Resin composition, power cable, and method for producing power cable

Abstract

The resin composition comprises: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the content of the copolymer is 0.5 parts by mass or more when the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the styrene-based elastomer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached due to thermal decomposition or hydrolysis at temperatures below 300°C.

Description

Technical Field

[0001] The present disclosure relates to a resin composition, a power cable, and a method for manufacturing the power cable.

[0002] This application claims priority based on Japanese patent application No. 2021-28226, filed on February 25, 2021, and incorporates by reference all the contents described in the aforementioned Japanese application. Background Art

[0003] In recent years, solid-insulated power cables (hereinafter simply referred to as "power cables") have been developed for use in direct current transmission (for example, Patent Document 1).

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 11-16421 Summary of the Invention

[0007] According to one embodiment of the present disclosure, a resin composition is provided, comprising: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the content of the copolymer is 0.5 parts by mass or more, when the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the styrene-based elastomer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached due to thermal decomposition or hydrolysis at temperatures below 300°C.

[0008] According to another embodiment of the present disclosure, a power cable is provided, comprising: a conductor; and an insulating layer configured to cover the conductor, the insulating layer comprising a resin composition comprising: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the content of the copolymer in the insulating layer is 0.5 parts by mass or more, when the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached due to thermal decomposition or hydrolysis at temperatures below 300°C.

[0009] According to another embodiment of the present disclosure, a power cable is provided, comprising: a conductor; and an insulating layer configured to cover the conductor, the insulating layer comprising a resin composition comprising: a base resin comprising a polyolefin; a styrene-based elastomer comprising styrene units; and a copolymer comprising styrene units and maleic anhydride units, wherein, when the combined content of the base resin and the styrene-based elastomer is 100 parts by mass, the total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more, the content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached due to thermal decomposition or hydrolysis at temperatures below 300°C.

[0010] According to another embodiment of the present disclosure, a method for manufacturing a power cable is provided, comprising the following steps: preparing a resin composition comprising a base resin comprising a polyolefin, a styrene-based elastomer comprising a styrene unit, and a copolymer comprising a styrene unit and a maleic anhydride unit; and forming an insulating layer using the resin composition to cover the outer periphery of a conductor, wherein in the step of preparing the resin composition, when the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the copolymer in the resin composition is set to 0.5 parts by mass or more, the content of the styrene-based elastomer in the resin composition is set to be greater than the content of the copolymer, and the copolymer is set to a material that does not contain side chains that are detached due to thermal decomposition or hydrolysis at a temperature below 300°C.

[0011] According to another embodiment of the present disclosure, a method for manufacturing a power cable is provided, comprising the following steps: preparing a resin composition comprising a base resin comprising a polyolefin, a styrene-based elastomer comprising a styrene unit, and a copolymer comprising a styrene unit and a maleic anhydride unit; and forming an insulating layer using the resin composition to cover the outer periphery of a conductor, wherein in the step of preparing the resin composition, when the combined content of the base resin and the styrene-based elastomer is 100 parts by mass, the total content of the maleic anhydride units in the resin composition is set to 0.1 parts by mass or more, the content of the styrene-based elastomer in the resin composition is set to be equal to or greater than the content of the copolymer, and the copolymer is made of a material that does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 1 is a schematic cross-sectional view perpendicular to the axial direction of a DC power cable according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0013] [Problems to be Solved by the Present Disclosure]

[0014] An object of the present disclosure is to obtain stable insulation properties of an insulating layer.

[0015] [Effects of the Present Disclosure]

[0016] According to the present disclosure, stable insulation properties of the insulating layer can be obtained.

[0017] [Description of Embodiments of the Present Disclosure]

[0018] <Insights Obtained by the Inventors>

[0019] First, the findings obtained by the inventors will be described.

[0020] In DC power cables, for example, when high voltage is applied, space charge is generated within the insulation layer, potentially degrading the insulation properties of the insulation layer. (Note that the "insulation properties" of the insulation layer referred to here refer to volume resistivity, DC breakdown electric field strength, and space charge characteristics, also known as "DC characteristics.")

[0021] Various countermeasures have been tried in the past to suppress the accumulation of space charge in the insulation layer of the DC power cable described above. However, the inventors have conducted extensive research and discovered that the following new problems may occur.

[0022] (i) When inorganic fillers are added

[0023] To suppress the accumulation of space charge within the insulation layer of a DC power cable, polar inorganic fillers such as carbon black and magnesium oxide (MgO) are sometimes added to the resin composition constituting the insulation layer (e.g., Patent Document 1). In this case, the insulation layer is formed by extruding the resin composition containing the inorganic filler through a mesh, for example.

[0024] However, when such inorganic fillers are added, depending on manufacturing conditions such as the particle size, surface treatment conditions, and content of the inorganic filler, the mesh may gradually become clogged during the insulation layer extrusion process due to agglomeration of the inorganic filler. This clogging can increase the resin pressure during the extrusion process. Consequently, the insulation properties of the insulation layer may become uneven along the length of the cable, or the moldability of the insulation layer itself may be reduced.

[0025] (ii) Modified polyolefin

[0026] To suppress the accumulation of space charge within the insulation layer of DC power cables, research has been conducted on introducing organic polar groups into the resin component. Examples of methods for introducing polar groups include adding modified polyolefins such as polyethylene modified with maleic anhydride as a polar group to the resin composition.

[0027] However, when modifying polyolefins with maleic anhydride as a side chain, peroxide is required. Using peroxide to increase the modification rate (modification amount) of maleic anhydride causes the polyolefins to react with each other, resulting in gelation. Consequently, the modified polyolefin may become unmoldable.

[0028] Due to the above reasons, it is difficult to increase the modification rate (modification amount) of maleic anhydride in the modified polyolefin. Therefore, it is difficult to fully ensure the total content of maleic anhydride in the entire resin composition. As a result, it may be impossible to suppress the local accumulation of space charge. In particular, there is a tendency for insulation properties to decrease at high temperatures.

[0029] The present disclosure is made based on the above-mentioned findings found by the inventors.

[0030] <Embodiments of the present disclosure>

[0031] Next, embodiments of the present disclosure will be described by way of examples.

[0032] [1] A resin composition according to one embodiment of the present disclosure comprises: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the content of the copolymer is 0.5 parts by mass or more, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer, the content of the styrene-based elastomer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C.

[0033] According to this configuration, stable insulation can be obtained.

[0034] [2] Another embodiment of the present disclosure provides a power cable comprising: a conductor; and an insulating layer configured to cover the periphery of the conductor, the insulating layer comprising a resin composition comprising: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the content of the copolymer in the insulating layer is 0.5 parts by mass or more when the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, and the copolymer does not contain a side chain that is detached by thermal decomposition or hydrolysis at a temperature below 300°C.

[0035] According to this configuration, stable insulation properties of the insulating layer can be obtained.

[0036] [3] In the power cable described in [2] above, the total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer.

[0037] According to this configuration, the maleic anhydride unit can sufficiently capture space charges.

[0038] [4] Another embodiment of the present disclosure provides a power cable comprising: a conductor; and an insulating layer configured to cover the periphery of the conductor, wherein the insulating layer comprises a resin composition, the resin composition comprising: a base resin comprising a polyolefin; a styrene-based elastomer comprising a styrene unit; and a copolymer comprising a styrene unit and a maleic anhydride unit, wherein the total content of the maleic anhydride unit in the insulating layer is 0.1 parts by mass or more when the combined content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, and the copolymer does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C.

[0039] According to this configuration, stable insulation properties of the insulating layer can be obtained.

[0040] [5] In the power cable described in any one of [2] to [4] above, the copolymer does not contain any of ester bonds, ether bonds, amide bonds, urethane bonds, and siloxane bonds.

[0041] According to this configuration, stable insulation properties of the insulating layer can be obtained.

[0042] [6] In the power cable described in any one of [2] to [5] above, the volume resistivity of the sheet of the insulating layer measured at a temperature of 90°C and a DC electric field of 75 kV / mm is 1.0×10 15 Ω·cm or more.

[0043] According to this configuration, stable DC power transmission can be performed.

[0044] [7] In the power cable described in any one of [2] to [6] above, the space charge storage amount of the sheet of the insulating layer measured under the conditions of a temperature of 90°C and a DC electric field of 75 kV / mm is 100% or less.

[0045] According to this configuration, stable DC power transmission can be performed.

[0046] [8] In the electric power cable according to any one of [2] to [7] above, the content of the copolymer is less than 20 parts by mass when the total content of the base resin and the styrene-based elastomer is 100 parts by mass.

[0047] According to this configuration, deformation at high temperatures can be suppressed.

[0048] [9] In the power cable described in [7] or [8] above, the heat deformation rate of the sheet of the insulating layer measured under the conditions of a temperature of 120° C. and a load of 2 kg is 40% or less.

[0049] According to this configuration, the heat resistance of the power cable can be improved even at high temperatures.

[0050]

[10] In the power cable according to any one of [2] to [9] above, the content of the inorganic compound contained in the insulating layer is less than 0.01 parts by mass when the total content of the base resin and the styrene-based elastomer is 100 parts by mass.

[0051] According to this configuration, clogging of the mesh can be suppressed during the extrusion step of the insulating layer.

[0052]

[11] In the power cable according to any one of [2] to [9] above, the insulating layer further contains less than 1 part by mass of an inorganic filler, when the total content of the base resin and the styrene-based elastomer is 100 parts by mass.

[0053] According to this configuration, clogging of the mesh during the extrusion process can be suppressed, and the effect of improving the insulation properties of the insulating layer can be stably obtained.

[0054]

[12] In the power cable described in

[10] or

[11] above, the insulating layer satisfies the following formula (1) for the variation rate of DC breakdown strength: (E MAX -E MIN ) / E AVE ≤0.2……(1), wherein the DC breakdown strength is the electric field strength when a DC electric field is applied to each of the plurality of sheets at a temperature of 90°C and insulation breakdown occurs in the sheet, wherein the plurality of sheets are collected at a plurality of locations of the insulating layer at predetermined intervals in the longitudinal direction of the conductor, E MAX 、E MIN and E AVE are respectively the maximum value, the minimum value and the average value of the DC breakdown strength of the plurality of sheets.

