Communication cable

Abstract

To provide a communication cable which has stable communication characteristics even in on-vehicle environment, and is excellent in peeling property of a sheath layer.SOLUTION: A communication cable 10 includes: a wire bundle 4 having a plurality of insulated wires 3 having conductors 1 and coating layers 2 coating the conductors; a sheath layer 5 coating the outer periphery of the wire bundle; and an intermediate layer 6 which is interposed between the wire bundle and the sheath layer, and coats the outer periphery of the wire bundle. The communication cable 10 has such a solid structure that the intermediate layer comes in close contact with the coating layers of the insulated wires, and the sheath layer comes in close contact with the intermediate layer. The melting point of a base layer constituting the intermediate layer is lower than the melting point of the base resin constituting the coating layer and the sheath layer by 20°C or more. The base resin constituting the intermediate layer is at least one of a polyethylene resin and a polyethylene copolymer, and the base resin constituting the coating layer and the sheath layer is a polypropylene resin.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Development has been ongoing for communication cables capable of performing the advanced electrical information communication required for autonomous driving of vehicles. Patent Document 1 discloses a communication electric cable having a signal line including a plurality of insulated electric wires, each having a conductor and an insulating coating covering the conductor, and a solid sheath covering the signal wire. The sheath is made of a material having a melt flow rate of 0.25 g / 10 min or more measured at 200°C under a load of 2.16 kg.

[0003] Patent Document 2 discloses a communication electric wire having a twisted pair formed by twisting together a pair of insulated electric wires, each of which is made of a conductor having a tensile strength of 400 MPa or more and an insulating coating covering the conductor. The communication electric wire has a characteristic impedance in the range of 100±10 Ω, and the difference in capacitance between the insulated electric wires constituting the twisted pair is 25 pF / m or less. The communication electric wire also has a sheath made of an insulating material covering the periphery of the twisted pair, with a gap between the sheath and the insulated electric wires constituting the twisted pair.

[0004] The communication wire of Patent Document 1 is a solid-structured wire in which there is substantially no gap between the signal wire and the sheath, and the constituent material of the sheath is in close contact with the surface of the insulated wire that constitutes the signal wire. In contrast, the communication wire of Patent Document 2 is a tube-structured wire in which there is a gap between the sheath and the insulated wire. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-136105 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-188431 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in Patent Document 1, a material having a melt flow rate of 0.25 g / 10 min or more is used as the sheath constituent material. However, even if such a material is used as the sheath constituent material, the sheath and the insulating coating of the insulated wire are fused together during extrusion molding of the sheath, which may make it difficult to strip the sheath.

[0007] In contrast, the communication electric wire of Patent Document 2 has a tube structure, and therefore the sheath is easy to strip. However, in this communication electric wire, the insulated electric wire is not constrained by a sheath, and therefore the structure of the twisted pair wire is prone to change, such as a loss of twist pitch or a change in inter-wire distance. Therefore, the communication electric wire of Patent Document 2 may have its communication characteristics affected by attachment to an exterior material, bending, etc. when mounted on a vehicle.

[0008] The present invention has been made in view of the problems inherent in the prior art, and an object of the present invention is to provide a communication cable that has stable communication characteristics even in a vehicle-mounted environment and has excellent sheath layer peelability. [Means for solving the problem]

[0009] A communication cable according to an embodiment of the present invention comprises a wire bundle including a plurality of insulated wires, each having a conductor and a coating layer covering the conductor; a sheath layer covering the outer periphery of the wire bundle; and an intermediate layer interposed between the wire bundle and the sheath layer and covering the outer periphery of the wire bundle. The intermediate layer is in close contact with the coating layer of the insulated wire, and the sheath layer is in close contact with the intermediate layer, forming a solid structure. The melting point of the base resin constituting the intermediate layer is at least 20°C lower than the melting points of the base resins constituting the coating layer and the sheath layer. The base resin constituting the intermediate layer is at least one of polyethylene resin and polyethylene copolymer, and the base resin constituting the coating layer and the sheath layer is polypropylene resin. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a communication cable that has stable communication characteristics even in an on-vehicle environment and has an excellent sheath layer that is easy to strip. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view illustrating an example of a communication cable according to an embodiment of the present invention. [Figure 2] 1 is a cross-sectional view illustrating an example of a communication cable according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The communication cable according to the present embodiment will be described in detail below with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0013] As shown in Fig. 1 , a communication cable 10 of this embodiment includes a wire bundle 4 including a plurality of insulated wires 3 each having a conductor 1 and a coating layer 2 coating the outer periphery of the conductor 1, and a sheath layer 5 coating the outer periphery of the wire bundle 4. In the communication cable 10 of Fig. 1 , the wire bundle 4 includes two insulated wires 3. The communication cable 10 further includes an intermediate layer 6 interposed between the wire bundle 4 and the sheath layer 5 and coating the outer periphery of the wire bundle 4.

