Resin composition, electric wire, and cable

Abstract

To provide a resin composition with excellent flame retardancy and suppressed changes in tensile strength during heat aging, and also to provide an electric wire and a cable each prepared using the resin composition.SOLUTION: A flame-retardant resin composition contains (A) an ethylenic polymer, and flame retardants as (B) a metal hydroxide and (C) at least one selected from a compound in which at least one of three hydroxyl groups of gallic acid is substituted with an alkoxy group, a phenoxy group, or a silyl ether group and a compound in which at least one of three hydroxyl groups of gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group. Relative to 100 pts.mass of the component (A), the component (C) is 2 pts.mass or more and 5 pts.mass or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a resin composition, an electric wire, and a cable. [Background technology]

[0002] An electric wire includes a conductor and a covering layer provided around the conductor. A cable includes, for example, a stranded wire formed by twisting together such electric wires and a sheath provided around the stranded wire. The covering layer of an electric wire and the sheath of a cable are generally formed from an electrically insulating material whose main raw material is rubber, resin, or the like.

[0003] The coating layer of electric wires and the sheath of cables are required to have various properties depending on their applications. For example, electric wires and cables for electronic devices and railway vehicles are required to be made of halogen-free materials that suppress the generation of toxic and corrosive gases when burned, and to have high flame retardancy.

[0004] As a material that satisfies such requirements, Patent Document 1 describes a resin composition in which a metal hydroxide such as magnesium hydroxide is added as a flame retardant to a resin component whose base polymer is an ethylene-based polymer. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-2062 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the investigations of the present inventors, when higher flame retardancy is required, the resin composition described in Patent Document 1 is sometimes not sufficient. Meanwhile, the present inventors have discovered that adding a compound having multiple phenolic hydroxyl groups in the molecule, such as a gallic acid ester, significantly improves flame retardancy due to the high radical trapping effect of the phenolic hydroxyl groups. The radical trapping effect refers to the effect of the phenolic hydroxyl groups capturing the generated radicals. This allows the flame retardant to capture the radicals generated from the combustion product during combustion, thereby suppressing the reaction between the resin composition and oxygen.

[0007] However, as a result of further investigations by the present inventors, it was newly discovered that when a resin composition containing a compound having multiple phenolic hydroxyl groups in the molecule is subjected to heat aging, the tensile strength increases, resulting in a large rate of change in tensile strength from the initial state.

[0008] One aspect of the present disclosure provides a resin composition that is excellent in flame retardancy and that suppresses change in tensile strength during heat aging, and an electric wire and a cable formed using the resin composition. [Means for solving the problem]

[0009] One aspect of the present disclosure is a flame-retardant resin composition comprising: (A) an ethylene-based polymer; (B) a metal hydroxide as a flame retardant; and (C) at least one compound selected from the group consisting of a compound in which at least one of three hydroxyl groups in gallic acid has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group, and a compound in which at least one of three hydroxyl groups in a gallic acid ester has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group, wherein the flame-retardant resin composition contains 2 to 5 parts by mass of the component (C) per 100 parts by mass of the component (A). [Effects of the Invention]

[0010] According to one aspect of the present disclosure, there are provided a resin composition that is excellent in flame retardancy and that suppresses change in tensile strength during heat aging, and an electric wire and a cable formed using the resin composition. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the structure of an electric wire according to a first embodiment. [Figure 2] FIG. 10 is a cross-sectional view showing the structure of an electric wire according to a second embodiment. [Figure 3] FIG. 1 is a cross-sectional view showing the structure of an example of a cable. DETAILED DESCRIPTION OF THE INVENTION

[0012] A resin composition according to one embodiment of the present disclosure includes (A) an ethylene-based polymer, (B) a metal hydroxide, and (C) at least one compound selected from the group consisting of a compound in which at least one of three hydroxyl groups in gallic acid has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group, and a compound in which at least one of three hydroxyl groups in a gallic acid ester has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group.

