insulated wire

Abstract

An insulation wire according to an aspect of the present disclosure comprises: a conductor obtained by twisting a plurality of strands; and an insulating layer covering the outer circumference of the conductor, wherein the insulating layer is a crosslinked product of a polymer composition, the polymer composition contains an ethylene-based copolymer, polyethylene, or a combination thereof as a main component, the gel content of the crosslinked product is 60% or more, and the tensile elongation of the crosslinked product is 150% or more.

Description

[Technical Field]

[0001] This disclosure relates to an insulated electric wire. This application claims priority to Japanese Patent Application No. 2020-132629, filed on August 4, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Insulated electric wires used in vehicles such as automobiles, and the insulating material that makes up their insulating layer, are required to have long-term heat resistance so that they do not deteriorate over long periods of time, even in high-temperature environments caused by heat generated when electricity is passed through them. Furthermore, when the ends of insulated electric wires are used as connectors, a method is used in which the insulating material is compressed and deformed using a rubber ring or similar, and the resulting rebound effect acts as a watertight seal to prevent water from seeping into the connection from the outside. To ensure this watertight performance, the insulating material is required to have creep deformation resistance.

[0003] In the prior art, there have been proposed a halogen-free resin composition containing a base resin made of a polypropylene-based resin, a propylene-α-olefin copolymer, or a low-density polyethylene resin, and a metal hydrate, a phenol-based antioxidant, and a hydrazine-based metal scavenger, an insulated wire having this resin composition as an insulating layer, and a wire harness including this insulated wire (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-127040 Summary of the Invention

[0005] An insulated wire according to one embodiment of the present disclosure includes a conductor formed by twisting together a plurality of strands and an insulating layer covering the outer periphery of the conductor, wherein the insulating layer is a crosslinked polymer composition, the polymer composition mainly containing an ethylene copolymer, polyethylene, or a combination thereof, the crosslinked polymer having a gel fraction of 60% or more, and a tensile elongation of 150% or more. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an insulated wire according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Problem to be solved by this disclosure] The insulating layer formed from the resin composition used in the insulated wires of the prior art does not have sufficient long-term heat resistance or water-stopping performance (terminal water-stopping performance), and there is a demand for improved long-term heat resistance and sufficient water-stopping performance (terminal water-stopping performance) to cope with the large heat generation caused by the passage of a large current.

[0008] The present disclosure has been made in light of the above-mentioned circumstances, and has an object to provide an insulated wire that is excellent in long-term heat resistance and waterproofing performance.

[0009] [Effects of this disclosure] The insulated wire according to one embodiment of the present disclosure has excellent long-term heat resistance and waterproofing performance.

[0010] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] An insulated wire according to one embodiment of the present disclosure includes a conductor formed by twisting together a plurality of strands and an insulating layer covering the outer periphery of the conductor, wherein the insulating layer is a crosslinked polymer composition, the polymer composition mainly containing an ethylene copolymer, polyethylene, or a combination thereof, the crosslinked polymer having a gel fraction of 60% or more, and a tensile elongation of 150% or more.

[0012] In the insulated wire, the insulating layer is a crosslinked product of a polymer composition mainly composed of an ethylene copolymer, polyethylene, or a combination thereof, and the crosslinked product has a gel fraction of 60% or more, which is thought to improve long-term heat resistance and creep characteristics. Furthermore, a tensile elongation of 150% or more improves flexibility and suppresses cracking and breakage under usage conditions, thereby further improving water-stopping performance (terminal water-stopping). Therefore, the insulated wire has excellent long-term heat resistance and water-stopping performance. The term "crosslinked body" refers to a material obtained by crosslinking a polymer composition. The term "main component" refers to the substance with the highest content among the constituent substances, for example, a content of 50% by mass or more. The term "creep modulus" refers to the ratio of creep strain to initial stress. The term "gel fraction" is an index of the degree of crosslinking of the base resin and is measured in accordance with JASO (Japan Automotive Engineering Society) D625 crosslinking degree measurement standard. The term "tensile elongation" refers to the tensile elongation (%) measured in accordance with JASO D625 insulator tensile test standard.

