Resin composition and power cable

Abstract

The resin composition contains a propylene-based resin (A) having a propylene unit and a thermoplastic elastomer (B), has a melting point of 110° C. or higher, and has a molecular weight of 1×10 4 The percentage of the following components is 3% or less:

Description

[Technical field]

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

[0002] In recent years, solid insulated power cables (hereinafter, abbreviated as "power cables") have been developed for DC transmission applications. In these power cables, cross-linked polyethylene is widely used as a component constituting the insulating layer (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-086634 Summary of the Invention

[0004] According to one aspect of the present disclosure, A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: A resin composition is provided.

[0005] According to another aspect of the present disclosure, A conductor; an insulating layer formed from a resin composition and covering the conductor; Equipped with The resin composition comprises A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: A power cable is provided. [Brief description of the drawings]

[0006] [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. [Diagram 2] FIG. 2 is a schematic configuration diagram of an extruder used in the power cable manufacturing method according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 is a schematic diagram for explaining the shape of the screw flight. [Figure 4] FIG. 4 is a schematic diagram for explaining the retention suppression member. [Diagram 5] FIG. 5 is a flow chart illustrating a method for manufacturing a power cable according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Problem to be solved by the invention] 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.

[0008] In recent years, therefore, polymer components having propylene units, such as polypropylene, have been attracting attention as resin components constituting the insulating layer. Polypropylene can achieve high insulating properties even without crosslinking. In other words, it is possible to achieve both insulating properties and recyclability.

[0009] On the other hand, when a polymer component having a propylene unit is used, it is sometimes difficult to obtain stable insulation properties in the insulating layer.

[0010] An object of the present disclosure is to provide a technique for obtaining stable insulation properties in a power cable.

[0011] [Effects of the invention] According to the present disclosure, stable insulation properties can be obtained in a power cable.

[0012] [Description of the embodiments of the present disclosure] <Knowledge gained by the inventors> First, the findings of the inventors will be outlined.

[0013] In the case of a power cable, when an insulating layer is formed of a polymer component having a propylene unit, for example, space charges are generated in the insulating layer when a high voltage is applied, and the insulating properties of the insulating layer may deteriorate. This tendency becomes more pronounced in a high temperature environment. Note that the insulating properties here refer to the volume resistivity, DC breakdown field strength, space charge characteristics, etc., of the insulating layer.

[0014] In order to improve the insulating properties of the insulating layer, a method of blending a modified polymer having a polar group has been considered. An example of such a modified polymer is modified propylene obtained by modifying propylene with an unsaturated carboxylic acid.

[0015] However, it was confirmed that the insulating properties of the resin composition and the insulating layer are not stable by merely adding the modified polymer. When this point was examined, it was found that the modified polymer contains low molecular weight components due to the generation of radicals and the cutting of molecular chains in the manufacturing process, and the low molecular weight components reduce the insulating properties. The low molecular weight components tend to behave as charge carriers, especially in high temperature environments. Therefore, it is considered that the low molecular weight components cause local accumulation of space charges in the resin composition, and move through the resin composition, especially in high temperature environments, causing further accumulation. Therefore, even if the modified polymer is added to the propylene-based resin, the effect of trapping space charges by the modified polymer may be difficult to obtain due to the influence of the low molecular weight components. As a result, the insulating layer may not be able to stably obtain high insulating properties.

[0016] For this reason, the inventors of the present invention have investigated a method for improving insulation without adding modified polymers, and have focused on a softening component added to the resin composition forming the insulation layer. Propylene-based resins tend to be highly crystalline and hard when used alone, so they may not be able to satisfy the flexibility required for the insulation layer of power cables. Various elastomers and wax components are used as the softening component.

[0017] However, when using softening ingredients, the following points are of concern:

[0018] First, the melting point of the soft component is lower than that of the propylene-based resin. The lower the melting point of the soft component, the higher the ratio of the region that becomes amorphous or melts in the resin composition in a high-temperature environment. Therefore, when a soft component with a low melting point is mixed, charge migration is likely to occur in a high-temperature environment, which may lead to a decrease in insulation.

[0019] Secondly, the molecular weight of the soft component is lower than that of the propylene-based resin. Generally, resins and elastomers have a specific molecular weight distribution according to their type. The lower the molecular weight of the soft component, the higher the ratio of low molecular weight components in the molecular weight distribution. The low molecular weight components have a lower melting point than the high molecular weight components, and move in the resin composition to cause localized space charge accumulation, which may cause a decrease in insulation properties in high temperature environments.

[0020] For this reason, we focused on thermoplastic elastomers with high melting points and few low molecular weight components as softening components to be added to propylene-based resins. We then developed a resin composition containing propylene-based resins and thermoplastic elastomers with a melting point of 110°C or higher and a molecular weight of 1×10 4 They found that by controlling the proportion of low molecular weight components to 3% or less, it is possible to suppress the accumulation of space charges in high temperature environments and achieve high insulation properties.

[0021] The present disclosure is based on the above-mentioned findings of the inventors.

[0022] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0023] [1] A resin composition according to one embodiment of the present disclosure, A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: According to this configuration, high insulation properties can be stably obtained.

[0024] [2] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer formed from a resin composition and covering the conductor; Equipped with The resin composition comprises A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: According to this configuration, a high withstand voltage can be achieved even in a high temperature environment, enabling stable DC power transmission.

[0025] [3] In the power cable according to the above [2], The thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit. According to this configuration, it is possible to improve the flexibility of the insulating layer and to stably obtain high insulating properties.

[0026] [4] The power cable according to the above [2] or [3], The melting point of the thermoplastic elastomer (B) is 110°C or higher and 160°C or lower. According to this configuration, the melting point of the resin composition can be easily adjusted to 110° C. or higher, and high insulating properties can be stably obtained.

[0027] [5] In the power cable according to any one of [2] to [4] above, The thermoplastic elastomer (B) has a molecular weight of 1×10 4 The percentage of the following components is 4.0% or less. According to this configuration, the proportion of low molecular weight components can be adjusted to be low, and high insulating properties can be stably obtained.

[0028] [6] The power cable according to any one of [2] to [5] above, The melting point of the propylene-based resin (A) is 130°C or higher and 170°C or lower. According to this configuration, the melting point of the resin composition can be easily adjusted to 110° C. or higher, and high insulating properties can be stably obtained.

[0029] [7] In the power cable according to any one of [2] to [6] above, The resin composition contains 50 parts by mass or more and 90 parts by mass or less of the propylene-based resin (A) and 10 parts by mass or more and 50 parts by mass or less of the thermoplastic elastomer (B). According to this configuration, the proportion of low molecular weight components can be reduced, and high insulating properties can be stably obtained.

[0030] [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.

