 100%.

[0040] Figure 4 A cross-sectional view is shown when the center of conductor 11 does not coincide with the center of insulated wire 10. First, straight lines L1, L2, and L3 are drawn to divide the insulated wire 10 into six equal parts circumferentially. Next, straight lines M1, M2, and M3 are drawn to divide conductor 11 into six equal parts circumferentially. At this point, straight lines L1 and M1, L2 and M2, and L3 and M3 are parallel to each other. Furthermore, a tangent is drawn at one intersection point between straight line M1 and the outer perimeter of conductor 11, and the thickness of the insulator 12, starting from the point where this tangent intersects with straight line L1, is defined as a1. Additionally, a tangent is drawn at another intersection point between straight line M1 and the outer perimeter of conductor 11, and the thickness of the insulator 12, starting from the point where this tangent intersects with straight line L1, is defined as b1 (assuming a1 ≥ b1).

[0041] Similarly, a tangent is drawn at one intersection between line M2 and the outer periphery of conductor 11, and the thickness of insulator 12 starting from the point where this tangent intersects with line L2 is defined as a2. A tangent is drawn at another intersection between line M2 and the outer periphery of conductor 11, and the thickness of insulator 12 starting from the point where this tangent intersects with line L2 is defined as b2 (assuming a2 ≥ b2). Furthermore, a tangent is drawn at one intersection between line M3 and the outer periphery of conductor 11, and the thickness of insulator 12 starting from the point where this tangent intersects with line L3 is defined as a3. A tangent is drawn at another intersection between line M3 and the outer periphery of conductor 11, and the thickness of insulator 12 starting from the point where this tangent intersects with line L3 is defined as b3 (assuming a3 ≥ b3). The concentricity of insulated wire 10 can be calculated using the values ​​of thicknesses a1 to a3 and b1 to b3 of insulator 12 obtained as described above using equation (1).

[0042] The characteristic impedance of the stranded wire can be calculated using the following formula (2).

[0043] [Mathematical Expression 2]

[0044]

[0045] In equation (2) above, Z0 represents the characteristic impedance (Ω), ε e Let represent the relative permittivity of insulator 12, d represent the outer diameter of conductor 11 (mm), and B represent the distance between the centers of conductors 11 (mm). In other words, the characteristic impedance theoretically depends on the distance between the centers of conductors 11. Thus, as described above, by setting the concentricity of each of the two insulated wires 10 to be above 91% and below 100%, the impedance variation can be reduced.

[0046] The twist pitch of the stranded wire is preferably 15 mm or more and 21 mm or less. By setting the twist pitch of the stranded wire to 15 mm or more and 21 mm or less, it is possible to prevent the inner wire (insulated wire 10) from being flattened and twisted, and to reduce the change in impedance.

[0047] The coupling ratio of the stranded wire can be calculated using the following formula (3).

[0048] [Mathematical Expression 3]

[0049]

[0050] In equation (3) above, CR represents the coupling rate (%), and Z odd Z represents the odd-mode impedance (Ω), and Z even Let represent the even-mode impedance (Ω). The odd-mode impedance and even-mode impedance can be calculated using the following equations (4) and (5).

[0051] [Mathematical Expression 4]

[0052]

[0053] In equation (4) above, Z diff This represents the differential-mode impedance (Ω). Differential-mode impedance is the impedance generated between two insulated wires 10 when current flows in opposite directions relative to signals in the two insulated wires 10, and is determined by the coupling between the two insulated wires 10, such as the conductor distance, conductor diameter, and material.

[0054] [Mathematical Expression 5]

[0055]

[0056] In equation (5) above, Z common This represents the common-mode impedance (Ω). Common-mode impedance refers to the impedance generated between the two insulated wires 10 and ground relative to the current flowing in the same direction relative to the signal on each of the two insulated wires 10.