[0013] The crosslinked body may have a creep modulus of 0.3% MPa or more, calculated under conditions of maintaining the crosslinked body at 150° C. for 1500 hours. When the crosslinked body has a creep modulus of 0.3% MPa or more, calculated under conditions of maintaining the crosslinked body at 150° C. for 1500 hours, the crosslinked body can have creep deformation resistance that can ensure sufficient water-stopping performance (terminal water-stopping).

[0014] The crosslinked body may have a tensile elongation of 50% or more after being held at 150° C. for 1500 hours. When the crosslinked body has a tensile elongation of 50% or more after being held at 150° C. for 1500 hours, the insulated wire can have a further improved long-term heat resistance.

[0015] The insulated wire is preferably used as a high-voltage wire for an automobile. By using the insulated wire as a high-voltage wire for an automobile, it is possible to provide a high-voltage wire for an automobile that has excellent long-term heat resistance and watertight performance. Here, "high-voltage wire for an automobile" means a high-voltage wire as an automobile part defined in JASO D624.

[0016] [Details of the embodiments of the present disclosure] Hereinafter, an insulated wire according to an embodiment of the present disclosure will be described in detail with reference to the drawings.

[0017] <Insulated wire> An insulated wire according to one embodiment of the present disclosure includes a conductor formed by twisting together a plurality of wires and an insulating layer that covers the conductor. The insulated wire 1 in Fig. 1 includes a linear conductor 3 formed by twisting together a plurality of wires 2 and an insulating layer 4 that is a protective layer that covers the conductor 3.

[0018] The cross-sectional shape of the insulated wire 1 is not particularly limited, but may be, for example, circular. When the cross-sectional shape of the insulated wire 1 is circular, its average outer diameter varies depending on the application, but may be, for example, 1 mm or more and 20 mm or less. Here, the "average outer diameter" refers to the average value of diameters measured at any ten points. The method for measuring the average outer diameter is not particularly limited, but, for example, the average value measured using a vernier caliper may be used as the average outer diameter.

[0019] (conductor) The conductor 3 is formed by twisting together a plurality of wires 2 at a fixed pitch. The wires 2 are not particularly limited, but examples include copper wires, copper alloy wires, aluminum wires, and aluminum alloy wires. The conductor 3 may be a twisted wire formed by twisting together a plurality of wires 2, and a twisted wire formed by further twisting together a plurality of twisted wires. The use of a twisted wire can improve the flexibility of the cable. The twisted wires may be formed by twisting together the same number of wires 2.

[0020] The number of wires 2 is appropriately designed depending on the use of the multi-core cable, the diameter of the wires 2, etc., but the lower limit is 7, and may be 19. On the other hand, the upper limit of the number of wires 2 is 2,450, and may be 2,000. Examples of twisted wires include a twisted wire having 247 wires 2 obtained by twisting together 19 stranded wires, each of which is obtained by twisting together 13 wires 2; a twisted wire having 798 wires 2 obtained by twisting together 42 wires 2, and a twisted wire having 1,998 wires 2 obtained by twisting together 37 stranded wires, each of which is obtained by twisting together 54 wires 2.

[0021] The lower limit of the average outer diameter of the wires 2 is 100 μm. On the other hand, the upper limit of the average outer diameter of the wires 2 is 600 μm. If the average outer diameter of the wires 2 is less than 100 μm or exceeds 600 μm, the effect of improving the bending resistance of the insulated wire 1 may not be fully exhibited. The lower limit of the average outer diameter of the wires 2 may be 150 μm or 180 μm, while the upper limit of the average outer diameter of the wires 2 may be 600 μm or 500 μm. There is no particular limitation on the method for measuring the average outer diameter of the wire 2, but for example, the average value obtained by measuring the outer diameter at any three points on the wire 2 using a micrometer with cylindrical ends may be used as the average diameter.

