JP6717073B2 - Insulated wire - Google Patents

Description

The present invention relates to an insulated wire.

Insulated electric wires used as wiring for railway vehicles and automobiles are required to have not only insulating properties but also flame retardancy that makes them difficult to burn in a fire. Therefore, a flame retardant is blended in the coating layer of the insulated wire. For example, Patent Document 1 discloses an insulated wire in which a flame-retardant layer containing a flame-retardant is laminated on the outer periphery of an insulating layer to form a coating layer. According to Patent Document 1, by forming a flame-retardant layer on the outer periphery of an insulating layer to form an insulated wire, it is possible to obtain a high level of insulation and flame retardancy in a well-balanced manner.

JP, 2013-214487, A

By the way, in recent years, the insulated wire is required to have a small outer diameter from the viewpoint of weight reduction. Therefore, it has been considered to reduce the thickness of the insulating layer located inside and the flame retardant layer located outside.

However, if the thickness of the flame retardant layer is reduced, it becomes difficult to maintain high flame retardancy. On the other hand, when the thickness of the insulating layer is reduced, the reliability of the insulation is reduced and it becomes difficult to maintain high DC stability. That is, in the insulated wire, it is difficult to achieve both flame retardancy and DC stability at a high level while reducing the outer diameter.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for reducing the outer diameter of an insulated wire while maintaining high flame retardancy and DC stability.

According to one aspect of the invention,
A conductor,
A coating layer disposed on the outer periphery of the conductor,
The coating layer is formed by alternately stacking a plurality of flame-retardant insulating layers formed of a resin composition containing a flame retardant and a plurality of water-impervious layers having a saturated water absorption of 0.5% or less in order from the conductor side. To be formed,
The thickness of the impermeable layer located on the surface of the coating layer is 25 μm or more,
Provided is an insulated wire in which the total thickness of the plurality of flame-retardant insulating layers is 250 μm or more.

According to the present invention, it is possible to reduce the outer diameter of an insulated wire while maintaining high flame retardancy and DC stability.

It is a figure which shows the cross section perpendicular|vertical to the length direction of the insulated wire concerning one Embodiment of this invention. It is a figure for demonstrating the difference in the penetration of the water to a coating layer by the difference in the number of water-blocking layers, (a) shows the case where there are two water-blocking layers, (b) shows the water-blocking layer 1 The case of layers is shown. It is a figure which shows the cross section perpendicular|vertical to the length direction of the conventional insulated wire.

First, a conventional insulated wire will be described with reference to FIG. FIG. 3 is a sectional view perpendicular to the length direction of a conventional insulated wire.

As shown in FIG. 3, a conventional insulated electric wire 100 includes a conductor 110, an insulating layer 120 arranged on the outer circumference of the conductor 110, and a flame retardant layer 130 arranged on the outer circumference of the insulating layer 120 and containing a flame retardant. , And are configured. That is, in the conventional insulated electric wire 100, the insulating layer 120 and the flame-retardant layer 130 are provided as a coating layer that covers the conductor 110.

In the conventional insulated wire 100, the flame-retardant layer 130, which is formed of resin like the insulating layer 120, exhibits a predetermined insulating property, but tends to have low insulation reliability and low DC stability. The DC stability is one of the electrical characteristics evaluated by a DC stability test in accordance with EN50305.6.7, as described later, and the insulated wire 100 was immersed in water to apply a predetermined voltage. It sometimes indicates that the insulation does not break down even after a lapse of a predetermined time, and is an index for the reliability of insulation.

According to the study by the present inventors, it was found that the DC stability of the flame retardant layer 130 is low because the water absorption rate is increased due to the blending of the flame retardant. As the cause, it is considered that the hydroxyl group of the flame retardant improves the water absorption, but for example, in the flame retardant layer 130, it is caused by the low adhesion between the resin forming the flame retardant layer 130 and the flame retardant. Therefore, it is considered that a minute gap is formed around the flame retardant, and the formation of the gap facilitates the permeation of water into the flame retardant layer 130 and the easier absorption of water. In such a flame-retardant layer 130, when the insulated wire 100 is immersed in water to evaluate the DC stability, a conductive path is formed due to water permeation and insulation breakdown is likely to occur, resulting in low insulation reliability. There is a tendency. In this way, the flame retardant layer 130 is likely to have reduced insulation due to water absorption, resulting in reduced DC stability.

On the other hand, since the insulating layer 120 is covered with the flame-retardant layer 130, the flame-retardant agent is not blended, or even if it is blended, the amount is small. Therefore, although the insulating layer 120 does not exhibit flame retardancy unlike the flame retardant layer 130, the insulating layer 120 is configured to have a low water absorption rate and contributes to DC stability.

As described above, in the conventional insulated electric wire 100, the insulating layer 120 contributes to the DC stability and the flame-retardant layer 130 contributes to the flame retardancy. Therefore, in order to achieve both high DC stability and high flame retardance, it is necessary to increase the thickness of each of the insulating layer 120 and the flame retardant layer 130, and to reduce the diameter of the insulated wire 100, reduce the thickness of each. It has become difficult.

