JP2020169282A - Electric insulation composition and power cable - Google Patents

Abstract

To improve water tree resistance.SOLUTION: An electric insulation composition contains: a base resin containing 100 pts.mass of the total of 40 pts.mass or more and 90 pts.mass or less of first polyethylene having a density of 0.91 g/cm3 or more and 0.93 g/cm3 or less, and 10 pts.mass or more and 60 pts.mass or less of second polyethylene having a density of 0.855 g/cm3 or more and 0.890 g/cm3 or less; 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
The first polyethylene and 40 parts by mass or more and 90 parts by weight or less of the density is less than 0.91 g / cm ³ or more 0.93 g / cm ^3, density of 0.855 g / cm ³ or more 0.890 g / cm ³ or less A base resin containing 10 parts by mass or more and 60 parts by mass or less of a second polyethylene in a total of 100 parts by mass.
Contains 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide.
An electrically insulating composition 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 40 parts by mass or more and 90 parts by mass or less of the first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ , and a density of 0.855 g / cm ³ or more and 0.890 g. A base resin containing 10 parts by mass or more and 60 parts by mass or less of the second polyethylene having a / cm ³ or less, and 100 parts by mass or less in total, and 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide. Consists of the contained electrical insulating composition,
A power cable 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 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 used for an electric insulation composition constituting an insulating layer of a power cable in order to further improve the water tree resistance. Specifically, the base resin and the lubricant added to the base resin were examined from various materials constituting the electrically insulating composition. As a result of the examination, it was found that at least two types of polyethylene having different densities should be used in combination as the base resin and fatty acid amide should be used as the lubricant. It has been found that the water tree resistance of the insulating layer can be remarkably improved by adopting such a composition.

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
The first polyethylene and 40 parts by mass or more and 90 parts by weight or less of the density is less than 0.91 g / cm ³ or more 0.93 g / cm ^3, density of 0.855 g / cm ³ or more 0.890 g / cm ³ or less A base resin containing 10 parts by mass or more and 60 parts by mass or less of a second polyethylene in a total of 100 parts by mass.
It contains 0.05 parts by mass or more and 1.0 parts by mass or less of fatty acid amide.
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],
An unsaturated dimer of α-aromatically substituted α-methylalkene is further contained in an amount of 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.
According to this configuration, the water tree resistance can be further improved.

[3] In the electrically insulating composition according to the above [1] or [2],
When the electric insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the electric insulating composition 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.

[4] In the electrically insulating composition according to any one of the above [1] to [3].
When the electrically insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the crosslinked product 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.

[5] In the electrically insulating composition according to any one of the above [1] to [4].
The melting point of the second polyethylene is 55 ° C. or higher and 100 ° C. or lower.
According to this configuration, the water tree resistance can be improved with a small content, so that the ratio of the first polyethylene can be increased and the various characteristics of the cable can be further improved.

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

[7] In the electrically insulating composition according to any one of the above [1] to [6].
The fatty acid amide is a monoamide.
According to this configuration, the effect of suppressing the local concentration of water by the polar group can be improved.

[8] In the electrically insulating composition according to any one of the above [1] to [7],
It further contains 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.

[9] In the electrically insulating composition according to any one of the above [1] to [8],
The base resin is crosslinked.
According to this configuration, the mechanical properties and electrical properties of the electrically insulating composition can be improved.

[10] 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 40 parts by mass or more and 90 parts by mass or less of the first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ , and a density of 0.855 g / cm ³ or more and 0.890 g. A base resin containing 10 parts by mass or more and 60 parts by mass or less of the second polyethylene having a / cm ³ or less, and 100 parts by mass or less in total, and 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide. It is composed of an electrically insulating composition contained therein.
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, a base resin, a fatty acid amide, and other components, if necessary. It has an additive and.

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 this embodiment contains at least two polyethylenes having different densities. Specifically, a first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ (hereinafter, also simply referred to as a first PE) and a density of 0.855 g / cm ³ or more and 0.890 g. Includes a second polyethylene of / cm ³ or less (hereinafter, also simply referred to as a second PE).

