JP6221782B2 - Semiconductive resin composition, power cable, and method of manufacturing power cable - Google Patents

Description

  The present invention relates to a semiconductive resin composition, a power cable, and a method for producing a power cable.

  The power cable includes a conductor, an internal semiconductive layer, an insulating layer, and an external semiconductive layer from the inside toward the outside. Until now, in a low-voltage power cable for private use, the external semiconductive layer has been formed by winding a semiconductive tape. An operator who lays the power cable peels off the external semiconductive layer around which the tape is wound, and connects the power cable. However, partial discharge may occur due to the unevenness of the external semiconductive layer wound with the tape, and the unevenness of the external semiconductive layer wrapped with the tape may promote water tree degradation. It has been desired to improve the coverage.

  Therefore, in recent years, in order to improve the coverage of the external semiconductive layer, a power cable in which the external semiconductive layer is simultaneously extruded together with an insulating layer or the like has been developed. In the power cable of 3.3 kV or more and 33 kV or less, it is required that the extruded outer semiconductive layer can be peeled from the insulating layer, and power cables having various compositions are provided. Moreover, in order to manufacture a power cable at low cost, a method of crosslinking an insulating layer by a silane graft / water crosslinking method after co-extrusion is used (for example, Patent Documents 1 and 2).

Japanese Patent No. 3551755 Japanese Patent No. 4399076

  However, the inventors, when wrapping the power cable around the drum in the water cross-linking process by the silane graft / water cross-linking method, depending on the composition of the external semi-conductive layer, the external semi-conductive layers of adjacent power cables are mutually connected. We found the problem that there is a possibility of adhesion.

  An object of the present invention is to provide a semiconductive resin that can easily peel an external semiconductive layer from an insulating layer and can prevent the external semiconductive layers of adjacent power cables from sticking to each other in a water-crosslinking process. It is to provide a composition, a power cable and a method for manufacturing the power cable.

According to a first aspect of the invention,
A semiconductive resin composition that forms an external semiconductive layer on the outer periphery of an insulating layer that is crosslinked by a silane graft / water crosslinking method,
A base resin having an ethylene-vinyl acetate copolymer containing vinyl acetate and a propylene-olefin copolymer;
Conductive carbon black,
Have
A semiconductive resin composition is provided, wherein a content of the vinyl acetate with respect to the base resin is 10% by mass or more and less than 25% by mass.

According to a second aspect of the invention,
When the base resin is 100 parts by weight, the content of the propylene-olefin copolymer is 1 part by weight or more and 50 parts by weight or less, and the semiconductive resin composition according to the first aspect is provided.

According to a third aspect of the invention,
The semiconductive resin composition according to the first or second aspect, in which the content of the vinyl acetate with respect to the ethylene-vinyl acetate copolymer is 25% by mass or more and 50% by mass or less, is provided.

According to a fourth aspect of the invention,
The melt flow rate of the ethylene-vinyl acetate copolymer is 0.1 g / 10 min or more and 10 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf. The described semiconductive resin composition is provided.

According to a fifth aspect of the present invention,
The melt flow rate of the propylene-olefin copolymer is a half according to any one of the first to fourth aspects, which is 1 g / 10 min or more and 20 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf. A conductive resin composition is provided.

According to a sixth aspect of the present invention,
The semiconductive resin composition according to any one of the first to fifth aspects, in which the melting point of the ethylene-vinyl acetate copolymer is 50 ° C. or higher and 100 ° C. or lower.

According to a seventh aspect of the present invention,
The semiconductive resin composition according to any one of the first to sixth aspects, wherein the propylene-olefin copolymer has a melting point of 140 ° C or higher and 180 ° C or lower.

According to an eighth aspect of the present invention,
The semiconductive resin composition according to any one of the first to seventh aspects, which has a melting point of 100 ° C. or higher and 180 ° C. or lower.

According to a ninth aspect of the present invention,
The semiconductive resin composition according to any one of the first to eighth aspects, in which the base resin includes polypropylene is provided.

According to a tenth aspect of the present invention,
The semiconductive resin composition according to any one of the first to ninth aspects, in which the content of the carbon black is 10 parts by weight or more and 300 parts by weight or less when the base resin is 100 parts by weight. Is done.

According to an eleventh aspect of the present invention,
The semiconductive resin composition according to any one of the first to tenth aspects, wherein the insulating layer is made of crosslinked polyethylene.

According to a twelfth aspect of the present invention,
Conductors,
An internal semiconductive layer provided to cover the outer periphery of the conductor;
An insulating layer provided so as to cover the outer periphery of the inner semiconductive layer, and crosslinked by a silane graft / water crosslinking method;
An external semiconductive layer provided to cover the outer periphery of the insulating layer;
Have
The external semiconductive layer is provided with a power cable formed of the semiconductive resin composition according to any one of the first to eleventh aspects.

According to a thirteenth aspect of the present invention,
Extrusion step of forming the cable intermediate by extruding the inner semiconductive layer, the insulating layer and the outer semiconductive layer from the inner side toward the outer side on the outer periphery of the conductor;
A winding step of winding the cable intermediate around a drum;
In a state where the cable intermediate is wound around the drum, a water crosslinking step of forming a power cable by crosslinking the insulating layer by a silane graft / water crosslinking method;
Have
In the extrusion process,
A base resin having an ethylene-vinyl acetate copolymer and a propylene-olefin copolymer containing vinyl acetate, and conductive carbon black, and the vinyl acetate content in the base resin is 10% by mass There is provided a method for producing a power cable for forming the external semiconductive layer using the semiconductive resin composition having a content of less than 25% by mass.

According to a fourteenth aspect of the present invention,
In the water crosslinking step,
A power cable manufacturing method according to a thirteenth aspect is provided, wherein the cable intermediate is exposed to an atmosphere of 70 ° C. or higher and 100 ° C. or lower and 80% RH or higher and 95% RH or lower.

  According to the present invention, the semiconductive resin that can easily peel the external semiconductive layer from the insulating layer and can prevent the external semiconductive layers of the adjacent power cables from sticking to each other in the water cross-linking step. Compositions, power cables and methods of manufacturing power cables are provided.

It is sectional drawing orthogonal to the axial direction of the power cable which concerns on one Embodiment of this invention. It is a figure which shows the peeling strength and the index value of mutual adhesiveness which concern on a present Example and a comparative example.

