Resin composition, resin coating material, insulated wire, automotive wire harness, and method for manufacturing insulated wire used in automotive wire harnesses.

Abstract

A resin composition including an ethylene / vinyl acetate copolymer resin as a resin component and containing an imidazole compound, a phenol compound, and a thioether compound as antioxidants and a bromine compound and an antimony compound as flame retardants, wherein the content of the imidazole compound is 14-24 parts by mass, the content of the phenol compound is 1.0-2.0 parts by mass, the content of the thioether component is 0.3-0.9 parts by mass, the content of the bromine compound is 15-30 parts by mass, and the content of the antimony compound is 5-15 parts by mass, per 100 parts by mass of the total content of the resin component in the resin composition.

Description

[[Technical Field]]

[0001] The present invention relates to a resin composition, a resin coating material, an insulated wire, an automobile wire harness, and a method for producing an insulated wire for use in an automobile wire harness. [[Background Art]]

[0002] Flame-retardant insulated wires are widely used in various white goods, office automation equipment, and the like. Insulated wires used in automobiles and the like are also required to have various properties such as flame retardancy, heat resistance, flexibility, and mechanical properties. Heretofore, resin compositions that can realize insulated wires having flame retardancy, heat resistance, flexibility and mechanical properties when used as a conductor coating material have been studied, and many reports have been made thereon. As resin compositions constituting insulated wires having such desired properties, those based on resins such as polyethylene and ethylene-vinyl acetate copolymer are widely used, for example.

[0003] For example, Patent Document 1 discloses that a resin composition containing specific amounts of an ethylene-vinyl acetate copolymer, a specific flame retardant, a plurality of specific anti-aging agents, a copper inhibitor, and a crosslinking co-agent respectively is prepared. In the preparation of this resin composition, the composition is less likely to adhere to a processing machine (excellent in processing adhesion), and the residual amount of the composition in the processing machine can be suppressed; further, when the resin composition is applied to the surface of a conductor or the like and crosslinked, an insulated wire exhibiting desired excellent properties in all of flexibility, hardness, crosslinking degree, abrasion resistance, flame retardancy, cold resistance and heat resistance can be obtained. This resin composition contains, based on 90 to 100 parts by mass of the ethylene-vinyl acetate copolymer, 15 to 30 parts by mass of a brominated flame retardant, 5 to 15 parts by mass of antimony trioxide, 6 to 12 parts by mass of a benzimidazole anti-aging agent, 2 to 4 parts by mass of a phenolic anti-aging agent, 2 to 4 parts by mass of a thioether anti-aging agent, 0.5 to 2 parts by mass of a copper inhibitor, and 3 to 6 parts by mass of a crosslinking co-agent.

[0004] Furthermore, Patent Document 2 describes a flame-retardant resin composition that, when used as a coating material for conductors, provides excellent heat resistance, flame retardancy, and coexistence with polyvinyl chloride (PVC), and does not cause problems such as the leaching of heavy metal compounds, the generation of large amounts of smoke, or the generation of corrosive gases during disposal such as landfill or incineration. This flame-retardant resin composition contains, per 100 parts by mass of an ethylene-vinyl acetate copolymer or a mixture of an ethylene-vinyl acetate copolymer and a polyolefin, with a vinyl acetate content of 10% by mass or more and less than 40% by mass, 50 to 160 parts by mass of a metal hydrate, 2 to 10 parts by mass of a phenolic antioxidant, 10 to 25 parts by mass of a benzimidazole antioxidant, and 0 to 10 parts by mass of a thioether antioxidant.

[0005] Furthermore, Patent Document 3 describes an insulated wire that has excellent flame retardancy, tensile properties, heat resistance, and electrical properties, and does not leach heavy metal compounds or generate large amounts of smoke or corrosive gases when disposed of by landfill, incineration, etc. In this insulated wire, the conductor is coated with a crosslinked body of a composition containing 150 to 300 parts by mass of a metal hydrate, 1 to 6 parts by mass of a phenolic antioxidant, and 12 to 30 parts by mass of a thioether antioxidant, with the vinyl acetate content of the base resin being 40% by mass or more, per 100 parts by mass of a base resin containing an ethylene-vinyl acetate copolymer.

[0006] Furthermore, Patent Document 4 describes a non-halogen flame-retardant electric wire / cable with excellent durability against corrosive gases such as NOx and SOx. This non-halogen flame-retardant electric wire / cable contains a non-halogen flame retardant in the insulator or sheath, and the insulator or sheath is characterized by a composition in which 300 parts by weight or less of the non-halogen flame retardant is mixed with 100 parts by weight of rubber or plastic, and 0.1 to 10 parts by weight each of a hindered phenol-based antioxidant and a thioether-based antioxidant are added. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-14794 [Patent Document 2] Japanese Patent Publication No. 2009-286903 [Patent Document 3] Japanese Patent Publication No. 2002-42574 [Patent Document 4] Japanese Patent Publication No. 2002-324442 [Overview of the project] [Problems that the invention aims to solve]

