Flame-retardant wire

Abstract

The present invention provides a flame-retardant electric wire which is excellent in the properties required of flame-retardant electric wires, such as mechanical properties, oil resistance, cold resistance, heat aging resistance, flexibility and operability, and has a halogen-free insulation layer. The flame-retardant electric wire (1) has a conductor (2) and an insulation layer (3) covering the outer periphery of the conductor (2) and composed of a resin composition. The resin composition contains 30 to 180 parts by mass of a flame retardant, 7 parts by mass or more of an antioxidant and 1 part by mass or more of a copper inhibitor relative to 100 parts by mass of a base polymer. The base polymer is composed of 50 to 90 parts by mass of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 45 to 60% by mass and 10 to 50 parts by mass of an ethylene-alpha-olefin copolymer. The flame retardant comprises a polymer surface-treated with a silane coupling agent and having a BET specific surface area of ​​6 m 2 / g or less of magnesium hydroxide and / or the above-mentioned aluminum hydroxide. In addition, the resin composition is cross-linked.

Description

Technical Field

[0001] The present invention relates to a flame-retardant electric wire, and more particularly to a flame-retardant electric wire having a halogen-free insulation layer. Background Art

[0002] Conventionally, polyolefin resins, which offer a good balance of oil resistance, fuel resistance, cold resistance, and flame retardancy, have been used as insulation materials for wires used in railway vehicles, automobiles, electrical equipment, and electronic devices. Furthermore, to further enhance flame retardancy, polyolefin resins containing halogen-based flame retardants are being used. Examples of polyolefin resins include polyvinyl chloride, polychloroprene rubber, chlorosulfonated polyethylene, chlorinated polyethylene, fluororubber, fluororesin, and polyethylene.

[0003] However, these materials containing a large amount of halogen produce a large amount of toxic and harmful gases when burned, and sometimes highly toxic dioxins are produced depending on the combustion conditions. Therefore, from the perspectives of fire safety and environmental load reduction, halogen-free materials that do not contain halogen have begun to be used as covering materials for electric wires.

[0004] Furthermore, wires used in railway vehicles and automobiles are being required to be thinner and lighter to save energy and improve fuel efficiency. Reducing the cross-sectional area of ​​the conductor while maintaining the same current capacity, and achieving thinner and lighter wires, increases the conductor's temperature, requiring the coating material to exhibit high heat aging resistance.

[0005] When electrical conductors reach high temperatures, wire coatings often use fluororubber or fluororesin, which offer excellent heat aging resistance. As mentioned above, these fluorochemical materials contain halogens. Therefore, in addition to fluorochemical materials, flame-retardant silicone rubber, which also offers excellent heat aging resistance, is used as a halogen-free coating material.

[0006] Because the base rubber itself is flame-retardant, silicone rubber does not require the addition of large amounts of flame retardants to achieve the high flame retardancy required for wires used in railway vehicles. Therefore, silicone rubber is an excellent material with both flame retardancy and electrical insulation properties.

[0007] For example, in Patent Document 1, a composition containing 50 to 200 parts by mass of a metal hydroxide, 0.5 parts by mass or more of a silicone rubber, 1 to 10 parts by mass of a hydroxybenzoyl isocyanurate compound, and 1 to 10 parts by mass of a thioester compound, per 100 parts by mass of a polyolefin, is used as a covering material for a flame-retardant electric wire.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 3-037908 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Silicone rubber is known to have inferior mechanical properties compared to other resins or rubbers. In particular, it is known to have low tear strength. For example, when using wires or cables coated with silicone rubber, the rubber will immediately crack if damaged, making it difficult to use in environments prone to damage.

[0013] Therefore, the Japanese Industrial Standard stipulates that in wires using silicone rubber (such as C3323 and C3315), if the tear strength of the silicone rubber used as the covering material is 25 kN / m or less, a reinforcement layer such as glass fiber braid must be provided on the outside of the silicone rubber.

