Resin compositions, insulated wires, and wire harnesses

Abstract

The present invention provides a resin composition having sufficient heat resistance and bleed resistance as a coating layer for electric wires, and coated electric wires and wire harnesses using the same. [Solution] The resin composition contains a polyolefin resin, a metal hydroxide-based flame retardant, an inorganic filler, and an antioxidant. The content of the metal hydroxide-based flame retardant is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the polyolefin resin. The inorganic filler is made by using a combination of zeolite and organically modified layered silicate. The content of zeolite is 0.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the polyolefin resin. The zeolite has a pore diameter of 3.0 Å or more and 6.5 Å or less, or a pore diameter exceeding 6.5 Å and 9.0 Å or less, and a silica / alumina ratio of 2 or more and 10 or less. The content of organically modified layered silicate is 1.0 part by mass or more and 14.0 parts by mass or less per 100 parts by mass of the polyolefin resin.

Description

[Technical Field]

[0001] This invention relates to resin compositions, insulated wires, and wire harnesses. [Background technology]

[0002] Conventionally, insulated electric wires used in automobiles have been those with a coating layer formed from a resin composition containing thermoplastic resins. Among thermoplastic resins, polyolefin resins are particularly widely used from the standpoint of cost and supply, and by applying a crosslinking treatment, they can be applied to electric wires intended for higher temperature environments.

[0003] A recent technological trend is the growing momentum towards electric vehicles. The challenge for electric vehicles is to improve their driving range, and research is underway to increase battery capacity. Consequently, it will be necessary to shorten charging time by increasing the current, which requires larger wires, a component of the wire harness, and wires that can withstand higher temperatures. On the other hand, fuel efficiency regulations are expected to become stricter year by year due to environmental regulations. To address these challenges, there is a need to thin the insulation covering the wire conductors. Challenges in thinning the insulation include long-term heat resistance and resistance to deformation due to heat.

[0004] In recent years, the use of inorganic flame retardants such as metal hydroxides has been considered from the perspective of reducing the burden on the global environment. However, high-filling formulations are required to achieve flame retardancy equivalent to that of brominated flame retardants. Since metal cations are known to accelerate the oxidative degradation of resins, there are concerns that adding large amounts will reduce long-term heat resistance. As a measure to improve long-term heat resistance, increasing the amount of antioxidant is generally considered first, but this makes the antioxidant more prone to bleed-out or blooming, which is a concern, especially in the case of electric wires, as it can cause deviations in wire length and lead to product defects. Therefore, as shown in Patent Document 1, a resin composition is disclosed in which magnesium hydroxide is added as a flame retardant and organic clay is added to suppress the bleed-out of the antioxidant. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-197040 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, as shown in Patent Document 1, the addition of organic clay alone is insufficient for heat resistance. Thus, the challenge remains in establishing a formulation that achieves both heat resistance and bleed resistance while using inorganic flame retardants.

[0007] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a resin composition having sufficient heat resistance and bleed resistance as a coating layer for electric wires, and coated electric wires and wire harnesses using the same. [Means for solving the problem]

[0008] The resin composition according to an aspect of the present invention is a resin composition containing a polyolefin resin, a metal hydroxide-based flame retardant, an inorganic filler, and an antioxidant. The content of the metal hydroxide-based flame retardant is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the polyolefin resin. The inorganic filler is made by using a combination of zeolite and organically modified layered silicate. The content of zeolite is 0.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the polyolefin resin. The zeolite has a pore diameter of 3.0 Å or more and 6.5 Å or less, or a pore diameter of more than 6.5 Å and 9.0 Å or less, and a silica / alumina ratio of 2.0 or more and 10.0 or less. The content of organically modified layered silicate is 1.0 part by mass or more and 14.0 parts by mass or less per 100 parts by mass of the polyolefin resin.

[0009] The coated electric wire according to another aspect of the present invention includes a conductor and a coating layer that coats the conductor and contains a resin composition.

[0010] The wire harness according to another aspect of the present invention includes a coated electric wire.

