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EP-4738388-A1 - RESIN COMPOSITION, POWER CABLE, AND METHOD FOR PRODUCING POWER CABLE

EP4738388A1EP 4738388 A1EP4738388 A1EP 4738388A1EP-4738388-A1

Abstract

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

Inventors

  • SAKAIDA, Hideaki
  • YAMASAKI, SATOSHI
  • YAMAZAKI, TAKANORI
  • ONODA, Takaaki

Assignees

  • Sumitomo Electric Industries, Ltd.

Dates

Publication Date
20260506
Application Date
20230630

Claims (9)

  1. A resin composition constituting an insulating layer disposed to cover a conductor of a power cable and having an inner peripheral surface facing the conductor and an outer peripheral surface opposite to the inner peripheral surface, the resin composition comprising: a base polymer including propylene units; a modified polymer including propylene units and modified with at least one selected from unsaturated organic acids and derivatives thereof; and a thermoplastic elastomer, wherein the resin composition is configured such that a ratio of a storage modulus of an inner-side sample of the insulating layer to a storage modulus of an outer-side sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of a volume resistivity of the inner-side sample to a volume resistivity of the outer-side sample is 1.0 or more and 1.5 or less, the outer-side sample of the insulating layer being collected from a position 0.3 mm away from the outer peripheral surface toward the conductor, the inner-side sample of the insulating layer being collected from a position 0.3 mm away from the inner peripheral surface toward the outer peripheral surface, the storage modulus of the outer-side sample and the storage modulus of the inner-side sample being measured by dynamic mechanical analysis at 25°C, the volume resistivity of the outer-side sample and the volume resistivity of the inner-side sample being measured at a temperature of 90°C and a DC electric field of 80 kV/mm.
  2. A power cable comprising: a conductor; and an insulating layer disposed to cover an outer periphery of the conductor and having an inner peripheral surface facing the conductor and an outer peripheral surface opposite to the inner peripheral surface, wherein the insulating layer contains a base polymer including propylene units, a modified polymer including propylene units and modified with at least one selected from unsaturated organic acids and derivatives thereof, and a thermoplastic elastomer, a ratio of a storage modulus of an inner-side sample of the insulating layer to a storage modulus of an outer-side sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of a volume resistivity of the inner-side sample to a volume resistivity of the outer-side sample is 1.0 or more and 1.5 or less, the outer-side sample of the insulating layer being collected from a position 0.3 mm away from the outer peripheral surface toward the conductor, the inner-side sample of the insulating layer being collected from a position 0.3 mm away from the inner peripheral surface toward the outer peripheral surface, the storage modulus of the outer-side sample and the storage modulus of the inner-side sample being measured by dynamic mechanical analysis at 25°C, the volume resistivity of the outer-side sample and the volume resistivity of the inner-side sample being measured at a temperature of 90°C and a DC electric field of 80 kV/mm.
  3. The power cable according to claim 2, wherein when a total content of the base polymer, the modified polymer, and the thermoplastic elastomer in the insulating layer is 100 parts by mass, a content of the modified polymer in the insulating layer is 1 part by mass or more and 10 parts by mass or less, and a content of the thermoplastic elastomer in the insulating layer is 10 parts by mass or more and 45 parts by mass or less.
  4. The power cable according to claim 2 or 3, wherein the thermoplastic elastomer includes a styrene-based elastomer.
  5. The power cable according to any one of claims 2 to 4, wherein the thermoplastic elastomer includes an olefin-based elastomer.
  6. The power cable according to any one of claims 2 to 5, wherein the storage modulus of the inner-side sample of the insulating layer is 650 MPa or more and 900 MPa or less, and the storage modulus of the outer-side sample of the insulating layer is 280 MPa or more and 670 MPa or less.
  7. The power cable according to any one of claims 2 to 6, wherein the insulating layer has a thickness of 3 mm or more.
  8. A method of manufacturing a power cable, the method comprising: preparing a resin composition; and forming an insulating layer with the resin composition to cover an outer periphery of a conductor, to form, in the insulating layer, an inner peripheral surface facing the conductor and an outer peripheral surface opposite to the inner peripheral surface, wherein in the preparing a resin composition, a composition containing a base polymer including propylene units, a modified polymer including propylene units and modified with at least one selected from unsaturated organic acids and derivatives thereof, and a thermoplastic elastomer is prepared as the resin composition, and the forming an insulating layer includes forming the insulating layer on the outer periphery of the conductor by extrusion molding, and cooling the insulating layer so that a ratio of a storage modulus of an inner-side sample of the insulating layer to a storage modulus of an outer-side sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of a volume resistivity of the inner-side sample to a volume resistivity of the outer-side sample is 1.0 or more and 1.5 or less, the outer-side sample of the insulating layer being collected from a position 0.3 mm away from the outer peripheral surface toward the conductor, the inner-side sample of the insulating layer being collected from a position 0.3 mm away from the inner peripheral surface toward the outer peripheral surface, the storage modulus of the outer-side sample and the storage modulus of the inner-side sample being measured by dynamic mechanical analysis at 25°C, the volume resistivity of the outer-side sample and the volume resistivity of the inner-side sample being measured at a temperature of 90°C and a DC electric field of 80 kV/mm.
  9. The method of manufacturing a power cable according to claim 8, wherein in the cooling the insulating layer, for at least a part of a period immediately after the forming the insulating layer by extrusion molding, the insulating layer is cooled from a region of the insulating layer near the outer peripheral surface while the conductor is subjected to electromagnetic induction heating.