[0022] The lower limit of the average area of ​​the cross section of the conductor 3 is 0.5 mm 2 On the other hand, the upper limit of the average area range of the cross section of the conductor 3 is 100 mm 2 By setting the average area of ​​the cross section of the conductor 3 within the above range, the insulated wire 1 can be suitably used as an in-vehicle high-voltage wire. The lower limit of the average area range of the cross section of the conductor 3 is 1.0 mm 2 may be 2.0 mm 2 may be 3.0 mm 2 The upper limit of the range of the average area of ​​the cross section of the conductor 3 is 95 mm 2 may be. The average area in the cross section of the conductor 3 is calculated by calculating the cross section area per wire 2 from the average outer diameter of the wires 2, and the product of the cross section area per wire 2 and the number of wires 2 is taken as the average area in the cross section of the conductor 3.

[0023] [Insulating layer] The insulating layer 4 is a crosslinked product of a polymer composition. Methods for crosslinking the polymer composition that constitutes the insulating layer 4 include a method of irradiating with ionizing radiation and a method using a thermal crosslinking agent. The insulating layer 4 is formed from a polymer composition and is laminated around the outer periphery of the conductor 3 to cover the conductor 3. The average thickness of the insulating layer 4 is not particularly limited, but is, for example, 0.1 mm or more and 5 mm or less. Here, the "average thickness" refers to the average value of thicknesses measured at any ten points using, for example, a vernier caliper. Note that the same definition is used below when referring to "average thickness" of other members, etc.

[0024] The main component of the polymer composition is an ethylene copolymer, polyethylene, or a combination thereof. When the main component of the polymer composition is an ethylene copolymer, polyethylene, or a combination thereof, the long-term heat resistance of the insulating layer 4 can be improved.

[0025] (ethylene copolymer) Examples of the ethylene copolymer include a copolymer of ethylene and an α-olefin having a carbonyl group, and an ethylene rubber.

[0026] <Copolymer of ethylene and α-olefin having a carbonyl group> Examples of the α-olefin having a carbonyl group in the copolymer of ethylene and an α-olefin having a carbonyl group include (meth)acrylic acid alkyl esters such as methyl (meth)acrylate and ethyl (meth)acrylate; (meth)acrylic acid aryl esters such as phenyl (meth)acrylate; vinyl esters such as vinyl acetate and vinyl propionate; unsaturated acids such as (meth)acrylic acid, crotonic acid, maleic acid, and itaconic acid; vinyl ketones such as methyl vinyl ketone and phenyl vinyl ketone; and (meth)acrylic acid amides.

[0027] Examples of the resins mainly composed of copolymers of ethylene and an α-olefin having a carbonyl group include ethylene-methyl acrylate copolymer (EMA), ethylene-butyl acrylate copolymer (EBA), ethylene-vinyl acetate copolymer (EVA), and ethylene-ethyl acrylate copolymer (EEA).

[0028] The lower limit of the carbonyl group-containing α-olefin content is 5% by mass. If the carbonyl group-containing α-olefin content is less than 5% by mass, the long-term heat resistance and water-stopping performance may be insufficient. On the other hand, the upper limit of the carbonyl group-containing α-olefin content is 45% by mass. If the carbonyl group-containing α-olefin content exceeds 45% by mass, the mechanical properties of the insulating layer 4, such as its strength, may be reduced. The lower limit of the carbonyl group-containing α-olefin content may be 10% by mass, because sufficient heat resistance and water-stopping performance can be obtained. On the other hand, the upper limit of the carbonyl group-containing α-olefin content may be 40% by mass, because sufficient mechanical strength can be obtained.

[0029] <Ethylene-based rubber> Examples of ethylene-based rubbers include ethylene-α-olefin copolymers, ethylene-α-olefin-non-conjugated polyene copolymers, and ethylene-acrylic acid ester copolymers.

[0030] Examples of the α-olefin in the ethylene-α-olefin copolymer and the ethylene-α-olefin-non-conjugated polyene copolymer include α-olefins having 3 to 20 carbon atoms. Examples of the α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-nonadecene, 1-eicosene-1, 9-methyl-1-decene, 11-methyl-1-dodecene, and 12-ethyl-1-tetradecene. These α-olefins can be used alone or in combination of two or more.

