JPH08111125A - Electric wire/cable - Google Patents

Abstract

PURPOSE: To provide a new electric wire/cable in which water tree formation is suppressed and which has improved dielectric breakdown strength even if defects such as voids, foreign matter exist inevitably. CONSTITUTION: An insulation layer 3 to be formed on a conductor 1 or a conductor shielding layer 2, 4 is made up of a resin composition consisting of mainly polyethylene with 0.930-0.945g/cm<3> density and 0.5-5.0g/10min MI and produced by polymerization with a single site catalyst, containing also an organic peroxide compound of 1-(2-tert-butylperoxyisopropyl)-4-isopropylbenzene, 1-(2-tert- butylperoxyisopropyl)-3-isopropylbenzene or its mixture, and crosslinked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric wire / cable that is often used in a wet atmosphere and uses crosslinked polyethylene as an insulating layer.

[0002]

2. Description of the Related Art Generally, polyolefin is widely used as an insulating material for high-voltage cables such as electric power cables, and particularly cross-linked polyethylene having excellent electrical insulation and heat resistance. However, the insulator made of this cross-linked polyethylene has a drawback that when used in a wet or flooded atmosphere, a water tree is generated inside the insulator, and the excellent electrical insulation performance of the material is significantly reduced. For example,
As shown in FIG. 1, in a general high-voltage electric wire cable, an inner semiconductive layer 2 is formed on a conductor 1, an insulator 3 is provided on the outer periphery thereof, and an outer semiconductive layer is provided on the outer periphery of the insulation layer 3. However, when exposed to a humid atmosphere for a long time, a bowtie-like water tree is generated inside the insulating layer 3, or the interfacial water tree is formed inside the semiconductive layer 2 or outside. It is generated from the semiconductive layer 4, and in the worst case, it may even penetrate the insulating layer 3 to cause dielectric breakdown.

It is known that such a water tree is generated by the agglomeration of water in a void or foreign matter in the insulator, or in a defective portion such as a local high electric field portion such as an irregularity of the interface between the insulator and the semiconductive layer. Has been. Therefore, in order to eliminate these defects in the insulator, many efforts have been made in various fields such as quality control of resins and improvement of electric wire / cable manufacturing technology.

[0004]

By the way, in addition to the large amount of labor and cost involved in improving the quality control and manufacturing technology of such a resin, in spite of these efforts, It has been extremely difficult to prevent such defects, that is, the generation of water trees. On the other hand, with the recent increase in the demand for electric power, the voltage of power cables has been increased, and it has been required to reduce the insulation thickness and to develop an insulating material having high reliability. Therefore, the present invention has the above-mentioned problems. The present invention has been devised in order to effectively solve the problem, and the purpose thereof is to prevent the generation of water trees even if defects such as voids and foreign substances are unavoidably present in the insulator. The purpose of the present invention is to provide a new electric wire / cable capable of improving the dielectric breakdown strength.

[0005]

In order to achieve the above object, the present invention provides a density of 0.9 or more when an insulating layer coated on a conductor or a conductor shielding layer is polymerized using a single site catalyst.
MI of 0.5 to 5.0 g at ³⁰ to 0.945 g / cm ³
/ 10 min resin composition mainly composed of polyethylene, 1- (2-tert-butylperoxy-isopropyl) -4-isopropylbenzene or 1- (2-t
ert-Butylperoxyisopropyl) -3-isopropylbenzene or an organic peroxide composed of a mixture thereof, or in addition to this, an unsaturated dimer of an aromatic α-methylalkenyl monomer is contained and crosslinked. In addition, the degree of crosslinking of the insulating layer is 70% or more.

[0006]

The single-site catalyst used in the polymerization of polyethylene according to the present invention has a uniform active site and has a transition metal (Ti, Z
(r, Hf, V, Cr) is a compound having a sandwiched structure of unsaturated cyclic compounds, and has, for example, the following chemical structure.

[0007]

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At this time, methylalumoxane (MAO), which is a compound of trimethylaluminum and water shown below, is used.
May be used as a promoter.

[0009]

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As an example, there are the following compounds.

