GB2524621A

GB2524621A - Radiation-resistant halogen-free resin composition, and electric wire and cable using the same

Info

Publication number: GB2524621A
Application number: GB1501019.2A
Authority: GB
Inventors: Yoshiaki Nakamura; Shuichi Tadokoro
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2014-01-22
Filing date: 2015-01-21
Publication date: 2015-09-30
Anticipated expiration: 2035-01-21
Also published as: GB2524621B; JP6152802B2; GB201501019D0; JP2015137315A

Abstract

A radiation-resistant halogen-free resin composition comprising 3-10 parts by mass of an aromatic amine-based antioxidant, 5-20 parts by mass of an aromatic process oil, 10-30 parts by mass of a melamine cyanurate compound and 100-200 parts by mass of a metal hydrate per 100 parts by mass of a base polymer mainly comprising an ethylene polymer, wherein the ethylene polymer comprises at least one of an ethylene-propylene-diene copolymer, an ethylene-alpha-olefin copolymer and an ethylene-vinyl acetate copolymer, and wherein the ethylene polymer further comprises an ethylene polymer modified with a polar functional group. The polar functional group may comprise an epoxy, carboxyl or maleic anhydride group. Preferably the ethylene polymer modified with the polar functional group comprises ethylene-alpha-olefin copolymer. Also disclosed is an electric wire 10 and also a cable, both comprising covering material 2 comprising the radiation-resistant halogen-free resin composition.

Description

Intellectual Property Office Application No. GB1501019.2 RTM Date:21 July 2015 The following terms are registered trade marks and should be read as such wherever they occur in this document: Tafiier Kisuma Evolue Intellectual Property Office is an operating name of the Patent Office www.gov.uk/ipo RADIATION-RESISTANT HALOGENFREE RESIN COMPOSITION, AND ELECTRIC WIRE AND CABLE USTh 0 THE SAME The invention relates to a radiation-resistant halogen-free resin composition usable in radiation environment, especially in nuclear power plants, and an electric wire and a cable which use the radiation --resistant haiogen4iee resin composition.

Radiations including y-ray are present in the environment of a radiation facility such as a nucEear power plant, a fast-breeder reactor, a nuclear fuel reprocessing plant, and a particle aceeleracor. i'hus wires and cables which are used for the power supply or signa.l transmission to the facility or equipment are needed to withstand the radiation.

TE'he wires and cables used especially in the nuclear power plant are needed to keep a specified electrical insulation effect the a certain period oftine under exposure to heat and radiation generated during steady operation and even under exposure to heat, radiation and boiling water or superheaed steam expected in loss-of-coolam ac.iJet (hereinatier, referred to as "LOCA"). FwThermore, considering a possible emergency fire, his required to have such high flame retardancy as enough 10 withstand cable fire simulated on a vertical tray.

By the way, halogen-free wires or cables without halogens such as chlorine and without producing poisonous gas when being burnt are increasingly demanded in terms cf safety in the event of fire and environmental concerns. To meet the demand, in recent years. wires and cables as defined by 115 C 3605 and 3401 and using "eco-friendly materials" as covering materials have been widely spread as cables fix equipments in buildings.

The "ecu-friendly material" is a gencral term fix halogen-free flame-retardant resin compositions formed by mixing a metal hydroxide flame retardant such as magnesium hydroxide or aluminum hydroxide to a soft ethylene polymer such as ethylene-ethyl acrylate (E.EA), ethylene vinyl acetate copolymer (EVA) or ethyiene-a-olefin random copolymer.

However, in resin compositions thnned using ecofiiendly materials and used for wires/cables, exposure to radiation causes main chain scission or crosslink due to oxidative degradation to proceed and this significantly decreases mechanical characteristics such as elongation and tensile strength. In addition, a covering material cracks due to oxida.tive degradation and electrical insulation thus cannot he maintained.

JPA2002**42552 discloses an insulating resin composition with a specific physical property and flame retardancy, in which a metal hydrate and a melamine cyanurate compound are included at a specific mass ratio with respect to a resin component such as ethylene propylene rubber and not less than 50 mass% of the metal hydra-.tc is treated with a silane coupling agent.

JP.AH04-268350 discloses a radiation-resistant composition formed by mixing an ethylene propylenediene rubber having an iodine value of Ito 10 and a process oil (naphthenic or aromatic).

