JP7666016B2 - Insulated wire and method for producing the same - Google Patents

Description

This disclosure relates to a resin composition for an outer layer waterproofing material, an insulated electric wire, and a method for manufacturing an insulated electric wire.

In overhead wiring applications, insulated electric wires are used that have waterproof materials between the conductor strands and between the conductor and the insulating layer to prevent corrosion of the conductor due to the infiltration of rainwater. Of the waterproof materials for insulated electric wires, the outer waterproof material provided between the conductor and the insulating layer is required to have watertight properties, adhesion to bond the conductor and the insulating layer, and peelability to strip the waterproof material and the insulating layer from the conductor (for example, Patent Document 1).

Patent No. 3688319

The purpose of this disclosure is to provide technology that can improve watertightness, adhesion, and peelability in a balanced manner.

According to one aspect of the present disclosure,
A resin composition for an outer layer water-tight material forming an outer layer water-tight material for an insulated electric wire,
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire gripping tool and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
The resin composition for an outer layer watertight material is provided, in which when the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated electric wire around the entire outer circumference of the conductor, the remaining portion of the outer layer watertight material remaining across the conductor wires is 5 or less pieces.

According to another aspect of the present disclosure,
a conductor formed by twisting together a plurality of conductor wires;
An outer watertight material provided to cover the outer periphery of the conductor;
An insulating layer provided to cover the outer periphery of the outer layer watertight material;
An insulated wire having
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire holder and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
The insulated wire provided has such a structure that when the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated wire around the entire outer circumference of the conductor, the remaining portion of the outer layer watertight material remaining across the conductor wires is 5 or less.

According to another aspect of the present disclosure,
A step of stranding a plurality of conductor wires to form a conductor;
forming an outer layer watertight material so as to cover an outer periphery of the conductor;
forming an insulating layer so as to cover the outer periphery of the outer layer watertight material;
cross-linking at least the insulating layer;
having
In the step of forming the outer layer water-tight material,
The conductor is preheated to a temperature of 20°C to 40°C, and the outer layer watertight material is extruded.
In the step of cross-linking the insulating layer,
The present invention provides a method for producing an insulated wire, in which the insulating layer is cross-linked with water at a cross-linking temperature of 75° C. or more and 82° C. or less.

This disclosure makes it possible to achieve a balanced improvement in watertightness, adhesion, and peelability.

FIG. 1 is a cross-sectional view perpendicular to an axial direction of an insulated wire according to an embodiment of the present disclosure. FIG. 2A is a schematic diagram illustrating a method for manufacturing an insulated wire according to one embodiment of the present disclosure. FIG. 2B is a schematic diagram illustrating a method for manufacturing an insulated wire according to one embodiment of the present disclosure. FIG. 2C is a schematic diagram illustrating a method for manufacturing an insulated wire according to one embodiment of the present disclosure. FIG. 2D is a schematic diagram illustrating a method for manufacturing an insulated wire according to one embodiment of the present disclosure. FIG. 3A is a schematic diagram showing an insulated wire of Sample 1 that was subjected to a peelability test. FIG. 3B is a schematic diagram showing an insulated wire of Sample 3 that was subjected to a peelability test. FIG. 3C is a schematic diagram showing an insulated wire of Sample 4 that was subjected to a peelability test. FIG. 3D is a schematic diagram showing an insulated wire of Sample 5 that was subjected to a peeling property test.

[Description of the embodiments of the present disclosure]
<Findings gained by the inventors>
First, the findings of the inventors will be described.

Of the three characteristics required for an outer layer waterproofing material, the watertightness (rainwater infiltration prevention or water running prevention) is a characteristic to suppress the propagation of rainwater between the conductor strands and between the conductor and the insulating layer, and to suppress corrosion of the conductor due to rainwater. Adhesion (wire gripping property, Camler property) is a property to prevent the insulating layer from shifting or breaking when the insulated wire is pulled with a wire gripping tool (wire gripper, Camler) by making the conductor and insulating layer adhere to each other. Strippability (peelability) is a property to strip the outer layer waterproofing material and insulating layer from the conductor at the end of the insulated wire when a pair of insulated wires are compressed and connected through a compression sleeve.

Regarding the peelability required for the outer layer waterproof material, it has been conventionally considered that even if at least a portion of the conductor remains, there is no problem as long as electrical continuity is established between the conductor and the compression sleeve when a pair of insulated electric wires are compressed and connected via the compression sleeve.

However, in recent years, from the viewpoint of improving power transmission efficiency and installation stability, it is desirable to reduce the contact resistance between the conductor and the compression sleeve when a pair of insulated electric wires are compressed and connected via the compression sleeve, and to improve the gripping ability (grip strength) of the compression sleeve. Therefore, there is a demand for more precise stripping ability of insulated electric wires.

Here, the inventors have discovered that depending on the shape of the remaining outer layer watertight material that remains when the insulating layer is stripped away, the following problems may occur.

For example, if a large amount of the outer layer waterproof material remains across the conductor wires when the insulation layer is stripped away, it becomes difficult for the conductor wires and the compression sleeve to be connected via the remaining portion. This can result in high contact resistance between the conductor and the compression sleeve.

For example, if many of the grooves formed between adjacent conductor wires when the insulation layer is stripped away contain residual outer layer watertight material, the remaining outer layer watertight material in the grooves will cause the compression sleeve to come into uneven contact with the outer circumference of the conductor when the compression sleeve is compressed and connected, making it difficult to sufficiently compress the compression sleeve. This may reduce the grip of the compression sleeve.

The inventors conducted extensive research into these issues and discovered that the above-mentioned peelability could be improved by preheating the conductor to a specified temperature during the outer waterproofing material formation process in the insulated wire manufacturing process.

This disclosure is based on the above-mentioned new findings discovered by the inventors.

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

[1] A resin composition for an outer layer watertight material according to one embodiment of the present disclosure,
A resin composition for an outer layer water-tight material forming an outer layer water-tight material for an insulated electric wire,
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire holder and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
When the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated wire around the entire outer circumference of the conductor, the remaining portions of the outer layer watertight material remaining across the conductor wires are 5 or less.
According to this configuration, it is possible to improve watertightness, adhesion and peelability in a well-balanced manner.

[2] An insulated wire according to another aspect of the present disclosure includes:
A resin composition for an outer layer water-tight material forming an outer layer water-tight material for an insulated electric wire,
a conductor formed by twisting together a plurality of conductor wires;
An outer watertight material provided to cover the outer periphery of the conductor;
An insulating layer provided to cover the outer periphery of the outer layer watertight material;
An insulated wire having
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire holder and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
When the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated wire around the entire outer circumference of the conductor, the remaining portions of the outer layer watertight material remaining across the conductor wires are 5 or less.
According to this configuration, it is possible to improve watertightness, adhesion and peelability in a well-balanced manner.

[3] The insulated wire according to the above [2],
When the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated wire around the entire outer circumference of the conductor, the ratio of the number of grooves in which the outer layer watertight material remains to the total number of grooves formed between adjacent conductor wires is 7/12 or less.
This configuration improves the grip of the compression sleeve.

[4] The insulated wire according to the above [2] or [3],
The outer layer watertight material is made of a resin composition containing an ethylene-(meth)acrylate copolymer.
According to this configuration, it is possible to preferably achieve a well-balanced watertightness, adhesion and peelability.

