JP3195027B2 - High insulator made of ethylene copolymer composition and power cable using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high insulator made of an ethylene copolymer composition having excellent high voltage characteristics and workability, and a high-voltage power cable using the same.

[0002]

2. Description of the Related Art Conventionally, high-pressure polyethylene and cross-linked polyethylene have been widely used as insulators for high-voltage power cables because of their excellent electrical properties. One of the problems with high-voltage power cables is power loss during high-voltage transmission, and reducing this is an important issue. One means for reducing the power loss can be achieved by increasing the high voltage characteristics of the insulating material, particularly the electrical insulation resistance.

As a method for improving the high voltage characteristics of an insulating material, a method has been proposed in which maleic anhydride is grafted onto low-pressure polyethylene (see, for example, JP-A-2-10610).
No.). However, when a low-pressure polyethylene is used as an insulator for a high-voltage power cable, there is a problem in that a metal compound which is inferior to the high-pressure polyethylene and has a bad effect on electric characteristics as a catalyst residue remains.
Further, there has been proposed a power cable having an insulating layer of a composition in which 2 to 40 parts by weight of a maleic anhydride grafted polyethylene having a maleic anhydride grafting amount of 0.5 to 10% by weight is mixed with 100 parts by weight of polyethylene ( JP 63
-150811).

[0004]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and as a result of diligent studies, it has been found that low-density polyethylene obtained by a high-pressure radical polymerization method and ethylene having a specific amount By blending a copolymer containing a dibasic acid anhydride group in a specific range with an insulator, it is possible to prevent an increase in the dielectric loss tangent and without lowering the reliability of the electrical characteristics. The first object of the present invention is to provide a high insulator made of an ethylene copolymer composition having an extremely high electrical insulation resistance. A second object is to provide a high-voltage power cable using the same and having extremely high electric insulation resistance.

[0005]

The first invention of the present invention relates to a low-density polyethylene (A) obtained by a high-pressure radical polymerization method and substantially ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method. 0.002% by weight of dibasic acid anhydride group consisting of 0.05 to 7% by weight of the copolymer (B)
It is a high insulator made of an ethylene copolymer composition containing at least 0.05% by weight.

[0006] The second invention of the present invention relates to a low-density polyethylene (A) obtained by a high-pressure radical polymerization method and 0.05 to 7% by weight of substantially ethylene and dibasic anhydride obtained by a high-pressure radical polymerization method. 0.002% by weight or more and 0.05% by weight of a dibasic acid anhydride group comprising the copolymer (B)
What is claimed is: 1. A power cable, comprising using an ethylene copolymer composition containing less than as an insulator. Hereinafter, the present invention will be described in detail.

The low-density polyethylene (A) and ethylene-dibasic anhydride copolymer (B) obtained by the high-pressure radical polymerization method of the present invention are mainly composed of ethylene and other unsaturated monomers, or mainly The polymerization pressure is 500 to 4000 using ethylene and a dibasic acid anhydride in the presence of 0.0001 to 1% by weight of a radical polymerization initiator based on the total weight of all monomers.
The monomers are simultaneously or stepwise contacted in a tank or tube reactor in the presence of a chain transfer agent and, if necessary, an auxiliary agent, under the conditions of kg / cm ² , preferably 100 to 350 ° C. And low-density polyethylene produced by polymerization.

Examples of the other unsaturated monomers include small amounts of propylene, butene-1, hexene-1, decene-
Olefins such as 1, octene-1, and styrene.

The low-density polyethylene (A) obtained by the high-pressure radical polymerization method of the present invention includes vinyl propionate mainly composed of ethylene produced by the high-pressure radical polymerization method, without departing from the gist of the present invention. Copolymers with vinyl ester monomers such as vinyl acetate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl stearate, ethylene-α, β-unsaturated carboxylic acid copolymer, ethylene-α, β -Unsaturated carboxylic acid ester copolymers, amides, imides and the like may be blended.

