JPH08236246A - Formation of connection part of cross-linked polyolefin-insulated cable - Google Patents

Abstract

PURPOSE: To heighten the adhesion strength between a cable insulating material and an extrusion-molded insulating material and form a connection part with high withstand voltage characteristics regarding EMJ formation of a cross-linked polyolefin-insulated cable. CONSTITUTION: After an inner semiconductive layer 11 is fitted on a conductive connection part of a CV cable 7, a part covering both sides of a cable insulating material 9 is stored in chamber 12 whose inside pressure is decreased and a penciling face 9a of the cable insulating material 9 is etched and activated by plasma generated by electric discharge between electrodes 14. Then, dies 15 are fitted in the outsides of these parts and polyethylene which is not yet cross-linked is extruded inside the dies 15 by an extruding apparatus 17 and cooled. After that, an external semiconductive layer is formed on the resulting molded body and a bridging tube is further installed and then the resulting body is heated in an inert gas atmosphere to carry out cross-linking and fusion of the polyethylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a connecting portion of a crosslinked polyolefin insulation cable, and particularly, to enhance the adhesiveness between a cable insulation and an insulation reinforcement formed by extrusion molding and to obtain a good pressure resistance. A method of forming a connection.

[0002]

2. Description of the Related Art Conventionally, there have been various methods for connecting a crosslinked polyolefin insulated cable such as a CV cable (crosslinked polyethylene insulated cable). The extrusion mold system shown is used.

That is, in forming a connection portion by the extrusion molding method, first, the cable end is stripped off, the cable insulator is cut (pencilling) into a pencil tip shape, and then the cable conductor is connected by a conductor sleeve or the like. , And an internal semiconductive layer is provided thereon. Next, after a metal mold is fitted over the cable insulators on both sides on the outside of such a conductor connecting portion, a polyolefin resin (composition) containing a crosslinking agent is injected into the metal mold by an extruder. After that, the mold body is heated to crosslink and fuse. FIG. 2 shows an essential part of the structure of the extrusion mold type connection part (EMJ) formed in this manner. In the figure, reference numeral 1 is a cross-linked polyolefin insulated cable, 2 is a cable insulator, 3 is a cable conductor,
Reference numeral 4 is a conductor sleeve, 5 is an inner semiconductive layer, and 6 is an extrusion mold insulator.

[0004]

However, in such a conventional EMJ, since the adhesion of the uncrosslinked polyolefin to the crosslinked polyolefin by heat crosslinking is poor, the uncrosslinked polyolefin forming the extrusion mold insulator 6 is not formed. Even when the polyolefin was heat-crosslinked, it did not sufficiently adhere to the cable insulator 2, which was one of the causes of dielectric breakdown.

Therefore, the inclined surface (pencilling surface 2a) of the cable insulator 2 that has been penciled is heated in advance to partially decompose the crosslinked polyolefin constituting the cable insulator 2 by heat, or at the same time as the decomposition, the surface is further decomposed. There is proposed a method of cleaning the resin with a solvent to improve the adhesiveness with the extrusion mold insulator 6.

However, this method has a problem that the work efficiency is poor because the thermal decomposition of the crosslinked polyolefin takes a very long time.

Further, conventionally, the penciling surface 2a of the cable insulator has been roughened by sanding it with sandpaper or an emery cloth (cloth file). With this method, shavings are scraped on the surface. Such foreign matter is likely to remain and adhere, and this foreign matter is one of the causes of destruction of the connection portion.

The present invention has been made in order to solve the above problems, and is an E of crosslinked polyolefin insulation cable.
It is an object of the present invention to provide a method for forming a connection part having good pressure resistance characteristics by improving the adhesiveness between a cable insulator and an extrusion molded insulator (insulation reinforcement) in a short time in forming an MJ.

[0009]

A method for forming a connecting portion of a crosslinked polyolefin insulated cable according to the present invention is an insulation made of a crosslinked polyolefin on the outer side of a conductor connecting portion of a crosslinked polyolefin insulated cable across both cable insulators. In forming the reinforcing body by extrusion molding, the penciling surfaces of the cable insulators on both sides of the pencil, which are cut and formed in the shape of the tip of the pencil, are surface-treated by plasma contact treatment, and then a crosslinkable polyolefin is extrusion-molded thereon. It is characterized by doing.

In the plasma contact treatment used in the present invention, the surface is cleaned or roughened by the impact of various components in the plasma generated by the gas discharge (glow discharge etc.) under a low pressure close to vacuum, and the adhesion is enhanced. Surface treatment is called nitrogen,
This can be performed by applying high-frequency power between flat plate electrodes arranged opposite to each other in an inert gas such as argon. Further, among such plasma contact treatments, the treatment with an inert gas molecule in an excited state is known as a CASING treatment, and this treatment can cause a crosslinking reaction on the surface to enhance the adhesiveness.

[0011]

In the present invention, the adsorbed gas on the surface is removed by plasma-treating the outer peripheral surface of the cable insulator, including the penciling surface, in an inert gas such as low pressure air, nitrogen or argon. Simultaneously with the cleaning and cleaning, minute irregularities of the order of μm are formed on the surface, and further, a part of the polymer bonding chains on the surface are cleaved to generate free radicals and are activated.

Further, particularly when the CASING treatment is performed, the excited inert gas molecules in the inert gas plasma collide with the surface of the polyolefin insulator to extract hydrogen molecules and generate active radicals. However, in most cases, unsaturated bonds occur on the surface and metastabilize. Then, in the extrusion molding step after the plasma contact treatment, the peroxide cross-linking agent contained in the mold insulator is decomposed by heating and attacks the unsaturated bond on the surface of the cable insulator. Crosslinking occurs at the interface with the body, and both are firmly bonded.

