Electrically insulating composition and power cable

Abstract

An electrical insulation composition comprising: a base resin comprising 100 parts by mass of polyethylene comprising 65 to 98 parts by mass and 2 to 35 parts by mass of styrene-containing resin; and a fatty acid amide comprising 0.05 to 1.0 parts by mass.

Description

Technical Field

[0001] This disclosure relates to electrical insulation compositions and power cables.

[0002] This patent application claims priority to Japanese Patent Application No. 2019-071786, filed on April 4, 2019, and invokes all the contents set forth in that Japanese patent application. Background Technology

[0003] Due to its excellent insulation properties, polyethylene is widely used as a base resin in electrical insulation compositions that form the insulation layer in power cables and the like (e.g., Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 57-69611 Summary of the Invention

[0007] According to one aspect of the present disclosure, an electrical insulating composition is provided, comprising:

[0008] The base resin comprising 100 parts by weight, including 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin; and

[0009] Fatty acid amides in amounts of 0.05 parts by weight to 1.0 parts by weight.

[0010] According to another aspect of this disclosure, a power cable is provided, comprising:

[0011] conductors; and

[0012] An insulating layer is configured to cover the outer periphery of the conductor.

[0013] The insulating layer is composed of an electrical insulating composition having a base resin and a fatty acid amide, wherein the base resin comprises 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin, totaling 100 parts by weight, and the fatty acid amide comprises 0.05 to 1.0 parts by weight. Attached Figure Description

[0014] [ Figure 1 [This is a schematic cross-sectional view perpendicular to the axis of an embodiment of the power cable involved in this disclosure.] Detailed Implementation

[0015] The problem to be solved by the present invention

[0016] When power cables are supplied in humid or submerged environments, water treeing may occur in the insulation layer. Therefore, it is necessary to improve the water treeing resistance of the insulation layer.

[0017] The purpose of this disclosure is to provide a technology that can ensure various properties of cables and improve their resistance to water and treeing.

[0018] Invention Effects

[0019] According to this disclosure, various properties of the cable can be ensured and water resistance can be improved.

[0020] [Description of embodiments of this disclosure]

[0021] <Discovery obtained by the inventor>

[0022] First, a summary of the discoveries made by the inventors is given.

[0023] Power cables are sometimes installed in, for example, humid or submerged environments. In such environments, when a specified electric field is applied to the insulation of the power cable, water treeing may occur within the insulation. If water treeing occurs, the insulation performance of the power cable may deteriorate.

[0024] Water trees are generated through mechanisms such as the following: In humid or submerged environments, water can seep into the insulation layer of power cables. During power supply to the cables, when water seeps into the insulation layer, it accumulates in areas where a localized electric field is concentrated. Examples of such localized electric field concentrations include voids in the insulation layer, foreign objects, and irregularities at the interface between the insulation and semiconductive layers. When water accumulates in such localized electric field concentrations, the increased pressure of the accumulated water causes mechanical strain around the area where the water has accumulated. As a result, dendritic or butterfly-shaped water trees form in the insulation layer.

[0025] In the prior art, various techniques have been studied, such as those described in Patent Document 1 above, in order to suppress the formation of water trees in the insulation layer of power cables.

[0026] However, in recent years, the specifications required for power cables laid in humid or submerged environments have become more stringent. Alternatively, there is a need to simplify the structure of power cables laid in humid or submerged environments to reduce costs. Therefore, there is a demand for a power cable with further improved resistance to water and tree penetration compared to existing power cables.

[0027] Therefore, the inventors investigated materials to be added to the electrical insulation composition constituting the insulation layer of power cables. Specifically, styrene-containing resins and fatty acid amides were investigated from various materials to be added to the electrical insulation composition. The results showed that by adding either a styrene-containing resin or a fatty acid amide, the density of water trees formed in the insulation layer could be reduced.

[0028] Further research by the inventors revealed that adding both styrene-containing resin and fatty acid amide significantly improves water-tree resistance. Specifically, it was found that the maximum length of water trees forming in the insulation layer can be shortened, and the density of water trees forming in the insulation layer can be significantly reduced.

[0029] This disclosure is based on the above-mentioned findings obtained by the inventors.

[0030] <Implementation Methods of This Disclosure>

[0031] The embodiments of this disclosure will now be listed and described.

[0032] [1] One aspect of the present disclosure relates to an electrical insulating composition having:

[0033] The base resin comprising 100 parts by weight, including 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin; and

[0034] Fatty acid amides in amounts of 0.05 parts by weight to 1.0 parts by weight.

[0035] This configuration ensures various cable performance characteristics and significantly improves resistance to water and tree growth.

[0036] [2] In the electrical insulation composition described in [1] above,

[0037] When the electrical insulation composition comprising the base resin and the fatty acid amide is impregnated in a 1-equivalent NaCl aqueous solution at room temperature, and an AC electric field of 4 kV / mm at a commercial frequency is applied to the electrical insulation composition for 1000 hours,

[0038] The maximum length of the water tree produced in the electrical insulation composition is less than 200 μm.

[0039] Based on this structure, insulation damage to the insulation layer caused by water treeing can be stably suppressed.

[0040] [3] In the electrical insulation composition described in [1] or [2] above,

[0041] When the electrical insulation composition comprising the base resin and the fatty acid amide is impregnated in a 1-equivalent NaCl aqueous solution at room temperature, and an AC electric field of 4 kV / mm at a commercial frequency is applied to the electrical insulation composition for 1000 hours,

[0042] The concentration of water trees with a length of 30 μm or more generated in the electrical insulation composition is less than 200 per cm³. 3 .

[0043] Based on this structure, it is possible to stably suppress insulation damage to the insulation layer caused by water treeing.

[0044] [4] In any of the electrical insulation compositions described in [1] to [3] above,

[0045] The styrene content in the styrene-containing resin is less than 45% by mass.

[0046] Based on this configuration, the maximum length of the water tree can be significantly shortened. Furthermore, dielectric losses can be significantly reduced. Additionally, mechanical properties (tensile strength and elongation) can be significantly improved.

[0047] [5] In any of the electrical insulation compositions described in [1] to [4] above,

[0048] The total styrene content in the base resin is between 0.15 and 11 parts by weight relative to 100 parts by weight of the base resin.

[0049] According to this composition, by setting the total styrene content to 0.15 parts by mass or more, the water-tree-inhibiting effect of styrene-containing resin can be fully obtained. By setting the total styrene content to 11 parts by mass or less, dielectric loss can be sufficiently reduced, and mechanical properties (tensile strength and elongation) can be sufficiently improved.

[0050] [6] In any of the electrical insulation compositions described in [1] to [5] above,

[0051] The ratio of the total styrene content in the base resin to the content of the fatty acid amide is more than 1.5 and less than 110.

[0052] Based on this composition, the significant water-tree-suppressing effect resulting from both the fatty acid amide and the styrene-containing resin can be fully achieved. Furthermore, the increase in dielectric loss and the decrease in mechanical properties (reduction in tensile strength and reduction in tensile elongation) can be stably suppressed.

[0053] [7] In any of the electrical insulation compositions described in [1] to [6] above,

[0054] It further includes 0.1 to 10 parts by mass of unsaturated dimers of α-aromatic substituted α-methyl olefins.

[0055] According to this composition, in addition to the water tree-inhibiting effect brought about by both styrene-containing resin and fatty acid amide, the formation of water trees in the insulation layer can be more stably suppressed.

[0056] [8] In any of the electrical insulation compositions described in [1] to [7] above,

[0057] The fatty acid amide is composed of fatty acid monoamides.

[0058] Based on this composition, the localized suppression effect of water concentration can be improved by using polar groups.

[0059] [9] In any of the electrical insulation compositions described in [1] to [8] above,

[0060] The fatty acid amide is composed of unsaturated fatty acid amides.

[0061] According to this structure, electrons can be trapped by dispersed unsaturated bonds (double bonds), thereby suppressing local electric field concentration.

[0062]

[10] In any of the electrical insulation compositions described in [1] to [9] above,

[0063] It has a crosslinking agent containing organic peroxides.

[0064] Based on this composition, the base resin can be crosslinked using a crosslinking agent. This improves the mechanical and electrical properties of the electrical insulation composition.

[0065]

[11] In any of the electrical insulating compositions described in [1] to [9] above, the base resin is crosslinked.

[0066] Based on this composition, the mechanical and electrical properties of the electrical insulation composition can be improved.

[0067]

[12] Other types of power cables covered by this disclosure include:

[0068] conductors; and

[0069] An insulating layer is configured to cover the outer periphery of the conductor.

[0070] The insulating layer is composed of an electrical insulating composition comprising a base resin and a fatty acid amide, wherein the base resin comprises 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin, totaling 100 parts by weight, and the fatty acid amide comprises 0.05 to 1.0 parts by weight.

[0071] This configuration ensures various cable properties and significantly improves resistance to water and tree growth.

[0072] [Detailed Implementation of this Disclosure]

[0073] Next, an embodiment of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present disclosure is not limited to these examples, but is indicated by the scope of the claims, and is intended to include all variations within the meaning and scope equivalent to the scope of the claims.

[0074] <One embodiment of this disclosure>

[0075] (1) Electrical insulation composition

[0076] The electrical insulation composition of this embodiment is the material constituting the insulation layer 130 of the power cable 10 described later, and has, for example, a base resin, fatty acid amides, and other additives.