[0055] According to this configuration, stable insulation can be obtained for the entire long power cable.

[0056]

[13] In the electric power cable according to any one of [2] to

[12] above, the glass transition temperature of the copolymer is 110° C. or higher.

[0057] According to this configuration, the mechanical characteristics of the power cable can be ensured.

[0058]

[14] In the electric power cable according to any one of [2] to

[13] above, the glass transition temperature of the copolymer is 140° C. or lower.

[0059] According to this configuration, the copolymer can be prevented from becoming glassy (filler-like).

[0060]

[15] Another embodiment of the present disclosure provides a method for manufacturing a power cable, comprising the following steps: preparing a resin composition comprising a base resin containing a polyolefin, a styrene-based elastomer containing a styrene unit, and a copolymer containing a styrene unit and a maleic anhydride unit; and using the resin composition to form an insulating layer in a manner that covers the outer periphery of a conductor, wherein in the step of preparing the resin composition, when the total content of the base resin and the styrene-based elastomer is set to 100 parts by mass, the content of the copolymer in the resin composition is set to 0.5 parts by mass or more, the content of the styrene-based elastomer in the resin composition is set to be greater than the content of the copolymer, and the copolymer is set to a material that does not contain side chains that will be detached due to thermal decomposition or hydrolysis at a temperature below 300°C.

[0061] According to this configuration, a power cable having an insulating layer with stable insulation properties can be obtained.

[0062]

[16] Another embodiment of the present disclosure provides a method for manufacturing a power cable, comprising the following steps: preparing a resin composition comprising a base resin comprising a polyolefin, a styrene-based elastomer comprising a styrene unit, and a copolymer comprising a styrene unit and a maleic anhydride unit; and using the resin composition to form an insulating layer in a manner that covers the periphery of a conductor, wherein in the step of preparing the resin composition, when the combined content of the base resin and the styrene-based elastomer is set to 100 parts by mass, the total content of the maleic anhydride unit in the resin composition is set to 0.1 parts by mass or more, the content of the styrene-based elastomer in the resin composition is set to be greater than the content of the copolymer, and the copolymer is set to be a material that does not contain side chains that will be detached due to thermal decomposition or hydrolysis at a temperature below 300°C.

[0063] According to this configuration, a power cable having an insulating layer with stable insulation properties can be obtained.

[0064] [Details of the embodiments of the present disclosure]

[0065] Next, an embodiment of the present disclosure will be described below with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to these examples, but is shown by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0066] <One embodiment of the present disclosure>

[0067] (1) Resin composition

[0068] The resin composition of this embodiment is a material that constitutes the insulating layer 130 of the power cable 10 described below. The resin composition comprises, for example, a base resin (A), a styrene-based elastomer (B), a copolymer (C), and other additives. Hereinafter, the base resin (A) is also referred to as "component (A)", the styrene-based elastomer (B) is also referred to as "component (B)", and the copolymer (C) is also referred to as "component (C)".

[0069] [Base resin (A)]

[0070] The base resin (base polymer) refers to the resin component constituting the main component of the resin composition. The "main component" refers to the component with the largest content.

[0071] The base resin of the present embodiment includes, for example, a polyolefin. Examples of the polyolefin constituting the base resin include polyethylene, polypropylene, ethylene-α-olefin copolymers, and thermoplastic elastomers (non-styrene elastomers) obtained by dispersing or copolymerizing ethylene-propylene rubber in polypropylene. Among them, polyethylene or polypropylene is preferred. It should be noted that two or more of these may be used in combination.

[0072] Examples of the polyethylene constituting the base resin include low-density polyethylene (LDPE), medium-density polyethylene (MDPE), and high-density polyethylene (HDPE). These polyethylenes may be linear or branched.

[0073] Examples of the polypropylene constituting the base resin include propylene homopolymers (homopolypropylene) and propylene random polymers (atactic polypropylene). The stereoregularity is not limited, but is preferably isotactic, for example.

[0074] Since the resin composition includes the above-mentioned base resin (A), the basic characteristics and mechanical characteristics of the power cable 10 can be ensured.

[0075] The elastic modulus of the polyolefin, as measured using a scanning probe microscope (SPM), is preferably between 300 MPa and 2000 MPa. The SPM elastic modulus measurement is performed under the following conditions: 60,000 taps are applied to a 10 μm square area of the polyolefin at 25°C using a cantilever made of silicon and having a tip with a curvature radius of less than 20 nm. When the elastic modulus of the polyolefin is within this range, both flexibility and rigidity can be achieved.

[0076] [Styrene elastomer (B)]

[0077] The styrene-based elastomer (B) contains, for example, at least a styrene unit as a monomer unit.

[0078] By including styrene units in the styrene-based elastomer (B), the compatibility between the styrene-based elastomer (B) and the copolymer (C) containing styrene units, described later, can be improved. That is, the styrene-based elastomer (B) can be incorporated into the base resin (A), and the copolymer (C) can be uniformly dispersed. This makes it easy to increase the content of the copolymer (C) in the resin composition.

[0079] Furthermore, since the styrene-based elastomer (B) contains styrene units, space charges can be trapped not only in the maleic anhydride units in the copolymer (C) described below, but also in the aromatic rings of the styrene units in the styrene-based elastomer (B). This can suppress localized accumulation of space charges.

[0080] The styrene-based elastomer (B) is, for example, a copolymer containing a styrene unit as a hard segment and at least one monomer unit selected from the group consisting of ethylene, propylene, butene, and isoprene as a soft segment.

[0081] Examples of the styrene-based elastomer (B) include styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, and styrene-ethylene-butylene-olefin crystalline block copolymer. Two or more of these may be used in combination.

[0082] It should be noted that the term "hydrogenated" as used herein refers to hydrogenation of double bonds. For example, a "hydrogenated styrene-butadiene-styrene block copolymer" refers to a polymer obtained by hydrogenating the double bonds of a styrene-butadiene-styrene block copolymer. It should be noted that the double bonds of the aromatic rings of styrene are not hydrogenated. A "hydrogenated styrene-butadiene-styrene block copolymer" may also be referred to as a styrene-ethylene-butylene-styrene block copolymer (SEBS).

[0083] When the base resin contains polyethylene, the styrene-based elastomer (B) preferably contains, for example, ethylene units among the above-mentioned materials. This can improve the compatibility between the base resin (A) and the styrene-based elastomer (B).

[0084] The ethylene unit content (hereinafter simply referred to as "ethylene content") in the styrene-based elastomer (B) is not particularly limited, but is preferably, for example, 10% by mass or more and 50% by mass or less. By setting the ethylene content to 10% by mass or more, the compatibility between the base resin (A) and the styrene-based elastomer (B) can be sufficiently improved. On the other hand, by setting the ethylene content to 50% by mass or less, a predetermined amount of styrene units can be ensured. This can substantially improve the compatibility between the styrene-based elastomer (B) and the copolymer (C) described below. As a result, the insulation properties at high temperatures can be stably improved.

[0085] Furthermore, among the above materials, hydrogenated materials, which contain no double bonds in their chemical structure other than aromatic rings, are preferred. Using non-hydrogenated materials can lead to thermal degradation of the resin component during molding of the resin composition, potentially degrading the properties of the resulting molded article. In contrast, using hydrogenated materials improves tolerance to thermal degradation, thereby maintaining high properties of the molded article.

[0086] In addition, the styrene elastomer (B) has a low elastic modulus. Specifically, the elastic modulus of the styrene elastomer (B) measured using SPM is, for example, preferably 10 MPa or more and 400 MPa or less. It should be noted that the measurement conditions are the same as those described in the base resin (A). By setting the elastic modulus of the styrene elastomer (B) to 10 MPa or more, the insulating layer 130 can be stably molded. On the other hand, by setting the elastic modulus of the styrene elastomer (B) to 400 MPa or less, the flexibility of the power cable 10 can be improved.

[0087] Furthermore, the styrene elastomer (B) has low crystallinity. Specifically, the styrene elastomer (B) has no melting point or a melting point lower than 100° C. Furthermore, the heat of fusion of the styrene elastomer (B) is, for example, 50 J / g or less, preferably 30 J / g or less.

[0088] It should be noted that styrene-modified polyethylene is not suitable as the styrene-based elastomer (B) in this embodiment. This is because, in order to suppress the local accumulation of space charge (showing good DC characteristics), it is necessary to finely disperse the copolymer (C) described later in the composition. However, in styrene-modified polyethylene, it is difficult to ensure the grafting amount of a specified amount of styrene units. For example, in a styrene-grafted polyethylene grafted with 0.1% by mass or more and 10% by mass or less of styrene, the styrene units are insufficient. Therefore, it is difficult to improve the compatibility of the styrene-based elastomer (B) and the copolymer (C) described later. As a result, the dispersibility of the copolymer (C) may decrease.

[0089] The content of the styrene-based elastomer (B) in the resin composition is, for example, greater than the content of the copolymer (C) described later. When the content of the component (B) is lower than the content of the component (C), the styrene-based elastomer (B) cannot be sufficiently mixed in the base resin (A), and it is difficult to uniformly disperse the copolymer (C). Therefore, it may be impossible to suppress the local accumulation of space charges. In particular, the insulation properties at high temperatures may decrease. In contrast, in this embodiment, by setting the content of the component (B) to greater than the content of the component (C), the styrene-based elastomer (B) can be sufficiently mixed in the base resin (A), and the copolymer (C) can be uniformly dispersed. Thus, the local accumulation of space charges can be suppressed. In particular, the insulation properties at high temperatures can be improved.

[0090] It should be noted that the upper limit of the content of the styrene-based elastomer (B) in the resin composition is not limited. However, preferably, when the total content of components (A) and (B) is set to 100 parts by mass, the content of the styrene-based elastomer (B) is, for example, 40 parts by mass or less, preferably 30 parts by mass or less. In other words, the content of the base resin (A) is preferably 60 parts by mass or more, preferably 70 parts by mass or more. This ensures that the basic properties and mechanical properties of the power cable 10 are consistently maintained.