[0057] In the relationship between frequency and insertion loss (IL), insertion loss is generally low in the low-frequency range but tends to increase in the high-frequency range. Furthermore, by increasing the coupling ratio of the stranded wires and strengthening the coupling between the two insulated wires 10, insertion loss in the high-frequency range can be suppressed. For example, when the cross-sectional area of ​​conductor 11 is 0.22 sq or less, the coupling ratio of the stranded wires is preferably 12.0% or more and 20.0% or less, more preferably 12.0% or more and 15.0% or less. By setting the coupling ratio of the stranded wires to 12.0% or more, insertion loss in the high-frequency range can be suppressed. For example, when the cross-sectional area of ​​conductor 11 is 0.22 sq, the insertion loss near the 9 GHz frequency in the high-frequency range is preferably -3 dB / m or more. Furthermore, when the cross-sectional area of ​​conductor 11 is 0.13 sq, the insertion loss near the 9 GHz frequency is preferably -3.5 dB / m or more. On the other hand, by setting the coupling ratio of the stranded wires to 20.0% or less, good manufacturability of the communication cable can be achieved.

[0058] [Metal Foil Shielding]

[0059] The communication cable 1 includes a metal foil shield 20 that is laterally wound around two insulated wires 10. The term "lateral winding" refers to the metal foil shield 20 being wound in a spiral manner, such as... Figure 1 As shown. Compared to the case where the metal foil shield 20 is laid longitudinally, by laterally winding the metal foil shield 20, the communication cable is easier to bend and can ensure alignment. Note that a retaining film can be arranged between the two insulated wires 10 and the metal foil shield 20, and this retaining film is configured to cover the outer periphery of the two insulated wires 10. In other words, the metal foil shield 20 can be arranged around the two insulated wires 10 by laterally winding it via the retaining film. For example, polyethylene terephthalate (PET) film can be used as the retaining film.

[0060] The metal foil shield 20 is a shielding component disposed around two insulated wires 10 by laterally winding. The metal foil shield 20 includes a resin layer and a metal layer. Furthermore, the metal foil shield 20 can be stacked and wound around the two insulated wires 10 such that the metal layer is on the outer side. Moreover, the metal foil shield 20 preferably has a three-layer structure, including a resin layer, an adhesive layer that integrally bonds the resin layer and the metal layer, and the metal layer. In other words, the metal layer, adhesive layer, and resin layer are preferably stacked in this order from the outer side, and are preferably stacked and wound around the two insulated wires 10.

[0061] The resin layer of the metal foil shield 20 is not particularly limited, as long as it is a non-conductive resin layer, but it may include, for example, PET, or it may be a PET film. In addition, the resin layer may be any of an unstretched film, a uniaxially stretched film, or a biaxially stretched film, but from the point of view of strength, a biaxially stretched film stretched in both the longitudinal and transverse directions is preferred.

[0062] The metal layer of the metal foil shield 20 is not particularly limited, as long as it is a conductive metal layer, but it is preferable to include at least one of aluminum or copper, and from a cost point of view, it is more preferable to include aluminum. Note that from the point of view of ensuring shielding performance, when the metal layer includes copper, the thickness of the metal layer is preferably 8 μm or more, and when the metal layer includes aluminum, it is preferably 10 μm or more.

[0063] The ratio of the thickness of the metal layer to the thickness of the resin layer in the metal foil shield 20 is 0.4 or more and 1.2 or less. By setting the ratio of the metal layer thickness to the resin layer thickness to be 0.4 or more, the rigidity of the resin layer is not too high, which can suppress damage to the insulated wire 10 when the metal foil shield 20 is wound along the stranded wire, and can prevent notch waves. Furthermore, by setting the ratio of the metal layer thickness to the resin layer thickness to be 1.2 or less, the resin layer is not too thin, and it is not easy to break during the manufacturing process of the communication cable.

[0064] The thickness of the metal foil shield 20 is preferably 15 μm or more and 50 μm or less. By setting the thickness of the metal foil shield 20 to 15 μm or more, breakage of the metal foil shield 20 is less likely to occur during the manufacturing process of the communication cable. Furthermore, by setting the thickness of the metal foil shield 20 to 50 μm or less, the metal foil shield 20 is not too rigid, and the metal foil shield body 20 can be easily wound along the stranded wire.

[0065] like Figure 1 As shown, the foil winding spacing P of the metal foil shield 20 is preferably 18.5 mm or less. The notch frequency of the stranded wire obtained by twisting two insulated wires 10 can be calculated by the following formula (6).

