Communication cable

Abstract

To provide a communication cable that suppresses performance degradation and reduces the amount of metal used. [Solution] The communication cables 1A and 1B comprise one or more pairs of internal conductors 10, a substantially flat connecting portion 14 that connects the one or more pairs of internal conductors 10 and has electrical insulating properties, an insulating coating layer 20 that covers the outer surfaces of the internal conductors 10 and the connecting portion 14, an external conductor 30 that covers the outer surface of the insulating coating layer 20, and a sheath 40 that covers the outer surface of the external conductor 30. The one or more pairs of internal conductors 10 are arranged to face each other in the diametrical direction of the communication cables 1A and 1B, and the internal conductors 10 are composed of an insulator 12 and a plating layer 16 that covers the outer surface of the insulator 12.

Description

Technical Field

[0001] The present invention relates to a communication cable.

Background Art

[0002] Typical examples of high-speed communication cables include coaxial cables or twisted pair cables. Further, in a communication system where noise resistance and signal stability are required, a balanced two-wire transmission line cable in which two conductors are arranged in contrast to each other and signals are transmitted in opposite phases through the respective conductors is widely used.

[0003] Patent Document 1 discloses a coaxial cable that can also be used for high-frequency transmission and is composed of an inner conductor, an insulator, an outer conductor, and a sheath. The inner conductor is composed of an optical fiber made of synthetic resin and a conductor layer formed on the outer peripheral surface of the optical fiber. Further, the conductor layer of the inner conductor and the second conductor layer of the outer conductor are formed by electroless plating.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In coaxial cables, it is known that current concentrates on the conductor surface due to the skin effect. This tendency is particularly strong in high-frequency transmission, and no current flows inside the central conductor. Therefore, if the central conductor is entirely metal, the area of ​​the metal portion that does not contribute to high-frequency transmission becomes large and is wasted. On the other hand, in coaxial cables such as those described in Patent Document 1, when constructing a balanced two-wire transmission line structure, two coaxial lines are prepared and placed side by side or twisted together. In this case, if the spacing between the two conductors or the twist pitch is misaligned due to bending of the cable, there is a problem that performance degradation occurs, such as a decrease in the noise cancellation effect of the cable.

[0006] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a communication cable that suppresses performance degradation of the cable and reduces the amount of metal used. [Means for solving the problem]

[0007] A communication cable according to an aspect of the present invention comprises one or more pairs of internal conductors, a substantially flat plate-shaped connector that connects one or more pairs of internal conductors and has electrical insulating properties, an insulating coating layer that covers the outer surfaces of the internal conductors and the connector, an external conductor that covers the outer surfaces of the insulating coating layer, and a sheath that covers the outer surfaces of the external conductor. The one or more pairs of internal conductors are arranged to face each other in the diametrical direction of the communication cable, and the internal conductors are composed of an insulator and a plating layer that covers the outer surfaces of the insulator. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a communication cable that suppresses performance degradation of the cable and reduces the amount of metal used. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing an example of a communication cable according to the first embodiment. [Figure 2]Figure 1 is a perspective view of the internal conductor and connection part of the communication cable shown. [Figure 3] This is a cross-sectional view showing an example of a communication cable according to the second embodiment. [Figure 4] Figure 3 is a perspective view of the internal conductor and connection part of the communication cable shown. [Figure 5] This is a cross-sectional view showing an example of a conventional communication cable. [Figure 6] This graph shows the relationship between frequency and epidermal depth. [Modes for carrying out the invention]

[0010] The following describes in detail a communication cable according to an embodiment of the present invention with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0011] The communication cable according to this embodiment comprises one or more pairs of internal conductors 10, and substantially flat plate-shaped connecting parts 14 that connect the one or more pairs of internal conductors 10 and have electrical insulating properties. Furthermore, the communication cable according to this embodiment comprises an insulating coating layer 20 that covers the outer surfaces of the internal conductors 10 and the connecting parts 14, an outer conductor 30 that covers the outer surface of the insulating coating layer 20, and a sheath 40 that covers the outer surface of the outer conductor 30. In addition, one or more pairs of internal conductors 10 are arranged to face each other in the diametrical direction of the communication cable.

