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 145°C or less and a molecular weight of from 200 to 500; and 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.

Description

[Technical field]

[0001] This application claims priority to Japanese application "Patent Application No. 2020-211490" filed on December 21, 2020, and incorporates all of the contents of the 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).

[0004] However, cross-linked polyethylene that has deteriorated over time cannot be recycled and must be incinerated, raising concerns about its impact on the environment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 57-69611 Summary of the Invention

[0006] 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 145° 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. A resin composition is provided.

[0007] 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 145° 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. A power cable is provided. [Brief description of the drawings]

[0008] [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

[0009] [Problem that this disclosure aims to solve] In recent years, 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 a resin component constituting an insulating layer, the insulating properties inherent to the propylene-based resin may not be obtained. Furthermore, according to the study by the present inventors, it has been found that the insulating properties of an insulating layer containing a propylene-based resin are significantly reduced when, for example, a power cable is bent and stress accompanying bending is applied to the insulating layer.

[0011] An object of the present disclosure is to provide a technique for improving the insulating properties of an insulating layer containing a propylene-based resin and suppressing a decrease in the insulating properties caused by external stress.

[0012] [Effects of this disclosure] According to the present disclosure, in a resin composition containing a propylene-based resin, it is possible to improve the insulating properties and suppress a decrease in the insulating properties caused by external stress.

[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 control the crystallinity of the propylene-based resin by mixing it with a low-crystalline resin or the like.

[0015] However, when an insulating layer is formed by mixing a propylene-based resin with a low-crystalline resin, very fine voids may be formed in the insulating layer, and the original insulating properties may not be obtained. Even if there are no apparent voids in the insulating layer and there are no problems in terms of characteristics, the insulating properties may be significantly reduced after a large external stress is applied, for example, by bending. The present inventors have studied this point and found that new voids are formed by external stress.

[0016] In the insulating layer containing such a propylene-based resin, high insulating properties cannot be obtained due to minute voids, and the insulating properties may be significantly reduced due to the generation of voids caused by bending.

[0017] The present inventors have studied the above-mentioned problems and found that the use of a specific additive can suppress the deterioration of insulation caused by fine voids and voids generated by bending. 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, with a molecular weight of 200 to 500 and a melting point lower than that of a propylene-based resin.

[0018] The above-mentioned monomer has been generally used as an antioxidant up to now, but according to the study by the present inventors, by having a specific chemical structure, molecular weight and melting point, it is possible to fill fine voids in the insulating layer or voids formed by bending. By filling the voids, it acts to mitigate a sudden change in resistance between the insulating layer and the voids, and as a result, it is possible to suppress the deterioration of insulation due to the voids. 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 voids to the insulating layer.

[0019] The inventors have discovered that by blending a predetermined amount of the above compound into a resin composition containing a propylene-based resin, the resistance-imparting agent can be filled into minute voids present in the insulating layer and voids formed by the application of external stress, thereby improving the insulating properties and suppressing the deterioration of the insulating properties due to bending.

[0020] The present disclosure is based on the above-mentioned findings of the inventors.

[0021] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0022] [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 145° 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. According to this configuration, the insulating properties of the resin composition containing the propylene-based resin can be improved and deterioration of the insulating properties due to bending can be suppressed.

[0023] [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 145° 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. According to this configuration, the insulating layer containing the propylene-based resin can have improved insulating properties, and can also be prevented from being deteriorated due to bending.

[0024] [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 formation of voids in the insulating layer can be suppressed.

[0025] [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.

[0026] [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.

[0027] [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 resistance imparting agent can be easily retained at locations in the insulating layer that will become the starting points of cracks or voids, and the resistance imparting agent can be more reliably filled into newly formed voids, etc.

[0028] [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.

[0029] [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 in the insulating layer.

[0030] [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 in the insulating layer.

[0031] [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 invention 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.