[0066] [Mathematical Expression 6]

[0067]

[0068] In equation (6) above, f represents the notch filter frequency (GHz), c represents the speed of light, and ε rP represents the relative permittivity of the inner wire (the relative permittivity of insulator 12), and P represents the foil winding pitch (mm) of the metal foil shield 20. As described above, when the relative permittivity of insulator 12 is 1.55 or higher and 2.07 or lower, the foil winding pitch P of the metal foil shield 20 is 18.5 mm or lower, and therefore the notch frequency is 9 GHz or higher. Thus, notch waves at frequencies up to 9 GHz can be prevented in the communication cable 1. To address the automotive industry's trend of CASE ("connected," "autonomous," "sharing and services," and "electric"), communication speeds are expected to increase to 25 Gbps. To achieve this communication speed, it is necessary to prevent notch waves in the communication cable in the high-frequency range up to 9 GHz.

[0069] [Metal woven fabric]

[0070] The communication cable 1 may include a metal braid 30 disposed between the metal foil shield 20 and the sheath 40 to cover the outer periphery of the metal foil shield 20. The metal braid 30 is formed, for example, by bundling multiple metal wires such as soft copper wire, silver-plated soft copper wire, tin-plated soft copper wire, or tin-plated copper alloy wire and weaving these bundles. Note that the metal wires may be coated fibers with metal plating applied to them. Furthermore, the metal braid 30 can be formed by weaving a flat bundle obtained by co-plating multiple metal wires.

[0071] [jacket]

[0072] The communication cable 1 includes a sheath 40 disposed on the outer periphery of the metal foil shield 20. When the metal braid 30 is disposed between the metal foil shield 20 and the sheath 40, the sheath 40 is configured to cover the outer periphery of the metal braid 30.

[0073] The material of the base resin forming the sheath 40 is not particularly limited, as long as electrical insulation can be ensured. However, for example, any known insulating resin can be used, such as cross-linked polyethylene, olefin resins such as polypropylene, and polyvinyl chloride. Note that the sheath 40 is not limited to a solid state and can be formed into a tubular shape, and can be arranged with a partial gap relative to the inner metal foil shield 20 or metal braid 30. Alternatively, some other intervening material can be provided in the gap.

[0074] To ensure the required flame retardancy for the wire's performance, it is preferable to add flame retardants, such as inorganic flame retardants including metal hydroxides and halogen-based flame retardants, to the base resin forming the sheath 40. Furthermore, similar to the insulator 12, additives such as antioxidants and plasticizers may be appropriately incorporated into the base resin forming the sheath 40 without impairing the effects of this embodiment.

[0075] The method of covering the metal foil shield 20 or the metal braid 30 with the sheath 40 can be carried out using the same known means as the insulator 12, and the sheath 40 can be manufactured by, for example, a common extrusion molding method. The thickness of the sheath 40 is not particularly limited, but can be, for example, from 0.1 mm to 1 mm.

[0076] As described above, the communication cable 1 includes two insulated wires 10 twisted together, each of the two insulated wires including a conductor 11 and an insulator 12 covering the conductor 11. Furthermore, the communication cable 1 includes a metal foil shield 20, which is laterally wound around the two insulated wires 10; and a sheath 40 disposed on the outer periphery of the metal foil shield 20. The insulator 12 is a foamed material with a foaming rate of 39% or less, and the concentricity of each of the two insulated wires 10 is 94% or more and 100% or less. Therefore, in the communication cable 1, damage to the insulated wires 10 caused by twisting and foil winding during the manufacturing process of the communication cable can be suppressed, and notch filtering can be prevented. Therefore, the communication cable 1 according to this embodiment provides a communication cable with improved manufacturability and communication stability. Furthermore, in the communication cable 1, by laterally winding the metal foil shield 20 and adjusting the foil winding spacing, wiring performance is ensured, and excellent communication stability is achieved in the high-frequency range up to 10 GHz.

[0077] [Example]

[0078] The present embodiment is further described below through examples and comparative examples. However, the present embodiment is not limited to these examples.

