Heat-shrinkable tube and wire harness

Abstract

To provide a heat-shrinkable tube which is excellent in adhesion between an inner layer and an adherend in heat shrinkage, and prevents outflow of the inner layer from an outer layer even during use under high temperature.SOLUTION: A heat-shrinkable tube includes a cylindrical outer layer having a melting point of 210°C or higher and 260°C or lower, and an inner layer stacked on the inner peripheral surface of the outer layer, wherein the outer layer and the inner layer contain a fluorine resin or a fluororubber as a main component, and in the inner layer, shear viscosity at a shear rate of 10 / s at 250°C is 300 Pa s or more and 10,000 Pa s or less, and shear viscosity at a shear rate of 1 / s at 215°C is 3,000 Pa s or more and 70,000 Pa s or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a heat shrink tube and a wire harness. [Background technology]

[0002] Heat-shrinkable tubing that is heat-shrinkable in the radial direction is used as a covering for protecting, insulating, waterproofing, and corrosion-preventing the joints of insulated electric wires, wiring terminals, metal pipes, etc. When the heat-shrinkable tubing is placed at the joint between insulated electric wires and heated, it shrinks to conform to the shape of the joint, adhering tightly to the joint, thereby protecting the joint. When a high degree of adhesion is required at the joint for waterproofing, etc., a heat-shrinkable tubing with an inner layer provided on the inner surface of a cylindrical outer layer is used.

[0003] The inner layer of such heat-shrinkable tubing is typically made of a hot-melt adhesive such as ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), or polyamide. Such heat-shrinkable tubing is manufactured by extruding an outer layer and an inner layer laminated on the inner surface into a tubular shape, expanding the diameter under heat, and then cooling to fix the shape (see Patent Document 1). Furthermore, in double-walled tubing in which fluororesin is used for the outer and inner layers of the heat-shrinkable tubing to enhance heat resistance, poor fluidity of the inner layer during heat shrinkage reduces waterproofing. Therefore, a shear viscosity suitable for improving fluidity has been proposed (see Patent Document 2). Furthermore, a shear viscosity suitable for controlling the fluidity of a sealing material in a connecting part using heat-shrinkable tubing has been proposed (see Patent Document 3).

[0004] Such a heat-shrinkable tube is attached to an adherend by, for example, heating the heat-shrinkable tube while it is positioned so as to cover the outer periphery of the adherend. When the heat-shrinkable tube is heated, the outer layer thermally shrinks and the inner layer simultaneously fluidizes. At this time, the fluidized inner layer fills the gap between the adherend and the outer layer, and subsequent cooling solidifies the inner layer, thereby allowing the heat-shrinkable tube to adhere tightly to the adherend. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-129042 [Patent Document 2] International Publication No. 2019 / 097820 [Patent Document 3] International Publication No. 2022 / 181142 Summary of the Invention

[0006] The heat-shrinkable tube of the present disclosure comprises a cylindrical outer layer having a melting point of 210°C or more and 260°C or less, and an inner layer laminated on the inner surface of the outer layer, the outer layer and the inner layer being primarily composed of a fluororesin or a fluororubber, and the inner layer having a shear viscosity of 300 Pa·s or more and 10,000 Pa·s or less at 250°C and a shear rate of 10 / s, and a shear viscosity of 3,000 Pa·s or more and 70,000 Pa·s or less at 215°C and a shear rate of 1 / s. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic perspective view showing a heat-shrinkable tube according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA of the heat-shrinkable tube of FIG. 1, showing a longitudinal cross section thereof. [Figure 3] 3 is a cross-sectional view taken along line BB of the heat-shrinkable tube of FIG. 1, showing a cross section perpendicular to the longitudinal direction thereof. [Figure 4] FIG. 4 is a schematic side view showing a wire harness according to an embodiment of the present disclosure. [Figure 5] FIG. 5 is a schematic cross-sectional view of the wire harness shown in FIG. 4, corresponding to FIG. [Figure 6] FIG. 6 is a schematic diagram illustrating a state in which conductors exposed from two wires are inserted into a heat-shrinkable tube in a wire harness according to another embodiment of the present disclosure. [Figure 7]FIG. 7 is a schematic diagram showing two connecting wires covered with heat-shrunk tubes in the wire harness shown in FIG. [Figure 8] FIG. 8 is a schematic cross-sectional view corresponding to FIG. 2, showing a heat-shrinkable tube according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Problem to be solved by this disclosure] The inner layer is desired to have high fluidity so that it can adhere tightly to recesses and the like of the adherend during heat shrinkage. However, in heat-shrinkable tubing whose main component is a highly heat-resistant fluororesin or fluororubber, if the inner layer has high fluidity, there are problems such as the inner layer easily flowing out from the end of the tubing during heat shrinkage, and the inner layer easily flowing out from the outer layer when used at high temperatures, resulting in a decrease in sealing performance. Furthermore, if a heat-shrinkable connecting part with a locally applied sealant is used instead of a heat-shrinkable tubing, there is a problem that it may not be usable depending on the length of the connecting part, limiting its applications.

