JPH09167521A - Reinforced insulating material for power cable connection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To snorten execution time and enhance reliability in electric insulation performance by forming a reinforced insulating material for power cable connection with a composition of the specified amount of specific material, previously partially crosslinking, and integrally forming with a power cable by heating. SOLUTION: A composition prepared by adding 1.2 pts.wt. 1,3-bis(t- butylperoxyisopropyl)-benzene and 0.3 pts.wt. octadecyl-3-(3,5-di-t-butyl-4-hydroxy phenyl)propionate to 100 pts.wt. low density polyethylene (melt index is 0.5g/10min.) is heated at 130 deg.C for 60min. with a compression molding machine, crosslinked, then molded in a cylinder having an outer diameter of 19cm and an inner diameter of 10cm, and further crosslinked at 270 deg.C for 5 hours with a compression molding machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reinforced insulator for connecting a power cable, which can reduce a construction time and is highly reliable in terms of electric insulation performance.

[0002]

2. Description of the Related Art
From the viewpoint of electrical insulation, crosslinked polyethylene is used for the insulating layer of the power cable, and the same is used for the power cable connecting portion. The above-mentioned crosslinked polyethylene uses an organic peroxide as a crosslinking agent, and crosslinks polyethylene by radicals generated by thermal decomposition of the organic peroxide. The organic peroxide has a decomposition temperature of polyethylene. It may be higher than the melting point, but it is preferable that the melting point and the decomposition temperature are not close to each other. This is because when the insulating layer is molded into a desired shape, it is heated to about the melting point in order to make the polyethylene have fluidity, but at this time, if the decomposition of the organic peroxide proceeds at the same time, the polyethylene is cross-linked early. This makes it difficult to mold. Further, when an organic peroxide having a high decomposition temperature is used, the crosslinking time becomes long. Therefore, it is preferable that the decomposition temperature is not too high. As an organic peroxide satisfying the above two conditions, dicumyl peroxide has been conventionally used for crosslinking polyethylene.

By the way, as one of the construction methods of the power cable connecting portion, a reinforcing insulator for the connecting portion is preformed in a specific shape and is arranged around the power cable connecting portion when connecting the power cable. However, there is a method in which the reinforcing insulation is melted and crosslinked by heating to be integrated with the insulation of the cable (hereinafter also referred to as the block mold method). However, in order to shorten the construction time, crosslinking is performed during the above heating. It has been proposed to raise the temperature to reduce the crosslinking time.

However, in the above-mentioned construction method, since the reinforcing insulator is reheated, water is easily generated from the decomposition residue of dicumyl peroxide used as a cross-linking agent, and in addition to this, When the crosslinking temperature, which was 160 to 230 ° C., is increased to 260 ° C., for example,
There is a problem that water is likely to be generated from the decomposition residue of dicumyl peroxide, and as a result, water remains inside the reinforcing insulator, which is not preferable in terms of insulating performance.

An object of the present invention is to provide a reinforced insulator for connecting an electric cable, which can shorten the construction time and is highly reliable in terms of electric insulation performance.

[0006]

The reinforcing insulator for connecting a power cable according to the present invention has an octadecyl-based content of 100 parts by weight of low density polyethylene having a melt index of 0.5 to 4.0 g / 10 min.
3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 4,4 ′ -Thiobis [(3-
Methyl-6-t-butylphenyl) -2-thioalkylpropionate], and 0.1 to 2.0 parts by weight of at least one antioxidant selected from the group, and 1,3 as a crosslinking agent.
-Bis (t-butylperoxyisopropyl) -benzene and / or 2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3 in an amount of 1.0 to 2.5 parts by weight. Composed of a composition. The composition having a shape having a hole into which a power cable can be inserted is preliminarily partially cross-linked and molded. To be integrated with the insulator of the power cable by arranging it around the connection part of the power cable and then melting and crosslinking by heating. By having the above conditions (1) to (3), the above object is achieved.

The present invention suppresses the generation of water by combining the above-mentioned specific cross-linking agent and a specific antioxidant. Conventionally, dicumyl peroxide, which has been used as a cross-linking agent, produces water from a decomposition residue when cross-linked at a high temperature of about 260 ° C. Therefore, it is attempted to suppress the production of water by another cross-linking agent. A cross-linking agent was used. However, since the above-mentioned reinforcing insulator is partially cross-linked in advance and then cross-linked again at a high temperature, water is more likely to be generated than when it is cross-linked at once, and even if the above-mentioned specific cross-linking agent is used, the generation of water can be sufficiently suppressed. There wasn't. However, among the antioxidants that originally have the role of increasing the heat resistance of polyethylene, if it is a composition containing a specific antioxidant and the specific crosslinking agent,
The present invention has been completed by finding that the generation of water can be suppressed even when crosslinking is performed at a high temperature of about 260 ° C.

