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

Abstract

This resin composition is provided so as to cover a conductor of a power cable, and constitutes an insulating layer having an inner peripheral surface facing the conductor and an outer peripheral surface opposite to the inner peripheral surface. The resin composition includes: a base polymer that contains a propylene unit; a modified polymer that contains the propylene unit and that is modified by at least one selected from an unsaturated organic acid and a derivative thereof; and a thermoplastic elastomer. The resin composition is configured such that the ratio of the storage elastic modulus of an inner sample of the insulating layer to the storage elastic modulus of an outer sample of the insulating layer is 1.1 or more and 2.5 or less, and the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less. Here, the outer sample of the insulating layer is collected from a position of 0.3 mm from the outer peripheral surface toward the conductor, the inner sample of the insulating layer is collected from a position of 0.3 mm from the inner peripheral surface toward the outer peripheral surface, and the storage elastic modulus of the outer sample and the storage elastic modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement.

Description

[Technical Field]

[0001] The present disclosure relates to a resin composition, a power cable, and a method for producing a power cable. [Background technology]

[0002] Cross-linked polyethylene has excellent insulating properties and has therefore been widely used as a resin component that constitutes the insulating layer of power cables (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 57-69611 Summary of the Invention

[0004] According to one aspect of the present disclosure, A resin composition constituting an insulating layer that is provided to cover a conductor of a power cable and has an inner circumferential surface facing the conductor and an outer circumferential surface opposite to the inner circumferential surface, a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, The resin composition comprises The ratio of the storage modulus of the inner sample of the insulating layer to the storage modulus of the outer sample of the insulating layer is 1.1 or more and 2.5 or less, and The ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is configured to be 1.0 or more and 1.5 or less. where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90°C and a DC electric field of 80 kV / mm. A resin composition is provided. [Brief explanation of the drawings]

[0005] [Figure 1] 1 is a schematic cross-sectional view perpendicular to the axial direction of a power cable according to an embodiment of the present disclosure. [Figure 2] FIG. 10 is a diagram showing the temperature at the collection position of the outer sample and the temperature at the collection position of the inner sample in the cooling process of sample A3. [Figure 3] FIG. 10 is a diagram showing the temperature at the sampling position of the outer sample and the temperature at the sampling position of the inner sample in the cooling process of sample B1. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] The present inventors have focused on polypropylene as a resin component constituting the insulating layer and have conducted extensive research to improve the properties of power cables.

[0007] An object of the present disclosure is to improve the flexibility, strength and insulating properties of insulating layers.

[0008] [Effects of this disclosure] According to the present disclosure, the flexibility, strength, and insulating properties of the insulating layer can be improved.

[0009] [Description of the embodiments of the present disclosure] <Knowledge gained by the inventors> First, the findings of the inventors will be outlined.

[0010] In the manufacturing process of a power cable, a resin composition molten in a heated extruder is extruded to form an insulating layer covering the outer periphery of a conductor. After the insulating layer is extruded, it is cooled by a predetermined cooling method.

[0011] At this time, the outer peripheral surface of the insulating layer is cooled with a predetermined refrigerant, so that cooling proceeds from the outer periphery of the insulating layer toward the inner periphery of the insulating layer in the radial direction of the conductor.

[0012] When the temperature at which the outer peripheral surface of the insulating layer is cooled is low, i.e., when the cooling rate of the outer peripheral surface of the insulating layer is high, the base polymer on the outside of the insulating layer is cooled rapidly, whereas the base polymer on the inside of the insulating layer is cooled more slowly than the base polymer on the outside of the insulating layer.

[0013] Therefore, when the cooling rate of the outer peripheral surface of the insulation layer is fast, a distribution (variation) of the crystallinity occurs in the thickness direction of the insulation layer. That is, the crystallinity of the base polymer is low on the outside of the insulation layer. On the other hand, the crystallinity of the base polymer is higher on the inside of the insulation layer than on the outside of the insulation layer. When such a distribution of the crystallinity occurs, the insulating properties gradually decrease from the inside to the outside of the insulation layer. As a result, it becomes difficult to ensure the sufficient insulating properties required for the entire insulation layer of the power cable.

[0014] Therefore, in the past, the cooling rate of the outer peripheral surface of the insulation layer was slowed down to make the cooling rate uniform in the thickness direction of the insulation layer. That is, the cooling rate of the base polymer on the outside of the insulation layer was made similar to the cooling rate of the base polymer on the inside of the insulation layer. This adjusted the crystallinity of the base polymer on the outside of the insulation layer to be similarly high. As a result, the required sufficient insulation properties of the insulation layer as a whole of the power cable were ensured.

[0015] However, when the rate at which the outer peripheral surface of the insulating layer is cooled is slowed down, the degree of crystallinity of the insulating layer is high and uniform in the thickness direction of the insulating layer, and therefore the elasticity of the insulating layer also becomes uniform in the thickness direction of the insulating layer.

[0016] For this reason, for example, the elasticity of the base polymer on the inside of the insulating layer may be high, as well as the elasticity of the base polymer on the outside of the insulating layer. In this case, it is difficult to ensure sufficient flexibility of the power cable when the power cable is bent. As a result, there is a restriction on the reel diameter when the power cable is wound around the reel.

[0017] Since the conventional methods have the above-mentioned problems, it has been desirable to achieve both the desired elasticity of the insulating layer and uniform insulating properties of the insulating layer in the thickness direction.

[0018] Therefore, after extensive research, the inventors have succeeded in improving the resin components and applying a new manufacturing method, thereby achieving the desired distribution of elasticity in the thickness direction of the insulating layer while making the insulating properties of the insulating layer uniform in the thickness direction of the insulating layer.

[0019] The present disclosure is based on the above-mentioned findings of the inventors.

[0020] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0021] [1] A resin composition according to one embodiment of the present disclosure comprises: A resin composition constituting an insulating layer that is provided to cover a conductor of a power cable and has an inner circumferential surface facing the conductor and an outer circumferential surface opposite to the inner circumferential surface, a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, The resin composition comprises The ratio of the storage modulus of the inner sample of the insulating layer to the storage modulus of the outer sample of the insulating layer is 1.1 or more and 2.5 or less, and The ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is configured to be 1.0 or more and 1.5 or less. where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0022] [2] A power cable according to one embodiment of the present disclosure includes: A conductor; an insulating layer provided to cover an outer periphery of the conductor, the insulating layer having an inner periphery facing the conductor and an outer periphery opposite to the inner periphery; Equipped with The insulating layer is a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, a ratio of the storage modulus of an inner sample of the insulating layer to the storage modulus of an outer sample of the insulating layer is 1.1 or more and 2.5 or less; a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0023] [3] In the power cable according to [2] above, When the total content of the base polymer, the modified polymer, and the thermoplastic elastomer in the insulating layer is 100 parts by mass, the content of the modified polymer in the insulating layer is 1 part by mass or more and 10 parts by mass or less; The content of the thermoplastic elastomer in the insulating layer is 10 parts by mass or more and 45 parts by mass or less. According to this configuration, it is possible to stably achieve both a desired distribution of elasticity and uniformity of insulation in the thickness direction of the insulating layer.

[0024] [4] In the power cable according to the above [2] or [3], The thermoplastic elastomer includes a styrene-based elastomer. This configuration allows short chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C), thereby improving the compatibility between the base polymer (A) and the thermoplastic elastomer (C).

[0025] [5] The power cable according to any one of [2] to [4] above, The thermoplastic elastomer includes an olefin-based elastomer. This configuration allows short chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C), thereby improving the compatibility between the base polymer (A) and the thermoplastic elastomer (C).

[0026] [6] The power cable according to any one of [2] to [5] above, the storage modulus of the inner sample of the insulating layer is 650 MPa or more and 900 MPa or less; The storage modulus of the outer sample of the insulating layer is 280 MPa or more and 670 MPa or less. This configuration allows the power cable 10 to have both rigidity and flexibility.

[0027] [7] The power cable according to any one of [2] to [6] above, The insulating layer has a thickness of 3 mm or more. With this configuration, even when the power cable is used in high voltage applications, it is possible to stably achieve both flexibility of the insulating layer and insulation properties of the insulating layer.

[0028] [8] A method for manufacturing a power cable according to another aspect of the present disclosure includes: preparing a resin composition; forming an insulating layer from the resin composition so as to cover an outer periphery of the conductor, and forming an inner circumferential surface of the insulating layer facing the conductor and an outer circumferential surface facing the inner circumferential surface; Equipped with In the step of preparing the resin composition, The resin composition includes: a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; providing a composition comprising: The step of forming the insulating layer includes: extruding the insulating layer around the outer periphery of the conductor; cooling the insulating layer so that a ratio of the storage modulus of the inner sample of the insulating layer to that of the outer sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to that of the outer sample is 1.0 or more and 1.5 or less; having where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. This configuration can improve the flexibility, strength, and insulating properties of the insulating layer.