[0009] An object of the present disclosure is to provide a heat-shrinkable tube that exhibits excellent adhesion between the inner layer and the adherend during heat shrinkage, and in which the inner layer is less likely to flow out from the outer layer even when used at high temperatures.

[0010] [Effects of this disclosure] According to the present disclosure, it is possible to provide a heat-shrinkable tube that has excellent adhesion between the inner layer and the adherend during heat shrinkage and in which the inner layer is less likely to flow out from the outer layer even when used at high temperatures.

[0011] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described.

[0012] The heat shrink tubing of the present disclosure comprises: (1) A cylindrical outer layer having a melting point of 210°C or higher and 260°C or lower, and an inner layer laminated on the inner surface of the outer layer, the outer layer and the inner layer being primarily composed of fluororesin or fluororubber, the inner layer having a shear viscosity of 300 Pa·s or higher and 10,000 Pa·s or lower at 250°C and a shear rate of 10 / s, and a shear viscosity of 3,000 Pa·s or higher and 70,000 Pa·s or lower at 215°C and a shear rate of 1 / s.

[0013] The heat-shrinkable tubing has excellent heat resistance because the outer layer and the inner layer are mainly composed of fluororesin or fluororubber. The melting point of the outer layer is 210°C or higher and 260°C or lower, ensuring heat resistance and reducing thermal damage to the adherend. Furthermore, in this heat-shrinkable tubing, the shear viscosity of the inner layer at 250°C and a shear rate of 10 / s is 300 Pa·s or more and 10,000 Pa·s or less, and the shear viscosity at 215°C and a shear rate of 1 / s is 3,000 Pa·s or more and 70,000 Pa·s or less, thereby providing excellent fluidity and durability during heat shrinkage and good shape retention during use at high temperatures. Therefore, the inner layer flows easily during heat shrinkage, ensuring close contact with the adherend and is less likely to flow out of the outer layer after heat shrinkage.

[0014] The "major component" refers to the component with the highest content, for example, a component with a content of 60 mass % or more. The "shear viscosity" is a value measured using a rotational rheometer.

[0015] (2) In the above (1), the outer layer may be primarily composed of an ethylene-tetrafluoroethylene copolymer, and the outer layer may have a storage modulus of 0.8 MPa to 2.8 MPa at 250°C to 280°C. When the outer layer is primarily composed of an ethylene-tetrafluoroethylene copolymer, the outer layer has good heat resistance. Furthermore, when the outer layer has a storage modulus of 250°C to 280°C within the above range, good shrinkage characteristics can be obtained, and the shape memory performance is excellent.

[0016] (3) In the above (1) or (2), the melting point of the inner layer may be 120° C. or higher and 180° C. or lower. By having the melting point of the inner layer be 120° C. or higher and 180° C. or lower, good fluidity can be obtained during heat shrinkage, and adhesion between the inner layer and the adherend during heat shrinkage can be improved.

[0017] (4) In any of the above (1) to (3), the main component of the inner layer may be an ethylene-tetrafluoroethylene copolymer, which can provide good fluidity during heat shrinkage and improve durability and shape retention.

[0018] (5) In any of (1) to (4) above, the main component of the inner layer may be an ethylene-tetrafluoroethylene copolymer, and the content of polyvinylidene fluoride in the inner layer may be 5% by mass or more and 40% by mass or less. By making the main component of the inner layer an ethylene-tetrafluoroethylene copolymer and the content of polyvinylidene fluoride in the inner layer be 5% by mass or more and 40% by mass or less, the fluidity during heat shrinkage can be further improved.

[0019] (6) In any of the above (1) to (5), the heat-shrinkable tube may have a transmittance of 10% or more at a wavelength of 550 nm. When the heat-shrinkable tube has a transmittance of 10% or more at a wavelength of 550 nm, which is visible light, the visibility of the inside of the heat-shrinkable tube is improved, making it easier to check the inside of the heat-shrinkable tube. The transmittance at a wavelength of 550 nm can be measured using a spectrophotometer.

[0020] (7) In any of the above (1) to (6), the heat-shrinkable tube may have a shrinkage rate of 50% or more. A shrinkage rate of 50% or more can further improve adhesion to the adherend. The "shrinkage rate" is calculated by finding the difference between the inner diameter of the heat-shrinkable tube before shrinkage and the inner diameter of the heat-shrinkable tube after shrinkage, and dividing the difference by the inner diameter before shrinkage.

[0021] (8) The wire harness of the present disclosure is a wire harness including a plurality of wires each having a conductor and an insulating layer covering the outer surface of the conductor, and a tube attached to the plurality of wires, wherein the tube is a heat-shrinkable tube according to any one of (1) to (7) above.