[0012] [First Embodiment] As shown in Figure 1, the communication cable 1A has two (a pair) internal conductors 10, and this is an example where the central conductor of the communication cable is a balanced two-wire transmission line. The communication cable 1A is used for differential transmission, and signals can be transmitted by the potential difference created by passing currents with opposite phases through the two internal conductors 10. In differential transmission, the two internal conductors 10 form a pair, and noise can be corrected by taking the difference between the two signals at the receiving end. Therefore, as will be described later, the communication cable may be a balanced four-wire transmission line with four (two pairs) internal conductors 10, or a balanced transmission line with six or more even-numbered internal conductors 10.

[0013] The internal conductor 10 is the central conductor of the communication cable 1A and is composed of an insulator 12 and a plating layer 16 that covers the outer surface of the insulator 12. In other words, the internal conductor 10 is manufactured by applying a plating treatment to the outer surface of the insulator 12 to form the plating layer 16.

[0014] Any electrically insulating resin, such as polyvinyl chloride resin or olefin resin, can be used as the material for the insulator 12. Specifically, as the base resin constituting the insulator 12, for example, polyvinyl chloride, heat-resistant polyvinyl chloride, cross-linked polyvinyl chloride, polyethylene, polypropylene, polyamide (nylon), polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene, perfluoroalkoxyalkane, natural rubber, chloroprene rubber, butyl rubber, ethylene propylene rubber, chlorosulfonated polyethylene rubber, and silicone rubber can be used. These materials may be used individually or in combination of two or more.

[0015] As the polyethylene used for the insulator 12, for example, resins with an ethylene component unit of 50 mol% or more can be mentioned. Specifically, as the polyethylene, high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer, ethylene-propylene copolymer, ethylene-propylene-butene-1 copolymer, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, ethylene-octene-1 copolymer, and further mixtures thereof, etc. can be mentioned. Also, crosslinked polyethylene, foamed polyethylene, crosslinked foamed polyethylene, or chlorinated polyethylene may be used.

[0016] As the polypropylene used for the insulator 12, homopolypropylene (homo-PP), random polypropylene (random-PP), block polypropylene (block-PP), or copolymers with other components such as other olefins copolymerizable with propylene can be mentioned. Examples of other olefins copolymerizable with propylene include α-olefins such as ethylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, etc.

[0017] The plating layer 16 is formed by performing a plating process on the outer peripheral surface of the insulator 12. As the material constituting the plating layer 16, a conductive metal material is used, and it is preferably at least one of gold, silver, copper, and tin, or an alloy containing at least one of these. Also, the method for forming the plating layer 16 is not particularly limited, and for example, electrolytic plating, electroless plating, direct plating, electroless etching plating, or vacuum evaporation, etc. can be used.

[0018] The thickness of the plating layer 16 is not particularly limited, but is preferably 2 μm to 20 μm, and more preferably 2 μm to 10 μm. By setting the thickness of the plating layer 16 to 2 μm or more, a sufficient conductor area for high-frequency transmission can be secured as shown in FIG. 6. Further, by setting the thickness of the plating layer 16 to 20 μm or less, the effect of reducing the amount of metal used can be sufficiently obtained.

[0019] The outer diameter of the inner conductor 10 is not particularly limited, and for example, it may be 0.5 mm to 3 mm, which is the outer diameter of the inner conductor of a standard coaxial cable.

[0020] Between one pair or a plurality of pairs of inner conductors 10, they are connected by a substantially flat connecting portion 14 having electrical insulation. In FIGS. 1 and 2, between the pair of inner conductors 10, they are connected by the connecting portion 14. As described above, the outer peripheral surface of the insulator 12 is subjected to a plating process to form the plating layer 16, but the connecting portion 14 is not plated. And since the pair of inner conductors 10 are connected by the connecting portion 14, the distance between the pair of inner conductors 10 is kept constant. Therefore, it is possible to suppress deterioration of the cable transmission performance without causing a deviation in the distance between the two conductors due to bending of the communication cable or the like.

[0021] As the material used for the connecting portion 14, the electrically insulating resin used for the insulator 12 can be used. Also, as described later, the connecting portion 14 and the insulator 12 may be integrally formed by the above-mentioned electrically insulating resin. Also, the size of the connecting portion 14 is not particularly limited.