Description

TECHNICAL FIELD The present disclosure relates to a resin composition, a power cable, and a method of manufacturing a power cable. BACKGROUND ART Cross-linked polyethylene has been widely used as a resin component constituting an insulating layer of a power cable because of its excellent insulating property (for example, Patent literature 1). CITATION LIST PATENT LITERATURE Patent literature 1: Japanese Unexamined Patent Application Publication No. S57-69611 SUMMARY OF INVENTION According to one aspect of the present disclosure, a resin composition constituting an insulating layer that is disposed to cover a conductor of a power cable and has an inner peripheral surface facing the conductor and an outer peripheral surface opposite to the inner peripheral surface is provided. The resin composition contains a base polymer including propylene units, a modified polymer including propylene units and modified with at least one selected from unsaturated organic acids and derivatives thereof, and a thermoplastic elastomer. The resin composition is configured such that a ratio of a storage modulus of an inner-side sample of the insulating layer to a storage modulus of an outer-side sample of the insulating layer is 1.1 or more and 2.5 or less, and a ratio of a volume resistivity of the inner-side sample to a volume resistivity of the outer-side sample is 1.0 or more and 1.5 or less, where the outer-side sample of the insulating layer is collected from a position 0.3 mm away from the outer peripheral surface toward the conductor, the inner-side sample of the insulating layer is collected from a position 0.3 mm away from the inner peripheral surface toward the outer peripheral surface, the storage modulus of the outer-side sample and the storage modulus of the inner-side sample is measured by dynamic mechanical analysis at 25°C, and the volume resistivity of the outer-side sample and the volume resistivity of the inner-side sample is measured at a temperature of 90°C and a DC electric field of 80 kV/mm. BRIEF DESCRIPTION OF THE DRAWINGS [FIG. 1] FIG. 1 is a schematic cross-sectional view orthogonal to an axial direction of a power cable according to an embodiment of the present disclosure.[FIG. 2] FIG. 2 is a diagram showing a temperature at a position where an outer-side sample is collected and a temperature at a position where an inner-side sample is collected in a cooling step of a sample A3.[FIG. 3] FIG. 3 is a diagram showing a temperature at a position where an outer-side sample is collected and a temperature at a position where an inner-side sample is collected in a cooling step of a sample B1. DETAILED DESCRIPTION [Problems to be Solved by Present Disclosure] The present inventors focused on polypropylene as a resin component forming an insulating layer, and have conducted intensive research to improve characteristics of a power cable. An object of the present disclosure is to improve the flexibility, strength and insulating property of the insulating layer. [Advantageous Effects of Present Disclosure] According to the present disclosure, the flexibility, strength and insulating property of the insulating layer can be improved. [Description of Embodiments of Present Disclosure] <Knowledge Obtained by the Inventors> First, the outline of knowledge obtained by the inventors will be described. In the manufacturing process of the power cable, the insulating layer is formed by extrusion molding to cover the outer periphery of the conductor with the resin composition melted in a heated extruder. After the insulating layer is formed by extrusion molding, the insulating layer is cooled by a predetermined cooling method. In this case, the outer peripheral surface of the insulating layer is cooled using a predetermined refrigerant. As a result, cooling proceeds from the outer periphery of the insulating layer toward the inner periphery of the insulating layer in a radial direction of the conductor. When a temperature used to cool the outer peripheral surface of the insulating layer is low, that is, a cooling rate of the outer peripheral surface of the insulating layer is high, a base polymer on an outer side of the insulating layer is rapidly cooled. The base polymer on an inner side of the insulating layer is less likely to be cooled than the base polymer on the outer side of the insulating layer, and is slowly cooled. Thus, when the cooling rate of the outer peripheral surface of the insulating layer is high, a distribution (variation) of the degree of crystallinity occurs in a thickness direction of the insulating layer. That is, the degree of the crystallinity of the base polymer is lowered on the outer side of the insulating layer. The degree of the crystallinity of the base polymer on the inner side of the insulating layer becomes higher than that on the outer side of the insulating layer. When such a distribution of the degree of crystallinity occurs, the insulating property gradually decreases from the inner sid