JPH10106356A - Insulating composition for electric power cable and 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 adding polyethylene produced by using a metallocene catalyst, dicumylperoxide, and a heat radiation-suppressing agent. SOLUTION: An insulating composition for an electric power cable is produced by adding polyethylene produced by polymerization using a metallocene catalyst, dicumylperoxide as a cross-linking agent, and a heat radiation suppressing agent. The heat radiation suppressing agent is a compound selected from fatty acids with 14-28 carbons, alkaline earth metal salts and their amides, saturated alkanes with 3000 or lower molecular weight. The addition amount of the heat radiation suppressing agent is preferably 0.1-5.0 pts.wt. to 100 pts.wt. of base polymer in the case the and a high temperature decomposable cross- linking agent selected from fatty acids and alkaline earth metals. A problem that the polymer is over-heated and decomposition of dicumylperoxide is started in an extruder can be solved by using the heat radiation suppressing agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a power cable having an insulating layer based on polyethylene obtained by polymerization using a metallocene catalyst. More specifically, the present invention relates to an insulating composition capable of providing an insulating layer having excellent electric insulation performance and a power cable having an insulating layer obtained from the composition.

[0002]

2. Description of the Related Art Polyethylene polymerized by a metallocene catalyst is used as a base polymer of a cross-linked insulating layer of a power cable, instead of polyethylene conventionally produced by a high-pressure method using a Ziegler-Natta catalyst. Has been proposed by the present inventors. Unlike the conventional Ziegler-Natta catalyst, the metallocene catalyst is soluble in a solvent, so that the polymerization reaction can be performed in the solvent (homogeneous system). Therefore, the obtained polyethylene has a homogeneous molecular weight, a branched structure, a crystal structure, and the like, and the insulating layer obtained from such a polyethylene has excellent electric strength with few local electric weak points. In addition, since the cross-linking occurs efficiently, the amount of the cross-linking agent can be greatly reduced. Therefore, the amount of the crosslinking agent decomposition residue in the insulating layer 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.

[0003]

However, in order to extrude an insulating composition containing polyethylene and dicumyl peroxide obtained using the above-mentioned metallocene catalyst onto a conductor, when kneading in an extruder, high pressure is applied. In the case of polyethylene obtained by the method, the temperature in the extruder only rises to at most 130 ° C., but polyethylene polymerized using a metallocene catalyst rises to 140 to 150 ° C. The present inventors have found for the first time that there is a problem that peroxide starts to decompose.

An object of the present invention is to solve the above-mentioned drawbacks of polyethylene obtained by using a metallocene catalyst, and to provide an insulating composition capable of providing an insulating layer having better electric insulating properties. . Another object of the present invention is
An object of the present invention is to provide a power cable having an insulating layer having excellent insulation performance.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that the above object can be attained when a heat generation inhibitor is added to an insulating composition. Thus, the present invention has been completed.

That is, the present invention provides (1) an insulating composition for a power cable containing polyethylene, dicumyl peroxide and a heat generation inhibitor obtained by polymerization using a metallocene catalyst; The insulating composition for a power cable according to the above (1), which is a compound selected from the group consisting of a fatty acid of 14 to 24, an alkaline earth metal salt thereof and an amide thereof, and a saturated alkane having a weight average molecular weight of 3,000 or less. (3) a power cable including an insulating layer manufactured from an insulating composition containing polyethylene, dicumyl peroxide and a heat generation inhibitor obtained by polymerization using a metallocene catalyst; and (4) the heat generation inhibitor having 14 carbon atoms. To 24 fatty acids, alkaline earth metal salts and amides thereof, and a weight average molecular weight of 3000
The power cable according to the above (3), which is a compound selected from the group consisting of the following saturated alkanes: (5)
The power cable according to the above (3), comprising an inner semiconductive layer and / or an outer semiconductive layer, and (6) a crosslinking agent used for the inner semiconductive layer and / or the outer semiconductive layer,
[1,3-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]

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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]

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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 (source gas) is sterically blocked by a substituent bonded to a five-membered ring bonded to a metal atom. Since the contact cannot be made from a certain direction, the metal and the monomer always come into contact from a certain direction, stereoregular polymerization occurs, and 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 crosslinking agent used is dicumyl peroxide. The amount of dicumyl peroxide is appropriately determined depending on the intended use of the resulting insulator and is not particularly limited, but is preferably 0.5 to 2.5 parts by weight, more preferably 1.50 parts by weight, based on 100 parts by weight of polyethylene. 0 to
2.0 parts by weight.

Polyethylene polymerized using a metallocene catalyst has a higher frictional heat with a screw than polyethylene obtained by a high-pressure method, so that the temperature in the extruder becomes high. Therefore, dicumyl peroxide, a cross-linking agent that has been conventionally used, partially decomposes, and the electrical properties of the obtained insulating layer,
Heat resistance is reduced. Therefore, an exothermic inhibitor is added to reduce the frictional heat and suppress the heat generation in the extruder. As the heat release inhibitor, any material can be used as long as it has a property of reducing frictional heat between the polyethylene and the screw in the extruder. For example, carbon number 14-24
Fatty acids, alkaline earth metal salts thereof, and having 14 to 24 carbon atoms
And saturated alkanes having a weight average molecular weight of 3000 or less. Specifically, examples of the fatty acid having 14 to 24 carbon atoms include stearic acid, oleic acid, palmitic acid, linoleic acid, linolenic acid, and the like. Examples of the alkaline earth metal include zinc salts, calcium salts, and magnesium salts of the above-mentioned fatty acids. The amides of the fatty acids having 14 to 24 carbon atoms include the amides of the above-described fatty acids. Weight average molecular weight of 30
AC polyethylene as a saturated alkane of 00 or less,
Micro wax, paraffin wax, liquid paraffin and the like can be mentioned.