[0077] It should be noted that the “electrical insulation composition” mentioned in this embodiment (for example) includes: a composition that does not contain the crosslinking agent described later and is in a non-crosslinked state, a composition that contains the crosslinking agent described later and is in a non-crosslinked state, and a composition in a crosslinked state.

[0078] (Base resin)

[0079] The base resin (base polymer) refers to the resin component that constitutes the main component of the electrical insulation composition. In this embodiment, the base resin includes, for example, polyethylene and styrene-containing resins.

[0080] Polyethylene, as a constituent of the base resin, includes, for example, low-density polyethylene (LDPE: density 0.91 g / cm³). 3 Above and below 0.93 g / cm 3 Linear low-density polyethylene (LLDPE: density 0.945 g / cm³) 3 The following), medium-density polyethylene (MDPE: density 0.93 g / cm³). 3 Above and below 0.942 g / cm³ 3 High-density polyethylene (HDPE: density 0.942 g / cm³) 3(Above) etc. Among them, at least one of LDPE and LLDPE is preferred. This improves the insulation performance and mechanical properties of the power cable.

[0081] The "styrene-containing resin" that constitutes the base resin refers to a polymer that contains styrene in at least a portion, and can also be called a styrene-based thermoplastic elastomer.

[0082] Since the base resin includes a styrene-containing resin, electrons can be trapped by the aromatic rings of styrene, thereby forming a stable resonant structure. Furthermore, by making the styrene-containing resin function as an elastomer, the generation of mechanical stress cracks can be suppressed. Thus, the formation of water trees in the insulating layer 130, described later, can be suppressed.

[0083] Specifically, examples of styrene-containing resins include styrene-butadiene-styrene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene copolymers, hydrogenated styrene-isoprene-styrene copolymers, hydrogenated styrene-butadiene rubber, hydrogenated styrene-isoprene rubber, and styrene-ethylene-butene-olefin crystalline block copolymers. Two or more of these can be used in combination.

[0084] It should be noted that "hydrogenation" here refers to the addition of hydrogen to the double bonds. For example, "hydrogenated styrene-butadiene-styrene block copolymer" refers to a polymer in which hydrogen is added to the double bonds of a styrene-butadiene-styrene block copolymer. It should be observed that no hydrogen is added to the double bonds of the aromatic rings in styrene. Therefore, "hydrogenated styrene-butadiene-styrene block copolymer" can be referred to as a styrene-ethylene-butene-styrene block copolymer.

[0085] When the total content of the base resin is set to 100 parts by mass, the content of polyethylene in the base resin is (for example) 65 parts by mass or more and 98 parts by mass or less, and the content of styrene-containing resin in the base resin is (for example) 2 parts by mass or more and 35 parts by mass or less.

[0086] When the content of styrene-containing resin is less than 2 parts by mass, the water-tree suppression effect provided by the styrene-containing resin may not be sufficiently obtained. Conversely, by setting the content of styrene-containing resin to 2 parts by mass or more, the water-tree suppression effect provided by the styrene-containing resin can be sufficiently obtained. On the other hand, when the content of styrene-containing resin exceeds 35 parts by mass, the aromatic rings of styrene trap excessive electrons, potentially increasing losses in the alternating current field. Therefore, dielectric loss may increase. Furthermore, when the content of styrene-containing resin exceeds 35 parts by mass, the polystyrene blocks, as hard segments, increase relatively excessively compared to the polyolefin blocks, as soft segments. Therefore, mechanical properties may decrease (resulting in at least one of a decrease in tensile strength and a reduction in tensile elongation). Conversely, by setting the content of styrene-containing resin to 35 parts by mass or less, the trapping of excessive electrons by the aromatic rings of styrene can be suppressed, and the increase in losses in the alternating current field can be suppressed. Thus, dielectric loss can be reduced. Furthermore, by setting the content of styrene-containing resin to 35 parts by mass or less, the relatively excessive increase of polystyrene blocks, as hard segments, can be suppressed. This can suppress the reduction in mechanical properties (reduction in tensile strength and reduction in tensile elongation).

[0087] In this embodiment, the styrene content in the styrene-containing resin (hereinafter also simply referred to as "styrene content") is preferably (for example) less than 45% by mass. It should be noted that "styrene content in the styrene-containing resin" refers to the mass ratio of styrene contained in one molecule of styrene-containing resin.

[0088] When the styrene content is 45% by mass or higher, the compatibility of polyethylene with styrene-containing resins decreases. When compatibility decreases, relatively dense portions of the polystyrene blocks, which are hard segments, may form. Therefore, in the case of water tree formation, stress cracking cannot be adequately suppressed in the relatively dense portions of the polystyrene blocks, and the effect of suppressing water tree propagation may not be sufficiently achieved. As a result, the maximum length of the water tree may not be sufficiently shortened. Furthermore, when the styrene content is 45% by mass or higher, electron capture occurs locally on the aromatic rings of styrene, which may not sufficiently reduce losses in the alternating current field. Therefore, the dielectric loss may not be sufficiently low. Additionally, when the styrene content is 45% by mass or higher, the number of polystyrene blocks, which are hard segments, relatively increases. Therefore, the mechanical properties (at least one of tensile strength and elongation at least) may not be sufficiently improved.

[0089] In contrast, by reducing the styrene content to less than 45% by mass, the decrease in compatibility between polyethylene and styrene-containing resins can be suppressed. By suppressing the decrease in compatibility, the formation of relatively dense portions in the polystyrene blocks, which are hard segments, can be prevented. This uniformly suppresses stress cracking in the electrical insulation composition and inhibits the spread of water trees. Consequently, the maximum length of water trees can be significantly shortened. Furthermore, by reducing the styrene content to less than 45% by mass, localized electron trapping on the aromatic rings of styrene can be suppressed, thereby significantly reducing losses in the alternating current field. This significantly reduces dielectric losses. Moreover, by reducing the styrene content to less than 45% by mass, the relative increase in the number of polystyrene blocks, which are hard segments, can be suppressed. This significantly improves mechanical properties (tensile strength and elongation).

[0090] It should be noted that there is no particular lower limit to the styrene content in styrene-containing resins. However, from the viewpoint of effectively exhibiting the water-tree-inhibiting effect of styrene-containing resins, the styrene content in styrene-containing resins is preferably, for example, 5% by mass or more.

[0091] Furthermore, in this embodiment, the total styrene content in the base resin (hereinafter also referred to as "total styrene content") relative to 100 parts by weight of the base resin is preferably, for example, 0.15 parts by weight or more and 11 parts by weight or less.

[0092] When the total styrene content is less than 0.15 parts by mass, the water-tree inhibition effect provided by the styrene-containing resin may not be sufficiently obtained. Conversely, by setting the total styrene content to 0.15 parts by mass or more, the water-tree inhibition effect provided by the styrene-containing resin can be sufficiently obtained. On the other hand, when the total styrene content exceeds 11 parts by mass, the electron trapping on the aromatic ring of styrene increases, thus the loss to the alternating current field may not be sufficiently reduced. Therefore, the dielectric loss may not be sufficiently reduced. Furthermore, when the total styrene content exceeds 11 parts by mass, the polystyrene blocks, which are hard segments, relatively increase compared to the polyolefin blocks, which are soft segments. Therefore, the mechanical properties (at least one of tensile strength and elongation at least) may not be sufficiently improved. Conversely, by setting the total styrene content to 11 parts by mass or less, the loss to the alternating current field caused by electron trapping on the aromatic ring of styrene can be sufficiently reduced. Thus, the dielectric loss can be sufficiently reduced. Furthermore, by setting the total styrene content to 11 parts by mass or less, the relative increase in the polystyrene blocks, which are hard segments, can be suppressed. This can significantly improve mechanical properties (tensile strength and elongation).

[0093] (Fatty acid amide)

[0094] By adding a fatty acid amide to the electrical insulation composition, the fatty acid amide acts as a lubricant, thereby improving the flowability of the electrical insulation composition during the extrusion step of the insulation layer 130. Furthermore, by dispersing the fatty acid amide, the dispersed polar groups (hydrophilic groups) can suppress localized water aggregation in the electrical insulation composition. This helps to prevent water treeing in the insulation layer 130.

[0095] Examples of fatty acid amides include saturated fatty acid monoamides, unsaturated fatty acid monoamides, saturated fatty acid diamides, and unsaturated fatty acid diamides.

[0096] Specifically, examples of saturated fatty acid monoamides include laurylamide, palmitamide, stearamide, and hydroxystearamide.

[0097] Examples of unsaturated fatty acid monoamides include oleamide and erucamide.

[0098] Examples of saturated fatty acid diamides include methylene bis-stearamide, ethylene bis-decanoic acid amide, ethylene bis-lauric acid amide, ethylene bis-stearamide, ethylene bis-hydroxystearamide, ethylene bis-codonoic acid amide, hexamethylene bis-stearamide, hexamethylene bis-hydroxystearamide, and N,N'-distearate adipamide.

[0099] Examples of unsaturated fatty acid diamides include ethylene dioleamide, ethylene dierucamide, hexamethylene dioleamide, N,N'-dioleenyl adipamide, and N,N'-dioleenyl sebacate amide.

[0100] It should be noted that two or more of these fatty acid amides can also be used in combination.

[0101] In this embodiment, the fatty acid amide added to the electrical insulation composition is preferably a fatty acid monoamide, for example. That is, the fatty acid amide preferably has one amide group, for example. This increases the polarity of the fatty acid amide. As a result, the local concentration suppression effect of water can be improved through the polar group.

