Power Cable

Abstract

A resin composition which contains a resin component that comprises a propylene unit, and a resistance imparting agent, wherein: the resistance imparting agent is composed of a monomer which has a phenolic skeleton wherein a hydrogen atom or an alkyl group having from 1 to 3 carbon atoms is bonded to at least one of the ortho positions of the hydroxyl group, and which has a melting point of 215°C or less and a molecular weight of from 200 to 500; the content of the resistance imparting agent is from 0.4 part by mass to 10 parts by mass relative to 100 parts by mass of the resin component; and the content ratio of metal impurities is 0.02% by volume or less.

Description

[Technical field]

[0001] This application claims priority to Japanese application "Patent Application No. 2020-211491" filed on December 21, 2020, and incorporates all of the contents of the above-mentioned Japanese application by reference.

[0002] The present disclosure relates to a resin composition and a power cable. [Background technology]

[0003] Cross-linked polyethylene has excellent insulating properties and has therefore been widely used as a resin component constituting the insulating layer in power cables and the like (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 57-69611 Summary of the Invention

[0005] According to one aspect of the present disclosure, Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metal impurities is 0.02% or less. A resin composition is provided.

[0006] According to another aspect of the present disclosure, A conductor; an insulating layer covering the outer periphery of the conductor; Equipped with The insulating layer is formed from a resin composition, The resin composition comprises Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metal impurities is 0.02% or less. A power cable is provided. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view perpendicular to the axial direction of a power cable according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Problem that this disclosure aims to solve] Cross-linked polyethylene that has deteriorated over time cannot be recycled and must be incinerated, which has raised concerns about its impact on the environment.

[0009] In recent years, therefore, resins containing propylene (hereinafter also referred to as "propylene-based resins") have been attracting attention as resin components constituting the insulating layer. Propylene-based resins can achieve high insulation even when they are not crosslinked. In other words, they can achieve both insulation and recyclability. Furthermore, the use of propylene-based resins can improve handling, processability, and ease of manufacture.

[0010] However, when a propylene-based resin is used as the resin component constituting the insulating layer, the insulating properties inherent to the propylene-based resin may not be obtained.

[0011] An object of the present disclosure is to provide a technique for improving the insulating properties of a resin composition containing a propylene-based resin.

[0012] [Effects of this disclosure] According to the present disclosure, it is possible to improve the insulating properties of a resin composition containing a propylene-based resin.

[0013] [Description of the embodiments of the present disclosure] <Knowledge gained by the inventors> First, the findings of the inventors will be outlined.

[0014] Generally, propylene-based resins have a large amount of crystals and tend to form coarse crystals. Therefore, when an insulating layer is formed using only propylene-based resin, the insulating layer tends to be hard. Therefore, when using propylene-based resin as a resin component constituting an insulating layer, it is necessary to mix a low-crystalline resin to control the crystallinity of the propylene-based resin.

[0015] The present inventors formed an insulating layer by low-crystallizing a propylene-based resin, but found that the insulating properties varied depending on when the power cable was produced, and the insulating properties inherent to the propylene-based resin were sometimes not obtained.

[0016] As a result of investigating this issue, it was found that the variation in insulation properties was caused by foreign matter mixed into the resin composition during the manufacturing process of the power cable. Such foreign matter included, for example, metallic impurities such as fine metal powder derived from the metal conductor and carbides (amber) generated by burning the resin components. Among these foreign matter, metallic impurities in particular had an effect on insulation properties, and depending on the amount of such impurities mixed in, the insulation properties of the power cable could vary greatly.

[0017] Metallic impurities have poor adhesion to the resin component, which causes a sudden change in resistance at the interface with the resin component and reduces the insulating properties. In addition, if the metallic impurities have a protruding shape, the electric field tends to concentrate, which reduces the insulating properties.

[0018] In the insulating layer containing such a propylene-based resin, metallic impurities mixed in during the manufacturing process can cause variations in the insulating properties.

[0019] The present inventors have studied the above-mentioned problem and found that the variation in insulation can be suppressed by using a specific additive. This additive is used as an antioxidant, and is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, a molecular weight of 200 to 500, and a melting point of 215°C or less, which is lower than the heating and mixing temperature of the propylene-based resin.

[0020] The above-mentioned monomer has been generally used as an antioxidant up to now, but according to the study by the present inventors, it has been found that the monomer has a chemical structure with high affinity for metal impurities and a predetermined molecular weight and melting point, and thus can melt and coat the surface of the metal impurities when the resin composition is heated and mixed. By coating the surface, it acts to alleviate the sudden resistance change at the interface between the metal impurities and the resin component, and also acts to alleviate the electric field concentration on the metal impurities. As a result, it is possible to suppress the deterioration of insulation due to metal impurities. In other words, the above-mentioned monomer acts not only as an antioxidant, but also as a resistance imparting agent that imparts resistance to the deterioration of insulation due to metal impurities to the insulating layer.

[0021] The inventors have also found that by blending a prescribed amount of the above compound in a resin composition containing a propylene-based resin, it is possible to suppress deterioration in insulating properties caused by metal impurities mixed into the resin composition.

[0022] The present disclosure is based on the above-mentioned findings of the inventors.

[0023] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0024] [1] A resin composition according to one embodiment of the present disclosure, Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metallic impurities is 0.02% or less. According to this configuration, the insulating properties of the resin composition containing the propylene-based resin can be improved.

[0025] [2] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer covering the outer periphery of the conductor; Equipped with The insulating layer is formed from a resin composition, The resin composition comprises Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metallic impurities is 0.02% or less. According to this configuration, the insulation properties of the power cable can be improved.

[0026] [3] In the power cable according to the above [2], The resin component includes at least one of an ethylene unit and a styrene unit. According to this configuration, excessive crystal growth of the propylene-based resin can be suppressed, and the insulating layer can have high insulation properties as well as desired flexibility.

[0027] [4] The power cable according to the above [2] or [3], The resistance-imparting agent has a linear carbon chain structure having 5 to 10 carbon atoms. This configuration can impart electrical stability to the insulating layer.

[0028] [5] In the power cable according to any one of [2] to [4] above, The resistance imparting agent contains a sulfur atom. This configuration can impart electrical stability to the insulating layer.

[0029] [6] The power cable according to any one of [2] to [5] above, The resistance imparting agent has a melting point such that it is in a liquid state at 27°C. According to this configuration, the surface of the metal impurities can be more reliably covered with the resistance imparting agent, and the deterioration of the insulation property due to the metal impurities can be more effectively suppressed.

[0030] [7] In the power cable according to any one of [2] to [6] above, The resistance imparting agent is a phenolic antioxidant. According to this configuration, the effect of the antioxidant can be imparted to the insulating layer.

