JP3341488B2 - Electrical insulating composition and electric wires and cables - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, polyolefins, particularly crosslinked polyethylene having excellent electrical insulation and heat resistance, are widely used as insulating materials for high-voltage cables such as power cables. However, the insulator made of the crosslinked polyethylene has a disadvantage that when used in a wet or submerged atmosphere, water trees are generated inside the insulator, and the excellent electrical insulation performance of the material is greatly reduced. That is, as shown in FIG. 1, a general high-voltage electric cable has, for example, an inner semiconductive layer 2 formed on a conductor 1, an insulating layer 3 on the outer periphery thereof, and an outer semiconductive layer 3 on the outer periphery of the insulating layer 3. Although it has a structure in which the semiconductive layer 4 is formed by coating, if it is exposed to a humid atmosphere for a long time, a bow-tie-like water tree is generated inside the insulating layer 3 or the interfacial water tree is formed by the internal semiconductive layer. 2 or from the external semiconductive layer 4, and in the worst case, may penetrate through the insulating layer 3 and even cause dielectric breakdown.

[0003] It is known that such water trees are generated by water agglomeration in voids and foreign matters in an insulator, or in defects such as local high electric field portions such as irregularities in the interface between an insulating layer and a semiconductive layer. Have been. Therefore, many efforts have been made in various fields such as quality control of resin and improvement of wire / cable manufacturing technology in order to remove these defects in the insulator.

[0004]

By the way, in order to improve the quality control and the manufacturing technique of such a resin, much labor and cost are required. It was extremely difficult to suppress the generation of a serious defect, namely, water trees. On the other hand, with the increase in power demand in recent years, the voltage of power cables has been increased, and there has been a demand for the development of an insulating material having a reduced insulation thickness and high reliability. It is devised to effectively solve the problem, the purpose is to prevent the occurrence of water trees even if defects such as voids and foreign substances are inevitable in the insulator, Another object of the present invention is to provide a novel electric insulating composition and an electric wire / cable capable of improving the dielectric breakdown strength.

[0005]

In order to achieve the above object, the present invention relates to a method for producing a polymer having a density of 0.910 to 0.945 g / cm ³ and an MI of 0.5 to 0.99, which is obtained by polymerization using a single-site catalyst.
5.0 g / 10 min polyethylene and density 0.91
An electrical insulating composition obtained by blending 0 to 0.945 g / cm ³ of a high-pressure radically polymerized polyethylene in the range of 95/5 parts by weight to 50/50 parts by weight, and an insulating layer comprising the electrical insulating composition, An electric wire or cable coated on a conductor or a conductor shielding layer, and the degree of crosslinking of the insulating layer is 70% or more.

[0006]

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

[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 having a uniform crystal thickness and a large number of tie molecules connecting the lamella. For this reason, it is considered that the strength of the amorphous portion is improved, and the progress of the tree, which is said to progress through the amorphous portion, is suppressed, and it is presumed that the dielectric breakdown strength is also improved.

In the present invention, the density is 0.910 to 0.9.
The reason for using polyethylene having 45 g / cm ³ and MI of 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,
If it exceeds g / cm ³ , molding becomes difficult. If the MI is less than 0.5 g / 10 min, the fluidity at the time of molding the cable is poor. If the MI exceeds 5.0 g / 10 min, the fluidity becomes too large, the liquid tends to sag, and molding becomes difficult.

The reason for using high-pressure radically polymerized polyethylene is that it has long chain branches in the molecule, has good fluidity, and has good extrudability. In addition, the compounding ratio is 95/5 to 50 /
The reason for limiting the amount to 50 parts by weight is that if the high-pressure radially polymerized polyethylene is less than 5 parts by weight, there is no effect of improving fluidity, and if 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 reduced. Because it disappears.

The crosslinking method includes dicumyl peroxide, 1.3-bis- (t-butylperoxy-isopropyl) benzene, 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 cross-linking using silanes such as vinyltriethoxysilane and irradiation cross-linking with ionizing radiation such as an electron beam.