[0102] Furthermore, in this embodiment, the fatty acid amide added to the electrical insulation composition is preferably an unsaturated fatty acid amide, for example. That is, the fatty acid amide preferably has, for example, unsaturated bonds (unsaturated groups, double bonds). Thus, the dispersed unsaturated bonds can trap electrons, thereby suppressing localized electric field concentration.

[0103] In this embodiment, the content of fatty acid amide in the electrical insulation composition is, for example, 0.05 parts by mass or more and 1.0 parts by mass or less, relative to 100 parts by mass of the base resin.

[0104] When the content of fatty acid amide is less than 0.05 parts by mass, the water-tree inhibition effect caused by fatty acid amide may not be sufficiently obtained. Conversely, by setting the content of fatty acid amide to 0.05 parts by mass or more, the water-tree inhibition effect caused by fatty acid amide can be sufficiently obtained. On the other hand, when the content of fatty acid amide exceeds 1.0 parts by mass, due to the compatibility difference between the base resin and fatty acid amide, fatty acid amide may precipitate on the surface of the insulation layer 130. This phenomenon is called "frost formation." Conversely, by setting the content of fatty acid amide to 1.0 parts by mass or less, the occurrence of frost formation caused by the compatibility difference between the base resin and fatty acid amide can be suppressed.

[0105] In this embodiment, by adding both fatty acid amide and the aforementioned styrene-containing resin, the water resistance can be significantly improved through their synergistic effect.

[0106] In this embodiment, the ratio of the total styrene content B in the base resin to the fatty acid amide content A, B / A (hereinafter also referred to as the content ratio B / A), is preferably (for example) 1.5 or more and 110 or less, more preferably 2.4 or more and 105 or less.

[0107] When the content ratio B / A is less than 1.5, the significant water-tree inhibition effect provided by both fatty acid amides and styrene-containing resins may not be sufficiently obtained. Conversely, by setting the content ratio B / A to 1.5 or higher, the significant water-tree inhibition effect provided by both fatty acid amides and styrene-containing resins can be sufficiently obtained. Furthermore, by setting the content ratio B / A to 2.4 or higher, the significant water-tree inhibition effect provided by both fatty acid amides and styrene-containing resins can be stably obtained.

[0108] On the other hand, when the B / A ratio exceeds 110, the flowability improvement effect caused by the fatty acid amide may not be sufficiently obtained. Therefore, it may be difficult to uniformly disperse the polystyrene blocks. Furthermore, when the B / A ratio exceeds 110, the localized water-curing inhibition effect caused by the polar groups of the fatty acid amide may not be sufficiently obtained. In contrast, by setting the B / A ratio to 110 or less, the flowability improvement effect caused by the fatty acid amide can be sufficiently obtained. This allows for uniform dispersion of the polystyrene blocks. As a result, the increase in dielectric loss and the decrease in mechanical properties (decrease in tensile strength and reduction in tensile elongation) can be stably suppressed. Furthermore, by setting the B / A ratio to 110 or less, the localized water-curing inhibition effect caused by the polar groups of the fatty acid amide can be sufficiently obtained. This allows for a significant water-curing inhibition effect from both the fatty acid amide and the styrene-containing resin. Moreover, by setting the B / A ratio to 105 or less, the increase in dielectric loss and the decrease in mechanical properties (decrease in tensile strength and reduction in tensile elongation) can be reliably suppressed. Furthermore, the significant water-tree-inhibiting effect brought about by both fatty acid amides and styrene-containing resins can be further fully obtained.

[0109] (An unsaturated dimer of α-aromatic substituted α-methyl olefins)

[0110] In this embodiment, the electrical insulating composition may also have, for example, an unsaturated dimer of an α-aromatic substituted α-methyl olefin.

[0111] By adding an α-aromatically substituted α-methylolefin unsaturated dimer to the electrical insulation composition, the formation of localized charring (burning) during the extrusion step of the electrical insulation composition can be suppressed. Furthermore, similar to styrene-containing resins, electrons are captured by the aromatic ring of the α-aromatically substituted α-methylolefin unsaturated dimer, thereby forming a stable resonant structure. This stably suppresses the formation of water treeing in the insulation layer 130. It should be noted that, hereinafter, the α-aromatically substituted α-methylolefin unsaturated dimer is sometimes simply referred to as the "unsaturated dimer".

[0112] Monomers of α-aromatic substituted α-methyl olefins are represented by, for example, the following formula (1).

[0113] [Chemical Formula 1]

[0114]

[0115] Wherein, R is any one of aryl, alkylaryl, halogen-substituted aryl, or halogen-substituted alkylaryl. It should be noted that, as used herein, "alkylaryl" refers to a combination of one or more aryl groups bonded with one or more alkyl groups.

[0116] Specifically, examples of monomers that are α-aromatic substituted α-methylolefins include, for example, α-methylstyrene, p-methyl-α-methylstyrene, p-isopropyl-α-methylstyrene, m-methyl-α-methylstyrene, m-ethyl-α-methylstyrene, ar-dimethyl-α-methylstyrene, ar-chloro-α-methylstyrene, ar-chloro-ar-methyl-α-methylstyrene, ar-diethyl-α-methylstyrene, and ar-methyl-ar-isopropyl-α-methylstyrene. Two or more of these can also be used in combination.

[0117] Examples of unsaturated dimers of α-aromatic substituted α-methylolefins include, for example, the unsaturated dimer of α-methylstyrene (2,4-diphenyl-4-methyl-1-pentene). It should be noted that two or more of the unsaturated dimers of α-methylstyrene, along with other unsaturated dimers, can be used in combination.

[0118] In this embodiment, the content of the unsaturated dimer of α-aromatic substituted α-methyl olefin in the electrical insulation composition is, for example, 0.1 parts by mass or less and 10 parts by mass or less, relative to 100 parts by mass of the base resin.

[0119] When the content of unsaturated dimer is less than 0.1 parts by mass, the water-tree inhibition effect produced by the unsaturated dimer may not be sufficiently obtained. Conversely, by setting the content of unsaturated dimer to 0.1 parts by mass or more, the water-tree inhibition effect produced by the unsaturated dimer can be sufficiently obtained. On the other hand, when the content of unsaturated dimer exceeds 10 parts by mass, the base resin is difficult to crosslink, and the gel fraction of the electrical insulation composition decreases. Therefore, when a specified alternating current electric field is applied, the dielectric loss may increase, or the tensile properties of the insulation layer 130 may decrease. Conversely, by setting the content of unsaturated dimer to 10 parts by mass or less, a specified amount of base resin can be crosslinked, thereby suppressing the decrease in the gel fraction of the electrical insulation composition. Thus, the increase in dielectric loss when a specified alternating current electric field is applied can be suppressed, and the decrease in the tensile properties of the insulation layer 130 can be suppressed.

[0120] (Cross-linking agent)

[0121] In this embodiment, the base resin of the electrical insulating composition is preferably crosslinked (for example) by a crosslinking agent. This improves the mechanical properties (tensile properties, etc.) and electrical properties of the electrical insulating composition.

[0122] As a crosslinking agent added to the electrical insulation composition, organic peroxides can be used, for example. Specifically, examples of organic peroxides include: dicumyl peroxide, 1-(2-tert-butylperoxyisopropyl)-1-isopropylbenzene, 1-(2-tert-butylperoxyisopropyl)-3-isopropylbenzene, 1,3-bis-(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, 2,5-dimethyl-2,5-(tert-butylperoxy)-hexyne-3, etc. It should be noted that two or more of these can be used in combination.

[0123] (Other additives)

[0124] Electrical insulation compositions may also contain, for example, antioxidants.

[0125] Examples of antioxidants include 4,4'-thiobis-(6-tert-butyl-3-methylphenol), 2,2-thio-diethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], pentaerythritol tetra[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, 2,4-bis-[(octylthio)methyl]-o-cresol, 2,4-bis-(n-octylthio)-6-(4-hydroxy-3,5-di-tert-butylaniline)-1,3,5-triazine, and bis[2-methyl-4-{3-n-alkyl(C12 or C14)thiopropionoxy}-5-tert-butylphenyl] sulfide. Furthermore, two or more of these can be used in combination.

[0126] It should be noted that, as a lubricant, the electrical insulating composition may also contain lubricants other than the fatty acid amides mentioned above. Furthermore, the electrical insulating composition may also contain, for example, a colorant.

[0127] (2) Power cables

[0128] Next, use Figure 1 The power cable of this embodiment will be described. Figure 1 This is a cross-sectional view of the power cable involved in this embodiment, perpendicular to the axial direction.

[0129] The power cable 10 in this embodiment is configured as a so-called solid-insulated power cable. Furthermore, the power cable 10 in this embodiment is configured to be laid in water or underwater, for example. It should be noted that the power cable 10 is used for, for example, alternating current.

[0130] Specifically, the power cable 10 (for example) has: a conductor 110, an inner semiconducting layer 120, an insulating layer 130, an outer semiconducting layer 140, a shielding layer 150, and an outer sheath 160.

[0131] Because the power cable 10 of this embodiment has the aforementioned significant effect in suppressing water treeing, there is no water-blocking layer made of metal such as an aluminum shield on the outer side of the shielding layer 150. In other words, the power cable 10 of this embodiment is constructed with a non-completely water-blocking structure.

[0132] (Conductor (Conductive Part))

[0133] The conductor 110 is constructed by twisting together multiple conductor cores (conductive cores) containing, for example, pure copper, copper alloys, aluminum or aluminum alloys.

