Direct-current cable, composition and method of manufacturing direct-current cable

Abstract

A direct-current cable of an embodiment includes a conductive portion; and an insulating layer covering an outer periphery of the conductive portion, the insulating layer containing cross-linked base resin and inorganic filler, the base resin containing polyethylene, a BET specific surface area of the inorganic filler being greater than or equal to 5 m 2 /g, and a mean volume diameter of the inorganic filler being less than or equal to 5 μm, the mass ratio of the inorganic filler with respect to the base resin being greater than or equal to 0.001 and less than or equal to 0.05, and the cross-linked base resin being cross-linked by a cross-linking agent containing organic peroxide.

What is claimed is: 
     
         1 . A direct-current cable comprising:
 a conductive portion; and   an insulating layer covering an outer periphery of the conductive portion,   the insulating layer containing cross-linked base resin and inorganic filler,   the base resin containing polyethylene,   a BET specific surface area of the inorganic filler being greater than or equal to 5 m 2 /g, and a mean volume diameter of the inorganic filler being less than or equal to 5 μm,   the mass ratio of the inorganic filler with respect to the base resin being greater than or equal to 0.001 and less than or equal to 0.05, and   the cross-linked base resin being cross-linked by a cross-linking agent containing organic peroxide.   
     
     
         2 . The direct-current cable according to  claim 1 , wherein the inorganic filler is one or more selected from a group consisting of magnesium oxide powder, aluminum oxide powder, silica powder, magnesium silicate powder, aluminum silicate powder and carbon black. 
     
     
         3 . The direct-current cable according to  claim 2 , wherein a surface of each of the magnesium oxide powder, the aluminum oxide powder, the silica powder, the magnesium silicate powder and the aluminum silicate powder is treated by a silane coupling agent. 
     
     
         4 . The direct-current cable according to  claim 1 ,
 wherein the base resin further contains copolymer of ethylene and polar monomer or polyethylene-graft-maleic anhydride, and   wherein the mass ratio of the copolymer of ethylene and polar monomer or the polyethylene-graft-maleic anhydride with respect to the polyethylene is less than or equal to 1/9.   
     
     
         5 . A composition comprising: base resin, inorganic filler and a cross-linking agent,
 the base resin containing polyethylene,   a BET specific surface area of the inorganic filler being greater than or equal to 5 m 2 /g, and a mean volume diameter of the inorganic filler being less than or equal to 5 μm,   the mass ratio of the inorganic filler with respect to the base resin being greater than or equal to 0.001 and less than or equal to 0.05, and   the cross-linking agent containing organic peroxide.   
     
     
         6 . The composition according to  claim 5 , wherein the inorganic filler is one or more selected from a group consisting of magnesium oxide powder, aluminum oxide powder, silica powder, magnesium silicate powder, aluminum silicate powder and carbon black. 
     
     
         7 . The composition according to  claim 6 , wherein a surface of each of the magnesium oxide powder, the aluminum oxide powder, the silica powder, the magnesium silicate powder and the aluminum silicate powder is treated by a silane coupling agent. 
     
     
         8 . The composition according to  claim 5 ,
 wherein the base resin further contains copolymer of ethylene and polar monomer or polyethylene-graft-maleic anhydride, and   wherein the mass ratio of the copolymer of ethylene and polar monomer or the polyethylene-graft-maleic anhydride with respect to the polyethylene is less than or equal to 1/9.   
     
     
         9 . A method of manufacturing a direct-current cable in which an outer periphery of a conductive portion is covered by an insulating layer, comprising:
 manufacturing an extrusion molded material by extrusion molding the composition as claimed in  claim 5  to cover an outer periphery of the conductive portion; and   forming the insulating layer by heating the extrusion molded material at a predetermined temperature to cross link the base resin.