[0031] Examples of the non-conjugated polyene in the ethylene-α-olefin-non-conjugated polyene copolymer include those having 5 to 20, preferably 5 to 10, carbon atoms, such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,4-octadiene, 1,5-octadiene, 1,6-octadiene, 1,7-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene, 7-methyl-1,6-octadiene, 4-ethylidene-8-methyl-1,7-nonadiene, and 4,8-dimethyl-1,4,8-decatriene. Examples of the alkylene include cyclopentadiene, cyclohexadiene, dicyclooctadiene, methylenenorbornene, 5-vinylnorbornene, 5-ethylidene-2-norbornene, 5-methylene-2-norbornene, 5-vinylidene-2-norbornene, 5-isopropylidene-2-norbornene, 6-chloromethyl-5-isopropenyl-2-norbornene, 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, and 2-propenyl-2,2-norbornadiene.

[0032] Examples of the acrylic acid ester in the ethylene-acrylic acid ester copolymer include ethyl acrylate.

[0033] Examples of the ethylene-based rubber include ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), and ethylene-acrylic rubber.

[0034] (polyethylene) Examples of polyethylene include linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE), high density polyethylene (HDPE), and low density polyethylene (LDPE).

[0035] From the viewpoint of improving long-term heat resistance and water-stopping performance, the main component of the polymer composition may be a polymer such as an ethylene-methyl acrylate copolymer, which is a copolymer of ethylene and an α-olefin having a carbonyl group, an ultra-low density polyethylene, which is a polyethylene, or a linear low density polyethylene, or an ethylene-based rubber such as EP rubber.

[0036] The insulating layer 4 may contain other resins in addition to the main component resin. The upper limit of the content of other resins is 50 mass %, or may be 30 mass %. Furthermore, the insulating layer 4 may be substantially free of other resins.

[0037] The insulating layer 4 may contain additives such as a flame retardant, an antioxidant, a cross-linking aid, and a thermal cross-linking agent.

[0038] (Flame retardant) The inclusion of a flame retardant can improve the flame retardancy of the insulated wire 1. Examples of flame retardants include bromine-based flame retardants, antimony trioxide, antimony pentoxide, zinc borate, and metal hydroxides, which can be used alone or in combination of two or more. However, in order to obtain sufficient flame retardancy, the amount of metal hydroxides to be filled must be increased. Since metal hydroxides often impair properties such as reduced mechanical strength and long-term heat resistance, a bromine-based flame retardant and antimony trioxide may be used in combination as the flame retardant.

[0039] Examples of bromine-based flame retardants include ethylenebis(pentabromophenyl), decabromodiphenylethane, etc. Examples of metal hydroxides include magnesium hydroxide, aluminum hydroxide, etc.

[0040] The content of the flame retardant in the polymer composition may be 10 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the polymer. If the content of the flame retardant is less than 10 parts by mass, sufficient flame retardancy may not be obtained. On the other hand, if the content of the flame retardant is more than 200 parts by mass, the mechanical strength of the insulating layer 4 may be reduced.

[0041] (antioxidant) Stability can be improved by adding an antioxidant, such as a sulfur-based antioxidant or a phenol-based antioxidant.

[0042] The content of the antioxidant in the polymer composition may be 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the polymer. If the content of the antioxidant is less than 1 part by mass, a sufficient effect of inhibiting oxidative degradation may not be obtained. On the other hand, if the content of the antioxidant is more than 10 parts by mass, the mechanical strength of the insulating layer 4 may be reduced.

[0043] (Crosslinking aid) The cross-linking aid is blended to promote cross-linking of the polymer by irradiation with ionizing radiation. Furthermore, by irradiating the polymer composition blended with the cross-linking aid with ionizing radiation to cross-link the polymer, the mechanical strength, such as the tensile strength, of the insulating layer 4 can be improved.

[0044] Examples of crosslinking aids include isocyanurates such as triallyl isocyanurate (TAIC) and diallyl monoglycidyl isocyanurate (DA-MGIC), and trimethylolpropane trimethacrylate. These may be used alone or in combination of two or more. Among them, trimethylolpropane trimethacrylate may be used to effectively crosslink.