Effects of the Invention

[0011] According to the present invention, it is possible to provide a resin composition having sufficient heat resistance and bleed resistance as a coating layer of an electric wire, a coated electric wire, and a wire harness using the same.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic cross-sectional view showing an example of the coated electric wire according to the present embodiment.

Modes for Carrying Out the Invention

[0013] Hereinafter, the resin composition, coated electric wire, and wire harness according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

[0014] [Resin Composition] The resin composition according to the present embodiment contains a polyolefin resin, a metal hydroxide-based flame retardant, an inorganic filler, and an antioxidant.

[0015] (Polyolefin Resin) The polyolefin resin is a polymer of a monomer containing olefin. The polyolefin resin may be a polymer of olefin alone or a copolymer of olefin and a monomer other than olefin. The polymer of olefin alone may be a polymer of one kind of olefin or a polymer of two or more kinds of olefins. The polyolefin resin may be modified with maleic acid or the like or may not be modified.

[0016] The olefin may include α-olefins, β-olefins, γ-olefins, etc. The α-olefin may include at least one monomer selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, etc.

[0017] The monomer other than the olefin may be a monomer having a carbon-carbon double bond. The monomer other than the olefin may include at least one of styrene and acrylate, etc.

[0018] The polyolefin resin may be at least one selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homopolypropylene (homo-PP), random polypropylene (random-PP), block polypropylene (block-PP), ethylene-butene copolymer, ethylene-propylene-butene copolymer, etc.

[0019] Polyolefin resins may also be ethylene copolymer resins polymerized using ethylene monomers and comonomers other than ethylene monomers. Ethylene copolymer resins are copolymers of ethylene monomers and olefin monomers other than ethylene monomers in amounts exceeding 5 mol%, and copolymers of ethylene monomers and non-olefin monomers in amounts exceeding 1 mol%. Examples of ethylene copolymer resins include ethylene-vinyl ester copolymers, ethylene-α,β-unsaturated carboxylic acid and / or its alkyl ester copolymers, ethylene-vinyl acetate copolymers (EVA), ethylene-methyl methacrylate copolymers (EMMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-methyl acrylate copolymers (EMA), ethylene-butyl acrylate copolymers (EBA), and ethylene-vinyl acetate-ethyl acrylate copolymers. These ethylene copolymer resins may be used individually or in combination. Furthermore, ethylene copolymer resins may or may not be modified with maleic acid and maleic anhydride.

[0020] (Metal hydroxide-based flame retardant) The resin composition contains a metal hydroxide-based flame retardant to improve flame retardancy. As the metal hydroxide-based flame retardant, one or more metal compounds having hydroxyl groups or crystal water can be used, such as magnesium hydroxide (Mg(OH)2), aluminum hydroxide (Al(OH)3), calcium hydroxide (Ca(OH)2), basic magnesium carbonate (mMgCO3·Mg(OH)2·nH2O), hydrated aluminum silicate (aluminum silicate hydrate, Al2O3·3SiO2·nH2O), and hydrated magnesium silicate (magnesium silicate pentahydrate, Mg2Si3O8·5H2O). Among these, magnesium hydroxide is particularly preferred as the metal hydroxide.

[0021] The content of the metal hydroxide-based flame retardant in the resin composition is 60 parts by mass or more and 140 parts by mass or less, preferably 60 parts by mass or more and 120 parts by mass or less, based on 100 parts by mass of the polyolefin resin. When the content of the metal hydroxide-based flame retardant is 60 parts by mass or more, the flame retardancy of the resin composition can be improved. Also, when the content of the metal hydroxide-based flame retardant is 140 parts by mass or less, the heat resistance and mechanical properties of the resin composition can be prevented from being affected.

[0022] (Zeolite) The resin composition contains an inorganic filler. The inorganic filler is a combination of zeolite and an organically modified layered silicate.

[0023] By adding zeolite to the resin composition, the temperature at which the resin composition decomposes can be increased. Zeolite is a type of aluminosilicate and can be represented by the general formula M x / n ·[(AlO2) x ·(SiO2) y ·zH2O. In the general formula, M is a cation with valence n, x + y is the number of tetrahedra per unit cell, z is the number of moles of water, and y is a value larger than x. Examples of cation species with valence 1 include Li + , Na + , K + , etc. Examples of cation species with valence 2 include Ca 2+ , Mg 2+ , Ba 2+ , etc.

[0024] Generally, zeolite is porous and has pores. Zeolite can adsorb molecules smaller than the pore diameter, but molecules larger than the pore diameter cannot enter the pores, so it is known to have a molecular sieve effect and an ion exchange function.

[0025] In this embodiment, the pore diameter of the zeolite is 3.0 Å or more and 9.0 Å or less. By using such zeolite, the consumption of the antioxidant is moderated and the antioxidant efficiency with respect to the addition amount is improved.

[0026] The cation species of zeolite are hydrogen ions (H + ), potassium ions (K + ), calcium ions (Ca 2+ ) and ammonium ions (NH4 + ) are some examples. Regarding the cation species of zeolite, the effect on the thermal decomposition behavior of polyolefin resin differs depending on the type. From the viewpoint of improving the thermal decomposition temperature of polyolefin resin, NH4 suppresses the effect of zeolite as a solid acid catalyst. + ,K + and Ca 2+ Cation species such as the above are preferred.

[0027] The average particle size of the zeolite is not particularly limited, but is preferably 0.1 μm to 50 μm, more preferably 1 μm to 30 μm, and even more preferably 5 μm to 20 μm. The average particle size of the zeolite can be measured by observing a cross-section of the resin composition with a scanning electron microscope (SEM) or the like.

[0028] Zeolites include natural zeolites, synthetic zeolites, and artificial zeolites. Natural zeolites are characterized by being naturally occurring and often inexpensive. Synthetic zeolites are characterized by being made from highly purified chemical substances and thus having high purity. Artificial zeolites are characterized by being made from unused resources such as coal ash and having higher purity than natural zeolites, and being less expensive than artificial zeolites. Among these, it is preferable that the zeolite be at least one of synthetic zeolites or artificial zeolites. This is because these zeolites have a more uniform structure compared to natural zeolites, and the thermal decomposition of thermoplastic resins is relatively easy to control.

[0029] The structure of zeolite is not particularly limited. Examples of zeolite structures include type A, beta, MCM-22, ZSM-5, Y, ferrielite, and mordenite types.

[0030] The pore size of a zeolite is determined by its crystal structure. The pore size of a zeolite can be measured, for example, by the Horvath-Kawazoe method. When the pore size of a zeolite is 6.5 Å or less, the ratio of silica to alumina in the zeolite, i.e., the SiO2 / Al2O3 ratio (hereinafter referred to as the silica / alumina ratio), is not particularly limited, but is, for example, between 2 and 10000.

[0031] On the other hand, when the pore size of the zeolite exceeds 6.5 Å and is 9.0 Å or less, the silica / alumina ratio is between 2 and 10 from the viewpoint of heat resistance of the resin composition.

[0032] Zeolite has hygroscopic properties, and there is a concern that the moisture content in the resin will increase with the amount added. Therefore, the zeolite content in the resin composition is 0.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of polyolefin resin. By having a zeolite content of 0.5 parts by mass or more, the heat resistance of the resin composition can be improved. On the other hand, by having a zeolite content of 2.0 parts by mass or less, the water absorption of the resin composition can be suppressed. On the other hand, there is a concern that high zeolite content may promote thermal degradation of the resin. Therefore, the ratio of zeolite content to antioxidant content is preferably 0.08 to 3.0, and more preferably 0.08 to 1.0. By setting the ratio of zeolite content to antioxidant content within the above range, it is possible to minimize the amount of antioxidant added, maintain bleed resistance, and ensure the heat resistance of the resin composition. Furthermore, the time during which the antioxidant is consumed during heat treatment can be extended, further improving the heat resistance of the resin composition.

