Crosslinkable semiconductive resin composition, semiconductive resin crosslinked product, and power cable

Abstract

To provide a crosslinkable semiconductive resin composition that is capable of forming a semiconductive resin crosslinked product having good conductivity and heat deformation resistance, and that is capable of reversible crosslinking.SOLUTION: A crosslinkable semiconductive resin composition of the present invention is a resin composition comprising an ethylene-(meth)acrylic acid ester copolymer, a specific amount of carbon black, and a crosslinking agent. 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 a resin crosslinked product obtained by crosslinking the copolymer 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 a crosslinkable semiconductive resin composition comprising an ethylene copolymer capable of performing reversible crosslinking, a semiconductive resin crosslinked body having good conductivity and heat distortion resistance, capable of undergoing de-crosslinking and excellent in recyclability, and a power cable provided with a semiconductive layer formed from such a semiconductive resin crosslinked body.

Background Art

[0002] For the semiconductive layers (inner semiconductive layer and outer semiconductive layer) of power cables, good conductivity capable of relaxing electrical stress and the like are required. As a resin composition for forming such a semiconductive layer, a semiconductive resin composition containing 5 to 80 parts by weight of carbon black with respect to 100 parts by weight of polyethylene having a density of 0.890 to 0.910 g / cm 3 has been proposed (see Patent Document 1 below). In addition, as a resin composition capable of forming a resin crosslinked body (semiconductive layer) having good conductivity, mechanical properties, heat distortion resistance, etc., and improved blocking properties, a crosslinkable semiconductive resin composition containing an ethylene copolymer, carbon black, a crosslinking agent, and a surfactant has been proposed by the present applicant (see Patent Document 2 below).

[0003] Also, recently, it has been demanded to effectively utilize (recycle) the waste materials of the resin crosslinked body generated during the manufacture or after the use of power cables as recycled resources. However, conventionally known crosslinked polyethylene cannot be melted by heat or a solvent, and its recycling method is limited. Therefore, methods of forcibly cutting carbon chains by water in a supercritical state (see Patent Documents 3 and 4 below) or shear by a twin-screw extruder (see Patent Documents 5 and 6 below) have been studied. However, these methods cannot avoid the newly introduction of equipment and the deterioration of quality, and have hardly reached industrialization.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Laid-Open No. 61-235444 [Patent Document 2] Japanese Patent Laid-Open No. 2002-363352 [Patent Document 3] Japanese Patent Laid-Open No. 2002-187976 [Patent Document 4] Japanese Patent Laid-Open No. 2001-192495 [Patent Document 5] Japanese Patent Laid-Open No. 2008-69209 [Patent Document 6] Japanese Patent Laid-Open No. 2018-35247 [Summary of the Invention] [Problems to be Solved by the Invention]

[0005] An object of the present invention is to provide a crosslinkable semiconductive resin composition capable of forming a semiconductive resin crosslinked body having good conductivity, heat resistance to deformation, etc., and capable of performing reversible crosslinking. Another object of the present invention is to provide a semiconductive resin crosslinked body having good conductivity, heat resistance to deformation, etc., and excellent recyclability capable of returning at least a part of the crosslinked structure to an uncrosslinked state. Still another object of the present invention is to provide a power cable provided with a semiconductive layer having good conductivity, heat resistance to deformation, etc., and excellent recyclability. [Means for Solving the Problems]

[0006] The crosslinkable semiconductive resin composition of the present invention is a resin composition containing 100 parts by mass of an ethylene-(meth)acrylate copolymer, 10 to 120 parts by mass of carbon black, and a crosslinking agent, 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 resin crosslinked body obtained by crosslinking treatment thereof is in the range represented by the following formula. Here, the crosslinking degree C is the crosslinking degree (gel fraction law) measured according to JIS C 3005.

[0007] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0008] It is preferable that the crosslinkable semiconductive resin composition of the present invention can obtain a resin crosslinked body having a crosslinking degree C of 45% or more and less than 75%, particularly 50 to 70%. Further, it is preferable that the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate (EEA). Further, it is preferable that the content ratio A (comonomer amount) of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is 1.5 to 16 mol%, particularly 2.0 to 13 mol%.

[0009] The semiconductive resin crosslinked body of the present invention is a crosslinked body of the ethylene-(meth)acrylate copolymer containing carbon black at a ratio of 10 to 120 parts by mass with respect to 100 parts by mass of the ethylene-(meth)acrylate copolymer, where when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol %), the crosslinking degree C (%) thereof is in the range represented by the following formula.