[5] A method for producing an insulated wire according to still another aspect of the present disclosure includes:
A step of stranding a plurality of conductor wires to form a conductor;
forming an outer layer watertight material so as to cover an outer periphery of the conductor;
forming an insulating layer so as to cover the outer periphery of the outer layer watertight material;
cross-linking at least the insulating layer;
having
In the step of forming the outer layer water-tight material,
The conductor is preheated to a temperature of 20°C to 40°C, and the outer layer watertight material is extruded.
In the step of cross-linking the insulating layer,
The insulating layer is crosslinked with water at a crosslinking temperature of 75°C or more and 82°C or less.
According to this configuration, it is possible to improve watertightness, adhesion and peelability in a well-balanced manner.

[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.

<One embodiment of the present disclosure>
(1) Insulated wire (watertight insulated wire)
An insulated wire according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a cross-sectional view of the insulated wire according to the embodiment, taken perpendicular to its axial direction.

As shown in FIG. 1, the insulated electric wire 10 of this embodiment is configured to be used as an electric wire for outdoor power distribution, and has, for example, from the center toward the outside, a conductor 100, an inner layer watertight material 220, an outer layer watertight material 240, and an insulating layer (insulator, insulating coating layer) 300.

The conductor 100 is formed by twisting together a number of conductor wires 110. The conductor 100 is made of, for example, hard copper wire, hard copper stranded wire, hard aluminum stranded wire, steel core aluminum stranded wire (ACSR), etc. The multiple conductor wires 110 are, for example, twisted concentrically, and the number of conductor wires 110 is, for example, 19.

The conductor 100 may or may not be compressed.

The inner layer watertight material 220 is filled between the multiple conductor wires 110. The inner layer watertight material 220 is configured to improve the watertight properties between the multiple conductor wires 110. The inner layer watertight material 220 will be described later.

The outer layer watertight material 240 is provided to cover the outer periphery of the conductor 100 (and the inner layer watertight material 220). The outer layer watertight material 240 is also configured to improve the watertightness mainly between the conductor 100 and the insulating layer 300. The outer layer watertight material 240 will be described in detail below together with the inner layer watertight material 220.

The insulating layer 300 is provided so as to cover the outer periphery of the outer layer waterproof material 240 (and the conductor 100). The insulating layer 300 is made of, for example, an insulating layer resin composition containing polyolefin as a base resin. The base resin of the insulating layer resin composition is, for example, polyethylene.

The insulating layer 300 is configured to be crosslinked, for example, by a silane grafting/water crosslinking method. The resin composition for the insulating layer that constitutes the insulating layer 300 contains, for example, a silane coupling agent, a crosslinking agent (free radical generator), and a catalyst (silanol condensation catalyst). In addition, the resin composition for the insulating layer may contain, for example, a color batch, an anti-aging agent, etc.

(Each dimension, etc.)
The outer diameter of the conductor wire 110 is, for example, 1 mm or more and 5 mm or less. The cross-sectional area of the conductor 100 is, for example, 14 ^mm2 or more and 500 ^mm2 or less. The thickness of the outer layer watertight material 240 is, for example, 0.1 mm or more and 2 mm or less. The thickness of the insulating layer 300 is, for example, 1 mm or more and 5 mm or less. The nominal voltage of the insulated wire 10 is, for example, 6.6 kV or more and 33 kV or less.

(2) Characteristics of the Insulated Wire As a result of diligent research by the inventors, for the first time, an insulated wire 10 having, for example, the following characteristics has been realized.

In the insulated electric wire 10 of this embodiment, when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire 10 cut to a predetermined length for 24 hours, the water permeation distance from one end of the insulated electric wire 10 is, for example, 1000 mm or less, preferably 600 mm or less. If the water permeation distance exceeds 1000 mm, the conductor 100 may corrode due to the penetration of rainwater. In contrast, in the insulated electric wire 10 of this embodiment, the water permeation distance is 1000 mm or less, so that the corrosion of the conductor 100 can be suppressed. This allows the insulated electric wire 10 to be stably maintained as a product. Furthermore, the water permeation distance is 600 mm or less, so that the corrosion of the conductor 100 can be stably suppressed.

The shorter the water penetration distance, the better. In other words, it is preferable that the lower limit of the water penetration distance is 0 mm, that is, it is preferable that no water penetrates at all from one end of the insulated electric wire 10.

In addition, in the insulated electric wire 10 of this embodiment, when the insulated electric wire 10 is held by a predetermined electric wire gripper (e.g., Camlar manufactured by Nagaki Seiki Co., Ltd.) and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length by which the insulating layer 300 shifts is, for example, 50 mm or less, preferably 5 mm or less. If the length by which the insulating layer 300 shifts exceeds 50 mm, for example, when the insulated electric wire 10 is held by a wire gripper during a work of replacing the insulated electric wire 10, the insulating layer 300 may slip along the conductor 100, and the insulated electric wire 10 may come off the wire gripper. This may increase the risk of the insulated electric wire 10 falling off. In contrast, in the insulated wire 10 of this embodiment, the length of displacement of the insulating layer 300 is 50 mm or less, so that when the insulated wire 10 is held by a wire gripper, slippage of the insulating layer 300 is suppressed, and the insulated wire 10 can be prevented from coming off the wire gripper. As a result, the insulated wire 10 can be prevented from falling off. Furthermore, because the length of displacement of the insulating layer 300 is 5 mm or less, it is possible to reliably suppress the insulated wire 10 from coming off the wire gripper.

The shorter the length of the displacement of the insulating layer 300, the better. In other words, it is preferable that the lower limit of the length of the displacement of the insulating layer 300 is 0 mm, that is, it is preferable that the insulating layer 300 does not displace.

In addition, the insulated wire 10 of this embodiment meets stricter stripping requirements than conventional wires.

Specifically, in the insulated wire 10 of this embodiment, when the outer layer watertight material 240 and the insulating layer 300 are stripped off 15 cm in the axial direction of the insulated wire 10 over the entire outer circumference of the conductor 100, the remaining portion of the outer layer watertight material 240 remaining to straddle the conductor wires 110 is, for example, 5 or less, preferably 3 or less, and more preferably 0. Note that the "remaining portion of the outer layer watertight material 240 remaining to straddle the conductor wires 110" refers to the remaining portion of the outer layer watertight material 240 remaining to connect from one conductor wire 110 (groove on the side) of a pair of conductor wires 110 adjacent to a specific conductor wire 110 on the outer circumference of the conductor 100 to the other conductor wire 110 (groove on the side) across the specific conductor wire 110. If the number of remaining outer layer watertight materials 240 remaining across the conductor wires 110 is more than five, it becomes difficult for the conductor wires 110 with the remaining portions to be connected to the compression sleeve through the remaining portions. This may increase the contact resistance between the conductor 100 and the compression sleeve. In contrast, in the insulated wire 10 of this embodiment, the number of remaining outer layer watertight materials 240 remaining across the conductor wires 110 is five or less, that is, the number of remaining outer layer watertight materials 240 interposed between the conductor wires 110 and the compression sleeve is reduced, so that each conductor wire 110 and the compression sleeve can be well connected. As a result, it is possible to prevent the contact resistance between the conductor 100 and the compression sleeve from increasing. Furthermore, the number of remaining outer layer watertight materials 240 remaining across the conductor wires 110 is preferably three or less, more preferably zero, so that each conductor wire 110 and the compression sleeve can be better and more reliably connected.