<One Embodiment of the Present Invention>
(1) Structure of Power Cable A power cable according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view orthogonal to the axial direction of the power cable 10 according to the present embodiment.

  In the power cable 10 of the present embodiment, the outer semiconductive layer 140 can be easily peeled from the insulating layer 130, and the outer semiconductive layers 140 of the adjacent power cables 10 are mutually connected in the water bridging process of the insulating layer 130. It is comprised so that sticking may be suppressed. Details will be described below.

(Overall structure)
As shown in FIG. 1, the power cable 10 has a conductor 110, an inner semiconductive layer 120, an insulating layer 130, and an outer semiconductive layer 140 from the inside toward the outside.

(conductor)
The conductor 110 is a copper conductor formed by twisting a plurality of conductive core wires made of, for example, pure copper (Cu) or a copper alloy.

(Internal semiconductive layer)
The internal semiconductive layer 120 is provided so as to cover the outer periphery of the conductor 110 in order to improve the adhesion between the conductor 110 and the insulating layer 130 and to suppress electric field concentration on the surface of the stranded wire of the conductor 110. The internal semiconductive layer 120 is formed of, for example, at least one of ethylene-vinyl acetate copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer, and conductive carbon. And black.

(Insulating layer)
The insulating layer 130 is provided so as to cover the outer periphery of the inner semiconductive layer 120. For example, a polyethylene resin obtained by graft copolymerization of a silane compound with a free radical generator is crosslinked in the presence of a silanol condensation catalyst and moisture. It consists of the crosslinked polyethylene formed by this. Such a crosslinking method is called a silane graft / water crosslinking method.

  Examples of the polyethylene resin used here include high pressure method low density polyethylene, high pressure method medium density polyethylene, low pressure method low density polyethylene (linear and metallocene catalyst polyethylene), and low pressure method medium density polyethylene (linear and metallocene catalyst). Polyethylene) or the like can be used alone or in admixture of two or more.

The silane compound used here has a general formula:
RR'SiY ₂
It is the alkoxysilane compound represented by these. In the formula, R is an olefinically unsaturated hydrocarbon group or a hydrocarbonoxy group, such as a vinyl group, an allyl group, a butenyl group, a dichlorohexenyl group, a cyclopentadienyl group, and preferably a vinyl group. Y is a hydrolyzable organic group, such as alkoxy group such as methoxy group, ethoxy group and butoxy group, acyloxy group such as formyloxy group, acetoxy group and propionoxy group, other oxime group, alkinoamino group, arylamino group A group or the like, preferably an alkoxy group. R ′ is an R group or a Y group. The most preferred silane compound is vinyl alkoxysilane, specifically vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, vinyldimethoxymethylsilane, vinyldiethoxymethylsilane, vinylmethoxydimethylsilane, vinyl At least one of ethoxydimethylsilane.

  The free radical generator used here is dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t -Butylperoxy) hexyne-3, α, α'-bis (t-butylperoxy-m-isopropyl) benzene, butylcumyl peroxide, isopropylcumyl-t-butyl peroxide and the like.

  The silanol condensation catalyst is added to the polyethylene resin, or is allowed to permeate into the polyethylene resin from the surface of the molded product. Examples of the silanol condensation catalyst include carboxylates of metals such as tin, zinc, iron, lead, and cobalt, organic bases, inorganic acids, and organic acids. Specifically, the silanol condensation catalyst includes dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, stannous acetate, stannous cablate, lead naphthenate, zinc cablate, cobalt naphthenate, Examples thereof include inorganic acids such as ethylamine, dibutylamine, hexylamine, pyridine, sulfuric acid and hydrochloric acid, and organic acids such as toluenesulfonic acid, acetic acid, stearic acid and maleic acid.

(External semiconductive layer)
The external semiconductive layer 140 is provided so as to cover the outer periphery of the insulating layer 130 in order to suppress external discharge from fine irregularities on the surface of the insulating layer 130, and has good peelability and non-adhesiveness as described above. Configured to have. Details of the semiconductive resin composition forming the external semiconductive layer 140 of the present embodiment will be described later.

(Other configuration of power cable)
In addition, a shielding layer or a sheath may be provided outside the external semiconductive layer 140 as necessary. The shielding layer is, for example, a copper tape wound around the outer periphery of the outer semiconductive layer 140, a wire shield covered with conductive wires such as a plurality of annealed copper wires, or the like. The covering layer is made of, for example, a covering material made of polyvinyl chloride.

(Each dimension)
As specific dimensions of the power cable 10, for example, the diameter of the conductor 110 is 3 mm or more and 60 mm or less, the thickness of the internal semiconductive layer 120 is 0.5 mm or more and 3 mm or less, and the thickness of the insulating layer 130. The thickness is 2 mm or more and 10 mm or less, and the thickness of the outer semiconductive layer 140 is 0.5 mm or more and 3 mm or less. The voltage applied to the power cable 10 of the present embodiment is, for example, 3.3 kV or more and 33 kV or less.

(2) Semiconductive resin composition The external semiconductive layer 140 of this embodiment is, for example, a base having an ethylene-vinyl acetate copolymer (EVA) containing vinyl acetate (VA) and a propylene-olefin copolymer. It is formed of a semiconductive resin composition having a resin and conductive carbon black.

(Ethylene-vinyl acetate copolymer)
The base resin of the semiconductive resin composition has an ethylene-vinyl acetate copolymer synthesized by multistage polymerization and having a large molecular weight. The melt flow rate (MFR) of the ethylene-vinyl acetate copolymer is 0.1 g / 10 min or more and 10 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf according to the test method of JISK7210. preferable. The melt flow rate of the ethylene-vinyl acetate copolymer is 10 g / 10 min or less, that is, the high molecular weight of the ethylene-vinyl acetate copolymer makes it possible to increase the interface at the interface between the insulating layer 130 and the external semiconductive layer 140. Molecular diffusion is suppressed, and the peelability from the insulating layer 130 is improved.

  The melting point of the ethylene-vinyl acetate copolymer is, for example, 50 ° C. or higher and 100 ° C. or lower, and preferably 60 ° C. or higher and 80 ° C. or lower. When the melting point of the ethylene-vinyl acetate copolymer is less than 50 ° C., the external semiconductive layer of the adjacent power cable may stick in the water crosslinking step. When the melting point of the ethylene-vinyl acetate copolymer is higher than 100 ° C., that is, when the content of vinyl acetate in the ethylene-vinyl acetate copolymer is small, the semiconductive resin composition constituting the outer semiconductive layer 140 Therefore, the outer semiconductive layer 140 is easily bonded to the insulating layer 130 made of nonpolar polyethylene. For this reason, the peelability of the outer semiconductive layer 140 from the insulating layer 130 may be insufficient.

