JPH01225004A - Electric insulation composition and power cable - Google Patents

Abstract

PURPOSE:To aim at improving insulation endurance of an insulator by using a polyolefin to which an antioxidant is grafted by means of an organic peroxide. CONSTITUTION:A polyolefin can be bridged by an organic peroxide, but when a specific antioxidant is coexistent, it is grafted to polyolefin chains antecedently to bridging. The antioxidants that are ready to be grafted such as thiobisphenol antioxidants or phenol antioxidants having vinyl base are used. Namely, the voltage withstand characteristic can be improved by suppressing acceleration of moving electrons within the crystal structure when insulation breaks as a result of more of less inhibition of polyolefin crystallization, and by suppressing acceleration of electrons due to aromatic rings having a resonant structure included in the antioxidant.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrical insulating composition used for electrical cables and electrical cables.

(Prior art) (Problems to be solved by the invention) With the recent increase in power transmission voltage, polyolefin electric capacitors are
Even 7S kV class cables have been put into practical use.

This poses an obstacle to winding, transportation, and facilities, and it is desired to reduce the insulation thickness.

In other words, it is required to reduce the insulation thickness as much as possible by improving the dielectric strength of polyolefin insulators.

(Means for solving the problems) The present invention has been made to achieve the above problems,
The outline is shown below.

We have discovered that the dielectric strength of an electrical insulating composition based on polyolefin grafted with an antioxidant using an organic peroxide is significantly improved when used as an external insulating layer of a conductor. .

Therefore, the antioxidant used here is preferably a thiobisphenol type or a vinyl group-containing phenol type.
Also, the amount added per 100 parts by weight of polyolefin is 0.
1 to 5 parts by weight is preferred.

(Function) Although polyolefins are crosslinked by organic peroxides, we have found that when a specific antioxidant coexists, the antioxidant grafts onto the polyolefin chains prior to crosslinking.

Examples of such antioxidants include thiobisphenols, 4,4'-thiobis=(6-tert-butyl-
3-methylphenol), 4-4'-thiobis-(6-
tert-butyl-0-cresol), 2,2'-thiobis-
(6-tert-butyl-4-methylphenol) and the like. In addition, phenolic antioxidants containing vinyl groups as shown in the chemical formula below are also antioxidants that can be easily grafted.

Bu Bu Bu H3CH3 Grafting of these antioxidants to polyolefin is thought to have the following mechanism.

(Thiobisphenol antioxidant) (Vinyl group-containing phenolic antioxidant) ■ H ■ PAO (PAO: Phenolic antioxidant) Here, the amount of antioxidant for grafting added is based on 100 parts by weight of polyolefin. 0.1 to 5 parts by weight is preferred;
If it is less than 0.1 part by weight, the withstand voltage performance will not be improved, and the effect of preventing thermal deterioration will not be improved.

If it exceeds 25.0 parts by weight, the dielectric properties of the insulator will be deteriorated and the crystallinity of the polyolefin will be significantly reduced due to grafting, resulting in poor withstand voltage performance.

Organic peroxides used for grafting antioxidants and crosslinking polyolefins include dicumyl peroxide (DCP), α-α'-bis(t-butylperoxy) diisopropylbenzene, and 1-butylcumyl peroxide. , 2,5-methyl-2,5-di(1-butyl-4-
Oxy)hexane-(3) and the like are listed.

When used as an uncrosslinked insulator, the amount added is equal to the number of moles of the antioxidant added - 1/4, and when used as a crosslinked insulator, it is necessary to add even more.

The reasons for the improvement in voltage resistance properties due to the grafting of antioxidants as described above are thought to be as follows.

(1) Suppression of acceleration of intracrystalline electrons during dielectric breakdown due to some inhibition of crystallinity of polyolefin (2J Suppression of electron acceleration due to aromatic rings with electronic resonance structure contained in antioxidants, and as a polyolefin Examples include polyethylene, polypropylene, polybutene-1, polymethylpentene-1, etc., and high-density polyethylene with a high degree of crystallinity is most preferred in terms of withstand voltage performance.