In addition, in the insulated wire 10 of this embodiment, when the outer layer watertight material 240 and the insulating layer 300 are stripped off 15 cm in the axial direction of the insulated wire 10 over the entire outer circumference of the conductor 100, the ratio of the number of grooves in which the outer layer watertight material 240 remains to the total number of grooves formed between adjacent conductor wires 110 (on the outer circumference of the conductor 100) is, for example, 7/12 or less, preferably 3/12 or less. If the ratio of the number of grooves in which the outer layer watertight material 240 remains exceeds 7/12, when the compression sleeve is compressed and connected, the compression sleeve abuts unevenly against the outer circumference of the conductor 100 due to the remaining outer layer watertight material 240 in the groove, making it difficult for the compression sleeve to be sufficiently compressed. This may reduce the grip of the compression sleeve. In contrast, in the insulated wire 10 of this embodiment, the ratio of the number of grooves in which the outer layer watertight material 240 remains is 7/12 or less, so that when the compression sleeve is compressed and connected, the compression sleeve can be abutted evenly against the outer circumference of the conductor 100, and the compression sleeve can be sufficiently compressed. As a result, the gripping ability of the compression sleeve can be improved. Furthermore, the ratio of the number of grooves in which the outer layer watertight material 240 remains is 3/12 or less, so that the compression sleeve can be firmly compressed.

The lower the percentage of the number of grooves in which the outer layer watertight material 240 remains, the better. In other words, it is preferable that the lower limit of the percentage of the number of grooves in which the outer layer watertight material 240 remains is 0.

(3) Watertight material (outer layer watertight material)
Next, a description will be given of the outer layer watertight material 240. The outer layer watertight material 240 of the present embodiment is configured, for example, as follows.

The outer layer watertight material 240 of this embodiment is composed of a resin composition (hereinafter also referred to as "resin composition for outer layer watertight material") that contains, for example, an ethylene-(meth)acrylate copolymer as a base resin. Note that "(meth)acrylate" here means acrylate or methacrylate.

Specific examples of base resins for the resin composition for the outer layer watertight material include ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer (EBA), and ethylene-methyl methacrylate copolymer (EMMA).

The base resin of the resin composition for the outer layer watertight material of this embodiment is, for example, EMMA. EMMA has the structure shown in the following formula (1).

EMMA has the same flexibility as ethylene vinyl acetate copolymer (EVA), rubber-like elasticity, excellent low-temperature properties, and excellent electrical properties. However, EMMA is designed not to be corroded by acids like EVA.

The base resin of the outer layer watertight material 240 of this embodiment is formed by mixing two resins (first resin and second resin) that contain, for example, EMMA and have different properties. The first resin has, for example, high mechanical strength and hard properties, good peelability, but poor adhesion. On the other hand, the second resin has, for example, low mechanical strength and soft properties, good watertightness and adhesion, but poor peelability. In this embodiment, the outer layer watertight material 240 contains a base resin that is a mixture of the first resin and the second resin, making it possible to improve the watertightness, adhesion, and peelability of the insulated electric wire 10 in a well-balanced manner.

Here, we will explain the first and second resins in detail.

The first resin has, for example, the following properties.
MMA content: 18% by weight or more and less than 22% by weight Melt flow rate: 1 g/10 min or more and less than 3 g/10 min Durometer hardness in type A: 75 or more and less than 92 Vicat softening temperature: 54°C or more and 66°C or less Melting temperature: 77°C or more and less than 95°C

Note that MMA stands for methyl methacrylate. The melt flow rate (MFR) is measured in accordance with JIS K7210 at a measurement temperature of 190°C and a load of 2.12N. The durometer hardness for Type A is measured in accordance with JIS K7215. The Vicat softening temperature is measured in accordance with JIS K7206. The melting temperature is measured by a differential scanning calorimeter (DSC) in accordance with JIS K7121.

On the other hand, the second resin has, for example, the following properties.
MMA content: 22% by weight or more and less than 28% by weight Melt flow rate: 6 g/10 min or more and less than 8 g/10 min Durometer hardness in type A: 70 or more and less than 86 Vicat softening temperature: 42°C or more and 52°C or less Melting temperature: 72°C or more and less than 88°C

In this embodiment, the ratio B/A of the weight B of the second resin to the weight A of the first resin in the base resin of the outer layer watertight material 240 is 1/4 or more and 4 or less (A:B = 80:20 to 20:80). If the ratio B/A of the weight B of the second resin to the weight A of the first resin is less than 1/4, that is, if the weight B of the second resin is smaller than the weight A of the first resin by a certain ratio, the outer layer watertight material 240 becomes excessively hard, and while the peelability is improved, the adhesion is reduced. In contrast, by setting the ratio B/A of the weight B of the second resin to the weight A of the first resin to 1/4 or more, the outer layer watertight material 240 is prevented from becoming excessively hard, and the watertightness and adhesion can be improved while maintaining the peelability. On the other hand, if the ratio B/A of the weight B of the second resin to the weight A of the first resin exceeds 4, that is, if the weight B of the second resin is greater than the weight A of the first resin by a certain ratio, the outer layer watertight material 240 becomes excessively soft, improving the watertightness and adhesion while decreasing the peelability. In contrast, by setting the ratio B/A of the weight B of the second resin to the weight A of the first resin to 4 or less, the outer layer watertight material 240 is prevented from becoming excessively soft, and the peelability can be improved while maintaining the watertightness and adhesion.

Moreover, in this embodiment, the ratio B/A of the weight A of the first resin to the weight B of the second resin in the base resin of the outer layer watertight material 240 is preferably 1 or more and 7/3 or less (A:B = 50:50 to 30:70). In this way, by mixing the relatively soft second resin in greater amounts than the first resin in the base resin of the outer layer watertight material 240, it is possible to stably improve watertightness and adhesion while maintaining peelability.

The resin composition that constitutes the outer layer watertight material 240 contains, in addition to the base resin described above, various additives such as the following:

The outer layer watertight material 240 is configured to be colored, for example. The resin composition constituting the outer layer watertight material 240 contains, for example, a color batch. The color batch contains, for example, a color batch base resin made of EMMA, carbon black, and a dispersant. For example, the content of the color batch base resin is 50 parts by weight, the content of the carbon black is 20 parts by weight, and the content of the dispersant is 30 parts by weight. The content of the color batch in the outer layer watertight material 240 is 0.5 parts by weight or more and 5 parts by weight or less, when the base resin of the outer layer watertight material 240 is 100 parts by weight. By containing a predetermined amount of color batch in the outer layer watertight material 240, the outer layer watertight material 240 can be colored to make the peeling property easier to visually recognize, and deterioration of the outer layer watertight material 240 over time can be suppressed.

The outer layer watertight material 240 is configured to be crosslinked by, for example, a silane grafting/water crosslinking method. The resin composition constituting the outer layer watertight material 240 contains, for example, a silane coupling agent, a crosslinking agent (free radical generator), a catalyst (silanol condensation catalyst), and an anti-aging agent. An alkoxysilane compound is used as the silane coupling agent. Specifically, the silane coupling agent is, for example, vinyltrimethoxysilane. The content of the silane coupling agent in the outer layer watertight material 240 is 0.5 parts by weight or more and 5 parts by weight or less when the base resin is 100 parts by weight. An organic peroxide is used as the crosslinking agent. Specifically, the crosslinking agent is, for example, dicumyl peroxide (DCP). The content of the crosslinking agent in the outer layer watertight material 240 is 0.05 parts by weight or more and 0.5 parts by weight or less when the base resin is 100 parts by weight. The catalyst may be a carboxylate of a metal such as tin, zinc, iron, lead, or cobalt, an organic base, an inorganic acid, or an organic acid. Specifically, the catalyst may be, for example, dibutyltin dilaurate. The content of the catalyst in the outer layer watertight material 240 is 0.01 parts by weight or more and 0.1 parts by weight or less when the base resin is 100 parts by weight. The antioxidant may be, for example, a phenol-based antioxidant. Specifically, the antioxidant may be, for example, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]. The content of the antioxidant in the outer layer watertight material 240 is 0.01 parts by weight or more and 0.3 parts by weight or less when the base resin is 100 parts by weight.

(Inner layer watertight material)
Next, the inner layer watertight material 220 will be described.

