Resin composition molded article and power cable

Abstract

To provide a resin composition molding of which insulation is improved.SOLUTION: A resin composition is a resin composition that is coated around a long object, contains propylene units, and in a molding containing resin composition after a predetermined flexure test, neither a void having a maximum length of 1 μm or more nor a crystal having a maximum length exceeding 10 μm is present. However, a bending test comprises: a first step of bending a power cable such that a bending rate of a bending radius of the power cable to an outer diameter of an insulation layer is 7 or less, and a second step of bending the power cable at a bending rate same as the bending rate of the first step in a direction opposite from the bending direction of the first step.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a resin composition, a resin composition molded article, a power cable, and a method for producing a power cable. This application claims priority to Japanese application "Patent Application No. 2020-211489" filed on December 21, 2020, and incorporates all of the contents of the above-mentioned Japanese application by reference. [Background technology]

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

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

[0004] According to one aspect of the present disclosure, A resin composition that is coated around a long object, Contains propylene units, In a molded product containing the resin composition after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the molded body so that a bending ratio of a bending radius of the molded body to an outer diameter of the molded body is 7 or less, and a second step of bending the molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. A resin composition is provided.

[0005] According to another aspect of the present disclosure, A resin composition molded article coated around a long object, Contains propylene units, In the resin composition molded body after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the resin composition molded body so that a bending ratio of a bending radius of the resin composition molded body to an outer diameter of the resin composition molded body is 7 or less, and a second step of bending the resin composition molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. A molded article of a resin composition is provided.

[0006] According to yet another aspect of the present disclosure, A resin composition molded article, Contains propylene units, The resin composition molded product satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded product obtained by measuring elasticity in a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the conditions of tapping 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C. using a cantilever having a tip made of silicon and a curvature radius of less than 20 nm, The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. A molded article of a resin composition is provided.

[0007] According to yet another aspect of the present disclosure, Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A molded article of a resin composition is provided.

[0008] According to yet another aspect of the present disclosure, Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A molded article of a resin composition is provided.

[0009] According to yet another aspect of the present disclosure, Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution A molded article of a resin composition is provided.

[0010] According to yet another aspect of the present disclosure, A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, In the insulating layer after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; A power cable is provided.

[0011] According to yet another aspect of the present disclosure, A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, the insulating layer satisfies the first, second and third requirements in a distribution of counts relative to the elastic modulus of the insulating layer, the distribution being obtained by micro-area elasticity measurement using a scanning probe microscope; A power cable is provided.

[0012] According to yet another aspect of the present disclosure, A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A power cable is provided.

[0013] According to yet another aspect of the present disclosure, A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A power cable is provided.

[0014] According to yet another aspect of the present disclosure, A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A power cable is provided.

[0015] According to yet another aspect of the present disclosure, Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The storage modulus of the resin A at 25°C measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A method for manufacturing a power cable is provided.

[0016] According to yet another aspect of the present disclosure, Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 5 to 200, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A method for manufacturing a power cable is provided.

[0017] According to yet another aspect of the present disclosure, A step of preparing a resin composition having a resin A containing a propylene unit and a resin B containing two or more monomer units; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 The following: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 The following: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A method for manufacturing a power cable is provided. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example of the molecular weight distribution of each of Resin A and Resin B according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 is a schematic cross-sectional view perpendicular to the axial direction of a power cable according to an embodiment of the present disclosure. [Diagram 3] FIG. 3 is a diagram showing an example of the results of micro-area elasticity measurement. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] [Problem that this disclosure aims to solve] Cross-linked polyethylene has been widely used in the insulating layer of power cables, but after deterioration over time, it cannot be recycled and must be incinerated, raising concerns about its impact on the environment.

[0020] In recent years, therefore, resins containing propylene (hereinafter also referred to as "propylene-based resins") have been attracting attention as resin components constituting the insulating layer. Even if the propylene-based resin is not crosslinked, it can satisfy the insulating properties required for a power cable. In other words, it can achieve both insulating properties and recyclability.

[0021] An object of the present disclosure is to provide a technique capable of improving the insulating properties of a molded article containing a propylene-based resin.

[0022] [Effects of this disclosure] According to the present disclosure, it is possible to improve the insulating properties of a molded article containing a propylene-based resin.

[0023] [Description of the embodiments of the present disclosure] <Knowledge gained by the inventors> First, the findings of the inventors will be outlined.

[0024] Generally, polypropylene alone is harder than polyethylene and the like.

[0025] For this reason, in the technical field of automobile bumpers, resin components made by adding ethylene propylene rubber (EPR) to polypropylene have been used in the past. By adding EPR to polypropylene, the resin component can be made flexible.

[0026] Therefore, in the technical field of power cables, the inventors have attempted to add a flexible resin such as EPR to a propylene-based resin as a resin component constituting the insulating layer in order to improve the flexibility of the insulating layer.

[0027] However, the inventors have investigated the addition of a flexible resin to the propylene-based resin in the insulating layer and have found that the insulating properties of the insulating layer may be reduced after the power cable is bent.

[0028] As a result of analyzing the insulating layer whose insulating properties had deteriorated due to bending, it was found that the cause of the deterioration of insulating properties after bending was due to the following mechanism.

[0029] As described above, the elastic modulus of the flexible resin is lower than that of the polypropylene-based resin. Each resin has a specific molecular weight distribution that is correlated with the elastic modulus. As a result, the molecular weight distribution of the flexible resin and the molecular weight distribution of the polypropylene-based resin are different from each other.

[0030] When two resins having different molecular weight distributions are mixed in this way, at least one of the resins may become locally biased.

[0031] For example, there is a possibility that a component having a high elastic modulus is locally concentrated due to the polypropylene resin. Hereinafter, the region where the component having a high elastic modulus is locally concentrated is also referred to as a "high elastic region". In the high elastic region derived from the polypropylene resin, the crystallinity is high and the high elastic region becomes hard.

[0032] On the other hand, for example, components having a low elastic modulus may be locally concentrated due to the flexible resin. The region where the components having a low elastic modulus are locally concentrated is hereinafter also referred to as a "low elastic region." In the low elastic region derived from the flexible resin, the crystallinity is low (becomes amorphous), and the low elastic region becomes soft.

[0033] Even if the resin is locally biased in the insulating layer as described above, there is no problem with the insulation immediately after manufacture. However, if the resin is locally biased in the insulating layer, the following phenomenon may occur when the power cable is bent.

[0034] When the power cable is bent, local stress is applied in the resin component. When local stress is applied, for example, inside the high elasticity region, crystals may crack or separate, which may cause microvoids. Or, at the interface between the crystalline high elasticity region and the amorphous low elasticity region, they may separate, which may cause microvoids. Or, even inside the amorphous low elasticity region, materials that are particularly poorly compatible may separate or peel along the material interface, which may cause microvoids. Note that the term "void" here also includes cracks.

[0035] Furthermore, when local stress is applied within the resin component, for example, within the highly elastic region derived from the polypropylene-based resin, coarse crystals (spherulites) may be generated as a trigger by mechanical strain.

[0036] The minute voids and coarse crystals generated during bending in this way reduce the insulating properties, and therefore, when a high electric field is applied to the power cable, the electric field may concentrate on the minute voids and coarse crystals in the insulating layer, causing a dielectric breakdown of the insulating layer.

[0037] As a result of intensive research into the above, the inventors have found that it is possible to suppress the deterioration of insulation properties after bending by suppressing the generation of minute voids and coarse crystals during bending.

[0038] The present disclosure is based on the above-mentioned findings of the inventors.

[0039] <Embodiments of the present disclosure> Next, embodiments of the present disclosure will be listed and described.

[0040] [1] A resin composition according to one embodiment of the present disclosure, A resin composition that is coated around a long object, Contains propylene units, In a molded product containing the resin composition after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the molded body so that the bending ratio of the bending radius of the molded body to the outer diameter of the molded body is 7 or less, and a second step of bending the molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0041] [2] A molded article of a resin composition according to one embodiment of the present disclosure, A resin composition molded article coated around a long object, Contains propylene units, In the resin composition molded product after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the resin composition molded body so that a bending ratio of the bending radius of the resin composition molded body to the outer diameter of the resin composition molded body is 7 or less, and a second step of bending the resin composition molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0042] [3] The resin composition molded article according to the above [2], The resin composition molded product satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded product obtained by measuring elasticity in a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the conditions of tapping 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C. using a cantilever having a tip made of silicon and a curvature radius of less than 20 nm, The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less, The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. According to this configuration, it is possible to suppress the occurrence of minute voids and coarse crystals when the substrate is bent.