[0022] The wire harness includes a tube obtained by heat-shrinking the heat-shrinkable tube, which provides excellent adhesion between the inner layer and the adherend during heat shrinkage, and the inner layer is less likely to flow out of the outer layer when used at high temperatures, so the tube can maintain good adhesion to and protect the wires.Furthermore, the wire harness includes a tube obtained by heat-shrinking the heat-shrinkable tube, which ensures waterproofing of the connection, resulting in good electrical properties.

[0023] [Details of the embodiments of the present disclosure] Hereinafter, a heat shrink tube and a wire harness according to an embodiment of the present disclosure will be described with reference to the drawings.

[0024] <Heat shrink tubing> The heat-shrinkable tube has a two-layer structure including a cylindrical outer layer and an inner layer laminated on the inner circumferential surface of the outer layer. The heat-shrinkable tube is used, for example, as a covering for protecting, insulating, waterproofing, and corrosion-preventing the connection between insulated electric wires, the terminals of wiring, metal pipes, etc. FIG. 1 is a schematic perspective view showing a heat-shrinkable tube according to one embodiment of the present disclosure. FIG. 2 is a cross-sectional view taken along line AA showing a longitudinal cross section of the heat-shrinkable tube of FIG. 1. FIG. 3 is a cross-sectional view taken along line BB showing a transverse cross section perpendicular to the longitudinal direction of the heat-shrinkable tube of FIG. 1. As shown in FIGS. 1 to 3, the heat-shrinkable tube 1 of this embodiment includes a cylindrical outer layer 2 and an inner layer 3 laminated on the inner circumferential surface of the outer layer 2.

[0025] The heat-shrinkable tube 1 has excellent heat resistance because the outer layer 2 and the inner layer 3 are mainly composed of a fluororesin or a fluororubber. Examples of fluororesins include tetrafluoroethylene-ethylene copolymer (ETFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polyethylene fluoride propylene (FEP), and polychlorotrifluoroethylene (PCTFE). Among these, the fluororesin may be tetrafluoroethylene-ethylene copolymer, which can provide good fluidity during heat shrinkage.

[0026] The heat-shrinkable tube 1 has excellent flexibility due to its main component being fluororubber. Examples of fluororubber include vinylidene fluoride rubber (FKM), tetrafluoroethylene-propylene rubber (FEPM), and tetrafluoroethylene-perfluorovinyl ether rubber (FFKM). Among these, vinylidene fluoride rubber may be used, as it has good heat resistance, processability, and cost performance.

[0027] The lower limit of the content of the fluororesin or fluororubber in the outer layer 2 and the inner layer 3 may be 60 mass %, 70 mass %, 80 mass %, or 90 mass %. When the content of the fluororesin or fluororubber in the outer layer 2 and the inner layer 3 is within the above range, the heat shrink force of the produced heat-shrinkable tube is good, allowing it to adequately adhere to the adherend. Furthermore, the heat-shrinkable tube 1 can adequately exhibit the heat resistance and other properties unique to the fluororesin or fluororubber.

[0028] The average inner diameter and average thickness of the heat-shrinkable tube 1 before heat shrinkage are appropriately selected depending on the application and the like.

[0029] Generally, it is necessary to check the shrinkage state, melting of the inner layer, and the connection state of electric wires, etc., of heat-shrinkable tubing, and transparency of the tubing is required to improve visibility inside the heat-shrinkable tubing. The heat-shrinkable tubing 1 may have a transmittance of 10% or more, 20% or more, or 30% or more at a wavelength of 550 nm, which is visible light. When the heat-shrinkable tubing 1 has a transmittance of 10% or more at a wavelength of 550 nm, visibility inside the heat-shrinkable tubing is improved, making it easier to check the inside of the heat-shrinkable tubing 1. To maintain transparency, it is better to adjust the transmittance by selecting a resin material or rubber material rather than adding an inorganic filler.

[0030] The upper limit of the secant modulus of the heat-shrinkable tube 1 may be 2000 MPa. When the upper limit of the secant modulus is 2000 MPa, the flexibility of the heat-shrinkable tube 1 can be improved and breakage can be reduced. On the other hand, the lower limit of the secant modulus of the heat-shrinkable tube 1 may be 300 MPa or 500 MPa. When the lower limit of the secant modulus is 300 MPa, the heat-shrinkable tube 1 becomes semi-rigid after shrinkage, which improves the shape retention of the tube and protects the connection portion of the adherend, such as an electric wire, from mechanical shock.

[0031] The shrinkage rate of the heat-shrinkable tube 1 may be 50% or more, 60% or more, or 70% or more. When the shrinkage rate of the heat-shrinkable tube 1 is 50% or more, the adhesion to the adherend can be further improved, and the adherend having large steps can be effectively waterproofed.

[0032] [Outer layer] The outer layer 2 is formed as a tube that shrinks in diameter when heated, and is mainly composed of a fluororesin or a fluororubber.

