JP3327341B2 - 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 that of high-pressure radical polymerization polyethylene, and a metal compound that adversely affects electric characteristics remains as a catalyst residue. .
In addition, 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 has been proposed ( JP 63
-150811).

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and as a result, has been obtained by copolymerizing ethylene and a small amount of a monomer having a specific polar group by a high-pressure radical polymerization method. By using an ethylene-based copolymer in which a small amount of dibasic acid anhydride is grafted onto the copolymer, or a composition of the ethylene-based copolymer and another polyolefin-based resin, the electrical insulation resistance characteristics are greatly improved. It has been found that improvement has been made,
An object is to provide a high insulator made of an ethylene copolymer having an extremely high electric insulation resistance, and a second object is to provide a high-voltage power cable using the same which has an extremely high electric insulation resistance.

[0004]

According to a first aspect of the present invention, there is provided a copolymer of ethylene and at least one of monomers having a carbonyl group, a nitrile group and a nitro group, which is obtained by a high-pressure radical polymerization method. An ethylene copolymer grafted with a dibasic acid anhydride, or a composition of the ethylene copolymer and another polyolefin resin, wherein the ethylene copolymer or other components in the composition are 0.001% to 0.05% by weight of the basic acid anhydride unit, and 0.002% of the total of the dibasic acid anhydride unit and the polar group unit.
It is a high insulator having an electrical insulation resistance improved by setting the dielectric loss tangent of the ethylene-based copolymer or its composition of from 5 % by weight to 0.2% by weight to 5 × 10 ⁻⁴ or less .

The second invention of the present invention is to provide a copolymer of ethylene and at least one of monomers having a carbonyl group, a nitrile group and a nitro group obtained by a high-pressure radical polymerization method with a dibasic anhydride. An ethylene-based copolymer grafted with a product, or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the dibasic acid anhydride unit in the ethylene-based copolymer or the composition is 0.0
Dielectric comprising an ethylene-based copolymer or a composition thereof in an amount of from 0.01% to 0.05% by weight, and a total of 0.002% to 0.2% by weight of a dibasic acid anhydride unit and the polar group unit. A power cable characterized in that a high insulator having an improved electrical insulation resistance with a tangent of 5 × 10 ⁻⁴ or less is used as an insulator. Hereinafter, the present invention will be described in detail.

[0006] The ethylene copolymer or the composition thereof according to the first invention of the present invention refers to an ethylene copolymer obtained by grafting a dibasic acid anhydride to a copolymer of ethylene and a monomer having the above-mentioned specific polar group. A copolymer in which another polyolefin-based resin is blended with the ethylene-based copolymer or the ethylene-based copolymer, and the ethylene-based copolymer or the composition thereof,
0.001% by weight to 0.05% by weight of the dibasic acid anhydride unit, and 0.002% by weight to 0.2% by weight of the total of the dibasic acid anhydride unit and the monomer unit having the polar group. %. The ethylene-based copolymer is obtained by a high-pressure radical polymerization method into a copolymer of ethylene and at least one monomer having a polar group comprising a carbonyl group, a nitrile group and a nitro group (hereinafter, referred to as a polar group). It can be produced by grafting a dibasic acid anhydride.

The high-pressure radical polymerization method for producing a copolymer of substantially ethylene and a monomer having the above-mentioned polar group used in the present invention includes, for example, ethylene 93 to 99.95.
% By weight, 0.05 to 7% by weight of the monomer having a polar group
In a mixture based on the total weight of all their monomers.
In the presence of 0001-1% by weight of a radical polymerization initiator, the polymerization pressure is 500-4000 kg / cm ² , preferably 100-100
This is a method in which the monomers are contacted and polymerized simultaneously or stepwise in a tank type or tube type reactor at 350 ° C. in the presence of a chain transfer agent and, if necessary, an auxiliary agent. Examples of the radical polymerization initiator include common 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, n-hexane, and n-hexane. Examples include heptane, cycloparaffins, chloroform, and carbon tetrachloride, aromatic compounds such as toluene, diethylbenzene and xylene. When copolymerizing the monomer having a polar group with ethylene, another unsaturated monomer can be further copolymerized as necessary. Examples of the other unsaturated monomer include propylene,
Butene-1, hexene-1, decene-1, octene-
1, olefins such as styrene.

