Crosslinkable resin composition and insulated wire

Abstract

To improve the oil resistance and flexibility of insulated wires that use metal hydroxide-based flame retardants. [Solution] A crosslinkable resin composition is provided which comprises a resin and a flame retardant, and further comprises a crosslinking agent and a crosslinking aid for crosslinking the resin, and is used as a coating material for insulated electric wires, wherein the resin is an ethylene-vinyl acetate copolymer with a vinyl acetate content of 40% by mass or more, the crosslinking agent is an organic peroxide-based crosslinking agent, the crosslinking aid is a nitrogen-containing organic compound, and the flame retardant is a metal hydroxide-based flame retardant.

Description

[Technical Field]

[0001] The present invention relates to a crosslinkable resin composition and an insulated wire, and more specifically, to a crosslinkable resin composition used as a coating material for an insulated wire, and an insulated wire whose coating material is formed of a crosslinked product of the crosslinkable resin composition. [Background Art]

[0002] Conventionally, in an insulated wire, a conductor is coated with a coating material referred to as an insulating material or the like. Insulated wires are sometimes also provided with a coating material called a sheath material that further covers the insulating material from the outside. Coating materials such as insulating materials and sheath materials are usually formed of a resin composition. Various base resins are known for the resin composition, and the selection of the specific resin is determined according to the application of the insulated wire and the like. For example, when heat resistance is required for an insulated wire, a coating material using a resin with a high glass transition temperature such as engineering plastics is employed, or the coating material is formed of a crosslinked product such as crosslinked polyethylene.

[0003] In addition to the base resin, the resin composition constituting the coating material of an insulated wire contains various compounding agents. For example, vehicle wires used in railway vehicles and electronic wires used in electronic devices are required to have flame retardancy specified in the Railway Vehicle Material Flammability Test (Shazai Nenshi) and UL standards. Therefore, the coating material of this type of insulated wire may contain a flame retardant in some cases.

[0004] As flame retardants used for coating materials of insulated wires, halogen-based flame retardants such as bromine-based flame retardants and chlorine-based flame retardants, and non-halogen flame retardants such as phosphorus-based flame retardants and metal hydroxide-based flame retardants are known. Among them, metal hydroxide-based flame retardants such as magnesium hydroxide are widely used as constituent materials for coating materials of insulated wires.

[0005] To achieve the same level of flame retardancy as halogen-based flame retardants using metal hydroxide-based flame retardants, it is usually necessary to include a larger amount of metal hydroxide-based flame retardant in the coating material than with halogen-based flame retardants. As a result, insulated wires containing metal hydroxide-based flame retardants in the coating material tend to be less flexible. Furthermore, in insulated wires using metal hydroxide-based flame retardants as a component material in the coating material, the amount of resin per unit volume is generally low. Therefore, if substances that can affect the mechanical properties of the resin, such as oil, adhere to the coating material, the ratio of oil to resin becomes high, and the effect can become more pronounced.

[0006] In this regard, Patent Document 1 below describes a method for improving the oil resistance and flexibility of insulated wires in which metal hydroxide-based flame retardants are used as flame retardants. Specifically, Patent Document 1 below describes a method in which a flame retardant consisting of magnesium hydroxide and / or aluminum hydroxide is contained in a ratio of 130 to 180 parts by mass per 100 parts by mass of base polymer, and a flame retardant that has undergone a specific surface treatment is used, a specific resin is used as the base polymer, and the conductor is coated with a resin composition that has crosslinking properties. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-158073 [Overview of the project] [Problems that the invention aims to solve]

[0008] Insulated wires using metal hydroxide-based flame retardants still have room for improvement in terms of oil resistance and flexibility. Although there is a demand for insulated wires with superior oil resistance and flexibility, such demands have not yet been met. Therefore, the present invention aims to satisfy such demands and addresses the challenge of improving the oil resistance and flexibility of insulated wires using metal hydroxide-based flame retardants. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides: A crosslinkable resin composition comprising a resin and a flame retardant, and further comprising a crosslinking agent and a crosslinking aid for crosslinking the resin, Used as a coating material for insulated wires, The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. The present invention provides a crosslinkable resin composition in which the flame retardant is a metal hydroxide-based flame retardant.

[0010] In order to solve the above problems, the present invention provides: An insulated electric wire comprising a conductor and a covering material that covers the conductor, The coating material is composed of a crosslinked product of a crosslinkable resin composition, The crosslinkable resin composition comprises a resin and a flame retardant, and further comprises a crosslinking agent and a crosslinking aid for crosslinking the resin. The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. The present invention provides an insulated wire in which the flame retardant is a metal hydroxide-based flame retardant. [Effects of the Invention]

[0011] According to the present invention, an insulated wire can be provided that has excellent oil resistance and flexibility, even while using a metal hydroxide-based flame retardant as the flame retardant. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing the structure of the vehicle access line. [Figure 2] Figure 2 is a schematic cross-sectional view showing the structure of a different vehicle access line than that shown in Figure 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing a different vehicle wiring structure from that shown in Figures 1 and 2. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below. In the following, examples will mainly be given when the insulated wire conforms to the specifications of JRIS J 1041:2006 "Railway vehicles - Halogen-free wires". More specifically, embodiments of the present invention will be described below using insulated wires used for connecting electrical equipment as an example. More specifically, the insulated wire in this embodiment is a lead wire used for power supply, and is used when one of the electrically connected electrical devices is a power supply source and the other is a rotating electric machine (motor, generator) or transformer. In addition, the vehicle lead wire in this embodiment is merely a specific example, and the insulated wire in this embodiment is not limited to lead wires, nor is it limited to vehicle wires that conform to the above standard.

