JP3133144B2 - High insulator made of ethylene copolymer or its 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 or a composition thereof excellent in high voltage characteristics and workability, and a high-voltage power cable using the same.

[0002]

2. Description of the Related Art Hitherto, 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 low-pressure polyethylene is used as an insulator for high-voltage power cables, there is a problem that flexibility is inferior to high-pressure radical polymerization polyethylene, metal compounds remain as catalyst residues and adversely affect electrical characteristics. I have. 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-A-63-150811).

[0003]

The present invention has been made in view of the above-mentioned problems, and as a result of intensive studies, it has been found that ethylene, a small amount of dibasic anhydride and a monomer having a specific polar group are produced by a high-pressure radical polymerization method. By using a multi-component random copolymer obtained by copolymerization or a composition of the multi-component random copolymer and another polyolefin, it has been found that the electrical insulation resistance is greatly improved. The first object is to provide an insulator having an extremely high electric insulation resistance, and the second object is to provide a high-voltage power cable using the same having an extremely high electric insulation resistance.

[0004]

According to a first aspect of the present invention, there is provided at least one of a monomer having substantially ethylene and a dibasic acid anhydride and a carbonyl group, a nitrile group and a nitro group obtained by a high-pressure radical polymerization method. A multi-component random copolymer with one or a composition of the multi-component random copolymer and another polyolefin resin, wherein the dibasic anhydride unit in the multi-component random copolymer or the composition is 0.
001-0.05% by weight, and a total amount of an ethylene-based copolymer or a composition thereof comprising 0.002% -0.2% by weight of a dibasic acid anhydride unit and the polar group unit. It is an insulator.

The second invention of the present invention relates to a multi-element randomization of substantially ethylene obtained by a high-pressure radical polymerization method and at least one of dibasic acid anhydride and a monomer having a carbonyl group, a nitrile group and a nitro group. A copolymer or a composition of the multi-component random copolymer and another polyolefin resin, wherein the multi-component random copolymer or the dibasic acid anhydride unit in the composition is 0.001% by weight or more.
An ethylene copolymer or a composition thereof containing 0.05% by weight and a total of 0.002% by weight to 0.2% by weight of a dibasic acid anhydride unit and the polar group unit is used as an insulator. It is a power cable characterized by the above. Hereinafter, the present invention will be described in detail.

[0006] The multi-component ethylene random copolymer (hereinafter referred to as a copolymer) or a composition thereof according to the first invention of the present invention includes ethylene, a dibasic acid anhydride, and a carbonyl group, a nitrile group and a nitro group. A multi-element random copolymer with at least one of the monomers, or a composition obtained by blending the copolymer with another polyolefin resin, wherein the copolymer or the composition contains a dibasic acid anhydride unit 0.001% by weight to 0.05% by weight, and the total of the dibasic acid anhydride unit and the monomer unit having a polar group is 0.002% by weight to 0.2% by weight. The copolymer can be produced by copolymerizing ethylene, a dibasic acid anhydride and a monomer having a specific polar group by high-pressure radical polymerization.

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 monomer containing a specific polar group (hereinafter referred to as a polar group) other than the dibasic acid anhydride which can be used in the present invention includes (a) a monomer having a carbonyl group, and (b) a nitrile. And a monomer having a nitro group (c). (A1) Examples of the monomer having a carbonyl group include:
and unsaturated carboxylic acid esters derived from α, β-unsaturated carboxylic acid esters. Specific examples thereof include methyl acrylate, methyl methacrylate,
Ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, Unsaturated carboxylic esters such as lauryl methacrylate, stearyl acrylate, stearyl methacrylate, monomethyl maleate, monoethyl maleate, diethyl maleate, monomethyl fumarate, glycidyl acrylate, glycidyl methacrylate, and the like. be able to. Of these, alkyl (meth) acrylate is particularly preferred. More preferred are methyl acrylate and ethyl acrylate.

(A2) Examples of other monomers having a carbonyl group include vinyl esters.
Specific examples thereof include vinyl ester monomers such as vinyl propionate, vinyl acetate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl stearate, and vinyl trifluoroacetate.
Among them, particularly preferred is vinyl acetate.

(A3) Examples of other monomers having a carbonyl group include carbon monoxide, methyl vinyl ketone, isopropenyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl ketone, t-butyl vinyl ketone, and isopropyl vinyl ketone. , Methylpropenyl ketone, methyl isopropenyl ketone, cyclohexyl vinyl ketone and the like.

(B) Monomers having a nitrile group include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, cinnamonitrile, crotononitrile, α-phenylcrotononitrile, fumaronitrile, allyl acetonitrile, −
Butenenitrile, 3-butenenitrile and the like can be mentioned.