Specific examples of the above α, β-unsaturated carboxylic acid or ester include unsaturated carboxylic acids such as acrylic acid and methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate and ethyl methacrylate. , Propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate,
Unsaturated carboxylic acids such as lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, monomethyl maleate, monoethyl maleate, diethyl maleate, monomethyl fumarate, glycidyl acrylate, glycidyl methacrylate Esters can be mentioned.
Of these, alkyl (meth) acrylate is particularly preferred. More preferably, ethyl acrylate can be mentioned. The content of these comonomers is desirably 5% by weight or less to prevent an increase in dielectric loss tangent.

Specific examples of the above copolymer include ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid-ethyl acrylate copolymer , Ethylene-
Examples include vinyl acetate copolymer, ethylene-vinyl acetate-ethyl acrylate copolymer, ethylene-glycidyl methacrylate copolymer, ethylene-glycidyl methacrylate-ethyl acrylate copolymer, and the like. These copolymers may be used as a mixture.

Examples of the radical polymerization initiator include conventional initiators such as peroxides, hydroperoxides, azo compounds, amine oxide compounds, and oxygen.

Examples of the chain transfer agent include hydrogen, propylene, butene-1, C1 to C20 or higher saturated aliphatic hydrocarbons and halogen-substituted hydrocarbons such as methane, ethane, propane, butane, isobutane and n-hexane. , N-heptane, cycloparaffins, chloroform, and carbon tetrachloride, aromatic compounds such as compounds such as toluene, diethylbenzene and xylene.

The ethylene-dibasic acid anhydride copolymer (B) in the present invention is prepared by a high-pressure radical polymerization method. It is an ethylene copolymer obtained by copolymerizing 5% by weight. When the content of the dibasic acid anhydride group is 7% by weight or more, the electrical properties of the composition of the present invention are undesirably deteriorated.

The dibasic acid anhydrides usable in the present invention include maleic anhydride, itaconic anhydride, hymic anhydride, methyl maleic anhydride, dimethyl maleic anhydride,
Phenyl maleic anhydride, diphenyl maleic anhydride,
Examples thereof include chloromaleic anhydride, dichloromaleic anhydride, fluoromaleic anhydride, difluoromaleic anhydride, bromomaleic anhydride, and dibromomaleic anhydride. Of these, maleic anhydride is particularly preferred.

The ethylene copolymer composition according to the first invention of the present invention is a blend of the ethylene-dibasic anhydride copolymer (B) with a low-density polyethylene (A) obtained by a high-pressure radical polymerization method. The ethylene polymer composition has a dibasic acid anhydride group in the composition of not less than 0.002% by weight and less than 0.05% by weight. The content of the dibasic acid anhydride group is 0.002 to 0.05 in the composition.
It is important to include the weight%. When the content of the dibasic acid anhydride group is less than 0.002% by weight, the effect of improving the insulation resistance is small, and when the content is 0.05% by weight or more, a material having a high insulation resistance can be obtained. tanδ)
Is not preferred because of the increase in The dielectric loss tangent value monotonically increases with an increase in the amount of dibasic acid anhydride. The dielectric loss tangent should be at most 5 to be used as an insulation material for power cables.
× 10 ^-4 or less, so that the amount of dibasic anhydride is less than 0.05% by weight, preferably 0.003%.
% By weight or less is desirable.

The density of the ethylene copolymer composition is generally in the range of 0.91 to 0.94 g / cm ³ . In addition, the melt index (hereinafter abbreviated as MI) is 0.05 to 0.05 in consideration of the extrudability of the cable.
10 g / 10 min is desirable.

In order to produce the ethylene copolymer composition of the present invention, first, a low-density polyethylene (A) obtained by a high-pressure radical polymerization method and an ethylene-dibasic acid copolymer (B), if necessary, are crosslinked. Ingredients, additives, etc., and dry-blending them with a normal tumbler or melt kneading with a normal kneading machine such as a Banbury mixer, pressure kneader, kneading extruder, twin-screw extruder, roll, etc. And may be used by being dispersed uniformly, or may be used as it is as an insulating layer of electric wires, power cables and the like.