[0022] The insulating coating layer 20 has a solid structure that covers the outer peripheral surfaces of the inner conductor 10 and the connecting portion 14. Since the inner conductor 10 and the connecting portion 14 are constrained by the insulating coating layer 20, the structure of the inner conductor 10 is less likely to change. And it is possible to prevent the communication characteristics from being affected by the attachment or bending of the exterior material when mounted on a vehicle or the like.

[0023] As the material used for the insulating coating layer 20, the same electrically insulating resin used for the insulator 12 described above can be used.

[0024] If the plating layer 16 of the internal conductor 10 contains copper or a copper alloy, contact between the insulator 12 and the insulating coating layer 20 and the plating layer 16 may cause oxidative degradation of the insulator 12 and the insulating coating layer 20, known as copper damage. Therefore, it is preferable to add antioxidants and copper damage inhibitors to the base resin constituting the insulator 12 and the insulating coating layer 20, to the extent that they do not degrade the communication characteristics.

[0025] The antioxidant suppresses the oxidation of the insulator 12 or the insulating coating layer 20. As antioxidants, known antioxidants used in thermoplastic resins and the like can be used, such as radical chain inhibitors including phenolic antioxidants, hindered phenolic antioxidants, and amine antioxidants; peroxide decomposing agents including phosphorus-based antioxidants and sulfur-based antioxidants; and metal deactivators including hydrazine-based antioxidants and amine-based antioxidants. Antioxidants may be used individually or in combination of multiple types.

[0026] The antioxidant content should be adjusted considering both the antioxidant effect and any problems caused by bleed-out. The antioxidant content added to the base resin constituting the insulator 12 or insulating coating layer 20 is preferably 0.5 to 10.0 parts by mass, and more preferably 1.0 to 5.0 parts by mass, per 100 parts by mass of the total base resin. Heat resistance can be improved by setting the antioxidant content to 0.5 parts by mass or more. Furthermore, bleed-out can be reduced by setting the antioxidant content to 10.0 parts by mass or less.

[0027] The copper damage inhibitor suppresses copper damage to the insulator 12 or the insulating coating layer 20. For example, salicylic acid-based copper damage inhibitors and hydrazine-based copper damage inhibitors can be used. The amount of copper damage inhibitor added to the base resin constituting the insulator 12 or the insulating coating layer 20 is preferably 0.5 to 10.0 parts by mass, and more preferably 1.0 to 3.0 parts by mass, per 100 parts by mass of the total base resin. By setting the copper damage inhibitor content to 0.5 parts by mass or more, an effective copper damage prevention effect can be provided. Furthermore, by setting the copper damage inhibitor content to 10.0 parts by mass or less, bleed-out can be reduced.

[0028] As additives to be added to the base resin constituting the insulator 12 or insulating coating layer 20, in addition to the antioxidant and copper damage inhibitor mentioned above, various additives can be blended in appropriate amounts as long as they do not hinder the effects of this embodiment. Examples of additives include 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, foaming agents, and the like.

[0029] Known methods can be used to incorporate the above-mentioned additives into the base resin constituting the insulator 12 or the insulating coating layer 20. For example, the resin composition can be obtained by kneading using a known kneader such as a Banbury mixer, kneader, roll mill, twin-screw extruder, or single-screw extruder.

[0030] The outer conductor 30 covers the outer surface of the insulating coating layer 20. By providing the outer conductor 30, a shielding effect can be provided to prevent signal leakage to the outside and the intrusion of radio waves from the outside. Conductive metal materials are used as the material constituting the outer conductor 30. The outer conductor 30 may include at least one selected from the group consisting of plating, metal foil, metal vapor deposition film, and metal vapor deposition sheet.

[0031] The material that constitutes the plating layer 16 described above can be used as the plating for the outer conductor 30.

[0032] For example, materials such as copper, aluminum, stainless steel, nickel, titanium, and platinum can be used as the metal foil for the outer conductor 30.

[0033] Examples of metal-deposited films or metal-deposited sheets used for the outer conductor 30 include those in which a metal film is deposited on the surface of a resin. Electrically insulating resins can be used as the resin, such as polyethylene terephthalate (PET), polyethylene, polypropylene, or polyamide. Furthermore, examples of metals deposited on the resin include aluminum, gold, silver, copper, or nickel.

[0034] The sheath 40 covers the outer surface of the outer conductor 30. The material used for the sheath 40 can be the same electrically insulating resin used for the insulator 12 described above.

