JPS6245643B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a semiconductive composition suitable for forming a semiconductive layer around the conductor or insulator of a power cable. The smoothness and adhesion of the interface between the semiconducting layer and the insulator in cross-linked polyethylene insulated power cables are important from the perspective of improving cable reliability. When interface irregularities exist, a high electric field is locally formed, which tends to cause water tree deterioration during corona discharge or water immersion, and deteriorates the electrical characteristics of the cable. To address this problem, studies have been made from the aspects of manufacturing and materials for semiconducting layers, and extruded semiconducting layers have been developed in place of semiconductive cloth tapes, which tend to have a lot of fuzz. Materials for the extruded semiconductive layer include those using polar ethylene-vinyl acetate copolymer or ethylene-ethyl acrylate copolymer as the base polymer, non-polar ethylene propylene rubber, polyethylene as the base polymer, Alternatively, a blend of these as a base polymer is used. A cross-linked polyethylene insulated power cable with such a semiconducting layer is
Although the breakdown voltage is significantly improved, under severe conditions such as water seepage inside the cable, water treeing occurs frequently when electricity is applied for a long period of time, resulting in a decrease in the breakdown voltage. The present invention was made in order to solve the above-mentioned problems, and an object of the present invention is to provide a semiconductive composition that can improve the water resistance of power cables. The semiconductive composition of the present invention comprises a crystalline ethylene polymer with a melting point of 120°C or higher and ethylene-butene-
It is characterized by adding a conductivity imparting material to a blend polymer of 1,4-hexadiene copolymerized elastomer. In the present invention, the crystalline ethylene polymers include polyethylene, polypropylene, polybutene-1, polyhexene-1, polyoctene-1,
Examples include homopolymers such as poly-4-methylpentene-1 and copolymers of these with ethylene, among which polyethylene and polypropylene are preferred. It has been found that remarkable water resistance can be exhibited by blending an ethylene-butene-1,4-hexadiene copolymer elastomer with such a crystalline ethylene-based polymer. Note that it is preferable that the content ratio of the crystalline ethylene polymer in the blend polymer is 50% by weight or more from the viewpoint of water tree suppression effect. As the conductivity imparting material, acetylene black,
Conductive carbon blacks, such as furnace blacks, are suitable. The amount of the conductivity imparting material added is preferably 40 parts by weight or more based on 100 parts by weight of the blend polymer. In the present invention, in addition to the above-mentioned components, anti-aging agents, lubricants, dispersants, etc. may also be added as necessary. As anti-aging agents, amine-based N,
N'-diphenyl-P-phenylenediamine, phenyl-α-naphthylamine, N-phenyl-
N'-isopropyl-phenylenediamine, poly(2,2-4-trimethyl-1,2-dihydroquinoline), phenolic 2,2'methylenebis(4-methyl-6-tert-butylphenol), 2 , 6-di-tert-butyl-4-methylphenol, 4,4'-thiobis(6-tert-butyl-3-methylphenol), etc., imidazole-based 2-mercaptobenzimidazole, zinc of 2-mercaptobenzimidazole Salts such as sulfur-based distearyl-thio-dipropionate, dilaurylthiopropionate, tetrakis (methyl-dodecylthiopropionate) methane, etc., and other anti-aging agents for rubber are used alone or in combination. be able to. The semiconductive composition containing the various components described above may be crosslinked after being molded into a predetermined shape, and crosslinking methods include crosslinking using peroxide or sulfur, crosslinking by electron beam irradiation, and silane graft water crosslinking. Things can be given. Examples of the present invention will be described below in comparison with comparative examples. A semiconductive composition having the formulation shown in each example in Table 1 was extruded and coated onto a copper stranded wire conductor with a cross-sectional area of 80 mm ² to a thickness of 1 mm.
100 parts by weight of low density polyethylene (density 0.920 g/cm ³ , melt index 1.0), dicumyl peroxide
An insulator composition containing 2.5 parts by weight and 0.25 parts by weight of an antioxidant was extrusion coated to form an insulator layer with a thickness of 4 mm. Next, a semiconductive composition having the same composition as the internal semiconductive layer was extruded around the outer periphery of this insulating layer to form an external semiconductive layer with a thickness of 1 mm, and heat crosslinking was performed to form a crosslinked polyethylene insulated power cable. was manufactured. Water was injected into the conductor of the power cable manufactured as described above, and after the water had soaked, an AC voltage of 50 Hz and 15 kV was applied between the conductor and the water electrode, the water temperature was set to 90°C, and electricity was applied for 18 months. After completion, the insulator was spirally cut to a thickness of 0.5 mm, boiled and stained with a methylene blue aqueous solution, and the number of water trees generated at the interface between the insulator and the internal semiconducting layer was observed using a microscope. The results are shown in the lower column of Table 1.

【table】

[Table] As is clear from the evaluation results in Table 1, Example 1
All of the semiconductive compositions according to the present invention shown in 3 to 3 in which inner and outer semiconductive layers were formed had a water tree number as compared to the case where the semiconductive compositions of Comparative Examples 1 to 4 were used. The amount was significantly reduced, indicating good results. As explained above, according to the present invention, it is possible to realize a power cable with significantly improved water resistance.

Claims (1)

[Claims] 1. A semiconductive composition comprising a blend polymer of a crystalline ethylene polymer with a melting point of 120° C. or higher and an ethylene-butene-1,4-hexadiene copolymer elastomer, and a conductivity-imparting material added thereto.