[0013] As described below, such a resin composition has excellent flame retardancy, and also suppresses changes in tensile strength and elongation during heat aging. As mentioned above, according to the research of the present inventors, compounds having multiple phenolic hydroxyl groups in the molecule, such as gallic acid esters, can improve the flame retardancy of resin compositions. However, when a resin composition containing such a compound is subjected to heat aging, the tensile strength increases from the initial state while the elongation decreases, resulting in large changes in these properties. This situation is undesirable because it contradicts the design concept that small changes in physical properties are desirable under relatively short heating conditions.

[0014] The reason for this phenomenon is thought to be that the phenolic hydroxyl groups capture radicals that may be generated during the production of the coating layer of the electric wire and the sheath of the cable, and release the captured radicals during heat aging, thereby accelerating the crosslinking reaction of the base polymer. For example, in some cases, resin compositions are crosslinked to improve the heat resistance of the coating layer of the electric wire and the sheath of the cable, and radicals may be generated during this crosslinking.

[0015] The present inventors have considered that, in order to simultaneously achieve both radical scavenging during combustion and suppression of radical donation during heat aging, it is effective to protect the phenolic hydroxyl group, thereby temporarily reducing the reactivity of the phenolic hydroxyl group and returning it to its original hydroxyl group during combustion. That is, by replacing only the hydrogen with a different structure while leaving the oxygen of the phenolic hydroxyl group, the reactivity of the phenolic hydroxyl group is suppressed, and changes in tensile strength, etc. during heat aging are thought to be suppressed. In addition, if the replaced moiety is eliminated in the high-temperature environment during combustion and returns to the original hydroxyl group, restoring the radical trapping effect, it is thought that high flame retardancy can be maintained. Therefore, the present inventors have conducted various studies on protecting the hydroxyl groups of compounds such as gallic acid esters.

[0016] As a result, they found that by substituting at least one of the three hydroxyl groups in gallic acid or a gallic acid ester with an alkoxy group, a phenoxy group, or a silyl ether group, it is possible to suppress changes in tensile strength and other properties during heat aging while maintaining high flame retardancy.

[0017] The resin composition, electric wire, and cable according to one embodiment of the present disclosure will be described in detail below. <Resin composition> The resin composition is a halogen-free flame-retardant resin composition. Each component contained in the resin composition will be described in detail below. Note that, below, component (B) and component (C) may be collectively described as a flame retardant. [Component (A)] Examples of the ethylene polymer of component (A) include ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and ethylene-α-olefin copolymer. Component (A) preferably contains an ethylene-vinyl acetate copolymer. Furthermore, component (A) is preferably the base polymer in the resin composition.

[0018] [(B) Component] Examples of metal hydroxides for component (B) include magnesium hydroxide, aluminum hydroxide, hydrotalcite, boehmite, calcium hydroxide, iron (II) hydroxide, iron (III) hydroxide, etc. Component (B) preferably contains magnesium hydroxide.

[0019] Magnesium hydroxide includes, for example, surface-untreated and surface-treated magnesium hydroxides. Examples of surface-untreated magnesium hydroxides include natural magnesium hydroxide obtained by crushing brucite ore and synthetic magnesium hydroxide. Examples of surface-treated magnesium hydroxides include those surface-treated with a silane coupling agent, a phosphate ester, a fatty acid (e.g., stearic acid, oleic acid, etc.), or a fatty acid salt.

[0020] The magnesium hydroxide is preferably surface-treated with a silane coupling agent, because magnesium hydroxide surface-treated with a silane coupling agent has high affinity with component (A), resulting in good tensile properties of the resin composition.

[0021] The content of component (B) in the resin composition is preferably 50 to 300 parts by mass, more preferably 100 to 250 parts by mass, per 100 parts by mass of component (A). When the content of component (B) is 50 parts by mass or more per 100 parts by mass of component (A), higher flame retardancy can be obtained in the resulting electric wire, cable, etc. Furthermore, when the content of component (B) is 300 parts by mass or less per 100 parts by mass of component (A), adhesion and aggregation between metal hydroxide particles is suppressed, which makes it less likely that the fluidity of the resin composition will decrease, resulting in good processability of the resin composition, for example, processability by extrusion molding.