[0035] In order to ensure the flame retardancy required for electric wire characteristics, it is preferable to add flame retardants such as metal hydroxides or halogen-based flame retardants to the base resin constituting the sheath 40. In addition, it is preferable to add antioxidants and the like, to the extent that they do not interfere with communication characteristics, similar to the insulator 12 and the insulating coating layer 20.

[0036] The flame retardant improves the flame retardancy of the sheath 40. The flame retardant may be, for example, at least one of an organic flame retardant and an inorganic flame retardant. Examples of organic flame retardants include halogenated flame retardants such as brominated flame retardants and chlorinated flame retardants, and phosphorus-based flame retardants such as phosphate esters, condensed phosphate esters, cyclic phosphorus compounds, and red phosphorus. Examples of inorganic flame retardants include at least one metal hydroxide selected from the group consisting of aluminum hydroxide, magnesium hydroxide, and calcium hydroxide. These flame retardants may be used individually or in combination. The flame retardant may, for example, contain both an organic flame retardant and an inorganic flame retardant.

[0037] The organic flame retardant preferably contains at least a halogen-based flame retardant. The halogen-based flame retardant can capture hydroxyl radicals that promote the combustion of the base resin constituting the sheath 40, thereby suppressing the combustion of the base resin. The halogen-based flame retardant may be, for example, a compound in which at least one halogen is substituted for an organic compound. Examples of halogen-based flame retardants include fluorine-based flame retardants, chlorine-based flame retardants, bromine-based flame retardants, and iodine-based flame retardants. The halogen-based flame retardant is preferably a bromine-based flame retardant.

[0038] Brominated flame retardants include, for example, 1,2-bis(bromophenyl)ethane, 1,2-bis(pentabromophenyl)ethane, hexabromobenzene, ethylenebis-dibromonolbornanedicarboxyimide, ethylenebis-tetrabromophthalimide, tetrabromobisphenol S, tris(2,3-dibromopropyl-1) isocyanurate, hexabromocyclododecane (HBCD), octabromophenyl ether, tetrabromobisphenol A (TBA), TBA epoxy oligomer or polymer, TBA-bis(2,3-dibromopropyl ether), decabromodiphenyl oxide, polydibromophenylene oxide, bis(tribromophenoxy)ethane, ethylenebis-pentabromolene, dib This includes romoethyl-dibromocyclohexane, dibromoneopentyl glycol, tribromophenol, tribromophenol allyl ether, tetradecabromodifenoxybenzene, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, 2,2-bis(4-hydroxyethoxy-3,5-dibromophenyl)propane, pentabromophenol, pentabromotoluene, pentabromodiphenyl oxide, hexabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, octabromodiphenyl oxide, dibromoneopentyl glycol tetracarbonate, bis(tribromophenyl) fumaamide, N-methylhexabromophenylamine, etc. The flame retardant preferably contains 1,2-bis(pentabromophenyl)ethane and tetrabromobisphenol A. Since such flame retardants have a low dielectric constant, they can impart flame retardancy while suppressing an increase in the viscosity and dielectric constant of the sheath 40.

[0039] The amount of halogen-based flame retardant added to the base resin constituting the sheath 40 is preferably 5 to 40 parts by mass, and more preferably 10 to 30 parts by mass, per 100 parts by mass of the total base resin. By setting the halogen-based flame retardant content to 10 parts by mass or more, the flame retardancy of the sheath 40 can be improved. Furthermore, by setting the halogen-based flame retardant content to 30 parts by mass or less, the manufacturing cost of the sheath 40 can be reduced because the mechanical properties of the sheath 40 can be maintained without using more flame retardant than necessary.

[0040] The amount of inorganic flame retardant added to the base resin constituting the sheath 40 is preferably 30 to 200 parts by mass, and more preferably 40 to 150 parts by mass, per 100 parts by mass of the total base resin. By setting the inorganic flame retardant content to 40 parts by mass or more, the flame retardancy of the sheath 40 can be improved. Furthermore, by setting the inorganic flame retardant content to 150 parts by mass or less, the processability of the sheath 40 can be improved.