  Further, the ethylene-vinyl acetate copolymer contains vinyl acetate. The content of vinyl acetate with respect to the ethylene-vinyl acetate copolymer as the precursor is 25% by mass or more and 50% by mass or less. Content of vinyl acetate with respect to base resin by mixing ethylene-vinyl acetate copolymer containing vinyl acetate at a predetermined content and propylene-olefin copolymer described later at a predetermined mixing ratio Can be adjusted to a desired value. Details of the vinyl acetate content will be described later.

  The hardness of the ethylene-vinyl acetate copolymer is from Shore A 65 to 80.

(Propylene-olefin copolymer)
The base resin of the semiconductive resin composition has a propylene-olefin copolymer in addition to the ethylene-vinyl acetate copolymer. By mixing a propylene-olefin copolymer having low compatibility (adhesiveness) with the insulating layer 130 made of polyethylene, the peelability of the outer semiconductive layer 140 from the insulating layer 130 is improved.

  The propylene-olefin copolymer in this embodiment is a copolymer in which the size of polypropylene crystals is controlled in nano order. The propylene-olefin copolymer in the present embodiment includes a structural unit derived from propylene and a structural unit derived from an olefin having 2 or more carbon atoms. Examples of the olefin having 2 or more carbon atoms include ethylene, propylene, 1-butene, 1-hexene, 4-methyl 1-pentene, 1-octene and 1-decene. Olefin having 2 or more carbon atoms may be used alone or in combination of two or more.

Further, the propylene - density olefin copolymer, 850 kg / ^{m 3} or more 900 kg / ^{m 3} or less, preferably 860 kg / ^{m 3} or more 880 kg / ^{m 3} or less.

  The Shore A hardness of the propylene-olefin copolymer is 70 or more and 85 or less. When the hardness of the propylene-olefin copolymer is within the above range, kneadability and compatibility with the ethylene-vinyl acetate copolymer can be improved.

  Further, the melting point of the propylene-olefin copolymer is higher than the melting point of the ethylene-vinyl acetate copolymer and is equal to or higher than the temperature in the water crosslinking step. Specifically, as described above, the melting point of the ethylene-vinyl acetate copolymer is 50 ° C. or more and 100 ° C. or less, whereas the melting point of the propylene-olefin copolymer is 140 ° C. or more and 180 ° C. or less. . Thus, since the melting point of the propylene-olefin copolymer contained in the base resin is high, the melting point of the entire semiconductive resin composition can be maintained high. Thereby, it can suppress that the external semiconductive layer 140 of the adjacent electric power cable 10 adheres in a water bridge | crosslinking process.

  The melt flow rate (MFR) of the propylene-olefin copolymer is 1 g / 10 min or more and 20 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf according to the test method of JISK7210. When the MFR of the propylene-olefin copolymer is within the above range, that is, the molecular weight of the propylene-olefin copolymer is large, molecular diffusion from the outer semiconductive layer 140 to the insulating layer 130 is suppressed, and the outer half The conductive layer 140 can be easily separated from the insulating layer 130.

  The mixing ratio of the propylene-olefin copolymer to the base resin is adjusted so that the content of vinyl acetate with respect to the base resin becomes a desired value. Specifically, when the base resin is 100 parts by weight, the content of the propylene-olefin copolymer is 1 part by weight or more and 50 parts by weight or less (that is, the content of the ethylene-vinyl acetate copolymer is 50 parts by weight or more and 99 parts by weight or less). When the content of the propylene-olefin copolymer is larger than the above upper limit value, the peeling strength when peeling the external semiconductive layer 140 from the insulating layer 130 is 50 N / 0.5 inch or more, and the external semiconductive layer is separated from the insulating layer 130. It becomes difficult to peel 140.

  In addition, as described above, the base resin has a high-melting-point propylene-olefin copolymer in a predetermined content as compared with the ethylene-vinyl acetate copolymer, so that the semiconductive resin composition as a whole can be obtained. The melting point can be increased. Specifically, the melting point as a whole of the semiconductive resin composition is adjusted to 100 ° C. or higher and 180 ° C. or lower. Thereby, adhesion and deformation of the external semiconductive layer 140 can be suppressed in the water cross-linking step, and deformation due to heating when the power cable 10 is used can be suppressed.

  Further, as will be described later, as the content of vinyl acetate with respect to the base resin is larger, the outer semiconductive layers 140 of the adjacent power cables 10 may stick to each other. In this embodiment, since the melting point of the propylene-olefin copolymer contained in the base resin is higher than the melting point of the ethylene-vinyl acetate copolymer, it is semiconductive even when the base resin contains a predetermined amount of vinyl acetate. The melting point of the entire resin composition can be maintained high, and the non-adhesiveness of the outer semiconductive layer 140 in the water crosslinking step can be improved. Therefore, the content of vinyl acetate with respect to the base resin can be optimized so that the peelability and non-adhesiveness of the external semiconductive layer 140 are compatible.

  The base resin may contain a plurality of types of propylene-olefin copolymers.

  The base resin may contain a homopolymer polypropylene in addition to the propylene-olefin copolymer. Here, the melting point of polypropylene is 140 ° C. or higher and 180 ° C. or lower, and the Rockwell hardness of polypropylene is 80 or higher. When the hardness of the polypropylene mixed with the base resin is higher than the hardness of the ethylene-vinyl acetate copolymer, the peelability of the outer semiconductive layer 140 from the insulating layer 130 is improved. Moreover, since the melting point of polypropylene mixed with the base resin is higher than that of the ethylene-vinyl acetate copolymer, the non-adhesiveness of the outer semiconductive layer 140 in the water crosslinking step is improved.

(Vinyl acetate content)
By adjusting the mixing ratio of the ethylene-vinyl acetate copolymer and the propylene-olefin copolymer as described above, the content of vinyl acetate with respect to the base resin is adjusted to 10% by mass or more and less than 25% by mass. .

