JPH09306265A - Power cable and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease melt fracture, critical surface misalignment, or generation of electric torry and obtain a long service life by providing an internal semiconductor layer, two layers i.e., insulation layer and external semiconductor layer of a specific resin composition, and an external semiconductor layer on a conductor and performing heating cross-linking after coating. SOLUTION: Each resin composition of an internal semiconductor layer, insulation layers A and B, and an external semiconductor layer is coated using a common four-layer extruder on a conductor, and heating cross-linking is performed on a conductor. Here, an insulation layer A is made of resin composition containing 100wt.% of a high-pressure method diverged low density ethylene based resin of 0.915 to 0.912g/cm<3> and of 0.3 to 3.0g/10 minutes in melt index and 0.1 to 5wt.% of organic peroxide. An insulation layer B contains 100wt.% of a straight chain shaped low density ethylene-α-olefin copolymer α of 0.91 to 0.93g/cm<3> in density and 0.1 to 5.0g/10 minutes in let index and 0.3 to 3wt.% of organic peroxide. In addition, the relationship between thickness a and thickness b of the insulation layers A and B is a<=b<=(1/2)a. Thus, misalignment of each boundary is eliminated, and longer service life is obtained.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power cable and a method for manufacturing the same. The power cable of the present invention is used as a means for transmitting medium-voltage or high-voltage electricity from a power plant to a power demand area such as a city or factory, and between or inside a city, factory, building or the like. It is used as a means of sending high voltage electricity.

[0002]

2. Description of the Related Art Power cables are roughly classified into OF cables (oil-impregnated paper-insulated cables) and CV cables (cross-linked polyethylene insulated vinyl chloride-coated cables). OF cables are installed space, maintenance, and fire countermeasures due to oil, etc. However, in recent years, CV cables that do not require these problems have been used in place of OF cables.

A CV cable is coated with a high-voltage polyethylene having excellent dielectric strength, low dielectric constant and low dielectric loss on a conductor through an internal semiconductive layer, and the high-voltage polyethylene is chemically crosslinked (organic peroxide). Although it is a power cable that is cross-linked with an insulating layer and covered with an external semiconductive layer or a sheath layer on it, since it is solid insulation, it does not require oiling equipment and is relatively easy to lay and maintain, Since it is also advantageous in disaster prevention, it is used in large quantities as an alternative to OF cables.

The high-pressure polyethylene used for the insulating layer of the CV cable is flexible, has relatively few impurities, and has high processability, so that it has been used in a large amount from the past, but the manufacturing cost is high, and Since the melting point is around 104 ° C., the heat resistance is insufficient and the heat deformation is large, and therefore, polyethylene which is improved or replaced therefor has been demanded.

In recent years, linear low-density ethylene-α-by a low pressure method using a Ziegler type catalyst or a Kaminsky type catalyst.
An olefin copolymer has come to be produced, and a CV cable using this instead of high-pressure polyethylene has been proposed (for example, JP-A-55-9677 discloses one using a Ziegler type catalyst). Japanese Patent Application Laid-Open No. 7-312118, which uses a Kaminsky catalyst.
Disclosed in the publication). This type of linear low-density ethylene-α-olefin copolymer has low cost, excellent heat resistance, and high cross-linking efficiency, so it has been expected that it can be immediately replaced with high-pressure polyethylene. When the wire is coated by extrusion, at the desired extrusion speed, the surface of the coating becomes extremely rough, so-called melt fracture,
There are problems that the electrical characteristics as an insulator are deteriorated, the appearance is poor, and the commercial value is significantly reduced. In addition, since the linear low-density ethylene-α-olefin copolymer has a low viscosity, it causes eccentricity when it is coated on an electric wire, and it is difficult to cover the electric wire with an insulating layer having a uniform thickness. It's difficult to get a power cable.

[0006]

As described above, a power cable having a linear low-density ethylene-α-olefin copolymer as an insulating layer has drawbacks such as eccentricity and melt fracture. However, the present invention has been made to solve these drawbacks and to provide a power cable of good quality and a manufacturing method thereof.

[0007]

The inventor of the present invention has assumed that the insulating layer of the conventional power cable is composed of a single layer, but if the insulating layer has a two-layer structure, the above problem can be solved. However, when the material for each layer was selected from various ethylene-based resins and many experiments were conducted, it was found that good results were obtained when two specific ethylene-based resins were coextruded to a specific thickness. After further studies, the present invention has been completed.