[0033] (Organic modified layered silicate) Inorganic fillers may be a combination of zeolite and organically modified layered silicate. Organically modified layered silicate is a layered silicate that has been organically modified. By peeling and dispersing organically modified layered silicate in polyolefin resin, it is possible to improve the long-term heat resistance life of coated wires coated with the resin composition, and further improve heat deformability by suppressing physical deformation. In other words, by using zeolite and organically modified layered silicate in combination with the resin composition, it is possible to achieve both bleed resistance, heat resistance, and low heat deformability.

[0034] Examples of layered silicates include bentonite, smectite, hectorite, montmorillonite, mica, talc, and kaolin. Organically modified layered silicates can be produced by causing an ion exchange reaction between the inorganic cations of the layered silicate and an organic modifier. Examples of organic modifiers include organic phosphonium salts, alkylammonium salts, and organic onium salts. From the viewpoint of heat resistance of the resin composition, the organically modified layered silicate is preferably bentonite or smectite modified with an organic onium salt, and more preferably trimethylstearylammonium bentonite.

[0035] When the inorganic filler is composed of zeolite and organically modified layered silicate in combination, the content of the organically modified layered silicate is 1.0 part by mass or more and 14.0 parts by mass or less per 100 parts by mass of polyolefin resin. By having an organically modified layered silicate content of 1.0 part by mass or more, it is possible to achieve both bleed resistance, heat resistance, and low heat deformation of the resin composition. Furthermore, by having an organically modified layered silicate content of 14.0 parts by mass or less, it is possible to avoid adversely affecting the heat resistance of the resin composition.

[0036] (Antioxidant) Because high concentrations of metal hydroxide-based flame retardants accelerate oxidative degradation of the resin, it is necessary to improve long-term heat resistance with antioxidants. Examples of antioxidants include phenolic antioxidants that scavenge radicals, phosphorus-based antioxidants that decompose peroxides, or sulfur-based antioxidants. To impart sufficient heat resistance to the resin composition as an antioxidant, a combination of an antioxidant such as hindered phenol (primary antioxidant) and a sulfur-based antioxidant such as thioether (secondary antioxidant) may be used.

[0037] While a higher amount of primary antioxidant can prevent oxidative degradation of the resin, there are concerns that high additions may lead to bleed-out or a decrease in the degree of crosslinking due to reactions during the crosslinking process. Therefore, it is preferable that the primary antioxidant content be between 1 and 6 parts by mass per 100 parts by mass of polyolefin resin. A primary antioxidant content of 1 part by mass or more provides sufficient heat resistance. Furthermore, a primary antioxidant content of 6 parts by mass or less suppresses the bleed-out of the antioxidant to the surface of the insulation layer of the electric wire, thus preventing adverse effects on workability during electric wire manufacturing.

[0038] While secondary antioxidants exhibit synergistic effects when used in combination with primary antioxidants, concerns arise, similar to those with primary antioxidants, such as bleed-out with high addition levels and a decrease in the smoke emission characteristics of electric wires. Therefore, it is preferable that the content of secondary antioxidants be 1 part by mass or less per 100 parts by mass of polyolefin resin. By limiting the secondary antioxidant content to 1 part by mass or less, it is possible to suppress the antioxidant from bleeding out onto the surface of the insulating layer of the electric wire.

[0039] (Other additives) In addition to the metal hydroxide-based flame retardants, zeolites, organically modified layered silicates, and antioxidants mentioned above, other additives include crosslinking agents, crosslinking aids, processing aids, plasticizers, copper damage inhibitors, metal deactivators, fillers, reinforcing agents, UV absorbers, stabilizers, pigments, lubricants, dyes, colorants, antistatic agents, and foaming agents.

[0040] In this embodiment, the polyolefin resin in the resin composition may be crosslinked. Crosslinking the polyolefin resin can improve the heat resistance of the resin composition. The method of crosslinking the polyolefin resin is not particularly limited, but for example, the polyolefin resin may be crosslinked by irradiation with radiation, or the polyolefin resin may be crosslinked by a crosslinking agent contained in the resin composition. It is preferable that the polyolefin resin is radiation crosslinked.