[0014] Furthermore, the European standards for railway vehicle wires, EN50264-3-1 (single-core cables with narrow cross-linked elastomer insulation) and EN50382-2 (single-core cables with 120°C / 150°C rating silicone rubber insulation), have the same rated voltage. However, EN50382-2, which uses silicone rubber, ensures mechanical properties (tear strength, tensile strength, and elongation at break) by making the insulation layer thicker. Furthermore, EN50382-2, which has a sheath, ensures mechanical properties by making the sheath thicker.

[0015] However, using a glass fiber braid as a reinforcement layer, as specified in Japanese Industrial Standards, complicates the process by requiring the glass fiber braid to be processed during the wire end processing. Furthermore, short glass fibers generated when the glass fiber braid is cut can enter the joint, increasing the insulation resistance and causing abnormal heat generation.

[0016] Furthermore, even if the coating is thickened, as is the case with railroad wires, if the silicone rubber is damaged, cracks in the silicone rubber will immediately propagate regardless of the coating thickness. Therefore, it is difficult to say that these methods are a fundamental solution.

[0017] The main object of the present application has been made in view of the above-mentioned problems, and is to provide a flame-retardant electric wire having excellent properties required of flame-retardant electric wires, such as mechanical properties, oil resistance, cold resistance, heat aging resistance, flexibility, and handleability, and having a halogen-free insulation layer.

[0018] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings.

[0019] Solutions to Problems

[0020] The flame-retardant wire in one embodiment has a conductor and a first insulating layer covering the periphery of the conductor and composed of a first resin composition. The first resin composition contains 130 to 180 parts by mass of a flame retardant, 7 parts by mass or more of an antioxidant, and 1 part by mass or more of a copper inhibitor relative to 100 parts by mass of a base polymer. The base polymer is composed of 50 to 90 parts by mass of an ethylene vinyl acetate copolymer having a vinyl acetate content of 45 to 60% by mass and 10 to 50 parts by mass of an ethylene alpha olefin copolymer. The flame retardant comprises a silane coupling agent that has been surface-treated and has a BET specific surface area of ​​6 m 2 / g or less of magnesium hydroxide and / or aluminum hydroxide. The first resin composition is cross-linked.

[0021] Effects of the Invention

[0022] According to one embodiment, a flame-retardant electric wire can be provided that is excellent in the properties required of a flame-retardant electric wire, such as mechanical properties, oil resistance, cold resistance, heat aging resistance, flexibility, and handleability, and includes a halogen-free insulation layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional view showing a flame-retardant electric wire in the embodiment.

[0024] Figure 2 It is a cross-sectional view showing a flame-retardant electric wire in a modified example.

[0025] Figure 3 This is a table showing the mixing ratios of the respective materials in Examples 1 to 9.

[0026] Figure 4 This is a table showing the mixing ratios of the respective materials in Comparative Examples 1 to 11.

[0027] Figure 5 This is a table showing the pass / fail evaluation results of Examples 1 to 9 and Comparative Examples 1 to 11.

[0028] Explanation of symbols

[0029] 1: Flame-retardant wire, 2: Conductor, 3: Insulation layer, 3a: First insulation layer, 3b: Second insulation layer. DETAILED DESCRIPTION

[0030] The following embodiments are described in detail based on the accompanying drawings. In all drawings used to illustrate the embodiments, components having the same functions are denoted by the same reference numerals, and their repeated descriptions are omitted. Furthermore, in the following embodiments, descriptions of identical or similar parts are not repeated in principle, except where specifically required.

[0031] In the following description, when a numerical range is specified, for example, as "1 to 10 parts by mass," "1 to 10 parts by mass" means "1 part by mass or more and 10 parts by mass or less." The same applies to other numerical ranges and other units.

[0032] Hereinafter, the flame-retardant electric wire (flame-retardant cable) 1 in this embodiment will be described.

[0033] like Figure 1 As shown, a flame-retardant wire 1 includes a conductor 2 and an insulating layer 3 covering the outer periphery of the conductor 2. The conductor 2 may be a single conductive wire or a stranded wire assembly consisting of a plurality of twisted conductive wires. Such a conductive wire is made of, for example, a metal material such as copper or a copper alloy. Alternatively, a plating layer made of a metal material such as tin or nickel may be formed on the surface of the conductive wire.