By adding the first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ to the electrical insulating composition, the insulating property and mechanical properties of the insulating layer in the power cable are improved, and the mechanical properties are also improved. The dielectric tangent can be kept low. Moreover, when mixed with the second polyethylene having a relatively low density, the effect of the second PE can be brought out more highly.

The first polyethylene is not particularly limited as long as it has a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ , and 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 or less) and the like can be used. Among these, LDPE is preferable. According to LDPE, the water tree resistance can be made higher in the insulating layer as well as the cable characteristics such as insulation and mechanical properties as compared with polyethylene having other densities.

Electrical insulating composition, by the density is added with 0.855 g / cm ³ or more 0.890 g / cm ³ or less is a second polyethylene (first 2PE) a first polyethylene (first 1PE), an insulating layer Not only can the insulation and mechanical properties be improved, but the occurrence of mechanical stress cracks in the insulating layer can be suppressed. Thereby, the water tree resistance of the insulating layer can be improved.

The second PE is not particularly limited as long as the density is within the above range, and for example, ultra-low density polyethylene (VLDPE) can be used. The crystallinity is not particularly limited, and either high crystallinity or low crystallinity can be used. Specifically, VLDPE having crystallinity such that the melting point is 55 ° C. or higher and 125 ° C. or lower can be used. As the second PE, one having a predetermined crystallinity may be used according to the characteristics required for the insulating layer. Specifically, from the viewpoint of improving the water tree resistance of the insulating layer, it has a lower crystallinity having a melting point of 55 ° C. or higher and 100 ° C. or lower than that of a highly crystalline VLDPE having a melting point of 115 ° C. or higher and 125 ° C. or lower. VLDPE is more preferred. According to the low crystallinity VLDPE, the water tree resistance of the insulating layer can be improved with a smaller content as compared with the highly crystalline one. Moreover, since the ratio of VLDPE to the electrically insulating composition can be lowered and the ratio of the first PE having a higher density can be increased, not only the insulating property and mechanical properties of the insulating layer can be further improved, but also the dielectric loss tangent can be suppressed low. Can be done. On the other hand, from the viewpoint of processability of the insulating layer, the second PE preferably has high crystallinity rather than low crystallinity. The melting point of the second polyethylene is a value measured by differential scanning calorimetry.

The contents of the first PE and the second PE in the base resin are 40 parts by mass or more and 90 parts by mass or less for the first PE and 10 parts by mass or more and 60 parts by mass or less for the second PE so that the total is 100 parts by mass. .. From the viewpoint of obtaining the cable characteristics of the insulating layer and the water tree resistance in a well-balanced manner at a high level, it is preferable that the first PE is 60 parts by mass to 90 parts by mass or less and the second PE is 10 parts by mass to 40 parts by mass or less. The content of the second PE may be appropriately changed depending on its melting point. For example, when the melting point of the second PE is 115 ° C. or higher and 125 ° C. or lower, it may be 10 parts by mass or more and 60 parts by mass or less. Further, for example, when the melting point is as low as 55 ° C. or higher and 100 ° C. or lower, it is preferably 10 parts by mass or more and 40 parts by mass in consideration of the crushability of the insulating layer 130.

(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. Thereby, the above-mentioned first and second polyethylenes can be uniformly dispersed. 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 preferably has one amide group and is preferably a monoamide from the viewpoint of improving the effect of suppressing the local concentration of water by the polar group. Specifically, it is preferably a saturated fatty acid monoamide or an unsaturated fatty acid monoamide. On the other hand, the fatty acid amide is preferably having an unsaturated group (double bond) from the viewpoint of trapping electrons in the insulating layer and suppressing local electric field concentration. Specifically, it is preferably unsaturated fatty acid monoamide or unsaturated fatty acid bisamide. Among these, unsaturated fatty acid monoamide is particularly preferable because it can suppress both local concentration of water due to polar groups and electric field concentration due to unsaturated groups at the same time.