[0079] [Experiment 1]

[0080] Examples 1-1 and 1-2, as well as Comparative Example 1-1, were used to verify the effect of differences in the concentricity of the insulated wires forming the stranded wires on communication stability.

[0081] As a method for manufacturing insulated wires, polypropylene is first foamed and extruded onto a stranded conductor (cross-sectional area: 0.13 sq, outer diameter: 0.48 mm) formed by twisting seven soft copper wires together, thereby forming an insulator (foamed polypropylene). The temperature of the extruder used for foaming extrusion molding is set to 170 to 220°C, and high-pressure nitrogen gas pressurized by a gas booster is injected and mixed from the middle part of the extruder. At this time, the foaming rate of the insulator is set to 35% in all cases. In addition, the concentricity of the insulated wires is set to 97% in Example 1-1, 94% in Example 1-2, and 90% in Comparative Example 1-1. In each case, two insulated wires were manufactured according to the above conditions.

[0082] The foaming rate was confirmed by acquiring CT images (in both the cross-sectional and length directions) of the insulated wire using an X-ray microscope (nano3DX). Imaging conditions were set as follows: spatial resolution of 4.31 μm / voxel, X-ray camera lens L1080, pixel binning setting of 3, exposure time of 4 seconds, Cu X-ray source (40 kV, 30 mA), field of view of 3.626 × 2.719 mm, and 400 images. Furthermore, the foaming rate was calculated as an average value for each acquired image using the ImageJ analysis software.

[0083] The obtained insulated wires are stranded together to manufacture a stranded wire. The twist pitch of the stranded wire is set to 17 mm. Furthermore, a metal foil shield is formed by laterally winding around the stranded wire. The resin layer of the metal foil shield is a PET film, and the resin layer thickness is 12 μm. The metal layer of the metal foil shield is aluminum, and the metal layer thickness is 10 μm. Thus, the ratio of the metal layer thickness to the resin layer thickness is 0.83. Note that the thickness of the metal foil shield is 50 μm or less.

[0084] In addition, after a metal braid formed of metal wire is placed on the outer periphery of the metal foil shield, the assembly is placed in an extruder (set temperature: 140 to 180°C) and covered with a sheath with a thickness of 0.4 mm by extrusion molding to manufacture a test sample of the communication cable.

[0085] To evaluate the communication stability of communication cables, insertion loss was measured. Specifically, the insertion loss of the communication cables was measured using a vector network analyzer (VNA) (E5071C manufactured by Keysight Technologies) under conditions of a measurement frequency of 1 MHz to 10 GHz and a measurement bandwidth of 1 kHz.

[0086] Figure 5 This is a graph comparing the communication stability of the communication cables according to Examples 1-1 and 1-2 and Comparative Example 1-1, showing the relationship between frequency and insertion loss (IL). In Examples 1-1 and 1-2, since the concentricity of the insulated wires is above 91%, no notch appeared, and the communication stability was good. On the other hand, in Comparative Example 1-1, a notch appeared near 5.9 GHz. In Comparative Example 1-1, since the concentricity of the insulated wires is less than 91%, a notch appeared at the frequency corresponding to the twist pitch of the stranded wires, and the communication stability was poor.

[0087] [Experiment 2]

[0088] Example 2-1 and Comparative Examples 2-1 and 2-2 were used to verify the effect of differences in the foaming rate of insulators on communication stability.

[0089] As a method for manufacturing insulated wires, polypropylene is first foamed and extruded onto a stranded conductor (cross-sectional area: 0.13 sq, outer diameter: 0.48 mm) formed by twisting seven soft copper wires together, thereby forming an insulator (foamed polypropylene). The temperature of the extruder used for foaming extrusion molding is set to 170 to 220°C, and high-pressure nitrogen gas pressurized by a gas booster is injected and mixed from the middle part of the extruder. At this time, the foaming rate of the insulator is set to 37% in Example 2-1, 40% in Comparative Example 2-1, and 45% in Comparative Example 2-2. In addition, in all cases, the concentricity of the insulated wire is set to 95% or more. In each case, two insulated wires were manufactured according to the above conditions.