The resin composition for the inner layer watertight material constituting the inner layer watertight material 220 of this embodiment is not particularly limited, but for example, like the resin composition for the outer layer watertight material, contains an ethylene-(meth)acrylate copolymer as a base resin.

The inner layer watertight material 220 is filled between the multiple conductor wires 110 and is not in contact with the insulating layer 300. For this reason, the inner layer watertight material 220 does not require peeling properties like the outer layer watertight material 240. Therefore, the inner layer watertight material 220 may be made of a material softer than the outer layer watertight material 240 to make it easier to penetrate between the conductor wires 110.

The resin composition for the inner layer watertight material also contains a color batch, similar to the resin composition constituting the outer layer watertight material 240, for example.

The inner layer watertight material 220 may be configured to be cross-linked by the silane graft/water cross-linking method, or may be configured not to be cross-linked by the cross-linking method.

(4) Manufacturing Method of Insulated Wire Next, a manufacturing method of the insulated wire 10 according to the present embodiment will be described with reference to Figures 2A to 2D. Figures 2A to 2D are schematic diagrams showing a manufacturing method of the insulated wire according to the present embodiment.

(Step 1: Conductor wire forming process)
First, a predetermined number of conductor wires 110 made of, for example, hard copper wire are formed by a wire drawing machine (not shown).

(Step 2: Conductor forming process and inner layer water tight material forming process)
2A, one conductor wire 110 that will form the center of the conductor 100 is fed out from a bobbin 511. After the conductor wire 110 is fed out from the bobbin 511, the conductor wire 110 is passed through a first inner-layer watertight material extruder 522 into which a resin composition for the inner-layer watertight material is charged while being conveyed along the axial direction. As a result, an inner-layer watertight material 220 is extruded to cover the outer periphery of the conductor wire 110.

After the inner layer watertight material 220 is formed to cover the outer circumference of the conductor wire 110, the six bobbins 512 are rotated around the conductor wire 110 coated with the inner layer watertight material 220, and the conductor wire 110 is fed out from each of the six bobbins 512. After the conductor wire 110 is fed out from each of the six bobbins 512, these conductor wires 110 are passed through a predetermined die 532 having a circular opening. In this way, the six conductor wires 110 are twisted together so that the inner layer watertight material 220 covers the outer circumference of the conductor wire 110 coated with the conductor wire 110, thereby forming the conductor intermediate body 120. After the conductor intermediate body 120 is formed, the conductor intermediate body 120 is wound up on a drum 542.

Next, as shown in FIG. 2B, the conductor intermediate 120 is sent out from the drum 542, and while conveying the conductor intermediate 120 along the axial direction, it is passed through the second inner-layer watertight material extruder 524 into which the resin composition for the inner-layer watertight material has been charged. This causes the inner-layer watertight material 220 to be extruded so as to cover the outer periphery of the conductor intermediate 120.

After the inner layer watertight material 220 is formed to cover the outer periphery of the conductor intermediate body 120, the conductor wires 110 are fed out from each of the 12 bobbins 513 while rotating the 12 bobbins 513 around the conductor intermediate body 120 coated with the inner layer watertight material 220. After the conductor wires 110 are fed out from each of the 12 bobbins 513, these conductor wires 110 are passed through a predetermined die 534 having a circular opening. In this way, the 12 conductor wires 110 are twisted together to cover the outer periphery of the conductor intermediate body 120 coated with the inner layer watertight material 220, thereby forming the conductor 100. After the conductor 100 is formed, the conductor 100 is wound up on a drum 544.

Immediately after the conductor 100 is formed, the temperature of the conductor 100 rises to a predetermined temperature by passing through the heated second inner layer watertight material extruder 524. However, after the conductor 100 is wound around the drum 544, the drum 544 is stored at room temperature for a predetermined time, whereby the conductor 100 is cooled, and the temperature of the conductor 100 drops to, for example, less than 20°C.

(Step 3: Outer layer water-tight material formation process)
2C, the conductor 100 is fed from the drum 544, and while being conveyed in the axial direction, the conductor 100 is preheated to a predetermined temperature by a heater 552. The term "preheating" here means that the conductor 100 is heated in advance before the outer layer watertight material 240 is extruded.

At this time, the temperature to which the conductor 100 is preheated is, for example, 20°C or higher and 40°C or lower.

In this case, the heater 552 is, for example, a lamp heater that irradiates infrared rays. This makes it possible to easily preheat the conductor 100 to a predetermined temperature while transporting the conductor 100 along the axial direction.

Next, the conductor 100 is conveyed along the axial direction and passed through the outer layer watertight material extruder 526 into which the resin composition for the outer layer watertight material is added. This causes the outer layer watertight material 240 to be extruded so as to cover the outer circumference of the conductor 100.

At this time, as described above, the outer layer watertight material 240 is extruded in a state where the conductor 100 is preheated to a temperature of, for example, 20°C or more and 40°C or less. If the conductor 100 is not preheated and the temperature at which the conductor 100 is preheated is less than 20°C, it becomes difficult to coat the resin composition for the outer layer watertight material according to the outer peripheral shape of the conductor 100 in which the conductor wires 110 are twisted together in a spiral shape when the outer layer watertight material 240 is extruded by the outer layer watertight material extruder 526. The reason for this is that fine gaps are formed between the conductor 100 and the outer layer watertight material 240, which may cause the conductor 100 and the outer layer watertight material 240 to not adhere well to each other. As a result, the watertightness and adhesion of the insulated electric wire 10 may be reduced. In contrast, by setting the temperature for preheating the conductor 100 to 20°C or higher, the covering property of the resin composition for the outer layer watertight material on the outer periphery of the conductor 100 can be improved when extruding the outer layer watertight material 240. The reason for this is that the formation of fine gaps between the conductor 100 and the outer layer watertight material 240 can be suppressed, and the conductor 100 and the outer layer watertight material 240 can be well adhered to each other. As a result, the watertightness and adhesion of the insulated electric wire 10 can be improved. On the other hand, if the temperature for preheating the conductor 100 is more than 40°C, the fluidity of the resin composition for the outer layer watertight material increases when extruding the outer layer watertight material 240, and the resin composition for the outer layer watertight material may be excessively adhered to the outer periphery of the conductor 100. For this reason, the peeling property of the outer layer watertight material 240 may be reduced. In contrast, by setting the temperature for preheating the conductor 100 to 40°C or lower, the resin composition for the outer layer watertight material can be suppressed from excessively adhering to the outer periphery of the conductor 100. As a result, the peelability of the outer layer watertight material 240 can be ensured.

At this time, for example, pellets of the first resin and pellets of the second resin are mixed in advance using a metering mixer (not shown) so that the ratio B/A of the weight B of the second resin to the weight A of the first resin is 1/4 or more and 4 or less. After the first resin and the second resin are mixed, the resin composition for the outer layer watertight material, which is a mixture of a base resin containing the first resin and the second resin and predetermined additives (color batch, silane coupling agent, crosslinking agent, catalyst, anti-aging agent), is poured into the hopper of the outer layer watertight material extruder 526. At this time, the silane coupling agent and the like to be added are poured into the lower part of the hopper by injection.

At this time, for example, the outer layer watertight material 240 is extruded in the outer layer watertight material extruder 526 by the so-called one-shot method (also called the monosil method) while grafting the silane coupling agent to the base resin. This simplifies the manufacturing process.

