JP2020169281A - Electric insulation composition and power cable - Google Patents

Abstract

To improve water tree resistance while securing various cable characteristics.SOLUTION: An electric insulation composition has 100 pts.mass of a base resin containing polyethylene, 0.1 pts.mass or more and 10 pts.mass or less of an unsaturated dimer of α-aromatic substituted α-methyl alkene, and 0.05 pts.mass or more and 1.0 pts.mass or less of fatty acid amide.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to electrically insulating compositions and power cables.

Since polyethylene has excellent insulating properties, it is widely used as a base resin for an electrical insulating composition constituting an insulating layer in power cables and the like (for example, Patent Document 1).

JP-A-57-69611

When the power cable is charged in a moist or flooded environment, water trees can form in the insulating layer. Therefore, it is required to improve the water tree resistance of the insulating layer.

An object of the present disclosure is to provide a technique capable of improving water tree resistance while ensuring various cable characteristics.

According to one aspect of the present disclosure
100 parts by mass of base resin containing polyethylene,
The unsaturated dimer of α-aromatically substituted α-methylalkene is 0.1 parts by mass or more and 10 parts by mass or less.
Fatty acid amide in an amount of 0.05 parts by mass or more and 1.0 part by mass or less.
An electrically insulating composition having the above is provided.

According to other aspects of the disclosure,
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 100 parts by mass of a base resin containing polyethylene, 0.1 parts by mass or more and 10 parts by mass or less of an unsaturated dimer of α-aromatically substituted α-methylalkene, and 0.05 parts by mass of fatty acid amide. A power cable composed of an electrically insulating composition having a mass of parts by mass or more and 1.0 part by mass or less is provided.

According to the present disclosure, it is possible to improve water tree resistance while ensuring various cable characteristics.

It is a schematic cross-sectional view orthogonal to the axial direction of the power cable which concerns on one Embodiment of this disclosure.

[Explanation of Embodiments of the present disclosure]
<Knowledge obtained by inventors>
First, the findings obtained by the inventors will be outlined.

The power cable may be laid, for example, in a moist or flooded environment. In such an environment, when a predetermined electric field is applied to the insulating layer of the power cable, a water tree may be generated in the insulating layer. If a water tree is generated in the insulating layer, the insulating property of the power cable may be deteriorated.

The water tree is generated by the following mechanism, for example. That is, in a moist environment or a flooded environment, water can infiltrate into the insulating layer of the power cable. When water enters the insulating layer during power supply of the power cable, the water aggregates in the portion of the insulating layer where the local electric field concentration occurs. Examples of the local electric field concentration portion include voids and foreign matter in the insulating layer, and an irregular interface between the insulating layer and the semiconductive layer. When water aggregates in such a local electric field concentration portion, mechanical strain occurs around the water-aggregated portion due to an increase in pressure of the aggregated water. As a result, tree-like or bow-tie-like water trees are generated in the insulating layer.

Conventionally, in order to suppress the generation of water trees in the insulating layer of a power cable, various techniques have been studied, for example, as in Patent Document 1 described above.

However, in recent years, the specifications required for power cables laid in a moist environment or a flooded environment have become stricter. Alternatively, it is required to simplify the configuration of the power cable laid in a moist environment or a flooded environment and reduce the cost of the power cable. For these reasons, a power cable having further improved water tree resistance is desired.

Therefore, the present inventors have studied a material to be added to the electrical insulating composition constituting the insulating layer of the power cable. Specifically, among various materials added to the electrically insulating composition, unsaturated dimers of α-aromatically substituted α-methylalkene and fatty acid amides were examined. As a result of the examination, it is possible to reduce the generation density of water trees in the insulating layer by adding either an unsaturated dimer of α-aromatically substituted α-methylalkene or a fatty acid amide. Do you get it.

As a result of further diligent studies by the present inventors, it is possible to significantly improve water tree resistance by adding both an unsaturated dimer of α-aromatically substituted α-methylalkene and a fatty acid amide. I found out what I could do. Specifically, it has been found that the maximum length of the water tree generated in the insulating layer can be shortened and the density of the number of water trees generated in the insulating layer can be remarkably reduced.

The present disclosure is based on the above-mentioned findings found by the inventors.

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

[1] The electrically insulating composition according to one aspect of the present disclosure is
100 parts by mass of base resin containing polyethylene,
The unsaturated dimer of α-aromatically substituted α-methylalkene is 0.1 parts by mass or more and 10 parts by mass or less.
Fatty acid amide in an amount of 0.05 parts by mass or more and 1.0 part by mass or less.
Have.
According to this configuration, the water tree resistance can be remarkably improved while ensuring various cable characteristics.

[2] In the electrically insulating composition according to the above [1],
The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
The maximum length of the water tree generated in the electrically insulating composition is less than 200 μm.
According to this configuration, dielectric breakdown of the insulating layer caused by the water tree can be stably suppressed.

[3] In the electrically insulating composition according to the above [1] or [2],
The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
Generation number concentration of water tree having a length of more than 30μm occurred while the electrically insulating composition is less than 200 / cm ^3.
According to this configuration, dielectric breakdown of the insulating layer caused by the water tree can be stably suppressed.

[4] In the electrically insulating composition according to any one of the above [1] to [3].
The fatty acid amide comprises a fatty acid monoamide.
According to this configuration, the effect of suppressing the local concentration of water by the polar group can be improved.

[5] In the electrically insulating composition according to any one of the above [1] to [4].
The fatty acid amide comprises an unsaturated fatty acid amide.
According to this configuration, electrons can be trapped in the dispersed unsaturated bond (double bond), and local electric field concentration can be suppressed.

[6] In the electrically insulating composition according to any one of the above [1] to [5].
It has a cross-linking agent containing an organic peroxide.
According to this configuration, the base resin can be crosslinked with a crosslinking agent. Thereby, the mechanical properties and the electrical properties of the electrically insulating composition can be improved.

[7] In the electrically insulating composition according to any one of the above [1] to [5],
The base resin is crosslinked.
According to this configuration, the mechanical properties and electrical properties of the electrically insulating composition can be improved.

[8] In the electrically insulating composition according to any one of the above [1] to [7],
The ratio of the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene to the content of the fatty acid amide is more than 0.5 and less than 15.
According to this configuration, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer can be sufficiently obtained. Further, it is possible to stably suppress an increase in the dielectric loss tangent and a decrease in the tensile property of the insulating layer (decrease in tensile strength and shortening in tensile elongation).

[9] The power cable according to another aspect of the present disclosure is
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 100 parts by mass of a base resin containing polyethylene, 0.1 parts by mass or more and 10 parts by mass or less of an unsaturated dimer of α-aromatically substituted α-methylalkene, and 0.05 parts by mass of fatty acid amide. It is composed of an electrically insulating composition having a mass of parts or more and 1.0 part by mass or less.
According to this configuration, the water tree resistance can be remarkably improved while ensuring various cable characteristics.

