Resin composition, wire, and cable

Abstract

Provided are a resin composition, an electric wire, and a cable, each having excellent flame retardancy and suppressed change in tensile strength during heat aging. The resin composition comprises (A) an ethylene-based polymer, (B) a metal hydroxide, and (C) at least one of a compound in which at least one of the 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 the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group.

Description

Technical Field

[0001] The present disclosure relates to resin compositions, electric wires, and cables. Background Art

[0002] An electric wire has a conductor and a coating provided around the conductor. Furthermore, a cable, for example, has stranded wires, which are twisted together, and a sheath provided around the stranded wires. The coating of an electric wire and the sheath of a cable are generally made of an electrically insulating material primarily made of rubber, resin, or the like.

[0003] The coatings of wires and cables require various properties depending on their intended use. For example, wires and cables used in electronic equipment and railway vehicles are required to be made of halogen-free materials that suppress the generation of toxic and corrosive gases during combustion, and to exhibit high flame retardancy.

[0004] As a material that meets 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 having an ethylene-based polymer as a base polymer.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-2062 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, according to the studies conducted by the present inventors, when higher flame retardancy is required, the resin composition described in Patent Document 1 may be insufficient.

[0010] On the other hand, the present inventors have discovered that by adding a compound having multiple phenolic hydroxyl groups within its molecule, such as a gallic acid ester, flame retardancy is significantly improved due to the high free radical scavenging effect of the phenolic hydroxyl groups. The free radical scavenging effect refers to the effect of the phenolic hydroxyl groups capturing generated free radicals. As a result, the flame retardant can capture free radicals generated from the combustion products during combustion, inhibiting the reaction of the resin composition with oxygen.

[0011] However, the present inventors have conducted further studies and have recently found that, when a resin composition containing a compound having a plurality of phenolic hydroxyl groups in its molecule is subjected to heat aging, the tensile strength increases, and thus the rate of change in tensile strength from the initial state increases.

[0012] One aspect of the present disclosure provides a resin composition that is excellent in flame retardancy while suppressing changes in tensile strength during heat aging, and an electric wire and a cable formed using the resin composition.

[0013] Methods for solving problems

[0014] One embodiment of the present disclosure is a resin composition comprising (A) an ethylene-based polymer, (B) a metal hydroxide, and (C) at least one of a compound in which at least one of the 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 the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group.

[0015] Effects of the Invention

[0016] According to one embodiment of the present disclosure, there are provided a resin composition having excellent flame retardancy and suppressed change in tensile strength during heat aging, and an electric wire and a cable formed using the resin composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a cross-sectional view showing the structure of the electric wire according to the first embodiment.

[0018] Figure 2 It is a cross-sectional view showing the structure of an electric wire according to the second embodiment.

[0019] Figure 3 This is a cross-sectional view showing the structure of an example cable.

[0020] Explanation of symbols

[0021] 1: Conductor, 2: Insulation layer (coating), 2a: Inner insulation layer, 2b: Outer insulation layer (coating), 3, 6: Diaphragm, 4: Cable core, 4a: Three-core twisted wire, 4b: Interlayer, 5: Sheath, 7: Shielding braid, 10, 20: Wire, 30: Cable. DETAILED DESCRIPTION

[0022] A resin composition according to one embodiment of the present disclosure contains (A) an ethylene-based polymer, (B) a metal hydroxide, and (C) at least one of a compound in which at least one of the 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 the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group.

[0023] As described below, such a resin composition has excellent flame retardancy and suppresses changes in tensile strength and elongation during heat aging.

[0024] As described above, according to research conducted by the present inventors, compounds containing multiple phenolic hydroxyl groups within their molecules, such as gallic acid esters, can improve the flame retardancy of resin compositions. However, when resin compositions containing such compounds are subjected to heat aging, the rate of change in tensile strength increases compared to the initial state while the elongation decreases, resulting in a significant increase in these changes. This situation contradicts the design philosophy that minimal changes in physical properties are desirable under short heating conditions and is therefore undesirable.