(C) As the monomer having a nitro group,
2,4-dinitrophenyl acrylate, 2-nitrostyrene, 3-nitrostyrene, 4-nitrostyrene, p
-Nitrophenyl methacrylate, m-nitrophenyl methacrylate, 2,4-dinitrophenyl methacrylate, 2,4,6-trinitrophenyl methacrylate and the like.

As a specific example of a multi-element ethylene random copolymer of substantially ethylene, a dibasic acid anhydride and another monomer having a specific polar group, obtained by the high-pressure radical polymerization method used in the present invention. Are ethylene / maleic anhydride / VA or carbon monoxide copolymer, ethylene / maleic anhydride / methyl vinyl ketone copolymer, ethylene /
Maleic anhydride / ethyl vinyl ketone copolymer, ethylene / maleic anhydride / acrylonitrile copolymer, ethylene / maleic anhydride / methacrylonitrile copolymer, ethylene / maleic anhydride / allyl acetonitrile copolymer, ethylene / maleic anhydride Acid / 2-nitrostyrene copolymer, ethylene / maleic anhydride / m-nitrostyrene copolymer, ethylene / maleic anhydride / p-nitrophenyl methacrylate copolymer, ethylene / maleic anhydride / methyl isopropenyl ketone Polymers, etc.
Examples include ethylene / maleic anhydride / EA or a carbon monoxide copolymer.

In the high pressure radical polymerization method, for example, ethylene 99.8 to 99.998% by weight, dibasic acid anhydride 0.0
01 to 0.05% by weight, a monomer having a polar group other than dibasic acid anhydride (an amount such that the sum with the dibasic acid anhydride becomes 0.002% by weight or more and 0.2% by weight or less) Of 0.0001 based on the total weight of their total monomers
Polymerization pressure of 5 to 1% by weight of radical polymerization initiator
00 to 4000 kg / cm ² , preferably 100 to 350 ° C.
Under the conditions (1) and (2), in the presence of a chain transfer agent and, if necessary, an auxiliary, the monomers are contacted and polymerized simultaneously or stepwise in a tank type or tube type reactor.

Examples of the radical polymerization initiator include conventional initiators such as peroxides, hydroperoxides, azo compounds, amine oxide compounds, and oxygen. As the chain transfer agent, hydrogen, propylene, butene-
1, C1 to C20 or higher saturated aliphatic and halogen-substituted hydrocarbons such as methane, ethane, propane, butane, isobutane, n-hexane, n-heptane, cycloparaffins, chloroform, and carbon tetrachloride; Aromatic compounds, such as compounds such as toluene, diethylbenzene and xylene, and the like.

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

In the present invention, other polyolefin resins to be blended with the above-mentioned multi-component ethylene random copolymer include homopolymers such as low-density, medium-density and high-density polyethylenes, ethylene-propylene copolymers and ethylene-propylene copolymers. −
Other α-olefins containing ethylene as a main component such as butene-1 copolymer, ethylene-hexene-1 copolymer, ethylene-4-methylpentene-1 copolymer, and ethylene-octene-1 copolymer; Linear low-density polyethylene, ultra-low-density polyethylene, ethylene-
Examples include propylene copolymer rubber and ethylene-propylene-diene copolymer rubber. Among these, it is preferable to use high-pressure radical polymerization polyethylene. As a method of melting and mixing these compositions, a kneading machine such as a Banbury mixer, a pressure kneader, a kneading extruder, a twin-screw extruder and a roll can be used.

In the present invention, the above-mentioned multi-component ethylene random copolymer may be used as an insulator, or a composition in which the multi-component ethylene random copolymer is mixed with another polyolefin resin may be used as the insulator. However, the content of the dibasic acid anhydride unit in the multi-component ethylene random copolymer or the composition thereof is 0.001 to 0.05% by weight, preferably 0.003 to 0.03% by weight,
The total of the dibasic acid anhydride unit and the other monomer unit having a specific polar group is in the range of 0.002 to 0.2% by weight, preferably 0.005 to 0.15% by weight. It is important to adjust the dibasic acid anhydride unit and the monomer unit having a specific polar group to a specific range, which has the effect of dramatically improving electrical insulation resistance.

