Insulated wire and heat shrinkable tube

Abstract

An insulated wire which comprises a conductor and an insulating layer that covers the conductor, wherein: the insulating layer is composed of a composition that contains a first component, a second component, a bromine-based flame retardant, and zinc oxide; the first component is composed of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer; and the second component is composed of at least one substance that is selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite. In the composition: the ratio M2 / M1 of the mass M2 of the ethylene-tetrafluoroethylene copolymer to the mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 to 40 / 60 inclusive; the content of the bromine-based flame retardant with respect to 100 parts by mass of the first component is 1.0 part by mass to 40 parts by mass inclusive; the content of the zinc oxide with respect to 100 parts by mass of the first component is 1.0 part by mass to 25 parts by mass inclusive; and the total content of the second component with respect to 100 parts by mass of the first component is 5.0 parts by mass to 50 parts by mass inclusive.

Description

Insulated wire and heat shrink tubing

[0001] The present disclosure relates to insulated wire and heat shrink tubing.

[0002] Flame retardancy is one of the required properties of an insulating layer that covers a conductor. Patent Document 1 discloses a coated electric wire that uses a composition with improved flame retardancy as an insulating layer, which is obtained by adding antimony trioxide to a blend polymer consisting of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer.

[0003] JP 2010-186585 A

[0004] An insulated wire according to the present disclosure includes: a conductor; and an insulating layer covering the conductor; wherein the insulating layer is made of a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide; the first component is made of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer; and the second component is made of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite; in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less; in the composition, a content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less; and in the composition, a content of the zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less. In the composition, the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

[0005] 1 is a schematic perspective view showing an insulated wire according to an embodiment of the present disclosure, and FIG. 2 is a schematic perspective view showing a heat-shrinkable tube according to an embodiment of the present disclosure.

[0006] [Problem to be Solved by the Present Disclosure] The insulating layer of an insulated wire is required to have flame retardancy as well as the ability to suppress smoke generation during combustion. Furthermore, the insulating layer of an insulated wire is also required to have excellent flexibility and tensile elongation.

[0007] Therefore, an object of the present disclosure is to provide an insulated wire having an insulating layer that is excellent in flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0008] Furthermore, an object of the present disclosure is to provide a heat-shrinkable tube that has excellent flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0009] Effect of the Present Disclosure According to the present disclosure, it is possible to provide an insulated wire including an insulating layer that is excellent in flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0010] Furthermore, according to the present disclosure, it is possible to provide a heat-shrinkable tube that has excellent flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) An insulated wire according to the present disclosure includes: a conductor; and an insulating layer covering the conductor; wherein the insulating layer is made of a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide; the first component is made of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer; and the second component is made of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite; in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less; in the composition, a content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less; and in the composition, a content of the zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less. In the composition, the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

[0012] According to the present disclosure, it is possible to provide an insulated wire having an insulating layer that is excellent in flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0013] (2) In the above (1), the second component may have an average particle size of 0.05 μm or more and 5 μm or less, thereby making it possible to obtain an insulating layer with a good appearance.

[0014] (3) In the above (1) or (2), the zinc oxide may have an average particle size of 0.05 μm or more and 5 μm or less, thereby making it possible to obtain an insulating layer with a good appearance.

[0015] (4) In any one of (1) to (3) above, the insulating layer may have a storage modulus of 0.1 MPa or more and 10 MPa or less at 250° C. This makes the insulating layer less susceptible to thermal deformation at high temperatures and has good flexibility at high temperatures.

[0016] (5) In any of (1) to (4) above, the heat of fusion of the insulating layer at 70°C or higher measured by a differential scanning calorimeter may be 1 J / g or more and 12 J / g or less. When the heat of fusion is 1 J / g or more, the crystalline components can prevent the electric wires from adhering to each other. When the heat of fusion is 12 J / g or less, the insulating layer can have good flexibility.

[0017] (6) In any one of (1) to (5) above, the content of the first component in the composition may be 50 mass % or more, thereby allowing the insulating layer to have sufficient strength and heat resistance.

[0018] (7) In any one of the above (1) to (6), the insulating layer may be an electron beam crosslinked product of the composition, thereby improving the strength of the insulating layer.

[0019] (8) A heat shrinkable tube according to the present disclosure comprises a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide, wherein the first component comprises a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer, and the second component comprises at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite, wherein in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less, wherein the content of the brominated flame retardant in the composition relative to 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less, and wherein the content of the zinc oxide in the composition relative to 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less, In the heat-shrinkable tube, the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

[0020] According to the present disclosure, it is possible to provide a heat-shrinkable tube that is excellent in flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0021] (9) In the above (8), the heat-shrinkable tube may be a covering material for the electric wire, thereby making it possible to provide an electric wire that produces less smoke when burned.

[0022] (10) In the above (8) or (9), the composition may be an electron beam crosslinked product, which improves the strength of the heat-shrinkable tube.

[0023] [Details of the embodiments of the present disclosure] Specific examples of the insulated wire and heat-shrinkable tubing of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0024] In this specification, the notation in the form of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0025] In the present specification, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is understood to include any conventionally known atomic ratio, and is not necessarily limited to only those within the stoichiometric range.

[0026] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0027] [Embodiment 1: Insulated Wire] An insulated wire according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") includes: a conductor; and an insulating layer covering the conductor; the insulating layer is made of a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide; the first component is made of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer; the second component is made of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite; in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less; and in the composition, a content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less; In the composition, the content of the zinc oxide is 1.0 part by mass or more and 25 parts by mass or less per 100 parts by mass of the first component, and the total content of the second component is 5.0 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the first component.

[0028] <Structure of Insulated Wire> As shown in Fig. 1 , the insulated wire 1 of the first embodiment has a conductor 2 and an insulating layer 3 that directly or indirectly covers the conductor 2. In the insulated wire, an additional layer, such as a primer treatment layer, may be provided between the conductor and the insulating layer. In the present disclosure, the insulated wire is a concept that includes an insulated wire in the narrow sense that is made up of a conductor and an insulating coating, and an insulated cable in which one or more insulated wires in the narrow sense are further covered with a protective coating.

[0029] <Conductor> The conductor 2 can be a conductor such as a copper wire that constitutes an insulated electric wire or an insulated cable used for wiring inside a device or an automobile. The conductor 2 is formed by twisting together a plurality of elemental wires at a constant pitch. The elemental wires are not particularly limited, but examples thereof include copper wire, copper alloy wire, aluminum wire, and aluminum alloy wire. The conductor 2 may also be a stranded wire formed by twisting together a plurality of elemental wires, and a stranded wire formed by further twisting together a plurality of stranded wires. The stranded wires may be formed by twisting together the same number of elemental wires.

[0030] The average area (including the gaps between the wires) of the cross section of the conductor 2 normal to the extending direction (hereinafter also referred to as the "cross section of the conductor 2") can be set appropriately depending on the application. The lower limit of the average area of ​​the cross section of the conductor 2 is 0.01 mm ２ The average area of ​​the cross section of the conductor 2 is 0.01 mm ２ If the average cross-sectional area of ​​the conductor 2 is less than 200 mm, the allowable current may be small. ２ The average area may be 200 mm or less. ２ If the average cross section of the conductor 2 exceeds 0.05 mm, the flexibility may be lost and the wiring may become difficult. ２ It may be 0.10 mm or more. ２ The upper limit of the average area of ​​the cross section of the conductor 2 (including the gaps between the wires) is 100 mm ２ Less than 80mm is also acceptable. ２ The average area of ​​the cross section of the conductor 2 may be 0.01 mm ２ More than 200 mm ２ It may be less than 0.05 mm ２ More than 100 mm ２ It may be less than 0.10 mm ２ Over 80mm ２ The following is also acceptable.

[0031] <Insulating Layer> In the insulated wire of the first embodiment, the insulating layer is made of a composition containing the first component, the second component, a brominated flame retardant, and zinc oxide.

[0032] <<First Component>> The first component includes a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer.

[0033] The first component contains a tetrafluoroethylene-propylene copolymer, which can improve the flexibility of the insulating layer. The tetrafluoroethylene-propylene copolymer is obtained by low-temperature emulsion copolymerization of tetrafluoroethylene and propylene. The tetrafluoroethylene-propylene copolymer may contain, as other components, an appropriate amount of one or more copolymerizable monomers, such as ethylene, isobutylene, acrylic acid and its alkyl esters, methacrylic acid and its alkyl esters, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, chloroethyl vinyl ether, chlorotrifluoroethylene, and perfluoroalkyl vinyl ethers. Tetrafluoroethylene-propylene copolymers are generally known and are readily available commercially.

[0034] The first component contains an ethylene-tetrafluoroethylene copolymer, which can improve the heat resistance and strength of the insulating layer. The ethylene-tetrafluoroethylene copolymer may contain, in addition to ethylene, an appropriate amount of one or more copolymerizable monomers, such as ethylene, isobutylene, acrylic acid and its alkyl esters, methacrylic acid and its alkyl esters, vinyl fluoride, vinylidene fluoride, hexafluoropropylene, chloroethyl vinyl ether, chlorotrifluoroethylene, and perfluoroalkyl vinyl ethers, as other components. Ethylene-tetrafluoroethylene copolymers are generally known and are readily available as commercial products.

[0035] In the composition constituting the insulating layer, the ratio M2 / M1 of the mass M2 of the ethylene-tetrafluoroethylene copolymer to the mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less. If the ratio M2 / M1 is less than 10 / 90, the heat resistance of the insulating layer may be insufficient. If the ratio M2 / M1 exceeds 40 / 60, the flexibility of the insulated wire 1 may be insufficient. The ratio M2 / M1 may be 15 / 85 or more and 37 / 63 or less, or may be 20 / 80 or more and 30 / 70 or less.

[0036] The ratio M2 / M1 is calculated by solid-state NMR measurement.

[0037] The lower limit of the content of the first component in the insulating layer 3 may be 50% by mass or more, 60% by mass or more, or 65% by mass or more. The upper limit of the content of the first component in the insulating layer 3 may be 97% by mass or less, or 95% by mass or less. If the content of the first component in the insulating layer 3 is less than 50% by mass, sufficient strength and heat resistance may not be obtained. On the other hand, if the content of the first component exceeds 97% by mass, the content of other compounding agents other than the first component will be insufficient, and the effects of the other compounding agents may be insufficient. The content of the first component in the insulating layer 3 may be 50% by mass or more and 97% by mass or less, 60% by mass or more and 97% by mass or less, or 65% by mass or more and 95% by mass or less.

[0038] The method for measuring the content of the first component in the insulating layer 3 is as follows: The mass concentration (%) of fluorine in the insulating layer 3 is measured by combustion ion chromatography, and the content of the first component in the insulating layer 3 is calculated from the ratio M2 / M1 measured by solid-state NMR.