[0031] [8] The power cable according to any one of [2] to [7] above, The resin composition contains, as a propylene-based resin, a propylene homopolymer having a melting point of 160° C. or more and 175° C. or less and a heat of fusion of 100 J / g or more and 120 J / g or less, The resin composition has a melting point of 158° C. or more and 168° C. or less, and a heat of fusion of 55 J / g or more and 110 J / g or less. According to this configuration, excessive crystal growth of the propylene-based resin in the insulating layer can be suppressed, and higher insulating properties can be obtained.

[0032] [9] The power cable according to any one of [2] to [7] above, The resin composition contains, as a propylene-based resin, a propylene random copolymer having a melting point of 140° C. or more and 155° C. or less and a heat of fusion of 90 J / g or more and 105 J / g or less, The resin composition has a melting point of 140° C. or more and 150° C. or less, and a heat of fusion of 55 J / g or more and 100 J / g or less. According to this configuration, excessive crystal growth of the propylene-based resin in the insulating layer can be suppressed, and higher insulating properties can be obtained.

[0033] [Details of the embodiment of the present disclosure] Next, an 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.

[0034] <One embodiment of the present disclosure> (1) Resin composition The resin composition of the present embodiment is a material for forming the insulating layer 130 of the power cable 10 described later, and contains, for example, a resin component containing a propylene unit, a resistance imparting agent, and other additives as necessary. The resin composition also contains metal impurities that are inevitably mixed in during the manufacturing process.

[0035] Metal impurities are mixed in, for example, during the polymerization stage of the material, or during the mixing and extrusion stage of the material, and are metal powders containing copper, iron, their alloys, or other metals used at the manufacturing site. The size of the metal powder is not particularly limited, but is, for example, 50 μm or more and 500 μm or less. The content of metal impurities, that is, the amount of contamination, is 0.02% or less by volume. The content of metal impurities is, for example, 100 mm from the resin composition. 3 The volume of a sample piece is calculated assuming that the metal impurities contained in the sample piece are spherical, and the volume ratio is obtained.

[0036] The resin composition of the present embodiment contains at least a propylene-based resin as a resin component. Therefore, when the resin composition is analyzed by a nuclear magnetic resonance (NMR) device, at least a propylene unit is detected. For example, when the propylene-based resin is a random polypropylene, a propylene unit and an ethylene unit are detected, and when the propylene-based resin is a propylene homopolymer, a propylene unit is detected.

[0037] The resin component preferably contains at least one of a low crystalline resin and a styrene resin as a soft component that reduces the crystallinity of the propylene resin and increases the flexibility of the insulating layer. When the resin component contains a low crystalline resin or a styrene resin, monomer units derived from these resins are detected when the resin composition is analyzed by NMR. For example, when the low crystalline resin contains ethylene propylene rubber (EPR) described later, propylene units and ethylene units derived from the low crystalline resin are detected. Also, when a styrene resin is contained, styrene units derived from the low crystalline resin are detected.

[0038] Each component will be described below.

[0039] (Propylene-based resin) The propylene-based resin is the base polymer of the resin composition and is the component with the highest content in the resin components. As the propylene-based resin, for example, a propylene homopolymer (hereinafter also referred to as homo PP) or a propylene random copolymer (hereinafter also referred to as random PP) can be used. From the viewpoint of obtaining higher insulation in the insulating layer, it is preferable to use random PP. Homo PP has a larger amount of crystals than random PP and can obtain high insulation, but since cracks occur in the crystals or between the crystals in the insulating layer, the inherent insulation may not be obtained. In contrast, since random PP contains ethylene units, the amount of crystals is low, but cracks due to coarse crystallization are unlikely to occur in the insulating layer, and higher insulation can be obtained compared to homo PP.

[0040] The stereoregularity of the propylene-based resin is not particularly limited, but is preferably isotactic. When mixed with a low-crystalline resin, the isotactic propylene-based resin can be crystallized to a lower degree than syndiotactic or atactic resins, thereby improving the brittleness of the insulating layer at low temperatures and improving the insulating properties.

[0041] The melting point and heat of fusion of the propylene-based resin are not particularly limited. For example, in the case of homo PP, the melting point is preferably 160°C to 175°C, and the heat of fusion is preferably 100 J / g to 120 J / g. Also, in the case of random PP, the melting point is preferably 140°C to 155°C, and the heat of fusion is preferably 90 J / g to 105 J / g.

[0042] (Low crystalline resin) The low crystalline resin is a component that controls the crystal growth (amount of crystals) of the propylene-based resin and imparts flexibility to the insulating layer. Here, the low crystalline resin refers to a component that has low crystallinity or is amorphous and does not have a melting point, or if it does have a melting point, the melting point is 100° C. or less. The heat of fusion of the low crystalline resin is, for example, 50 J / g or less, preferably 30 J / g or less.

[0043] From the viewpoint of improving the controllability of crystal growth and the flexibility of the insulating layer, the low crystalline resin is preferably a copolymer of at least two of ethylene, propylene, butene, hexene, and octene. Note that the carbon-carbon double bond in the monomer unit constituting the low crystalline resin is preferably at the α-position, for example.

[0044] Examples of low crystalline resins include ethylene propylene rubber (EPR) and very low density polyethylene (VLDPE). Very low density polyethylene has a density of, for example, 0.91 g / cm 3 Less than or equal to 0.855 g / cm 3 ~0.890g / cm 3It is polyethylene.

[0045] From the viewpoint of compatibility with propylene-based resins, the low crystalline resin is preferably a copolymer containing propylene, and among the above-mentioned copolymers containing propylene, EPR can be given.

[0046] The ethylene content of the EPR is, for example, 20% by mass or more, preferably 40% by mass or more, and more preferably 55% by mass or more. If the ethylene content is less than 20% by mass, the compatibility of the EPR with the propylene-based resin becomes excessively high. Therefore, even if the content of the EPR in the insulating layer is reduced, the insulating layer can be made flexible. However, the crystallization of the propylene-based resin cannot be sufficiently controlled, and the insulating properties may be reduced. In contrast, by setting the ethylene content to 20% by mass or more, it is possible to suppress the compatibility of the EPR with the propylene-based resin from becoming excessively high. This allows the crystallization of the propylene-based resin by the EPR to be sufficiently controlled while obtaining the softening effect by the EPR. As a result, the insulating properties can be suppressed from decreasing. Furthermore, by setting the ethylene content to preferably 40% by mass or more, and more preferably 55% by mass or more, it is possible to more stably control the crystallization and stably suppress the insulating properties from decreasing. The ethylene content indicates the mass ratio of the ethylene units to the ethylene units and propylene units constituting the EPR.

[0047] On the other hand, the low crystalline resin may be, for example, a copolymer that does not contain propylene. As the copolymer that does not contain propylene, for example, VLDPE is preferable from the viewpoint of easy availability. Examples of VLDPE include PE composed of ethylene and 1-butene, and PE composed of ethylene and 1-octene.