[0008] With the recent advancements in the development of hybrid vehicles and other electronic devices, insulated wires used in automobiles and other applications are now required to possess superior properties in terms of flexibility, hardness, degree of crosslinking, abrasion resistance, flame retardancy, cold resistance, and heat resistance. Regarding heat resistance, it is now required that the wires meet the heat resistance class 150°C specified in the automotive standard (JASO) D624 (2015) or the heat resistance class D specified in ISO 6722 (2006). Furthermore, from the perspective of terminal sealing characteristics of insulated wires (preventing water from entering the connection from the outside), it is known that the wire coating is compressed and deformed using rubber material or the like to ensure its watertight performance. In order to ensure such watertight performance, it is necessary to design with a high degree of crosslinking (gel fraction). In particular, many resins tend to have a high rate of thermal deformation in high-temperature environments, and if the insulating coating of an insulated wire is crushed (deformed) under such conditions, it can be a factor that impairs the sealing characteristics with the connector. Furthermore, when processing wire harnesses or assembling them, harness processing such as cable termination, connector insertion, and cable routing is often done manually. In particular, when processing harnesses during periods of significant environmental change, such as in summer, the ease of routing (slipperiness) between wire harness components and electric cables or between electric cables is important from the perspective of work efficiency, worker load, and assembly accuracy.

[0009] In view of the above circumstances, the present invention aims to provide a resin composition that, when used to form an insulating film (resin coating layer) on an insulated wire, can produce an insulated wire that is excellent in heat resistance, has excellent crosslinking properties within the insulating film, and also has excellent wire-passability (slipperiness) in high-temperature environments. The present invention also aims to provide a resin coating material using the above resin composition, an insulated wire having the resin coating material around a conductor, an automotive wire harness having the insulated wire, and a method for manufacturing an insulated wire used in an automotive wire harness. [Means for solving the problem]

[0010] The inventors of the present invention conducted diligent studies to solve the above problems and found that by using an ethylene-vinyl acetate copolymer resin as the base resin, and blending it with specific amounts of an imidazole compound, a phenol compound, and a thioether compound, and further blending it with specific amounts of a bromine compound and an antimony compound, the resulting resin composition can be used to form an insulating coating on an insulated wire, thereby providing an insulated wire with excellent heat resistance, high crosslinkability, and excellent wire ductility. The present invention was completed after further studies based on these findings.

[0011] In other words, the above problems were solved by the following means. <1> A resin composition containing an ethylene-vinyl acetate copolymer resin as a resin component, The resin composition contains imidazole compounds, phenol compounds, and thioether compounds as antioxidants, and bromine compounds and antimony compounds as flame retardants. A resin composition in which, per 100 parts by mass of the total content of the resin components, the imidazole compound is contained in 14 to 24 parts by mass, the phenol compound in 1.0 to 2.0 parts by mass, the thioether compound in 0.3 to 0.9 parts by mass, the bromine compound in 15 to 30 parts by mass, and the antimony compound in 5 to 15 parts by mass. <2> The resin composition according to <1> above, wherein the resin composition contains 0.5 to 6.0 parts by mass of a dispersant based on 100 parts by mass of the total content of the resin components in the resin composition. <3> The resin composition according to <1> or <2> above, which comprises a maleic acid-modified polyethylene resin and / or a low-density polyethylene resin as the resin component. <4> The resin composition according to any one of <1> to <3> above, wherein the proportion of vinyl acetate components in the ethylene-vinyl acetate copolymer resin is 30% by mass or less. <5> The resin composition according to any one of <1> to <4> above, wherein the total content of the antioxidant is 20 to 26 parts by mass based on 100 parts by mass of the total content of the resin components in the resin composition. <6> The resin composition according to any one of <1> to <5> above, wherein the resin composition contains at least one of a crosslinking auxiliary agent and a processing auxiliary agent. <7> The resin composition according to any one of <1> to <6> above, which is used for automobile wire harnesses. <8> A resin coating material obtained by crosslinking the resin composition according to any one of <1> to <7> above. <9> An insulated wire, wherein an insulating coating comprises the resin coating material according to <8> above. <10> An automobile wire harness, comprising the insulated wire according to <9> above. <11> A method for producing an insulated wire used for an automobile wire harness, comprising the steps of: extrusion-coating the resin composition according to any one of <1> to <7> above on a conductor to form a layer of the resin composition; and irradiating the layer of the resin composition with an electron beam of 80 to 250 kGy.

[0012] In the present invention, a numerical range expressed using "~" means a range that includes the numerical values described before and after it as the lower limit and the upper limit. Effects of the Invention

[0013] When the resin composition of the present invention is used for forming an insulating coating (resin coating material layer) of an insulated electric wire, an insulated electric wire excellent in heat resistance, excellent in crosslinkability within the insulating coating, and also excellent in wire-passing performance between the obtained insulated electric wires can be obtained. When the resin coating material of the present invention is used as a constituent material for an insulating coating of an insulated electric wire, an insulated electric wire exhibiting the aforementioned desired excellent properties can be obtained. In the automotive wire harness of the present invention, the insulated electric wires constituting the automotive wire harness have the aforementioned resin coating material in the insulating coating thereof, and the wire harness is excellent in heat resistance, excellent in crosslinkability within the insulating coating, and further excellent in wire-passing performance under high temperature environments. According to the method for producing an insulated electric wire used in the automotive wire harness of the present invention, an insulated electric wire having the aforementioned excellent properties can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0014] [Resin Composition] The resin composition of the present invention contains, as a base resin, an ethylene-vinyl acetate copolymer resin, as an antioxidant, an imidazole compound, a phenol compound and a thioether compound, and as a flame retardant, a bromine compound and an antimony compound, each in a specific amount. Each of the aforementioned components and optional components described below may be used alone as one kind, or may be used in combination of two or more kinds. Hereinafter, each component contained in the resin composition of the present invention will be described.

