JP3229638B2 - High insulator made of ethylene copolymer 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 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 the insulating material, a method has been proposed in which maleic anhydride is grafted to low-pressure polyethylene (for example, Japanese Patent Application Laid-Open No. 2-10610). 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.

[0003]

SUMMARY OF THE INVENTION The present invention has been intensively studied in view of the above problems, and as a result, it has been found that ethylene and a small amount of dibasic anhydride are copolymerized by a high pressure radical polymerization method, By graft copolymerizing a small amount of dibasic acid anhydride, the electric insulation resistance characteristics have been greatly improved without increasing the dielectric loss tangent, and the first object is to have an extremely high electric insulation resistance. A second object of the present invention is to provide a high-insulation material made of an ethylene copolymer, and a second object of the invention is to provide a high-voltage power cable having an extremely high electric insulation resistance using the same.

[0004]

The first invention of the present invention relates to a copolymer of ethylene and dibasic anhydride obtained by a high-pressure radical polymerization method or a low-density polyethylene obtained by a high-pressure radical polymerization method. A copolymer obtained by grafting a dibasic acid anhydride to a dibasic acid anhydride group 0.0
An inner semiconductive layer and / or an outer layer made of an ethylene copolymer containing at least 02% by weight and less than 0.05% by weight and having an improved dielectric tangent characteristic of a dielectric loss tangent of 5 × 10 ⁻⁴ or less;
It is a high insulator for a high voltage power cable having an insulating layer together with a semiconductive layer .

The second invention of the present invention relates to a copolymer of substantially ethylene and a dibasic anhydride obtained by a high-pressure radical polymerization method or a low-density polyethylene obtained by a high-pressure radical polymerization method to a dibasic acid anhydride. Which is an ethylene copolymer containing 0.002% by weight or more and less than 0.05% by weight of dibasic acid anhydride groups, having a dielectric loss tangent of 5 × 10 ⁻⁴ or less and an electrical insulation resistance of among the characterized by using an improved high-insulation characteristic as an insulator
An insulating layer together with a part semiconductive layer and / or an outer semiconductive layer.
High-voltage power cable. Hereinafter, the present invention will be described in detail.

The ethylene copolymer for forming a high insulator according to the first invention of the present invention is defined as having a dibasic acid anhydride group content of 0.002% by weight or more. An ethylene copolymer obtained by a high-pressure radical polymerization method containing less than 05% by weight, wherein a dibasic acid anhydride and ethylene are copolymerized by high-pressure radical polymerization, It is an ethylene copolymer having a dibasic acid anhydride group introduced by graft copolymerization of an acid anhydride.

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.

Specific examples of the ethylene copolymer containing a dibasic acid anhydride group of the present invention include ethylene / maleic anhydride copolymer, ethylene / itaconic anhydride copolymer, ethylene / hymic anhydride copolymer. , Ethylene / methyl maleic anhydride copolymer, ethylene / dimethyl maleic anhydride copolymer, ethylene / phenyl maleic anhydride copolymer, ethylene / diphenyl maleic anhydride copolymer, ethylene / chloromaleic anhydride copolymer , Ethylene / dichloromaleic anhydride copolymer, ethylene / fluoromaleic anhydride copolymer, ethylene / difluoromaleic anhydride copolymer, ethylene / bromomaleic anhydride copolymer, ethylene / dibromomaleic anhydride copolymer And the like.

In copolymerizing the above dibasic acid anhydride with ethylene, a small amount of another unsaturated monomer can be further copolymerized if necessary. Examples of the other unsaturated monomer include olefins such as propylene, butene-1, hexene-1, decene-1, octene-1, and styrene.

In the high-pressure radical polymerization method, for example, ethylene is used in an amount of 99.95 to 99.998% by weight, and a dibasic acid anhydride is used in an amount of 0.9%.
002-0.05% by weight of the mixture are subjected to a polymerization pressure of 500-4000 kg / cm in the presence of 0.0001-1% by weight, based on the total weight of their total monomers, of a radical polymerization initiator.
^{2. The} monomers are contacted and polymerized simultaneously or stepwise in a tank-type or tube-type reactor in the presence of a chain transfer agent and, if necessary, an auxiliary agent, preferably at 100 to 350 ° C. Is the way. The low-density polyethylene obtained by polymerization by the high-pressure radical polymerization method of graft-copolymerizing the dibasic acid anhydride used in the present invention is a low-density polyethylene produced mainly by ethylene and polymerized by the high-pressure radical polymerization method described above. is there.

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 toluene, diethylbenzene and xylene.