[0029] [9] In the method for producing a power cable according to the above [8], In the step of cooling the insulating layer, During at least a portion of the period immediately after the step of extruding the insulating layer, the insulating layer is cooled from a region close to the outer circumferential surface of the insulating layer while the conductor is being heated by electromagnetic induction. This configuration allows the inside of the insulating layer to be slowly cooled.

[0030] [Details of the embodiments of the present disclosure] Next, one embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0031] <One embodiment of the present disclosure> (1) Resin composition The resin composition of this embodiment is a material that constitutes the insulating layer 130 of the power cable 10, which will be described later. The resin composition contains, for example, a base polymer (A), a modified polymer (B), a thermoplastic elastomer (C), and other additives.

[0032] Hereinafter, the base polymer (A), the modified polymer (B), and the thermoplastic elastomer (C) are also referred to as "resin components."

[0033] (Base polymer (A)) The base polymer (base resin) (A) refers to the resin component that constitutes the main component of the resin composition. The "main component" refers to the component that is contained in the largest amount.

[0034] The base polymer (A) of this embodiment contains, for example, at least a propylene unit as a monomer unit.

[0035] That is, when the resin composition of this embodiment is analyzed by a nuclear magnetic resonance (NMR) device, propylene units are detected as monomer units derived from the base polymer (A).

[0036] The base polymer (A) is, for example, made of polypropylene (propylene-based resin, also called PP) having propylene units in the main chain. Examples of polypropylene include homopolypropylene (homoPP), random polypropylene (randomPP), and block polypropylene (blockPP).

[0037] By analyzing the resin composition of this embodiment by NMR, for example, when the base polymer (A) is a random PP or a block PP, propylene units and ethylene units derived from the random PP or the block PP are detected, and when the base polymer (A) is a homo PP, propylene units derived from the homo PP are detected.

[0038] From the viewpoint of obtaining high insulating properties in the insulating layer 130, the base polymer (A) may be random PP. Homo PP has a higher crystalline content than random PP and can obtain high insulating properties. However, an insulating layer 130 containing homo PP may cause cracks within or between crystals. For this reason, homo PP may not obtain the insulating properties it inherently possesses. In contrast, random PP contains ethylene units, resulting in a low crystalline content. However, an insulating layer 130 containing random PP is less likely to crack due to coarse crystallization. As a result, random PP can obtain higher insulating properties than homo PP.

[0039] When the base polymer (A) is a random PP, the ethylene unit content in the random PP may be, for example, 0.5% by mass or more and 15% by mass or less. By setting the ethylene unit content to 0.5% by mass or more, it is possible to suppress the growth of coarse spherulites. On the other hand, by setting the ethylene unit content to 15% by mass or less, it is possible to suppress a decrease in melting point and to stably realize use in a non-crosslinked or slightly crosslinked state.

[0040] In this embodiment, the stereoregularity of the polypropylene is not particularly limited, but may be, for example, isotactic. Here, if the stereoregularity of the polypropylene is atactic, the polypropylene will not crystallize. In contrast, isotactic polypropylene is polymerized with a Ziegler-Natta catalyst and is a versatile material. The isotactic stereoregularity of the composition can suppress a decrease in melting point. This allows a predetermined crystallinity to be easily obtained, resulting in high insulating properties.

[0041] In this embodiment, the storage modulus of the base polymer (A) alone is, for example, 800 MPa or more and 1700 MPa or less. The measurement method and conditions for the "storage modulus of the base polymer (A) alone" here are the same as those for the storage modulus of the insulating layer described later.

[0042] The melt flow rate (MFR) of the base polymer (A) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 5.0 g / 10 min or less, or 0.1 g / 10 min or more and 2.0 g / 10 min or less. The "MFR" here refers to a value measured in accordance with JIS K7210 at a temperature of 190°C and a load of 2.16 kg. By setting the MFR of the base polymer (A) within the above range, the phase structure described below can be easily formed in the insulating layer 130.

[0043] The melting point of the base polymer (A) is not particularly limited, but may be, for example, 130° C. or higher and 165° C. or lower. This makes it possible to easily form a phase structure described below when the base polymer (A) is mixed with at least one of the modified polymer (B) and the thermoplastic elastomer (C).

[0044] (Modified polymer (B)) The modified polymer (B) is a resin containing propylene units as the main chain and modified with at least one selected from unsaturated organic acids and derivatives thereof.

[0045] When the modified polymer (B) contains a propylene unit, the compatibility of the base polymer (A) and the modified polymer (B) when they are mixed can be improved.

[0046] By modifying the modified polymer (B) with an unsaturated organic acid containing a polar group, a polar group can be introduced into the resin composition. This allows the polar groups dispersed in the insulating layer 130 formed from the resin composition to trap space charge. In other words, local accumulation of space charge in the insulating layer 130 can be suppressed. As a result, the insulating properties of the insulating layer 130 can be improved.

[0047] Specifically, the modified polymer (B) may be, for example, an unsaturated carboxylic acid-modified polypropylene in which polypropylene is modified with at least one of an unsaturated carboxylic acid and its derivatives. Examples of unsaturated carboxylic acids and their derivatives include acrylic acid, methacrylic acid, crotonic acid, maleic acid, cinnamic acid, itaconic acid, citraconic acid, fumaric acid, and anhydrides thereof.

[0048] Among these, the modified polymer (B) may be modified with, for example, maleic anhydride. Maleic anhydride has a large number of polar groups per molecular weight. This ensures that the number of polar groups in the modified polymer (B) is sufficient even if the content of maleic anhydride in the modified polymer (B) is small.

[0049] The modification amount of at least one of the unsaturated carboxylic acid and its derivative in the modified polymer (B) (hereinafter simply referred to as the modification amount) is not particularly limited, but may be, for example, 0.1% by mass or more and 10% by mass or less. The "modification amount" here refers to the copolymerization ratio (content) of at least one of the unsaturated carboxylic acid and its derivative in the modified polymer (B). By setting the modification amount to 0.1% by mass or more, it is possible to stably suppress the accumulation of space charge in the insulating layer 130. On the other hand, by setting the modification amount to 10% by mass or less, it is possible to improve the compatibility between the modified polymer (B) and the base polymer (A).

[0050] In this embodiment, the storage modulus of the modified polymer (B) alone is, for example, 1000 MPa or more and 1900 MPa or less. The measurement method and conditions for the "storage modulus of the modified polymer (B) alone" here are the same as those for the storage modulus of the insulating layer described below.

[0051] The MFR of the modified polymer (B) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 500 g / 10 min or less, or 1 g / 10 min or more and 300 g / 10 min or less. The measurement conditions for the MFR of the modified polymer (B) here are the same as those described for the MFR of the base polymer (A). When the MFR of the modified polymer (B) is within the above range, the phase structure described below can be easily formed when the base polymer (A) and the modified polymer (B) are mixed.

[0052] The melting point of the modified polymer (B) is not particularly limited, but may be, for example, 130° C. or higher and 165° C. or lower, which allows the phase structure described below to be easily formed when the base polymer (A) and the modified polymer (B) are mixed.

[0053] (Thermoplastic elastomer (C)) The thermoplastic elastomer (C) has lower crystallinity than the base polymer (A) having propylene units, and the thermoplastic elastomer (C) can suppress excessive crystal growth of the base polymer (A) and impart flexibility to the insulating layer 130.

[0054] Examples of the thermoplastic elastomer (C) include amide-based, ester-based, olefin-based, styrene-based, urethane-based, vinyl chloride-based, fluorine-based, etc. Among these, the thermoplastic elastomer (C) may be at least one of a styrene-based polymer and an olefin-based elastomer.

[0055] (styrene elastomer) The thermoplastic elastomer (C) may contain, for example, a styrene-based elastomer. This allows short-chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C). As a result, the compatibility between the base polymer (A) and the thermoplastic elastomer (C) can be improved.

[0056] In this embodiment, the styrene-based elastomer is, for example, a copolymer containing styrene units as hard segments and at least one type of monomer unit selected from ethylene units, propylene units, butylene units, and isoprene units as soft segments.

