JPH06203651A - Power cable - Google Patents

Abstract

PURPOSE:To provide such a power cable that the adhesion of an outer semiconducting layer to an insulator may be improved and also the workability of peeling the outer semiconducting layer off the insulator may be improved by using, for the outer semiconducting layer of the cable, a composition comprising conductive carbon black and an epoxy compound contained in a specific copolymer in a specific quantity ratio of the carbon black to the compound. CONSTITUTION:In a power cable, its outer semiconducting layer is formed out of a composition comprising 20 to 100 pts. of conductive carbon black and 0.5 to 50 pts. of an epoxy compound with its melting point of not less than 40 deg.C both against 100 pts. of at least one kind of an ethylene vinyl acetate copolymer which contains 30 to 70wt.% of vinyl acetate and ethylene-ethyl acrylate which contains 20 to 40wt.% of ethyl acrylate respectively contained therein. Extrusion coating of the composition forming the outer semiconducting layer is given to a cross-linked polyolefine insulator layer covering a wire so as to form the power cable. The outer semiconducting layer can thus be excellently stuck fast to the insulator layer. Moreover, the outer semiconducting layer can be peeled off the insulator layer without difficulty in any environment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a power cable having an outer semiconductive layer on a crosslinked polyolefin insulation, and more particularly, to improve adhesion at the interface between the crosslinked polyolefin insulation and the outer semiconductive layer. The present invention relates to a power cable which is excellent and has good workability for peeling the outer semiconductive layer.

[0002]

2. Description of the Related Art There are many types of power cables using cross-linked polyethylene as an insulator, such as single-core CV cables, 3-core CV cables, and triplex CV cables.
These power cables generally have a structure in which a conductor is coated with an inner semiconductive layer, a crosslinked polyethylene insulator (insulating layer), and an outer semiconductive layer in this order. The withstand voltage characteristics of the CV cable are as follows:
Alternatively, it relies heavily on defects such as interface irregularities between the insulator and the outer semiconductive layer. Therefore, in this type of power cable, it is necessary for electrical performance that the inner semiconductive layer and the outer semiconductive layer are in close contact with the insulating layer without a gap when the cable is energized.

Conventionally, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene propylene rubber and the like have been used alone or as a mixture of two or more as materials for forming the inner semiconductive layer and the outer semiconductive layer. A composition in which conductive carbon black is added to a material is used. Then, in order to reduce defects at the interface between the insulator and the inner semiconductive layer and the outer semiconductive layer, a three-layer coextrusion method is adopted, a liquid epoxy resin is added to the semiconductive layer forming material, etc. Measures are taken. As a result, the adhesion between the insulator and the inner semi-conducting layer and the outer semi-conducting layer has been improved, but the adhesion force (peeling force) becomes too large, resulting in a new problem of poor peeling workability. There is.

In other words, it is sometimes necessary to peel off the outer semiconductive layer from the insulator when connecting the power cable or terminating the power cable. In this case, it is desired from the viewpoint of workability that the outer semiconductive layer be easily peeled off from the insulator. However, the conventional material for forming an external semiconductive layer has a large adhesive force with the crosslinked polyolefin insulator, and a good peeling workability cannot be obtained. In particular, this problem was remarkable at a low temperature of about 0 ° C. or a high temperature of about 40 ° C. Therefore, there is a demand for a power cable having an external semiconductive layer that is excellent in adhesion to an insulator and is excellent in peeling workability, but conventionally, it is difficult to satisfy both of these contradictory characteristics. there were.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to provide a power cable having a structure in which an outer semiconductive layer is coated on a crosslinked polyolefin insulator, which has excellent adhesion to the insulator and has good peeling workability. An object is to provide a power cable having a good outer conductive layer. The present inventors, as a result of earnest research to overcome the problems of the prior art,
As a material for forming the external semiconductive layer, ethylene-vinyl acetate copolymer (EVA) and / or ethylene-ethyl acrylate copolymer (EEA) are mixed with conductive carbon black and an epoxy compound having a melting point of 40 ° C. or higher. It has been found that the above object can be achieved by using a composition containing a specific ratio, and the present invention has been completed based on the findings.