[0048] By using a copolymer not containing propylene as the low crystalline resin, it is possible to suppress complete compatibility with the propylene-based resin while mixing the low crystalline resin in a predetermined amount, and therefore, by making the content of such a copolymer equal to or more than a predetermined amount, it is possible to stably control the crystallization of the propylene-based resin.

[0049] (styrene resin) The styrene resin is a styrene thermoplastic elastomer containing styrene as a hard segment and at least one of ethylene, propylene, butylene, and isoprene as a soft segment. The styrene resin can be dispersed in a resin composition to control the crystal growth of the propylene resin, similar to the low crystalline resin. Specifically, when the styrene resin is mixed with the propylene resin together with the low crystalline resin, it is considered that the styrene resin forms a unique phase structure by finely dispersing the low crystalline resin in the propylene resin starting from the low crystalline resin, and this phase structure can suppress excessive crystal growth of the propylene resin. In addition, the styrene resin can trap electrons by the aromatic ring to form a stable resonance structure, so that the insulation of the insulating layer can be further improved. The styrene resin does not have a melting point or heat of fusion.

[0050] Examples of styrene-based resins include styrene-butadiene-styrene block copolymers (SBS), hydrogenated styrene-butadiene-styrene block copolymers, 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, etc. Two or more of these may be used in combination.

[0051] In this case, "hydrogenation" 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).

[0052] As the styrene-based resin, those that do not contain double bonds in the chemical structure except for the benzene ring are preferred. When those that have double bonds are used, the resin components may be thermally deteriorated during molding of the resin composition, and the properties of the resulting molded product may be reduced. In this respect, those that do not contain double bonds have high resistance to thermal deterioration, and therefore can maintain the properties of the molded product at a higher level.

[0053] The styrene content of the styrene resin is not particularly limited, but is preferably 5% by mass or more and 35% by mass or less from the viewpoints of controlling the crystal growth of the propylene resin and softening the molded body. The styrene content indicates the mass ratio of styrene units to the component units constituting the styrene resin.

[0054] (Resistance imparting agent) The resistance imparting agent is a component that covers metal impurities present in the insulating layer and alleviates a sudden change in resistance at the interface between the metal impurities and the insulating layer. Specifically, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, and having a melting point of 215° C. or less and a molecular weight of 200 to 500. Preferably, the resistance imparting agent is a phenol-based antioxidant having the above melting point, molecular weight and chemical structure.

[0055] The mechanism by which the resistance imparting agent covers the metal impurities and reduces the resistance change at the interface is presumed to be as follows.

[0056] In general, a resin component containing a resistance imparting agent and a propylene-based resin is mixed while being heated at, for example, 200°C to 220°C, since the melting point of the propylene-based resin is about 140°C to 160°C. Therefore, a resistance imparting agent having a melting point of 215°C or less tends to melt and become liquid during heating and mixing. This resistance imparting agent has polarity due to the phenol skeleton and has high affinity with metal impurities, so it is presumed that when heated and mixed with the resin component, it gathers around the metal impurities mixed in the resin component and covers the metal impurities.

[0057] Moreover, the resistance imparting agent has hydrogen or an alkyl group having 1 to 3 carbon atoms at at least one of the ortho positions of the hydroxyl group constituting the phenol skeleton, and no bulky substituent is arranged at at least one side of the ortho position of the hydroxyl group. In other words, the resistance imparting agent has little steric hindrance around the hydroxyl group. Therefore, the reactivity of the hydroxyl group in the resistance imparting agent tends to be high. In contrast, for example, in a monomer (so-called hindered phenol antioxidant) in which a bulky substituent (such as a t-butyl group) is arranged at two ortho positions of the hydroxyl group, the steric hindrance is large. In such a monomer, the reactivity of the hydroxyl group is inhibited by the steric hindrance, and the affinity with metal impurities is low. In this respect, according to the resistance imparting agent of the present embodiment, the steric hindrance is small and the reactivity of the hydroxyl group is high, so that the metal impurities can be covered more reliably than a component with a large steric hindrance such as a hindered phenol antioxidant.

[0058] Furthermore, by making the molecular weight of the resistance imparting agent 200 or more, it is possible to suppress the volatilization of the resistance imparting agent when the resin composition is heated and mixed. Furthermore, by making the molecular weight 500 or less, it is possible to suitably move the resistance imparting agent in the resin component. As a result, the aggregation of the resistance imparting agent in the resin composition is suppressed and the resistance imparting agent is uniformly dispersed, and the surface of the metal impurities present in the resin composition can be coated with the resistance imparting agent.

[0059] In addition, since the resistance imparting agent has polarity due to the phenol skeleton, it can provide a gradient to alleviate the sudden resistance change at the interface between the metal impurity and the insulating layer, and since it has an aromatic ring derived from the phenol skeleton, it can impart electrical stability to the periphery of the metal impurity due to the electron trapping effect.

[0060] In this way, the resistance imparting agent can act to cover the metal impurities in the insulating layer and to reduce the resistance change at the interface between the metal impurities and the insulating layer and the electric field concentration on the metal impurities.

[0061] The molecular weight of the resistance imparting agent is from 200 to 500. From the viewpoint of suppressing volatilization of the resistance imparting agent and suppressing aggregation of the resistance imparting agent to disperse it in the resin composition, the molecular weight of the resistance imparting agent is preferably from 300 to 450.

[0062] The melting point of the resistance imparting agent is not particularly limited as long as it is 215°C or less, but is preferably 130°C or less. By having a melting point of 130°C or less, the metal impurities can be more reliably covered with the resistance imparting agent when the resin composition is heated and mixed. Furthermore, the melting point is preferably a temperature at which the resistance imparting agent is in a liquid state at room temperature (27°C), and more specifically, it is more preferably 27°C or less. By having a melting point of 27°C or less, the resistance imparting agent can be made to flow even in the insulating layer and remain around the metal impurities. As a result, the surface of the metal impurities can be more reliably covered, so that the deterioration of insulation due to the metal impurities can be more suppressed. The lower limit is not particularly limited, but is preferably -30°C or more.

[0063] In the resistance-imparting agent, the number of phenol skeletons is not particularly limited as long as the molecular weight of the resistance-imparting agent is within the range of 200 or more and 500 or less.