[0025] This phenomenon is believed to occur because phenolic hydroxyl groups capture free radicals generated during the production of wire coatings and cable sheaths, releasing these captured radicals during thermal aging, thereby promoting the crosslinking reaction of the base polymer. For example, resin compositions are sometimes crosslinked to improve the heat resistance of wire coatings and cable sheaths, but this crosslinking may generate free radicals.

[0026] The present inventors believe that, in order to balance the capture of free radicals during combustion and the suppression of the supply of free radicals during thermal aging, it is effective to protect the phenolic hydroxyl group, temporarily reducing its reactivity and allowing it to return to its original hydroxyl group during combustion. Specifically, they believe that by replacing only the hydrogen with other structures while leaving the oxygen in the phenolic hydroxyl group, the reactivity of the phenolic hydroxyl group can be suppressed, thereby suppressing changes in tensile strength, etc., during thermal aging. Furthermore, it is believed that if the substituted portion dissociates under high temperature during combustion and returns to its original hydroxyl group, thereby restoring the free radical capture effect, high flame retardancy can be maintained. Therefore, the present inventors have conducted various studies on the protection of the hydroxyl groups in compounds such as gallic acid esters.

[0027] As a result, it was found that by replacing at least one of the three hydroxyl groups of gallic acid or a gallic acid ester with an alkoxy group, a phenoxy group, or a silyl ether group, changes in tensile strength and the like during heat aging can be suppressed while maintaining high flame retardancy.

[0028] The resin composition, electric wire, and cable according to one embodiment of the present disclosure will be described in detail below.

[0029] <Resin composition>

[0030] The resin composition is a halogen-free flame-retardant resin composition.

[0031] Hereinafter, each component contained in the resin composition will be described in detail. In the following description, the component (B) and the component (C) may be described together as a flame retardant.

[0032] [(A) ingredient]

[0033] As the ethylene polymer of component (A), for example, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ethylene-α-olefin copolymer etc. can be mentioned. As component (A), it is preferred to contain ethylene-vinyl acetate copolymer. In addition, component (A) is preferably the base polymer of the resin composition.

[0034] [(B) ingredient]

[0035] Examples of the metal hydroxide of the component (B) include magnesium hydroxide, aluminum hydroxide, hydrotalcite, boehmite, calcium hydroxide, iron (II) hydroxide, and iron (III) hydroxide. Component (B) preferably contains magnesium hydroxide.

[0036] Examples of magnesium hydroxide include non-surface-treated magnesium hydroxide and surface-treated magnesium hydroxide. Examples of non-surface-treated magnesium hydroxide include natural magnesium hydroxide obtained by crushing brucite ore and synthetic magnesium hydroxide. Examples of surface-treated magnesium hydroxide include magnesium hydroxide 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.

[0037] The magnesium hydroxide is preferably surface-treated with a silane coupling agent. Since the magnesium hydroxide surface-treated with a silane coupling agent has a high affinity with the component (A), the tensile properties of the resin composition are improved.

[0038] Relative to 100 mass parts (A) components, in resin combination, the content of (B) component is preferably below 300 mass parts above 50 mass parts, more preferably below 250 mass parts above 100 mass parts.The content of (B) component is that more than 50 mass parts can obtain higher flame retardancy in the electric wire, cable etc. obtained relative to 100 mass parts (A) components.In addition, the content of (B) component is that below 300 mass parts then metal hydroxide particles close together and agglomeration are suppressed each other so that the flowability of resin combination is difficult to decline relative to 100 mass parts (A) components, so the processability of resin combination, such as the processability of extrusion molding etc. are good.

[0039] [(C) ingredient]

[0040] The compound of component (C) is at least one of a compound in which at least one of the 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 the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group. Gallic acid is a compound represented by the following formula (1).

[0041] [Chemistry 1]

[0042]

[0043] The carboxylic acid group in gallic acid may be a carboxylic acid structure or an esterified one as long as the hydroxyl group is protected. As the ester, an alkyl ester having a small number of carbon atoms, such as 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.