[0014] The conductor 1 may be composed of only one wire, or may be a bunched stranded wire composed of a bundle of multiple wires. The conductor 1 may also be composed of only one twisted wire, or may be a concentric stranded wire composed of a bundle of multiple bunched twisted wires. Furthermore, the conductor 1 may be a compacted conductor or a non-compacted conductor. The material constituting the conductor 1 is not particularly limited, but is preferably at least one conductive metal material selected from the group consisting of copper, copper alloy, aluminum, and aluminum alloy.

[0015] The outer diameter of the conductor 1 is not particularly limited, but is preferably 0.435 mm or more, and more preferably 0.440 mm or more. By setting the outer diameter of the conductor 1 as described above, it is possible to reduce the resistance of the conductor 1. Furthermore, the outer diameter of the conductor 1 is not particularly limited, but is preferably 0.465 mm or less, and more preferably 0.460 mm or less.

[0016] The thickness of the coating layer 2 is not particularly limited, but is preferably 0.15 mm or more, and more preferably 0.18 mm or more. By setting the thickness of the coating layer 2 as described above, the conductor 1 can be effectively protected. Furthermore, the thickness of the coating layer 2 is not particularly limited, but is preferably 0.32 mm or less.

[0017] The covering layer 2 covers the entire outer periphery of the conductor 1. In the communication cable 10 of FIG.

[0018] The wire bundle 4 includes a plurality of insulated wires 3 each having a conductor 1 and a coating layer 2 and constituting a signal line. The plurality of insulated wires 3 may be twisted together. Alternatively, the plurality of insulated wires 3 may be parallel to one another without being twisted. However, by forming the plurality of insulated wires 3 into twisted wires, the plurality of insulated wires 3 are less susceptible to external noise and are less likely to affect the outside world compared to parallel wires. For this reason, it is preferable that the plurality of insulated wires 3 in the wire bundle 4 be twisted wires.

[0019] The sheath layer 5 covers the outer periphery of the wire bundle 4, thereby protecting the insulated wires 3 and stabilizing the relative positions of the multiple insulated wires 3 in the wire bundle 4. The sheath layer 5 has a solid structure in which there is substantially no gap between the sheath layer 5 and the intermediate layer 6, and the constituent material of the sheath layer 5 is in close contact with the surface of the intermediate layer 6. As will be described later, the intermediate layer 6 covers the entire outer periphery of the wire bundle 4 and is in close contact with the entire surface of the wire bundle 4. Therefore, the solid sheath layer 5 and intermediate layer 6 can stabilize the relative positions of the multiple insulated wires 3. Note that it is preferable that there is no gap between the sheath layer 5 and the intermediate layer 6; however, if the relative positions of the multiple insulated wires 3 do not change substantially, a slight gap may exist.

[0020] In the communication cable 10, an intermediate layer 6 is interposed between the wire bundle 4 and the sheath layer 5, and the intermediate layer 6 covers the entire surface of the wire bundle 4. The presence of such an intermediate layer 6 makes it easy to strip the sheath layer 5.

[0021] The resin compositions constituting the coating layer 2 and sheath layer 5 of the insulated wire 3 contain a base resin as a main component. Similarly, the resin composition constituting the intermediate layer 6 contains a base resin as a main component. In this specification, the base resin refers to a resin that accounts for 50% by mass or more of the total resin content of the resin composition constituting each layer.

[0022] The base resins constituting the coating layer 2 and the sheath layer 5 may be the same. However, the base resins constituting the coating layer 2 and the sheath layer 5 and the base resin constituting the intermediate layer 6 are different from each other. Because the base resins of the coating layer 2 and the intermediate layer 6 are different, these resins are less likely to fuse together. Similarly, because the base resins of the sheath layer 5 and the intermediate layer 6 are different, these resins are less likely to fuse together. Therefore, when a load is applied to the sheath layer 5 to peel it, peeling occurs between the coating layer 2 and the intermediate layer 6 and / or between the sheath layer 5 and the intermediate layer 6, easily generating voids. As a result, the sheath layer 5 can be easily separated from the coating layer 2 and / or the intermediate layer 6.

