Insulating resin composition for cable and cable

Abstract

Provided is an insulating resin composition for a cable, comprising a component (a), a component (b), a component (c), and a component (d), the component (a) being polyethylene, the component (b) being at least one resin selected from the group consisting of resins (b1) and (b2), the resin (b1) being a resin grafted with at least one modified monomer selected from the group consisting of unsaturated organic acids and derivatives thereof, and the resin (b2) being a resin grafted with at least one modified monomer selected from the group consisting of unsaturated organic acids and derivatives thereof. The resin (b2) is at least one ethylene copolymer selected from the group consisting of ethylene-acrylate copolymers, ethylene-acrylic acid copolymers, and ethylene-vinyl acetate copolymers, the component (c) is a water tree inhibitor, and the component (d) is a crosslinking agent.

Description

Technical Field

[0001] This disclosure relates to insulating resin compositions for cables and cables. Background Technology

[0002] Cross-linked polyethylene (XLPE), which was used in traditional cables, can develop water treeing when used as cable insulation in environments with high moisture content. Water treeing is a dendritic defect caused by foreign matter or air bubbles (voids) in the resin.

[0003] Dielectric electrophoresis of water generated when current is applied to the cable causes water in the resin to concentrate at the interface of foreign objects or voids, leading to water tree growth. Since water treeing can damage the cable, it is necessary to inhibit its growth.

[0004] To inhibit the growth of water trees, hydrophilic molecules, such as polyethylene glycol, are added to XLPE resin, which is composed of hydrophobic polyethylene. Because of these hydrophilic molecules, water is evenly dispersed within the XLPE resin, thus inhibiting the concentration of water at the interface of foreign matter and voids, thereby suppressing the growth of water trees.

[0005] Furthermore, Patent Document 1 discloses a polyolefin composition for electrical insulation, comprising a polyolefin or cross-linked polyolefin and a small amount of high molecular weight polyethylene glycol. It also discloses a technique that materials with low hydrophilicity or hydrophobicity, such as polypropylene glycol, do not prevent the formation of water trees in the insulator.

[0006] As mentioned above, the addition of hydrophilic molecules inhibits the growth of water trees. However, the addition of hydrophilic molecules increases the dielectric loss tangent (tanδ) of the resin, thus reducing the power transmission efficiency of the cable.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: US Patent No. 4,305,849 Summary of the Invention

[0010] [The problem the invention aims to solve]

[0011] The purpose of this disclosure is to provide an insulating resin composition for cables and a cable that can suppress the growth of water trees and reduce the dielectric loss tangent.

[0012] [Technical means to solve the problem]

[0013] [1] An insulating resin composition for cables, comprising component (a), component (b), component (c), and component (d), wherein component (a) is polyethylene, component (b) is at least one resin selected from resin (b1) and resin (b2), resin (b1) is a resin grafted with at least one modified monomer selected from unsaturated organic acids and their derivatives, resin (b2) is at least one ethylene copolymer selected from ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer, component (c) is a water tree inhibitor, and component (d) is a crosslinking agent.

[0014] [2] According to the above [1] insulating resin composition for cables, wherein the aforementioned component (c) is at least one compound selected from polyalkylene glycols and their derivatives, polyglycerol, glycerol fatty acid esters, and sorbitol esters.

[0015] [3] According to the above [1] or [2], the crosslinked product formed by crosslinking the aforementioned cable insulating resin composition has a dielectric loss tangent of less than 1.0% at 90°C and 30 kV / mm.

[0016] [4] The cable insulating resin composition according to any one of [1] to [3] above, wherein, in the aforementioned resin (b1), at least one modified monomer selected from unsaturated dicarboxylic acid, unsaturated dicarboxylic anhydride, and unsaturated dicarboxylic acid derivatives has been added to at least one resin selected from polypropylene, polyethylene, and olefin copolymers.

