JPH1064338A - Electric insulating composite, and wire and cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep excellent electric characteristics and improve water tree resistance, particularly bowtie tree resistance by covering a conductor with an insulator formed of a specified electric insulating composite. SOLUTION: In a wire and cable formed of a conductor 1 consisting of a soft copper stranded were, an internal semiconductive layer 2, an insulator 3 consisting of a resin composite, and an external semiconductive layer 4, a specified electric insulating composite is used as the composite constituting the insulator 3. Namely, an electric insulating composite obtained by mixing a styrene graft polyethylene in which 0.1-10wt % of styrene is grafted with a polyethylene or ethylene copolymer, or a mixture thereof with a styrene-maleic anhydride copolymer, or an electric insulating composite obtained by additionally mixing a maleic anhydride graft polyethylene in which 0.05-5wt % of maleic anhydride is grafted is used. Thus, excellent electric characteristics and water tree resistance, particularly, bowtie tree resistance can be exhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical insulating composition and an electric wire / cable using the same as an insulator.

[0002]

2. Description of the Related Art So-called cross-linked polyethylene obtained by cross-linking polyolefin, particularly polyethylene, has been widely used as an insulating material for electric wires and cables because of its excellent electric insulation and heat resistance.

[0003] However, the wires and cables coated with the cross-linked polyethylene have a disadvantage that when used in a wet or submerged atmosphere, water trees are generated in the insulator and the excellent electrical insulation performance of the material is greatly reduced.

[0004] The water tree that causes the deterioration of the electric insulation performance is formed by condensation of water on voids and foreign matters in the insulator and defects such as local high electric field portions such as irregularities in the interface between the insulator and the semiconductive layer. It is known that this is caused by things. For this reason, much effort has been made to eliminate these defects in wires and cables, for example,
Improvement of resin quality and improvement of manufacturing technology of electric wires and cables have improved the effect of suppressing the generation of water trees.

[0005]

However, despite efforts to suppress the generation of water trees over various areas, the generation of water trees can be greatly reduced. At present, it has not reached the stage.

Accordingly, the present invention has been devised in order to effectively solve such a problem, and an object of the present invention is to provide a water resistant tree even if a defect such as a void, a foreign substance, or irregularity occurs in an insulator. It is intended to provide a novel electric insulating composition and a wire / cable capable of greatly improving the properties, particularly the bow titley resistance.

[0007]

In order to solve the above-mentioned problems, the present invention relates to a method for preparing polyethylene or ethylene copolymer or a mixture of polyethylene and ethylene copolymer in 0.1 to 0.1%.
An electrical insulating composition comprising a styrene-grafted polyethylene grafted with 10% by weight of styrene and a styrene-maleic anhydride copolymer;
An electrical insulating composition comprising 5% by weight of maleic anhydride grafted with maleic anhydride-grafted polyethylene, and an electric wire or cable obtained by coating an insulator made of any of these electrical insulating compositions on a conductor It is.

As a result, excellent electrical properties are maintained, and the water-resistant tree, especially the bow titley resistance, is improved.

[0009]

Next, a preferred embodiment of the present invention will be described.

FIG. 1 is an enlarged sectional view showing an embodiment of an electric cable according to the present invention, in which 1 is a conductor made of annealed copper or the like, 2 is an internal semiconductive layer, and 3 is a resin composition. The insulator 4 is an external semiconductive layer.

The composition constituting the insulator 3 is a styrene-grafted polyethylene obtained by grafting 0.1 to 10% by weight of styrene onto polyethylene or an ethylene copolymer or a mixture thereof, and a styrene-maleic anhydride copolymer. And an electrical insulating composition obtained by further adding a maleic anhydride-grafted polyethylene obtained by grafting 0.05 to 5% by weight of maleic anhydride thereto. It can exhibit excellent electrical properties and water-tree resistance, and in particular, excellent bow-tree resistance.

Here, the graft amount of styrene is 0.1 to
The reason why the amount is specified as 10% by weight is that if it is less than 0.1% by weight, there is no effect on water tree suppression, and if it exceeds 10% by weight, the dielectric properties deteriorate.

Further, when maleic anhydride-grafted polyethylene is used in combination with the above-mentioned components, it has a function of improving the adhesion at the interface between foreign matter and irregular parts, and can further suppress the generation of water trees. Here, the reason why the grafting amount of maleic anhydride was set to 0.05 to 5% by weight was 0.05%.
When the amount is less than 5% by weight, the effect of suppressing water tree is not obtained, and when the amount is more than 5% by weight, the dielectric properties are deteriorated.

The following is a typical example of the styrene-maleic anhydride copolymer used in the present invention.

[0015]

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The styrene-maleic anhydride copolymer is preferably added in the range of 0.05 to 5 parts by weight based on 100 parts by weight of polyethylene or the ethylene copolymer component. The effect of suppressing the tree is small, and if it exceeds 5 parts by weight, the dielectric properties tend to deteriorate.

The polyethylene or ethylene copolymer of the present invention includes low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, high-density polyethylene, ethylene-propylene copolymer, ethylene-ethyl acrylate copolymer, ethylene -Polyolefin corresponds to a majority of ethylene such as vinyl acetate copolymer and ethylene-styrene copolymer.