  Here, the peel strength when peeling the outer semiconductive layer 140 from the insulating layer 130 monotonously decreases with respect to the vinyl acetate content relative to the base resin. As the content of vinyl acetate with respect to the base resin increases, the polarity of the semiconductive resin composition constituting the external semiconductive layer 140 increases, so that the external semiconductive layer 140 is easily peeled from the insulating layer 130. Therefore, when the content of vinyl acetate with respect to the base resin is not less than the above lower limit value, the peel strength when peeling the outer semiconductive layer 140 from the insulating layer 130 can be 50 N / 0.5 inches or less.

  On the other hand, the higher the vinyl acetate content relative to the base resin, the lower the melting point of the semiconductive resin composition. For this reason, when the content of vinyl acetate with respect to the base resin exceeds a predetermined amount, the external semiconductive layer 140 of the adjacent power cable 10 is easily adhered in the water crosslinking step. In this embodiment, when the content of vinyl acetate with respect to the base resin is equal to or less than the above upper limit value, adhesion of the external semiconductive layer 140 of the adjacent power cable 10 in the water crosslinking step can be suppressed.

(Carbon black)
The semiconductive resin composition has conductive carbon black. The carbon black is, for example, at least one of furnace black, acetylene black, and ketjen black. The carbon black content is set according to the desired conductivity. For example, when the base resin is 100 parts by weight, the carbon black content is 10 parts by weight or more and 300 parts by weight or less, preferably 10 parts by weight. It is not less than 100 parts by weight. When the content of carbon black is 10 parts by weight or more, the volume specific resistance value of the external semiconductive layer 140 is less than 100 Ω · cm, and sufficient conductivity as the external semiconductive layer 140 is obtained. On the other hand, when the content of carbon black is 300 parts by weight or less, the power cable 10 can be stably extruded, and good mechanical characteristics of the power cable 10 can be obtained.

(Other configurations of semiconductive resin composition)
The semiconductive resin composition may contain an antioxidant, a copper damage inhibitor, an acid acceptor, and the like as additives in addition to the above-described components. Antioxidants include, for example, 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], pentaerythrityl-tetrakis [3- (3,5-di -T-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, N, N′-hexamethylenebis (3,5-di-) t-butyl-4-hydroxy-hydrocinnamamide), 4,4′-thiobis (3-methyl-6-tert-butylphenol, etc. Examples of copper damage inhibitors include 1,2-bis (3,5 -Di-t-butyl-4-hydroxyhydrocinnamoyl) hydrazine, 2-hydroxy-N-1H-1,2,4-triazol-3-ylbenzamide, N'1, N'12-bis (2- Such as droxybenzoyl) dodecanedihydrazide, N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine, etc. The acid acceptor is used in a humid heat environment. For example, hydrotalcite, magnesium oxide, magnesium carbonate, calcium carbonate, magnesium silicate, and the like are used to suppress discoloration of the conductor 110.

  The outer semiconductive layer 140 may be non-crosslinked or crosslinked. As a method for crosslinking the outer semiconductive layer 140, for example, a crosslinking method similar to that for the insulating layer 130, that is, a silane graft / water crosslinking method is used. In this case, the semiconductive resin composition may contain the above-mentioned silane compound, a free radical generator, and a silanol condensation catalyst.

(3) Manufacturing method of semiconductive resin composition The manufacturing method of the semiconductive resin composition which concerns on one Embodiment of this invention is demonstrated.

  Using a Banbury mixer, the materials constituting the semiconductive resin composition are kneaded as follows. First, from a hopper part of a Banbury mixer, a base resin having an ethylene-vinyl acetate copolymer and a propylene-olefin copolymer containing vinyl acetate and conductive carbon black are charged.

  At this time, the content of vinyl acetate with respect to the ethylene-vinyl acetate copolymer as a precursor is previously set to 25% by mass or more and 50% by mass or less depending on the composition of the material to be used. When the base resin is 100 parts by weight, the propylene-olefin copolymer is mixed with the ethylene-vinyl acetate copolymer and the propylene-olefin copolymer in the range of 1 part by weight to 50 parts by weight. Thereby, content of vinyl acetate with respect to base resin is adjusted so that it may become 10 mass% or more and less than 25 mass%. In addition, as an additive for the semiconductive resin composition, an antioxidant, a copper damage inhibitor, an acid acceptor, and the like may be simultaneously added.

  Next, the above material is pushed into the casing from the hopper portion of the Banbury mixer. By rotating the rotor so as to bite the material, a shearing force generated between the rotor and the casing is applied to the material to knead the material.

  Next, when the materials are kneaded for a predetermined time, the outlet of the Banbury mixer is opened and the kneaded material is discharged. Next, the kneaded material discharged from the Banbury mixer is formed into pellets. The semiconductive resin composition is manufactured by the above.

(4) Method for Manufacturing Power Cable A method for manufacturing the power cable 10 according to an embodiment of the present invention will be described.

(Extrusion step S110)
First, among the three-layer co-extruder, an extruder A for forming the inner semiconductive layer 120 is mixed with pellets obtained by mixing, for example, ethylene-vinyl acetate copolymer and conductive carbon black at a predetermined ratio. throw into. The temperature of the extruder A is, for example, 150 ° C. or higher and 230 ° C. or lower.

  Next, in the extruder B for forming the insulating layer 130, for example, a polyethylene-based resin such as linear polyethylene, a silane compound such as vinylalkoxysilane, a free radical generator such as dicumyl peroxide, and dibutyltin dilaurate The silanol condensation catalyst is added at a predetermined ratio, and is heated and kneaded. The temperature of the extruder B is, for example, 150 ° C. or higher and 230 ° C. or lower. Thus, the polyethylene resin is graft-copolymerized with the free radical generator.

  Next, the extruder C for forming the outer semiconductive layer 140 is provided with a base resin having an ethylene-vinyl acetate copolymer containing vinyl acetate and a propylene-olefin copolymer, and conductive carbon black. Then, the semiconductive resin composition kneaded into pellets as described above is charged. Moreover, the temperature of the extruder C is 150 degreeC or more and 230 degrees C or less, for example.

  Next, the respective mixtures from the extruders A to C are guided to the common head, and the inner semiconductive layer 120, the insulating layer 130, and the outer semiconductive layer 140 are simultaneously pressed on the outer periphery of the conductor 110 from the inner side toward the outer side. By taking out, a cable intermediate (extruded product) is formed.

(Wounding step S120)
Next, the cable intermediate is wound around the drum while the cable intermediate is extruded from the three-layer co-extruder.

(Water crosslinking step S130)
Next, in a state where the cable intermediate is wound around the drum, the cable intermediate is put into a constant temperature and humidity chamber maintained at a predetermined temperature and humidity. Thus, the power cable 10 is formed by crosslinking the insulating layer 130 by a silane graft / water crosslinking method.