[0041] The radiation used for crosslinking may be, for example, gamma rays or electron beams. By irradiating the coating layer with radiation, radicals are generated in the molecules, and crosslinking bonds are formed between the molecules. The radiation irradiation conditions are not particularly limited, but for example, the accelerating voltage is 500kV to 1000kV and the irradiation dose is 100kGy to 250kGy.

[0042] For example, organic peroxides can be used as crosslinking agents. The crosslinking agent may be at least one selected from the group consisting of, for example, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-di-(tert-butylperoxy)hexine-3, 1,3-bis(tert-butylperoxyisopropyl)benzene, 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, n-butyl-4,4-bis(tert-butylperoxy)valerate, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxybenzoate, tert-butylperoxyisopropyl carbonate, diacetyl peroxide, lauroyl peroxide, and tert-butylcumyl peroxide. The crosslinking agent may be used individually or in combination of multiple types. In the resin composition, the crosslinking agent content is preferably 0.05 to 0.10 parts by mass per 100 parts by mass of polyolefin resin.

[0043] The resin composition may contain a crosslinking aid in addition to the crosslinking agent to improve crosslinking efficiency. A polyfunctional compound can be used as the crosslinking aid. The crosslinking aid may be at least one compound selected from the group consisting of, for example, acrylate compounds, methacrylate compounds, allyl compounds, and vinyl compounds. These polyfunctional compounds may be used individually or in combination. Among these compounds, trimethylolpropane trimethacrylate is preferred due to its high affinity with polyolefin resins.

[0044] Furthermore, the content of the crosslinking aid in the resin composition is preferably 0.1 to 5 parts by mass, and more preferably 0.8 to 2 parts by mass, per 100 parts by mass of polyolefin resin. By setting the content within this range, the heat resistance, processability, and bleed resistance of the resin composition can be further improved.

[0045] Examples of processing aids include petroleum-based oils such as paraffinic oils and naphthenic oils, which are added to rubber materials.

[0046] The resin composition is prepared by melt-kneading the above-mentioned polyolefin resin and metal hydroxide-based flame retardant, and known methods can be used for this preparation. For example, after pre-blending using a high-speed mixing device such as a Henschel mixer, the mixture can be kneaded using a known kneader such as a Banbury mixer, kneader, or roll mill, and the polyolefin resin can be crosslinked as described above to obtain the resin composition.

[0047] As described above, the resin composition contains a polyolefin resin, a metal hydroxide-based flame retardant, an inorganic filler, and an antioxidant. The content of the metal hydroxide-based flame retardant is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the polyolefin resin. The inorganic filler is made by using a combination of zeolite and organically modified layered silicate. The content of zeolite is 0.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the polyolefin resin. The zeolite has a pore diameter of 3.0 Å or more and 6.5 Å or less, or a pore diameter exceeding 6.5 Å and 9.0 Å or less, and a silica / alumina ratio of 2 or more and 10 or less. The content of organically modified layered silicate is 1.0 part by mass or more and 14.0 parts by mass or less per 100 parts by mass of the polyolefin resin. Therefore, the resin composition has sufficient heat resistance and bleed resistance as a coating layer for electric wires.

[0048] [Insulated wire] Figure 1 is a cross-sectional view showing an example of a coated electric wire 10 according to this embodiment. As shown in Figure 1, the coated electric wire 10 of this embodiment comprises a conductor 11 and a coating layer 12 that covers the conductor 11 and contains the resin composition according to the above embodiment. The resin composition according to the above embodiment has sufficient heat resistance and bleed resistance as a coating layer for an electric wire. Therefore, a coated electric wire 10 having such a coating layer 12 can be preferably used, for example, as a coated electric wire 10 for automobiles.

[0049] The conductor 11 may consist of only one strand, or it may be a stranded wire made by bundling multiple strands together. Alternatively, the conductor 11 may consist of only one strand, or it may be a composite stranded wire made by bundling multiple stranded wires together. The configuration and size of the conductor 11 are preferably those specified in at least one of JASO D624 and ISO 19642-5.

