JPH05298928A - Highly insulating body made of ethylene-based copolymer or its composition and electric cable using thereof - Google Patents

Abstract

PURPOSE:To heighten the electric insulation resistance greatly by specifying a dibasic acid anhydride unit and a monomer unit having specified polar groups regarding an ethylene-based copolymer or its composition mixed with another polyolefine-based resin. CONSTITUTION:An ethylene-based copolymer or a composition of the ethylene- based copolymer and another polyolefine-based resin is prepared wherein the copolymer is obtained by grafting a dibasic acid adhydride and at least one kind of monomers having carbonyl, nitryl, and nitro group to ethylene (co)polymer prepared by high pressure radical polymerization. A highly insulating material is made of the ethylene-based copolymer or ethylene-based copolymer composition containing 0.001-0.05wt.% of dibasic acid anhydride unit and 0.002-0.2wt.% in total of dibasic acid anhydride unit and the polar group unit. In this case, the electric insulation resistance is greatly heightened by specifying the dibasic acid anhydride unit and the monomer unit having the specified polar groups and the electric power loss at the time of transmission of electricity with high voltage is lowered.

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, which is excellent in high voltage characteristics and workability, and a high voltage power cable using the same.

[0002]

2. Description of the Related Art Conventionally, high-voltage polyethylene and cross-linked polyethylene have been widely used as insulators for high-voltage power cables because of their excellent electrical characteristics. One of the problems of high voltage power cables is power loss during high voltage power transmission, and reducing it is an important issue. One means of reducing this power loss can be achieved by increasing the high voltage characteristics of the insulating material, especially the electrical insulation resistance.
As a method for improving the high voltage characteristics of the insulating material, a method of grafting maleic anhydride onto low-pressure polyethylene has been proposed (for example, JP-A-2-10610).
However, when low-pressure polyethylene is used as an insulator for high-voltage power cables, it has a problem that it is inferior in flexibility as compared with high-pressure radical-polymerized polyethylene, and metal compounds that adversely affect electric properties remain as catalyst residues. ..
Further, a power cable having an insulating layer of a composition in which 100 parts by weight of polyethylene is mixed with 2 to 40 parts by weight of maleic anhydride grafted polyethylene having a maleic anhydride graft amount of 0.5 to 10% by weight has been proposed ( 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, an ethylene (co) polymer obtained by a high-pressure radical polymerization method has a small amount of dibasic acid anhydride and a small amount of dibasic acid anhydride. By using an ethylene-based polymer grafted with a monomer having a specific polar group or a composition of the ethylene-based polymer and another polyolefin-based resin, the electrical insulation resistance characteristics are significantly improved. The first purpose thereof is to provide a high insulator made of an ethylene polymer having a very high electric insulation resistance, and the second purpose thereof is to use a very high electric resistance. A high-voltage power cable having high insulation resistance is provided.

[0004]

The first invention of the present invention is that an ethylene (co) polymer obtained by a high pressure radical polymerization method is a monomer having a dibasic acid anhydride and a carbonyl group, a nitrile group and a nitro group. An ethylene-based copolymer grafted with at least one of the polymers, or a composition of the ethylene-based copolymer and another polyolefin-based resin, wherein the ethylene-based copolymer or the dibasic acid in the composition The anhydride unit is 0.001% by weight to 0.05% by weight, and the total amount of the dibasic acid anhydride unit and the polar group unit is 0.002% by weight to
It is a high insulator composed of 0.2% by weight of an ethylene copolymer or its composition.

A second invention of the present invention is to add an ethylene (co) polymer obtained by a high pressure radical polymerization method to a dibasic acid anhydride and at least one kind of a monomer having a carbonyl group, a nitrile group and a nitro group. A grafted ethylene-based copolymer 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. 001 wt% to 0.05 wt%, and the total amount of the dibasic acid anhydride unit and the polar group unit is 0.002 wt% to 0.2 wt% ethylene-based copolymer or its composition as an insulator It is a power cable characterized by being used as. The present invention will be described in detail below.

The ethylene polymer or the composition thereof in the first invention of the present invention means an ethylene (co) polymer obtained by a high-pressure radical polymerization method, a dibasic acid anhydride, a carbonyl group, a nitrile group and a nitro group. An ethylene-based copolymer grafted with at least one of monomers having
Alternatively, it is a composition in which another polyolefin resin is mixed with the ethylene copolymer, and the dibasic acid anhydride unit is 0.001 in the ethylene copolymer or the composition.
% To 0.05% by weight, and the total amount of the dibasic acid anhydride unit and the polar group-containing monomer unit is 0.002% to 0.2% by weight.

