JPH01229058A - Insulating composition and power cable - Google Patents

Abstract

PURPOSE:To obtain an insulating composition, excellent in water treeing resistance and suitable as insulators for power cables, by blending a mixture consisting of a maleic acid-modified low-density polyethylene and ethylene-vinyl acetate copolymer with a crosslinking agent and antioxidant. CONSTITUTION:An insulating composition obtained by blending (A) 100 pts.wt. mixture, consisting of (A1) a maleic acid-modified low-density polyethylene, preferably having 0.5-5wt.% amount of modification and (A2) ethylene-vinyl acetate copolymer and having 0.5-10wt.%, preferably 0.54-5wt.% vinyl acetate content of the total mixture with (B) 1.5-3 pts.wt. crosslinking agent (e.g., dicumyl peroxide) and (C) 0.2-0.3 pt.wt. antioxidant [e.g., 4,4'-thiobis(6-tert- butyl-3-methylphenol)].

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement of a crosslinked polyethylene insulation composition and an electric cable using this composition as an insulator, and particularly to one in which the occurrence of water trees is suppressed.

<Conventional technology> Due to its excellent insulation properties and ease of processing, polyethylene is the main insulator for power cables today, and in particular, cross-linked polyethylene cables with improved thermal properties through cross-linking are used. (XLPE cable) is widely used.

The weak point of this XLPE cable is that water treeing occurs due to moisture in the insulator and the presence of local abnormal electric fields, which is a phenomenon unique to the cable, and the insulation performance of the cable deteriorates.

Water trees in XLPE insulators are thought to occur when water is concentrated in polyethylene, which is a hydrophobic polymer, when there is an abnormal electric field locally.

Therefore, it is considered that by blending a polymer that has a scratchable group and is hydrophilic to some extent, it is possible to prevent water from concentrating in the local abnormal electric field and to improve water tree resistance. In fact, there have already been some proposals to improve water resistance by blending EVA or ethylene-ethyl acrylate copolymer (EEA).

<Problems to be Solved by the Invention> However, even with the above-mentioned insulating composition, the water tree prevention effect is still incomplete, especially in cases where the insulation composition is immersed in water, such as distribution class electric cables. In cases where conditions are severe, further improvement in water resistance is desired.

Therefore, as a result of intensive studies on the polyethylene to be used and the EVA to be mixed with, the present inventors found that maleic acid-modified P
When E and EVA are mixed and the VA% of the entire mixture is set to be in a specific range (0.5 to 10%),
It has been found that water resistance can be significantly improved.

The present invention has been made from such a viewpoint, and an object of the present invention is to provide an insulating composition with further improved water resistance and an electric cable using the same.

The insulating composition of the present invention, which achieves the above objects, is made of maleic acid-modified PE.
and EVA, and the total VA% is 0.5 to 10.
%, and a crosslinking agent and an anti-aging agent are added to 100 parts by weight of the mixture.The electric cable of the present invention is a cable using this insulating composition as an insulator.

Here, the maleic acid-modified PE used is not particularly limited, but the amount of maleic acid modification is 0. 5 to 5% is preferred. This is because the amount of maleic acid modification is 0.5%.
If the amount is less than 5%, the effect of suppressing water tree is small, and if the amount of maleic acid modification exceeds 5%, the electrical properties (for example, tan δ
) becomes worse.

Further, the VA% of EVA itself used in the present invention is not particularly limited, but when blended with the maleic acid-modified PE, the VA% of the entire mixture is 0.5 to 10%, preferably 5% or less. Must. because,
This is because when VA% is less than 0.5, almost no water tree suppression effect is obtained, and on the other hand, when it exceeds 10%, electrical characteristics (for example, Lan δ) deteriorate.

In addition, examples of the crosslinking agent added in the present invention include dicumyl peroxide (DCP), 2.5-dimethyl-2
, 5-di(t-butylperoxy)hexyne-3, etc. can be used, and the amount added is preferably about 1.5 to 3.0 parts by weight per 100 parts by weight of the above-mentioned mixture.