[0057] Examples of styrene-based elastomers include styrene-butadiene-styrene block copolymer (SBS), hydrogenated styrene-butadiene-styrene block copolymer, styrene-ethylene-styrene block copolymer (SES), styrene-ethylene-propylene copolymer (SEP), 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, etc. Two or more of these may be used in combination.

[0058] "Hydrogenated" here means that hydrogen has been added to the double bond. For example, "hydrogenated styrene butadiene styrene block copolymer" means a polymer in which hydrogen has been added to the double bond of a styrene butadiene styrene block copolymer. No hydrogen has been added to the double bond of the aromatic ring of styrene. "Hydrogenated styrene butadiene styrene block copolymer" can be rephrased as styrene ethylene butylene styrene block copolymer (SEBS).

[0059] The styrene-based elastomer may be, for example, a hydrogenated material that does not contain double bonds in its chemical structure except for aromatic rings. If a non-hydrogenated material is used, the resin component may be thermally degraded during molding of the resin composition. This may result in a deterioration in the properties of the resulting insulating layer 130. In contrast, the use of a hydrogenated material can improve resistance to thermal degradation. This allows the properties of the insulating layer 130 to be maintained at a higher level.

[0060] Furthermore, the styrene-based elastomer may contain, for example, a styrene unit and at least one of a propylene unit and a butene unit. This allows the compatibility between the polypropylene as the base polymer (A) and the styrene-based elastomer to be stably improved. As a result, the polypropylene and the styrene-based elastomer can be uniformly mixed.

[0061] The content of styrene units in the styrene-based elastomer (content rate; hereinafter simply referred to as "styrene unit content") is not particularly limited, but the styrene unit content may be, for example, 5% by mass or more and 35% by mass or less. By setting the styrene unit content to 5% by mass or more and 35% by mass or less, it is possible to stably prevent the material from becoming excessively hard. This makes it possible to stably prevent separation and cracking between the polypropylene and the thermoplastic elastomer (C).

[0062] (olefin elastomer) The thermoplastic elastomer (C) may contain, for example, an olefin-based elastomer. This allows short-chain branches to be easily incorporated into the molecular structure of the flexible thermoplastic elastomer (C). As a result, the compatibility between the base polymer (A) and the thermoplastic elastomer (C) can be improved.

[0063] The olefin-based elastomer as the thermoplastic elastomer (C) is, for example, a copolymer of two olefin units, such as a copolymer of an ethylene unit and an α-olefin unit having 3 or more carbon atoms, or a copolymer of a propylene unit and an α-olefin unit having 4 or more carbon atoms.

[0064] Specifically, olefin elastomers include ethylene propylene rubber (EPR), very low density polyethylene (VLDPE), and propylene-1-butene copolymer (propylene-1-butene rubber (PBR)). Ethylene-1-butene copolymer (ethylene-1-butene rubber (EBR)) is a type of VLDPE.

[0065] The olefinic elastomer may contain, for example, at least one of a propylene unit and a butene unit. This allows the compatibility between the polypropylene as the base polymer (A) and the olefinic elastomer to be stably improved. As a result, the polypropylene and the olefinic elastomer can be uniformly mixed.

[0066] When the olefin elastomer contains ethylene units, the content of the ethylene units in the olefin elastomer is not particularly limited, but may be, for example, 5% by mass or more and 90% by mass or less, which allows the olefin elastomer to stably provide the softening effect and crystallization inhibition effect.

[0067] (Characteristics of thermoplastic elastomers) In this embodiment, the storage modulus of the thermoplastic elastomer (C) alone is, for example, 20 MPa or more and 500 MPa or less. The measurement method and conditions for the "storage modulus of the thermoplastic elastomer (C) alone" here are the same as those for the storage modulus of the insulating layer described below.

[0068] The MFR of the thermoplastic elastomer (C) is not particularly limited, but may be, for example, 0.1 g / 10 min or more and 5.0 g / 10 min or less, or 0.1 g / 10 min or more and 2.0 g / 10 min or less. The conditions for measuring the MFR of the thermoplastic elastomer (C) here are the same as those described for the MFR of the base polymer (A). When the MFR of the thermoplastic elastomer (C) is within the above range, the phase structure described below can be easily formed when the base polymer (A) and the thermoplastic elastomer (C) are mixed.

[0069] The thermoplastic elastomer (C) may, for example, have no melting point or may have a melting point lower than 165° C. This makes it possible to easily form a phase structure described below when the base polymer (A) and the thermoplastic elastomer (C) are mixed.

[0070] (Content of modified polymer (B) and thermoplastic elastomer (C)) The contents of the modified polymer (B) and thermoplastic elastomer (C) will be explained. Here, the total content of the resin component consisting of the base polymer (A), modified polymer (B), and thermoplastic elastomer (C) is taken as 100 parts by mass. The remainder of the resin component other than the modified polymer (B) and thermoplastic elastomer (C) is the base polymer (A).

[0071] In this embodiment, the content of the modified polymer (B) in the resin composition (i.e., the insulating layer 130) may be, for example, 1 part by mass or more and 10 parts by mass or less. By setting the content of the modified polymer (B) to 1 part by mass or more, it is possible to suppress a decrease in the insulating properties of the insulating layer 130. On the other hand, by setting the content of the modified polymer (B) to 10 parts by mass or less, it is possible to suppress a decrease in the formability of the insulating layer 130. This makes it possible to suppress a decrease in the insulating properties of the insulating layer 130 due to a decrease in formability.

[0072] The content of the thermoplastic elastomer (C) in the resin composition (i.e., the insulating layer 130) may be, for example, 10 parts by mass or more and 45 parts by mass or less. By setting the content of the thermoplastic elastomer (C) to 10 parts by mass or more, it is possible to prevent the elasticity of the insulating layer 130 from becoming excessively high, and to impart flexibility to the insulating layer 130. On the other hand, by setting the content of the thermoplastic elastomer (C) to 45 parts by mass or less, that is, by preventing excessive incorporation of the amorphous thermoplastic elastomer (C), it is possible to prevent a decrease in the insulating properties and mechanical properties that are originally required of polypropylene having a high melting point as the base polymer (A).

[0073] Furthermore, by setting the contents of the modified polymer (B) and the thermoplastic elastomer (C) within the above-mentioned ranges, a phase structure, which will be described later, can be easily formed.

[0074] In this way, by setting the content of each of the modified polymer (B) and the thermoplastic elastomer (C) within the above-mentioned ranges, it is possible to stably achieve both the desired distribution of elasticity and uniformity of insulating properties in the thickness direction of the insulating layer 130.

[0075] (inorganic filler) In this embodiment, the resin composition contains the modified polymer (B), and as described above, the space charge trapping effect of the modified polymer (B) can be uniformly obtained throughout the resin composition. This allows high insulating properties to be stably obtained without adding an inorganic filler. Therefore, in this embodiment, the resin composition does not need to contain an inorganic filler.

[0076] On the other hand, the resin composition may contain a trace amount of inorganic filler to the extent that it does not cause clogging of the mesh in the extruder.

[0077] Specifically, the resin composition contains an inorganic filler, and the content of the inorganic filler may be, for example, less than 1 part by mass when the total content of the resin components is 100 parts by mass. The lower limit of the content of the inorganic filler is not limited as long as the inorganic filler can be added.

[0078] Examples of inorganic fillers include magnesium oxide (MgO), silicon dioxide, zinc oxide, aluminum oxide, titanium oxide, zirconium oxide, carbon black, and mixtures of two or more of these.

[0079] The volume average particle diameter (MV) of the inorganic filler is not particularly limited, but may be, for example, 1 μm or less, or 700 nm or less, or 100 nm or less. The "volume average particle diameter (MV)" here refers to the particle diameter of the particles di , the volume of the particle V i When this is the case, it can be calculated using the following formula: MV=Σ(V i d i ) / ΣV i The volume average particle size is measured using a dynamic light scattering particle size / particle size distribution measuring device.

[0080] The lower limit of the volume average particle diameter of the inorganic filler is not particularly limited, but from the viewpoint of stably forming the inorganic filler, the volume average particle diameter of the inorganic filler may be, for example, 1 nm or more, or 5 nm or more.

[0081] At least a portion of the inorganic filler may be surface-treated with a silane coupling agent, which can improve the adhesion at the interface between the inorganic filler and the base polymer (A), etc., and can improve the mechanical properties and insulating properties of the insulating layer 130.

[0082] (Crosslinking agent) In this embodiment, the resin component that constitutes the insulating layer 130 may be non-crosslinked from the viewpoint of recycling. In this case, the resin composition may not contain a crosslinking agent.