[Details of Embodiments of the present disclosure]
Next, one embodiment of the present disclosure will be described below with reference to the drawings. It should be noted that the present invention is not limited to these examples, and is indicated by the scope of claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

<One Embodiment of the present disclosure>
(1) Electrical Insulation Composition The electrical insulation composition of the present embodiment is a material constituting the insulating layer 130 of the power cable 10 described later, and is, for example, an unsaturated base resin and an α-aromatically substituted α-methylalkene. It has a saturated dimer, a fatty acid amide, and other additives.

The "electrically insulating composition" in the present embodiment means, for example, a composition in an uncrosslinked state without a crosslinking agent described later, a composition in an uncrosslinked state containing a crosslinking agent described below, and a crosslinked composition. Contains the composition in the state of cross-linking.

(Base resin)
The base resin (base polymer) refers to a resin component that constitutes the main component of the electrically insulating composition. The base resin of the present embodiment contains, for example, polyethylene.

The polyethylene constituting the base resin, for example, low density polyethylene (LDPE: density 0.91 g / cm ³ or more 0.93 g / cm less than ^3), linear low density polyethylene (LLDPE: density 0.945 g / cm ³ below) medium density polyethylene (MDPE: density below 0.93 g / cm ³ or more 0.942 g / cm ^3), high density polyethylene (HDPE: density 0.942 g / cm ³ or higher), and the like. Among these, at least one of LDPE and LLDPE is preferable. As a result, the mechanical properties can be improved while improving the insulation property of the power cable.

(Α-aromatically substituted α-methylalkene unsaturated dimer)
By adding an unsaturated dimer of α-aromatically substituted α-methylalkene to the electrically insulating composition, it is possible to suppress the generation of local scorch in the extrusion process of the electrically insulating composition. .. In addition, electrons can be trapped in the aromatic ring of the unsaturated dimer of the α-aromatically substituted α-methylalkene to form a stable resonance structure. As a result, the generation of water trees in the insulating layer 130 can be suppressed. In the following, the unsaturated dimer of the α-aromatically substituted α-methylalkene may be abbreviated as “unsaturated dimer”.

The α-aromatically substituted α-methylalkene monomer is represented by, for example, the following formula (1).

However, R is any one of an aryl group, an alkaline group, a halogen-substituted aryl group, and a halogen-substituted alkaline group. The term "alkaline group" as used herein refers to a combination of one or more aryl groups bonded to one or more alkyl groups.

Specifically, examples of the α-aromatically substituted α-methylalkene monomer include α-methylstyrene, para-methyl-α-methylstyrene, para-isopropyl-α-methylstyrene, and meta-methyl-. α-Methylstyrene, Meta-ethyl-α-Methylstyrene, ar-dimethyl-α-methylstyrene, ar-chlor-α-methylstyrene, ar-chlor-ar-methyl-α-methylstyrene, ar-diethyl-α -Methylstyrene, ar-methyl-ar-isopropyl-α-methylstyrene and the like can be mentioned.

Examples of the unsaturated dimer of the α-aromatically substituted α-methylalkene include an unsaturated dimer of α-methylstyrene (2,4-diphenyl-4-methyl-1-pentene). In addition, two or more kinds of unsaturated dimers of α-methylstyrene and other unsaturated dimers may be used in combination.

In the present embodiment, the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene in the electrically insulating composition is, for example, 0.1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the base resin. It is less than a part.

If the content of the unsaturated dimer is less than 0.1 parts by mass, the effect of suppressing the water tree by the unsaturated dimer may not be sufficiently obtained. On the other hand, when the content of the unsaturated dimer is 0.1 parts by mass or more, the effect of suppressing the water tree by the unsaturated dimer can be sufficiently obtained. On the other hand, if the content of the unsaturated dimer is more than 10 parts by mass, the base resin is less likely to be crosslinked, and the gel content of the electrically insulating composition is lowered. Therefore, there is a possibility that the dielectric loss tangent when a predetermined AC electric field is applied may increase, or the tensile characteristics of the insulating layer 130 may decrease (at least one of a decrease in tensile strength and a decrease in tensile elongation occurs). There is. On the other hand, by setting the content of the unsaturated dimer to 10 parts by mass or less, it is possible to crosslink a predetermined amount of the base resin and suppress a decrease in the gel fraction of the electrically insulating composition. As a result, it is possible to suppress an increase in the dielectric loss tangent when a predetermined AC electric field is applied, and it is possible to suppress a decrease in the tensile characteristics of the insulating layer 130 (decrease in tensile strength and shortening in tensile elongation).

(Fatty acid amide)
By adding the fatty acid amide to the electrically insulating composition, the fatty acid amide can act as a lubricant to improve the fluidity of the electrically insulating composition in the extrusion step of the insulating layer 130. Further, by dispersing the fatty acid amide, local concentration of water in the electrically insulating composition can be suppressed by the dispersed polar groups (hydrophilic groups). Thereby, the generation of the water tree in the insulating layer 130 can be suppressed.

Examples of fatty acid amides include saturated fatty acid monoamides, unsaturated fatty acid monoamides, saturated fatty acid bisamides and unsaturated fatty acid bisamides.

Specifically, examples of the saturated fatty acid monoamide include lauric acid amide, palmitic acid amide, stearic acid amide, and hydroxystearic acid amide.

Examples of unsaturated fatty acid monoamides include oleic acid amides and erucic acid amides.

Examples of the saturated fatty acid bisamide include methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, ethylene bisstearic acid amide, ethylene bishydroxystearic acid amide, ethylene bisbechenic acid amide, and hexamethylene bisstearic acid. Examples thereof include amides, hexamethylene bishydroxystearic acid amides, and N, N'-distearyl adipate amides.

Examples of the unsaturated fatty acid bisamide include ethylene bisoleic acid amide, ethylene biserucic acid amide, hexamethylene bisoleic acid amide, N, N'-diorail adipic acid amide, and N, N'-diorail sebacic acid amide. Can be mentioned.

Two or more of these fatty acid amides may be used in combination.

In the present embodiment, the fatty acid amide added to the electrically insulating composition is preferably, for example, a fatty acid monoamide. Thereby, the polarity of the fatty acid amide can be improved. As a result, the effect of suppressing the local concentration of water by the polar group can be improved.

Further, in the present embodiment, the fatty acid amide added to the electrically insulating composition is preferably, for example, an unsaturated fatty acid amide. As a result, electrons can be trapped in the dispersed unsaturated bond (double bond), and local electric field concentration can be suppressed.

In the present embodiment, the content of fatty acid amide in the electrically insulating composition is, for example, 0.05 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the base resin.