[0134] (Internal semiconductive layer)

[0135] An internal semiconducting layer 120 is configured to cover the outer periphery of the conductor 110. Furthermore, the internal semiconducting layer 120 is semiconducting and is configured to suppress electric field concentration on the surface side of the conductor 110. The internal semiconducting layer 120 includes, for example, at least one of ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-butyl acrylate copolymer, and ethylene-vinyl acetate copolymer, as well as conductive carbon black.

[0136] (Insulating layer)

[0137] The insulating layer 130 is configured to cover the outer periphery of the inner semiconductive layer 120 and is composed of the aforementioned electrical insulating composition. The insulating layer 130 is cross-linked by, for example, extruding the electrical insulating composition as described above and then heating it.

[0138] (Outer semiconductive layer)

[0139] The outer semiconductive layer 140 is configured to cover the outer periphery of the insulating layer 130. Furthermore, the outer semiconductive layer 140 is semiconductive and is configured to suppress electric field concentration between the insulating layer 130 and the shielding layer 150. The outer semiconductive layer 140 is made of, for example, the same material as the inner semiconductive layer 120.

[0140] (Shielding layer)

[0141] The shielding layer 150 is configured to cover the outer periphery of the outer semiconductive layer 140. The shielding layer 150 is formed by, for example, winding copper strip, or is configured as a shielding wire obtained by winding multiple soft copper wires, etc. Alternatively, a strip made of adhesive tape or the like can be wound on the inner or outer side of the shielding layer 150.

[0142] (Outer skin)

[0143] The outer skin 160 is configured to cover the outer periphery of the shielding layer 150. The outer skin 160 is made of, for example, polyvinyl chloride or polyethylene.

[0144] (Water-tolerant tree)

[0145] In this embodiment, as described above, the water resistance of the insulation layer 130 is significantly improved by adding both styrene resin and fatty acid amide to the insulation layer 13.

[0146] Specifically, in this embodiment, when the electrical insulating composition constituting the insulating layer 130 is immersed in a NaCl aqueous solution with a concentration of 1 equivalent at room temperature (27°C), and an AC electric field of 4 kV / mm at a commercial frequency (e.g., 60 Hz) is applied to the electrical insulating composition for 1000 hours, the maximum length of water trees generated in the electrical insulating composition is (e.g.) less than 200 μm, preferably less than 120 μm, and more preferably less than 100 μm. Therefore, insulation damage to the insulating layer 130 caused by water trees can be stably suppressed.

[0147] It should be noted that the maximum length of the water tree generated in the electrical insulation composition should be as small as possible, and therefore there is no limitation. However, in this embodiment, since no water tree occurs, the maximum length of the water tree generated in the electrical insulation composition is, for example, 0 μm or more.

[0148] Furthermore, in this embodiment, when the electrical insulation composition constituting the insulation layer 130 is immersed in a NaCl aqueous solution with a concentration of 1 equivalent at room temperature (27°C), and an AC electric field of 4 kV / mm at a commercial frequency (e.g., 60 Hz) is applied to the electrical insulation composition for 1000 hours, the concentration of water trees with a length of 30 μm or more generated in the electrical insulation composition is (e.g.) less than 200 per cm. 3 Preferably 100 pieces / cm 3 The following is more preferred: 60 pieces / cm 3 Therefore, it is possible to stably suppress insulation failure of the insulation layer 130 caused by water treeing.

[0149] It should be noted that a lower concentration of water trees is better, and therefore there is no limitation. However, in this embodiment, since no water trees appear, the concentration of water trees is (for example) 0 per cm³. 3 above.

[0150] (Gel fraction (degree of cross-linking))

[0151] In this embodiment, as described above, for example, the insulating layer 130 is crosslinked. Furthermore, in the electrical insulating composition constituting the insulating layer 130, by not containing unsaturated dimers of α-aromatic substituted α-methyl olefins, or by setting the content of unsaturated dimers of α-aromatic substituted α-methyl olefins to 10 parts by mass or less, it is possible to suppress the decrease in the gel fraction of the electrical insulating composition.

[0152] Specifically, in this embodiment, the gel fraction of the electrical insulating composition constituting the insulating layer 130 is, for example, more than 68%, preferably more than 70%, and more preferably more than 74%.

[0153] It should be noted that a higher gel fraction of the electrical insulation composition is better, and therefore there is no limitation. However, in this embodiment, the gel fraction of the electrical insulation composition is, for example, 95% or less.

[0154] (Dielectric loss)

[0155] Here, when an alternating electric field is applied to the electrical insulation composition, losses may occur. These losses include, for example, losses due to leakage current, losses based on dielectric polarization, and losses based on partial discharge. Due to these losses, the current phase lags behind the ideal lossless current flowing into the electrical insulation composition. This delay angle δ is called the dielectric loss angle, and its tangent is called the dielectric loss tangent (tanδ).

[0156] In this embodiment, by setting the content of styrene-containing resin to 35 parts by mass or less, the increase in dielectric loss can be suppressed.

[0157] Specifically, in this embodiment, under conditions of 90°C, commercial frequency (e.g., 60Hz), and 9kV / mm, the dielectric loss when an alternating electric field is applied to the electrical insulation composition constituting the insulation layer 130 is, for example, 0.05% or less, preferably 0.04% or less.

[0158] It should be noted that lower dielectric loss is better, and therefore there is no limitation. However, in the electrical insulation composition of this embodiment, the dielectric loss is, for example, 0.001% or more.

[0159] (Alternating current disrupts the electric field)

[0160] In this embodiment, the specified alternating current destructive electric field is ensured by setting the content of styrene resin to 35 parts by mass or less.

[0161] Specifically, in this embodiment, the alternating destructive electric field of the electrical insulation composition constituting the insulation layer 130, measured at room temperature (27°C) and commercial frequency (e.g., 60Hz), is, for example, 55kV / mm or more, preferably 58kV / mm or more.

[0162] It should be noted that a larger AC disruptive electric field is better, and therefore there is no limitation. However, in the electrical insulation composition of this embodiment, the AC disruptive electric field is, for example, 100 kV / mm or less.

[0163] (Tensile properties (mechanical properties))

[0164] In this embodiment, the tensile strength of the electrical insulation composition can be improved by including a styrene-containing resin as an elastomer.

[0165] Specifically, in this embodiment, the tensile strength of the electrical insulation composition constituting the insulation layer 130 is, for example, 12.5 MPa or more, preferably 14 MPa or more, and more preferably 17 MPa or more.

[0166] It should be noted that the higher the tensile strength of the electrical insulation composition, the better, and therefore there is no limitation. However, in the electrical insulation composition of this embodiment, the tensile strength is, for example, 50 MPa or less.

[0167] Furthermore, in this embodiment, by setting the content of styrene resin to 35 parts by weight or less, the tensile elongation of the electrical insulation composition can be ensured.

[0168] Specifically, in this embodiment, the tensile elongation of the electrical insulating composition constituting the insulating layer 130 is, for example, 350% or more, preferably 430% or more.

[0169] It should be noted that a higher elongation at break of the electrical insulation composition is better, and therefore there is no limitation. However, in the electrical insulation composition of this embodiment, the elongation at break is, for example, 1000% or less.

[0170] Thus, in this embodiment, the specified tensile properties can be ensured. Consequently, the power cable 10 can be properly laid out even in environments where it stretches or bends. Specifically, the power cable 10 of this embodiment can be applied, for example, to array cables (dynamic cables, riser cables) that can be bent and connected to floating aquatic equipment in water.

[0171] (Frost)

[0172] In this embodiment, as described above, by setting the content of fatty acid amide to 1.0 parts by mass or less, frosting caused by the compatibility difference between the base resin and the fatty acid amide will not be detected on the surface of the insulating layer 130.

[0173] (Specific dimensions, etc.)

[0174] The specific dimensions of the power cable 10 are not particularly limited. For example, the diameter of the conductor 110 is 5 mm to 60 mm, the thickness of the inner semi-conductive layer 120 is 0.5 mm to 3 mm, the thickness of the insulation layer 130 is 1 mm to 35 mm, the thickness of the outer semi-conductive layer 140 is 0.5 mm to 3 mm, the thickness of the shielding layer 150 is 1 mm to 5 mm, and the thickness of the outer sheath 160 is 1 mm or more. The AC voltage used in the power cable 10 of this embodiment is, for example, 20 kV or more.

[0175] (3) Manufacturing method of power cables

[0176] Next, the method for manufacturing the power cable according to this embodiment will be described. Hereinafter, the steps will be referred to as "S".

[0177] (S100: Preparation steps for electrical insulation composition)

[0178] First, prepare the electrical insulation composition.

[0179] In this embodiment, a mixer such as a Banbury mixer or a kneader is used to mix (blend) a base resin containing polyethylene and styrene-containing resin, fatty acid amides, and other additives (crosslinking agents, antioxidants, etc.) to form a blended material. At this time, when the total content of the base resin is set to 100 parts by mass, the content of polyethylene in the base resin is set to (for example) 65 parts by mass or more and 98 parts by mass or less, and the content of styrene-containing resin in the base resin is set to (for example) 2 parts by mass or more and 35 parts by mass or less. Furthermore, relative to 100 parts by mass of the base resin, the content of fatty acid amides is set to (for example) 0.05 parts by mass or more and 1.0 parts by mass or less.

[0180] It should be noted that, in this case, an unsaturated dimer of α-aromatic substituted α-methyl olefin can also be added. In this case, the content of the unsaturated dimer of α-aromatic substituted α-methyl olefin is set to, for example, 0.1 parts by mass to 10 parts by mass less than 100 parts by mass of the base resin.

