JP3133145B2 - 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 a high-voltage power cable, there is a problem that flexibility is inferior to high-pressure radical polymerization polyethylene, and a metal compound that adversely affects electric characteristics remains as a catalyst residue. .
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).

[0003]

DISCLOSURE OF THE INVENTION The present invention has been intensively studied in view of the above problems, and as a result, a copolymer obtained by copolymerizing ethylene and a small amount of a dibasic acid anhydride by a high-pressure radical polymerization method has been developed. By using an ethylene-based copolymer grafted with at least one kind of monomer having a specific polar group, or a composition of the ethylene-based copolymer and another polyolefin-based resin, the electric insulation resistance characteristic is greatly improved. It was found to be improved,
The first object is to provide a high insulator made of an ethylene copolymer having extremely high electric insulation resistance.
It is an object of the present invention to provide a high-voltage power cable having extremely high electric insulation resistance using the same.

[0004]

According to a first aspect of the present invention, a copolymer of ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method has a carbonyl group, a nitrile group and a nitro group. An ethylene copolymer grafted with at least one of monomers, or a composition of the ethylene copolymer and another polyolefin resin,
0.001% by weight to 0.05% by weight of a dibasic acid anhydride unit in the ethylene copolymer or the composition, and 0.002% by weight of a total of the dibasic acid anhydride unit and the polar group unit. % To 0.2% by weight of the ethylene-based copolymer or its composition.

The second invention of the present invention relates to a copolymer of ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method, wherein at least one of a monomer having a carbonyl group, a nitrile group and a nitro group is provided. Or a composition of the ethylene copolymer and another polyolefin resin, wherein the dibasic acid anhydride unit in the ethylene copolymer or the composition is 0. .00
1% to 0.05% by weight, and the total of the dibasic acid anhydride unit and the polar group unit is 0.002% to 0.2% by weight
A power cable using the ethylene copolymer or its composition as an insulator. Hereinafter, the present invention will be described in detail.

The ethylene copolymer or the composition thereof according to the first invention of the present invention is obtained by grafting a monomer having a carbonyl group, a nitrile group and a nitro group to a copolymer of ethylene and a dibasic acid anhydride. Ethylene copolymer,
Or a composition obtained by blending another polyolefin resin with the ethylene-based copolymer, wherein the ethylene-based copolymer or the composition contains 0.001 of dibasic acid anhydride units.
% By weight, and a total of 0.002% by weight to 0.2% by weight of the dibasic acid anhydride unit and the monomer unit having the polar group. The ethylene-based copolymer can be produced by grafting a monomer having a carbonyl group, a nitrile group and a nitro group to a copolymer obtained by copolymerizing ethylene and a dibasic anhydride by high-pressure radical polymerization. it can.

The high-pressure radical polymerization method for producing a copolymer of substantially ethylene and a dibasic anhydride used in the present invention comprises, for example, 93 to 99.95% by weight of ethylene and 0 to 99% by weight of a dibasic anhydride. From 0.05 to 7% by weight of the mixture in the presence of from 0.0001 to 1% by weight, based on the total weight of their total monomers, of a radical polymerization initiator and a polymerization pressure of from 500 to 400%.
The monomers are contacted 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, under the conditions of 0 kg / cm ² , preferably 100 to 350 ° C. ,
This is a method of polymerizing. As the radical polymerization initiator, peroxides, hydroperoxides, azo compounds,
Customary initiators such as amine oxide compounds, oxygen and the like can be mentioned. As the chain transfer agent, hydrogen, propylene,
Butene-1, a C1 to C20 or higher saturated aliphatic hydrocarbon and a halogen-substituted hydrocarbon such as methane, ethane, propane, butane, isobutane, n-hexane,
Examples include n-heptane, cycloparaffins, chloroform, and carbon tetrachloride, aromatic compounds such as toluene, diethylbenzene and xylene. When copolymerizing the dibasic acid anhydride 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, the grafting method of grafting a monomer having a carbonyl group, a nitrile group and a nitro group to a copolymer of ethylene and a dibasic acid anhydride can be performed by a generally well-known method. . That is, a method in which an ethylene / dibasic acid anhydride copolymer obtained by high-pressure radical polymerization and the above monomer are reacted under melt-kneading using a crosslinking agent such as an organic peroxide, Various methods such as a method of performing a graft reaction in a solution state by dissolving the same in a solution state, a method of dispersing the ethylene / dibasic anhydride copolymer in water, supplying the monomers and a reaction initiator, and performing a graft reaction. Method can be implemented. However, the melt-kneading method is preferred from the viewpoint of practicality.