[0014] The vehicle outlet wire exemplified in the present embodiment may be a low-voltage vehicle outlet wire used for direct current of 750 V or less, or alternating current of 600 V or less, or may be a high-voltage vehicle outlet wire used for direct current exceeding 750 V and 7000 V or less, or alternating current exceeding 600 V and 7000 V or less. In general, the electricity commonly used in railway vehicles is 600 V, 750 V, 1000 V, 1500 V, etc. for direct current, and 600 V, etc. for alternating current, and vehicle outlet wires are in many cases roughly classified into a 600 V class and a 1500 V class. The vehicle outlet wire exemplified in the present embodiment may be of the 600 V class, or may be of the 1500 V class.

[0015] Figure 1 is a schematic cross-sectional view of the vehicle outlet wire 100 of the present embodiment, which shows a cross-section when the vehicle outlet wire 100 arranged in a straight line along the length direction DL is cut along a plane orthogonal to the central axis CX. As shown in the figure, the vehicle outlet wire 100 of the present embodiment is a round wire with a circular cross-sectional shape, and includes the conductor 10, which serves as an electricity flow path when supplying power to electrical equipment, at the center in the radial direction DD.

[0016] As the conductor 10, for allowing the vehicle outlet wire 100 to exhibit good flexibility, for example, a conductor composed of a plurality of strands can be employed. The strand may be a soft copper wire having a diameter that falls within a range of 0.1 mm to 1.0 mm (for example, 0.18 mm, 0.26 mm, 0.32 mm, 0.45 mm, etc.). The strand may be, for example, a plated wire such as a tin-plated soft copper wire. The conductor 10 may be formed by taking a stranded wire composed of a plurality of strands as secondary stranded wires, and stranding (primary stranding) a plurality of (for example, 7, 19, 27, etc.) secondary stranded wires together.

[0017] As the conductor 10, for example, the nominal cross-sectional area is 2.0 mm 2 to 150 mm 2 the following can be employed.

[0018] The vehicle lead wire 100 illustrated in Figure 1 has a tape layer 20 made of tape spirally wrapped around the outer circumference of the conductor 10 in order to prevent the covering material from digging into the spaces between the strands of the conductor 10 and to prevent the conductor 10 and the covering material from becoming too strongly bonded and exhibiting excessively high bending rigidity. The tape layer 20 may be made of tape that is wrapped in a wrap-around fashion so that both ends in the width direction overlap to prevent the conductor 10 from being exposed. The tape layer 20 may be made of paper tape, resin tape, cloth tape, etc.

[0019] The vehicle lead wire 100 further comprises an insulating material 30 covering the tape layer 20 and a sheath material 40 covering the insulating material 30. Both the insulating material 30 and the sheath material 40 are cylindrical in shape, with a thickness that is approximately constant in the circumferential direction DR and the longitudinal direction DL. Thus, the vehicle lead wire 100 has a double layer of covering material, consisting of the insulating material 30 and the sheath material 40, as a covering material for the conductor 10. The sheath material 40 is arranged to be the outermost layer in the radial direction DD of the vehicle lead wire 100. That is, the outer surface of the sheath material 40 constitutes the surface of the vehicle lead wire 100, and the inner surface is arranged to be in contact with the outer surface of the insulating material 30. Furthermore, the outer surface of the insulating material 30 is in contact with the inner surface of the sheath material 40, and the inner surface is in contact with the outer surface of the tape layer 20.

[0020] The lead wire 100 for vehicles may have a small amount of inorganic powder (e.g., talc, clay, etc.) interposed between the sheath material 40 and the insulating material 30. When bending stress is applied to the lead wire 100 for vehicles, the tape layer 20 allows for good relative movement (slip) between the insulating material 30 and the conductor 10 in the longitudinal direction of the wire, and the interposition of talc or clay can also improve the slip between the sheath material 40 and the insulating material 30. In other words, in the lead wire 100 for vehicles, when bending, the frictional force between the insulating material 30 and the conductor 10 and the frictional force between the sheath material 40 and the insulating material 30 is suppressed, and good flexibility can be achieved.

[0021] The sheath material 40 is made of a resin composition containing a crosslinked resin. That is, the sheath material 40 is composed of a crosslinked product of a crosslinkable resin composition containing a resin and a crosslinking agent. The crosslinkable resin composition used in the composition of the sheath material 40 further contains a flame retardant and a crosslinking aid.

[0022] The crosslinking agent contained in the crosslinkable resin composition is an organic peroxide-based crosslinking agent, and the crosslinking aid contained in the crosslinkable resin composition is a nitrogen-containing organic compound. As will be described later, the crosslinkable resin composition in this embodiment contains an ethylene-vinyl acetate copolymer. When heated, the organic peroxide-based crosslinking agent undergoes molecular cleavage and generates radicals, which act to create crosslinking sites in the ethylene-vinyl acetate copolymer. The crosslinking aid then enters between adjacent ethylene-vinyl acetate copolymer molecules and acts to chemically bond (covalently bond) both ends of the nitrogen-containing organic compound molecule to the crosslinking sites created on each of the adjacent ethylene-vinyl acetate copolymer molecules, thereby creating intermolecular crosslinking.

