JPH04220906A - Ethylene type polymeride or its compound excellent in anti-water tree property and electric insulation, and power cable using the same - Google Patents

Abstract

PURPOSE:To provide an ethylene type polymeride or compound incl. it, which has a high dielectric breakdown voltage and with which generation of water-tree is prevented, and fabricate a high voltage power cable using the substance. CONSTITUTION:Ethylene type polymeride or a compound including it is prepared from (a), (b), (c) as named below, and a power cable is fabricated using this substance as insulation. That is, (a) 87-98.99wt.% of ethylene, (b) 1-10wt.% of unsaturated carbonic acid ester and/or vinyl-ester, and (c) 0.01-3wt.% of at least one of the aromatic substances consisting of monomers incl. stylene and its derivative. Thereby the intended purpose can be achieved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ethylene polymer composition having a high dielectric breakdown voltage and excellent water tree resistance, and a high-voltage power cable using the same. For more details,
The present invention relates to an ethylene polymer or an ethylene polymer composition that prevents the occurrence of water trees and has a high dielectric breakdown voltage, and a high-voltage power cable using the same.

0002

2. Description of the Related Art Hitherto, high-voltage polyethylene and cross-linked polyethylene have been widely used as insulators for high-voltage power cables because of their excellent electrical properties. However, when high-voltage power cables made of polyethylene or cross-linked polyethylene are used for long periods of time, insulation breakdown occurs due to water trees, etc., so improvements are needed. Furthermore, if the power transmission voltage increases as the power transmission capacity is expected to increase in the future, there is a problem in that the thickness of the insulator must be increased to correspond to the increased voltage. That is, with current materials such as polyethylene, dielectric breakdown will occur if the insulating layer is not made very thick in response to high voltages. Various methods have been attempted to improve the above problems. for example,
Ethylene and vinyl acetate (VA) for polyethylene
Ethylene-vinyl acetate copolymer (EV
A), ethylene-ethyl acrylate copolymer (EE), which is a copolymer of ethylene and ethyl acrylate (EA).
There is a method of blending polar polymers such as A).

[0003] According to this method, the generation of water trees (bowtie-shaped trees) generated from microvoids and foreign matter parts has been suppressed, but on the other hand, it has the disadvantage that electrical insulation resistance decreases due to the introduction of polar groups. There is. Also,
In order to achieve thinning of the insulating layer, there are methods such as copolymerizing an ethylenically unsaturated monomer with a styrene monomer to improve the breakdown strength against impact voltage.

0004

[Problems to be Solved by the Invention] The present invention has been made as a result of intensive studies in view of the above problems, and its first purpose is to prevent the occurrence of water trees and increase dielectric breakdown voltage. A second object of the present invention is to provide a high-voltage power cable using the same as an insulator.

[0005]

A first aspect of the present invention is an ethylene polymer or an ethylene polymer composition comprising the following (a), (b), and (c). (a) Ethylene units 87-98.99% by weight (b) Unsaturated carboxylic acid ester and/or vinyl ester units 1-10% by weight (c) At least one selected from the group consisting of styrene and monomers containing styrene derivatives a type of aromatic unit
0.01-3% by weight The second invention of the present invention has the following (a
), (b), and (c) as an insulator. (a) Ethylene unit 87-98.99
Weight % (b) Unsaturated carboxylic acid ester and/or vinyl ester unit 1 to 10 weight % (c) At least one aromatic unit selected from the group consisting of styrene and monomers containing styrene derivatives
0.01-3% by weight

The present invention will be explained in detail below. The present inventors randomly added at least one aromatic unit selected from the group consisting of a very small amount of unsaturated carboxylic acid ester and/or vinyl ester units and styrene and monomers containing styrene derivatives to the ethylene unit. The present inventors have surprisingly found that the ethylene polymer contained therein increases the dielectric breakdown voltage and also prevents water trees. The unsaturated carboxylic acid ester unit of component (b) used in the present invention is a unit derived from α,β-unsaturated carboxylic acid ester, and 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, Examples include unsaturated carboxylic acid esters such as lauryl methacrylate, stearyl acrylate, stearyl methacrylate, monomethyl maleate, monoethyl maleate, diethyl maleate, monomethyl fumarate, glycidyl acrylate, and glycidyl methacrylate. be able to. Among these, (meth)acrylic acid alkyl esters are particularly preferred. More preferred are methyl acrylate and ethyl acrylate.

Examples of specific monomers for inducing the vinyl ester unit of component (b) used in the present invention include vinyl propionate, vinyl acetate, vinyl caproate, vinyl caprylate, vinyl laurate, and stearin. Examples include vinyl ester monomers such as vinyl acid and vinyl trifluoroacetate. Among these, vinyl acetate is particularly preferred. The content of unsaturated carboxylic acid ester and/or vinyl ester units as component (b) used in the present invention is 1 to 10% by weight. If the content is less than 1% by weight, the effect will be small, and if the content is more than 10% by weight, the insulation will deteriorate, which is not preferable.