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 above-mentioned monomers which can be used for the graft reaction in the present invention include (a) a monomer having a carbonyl group,
(B) a monomer having a nitrile group and (c) a monomer having a nitro group. (A1) Examples of the monomer having a carbonyl group include:
Unsaturated carboxylic esters derived from α, β-unsaturated carboxylic esters can be mentioned. Specific examples thereof include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, and acrylic acid. Propyl, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-acrylic acid
Butyl, n-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, monomethyl maleate, monoethyl maleate, diethyl maleate, fumarate And unsaturated carboxylic acid esters such as acid monomethyl ester, glycidyl acrylate and glycidyl methacrylate. 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 include vinyl propionate, vinyl acetate,
Examples include vinyl ester monomers such as 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, isopropyl vinyl ketone, Methyl propenyl ketone, methyl isopropenyl ketone, cyclohexyl vinyl ketone and the like can be mentioned.

(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.

Specific examples of the ethylene-based copolymer obtained by grafting the above-mentioned monomer to a copolymer of substantially ethylene and a dibasic acid anhydride obtained by the high-pressure radical polymerization method used in the present invention include 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 / 2-nitrostyrene copolymer, ethylene / maleic anhydride / m-nitrostyrene copolymer Polymer, ethylene / maleic anhydride / p-nitrophenyl methacrylate copolymer , And ethylene / maleic anhydride / methyl isopropenyl ketone copolymer, ethylene / maleic anhydride / EA or carbon monoxide copolymer.

In the present invention, other polyolefin resins to be mixed with the above-mentioned ethylene copolymer include homopolymers such as low density, medium density and high density polyethylene,
Ethylene-propylene copolymer, ethylene-butene-1
Other α-containing ethylene as a main component such as a copolymer, an ethylene-hexene-1 copolymer, an ethylene-4-methylpentene-1 copolymer, and an ethylene-octene-1 copolymer.
Examples include linear low-density polyethylene, ultra-low-density polyethylene, ethylene-propylene copolymer rubber, and ethylene-propylene-diene copolymer rubber composed of a copolymer with an olefin. 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 ethylene copolymer may be used as an insulator, or a composition obtained by blending another polyolefin resin with the ethylene copolymer may be used as an insulator. The content of the dibasic acid anhydride unit in the copolymer or its composition is 0.00
1 to 0.05% by weight, preferably 0.003 to 0.03
%, And the total of the dibasic acid anhydride unit and the other monomer unit having a specific polar group is 0.002% by weight or more.
0.2% by weight, preferably 0.005 to 0.15% by weight
It is important to adjust the above-mentioned 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 total content of the dibasic acid anhydride unit and the monomer unit having the 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 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 dielectric insulation is high, but the dielectric strength is high. It is not preferable because it increases the tangent (tan δ). The dielectric loss tangent value monotonically increases with the amount of the dibasic acid anhydride unit and the amount of the monomer unit containing 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 a polar group is limited to 0.002% by weight to 0.2% by weight.

The density of the above ethylene copolymer 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.
20 g / 10 min is desirable.

The above-mentioned ethylene copolymer or its composition of the present invention is used not only as an insulating layer of ordinary electric wires and power cables, but also alone or blended with another synthetic resin, rubber or the like. , Film or sheet,
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, if desired. It has an insulating layer made of the above-mentioned ethylene-based 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.

[0024]

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 11 g of a maleic anhydride acetone solution (0.1 g as maleic anhydride) were placed in a 3.8-liter autoclave equipped with a stirrer and purged with nitrogen.
1 g) and ditertiary butyl peroxide as a polymerization initiator, and then 1,700 g of ethylene was charged. 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 copolymer obtained by this polymerization was obtained. After reprecipitation purification with a toluene-acetone solvent, analysis with an infrared spectrophotometer revealed that maleic anhydride was 0.03% by weight.
Met. This ethylene-maleic anhydride copolymer 50
0 g, 0.1 g of ethyl acrylate (abbreviated as EA) and 2,
After dry blending 0.03 g of 5-dimethyl-2,5-di (t-butylperoxy) hexane, a single screw extruder (L / D = 26,
C. R. = 3.0), and after extrusion, granulated.
The granulated ethylene copolymer was purified by reprecipitation with a toluene-acetone solution and analyzed by an infrared spectrophotometer. As a result, maleic anhydride was 0.03% by weight and ethyl acrylate was 0.01% by weight. % By weight. When the electrical characteristics of this copolymer were measured, the volume resistance was 30 times that of the low-density polyethylene of Comparative Example 1. Also,
The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 2 The electrical properties of an ethylene copolymer (maleic anhydride: 0.03% by weight, ethyl acrylate: 0.12% by weight) obtained by the same production method as in Example 1 were measured. As a result, the volume resistance was 4 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 ten 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, 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 manner as in Example 3, 60 g of a copolymer (0.15% by weight of maleic anhydride and 0.5% by weight of ethyl acrylate) were mixed with 2000 g of low-density polyethylene. Ethylene copolymer composition obtained by blending (maleic anhydride is 0.001% by weight, ethyl acrylate is
(0.005% by weight), the volume resistance was 7 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 6 An ethylene copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.001% by weight, vinyl acetate (VA
(Abbreviated as 0.05% by weight), the volume resistivity was 11 times higher than that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is 5 × 10
^-4 or less.

