JPH09111089A - Semiconductive composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductive composition excellent in adhesivity to and releasability from an insulator of a power cable, extrusion processability, surface smoothness and electroconductivity, capable of forming an external semiconductive layer excellent in electroconductivity as well. SOLUTION: This semiconductive composition is obtained by blending 100 pts.wt. of a styrene-modified ethylene-vinyl acetate copolymer prepared by grafting 3-10wt.% of a styrene-based monomer onto an ethylene-vinyl acetate copolymer having 20-30wt.% vinyl acetate content with 40-80 pts.wt. of oil furnace carbon black having 35-45nm average particle diameter and 55-65mg/g iodine adsorption and 155-180cc/100g DBP oil absorption and 1.5-5 pts.wt. of an antioxidant.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a semiconductive composition useful in the outer semiconductive layer of plastic insulated power cables,
In particular, the present invention relates to a semiconductive composition capable of forming an external semiconductive layer which is excellent in both adhesiveness and peelability with respect to a crosslinked polyethylene insulator and is also excellent in extrusion processability and surface smoothness.

[0002]

BACKGROUND OF THE INVENTION Plastic insulated power cables, especially
The outer semiconductive layer of the crosslinked polyethylene insulated power cable is
It is generally formed by extrusion coating. This outer semiconductive layer must be in close contact with the crosslinked polyethylene insulator so that corona discharge does not occur. On the other hand, however, it is required that the outer semiconductive layer be easily removed without damaging the insulator when terminating the cable. Therefore, there is a demand for an external semiconductive layer that normally adheres well to an insulator and can be easily peeled off when necessary. In order to obtain such a semiconductive layer, it is effective to use a polymer having no affinity with the crosslinked polyethylene insulator as a base, and conventionally, a composition based on an ethylene-vinyl acetate copolymer has been used. Has been done.

As such a semiconductive composition, there is one disclosed in Japanese Patent Publication No. 5-77123. This semiconductive composition comprises a base polymer mainly composed of an ethylene-vinyl acetate copolymer, a wax-like hydrocarbon such as paraffin wax and an average particle size of 25 to 40 nm, an iodine adsorption amount of 40 to 60 mg / g, a DBP oil absorption. Quantity 120-150m
It is a blend of 1/100 g of furnace carbon black, and it is said that excellent peelability and extrusion processability can be obtained by the synergistic action of waxy hydrocarbon and furnace carbon black.

However, in this semiconductive composition, the heat resistance of the composition may be lowered by the addition of a waxy hydrocarbon, and the above-mentioned furnace carbon black is not well dispersed in the base polymer. However, when the outer semiconductive layer is formed, a large number of minute projections are formed on the surface thereof, water particles may be induced by the minute projections, and sufficient conductivity is difficult to obtain.

[0005]

Therefore, an object of the present invention is to provide an external semiconductive layer having excellent extrusion processability, surface smoothness and conductivity while ensuring both good adhesion and easy peeling property. To obtain a semiconductive composition that can be

[0006]

The object of the present invention is to provide a styrene-modified ethylene-obtained by graft-treating an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 30% by weight with a styrene-based monomer in an amount of 3 to 10% by weight. An average particle diameter of 35 to 45 nm, relative to 100 parts by weight of the vinyl acetate copolymer,
Iodine adsorption amount 55-65 mg / g, DBP oil absorption amount 155
The problem is solved by a semiconductive composition containing 40 to 80 parts by weight of oil furnace carbon black of 180 cc / 100 g and 1.5 to 5 parts by weight of an antioxidant.