[0181] After the mixture is formed, it is granulated using an extruder. This results in a granular electrical insulation composition constituting the insulating layer 130. It should be noted that a biaxial extruder with high mixing efficiency can be used to perform the mixing and granulation steps simultaneously.

[0182] (S200: Conductor preparation steps)

[0183] On the other hand, a conductor 110 is prepared, which is formed by twisting together multiple conductor cores.

[0184] (S300: Steps for forming the cable core (extrusion step))

[0185] After the electrical insulation composition preparation step S100 and the conductor preparation step S200 are completed, in a three-layer simultaneous extruder, the composition for the internal semi-conductive layer, obtained by premixing ethylene-ethyl acrylate copolymer and conductive carbon black, is fed into the extruder A for forming the internal semi-conductive layer 120.

[0186] The above-mentioned granular electrical insulating composition is fed into an extruder B used to form the insulating layer 130.

[0187] In the extruder C used to form the outer semiconductive layer 140, an outer semiconductive layer composition containing the same material as the inner semiconductive layer electrical insulation composition fed into the extruder A is fed.

[0188] Next, the extrudates from extruders A to C are guided to a common head, where an inner semiconductive layer 120, an insulating layer 130, and an outer semiconductive layer 140 are simultaneously extruded from the inside to the outside around the conductor 110.

[0189] After extrusion, the insulation layer 130 is cross-linked within a cross-linking tube pressurized with nitrogen or similar gas by radiation from an infrared heater, or by heat transfer through a heat medium such as high-temperature nitrogen or silicone oil. Subsequently, the cross-linked cable core is cooled, for example, with water.

[0190] Through the above core forming step S300, a core consisting of conductor 110, inner semiconductive layer 120, insulation layer 130 and outer semiconductive layer 140 is formed.

[0191] (S400: Steps for forming the shielding layer)

[0192] After the cable core is formed, a shielding layer 150 is formed by winding (for example) copper tape around the outside of the outer semiconductive layer 140.

[0193] (S500: Skin formation step)

[0194] After the shielding layer 150 is formed, vinyl chloride is fed into an extruder and extruded to form an outer skin 160 on the outer periphery of the shielding layer 150.

[0195] As described above, a power cable 10 was manufactured as a solid insulated power cable.

[0196] (4) Effects of this implementation method

[0197] According to this embodiment, one or more effects as shown below are obtained.

[0198] (a) In this embodiment, by adding a styrene-containing resin as a base resin to the electrical insulation composition, electrons are trapped by the aromatic rings of styrene, forming a stable resonant structure. This suppresses localized non-uniformity of electrons, i.e., suppresses the formation of localized electric field concentrations. By suppressing the formation of localized electric field concentrations, water accumulation in these concentrations can be suppressed. Consequently, the occurrence of mechanical strain caused by water accumulation can be suppressed. As a result, water treeing in the insulation layer 130 can be suppressed.

[0199] Furthermore, in this embodiment, by adding a styrene-containing resin as a base resin to the electrical insulation composition, the styrene-containing resin can function as an elastomer. By enabling the styrene-containing resin to function as an elastomer, even if the aforementioned water aggregates are formed in the electrical insulation composition, the mechanical strain caused by the water aggregates can be mitigated. Therefore, the formation of mechanical stress cracks can be suppressed in the electrical insulation composition. As a result, the spread and development of water trees can be suppressed.

[0200] (b) In this embodiment, by adding a fatty acid amide to the electrical insulation composition, the fatty acid amide acts as a lubricant, thereby improving the flowability of the electrical insulation composition during the extrusion step of the insulation layer 130. This allows for uniform dispersion of the materials in the electrical insulation composition. By uniformly dispersing the fatty acid amide in the electrical insulation composition, the polar groups (hydrophilic groups) of the fatty acid amide are dispersed. This disperses water entering the electrical insulation composition through the polar groups, suppressing localized water concentration in the electrical insulation composition. By suppressing localized water concentration, mechanical strain caused by water concentration points (water accumulation points) can be suppressed. As a result, water treeing in the insulation layer 130 can be suppressed.

[0201] (c) According to this embodiment, the water-tolerant nature of trees can be significantly improved through the synergistic effect of (a) and (b) above.

[0202] Here, when only one of styrene resin or fatty acid amide is added to the electrical insulation composition, although the number density of water trees generated in the insulation layer 130 is reduced to a certain extent, the maximum length of the water trees generated in the insulation layer 130 may not be shortened.

[0203] In contrast, in this embodiment, by adding both the styrene-containing resin and the fatty acid amide to the electrical insulation composition, the synergistic effects of (a) and (b) described above can be obtained. That is, by adding the fatty acid amide, the flowability of the electrical insulation composition is improved, thereby allowing the polystyrene blocks of the styrene-containing resin to be uniformly dispersed in the electrical insulation composition.

[0204] By uniformly dispersing polystyrene blocks, the electron-trapping effect of the aromatic rings in styrene can be uniformly exhibited, and the formation of localized electric field concentrations can be stably suppressed. Furthermore, the polar groups of the fatty acid amides disperse water entering the electrical insulation composition, thereby reducing the probability of water concentration in localized electric field concentrations. Thus, water treeing in the insulation layer 130 can be stably suppressed.

[0205] Furthermore, by uniformly dispersing polystyrene blocks as hard segments and polyolefin blocks as soft segments, mechanical strain cracking can be uniformly suppressed in the electrical composition. This, in turn, stably suppresses the diffusion and development of water trees.

[0206] Based on these results, in this embodiment, the maximum length of the water tree generated in the insulating layer 130 can be shortened, and the number density of water trees generated in the insulating layer 130 can be significantly reduced.

[0207] By significantly improving resistance to water treeing, it can be appropriately applied to underwater cables or submersible cables that are frequently exposed to water. Furthermore, by significantly improving resistance to water treeing, the structure of the water-shielding layer of the power cable 10 can be simplified. For example, a water-shielding layer may be omitted, or a simple shielding layer may be constructed. As a result, the cost of the power cable 10 can be reduced.

[0208] (d) By setting the content of styrene-containing resin to 2 parts by mass or more, the water-tree suppression effect brought about by the styrene-containing resin can be sufficiently obtained. On the other hand, by setting the content of styrene-containing resin to 35 parts by mass or less, excessive electron trapping by the aromatic rings of styrene can be suppressed, and the increase in losses to the alternating electric field can be suppressed. As a result, dielectric loss can be reduced. Furthermore, by setting the content of styrene-containing resin to 35 parts by mass or less, the relatively excessive increase of polystyrene blocks as hard segments can be suppressed. As a result, the decrease in mechanical properties (decrease in tensile strength and reduction in tensile elongation) can be suppressed.

[0209] (e) By setting the content of fatty acid amide to 0.05 parts by mass or more, the effect of inhibiting water treeing caused by fatty acid amide can be fully obtained. On the other hand, by setting the content of fatty acid amide to 1.0 parts by mass or less, blooming caused by the compatibility difference between the base resin and fatty acid amide can be suppressed.

[0210] According to this embodiment, as described in (a) to (e) above, various properties of the cable (electrical properties, tensile properties, anti-frost properties) can be ensured, and water resistance can be improved.

[0211] (f) In this embodiment, the styrene content in the styrene-containing resin is preferably less than 45% by mass. By keeping the styrene content less than 45% by mass, the decrease in compatibility between polyethylene and the styrene-containing resin can be suppressed. By suppressing the decrease in compatibility, the formation of relatively dense portions of the polystyrene blocks as hard segments can be suppressed. As a result, stress cracking in the electrical insulation composition can be uniformly suppressed, and the diffusion of water trees can be suppressed. Consequently, the maximum length of water trees can be sufficiently shortened. Furthermore, by keeping the styrene content less than 45% by mass, the local non-uniformity of electron trapping on the aromatic ring of styrene can be suppressed, thereby sufficiently reducing losses to the alternating current field. As a result, dielectric losses can be sufficiently reduced. Furthermore, by keeping the styrene content less than 45% by mass, the relative increase of polystyrene blocks as hard segments can be suppressed. As a result, mechanical properties (tensile strength and elongation at break) can be sufficiently improved.

[0212] (g) In this embodiment, the total styrene content in the base resin is preferably, for example, 0.15 parts by mass or more and 11 parts by mass or less, relative to 100 parts by mass of the base resin. By setting the total styrene content to 0.15 parts by mass or more, the water-tree suppression effect provided by the styrene-containing resin can be sufficiently obtained. On the other hand, by setting the total styrene content to 11 parts by mass or less, the loss to the alternating electric field caused by electron capture on the aromatic ring of styrene can be sufficiently reduced. As a result, dielectric loss can be sufficiently reduced. Furthermore, by setting the total styrene content to 11 parts by mass or less, the relative increase of polystyrene blocks as hard segments can be suppressed. As a result, mechanical properties (tensile strength and elongation at break) can be sufficiently improved.