Further, additives such as an antioxidant, a lubricant and a coloring agent may be added to the electrical insulating composition of the present invention. The effect of moisture on the bow title tree is extremely large, and a bow title tree is also found in a cable imposed in the air or a cable shielded by a metal sheath or the like.
These are considered to be due to moisture that has permeated from the outside. It goes without saying that the insulator according to the present invention also exerts an effective tree-suppressing effect on such bow title trees.

[0017]

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

(Embodiments) Eight compositions as shown in Table 1 were kneaded with a 22-inch mixing roll to form a sheet, which was pelletized with a pelletizer. Then, the pellets were introduced into an extruder and, as shown in FIG. 1, a 4 mm thick insulating layer was formed on a 60 mm ² soft copper stranded wire 1 together with a 0.7 mm thick inner semiconductive layer 2 and an outer semiconductive layer 4. Extruded as 3. After that, the cable 5 was immediately cross-linked in a dry cross-linking tube using nitrogen gas as a heat medium, and then pressurized and cooled to complete the cable 5 to obtain a sample.

The extrudability, the gel fraction, the number of bow title trees generated, and the AC breakdown voltage of each of these samples were examined. In addition, as for the extrudability, the cable is 14
The extrusion appearance at a 5 ° C. extrusion temperature was checked and judged, and the gel fraction was measured according to JIS-C3005. As an evaluation method of the number of bow title trees generated, the electric wire 5 is immersed in warm water of 90 ° C., and AC3k is applied between the conductor and the water.
After applying V for 500 days, the slice was thinly sliced, stained by boiling in an aqueous methylene blue solution, and the presence or absence and the number of bow title trees (0.2 mm or more) were observed using an optical microscope.
Was examined. Further, as an AC breakdown test, each sample was boosted at a rate of 5 kV / 10 minutes after 17 kV / 10 minutes at room temperature, and its breakdown voltage value was measured.

[0020]

[Table 1]

(Comparative Example) Five kinds of samples were obtained in the same manner as in the examples by using compositions of six kinds as shown in Table 2, and the same evaluation was performed.

[0022]

[Table 2]

As a result, as shown in Table 1, in the examples according to the present invention, excellent extrudability was excellent.
The generation of bow titleeries is very small, and a high AC breakdown voltage is exhibited. On the other hand, in the case of Comparative Example 1 consisting only of polyethylene polymerized with a single-site catalyst, the extrusion moldability was poor, and Comparative Example 2 in which the blending amount of high-pressure polymerized polyethylene was greater than the specified value (5 to 50 parts by weight). In this case, the generation of bow titles is remarkably large and the AC breakdown voltage is low. Further, the density is a specified value of the present invention (density = 0.910 g / cm ^{3 to} 0.945 g / cm ³ ).
Comparative Example 3 using other polyethylene, and MI was the specified value of the present invention (MI = 1.0 g / 10 min to 5.0 g / 10
min), Comparative Examples 5 and 6 have poor extrusion processability. In particular,
In the case of using low-density polyethylene as in Comparative Example 4, many bow titles are generated and the AC breakdown voltage is low.

[0024]

In summary, according to the present invention, even if there are unavoidable defects such as voids and foreign substances in the insulator, the occurrence 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 exhibit an excellent effect such as that it is possible to contribute to the weight reduction of the power cable by making the insulating layer thinner.

[Brief description of the drawings]

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01B 3/16-3/56

Claims (3)

(57) [Claims] 1. A polymer obtained by using a single-site catalyst and having a density of 0.910 to 0.945 g / cm ³ and an MI of 0.5 to
5.0 g / 10 min polyethylene and density 0.91
An electrical insulating composition comprising a high pressure radically polymerized polyethylene of 0 to 0.945 g / cm ³ in a range of 95/5 parts by weight to 50/50 parts by weight. 2. An electric wire or cable comprising an insulating layer comprising the electrical insulating composition according to claim 1 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.