[0091] [Copolymer (C)]

[0092] The copolymer (C) comprises, for example, styrene units and maleic anhydride units as monomeric units. By introducing the maleic anhydride unit as a monomeric unit constituting the main chain into the copolymer (C) comprising the styrene unit, the copolymer (C) can be freely molecularly designed. Thus, the content of the maleic anhydride unit in one molecule can be easily increased. As a result, the total content of the maleic anhydride units in the entire resin composition can be increased.

[0093] In addition, the copolymer (C) does not contain side chains that may be detached due to thermal decomposition or hydrolysis at temperatures below 300°C. The "side chains that may be detached due to thermal decomposition or hydrolysis at temperatures below 300°C" mentioned herein refer to side chains that may be detached from the main chain during at least one of the extrusion process of the insulating layer 130, the cross-linking process, and the laying environment in which the insulating layer 130 absorbs moisture. By not containing such side chains in the copolymer (C), even if the resin composition is exposed to high temperature or high humidity during the extrusion process, the cross-linking process, and the laying environment in high humidity, the detachment of the side chains can be suppressed, and the generation of low-molecular-weight components caused by the side chains can be suppressed. As a result, the accumulation of space charges in the low-molecular-weight components can be suppressed.

[0094] Specifically, the copolymer (C) preferably does not contain any of the following bonds: ester bonds, ether bonds, amide bonds, urethane bonds, and siloxane bonds. If ester bonds, ether bonds, amide bonds, urethane bonds, and siloxane bonds exist as side chains, they may be removed by thermal decomposition or hydrolysis at temperatures below 300°C.

[0095] Examples of the monomer unit containing the side chain that is decomposed or hydrolyzed at 300° C. or lower include vinyl acetate, allyl ether, and acrylamide.

[0096] On the other hand, examples of monomer units that do not include the aforementioned detachable side chains, that is, other monomer units that may be included in the copolymer (C) include olefins, styrene, maleic anhydride, and the like.

[0097] Furthermore, the copolymer (C) preferably has no polar groups other than the maleic anhydride units, for example. This can suppress the generation of low-molecular-weight components caused by polar groups other than the maleic anhydride units.

[0098] Furthermore, the copolymer (C) is more preferably composed of, for example, styrene units and maleic anhydride units only. In other words, the copolymer (C) is more preferably a styrene maleic anhydride copolymer. That is, by not having other monomer units other than styrene units and maleic anhydride units in the copolymer (C), the content of maleic anhydride units in one molecule can be increased. As a result, the total content of maleic anhydride units in the entire resin composition can be easily increased.

[0099] The content of styrene units in the copolymer (C) (hereinafter, also referred to as "styrene content") is preferably, for example, 50% by mass or more and 90% by mass or less. When the styrene content is less than 50% by mass, the compatibility of the copolymer (C) with the styrene-based elastomer (B) may decrease. In contrast, by setting the styrene content to 50% by mass or more, the compatibility of the copolymer (C) with the styrene-based elastomer (B) can be improved. On the other hand, when the styrene content exceeds 90% by mass, the insulating layer 130 may become soft and deform easily under high temperature conditions. When the styrene content exceeds 90% by mass, it is difficult to ensure a specified amount of maleic anhydride units. In contrast, by setting the styrene content to 90% by mass or less, excessive softening of the insulating layer 130 and excessive deformation of the insulating layer 130 under high temperature conditions can be suppressed. That is, mechanical properties can be ensured. In addition, by setting the styrene content to 90% by mass or less, a specified amount of maleic anhydride units can be ensured. The total content of maleic anhydride units in the resin composition will be described later.

[0100] On the other hand, the content of the maleic anhydride units in the copolymer (C) (hereinafter, also simply referred to as "maleic anhydride content") is, for example, preferably 10% by mass or more and 50% by mass or less. By setting the maleic anhydride content to 10% by mass or more, the total content of the maleic anhydride units in the resin composition can be ensured. The total content of the maleic anhydride units in the resin composition will be described later. On the other hand, by setting the maleic anhydride content to 50% by mass or less, a predetermined amount of styrene units can be ensured. Thus, the compatibility of the copolymer (C) and the styrene-based elastomer (B) can be improved.

[0101] In addition, the copolymer (C) may contain a predetermined amount of other monomer units other than the styrene unit and the maleic anhydride unit.

[0102] The glass transition temperature of the copolymer (C) is, for example, 110° C. or higher. This can suppress excessive softening of the power cable 10. As a result, the mechanical properties of the power cable 10 can be ensured.

[0103] On the other hand, the glass transition temperature of the copolymer (C) is, for example, 140°C or lower. This prevents the copolymer (C) from becoming glassy (filler-like) even at the processing temperatures during the extrusion process of the insulating layer 130, and suppresses localized aggregation of the copolymer (C). As a result, the copolymer (C) can be uniformly dispersed throughout the insulating layer 130.

[0104] In addition, the elastic modulus of the multipolymer (C) measured by SPM is, for example, preferably more than 1300MPa and less than 3000MPa. It should be noted that the measurement conditions are identical with the conditions described in the base resin (A). By making the elastic modulus of multipolymer (C) more than 1300MPa, rigidity can be ensured. On the other hand, by making the elastic modulus of multipolymer (C) less than 3000MPa, flexibility can be ensured.

[0105] Here, in the present embodiment, the content of the copolymer (C) in the resin composition is large, that is, the total content of the maleic anhydride units in the resin composition is larger than conventional ones.

[0106] Specifically, when the total content of base resin (A) and styrene-based elastomer (B) is set to 100 mass parts, the content of the copolymer (C) in the resin combination is, for example, more than 0.5 mass parts, preferably more than 4 mass parts. When the content of copolymer (C) is less than 0.5 mass parts, it is difficult to fully ensure the total content of the maleic anhydride units in the resin combination. Therefore, it may be impossible to make the maleic anhydride units fully capture space charge. In contrast, by making the content of copolymer (C) more than 0.5 mass parts, it is possible to fully ensure the total content of the maleic anhydride units in the resin combination. Thus, it is possible to make the maleic anhydride units fully capture space charge. And then, by making the content of copolymer (C) more than 4 mass parts, it is possible to make the maleic anhydride units stably capture space charge.

[0107] Furthermore, when the combined content of the base resin (A) and the styrene-based elastomer (B) is 100 parts by mass, the total content of the maleic anhydride units in the resin composition is, for example, 0.1 parts by mass or more, preferably 0.8 parts by mass or more. This allows the maleic anhydride units to fully capture space charge, as described above. As a result, stable insulation properties can be achieved for the insulating layer 130. The insulating properties of the insulating layer 130 will be described in detail later.

[0108] On the other hand, in the present embodiment, the content of the copolymer (C) in the resin composition is suppressed from being excessive.

[0109] Specifically, when the total content of the base resin (A) and the styrene-based elastomer (B) is set to 100 parts by mass, the content of the copolymer (C) in the resin composition is less than 20 parts by mass, preferably less than 15 parts by mass. When the content of the copolymer (C) is more than 20 parts by mass, the styrene units in the copolymer (C) promote deformation and become larger. As a result, the power cable 10 is easily deformed at high temperatures. In contrast, by setting the content of the copolymer (C) to less than 20 parts by mass, the promotion of the styrene units in the copolymer (C) to deformation can be reduced. As a result, the deformation of the power cable 10 at high temperatures can be suppressed. Furthermore, by setting the content of the copolymer (C) to less than 15 parts by mass, the deformation of the power cable 10 at high temperatures can be stably suppressed.

[0110] [Other additives]

[0111] The resin composition of the present embodiment may contain the following materials as other additives.

[0112] [Crosslinking agent]

[0113] The crosslinking agent is, for example, an organic peroxide. Examples of the organic peroxide include dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, and 1,3-bis(tert-butylperoxyisopropyl)benzene. It should be noted that two or more of these can be used in combination.

[0114] When the resin composition contains a crosslinking agent, the content of the crosslinking agent is not limited. However, the content of the crosslinking agent is preferably 0.5 parts by mass or more and 3.0 parts by mass or less, based on 100 parts by mass of the total content of component (A) and component (B). By setting the crosslinking agent content to 3.0 parts by mass or less, resistance to scorch can be ensured.

[0115] [Antioxidants]

[0116] Examples of the antioxidant include 2,2-thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,4-bis[(octylthio)methyl]-o-cresol, 2,4-bis(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylanilino)-1,3,5-triazine, bis[2-methyl-4-{3-n-alkyl(C12 or C14)thiopropionyloxy}-5-tert-butylphenyl]sulfide, and 4,4′-thiobis(3-methyl-6-tert-butylphenol). Two or more of these may be used in combination.

[0117] When the resin composition contains an antioxidant, the content of the antioxidant is not limited. However, when the total content of the components (A) and (B) is 100 parts by mass, the content of the antioxidant is preferably 0.1 parts by mass or more and 0.5 parts by mass or less.

[0118] [Lubricant]

[0119] The lubricant acts to improve the fluidity of the resin composition during the extrusion process of the insulating layer 130. The lubricant of this embodiment is, for example, a fatty acid metal salt or a fatty acid amide. Examples of fatty acid metal salts include magnesium stearate, zinc stearate, aluminum stearate, and magnesium montanate. In addition, examples of fatty acid amides include oleamide and stearamide. It should be noted that two or more of these may be used in combination.

[0120] When the resin composition contains a lubricant, the content of the lubricant is not limited, but is preferably 0.01 parts by mass or more and 0.5 parts by mass or less, based on 100 parts by mass of the total content of the components (A) and (B).

[0121] In addition, the resin composition may further contain a colorant, for example.

[0122] On the other hand, the resin composition of the present embodiment does not include inorganic compounds such as inorganic fillers. The "inorganic compound" mentioned here refers to a compound other than an organic compound containing an organic substituent, and does not include the above-mentioned fatty acid metal salts, etc. That is, the resin composition of the present embodiment is not intentionally mixed with inorganic fillers added to the insulating layer of a general DC power cable, and hardly contains inorganic compounds. Even if an inorganic compound is included in the resin composition of the present embodiment, it is only included in the resin composition in a trace amount as an inevitable impurity. Specifically, when the total content of the base resin (A) and the styrene-based elastomer (B) is set to 100 parts by mass, the content of the inorganic compound included in the resin composition is less than 0.01 parts by mass. Thus, the clogging of the mesh can be suppressed in the extrusion process of the insulating layer 130.