[0031] <One embodiment of the present disclosure> (1) Resin composition The resin composition of the present embodiment can be used, for example, as a material for forming an insulating layer of a power cable, which will be described later. The resin composition contains a propylene-based resin (A) having a propylene unit, a thermoplastic elastomer (B), and other additives as necessary. In the following, the propylene-based resin (A) is also referred to as component (A), and the thermoplastic elastomer (B) is also referred to as component (B).

[0032] The resin composition is formed by mixing a propylene-based resin (A) and a thermoplastic elastomer (B) having different melting points and molecular weight distributions. 4 The ratio of the following components (hereinafter also referred to as low molecular weight components) is 3% or less. The resin composition has a predetermined phase structure due to the mixture of components (A) and (B). The phase structure may be, for example, a structure in which component (B) is finely dispersed in component (A) (a so-called sea-island structure), or a structure in which components (A) and (B) are compatible with each other.

[0033] (Melting point of resin composition) The resin composition contains a thermoplastic elastomer (B) having a melting point lower than that of the propylene-based resin (A), so that the melting point of the resin composition is lower than that of the (A) component. The melting point of the resin composition is an index showing the addition ratio of the (A) component and the (B) component. The melting point of the resin composition is 110°C or higher, so that the ratio of the (B) component having a low melting point can be controlled to a predetermined amount. This can reduce the influence of the (B) component becoming amorphous or melting in a high-temperature environment. The upper limit of the melting point of the resin composition is not particularly limited, but it is preferably 170°C or lower, for example. In addition, as described later, when an olefin-based thermoplastic elastomer is used as the (B) component, the melting point of the resin composition is preferably 130°C or higher and 170°C or lower, for example. In addition, when a styrene-based thermoplastic elastomer is used as the (B) component, the melting point of the resin composition is preferably 110°C or higher and 170°C or lower, for example.

[0034] In this specification, the melting point is measured as follows. First, a sample is subjected to differential scanning calorimetry (DSC) in accordance with, for example, JIS-K-7121 (1987). Specifically, in a DSC device, the temperature is raised from room temperature (normal temperature, for example, 27°C) to 220°C at a rate of 10°C / min. This allows the amount of heat absorbed (heat flow) per unit time to be plotted against the temperature to obtain a DSC curve. At this time, the temperature at which the amount of heat absorbed per unit time in the sample is maximized (peak) is defined as the "melting point (melting peak temperature)."

[0035] (Molecular Weight Distribution of Resin Composition) When the molecular weight distribution of the resin composition is measured, the resin composition has a molecular weight distribution of a predetermined width derived from the propylene-based resin (A) and the thermoplastic elastomer (B) contained in the resin composition. In this embodiment, the molecular weight distribution of the resin composition has a molecular weight of 1×10 4 The proportion of low molecular weight components is 3% or less. The proportion of low molecular weight components may be 2.5% or less, or 1.5% or less. The lower limit of the proportion of low molecular weight components is not particularly limited, but is, for example, 0.0001%.

[0036] The low molecular weight component has a molecular weight of 1×10 4 The following components are shown. The low molecular weight components are components derived from the thermoplastic elastomer (B) with a relatively low molecular weight, or components derived from the thermal decomposition products of component (B) or the propylene-based resin (A). The proportion of low molecular weight components indicates the proportion of low molecular weight components in the entire resin composition, and in the molecular weight distribution, the proportion of low molecular weight components with a molecular weight of 1 x 10 relative to the area of ​​the entire molecular weight distribution is shown. 4 The ratio is the area of ​​the following region. As described above, the low molecular weight component has a low melting point and may cause a decrease in insulation in a high temperature environment. In this respect, in this embodiment, the ratio of the low molecular weight component in the resin composition is set to 3% or less, so that the decrease in insulation can be suppressed. The measurement of the molecular weight distribution will be described later in the examples.

[0037] The molecular weight distribution of the resin composition is determined by the molecular weight distribution of the propylene-based resin (A) and the thermoplastic elastomer (B). The molecular weight range is not particularly limited, but is, for example, 1×10 3 More than 1×10 8 The ratio of the low molecular weight component in the resin composition can be adjusted by the content of the low molecular weight thermoplastic elastomer (B) and the molecular weight of the (B) component used.

[0038] (Components) Next, the propylene-based resin (A), the thermoplastic elastomer (B) and other additives that constitute the resin composition will be described.

[0039] (Propylene-based resin (A)) The propylene-based resin (A) is a resin material constituting the main component in the resin composition, and is a component having a propylene unit. As the (A) component, at least one of a propylene homopolymer (hereinafter also referred to as homo PP) and a propylene random polymer (hereinafter also referred to as random PP) can be used. The homo PP contains a propylene unit, and the random PP has a propylene unit and an ethylene unit. The content of the ethylene unit in the random PP may be, for example, 0.5% by mass or more and 15% by mass or less, and may be 0.5% by mass or more and 10% by mass or less. By making the content of the ethylene unit 0.5% by mass or more, it is possible to suppress the growth of spherulites (the generation of coarse crystals) and maintain high insulation properties. On the other hand, by making the content of the ethylene unit 15% by mass or less, it is possible to suppress the decrease in melting point and stably realize use in non-crosslinked or slightly crosslinked state.

[0040] From the viewpoint of obtaining higher insulation in the resin composition, the propylene-based resin (A) is preferably random PP. Homo PP has a larger amount of crystals than random PP and can obtain high insulation, but it may not obtain the inherent insulation because it causes cracks in the crystals or between crystals in the insulating layer. In contrast, random PP contains ethylene units, so although it has a lower amount of crystals, it is less likely to cause cracks due to coarse crystallization in the insulating layer, and it can obtain higher insulation than homo PP.

[0041] The stereoregularity of the propylene-based resin (A) may be isotactic, syndiotactic, or atactic. The stereoregularity is not particularly limited, but isotactic is preferable. The stereoregularity of the resin composition is isotactic, which can suppress the melting point of the resin composition from decreasing. As a result, the resin composition can be used stably in a non-crosslinked or slightly crosslinked state.

[0042] The melting point of the propylene-based resin (A) is not particularly limited, but it is preferable that the melting point is 130° C. or more and 170° C. or less. When the propylene-based resin (A) is homo PP, it is preferable that the melting point is 120° C. or more and 165° C. or less, and when it is random PP, it is preferable that the melting point is 130° C. or more and 170° C. or less. By using a propylene-based resin (A) having such a melting point, it is possible to increase the melting point of the resin composition while decreasing the proportion of low molecular weight components.

[0043] The number average molecular weight of the propylene-based resin (A) is not particularly limited, but is preferably 5.0×10 4 It is better to use 8.0×10 or more. 4 Above 5.0×10 5 If the component (A) has such a number average molecular weight, the amount of low molecular weight components is small, and the proportion of low molecular weight components in the resin composition can be adjusted to be smaller.

[0044] The number average molecular weight is calculated from the molecular weight distribution of the propylene-based resin (A) measured by gel permeation chromatography (GPC) based on a calibration curve prepared using polystyrene (PS) as a standard sample. The number average molecular weight of the thermoplastic elastomer (B) can be calculated in the same manner. A detailed calculation method will be described later in the Examples.