[0039] The tetrafluoroethylene-propylene copolymer and the ethylene-tetrafluoroethylene copolymer can be crosslinked by irradiation with an electron beam, and therefore the insulating layer may be an electron beam crosslinked product of a composition containing the first component, the second component, a brominated flame retardant, and zinc oxide.

[0040] <Second Component> The second component comprises at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite. In the composition constituting the insulating layer, the total content of the second component per 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less. The lower limit of the total content of the second component per 100 parts by mass of the first component is 5.0 parts by mass or more, or may be 10 parts by mass or more, or 20 parts by mass or more. The upper limit of the total content of the second component per 100 parts by mass of the first component is 50 parts by mass or less, or may be 45 parts by mass or less, or may be 40 parts by mass or less. If the total content of the second component per 100 parts by mass of the first component is less than 5.0 parts by mass, the flame retardant effect may not be sufficiently obtained. On the other hand, if the total content of the second component per 100 parts by mass of the first component exceeds 50 parts by mass, the mechanical strength of the insulating layer, such as tensile strength and tensile elongation, may be reduced. In the composition constituting the insulating layer, the total content of the second component relative to 100 parts by mass of the first component may be 10 parts by mass or more and 45 parts by mass or less, or may be 20 parts by mass or more and 40 parts by mass or less.

[0041] In the composition constituting the insulating layer, the total content of the second component relative to 100 parts by mass of the first component is calculated by measuring the mass concentration (%) of each filler in the composition constituting the insulating layer by fluorescent X-ray analysis.

[0042] The lower limit of the average particle size of the second component may be 0.05 μm or more, or 0.5 μm or more. The upper limit of the average particle size of the second component may be 5 μm or less, or 3 μm or less. If the lower limit of the average particle size of the second component is less than 0.05 μm, aggregation may occur due to poor dispersion, and the mechanical strength of the insulating layer, such as tensile strength and tensile elongation, may be reduced. If the upper limit of the average particle size of the second component is more than 5 μm, die scuffs may be easily generated during molding, and an insulating layer with a good appearance may not be obtained. The average particle size of the second component may be 0.05 μm or more and 5 μm or more, or 0.5 μm or more and 5 μm or less.

[0043] The average particle size of the second component contained in the insulating layer is measured as follows: A cross section of the insulating layer is observed using an SEM. In the cross-sectional SEM image, the diameters of 100 particles of the second component are measured and the average is calculated. This average corresponds to the average particle size of the second component contained in the insulating layer.

[0044] Brominated flame retardants include decabromodiphenyl ether, hexabromobenzene, ethylene bistetrabromophthalimide, 2,2-bis(4-bromoethyl ether-3,5-dibromophenyl)propane, ethylene bis-dibromonorbornanedicarboximide, tetrabromo-bisphenol S, tris(2,3-dibromopropyl-1)isocyanurate, hexabromocyclododecane (HBCD), octabromophenyl ether, tetrabromobisphenol A (TBA) epoxy oligomer or polymer, TBA-bis(2,3-dibromopropyl ether), polydibromophenylene oxide, bis(tribromophenoxy)ethane, ethylene bis-pentabromobenzene, dibromoethyl-dibromocyclohexane, and dibromoneopentyl glycol. Examples of the bromophenol include bromophenol aliphatic phenol, ...

[0045] In the composition constituting the insulating layer, the content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less. The lower limit of the content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more, or may be 3 parts by mass or more, or 5 parts by mass or more. The upper limit of the content of the brominated flame retardant per 100 parts by mass of the first component is 40 parts by mass or less, or may be 30 parts by mass or less, or may be 20 parts by mass or less. If the content of the brominated flame retardant per 100 parts by mass of the first component is less than 1.0 part by mass, the flame retardant effect may not be sufficiently obtained. On the other hand, if the content of the brominated flame retardant per 100 parts by mass of the first component exceeds 40 parts by mass, the mechanical strength of the insulating layer, such as tensile strength and tensile elongation, may be reduced. The content of the brominated flame retardant relative to 100 parts by mass of the first component may be 3 parts by mass or more and 30 parts by mass or less, or may be 5 parts by mass or more and 20 parts by mass or less.

[0046] The method for measuring the content of the brominated flame retardant per 100 parts by mass of the first component in the composition constituting the insulating layer is as follows: The type of brominated flame retardant is identified by IR measurement, and the content of the brominated flame retardant per 100 parts by mass of the first component is calculated from the mass concentration (%) of bromine in the composition constituting the insulating layer determined by combustion ion chromatography measurement.

[0047] <Zinc Oxide> Zinc oxide can be used without any particular limitation, and may be obtained, for example, by adding a reducing agent such as coke to zinc ore and calcining the resulting zinc vapor, which is then oxidized with air, or by using zinc sulfate or zinc chloride as a raw material.

[0048] In the composition constituting the insulating layer, the content of zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less. The lower limit of the content of zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more, or may be 3 parts by mass or more, or 5 parts by mass or more. The upper limit of the content of zinc oxide per 100 parts by mass of the first component is 25 parts by mass or less, or may be 20 parts by mass or less, or may be 10 parts by mass or less. If the content of zinc oxide per 100 parts by mass of the first component is less than 1.0 part by mass, burns may occur during the mixing process or extrusion process. If the content of zinc oxide per 100 parts by mass of the first component exceeds 25 parts by mass, the mechanical strength of the insulating layer, such as tensile strength and tensile elongation, may be reduced. In the composition constituting the insulating layer, the content of zinc oxide per 100 parts by mass of the first component may be 3 parts by mass or more and 20 parts by mass or less, or may be 5 parts by mass or more and 10 parts by mass or less.