[0023] The crosslinked product obtained by crosslinking the above crosslinkable resin composition contains a crosslinked ethylene-vinyl acetate copolymer, which includes a first crosslinked structure in which molecules are directly bonded to each other, and a second crosslinked structure in which molecules of the ethylene-vinyl acetate copolymer are bonded to each other via a crosslinking aid. In this second crosslinked structure, the spacing between the molecules of the ethylene-vinyl acetate copolymer is increased, so the van der Waals forces acting between the ethylene-vinyl acetate copolymers are reduced, and hydrogen bonding between molecules becomes less likely. Moreover, in this second crosslinked structure, not only is a wide spacing between molecules provided, but the intermolecular forces can be further reduced by interposing nitrogen-containing organic compounds, which are more polar than the polyethylene chains of the main chain, between the molecules. As a result, the crosslinked resin itself has excellent flexibility and improved receptivity of flame retardants, so that the sheath material 40 can also exhibit high flexibility. Furthermore, the presence of highly polar bonding sites can result in excellent oil resistance.

[0024] Examples of nitrogen-containing organic compounds that can be used as crosslinking aids include trialyl isocyanurate, trialyl cyanurate, trimetallyl isocyanurate, N,N'-m-phenylene bismaleimide, bismaleimide, fluorinated trialyl isocyanurate (1,3,5-tris(2,3,3-trifluoro-2-propenyl)-1,3,5-triazine-2,4,6-trione), tris(diallylamine)-S-triazine, trialyl phosphite, N,N-diallylacrylamide, hexaarylphosphoramide, N,N,N',N'-tetraallylphthalamide, N,N,N',N'-tetraallylmalonamide, trivinyl isocyanurate, tri(5-norbornene-2-methylene)cyanurate, and triacryloylhexahydro-1,3,5-triazine. Nitrogen-containing heterocyclic compounds such as isocyanurate trialyl and cyanurate trialyl are suitable as crosslinking aids used in this embodiment due to their bulky molecular structure. The crosslinking aid preferably contains one or both of isocyanurate trialyl and cyanurate trialyl.

[0025] The nitrogen-containing heterocyclic compound may be included in the crosslinkable resin composition in a proportion of, for example, 0.1 parts by mass or more per 100 parts by mass of the ethylene-vinyl acetate copolymer. The nitrogen-containing heterocyclic compound is preferably included in a proportion of 0.2 parts by mass or more, more preferably in a proportion of 0.3 parts by mass or more, and even more preferably in a proportion of 0.4 parts by mass or more, per 100 parts by mass of the ethylene-vinyl acetate copolymer. The nitrogen-containing heterocyclic compound may be included in the crosslinkable resin composition in a proportion of, for example, 2.4 parts by mass or less per 100 parts by mass of the ethylene-vinyl acetate copolymer. The nitrogen-containing heterocyclic compound is more preferably included in a proportion of 2.2 parts by mass or less, and even more preferably in a proportion of 2.0 parts by mass or less, per 100 parts by mass of the ethylene-vinyl acetate copolymer.

[0026] Examples of organic peroxide-based crosslinking agents to be included in the crosslinkable resin composition include dialkyl peroxides, hydroperoxides, peroxyesters, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides.

[0027] Examples of the dialkyl peroxides include dicumyl peroxide, di-t-butyl peroxide, and 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

[0028] Examples of the aforementioned hydroperoxides include permethane hydroperoxide, diisopropylbenzene hydroperoxide, cumene hydroperoxide, and t-butyl hydroperoxide.

[0029] Examples of the peroxyesters include t-butyl peroxy 2-ethylhexyl carbonate, t-hexyl peroxyisopropyl monocarbonate, t-hexyl peroxybenzoate, t-butyl peroxybenzoate, t-butyl peroxylaurate, t-butyl peroxy-3,5,5-trimethylhexanoate, t-butyl peroxyacetate, 2,5-dimethyl 2,5-di(benzoyl peroxy)hexane, and t-butyl peroxyisopropyl monocarbonate.

[0030] Examples of the aforementioned diacyl peroxides include dibenzoyl peroxide, di(4-methylbenzoyl) peroxide, and di(3-methylbenzoyl) peroxide.

[0031] Examples of the peroxydicarbonate include di(2-ethylhexyl)peroxydicarbonate and diisopropylperoxydicarbonate.

[0032] Examples of the peroxyketal include 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 1,1-di-t-butylperoxycyclohexane, 2,2-di(t-butylperoxy)-butane, n-butyl4,4-di-(t-butylperoxy)valerate, and 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane.

[0033] Examples of the ketone peroxide include methyl ethyl ketone peroxide and acetylacetone peroxide.

[0034] The organic peroxide-based crosslinking agent to be included in the crosslinkable resin composition is preferably a dialkyl peroxide, and more preferably a dicumyl peroxide.