In the conventional insulated wire 100, the present inventors provide a flame-retardant layer 130 that easily absorbs water on the surface, so that the DC stability (reliability of insulation) is lowered, so that water does not penetrate into the flame-retardant layer 130. With such a configuration, the flame-retardant layer 130 can contribute not only to flame retardancy but also to DC stability, and finally the thickness of the insulating layer 120 can be reduced to reduce the outer diameter of the insulated wire 100. I thought it could be thinner.

Therefore, a method for suppressing the permeation of water into the flame retardant layer 130 was examined. As a result, it has been found that it is preferable to provide a water shield layer having a low water absorption rate on the outer periphery of the flame retardant layer. Since the water-blocking layer can suppress the permeation of water into the flame-retardant layer, the flame-retardant layer can function as a flame-retardant insulating layer having not only flame retardancy but also DC stability. As a result, the insulating layer 120 that has been conventionally formed can be omitted. That is, the conventional laminated structure including the insulating layer 120 and the flame retardant layer 130 can be configured by the flame retardant insulating layer and the water impervious layer. The water-blocking layer has a thickness that prevents water from penetrating and does not need to be formed as thick as the conventional insulating layer 120. Therefore, the outer diameter of the insulated wire can be reduced.

Also, when only one water barrier layer is provided outside the flame retardant insulation layer, when the water barrier layer breaks and pinholes occur, water permeates into the flame retardant insulation layer and stabilizes the direct current by the flame retardant insulation layer. Since it may not be possible to obtain stable properties, it was found that it is better to provide a plurality of impermeable layers. The use of a plurality of water-impervious layers makes it possible to suppress water permeation in multiple layers, so that it is possible to suppress a decrease in DC stability due to the occurrence of pinholes.

The present invention has been made based on the above findings.

<Structure of insulated wire>
Hereinafter, an insulated wire according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view perpendicular to the length direction of an insulated wire according to an embodiment of the present invention. In addition, in this specification, the numerical range represented using "-" means the range which includes the numerical value described before and after "-" as a lower limit and an upper limit.

As shown in FIG. 1, the insulated wire 1 according to the present embodiment includes a conductor 10 and a coating layer 20.

〔conductor〕
As the conductor 10, a commonly used metal wire, for example, a copper wire, a copper alloy wire, an aluminum wire, a gold wire, a silver wire, or the like can be used. Alternatively, a metal wire having an outer periphery plated with a metal such as tin or nickel may be used. Further, a collective twisted conductor in which metal wires are twisted together can be used. The outer diameter of the conductor 10 can be appropriately changed according to the electric characteristics required for the insulated wire 1, and is, for example, 1.0 mm to 20.0 mm.

[Coating layer]
A coating layer 20 is provided on the outer periphery of the conductor 10. In the present embodiment, the coating layer 20 has a laminated structure in which two flame-retardant insulating layers 21 and two impermeable layers 22 are alternately laminated so that the impermeable layers 22 are located on the surface. ..

(Flame-retardant insulation layer)
The flame-retardant insulating layer 21 is formed of a resin composition containing a flame retardant and contributes to the flame retardancy of the coating layer 20. In addition, the flame-retardant insulating layer 21 is covered with the water-impervious layer 22 described later, so that when the insulated wire 1 is immersed in water to evaluate the DC stability, the permeation of water is suppressed, and the coating layer 20 has This will contribute to DC stability.

The resin composition forming the flame-retardant insulating layer 21 contains a resin and a flame retardant.

The type of the resin forming the flame-retardant insulating layer 21 may be appropriately changed according to the characteristics required for the insulated wire 1, such as elongation and strength. For example, a polyolefin resin or a polyamide-imide resin (PAI resin) can be used. As the polyolefin resin, a polyethylene resin, a polypropylene resin or the like can be used, and a polyethylene resin is particularly preferable. Examples of the polyethylene resin include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), high density polyethylene (HDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer. , Ethylene-methyl acrylate copolymer, ethylene-glycidyl methacrylate copolymer and the like can be used. These polyolefin resins may be used alone or in combination of two or more.

From the viewpoint of obtaining higher DC stability in the flame-retardant insulating layer 21, high-density polyethylene (HDPE) is preferable, and for example, HDPE having a density of 0.95 g/cm ³ or more and 0.98 g/cm ³ or less is used. be able to. From the viewpoint of obtaining higher flame retardancy, EVA is particularly preferable, and for example, EVA having a high vinyl acetate content can be used.

As the flame retardant, a non-halogen flame retardant is preferable because it does not generate a toxic gas, and for example, a metal hydroxide can be used. The metal hydroxide is decomposed and dehydrated when the flame-retardant insulating layer 21 is heated and burned, and the moisture released lowers the temperature of the flame-retardant insulating layer 21 to suppress the combustion. .. As the metal hydroxide, for example, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and metal hydroxide in which nickel is solid-solved therein can be used. These flame retardants may be used alone or in combination of two or more.

The flame retardant is a silane coupling agent, a titanate coupling agent, a fatty acid such as stearic acid, a fatty acid such as stearate, from the viewpoint of controlling the mechanical properties (balance between tensile strength and elongation) of the flame retardant insulating layer 21. The surface treatment is preferably performed with a salt, a fatty acid metal such as calcium stearate, or the like.