[0034] It should be noted that, in the present application, expressions such as "insulating layer 3 covering the outer periphery of conductor 2" mean that insulating layer 3 is located around conductor 2. Furthermore, the above expression includes a case where conductor 2 and insulating layer 3 are in direct contact, and also includes a case where a space or other structure exists between conductor 2 and insulating layer 3, and conductor 2 and insulating layer 3 are adjacent to each other through the space or other structure.

[0035] Insulating layer 3 is composed of a halogen-free resin composition. This resin composition uses a polyolefin as its base polymer, which exhibits superior mechanical properties (tear strength, tensile strength, and elongation at break) compared to silicone rubber. The base polymer contains 50-90 parts by mass of an ethylene-vinyl acetate copolymer (45-60% by mass of vinyl acetate) and 10-50 parts by mass of an ethylene-alpha-olefin copolymer.

[0036] The properties of ethylene-vinyl acetate copolymers vary depending on the vinyl acetate content. It is known that high vinyl acetate content improves flexibility and oil resistance, but deteriorates cold resistance and makes handling difficult due to stickiness. For example, when the vinyl acetate content is less than 45% by mass, the flexibility and oil resistance of the ethylene-vinyl acetate copolymer deteriorate, while when the vinyl acetate content exceeds 60% by mass, the cold resistance of the ethylene-vinyl acetate copolymer deteriorates.

[0037] Ethylene-vinyl acetate copolymers containing 45% by mass or more of vinyl acetate do not exhibit crystallinity, thereby improving flexibility and oil resistance as described above, while maintaining cold resistance. However, due to stickiness, handling during and after molding becomes difficult. Therefore, by blending an ethylene-α-olefin copolymer with the ethylene-vinyl acetate copolymer, the difficulty in handling caused by stickiness can be eliminated.

[0038] On the other hand, when the ethylene-α-olefin copolymer is less than 10 parts by mass, stickiness cannot be improved. In addition, when the ethylene-α-olefin copolymer is more than 50 parts by mass, the overall properties of the base polymer deteriorate and oil resistance cannot be satisfactory.

[0039] The hardness of the ethylene-α-olefin copolymer is not particularly limited, but in order to obtain flexibility, the durometer A hardness of the ethylene-α-olefin copolymer is preferably 60 or less. This allows the flame-retardant wire 1 to have a durometer A hardness of 80 or less.

[0040] Furthermore, when the ethylene-α-olefin copolymer is a block copolymer and the melting point of the crystal of the ethylene-α-olefin copolymer is 110° C. or higher, the oil resistance of the flame-retardant electric wire 1 can be further improved.

[0041] Furthermore, by introducing or grafting an organic acid such as maleic acid, maleic anhydride, fumaric acid, or carboxylic acid to the terminal of a base polymer in a portion of the ethylene-α-olefin copolymer, the mechanical properties and cold resistance of the flame-retardant electric wire 1 can be improved.

[0042] Furthermore, when the ethylene-α-olefin copolymer is an acid-modified ethylene-α-olefin copolymer copolymerized with an organic acid such as maleic acid, maleic anhydride, fumaric acid, or carboxylic acid, the mechanical properties and cold resistance of the flame-retardant electric wire 1 can also be improved.

[0043] 130 to 180 parts by mass of a flame retardant is added to the base polymer relative to 100 parts by mass of the base polymer. This imparts high flame retardancy to the flame-retardant wire 1, which passes the vertical tray flame retardancy test specified in IEEE 1202 or IEC 60332. Furthermore, surface treatment with a silane coupling agent is effective for imparting oil resistance to the flame-retardant wire 1. By using a silane coupling agent to firmly bond the flame retardant particles to the base polymer, the resin composition's oil absorption can be reduced, thereby imparting oil resistance to the flame-retardant wire 1.

[0044] The flame retardant is, for example, magnesium hydroxide and / or aluminum hydroxide surface-treated with a silane coupling agent. When the flame retardant is less than 130 parts by mass, the flame retardancy is deteriorated, and when the flame retardant is more than 180 parts by mass, the mechanical properties, flexibility, and cold resistance are deteriorated.