[0043] [4] A resin composition molded article according to another embodiment of the present disclosure, A resin composition molded article, Contains propylene units, The resin composition molded product satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded product obtained by measuring elasticity in a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the conditions of tapping 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C. using a cantilever having a tip made of silicon and a curvature radius of less than 20 nm, The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0044] [5] In the resin composition molded article according to any one of the above [2] to [4], Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; has. This configuration allows the molded body to be flexible.

[0045] [6] The resin composition molded article according to the above [5], The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. According to this configuration, it is possible to suppress the occurrence of minute voids and coarse crystals when the substrate is bent.

[0046] [7] The resin composition molded article according to the above [5] or [6], The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25° C. measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less. According to this configuration, resin A and resin B can be mixed uniformly.

[0047] [8] A resin composition molded article according to another embodiment of the present disclosure, Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0048] [9] The resin composition molded article according to any one of [5] to [8] above, Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25° C., as measured by dynamic viscoelasticity measurement, is 5 or more and 200 or less. According to this configuration, resin A and resin B can be mixed uniformly.

[0049]

[10] A resin composition molded article according to another embodiment of the present disclosure, Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0050]

[11] The resin composition molded article according to any one of [5] to

[10] above, The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution. According to this configuration, resin A and resin B can be mixed uniformly.

[0051]

[12] A resin composition molded article according to another embodiment of the present disclosure, Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0052]

[13] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, In the insulating layer after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the power cable so that a bending ratio of the bending radius of the power cable to the outer diameter of the insulating layer is 7 or less, and a second step of bending the power cable in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0053]

[14] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, the insulating layer satisfies the first, second and third requirements in a distribution of counts relative to the elastic modulus of the insulating layer, the distribution being obtained by micro-area elasticity measurement using a scanning probe microscope; however, In the micro-area elasticity measurement, the elastic modulus is measured under the condition that a cantilever having a tip made of silicon and a curvature radius of less than 20 nm is tapped 60,000 times within a 10 μm square area of ​​the insulating layer at 25° C., The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0054]

[15] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0055]

[16] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0056]

[17] A power cable according to another aspect of the present disclosure includes: A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0057]

[18] A method for producing a power cable according to another aspect of the present disclosure includes the steps of: Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The storage modulus of the resin A at 25°C measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is set to 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is taken as 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0058]

[19] A method for producing a power cable according to another aspect of the present disclosure includes the steps of: Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 5 to 200, The content of the resin A is set to 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is taken as 100 parts by mass. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0059]

[20] A method for producing a power cable according to another aspect of the present disclosure includes the steps of: A step of preparing a resin composition having a resin A containing a propylene unit and a resin B containing two or more monomer units; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 The following: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 The following: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of the resin A or the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution. According to this configuration, it is possible to suppress the deterioration of the insulation property after bending.

[0060] [Details of the embodiment of the present disclosure] Next, an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0061] <One embodiment of the present disclosure> (1) Resin composition molded article The resin composition molded body of this embodiment (hereinafter, also simply referred to as "molded body") contains, for example, a resin composition and is coated around a long object. Specifically, the resin composition molded body constitutes, for example, the insulating layer 130 of the power cable 10 described later. The object of the resin composition molded body is, for example, a long linear conductor 110. The resin composition molded body is, for example, extrusion molded so as to cover the outer periphery of the conductor 110. That is, the resin composition molded body has, for example, the same shape in the longitudinal direction of the object. In addition, the length of the resin composition molded body in the longitudinal direction of the object is, for example, 30 cm or more, preferably 50 cm or more. The thickness of the resin composition molded body coated on the object is, for example, 3 mm or more.

[0062] The resin composition molded product of the present embodiment contains, for example, at least a propylene unit as a resin component. The term "resin component" as used herein means a resin material (polymer) constituting the main component of the resin composition molded product. The term "main component" means a component with the highest content.

[0063] More specifically, the resin components constituting the resin composition molded product include, for example, resin A, which is a propylene-based resin, and resin B, which is a flexible resin. By mixing these, excessive crystal growth of the propylene-based resin can be inhibited, and the flexibility of the insulating layer can be improved.

[0064] In addition, the resin composition molded article of this embodiment is, for example, non-crosslinked, or even if crosslinked, has a low gel fraction (degree of crosslinking). Specifically, the residue of the crosslinking agent in the resin composition molded article is, for example, less than 300 ppm. When dicumyl peroxide is used as the crosslinking agent, the residue is, for example, cumyl alcohol, α-methylstyrene, etc. As described above, by making the molded article non-crosslinked or reducing the degree of crosslinking, the recyclability of the resin composition molded article can be improved.

[0065] (Resin A: Propylene-based resin) As described above, the resin A of the present embodiment contains at least propylene units as a main component. Examples of the resin A include a propylene homopolymer (homopolypropylene) and a propylene random polymer (random polypropylene).

[0066] In addition, by analyzing the resin composition of the present embodiment with a nuclear magnetic resonance (NMR) device, at least a propylene unit is detected as a monomer unit derived from resin A. For example, when resin A is a propylene random polymer, a propylene unit and an ethylene unit are detected, and when resin B is a propylene homopolymer, a propylene unit is detected.

[0067] In this embodiment, the stereoregularity of the propylene-based resin as resin A is preferably, for example, isotactic. The propylene-based resin is polymerized with a Ziegler-Natta catalyst and is versatile. The stereoregularity is isotactic, so that the melting point of the composition in which resin A and low-crystalline resin B are mixed can be suppressed from decreasing. As a result, the use of non-crosslinking or slight crosslinking can be stably realized.

[0068] For reference, other stereoregularities include syndiotactic and atactic, but neither is preferable as the stereoregularity of the propylene resin of this embodiment. PP resins having these stereoregularities do not obtain a predetermined crystal structure, and the melting point of the single unit is low. In addition, in a composition in which the PP resin is mixed with resin B, the crystals of the PP resin are easily eroded by resin B. For this reason, the melting point of the composition is lower than the melting point of the PP resin alone. As a result, it is difficult to use the composition in a non-crosslinked or slightly crosslinked state. For these reasons, syndiotactic and atactic are not preferable.

[0069] When the resin A is a propylene random polymer, the resin A has a propylene unit and an ethylene unit as described above. The ethylene content (ethylene unit content) in the propylene random polymer is, for example, 0.5% by mass or more and 15% by mass or less. By setting the ethylene content to 0.5% by mass or less, it is possible to suppress the growth of spherulites. On the other hand, by setting the ethylene content to 15% by mass or less, it is possible to suppress the decrease in melting point and stably realize the use in a non-crosslinked or slightly crosslinked state.

[0070] The storage modulus, molecular weight and content of Resin A, together with those of Resin B, will be described in detail later.

[0071] (Resin B: Flexible resin) Resin B in this embodiment is, for example, a resin material that has a lower elastic modulus than that of resin A and imparts flexibility to a resin composition molded product. From the viewpoint of suppressing excessive crystal growth of resin A, resin B may be considered as a low-crystalline resin (amorphous resin).

[0072] Resin B of this embodiment contains, for example, two or more monomer units. Specifically, Resin B is made of, for example, a copolymer of at least two of ethylene, propylene, butene (butylene), hexene, octene, isoprene, and styrene. By analyzing the resin composition of this embodiment with an NMR device, each monomer unit derived from Resin B is detected.

[0073] The carbon-carbon double bond in the olefin monomer unit is preferably, for example, at the α-position.

[0074] Moreover, it is preferable that resin B is a solid at, for example, 25°C. When resin B is liquid at 25°C, this corresponds to an excessively low molecular weight, which will be described later. In this case, it becomes difficult to mix resin A and resin B uniformly. In contrast, when resin B is solid at 25°C, it is possible to suppress an excessive decrease in molecular weight. This allows resin A and resin B to be mixed uniformly.

[0075] Examples of resin B that meets the above requirements include ethylene propylene rubber (EPR), very low density polyethylene (VLDPE), and styrene-based resins (styrene-containing resins). Two or more of these may be used in combination. The density of VLDPE is, for example, 0.855 g / cm. 3 More than 0.890g / cm 3 The following is the result.

[0076] Resin B is preferably a copolymer containing a propylene unit from the viewpoint of compatibility with, for example, a propylene-based resin, Resin A. Among the above, examples of the copolymer containing a propylene unit include EPR.