From the viewpoint of flame retardancy, the blending amount of the flame retardant is preferably 50 parts by mass to 300 parts by mass with respect to 100 parts by mass of the resin. If the blending amount is less than 50 parts by mass, the desired high flame retardancy may not be obtained in the insulated wire 1. If the blending amount exceeds 300 parts by mass, the mechanical properties of the flame-retardant insulating layer 21 may deteriorate, and the elongation rate may decrease.

The resin composition forming the flame-retardant insulating layer 21 may contain other additives, if necessary. For example, when the flame-retardant insulating layer 21 is cross-linked, a cross-linking agent or a cross-linking aid may be contained. Further, for example, in addition to the cross-linking agent, a flame retardant auxiliary agent, an antioxidant, a lubricant, a softening agent, a plasticizer, an inorganic filler, a compatibilizer, a stabilizer, carbon black, a colorant and the like may be contained. These can be contained in a range that does not impair the characteristics of the flame-retardant insulating layer 21.

The flame-retardant insulating layer 21 can be formed by, for example, extrusion molding a resin composition containing a flame retardant. When the flame-retardant insulating layer 21 is cross-linked, it may be cross-linked by a conventionally known method.

(Impermeable layer)
The water shield layer 22 has a saturated water absorption rate of 0.5% or less, and is configured to have a small water absorption amount and a small water diffusion coefficient. Since the water-impervious layer 22 has high water impermeability and water hardly permeates, it is possible to suppress permeation of water into the inside of the coating layer 20. The lower limit of the saturated water absorption is not particularly limited and may be 0%. In the present specification, the saturated water absorption rate is a water saturation rate obtained from Fick's law in accordance with JIS K7209:2000.

From the viewpoint of water impermeability, the impermeable layer 22 is preferably formed, for example, in a tubular shape so that it is seamless and has no joints. The material for forming the water shield layer 22 is not particularly limited as long as it has a low saturated water absorption rate and can form the water shield layer 22 without a joint. As such a material, a resin is preferable from the viewpoint of moldability of the water shield layer 22. The resin, from the viewpoint of safety is preferably a polyolefin resin is halogen-free, resin density in terms of impermeability and mechanical properties are 0.85g ^/ cm ³ ~1.20g ^/ cm 3 are preferred. For example, high density polyethylene (HDPE) or low density polyethylene (LDPE) can be used. Further, for example, a fluorine-containing resin (for example, PFA) or the like may be used because it has a low water absorption rate.

Further, when the water-blocking layer 22 is formed of resin, it is preferable to crosslink the resin in order to further improve the water-blocking property. That is, the water-blocking layer 22 is preferably formed of a cross-linked body obtained by cross-linking a resin. By crosslinking, the molecular structure of the resin can be strengthened and the water impermeability of the water impervious layer 22 can be improved. Moreover, since the strength of the water-impervious layer 22 can be improved, even if the thickness of the water-impermeable layer 22 is reduced, the water impermeability can be maintained high without impairing the strength.

It is preferable that the crosslinked body forming the water shield layer 22 is crosslinked so that the gel fraction is 40% to 100%. Since the strength and the water impermeability can be increased as the gel fraction of the crosslinked body is increased, the water shield layer 22 can be made thinner.

When the water shield layer 22 is formed of a resin such as HDPE, a resin composition containing HDPE may be formed by extrusion molding on the outer periphery of the flame retardant insulating layer 21. When cross-linking, a cross-linking agent or a cross-linking aid may be added to the resin composition. The crosslinking can be performed by a known method such as chemical crosslinking or electron beam crosslinking.

(Layered structure)
Next, the laminated structure of the coating layer 20 will be described.
As described above, in the present embodiment, the two flame-retardant insulating layers 21 and the two water-impermeable layers 22 are formed in order to suppress the deterioration of the DC stability due to the generation of pinholes in the water-impermeable layer 22 in the coating layer 20. Are alternately laminated so that the water-impervious layers 22 are located on the surface to form the coating layer 20. Specifically, as shown in FIG. 1, the coating layer 20 includes a first water-blocking layer 22a, a first flame-retardant insulating layer 21a, a second water-blocking layer 22b, and a second water-blocking layer 22b in order from the front surface side. The flame retardant insulating layer 21b is provided, the first water impervious layer 22a is provided so as to cover the first flame retardant insulating layer 21a, and the second water impervious layer 21b is the first flame retardant insulating layer 21a. And the second flame-retardant insulating layer 21b.

In the coating layer 20, not only the first water-impervious layer 22a is provided on the outermost surface, but also the second water-impervious layer 21a is provided so as to be interposed between the first flame-retardant insulating layer 21a and the second flame-retardant insulating layer 21b. By providing the water-impervious layer 22b, it is possible to suppress a decrease in DC stability due to pinholes, as compared with the case where one water-impervious layer 22 is provided on the outermost surface. For example, in the coating layer 20, the direct current stability is reduced by including two water-impermeable layers 22 having a thickness of 50 μm rather than providing only one water-impermeable layer 22 having a thickness of 100 μm on the outermost surface. Can be suppressed.