[0023] Furthermore, the melting point of the base resin constituting the intermediate layer 6 is preferably at least 20°C lower than the melting points of the base resins constituting the coating layer 2 and the sheath layer 5. As will be described later, the sheath layer 5 and the intermediate layer 6 can be formed around the outer periphery of the electric wire bundle 4 by extrusion molding the resin composition of the sheath layer 5 and the resin composition of the intermediate layer 6 around the outer periphery of the electric wire bundle 4. In this case, if the melting point of the base resin of the intermediate layer 6 is at least 20°C lower than the melting points of the base resins of the coating layer 2 and the sheath layer 5, the melting point of the coating layer 2 will be higher than the melting point of the intermediate layer 6, and therefore the coating layer 2 is unlikely to melt due to the heat of the intermediate layer 6 during extrusion molding. As a result, the thickness of the coating layer 2 is unlikely to be partially thin, and the conductor 1 can be effectively protected by the coating layer 2.

[0024] The base resin of the coating layer 2 and the sheath layer 5 is preferably a polypropylene resin. The base resin constituting the intermediate layer 6 is preferably at least one of a polyethylene resin and a polyethylene copolymer. Polypropylene resin, polyethylene resin, and polyethylene copolymer are resins with relatively high melting points and therefore have excellent instantaneous heat resistance. Therefore, the coating layer 2, the sheath layer 5, and the intermediate layer 6 can be easily formed by extrusion molding.

[0025] Examples of polypropylene resins include homopolypropylene (homoPP), random polypropylene (randomPP), block polypropylene (blockPP), and copolymers of propylene with other olefins copolymerizable with propylene. 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, and 3-methyl-1-hexene. Examples of polyethylene resins include high-density polyethylene resin (HDPE), low-density polyethylene resin (LDPE), and linear low-density polyethylene resin (LLDPE). Examples of polyethylene copolymers include 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 mixtures thereof.

[0026] Here, the base resin constituting the coating layer 2 and the sheath layer 5 may be a polypropylene resin having a melting point of 160°C or higher. Furthermore, the base resin constituting the intermediate layer 6 may be at least one of a polyethylene resin and a polyethylene copolymer having a melting point of 140°C or lower. Even with such a configuration, the instantaneous heat resistance can be increased, and therefore the coating layer 2, the sheath layer 5, and the intermediate layer 6 can be easily formed by extrusion molding.

[0027] To increase the flexibility of the communication cable 10, the coating layer 2 and the sheath layer 5 may contain a flexible resin in addition to the base resin. The flexible resin may be one or more of chlorinated polyolefins such as chlorinated polyethylene resin, acrylic rubbers such as NBR (nitrile rubber), and the olefin-based and styrene-based thermoplastic elastomers listed below. The flexible resin may be modified with maleic acid or the like, or it may be unmodified.

[0028] Olefin-based thermoplastic elastomers contain hard segments made of olefin-based resins and soft segments made of rubber. Typical olefin-based thermoplastic elastomers are polymer alloys in which soft segments are finely dispersed as domains in a matrix of hard segments, but copolymers of hard and soft segments can also be used. Examples of olefin-based resins that can be used include polyethylene resins and polypropylene resins. Examples of rubbers that can be used include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene copolymer rubber (SBR), acrylonitrile-butadiene copolymer rubber (NBR), chloroprene rubber (CR), butyl rubber (IIR), ethylene-propylene rubber (EPM), and ethylene-propylene-diene rubber (EPDM). These may be used alone or in combination.

[0029] Examples of styrene-based thermoplastic elastomers include block copolymers or random copolymers having hard segments made of aromatic vinyl polymers and soft segments made of conjugated diene polymers. Monomers constituting the aromatic vinyl polymers may include styrene, α-alkyl-substituted styrenes such as α-methylstyrene, α-ethylstyrene, and α-methyl-p-methylstyrene, and aromatic alkyl-substituted styrenes such as o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, ethylstyrene, 2,4,6-trimethylstyrene, ot-butylstyrene, pt-butylstyrene, and p-cyclohexylstyrene. Examples of conjugated diene polymers include copolymers of at least one of butadiene and isoprene, and partially hydrogenated versions of these copolymers.

[0030] The styrene-based thermoplastic elastomer may be at least one block copolymer selected from the group consisting of polystyrene-polybutadiene-polystyrene (SBS), polystyrene-polyisoprene-polystyrene (SIS), polystyrene-polyisobutylene-polystyrene (SIBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), polystyrene-poly(ethylene-butylene)-crystalline polyolefin (SEBC), and polystyrene-poly(ethylene-propylene)-polystyrene (SEPS).

[0031] The sheath layer 5 may contain 49 to 0 parts by mass of soft resin relative to 1 to 100 parts by mass of base resin 5. That is, the content of the soft resin may be 0 to 49 parts by mass relative to 100 parts by mass of the total of the base resin and soft resin. By containing the soft resin in an amount of 49 parts by mass or less, it is possible to maintain abrasion resistance while increasing the flexibility of the resin composition.