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.

(Other additives)
In addition to the base resin and fatty acid amide described above, the electrically insulating composition may further contain other additives, if necessary. As other additives, for example, an unsaturated dimer of α-aromatically substituted α-methylalkene, a cross-linking agent, an antioxidant and the like can be used.

(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. Thereby, the generation of the water tree in the insulating layer 130 can be suppressed. Moreover, since the fatty acid amide is added in the present embodiment, the water tree resistance can be remarkably improved by the synergistic action of the unsaturated dimer and the fatty acid amide. 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.

The content of the unsaturated dimer of the α-aromatically substituted α-methylalkene is not particularly limited, but if it is excessively small, the scorch in the electrically insulating composition and the generation of water tree in the insulating layer are sufficient. It may not be suppressed. On the other hand, if it is excessively large, it becomes difficult to crosslink the electrically insulating composition, and the degree of cross-linking (gel fraction) of the insulating layer may decrease. As a result, the dielectric loss tangent when a predetermined AC electric field is applied to the insulating layer is increased, or the tensile characteristics of the insulating layer 130 are deteriorated (at least one of a decrease in tensile strength and a shortening in tensile elongation occurs. )there is a possibility. Therefore, from the viewpoint of suppressing the generation of scorch and water tree and maintaining a high gel content of the insulating layer, the content of the unsaturated dimer is 0.1 part by mass with respect to 100 parts by mass of the base resin. It is preferably 10 parts by mass or less, and more preferably 0.3 parts by mass or more and 8 parts by mass or less. By setting such a content, 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 reduce the tensile characteristics of the insulating layer 130 (decrease in tensile strength and shortening in tensile elongation). It can be suppressed.

(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.

Examples of the antioxidant added to the electrically insulating composition 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 ] Butyl 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, the insulating layer 130 contains the fatty acid amide with respect to the base resin containing the first and second PEs in a predetermined ratio, so that the water tree resistance of the insulating layer 130 is remarkable. Has improved. As a result, the concentration of the number of generated water trees in the insulating layer 130 can be kept low, and the length of the generated water trees can be shortened.

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. If no water tree is generated, the maximum length of the water tree is 0 μm.

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, more preferably 100 pieces / 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. If the water trees is not generated generated number concentration becomes 0 / cm ^3.

(Gel fraction (crosslinking degree))
In this embodiment, as described above, the insulating layer 130 is, for example, crosslinked. The degree of cross-linking of the insulating layer 130 is not particularly limited, but the gel fraction is preferably 75% or more from the viewpoint of keeping the dielectric loss tangent described later small while maintaining high insulating properties and mechanical properties. The gel fraction of the electrically insulating composition is better, and is not limited, but is, for example, 95% or less.

(Dissipation factor)
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.

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).

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, 0.04% 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, 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, the insulating property can be maintained high and a predetermined AC breaking electric field is secured. ing.

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 preferably 65 kV / mm or more, for example.

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, the insulating layer 130 is composed of the above-mentioned electrical insulating composition, and is preferably further crosslinked to have high tensile properties as mechanical properties.

Specifically, in the present embodiment, the tensile strength of the electrically insulating composition constituting the insulating layer 130 is, for example, 12 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, 550% 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 the present embodiment, the base resin containing the first and second polyethylenes, the fatty acid amide, and other additives are mixed so as to have the above-mentioned predetermined composition, and the mixture is mixed with a Banvarimixer, a kneader, or the like. Mix (knead) with a machine to form a mixed material.