[0015] <Ethylene-Vinyl Acetate Copolymer Resin> The resin composition of the present invention contains at least an ethylene-vinyl acetate copolymer resin as a resin component constituting the base resin. The polymerization mode of the ethylene-vinyl acetate copolymer resin used in the present invention may be any of block, random and graft polymerization.

[0016] From the viewpoint of adhesion between the resin coating material and the conductor, and the ease of wire passage (slipperiness) between the wire harness member and the electric wire cable or between electric wires themselves, the content of the vinyl acetate component constituting the ethylene-vinyl acetate copolymer is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less. Also, from the same viewpoint as above, the content of the vinyl acetate component is preferably 7% by mass or more, and more preferably 9% by mass or more. Furthermore, by setting the content of the vinyl acetate component within the above range, the resin coating material made using the resin composition of the present invention can acquire sufficient mechanical properties such as tensile strength and tensile elongation, and the flame retardancy of the insulated wire can be further improved. The content of the vinyl acetate component can be determined, for example, from the mass ratio of the raw materials (monomers) used in synthesis.

[0017] The melt flow rate (MFR) of the ethylene-vinyl acetate copolymer resin used in the present invention is preferably 0.1 to 10 g / 10 min (load 2.16 kg, temperature 190 °C), and more preferably 0.5 to 5 g / 10 min. By setting the melt flow rate of the ethylene-vinyl acetate copolymer resin within the preferred range described above, the load on the kneading equipment and extruder can be further reduced during the preparation of the resin composition and the manufacture of insulated wires or wire harnesses. Furthermore, the dispersibility of each component in the resin composition can be improved. The melt flow rate (MFR) can be measured according to the method specified in JIS K 7210:2014.

[0018] The ethylene-vinyl acetate copolymer resin used in the present invention can be synthesized by conventional methods, or a commercially available product may be used. Specific examples of commercially available products include, for example, Evaflex V5274 and Evaflex V422 (both trade names) manufactured by Mitsui DuPont Polychemicals.

[0019] In the resin composition of the present invention, the content of the ethylene-vinyl acetate copolymer resin in the resin components is preferably 80% by mass or more, more preferably 85% by mass or more, and even more preferably 90% by mass or more, from the viewpoint of improving flame retardancy and crosslinkability. Furthermore, all of the resin components contained in the resin composition of the present invention may be ethylene-vinyl acetate copolymer resin.

[0020] <Polyethylene resin> The resin composition of the present invention may contain polyethylene resin as a resin component other than the ethylene-vinyl acetate copolymer resin described above. Examples of such polyethylene resins include maleic acid-modified polyethylene resin and low-density polyethylene resin. Such polyethylene resins may be used individually or in combination of two or more types. The content of polyethylene resin in the resin components constituting the resin composition of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, and can also be 1 to 10% by mass, 2 to 8% by mass, or 3 to 5% by mass.

[0021] (Maleic acid-modified polyethylene resin) When the resin composition of the present invention contains a maleic acid-modified polyethylene resin component as a resin component, the content of the maleic acid-modified polyethylene resin in the resin components constituting the resin composition of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, and can also be 1 to 10% by mass, 2 to 8% by mass, or 3 to 5% by mass. By setting the content of the maleic acid-modified polyethylene resin within the above preferred range, sufficient flexibility can be imparted to the insulated wire having a resin coating material made using the resin composition of the present invention. Furthermore, since the resin composition does not adhere easily to the processing machine (excellent processing adhesion), the amount of composition remaining inside the processing machine can be reduced. In addition, the compatibility between the resin component in the composition and fillers can be improved, and the wear resistance of the resulting insulated wire can be further improved.

[0022] (Low-density polyethylene resin) In this invention, "low-density polyethylene resin" refers to a resin with a density of 0.929 g / cm³. 3 This refers to the following polyethylene resins. Therefore, in this invention, "low-density polyethylene resin" includes not only "low-density polyethylene (LDPE)" but also "very low-density polyethylene (VLDPE)" and the like. The low-density polyethylene resin used in this invention preferably has a density range of 0.870 to 0.929 g / cm³. 3 Preferably, the density range is 0.910 to 0.929 cm³. 3 The density of polyethylene resin can be determined in accordance with JIS K 7112:1999. Furthermore, the low-density polyethylene resin may be, for example, a high-pressure radical-process (high-pressure method) low-density polyethylene resin, or a metallocene-catalyzed linear low-density polyethylene resin. Details of such polyethylene resins can be found, for example, in the description in Japanese Patent Application No. 2016-072380.

[0023] When the resin composition of the present invention contains low-density polyethylene resin as a resin component, the content of low-density polyethylene resin in the resin component constituting the resin composition of the present invention is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, and may also be 1 to 10% by mass, 2 to 8% by mass, or 3 to 5% by mass.