[0213] (h) In this embodiment, by adding an unsaturated dimer of α-aromatic substituted α-methyl olefin to the electrical insulation composition, localized charring (burning) during the extrusion step of the electrical insulation composition can be suppressed. This suppresses the formation of localized electric field concentrations caused by charring. Furthermore, by adding an unsaturated dimer of α-aromatic substituted α-methyl olefin to the electrical insulation composition, electrons are trapped by the aromatic ring of the unsaturated dimer of α-aromatic substituted α-methyl olefin, based on the same principle as with styrene-containing resins, thereby suppressing the formation of localized electric field concentrations. By suppressing the formation of localized electric field concentrations, water accumulation in the electric field concentrations can be suppressed. This suppresses mechanical strain caused by water accumulation. As a result, in addition to the water-tree-suppressing effect of both the styrene-containing resin and the fatty acid amide, water treeing in the insulation layer 130 is more stably suppressed.

[0214] (i) By setting the content of the unsaturated dimer of α-aromatic substituted α-methyl olefin to 0.1 parts by mass or more, the effect of suppressing water treeing produced 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, and crosslinking a specified amount of base resin, the decrease in the gel fraction of the electrical insulation composition can be suppressed. As a result, the increase in dielectric loss when a specified alternating electric field is applied can be suppressed, thereby suppressing the decrease in the tensile properties of the insulation layer 130.

[0215] (j) The fatty acid amide added to the electrical insulation composition is preferably a fatty acid monoamide. This increases the polarity of the fatty acid amide. By increasing the polarity of the fatty acid amide, the local concentration suppression effect of water can be improved through the polar groups. As a result, water treeing in the insulation layer 130 can be stably suppressed.

[0216] (k) The fatty acid amide added to the electrical insulation composition is preferably an unsaturated fatty acid amide. This allows electrons to be trapped by the dispersed unsaturated bonds (double bonds) and suppresses localized electric field concentration. By suppressing the formation of localized electric field concentrations, water accumulation in these concentrations can be suppressed. Consequently, water treeing in the insulation layer 130 can be stably suppressed.

[0217] <Other embodiments of this disclosure>

[0218] The embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the above embodiments, and various changes can be made without departing from its spirit.

[0219] In the above embodiments, the case where the base resin contains polyethylene has been described, but this disclosure is not limited to this case. For example, the base resin may contain an ethylene copolymer. Examples of ethylene copolymers include ethylene-propylene copolymers, ethylene-methyl acrylate copolymers, ethylene-ethyl acrylate copolymers, and ethylene-vinyl acetate copolymers. Two or more of these can be used in combination. By including an ethylene copolymer in the base resin, the dispersibility of the unsaturated dimer containing styrene resin, fatty acid amide, and α-aromatic substituted α-methyl olefin can be improved when the electrical insulating composition is mixed.

[0220] In the above embodiments, the case where the power cable 10 does not have a water-shielding layer has been described, but this disclosure is not limited to this case. Since the power cable 10 has the aforementioned significant effect in suppressing water treeing, it can have a simple water-shielding layer. Specifically, the simple water-shielding layer is made of, for example, a metal laminate. The metal laminate has, for example, a metal layer made of aluminum or copper, and an adhesive layer disposed on one or both sides of the metal layer. For example, the metal laminate is wound longitudinally to surround the outer periphery of the cable core (the outer periphery further out than the outer semiconductive layer). Alternatively, this water-shielding layer can be disposed further out of the shielding layer, or it can also serve as a shielding layer. With such a structure, the cost of the power cable 10 can be reduced.

[0221] In the above embodiments, the power cable 10 was described as being laid in water or on the seabed, but this disclosure is not limited to this case. For example, the power cable 10 may also be configured as a so-called overhead wire (overhead insulated wire).

[0222] Example

[0223] The following describes embodiments relating to this disclosure. These embodiments are examples of this disclosure. This disclosure is not limited to these embodiments.

[0224] (1) Preparation of electrical insulation composition

[0225] The following samples A1 to A14 and B1 to B11 were mixed at 120°C using an open roller to obtain an electrical insulation composition.

[0226] [Samples A1~A14]

[0227] (Base resin) 100 parts by weight in total

[0228] Low-density polyethylene (LDPE) (density d = 0.92 g / cm³) 3 MFR = 1.0 g / 10 min: 65 parts by weight or more, 98 parts by weight or less

[0229] Styrene-containing resin: 2 to 35 parts by weight

[0230] Styrene-butadiene-styrene block copolymer (SBS) (density d = 0.95 g / cm³) 3 MFR = 2.6 g / 10 min, styrene content 40% by mass)

[0231] • Hydrogenated styrene-butadiene-styrene block copolymer (SEBS: styrene-ethylene-butadiene-styrene block copolymer) (density d = 0.91 g / cm³) 3 MFR = 5g / 10min, styrene content 30% by mass)

[0232] • Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (density d = 0.89 g / cm³) 3 MFR = 4.5 g / 10 min, styrene content 12% by mass)

[0233] • Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (density d = 0.93 g / cm³) 3 MFR = 3.0 g / 10 min, styrene content 43% by mass)

[0234] (Fatty acid amide)

[0235] Stearamide, oleamide, erucamide, ethylene bis-stearamide, ethylene bis-oleamide: 0.1 parts by weight

[0236] (Unsaturated dimer)

[0237] Unsaturated dimer of α-methylstyrene (2,4-diphenyl-4-methyl-1-pentene): 0.3 parts by weight (sample A9 only)

[0238] (Cross-linking agent)

[0239] Dicumyl peroxide: 2 parts by mass, or

[0240] 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane: 1.3 parts by weight

[0241] (Antioxidants)

[0242] 4,4'-Thiobis-(6-tert-butyl-3-methylphenol): 0.2 parts by weight

[0243] [Sample B1]

[0244] The base resin does not contain styrene-containing resin, but contains 100 parts by weight of polyethylene and does not contain fatty acid amides. Apart from these aspects, it is prepared in the same manner as sample A3.

[0245] [Sample B2]

[0246] Except for the absence of fatty acid amides, it was prepared in the same manner as sample A3.

[0247] [Sample B3]

[0248] The base resin does not include styrene-containing resin, but contains 100 parts by weight of polyethylene. Apart from this, it is prepared in the same manner as sample A3.

[0249] [Sample B4]

[0250] Except for the fact that the content of styrene resin is 1.5 parts by mass, it was prepared in the same manner as sample A3.

[0251] [Sample B5]

[0252] Except for the fact that the content of styrene resin is 38 parts by mass, it was prepared in the same manner as sample A3.

[0253] [Sample B6]

[0254] Except for the use of the following styrene-containing resin, it is prepared in the same manner as sample A3.

[0255] • Hydrogenated styrene-butadiene-styrene block copolymer (SEBS) (density d = 0.97 g / cm³) 3 MFR = 2.0 g / 10 min, styrene content 67% by mass: 20 parts by mass

[0256] [Sample B7]

[0257] Except for the fact that the total styrene content in the base resin is 0.12 parts by mass, it was prepared in the same manner as sample A7.

[0258] [Sample B8]

[0259] Except for the fact that the total styrene content in the base resin is 12.9 parts by mass, it was prepared in the same manner as sample A8.

[0260] [Sample B9]

[0261] Except for the fact that the content of SEBS is 10 parts by mass with a styrene content of 67% by mass, it was prepared in the same manner as sample B6.

[0262] [Sample B10]

[0263] Except for the fact that the content of fatty acid amide is 0.02 parts by mass, it was prepared in the same manner as sample A3.

[0264] [Sample B11]

[0265] Except for the fact that the content of fatty acid amide is 1.5 parts by mass, it was prepared in the same manner as sample A3.

[0266] (2) Evaluation

[0267] Insulating sheets were prepared using the above-described electrical insulating composition, and each evaluation was conducted.

[0268] (Evaluation 1: Water-resistant tree)

[0269] After forming the above-mentioned electrical insulation composition, two insulating sheets with a thickness of 1 mm were produced by pressing the electrical insulation composition at 120°C for 10 minutes. After preparing the insulating sheets, a specified semiconducting sheet was sandwiched between the two insulating sheets to form a laminate. After forming the laminate, the laminate was pressed at 180°C for 30 minutes to crosslink the base resin in the insulating sheets. After the insulating sheets were crosslinked, wiring was formed on the semiconducting sheet.

[0270] Next, while the laminated sheet was immersed in a NaCl aqueous solution with a concentration of 1 equivalent at room temperature (27°C), an AC electric field of 4kV / mm at 60Hz was applied to the insulating sheet between the semiconducting sheet and the aqueous solution for 1000 hours.

[0271] After applying a predetermined alternating electric field, the laminated sheet was dried and stained with methylene blue aqueous solution while boiling. After staining, the laminated sheet was cut into 30 μm thicknesses along the lamination direction (i.e., the direction perpendicular to the main surface of the laminated sheet), thus forming observation sections. The observation sections were then observed using an optical microscope. Water trees were observed in the insulating sheet of the observation sections, either along the surface direction of the semiconducting sheet or perpendicular to the main surface of the semiconducting sheet. The maximum length of the water trees generated in the insulating sheet was measured. Furthermore, the concentration of water trees with a length of 30 μm or more generated in the insulating sheet was measured. It should be noted that in Tables 1 and 2 described later, the "maximum length of water trees" is calculated by rounding the length of the longest water tree among 10 randomly selected observation sections, and the "concentration of the number of water trees generated" is calculated by rounding the average concentration of the number of water trees generated in the 10 randomly selected observation sections.

[0272] It should be noted that, for reference, in existing water tree resistance evaluations, power cables with an insulation layer composed of a specified electrical insulation composition are prepared, and the power cables are immersed in water to evaluate water tree resistance. In this case, a shielding layer and an outer sheath are provided on the outside of the insulation layer of the power cable. Therefore, the insulation layer does not directly contact the water. In contrast, in this embodiment, as described above, the laminated sheet is directly immersed in a predetermined aqueous solution to evaluate water tree resistance. Therefore, the insulation sheet is in direct contact with the aqueous solution. Therefore, compared to evaluations using existing power cables, the water tree resistance evaluation of this embodiment is conducted under more severe conditions.