[0017] [5] The cable insulating resin composition according to any one of [1] to [4] above, wherein the content of the aforementioned component (b) in the aforementioned cable insulating resin composition is 3.0 wt% or more and 25.0 wt% or less.

[0018] [6] A cable comprising: a conductor; an inner semiconductive layer disposed on the outside of the conductor and surrounding the conductor; an insulation layer disposed on the outside of the inner semiconductive layer and surrounding the inner semiconductive layer, formed by crosslinking of the cable insulating resin composition described in any one of [1] to [5] above; and an outer semiconductive layer disposed on the outside of the insulation layer and surrounding the insulation layer.

[0019] (The effect of the invention)

[0020] According to this disclosure, it is possible to provide an insulating resin composition for cables and a cable that can suppress the growth of water trees and reduce the dielectric loss tangent. Attached Figure Description

[0021] Figure 1This is a cross-sectional view of an example of a cable using the insulating resin composition of the embodiment.

[0022] Figure 2 This is a schematic diagram illustrating a water tree experiment. Detailed Implementation

[0023] The following is a detailed description based on the implementation method.

[0024] After repeated and in-depth research, the inventors discovered that even if a water tree inhibitor is included in order to suppress the growth of water trees, the increase in dielectric loss tangent caused by the water tree inhibitor can still be suppressed by including specific components. Based on this insight, this disclosure was completed.

[0025] The cable insulating resin composition of the embodiment (hereinafter also simply referred to as the insulating resin composition) comprises component (a), component (b), component (c), and component (d), wherein component (a) is polyethylene, component (b) is at least one resin selected from resin (b1) and resin (b2), resin (b1) is a resin grafted with at least one modified monomer selected from unsaturated organic acids and their derivatives, resin (b2) is at least one ethylene copolymer selected from ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer, component (c) is a water tree inhibitor, and component (d) is a crosslinking agent.

[0026] The insulating resin composition of the embodiment comprises components (a), (b), (c), and (d) as constituent elements. The crosslinked product formed by crosslinking the insulating resin composition (hereinafter also simply referred to as the crosslinked product) is an insulator and is suitable for the insulation layer of cables.

[0027] The insulating resin composition contains component (a) which is polyethylene. Polyethylene can be manufactured using either a low-pressure process or a high-pressure process, but low-density polyethylene (LDPE) manufactured using a high-pressure process is preferred.

[0028] The insulating resin composition contains component (b) which is at least one resin selected from resin (b1) and resin (b2). Component (b) inhibits the increase of dielectric loss tangent in the crosslinked product of the insulating resin composition caused by component (c), i.e., the water tree inhibitor.

[0029] Resin (b1) is a resin grafted with at least one modified monomer selected from unsaturated organic acids and their derivatives (hereinafter also referred to as grafted resin).

[0030] The functional group introduced into the resin by grafting a modified monomer is preferably a functional group having a C=O bond. Preferably, it is a carbonyl, carboxyl, ester, anhydride, amide, or imide group. Component (c), the water tree inhibitor, is bound by hydrogen bonds to the C=O group in the molecule grafted into the resin, thereby suppressing molecular motion induced by the electric field. In other words, since the permanent dipole of the water tree inhibitor does not follow the frequency vibration of the alternating current field and does not generate orientation polarization, energy loss due to molecular motion for molecular orientation is reduced. Furthermore, since the C=O structure captures space charge within the insulator, interfacial polarization caused by the movement of space charge in response to the electric field is suppressed, thus reducing energy loss due to charge movement. In this way, the C=O group in the molecule grafted into the resin effectively reduces the dielectric loss tangent of the crosslinked material by suppressing the molecular motion of the water tree inhibitor and the movement of space charge. In addition, the grafted resin can improve the dispersibility of the water tree inhibitor and suppress the exudation of the crosslinked material.

