Halogen-free flame-retardant resin composition, electric wire, and cable

Abstract

To provide a non-halogen flame-retardant resin composition having excellent flexibility and excellent oil resistance and processability, and to provide an electric wire and a cable.SOLUTION: The non-halogen flame-retardant resin composition comprises a base polymer comprising (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of ≥ 60 mass%, (b) an ethylene-based copolymer having a melting point of ≥ 115 °C and a specific gravity of ≤ 0.9, and (c) an acid-modified ethylene-based copolymer, a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a halogen-free flame-retardant resin composition, an electric wire, and a cable. [Background technology]

[0002] Electric wires and cables used in vehicles such as railway cars and automobiles are required to have oil resistance, heat resistance, flame retardancy, etc., depending on the environment in which they are used. It is known that adding halogen-based flame retardants or phosphorus-based flame retardants such as red phosphorus can provide high flame retardancy.

[0003] However, halogen-based flame retardants generate halogen gases during combustion, which makes them inadequate for addressing growing environmental concerns worldwide. Phosphorus-based flame retardants, such as red phosphorus, also generate phosphine during combustion and phosphoric acid during disposal, which can contaminate groundwater veins.

[0004] On the other hand, metal hydroxides do not cause the problems described above compared to halogen-based flame retardants or phosphorus-based flame retardants, but they require high loadings. Also, it is known that polar polymers such as ethylene vinyl acetate copolymers can be used to achieve high fuel resistance (e.g., Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2024-25002 [Patent Document 2] Patent No. 5907015 Publication [Patent Document 3] Patent No. 5733352 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when ethylene vinyl acetate copolymer is highly filled with metal magnesium hydroxide, the mechanical properties and heat resistance are reduced, and the moldability is also reduced due to the increased viscosity.

[0007] Furthermore, with the recent advancement of technology, the number of electrical wiring circuits has increased, leading to a growing need for space savings. One way to achieve this is to reduce the diameter of electrical wires. While this can be achieved by reducing the thickness of the insulation, it becomes difficult to ensure resistance to external damage. While it is possible to reduce the diameter by reducing the conductor size while maintaining the same thickness, this increases the conductor resistance and leads to more pronounced heat generation, necessitating further improvements in the heat resistance of the insulation material. The instantaneous improvement in the heat resistance of polymer-based insulation materials can be achieved by crosslinking, which maintains their shape and simultaneously improves properties such as oil resistance. Furthermore, long-term heat resistance, such as heat aging resistance, can be achieved by adding antioxidants. However, antioxidants can capture radicals generated during the crosslinking process and inhibit crosslinking. Insufficient crosslinking can lead to problems such as thermal deformation and reduced oil resistance.

[0008] An object of the present invention is to provide a halogen-free flame-retardant resin composition, an electric wire, and a cable that have excellent flexibility, oil resistance, and processability.

[0009] Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0010] A halogen-free flame-retardant resin composition according to one embodiment includes a base polymer having (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant, wherein the content of the metal hydroxide is 130 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the base polymer, the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer, the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base polymer, and the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer, and the maximum bending stress is 2.0 MPa or less.

[0011] An electric wire according to one embodiment includes a conductor and an insulating layer provided around the conductor, wherein the insulating layer is made of a halogen-free flame-retardant resin composition including a base polymer having (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant, and the content of the metal hydroxide in the base polymer is the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer; the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base polymer; the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer; and the maximum bending stress of the halogen-free flame-retardant resin composition is 2.0 MPa or less.

[0012] A cable according to one embodiment includes a conductor, an insulating layer disposed around the conductor, and a coating layer disposed around the insulating layer, wherein the coating layer is made of a halogen-free flame-retardant resin composition including a base polymer having (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant, and wherein the metal hydroxide The content is 130 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the base polymer, the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer, the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base polymer, the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer, and the maximum bending stress of the halogen-free flame-retardant resin composition is 2.0 MPa or less. [Effects of the Invention]

[0013] According to one embodiment, it is possible to provide a halogen-free flame-retardant resin composition, an electric wire, and a cable that have excellent flexibility, oil resistance, and processability. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing an example of the structure of an electric wire according to an embodiment; [Figure 2] 1 is a cross-sectional view showing an example of the structure of a cable according to an embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described below with reference to the drawings. In all the drawings for explaining the embodiment, components having the same functions are designated by the same reference numerals, and repeated explanations thereof will be omitted. Furthermore, in the following embodiment, explanations of identical or similar parts will not be repeated unless specifically required.