[0024] Polyethylene resins such as maleic acid-modified polyethylene resin and low-density polyethylene resin that can be used in the present invention can be synthesized by conventional methods, or commercially available products can be used. Specific examples of commercially available products include, for example, Petrocene 180R, Petrocene 170R, Petrocene 173R from Tosoh Corporation; Sumikasen F218-0, Sumikasen F200, Sumikasen G401 from Sumitomo Chemical Co., Ltd.; Novatec UE320, Novatec LF443, Novatec LF280H, Novatec LF448K1, Adtex L6100M from Nippon Polyethylene Co., Ltd.; NUC-9060, ENGAGE-8100 from NUC Corporation; and NUCG-5130 from Dow Elastomer Corporation (all are product names).

[0025] The total content of resin components in the resin composition of the present invention is usually 30 to 80% by mass, but can also be 40 to 75% by mass, or 50 to 75% by mass.

[0026] <Antioxidant> The resin composition of the present invention contains specific amounts of imidazole compounds (imidazole-based antioxidants), phenol compounds (phenol-based antioxidants), and thioether compounds (thioether-based antioxidants) as antioxidants (anti-aging agents). By incorporating specific amounts of each of these antioxidants, it is possible to suppress the occurrence of bleeding in the resulting resin coating while further improving heat resistance, crosslinkability, and slipperiness. Each of the above antioxidants is described below.

[0027] (Imidazole compounds) Examples of imidazole compounds (compounds having a benzimidazole skeleton) used in the resin composition of the present invention include 2-sulfanylbenzimidazole, 2-sulfanylmethylbenzimidazole, 4-sulfanylmethylbenzimidazole, 5-sulfanylmethylbenzimidazole, and their zinc salts, with 2-sulfanylbenzimidazole and its zinc salt being preferred. The present invention may also use commercially available imidazole compounds. Examples of commercially available products include Nocrack MBZ (trade name, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.). The imidazole compound content is 14 to 24 parts by mass per 100 parts by mass of the total resin components constituting the resin composition of the present invention. From the viewpoint of further improving heat resistance and crosslinking properties, and from the viewpoint of dispersibility in the resin and suppressing the occurrence of bleeding, the content is preferably 16 to 24 parts by mass, and more preferably 16 to 20 parts by mass.

[0028] (Phenol compounds) Examples of phenol compounds (compounds having a phenol skeleton) used in the resin composition of the present invention include triethylene glycol-bis(3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate), 1,6-hexanediol-bis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), pentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), and Examples include kutadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5,-di-t-butyl-4-hydroxybenzyl)benzene, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanuric acid, and isooctyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, and one or more of these can be used. Among these, those having two or more 3,5-di-t-butyl-4-hydroxyphenyl groups or 3,5-di-t-butyl-4-hydroxybenzyl groups are preferred from the viewpoint of providing high heat resistance to automotive wire harnesses, and 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanuric acid and pentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) are particularly preferred. Even if a compound has a phenol skeleton (phenolic antioxidant), as described later, if it falls under the category of triazole compounds, N,N'-diacylhydrazine compounds, or dihydrazide compounds and is used as a copper damage inhibitor, it will be treated as a copper damage inhibitor rather than a phenolic compound in this invention. The present invention may also use commercially available phenol compounds. Examples of commercially available products include Irganox 1010 (trade name, manufactured by BASF) and Adeka Stab AO-20 (trade name, manufactured by ADEKA). The content of the phenol compound in the resin composition of the present invention is 1.0 to 2.0 parts by mass per 100 parts by mass of the total content of the resin components. From the viewpoint of further improving heat resistance and crosslinking properties, and from the viewpoint of suppressing the occurrence of bleeding, the content is preferably 1.5 to 2.0 parts by mass.

[0029] (Thioether compounds) Examples of thioether compounds (compounds having a thioether bond) used in the resin composition of the present invention include thioether compounds used as antioxidants for wire coatings. For example, dilauryl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearyl 3,3'-thiodipropionate, 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-dodecylthiopropionate] (also known as bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropyloxy]methyl]-1,3-propanediyl) can be used, and one or more of these can be used. Among these, 2,2-bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-dodecylthiopropionate] is preferred from the viewpoint of long-term thermal stability. The resin composition of the present invention may also use commercially available thioether compounds. Examples of commercially available products include ADEKA stab AO-412S (trade name, manufactured by ADEKA).

[0030] The content of the thioether compound is 0.3 to 0.9 parts by mass per 100 parts by mass of the total content of the resin components constituting the resin composition of the present invention. Insulated wires having a resin composition with a high concentration of the thioether compound are prone to the thioether compound bleeding onto the surface of the insulating film. When such insulated wires are stored at high temperatures, their lubricity is significantly impaired (the coefficient of dynamic friction increases significantly), which hinders the assembly of the wires. Therefore, by keeping the content of the thioether compound within the above range, a resin composition with excellent heat resistance and lubricity can be obtained. Furthermore, from the viewpoint of improving heat resistance and improving lubricity while suppressing crosslinking inhibition, the content is preferably 0.3 to 0.6 parts by mass.

[0031] (Other antioxidants) Furthermore, the resin composition of the present invention may contain antioxidants other than the imidazole compound, phenol compound, and thioether compound mentioned above. Examples of such antioxidants include copper damage inhibitors and zinc compounds, and one or more of these can be used. Specific examples of zinc compounds include zinc sulfide and zinc oxide.

