Outdoor insulated electric wire

Abstract

To provide an outdoor insulated electric wire having a conductor covered with an insulating layer that has good electrical insulation, mechanical properties, heat deformation resistance, and weather resistance, and also has superior recyclability.SOLUTION: An insulated wire having a conductor coated with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylic acid ester copolymer containing a specific amount of carbon black, 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 within a 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 an outdoor insulated wire, and more particularly to an outdoor insulated wire having an insulating layer with good electrical insulation, weather resistance, and excellent recyclability.

Background Art

[0002] For the insulating layer (insulating coating layer) of outdoor insulated wires such as outdoor crosslinked polyethylene insulated wires and pole transformer drop wire crosslinked polyethylene insulated wires, good electrical insulation, mechanical properties, heat deformation resistance, and weather resistance are required.

[0003] In order to impart weather resistance to the insulating layer of outdoor insulated wires, the applicant has proposed forming an insulating layer by crosslinking a crosslinkable resin composition obtained by blending carbon black with an ethylene-based resin at a certain ratio (see Patent Document 1 below).

[0004] Recently, it has been required to effectively utilize (recycle) the waste material of the insulating layer after use of outdoor insulated wires as a renewable resource. However, the crosslinked polyethylene constituting the conventionally known insulating layer cannot be melted by heat or a solvent, and its recycling method is limited. Therefore, methods of forcibly cutting carbon chains by supercritical water (see Patent Documents 2 and 3 below) or shear by a twin-screw extruder (see Patent Documents 4 and 5 below) have been studied. However, these methods inevitably involve new introduction of equipment and deterioration of quality, and have hardly reached industrialization.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide an outdoor insulated electric wire in which a conductor is coated with an insulating layer having good electrical insulation properties, mechanical properties, heat distortion resistance, and weather resistance, and excellent recyclability.

Means for Solving the Problems

[0007] The outdoor insulated electric wire of the present invention is an insulated electric wire in which a conductor is coated with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylate copolymer containing carbon black in a proportion of 0.2 to 4.0 parts by mass with respect to 100 parts by mass of the 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 product is in the range represented by the following formula.

[0008] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0009] In the outdoor insulated electric wire of the present invention, it is preferable that the crosslinking degree C of the crosslinked product is 45% or more.

[0010] In the outdoor insulated electric wire 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 product of ethylene-ethyl acrylate containing carbon black).

[0011] The outdoor insulated electric wire of the present invention is preferably formed by coating the conductor with the insulating layer formed by crosslinking a crosslinkable resin composition containing 100 parts by mass of an ethylene-(meth)acrylate copolymer, 0.2 to 4.0 parts by mass of carbon black, and a crosslinking agent.

[0012] In the outdoor insulated electric wire of the present invention, it is preferable that when the crosslinked product constituting the insulating layer is heated at 350 °C, the degree of crosslinking thereof decreases to less than 15%.

Effect of the Invention

[0013] According to the outdoor insulated electric wire of the present invention, it has good electrical insulation properties, mechanical properties, heat resistance to deformation, and weather resistance, and is also excellent in recyclability. That is, by heating the crosslinked product constituting the insulating layer of the outdoor insulated electric wire 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 outdoor insulated electric wire of the present invention has good electrical insulation properties, mechanical properties, heat resistance to deformation, and weather resistance.

Brief Description of the Drawings

[0014]

Figure 1

Embodiments for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail. The outdoor insulated electric wire of the present invention has an outer peripheral surface of a conductor coated with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylic acid ester copolymer containing carbon black.

[0016] FIG. 1 is a cross-sectional view showing an example of the outdoor insulated electric wire of the present invention. In the outdoor insulated electric wire 10 shown in FIG. 1, an insulating layer 13 is not formed on the outer peripheral surface of the conductor 11.

[0017] The insulating layer of the outdoor insulated electric wire of the present invention is formed of a crosslinked product of an ethylene-(meth)acrylic acid ester copolymer containing carbon black having a degree of crosslinking within the range represented by the above formula (hereinafter, also referred to as "specific resin crosslinked product").

[0018] The degree of crosslinking of the specific resin crosslinked product constituting the insulating layer is 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 melt and deform 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)acrylic acid ester unit in the ethylene-(meth)acrylic acid ester copolymer is higher. As shown in the above formula, when the content ratio of the (meth)acrylic acid ester unit is A, the upper limit degree of crosslinking of the specific resin crosslinked product is 2.3A + 77 (%) when the content ratio A is 1.5 to 8.0 mol%, and 95% when the content ratio A exceeds 8.0 mol%.