[0045] The melt flow rate (MFR) of the propylene-based resin (A) is preferably 0.1 g / 10 min to 5.0 g / 10 min from the viewpoint of compatibility with the thermoplastic elastomer (B), and may be 0.1 g / 10 min to 2.0 g / 10 min. By setting the MFR at such a value, the phase structure of the resin composition can be formed into a structure in which each component is compatible with the other components or a structure in which each component is finely dispersed. This can improve the flexibility and insulating properties of the resin composition. The MFR here is a value measured in accordance with JIS K7210 at a temperature of 190° C. and a load of 2.16 kg.

[0046] (Thermoplastic elastomer (B)) The thermoplastic elastomer (B) has lower crystallinity compared to the propylene-based resin (A) having propylene units, and can control the crystal growth of the (A) component, thereby imparting flexibility to the resin composition and insulating layer.

[0047] The thermoplastic elastomer (B) has a lower melting point and tends to have a higher ratio of low molecular weight components than the propylene-based resin (A), which tends to lower the melting point of the resin composition and increase the ratio of low molecular weight components in the resin composition. In this respect, in this embodiment, it is preferable to select component (B) that has a higher melting point and a lower ratio of low molecular weight components.

[0048] Specifically, the melting point of the thermoplastic elastomer (B) is preferably 110° C. or more and 160° C. or less. By using component (B) having such a melting point, it is easy to adjust the melting point to 110° C. or more without excessively lowering the melting point of the resin composition.

[0049] In addition, when the molecular weight distribution of the thermoplastic elastomer (B) was measured, the molecular weight was 1×10 4 It is preferable that the proportion of low molecular weight components that are 4.0% or less is 4.0% or less. By using the (B) component having such a molecular weight distribution, the proportion of low molecular weight components in the resin composition can be stably adjusted to 3% or less. In addition, the proportion of low molecular weight components contained in the (B) component is preferably as low as possible from the viewpoint of reducing the proportion of the low molecular weight components in the resin composition. The lower limit is not particularly limited, but may be, for example, 0.001%.

[0050] The number average molecular weight of the thermoplastic elastomer (B) is not particularly limited, but is preferably 5.0×10 4 It is better to use 8.0×10 or more. 4 Above 7.0×10 5 According to the component (B) having such a number average molecular weight, the ratio of low molecular weight components is small, and the proportion of low molecular weight components contained in the resin composition can be kept low.

[0051] The thermoplastic elastomer (B) may be any component capable of improving the flexibility of the resin composition, and may be, for example, a known component such as an amide, ester, olefin, styrene, urethane, vinyl chloride, or fluorine. Among these, at least one of an olefin and a styrene is preferably used from the viewpoint of finely dispersing or being compatible when mixed with the propylene-based resin (A). From the viewpoint of further improving the insulating properties, an olefin is preferably used. Compared with a styrene-based resin, an olefin-based resin has a higher compatibility with the propylene-based resin (A), and it is easy to select one having a high melting point and a high molecular weight, so that the insulating properties can be further improved.

[0052] The olefin-based thermoplastic elastomer (so-called TPO) is composed of at least one olefin unit of polyethylene and polypropylene as a hard segment, and an ethylene-α-olefin copolymer unit as a soft segment. The olefin-based thermoplastic elastomer may be a copolymer type of an olefin unit and an ethylene-α-olefin copolymer unit, or may be a mixed type of an olefin and an ethylene-α-olefin copolymer. Among these, it is preferable to use a copolymer from the viewpoint of mixability with the (A) component. The α-olefin is a linear or branched α-olefin having 2 to 8 carbon atoms, and for example, ethylene, propylene, 1-butene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 1-octene, etc. can be used. Among these, it is preferable that the TPO has polypropylene as a hard segment and ethylene-propylene rubber as a soft segment. The olefin-based thermoplastic elastomer may be used alone or in combination of two or more types.

[0053] The styrene-based thermoplastic elastomer is a copolymer containing a styrene unit as a hard segment and at least one monomer unit of ethylene, propylene, butylene, isoprene, etc. as a soft segment.

[0054] Examples of styrene-based thermoplastic elastomers 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.

[0055] 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).

[0056] The styrene-based thermoplastic elastomer is preferably one that does not contain a double bond in the chemical structure except for the benzene ring. When a double bond-containing elastomer is used, the resin component may be thermally deteriorated during molding of the resin composition, which may deteriorate the properties of the resulting insulating layer. In this respect, a double bond-free elastomer has high resistance to thermal deterioration, and therefore can maintain the properties of the insulating layer at a high level.

[0057] The content of styrene units in the styrene-based thermoplastic elastomer is not particularly limited, but from the viewpoint of controlling the crystal growth of the propylene-based resin (A) and softening the insulating layer, it is preferable that the content of styrene units is 5% by mass or more and 35% by mass or less. In addition, by keeping the content of styrene units within the above range, a predetermined amount of monomer units such as ethylene units can be secured as soft segments, so that the compatibility between the styrene-based thermoplastic elastomer and the (A) component can be improved. This allows the insulating properties of the insulating layer to be stably improved.

[0058] The melting points of the olefin-based thermoplastic elastomer and the styrene-based thermoplastic elastomer are not particularly limited. For example, the melting point of the olefin-based thermoplastic elastomer may be 130°C or more and 160°C or less. For example, the melting point of the styrene-based thermoplastic elastomer may be 110°C or more and 130°C or less. By using a component having such a melting point, it is easy to adjust the melting point of the resin composition to 110°C or more and 170°C or less without excessively lowering the melting point of the resin composition.

[0059] The MFR of the thermoplastic elastomer (B) is preferably 0.1 g / 10 min to 5.0 g / 10 min from the viewpoint of compatibility with the propylene-based resin (A), and may be 0.1 g / 10 min to 2.0 g / 10 min. By setting the MFR in this range, the above-mentioned phase structure can be stably formed in the resin composition.

[0060] From the viewpoint of finely dispersing or dissolving the thermoplastic elastomer (B) in the propylene-based resin (A) when mixed with the latter, it is preferable that the MFR of the thermoplastic elastomer (B) is small in difference from the MFR of the component (A). Specifically, it is preferable that the difference in MFR between the components (A) and (B) of the resin composition is 300 g / 10 min or less.

[0061] (Other additives) The resin composition may contain other additives as necessary, such as an antioxidant, a crosslinking agent, a lubricant, and a colorant.

[0062] The antioxidant may be, for example, a known antioxidant such as a phenol-based, sulfur-based, amine-based, etc. The content of the antioxidant is not particularly limited, but may be, for example, 0.1 part by mass or more and 1.0 part by mass or less when the total content of the propylene-based resin (A) and the thermoplastic elastomer (B) is 100 parts by mass.

[0063] 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. When dicumyl peroxide is used as the crosslinking agent, the residue is, for example, cumyl alcohol, α-methylstyrene, etc.