[0022] [(C) component] The compound of component (C) is at least one of a compound in which at least one of three hydroxyl groups in gallic acid has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group, and a compound in which at least one of three hydroxyl groups in a gallic acid ester has been substituted with an alkoxy group, a phenoxy group, or a silyl ether group. Gallic acid is a compound represented by the following formula (1):

[0023] [ka]

[0024] The carboxylic acid group in gallic acid may remain as a carboxylic acid structure or may be esterified as long as the hydroxyl group is protected. As the ester, an alkyl ester having a small number of carbon atoms, for example, a lower alkyl ester having 1 to 4 carbon atoms, is preferred. As the gallic acid ester, at least one selected from methyl gallate represented by the following formula (2) and propyl gallate represented by the following formula (3) is particularly preferred.

[0025] [ka]

[0026] [ka]

[0027] In the compound of component (C), at least one of the three hydroxyl groups may be substituted. The position of the substituent may be any of the 3-, 4-, and 5-positions. From the viewpoint of further suppressing radical donation during heat aging, it is preferable that multiple (i.e., two or three) hydroxyl groups are substituted, and it is more preferable that all hydroxyl groups are substituted. While the reason why the radical donation suppression effect during heat aging is exhibited even when not all hydroxyl groups are necessarily protected is unclear, the present inventors believe that this is due to a decrease in radical scavenging power due to steric hindrance.

[0028] The alkoxy group of the substituent is preferably an alkoxy group having 1 to 4 carbon atoms, such as a methoxy group, an ethoxy group, or a butoxy group, and a methoxy group is more preferred from the viewpoint of availability. Examples of compounds substituted with an alkoxy group include 3,4,5-trimethoxybenzoic acid (also known as eudesmic acid) and its alkyl esters, 3,5-dimethoxy-4-hydroxybenzoic acid (also known as syringic acid) and its alkyl esters, etc. Examples of alkyl esters of eudesmic acid include alkyl esters having 1 to 4 carbon atoms, such as methyl eudesmate and propyl eudesmate. Examples of alkyl esters of syringic acid include alkyl esters having 1 to 4 carbon atoms, such as methyl syringate.

[0029] As the compound substituted with an alkoxy group, eudesmic acid and alkyl esters thereof are preferred, and eudesmic acid is more preferred, from the viewpoint of further suppressing radical donation during heat aging. Examples of compounds substituted with a phenoxy group include 3,4,5-triphenoxybenzoic acid and its alkyl esters, 4-phenoxy-3,5-dihydroxybenzoic acid and its alkyl esters, 3-phenoxy-4,5-dihydroxybenzoic acid and its alkyl esters, 3,4-diphenoxy-5-dihydroxybenzoic acid and its alkyl esters, etc. In these cases, the alkyl ester is preferably an alkyl ester having from 1 to 4 carbon atoms.

[0030] Examples of the silyl ether group as a substituent include trialkylsilyloxy groups having 1 to 4 carbon atoms, such as trimethylsilyloxy, triethylsilyloxy, and tri-t-butylsilyloxy. The silyl ether group is more preferably a trimethylsilyloxy group because it is easily deprotected during combustion.

[0031] A silyl ether group can be introduced into a compound by silyl-etherifying a hydroxyl group using a silane compound. Examples of silane compounds used for silyl-etherification include chlorosilane compounds such as trimethylchlorosilane, triethylchlorosilane, and tri-t-butylchlorosilane. Protection with a silyl ether group can be easily achieved, for example, by adding a chlorosilane compound dropwise to a solution in which gallic acid or a gallic acid ester is dissolved together with a base, and allowing the reaction to occur.

[0032] When an ethylene-vinyl acetate copolymer is used as the ethylene-based polymer of component (A), the substituent is preferably a silyl ether group, because in an acidic environment caused by elimination of acetic acid during combustion, the silyl ether group is rapidly deprotected, and the compound quickly returns to the original gallic acid or gallate ester, making it easier to maintain flame retardancy.