[0016] <Halogen-free flame-retardant resin composition> The halogen-free flame-retardant resin composition of this embodiment will be described in detail below.

[0017] The halogen-free flame-retardant resin composition according to the present embodiment contains a base polymer, a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant.

[0018] (Base polymer) In this embodiment, the base polymer includes (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer. The base polymer may further include a polyolefin.

[0019] (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more; Ethylene-vinyl acetate copolymer (EVA) is composed of a non-polar ethylene moiety and a polar vinyl acetate moiety. Because the IRM902 or IRM903 test oil used in oil resistance tests is a non-polar oil, the presence of a large amount of polar EVA moieties reduces the affinity between the resin composition and the test oil. This improves the oil resistance of the resin composition. Therefore, the vinyl acetate content of the ethylene-vinyl acetate copolymer is 60% by mass or more. Furthermore, when the vinyl acetate content of the ethylene-vinyl acetate copolymer is 60% by mass or more, the filler acceptance of the resin composition can be improved. As a result, the elongation properties of the resin composition can be improved.

[0020] The ratio of (a) ethylene vinyl acetate copolymer with a vinyl acetate content of 60% by mass or more to the base polymer is preferably 40% by mass or more and 80% by mass or less. If (a) ethylene vinyl acetate copolymer with a vinyl acetate content of 60% by mass or more exceeds 80% by mass, EVA with a high vinyl acetate content has high polarity, which may cause materials to stick together. This may make the materials difficult to handle. If (a) ethylene vinyl acetate copolymer with a vinyl acetate content of 60% by mass or more is less than 40% by mass, the receptivity of flame retardants may decrease. The material used in the outermost layer of electric wires and cables preferably contains ethylene vinyl acetate copolymer (EVA).

[0021] (b) an ethylene copolymer having a melting point of 115°C or higher and a specific gravity of 0.9 or lower; The affinity between non-polar oils and resin compositions can also be suppressed by crystallization. Ethylene-based copolymers with high melting points have a large amount of crystals, which can prevent the IRM902 or IRM903 test oil used in oil resistance tests from penetrating between polymer molecules, thereby suppressing changes in physical properties. Therefore, the base polymer contains an ethylene-based copolymer with a melting point of 115°C or higher. The melting point of the ethylene-based copolymer is a value measured by differential scanning calorimetry (DSC). The ethylene-based polymer may be any polymer containing ethylene as a monomer, and includes polyethylene as well as ethylene-based copolymers containing ethylene and other monomers. The ethylene-based copolymer is preferably a copolymer having ethylene and an α-olefin as structural units.

[0022] Polyolefins and ethylene copolymers with a melting point of 115°C or higher include low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), linear very-low-density polyethylene (VLDPE), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-glycidyl methacrylate copolymer (EGMA), ethylene-butene-hexene terpolymer, ethylene-propylene-diene terpolymer (EPDM), ethylene-octene copolymer (EOR), ethylene copolymer polypropylene, ethylene-propylene copolymer (EPR), poly-4-methyl-pentene-1, maleic acid grafted low-density poly Examples of such copolymers include ethylene, hydrogenated styrene-butadiene copolymer (H-SBR), maleic acid grafted linear low-density polyethylene, copolymers of ethylene and an α-olefin having 3 to 30 carbon atoms, ethylene-styrene copolymer, maleic acid grafted ethylene-methyl acrylate copolymer, maleic acid grafted ethylene-vinyl acetate copolymer, ethylene-maleic anhydride copolymer, ethylene-ethyl acrylate-maleic anhydride terpolymer, ethylene-propylene-butene-1 terpolymers with butene-1 as the main component, ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-octene-1 copolymer, and other ethylene-α-olefin copolymers and olefin block copolymers.

[0023] The base polymer preferably contains an ethylene copolymer having a density of 0.9 g / cm or less. That is, the base polymer preferably contains an ethylene copolymer having a specific gravity of 0.9 or less. When the base polymer contains an ethylene copolymer having a density of 0.9 g / cm or less, the flexibility and oil resistance imparted to the resin composition are good.