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, as the base resin of the electrical insulation composition, and density of 0.91 g / cm ³ or more 0.93 g / cm second 1PE 40 parts by mass to 90 parts by weight is less than ^3, the density is 0 .855g / cm ³ or more 0.890 g / cm ³ and in which the 2PE below are used so that 100 parts by weight in total of 10 parts by mass to 60 parts by weight. According to the first PE having a relatively high density, the insulating property and mechanical properties of the insulating layer 130 can be improved, and the dielectric loss tangent can be suppressed low. On the other hand, according to the second PE having a relatively low density, not only the insulating property and the mechanical properties can be improved, but also the occurrence of mechanical stress cracks in the insulating layer 130 can be suppressed. Specifically, even when the electric field is locally concentrated in the insulating layer 130 and water aggregates, the occurrence of mechanical distortion due to the aggregation of water is suppressed to allow water to permeate into the insulating layer 130. It can be suppressed. As a result, the generation of water trees in the insulating layer 130 can be suppressed. Then, by mixing the first and second PEs with a predetermined composition, various cable characteristics required for the cable such as insulation, mechanical properties, and dielectric loss tangent, and water tree resistance can be obtained in a well-balanced manner at a high level. be able to.

(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. .. As a result, the first and second PEs and other additives in the electrically insulating composition can be uniformly dispersed, and the effects of each PE can be synergistically obtained. Further, 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. By dispersing the polar groups, it is possible to suppress the local concentration of water, thus reducing the permeation of water into the insulating layer and suppressing the mechanical strain in the insulating layer due to the concentration of water. Can be done. As a result, the generation of mechanical stress cracks in the insulating layer can be suppressed, and the generation of water trees can be suppressed.

(C) According to the present embodiment, the water tree resistance of the insulating layer can be remarkably improved by the synergistic effect of (a) and (b) described above, and the concentration of the number of generated water trees is reduced. At the same time, the maximum length of the water tree can be shortened.

Here, when only one of the first and second PEs is used as the base resin and only one of them is not added, or when the fatty acid amide is not added, the concentration of the number of generated water trees in the insulating layer 130 is increased. Although it can be reduced to a certain extent, the maximum length of the water tree may increase due to the locally concentrated permeation of water.

On the other hand, by configuring the insulating layer 130 as described above, the synergistic effect of (a) and (b) can be obtained. That is, the fatty acid amide prevents water from being locally attracted to the insulating layer 130, thereby suppressing the local concentration of water and the resulting mechanical strain in the insulating layer. can do. Further, by using the first and second PEs in combination as the base resin in a predetermined ratio, even if local concentration of water occurs, mechanical stress cracks due to mechanical strain occur in the insulating layer 130. Occurrence can be suppressed. As a result, in the insulating layer 130, the concentration of the number of generated water trees can be remarkably reduced, and the maximum length of the water trees can be significantly shortened.

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 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 (d) above, it is possible to improve the water tree resistance while ensuring various cable characteristics (electrical characteristics, tensile characteristics, bloom suppression characteristics). ..

(E) In the present embodiment, it is preferable to further add an unsaturated dimer of α-aromatically substituted α-methylalkene to the electrically insulating composition. According to the unsaturated dimer, the generation of local scorch (burnt) can be suppressed in the extrusion process of the electrically insulating composition. 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.

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.

(F) In the present embodiment, the melting point of the second polyethylene is preferably 55 ° C. or higher and 100 ° C. or lower. According to the second PE having such a melting point, since it has low crystallinity, the water tree resistance of the insulating layer 130 can be improved even with a small content. Moreover, since the ratio of the first PE can be increased by the amount of the reduced content, not only the insulating property and mechanical properties of the insulating layer 130 can be further improved, but also the dielectric loss tangent can be suppressed low.

(G) Further, in the present embodiment, the melting point of the second polyethylene is preferably 115 ° C. or higher and 125 ° C. or lower. By using a second PE having a relatively high crystallinity, the processability of the electrically insulating composition can be improved. Thereby, for example, the insulating layer 130 can be formed to have a uniform thickness, or can be easily formed to improve the production efficiency.

(H) The fatty acid amide added to the electrically insulating composition is preferably a monoamide having one amide group. According to monoamide, the polarity of fatty acid amide can be improved as compared with bisamide having two amide groups. 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.

(I) The fatty acid amide added to the electrically insulating composition preferably has an unsaturated group. According to such a fatty acid amide, 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 In this example, the following materials were used as the materials for the electrical insulation materials.