[0064] In addition, from the viewpoint of improving compatibility with the resin component, the resistance imparting agent preferably has a straight-chain carbon chain structure having 5 to 10 carbon atoms in the phenol skeleton. By increasing the compatibility of the resistance imparting agent, the resistance imparting agent can be uniformly present in the resin composition, so that metal impurities can be covered more reliably. The number of straight-chain carbon chain structures is not particularly limited as long as the molecular weight of the resistance imparting agent is within the above range, but may be, for example, one or two. From the viewpoint of improving compatibility while satisfying the molecular weight range, the number of straight-chain carbon chain structures is preferably two. In addition, the straight-chain carbon chain structure may be located at the other side of the ortho position of the hydroxyl group. This is because if at least one of the ortho positions of the hydroxyl group has hydrogen or an alkyl group having 1 to 3 carbon atoms, the decrease in reactivity due to steric hindrance can be suppressed. In addition, the straight-chain carbon chain structure may be directly bonded to the aromatic ring, or may be bonded via another atom such as a sulfur atom or a nitrogen atom.

[0065] The resistance-imparting agent is a monomer containing carbon, hydrogen and oxygen atoms, and may contain sulfur and nitrogen atoms in addition to these atoms, and preferably contains sulfur atoms.

[0066] The resistance-imparting agent is not particularly limited as long as it satisfies the above-mentioned chemical structure, molecular weight and melting point. For example, 2-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol, 2-hydroxy-4-n-octyloxybenzophenone, 2,4-dihydroxybenzophenone, 2,2'-dihydroxy-4,4'-dimethoxybenzophenone, 2,4-bis(octylthiomethyl)-6-methylphenol, nonylphenol, dinonylphenol, etc. can be used. Among these, 2,4-bis(octylthiomethyl)-6-methylphenol is preferred because it has a sulfur atom and a linear carbon chain structure having 5 to 10 carbon atoms in its chemical structure and has high compatibility with the resin component.

[0067] The content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component. Preferably, it is 0.5 parts by mass or more and 8 parts by mass or less. By making it 0.4 parts by mass or more, it becomes easier to cover metal impurities with the resistance imparting agent, so that it is possible to mitigate the deterioration of insulation caused by metal impurities. In addition, if the amount of the resistance imparting agent added is excessively large, it becomes difficult to mold the resin composition into an insulating layer, but by making it 10 parts by mass or less, it is possible to ensure the moldability of the resin composition.

[0068] (Other additives) The resin composition may contain other additives as necessary, such as antioxidants, copper inhibitors, lubricants, and colorants other than the above-mentioned resistance imparting agents.

[0069] However, the resin composition preferably contains a small amount of additives that function as nucleating agents for generating propylene crystals, and more preferably does not contain such additives substantially. Specifically, the amount of additives that function as nucleating agents is preferably less than 1 part by mass, and more preferably 0 part by mass, when the total amount of the resin components is 100 parts by mass. This makes it possible to suppress the occurrence of unexpected abnormal crystallization caused by the nucleating agent and to easily control the amount of crystals.

[0070] From the viewpoint of recycling, the resin composition is preferably not crosslinked but may contain a crosslinking agent for crosslinking. However, even if crosslinking is performed, it is preferable to perform crosslinking so that the gel fraction (degree of crosslinking) is low. Specifically, it is preferable to perform crosslinking at a degree of crosslinking such that the residue of the crosslinking agent in the resin composition is less than 300 ppm by mass. When dicumyl peroxide is used as the crosslinking agent, the residue is, for example, cumyl alcohol, α-methylstyrene, etc.

[0071] (Melting point and heat of fusion of resin composition) The melting point and heat of fusion of the resin composition change depending on the content of each of the propylene-based resin and low crystalline resin used as the resin component, and are indicators of the resin composition. The melting point and heat of fusion of the resin composition are not particularly limited, but when the propylene-based resin contains random PP, the melting point is preferably 140°C or more and 150°C or less, and the heat of fusion is preferably 55J / g or more and 100J / g or less. More preferably, the melting point is 140°C or more and 148°C or less, and the heat of fusion is 55J / g or more and 95J / g or less. On the other hand, when the propylene-based resin contains homo PP, the melting point is preferably 158°C or more and 168°C or less, and the heat of fusion is preferably 55J / g or more and 110J / g or less. More preferably, the melting point is 158°C or more and 165°C or less, and the heat of fusion is 55J / g or more and 100J / g or less. By blending a propylene-based resin with at least one of a low crystalline resin and a styrene-based resin so as to obtain such a melting point and heat of fusion, excessive crystal growth of the propylene-based resin can be suppressed, and the characteristics of each resin can be obtained.

[0072] The "melting point" and "heat of fusion" referred to here are measured by differential scanning calorimetry (DSC). "Differential scanning calorimetry" is performed, for example, in accordance with JIS-K-7121 (1987). Specifically, in a DSC device, a measurement sample is heated from room temperature (normal temperature, for example, 27°C) to 220°C at a rate of 10°C / min. A DSC curve is obtained by plotting the amount of heat absorbed (heat flow) per unit time against the temperature.

[0073] The temperature at which the amount of heat absorbed per unit time in the sample is maximized (highest peak) is defined as the "melting point (peak melting temperature)." Assuming that all of the heat absorbed by the sample is caused by the resin components, the amount of heat absorbed by the sample from room temperature to 220°C (J) divided by the total mass (g) of the resin components in the sample (J / g) is defined as the "heat of fusion." The degree of crystallinity (%) of the sample can be calculated based on the heat of fusion of the sample and the theoretical value of the heat of fusion of a perfect crystal.

[0074] (Resin Composition) The content of each component contained in the resin composition is preferably appropriately changed so that the melting point and heat of fusion of the resin composition are within the above-mentioned range. For example, when the total of the propylene-based resin and the soft component containing at least one of the low crystalline resin and the styrene-based resin is 100 parts by mass, the resin composition preferably contains 55 parts by mass or more and 95 parts by mass or less of the propylene-based resin and 5 parts by mass or less and 45 parts by mass or less of the soft component. More preferably, the resin composition contains 60 parts by mass or more and 95 parts by mass or less of the propylene-based resin and 5 parts by mass or less and 40 parts by mass or less of the soft component. By setting the addition amount as such, the amount of crystals in the resin composition can be adjusted to an appropriate range. As a result, when an insulating layer is formed from the resin composition, the formation of voids in the insulating layer can be suppressed. The addition ratio of the low crystalline resin and the styrene-based resin is not particularly limited, and it is sufficient that the total addition amount of these satisfies the above-mentioned range.

[0075] (2) Power cable Next, the power cable of this embodiment will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view perpendicular to the axial direction of the power cable according to this embodiment.

[0076] 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 pipe), underwater, or at the bottom of the water. The power cable 10 is used, for example, for alternating current.

[0077] 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 .

[0078] (Conductor (conductive part)) The conductor 110 is formed by twisting together a plurality of conductor core wires (conductive core wires) containing, for example, pure copper, a copper alloy, aluminum, an aluminum alloy, or the like.

[0079] (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 has semiconductivity and is 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, and an ethylene-vinyl acetate copolymer, an olefin-based elastomer, the above-mentioned low crystalline resin, and the like, and conductive carbon black.