[0010] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

[0011] The crosslinked semiconductive resin of the present invention preferably has a crosslinking degree C of 45% or more and less than 75%, particularly preferably 50 to 70%. Further, it is preferable that the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate (EEA). Also, according to JIS K 7194, the volume resistivity measured under the conditions of the two-terminal method, a temperature of 90°C, and a current of 1 mA is preferably 500 Ω·cm or less. Further, when heated at 350°C, it is preferable that the crosslinking degree decreases to less than 15%, particularly less than 10%.

[0012] The power cable of the present invention is characterized by comprising a semiconductive layer formed from the crosslinked semiconductive resin of the present invention. The power cable of the present invention is formed from a crosslinked product of an ethylene-(meth)acrylate copolymer. When the content ratio of the (meth)acrylate ester unit in the ethylene-(meth)acrylate copolymer is A (mol%), it preferably includes an insulating layer (hereinafter referred to as "specific insulating layer") in which the crosslinking degree C (%) of the crosslinked product is in the range represented by the following formula.

[0013] ·25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ·25 ≦ C ≦ 95 (where 8.0 < A)

Advantages of the Invention

[0014] The crosslinkable semiconductive resin composition of the present invention 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. According to the crosslinkable semiconductive resin composition of the present invention, at a predetermined temperature (relatively low temperature), the crosslinking reaction of the crosslinkable resin composition occurs, and thereby, a resin crosslinked product (the crosslinked semiconductive resin of the present invention) can be preferably produced.

[0015] The crosslinked semi-conductive resin of the present invention can return at least a part of the crosslinked structure to an uncrosslinked state by a de-crosslinking reaction. According to the crosslinked semi-conductive resin of the present invention, without using a special additive or applying a high shear force, the de-crosslinking reaction of the resin crosslinked body occurs only by heating to a predetermined temperature (relatively high temperature), and thereby, an uncrosslinked or low crosslinked resin composition can be suitably recycled. Also, as is clear from the results of the examples described later, the crosslinked semi-conductive resin of the present invention can have good conductivity, heat resistance deformation resistance, etc. required for the semi-conductive layer of a power cable.

[0016] The semi-conductive layer constituting the power cable of the present invention has good conductivity, heat resistance deformation resistance, etc., and is also excellent in recyclability. Also, according to the power cable of the present invention provided with a specific insulating layer, the resin crosslinked body constituting the specific insulating layer can also return at least a part of the crosslinked structure to an uncrosslinked state by a de-crosslinking reaction, and the specific insulating layer (resin crosslinked body) also has excellent recyclability. As a result, since the recycling process can be performed without separating the specific insulating layer and the semi-conductive layer, the recycling efficiency can be improved.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] <Crosslinkable Semi-conductive Resin Composition> The crosslinkable semi-conductive resin composition of the present invention contains an ethylene-(meth)acrylate copolymer, carbon black, and a crosslinking agent. The crosslinkable semi-conductive resin composition of the present invention can perform reversible crosslinking (crosslinking reaction and de-crosslinking reaction).

[0019] The de-crosslinking reaction of the resin composition (resin crosslinked body) is important for the structure of the polymer side chain, 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 crosslinkable 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 crosslinkable resin composition that can be melt-molded cannot be produced (recycled). On the other hand, in the case of ethylene-(meth)acrylate copolymer, such side reactions do not occur, and thus the de-crosslinking reaction proceeds efficiently by heating at a predetermined temperature.

[0020] Examples of the ethylene-(meth)acrylate copolymer contained in the crosslinkable semiconductive resin composition of the present invention 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.

[0021] Here, since the ethylene-acrylic acid ester copolymer is less likely to undergo a disintegrating reaction with radicals, a high degree of crosslinking can be easily obtained mainly by peroxide crosslinking, and the crosslinking efficiency can be higher than that using an ethylene-methacrylic acid ester copolymer as the resin component. Also, from the viewpoint of obtaining a resin composition having a well-balanced combination of 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 preferred from the viewpoints of high crosslinking efficiency and excellent physical property balance.

[0022] In the ethylene-(meth)acrylic acid ester copolymer, 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%, and particularly preferably 4.0 to 9.0 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 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 characteristics of the resin crosslinked body obtained by crosslinking the resin composition may be impaired.

