JPH09115367A - Crosslinked-polyethylene-insulated power cable and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an application to the transport of electric power over a range from low voltage approximately equal to 6kV to high voltage equal to or above 500kV. SOLUTION: Regarding a method for manufacturing crosslinked-polyethylene- insulated power cable where an extruding device with a three-layer common crosshead having each extruder arranged for an inner semiconductor layer, an insulation layer and an outer semielectricconductor layer is used to concurrently extrude the three layers to a conductor for the coverage thereof for bridging under the application of heat, an ethylene resin composition without any organic peroxide contained is used for the inner semiconductor layer. Furthermore, an ethylene resin composition containing organic peroxide is used for the insulation layer and the outer semielectricconductor layer. In this case. the composition of the inner semielectricconductor layer is heated and melted in an extruding machine therefor at temperature between 150 and 250 deg.C. Thereafter, the composition is filtrated through a screen pack having 500 meshes or more on a die plate for the removal of foreign materials. Also, a part of the organic peroxide contained in the insulation layer is caused to shift to the inner semiconductor layer at the time of extrusion to and coverage of the conductor at that temperature.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cross-linked polyethylene insulated power cable and a method for manufacturing the same. The power cable produced in the present invention can be used for a wide range of power transportation ranging from low voltage (about 6 kV) to high voltage (about 500 kV) or higher.

[0002]

2. Description of the Related Art Crosslinked polyethylene insulated power cables are:
Polyethylene with excellent dielectric strength, low dielectric constant and low dielectric loss is coated on the conductor through the inner semiconductive layer, the polyethylene is crosslinked to form an insulating layer, and the outer semiconductive layer or sheath layer is coated thereon. Although it is a power cable, since it is solid insulation, it does not require the installation space, maintenance, and fire protection measures due to oil that are required for OF cables (oil-impregnated paper-insulated cables). It has started to be done.

The semi-conductive layer of the cross-linked polyethylene insulated power cable (hereinafter also referred to as CV cable) is for improving the potential gradient and equalizing the potential to improve the withstand voltage property, and is used at high temperature. It is chemically crosslinked with an organic peroxide for the purpose of preventing deformation at the time, reducing the brittle temperature, and preventing brittle fracture at low temperatures. Therefore, the resin composition for a semiconductive layer should be kept below the temperature at which the crosslinking agent does not cause a crosslinking reaction between the step of kneading the crosslinking agent (organic peroxide) and the step of extrusion coating the cable. Although it is necessary to work, since a large amount of carbon black is blended to make it semi-conductive, the melt viscosity increases during kneading, heat is generated, and premature crosslinking occurs, so in order to avoid this, as a resin An ethylene-vinyl acetate copolymer having a low melting temperature, excellent miscibility with carbon black, a low melt viscosity, and a high extrusion processability (hereinafter sometimes referred to as EVA).
Ethylene-ethyl acrylate copolymers (hereinafter sometimes referred to as EEA) have been used.

That is, in the above-mentioned conventional method, in order to avoid premature crosslinking, EVA or EEA is used, and the coating process is performed at a low temperature. Therefore, the coating speed is slow and the productivity is poor, and EVA, EEA, etc. are used. Has a polar group in the molecule, so its dielectric constant and dielectric loss are large, and further, when the power cable is immersed in water or left in a conductor-filled state for a long period of time, water tree generation, a decrease in AC breakdown voltage, etc. occur, Since the life of the power cable is shortened and EVA and EEA have a low melting point, there is a problem that the upper limit of the operating temperature of the power cable is limited.

Further, if a small amount of foreign matter is present in the resin composition for a semiconductive layer, irregularities will occur at the interface between the semiconductive layer and the insulating layer even if the amount of the foreign matter is very small, resulting in an irregular portion. A high electric field is formed at a critical point, which causes corona discharge and water tree deterioration when the cable is flooded, which shortens the cable life and is not desirable.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional method for producing a crosslinked polyethylene insulated power cable described above. To prevent the occurrence of irregularities in the power cable and extend the cable life,
(B) If low-temperature decomposable organic peroxide is used to avoid premature crosslinking, productivity will be reduced. (C) In order to avoid premature crosslinking, EVA or EEA
If a resin having a low melting point such as is used, the electrical characteristics of the cable are deteriorated and the life of the cable is shortened. However, to solve this, (d) the semiconductive layer due to the presence of foreign matter in the resin composition for the semiconductive layer. Eliminates irregularities at the interface between the insulation layer and the insulation layer, and extends the cable life. (E) The internal semiconductive layer allows a relatively long time for external heat to reach the inside by external heat and pressure crosslinking. In addition, since productivity is deteriorated, it is possible to use dielectric heating together and heat from the center conductor side to increase the cross-linking speed.However, this requires equipment cost and operation control is difficult, which leads to cost increase. However, to solve these problems, (F) EVA and E
Electric power produced using metallocene-catalyzed polyethylene, linear low-density polyethylene (eg, LLDPE, VLDPE), etc., which has good electrical characteristics, withstands high-temperature use of the cable, and extends the life of the cable, instead of EA, etc. The objectives were to provide a cable, to provide a method for manufacturing a power cable that can be easily removed even if foreign matter is present in the (g) raw material ethylene resin, and to reduce costs. It is a thing.