[0045] The type of silane coupling agent is not particularly limited. However, when crosslinking is performed using ionizing radiation or an organic peroxide, the functional group of the silane coupling agent is preferably a vinyl group, a methacryloyl group, or an acryloyl group in order to facilitate bonding with the base polymer.

[0046] Fluctuations in the oil resistance of the flame-retardant wire 1 are primarily caused by swelling of the resin composition due to oil absorption and the associated changes in its mechanical properties (tensile strength and elongation at break). In the resin composition of the present application, elongation at break may decrease after oil resistance testing. While treatments to minimize oil absorption into the resin composition are necessary for swelling and tensile strength, additional treatments are required to reduce elongation at break.

[0047] Regarding the reduction of elongation at break in oil resistance, the inventors of this application focused on the BET specific surface area of ​​the flame retardant (magnesium hydroxide and / or aluminum hydroxide surface-treated with a silane coupling agent). The clear reason cannot be determined, but it is known that by using a flame retardant with a BET specific surface area of ​​6 m 2 / g or less, can suppress the decrease in elongation at break.

[0048] It should be noted that the BET specific surface area described here is measured using the nitrogen adsorption method, which uses the BET equation to calculate the specific surface area from the isothermal absorption curve of nitrogen gas at liquid nitrogen temperature (77K). The BET equation was proposed by S. Brunauer, P.H. Emmett, E. Teller, and others and is represented by the following "Equation 1." Vm is the volume of the gas adsorbed in the first layer, V is the volume of the adsorbed gas, P is the pressure within the sample cell, and P0 is the saturated vapor pressure.

[0049] P / V(P0-P)=(1 / VmC)+((C-1) / VmC)×P / P0 Formula 1

[0050] This "Formula 1" is applied in the range of P / P0 from 0.05 to 0.35. When P / P0 is plotted on the horizontal axis and P / V (P0 to P) is plotted on the vertical axis, a straight line is obtained. Vm can be calculated from the intercept and slope of this straight line. In addition, the BET specific surface area is calculated using the following "Formula 2". SA is the surface area of ​​the sample, Vm is the volume of the gas adsorbed in the first layer, N is Avogadro's constant, and Am is the area occupied by one molecule of nitrogen (0.162 nm 2 ).

[0051] SA=Vm×N×Am Formula 2

[0052] There is no specific lower limit for the BET specific surface area. However, the average particle size of the flame retardant particles (the average particle size of the magnesium hydroxide and / or aluminum hydroxide particles surface-treated with a silane coupling agent) that is relevant to the BET specific surface area is preferably approximately 1 to 2 μm. When the average particle size is less than 1 μm, dispersibility is poor, particles agglomerate, processability deteriorates, and elongation at break decreases. When the average particle size is greater than 2 μm, cold resistance deteriorates and elongation at break decreases.

[0053] The flame-retardant wire 1 of this embodiment is intended to be used in applications requiring high heat aging resistance at a rated temperature of 120°C or higher. Therefore, the resin composition constituting the insulating layer 3 preferably maintains an elongation at break of 50% after a heat aging test equivalent to 20,000 hours at 140°C in accordance with EN50305.

[0054] To impart heat aging resistance as high as that of silicone rubber to the flame-retardant wire 1, 7 parts by mass or more of an antioxidant is added to the resin composition per 100 parts by mass of the base polymer. The antioxidant is preferably a phenolic antioxidant or a sulfur-based antioxidant, or a mixture thereof.

[0055] When the antioxidant content is less than 7 parts by mass, an elongation at break of 50% cannot be maintained after a heat aging test equivalent to 20,000 hours at 140°C. There is no particular upper limit on the amount of antioxidant added. However, when the antioxidant content exceeds 10 parts by mass, crosslinking may be hindered during crosslinking using ionizing radiation or an organic peroxide, and the oozing antioxidant may impair the appearance of the flame-retardant wire 1. Therefore, when crosslinking the resin composition, it is most preferred to add 7 to 10 parts by mass of the antioxidant to the resin composition relative to 100 parts by mass of the base polymer.