If the content of the fatty acid amide is less than 0.05 parts by mass, the effect of suppressing the water tree by the fatty acid amide may not be sufficiently obtained. On the other hand, when the content of the fatty acid amide is 0.05 parts by mass or more, the effect of suppressing the water tree by the fatty acid amide can be sufficiently obtained. On the other hand, if the content of the fatty acid amide is more than 1.0 part by mass, the fatty acid amide may be precipitated on the surface of the insulating layer 130 due to the difference in compatibility between the base resin and the fatty acid amide. There is. This phenomenon is called "bloom". On the other hand, by setting the content of the fatty acid amide to 1.0 part by mass or less, it is possible to suppress the generation of bloom due to the difference in compatibility between the base resin and the fatty acid amide.

In the present embodiment, by adding both the fatty acid amide and the unsaturated dimer of the α-aromatically substituted α-methylalkene described above, the synergistic action thereof significantly improves the water tree resistance. Can be made to.

In the present embodiment, the ratio B / A of the content B of the unsaturated dimer of the α-aromatically substituted α-methylalkene to the content A of the fatty acid amide is B / A (hereinafter, also referred to as content ratio B / A). For example, it is preferably more than 0.5 and less than 15, and more preferably 2 or more and less than 9.

When the content ratio B / A is 0.5 or less, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer may not be sufficiently obtained. On the other hand, when the content ratio B / A is more than 0.5, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer can be sufficiently obtained. Further, by setting the content ratio B / A to 2 or more, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer can be stably obtained.

On the other hand, if the content ratio B / A is 15 or more, the effect of improving the fluidity of the fatty acid amide may not be sufficiently obtained. Therefore, it becomes difficult to uniformly disperse the unsaturated dimer, and it may be difficult to improve the gel fraction. Further, when the content ratio B / A is 15 or more, the effect of suppressing the local concentration of water by the polar group of the fatty acid amide may not be sufficiently obtained. On the other hand, when the content ratio B / A is less than 15, the effect of improving the fluidity of the fatty acid amide can be sufficiently obtained. As a result, the unsaturated dimer can be uniformly dispersed, and the gel fraction can be stably improved. As a result, an increase in the dielectric loss tangent and a decrease in the tensile property of the insulating layer 130 (decrease in tensile strength and shortening in tensile elongation) can be stably suppressed. Further, by setting the content ratio B / A to less than 15, it is possible to sufficiently obtain the effect of suppressing the local concentration of water by the polar group of the fatty acid amide. As a result, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer can be sufficiently obtained. Further, by setting the content ratio B / A to less than 9, it is possible to surely suppress an increase in the dielectric loss tangent and a decrease in the tensile characteristics of the insulating layer 130 (decrease in tensile strength and shortening in tensile elongation). .. Further, by setting the content ratio B / A to less than 9, it is possible to stably obtain the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer.

(Crosslinking agent)
In the present embodiment, the base resin of the electrically insulating composition is preferably crosslinked with, for example, a crosslinking agent. As a result, the mechanical properties (tensile properties, etc.) and electrical properties of the electrically insulating composition can be improved.

As the cross-linking agent added to the electrically insulating composition, for example, an organic peroxide is used. Specifically, examples of the organic peroxide include dicumyl peroxide, 1- (2-tert-butylperoxyisopropyl) -1-isopropylbenzene, and 1- (2-tert-butylperoxyisopropyl)-. 3-Isopropylbenzene, 1,3-bis- (tert-butylperoxy-isopropyl) benzene, 2,5-dimethyl-2.5-di (t-butylperoxy) hexane, 2,5-dimethyl-2, Examples thereof include 5- (tert-butylperoxy) -hexin-3. Two or more of these may be used in combination.

(Other additives)
The electrically insulating composition may further contain, for example, an antioxidant.

Examples of the antioxidant include 4,4'-thiobis- (6-t-butyl-3-methylphenol) and 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-). 4-Hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl 3- (3,5-di-t-butyl-4) -Hydroxyphenyl) propionate, 2,4-bis-[(octylthio) methyl] -o-cresol, 2,4-bis- (n-octylthio) -6- (4-hydroxy-3,5-di-t-) Butylanilino) -1,3,5-triazine, bis [2-methyl-4- {3-n-alkyl (C12 or C14) thiopropionyloxy} -5-t-butylphenyl] sulfide and the like can be mentioned. Two or more of these may be used in combination.

The electrically insulating composition may contain a lubricant other than the above-mentioned fatty acid amide as a lubricant. Further, the electrically insulating composition may further contain, for example, a colorant.

(2) Power Cable Next, the power cable of the present embodiment will be described with reference to FIG. FIG. 1 is a cross-sectional view orthogonal to the axial direction of the power cable according to the present embodiment.

The power cable 10 of this embodiment is configured as a so-called solid-state insulated power cable. Further, the power cable 10 of the present embodiment is configured to be laid underwater or underwater, for example. The power cable 10 is used for alternating current, for example.

Specifically, the power cable 10 has, for example, a conductor 110, an inner semi-conductive layer 120, an insulating layer 130, an outer semi-conductive layer 140, a shielding layer 150, and a sheath 160.

The power cable 10 of the present embodiment has the above-mentioned remarkable water tree suppressing effect, and thus has, for example, a metal water-shielding layer such as a so-called aluminum cover outside the shielding layer 150. Absent. That is, the power cable 10 of the present embodiment is configured by a non-complete impermeable structure.

(Conductor (conductive part))
The conductor 110 is formed by twisting a plurality of conductor core wires (conductive core wires) including, for example, pure copper, a copper alloy, aluminum, an aluminum alloy, or the like.

(Internal semi-conductive layer)
The inner semi-conductive layer 120 is provided so as to cover the outer periphery of the conductor 110. Further, the internal semiconductive layer 120 has semiconductivity and is configured to suppress electric field concentration on the surface side of the conductor 110. The internal semi-conductive layer 120 is conductive with at least one of, for example, an ethylene-ethyl acrylate copolymer, an ethylene-methyl acrylate copolymer, an ethylene-butyl acrylate copolymer, and an ethylene-vinyl acetate copolymer. Includes carbon black and.

(Insulation layer)
The insulating layer 130 is provided so as to cover the outer periphery of the inner semi-conductive layer 120, and is composed of the above-mentioned electrical insulating composition. The insulating layer 130 is crosslinked by heating the electrically insulating composition after being extruded, for example, as described above.

(External semi-conductive layer)
The outer semi-conductive layer 140 is provided so as to cover the outer periphery of the insulating layer 130. Further, the external semi-conductive layer 140 has semi-conductive property and is configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semi-conductive layer 140 is made of, for example, the same material as the inner semi-conductive layer 120.

(Shielding layer)
The shielding layer 150 is provided so as to cover the outer periphery of the outer semi-conductive layer 140. The shielding layer 150 is, for example, configured by winding a copper tape, or is configured as a wire shield in which a plurality of annealed copper wires or the like are wound. A tape made of a rubberized cloth or the like may be wound around the inside or outside of the shielding layer 150.

(sheath)
The sheath 160 is provided so as to cover the outer periphery of the shielding layer 150. The sheath 160 is made of, for example, polyvinyl chloride or polyethylene.

(Water tree resistance)
In the present embodiment, as described above, both the unsaturated dimer of the α-aromatically substituted α-methylalkene and the fatty acid amide are added to the insulating layer 130, whereby the water in the insulating layer 130 is added. Tree resistance is significantly improved.

Specifically, in the present embodiment, the electric insulating composition constituting the insulating layer 130 is immersed in a 1N NaCl aqueous solution at room temperature (27 ° C.) and has a commercial frequency (for example, for example) with respect to the electric insulating composition. When an AC electric field of (60 Hz) 4 kV / mm is applied for 1000 hours, the maximum length of the water tree generated in the electrically insulating composition is, for example, less than 200 μm, preferably 180 μm or less. As a result, dielectric breakdown of the insulating layer 130 caused by the water tree can be stably suppressed.

The maximum length of the water tree generated in the electrically insulating composition is not limited as it is smaller. However, in the present embodiment, since a predetermined amount of water tree can be generated by the above-mentioned test, the maximum length of the water tree generated in the electrically insulating composition is, for example, 30 μm or more.

Further, in the present embodiment, the electrical insulating composition constituting the insulating layer 130 is immersed in a 1N NaCl aqueous solution at room temperature (27 ° C.) and has a commercial frequency (for example, 60 Hz) of 4 kV with respect to the electrical insulating composition. / mm alternating electric field upon application 1000 hours, generation number concentration of water tree having electrical insulation composition occurred or longer 30μm in, for example, less than 200 pieces / cm ^3, preferably 150 / It is cm ³ or less. As a result, dielectric breakdown of the insulating layer 130 caused by the water tree can be stably suppressed.

The concentration of the number of generated water trees is not limited as it is lower. However, in the present embodiment, since the predetermined amount of water trees can occur by the test described above, generation number concentration of water trees, for example, the 10 pieces / cm ³ or more.

(Gel fraction (crosslinking degree))
In this embodiment, as described above, the insulating layer 130 is, for example, crosslinked. Further, by setting the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene to 10 parts by mass or less in the electrically insulating composition constituting the insulating layer 130, the gel content of the electrically insulating composition is set. The decrease in the rate is suppressed.

Specifically, in the present embodiment, the gel fraction of the electrically insulating composition constituting the insulating layer 130 is, for example, more than 68%, preferably 70% or more, and more preferably 74% or more.

The gel fraction of the electrically insulating composition is not limited as it is higher. However, since the electrically insulating composition contains a predetermined amount of an unsaturated dimer of α-aromatically substituted α-methylalkene, the gel fraction of the electrically insulating composition is, for example, 95% or less.

(Dissipation factor)
Here, if an AC electric field is applied to the electrically insulating composition, a loss may occur. The loss when an AC electric field is applied includes, for example, a loss due to leakage current, a loss due to dielectric polarization, and a loss due to partial discharge. Due to such loss, the current phase lags behind the lossless current flowing through the ideal electrically insulating composition. The delay angle δ in this case is called the dielectric loss angle, and the tangent is called the dielectric loss tangent (tan δ).

In the present embodiment, the dielectric loss tangent becomes smaller when the gel fraction of the electrically insulating composition constituting the insulating layer 130 is equal to or more than a predetermined value as described above.

Specifically, in the present embodiment, the dielectric loss tangent when an AC electric field of 9 kV / mm is applied to the electrically insulating composition constituting the insulating layer 130 at 90 ° C. is, for example, 0.05% or less. ..

The dielectric loss tangent is not limited as it is smaller. However, in the electrically insulating composition of the present embodiment, the dielectric loss is, for example, 0.001% or more.

(AC fracture electric field)
In the present embodiment, a predetermined AC breaking electric field is secured when the gel fraction of the electrically insulating composition constituting the insulating layer 130 is equal to or higher than a predetermined value as described above.

Specifically, in the present embodiment, the AC breaking electric field of the electrically insulating composition constituting the insulating layer 130 measured at room temperature (27 ° C.) is, for example, 55 kV / mm or more, preferably more than 61 kV / mm. It is preferably 64 kV / mm or more.

The larger the AC fracture electric field, the better, so the AC breakdown electric field is not limited. However, in the electrically insulating composition of the present embodiment, the AC breaking electric field is, for example, 100 kV / mm or less.

(Tensile characteristics)
In the present embodiment, when the gel fraction of the electrically insulating composition constituting the insulating layer 130 is at least a predetermined value as described above, the tensile properties of the electrically insulating composition can be improved.

Specifically, in the present embodiment, the tensile strength of the electrically insulating composition constituting the insulating layer 130 is, for example, 12.5 MPa or more, preferably 14 MPa or more.

The tensile strength of the electrically insulating composition is not limited as it is higher. However, in the electrically insulating composition of the present embodiment, the tensile strength is, for example, 50 MPa or less.

Further, in the present embodiment, the tensile elongation of the electrically insulating composition constituting the insulating layer 130 is, for example, 350% or more, preferably more than 380%, and more preferably 430% or more.

The tensile elongation of the electrically insulating composition is not limited as it is larger. However, in the electrically insulating composition of the present embodiment, the tensile elongation is, for example, 1000% or less.

As described above, in the present embodiment, a predetermined tensile property can be secured. As a result, the power cable 10 can be suitably laid even in an environment where the power cable 10 expands and contracts or bends. Specifically, the power cable 10 of the present embodiment can be applied to, for example, an array cable (dynamic cable, riser cable) that is flexibly connected to a floating water turbine in water.

(Bloom)
In the present embodiment, as described above, by setting the fatty acid amide content to 1.0 part by mass or less, bloom caused by the difference in compatibility between the base resin and the fatty acid amide is generated on the surface of the insulating layer 130. Not detected.

(Specific dimensions, etc.)
The specific dimensions of the power cable 10 are not particularly limited, but for example, the diameter of the conductor 110 is 5 mm or more and 60 mm or less, and the thickness of the internal semiconductive layer 120 is 0.5 mm or more and 3 mm or less. The thickness of the insulating layer 130 is 1 mm or more and 35 mm or less, the thickness of the external semi-conductive layer 140 is 0.5 mm or more and 3 mm or less, the thickness of the shielding layer 150 is 1 mm or more and 5 mm or less, and the sheath. The thickness of 160 is 1 mm or more. The AC voltage applied to the power cable 10 of the present embodiment is, for example, 20 kV or more.

(3) Method of Manufacturing Power Cable Next, the method of manufacturing the power cable of the present embodiment will be described. Hereinafter, the step is abbreviated as "S".