[0064] The resin composition may also contain a lubricant to improve the fluidity of the resin composition in the extrusion process of the insulating layer. As the lubricant, for example, a conventionally known component such as a fatty acid metal salt or a fatty acid amide can be used. These may be used alone or in combination of two or more.

[0065] In addition, the resin composition of the present embodiment can maintain high insulation by controlling the melting point and the ratio of low molecular weight components within a predetermined range, so there is no need to add inorganic fillers. As described below, inorganic fillers may cause clogging of the mesh during the extrusion process of the resin composition, and the remaining resin composition may be excessively heated, promoting the formation of low molecular weight components. In this regard, by not adding inorganic fillers, the ratio of low molecular weight components can be adjusted to be low.

[0066] (composition ratio) The compounding ratio of the propylene-based resin (A) and the thermoplastic elastomer (B) in the resin composition is not particularly limited as long as the melting point of the resin composition can be 110°C or higher. The content of each component may be adjusted depending on the (A) component and (B) component used. Specifically, when the total content of the propylene-based resin (A) and the thermoplastic elastomer (B) is taken as 100 parts by mass, the content of the (A) component may be 50 parts by mass or more and 90 parts by mass or less, and the content of the (B) component may be 10 parts by mass or more and 50 parts by mass or less. By setting the contents in this range, it is easy to adjust the melting point of the resin composition and the ratio of the low molecular weight component to the above-mentioned range.

[0067] (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.

[0068] 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 direct current.

[0069] 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 .

[0070] (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.

[0071] (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, a thermoplastic elastomer, the above-mentioned low crystalline resin, and the like, and conductive carbon black.

[0072] (insulating layer) The insulating layer 130 is provided so as to cover the outer periphery of the internal semiconductive layer 120, and is formed from the above-mentioned resin composition. For example, the insulating layer 130 is formed by extruding the resin composition.

[0073] (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.

[0074] (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.

[0075] (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.

[0076] 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.

[0077] 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.

[0078] (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 DC voltage applied to the power cable 10 of this embodiment is, for example, 20 kV or more.

[0079] (3) Cable characteristics In this embodiment, as described above, the resin composition contains a propylene-based resin (A) and a thermoplastic elastomer (B), and the melting point of the resin composition and the proportion of low molecular weight components in the molecular weight distribution satisfy predetermined requirements, making it possible to stably obtain high insulation properties in the insulating layer 130.

[0080] Specifically, the insulating layer 130 of this embodiment satisfies the following insulating requirements measured, for example, under high temperature and high electric field conditions. The measurement is performed, for example, on a sheet taken from the center in the thickness direction of the insulating layer 130. The sheet thickness of the insulating layer 130 at this time is, for example, 0.2 mm.

[0081] The amount of space charge accumulation measured in the insulating layer 130 under conditions of a temperature of 90° C. and a DC electric field of 40 kV / mm may be, for example, 100% or less, or may be 25% or less. Also, the amount of space charge accumulation measured under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm may be, for example, 100% or less, or may be 40% or less.

[0082] The amount of space charge accumulation is determined by the current integral charge method. In this method, charge is accumulated in a measuring capacitor connected in series to a sample sheet, and the amount of charge, which is the integral value of the current, is evaluated. Specifically, a DC electric field of 40 kV / mm or 80 kV / mm is continuously applied to the sample at a temperature of 90°C, and the amount of charge Q after 300 seconds is 300 Based on the charge amount Q0 immediately after application (0 seconds), the amount of space charge accumulation is calculated using the following formula. Space charge accumulation amount = (Q 300 / Q0-1)×100

[0083] The volume resistivity of the sheet of the insulating layer 130 measured under conditions of a temperature of 90° C. and a DC electric field of 40 kV / mm, or under conditions of a temperature of 90° C. and a DC electric field of 80 kV / mm, is, for example, 5.0×10 14 It is recommended that the resistance be 1.0×10 Ω cm or more. 15 It may be Ω·cm or more.

[0084] Furthermore, the DC breakdown field strength of the sheet of insulating layer 130 measured under a condition of a temperature of 90° C. may be, for example, 160 kV / mm or more, and may be 200 kV / mm or more.

[0085] (4) Extruder Next, prior to the method for producing a power cable according to the present embodiment, an extruder used in the production of the power cable will be described with reference to Fig. 2. Fig. 2 is a schematic configuration diagram of the extruder used in the method for producing a power cable according to an embodiment of the present disclosure.

[0086] The extruder 200 is a device for preparing the above-mentioned resin composition. In the extruder 200, the resin composition is prepared by mixing the components while heating them. At this time, the resin components may be thermally decomposed by heating and become low molecular weight. For example, when the heating and mixing is performed in an atmosphere containing oxygen, the resin components may be thermally decomposed. In addition, for example, if the resin components are retained in the extruder 200 and the heating time is extended, the resin components may be thermally decomposed. For this reason, the proportion of low molecular weight components in the resin composition may be higher than the original value of the contained components.

[0087] In this embodiment, from the viewpoint of adjusting the ratio of the low molecular weight component in the resin composition to a predetermined range, the extruder 200 may be configured so that the resin composition is extruded while adjusting the inside of the extruder to an inert gas atmosphere, or so that the screw and the extrusion port of the extruder are not likely to cause the resin composition to stagnate. The specific configuration of the extruder 200 will be described below.

[0088] As shown in Fig. 2, the extruder 200 is configured to include a cylindrical cylinder 210 to which the resin composition material is supplied, a hopper 220 for supplying the material into the cylinder 210, a screw 230 inserted from a first direction (left side in Fig. 2) of the cylinder 210 and arranged to be freely rotatable, a rotation drive mechanism 240 for rotating the screw 230, a discharge section 250 attached to a second direction (right side in Fig. 2) of the cylinder 210 and provided with a hole for discharging the resin composition, and an atmosphere adjustment section 260 for adjusting the inside of the cylinder 210 to an inert gas atmosphere. In the following, the first direction is also referred to as the upstream side in the heat mixing of the resin composition, and the second direction is also referred to as the downstream side.

[0089] The cylindrical cylinder 210 has a space therein for accommodating and mixing materials. In the cylindrical cylinder 210, the materials supplied to the internal space are mixed by the screw 230. The screw 230 is inserted from the end of the cylinder 210 in the first direction and disposed at the center of the axial direction of the cylinder 210. The screw 230 is connected to the rotation drive mechanism 240 and rotatably supported. The screw 230 is configured to be rotated by the rotation drive mechanism 240 and to push out the materials toward the discharge section 250 while mixing them. The screw 230 may be a single-shaft or a double-shaft screw. In FIG. 2, the double-shaft screws 230 are disposed in parallel in the depth direction of the paper, and one of the screws 230 is shown. As the rotation drive mechanism 240, for example, a known rotation motor or the like can be used.