[0031] Preferred modifying monomers are unsaturated dicarboxylic acids, unsaturated dicarboxylic anhydrides, and unsaturated dicarboxylic acid derivatives. Preferably, as the resin (b1) grafted with such a modifying monomer, at least one modifying monomer selected from unsaturated dicarboxylic acids, unsaturated dicarboxylic anhydrides, and unsaturated dicarboxylic acid derivatives has been added to at least one resin selected from polypropylene, polyethylene, and olefin copolymers. As the polyethylene, low-density polyethylene produced by a high-pressure process is preferred.

[0032] As unsaturated dicarboxylic acids, maleic acid, fumaric acid, and itaconic acid are preferred. As unsaturated dicarboxylic acid anhydrides, maleic anhydride and itaconic anhydride are preferred. As unsaturated dicarboxylic acid derivatives, monomethyl maleate, monoethyl maleate, diethyl maleate, monomethyl fumarate, dimethyl fumarate, diethyl fumarate, maleic acid monoamide, maleimide, N-phenylmaleimide, and N-cyclohexylmaleimide are preferred. These can be used alone or in combination of two or more. Among them, five-membered ring cyclic anhydrides, i.e., maleic anhydride, are preferred.

[0033] The grafting amount of the modified monomer is preferably 0.25 wt% or more and 2.00 wt% or less in the grafted resin. If the modified monomer is grafted within this range, the modified monomer is uniformly dispersed in the insulating resin composition, thus enabling a uniform reduction in the dielectric loss tangent within the system.

[0034] When the modified monomer is maleic anhydride, the content of the modified monomer in the insulating resin composition is preferably 0.01 wt% or more and 0.50 wt% or less. If the insulating resin composition contains maleic anhydride within this range, the dielectric loss tangent within the system can be uniformly suppressed. In particular, when the content of maleic anhydride exceeds 0.50 wt%, the grafted resin may adhere to the inner metal wall of the mixing or extrusion apparatus, potentially reducing the uniformity of the resin composition. As a result, water tree growth may be promoted.

[0035] As a method for preparing grafted resin, for example, it can be obtained by mixing and heating the raw material polyethylene, antioxidant, modified monomer and organic peroxide in an extruder and reacting them according to the method described in paragraph

[0098] of Japanese Patent No. 6205032.

[0036] Resin (b2) is at least one ethylene copolymer selected from ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer.

[0037] The preferred ethylene-acrylate copolymers are ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-butyl acrylate copolymers.

[0038] Regarding the content ratio of component (b) in the insulating resin composition, the lower limit is preferably 3.0 wt% or more, more preferably 4.0 wt% or more, and the upper limit is preferably 25.0 wt% or less, more preferably 15.0 wt% or less. When the content ratio of component (b) is within the above range, the dielectric loss tangent of the crosslinked product of the insulating resin composition can be sufficiently reduced.

[0039] Regarding component (b), resin (b1) is more effective than resin (b2) in reducing the dielectric loss tangent of the crosslinked material. Therefore, the insulating resin composition preferably includes resin (b1).

[0040] The insulating resin composition contains component (c), which is a water tree inhibitor. Component (c), the water tree inhibitor, is a hydrophilic molecule that imparts hygroscopic properties to the crosslinked components of the insulating resin composition. By imparting hygroscopic properties to the crosslinked components, the moisture in the crosslinked components is evenly dispersed, thus inhibiting the concentration of moisture at the interfaces of foreign matter and voids, thereby inhibiting the growth of water trees in the crosslinked components.

[0041] The water tree inhibitor is preferably at least one compound selected from polyalkylene glycols and their derivatives, polyglycerol, glycerol fatty acid esters, and sorbitol esters.