[0032] <One embodiment of the present disclosure> (1) Resin composition The resin composition of the present embodiment is a material that constitutes the insulating layer 130 in the power cable 10 described later, and contains, for example, a resin component containing propylene units, a resistance imparting agent, and other additives as necessary.

[0033] The resin composition of the present embodiment contains at least a propylene-based resin as a resin component, and 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.

[0034] 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.

[0035] Each component will be described below.

[0036] (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. 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 as the propylene-based resin. It is preferable to use random PP as the propylene-based resin. When comparing homo PP with random PP, random PP tends to have a lower crystal content due to the inclusion of ethylene units, but the formation of cracks and voids in the insulating layer due to coarse crystallization can be suppressed. Therefore, the random PP can obtain higher insulation properties than homo PP. In addition, when an external stress such as bending is applied to the insulating layer, the formation of voids can be suppressed, and the variation in insulation properties before and after bending can be reduced.

[0037] 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.

[0038] 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.

[0039] (Low crystalline resin) The low crystalline resin is a component that controls the crystal growth (amount of crystals) of the propylene-based resin to impart 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.

[0040] 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.

[0041] 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 0.855 g / cm 3 ~0.890g / cm 3 It is polyethylene.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] (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. In particular, 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.

[0047] 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.

[0048] 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).

[0049] 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.

[0050] 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.

[0051] (Resistance imparting agent) The resistance imparting agent is a component that fills voids present in the insulating layer and suppresses the deterioration of insulation caused by the voids. The resistance imparting agent also functions as an antioxidant, and can suppress deterioration during heating and mixing of the resin composition. 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 the hydroxyl group in the phenol skeleton, having a melting point lower than that of the resin component, and having a molecular weight of 200 to 500. Preferably, the resistance imparting agent is a phenol-based antioxidant having the above chemical structure, melting point, and molecular weight.

[0052] The mechanism by which the resistance imparting agent fills the voids and suppresses the deterioration of insulation due to the voids is presumed to be as follows.

[0053] The resistance imparting agent has a melting point of 145°C or less, which tends to be lower than that of the resin component, so it melts and becomes liquid when heated and mixed with the resin component. When the resin composition obtained by heating and mixing is molded into an insulating layer and cooled, the resin component begins to solidify first. At this time, crystal growth of the propylene-based resin progresses, and fine voids may be generated. Since the resistance imparting agent has a melting point lower than that of the resin component and exists in a liquid state at the stage when the resin component begins to solidify, it can move to the voids and fill them.

[0054] Moreover, since the molecular weight of the resistance imparting agent is 200 or more, volatilization of the resistance imparting agent can be suppressed when the resin composition is heated and mixed, and the resistance imparting agent can be stably embedded in the voids. Furthermore, since the molecular weight is 500 or less, the resistance imparting agent can be suitably moved within the resin component, and aggregation of the resistance imparting agent can be suppressed. As a result, the resistance imparting agent can be uniformly dispersed in the resin composition, and the resistance imparting agent can be stably embedded in the voids.

[0055] In addition, since the resistance imparting agent has an aromatic ring derived from the phenol skeleton, it can fill the voids and impart electrical stability to the insulating layer. Furthermore, since the resistance imparting agent has polarity due to the phenol skeleton, when the resistance imparting agent fills the voids, it can mitigate a sudden change in resistance between the insulating layer and the resistance imparting agent, thereby maintaining insulation. 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. Therefore, the resistance imparting agent has little steric hindrance around the hydroxyl group. On the other hand, in the case of a monomer in which bulky substituents (such as t-butyl groups) are arranged at the ortho positions on both sides of the hydroxyl group, for example, a hindered phenol-based antioxidant, the steric hindrance around the hydroxyl group becomes large. In such a monomer, the reactivity of the hydroxyl group is inhibited by the steric hindrance, and the originally obtained characteristics may not be exhibited. In this regard, the resistance imparting agent of the present embodiment has little steric hindrance and high reactivity of the hydroxyl group, so that the characteristic of maintaining the insulating property can be stably exhibited.

