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EP-4741150-A1 - HEAT-SHRINKABLE TUBE, HEAT-SHRINKABLE TUBE MEMBER, WIRE SPLICE, AND WIRE HARNESS

EP4741150A1EP 4741150 A1EP4741150 A1EP 4741150A1EP-4741150-A1

Abstract

A heat-shrinkable tube includes an outer layer having a cylindrical shape, and an inner layer disposed on an inner peripheral surface of the outer layer. The outer layer contains a first fluororesin, the inner layer contains a second fluororesin as a main component, the inner layer has a shear viscosity of 300 Pa·s to 10,000 Pa·s at 215°C and a shear rate of 10/s, and the inner layer has a shear viscosity of 3,000 Pa·s to 70,000 Pa·s at 200°C and a shear rate of 1/s.

Inventors

  • KUDO, Mayumi
  • ISHIBASHI, KEIJI
  • FUKUMOTO, RYOTA
  • EMOTO, Yasutaka

Assignees

  • Sumitomo Electric Fine Polymer, Inc.
  • Sumitomo Electric Industries, Ltd.

Dates

Publication Date
20260513
Application Date
20251105

Claims (13)

  1. A heat-shrinkable tube comprising: an outer layer having a cylindrical shape; and an inner layer disposed on an inner peripheral surface of the outer layer, wherein the outer layer contains a first fluororesin, the inner layer contains a second fluororesin as a main component, the inner layer has a shear viscosity of 300 Pa·s to 10,000 Pa·s at 215°C and a shear rate of 10/s, and the inner layer has a shear viscosity of 3,000 Pa·s to 70,000 Pa·s at 200°C and a shear rate of 1/s.
  2. The heat-shrinkable tube according to claim 1, wherein the outer layer contains, as a main component, a mixture consisting of the first fluororesin and a fluoro-rubber, and the outer layer has a storage modulus of 0.5 MPa to 5.0 MPa at 215°C.
  3. The heat-shrinkable tube according to claim 2, wherein the fluoro-rubber is a VDF-HFP-TFE copolymer.
  4. The heat-shrinkable tube according to any one of claims 1 to 3, wherein in a DSC curve of the inner layer, one or more melting peaks are present in a range of 120°C to 195°C, and the DSC curve is obtained by performing a measurement using a differential scanning calorimeter in a range of -50°C to 300°C at a heating rate of 10°C/min.
  5. The heat-shrinkable tube according to any one of claims 1 to 4, wherein the second fluororesin contains an ethylene-tetrafluoroethylene copolymer.
  6. The heat-shrinkable tube according to claim 5, wherein the second fluororesin further contains polyvinylidene fluoride, and the inner layer contains 5 mass% to 40 mass% of the polyvinylidene fluoride.
  7. The heat-shrinkable tube according to any one of claims 1 to 6, wherein the heat-shrinkable tube has a shrinkage ratio of 50% or more.
  8. A heat-shrinkable tube member having a cylindrical shape, wherein the heat-shrinkable tube member contains a fluororesin as a main component, the heat-shrinkable tube member has a shear viscosity of 300 Pa·s to 10,000 Pa·s at 215°C and a shear rate of 10/s, and the heat-shrinkable tube member has a shear viscosity of 3,000 Pa·s to 70,000 Pa·s at 200°C and a shear rate of 1/s.
  9. The heat-shrinkable tube member according to claim 8, wherein in a DSC curve of the heat-shrinkable tube member, one or more melting peaks are present in a range of 120°C to 195°C, and the DSC curve is obtained by performing a measurement using a differential scanning calorimeter in a range of -50°C to 300°C at a heating rate of 10°C/min.
  10. The heat-shrinkable tube member according to claim 8 or 9, wherein the fluororesin is an ethylene-tetrafluoroethylene copolymer.
  11. The heat-shrinkable tube member according to claim 10, wherein the heat-shrinkable tube member contains 5 mass% to 40 mass% of polyvinylidene fluoride.
  12. A wire splice comprising: a plurality of wires including conductors and insulating layers disposed on outer sides of the conductors; and a heat-shrunk product of the heat-shrinkable tube according to any one of claims 1 to 7 or a heat-shrunk product of the heat-shrinkable tube member according to any one of claims 8 to 11, each of the heat-shrunk products covering a portion where the conductors of the plurality of wires are connected together.