[0049] In the composition constituting the insulating layer, the content of zinc oxide per 100 parts by mass of the first component is measured by calculating the content of zinc oxide from the mass concentration (%) of zinc in the composition constituting the insulating layer determined by fluorescent X-ray analysis.

[0050] The lower limit of the average particle size of zinc oxide may be 0.05 μm or more, or 0.5 μm or more. The upper limit of the average particle size of zinc oxide may be 5 μm or less, or 3 μm or less. If the lower limit of the average particle size of zinc oxide is less than 0.05 μm, aggregation may occur due to poor dispersion, and the mechanical strength of the insulating layer, such as tensile strength and tensile elongation, may be reduced. If the upper limit of the average particle size of zinc oxide is more than 5 μm, die scuffs may be easily generated during molding, and an insulating layer with a good appearance may not be obtained. The average particle size of zinc oxide may be 0.05 μm or more and 5 μm or less, or 0.5 μm or more and 3 μm or less.

[0051] The average particle size of zinc oxide contained in the insulating layer is measured as follows: A cross section of the insulating layer is observed using an SEM. In the cross-sectional SEM image, the diameters of 100 zinc oxide particles are measured and the average is calculated. This average corresponds to the average particle size of zinc oxide contained in the insulating layer.

[0052] <Storage Modulus of Insulating Layer at 250°C> The lower limit of the storage modulus of the insulating layer 3 at 250°C may be 0.1 MPa or more, 0.5 MPa or more, or 1.0 MPa or more. The upper limit of the storage modulus of the insulating layer 3 at 250°C may be 10 MPa or less, 8 MPa or less, or 6 MPa or less. If the storage modulus of the insulating layer 3 at 250°C is less than 0.1 MPa, the insulating layer 3 may be prone to thermal deformation at high temperatures. On the other hand, if the storage modulus of the insulating layer 3 at 250°C exceeds 10 MPa, the flexibility of the insulating layer 3 at high temperatures may be reduced. The storage modulus of the insulating layer 3 at 250°C may be 0.1 MPa or more and 10 MPa or less, 0.5 MPa or more and 8 MPa or less, or 1.0 MPa or more and 6 MPa or less.

[0053] In the present disclosure, the "storage modulus at 250°C" is a value measured in accordance with the dynamic mechanical property test method described in JIS K7244-4:1999. A sample is prepared by removing the insulating layer from an electric wire. The storage modulus of the sample at 250°C is measured using a viscoelasticity measuring device under the conditions of tensile mode, strain of 0.08%, and frequency of 10 Hz. The heating rate from room temperature to 250°C is 10°C / min. As the viscoelasticity measuring device, for example, the "DVA-220" manufactured by IT Measurement & Control Co., Ltd. can be used.

[0054] <<Heat of Fusion of Insulating Layer at 70°C or Higher, Measured by Differential Scanning>> The lower limit of the heat of fusion of the insulating layer 3 at 70°C or higher, measured by a differential scanning calorimeter, may be 1 J / g or higher, or may be 2 J / g or higher. When the heat of fusion is 1 J / g or higher, the crystalline components can prevent the electric wires from adhering to each other. On the other hand, the upper limit of the heat of fusion may be 12 J / g or lower, or may be 10 J / g or lower. When the upper limit of the heat of fusion is 12 J / g or lower, the insulating layer can have good flexibility. The heat of fusion of the insulating layer 3 at 70°C or higher, measured by a differential scanning calorimeter, may be 1 J / g or higher and 12 J / g or lower, or may be 2 J / g or higher and 10 J / g or lower.

[0055] The heat of fusion can be obtained from a melting curve obtained by differential scanning calorimetry. The melting curve is determined by performing differential scanning calorimetry under the following conditions. Using a differential scanning calorimeter, a sample made of a 5 mg insulating layer is heated from -50°C to 300°C at a heating rate of 10°C / min in a nitrogen atmosphere, and the area of ​​all endothermic peaks appearing after 70°C is calculated. When the peaks are multimodal, the area of ​​all peaks is calculated.

[0056] <<Thickness of Insulating Layer>> The average thickness of the insulating layer 3 is not particularly limited, but may be, for example, 0.1 mm to 10 mm, 0.2 mm to 5 mm, or 0.5 mm to 2 mm. Here, the "average thickness" refers to the average value of thicknesses measured at any ten points. Note that the same definition is used below when referring to "average thickness" of other members, etc.

[0057] The composition constituting the insulating layer may contain other components in addition to the first component, the second component, the brominated flame retardant, and zinc oxide, as long as the effects of the present disclosure are not impaired. Examples of other components include the crosslinking aids described below and other additives.

[0058] The composition constituting the insulating layer may contain a crosslinking aid to promote crosslinking of the resin by electron beam irradiation. The content of the crosslinking aid varies depending on the type of crosslinking aid, but may usually be 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the first component. Examples of the crosslinking aid include oximes such as p-quinone dioxime and p,p'-dibenzoylquinone dioxime; acrylates or methacrylates such as ethylene dimethacrylate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, cyclohexyl methacrylate, acrylic acid / zinc oxide mixture, allyl methacrylate, and trimethacrylic isocyanurate (hereinafter also referred to as TMIC); vinyl monomers such as divinylbenzene, vinyltoluene, and vinylpyridine; allyl compounds such as hexamethylenediallylnadimide, diaryl itaconate, diallyl phthalate, diallyl isophthalate, diallyl monoglycidyl isocyanurate, triallyl cyanurate, and triallyl isocyanurate (hereinafter also referred to as TAIC); and maleimide compounds such as N,N'-m-phenylene bismaleimide and N,N'-(4,4'-methylenediphenylene)dimaleimide. These crosslinking aids may be used alone or in combination.