The following was used as the polyethylene constituting the base resin.
-Low density polyethylene (LDPE, density d = 0.920 g / cm ³ , MFR = 1 g / 10 min)
Ultra-low density polyethylene 1 (VLDPE 1, density d = 0.857 g / cm ³ , MFR = 1 g / 10 min, mp = 38 ° C)
-Ultra low density polyethylene 2 (VLDPE2, density d = 0.885 g / cm ³ , MFR = 1 g / 10 min, mp = 77 ° C)
Ultra-low density polyethylene 3 (VLDPE3, density d = 0.866 g / cm ³ , MFR = 1 g / 10 min, mp = 121 ° C)
Ultra-low density polyethylene 4 (VLDPE 4, density d = 0.902 g / cm ³ , MFR = 1 g / 10 min, mp = 104 ° C)

The following were used as fatty acid amides.
-Stearic acid amide, oleic acid amide, erucic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide

The following were used as unsaturated dimers.
・ Α-Methylstyrene dimer

The following were used as the cross-linking agent.
・ Dicumyl peroxide ・ 2,5-dimethyl-2,5-di (t-butylperoxy) hexane

The following were used as antioxidants.
4,4'-thiobis- (6-t-butyl-3-methylphenol)

(Samples A1 to A5)
As shown in Table 1 below, sample A1 contains 80 parts by mass of LDPE as the first polyethylene, 20 parts by mass of VLDPE2 as the second polyethylene, 0.1 parts by mass of stearate amide as the fatty acid amide, and 0.1 parts by mass as the cross-linking agent. 2 parts by mass of dicumyl peroxide and 0.2 parts by mass of 4,4'-thiobis- (6-t-butyl-3-methylphenol) as an antioxidant are mixed and 120 by mass on an open roll. It was prepared by kneading at ° C. Samples A2 to A5 were prepared in the same manner as Sample A1 except that the type of fatty acid amide was changed. In Table 1 below, the unit of the content of the compounding agent is "part by mass".

(Samples A6 and A7)
Samples A6 and A7 were prepared in the same manner as Sample A3, except that the type of the second polyethylene was changed from VLDPE2 to VLDPE1 or VLDPE3, respectively.

(Samples A8 to A11)
Samples A8 and A9 were prepared in the same manner as Sample A6 except that the ratio of the first and second polyethylenes was changed from 80:20 to 90:10 or 40:60.
Samples A10 and A11 were prepared in the same manner as Sample A7 except that the ratio of the first and second polyethylenes was changed from 80:20 to 90:10 or 40:60.

(Samples A12, A13)
Sample A12 was prepared in the same manner as Sample A3 except that an unsaturated dimer was added to Sample A3.
Sample A13 was prepared in the same manner as Sample A3 except that the type of cross-linking agent was changed.

(Sample B1)
As shown in Table 2 below, sample B1 was prepared in the same manner as sample A3, except that the second polyethylene was not used in combination and only LDPE was used as the first polyethylene. In Table 2 below, the unit of the content of the compounding agent is "part by mass".

(Samples B2 and B3)
Samples B2 and B3 were prepared in the same manner as Sample A3 except that the ratio of the first and second polyethylenes was changed from 80:20 to 93: 7 or 35:65.

(Samples B4 and B5)
Sample B4 was prepared in the same manner as Sample A3 except that VLDPE4 having a density of 0.902 g / cm ³ was used instead of the second polyethylene.
Sample B5 was prepared in the same manner as Sample B4 except that the amount of VLDPE4 added was changed to 55 parts by mass and the amount of LDPE added was changed to 45 parts by mass.

(Samples B6 and B7)
Samples B6 and B7 were prepared in the same manner as Sample A3, except that the amounts of fatty acid amide added were changed to 0.02 parts by mass and 1.5 parts by mass, respectively.

(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 are shown in Tables 1 and 2 above.

As shown in Table 2, in sample B1, since only the first polyethylene was used without using the second polyethylene in combination, the concentration of the number of water trees generated was high and the maximum length of the water tree was also large. confirmed.