Component (c) used in the present invention is at least one aromatic unit selected from the group consisting of monomers including styrene and styrene derivatives. However, among these, styrene, α-methylstyrene, etc. are preferred. The styrene derivative monomer inducing the aromatic unit of component (c) that can be used in the present invention includes Compound 1 represented by the following general formula.

[Formula 1] However, R1, R2, and R3 may be the same or different, H, methyl group, ethyl group, propyl group, butyl group, naphthene group, substituted naphthene group, phenyl group, substituted phenyl group, biphenyl group, substituted biphenyl group,
Hydrocarbon groups such as naphthalene groups and substituted naphthalene groups. The benzene nucleus of the styrene derivative may be substituted with one or more of the above substituents.

Specific examples of styrene derivatives include α-
Methylstyrene, α-methyl-p-methylstyrene, α
-Methyl-o-methylstyrene, α-methyl-m-methylstyrene, α-methyl-p-ethylstyrene, p-methylstyrene, o-methylstyrene, m-methylstyrene, p-ethylstyrene, o-ethylstyrene , m-ethylstyrene, p-phenylstyrene, p-propylstyrene, and the like.

In the present invention, the content of aromatic units in the ethylene polymer containing 0.01 to 3% by weight of aromatic units derived from styrene or styrene derivatives is 0.01 to 3% by weight.
If it is less than 0.01% by weight, the effect of increasing the dielectric breakdown voltage will be small, and if it is more than 3% by weight, the dielectric breakdown voltage will decrease, which is not preferable.

Specific examples of the ethylene polymer of the present invention, which is a copolymer of ethylene and at least one monomer containing unsaturated carboxylic acid ester and/or vinyl ester units and styrene and styrene derivatives, include: , ethylene/VA/styrene copolymer, ethylene/V
A/α-methylstyrene copolymer, ethylene/VA/α
-Methyl-p-methylstyrene copolymer, ethylene/V
A/α-methyl-o-methylstyrene copolymer, ethylene/VA/α-methyl-m-methylstyrene copolymer,
Ethylene/VA/α-methyl-p-ethylstyrene copolymer, ethylene/VA/p-methylstyrene copolymer,
Ethylene/VA/o-methylstyrene copolymer, ethylene/VA/m-methylstyrene copolymer, ethylene/V
A/p-ethylstyrene copolymer, ethylene/VA/o
- Ethylstyrene copolymer, ethylene/VA/m-ethylstyrene copolymer, ethylene/VA/p-phenylstyrene copolymer, ethylene/VA/p-propylstyrene copolymer, etc.

Ethylene/EA/styrene copolymer, ethylene/EA/α-methylstyrene copolymer, ethylene/
EA/α-methyl-p-methylstyrene copolymer, ethylene/EA/α-methyl-o-methylstyrene copolymer, ethylene/EA/α-methyl-m-methylstyrene copolymer, ethylene/EA/ α-Methyl-p-ethylstyrene copolymer, ethylene/EA/p-methylstyrene copolymer, ethylene/EA/o-methylstyrene copolymer, ethylene/EA/m-methylstyrene copolymer, ethylene/ EA/p-ethylstyrene copolymer, ethylene/
EA/o-ethylstyrene copolymer, ethylene/EA/
m-ethylstyrene copolymer, ethylene/EA/p-phenylstyrene copolymer, ethylene/EA/p-propylstyrene copolymer, etc.

Ethylene/VA/EA/styrene copolymer, ethylene/VA/EA/α-methylstyrene copolymer, ethylene/VA/EA/α-methyl-p-methylstyrene copolymer, ethylene/VA/ EA/α-methyl-o
-Methylstyrene copolymer, ethylene/VA/EA/α
-Methyl-m-methylstyrene copolymer, ethylene/V
A/EA/α-methyl-p-ethylstyrene copolymer,
Ethylene/VA/EA/p-methylstyrene copolymer,
ethylene/VA/EA/o-methylstyrene copolymer,
ethylene/VA/EA/m-methylstyrene copolymer,
ethylene/VA/EA/p-ethylstyrene copolymer,
ethylene/VA/EA/o-ethylstyrene copolymer,
ethylene/VA/EA/m-ethylstyrene copolymer,
Examples include ethylene/VA/EA/p-phenylstyrene copolymer and ethylene/VA/EA/p-propylstyrene copolymer.