JPA2009845?l descihes a radiationresistant resin composition in which l 5 salicylate-hased, henzotriazole-hased or triazinehased ultraviolet absorbers are added to a polyolefin resin.

J.P.*A-2002-42552 makes no reference to the radiation resistance and it is difficult to keep the electrical insulation when the resin composition disclosed therein is used under the radiation environment, especially in case of LOCA.

JP.A4104258350 only relates to a radiation resistance of about 0.8 to I MGy. A higher level of radiation resistance has been required in recent years.

JP-A-2009-84571 relates to a radiation resistance of about 23 MGy hut makes no consideration to the exposure to boiling water or superheated steam in case of LOCA, Known radiation-resistant resin compositions, and so also electric wire and cable employing the same, exhibil disadvantages and limitations.

in particular, the electrical insulation may not be kept when the accident occurs, The invention seeks to provide for a radiationresistant resin composition, and electric wire and cable using the same, and having advantages over known resin compositions, wires and cables.

It is a particular obiect of the invention to provide a radiation-resistant halogen-free resin composition that is effective in keeping the electrical insulation even if exposed to boiling water or superheated steam in case of LOCA, as well as an electric wire S and a cable using the radiation-resistant halogen-free resin composition.

Accordin to an aspect of the invention, a radiation-resistant halogen-free resin composition comprises 3 to 10 parts by mass of an aromatic amine--based antioxidant, 5 to parts by mass of an aromatic process oil, 10 to 30 parts by mass of a melanñne cyanutate compound and 100 to 200 parts by mass of a metal hydrate per 10-3 parts by mass of a base polymer mainly comprising an ethylene polymer, wherein the ethylene polymer coniprises at least one of an ethyiene-pronylene-diene copolymer. an ethylene-a--oietin copolyiner and an ethylene-vinyl acetate copolymer, and wherein the ethylene polymer further comprises an ethylene polymer modified with a polar functional group.

In the above aspect of the invention, the following modifications and changes can he made.

The polar functional group can comprise an epoxy group, a carhoxyl group or a maleic anhydride group.

The ethylene polymer rncdified with the polar functional group can comprise an ethylene*-*a-oefin copolviner.

According to another aspect of the invention, there is provided art electric wire comprising a covering material comprising a radiation-resistant halogen-free resin composition as outlined above.

According to a further aspect of the invention, there is provided a cable comprising a covering material comprising a radiation-resistant halogen-free resin composition as outlined above.

Effects of the invention According to an aspect of the invention, a radiation-resistant halogen-free resin composition having advantages over known compositions can be provided and in particular that is effective in keeping the electrical insulation even if exposed to boiling water or superheated steam in case of LOCA, as well as an electric wire and a cable using the radiation-resistant halogen-free resin composition.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings in which: FIG.1 is a cross sectional view showing an electric wire in an embodiment of the present invention; FIQ2 is a cross sectional view showing a cable in an embodiment of the invention; and FIGS is a diagram illustrating the conditions (i.e., change in temperature and pressure over time) of radiation resistance test (or high-pressure steam exposure test).

Radiation-resistant halo2en-free resin cOmDOSitiOfl A radiation-resistant halogen-free resin composition in an embodiment of the invention includes 3 to 14) parts by mass of aromatic amine-based antioxidant, 5 to 20 parts by mass of aromatic process oil, lOto 30 parts by mass of melamine cyanurate compound and 100 to 200 parts by mass of metal hydrate per 100 parts by mass of base polymer mainly including an ethylene polymer, wherein the ethylene polymer includes at least one of ethylene-propylene-diene copolymer, ethylene-a-olefin copolymer and ethylene-vinyl acetate copolymer and further includes an ethylene polymer modified with a polar functional group.

Base polymer mainly including ethylene colymer The base polymer used in the embodiment of the invention mainly includes an ethylene polymer and the amount of the ethylene polymer included in the base polymer can be not less than 60 mass%, or not less than 80 mass%, or not less than 90 ntass%, or even mass%. Other types of polymers may be included as long as the effects of the invention are exerted.