In addition, at this time, the extrusion temperature of the outer layer watertight material 240 in the outer layer watertight material extruder 526 is, for example, 180 ° C or more and 240 ° C or less. If the extrusion temperature of the outer layer watertight material 240 is less than 180 ° C, the coverage of the resin composition for the outer layer watertight material on the outer circumference of the conductor 100 may decrease. In addition, the graft rate of the silane coupling agent to the base resin may be reduced. In contrast, by setting the extrusion temperature of the outer layer watertight material 240 to 180 ° C or more, the coverage of the resin composition for the outer layer watertight material on the outer circumference of the conductor 100 can be improved. In addition, the graft rate of the silane coupling agent to the base resin can be set to a predetermined value or more. On the other hand, if the extrusion temperature of the outer layer watertight material 240 is more than 240 ° C, the fluidity of the resin composition for the outer layer watertight material increases, and the resin composition for the outer layer watertight material may adhere excessively to the outer circumference of the conductor 100. In response to this, by setting the extrusion temperature of the outer layer watertight material 240 to 240°C or less, it is possible to prevent the resin composition for the outer layer watertight material from excessively adhering to the outer circumference of the conductor 100.

(Step 4: Insulating layer formation process)
2C, the conductor 100 coated with the outer-layer watertight material 240 is conveyed in the axial direction and passed through an insulating layer extruder 528 into which an insulating layer resin composition having a base resin containing polyolefin and a predetermined additive is charged. In this way, the insulating layer 300 is extruded to cover the outer periphery of the outer-layer watertight material 240, and the insulated wire intermediate body 12 in which the outer-layer watertight material 240 and the insulating layer 300 are in an uncrosslinked state is formed. After the insulated wire intermediate body 12 is formed, the insulated wire intermediate body 12 is wound around a drum 546.

At this time, for example, the insulating layer 300 is extruded in the insulating layer extruder 528 by the so-called one-shot method while grafting the silane coupling agent to the base resin of the insulating layer resin composition. This simplifies the manufacturing process.

(Step 5: Cross-linking process)
2D, the drum 546 around which the insulated wire intermediate body 12 is wound is immersed for a predetermined time in a hot water bath 560 containing hot water. This causes water cross-linking of at least the insulating layer 300 (in this embodiment, both the outer layer water-tight material 240 and the insulating layer 300).

At this time, the outer layer watertight material 240 and the insulating layer 300 are water-crosslinked at a crosslinking temperature of, for example, 75°C or higher and 82°C or lower. If the crosslinking temperature is lower than 75°C, the outer layer watertight material 240 and the insulating layer 300 may not be sufficiently water-crosslinked. In contrast, by setting the crosslinking temperature to 75°C or higher, the outer layer watertight material 240 and the insulating layer 300 can be sufficiently water-crosslinked. In addition, by combining the preheating in step 3, the resin composition for the outer layer watertight material that is moderately adhered to the outer circumference of the conductor 100 can be melted to an optimal temperature, and the peelability of the outer layer watertight material 240 can be ensured while also satisfying the watertightness characteristics.

On the other hand, if the crosslinking temperature exceeds 82°C, the outer layer watertight material 240 may melt excessively again during the crosslinking process of step 5, and the outer layer watertight material 240 may flow into and become stuck in the grooves formed between adjacent conductor wires 110. In contrast, by setting the crosslinking temperature to 82°C or lower, it is possible to prevent the outer layer watertight material 240 from melting excessively again during the crosslinking process of step 5, and to prevent the outer layer watertight material 240 from flowing into and becoming stuck in the grooves.

When the inner layer watertight material 220 is configured to be crosslinked by the silane grafting/water crosslinking method, a silane coupling agent is grafted to the base resin of the inner layer watertight material 220 in advance in the conductor forming process and the inner layer watertight material forming process of step 2, and then in the crosslinking process of step 5, the inner layer watertight material 220 is water-crosslinked together with the outer layer watertight material 240 and the insulating layer 300.

This is how the insulated electric wire 10 of this embodiment is manufactured.

(5) Effects of the Present Embodiment According to the present embodiment, one or more of the following effects can be obtained.

(a) In the outer layer watertight material forming process of step 3 of this embodiment, the conductor 100 is preheated to a temperature of 20°C or more and 40°C or less, and the outer layer watertight material 240 is extrusion molded. By setting the temperature for preheating the conductor 100 to 20°C or more, the coating property of the resin composition for the outer layer watertight material on the outer periphery of the conductor 100 can be improved when extruding the outer layer watertight material 240. This makes it possible to suppress the formation of fine gaps between the conductor 100 and the outer layer watertight material 240, and to ensure good adhesion between the conductor 100 and the outer layer watertight material 240. As a result, the watertightness and adhesion of the insulated electric wire 10 can be improved. In addition, by setting the temperature for preheating the conductor 100 to 40°C or less, it is possible to suppress excessive adhesion of the resin composition for the outer layer watertight material to the outer periphery of the conductor 100. As a result, the peelability of the outer layer watertight material 240 can be ensured. Specifically, when the insulating layer 300 is peeled off, the remaining portion of the outer layer waterproof material 240 that remains across the conductor wire 110 can be reduced. In this way, according to this embodiment, it is possible to improve the watertightness, adhesion, and peelability of the insulated wire 10 in a well-balanced manner.

(b) In the crosslinking process of step 5 of this embodiment, the outer layer watertight material 240 and the insulating layer 300 are water-crosslinked at a crosslinking temperature of 75°C or higher and 82°C or lower. By setting the crosslinking temperature to 75°C or higher, the outer layer watertight material 240 and the insulating layer 300 can be sufficiently water-crosslinked. In addition, by setting the crosslinking temperature to 82°C or lower, excessive melting of the outer layer watertight material 240 again during the crosslinking process of step 5 can be suppressed, and the outer layer watertight material 240 can be suppressed from flowing excessively into the groove formed between adjacent conductor wires 110 and becoming stuck there. As a result, the peelability of the outer layer watertight material 240 can be improved. Specifically, when the insulating layer 300 is peeled off, the remaining portion of the outer layer watertight material 240 remaining in the groove between adjacent conductor wires 110 can be reduced. In this way, in this embodiment, it is possible to improve the watertightness and adhesion while meeting recent strict requirements for peelability.

(c) In the insulated wire 10 of this embodiment, when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated wire 10 cut to a predetermined length for 24 hours, the penetration distance of water from one end of the insulated wire 10 is 1000 mm or less. This makes it possible to suppress corrosion of the conductor 100. As a result, the insulated wire 10 can be stably maintained as a product.

(d) In the insulated electric wire 10 of this embodiment, when the insulated electric wire 10 is held by a specified electric wire gripper and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length by which the insulating layer 300 shifts is 50 mm or less. This makes it possible to suppress slippage of the insulating layer 300 when the insulated electric wire 10 is held by the electric wire gripper, and to suppress the insulated electric wire 10 from coming off the electric wire gripper. As a result, it is possible to suppress the insulated electric wire 10 from falling off.

(e) In the insulated wire 10 of this embodiment, when the outer layer watertight material 240 and the insulating layer 300 are stripped 15 cm in the axial direction of the insulated wire 10 around the entire outer circumference of the conductor 100, the remaining portion of the outer layer watertight material 240 remaining across the conductor wires 110 is 5 or less. In other words, by reducing the remaining portion of the outer layer watertight material 240 interposed between the conductor wires 110 and the compression sleeve, each conductor wire 110 and the compression sleeve can be well connected. As a result, the contact resistance between the conductor 100 and the compression sleeve can be prevented from increasing.

(f) In the insulated wire 10 of this embodiment, when the outer layer watertight material 240 and the insulating layer 300 are stripped off over 15 cm in the axial direction of the insulated wire 10 around the entire outer circumference of the conductor 100, the ratio of the number of grooves in which the outer layer watertight material 240 remains to the total number of grooves formed between adjacent conductor wires 110 is 7/12 or less. As a result, when the compression sleeve is compressed and connected, the compression sleeve can be uniformly abutted against the outer circumference of the conductor 100 and the compression sleeve can be sufficiently compressed. As a result, the gripping ability of the compression sleeve can be improved.