[0032] (Copper damage inhibitor) Examples of copper-damaging inhibitors that can be used in the resin composition of the present invention include triazole compounds, N,N'-diacylhydrazine compounds, and dihydrazide compounds. Examples of commercially available products include the heavy metal deactivator ADEKA's CDA series (CDA-1, CDA-6, CDA-10 (all trade names)) and BASF's Irganox MD1024 (trade name). When the resin composition of the present invention contains a copper damage inhibitor, the amount of the copper damage inhibitor is preferably 0.5 to 2.0 parts by mass per 100 parts by mass of the total resin component, from the viewpoint of reducing heat resistance due to contact with metal ions such as copper.

[0033] (Zinc compounds) Examples of zinc compounds that can be used in the resin composition of the present invention include zinc sulfide and zinc oxide. In particular, it is preferable that the resin composition of the present invention contains zinc sulfide and / or zinc oxide. Examples of commercially available zinc sulfide and zinc oxide include SachtolithHD-S (trade name) from Sachtleben Chemie GmbH and Zinc sulfide from Taizhou ATS Optical Material. In the present invention and this specification, zinc compounds do not include zinc salts with imidazole compounds used as imidazole compounds, nor zinc stearate used as a processing aid (lubricant). When the resin composition of the present invention contains a zinc compound, the content of the zinc compound is preferably 1.0 to 10 parts by mass, and more preferably 3.0 to 5.0 parts by mass, per 100 parts by mass of the total content of the resin components, from the viewpoint of heat resistance.

[0034] The total content of the antioxidant is preferably 10 to 35 parts by mass, more preferably 15 to 30 parts by mass, and even more preferably 20 to 26 parts by mass, relative to 100 parts by mass of the total content of the resin components constituting the resin composition of the present invention.

[0035] <Flame retardant> The resin composition of the present invention contains a bromine compound (bromine-based flame retardant) and an antimony compound (antimony-based flame retardant) as flame retardants. The preferred ratio of the bromine compound to the antimony compound in the resin composition is 2 to 5 moles of bromine element per mole of antimony element. The total amount of flame retardant in the resin composition of the present invention is preferably 20 to 45 parts by mass, more preferably 30 to 45 parts by mass, and even more preferably 31 to 42 parts by mass, based on 100 parts by mass of the total resin content.

[0036] (Bromine compounds) Examples of bromine compounds used as flame retardants in the present invention include brominated N,N'-ethylenebisphthalimide or compounds derived therefrom (collectively referred to as "brominated N,N'-ethylenebisphthalimide compounds"), N,N'-bis(bromophenyl)terephthalamide or compounds derived therefrom (collectively referred to as "N,N'-bis(bromophenyl)terephthalamide compounds"), brominated bisphenol or compounds derived therefrom (collectively referred to as "brominated bisphenol compounds"), and organic bromine-containing flame retardants such as 1,2-bis(bromophenyl)alkanes. Among these, for example, brominated N,N'-ethylenebisphthalimide and / or 1,2-bis(bromophenyl)ethane are preferred. A commercially available bromine compound may be used as the bromine compound in the resin composition of the present invention. An example of a commercially available product is Cytex 8010 (trade name, manufactured by Albemarle).

[0037] The bromine compound content in the resin composition of the present invention is 15 to 30 parts by mass per 100 parts by mass of the total resin component content. From the viewpoint of flame retardancy, the content is preferably 20 to 30 parts by mass, and more preferably 24 to 30 parts by mass.

[0038] (Antimony compound) Examples of antimony compounds include antimony trioxide, antimony tetroxide, antimony pentoxide, and sodium antimonate. Antimony reacts with chlorine (halogen), and the resulting gas is thought to block oxygen, thereby promoting the formation of a carbonized layer and trapping free radicals (stopping the thermal decomposition chain reaction). In particular, from the viewpoint of forming a more stable carbonized layer, it is preferable to include antimony trioxide in the present invention. Commercially available antimony trioxide may be used in this invention. Examples of commercially available products include PATOX-C (trade name, manufactured by Nippon Seikou Co., Ltd.).

[0039] When the resin composition of the present invention contains an antimony compound, the amount is 5 to 15 parts by mass per 100 parts by mass of the total resin components. From the viewpoint of flame retardancy, the amount is preferably 8 to 13 parts by mass, more preferably 9 to 12 parts by mass, and even more preferably 10 to 12 parts by mass.

[0040] (Other flame retardants) In addition to the bromine and antimony compounds mentioned above, the resin composition of the present invention may also contain other flame retardants that can be commonly used in insulating coatings for insulated wires. Examples of such flame retardants include metal hydroxides (hydroxide-based flame retardants) such as magnesium hydroxide and aluminum hydroxide. When the resin composition of the present invention contains a hydroxide-based flame retardant, the amount is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of the total resin component.

[0041] <Other ingredients> In addition to the components described above, the resin composition of the present invention may contain other components, such as the following crosslinking aids and processing aids, to the extent that they do not impair the effects of the present invention. Furthermore, it may contain components such as plasticizers, fillers, and pigments as needed.

[0042] <Crosslinking agent> The resin composition of the present invention may also preferably contain a crosslinking aid. Examples of crosslinking aids include polyfunctional compounds, and compounds having two or more (preferably three or more, more preferably three to six) ethylenically unsaturated bonds (carbon-carbon double bonds) in the molecule are preferred. Specific examples of crosslinking aids include (meth)acrylate compounds such as polypropylene glycol di(meth)acrylate and trimethylolpropane tri(meth)acrylate, allyl compounds such as triallyl cyanurate, maleimide compounds, and divinyl compounds. The present invention may also utilize commercially available crosslinking aids. Examples of commercially available products include Ogmont T200 (trade name, manufactured by Shin-Nakamura Chemical Industry Co., Ltd.). The resin composition of the present invention preferably contains 2 to 6 parts by mass of a crosslinking aid, and more preferably 3 to 5 parts by mass, per 100 parts by mass of the total resin component content.