In the present invention, the grafting method of grafting a dibasic acid anhydride to a copolymer of ethylene and the above-mentioned monomer having a polar group can be performed by a generally well-known method.
That is, a method in which ethylene / a monomer copolymer having a polar group obtained by high-pressure radical polymerization and a dibasic acid anhydride are reacted under melt-kneading using a crosslinking agent such as an organic peroxide, A method in which these are dissolved in an appropriate solvent to carry out a graft reaction in a solution state, the ethylene / monomer copolymer having a polar group is dispersed in water, and a dibasic acid anhydride and a reaction initiator are supplied. Then, various methods such as a method of performing a graft reaction can be performed. However, the melt-kneading method is preferred from the viewpoint of practicality.

The dibasic acid anhydride which can be used in the graft reaction in the present invention includes maleic anhydride, itaconic anhydride,
Hymic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, phenyl maleic anhydride, diphenyl maleic anhydride, chloromaleic anhydride, dichloromaleic anhydride, fluoromaleic anhydride, difluoromaleic anhydride, bromomaleic anhydride, dibromo Maleic anhydride and the like can be mentioned. Of these, maleic anhydride is particularly preferred.

The above-mentioned monomer having a polar group which can be used for copolymerization with ethylene in the present invention includes (a) a monomer having a carbonyl group, (b) a monomer having a nitrile group, c) Monomers having a nitro group can be exemplified. (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 polymer obtained by grafting a dibasic acid anhydride to a copolymer of substantially ethylene and the above-mentioned monomer having a polar group 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 / allylacetonitrile copolymer, ethylene / maleic anhydride / 2-nitrostyrene copolymer, ethylene / anhydride Ethylene / maleic anhydride / EA or copolymer such as maleic acid / m-nitrostyrene copolymer, ethylene / maleic anhydride / p-nitrophenyl methacrylate copolymer, ethylene / maleic anhydride / methyl isopropenyl ketone copolymer Examples include a carbon oxide 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 copolymer, ethylene-hexene-1 copolymer, ethylene-
4-methylpentene-1 copolymer, linear low-density polyethylene consisting of a copolymer with other α-olefin containing ethylene as a main component such as ethylene-octene-1 copolymer, ultra-low-density polyethylene, Ethylene-propylene copolymer rubber and ethylene-propylene-diene copolymer rubber are exemplified. 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 that the content is within the range described above, and by adjusting the above-mentioned dibasic acid anhydride unit and the monomer unit having a specific polar group to a specific range, there is an effect of dramatically improving electric 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 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 make it an insulating material for power cables, it is desirable that the dielectric loss tangent value be 5 × 10 ⁻⁴ or less at the maximum,
Therefore, the amount of the dibasic acid anhydride unit is 0.05% by weight or less, and the total of the dibasic acid anhydride unit and the monomer unit having the polar group is 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, 0.4 g of ethyl acrylate (abbreviated as EA), and ditertiary butyl peroxide as a polymerization initiator were added into a 3.8-liter autoclave equipped with a stirrer and purged with nitrogen. Then, after charging 1,700 g of ethylene, the polymerization pressure was 1,600 kg.
f / cm ² Temperature 190 ° C., was polymerized at a polymerization time of 1 hour. By this polymerization, an ethylene-ethyl acrylate copolymer was obtained. After performing reprecipitation purification with a toluene-acetone solvent, analysis with an infrared spectrophotometer revealed that ethyl acrylate was 0.1% by weight. 500 g of this ethylene-ethyl acrylate copolymer and 0.08 maleic anhydride
After dry-blending 4 g and 0.02 g of 2,5-demethyl-2,5-de (t-butylperoxy) hexane,
Single screw extruder (L / D
= 26, C.I. R. = 3.0), and after extrusion, granulated. The granulated ethylene polymer was purified by reprecipitation with a toluene-acetone solution, and then analyzed by an infrared spectrophotometer. As a result, maleic anhydride was 0.01% by weight and ethyl acrylate was 0.1% by weight. % By weight. When the electrical properties of this copolymer were measured, the volume resistance was 20 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 2 The electrical properties of an ethylene polymer (maleic anhydride: 0.04% by weight, ethyl acrylate: 0.1% by weight) obtained by the same production method as in Example 1 were measured. As a result, the volume resistance was 50% lower than that of the low-density polyethylene
Had doubled. 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 (0.4% by weight of maleic anhydride and 0.2% by weight of ethyl acrylate) were mixed with 2000 g of low-density polyethylene. Ethylene copolymer composition obtained by blending (maleic anhydride is 0.01% by weight, ethyl acrylate is 0.0%
06% by weight), the volume resistance was 25 times as high as that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent is 5
× 10 ^-4 or less.