(S100: Electrical insulation composition preparation step)
First, an electrically insulating composition is prepared.

In this embodiment, a base resin containing polyethylene, an unsaturated dimer of α-aromatically substituted α-methylalkene, a fatty acid amide, and other additives (crosslinking agent, antioxidant, etc.) are used as a banvarimixer. Mix (knead) with a mixer such as or kneader to form a mixed material. At this time, the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene is set to, for example, 0.1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the base resin. The fatty acid amide content is, for example, 0.05 parts by mass or more and 1.0 parts by mass or less with respect to 100 parts by mass of the base resin.

After forming the mixed material, the mixed material is granulated by an extruder. As a result, a pellet-shaped electrically insulating composition that constitutes the insulating layer 130 is formed. A twin-screw extruder having a high kneading action may be used to collectively perform the steps from mixing to granulation.

(S200: Conductor preparation process)
On the other hand, a conductor 110 formed by twisting a plurality of conductor core wires is prepared.

(S300: Cable core forming step (extrusion step))
After the electrical insulation composition preparation step S100 and the conductor preparation step S200 are completed, the extruder A for forming the internal semi-conductive layer 120 among the three-layer simultaneous extruders is, for example, conductive with an ethylene-ethyl acrylate copolymer. The composition for the internal semi-conductive layer, which is premixed with the carbon black of the above, is added.

The pellet-shaped electrically insulating composition described above is put into the extruder B that forms the insulating layer 130.

The composition for the outer semiconductive layer containing the same material as the electrically insulating composition for the inner semiconductive layer charged in the extruder A is charged into the extruder C forming the outer semiconductive layer 140.

Next, each extruded product from the extruders A to C is guided to the common head, and the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 are simultaneously formed on the outer periphery of the conductor 110 from the inside to the outside. Extrude.

After extrusion, at least the insulating layer 130 is crosslinked by heating by radiation from an infrared heater or by transferring heat through a heat medium such as high-temperature nitrogen gas or silicone oil in a crosslinked tube pressurized with nitrogen gas or the like. Let me. Then, the cable core after cross-linking is cooled by, for example, water.

By the above cable core forming step S300, a cable core composed of the conductor 110, the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 is formed.

(S400: Shielding layer forming step)
After the cable core is formed, the shielding layer 150 is formed on the outside of the outer semi-conductive layer 140, for example, by winding a copper tape.

(S500: sheath forming step)
After the shielding layer 150 is formed, vinyl chloride is put into an extruder and extruded to form a sheath 160 on the outer periphery of the shielding layer 150.

As described above, the power cable 10 as a solid-state insulated power cable is manufactured.

(4) Effects of the present embodiment According to the present embodiment, one or more of the following effects are exhibited.

(A) In the present embodiment, by adding an unsaturated dimer of α-aromatically substituted α-methylalkene to the electrically insulating composition, a local scorch is formed in the extrusion process of the electrically insulating composition. Can be suppressed. As a result, it is possible to suppress the formation of a local electric field concentration portion caused by the scorch. In addition, by adding an unsaturated dimer of α-aromatically substituted α-methylalkene to the electrically insulating composition, electrons are added to the aromatic ring of the unsaturated dimer of α-aromatically substituted α-methylalkene. Can be trapped to form a stable resonance structure. As a result, the local bias of electrons can be suppressed, that is, the formation of a local electric field concentration portion can be suppressed. By suppressing the formation of the local electric field concentration portion, it is possible to suppress the aggregation of water in the electric field concentration portion. As a result, it is possible to suppress the occurrence of mechanical strain caused by the water agglomerated portion. As a result, the generation of water trees in the insulating layer 130 can be suppressed.

(B) In the present embodiment, by adding the fatty acid amide to the electrically insulating composition, the fatty acid amide can act as a lubricant and the fluidity of the electrically insulating composition in the extrusion step of the insulating layer 130 can be improved. .. Thereby, each material in the electrically insulating composition can be uniformly dispersed. By uniformly dispersing the fatty acid amide in the electrically insulating composition, the polar group (hydrophilic group) of the fatty acid amide can be dispersed. As a result, the water that has entered the electrically insulating composition can be dispersed by the polar groups, and the local concentration of water in the electrically insulating composition can be suppressed. By suppressing the local concentration of water, it is possible to suppress the occurrence of mechanical strain caused by the water concentration portion (water agglomeration portion). As a result, the generation of water trees in the insulating layer 130 can be suppressed.

(C) According to the present embodiment, the water tree resistance can be remarkably improved by the synergistic effect of (a) and (b) described above.

Here, when only one of the unsaturated dimer of the α-aromatically substituted α-methylalkene or the fatty acid amide is added to the electrically insulating composition, the number of water trees generated in the insulating layer 130. Although the density is reduced to some extent, the maximum length of the water tree generated in the insulating layer 130 may not be shortened.

On the other hand, in the present embodiment, by adding both the unsaturated dimer of the α-aromatically substituted α-methylalkene and the fatty acid amide to the electrically insulating composition, the above-mentioned (a) and ( The synergistic effect of b) can be obtained. That is, by adding the fatty acid amide, the fluidity of the electrically insulating composition can be improved, and the unsaturated dimer of the α-aromatically substituted α-methylalkene can be uniformly dispersed in the electrically insulating composition. By uniformly dispersing the unsaturated dimer, the electron trap effect due to the aromatic ring of the unsaturated dimer can be uniformly expressed, and the formation of a local electric field concentration portion can be stably suppressed. Can be done. Furthermore, by dispersing the water that has entered the electrically insulating composition with the polar groups of the fatty acid amide, the probability that the water will concentrate in the local electric field concentration portion can be reduced. As a result, the generation of water trees in the insulating layer 130 can be stably suppressed. As a result, in the present embodiment, the maximum length of the water tree generated in the insulating layer 130 can be shortened, and the density of the number of water trees generated in the insulating layer 130 can be significantly reduced.

By significantly improving the water tree resistance in this way, it can be suitably applied to an underwater cable or a bottom cable that is constantly exposed to water. Further, by remarkably improving the water tree resistance, the configuration of the impermeable layer of the power cable 10 can be simplified. For example, the impermeable layer can be eliminated or the shielding layer can be simply configured. As a result, the cost of the power cable 10 can be reduced.

(D) By setting the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene to 0.1 parts by mass or more, the effect of suppressing the water tree by the unsaturated dimer can be sufficiently obtained. .. On the other hand, by setting the content of the unsaturated dimer to 10 parts by mass or less, it is possible to crosslink a predetermined amount of the base resin and suppress a decrease in the gel fraction of the electrically insulating composition. As a result, it is possible to suppress an increase in the dielectric loss tangent when a predetermined AC electric field is applied, and it is possible to suppress a decrease in the tensile characteristics of the insulating layer 130 (decrease in tensile strength and shortening in tensile elongation).