[0035] Organic peroxide-based crosslinking agents such as dicumyl peroxide may be included in the crosslinkable resin composition in a proportion of, for example, 1.8 parts by mass or more per 100 parts by mass of ethylene-vinyl acetate copolymer. It is preferable that the organic peroxide-based crosslinking agent, such as dicumyl peroxide, be included in a proportion of 2.0 parts by mass or more, and more preferably 2.2 parts by mass or more, per 100 parts by mass of ethylene-vinyl acetate copolymer. The organic peroxide-based crosslinking agent, such as dicumyl peroxide, may be included in the crosslinkable resin composition in a proportion of, for example, 5.5 parts by mass or less per 100 parts by mass of ethylene-vinyl acetate copolymer. It is more preferable that the organic peroxide-based crosslinking agent, such as dicumyl peroxide, be included in a proportion of 5.0 parts by mass or less, and even more preferably 4.5 parts by mass or less, per 100 parts by mass of ethylene-vinyl acetate copolymer.

[0036] The crosslinkable resin composition constituting the sheath material 40 contains a metal hydroxide-based flame retardant as a flame retardant. The base resin of the crosslinkable resin composition can be an ethylene-vinyl acetate copolymer that has high acceptance for the metal hydroxide-based flame retardant and can provide good flexibility to the sheath material 40 even when the metal hydroxide-based flame retardant is contained in a high proportion to exhibit excellent flame retardancy. In particular, in this embodiment, an ethylene-vinyl acetate copolymer with a vinyl acetate content of 40% by mass or more is considered a suitable base resin for the crosslinkable resin composition and the sheath material 40 which is its crosslinked product.

[0037] The vinyl acetate content of the ethylene-vinyl acetate copolymer may be, for example, 41% by mass or more. The vinyl acetate content of the ethylene-vinyl acetate copolymer may be, for example, 42% by mass or more, 43% by mass or more, 44% by mass or more, 45% by mass or more, or 46% by mass or more. The vinyl acetate content of the ethylene-vinyl acetate copolymer may be, for example, less than 80% by mass. The vinyl acetate content of the ethylene-vinyl acetate copolymer may be, for example, less than 75% by mass, less than 70% by mass, less than 65% by mass, less than 60% by mass, or less than 55% by mass.

[0038] The vinyl acetate content can be measured based on JIS K7192:1999 "Plastics - Ethylene-vinyl acetate resin (EVAC) - Method for measuring vinyl acetate content". Furthermore, if the crosslinkable resin composition and its crosslinked sheath material 40 contain multiple ethylene-vinyl acetate copolymers, the vinyl acetate content refers to the vinyl acetate content in a mixed state of the multiple ethylene-vinyl acetate copolymers. The vinyl acetate content in the mixed state can also be predicted based on calculations. For example, the vinyl acetate content in an ethylene-vinyl acetate copolymer mixture containing a first ethylene-vinyl acetate copolymer (EVA1) with a vinyl acetate content of X1 mass% and a second ethylene-vinyl acetate copolymer (EVA2) with a vinyl acetate content of X2 mass% in a mass ratio of Y1:Y2 (EVA1:EVA2) can be determined based on the following calculation. Vinyl acetate content (mass%) = (X1·Y1 + X2·Y2) ÷ (Y1 + Y2)

[0039] The resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) may include resins other than ethylene-vinyl acetate copolymer. However, it is preferable that 90% by mass or more of the resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) is ethylene-vinyl acetate copolymer. The proportion of ethylene-vinyl acetate copolymer in the resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) may be 95% by mass or more, or 98% by mass or more. The resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) may be substantially ethylene-vinyl acetate copolymer only.

[0040] Examples of metal hydroxide-based flame retardants contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) include magnesium hydroxide and aluminum hydroxide. Magnesium hydroxide and aluminum hydroxide can be contained in the sheath material 40 in the form of particles with a median diameter (D50) on a volume basis measured by laser diffraction scattering, for example, of 0.5 μm or more and 10 μm or less. The metal hydroxide-based flame retardant can be contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) in a proportion of 60 parts by mass or more when the proportion of resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) is 100 parts by mass. The proportion of metal hydroxide-based flame retardant per 100 parts by mass of resin may be 70 parts by mass or more, or 80 parts by mass or more. The proportion of metal hydroxide-based flame retardant per 100 parts by mass of resin may be greater than 80 parts by mass, greater than 82 parts by mass, or greater than 84 parts by mass. The ratio of metal hydroxide-based flame retardant to 100 parts by mass of resin may be, for example, 180 parts by mass or less. The ratio of metal hydroxide-based flame retardant may be 160 parts by mass or less, 140 parts by mass or less, or 120 parts by mass or less. The ratio of metal hydroxide-based flame retardant may be less than 120 parts by mass or less than 100 parts by mass.

[0041] The crosslinkable resin composition and its crosslinked product (sheath material 40) may contain non-halogen flame retardants other than metal hydroxide-based flame retardants. Examples of non-halogen flame retardants other than metal hydroxide-based flame retardants include phosphorus-based flame retardants such as red phosphorus, ammonium phosphate, and phosphate esters; nitrogen-based flame retardants such as ammonium carbonate and melamine cyanurate; silicone-based flame retardants such as polyorganosiloxane; and graphite-based flame retardants such as thermally expandable graphite. When a non-halogen flame retardant other than a metal hydroxide-based flame retardant is included, the non-halogen flame retardant other than a metal hydroxide-based flame retardant may be included in a proportion of, for example, 1 part by mass or more and 50 parts by mass or less, when the proportion of resin contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) is 100 parts by mass. The content of the non-halogen flame retardant other than a metal hydroxide-based flame retardant may be, for example, 2 parts by mass or more, or 3 parts by mass or more. The content of non-halogen flame retardants other than metal hydroxide flame retardants may be, for example, 40 parts by mass or less, 30 parts by mass or less, or 20 parts by mass or less. The content of non-halogen flame retardants other than metal hydroxide flame retardants may be, for example, 10 parts by mass or less, or 5 parts by mass or less. The flame retardants contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) may consist substantially only of metal hydroxide flame retardants.