The amount of the heat generation inhibitor is not particularly limited,
In the case of a fatty acid and its alkaline earth metal, it is preferably 0.1 to 5.0 parts by weight, more preferably 1.0 to 5.0 parts by weight, based on 100 parts by weight of the base polymer.
In the case of an amide of a fatty acid, the amount is preferably 0.01 to 3.0 parts by weight, more preferably 0.03 to 1.0 part by weight, based on 100 parts by weight of the base polymer. In the case of a saturated alkane, It is preferably 0.5 to 10 parts by weight, more preferably 1.10 parts by weight, based on 100 parts by weight of the base polymer.
0 to 3.0 parts by weight.

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.

Any antioxidant can be used without particular limitation as long as it is commonly used for cable insulators.
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 reduce a drastic change of an electric field generated between the conductor / insulating layer and 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 [1,3-bis (t-butylperoxyisopropyl) -benzene],
[2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3] and the like are used.

Acetylene black is mainly used as the conductive carbon black. The amount is preferably 10 to 80 parts by weight, more preferably 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 100 parts by weight of the base polymer.
3.0 parts by weight, more preferably 1.5 to 2.0 parts by weight.

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

The method for manufacturing the power cable of the present invention is not particularly limited, and the power cable 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)- 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.

[0025]

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 Insulation containing 100 parts by weight of metallocene polyethylene (Kernel 54FT, manufactured by Mitsubishi Chemical Corporation), 0.5 parts by weight of dicumyl peroxide (Park Mill D, manufactured by NOF Corporation) and 2 parts by weight of stearic acid Insulating composition for forming layer and ethylene-vinyl acetate copolymer (Evaflex P1207, manufactured by DuPont Mitsui Polychemicals) 100
60 parts by weight of acetylene black (manufactured by Denki Kagaku Co., Ltd.), and [1,3-bis (t-butylperoxyisopropyl) -benzene] (Percadox 14,
1.2 parts by weight of a composition for forming the inner and outer semiconductive layers, which were compounded in an amount of 1.2 parts by weight, were continuously extruded to a thickness of 1 mm on a copper stranded conductor (diameter: 2 mm) by a 30 mmφ extruder. Thereafter, crosslinking was performed at 180 ° C. to obtain a power cable.

Example 2 Metallocene polyethylene (kernel 54FT) 100
Parts by weight, 2.0 parts by weight of Parkmill D and a molecular weight of 360
An insulating composition for forming an insulating layer containing 5 parts by weight of paraffin of about 500 to 500 parts by weight of ethylene-ethyl acrylate copolymer (Evaflex EEA A-707, manufactured by DuPont-Mitsui Polychemicals) and acetylene black (electrochemical 60 parts by weight, a crosslinking agent [2,5
-Dimethyl-2,5-di (t-butylperoxy) -hexyne-3] (Kayahexa YD, manufactured by Kayaku Nuuri)
1.2 parts by weight of the mixture was used as an inner and outer semiconductive layer by a 30 mmφ extruder using a copper stranded conductor (diameter: 2 m).
m) was continuously extruded and coated to a thickness of 1 mm, and then crosslinked at 180 ° C. to obtain a power cable.

Comparative Example 1 An insulating layer containing 100 parts by weight of high-pressure low-density polyethylene (ZF-33, manufactured by Mitsubishi Chemical Corporation), 0.5 parts by weight of dicumyl peroxide (Parkmill D) and 2 parts by weight of stearic acid was used. An insulating composition to be made and an ethylene-ethyl acrylate copolymer (Evaflex EEA A-7)
07) 60 parts by weight of acetylene black (manufactured by Denki Kagaku) and 1.2 parts by weight of Kayahexa YD as a cross-linking agent were mixed with 100 parts by weight as inner and outer semiconductive layers.
After continuous extrusion coating to a thickness of 1 mm on a copper stranded wire conductor (diameter: 2 mm) by a 0 mmφ extruder, crosslinking was performed at 180 ° C.
Got the power cable.

Comparative Example 2 A power cable was obtained in the same manner as in Example 1 except that no heat generation inhibitor was used.

With respect to the cables obtained in Examples 1 and 2 and Comparative Examples 1 and 2, 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.

[0031]

[Table 1]

[0032]

As described above, the insulating composition of the present invention has a problem that decomposition of dicumyl peroxide starts due to an excessive rise in the temperature of the polymer in an extruder of a low-density polyethylene polymerized using a metallocene catalyst. It is possible to provide an insulating layer which has solved the above and makes full use of the advantages of the polyethylene, has excellent electric strength, and is capable of suppressing a decrease in insulating performance.

Claims (6)

[Claims] 1. An insulating composition for power cables, comprising polyethylene, dicumyl peroxide and a heat generation inhibitor obtained by polymerization using a metallocene catalyst. 2. The heat generation inhibitor is a compound selected from the group consisting of fatty acids having 14 to 24 carbon atoms, alkaline earth metal salts and amides thereof, and saturated alkanes having a weight average molecular weight of 3000 or less. The insulating composition for a power cable according to the above. 3. A power cable including an insulating layer manufactured from an insulating composition containing polyethylene, dicumyl peroxide, and a heat generation inhibitor obtained by polymerization using a metallocene catalyst. 4. The exothermic inhibitor is a compound selected from the group consisting of fatty acids having 14 to 24 carbon atoms, alkaline earth metal salts and amides thereof, and saturated alkanes having a weight average molecular weight of 3000 or less. The described power cable. 5. The 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].