Example 7 The electricity of an ethylene copolymer (maleic anhydride: 0.001% by weight, methyl vinyl ketone (abbreviated as MVK) 0.05% by weight) obtained by the same production method as in Example 1 was used. When the characteristics were measured, the volume resistance was ten times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is
It was 5 × 10 ⁻⁴ or less.

Example 8 The electrical properties of an ethylene copolymer (maleic anhydride: 0.001% by weight, acrylonitrile (abbreviated as AN): 0.01% by weight) obtained by the same production method as in Example 1 were measured. As a result of measurement, the volume resistance was 16 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is 5 ×
It was 10 ^-4 or less.

Example 9 An ethylene copolymer (maleic anhydride, 0.001% by weight, 0.01% by weight of 2-nitrostyrene (abbreviated as NSt), 0.01% by weight) obtained in the same manner as in Example 1 was used. When the electrical characteristics were measured, 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.

Comparative Example 1 Comparative example 1 was a commercially available low-density polyethylene (trade name: Nisseki Lexlon W2000, manufactured by Nippon Petrochemical Co., Ltd.) produced by the high-pressure radical method.

Comparative Example 2 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.15% by weight, ethyl acrylate was 0.0
An ethylene copolymer composition (maleic anhydride was 0.0007% by weight, obtained by the same production method as in Example 3) using 10 g of 5% by weight and 2000 g of low-density polyethylene.
Ethyl acrylate (0.0002% by weight) does not show a remarkable improvement in volume resistance as compared with the low-density polyethylene of Comparative Example 1.

Comparative Example 3 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.15% by weight and ethyl acrylate was 0.5% by weight)
(% By weight) and 60 g of low-density polyethylene and 2000 g of low-density polyethylene in the same production method as in Example 3 (maleic anhydride was 0.05% by weight, ethyl acrylate was 0%) .17% by weight), the volume resistance is 50 times as large as that of the low-density polyethylene of Comparative Example 1, but the dielectric loss tangent is 5 × 10 ^-4 or more. Not suitable for insulators. The results are summarized in Table 1 below.

(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, an ethylene copolymer obtained by grafting a monomer having a specific polar group onto the ethylene / dibasic anhydride copolymer produced by the high-pressure radical polymerization method of the present invention or The composition of the ethylene copolymer and other polyolefin resin has the effect of dramatically increasing the electrical insulation resistance by specifying dibasic acid anhydride units and monomer units having a specific polar group. Thus, 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 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] An ethylene copolymer obtained by grafting at least one of a monomer having a carbonyl group, a nitrile group and a nitro group to a copolymer of substantially ethylene and a dibasic acid anhydride obtained by a high-pressure radical polymerization method. A polymer or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the ethylene-based copolymer or the dibasic acid anhydride unit in the composition is 0.001% by weight to 0%. .05
A high insulator comprising an ethylene-based copolymer or a composition thereof in which the total amount of the dibasic acid anhydride unit and the polar group unit is 0.002 to 0.2% by weight. 2. An ethylene copolymer obtained by grafting at least one of a monomer having a carbonyl group, a nitrile group and a nitro group to a copolymer of substantially ethylene and a dibasic anhydride obtained by a high-pressure radical polymerization method. A polymer or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the ethylene-based copolymer or the dibasic acid anhydride unit in the composition is 0.001% by weight to 0%. .05
% By weight, and an ethylene-based copolymer or a composition thereof having a total of 0.002% to 0.2% by weight of a dibasic acid anhydride unit and the polar group unit is used as an insulator. Power cable.