When the content of the dibasic acid anhydride unit is 0.001
When the amount is less than 0.002% by weight and the total of the dibasic acid anhydride unit and the monomer unit having a polar group is less than 0.002% by weight, the effect of improving the electrical insulation resistance is small, and the dibasic acid anhydride unit is reduced. If the content exceeds 0.05% by weight and the sum of the dibasic acid anhydride unit and the monomer unit having the polar group exceeds 0.2% by weight, the electrical insulation resistance is high, It is not preferable because it causes an increase in the dielectric loss tangent (tan δ). The dielectric loss tangent value monotonically increases with an increase in the amount of the dibasic acid anhydride unit and the amount of the monomer unit having the polar group. In order to be used as an insulating material for power cables, it is desirable that the dielectric loss tangent is at most 5 × 10 ⁻⁴ or less, so that the amount of dibasic anhydride units is 0.05% by weight or less and The total of the basic acid anhydride unit and the monomer unit having the polar group is 0.002% by weight to 0.2% by weight.
It is limited to.

The density of the multi-element ethylene random copolymer is generally in the range of 0.91 to 0.94 g / cm ³ . The melt index (hereinafter abbreviated as MI) is desirably 0.05 to 20 g / 10 minutes in consideration of the extrudability of the cable.

The above-mentioned multi-component ethylene random copolymer or its composition of the present invention is used not only as an insulating layer for ordinary electric wires and power cables, but also alone or blended with other synthetic resins, rubbers and the like. Then, it is processed into a film or a sheet, a tape, a yarn or the like, and laminated with another base material as necessary, and is used for an insulating film or a sheet, an insulating tape, an insulating cover, an insulating garment, and the like.

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 external metal shielding layer of copper, aluminum, lead or the like, or an aluminum tape or the like, if desired. It has an insulation layer made of the above-mentioned multi-element random copolymer or its 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. In addition, in the cross-linking, a usual method such as silane cross-linking and electron beam cross-linking can be used in addition to peroxide and sulfur.

In the present invention, other synthetic resins, rubbers or antioxidants,
Conventional additives such as UV inhibitors, pigments, dyes, lubricants, foaming agents, flame retardants, fillers and the like may be added.

[0025]

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. Example 1 380 g of n-hexane and 0.38 g of maleic anhydride in acetone were placed in a 3.8-liter autoclave equipped with a stirrer and purged with nitrogen.
0.0038 g) Ethyl acrylate (abbreviated as EA)
After adding 2 g and ditertiary butyl peroxide as a polymerization initiator, and then charging 1,700 g of ethylene, the polymerization pressure was 1,600 kgf / cm ^{2 and the} temperature was 190.
The polymerization was carried out at a temperature of 1 ° C. for a polymerization time of 1 hour. An ethylene-maleic anhydride-ethyl acrylate copolymer obtained by this polymerization was obtained. After performing reprecipitation purification with a toluene-acetone solvent, analysis with an infrared spectrophotometer revealed that maleic anhydride was 0.001% by weight and ethyl acrylate was 0.0% by weight.
It was 5% by weight. When the electrical properties of this copolymer were measured, the volume resistance was 10 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is 5 ×
It was 10 ^-4 or less.

Example 2 The electrical properties of an ethylene copolymer (maleic anhydride: 0.02% by weight, ethyl acrylate: 0.01% by weight) obtained by the same production method as in Example 1 were measured. As a result, the volume resistivity was 2 compared to the low-density polyethylene of Comparative Example 1.
It was 0 times. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 3 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.15% by weight, ethyl acrylate was 0.1% by weight)
After dry blending 40 g of 5% by weight) and 2000 g of low-density polyethylene, the mixture was fed to a single-screw extruder (L / D = 26, CR = 3.0) set at a cylinder temperature of 200 ° C., and extruded. , Granulated. The granulated ethylene copolymer composition was purified by reprecipitation with a toluene-acetone solution, and then analyzed by an infrared spectrophotometer. As a result, it was found that maleic anhydride was 0.003% by weight and ethyl acrylate was 0% by weight. .
003% by weight. When the electrical properties of this copolymer composition were measured, the volume resistance was 10 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 4 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.15% by weight and ethyl acrylate was 0.1% by weight)
An ethylene copolymer composition (maleic anhydride was 0.03% by weight, and ethyl acrylate was obtained by the same production method as in Example 3 using 500 g of 5% by weight) and 2000 g of low-density polyethylene. 0.03% by weight), the volume resistance was 40 times higher than that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 5 In the same production method as in Example 3, 60 g of a copolymer (0.4% by weight of maleic anhydride and 0.15% by weight of ethyl acrylate) were mixed with 2000 g of low-density polyethylene. The ethylene copolymer composition obtained by blending (maleic anhydride is 0.01% by weight and ethyl acrylate is 0.1% by weight).
004% by weight), the volume resistance was 15 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is
It was 5 × 10 ⁻⁴ or less.