[0043] <Processing aid> The resin composition of the present invention may also preferably contain a processing aid. A preferred example of a processing aid is a metal soap (lubricant). Examples of metal soaps (lubricants) that can be used in the resin composition of the present invention include calcium stearate, zinc stearate, and magnesium stearate. The present invention may also use commercially available metal soaps. An example of a commercially available product is Shinaka Red ZS-101 (product name, manufactured by Shinagawa Chemical Co., Ltd.).

[0044] When the resin composition of the present invention contains a lubricant, it is preferable that the lubricant be present in an amount of 0.5 to 2 parts by mass per 100 parts by mass of the total resin component.

[0045] <Dispersant> The resin composition of the present invention may also preferably contain a dispersant. By including a dispersant in the resin composition of the present invention, it is possible to prevent the re-aggregation of additives such as flame retardants and antioxidants, improve the dispersibility of each component in the polymer, and make it possible to achieve excellent processability for compound manufacturing using feeder-rulers and twin-screw extruders, as well as further enhance heat resistance. The dispersant that can be used in the present invention is not particularly limited, and dispersants that are normally blended into resin compositions can be used. From the viewpoint of further suppressing the re-aggregation of additives, the dispersant is preferably a wetting dispersant. A wetting dispersant is an additive that has both the function of a wetting agent, which acts as a surfactant to increase the wettability of the dispersed phase to the resin component, and the function of preventing aggregation of the dispersed phase through actions such as electrical repulsion and steric hindrance. Typically, the function of a wetting agent is carried out by a chain that is compatible with the resin component, and the function of preventing aggregation of the dispersed phase is carried out by an adsorbent group that is attached to the dispersed phase. Examples of commercially available wetting dispersants include BYK-MAX D4221 and BYK-MAX P4102 (both trade names, manufactured by BYK-Chemie Japan).

[0046] When the resin composition of the present invention contains a dispersant, from the viewpoint of further improving heat resistance and suppressing the occurrence of bloom and inhibition of crosslinking, it is preferable to contain 0.5 to 6.0 parts by mass, and more preferably 1.0 to 6.0 parts by mass, per 100 parts by mass of the total content of the resin component.

[0047] <Additives> The resin composition of the present invention may contain various additives, such as ultraviolet absorbers, plasticizers, fillers, and pigments, as needed, within limits that do not impair the effects of the present invention.

[0048] [Method for producing resin compositions] The resin composition of the present invention can be obtained by blending a resin, an antioxidant, a flame retardant, and other components, and optionally the aforementioned optional components, and then melt-kneading them in a batch-type kneader such as a roll, kneader, or Banbury mixer, or a commonly used kneading device such as a twin-screw extruder.

[0049] [Insulated wire] The insulated wire of the present invention has a layer on the surface of the conductor (including conductor bundles and fiber cores) made of a resin coating material formed by crosslinking the resin composition of the present invention. The insulated wire of the present invention may also have an intermediate layer or a shielding layer between the conductor and the layer made of the resin coating material.

[0050] The conductor's shape and material can be any shape and material commonly used in insulated wires for automotive wire harnesses. The conductor can be single-strand or stranded, and can be bare or tinned or enamel coated. Examples of metal materials for forming the conductor include soft copper, copper alloys, and aluminum. Furthermore, the thickness of the layer made of resin coating material formed around the conductor is not particularly limited, but is usually about 0.15 to 5 mm. When using the resin composition of the present invention, an advantage is that an insulated wire with excellent flexibility, hardness, degree of crosslinking, flame retardancy, cold resistance, and heat resistance can be obtained even if the thickness of the resin coating layer is reduced.

[0051] [Automotive Wire Harness] In the present invention and this specification, an automotive wire harness is a general term for bundles of wires routed in various parts of a vehicle, such as the engine compartment, instrument panel, and inside the doors, according to environmental performance requirements. The automotive wire harness of the present invention has the insulated wire of the present invention. The resin composition of the present invention has excellent appearance and also possesses excellent flame retardancy and mechanical properties. Therefore, a wire harness incorporating an insulated wire having a layer made of a resin coating material formed by crosslinking the resin composition of the present invention can be suitably used for automotive applications. Hereafter, automotive wire harnesses may simply be referred to as "wire harnesses."

[0052] [Manufacturing method for insulated wires used in automotive wire harnesses] The insulated wire used in the automotive wire harness of the present invention can be obtained by extruding the resin composition of the present invention onto a conductor to form a layer of the resin composition, and then irradiating the layer of the resin composition with an electron beam of 80 to 250 kGy. This electron beam irradiation causes a crosslinking reaction in the layer of the resin composition, forming a resin coating layer. The crosslinking reaction by electron beam irradiation can be carried out using conventional methods and conditions. The electron beam irradiation conditions are preferably an irradiation dose of 80 to 200 kGy, and more preferably 80 to 160 kGy. The acceleration voltage is preferably 300 to 3000 keV, and more preferably 500 to 2500 keV. Furthermore, a multilayer structure may be adopted, such as having an intermediate layer or shielding layer between the conductor and the coating layer, and between the coating layers themselves.