[0080] (insulating layer) The insulating layer 130 is provided so as to cover the outer periphery of the internal semiconducting layer 120, and is configured as the above-mentioned resin composition molded article. The insulating layer 130 is, for example, extrusion molded from the resin composition as described above.

[0081] (Outer semiconducting 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.

[0082] (shielding layer) The shielding layer 150 is provided so as to cover the outer periphery of the outer semiconductive layer 140. The shielding layer 150 is formed, for example, by winding a copper tape, or is formed as a wire shield in which a plurality of soft copper wires or the like are wound. Note that a tape made of a material such as a rubber-coated cloth may be wound on the inside or outside of the shielding layer 150.

[0083] (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.

[0084] If the power cable 10 of this embodiment is an underwater cable or an underwater cable, it may have a metal waterproof layer such as an aluminum sheath or an iron wire armor outside the shielding layer 150.

[0085] On the other hand, the power cable 10 of the present embodiment may not have a water-impermeable layer outside the shielding layer 150. In other words, the power cable 10 of the present embodiment may be configured to have a non-completely water-impermeable structure.

[0086] (Specific dimensions, etc.) Although there are no particular limitations on the specific dimensions of the power cable 10, for example, the diameter of the conductor 110 is 5 mm or more and 60 mm or less, the thickness of the inner semiconductive layer 120 is 0.5 mm or more and 3 mm or less, the thickness of the insulating layer 130 is 3 mm or more and 35 mm or less, the thickness of the outer semiconductive layer 140 is 0.5 mm or more and 3 mm or less, the thickness of the shielding layer 150 is 0.1 mm or more and 5 mm or less, and the thickness of the sheath 160 is 1 mm or more. The AC voltage applied to the power cable 10 of this embodiment is, for example, 20 kV or more.

[0087] (3) Cable characteristics In this embodiment, the insulating layer 130 (resin composition molded product) is configured to contain the above-mentioned resistance imparting agent, so that the following insulating properties can be obtained.

[0088] The insulating layer 130 of this embodiment exhibits high insulation properties when the content ratio of metal impurities is within the range of 0.02% or less by volume. Specifically, when a sample is formed from the above-mentioned resin composition and has a thickness of 0.4 mm, and copper pieces having a diameter of 200 μm or less are embedded as metal impurities, and an AC voltage of a commercial frequency (for example, 60 Hz) is applied at room temperature at 10 kV for 10 minutes, and then the voltage is increased by 1 kV and applied for 10 minutes repeatedly, the AC breakdown field strength is 45 kV / mm or more. In other words, if the content ratio of metal impurities is within the range of 0.02% or less by volume, the desired AC breakdown field strength can be obtained in the insulating layer, and high insulation properties can be ensured.

[0089] (4) Manufacturing method of power cables Next, a method for manufacturing the power cable according to the present embodiment will be described. Hereinafter, steps are abbreviated as "S".

[0090] (S100: Resin composition preparation step) First, a resin composition for forming the insulating layer 130 is prepared.

[0091] In this embodiment, a propylene-based resin as a resin component, a soft component containing at least one of a low crystalline resin and a styrene-based resin, a resistance imparting agent, and other additives as necessary are mixed (kneaded) by a mixer to form a mixture. During kneading, the molten resistance imparting agent gathers around the metal impurities contained in the resin component, thereby covering the metal impurities. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-shaft mixer, and a multi-shaft mixer.

[0092] In this case, the amount of each resin added may be, for example, 55 to 95 parts by mass of the propylene resin and 5 to 45 parts by mass of the soft component when the total content of the propylene resin and the soft component containing at least one of the low crystalline resin and the styrene resin is taken as 100 parts by mass. Also, the content of the resistance imparting agent is 0.4 to 10 parts by mass when the total content of the propylene resin and the low crystalline resin is taken as 100 parts by mass.

[0093] After the mixture is prepared, it is granulated by an extruder, thereby forming a pellet-like resin composition that will form the insulating layer 130. Note that the steps from mixing to granulation may be performed in one step using a twin-screw extruder that has a high kneading effect.

[0094] In the present embodiment, when the resin component and the resistance imparting agent are heated and mixed, the resistance imparting agent is melted to coat the surfaces of the metal impurities mixed in the resin component. In the resin composition, the resistance imparting agent is dispersed in the resin component and is present at the interface between the metal impurities and the resin component.

[0095] (S200: Conductor preparation process) On the other hand, conductor 110 is prepared by twisting together a plurality of conductor core wires.

[0096] (S300: Cable core forming process (extrusion process, insulation layer forming process)) After the resin composition preparing step S100 and the conductor preparing step S200 are completed, the above-mentioned resin composition is used to form an insulating layer 130 so as to cover the outer periphery of the conductor 110 to a thickness of 3 mm or more.

[0097] At this time, 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.

[0098] 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.

[0099] The above-mentioned pellet-shaped resin composition is fed into extruder B which forms insulating layer 130. The set temperature of extruder B is set to a temperature which is 10° C. to 50° C. higher than the desired melting point. It is preferable to appropriately adjust the set temperature based on the linear speed and extrusion pressure.

[0100] An outer semiconductive layer composition containing the same materials as the inner semiconductive layer resin composition charged in extruder A is charged in extruder C which forms the outer semiconductive layer 140 .

[0101] Next, the extrudates from the extruders A to C are guided 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 around the periphery of the conductor 110. This forms an extruded material that will become the cable core.

[0102] The extrusion is then cooled, for example with water.

[0103] Through the above cable core formation 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.

[0104] (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, for example by wrapping copper tape around it.

[0105] (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 .

[0106] In this manner, the power cable 10 is manufactured as a solid insulated power cable.

[0107] (4) Effects of this embodiment According to this embodiment, one or more of the following advantages are achieved.

[0108] (a) The insulating layer of the present embodiment is formed from a resin composition containing a resin component including a propylene-based resin, at least one of a low-crystalline resin and a styrene-based resin, and a resistance-imparting agent having a predetermined molecular weight, melting point, and chemical structure, with the content of the resistance-imparting agent being 0.4 parts by mass to 10 parts by mass per 100 parts by mass of the resin component. The low-crystalline resin and the styrene-based resin can suppress excessive crystal growth of the propylene-based resin, thereby improving the insulating properties of the insulating layer. The resistance-imparting agent having a predetermined melting point and chemical structure can be melted when heated and mixed with the resin component to coat the surface of metal impurities mixed into the resin component. In other words, the resistance-imparting agent can be interposed at the interface between the metal impurities and the resin component. The resistance-imparting agent has an aromatic ring and polarity derived from a phenol skeleton, and therefore can mitigate a sudden resistance change between the resin component and the metal impurities, and can mitigate electric field concentration on the metal impurities, thereby suppressing the deterioration of insulating properties caused by the metal impurities. Thus, according to the insulating layer of the present embodiment, when the content of metal impurities is within a range of 0.02% or less by volume, the metal impurities can be covered with a resistance imparting agent to suppress deterioration of insulating properties caused by the metal impurities, thereby achieving stable high insulating properties.