Example 6 A copolymer was prepared in the same manner as in Example 3 (maleic anhydride was 0.2% by weight and ethyl acrylate was 7% by weight).
An ethylene copolymer composition obtained by blending 10 g with low-density polyethylene 2000 g (maleic anhydride is 0.001% by weight, ethyl acrylate is 0.0
3% by weight), the volume resistance was 10 times higher than that of the low-density polyethylene of Comparative Example 1. Dielectric tangent is 5 ×
It was 10 ^-4 or less.

Examples 7 to 10 Ethyl acrylate of Example 1 was obtained by converting vinyl acetate (abbreviated as VA), methyl vinyl ketone (abbreviated as MVK), acrylonitrile (abbreviated as AN) and 2-nitrostyrene (N
A copolymer was produced in the same manner as in Example 1 except that the copolymer was changed to St.).

Comparative Example 1 A low-density polyethylene (trade name: Nisseki Lexlon W2000, manufactured by Nippon Petrochemical Co., Ltd.) currently available on the market by the high-pressure radical method was used as a comparative example.

Comparative Example 2 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.04% by weight and ethyl acrylate was 0.2%
(% By weight), the volume resistance was 60 times higher than that of the low-density polyethylene of Comparative Example 1, but the dielectric loss tangent was 5 × 10 ⁻⁴ or more. It is not suitable for insulators for electric wires and cables.

Comparative Example 3 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.15% by weight, ethyl acrylate was 0.1% by weight)
% By weight) and 10 g of low-density polyethylene and 2000 g of low-density polyethylene in the same production method as in Example 3 (maleic anhydride is 0.0007% by weight, ethyl acrylate is 0% by weight). 0.0005% by weight)
No remarkable improvement in volume resistance is observed as compared with the low-density polyethylene.

Comparative Example 4 60 g of a copolymer (0.2% by weight of maleic anhydride and 7% by weight of ethyl acrylate) obtained by the same production method as in Example 1 were mixed with 2000 g of low-density polyethylene. The ethylene copolymer composition (maleic anhydride was 0.01% by weight and ethyl acrylate was 0.2% by weight) obtained by the same production method as in Example 3 was used in Comparative Example 1. Volume resistance is 20 times higher than low density polyethylene, but dielectric loss tangent is 5 × 10 ^-4 or more,
It is not suitable for insulators for electric wires and cables. The results are summarized in Table 1.

(Test method) Insulation resistance (volume resistivity); applied voltage 3 kV, time 10
And the sample thickness was 0.3 mm. Dielectric loss tangent (tan δ); YHP4194A impedance analyzer manufactured by Yokogawa Hewlett-Packard Co., Ltd., sample thickness 1 mm, 100 kHz.

[0037]

[Table 1]

[0038]

As described above, the ethylene / dibasic anhydride / monomer having a specific polar group according to the present invention is a multi-component ethylene random copolymer or a multi-component ethylene random copolymer and another multi-component ethylene random copolymer. The composition with the polyolefin resin has the effect of dramatically increasing the electrical insulation resistance by specifying the dibasic acid anhydride unit and the monomer unit having a specific polar group. When used, power loss during high-voltage transmission can be reduced without increasing the thickness of the insulating layer.

Continuation of the front page (72) Inventor Junichi Yokoyama 2-25-26 Takafunai, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-4-39815 (JP, A) JP-A-63-297441 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01B 3/16-3/56 H01B 9/00-9/06

Claims (2)

(57) [Claims] 1. A method according to claim 1, wherein substantially at least one of ethylene and a dibasic acid anhydride and a monomer having a carbonyl group, a nitrile group and a nitro group obtained by a high-pressure radical polymerization method is used.
A multi-component random copolymer with a seed, or a composition of the multi-component random copolymer and another polyolefin-based resin, wherein the multi-component random copolymer or the dibasic acid anhydride unit in the composition is 0% 0.001% by weight to 0.05% by weight, and the total of the dibasic acid anhydride unit and the polar group unit is 0.00
A high insulator comprising an ethylene-based copolymer or a composition thereof in an amount of 2% by weight to 0.2% by weight. 2. At least one of ethylene and a dibasic acid anhydride and a monomer having a carbonyl group, a nitrile group and a nitro group obtained by a high-pressure radical polymerization method.
A multi-component random copolymer with a seed, or a composition of the multi-component random copolymer and another polyolefin-based resin, wherein the multi-component random copolymer or the dibasic acid anhydride unit in the composition is 0% 0.001% by weight to 0.05% by weight, and the total of the dibasic acid anhydride unit and the polar group unit is 0.00
A power cable using an ethylene copolymer or a composition thereof in an amount of 2% by weight to 0.2% by weight as an insulator.