  At this time, the cable intermediate is exposed to an atmosphere of 70 ° C. or more and 100 ° C. or less and 80% RH or more and 95% RH or less for 12 hours or more and 48 hours or less in a constant temperature and humidity chamber. By exposing the cable intermediate to the above atmosphere, water vapor can be transmitted to the insulating layer 130 via the external semiconductive layer 140, and the insulating layer 130 can be stably hydrobridged.

  As described above, the power cable 10 according to this embodiment is manufactured.

(5) Effects according to the present embodiment According to the present embodiment and its modifications, the following one or more effects are achieved.

(A) According to this embodiment, the outer semiconductive layer is formed on the outer periphery of the insulating layer that is crosslinked by the silane graft / water crosslinking method, so that the vinyl acetate content relative to the base resin is 10 mass% or more and 25 mass%. A semiconductive resin composition that is less than is used.

  Here, the peeling strength (peeling force) when peeling the external semiconductive layer 140 from the insulating layer 130 monotonously decreases with respect to the content of vinyl acetate with respect to the base resin. The greater the vinyl acetate content relative to the base resin, the greater the polarity of the semiconductive resin composition constituting the external semiconductive layer 140, and the greater the difference in solubility parameter between the insulating layer 130 and the external semiconductive layer 140. . Thereby, the outer semiconductive layer 140 can be easily peeled from the insulating layer 130. In the present embodiment, when the content of vinyl acetate with respect to the base resin is 10% by mass or more, the peel strength when peeling the outer semiconductive layer 140 from the insulating layer 130 may be 50 N / 0.5 inch or less. it can.

  On the other hand, the inventors have found that the larger the content of vinyl acetate with respect to the base resin, the more likely that the outer semiconductive layers 140 of the adjacent power cables 10 stick to each other in the water crosslinking step. . The higher the vinyl acetate content relative to the base resin, the lower the melting point of the semiconductive resin composition. For this reason, when the content of vinyl acetate with respect to the base resin exceeds a predetermined amount, the external semiconductive layer 140 of the adjacent power cable 10 is easily adhered in the water crosslinking step. In this embodiment, when the content of vinyl acetate with respect to the base resin is less than 25% by mass, the outer semiconductive layer 140 of the adjacent power cable 10 adheres when the cable is wound around the drum in the water crosslinking step. Can be suppressed.

  Therefore, when the content of vinyl acetate with respect to the base resin is 10% by mass or more and less than 25% by mass, the external semiconductive layer 140 can be peeled from the insulating layer 130 (peelability) and adjacent in the water crosslinking step. It is possible to achieve both prevention of adhesion of the external semiconductive layer 140 of the power cable 10 to each other (non-adhesiveness).

(B) According to this embodiment, the base resin of the semiconductive resin composition has a propylene-olefin copolymer.

  Here, as a comparative example, a case where high-density polyethylene or ethylene-olefin copolymer is used as the base resin in addition to the ethylene-vinyl acetate copolymer will be considered. Ethylene polymers such as high-density polyethylene and ethylene-olefin copolymers are highly compatible (adhesive) with the insulating layer 130 made of polyethylene as an ethylene-based polymer. For this reason, it may be difficult to peel the external semiconductive layer using high-density polyethylene or ethylene-olefin copolymer as the base resin from the insulating layer. Moreover, although melting | fusing point of a high density polyethylene is 120-140 degreeC, and higher than melting | fusing point (50-100 degreeC) of an ethylene-vinyl acetate copolymer, melting | fusing point of an ethylene-olefin copolymer is 50-100 degreeC, It is close to the melting point of the ethylene-vinyl acetate copolymer. For this reason, when an ethylene-olefin copolymer is used as the base resin, the external semiconductive layers of the adjacent power cables may stick to each other in the water crosslinking step. Thus, when an ethylene-based polymer such as high-density polyethylene or ethylene-olefin copolymer is used as the base resin, it may be difficult to achieve both the peelability and non-adhesiveness of the external semiconductive layer. There is sex.

  On the other hand, according to this embodiment, by mixing a propylene-olefin copolymer as a propylene-based polymer having low compatibility (adhesiveness) with the insulating layer 130 made of polyethylene, the external semiconductive layer The peelability from the 140 insulating layer 130 can be improved. In addition, since the melting point of the propylene-olefin copolymer contained in the base resin is higher than the melting point of the ethylene-vinyl acetate copolymer, the semiconductive resin composition can be used even when the base resin contains a predetermined amount of vinyl acetate. The melting point as a whole can be kept high, and the non-adhesiveness of the outer semiconductive layer 140 in the water crosslinking step can be improved. Therefore, in this embodiment, the content of vinyl acetate with respect to the base resin can be optimized so as to achieve both peelability and non-adhesiveness.

(C) According to this embodiment, the melt flow rate (MFR) of the ethylene-vinyl acetate copolymer is 0.1 g / 10 min when the measurement temperature is 190 ° C. and the load is 2.16 kgf according to the test method of JIS K7210. It is 10 g / 10 min or less. The melt flow rate of the ethylene-vinyl acetate copolymer is 10 g / 10 min or less, that is, the high molecular weight of the ethylene-vinyl acetate copolymer makes it possible to increase the interface at the interface between the insulating layer 130 and the external semiconductive layer 140. Molecular diffusion is suppressed, and the peelability from the insulating layer 130 is improved.

(D) According to this embodiment, the melt flow rate (MFR) of the propylene-olefin copolymer is 1 g / 10 min or more and 20 g / 10 min or less at a measurement temperature of 190 ° C. and a load of 2.16 kgf. When the MFR of the propylene-olefin copolymer is within the above range, that is, the molecular weight of the propylene-olefin copolymer is large, molecular diffusion from the outer semiconductive layer 140 to the insulating layer 130 is suppressed, and the outer half The conductive layer 140 can be easily separated from the insulating layer 130.

(E) According to this embodiment, by forming the outer semiconductive layer 140 using the above-described semiconductor resin composition together with the inner semiconductive layer 120 and the insulating layer 130 by, for example, three-layer simultaneous extrusion, Form the body. Thereafter, the insulating layer 130 is crosslinked by a silane graft / water crosslinking method with the cable intermediate wound around the drum. Thereby, the big equipment used for thermal bridge | crosslinking is not required, but the power cable 10 can be manufactured at low cost.