[0123] (2) DC power cable

[0124] Next, use Figure 1 A DC power cable according to this embodiment will be described. Figure 1 This is a cross-sectional view perpendicular to the axial direction of the DC power cable according to the present embodiment.

[0125] The power cable 10 of this embodiment is configured as a so-called solid insulated DC power cable, and includes, for example, a conductor 110 , an inner semiconductive layer 120 , an insulating layer 130 , an outer semiconductive layer 140 , a shield layer 150 , and a sheath 160 .

[0126] (Conductor (conductive part))

[0127] The conductor 110 is formed by twisting together a plurality of conductor core wires (conductive core wires) made of, for example, pure copper, a copper alloy, aluminum, or an aluminum alloy.

[0128] (Inner semiconducting layer)

[0129] Internal semiconductive layer 120 is provided to cover the outer periphery of conductor 110. Furthermore, internal semiconductive layer 120 is configured to have semiconductivity and to suppress electric field concentration on the surface side of conductor 110. Internal semiconductive layer 120 may include, for example, at least one of ethylene-based copolymers such as ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, an olefin-based elastomer, and the aforementioned low-crystalline resin, and conductive carbon black.

[0130] (Insulation layer)

[0131] Insulating layer 130 is provided to cover the outer periphery of internal semiconductive layer 120. Insulating layer 130 contains the resin composition of this embodiment described above.

[0132] When the insulating layer 130 of this embodiment is cross-linked with a cross-linking agent, at least a portion of the base resin (A), the styrene-based elastomer (B), and the copolymer (C) is cross-linked. It should be noted that uncross-linked portions may remain in other portions of the components (A), (B), and the copolymer (C).

[0133] (Outer semiconducting layer)

[0134] External semiconductive layer 140 is provided to cover the outer periphery of insulating layer 130. Furthermore, external semiconductive layer 140 is configured to have semiconductivity and to suppress electric field concentration between insulating layer 130 and shielding layer 150. External semiconductive layer 140 is formed of, for example, the same material as internal semiconductive layer 120.

[0135] (Shielding layer)

[0136] Shielding layer 150 is provided to cover the outer periphery of outer semiconductive layer 140. Shielding layer 150 is formed, for example, by winding copper tape or as a wire shield formed by winding multiple soft copper wires. It should be noted that tape, such as adhesive tape, may be wound around the inside and outside of shielding layer 150.

[0137] (jacket)

[0138] The sheath 160 is provided to cover the outer periphery of the shield layer 150. The sheath 160 is made of, for example, polyvinyl chloride or polyethylene.

[0139] (Insulation properties of the insulation layer)

[0140] In this embodiment, since the insulating layer 130 is formed of the above-mentioned resin composition, stable insulation can be obtained.

[0141] Specifically, the insulating layer 130 of this embodiment satisfies the following insulation requirements, as measured under high temperature and high electric field conditions. This measurement is performed, for example, using a sheet sampled from the center of the thickness of the insulating layer 130. The thickness of the insulating layer 130 sheet is, for example, 0.2 mm.

[0142] The volume resistivity of the sheet of the insulating layer 130 measured under the conditions of a temperature of 90° C. and a DC electric field of 50 kV / mm is, for example, 1.0×10 15 Ω·cm or more, preferably 1.0×10 16 Ω·cm or more.

[0143] Furthermore, the amount of space charge storage of the sheet of the insulating layer 130 measured under the conditions of a temperature of 90° C. and a DC electric field of 50 kV / mm is, for example, 100% or less, or preferably 25% or less.

[0144] The amount of space charge accumulation is determined using the current-integrated charge method. In the current-integrated charge method, charge is accumulated in a measuring capacitor connected in series with a sample sheet, and the charge amount is evaluated as the integral value of the current. Specifically, a DC electric field of 50 kV / mm is continuously applied to the sample at a temperature of 90°C, and the charge amount Q after 300 seconds is calculated. 300 The amount of space charge accumulation is calculated using the following equation using the charge amount Q0 immediately after the application (0 seconds).

[0145] Space charge accumulation = (Q 300 / Q0-1)×100

[0146] The insulating layer 130 of this embodiment satisfies the following necessary conditions for insulation even under more severe electric field conditions.

[0147] The volume resistivity of the insulating layer 130 sheet measured under the conditions of a temperature of 90°C and a DC electric field of 75 kV / mm is 1.0×10 15 Ω·cm or more, preferably 1.0×10 16 Ω·cm or more.

[0148] Furthermore, the space charge storage amount of the sheet of insulating layer 130 measured under the conditions of a temperature of 90° C. and a DC electric field of 75 kV / mm is 100% or less, preferably 25% or less.

[0149] (Shape stability)

[0150] Furthermore, the insulating layer 130 of the present embodiment satisfies the following requirements for shape stability under high temperature conditions, for example.

[0151] The heating deformation rate of the sheet of the insulating layer 130 measured under the conditions of a temperature of 120° C. and a load of 2 kg in accordance with JIS C3005 is 40% or less.

[0152] (Extrusion stability: insulation in the longitudinal direction)

[0153] Furthermore, the insulating layer 130 of the present embodiment suppresses clogging of the mesh during the extrusion process, thereby satisfying the requirement for uniform insulation in the longitudinal direction.

[0154] Specifically, the insulating layer 130 satisfies, for example, the following equation (1) for the variation rate of DC breakdown strength.

[0155] (E MAX -E MIN ) / E AVE ≤0.2……(1)

[0156] The DC breakdown strength herein refers to the electric field strength at which insulation breakdown occurs in each of the plurality of sheets when a DC electric field is applied at a temperature of 90°C. The plurality of sheets are collected at a plurality of locations of the insulating layer 130 at predetermined intervals in the longitudinal direction of the conductor 110. MAX 、E MIN and E AVE are the maximum value, minimum value, and average value of the DC breakdown strength of the plurality of sheets, respectively.

[0157] (Specific dimensions, etc.)

[0158] The specific dimensions of power cable 10 are not particularly limited. For example, the diameter of conductor 110 is 5 mm to 75 mm, the thickness of inner semiconductive layer 120 is 0.5 mm to 3 mm, the thickness of insulating layer 130 is 1 mm to 35 mm, the thickness of outer semiconductive layer 140 is 0.5 mm to 3 mm, the thickness of shielding layer 150 is 1 mm to 5 mm, and the thickness of jacket 160 is 1 mm or more. The DC voltage applicable to power cable 10 of this embodiment is, for example, 20 kV or more.

[0159] (3) Manufacturing method of DC power cable

[0160] Next, a method for manufacturing a DC power cable according to this embodiment will be described. Hereinafter, the step will be simply referred to as "S".

[0161] (S100: Resin Composition Preparation Step)

[0162] First, a resin composition is prepared. The resin composition comprises: a base resin (A) comprising a polyolefin; a styrene-based elastomer (B) comprising a styrene unit; and a copolymer (C) comprising a styrene unit and a maleic anhydride unit.

[0163] The base resin (A), styrene elastomer (B), copolymer (C), and other additives are mixed (kneaded) using a mixer such as a Banbury mixer or a kneader to form a mixed material. After the mixed material is formed, the mixed material is granulated using an extruder. This forms a granular resin composition that will constitute the insulating layer 130. It should be noted that a twin-screw extruder with a high kneading action can also be used to perform the steps from mixing to granulation.

[0164] In this embodiment, the content of the copolymer (C) in the resin composition is set to 0.5 parts by mass or more and less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin (A) and the styrene elastomer (B).

[0165] Alternatively, the total content of maleic anhydride units in the resin composition may be 0.1 parts by mass or more and less than 4 parts by mass, based on 100 parts by mass of the total content of the base resin (A) and the styrene elastomer (B).

[0166] In this case, in the present embodiment, the content of the styrene-based elastomer (B) in the resin composition is set to be equal to or greater than the content of the copolymer (C).

[0167] In this embodiment, the copolymer (C) is made of a material that does not include a side chain that is decomposed or hydrolyzed at 300° C. or lower.

[0168] (S200: Conductor Preparation Process)

[0169] On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

[0170] (S300: Cable core forming process (extrusion process))

[0171] Next, in a three-layer simultaneous extruder, a resin composition for the inner semiconductive layer, for example, prepared by pre-mixing an ethylene-ethyl acrylate copolymer and conductive carbon black, is fed into the extruder A for forming the inner semiconductive layer 120 .

[0172] The pelletized resin composition is fed into the extruder B for forming the insulating layer 130 .

[0173] The outer semiconductive layer resin composition composed of the same material as the inner semiconductive layer resin composition fed into the extruder A is fed into the extruder C for forming the outer semiconductive layer 140 .

[0174] Next, the extrudates from the extruders A to C are directed to a common head, and the inner semiconductive layer 120 , the insulating layer 130 , and the outer semiconductive layer 140 are simultaneously extruded from the inside to the outside onto the outer periphery of the conductor 110 .

[0175] In this embodiment, insulation layer 130 is then cross-linked by heating it within a cross-linking tube pressurized with nitrogen or the like, either by radiation from an infrared heater or by heat transfer via a heat medium such as high-temperature nitrogen or silicone oil. This forms a cable core composed of conductor 110, inner semiconductive layer 120, insulation layer 130, and outer semiconductive layer 140.

[0176] (S400: Shielding Layer Forming Step)

[0177] Next, the shielding layer 150 is formed by winding, for example, a copper tape around the outer side of the outer semiconducting layer 140 .

[0178] (S500: Sheath Forming Step)

[0179] Next, vinyl chloride is fed into an extruder and extruded, thereby forming the sheath 160 on the outer periphery of the shield layer 150 .

[0180] In the above manner, the power cable 10 as a solid-insulated DC power cable is manufactured.

[0181] (4) Effects of this embodiment

[0182] According to this embodiment, one or more of the following effects are achieved.

