JPH10106353A - Insulating composition for high voltage electric power cable and high voltage electric power cable using the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition having high electric strength and excellent electric insulating property by using polyethylene, which is produced by using a metallocene catalyst, as a base polymer of an insulating layer of a high voltage electric power cable. SOLUTION: An insulating composition for an electric power cable for high voltage not lower than 6.6kV is produced by adding polyethylene produced by polymerization using a metallocene catalyst and a cross-linking agent. As the cross-linking agent, dicumyl peroxide is preferably used. The metallocene used as a catalyst is a general term for non-electrolytic complexes of bis(cyclopentadienyl) metal compounds and molecules with a sandwich structure comprising two paralleled cyclopentadienyl rings with right pentagonal shape on the opposite to each other and sandwiching a metal atom between them and the metallocene is expressed with a formula as a representative. The metallocene catalyst is soluble in a solvent and polymerization reaction can be carried out in the solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved crosslinked polyethylene insulated power cable. More specifically, the present invention relates to an insulating composition for a high-voltage power cable capable of providing an insulating layer having excellent electrical insulation properties, and a high-voltage power cable of 6.6 kV or higher having an insulating layer obtained from the composition.

[0002]

2. Description of the Related Art At present, as a polyethylene used as a base polymer of an insulating layer of a power cable, a low-density polyethylene manufactured by a high-pressure method is generally used. However, since the high-pressure method is a gas phase polymerization, the resulting polyethylene has variations in molecular weight, branched structure, crystal structure, and the like, and the crosslinked structure is heterogeneous.
Therefore, the insulating layer using high-pressure low-density polyethylene as a base polymer has a portion that is locally an electrical weak point.

The insulating layer is formed by extruding a composition containing low-density polyethylene, an organic peroxide as a crosslinking agent and an antioxidant such as a hindered phenol type on a conductor,
Crosslink by heating to 60-240 ° C. Further, the insulating layer near the cable connection portion is also capable of forming a 160 to 2
Heat again to 40 ° C. As described above, since the power cable is subjected to a heating condition during manufacture and connection, alcohol which is a decomposition residue of the cross-linking agent present in the insulating layer, for example, when dicumyl peroxide is used as the cross-linking agent, dichyl peroxide is used. There was a problem that mill alcohol caused a dehydration reaction by heat, increasing the amount of water in the insulating layer, and deteriorating its electrical insulation performance. Problems such as the presence of local electrical weaknesses in the insulating layer and the presence of a large amount of moisture in the insulating layer are particularly problematic when used as an insulating layer in high-voltage power cables of 6.6 kV or higher. .

An object of the present invention is to solve the above-mentioned drawbacks of the high-pressure process low-density polyethylene and to provide a high-pressure insulating layer which can be suitably used as an insulating layer of a high-voltage power cable. An object of the present invention is to provide an insulating composition for a power cable. Another object of the present invention is to provide a high voltage power cable of 6.6 kV or more having an insulating layer having excellent insulating performance.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, when polyethylene produced using a metallocene catalyst is used as a base polymer of an insulating layer, Have been achieved, and the present invention has been completed.

That is, the present invention provides (1) an insulating composition for a high-voltage power cable of 6.6 kV or more containing a polyethylene obtained by polymerization using a metallocene catalyst and a crosslinking agent, and (2) a dicumyl peroxide as a crosslinking agent. (3) the insulating composition for a high-voltage power cable according to the above (1),
(4) a high-voltage power cable of 6.6 kV or more including an insulating layer produced from an insulating composition containing polyethylene and a cross-linking agent obtained by polymerization using a metallocene catalyst;
(5) the high-voltage power cable according to the above (3), wherein the crosslinking agent is dicumyl peroxide; (5) the high-voltage power cable according to the above (3), further comprising an inner semiconductive layer and / or an outer semiconductive layer; ) The crosslinker used in the production of the inner and / or outer semiconductive layer is [1,3-
The high-voltage power cable according to the above (5), which is bis (t-butylperoxyisopropyl) -benzene] or [2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3].

[0007]

DETAILED DESCRIPTION OF THE INVENTION The polyethylene used in the present invention is a polyethylene polymerized with a metallocene catalyst. Metallocene is a bis (cyclopentadienyl) metal compound, a non-electrolyte complex, in which two cyclopentadienyl rings have a regular pentagonal structure and are parallel to each other, with a metal atom sandwiched between them. It is a generic term for molecules consisting of sandwiched molecules. As a typical example, the following formula

[0008]

Embedded image

Wherein M represents a metal, for example, Zr,
Ti, Vi, Cr, Fe, Co, Ni, Ru, Pd, etc.
Among them, Zr is preferable from the viewpoint of polymerization uniformity, Hal represents halogen, and particularly preferably Cl from the viewpoint of polymerization uniformity.

