Power cable

Abstract

To provide a power cable having a conductor covered with an insulating layer that has good electrical insulation performance and heat deformation resistance, and has superior recyclability.SOLUTION: A power cable having a conductor coated with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylic acid ester copolymer, wherein when the content proportion of (meth)acrylic acid ester unit in the ethylene-(meth)acrylic acid ester copolymer is represented by A (mol%), the crosslinking degree C (%) of the crosslinked product is in the range represented by the following formulae: 25≤C≤2.3A+77 (where 1.5≤A≤8.0) and 25≤C≤95 (where 8.0<A).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a power cable, and more particularly to a power cable having an insulating layer with good electrical insulation and heat deformation resistance and excellent recyclability.

Background Art

[0002] The insulating layer (insulating coating layer) of a power cable is required to have electrical insulation and heat deformation resistance, and it is also required to effectively utilize (recycle) the waste material of the insulating layer after the use of the power cable as a renewable resource. However, the cross-linked polyethylene that constitutes the conventionally known insulating layer cannot be melted by heat or a solvent, and its recycling method is limited. Therefore, methods of forcibly cutting the carbon chain by water in a supercritical state (see Patent Documents 1 and 2 below) or shear by a twin-screw extruder (see Patent Documents 3 and 4 below) have been studied. However, these methods cannot avoid the new introduction of equipment or the deterioration of quality, and have hardly reached industrialization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] An object of the present invention is to provide a power cable in which a conductor is covered with an insulating layer having good electrical insulation and heat deformation resistance and excellent recyclability.

Means for Solving the Problem

[0005] The power cable of the present invention is a power cable in which a conductor is coated with an insulating layer formed from a crosslinked body of an ethylene-(meth)acrylate copolymer, when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol %), the crosslinking degree C (%) of the crosslinked body is in the range represented by the following formula.

[0006] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0007] In the power cable of the present invention, it is preferable that the crosslinking degree C of the crosslinked body is 45% or more.

[0008] In the power cable of the present invention, it is preferable that the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate (the conductor is coated with an insulating layer formed from a crosslinked body of ethylene-ethyl acrylate).

[0009] The power cable of the present invention is preferably one in which the conductor is coated with the insulating layer formed by peroxide crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer and a peroxide crosslinking agent.

[0010] The power cable of the present invention may be one in which the conductor is coated with the insulating layer formed by silane crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer and a silane crosslinking agent.

[0011] The power cable of the present invention may be one in which the conductor is coated with the insulating layer formed by electron beam crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer.

[0012] In the power cable of the present invention, it is preferable that the degree of crosslinking of the crosslinked body constituting the insulating layer decreases to less than 15% when heated at 350°C.

Advantages of the Invention

[0013] According to the power cable of the present invention, the insulating layer constituting the same has good electrical insulation and heat resistance deformation properties, and is also excellent in recyclability. That is, by heating the crosslinked body constituting the insulating layer of the power cable to a predetermined temperature (usually higher than the crosslinking temperature), a de-crosslinking reaction occurs, and at least a part of the crosslinked structure can be returned to an uncrosslinked state (a recyclable state). Also, as is clear from the results of the examples described later, the insulating layer of the power cable of the present invention has good electrical insulation and heat resistance deformation properties.

Brief Description of the Drawings

[0014]

Figure 1

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail. In the power cable of the present invention, the outer peripheral surface of the conductor is covered by an insulating layer formed from a crosslinked body of an ethylene-(meth)acrylate copolymer, either directly or via a semiconductive layer.

[0016] FIG. 1 is a cross-sectional view showing an example of the power cable of the present invention. The power cable 10 shown in FIG. 1 has an inner semiconductive layer 12, an insulating layer 13, and an outer semiconductive layer 14 laminated on the outer peripheral surface of a conductor 11, and further, a metal shielding layer 15 and a sheath 16 are laminated and arranged on the outer peripheral surface of the outer semiconductive layer 14.

[0017] The insulating layer of the power cable of the present invention is formed of a crosslinked product of an ethylene-(meth)acrylate copolymer (hereinafter, also referred to as "specific resin crosslinked product") having a degree of crosslinking within the range represented by the above formula.

[0018] The degree of crosslinking of the specific resin crosslinked product constituting the insulating layer is set to 25% or more, preferably 45% or more, and more preferably 70% or more. A resin crosslinked product with an excessively low degree of crosslinking (less than 25%) cannot exhibit sufficient heat resistance to deformation and will undergo melt deformation under temperature conditions exceeding the melting point of the resin (see Comparative Example 2 described later).