[0044] [Chemistry 2]

[0045]

[0046] [Chemistry 3]

[0047]

[0048] In the compound of component (C), at least one of the three hydroxyl groups may be substituted. In addition, the position of the substituent may be any of the 3, 4, and 5 positions. From the perspective of further suppressing the provision of free radicals during heat aging, it is preferred that multiple (i.e., two or three) hydroxyl groups be substituted, and more preferably all hydroxyl groups be substituted. It should be noted that it is not known why the inhibitory effect of free radicals provided during heat aging is exerted even if not all hydroxyl groups are protected. The present inventors believe that the reason is that the free radical capture ability is reduced due to steric hindrance.

[0049] As the alkoxy group of the substituent, it is preferably an alkoxy group having 1 or more carbon atoms and 4 or less such as methoxy, ethoxy, butoxy, and from the point of view of the ease of obtaining, methoxy is more preferred. As the compound substituted by the alkoxy group, for example, 3,4,5-trimethoxybenzoic acid (another name: eucalyptol) and its alkyl esters, 3,5-dimethoxy-4-hydroxybenzoic acid (another name: syringic acid) and its alkyl esters can be listed. As the alkyl esters of eucalyptol, for example, alkyl esters having 1 or more carbon atoms and 4 or less such as methyl eucalyptol and propyl eucalyptol can be listed. As the alkyl esters of syringic acid, for example, alkyl esters having 1 or more carbon atoms and 4 or less such as methyl eucalyptol can be listed.

[0050] As the compound substituted with an alkoxy group, from the viewpoint of further suppressing the generation of free radicals during heat aging, eucalyptol and its alkyl esters are preferred, and eucalyptol is more preferred.

[0051] Examples of phenoxy-substituted compounds 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, and 3,4-diphenoxy-5-dihydroxybenzoic acid and its alkyl esters. In this case, the alkyl ester is preferably one having 1 to 4 carbon atoms.

[0052] Examples of the silyl ether group as a substituent include trialkylsilyloxy groups having 1 to 4 carbon atoms, such as trimethylsilyloxy, triethylsilyloxy, and tri-tert-butylsilyloxy. As the silyl ether group, trimethylsilyloxy is more preferred because it is easily deprotected during combustion.

[0053] Silyl ether groups can be introduced into compounds by silyl-etherifying hydroxyl groups using a silane compound. Examples of silane compounds used for silyl-etherification include chlorosilane compounds such as trimethylsilyl chloride, triethylsilyl chloride, and tri-tert-butylsilyl chloride. Protection of silyl ether groups can be facilitated, for example, by dropwise addition of the chlorosilane compound to a solution containing gallic acid or a gallic acid ester dissolved in a base.

[0054] When an ethylene-vinyl acetate copolymer is used as the vinyl polymer of component (A), the substituent is preferably a silyl ether group. This is because in an acidic environment created by the release of acetic acid during combustion, the silyl ether group is rapidly deprotected, and the compound quickly returns to its original gallic acid or gallic acid ester, thereby easily maintaining flame retardancy.

[0055] Examples of compounds substituted with a silyl ether group include 3,4,5-tris(trimethylsilyloxy)benzoic acid and its alkyl esters, 3,5-bis(trimethylsilyloxy)-4-hydroxybenzoic acid and its alkyl esters, 3-trimethylsilyloxy-4,5-dihydroxybenzoic acid and its alkyl esters, and 3,4,5-tris(tri-tert-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-bis(trimethylsilyloxy)-4-hydroxybenzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3,5-bis(trimethylsilyloxy)-4-hydroxybenzoate. Examples of the 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 the alkyl esters of 3,4,5-tris(tri-tert-butylsilyloxy)benzoic acid include alkyl esters having 1 to 4 carbon atoms, such as propyl 3,4,5-tris(tri-tert-butylsilyloxy)benzoate.

[0056] As the substituent, from the viewpoint of further suppressing the generation of radicals during heat aging, among alkoxy groups, phenoxy groups and silyl ether groups, alkoxy groups and silyl ether groups are preferred, and alkoxy groups are more preferred.