[0033] In the heat-shrinkable tube 1, the melting point of the outer layer 2 is 210°C or higher and 260°C or lower, thereby ensuring heat resistance and suppressing thermal damage to the adherend. If the melting point of the outer layer 2 is lower than 210°C, sufficient heat resistance may not be obtained. On the other hand, if the melting point of the outer layer 2 exceeds 260°C, the heat-shrinkable tube 1 has a high heat shrinkage temperature, which may cause deterioration of the adherend.

[0034] The outer layer 2 may contain an ethylene-tetrafluoroethylene copolymer as a main component, and the storage modulus of the outer layer 2 at 250°C or higher and 280°C or lower may be 0.8 MPa or higher and 2.8 MPa or lower. When the outer layer 2 contains an ethylene-tetrafluoroethylene copolymer as a main component, the heat resistance of the outer layer 2 is good. When the storage modulus of the outer layer 2 at 250°C or higher and 280°C or lower is within the above range, good shrinkage properties can be obtained, and the shape memory performance is excellent.

[0035] Other additives may be added as needed to the outer layer 2. Examples of such additives include crosslinking aids, antioxidants, flame retardants, copper inhibitors, lubricants, colorants, heat stabilizers, and ultraviolet absorbers.

[0036] The outer layer 2 may be a crosslinked product obtained by irradiation with ionizing radiation. When the outer layer 2 is a crosslinked product obtained by irradiation with ionizing radiation, the outer layer 2 can stably maintain its shape for a long period of time even in an environment where it is subjected to external stress or high temperatures.

[0037] Inner Layer The inner layer 3 is intended to enhance adhesion to the adherend and improve waterproofing, etc. The inner layer 3 is mainly composed of a fluororesin or fluororubber.

[0038] When the shear viscosity of the inner layer 3 at 250°C and a shear rate of 10 / s is 300 Pa·s or more and 10,000 Pa·s or less, and when the shear viscosity at 215°C and a shear rate of 1 / s is 3,000 Pa·s or more and 70,000 Pa·s or less, the heat-shrinkable tubing 1 has excellent fluidity and durability during heat shrinkage and good shape retention when used at high temperatures, thereby suppressing dripping. In other words, when the shear viscosity of the inner layer 3 is in the above ranges, the heat-shrinkable tubing 1 has good sealing properties during heat shrinkage, as well as good durability and sealing properties when used at high temperatures.

[0039] The lower limit of the shear viscosity of the inner layer 3 at 250°C and a shear rate of 10 / s is 300 Pa·s, or may be 400 Pa·s, or 500 Pa·s. A shear viscosity of 300 Pa·s or more at a shear rate of 10 / s reduces outflow of the inner layer 3 during heat shrinkage, improving sealing performance. On the other hand, the upper limit of the shear viscosity at 250°C and a shear rate of 10 / s is 10,000 Pa·s, or may be 9,000 Pa·s, 8,000 Pa·s, 7,000 Pa·s, or 6,000 Pa·s. A shear viscosity of 10,000 Pa·s or less at a shear rate of 10 / s improves the fluidity of the inner layer 3 during heat shrinkage of the heat-shrinkable tube 1, allowing gaps at the ends of the heat-shrinkable tube 1 to be filled, improving sealing performance.

[0040] The lower limit of the shear viscosity of the inner layer 3 at 215°C and a shear rate of 1 / s is 3000 Pa·s, or may be 4000 Pa·s, or 5000 Pa·s. A shear viscosity of 3000 Pa·s or more at a shear rate of 1 / s reduces outflow of the inner layer 3 during use at high temperatures, improving sealing performance. On the other hand, the upper limit of the shear viscosity at 215°C and a shear rate of 1 / s is 70000 Pa·s, or may be 60000 Pa·s, or 55000 Pa·s. A shear viscosity of 70000 Pa·s or less at a shear rate of 1 / s ensures durability of the heat-shrinkable tube 1 during use at high temperatures and maintains its sealing effect.

[0041] The shear viscosity of the inner layer 3 can be adjusted by further containing an inorganic filler such as silica, hydrotalcite, clay, etc. The shear viscosity of the inner layer 3 can also be adjusted by irradiating it with ionizing radiation.

[0042] The melting point of the inner layer 3 may be 120° C. or higher and 180° C. or lower. When the melting point of the inner layer 3 is 120° C. or higher and 180° C. or lower, good fluidity can be obtained during heat shrinkage, and the adhesion between the inner layer 3 and the adherend during heat shrinkage can be improved.

[0043] To obtain good fluidity during heat shrinkage, the main component of the inner layer 3 may be any of ethylene-tetrafluoroethylene copolymer (ETFE), acid-modified ethylene-tetrafluoroethylene-hexafluoropropylene copolymer (acid-modified EFEP), polyvinylidene fluoride (PVDF), and vinylidene fluoride rubber (FKM). These may be used alone or as a mixture of two or more. Among these, the main component of the inner layer 3 may be ethylene-tetrafluoroethylene copolymer, from the viewpoint of improving durability and shape retention as well as fluidity during heat shrinkage.