Examples of the ethylene polymer used in the embodiment of the invention can include higftdensity polyethylene (HOPE), mediutmdensity polyethylene (MDPE), iowdcnsiiy polyethylene (i.DPE), linear lowdeusity polyethylene (LLDPE). Linear very low-density polyethylene, high-density polyethylene (FIDPE), ethylene-methyl methacryiate copolymer (EMMA), ethyleneethyl acrylate copolymer (PEA), ethyienchutyi ucrylate (ERA). ethylene vinyl acetate copolymer (EVA), ethylene-glycidyl rnethacrylate eopolymer, ethylenebutene-1 copolymer, ethylenebutenehexene terpolymer, ethylene-propylene-diene tcrpolymer (EPDM), ethyieneoctene copolymer (FOR), ethylene copolymerized polypropylene, ethyienepropylene copolymer (EPM).

poly4-niethylpentene-1, maleic acid grafted low density polyethylene, hydrogenated styrenehutadiene copolyrner (HSBR), inaleic acid grafted linear low density polyethylene.

maleic acid grafted linear very low-density polyethylene, ethylene-a-olcfin copolymer (especially exemplarily a copo]ymer of ethylene and uolefin having a carbon number of 4 to 20), ethyienestyreiie copolymer, maleic acid grafted ethylene-styrene copo1ymei 13 maleic acid grafted ethylene-methyl acrylate copoiyrnei maleic acid grafted ethyienevinyi acetate copolymer, ethylene-mateic anhydride copolymer, etli leneethyl aery]ateinaleic anhydride terpolyrner and ethyiene-propylene-butcr.e-1 ternolymer mainly including butene4 etc. These can be used alone or as a mixture of two or more.

Among the ethylene polymers listed above, one or more selected from ethyienepropylene--diene copolymer (EPDM'). ethylenea-olefir. copolymer and ethylene vinyi acetate copolyrner (EVA) can. he included in the radiation-resistant halogen4±ee resin composition in the embodiment of the invention. Thus even when large amounts of rnelaminc cyanurate compound and metal hydrate are added, such ethylene polymers receive additives and prevent mechanical strength from decreasing.

The resin composition, when used especially as an insulation material for wires and cables, can include ethylene-propylene--diene copolymer (EPDM) and ethyienea-oiefin copolynier which have good radiation resistance and also allow electrical insulation to be maintained. On the other hand, when used as a sheath material for cables, the resin composition can include ethylene vinyl acetate copolymer (E'vA) having flame retardancy.

In the ethylene polymer constituting the base polymei one or more selected from ethylene-propylene-diene copolymer (EPDM), ethylene-a-olefin copotymer and ethylene vinyl acetate copolymer (EVA) can be included in an amount of 70 to 97 mass%, more exemplarily 75 to 96 mass%, further exemplarily 80 to 95 mass%, and the most exemplarily 85 to 95 mass%.

The radiation-resistant halogen-free resin composition in the embodiment of the invention can also include an ethylene polymer modified with a polar functional group.

The above listed polymers can be used as an ethylene polymer to be modified, and an ethylene-a-olefin copolynier is exemplary. This provides excellent mechanical characteristics and also provides radiation resistance which allows electrical insulation to be maintained even i1 after degradation, exposed to boiling water or superheated steam generated in the event of LOCA. It is considered that the polar functional group in the polymer electrostatically absorbs a hydroxyl group on a particle surface of the additive and this increases adhesion between the polymer and the particle surfkce, inhibits water penetration and thus maintains electrical insulation.

An epoxy group, a carboxyl group or a maleic anhydride group can comprise the polar functional group. It is particularly exemplary to use an ethylene-a-olefln copolymer modified with a ntaleic anhydride.

In the ethylene polymer constituting the base polymer, the ethylene polymer modified with a polar functional group can be included in an amount of 2 to 20 mass%, more exemplarily 3 to 18 mass%, further exemplarily S to 15 mass%, and the most exemplarily 7 to 12 mass%.

The base polymer can be crosslinked by a conventional method such as addition of a sulfur compound or an organic peroxide, clcctron beam irradiation or silane-grafted water crosslinking to improve heat resistance. Since the ethylene polymer is used in the present embodiment, crosslinking can be by electron beam irradiation or organic peroxide.

The crosslinking by organic peroxide can be particularly usefully employed to increase the degree of crosslinking.

Aromatic amine-based antioxidant The radiation-resistant halogen-free resin composition in the embodiment of the invention includes 3 to 10 parts by mass of aromatic amine-based antioxidant per 100 parts by mass of the base polymer.