[0041] As an inorganic flame retardant, it is preferable to include at least a metal hydroxide. Metal hydroxides are widely used as flame retardants and are relatively less expensive than brominated flame retardants. Furthermore, because metal hydroxides have a higher dielectric constant than typical polyolefin resins, they act as dielectric constant modifiers. Therefore, it is preferable that the sheath 40 of this embodiment contains a metal hydroxide. As the metal hydroxide, one or more metal compounds having hydroxyl groups or crystal water can be used, such as magnesium hydroxide (Mg(OH)2), aluminum hydroxide (Al(OH)3), calcium hydroxide (Ca(OH)2), basic magnesium carbonate (mMgCO3·Mg(OH)2·nH2O), hydrated aluminum silicate (aluminum silicate hydrate, Al2O3·3SiO2·nH2O), and hydrated magnesium silicate (magnesium silicate pentahydrate, Mg2Si3O8·5H2O). Among these, magnesium hydroxide is particularly preferred as the metal hydroxide.

[0042] The base resin constituting the sheath 40 preferably contains 40 to 150 parts by mass of metal hydroxide per 100 parts by mass of the total base resin, and more preferably contains 100 to 150 parts by mass of metal hydroxide. By having a metal hydroxide content of 40 parts by mass or more, the flame retardancy of the sheath 40 can be improved. By having a metal hydroxide content of 150 parts by mass or less, the flexibility and processability of the sheath 40 can be improved.

[0043] To suppress oxidation of the sheath 40, an antioxidant may be added to the base resin constituting the sheath 40. As an antioxidant, for example, an antioxidant used in the insulator 12 and the insulating coating layer 20 can be used.

[0044] The amount of antioxidant added should be adjusted considering the antioxidant effect and any problems caused by bleed-out. The amount of antioxidant added to the base resin constituting the sheath 40 is preferably 0.5 to 10.0 parts by mass, and more preferably 1.0 to 8.0 parts by mass, per 100 parts by mass of the total base resin. Heat resistance can be improved by increasing the antioxidant content to 0.5 parts by mass or more. Furthermore, bleed-out can be reduced by decreasing the antioxidant content to 10.0 parts by mass or less.

[0045] In addition to the flame retardants and antioxidants mentioned above, various additives can be added to the base resin constituting the sheath 40 in appropriate amounts, as long as they do not hinder the effects of this embodiment. Examples of additives include inorganic fillers, flame retardant aids, processing aids, crosslinking agents, metal deactivators (copper damage inhibitors), anti-aging agents, fillers, reinforcing agents, ultraviolet absorbers, stabilizers, plasticizers, pigments, dyes, colorants, antistatic agents, and foaming agents.

[0046] To adjust the dielectric constant of the sheath 40, an inorganic filler may be added to the base resin constituting the sheath 40. The inorganic filler may be, for example, metal oxides such as the metal hydroxides, aluminum oxide, and titanium oxide mentioned above, as well as titanate compounds such as barium titanate and strontium titanate.

[0047] The amount of inorganic filler added to the base resin constituting the sheath 40 is preferably 30 to 200 parts by mass, and more preferably 40 to 150 parts by mass, per 100 parts by mass of the total base resin. By setting the inorganic filler content to 30 parts by mass or more, it is possible to suppress the dielectric constant of the sheath 40 from becoming too low. By setting the inorganic filler content to 200 parts by mass or less, it is possible to suppress the dielectric constant from becoming too high and to suppress a decrease in the flexibility of the sheath 40.

[0048] The flame retardant enhancer improves the flame retardancy of the sheath 40, similar to the flame retardant itself. The flame retardant enhancer may be, for example, antimony trioxide. Antimony trioxide can improve the flame retardancy of the sheath 40 when used in combination with a halogen-based flame retardant. The amount of the flame retardant enhancer added to the base resin constituting the sheath 40 is preferably 0.1 to 30 parts by mass, and more preferably 1 to 15 parts by mass, per 100 parts by mass of the total base resin.

[0049] Processing aids are added to remove grease generated during extrusion molding and to maintain the shape of the extruded product. Processing aids may contain at least one of a metal soap and a polymer lubricant. The amount of processing aid added to the base resin constituting the sheath 40 is preferably 0.01 to 10 parts by mass, and more preferably 0.1 to 5 parts by mass, per 100 parts by mass of the total base resin.