[0077] The ethylene content (ethylene unit content) of 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 EPR with the propylene-based resin becomes excessively high. Therefore, even if the content of EPR in the molded body is reduced, the molded body can be made flexible. However, the effect of inhibiting the crystallization of the propylene-based resin (also called the "crystallization inhibition effect") is not manifested, and the insulating properties may be reduced due to microcracks of the spherulites. In contrast, in this embodiment, by setting the ethylene content to 20% by mass or more, it is possible to suppress the compatibility of EPR with the propylene-based resin from becoming excessively high. This allows the softening effect of EPR to be obtained while the crystallization inhibition effect of EPR to be manifested. As a result, the deterioration of the insulating properties can be suppressed. Furthermore, by setting the ethylene content to preferably 40% by mass or more, and more preferably 55% by mass or more, the crystallization inhibition effect can be stably manifested, and the deterioration of the insulating properties can be stably suppressed.

[0078] On the other hand, resin B may be, for example, a copolymer that does not contain a propylene unit. As a copolymer that does not contain a propylene unit, 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. By adding a copolymer that does not contain a propylene unit as resin B in this way, complete compatibility can be suppressed while mixing a predetermined amount of resin B with the propylene-based resin. By making the content of such a copolymer that does not contain a propylene unit equal to or more than a predetermined amount, a crystallization inhibition effect can be exhibited.

[0079] Resin B may be, for example, a styrene-based resin as described above. A styrene-based resin is a copolymer containing a styrene unit as a hard segment and at least one monomer unit selected from ethylene, propylene, butylene, and isoprene as a soft segment. A styrene-based resin can also be called a styrene-based thermoplastic elastomer. When a styrene-based resin contains a relatively flexible monomer unit and a relatively rigid monomer unit, moldability can be improved. When a styrene-based resin contains a monomer unit (e.g., butylene) that is compatible with resin A, which is a PP resin, resin A and resin B can be mixed uniformly.

[0080] 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.

[0081] In this context, "hydrogenated" 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).

[0082] Among styrene-based resins, hydrogenated materials that do not contain double bonds in the chemical structure except for aromatic rings are preferred. When a non-hydrogenated material is used, the resin component may be thermally deteriorated during molding of the resin composition, and the properties of the resulting molded product may be reduced. In contrast, the use of a hydrogenated material can improve resistance to thermal deterioration. This allows the properties of the molded product to be maintained at a higher level.

[0083] The content of styrene in the styrene-based resin (hereinafter, simply referred to as "styrene content") is not particularly limited, but is preferably, for example, 5% by mass or more and 35% by mass or less. By setting the styrene content within the above range, it is possible to prevent the material from becoming excessively hard. This makes it possible to prevent separation and cracking of the PP-based resin and the styrene-containing resin.

[0084] (molecular weight distribution) As a result of extensive research, the inventors have discovered that the local bias of each of the above-mentioned resins A and B can be suppressed by adjusting the molecular weight distribution of each of the resins A and B alone.

[0085] Here, the molecular weight distribution of each of the resins A and B in this embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the molecular weight distribution of each of the resins A and B in this embodiment. In Fig. 1, the vertical axis represents the differential distribution value (frequency) (%) normalized by 100.

[0086] The molecular weight distribution of each of Resin A and Resin B in Fig. 1 is measured, for example, by gel permeation chromatography (GPC) based on a calibration curve prepared using polystyrene (PS) as a standard sample. In other words, the "molecular weight distribution" referred to here is a distribution curve obtained by plotting a differential distribution value corresponding to the number of molecules against the molecular weight, for example, as shown in Fig. 1.

[0087] In the following, Mw is the weight average molecular weight in the molecular weight distribution, and Mn is the number average molecular weight in the molecular weight distribution. Mw / Mn is a value also called polydispersity index, and is defined as an index value (numerical value) indicating the degree of spread of the above-mentioned molecular weight distribution. The larger Mw / Mn is, the broader the molecular weight distribution is.

[0088] As shown in FIG. 1, in this embodiment, resin A and resin B have different molecular weight distributions. At least a part of the molecular weight distribution of resin A overlaps with the molecular weight distribution of resin B, for example. On the other hand, the molecular weight distribution of resin A is relatively wide, and the molecular weight distribution of resin B is relatively narrow. Due to such molecular weight distribution of resin A or resin B, resin A and resin B can be mixed uniformly. This makes it possible to suppress localized bias of resin A and resin B in the insulating layer 130. As a result, it is possible to suppress the generation of minute voids and coarse crystals when bending.

[0089] Specifically, the peak molecular weight in the molecular weight distribution of resin A is, for example, 6×10 4 More than 6×10 5 The peak molecular weight of resin A is 6×10 4 If the peak molecular weight of resin A is less than 6×10, resin A becomes brittle. Therefore, it becomes difficult to uniformly mix resin A and resin B. 4 By setting the peak molecular weight of resin A at 6×10 or more, embrittlement of resin A can be suppressed. This allows resin A and resin B to be mixed uniformly. On the other hand, if the peak molecular weight of resin A is 6×10 or more, 5 If the peak molecular weight of resin A is more than 6×10, the flowability is low, making it difficult to mold the insulating layer 130. In addition, the overlapping range of the molecular weight distribution of resin A and the molecular weight distribution of resin B becomes narrow. This makes it difficult to uniformly mix resin A and resin B. 5By setting the above, it is possible to ensure fluidity and stably mold the insulating layer 130. In addition, it is possible to make the molecular weight distribution of resin A overlap with the molecular weight distribution of resin B over a predetermined range. This allows resin A and resin B to be mixed uniformly.

[0090] Moreover, the Mw / Mn of the resin A is, for example, 3.0 or more and 8.0 or less. If the Mw / Mn of the resin A is less than 3.0, it is difficult to mold the insulating layer 130. In contrast, by setting the Mw / Mn of the resin A to 3.0 or more, the insulating layer 130 can be stably molded. On the other hand, if the Mw / Mn of the resin A is more than 8.0, the molecular weight distribution of the resin A becomes excessively wide. Therefore, the compatibility between the resin A and the resin B becomes poor in some parts. Therefore, it becomes difficult to mix them uniformly. In contrast, by setting the Mw / Mn of the resin A to 8.0 or less, the molecular weight distribution of the resin A can be made wider than that of the resin B while suppressing excessive expansion of the molecular weight distribution of the resin A. This makes it possible to suppress the occurrence of parts in which the compatibility between the resin A and the resin B is poor. As a result, the resin A and the resin B can be mixed uniformly.

[0091] On the other hand, the peak molecular weight in the molecular weight distribution of resin B is, for example, 4 × 10 4 More than 4×10 5 The peak molecular weight of resin B is 4×10 4 Less than or 4×10 5 If the peak molecular weight of resin B is more than 4×10, there is a possibility that non-uniform parts will occur in which only resin A or resin B solidifies. 4 More than 4×10 5 By doing the following, it is possible to prevent the occurrence of non-uniform parts where only one of resin A or resin B hardens. In other words, resin A and resin B can be mixed uniformly.

[0092] Moreover, the Mw / Mn of resin B is, for example, 1.1 or more and 3.0 or less. If the Mw / Mn of resin B is less than 1.1, the molecular weight distribution of resin B becomes excessively narrow. For this reason, there is a possibility that a non-uniform portion solidified by only one of resin A or resin B occurs. In contrast, by making the Mw / Mn of resin B 1.1 or more, it is possible to suppress the excessive narrowing of the molecular weight distribution of resin B while making the molecular weight distribution of resin B narrower than that of resin A. This makes it possible to suppress the occurrence of a non-uniform portion solidified by only one of resin A or resin B. That is, resin A and resin B can be mixed uniformly. On the other hand, if the Mw / Mn of resin B is more than 3.0, the molecular weight distribution of resin B becomes wide. Resin B, which is mixed with resin A in a wide molecular weight distribution, is mixed only in a specific molecular weight region in resin A. For this reason, there is a possibility that a non-uniform portion solidified by only one of resin A or resin B occurs. In contrast, by setting the Mw / Mn of resin B to 3.0 or less, the molecular weight distribution of resin B can be made narrower than that of resin A. This makes it possible to suppress the occurrence of non-uniform portions where only one of resin A or resin B solidifies. As a result, resin B, which is mixed with a narrow molecular weight distribution, can be mixed uniformly throughout resin A, regardless of the local molecular weight within resin A.

[0093] (Elasticity Modulus) In this embodiment, as described above, the elastic modulus of resin B is lower than that of resin A. Furthermore, in this embodiment, resin A and resin B each satisfy the above-mentioned molecular weight distribution requirements, and therefore resin A and resin B each satisfy the storage modulus requirements measured by dynamic viscoelasticity measurement (DMA: Dynamic Mechanical Analysis) below.