When the ethylene polymer is exposed to radiation (mainly y-rays), hydrogen is abstracted from the polymer and radicals are produced even at room temperature, unlike typical degradation caused by heat. Then, the radicals bind to oxygen, causing oxidative degradation of the polymer. This causes crosslink of or molecular chain scission in the polymer and a resulting sharp decrease in mechanical characteristics of the resin composition. As a countermeasure against the degradation phenomenon, it is considered to be important to suppress chain oxidative degradation by promptly capturing radicals produced in the polymer and transforming hydroperoxide produced in the polymer due to oxidative degradation into stable alcohoL Then, it was found that an aromatic amine-based antioxidant is effective against the degradation.

The aromatic amine-based antioxidant may be compounds marketed as antioxidants for rubber or plastic and examples thereof include monoamine compounds such as diphenylamine compound, quinoline compound and naphthylamine compound, and diamine compounds such as phenylenediamine compound and benzimidazole compound.

The diphenylamine compound can include p-(p-toluene sulfonylamido)-diphenylamine (trade name: Nocrac TD, etc.), 4,4'.(a,a-dirnethylbenzyl) diphenylamine (trade name: Nocrac CD, Naugard 445, etc.) and 4,4'-dioctyldiphenylamine derivative (trade name: Nocrac ODA-N, Antage OD-?, Antage DDP, etc.), etc. The quinoline compound can include 2,2,4-trimethyl-1,2-dihydroquinoline poLymer (trade name: Nocrac 224, brevity code in 313: TMDQ), ctc.

The naphthylamine compound can include phenyl-a-naphthylamine (trade name: Nocrac PA, etc., brevity code in JIS: PAN), N,N*di2naphthyl.pphenylenediamine (trade name: Nocrac White, etc., brevity code in 315: DNPD), etc. The phenylenediamine compound can include N,N'-diphenyl-p-phenylenediamine (trade name: Nocrac DP, etc., brevity code in JIS: DPPD), N-isopropyl-N'-phenyl-p-phenylenediamIne (Antage 3C, Nocrac S1ONA, etc., brevity code in JIS: IPPD), N-phenyl-N'-(3-methacryloyloxy-2-hydroxypropyl -p-phcnylenediamine (trade name: Nocrac 0-1, etc,), N-phenyl-N'41,3-diinethylbutyl)-p-phenylenediamine (Antage 6C, Nocrac 6C, etc.), mixtures (trade name: Nocrac 500, Antage DPi, etc.) including N-N'-diphenyl-p-phenylenediamine (trade name: Nocrac DP, etc., brevity code in JIS: DPPD), and diaryl-p-phenylenediamine derivatives or mixtures including thereof (trade name: Nocrac 630, Antage STE etc.).

The benzimidazole compound can include 2-mercapto benzimidazole (trade name: Antage MB, etc., brevity code in 315: MN), 2-mercapto methyl benzimidazole (trade name: Nocrac MMB, etc.), zinc salt of 2-mercapto benzimidazole (trade name: Nocrac MBZ, etc., brevity code in JIS: ZnMBI) and zinc salt of 2-mercapto methyl benzimidazole (trade name: Nocrac MMBZ, etc.), etc. The above Listed aromatic amine-based antioxidants may be used alone or as a mixture of two or more. Particularly, the diphenylamine compound and the quinoline compound are suitable for capturing radicals and the benzimidazole compound is suitable for stabilization of hydroperoxide in addition to capture of radicals. Therefore, the diphenylamine compound and/or the quinoline compound can be used together with the benzimidazole compound.

The added amount of the aromatic amine-based antioxidant can be 3 to 10 parts by mass, or S to Spurts by mass, per 100 parts by mass of the base polymet When the added amount is less than 3 parts by mass, a degradation prevention effect under radiation environment is small. On the other hand, when more than 10 parts by mass, cross-linking is inhibited when crosslinking the composition by electron beam or organic peroxide since the antioxidant captures even radicals necessary for crosslink and mechanical characteristics thus decrease.

Aromatic process 9jj The radiation-resistant halogen-free resin composition in the embodiment of the invention includes 5 to 20 parts by mass of aromatic process oil per 100 parts by mass of the base polymer.

Radiation resistance is further improved by adding the aromatic process oil. The reason therefor is not known but it is presumed that shared it-electrons included in an aromatic compound in the aromatic process oil resonance-stabilizes energy from radiation.

The added amount of the aromatic process oil is 5 to 20 parts by mass, exemplarily 5 to 15 parts by mass, per 100 parts by mass of the base polymer. If less than S parts by mass, radiation resistance is not remarkably exhibited. If more than 20 parts by mass, a decrease in tensile strength may occur.