(E) By setting the content of the fatty acid amide to 0.05 parts by mass or more, the effect of suppressing the water tree by the fatty acid amide can be sufficiently obtained. On the other hand, by setting the content of the fatty acid amide to 1.0 part by mass or less, it is possible to suppress the generation of bloom due to the difference in compatibility between the base resin and the fatty acid amide.

According to the present embodiment, as described in (a) to (e) above, it is possible to improve the water tree resistance while ensuring various cable characteristics (electrical characteristics, tensile characteristics, bloom suppression characteristics). ..

(F) The fatty acid amide added to the electrically insulating composition is preferably a fatty acid monoamide. Thereby, the polarity of the fatty acid amide can be improved. By improving the polarity of the fatty acid amide, the effect of suppressing the local concentration of water by the polar group can be improved. As a result, the generation of water trees in the insulating layer 130 can be stably suppressed.

(G) The fatty acid amide added to the electrically insulating composition is preferably an unsaturated fatty acid amide. As a result, electrons can be trapped in the dispersed unsaturated bond (double bond), and local electric field concentration can be suppressed. By suppressing the formation of the local electric field concentration portion, it is possible to suppress the aggregation of water in the electric field concentration portion. As a result, the generation of water trees in the insulating layer 130 can be stably suppressed.

<Other Embodiments of the present disclosure>
Although the embodiments of the present disclosure have been specifically described above, the present disclosure is not limited to the above-described embodiments, and various changes can be made without departing from the gist thereof.

In the above-described embodiment, the case where the base resin contains polyethylene has been described, but the present disclosure is not limited to this case. For example, the base resin may contain an ethylene copolymer. Examples of the ethylene copolymer include an ethylene-propylene copolymer, an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, and an ethylene-vinyl acetate copolymer. Two or more of these may be used in combination. When the base resin contains an ethylene copolymer, the dispersibility of the unsaturated dimer of the α-aromatically substituted α-methylalkene and the fatty acid amide can be improved when the electrically insulating composition is mixed.

In the above-described embodiment, the case where the power cable 10 does not have the impermeable layer has been described, but the present disclosure is not limited to this case. The power cable 10 may have a simple water-impervious layer because it has the above-mentioned remarkable water tree suppressing effect. Specifically, the simple impermeable layer is made of, for example, a metal laminate tape. The metal laminate tape has, for example, a metal layer made of aluminum, copper, or the like, and an adhesive layer provided on one side or both sides of the metal layer. The metal laminated tape is wound by vertical attachment so as to surround the outer circumference of the cable core (outer circumference than the outer semi-conductive layer), for example. The water-impervious layer may be provided outside the shielding layer, or may also serve as a shielding layer. With such a configuration, the cost of the power cable 10 can be reduced.

In the above-described embodiment, the case where the power cable 10 is configured to be laid underwater or underwater has been described, but the present disclosure is not limited to this case. For example, the power cable 10 may be configured as a so-called overhead electric wire (overhead insulated wire).

Next, an example according to the present disclosure will be described. These examples are examples of the present disclosure, and the present disclosure is not limited to these examples.

(1) Preparation of Electrical Insulation Composition The following materials of Samples A1 to A8 and B1 to B7 were mixed by an open roll at 120 ° C. to obtain an electrical insulation composition.

[Samples A1 to A8]
(Base resin)
Low Density Polyethylene (LDPE):
(Density d = 0.92 g / cm ³ , MFR = 1.0 g / 10 min) 100 parts by mass (unsaturated dimer)
Unsaturated dimer of α-methylstyrene (2,4-diphenyl-4-methyl-1-pentene): 0.12 parts by mass or more and 8 parts by mass or less (fatty acid amide)
Stearic acid amide, oleic acid amide, erucic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide: 0.06 parts by mass or more and 0.9 parts by mass or less (crosslinking agent)
Dicumyl peroxide: 2 parts by mass, or 2,5-dimethyl-2,5-di (t-butylperoxy) hexane: 1.3 parts by mass (antioxidant)
4,4'-thiobis- (6-t-butyl-3-methylphenol): 0.2 parts by mass

[Sample B1]
It was prepared in the same manner as sample A3 except that it did not contain unsaturated dimers and fatty acid amides.
[Sample B2]
It was prepared in the same manner as sample A3 except that it did not contain fatty acid amide.
[Sample B3]
It was prepared in the same manner as sample A3 except that it did not contain an unsaturated dimer.
[Sample B4]
It was prepared in the same manner as sample A3 except that the content of the unsaturated dimer was 0.05 parts by mass.
[Sample B5]
It was prepared in the same manner as sample A3 except that the content of the unsaturated dimer was 12 parts by mass.
[Sample B6]
It was prepared in the same manner as Sample A3 except that the fatty acid amide content was 0.02 parts by mass.
[Sample B7]
It was prepared in the same manner as Sample A3 except that the fatty acid amide content was 1.5 parts by mass.

(2) Evaluation Using the above-mentioned electrical insulating composition, an insulating sheet was prepared according to each evaluation, and each evaluation was performed.

(Evaluation 1: Water tree resistance)
After forming the above-mentioned electric insulating composition, the electric insulating composition was pressed at 120 ° C. for 10 minutes by press molding to prepare two insulating sheets having a thickness of 1 mm. After producing the insulating sheet, a predetermined semi-conductive sheet was sandwiched between two insulating sheets to form a laminated sheet. After forming the laminated sheet, the base resin of the insulating sheet was crosslinked by pressing the laminated sheet at 180 ° C. for 30 minutes by press molding. After cross-linking the insulating sheet, wiring was formed for the semi-conductive sheet.

Next, with the laminated sheet immersed in a 1N NaCl aqueous solution at room temperature (27 ° C.), an AC electric field of 60 Hz 4 kV / mm was applied to the insulating sheet between the semiconductive sheet and the aqueous solution for 1000 hours.

After applying a predetermined AC electric field, the laminated sheet was dried, and the laminated sheet was boil-stained with an aqueous methylene blue solution. After dyeing the laminated sheet, the laminated sheet was sliced along the laminating direction (that is, the direction orthogonal to the main surface of the laminated sheet) to a thickness of 30 μm to form an observation slice piece. Then, by observing the observation slice piece with an optical microscope, the water tree generated in the creeping direction of the semiconductive sheet or in the direction orthogonal to the main surface of the semiconductive sheet was observed in the insulating sheet of the observation slice piece. At this time, the maximum length of the water tree generated in the insulating sheet was measured. In addition, the concentration of the number of generated water trees generated in the insulating sheet and having a length of 30 μm or more was measured. In Tables 1 and 2 described later, the "maximum length of the water tree" is obtained by rounding off the length of the water tree that was the longest among the 10 randomly selected observation slices. The “concentration of the number of generated water trees” was obtained by rounding off the average value of the concentration of the number of generated numbers of water trees in 10 randomly selected observation slice pieces.