[0109] The melting point of the (b) resistance imparting agent is preferably 130° C. or lower, and more preferably has a melting point at which the agent is in a liquid state at 27° C. If the resistance imparting agent has such a melting point, the surface of metal impurities can be more reliably covered during heating and mixing of the resin composition, and the insulating properties of the insulating layer can be further improved.

[0110] (c) The resistance imparting agent preferably has a linear carbon chain structure having 5 to 10 carbon atoms. The resistance imparting agent preferably contains a sulfur atom. Such a resistance imparting agent has excellent compatibility with the resin component, and therefore can easily cover metal impurities during heating and mixing of the resin composition, thereby imparting electrical stability to the insulating layer.

[0111] (d) The resin composition preferably contains random PP as the propylene-based resin, which can suppress cracks in the insulating layer compared to homogeneous PP, thereby providing higher insulating properties.

[0112] (e) The resin composition preferably contains random PP and a styrene-based resin, or random PP, a low crystalline resin, and a styrene-based resin. By using at least random PP and a styrene-based resin, it is easy to suppress the growth of coarse crystals in the propylene-based resin, and high insulation properties can be obtained in the insulating layer.

[0113] (f) The resin composition preferably contains random PP as a propylene-based resin and a soft component which is a low crystalline resin or a styrene-based resin in a ratio such that the melting point of the resin composition is 140°C or more and 150°C or less, and the heat of fusion is 55 J / g or more and 100 J / g or less. The resin composition preferably contains homo PP as a propylene-based resin and a soft component which is a low crystalline resin or a styrene-based resin in a ratio such that the melting point of the resin composition is 158°C or more and 168°C or less, and the heat of fusion is 55 J / g or more and 110 J / g or less. By containing each component in a ratio such that the heat of fusion and the melting point of the resin composition are in the above ranges, excessive crystal growth of the propylene-based resin in the insulating layer can be suppressed, and higher insulation can be obtained in the insulating layer.

[0114] (g) The resin composition preferably contains a propylene-based resin, a low crystalline resin, and a styrene-based resin as resin components, which makes it possible to better control the crystal growth of the propylene-based resin compared to the case where only the low crystalline resin or the styrene-based resin is added, and thus makes it possible to obtain higher insulation properties in the insulating layer.

[0115] <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 and scope of the present disclosure.

[0116] In the above-described embodiment, the resin composition molded body as the insulating layer is described as being one which is mechanically mixed and extrusion molded, but the resin composition molded body may also be one which is polymerized and extrusion molded.

[0117] In the above embodiment, the case where the power cable 10 does not need to have a water-shielding layer has been described, but the present disclosure is not limited to this case. The power cable 10 may have a simple water-shielding layer because it has the above-mentioned remarkable water tree suppression effect. Specifically, the simple water-shielding layer is made of, for example, a metal laminate tape. The metal laminate tape has, for example, a metal layer made of aluminum or copper, and an adhesive layer provided on one or both sides of the metal layer. The metal laminate tape is, for example, wound vertically so as to surround the outer periphery of the cable core (outer periphery than the outer semiconductive layer). The water-shielding layer may be provided outside the shielding layer, or may also serve as the shielding layer. With such a configuration, the cost of the power cable 10 can be reduced.

[0118] In the above 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).

[0119] In the above embodiment, three layers are simultaneously extruded in the cable core forming step S300, but each layer may be extruded one at a time. EXAMPLES

[0120] Next, examples according to the present disclosure will be described. These examples are merely examples of the present disclosure, and the present disclosure is not limited to these examples.

[0121] (1) Preparation of evaluation samples In this example, an evaluation sample simulating an insulating layer of a power cable was prepared by the following procedure: In this example, in order to evaluate the change in insulation property due to the inclusion of metal impurities, a metal powder was added to the resin composition as a metal impurity to prepare an evaluation sample.

[0122] (1-1) Material The following components were prepared as materials for a resin composition for forming an evaluation sample.

[0123] As the propylene-based resin (A), the following was used. Isotactic propylene homopolymer (homo PP): Melt flow rate: 0.5g / 10min, density: 0.9g / ml, melting point: 165℃, heat of fusion: 115J / g Random polypropylene (random PP): Melt flow rate: 1.3g / 10min, density: 0.9g / ml, melting point: 145℃, heat of fusion: 100J / g

[0124] As the low crystalline resin (B), the following was used. Ethylene propylene rubber (EPR): Ethylene content: 52% by mass, Mooney viscosity ML (1+4) 100℃: 40, Melting point: None, Heat of fusion: None

[0125] As the styrene-based resin (C), the following was used. Hydrogenated styrene-based thermoplastic elastomer (SEBS): Styrene content: 12% by mass, Hardness: A42, Melt flow rate: 4.5g / 10min (230℃, 2.16kg), Melting point: None, Heat of fusion: None

[0126] The following were used as the resistance imparting agent (D) and the comparative component (D') which is a comparative form of the component (D).

[0127] The metal powder used was obtained by scraping a copper material with a metal file to obtain copper powder, which was then separated through a sieve with 200 μm openings.

[0128] [Table 1]

[0129] In Table 1, the number of phenols indicates the number of phenol skeletons in the compound, with 0 indicated by "-". The area around the hydroxyl group indicates the presence or absence of steric hindrance at the hydroxyl group, with "-" indicating small steric hindrance, "single-hindered" when a bulky substituent is on one side of the ortho position of the hydroxyl group, and "hindered" when on both ortho positions. Additionally, since resistance-imparting agent (d6) and resistance-imparting agent (d'9) are liquid at room temperature (27°C), the boiling points (bp) are indicated.

[0130] (1-2) Preparation of resin composition The above-mentioned materials were mixed under heating in the compositions shown in Tables 2 to 7 below to prepare resin compositions.

[0131] [Table 2]

[0132] [Table 3]

[0133] [Table 4]

[0134] [Table 5]

[0135] [Table 6]

[0136] [Table 7]

[0137] (Samples 1-6) In sample 1, as shown in Table 2, 75 parts by mass of isotactic propylene homopolymer (homo PP) was mixed as polypropylene resin (A), 25 parts by mass of ethylene propylene rubber (EPR) was mixed as low crystalline resin (B), and 6 parts by mass of component (d1) shown in Table 1 was mixed as resistance imparting agent (D). Furthermore, copper powder was added to this mixture so that its content was 0.02% by volume of the resin composition. Then, this mixture was heated and mixed at 220°C using a kneader to prepare a resin composition. In addition, in sample 2, a resin composition was prepared in the same manner as sample 1, except that the resistance imparting agent (D) was not added. In samples 3 to 6, a resin composition was prepared in the same manner as sample 1, except that the amount of component (d1) added was changed to 0.3 parts by mass, 0.5 parts by mass, 9 parts by mass, and 12 parts by mass, respectively.