[0024] The base polymer preferably contains an ethylene-α-olefin having a density of 0.9 g / cm3 or less, which can further improve the flexibility and oil resistance of the resin composition. Specific examples of olefin block copolymers include D9000, D9007, D9100, D9107, D9500, D9507, D9530, D9807, and D9817 from the INFUSE series, trade name of The Dow Chemical Company.

[0025] The base polymer can be a single or multiple blend of ethylene-α-olefin copolymers having a melting point of 115° C. or higher.

[0026] The total proportion of components (a) and (b) relative to the base polymer is preferably 70% by mass or more. If the total proportion of components (a) and (b) relative to the base polymer is less than 70% by mass, the oil resistance of the resin composition may be insufficient. The total proportion of components (a) and (b) relative to the base polymer is preferably 90% by mass or less. If the total proportion of components (a) and (b) relative to the base polymer exceeds 90% by mass, the low-temperature properties of the resin composition may be reduced.

[0027] (c) Acid-modified ethylene copolymer The acid-modified ethylene copolymer is an ethylene copolymer that has been acid-modified. The acid-modified ethylene copolymer can strengthen adhesion to fillers such as flame retardants and can also improve mechanical properties such as tensile strength. Therefore, the base polymer contains an acid-modified ethylene copolymer.

[0028] Ethylene copolymers before acid modification include low-density polyethylene (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), linear very-low-density polyethylene (VLDPE), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), ethylene-glycidyl methacrylate copolymer (EGMA), ethylene-butene-hexene terpolymer, ethylene-propylene-diene terpolymer (EPDM), ethylene-octene copolymer (EOR), and ethylene copolymer polyethylene. Examples of suitable olefin copolymers include polypropylene, ethylene-propylene copolymer (EPR), poly-4-methyl-pentene-1, hydrogenated styrene-butadiene copolymer (H-SBR), copolymers of ethylene with α-olefins having 3 to 30 carbon atoms, ethylene-styrene copolymers, ethylene-propylene-butene-1 terpolymers containing butene-1 as the main component, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers, ethylene-octene-1 copolymers, and low-density polyethylene olefin block copolymers. Among these, ethylene-butene-1 copolymers, ethylene-hexene-1 copolymers, and ethylene-octene-1 copolymers are preferred because they have little crystallinity, can accept fillers, and can achieve flexibility. Examples of acids used for modification include maleic acid, maleic anhydride, and fumaric acid.

[0029] The ratio of component (a) to component (b) in the base polymer ((a):(b)) is not particularly limited, but is preferably 1:1 to 5:1, and more preferably 2:1 to 4:1. Component (c) may or may not be added, but its addition is preferred as it is expected to improve mechanical properties. The ratio of component (b) to component (c) in the base polymer ((b):(c)) is not particularly limited, but is preferably 1:1 to 10:1, and more preferably 2:1 to 3:1.

[0030] (metal hydroxide) The metal hydroxide is added as a flame retardant. Examples of the metal hydroxide include magnesium hydroxide, aluminum hydroxide, and calcium hydroxide. The metal hydroxide is preferably at least one selected from magnesium hydroxide and aluminum hydroxide. Among the metal hydroxides, magnesium hydroxide has a decomposition temperature close to that of the polymer, so it can effectively exhibit high flame retardancy. The content of the metal hydroxide is 130 parts by mass or more and 200 parts by mass or less per 100 parts by mass of the base polymer. If the content of the metal hydroxide is less than 130 parts by mass, the resin composition may not have sufficient flame retardancy. If the content of the metal hydroxide is more than 200 parts by mass, the breaking elongation of the resin composition may be reduced.

[0031] Taking into consideration dispersibility, etc., the metal hydroxide can be surface-treated with a silane coupling agent, a titanate coupling agent, a fatty acid such as stearic acid, etc. Since the silane coupling agent has excellent reinforcing effect and aging properties, it is preferable that the metal hydroxide be surface-treated with a silane coupling agent.