[0007]

The use of the above oil furnace carbon black provides good conductivity, extrusion processability and surface smoothness, and the use of an antioxidant inhibits co-crosslinking at the interface between the insulator and the outer semiconductive layer. Excellent peelability can be obtained.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The styrene-modified ethylene-vinyl acetate copolymer used in the present invention is an ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 30% by weight,
It is obtained by graft-copolymerizing styrene-based monomers such as styrene, methylstyrene, α-methylstyrene and chloromethylstyrene. This graft copolymerization is carried out by a method of impregnating ethylene-vinyl acetate copolymer particles with most of the styrene-based monomer, and then performing aqueous suspension polymerization. The amount of the styrene-based monomer in this graft copolymer is 3 to 10% by weight, and if it is less than 3% by weight, the releasability is lowered, and if it exceeds 10% by weight, the melt viscosity of the composition is increased and the extrusion processability is increased. Is reduced. If the content of vinyl acetate in the ethylene-vinyl acetate copolymer is less than 20% by weight, the releasability is low, and if it exceeds 30% by weight, fusion between pellets is likely to occur and workability is impaired.

The average particle size of the oil-furnace carbon black used in the present invention is measured by an electron microscope. If the average particle size is less than 35 nm, the viscosity of the compound increases and the workability deteriorates. I can not get sex. Also, the iodine adsorption amount is JIS
This is due to -K-6221. If it is less than 55 mg / g, the conductivity is insufficient, and if it exceeds 65 mg / g, the melt viscosity becomes large and the extrusion processability deteriorates. DBP oil absorption is
According to JIS-K-6221, 155cc / 10
If it is less than 0 g, the conductivity becomes insufficient, and 180 cc / 100
If it exceeds g, the viscosity of the compound increases, which is inconvenient.

The blending amount of this oil furnace carbon black is in the range of 40 to 80 parts by weight with respect to 100 parts by weight of the styrene-modified ethylene-vinyl acetate copolymer. If it is less than 40 parts by weight, the conductivity will be insufficient. If it exceeds 80 parts by weight, the viscosity of the compound increases, which is inconvenient. In addition to the above specific oil furnace carbon black, acetylene black may be used in combination as long as it does not hinder the kneading workability and peeling property.

In the present invention, the antioxidant is also an essential component, and 1.5 to 5 parts by weight of the antioxidant is added to 100 parts by weight of the styrene-modified ethylene-vinyl acetate copolymer. If it is less than 1.5 parts by weight, co-crosslinking at the interface between the insulator and the outer semiconductive layer cannot be inhibited and sufficient releasability cannot be obtained. If it exceeds 5 parts by weight, the kneading property and mechanical strength are poor. It is not preferable because it decreases. As this anti-aging agent,
4,4'-thiobis- (6-tert-butyl-3-methylphenol) is the most preferable for obtaining the above-mentioned effect, but other than this, 2,6, -di-tert-butyl-4-methylphenol, 2,2'-methylene-bis- (4-methyl-
6-tert-butylphenol) styrenated phenol, phenyl-α-naphthylamine, phenyl-β-naphthylamine, N-isopropyl-N′-phenyl-p-phenyldiamine, N, N′-di-2-naphthyl-p-phenylene Diamine and the like also have good effects and can be used.

The semiconductive composition of the present invention may be crosslinked or non-crosslinked. When the cross-linking type is used, dicumyl peroxide, 2,5-dimethyl-2,5-di (tertiary butyl-peroxy) hexane, 2,5-dimethyl-2,5-
Peroxides such as di (tertiary butyl-peroxy) hexyne and 1,3-bis (tertiary butyl-peroxyisopropyl) benzene are added in an amount of 0.
The amount may be about 2 to 2 parts by weight. Further, in the composition of the present invention, a lubricant such as a fatty acid metal salt such as zinc stearate, lead stearate, magnesium stearate or a fatty acid ester can be blended, if necessary.

The power cable of the present invention is obtained by kneading the above-mentioned semiconductive composition with a Banbury mixer or the like, and extrusion-coating this on an insulator such as polyethylene to form an external semiconductive layer. The outer semiconductive layer can be extruded by coextrusion at the same time as the insulator is extruded. The thickness of this outer semiconductive layer is usually about 0.2 to 2 mm.

When the semiconductive composition of the present invention is used as an external semiconductive layer, it is in good contact with the insulator and can be easily peeled off from the insulator if necessary. Further, it has excellent mechanical properties, the surface is smooth and there are no minute projections, it has excellent thermal stability, low melt viscosity, and good extrusion processability. Also, the conductivity becomes good.