[0019] The upper limit value of the degree of crosslinking of the specific resin crosslinked product (hereinafter, also referred to as "upper limit degree of crosslinking") is defined from the viewpoint of allowing the de-crosslinking reaction to proceed sufficiently. Here, the de-crosslinking reaction of the specific resin crosslinked product proceeds more easily as the content ratio (comonomer amount) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is higher. As shown in the above formula, when the content ratio A of the (meth)acrylate unit is 1.5 to 8.0 mol%, the upper limit degree of crosslinking of the specific resin crosslinked product is 2.3A + 77 (%), and when the content ratio A exceeds 8.0 mol%, it is 95%.

[0020] If the degree of crosslinking of the resin crosslinked product is excessive (exceeding the upper limit degree of crosslinking), the de-crosslinking reaction will not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (regenerated) (see Comparative Example 1 described later).

[0021] The specific resin crosslinked product constituting the insulating layer can be obtained by crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer (uncrosslinked resin) and a crosslinking agent.

[0022] The crosslinkable resin composition (hereinafter, also referred to as "specific resin composition") for obtaining the specific resin crosslinked product has its crosslinking agent content adjusted so that a resin crosslinked product having a degree of crosslinking within the range represented by the above formula can be obtained, thereby enabling reversible crosslinking (crosslinking reaction and de-crosslinking reaction).

[0023] Here, in the de-crosslinking reaction of the resin composition (resin crosslinked body), the structure of the polymer side chain is important, and it is necessary to have an atomic group containing a heteroatom. Therefore, ethylene homopolymers and copolymers, such as ethylene-α-olefin copolymers which are hydrocarbon compounds (for example, propylene, butene-1, 1-hexene, etc. as α-olefins), are not suitable. Furthermore, even for ethylene-α-olefin copolymers containing a heteroatom group, when vinyl alcohol esters such as ethylene-vinyl acetate copolymer (EVA) are used as copolymer components, it is well known that decarboxylation reaction, generation of main chain double bonds, and subsequent crosslinking reaction occur upon heating, and the heat resistance at the de-crosslinking temperature is insufficient. For this reason, the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (recycled). Also, when (meth)acrylic acid such as ethylene-(meth)acrylic acid copolymer (EAA, EMAA) is used as a copolymer component, it is well known that intermolecular dehydration reaction and crosslinking reaction due to the formation of acid anhydride occur upon heating, and similarly the heat resistance is insufficient. For this reason, the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (recycled). In contrast, such side reactions do not occur in ethylene-(meth)acrylate copolymers, so the de-crosslinking reaction proceeds efficiently by heating at a predetermined temperature.

[0024] Examples of the ethylene-(meth)acrylate copolymer contained in a specific resin composition include ethylene-methyl acrylate, ethylene-ethyl acrylate, ethylene-propyl acrylate, ethylene-butyl acrylate, ethylene-2-ethylhexyl acrylate, ethylene-methyl methacrylate, ethylene-ethyl methacrylate, ethylene-propyl methacrylate, ethylene-butyl methacrylate, and ethylene-2-ethylhexyl methacrylate.

[0025] Here, since the ethylene-acrylic acid ester copolymer is less likely to exhibit a disintegrating reaction with respect to radicals, a high degree of crosslinking is easily obtained mainly by peroxide crosslinking, and the crosslinking efficiency can be higher than that of a resin component composed of an ethylene-methacrylic acid ester copolymer. Also, from the viewpoint of obtaining a resin crosslinked body that well balances high mechanical strength and good flexibility, the copolymer component of the resin component is preferably an ethyl ester of (meth)acrylic acid. From the above, among the ethylene-(meth)acrylic acid ester copolymers exemplified above, ethylene-ethyl acrylate (EEA) is particularly preferable from the viewpoints of high crosslinking efficiency and excellent physical property balance.

[0026] In the ethylene-(meth)acrylic acid ester copolymer contained in a specific resin composition, the content ratio (comonomer amount) of the (meth)acrylic acid ester unit is 1.5 mol% or more, preferably 1.5 to 16 mol%, more preferably 2.0 to 13 mol%. When the content ratio of the (meth)acrylic acid ester unit is too small, the de-crosslinking reaction of the resin crosslinked body obtained by crosslinking the resin composition does not proceed sufficiently, so that a resin composition that can be melt-molded cannot be manufactured (recycled). On the other hand, when this ratio is too large, properties such as the mechanical strength and electrical insulation properties of the resin crosslinked body obtained by crosslinking the resin composition may be impaired.