Specifically, as shown in FIG. 2B, when only one water shield layer 22 is provided on the outermost surface of the coating layer 20, if the water shield layer 22 is broken and a pinhole 50 is generated, the DC stability is improved. At the time of evaluation, the water 60 penetrates into the flame-retardant insulating layer 21 located inside thereof. At this time, the permeation path of the water 60 becomes a conductive path, and if the water 60 permeates to the conductor 10, dielectric breakdown occurs. In FIG. 2B, since the permeation path (dotted line in the figure) is short, if the pinhole 50 were formed in the water-blocking layer 22, the time until dielectric breakdown would be short, and the DC stability would be easily deteriorated. ..

On the other hand, when the two water shield tanks 22 are provided, even if water is permeated into the first flame-retardant insulating layer 21a located inside the pinholes on the outer first water shield layer 22a, the second The water-blocking layer 22b can suppress permeation of water into the second flame-retardant insulating layer 21b located inside thereof. Even if pinholes are formed on both sides, as shown in FIG. 2A, since the regions where the pinholes 50 are formed are different from each other, the permeation path of water 60 (dotted line in the figure) becomes longer, It is possible to extend the time until dielectric breakdown. As described above, by providing a plurality of water-impervious layers 22, it is possible to delay the formation of a conductive path due to water absorption and prolong the time until dielectric breakdown. As a result, it is possible to obtain stable DC stability in the coating layer 20.

In the laminated structure of the coating layer 20, from the viewpoint of water impermeability, among the plurality of impermeable layers 22, the impermeable layer 22 located on the surface, that is, the first impermeable layer 22a has a thickness of 25 μm or more. With such a thickness, the strength of the first water-impervious layer 22a can be increased, so that the first water-impervious layer 22a can be prevented from breaking when the insulated wire 1 is bent, that is, a pinhole can be suppressed. .. Further, since the water impermeability can be increased by increasing the thickness, it is possible to suppress the permeation of water into the inside of the coating layer 20.

The thickness of the water shield layer 22 inside the coating layer 20, that is, the second water shield layer 22b is not particularly limited, and is appropriately changed within a range in which the total thickness of the plurality of water shield layers 22 is 120 μm or less. Good to do. Since the water-impervious layer 22 does not contain a flame retardant, it may reduce the flame retardancy of the coating layer 20 as a whole. However, by setting the total thickness of the plurality of water-impervious layers 22 to 120 μm or less, the coating layer Since the proportion of the water-impervious layer 22 in 20 can be reduced, it can be maintained high without impairing the flame retardancy of the coating layer 20. The lower limit of the total thickness of the plurality of water-impervious layers 22 is not particularly limited, but may be 30 μm (0.03 mm), for example.

In the laminated structure of the coating layer 20, the thickness of each of the plurality of flame-retardant insulating layers 21 is not particularly limited, but the total thickness of the plurality of flame-retardant insulating layers 21 is 250 μm (0.25 mm) or more. With such a thickness, it is possible to maintain high flame retardancy in the coating layer 20. The upper limit of the total thickness is not particularly limited, but it is preferably 0.5 mm or less from the viewpoint of reducing the diameter of the insulated wire 1. With such a thickness, it is possible to obtain direct current stability and high flame retardancy while reducing the diameter of the insulated wire 1. The plurality of flame-retardant insulating layers 21 may have different thicknesses.

In the laminated structure of the coating layer 20, from the viewpoint of achieving both flame retardancy and DC stability at a higher level, the ratio of the total thickness of the impermeable layer 22 to the thickness of the coating layer 20 is 14% or less. Is preferable, and more preferably 10% to 12%. As described above, the impermeable layer 22 does not contain a flame retardant and may reduce the flame retardancy of the insulated wire 1 as a whole, but by setting the ratio of the thickness of the impermeable layer 22 to the above range, By setting the total thickness of the flame-retardant insulating layer 21 and the total thickness of the water-impervious layer 22 to a predetermined ratio, it is possible to achieve both flame retardancy and DC stability at a high level in the insulated wire 1. The thickness of the coating layer 20 is the total thickness of the flame-retardant insulating layer 21 and the water shield layer 22 forming the coating layer 20.

<Effects of this embodiment>
According to this embodiment, one or more of the following effects are exhibited.

According to the present embodiment, from the viewpoint of obtaining flame retardancy, a resin layer containing a flame retardant is provided on the outer periphery of the conductor 10. However, the outer periphery of the resin layer has a small saturated water absorption formed from HDPE or LDPE. The impermeable layer 22 is laminated. As a result, when the insulated electric wire 1 is immersed in water to evaluate the DC stability, it is possible to suppress the permeation of water into the resin layer, so that the resin layer containing the flame retardant is not only flame retardant but also DC stable. It can be made to function as the flame-retardant insulating layer 21 that also contributes to the properties. Therefore, it is not necessary to form an insulating layer that contributes to DC stability inside the flame-retardant layer as in the related art, and the thickness can be reduced by that amount. Therefore, according to the present embodiment, it is possible to reduce the outer diameter of the insulated wire 1 while achieving both flame retardancy and DC stability at a high level.