[0042] As polyalkylene glycols, polyethylene glycol, polypropylene glycol, block copolymers of polyethylene glycol and polypropylene glycol, and alkyl ethers or carboxylic esters of these compounds are preferred. More preferred derivatives of polyalkylene glycols include: alkoxy polyethylene glycol methacrylate, alkoxy polyethylene glycol acrylate, polyoxyethylene alkyl ether, and polyethylene glycol fatty acid ester. The purpose of these water tree inhibitors is to impart hygroscopicity to the crosslinked components of the insulating resin composition by utilizing hydrogen bonds with water molecules; polyalkylene glycol derivatives exert the same effect as polyalkylene glycols. Thus, by methacrylating, acrylate-acrylating, alkoxy-etherifying, and esterifying polyalkylene glycols, crosslinking of polyalkylene glycol derivatives with polyethylene can occur during the crosslinking of cable insulation, reducing leakage. When polyalkylene glycols and their derivatives are absorbed by resin particles during dry mixing, they are preferably used as liquids at 60°C. Polyglycerol is a compound formed by the polymerization of multiple glycerols using ether bonds and can adopt linear, cyclic, or branched structures. Furthermore, the dispersibility in the insulating resin composition disclosed herein can be improved by alkylating and carboxylating these polyglycerols. In particular, regarding the stability of the compound manufacturing process, it is preferable to incorporate fatty acid esterification into the insulating resin composition. Sorbitol is a glucose-derived polyol, and sorbitol esters are compounds formed by esterifying one or more hydroxyl groups of sorbitol with fatty acids. Sorbitol can be dispersed in the insulating resin composition via esterification.

[0043] To suppress exudation from the crosslinked components of the insulating resin composition, the number average molecular weight of the water tree inhibitor is preferably 1000 or more, more preferably 3000 or more, and even more preferably 9000 or more. On the other hand, to ensure good dispersibility of the water tree inhibitor during melt mixing, the number average molecular weight of the water tree inhibitor is preferably 30000 or less. Furthermore, from the perspective of ease of operation, the number average molecular weight of the water tree inhibitor is preferably 20000 or less.

[0044] Regarding the proportion of water tree inhibitor in the insulating resin composition, the lower limit is preferably 0.1 wt% or more, more preferably 0.2 wt% or more, and the upper limit is preferably 2.0 wt% or less, more preferably 1.0 wt% or less. When the proportion of water tree inhibitor is within the above range, the growth of water trees in the crosslinked product of the insulating resin composition can be sufficiently suppressed. Furthermore, when the proportion of water tree inhibitor is 1.0 wt% or less, the exudation of the crosslinked product can be further suppressed.

[0045] The insulating resin composition contains component (d) as a crosslinking agent, which crosslinks component (a), i.e., polyethylene. Component (d), i.e., the crosslinking agent, is preferably: di-tert-hexyl peroxide (Perhexyl D, manufactured by Nippon Oil Co., Ltd.), dicumyl peroxide (Percumyl D, manufactured by Nippon Oil Co., Ltd.), 2,5-dimethyl-2,5-di(tert-butyl peroxide)hexane (Perhexa 25B, manufactured by Nippon Oil Co., Ltd.), α,α'-di(tert-butyl peroxide)diisopropylbenzene (Perbutyl P, manufactured by Nippon Oil Co., Ltd.), tert-butylcumyl peroxide (Perbutyl C, manufactured by Nippon Oil Co., Ltd.), or di-tert-butyl peroxide (Perbutyl D, manufactured by Nippon Oil Co., Ltd.). These can be used alone or in combination of two or more. Dicumyl peroxide is preferred.

[0046] Regarding the proportion of the crosslinking agent in the insulating resin composition, the lower limit is preferably 0.1 wt% or more, more preferably 0.5 wt% or more, and the upper limit is preferably 5.0 wt% or less, more preferably 3.0 wt% or less. When the proportion of the crosslinking agent is within the above range, the insulating resin composition can be well crosslinked.

[0047] In addition to the components (a), (b), (c), and (d) mentioned above, the insulating resin composition may also contain an antioxidant. As an antioxidant, it is preferable to use a combination of hindered phenolic antioxidants, which are primarily used to scavenge free radicals, and phosphorus-based or sulfur-based antioxidants, which are primarily used to decompose peroxides.