  13. A wire harness comprising: a plurality of wires including conductors and insulating layers disposed on outer sides of the conductors; and a heat-shrunk product of the heat-shrinkable tube according to any one of claims 1 to 7 or a heat-shrunk product of the heat-shrinkable tube member according to any one of claims 8 to 11, each of the heat-shrunk products covering the plurality of wires.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application claims priority based on Japanese Patent Application No. 2024-196654 filed on November 11, 2024, and the entire contents of the Japanese patent application are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a heat-shrinkable tube, a heat-shrinkable tube member, a wire splice, and a wire harness. BACKGROUND The heat-shrinkable tube, when heated with the heat-shrinkable tube covering connection portions between insulated wires and the like, shrinks along the shape of the covered portion and conforms tightly to that portion. The heat-shrinkable tube is used for protection, insulation, waterproofing, oil proofing, corrosion protection, and the like of a connection portion between insulated wires. As a heat-shrinkable tube, a two layer heat-shrinkable tube in which an adhesive layer (inner layer) is provided on an inner peripheral surface of a heat-shrinkable outer layer in order to improve adhesion to a connection portion of insulated wires is known (for example, Patent Literature 1: WO 2019/097820 and Patent Literature 2: WO 2021/243036). SUMMARY For applications requiring high heat resistance, such as in automotive and aerospace uses, insulated wires coated with high heat-resistant resins are utilized, such as ETFE wires coated with a copolymer of tetrafluoroethylene and ethylene (ETFE). A heat-shrinkable tube used for protection of a connection portion between insulated wires having such high heat resistance, waterproofing, oil proofing, and the like is required to maintain excellent sealing properties under a high-temperature environment. In the present disclosure, the high temperature means 150°C to 200°C which is the use temperature of a high heat-resistant insulated wire such as an ethylene-tetrafluoroethylene copolymer (ETFE) wire to be covered. Further, there is also a demand for improvement in sealing properties of the heat-shrinkable tube during heat shrinkage. In the present disclosure, the temperature of the heat-shrinkable tube during heat shrinkage is 150°C to 215°C. Thus, an object of the present disclosure is to provide a heat-shrinkable tube and a heat-shrinkable tube member that have excellent sealing properties when the heat-shrinkable tube is heated and shrunk and can maintain excellent sealing properties even in use under the high-temperature environment, and a wire splice and a wire harness that include a shrunk product of the heat-shrinkable tube or a shrunk product of the heat-shrinkable tube member. First, embodiments of the present disclosure will be listed and described. (1) A heat-shrinkable tube of the present disclosure includes an outer layer having a cylindrical shape, and an inner layer disposed on an inner peripheral surface of the outer layer. The outer layer contains a first fluororesin. The inner layer contains a second fluororesin as a main component. The inner layer has a shear viscosity of 300 Pa·s to 10,000 Pa·s at 215°C and a shear rate of 10/s. The inner layer has a shear viscosity of 3,000 Pa·s to 70,000 Pa·s at 200°C and a shear rate of 1/s. The heat-shrinkable tube of the present disclosure has excellent sealing properties during heat shrinkage, and can maintain excellent sealing properties even when used in the high-temperature environment. The reason for this is inferred to be as follows. The outer layer of the heat-shrinkable tube of the present disclosure includes a first fluororesin. Fluororesin has a melting point of 100°C or higher and has a strong fluorine bond, and thus has high heat resistance. Thus, the outer layer can contribute to maintaining excellent sealing properties of the heat-shrinkable tube in use under the high-temperature environment of about 200°C. Further, since the fluororesin has high chemical resistance, the outer layer can contribute to blocking the penetration of acid, alkali, and oil. The inner layer of the heat-shrinkable tube of the present disclosure includes a second fluororesin as a main component. Fluororesin has a melting point of 100°C or higher and has a strong fluorine bond, and thus has high heat resistance. Thus, the inner layer can contribute to maintaining excellent sealing properties of the heat-shrinkable tube in use under the high-temperature environment of about 200°C. Further, since the fluororesin has high chemical resistance, the inner layer can contribute to blocking the penetration of acid, alkali, and oil. The shear viscosity of the inner layer of the heat-shrinkable tube of the present disclosure at 215°C and a shear rate of 10/s is 300 Pa·s to 10,000 Pa·s. According to this, when the heat-shrinkable tube is heated and shrunk, the fluidity of the inner layer is appropriate, a gap is hardly generated between the covering target and the heat-shrinkable tube, and can obtain good sealing properties. Since the fluidity of the inner layer of the heat-shrinkable tube during heat shrinkage corresponds to rapid shear, in the h