[0033] Examples of compounds substituted with a silyl ether group include 3,4,5-tris(trimethylsilyloxy)benzoic acid and its alkyl esters, 3,5-di(trimethylsilyloxy)-4-hydroxybenzoic acid and its alkyl esters, 3-trimethylsilyloxy-4,5-dihydroxybenzoic acid and its alkyl esters, and 3,4,5-tris(tri-t-butylsilyloxy)benzoic acid and its alkyl esters. Examples of alkyl esters of 3,4,5-tris(trimethylsilyloxy)benzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3,4,5-tris(trimethylsilyloxy)benzoate. Examples of alkyl esters of 3,5-di(trimethylsilyloxy)-4-hydroxybenzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3,5-di(trimethylsilyloxy)-4-hydroxybenzoate. Examples of alkyl esters of 3-trimethylsilyloxy-4,5-dihydroxybenzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3-(trimethylsilyloxy)-4,5-dihydroxybenzoate. Examples of alkyl esters of 3,4,5-tris(tri-t-butylsilyloxy)benzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3,4,5-tris(tri-t-butylsilyloxy)benzoate.

[0034] As the substituent, from the viewpoint of further suppressing radical donation during heat aging, of the alkoxy group, phenoxy group and silyl ether group, the alkoxy group and silyl ether group are preferred, and the alkoxy group is more preferred.

[0035] The content of component (C) is preferably 1 part by mass or more and 50 parts by mass or less, and more preferably 2 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of component (A). When the content of component (C) is 1 part by mass or more per 100 parts by mass of component (A), high flame retardancy is obtained in the resulting electric wire, cable, etc. Furthermore, when the content of component (C) is 50 parts by mass or less per 100 parts by mass of component (A), the tensile strength of the resin composition is improved.

[0036] [Other ingredients] The resin composition may contain other components in addition to the above components as needed to the extent that the above properties are not affected. Examples of other components include flame retardants, flame retardant assistants, crosslinking agents, crosslinking assistants, processing aids, coupling agents, surface treatment agents, colorants, lubricants, compatibilizers, antioxidants, antiozonants, ultraviolet absorbers, light stabilizers, metal chelators, softeners, plasticizers, and the like.

[0037] <Electric wire> [First embodiment] 1 is a halogen-free, flame-retardant insulated wire according to the first embodiment. The wire 10 includes a conductor 1, an insulating layer 2 as a coating layer that coats the conductor 1, and a separator 3 provided between the conductor 1 and the insulating layer 2.

[0038] The conductor 1 can be a commonly used metal wire, such as a copper wire, a copper alloy wire, an aluminum wire, a gold wire, or a silver wire. Alternatively, the conductor 1 can be a metal wire plated with a metal such as tin or nickel. Alternatively, the conductor 1 can be a twisted wire made by twisting metal wires together. Examples of twisted wires that can be used include concentric twisted wires, bunched twisted wires, and composite twisted wires made by further twisting these concentrically. Alternatively, the conductor 1 can be a compressed conductor made by compressing twisted wires. Compressed conductors are preferable because they allow the diameter of the electric wire to be reduced.

[0039] The insulating layer 2 is formed from the above resin composition. There are no particular limitations on the thickness of the insulating layer 2, but it is preferably 0.15 mm or more and 2 mm or less. The separator 3 is formed of, for example, a polyester tape. When a stranded conductor is used as the conductor 1, the provision of the separator 3 can prevent the resin composition from penetrating into the inside of the conductor 1 when the resin composition is extruded, i.e., when the insulating layer 2 is formed. Note that the electric wire 10 does not necessarily have to include the separator 3.

[0040] The electric wire 10 can be manufactured, for example, as follows. First, the components (A) to (C) and other components are melt-kneaded to obtain a resin composition. The kneading device may be a known kneading device, such as a batch kneader (e.g., a Banbury mixer or a pressure kneader), or a continuous kneader (e.g., a twin-screw extruder).

[0041] Then, the conductor 1 is prepared, and the separator 3 is wound around the conductor 1. After that, the separator 3 is covered with a resin composition using an extrusion molding machine, thereby forming an insulating layer 2 of a predetermined thickness.