[0056] In this way, the resistance imparting agent can fill the voids in the insulating layer and impart electrical stability to the insulating layer, so that even if the insulating layer has fine voids or voids are formed due to bending of the insulating layer, the deterioration of insulating properties due to the voids can be mitigated and the insulating properties can be maintained at a high level.

[0057] 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.

[0058] The melting point of the resistance imparting agent may be 145°C or lower, but is preferably 130°C or lower. By having a melting point of 130°C or lower, the resistance imparting agent can be filled more reliably into voids that occur in the insulating layer. Furthermore, the melting point is preferably a temperature at which the resistance imparting agent becomes liquid at room temperature (27°C), and more preferably 27°C or lower. A resistance imparting agent that becomes liquid at 27°C is likely to accumulate in areas in the insulating layer where the molecular chains that are the starting points of cracks and voids are sparse. Therefore, when an external stress is applied to the insulating layer, the resistance imparting agent can be filled more reliably into voids that are newly formed. The lower limit is not particularly limited, but is preferably -30°C or higher.

[0059] 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.

[0060] In addition, from the viewpoint of increasing 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, it can be stably present in a place where voids are likely to occur, and when voids occur, the resistance imparting agent can fill the voids 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 it is preferable that it is 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.

[0061] 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.

[0062] 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.

[0063] The content of the resistance imparting agent is 0.4 parts by mass or more and 10 parts by mass or less relative 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, the resistance imparting agent can be easily embedded in voids, so that the decrease in insulation due to voids can be mitigated. 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, the moldability of the resin composition can be ensured.

[0064] (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.

[0065] 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.

[0066] 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.

[0067] (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.

[0068] 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.

[0069] 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.

[0070] (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.

[0071] (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.

[0072] 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.

[0073] 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 .

[0074] (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.

[0075] (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.

[0076] (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.

[0077] (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.

[0078] (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.

[0079] (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.

[0080] 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.

[0081] 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.

[0082] (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.

[0083] (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.

[0084] The insulating layer 130 of this embodiment can maintain high insulation even when external stress is applied by bending. Specifically, a 180° bending test described later is performed on a 0.4 mm thick sheet formed from the above-mentioned resin composition, and an AC voltage of a commercial frequency (e.g., 60 Hz) is applied to the sheet to which external stress 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. When this is repeated, the AC breakdown electric field strength is 45 kV / mm or more even when voids are confirmed, and 70 kV / mm or more when no voids are confirmed.

[0085] Furthermore, the insulating layer 130 can maintain a high AC breakdown field strength even when voids are formed due to external stress such as bending. In other words, the AC breakdown field strength of the insulating layer 130 has a small difference between a state before an external stress such as bending is applied and a state after an external stress such as bending is applied. Specifically, the rate of change in the AC breakdown field strength due to bending is 30% or less. Here, the rate of change in the AC breakdown field strength is a ratio indicating the difference between the AC breakdown field strength before and after bending, relative to the AC breakdown field strength in the normal state before bending.

[0086] (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".

[0087] (S100: Resin composition preparation step) First, a resin composition for forming the insulating layer 130 is prepared.

[0088] In this embodiment, a propylene-based resin as a resin component, a softening 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. Examples of the mixer include an open roll, a Banbury mixer, a pressure kneader, a single-shaft mixer, and a multi-shaft mixer.

[0089] 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.

[0090] 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.

[0091] (S200: Conductor preparation process) On the other hand, conductor 110 is prepared by twisting together a plurality of conductor core wires.

[0092] (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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 .

[0097] 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.

[0098] The extrusion is then cooled, for example with water.

[0099] During this cooling, the resin component containing the propylene-based resin begins to solidify first in the resin composition constituting the insulating layer 130. At this time, the resistance imparting agent, which has a lower melting point than the resin component, exists in a molten liquid state, and therefore moves to and fills the minute voids formed during solidification.

[0100] 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.

[0101] (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.

[0102] (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 .