<Other embodiments of the present disclosure>
Although the embodiments and modified examples of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments and modified examples, and various modifications are possible without departing from the gist of the present disclosure.

In the above embodiment, the number of conductor wires 110 is described as 19, but the number of conductor wires 110 is not limited to this number and may be, for example, 7.

In the above embodiment, the base resin of the outer layer watertight material 240 is described as being EMMA only, but the base resin of the outer layer watertight material 240 may be a material other than EMMA, or may be a mixture of EMMA and another material.

In the above embodiment, the base resin of the outer layer watertight material 240 is described as being composed of a mixture of a first resin and a second resin, but the base resin of the outer layer watertight material 240 may be composed of one resin or three or more types of resin.

In the above embodiment, the outer layer watertight material 240 is configured to be cross-linked by the silane grafting/water cross-linking method, but the outer layer watertight material 240 may be configured not to be cross-linked.

In the above embodiment, the resin composition for the outer layer watertight material contains vinyltrimethoxysilane as a silane coupling agent, but the resin composition for the outer layer watertight material may contain other materials as silane coupling agents.

In the above embodiment, the resin composition for the outer layer watertight material contains dicumyl peroxide as a crosslinking agent, but the resin composition for the outer layer watertight material may contain other materials as crosslinking agents.

In the above embodiment, the resin composition for the outer layer watertight material contains dibutyltin dilaurate as a catalyst, but the resin composition for the outer layer watertight material may contain other materials as catalysts.

In the above embodiment, the resin composition for the outer layer watertight material contains thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as an anti-aging agent, but the resin composition for the outer layer watertight material may contain other materials as anti-aging agents.

In the above embodiment, the case where the conductor forming process and the inner layer water-tight material forming process are performed simultaneously in step 2 has been described, but the inner layer water-tight material may be pressed in from the outside of the conductor after the conductor forming process has been performed.

In the above embodiment, the case where the conductor intermediate body 120 is formed in step 2 and then wound around the drum 542 has been described, but the conductor intermediate body 120 may be passed through the second inner layer watertight material extruder 524 while being conveyed along the axial direction without being wound around the drum 542. In other words, the process may be continued without winding around the drum until the conductor 100 is formed.

In the above embodiment, a lamp heater is used as the heater 552 in the outer layer watertight material forming process in step 3 to preheat the conductor 100, but the heater 552 may be something other than a lamp heater. For example, a thermostatic bath that heats the entire drum 544 to a predetermined temperature may be used as the heater 552, and then processing may be immediately performed in the process following the outer layer watertight material extruder 526 in step 3.

In the above embodiment, in the outer layer watertight material forming process in step 3, the pellets of the first resin and the pellets of the second resin are mixed using a measuring mixer. However, resin pellets in which the first resin and the second resin are mixed in a predetermined ratio may be prepared in advance.

In the above embodiment, the outer watertight material 240 and the insulating layer 300 are extrusion molded by the one-shot method in steps 3 and 4, but this is not limited to the above case. For example, the outer watertight material 240 and the insulating layer 300 may be extrusion molded by the two-shot method by feeding a base resin to which a silane coupling agent has been grafted, a master batch containing a silanol condensation catalyst, and other additives into an extruder.

Next, we will explain examples of this disclosure along with comparative examples.

(1) Production of Insulated Wire Insulated wires according to Samples 1 to 6 were produced as follows.

[Configuration of insulated wire]
In Samples 1 to 6, the insulated wire had the following common configuration.
(conductor)
Conductor wire: hard copper wire Outer diameter of conductor wire: 2.00 mm
Number of conductor wires: 19 Conductor cross-sectional area: 80 mm ²
(Inner layer watertight material)
Base resin: Second resin Additives are the same as the outer layer water-tight material below (Outer layer water-tight material)
Base resin: Mixture of first resin and second resin (total 100 parts by weight)
First resin: Acryft (registered trademark) WH206 manufactured by Sumitomo Chemical Co., Ltd.
Second resin: Acryft (registered trademark) WK307 manufactured by Sumitomo Chemical Co., Ltd.
Ratio of weight B of the second resin to weight A of the first resin: B/A: 1/4 to 4
Color batch: PE-M 10H397 (1.2 parts by weight) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.
Silane coupling agent: KBM-1003 (1.25 parts by weight) manufactured by Shin-Etsu Chemical Co., Ltd.
Crosslinking agent: DCP (0.094 parts by weight) manufactured by NOF Corporation
Catalyst: Neostan (registered trademark) U-100 (0.05 parts by weight) manufactured by Nitto Kasei Co., Ltd.
Antioxidant: Irganox (registered trademark) 1035 (manufactured by BASF) (0.15 parts by weight)
Outer watertight material thickness: 0.2 mm
(Insulating layer)
Material: Cross-linked polyethylene Insulation layer thickness: 2.5 mm

[Insulated wire manufacturing conditions]
(Inner layer water tight material formation process)
Extrusion temperature: 180 to 240°C
(Outer layer watertight material formation process)
Conductor preheating temperature: no heating (about 18°C), 25-50°C
Extrusion temperature: 180 to 240°C
(Insulating layer forming process)
Extrusion temperature: 180 to 240°C
(Crosslinking process)
Method: Hot water bath immersion Crosslinking temperature: 73-85℃

The manufacturing conditions for the insulated wires in samples 1 to 6 and their evaluation results are shown in Table 1 below.

(2) Evaluation (watertightness characteristic test (rainwater infiltration test))
The insulated wires of Samples 1 to 6 were cut to a predetermined length (for example, 2.0 m). A water pressure of 0.5 atm was applied to one axial end of the cut insulated wire for 24 hours, and the permeation distance of water from the one end was measured.

(Adhesion test (wire gripping tool tensile test))
The insulated wires of Samples 1 to 6 were held by a wire holder (Camlar, manufactured by Nagaki Seiki Co., Ltd.) and subjected to a tensile test under the following conditions: temperature 40° C., tensile load 4.17 kN, and application time 10 minutes. As a result of the test, cases in which the insulation layer was displaced for a length of 0 mm or more and 50 mm or less were rated as “A”, and cases in which the insulation layer was displaced for a length of more than 50 mm were rated as “B”.

(Skinning test)
A peeling test was conducted on the insulated wires of Samples 1 to 6, in which the outer watertight material and the insulating layer were peeled off with a knife at a temperature of 40° C. However, the speed at which the outer watertight material and the insulating layer were peeled off by 15 cm was set to 60 seconds or less. When the outer watertight material and the insulating layer were peeled off at a speed exceeding 60 seconds, the remaining outer watertight material tends to decrease, but considering the work efficiency at the site where the wire is used, it is difficult to apply this method.

As a result of the test, the shape of the remaining outer layer of waterproof material that remained when the insulation layer was stripped away was evaluated in two categories.

(i) Straddling Part When the insulating layer was peeled off, the number of remaining parts of the outer layer watertight material that remained straddling the conductor wires (hereinafter also referred to as "straddling parts") was 0 to 5, and was evaluated as "A", and the number of parts was more than 5, as "B". Note that when the remaining parts of the outer layer watertight material that remained straddling the conductor wires covered a wide area, a square area with one side having a length equal to the diameter of the conductor wires was counted as one straddling part.

(ii) Groove with Remainder When the insulating layer was peeled off, the ratio of the number of grooves in which the outer layer watertight material remained (hereinafter also referred to as "groove with remainder") to the total number of grooves formed between adjacent conductor wires was 7/12 or less, and was evaluated as "A", and the ratio of the number of grooves exceeding 7/12 was evaluated as "B". Note that in Samples 1 to 5, the number of conductor wires in the outermost layer of the conductor was 12, so the total number of grooves was 12.