[0057] The content of component (C) is preferably 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of component (A), and more preferably 2 parts by mass or more and 30 parts by mass or less. When the content of component (C) is 1 part by mass or more relative to 100 parts by mass of component (A), high flame retardancy can be obtained in the resulting wires, cables, etc. In addition, when the content of component (C) is 50 parts by mass or less relative to 100 parts by mass of component (A), the tensile strength of the resin composition is improved.

[0058] [Other ingredients]

[0059] In addition to the above-mentioned components, the resin composition may further contain other components as needed, within a range that does not affect the above-mentioned properties. Examples of other components include flame retardants, flame retardant aids, crosslinking agents, crosslinking aids, processing aids, coupling agents, surface treatment agents, colorants, lubricants, compatibilizers, antioxidants, ozone inhibitors, ultraviolet absorbers, light stabilizers, metal chelating agents, softeners, plasticizers, and the like.

[0060] <Electric wire>

[0061] [First embodiment]

[0062] Figure 1 The illustrated electric wire 10 is a halogen-free flame-retardant insulated electric wire according to Embodiment 1. The electric wire 10 includes a conductor 1, an insulating layer 2 as a coating covering the conductor 1, and a separator 3 provided between the conductor 1 and the insulating layer 2.

[0063] As the conductor 1, commonly used metal wires such as copper wire, copper alloy wire, aluminum wire, gold wire, silver wire, etc. can be used. In addition, as the conductor 1, a conductor coated with a metal such as tin or nickel can be used. In addition, as the conductor 1, a stranded wire formed by twisting metal wires can be used. As the stranded wire, concentric stranded wires, aggregate stranded wires, and composite stranded wires formed by further concentrically twisting these can be used. In addition, as the conductor 1, a compressed conductor formed by compressing stranded wires can be used. Compressed conductors are preferred because they can reduce the diameter of the wire.

[0064] The insulating layer 2 is formed from the above-mentioned resin composition. The thickness of the insulating layer 2 is not particularly limited, but is preferably 0.15 mm to 2 mm.

[0065] The separator 3 is formed of, for example, a polyester tape. Providing the separator 3 can prevent the resin composition from penetrating into the conductor 1 during extrusion of the resin composition, i.e., during formation of the insulating layer 2, when a stranded conductor is used as the conductor 1. Note that the wire 10 does not necessarily have the separator 3.

[0066] The electric wire 10 can be manufactured, for example, as follows.

[0067] First, materials containing the above-mentioned components (A) to (C) and other components are melt-kneaded to obtain a resin composition. As a kneading apparatus, for example, a batch kneading apparatus such as a Banbury mixer and a pressure kneader, or a continuous kneading apparatus such as a twin-screw extruder can be used.

[0068] Next, a conductor 1 is prepared, and a separator 3 is wound around the conductor 1. Then, an extruder is used to cover the periphery of the separator 3 with a resin composition. In this way, an insulating layer 2 having a predetermined thickness can be formed.

[0069] Then, the insulating layer 2 is cross-linked by, for example, an electron beam cross-linking method, a chemical cross-linking method, or the like. Cross-linking is not essential, but by subjecting the insulating layer 2 to a cross-linking method, the heat resistance of the insulating layer 2 is improved, so it is preferable to subject the insulating layer 2 to a cross-linking method. When the electron beam cross-linking method is used, the insulating layer 2 is irradiated with electron beams of, for example, 1 Mrad to 30 Mrad (0.01 MGy to 0.3 MGy). When the chemical cross-linking method is used, for example, a cross-linking agent is pre-added to the resin composition, and after the resin composition is molded as the insulating layer 2 of the electric wire 10, the insulating layer 2 is heat-treated. In the examples described below, the electron beam cross-linking method is used.

[0070] [Second embodiment]

[0071] Figure 2 The illustrated wire 20 is a halogen-free, flame-retardant insulated wire according to the second embodiment. Wire 20 differs from wire 10 according to the first embodiment in that its insulation layer 2 consists of two layers and lacks a separator 3. Specifically, wire 20 comprises a conductor 1, an inner insulating layer 2a disposed around conductor 1, and an outer insulating layer 2b disposed around inner insulating layer 2a. Inner insulating layer 2a is formed from an insulating resin such as polyethylene. Outer insulating layer 2b is formed from the aforementioned resin composition. It should be noted that outer insulating layer 2b serves as a coating. As with wire 10, wire 20 may also include a separator 3. Furthermore, the insulating layer 2 may comprise three or more layers.