Carbons constituting the aromatic process oil are categorized into carbons in an aromatic ring, carbons in a naphthalene ring and carbons in a paraffin chain, and it is more effective to protect from radiation when more carbons, exemplarily not less than 25 mass%, are included in the aromatic ring.

Mejamine cyanurate compound The radiation-resistant halogen-free resin composition in the embodiment of the invention can include 10 to 30 parts by mass of melamine cyanurate compound (adduct of melamine and cyanuric acid) per 100 parts by mass of the base polymer.

It was found that melamine cyanurate compounds, which are widely known as flame retardants and can provide flame retardancy, can also provide radiation resistance when used together with the aromatic process oil. The reason for this is considered as follows: the melaniine cyanurate compounds have properties of absorbing ultraviolet rays with a wavelength of around 200 to 230 nit and the y-ray is radiation with a shorter wavelength of about 10pm. When it is expected that the y-ray collides with some atoms in the composition and the wavelength thereof is increased by the Compton effect, the melamine cyanurate compound absorbs an electromagnetic wave with a wavelength reached the ultraviolet range and this suppresses the degradation. In addition, it is also considered that dispersibility of melamine cyanurate is improved by combining the aromatic process oil which also has the shared it-electrons in the same manner as the melamine cyanurate compound, and ftwthennore, the shared ic-electrons of the aromatic process oil and those of the melamine cyanurate compound are stuck and this increases an 9.

effect of resonancestabiIizing energy from the. radiation.

[he added amount of the melamine cyanurate compound can be 10 to 30 parts by mass, or 15 to 25 parts by mass, per 100 parts by mass of the base polymer. Radiation resistance is not exerted when ess than 10 parts by mass, whlle addition of more than 30 parts by mass causes ioor dispersibility and a decrease ifl tensile characteristics. In such cases, deterioration under radiation environment is likely to occur.

The radanonresistant halogen-free resin composition in the embodiment of the invention includes 100 to 200 parts by mass of metal hydrate per 100 parts by mass of the base polymer.

Magnesium hydroxide, a'uminum hydroxide or hydrotaleite, etc., can he used as the metal hydrate, Of those, magnesium hydroxide and. alurninuni hydroxide have a larger flame retardant effect, considering disnersibility of particles thereof and adhesion between the polymer arid the particle surface, a surface can be treated with fatty acid, fatty acid metal salt, a silane coupling agent, a titanate-hased coupling agent, an acrylic resin, a phenoiic resin, a silicone resin, a silicone elastomer or a water-soluble eationic or nonionic resin, etc,A particular example is to treat the surface with a silane coupling agent.

The added amount of the metal hydrate is 100 to 200 parts by mass. can he 120 to pans by mass, per 100 parts by mass of the base polymer. When the added amount of the metal hydrate is less than 100 parts by mass, it is not possible to obtain a high flame retardancy which is enough to pass a vertical tray flame test, On the other hand, when adding more than 200 parts by mass, mechanical characteristics significantly decrease.

Other additives lb the resin composition in the embodiment of the invention, it is possible, if necessary, to add additives such as flame-retardant aids, anuoxidants, lubricants, surface active agents, softenens, plasticizers, inorganic fillers, compatibilizing agents, stabilizers, metaE cheators (copper inhibitors), crossliriking agents, ultraviolet absorbers, light stabilizers (hindered amine compounds) and colorants, besides the additives described above. it is particularly exemplary to add a flame-retardant aid. Examples of the 1*0 flame-retardant aid include phosphorus flame retardants such as red phosphorus or phosphoric ester compounds, silicone flame retardants, nitrogen-based flame retardants, boric-acid compounds and stannic acid compounds, etc. $lectric wire An electric wire in the embodiment of the invention is characterized in that the radiation-resistant halogen-free resin composition in the embodiment of the invention is used as a covering material (insulation).

FIC.1 is a cross sectional view showing the electric wire of an embodiment of the invention.

As shown in H&1, an insulated wire 10 in the present embodiment is provided with a conductor 1 formed of a general-purpose material, e.g., pure copper or tin-plated copper, etc., and an insulation 2 formed to cover the outer periphery of the conductor 1.