[0023] The carbon black contained in the crosslinkable semiconductive resin composition of the present invention becomes a constituent component of the resin crosslinked body after crosslinking, and imparts good conductivity (electrical conduction characteristics capable of relaxing the electrical stress required for the semiconductive layer of the power cable) to the resin crosslinked body. The carbon black is not particularly limited, and examples thereof include graphitized carbon, furnace black, acetylene black, and ketjen black.

[0024] The content of carbon black in the crosslinkable semiconductive resin composition of the present invention is 10 to 120 parts by mass, preferably 10 to 100 parts by mass, based on 100 parts by mass of the ethylene-(meth)acrylate copolymer. When the content of carbon black is less than 10 parts by mass, the conductivity required for the semiconductive layer cannot be imparted to the resin crosslinked body obtained by crosslinking the resin composition (see Comparative Example 3 described later). On the other hand, when the content of carbon black exceeds 120 parts by mass, the recyclability of the resin crosslinked body obtained by crosslinking the resin composition is impaired (see Comparative Example 4 described later).

[0025] Examples of the crosslinking agent contained in the crosslinkable semiconductive resin composition of the present invention include peroxide crosslinking agents and silane crosslinking agents, 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.

[0026] 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 preferable.

[0027] 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.

[0028] The content of the crosslinking agent in the crosslinkable semiconductive resin composition of the present invention is adjusted so that the crosslinking degree (C) of the resin crosslinked body 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 contained. 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.

[0029] The crosslinkable semiconductive resin composition of the present invention 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. According to the crosslinkable semiconductive resin composition of the present invention, by simply heating to a predetermined temperature (relatively low temperature), the crosslinking reaction of the crosslinkable resin composition occurs, whereby the semiconductive resin crosslinked body of the present invention can be produced.

[0030] By subjecting the crosslinkable semiconductive resin composition of the present invention to a crosslinking treatment, a resin crosslinked body (the semiconductive resin crosslinked body of the present invention) in which the crosslinking degree C (%) is within the range represented by the above formula can be obtained.

[0031] The crosslinkable semiconductive resin composition of the present invention can optionally contain components used in resin compositions for forming the semiconductive layer and insulating layer of power cables as required. These optional components, together with carbon black, become the constituent components of the semiconductive resin crosslinked body of the present invention.

[0032] Examples of such optional components include inorganic fillers (e.g., calcium carbonate, clay, diatomaceous earth, metal oxides, silica, glass fibers, carbon fibers), plasticizers (phthalic esters, trimellitic 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, alkyl sulfonic 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.

[0033] <Semiconductive resin crosslinked body> The semiconductive resin crosslinked body of the present invention is a crosslinked body of an ethylene-(meth)acrylate copolymer containing carbon black, and is composed of a semiconductive resin crosslinked body having a specific degree of crosslinking within the range represented by the above formula. The degree of crosslinking C(%) of the semiconductive resin crosslinked body of the present invention 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 to prepare a resin composition (the crosslinkable semiconductive resin composition of the present invention). In addition, the degree of crosslinking C(%) of the semiconductive resin crosslinked body by electron beam crosslinking described later can be adjusted by appropriately adjusting the irradiation conditions of the electron beam irradiated to the ethylene-(meth)acrylate copolymer according to the content ratio A (mol%).

[0034] The content of carbon black in the semiconductive resin crosslinked body of the present invention is 10 to 120 parts by mass, preferably 10 to 100 parts by mass, based on 100 parts by mass of the ethylene-(meth)acrylate copolymer. When the content of carbon black is less than 10 parts by mass, the conductivity required for the semiconductive layer cannot be exhibited (see Comparative Example 3 described later). On the other hand, when the content of carbon black exceeds 120 parts by mass, the recyclability is impaired (see Comparative Example 4 described later).

[0035] Here, from the viewpoint of exhibiting the conductivity required for the semiconductive layer, the semiconductive resin crosslinked body preferably has a volume resistivity of 500 Ω·cm or less, particularly 300 Ω·cm or less, measured according to JIS K 7194 under the conditions of the two-terminal method, a temperature of 90 °C, and a current of 1 mA.

[0036] The semiconductive resin crosslinked body of the present invention is obtained by crosslinking the crosslinkable semiconductive resin composition of the present invention. The crosslinking method for producing the semiconductive resin crosslinked body of the present invention is not particularly limited. For example, (1) A method of chemically crosslinking the resin composition of the present invention containing a peroxide crosslinking agent by heating at a predetermined temperature. (2) A method of silane crosslinking the resin composition of the present invention containing a silane crosslinking agent by heating at a predetermined temperature. (3) A method of electron beam crosslinking by irradiating an ethylene-(meth)acrylate copolymer with an electron beam can be mentioned.