Organic peroxides used for grafting antioxidants include dicumyl parent oxide (DCP), α, α
'-bis(1-butylperoxy)diisopropylbenzene, t-butylcumyl peroxide, 2.5 dimethyl-2.5 di(t-butyloxy)hexane,
2.5-methyl-2,5-di(1-butylperoxy)
hexane-CB), etc.

When used as an uncrosslinked insulator, the amount added should be equal to the number of moles of the antioxidant added - 1/4, and when used as a crosslinked insulator, it needs to be even larger than this.

(Example) Next, embodiments of the present invention will be described.

Examples 1 to 3 High-density polyethylene with a density of 0.953 and MI=0.5 was kneaded with an antioxidant and DCP of a predetermined tone to prepare a mixture. The antioxidant is one of the following formula k0. 1-5
．． It was used within the range of 0-layer lid.

Further, DCP was set at A mole relative to the antioxidant.

Comparative Example 1 Same as Example 1 except that no antioxidant was added.

Comparative Examples 2 and 3 The same as Example 1 except that the total amount of antioxidant used was less than 0.1 parts by weight and 5.0 parts by weight.

Examples 4 to 6 n except that the following formula was used as the antioxidant
This is the same as Examples 1 to 3.

-Bu The addition cap of DCP is A mole of antioxidant.

Comparative Example 4.5 Use of antioxidant! : Same as Example 4 except that the total was less than 0.1 part by weight and 5.0 parts by weight. In order to examine the characteristics of these Examples and Comparative Examples, recessed sheet samples for destructive testing and 1 for dielectric property measurement as shown in Figure 1 were used.
fil! A thick sheet was press-crosslinked at 180°C for 30 minutes.

Using the electrode configuration shown in Figure 1 for each sample, a breakdown test using standard impulse (IX40μB) voltage and AC30
The dielectric loss tangent (tan δ) was measured in Hz.

In Figure 1, 1 is the sample, 2 is the conductive paint on the upper and lower surfaces, 3 is the insulating oil, and 4 is the electrode, and the thickness of the recess is 200~3.
0 0 ttm, and the effective diameter of the recess is 10 mm.

Antioxidant analysis was performed by solvent extraction, but no antioxidant was detected in the extraction solvent, confirming that the antioxidant was grafted onto the polyethylene.

Table 1 Note: ■ and ■ represent the above-mentioned antioxidants.

Next, in the present invention, electric cables were made using the valley insulators of Example 2.5 and Comparative Example 2 in Table 1 above as an insulating layer outside the conductor. The cable structure has a conductor cross section of 250
y+i'', an insulating layer thickness of 9 mm, a 3-no structure having an inner semiconducting layer of 1- and an outer semiconducting layer.

Commercial frequency (AC) of each cable above! Table 2 shows the results of destructive tests using pressure and standard pressure (Imp).
This was the general rule.

Table 2 (Effects of the Invention) According to the present invention, as is clear from the comparative test drive described above, unlike the case where the antioxidant is completely cooled, the withstand voltage performance can be significantly improved by grafting the polyolefin. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a method for destructive testing of an admixture sheet. Agent Patent Attorney Mamoru Takeuchi Figure 1

Claims (5)

[Claims] (1) Electrical insulation composition based on polyolefin grafted with antioxidant by organic peroxide (2) The electrical insulation composition according to claim 1, wherein the antioxidant is a thiobisphenol type or a vinyl group-containing phenol type. (3) Claim 1 in which the polyolefin is high-density polyethylene, polypropylene, or ethylene-propylene copolymer.
electrical insulation composition (4) The electrical insulation composition according to claim 1, wherein the amount of the antioxidant added is 0.1 to 5 parts by weight per 100 parts by weight of the polyolefin. (5) A power cable characterized in that the external insulating layer of the conductor is made of a crosslinked polyolefin grafted with an antioxidant using an organic peroxide.