[0010]

Embedded image

Wherein M and Hal are as defined above, and (C) is added to the five-membered ring of these compounds.
H _{3) 2} CH- alkyl group or the like, and the like have been substituted.

The metallocene catalyst used in the present invention has a steric structure as described above. Ethylene gas (raw material gas) is sterically blocked by a substituent bonded to a 5-membered ring bonded to a metal. Since the contact cannot be made from a certain direction, the metal and the monomer come into contact with each other from a certain direction, and stereoregular polymerization occurs. Therefore, the molecular weight, branched structure and crystal structure of the obtained polyethylene become constant. Further, since the metallocene catalyst is soluble in the solvent, the polymerization reaction can be performed in the solvent (homogeneous system).

The polyethylene used in the present invention has a melt flow rate (MFR) [190 ° C., 2.16 kg (J
IS K 6760)], preferably 0.1 to 20 g / 10 min, more preferably 1.0 to 1 g / min.
0 g / 10 minutes. The density (value specified in JIS K 6760) is preferably 0.914 to 0.924 g /
cm ³ , more preferably 0.918 to 0.922 g /
cm ³ . Further, the molecular weight distribution and Mw (weight average molecular weight) / Mn (number average molecular weight) are preferably 1 to 20, and more preferably 1 to 10.

The cross-linking agent to be used can be used without any particular limitation as long as it is generally used in a polyethylene resin composition as an insulator material of a cable. For example, dicumyl peroxide, [1,3-bis (t-butylperoxyisopropyl) -benzene], [2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-
3]. Preferred crosslinkers include dicumyl peroxide. The amount of the crosslinking agent is appropriately determined depending on the purpose of use of the obtained insulator and is not particularly limited, but is preferably 0.5 to 2.5 parts by weight, more preferably 0.8 to 2.5 parts by weight based on 100 parts by weight of polyethylene.
1.5 parts by weight.

Further, if necessary, antioxidants, lubricants such as higher fatty acids and metal salts, processing aids such as higher fatty acid amides, organic and inorganic pigments, fillers such as silica and clay,
Additives such as stabilizers, copper harm inhibitors such as amides and hydrazides, ultraviolet inhibitors such as benzophenones and benzoins, and polyfunctional crosslinking assistants can also be added.

As the antioxidant, any one can be used without particular limitation as long as it is generally used for an insulator of a cable.
For example, 4,4'-thiobis (6-tert-butyl-
3-methylphenol, 2,2′-methylenebis (4-
Hindered phenol-type antioxidants such as ethyl-6-tert-butylphenol, amine-type antioxidants, thioether-type antioxidants and the like can be mentioned. Among them, hindered antioxidants are preferred.

Further, in order to mitigate a drastic change of an electric field generated between the conductor / insulating layer and between the insulating layer / sheath, an inner semiconductive layer is provided around the conductor and / or an outer semiconductive layer is provided around the insulating layer. Is preferred. Examples of the base polymer constituting the inner and outer semiconductive layers include styrene-butadiene-based thermoplastic elastomer, polyester-based thermoplastic elastomer, ethylene-vinyl acetate copolymer (EVA), ethylene-ethyl acrylate copolymer (EEA), Soft polyolefins such as ethylene-methyl acrylate copolymer (EMA),
EP rubber and butyl rubber are exemplified. A conductive carbon black and a crosslinking agent are added thereto.

Examples of the crosslinking agent include dicumyl peroxide, [1,3-bis (t-butylperoxyisopropyl) -benzene], [2,5-dimethyl-2,5
-Di (t-butylperoxy) -hexyne-3] and the like.

As the conductive carbon black, acetylene black is mainly used. The amount used is preferably from 10 to 80 parts by weight, more preferably from 40 to 60 parts by weight, based on 100 parts by weight of the base polymer. The amount of the crosslinking agent is preferably from 1.0 to 3.0 parts by weight, more preferably from 1.5 to 2.0 parts by weight, based on 100 parts by weight of the base polymer.
0 parts by weight.

In the composition for forming the above-mentioned semiconductive layer, in addition to the above-mentioned components, graphite, a lubricant, a filler, a metal fine powder, a stabilizer, an antioxidant, a crosslinking aid, a processing aid Agents and the like may be blended.

[0021] The insulating composition of the present invention is particularly suitable for use at a pressure of 6.6 kV.
It is preferably used as an insulating layer of the above high voltage power cable.

The method for manufacturing the power cable of the present invention is not particularly limited, and is manufactured by a method known per se. For example, a composition for forming an internal semiconductive layer on a conductor, an insulating composition for forming an insulating layer, and a composition for forming an external semiconductive layer are formed by continuously extruding each layer with an extruder, and thereafter, At a temperature of 160 to 240 ° C. for crosslinking.

The crosslinking agent used for the insulating layer is dicumyl peroxide, and the crosslinking agent used for the inner and / or outer semiconductive layer is [1,3-bis (t-butylperoxyisopropyl)- High-voltage power cables having a layer of [benzene] or [2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3] are particularly preferred in terms of electrical strength and degree of crosslinking.