[0138] (Samples 7-15) In samples 7 to 15, the resin compositions were prepared in the same manner as in sample 1, except that the type of resistance imparting agent (D) was changed to (d2) to (d8) as shown in Tables 3 and 4, and the amount of each resistance imparting agent added was appropriately changed.

[0139] (Samples 16-18) For Samples 16 and 17, the resin compositions were prepared in the same manner as for Sample 1, except that the type of propylene-based resin (A) was changed from homo-PP to random polypropylene (random PP) and the amount of each component added was changed as shown in Table 5. For Sample 18, the resin composition was prepared in the same manner as for Samples 16 and 17, except that the resistance imparting agent (D) was not added.

[0140] (Samples 19-21) For Samples 19 and 20, resin compositions were prepared in the same manner as for Sample 16, except that a styrene-based resin (C) was further added as a resin component and the amount of each component added was appropriately changed as shown in Table 5. For Sample 21, a resin composition was prepared in the same manner as for Samples 19 and 20, except that the resistance imparting agent (D) was not added.

[0141] (Samples 22-31) For samples 22 to 31, as shown in Tables 6 and 7, components (d'1) to (d'10) were used as comparative components (D') instead of the resistance imparting agent (D), and the amounts added were appropriately changed, and the resin compositions were prepared in the same manner as for sample 1.

[0142] (1-3) Preparation of evaluation samples Next, the prepared resin compositions of Samples 1 to 31 were press-molded at 220°C and slowly cooled by water cooling under pressure to prepare sheet-shaped evaluation samples with a thickness of 0.4 mm. In addition, in the preparation of the evaluation samples, the resin compositions were extrusion-molded so that copper powder having a diameter of 200 μm or less was placed in the center of the sheet. In addition, in Samples 18 and 21, the evaluation samples were prepared without placing copper powder.

[0143] (2) Evaluation The evaluation samples thus prepared were evaluated for the following items.

[0144] (Melting point and heat of fusion) The melting point and heat of fusion of the resin composition were measured for the prepared evaluation sample.

[0145] The melting point of each evaluation sample was determined by DSC measurement. The DSC measurement was performed in accordance with JIS-K-7121 (1987). Specifically, a PerkinElmer DSC8500 (input compensation type) was used as the DSC device. The reference sample was, for example, α-alumina. The mass of the evaluation sample was 8 to 10 g. In the DSC device, the temperature was raised from room temperature (27°C) to 220°C at a rate of 10°C / min. Thus, the amount of heat absorbed (heat flow) per unit time was plotted against the temperature to obtain a DSC curve.

[0146] The temperature at which the amount of heat absorbed per unit time for each evaluation sample was maximized (highest peak) was defined as the "melting point." The area of ​​the region surrounded by the melting peak and the baseline in the DSC curve was calculated to determine the "heat of fusion."

[0147] (AC breakdown field strength) The insulation of the prepared evaluation sample was measured for AC breakdown field strength. The AC breakdown field strength was determined by an AC breakdown test. Specifically, at room temperature (27°C), an AC voltage of commercial frequency (e.g., 60Hz) was applied to the evaluation sample at 10kV for 10 minutes, and then increased by 1kV and applied for 10 minutes, and this was repeated. The field strength was measured when the evaluation sample broke down. In this example, an AC breakdown field strength of 45kV / mm or more was considered to be good.

[0148] (3) Evaluation results The results of the above evaluations for each evaluation sample are shown in Tables 2 to 7.

[0149] According to Samples 1 to 6, Samples 1, 4, and 5, in which the amount of the resistance imparting agent (D) was 0.4 parts by mass to 10 parts by mass, were confirmed to have high AC breakdown field strength and excellent insulation properties compared to Sample 2, in which the resistance imparting agent (D) was not added, and Sample 3, in which the amount was 0.3 parts by mass. This is considered to be because, in Samples 1, 4, and 5, the resistance imparting agent (D) was able to cover metal impurities, and the deterioration of insulation properties due to the metal impurities was able to be suppressed. Note that, in Sample 6, the amount of the resistance imparting agent (D) was excessive at 12 parts by mass, so the evaluation sample could not be formed into a sheet, and the insulation properties could not be evaluated.

[0150] In addition, in Samples 1, 7 to 10, and 13 to 15, the type of resistance imparting agent (D) was appropriately changed, and it was confirmed that all of them had high AC breakdown field strength and high insulation. In addition, it was confirmed that Sample 10 had a higher AC breakdown field strength than the other samples. From this, it was confirmed that the resistance imparting agent (D) is preferably one having a sulfur atom or a linear carbon chain structure having 5 to 10 carbon atoms in its chemical structure.

[0151] Moreover, according to Samples 10 to 12, it was confirmed that, similarly to Samples 1 to 7, high insulating properties could be obtained by adding an appropriate amount of the resistance imparting agent (D).

[0152] According to Samples 16 and 17, it was confirmed that the AC breakdown field strength could be increased by using random PP as the propylene-based resin, compared to Sample 1, which used homo-PP. Also, according to Samples 19 and 20, it was confirmed that the AC breakdown field strength could be increased, as in Samples 16 and 17, by adding a styrene-based resin together with a low-crystalline resin to the propylene-based resin. In contrast, it was confirmed that Samples 18 and 21, which did not contain the resistance-imparting agent (D), had an AC breakdown field strength of less than 45 kV / mm due to the influence of metal impurities, and had lower insulation properties compared to Samples 16, 17, 19, and 20. In addition, when the resin composition was the same as Samples 18 and 21 and copper powder was not added, the AC breakdown field strength was 66 kV / mm and 68 kV / mm, and it was confirmed that the desired insulation properties could be obtained in the absence of metal impurities.

[0153] As shown in Table 6, samples 22 to 31 were found to have significantly lower insulation properties due to the use of comparative component (D') that has a molecular weight outside the range of 200 to 500, does not have a phenol skeleton, generates steric hindrance around the hydroxyl group, or has a melting point higher than 215°C. This is thought to be because comparative component (D') is unable to adequately cover the surfaces of metal impurities during heating and mixing, or, even if it does cover them, is unable to adequately alleviate the resistance change between the metal impurities and the resin component.

[0154] As described above, it has been confirmed that by adding a predetermined amount of a resistance imparting agent having a predetermined chemical structure, molecular weight and melting point to a resin component containing propylene units, high insulation properties can be stably achieved in the insulating layer, provided that the content of metal impurities is within a range of 0.02% or less by volume.