As a method for cross-linking the electrical insulating composition mainly composed of polyethylene, dicumyl peroxide, 1- (2-tert-butylperoxyisopropyl) -1-isopropylbenzene or 1- (2-
tert-butylperoxyisopropyl) -3-isopropylbenzene, 1,3-bis- (tert-butylperoxy-isopropyl) benzene, 2,5-dimethyl-2,
Chemical crosslinking with an organic peroxide such as 5- (tert-butylperoxy) -hexyne-3 can be mentioned, and these can be used alone or in combination of two or more.

Further, together with such an organic peroxide,
It is also possible to use an aromatic α-methylalkenyl dimer in combination. Here, such a dimer includes α-methylstyrene, para-methyl-α-methylstyrene,
Isopropyl-α-methylstyrene, meta-ethyl-α
-Methylstyrene, meta-methyl-α-methylstyrene, ar-dimethyl-α-methylstyrene, ar-chloro-α-methylstyrene, ar-chloro-ar-methyl-α-methylstyrene, ar-diethyl-α- Unsaturated dimers such as methylstyrene, ar-methyl-ar-isopropyl-α-methylstyrene are included.

Further, these dimers may be used alone or in combination of two or more. This dimer has a function of preventing cross-linking of polyethylene at the time of extrusion molding, can prevent scorch at the time of extrusion molding, and can obtain wires and cables having good appearance.

Further, as a crosslinking method other than those described above, silane water crosslinking using a silane such as vinyltriethoxysilane or irradiation crosslinking by ionizing radiation such as an electron beam can be used.

[0022] In addition to the above components, additives such as an antioxidant, a lubricant, and a coloring agent may be appropriately added to the electrical insulating composition.

The effect of moisture on the bow title tree is extremely large, and a bow title tree has been found in a cable charged in the air or a cable shielded by a metal sheath or the like. It is considered that these are not due to moisture permeating from the outside, but to trace amounts of moisture contained inside the crosslinked polyethylene during cable production. It is needless to say that the present invention is also effective for such bow titles.

[0024]

EXAMPLES Hereinafter, specific examples of the present invention will be described in detail along with comparative examples.

First, the components 9 were mixed as shown in Table 1 below.
Each composition (Examples 1 to 5 and Comparative Examples 1 to 4) was kneaded with a hot roll at 120 ° C. to form a sheet, and pelletized with a pelletizer. Next, each of these pellets was introduced into an extruder and, as shown in FIG. 1, a 4 mm-thick inner semiconductive layer 2 and an outer semiconductive layer 4 each having a thickness of 0.7 mm were placed on a conductor 1 made of a 60 mm ² soft copper stranded wire. After being extruded as an insulator 3, this was immediately cross-linked in a dry cross-linking tube using nitrogen gas as a medium, and then cooled to form cables.

These nine types of cables were used as samples, and the bow titley resistance and electrical characteristics of each sample were examined, and the respective characteristics were evaluated.

In order to evaluate the anti-bow titleile characteristics, the above sample was immersed in warm water at 90 ° C., and an AC voltage of 50 Hz and 9 kV was applied between the conductor and water for 500 days. Was sliced thinly and stained by boiling with an aqueous methylene blue solution, and the presence or absence and the number (200 μm or more) of bow title trees were counted using an optical microscope. On the other hand, as a method for evaluating electric characteristics, a sharing bridge is used, and an electric field applied to the cable insulator is reduced by 10 k.
V / mm, and the dielectric loss tangent at that time was measured. If the value of the dielectric loss tangent was 0.05% or less, the result was marked as "O" if the value was acceptable, and "x" if it was not acceptable.

[0028]

[Table 1]

As a result, as is apparent from Table 1, in all of Examples 1 to 5 according to the present invention, the number of bow title trees generated was small and the dielectric loss tangent was good.

On the other hand, in Comparative Example 1 in which the styrene-grafted polyethylene and the styrene-maleic anhydride copolymer were not added, and in Comparative Example 2 in which the styrene-maleic anhydride copolymer was not added, the number of bow title trees generated was extremely low. There were many. In Comparative Examples 3 and 4, in which polyethylene having a high graft concentration of styrene or maleic anhydride was blended, the dielectric loss tangent was deteriorated.

[0031]

In summary, according to the present invention, the water tree resistance, especially the bow titley resistance, is greatly improved irrespective of the occurrence of defects such as voids, foreign matters, irregularities, etc. in the insulator. Excellent effects such as excellent electric performance can be maintained over a long period of time.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of an embodiment of an electric wire / cable according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductor 2 inner semiconductive layer 3 insulator 4 outer semiconductive layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 51/06 LLE C08L 51/06 LLE H01B 7/02 H01B 7 / 02F

Claims (3)

[Claims] A styrene-grafted polyethylene obtained by grafting 0.1 to 10% by weight of styrene and a styrene-maleic anhydride copolymer to polyethylene or an ethylene copolymer or a mixture thereof. An electrical insulating composition characterized by the following: 2. A styrene-grafted polyethylene obtained by grafting 0.1 to 10% by weight of styrene to polyethylene or an ethylene copolymer or a mixture thereof;
An electrical insulating composition comprising a maleic anhydride-grafted polyethylene grafted with 0.5 to 5% by weight of maleic anhydride and a styrene-maleic anhydride copolymer. 3. An electric wire or cable comprising an insulator made of the electrical insulating composition according to claim 1 coated on a conductor.