[0042] The insulating layer 2 is then crosslinked, for example, by electron beam crosslinking or chemical crosslinking. Although crosslinking is not essential, crosslinking the insulating layer 2 is preferable because crosslinking the insulating layer 2 improves the heat resistance of the insulating layer 2. When using the electron beam crosslinking method, the insulating layer 2 is irradiated with an electron beam of, for example, 1 Mrad to 30 Mrad (0.01 MGy to 0.3 MGy). When using the chemical crosslinking method, for example, a crosslinking agent is added to the resin composition in advance, and the resin composition is molded into the insulating layer 2 of the electric wire 10, and then the insulating layer 2 is heat-treated. Note that the electron beam crosslinking method is used in the examples described below.

[0043] [Second embodiment] The electric wire 20 shown in FIG. 2 is a halogen-free, flame-retardant insulated wire according to the second embodiment. The electric wire 20 differs from the electric wire 10 according to the first embodiment in that the insulating layer 2 is composed of two layers and in that the electric wire 20 does not include a separator 3. Specifically, the electric wire 20 includes a conductor 1, an insulating inner layer 2a provided around the conductor 1, and an insulating outer layer 2b provided around the insulating inner layer 2a. The insulating inner layer 2a is formed of an insulating resin such as polyethylene. The insulating outer layer 2b is formed of the above-mentioned resin composition. The insulating outer layer 2b corresponds to a coating layer. The electric wire 20 may include a separator 3, similar to the electric wire 10. The insulating layer 2 may also include three or more layers.

[0044] <Cable> 3 is a halogen-free, flame-retardant cable. The cable 30 includes a core 4, a sheath 5 as a covering layer that covers the core 4, and a separator 6 and a shield braid 7 provided between the core 4 and the sheath 5.

[0045] The core 4 has a three-core stranded wire 4a formed by twisting together three of the electric wires 10, and a filler 4b provided around the three-core stranded wire 4a. The filler 4b is made of staple yarn, paper tape, jute, etc. The core 4 does not necessarily have to have the filler 4b.

[0046] The sheath 5 is formed from the resin composition. The separator 6 is the same as the separator 3 in the electric wire 10. The shielding braid 7 is provided around the separator 6 and has an electrical shielding function. The shielding braid 7 is formed, for example, from a mesh-like woven metal tape, copper wire, or the like. The shielding braid 7 may be provided inside the separator 6, and the cable 30 may not have the shielding braid 7.

[0047] The cable 30 can be manufactured, for example, as follows. First, three electric wires 10 are produced by the same method as above. Then, the three electric wires 10 are twisted together with the fillers 4b to form the core 4, and the separator 6 and the shield braid 7 are provided around the core 4. Then, the surroundings of these are covered with a resin composition using an extrusion molding machine. This allows the sheath 5 to be formed with a predetermined thickness.

[0048] Then, if necessary, the sheath 5 is cross-linked in the same manner as above, whereby the cable 30 can be manufactured. Note that other electric wires may be used instead of the electric wire 10. Furthermore, instead of the three-core stranded wire 4a, a single core consisting of one electric wire may be used, or a multi-core stranded wire other than a three-core stranded wire may be used. Furthermore, another layer, for example, another insulating layer, may be provided between the core 4 and the sheath 5.

[0049] <Other uses of resin compositions> The resin composition can be used for electric wires and cables of various applications and sizes. Examples of applications for the electric wires and cables include those for electronic devices, railway vehicles, automobiles, in-panel wiring, in-device wiring, and in-building wiring. Since wires and cables for electronic devices or railway vehicles require particularly high flame retardancy, the resin composition can be suitably used for electric wires and cables for electronic devices or railway vehicles. The type of cable is also not particularly limited, and may be, for example, a power cable, a signal cable, or the like.

[0050] The resin composition can be used not only for the electric wires and cables but also for other applications, such as films, panels, mats, pipes, protective materials, fillers, fibers, resin molded products, resin substrates, stationery, building materials, connectors, bushings, grommets, terminal blocks, and terminal internal insulators. [Example]

[0051] Hereinafter, one embodiment of the present disclosure will be described with reference to an example, but the present disclosure is not limited to the following example. <Production of Resin Composition for Cable Sheath> Resin compositions for cable sheaths were produced by dry-blending the materials of Examples 1 to 8 and Comparative Examples 1 to 4 shown in Table 1 below at room temperature, and then melt-kneading the mixed materials using a pressure kneader at a discharge temperature of 190° C. The content of each material in Table 1 is expressed in parts by mass.