[0037] In the crosslinking methods (1) and (2) above, the heating temperature for crosslinking the crosslinkable semiconductive resin composition is preferably 20 to 260 °C, and more preferably 25 to 240 °C. As the heat treatment method for crosslinking, various methods can be adopted according to the form of the resin crosslinked body, such as a method of heating in an atmosphere of nitrogen, steam, silicone oil, molten salt, etc., and a method of heating during molding with a hot press or an injection molding machine.

[0038] As an example of the heat treatment method for forming the semiconductive layer of a power cable, under a nitrogen atmosphere, at a pressure of 4 to 10 kg / cm 2 , at a temperature of 160 to 260 °C, by pressurized heating of the semiconductive layer forming layer (crosslinkable semiconductive resin composition), the crosslinking of the resin composition can be advanced.

[0039] The lower limit value of the crosslinking degree of the semiconductive resin crosslinked body of the present invention is set to 25%, preferably 45%. A resin crosslinked body with an excessively small crosslinking degree (less than 25%) cannot exhibit sufficient heat resistance to deformation, and may melt and deform under temperature conditions exceeding the melting point of the resin (see Comparative Example 2 described later).

[0040] The upper limit value of the crosslinking degree of the semiconductive resin crosslinked body of the present invention (hereinafter, also referred to as "upper crosslinking degree") is defined from the viewpoint of sufficiently advancing the de-crosslinking reaction of the resin crosslinked body. Here, the de-crosslinking reaction of the resin crosslinked body 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. The upper limit crosslinking degree of the semiconductive resin crosslinked body of the present invention is 2.3A + 77% when the content ratio of the (meth)acrylic acid ester unit is A and A is 1.5 to 8.0 mol%, and 95% when the content ratio A exceeds 8.0 mol%.

[0041] When the crosslinking degree of the resin crosslinked body is excessive (exceeding the upper limit crosslinking degree), the de-crosslinking reaction does not proceed sufficiently, and a resin composition that can be melt-molded cannot be produced (recycled) (see Comparative Example 1 described later).

[0042] From the viewpoint of good mechanical properties and heat distortion resistance and sufficient progress of the de-crosslinking reaction, the preferable crosslinking degree C in the semiconductive resin crosslinked body of the present invention is 45% or more and less than 75%, and particularly preferably 50 to 70%.

[0043] By heating the semiconductive resin crosslinked body of the present invention at a predetermined temperature, at least a part of the crosslinked structure is de-crosslinked.

[0044] The heating temperature for de-crosslinking the semiconductive resin crosslinked body of the present invention is preferably 300 to 400°C, and more preferably 320 to 380°C.

[0045] The semiconductive resin crosslinked body of the present invention preferably has a crosslinking degree that decreases to less than 15%, particularly less than 10% when heated at 350°C.

[0046] The resin (ethylene-(meth)acrylic acid ester copolymer) with a crosslinking degree decreased to less than 15% can be subjected to re-melt molding by heating and can be suitably used as a recycled resin.

[0047] <Power cable> 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 internal semiconductive layer 12, an insulating layer 13, and an external semiconductive layer 14 laminated on the outer peripheral surface of a conductor 11. Further, a metal shielding layer 15 and a sheath 16 are laminated and arranged on the outer peripheral surface of the external semiconductive layer 14.

[0048] The internal semiconductive layer 12 and the external semiconductive layer 14 of the power cable of the present invention are formed of the semiconductive resin crosslinked body of the present invention. According to the power cable of the present invention, the semiconductive layers (internal semiconductive layer and external semiconductive layer) constituting the same have good conductivity and heat deformation resistance, and are also excellent in recyclability. That is, by heating the semiconductive resin crosslinked body constituting the semiconductive 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 (recyclable state). Further, when the insulating layer 13 is a specific insulating layer, a recycling process can be performed without separating the internal semiconductive layer 12, the insulating layer 13, and the external semiconductive layer 14, so that the efficiency of recycling can be improved.

Example

[0049] 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, conductive carbon black, antioxidant, and crosslinking agent constituting the resin component.

[0050] · Copolymer (EEA-1) Density = 0.93 g / cm 3 , An ethylene-ethyl acrylate copolymer with MFR (190 ° C, 2.16 kg) = 20 g / 10 min and an EA content ratio of 6.5 mol%.