[0044] The main component of the inner layer 3 may be an ethylene-tetrafluoroethylene copolymer, and the polyvinylidene fluoride content in the inner layer 3 may be 5% by mass or more and 40% by mass or less. When the main component of the inner layer 3 is an ethylene-tetrafluoroethylene copolymer, and the polyvinylidene fluoride content is 5% by mass or more and 40% by mass or less, the fluidity during heat shrinkage can be further improved. The lower limit of the polyvinylidene fluoride content in the inner layer 3 may be 5% by mass, 6% by mass, or 7% by mass. The upper limit of the polyvinylidene fluoride content in the inner layer 3 may be 40% by mass or 35% by mass.

[0045] Other additives may be added as needed to the inner layer 3. Examples of such additives include crosslinking inhibitors, antioxidants, copper inhibitors, viscosity property improvers, deterioration inhibitors, flame retardants, lubricants, colorants, heat stabilizers, UV absorbers, and adhesives.

[0046] [Heat shrink tubing manufacturing method] The heat-shrinkable tube can be manufactured, for example, by the following steps. (1) A step of preparing an outer layer composition for forming an outer layer (2) A step of producing an inner layer composition for forming the inner layer (3) A step of forming a two-layer molded product by extruding the outer layer composition and the inner layer composition using a melt extruder. (4) Expanding the diameter of the two-layer molded product

[0047] (1) Step of preparing an outer layer composition The outer layer composition can be prepared by mixing the fluororesin or fluororubber as the main component with optional additives using, for example, a melt mixer. As the melt mixer, a known mixer such as an open roll, a Banbury mixer, a pressure kneader, a single-screw mixer, or a multi-screw mixer can be used.

[0048] (2) Step of preparing the inner layer composition The inner layer composition can be prepared by mixing the fluororesin or fluororubber as the main component with optional additives, for example, using a melt mixer. The melt mixer can be the same as that used to prepare the outer layer composition.

[0049] (3) Process for forming two-layer molded products In this process, a two-layer molded product may be formed by extruding the outer layer and the inner layer separately, or by co-extruding the inner layer and the outer layer. When the outer layer and the inner layer are extruded separately, there are fewer restrictions on the combination of resins for the inner layer and the outer layer, making production easier. On the other hand, when the inner layer and outer layer are co-extruded, it is possible to easily produce a tube of the desired length with excellent cost and productivity. The co-extrusion molded product is formed by co-extrusion molding the outer layer composition and the inner layer composition using a known melt extruder, with the inner layer laminated on the inner peripheral surface of the outer layer.

[0050] The dimensions of the two-layer molded product can be designed according to the application, etc.

[0051] (4) Expanding the diameter of the two-layer molded product In this process, the two-layer molded article is expanded in diameter to form a heat-shrinkable tube. The two-layer molded article is expanded in diameter by, for example, heating the two-layer molded article to a temperature above its melting point and then introducing compressed air into the interior to expand it to a predetermined inner diameter, and then cooled to fix the shape. The two-layer molded article is expanded in diameter, for example, so that the inner diameter of the two-layer molded article becomes about two to four times its original size. The two-layer molded article expanded in diameter and fixed in shape in this way becomes the heat-shrinkable tube. On the other hand, when the outer layer and the inner layer are extrusion molded separately, the inner layer is placed on the inner surface of the outer layer, which has been expanded after extrusion molding, and this is then attached to the adherend, and the outer layer is then shrunk to form a two-layer molded product.

[0052] When the outer layer is primarily composed of ethylene-tetrafluoroethylene copolymer, a storage modulus of the outer layer between 0.8 MPa and 2.8 MPa at 250°C and 280°C can provide good diameter expandability, improve the wall thickness distribution, and control the length change rate. Furthermore, uniform shrinkage in the longitudinal direction can suppress the inclination of the end face during shrinkage.

[0053] This step may include a step of irradiating the extruded outer layer and inner layer with ionizing radiation. By crosslinking the outer layer by irradiating with ionizing radiation, the shape retention and heat resistance of the outer layer can be improved. Examples of the ionizing radiation to be irradiated include electron beams and gamma rays, but electron beams are preferred because the equipment required for their preparation is relatively easy.

[0054] In this way, a heat-shrinkable tube is produced which has an outer layer having a melting point of 210°C or more and 260°C or less, and an inner layer having a shear viscosity of 300 Pa·s or more and 10,000 Pa·s or less at 250°C and a shear rate of 10 / s, and a shear viscosity of 3,000 Pa·s or more and 70,000 Pa·s or less at 215°C and a shear rate of 1 / s.

[0055] According to this heat-shrinkable tube, the inner layer easily flows during heat shrinkage, ensuring close contact with the adherend, and the inner layer has excellent close contact with the adherend during heat shrinkage. In addition, the inner layer is less likely to flow out from the outer layer when used at high temperatures.