[0014] Unsaturated carboxylic acid ester monomer and/or
Alternatively, when copolymerizing ethylene with at least one of a vinyl ester monomer and a monomer containing styrene and styrene derivatives, other unsaturated monomers may be further copolymerized as necessary. Examples of the other unsaturated monomers include olefins such as propylene, butene-1, hexene-1, decene-1, octene-1, and the like. A preferred method for producing the ethylene copolymer of the present invention is a high-pressure radical polymerization method, which does not leave any metal compound as a catalyst residue and is said to have no adverse effect on electrical properties.

[0015] The high-pressure radical polymerization method uses, for example, 87 to 98.99% by weight of ethylene and 1 to 10% of unsaturated carboxylic acid ester monomer and/or vinyl ester monomer.
% by weight and 0.01 to 3% by weight of at least one of the monomers, including styrene and styrene derivatives, based on the total weight of all those monomers.
Polymerization pressure of 500 to 4000 kg/cm2, preferably 100 kg/cm2 in the presence of 1 to 1% by weight of a radical polymerization initiator
0~3500kg/cm2, reaction temperature 50~400
℃, preferably 100 to 350 ℃ in the presence of a chain transfer agent and optionally an auxiliary agent in a tank or tubular reactor, the monomers are contacted and polymerized simultaneously or in stages. It's a method.

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

Another method for producing the ethylene polymer of the present invention is to add at least one of styrene and styrene derivatives to a conventional ethylene homopolymer or copolymer, and an unsaturated carboxylic acid ester monomer and/or There is a method of grafting vinyl ester monomers.

The above-mentioned ethylene homopolymers or copolymers include homopolymers such as low density and medium density polyethylene, ethylene/propylene copolymers, ethylene/butene-1 copolymers, ethylene/hexene-1 copolymers, Copolymers containing ethylene as a main component with other α-olefins, such as ethylene/4-methylpentene-1 copolymer and ethylene/octene-1 copolymer, and mixtures thereof can be used.

The grafting method may be any of the generally well-known methods such as a chain transfer method such as graft modification without a solvent or in a solvent in the presence of a crosslinking agent such as an organic peroxide, or irradiation with ionizing radiation. It may also be done by

[0020] As the crosslinking agent, organic peroxides such as hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxy ester, and ketone peroxide;
Vulcanizing agents such as dihydroaromatic compounds and sulfur can be mentioned. It is important that the amount of styrene and styrene derivatives grafted is 0.01 to 3% by weight based on the resin component.

The ethylene polymer composition of the present invention is a blend of an ethylene (co)polymer having an aromatic group such as styrene and an ethylene homopolymer or copolymer;
It includes a blend of a predetermined amount of a polymer such as styrene with the ethylene homopolymer or copolymer. Specifically, a terpolymer containing (a) ethylene units, (b) unsaturated carboxylic acid ester and/or vinyl ester units, and (c) aromatic units such as styrene is blended into an ethylene homopolymer. or (a
) a binary copolymer containing an ethylene unit and (b) an unsaturated carboxylic acid ester and/or vinyl ester unit; and a binary copolymer containing (a) an ethylene unit and (c) an aromatic unit such as styrene. It may also be made by blending. However, in both cases, (a) in the blend
87 to 98.99% by weight of ethylene units, (b) 1 to 10% by weight of unsaturated carboxylic acid ester and/or vinyl ester units, and (c) 0.01 to 3% by weight of aromatic units such as styrene. It is important to become

[0022] The ethylene polymer or ethylene polymer composition of the present invention can be used to produce a power cable by applying an insulating coating onto a conductor using a conventional crosshead extrusion coating method. In this case, it is preferable to provide an inner and an outer semiconducting layer. In the present invention, antioxidants, crosslinking agents, ultraviolet absorbers, pigments, dyes, lubricants, etc. may be added to the ethylene polymer or ethylene polymer composition without departing from the gist of the present invention. . The ethylene polymer or ethylene polymer composition of the present invention described above is not only used as an insulating layer for ordinary electric wires and power cables, but also used alone or blended with other synthetic resins, rubber, etc. It is processed into films, sheets, tapes, yarns, etc., laminated with other base materials as necessary, and used for insulating films, sheets, insulating tapes, insulating covers, insulating clothing, etc.

[0023] The power cable, which is the second invention of the present invention, includes an extruded inner semiconducting layer and/or outer semiconducting layer, or optionally an outer metal shielding layer made of copper, aluminum, lead, etc., or wrapped with aluminum tape or the like. It has an insulating layer made of the above-mentioned ethylene polymer or ethylene polymer composition together with a coating layer, such as a twisted water-shielding layer, which is usually provided in power cables. The insulating layer includes a crosslinked body,
Any uncrosslinked form may be used. In addition, in crosslinking, in addition to crosslinking agents such as peroxide and sulfur, or vulcanizing agents,
Conventional methods such as silane crosslinking, electron beam crosslinking, etc. can be used.