[0094] In the dynamic viscoelasticity measurement described below, for example, the storage modulus of a sample is measured while heating the sample from -50°C to 100°C in a state where a stretch of 0.08% is applied to the target resin sample (a state where a stretching vibration with an amplitude of 0.08% is applied). At this time, the measurement frequency is 10Hz. Also, the heating rate is 10°C / min.

[0095] In the case of Resin A, which is a polypropylene resin, the elastic modulus increases as the molecular weight increases. The storage elastic modulus of Resin A at 25°C measured by dynamic viscoelasticity measurement is, for example, 600 MPa or more and 1200 MPa or less based on the above-mentioned molecular weight distribution of Resin A. This provides an effect equivalent to the effect of Resin A satisfying the above-mentioned requirements for molecular weight distribution. In other words, resin A and resin B can be mixed uniformly.

[0096] On the other hand, for resin B, which is a flexible resin, the correspondence relationship between molecular weight and elastic modulus depends on whether resin B is a styrene-based resin or not. When resin B is a non-styrene-based resin, the elastic modulus increases as the molecular weight increases. Conversely, when resin B is a styrene-based resin, the elastic modulus decreases as the molecular weight increases.

[0097] In either case of resin B, the storage modulus of resin B at 25°C measured by dynamic viscoelasticity measurement is, for example, 1 MPa or more and 200 MPa or less based on the above-mentioned molecular weight distribution of resin B. This makes it possible to obtain an effect equivalent to the effect of resin B satisfying the above-mentioned requirements for molecular weight distribution. That is, resin A and resin B can be mixed uniformly.

[0098] Alternatively, the ratio of the storage modulus of resin A to the storage modulus of resin B at 25° C. measured by dynamic viscoelasticity measurement is, for example, 5 or more and 200 or less, based on the molecular weight distributions of the above-mentioned resins A and B. This also provides an effect equivalent to the effect of satisfying the above-mentioned molecular weight distribution requirement.

[0099] (composition ratio) In this embodiment, it is further preferable that the compounding ratio of resin A and resin B satisfies the following requirement.

[0100] Specifically, the content of resin A is, for example, 52 parts by mass or more and 95 parts by mass or less when the total content of resin A and resin B is 100 parts by mass.

[0101] If the content of resin A is less than 52 parts by mass, the content of resin B, which is a flexible resin, becomes relatively large. This makes it easier for low elasticity regions in which resin B is locally concentrated to occur. As a result, when the sheet is bent, there is a possibility that minute voids will occur at the interface between the high elasticity region and the low elasticity region, or within the low elasticity region. In contrast, by making the content of resin A 52 parts by mass or more, it is possible to suppress the excessive occurrence of low elasticity regions. This makes it possible to suppress the occurrence of minute voids at the interface between the high elasticity region and the low elasticity region, or within the low elasticity region, when the sheet is bent.

[0102] On the other hand, if the content of resin A is more than 95 parts by mass, the amount of resin A, which is a propylene-based resin, becomes excessively large relative to resin B. This makes it easier for high elasticity regions to occur where resin A is locally concentrated. As a result, when bending, there is a possibility that minute voids will occur due to separation between crystals in the high elasticity region. In contrast, by setting the content of resin A to 95 parts by mass or less, it is possible to suppress the excessive occurrence of high elasticity regions. This makes it possible to suppress the occurrence of minute voids due to separation between crystals in the high elasticity region when bending.

[0103] (Other additives) The resin composition molded article may contain, in addition to the above-mentioned resin components, for example, an antioxidant, a copper inhibitor, a lubricant, and a colorant.

[0104] However, the resin composition molded product of the present embodiment preferably contains a small amount of additives that function as nucleating agents that generate propylene crystals. Examples of additives that function as nucleating agents include inorganic or organic substances such as flame retardants. Specifically, the content of the additives that function as nucleating agents is preferably less than 1 part by mass when the total content of the propylene-based resin and the low crystalline resin 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.

[0105] (2) Power cable Next, the power cable of this embodiment will be described with reference to Fig. 2. Fig. 2 is a cross-sectional view perpendicular to the axial direction of the power cable according to this embodiment.

[0106] 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.

[0107] 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 .

[0108] (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.

[0109] (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.

[0110] (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.

[0111] (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.

[0112] (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.

[0113] (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.

[0114] 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.

[0115] 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.

[0116] (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.

[0117] (3) Cable characteristics In this embodiment, as described above, by satisfying the requirements for the molecular weight distribution, elastic modulus, and compounding ratio of each of resin A and resin B, the following characteristics of insulating layer 130 can be obtained.

[0118] (Micro-area Elasticity) The possibility of the occurrence of microvoids and coarse crystals during bending as described above cannot be grasped by simply measuring the elastic modulus of the molded body using dynamic mechanical analysis (DMA) or the like as a measure of macroscopic hardness.

[0119] As a result of intensive research, the inventors attempted to measure the microscopic hardness (microscopic hardness) by measuring the elasticity of a small area of ​​a molded body. As a result, they found that it was possible to grasp the possibility of the generation of small voids and coarse crystals during bending.

[0120] Here, the micro-area elasticity measurement will be described with reference to Fig. 3. Fig. 3 is a diagram showing an example of the result of the micro-area elasticity measurement.

[0121] The "micro-area elasticity measurement" in Fig. 3 is performed using a scanning probe microscope (SPM). In the micro-area elasticity measurement, for example, at 25°C, a cantilever having a tip made of silicon (single crystal) with a radius of curvature of 1 nm or more and less than 20 nm is used to tap an area of ​​10 µm square of the molded body 60,000 times. As the molded body for this measurement, for example, a sheet having a predetermined thickness cut out from the center in the thickness direction of the insulating layer 130 is used. By such micro-area elasticity measurement, a distribution of the count number for the elasticity of the molded body is obtained.

[0122] The insulating layer 130 of this embodiment satisfies the first, second and third requirements described below, for example, in the distribution of count numbers versus elastic modulus of the insulating layer 130 obtained by micro-area elasticity measurement.

[0123] First, a comparative example that does not satisfy at least any one of the first, second and third requirements will be described.

[0124] As a comparative example, for example, as shown in (ii) of FIG. 3, two or more peaks may appear in the region where the count number is 4000 or more. In this case, resin A and resin B are not mixed uniformly, and at least one of resin A and resin B is locally biased. In this case, minute voids or coarse crystals may occur when bending.

[0125] As another comparative example, for example, as shown in FIG. 3(iii), even if there is only one peak of the normal distribution, the elastic modulus at the peak of the normal distribution may exceed 2000 MPa. This corresponds to a case where the content of resin A is high and a high elasticity region where resin A is locally concentrated is generated. In this case, there is a possibility that minute voids or coarse crystals may be generated when bending.

[0126] As another comparative example, for example, as shown in (iv) of FIG. 3, even if there is only one peak in the normal distribution and the elastic modulus at the peak is 2000 MPa or less, the count number at the peak of the normal distribution may be 25% or more of the total number of tappings (i.e., 15000 or more). This case corresponds to, for example, a case where the elastic modulus of resin B is excessively low and resin A and resin B are not mixed uniformly. In this case, there is also a possibility that minute voids or coarse crystals may be generated when bending.

[0127] In contrast to this, in this embodiment, as shown in FIG. 3(i), for example, a normal distribution having only one peak appears in a region where the count number is 4000 or more, as a first requirement. The second requirement is that the modulus of elasticity at the peak of the normal distribution is 2000 MPa or less, and the third requirement is that the count number at the peak of the normal distribution is less than 25% of the total number of tappings.

[0128] Thus, in this embodiment, the distribution of elastic modulus in the minute region of the insulating layer 130 is shifted to the low side and is distributed widely from low to high elastic modulus. In other words, resin A and resin B are mixed uniformly, so that the hardness is uniform even in the minute region of the molded body. This makes it possible to suppress the generation of minute voids and coarse crystals when bending.

[0129] In the second requirement, the lower limit of the elastic modulus at the peak of the normal distribution is not limited, but is, for example, 500 MPa, which corresponds to the elastic modulus when the amount of propylene-based resin is small. In the third requirement, the lower limit of the count number at the peak of the normal distribution is not limited. However, if the first requirement is satisfied, the lower limit of the count number in the third requirement will not be smaller than the count number (4000 times) that is the standard for the first requirement. Therefore, the lower limit of the count number in the third requirement is, for example, 6.7% of the total number of tappings.

[0130] (Bending resistance) In this embodiment, the insulating layer 130 satisfies all of the requirements in the micro-area elasticity measurement described above, and thus has resistance to a predetermined bending test.