[0051] · Copolymer (EEA-2) Density = 0.94 g / cm 3,An ethylene-ethyl acrylate copolymer with MFR (190 °C, 2.16 kg) = 20 g / 10 min and an EA content ratio of 8.5 mol%.

[0052] · Conductive carbon black (CB-1) Acetylene black with the trade name "Denka Black Granular Product" (manufactured by Denka Co., Ltd.).

[0053] · Conductive carbon black (CB-2) Furnace black with the trade name "Seast SO" (manufactured by Tokai Carbon Co., Ltd.).

[0054] · Conductive carbon black (CB-3) Ketjen black with the trade name "LIONITE EC-200L" (manufactured by Lion Specialty Chemicals Co., Ltd.).

[0055] · Antioxidant (AO-1) Hindered phenol type stabilizer, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]

[0056] · Crosslinking agent (PO-1) Peroxide crosslinking agent composed of dicumyl peroxide

[0057] <Production of crosslinkable resin composition> 〔Example 1〕 According to the formulation shown in Table 1 below, 100 parts by mass of copolymer (EEA-1), 60 parts by mass of conductive carbon black (CB-1), and 0.15 parts by mass of antioxidant (AO-1) were melt-kneaded. Then, 0.6 parts by mass of crosslinking agent (PO-1) was added to the obtained kneaded product, and after mixing at 60 °C for 12 hours, it was cooled to room temperature to obtain a resin composition (the crosslinkable semiconductive resin composition of the present invention).

[0058] 〔Example 2〕 According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-2), 100 parts by mass of conductive carbon black (CB-2), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 0.4 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours while heating, it was cooled to room temperature to obtain a resin composition (the crosslinkable semiconductive resin composition of the present invention).

[0059] [Example 3] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-2), 10 parts by mass of conductive carbon black (CB-3), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 0.4 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours while heating, it was cooled to room temperature to obtain a resin composition (the crosslinkable semiconductive resin composition of the present invention).

[0060] [Comparative Example 1] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-1), 60 parts by mass of conductive carbon black (CB-1), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 1.5 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours while heating, it was cooled to room temperature to obtain a comparative resin composition. This Comparative Example 1 is a comparative example in which the amount of the crosslinking agent used is excessive, and the crosslinking degree of the resin crosslinked body obtained by crosslinking the resin composition becomes too large.

[0061] [Comparative Example 2] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-1), 60 parts by mass of conductive carbon black (CB-1), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 0.1 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours while heating, it was cooled to room temperature to obtain a comparative resin composition. This Comparative Example 2 is a comparative example in which the amount of the crosslinking agent used is too small, and the crosslinking degree of the resin crosslinked body obtained by crosslinking the resin composition becomes too small.

[0062] [Comparative Example 3] According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-1), 5 parts by mass of conductive carbon black (CB-1), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 0.6 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours, it was cooled to room temperature to obtain a resin composition for comparison. This Comparative Example 3 is a comparative example in which the amount of conductive carbon used is too small.

[0063] 〔Comparative Example 4〕 According to the formulation shown in Table 1 below, 100 parts by mass of a copolymer (EEA-1), 200 parts by mass of conductive carbon black (CB-1), and 0.15 parts by mass of an antioxidant (AO-1) were melt-kneaded. Then, 0.6 parts by mass of a crosslinking agent (PO-1) was added to this kneaded product, and after mixing at 60 °C for 12 hours, it was cooled to room temperature to obtain a resin composition for comparison. This Comparative Example 4 is a comparative example in which the amount of conductive carbon used is excessive.

[0064] <Manufacture of Power Cable (Crosslinking Reaction)> Using a general-purpose wire manufacturing extrusion molding machine, the outer peripheral surface of the conductor was extrusion-coated with an internal semiconductive layer forming layer made of each of the resin compositions obtained in the examples and comparative examples, an insulating layer forming layer (HFDJ-4201 manufactured by ENEOS NUC), and an external semiconductive layer forming layer made of the same resin composition as the resin composition forming the internal semiconductive layer. Next, under a nitrogen atmosphere, a pressure heat treatment was performed at a temperature of 260 °C to crosslink the internal semiconductive layer forming layer, the insulating layer forming layer, and the external semiconductive layer forming layer, and the internal semiconductive layer, the insulating layer, and the external semiconductive layer were laminated and formed on the outer peripheral surface of the conductor. Next, a power cable having a laminated structure as shown in FIG. 1 was manufactured by providing a metal shielding layer made of a copper tape and a sheath made of a vinyl chloride resin.