In addition, the coating layer 20 is configured by alternately stacking two flame-retardant insulating layers 21a and 21b and two water-impervious layers 22a and 22b so that the first water-impervious layer 22a is on the surface. That is, not only the first water-impervious layer 22a is provided on the surface of the coating layer 20, but also the second water-impermeable layer 22b is provided so as to be interposed between the two flame-retardant insulating layers 21a and 21b. Thereby, for example, even when a pinhole is generated in the first water-impervious layer 22a on the front surface side and the first flame-retardant insulating layer 21a located inside is inundated, the second water-impermeable layer 22b does not Since the infiltration of water can be suppressed, it is possible to maintain the DC stability by the flame-retardant insulating layer 21 located inside the second water-blocking layer 22b. Further, for example, even if pinholes are formed in both of the two water-impervious layers 22a and 22b, since the regions where the pinholes 50 are formed are different from each other, the permeation path of the water 60 is lengthened to thereby cause dielectric breakdown. It is possible to extend the time, and it is possible to suppress a decrease in DC stability.

Further, the thickness of the first water shield layer 22a located on the surface of the coating layer 20 is at least 25 μm. As a result, the strength of the first water-impervious layer 22a can be increased, so that the first water-impervious layer 22a can be prevented from breaking when the insulated wire 1 is bent, that is, pinholes can be suppressed. Further, since the water impermeability can be increased by increasing the thickness, it is possible to suppress the permeation of water into the inside of the coating layer 20. Moreover, in the coating layer 20, the total thickness of the two flame-retardant insulating layers 21a and 21b is at least 250 μm. As a result, it is possible to suppress a decrease in flame retardancy due to the water-impervious layer 22 and maintain high flame retardancy. Therefore, it is possible to obtain a high level of DC stability and flame retardance in a well-balanced manner while reducing the diameter of the insulated wire 1.

For example, in the case of achieving both high flame retardancy according to EN60332-1-2 and direct current stability according to EN50305.6.7, the conventional insulated wire 100 as shown in FIG. 3 has an outer diameter of 1. It is necessary to set the thickness of the insulating layer 120 to 0.6 mm to 2.0 mm and the thickness of the flame retardant layer 130 containing a flame retardant to 0.2 mm to 2.1 mm for the conductor 110 of 0 mm to 20.0 mm. Therefore, the outer diameter of the insulated wire 100 is 2.6 mm to 28.2 mm.
On the other hand, in the present embodiment, for the conductor 11 having the same outer diameter, the total thickness of the plurality of water-impervious layers 22 is 0.03 mm to 0.12 mm, and the total thickness of the plurality of flame-retardant insulating layers is the same. The outer diameter of the insulated wire 1 can be reduced to a range of 1.56 mm to 21.24 mm.

Each impermeable layer 22 is preferably formed of resin, the density is preferably formed from a polyolefin resin is ^{0.85g / cm 3 ~1.20g / cm 3} . These polyolefin resins can be easily formed as the water shield layer 22 by extrusion molding. In particular, since HDPE has a high density and is less likely to allow water to permeate, it is possible to increase the water impermeability of the impermeable layer 22. Further, since LDPE can increase the degree of cross-linking, it can increase the water impermeability of the water-impervious layer 22.

Each water impermeable layer 22 is formed of a crosslinked body obtained by crosslinking HDPE or LDPE, and the gel fraction of the crosslinked body is preferably 40% to 100%. By setting such a gel fraction, the strength and the water impermeability of the water-impervious layer 22 can be enhanced, so that the thickness of the water-impermeable layer 22 can be formed thin. As a result, the outer diameter of the insulated wire 1 can be made thinner.

According to the present embodiment, the insulated wire 1 may be formed to have the same outer diameter as the conventional one without reducing the diameter. In this case, by increasing the thickness of the flame-retardant insulating layer 21, it becomes possible to further improve the flame retardancy and the DC stability.

<Other Embodiments of the Present Invention>
Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above-described embodiment and can be appropriately modified without departing from the scope of the invention.

In the above-described embodiment, the case where the coating layer 20 is configured by alternately stacking two flame-retardant insulating layers 21 and two water-impervious layers 22 is exemplified, but, for example, three or more water-impervious layers 22 may be included. Alternatively, the coating layer 20 may be configured.

Further, FIG. 1 shows a case where the flame-retardant insulating layer 21 and the water shield layer 22 are laminated, but the present invention is not limited to this. For example, the coating layer 20 may be provided with a resin layer having characteristics different from those of the flame-retardant insulating layer 21 and the water shield layer 22. Further, another functional layer may be provided on the outer periphery of the coating layer 20, that is, on the outer periphery of the water blocking layer 22, and for example, a flame retardant layer containing a flame retardant and having flame retardancy may be provided.

Further, in the above-described embodiment, the case where the water shield layer 22 is formed of resin such as HDPE has been described, but the present invention is not limited to this. The water blocking layer 22 may be formed of a material other than resin, and may be formed of, for example, metal, ceramics, glass, or the like.
When the water-blocking layer 22 is made of metal, it can be formed, for example, by winding a metal foil made of copper or aluminum around the outer periphery of the flame-retardant insulating layer 21.
When formed of ceramics or glass, for example, the outer periphery of the flame-retardant insulating layer 21 may be surface-treated with alumina, zirconia, or diamond-like carbon (DLC) by a plasma CVD method or the like.