The composition used in the present invention comprises low-density polyethylene mixed with an antioxidant. The low-density polyethylene has a melt index of 0.5 to 4.0 g / 10 min in view of processability. A melt index of 0.6 to 2.5 g / 1 is particularly used from the viewpoint of extrudability.
A time of 0 minutes is preferred. Melt index is 0.5
If it is less than g / 10 minutes, extrusion failure will occur and 4.0 g / 1.
If it exceeds 0 minutes, it is not preferable from the viewpoint of heat deformation characteristics. In the present invention, the melt index is JIS
It is a value measured according to K6760. The density of the low density polyethylene is 0.918 to 0.9.
40 g / cm ³ is preferred.

Further, as the above-mentioned antioxidant, octadecyl-3- (3,3,3) is used from the viewpoint of suppressing the production of water.
5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3-
(3,5-di-t-butyl-4-hydroxyphenyl) propionate], 4,4'-thiobis [(3-methyl-6-t-butylphenyl) -2-thioalkylpropionate] Use at least one
The blending amount of the above-mentioned antioxidant is 0.1 to 2.0 parts by weight with respect to 100 parts by weight of low density polyethylene, and 0.15 to 1.5 parts by weight is preferable from the viewpoint of suppressing the generation of water. . If the compounding amount of the antioxidant is less than 0.1 parts by weight, the antioxidant effect will be insufficient, and if it exceeds 2.0 parts by weight, the degree of crosslinking will be reduced, which is not preferable.

The cross-linking agent used in the present invention is 1,3-bis (t-butylperoxyisopropyl) -benzene and / or 2,5-dimethyl-2,5-from the viewpoint of suppressing the production of water. It is di (t-butylperoxy) -hexyne-3. The amount of the cross-linking agent to be blended is preferably 1.0 to 2.5 parts by weight with respect to 100 parts by weight of low-density polyethylene, and is 1.2 to 1.2 in terms of the degree of crosslinking and the amount of water.
2.0 parts by weight is more preferred. The amount of the crosslinking agent is 1.
If the amount is less than 0 parts by weight, the degree of crosslinking will decrease, and if it exceeds 2.5 parts by weight, the effect of suppressing water generation is insufficient, which is not preferable.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As an embodiment of the reinforcing insulator for connecting a power cable of the present invention, FIG. 1 shows a sectional view of a power cable connecting portion after the reinforcing insulator is applied. Construction of the reinforced insulator may be performed as follows, for example. First, after correcting the bending tendency of the power cable, the metal jacket pipe and the like are removed to expose the insulator. Next, the insulator of the exposed portion is removed from the end portion by a predetermined size to expose the conductor,
Further, the remaining insulator is processed so that its outer diameter becomes narrower toward the axial end. After that, the above-mentioned cable end portion and another cable end portion processed in the same manner as above are connected and fixed by a conductor connecting pipe, and a cable inner semiconductive layer is connected and formed on the conductor connecting pipe. Then pre-partially cross-linked into a shape with holes into which power cables can be inserted,
A molded reinforced insulator is placed around the connection,
The reinforcing insulator and the power cable insulator are brought into close contact with and integrated with each other by melting and cross-linking this by heating.

In the present invention, it is preferable that the reinforcing insulator has a shape that can be easily arranged in the connection portion of the power cable, and therefore, it is preformed into a shape having a hole into which the power cable can be inserted. The size, shape, etc. of the cable insertion hole formed in the above-mentioned reinforcing insulator may be appropriately designed according to the size, shape, etc. of the tip portion of the cable to be inserted. However, in order to allow the power cable to be easily inserted into the cable insertion hole even if the power cable has a certain degree of bending, a certain degree of clearance is provided between the inner surface of the cable insertion hole and the cable insulator. It is preferable. This gap is 1 to 4 mm
It is suitable that it is about 2 mm to 3 mm. If the gap is less than 2 mm, the assembling of the connecting portion tends to be difficult, and if it is larger than 4 mm, the amount of gas in the gap increases, and the holes are formed at the interface between the reinforcing insulator and the cable insulator. It tends to be difficult to suppress the formation of (voids).

The shape of the reinforcing insulator is not particularly limited, but a tubular shape is preferable from the viewpoint of ease of constructing the connection portion. In this case, the inner cavity of the cylindrical reinforcing insulator is inserted into the cable. It can be a hole. Further, in this tubular reinforced insulator, the outer diameter is narrower toward the axial end as shown in FIG. 1 from the viewpoint of suppressing voids generated at the interface between the reinforced insulator and the cable insulator. It is preferably formed so that Further, the wall thickness of the reinforcing insulator (for example, the wall thickness in the central portion of the shaft) varies depending on the type of cable to be connected, and may be appropriately designed.