Plural conductors 1 may be provided as shown in FIG1, or only one conductor I may be provided.

iS The insulation 2 is formed of the radiation-resistant halogen-free resin composition embodying the invention.

In the present embodiment, the insulation may be a single layer or may have a rnultilayer structure. A separator or a braid, etc., may be further provided, if required. Cable

A cable in the embodiment of the invention is characterized in that the radiation-resistant halogen-free resin composition in the embodiment of the invention is used as a covering material (insulation and/or sheath).

FIG.2 is a cross sectional view showing the cable of an embodiment of the invention.

As shown in FIG.2, a cable 100 in the present embodiment is provided with a three-core twisted wire formed of three electric wires, each formed of covering the conductor I with the insulation 2, twisted together with an inclusion 4 such as paper, a binding tapeS provided on the outer periphery of the three-core twisted wire, and a sheath 3 formed by extrusion to cover the outer periphery of the binding tape 5. A single-core wire or a multi-core twisted wire other than three-core may be alternatively used.

T he insulation 2 and the sheath 3 are formed of the radiation-resistant halogen-free resin composition embodying the invention, The radiation-resistant halogen-free resin composition may be used for only one of the insulation 2 and the sheath 3 but is exemplarily used for both.

in the present embodiment, the sheath may be a single layer or may have a multilayer structure. A separator or a braid, etc., may be further provided, if required.

Effects of the embodiment of the invention As described above, according to the embodiment of the invention, it is possible to obtain a highly radiation-resistant halogen-free resin composition capable of maintaining electrical insulation even if exposed to boiling water or superheated steam in the event of LOCA. The radiation-resistant halogen-free resin composition in the embodiment of the invention does not produce poisonous gas when being burnt and a decrease in mechanical characteristics thereof is small even when used under radiation environment. In addition, by using such a resin composition for insulation and/or sheath, it is possible to obtain electric wires/cables which have flame retardancy high enough to pass the vertical tray flame test, do not produce poisonous gas when being burnt, have high radiation resistance and can maintain the specific electrical insulation for a certain period of time even in the event of LOCA.

Examples

The invention will be described in more detail below in reference to Examples.

However, the invention is not limited to these Examples.

The electric wire 10 having a structure shown in FIQI was made by the following method.

Components other than organic peroxide were mixed at respective ratios shown in Examples I to 10 in Table 1 and Comparative Examples 1 to 11 in Table 2 and were kneaded by a 25-litre pressure kneader at a start temperature of 40°C and an end temperature of 200°C, and each kneaded mixture was then pelletized. After that, each kneaded mixture was impregnated with the organic peroxide using a blender, thereby obtaining resin compositions to be used. as an insulation.

The obtained resin composition was extruded on a copper conductor having a conductor cross section of 3,5 SQ at a preset temperature of 130°C so as to have a thickness of 0.8 mm and was then crosslinked in saturated vapor at about 200°C, thereby obtaining an electric wire shown in FIGI.

Each of the obtained wires was evaluated by the tollowing methods. Tables I and 2 show the evaluation results.:.

The tensile test was conducted on the obtained wires in accordance with IEC 60811-1. For tensile strength (Tb), not less than 9.0 MPa was regarded as Fail and not less than 9,0 MPa was regarded as Pass. For breaking elongation (Eb), less than 200% was regarded as Fail and not less than 200% was regarded as Pass, (21 Flame test The vertical tray flame test was conducted on the obtained wires in accordance IS with IEEE Std. 383 (2003). The wires with a char length of not more than 150 em were regarded as Pass, (31 Radiation resistance test After thermally accelerated degradation equivalent to 60 years of natural aaing on the obtained wire in accordance with Arrhenius equation, the yray was uTadrated and vapor exposure was carried out using the profile shown in FIG3. FIG3 is a diagram illustrating conditions (change in temperature and pressure over time) of radiation resistance test (highpressure steam exposure test). During the vapor exposure period, voltage is applied at 600 volts AC and a short circuit must not occur. Then, each wire was wound around a mandrel having a diameter 40 times the own diameter and a wet withstand voltage test was conducted at 3200 volts AC/mm for 5 minutes, The wires which were not broken passed the test. The yray was irradiated up to 2 NiGy at a dose rate of S kGy/h at room temperature.

(4) QiicraU evaluation lEe wires which passed all of the above tests (1) 10 (3) were evaluated as Pass and 1:3 the wires which thiled even one of the tests (1) to (3) were evaluated as Fail.