[0090] In the screw 230, the screw flight 232 is arranged in a spiral shape on the surface of the screw body 231. The cross-sectional shape of the screw flight 232 is not particularly limited, but may be tapered as shown in FIG. 3. FIG. 3 is a schematic diagram for explaining the shape of the screw flight, and is a cross-sectional view along the axial direction of the screw 230. In FIG. 3, the right side is the tip direction of the screw 230 (the second direction of the cylinder 210), and the left side is the end direction of the screw 230 (the first direction of the cylinder 210). When the screw flight 232 has a rectangular shape as shown by the dashed line in FIG. 3, the resin composition is likely to remain on the end side of the screw flight 232, and the remaining resin composition may be thermally decomposed. Therefore, from the viewpoint of suppressing the retention of the resin composition on the surface of the screw 230, the cross-sectional shape of the screw flight 232 may be tapered on the side surface on the end side as shown in FIG. 3. In other words, it is preferable that the angle formed between the side surface of the screw flight 232 on the first direction side and the surface of the screw main body 231 is an obtuse angle. The angle is preferably set to, for example, 120° to 145°.

[0091] The discharge section 250 is disposed at an end of the cylinder 210 in the second direction. The discharge section 250 has a plurality of holes penetrating in the thickness direction, for example, and is configured to push out the resin composition prepared by mixing inside the cylinder 210 to the outside. For example, a breaker plate can be used as the discharge section 250. Note that a mesh or the like may be disposed between the cylinder 210 and the discharge section 250 for the purpose of removing foreign matter contained in the resin composition.

[0092] As shown in FIG. 4, a retention suppression member 270 may be disposed at the end of the cylinder 210 in the second direction at a position where the retention suppression member 270 contacts the discharge portion 250. FIG. 4 is a schematic diagram for explaining the retention suppression member, and is a cross-sectional view of the end of the cylinder 210 in the second direction. As shown in FIG. 4, the retention suppression member 270 suppresses the resin composition from staying in the cylinder 210 and promotes extrusion from the discharge portion 250. The retention suppression member 270 has a plurality of tapered holes 271 that penetrate in the thickness direction and have a smaller diameter toward the thickness direction. The retention suppression member 270 is disposed so that the small diameter side of the tapered hole 271 communicates with the hole 251 of the discharge portion 250. The retention suppression member 270 can suppress the resin composition from staying at the edge of the hole 251 of the discharge portion 250 or at the corner between the inner wall of the cylinder 210 and the discharge portion 250. The retention suppression member 270 may be made of the same material as the breaker plate, for example.

[0093] An atmosphere adjustment unit 260 that adjusts the inside of the cylinder 210 to an inert gas atmosphere is connected to the cylinder 210. The atmosphere adjustment unit 260 is configured to supply an inert gas to the inside of the cylinder 210. Although air may be mixed into the inside of the cylinder 210 as the material is supplied from the hopper 220, the atmosphere adjustment unit 260 can adjust the inside of the cylinder 210 to an inert gas atmosphere. This makes it possible to prevent the mixed materials and the resulting resin composition from being oxidized and thermally decomposed by air. In other words, it is possible to prevent an increase in the ratio of low molecular weight components in the resin composition while maintaining a high ratio of high molecular weight components.

[0094] The inert gas is not particularly limited, but may be, for example, nitrogen gas or argon gas.

[0095] The extruder 200 may include a heating section (not shown) for heating the inside of the cylinder 210. As the heating section, a conventionally known one can be used.

[0096] (5) Manufacturing method of power cables Next, a method for manufacturing a power cable according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a flowchart showing a method for manufacturing a power cable according to an embodiment of the present disclosure. Hereinafter, steps are abbreviated as "S".

[0097] (S100: Resin composition preparation step) First, a resin composition for forming the insulating layer 130 is prepared.

[0098] In this embodiment, for example, a propylene-based resin (A), a thermoplastic elastomer (B), and other additives (such as an antioxidant) as necessary are supplied to an extruder 200 shown in FIG. 2. Then, the materials supplied from a hopper 220 are mixed while being heated inside a cylinder 210. At this time, the inside of the cylinder 210 is adjusted to an inert gas atmosphere by an atmosphere adjustment unit 260. Then, the resin composition obtained by heating and mixing is extruded from a discharge unit 250 and granulated. As a result, a pellet-shaped resin composition that will constitute the insulating layer 130 is obtained.

[0099] The content of each component may be appropriately adjusted so that the melting point of the resin composition is 110° C. or higher and the proportion of low molecular weight components is 3% or less. For example, the content of the propylene-based resin (A) may be 50 parts by mass or more and 90 parts by mass or less, and the content of the thermoplastic elastomer (B) may be 10 parts by mass or more and 50 parts by mass or less.

[0100] In the resin composition preparation step S100, the components are heated, mixed, and extruded in an inert gas atmosphere, thereby making it possible to suppress and reduce the proportion of low molecular weight components that are caused by heating the resin composition.

[0101] (S200: Conductor preparation process) On the other hand, conductor 110 is prepared by twisting together a plurality of conductor core wires.

[0102] (S300: Cable core forming process (extrusion process, insulation layer forming process)) After the resin composition preparation step S100 and the conductor preparation 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, for example, 3 mm or more.

[0103] At this time, in this embodiment, for example, a three-layer co-extruder is used to simultaneously form the inner semiconductive layer 120, the insulating layer 130 and the outer semiconductive layer 140.

[0104] Specifically, for example, the composition for the internal semiconductive layer is put into the extruder A that forms the internal semiconductive layer 120 among the three-layer simultaneous extruders. The above-mentioned pellet-shaped resin composition is put into the extruder 200 shown in FIG. 2 as the extruder B that forms the insulating layer 130. At this time, the inside of the cylinder 210 of the extruder 200 is adjusted to an inert gas atmosphere. The set temperature of the extruder B is set to a temperature that is, for example, 10°C to 80°C higher than the desired melting point. The set temperature may be appropriately adjusted based on the linear speed and extrusion pressure. The composition for the external semiconductive layer, which contains the same material as the resin composition for the internal semiconductive layer put into the extruder A, is put into the extruder C that forms the external semiconductive layer 140.

[0105] 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.

[0106] The extrusion is then cooled, for example with water.

[0107] In the cable core forming step S300, the pellet-shaped resin composition is mixed and extruded while being heated in an inert gas atmosphere, thereby suppressing an increase in the proportion of low molecular weight components due to heating. As a result, the proportion of low molecular weight components in the insulating layer 130 can be suppressed to be low.

[0108] 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.

[0109] (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.

[0110] (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 .

[0111] In this manner, the power cable 10 is manufactured as a solid insulated power cable.

[0112] (6) Effects of this embodiment According to this embodiment, one or more of the following advantages are achieved.