[0042] The crosslinkable resin composition and its crosslinked product (sheath material 40) may contain a plasticizer. Examples of plasticizers include phthalate ester plasticizers such as diisononyl phthalate, di-2-ethylhexyl phthalate, di-n-octyl phthalate, and dibutyl phthalate; adipate ester plasticizers such as octyl adipate and diisononyl adipate; phosphate ester plasticizers such as triphenyl phosphate and tricresyl phosphate; trimellitic acid ester plasticizers such as tri-2-ethylhexyl trimellitate and tri-n-octyl trimellitate; and epoxidized vegetable oil plasticizers such as epoxidized soybean oil. When a plasticizer is included, the plasticizer may be included in a proportion of, for example, 1 part by mass or more and 50 parts by mass or less, when the proportion of resin in the crosslinkable resin composition and its crosslinked product (sheath material 40) is 100 parts by mass. The plasticizer content may be, for example, 2 parts by mass or more, or 3 parts by mass or more. The plasticizer content may be, for example, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, or 10 parts by mass or less.

[0043] The crosslinkable resin composition and its crosslinked product (sheath material 40) may contain an antioxidant to suppress the deacetic acid reaction in the ethylene-vinyl acetate copolymer. Furthermore, the crosslinkable resin composition and its crosslinked product (sheath material 40) may also contain a lead-based stabilizer.

[0044] Examples of antioxidants include one or more selected from the group consisting of aromatic amine antioxidants, hindered phenol antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants, with aromatic amine antioxidants being particularly preferred.

[0045] Specific examples of aromatic amine antioxidants include, for example, 4,4'-bis(α,α-dimethylbenzyl)diphenylamine, 4,4'-dimethoxydiphenylamine, 4-isopropoxydiphenylamine, phenylnaphthylamine, and 2,2,4-trimethyl-1,2-dihydroquinoline polymer.

[0046] Examples of hindered phenol antioxidants include 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butylphenol, 2,6-di-t-butyl-p-cresol, hydroxymethyl-2,6-di-t-butylphenol, 2,6-di-t-α-dimethylamino-p-cresol, 2,5-di-t-butyl-4-ethylphenol, 4,4'-bis(2,6-di-t-butylphenol), 2,2'-methylene-bis-4-methyl-6-t-butylphenol, 2,2'-methylene-bis(4-ethyl-6-t-butylphenol), 4,4'-methylene-bis(6-t-butyl-o-cresol), 4,4'-methylene-bis(2,6-di-t-butylphenol), and 2,2'-methylene-bis (4-methyl-6-cyclohexylphenol), 4,4'-butylidene-bis(3-methyl-6-t-butylphenol), 4,4'-thiobis(6-t-butyl-3-methylphenol), bis(3-methyl-4-hydroxy-5-t-butylbenzyl) sulfide, 4,4'-thiobis(6-t-butyl-o-cresol), 2,2'-thiobis(4-methyl-6-t-butylphenol), 2,6-bis(2'-hydroxy-3'-t-butyl-5'-methylbenzyl)-4-methylphenol, diethyl ester of 3,5-di-t-butyl-4-hydroxybenzenesulfonic acid, 2,2'-dihydroxy-3,3'-di(α-methylcyclohexyl)-5,5'-dimethyl-diphenylmethane, octadecyl 3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 6-(hydroxy-3,5-di-t-butylanilino)-2,4-bis-octyl-thio-1,3,5-triazine, hexamethylene glycol-bis[β-(3,5-di-t-butyl-4-hydroxyphenol)propionate], N,N'-hexamethylene-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamic acid amide), 2,2-thio[diethyl-bis-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate], dioctadecyl ester of 3,5-di-t-butyl-4-hydroxybenzenephosphonic acid, tetrakis[methylene-3(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, 1,3,5-trimethyl-2,4,6-tris(3,Examples include 5-di-t-butyl-4-hydroxybenzyl)benzene, 1,1,3-tris(2-methyl-4-hydroxy-5-di-t-butylphenyl)butane, tris(3,5-di-t-butyl-4-hydroxyphenyl)isocyanurate, and tris[β-(3,5-di-t-butyl-4-hydroxyphenyl)propionyl-oxyethyl]isocyanurate.

[0047] Examples of sulfur-based antioxidants include mercaptobenzimidazole antioxidants, thioether antioxidants, dithioate antioxidants, thiocarbanilide antioxidants, and thiodipropion ester antioxidants.

[0048] Examples of phosphorus-based antioxidants include phosphoric acid, phosphorous acid, hypophosphorous acid derivatives, phenylphosphonic acid, polyphosphonates, dialkylpentaerythritol diphosphite, and dialkylbisphenol A diphosphite, which are phosphorus-containing compounds.

[0049] Examples of lead-based stabilizers include tribasic lead sulfate and lead stearate.