[0103] In this manner, the power cable 10 is manufactured as a solid insulated power cable.

[0104] (4) Effects of this embodiment According to this embodiment, one or more of the following advantages are achieved.

[0105] (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. The resistance-imparting agent can enter voids present in the resin composition, for example, minute voids that cannot be observed, and can suppress a sudden resistance change occurring between the resin component and the voids. Therefore, high insulation can be obtained in the insulating layer. Moreover, although the insulating layer may be bent to form voids, the resistance-imparting agent can fill the voids and suppress the decrease in insulation caused by the formation of voids. Thus, according to the insulating layer of the present embodiment, the insulating property before the application of external stress can be improved, and the difference in AC breakdown field strength before and after the application of external stress due to bending can be kept small, thereby suppressing the change in insulation property before and after bending.

[0106] (b) The melting point of the 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. A resistance imparting agent having such a melting point can more reliably fill voids formed in the propylene-based resin, and can further suppress fluctuations in the insulating properties of the insulating layer before and after bending.

[0107] (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, so that it can fill voids in the insulating layer more stably and can impart electrical stability to the insulating layer. As a result, the insulating properties of the insulating layer in the initial state can be improved and the fluctuation in insulating properties before and after bending can be further suppressed.

[0108] (d) When homo PP is used as the propylene-based resin, since homo PP has a large amount of crystals, cracks and voids are likely to occur in or between the crystals in the insulating layer. Therefore, not only does the insulating layer tend to have low insulation to begin with, but the insulating layer is also likely to deteriorate when it is bent. In this regard, the resistance imparting agent can fill not only the voids that are initially present in the insulating layer, but also the voids that are formed by bending. This can improve the insulating properties of the insulating layer, and can suppress deterioration of the insulating properties due to bending, thereby maintaining high insulating properties.

[0109] On the other hand, random PP has a smaller amount of crystals than homo-PP, so cracks and voids are less likely to occur in the insulating layer, and new voids are less likely to form when the insulating layer is bent. However, even in the case of random PP, there is a tendency that the inherent insulating properties of random PP cannot be obtained due to the presence of minute voids that cannot be observed. In this regard, the resistance imparting agent can fill the minute voids and suppress the deterioration of insulating properties due to the voids.

[0110] In this way, the resistance imparting agent can achieve high insulation in the insulating layer regardless of the type of propylene-based resin, such as homo-PP or random PP, while suppressing the deterioration of insulation due to bending of the insulating layer and minimizing the fluctuation in insulation before and after bending.

[0111] (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 possible to suppress the generation of large voids during the formation of the insulating layer, and to suppress the generation of new voids when the obtained insulating layer is bent. This makes it possible to increase the insulating property of the insulating layer before the external stress is applied, and to maintain the high insulating property even after bending.

[0112] (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.

[0113] (g) The resin composition preferably contains a propylene-based resin, a low crystalline resin, and a styrene-based resin as resin components. This makes it possible to better control the crystal growth of the propylene-based resin, and to reduce the number of voids and the size of the voids, compared to the case where only the low crystalline resin or the styrene-based resin is added. In addition, the formation of voids due to bending of the insulating layer can be more suppressed. Moreover, by adding a resistance imparting agent to the resin composition, the resistance imparting agent can be filled into fine voids, and the insulation properties can be improved. Even in the case where fine voids are formed due to bending of the insulating layer, the decrease in insulation properties can be mitigated, and the fluctuation in insulation properties before and after bending can be suppressed. In addition, the resistance imparting agent can mitigate the decrease in insulation properties due to the formation of voids, so that the amount of styrene-based resin that suppresses the formation of voids can be reduced.

[0114] <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.

[0115] 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.

[0116] 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. 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.

[0117] 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).

[0118] 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

[0119] 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.

[0120] (1) Preparation of evaluation samples In this example, an evaluation sample simulating an insulating layer of a power cable was produced by the following procedure.

[0121] (1-1) Material The following components were prepared as materials for a resin composition for forming an evaluation sample.

