JPH08264029A - Cross-linked polyolefin insulated cable - Google Patents

Abstract

PURPOSE: To effectively suppress the deterioration of electric insulation due to the water generated by the decomposition of a cross-linking agent and the generation of a water tree by making the cross-linked polyolefin containing a specific quantity of a specific oxidant an insulator. CONSTITUTION: A cross-linked polyolefin insulator with dicumyl peroxide cross- linked as a cross-linking agent contains an oxidation inhibitor having the hindered phenol group and an ester bond section within the range of 0.05-3pHR. When the content of the oxidation inhibitor is below 0.05pHR, the effect to prevent the generation of water is insufficient. When the content exceeds 3pHR, the nature of the insulator is affected, and blooming easily occurs. A cable using this insulator can prevent the deterioration of the electrical insulation performance due to the water generated by the decomposition of the cross- linking agent and the generation of a water tree under heating conditions during its use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross-linked polyolefin insulation cable, and in particular, dicumyl peroxide (hereinafter referred to as "DCP") as a cross-linking agent for an insulator.
In the crosslinked polyolefin insulated cable using, the crosslinked polyolefin insulated cable in which deterioration of the electrical insulating performance due to water generated by decomposition of the crosslinking agent under actual heating conditions and generation of water trees is prevented.

[0002]

2. Description of the Related Art Electric wires or power cables using polyethylene crosslinked with DCP as an insulator are often used as crosslinked polyolefin insulated cables. However, the insulator cross-linked by this method generates water inside when the cable connection part is assembled and is heated by a heat cycle during actual use, which deteriorates the electrical insulation performance, or causes so-called water tree formation. It may cause serious damage to the characteristics of the cable.

Therefore, a method for suppressing the generation of water in this insulator has been searched for. It is known that the water generated in the crosslinked polyolefin insulator is generated by the decomposition of DCP. That is, at the time of crosslinking, DCP decomposes according to the following formula (I) to generate cumyloxy radicals and to withdraw hydrogen from polyethylene, thereby promoting crosslinking and producing acetophenone, methane, cumyl alcohol and the like.

[0004]

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The produced cumyl alcohol undergoes a secondary decomposition reaction as shown in the following formula (II) when heated, and α
-Produces methylstyrene and water.

[0006]

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[0007]

As a method of removing this water, for example, JP-A-4-342731 discloses that the secondary decomposition reaction (II) of cumyl alcohol is suppressed.
A method is proposed in which the content of water in the insulator is reduced in advance by heating to a temperature of 5 ° C. or lower and the temperature is newly heated to 85 to 95 ° C. However, this method is for preventing the water from temporarily increasing and accumulating, and is not efficient in that it requires a long drying time. In addition, JP-A-4-35
5013 describes a method of volatilizing and removing a decomposition residue of DCP, which is a causative substance of water generation, by heating and drying a crosslinked insulator. However, this method is also inefficient in that it requires an additional heat drying step to remove the decomposition residue and the produced water.

As a method which does not require a step of removing cumyl alcohol and / or generated water by heating for a long time,
A method has been proposed in which a basic antioxidant such as an aliphatic amine or isocyanic acid ester is added to the insulator to suppress the secondary decomposition reaction (II) (JP-A-1-243306, respectively). JP-A-63-289
715). However, these antioxidants
In addition to causing problems such as contamination, blooming, and delamination, it expires relatively quickly due to migration and if mixed in in large amounts, it also causes problems with the insulation performance of cables. The present invention has been made to solve the above problems, and therefore an object thereof is a crosslinked polyolefin in which deterioration of electric insulation performance due to water produced by decomposition of a crosslinking agent and generation of water trees are effectively suppressed. To provide an insulated cable.

[0009]

[Means for Solving the Problems] The above-mentioned problem is to provide an antioxidant in which a crosslinked polyolefin insulator crosslinked with DCP has a hindered phenol group and an ester bond portion.
The solution can be provided by providing a crosslinked polyolefin insulated cable comprising within the range of 0.05 PHR to 3 PHR. This antioxidant is tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane (hereinafter referred to as “TMP”).
M ”), 2,2′-thiodiethylenebis- [3-
(3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] (hereinafter referred to as "TDBP")
Or n-octadecyl-3- (3 ', 5'-di-t-
It is preferable that it is any one or more of butyl-4′-hydroxyphenyl) propionate (hereinafter referred to as “NODP”).

[0010]

It is known that the decomposition of cumyl alcohol according to the above formula (II) proceeds in the presence of active oxygen. It is considered that the above-mentioned antioxidants effectively inactivate oxygen in the insulator to suppress the decomposition of cumyl alcohol and prevent the generation of water.

In particular, the antioxidant having a hindered phenol group and an ester bond has an effect of preventing scorch by being stably held in crosslinked polyethylene without causing problems such as contamination of polyethylene. From these viewpoints T
MPM, TDBP, and NODP have been found to be particularly preferred antioxidants. If the content of the antioxidant is less than 0.05 PHR, the effect of preventing the generation of water is insufficient, and if it exceeds 3 PHR, the physical properties of the insulator are affected, and blooming is likely to occur.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. The cable samples used in the following Examples and Comparative Examples are all low-density polyethylene having a specific gravity of 0.92, which contains 2 PHR of DCP as a cross-linking agent and 0.3 PHR of the following antioxidant on a conductor having a diameter of 60 mm. 2
It is coated to a thickness of 5 mm and crosslinked under the same conditions at 200 ° C.

The antioxidants used for each sample are as follows. (Example 1) TMPM (Example 2) TDBP (Example 3) NODP (Comparative Example 1) 4,4'-thiobis- (3-methyl-6-
t-butylphenol). Hereinafter, it is referred to as "TBMP".
This compound is an antioxidant having a hindered phenol group but no ester bond.

Each of the above cable samples was heated in an air oven at 180 ° C. for 2 hours and heated, and then the water content in the insulator was measured by the Karl Fischer method and compared with the water content before heating. The results are shown in Table 1.

[0015]

[Table 1]

From the results of Table 1, TMP which is an antioxidant having a hindered phenol group and an ester bond part
It is clear that M, TDBP, and NODP effectively suppress the generation of moisture after heating.

[0017]

INDUSTRIAL APPLICABILITY In the crosslinked polyolefin insulation cable of the present invention, the crosslinked polyolefin insulation crosslinked using DCP as a crosslinking agent contains an antioxidant having a hindered phenol group and an ester bond portion. It is possible to prevent deterioration of electrical insulation performance and generation of water trees due to water produced by decomposition of the cross-linking agent under all conditions of use.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiaki Mabuchi 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Izumi Ishikawa 1-1-5 Kiba, Koto-ku, Tokyo Shareholders Inside Fujikura

Claims (2)

[Claims] 1. An antioxidant in which a crosslinked polyolefin insulator crosslinked using dicumyl peroxide as a crosslinking agent has a hindered phenol group and an ester bond portion,
A cross-linked polyolefin insulated cable comprising in the range of 0.05 PHR to 3 PHR. 2. The antioxidant is tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, 2,2′-.
Thiodiethylenebis- [3- (3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] or n-octadecyl-3- (3', 5'-di-t-butyl-4 ' The crosslinked polyolefin insulated cable according to claim 1, which is any one or more of -hydroxyphenyl) propionate.