[0273] (Evaluation 2: Dielectric loss)

[0274] After forming the above-mentioned electrical insulation composition, an insulating sheet with a thickness of 0.2 mm was prepared by pressing the electrical insulation composition at 180°C for 30 minutes. At this time, the base resin of the insulating sheet was crosslinked by pressing the insulating sheet at 180°C for 30 minutes.

[0275] Next, using a Schering bridge, an alternating electric field was applied to the insulating sheet at 90°C, a commercial frequency (e.g., 60 Hz), and 9 kV / mm to measure the dielectric loss.

[0276] (Evaluation 3: Alternating current disrupts the electric field)

[0277] The same insulating sheet as in Evaluation 2 above was prepared. Next, an AC voltage of 5 kV was applied to the insulating sheet for 1 minute at room temperature (27°C) and a commercial frequency (e.g., 60 Hz). Afterward, the AC voltage was increased by 1 kV increments, and the cycle of applying the AC voltage to the insulating sheet for 1 minute was repeated. Then, the electric field at which insulation failure occurred in the insulating sheet was measured.

[0278] (Evaluation 4: Gel fraction (degree of cross-linking))

[0279] After forming the above-mentioned electrical insulation composition, an insulating sheet with a thickness of 1 mm was produced by pressing the electrical insulation composition at 180°C for 30 minutes. In this case, the base resin of the insulating sheet is crosslinked by pressing the insulating sheet at 180°C for 30 minutes.

[0280] After the insulating sheet is prepared, the gel fraction is measured according to JIS C3005. Specifically, first, the mass of the insulating sheet is measured. Next, the insulating sheet is immersed in a specified solvent (e.g., hot xylene) to dissolve it. At this point, the cross-linked portion of the base resin in the insulating sheet remains as a gel and does not dissolve. After the insulating sheet is dissolved, the mass of the undissolved gel is measured. As a result, the "gel fraction" is determined by calculating the ratio (%) of the mass of the residual gel to the mass of the insulating sheet before dissolution.

[0281] (Evaluation 5: Tensile Properties)

[0282] The same insulating sheet as evaluated in section 4 above was fabricated. Next, the tensile strength and elongation of the insulating sheet were measured according to JIS C3005. Specifically, the tensile strength and elongation of the insulating sheet were measured by stretching the sheet at a tensile speed of 200 mm / min using a JIS-3 dumbbell.

[0283] (Rating 6: Frosty)

[0284] After the granules of the electrical insulation composition were kept in a constant temperature bath at 80°C for 10 days, their surface was visually observed. The presence or absence of frost on the granule surface was evaluated by observation. The case without frost was designated as "A", and the case with frost was designated as "B".

[0285] (3) Results

[0286] The evaluation results for each sample are explained using Tables 1 and 2 below. It should be noted that the unit of measurement for the content of each compounding agent in Tables 1 and 2 is "parts by mass". Furthermore, in Tables 1 and 2, the "St" in parentheses for styrene-containing resins refers to the styrene content.

[0287]

[0288]

[0289] As shown in Table 2, in sample B1, which did not contain either styrene resin or fatty acid amide, the concentration of water tree formation was high, and the maximum length of the water tree was also long. Furthermore, in sample B2, which only contained styrene resin, the concentration of water tree formation was lower than that of sample B1, and the maximum length of the water tree was slightly shorter than that of sample B1, but the maximum length of the water tree was longer. Additionally, in sample B3, which only contained fatty acid amide, the concentration of water tree formation was lower than that of sample B1, but the maximum length of the water tree was the same as that of sample B1.

[0290] In contrast, as shown in Table 1, in samples A1–A14 containing both styrene resin and fatty acid amide, the concentration of water trees was significantly lower than in samples B1–B3, at 60 trees / cm³. 3 Furthermore, in samples A1 to A14, the maximum length of the water tree is shorter than that in samples B1 to B3, being less than 100 μm.

[0291] These results confirm that by adding styrene-containing resin and fatty acid amide, the maximum length of water trees generated in the insulation layer can be shortened due to their synergistic effect, and the number density of water trees generated in the insulation layer can be significantly reduced.

[0292] Furthermore, as shown in Table 2, in samples B4 (and B7) containing less than 2 parts by mass of styrene resin, the concentration of water trees formed was lower than that in sample B1, but still 200 trees / cm³. 3 That's all. Furthermore, in sample B4, although the maximum length of the water tree was shorter than that of each of samples B1 to B3, it was still over 120 μm.

[0293] In contrast, as shown in Table 1, in samples A1 to A14 containing 2 or more parts by mass of styrene resin, the concentration of water trees was significantly lower than that in sample B4. Furthermore, in samples A1 to A14, the maximum length of the water trees was shorter than that in sample B4.

[0294] These results confirm that by setting the content of styrene-containing resin to 2 parts by mass or more, the water tree-inhibiting effect brought about by styrene-containing resin can be fully obtained.

[0295] Furthermore, as shown in Table 2, in sample B5 containing more than 35 parts by mass of styrene resin, the dielectric loss is high and the tensile elongation is short.

[0296] In contrast, as shown in Table 1, in samples A1 to A14 with a styrene resin content of 35 parts by mass or less, the dielectric loss was less than that of sample B5, being less than 0.05%. Furthermore, in samples A1 to A14, the tensile elongation was greater than that of sample B5, being more than 430%.

[0297] Based on these results, by setting the content of styrene-containing resin to 35 parts by mass or less, excessive electron capture by the aromatic rings of styrene can be suppressed, and the increase in losses to the alternating electric field can be suppressed. This confirms that dielectric loss can be reduced. Furthermore, by setting the content of styrene-containing resin to 35 parts by mass or less, the relative excess of polystyrene blocks as hard segments can be suppressed. This confirms that the shortening of tensile elongation can be suppressed.

[0298] Furthermore, as shown in Table 2, in samples B6 and B9, where the styrene content in the styrene-containing resin is 45% by mass or more, although the maximum length of the water tree is within the aforementioned specified range (less than 200 μm), it is close to its upper limit. Additionally, in samples B6 and B9, although the dielectric loss is within the aforementioned specified range (less than 0.05%), it is at its upper limit. Furthermore, in samples B6 and B9, although the tensile elongation is within the aforementioned specified range (more than 350%), it is at or close to its lower limit.

[0299] In contrast, as shown in Table 1, in samples A1 to A14, where the styrene content in the styrene-containing resin is less than 45% by mass, the maximum length of the water tree is shorter than that of each of samples B6 and B9, being less than 100 μm. Furthermore, in samples A1 to A14, the dielectric loss is lower than that of each of samples B6 and B9, being less than 0.04%. Additionally, in samples A1 to A14, the tensile elongation is greater than that of each of samples B6 and B9, exceeding 430%.

[0300] Based on these results, by reducing the styrene content to less than 45% by mass, stress cracking in the electrical insulation composition can be uniformly suppressed, and the propagation of water trees can be inhibited. The results confirm that the maximum length of water trees can be sufficiently shortened. Furthermore, by reducing the styrene content to less than 45% by mass, the localized non-uniformity of electron trapping on the aromatic rings of styrene can be suppressed, thereby significantly reducing losses to the alternating current field. This confirms that dielectric losses can be sufficiently reduced. Moreover, by reducing the styrene content to less than 45% by mass, the relative increase in polystyrene blocks as hard segments can be suppressed. This confirms that tensile elongation can be sufficiently extended.

[0301] Furthermore, as shown in Table 2, in sample B7, where the total styrene content in the base resin was less than 0.15 parts by mass, the concentration of water trees formed was lower than that of each of samples B1 to B3, but still 200 trees / cm³. 3 That's all. Furthermore, although the maximum length of the water tree in sample B7 was shorter than that in samples B1-B3, it was still over 200 μm. It should be noted that the fact that the styrene resin content in sample B7 was less than 2 parts by mass is believed to be another reason for the low water tree resistance.

[0302] In contrast, as shown in Table 1, in samples A1 to A14 where the total styrene content in the base resin was 0.15 parts by mass or more, the concentration of water trees formed was significantly lower than that in sample B7. Furthermore, the maximum length of the water trees in samples A1 to A14 was shorter than that in sample B7.

[0303] These results confirm that by setting the total styrene content in the base resin to 0.15 parts by mass or more, the water tree inhibition effect of styrene-containing resin can be fully obtained.

[0304] Furthermore, as shown in Table 2, in sample B8, where the total styrene content in the base resin exceeds 11 parts by mass, although the dielectric loss is within the aforementioned specified range (less than 0.05%), it is at its upper limit. Additionally, in sample B8, although the tensile elongation is within the aforementioned specified range (more than 350%), it is at its lower limit.

[0305] In contrast, as shown in Table 1, in samples A1 to A14 where the total styrene content in the base resin is less than 11 parts by mass, the dielectric loss is less than that of sample B8, being less than 0.04%. Furthermore, in samples A1 to A14, the tensile elongation is greater than that of sample B8, being more than 430%.