[0056] To further improve the heat aging resistance of the flame-retardant wire 1, a copper inhibitor is added to the resin composition at a ratio of 1 part by mass to 100 parts by mass of the base polymer. The copper inhibitor is preferably bis[2-(2-hydroxybenzoyl)hydrazide]dodecanediol (e.g., CDA-6 manufactured by ADEKA), bis(2-phenoxypropionohydrazide)isophthalic acid (e.g., QuinoxAX manufactured by MITSUIFINE CHEMICAL), or a mixture thereof.

[0057] By using such a copper inhibitor, copper ions transferred from the conductor 2 can be captured, thereby suppressing degradation of the conductor 2 due to oxidation. A copper inhibitor is also added to the resin composition to capture metal ions contained as impurities in the antioxidant. There is no particular upper limit on the amount of copper inhibitor added. However, due to the high cost of copper inhibitors, the amount of copper inhibitor added is preferably as small as possible.

[0058] To prevent deformation caused by heating and improve mechanical properties, the resin composition is preferably crosslinked. The crosslinking agent and crosslinking method are not particularly limited, but preferred methods include peroxide crosslinking using an organic peroxide crosslinking agent, radiation crosslinking using ionizing radiation, or silane hydrocrosslinking, in which a silane coupling agent is grafted onto a base polymer using an organic peroxide and crosslinked hydrothermally. Peroxide crosslinking and radiation crosslinking are particularly preferred.

[0059] As required, additives such as lubricants, flame retardant aids, crosslinking agents, crosslinking aids, crosslinking accelerators, surfactants, compatibilizers, ultraviolet light absorbers, or hindered amine light stabilizers (HALS) may also be suitably added to the resin composition. Particularly when high flame retardancy is required, it is preferred to add, in the resin composition, phosphorus-based flame retardants represented by red phosphorus, phosphate derivatives, or intumescent flame retardants, nitrogen-based flame retardants represented by melamine cyanurate derivative mixtures, catechol, gallic acid derivatives, or polyphenol compounds or silicone-based flame retardants as flame retardant aids.

[0060] (Variation)

[0061] Figure 2 A flame-retardant electric wire 1 according to a modified example of the present embodiment is shown.

[0062] like Figure 2 As shown in FIG. 1 , in a modified example, the insulating layer 3 is composed of multiple layers. Figure 2 , the outermost first insulating layer 3 a and the second insulating layer 3 b provided between the first insulating layer 3 a and the conductor 2 are shown, but the insulating layer 3 may be composed of three or more layers.

[0063] The outermost first insulating layer 3a is composed of the same resin composition as the insulating layer 3 described in the embodiment. The inner second insulating layer 3b may be composed of the same composition as the resin composition of the first insulating layer 3a, or may be composed of a different composition from the resin composition of the first insulating layer 3a, such as flame-retardant silicone rubber or a polyolefin-based composition with high electrical insulation properties.

[0064] Specifically, if the flame-retardant wire 1 is exposed to a harsh external environment, it is preferable to provide a first insulating layer 3a having excellent mechanical properties, oil resistance, cold resistance, and heat aging resistance on the outermost periphery. Thus, the resin composition is applied to at least the outermost first insulating layer 3a of the multilayer insulating layer.

[0065] (Example)

[0066] Below, use Figure 3 and Figure 4 , Examples 1 to 9 and Comparative Examples 1 to 11 of the flame-retardant electric wire 1 are described, using Figure 5 , and explain the judgment of whether they are qualified or not.

[0067] like Figure 3 As shown, in Examples 1 to 9, the compounding ingredients for forming the insulating layer 3 (resin composition) were distributed so as to have a compounding ratio within the following numerical ranges.