Example 6 10 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 0.001% by weight and ethyl acrylate was 0.03% by weight) obtained by the same production method as in Example 3 was used in Comparative Example 1. The volume resistance was ten times higher than that of the low-density polyethylene. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 7 A copolymer obtained by the same production method as in Example 1 (maleic anhydride is 0.01% by weight, vinyl acetate (abbreviated as VA))
An ethylene copolymer composition (maleic anhydride was 0.001% by weight, obtained by the same production method as in Example 3) using 10 g of 0.5% by weight) and 100 g of low-density polyethylene.
(VA: 0.05% by weight) had a volume resistance 13 times that of the low-density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 8 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.01% by weight and methyl vinyl ketone (MVK
Is an ethylene copolymer composition (maleic anhydride is 0.00%) obtained by the same production method as in Example 3 using 10 g of 0.5% by weight) and 100 g of low-density polyethylene.
1% by weight, MVK is 0.05% by weight)
Of the low-density polyethylene was 10 times as large. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 9 10 g of a copolymer (maleic anhydride was 0.01% by weight and acrylonitrile (abbreviated as AN) was 0.1% by weight) obtained by the same production method as in Example 1 were as low as 10 g. Density polyethylene 1
The ethylene copolymer composition (maleic anhydride was 0.001% by weight and AN was 0.01% by weight) obtained in the same production method as in Example 3 using Comparative Example 1 was prepared using Comparative Example 1 Had a volume resistance 20 times higher than that of the low density polyethylene. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 10 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.01% by weight, 2-nitrostyrene (NSt)
Is an ethylene copolymer composition (maleic anhydride: 0.00 g) obtained by the same production method as in Example 3 using 10 g of 0.1% by weight) and 100 g of low-density polyethylene.
1% by weight, NSt is 0.01% by weight)
Had a volume resistance 18 times higher than that of low density polyethylene. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

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

Comparative Example 2 A copolymer obtained by the same production method as in Example 1 (maleic anhydride was 0.04% by weight, 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 (maleic anhydride was 0.2% by weight and ethyl acrylate was 7% by weight) obtained by the same production method as in Example 1 was 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.

[0038]

(Test method) Insulation resistance (volume specific resistance); 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.

[0040]

[Table 1]

[0041]

As described above, an ethylene copolymer obtained by grafting a dibasic acid anhydride to a copolymer comprising ethylene / a monomer having a specific polar group produced by the high-pressure radical polymerization method of the present invention. The composition of the polymer, or its ethylene copolymer and other polyolefin-based resin, has the potential to increase electrical insulation resistance by specifying dibasic acid anhydride units and monomer units having specific polar groups. 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.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Junichi Yokoyama 2-25-26 Takafunai, Kanazawa-ku, Yokohama-shi, Kanagawa (56) References JP-A-49-110740 (JP, A) JP-A-4-39815 (JP) , A) JP-A-61-296045 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 3/44 H01B 9/00 C08L 23/26 C08L 51/06

Claims (2)

(57) [Claims] 1. An ethylene-based polymer obtained by grafting a dibasic acid anhydride onto a copolymer of substantially ethylene obtained by a high-pressure radical polymerization method and at least one monomer having a carbonyl group, a nitrile group and a nitro group. A copolymer or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the ethylene-based copolymer or the dibasic anhydride unit in the composition is 0.001% by weight or more. 0.0
The dielectric loss tangent of the ethylene copolymer or its composition is 5 × 10 % and the total of the dibasic acid anhydride unit and the polar group unit is 0.002% to 0.2% by weight.
A high insulator with an electrical insulation resistance of ^-4 or less . 2. An ethylene-based copolymer obtained by grafting a dibasic acid anhydride to a copolymer of substantially ethylene obtained by a high-pressure radical polymerization method and at least one monomer having a carbonyl group, a nitrile group and a nitro group. A copolymer or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the ethylene-based copolymer or the dibasic anhydride unit in the composition is 0.001% by weight or more. 0.0
The dielectric loss tangent of the ethylene copolymer or its composition is 5 × 10 % 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 characterized in that a high insulator having an electric insulation resistance of ^-4 or less is used as an insulator.