On the other hand, as shown in Table 1, in the samples A1 to A13 in which the first and second polyethylenes were used in combination and the fatty acid amide was added, the concentration of the number of water trees generated was significantly lower than that in the sample B1. cage, was less than 200 / cm ^3. Further, in Samples A1 to A13, the maximum length of the water tree was shorter than that of Sample B1, and it was confirmed that Sample B1 was 270 μm, whereas it was 200 μm or less.

According to these results, by using the first and second polyethylenes in combination and adding the fatty acid amide, the maximum length of the water tree generated in the insulating layer can be shortened due to these synergistic effects. It was confirmed that the concentration of the number of generated water trees in the insulating layer can be significantly reduced.

Further, according to the samples A1 to A5, the samples A2 and A3 using the unsaturated fatty acid monoamide having an unsaturated group as the saturated fatty acid and being a monoamide are the samples A1 using the saturated fatty acid amide and saturated or unsaturated. It was confirmed that the concentration of the number of water trees generated can be reduced and the maximum length of the water tree can be shortened as compared with the samples A4 and A5 using the saturated fatty acid bisamide.

Further, according to the samples A3, A6, and A7, it was confirmed that the lower the melting point and the lower the crystallinity of the second polyethylene, the higher the cable characteristics can be maintained and the water tree resistance can be improved. .. Specifically, the maximum length of the water tree is 50 μm for sample A3 using VLDPE2 having a melting point of 77 ° C. and 40 μm for sample A7 using VLDPE3 having a melting point of 121 ° C., whereas the melting point is 38 ° C. It was confirmed that the maximum length of sample A6 using VLDPE1 was 30 μm, which was shorter. Moreover, the generation number concentration of water trees, whereas a sample in A3 and A7 50 pieces / cm ^3, a sample A6 the 40 / cm ^3, can be reduced more also generated number was confirmed.

Further, according to Samples A3, A8 and A9, or Samples A7, A10 and A11, the higher the ratio of the first polyethylene having a high density, the more various cable characteristics such as dielectric tangent, insulating property and tensile property can be improved. It was confirmed that the higher the ratio of the second polyethylene having a lower density, the higher the water tree resistance.

Further, according to the samples A3 and A12, the sample A12 to which the unsaturated dimer is further added has a shorter maximum length of the water tree and a lower concentration of the number of occurrences than the sample A3 without the addition. Was confirmed. From this, it was confirmed that the addition of the unsaturated dimer can further improve the water tree resistance.

Further, according to the samples A3 and A13, it was confirmed that various cable characteristics and water tree resistance can be obtained in a well-balanced manner at a high level regardless of the type of the cross-linking agent.

Further, according to the samples B2 and B3, the ratio of the second polyethylene is excessively small or high, so that the water tree resistance is lower than that of the sample A3, and the characteristics in terms of dielectric loss tangent and tensile characteristics are improved. It was confirmed that it was low.

Further, according to the samples B4 and B5, it was confirmed that the water tree resistance could not be sufficiently improved when VLDPE4 having a density of 0.902 g / cm ³ and a density higher than that of the second polyethylene was used.

Further, according to the samples B6 and B7, it was confirmed that the water tree could not be sufficiently suppressed when the fatty acid amide content was excessively low, while bloom was generated when the fatty acid amide content was excessively high.

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

(Appendix 1)
The first polyethylene and 40 parts by mass or more and 90 parts by weight or less of the density is less than 0.91 g / cm ³ or more 0.93 g / cm ^3, density of 0.855 g / cm ³ or more 0.890 g / cm ³ or less A base resin containing 10 parts by mass or more and 60 parts by mass or less of a second polyethylene in a total of 100 parts by mass.
Contains 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide.
Electrical insulation composition.

(Appendix 2)
An unsaturated dimer of α-aromatically substituted α-methylalkene is further contained in an amount of 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 electrically insulating composition according to Appendix 1.