[0090] The obtained insulated wires were stranded together to manufacture a stranded wire. In Example 2-1 and Comparative Example 2-1, the twist pitch of the stranded wire was set to 17 mm, and in Comparative Example 2-2 it was set to 23 mm. Furthermore, a metal foil shield was provided by laterally winding around the stranded wire. The resin layer of the metal foil shield was a PET film, and the thickness of the resin layer was 12 μm. The metal layer of the metal foil shield was aluminum, and the thickness of the metal layer was 10 μm. Thus, the ratio of the thickness of the metal layer to the thickness of the resin layer was 0.83. Note that the thickness of the metal foil shield was 50 μm or less.

[0091] In addition, after a metal braid formed of metal wire is placed on the outer periphery of the metal foil shield, the assembly is placed in an extruder (set temperature: 140 to 180°C) and covered with a sheath with a thickness of 0.4 mm by extrusion molding to manufacture a test sample of the communication cable.

[0092] Figure 6 This is a graph comparing the communication stability of the communication cables according to Examples 2-1, 2-1, and 2-2, and showing the relationship between frequency and insertion loss (IL). In Example 2-1, since the foaming rate of the insulator is less than 39%, no notch appeared, and the communication stability was good. On the other hand, in Comparative Example 2-1, notch appeared near 6.3 to 6.7 GHz, while in Comparative Example 2-2, notch appeared near 5 GHz. In Comparative Examples 2-1 and 2-2, since the foaming rate of the insulator is greater than 39%, the insulator is easily flattened, notch appears, and the communication stability is poor.

[0093] [Experiment 3]

[0094] Examples 3-1 to 3-5 and Comparative Examples 3-1 to 3-7 were used to verify the effect of the difference in D-hardness of the insulator and the metal foil shielding on communication stability.

[0095] As a method for manufacturing insulated electric wires, first, polypropylene is foam-extruded onto a stranded conductor (cross-sectional area: 0.13 sq, outer diameter: 0.48 mm) formed by stranding seven soft copper elemental wires together, so as to form an insulator (foamed polypropylene). The temperature of the extruder for foam extrusion molding is set to 170 to 220°C, and high-pressure nitrogen gas pressurized by a gas booster is injected and mixed from the middle part of the extruder. At this time, the foaming rate of the insulator is set to 35% in all cases. In addition, the concentricity of the insulated electric wire is set to 95% or more in all cases. In each case, two insulated electric wires were manufactured under the above conditions. The measurement results of the D hardness of the insulator are shown in Table 1.

[0096] The obtained insulated electric wires are stranded together to manufacture a stranded wire. The twist pitch of the stranded wire is set to 17 mm. Further, a metal foil shield is provided around the stranded wire by lateral winding. The resin layer of the metal foil shield is a PET film, and the metal layer of the metal foil shield is aluminum. Further, the ratio of the thickness of the metal layer to the thickness of the resin layer in the metal foil shield is set as shown in Table 1. Note that the thickness of the metal foil shield is 50 μm or less in all cases.

[0097] Further, after a metal braid formed of metal wires is provided on the outer periphery of the metal foil shield, the assembly is placed into an extruder (set temperature: 140 to 180°C) and covered with a sheath having a thickness of 0.4 mm by extrusion molding, so as to manufacture a test sample of a communication cable.

[0098] (Manufacturability)

[0099] In each case, those in which the communication cable was successfully manufactured by the above method were evaluated as acceptable (pass), and those in which the communication cable could not be manufactured or a defect occurred during the manufacturing process were evaluated as unacceptable (fail). The evaluation results are shown in Table 1.

[0100] (Communication stability)

[0101] In each case, when the communication stability of the communication cable manufactured by the above method was evaluated, the communication cable in which no notch occurred was evaluated as acceptable (pass), and the communication cable in which a notch occurred was evaluated as unacceptable (fail). The evaluation results are shown in Table 1. Note that for the case where the communication cable could not be manufactured and the communication stability was not evaluated, the result was determined as "unmeasurable" and regarded as unacceptable.

[0102] (Comprehensive evaluation)

[0103] The case where both the manufacturability evaluation and the communication stability evaluation are acceptable is evaluated as acceptable (pass), and the case where either evaluation is unacceptable is evaluated as unacceptable (fail). The evaluation results are shown in Table 1.