[0306] Based on these results, by setting the total styrene content in the base resin to 11 parts by mass or less, the loss to the alternating electric field caused by electron capture on the aromatic ring of styrene can be sufficiently reduced. This confirms that dielectric loss can be sufficiently reduced. Furthermore, by setting the total styrene content to 11 parts by mass or less, the relative increase of polystyrene blocks as hard segments can be suppressed. This confirms that tensile elongation can be sufficiently extended.

[0307] Furthermore, as shown in Table 2, in sample B10, where the content of fatty acid amide was less than 0.05 parts by mass, although the concentration of water trees formed was lower than that in sample B1, it was still 200 trees / cm³. 3 That's all. Furthermore, in sample B10, although the maximum length of the water tree was slightly shorter than that of each of samples B1 to B3, it still exceeded 200 μm.

[0308] In contrast, as shown in Table 1, the concentration of water trees formed in samples A1 to A14, where the content of fatty acid amide was 0.05 parts by mass or more, was significantly lower than that in sample B10. Furthermore, the maximum length of the water trees in samples A1 to A14 was shorter than that in sample B10.

[0309] These results confirm that by setting the content of fatty acid amide to 0.05 parts by mass or more, the inhibitory effect of fatty acid amide on water trees can be fully obtained.

[0310] Furthermore, as shown in Table 2, blooming occurred in sample B11 where the content of fatty acid amide exceeded 1.0 parts by mass.

[0311] In contrast, as shown in Table 1, no frosting occurred in samples A1 to A14 with a fatty acid amide content of less than 1.0 parts by mass.

[0312] These results confirm that setting the content of fatty acid amide to less than 1.0 parts by weight can suppress blooming caused by differences in compatibility between the base resin and the fatty acid amide.

[0313] Furthermore, as shown in Table 1, in samples A1 to A14, the ratio of the total styrene content B in the base resin to the fatty acid amide content A, B / A, was 1.5 to 110. As described above, it can be confirmed that by setting the content ratio B / A to 1.5 or higher, a significant water-tree-inhibiting effect from both the fatty acid amide and the styrene-containing resin can be stably obtained. Furthermore, by setting the content ratio B / A to 110 or lower, the polystyrene blocks can be uniformly dispersed. The results confirmed a stable suppression of the increase in dielectric loss and the decrease in tensile elongation. It was also confirmed that by setting the content ratio B / A to 110 or lower, the significant water-tree-inhibiting effect from both the fatty acid amide and the styrene-containing resin can be fully obtained through the inhibition of localized water concentration caused by the polar groups of the fatty acid amide.

[0314] As described above, based on samples A1 to A14, it can be confirmed that under harsh conditions where the insulating sheet is in direct contact with the aqueous solution, there is a significant effect in suppressing water treeing. This confirms that by manufacturing power cables having an insulating layer composed of the respective electrical insulating compositions of samples A1 to A14, the formation of water treeing in the insulating layer can be stably suppressed.

[0315] <Preferred methods of this disclosure>

[0316] The preferred embodiments of this disclosure are listed below.

[0317] (Postscript 1)

[0318] An electrical insulation composition comprising:

[0319] The base resin comprising 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin, totaling 100 parts by weight; and

[0320] Fatty acid amides in amounts of 0.05 parts by weight to 1.0 parts by weight.

[0321] (Postscript 2)

[0322] According to the electrical insulation composition described in Appendix 1, when the electrical insulation composition having the base resin and the fatty acid amide is impregnated in a 1 equivalent concentration NaCl aqueous solution at room temperature, and an AC electric field of 4 kV / mm at a commercial frequency is applied to the electrical insulation composition for 1000 hours,

[0323] The maximum length of the water tree generated in the electrical insulation composition is less than 200 μm.

[0324] (Note 3)

[0325] According to Appendix 1 or Appendix 2, the electrical insulating composition, wherein when the electrical insulating composition having the base resin and the fatty acid amide is impregnated in a 1 equivalent concentration NaCl aqueous solution at room temperature, is subjected to a commercial frequency AC electric field of 4 kV / mm for 1000 hours,

[0326] The concentration of water trees with a length of 30 μm or more generated in the electrical insulation composition is less than 200 per cm³. 3 .

[0327] (Note 4)

[0328] The electrical insulating composition according to any one of Annexes 1 to 3, wherein the styrene content in the styrene-containing resin is less than 45% by mass.

[0329] (Note 5)

[0330] The electrical insulating composition according to any one of Annexes 1 to 4, wherein the total styrene content in the base resin is 0.15 parts by mass to 11 parts by mass relative to 100 parts by mass of the base resin.

[0331] (Note 6)

[0332] The electrical insulating composition according to any one of Annexes 1 to 5, wherein the total styrene content in the base resin is in a ratio of 1.5 to 110 to the content of the fatty acid amide.

[0333] (Note 7)

[0334] The electrical insulating composition according to any one of Annexes 1 to 6 further comprises 0.1 to 10 parts by mass of an unsaturated dimer of an α-aromatic substituted α-methyl olefin.

[0335] (Postscript 8)

[0336] The electrical insulating composition according to any one of Annexes 1 to 7, wherein the fatty acid amide is a fatty acid monoamide.

[0337] (Note 9)

[0338] The electrical insulating composition according to any one of Annexes 1 to 8, wherein the fatty acid amide is an unsaturated fatty acid amide.

[0339] (Postscript 10)

[0340] The electrical insulating composition according to any one of Annexes 1 to 9, wherein it comprises a crosslinking agent having an organic peroxide.

[0341] (Postscript 11)

[0342] The electrical insulating composition according to any one of Annexes 1 to 9, wherein the base resin is cross-linked.

[0343] (Postscript 12)

[0344] An electrical cable comprising

[0345] conductors; and

[0346] An insulating layer is configured to cover the outer periphery of the conductor.

[0347] The insulating layer is composed of an electrical insulating composition resin having a base resin and a fatty acid amide, wherein the base resin comprises 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin, totaling 100 parts by weight, and the fatty acid amide comprises 0.05 to 1.0 parts by weight.

[0348] (Postscript 13)

[0349] A method for manufacturing an electrical cable, comprising:

[0350] The steps for preparing an electrical insulation composition; and

[0351] The step of forming an insulating layer by using the electrical insulating composition to cover the outer periphery of a conductor.

[0352] In the step of preparing the electrical insulation composition, a base resin comprising 100 parts by mass of polyethylene (65 to 98 parts by mass) and styrene-containing resin (2 to 35 parts by mass) is mixed with fatty acid amide (0.05 to 1.0 parts by mass) to form the electrical insulation composition.

[0353] Symbol Explanation

[0354] 10. Power cables

[0355] 110 conductor

[0356] 120 Internal Semiconductor Layer

[0357] 130 insulation layer

[0358] 140 External Semiconductor Layer

[0359] 150 shielding layers

[0360] 160 outer skin

Claims

1. An electrical insulation composition comprising: The base resin comprising 100 parts by weight, including 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin; and Fatty acid amides, ranging from 0.05 parts by weight to 1.0 parts by weight. The styrene content in the styrene-containing resin is less than 45% by mass. The ratio of the total styrene content in the base resin to the fatty acid amide content is between 1.5 and 110. When the electrical insulation composition comprising the base resin and the fatty acid amide is directly impregnated in a 1-equivalent NaCl aqueous solution at room temperature, and an AC electric field of 4 kV / mm at a commercial frequency is applied to the electrical insulation composition for 1000 hours, The number density of water trees having a length of 30 μm or more generated in the electrical insulating composition is less than 60 per cm 3 .

2. The electrical insulation composition according to claim 1, wherein, When the electrical insulation composition comprising the base resin and the fatty acid amide is impregnated in a 1-equivalent NaCl aqueous solution at room temperature, and an AC electric field of 4 kV / mm at a commercial frequency is applied to the electrical insulation composition for 1000 hours, The maximum length of the water tree generated in the electrical insulation composition is less than 200 μm.

3. The electrical insulation composition according to claim 1 or claim 2, wherein, The total styrene content in the base resin is between 0.15 and 11 parts by weight relative to 100 parts by weight of the base resin.

4. The electrical insulation composition according to claim 1 or claim 2, wherein, It also includes unsaturated dimers of α-aromatic substituted α-methyl olefins, ranging from 0.1 parts by mass to 10 parts by mass.

5. The electrical insulation composition according to claim 1 or claim 2, wherein, The fatty acid amide is a fatty acid monoamide.

6. The electrical insulation composition according to claim 1 or claim 2, wherein, The fatty acid amide is an unsaturated fatty acid amide.

7. The electrical insulating composition according to claim 1 or claim 2, wherein it comprises a crosslinking agent containing an organic peroxide.

8. The electrical insulation composition according to claim 1 or claim 2, wherein, The base resin is cross-linked.

9. A power cable, comprising: conductor; as well as An insulating layer is configured to cover the outer periphery of the conductor. The insulating layer is composed of an electrical insulating composition having a base resin and a fatty acid amide, wherein the base resin comprises 65 to 98 parts by weight of polyethylene and 2 to 35 parts by weight of styrene-containing resin, totaling 100 parts by weight, and the fatty acid amide comprises 0.05 to 1.0 parts by weight. The styrene content in the styrene-containing resin is less than 45% by mass. The ratio of the total styrene content in the base resin to the fatty acid amide content is between 1.5 and 110. When the electrical insulation composition is directly immersed in a 1-equivalent NaCl aqueous solution at room temperature, and a commercial frequency AC electric field of 4 kV / mm is applied to the electrical insulation composition for 1000 hours, The concentration of water trees with a length of 30 μm or more generated in the electrical insulation composition is less than 60 per cm³. 3 .

Images