The above-mentioned ethylene copolymer composition of the present invention is used not only as an insulating layer of ordinary electric wires and electric power cables, but also as a single film or blended with another synthetic resin, rubber or the like. Processed into sheets, tapes, yarns, etc., laminated with other base materials as necessary, and used for insulating films and sheets, insulating tapes, insulating covers, insulating clothing, etc.

The power cable according to the second invention of the present invention is formed by winding an inner semiconductive layer and / or an outer semiconductive layer by extrusion, or an outer metal shielding layer of copper, aluminum, lead or the like, or an aluminum tape or the like, if desired. It has an insulating layer made of the above-mentioned ethylene copolymer composition together with a coating layer usually provided in a power cable such as a turned water-impervious layer.

The insulating layer may be a crosslinked body or an uncrosslinked body. For the crosslinking, a conventional method such as silane crosslinking or electron beam crosslinking can be used in addition to peroxide, dicumyl compound, sulfur and the like.

In the present invention, other synthetic resins, rubbers, antioxidants, and the like can be used without departing from the gist of the present invention.
Conventional additives such as UV inhibitors, pigments, dyes, lubricants, foaming agents, flame retardants, fillers and the like may be added.

[0023]

The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention. (Examples 1 to 5 and Comparative Examples 1 to 4) Ethylene copolymers having different copolymerization amounts of dibasic acid anhydrides (Examples 1 to 5 and Comparative Examples 2 to 4). The density, MI, maleic anhydride concentration, and insulation resistance (volume resistivity) and dielectric loss tangent (tan δ) of the density polyethylene (trade name: Nisseki Lexlon W2000, manufactured by Nippon Petrochemical Co., Ltd.) were measured. Collectively (Table 1)
Shown in

Measurement method of insulation resistance (volume specific resistance) and dielectric loss tangent (tan δ): insulation resistance (volume specific resistance); applied voltage 3 KV, time 10
min. Was measured at a sample thickness of 0.3 mm. Dielectric loss tangent (tan δ); YHP4194A impedance analyzer manufactured by Yokogawa Hewlett-Packard Co., Ltd., sample thickness 1 mm, 100 kHz.

[0025]

[Table 1]

[0026]

As described above, the high insulator comprising the ethylene copolymer composition of the present invention comprises a low-density polyethylene obtained by a high-pressure radical polymerization method and a specific amount of dibasic acid obtained by the high-pressure radical polymerization. By blending with a copolymer obtained by copolymerizing anhydride and using a composition containing a specific range of dibasic anhydride groups as an insulator, the dielectric loss tangent is prevented from increasing and the reliability of electrical characteristics is reduced. Without this, the effect of greatly improving the electrical insulation resistance characteristics is obtained, and when used as an insulating layer of a power cable, power loss during high-voltage power transmission can be reduced without increasing the thickness of the insulating layer.

Continuation of the front page (72) Inventor Junichi Yokoyama 2-25-26 Takafunadai, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-62-225541 (JP, A) JP-A-61-206108 (JP, A) JP-A-62-97206 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 3/44 H01B 7/02 H01B 9/00 C08L 23/08

Claims (2)

(57) [Claims] A low-density polyethylene (A) obtained by a high-pressure radical polymerization method, and substantially ethylene and a dibasic anhydride obtained by a high-pressure radical polymerization method.
A high insulator comprising an ethylene copolymer composition containing 0.002% by weight or more and less than 0.05% by weight of a dibasic acid anhydride group comprising the copolymer (B). 2. A low-density polyethylene (A) obtained by a high-pressure radical polymerization method and substantially ethylene and a dibasic anhydride obtained by a high-pressure radical polymerization method.
An ethylene copolymer composition containing 0.002% by weight or more and less than 0.05% by weight of a dibasic acid anhydride group composed of the copolymer (B) and 1% by weight is used as an insulator. Power cable.