[0011]

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Polyethylene polymerized using such a single-site catalyst is characterized by a uniform crystal thickness and a large number of tie molecules connecting lamellas. Therefore, it is considered that the strength of the amorphous portion is improved, the progress of the tree which is said to proceed through the amorphous portion is suppressed, and the dielectric breakdown strength is also improved.

The polyethylene used in the present invention is a low density polyethylene (LDP) polymerized by a high pressure radical polymerization method.
E) and medium density polyethylene (MDPE), ultra low density polyethylene polymerized with martensite catalyst (VLDP)
E), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and ethylene-propylene copolymers, ethylene-ethylene acrylate copolymers, ethylene-vinyl acetate copolymers, and other polyolefins containing a majority of ethylene. You may use 1 type or 2 types or more blended. Here, the density of polyethylene polymerized using a single-site catalyst was set to 0.930 to 0.94.
The 5 g / cm ^3, MI was a 0.5 to 5.0 g / 10min, the density is small dielectric breakdown strength is less than 0.930 g / cm ^3, difficult molding exceeds 0.945 g / cm ³ Because it will be. Also, MI is 0.5 g / 10
If it is less than min, the fluidity at the time of cable molding is poor, and 5.0
This is because if it exceeds g / 10 min, the fluidity becomes so large that it tends to sag and molding becomes difficult.

The 1- (2-tert-butylperoxyisopropyl) -4-isopropylbenzene and 1- (2-tert-butylperoxyisopropyl) -3-isopropylbenzene can be represented by the following formula. is there.

[0015]

[Chemical 4]

[0016]

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These cross-linking agents have a higher decomposition temperature than conventionally used dicumyl peroxide, prevent premature cross-linking (scorch) at the time of molding a cable / electric wire, and have a good appearance. Can be manufactured. However, the organic peroxide of the present invention is dicumyl peroxide, 1.3-bis- (tert-butylperoxyisopropyl) benzene or 2,5-dimethyl-2,5, which has been conventionally used for crosslinking polyolefins. It is also possible to use it together with -di-tert-butyl-hexyne-3 and the like, but in that case, it is desirable that the addition amount is less than 1/2 of the organic peroxide specified in the present invention.

The aromatic α-methylalkenyl monomer is represented by the following formula.

[0019] Here, R is an allyl group, an alkaryl group, a halogen-substituted allyl group, or a halogen-substituted alkaryl group.

The unsaturated dimer includes α-methylstyrene,
Para-methyl-α-methylstyrene, para-ethyl-α
-Methylstyrene, para-isopropyl-α-methylstyrene, meta-ethyl-α-methylstyrene, meta-methyl-α-methylstyrene, ar-dimethyl-α-methylstyrene, ar-chloro-α-methylstyrene, ar-
Unsaturated dimers such as chloro-ar-methyl-α-methylstyrene, ar-diethyl-α-methylstyrene, ar-methyl-ar-isopropyl-α-methylstyrene are included.

Further, these dimers may be used alone or in combination of two or more kinds. Further, it has been found that the dimer has a function of crosslinking polyethylene during extrusion molding.
That is, scorch at the time of extrusion molding can be prevented, and an electric wire / cable having a good appearance can be obtained. Although the amount of this organic peroxide added is not specified, as a result of examining the relationship between the degree of cross-linking and the water-immersion potential of cross-linked polyolefin insulated wires / cables, the effect of improving the water-immersion potential when the degree of cross-linking is 70% or more. Admit that is large. It is all right to add additives such as an antioxidant, a lubricant and a coloring agent to the resin composition of the present invention. In addition, the influence of water on the bow tie tree is extremely large, and the vault tie tree is also found in a cable that is electrically charged in the air or a cable that is shielded by a metal sheath. It is considered that these are due to moisture that has penetrated from the outside. It is needless to say that the insulator according to the present invention exerts an effective tree suppressing effect even on such a bowtie tree.

[0022]

EXAMPLES Examples and comparative examples of the present invention will be described below.