As described above, the crosslinkable polyolefin is extrusion-molded on the activated cable insulator whose outer peripheral surface has been roughened by the plasma treatment, whereby adhesion between the cable insulator and the mold insulator is achieved. Property is greatly improved, and dielectric breakdown at these interfaces is prevented.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a method for forming a connecting portion of a crosslinked polyolefin insulated cable of the present invention will be described below with reference to the drawings.

In the embodiment, as shown in FIG. 1 (a), first, the end portion of the CV cable 7 is stepped off to expose the cable conductor 8, and the cable insulator 9 is penciled, and then the cable conductor 8 are connected via a conductor sleeve 10 and the inner semiconductive layer 11 is mounted thereon.

Then, as shown in FIG. 1 (b), a chamber whose inside is depressurized to 0.1 to 1 Torr in a portion having a predetermined length extending from the conductor connecting portion as a center to the cable insulators 9 on both sides. 12 and the contact portion between the outer peripheral surface of the cable insulator 9 and the end surface of the chamber 12 is sealed by the seal layer 13
To hermetically seal. Then, high-frequency power (for example, 13.56 MHz, 20 to 50 W) is applied between the pair of electrodes 14 which are vertically opposed to each other in the chamber 12, and the plasma generated by the discharge between the electrodes 14 causes the surface of the cable insulator 9. Etching to form minute irregularities on the surface (roughening)
And activates. Here, by moving the pair of electrodes 14 in the chamber 12 in the axial direction of the cable at an appropriate speed, the outer peripheral surface of the cable insulator 9 on both sides of the conductor connecting portion, particularly the pencil ring surface 9a, is roughened. Surface.

Next, as shown in FIG. 1C, a mold 15 having a spindle-shaped internal shape is provided outside the conductor connecting portion across the cable insulators 9 on both sides which have been surface-treated in this way.
After pre-heating the mold 15 and the like, an uncrosslinked polyethylene 16 containing a crosslinking agent such as an organic peroxide is extruded, filled and cooled in the extruder 17 in the mold 15. . After that, an outer semiconductive layer is attached to the outer periphery of the thus obtained mold body, and a cross-linking tube is further attached. Then, an inert gas such as high-pressure nitrogen gas is sealed, and the cross-linking and fusion are performed by heating. The illustration of the crosslinking step is omitted.

In the extruded mold type connection portion (EMJ) of the CV cable thus formed, the outer peripheral surfaces of the cable insulators 9 on both sides including the inclined penciling surface 9a are roughened by the plasma surface treatment. Since it has been activated and activated, as is clear from the following specific examples, the adhesion between the insulation reinforcement body extruded and molded thereon is significantly improved, and the dielectric breakdown at these interfaces is prevented. To be prevented. Further, as compared with the conventional method of roughening the surface of the pencil insulator 9a of the cable insulator 9 using the emery cloth, foreign matter is not attached and a cleaner surface finish is possible.

That is, the EMJ of the CV cable formed according to the present example and the EMJ formed in the same manner as the example after the surface of the cable insulator was roughened using an emery cloth instead of the plasma surface treatment. (Comparative Example 1),
Also, regarding EMJ (Comparative Example 2) formed by extrusion molding without performing any surface treatment of the cable insulator, the adhesiveness (interfacial peeling force) at the interface between the cable insulator and the extrusion mold insulator and the foreign matter at the interface When the presence and absence and the dielectric breakdown voltage were examined, the measurement results shown in Table 1 were obtained.

[0020]

[Table 1] In the above-mentioned examples, the plasma surface treatment was performed on the pensioning surface 9a of the cable insulator in the chamber 12 whose pressure was reduced to 0.1 to 1 Torr. However, the plasma treatment method is not limited to such a method. It is also possible to activate the penciling surface 9a and enhance the adhesiveness by generating plasma and performing a CASING process in a chamber (pressure: 0.01 to 1 Torr) in which gas is enclosed in the same manner as in the embodiment.

[0021]

As described above, according to the method of the present invention, the outer peripheral surface of the cable insulator, particularly the pencil ring surface, is roughened or activated by plasma surface treatment, and then a crosslinkable polyolefin is applied thereon. Since it is extrusion-molded, the adhesiveness between the cable insulator and the mold insulator is significantly improved, and a connection portion having good withstand voltage characteristics such as dielectric breakdown voltage can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view for explaining an embodiment of a method for forming a crosslinked polyolefin insulated cable connection portion of the present invention, where (a) is a pretreatment step, (b) is a surface treatment step of a cable insulator, (C) has shown the extrusion process, respectively.

FIG. 2 is a cross-sectional view showing the main part of the structure of a conventional extrusion mold type connection (EMJ).

[Explanation of symbols]

 7 ... CV cable 9 ... Cable insulator 9a ... Pencilling surface 10 ... Conductor sleeve 11 ... Chamber 14 ... High frequency electrode 15 ... Mold 16 ... Uncrosslinked polyethylene 17 ... Extruder

Claims (1)

[Claims] 1. When forming an insulation reinforcement made of crosslinked polyolefin by extrusion molding on the outside of the conductor connection portion of the crosslinked polyolefin insulated cable across the cable insulators on both sides, a pencil of the cable insulators on both sides is formed. A method for forming a connecting portion of a crosslinked polyolefin insulated cable, which comprises subjecting a penciling surface cut and formed in a tip shape to a surface treatment by plasma contact treatment, and then extrusion-molding a crosslinkable polyolefin onto the surface.