[0052] In the resin compositions of Examples 1, 2, and 6 to 8, (C1) eudesmic acid represented by the following formula (4) was used as component (C). Note that the content of (C1) eudesmic acid was varied among the resin compositions of Examples 1, 2, and 6 to 8.

[0053] [ka]

[0054] In the resin composition according to Example 3, (C2) methyl syringate represented by the following formula (5) was used as the component (C).

[0055] [ka]

[0056] In the resin composition of Example 4, (C3) silyl-protected propyl gallate 1 (propyl 3,4,5-tris(trimethylsilyloxy)benzoate represented by the following formula (6)) was used as component (C). Silyl-protected propyl gallate 1 was synthesized as follows: Propyl gallate was dissolved in acetone, and 5 equivalents of triethylamine per equivalent of hydroxyl groups of the propyl gallate and 5 equivalents of trimethylchlorosilane per equivalent of hydroxyl groups of the propyl gallate were added and reacted. Thereafter, acetone and triethylamine were removed to obtain silyl-protected propyl gallate 1. It was confirmed by FT-IR that the original hydroxyl groups in the obtained silyl-protected propyl gallate 1 were protected.

[0057] [ka]

[0058] In the resin composition of Example 5, (C4) silyl-protected propyl gallate 2 (propyl 3,4,5-tris(tri-t-butylsilyloxy)benzoate represented by the following formula (7)) was used as component (C). Silyl-protected propyl gallate 2 was synthesized in the same manner as silyl-protected propyl gallate 1, except that tri-t-butylchlorosilane was used instead of trimethylchlorosilane.

[0059] [ka]

[0060] The resin composition of Comparative Example 1 did not contain component (C), unlike the resin compositions of Examples 1 to 8. The resin compositions of Comparative Examples 2 to 4 used propyl gallate in which no hydroxyl groups were protected, instead of component (C).

[0061] <Cable manufacturing> By extrusion molding using a 20mm single-screw extruder of "Labo Plastomill (registered trademark)" manufactured by Toyo Seiki Seisakusho, which is an extrusion coating device for electric wire manufacturing, a cross-sectional area of ​​0.5mm 2 An insulating layer having a coating thickness of 0.2 mm was formed around the compressed tin-plated copper stranded wire. To form the insulating layer, a resin composition was used, which was produced by melt-kneading each material according to Comparative Example 1 shown in Table 1 in the same manner as for the resin composition for the sheath. The cylinder temperature was 160°C, and the wire take-up speed was 4.0 m / min. The insulating layer of the produced electric wire was then subjected to a crosslinking treatment by an electron beam crosslinking method under conditions of 7.5 Mrad, thereby crosslinking the resin composition constituting the insulating layer.

[0062] Three of the obtained electric wires were twisted together, and a polyester tape was wound around them as a separator, and then a shielding braid was applied therearound. Then, a 60 mm single-screw extruder was used to extrude a 0.45 mm thick sheath around the shield braid, which was made from the resin composition for the sheath according to Examples 1 to 8 and Comparative Examples 1 to 4. The sheath was then crosslinked by electron beam crosslinking under conditions of 7.5 Mrad, to produce a cable with an outer diameter of 4.5 mm.

[0063] [Table 1]

[0064] <Evaluation method> (1) Initial tensile test The sheath was stripped from the prepared cable, and a dumbbell-shaped test piece was punched out from the stripped sheath. Using the dumbbell-shaped test piece, a tensile test was performed in accordance with JIS C3005:2000 to measure the tensile strength and elongation. The tensile test was performed at a pulling speed of 250 mm / min.