[0059] The composition constituting the insulating layer may contain other additives as needed. Examples of such additives include strength-retaining agents, antioxidants, copper inhibitors, colorants, heat stabilizers, and UV absorbers. The content of the additives in the composition constituting the insulating layer may be less than 40% by mass or less than 25% by mass. If the content of the additives is 40% by mass or more, the ratio of the first component in the insulating layer may decrease, which may result in a decrease in strength.

[0060] <Uses of Insulated Wire> The insulated wire of the first embodiment can be used as wiring inside a device or inside an automobile.

[0061] <Method for Producing Insulated Wire> The method for producing an insulated wire of the first embodiment is not particularly limited, but may include, for example, the following steps: (1) a step of preparing a resin composition for forming an insulating layer (resin composition preparation step), (2) a step of coating a conductor with the resin composition (coating step), and (3) a step of crosslinking the resin composition by irradiation (crosslinking step).

[0062] (1) Resin Composition Preparation Step In the resin composition preparation step, the first component, the second component, the brominated flame retardant, zinc oxide, and other additives as necessary are mixed using a melt mixer, etc., to prepare a resin composition for forming an insulating layer. As the melt mixer, a known mixer, such as an open roll, a Banbury mixer, a pressure kneader, a single-screw mixer, or a multi-screw mixer, can be used.

[0063] (2) Coating Step In the coating step, the resin composition is extruded onto the conductor using, for example, a melt extruder to coat the conductor with the resin composition.

[0064] (3) Crosslinking Step In the crosslinking step, the resin composition that coats the conductor is crosslinked by irradiation. Crosslinking the first component of the resin composition (tetrafluoroethylene-propylene copolymer and ethylene-tetrafluoroethylene copolymer) provides the insulating layer with shape retention at high temperatures. A method of crosslinking the first component may be a method of irradiating the resin composition with an electron beam. Since molding becomes difficult after crosslinking the first component by electron beam irradiation, electron beam irradiation is performed after the extrusion molding step. By irradiating with an electron beam after extrusion molding, molding can be carried out reliably and the effects of electron beam irradiation can be fully obtained.

[0065] The electron beam irradiation dose may be in the range of 50 kGy to 400 kGy. If the electron beam irradiation dose is less than 50 kGy, the degree of crosslinking may be small, and the shape retention at high temperatures may be reduced. On the other hand, if the electron beam irradiation dose is more than 400 kGy, it takes a long time to produce the product.

[0066] [Embodiment 2: Heat Shrink Tubing] A heat shrink tubing according to another embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") comprises a composition including a first component, a second component, a brominated flame retardant, and zinc oxide, wherein the first component comprises a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer, and the second component comprises at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite, wherein in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less, wherein the content of the brominated flame retardant in the composition is 1.0 part by mass or more and 40 parts by mass or less per 100 parts by mass of the first component, and wherein the content of the zinc oxide in the composition is 1.0 part by mass or more and 25 parts by mass or less per 100 parts by mass of the first component, In the heat-shrinkable tube, the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

[0067] <Structure of Heat-Shrinkable Tube> As shown in FIG. 2 , the heat-shrinkable tube 10 of the second embodiment is composed of a cylindrical single-layer base material layer. The heat-shrinkable tube 10 is used to protect, insulate, waterproof, and protect against corrosion of, for example, the connection between objects to be covered, the terminals of wiring, metal pipes, etc. The heat-shrinkable tube of the second embodiment is not limited to the cylindrical single-layer base material layer shown in FIG. 2 , but may also be a heat-shrinkable tube having a cap-shaped base material layer, for example. Such a heat-shrinkable tube can be manufactured by heat-shrinking and closing one end of a cylindrical heat-shrinkable tube. This heat-shrinkable tube can be suitably used, for example, for processing the terminals of wiring.

[0068] The average inner diameter and average thickness of the heat-shrinkable tube 10 are appropriately selected depending on the application, etc. The average inner diameter of the heat-shrinkable tube 10 before heat shrinkage may be, for example, 1 mm or more and 60 mm or less. The average inner diameter of the heat-shrinkable tube 10 after heat shrinkage may be, for example, 30% or more and 50% or less of the average inner diameter before heat shrinkage. The average thickness of the heat-shrinkable tube 10 may be, for example, 0.1 mm or more and 5 mm or less.

[0069] <Composition> The composition constituting the heat-shrinkable tube of embodiment 2 is a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide. The composition constituting the heat-shrinkable tube of embodiment 2 can have the same configuration as the composition constituting the insulating layer of the insulated wire of embodiment 1, and therefore the description thereof will not be repeated. The heat-shrinkable tube of embodiment 2 has excellent flame retardancy, suppresses smoke generation during combustion, and has excellent flexibility and tensile elongation.