[0131] The "bending test" here includes, for example, a first step of bending the power cable 10 so that the bending ratio of the bending radius (bending radius of the molded body) of the power cable 10 to the outer diameter (outer diameter of the molded body) of the insulating layer 130 is 7 or less, and a second step of bending the power cable in the opposite direction to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. In a bending test based on a normal cable standard, the bending ratio of the bending radius of the power cable to the outer diameter of the insulating layer is, for example, about 20. In contrast, the bending ratio in the bending test of this embodiment is smaller than the bending ratio in the bending test based on the normal cable standard. Therefore, in this embodiment, the bending stress applied to the insulating layer 130 is strong. Therefore, the bending test in this embodiment is considered to be a severe test for the insulating layer 130.

[0132] The resistance to the bending test is evaluated by evaluating the presence or absence of voids and coarse crystals in the insulating layer 130. The evaluation of voids is performed, for example, by a scanning electron microscope (SEM), and the evaluation of coarse crystals is performed, for example, by an optical microscope.

[0133] In this embodiment, after the bending test, there are no voids with a maximum length of 1 μm or more, and no crystals with a maximum length of more than 10 μm in the insulating layer 130. By suppressing the generation of minute voids and coarse crystals during bending in this manner, it is possible to suppress the deterioration of the insulating properties after bending.

[0134] (Insulating) In this embodiment, the AC breakdown field strength of the insulating layer 130 at room temperature (e.g., 25° C.) before the bending test is, for example, 60 kV / mm or more. More specifically, when a commercial frequency (e.g., 60 Hz) AC voltage is applied to a sample having a thickness of 0.2 mm at room temperature under the condition that the AC voltage is applied at 10 kV for 10 minutes, and then increased by 1 kV and applied for 10 minutes, the AC breakdown field is 60 kV / mm or more.

[0135] Furthermore, in this embodiment, the AC breakdown electric field is maintained high even after the above-mentioned bending test.

[0136] That is, in this embodiment, the AC breakdown field strength of the insulating layer 130 at room temperature (e.g., 25° C.) after the above-mentioned bending test is, for example, 60 kV / mm or more. The test method for the AC breakdown field strength after the bending test is the same as that before the above-mentioned bending test.

[0137] (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".

[0138] (S100: Resin composition preparation step) First, a resin composition containing propylene units is prepared.

[0139] In this embodiment, the resin components including resin A, which is a propylene-based resin, resin B, which is a flexible resin, and other additives (antioxidants, etc.) 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.

[0140] In this case, resin A and resin B that satisfy at least one of the requirements for molecular weight distribution and the requirements for elastic modulus described above are used.

[0141] Specifically, the peak molecular weight in the molecular weight distribution of resin A is 6×10 4 More than 6×10 5The Mw / Mn of resin A is 3.0 or more and 8.0 or less. The peak molecular weight in the molecular weight distribution of resin B is 4×10 4 More than 4×10 5 and the Mw / Mn of resin B is 1.1 or more and 3.0 or less.

[0142] Alternatively, the storage modulus of resin A at 25°C measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, and the storage modulus of resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less.

[0143] Alternatively, the ratio of the storage modulus of resin A to the storage modulus of resin B at 25° C. measured by dynamic viscoelasticity measurement is set to 5 or more and 200 or less.

[0144] In this case, the content of resin A is set to 52 parts by mass or more and 95 parts by mass or less when the total content of resin A and resin B is 100 parts by mass.

[0145] After the mixture is prepared, it is granulated by an extruder, thereby forming a pellet-shaped 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.

[0146] (S200: Conductor preparation process) On the other hand, conductor 110 is prepared by twisting together a plurality of conductor core wires.

[0147] (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, for example, 3 mm or more.

[0148] At this time, in this embodiment, by using the above-mentioned resin composition, the insulating layer 130 is formed so as to satisfy the first, second and third requirements in the distribution of the count number relative to the elastic modulus obtained by the micro-area elasticity measurement.

[0149] In addition, in this embodiment, by using the above-mentioned resin composition, the insulating layer 130 is formed so that there are no voids with a maximum length of 1 μm or more in the insulating layer 130 after the above-mentioned bending test, and there are no crystals with a maximum length of more than 10 μm.

[0150] In this embodiment, the inner semiconductive layer 120, the insulating layer 130 and the outer semiconductive layer 140 are simultaneously formed using, for example, a three-layer co-extruder.

[0151] 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.

[0152] 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.

[0153] 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 .

[0154] 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.

[0155] The extrusion is then cooled, for example with water.

[0156] 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.

[0157] (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.

[0158] (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 .

[0159] In this manner, the power cable 10 is manufactured as a solid insulated power cable.

[0160] (5) Effects of this embodiment According to this embodiment, one or more of the following advantages are achieved.

[0161] (a) In this embodiment, at least a part of the molecular weight distribution of resin A overlaps with the molecular weight distribution of resin B. Meanwhile, the molecular weight distribution of resin A is relatively broad, and the molecular weight distribution of resin B is relatively narrow. This allows resin A and resin B to be mixed uniformly.

[0162] Here, a case will be considered in which neither Resin A nor Resin B satisfies the above-mentioned requirements for molecular weight distribution.

[0163] A case in which the above-mentioned molecular weight distribution requirement is not satisfied may be when the molecular weight distribution of resin A does not overlap with the molecular weight distribution of resin B. In this case, the compatibility between resin A and resin B may be low, and they may not be mixed sufficiently.

[0164] In addition, even if the molecular weight distribution of resin A and the molecular weight distribution of resin B overlap, it is possible that both the molecular weight distribution of resin A and the molecular weight distribution of resin B are broad. In this case, it is expected that resin A and resin B will be mixed uniformly according to their respective broad molecular weight distributions, but in reality, resin A and resin B will be in a non-uniform state contrary to the above-mentioned expectation. That is, there will be parts where resin A and resin B do not mix, and there is a possibility that at least one of resin A and resin B will be locally biased. For example, it is possible that all of resin B will be concentrated and mixed into a part of resin A having a certain molecular weight.

[0165] In contrast, in this embodiment, due to the molecular weight distribution of each of resin A and resin B as described above, resin B having a narrow molecular weight distribution can be mixed uniformly throughout resin A, regardless of the local molecular weight within resin A. This makes it possible to suppress local bias of resin A and resin B in insulating layer 130.

[0166] By suppressing the localized bias of resin A and resin B, even in a small area of ​​the insulating layer 130, it is possible to shift the elastic modulus to the lower side and distribute the soft and hard parts evenly. This makes it possible to suppress the generation of micro voids and coarse crystals when bending. As a result, it is possible to suppress the deterioration of the insulating properties of the insulating layer 130 after bending.

[0167] (b) In this embodiment, the peak molecular weight in the molecular weight distribution of resin A is 6×10 4 More than 6×10 5or less. This allows resin A and resin B to be mixed uniformly. Furthermore, Mw / Mn of resin A is 3.0 or more and 8.0 or less. By making Mw / Mn of resin A 3.0 or more, insulating layer 130 can be stably molded. Furthermore, by making Mw / Mn of resin A 8.0 or less, it is possible to suppress excessive expansion of the molecular weight distribution of resin A while making the molecular weight distribution of resin A wider than that of resin B. This makes it possible to suppress the occurrence of portions where compatibility between resin A and resin B is poor. As a result, resin A and resin B can be mixed uniformly.

[0168] The peak molecular weight in the molecular weight distribution of resin B is 4×10 4 More than 4×10 5 This allows resin A and resin B to be mixed uniformly. Furthermore, the Mw / Mn of resin B is 1.1 or more and 3.0 or less. By making the Mw / Mn of resin B 1.1 or more and 3.0 or less, it is possible to suppress the occurrence of non-uniform portions where only one of resin A or resin B hardens. In other words, resin A and resin B can be mixed uniformly.

[0169] In this way, by making resin A and resin B satisfy the above-mentioned requirements for molecular weight distribution, it is possible to suppress localized bias of resin A and resin B in insulating layer 130. As a result, it is possible to suppress the occurrence of minute voids and coarse crystals when bending.

[0170] (c) In this embodiment, based on the molecular weight distribution of the resin A described above, the storage modulus of the resin A at 25°C is 600 MPa or more and 1200 MPa or less. This makes it possible to obtain an effect equivalent to the effect that the resin A satisfies the requirements of the molecular weight distribution described above. In other words, the resin A and the resin B can be mixed uniformly.