Next, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

The materials used in the examples and comparative examples are as follows.
-Ethylene-vinyl acetate copolymer (EVA1): "Evaflex EV260" manufactured by Mitsui DuPont Polychemical Co., Ltd. (VA amount: 28%, MFR: 6)
-Ethylene-vinyl acetate copolymer (EVA2): "Eva Flex 45X" manufactured by Mitsui DuPont Polychemical Co., Ltd. (VA amount: 46%, MFR: 100)
-Maleic acid modified polymer: "Toughmer MH7020" manufactured by Mitsui Chemicals, Inc.
High density polyethylene (HDPE, d: 0.951 g/cm ³ , MFR: 0.8): "Hi-Zex 5305E" manufactured by Prime Polymer Co., Ltd.
・Low-density polyethylene (LDPE, d: 0.921 g/cm ³ , MFR: 1): "UBE C450" manufactured by Ube Industries, Ltd.
・Magnesium hydroxide (silane treatment): "H10A" manufactured by Albemarle Corporation
・Magnesium hydroxide (fatty acid treatment): "H10C" manufactured by Albemarle Corporation
・Mixed antioxidant: "AO-18" manufactured by ADEKA CORPORATION
-Phenolic antioxidant: "IRGANOX 1010" manufactured by BASF Corporation
・Colorant: "FT carbon" manufactured by Asahi Carbon Co., Ltd.
・Lubricant (zinc stearate): Nitto Kasei Co., Ltd.

<Production of insulated wire>
(Example 1)
First, a resin composition A for forming a flame-retardant insulating layer was prepared using the above materials.
Specifically, 70 parts by mass of EVA1, 15 parts by mass of EVA2, 15 parts by mass of a maleic acid-modified polymer, 80 parts by mass of silanized magnesium hydroxide, and fatty acid-treated magnesium hydroxide were used. A resin composition A was prepared by kneading 120 parts by mass, 1 part by mass of a mixed antioxidant, 2 parts by mass of a colorant, and 1 part by mass of a lubricant.

Then, the resin composition B for forming a water-impervious layer was prepared.
Specifically, a resin composition B was prepared by kneading 100 parts by mass of HDPE and 1 part by mass of a phenolic antioxidant.

Subsequently, an insulated wire was produced using the prepared resin compositions A and B.
Specifically, first, the resin composition A is extruded on the outer periphery of a twisted copper wire having a diameter of 1.23 mm obtained by twisting a plurality of copper strands to form a second flame-retardant insulating layer having a thickness of 0.2 mm. did. Then, the resin composition B was extruded on the outer periphery of the second flame-retardant insulating layer to form a second water-impervious layer having a thickness of 0.025 mm. Then, the resin composition A was extruded on the outer periphery of the second water-impervious layer to form a first flame-retardant insulating layer having a thickness of 0.1 mm. Then, the resin composition B was extruded on the outer periphery of the first flame-retardant insulating layer to form a first water-impervious layer having a thickness of 0.025 mm. Then, it was crosslinked by electron beam irradiation. Thus, an insulated electric wire having an outer diameter of 1.93 mm was prepared, which was provided with a coating layer in which two water-impermeable layers and two flame-retardant insulating layers were alternately laminated so that the water-impermeable layer was located on the surface. It was confirmed that the water-impervious layer had a degree of crosslinking such that the gel fraction was 41.2%. Table 1 below summarizes each constitution of the insulated electric wire of Example 1.

(Example 2)
In Example 2, the insulated wire was the same as in Example 1 except that the thicknesses of the flame-retardant insulating layer and the water-impervious layer were changed as shown in Table 1 so that the outer diameter of the wire was smaller than that of Example 1. Was produced.

(Example 3)
In Example 3, LDPE was used in place of HDPE to prepare a resin composition B for forming a water shield layer, and as shown in Table 1, the thickness of the water shield layer and the flame retardant insulating layer was appropriately changed. An insulated wire was produced in the same manner as in Example 1 except for the above.

(Example 4)
In Example 4, as shown in Table 1, except that the thicknesses of the flame-retardant insulating layer and the water-impervious layer were appropriately changed as shown in Table 1 so that the outer diameter of the wire was smaller than that of Example 3, execution was performed. An insulated wire was produced in the same manner as in Example 1.

(Comparative Example 1)
In Comparative Example 1, as shown in Table 1, the thickness of the first impermeable layer located on the surface of the coating layer was changed to 0.005 mm (5 μm), and the thicknesses of the other layers were changed appropriately. An insulated wire was produced in the same manner as in Example 1 except for the above.

(Comparative example 2)
In Comparative Example 2, as shown in Table 1, an insulated wire was manufactured in the same manner as in Example 1 except that the thickness of each layer was appropriately changed so that the total thickness of the flame-retardant insulating layers was 0.2 mm. did.

(Comparative Examples 3 and 4)
In Comparative Examples 3 and 4, the same resin composition A and resin composition B as in Example 1 were used to form one water shield layer on the outer periphery of the flame-retardant insulating layer, as shown in FIG. 2(b). An insulated wire was produced in the same manner as in Example 1 except that the above was performed. The thickness of each layer is shown in Table 2 below.