[0006]

Thus, according to the present invention, in a power cable having a structure in which a crosslinked polyolefin insulation is coated with an outer semiconductive layer, the outer semiconductive layer comprises (A) vinyl acetate. At least one copolymer selected from the group consisting of ethylene-vinyl acetate copolymer having a content of 30 to 70% by weight and ethylene-ethyl acrylate copolymer having a content of ethyl acrylate of 20 to 40% by weight. With respect to 100 parts by weight, (B) 20 to 100 parts by weight of electrically conductive carbon black, and (C) an epoxy compound having at least one epoxy group in the molecule and having a melting point of 40 ° C. or higher 0.5 to 50 A power cable is provided that is formed from a composition that includes parts by weight.

The present invention will be described in detail below. The power cable of the present invention may have any structure as long as it has a structure in which an outer semiconductive layer is coated on a crosslinked polyolefin insulator, and in addition to it, for example, an additional inner semiconductive layer, a shielding layer, a vinyl sheath, or the like is added. It may include layers. Of course, a conductor is used in the center layer of the power cable. Various types of power cables can be used including a single-core CV cable. Also, regarding the crosslinked polyolefin, various ones such as crosslinked polyethylene can be used,
There is no particular limitation.

The composition forming the outer semiconductive layer is extrusion coated onto the insulator (insulating layer). The insulator and the outer semiconductive layer may be coextruded. By using the composition (external semiconductive composition) as a material for forming the external semiconductive layer, the external semiconductive layer and the insulator are in good contact with each other when the cable is energized, and terminal work is performed. 0 at times
A crosslinked polyolefin insulated power cable can be obtained in which the outer semiconductive layer can be easily peeled off in any environment in the temperature range of 40 ° C to 40 ° C.

In the present invention, an ethylene-vinyl acetate copolymer having a vinyl acetate content of 30 to 70% by weight and a ethyl acrylate content of 20 to 40% by weight are used as the polymer material for forming the outer semiconductive layer. Ethylene-ethyl acrylate copolymer, and mixtures thereof are used. These copolymers have been conventionally used as a semiconductive material in combination with conductive carbon black.

Examples of the conductive carbon black used in the present invention include acetylene black, furnace black and Ketjen black. The blending ratio is 20 to 100 parts by weight with respect to 100 parts by weight of the copolymer component, and within this range, a preferred blending amount is determined depending on the conductivity of each conductive carbon black.

The epoxy compound used in the present invention includes
There is no particular limitation as long as it is a compound having at least one, preferably two or more epoxy groups in the molecule and having a melting point of 40 ° C. or higher. Specific examples of epoxy compounds include
Examples include bisphenol A uncured epoxy resin, cresol novolac type or phenol novolac type uncured epoxy resin, and among these, cresol novolac type or phenol novolac type uncured epoxy resin has low peeling force. This is particularly preferable because the effect of doing so is remarkable. It is not clear why the peeling force of the outer semiconductive layer is remarkably reduced when these two epoxy compounds are mixed, but the cresol novolac type or phenol novolac type epoxy compound has an epoxy equivalent generally used. It is presumed that the effect is particularly small compared to the existing bisphenol A type epoxy compound. The epoxy compound used in the present invention needs to have a melting point of 40 ° C. or higher. If a liquid epoxy compound or an epoxy compound having a melting point of 40 ° C. or lower even if it is a solid at room temperature is mixed, the peeling workability at high temperature deteriorates.

The epoxy compound is added in an amount of 0.5 to 0.5 with respect to 100 parts by weight of the copolymer component in the external semiconductive composition.
It is mixed in a ratio of 50 parts by weight. If the blending ratio of the epoxy compound is too small, easy peeling properties cannot be obtained, and conversely,
If it is too large, the peeling property deteriorates especially at low temperatures. The compounding ratio of the epoxy compound is preferably 10 to 45 parts by weight, more preferably 20 to 40 parts by weight.