[0032] In addition to metal hydroxides, flame retardant aids can be added to enhance the flame retardant effect. However, it is preferable not to add phosphorus-based flame retardants such as red phosphorus or triazine-based flame retardants such as melamine cyanurate because they generate phosphine gas and cyanide gas, which are harmful to the human body. Examples of flame retardant aids other than phosphorus-based flame retardants and triazine-based flame retardants include clay, silica, zinc stannate, zinc borate, calcium borate, hydroxide dolomide, and silicone.

[0033] (metal chelating agent) Metal chelating agents can suppress metal damage caused by impurities contained in fillers, etc. For this reason, metal chelating agents are added to resin compositions. The metal chelating agent is preferably at least one selected from dodecanedioic acid bis[N2-(2-hydroxybenzoyl)hydrazide] and isophthalic acid bis(2-phenoxypropionylhydrazide). An example of dodecanedioic acid bis[N2-(2-hydroxybenzoyl)hydrazide] is CDA-6 manufactured by ADEKA. An example of isophthalic acid bis(2-phenoxypropionylhydrazide) is Qunox AX manufactured by Mitsui Chemicals Fine Chemicals.

[0034] The content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base polymer.

[0035] (acrylic plasticizer) High loading of metal hydroxides may increase the viscosity of the resin composition, potentially reducing the processability of the resin composition. Adding process oil is effective for reducing the viscosity of the resin composition. Typical non-polar hydrocarbon oils have poor affinity with the EVA used in this embodiment, which may lead to bleed-out. Acrylic oils are highly polar and have good affinity with EVA with a high VA content. Therefore, an acrylic plasticizer is added to the resin composition.

[0036] The content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base polymer. If the content of the acrylic plasticizer is less than 1 part by mass, the viscosity of the resin composition may increase. If the content of the acrylic plasticizer is more than 10 parts by mass, the resin composition may become sticky and the handleability of the resin composition may decrease.

[0037] (antioxidant) To achieve high heat aging resistance, an antioxidant is added to the resin composition. The antioxidant is preferably at least one selected from phenolic antioxidants and sulfur-based antioxidants. The content of the antioxidant is 5 to 10 parts by mass per 100 parts by mass of the base polymer.

[0038] (others) In addition to the above, the resin composition may contain, as necessary, a crosslinking agent, a crosslinking aid, a flame retardant, a flame retardant aid, an ultraviolet absorber, a light stabilizer, a softener, a lubricant, a colorant, a reinforcing agent, a surfactant, an inorganic filler, an antioxidant, a plasticizer, a metal chelating agent, a foaming agent, a compatibilizer, a processing aid, a stabilizer, or the like.

[0039] The resin composition is preferably crosslinked. Crosslinking is an important property for ensuring the oil resistance of the resin composition. Examples of crosslinking treatments include, but are not limited to, chemical crosslinking using organic peroxides, sulfur compounds, silanes, etc., irradiation crosslinking using electron beams, radiation, etc., and crosslinking using other chemical reactions. Among these, chemical crosslinking types crosslink while the material is in a molten state, so crosslinking efficiency is high and the effect can be more pronounced.

[0040] The degree of crosslinking can be defined by the gel fraction. The gel fraction can be calculated, for example, as follows: When measuring the gel fraction, the material to be used is weighed in advance. Next, the material is immersed in xylene heated to 110°C for 24 hours. After immersion, the material is left at atmospheric pressure at 20°C for 3 hours and vacuum dried at 80°C for 4 hours. The mass of the treated material is then weighed, and the gel fraction can be calculated as the ratio (percentage) of the mass after immersion (after treatment) to the mass before immersion in xylene (before treatment). The gel fraction of the resin composition is preferably 80% or more. This can further improve the oil resistance of the resin composition.

[0041] (Maximum bending stress) The maximum bending stress of the resin composition is 2.0 MPa or less, which allows the resin composition to have sufficient processability.

[0042] <Electric wire> Next, an electric wire according to an embodiment will be described. Fig. 1 is a cross-sectional view showing an example of the structure of an electric wire according to an embodiment.

[0043] 1, an electric wire 11 according to this embodiment includes a conductor 11a and an insulating layer 11b that covers the conductor 11a. The insulating layer 11b may have a single layer structure or a multi-layer structure of two or more layers.