[0068] Vinyl acetate content: 45-60% by mass

[0069] Ethylene vinyl acetate copolymer: 50-90 parts by mass

[0070] Ethylene α-olefin copolymer: 10-50 parts by mass

[0071] Magnesium hydroxide (flame retardant): 130-180 parts by mass

[0072] Antioxidant: 7 parts by mass or more

[0073] Copper inhibitor: 1 part by mass or more

[0074] On the other hand, Figure 4 As shown, in Comparative Examples 1 to 11, the compounding ratios of the compounding ingredients used to form the insulating layer 3 (resin composition) were distributed so that at least one of the compounding ratios was outside the above numerical range. It should be noted that the compounding ratios of carbon, crosslinking aid, and crosslinking agent were distributed identically in Examples 1 to 9 and Comparative Examples 1 to 11.

[0075] First, Figure 3 and Figure 4 The compounding ingredients were weighed in the indicated proportions and kneaded in a 75L pressure kneader to form a kneaded product. The kneaded product was then extruded into a long strip, cooled, and then processed into pellets.

[0076] Next, a predetermined amount of a liquid crosslinking agent heated to 40° C. is prepared. Next, the pelletized kneaded material and the crosslinking agent are stirred with a stirrer to impregnate the pelletized kneaded material with the crosslinking agent, thereby forming a pelletized resin composition.

[0077] Next, prepare the conductor 2. The conductor 2 can be a single conductive wire or a stranded wire formed by twisting multiple conductive wires. Such a conductive wire is made of a metal material such as copper or a copper alloy. Furthermore, if necessary, a plating layer made of a metal material such as tin or nickel can be formed on the surface of the conductive wire. The cross-sectional area of ​​the conductor 2 thus formed is, for example, 70 mm. 2 The outer diameter of the conductor 2 (the diameter of the outer circumference of the conductor 2) is, for example, 11 mm.

[0078] Next, in order to prevent the resin composition from sinking into the conductor 2, a film tape made of polyethylene terephthalate is wound around the outer periphery of the conductor 2. The thickness of the film tape is, for example, 0.15 mm. Figure 1 Next, using an extruder, the resin composition is coated on the outer periphery of the conductor 2 via the film tape so that the thickness of the resin composition becomes, for example, 3.6 mm.

[0079] Next, the internal pressure is set to 1.8 MPaG, and the resin composition is heated for 5 minutes in a chamber filled with saturated water vapor. Figure 1 The flame-retardant electric wire 1 has an outer diameter (a diameter of the outer periphery of the flame-retardant electric wire 1) of, for example, 18.5 mm.

[0080] Hereinafter, evaluation items and evaluation methods of the flame-retardant electric wire 1 will be described.

[0081] <Initial tensile test>

[0082] First, the flame-retardant wire 1 was disassembled by removing the conductor 2 and separating the insulating layer 3 from the conductor 2. Next, the insulating layer 3 was ground to a smooth inner circumference, adjusting its thickness to approximately 1 mm. The ground insulating layer 3 was then punched out to form a dumbbell shape as specified in IEC 60811-1-1, which served as a test specimen. The specimen was pulled at a speed of 250 mm / min using a tensile testing machine, and the tensile strength and elongation at break were measured.

[0083] <Oil resistance>

[0084] An oil resistance test was conducted in accordance with Item 10 of EN60811-2-1. First, a dumbbell-shaped specimen was prepared in the same manner as in the initial tensile test, and the specimen was immersed in IRM903 oil at 70°C for 168 hours. Next, the specimen was stretched at a speed of 250 mm / min using a tensile testing machine to measure the tensile strength and elongation at break. Next, the rate of change between the results of the initial tensile test and the results of the oil resistance test was calculated. For tensile strength, specimens with a rate of change of within ±30% were considered qualified, and for elongation at break, specimens with a rate of change of within ±40% were considered qualified.

[0085] <Determination of Durometer A Hardness>

[0086] A type A durometer specified in JIS K6253-3 was pressed against the produced flame-retardant electric wire 1, and after 3 seconds, the durometer A hardness was measured with the durometer. A flame-retardant electric wire 1 having a durometer A hardness of 80 or less was considered acceptable.