[0007]

The present inventor has studied the above-mentioned problems in the production of conventional power cables, and found that the above-mentioned problems are the organic peroxides in the ethylene-based resin composition for the inner semiconductive layer. Clarified that it is due to
Despite not using an organic peroxide in the ethylene-based resin composition for the inner semi-conductive layer, that the inner semi-conductive layer can be cross-linked equally to the inner semi-conductive layer of a conventional power cable,
The present invention has been completed by finding out by applying the phenomenon of high-speed dispersibility of an organic peroxide.

That is, the present invention uses a three-layer common extruder having a three-layer common crosshead in which an inner semiconductive layer extruder, an insulating layer extruder, and an outer semiconductive layer extruder are arranged to crosslink polyethylene insulated power cable. In the method for producing, an ethylene-based resin composition for an internal semiconductive layer containing no organic peroxide, an ethylene-based resin composition for an insulating layer containing an organic peroxide, and an external semiconductive material containing an organic peroxide. Using an ethylene resin composition for layers, and,
A screen pack of 500 mesh or more is provided on the die plate of the internal semiconductive layer extruder, and the ethylene-based resin composition for the internal semiconductive layer is used in the internal semiconductive layer extruder at 150 to
After being heated and melted at 250 ° C., foreign matter is removed by passing through the screen pack, and then the ethylene-based resin composition for the inner semiconductive layer, the ethylene-based resin composition for the insulating layer, and the ethylene-based resin composition for the outer semiconductive layer. The present invention relates to a method for producing a crosslinked polyethylene insulated power cable, which comprises extruding and coating a resin composition on the outside of a conductor, introducing the resin composition into a crosslinking cylinder, and performing external heating crosslinking. The invention also relates to a crosslinked polyethylene insulated power cable produced by the method of the invention.

The three-layer common extruder used in the present invention has a three-layer common crosshead in which an inner semiconductive layer extruder, an insulating layer extruder and an outer semiconductive layer extruder are arranged. Known materials can be used as they are.

In the present invention, the ethylene-based resin composition for the internal semiconductive layer is a composition in which 70 parts by weight or more of the conductivity-imparting agent is mixed with 100 parts by weight of the ethylene-based resin,
It is essential that no organic peroxide is added. The reason is that when an organic peroxide is blended, premature crosslinking occurs. The conductivity-imparting agent is carbon black, such as furnace black, acetylene black, and Ketjen black.

Examples of ethylene resins include EVA and EE
A, high pressure low density polyethylene (HP-LDPE), low pressure high density polyethylene (HDPE), linear low density ethylene-α olefin copolymer (LLDPE), linear ultra low density ethylene-α olefin copolymer Coalescence (VLDP
E), ethylene-α olefin copolymer produced by a metallocene single site catalyst, and the like can be used.

In the present invention, it is an essential requirement that the ethylene resin composition for an insulating layer be blended with an organic peroxide. The organic peroxide preferably has a decomposition temperature of 150 to 200 ° C. until a half-life of 1 minute is obtained, and examples thereof include 1,1-bis-tert-butylperoxycyclohexane and 2,2-bis-tert-butyl. Peroxybutane, tert-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-tert-butyl peroxyhexane, tert-butyl cumyl peroxide, 2,
Examples thereof include 5-dimethyl-2,5-di-tert-butylperoxyhexyne-3 and the like, and dicumyl peroxide is particularly preferable.

The blending amount of the organic peroxide is ethylene resin 1
The amount is 1.0 to 5.0 parts by weight, preferably 2.0 to 4.0 parts by weight, relative to 00 parts by weight. The organic peroxide in the ethylene-based resin composition for the insulating layer migrates to the molten ethylene-based resin composition for the inner semiconductive layer, and therefore the amount of the organic peroxide in the inner semiconductive layer and the insulating layer is expected. It is necessary to mix them in consideration of the required degree of crosslinking (gel fraction).

In the present invention, it is essential that the ethylene-based resin composition for the outer semiconductive layer contains an organic peroxide. The reason is that cross-linking with an organic peroxide provides mechanical strength and heat deformation resistance when the outer semiconductive layer is used.

The ethylene resin used for the insulating layer and the outer semiconductive layer may be selected from the ethylene resins listed for the inner semiconductive layer. The organic peroxide used for the outer semiconductive layer can be selected from those listed for the insulating layer.