[0072] Cable

[0073] Figure 3 The cable 30 shown is a halogen-free flame-retardant cable and includes a core 4 , a sheath 5 as a coating covering the core 4 , and a diaphragm 6 and a shielding braid 7 provided between the core 4 and the sheath 5 .

[0074] The cable core 4 comprises a three-core stranded wire 4a formed by twisting the three wires 10 together, and an interlayer 4b disposed around the three-core stranded wire 4a. The interlayer 4b is made of rayon, paper tape, jute, etc. It should be noted that the cable core 4 may not have the interlayer 4b.

[0075] The jacket 5 is formed from the aforementioned resin composition. The separator 6 is the same as the separator 3 in the aforementioned electrical cable 10. A shielding braid 7 is disposed around the separator 6 and provides an electrical shielding function. The shielding braid 7 is formed, for example, from a mesh of metal tape or copper wire. It should be noted that the shielding braid 7 can be disposed inside the separator 6, and the cable 30 may not include the shielding braid 7.

[0076] The cable 30 can be manufactured, for example, as follows.

[0077] First, three wires 10 are manufactured using the same method as described above. The three wires 10 are then twisted together with the interlayer 4b to form a cable core 4. A separator 6 and a shielding braid 7 are placed around the cable core 4. These are then coated with a resin composition using an extruder. This forms a sheath 5 of a predetermined thickness.

[0078] Then, as needed, the sheath 5 is cross-linked using the same method as described above. This allows the manufacture of the cable 30. It should be noted that other wires can be used in place of the wire 10. Furthermore, a single-core wire consisting of a single wire can be used in place of the three-core twisted wire 4a, or a multi-core twisted wire other than a three-core twisted wire can be used. Furthermore, other layers, such as other insulating layers, can be provided between the cable core 4 and the sheath 5.

[0079] <Other uses of the resin composition>

[0080] The resin composition can be used for wires and cables of various applications and sizes. For example, the applications of the wires and cables include electronic equipment, railroad vehicles, automobiles, wiring within trays, wiring within machines, and wiring within buildings. For wires and cables used in electronic equipment or railroad vehicles, particularly high flame retardancy is required, so the resin composition can be suitably used for wires and cables used in electronic equipment or railroad vehicles. Furthermore, the type of cable is not particularly limited, and examples thereof include power cables, signal cables, and the like.

[0081] Furthermore, the resin composition can be used not only for the aforementioned wires and cables but also for other applications. For example, the resin composition can be used for films, panels, mats, tubes, protective materials, fillers, fibers, resin molded articles, resin substrates, stationery, building materials, connectors, bushings, grommets, terminal blocks, terminal internal insulators, and the like.

[0082] Example

[0083] The following examples are given to illustrate one embodiment of the present disclosure, but the present disclosure is not limited to the following examples.

[0084] <Production of Resin Composition for Cable Sheath>

[0085] The materials described in Examples 1 to 8 and Comparative Examples 1 to 4 shown in Table 1 below were dry-blended at room temperature and melt-kneaded using a pressure kneader at a take-off temperature of 190°C to produce resin compositions for cable sheaths. The amounts of the materials in Table 1 are expressed in parts by mass.

[0086] In the resin compositions of Examples 1, 2, and 6 to 8, (C1) eucalyptol represented by the following formula (4) was used as the component (C). However, the content of (C1) eucalyptol in the resin compositions of Examples 1, 2, and 6 to 8 was varied.

[0087] [Chemistry 4]

[0088]

[0089] In the resin composition according to Example 3, (C2) methyl syringate represented by the following formula (5) was used as the component (C).