[0050] Antioxidants and lead-based stabilizers may be included individually or in combination of multiple types. When antioxidants and lead-based stabilizers are included, when the proportion of resin in the crosslinkable resin composition and its crosslinked product (sheath material 40) is 100 parts by mass, the antioxidant and lead-based stabilizer may be included in proportions of, for example, 0.1 parts by mass or more and 10.0 parts by mass or less. The respective content may be, for example, 0.5 parts by mass or more, or 1.0 part by mass or more. The respective content may be, for example, 8.0 parts by mass or less, or 6.0 parts by mass or less.

[0051] The crosslinkable resin composition and its crosslinked product (sheath material 40) may contain a reinforcing agent such as carbon black. The carbon black may be, for example, furnace black, thermal black, channel black, or acetylene black, but furnace black is preferred. The furnace black may be, for example, SAF, ISAF, HAF, MAF, FEF, GPF, SRF, etc., according to the classification in ASTM D 1765.

[0052] From the viewpoint of reinforcing effect, the furnace black contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) is preferably of a fine particle size, and is more preferably SAF, ISAF, HAF, etc. than MAF, FEF, GPF, SRF, etc. From the viewpoint of reinforcing effect, the furnace black contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) is preferably of a fine particle size. On the other hand, the furnace black contained in the crosslinkable resin composition and its crosslinked product (sheath material 40) disperses better in the resin if the particle size is above a certain level. From this viewpoint, the furnace black is preferably ISAF, HAF, etc., and more preferably HAF. When HAF is used as the furnace black to be contained in the crosslinkable resin composition and its crosslinked product (sheath material 40), the high-structure type (HAF-HS:N-347) has a DBP oil absorption capacity (old JIS K6221 A method) of 110 cm³ compared to the normal-structure type (HAF:N-330) and the low-structure type (HAF-LS:N-327). 3 A quantity exceeding 100g is preferable.

[0053] When carbon black such as HAF-HS is included in a crosslinkable resin composition and its crosslinked product (sheath material 40), the carbon black content can be, for example, 1 part by mass or more and 40 parts by mass or less when the resin content is 100 parts by mass. The carbon black content may be, for example, 2 parts by mass or more, or 3 parts by mass or more. The carbon black content may be, for example, 35 parts by mass or less, 30 parts by mass or less, or 25 parts by mass or less.

[0054] The crosslinkable resin composition and its crosslinked product (sheath material 40) may further contain: a vulcanization accelerator such as zinc oxide; a lubricant such as fatty acids, fatty acid salts, or fatty acid esters; and a bioagent such as an antibacterial agent, antifungal agent, rodenticide, or termite repellent.

[0055] The crosslinkable resin composition may be prepared such that the tensile strength (T) of the crosslinked material (sheath material 40) is, for example, 9 MPa or higher. The tensile strength of the crosslinked material (sheath material 40) may be 10 MPa or higher, or 11 MPa or higher. The tensile strength of the crosslinked material (sheath material 40) is usually 30 MPa or lower. The tensile strength of the crosslinked material (sheath material 40) may be, for example, 25 MPa or lower.

[0056] The crosslinkable resin composition may be prepared such that the 100% modulus (stress at 100% elongation: M100) of the crosslinked material (sheath material 40) is, for example, 4.0 MPa or less. The 100% modulus (M100) of the crosslinked material (sheath material 40) may be 3.5 MPa or less, or 3.0 MPa or less. The 100% modulus (M100) of the crosslinked material (sheath material 40) is usually 1.0 MPa or more.

[0057] The crosslinkable resin composition can be prepared such that the elongation (Eb) at break of the crosslinked material (sheath material 40) is, for example, 200% or more. The elongation at break of the crosslinked material (sheath material 40) may be 250% or more, or 300% or more.

[0058] The above properties of the crosslinked material (sheath material 40) can be determined by conducting a tensile test at a speed of 200 mm / min in a room temperature environment (e.g., 23°C) using a dumbbell-shaped test specimen (e.g., type 3 test specimen), in accordance with JIS K6251:2017 "Vulcanized rubber and thermoplastic rubber - Method for determining tensile properties".

[0059] The crosslinkable resin compositions exemplified above can be used not only for the sheath material 40 but also for the insulating material 30 and the like. When using the crosslinkable resin compositions exemplified above for both the sheath material 40 and the insulating material 30, the crosslinkable resin compositions used for the sheath material 40 and the crosslinkable resin compositions used for the insulating material 30 may or may not have the same composition. For example, when using the crosslinkable resin compositions exemplified above for the insulating material 30, carbon black and the like may not be included.

[0060] Crosslinkable resin compositions can be prepared using common mixing equipment such as kneaders, Banbury mixers, and extruders. Furthermore, when using liquid crosslinking agents or crosslinking aids, pellets may be prepared with the other formulations first, and then the crosslinking agents and crosslinking aids may be adsorbed onto the pellets using a Henschel mixer or ribbon blender.

[0061] The insulating material 30 and the sheathing material 40 can be sequentially coated onto the laminated conductor 10 of the tape layer 20 using an extruder equipped with a crosshead. The crosslinking of the crosslinkable resin composition may be completed in the extruder, or additional crosslinking may be performed after extrusion in a semi-crosslinked state.