[0050] The plasticizer enhances the flexibility of the sheath 40. Any known plasticizer can be used. The plasticizer may be at least one selected from the group consisting of trimellitic acid plasticizers, aliphatic dibasic acid plasticizers, epoxy plasticizers, phthalic acid plasticizers, pyromellitic acid ester plasticizers, phosphate ester plasticizers, and ether ester plasticizers.

[0051] The phthalate-based plasticizer may be at least one phthalate ester selected from the group consisting of di-2-ethylhexyl phthalate (DEHP), di-n-octyl phthalate (DNOP), diisononyl phthalate (DINP), dinonyl phthalate (DNP), diisodecyl phthalate (DIDP), and ditridecyl phthalate.

[0052] The trimellitic acid plasticizer may be, for example, at least one trimellitic acid ester selected from the group consisting of trioctyl trimellitic acid (TOTM) and triisodecyl trimellitic acid.

[0053] The thickness of the sheath 40 is not particularly limited, but may be, for example, 0.1 mm to 1.0 mm. By making the thickness of the sheath 40 0.1 mm or more, the outer conductor 30 can be effectively protected. Also, by making the thickness of the sheath 40 1.0 mm or less, the routing of the communication cable 1A can be made easier even in narrow and short paths.

[0054] Conventional communication cables 100 have a single-wire coaxial structure as shown in Figure 5. Communication cables 100 include one internal conductor 10, an insulating coating layer 20 covering the outer surface of the internal conductor 10, an external conductor 30 covering the outer surface of the insulating coating layer 20, and a sheath 40 covering the outer surface of the external conductor 30. The internal conductor 10 is the central conductor of the communication cable 100 and is composed of an insulator 12 and a plating layer 16 covering the outer surface of the insulator 12. Conventional communication cables 100 differ from communication cables 1A in that they have one internal conductor 10 instead of two (a pair) internal conductors 10, and do not have a connection part 14. Other parts that are the same as communication cables 1A will not be explained.

[0055] In high-frequency transmission, it is known that current concentrates on the conductor surface due to the skin effect. The skin effect is a phenomenon in which, as the frequency of the current increases, it becomes more difficult for current to flow through the center of the conductor, and easier for current to flow through the conductor surface. As a measure of the effect of the skin effect, the depth from the conductor surface at which the current value decreases to approximately 36.7% of the current value at the conductor surface where the most current flows is defined as the "skin depth."

[0056] The epidermal depth can be calculated using the following formula (1). δ = √{2ρ / (ω×μ) r (1) In the above calculation formula (1), δ is the skin depth (m), ρ is the electrical resistivity of the conductor (Ω·m), ω is the angular frequency of the alternating current (rad / s), and μ r μ0 represents the relative permeability of the material, and μ0 represents the permeability of vacuum (H / m).

[0057] Furthermore, the angular frequency ω can be calculated using the following formula (2). ω = 2π × f (2) In the above calculation formula (2), f represents frequency (Hz).

[0058] When copper is used as a conductor, the skin depth δ is calculated using the above formulas (1) and (2), with the electrical resistivity ρ of copper being 1.69 × 10⁻⁶. -8(Ω m), relative magnetic permeability μ of copper r Let μ0 be 1, and the permeability of vacuum be 1.26 × 10⁻⁶. -6 It can be calculated as (H / m). Figure 6 shows the relationship between frequency and skin depth in a communication cable with a single-wire coaxial structure using copper as the conductor. Specifically, it shows that signals with frequencies of 0.1 GHz (100 MHz) or higher can be transmitted at a skin depth of 6.5 μm, signals with frequencies of 1 GHz or higher at a skin depth of 2 μm, and signals with frequencies of several GHz or higher at a skin depth of a few μm. When transmitting signals with even higher frequencies, for example, at frequencies of 20 GHz or higher, the skin depth becomes 0.47 μm. The outer diameter of the central conductor of a typical coaxial cable is 0.2 mm to 1.0 mm, but due to the skin effect in high-frequency transmission, no current flows inside the central conductor. Assuming that the central conductor is all metal and has an outer diameter of 0.2 mm, the proportion of the conductor area where almost no current flows is about 99% of the entire conductor, and this part does not contribute to high-frequency transmission and is wasted. On the other hand, in the case of the internal conductor 10 of a conventional communication cable 100 as shown in Figure 5, assuming that the plating layer 16 has a typical plating thickness of 10 μm, considering the above-mentioned skin depth, it is quite possible to perform high-frequency transmission in the portion of the plating layer 16.