[0024]

EXAMPLES Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto. Examples 1 to 5 and Comparative Examples 1 to 4 In Table 1, as Example 1, ethylene/vinyl acetate (V
A)/styrene copolymer (VA content 3% by weight, styrene content 0.2% by weight), as Example 2, ethylene/vinyl acetate (VA) copolymer (VA content 10% by weight) and ethylene/vinyl acetate (VA) copolymer (VA content 10% by weight). Blend (1:1 weight ratio) with styrene copolymer (styrene content 0.5% by weight), ethylene/vinyl acetate (VA)/styrene copolymer (1:1 weight ratio) as Example 3;
(VA content 10% by weight, styrene content 0.5% by weight)
and low-density homopolyethylene (product name = Nisseki Rexron W
2000, manufactured by Japan Petrochemical Co., Ltd.) (LDPE) (1:1 weight ratio), Example 4: ethylene/
Vinyl acetate (VA)/styrene copolymer (VA content 1
0% by weight, styrene content 0.2% by weight), ethylene/vinyl acetate (VA)/styrene copolymer (VA content 3% by weight, styrene content 0.5% by weight) as Example 5.
,

As Comparative Example 1, low density homopolyethylene (
(Product name = Nisseki Rexron W2000, manufactured by Nippon Petrochemical Co., Ltd.); as comparative example 2, ethylene/vinyl acetate copolymer was added to low-density homopolyethylene (Product name = Nisseki Rexron W2000, manufactured by Nippon Petrochemical Co., Ltd.) (EVA) (VA content 15% by weight) was blended to make the VA content of the blend 3% by weight, and Comparative Example 3 was an ethylene/vinyl acetate (VA)/styrene copolymer (VA content 15%).
% by weight, styrene content 0.5% by weight), and as Comparative Example 4, ethylene/vinyl acetate (VA)/styrene copolymer (
The measurement results of the number of water tree occurrences, volume resistivity, and dielectric breakdown voltage for VA content of 5% by weight and styrene content of 15% by weight are shown.

[Method for Measuring Insulation Resistance and Dielectric Breakdown Voltage] The ethylene polymer (composition) shown in Table 1 was made into a 0.3 mm thick press sheet, and the insulation resistance was determined after applying 1000 V DC for 10 minutes. Moreover, the method of the impulse destruction test is as follows. A fixed electrode, a so-called McKeon electrode (Fig. 1), was used as the electrode system. The electrode system substrate was made of polymethyl methacrylate 4 and had a hole with a diameter of 1/2 inch in its center. The electrode is a 1/2 inch stainless steel bulb.
was used. Sample 2 was cut into approximately 8 to 10 mm squares and sandwiched between the electrodes. A degassed epoxy resin 3 was filled between the sample 2 and the electrode and cured. The McKeon electrode was immersed in a container filled with silicone oil and placed in a constant temperature bath for measurements. The voltage waveform used for destruction was a negative polarity, 1 x 40 μS impulse waveform. The waveform was observed with an oscilloscope, and the data that broke at the top of the wave was taken as data, and the average value of 20 points or more was taken.

[Method for measuring the number of water trees generated] A sheet with a thickness of 3 mm was placed in water at 70°C and charged with a sinusoidal alternating current of a voltage of 6 KV and a frequency of 1 KHz for 320 hours.The sample was stained with methylene blue and water trees were measured. I counted the numbers.

[Table 1]

[0028]

Effects of the Invention As described above, the ethylene polymer or the ethylene polymer composition of the present invention contains at least one aromatic unit selected from the group consisting of a small amount of styrene and a monomer containing a styrene derivative. and unsaturated carboxylic acid ester and/or vinyl ester units, it has the effect of increasing dielectric breakdown voltage and preventing the occurrence of water tree, and when used as an insulating layer of power cables. , it is possible to reduce power loss during high voltage transmission without increasing the thickness of the insulating layer.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view showing a McKeon electrode for impulse breakdown testing in the present invention.

[Explanation of symbols]

1. stainless steel ball 2. sample 3. Epoxy resin 4. polymethyl methacrylate

Claims (2)

[Claims] 1. An ethylene polymer or an ethylene polymer composition comprising the following (a), (b), and (c). (a) Ethylene units 87-98.99% by weight (b) Unsaturated carboxylic acid ester and/or vinyl ester units 1-10% by weight (c) At least one selected from the group consisting of styrene and monomers containing styrene derivatives a type of aromatic unit
0.01-3% by weight 2. A power cable characterized in that an ethylene polymer composition consisting of the following (a), (b), and (c) is used as an insulator. (a) Ethylene unit 87-98.99
Weight % (b) Unsaturated carboxylic acid ester and/or vinyl ester unit 1 to 10 weight % (c) At least one aromatic unit selected from the group consisting of styrene and monomers containing styrene derivatives
0.01-3% by weight