[0122] 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

[0123] 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

[0124] 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

[0125] The following were used as the resistance imparting agent (D) and the comparative component (D') which is a comparative form of the component (D).

[0126] [Table 1]

[0127] 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.

[0128] (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.

[0129] [Table 2]

[0130] [Table 3]

[0131] [Table 4]

[0132] [Table 5]

[0133] [Table 6]

[0134] [Table 7]

[0135] (Samples 1-6) In sample 1, as shown in Table 2, 75 parts by mass of isotactic propylene homopolymer (homo PP) as polypropylene resin (A), 25 parts by mass of ethylene propylene rubber (EPR) as low crystalline resin (B), and 6 parts by mass of component (d1) shown in Table 1 as resistance imparting agent (D) were mixed and 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.

[0136] (Samples 7-14) For samples 7 to 14, the resin compositions were prepared in the same manner as for sample 1, except that the type of resistance imparting agent (D) was changed to (d2) to (d7) as shown in Tables 3 and 4, and the amount of each resistance imparting agent added was appropriately changed.

[0137] (Samples 15-17) For Samples 15 and 16, 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 17, the resin composition was prepared in the same manner as for Samples 15 and 16, except that the resistance imparting agent (D) was not added.

[0138] (Samples 18-20) For Samples 18 and 19, resin compositions were prepared in the same manner as for Sample 15, 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 20, a resin composition was prepared in the same manner as for Samples 18 and 19, except that the resistance imparting agent (D) was not added.

[0139] (Samples 21-30) For samples 21 to 30, 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.

[0140] (1-3) Preparation of evaluation samples Next, each of the prepared resin compositions of Samples 1 to 30 was press-molded at 220° C. and slowly cooled by water cooling under pressure to prepare a sheet-like evaluation sample having a thickness of 0.4 mm.

[0141] (2) Evaluation The prepared evaluation samples were evaluated for the following items.

[0142] (Melting point and heat of fusion) The melting point and heat of fusion of the resin composition were measured for the prepared evaluation sample.

[0143] 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.

[0144] 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."

[0145] (AC breakdown field strength) The AC breakdown field strength was measured for the insulation of the prepared evaluation sample. The AC breakdown field strength was obtained by an AC breakdown test. Specifically, at room temperature (27°C), an AC voltage of a commercial frequency (for example, 60 Hz) was applied to the evaluation sample at 10 kV for 10 minutes, and then the voltage was increased by 1 kV and applied for 10 minutes repeatedly. The field strength was measured when the evaluation sample experienced insulation breakdown. In this example, the AC breakdown field strength of the evaluation sample was measured before and after the bending test described below. In this example, the evaluation sample after the bending test was evaluated as good if 45 kV / mm or more was found to have voids larger than 10 μm, and as good if 70 kV / mm or more was found to have no voids larger than 10 μm.

[0146] (Bending test) In order to confirm the generation of voids in the evaluation sample, a 180° bending test was performed on the evaluation sample. Specifically, the evaluation sample was bent 180° at a diameter of 500 mm, and then the bent portion was cut out and its surface was observed by SEM. In Tables 2 to 4, the case where voids larger than 10 μm were confirmed is indicated as A, and the case where they were not confirmed is indicated as B.

[0147] (3) Evaluation results The results of the above evaluations for each evaluation sample are shown in Tables 2 to 7.

[0148] 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 before the bending test and excellent insulation properties, compared with 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. In addition, when each sample was subjected to a bending test, it was confirmed that voids of a size exceeding 10 μm were formed in all of them. In addition, in Samples 2 and 3, the AC breakdown field strength before the bending test was low, and the AC breakdown field strength significantly decreased before and after the bending test. In contrast, in Samples 1, 4, and 5, the AC breakdown field strength before the bending test was high, and although voids were formed by bending, the fluctuation of the AC breakdown field strength was small, and it was confirmed that the decrease in insulation due to bending could be mitigated. This is considered to be because in Samples 1, 4, and 5, the resistance imparting agent (D) was able to be sufficiently embedded in the voids present in the sample. In addition, 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.