The high-pressure radical polymerization method for producing the ethylene (co) polymer used in the present invention includes, for example, 93 to 100% by weight of ethylene and 0 to 7% by weight of an unsaturated monomer copolymerizable with ethylene. The mixture is subjected to a polymerization pressure of 500 to 4000 kg / cm ² , preferably 100 to 350 ° C., in the presence of 0.0001 to 1% by weight of a radical polymerization initiator, based on the total weight of all the monomers. In this method, the monomers are contacted or polymerized simultaneously or stepwise in a tank or tube reactor in the presence of a chain transfer agent and, if necessary, an auxiliary agent. Examples of the radical polymerization initiator include conventional initiators such as peroxides, hydroperoxides, azo compounds, amine oxide compounds and oxygen. Further, as the chain transfer agent, hydrogen, propylene, butene-1, C
1 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 Examples of the compound include compounds such as toluene, diethylbenzene and xylene. Examples of unsaturated monomers copolymerizable with ethylene include olefins such as propylene, butene-1, hexene-1, decene-1, octene-1, and styrene.

In the present invention, the grafting method of grafting the polar group-containing monomer and the dibasic acid anhydride onto the ethylene (co) polymer can be carried out by a generally well-known method. That is, ethylene (co) obtained by high pressure radical polymerization
A method of reacting the polymer, the monomer having the polar group and the dibasic acid anhydride under melt-kneading using a crosslinking agent such as an organic peroxide, and dissolving these in a suitable solvent. A method of carrying out a graft reaction in a solution state, an ethylene (co) polymer obtained by high-pressure radical polymerization is dispersed in water, and a monomer having the above polar group, a dibasic acid anhydride and a reaction initiator are supplied to carry out grafting. Various methods such as a method of carrying out the reaction can be carried out. However, the melt-kneading method is preferable from the viewpoint of practicality.

The dibasic acid anhydride usable 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 etc. can be mentioned. Among these, maleic anhydride can be mentioned as a particularly preferable one.

The polar group-containing monomer which can be used in the graft reaction in the present invention includes (a) a carbonyl group-containing monomer, (b) a nitrile group-containing monomer,
(C) The monomer which has a nitro group can be mentioned. Examples of the (a1) carbonyl group-containing monomer include:
Unsaturated carboxylic acid esters derived from α, β-unsaturated carboxylic acid esters can be mentioned, and specific examples thereof include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, acrylic acid. Propyl, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, acrylic acid-n-
Butyl, n-butyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid diethyl ester, fumar Examples thereof include unsaturated carboxylic acid esters such as acid monomethyl ester, glycidyl acrylate and glycidyl methacrylate. Among these, (meth) acrylic acid alkyl ester is particularly preferable. More preferably, methyl acrylate and ethyl acrylate can be mentioned.

Examples of (a2) another monomer having a carbonyl group include vinyl ester. Specific examples thereof include vinyl propionate, vinyl acetate,
Examples thereof include vinyl ester monomers such as vinyl caproate, vinyl caprylate, vinyl laurate, vinyl stearate and vinyl trifluoroacetate. Among these, vinyl acetate is particularly preferable.

(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, Mention may be made of methyl propenyl ketone, methyl isopropenyl ketone, cyclohexyl vinyl ketone.

(B) Monomers having a nitrile group include acrylonitrile, methacrylonitrile, α-methoxyacrylonitrile, vinylidene cyanide, cinnamonitrile, crotononitrile, α-phenylcrotononitrile, fumaronitrile, allylacetonitrile, 2 −
Butene nitrile, 3-butene nitrile, etc. can be mentioned.

Examples of the monomer (c) having a nitro group include
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 can be mentioned.

Specific examples of the ethylene-based copolymer obtained by grafting the above polar group-containing monomer and dibasic acid anhydride onto the ethylene (co) polymer 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 / maleic anhydride / m
-Nitrostyrene copolymer, ethylene / maleic anhydride / p-nitrophenyl methacrylate copolymer, ethylene / maleic anhydride / methyl isopropenyl ketone copolymer, ethylene / maleic anhydride / EA or carbon monoxide copolymer Examples include coalescence.

In the present invention, other polyolefin resins to be added to the above 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-
Linear low-density polyethylene, ultra-low-density polyethylene composed of a copolymer with other α-olefins containing ethylene as a main component, such as 4-methylpentene-1 copolymer and ethylene-octene-1 copolymer. Examples thereof include ethylene-propylene copolymer rubber and ethylene-propylene-diene copolymer rubber. Among these, high-pressure radical polymerization polyethylene is preferably used. As a method for melt-mixing these compositions, a kneading machine that is commonly used, such as a Banbury mixer, a pressure kneader, a kneading extruder, a twin-screw extruder, or a roll, can be used.