[0048] Regarding the proportion of antioxidants in the insulating resin composition, the lower limit is preferably 0.01 wt% or more, more preferably 0.20 wt% or more, and the upper limit is preferably 1.00 wt% or less, more preferably 0.60 wt% or less. When the proportion of antioxidants is within the above range, oxidative degradation in the crosslinked products of the insulating resin composition can be effectively suppressed.

[0049] Furthermore, as long as it does not hinder the inhibition of water tree growth and the reduction of dielectric loss tangent in the crosslinked components of the insulating resin composition, the insulating resin composition may contain various substances in addition to the above-mentioned components. Examples of such substances include: stabilizers, lubricants, inorganic fillers, surface treatment agents, flame retardants, acid removers, voltage stabilizers, etc.

[0050] An insulating resin composition can be obtained by melt-kneading components (b), (c), and (d) relative to component (a) after drying and mixing them in a Henschel mixer or similar equipment. As the melt-kneading apparatus, a single-screw or twin-screw extruder, a Banbury internal mixer, a kneader, or similar mixer can be used. Particularly preferred is that, in order to remove foreign matter, a metal mesh filter with a pore size of 100 μm or less is installed on a single-screw or twin-screw extruder capable of continuous processing during resin extrusion. The insulating resin composition after adding component (d) is preferably kneaded at a temperature of 120°C or higher and 135°C or lower.

[0051] The specific gravity of the insulating resin composition is preferably 0.91 or more and 0.93 or less.

[0052] Furthermore, the dielectric loss tangent of the crosslinked product formed by crosslinking the insulating resin composition at 90°C and 30 kV / mm is preferably 1.0% or less, more preferably 0.5% or less. When the dielectric loss tangent of the crosslinked product is within the above range, for cables in which the crosslinked product of the insulating resin composition is applied to the insulation layer, the power transmission efficiency can be improved due to the small dielectric loss tangent.

[0053] The dielectric loss tangent of the crosslinked compound is the value measured according to JIS C 2138 standard at 90°C and 30 kV / mm. Furthermore, the dielectric loss tangent is temperature- and field-dependent; when the crosslinked compound of the above-mentioned insulating resin composition was measured at 23°C and 10 kV / mm, the dielectric loss tangent of the crosslinked compound was 0.1% or less.

[0054] Furthermore, in order to suppress the growth of water trees in the crosslinked material of the insulating resin composition, the moisture absorption rate of the crosslinked material is preferably 500 ppm or more, more preferably 800 ppm or more. By imparting hygroscopicity to the crosslinked material, the moisture in the crosslinked material is uniformly dispersed, thereby suppressing the growth of water trees in the crosslinked material. In addition, from the perspective of the insulation resistance of the crosslinked material, the moisture absorption rate of the crosslinked material is preferably 2000 ppm or less.

[0055] Furthermore, according to JIS K 7210 standard, when measured at a melt temperature of 190°C and a load of 2.16 kgf, the resin flowability of the crosslinked compound is preferably 0.5 g / 10 min or more and 5.0 g / 10 min or less, more preferably 0.5 g / 10 min or more and 3.0 g / 10 min or less. When the resin flowability is within the above range, the exudation of water tree inhibitors from the crosslinked compound can be suppressed, and the shape of the crosslinked compound can be maintained for a long time.

[0056] The cross-linked product obtained by cross-linking the insulating resin composition of the embodiment is an insulator. When such a cross-linked insulating resin composition is applied to a cable with an insulation layer, the growth of water trees in the insulation layer can be suppressed and the dielectric loss tangent can be reduced. Therefore, even when used under high or ultra-high voltage conditions, the cable can transmit electricity efficiently. Such cables are suitable for underground cables and submarine cables. When the cable is an AC cable, the effects of suppressing water tree growth and reducing the dielectric loss tangent are even more effective.