[0090] [Chemistry 5]

[0091]

[0092] In the resin composition involved in Example 4, as the (C) component, (C3) silyl-protected propyl gallate 1 (3,4,5-tris(trimethylsilyloxy)benzoic acid propyl ester represented by the following formula (6)) is used. The silyl-protected propyl gallate 1 is synthesized as follows. Propyl gallate is dissolved in acetone, and 5 equivalents of triethylamine are added to 1 equivalent of the hydroxyl group of propyl gallate, and 5 equivalents of trimethylchlorosilane are added to 1 equivalent of the hydroxyl group of propyl gallate, and the mixture is reacted. Then, the acetone and triethylamine are removed to obtain the silyl-protected propyl gallate 1. It should be noted that the protection of the original hydroxyl group in the obtained silyl-protected propyl gallate 1 was confirmed using FT-IR.

[0093] [Chemistry 6]

[0094]

[0095] In the resin composition of Example 5, (C4) silyl-protected propyl gallate 2 (3,4,5-tris(tri-tert-butylsilyloxy)benzoic acid propyl ester represented by the following formula (7)) was used as component (C). Silyl-protected propyl gallate 2 was synthesized by the same method as silyl-protected propyl gallate 1, except that tri-tert-butylchlorosilane was used instead of trimethylchlorosilane.

[0096] [Chemistry 7]

[0097]

[0098] Unlike the resin compositions of Examples 1 to 8, the resin composition of Comparative Example 1 did not use the component (C). In the resin compositions of Comparative Examples 2 to 4, propyl gallate having completely unprotected hydroxyl groups was used instead of the component (C).

[0099] Cable Production

[0100] Extrusion molding was performed using a 20 mm single screw extruder "LaboPlastoMill (registered trademark)" manufactured by Toyo Seiki Co., Ltd., which is an extrusion coating device for producing electric wires, to form a 0.5 mm cross-sectional area. 2 An insulating layer with a thickness of 0.2 mm was formed around the compressed tinned copper strands. The insulating layer was formed using a resin composition produced by melt-kneading the materials described in Comparative Example 1 shown in Table 1 using the same method as for the sheathing resin composition. The barrel temperature was 160°C, and the wire pulling speed was 4.0 m / min. The insulating layer of the resulting wire was then crosslinked using an electron beam crosslinking method at 7.5 Mrad to crosslink the resin composition constituting the insulating layer.

[0101] The three resulting wires were twisted and wrapped around a polyester tape serving as a separator. A shield braid was then placed around the braid. A 0.45 mm thick sheath composed of the sheathing resin compositions described in Examples 1 to 8 and Comparative Examples 1 to 4 was then formed using a 60 mm single-screw extruder. The sheath was then cross-linked using an electron beam cross-linking method at 7.5 Mrad to produce a cable with an outer diameter of 4.5 mm.

[0102] [Table 1]

[0103]

[0104] Evaluation Method

[0105] (1) Initial tensile test

[0106] The sheath was stripped from the prepared cable, and dumbbell-shaped test pieces were punched out from the stripped sheath. Tensile tests were performed using the dumbbell-shaped test pieces in accordance with JIS C3005:2000 to measure tensile strength and elongation. The tensile tests were conducted at a tensile speed of 250 mm / min.

[0107] (2) Heating aging test

[0108] A dumbbell-shaped test piece, prepared in the same manner as in the initial tensile test (1) above, was heated in a Gir oven at 135°C for 168 hours. A tensile test was then conducted using the heat-aged dumbbell-shaped test piece in the same manner as in the initial tensile test to measure the tensile strength and elongation. The rate of change in tensile strength and elongation after heat aging relative to the values before heat aging (i.e., during the initial tensile test) was calculated.

[0109] (3) Cable combustion test

[0110] A 600mm length was taken from the prepared cable to serve as a test sample. Using this sample, a combustion test was conducted according to IEC 60332-1, measuring the distance from the upper support to the burned portion. A longer distance from the upper support to the burned portion indicates a shorter spread of flame, indicating higher flame retardancy. When the test sample was completely burned, the distance from the upper support to the burned portion was 0mm.