[0056] <Wire harness> The heat-shrinkable tube can be used to protect, insulate, waterproof, and protect against corrosion of wires such as fluororesin electric wires whose insulating layer covering the conductor is fluororesin, fluororubber electric wires whose insulating layer is fluororubber, PE electric wires or PE cables whose insulating layer is polyethylene (PE), and PVC electric wires or PVC cables whose insulating layer is polyvinyl chloride (PVC). For example, the heat-shrinkable tube can be used in wire harnesses. Specifically, the wire harness includes multiple wires each having a conductor and an insulating layer covering the outer circumferential surface of the conductor, and a tube attached to the multiple wires, and the tube is made of the heat-shrinkable tube. In other words, the tube is obtained by heat-shrinking the heat-shrinkable tube.

[0057] The wire harness includes a tube obtained by heat-shrinking the heat-shrinkable tube, which provides excellent adhesion between the inner layer and the adherend during heat shrinkage. The inner layer is less likely to flow out of the outer layer during use at high temperatures, allowing the tube to maintain good adhesion to and protect the wires. Furthermore, the wire harness includes a tube obtained by heat-shrinking the heat-shrinkable tube, which ensures waterproofing of the connection, resulting in good electrical properties. The wire harness exhibits particularly good properties with fluororesin electric wires and fluororubber electric wires.

[0058] 4 and 5 show an example in which the heat-shrinkable tube 1 is applied to a wire harness 50. The wire harness 50 in FIGS. 4 and 5 includes a plurality of wires 30 bundled together by a tube 1a formed by heat-shrinking the heat-shrinkable tube 1 of FIG. 1, and a multi-pin connector 31 attached to the ends of the plurality of wires 30. The tube 1a includes a heat-shrunk outer layer 2a and inner layer 3a. The wires 30 are insulated wires or cables such as fluororesin wires, polyethylene wires, and PVC wires. For example, the wires 30 may have an insulating layer 25 covering the conductors 20, the insulating layer 25 containing an ethylene-tetrafluoroethylene copolymer as a main component. The content of the ethylene-tetrafluoroethylene copolymer in the insulating layer 25 is, for example, 50% by mass or more and 95% by mass or less. In the wire harness 50, the tube 1a can contribute to protecting, insulating, waterproofing, and corrosion prevention of the connection parts. In the wire harness 50, the tube 1a not only serves to bundle the wires 30 but also to protect each individual wire 30. There is no restriction on the number of wires 30 that can be covered by the heat-shrinkable tube 1, and the heat-shrinkable tube 1 can be used to connect one wire or multiple wires.

[0059] [Other embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0060] The wire harness of the present disclosure may be configured as a so-called flat harness in which a plurality of wires are bundled in a flat shape, or may have other forms.

[0061] The wire harness of the present disclosure also includes a wire splice. A wire splice is formed by twisting and connecting the conductors of a pair of wires, and covering the connection with a tube obtained by heat-shrinking the heat-shrink tube. The wires are similar to the wire harness described above. In such a wire splice, the tube can contribute to protecting, insulating, waterproofing, and corrosion prevention of the connection. The wire splice may be formed by covering the connection between the wires with a heat-shrink tube, and may be formed by connecting one wire to multiple wires, connecting multiple wires together, or connecting the ends of multiple wires together as in wiring terminal processing, or may be formed in other forms.

[0062] 6 and 7 show an example in which the heat shrinkable tube 1 is applied to a wire splice as a wire harness according to another embodiment. FIG. 6 shows the wire harness 60 with the exposed conductors of two wires inserted into a heat-shrinkable tube, and FIG. 7 shows the two connecting wires 30 in the wire harness 60 covered with the shrunk tube. The wire harness 60 in FIG. 7 has the conductors 20 of the two wires 30 twisted together to connect them, and the connection is covered with a tube 1a obtained by heat-shrinking the heat-shrinkable tube 1. The tube 1a has a heat-shrunk outer layer 2a and inner layer 3a. In the wire harness 60, the tube 1a can also contribute to protecting the connection, insulating it, waterproofing it, preventing corrosion, and so on. In the wire harness 60, the tube 1a not only serves to bundle the two wires 30 together but also serves to protect each individual wire 30.

[0063] The heat-shrinkable tube of the present disclosure is not limited to the heat-shrinkable tube having an outer layer formed in a tubular shape as shown in Figures 1 to 3, but may also be a heat-shrinkable tube 10 having an outer layer 12 formed in a cap shape, as shown in Figure 8. This heat-shrinkable tube 10 is formed by heat-shrinking one end of the heat-shrinkable tube 10 to close the end, thereby disposing the inner layer 13 on the inner peripheral surface of the cap-shaped outer layer 12. This heat-shrinkable tube 10 can be suitably used, for example, for terminal processing of wiring. [Example]