In the present invention, a grafting method for graft copolymerizing a dibasic acid anhydride with a high-pressure radical polymerization method low-density polyethylene includes a method using a crosslinking agent such as an organic peroxide or a dicumyl compound, an electron beam, a β The irradiation can be performed by a generally well-known method such as a method of irradiating high-energy radiation such as X-rays or γ-rays. For example, a method in which a high-pressure radical polymerization method low-density polyethylene and a dibasic acid anhydride are reacted under melt-kneading using a crosslinking agent such as an organic peroxide, etc., a high-pressure radical polymerization method low-density polyethylene and a dibasic acid anhydride. A method of dissolving a radical reaction initiator such as an organic oxide in an appropriate solvent and performing a graft reaction in a solution state, dispersing the polymer in water, supplying a dibasic acid anhydride and a reaction initiator And various methods such as a method of performing a graft reaction. However, the melt-kneading method is preferred from the viewpoint of practicality.

It is important that the content of the dibasic anhydride group in the ethylene copolymer of the present invention contains 0.002 to less than 0.05% by weight. When the content of the dibasic acid anhydride group is 0.
When the content is less than 002% by weight, the effect of improving the insulation resistance is small, and when the content is more than 0.05% by weight, a material having a high insulation resistance can be obtained, but the dielectric loss tangent (tan δ) is undesirably increased. The dielectric loss tangent value monotonically increases with an increase in the amount of dibasic acid anhydride. In order to use it as an insulating material for power cables, the dielectric loss tangent should be at most 5 × 10 ^-4
It is desirable that the content is not more than the above, and therefore, the amount of the dibasic anhydride is limited to 0.05% by weight or less.

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

The ethylene copolymer of the present invention described above is used not only as an insulating layer of ordinary electric wires and power cables, but also alone or blended with other synthetic resins, rubbers, etc. to form films or sheets, Processed into tapes, yarns and the like, laminated with other substrates as necessary, and used for insulating films and sheets, insulating tapes, insulating covers, insulating garments and the like.

The power cable according to the second invention of the present invention is formed by winding an internal semiconductive layer and / or an external semiconductive layer by extrusion, or an external metal shielding layer of copper, aluminum, lead or the like, or an aluminum tape or the like as required. It has an insulating layer made of the above-mentioned ethylene copolymer 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.

[0020]

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 7 and Comparative Examples 1 to 3) Ethylene copolymers having different dibasic acid anhydride contents (Examples 1 to 7, Comparative Examples 2 to 7)
3) As Comparative Example 1, density, MI, maleic anhydride concentration of high-pressure radical method low-density polyethylene (trade name: Nisseki Lexlon W2000, manufactured by Nippon Petrochemical Co., Ltd.), and insulation resistance (volume resistivity) as electrical characteristics ) And dielectric loss tangent (tan δ) are summarized in Table 1 below. Example 8 A sheet (15 cm × 15 cm) having a sample thickness of 0.3 mm was formed using the maleic anhydride-grafted ethylene copolymer used in Example 2, and an EPS manufactured by Nissin High Voltage Co., Ltd. Crosslinking was carried out by irradiating an electron beam with 15 Mrad in air using -750. Gel fraction (sample 20
(Referred to as a residual ratio after grinding to ~ 35 mesh and extracting with xylene) was 80%. The insulation resistance (volume specific resistance) is 6.0 × 10 ¹⁸ Ω · cm, and the dielectric loss tangent (tan δ) is 1.
It was 6 × 10 ^-4 .

Measurement method of insulation resistance (volume resistivity) and dielectric loss tangent (tan δ): insulation resistance (volume resistivity); 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.

[0022]

[Table 1]

[0023]

As described above, the ethylene-dibasic anhydride copolymer polymerized by the high-pressure radical polymerization method of the present invention or the ethylene obtained by grafting the dibasic anhydride to the low-density polyethylene obtained by the high-pressure radical polymerization method The high-insulator made of a copolymer contains a small amount of dibasic acid anhydride, which has the effect of dramatically increasing the electrical insulation resistance without increasing the dielectric loss tangent, and is used as an insulation layer for power cables. In this case, 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 (56) References JP-A-61-53611 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 3/44 H01B 7/02 H01B 9/00 C08L 23/26

Claims (2)

(57) [Claims] 1. A copolymer of substantially ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method or a copolymer obtained by grafting a dibasic acid anhydride to low-density polyethylene obtained by a high-pressure radical polymerization method Comprising an ethylene copolymer containing 0.002% by weight or more and less than 0.05% by weight of a dibasic acid anhydride group,
^-4 or less , the inner semiconductive layer and
High-voltage with insulating layer together with and / or outer semiconductive layer
High insulation for power cables . 2. A copolymer of substantially ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method or a copolymer obtained by grafting a dibasic acid anhydride to low-density polyethylene obtained by a high-pressure radical polymerization method Comprising an ethylene copolymer containing 0.002% by weight or more and less than 0.05% by weight of a dibasic acid anhydride group,
Inner semiconducting layer, characterized in that it uses ^-4 with improved electrical insulation resistance properties below the high insulator as an insulator and / or
Or a high-voltage power cable having an insulating layer together with an outer semiconductive layer .