That is, according to the present invention, a high pressure branched low density ethylene having an inner semiconductive layer, a density of 0.915 to 0.925 g / cm ³ , and a melt index of 0.3 to 3.0 g / 10 min is formed on a conductor. Insulating layer (A) made of a resin composition containing 100 parts by weight of a base resin and 0.1 to 5 parts by weight of an organic peroxide, a density of 0.91 to 0.93 g / cm ³ , and a melt index of 0.1 to 5 An insulating layer (B) composed of a resin composition containing 100 parts by weight of a linear low-density ethylene-α-olefin copolymer of 0.0 g / 10 minutes and 0.3 to 3 parts by weight of an organic peroxide [however, The thicknesses of the insulating layer (A) and the insulating layer (B) (respectively a and b) are a ≧ b
≧ (1/2) a] and the external semiconducting layer is coated using a common four-layer extruder, and then heat crosslinking is performed. The invention also relates to a power cable produced by the method of the invention.

In the present invention, the inner semi-conductive layer and the outer semi-conductive layer are for improving the potential gradient and attaining the same potential, and for improving the withstanding voltage property. The ethylene-vinyl acetate copolymer, ethylene- Ethyl acrylate copolymer,
High pressure method low density polyethylene, linear low density ethylene-α
-Conductivity-imparting agent 3 such as furnace black, acetylene black or Ketjen black to 100 parts by weight of an ethylene resin such as an olefin copolymer or medium density polyethylene.
0 to 100 parts by weight, if necessary, 1,1-bis-tert-butylperoxybenzoate, 2,2-bis-tert-butylperoxybutane, tert-butylperoxybenzoate, dicumyl peroxide, 2,5 -Dimethyl-2,
The decomposition temperature of 5-di-tert-butylperoxyhexane, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di-tert-butylperoxyhexyne-3, etc. until the one-minute half-life is obtained is A resin composition comprising an organic peroxide of 150 to 200 ° C. at a maximum of 5 parts by weight and, if necessary, an antioxidant, a processing aid, a peelability improver, etc., on the conductor or insulating layer is 0.1 to 2 mm. It is coated to the thickness of
It is generally used in the art.

In the present invention, a high-pressure branched low-density ethylene-based resin having a density of 0.915 to 0.925 g / cm ³ and a melt index of 0.3 to 3.0 g / 10 min, which constitutes the insulating layer (A), Was obtained by polymerizing ethylene alone or ethylene and propylene, butene-1 or the like under a high pressure of 2000 to 3000 atmospheres using oxygen or an organic peroxide as a catalyst, with or without a chain transfer agent. It is a polymer with long chain branching and very high processability. If the density of the high-pressure branched low-density ethylene resin is less than 0.915 g / cm ³ , the heat resistance and mechanical strength of the obtained power cable are insufficient, and if it exceeds 0.925 g / cm ³ , it is flexible. It is inferior in nature and is not desirable. Further, the melt index is 0.
Less than 3 g / 10 min has low workability, coating speed is very slow or uncoatable, undesired, 3.0 g
If it exceeds / 10 minutes, heat resistance and mechanical strength become insufficient, which is not desirable.

In the insulating layer (A), the organic peroxide compounded in the high-pressure branched low-density ethylene resin is selected from the same ones as described above for the inner and outer semiconductive layers, The blending amount is 0.1 to 5 parts by weight with respect to 100 parts by weight of the high pressure branched low density ethylene resin. If the blending amount is less than 0.1 parts by weight, heat resistance and mechanical strength are insufficient, and even if it is used in excess of 5 parts by weight, heat resistance, mechanical strength, etc. reach a saturation point. However, it does not improve, resulting in cost increase and deterioration of electrical characteristics due to decomposition residues, which is not desirable.

In the present invention, the insulating layer (B) is formed.
Density 0.91 to 0.93 g / cm^Three, Melt index
0.1 to 5.0 g / 10 min linear low density ethylene-
α-Olefin copolymer means Ziegler catalyst, Phili
Up catalyst, Kaminsky catalyst, single-site catalyst, etc.
Using gas phase method, liquid phase method, slurry method, suspension method, etc.
Ethylene, propylene, butene-1, pentene-
1, hexene-1, 4-methylpentene-1, heptene
-1,4-methylhexene-1,4,4-dimethyl pen
Ten-1, Octene-1, Decene-1, Dodecene-1, etc.
It is obtained by copolymerizing. Linear low density Eth
The density of the ren-α-olefin copolymer is 0.91 g / c.
m^ThreeIf it is less than 1, the heat resistance of the obtained power cable is insufficient.
Minutes, 0.93 g / cm ^ThreeIs less flexible
Not desirable. The melt index is 0.1 g /
If it is less than 10 minutes, the workability is low and the coating speed is very slow.
Squid, uncoverable, undesired, 5.0 g / 10
If it exceeds the limit, heat resistance and mechanical strength become insufficient, which is desirable.
No