[0053] The conditions for extruding the resin composition of the present invention are not particularly limited as long as the resin composition of the present invention can be extruded. However, in order to reduce the load on the extruder (extruder) and ensure shape retention, the extrusion temperature (head portion) is preferably 100 to 230°C, and more preferably 120 to 200°C. Furthermore, other conditions for extrusion molding can be set as appropriate depending on the purpose. The screw configuration of the extruder is not particularly limited, and standard full-flight screws, double-flight screws, tip-double-flight screws, Maddock screws, etc., can be used. [Examples]

[0054] The present invention will be described in more detail based on the following examples and comparative examples, but the present invention is not limited thereto.

[0055] [Examples 1-13 and Comparative Examples 1-12] The materials used to prepare the resin compositions of Examples 1-13 and Comparative Examples 1-12 are shown in Tables 1 and 2 below. Details of the materials used are as follows. Note that (1)-(14) below correspond to (1)-(14) in Tables 1 and 2 below.

[0056] <Materials used> (resin) (1): Ethylene-vinyl acetate copolymer 1, Evaflex V5274 (trade name), vinyl acetate content: 17% by mass, manufactured by Mitsui DuPont Polychemicals. (2): Ethylene-vinyl acetate copolymer 2, Evaflex V422 (trade name), vinyl acetate content: 20% by mass, manufactured by Mitsui DuPont Polychemicals. (3): Maleic acid-modified polyethylene, Adtex L6100M (product name), manufactured by Nippon Polyolefin Co., Ltd. (4): Linear low-density polyethylene (LLDPE), Novatec UE320 (product name), density 0.922 g / cm³ 3 , Manufactured by Japan Polyethylene Co., Ltd.

[0057] (Flame retardant) (5): 1,2-Bis(pentabromophenyl)ethane, Cytex 8010 (trade name), manufactured by Albemarle. (6): Antimony trioxide, PATOX-C (trade name), manufactured by Nippon Seikou Co., Ltd.

[0058] (Antioxidant) (7): Zinc salt of 2-mercaptobenzimidazole, Nocrack MBZ (trade name), manufactured by Ouchi Shinko Chemical Industry Co., Ltd. (8): Pentaerythrityl-tetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate), Irganox 1010 (trade name), manufactured by BASF. (9): 2,2-Bis{[3-(dodecylthio)-1-oxopropoxy]methyl}propane-1,3-diyl bis[3-(dodecylthio)propionate], Adekastab AO-412S (trade name), manufactured by ADEKA Corporation. (10): 2',3-Bis{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl}propionohydrazide, Irganox MD1024 (trade name), manufactured by BASF. (11): Zinc sulfide, SachtolithHD-S (trade name), manufactured by Sachtleben Chemie GmbH. (12): Zinc oxide, two types of zinc oxide, manufactured by Mitsui Mining & Smelting Co., Ltd.

[0059] (Crosslinking agent) (13): Trimethylolpropane trimethacrylate, Ogmont T200 (product name), manufactured by Shin Nakamura Chemical Industry Co., Ltd.

[0060] (Lubricant) (14): Zinc stearate, Shinakared ZS-101 (product name), manufactured by Shinagawa Chemical Co., Ltd.

[0061] (Dispersant) (15): BYK-MAX D4221 (product name), manufactured by Big Chemie Japan Co., Ltd.

[0062] <Manufacturing of resin composition sheets> The mixture was melt-kneaded at 160°C using a 1.7-liter Banbury mixer according to the compositions shown in Tables 1 and 2 below, and the resulting mixture was formed into a sheet using a 6-inch roll press. Each of the obtained resin composition sheets was pressurized to a thickness of 1 mm using a pressure press set to a temperature of 160°C, and the molded sheets after pressurization were crosslinked with an electron beam to obtain test samples (Examples 1-13, Comparative Examples 1-12). The electron beam crosslinking was performed at an acceleration voltage of 750 keV and under conditions of 80 kGy or 120 kGy.

[0063] [Performance evaluation] The following performance evaluations were performed using each test sample manufactured as described above.

[0064] <Slipperiness Evaluation> The coefficient of dynamic friction was measured for each test sample (Examples 1-13, Comparative Examples 1-12) in accordance with the method of JIS K 7125:1999 under the following conditions. Each test sample was cut to a size of 320mm (length) x 200mm (width) x 1mm (thickness). A 100mm square low-density polyethylene sheet (model number: UBEC130, manufactured by Ube Maruzen Polyethylene Co., Ltd.) was placed on top of it, and a 100mm square acrylic plate was placed on top of the low-density polyethylene sheet. A test load (30N) was placed on the acrylic plate, and the low-density polyethylene sheet was pulled at a tensile speed of 100mm / min. The frictional force generated between each test sample and the low-density polyethylene sheet during movement over a measurement distance of 80mm was measured, and the coefficient of dynamic friction (before heating) was determined. Furthermore, each test sample used for measurement was heated at 50°C for 2 hours, then allowed to stand until its temperature returned to room temperature, and the coefficient of dynamic friction (after heating) was measured again under the same conditions. From the obtained coefficients of dynamic friction (before and after heating), the ratio of the coefficient of dynamic friction after heating to the coefficient of dynamic friction before heating (coefficient of dynamic friction after heating / coefficient of dynamic friction before heating) was calculated, and the slipperiness was evaluated by applying the obtained value to the evaluation criteria below. A larger value indicates that the slipperiness has decreased due to heating. -Evaluation Criteria- A: Less than 1.2 B: 1.2 or higher, less than 1.5 C:1.5 or more