[0104] [Table 1]

[0105]

[0106] As can be seen from Table 1, in the communication cables of Examples 3-1 to 3-5, the D-hardness of the insulation is 60 or higher and 70 or lower, and the ratio of the thickness of the metal layer to the thickness of the resin layer is 0.4 or higher and 1.2 or lower. Therefore, the manufacturability evaluation and the communication stability evaluation are both satisfactory, and the overall evaluation is satisfactory in all cases.

[0107] In the communication cable of Comparative Example 3-1, the D-hardness of the insulation is less than 60, and the ratio of the thickness of the metal layer to the thickness of the resin layer is greater than 1.2. Consequently, the resin layer of the metal foil shield is thin and easily broken, resulting in defects during the manufacturing process of the communication cable and failing the manufacturability evaluation. Furthermore, Figure 7 This is a graph comparing the communication stability of the communication cables according to Examples 3-1 and 3-2 and Comparative Example 3-1, showing the relationship between frequency and insertion loss (IL). No notch was observed in Examples 3-1 and 3-2, while in Comparative Example 3-3, a notch occurred near 6.2 to 6.6 GHz. In Comparative Example 3-1, a notch occurred in the communication stability evaluation because the insulated wires were flattened through twisting and foil winding during the manufacturing process of the communication cable, resulting in a substandard result.

[0108] In the communication cable of Comparative Example 3-2, the D hardness of the insulation is less than 60, but the ratio of the thickness of the metal layer to the thickness of the resin layer is 0.4 or more and 1.2 or less. Thus, a communication cable is manufactured. However, because the insulated wires are flattened by twisting and foil winding during the manufacturing process of the communication cable, notch filtering occurs in the communication stability evaluation, and the result is unacceptable.

[0109] In the communication cable of Comparative Example 3-3, the D-hardness of the insulation was 60 or higher and 70 or lower, but the ratio of the metal layer thickness to the resin layer thickness was less than 0.4. Therefore, a communication cable was manufactured. However, the communication stability evaluation failed. Meanwhile, Figure 8 This is a graph comparing the communication stability of the communication cables according to Example 3-1 and Comparative Example 3-3, showing the relationship between frequency and insertion loss (IL). No notch was observed in Example 3-1, while in Comparative Example 3-3, a notch occurred near 5.7 to 6.8 GHz. In Comparative Example 3-3, due to the increased foil winding tension required during the manufacturing process of the communication cable, which resulted in damage to the insulated wires, a notch occurred in the communication stability evaluation, and the result was unsatisfactory.

[0110] In the communication cables of Comparative Examples 3-4, the D-hardness of the insulation was 60 or higher and 70 or lower, but the ratio of the thickness of the metal layer to the thickness of the resin layer was less than 0.4. In Comparative Examples 3-4, since the ratio of the thickness of the metal layer to the thickness of the resin layer was even lower than that of Comparative Example 3-3, the rigidity of the resin layer was very high, and the metal foil shielding became hard. Therefore, it was impossible to wind along the strands, and the communication cable could not be manufactured. As a result, the manufacturability evaluation failed. The communication cable was not manufactured, and therefore, the communication stability was not evaluated.

[0111] In the communication cables of Comparative Examples 3-5, the D-hardness of the insulation was 60 or higher and 70 or lower, but the ratio of the thickness of the metal layer to the thickness of the resin layer was greater than 1.2. Consequently, the resin layer of the metal foil shield was thin and easily broken, while the metal layer was thick and prone to wrinkling. Therefore, defects occurred during the manufacturing process of the communication cable, and the manufacturability evaluation was unsatisfactory. On the other hand, no notch filtering occurred in the communication stability evaluation, and the result was satisfactory.

[0112] In the communication cables of Comparative Examples 3-6, the D-hardness of the insulation was greater than 70, but the ratio of the metal layer thickness to the resin layer thickness was between 0.4 and 1.2. Therefore, during the manufacturing process of the communication cable, deformation during the twisting process increased, leading to problems such as the strands unraveling, and no communication cable was manufactured. Therefore, the manufacturability evaluation was unsuccessful. No communication cable was manufactured, and therefore, communication stability was not evaluated.

