JPH0241844B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvement of polyethylene-based power cables Polyethylene and its copolymers are widely used as power cables due to their excellent properties as insulators and ease of processing, as well as improvements in cable manufacturing technology. There is. A typical structure of such a power cable has an insulating structure consisting of an inner semiconducting layer, a polyethylene insulating layer, and an outer semiconducting layer on a conductor. In particular, the outer semiconducting layer is made of a semiconducting composition. It is obtained by extrusion coating on a polyethylene insulating layer or by wrapping a tape made of a semiconductive material on the insulating layer, and this semiconductive tape uses an adhesive containing conductive carbon black. Impregnated cloth tape was commonly used. When the external semiconducting layer of such conventional power cables is constructed by wrapping with semiconducting tape, gaps are likely to be formed between the insulating layer and the semiconducting tape wrapping layer, which can cause ionization phenomena. In addition, extrusion coatings with semiconductive compositions do not have the problem of void formation that occurs in the case of semiconductive tape, but they usually contain conductive material in a resin material that is the same or similar to the insulator. Because it is a semiconductive composition containing carbon black, it has the advantage of adhering easily to the insulation layer of the cable, but on the other hand, it is difficult to remove the semiconductivity cleanly when connecting cables.
The disadvantage is that the cable connection work becomes difficult. For this purpose, a semiconductive composition containing an ethylene-vinyl acetate copolymer with a vinyl acetate content of 15-55% by weight, an ethylene-vinyl acetate-vinyl chloride terpolymer, a crosslinking agent, and carbon black is used for the exterior of polyethylene power cables. It was considered to be preferable as a semiconducting layer due to its low peel strength (Special Publication Publication 19907-1979).
However, it is still considered to be insufficient, and a polymer based on a graft polymerization of vinyl chloride to an ethylene/vinyl acetate copolymer and an ethylene/vinyl acetate copolymer is used as a base, and ethylene/vinyl acetate copolymer and carbon black are added to this. When the blended conductive composition is used as an external semiconductive layer, the peel strength can be further reduced (Japanese Patent Publication No. 54-23436). However, even with this, it was still not possible to satisfy the requirements for lowering the peel strength and from the viewpoint of cost. As a result of further study, the inventors found that a composition containing an ethylene/vinyl acetate/vinyl chloride terpolymer with a vinyl acetate content of 60% or more by weight and conductive carbon black was extremely simple. It has been found that when used as an external semiconductive layer, the peel strength is low and the cost is low, which is preferable. In other words, although the Japanese Patent Publication No. 49-19907 uses a terpolymer of ethylene, vinyl acetate, and vinyl chloride, the objective of reducing tear strength cannot be achieved unless an ethylene-vinyl acetate copolymer is used in combination. Although this invention achieves a reduction in tear strength without using an ethylene/vinyl acetate copolymer, the biggest difference between the two is that the vinyl acetate component of the terpolymer The content of That is, in the former case, the vinyl acetate component is 55% by weight or less, whereas in this invention, the tear strength of the external semiconductive layer can be increased more easily than before by using a terpolymer with a vinyl acetate content of 60% by weight or more as the outer semiconductive layer. We succeeded in obtaining a polyethylene-based power cable (a power cable having a polyethylene-based insulating layer made of polyethylene, ethylene-propylene terpolymer, etc., and cross-linked if necessary) with a small diameter. The amount of conductive carbon black used here can be selected according to the conductivity required in the design, but in the case of ordinary 20 to 60 kV class polyethylene cables, ethylene, vinyl acetate, and chloride are used. The amount of conductive carbon black is 10 to 100 parts by weight per 100 parts by weight of the vinyl terpolymer. As in the case of insulators, crosslinking agents such as peroxides, anti-aging agents, processing aids, etc. can be added in appropriate amounts. An example of a polyethylene cable with an outer semiconducting layer according to the invention is shown in the figure. 1 is a conductor, 2 is an internal semiconducting layer, and 3 is a polyethylene insulating layer, which is usually crosslinked. 4 is an outer semiconducting layer, and 5 is a protective coating. Next, Examples and Comparative Examples are shown below. In addition,
The materials and test methods used in this test are as follows. A normal inner semiconducting layer is extruded onto a stranded conductor with a cross-sectional area of 250 mm ² , and then an insulating layer and an outer semiconducting layer shown in the table below are extruded and cross-linked in saturated steam at 10 atm. The reaction was completed. The outer semiconducting layer coated on the surface of the obtained wire has a width of 12.5 mm.
A peel test was performed by making a cut.

【table】

【table】 [Brief explanation of drawings]

The figure is a cross-sectional view showing an example of the polyethylene power cable of the present invention. 1...Conductor, 2...Inner semiconducting layer, 3...Insulating layer, 4...Outer semiconducting layer.

Claims (1)

[Claims] 1. An external semiconductive layer made of a conductive composition prepared by blending conductive carbon black with an ethylene-vinyl acetate-vinyl chloride ternary copolymer with a vinyl acetate content of 60% or more is provided on the surface of the polyethylene insulator. A polyethylene power cable featuring: