JPH08111121A - Electric insulating composition and electric wire/cable - Google Patents

Abstract

PURPOSE: To suppress water tree formation in an insulating body by mixing a specified range of parts by weight of polyethylene polymerized while using a single site catalyst and having a specified density and MI and a specified range of parts by weight of high pressure polymerized polyethylene with a specified density. CONSTITUTION: Polyethylene having 0.910-0.945g/cm<3> density and 0.5-5.0g/10min MI is produced by polymerization while using a single site catalyst having uniform active sites and a structure in which transition metals (Ti, Zr) are sandwiched by unsaturated cyclic compounds. Also polyethylene having 0.910-0.945g/cm<3> is produced by high pressure radical polymerization. Both polyethylenes are mixed in a range from (95:5) to (50:50) by weight ratio (the former: the latter) to give an electric insulating/composition. Together with semiconductive layers 2, 4, an insulating layer 3 is formed on a conductor 1 to give an electric wire/cable. The polyethylenes have high strength in amorphous parts and suppress the progress of water tree formation.

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. That is, as shown in FIG. 1, in a general high-voltage electric wire cable, for example, an inner semiconductive layer 2 is formed on a conductor 1, an insulating layer 3 is formed on the outer periphery thereof, and an outer layer is formed on the outer periphery of the insulating layer 3. Although it has a structure in which the semiconductive layer 4 is formed by coating, when exposed to a moist atmosphere for a long time, a bowtie-like water tree is generated inside the insulating layer 3 or an interfacial water tree is formed inside the semiconductive layer. 2 or from the external 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 at the interface between the insulating layer 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 resin and improvement of electric wire / cable manufacturing technology.

[0004]

By the way, it takes a lot of labor and cost to improve the quality control and manufacturing technique of such a resin, and in spite of such labor, It was extremely difficult to prevent the generation of such defects, that is, 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 present invention provides a novel electric insulating composition and electric wire / cable capable of improving the dielectric breakdown strength.

[0005]

In order to achieve the above object, the present invention provides a polymerized using a single-site catalyst having a density of 0.910 to 0.945 g / cm ³ and an MI of 0.5 to.
5.0g / 10min polyethylene and density 0.91
An electrically insulating composition obtained by blending 0 to 0.945 g / cm ³ of high-pressure radical-polymerized polyethylene in the range of 95/5 parts by weight to 50/50 parts by weight, and an insulating layer comprising the electrically insulating composition, This is an electric wire / cable formed by coating a conductor or a conductor shielding layer, and the degree of crosslinking of this 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.

In the present invention, the density is 0.910 to 0.9.
The reason for using polyethylene of 45 g / cm ³ and MI 0.5 to 5.0 g / 10 min is that the density is 0.910.
If it is less than g / cm ³ , the dielectric breakdown strength is small and is 0.945.
This is because if it exceeds g / cm ³ , molding becomes difficult. Also, if the MI is less than 0.5 g / 10 min, the fluidity at the time of molding the cable is poor, and if it exceeds 5.0 g / 10 min, the fluidity becomes so large that it tends to sag and molding becomes difficult.

The high-pressure radical-polymerized polyethylene is used because it has a long chain branch in the molecule and has good fluidity and good extrusion processability. Also, the compounding ratio is 95/5 to 50 /
The range of 50 parts by weight is limited so that when the high-pressure radial polymerized polyethylene is less than 5 parts by weight, there is no effect of improving the fluidity, and when it exceeds 50 parts by weight, the effect of suppressing the generation of water trees and the effect of improving the dielectric breakdown strength are achieved. Because it disappears.

The cross-linking method includes dicumyl peroxide, 1.3-bis- (t-butylperoxy-isopropyl) benzene and 2,5-dimethyl-2,5-di- (t.
-Butylperoxy) -hexyne-3,1- (2-te
Chemical crosslinking with an organic peroxide such as rt-butylperoxyisopropyl) -4-isopropylbenzene and 1- (2-tert-butylperoxyisopropyl) -3-isopropylbenzene is common. In addition, there are silane water crosslinking using silanes such as vinyltriethoxysilane, and irradiation crosslinking using ionizing radiation such as electron beam.

In addition, additives such as antioxidants, lubricants and colorants may be added to the electrical insulation 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.

[0017]

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

(Example) A composition was prepared by kneading compositions of 8 kinds as shown in Table 1 with 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 votitley generation, 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. was checked and judged, and the gel fraction was measured according to JIS-C3005. As an evaluation method of the number of occurrence of bow-tightly, the electric wire 5 is immersed in warm water of 90 ° C. and AC3k is applied between the conductor and water.
After applying V for 500 days, it was sliced thinly, boiled and dyed with an aqueous solution of methylene blue, and the presence or absence of occurrence of bow tie and number (0.2 mm or more) using an optical microscope.
I checked. Further, as an AC dielectric breakdown test, each sample was boosted at a rate of 5 kV / 10 minutes after being heated at room temperature for 17 kV / 10 minutes, and the dielectric breakdown voltage value was measured.

[0020]

[Table 1]

(Comparative Example) Using the compositions of 6 kinds as shown in Table 2, 5 kinds of samples were obtained by the same method as in the example, and then the same evaluation was carried out.

[0022]

[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,
The occurrence of bow tie tree is very small and the AC breakdown voltage is high. On the other hand, in the case of Comparative Example 1 consisting only of polyethylene polymerized with a single-site catalyst, extrusion moldability was poor and Comparative Example 2 in which the amount of high-pressure polymerized polyethylene compounded was more than the specified value (5 to 50 parts by weight). In this case, the occurrence of bow tie tree is extremely large and the AC breakdown voltage is low. Further, the density is the specified value of the present invention (density = 0.910 g / cm ^{3 to} 0.945 g / cm ³ ,).
Comparative Example 3 in which polyethylene other than the above is used, and MI is a specified value of the present invention (MI = 1.0 g / 10 min to 5.0 g / 10
min) and Comparative Examples 5 and 6 have poor extrusion processability. In particular,
In the case of using low-density polyethylene as in Comparative Example 4, the occurrence of votitley is large and the AC breakdown voltage is low.

[0024]

In summary, according to the present invention, even if there is an unavoidable defect such as a void or a foreign substance in the insulator, the generation of trees is suppressed, so that the reliability of the insulating layer is improved and 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. A density of 0.910 to 0.945 g / cm ³ polymerized using a single-site catalyst and an MI of 0.5 to.
5.0g / 10min polyethylene and density 0.91
An electrically insulating composition, characterized in that it is blended with 0 to 0.945 g / cm ³ of high-pressure radical-polymerized polyethylene in the range of 95/5 parts by weight to 50/50 parts by weight, respectively. 2. An electric wire / cable in which an insulating layer made of the electrical insulating composition according to claim 1 is coated on a conductor or a conductor shielding layer. 3. The electric wire / cable according to claim 2, wherein the degree of crosslinking of the insulating layer is 70% or more.