[0083] On the other hand, the resin composition may contain a small amount of crosslinking agent to reduce the gel fraction (degree of crosslinking). Specifically, the resin composition may contain a crosslinking agent so that the crosslinking agent residue in the insulating layer 130 is less than 300 ppm. When dicumyl peroxide is used as the crosslinking agent, the residue is, for example, cumyl alcohol, α-methylstyrene, or the like.

[0084] (Other additives) The resin composition may contain other additives as needed, such as antioxidants, lubricants, and colorants.

[0085] (2) Power cable Next, the power cable of this embodiment will be described with reference to FIG.

[0086] The power cable 10 of this embodiment is configured as a so-called solid insulated power cable. The power cable 10 of this embodiment is configured to be laid, for example, on land (in a conduit), underwater, or at the bottom of a body of water. The power cable 10 may be used, for example, for direct current.

[0087] Specifically, the power cable 10 includes, for example, a conductor 110 , an inner semiconductive layer 120 , an insulating layer 130 , an outer semiconductive layer 140 , a shielding layer 150 , and a sheath 160 .

[0088] (Conductor (conductive part)) The conductor 110 is formed by twisting together a plurality of conductor core wires (conductive core wires) made of, for example, pure copper, copper alloy, aluminum, or aluminum alloy.

[0089] (internal semiconductive layer) The internal semiconductive layer 120 is provided so as to cover the outer periphery of the conductor 110. The internal semiconductive layer 120 is semiconductive and configured to suppress electric field concentration on the surface side of the conductor 110. The internal semiconductive layer 120 contains, for example, at least one of an ethylene-based copolymer such as an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-butyl acrylate copolymer, or an ethylene-vinyl acetate copolymer, an olefin-based elastomer, or the above-mentioned low-crystalline resin, and conductive carbon black.

[0090] (insulating layer) The insulating layer 130 is provided so as to cover the outer periphery of the internal semiconductive layer 120. The insulating layer 130 is formed, for example, by extrusion molding using a resin composition as described above. The insulating layer 130 has an inner circumferential surface facing the conductor 110 and an outer circumferential surface opposite the inner circumferential surface.

[0091] In this embodiment, the elasticity of the insulating layer 130 varies in the thickness direction of the insulating layer 130. On the other hand, the insulating property of the insulating layer 130 is uniform in the thickness direction of the insulating layer 130. This point will be described in detail later.

[0092] In this embodiment, the insulating layer 130 has a predetermined phase structure by mixing a base polymer (A), a modified polymer (B), and a thermoplastic elastomer (C).

[0093] Specifically, the inclusion of the modified polymer (B) in the insulating layer 130 forms a structure in which the base polymer (A) and the modified polymer (B) are compatible with each other, or a sea-island structure in which the modified polymer (B) is finely dispersed in the base polymer (A). The "compatible structure" here means that, for example, when the phase structure is observed with a transmission electron microscope, no phase separation can be confirmed and each component is uniformly dispersed.

[0094] The more finely the modified polymer (B) is dispersed in the insulating layer 130, the more the accumulation of space charge can be suppressed. From this viewpoint, a structure in which the resin components are compatible with each other may be formed in the insulating layer 130. Alternatively, when a sea-island structure is formed in the insulating layer 130, the diameter of the island phases formed from the modified polymer (B) may be less than 0.5 μm.

[0095] Furthermore, since the insulating layer 130 contains not only the base polymer (A) and the modified polymer (B) but also the thermoplastic elastomer (C), a sea-island structure in which the thermoplastic elastomer (C) is finely dispersed is formed in the above-mentioned phase structure of the two-component system in which the insulating layer 130 contains the base polymer (A) and the modified polymer (B).

[0096] By forming the above-described phase structure in the insulating layer 130, the polar groups in the modified polymer (B) can be uniformly dispersed in the insulating layer 130. This allows the space charge trapping effect to be obtained uniformly in the insulating layer 130.

[0097] Furthermore, by forming the above-mentioned phase structure in the insulating layer 130, the thermoplastic elastomer (C) can be uniformly dispersed in the insulating layer 130. This makes it possible to obtain a stable distribution of elasticity in the insulating layer 130 according to the difference in cooling rate in the thickness direction of the insulating layer 130.

[0098] In this embodiment, as described above, the insulating layer 130 is non-crosslinked, or even if the insulating layer 130 is crosslinked, the gel fraction (degree of crosslinking) is low. Specifically, the residue of the crosslinking agent in the insulating layer 130 is, for example, less than 300 ppm. In other words, the insulating layer 130 is slightly crosslinked so that the decomposition residue of the crosslinking agent is, for example, less than 300 ppm. In this way, by making the insulating layer 130 non-crosslinked or with a low degree of crosslinking, recyclability can be improved.

[0099] (Outer semiconductive layer) The outer semiconductive layer 140 is provided so as to cover the outer periphery of the insulating layer 130. The outer semiconductive layer 140 has semiconductivity and is configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semiconductive layer 140 is configured, for example, from the same material as the inner semiconductive layer 120.

[0100] (shielding layer) The shielding layer 150 is provided so as to cover the outer periphery of the outer semiconducting layer 140. The shielding layer 150 is formed, for example, by winding copper tape, or is formed as a wire shield made by winding a plurality of annealed copper wires or the like. Tape made of a material such as rubberized cloth may be wound on the inside or outside of the shielding layer 150.

[0101] (sheath) The sheath 160 is provided so as to cover the outer periphery of the shielding layer 150. The sheath 160 is made of, for example, polyvinyl chloride or polyethylene.

[0102] If the power cable 10 of this embodiment is an underwater cable or an underwater cable, it may have, outside the shielding layer 150, a metal waterproof layer such as aluminum sheath or iron wire armor.

[0103] On the other hand, the power cable 10 of this embodiment may not have a water-shielding layer outside the shielding layer 150. In other words, the power cable 10 of this embodiment may have a non-completely water-shielding structure.

[0104] (Specific dimensions, etc.) The specific dimensions of the power cable 10 are not particularly limited, but for example, the diameter of the conductor 110 is 5 mm to 60 mm, the thickness of the inner semiconductive layer 120 is 0.5 mm to 3 mm, the thickness of the insulating layer 130 is 3 mm to 35 mm, the thickness of the outer semiconductive layer 140 is 0.5 mm to 3 mm, the thickness of the shielding layer 150 is 0.1 mm to 5 mm, and the thickness of the sheath 160 is 1 mm or more. The DC voltage applied to the power cable 10 of this embodiment is, for example, 20 kV or more.

[0105] (3) Cable characteristics In this embodiment, the insulating layer 130 ensures the following cable characteristics.

[0106] Hereinafter, the term "outer sample" refers to a sheet taken from a position 0.3 mm from the outer peripheral surface of the insulating layer 130 toward the conductor 110 in the radial direction of the conductor 110. The term "inner sample" refers to a sheet taken from a position 0.3 mm from the inner peripheral surface of the insulating layer 130 toward the outer peripheral surface of the insulating layer 130 in the radial direction of the conductor 110.

[0107] (elasticity) In this embodiment, the elasticity of the insulating layer 130 varies in the thickness direction of the insulating layer 130 by performing a cooling process, which will be described later, after the extrusion process of the insulating layer 130.

[0108] Specifically, the ratio of the storage modulus of the inner sample of insulating layer 130 to the storage modulus of the outer sample of insulating layer 130 (hereinafter also referred to as "elastic modulus ratio") is, for example, 1.1 or more and 2.5 or less.

[0109] The "storage modulus" referred to here is measured by dynamic mechanical analysis (DMA) in accordance with JIS K7244-4:1999.

[0110] The dynamic viscoelasticity measurement is carried out under the following conditions. Measurement mode: Tensile mode Distortion: 0.08% Frequency: 10Hz Temperature range: 0°C to 200°C Heating rate: 10℃ / min

[0111] The "storage modulus of the outer sample" and the "storage modulus of the inner sample" in the definition of the elastic modulus ratio above are values ​​measured by the dynamic viscoelasticity measurement at 25°C. In the dynamic viscoelasticity measurement, the thickness of each sample is 0.5 mm.

[0112] In this embodiment, by setting the elastic modulus ratio to 1.1 or more, it is possible to make the outside of the insulating layer 130 relatively soft, while making the inside of the insulating layer 130 relatively hard. As a result, in this embodiment, it is possible to achieve both flexibility and strength of the insulating layer 130.

[0113] On the other hand, in this embodiment, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress the generation of voids due to the stress difference in the insulating layer 130. This makes it possible to suppress a decrease in the dielectric breakdown strength (for example, DC breakdown field strength) of the insulating layer 130.