In the present invention, the ethylene-based copolymer described above may be used as an insulator, or a composition prepared by mixing the ethylene-based copolymer with another polyolefin resin may be used as an insulator. Content of the dibasic acid anhydride unit in the system copolymer or its composition is 0.00
1 to 0.05% by weight, preferably 0.003 to 0.03
% By weight, and the total amount of dibasic acid anhydride units and other monomer units having polar groups is 0.002% by weight to 0.2%.
It is important that the content of the dibasic acid anhydride unit and the polar group-containing monomer unit is adjusted to a specific range by adjusting the content of the dibasic acid anhydride unit to a specific range. It has the effect of dramatically improving the insulation resistance.

The content of the dibasic acid anhydride unit is 0.001
If the total amount 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 of When the content exceeds 0.05% by weight and the total amount 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 but the dielectric It is not preferable because it increases the tangent (tan δ). The dielectric loss tangent value monotonically increases as the amount of the dibasic acid anhydride unit and the amount of the monomer unit having the polar group increase. In order to use it as 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 amount of the dibasic acid anhydride unit and the monomer unit containing the polar group is 0.002% by weight to 0.2% by weight. It is limited.

The density of the above ethylene copolymer is generally applied in the range of 0.91 to 0.94 g / cm ³ . Further, regarding the melt index (hereinafter abbreviated as MI), considering the extrudability into a cable, it is 0.05 to
20 g / 10 minutes is desirable.

The above-mentioned ethylene-based copolymer of the present invention or a composition thereof is not only used as an insulating layer for a usual electric wire / power cable, but also alone or blended with another synthetic resin, rubber or the like. , Film or sheet,
It is processed into tapes, yarns, etc., and if necessary, laminated with other base materials, and is utilized for insulating films and sheets, insulating tapes, insulating covers, insulating garments, etc.

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

The insulating layer may be a crosslinked body or an uncrosslinked body. In addition, in the crosslinking, in addition to peroxide, sulfur, etc., a usual method such as silane crosslinking, electron beam crosslinking, etc. can be used.

In the present invention, other synthetic resins or rubbers or antioxidants, within the range not departing from the gist of the present invention,
It is possible to add usual additives such as an anti-UV agent, a pigment, a dye, a lubricant, a foaming agent, a flame retardant and a filler.

[0024]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention. Example 1 Low-density polyethylene obtained by high-pressure radical polymerization, 0.25 g of maleic anhydride, 0.1 g of ethyl acrylate (abbreviated as EA) and 2,5-dimethyl-2,5-di (t-butylperoxy) hexane. After 0.08 g was dry blended, the mixture was fed to a single-screw extruder (L / D = 26, CR = 3.0) set to a cylinder temperature of 230 ° C., extruded and then granulated. Toluene the granulated ethylene polymer
After reprecipitation purification with an acetone solution, analysis by an infrared spectrophotometer showed that maleic anhydride was 0.03% by weight.
Thus, ethyl acrylate was 0.01% by weight. When the electrical properties of this copolymer were measured, the volume resistance was
Compared with the low density polyethylene of Comparative Example 1, it was 30 times. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 2 An ethylene polymer obtained by the same production method as in Example 1 (maleic anhydride was 0.03% by weight and ethyl acrylate was
When the electrical characteristics of 0.1% by weight) were measured, the volume resistance was 40 times that of the low density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 3 A copolymer obtained by the same production method as in Example 1 (0.15% by weight of maleic anhydride and 0.1% by weight of ethyl acrylate).
(5 wt%) 40 g and low-density polyethylene 2000 g were dry-blended and then fed to a single-screw extruder (L / D = 26, CR = 3.0) set to a cylinder temperature of 200 ° C., and after extrusion , Granulated. After reprecipitation purification of the granulated ethylene-based copolymer composition with a toluene-acetone solution, analysis with an infrared spectrophotometer showed that maleic anhydride was 0.003% by weight and ethyl acrylate was
It was 0.003% by weight. When the electrical characteristics of this copolymer were measured, the volume resistance was 10 times that of the low density polyethylene of Comparative Example 1. Also, the dissipation factor is
It was 5 × 10 ⁻⁴ or less.

Example 4 A copolymer obtained by the same production method as in Example 1 (0.15% by weight of maleic anhydride and 0.1% by weight of ethyl acrylate).
5% by weight) and 2000 g of low-density polyethylene, and an ethylene copolymer composition obtained by the same production method as in Example 3 (0.03% by weight of maleic anhydride and 0% of ethyl acrylate). (0.03% by weight), the volume resistance was 40 times that of the low density polyethylene of Comparative Example 1. The dielectric loss tangent was 5 × 10 ⁻⁴ or less.