There are no particular restrictions on the molding method for preliminarily molding the reinforcing insulator of the present invention into the above-mentioned shape, and examples thereof include extrusion molding, tape winding molding, and injection molding.
Further, the reinforced insulator of the present invention is preferably formed by being divided in the axial direction and / or the radial direction from the viewpoint of easy construction.

In the present invention, the reinforcing insulating material, which has been partially cross-linked in advance to the specific shape as described above, is placed in the power cable connecting portion and then melted and cross-linked by heating. However, it is necessary that some of them remain unreacted even after being partially crosslinked. Therefore, the molding of the reinforcing insulator is performed under the condition that the crosslinking reaction is not completed. As such molding conditions, for example, a molding temperature of 110 to
The temperature is 140 ° C., preferably 120 to 135 ° C., and the molding time is 3 hours or less, preferably 2 hours or less.

The reinforcing insulation body formed by partially cross-linking in advance has a cross-linking degree of about 0.1 to 75%, and the fusion insulation between the reinforcing insulation body and the power cable insulation body is suitable. From the viewpoint of the above, it is preferably about 0.1 to 50%, and more preferably about 0.1 to 20%. If the degree of cross-linking is too small, the strength of the reinforcing insulator decreases, and the degree of deformation of the reinforcing insulator tends to increase during construction, and if the degree of cross-linking is too large, the fluidity of the reinforcing insulator decreases, In addition, the fusion bond between the reinforced insulator and the power cable insulator tends to decrease. The degree of crosslinking is the degree of crosslinking (gel fraction) measured by extraction with xylene (120 ° C for 24 hours).

The reinforced insulator of the present invention is disposed around the power cable, and is then melted and crosslinked by heating to be integrated with the power cable insulator. The heating temperature at this time is usually about 160 to 230 ° C., but in the present invention, it is 2
Generation of water can be suppressed even when cross-linked at a high temperature of about 30 to 300 ° C. Further, it is preferable to apply a pressure from the viewpoint of suppressing voids during the heating, and the applied pressure is 1
About 10 kg / cm ² G is suitable. Further, at this time, since the reinforcing insulator preferably has sufficient fluidity, the viscosity at 90 to 140 ° C. is 1 × 10 ⁴ to 1 ×.
It is preferably about 10 ¹² poise and 1 × 10 ⁴ to 1
More preferably, it is approximately 10 ¹⁰ poise. After being integrated with the power cable insulation, the degree of crosslinking of the reinforced insulation is
From the viewpoint of heat deformation characteristics, it is preferably 80% or more.

In order to prevent the deterioration of various properties of the reinforced insulator, the exposure of the cross-linking agent, the antioxidant and the like to the surface of the reinforced insulator during the period from the manufacture of the reinforced insulator to the construction at the connection site. It is preferable to prevent it. As a method for preventing exposure, for example, the reinforced insulator is stored at a temperature of 40 ° C. or lower from the time it is manufactured until it is assembled / molded at a connection site, or a vacuum or an inert gas atmosphere is used. It can be stored in.

[0019]

【Example】

(Example 1) 100 parts by weight of low-density polyethylene (melt index 0.5 g / 10 minutes) was added with 1,3-bis (t
-Butylperoxyisopropyl) -benzene 1.2 parts by weight, octadecyl-3- (3,5-di-t-butyl-
The composition, to which 0.3 part by weight of 4-hydroxyphenyl) propionate was added, was mixed with a compression molding machine at 130 ° C.
Heated for a minute and partially cross-linked beforehand to give an outer diameter of 19 cm and an inner diameter of 1
It was molded into a 0 cm tubular shape. Using a compression molding machine 2
Crosslinking was performed at 70 ° C. for 5 hours.

(Example 2) 100 parts by weight of low-density polyethylene (melt index 1.0 g / 10 minutes), 2,
5-Dimethyl-2,5-di (t-butylperoxy)-
A composition containing 2.0 parts by weight of hexyne-3 and 0.3 part by weight of pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] was prepared in Example 1. Under the same conditions as above, partial cross-linking was performed in advance to form a cylinder having an outer diameter of 19 cm and an inner diameter of 10 cm. This was crosslinked at 300 ° C. for 5 hours using a compression molding machine.

(Example 3) 100 parts by weight of low-density polyethylene (melt index 4.0 g / 10 minutes), 2,
5-Dimethyl-2,5-di (t-butylperoxy)-
A composition was prepared by adding 2.0 parts by weight of hexyne-3 and 1.0 part by weight of 4,4'-thiobis [(3-methyl-6-t-butylphenyl) -2-thioalkylpropionate]. Under the same conditions as in Example 1, partial cross-linking was performed in advance to form a tubular shape having an outer diameter of 19 cm and an inner diameter of 10 cm. This was crosslinked at 300 ° C. for 5 hours using a compression molding machine.