[0057] Figure 1 This is a cross-sectional view illustrating an example of an insulating resin composition used in an application embodiment of the cable.

[0058] like Figure 1 As shown, the cable 1 includes: a conductor 2; an inner semiconductive layer 3 disposed on the outside of the conductor 2; an insulation layer 4 disposed on the outside of the inner semiconductive layer 3, formed by cross-linking the aforementioned insulating resin composition; and an outer semiconductive layer 5 disposed on the outside of the insulation layer 4. The inner semiconductive layer 3 surrounds the conductor 2. The insulation layer 4 surrounds the inner semiconductive layer 3. The outer semiconductive layer 5 surrounds the insulation layer 4. Thus, in the cable 1, the inner semiconductive layer 3, the insulation layer 4, and the outer semiconductive layer 5 are sequentially stacked on the conductor 2, which is made of a metal such as copper or aluminum.

[0059] The inner semiconductive layer 3 and the outer semiconductive layer 5 comprise, for example: ethylene-based copolymers such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, or ethylene-vinyl acetate copolymer; olefin-based elastomers; and conductive carbon black.

[0060] In addition, cable 1 may also have a metallic shielding layer (not shown), which is disposed outside the outer semiconductive layer 5 and surrounds the outer semiconductive layer 5. Furthermore, cable 1 may also have a sheath (not shown), which is disposed outside the metallic shielding layer and surrounds the metallic shielding layer.

[0061] Conductor 2 is continuously supplied to the resin extrusion port, where it is coated with an inner semiconductive layer 3, an insulating resin composition layer, and an outer semiconductive layer 5. These three layers can be extruded and coated simultaneously or sequentially. Since the conductor is heated by heat transfer from the previously coated resin during coating, the cooling rate of the resin near the conductor will be slower. Therefore, it is preferable to supply the conductor to the resin extrusion port after adjusting the conductor temperature to above 1°C and below 100°C using cooling.

[0062] The coating of the insulating resin composition is carried out by extruding it from the resin extrusion port of a resin extruder equipped with a metal mesh filter with a pore size of 100 μm or less for the purpose of removing foreign matter onto the conductor 2 (on the inner semiconductive layer 3). The temperature of the insulating resin composition during extrusion is preferably above the melting point of the insulating resin composition, specifically, preferably 110°C or higher, more preferably 120°C or higher. Furthermore, to suppress charring, the temperature of the insulating resin composition during extrusion is preferably 140°C or lower.

[0063] After coating conductor 2 with an insulating resin composition layer, the insulating resin composition layer is subjected to a cross-linking reaction under pressure and heat to form an insulating layer 4 formed by cross-linking of the insulating resin composition. This yields cable 1. Cable 1 is then cooled by a cooling pipe or cooling water tank, and, if necessary, a metallic shielding layer or sheath (not shown) is formed using conventional methods.

[0064] When forming a metal shielding layer or sheath on the cooled cable 1, the temperature of the insulation layer 4 is preferably below 300°C to prevent deformation of the insulation layer 4.

[0065] Regarding the thickness of the insulation layer 4, from the perspective of insulation characteristics, it is preferably 2 mm or more, more preferably 5 mm or more, and even more preferably 10 mm or more. From the perspective of laying workability, it is preferably 50 mm or less, and more preferably 40 mm or less.

[0066] Furthermore, regarding the thickness of the inner semiconductive layer 3 and the outer semiconductive layer 5, from the perspective of insulation properties, both are preferably 0.1 mm or more, more preferably 0.5 mm or more, and from the perspective of conductivity properties, both are preferably 5.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less.