[0114] For example, the elastic modulus of the insulating layer 130 may gradually decrease from the inner peripheral surface of the insulating layer 130 toward the outer peripheral surface of the insulating layer 130 in the radial direction of the conductor 110. By suppressing a sudden change in the elasticity of the insulating layer 130 in this way, it is possible to suppress the occurrence of cracks in the insulating layer 130 due to a difference in the elastic modulus.

[0115] The storage modulus of the inner sample of the insulating layer 130 is, for example, 650 MPa or more and 900 MPa or less. By setting the storage modulus of the inner sample to 650 MPa or more, it is possible to ensure the rigidity of the power cable 10. On the other hand, by setting the storage modulus of the inner sample to 900 MPa or less, it is possible to suppress a decrease in the flexibility of the power cable 10.

[0116] The storage modulus of the outer sample of the insulating layer 130 is, for example, 280 MPa or more and 670 MPa or less. By setting the storage modulus of the outer sample to 280 MPa or more, it is possible to prevent the outer side of the insulating layer 130 from becoming excessively soft. This makes it possible to prevent the occurrence of cracks in the insulating layer 130 due to impacts when the power cable 10 is laid. On the other hand, by setting the storage modulus of the outer sample to 670 MPa or less, it is possible to ensure the flexibility of the power cable 10.

[0117] (insulating) In this embodiment, since the insulating layer 130 contains the modified polymer (B), the space charge trapping effect of the modified polymer (B) can be obtained uniformly throughout the insulating layer 130. As a result, the insulating properties of the insulating layer 130 are uniform in the thickness direction of the insulating layer 130.

[0118] Specifically, the ratio of the volume resistivity of the inner sample of the insulating layer 130 to the volume resistivity of the outer sample of the insulating layer 130 (hereinafter also referred to as "volume resistivity ratio") is, for example, 1.0 or more and 1.5 or less.

[0119] The "volume resistivity of the outer sample" and the "volume resistivity of the inner sample" are measured at a temperature of 90°C and in a DC electric field of 80 kV / mm.

[0120] In this embodiment, by setting the volume resistivity ratio to be 1.0 or more and 1.5 or less, the insulating layer 130 of the power cable 10 as a whole can obtain sufficient insulating properties required.

[0121] The volume resistivity of the outer sample of the insulating layer 130 and the volume resistivity of the inner sample of the insulating layer 130 measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm are, for example, 7.0×10 14 Ω·cm or more, or 3.6×10 15 It may be Ω·cm or more, or 5.0×10 15 It may be Ω·cm or more, or 7.0×10 15 It may be Ω·cm or more. In measuring the volume resistivity, the thickness of each sample shall be 0.2 mm.

[0122] The DC breakdown field strength of the outer sample of insulating layer 130 and the DC breakdown field strength of the inner sample of insulating layer 130 measured at a temperature of 90° C. may be, for example, 160 kV / mm or more, or 200 kV / mm or more. In measuring the DC breakdown field strength, the thickness of each sample is 0.2 mm.

[0123] (4) Power cable manufacturing method Next, a method for manufacturing the power cable of this embodiment will be described. Hereinafter, steps will be abbreviated as "S."

[0124] (S100: Resin composition preparation step) First, the resin composition of this embodiment is prepared.

[0125] In this embodiment, a resin component including a base polymer (A), a modified polymer (B), and a thermoplastic elastomer (C) is mixed (kneaded) with other additives (antioxidants, etc.) using a mixer to form a mixture. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-screw mixer, and a multi-screw mixer.

[0126] Once the mixture is formed, it is granulated using an extruder, thereby forming a pellet-like resin composition that will form the insulating layer 130. The steps from mixing to granulation may be carried out all at once using a twin-screw extruder that has a high kneading effect.

[0127] (S200: Conductor preparation process) On the other hand, a conductor 110 is prepared by twisting together a plurality of conductor core wires.

[0128] (S300: Cable core forming process (insulating layer forming process)) After the resin composition preparation step S100 and the conductor preparation step S200 are completed, the insulating layer 130 is formed in the cable core formation step S300 using the resin composition described above so as to cover the outer periphery of the conductor 110.

[0129] The cable core forming step S300 of this embodiment includes, for example, an extruding step S320 and a cooling step S340.

[0130] (S320: Extrusion process) In this embodiment, for example, a three-layer co-extruder is used to simultaneously form the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140.

[0131] Specifically, for example, the composition for the inner semiconductive layer is charged into extruder A, which forms the inner semiconductive layer 120, of the three-layer co-extruder.

[0132] The above-described pellet-shaped resin composition is fed into extruder B, which forms insulating layer 130. At this time, the set temperature of extruder B is set to a temperature that is 10°C to 80°C higher than the melting point of base polymer (A). The set temperature is adjusted appropriately based on the linear velocity and extrusion pressure.

[0133] An outer semiconductive layer composition containing the same materials as the inner semiconductive layer resin composition charged into extruder A is charged into extruder C which forms the outer semiconductive layer 140 .

[0134] Next, the extrudates from extruders A to C are introduced into a common head, and inner semiconductive layer 120, insulating layer 130, and outer semiconductive layer 140 are simultaneously extruded from the inside to the outside around conductor 110. This forms an extruded material that will become the cable core.

[0135] (S340: Cooling process) After the extrusion step S320 is completed, the extruded material is cooled.

[0136] In this embodiment, the insulating layer 130 is cooled so that the ratio of the storage modulus of the inner sample of the insulating layer 130 to the storage modulus of the outer sample of the insulating layer 130 is 1.1 or more and 2.5 or less, and the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less. In other words, the cable core is cooled so that a temperature difference is intentionally generated between the inside and outside of the insulating layer 130.

[0137] Specifically, the cable cores formed in the extrusion step S320 are successively immersed in a water tank containing water cooled to a predetermined temperature by a chiller (hereinafter also referred to as cooling water), thereby rapidly cooling the insulating layer 130 from the region close to the outer circumferential surface of the insulating layer 130.

[0138] At this time, at a position 0.3 mm from the outer peripheral surface of the insulating layer 130 toward the conductor 110, i.e., at the position where the outer sample was taken, the cooling rate (temperature drop rate) at a temperature of 110°C may be, for example, 30°C / min or more, or 75°C / min or more, or 100°C / min or more. This makes it possible to suppress excessive crystallization on the outer side of the insulating layer 130. As a result, it is possible to reduce the elasticity of the outer side of the insulating layer 130. The "cooling rate at a temperature of 110°C" here is calculated as the absolute value of the gradient of temperature with respect to time at a temperature of 110°C.

[0139] At this time, the cooling rate at the temperature of 110°C at the location where the outer sample of the insulating layer 130 is taken may be, for example, 310°C / min or less. This makes it possible to suppress excessive variations in the crystallinity in the thickness direction of the insulating layer 130. As a result, it is possible to suppress the occurrence of excessive differences in elasticity in the thickness direction of the insulating layer 130.

[0140] At this time, the temperature of the cooling water in the water tank is set to, for example, −50° C. or higher and 50° C. or lower, thereby making it possible to cool the outside of the insulating layer 130 at the above-mentioned cooling rate.

[0141] Meanwhile, during at least a portion of the period immediately following the extrusion step S320 in which the insulating layer 130 is extruded, the conductor 110 is electromagnetically heated while the insulating layer 130 is cooled starting from a region close to the outer circumferential surface of the insulating layer 130. Here, "electromagnetic induction heating" refers to heating the conductor 110 by heat generated in the conductor 110 due to eddy current loss caused by electromagnetic induction and heat generated in the conductor 110 due to hysteresis loss. Electromagnetic induction heating can heat the conductor 110 of the cable core immersed in a water tank without contact. This allows the outer surface of the insulating layer 130 to be rapidly cooled, while the cooling of the inner surface of the insulating layer 130 can be suppressed. In other words, the inner surface of the insulating layer 130 can be slowly cooled.

[0142] At this time, the conductor 110 is heated by electromagnetic induction so that the temperature of the conductor 110 is between 80°C and 110°C. This allows the inside of the insulating layer 130 to be heated to a temperature close to the crystallization temperature of the polypropylene used as the base polymer (A), and the inside of the insulating layer 130 to be gradually cooled. As a result, the elasticity of the inside of the insulating layer 130 can be made relatively high.

[0143] The period during which the conductor 110 is heated by electromagnetic induction to the above temperature may be shorter than the period during which the cable core is water-cooled, for example.

[0144] By the cooling step S340 as described above, the insulating layer 130 is cooled, for example, as shown in FIG.