[0113] In the communication cables of Comparative Examples 3-7, the D hardness of the insulator was 60 or higher and 70 or lower, but the ratio of the thickness of the metal layer to the thickness of the resin layer was greater than 1.2. As a result, the resin layer of the metal foil shield was thin and prone to breakage, leading to defects during the manufacturing process of the communication cable and failing the manufacturability evaluation. On the other hand, no notch filtering occurred in the communication stability evaluation, and the result was satisfactory.

[0114] Therefore, since the communication cables of Comparative Examples 3-1 to 3-7 failed the manufacturability evaluation or communication stability evaluation, the overall evaluation was unqualified in all cases.

[0115] [Experiment 4]

[0116] Examples 4-1 and 4-2, as well as Comparative Examples 4-1 and 4-2, were used to verify the effect of differences in twist pitch of stranded wires on communication stability.

[0117] As a method for manufacturing insulated wires, polypropylene is first foamed and extruded onto a stranded conductor (cross-sectional area: 0.13 sq, outer diameter: 0.48 mm) formed by twisting seven soft copper wires together, thereby forming an insulator (foamed polypropylene). The temperature of the extruder used for foaming extrusion molding is set to 170 to 220°C, and high-pressure nitrogen gas, pressurized by a gas booster, is injected and mixed from the middle section of the extruder. The foaming rate of the insulator is set to 35% in all cases. Furthermore, the concentricity of the insulated wire is set to 95% or higher in all cases. Two insulated wires are manufactured according to the above conditions in each case.

[0118] The obtained insulated wires were stranded together to manufacture a stranded wire. The twist pitch of the stranded wire was set to 15 mm in Example 4-1, 17 mm in Example 4-2, 11 mm in Comparative Example 4-1, and 23 mm in Comparative Example 4-2. Furthermore, a metal foil shield was provided by laterally winding around the stranded wire. The resin layer of the metal foil shield was a PET film, and the thickness of the resin layer was 12 μm. The metal layer of the metal foil shield was aluminum, and the thickness of the metal layer was 10 μm. Thus, the ratio of the thickness of the metal layer to the thickness of the resin layer was 0.83. Note that the thickness of the metal foil shield was 50 μm or less.

[0119] In addition, after a metal braid formed of metal wire is placed on the outer periphery of the metal foil shield, the assembly is placed in an extruder (set temperature: 140 to 180°C) and covered with a sheath with a thickness of 0.4 mm by extrusion molding to manufacture a test sample of the communication cable.

[0120] Figure 9 and Figure 10 It is a graph comparing the communication stability of the communication cables according to Examples 4-1 and 4-2 and Comparative Examples 4-1 and 4-2, and illustrating the relationship between frequency and insertion loss (IL). Figure 10 It has changed. Figure 9The graph shows the proportion of the vertical axis. In Examples 4-1 and 4-2, since the twist pitch of the stranded wire is 15 mm or more and 21 mm or less, no notch appeared, and the communication stability was good. On the other hand, in Comparative Example 4-1, notch appeared near 8 to 10 GHz. In Comparative Example 4-1, since the twist pitch of the stranded wire is less than 15 mm, the inner wire is easily flattened, resulting in notch, and the communication stability is poor. Furthermore, in Comparative Example 4-2, the communication performance deteriorated in the region above 5 GHz, and deteriorated by about 9% near 10 GHz compared to Examples 4-1 and 4-2. In Comparative Example 4-2, since the twist pitch of the stranded wire is greater than 21 mm, the metal foil easily enters the twist valley, the area occupancy of the air layer between the stranded wire and the metal foil shielding is reduced, the effective relative permittivity of the communication cable deteriorates, and the communication stability is poor.

[0121] [Experiment 5]

[0122] Examples 5-1 and 5-2, as well as Comparative Examples 5-1 and 5-2, were used to verify the impact of differences in the coupling rate of the stranded wires on communication stability.

