JP2000003627A - Power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent projections, eruptions, etc., from arising on a surface of an easily peelable outer semiconductive layer, in the case of a power cable having an easily peelable outer semiconductive layer comprising a composition made by mixing a base polymer mainly composed of an EVA with carbon black and a nonorganic filler. SOLUTION: An easily peelable outer semiconductive layer 4 comprises a composition made by mixing an ethylene-vinyl acetate copolymer with carbon black and a surface treated nonorganic filler, and the number of projections not less than 20 μm in height is one or less per 10 cm2 of its surface. As the nonorganic filler, a filler surface-treated by a higher fatty acid such as stearic acid or by a surfactant is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a power supply having a working voltage of 6 to
It relates to a 33 kv class power cable.

[0002]

2. Description of the Related Art In this type of power cable, an inner semiconductive layer and an insulator made of crosslinked polyethylene are provided on a conductor, an easily peelable outer semiconductive layer is provided thereon, and a copper tape is wound thereon. A shielding layer is provided, and a sheath made of polyethylene, polyvinyl chloride, or the like is further covered. The easily peelable outer semiconductive layer is made of an ethylene-vinyl acetate copolymer (EVA) as a base polymer, and is blended with carbon black, an antioxidant and the like to weaken the adhesive strength to an insulator made of cross-linked polyethylene. Semiconductive compositions are mainly used.

When this semiconductive composition is heated, the base polymer EVA is partially decomposed to generate acetic acid. Therefore, when the cable is placed in a high-temperature environment, acetic acid generated in the easily peelable outer semiconductive layer corrodes the copper tape of the shielding layer and produces patina. In order to prevent such inconvenience, an acid acceptor for capturing and neutralizing acetic acid generated is blended in the semiconductive composition forming the easily peelable external semiconductive layer. As the acid acceptor, an inorganic filler such as calcium carbonate is used, and the inorganic filler particles are aggregated in the semiconductive composition to form a large lump, which is extruded and coated to form an easily peelable external semiconductive material. It appeared as protrusions or bumps on the surface of the layer, and sometimes caused electrical defects in which the electric field was concentrated.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an easy-to-separate outer semiconductive layer for an electric power cable, in which a composition containing an acid acceptor of an inorganic filler is used. An object of the present invention is to prevent projections and bumps from being formed on the surface of the peelable external semiconductive layer.

[0005]

The object of the present invention is to use a surface-treated inorganic filler as an inorganic filler used as an acid acceptor to enhance dispersibility and prevent agglomeration of particles. The problem can be solved by reducing the number of projections having a height of 20 μm or less to one or less per 10 cm ² of the surface of the semiconductive layer.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 shows an example of a power cable according to the present invention, in which reference numeral 1 denotes a conductor. An inner semiconductive layer 2 is provided on the conductor 1, and an insulator 3 made of cross-linked polyethylene is provided on the inner semiconductive layer 2. On the insulator 3, an easily peelable outer semiconductive layer is provided. 4 are provided. Further, a copper tape is wound around the easily peelable outer semiconductive layer 4 to provide a shielding layer 5, on which polyethylene,
A sheath 6 made of polyvinyl chloride or the like is covered.

The easily peelable external semiconductive layer 4 is made of EVA7
40 to 80 parts by weight of carbon black based on 100 parts by weight of a base polymer consisting of 0 to 100% by weight and 0 to 30% by weight of styrene-modified EVA, and a surface-treated inorganic filler of 0.
5 to 10 parts by weight, antioxidant 0.5 to 5 parts by weight, lubricant 0
~ 3 parts by weight of a composition formed by extrusion coating.

EVA as a base polymer has a vinyl acetate content of 20 to 30% by weight and a melt index of 1
Approximately 50 are used. Styrene-modified EVA
Is obtained by grafting 3 to 10% by weight of a styrene monomer to EVA having a vinyl acetate content of 20 to 30% by weight. By adding this styrene-modified EVA,
The adhesion to the crosslinked polyethylene is reduced, and the releasability of the external semiconductive is improved. The upper limit is 30% by weight in the base polymer, and if it exceeds this, the adhesion is excessively reduced. This styrene-modified EVA is not always required.

The surface-treated inorganic filler includes calcium carbonate,
Coating the surface of inorganic filler particles such as magnesium oxide, magnesium hydroxide, zinc oxide, etc., with a higher fatty acid such as stearic acid, oleic acid, palmitic acid or a cationic or anionic surfactant to a thickness of about 10 to 100 nm. It was done. As a specific method of the surface treatment, a method in which a liquid treatment agent is dropped or sprayed in a mist state while stirring the inorganic filler at a high speed is performed. The amount of the treatment agent attached to the inorganic filler particles is 5 to 10
% By weight. The amount of the surface-treated inorganic filler is 0.5 to 1 with respect to 100 parts by weight of the base polymer.
When the amount is less than 0.5 part by weight, the effect as an acid acceptor cannot be obtained. When the amount exceeds 10 parts by weight, the water absorption of the semiconductive material increases, which causes foaming during extrusion molding.

[0010] The carbon black is not particularly limited, but preferably has fine particles and is hardly aggregated, and furnace black is particularly preferred. The amount of the carbon black is in the range of 40 to 80 parts by weight based on 100 parts by weight of the base polymer, and is determined by the conductivity required for the external semiconductive layer 4. Also,
As the antioxidant, a phenolic antioxidant such as 4,4'-thiobis- (6-tert-butyl-3-methylphenol) is used, and as the lubricant, a metallic soap such as zinc stearate is used.