[0032] 1 and 2, when the wire bundle 4 includes two insulated wires 3, the thickness of the intermediate layer 6 is preferably 20 to 80% of the thickness of the sheath layer 5. When the thickness of the intermediate layer 6 is 20% or more of the thickness of the sheath layer 5, melting of the coating layer 2 of the insulated wire 3 is suppressed when the intermediate layer 6 and the sheath layer 5 are extrusion-molded, as described below. This prevents partial reduction in the thickness of the coating layer 2. Furthermore, when the thickness of the intermediate layer 6 is 80% or less of the thickness of the sheath layer 5, deterioration in the flame retardancy of the communication cable 10 is suppressed. The thickness of the sheath layer 5 is defined as the average value of thicknesses A and B at four locations perpendicular to the center line passing through the centers of the two conductors 1 and along the joining surface of the two insulated wires 3, and thicknesses C and D at four locations along the center line passing through the centers of the two conductors, as shown in FIG. The thickness of the intermediate layer 6 is the average value of the thicknesses E and F of the portions perpendicular to the center line passing through the centers of the two conductors 1 and along the joint surface of the two insulated wires 3, and the thicknesses G and H of the portions along the center line passing through the centers of the two conductors 1, as shown in Figure 2.

[0033] In addition to the base resin and soft resin, the resin compositions constituting the coating layer 2, the sheath layer 5, and the intermediate layer 6 may contain various additives in appropriate amounts within the range that does not impair the effects of this embodiment. Examples of additives include antioxidants, copper inhibitors, flame retardants, processing aids, crosslinking agents, metal deactivators, antioxidants, fillers, reinforcing agents, UV absorbers, stabilizers, plasticizers, pigments, dyes, colorants, antistatic agents, and foaming agents.

[0034] When the sheath layer 5 has a solid structure, it is necessary to keep the dielectric constant of the insulated wire 3 low, so it is preferable to add as little additive as possible to the base resin of the coating layer 2. However, when copper or a copper alloy is used for the conductor 1, contact between the coating layer 2 and the conductor 1 can cause oxidation degradation of the coating layer 2, known as copper damage. Therefore, it is preferable to add an antioxidant and a copper damage inhibitor to the base resin constituting the coating layer 2 to an extent that does not deteriorate the communication characteristics.

[0035] The antioxidant suppresses oxidation of the coating layer 2. Examples of the antioxidant that can be used include known antioxidants used in thermoplastic resins, such as radical chain inhibitors such as phenolic antioxidants, hindered phenolic antioxidants, and amine antioxidants, peroxide decomposers such as phosphorus-based antioxidants and sulfur-based antioxidants, and metal deactivators such as hydrazine-based antioxidants and amine-based antioxidants. The antioxidants may be used alone or in combination.

[0036] The content of the antioxidant may be adjusted taking into consideration the antioxidant effect and the influence on communication characteristics. The content of the antioxidant in the resin composition constituting the coating layer 2 is preferably 0.1 to 5.0 parts by mass per 100 parts by mass of polypropylene resin. By setting the content of the antioxidant to 0.1 part by mass or more, it is possible to improve heat resistance. Furthermore, by setting the content of the antioxidant to 5.0 parts by mass or less, it is possible to suppress the influence on communication characteristics.

[0037] The copper inhibitor suppresses oxidation degradation of the coating layer 2, known as copper damage, caused by contact of the coating layer 2 with the conductor 1 (copper or copper alloy). Examples of copper inhibitors that can be used include salicylic acid-based copper inhibitors and hydrazine-based copper inhibitors. The content of the copper inhibitor in the resin composition constituting the coating layer 2 is preferably 0.1 to 3.0 parts by mass per 100 parts by mass of polypropylene resin. By setting the content of the copper inhibitor to 0.1 part by mass or more, the copper damage prevention effect can be effectively imparted. Furthermore, by setting the content of the copper inhibitor to 3.0 parts by mass or less, the effect on communication characteristics can be suppressed.

[0038] To ensure flame retardancy required for the wire characteristics, a flame retardant is preferably added to the resin composition constituting the sheath layer 5. Similarly to the coating layer 2, an antioxidant or the like is preferably added to the resin composition constituting the sheath layer 5 within a range that does not impair the communication characteristics.

[0039] The flame retardant improves the flame retardancy of the sheath layer 5. By improving the flame retardancy of the sheath layer 5, even if a fire breaks out in a vehicle, the sheath layer 5 can suppress the spread of fire.

[0040] 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 that can be used include halogen-based flame retardants such as bromine-based flame retardants and chlorine-based 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 that can be used 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 alone or in combination. The flame retardant may include, for example, an organic flame retardant and an inorganic flame retardant.

[0041] The organic flame retardant preferably contains at least a halogen-based flame retardant. The halogen-based flame retardant can capture hydroxyl radicals that promote combustion of the base resin constituting the sheath layer 5, 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 on an organic compound. Examples of the halogen-based flame retardant 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.