Example 5 A copolymer obtained by the same production method as in Example 3 (0.15% by weight of maleic anhydride and 0.5% of ethyl acrylate)
(Wt%) 60 g and 2000 g of low-density polyethylene blended to obtain an ethylene copolymer composition (maleic anhydride is 0.001 wt% and 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 The electrical characteristics of an ethylene polymer (maleic anhydride: 0.001% by weight, vinyl acetate (abbreviated as VA): 0.05% by weight) obtained by the same production method as in Example 1 were measured. When I 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 7 Electrical characteristics of ethylene polymer (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 The volume resistance was 13 times higher than that of the low density polyethylene of Comparative Example 1. The dielectric loss tangent is 5
It was less than × 10 ^-4 .

Example 8 The electrical properties of an ethylene polymer (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, the volume resistance was 21 times that of the low-density polyethylene of Comparative Example 1. Also, the dielectric loss tangent is 5 ×
It was 10 ⁻⁴ or less.

Example 9 Electricity of an ethylene polymer (maleic anhydride: 0.001% by weight, 2-nitrostyrene (abbreviated as NSt): 0.01% by weight) obtained by the same production method as in Example 1 When the characteristics were measured, the volume resistance was 18 times that of the low density polyethylene of Comparative Example 1. The dielectric loss tangent is 5
It was less than × 10 ^-4 .

Comparative Example 1 Low-density polyethylene (trade name: Nisseki Lexron W2000, manufactured by Nippon Petrochemical Co., Ltd.) manufactured by the high pressure radical method, which is currently on the market, was used as Comparative Example 1.

Comparative Example 2 A copolymer obtained by the same production method as in Example 1 (0.15% by weight of maleic anhydride and 0.05% of ethyl acrylate).
5% by weight) 10 g and low-density polyethylene 2000 g, and an ethylene copolymer composition obtained by the same production method as in Example 3 (maleic anhydride is 0.0007% by weight,
0.0002% by weight of ethyl acrylate) does not show a significant 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 (0.15% by weight of maleic anhydride and 0.5% of ethyl acrylate).
% By weight) and 2000 g of low-density polyethylene, and an ethylene copolymer composition obtained by the same production method as in Example 3 (maleic anhydride: 0.05% by weight; ethyl acrylate: 0% by weight). .17% by weight) has a volume resistance 50 times that of the low-density polyethylene of Comparative Example 1, but has a dielectric loss tangent of 5 × 10 ⁻⁴ or more, so that Not suitable for insulators. The results are summarized in (Table 1).

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

[0037]

[Table 1]

[0038]

Industrial Applicability The ethylene-based ethylene (co) polymer produced by the high pressure radical polymerization method as described above is grafted with a monomer having a specific polar group and a dibasic acid anhydride. The composition of the copolymer or its ethylene-based copolymer and other polyolefin-based resin has a significantly improved electrical insulation resistance by specifying the dibasic acid anhydride unit and the monomer unit having a specific polar group. When it is used as an insulating layer of a power cable, it is possible to reduce power loss during high-voltage power transmission without thickening the insulating layer.

(72) Inventor Hideo Kawabata 3-35-2, Okubo, Konan-ku, Yokohama-shi, Kanagawa Prefecture (72) Junichi Yokoyama 2-25-26 Takafunedai, Kanazawa-ku, Yokohama-shi, Kanagawa Prefecture

Claims (2)

[Claims] 1. An ethylene (co) polymer obtained by a high-pressure radical polymerization method, a dibasic acid anhydride and a carbonyl group,
An ethylene copolymer grafted with at least one monomer having a nitrile group and a nitro group, or a composition of the ethylene copolymer and another polyolefin resin, the ethylene copolymer Alternatively, the dibasic acid anhydride unit in the composition is 0.001% to 0.05% by weight, and the total amount of the dibasic acid anhydride unit and the polar group unit is 0.002% to 0.2% by weight. % High insulator comprising an ethylene-based copolymer or a composition thereof. 2. An ethylene (co) polymer obtained by a high-pressure radical polymerization method, a dibasic acid anhydride and a carbonyl group,
An ethylene copolymer grafted with at least one monomer having a nitrile group and a nitro group, or a composition of the ethylene copolymer and another polyolefin resin, the ethylene copolymer Alternatively, the dibasic acid anhydride unit in the composition is 0.001% to 0.05% by weight, and the total amount of the dibasic acid anhydride unit and the polar group unit is 0.002% to 0.2% by weight. %, An ethylene-based copolymer or a composition thereof is used as an insulator.