The ethylene-based resin composition of the insulating layer and the outer semiconductive layer is also blended with a conductivity-imparting agent. The conductivity-imparting agent is carbon black, such as furnace black, acetylene black, Ketjen black and the like. Means In the case of Ketjen black, 15 parts by weight or more is added to 100 parts by weight of the resin component, and in the case of other carbon black, 40 parts by weight or more is added. If the amount is less than the above amount, sufficient conductivity cannot be obtained.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a die pack of an internal semiconductive layer extruder is provided with a screen pack of 500 mesh or more, and the ethylene-based resin composition for the internal semiconductive layer is used in the internal semiconductive layer extruder. At 150 to 250 ° C., preferably 200 to 250 ° C., and then integrated with the insulating layer heated and melted at 150 to 250 ° C., preferably 200 to 250 ° C. As described above, the ethylene-based resin composition for the internal semiconductive layer is passed through the screen pack at a high temperature, so that the melt viscosity is low and the screen pack having fine meshes can easily pass with low resistance. Even if foreign matter is present inside, it can be removed with a screen pack and no irregularities are generated at the interface between the internal semi-conductive layer and insulating layer, which has the effect of extending the life of the power cable. Also, the inner semiconductive layer and the insulating layer are formed at 150 to 250 ° C., preferably 200 to 250 ° C.
Since they are integrated in a molten state at 250 ° C., the organic peroxide contained in the insulating layer migrates across the interface at a high speed to the inner semiconductive layer and is uniformly dispersed in the inner semiconductive layer. A crosslinking reaction occurs in the crosslinking cylinder, which is the process of
Crosslinking the inner semiconductive layer, more uniform crosslinking occurs than when a conventional resin composition for the inner semiconductive layer is mixed with an organic peroxide in advance, and a high quality and long life power cable can be manufactured. .

In the present invention, as described above, the inner semiconductive layer can be coated at a high temperature, and the crosslinking reaction can also be performed at a high temperature, so that the speed of the manufacturing process can be greatly increased and the cost can be reduced. Can be down. Also,
In the conventional crosslinking method in which the internal semiconductive layer itself contains an organic peroxide in advance, the melt viscosity is too high and the productivity is poor, and the ethylene-α-olefin copolymerization produced by the metallocene single-site catalyst that could not be used. Coalescing, LLD
It is possible to use PE, VLDPE, HDPE, etc., and it is possible to further enhance the effects of preventing deterioration and deformation when the power cable is used at high temperatures.

In the present invention, the above-mentioned ethylene resin composition for the inner semiconductive layer, the ethylene resin composition for the insulating layer and the ethylene resin composition for the outer semiconductive layer are combined with a three-layer common crosshead. It is supplied to a layer common extruder, and the above three kinds of resin compositions are simultaneously extrusion-coated and then introduced into a cross-linking cylinder and heated from the outside to cross-link,
Manufacture power cables.

[0020]

Next, the present invention will be described based on examples.
The present invention is not limited to these. Example 1 A. Preparation of ethylene-based resin composition for internal semiconductive layer Linear low-density ethylene-butene-1 copolymer (density 0.
92 g / ml, melt index 3.7 g / 10 minutes,
100 parts by weight of a melting point of 121 ° C.), 0.3 parts by weight of an antioxidant [Irganox 1010] (trade name, Irganox 1010) and 80 parts by weight of acetylene black at 10 ° C.
After kneading for a minute, pellets (3 mm × 3 mm) were obtained to obtain an ethylene-based resin composition for the internal semiconductive layer. B. Preparation of Ethylene Resin Composition for Insulating Layer High Pressure Low Density Polyethylene (Density 0.92 g / ml, Melt Index 3.5 g / 10 min, Melting Point 101 ° C.) 1
100 parts by weight of 0.18 parts by weight of an antioxidant [Seenox BCS (trade name: Seenox BCS)] was kneaded at 130 ° C. for 10 minutes to obtain pellets (3 mm × 3 mm). 3 parts by weight of mil peroxide) 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 an ethylene resin composition for an insulating layer. C. Preparation of Ethylene Resin Composition for External Semiconductive Layer High-pressure method ethylene-vinyl acetate copolymer (vinyl acetate content 28% by weight, melt index 20 g / 10 minutes, melting point 91 ° C.) 100 parts by weight of antioxidant [IRGA Knox 1010 (trade name, Irganox 1010)] 0.3 parts by weight and 80 parts by weight of acetylene black were 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 an external semiconductive layer.

D. Three-layer common extruder Extruder having a three-layer common crosshead in which an internal semiconductive layer extruder having a screen pack of 500 mesh or more on a die plate, an insulating layer extruder and an external semiconductive layer extruder are sequentially arranged. did.