[0024]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 An insulating composition for forming an insulating layer containing 100 parts by weight of metallocene polyethylene (Kernel 54FT, manufactured by Mitsubishi Chemical Corporation) and 1.0 part by weight of dicumyl peroxide (Park Mill D, Nippon Oil & Fats Co., Ltd.) , 100 parts by weight of ethylene-vinyl acetate copolymer (Evaflex P1207, manufactured by DuPont Mitsui Polychemicals), 60 parts by weight of acetylene black (manufactured by Denki Kagaku), a crosslinking agent [1,3-bis (t-butylperoxyisopropyl) ) -Benzene]
(Parkadox 14, manufactured by Kayaku Nury Co.) 1.2 parts by weight of a composition for forming internal and external semiconductive layers,
After continuous extrusion coating to a thickness of 1 mm on a copper stranded wire conductor (diameter: 2 mm) by a 30 mmφ extruder, it was crosslinked at 180 ° C. to obtain a power cable.

Example 2 Metallocene polyethylene (kernel 54FT) 100
Parts by weight and dicumyl peroxide (Park Mill D)
2.5 parts by weight of an insulating composition for forming an insulating layer and 100 parts by weight of ethylene-ethyl acrylate copolymer (Evaflex EEA A-707, manufactured by DuPont Mitsui Polychemicals) and acetylene black (manufactured by Denki Kagaku) 60 parts by weight, a crosslinking agent [2,5-dimethyl-2,5-
Di (t-butylperoxy) -hexyne-3] (Kayahexa YD, manufactured by Kayaku Nuuri Co., Ltd.) was used as an internal and external semiconductive layer by using a 30 mmφ extruder to form a copper stranded wire conductor ( (Diameter: 2 mm), and then continuously extrusion-coated to a thickness of 1 mm, followed by crosslinking at 180 ° C to obtain a power cable.

Comparative Example 1 A power cable was obtained in the same manner as in Example 2 except that a low-density polyethylene produced by a high-pressure method (ZF-33, manufactured by Mitsubishi Chemical Corporation) was used.

With respect to the cables obtained in Examples 1 to 3 and Comparative Example 1, the gel fraction, the water content and the AC withstand voltage were measured. Gel fraction (% by weight): Measured according to JIS C 3005. ：: 80% by weight or more ×: Less than 80% by weight Water content (ppm): Using a Karl Fischer moisture meter, 1 g of a sample was cut out from the surface of the insulating layer 1 mm from the inside, and the water content was measured. ：: 200 ppm or more ×: less than 200 ppm AC withstand voltage (kV / mm): Measured in accordance with JIS C 3005. ：: 30 kV / mm or more ×: less than 30 kV / mm The results are shown in Table 1.

[0029]

[Table 1]

[0030]

The metallocene catalyst is a conventional Ziegler catalyst.
Unlike the Natta catalyst, it is soluble in a solvent, so that the polymerization reaction can be performed in the solvent (homogeneous system). The polyethylene obtained in a homogeneous system is different in the molecular weight, the branched structure, the crystal structure, and the like from those produced by the high-pressure method. Accordingly, the insulating layer has extremely few local electric weak points as compared with the related art, so that the insulating layer has extremely excellent electric strength. In addition, since the cross-linking occurs efficiently, the amount of the cross-linking agent used to obtain the desired degree of cross-linking can be significantly reduced. Therefore, the amount of the decomposition residue of the crosslinking agent is reduced, and the amount of water generated in the insulating layer during the crosslinking reaction is reduced. That is, the insulating layer has a reduced insulating performance.
That is, the insulating composition of the present invention comprising polyethylene polymerized with a metallocene catalyst as a constituent component provides an insulating layer that is extremely excellent in electric strength and insulating performance, and thus can be suitably used as an insulating layer of a high-voltage power cable. sell.

Claims (6)

[Claims] 1. An insulating composition for a high-voltage power cable of 6.6 kV or more, comprising polyethylene and a crosslinking agent obtained by polymerization using a metallocene catalyst. 2. The insulating composition for a high-voltage power cable according to claim 1, wherein the crosslinking agent is dicumyl peroxide. 3. A high-voltage power cable of 6.6 kV or more comprising an insulating layer produced from an insulating composition containing polyethylene obtained by polymerization using a metallocene catalyst and a crosslinking agent. 4. The high-voltage power cable according to claim 3, wherein the crosslinking agent is dicumyl peroxide. 5. The high-voltage power cable according to claim 3, further comprising an inner semiconductive layer and / or an outer semiconductive layer. 6. The crosslinking agent used in the inner semiconductive layer and / or the outer semiconductive layer is [1,3-bis (t-butylperoxyisopropyl) -benzene] or [2,5
-Dimethyl-2,5-di (t-butylperoxy) -hexyne-3].