[0050] The diameter of the conductor 11 is not particularly limited, but is preferably 4.0 mm or more, and more preferably 5.0 mm or more. By setting the diameter of the conductor 11 as described above, the resistance of the conductor is reduced, and for example, even with a large-capacity battery, the charging time can be shortened. Furthermore, although the diameter of the conductor 11 is not particularly limited, is preferably 25 mm or less, and more preferably 20 mm or less. By setting the diameter of the conductor 11 as described above, the routing of the insulated wire 10 can be made easier even in narrow and short paths.

[0051] The diameter of the wire strands is not particularly limited, but is preferably 0.1 mm or more, and more preferably 0.2 mm or more. By setting the wire strand diameter as described above, wire breakage can be suppressed. Furthermore, although the diameter of the wire strands is not particularly limited, is preferably 0.5 mm or less, and more preferably 0.4 mm or less. By setting the wire strand diameter as described above, the insulated wire 10 can be easily routed even in narrow and short paths.

[0052] The material constituting the conductor 11 is not particularly limited, but it is preferably at least one conductive metallic material selected from the group consisting of copper, copper alloys, aluminum, and aluminum alloys.

[0053] The thickness of the coating layer 12 is not particularly limited, but is preferably 0.5 mm or more, and more preferably 0.65 mm or more. By setting the thickness of the coating layer 12 as described above, the conductor 11 can be effectively protected. Alternatively, the thickness of the coating layer 12 is not particularly limited, but is preferably 2.0 mm or less, and more preferably 1.85 mm or less. By setting the thickness of the coating layer 12 as described above, the insulated wire 10 can be easily routed even in narrow and short paths.

[0054] The insulated wire 10 may further comprise a shield layer covering the insulated layer 12 and a sheath layer further covering the shield layer. The shield layer can prevent the emission of unnecessary electromagnetic waves from the conductor 11. The shield layer can be formed by weaving conductive metal foil or metal-containing foil or metal wire (metal conductor) in a mesh-like structure. The sheath layer can effectively protect and bundle the shield layer. The sheath layer is not particularly limited, but may be made of an olefin resin such as polyethylene, or a resin composition according to the above embodiment may be used.

[0055] Known methods can be used to cover the conductor 11 with the coating layer 12. For example, the coating layer 12 can be formed by a general extrusion molding method. As the extruder used in the extrusion molding method, for example, a single-screw extruder or a twin-screw extruder can be used, and it can be one that has a screw, breaker plate, crosshead, distributor, nipple and die.

[0056] When preparing the resin composition that constitutes the coating layer 12, polyolefin resin, flame retardant, inorganic filler, and antioxidant are fed into an extruder set to a temperature at which the resin is sufficiently melted. At this time, other additives are also added to the extruder as needed. The resin composition is then melted and kneaded by a screw, and a certain amount is supplied to the crosshead via a breaker plate. The molten resin composition flows onto the circumference of the nipple by a distributor and is extruded by a die in a state that covers the outer circumference of the conductor 11, thereby obtaining the coating layer 12 that covers the outer circumference of the conductor 11.

[0057] Thus, in the coated wire 10 of this embodiment, the coating layer 12 can be formed by extrusion molding, similar to general resin compositions for electric wires. In order to improve the strength of the coating layer 12, after forming the coating layer 12 on the outer circumference of the conductor 11, the resin composition may be crosslinked by methods such as the radiation irradiation described above.

[0058] [Wire harness] The wire harness according to this embodiment comprises a coated wire 10. The resin composition according to the above embodiment has sufficient heat resistance and bleed resistance as a coating layer for the wire. Therefore, a coated wire 10 having a coating layer 12 made of such a resin composition can be preferably used, for example, as a wire harness in the engine compartment of an automobile. [Examples]

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

[0060] (Polyolefin resin) Engage® 7256, ethylene-butene copolymer, manufactured by Dow Chemical Japan Ltd.

[0061] (Metal hydroxide-based flame retardant) Kyowa Chemical Industry Co., Ltd.'s Kisma (registered trademark) 5A, stearic acid surface-treated magnesium hydroxide.