[0171] Based on the molecular weight distribution of the resin B, the storage modulus of the resin B at 25° C. is 1 MPa or more and 200 MPa or less. This makes it possible to obtain an effect equivalent to the effect of the resin B satisfying the above-mentioned molecular weight distribution requirement. That is, the resin A and the resin B can be mixed uniformly.

[0172] Alternatively, based on the molecular weight distributions of the above-mentioned resins A and B, the ratio of the storage modulus of resin A to the storage modulus of resin B at 25° C. is from 5 to 200. This also makes it possible to obtain an effect equivalent to the effect of satisfying the above-mentioned molecular weight distribution requirement.

[0173] (d) In this embodiment, the content of resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of resin A and resin B is 100 parts by mass. By making the content of resin A 52 parts by mass or more, it is possible to suppress the excessive generation of low elasticity regions. This makes it possible to suppress the generation of minute voids at least in the interface between the high elasticity region and the low elasticity region or in the low elasticity region when bending. On the other hand, by making the content of resin A 95 parts by mass or less, it is possible to suppress the excessive generation of high elasticity regions. This makes it possible to suppress the generation of minute voids caused by separation of crystals in the high elasticity region when bending.

[0174] (e) In this embodiment, resin A and resin B satisfy the above-mentioned requirements for molecular weight distribution, elastic modulus, and compounding ratio, so that the insulating layer 130 satisfies the above-mentioned first, second, and third requirements in the distribution of the count number for the elastic modulus of the insulating layer 130 obtained by the micro-area elasticity measurement. That is, in the insulating layer 130 of this embodiment, the distribution of the elastic modulus in the micro-area is widely distributed from low to high elastic modulus while shifting to the low side. In other words, by uniformly mixing resin A and resin B, it is possible to distribute soft and hard parts evenly even in the micro-area of ​​the molded body. This makes it possible to suppress the occurrence of minute voids and coarse crystals when bending.

[0175] (f) In this embodiment, there are no voids with a maximum length of 1 μm or more in the insulating layer 130 after the bending test described above, and no crystals with a maximum length of more than 10 μm. By suppressing the generation of minute voids and coarse crystals during bending in this way, it is possible to suppress localized electric field concentration when a high electric field is applied. As a result, it is possible to suppress the deterioration of insulation after bending.

[0176] <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.

[0177] 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.

[0178] 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.

[0179] 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).

[0180] 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

[0181] 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.

[0182] (1) Power cable production First, a given resin composition was mixed in a Banbury mixer and granulated into pellets using an extruder. 2 The conductor was prepared. After the conductor was prepared, the resin composition for the internal semiconductive layer containing an ethylene-ethyl acrylate copolymer, the above-mentioned resin composition, 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 the 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. At this time, the thicknesses of the internal semiconductive layer, the insulating layer, and the external semiconductive layer were set to 0.5 mm, 3.5 mm, and 0.5 mm, respectively. After extrusion, the extruded material was water-cooled. As a result, the power cables of samples A1 to A7 and B1 to B9 having the conductor, the internal semiconductive layer, the insulating layer, and the external semiconductive layer from the center to the periphery were manufactured.

[0183] [Samples A1 to A7, B1 to B9] (Molding method) Extrusion Extrusion temperature: 170℃ Insulation layer thickness: 3.5mm Final power cable outer diameter: 20.3mm

[0184] (Resin A) Content: 40~100 parts by mass (The total content of resin A and resin B is 100 parts by mass.) PP1 to PP3: Propylene random polymer (random PP) (The following corresponds to PP1 to PP3 in the order listed) Each stereoregularity: isotactic Styrene equivalent molecular weight peaks: 230000, 480000, 720000 Mw / Mn: 6.7, 6.2, 5.1 Storage modulus of the single material measured by dynamic viscoelasticity measurement at 25℃: 850MPa, 1050MPa, 1300MPa Incidentally, PP1 contains 10 mass % EPR.

[0185] (Resin B) Content: 0~60 parts by mass material: EPR1, EPR2: Ethylene propylene rubber (EPR) (The following corresponds to EPR1 and EPR2 in the order listed.) Ethylene content: 52% by mass, 68% by mass Styrene equivalent molecular weight peak: 200,000, 700,000 Mw / Mn: 2.3, 2.5 Storage modulus of the single material measured by dynamic viscoelasticity measurement at 25℃: 40MPa, 210MPa

[0186] ·VLDPE1, VLDPE2: Very low density polyethylene (The following corresponds to VLDPE1 and VLDPE2 in the order listed.) Copolymers of ethylene and 1-butene, Copolymers of ethylene and 1-octene 1-Butene content: 25% by mass, 1-octene content: 10% by mass Styrene equivalent molecular weight peak: 120000, 270000 Mw / Mn: 1.4, 1.7 Storage modulus of the single material measured by dynamic viscoelasticity measurement at 25℃: 80MPa, 180MPa

[0187] SEBS1~SEBS3: Hydrogenated styrene butadiene styrene block copolymers (The following corresponds to SEBS1 to SEBS3 in the order listed) Styrene content: 40% by mass, 20% by mass, 10% by mass Styrene equivalent molecular weight peaks: 30000, 70000, 150000 Mw / Mn: 1.2, 1.1, 1.1 Storage modulus of the single material measured by dynamic viscoelasticity measurement at 25℃: 330MPa, 70MPa, 5MPa

[0188] -Butyl rubber 1, butyl rubber 2: isobutylene-isoprene copolymer (The following corresponds to Butyl Rubber 1 and Butyl Rubber 2 in the order listed.) Styrene equivalent molecular weight peak: 600,000, 800,000 Mw / Mn: 5.2, 5.2 Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25℃: 230MPa, 350MPa

[0189] Polybutene Styrene equivalent molecular weight peak: 10000 Mw / Mn: 2.1 Storage modulus of the single substance measured by dynamic viscoelasticity measurement at 25°C: 0.1MPa Furthermore, only polybutene is liquid at 25°C.

[0190] (2) Evaluation [Resin evaluation] The following analyses were carried out on each of the above-mentioned resins A and B.

[0191] (molecular weight distribution) The molecular weight distribution of each of Resin A and Resin B was measured by GPC based on a calibration curve prepared using PS as a standard sample under the following conditions. Equipment: Tosoh HLC-8321GPC / HT Eluent: o-dichlorobenzene Temperature: 145℃ Concentration: 0.1wt% / vol% 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.

[0192] (Storage modulus) Resin A and resin B were used alone to prepare press sheets for evaluation. Dynamic mechanical analysis (DMA) was performed on the press sheets of the target resins. Specifically, the storage modulus of the press sheets was measured while heating them from -50°C to 100°C while applying a 0.08% expansion and contraction to the press sheets. The measurement frequency was 10Hz. The heating rate was 10°C / min. The storage modulus at 25°C was compared based on the measurement results.

[0193] [Post-manufacturing evaluation] Furthermore, for each of the above-mentioned samples A1 to A7 and B1 to B9, two power cables were manufactured, and then one of the two power cables was evaluated immediately after manufacturing, and the other was evaluated after a bending test.

[0194] (i) Evaluation immediately after manufacturing (before bending test) (Sample collection) The insulating layer of each of the power cables of the samples A1 to A7 and B1 to B9 was thinly sliced ​​in the circumferential direction, and a sheet was taken from the center of the insulating layer in the thickness direction. The thickness of the sheet was 0.5 mm. (Void observation) The above-mentioned insulating layer sheet was observed by SEM. If voids were present in the observed image, the maximum length of the void was measured. As a result, if there were no voids with a maximum length of 1 μm or more in the insulating layer sheet, it was rated as "A (good)", and if there were voids with a maximum length of 1 μm or more in the insulating layer sheet, it was rated as "B (poor)". (Crystallization) The insulating layer sheet was observed using an optical microscope. If crystals were present in the observed image, the maximum length of the crystals was measured. If the crystals overlapped and it was difficult to measure the maximum length of the lower crystal, the crystal exposed on the upper side was measured. As a result, if there were no crystals with a maximum length of more than 10 μm in the insulating layer sheet, it was rated as "A (good)", and if there were crystals with a maximum length of more than 10 μm in the insulating layer sheet, it was rated as "B (poor)".

[0195] (Storage modulus) Dynamic viscoelasticity measurements were performed on the above-mentioned insulating layer sheets in the same manner as the measurements on the respective resins A and B alone, thereby evaluating the storage modulus of the molded product.