(Example) Compositions of 10 kinds of compounds as shown in Table 1 were kneaded by a 22 inch mixing roll to prepare a sheet, which was pelletized by a pelletizer. Then, the pellets were introduced into an extruder, and as shown in FIG. 1, a 4 mm thick insulating layer with a 0.7 mm thick inner semiconductive layer 2 and an outer semiconductive layer 4 on a 60 mm ² annealed copper stranded wire 1. Extruded as 3. Immediately thereafter, the cable 5 was completed by crosslinking in a dry crosslinking tube using nitrogen gas as a heating medium, and then pressure cooling was completed to obtain a sample.

Then, with respect to each of these samples, the extrusion processability, the gel fraction, the number of votitleys generated, and the AC breakdown voltage were examined. As for the extrudability, the cable should be 14
The appearance of extrusion at an extrusion temperature of 5 ° C, that is, the presence or absence of burning was determined, and the gel fraction was measured according to JIS-C3005. In addition, as an evaluation method of the number of occurrence of boutite trie, the electric wire 5 is immersed in warm water of 90 ° C., AC3 kV is applied between the conductor and water for 500 days, then, this is sliced into thin pieces, boiled and dyed with an aqueous solution of methylene blue, and the optical Use a microscope to determine the presence and number of occurrence of bow tie tree (0.
2 mm or more). Furthermore, as an AC dielectric breakdown test, each sample was tested at room temperature for 17 kV / 10 minutes and then 5 kV /
The voltage was increased at a rate of 10 minutes, and the dielectric breakdown voltage value was measured.

[0025]

[Table 1]

(Comparative Example) Using compositions of 5 kinds as shown in Table 2, 5 kinds of samples were obtained by the same method as the example, and then the same evaluation was carried out.

[0027]

[Table 2]

As a result, as shown in Table 1, in each of the examples according to the present invention, excellent extrusion moldability was obtained,
In addition, there is little occurrence of bow tie tree, and high AC breakdown voltage is exhibited. On the other hand, the density is low (0.9
30 g / cm ³ or less) Comparative Example 1 using polyethylene D
Then, the AC breakdown voltage is lower than any of the examples,
Further, Comparative Example 2 using polyethylene E having a high density (0.945 g / cm ³ or more), Comparative Example 3 and Comparative Example in which MI is out of the specified value (0.5 to 5.0 g / 10 min) of the present invention. In Comparative Example 5 in which dicumyl peroxide other than the present invention was used as the crosslinking agent, extrusion was difficult in all cases.

[0029]

In summary, according to the present invention, even if there are unavoidable defects such as voids and foreign substances in the insulator, the generation of trees is suppressed, so that the reliability of the insulating layer is greatly improved. Further, since the dielectric breakdown voltage is also greatly improved, it is possible to exert an excellent effect such as contributing to weight reduction of the power cable due to the thinning of the insulating layer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a high-voltage electric wire cable according to the present invention.

[Explanation of symbols]

 1 conductor 2 inner semiconductive layer 3 insulating layer 4 outer semiconductive layer 5 cable

Claims (3)

[Claims] 1. The density of an insulating layer coated on a conductor or a conductor shielding layer is 0.930 to which is polymerized using a single-site catalyst.
MI of 0.5 to 5.0 g / 10 at 0.945 g / cm ³
1-min resin composition containing mainly polyethylene
(2-tert-butylperoxyisopropyl) -4
An electric wire / cable comprising: an isopropylbenzene or 1- (2-tert-butylperoxyisopropyl) -3-isopropylbenzene or a mixture thereof containing an organic peroxide and crosslinking the organic peroxide. 2. The density of the insulating layer coated on the conductor or the conductor shielding layer is 0.930 to which is polymerized by using a single-site catalyst.
MI of 0.5 to 5.0 g / 10 at 0.945 g / cm ³
1-min resin composition containing mainly polyethylene
(2-tert-butylperoxy-isopropyl)-
4-isopropylbenzene or 1- (2-tert-
Butylperoxyisopropyl) -3-isopropylbenzene or an organic peroxide composed of a mixture thereof, and an unsaturated dimer of an aromatic α-methylalkenyl monomer, which are crosslinked. Characteristic electric wire
cable. 3. The electric wire / cable according to claim 1, wherein the degree of crosslinking of the insulating layer is 70% or more.