[0045] The content of the cross-linking aid in the polymer composition may be 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the polymer. If the content of the cross-linking aid is less than 1 part by mass, cross-linking may not proceed sufficiently, which may reduce the mechanical strength of the insulating layer 4. On the other hand, if the content of the cross-linking aid is more than 10 parts by mass, the cross-linking density may become too high, which may harden the insulating layer 4 and reduce its flexibility.

[0046] (thermal crosslinking agent) Thermal crosslinking agents are used in a method of thermal crosslinking in which a crosslinking agent is mixed into a polymer and heated to cause a reaction. Organic peroxides are primarily used as thermal crosslinking agents. Examples of organic peroxides include dicumyl peroxide (DCP) and 2,5-dimethylditertiarybutylperoxyhexane. Addition-type crosslinking agents containing a platinum catalyst or a curing agent may also be used as thermal crosslinking agents.

[0047] The content of the thermal crosslinking agent in the polymer composition may be 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of the polymer. If the content of the thermal crosslinking agent is less than 1 part by mass, crosslinking may not proceed sufficiently, which may reduce the mechanical strength of the insulating layer 4. On the other hand, if the content of the thermal crosslinking agent is more than 5 parts by mass, the crosslinking density may become too high, which may harden the insulating layer 4 and reduce its flexibility.

[0048] In addition to the flame retardant, antioxidant, crosslinking aid, and thermal crosslinking agent, the insulating layer 4 may contain additives such as a flame retardant aid, a lubricant, a colorant, a reflectivity imparting agent, an opacifying agent, a processing stabilizer, and a plasticizer.

[0049] [Physical properties of cross-linked body] (Creep modulus calculated by holding the crosslinked product at 150°C for 1500 hours) The lower limit of the creep modulus calculated under the condition of maintaining the crosslinked body at 150° C. for 1500 hours is 0.3 MPa. When the creep modulus calculated under the condition of maintaining the crosslinked body at 150° C. for 1500 hours is 0.3 MPa or more, the crosslinked body can have creep deformation resistance that can ensure sufficient water-stopping performance (terminal water-stopping). The lower limit of the creep modulus calculated under the condition that the crosslinked body is maintained at 150° C. for 1500 hours may be 0.32 MPa, which can further improve the waterproofing performance.

[0050] The creep modulus calculated under the condition of holding the crosslinked material at 150°C for 1500 hours can be determined as follows. Measurements are taken using a viscoelasticity measuring device while changing the temperature and frequency, and a double logarithmic graph of frequency and storage modulus is created by moving parallel to 150°C as the reference in accordance with temperature-time conversion. This data is power-approximated, and from the approximation formula, the frequency corresponding to 1500 hours, 1.9 x 10 -7 The storage modulus in Hz is determined. The "storage modulus" is a value measured in accordance with the dynamic mechanical property testing method described in JIS-K7244-4 (1999), and is a value measured using a viscoelasticity measuring device at the above temperature and frequency under the conditions of tensile mode and strain of 0.08%. As the viscoelasticity measuring device, for example, the "DVA-220" manufactured by IT Instrument & Control Co., Ltd. can be used.

[0051] (gel fraction) The "gel fraction" is an index of the degree of crosslinking of the base resin, and is measured in accordance with the crosslinking degree measurement method of JASO D625. The lower limit of the gel fraction of the crosslinked body is 60%. A lower limit of 60% for the gel fraction of the crosslinked body can improve long-term heat resistance and creep properties. On the other hand, the upper limit of the gel fraction of the crosslinked body is 95%. A higher limit of 95% for the gel fraction of the crosslinked body can suppress cracking and breakage in the usage environment due to reduced flexibility. The lower limit of the gel fraction of the crosslinked body may be 63%. This is because sufficient heat resistance and creep properties can be obtained. The upper limit of the gel fraction of the crosslinked body may be 90%. This is because cracking and breakage due to reduced flexibility can be suppressed.