[0113] (a) The resin composition of the present embodiment contains a propylene-based resin (A) having a propylene unit and a thermoplastic elastomer (B), and the resin composition has a melting point of 110° C. or higher, and a molecular weight distribution of 1×10 4The ratio of the following low molecular weight components is 3% or less. The resin composition may contain low molecular weight components derived from the (B) component, and the low molecular weight components may become amorphous or melt in a high temperature environment. The melted low molecular weight components may move in the resin composition, causing the accumulation of space charges, behave as charge carriers, and may deteriorate the insulating properties. In this regard, by increasing the melting point of the resin composition to 110°C or more, the melting of the resin components and the associated flow can be suppressed, and the low molecular weight components can be fixed in the resin composition. In other words, the low molecular weight components can be maintained in a state in which they are finely dispersed or in a compatible state in the resin composition. Moreover, by reducing the ratio of the low molecular weight components in the resin composition, the deterioration of the insulating properties due to the low molecular weight components can be further suppressed. As a result, the resin composition can maintain high insulating properties even in a high temperature environment. Therefore, by forming the insulating layer 130 from the above resin composition, it is possible to make the insulating layer 130 have high voltage resistance even at high temperatures. As a result, the power cable 10 of this embodiment enables stable DC transmission.

[0114] In the (b) resin composition, the thermoplastic elastomer (B) can be finely dispersed or dissolved in the propylene-based resin (A). In other words, the (B) component can be uniformly distributed in the resin composition. As a result, the (B) component can suppress excessive crystal growth of the (A) component, and flexibility can be imparted to the resin composition. In other words, the flexibility of the resin composition can be expressed more stably than ever before.

[0115] (c) The thermoplastic elastomer (B) may be at least one of an olefin-based thermoplastic elastomer and a styrene-based thermoplastic elastomer. The olefin-based thermoplastic elastomer can be finely dispersed or dissolved in the propylene-based resin (A) and has a higher melting point than the styrene-based thermoplastic elastomer, so that the above-mentioned effect (a) can be obtained more reliably. On the other hand, the styrene-based thermoplastic elastomer can trap electrons by the aromatic ring to form a stable resonance structure, so that the insulating properties of the resin composition can be further improved.

[0116] (d) The melting point of the thermoplastic elastomer (B) is preferably 110° C. or higher and 160° C. or lower. When such a (B) component is mixed with the propylene-based resin (A) to prepare a resin composition, the melting point of the resin composition can be adjusted to 110° C. or higher without excessively lowering the melting point. This makes it possible to more reliably obtain the above-mentioned effect (a).

[0117] (e) Thermoplastic elastomer (B) has a molecular weight of 1×10 4 The ratio of the following component is preferably 4.0% or less. By using such component (B), the ratio of the low molecular weight component can be more reliably adjusted to 3% or less when the resin composition is prepared. This makes it possible to more reliably obtain the above-mentioned effect (a).

[0118] The melting point of the (f) propylene-based resin is preferably 130° C. or higher and 170° C. or lower. When mixed with the thermoplastic elastomer (B), such component (A) can maintain the melting point of the resin composition at 110° C. or higher and achieve the flexibility required for a power cable.

[0119] (g) The resin composition may contain 50 to 90 parts by mass of the (A) component and 10 to 50 parts by mass of the (B) component, when the total content of the propylene-based resin (A) and the thermoplastic elastomer (B) is taken as 100 parts by mass. By using these blending amounts, the melting point of the resin composition can be more reliably adjusted to 110°C or higher and the proportion of low molecular weight components in the resin composition to 3% or less, and the above-mentioned effect (a) can be more reliably obtained.

[0120] (h) The number average molecular weight of the thermoplastic elastomer (B) is 8.0×10 4 The content of low molecular weight components in the (B) component is low, so that when the (B) component is mixed with the (A) propylene-based resin to prepare a resin composition, the content of low molecular weight components in the resin composition can be reduced. This makes it possible to more reliably obtain the above-mentioned effect (a).

[0121] (i) The resin composition may be substantially free of modified polymers or inorganic fillers that improve insulation. The resin composition is formed so that the melting point and the ratio of low molecular weight components are within a predetermined range, so that high insulation can be achieved without including modified polymers or inorganic fillers. In addition, when the resin composition includes an inorganic filler, the resin composition is likely to clog the mesh when extruded from the extruder 200, and the resin composition is likely to remain in the extruder 200. In this respect, by not including an inorganic filler, the retention of the resin composition and the reduction in molecular weight due to the retention can be more reliably suppressed. In addition, modified polymers tend to be easily thermally deteriorated, but by not including a modified polymer, the deterioration of the resin composition during the manufacture of a power cable over a long period of time can be suppressed. As a result, for example, when a long power cable is manufactured, the thermal deterioration of the resin composition can be suppressed, and the variation in characteristics can be reduced and maintained high over the longitudinal direction of the insulation layer.

[0122] (j) When preparing the resin composition, the propylene-based resin (A), the thermoplastic elastomer (B), and other additives, if necessary, may be supplied to the cylinder 210 of the extruder 200 and heated and mixed in an inert gas atmosphere. Alternatively, the screw flight 232 of the screw 230 in the extruder 200 may be configured so that the first direction side is tapered. Alternatively, a retention suppression member 270 having a plurality of tapered holes 271 penetrating in the thickness direction and having a diameter that decreases from the first direction to the second direction may be disposed between the cylinder 210 and the discharge section 250 of the extruder 200. According to at least one of these configurations, it is possible to suppress the resin component from being thermally decomposed and becoming low molecular weight during the preparation of the resin composition, and thus it is possible to more reliably adjust the ratio of low molecular weight components in the resin composition to 3% or less, and obtain the above-mentioned effect (a).

[0123] <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.

[0124] 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.

[0125] 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).

[0126] 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

[0127] 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.

[0128] (1) Materials The materials used in preparing the resin composition are listed below.

[0129] Propylene random polymer (PP1) was prepared as the propylene resin (A), and olefin elastomers (TPO1)-(TPO2) and styrene thermoplastic elastomers (SEBS1)-(SEBS2) were prepared as the thermoplastic elastomers (B). The physical properties of each component are as follows. The melting point, number average molecular weight, MFR, and proportion of low molecular weight components were measured in advance using the methods described below. PP1: Melting point 160°C, number average molecular weight 1.5×10 5 , MFR 0.6g / 10min TPO1: An olefin-based thermoplastic elastomer with hard segments of polypropylene and soft segments of ethylene-propylene rubber, melting point 135°C, low molecular weight component ratio 5.1%, number average molecular weight 9.0×10 4 , MFR4.7g / 10min TPO2: Olefin-based thermoplastic elastomer with hard segments of polypropylene and soft segments of ethylene-propylene rubber, melting point 140°C, low molecular weight component ratio 1.5%, number average molecular weight 1.6×10 5 , MFR3.2g / 10min SEBS1: Melting point 115°C, low molecular weight component ratio 5.4%, number average molecular weight 1.2×10 5 , MFR 4.5g / 10min, styrene content 10% by mass SEBS2: Melting point 120°C, low molecular weight component ratio 2.0%, number average molecular weight 1.5×10 5 , MFR 3.7g / 10min, styrene content 12% by mass

[0130] As another additive, a hindered phenol, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], was prepared as an antioxidant.