[0062] In this embodiment, a vehicle lead wire 100 is illustrated in which a conductor 10 is covered with a double layer of insulating material 30 and sheathing material 40. However, the crosslinkable resin composition may also be used in a vehicle lead wire 100 in which the conductor 10 is covered with only insulating material 30, as shown in Figure 2. Furthermore, the crosslinkable resin composition may be used not only in lead wires but also in multi-core signal lines 101 as shown in Figure 3.

[0063] In the signal line 101, for example, the crosslinkable resin composition exemplified above may be used to form the tape layer 20 that bundles a plurality of core wires, each having an insulating material 30 directly covering the conductor 10, with an intervening layer 50, and the sheath material 40 that covers the braid 60.

[0064] The insulated wire in this embodiment is not limited to vehicle wires, but may be a general-purpose wire such as EM-IE / F or NH-IE. Furthermore, the insulated wire in this embodiment does not have to be a round wire, but may be a flat wire such as EM-EEF.

[0065] The crosslinkable resin composition in this embodiment, as described above, is composed of specific components, which is advantageous for providing various insulated wires with excellent flexibility and oil resistance. In other words, insulated wires equipped with a coating material using such a crosslinkable resin composition can exhibit excellent flexibility and oil resistance even when metal hydroxide-based flame retardants are used. It should be noted that the above description is merely a specific example, and the present invention is not limited in any way to the above example, and the above description includes the following disclosures.

[0066] [1] A crosslinkable resin composition comprising a resin and a flame retardant, and further comprising a crosslinking agent and a crosslinking aid for crosslinking the resin, Used as a coating material for insulated wires, The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. A crosslinkable resin composition in which the flame retardant is a metal hydroxide-based flame retardant.

[0067] [2] The nitrogen-containing organic compound is a nitrogen-containing heterocyclic compound, The nitrogen-containing heterocyclic compound contains at least one of isocyanurate trialyl and cyanurate trialyl, The aforementioned organic peroxide-based crosslinking agent includes dicumyl peroxide, In relation to 100 parts by mass of the ethylene-vinyl acetate copolymer, The nitrogen-containing heterocyclic compound is present in an amount of 0.2 parts by mass or more and 2.2 parts by mass or less. The crosslinkable resin composition according to [1], wherein the dicumyl peroxide is contained in a proportion of 2.0 parts by mass or more and 5.0 parts by mass or less.

[0068] [3] An insulated electric wire comprising a conductor and a covering material that covers the conductor, The coating material is composed of a crosslinked product of a crosslinkable resin composition, The crosslinkable resin composition comprises a resin and a flame retardant, and further comprises a crosslinking agent and a crosslinking aid for crosslinking the resin. The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. An insulated wire in which the flame retardant is a metal hydroxide-based flame retardant. [Examples]

[0069] The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the specific cases shown in the examples.

[0070] [Preparation of crosslinkable resin compositions] Eleven types of ethylene-vinyl acetate copolymers, indicated by the following abbreviations, were prepared as base resins for the crosslinkable resin compositions. The abbreviations and details of the other compounding agents are also shown below.

[0071] <Ethylene-vinyl acetate copolymer> • EVA1: Vinyl acetate (VA) content 33% by mass, MFR 1g / 10min • EVA2: Vinyl acetate (VA) content 33% by mass, MFR 14g / 10min • EVA3: Vinyl acetate (VA) content 14% by mass, MFR 14g / 10min • EVA4: Vinyl acetate (VA) content 25% by mass, MFR 2g / 10min • EVA5: Vinyl acetate (VA) content 19% by mass, MFR 2.5g / 10min • EVA6: Vinyl acetate (VA) content 28% by mass, MFR 4g / 10min • EVA7: Vinyl acetate (VA) content 5% by mass, MFR 0.4g / 10min • EVA8: Vinyl acetate (VA) content 14% by mass, MFR 15g / 10min • EVA9: Vinyl acetate (VA) content 28% by mass, MFR 15g / 10min • EVA10: Vinyl acetate (VA) content 46% by mass, MFR 2.5g / 10min • EVA11: Vinyl acetate (VA) content 41% by mass, MFR 2g / 10min

[0072] In addition, the following were prepared as compounding agents other than ethylene-vinyl acetate copolymer. <Plasticizer> • OL: Diisononylphthalate <Antioxidant> • AO1: 4,4'-bis(α,α-dimethylbenzyl)diphenylamine • AO2:2-mercaptobenzimidazole AO3: 2,2,4-trimethyl-1,2-dihydroquinoline polymer <Flame retardant> ·P1: Red phosphorus M1: Magnesium hydroxide • M2: Magnesium hydroxide (different grade from M1) <Carbon Black> ·CB1:DBP oil absorption approximately 126cm 3 HAF-HS / 100g ·CB2:DBP oil absorption approximately 75cm 3 ISAF-LS / 100g <Vulcanization promoter> • ZO1: Three types of zinc oxide • ZO2: Three types of zinc oxide (different grade from ZO1) <Stabilizer> ·S1: Granular lead stearate S2: Tribasic lead sulfate <Lubricant> L1: Stearic acid • L2: Zinc stearate <Crosslinking agent> • XA1: Triallyl isocyanurate (TAIC) <Crosslinking agent> • PO1: Dicumyl peroxide (DCP)

[0073] [Base resin settings] By using ethylene-vinyl acetate copolymers from EVA1 to EVA11 individually or in blends, 34 different base resin formulations (BP1 to BP34) were established, as shown in Table 1 below. The rightmost column of Table 1 shows the vinyl acetate content for each base resin. As shown here, only BP24, BP26, and BP28 to BP32 (7 types in total) have a vinyl acetate content of 40% by mass or more.