[0062] (Antioxidant) • Antioxidant 1: Irganox® 1010, manufactured by BASF Ltd., a hindered phenol-based antioxidant (primary antioxidant). • Antioxidant 2: Nocrack® 400, manufactured by Ouchi Shinko Chemical Industry Co., Ltd., sulfur-based antioxidant (secondary antioxidant)

[0063] (Copper damage inhibitor) BASF Ltd.'s Irganox® MD1024, a hydrazine-based copper corrosion inhibitor.

[0064] (Zeolite) • Type A zeolite: Zeolam® A-5, manufactured by Tosoh Corporation, pore size 5 Å, silica / alumina ratio 2 • Beta-type zeolite: HSZ (registered trademark) 940HOA, manufactured by Tosoh Corporation, pore size 6.5Å, silica / alumina ratio 40 • Y-type zeolite 1: HSZ 320HOA, manufactured by Tosoh Corporation, pore size 9 Å, silica / alumina ratio 5.5 • Y-type zeolite 2: HSZ 385HUA, manufactured by Tosoh Corporation, pore size 9 Å, silica / alumina ratio 100

[0065] (Organic modified layered silicate) • Organically modified bentonite: Kunibis®-110, manufactured by Kunimine Industries Co., Ltd., trimethylstearylammonium bentonite • Refined bentonite: Manufactured by Kunimine Industries Co., Ltd., Kunipia (registered trademark)-F • Mica: M-XF manufactured by Repco Co., Ltd. • Calcined kaolin clay: Manufactured by Shiraishi Calcium Co., Ltd. ST-100 • Wollastonite (Wollastonite): Manufactured by Shiraishi Calcium Co., Ltd. ST-40FK

[0066] [evaluation] The properties of the resin compositions in the examples and comparative examples were evaluated using the following method. Based on the formulations (unit: parts by mass) shown in Tables 1 and 2, the resin compositions were crosslinked by electron beam irradiation under conditions of 750 kV × 160 kGy. These crosslinked resin compositions were used as test samples, and their heat resistance, bleed resistance, heat deformation resistance, and water absorption were evaluated. The evaluation results are shown in Tables 1 and 2.

[0067] (Wire heat resistance) The test samples were prepared by fabricating wires with a conductor outer diameter of 2.1-2.2 mm and a coating layer thickness of 0.4 mm, then performing a cross-linking treatment and cutting them to a length of 200 mm. These test samples were placed in a gear oven set to a temperature of 170°C and subjected to heat treatment for a predetermined time. After that, they were removed from the gear oven and left at room temperature (approximately 23°C) for 12 hours. Furthermore, the heat-treated test samples were wound around a mandrel with an outer diameter 1.5 times that of the finished outer diameter of the wire, and the heat treatment time required until cracking occurred was determined. A sample was evaluated as a pass ("○") if no cracking occurred after heating at 170°C for 250 hours, and as a fail ("×") if cracking occurred after heating at 170°C for 250 hours or less.

[0068] (Bleed resistance) The test samples were prepared by molding the resin composition into a 0.5 mm thick, 50 mm wide resin sheet, and then cutting it into 200 mm lengths. After wiping the resin sheet with acetone, it was left for 1000 hours at room temperature (23°C) and 40-60% humidity. The resin sheet was then wiped again with acetone, and the weight change before and after wiping was measured. The bleed amount per unit area (mg / cm²) was then calculated using the length and width values ​​of the resin sheet. 2 The weight change in the measurement result was 0.150 mg / cm³. 2 A value less than 0.150 mg / cm³ is considered a pass ("〇"). 2 In the above cases, the result was marked as a failure ("×").

[0069] (Heat-deformable) The test samples were prepared by molding the resin composition into a 2 mm thick resin sheet and then cutting it to the size specified in JIS K6723 6.5 (heat deformation test). For the measurement, the sample was preheated at 150°C for 30 minutes, then a load of 9.8067 N was applied at 150°C for 30 minutes, and the rate of heat deformation from the initial thickness was measured. A heat deformation rate of 8.0% or less was considered a pass ("○"), and a rate of 8.0% or more was considered a fail ("×").