[0111] (4) Comprehensive judgment

[0112] Regarding the tensile strength of the initial tensile test, samples with a tensile strength of 8 MPa or more were considered acceptable, while samples with a tensile strength of less than 8 MPa were considered unacceptable. Regarding the elongation of the initial tensile test, samples with a tensile strength of 125% or more were considered acceptable, while samples with a tensile strength of less than 125% were considered unacceptable.

[0113] For the rate of change in tensile strength and elongation during the heat aging test, samples with a change of ±30% or less were considered acceptable, while samples with a change of more than ±30% were considered unacceptable. For the combustion test, similar to IEC60332-1, samples with a distance from the upper support to the burned portion of 50 mm or greater were considered acceptable, while samples with a distance less than 50 mm were considered unacceptable.

[0114] Furthermore, samples that passed all of the tensile strength and elongation in the final initial tensile test, the rate of change in tensile strength and elongation in the heat aging test, and the combustion test were considered qualified, while samples that failed any of these tests were considered unqualified. The evaluation results are shown in Table 1. In Table 1, qualified samples are indicated by 0, and unqualified samples are indicated by x.

[0115] <Evaluation Results>

[0116] As shown in Table 1, Examples 1 to 8 passed all the tests of the initial tensile test, the heat aging test, and the combustion test.

[0117] On the other hand, Comparative Example 1, which did not contain component (C), failed the combustion test. Furthermore, Comparative Examples 2 and 3, which contained propyl gallate (with completely unprotected hydroxyl groups) instead of component (C), passed the initial tensile test and the combustion test but failed the heat aging test. Furthermore, Comparative Example 4, which contained only a relatively small amount of propyl gallate, failed not only the heat aging test but also the combustion test.

[0118] <Inspection>

[0119] As shown in Comparative Examples 1 to 4, it is believed that only when gallic acid esters are added to the resin composition will the resin composition pass the combustion test. However, as shown in Comparative Examples 2 to 4, the resin composition fails the heat aging test because the hydroxyl groups of the gallic acid esters are not protected.

[0120] Comparing Example 1 and Comparative Example 2, it is believed that the gallic acid ester and component (C) exhibit comparable flame retardancy. In other words, whether the hydroxyl group of the gallic acid ester is protected has little effect on flame retardancy. This suggests that the substituent may be released during combustion.

[0121] In addition, when comparing Examples 1, 2, 6, and 7 with Example 8, based on the improvement in tensile strength in the initial tensile test, it can be considered that the resin composition preferably contains 2 parts by mass or more and 30 parts by mass or less of the component (C) relative to 100 parts by mass of the total amount of the component (A).

Claims

1. A resin composition comprising: (A) an ethylene 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 the 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 the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group, a phenoxy group, or a silyl ether group.

2. The resin composition according to claim 1, wherein The component (C) contains at least one of a compound in which at least one of the three hydroxyl groups of gallic acid is substituted with an alkoxy group or a silyl ether group, and a compound in which at least one of the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group or a silyl ether group.

3. The resin composition according to claim 1 or 2, wherein The component (C) contains at least one compound selected from the group consisting of a compound in which at least one of the three hydroxyl groups of gallic acid is substituted with an alkoxy group and a compound in which at least one of the three hydroxyl groups of a gallic acid ester is substituted with an alkoxy group.

4. The resin composition according to claim 1 or 2, wherein The component (C) contains at least one compound selected from the group consisting of a compound in which two or three of the three hydroxyl groups of gallic acid are substituted with alkoxy groups and a compound in which two or three of the three hydroxyl groups of a gallic acid ester are substituted with alkoxy groups.

5. The resin composition according to claim 1 or 2, wherein The component (C) contains at least one of 3,4,5-trimethoxybenzoic acid, eucalyptol, and its alkyl ester.

6. The resin composition according to claim 1 or 2, wherein The resin composition contains 2 parts by mass or more and 30 parts by mass or less of the component (C) relative to 100 parts by mass of the component (A).

7. An electric wire, A conductor and a coating layer covering the conductor are provided. The covering layer is formed from the resin composition according to any one of claims 1 to 6. 8 . A cable comprising a sheath formed from the resin composition according to claim 1 .

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