(F) According to the present embodiment, the content of vinyl acetate with respect to the ethylene-vinyl acetate copolymer as the precursor is predetermined from 25 mass% to 50 mass% depending on the composition of the material used. When the base resin is 100 parts by weight, the propylene-olefin copolymer is mixed with the ethylene-vinyl acetate copolymer and the propylene-olefin copolymer in the range of 1 part by weight to 50 parts by weight. Thereby, content of vinyl acetate with respect to base resin is adjusted so that it may become 10 mass% or more and less than 25 mass%. Thus, by mixing an ethylene-vinyl acetate copolymer containing vinyl acetate in a predetermined content and a propylene-olefin copolymer at a predetermined mixing ratio, acetic acid with respect to the base resin can be easily obtained. The vinyl content can be adjusted to a desired value.

<Other Embodiments of the Present Invention>
As mentioned above, although embodiment of this invention was described concretely, this invention is not limited to the above-mentioned embodiment, It can change variously in the range which does not deviate from the summary.

  In the above-described embodiment, a cable intermediate is formed by simultaneously extruding the inner semiconductive layer, the insulating layer, and the outer semiconductive layer from the inner side to the outer side of the outer periphery of the conductor. Although the method has been described, it is also possible to extrude in the tandem method in which the outer semiconductive layer is extruded immediately after the inner semiconductive layer and the insulating layer are simultaneously extruded.

  Next, examples according to the present invention will be described together with comparative examples.

(1) Preparation of semiconductive resin composition As shown in the following Tables 1-4, the semiconductive resin composition of Examples 1-22 and Comparative Examples 1-6 was produced.

  As Examples 1-7, a semiconductive resin composition using one kind of propylene-olefin copolymer was prepared, and as Examples 8-13, semiconductive having a plurality of propylene-olefin copolymers mixed. The resin composition was produced and the semiconductive resin composition which mixed the polypropylene with the propylene-olefin copolymer as Examples 14-22 was produced. As Comparative Examples 1 to 3, a semiconductive resin composition having a VA concentration outside the predetermined range with respect to the base resin was prepared. As Comparative Example 4, a semiconductive resin composition not containing a propylene-olefin copolymer was prepared. In Comparative Example 5, a semiconductive resin composition using high-density polyethylene instead of the propylene-olefin copolymer was prepared. In Comparative Example 6, ethylene-olefin copolymer was used instead of the propylene-olefin copolymer. A semiconductive resin composition using a polymer was prepared.

Details of each material are as follows.
Ethylene-vinyl acetate copolymer (EVA): Made by Mitsui DuPont Polychemical EV170 Vinyl acetate content 33% by mass MFR 1.0 g / 10 min
EV270 Vinyl acetate content 28% by mass MFR 1.0 g / 10 min
EV45LX Vinyl acetate content 46% by mass MFR 2.5g / 10min
V523 Vinyl acetate content 33% by mass MFR 14.0 g / 10 min

Propylene-olefin copolymer: Mitsui Chemicals Toughmer PN-2070
Melting point 140 ° C. Shore A hardness 75 MFR 3.2 g / 10 min
Toughmer PN-3560
Melting point 160 ° C. Shore A hardness 72 MFR 2.7 g / 10 min
Toughmer PN-2060
Melting point 160 ° C. Shore A hardness 84 MFR 2.7 g / 10 min
Toughmer PN-20300
Melting point 160 ° C Shore D hardness 84 MFR14g / 10min

Polypropylene in Examples 13 to 21: Novatec PP EC7 manufactured by Nippon Polypro Co., Ltd. Melting point 140 ° C. or higher and 170 ° C. or lower Rockwell hardness 80
Novatec PP EC9 Melting point 140 ° C to 170 ° C Rockwell hardness 80

High density polyethylene in Comparative Example 5: made of prime polymer Hi-Zex 5305E

Ethylene-olefin copolymer in Comparative Example 6 Ethylene-based Tuffmer Tuffmer DF

Carbon black: Toast carbon carbon seast G117

In addition, antioxidant: Nouchi 300 from Ouchi Shinsei Chemical Industry

Copper damage prevention agent:
Lowurax MD24 made by Chemtura
CDA-1 made by ADEKA

Acid acceptor:
Hydrotalcite manufactured by Sakai Chemical Industry Magnesium oxide manufactured by Kamishima Chemical Industry

(2) Preparation of test piece In order to evaluate the semiconductive resin compositions shown in Tables 1 to 4, sheet samples were prepared as follows.

  First, a polyethylene resin such as linear polyethylene, a silane compound such as vinyl alkoxysilane, a free radical generator such as dicumyl peroxide, and a silanol condensation catalyst such as dibutyltin dilaurate are kneaded at a predetermined ratio at 190 ° C. And the sheet | seat corresponded to an insulating layer was produced with the hot press molding machine.

  Next, the semiconductive resins of Examples 1 to 22 and Comparative Examples 1 to 6 were kneaded with a Banbury mixer, and a sheet corresponding to the external semiconductive layer was produced with a hot press molding machine.

  Next, in a state where the two sheets described above were compressed at a predetermined pressure, the insulating layer was subjected to water crosslinking by exposing it to a constant temperature and humidity chamber at 80 ° C. and 95% RH for 12 hours. Thus, a sheet sample was produced.

(3) Test Using the sheet sample described above, the following test was performed.
(Peel test)
Using a method specified by AEIC-CS5, using a sheet sample having a width of 0.5 inch, the peeling force (peel strength) between the insulating layer and the external semiconductive layers according to Examples 1 to 22 and Comparative Examples 1 to 6 ) Was measured.

(Mutual adhesion test)
Two sheet samples were overlapped so that the external semiconductive layers were opposed to each other, put in a constant temperature bath maintained at the same temperature as that during water crosslinking, with a constant load applied, and left for 12 hours. Thereafter, the two sheet samples were peeled, and index values were given to the respective examples depending on the degree of peeling at that time. The index value 0 is a state in which the adhesive is not adhered at all, the index value 10 is a state in which the adhesive is partially adhered but can be peeled off, the index value 20 is a state in which the whole is adhered but is peelable, and the index value 30 is It is in a state where it cannot adhere and peel off at all. The cases of peeling 0 and 10 were evaluated as having good non-adhesiveness.

(4) Results (VA content)
FIG. 2 is a view showing index values of peel strength and mutual adhesiveness according to the present example and a comparative example. The horizontal axis of FIG. 2 shows the content (% by mass) of VA with respect to the base resin, the left axis of FIG. 2 shows the peel strength (peel force) (N / 0.5 inch), and the right axis of FIG. Indicates an index value of mutual adhesiveness. Note that Comparative Examples 4 to 7 are not plotted in FIG.

  As shown in FIG. 2, the peel strength when peeling the external semiconductive layer from the insulating layer monotonously decreases with respect to the vinyl acetate content relative to the base resin. When the content of VA with respect to the base resin was 9.9% by mass (Comparative Example 2), the peeling force was 50 N / 0.5 inches or more. Therefore, since it decreases monotonously with respect to the content of vinyl acetate with respect to the base resin, the peel strength is 50 N / 0.5 inch or less when the content of vinyl acetate with respect to the base resin is 10% by mass or more.

  On the other hand, the greater the vinyl acetate content relative to the base resin, the greater the index value for mutual adhesion. When the content of VA with respect to the base resin was 23.1% by mass (for example, Examples 1 to 3), the sheet sample was partly adhered, but could be peeled off, and the index value was 10. On the other hand, when the content of VA with respect to the base resin was 26.4% by mass (Comparative Example 3), the sheet sample was in a state of being peeled although it was totally adhered, and the index value was 20. That is, when the content of VA with respect to the base resin is 25% by mass or more, the mutual adhesiveness of the sheet sample is changed, and the index value is increased.

  From the above results, in Examples 1 to 22, it can be seen that when the content of vinyl acetate with respect to the base resin is 10% by mass or more and less than 25% by mass, both peelability and non-adhesiveness can be achieved.

(Propylene-olefin copolymer)
As shown in Table 4, in Comparative Example 4 not including the propylene-olefin copolymer, the vinyl acetate content relative to the base resin is in the range of 10% by mass or more and less than 25% by mass, but the peel strength is Was low, but the index value of mutual adhesiveness was high. This is probably because the base resin had a low melting point because it did not contain a propylene-olefin copolymer.

  Further, in Comparative Example 5 in which high-density polyethylene was used instead of the propylene-olefin copolymer, although the vinyl acetate content relative to the base resin was within the range of 10% by mass or more and less than 25% by mass, The adhesive strength was low, but the peel strength was high. Since the high density polyethylene is the same polyethylene as the insulating layer, the compatibility of the high density polyethylene with the insulating layer is high. For this reason, it is considered that the peel strength was high. Although not shown, even when high-density polyethylene is used, the peel strength when peeling the outer semiconductive layer from the insulating layer is similar to the vinyl acetate content relative to the base resin, as in the examples. It showed a tendency to decrease monotonously, and it was found that the higher the vinyl acetate content relative to the base resin, the worse the mutual tackiness. However, when high-density polyethylene is used, it has been difficult to optimize the composition of the base resin, the vinyl acetate content relative to the base resin, etc. so as to achieve both peelability and non-adhesiveness.

  Further, in Comparative Example 6 in which an ethylene-olefin copolymer was used instead of the propylene-olefin copolymer, the vinyl acetate content relative to the base resin was in the range of 10% by mass to less than 25% by mass. In addition, the index value of mutual adhesiveness was high, and the peel strength was also high. Since the ethylene-olefin copolymer is the same ethylene polymer as the insulating layer, the compatibility of the ethylene-olefin copolymer with the insulating layer is increased. For this reason, it is considered that the peel strength was high. In addition, since the melting point of the ethylene-olefin copolymer is low, it is considered that the semiconductive resin compositions easily adhere to each other, and the index value of mutual adhesiveness was high. In addition, when using an ethylene-olefin copolymer, the composition of the base resin and the content of vinyl acetate in the base resin so as to achieve both peelability and non-adhesiveness in the same manner as when using high-density polyethylene. It was difficult to optimize the amount and the like.

  On the other hand, in Examples 1 to 22, the base resin has a tafmer PN that is a propylene-olefin copolymer as a propylene-based polymer that has low compatibility (adhesiveness) with the insulating layer 130, thereby peeling off. The optimum range of the vinyl acetate content relative to the base resin could be found so as to achieve both compatibility and non-adhesiveness.

(About MFR of ethylene-vinyl acetate copolymer)
As shown in Table 1, in Example 7 where the MFR of the ethylene-vinyl acetate copolymer is 14 g / 10 min, the peel strength was 40 N / 0.5 inch, although the index value of mutual adhesiveness was low. It was. Since the MFR of the ethylene-vinyl acetate copolymer is high, that is, the molecular weight of the ethylene-vinyl acetate copolymer is low, molecular diffusion of the polymer occurs at the interface between the insulating layer and the external semiconductive layer, and the insulating layer and the external semiconductive layer It is thought that the conductive layer has adhered.

  On the other hand, in Examples 1-6 and 8-22, when the MFR of the ethylene-vinyl acetate copolymer is 10 g / 10 min or less, the peel strength is 30 N / 0.5 inch or less. It was lower than the peel strength at. The MFR of the ethylene-vinyl acetate copolymer is 10 g / 10 min or less, that is, the molecular diffusion of the polymer at the interface between the insulating layer and the external semiconductive layer due to the high molecular weight of the ethylene-vinyl acetate copolymer. Is suppressed, and the peelability from the insulating layer is considered to be improved.

(Other)
In addition, when Examples 1-13 were compared, although melting | fusing point and MFR of Toughmer PN used in each Example differed, Examples 1-13 showed the substantially equivalent peelability and mutual adhesiveness. From this, it is considered that the influence on the peelability and the mutual adhesiveness due to the difference in the material of the Tafmer PN, that is, the difference in the material of the propylene-olefin copolymer is small.

  Moreover, when Examples 14-22 were compared, although melting | fusing point and MFR of Novatec PP used in each Example differed, Examples 14-22 showed substantially the same peelability and mutual adhesiveness. From this, it is considered that the influence on the peelability and mutual adhesiveness due to the difference in the material of Novatec PP, that is, the difference in the material of polypropylene, is small.

  Examples (6, 13, and 22) that do not include an antioxidant, a copper damage inhibitor, and an acid acceptor, examples that include different antioxidants, a copper damage preventive, and an acid acceptor, and these Since examples having different blending parts also showed the same tendency, it is considered that the antioxidant, copper damage inhibitor, and acid acceptor do not affect the peelability and mutual adhesiveness.

(5) Production of semiconductive resin composition Based on the above results, a semiconductive resin composition was produced as follows.