[0027] A specific resin composition usually contains a crosslinking agent. As the crosslinking agent contained in a specific resin composition, a peroxide crosslinking agent and a silane crosslinking agent can be used, and it is preferable to use a peroxide crosslinking agent from the viewpoint of obtaining a resin crosslinked body with a high degree of crosslinking.

[0028] The peroxide crosslinking agent is not particularly limited, and examples thereof include bis(t-butylperoxyisopropyl)benzene, t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, etc. Among these, dicumyl peroxide is preferred.

[0029] Examples of the silane crosslinking agent include compounds having a functional group reactive with an ethylene-(meth)acrylate copolymer and a plurality of alkoxy groups. Specifically, vinylsilane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane; aminosilane compounds such as γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β-(aminoethyl)γ-aminopropyltrimethoxysilane, β-(aminoethyl)γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane; epoxy silane compounds such as β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane; acrylic silane compounds such as γ-methacryloxypropyltrimethoxysilane; polysulfide silane compounds such as bis(3-methacryloxysilyl)propyl)disulfide, bis(3-(triethoxysilyl)propyl)tetrasulfide; mercapto silane compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, etc. can be exemplified.

[0030] The content of the crosslinking agent in the specific resin composition is adjusted so that the degree of crosslinking (C) of the specific resin crosslinked product obtained by crosslinking the resin composition falls within the range represented by the above formula, and it varies depending on the content ratio (A) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer which is the resin component. However, it is preferably 0.25 to 4.5 parts by mass, more preferably 0.3 to 4.0 parts by mass, based on 100 parts by mass of the resin component.

[0031] The specific resin composition can contain, as optional components, components used in the resin composition for forming the insulating layer of a power cable as needed. These optional components become the constituent components of the specific resin crosslinked product.

[0032] Examples of such optional components include inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, carbon black, glass fibers, carbon fibers), plasticizers (phthalic acid esters, trimellitic acid esters, polyesters), softeners (mineral oils, process oils, fatty acids), antioxidants (hindered phenol-based stabilizers, sulfur-based stabilizers, amine-based stabilizers), ultraviolet absorbers (benzophenone-based UVA, benzotriazole-based UVA, salicylic acid ester-based UVA), antistatic agents (glycerin fatty acid esters, alkyl sulfonic acids, tetraalkylammonium salts), flame retardants (metal hydroxides, phosphorus compounds, halogen compounds), lubricants (fatty acid amides, zinc stearate, silicones), foaming agents [azodicarbonamide (ADCA), sodium hydrogen carbonate, 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH)], colorants (azo compounds, anthraquinone compounds, phthalocyanine compounds, titanium oxide, carbon black), crosslinking aids [trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate (TMPTM), triallyl isocyanurate (TAIC), triallyl cyanurate (TAC)], light stabilizers (hindered amine-type compounds, hindered piperidine-type compounds), etc.

[0033] A specific resin composition can perform reversible crosslinking (crosslinking reaction and de-crosslinking reaction). Here, the crosslinking reaction is carried out at a relatively low temperature, and the de-crosslinking reaction is carried out at a relatively high temperature.

[0034] The crosslinking degree C (%) of a specific resin crosslinked body constituting the insulating layer can be adjusted by appropriately adjusting the content of the crosslinking agent according to the content ratio A (mol%) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer. In addition, the crosslinking degree C (%) of a specific resin crosslinked body by electron beam crosslinking can be adjusted by appropriately adjusting the irradiation conditions of the electron beam irradiated to the specific resin composition according to the content ratio A (mol%).

[0035] The power cable 10 shown in FIG. 1 is manufactured by simultaneously extrusion-molding an internal semiconductive layer 12 covering a conductor 11, an insulating layer forming layer made of a specific resin composition, and an external semiconductive layer 14, crosslinking the insulating layer forming layer (specific resin composition) to form an insulating layer 13 (specific resin crosslinked body), and then providing a metal shielding layer 15 and a sheath 16 on the outer peripheral surface of the external semiconductive layer 14 according to a conventional method.

[0036] The crosslinking method for forming the insulating layer (specific resin crosslinked body) is not particularly limited. For example, (1) A method of performing chemical crosslinking (peroxide crosslinking) by heating a specific resin composition containing an ethylene-(meth)acrylate copolymer and a peroxide crosslinking agent at a predetermined temperature. (2) A method of performing silane crosslinking by heating a specific resin composition containing an ethylene-(meth)acrylate copolymer and a silane crosslinking agent at a predetermined temperature. (3) A method of performing electron beam crosslinking by irradiating a specific resin composition containing an ethylene-(meth)acrylate copolymer with an electron beam can be mentioned.