[0044] Conductor 11a can be any commonly used metal wire, such as copper wire or copper alloy wire, as well as aluminum wire, gold wire, or silver wire. Conductor 11a may also be a metal wire plated with metal such as tin or nickel. Conductor 11a may have a single wire structure, or a stranded conductor formed by twisting metal wires together. Examples of stranded conductors that can be used include concentric twisted wires, bunched twisted wires, and composite twisted wires formed by twisting these concentrically. Lightly compressed conductors formed by compressing these twisted wires are preferred because they allow the diameter of the electric wire to be reduced.

[0045] The insulating layer 11b is made of the resin composition described above. That is, the halogen-free flame-retardant resin composition according to this embodiment can be used for the insulating layer 11b. In this case, it is preferable to use a resin composition that has been subjected to a cross-linking treatment as described above. That is, it is preferable that the insulating layer 11b is made of a resin composition having a cross-linked structure. The thickness of this insulating layer 11b is not particularly limited, but is preferably 0.15 to 2 mm.

[0046] The electric wire 11 of this embodiment is manufactured, for example, as follows: First, materials containing the components of the base polymer and a metal hydroxide as a flame retardant are melt-kneaded to obtain the resin composition of this embodiment.

[0047] Thereafter, the conductor 11a is prepared. Then, the resin composition of the present embodiment is extruded by an extrusion molding machine so as to cover the periphery of the conductor 11a, thereby forming the insulating layer 11b of a predetermined thickness. In this way, the electric wire 11 can be manufactured.

[0048] In the present embodiment, after the electric wire 11 is manufactured, the flame-retardant resin composition constituting the insulating layer 11b is crosslinked by, for example, an electron beam crosslinking method or a chemical crosslinking method. This crosslinking allows the insulating layer 11b to have a crosslinked structure. This crosslinking is preferable because it improves the oil resistance of the insulating layer 11b made of the flame-retardant resin composition.

[0049] When an electron beam crosslinking method is used as the crosslinking treatment, the resin composition is molded into the insulating layer 11b of the electric wire 11, and then crosslinked by irradiating with an electron beam of, for example, 1 to 30 Mrad. When a chemical crosslinking method is used, a crosslinking agent is added to the flame-retardant resin composition in advance, and the flame-retardant resin composition to which the crosslinking agent has been added is molded into the insulating layer 11b of the electric wire 11, and then crosslinked by heat treatment.

[0050] <Cable> A cable according to one embodiment of the present invention is a cable in which a single-core or multi-core stranded wire formed by twisting together one or more electric wires is covered with a covering layer. The cable according to one embodiment will be described in detail with reference to Fig. 2. Fig. 2 is a cross-sectional view showing the structure of a cable according to this embodiment.

[0051] 2, cable 12 according to this embodiment includes conductor 12a, insulating layer 12b covering conductor 12a, and covering layer (sheath) 12c covering insulating layer 12b. Covering layer 12c is made of the resin composition of this embodiment described above. That is, covering layer 12c uses the halogen-free flame-retardant resin composition of this embodiment.

[0052] If necessary, the resin composition constituting the coating layer 12c may contain added crosslinking agents, crosslinking aids, flame retardant aids, ultraviolet absorbers, light stabilizers, softeners, lubricants, colorants, reinforcing materials, surfactants, inorganic fillers, plasticizers, metal chelating agents, foaming agents, compatibilizers, processing aids, stabilizers, etc.

[0053] From the viewpoint of oil resistance, it is preferable to crosslink the coating layer 12c. As described above for the insulating layer, the crosslinking treatment can be chemical crosslinking using organic peroxides or silane compounds, irradiation crosslinking using electron beams or radiation, or crosslinking using other chemical reactions, and any crosslinking method can be applied. By crosslinking, the coating layer 12c can have a crosslinked structure.

[0054] Here, the thickness of the coating layer 12c is not particularly limited, but a thickness of 0.5 to 2 mm is preferable in terms of achieving the effects of the present invention.

[0055] Although the present embodiment has been described with reference to an example in which the core wire of cable 12 is a single-core wire, the core wire may be a two-core twisted wire in which two wires are twisted together, or a multi-core twisted wire other than a two-core twisted wire.