[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] A specific resin crosslinking product that constitutes the insulating layer can be obtained by crosslinking a crosslinkable resin composition containing an ethylene-(meth)acrylate copolymer (uncrosslinked resin), carbon black, and a crosslinking agent.

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

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

[0024] Examples of the ethylene-(meth)acrylate copolymer contained in the 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-(meth)acrylate 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 using an ethylene-methacrylate copolymer as a resin component. 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)acrylate copolymers exemplified above, ethylene-ethyl acrylate (EEA) is particularly preferred from the viewpoints of high crosslinking efficiency and excellent physical property balance.

[0026] In the ethylene-(meth)acrylate copolymer contained in the specific resin composition, the content ratio (comonomer amount) of the (meth)acrylate unit is 1.5 mol% or more, preferably 1.5 to 16 mol%, more preferably 2.0 to 13 mol%, and particularly preferably 3.0 to 9.0 mol%. When the content ratio of the (meth)acrylate 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 melt-moldable resin composition cannot be produced (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] The carbon black contained in a specific resin composition becomes a constituent of a specific resin crosslinked body after crosslinking, and imparts good weather resistance to an insulating layer made of the specific resin crosslinked body. The carbon black is not particularly limited, and examples thereof include graphitized carbon, furnace black, acetylene black, ketjen black, and the like. Among these, furnace black is preferred because it can balance the electrical insulation properties and weather resistance of the formed insulating layer.

[0028] The content of carbon black in the specific resin composition / specific resin crosslinked body is 0.2 to 4.0 parts by mass, preferably 0.5 to 2.5 parts by mass, based on 100 parts by mass of the ethylene-(meth)acrylate copolymer. When the content of carbon black is less than 0.2 parts by mass, good weather resistance cannot be imparted to the formed insulating layer (see Comparative Example 3 described later). On the other hand, when the content of carbon black exceeds 4.0 parts by mass, the electrical insulation properties of the insulating layer tend to be impaired (see Comparative Example 4 described later).

[0029] As the crosslinking agent contained in the 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.

[0030] 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, and the like. Among these, dicumyl peroxide is preferred.

[0031] 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.

[0032] The content of the crosslinking agent in a specific resin composition is adjusted so that the crosslinking degree (C) of a specific resin crosslinked product obtained by crosslinking the resin composition falls within the range shown by the above formula, and it also 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, and particularly preferably 0.4 to 2.0 parts by mass with respect to 100 parts by mass of the resin component.

[0033] The specific resin composition may contain, as optional components, components used in the resin composition for forming the insulating layer of an insulated electric wire as needed. These optional components, together with carbon black, become the constituent components of a specific resin crosslinked product.

[0034] Examples of such optional components include inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, glass fibers, carbon fibers), plasticizers (phthalic acid esters, trimellitic acid esters, polyesters), softeners (mineral oil, process oil, 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, alkylsulfonic acids, tetraalkylammonium salts), flame retardants (metal hydroxides, phosphorus compounds, halogen compounds), lubricants (fatty acid amides, zinc stearate, silicone), foaming agents [azodicarbonamide (ADCA), sodium hydrogen carbonate, 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH)], colorants (azo compounds, anthraquinone compounds, phthalocyanine compounds, titanium oxide), 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.

[0035] 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.

[0036] 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 to prepare a specific resin composition according to the content ratio A (mol%) of the (meth)acrylate ester unit in the ethylene-(meth)acrylate ester 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%).

[0037] The outdoor insulated electric wire 10 shown in Fig. 1 can be manufactured by extruding an insulating layer forming layer made of a specific resin composition on the outer peripheral surface of a conductor 11 and crosslinking the insulating layer forming layer (specific resin composition) to form an insulating layer 13 (specific resin crosslinked product).

[0038] The crosslinking method for forming the insulating layer (specific resin crosslinked product) 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 resin composition containing an ethylene-(meth)acrylate copolymer with an electron beam can be mentioned.

[0039] Also, the crosslinking treatment method is not particularly limited, but usually, pressure heating treatment or the like is used. As an example, in a nitrogen atmosphere, at a pressure of 4 to 10 kg / cm 2 , and at a temperature of 160 to 260°C, the crosslinking of the specific resin composition can be advanced by pressure heating the insulating layer forming layer.

[0040] By heating the specific resin crosslinked product constituting the insulating layer of the outdoor insulated electric wire of the present invention at a predetermined temperature, at least a part of the crosslinked structure can be de-crosslinked.

[0041] The heating temperature for de-crosslinking the specific resin crosslinked product constituting the insulating layer is preferably in the range of 300 to 400°C, more preferably in the range of 320 to 380°C.