[0042] The inorganic flame retardant preferably contains at least a metal hydroxide. Metal hydroxides are commonly used as flame retardants and are relatively less expensive than bromine-based flame retardants. Furthermore, metal hydroxides have a higher dielectric constant than typical polyolefin resins, so they act as a dielectric constant adjuster. Therefore, the sheath layer 5 of this embodiment preferably contains a metal hydroxide. Examples of metal hydroxides that can be used include one or more metal compounds having a hydroxyl group or crystal water, such as magnesium hydroxide (Mg(OH)), aluminum hydroxide (Al(OH)), calcium hydroxide (Ca(OH)), basic magnesium carbonate (mMgCO·Mg(OH)·nH2O), hydrated aluminum silicate (aluminum silicate hydrate, Al2O3·3SiO2·nH2O), and hydrated magnesium silicate (magnesium silicate pentahydrate, Mg2SiO8·5H2O). Among these, magnesium hydroxide is particularly preferred as the metal hydroxide.

[0043] The content of the flame retardant in the resin composition constituting the sheath layer 5 is preferably 60 to 150 parts by mass relative to 100 parts by mass of the total of the polypropylene resin and the soft resin. By setting the content of the flame retardant to 60 parts by mass or more, it is possible to improve the flame retardancy of the sheath layer 5. Furthermore, by setting the content of the flame retardant to 150 parts by mass or less, it is possible to maintain the mechanical properties of the sheath layer 5 while not using more flame retardant than necessary, thereby reducing the manufacturing cost of the sheath layer 5.

[0044] As the antioxidant contained in the sheath layer 5, for example, the antioxidant used in the coating layer 2 can be used.

[0045] The amount of antioxidant added may be adjusted taking into consideration the antioxidant effect and the influence on communication characteristics. The content of the antioxidant in the resin composition constituting the sheath layer 5 is preferably 0.1 to 5.0 parts by mass per 100 parts by mass of the polypropylene resin and the soft resin combined. By setting the content of the antioxidant to 0.1 part by mass or more, it is possible to improve heat resistance. Furthermore, by setting the content of the antioxidant to 5.0 parts by mass or less, it is possible to suppress the influence on communication characteristics.

[0046] The communication cable 10 of this embodiment can be produced by the following method. First, resin compositions constituting the coating layer 2, sheath layer 5, and intermediate layer 6 are prepared. These resin compositions are produced by melt-kneading the raw materials of the resin compositions described above, and any known method can be used for this. For example, the resin compositions can be obtained by pre-blending the raw materials in advance using a high-speed mixer such as a Henschel mixer, and then kneading them using a known kneading machine such as a Banbury mixer, kneader, or roll mill.

[0047] Next, the conductor 1 is coated with the coating layer 2 to obtain the insulated wire 3. There are no particular limitations on the method for coating the conductor 1 with the coating layer 2, and for example, a general extrusion molding method can be used. Note that the extruder used in the extrusion molding method may be, for example, a single-screw extruder or a twin-screw extruder having a screw, a breaker plate, a crosshead, a distributor, a nipple, and a die.

[0048] Next, a plurality of the obtained insulated electric wires 3 are bundled together to obtain an electric wire bundle 4. At this time, a plurality of the insulated electric wires 3 may be twisted together to form a twisted wire.

[0049] Then, the sheath layer 5 and the intermediate layer 6 are formed around the wire bundle 4. The method for forming the sheath layer 5 and the intermediate layer 6 is not particularly limited, but the sheath layer 5 and the intermediate layer 6 can be formed by twin-screw extrusion molding the resin composition of the sheath layer 5 and the resin composition of the intermediate layer 6. At this time, the extrusion molding conditions are adjusted so that the sheath layer 5 has a solid structure.

[0050] When the sheath layer 5 and the intermediate layer 6 are formed by twin-screw extrusion, the resin composition of the sheath layer 5 and the resin composition of the intermediate layer 6 are extruded simultaneously, so that the intermediate layer 6 adheres closely to the sheath layer 5. Therefore, when peeling the sheath layer 5, the intermediate layer 6 can be peeled together with the sheath layer 5, thereby improving work efficiency.

[0051] By this method, the communication cable 10 of this embodiment can be obtained.