In the easily peelable outer semiconductive layer 4 of such a power cable, the inorganic filler compounded as an acid acceptor is a surface-treated inorganic filler. The dispersibility in the polymer is increased, the particles do not agglomerate in the composition, and the surface does not appear as projections or bumps, and the surface becomes flat. For this reason, the number of protrusions having a height of 20 μm or less per one 10 cm ² of the surface of the easily peelable external semiconductive layer 4 is one or less, almost zero, and an electric defect in which an electric field is concentrated does not occur.

The power cable is placed in a high temperature environment, and the EVA of the base polymer of the easily peelable outer semiconductive layer 4 is used.
Even when acetic acid is generated, the acetic acid is similarly trapped and neutralized by the surface-treated inorganic filler, so that the outer shielding layer 5 made of copper tape does not corrode or deteriorate. Further, EVA or EVA and styrene-modified E
Since a mixture with VA is used, it exhibits good releasability from an insulator made of cross-linked polyethylene.

Hereinafter, the operation and effects will be clarified by showing specific examples, but the present invention is not limited to these specific examples. As a base polymer, EVA having a vinyl acetate content of 28% by weight and a melt index of 4.0;
The styrene monomer is graft-copolymerized at various ratios to the styrene monomer content of 3% by weight, 7% by weight,
% By weight of styrene-modified EVA (hereinafter, S-EVA-3,
It is described as S-EVA-7 or S-EVA-10. ), And furnace carbon black, a surface-treated inorganic filler, an untreated inorganic filler, an antioxidant, and a lubricant as shown in Tables 1 and 2 were blended into a composition.

As the surface-treated inorganic filler, a surface-treated one using stearic acid was used. A phenolic antioxidant was used as an antioxidant, and zinc stearate was used as a lubricant. .

These compositions were extrusion coated onto a crosslinked polyethylene insulator to form an easily releasable outer semiconductive layer, comprising 6 kv 1
A crosslinked polyethylene insulated power cable of × 100 mm ² was manufactured. The peelability, extrusion workability, and smoothness of the easily peelable outer semiconductive layer of this power cable were examined.

The peelability of the obtained power cable was determined by making parallel cuts of 0.5 inch width in the longitudinal direction of the cable in the easily peelable outer semiconductive layer of the obtained power cable, and at 50 ° C. for easy peeling from the insulator. evaluated. The extrudability was evaluated as x when the composition was not extruded or the load on the motor was extremely high when the composition was extruded with an extruder.

The smoothness is evaluated by observing the surface of the easily peelable external semiconductive layer of the obtained cable over an area of 10 cm ^{2 under a} microscope and detecting the presence of projections having a height of 20 μm or more.
When there were no protrusions, the result was indicated by ○, and when there were five or more protrusions, the result was indicated by ×.

Further, a copper discoloration test was carried out as follows. The above composition was extruded into a test sheet having a thickness of about 1 mm, and this test sheet and a sheet made of crosslinked polyethylene having a thickness of 5 mm were bonded by hot pressing, and a copper foil was further placed on the test sheet side of the bonded sheet. (Thickness: 0.1 mm) was bonded at 250 ° C. to obtain a sample for a copper discoloration test. This sample was subjected to a humidity of 70% RH.
Leave constant for 2 weeks while giving a heat cycle of room temperature to 60 ° C., and visually observe the discoloration of the copper foil after 2 weeks. Those with patina were recognized as x.

The above results are summarized in Tables 1 and 2. In Tables 1 and 2, all amounts are parts by weight.

[0020]

[Table 1]

[0021]

[Table 2]

As is clear from Tables 1 and 2, the use of the surface-treated inorganic filler as the acid acceptor can prevent the occurrence of projections and bumps on the surface of the easily peelable external semiconductive layer. .

[0023]

As described above, in the power cable of the present invention, an easily peelable external cable made of a composition containing a base polymer mainly composed of an ethylene-vinyl acetate copolymer and a surface-treated inorganic filler. Since it has a semiconductive layer, no protrusions or bumps appear on the surface of the easily peelable external semiconductive layer, and no electrical defect occurs. Also, acetic acid generated by the decomposition of the ethylene-vinyl acetate copolymer is trapped and neutralized by the surface-treated inorganic filler, thereby preventing corrosion of the copper tape of the shielding layer.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a power cable of the present invention.

[Explanation of symbols]

 4: Easy peeling outer semiconductive layer, 5: Shielding layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J002 BB061 BN072 DA036 DE077 DE107 DE237 FB087 FB237 FD017 FD030 FD170 GQ01 GQ02 5G301 DA18 DA32 DA33 DA45 DD04

Claims (3)

[Claims] 1. A power cable having an easily peelable external semiconductive layer, wherein the easily peelable external semiconductive layer is a composition in which carbon black and a surface-treated inorganic filler are blended in an ethylene-vinyl acetate copolymer. A power cable, comprising: a projection having a height of 20 μm or more per surface 10 cm ² . 2. The power cable according to claim 1, wherein the surface-treated inorganic filler is surface-treated with a higher fatty acid. 3. The power cable according to claim 1, wherein a copper tape is wound on the easily peelable outer semiconductive layer.