[0155] <Preferred aspects of the present disclosure> Preferred aspects of the present disclosure are described below.

[0156] (Appendix 1) Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metal impurities is 0.02% or less. Resin composition.

[0157] (Appendix 2) A conductor; an insulating layer covering the outer periphery of the conductor; Equipped with The insulating layer is formed from a resin composition, The resin composition comprises Contains a resin component containing propylene units and a resistance imparting agent, the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, the content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, The volume ratio of metal impurities is 0.02% or less. Power cable.

[0158] (Appendix 3) The resin component contains at least one of an ethylene unit and a styrene unit. 2. A power cable as defined in claim 2.

[0159] (Appendix 4) The resistance imparting agent has a melting point such that it is in a liquid state at 27°C. 1. The power cable according to claim 2 or 3.

[0160] (Appendix 5) The resistance imparting agent has a linear carbon chain structure having 5 to 10 carbon atoms. 5. The power cable according to any one of claims 2 to 4.

[0161] (Appendix 6) The resistance imparting agent contains a sulfur atom. 10. The power cable according to claim 2,

[0162] (Appendix 7) The resistance imparting agent is a phenolic antioxidant. 7. The power cable according to any one of appendix 2 to appendix 6.

[0163] (Appendix 8) The resin composition contains, as a propylene-based resin, a propylene homopolymer having a melting point of 160° C. or more and 175° C. or less and a heat of fusion of 100 J / g or more and 120 J / g or less, The melting point of the resin composition is 158°C or more and 168°C or less, and the heat of fusion is 55 J / g or more and 110 J / g or less. 8. The power cable according to any one of appendices 2 to 7.

[0164] (Appendix 9) The resin composition contains, as a propylene-based resin, a propylene random copolymer having a melting point of 140° C. or more and 155° C. or less and a heat of fusion of 90 J / g or more and 105 J / g or less, The melting point of the resin composition is 140° C. or more and 150° C. or less, and the heat of fusion is 55 J / g or more and 100 J / g or less. 8. The power cable according to any one of appendices 2 to 7.

[0165] (Appendix 10) A step of preparing a resin composition by mixing a propylene-based resin, a soft component including at least one of a low crystalline resin and a styrene-based resin, and a resistance imparting agent; and a step of coating an insulating layer around a conductor using the resin composition. the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point of 215° C. or less and a molecular weight of 200 or more and 500 or less, In the step of preparing the resin composition, the resistance imparting agent is added in an amount of 0.4 parts by mass or more and 10 parts by mass or less to 100 parts by mass of a resin component including the propylene-based resin and the soft component. A method for manufacturing power cables.

[0166] (Appendix 11) In the step of preparing the resin composition, when the total amount of the propylene-based resin and the soft component is 100 parts by mass, the propylene-based resin is mixed in an amount of 55 parts by mass or more and 95 parts by mass or less, and the soft component is mixed in an amount of 5 parts by mass or more and 45 parts by mass or less. 11. A method for manufacturing a power cable according to claim 10.

[0167] (Appendix 12) The propylene-based resin is a propylene homopolymer having a melting point of 160° C. or more and 175° C. or less and a heat of fusion of 100 J / g or more and 120 J / g or less, In the step of preparing the resin composition, the propylene-based resin and the soft component are mixed so that the melting point of the resin composition is 158° C. or more and 168° C. or less and the heat of fusion is 55 J / g or more and 110 J / g or less. A method for producing a power cable according to claim 10 or 11.

[0168] (Appendix 13) The propylene-based resin is a propylene random copolymer having a melting point of 140° C. or more and 155° C. or less and a heat of fusion of 90 J / g or more and 105 J / g or less, In the step of preparing the resin composition, the propylene-based resin and the soft component are mixed so that the melting point of the resin composition is 140° C. or more and 150° C. or less, and the heat of fusion is 55 J / g or more and 100 J / g or less. A method for producing a power cable according to claim 10 or 11. [Explanation of symbols]

[0169] 10 Power Cable 110 Conductor 120 Inner semiconducting layer 130 Insulating layer 140 Outer semiconducting layer 150 Shielding layer 160 Sheath

Claims

1. A conductor; an insulating layer covering the outer periphery of the conductor; Equipped with The insulating layer is formed from a resin composition, The resin composition comprises Contains a resin component containing propylene units and a resistance imparting agent, The resin component contains a propylene-based resin and a soft component containing at least one of a low-crystalline resin and a styrene-based resin, The propylene-based resin is a propylene homopolymer having a melting point of 160° C. or more and 175° C. or less, or a propylene random copolymer having a melting point of 140° C. or more and 155° C. or less, The low crystalline resin is a copolymer of at least two of ethylene, propylene, butene, hexene, and octene, and has no melting point or a melting point of 100° C. or less; The styrene-based resin is a styrene-based thermoplastic elastomer containing styrene as a hard segment and at least one of ethylene, propylene, butylene, and isoprene as a soft segment; the resistance imparting agent is a monomer having a phenol skeleton, in which hydrogen or an alkyl group having 1 to 3 carbon atoms is bonded to at least one of the ortho positions of a hydroxyl group in the phenol skeleton, the monomer having a melting point such that the monomer is in a liquid state at 27° C., and a molecular weight of 200 or more and 500 or less; The resin component contains the propylene-based resin in an amount of 60 parts by mass or more and 95 parts by mass or less, and the soft component in an amount of 5 parts by mass or more and 40 parts by mass or less, The content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the resin component, Contains metal impurities, and the content of the metal impurities is 0.02% or less by volume ratio; Power cable.

2. The resin component contains at least one of an ethylene unit and a styrene unit.

2. The power cable according to claim 1.

3. The resistance imparting agent has a linear carbon chain structure having 5 to 10 carbon atoms.

3. The power cable according to claim 1 or 2.

4. The resistance imparting agent contains a sulfur atom. The power cable according to any one of claims 1 to 3.

5. The resistance imparting agent is a phenolic antioxidant.

5. The power cable according to claim 1 .

6. The propylene-based resin is a propylene homopolymer having a melting point of 160°C or more and 175°C or less and a heat of fusion of 100 J / g or more and 120 J / g or less, The melting point of the resin composition is 158° C. or more and 168° C. or less, and the heat of fusion is 55 J / g or more and 110 J / g or less.

6. The power cable according to claim 1 .

7. The propylene-based resin is a propylene random copolymer having a melting point of 140°C or more and 155°C or less and a heat of fusion of 90 J / g or more and 105 J / g or less, The melting point of the resin composition is 140° C. or more and 150° C. or less, and the heat of fusion is 55 J / g or more and 100 J / g or less.

6. The power cable according to claim 1 .

8. The styrene resin has no melting point and no heat of fusion. A power cable according to any one of claims 1 to 7.

9. The metal impurities are metal powders.

9. The power cable according to claim 1 .

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