The external semiconductive composition in the present invention includes:
4,4'-thiobis- (6-t-butyl-3-methylphenol), pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, if necessary. ], 2,2-thio-diethylenebis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and the like from the viewpoint of obtaining long-term thermal stability by adding an antioxidant. desirable.
Also, dicumyl peroxide, 2,5-dimethyl-
2,5-bis (t-butylperoxy) hexyne-3,
1,3-bis (t-butylperoxy-isopropyl)
Crosslinking by a method of adding a peroxide such as benzene and heating, or a method of irradiating with an electron beam is desirable from the viewpoint of obtaining stability with respect to use temperature and use environment.

Further, compounding agents such as lubricants such as stearic acid, zinc stearate, lead stearate, magnesium stearate and oleic acid amide, and fillers such as calcium carbonate, clay and talc may be added.

[0015]

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Examples 1 to 5 and Comparative Examples 1 to 3] An ethylene-vinyl acetate copolymer was used as a polymer material, and each component was mixed with a Banbury mixer according to the compounding recipe shown in Table 1 to give semiconductivity. A composition was obtained. These compositions were extrusion-coated on a cross-linked polyethylene layer (insulator), and then heat-crosslinked using an infrared heater in a nitrogen gas atmosphere, and 2
A 2 kV 1 × 100 SQ crosslinked polyethylene insulated cable was obtained. The outer semiconductive layer of the obtained cable was provided with a parallel cut having a width of 0.5 inch in the cable longitudinal direction, and the peeling force from the insulator was measured. The results are shown in Table 1.

[0017]

[Table 1]

As is clear from the results shown in Table 1, the melting point is 40
It was found that by adding an epoxy compound at a temperature of ℃ or higher, a crosslinked polyethylene insulation cable having an outer semiconductive layer having excellent peelability from an insulator can be obtained. In particular, when a cresol novolac type epoxy compound or a phenol novolac type epoxy compound is used (Examples 1, 2, 4, 5), the peeling property is more excellent than that when a bisphenol A type epoxy compound that is most commonly used is used. It turned out that a good cable is obtained.

[Examples 6 to 8 and Comparative Examples 3 to 6] An ethylene-ethyl acrylate copolymer was used as a polymer material.
Each component was mixed with a Banbury mixer according to the formulation shown in Table 2 to obtain a semiconductive composition. These compositions are extrusion-coated on a cross-linked polyethylene layer (insulator),
It was heat-crosslinked using an infrared heater in a nitrogen gas atmosphere to obtain a crosslinked polyethylene insulated cable of 22 kV 1 × 100 SQ. On the outer semiconductive layer of the obtained cable,
A parallel cut having a width of 0.5 inch was made in the longitudinal direction of the cable and the peeling force from the insulator was measured. The results are shown in Table 2.

[0020]

[Table 2]

As is clear from the results shown in Table 2, the melting point of 40
It was found that by adding an epoxy compound at a temperature of ℃ or higher, a crosslinked polyethylene insulation cable having an outer semiconductive layer having excellent peelability from an insulator can be obtained. In particular, when the cresol novolac type epoxy compound or the phenol novolac type epoxy compound is used (Examples 6 and 7), a cable having more excellent peeling property can be obtained as compared with the case where the bisphenol A type epoxy compound which is most commonly used is used. It turned out to be obtained.

[0022]

EFFECTS OF THE INVENTION According to the present invention, in a power cable having a structure in which an outer semiconductive layer is coated on a crosslinked polyolefin insulating material, the external conductive material has excellent adhesion to the insulating material and good peeling workability. A power cable having layers is provided.

Claims (1)

[Claims] 1. A power cable having a structure in which an outer semiconductive layer is coated on a crosslinked polyolefin insulator,
The outer semiconductive layer has a vinyl acetate content of (A) 30 to 70.
At least 1 selected from the group consisting of an ethylene-vinyl acetate copolymer having a weight percentage of 20% and an ethyl acrylate content of 20-40% by weight.
20 to 100 parts by weight of (B) conductive carbon black, and (C) at least one epoxy group in the molecule, and a melting point of 40 with respect to 100 parts by weight of the copolymer.
A power cable, which is formed from a composition containing 0.5 to 50 parts by weight of an epoxy compound having a temperature of not less than 0 ° C.