[0059] Thus, in high-speed communication cables that transmit high-frequency signals, it is entirely possible to communicate using a metal-plated resin wire with a plated outer surface of the insulator, i.e., a structure like the internal conductor 10 described above. Compared to cases where the central conductor is entirely metal, the amount of metal used is significantly reduced, and the proportion of conductor area where almost no current flows can be suppressed. The higher the expected frequency, the thinner the plating can be made, further reducing the amount of metal used. In this way, a significant reduction in the amount of metal used in communication cables can be expected, which can contribute to achieving carbon neutrality in high-speed communication lines. In addition, this technology also contributes to improving the flexibility or reducing the weight of communication cables.

[0060] When constructing a balanced two-wire transmission line structure based on conventional communication cable 100, two coaxial cables are prepared and placed side by side or twisted together. If the twist pitch is constant and there is no space between the two wires, losses such as suck-out (a phenomenon in which abrupt attenuation occurs at a specific frequency) can be suppressed. However, if the distance between the two conductors or the twist pitch is misaligned due to bending of the communication cable, the noise cancellation effect of the communication cable may decrease, potentially degrading the cable transmission performance.

[0061] As described above, when the communication cable 1A is used as a balanced two-wire transmission line, the distance between the pair of internal conductors 10 is kept constant because they are connected by the connector 14. Therefore, the distance between the two conductors does not shift due to bending of the communication cable, and deterioration of the cable transmission performance can be suppressed.

[0062] A method for manufacturing the communication cable 1A according to this embodiment will now be described. First, a pair of insulators 12 and a connecting portion 14 connected to the pair of insulators 12 are molded using an electrically insulating resin by injection molding or the like. Preferably, the connecting portion 14 is molded into a substantially flat plate shape, and the insulators 12 are molded into a cylindrical shape. Alternatively, the connecting portion 14 and the insulators 12 may be molded integrally. In addition, various additives can be added to the base resin as needed during molding.

[0063] Subsequently, by applying a pre-plating treatment such as roughening only to the insulator 12, the plating treatment is applied only to the insulator 12, and a plating layer 16 that covers the outer surface of the insulator 12 is formed. In this way, a pair of internal conductors 10 and a connecting portion 14 are manufactured as shown in Figure 2.

[0064] The insulating coating layer 20 can be manufactured by known methods, for example, by a general extrusion molding method. Specifically, the insulating coating layer 20 can be formed by extruding the insulating coating layer 20 material onto the outer surfaces of the pair of internal conductors 10 and connection parts 14 manufactured as described above. As the extruder used in the extrusion molding method, for example, a single-screw extruder or a twin-screw extruder can be used, and it can be equipped with a screw, breaker plate, crosshead, distributor, nipple and die. When performing extrusion molding, the base resin is fed into the extruder set to a temperature at which the base resin is sufficiently melted. At this time, various additives can be added to the extruder in addition to the base resin as needed.

[0065] Subsequently, the outer surface of the insulating coating layer 20 is covered with the outer conductor 30. As described above, the outer conductor 30 may include at least one selected from the group consisting of plating, metal foil, metal vapor-deposited film, and metal vapor-deposited sheet.

[0066] The sheath 40 can be manufactured by known methods, for example, by a general extrusion molding method similar to that used for the insulating coating layer 20. Specifically, the sheath 40 can be formed by extruding the sheath 40 material onto the outer surface of the outer conductor 30 manufactured as described above. When performing extrusion molding, the base resin is fed into an extruder set to a temperature at which the base resin is sufficiently melted. At this time, various additives can be added to the extruder in addition to the base resin as needed. In this way, the communication cable 1A can be manufactured.

[0067] As described above, the communication cable 1A according to this embodiment comprises one or more pairs of internal conductors 10, and a substantially flat plate-shaped connecting portion 14 that connects the one or more pairs of internal conductors 10 and has electrical insulating properties. Furthermore, the communication cable 1A according to this embodiment comprises an insulating coating layer 20 that covers the outer surfaces of the internal conductors 10 and the connecting portion 14, an outer conductor 30 that covers the outer surface of the insulating coating layer 20, and a sheath 40 that covers the outer surface of the outer conductor 30. The one or more pairs of internal conductors 10 are arranged to face each other in the diametrical direction of the communication cable 1A, and the internal conductors 10 are composed of an insulator 12 and a plating layer 16 that covers the outer surface of the insulator 12. Since the pair of internal conductors 10 are connected by the connecting portion 14, the distance between the pair of internal conductors 10 is kept constant, and thus deterioration of cable transmission performance can be suppressed. Furthermore, since the communication cable 1A has a central conductor with a plated insulator 12, the amount of metal used is significantly reduced, which contributes to lower cable costs and energy savings during manufacturing. Therefore, according to the present invention, it is possible to provide a communication cable that suppresses performance degradation and reduces the amount of metal used.

[0068] [Second Embodiment] Figure 3 shows an example of an extension to a balanced four-wire transmission line by using a pair structure of balanced two-wire transmission lines for the central conductor of the communication cable. The communication cable 1B has four (two pairs) internal conductors 10. In the description of the second embodiment, the description of parts that are the same as in the first embodiment will be omitted or simplified.

[0069] The internal conductor 10 is the central conductor of the communication cable 1B and is composed of an insulator 12 and a plating layer 16 that covers the outer surface of the insulator 12.

[0070] As shown in Figures 3 and 4, the two pairs of internal conductors 10 are connected by connectors 14. From the viewpoint of suppressing deterioration of cable transmission performance, it is preferable that the connectors 14 connecting the two pairs of internal conductors 10 intersect perpendicularly in a cross-sectional view. As described above, the outer surface of the insulator 12 is plated to form a plating layer 16, but the surface of the connectors 14 is not plated. Because the two pairs of internal conductors 10 are connected by connectors 14, the distance between the two pairs of internal conductors 10 is kept constant. Therefore, the distance between the four conductors does not shift due to bending of the communication cable, and deterioration of cable transmission performance can be suppressed.

[0071] The insulating coating layer 20 has a solid structure that covers the outer surfaces of the two pairs of internal conductors 10 and the connection parts 14. Because the two pairs of internal conductors 10 and the connection parts 14 are constrained by the insulating coating layer 20, the structure of the internal conductors 10 is less likely to change. The outer conductor 30 is covered by the outer surface of the insulating coating layer 20. Furthermore, the sheath 40 covers the outer surface of the outer conductor 30.

[0072] As described above, when the communication cable 1B is used as a balanced four-wire transmission line, the distance between the two pairs of internal conductors 10 is kept constant because the two pairs of internal conductors 10 are connected by the connection parts 14, thereby suppressing deterioration of the cable transmission performance. Furthermore, since the communication cable 1B has a central conductor with a plated insulator 12, the amount of metal used is significantly reduced, which contributes to lower cable costs and energy savings during manufacturing. Therefore, according to the present invention, it is possible to provide a communication cable that suppresses deterioration of cable performance and reduces the amount of metal used.

[0073] Although this embodiment has been described above with reference to examples, this embodiment is not limited to these examples, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of symbols]

[0074] 1A, 1B communication cable 10 Inner conductor 12 Insulators 14 Connection part 16 Plating layer 20 Insulating coating layer 30 Outer conductor 40 sheaths

Claims

1. One or more pairs of internal conductors, A substantially flat connecting portion having electrical insulation properties connects one or more pairs of internal conductors, An insulating coating layer covering the inner conductor and the outer surface of the connection part, An outer conductor covering the outer surface of the insulating coating layer, A communication cable comprising a sheath covering the outer surface of the outer conductor, The pair or more pairs of internal conductors are arranged to face each other in the diametrical direction of the communication cable. The communication cable comprises an internal conductor composed of an insulator and a plating layer covering the outer surface of the insulator.

2. The communication cable according to claim 1, wherein the outer conductor includes at least one selected from the group consisting of plating, metal foil, metal vapor-deposited film, and metal vapor-deposited sheet.

3. The communication cable according to claim 1 or 2, wherein the pair or more pairs of internal conductors are a single internal conductor.

4. The aforementioned pair or multiple pairs of internal conductors are two pairs of internal conductors, The communication cable according to claim 1 or 2, wherein the connecting portions that link the two pairs of internal conductors intersect perpendicularly in a cross-sectional view.

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