[0183] (a) In the present embodiment, the resin composition constituting the insulating layer 130 comprises: a base resin (A) comprising a polyolefin; a styrene elastomer (B) comprising a styrene unit; and a copolymer (C) comprising a styrene unit and a maleic anhydride unit. By introducing a maleic anhydride unit as a monomer unit constituting the main chain into the copolymer (C) comprising the styrene unit, the copolymer (C) can be freely molecularly designed. Thus, the content of the maleic anhydride unit in one molecule can be easily increased. By mixing the copolymer (C) and the above-mentioned styrene elastomer (B) together with the base resin (A), maleic anhydride can be uniformly dispersed in the insulating layer 130, and the total content of maleic anhydride units in the entire insulating layer 130 can be increased. Thus, the maleic anhydride units as polar groups uniformly dispersed in the insulating layer 130 can capture space charges. That is, the local accumulation of space charges can be suppressed in the insulating layer 130.

[0184] By suppressing the local accumulation of space charge in this manner, stable insulation properties can be obtained for the insulating layer 130. Specifically, the insulating layer 130 can have a high withstand voltage even at high temperatures. As a result, the power cable 10 of this embodiment enables stable DC power transmission.

[0185] (b) The content of the copolymer (C) in the resin composition (i.e., in the insulating layer 130) is 0.5 parts by mass or more, based on 100 parts by mass of the combined content of the base resin (A) and the styrene-based elastomer (B). This makes it easy to ensure the total content of maleic anhydride units in the insulating layer 130. Specifically, the total content of maleic anhydride units in the resin composition can be set to 0.1 parts by mass or more.

[0186] By setting the total content of maleic anhydride units to 0.1 parts by mass or more, the maleic anhydride units can sufficiently capture space charges, thereby enabling the insulating layer 130 to have a high withstand voltage even at high temperatures.

[0187] (c) The content of the styrene-based elastomer (B) in the resin composition (i.e., in the insulating layer 130) is greater than or equal to the content of the copolymer (C). This allows the styrene-based elastomer (B) to be sufficiently incorporated into the base resin (A), while also allowing the copolymer (C) to be uniformly dispersed. As a result, localized accumulation of space charge can be suppressed. As described above, insulation properties can be particularly improved at high temperatures.

[0188] (d) The copolymer (C) does not contain side chains that may be detached by thermal decomposition or hydrolysis at 300° C. or lower.

[0189] Here, consider the case where the copolymer (C) contains side chains that will detach due to thermal decomposition or hydrolysis at high temperatures. In this case, when the resin composition is exposed to high temperature or high humidity in at least one of the extrusion process, the cross-linking process, and the laying environment where the insulating layer absorbs moisture, the side chains will detach, and low-molecular-weight components caused by the side chains will be generated in the insulating layer. When such low-molecular-weight components are generated, space charge is locally accumulated in the low-molecular-weight components in the insulating layer. That is, even if the maleic anhydride units as the polar groups of the above-mentioned copolymer (C) are dispersed, parts may be generated that cannot obtain the space charge capture effect achieved by the dispersed maleic anhydride.

[0190] In contrast, in this embodiment, copolymer (C) does not contain the aforementioned side chains. Thus, even when the resin composition is exposed to high temperatures during the extrusion and crosslinking steps, the side chains can be prevented from detaching, thereby suppressing the generation of low-molecular-weight components caused by these side chains. Consequently, the accumulation of space charge in the low-molecular-weight components can be suppressed. In other words, the space charge capture effect achieved by the dispersed maleic anhydride can be uniformly achieved.

[0191] (e) The content of the copolymer (C) in the resin composition (i.e., in the insulating layer 130) is less than 20 parts by mass, based on 100 parts by mass of the combined content of the base resin (A) and the styrene-based elastomer (B). This reduces the contribution of the styrene units in the copolymer (C) to deformation. Consequently, deformation of the power cable 10 at high temperatures can be suppressed. In other words, heat resistance can be improved even in the case of high-temperature deformation of the power cable 10.

[0192] (f) In this embodiment, insulating layer 130 does not contain inorganic compounds such as inorganic fillers. Specifically, the content of inorganic compounds in insulating layer 130 is less than 0.01 parts by mass, based on 100 parts by mass of the combined content of base resin (A) and styrene elastomer (B). This prevents clogging of the mesh during the extrusion process of insulating layer 130.

[0193] By suppressing clogging of the mesh during the extrusion process of the insulating layer 130, it is possible to suppress variations in the insulation properties of the insulating layer 130 in the longitudinal direction of the conductor 110. Furthermore, it is possible to suppress a decrease in the moldability of the insulating layer 130 itself.

[0194] As a result, a long power cable can be manufactured by a continuous extrusion process, and stable insulation properties can be obtained for the entire long power cable.

[0195] (5) Modification of one embodiment of the present disclosure

[0196] The above-described embodiment can be modified as needed as shown in the following modified examples.

[0197] Hereinafter, only elements that are different from those in the above-described embodiment will be described, and description of elements that are substantially the same as those described in the above-described embodiment will be omitted.

[0198] [Variation 1]

[0199] In Modification 1, the base resin (A) may further contain, for example, a maleic anhydride-modified polyolefin in which maleic anhydride is grafted onto a polyolefin.

[0200] The polyolefin constituting the maleic anhydride-modified polyolefin is, for example, the same as the other polyolefins contained in the base resin (A). Specifically, the polyolefin constituting the maleic anhydride-modified polyolefin is, for example, polyethylene.

[0201] The modification ratio (copolymerization ratio) of maleic anhydride relative to the polyolefin in the maleic anhydride-modified polyolefin is not particularly limited, but may be, for example, 0.1% or higher and 5% or lower. By setting the modification ratio of maleic anhydride relative to the polyolefin to 0.1% or higher, the compatibility between the base resin (A) and the copolymer (C) can be improved, allowing the copolymer (C) to be evenly dispersed. On the other hand, by setting the modification ratio of maleic anhydride relative to the polyolefin to 5% or lower, the insulating layer 130 can be stably molded.

[0202] The content of the maleic anhydride-modified polyolefin in the resin composition is not particularly limited, and is, for example, 1 part by mass or more and 10 parts by mass or less, based on the combined content of components (A) and (B) being 100 parts by mass. By setting the content of the maleic anhydride-modified polyolefin to 1 part by mass or more, the compatibility between the base resin (A) and the copolymer (C) is improved, allowing the copolymer (C) to be uniformly dispersed. On the other hand, by setting the content of the maleic anhydride-modified polyolefin to 10 parts by mass or less, the insulating layer 130 can be stably molded.

[0203] According to Modification 1, by further including maleic anhydride-modified polyethylene in the base resin (A), the total content of maleic anhydride units in the entire insulating layer 130 can be further increased. Furthermore, by further including maleic anhydride-modified polyethylene in the base resin (A), the compatibility of the copolymer (C) containing maleic anhydride units with the base resin (A) can be improved. This allows the maleic anhydride to be uniformly dispersed in the insulating layer 130. As a result, localized accumulation of space charge in the insulating layer 130 can be stably suppressed.

[0204] [Variation 2]

[0205] In Modification 2, the resin composition may further contain a trace amount of an inorganic filler to such an extent that clogging of the mesh does not occur during the extrusion step.

[0206] Examples of the inorganic filler include at least one of magnesium oxide (MgO), silicon dioxide, zinc oxide, aluminum oxide, titanium oxide, zirconium oxide, carbon black, and a mixture of two or more thereof.

[0207] Examples of methods for forming magnesium oxide include a vapor phase method in which Mg vapor is brought into contact with oxygen and a seawater method using seawater as a raw material. The inorganic filler in this embodiment may be formed by either the vapor phase method or the seawater method.

[0208] Examples of silica include at least one of fumed silica, colloidal silica, precipitated silica, and deflagration silica. Of these, fumed silica is preferred.

[0209] In this modification, the content of the inorganic filler in the resin composition is, for example, less than 1 part by mass when the total content of the components (A) and (B) is 100 parts by mass. By setting the content to a trace amount, clogging of the mesh during the extrusion process can be suppressed.

[0210] In addition, in this modification, as long as an inorganic filler can be added, the lower limit of the content of the inorganic filler is not limited.

[0211] In this modification, the volume average particle size (MV: Mean Volume Diameter) of the inorganic filler is not particularly limited, but is, for example, 1 μm or less, preferably 700 nm or less, and more preferably 100 nm or less.

[0212] It should be noted that when the particle size is set to d i , set the volume of the particle to V i When , the "volume average particle size (MV)" referred to herein is calculated by the following formula.

[0213] MV=Σ(V i d i ) / ΣV i

[0214] In addition, the volume average particle diameter was measured using a dynamic light scattering particle size / particle size distribution measuring device.

[0215] In addition, the lower limit of the volume average particle size of the inorganic filler is not particularly limited.

[0216] However, from the viewpoint of stably forming the inorganic filler, the volume average particle size of the inorganic filler is, for example, 1 nm or more, or preferably 5 nm or more.

[0217] In this modification, at least a portion of the inorganic filler may be surface-treated with a silane coupling agent, thereby improving the adhesion of the interface between the inorganic filler and the base resin and enhancing the mechanical properties and insulation of the insulating layer 130 .

[0218] According to Modification 2, since the resin composition further contains a trace amount of inorganic filler, clogging of the mesh during the extrusion process can be suppressed, and the effect of improving the insulation properties of the insulating layer 130 can be stably obtained.

[0219] <Other embodiments of the present disclosure>

[0220] As mentioned above, although embodiment of this disclosure was specifically described, this disclosure is not limited to the said embodiment, Various changes are possible within the range which does not deviate from the summary.

[0221] In the above embodiments and modifications, the base resin (A) is described as comprising a polyolefin and as further comprising a maleic anhydride-modified polyolefin. However, the resin composition may also comprise a copolymer of an olefin and a polar monomer as the base resin (A). Examples of copolymers of an olefin and a polar monomer include ethylene-ethyl acrylate copolymers, ethylene-methyl acrylate copolymers, ethylene-butyl acrylate copolymers, ethylene-methyl methacrylate copolymers, and ethylene-glycidyl methacrylate copolymers. It should be noted that two or more of these copolymers may be used in combination.

[0222] In the above-described embodiment and modified examples, the resin composition contains an additive such as a crosslinking agent, and the insulating layer 130 is crosslinked by the crosslinking agent. However, the insulating layer 130 may not be crosslinked.