In the insulating layer (B), the organic peroxide compounded in the linear low-density ethylene-α-olefin copolymer is also the same as that described above for the inner and outer semiconductive layers. The blending amount thereof is 0.3 to 3 parts by weight with respect to 100 parts by weight of the linear low-density ethylene-α-olefin copolymer. This blend amount is 0.3
If it is less than parts by weight, the heat resistance and mechanical strength are insufficient, and even if it is used in excess of 3 parts by weight, the heat resistance and mechanical strength, etc. reach the saturation point and there is no further improvement, and the cost is reduced. This is not desirable because it causes an increase or deterioration of electrical characteristics due to decomposition residues.

In the present invention, the thicknesses of the insulating layer (A) and the insulating layer (B) have a relationship of a ≧ b ≧ (1/2) a, where the respective thicknesses are a and b. is necessary. When b exceeds a, eccentricity occurs, melt fracture occurs at the time of coating, a power cable with good electrical characteristics cannot be obtained, and the coating speed decreases and the cost increases, which is not desirable. When b is less than (1/2) a, that is, less than half of a, heat resistance and mechanical strength deteriorate, and the amount of relatively expensive high-pressure branched low-density ethylene resin used is relatively high. This increases cost, which is undesirable. Further, the total thickness of the insulating layer (A) and the insulating layer (B), that is, a + b is preferably in the range of 3 mm to 30 mm.

The four-layer common extruder used in the present invention is a four-layered one in which an internal semiconductive layer extruder, an insulating layer (A) extruder, an insulating layer (B) extruder and an external semiconductive layer extruder are arranged. It has a common crosshead.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A power cable of the present invention comprises a resin composition of each of the above-mentioned inner semiconductive layer, insulating layer (A), insulating layer (B) and outer semiconductive layer, which is prepared by using a common four-layer extruder. It can be produced by supplying each extruder, coating each of the above layers on the conductor, preferably at the same time, then introducing it into a cross-linking tube, and heating from the outside to perform cross-linking.

[0017]

Next, the present invention will be described based on examples.
The present invention is not limited to these.

Example 1 A. Preparation of Resin Composition for Inner and Outer Semiconducting Layer 100 parts by weight of a high-pressure ethylene-vinyl acetate copolymer (vinyl acetate content 28% by weight, melt index 20 g / 10 minutes, melting point 91 ° C.) was added with an antioxidant [IRGA Knox 1010 (trade name, Irganox 1010)] 0.5 part by weight and 80 parts by weight of acetylene black are kneaded at 130 ° C. for 10 minutes to obtain pellets (3 mm × 3 mm), and organic peroxide [2,5- Dimethyl-2,5-di (tert-butylperoxy) hexyne] 0.5 part by weight was added,
The mixture was slowly stirred at 0 ° C. for 5 hours to uniformly impregnate the inside of the pellet with an organic peroxide to obtain a resin composition for the inner and outer semiconductive layers.

B. Preparation of resin composition for insulating layer (A) Density 0.922 g / cm ³ , melt index 2.5
Antioxidant [Cynox BCS (trade name, Seenox BC
S)] After kneading 0.2 parts by weight at 130 ° C. for 10 minutes,
Pellet (3 mm x 3 mm), 3.5 parts by weight of organic peroxide (dicumyl peroxide) was added to this, and 6
The mixture was slowly stirred at 8 ° C. for 5 hours to uniformly impregnate the inside of the pellet with an organic peroxide to obtain a resin composition for the insulating layer (A).

C. Preparation of Resin Composition for Insulating Layer (B) Density 0.923 g / cm ³ , Melt Index 0.8
g / 10 min gas phase linear low density ethylene-butene-1
Antioxidant [Cynox BC
0.2 parts by weight of S (trade name, Seenox BCS)] is kneaded at 150 ° C. for 10 minutes to obtain pellets (3 mm × 3 mm), and organic peroxide (dicumyl peroxide) is added to the pellets.
2.5 parts by weight was added, and the mixture was slowly stirred at 70 ° C. for 5 hours to uniformly impregnate the inside of the pellet with an organic peroxide to obtain a resin composition for the insulating layer (B).

D. Four-layer common extruder: An internal semi-conductive layer extruder, an insulating layer (A) extruder, an insulating layer (B) extruder, and an external semi-conductive layer extruder in which a screen pack of 500 mesh or more is provided on each die plate are sequentially arranged. An extruder having the above-mentioned four-layer common crosshead was prepared.

