JPH02309580A - Formation method of mould connection for bridging polyolefine insulating cable - Google Patents

Abstract

PURPOSE:To improve the insulating property by bridging a spindleshaped insulating reinforcement body which consists of a polyolefine composition mixed with a peroxide for bridging, and after that, continuing the heating until the decomposing leftovers of the peroxide for bridging is decomposed perfectly. CONSTITUTION:On a conductor connection where a conductor connecting sleeve 3 is pressed on the exposed conductors 2 of a pair of CV cables 1, a metal mould 5 is set striding on both insulators 4, and after that, a spindle-shaped insulating reinforcement body 6 which consists of a bridgeable polyolefine composition mixed with a peroxide for bridging is filled. Then, after the whole body of the metal mould 5 is heated at 200 deg.C for 8-13 hours to bridge, it is kept for 4-15 hours as at the same temperature to decompose the decomposing leftovers of the peroxide for bridging perfectly, and at the same time, the decomposed product is exhausted to the outside. As a result, the moisture in the insulating reinforcement body 6 is never increased during the current is applied, and no deterioration of the insulating property with the passage of time is generated. Consequently, a high insulating property is maintained for a long period.

Description

[Detailed Description of the Invention] [Objective of the Invention 1 (Industrial Application Field) The present invention provides a molded joint for a crosslinked polyolefin insulated cable that has good water resistance and long-term reliability of insulation properties. Regarding the method.

(Prior Art) Conventionally, as a method for forming connections of cross-linked polyolefin insulated cables such as Cv cables (cross-linked polyethylene insulated cables), a cross-linkable polyolefin composition containing a cross-linking peroxide is mixed with a predetermined shape of gold. Extrusion mold joint method (EMJ method) in which the material is extruded and filled into a mold and then heat-crosslinked to form a connection insulator (insulation reinforcement);
A tape mold joint method (TMJ method) is used in which a tape made of the above-mentioned polyolefin composition is wound onto a conductor connection portion and then heated to crosslink and integrate the wound layers.

In the formation of such connections, the heating for crosslinking is carried out for the minimum time required to complete the crosslinking reaction after reaching the set temperature, which is the decomposition temperature of the peroxide, which is the crosslinking agent.
For example, it is limited to 8 to 13 hours.

(Problem to be Solved by the Invention) However, in such a heating method, a large amount of decomposition residue of the crosslinking peroxide and water are present in the insulation reinforcing body after the completion of crosslinking, and furthermore, this decomposition residue is As the temperature rises due to this, the water is decomposed into water, so the amount of water in the insulation reinforcement gradually increases.

That is, when dicumyl peroxide (DCP) is used as a crosslinking peroxide, cumyloxy radicals are generated by decomposition of DCP, and these cumyloxy radicals generate cumyl alcohol by reaction with polyethylene, for example. However, some of it becomes acetophenone. Furthermore, cumyl alcohol, which is a decomposed KM, generates α-methylstyrene and water, respectively, by applying thermal energy.

Since the amount of water in the insulation reinforcing body gradually increases during energization, voids and water trees are likely to occur, which may significantly reduce the insulation performance.

The present invention was made to solve this problem, and since no decomposition residue of cross-linking peroxide or water remains in the insulation reinforcement, there is no water tree generation and the long-term high It is an object of the present invention to provide a method for forming a molded connection part of a crosslinked polyolefin insulated cable that exhibits insulation properties.

[Structure of the Invention] (Means for Solving the Problems) A method for forming a molded connection portion of a crosslinked polyolefin insulated cable of the present invention is to form a crosslinked polyolefin insulated cable on the conductor connection portion of the cable, spanning the cable insulators on both sides. After molding a spindle-shaped insulation reinforcement made of a crosslinkable polyolefin composition containing a peroxide, and then heating and crosslinking the insulation reinforcement, the crosslinking peroxide in the insulation reinforcement is The heating is continued for a time sufficient for the decomposition residue to be further completely decomposed and for the decomposition products to be discharged to the outside.

In the present invention, the polyolefin that is the base of the crosslinkable composition for forming the insulation reinforcement includes polyethylene, polypropylene, ethylene-propylene copolymer,
Ethylene-vinyl acetate polymer (EvA), ethylene-
Examples include ethyl acrylate copolymer (EEA) and the like, and Dcp, t-butyl peroxide, etc. can be used as a crosslinking peroxide to be blended with these polyolefins.

In the present invention, a spindle-shaped insulating reinforcement made of such a polyolefin composition is molded on the conductor connection portion of a cable, and the molding is usually performed by the following method.