[0052] As described above, the communication cable 10 of this embodiment includes a wire bundle 4 having a plurality of insulated wires 3, each having a conductor 1 and a coating layer 2 that coats the conductor, a sheath layer 5 that coats the outer periphery of the wire bundle, and an intermediate layer 6 that is interposed between the wire bundle 4 and the sheath layer 5 and coats the outer periphery of the wire bundle. The intermediate layer 6 is in close contact with the coating layer 2 of the insulated wire 3, and the sheath layer 5 is in close contact with the intermediate layer 6, forming a solid structure. The melting point of the base resin that constitutes the intermediate layer 6 is at least 20°C lower than the melting points of the base resins that constitute the coating layer 2 and the sheath layer 5. The base resin that constitutes the intermediate layer 6 is at least one of a polyethylene resin and a polyethylene copolymer, and the base resin that constitutes the coating layer 2 and the sheath layer 5 is a polypropylene resin.

[0053] In the communication cable 10, the sheath layer 5 has a solid structure, which stabilizes the relative positions of the multiple insulated wires 3. Therefore, even when the communication cable 10 is mounted on a vehicle, the communication characteristics can be stabilized. Furthermore, the communication cable 10 has an intermediate layer 6 provided between the coating layer 2 and the sheath layer 5 of the insulated wires 3. Therefore, the sheath layer 5 can be easily peeled off, which makes it easy to strip the sheath layer 5.

[0054] In the communication cable 10, the wire bundle 4 may be a twisted wire formed by twisting a plurality of insulated wires 3. A twisted wire is less susceptible to the influence of external noise and is less likely to affect the outside world, so that the functionality of the communication cable 10 can be further improved by using the wire bundle 4 as a twisted wire.

[0055] In the communication cable 10, the base resin constituting the intermediate layer 6 may be at least one of a polyethylene resin and a polyethylene copolymer having a melting point of 140°C or lower, and the base resin constituting the coating layer 2 and the sheath layer 5 may be a polypropylene resin having a melting point of 160°C or higher. This configuration makes it difficult for the coating layer 2 to melt due to the heat of the intermediate layer 6 during extrusion molding. As a result, the thickness of the coating layer 2 is unlikely to be partially thinned, and the conductor 1 can be effectively protected by the coating layer 2.

[0056] In the communication cable 10, the coating layer 2 may contain 0.1 to 5.0 parts by mass of an antioxidant and 0.1 to 3.0 parts by mass of a copper inhibitor per 100 parts by mass of polypropylene resin. With this configuration, the coating layer 2 can be effectively imparted with antioxidant effects and copper damage prevention effects.

[0057] In the communication cable 10, the sheath layer 5 may contain 1 to 100 parts by mass of polypropylene resin and 49 to 0 parts by mass of soft resin. The sheath layer 5 may also contain 0.1 to 5.0 parts by mass of an antioxidant and 60 to 150 parts by mass of a flame retardant, relative to 100 parts by mass of the polypropylene resin and soft resin combined. This configuration can effectively impart antioxidant and flame retardant effects to the sheath layer 5 while imparting flexibility.

[0058] In the communication cable 10, when the wire bundle 4 includes two insulated wires 3, the thickness of the intermediate layer 6 may be 20 to 80% of the thickness of the sheath layer. With this configuration, the covering layer 2 is less likely to melt due to the heat of the intermediate layer 6 during extrusion molding. As a result, the covering layer 2 is less likely to become thin in parts, and the covering layer 2 can effectively protect the conductor 1. [Example]

[0059] Hereinafter, the present embodiment will be described in more detail with reference to examples, comparative examples and reference examples, but the present embodiment is not limited to these examples.

[0060] [Preparation of test samples] To prepare the test samples of Examples 1 to 4, Comparative Example 1, and Reference Examples 1 and 2, the following materials were prepared as the resin compositions for the coating layer, sheath layer, and intermediate layer of the insulated wire.

[0061] Polypropylene resin (PP): Prime Polypro (registered trademark) E-150GK, manufactured by Prime Polymer Co., Ltd., melting point 162°C Polyethylene resin (PE): Novatec (registered trademark) HE122R, high-density polyethylene resin, manufactured by Japan Polypropylene Corporation, melting point 128°C Ethylene-vinyl acetate copolymer (EVA): Evaflex® P1007, manufactured by Dow Mitsui Polychemicals Co., Ltd., melting point 94°C Styrene-ethylene-butylene-styrene block copolymer (SEBS): Septon (registered trademark) 8007L, manufactured by Kuraray Co., Ltd. Phenolic antioxidant: Adekastab® AO-60, Pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], manufactured by ADEKA Corporation Copper inhibitor: Adekastab (registered trademark) CDA-10, N,N'-Bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine, manufactured by ADEKA Corporation Flame retardant: Magnesium hydroxide, manufactured by Konoshima Chemical Co., Ltd.

[0062] Example 1 First, each raw material was weighed according to the blending amounts shown in Table 1, and then the raw materials were melt-kneaded to prepare resin compositions for the coating layer, intermediate layer, and sheath layer.