[0052] The gel fraction is measured in accordance with the cross-linking degree measurement method of JASO D625. A sample is prepared by cutting out the insulating layer 4 from the insulated wire 1 and immersing the sample in 20 ml of xylene at 120°C for 24 hours. The sample is then removed and dried at 100°C for 6 hours. The gel fraction is the value calculated by the following formula, where W1 [g] is the mass of the solid content and W2 [g] is the mass of the heat-shrinkable layer before immersion in xylene. Gel fraction [mass%] = [W1 / W2] x 100

[0053] (Tensile elongation and tensile strength) The lower limit of the tensile elongation of the crosslinked body measured in accordance with the JASO D625 insulator tensile test is 150%. A tensile elongation of 150% or more improves flexibility and suppresses cracking and breakage under usage conditions, thereby improving water-stopping performance (terminal water-stopping). The lower limit of the tensile elongation of the crosslinked body may be 200% or 250%. Furthermore, water-stopping performance (terminal water-stopping) can be improved.

[0054] The lower limit of the tensile strength of the crosslinked body measured in accordance with the JASO D625 insulator tensile test is 10 MPa. A tensile strength of 10 MPa can increase the mechanical strength. The lower limit of the tensile strength of the crosslinked body may be 12 MPa. Furthermore, the mechanical strength of the insulated wire 1 can be increased.

[0055] The lower limit of the tensile elongation of the crosslinked body after being held at 150°C for 1500 hours, as measured in accordance with the tensile test for insulators of JASO D625, is 50%. When the tensile elongation of the crosslinked body after being held at 150°C for 1500 hours is 50% or more, the long-term heat resistance of the insulated wire 1 can be improved. The lower limit of the tensile elongation may be 60%, which can further improve the long-term heat resistance of the insulated wire 1.

[0056] [Insulated wire manufacturing method] The insulated wire 1 can be obtained by a manufacturing method including a step of twisting a plurality of wires together (twisting step), a step of forming an insulating layer 4 that covers the outer periphery of a conductor 3 formed by twisting a plurality of wires 2 (insulating layer forming step), and a step of crosslinking the polymer composition that constitutes the insulating layer 4 (crosslinking step). This crosslinking step may be performed before or after the conductor 3 is covered with the composition that forms the insulating layer 4 (after the insulating layer 4 is formed).

[0057] The insulating layer 4 may be formed on the outer periphery of the conductor 3 by extruding a polymer composition onto the outer periphery of the conductor 3, for example.

[0058] Methods for crosslinking the polymer composition of the insulating layer 4 include a method of irradiating with ionizing radiation and a method of thermal crosslinking.

[0059] In the method of irradiating ionizing radiation, for example, gamma rays, electron beams, X-rays, neutron beams, high-energy ion beams, etc. can be used as the ionizing radiation. The lower limit of the exposure dose of ionizing radiation is 10 kGy. If the exposure dose is less than 10 kGy, the crosslinking reaction may not proceed sufficiently. On the other hand, the upper limit of the exposure dose of ionizing radiation is 400 kGy. If the exposure dose exceeds 400 kGy, decomposition of the polymer component may occur. The lower limit of the exposure dose of ionizing radiation may be 30 kGy. The upper limit of the exposure dose of ionizing radiation may be 360 ​​kGy.

[0060] In the thermal crosslinking method, a thermal crosslinking agent such as an organic peroxide, a metal oxide, or an organic amine compound is used to decompose and link molecules.

[0061] The insulated wire 1 of the present disclosure has excellent long-term heat resistance and waterproofing performance, and is therefore suitable for use as a high-voltage electrical wire for automobiles.

[0062] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is not limited to the configuration of the embodiments, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

[0063] The insulating layer 4 of the insulated wire 1 of the present disclosure may have a multi-layer structure.

[0064] The insulated wire 1 of the present disclosure may also have a primer layer laminated directly on the conductor. This primer layer can be preferably made of a crosslinked resin, such as ethylene, that does not contain metal hydroxide. Providing such a primer layer can prevent deterioration over time in the peelability of the insulating layer 4 and the conductor 3. [Example]

[0065] EXAMPLES Hereinafter, the insulated wire according to one aspect of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following production examples.