(Comparative Examples 5 and 6)
In Comparative Examples 5 and 6, LDPE was used instead of HDPE to prepare a resin composition B for forming a water shield layer, and as shown in Table 2, the thickness of the water shield layer and the flame retardant insulating layer were appropriately adjusted. An insulated electric wire was produced in the same manner as in Comparative Example 3 except that it was changed.

(Comparative Example 7)
In Comparative Example 7, an insulated wire having the structure shown in FIG. 3 was produced.
Specifically, first, 100 parts by mass of LDPE, 100 parts by mass of clay, 7 parts by mass of a crosslinking aid, and 1.5 parts by mass of a phenolic antioxidant are kneaded to form an insulating layer. A resin composition for use was prepared. Further, 100 parts by mass of EVA1 and 200 parts by mass of magnesium hydroxide were kneaded to prepare a resin composition for forming a flame retardant layer. Subsequently, the same twisted copper wire as in Example 1 was prepared, and the resin composition for forming an insulating layer was extruded on the outer periphery thereof to form an insulating layer having a thickness of 0.3 mm. Subsequently, a resin composition for forming a flame retardant layer was extruded on the outer periphery of the insulating layer and crosslinked by electron beam irradiation to form a flame retardant layer having a thickness of 0.4 mm. In this way, an insulated electric wire having an electric wire outer diameter of 2.62 mm was produced. It was confirmed that the flame-retardant layer on the surface of the insulated wire had a degree of crosslinking such that the gel fraction was 82.3%, but the saturated water absorption was 5%. The production conditions of Comparative Example 7 are shown in Table 3 below.

(Comparative Examples 8 and 9)
In Comparative Examples 8 and 9, as shown in Table 3, insulated wires were produced in the same manner as Comparative Example 7 except that the thickness of each of the insulating layer and the flame retardant layer was changed.

(Comparative Example 10)
In Comparative Example 10, as shown in Table 3, an insulated wire was produced in the same manner as in Comparative Example 7 except that the flame retardant layer was directly formed on the conductor without forming the insulating layer.

<Evaluation method>
The produced insulated wire was evaluated by the following methods. The evaluation results are summarized in Table 1.

(DC stability)
The DC stability of the insulated wire was evaluated by a DC stability test in accordance with EN50305.6.7. Specifically, the insulated electric wire was immersed in salt water having a concentration of 3% at 85° C. to apply electric power, and the time until dielectric breakdown was measured. In this example, if the time until dielectric breakdown was 60 hours or more, the DC stability was high, and if it was less than 60 hours, the DC stability was low.

(Flame retardance)
The flame retardancy of the insulated wire was evaluated by the vertical combustion test shown below.
First, a VFT test was carried out according to the vertical flame propagation for a single insulated wire or cable defined in EN603332-1-2. Specifically, an insulated electric wire having a length of 600 mm was held vertically, and a flame was applied to the insulated electric wire for 60 seconds. After extinguishing the flame, those extinguished within 30 seconds were marked with ⊚, those extinguished within 60 seconds were marked with ◯, and those not extinguished within 60 seconds were marked with x.
Further, the VTFT test was carried out in accordance with the multi-strand cable vertical combustion test (Flame propagation (bunched cables)) specified in EN50266-2-4. Specifically, 7 insulated wires with a total length of 3.5 m are twisted together to form one bundle, 11 bundles are arranged vertically at equal intervals, burned for 20 minutes, self-extinguished, and then the carbonized length from the lower end is It was measured. In this example, the carbonization length was 1.5 m or less, ⊚, the carbonization length was 2.5 m or less, and the carbonization length was more than 2.5 m.

<Evaluation result>
As shown in Table 1, in Examples 1 to 4, it was confirmed that it is possible to achieve both high DC stability and high flame retardancy while reducing the outer diameter of the wire.

On the other hand, in Comparative Example 1, although the two water shield layers were provided in the coating layer, the thickness of the first water shield layer located on the surface of the coating layer was less than 0.025 mm, which was less than 0.025 mm. Since it was 005 mm, it was confirmed that the water absorption of the flame-retardant insulating layer could not be sufficiently suppressed and the DC stability was low.

In Comparative Example 2, it was confirmed that sufficient flame retardancy could not be obtained because the total thickness of the flame-retardant insulating layers provided in the coating layer was thinner than 0.25 mm and 0.20 mm.

In Comparative Examples 3 to 6, direct current stability and flame retardancy were obtained in a well-balanced manner by providing the water blocking layer only on the surface of the coating layer, but the time until dielectric breakdown was 60 hours or more. It was also confirmed that it was short and was insufficient in terms of DC stability.

In Comparative Example 7, a flame-retardant layer was laminated on the outer periphery of the insulating layer to produce an insulated wire having a conventional structure. However, by forming each layer thicker, flame retardancy and DC stability were well balanced at a high level. It was confirmed to be obtained. However, it was confirmed that the outer diameter of the electric wire was excessively large, for example, about 35% larger than that of the insulated electric wire of Example 1.