[0056] In the case of a multi-core stranded wire in which two or more electric wires are twisted together, the wires are twisted together with an intervening material such as staple yarn, paper tape, or jute, and then the resin composition of this embodiment is extruded in the same manner as in the above-mentioned electric wire manufacturing method to cover the twisted wire, thereby forming a coating layer (sheath) 12c of a predetermined thickness.

[0057] In addition, in the cable 12 of this embodiment, the resin composition of this embodiment described above may be used as the insulating layer 12b, or an electric wire obtained by using a general-purpose material for the insulating layer may be used. When the resin composition of this embodiment is used, the obtained cable 12 has a configuration in which a covering layer (sheath) 12c is provided on the outer periphery of the electric wire 11.

[0058] Furthermore, when a general-purpose material is used for the insulating layer 12b, adding a flame retardant to the insulating layer 12b is preferable because it can provide higher flame retardancy. However, the flame retardant must be a halogen-free material, and even if a halogen-free flame retardant is used, it is preferable not to add a phosphorus-based flame retardant such as red phosphorus or a triazine-based flame retardant such as melamine cyanurate.

[0059] The polymer used for the insulating layer 12b is not particularly limited as long as it is a halogen-free resin, and examples thereof include polyolefins such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, and ethylene-acrylic acid ester copolymer.

[0060] Furthermore, a rubber material can also be used for the insulating layer 12b, such as ethylene-propylene copolymer rubber, ethylene-propylene-diene terpolymer rubber, acrylic rubber, ethylene-acrylate copolymer rubber, ethylene-octene copolymer rubber, ethylene-acrylate copolymer rubber, ethylene-octene copolymer rubber, ethylene-vinyl acetate copolymer rubber, ethylene-butene-1 copolymer rubber, butadiene-styrene copolymer rubber, isobutylene-isoprene copolymer rubber, and block copolymer rubber having a polystyrene block.

[0061] Furthermore, engineering plastics can also be used for the insulating layer 12b, such as polyethylene terephthalate, polybutylene terephthalate, polyphenylene ether, polycarbonate, polyamide, polyphenyl sulfide, polyether ether ketone, polyethylene naphthalate, polybutylene naphthalate, polyether sulfone, etc. Thermoplastic elastomers of these can also be used. The base polymer of this insulating layer 12b can be a single polymer or a blend of two or more polymers.

[0062] The cable 12 may have a structure in which, for example, a shield braid is provided on the outside of a single-core or multi-core stranded wire made by twisting together one or more electric wires, and a covering layer is provided on the outside of the shield braid. However, the separator can be freely installed and can be used on either the inside or outside in contact with the shield braid. There are no particular restrictions on the material of the separator. The cable 12 may also have a structure in which no separator is provided. [Example]

[0063] To obtain mechanical properties, the resin compositions shown in Tables 1 and 2 were kneaded in a 6-inch roll, and then crosslinked and molded into 1 mm and 2 mm sheets using a hot press. For the initial tensile test, the 1 mm crosslinked sheets were punched out into No. 6 dumbbell test pieces, and tensile tests were performed at a displacement rate of 250 mm / min to measure tensile strength and elongation at break. A tensile strength of 9 MPa or more was rated as good, and a tensile strength of less than 10 MPa was rated as bad.

[0064] For the oil resistance test, a 1 mm crosslinked sheet was punched into a No. 6 dumbbell test piece and immersed in IRM903 test oil heated to 70°C for 168 hours. After that, a tensile test was carried out at a displacement rate of 250 mm / min to measure the tensile strength. A tensile strength change rate of -30% or more was marked as ◯, and a rate of less than -30% was marked as ×.

[0065] To evaluate flexibility, the maximum bending stress was measured using a 2mm crosslinked sheet as a strip specimen, 30mm wide and 80mm long, at a support distance of 60mm and a pressing speed of 50mm / min. The bending stress was calculated by (3 x bending load x support distance) / (2 x thickness x width squared). A maximum stress of 2MPa or less was marked as ◯, and one exceeding 2MPa was marked as ×.

[0066] To evaluate processability, Mooney viscosity was evaluated at 130°C in accordance with JIS K6300-1. If the Mooney viscosity was 40 or less, it was marked as ◯, and if it was over 40, it was marked as ×.