[0223] In particular, when the base resin (A) contains polypropylene, the insulating layer 130 may be non-crosslinked. In this case, even if the insulating layer 130 is non-crosslinked, it can still meet the insulation properties required of the power cable 10. Furthermore, since the insulating layer 130 is non-crosslinked, it can be recycled.

[0224] When the base resin comprises polypropylene, the styrene elastomer (B) preferably comprises at least one of propylene units and butene units among the above materials. This improves the compatibility between the base resin (A) and the styrene elastomer (B).

[0225] Example

[0226] Next, embodiments of the present disclosure will be described. These embodiments are examples of the present disclosure, and the present disclosure is not limited to these embodiments.

[0227] (1) Power cable samples

[0228] Power cables of samples A1 to A11 and B1 to B9 were manufactured by the following process.

[0229] (1-1) Production of resin composition

[0230] The following compounding ingredients were mixed using a Banbury mixer and pelletized using an extruder to produce a pelletized resin composition.

[0231] [Base resin (A)]

[0232] Low density polyethylene (LDPE) (density d = 0.920 g / cm 3 , MFR = 1 g / 10 min, SPM elastic modulus 500 MPa): 0 parts by mass or more and 100 parts by mass or less

[0233] Polypropylene (propylene random polymer, isotactic, density d = 0.900g / cm 3 , MFR = 0.6g / 10min, SPM elastic modulus 1100MPa): 0 or 98 parts by mass

[0234] Maleic anhydride-modified polyethylene (modification rate 0.3%, SPM elastic modulus 500 MPa): 0 or 5 parts by mass

[0235] [Styrene elastomer (B)]

[0236] B1, B2 and B3: hydrogenated styrene butadiene styrene block copolymer (SEBS)

[0237] (Hereinafter, in order of description, they are B1, B2, and B3)

[0238] Ethylene content in component (B): 20 mass%, 37 mass%, 44 mass%

[0239] Styrene content in component (B): 65 mass%, 40 mass%, 30 mass%

[0240] (B) SPM elastic modulus: 50 MPa, 300 MPa, 100 MPa

[0241] Content of component (B): 0 parts by mass or more and 30 parts by mass or less

[0242] In addition, the total content of (A) component and (B) component is set to 100 parts by mass.

[0243] [Copolymer (C)]

[0244] C1 and C2: Styrene-maleic anhydride copolymer (glass transition temperature: 115°C)

[0245] Others: Styrene-maleic anhydride-allyl ether copolymer (glass transition temperature: 115°C)

[0246] Styrene content of C1 and C2: 75% by mass, 80% by mass

[0247] Maleic anhydride content of C1 and C2: 25% by mass, 20% by mass

[0248] SPM elastic modulus of C1 and C2 respectively: 1500MPa and 1300MPa

[0249] Content of component (C): 0 parts by mass or more and 20 parts by mass or less

[0250] The maleic anhydride content of the styrene-maleic anhydride-allyl ether copolymer is 25% by mass.

[0251] The "SPM elastic modulus" mentioned above refers to the elastic modulus measured using an SPM. The SPM elastic modulus measurement was performed under the following conditions: 60,000 taps were performed on a 10 μm square area of polyolefin at 25°C using a silicon cantilever with a tip having a curvature radius of less than 20 nm.

[0252] [Other additives]

[0253] (Inorganic filler)

[0254] Material: Fumed magnesium oxide (MgO) (volume average particle size: 50nm)

[0255] Inorganic filler content: 0 parts by mass or more and 2 parts by mass or less

[0256] (Antioxidant)

[0257] Ingredients: Phenolic antioxidant (4,4'-thiobis(3-methyl-6-tert-butylphenol))

[0258] Content of antioxidant: 0 parts by mass or more and 0.3 parts by mass or less

[0259] (Lubricant)

[0260] Material: Fatty amide

[0261] Lubricant content: 0 parts by mass or more and 0.01 parts by mass or less

[0262] (cross-linking agent)

[0263] Material: Organic peroxide (2,5 - dimethyl - 2,5 - bis(tert - butylperoxy)hexane)

[0264] Content of cross - linker: 0 parts by mass or more and 1.5 parts by mass or less

[0265] (1 - 2) Manufacture of samples of power cables

[0266] Next, a conductor formed by stranding a conductor core wire made of a low - concentration copper alloy (corresponding to "dilute copper alloy" in Japanese) with a diameter of 14 mm was prepared. After preparing the conductor, a resin composition for the inner semiconductive layer containing an ethylene - ethyl acrylate copolymer, the resin composition for the insulating layer prepared in (1 - 1) above, and a resin composition for the outer semiconductive layer made of the same material as the resin composition for the inner semiconductive layer were respectively fed into extruders A - C. The extrudates from extruders A - C were guided to a common head, and the inner semiconductive layer, insulating layer, and outer semiconductive layer were simultaneously extruded onto the outer circumference of the conductor from the inside to the outside. At this time, the thicknesses of the inner semiconductive layer, insulating layer, and outer semiconductive layer were set to 1 mm, 14 mm, and 1 mm, respectively. After that, the above - mentioned extruded product was heated at about 250 °C to cross - link the resin composition for the insulating layer. As a result, samples of power cables having a conductor, an inner semiconductive layer, an insulating layer, and an outer semiconductive layer from the center to the outer circumference were manufactured.

[0267] Through the above processes, specimens A1 - A11 and specimens B1 - B9 of power cables with different resin compositions were manufactured.

[0268] (2) Evaluation

[0269] The following evaluations were respectively carried out on specimens A1 - A11 and specimens B1 - B9 of power cables. It should be noted that the "resin pressure rise rate" described later was evaluated during the extrusion process of the insulating layer.

[0270] [Sample processing]

[0271] The insulating layer at positions within 100 m from the initial extrusion position of the insulating layer was thinly sliced from the outer circumference of specimens A1 - A11 and specimens B1 - B9 of power cables respectively. Then, sheets of the insulating layer with a thickness of 0.20 mm were formed from the central part in the thickness direction of the insulating layer. At this time, multiple sheets were formed from approximately the same circumference.

[0272] Note that in the evaluation of insulation in the longitudinal direction described later, sheets were collected at 10 locations on the insulation layer at intervals of 100 m along the longitudinal direction of the conductor, resulting in a total of 10 sheets. Note that at each collection location, a sheet was collected from the center of the thickness direction.

[0273] [Space Charge Characteristics]

[0274] The amount of space charge accumulation was determined by the above-mentioned current integral charge method. Specifically, a DC electric field of 50 kV / mm was continuously applied to each sample at a temperature of 90°C, and the charge amount Q after 300 seconds was calculated. 300 The space charge accumulation amount (%) is calculated using the above formula using the charge amount Q0 immediately after application (0 seconds). A space charge accumulation amount of 25% or less is rated A (optimal), a space charge accumulation amount exceeding 25% and falling below 100% is rated B (good), and a space charge accumulation amount exceeding 100% is rated C (poor).

[0275] [Volume resistivity]

[0276] The insulating layer sheet was immersed in silicone oil at a temperature of 90°C and a DC electric field of 50 kV / mm or 75 kV / mm was applied to the insulating layer sheet using a flat electrode with a diameter of 25 mm to measure the volume resistivity. 16 The case with a resistance of 1×10 15 Ω·cm or more and less than 1×10 16 Ω·cm was evaluated as B (good), and the volume resistivity was less than 1×10 15 The case with a value less than Ω·cm was evaluated as C (poor).

[0277] [DC breakdown strength]

[0278] The insulating layer sheet was immersed in silicone oil at 90°C. Using a 25mm diameter flat electrode, the applied voltage was increased at a rate of 4kV / min. The DC breakdown strength of the insulating layer sheet was determined by dividing the applied voltage at the point of dielectric breakdown by the sheet thickness. A DC breakdown strength of 200kV / mm or greater was rated A (excellent), a DC breakdown strength of 160kV / mm or greater but less than 200kV / mm was rated B (good), and a DC breakdown strength of less than 160kV / mm was rated C (poor).

[0279] [Heating deformation rate]

[0280] The heat deformation rate of the insulating layer 130 sheet was measured at a temperature of 120°C and a load of 2 kg in accordance with JIS C3005. A heat deformation rate of 40% or less was rated A (good), and a heat deformation rate exceeding 40% was rated B (poor).

[0281] [Extrusion stability: Resin pressure rise rate]

[0282] During the insulation layer extrusion process, the resin pressure rise rate was measured. The resin pressure rise rate is the ratio (%) of the resin pressure after two hours relative to the initial resin pressure. A resin pressure rise rate of 1% or less was rated A (good), while a resin pressure rise rate exceeding 1% was rated B (poor).

[0283] [Extrusion stability: insulation in the longitudinal direction]

[0284] As described above, the DC breakdown strength of each of the ten sheets collected at ten locations on the insulation layer at predetermined intervals in the longitudinal direction of the conductor was measured under the same measurement conditions as those described in the above-mentioned [DC breakdown strength]. In other words, the DC breakdown strength is the electric field strength at which the insulation of the sheet breaks down when a DC electric field is applied at a temperature of 90°C. Based on these results, {(E MAX -E MIN ) / E AVE The variation rate (%) of the DC breakdown strength was calculated by multiplying the DC breakdown strength by 100. A variation rate of 20% or less was evaluated as A (good), and a variation rate of more than 20% was evaluated as B (poor).

[0285] (3) Results

[0286] The results of the evaluation of the power cable samples are shown in Tables 1 and 2 below. In Tables 1 and 2, the units for the content of the compounding ingredients are "parts by mass." The "ratio of component (B) / component (C)" refers to the ratio of the content of component (B) to the content of component (C).

[0287] [Table 1]

[0288]

[0289] [Table 2]

[0290]

[0291] (Sample B6)

[0292] Sample B6, which did not contain the styrene-based elastomer (B), the copolymer (C), or the inorganic filler, showed poor results in terms of space charge accumulation, volume resistivity, and DC breakdown strength measured under a DC electric field of 50 kV / mm. This is presumably because Sample B6 lacked a material that suppresses localized space charge accumulation, resulting in reduced insulation properties.