[0123] As a method for manufacturing insulated wires, polypropylene is first foamed and extruded onto a stranded conductor (cross-sectional area: 0.22 sq, outer diameter: 0.60 mm) formed by twisting seven soft copper wires together, thereby forming an insulator (foamed polypropylene). The temperature of the extruder used for foaming extrusion molding is set to 170 to 220°C, and high-pressure nitrogen gas, pressurized by a gas booster, is injected and mixed from the middle section of the extruder. The foaming rate of the insulator is set to 35% in all cases. Furthermore, the concentricity of the insulated wire is set to 95% or higher in all cases. Two insulated wires are manufactured according to the above conditions in each case.

[0124] The obtained insulated wires were stranded together to manufacture a stranded wire. The twist pitch of the stranded wire was set to 17 mm. The coupling rate of the stranded wire was set to 14.01% in Example 5-1, 12.05% in Example 5-2, 11.98% in Comparative Example 5-1, and 11.00% in Comparative Example 5-2. Furthermore, a metal foil shield was provided by laterally winding around the stranded wire. The resin layer of the metal foil shield was a PET film, and the thickness of the resin layer was 12 μm. The metal layer of the metal foil shield was aluminum, and the thickness of the metal layer was 10 μm. Thus, the ratio of the thickness of the metal layer to the thickness of the resin layer was 0.83. Note that the thickness of the metal foil shield was 50 μm or less.

[0125] In addition, after a metal braid formed of metal wire is placed on the outer periphery of the metal foil shield, the assembly is placed in an extruder (set temperature: 140 to 180°C) and covered with a sheath with a thickness of 0.4 mm by extrusion molding to manufacture a test sample of the communication cable.

[0126] Figure 11 This is a graph comparing the communication stability of the communication cables according to Examples 5-1 and 5-2 and Comparative Examples 5-1 and 5-2, and showing the relationship between frequency and insertion loss (IL). In Examples 5-1 and 5-2, since the coupling rate of the stranded wire is above 12.0% and below 20.0%, the insertion loss near the 9 GHz frequency is successfully maintained above -3 dB / m, and the communication stability is good. On the other hand, in Comparative Examples 5-1 and 5-2, the insertion loss near the 9 GHz frequency is not maintained above -3 dB / m, and the communication stability is poor.

[0127] These results demonstrate that by appropriately selecting the material properties of the communication cable and the specifications of the metal foil shielding, it is possible to achieve communication cables with improved manufacturability and communication stability.

[0128] Although the present invention has been described above with reference to embodiments, the present invention is not limited thereto. Within the scope of the claims, the construction of the components can be replaced with any construction having the same function.

Claims

1. A communication cable, comprising: Two insulated wires twisted together, each of the two insulated wires comprising a conductor and an insulator covering the conductor; A metal foil shielding element, which is disposed around the two insulated wires by transverse winding; and A protective sleeve is disposed on the outer periphery of the metal foil shielding member, wherein, The insulator is a foamed material, and the foaming rate of the insulator is less than 39%. The concentricity of each of the two insulated wires is above 94% and below 100%.

2. The communication cable according to claim 1, wherein, The coupling rate of the two insulated wires is greater than 12.0%.

3. The communication cable according to claim 1 or 2, wherein, The metal foil shielding component includes a resin layer and a metal layer, wherein the ratio of the thickness of the metal layer to the thickness of the resin layer is 0.4 or more and 1.2 or less. The D hardness of the insulator is above 60 and below 70.

4. The communication cable according to claim 1 or 2, wherein, A metal braid is arranged between the metal foil shield and the sheath, the metal braid being configured to cover the outer periphery of the metal foil shield.

5. The communication cable according to claim 3, wherein, The metal layer of the metal foil shield comprises at least one of aluminum and copper.

6. The communication cable according to claim 3, wherein, The resin layer of the metal foil shield comprises polyethylene terephthalate.

7. The communication cable according to claim 1 or 2, wherein, The base resin forming the insulator is foamed polypropylene.

8. The communication cable according to claim 1 or 2, wherein, The twist pitch of the two insulated wires is more than 15 mm and less than 21 mm.

9. The communication cable according to claim 1 or 2, wherein, The foil winding spacing of the metal foil shield is less than 18.5 mm.

10. The communication cable according to claim 1 or 2, wherein, The material forming the conductor was not plated.

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