[0145] 2, the temperature of the outside of the insulating layer 130 drops rapidly from the temperature immediately after the extrusion step S320 to near the temperature of the cooling water. Meanwhile, the temperature of the inside of the insulating layer 130 near the conductor 110 drops gradually to the temperature of the electromagnetically-heated conductor 110. After the electromagnetic induction heating of the conductor 110 is stopped, the temperature of the inside of the insulating layer 130 gradually drops to the temperature of the cooling water. In this way, the outside of the insulating layer 130 is cooled rapidly, while the inside of the insulating layer 130 is cooled slowly.

[0146] In this way, by rapidly cooling the outside of the insulating layer 130, crystallization of the base polymer (A) can be suppressed on the outside of the insulating layer 130, and the resin component can be solidified in a state close to amorphous. In other words, the degree of crystallization on the outside of the insulating layer 130 can be reduced. On the other hand, by slowly cooling the inside of the insulating layer 130, the base polymer (A) can be sufficiently crystallized on the inside of the insulating layer 130. In other words, the degree of crystallization on the inside of the insulating layer 130 can be increased. As a result, the above-mentioned elasticity distribution can be obtained in the thickness direction of the insulating layer 130.

[0147] By the above-described cable core forming step S300, a cable core composed of the conductor 110, the inner semiconductive layer 120, the insulating layer 130 and the outer semiconductive layer 140 is formed.

[0148] (S400: Shielding layer formation process) Once the cable core is formed, a shielding layer 150 is formed on the outside of the outer semiconducting layer 140 by wrapping, for example, copper tape.

[0149] (S500: Sheath forming process) After the shielding layer 150 is formed, vinyl chloride is put into an extruder and extruded to form a sheath 160 around the outer periphery of the shielding layer 150 .

[0150] In this manner, the power cable 10 is manufactured as a solid insulated power cable.

[0151] (5) Summary of this embodiment According to this embodiment, one or more of the following effects are achieved.

[0152] (a) In this embodiment, in the cooling step S340 after the extrusion step S320 of the insulating layer 130, the inside of the insulating layer 130 is slowly cooled while the outside of the insulating layer 130 is rapidly cooled, so that a predetermined amount of the base polymer (A) is crystallized inside the insulating layer 130, whereas the resin component is solidified in a nearly amorphous state outside the insulating layer 130. This allows the elasticity of the insulating layer 130 to vary in the thickness direction of the insulating layer 130.

[0153] On the other hand, since the insulating layer 130 contains a predetermined amount of modified polymer (B), the polar groups in the modified polymer (B) can be uniformly dispersed in the insulating layer 130. This allows the space charge trapping effect of the modified polymer (B) to be uniformly achieved in the insulating layer 130. That is, even if the crystallinity of the insulating layer 130 varies in the thickness direction of the insulating layer 130 as described above, variations in the insulating properties due to the crystallinity distribution can be suppressed. As a result, the insulating properties of the insulating layer 130 can be made uniform in the thickness direction of the insulating layer 130.

[0154] As described above, according to this embodiment, it is possible to obtain a desired distribution of elasticity in the thickness direction of the insulating layer 130, while making the insulating properties of the insulating layer 130 uniform in the thickness direction of the insulating layer 130. As a result, it is possible to obtain a power cable 10 in which the flexibility, strength, and insulating properties of the insulating layer 130 are improved.

[0155] (b) In this embodiment, the ratio of the storage modulus of the inner sample of the insulating layer 130 to the storage modulus of the outer sample of the insulating layer 130 can be set to 1.1 or more and 2.5 or less.

[0156] By setting the elastic modulus ratio to 1.1 or more, the outside of the insulating layer 130 can be made relatively soft, while the inside of the insulating layer 130 can be made relatively hard. By making the outside of the insulating layer 130 relatively soft, the flexibility of the power cable 10 can be improved. For example, excessive restrictions on the reel diameter when winding the power cable 10 around a reel can be avoided. Furthermore, by making the inside of the insulating layer 130 relatively hard, the rigidity of the power cable 10 can be ensured. In this way, it is possible to achieve both flexibility and strength of the insulating layer 130.

[0157] On the other hand, by setting the elastic modulus ratio to 2.5 or less, it is possible to suppress the occurrence of voids due to stress differences within the insulating layer 130. This makes it possible to suppress a decrease in the dielectric breakdown strength (for example, DC breakdown field strength) of the insulating layer 130.

[0158] (c) In this embodiment, by uniformly dispersing a predetermined amount of polar groups in the modified polymer (B) that trap space charges in the insulating layer 130, the ratio of the volume resistivity of the inner sample of the insulating layer 130 to the volume resistivity of the outer sample of the insulating layer 130 can be set to 1.0 or more and 1.5 or less. For example, by rapidly cooling the insulating layer 130 after the extrusion step S320, even if the crystallinity of the outer portion of the insulating layer 130 becomes relatively low, it is possible to suppress a decrease in the insulating properties of the outer portion of the insulating layer 130. As a result, the insulating layer 130 of the power cable 10 as a whole can achieve the required sufficient insulating properties.

[0159] (d) In this embodiment, even when the thickness of the insulating layer 130 is set to 3 mm or more, it is possible to obtain a desired distribution of elasticity in the thickness direction of the insulating layer 130, while making the insulating properties of the insulating layer 130 uniform in the thickness direction of the insulating layer 130. Therefore, even when the power cable 10 of this embodiment is applied to high-voltage applications, it is possible to stably achieve both the flexibility of the insulating layer 130 and the insulating properties of the insulating layer 130.

[0160] <Other Embodiments of the Present Disclosure> Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present disclosure.

[0161] In the above-described embodiment, the power cable 10 does not necessarily have a water-shielding layer. However, the present disclosure is not limited to this case. The power cable 10 may have a simple water-shielding layer. Specifically, the simple water-shielding layer may be, for example, a metal laminate tape. The metal laminate tape has a metal layer made of, for example, aluminum or copper, and an adhesive layer provided on one or both sides of the metal layer. The metal laminate tape is, for example, wrapped longitudinally around the outer periphery of the cable core (outer than the outer semiconductive layer). The water-shielding layer may be provided outside the shielding layer or may also serve as the shielding layer. This configuration can reduce the cost of the power cable 10.

[0162] In the above-described embodiment, the power cable 10 is configured to be laid on land, underwater, or on the bottom of the water, but the present disclosure is not limited to this. For example, the power cable 10 may be configured as a so-called overhead electric wire (overhead insulated electric wire).

[0163] In the above embodiment, three layers are simultaneously extruded in the cable core forming step S300, but each layer may be extruded one by one. [Example]

[0164] Next, examples according to the present disclosure will be described. These examples are examples of the present disclosure, and the present disclosure is not limited to these examples.

[0165] (1) Power cable production As shown in Tables 1 and 2 below, for each of Samples A1 to A8 and B1 to B9, the resin composition was mixed in a Banbury mixer and granulated into pellets using an extruder. Next, a 2500 mm cross-sectional area conductor was formed by twisting together conductor core wires made of dilute copper alloys and having a diameter of 14 mm.2 The conductors were prepared. After the conductors were prepared, a resin composition for the inner semiconductive layer containing an ethylene-ethyl acrylate copolymer, the above-mentioned resin composition, and a resin composition for the outer semiconductive layer composed of the same materials as the resin composition for the inner semiconductive layer were fed into extruders A to C, respectively. The extrudates from extruders A to C were guided to a common head, and the inner semiconductive layer, insulating layer, and outer semiconductive layer were simultaneously extruded from the inside to the outside around the conductor. The thicknesses of the inner semiconductive layer, insulating layer, and outer semiconductive layer were set to 0.5 mm, 9 mm, and 0.5 mm, respectively. After the extrusion process, the extruded material was cooled using a cooling method appropriate for each sample. As a result, power cables A1 to A8 and B1 to B9 were manufactured.

[0166] The conditions for each sample are as shown in Tables 1 and 2 and below.

[0167] <Samples A1~A8> (Base polymer (A)) Random Polypropylene (r-PP): Stereoregularity: Isotactic Density: 0.9g / ml, Melting point: 150℃, Heat of fusion: 60J / g Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 1150 MPa

[0168] (Modified polymer (B)) Maleic anhydride modified polypropylene (MAH-PP): Maleic anhydride modification amount: 5% by mass, Melting point: 160℃ Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 1300 MPa

[0169] (Thermoplastic elastomer (C)) Styrene-ethylene-butylene-styrene block copolymer (SEBS): Styrene unit content: 25% by mass, Melting point: None Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 120 MPa

[0170] Ethylene Propylene Rubber (EPR): Ethylene unit content: 25% by mass, Melting point: None, Heat of fusion: None Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 80 MPa

[0171] (Extrusion process) Extrusion temperature: 190℃

[0172] (cooling process) In the cooling process for samples A1 to A8, rapid cooling was performed as follows: The cable cores formed by the extrusion process were successively immersed in a water tank containing cooling water cooled by a chiller, thereby rapidly cooling the insulating layer starting from the region close to the outer circumferential surface of the insulating layer.