[0067] According to the above embodiments, even if component (c), i.e., a water tree inhibitor, is included to suppress water tree growth, the increase in dielectric loss tangent caused by the water tree inhibitor can also be suppressed by including component (b). Furthermore, by applying a crosslinked version of an insulating resin composition that can suppress water tree growth and reduce dielectric loss tangent to the insulation layer, the power transmission efficiency of the cable can be improved.

[0068] While the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all the methods included in the concept of this disclosure and the scope of the claims, and various modifications can be made within the scope of this disclosure.

[0069] Example

[0070] Next, embodiments and comparative examples will be described, but the present invention is not limited to these embodiments.

[0071] The raw materials used in the examples and comparative examples are shown below.

[0072] • Composition (a): Polyethylene (CE1559; LDPE manufactured by Sumitomo Chemical Co., Ltd., MFR0.8)

[0073] • Resin (b1-1): Maleic anhydride grafted resin (resin grafted with 2.00 wt% maleic anhydride onto CE1559)

[0074] • Resin (b1-2): Maleic anhydride grafted resin (resin grafted with 0.25 wt% maleic anhydride onto CE1559)

[0075] • Resin (b1-3): Maleic anhydride grafted resin (resin grafted with 1.00 wt% maleic anhydride onto CE1559)

[0076] • Resin (b2-1): Ethylene copolymer (NUC-6520; ethylene-ethyl acrylate copolymer manufactured by ENEOS NUC, containing 24 wt% acrylate, MFR 1.6)

[0077] • Ingredient (c-1): Water tree inhibitor (PEG-20000; polyethylene glycol manufactured by ADEKA, number average molecular weight 20000)

[0078] • Ingredient (c-2): Water tree inhibitor (polypropylene glycol 4000; polypropylene glycol manufactured by ADEKA, number average molecular weight 4000)

[0079] • Ingredient (c-3): Water tree inhibitor (polypropylene glycol 400; polypropylene glycol manufactured by ADEKA, number average molecular weight 400)

[0080] • Component (d): Crosslinking agent (Percumyl D; dicumyl peroxide manufactured by Nippon Oil Company)

[0081] • Antioxidant (Irganox 1010; hindered phenolic antioxidant manufactured by BASF)

[0082] (Examples 1-8 and Comparative Examples 1-2)

[0083] After the raw materials are dried and mixed using a Henschel mixer, they are extruded using a single-screw extruder (L / D=24, 120°C) equipped with a flat woven mesh with a aperture of 0.091 mm to obtain a granular insulating resin composition (hereinafter also referred to as resin granules) having the composition shown in Table 1.

[0084] [Measurement and Evaluation]

[0085] The insulating resin compositions obtained in the above examples and comparative examples were subjected to the following measurements and evaluations. The results are shown in Table 1.

[0086] [1] Moisture absorption rate

[0087] Resin granules were molded at 120°C into samples 100 mm long, 150 mm wide, and 1 mm high. The samples were crosslinked at 160°C. The crosslinked material was divided into six test pieces and stored in a constant temperature and humidity bath at 70°C and 90% relative humidity for 4 hours. The moisture content was then determined using the Karl Fischer method (method B, moisture vaporization method) of JIS K7251, and the moisture absorption rate was calculated.

[0088] [2] Resin flowability

[0089] Using resin granules, resin flowability was determined by the amount of resin extruded (g) per 10 minutes under the conditions of a melt temperature of 190°C and a load of 2.16 kgf, according to JIS K7210 standard.

[0090] [3] Length of the water tree

[0091] First, a small cable is manufactured. Using resin granules, an insulating resin composition is extruded using a single-screw extruder (L / D=24, 120°C, fully threaded screw) equipped with a flat braided mesh of 0.091 mm aperture. This composition, along with a semi-conductive resin (based on NUCV-9590, a semi-conductive resin composition of ethylene-ethyl acrylate copolymer manufactured by ENEOS NUC) extruded using another single-screw extruder (L / D=24, 120°C, fully threaded screw) equipped with a flat braided mesh of 0.091 mm aperture, is then coated onto a copper conductor using a three-layer co-extrusion head (120°C). The coated cable is then passed through a pressure cross-linking tube and subsequently cooled in a water bath. This yields a small cable with a copper conductor approximately 2 mm in diameter, an inner semi-conductive layer approximately 0.5 mm thick, an insulation layer approximately 2 mm thick, and an outer semi-conductive layer approximately 0.5 mm thick.