Comparative Example 1 100 parts by weight of low-density polyethylene (melt index 0.5 g / 10 minutes), 2.0 parts by weight of dicumyl peroxide, 4,4'-thiobis (6-t-butyl-3) -Methylphenol) was added to the composition in an amount of 0.3 parts by weight under the same conditions as in Example 1 to partially cross-link the composition beforehand to form a tube having an outer diameter of 19 cm and an inner diameter of 10 cm. This was crosslinked at 300 ° C. for 5 hours using a compression molding machine.

(Comparative Example 2) 100 parts by weight of low-density polyethylene (melt index 1.0 g / 10 minutes) was added with 1,
1.2 parts by weight of 3-bis (t-butylperoxyisopropyl) -benzene, octadecyl-3- (3,5-di-)
2.5 parts by weight of t-butyl-4-hydroxyphenyl) propionate was added, and the composition was partially crosslinked in advance under the same conditions as in Example 1 to form a tube having an outer diameter of 19 cm and an inner diameter of 10 cm. This was crosslinked at 300 ° C. for 5 hours using a compression molding machine.

With respect to the above samples, the degree of partial crosslinking after partial crosslinking, and the degree of crosslinking and water content after recrosslinking were evaluated.
Table 1 shows the results. The evaluation criteria are as follows. (Partial cross-linking degree) For the above sample, ASTM D27
The degree of crosslinking was evaluated by the gel fraction measured according to 65. A gel fraction of 20% or more was evaluated as ◯, and a gel fraction of less than 20% was evaluated as x. (Crosslinking degree) For the above samples, ASTM D2765
The degree of crosslinking was evaluated by the gel fraction measured according to A sample having a gel fraction of 85% or more was evaluated as ◯, and a sample having a gel ratio of less than 85% was evaluated as x. (Water content) With respect to the above samples, the water content inside the samples was measured using a Karl Fischer moisture meter. When the water content was 200 ppm or less, it was evaluated as ◯, and when it exceeded 200 ppm, it was evaluated as x.

[0025]

[Effect] The reinforced insulator for connecting a power cable of the present invention is octadecyl-based on 100 parts by weight of low-density polyethylene having a melt index of 0.5 to 4.0 g / 10 min.
3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 4,4 ′ -Thiobis [(3-
Methyl-6-t-butylphenyl) -2-thioalkylpropionate], and 0.1 to 2.0 parts by weight of at least one antioxidant selected from the group, and 1,3 as a crosslinking agent.
-Bis (t-butylperoxyisopropyl) -benzene and / or 2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3 in an amount of 1.0 to 2.5 parts by weight. Composed of a composition. The composition having a shape having a hole into which a power cable can be inserted is preliminarily partially cross-linked and molded. To be integrated with the insulator of the power cable by arranging it around the connection part of the power cable and then melting and crosslinking by heating. By having the above conditions (1) to (3), it is possible to suppress the generation of water even if the crosslinking temperature is raised, so that the construction time can be shortened, and the reinforcing insulator for power cable connection is excellent in terms of electrical insulation performance. be able to.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a reinforcing insulator for connecting a power cable of the present invention.

[Explanation of symbols]

 1: Power cable insulator 2: Conductor 3: Conductor connecting pipe 4: Internal semiconductive layer 5: Reinforcement insulator

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H02G 1/14 H02G 1/14 B 15/08 15/08 J (72) Inventor Shigeto Nakamura Saitama Saitama Prefectural Kumagaya City, Kumagaya 1008, Mitsubishi Cable Industries, Ltd., Kumagaya Plant (72) Inventor Iwao Otaka, Kumagaya, Saitama Prefecture 1008 Shinobori, Mitsubishi Cable Industries, Ltd., Kumagaya Plant (72) Inventor, Kunihiko Kondo, Kumagaya, Saitama Prefecture 1008 Shinbori Shinbori, Kumagaya Works, Mitsubishi Cable Industries, Ltd.

Claims (1)

[Claims] 1. A reinforcing insulator for connecting a power cable, which has the following conditions. Octadecyl-based on 100 parts by weight of low-density polyethylene having a melt index of 0.5 to 4.0 g / 10 min.
3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], 4,4 ′ -Thiobis [(3-
Methyl-6-t-butylphenyl) -2-thioalkylpropionate], and 0.1 to 2.0 parts by weight of at least one antioxidant selected from the group, and 1,3 as a crosslinking agent.
-Bis (t-butylperoxyisopropyl) -benzene and / or 2,5-dimethyl-2,5-di (t-butylperoxy) -hexyne-3 in an amount of 1.0 to 2.5 parts by weight. Composed of a composition. The composition having a shape having a hole into which a power cable can be inserted is preliminarily partially cross-linked and molded. To be integrated with the insulator of the power cable by arranging it around the connection part of the power cable and then melting and crosslinking by heating.