[0087] <Cold resistance at -50℃>

[0088] Cold resistance testing was conducted in accordance with Section 8.3 of EN60811-1-4. First, dumbbell-shaped specimens were prepared in the same manner as for the initial tensile test and cooled at -50°C for at least 4 hours. Next, the specimens were stretched at a rate of 25 mm / min at -50°C using a tensile testing machine. Samples with an elongation at break of 30% or greater were considered acceptable.

[0089] <Heat aging resistance at 140°C>

[0090] Dumbbell-shaped specimens were prepared in the same manner as for the initial tensile test and subjected to long-term heat aging testing using the method specified in Section 7.3 of EN50305. After the heat aging test, an Arrhenius plot was generated based on the time required to reach 50% elongation at break. The plotted points were extrapolated, and specimens that maintained 20,000 hours or more of elongation at 140°C after the heat aging test were considered acceptable. In other words, specimens that maintained 50% elongation at break after 20,000 hours of heat aging at 140°C were considered acceptable.

[0091] <Flame retardancy>

[0092] The flame-retardant electric wire 1 produced was subjected to a vertical tray burning test in accordance with IEC 60332-3, and the flame-retardant electric wire 1 was judged to be acceptable.

[0093] <Sticky>

[0094] The operator palpated the produced flame-retardant electric wire 1 and determined that the flame-retardant electric wire 1 was clearly sticky to be unacceptable.

[0095] As described above, comprehensive evaluation was performed on the evaluation items of oil resistance, durometer A hardness, cold resistance at -50°C, heat aging resistance at 140°C, flame retardancy, and tack.

[0096] like Figure 5 As shown, all flame-retardant wires 1 of Examples 1 to 9 passed the comprehensive evaluation. On the other hand, all flame-retardant wires 1 of Comparative Examples 1 to 11 failed some evaluation items and were therefore comprehensively evaluated as unqualified. Therefore, the following results indicate that the flame-retardant wire 1 of this embodiment not only has a halogen-free insulation layer 3 but also exhibits excellent properties required of a flame-retardant wire 1, including mechanical properties, oil resistance, cold resistance, heat aging resistance, flexibility, and ease of handling.

[0097] As mentioned above, although this invention was specifically described based on the said embodiment, this invention is not limited to the said embodiment, Various changes are possible within the range which does not deviate from the summary.

Claims

1. A flame-retardant electric wire comprising a conductor and a first insulating layer covering the outer periphery of the conductor and comprising a first resin composition, The first resin composition contains 130 to 180 parts by mass of a flame retardant, 7 parts by mass or more of an antioxidant, and 1 part by mass or more of a copper inhibitor relative to 100 parts by mass of a base polymer. The base polymer is composed of 50 to 90 parts by mass of an ethylene vinyl acetate copolymer having a vinyl acetate content of 45 to 60% by mass and 10 to 50 parts by mass of an ethylene α-olefin copolymer. The flame retardant comprises a silane coupling agent that is surface treated and has a BET specific surface area of ​​6 m 2 / g or less of magnesium hydroxide and / or aluminum hydroxide, The first resin composition is cross-linked.

2. The flame-retardant electric wire according to claim 1, wherein The ethylene alpha olefin copolymer is a block copolymer, The melting point of the crystal of the ethylene-α-olefin copolymer is 110° C. or higher.

3. The flame-retardant electric wire according to claim 1, wherein The ethylene α-olefin copolymer is an acid-modified ethylene α-olefin copolymer copolymerized with maleic acid, maleic anhydride, fumaric acid or carboxylic acid.

4. The flame-retardant electric wire according to claim 1, wherein The flame retardant particles have an average particle size of 1 μm or more and 2 μm or less.

5. The flame-retardant electric wire according to claim 1, wherein A second insulating layer is provided between the first insulating layer and the conductor, The second insulating layer may be made of the same composition as the first resin composition or a composition different from the first resin composition.

6. The flame-retardant electric wire according to claim 1, wherein The flame-retardant electric wire has a Durometer A hardness of 80 or less.

7. The flame-retardant electric wire according to claim 1, wherein In a long-term heat aging test specified in EN50305, the first insulating layer maintains an elongation at break of 50% after a heat aging test at 140° C. for 20,000 hours.

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