[0131] (2) Preparation of resin composition The above materials were fed to an extruder in the amounts shown in Table 1 below, and were heated, mixed, and granulated by the extruder to produce Samples 1 to 5. When preparing the resin compositions, the extrusion conditions were changed as follows. In Samples 1 to 4, the above-mentioned extruder was used, the inside of the cylinder was purged with nitrogen gas, and a screw with a tapered side surface on the first direction side of the screw flight was used to perform extrusion. On the other hand, in Sample 5, the inside of the cylinder was not purged with nitrogen gas, and a rectangular screw was used to perform extrusion. In each sample, the amount of antioxidant was 0.1 parts by mass.

[0132] [Table 1]

[0133] (3) Power cable production Next, a conductor was prepared by twisting together conductor core wires made of dilute copper alloy with a diameter of 14 mm. After the conductor was prepared, the resin composition for the internal semiconductive layer containing an ethylene-ethyl acrylate copolymer, the resin composition for the insulating layer prepared in Table 1, and the resin composition for the external semiconductive layer made of the same material as the resin composition for the internal semiconductive layer were respectively fed into extruders A to C. The extrudates from extruders A to C were guided to a common head, and the internal semiconductive layer, the insulating layer, and the external semiconductive layer were simultaneously extruded from the inside to the outside around the conductor. This produced a sample of a power cable having a conductor, an internal semiconductive layer, an insulating layer, and an external semiconductive layer from the center to the periphery.

[0134] (4) Evaluation The prepared resin composition and a sample cut from the insulation layer of the manufactured power cable were evaluated for melting point, proportion of low molecular weight components, space charge characteristics, volume resistivity, and DC breakdown strength. Each evaluation method is as follows.

[0135] (Melting Point) The melting point of the resin composition prepared in each 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. For example, α-alumina was used as the reference sample. The mass of the measurement 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. At this time, the temperature at which the amount of heat absorbed per unit time in each measurement sample was maximized (highest peak) was defined as the "melting point".

[0136] (molecular weight distribution) The molecular weight distribution of the resin composition forming the insulating layer was measured by measuring the number average molecular weight of the base resin based on a calibration curve prepared by GPC using PS as a standard sample under the following conditions. In this example, based on the obtained molecular weight distribution, the molecular weight of 1×10 4 Calculate the area ratio of the following regions, and calculate the molecular weight of 1×10 4 The proportions of the following low molecular weight components were determined. Equipment: Tosoh HLC-8321GPC / HT Eluent: 1,2,4-trichlorobenzene Temperature: 140℃ Concentration: 1.0mg / mL Flow rate: 1.0mL / min The calibration curve for PS was prepared based on the results within the molecular weight range of 1,000 to 5.5 million.

[0137] (Space charge characteristics) The space charge characteristics of the insulating layer were evaluated by the amount of space charge accumulated in the insulating layer. The amount of space charge accumulated was measured by a current integration charge method. Specifically, a sheet-shaped sample was first taken from the insulating layer of the power cable. Then, this sample was connected in series to a measuring capacitor, and then a charge was accumulated in the measuring capacitor, and the amount of charge, which is the integral value of the current, was measured. In this example, a DC electric field of 40 kV / mm or 80 kV / mm was continuously applied to the sample at a temperature of 90°C, and the amount of charge Q after 300 seconds had elapsed was measured. 300 Based on the charge amount Q0 immediately after application (0 seconds), the spatial charge accumulation amount at a temperature of 90°C and a DC electric field of 40 kV / mm and the spatial charge accumulation amount at a temperature of 90°C and a DC electric field of 80 kV / mm were calculated by the following formula. In this example, the spatial charge accumulation amount at a temperature of 90°C and a DC electric field of 40 kV / mm was evaluated as A (best), the spatial charge accumulation amount was evaluated as more than 25% and less than 100%, and the spatial charge accumulation amount was evaluated as C (poor). In addition, the spatial charge accumulation amount at a temperature of 90°C and a DC electric field of 80 kV / mm was evaluated as A (best), the spatial charge accumulation amount was evaluated as more than 40% and less than 100%, and the spatial charge accumulation amount was evaluated as C (poor). Space charge accumulation amount = (Q 300 / Q0-1)×100

[0138] (Volume resistivity) The volume resistivity of the insulating layer was measured using a sheet-shaped sample taken from the insulating layer of a power cable in the same manner as for the space charge characteristics. Specifically, the sample was immersed in silicone oil at a temperature of 90°C, and a direct current electric field of 40 kV / mm or 80 kV / mm was applied to the sample using a flat electrode with a diameter of 25 mm to measure the volume resistivity. 15 Ω cm or more is rated A (best), and the volume resistivity is 5×10 14 Ω cm or more 1×10 15 If the volume resistivity is less than 5×10 14 If it was less than Ω·cm, it was rated as C (poor).

[0139] (DC breakdown strength) The DC breakdown strength of the insulating layer was measured using a sheet-shaped sample taken from the insulating layer of a power cable in the same manner as the space charge characteristics. Specifically, the sample was first immersed in silicone oil at a temperature of 90°C, and a flat electrode with a diameter of 25 mm was used to increase the applied voltage at a rate of 4 kV / min. Then, when the sample reached dielectric breakdown, the voltage applied at this time was divided by the thickness of the sample to obtain the DC breakdown strength of the sample. The DC breakdown strength was evaluated as A (best) when it was 200 kV / mm or more, B (good) when it was 160 kV / mm or more and less than 200 kV / mm, and C (poor) when it was less than 160 kV / mm.

[0140] (5) Evaluation results The above-mentioned evaluations were carried out for each sample, and the evaluation results are summarized in Table 1.

[0141] As shown in Table 1, in Sample 1 and Sample 2, TPO1 and SEBS1, which have high melting points but high proportions of low molecular weight components, were used, and it was confirmed that although the melting point of the resin composition can be made 110°C or higher, the proportion of low molecular weight components cannot be maintained at 3% or less. As a result, it was confirmed that the insulation properties are reduced in a high temperature environment. It is presumed that these samples have a high proportion of low molecular weight components, which melt in a high temperature environment and flow in the resin composition, causing localized charge accumulation. In particular, it is presumed that Sample 2 has a lower melting point of the resin composition than Sample 1, and therefore the low molecular weight components melt more easily, resulting in a further reduction in insulation properties.

[0142] On the other hand, in Samples 3 and 4, TPO2 and SEBS2, which have high melting points and low proportions of low molecular weight components, were used, and it was confirmed that the melting point of the resin composition could be 110°C or higher and the proportion of low molecular weight components could be 3% or lower. In particular, it was confirmed that by using TPO2, which has a higher melting point than SEBS2, the melting point of the resin composition could be made higher, and as a result, the insulation properties in a high temperature environment could be made higher. This is presumably because the melting of the resin components contained in the resin composition in a high temperature environment could be further suppressed, and the dispersion and compatibility of the low molecular weight components could be maintained.