(3) Results Using the above Table 1 and Figs. 3A to 3D, Figs. 3A to 3D are schematic diagrams showing insulated electric wires of Samples 1 and 3 to 5, respectively, which were subjected to the peelability test.

(Sample 2)
In sample 2, in which the conductor was not preheated in the outer layer water-tight material forming process and the crosslinking temperature was 78 to 82°C in the crosslinking process, good results equivalent to those of sample 1 described below were obtained in the peelability test.

However, in the watertightness test for sample 2, the water penetration distance exceeded 2,000 mm, and the results of the watertightness test were significantly inferior to those of the other samples. In addition, in the adhesion test for sample 2, the length of displacement of the insulating layer exceeded 50 mm, and the results of the adhesion test were inferior to those of the other samples.

In Sample 2, the crosslinking temperature in the crosslinking process was appropriate, but the conductor was not preheated in the outer layer watertight material forming process. For this reason, it is believed that it was difficult to coat the resin composition for the outer layer watertight material in accordance with the outer peripheral shape of the conductor when extruding the outer layer watertight material. As a result, it is believed that the watertightness and adhesion of Sample 2 were reduced.

(Sample 3)
In sample 3, in which the conductor preheating temperature in the outer layer watertight material forming process was set to more than 50°C and the crosslinking temperature in the crosslinking process was set to 78 to 82°C, good results were obtained in the watertight property test and the adhesion test.

However, in the case of Sample 3, the results shown in FIG. 3B were obtained in the peelability test. As shown in FIG. 3B, in Sample 3, many remnants 242 of the outer layer watertight material 240 were found on the surface of the conductor 100 from which the insulating layer 300 of the insulated electric wire 10 was stripped. The number of "straddling portions 244", which are the remnants 242 of the outer layer watertight material 240 remaining across the conductor wires 110, was more than five. In addition, the ratio of the number of "groove portions 112a with remnants", which are the groove portions 112 in which the remnants 242 of the outer layer watertight material 240 remain, to the total number of groove portions 112 formed between adjacent conductor wires 110, was more than 7/12. Thus, the results of the peelability test for Sample 3 were inferior to those of the other samples.

In Sample 3, the crosslinking temperature in the crosslinking process was appropriate, but the conductor preheating temperature in the outer layer watertight material forming process was set to above 50°C. This is thought to have increased the fluidity of the resin composition for the outer layer watertight material when the outer layer watertight material was extrusion molded, causing the resin composition for the outer layer watertight material to adhere excessively to the outer circumference of the conductor. As a result, it is thought that Sample 3 had improved watertightness and adhesion, but reduced peelability.

(Sample 4)
In sample 4, in which the conductor was not preheated in the outer layer watertight material forming process and the crosslinking temperature was 85° C. in the crosslinking process, good results were obtained in the watertight property test and the adhesion test.

In the peelability test for sample 4, the results shown in Figure 3C were obtained. As shown in Figure 3C, there were six straddling sections 244 in the outer layer waterproof material 240. In addition, there were many remaining groove sections 112a, with the proportion exceeding 7/12 (specifically, approximately 10/12). Thus, the results of the peelability test for sample 4 were inferior to those of sample 1, which will be described later.

In Sample 4, the conductor was not preheated in the outer layer watertight material formation process, so it is believed that the coverage of the outer layer watertight material on the outer periphery of the conductor was not necessarily good at the time of this process. However, because the crosslinking temperature in the crosslinking process was set to over 82°C, it is believed that the outer layer watertight material melted again during this process. For this reason, while the adhesion of the outer layer watertight material to the outer periphery of the conductor improved, it is believed that the outer layer watertight material flowed into the grooves between adjacent conductor wires and became fixed. As a result, it is believed that the watertight properties and adhesion were improved in Sample 4, but the peelability was reduced.

(Sample 5)
In sample 5, in which the conductor preheating temperature was set to 25 to 35°C in the outer layer watertight material forming process and 85°C in the crosslinking process, good results were obtained in the watertight property test and the adhesion test.

However, in the peelability test for sample 5, the results shown in Figure 3D were obtained. As shown in Figure 3D, there were 11 straddling sections 244 in the outer layer waterproof material 240. In addition, there were many remaining groove sections 112a, with the proportion exceeding 7/12 (specifically, approximately 12/12). Thus, the results of the peelability test for sample 5 were inferior to those of sample 1, which will be described later.

In sample 5, the conductor was preheated at an appropriate temperature in the outer layer watertight material formation process, so it is believed that the outer layer watertight material had good coverage over the conductor's outer circumference at the time of this process. However, because the crosslinking temperature in the crosslinking process was set to over 82°C, it is believed that the outer layer watertight material melted again during this process. This increased the adhesion of the outer layer watertight material to the conductor's outer circumference, and it is believed that the outer layer watertight material flowed into and fixed in the grooves formed between adjacent conductor wires. As a result, it is believed that in sample 5, the watertight properties and adhesion were improved, but the peelability was reduced.

(Sample 6)
In sample 6, in which the conductor preheating temperature was set to 25 to 35° C. in the outer layer water-tight material forming process and 73° C. in the crosslinking process, good results were obtained in the adhesion test and peelability.

However, in the watertightness test for sample 6, the water penetration distance exceeded 1,000 mm, and the results of the watertightness test were inferior to those of the other samples.

In Sample 6, the conductor preheating was performed at an appropriate temperature in the outer layer watertight material formation process, so it is believed that the outer layer watertight material had good coverage over the outer circumference of the conductor at the time of this process. However, because the crosslinking temperature in the crosslinking process was set to less than 75°C, the outer layer watertight material and the insulating layer were not sufficiently water-crosslinked, and in addition, it is believed that the outer layer watertight material did not optimally remelt sufficiently. As a result, it is believed that the watertight properties of Sample 6 were reduced.

(Sample 1)
In comparison with the above-mentioned samples 2 to 5, sample 1, in which the conductor preheating temperature was set to 25 to 35°C in the outer layer watertight material forming process and 78 to 82°C in the crosslinking process, obtained good results in the watertightness property test and the adhesion test.

Furthermore, in the peelability test, sample 1 obtained the results shown in Figure 3A. As shown in Figure 3A, the outer layer watertight material 240 had no straddling parts 244 at all, with at most five or less. There were also few remaining groove parts 112a, with the proportion being 7/12 or less (at most about 2/12). Furthermore, the length of the remaining part 242 in the remaining groove part 112a was 10 mm or less. Thus, sample 1 had the best results in the peelability test.

In sample 1, it was confirmed that by setting the conductor preheating temperature to 20°C or higher in the outer layer watertight material forming process, it was possible to improve the covering ability of the resin composition for the outer layer watertight material on the outer circumference of the conductor when extruding the outer layer watertight material. As a result, it was confirmed that it was possible to improve the watertightness and adhesion of the insulated electric wire.

In addition, in sample 1, it was confirmed that excessive adhesion of the resin composition for the outer layer watertight material to the outer circumference of the conductor could be suppressed by setting the conductor preheating temperature to 40°C or less in the outer layer watertight material forming process. As a result, it was confirmed that the peelability of the outer layer watertight material could be ensured. Specifically, it was confirmed that the straddling portion could be reduced in the peelability test.

In addition, in sample 1, by setting the crosslinking temperature in the crosslinking process to 75°C or higher and 82°C or lower, it was possible to sufficiently water-crosslink the outer layer watertight material and the insulating layer. It was also confirmed that during the crosslinking process, excessive remelting of the outer layer watertight material was suppressed, and that it was possible to suppress the outer layer watertight material from flowing into and adhering to the grooves between adjacent conductor wires. As a result, it was confirmed that it was possible to improve the watertight properties of the insulated electric wire while improving the peelability of the outer layer watertight material. Specifically, it was confirmed that it was possible to reduce the number of remaining grooves in the peelability test.