[0070] <Uses of Heat Shrink Tubing> The heat shrink tubing according to the second embodiment is used as a covering material for protecting an object to be covered. More specifically, it can be a heat shrink tubing that shrinks in the inner diameter direction when heated at a temperature equal to or higher than the melting point of an ethylene-tetrafluoroethylene copolymer. The heat shrink tubing with the object to be covered inserted therein is heated on the object to be covered, causing the heat shrink tubing to shrink. This protects the object to be covered. The heat shrink tubing is used as a covering material for protecting the object to be covered, such as the connection parts of electric wires, pipes, etc.

[0071] <Method for Manufacturing Heat-Shrinkable Tube> The method for manufacturing the heat-shrinkable tube of the second embodiment is not particularly limited, but may include, for example, the following steps: (1) a step of preparing a resin composition for forming the heat-shrinkable tube (resin composition preparation step), (2) a step of extruding the resin composition using a melt extruder (extrusion molding step), (3) a step of crosslinking the extrusion-molded product by irradiation (crosslinking step), and (4) a step of expanding the diameter of the extrusion-molded product after crosslinking to obtain the heat-shrinkable tube (diameter expansion step).

[0072] (1) Resin Composition Preparation Step In the resin composition preparation step, a resin composition for forming heat-shrinkable tubing is prepared by mixing the first component, the second component, the brominated flame retardant, zinc oxide, and, if necessary, other additives using a melt mixer, etc. As the melt mixer, a known one, for example, an open roll, a Banbury mixer, a pressure kneader, a single-screw mixer, a multi-screw mixer, etc. can be used.

[0073] (2) Extrusion Molding Step In the extrusion molding step, the resin composition is extruded using a melt extruder. Specifically, the resin composition is extruded into a cylindrical shape using an extrusion die having a cylindrical space. This results in an extrusion molded product. The dimensions of the extrusion molded product can be designed depending on the application, etc.

[0074] (3) Crosslinking Step In the crosslinking step, the extrusion molded article is crosslinked by irradiation. The irradiation conditions may be the same as those in the crosslinking step in the above-mentioned method for producing an insulated electric wire.

[0075] (4) Diameter Expansion Step In the diameter expansion step, the crosslinked extrusion-molded product is expanded in diameter. The diameter expansion method for the extrusion-molded product can be any known method commonly used in the production of conventional heat-shrinkable tubing. For example, the extrusion-molded product can be expanded to a predetermined inner diameter by heating the extrusion-molded product to a temperature above its melting point and then introducing compressed air into the extrusion-molded product, reducing pressure from the outside, or inserting a metal rod into the extrusion-molded product, and then cooling the extrusion-molded product to fix the shape. The diameter expansion of the extrusion-molded product is performed, for example, so that the inner diameter of the extrusion-molded product becomes 1.2 times or more and 4 times or less. The shape of the expanded extrusion-molded product is fixed to obtain a heat-shrinkable tubing. Examples of such a fixing method include cooling the extrusion-molded product to a temperature below the melting point of the base resin component. In the diameter expansion step, the roughness of the metal rod can be reduced, or a coating or lubricant can be applied to minimize the effect on the surface roughness of the inner surface of the heat-shrinkable tubing. The effect on the surface roughness of the inner surface of the heat-shrinkable tubing can also be reduced by reducing the rate of diameter expansion. In this way, the cross-linked extrusion molding is expanded in diameter and fixed in shape to form a heat-shrinkable tube.

[0076] [Supplementary Note 1] The present invention relates to a composition comprising a first component, a second component, a brominated flame retardant, and zinc oxide, wherein the first component comprises a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer, and the second component comprises at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite, wherein in the composition, a ratio M2 / M1 of a mass of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less, wherein the content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less, and wherein the content of the zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less, In the composition, the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

[0077] [Appendix 2] The heat-shrinkable tube according to Appendix 1, wherein the second component has an average particle size of 0.05 μm or more and 5 μm or less.

[0078] [Appendix 3] The heat-shrinkable tube according to appendix 1 or 2, wherein the zinc oxide has an average particle size of 0.05 μm or more and 5 μm or less.

[0079] [Appendix 4] The heat-shrinkable tube according to any one of Appendices 1 to 3, wherein the insulating layer has a storage modulus at 250°C of 0.1 MPa or more and 10 MPa or less.

[0080] [Appendix 5] The heat-shrinkable tube according to any one of Appendices 1 to 4, wherein the insulating layer has a heat of fusion of 1 J / g or more and 12 J / g or less at 70°C or higher as measured by a differential scanning calorimeter.

[0081] [Appendix 6] The heat-shrinkable tube according to any one of Appendices 1 to 5, wherein the content of the first component in the composition is 50 mass % or more.

[0082] [Appendix 7] The heat-shrinkable tube according to any one of Appendices 1 to 6, wherein the insulating layer is an electron beam crosslinked product of the composition.

[0083] [Appendix 8] The heat-shrinkable tube according to any one of Appendices 1 to 7, wherein the composition does not contain antimony trioxide.

[0084] [Supplementary Note 9] A conductive material comprising: a conductor; and an insulating layer covering the conductor, wherein the insulating layer is made of a composition containing a first component, a second component, a brominated flame retardant, and zinc oxide; the first component is made of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer; and the second component is made of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite; in the composition, a ratio M2 / M1 of a mass M2 of the ethylene-tetrafluoroethylene copolymer to a mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less; in the composition, the content of the brominated flame retardant per 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less; and in the composition, the content of the zinc oxide per 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less. an insulated wire in which the total content of the second component relative to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less, and the composition does not contain antimony trioxide.

[0085] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0086] [Preparation of insulated wires] <Samples 1 to 16, Samples 101 to 108> ２ A copper wire was prepared.