That is, a method in which the above-mentioned crosslinkable polyolefin composition is extruded and filled into a mold having a predetermined shape that is fitted over the conductor connection portion of the cable across the cable insulators on both sides; A method may be adopted in which an insulating tape formed by forming a material into a tape shape is wound around the conductor connection portion of the cable.

The insulating reinforcing body thus formed is then heated to a temperature at which the crosslinking peroxide decomposes (170 to 200°C) to completely crosslink the polyolefin composition, and then heated for several hours to 10 minutes. By continuing heating for several hours, the decomposition residue of peroxide is almost completely decomposed, and the final decomposition products such as water and the remainder of the decomposition residue thus generated are all transferred to the outside of the insulation reinforcement. Let it drain.

Here, the heating time in the heating step after the completion of crosslinking is not particularly limited, but it is necessary to ensure that the decomposition residue of peroxide is completely decomposed and the final decomposition products etc. are completely dissipated to the outside of the insulation reinforcement. It is desirable that the time is sufficient for the liquid to be drained and removed.

(Function) In the method for forming a molded connection part of a crosslinked polyolefin insulated cable of the present invention, the insulation reinforcing body made of polyolefin that has been molded onto the cable conductor connection part and crosslinked by heating is further heated as it is after the completion of crosslinking. Since the temperature is maintained, the peroxide decomposition residue remaining inside the insulation reinforcement is completely decomposed, and at the same time, the decomposition products such as water that are finally generated are completely discharged outside the insulation reinforcement. removed.

Therefore, during energized use, the amount of water in the insulation reinforcing body does not increase, and the insulation performance does not deteriorate over time due to occurrence of water tree or the like.

(Example) Examples of the present invention will be described below.

EXAMPLE First, as shown in FIG. 1, a conductor connection sleeve 3 was crimped by a conventional method onto the exposed conductor 2 of a pair of Cv cables 1 whose ends were butted together to form a conductor connection part.

Next, a mold 5 having a spindle-shaped cavity is placed over the conductor connection portion, spanning the insulators 4 of the CV cable 1 on both sides.
After fitting, a polyethylene composition 6 shown below was extruded and filled into the mold 5.

That is, melt index 3.2, density 0.92
A polyethylene composition containing 8% by weight of DCPl and 0 to 18% by weight of an anti-aging agent was added to the low-density polyethylene of No. 2 (manufactured by Nippon Unicar Co., Ltd., trade name NUL9205).
The mixture was heated and melted using an extruder, and then extruded and filled into the cavity of the mold 5.

Next, as shown in FIG. 2, the entire mold 5 is heated to 200°C (±
20° C.) for 8 to 13 hours to completely crosslink the polyethylene composition 6 in the mold 5, and then kept at this temperature for 4 to 15 hours to remove cumyl alcohol, which is a decomposition residue of DCP. was decomposed again, and the finally produced decomposition products such as water and the remaining cumyl alcohol were completely diffused and discharged to the outside.

When the moisture content in the molded insulation reinforcement of the Cv cable thus formed was determined to be 111J using a conventional method, an extremely small value was obtained.

Furthermore, when this insulation reinforcement was subjected to the following accelerated test and the number of water trees generated was measured, almost no water trees were observed.

That is, after applying silver paint to the lower surface of the insulation reinforcement sample and placing a vinyl chloride pipe filled with saline on the upper surface, a high-frequency voltage was applied between them for a long time. Thereafter, the sample was taken out and the number of water trees in the small piece sliced into In thickness was examined under a microscope, and no water trees were observed.

[Effects of the Invention] As explained above, according to the forming method of the present invention, there is no decomposition residue of crosslinking peroxide or residual water which is a decomposition product, and a mold for a crosslinked polyolefin insulated cable with good insulation properties can be formed. A connection is obtained.

Further, the molded connection portion formed according to the present invention does not increase the moisture content during use with electricity and does not generate water trees, so high insulation performance is maintained over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view for explaining a method of forming a molded connection part of a Cv cable according to an embodiment of the present invention, and FIG.
It is a graph showing a change in mold heating temperature over time in an example. 1... Cv cable 2... Cable conductor 4... Cable insulator 5... Mold 6... Polyethylene composition 1st = Fig. 2

Claims (1)

[Claims] (1) A spindle-shaped insulation reinforcement made of a crosslinkable polyolefin composition containing a crosslinking peroxide is formed on the conductor connection portion of the cable, spanning the cable insulators on both sides, and then After heating and crosslinking the insulation reinforcement, for a sufficient period of time for the decomposition residue of the crosslinking peroxide in the insulation reinforcement to be further completely decomposed and for the decomposition products to be discharged to the outside. , a method for forming a mold connection part of a crosslinked polyolefin insulated cable, characterized by continuing heating as it is.