[0064] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0065] <Test Example 1> Heat-shrinkable tubes No. 1 to No. 15 in Table 1 were produced through the following steps: selecting raw materials, preparing an outer layer composition, preparing an inner layer composition, forming a two-layer molded article, irradiating, and expanding the diameter of the two-layer molded article. Table 1 shows the compositions and physical properties of the outer and inner layers. Heat-shrinkable tubes No. 1 to No. 15 were produced by molding the outer and inner layers separately and then inserting the inner layer into the outer layer. The outer layer was extruded at a die temperature of 280°C, a drawdown ratio of 10, and a linear speed of 20 m / min. Then, as shown in Table 1, the outer layer was crosslinked by electron beam irradiation at a dose of 60 kGy, except for tube No. 14. After irradiation, the tube was heated to 250 to 280°C and expanded using an expansion die, applying higher pressure to the inside of the tube than to the outside. The expansion die was coated with a fluororesin. The melting point and high-temperature storage modulus of the outer layer were adjusted by selecting the raw materials and the degree of crosslinking. The inner layer was extruded at a die temperature of 285°C, a drawdown ratio of 10, and a linear speed of 6 m / min. The inner layer was then crosslinked by electron beam irradiation at doses ranging from 60 kGy to 180 kGy. The shear viscosity of the inner layer was adjusted by selecting the raw materials and the degree of crosslinking. Two-layer heat-shrinkable tubing was then fabricated by inserting the inner layer into the outer layer. Heat shrinkage was performed by heating at 270°C for 15 minutes. For heat-shrinkable tubing No. 1 to No. 15, the shear viscosity of the inner layer at an actual temperature of 250°C, the shear viscosity of the inner layer at 215°C (simulating high-temperature use), and the sealing performance of the heat-shrinkable tubing are shown. The shear viscosity was measured using a rotational rheometer (Anton Paar MCR302). The melting point of the outer layer and the storage modulus [MPa] at temperatures between 250°C and 280°C are also shown. The inner layer used THV with a melting point of 115°C, EVA with a melting point of 90°C, ETFE with a melting point of 170°C, PVDF with a melting point of 115°C, and FKM that is liquid at room temperature. In Table 1, "THV" is tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer, "PTFE" is polytetrafluoroethylene, and "EVA" is ethylene-vinyl acetate copolymer.

[0066] The sealing performance of the heat-shrinkable tubing was evaluated by an air leak test. The air leak test was conducted after heating the heat-shrunk sample at 215°C for 500 hours. The air leak test involves introducing air into the test sample underwater to check for air leakage. Specifically, the insulation layer of an insulated electric wire is peeled off and the sample heat-shrinkable tubing is shrunk to cover the exposed conductor. One end of the insulated electric wire is then sealed, and a tube for introducing air is attached to the other end to evaluate air leakage. The standard for air leakage is no air leakage after 30 seconds at an air pressure of 200 kPa. The evaluation criteria for the sealing performance of heat shrink tubing are as follows: A to C are considered pass. A: The pass rate for air leak testing is over 90%. B: The pass rate for the air leak test is between 80% and 90%. C: The pass rate for the air leak test is 70% or more but less than 80%. D: The pass rate for the air leak test is less than 70%.

[0067] Table 1 shows the evaluation results of the sealing performance of the heat-shrinkable tubing.

[0068] [Table 1]

[0069] As shown in Table 1, good results were obtained in the sealing performance of heat-shrinkable tubes No. 4 to No. 10, which have an outer layer with a melting point of 210°C or higher and 260°C or lower and an inner layer with a shear viscosity of 300 Pa·s or higher and 10,000 Pa·s or lower at 250°C and a shear rate of 10 / s, and a shear viscosity of 3,000 Pa·s or higher and 70,000 Pa·s or lower at 215°C and a shear rate of 1 / s. The heat-shrinkable tubing No. 14 had a high melting point for the outer layer, which meant that the shrinkage performance was insufficient and the sealing performance of the heat-shrinkable tubing was poor.The heat-shrinkable tubing No. 15 had a low melting point for the outer layer, which meant that the heat resistance was insufficient and the sealing performance of the heat-shrinkable tubing was poor.

[0070] <Test Example 2> Heat-shrinkable tubes No. 16 to No. 23 were produced in the same manner as in Test Example 1, except that the storage modulus of the outer layer was adjusted by selecting the raw material and the degree of crosslinking of the ethylene-tetrafluoroethylene copolymer resin in the outer layer.

[0071] The sealing performance of the heat shrinkable tube was evaluated by the same air leak test as in Test Example 1. Table 2 shows the evaluation results of the sealing performance of the heat shrinkable tube.

[0072] [Table 2]

[0073] As shown in Table 2, good sealing performance was obtained by setting the storage modulus at 250°C to 280°C to 0.8MPa to 2.8MPa. On the other hand, No. 16, which had a storage modulus of less than 0.8MPa, and No. 23, which had a storage modulus of more than 2.8MPa, did not exhibit good properties as a shrinkable connecting part.