Hereinafter, specific examples will be described. As base polymer, vinyl acetate content 28% by weight, melt flow rate 4
Styrene-modified ethylene having a styrene monomer content of 0% by weight, 2% by weight, 5% by weight, 7% by weight and 12% by weight is obtained by graft-copolymerizing a styrene monomer at various ratios with the ethylene-vinyl acetate copolymer of. -Vinyl acetate copolymer (hereinafter referred to as S-EVA-0, S-EVA-2, S-E
Notated as VA-5, S-EVA-7, S-EVA-12. ), Oil furnace carbon black shown in Tables 1 to 3, an antioxidant, an organic peroxide,
A lubricant was blended and kneaded with a Banbury mixer to obtain a semiconductive composition.

These semiconductive compositions were extrusion-coated on a crosslinked polyethylene insulator to form an external semiconductive layer, which was then heated and crosslinked by using an infrared heater in a nitrogen gas atmosphere to obtain 6 kV 1 × 100 mm ² . A crosslinked polyethylene insulated power cable was manufactured. The outer semiconductive layer of this power cable was examined for peelability, extrudability, smoothness, and conductivity.

The peeling property was evaluated by making parallel cuts having a width of 0.5 inch in the longitudinal direction of the cable in the outer semiconductive layer of the obtained power cable and by peeling from the insulator at 50 ° C. The extrusion processability was evaluated as x when the semiconductive composition was extruded by an extruder or the composition did not come out of the extruder or the load of the electric motor was extremely high.

The smoothness was determined by observing the surface of the outer semiconductive layer of the obtained cable with a microscope over an area of 10 cm ^2.
The evaluation was made based on the presence or absence of protrusions having a height of 0 μm or more. When there were no protrusions, the result was indicated by ◯, when there were less than 5 protrusions, it was indicated by Δ, and when there were 5 or more protrusions, it was indicated by x. For the conductivity, the volume resistivity of the outer semiconductive layer is measured, and the value less than 10 ⁴ Ω · cm is ◯, and the value of 10 ⁴ to 10 ⁵ Ω · cm is Δ, 10 ⁵ Ω · cm Those exceeding the above are displayed as x.

In Tables 1 to 3, FCB-
A has an average particle size of 40 nm, an iodine adsorption amount of 60 mg / g,
It shows an oil furnace carbon black having a DBP oil absorption of 170 cc / 100 g, and FCB-X has an average particle size of 30.
nm, iodine adsorption amount 50 mg / g, DBP oil absorption amount 135
cc / 100 g of oil furnace carbon black is shown. Further, the antiaging agent is 4,4'-thiobis-
(6-tert-butyl-3-methylphenol) was used, zinc stearate was used as the lubricant, and dicumyl peroxide was used as the organic peroxide. All blending amounts are expressed in parts by weight. The results are shown in Tables 1 to 3.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

From the results shown in Tables 1 to 3, it is clear that the semiconductive composition of the present invention can form an external semiconductive layer excellent in extrusion processability, peelability, smoothness and conductivity. .

[0024]

As described above, according to the semiconductive composition of the present invention, it has both good adhesion to an insulator and easy peeling property, and excellent extrusion processability and surface smoothness. ,
An outer semiconducting layer for the power cable can be obtained which is electrically conductive.

Claims (3)

[Claims] 1. An ethylene-vinyl acetate copolymer having a vinyl acetate content of 20 to 30% by weight and 3 to 3 of a styrene-based monomer.
An average particle diameter of 35 to 45 nm and an iodine adsorption amount of 55 to 65 mg / 100 parts by weight of a styrene-modified ethylene-vinyl acetate copolymer obtained by 10% by weight graft treatment.
g, 40 to 80 parts by weight of oil furnace carbon black having a DBP oil absorption of 155 to 180 cc / 100 g,
A semiconductive composition containing 1.5 to 5 parts by weight of an antioxidant. 2. The semiconductive composition according to claim 1, wherein the antiaging agent is 4,4′-thiobis- (6-tert-butyl-3-methylphenol). 3. A power cable having an outer semiconducting layer comprising the semiconducting composition of claim 1 or 2.