E. Manufacture of power cable The resin composition for the inner semiconductive layer, the resin composition for the insulating layer (A), the resin composition for the insulating layer (B), and the resin composition for the outer semiconductive layer, which are described above, are each prepared by using the above-mentioned extruder. It is supplied to the extruder and heated and kneaded at 200 ° C. in the internal semiconductive layer extruder,
The insulating layer (A) extruder is heated and kneaded at 130 ° C., the insulating layer (B) extruder is heated and kneaded at 140 ° C., and the external semiconductive layer extruder is heated and kneaded at 110 ° C. Extruded and simultaneously extruded and coated on the conductor from the die of the four-layer common crosshead (However, the thickness of each semiconductive layer is 1
mm, the thickness of the insulating layer (A) is 15 mm, the thickness of the insulating layer (B) is 10 mm), 230 ° C. located downstream thereof.
A cross-linking reaction was carried out with a cross-linking tube heated to 0.degree. C. to obtain a power cable in which the inner semi-conductive layer, the insulating layer (A), the insulating layer (B) and the outer semi-conductive layer were coated on the conductor from the inside. When the degree of crosslinking (gel fraction) of each layer of this power cable was measured,
The inner semiconductive layer, the insulating layer (A), the insulating layer (B) and the outer semiconductive layer are 76%, 82%, 80% and 78, respectively.
%, No irregularity due to melt fracture was observed at the interface of each layer, and a high quality power cable was obtained.

Example 2 In Example 1, the linear low density ethylene-butene-1 was used.
An ethylene-octene-1 copolymer produced by using a metallocene-based single-site catalyst instead of the copolymer (density 0.910 g / cm ³ , melt index 3.5 g /
The same experiment as in Example 1 was performed except that 10 minutes) was used, and the degree of crosslinking (gel fraction) of each layer was 76% for the inner semiconductive layer, 83% for the insulating layer (A), and 8 layers (B)
5%, and the outer semiconductive layer was 78%, and a high-quality power cable was obtained in which irregularities due to melt fracture were not observed at the interface between the layers.

Comparative Example 1 A power cable having only the inner semiconducting layer, the insulating layer (A) and the outer semiconducting layer described in Example 1 was manufactured, and an interface between the insulating layer (A) and the outer semiconducting layer was obtained. It had irregularities, electrical trees, and had a short life as a power cable, making it impractical. Moreover, it was not desirable in that eccentricity was generated.

Comparative Example 2 A power cable was manufactured in the same manner as in Example 1 except that the insulating layer (A) had a thickness of 20 mm and the insulating layer (B) had a thickness of 30 mm. Not only
The power cable was inferior in flexibility and was not desirable. Further, melt fracture occurred on both surfaces of the insulating layer (B), and the interface characteristics deteriorated.

Comparative Example 3 A power cable was manufactured in the same manner as in Example 1 except that the insulating layer (A) had a thickness of 30 mm and the insulating layer (B) had a thickness of 10 mm. Not only was a power cable with inferior mechanical strength obtained, but the cost increased, which was not desirable.

[0027]

The power cable of the present invention and the method for manufacturing the same have the following remarkable effects as compared with the conventional ones by adopting the structure described in detail above: (a) Between layers Since melt fracture does not occur, there is no irregularity at each interface, no electrical tree occurs, and the life of the power cable is long. (B) The conventional power cable was manufactured only from the high-pressure low-density ethylene-based resin, but in the present invention, since this is used in combination with the linear low-density ethylene-α-olefin copolymer, A power cable having high cross-linking efficiency, heat resistance, mechanical properties, and flexibility can be obtained. Since the crosslinking efficiency is high, the amount of the organic peroxide compounded can be reduced, and the cost can be reduced. (C) A high-quality power cable can be obtained without causing eccentricity.

Claims (2)

[Claims] 1. An inner semiconductive layer on a conductor, having a density of 0.91.
5 to 0.925 g / cm ³ , melt index 0.3
Insulation layer (A) composed of a resin composition containing 100 parts by weight of a high-pressure branched low-density ethylene resin of 0.1 to 3.0 g / 10 min and 0.1 to 5 parts by weight of an organic peroxide, and a density of 0.9.
1 to 0.93 g / cm ³ , melt index 0.1 to
100 parts by weight of a linear low-density ethylene-α-olefin copolymer at 5.0 g / 10 minutes and an organic peroxide of 0.3 to
Insulating layer (B) made of a resin composition containing 3 parts by weight
[However, the thicknesses of the insulating layer (A) and the insulating layer (B) (respectively a and b) are a ≧ b ≧ (1/2) a], and the external semiconductive layer is common. A method for producing an electric power cable, which comprises performing heating crosslinking after coating using a four-layer extruder. 2. A power cable manufactured by the method of claim 1.