[0196] (AC breakdown test) At room temperature (25°C), an AC voltage of commercial frequency (e.g., 60Hz) was applied to the insulating layer sheet at 10kV for 10 minutes, and then the voltage was increased by 1kV and applied for 10 minutes repeatedly. The electric field strength was measured when the insulating layer sheet experienced dielectric breakdown. As a result, an AC breakdown strength of 60kV / mm or more was evaluated as good, and an AC breakdown strength of less than 60kV / mm was evaluated as bad.

[0197] (Micro-area elasticity measurement) A scanning probe microscope (SPM) was used to measure the elasticity of a micro-area of ​​the insulating layer sheet. The SPM device used was a Burka MultiMode8. In the micro-area elasticity measurement, the elastic modulus was measured at 25°C under conditions where a cantilever with a tip made of silicon and a radius of curvature of less than 20 nm was used to tap an area of ​​10 μm square on the sheet 60,000 times. This gave a distribution of the counts relative to the elastic modulus of the sheet.

[0198] As a result, a case where the first, second and third requirements below were met was rated as good, and a case where any of these requirements were not met was rated as poor. First requirement: A normal distribution with only one peak appears in the region where the count number is 4000 or more. Second requirement: The elastic modulus at the peak of the normal distribution is 2000 MPa or less. Third requirement: The number of counts at the peak of the normal distribution is less than 25% of the total number of taps. In addition, in Table 2 described below, if the first requirement is not met, the columns for the second and third requirements are omitted.

[0199] (ii) Evaluation after bending test (Bending test: 7D bending test) A bending test was performed on each of the power cables of the above-mentioned samples A1 to A7 and B2 to B9. Note that, for sample B1, since the above-mentioned evaluation immediately after production was poor, no evaluation was performed after the bending test.

[0200] In the first step of the bending test, a power cable with an outer diameter of 20.3 mm was pressed along half the circumference of a SUS ring with a radius of 140 mm. In other words, the power cable was bent so that the bending ratio of the bending radius of the power cable to the outer diameter of the insulation layer (outer diameter of the power cable) was 7 or less. In the second step that followed, the power cable was bent in the opposite direction to the bending direction in the first step, at the same bending ratio as in the first step. (Sample collection) After the bending test, the insulating layer sheets were taken from each of the power cables of the samples A1 to A7 and B2 to B9 in the same manner as in the evaluation immediately after manufacture described above. (Void and crystal observation) The insulating layer sheets taken after the bending test were observed and evaluated for voids and crystals in the same manner as in the evaluation immediately after production described above. (Alternating Current Breakdown Test (AC Breakdown Test)) The insulating layer sheets taken after the bending test were subjected to an AC breakdown test in the same manner as in the evaluation immediately after production described above.

[0201] (3) Results The results of the evaluation of each sample are explained using the following Tables 1 and 2. In Tables 1 and 2, the elastic modulus at the peak of the SPM measurement results is referred to as the "peak elastic modulus," and the count number at the peak is referred to as the "peak count number."

[0202] [Table 1]

[0203] [Table 2]

[0204] (Sample B1 and Sample B9) In the micro-area elasticity measurement of sample B1, which did not contain resin B, and sample B9, which contained more than 95 parts by mass of resin A, a normal distribution with one peak was obtained, but the elastic modulus at the peak was high and the count at the peak was also high. In sample B1, many voids were generated before the bending test. As a result, the AC breakdown electric field of sample B1 was low before the bending test. In addition, micro-voids were generated during the bending test of sample B9. As a result, the AC breakdown electric field of sample B9 after the bending test was low. It is believed that micro-voids were generated during bending in sample B1 and sample B9 because an excessive amount of high elasticity region derived from resin A was formed.

[0205] (Sample B3) In sample B3, in which the content of resin A was less than 52 parts by mass, the storage modulus of the molded body was lower than that of resin A alone. However, two peaks appeared in the micro-area elasticity measurement of sample B3. In sample B3, many micro-voids were generated in the bending test. As a result, the AC breakdown electric field after the bending test was low in sample B3. It is believed that micro-voids were generated when the sample B3 was bent because an excessive amount of low elasticity areas derived from resin B were formed.

[0206] (Sample B4) Resin A has a peak molecular weight of 6×10 5 In sample B4, in which the storage modulus of resin A was over 1200 MPa, resin B with a low modulus was used, so the ratio of the storage modulus of resin A to that of resin B was within the specified range. In addition, the storage modulus of the molded body was lower than that of resin A alone. However, two peaks appeared in the micro-area elasticity measurement of sample B4. In sample B4, many micro-voids and coarse crystals were generated in the bending test. As a result, the AC breakdown field of sample B4 after the bending test was low. In sample B4, a high elasticity region with an excessively high elastic modulus derived from resin A was formed, which is thought to have caused micro-voids and coarse crystals to be generated when bent.

[0207] (Samples B5 to B7) Resin B has a peak molecular weight of 4×10 5 In samples B5 to B7, in which the storage modulus of resin A was greater than 100 MPa and the storage modulus of resin B was greater than 200 MPa, the ratio of the storage modulus of resin A to the storage modulus of resin B was less than 5. Samples B6 and B7 did not satisfy the Mw / Mn requirement either. For this reason, two peaks appeared in the micro-area elasticity measurement of samples B5 to B7. Many micro-voids were generated in samples B5 to B7 during the bending test. As a result, the AC breakdown electric field after the bending test was low in samples B5 to B7. It is believed that in samples B5 to B7, resin A and resin B were not mixed sufficiently due to resin B not satisfying the above-mentioned requirement, and thus micro-voids were generated during bending.

[0208] (Samples B2 and B8) Resin B, which is made of SEBS, has a peak molecular weight of 4×10 4 In sample B2, in which the storage modulus of resin A was less than 100 MPa and the storage modulus of resin B was more than 200 MPa, the ratio of the storage modulus of resin A to the storage modulus of resin B was less than 5. Therefore, two peaks appeared in the micro-area elasticity measurement of sample B2. In sample B2, many micro-voids were generated in the bending test. As a result, the AC breakdown electric field after the bending test was low in sample B2. In sample B2, it is considered that resin A and resin B were not sufficiently mixed due to resin B not satisfying the above-mentioned requirements, and therefore micro-voids were generated when bending.

[0209] On the other hand, the peak molecular weight of resin B, which is made of polybutene as liquid oil, is 4 × 10 4In sample B8, in which the storage modulus of resin A was less than 100 and the storage modulus of resin B was less than 1 MPa, the ratio of the storage modulus of resin A to the storage modulus of resin B was more than 200. In the micro-area elasticity measurement of sample B8, a normal distribution with one peak was obtained, but the count number at the peak was high. In sample B8, many microvoids and coarse crystals were generated in the bending test. As a result, the AC breakdown electric field after the bending test was low in sample B8. In sample B8, due to the excessively low storage modulus of resin B, resin A and resin B were not mixed sufficiently, and only resin A, which is a PP resin, aggregated and crystallized. It is believed that this is why microvoids and coarse crystals were generated when bending.

[0210] (Samples A1 to A7) In the micro-area elasticity measurement of samples A1 to A7, which satisfied the requirements for molecular weight distribution, storage modulus, and compounding ratio, the first requirement was that a normal distribution with only one peak appeared in the region where the count number was 4000 or more. The second requirement was that the modulus at the peak of the normal distribution was 2000 MPa or less. The third requirement was that the count number at the peak of the normal distribution was less than 25% of the total number of tappings. In samples A1 to A7, no microvoids or coarse crystals were present in the bending test. As a result, the AC breakdown electric field after the bending test was 60 kV / mm or more in samples A1 to A7.

[0211] According to samples A1 to A7, the content of resin A was set to 52 parts by mass or more and 95 parts by mass or less when the total content of resin A and resin B was 100 parts by mass. By setting the content of resin A to 52 parts by mass or more, it was possible to suppress the excessive generation of low elasticity regions. It was confirmed that this made it possible to suppress the generation of minute voids when bending. On the other hand, by setting the content of resin A to 95 parts by mass or less, it was possible to suppress the excessive generation of high elasticity regions. It was confirmed that this made it possible to suppress the generation of minute voids when bending.

[0212] According to the samples A1 to A7, the peak molecular weight in the molecular weight distribution of the resin A was 6×10 4 More than 6×105 The Mw / Mn of resin A was set to 3.0 or more and 8.0 or less. The peak molecular weight in the molecular weight distribution of resin B was set to 4×10 4 More than 4×10 5 or less, and the Mw / Mn of resin B is set to 1.1 or more and 3.0 or less. These enable the insulating layer to be stably molded, resin A and resin B to be mixed uniformly, and localized bias of resin A and resin B to be suppressed. As a result, it was confirmed that the generation of minute voids and coarse crystals during bending could be suppressed.