[0037] Also, the crosslinking treatment method is not particularly limited, but usually, a pressure heating treatment or the like can be adopted. As an example, under a nitrogen atmosphere, at a pressure of 4 to 10 kg / cm 2 , by heating the insulating layer forming layer under the conditions of a temperature of 160 to 260°C, the crosslinking of a specific resin composition can be advanced.

[0038] By heating a specific resin crosslinked body constituting the insulating layer of the power cable of the present invention at a predetermined temperature, at least a part of the crosslinked structure can be de-crosslinked.

[0039] The heating temperature for de-crosslinking the specific resin crosslinked body constituting the insulating layer is preferably in the range of 300 to 400°C, and more preferably in the range of 320 to 380°C.

[0040] The specific resin crosslinked body constituting the insulating layer preferably has a crosslinking degree that decreases to less than 15%, particularly less than 10% when heated at 350°C. The resin (ethylene-(meth)acrylate copolymer) with a crosslinking degree reduced to less than 15% can be subjected to remelting and molding by heating and can be suitably used as a recycled resin.

[0041] In the power cable 10 shown in FIG. 1, the internal semiconductive layer 12 and the external semiconductive layer 14 may be made of a specific resin crosslinked body containing conductive particles such as carbon black. In this case, since the recycling process can be performed without separating the internal semiconductive layer 12, the insulating layer 13, and the external semiconductive layer 14, the recycling efficiency can be improved.

Examples

[0042] Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto. In the following examples and comparative examples, the following compounds were used as the (co)polymers and crosslinking agents constituting the resin components.

[0043] · Copolymer (EEA-1) Density = 0.93 g / cm 3, Ethylene-ethyl acrylate copolymer with MFR(190℃, 2.16kg) = 1.5 g / 10min and EA content ratio = 4.7 mol%.

[0044] · Copolymer (EEA-2) Density = 0.94 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR(190℃, 2.16kg) = 1.6 g / 10min and EA content ratio = 8.1 mol%.

[0045] · Copolymer (EEA-3) Density = 0.93 g / cm 3 , Ethylene-ethyl acrylate copolymer with MFR(190℃, 2.16kg) = 4.0 g / 10min and EA content ratio = 2.1 mol%.

[0046] · Antioxidant (AO-1) Hindered phenolic stabilizer, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]

[0047] · Crosslinking agent (PO-1) Peroxide crosslinking agent consisting of dicumyl peroxide

[0048] <Manufacture of crosslinkable resin composition> 〔Example 1〕 According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-1) and 0.15 parts by mass of antioxidant (AO-1) were melt-kneaded. Then, 1.3 parts by mass of crosslinking agent (PO-1) was added to the obtained kneaded product, and after mixing at 60℃ for 12 hours, it was cooled to room temperature to obtain a specific resin composition. Next, using a general-purpose wire manufacturing extrusion molding machine, the outer peripheral surface of the conductor was extrusion-coated with an inner semiconductive layer (NUCV-9563 manufactured by ENEOS NUC), an insulating layer forming layer made of the specific resin composition obtained as described above, and an outer semiconductive layer (NUCV-9563 manufactured by ENEOS NUC). Next, under a nitrogen atmosphere, a pressure heat treatment was performed at a temperature of 260 °C to crosslink the insulating layer forming layer (specific resin composition) to form an insulating layer (specific resin crosslinked body). Next, the power cable of the present invention was manufactured by providing a metal shielding layer made of a copper tape and a sheath made of a vinyl chloride resin.

[0049] [Example 2] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-2), 0.15 parts by mass of an antioxidant (AO-1), and 1.2 parts by mass of a crosslinking agent (PO-1) were mixed to obtain a specific resin composition. A power cable of the present invention was manufactured in the same manner as in Example 1 except that this resin composition was used to form an insulating layer (specific resin crosslinked body).

[0050] [Example 3] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-3), 0.15 parts by mass of an antioxidant (AO-1), and 0.4 parts by mass of a crosslinking agent (PO-1) were mixed to obtain a specific resin composition. A power cable of the present invention was manufactured in the same manner as in Example 1 except that this resin composition was used to form an insulating layer (specific resin crosslinked body).

[0051] [Comparative Example 1] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-3), 0.15 parts by mass of an antioxidant (AO-1), and 1.8 parts by mass of a crosslinking agent (PO-1) were mixed to obtain a crosslinkable resin composition. A comparative power cable was manufactured in the same manner as in Example 1 except that this resin composition was used to form an insulating layer (resin crosslinked body). This Comparative Example 1 is a comparative example in which the degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is excessive.