[0293] (Sample B8)

[0294] Sample B8, which did not contain the styrene-based elastomer (B), the copolymer (C), or the inorganic filler but contained maleic anhydride-modified polyethylene, showed good values for space charge accumulation, volume resistivity, and DC breakdown strength measured under a DC electric field of 50 kV / mm. However, under the more stringent conditions of a DC electric field of 75 kV / mm, the space charge accumulation and volume resistivity were poor. This suggests that in Sample B8, the total content of polar groups in the composition could not be sufficiently ensured, and therefore, localized space charge accumulation could not be suppressed under these harsh conditions.

[0295] (Sample B9)

[0296] In the sample B9 that does not include styrene-based elastomer (B) and copolymer (C) but includes inorganic filler, the evaluation result related to insulation is good. However, the rate of change of the resin pressure rise rate in the extrusion process and the DC breakdown strength in the length direction of the cable is poor. It can be considered that: in sample B9, in the extrusion process of the insulating layer, due to the cohesion of the inorganic filler, the mesh is clogged, so the insulation has been uneven in the length direction of the cable.

[0297] (Samples B1 and B4)

[0298] In Sample B1, in which the copolymer (C) content was set to less than 0.5 parts by mass, and Sample B4, which did not contain copolymer (C), the total content of maleic anhydride units in the composition was less than 0.1 parts by mass. These samples had good DC breakdown strength, but poor space charge accumulation and volume resistivity measured under a DC electric field of 50 kV / mm. This is believed to be due to insufficient total content of maleic anhydride units in the composition in Samples B1 and B4, which prevented the maleic anhydride units from adequately capturing space charge.

[0299] (Samples B3 and B5)

[0300] In sample B3 in which the content of styrene-based elastomer (B) is set to be lower than the content of copolymer (C) (i.e., the ratio of component (B) / component (C) is set to be lower than 1), and in sample B5 which does not contain styrene-based elastomer (B), the DC breakdown strength is good. However, in sample B5, the space charge accumulation and volume resistivity measured under the condition of a DC electric field of 50 kV / mm are poor. On the other hand, in sample B3, although the insulation is slightly better, the space charge accumulation and volume resistivity measured under the condition of a DC electric field of 75 kV / mm are respectively poor. It can be considered that in samples B3 and B5, the styrene-based elastomer (B) cannot be fully mixed into the base resin (A), and the copolymer (C) cannot be evenly dispersed. Therefore, the local accumulation of space charge cannot be suppressed.

[0301] (Sample B2)

[0302] Sample B2, in which the copolymer (C) content was 20 parts by mass or greater, showed good insulation properties but poor heat deformation rate. This is presumably because the styrene units in the copolymer (C) significantly promoted deformation in Sample B2, resulting in the insulation layer being easily deformed at high temperatures.

[0303] (Sample B7)

[0304] Sample B7, containing a styrene-maleic anhydride-allyl ether copolymer as copolymer (C), showed poor space charge accumulation, volume resistivity, and DC breakdown strength measured under a DC electric field of 50 kV / mm. This is presumably because the allyl ether in copolymer (C) in Sample B7 was released and decomposed during the extrusion or crosslinking process, producing low-molecular-weight components. Consequently, space charge accumulated locally in these low-molecular-weight components, resulting in a decrease in insulation properties.

[0305] (Samples A1 to A11)

[0306] Samples A1 to A11 met the requirements for the content of copolymer (C), the total content of maleic anhydride units in the composition, and the side chains of copolymer (C). The results for samples A1 to A11 showed that the space charge accumulation, volume resistivity, and DC breakdown strength measured under the conditions of a DC electric field of 50 kV / mm and 75 kV / mm were respectively good. Furthermore, the heat deformation rate was good. Furthermore, the resin pressure rise rate during the extrusion process and the rate of change of the DC breakdown strength along the length of the cable were also good.

[0307] In samples A1 to A11, by increasing the content of copolymer (C) to 0.5 parts by mass or greater, the total content of maleic anhydride units in the composition can be reduced to 0.1 parts by mass or greater. This allows the maleic anhydride units to adequately capture space charge. As a result, it was confirmed that the insulating layer has a high withstand voltage even at high temperatures.

[0308] Among them, in samples A1 to A3 in which the content of the copolymer (C) was 4 parts by mass or more, the space charge storage amount and volume resistivity measured under the conditions of a DC electric field of 75 kV / mm were the best.

[0309] In samples A1 to A3, the total content of maleic anhydride units in the composition can be set to 0.8 parts by mass or more. This allows the maleic anhydride units to stably capture space charge, resulting in more stable insulation properties.

[0310] In samples A1 to A11, it was confirmed that the accumulation of space charge in the low molecular weight component can be suppressed because the copolymer (C) does not contain a side chain that is decomposed or hydrolyzed at 300° C. or lower.

[0311] In samples A1 to A11, by setting the content of copolymer (C) to less than 20 parts by mass, the styrene units in the copolymer (C) can reduce the acceleration of deformation. As a result, it was confirmed that deformation of the power cable at high temperatures can be suppressed.

[0312] In samples A1 to A10, by setting the content of the inorganic compound (inorganic filler) in the composition to less than 0.01 parts by mass, clogging of the mesh during the extrusion step of the insulating layer was suppressed. As a result, it was confirmed that variations in insulation properties in the longitudinal direction were suppressed.

[0313] On the other hand, in Sample A11, it was confirmed that by including less than 1 part by mass of the inorganic filler, clogging of the mesh during the extrusion process can be suppressed, and the effect of improving the insulation properties of the insulating layer can be stably obtained.

[0314] In Sample A9, since the base resin (A) further contains maleic anhydride-modified polyethylene, the total content of maleic anhydride units can be increased. As a result, it was confirmed that localized accumulation of space charge can be stably suppressed.

[0315] <Preferred embodiment of the present disclosure>

[0316] Preferred aspects of the present disclosure are described below.

[0317] (Note 1)

[0318] A resin composition comprising: a base resin (A) comprising a polyolefin; a styrene-based elastomer (B) comprising styrene units; and a copolymer (C) comprising styrene units and maleic anhydride units, wherein the content of the copolymer (C) is 0.5 parts by mass or more, based on 100 parts by mass of the total content of the base resin (A) and the styrene-based elastomer (B); the content of the styrene-based elastomer (B) is equal to or greater than the content of the copolymer (C); and the copolymer (C) does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C.

[0319] (Note 2)

[0320] A power cable comprises: a conductor; and an insulating layer configured to cover the conductor, the insulating layer comprising a resin composition comprising: a base resin (A) comprising a polyolefin; a styrene-based elastomer (B) comprising styrene units; and a copolymer (C) comprising styrene units and maleic anhydride units. The content of the copolymer (C) in the insulating layer is 0.5 parts by mass or more, based on 100 parts by mass of the combined content of the base resin (A) and the styrene-based elastomer (B). The content of the styrene-based elastomer (B) in the insulating layer is equal to or greater than the content of the copolymer (C). The copolymer (C) does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C.

[0321] (Note 3)

[0322] The electric power cable according to Supplementary Note 2, wherein the total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more, based on 100 parts by mass of the total content of the base resin (A) and the styrene-based elastomer (B).

[0323] (Note 4)

[0324] A power cable comprises: a conductor; and an insulating layer configured to cover the conductor, the insulating layer comprising a resin composition comprising: a base resin (A) comprising a polyolefin; a styrene-based elastomer (B) comprising styrene units; and a copolymer (C) comprising styrene units and maleic anhydride units, wherein the total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more, based on 100 parts by mass of the combined content of the base resin (A) and the styrene-based elastomer (B), the content of the styrene-based elastomer (B) in the insulating layer is equal to or greater than the content of the copolymer (C), and the copolymer (C) does not contain side chains that are detached by thermal decomposition or hydrolysis at temperatures below 300°C.

[0325] (Note 5)

[0326] The electric power cable according to any one of Supplementary Notes 2 to 4, wherein the copolymer does not include any of an ester bond, an ether bond, an amide bond, a urethane bond, and a siloxane bond.

[0327] (Note 6)

[0328] The power cable according to any one of Supplementary Notes 2 to 5, wherein the volume resistivity of the sheet of the insulating layer measured under conditions of a temperature of 90° C. and a DC electric field of 75 kV / mm is 1.0×10 15 Ω·cm or more.

[0329] (Note 7)

[0330] The electric power cable according to any one of Supplementary Notes 2 to 6, wherein a space charge storage amount of the sheet of the insulating layer measured under the conditions of a temperature of 90° C. and a DC electric field of 75 kV / mm is 100% or less.

[0331] (Note 8)

[0332] The electric power cable according to any one of Supplementary Notes 2 to 7, wherein the content of the copolymer (C) is less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin (A) and the styrene-based elastomer (B).

[0333] (Note 9)

[0334] The power cable according to Supplementary Note 7 or 8, wherein a heat deformation rate of the sheet of the insulating layer measured under conditions of a temperature of 120° C. and a load of 2 kg is 40% or less.

[0335] (Note 10)

[0336] The electric power cable according to any one of Supplementary Notes 2 to 9, wherein the content of the inorganic compound contained in the insulating layer is less than 0.01 parts by mass when the total content of the base resin (A) and the styrene-based elastomer (B) is 100 parts by mass.

[0337] (Note 11)

[0338] The electric power cable according to any one of Supplementary Notes 2 to 9, wherein the insulating layer further contains less than 1 part by mass of an inorganic filler, based on 100 parts by mass of the total content of the base resin (A) and the styrene-based elastomer (B).

[0339] (Note 12)

[0340] The power cable according to Supplementary Note 10 or 11, wherein the insulating layer satisfies the following formula (1) for the variation rate of DC breakdown strength: (EMAX -E MIN ) / E AVE ≤0.2……(1), wherein the DC breakdown strength is the electric field strength when a DC electric field is applied to each of the plurality of sheets at a temperature of 90°C and insulation breakdown occurs in the sheet, wherein the plurality of sheets are collected at a plurality of locations of the insulating layer at predetermined intervals in the longitudinal direction of the conductor, E MAX 、E MIN and E AVE are respectively the maximum value, the minimum value and the average value of the DC breakdown strength of the plurality of sheets.

[0341] (Note 13)

[0342] The electric power cable according to any one of Supplementary Notes 2 to 12, wherein the glass transition temperature of the copolymer (C) is 110° C. or higher.