[0042] The specific resin crosslinked product constituting the insulating layer preferably has its crosslinking degree reduced to less than 15%, particularly less than 10% when heated at 350°C.

[0043] A 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.

Examples

[0044] 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 copolymer, carbon black, antioxidant, and crosslinking agent constituting the resin composition.

[0045] · Copolymer (EEA-1) Density = 0.93 g / cm 3 , an ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 1.5 g / 10 min and EA content ratio = 4.7 mol%.

[0046] · Copolymer (EEA-2) Density = 0.94 g / cm 3 , an ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 0.5 g / 10 min and EA content ratio = 8.1 mol%.

[0047] · Copolymer (EEA-3) Density = 0.93 g / cm 3 , an ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 4.0 g / 10 min and EA content ratio = 2.1 mol%.

[0048] · Carbon black (CB-1) Furnace black with the trade name "VULCAN 9A32" (manufactured by Cabot Corporation).

[0049] · Carbon black (CB-2) Furnace black with the trade name "VULCAN XCmax22" (manufactured by Cabot Corporation).

[0050] · Antioxidant (AO-1) Hindered phenol stabilizer, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]

[0051] ·Crosslinking agent (PO-1) Peroxide crosslinking agent consisting of dicumyl peroxide

[0052] <Production of crosslinkable resin composition> [Example 1] According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-1), 0.5 part by mass of carbon black (CB-1), and 0.15 part by mass of antioxidant (AO-1) were melt-kneaded. 0.8 part by mass of crosslinking agent (PO-1) was added to the obtained kneaded product, and after mixing for 12 hours while heating to 60°C, 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 insulating layer forming layer made of the specific resin composition obtained as described above. Next, in a nitrogen atmosphere, 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), thereby manufacturing the outdoor insulating wire of the present invention.

[0053] [Example 2] According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-2) was used instead of copolymer (EEA-1), and a specific resin composition was obtained in the same manner as in Example 1 except that the amount of carbon black (CB-1) used was changed to 2.5 parts by mass. The outdoor insulating wire 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).

[0054] [Example 3] According to the formulation shown in Table 1 below, a specific resin composition was obtained in the same manner as in Example 1, except that 100 parts by mass of copolymer (EEA-3) was used instead of copolymer (EEA-1), and the amount of crosslinking agent (PO-1) used was changed to 0.4 parts by mass. An outdoor insulated electric wire of the present invention was manufactured in the same manner as in Example 1, except that an insulating layer (specific resin crosslinked body) was formed using this resin composition.

[0055] [Comparative Example 1] According to the formulation shown in Table 1 below, a crosslinkable resin composition was obtained in the same manner as in Example 3, except that the amount of crosslinking agent (PO-1) used was changed to 1.8 parts by mass. A comparative outdoor insulated electric wire 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 1 is a comparative example in which the degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is excessive.

[0056] 〔Comparative Example 2〕 According to the formulation shown in Table 1 below, a crosslinkable resin composition was obtained in the same manner as in Example 3, except that the amount of crosslinking agent (PO-1) used was changed to 0.2 parts by mass. A comparative outdoor insulated electric wire 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 degree of crosslinking of the resin crosslinked body obtained by crosslinking the resin composition is too small.

[0057] 〔Comparative Example 3〕 According to the formulation shown in Table 1 below, a crosslinkable resin composition was obtained in the same manner as in Example 3, except that the amount of carbon black (CB-1) used was changed to 0.05 parts by mass. A comparative outdoor insulated electric wire 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 3 is a comparative example in which the content of carbon black in the resin composition (resin crosslinked body) is too small.

[0058] 〔Comparative Example 4〕 A crosslinkable resin composition was obtained in the same manner as in Example 3, except that 10 parts by mass of carbon black (CB-2) was used instead of carbon black (CB-1) according to the formulation shown in Table 1 below. A comparative outdoor insulated electric wire 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 4 is a comparative example in which the content of carbon black in the resin composition (resin crosslinked body) is excessive.

[0059] <Measurement of the degree of crosslinking of the resin crosslinked body> Test pieces were prepared from the insulating layers (resin crosslinked bodies) collected from each of the outdoor insulated electric wires manufactured in Examples 1 to 3 and Comparative Examples 1 to 4, and the degree of crosslinking (gel fraction) was measured according to JIS C3005 using these test pieces. The results are shown in Table 1 below together.