[0065] (2) Heat aging test Dumbbell-shaped test pieces prepared in the same manner as in the initial tensile test in (1) above were heated in a Geer oven at 135°C for 168 hours. Then, a tensile test was performed in the same manner as in the initial tensile test using the dumbbell-shaped test pieces after heat aging, and the tensile strength and elongation were measured. The percentage change in tensile strength and elongation after heat aging compared to those before heat aging (i.e., at the time of the initial tensile test) was calculated.

[0066] (3) Cable combustion test A 600mm length was taken from the manufactured cable and used as a test sample. Using the test sample, a combustion test was conducted in accordance with IEC60332-1, and the distance from the upper support material to the burned area was measured. The longer the distance from the upper support material to the burned area, the shorter the fire spread distance and the higher the flame retardancy. If the test sample is completely burned, the distance from the upper support material to the burned area will be 0mm.

[0067] (4) Overall Judgment For the tensile strength in the initial tensile test, samples with a tensile strength of 8 MPa or more were judged as passing, and samples with a tensile strength of less than 8 MPa were judged as failing. For the elongation in the initial tensile test, samples with an elongation of 125% or more were judged as passing, and samples with an elongation of less than 125% were judged as failing.

[0068] The change rates of tensile strength and elongation in the heat aging test were judged as pass if they were ±30% or less, and fail if they were greater than ±30%. For the combustion test, similar to IEC60332-1, those with a distance of 50 mm or more from the upper support to the burned area were judged to have passed, and those with a distance of less than 50 mm were judged to have failed.

[0069] Finally, specimens that passed all of the tensile strength and elongation in the initial tensile test, the rate of change in tensile strength and elongation in the heat aging test, and the combustion test were rated as "pass," while specimens that failed any of the tests were rated as "fail." The evaluation results are shown in Table 1. In Table 1, specimens that passed were marked with a "◯" and specimens that failed were marked with an "×."

[0070] <Evaluation results> As shown in Table 1, Examples 1 to 8 passed all the tests including the initial tensile test, heat aging test, and combustion test.

[0071] On the other hand, Comparative Example 1, which did not contain component (C), failed the combustion test. Comparative Examples 2 and 3, which contained propyl gallate with no protected hydroxyl groups instead of component (C), passed the initial tensile test and the combustion test, but failed the heat aging test. Comparative Example 4, which contained only a relatively small amount of propyl gallate, failed both the heat aging test and the combustion test.

[0072] <Consideration> As shown in Comparative Examples 1 to 4, it can be said that the resin composition passes the combustion test only when a gallic acid ester is blended with the resin composition. However, as shown in Comparative Examples 2 to 4, the gallic acid ester fails the heat aging test because the hydroxyl groups are not protected.

[0073] Comparing Example 1 and Comparative Example 2, it can be said that the gallic acid ester and component (C) have the same flame retardant effect. In other words, it can be said that whether or not the hydroxyl group of the gallic acid ester is protected has almost no effect on the flame retardancy. This suggests that the substituent may be eliminated during combustion.

[0074] Furthermore, when Examples 1, 2, 6, and 7 are compared with Example 8, the tensile strength in the initial tensile test is higher, and therefore it can be said that it is preferable for the resin composition to contain 2 to 30 parts by mass of component (C) per 100 parts by mass of the total amount of component (A). [Explanation of symbols]

[0075] 1...conductor, 2...insulating layer (coating layer), 2a...insulating inner layer, 2b...insulating outer layer (coating layer), 3, 6...separator, 4...core, 4a...three-core stranded wire, 4b...interposer, 5...sheath, 7...shield braid, 10, 20...electric wire, 30...cable.

Claims

1. (A) an ethylene-based polymer; As a flame retardant (B) a metal hydroxide; (C) a compound in which at least one of three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group, The (C) component is contained in an amount of 2 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the (A) component, A flame-retardant resin composition comprising 50 parts by mass or more and 300 parts by mass or less of the component (B) per 100 parts by mass of the component (A).

2. An electric wire comprising a conductor and a coating layer that coats the conductor, An electric wire, wherein the coating layer is formed from the flame-retardant resin composition according to claim 1.

3. A cable comprising a sheath formed from the flame-retardant resin composition according to claim 1 or 2.

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