[0143] In addition, in sample 5, the same material as in sample 3 was used, but it was confirmed that the proportion of low molecular weight components was higher than that of sample 3. As a result, it was confirmed that the insulating properties in a high temperature environment were lower than those of sample 3. The reason why the proportion of low molecular weight components was higher than that of sample 3 is presumed to be that in sample 5, the resin composition is likely to remain in the extruder in which the materials are heated and mixed, and the resin composition is reduced in molecular weight due to thermal decomposition, because the extruder does not use nitrogen gas purging or a screw flight having a tapered shape. And, it is presumed that the low molecular weight components melt and flow in a high temperature environment, causing localized accumulation of charges and reducing the insulating properties.

[0144] As described above, it was confirmed that by using a propylene-based resin (A) having propylene units and a thermoplastic elastomer (B) in a resin composition and by making the melting point and the ratio of low molecular weight components of the resin composition satisfy the specified requirements, it is possible to suppress the accumulation of space charges and improve the volume resistivity and the DC breakdown field strength even in a high temperature environment. In other words, it was confirmed that high insulation properties can be stably obtained in the resin composition. As a result, the insulation layer can be made to have high voltage resistance even in a high temperature environment, and stable DC transmission is possible with the power cable.

[0145] <Preferred aspects of the present disclosure> Preferred aspects of the present disclosure are described below.

[0146] (Appendix 1) A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: Resin composition.

[0147] (Appendix 2) A conductor; an insulating layer formed from a resin composition and covering the conductor; Equipped with The resin composition comprises A propylene-based resin (A) having a propylene unit; A thermoplastic elastomer (B), The melting point is 110°C or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 4 The percentage of the following ingredients is 3% or less: Power cable.

[0148] (Appendix 3) In Appendix 2, preferably, The thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit.

[0149] (Appendix 4) In Supplementary Note 3, preferably, The thermoplastic elastomer (B) is an olefin-based thermoplastic elastomer having an olefin unit.

[0150] (Appendix 5) In any one of Supplementary Note 2 to Supplementary Note 4, preferably The melting point of the thermoplastic elastomer (B) is 110°C or higher and 160°C or lower.

[0151] (Appendix 6) In any one of Supplementary Note 2 to Supplementary Note 5, preferably The thermoplastic elastomer (B) has a molecular weight of 1×10 4 The percentage of the following components is 4.0% or less.

[0152] (Appendix 7) In any one of Supplementary Note 2 to Supplementary Note 6, preferably The propylene-based resin (A) is a propylene random polymer.

[0153] (Appendix 8) In any one of Supplementary Note 2 to Supplementary Note 7, preferably The melting point of the propylene-based resin (A) is 130°C or higher and 170°C or lower.

[0154] (Appendix 9) In any one of Supplementary Note 2 to Supplementary Note 8, preferably The resin composition contains 50 parts by mass or more and 90 parts by mass or less of the propylene-based resin (A) and 10 parts by mass or more and 50 parts by mass or less of the thermoplastic elastomer (B).

[0155] (Appendix 10) In any one of Supplementary Note 2 to Supplementary Note 9, preferably The number average molecular weight of the thermoplastic elastomer (B) is 5.0×10 4 That's all.

[0156] (Appendix 11) In any one of Supplementary Note 2 to Supplementary Note 10, preferably The number average molecular weight of the propylene-based resin (A) is 5.0×10 4 That's all.

[0157] (Appendix 12) A method for producing a power cable comprising: a conductor; and an insulating layer formed from a resin composition and covering the conductor, A preparation step of preparing the resin composition; and forming an insulating layer by extruding the resin composition so as to cover the conductor, thereby forming the insulating layer. In the preparation step, a propylene-based resin (A) having a propylene unit and a thermoplastic elastomer (B) are added so that the melting point of the resin composition is 110° C. or higher. When the molecular weight distribution of the resin composition is measured, the molecular weight is 1×10 4 Heat and mix the following ingredients so that their ratio is 3% or less. A method for manufacturing power cables.

[0158] (Appendix 13) In Supplementary Note 12, preferably, In the preparation step, the heating and mixing are carried out in an inert gas atmosphere.

[0159] (Appendix 14) In addition, preferably, In the preparation process, the resin composition is prepared using an extruder including a cylindrical cylinder, a screw inserted from a first direction of the cylinder and arranged to be freely rotatable, a discharge section attached to a second direction of the cylinder and provided with an outlet for discharging the resin composition, and an atmosphere adjustment section that adjusts the inside of the cylinder to an inert gas atmosphere.

[0160] (Appendix 15) In Supplementary Note 14, preferably, The screw comprises a screw body and a screw flight arranged helically on the surface of the screw body, The screw flight is configured so that a side surface on the first direction side is tapered. [Explanation of symbols]

[0161] 10 Power Cable 110 Conductor 120 Inner semiconducting layer 130 Insulating layer 140 Outer semiconducting layer 150 Shielding layer 160 Sheath 200 Extruder 210 Cylinder 220 Hopper 230 Screw 231 Screw body 232 Screw Flight 240 Rotational Drive Mechanism 250 Discharge section 251 Hole 260 Atmosphere Control Unit 270 Retention control member 271 Tapered hole

Claims

1. A composition comprising only a propylene-based resin (A) having a propylene unit and a thermoplastic elastomer (B) as resin components, The melting point is 110° C. or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 ４ The percentage of the following components is 3% or less: Resin composition.

2. A conductor; an insulating layer formed from a resin composition and covering the conductor; Equipped with The resin composition comprises The resin component contains only a propylene-based resin (A) having a propylene unit and a thermoplastic elastomer (B), The melting point is 110° C. or higher, When the molecular weight distribution was measured, the molecular weight was 1×10 ４ The percentage of the following components is 3% or less: Power cable.

3. The thermoplastic elastomer (B) is at least one of an olefin-based thermoplastic elastomer having an olefin unit and a styrene-based thermoplastic elastomer having a styrene unit.

3. The power cable according to claim 2.

4. The melting point of the thermoplastic elastomer (B) is 110° C. or more and 160° C. or less.

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

5. The thermoplastic elastomer (B) has a molecular weight of 1×10 ４ The percentage of the following components is 4.0% or less: The power cable according to any one of claims 2 to 4.

6. The melting point of the propylene-based resin (A) is 130° C. or higher and 170° C. or lower.

6. The power cable according to claim 2 .

7. The resin composition contains the propylene-based resin (A) in an amount of 50 parts by mass or more and 90 parts by mass or less, and the thermoplastic elastomer (B) in an amount of 10 parts by mass or more and 50 parts by mass or less. The power cable according to any one of claims 2 to 6.

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