[0066] [Preparation of insulated wires No. 1 to No. 11] A conductor (average outer diameter 6.5 mm) was prepared by twisting 19 stranded wires, each of which was made by twisting 13 annealed copper wires, with an average outer diameter of 450 μm. A polymer composition mixed in the blending ratio shown in Table 1 was extrusion coated onto the conductor to form an insulating layer with an average outer diameter of 8.7 mm, thereby obtaining an insulated wire having the above-described wire configuration. For Nos. 1 to 9, the insulating layer was irradiated with 240 kGy of electron beam to crosslink the polymer composition, thereby obtaining a crosslinked wire. For Nos. 10 to 11, the polymer composition mixed in the blending ratio shown in Table 1 was extrusion coated onto the conductor to form an insulating layer of the specified thickness, and then thermally crosslinked at the crosslinking temperature shown in Table 1, thereby obtaining an insulated wire having the specified wire configuration. In Table 1, "-" indicates that the corresponding component was not used.

[0067] The components of the polymer composition are as follows: (copolymer of ethylene and α-olefin having a carbonyl group) In Table 1, the copolymers of ethylene and α-olefins having a carbonyl group used are as follows: In the following, MA stands for methyl acrylate. (1) EMA (MA: 18%) (ethylene-methyl acrylate copolymer) "Rexpearl EB230X" (registered trademark) manufactured by Japan Polyethylene Corporation MA unit content 18% by mass (2) EMA (MA: 24%) (ethylene-methyl acrylate copolymer) "Rexpearl EB050S" (registered trademark) manufactured by Japan Polyethylene Corporation MA unit content: 24% by mass

[0068] (polyethylene) (1) VLDPE (Very Low Density Polyethylene) Mitsui Chemicals "Tafmer DF110" (registered trademark) (2) LLDPE (linear low-density polyethylene) "DFDJ7540" manufactured by NUC Corporation

[0069] (ethylene rubber) Ethylene-propylene-diene rubber Sumitomo Chemical's "ESPLENE 301" (registered trademark)

[0070] (silicone polymer) Shin-Etsu Silicone "KE-5634-U"

[0071] (Flame retardant) (1) Brominated flame retardant: Ethylenebis(pentabromophenyl) Albemarle "Saytex 8010" (registered trademark) (2) Antimony trioxide "PATOX-M" (registered trademark) manufactured by Nippon Seiko Co., Ltd.

[0072] (antioxidant) (1) Hindered phenol antioxidants BASF "Irganox 1010" (registered trademark) (2) Sulfur-based antioxidants BASF "Irganox PS802" (registered trademark)

[0073] (Crosslinking aid) Trimethylolpropane trimethacrylate DIC "TD1500s"

[0074] (thermal crosslinking agent) (1) Dicumyl peroxide "Perkmill D" (registered trademark) manufactured by Nippon Oil & Fats Co., Ltd. (2) Metal complex-containing addition-type crosslinking agent Shin-Etsu Silicone "C-25A" (3) Curing agent-containing addition-type crosslinking agent Shin-Etsu Silicone "C-25B"

[0075] Next, the creep modulus of elasticity, gel fraction, tensile strength, tensile elongation, and waterproofing performance of the insulated wires No. 1 to No. 11 were evaluated by the following methods. The evaluation results are shown in Table 1.

[0076] (Creep modulus) Based on the above calculation method, the elastic modulus was calculated for the insulating layer of the insulated wire under the condition of holding at 150°C for 1500 hours.

[0077] (gel fraction) The measurement was performed in accordance with JASO D625, the degree of cross-linking measurement. A sample was cut out of the insulated wire and immersed in 20 ml of xylene at 120°C for 24 hours. The sample was then removed and dried at 100°C for 6 hours. The gel fraction was calculated by the following formula, where W1 [g] is the mass of the solid content and W2 [g] is the mass of the heat-shrinkable layer before immersion in xylene. Gel fraction [mass%] = [W1 / W2] x 100

[0078] (Tensile strength and tensile elongation) Measurements were made in accordance with the JASO D625 insulation tensile test. The insulation was taken from the insulated wire, punched into a No. 3 dumbbell shape as specified in JIS K6251 (2017), and the surface was smoothed before testing at a speed of 500 mm / min using a tensile testing machine.