[0060] <Manufacture of sheet-like resin crosslinked body> Each of the crosslinkable resin compositions prepared in Examples 1 to 3 and Comparative Examples 1 to 4 was crosslinked by pressing at 180 °C for 15 minutes using a hot press machine (manufactured by Toho Machinery, model TBD-50), and a sheet-like resin crosslinked body made of the same insulating material as the insulating layer of each of the outdoor insulated electric wires manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was obtained.

[0061] <Evaluation of heat resistance deformation of resin crosslinked body (measurement of heat deformation rate)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and the heat deformation rate was measured according to JIS C3005 using these test pieces to evaluate the heat resistance deformation of the resin crosslinked body constituting the insulating layer. As the evaluation criteria, when the heat deformation rate was 40% or less, it was rated as "pass (○)", and when it exceeded 40%, it was rated as "fail (×)". The results are shown in Table 1 below together.

[0062] <Evaluation of electrical properties of insulating layer (measurement of volume resistivity)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and using the test pieces, in accordance with JIS C2139-3-1, the volume resistivity was measured under the conditions of a temperature of 90°C and an electric field of 10 kV / mm to evaluate the electrical properties. As the evaluation criteria, when the volume resistivity is 10 12 Ω·cm or more, it was regarded as "qualified (○)", and when it is less than 10 12 Ω·cm, it was regarded as "unqualified (×)". The results are shown in Table 1 below.

[0063] <Evaluation of the Mechanical Properties of the Resin Crosslinked Body (Measurement of Tensile Strength and Elongation)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and using the test pieces, a tensile test was conducted in accordance with JIS C3005 to measure the tensile strength and tensile elongation, and the mechanical properties of the resin crosslinked body were evaluated. As the evaluation criteria, when the tensile strength is 10 MPa or more and the tensile elongation is 350% or more, it was regarded as "qualified (○)", and when either of these is not satisfied, it was regarded as "unqualified (×)". The results are shown in Table 1 below.

[0064] <Evaluation of the Weather Resistance of the Resin Crosslinked Body (Measurement of the Retention Rate of Tensile Strength)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and for the test pieces, using a sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.), a deterioration acceleration treatment was performed by light exposure for 1000 hours at a black panel temperature of 63°C, water spray for 12 minutes / 60 cycles. Using the test pieces subjected to the deterioration acceleration treatment, a tensile test was conducted in accordance with JIS C3005 to measure the tensile strength and tensile elongation, and the retention rates of the tensile strength and tensile elongation with respect to the test pieces not subjected to the deterioration acceleration treatment were calculated to evaluate the weather resistance of the resin crosslinked body. As the evaluation criteria, when the retention rates of both the tensile strength and the tensile elongation are 80% or more, it was regarded as "qualified (○)", and when either of these is not satisfied, it was regarded as "unqualified (×)". The results are shown in Table 1 below.

[0065] <Evaluation of the Recyclability of the Resin Crosslinked Body (Crosslink Removal Treatment)> From each of the outdoor insulated electric wires obtained in Examples 1 to 3 and Comparative Examples 1 to 4, an insulating layer (resin crosslinked body) was collected, and for each of the collected resin crosslinked bodies, a devulcanization treatment (regeneration 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 devulcanization 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 devulcanization treatment was less than 15%, it was rated as "qualified (○)", and when it was 15% or more, it was rated as "unqualified (×)". 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.

[0066]

Table 1

Explanation of Symbols

[0067] 10 Outdoor insulated electric wire 11 Conductor 13 Insulating layer

Claims

1. An insulated electric wire obtained by coating a conductor with an insulating layer formed from a crosslinked product of an ethylene-(meth)acrylate copolymer containing carbon black in a proportion of 0.2 to 4.0 parts by mass based on 100 parts by mass of the 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. An outdoor insulated electric wire. ・25 ≤ C ≤ 2.3A + 77 (where 1.5 ≤ A ≤ 8.0) ・25 ≤ C ≤ 95 (where 8.0 < A)

2. The outdoor insulated electric wire according to Claim 1, wherein the crosslinking degree C of the crosslinked product is 45% or more.

3. The outdoor insulated electric wire according to Claim 1 or 2, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

4. The outdoor insulated electric wire according to Claim 1 or 2, obtained by coating the conductor with the insulating layer formed by crosslinking a crosslinkable resin composition containing 100 parts by mass of an ethylene-(meth)acrylate copolymer, 0.2 to 4.0 parts by mass of carbon black, and a crosslinking agent.

5. The outdoor insulated electric wire according to Claim 1 or 2, wherein when the crosslinked product constituting the insulating layer is heated at 350°C, the crosslinking degree thereof decreases to less than 15%.

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