(Appendix 3)
When the electric insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the electric insulating composition for 1000 hours,
The maximum length of the water tree generated in the electrically insulating composition is less than 200 μm.
The electrically insulating composition according to Appendix 1 or Appendix 2.

(Appendix 4)
When the electrically insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the crosslinked product 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,
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 3.

(Appendix 5)
The melting point of the second polyethylene is 55 ° C. or higher and 100 ° C. or lower.
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 4.

(Appendix 6)
The content of the second polyethylene is 10 parts by mass or more and 40 parts by mass or less.
The electrically insulating composition according to Appendix 5.

(Appendix 7)
The fatty acid amide has an unsaturated group.
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 6.

(Appendix 8)
The fatty acid amide is a monoamide.
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 7.

(Appendix 9)
The fatty acid amide is an unsaturated fatty acid monoamide.
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 8.

(Appendix 10)
Further containing a cross-linking agent containing an organic peroxide,
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 9.

(Appendix 11)
The base resin is crosslinked.
The electrically insulating composition according to any one of Supplementary note 1 to Supplementary note 10.

(Appendix 12)
With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 40 parts by mass or more and 90 parts by mass or less of the first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ , and a density of 0.855 g / cm ³ or more and 0.890 g. A base resin containing 10 parts by mass or more and 60 parts by mass or less of the second polyethylene having a / cm ³ or less, and 100 parts by mass or less in total, and 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide. Consists of the contained electrical insulating composition,
Power cable.

(Appendix 13)
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,
The first polyethylene and 40 parts by mass or more and 90 parts by weight or less of the density is less than 0.91 g / cm ³ or more 0.93 g / cm ^3, density of 0.855 g / cm ³ or more 0.890 g / cm ³ or less A base resin containing 10 parts by mass or more and 60 parts by mass or less of a second polyethylene, and 100 parts by mass or less in total, and 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide are mixed, and the electricity Forming an insulating composition,
How to make a power cable.

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

Claims (10)

The first polyethylene and 40 parts by mass or more and 90 parts by weight or less of the density is less than 0.91 g / cm ³ or more 0.93 g / cm ^3, density of 0.855 g / cm ³ or more 0.890 g / cm ³ or less A base resin containing 10 parts by mass or more and 60 parts by mass or less of a second polyethylene in a total of 100 parts by mass.
Contains 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide.
Electrical insulation composition. An unsaturated dimer of α-aromatically substituted α-methylalkene is further contained in an amount of 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 electrically insulating composition according to claim 1. When the electric insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the electric insulating composition for 1000 hours,
The maximum length of the water tree generated in the electrically insulating composition is less than 200 μm.
The electrically insulating composition according to claim 1 or 2. When the electrically insulating composition is immersed in a 1N NaCl aqueous solution at room temperature and an AC electric field having a commercial frequency of 4 kV / mm is applied to the crosslinked product 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,
The electrically insulating composition according to any one of claims 1 to 3. The melting point of the second polyethylene is 55 ° C. or higher and 100 ° C. or lower.
The electrically insulating composition according to any one of claims 1 to 4. The fatty acid amide has an unsaturated group.
The electrically insulating composition according to any one of claims 1 to 5. The fatty acid amide is a monoamide.
The electrically insulating composition according to any one of claims 1 to 6. Further containing a cross-linking agent containing an organic peroxide,
The electrically insulating composition according to any one of claims 1 to 7. The base resin is crosslinked.
The electrically insulating composition according to any one of claims 1 to 8. With the conductor
An insulating layer provided so as to cover the outer periphery of the conductor,
With
The insulating layer contains 40 parts by mass or more and 90 parts by mass or less of the first polyethylene having a density of 0.91 g / cm ³ or more and less than 0.93 g / cm ³ , and a density of 0.855 g / cm ³ or more and 0.890 g. A base resin containing 10 parts by mass or more and 60 parts by mass or less of the second polyethylene having a / cm ³ or less, and 100 parts by mass or less in total, and 0.05 parts by mass or more and 1.0 part by mass or less of fatty acid amide. Consists of the contained electrical insulating composition,
Power cable.

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