[0074] <Test Example 3> Except for adjusting the ratio of ETFE to PVDF in the composition of the inner layer, heat-shrinkable tubes No. 24 to No. 28 were produced in the same manner as in Test Example 1. The PVDF used had a melt flow rate of 93.4 g / 10 min at 232°C under a load of 1.2 kg.

[0075] The sealing performance of the heat shrinkable tube was evaluated by the same air leak test as in Test Example 1. Table 3 shows the evaluation results of the sealing performance of the heat shrinkable tube.

[0076] [Table 3]

[0077] As shown in Table 3, the inner layer containing PVDF and ETFE as the main component improved the sealing performance of the heat shrinkable tube.

[0078] <Test Example 4> The melting point of the inner layer was adjusted by selecting the resin for the inner layer, and heat-shrinkable tubing Nos. 29 to 34 were produced by co-extrusion. Extrusion was performed at a die temperature of 280°C, a drawdown ratio of 10, and a linear speed of 20 m / min. The outer layer was then crosslinked by electron beam irradiation at a dose of 25 kGy to 400 kGy. After irradiation, the tubing was heated to 250°C to 280°C and expanded using an expansion die, applying a higher pressure to the inside of the tubing than to the outside. The expansion die was coated with a fluororesin.

[0079] The sealing performance of the heat shrinkable tube was evaluated by the same air leak test as in Test Example 1. Table 4 shows the evaluation results of the sealing performance of the heat shrinkable tube.

[0080] [Table 4]

[0081] As shown in Table 4, by having the melting point of the inner layer be 120°C or higher and 180°C or lower, fluidity was obtained during heat shrinkage, and good results were obtained in the sealing performance of the heat shrinkable tube.

[0082] <Test Example 5> Heat-shrinkable tubes Nos. 35 to 38 were produced in the same manner as No. 5 in Test Example 1, except that crosslinking was performed by electron beam irradiation at an irradiation dose of 60 kGy so that the resin compositions of the outer layer and inner layer and the transmittance of the heat-shrinkable tube would be the values ​​shown in Table 5.

[0083] The evaluation results of the visibility of the inside of the heat shrinkable tubes No. 35 to No. 38 are shown in Table 5. The visibility of the inside of the heat shrinkable tubes was evaluated according to the following criteria. A: The interior is clearly visible. B: The interior is visible. C: The interior cannot be seen.

[0084] [Table 5]

[0085] As shown in Table 5, heat shrinkable tubes No. 36 to No. 38, which had a transmittance of 10% or more at a wavelength of 550 nm, had good visibility inside the heat shrinkable tube.

[0086] From the above results, it can be seen that the inner layer of the heat-shrinkable tube flows easily during heat shrinkage, ensuring close contact with the adherend, providing excellent adhesion between the inner layer and the adherend during heat shrinkage, and that the inner layer is less likely to flow out from the outer layer when used at high temperatures. [Explanation of symbols]

[0087] 1, 10 Heat shrink tubing 1a tube 2, 12 outer layer 2a Outer layer after shrinkage 3, 13 inner layer 3a Inner layer after shrinkage 20 Conductors 25 insulating layer 30 wire 31 Multi-pin connector 50, 60 Wire harness

Claims

1. a cylindrical outer layer having a melting point of 210°C or higher and 260°C or lower; an inner layer laminated on the inner circumferential surface of the outer layer; Equipped with the outer layer and the inner layer are each composed mainly of a fluororesin or a fluororubber, The heat-shrinkable tube has a shear viscosity of the inner layer at 250°C and a shear rate of 10 / s of 300 Pa·s or more and 10,000 Pa·s or less, and a shear viscosity of 215°C and a shear rate of 1 / s of 3,000 Pa·s or more and 70,000 Pa·s or less.

2. the outer layer is mainly composed of an ethylene-tetrafluoroethylene copolymer, 2. The heat-shrinkable tube according to claim 1, wherein the outer layer has a storage modulus of 0.8 MPa or more and 2.8 MPa or less at 250°C or more and 280°C or less.

3. 3. The heat-shrinkable tube according to claim 1, wherein the melting point of the inner layer is 120° C. or higher and 180° C. or lower.

4. 3. The heat-shrinkable tube according to claim 1, wherein the main component of the inner layer is an ethylene-tetrafluoroethylene copolymer.

5. the main component of the inner layer is an ethylene-tetrafluoroethylene copolymer, 3. The heat-shrinkable tube according to claim 1, wherein the content of polyvinylidene fluoride in the inner layer is 5% by mass or more and 40% by mass or less.

6. 3. The heat-shrinkable tube according to claim 1, wherein the transmittance at a wavelength of 550 nm is 10% or more.

7. 3. The heat-shrinkable tube according to claim 1, wherein the shrinkage rate is 50% or more.

8. A wire harness comprising: a plurality of wires each having a conductor and an insulating layer covering an outer peripheral surface of the conductor; and a tube attached to the plurality of wires, 3. A wire harness using the heat-shrinkable tube according to claim 1 or 2 as the tube.

Images