[0070] (Water absorption) The test samples used were pellets obtained by granulating a resin composition. The pellets were degassed under vacuum using a vacuum dryer at a temperature of 40°C, and then left to stand for 168 hours at room temperature (23°C) and a humidity of 40-60%. The measurements were performed using Method A (anhydrous methanol extraction method) as specified in JIS K7251:2002 (Plastics - Method for determining moisture content). A moisture content of less than 1500 ppm was marked as a pass ("○"), and a moisture content of 1500 ppm or more was marked as a fail ("×").

[0071] [Table 1]

[0072] [Table 2]

[0073] As shown in Table 1, the resin compositions of Examples 1 to 10 exhibited excellent heat resistance, bleed resistance, heat deformation resistance, and water absorption properties for electric wires. From these results, it is presumed that the resin compositions of Examples 1 to 10 have sufficient heat resistance and bleed resistance to be used as a coating layer for electric wires.

[0074] On the other hand, as shown in Table 2, the resin compositions related to Comparative Examples 1 to 13 lacked sufficient heat resistance, bleed resistance, heat deformation resistance, and water absorption for electrical wires. Comparative Examples 1 to 4 failed to pass the electrical wire heat resistance test because they did not contain organically modified layered silicates and instead contained unmodified purified bentonite, mica, calcined kaolin clay, or wollastonite. Comparative Example 5 failed to pass the electrical wire heat resistance test because the content of organically modified layered silicates per 100 parts by mass of polyolefin resin was greater than 14.0 parts by mass. Comparative Example 6 failed to pass the electrical wire heat resistance test because the content of metal hydroxide-based flame retardants per 100 parts by mass of polyolefin resin was greater than 140 parts by mass. Comparative Example 7 failed to pass the water absorption test because the zeolite content was greater than 2.0 parts by mass. In Comparative Examples 8-11, since only zeolite was used as the inorganic filler and no organically modified layered silicate was used, at least one of the following aspects—heat resistance, bleed resistance, and heat deformation resistance—was unsatisfactory. In Comparative Example 12, since only organically modified layered silicate was used as the inorganic filler and no zeolite was used, the heat resistance of the wire was unsatisfactory. In Comparative Example 13, since zeolite with a pore size of 9 Å and a silica / alumina ratio exceeding 10 was used, the heat resistance of the wire was unsatisfactory.

[0075] These results indicate that sufficient heat resistance and bleed resistance can be obtained for use as a wire coating layer by formulating a resin composition with specific components and a specific composition.

[0076] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of symbols]

[0077] 10 Insulated wires 11 Conductors 12 Covering layer

Claims

1. A resin composition containing a polyolefin resin, a metal hydroxide-based flame retardant, an inorganic filler, and an antioxidant, The content of the metal hydroxide-based flame retardant is 60 parts by mass or more and 140 parts by mass or less per 100 parts by mass of the polyolefin resin. The inorganic filler is made by using a zeolite and an organically modified layered silicate in combination. The zeolite content is 0.5 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of the polyolefin resin. The zeolite has a pore diameter of 3.0 Å or more and 6.5 Å or less, or a pore diameter greater than 6.5 Å and 9.0 Å or less, and a silica / alumina ratio of 2 or more and 10 or less. The resin composition is characterized in that the content of the organically modified layered silicate is 1.0 part by mass or more and 14.0 parts by mass or less per 100 parts by mass of the polyolefin resin.

2. The resin composition according to claim 1, wherein the polyolefin resin is a crosslinked polyethylene or ethylene copolymer resin.

3. The resin composition according to claim 1 or 2, wherein the metal hydroxide-based flame retardant is magnesium hydroxide.

4. The resin composition according to claim 1 or 2, wherein the organically modified layered silicate is bentonite or smectite modified with an organic onium salt.

5. A conductor and A coating layer comprising the resin composition described in claim 1 or 2, covering the conductor, Insulated wire equipped with a protective coating.

6. A wire harness comprising the insulated wire described in claim 5.

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