For reference, in the conventional evaluation of water tree resistance, a power cable having an insulating layer made of a predetermined electrical insulation composition was produced, and the power cable was immersed in water to evaluate the water tree. .. At this time, a shielding layer and a sheath were provided on the outside of the insulating layer of the power cable. Therefore, the insulating layer did not come into direct contact with water. On the other hand, in this example, as described above, the laminated sheet was directly immersed in a predetermined aqueous solution to evaluate the water tree. Therefore, the insulating sheet was brought into direct contact with the aqueous solution. Therefore, the evaluation of the water tree resistance in this example was performed under stricter conditions as compared with the evaluation using the conventional power cable.

(Evaluation 2: Dissipation factor)
After forming the above-mentioned electric insulating composition, the electric insulating composition was pressed at 180 ° C. for 30 minutes by press molding to prepare an insulating sheet having a thickness of 0.2 mm. At this time, the base resin of the insulating sheet was crosslinked by pressing the insulating sheet at 180 ° C. for 30 minutes.

Next, using a shaving bridge, an AC electric field of 9 kV / mm was applied to the insulating sheet at 90 ° C., and the dielectric loss tangent was measured.

(Evaluation 3: AC breaking electric field)
An insulating sheet similar to Evaluation 2 described above was produced. Next, at room temperature (27 ° C.), an AC voltage of 5 kV was applied to the insulating sheet for 1 minute. After that, the AC voltage to the insulating sheet was boosted by 1 kV, and the cycle of applying the AC voltage to the insulating sheet for 1 minute was repeated. Then, the electric field when dielectric breakdown occurred in the insulating sheet was measured.

(Evaluation 4: Gel fraction (crosslinking degree))
After forming the above-mentioned electric insulating composition, the electric insulating composition was pressed at 180 ° C. for 30 minutes by press molding to prepare an insulating sheet having a thickness of 1 mm. At this time, the base resin of the insulating sheet was crosslinked by pressing the insulating sheet at 180 ° C. for 30 minutes.

After preparing the insulating sheet, the gel fraction was measured according to JIS C3005. Specifically, first, the mass of the insulating sheet was measured. Next, the insulating sheet was immersed in a predetermined solvent (for example, thermal xylene) to dissolve the insulating sheet. At this time, the portion of the insulating sheet in which the base resin was crosslinked remained as a gel without being dissolved. After the insulating sheet was dissolved, the mass of the gel remaining undissolved was measured. As a result, the "gel fraction" was obtained by calculating the ratio (%) of the mass of the remaining gel to the mass of the insulating sheet before dissolution.

(Evaluation 5: Tensile characteristics)
An insulating sheet similar to the above-mentioned evaluation 4 was produced. Next, the tensile strength and tensile elongation of the insulating sheet were measured according to JIS C3005. Specifically, the tensile strength and tensile elongation of the insulating sheet were measured by pulling the insulating sheet at a tensile speed of 200 mm / min using a JIS-3 dumbbell.

(Evaluation 6: Bloom)
The pellets of the electrically insulating composition were kept in a constant temperature bath at 80 ° C. for 10 days, and then the surface thereof was visually observed. By observing the pellets, the presence or absence of bloom deposited on the pellet surface was evaluated. The case where there was no bloom was given as "A", and the case where there was bloom was given as "B".

(3) Results The results of evaluation of each sample will be described using Tables 1 and 2 below. In Table 1 below, the unit of the content of the compounding agent is "part by mass".

As shown in Table 2, in sample B1 to which both the unsaturated dimer and the fatty acid amide were not added, the concentration of the number of generated water trees was high, and the maximum length of the water trees was also long. Further, in the samples B2 and B3 to which only one of the unsaturated dimer and the fatty acid amide was added, the concentration of the number of water trees generated was lower than that of the sample B1, but the maximum length of the water tree was the sample B1. It was as long as.

On the other hand, as shown in Table 1, in the samples A1 to A8 to which both the unsaturated dimer and the fatty acid amide were added, the concentration of the number of water trees generated was significantly lower than that in the samples B1 to B3. , 150 pieces / cm ³ or less. Further, in the samples A1 to A8, the maximum length of the water tree was shorter than that of the samples B1 to B3, and was 180 μm or less.

According to these results, the addition of both unsaturated dimers and fatty acid amides reduced the maximum length of the water tree generated in the insulating layer due to their synergistic effect. At the same time, it was confirmed that the density of the number of water trees generated in the insulating layer could be significantly reduced.

Further, as shown in Table 2, in the sample B4 in which the content of the unsaturated dimer was less than 0.1 parts by mass, the concentration of the number of generated water trees was lower than that of the sample B1, but 200 pieces. It was / cm ³ or more. Further, in sample B4, the maximum length of the water tree was slightly shorter than that of each of samples B1 to B3, but it was more than 200 μm.

On the other hand, as shown in Table 1, in the samples A1 to A8 in which the content of the unsaturated dimer was 0.1 parts by mass or more, the concentration of the number of water trees generated was significantly lower than that of the sample B4. Was there. Further, in the samples A1 to A8, the maximum length of the water tree was shorter than that of the sample B4.

Based on these results, it was confirmed that by setting the content of the unsaturated dimer to 0.1 parts by mass or more, the effect of suppressing the water tree by the unsaturated dimer could be sufficiently obtained.

Further, as shown in Table 2, the gel fraction was low in sample B5 in which the content of the unsaturated dimer was more than 10 parts by mass. Therefore, in sample B5, the dielectric loss tangent was large and the AC fracture electric field was low. Further, in sample B5, the tensile characteristics were deteriorated.

On the other hand, as shown in Table 1, in the samples A1 to A8 in which the content of the unsaturated dimer was 10 parts by mass or less, the gel fraction was higher than that of the sample B5 and was 74% or more. As a result, in the samples A1 to A8, the dielectric loss tangent was smaller than that of the sample B5 and was 0.05 or less. Further, in the samples A1 to A8, the AC breaking electric field was higher than that of the sample B5 and was 64 kV / mm or more. Further, in the samples A1 to A8, the tensile properties were improved as compared with the sample B5. Specifically, in the samples A1 to A8, the tensile strength was 14 MPa or more and the tensile elongation was 430% or more.

According to these results, by setting the content of the unsaturated dimer to 10 parts by mass or less, it is possible to crosslink a predetermined amount of the base resin and suppress a decrease in the gel fraction of the electrically insulating composition. I confirmed that. As a result, it was confirmed that the increase in the dielectric loss tangent when a predetermined AC electric field was applied could be suppressed, and the decrease in the tensile characteristics of the insulating layer could be suppressed.