In Comparative Examples 8 and 9, the insulated wire was manufactured such that the outer diameter of the wire was about the same as in Example 1 by reducing the thickness of the flame retardant layer or the insulating layer. It was confirmed that they were not compatible. According to Comparative Examples 7 to 9, when a flame-retardant layer having a high saturated water absorption rate of 5% is provided on the surface of the insulated wire, a thick insulating layer is formed inside the flame-retardant layer in order to maintain high DC stability. Since it is necessary to form a thick flame-retardant layer in order to maintain high flame retardancy, it was confirmed that the insulated wire cannot be made thinner while satisfying these characteristics.

In Comparative Example 10, since only the flame retardant layer was provided without providing the insulating layer, high flame retardancy was obtained, but it was confirmed that the DC stability was low.

Thus, in the insulated wire, by providing the water-impervious layer of a predetermined thickness on the outer periphery of the resin layer containing the flame retardant, it is possible to suppress the permeation of water into the resin layer located inside, the flame retardant The resin layer to be blended can contribute to not only flame retardancy but also DC stability and function as a flame retardant insulating layer. Further, by forming a coating layer by laminating a plurality of flame-retardant insulating layers and water-impervious layers, it is possible to achieve both DC stability and flame retardancy while reducing the outer diameter of the insulated wire. Becomes

<Preferred embodiment of the present invention>
Hereinafter, the preferred embodiments of the present invention will be additionally described.

[Appendix 1]
According to one aspect of the invention,
A conductor,
A coating layer disposed on the outer periphery of the conductor,
The coating layer is formed by alternately stacking a plurality of flame-retardant insulating layers formed of a resin composition containing a flame retardant and a plurality of water-impervious layers having a saturated water absorption of 0.5% or less in order from the conductor side. To be formed,
The thickness of the impermeable layer located on the surface of the coating layer is 25 μm or more,
Provided is an insulated wire in which the total thickness of the plurality of flame-retardant insulating layers is 250 μm or more.

[Appendix 2]
In the insulated wire of Appendix 1, preferably,
The total thickness of the plurality of water shield layers is 120 μm or less.

[Appendix 3]
In the insulated wire of Appendix 1 or 2, preferably
The material forming the water blocking layer is at least one of resin, metal, ceramics and glass.

[Appendix 4]
In the insulated wire according to any one of appendices 1 to 3, preferably,
Each of the plurality of water blocking layers is formed of a crosslinked body obtained by crosslinking a resin, and the gel fraction of the crosslinked body is 40% or more and 100% or less.

[Appendix 5]
In the insulated wire according to any one of appendices 1 to 4, preferably,
Each of the plurality of water blocking layers is formed of at least one of high density polyethylene and low density polyethylene.

[Appendix 6]
In the insulated wire of Appendix 5, preferably,
Density of the resin is not more than 0.85 g / cm ³ or more 1.20 g / cm ^3.

[Appendix 7]
In the insulated wire according to any one of appendices 1 to 6, preferably,
The total thickness of the plurality of flame-retardant insulating layers is 250 μm or more and 500 μm or less.

[Appendix 8]
In the insulated wire according to any one of appendices 1 to 7, preferably,
The outer diameter is 1.8 mm or more and 32.9 mm or less.

[Appendix 9]
In the insulated wire according to any one of appendices 1 to 8, preferably,
The outer diameter of the conductor is 1.0 mm or more and 20.0 mm or less.

[Appendix 10]
In the insulated wire according to any one of appendices 1 to 9, preferably,
The ratio of the total thickness of the water shield layer 22 to the thickness of the coating layer 20 is 14% or less.

[Appendix 11]
In the insulated wire according to any one of appendices 1 to 9, preferably,
In a vertical combustion test according to EN60332-1-2, after removing the flame, flame retardancy to extinguish within 60 seconds,
In a DC stability test based on EN50305.6.7, it has DC stability such that dielectric breakdown does not occur when immersed in water and charged with electricity for 240 hours.

1 Insulated Wire 10 Conductor 20 Covering Layer 21 Flame Retardant Insulating Layer 22 Water Impermeable Layer

Claims (5)

A conductor,
A coating layer disposed on the outer periphery of the conductor,
The coating layer is formed by alternately stacking a plurality of flame-retardant insulating layers formed of a resin composition containing a flame retardant and a plurality of water-impervious layers having a saturated water absorption of 0.5% or less in order from the conductor side. To be formed,
The thickness of the impermeable layer located on the surface of the coating layer is 25 μm or more,
An insulated wire in which the total thickness of the plurality of flame-retardant insulating layers is 250 μm or more. The insulated wire according to claim 1, wherein the total thickness of the plurality of water-impermeable layers is 120 μm or less. The insulated wire according to claim 1 or 2, wherein each of the plurality of water blocking layers is formed of a crosslinked body obtained by crosslinking a resin, and the gel fraction of the crosslinked body is 40% or more and 100% or less. The insulated wire according to any one of claims 1 to 3, wherein each of the plurality of water blocking layers is formed of at least one of high-density polyethylene and low-density polyethylene. Density of the resin is not more than 0.85 g / cm ³ or more 1.20 g / cm ^3, claim 3 also

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