[0067] In the above test method, the overall evaluation was as follows: ⊚ indicates that all evaluations were ◯; ◯ indicates that some evaluations were △; and × indicates that some evaluations were ×.

[0068] [Table 1] 1): Lanxess, Levaprene 600 2) Dow Infuse 9000 (melting point: 120°C, density: 0.877 g / cm 3 ) 3): Mitsui Chemicals, Toughma MA7020 4): Aflon UC3510, manufactured by Toa Gosei 5): Aflon UC1020, manufactured by Toa Gosei 6): ADEKA, CDA-6S 7):ADEKA, AO-18 8): BASF Irganox 1010 9): Kyowa Chemical Industry Co., Ltd., Kisuma 5L

[0069] [Table 2]

[0070] Examples 1 to 3 Various evaluations were carried out on the resin composition shown in Table 1. The results are shown in Table 1. All evaluations were rated as ○, so the overall evaluation was rated as ⊚.

[0071] Comparative Example 1 Various evaluations were carried out on the resin composition shown in Table 1. The results are shown in Table 1. Because no plasticizer was added, the Mooney viscosity was high and the composition failed.

[0072] In an electric wire having a conductor and an insulating layer formed on the outer periphery of the conductor, a flame-retardant crosslinked electric wire cable having excellent processability, high oil resistance, and flexibility can be obtained if the resin composition is (a) a base polymer composed of an ethylene-based copolymer having a vinyl acetate VA content of 60% by mass or more as the main component, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, and 130 to 200 parts by mass of a metal hydroxide, and the maximum bending stress of the resin composition is 2.0 MPa or less.

[0073] Although the present invention has been described with reference to the above embodiments and examples, the present invention is not limited to the above embodiments and examples and can be modified in various ways without departing from the spirit of the present invention. [Industrial Applicability]

[0074] According to the present invention, it is possible to provide a halogen-free flame-retardant cable that is easy to process and has both oil resistance and flexibility. [Explanation of symbols]

[0075] 11 Electric wire 11a conductor 11b Insulating layer 12 Cable 12a conductor 12b Insulating layer 12c coating layer

Claims

1. a base polymer comprising: (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more; (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less; and (c) an acid-modified ethylene-based copolymer; a metal hydroxide; an acrylic plasticizer; A metal chelating agent; an antioxidant, the content of the metal hydroxide is 130 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the base polymer, the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base polymer; A halogen-free flame-retardant resin composition having a maximum bending stress of 2.0 MPa or less.

2. In claim 1, The halogen-free flame-retardant resin composition, wherein the metal hydroxide is at least one selected from the group consisting of silane-treated aluminum hydroxide and silane-treated magnesium hydroxide.

3. An electric wire having a conductor and an insulating layer provided around the conductor, the insulating layer is composed of a base polymer having (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, a halogen-free flame-retardant resin composition including a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant; the content of the metal hydroxide is 130 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the base polymer, the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base polymer; The electric wire, wherein the maximum bending stress of the halogen-free flame-retardant resin composition is 2.0 MPa or less.

4. In claim 3, The electric wire, wherein the metal hydroxide is at least one selected from silane-treated aluminum hydroxide and silane-treated magnesium hydroxide.

5. A cable having a conductor, an insulating layer provided on the outer periphery of the conductor, and a coating layer provided on the outer periphery of the insulating layer, the coating layer is composed of a base polymer having (a) an ethylene-vinyl acetate copolymer having a vinyl acetate content of 60% by mass or more, (b) an ethylene-based copolymer having a melting point of 115°C or more and a specific gravity of 0.9 or less, and (c) an acid-modified ethylene-based copolymer, a halogen-free flame-retardant resin composition including a metal hydroxide, an acrylic plasticizer, a metal chelating agent, and an antioxidant; the content of the metal hydroxide is 130 parts by mass or more and 200 parts by mass or less relative to 100 parts by mass of the base polymer, the content of the acrylic plasticizer is 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the metal chelating agent is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the base polymer, the content of the antioxidant is 5 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the base polymer; A cable, wherein the maximum bending stress of the halogen-free flame-retardant resin composition is 2.0 MPa or less.

6. In claim 5, The cable, wherein the metal hydroxide is at least one selected from silane-treated aluminum hydroxide and silane-treated magnesium hydroxide.

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