[0079] [Water stopping performance] A waterproof silicone rubber stopper with an inner diameter 20% smaller than the outer diameter of the wire was attached to the outer periphery of the wire, and a connector housing was formed around it to create a waterproof connector. This was placed in a heat resistance tester at 150°C for 1,500 hours, after which the terminal end of the housing was sealed, and compressed air at 0.2 MPa was sent through the rear end of the wire in water. The waterproof rubber stopper was evaluated on a two-level scale (A or B) based on the presence or absence of air bubbles. The waterproof performance of the insulation layer was evaluated as follows: A was good; A: No bubbles are visible. B: Air bubbles are observed and the waterproofing performance is insufficient.

[0080] (long-term heat resistance) The insulation layer of the insulated wire was measured for tensile elongation [%] in accordance with the JASO D625 insulation tensile test after 1500 hours at 150°C, and was evaluated on a two-level scale of A or B based on the tensile elongation. The evaluation criteria for the long-term heat resistance of the insulation layer were as follows: A is good. A: Tensile elongation is 50% or more. B: The tensile elongation is less than 50%.

[0081] [Table 1]

[0082] As shown in Table 1, insulated wires No. 1, No. 5 to No. 7, No. 9, and No. 11, whose insulating layer was made of a crosslinked polymer composition primarily composed of an ethylene copolymer, polyethylene, or a combination thereof, had a creep modulus of 0.3 MPa or more, a gel fraction of 60% or more, and a tensile elongation of 150% or more, all calculated at 1500 hours at 150°C. These wires exhibited excellent long-term heat resistance and watertightness. On the other hand, insulated wires No. 2 to No. 4, whose creep modulus was less than 0.3 MPa and whose gel fraction was less than 60%, all calculated at 1500 hours at 150°C, exhibited poor watertightness. Insulated wire No. 8, whose tensile elongation was less than 150%, exhibited poor long-term heat resistance and watertightness. Furthermore, wire No. 10, whose insulating layer was made of a crosslinked polymer composition primarily composed of a silicone polymer, exhibited good long-term heat resistance and watertightness, but had very poor tensile strength.

[0083] From the above, it can be seen that the insulated wire of the present disclosure has excellent long-term heat resistance and waterproof performance. [Explanation of symbols]

[0084] 1. Insulated wire 2 wires 3 Conductors 4. Insulation layer

Claims

1. a conductor formed by twisting together a plurality of wires; an insulating layer covering the outer periphery of the conductor; It is equipped with the insulating layer is formed from a crosslinked polymer composition and a flame retardant, the polymer composition is composed primarily of an ethylene copolymer, polyethylene, or a combination thereof; the flame retardant contains a brominated flame retardant and antimony trioxide, the insulating layer has a gel fraction of 60% or more; The insulating layer has a tensile elongation of 150% or more.

2. 2. The insulated wire according to claim 1, wherein the insulating layer has a creep modulus of elasticity of 0.3 MPa or more when calculated under conditions of maintaining the insulating layer at 150° C. for 1500 hours.

3. 3. The insulated wire according to claim 1, wherein the insulating layer has a tensile elongation of 50% or more after being held at 150°C for 1,500 hours.

4. 4. The insulated wire according to claim 1, wherein the insulating layer has a tensile strength of 10 MPa or more.

5. The insulated wire according to claim 1 , wherein the number of the wires is 7 or more and 2,450 or less.

6. 6. The insulated wire according to claim 1, wherein the average outer diameter of the wire is 100 μm or more and 600 μm or less.

7. The average cross-sectional area of ​​the conductor is 0.5 mm ２ More than 100 mm ２ The insulated wire according to any one of claims 1 to 6, wherein:

8. The insulated wire according to claim 1 or 7, which is used as a high-voltage wire for an automobile.

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