E. Production of power cable The above-mentioned internal semiconductive layer ethylene-based resin composition, insulating layer ethylene-based resin composition and external semiconductive layer ethylene-based resin composition are supplied to respective extruders of the above-mentioned extruder, and internal Semi-conductive layer extruder heat kneads at 200 ℃, insulation layer extruder heat kneaded at 130 ℃, external semi-conductive layer extruder heat kneaded at 110 ℃, extruded from each extruder, three-layer common cloth The conductor was simultaneously extrusion-coated from the die of the head, and the cross-linking reaction was performed in the cross-linking cylinder located at the downstream of the head and heated to 230 ° C. to obtain a power cable. When the degree of crosslinking (gel fraction) of each layer of this power cable was measured, the inner semiconductive layer, the insulating layer and the outer semiconductive layer were 78%, 82% and 80%, respectively, and irregularity was recognized 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 using a mecolocene-based single-site catalyst instead of the copolymer (density 0.910 g / ml, melt index 3.5 g / 1
When the same experiment as in Example 1 was performed except that 0 min, melting point 103 ° C.) was used, the degree of crosslinking (gel fraction) of each layer was
78% of the inner semiconductive layer, 82% of the insulating layer, and 80% of the outer semiconductive layer, and a high quality power cable having no irregularity at the interface of each layer was obtained.

[0024]

EFFECTS OF THE INVENTION The crosslinked polyethylene insulated power cable of the present invention and the method of manufacturing the same have the following remarkable effects as compared with the conventional ones by adopting the configuration described in detail above: (a) Since the ethylene resin composition for the internal semiconductive layer does not contain an organic peroxide, it can be extrusion-coated at a higher temperature than conventional ones, so that productivity can be improved and foreign matter can be easily removed. Moreover, it is possible to reduce the level of foreign matter. (B) Since the inner semiconductive layer and the insulating layer are extrusion-coated at a high temperature, a part of the organic peroxide of the insulating layer moves to the inner semiconductive layer side at a high speed and crosslinks the inner semiconductive layer. Despite not containing an organic peroxide in the ethylene-based resin composition for the semiconductive layer, the internal semiconductive layer is crosslinked,
It is possible to obtain a power cable with lower cost and equivalent performance as compared with the conventional power cable. (C) Polyethylene resin, which has poor extrudability at high temperatures and has been forced to be used at the expense of conventional productivity,
For example, LLDPE, VLDPE, polyethylene with a metallocene single-site catalyst, etc. can be used as the resin for the internal semiconductive layer according to the present invention without sacrificing the productivity. ,
It is possible to manufacture power cables with excellent heat resistance (usable even at high temperatures). (D) In the extrusion coating of the inner semiconductive layer, high-quality power cables are obtained because premature crosslinking does not occur. (E) A screen pack of 500 mesh or more is attached to the extruder for the inner semiconductive layer, and high temperature operation is possible, so that the level of foreign matter can be lowered and irregularity at the interface between the inner semiconductive layer and the insulating layer can be achieved. Can be prevented, corona discharge and water tree generated from the irregular portion (protrusion) of the interface can be prevented, and the life of the power cable can be extended. (F) In conventional cross-linking by external heating, heat is conducted to the inside, which requires a relatively long time and productivity is poor. However, in the present invention, the coating temperature of the internal semi-conductive layer is higher than that in the past. Therefore, extrusion coating is possible with high productivity. Further, the higher the coating temperature is,
The half-life of the organic peroxide is shortened and the productivity can be improved.

Claims (2)

[Claims] 1. A method for producing a crosslinked polyethylene insulated power cable using a three-layer common extruder having a three-layer common crosshead in which an inner semiconductive layer extruder, an insulating layer extruder and an outer semiconductive layer extruder are arranged. In, an ethylene-based resin composition for an internal semiconductive layer containing no organic peroxide, an ethylene-based resin composition for an insulating layer containing an organic peroxide, and an ethylene-based resin composition for an external semiconductive layer containing an organic peroxide A resin composition is used, and a screen pack of 500 mesh or more is provided on the die plate of the internal semiconductive layer extruder, and the ethylene-based resin composition for the internal semiconductive layer is used in the internal semiconductive layer extruder for 150 times. After heating and melting at ~ 250 ° C., the foreign matter is removed by passing through the screen pack, and then the ethylene-based resin composition for the internal semiconductive layer and the ethylene-based resin for the insulating layer. After extrusion-coating the resin composition and the external semiconductive layer ethylene-based resin composition to the outside of the conductor,
A method for producing a cross-linked polyethylene insulated power cable, which comprises introducing into a cross-linking cylinder and performing external heating cross-linking. 2. A cross-linked polyethylene insulated power cable produced by the method of claim 1.