[0052] [Comparative Example 2] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-3), 0.15 parts by mass of an antioxidant (AO-1), and 0.2 parts by mass of a crosslinking agent (PO-1) were mixed to obtain a crosslinkable resin composition. A comparative power cable was manufactured in the same manner as in Example 1 except that an insulating layer (resin crosslinked body) was formed using this resin composition. This Comparative Example 2 is a comparative example in which the crosslinking degree of the resin crosslinked body obtained by crosslinking the resin composition is too small.

[0053] <Measurement of the crosslinking degree of the resin crosslinked body> Test pieces were prepared by collecting the insulating layer (resin crosslinked body) from each of the power cables obtained in Examples 1 to 3 and Comparative Examples 1 and 2, and the crosslinking degree (gel fraction) was measured according to JIS C3005 except that the test pieces were used. The results are shown in Table 1 below.

[0054] <Evaluation of the heat resistance deformation of the insulating layer (measurement of the heating deformation rate)> Arc-shaped test pieces were prepared by collecting the insulating layer (resin crosslinked body) from each of the power cables obtained in Examples 1 to 3 and Comparative Examples 1 and 2, and the heat resistance deformation of the resin crosslinked body was evaluated by measuring the thickness reduction rate after heating according to JIS C3005 using the test pieces. As the evaluation criteria, when the heating deformation rate was 40% or less, it was regarded as "qualified (○)", and when it exceeded 40%, it was regarded as "unqualified (×)". The results are shown in Table 1 below.

[0055] <Evaluation of the electrical properties of the insulating layer (measurement of the volume resistivity)> Each of the crosslinkable resin compositions prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was crosslinked by pressing at 180 °C for 15 minutes using a hot press machine (manufactured by Toho Machinery, model TBD-50) to obtain a sheet-shaped resin crosslinked body. Test pieces were prepared from each of the obtained resin crosslinked bodies, and the volume resistivity was measured under the conditions of a temperature of 90 °C and an electric field of 10 kV / mm according to JIS C2139-3-1 using the test pieces to evaluate the electrical properties. As the evaluation criteria, when the volume resistivity was 10 12 Ω·cm or more, it was regarded as "qualified (○)", and 10 12When it was less than Ω·cm, it was regarded as "failed (×)". The results are shown in Table 1 below.

[0056] <Evaluation of Recyclability of Resin Crosslinked Body (Depolymerization Treatment)> The insulating layer (resin crosslinked body) was collected from each of the power cables obtained in Examples 1 to 3 and Comparative Examples 1 and 2, and for each of the collected resin crosslinked bodies, a depolymerization treatment was performed using a Laboplastmill single-screw extruder (manufactured by Toyo Seiki Seisakusho, main body model 4C150, extruder model D2025) at a rotational speed of 50 rpm and a temperature of 350 °C for 2 minutes. For each of the resins after the depolymerization treatment, the crosslinking degree (gel fraction) was measured according to JIS C3005 to evaluate the recyclability. As the evaluation criteria, when the crosslinking degree after the depolymerization treatment was less than 15%, it was regarded as "passed (○)", and when it was 15% or more, it was regarded as "failed (×)". If it was less than 15%, there were no lumps or roughness on the surface of the tape or strand made from the recycled copolymer, and a molded body with a good appearance could be obtained. The results are shown in Table 1 below.

[0057]

Table 1

Explanation of Symbols

[0058] 10 Power cable 11 Conductor 12 Inner semiconductive layer 13 Insulating layer 14 Outer semiconductive layer 15 Metal shielding layer 16 Sheath

Claims

1. A power cable in which a conductor is coated with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylate copolymer, wherein when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), the crosslinking degree C (%) of the crosslinked product is in the range represented by the following formula. ・25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) ・25 ≤ C ≤ 95 (where 8.0 < A)

2. The power cable according to claim 1, wherein the crosslinking degree C of the crosslinked product is 45% or more.

3. The power cable according to claim 1 or 2, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

4. The power cable according to claim 1 or 2, wherein the conductor is coated with the insulating layer formed by peroxide crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer and a peroxide crosslinking agent.

5. The power cable according to claim 1 or 2, wherein the conductor is coated with the insulating layer formed by silane crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer and a silane crosslinking agent.

6. The power cable according to claim 1 or 2, wherein the conductor is coated with the insulating layer formed by electron beam crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer.

7. The power cable according to claim 1 or 2, wherein when the crosslinked product constituting the insulating layer is heated at 350°C, its crosslinking degree decreases to less than 15%.

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