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C 2 N --9 0 E - -C 7-'-N -?-C7 C--------) rfl ---: -1CC -> a -0 t 73 CL -H <»= C) : 0 C -H-ed H nwXod;se-j As shown in Table 1, the wires of Examples 1 to 10 using the radiation-resistant halogen-free resin composition for the insulation satis1' all characteristics and are excellent in mechanical characteristics, flame retardancy and radiation resistance.

On the other hand, in Comparative Examples 1 and 2, an ethylene-propylene-diene copolymer, an ethylene-a-olefln copolymer and an ethylene-vinyl acctate copolymer are not used but representative ethylene polymers, LLDPE and LDPE, are used. Therefore, the wires had a small initial breaking elongation and were evaluated as Fail. In addition, radiation resistance was insufficient.

The wire in Comparative Example 3 has enough breaking elongation after degradation due to no addition of the ethylene polymer modified with a polar functional group, but did not pass the vapor exposure test simulating an loss-of-coolant accident.

In Comparative Example 4, the added amount of the aromatic process oil was small and radiation resistance was not sufficient. On the other hand, in Comparative Example 5, the added amount of the aromatic process oil was large and initial tensile strength was not sufficient The added amount of the melamine cyanurate compound was not sufficient in Comparative Example 6 and that of the metal hydrate was not sufficient in Comparative ExampleS, hence, the wires of Comparative Examples 6 and S did not pass the vertical tray flame test. In addition, the wire of Comparative Example 6 was poor in radiation resistance even though the amounts of the aromatic process oil and the aromatic amine-based antioxidants were sufficient.

In Comparative Example 7, the added amount of the melamine cyanurate compound was large and initial breaking elongation was not sufficient.

In Comparative Example 9, the added amount of the metal hydrate was large and 2$ initial breaking elongation was not sufficient. And also, the wire in Comparative Example 9 failed the withstand voltage test after degradation.

In Comparative Example 10, the added amount of the aromatic amine-based antioxidant was small and radiation resistance was not sufficient. On the other hand, in Comparative Example 11, cross-linking was inhibited due to too large amount of aromatic F? aminehased antioxid.ants. resulting in insufficient initial tensile strength.

Aithough the invention has been described with respect to the specific.

emhothnrents and. examples for complete and dear disclosure, the invention is not restricted to the exact combinatton of features disclosed in the embodiments and examples and any appropriate conibmation can be employed. Also, the appended dairns are not to be therefore Umited hut are to be construed as embodying nil modifications and alternative constructions that may occur to one sidlied in the art which Ihirly fail within the basic teaching herein set forth.

Claims

CLAIMS: 1 1. A radiation-resistant halogen-free resin composition, comprising 3 to 10 parts by mass of 2 an aromatic amine-based antioxidant, 5 to 20 parts by mass of an aromatic process oil, 10 3 to 30 pails by mass of a melamine cyanurate compound and 100 to 200 parts by mass of a 4 metal hydrate per 100 parts by mass of a base polymer mainly comprising an ethylene polymer.6 wherein the ethylene polymer comprises at least one of an 7 ethylene-propylene-diene copolymer, an ethylene-a-olefin copolymer and an 8 ethylene-vinyl acetate copolymer, and 9 wherein the ethylene polymer further comprises an ethylene polymer modified with a polar functional group.1
2. The radiation-resistant halogen-free resin composition according to Claim 1, wherein the 2 polar functional group comprises an epoxy group, a carboxyl group or a maleic anhydride 3 group.1
3. The radiation-resistant halogen-free resin composition according to Claim 1 or 2, 2 wherein the ethylene polymer modified with the polar functional group comprises an 3 ethylene-a-oletin copolyrner.

1
4. An electric wire, comprising a covering material comprising the radiation-resistant 2 halogen-free resin composition according to any one or more of Claims ito 3.

1
5. A cable, comprising a covering material comprising the radiation-resistant halogen-free 2 resin composition according to any one or more of Claims I to 3.

4
6. A cable including at least one electric wire according to Claim 4.6
7. A radiation-resistant ha)ogen-free composition suhstantiafly as described herein with 7 reference to the ac.comnanying draings. $9
8. An electric wire substantially as hercinbefore described with reference to Firs, I and 2 of the. accompanying drawings.12
9. A chk substantially as hereinhefore described with reference to Fig. 2 of the 13 accompanying drawings.