In this way, it was confirmed that Sample 1 can improve watertightness and adhesion while meeting the strict requirements for peelability in recent years.

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

(Appendix 1)
A resin composition for an outer layer water-tight material forming an outer layer water-tight material for an insulated electric wire,
when a water pressure of 0.5 atmospheres is applied for 24 hours to one axial end of the insulated electric wire cut to a predetermined length, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire gripping tool and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
A resin composition for an outer layer watertight material, wherein when the outer layer watertight material and the insulating layer are stripped off 15 cm in the axial direction of the insulated electric wire around the entire outer circumference of the conductor, the remaining portion of the outer layer watertight material remaining across the conductor wires is 5 or less pieces.

(Appendix 2)
a conductor formed by twisting together a plurality of conductor wires;
An outer watertight material provided to cover the outer periphery of the conductor;
An insulating layer provided to cover the outer periphery of the outer layer watertight material;
An insulated wire having
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire holder and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
An insulated electric wire in which, when the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated electric wire around the entire outer circumference of the conductor, the remaining portion of the outer layer watertight material remaining across the conductor wires is 5 or less.

(Appendix 3)
3. The insulated wire according to claim 2, wherein when the outer layer watertight material and the insulating layer are stripped off over 15 cm in the axial direction of the insulated wire around the entire outer circumference of the conductor, a ratio of the number of grooves in which the outer layer watertight material remains to the total number of grooves formed between adjacent conductor wires is 7/12 or less.

(Appendix 4)
The insulated wire according to claim 2 or 3, wherein the outer layer waterproof material is composed of a resin composition containing an ethylene-(meth)acrylate copolymer.

(Appendix 5)
The resin composition comprises
a first resin including an ethylene methyl methacrylate copolymer having a methyl methacrylate content of 18% by weight or more and less than 22% by weight;
and a second resin including an ethylene methyl methacrylate copolymer having a methyl methacrylate content of 22% by weight or more and less than 28% by weight,
5. The insulated wire according to claim 2, wherein a ratio B/A of a weight B of the second resin to a weight A of the first resin in the base resin is ¼ to 4.

(Appendix 6)
A step of stranding a plurality of conductor wires to form a conductor;
forming an outer layer watertight material so as to cover an outer periphery of the conductor;
forming an insulating layer so as to cover the outer periphery of the outer layer watertight material;
cross-linking at least the insulating layer;
having
In the step of forming the outer layer water-tight material,
The conductor is preheated to a temperature of 20°C to 40°C, and the outer layer watertight material is extruded.
In the step of cross-linking the insulating layer,
The method for producing an insulated wire includes water-crosslinking the insulating layer at a crosslinking temperature of 75° C. or higher and 82° C. or lower.

10 Insulated wire 12 Insulated wire intermediate body 100 Conductor 110 Conductor wire 112 Groove portion 112a Remaining groove portion 120 Conductor intermediate body 220 Inner layer watertight material 240 Outer layer watertight material 242 Remaining portion 244 Straddling portion 300 Insulating layer 511 Bobbin 512 Bobbin 513 Bobbin 522 First inner layer watertight material extruder 524 Second inner layer watertight material extruder 526 Outer layer watertight material extruder 528 Insulating layer extruder 532, 534 Die 542, 544, 546 Drum 552 Heater 560 Hot water tank

Claims (5)

a conductor formed by twisting together a plurality of conductor wires;
An outer watertight material provided to cover the outer periphery of the conductor;
An insulating layer provided to cover the outer periphery of the outer layer watertight material;
An insulated wire having
The conductor is made of a hard copper wire, a hard copper stranded wire, a hard aluminum stranded wire, or a steel-core aluminum stranded wire;
The outer layer watertight material is
A first resin including an ethylene-methyl methacrylate copolymer having a methyl methacrylate content of 18% by weight or more and less than 22% by weight;
a second resin including an ethylene-methyl methacrylate copolymer having a methyl methacrylate content of 22% by weight or more and less than 28% by weight;
The base resin is a mixture of
a ratio B/A of a weight B of the second resin to a weight A of the first resin in the base resin is 1/4 or more and 4 or less;
The melting temperature of the base resin is greater than 80° C. and less than 86° C.
the insulating layer comprises polyethylene;
The outer layer watertight material is extruded in a state where the conductor is preheated to a temperature of 20°C or more and 40°C or less,
The outer water-tight material and the insulating layer are crosslinked by a silane graft water crosslinking method at a crosslinking temperature of 75° C. or more and 82° C. or less ;
when a water pressure of 0.5 atmospheres is applied to one axial end of the insulated electric wire cut to a predetermined length for 24 hours, a water permeation distance from the one end of the insulated electric wire is 1000 mm or less;
when the insulated wire is held by a wire holder and a tensile test is performed under conditions of a tensile load of 4.17 kN and an application time of 10 minutes, the length of displacement of the insulating layer is 50 mm or less;
An insulated electric wire in which, when the outer watertight material and the insulating layer are stripped off 15 cm in the axial direction of the insulated electric wire around the entire outer circumference of the conductor at a temperature of 40°C and at a speed of 60 seconds or less using a knife, the number of remnants of the outer watertight material remaining across the conductor wires is 5 or less. 2. The insulated wire according to claim 1, wherein when the outer layer water-tight material and the insulating layer are stripped off over 15 cm in an axial direction of the insulated wire around the entire outer circumference of the conductor, a ratio of the number of grooves in which the outer layer water-tight material remains to the total number of grooves formed between adjacent conductor wires is 7/12 or less. The melt flow rate of the first resin is 1 g/10 min or more and less than 3 g/10 min when the measurement temperature is 190° C. and the load is 2.12 N,
3. The insulated wire according to claim 1, wherein the second resin has a melt flow rate of 6 g/10 min or more and less than 8 g/10 min when measured at a temperature of 190° C. and under a load of 2.12 N. The melting temperature of the first resin is 77° C. or higher and lower than 95° C.
The insulated wire according to claim 1 , wherein the second resin has a melting temperature of 72° C. or higher and lower than 88° C. A step of stranding a plurality of conductor wires to form a conductor;
forming an outer layer watertight material so as to cover an outer periphery of the conductor;
forming an insulating layer so as to cover the outer periphery of the outer layer watertight material;
A step of cross-linking the outer layer water-tight material and the insulating layer by a silane grafting/water cross-linking method;
having
In the step of forming a conductor,
The conductor is formed of a hard copper wire, a hard copper stranded wire, a hard aluminum stranded wire, or a steel-core aluminum stranded wire;
In the step of forming the outer layer water-tight material,
A first resin including an ethylene-methyl methacrylate copolymer having a methyl methacrylate content of 18% by weight or more and less than 22% by weight;
a second resin including an ethylene-methyl methacrylate copolymer having a methyl methacrylate content of 22% by weight or more and less than 28% by weight;
The outer layer watertight material is formed so as to include a base resin obtained by mixing
a ratio B/A of a weight B of the second resin to a weight A of the first resin in the base resin is set to 1/4 or more and 4 or less;
The melting temperature of the base resin is more than 80° C. and less than 86° C.
The conductor is preheated to a temperature of 20°C to 40°C, and the outer layer watertight material is extruded.
In the step of forming the insulating layer,
forming the insulating layer to include polyethylene;
In the step of cross-linking the outer water-tight material and the insulating layer,
The method for producing an insulated wire includes water-crosslinking the outer-layer water-tight material and the insulating layer at a crosslinking temperature of 75° C. or higher and 82° C. or lower.

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