[0065] <Evaluation of crosslinking properties> 0.1 g of each test sample (Examples 1-13, Comparative Examples 1-12) was taken and used as the sample, and the test was carried out according to the method specified in the Japan Society of Automotive Engineers of Japan (JASO) standard D618 6.14.2. Specifically, the sample was placed in a test tube, 20 ml of xylene was added, and it was heated at 120°C for 24 hours. After that, the sample was removed, dried in a 100°C drying oven for 6 hours, and then allowed to cool to room temperature (23°C) before the mass was accurately weighed. The gel fraction was defined as the percentage of the mass of the sample after xylene immersion and drying relative to the mass of the sample before xylene immersion ([mass of sample after xylene immersion and drying / mass of sample before xylene immersion] × 100), and the crosslinking properties were evaluated according to the following criteria. -Evaluation Criteria- A: Gel fraction of 70% or more B: Gel fraction 50% or more, less than 70% C: Gel fraction less than 50%

[0066] <Heat resistance evaluation> The heat resistance was evaluated based on the continuous heat resistance temperature according to the method specified in the Japan Society of Automotive Engineers of Japan (JASO) standard D618. Specifically, each test sample (Examples 1-13, Comparative Examples 1-12) was punched out into a dumbbell-shaped No. 3 as described in JIS K6251:2017 to make test specimens, and aging tests were conducted at temperatures of 170°C, 180°C, 190°C, and 200°C. The time until fracture occurred when the tensile elongation reached 100% (100% is the state when the elongation is twice as long) was determined, and the temperature at which fracture occurred after 10,000 hours with tensile elongation set to 100% was determined using an Arrhenius plot, and this was defined as the heat resistance life temperature. The heat resistance was evaluated by applying the heat resistance life temperature to the following criteria. -Evaluation Criteria- A: Items with a temperature of 151℃ or higher B: Items with a temperature of 150℃ or higher but less than 151℃ C: Items below 150℃

[0067] The results obtained are summarized in Tables 1 and 2 below.

[0068] [Table 1]

[0069] [Table 2]

[0070] The content of each component in the table is in parts by mass. "-" indicates that the component is not present.

[0071] Table 2 shows that resin composition sheets using resin compositions that did not satisfy the provisions of the present invention were inferior in at least one evaluation item of slipperiness, crosslinkability, and heat resistance. In contrast, as is clear from Table 1, the resin composition sheet prepared using the resin composition of the present invention performed superiorly in all evaluation items. From this, it can be seen that the resin composition of the present invention can achieve excellent properties as a resin coating layer for automotive wire harnesses.

[0072] Although we have described the present invention along with its embodiments, we do not intend to limit our invention in any detail of the description unless specifically designated, and we believe that it should be interpreted broadly without contradicting the spirit and scope of the invention as set forth in the appended claims.

[0073] This application claims priority based on Japanese Patent Application No. 2021-194495, filed in Japan on November 30, 2021, the contents of which are incorporated herein by reference as part of this specification.

Claims

1. A resin composition containing an ethylene-vinyl acetate copolymer resin as a resin component, The resin composition contains imidazole compounds, phenol compounds, and thioether compounds as antioxidants, and bromine compounds and antimony compounds as flame retardants. A resin composition wherein, per 100 parts by mass of the total content of the resin components in the resin composition, the content of the imidazole compound is 14 to 24 parts by mass, the content of the phenol compound is 1.0 to 2.0 parts by mass, the content of the thioether compound is 0.3 to 0.9 parts by mass, the content of the bromine compound is 15 to 30 parts by mass, and the content of the antimony compound is 5 to 15 parts by mass.

2. The resin composition according to claim 1, wherein the resin composition contains 0.5 to 6.0 parts by mass of a dispersant with respect to 100 parts by mass of the total content of the resin components in the resin composition.

3. The resin composition according to claim 1, comprising maleic acid-modified polyethylene resin and / or low-density polyethylene resin as the resin component.

4. The resin composition according to claim 1, wherein the proportion of vinyl acetate component in the ethylene-vinyl acetate copolymer resin is 30% by mass or less.

5. The resin composition according to claim 1, wherein the total content of the antioxidant in the resin composition is 20 to 26 parts by mass relative to 100 parts by mass of the total content of the resin component.

6. The resin composition according to claim 4, wherein the resin composition contains at least one crosslinking aid and a processing aid.

7. A resin composition according to any one of claims 1 to 6, for use in automotive wire harnesses.

8. A resin coating material obtained by crosslinking the resin composition according to any one of claims 1 to 6.

9. An insulated wire having an insulating coating made of the resin coating material described in claim 8.

10. An automotive wire harness having the insulated wire described in claim 9.

11. A method for manufacturing an insulated wire for use in an automobile wire harness, comprising the steps of: extruding a resin composition according to any one of claims 1 to 6 onto a conductor to form a layer of the resin composition; and irradiating the layer of the resin composition with an electron beam of 80 to 250 kGy.

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