Furthermore, as the anti-aging agent added in the present invention, phenol-based or amine-based ones can be used, such as 4.4'
-thiobis(6-tert-butyl-3-methylphenol), bis[2-methyl-4-(3-n-alkyl(C, or C14)thiopropionyloxy)-5
-t-butylphenyl]furphyto, 2,4-bis-(
n-Othylthio)-6-(4-hydroxy-3,5-di-butylaniline)-1,3,5-) riazine, etc. can be used, and the amount added is 100 parts by weight of the above mixture. The amount is preferably about 0.2 to 0.3 parts by weight.

In addition, other additives etc. which are usually added as necessary can be appropriately added to the composition of the present invention.

In this way, in the composition of the present invention, maleic acid-modified P
By combining E and EVA and by limiting the total VA% to a specific range, an excellent water tree inhibiting effect can be obtained. A possible reason for this is to prevent water from concentrating on the local abnormal electric field.

This insulating composition is coated on a cable core as an insulator by extrusion or the like to obtain the intended electrical cable.

<Example> Next, as shown in Table 1, maleic acid-modified PE (
MI=3, amount of maleic acid modification=2%), EVA
(MI=2, VA%=20%) in various proportions,
Values where the overall VA% satisfies the conditions of the present invention (0.5%, 5%
, 10%) was obtained, and to 100 parts by weight of this mixture,
2.0 parts by weight of DCP as a crosslinking agent and 4.4 parts by weight as an anti-aging agent.
0.3 parts by weight of '-thiobis(6-tert-butyl-3-methylphenol) was added and kneaded to obtain insulating compositions of the present invention (Examples 1 to 2).

For comparison, we also used the same maleic acid-modified PE as above (
MI = 3, maleic acid modification amount = 2%) or EVA (M1 = 2,
VA% = 20%) in various proportions, and the total VA%
A mixture with a value (0%, 0.3%, 15%) that lacks the conditions of the present invention was obtained, and a crosslinking agent and an anti-aging agent were added and kneaded to 100 parts by weight of this mixture in the same manner as above to obtain a comparative product. Insulating compositions were obtained (Comparative Examples ■ to ■).

Each of the above-mentioned insulating compositions (Examples 1 to 2, Comparative Examples 1 to 2) was press-molded at 160° C. for 140 minutes, and the following water tree test and dielectric loss tangent (tan δ) measurement test were conducted. The results are also listed in Table 1.

After this press molding, the gel fraction was measured by immersing it in xylene at 110°C for 24 hours, and the gel fraction was 85.
% or more, indicating that the crosslinking was sufficient.

(1) Water tree test As shown in Figure 1, a paint layer 2 of conductive paint is provided on the bottom surface of the test sample 1 with a thickness of 5 mm to serve as a ground electrode, and a water tank 3 is placed on the top surface of the test sample 1. A water electrode was formed by providing a water electrode, which was configured to be able to apply a voltage of 1 OKv, 1KH2, and after applying the above voltage for 30 days, the sample was boiled and the water tree was observed. The occurrence density of water trees of 50μ or more was observed and expressed as a relative number to the number of occurrences of 100 in the sample of Comparative Example (2) (XLPE only).

(2) Dielectric loss tangent (tan δ) measurement test A sheet sample with a thickness of 1 mm is used, and IKv, 50KH
A voltage of z was applied and measured using a Schering bridge.

From Table 1, it can be seen that in the case of the products according to the present invention, the density of water tree generation is extremely low, and there is no deterioration in electrical properties. On the other hand, in the case of comparative height measurement, the density of water tree generation was extremely high, and a decrease in electrical properties was observed in some samples.

<Effects of the Invention> As is clear from the above description, according to the present invention, it is possible to obtain an insulating composition that effectively suppresses the occurrence of water tree and has good electrical properties. By using it as an insulator, an excellent power cable can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the water tree test method performed in the present invention. In the figure, 1 is the test sample, 2 is the paint layer, and 3 is the water tank. Patent applicant: Fujikura Electric Wire Co., Ltd.

Claims (2)

[Claims] (1) Consists of low-density polyethylene modified with maleic acid (hereinafter referred to as maleic acid-modified PE) and ethylene vinyl acetate copolymer (hereinafter referred to as EVA), and has a total vinyl acetate content (hereinafter referred to as VA%). ) is 0.5 to 1
An insulating composition prepared by adding a crosslinking agent and an anti-aging agent to 100 parts by weight of a 0% mixture. (2) A power cable using the insulating composition according to claim 1 as an insulator.