[0065] <Manufacture of Sheet-like Resin Crosslinked Body (Crosslinking Reaction)> Each of the resin compositions obtained in the examples and comparative examples 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-like resin crosslinked body.

[0066] <Measurement of the Crosslinking Degree of the Resin Crosslinked Body> Test pieces were prepared from the semiconductive layers (resin crosslinked bodies) collected from each of the power cables manufactured as described above, and using these test pieces, the crosslinking degree (gel fraction) was measured in accordance with JIS C3005. The results are shown together in Table 1 below.

[0067] <Evaluation of the Heat Resistance Deformability of the Resin Crosslinked Body (Measurement of the Heat Deformation Rate)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and using these test pieces, the heat deformation rate was measured in accordance with JIS C3005 to evaluate the heat resistance deformability of the resin crosslinked body constituting the insulating layer. As the evaluation criteria, when the heat 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 together in Table 1 below.

[0068] <Evaluation of the Electrical Characteristics of the Resin Crosslinked Body (Measurement of the Volume Resistivity)> Test pieces were prepared from each of the sheet-like resin crosslinked bodies obtained as described above, and using these test pieces, with reference to JIS K 7194, the volume resistivity was measured under the conditions of the two-terminal method, a temperature of 90°C, and a current of 1 mA to evaluate the electrical characteristics (conductivity). As the evaluation criteria, when the volume resistivity was 500 Ω·cm or less, it was regarded as "qualified (○)", and when it exceeded 500 Ω·cm, it was regarded as "unqualified (×)". The results are shown together in Table 1 below.

[0069] <Evaluation of the Recyclability of the Resin Crosslinked Body (Crosslink Removal Treatment)> The semiconductive layers (resin crosslinked bodies) were collected from each of the power cables manufactured as described above, and for each of the collected resin crosslinked bodies, a crosslink removal 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 degree of crosslinking (gel fraction) was measured in accordance with JIS C3005, and the recyclability was evaluated. As the evaluation criteria, when the degree of crosslinking 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 is less than 15%, there will be 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 can be obtained. The results are shown in Table 1 below.

[0070]

Table 1

Explanation of Symbols

[0071] 10 Power cable 11 Conductor 12 Inner semiconductive layer 13 Insulation layer 14 Outer semiconductive layer 15 Metal shielding layer 16 Sheath

Claims

1. A resin composition containing 100 parts by mass of an ethylene-(meth)acrylate copolymer, 10 to 120 parts by mass of carbon black, and a crosslinking agent, 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 resin crosslinked body obtained by crosslinking this is in the range represented by the following formula: a crosslinkable semiconductive resin composition. ・ 25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ・ 25 ≦ C ≦ 95 (where 8.0 < A)

2. The crosslinkable semiconductive resin composition according to claim 1, wherein a resin crosslinked body having a crosslinking degree C of 45% or more and less than 75% can be obtained.

3. The crosslinkable semiconductive resin composition according to claim 1 or 2, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

4. The crosslinkable semiconductive resin composition according to claim 1 or 2, wherein the content ratio A of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is 1.5 to 16 mol%.

5. A crosslinked body of the ethylene-(meth)acrylate copolymer containing carbon black at a ratio of 10 to 120 parts by mass with respect to 100 parts by mass of the ethylene-(meth)acrylate copolymer, where when the content ratio of the (meth)acrylate unit in the ethylene-(meth)acrylate copolymer is A (mol%), the crosslinking degree C (%) thereof is in the range represented by the following formula: a semiconductive resin crosslinked body. ・ 25 ≦ C ≦ 2.3A + 77 (where 1.5 ≦ A ≦ 8.0) ・ 25 ≦ C ≦ 95 (where 8.0 < A)

6. The semiconductive resin crosslinked body according to claim 5, wherein the crosslinking degree C is 45% or more and less than 75%.

7. The semiconductive resin crosslinked body according to claim 5, wherein the ethylene-(meth)acrylate copolymer is ethylene-ethyl acrylate.

8. The semiconductive resin crosslinked body according to claim 5, wherein the volume resistivity measured according to JIS K 7194 under the conditions of the two-terminal method, a temperature of 90 ° C, and a current of 1 mA is 500 Ω·cm or less.

9. The semiconductive resin crosslinked body according to claim 5, wherein when heated at 350 ° C, the crosslinking degree decreases to less than 15%.

10. A power cable provided with a semiconductive layer formed from the semiconductive resin crosslinked body according to any one of claims 5 to 9.

11. The power cable according to claim 10, comprising 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)

Images