[0149] In addition, in samples 1, 7 to 10, 13, and 14, the type of resistance imparting agent (D) was appropriately changed, and it was confirmed that all of them had high insulation in the initial state, and although voids were formed by bending, the decrease in insulation due to the voids was mitigated, and high insulation could be maintained. In addition, it was confirmed that sample 10 had a high AC breakdown field strength in the initial state and a small fluctuation in AC breakdown field strength due to bending compared to 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.

[0150] Furthermore, according to Samples 10 to 12, it was confirmed that, similarly to Samples 1 to 6, by adding an appropriate amount of the resistance imparting agent (D), high insulating properties could be obtained and deterioration of insulating properties due to bending could be mitigated.

[0151] According to Samples 15 and 16, it was confirmed that the AC breakdown field strength before the bending test can be increased by using random PP as the propylene-based resin, compared to Sample 1, which uses homo-PP. It was also confirmed that the use of random PP prevents large voids with a size exceeding 10 μm from being formed even when the sample is bent. It was also confirmed that the fluctuation of the AC breakdown field strength due to bending can be reduced. It was also confirmed that Sample 17, which does not contain the resistance imparting agent (D), has a smaller AC breakdown field strength in the initial state compared to Samples 15 and 16, which contain the resistance imparting agent (D). This is thought to be because, while fine voids exist in Sample 17, the resistance imparting agent (D) is filled into the fine voids in Samples 15 and 16, which suppresses the deterioration of insulation.

[0152] According to Samples 18 and 19, it was confirmed that the AC breakdown field strength in the initial state can be increased compared to Sample 1 by adding a styrene-based resin together with a low-crystalline resin to a propylene-based resin. It was also confirmed that even when the sample was bent, large voids with a size exceeding 10 μm were not formed, and the AC breakdown field strength did not vary significantly before and after bending. It was confirmed that Sample 20, to which the resistance imparting agent (D) was not added, had a smaller AC breakdown field strength in the initial state compared to Samples 18 and 19, to which the resistance imparting agent (D) was added. This is believed to be because, while fine voids exist in Sample 20, the resistance imparting agent (D) was filled into the fine voids in Samples 18 and 19, suppressing the deterioration of insulation.

[0153] As shown in Table 4, in samples 21 to 30, comparative component (D') was used, which has a molecular weight outside the range of 200 to 500, does not have a phenol skeleton, has steric hindrance around the hydroxyl group, or has a melting point higher than that of the resin component, and therefore it was confirmed that the insulation before the bending test was low and the insulation significantly decreased before and after bending. This is considered to be because the comparative component (D') could not be sufficiently embedded in the voids, or even if it could be embedded in the voids, the comparative component (D') could not sufficiently mitigate the sudden resistance change between the insulating layer and the voids. The reason why the comparative component (D') was not sufficiently embedded in the voids is presumed to be that the molecular weight of the comparative component (D') was too small and therefore volatilized during heat mixing, the molecular weight was too large and therefore it could not be dispersed in the resin composition during heat mixing, or the melting point was higher than that of the resin component and therefore it could not be sufficiently melted during heat mixing. In addition, it is presumed that the reason why comparative component (D') cannot mitigate the sudden change in resistance between the insulating layer is that comparative component (D') does not have a phenol skeleton that contributes to electrical stability, or that it has steric hindrance, which results in low reactivity of the hydroxyl group.

[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, the initial insulating properties of the insulating layer can be improved and the deterioration of insulating properties before and after bending can be suppressed.

[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 145° 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. 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 145° 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. Power cable.

[0158] (Appendix 3) 3. The power cable of claim 2, wherein the resin component further contains at least one of ethylene units and styrene units.

[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 145° 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 containing a sulfur atom, a melting point of 145° C. or less, 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. Power cable.

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 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. Power cable.

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

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

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

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