[0213] According to the samples A1 to A7, the storage modulus of resin A at 25°C was set to 600 MPa or more and 1200 MPa or less, and the storage modulus of resin B at 25°C was set to 1 MPa or more and 200 MPa or less. Alternatively, the ratio of the storage modulus of resin A to the storage modulus of resin B at 25°C was set to 5 or more and 200 or less. As a result, it was possible to obtain an effect equivalent to the effect that resin A and resin B satisfy the above-mentioned molecular weight distribution requirements. That is, resin A and resin B could be mixed uniformly, and local deviations of resin A and resin B could be suppressed. As a result, it was confirmed that the generation of minute voids and coarse crystals during bending could be suppressed.

[0214] In this way, it was confirmed from the results of Samples A1 to A7 that it was possible to suppress the deterioration of insulation properties after bending.

[0215] <Preferred aspects of the present disclosure> Preferred aspects of the present disclosure are described below.

[0216] (Appendix 1) A resin composition that is coated around a long object, Contains propylene units, In a molded product containing the resin composition after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the molded body so that a bending ratio of a bending radius of the molded body to an outer diameter of the molded body is 7 or less, and a second step of bending the molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. Resin composition.

[0217] (Appendix 2) A resin composition molded article coated around a long object, Contains propylene units, In the resin composition molded body after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the resin composition molded body so that a bending ratio of a bending radius of the resin composition molded body to an outer diameter of the resin composition molded body is 7 or less, and a second step of bending the resin composition molded body in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. Resin composition molded body.

[0218] (Appendix 3) The resin composition molded product satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded product obtained by measuring elasticity in a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the conditions of tapping 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C. using a cantilever having a tip made of silicon and a curvature radius of less than 20 nm, The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. Attachment 2: A molded article of the resin composition according to claim 2.

[0219] (Appendix 4) A resin composition molded article, Contains propylene units, The resin composition molded product satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded product obtained by measuring elasticity in a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the conditions of tapping 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C. using a cantilever having a tip made of silicon and a curvature radius of less than 20 nm, The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less, The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. Resin composition molded body.

[0220] (Appendix 5) Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; have 5. A molded article of the resin composition according to any one of claims 2 to 4.

[0221] (Appendix 6) The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. 6. A molded article of the resin composition according to claim 5.

[0222] (Appendix 7) The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less. 7. A molded article of the resin composition according to claim 5 or 6.

[0223] (Appendix 8) Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. Resin composition molded body.

[0224] (Appendix 9) 9. The resin composition molded article according to any one of claims 5 to 8, wherein a ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 5 or more and 200 or less.

[0225] (Appendix 10) Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. Resin composition molded body.

[0226] (Appendix 11) The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution 11. A molded article of the resin composition according to any one of claims 5 to 10.

[0227] (Appendix 12) Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution Resin composition molded body.

[0228] (Appendix 13) The resin B is a copolymer of at least two of ethylene, propylene, butene, hexene, octene, isoprene, and styrene. Attachment 5 to Attachment 12. A molded article of a resin composition according to any one of claims 5 to 12.

[0229] (Appendix 14) The AC breakdown field at room temperature is 60kV / mm or more. 14. A molded article of a resin composition according to any one of claims 1 to 13.

[0230] (Appendix 15) A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, In the insulating layer after a predetermined bending test, There are no voids with a maximum length of 1 μm or more, and There are no crystals with a maximum length greater than 10 μm; However, the bending test includes a first step of bending the power cable so that a bending ratio of a bending radius of the power cable to an outer diameter of the insulating layer is 7 or less, and a second step of bending the power cable in a direction opposite to the bending direction of the first step at the same bending ratio as the bending ratio of the first step. Power cable.

[0231] (Appendix 16) A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer includes propylene units, the insulating layer satisfies the first, second and third requirements in a distribution of counts relative to the elastic modulus of the insulating layer, the distribution being obtained by micro-area elasticity measurement using a scanning probe microscope; however, In the micro-area elasticity measurement, the elastic modulus is measured under the condition that a cantilever having a tip made of silicon and a curvature radius of less than 20 nm is tapped 60,000 times within a 10 μm square area of ​​the insulating layer at 25° C., The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less, The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. Power cable.

[0232] (Appendix 17) A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The storage modulus of the resin A at 25°C as measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. Power cable.

[0233] (Appendix 18) A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B, which contains two or more monomer units and is solid at 25° C.; having The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C as measured by dynamic viscoelasticity measurement is 5 or more and 200 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. Power cable.

[0234] (Appendix 19) A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A containing propylene units; Resin B containing two or more monomer units; having The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 is as follows: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 is as follows: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of each of the resin A and the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution Power cable.

[0235] (Appendix 20) Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The storage modulus of the resin A at 25°C measured by dynamic viscoelasticity measurement is 600 MPa or more and 1200 MPa or less, The storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 1 MPa or more and 200 MPa or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A method for manufacturing power cables.

[0236] (Appendix 21) Providing a resin composition having a resin A containing propylene units and a resin B containing two or more monomer units and being solid at 25°C; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The ratio of the storage modulus of the resin A to the storage modulus of the resin B at 25°C measured by dynamic viscoelasticity measurement is 5 to 200, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. A method for manufacturing power cables.

[0237] (Appendix 22) A step of preparing a resin composition having a resin A containing a propylene unit and a resin B containing two or more monomer units; A step of coating an insulating layer around a conductor using the resin composition; Equipped with In the step of preparing the resin composition, The peak molecular weight in the molecular weight distribution of the resin A is 6×10 4 More than 6×10 5 The following: The Mw / Mn of the resin A is 3.0 or more and 8.0 or less, The peak molecular weight in the molecular weight distribution of the resin B is 4×10 4 More than 4×10 5 The following: The Mw / Mn of the resin B is 1.1 or more and 3.0 or less, The content of the resin A is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass. however, The molecular weight distribution of the resin A or the resin B is measured by gel permeation chromatography based on a calibration curve prepared using polystyrene as a standard sample; Mw is the weight average molecular weight in the molecular weight distribution, Mn is the number average molecular weight in the molecular weight distribution A method for manufacturing power cables. [Explanation of symbols]

[0238] 10 Power Cable 110 Conductor 120 Inner semiconducting layer 130 Insulating layer 140 Outer semiconducting layer 150 Shielding layer 160 Sheath

Claims

1. A resin composition molded article, Resin A consisting of at least one of homopolypropylene and random polypropylene; Resin B, which is a copolymer of at least two different members selected from ethylene, propylene, butene, hexene, octene, isoprene, and styrene, and is a solid at 25° C.; The resin component comprises The content of the resin A in the resin composition molded product is 52 parts by mass or more and 95 parts by mass or less when the total content of the resin A and the resin B is 100 parts by mass, The resin composition molded article satisfies the first, second and third requirements in a distribution of count numbers relative to the elastic modulus of the resin composition molded article, which is obtained by measuring the elasticity of a micro-area using a scanning probe microscope. however, In the micro-area elasticity measurement, the elastic modulus is measured under the condition that a cantilever having a tip made of silicon and a radius of curvature of less than 20 nm is tapped 60,000 times within a 10 μm square area of ​​the resin composition molded product at 25° C., The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. Resin composition molded body.

2. The storage modulus of the resin B at 25° C. measured by dynamic viscoelasticity measurement is lower than that of the resin A. A molded article made from the resin composition according to claim 1.

3. A conductor; an insulating layer coated around the conductor; Equipped with The insulating layer is Resin A consisting of at least one of homopolypropylene and random polypropylene; Resin B, which is a copolymer of at least two different members selected from ethylene, propylene, butene, hexene, octene, isoprene, and styrene, and is a solid at 25° C.; The resin component comprises a content of the resin A in the insulating layer is 52 parts by mass or more and 95 parts by mass or less when a total content of the resin A and the resin B is 100 parts by mass; the insulating layer satisfies the first, second and third requirements in a distribution of counts relative to the elastic modulus of the insulating layer, the distribution being obtained by micro-area elasticity measurement using a scanning probe microscope; however, In the micro-area elasticity measurement, the elastic modulus is measured under the condition that a cantilever having a tip made of silicon and a radius of curvature of less than 20 nm is tapped 60,000 times within a 10 μm square area of ​​the insulating layer at 25° C., The first requirement is that a normal distribution having only one peak appears in a region where the count number is 4000 or more, The second requirement is that the elastic modulus at the peak of the normal distribution is 2000 MPa or less; The third requirement is that the number of counts at the peak of the normal distribution is less than 25% of the total number of tappings. Power cable.

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