[0087] The raw materials for the resin composition will be described. First Component The following were prepared as raw materials for the first component. Tetrafluoroethylene-propylene copolymer (referred to as "TFE-P" in the tables): "Aflas 150CS" manufactured by AGC Ethylene-tetrafluoroethylene copolymer (referred to as "ETFE" in the tables): "Fluon LM730AP" manufactured by AGC

[0088] <<Second Component>> The following raw materials for the second component were prepared: Calcium carbonate (1): "Whiten SB" manufactured by Shiraishi Calcium Co., Ltd. Calcium carbonate (2): "Bigot 15" manufactured by Shiraishi Kogyo Co., Ltd. Calcium carbonate (3): "BF300" manufactured by Bihoku Funka Co., Ltd. Magnesium oxide: "Kyowamag 150" manufactured by Kyowa Chemical Industry Co., Ltd. Hydrotalcite: "DHT-4A" manufactured by Kyowa Chemical Industry Co., Ltd. The average particle size of the second component used in each sample is as shown in the "Average particle size" column of "Second component" in Tables 1 to 3.

[0089] <Brominated Flame Retardants> The following brominated flame retardants were prepared. Brominated Flame Retardant (1): "SAYTEX8010" (ethylene bis pentabromobenzene) manufactured by Albemarle Japan. Brominated Flame Retardant (2): "SAYTEXBT-93" (ethylene bis tetrabromophthalimide) manufactured by Albemarle Japan.

[0090] <Zinc Oxide> The following zinc oxides were prepared: Zinc oxide (1): "Zinc oxide type 1" manufactured by Sakai Chemical Industry Co., Ltd. Zinc oxide (2): "Fine zinc oxide" manufactured by Sakai Chemical Industry Co., Ltd. The average particle size of the zinc oxide used in each sample is as shown in the "Average particle size" column of "Zinc oxide" in Tables 1 to 3.

[0091] Each raw material was mixed according to the formulation shown in the table to prepare a resin composition. In the table, "-" indicates that the corresponding component was not used.

[0092]

[0093]

[0094]

[0095] The resin composition was extruded onto the conductor to coat the conductor with the resin composition. An extrusion die was used for extrusion molding. The extrusion molding was performed at a die temperature of 250°C and a linear velocity of 5 m / min. Next, for samples other than sample 16, the resin composition was irradiated with an electron beam to obtain an insulated electric wire for each sample. The electron beam irradiation dose was 100 kGy. Sample 16 was not irradiated with an electron beam. In all samples, the average thickness of the insulating layer was 1 mm.

[0096] Although multiple insulated wires of Sample 102 were produced, they adhered to each other before the various measurements were performed, and the shape of the insulated wire could not be maintained. For this reason, the following various measurements were not performed on Sample 102. In Table 3, items for which measurements were not performed are indicated as "N / A."

[0097] For Sample 105, resin burn occurred during extrusion of the insulating layer, and a good insulating layer could not be formed. Therefore, the following measurements were not performed on Sample 105.

[0098] [Evaluation of Insulating Layer] The insulating layer of each sample of insulated wire was evaluated for storage modulus at 250°C, heat of fusion at 70°C or higher, 2% secant modulus, tensile strength and tensile elongation.

[0099] <Storage Modulus of Insulating Layer at 250° C.> The storage modulus of the insulating layer at 250° C. was measured based on the method described in embodiment 1 in accordance with the dynamic mechanical property testing method described in JIS K7244-4:1999.

[0100] <<Heat of Fusion of Insulating Layer at 70°C or Higher, Measured with a Differential Scanning Calorimeter>> The heat of fusion of the insulating layer at 70°C or higher, measured with a differential scanning calorimeter, was determined using a differential scanning calorimeter (trade name "DSC8500", manufactured by Perkin-Elmer) based on the method described in embodiment 1.

[0101] <Tensile Strength and Tensile Elongation of Insulating Layer> The tensile strength [MPa] and tensile elongation [%] of the insulating layer were measured in accordance with JIS K7161-2:2014. The test temperature was 23±2°C, the test humidity was 50±10%, and the test speed was 500 mm / min. In the present disclosure, an insulating layer is considered to have excellent tensile strength when the tensile strength is 10.3 MPa or more. In the present disclosure, an insulating layer is considered to have excellent tensile elongation when the tensile elongation is 200% or more.

[0102] <2% Secant Modulus of Insulating Layer> A 100 mm long insulating layer was pulled at a pulling rate of 50 mm / min using a tensile tester, and the load at which the elongation reached 2% was divided by the cross-sectional area to measure the tensile strength, which was then multiplied by 50 to obtain the 2% secant modulus. The test temperature was 23±2°C, the test humidity was 50±10%, and the test speed was 50 mm / min. In the present disclosure, an insulating layer is considered to have excellent flexibility when the 2% secant modulus is 120 MPa or less.

[0103] The evaluation results of the insulating layer are shown in Tables 1 to 3.

[0104] [Flame Retardancy Test] Five test samples were prepared for each insulated wire. The VW-1 vertical flame retardancy test described in UL Standards 1581, 1080 was performed on the five test samples. The test was conducted by repeatedly igniting the test sample for 15 seconds five times. The test passed if the fire was extinguished within 60 seconds, the absorbent cotton placed underneath was not burned by falling burning material, and the kraft paper attached to the top of the test sample was not burned or scorched. If all five samples passed the test, the test was evaluated as passing (OK). If even one of the five samples did not meet the passing level, the test was evaluated as failing (NG). The results are shown in the "Flame Retardancy Test" column of Tables 1 to 3.