Further, as shown in Table 2, in sample B6 in which the fatty acid amide content was less than 0.05 parts by mass, the concentration of the number of water trees generated was lower than that in sample B1, but 200 pieces / cm ³ That was all. Further, in sample B6, the maximum length of the water tree was slightly shorter than that of each of samples B1 to B3, but it was more than 200 μm.

On the other hand, as shown in Table 1, in the samples A1 to A8 having the fatty acid amide content of 0.05 parts by mass or more, the concentration of the number of generated water trees was significantly lower than that of the sample B6. Further, in the samples A1 to A8, the maximum length of the water tree was shorter than that of the sample B6.

From these results, it was confirmed that the effect of suppressing the water tree by the fatty acid amide could be sufficiently obtained by setting the content of the fatty acid amide to 0.05 parts by mass or more.

Further, as shown in Table 2, bloom was generated in the sample B7 in which the fatty acid amide content was more than 1.0 part by mass.

On the other hand, as shown in Table 1, blooms were not generated in the samples A1 to A8 having the fatty acid amide content of 1.0 part by mass or less.

According to these results, by setting the fatty acid amide content to 1.0 part by mass or less, it was possible to suppress the generation of bloom due to the difference in compatibility between the base resin and the fatty acid amide. confirmed.

Further, as shown in Table 1, in the samples A1 to A8, the ratio B / A of the content B of the unsaturated dimer of the α-aromatically substituted α-methylalkene to the content A of the fatty acid amide is 0. It was more than .5 and less than 15. By setting the content ratio B / A to more than 0.5, as described above, the remarkable effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer could be stably obtained. It was confirmed. Further, it was confirmed that by setting the content ratio B / A to less than 15, the unsaturated dimer could be uniformly dispersed and the decrease in the gel fraction could be stably suppressed. As a result, it was confirmed that the increase in the dielectric loss tangent and the decrease in the tensile property of the insulating layer could be stably suppressed. In addition, by setting the content ratio B / A to less than 15, the effect of suppressing the local concentration of water by the polar group of the fatty acid amide makes the effect of suppressing the water tree by both the fatty acid amide and the unsaturated dimer remarkable. It was confirmed that it was sufficiently obtained.

As described above, according to the samples A1 to A8, a remarkable water tree suppressing effect could be confirmed under severe conditions in which the insulating sheet was in direct contact with the aqueous solution. Therefore, it was confirmed that the generation of water tree in the insulating layer can be stably suppressed by producing the power cable having the insulating layer composed of the respective electrical insulating compositions of the samples A1 to A8.

<Preferable aspect of the present disclosure>
Hereinafter, preferred embodiments of the present disclosure will be added.

(Appendix 1)
100 parts by mass of base resin containing polyethylene,
The unsaturated dimer of α-aromatically substituted α-methylalkene is 0.1 parts by mass or more and 10 parts by mass or less.
Fatty acid amide in an amount of 0.05 parts by mass or more and 1.0 part by mass or less.
An electrically insulating composition having.

(Appendix 2)
The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
The electrical insulation composition according to Appendix 1, wherein the maximum length of the water tree generated in the electrical insulation composition is less than 200 μm.

(Appendix 3)
The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
The electrical insulation composition according to Appendix 1 or Appendix 2, wherein the concentration of the number of generated water trees generated in the electrical insulation composition and having a length of 30 μm or more is less than 200 cells / cm ³ .

(Appendix 4)
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 3, wherein the fatty acid amide is composed of a fatty acid monoamide.

(Appendix 5)
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 4, wherein the fatty acid amide comprises an unsaturated fatty acid amide.

(Appendix 6)
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 5, which has a cross-linking agent containing an organic peroxide.

(Appendix 7)
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 5, wherein the base resin is crosslinked.

(Appendix 8)
The ratio of the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene to the content of the fatty acid amide is more than 0.5 and less than 15, in any one of Supplements 1 to 7. The electrically insulating composition according to the description.

(Appendix 9)
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 100 parts by mass of a base resin containing polyethylene, 0.1 parts by mass or more and 10 parts by mass or less of an unsaturated dimer of α-aromatically substituted α-methylalkene, and 0.05 parts by mass of fatty acid amide. A power cable composed of an electrically insulating composition having a mass of parts or more and 1.0 part by mass or less.

(Appendix 10)
The process of preparing the electrical insulation composition and
A step of forming an insulating layer so as to cover the outer periphery of the conductor using the electrically insulating composition, and
With
In the step of preparing the electrically insulating composition,
1. 100 parts by mass or more of the base resin containing polyethylene, 0.1 parts by mass or more and 10 parts by mass or less of the unsaturated dimer of the α-aromatically substituted α-methylalkene, and 0.05 parts by mass or more of the fatty acid amide. A method for producing a power cable, which is formed by mixing 0 parts by mass or less with 0 parts by mass or less to form the electrically insulating composition.

10 Power cable 110 Conductor 120 Inner semi-conductive layer 130 Insulation layer 140 External semi-conductive layer 150 Shielding layer 160 Sheath

Claims (9)

100 parts by mass of base resin containing polyethylene,
The unsaturated dimer of α-aromatically substituted α-methylalkene is 0.1 parts by mass or more and 10 parts by mass or less.
Fatty acid amide in an amount of 0.05 parts by mass or more and 1.0 part by mass or less.
An electrically insulating composition having. The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
The electrically insulating composition according to claim 1, wherein the maximum length of the water tree generated in the electrically insulating composition is less than 200 μm. The electrically insulating composition having the base resin, the unsaturated dimer of the α-aromatically substituted α-methylalkene, and the fatty acid amide is immersed in a 1N NaCl aqueous solution at room temperature. When an AC electric field with a commercial frequency of 4 kV / mm was applied for 1000 hours,
The generation number concentration of electrical insulation occurred composition water trees having longer than 30μm, the electrical insulation composition according to claim 1 or claim 2 which is less than 200 atoms / cm ^3. The electrically insulating composition according to any one of claims 1 to 3, wherein the fatty acid amide comprises a fatty acid monoamide. The electrically insulating composition according to any one of claims 1 to 4, wherein the fatty acid amide comprises an unsaturated fatty acid amide. The electrically insulating composition according to any one of claims 1 to 5, which has a cross-linking agent containing an organic peroxide. The electrically insulating composition according to any one of claims 1 to 5, wherein the base resin is crosslinked. The ratio of the content of the unsaturated dimer of the α-aromatically substituted α-methylalkene to the content of the fatty acid amide is more than 0.5 and less than 15, any one of claims 1 to 7. The electrically insulating composition according to the section. With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 100 parts by mass of a base resin containing polyethylene, 0.1 parts by mass or more and 10 parts by mass or less of an unsaturated dimer of α-aromatically substituted α-methylalkene, and 0.05 parts by mass of fatty acid amide. A power cable composed of an electrically insulating composition having a mass of parts or more and 1.0 part by mass or less.

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