[0092] Next, as Figure 2 As shown, a small cable 1 was immersed in a 3.5 wt% NaCl aqueous solution, and a 4 kV 1000 Hz AC voltage was applied between the conductor and the NaCl aqueous solution for 200 hours to conduct a water tree test. Ten samples were obtained by cutting the tested cable into 1 mm thick circular pieces along the axial direction, and the length of the water tree was observed using an optical microscope and measured.

[0093] [4] Dielectric loss tangent

[0094] Using resin particles, a 0.3 mm thick film sample was formed by molding at 120°C for 10 minutes. The sample was then crosslinked at 160°C for 30 minutes. The dielectric loss tangent of the crosslinked material was measured at 90°C and 30 kV / mm according to JIS C 2138 standard.

[0095] [Table 1]

[0096]

[0097] As shown in Table 1, in Examples 1-8, since the insulating resin composition includes components (a), (b), (c), and (d), it is possible to suppress the growth of water trees and reduce the dielectric loss tangent. On the other hand, in Comparative Examples 1-2, since the insulating resin composition does not include at least one of components (a) to (d), it is not possible to suppress the growth of water trees and reduce the dielectric loss tangent.

[0098] Figure Labels

[0099] 1. Cable

[0100] 2 conductors

[0101] 3. Internal semiconductive layer

[0102] 4 Insulation layer

[0103] 5. External semiconductive layer

Claims

1. An insulating resin composition for cables, comprising component (a), component (b), component (c), and component (d), The aforementioned component (a) is polyethylene. Component (b) is at least one resin selected from resin (b1) and resin (b2), wherein resin (b1) is a resin grafted with at least one modified monomer selected from unsaturated organic acids and their derivatives, and resin (b2) is at least one ethylene copolymer selected from ethylene-acrylate copolymer, ethylene-acrylic acid copolymer, and ethylene-vinyl acetate copolymer. The aforementioned component (c) is a water tree inhibitor. The aforementioned component (d) is a crosslinking agent.

2. The insulating resin composition for cables according to claim 1, wherein, The aforementioned component (c) is at least one compound selected from polyalkylene glycols and their derivatives, polyglycerol, glycerol fatty acid esters, and sorbitol esters.

3. The insulating resin composition for cables according to claim 1 or 2, wherein, The crosslinked product formed by crosslinking the aforementioned insulating resin composition for cables has a dielectric loss tangent of less than 1.0% at 90°C and 30 kV / mm.

4. The insulating resin composition for cables according to any one of claims 1 to 3, wherein, In the aforementioned resin (b1), at least one modifying monomer selected from unsaturated dicarboxylic acids, unsaturated dicarboxylic anhydrides, and unsaturated dicarboxylic acid derivatives has been added to at least one resin selected from polypropylene, polyethylene, and olefin copolymers.

5. The insulating resin composition for cables according to any one of claims 1 to 4, wherein, The aforementioned component (b) in the aforementioned cable insulating resin composition is present in an amount of 3.0 wt% or more and 25.0 wt% or less.

6. A cable comprising: conductor; An internal semiconductive layer is disposed on the outside of the aforementioned conductor, surrounding the aforementioned conductor; An insulating layer, disposed outside the aforementioned inner semiconductive layer and surrounding the aforementioned inner semiconductive layer, is cross-linked from the cable insulating resin composition according to any one of claims 1 to 5; and, An external semiconductive layer is disposed outside the aforementioned insulating layer and surrounds the aforementioned insulating layer.

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