[0063] Next, a copper alloy conductor having a stranded wire outer diameter φ of 0.45 mm was prepared. A resin composition for the coating layer was extrusion-molded around the conductor to form a coating layer with a thickness of 0.2 mm. In this way, an insulated wire was obtained in which the entire conductor was coated with the coating layer. Two such insulated wires were then prepared and twisted to obtain a wire bundle.

[0064] Next, the resin composition for the intermediate layer and the resin composition for the sheath layer were formed around the outer periphery of the electric wire bundle by twin-screw extrusion molding. During extrusion molding, the thickness of the sheath layer was adjusted to 0.75 mm, and the thickness of the intermediate layer was adjusted to the values ​​shown in Table 1. Furthermore, the sheath layer was adjusted to have a solid structure. In this way, a test sample of this example was obtained in which the entire outer periphery of the electric wire bundle was covered with the intermediate layer and the sheath layer. The outer diameter φ of the obtained test sample was 3.2 mm.

[0065] The thickness of the sheath layer was determined as the average of four thicknesses A and B along the joining surface of the two insulated wires, which are perpendicular to the center line passing through the centers of the two conductors, and thicknesses C and D along the center line passing through the centers of the two conductors, as shown in Figure 1. The thickness of the intermediate layer was determined as the average of four thicknesses E and F along the joining surface of the two insulated wires, which are perpendicular to the center line passing through the centers of the two conductors, and thicknesses G and H along the center line passing through the centers of the two conductors, as shown in Figure 2.

[0066] Examples 2 to 4 Test samples for each example were obtained in the same manner as in Example 1, except that the raw materials and blending amounts of the coating layer, intermediate layer, and sheath layer were changed as shown in Table 1.

[0067] (Comparative Example 1) The test samples of this example were obtained in the same manner as in Example 1, except that the raw materials and compounding amounts of the coating layer and sheath layer were changed as shown in Table 2. In Comparative Example 1, no intermediate layer was formed, and the sheath layer had a solid structure in which it was arranged so as to be in close contact with the coating layer of the insulated wire.

[0068] (Reference examples 1~2) Test samples for each example were obtained in the same manner as in Example 1, except that the raw materials and compounding amounts of the coating layer, intermediate layer, and sheath layer were changed as shown in Table 2. During extrusion molding, the thickness of the sheath layer was adjusted to 0.75 mm, the thickness of the intermediate layer was adjusted to the value shown in Table 2, and the sheath layer was adjusted to have a solid structure.

[0069] [Table 1]

[0070] [Table 2]

[0071] [evaluation] The test samples of each example obtained as described above were subjected to an adhesion test, a structural test, and a flame retardancy test.

[0072] (Adhesion test) The load required to peel a 20 mm long sheath layer at the end of each test sample was measured. As a result of the measurement, those where the load required for peeling was less than 50 N were evaluated as "Good", and those where it was 50 N or more were evaluated as "Poor". The measurement results are shown in Tables 1 and 2.

[0073] Tables 1 and 2 show that the test samples of Examples 1 to 4 have excellent peelability, with the load required to peel the sheath layer being less than 50 N. That is, in the test samples of Examples 1 to 4, the base resin of the intermediate layer is polyethylene resin or polyethylene copolymer, and the base resin of the coating layer and sheath layer is polypropylene resin, and further, the difference in melting point between them is 20°C or more. As a result, fusion between the coating layer and the intermediate layer is less likely to occur, resulting in excellent peelability.

[0074] In contrast, the test sample of Comparative Example 1 required a load of 50 N or more to peel the sheath layer, indicating poor peelability. That is, the test sample of Comparative Example 1 did not have an intermediate layer, the coating layer and the sheath layer were in close contact, and the base resins of both the coating layer and the sheath layer were polypropylene resins, so the coating layer and the sheath layer fused together, resulting in poor peelability of the sheath layer.

[0075] (Structural testing) The cross section of each test sample was observed to measure the thickness of the coating layer of the insulated wire. Specifically, the thickness of the coating layer of each insulated wire was measured at four locations per wire, for a total of eight locations for two wires. A sample with a thickness of 0.16 mm or more at all eight locations was evaluated as "Good," and a sample with a thickness of less than 0.16 mm at any one of the eight locations was evaluated as "Poor." The evaluation results are shown in Tables 1 and 2.

[0076] Tables 1 and 2 show that the thickness of the coating layer at all eight locations in the test samples of Examples 1 to 4 was 0.16 mm or more. That is, when preparing the test sample for each example, an insulated electric wire with a coating layer thickness of 0.2 mm was used, and an intermediate layer and a sheath layer were extrusion-molded around the outer periphery of a wire bundle formed by twisting two insulated electric wires. Here, if the thickness of the intermediate layer is insufficient, the coating layer will melt when the intermediate layer and the sheath layer are extrusion-molded, resulting in a thin coating layer.