[0105] [Smoke Generation Test] Test samples were prepared having the same composition as the insulating layer of each sample. All test samples except for sample 16 were irradiated with an electron beam. The test sample for sample 16 was not irradiated with an electron beam. Using the test samples, a smoke generation test was conducted using an NBS smoke chamber. The maximum value Dm of the specific optical density (Ds) specified in JIS C0081:2002 (IEC60695-6-31:1000) was measured. The results are shown in the "Smoke Generation Test Dm" column in Tables 1 to 3. If the maximum value Dm is 100 or less, it is determined that the smoke generation of the test sample during combustion is suppressed.

[0106] [Heat Deformation Test] In accordance with ISO 6722, a 0.7 mm thick edge was pressed against the surface of the insulating layer of each sample insulated wire, with a load according to the following formula 1, and the test was held in a 200°C atmosphere for 4 hours. Next, a voltage of 1 kV was applied to the insulated wire in water for 1 minute, and the presence or absence of dielectric breakdown was confirmed. Load [N] = 0.8 × √{i × (2D - i)} Formula 1 In the above formula 1, D: finished outer diameter of insulated wire [mm], i: thickness of insulator [mm].

[0107] If no dielectric breakdown occurred, the test was evaluated as passing (OK). If dielectric breakdown occurred, the test was evaluated as failing (NG). The results are shown in the "Thermal Deformation Test" column of Tables 1 to 3.

[0108] [Discussion] The insulated wires of Samples 1 to 16 correspond to Examples. It was confirmed that the insulated wires of Samples 1 to 16 (Examples) had an insulating layer with a 2% secant modulus of 120 MPa or less, excellent flexibility, an insulating layer with a tensile elongation of 200% or more, excellent flame retardancy that passed the flame retardancy test, and suppressed smoke generation during combustion.

[0109] The insulated wires of Samples 101 to 108 correspond to comparative examples. The insulated wire of Sample 101 had a 2% secant modulus of more than 120 MPa and was insufficient in flexibility. Multiple insulated wires of Sample 102 were produced, but they stuck together before various measurements were performed, and the insulated wire shape could not be maintained. Therefore, various measurements were not performed on Sample 102. In the smoke generation test, Sample 103 had a maximum Dm of 118, and smoke generation during combustion was not suppressed. Samples 104, 106, and 108 had insufficient tensile elongation, with tensile elongation less than 200%. In Sample 105, resin burn occurred during extrusion of the insulating layer, and a good insulating layer could not be formed. Therefore, various measurements were not performed on Sample 105. Sample 107 failed the flame retardancy test (NG).

[0110] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0111] 1 insulated wire, 2 conductor, 3 insulating layer, 10 heat shrinkable tube

Claims

1. An insulated wire comprising a conductor and an insulating layer covering the conductor, wherein the insulating layer is made of a composition containing a first component, a second component, a bromine-based flame retardant, and zinc oxide, the first component is composed of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer, the second component is composed of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite, in the composition, the ratio M2 / M1 of the mass M2 of the ethylene-tetrafluoroethylene copolymer to the mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less, in the composition, the content of the bromine-based flame retardant with respect to 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less, in the composition, the content of zinc oxide with respect to 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less, and in the composition, the total content of the second component with respect to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less.

2. The insulated wire according to claim 1, wherein the average particle size of the second component is 0.05 μm or more and 5 μm or less.

3. The insulated wire according to claim 1 or 2, wherein the average particle size of the zinc oxide is 0.05 μm or more and 5 μm or less.

4. The insulated wire according to any one of claims 1 to 3, wherein the storage modulus of the insulating layer at 250°C is 0.1 MPa or more and 10 MPa or less.

5. The insulated wire according to any one of claims 1 to 4, wherein the heat of fusion at 70°C or higher measured by a differential scanning calorimeter of the insulating layer is 1 J / g or more and 12 J / g or less.

6. The insulated wire according to any one of claims 1 to 5, wherein the content of the first component in the composition is 50% by mass or more.

7. The insulated wire according to any one of claims 1 to 6, wherein the insulating layer is an electron beam crosslinked product of the composition.

8. A composition comprising a first component, a second component, a brominated flame retardant, and zinc oxide, wherein the first component consists of a tetrafluoroethylene-propylene copolymer and an ethylene-tetrafluoroethylene copolymer, wherein the second component consists of at least one selected from the group consisting of magnesium oxide, calcium carbonate, and hydrotalcite, in the composition, the ratio M2 / M1 of the mass M2 of the ethylene-tetrafluoroethylene copolymer to the mass M1 of the tetrafluoroethylene-propylene copolymer is 10 / 90 or more and 40 / 60 or less, in the composition, the content of the brominated flame retardant with respect to 100 parts by mass of the first component is 1.0 part by mass or more and 40 parts by mass or less, in the composition, the content of zinc oxide with respect to 100 parts by mass of the first component is 1.0 part by mass or more and 25 parts by mass or less, in the composition, the total content of the second component with respect to 100 parts by mass of the first component is 5.0 parts by mass or more and 50 parts by mass or less, a heat-shrinkable tube.

9. The heat-shrinkable tube according to claim 8, which is a coating material for an electric wire.

10. The heat-shrinkable tube according to claim 8 or claim 9, wherein the composition is an electron beam crosslinked body.

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