  Using a Banbury mixer, for example, the materials constituting the semiconductive resin composition of Example 1, 8, or 17 were kneaded, and the kneaded material discharged from the Banbury mixer was formed into pellets. This obtained the semiconductive resin composition which concerns on Example 1, 8, or 17.

(6) Production of power cable Based on the above results, a power cable was produced as follows.

  First, among three-layer co-extruders, an extruder A for forming an internal semiconductive layer was charged with pellets obtained by mixing ethylene-vinyl acetate copolymer and conductive carbon black at a predetermined ratio. The temperature of the extruder A was set to 230 ° C. or less, for example.

  Next, linear polyethylene, vinylalkoxysilane, dicumyl peroxide, and dibutyltin dilaurate were charged at a predetermined ratio into an extruder B that forms an insulating layer, and heated and kneaded. The temperature of the extruder B was set to 230 ° C. or less, for example.

  Next, each pellet of the semiconductive resin composition of Example 1, 8, or 17 was put into an extruder C for forming an external semiconductive layer. The temperature of the extruder C was set to 230 ° C. or less, for example.

  Next, a cable intermediate was formed by simultaneously extruding the inner semiconductive layer, the insulating layer, and the outer semiconductive layer, and the cable intermediate was wound around a drum.

  Next, in a state where the cable intermediate was wound around the drum, it was put into a constant temperature and humidity chamber maintained at 70 ° C. and 95% RH. Thereby, the insulating layer was crosslinked by a silane graft / water crosslinking method. Thus, the power cable according to Example 1, 7, or 16 was obtained.

  At this time, after the water cross-linking step, the adjacent power cables could be peeled without sticking to each other. In addition, in the manufactured power cable, the external semiconductive layer could be easily peeled from the insulating layer.

10 Power cable 110 Conductor 120 Internal semiconductive layer 130 Insulating layer 140 External semiconductive layer

Claims (17)

A semiconductive resin composition that forms an external semiconductive layer on the outer periphery of an insulating layer that is crosslinked by a silane graft / water crosslinking method,
A base resin having an ethylene-vinyl acetate copolymer containing vinyl acetate and a propylene-olefin copolymer;
Conductive carbon black,
Have
The melting point of the propylene-olefin copolymer is higher than the melting point of the ethylene-vinyl acetate copolymer, and is equal to or higher than the water crosslinking temperature of the insulating layer;
The semiconductive resin composition, wherein the content of the vinyl acetate with respect to the base resin is 10% by mass or more and less than 25% by mass. The semiconductive resin composition according to claim 1, wherein the content of the propylene-olefin copolymer is 1 part by weight or more and 50 parts by weight or less when the base resin is 100 parts by weight. The semiconductive resin composition according to claim 1 or 2, wherein a content of the vinyl acetate with respect to the ethylene-vinyl acetate copolymer is 25% by mass or more and 50% by mass or less. The melt flow rate of the ethylene-vinyl acetate copolymer is 0.1 g / 10 min or more and 10 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf. The semiconductive resin composition according to any one of the above. The melt flow rate of the ethylene-vinyl acetate copolymer is 0.1 g / 10 min or more and 1.0 g / 10 min or less when the measurement temperature is 190 ° C. and the load is 2.16 kgf.
The semiconductive resin composition according to claim 4. The propylene - melt flow rate of the olefin copolymer, measured temperature 190 ° C., when a load 2.16 kgf, any one of the claims 1-5, characterized in that at most 1 g / 10min or more 20 g / 10min The semiconductive resin composition according to Item. The melt flow rate of the propylene-olefin copolymer is 1.58 g / 10 min to 20 g / 10 min when the measurement temperature is 190 ° C. and the load is 2.16 kgf.
The semiconductive resin composition according to claim 6. The ethylene - the melting point of the vinyl acetate copolymer, semi-conductive resin composition according to any one of claims 1 to 7, characterized in that at 50 ° C. or higher 100 ° C. or less. The propylene - melting point of the olefin copolymer, the semi-conductive resin composition according to any one of claims 1-8, characterized in that at 140 ° C. or higher 180 ° C. or less. The melting point of the semiconductive resin composition, a semi-conductive resin composition according to any one of claims 1 to 9, characterized in that at 100 ° C. or higher 180 ° C. or less. The propylene-olefin copolymer has a Shore A hardness of 70 or more and 85 or less.
The semiconductive resin composition according to any one of claims 1 to 10, wherein: The semiconductive resin composition according to any one of claims 1 to 11 , wherein the base resin includes polypropylene. The semiconductive property according to any one of claims 1 to 12 , wherein the content of the carbon black is 10 parts by weight or more and 300 parts by weight or less when the base resin is 100 parts by weight. Resin composition. The semiconductive resin composition according to any one of claims 1 to 13 , wherein the insulating layer is made of crosslinked polyethylene. Conductors,
An internal semiconductive layer provided to cover the outer periphery of the conductor;
An insulating layer provided so as to cover the outer periphery of the inner semiconductive layer, and crosslinked by a silane graft / water crosslinking method;
An external semiconductive layer provided to cover the outer periphery of the insulating layer;
Have
The outer semiconductive layer, the electric power cable, characterized in that it is formed by a semi-conductive resin composition according to any one of claims 1-14. Extrusion step of forming the cable intermediate by extruding the inner semiconductive layer, the insulating layer and the outer semiconductive layer from the inner side toward the outer side on the outer periphery of the conductor;
A winding step of winding the cable intermediate around a drum;
In a state where the cable intermediate is wound around the drum, a water crosslinking step of forming a power cable by crosslinking the insulating layer by a silane graft / water crosslinking method;
Have
In the extrusion process,
A base resin having an ethylene-vinyl acetate copolymer containing vinyl acetate and a propylene-olefin copolymer, and conductive carbon black, wherein the propylene-olefin copolymer has a melting point of the ethylene-acetic acid A semiconductive resin composition that is higher than the melting point of the vinyl copolymer, is equal to or higher than the water crosslinking temperature of the insulating layer, and the vinyl acetate content relative to the base resin is 10% by mass or more and less than 25% by mass. A method of manufacturing a power cable, characterized in that the outer semiconductive layer is formed by using the method. In the water crosslinking step,
The method of manufacturing a power cable according to claim 16 , wherein the cable intermediate is exposed to an atmosphere of 70 ° C. to 100 ° C. and 80% RH to 95% RH.