[0077] However, in the test sample of Example 1, the thickness of the intermediate layer was 0.15 mm and the thickness of the sheath layer was 0.75 mm, which means that the thickness of the intermediate layer was 20% of the thickness of the sheath layer. Therefore, since the thickness of the intermediate layer was sufficiently ensured, it was found that the coating layer was prevented from melting during extrusion molding, and a decrease in the thickness of the coating layer could be suppressed.

[0078] In addition, the test samples of Examples 2 and 3 also had an intermediate layer thickness of 0.15 mm and a sheath layer thickness of 0.75 mm, which means that the intermediate layer thickness was 20% of the sheath layer thickness. In addition, the test sample of Example 4 had an intermediate layer thickness of 0.6 mm and a sheath layer thickness of 0.75 mm, which means that the intermediate layer thickness was 80% of the sheath layer thickness. Therefore, it can be seen that these test samples can also suppress a decrease in the thickness of the coating layer.

[0079] In contrast, the test sample of Comparative Example 1 did not have an intermediate layer, so the coating layer melted when the sheath layer was extruded, resulting in a reduction in the thickness of the coating layer. The test sample of Reference Example 1 had an intermediate layer thickness of 0.10 mm and a sheath layer thickness of 0.75 mm, so the thickness of the intermediate layer was 13% of the thickness of the sheath layer. Therefore, because the thickness of the intermediate layer was insufficient, the coating layer melted during extrusion, resulting in a reduction in the thickness of the coating layer.

[0080] (Flame retardancy test) Each test sample was subjected to a wire flame retardancy test in accordance with ISO 19642. The wire flame retardancy test was conducted by placing the test sample at a 45° angle. As a result of the wire flame retardancy test, samples in which the fire was extinguished within 70 seconds and 50 mm or more of the test sample remained unburned were evaluated as "Good," while samples that continued to burn for more than 70 seconds or where the remaining unburned portion of the test sample was less than 50 mm were evaluated as "Poor." The test results are shown in Tables 1 and 2.

[0081] As can be seen from Tables 1 and 2, the test sample of Reference Example 2 was found to have poor flame retardancy. This is presumably because the thickness of the intermediate layer was greater than that of the test samples of the other examples, resulting in poor flame retardancy. In other words, the test sample of Reference Example 2 had an intermediate layer thickness of 0.65 mm and a sheath layer thickness of 0.75 mm, which means that the thickness of the intermediate layer was 87% of the sheath layer thickness, and therefore it is presumed to have poor flame retardancy.

[0082] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment. [Explanation of symbols]

[0083] 1 conductor 2 Covering layer 3. Insulated wire 4 Wire bundle 5 Sheath layer 6. Middle class 10 Communication Cable

Claims

1. a wire bundle including a plurality of insulated wires each having a conductor and a coating layer that coats the conductor; a sheath layer covering the outer periphery of the electric wire bundle; an intermediate layer interposed between the electric wire bundle and the sheath layer and covering the outer periphery of the electric wire bundle; Equipped with the intermediate layer is in close contact with the coating layer of the insulated wire, and the sheath layer is in close contact with the intermediate layer; the melting point of the base resin constituting the intermediate layer is lower by 20° C. or more than the melting points of the base resins constituting the coating layer and the sheath layer; A communication cable, wherein the base resin constituting the intermediate layer is at least one of a polyethylene resin and a polyethylene copolymer, and the base resin constituting the coating layer and the sheath layer is a polypropylene resin.

2. The communication cable according to claim 1 , wherein the bundle of electric wires is a twisted wire formed by twisting a plurality of the insulated electric wires.

3. the base resin constituting the intermediate layer is at least one of a polyethylene resin and a polyethylene copolymer having a melting point of 140°C or less, 3. The communication cable according to claim 1, wherein the base resin constituting the coating layer and the sheath layer is a polypropylene resin having a melting point of 160°C or higher.

4. 3. The communication cable according to claim 1, wherein the coating layer contains 0.1 to 5.0 parts by mass of an antioxidant and 0.1 to 3.0 parts by mass of a copper inhibitor per 100 parts by mass of polypropylene resin.

5. The sheath layer contains 51 to 100 parts by mass of polypropylene resin and 49 to 0 parts by mass of soft resin, 3. The communication cable according to claim 1, wherein the sheath layer contains 0.1 to 5.0 parts by mass of an antioxidant and 60 to 150 parts by mass of a flame retardant per 100 parts by mass of the polypropylene resin and the soft resin combined.

6. 3. The communication cable according to claim 1, wherein when the wire bundle includes two insulated wires, the thickness of the intermediate layer is 20 to 80% of the thickness of the sheath layer.

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