[0173] In each of the samples A1 to A8, the temperature of the water bath was adjusted within the range of -50°C to 50°C, so that the cooling rate at the temperature of 110°C on the outside of the insulating layer was 40°C / min to 300°C / min.

[0174] Meanwhile, for a period of 800 seconds immediately after the extrusion process for extruding the insulating layer, the conductor was heated by electromagnetic induction so that the temperature of the conductor reached 110°C, while the insulating layer was cooled starting from the region close to the outer periphery of the insulating layer.

[0175] <Samples B1~B4> Samples B1 to B4 were prepared in the same manner as samples A1 to A4, respectively, except that the following slow cooling was carried out in the cooling step.

[0176] (cooling process) In the cooling process for Samples B1 to B4, the cable cores formed by the extrusion process were first air-cooled for 700 seconds. Then, the cable cores formed by the extrusion process were sequentially immersed in a water bath containing cooling water cooled by a chiller. This cooled the insulating layer starting from the region close to the outer circumferential surface of the insulating layer. The temperature of the water bath at this time was set to 25°C.

[0177] <Sample B5~B8> Samples B5 to B8 were prepared in the same manner as sample A3, except that the content of the modified polymer (B) and the content of the thermoplastic elastomer (C) were different from those of sample A3.

[0178] <Sample B9> Sample B9 was produced in the same manner as Sample A3, except that in the cooling process, the temperature of the water bath was adjusted to -25°C, so that the cooling rate at an insulating layer temperature of 110°C was 312°C / min.

[0179] (2) Evaluation (Temperature transition) For each of Sample A3 and Sample B1, the temperature transition during the cooling process was measured as follows. Immediately after the extrusion process for each sample, a thermocouple was placed (pierced) at the location where the outer sample of the insulating layer was taken and at the location where the inner sample of the insulating layer was taken. Then, during the cooling process, the temperature transition at each location was measured using the thermocouple. From the measurement results, the cooling rate at a temperature of 110°C at the location where the outer sample was taken was calculated.

[0180] (Sample collection after cooling process) After the cooling process, the insulation layer of each of the power cables, samples A1 to A8 and B1 to B9, was thinly sliced ​​circumferentially. The outer samples were taken from a position 0.3 mm from the outer surface of the insulation layer toward the conductor. The inner samples were taken from a position 0.3 mm from the inner surface toward the outer surface of the insulation layer. The size of each sample for dynamic viscoelasticity measurement was 5 mm long, 42 mm wide, and 0.5 mm thick. The size of each sample for volume resistivity and DC breakdown field strength measurement was 50 mm long, 50 mm wide, and 0.2 mm thick.

[0181] (storage modulus) The storage modulus of the insulating layer in each sample was measured by dynamic viscoelasticity measurement (DMA) in accordance with JIS K7244-4:1999 under the following conditions. Measuring device: DVA-200 manufactured by IT Measurement and Control Co., Ltd. Measurement mode: Tensile mode Distortion: 0.08% Frequency: 10Hz Temperature range: 0°C to 200°C Heating rate: 10℃ / min

[0182] At this time, the storage modulus of the outer sample and the elastic modulus of the inner sample were measured at 25°C by the above-mentioned DMA.

[0183] (volume resistivity) The volume resistivity of the insulating layer in each sample was measured as follows. First, flat electrodes with a diameter of 25 mm were placed on the first surface of the sheet serving as the outer or inner sample and on the second surface opposite the first surface. After the electrodes were placed, the sheet was immersed in silicone oil at a temperature of 90°C. In this state, a DC electric field of 80 kV / mm was applied to the sheet. This allowed the volume resistivity to be measured.

[0184] (DC breakdown field strength) The DC breakdown field strength of the insulating layer of each sample was measured as follows. Specifically, as in the measurement of volume resistivity, flat electrodes with a diameter of 25 mm were placed on the first surface of the sheet serving as the outer or inner sample and on the second surface opposite the first surface. After the electrodes were placed, the sheet was immersed in silicone oil at a temperature of 90°C. In this state, the applied voltage was increased at a rate of 4 kV / min. The DC breakdown field strength of the sheet was then measured when the sheet reached dielectric breakdown. For both the outer and inner samples, a DC breakdown field strength of 160 kV / mm or greater was evaluated as A (good). On the other hand, a DC breakdown field strength of less than 160 kV / mm for at least either the outer or inner sample was evaluated as B (poor).

[0185] (3) Results The evaluation results of each sample are explained with reference to Figures 2 and 3 and the following Tables 1 and 2. In the "Cooling Method" section of each table, "slow cooling" means that slow cooling was performed in the same manner as for Sample B1. "Rapid cooling" means that rapid cooling was performed in the same manner as for Sample A3.

[0186] [Table 1]

[0187] [Table 2]

[0188] <Comparison of temperature changes> (Sample B1) During the air-cooling period after the extrusion process of sample B1, the temperature gradually decreased at both the outer and inner sample locations, as shown in Figure 3. At the outer sample location, the cooling rate from a temperature of 110°C was 2.5°C / min.

[0189] After that, the cable core was water-cooled, which accelerated the cooling rate at the outer sample collection position. However, the cable core was water-cooled after the temperature had already dropped to around 100°C at both the outer sample collection position and the inner sample collection position. Therefore, the temperature difference between these positions did not increase.

[0190] Thus, in sample B1, the cooling rate of the base polymer on the outside of the insulating layer was close to the cooling rate of the base polymer on the inside of the insulating layer.

[0191] (Sample A3) In contrast, as shown in Figure 2, for sample A3, the cable core was water-cooled immediately after the extrusion process. This resulted in a rapid drop in temperature at the outer sample extraction position. The cooling rate at the outer sample extraction position from a temperature of 110°C was 150°C / min.

[0192] On the other hand, for a period of 800 seconds immediately after the extrusion process of sample A3, the conductor was subjected to electromagnetic induction heating so that the conductor temperature reached 110°C. As a result, the temperature at the location where the inner sample was taken gradually decreased. After that, the electromagnetic induction heating was stopped, and the temperature at the location where the inner sample was taken also began to decrease below 100°C due to water cooling of the cable core. However, the temperature at the location where the inner sample was taken had already decreased to around 110°C, and the temperature at the location where the inner sample was taken gradually decreased.

[0193] Thus, in sample A3, the outside of the insulating layer was cooled rapidly, whereas the inside of the insulating layer was cooled slowly.

[0194] <Comparison of each characteristic> (Samples B1 to B4) In samples B1 to B4, the contents of the base polymer (A), the modified polymer (B) and the thermoplastic elastomer (C) were the same as those in samples A1 to A4, respectively, but the insulating layer was slowly cooled.

[0195] For this reason, in samples B1 to B4, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was close to 1. However, in samples B1 to B4, the ratio of the storage modulus of the inner sample to the storage modulus of the outer sample was also close to 1.

[0196] In Samples B1 to B4, the degree of crystallinity of the insulating layer was high and uniform in the thickness direction due to the slow cooling of the insulating layer, which is thought to be why the elasticity of the insulating layer was also uniform in the thickness direction in Samples B1 to B4.

[0197] (Sample B5) In sample B5, the outer side of the insulating layer was quenched as in sample A3, but the modified polymer (B) was not added to the insulating layer.

[0198] Therefore, in sample B5, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was greater than 1.5. The outer sample of sample B5 had a DC breakdown field strength of less than 160 kV / mm.

[0199] In sample B5, the rapid cooling of the insulating layer caused a distribution (variation) in the degree of crystallinity across the thickness of the insulating layer. Furthermore, because modified polymer (B) was not added to the insulating layer, the space charge trapping effect of modified polymer (B) was not obtained. This is thought to have resulted in a decrease in the insulating properties of the insulating layer in sample B5 and variations across the thickness of the insulating layer.

[0200] (Sample B6) In sample B6, the outer side of the insulating layer was rapidly cooled in the same manner as in sample A3, but the content of the modified polymer (B) in the insulating layer was more than 10 parts by mass.

[0201] Therefore, in sample B6, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was more than 1.5. The DC breakdown field strength of both the outer and inner samples of sample B6 was less than 160 kV / mm.