[0343] (Note 14)

[0344] The electric power cable according to any one of Supplementary Notes 2 to 13, wherein the glass transition temperature of the copolymer (C) is 140° C. or lower.

[0345] (Note 15)

[0346] The power cable according to any one of Supplementary Notes 2 to 14, wherein the elastic modulus of the polyolefin measured by a scanning probe microscope is 200 MPa or more and 2000 MPa or less.

[0347] (Note 16)

[0348] The electric power cable according to any one of Supplementary Notes 2 to 15, wherein the elastic modulus of the styrene-based elastomer (B) measured with a scanning probe microscope is 10 MPa or more and 200 MPa or less.

[0349] (Note 17)

[0350] The electric power cable according to any one of Supplementary Notes 2 to 16, wherein the base resin (A) further contains a maleic anhydride-modified polyolefin.

[0351] (Note 18)

[0352] The electric power cable according to any one of Supplementary Notes 2 to 17, wherein the base resin comprises polyethylene, and the styrene-based elastomer (B) comprises ethylene units.

[0353] (Note 19)

[0354] A method for producing a power cable comprises the following steps: preparing a resin composition comprising a base resin (A) comprising a polyolefin, a styrene-based elastomer (B) comprising styrene units, and a copolymer (C) comprising styrene units and maleic anhydride units; and forming an insulating layer using the resin composition to cover the outer circumference of a conductor, wherein in the step of preparing the resin composition, the content of the copolymer (C) in the resin composition is set to 0.5 parts by mass or more, based on 100 parts by mass of the total content of the base resin (A) and the styrene-based elastomer (B), the content of the styrene-based elastomer (B) in the resin composition is set to be equal to or greater than the content of the copolymer (C), and the copolymer (C) is a material that does not contain side chains that are decomposed or hydrolyzed at temperatures below 300°C.

[0355] (Note 20)

[0356] A method for producing a power cable comprises the following steps: preparing a resin composition comprising a base resin (A) comprising a polyolefin, a styrene-based elastomer (B) comprising styrene units, and a copolymer (C) comprising styrene units and maleic anhydride units; and forming an insulating layer using the resin composition to cover the outer circumference of a conductor, wherein in the step of preparing the resin composition, the total content of the maleic anhydride units in the resin composition is set to 0.1 parts by mass or more, based on 100 parts by mass of the combined content of the base resin (A) and the styrene-based elastomer (B), the content of the styrene-based elastomer (B) in the resin composition is set to be equal to or greater than the content of the copolymer (C), and the copolymer (C) is a material that does not contain side chains that are decomposed or hydrolyzed at temperatures below 300°C.

[0357] Description of Reference Numerals

[0358] 10: DC power cable

[0359] 110: Conductor

[0360] 120: Inner semi-conductive layer

[0361] 130: Insulation layer

[0362] 140: Outer semi-conductive layer

[0363] 150: Shielding layer

[0364] 160: Sheath.

Claims

1. A resin composition comprising: A base resin consisting of a polyolefin or a polyolefin and a maleic anhydride-modified polyolefin; Styrene-based elastomers selected from styrene butadiene styrene block copolymers (SBS), hydrogenated styrene butadiene styrene block copolymers, styrene-ethylene-ethylene-propylene-styrene block copolymers (SEEPS), styrene-ethylene-propylene-styrene block copolymers (SEPS), styrene isoprene styrene copolymers (SIS), hydrogenated styrene isoprene styrene copolymers, hydrogenated styrene butadiene rubber, hydrogenated styrene isoprene rubber, styrene ethylene butylene olefin crystalline block copolymers, or any combination thereof; and A copolymer comprising styrene units and maleic anhydride units, The content of the copolymer is 0.5 parts by mass or more and less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer. The content of the styrene-based elastomer is greater than or equal to the content of the copolymer, The copolymer does not contain side chains that will be detached due to thermal decomposition or hydrolysis below 300°C. The maleic anhydride unit is introduced as one monomer unit constituting a main chain into the copolymer including the styrene unit.

2. The resin composition according to claim 1, wherein The content of the maleic anhydride unit in the copolymer is 10% by mass or more and 50% by mass or less.

3. A power cable comprising: conductors; and an insulating layer, arranged to cover the periphery of the conductor, The insulating layer comprises a resin composition, wherein the resin composition comprises: a base resin composed of a polyolefin or a polyolefin and a maleic anhydride-modified polyolefin; a styrene-based elastomer selected from styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, styrene-ethylene-butylene-olefin crystalline block copolymer, or any combination thereof; and a copolymer comprising a styrene unit and a maleic anhydride unit. The content of the copolymer in the insulating layer is 0.5 parts by mass or more and less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer. The content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, The copolymer does not contain side chains that will be detached due to thermal decomposition or hydrolysis below 300°C. The maleic anhydride unit is introduced as one monomer unit constituting a main chain into the copolymer including the styrene unit.

4. The power cable according to claim 3, wherein: When the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more.

5. The power cable according to claim 3, wherein: The content of the maleic anhydride unit in the copolymer is 10% by mass or more and 50% by mass or less.

6. A power cable comprising: conductors; and an insulating layer, arranged to cover the periphery of the conductor, The insulating layer comprises a resin composition, wherein the resin composition comprises: a base resin composed of a polyolefin or a polyolefin and a maleic anhydride-modified polyolefin; a styrene-based elastomer selected from styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, styrene-ethylene-butylene-olefin crystalline block copolymer, or any combination thereof; and a copolymer comprising a styrene unit and a maleic anhydride unit. The total content of the maleic anhydride units in the insulating layer is 0.1 parts by mass or more, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer. The content of the styrene-based elastomer in the insulating layer is equal to or greater than the content of the copolymer, The copolymer does not contain side chains that will be detached due to thermal decomposition or hydrolysis below 300°C. The maleic anhydride unit is introduced into the copolymer containing the styrene unit as a monomer unit constituting the main chain, The content of the copolymer is less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer.

7. The power cable according to claim 6, wherein: The content of the maleic anhydride unit in the copolymer is 10% by mass or more and 50% by mass or less.

8. The power cable according to any one of claims 3 to 7, wherein: The copolymer does not contain any of ester bonds, ether bonds, amide bonds, urethane bonds, and siloxane bonds.

9. The power cable according to any one of claims 3 to 7, wherein: The volume resistivity of the insulating layer sheet measured under the conditions of a temperature of 90°C and a DC electric field of 75 kV / mm was 1.0×10 15 Ω·cm or more.

10. The power cable according to any one of claims 3 to 7, wherein: The space charge storage amount of the insulating layer sheet measured under the conditions of a temperature of 90° C. and a DC electric field of 75 kV / mm is 100% or less.

11. The power cable according to claim 10, wherein: The heating deformation rate of the sheet of the insulating layer measured under the conditions of a temperature of 120° C. and a load of 2 kg is 40% or less.

12. The power cable according to any one of claims 3 to 7, wherein: When the total content of the base resin and the styrene-based elastomer is 100 parts by mass, the content of the inorganic compound contained in the insulating layer is less than 0.01 parts by mass.

13. The power cable according to any one of claims 3 to 7, wherein: The insulating layer further contains less than 1 part by mass of an inorganic filler, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer.

14. The power cable according to claim 12, wherein: The insulating layer satisfies the following formula (1) for the variation rate of DC breakdown strength: (AND MAX -AND MIN ) / AND AVE ≤0.2……(1), The DC breakdown strength is the electric field strength when a DC electric field is applied to each of the plurality of sheets at a temperature of 90°C and insulation breakdown occurs in the sheet, wherein the plurality of sheets are collected at a plurality of locations of the insulating layer at predetermined intervals in the longitudinal direction of the conductor. E MAX 、E MIN and E AVE are respectively the maximum value, the minimum value and the average value of the DC breakdown strength of the plurality of sheets.

15. The power cable according to any one of claims 3 to 7, wherein: The glass transition temperature of the copolymer is 110° C. or higher.

16. The power cable according to any one of claims 3 to 7, wherein: The glass transition temperature of the copolymer is 140° C. or lower.

17. A method for manufacturing a power cable, comprising the following steps: preparing a resin composition comprising a base resin composed of a polyolefin or a polyolefin and a maleic anhydride-modified polyolefin, a styrene-based elastomer selected from styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, styrene-ethylene-butylene-olefin crystalline block copolymer, or any combination thereof, and a copolymer comprising a styrene unit and a maleic anhydride unit; and Using the resin composition, an insulating layer is formed so as to cover the outer periphery of the conductor; In the step of preparing the resin composition, The content of the copolymer in the resin composition is set to 0.5 parts by mass or more and less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer. The content of the styrene-based elastomer in the resin composition is set to be equal to or greater than the content of the copolymer, The copolymer is made of a material that does not contain side chains that are released by thermal decomposition or hydrolysis at 300° C. or lower. The maleic anhydride unit is introduced as one monomer unit constituting a main chain into the copolymer including the styrene unit.

18. A method for manufacturing a power cable, comprising the following steps: preparing a resin composition comprising a base resin composed of a polyolefin or a polyolefin and a maleic anhydride-modified polyolefin, a styrene-based elastomer selected from styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isoprene-styrene copolymer (SIS), hydrogenated styrene-isoprene-styrene copolymer, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, styrene-ethylene-butylene-olefin crystalline block copolymer, or any combination thereof, and a copolymer comprising a styrene unit and a maleic anhydride unit; and Using the resin composition, an insulating layer is formed so as to cover the outer periphery of the conductor; In the step of preparing the resin composition, The total content of the maleic anhydride units in the resin composition is set to 0.1 parts by mass or more, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer. The content of the styrene-based elastomer in the resin composition is set to be equal to or greater than the content of the copolymer, The copolymer is made of a material that does not contain side chains that are released by thermal decomposition or hydrolysis at 300° C. or lower. The maleic anhydride unit is introduced into the copolymer containing the styrene unit as a monomer unit constituting the main chain, The content of the copolymer is less than 20 parts by mass, based on 100 parts by mass of the total content of the base resin and the styrene-based elastomer.

19. The method for manufacturing a power cable according to claim 17 or 18, wherein: The content of the maleic anhydride unit in the copolymer is 10% by mass or more and 50% by mass or less.

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