[0074] [Table 1]

[0075] [evaluation] <Sample Preparation> Crosslinkable resin compositions were prepared using 97 different formulations shown in Tables 2 to 5 below. Uncrosslinked sheets were made using these crosslinkable resin compositions, and these uncrosslinked sheets were crosslinked by heat pressing to produce crosslinked resin sheets composed of crosslinked products of the crosslinkable resin compositions.

[0076] <Tensile Test> Dumbbell-shaped test specimens (Type 3) for tensile testing were taken from the cross-linked resin sheet. After conditioning the obtained specimens under normal temperature and humidity conditions, tensile tests were conducted, and the initial values ​​of tensile strength (T), elongation at break (Eb), and 100% modulus (stress at 100% elongation: M100) were measured. Similarly, dumbbell-shaped test specimens prepared in the same manner were immersed in IRM902 oil at 100°C for 24 hours. After removing them from the oil and wiping off any adhering oil, they were conditioned under normal temperature and humidity conditions, and tensile tests were conducted to measure the tensile strength (T) and elongation at break (Eb) of the dumbbell-shaped test specimens after the oil resistance test. The residual values ​​(T residual value, Eb residual value) were then calculated by dividing each measured value by the initial value. The results are shown in Tables 2 to 5.

[0077] <Flame-retardant> Six samples, No. 26 to 31, which do not contain phosphorus-based flame retardants and contain only 80 parts by mass or 85 parts by mass of magnesium hydroxide as a flame retardant, underwent combustion tests for railway vehicle materials (45-degree combustion tests). It was confirmed that they met the "flame retardancy" level or higher among the five categories: "flammable," "slow-burning," "flame retardant," "extremely flame retardant," and "non-flammable."

[0078] [Table 2]

[0079] [Table 3]

[0080] [Table 4]

[0081] [Table 5]

[0082] Focusing on the amount of flame retardant in the results shown in Tables 2 to 5, as shown in Tables 6 and 7 below, the decrease in tensile strength after the oil resistance test is significant if a certain amount or more of metal hydroxide-based flame retardant is not included. However, it was suggested that if the metal hydroxide-based flame retardant is included in a proportion exceeding 120 parts by mass, the initial value of the tensile strength may fall below the value required for wire coating material.

[0083] [Table 6]

[0084] [Table 7]

[0085] Considering the inclusion of a certain amount of metal hydroxide-based flame retardant, the results in Tables 2 to 5 show that in formulations using a base resin with a vinyl acetate content of less than 40% by mass, it tends to be difficult to suppress both the decrease in tensile strength after the oil resistance test and the increase in the 100% modulus value.

[0086] Focusing on carbon black, as shown in Table 8 below, high-structure carbon black (CB1: DBP oil absorption capacity approximately 126 cm³) 3 HAF-HS (100g) is better than the low-structured type (CB2:DBP oil absorption capacity approx. 75cm 3 A tendency towards better results was observed compared to ISAF-LS (100g).

[0087] [Table 8]

[0088] Furthermore, the above results confirm that good results tend to be obtained when organic peroxide-based crosslinking agents or nitrogen-containing organic compounds used in combination with ethylene-vinyl acetate copolymers having a vinyl acetate content of 40% by mass or more.

[0089] From the above, it can be understood that the present invention makes it possible to provide an insulated wire that is excellent in oil resistance and flexibility, even while using a metal hydroxide-based flame retardant as the flame retardant. [Explanation of Symbols]

[0090] 10: Conductor, 20: Tape layer, 30: Insulating material, 40: Sheath material, 50: Intervention, 60: Braid, 100: Vehicle access line, 101: Signal line

Claims

1. A crosslinkable resin composition comprising a resin and a flame retardant, and further comprising a crosslinking agent and a crosslinking aid for crosslinking the resin, Used as a coating material for insulated wires, The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. A crosslinkable resin composition in which the flame retardant is a metal hydroxide-based flame retardant.

2. The nitrogen-containing organic compound is a nitrogen-containing heterocyclic compound, The nitrogen-containing heterocyclic compound contains at least one of isocyanurate trialyl and cyanurate trialyl, The aforementioned organic peroxide-based crosslinking agent includes dicumyl peroxide, In relation to 100 parts by mass of the ethylene-vinyl acetate copolymer, The nitrogen-containing heterocyclic compound is present in an amount of 0.2 parts by mass or more and 2.2 parts by mass or less. The crosslinkable resin composition according to claim 1, wherein the dicumyl peroxide is contained in a proportion of 2.0 parts by mass or more and 5.0 parts by mass or less.

3. An insulated electric wire comprising a conductor and a covering material that covers the conductor, The coating material is composed of a crosslinked product of a crosslinkable resin composition, The crosslinkable resin composition comprises a resin and a flame retardant, and further comprises a crosslinking agent and a crosslinking aid for crosslinking the resin. The aforementioned resin is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 40% by mass or more. The crosslinking agent is an organic peroxide-based crosslinking agent, and the crosslinking aid is a nitrogen-containing organic compound. An insulated wire in which the flame retardant is a metal hydroxide-based flame retardant.

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