[0202] In sample B6, the content of modified polymer (B) in the insulating layer exceeded 10 parts by mass, which reduced the moldability of the insulating layer. This reduced moldability also reduced the insulating properties of the insulating layer. As a result, it is believed that the insulating properties of the insulating layer in sample B6 were reduced and varied in the thickness direction of the insulating layer.

[0203] (Sample B7) In sample B7, the outer side of the insulating layer was quenched as in sample A3, but the content of the thermoplastic elastomer (C) in the insulating layer was less than 10 parts by mass.

[0204] Therefore, in sample B7, the storage modulus of the inner specimen was particularly high. As a result, the ratio of the storage modulus of the inner specimen to that of the outer specimen exceeded 2.5. The DC breakdown field strength of the outer specimen of sample B7 was less than 160 kV / mm.

[0205] In sample B7, the content of thermoplastic elastomer (C) in the insulating layer was less than 10 parts by mass, so the thermoplastic elastomer (C) did not provide sufficient flexibility. As a result, the elasticity of the insulating layer varied greatly in the thickness direction of the insulating layer. Furthermore, voids occurred due to stress differences within the insulating layer. As a result, it is believed that the dielectric breakdown strength of sample B7 decreased due to the occurrence of voids in the insulating layer.

[0206] (Sample B8) In sample B8, the outer side of the insulating layer was quenched as in sample A3, but the content of the thermoplastic elastomer (C) in the insulating layer was more than 45 parts by mass.

[0207] Therefore, in sample B8, the volume resistivity was low overall, and the ratio of the volume resistivity of the inner sample to that of the outer sample exceeded 1.5. The DC breakdown field strength of both the outer and inner samples of sample B8 was less than 160 kV / mm.

[0208] In sample B8, the content of amorphous thermoplastic elastomer (C) in the insulating layer exceeded 45 parts by mass, which reduced the insulating properties that are inherently required of polypropylene with a high melting point as the base polymer (A). As a result, it is believed that the insulating properties of the insulating layer in sample B8 were reduced and varied in the thickness direction of the insulating layer.

[0209] (Sample B9) In sample B9, the cooling rate at the temperature of 110°C at the outer sample collection position of the insulating layer was more than 310°C / min.

[0210] Therefore, in sample B9, the ratio of the storage modulus of the inner sample to the storage modulus of the outer sample was more than 2.5. The DC breakdown field strength of the outer sample of sample B9 was less than 160 kV / mm.

[0211] In sample B9, the cooling rate of the outer insulating layer was too fast, resulting in excessive variation in the crystallinity of the insulating layer along its thickness. This resulted in significant variation in the elasticity of the insulating layer along its thickness. Furthermore, voids were generated due to stress differences within the insulating layer. As a result, it is believed that the generation of voids in the insulating layer caused a decrease in the dielectric breakdown strength of sample B9.

[0212] (Samples A1 to A8) In contrast, in samples A1 to A8, a modified polymer (B) and a thermoplastic elastomer (C) were added to the insulating layer. In samples A1 to A8, the content of the modified polymer (B) in the insulating layer was 1 part by mass or more and 10 parts by mass or less, and the content of the thermoplastic elastomer (C) in the resin composition was 10 parts by mass or more and 45 parts by mass or less. Furthermore, in samples A1 to A8, the outside of the insulating layer was rapidly cooled as described above. At this time, the cooling rate at a temperature of 110°C at the sampling position of the outer sample of the insulating layer was 30°C / min or more and 310°C / min or less.

[0213] As a result, for samples A1 to A8, the ratio of the storage modulus of the inner sample to the storage modulus of the outer sample was 1.1 or more and 2.5 or less. For samples A1 to A8, the ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample was 1.0 or more and 1.5 or less. For samples A1 to A8, the DC breakdown field strength was 160 kV / mm or more.

[0214] From the results of the above samples A1 to A8, it was confirmed that it is possible to obtain a power cable in which the desired distribution of elasticity in the thickness direction of the insulating layer is achieved while the insulating properties of the insulating layer are made uniform in the thickness direction of the insulating layer.

[0215] <Additional Notes> The following appendix describes aspects of the present disclosure. The aspects referenced by the numbers in brackets [ ] to which the appendix follows correspond to the aspects described in <Embodiments of the present disclosure>.

[0216]

[10] The styrene elastomer contains a styrene unit and at least one of a propylene unit and a butene unit. The power cable according to [4] above.

[0217]

[11] The olefin-based elastomer contains at least one of a propylene unit and a butene unit. The power cable according to [5] above.

[0218]

[12] The volume resistivity of the outer sample and the volume resistivity of the inner sample were each 7.0×10 14 Ω·cm or more, Here, the volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90°C and a DC electric field of 80 kV / mm. A power cable according to any one of [2] to [7],

[10] and

[11] above.

[0219]

[13] At the location where the outer sample of the insulating layer is taken, the cooling rate at a temperature of 110°C is 30°C / min or more. A method for manufacturing a power cable according to [8] above.

[0220]

[14] In the step of cooling the insulating layer, The conductor is heated by electromagnetic induction so that the temperature of the conductor is 80°C or more and 110°C or less. A method for manufacturing a power cable according to [9] above. [Explanation of symbols]

[0221] 10 Power Cable 110 Conductor 120 Internal semiconductive layer 130 Insulating layer 140 outer semiconductive layer 150 Shielding layer 160 Sheath

Claims

1. A resin composition constituting an insulating layer that is provided to cover a conductor of a power cable and has an inner circumferential surface facing the conductor and an outer circumferential surface opposite to the inner circumferential surface, a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, The resin composition comprises The ratio of the storage modulus of the inner sample of the insulating layer to the storage modulus of the outer sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is set to be 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. Resin composition.

2. A conductor; an insulating layer provided to cover an outer periphery of the conductor, the insulating layer having an inner periphery facing the conductor and an outer periphery opposite to the inner periphery; Equipped with The insulating layer is a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; Including, a ratio of the storage modulus of an inner sample of the insulating layer to the storage modulus of an outer sample of the insulating layer is 1.1 or more and 2.5 or less; a ratio of the volume resistivity of the inner sample to the volume resistivity of the outer sample is 1.0 or more and 1.5 or less; where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. Power cable.

3. When the total content of the base polymer, the modified polymer, and the thermoplastic elastomer in the insulating layer is 100 parts by mass, the content of the modified polymer in the insulating layer is 1 part by mass or more and 10 parts by mass or less; The content of the thermoplastic elastomer in the insulating layer is 10 parts by mass or more and 45 parts by mass or less. The power cable according to claim 2.

4. The thermoplastic elastomer includes a styrene-based elastomer. The power cable according to claim 2 or 3.

5. The thermoplastic elastomer includes an olefin-based elastomer. The power cable according to claim 2 or 3.

6. the storage modulus of the inner sample of the insulating layer is 650 MPa or more and 900 MPa or less; The storage modulus of the outer sample of the insulating layer is 280 MPa or more and 670 MPa or less. The power cable according to claim 2 or 3.

7. The thickness of the insulating layer is 3 mm or more. The power cable according to claim 2 or 3.

8. preparing a resin composition; forming an insulating layer from the resin composition so as to cover an outer periphery of the conductor, and forming an inner circumferential surface of the insulating layer facing the conductor and an outer circumferential surface facing the inner circumferential surface; Equipped with In the step of preparing the resin composition, The resin composition includes: a base polymer comprising propylene units; a modified polymer containing a propylene unit and modified with at least one selected from an unsaturated organic acid and a derivative thereof; a thermoplastic elastomer; providing a composition comprising: The step of forming the insulating layer includes: extruding the insulating layer around the outer periphery of the conductor; cooling the insulating layer so that a ratio of the storage modulus of the inner sample of the insulating layer to that of the outer sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of the volume resistivity of the inner sample to that of the outer sample is 1.0 or more and 1.5 or less; having where: the outer sample of the insulating layer is taken from a position 0.3 mm from the outer peripheral surface toward the conductor; the inner sample of the insulating layer is taken from a position 0.3 mm from the inner circumferential surface toward the outer circumferential surface, The storage modulus of the outer sample and the storage modulus of the inner sample are measured at 25°C by dynamic viscoelasticity measurement, The volume resistivity of the outer sample and the volume resistivity of the inner sample are measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm. Power cable manufacturing method.

9. In the step of cooling the insulating layer, During at least a part of the period immediately after the step of extruding the insulating layer, the insulating layer is cooled from a region close to the outer circumferential surface of the insulating layer while the conductor is being electromagnetically induction heated. The method for manufacturing a power cable according to claim 8.

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