JPH04342732A - Production of crosslinked polyolefin insulated cable - Google Patents

Abstract

PURPOSE:To shorten drying time for removing residue in decomposition of DCP and improve productivity of a crosslinked polyolefin insulating cable using DCP as a crosslinking agent in production of the capable. CONSTITUTION:When a polyolefin composition having dicumyl peroxide blended as a crosslinking agent is subjected to extrusion coating onto a conductor and crosslinked to form a crosslinked polyolefin insulated coating and then heat- dried, the composition is heated in oxygen atmosphere and then heated while evacuating.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a crosslinked polyolefin insulated cable using dicumyl peroxide as a crosslinking agent.

0003

[Prior Art] Conventionally, in manufacturing cross-linked polyolefin insulated cables, a polyolefin composition containing an organic peroxide as a cross-linking agent is extruded and coated on a continuously fed conductor, and then cross-linked to insulate the cross-linked polyolefin insulated cable. Forming a coating is carried out, and the crosslinking agent includes
Dicumyl peroxide (DCP) as an organic peroxide
is commonly used.

However, this method using DCP has the problem that decomposition residues of DCP, which is a crosslinking agent, such as cumyl alcohol, α-methylstyrene, and water remain in the insulation coating, impairing the long-term reliability of the cable. was there.

For this reason, conventionally, after forming the insulation coating, the cable wound around a drum is heated and dried at a temperature of about 70 to 90°C, usually in the air, but in the case of large-sized cables, under vacuum. , decomposition residues such as cumyl alcohol are removed.

[0006]

[Problems to be Solved by the Invention] However, in such conventional drying methods, decomposition residue is diffused and released for each component individually, so substances with small molecular weights such as water can be relatively easily diffused and removed. However, residues other than water have large molecular weights, so diffusion is slow; in particular, cumyl alcohol
It takes time to remove the oil, which is a factor that hinders productivity.

[0007] The present invention was made in response to the problems of the prior art, and it is difficult to remove cumyl alcohol by diffusion.
It is an object of the present invention to provide a method for manufacturing high-quality cross-linked polyolefin insulated cables with excellent long-term reliability and high productivity by removing dirt in a short time.

[Configuration of the invention]

[0009]

[Means for Solving the Problems] The present invention provides D
A polyolefin composition containing CP as a crosslinking agent is extrusion coated, crosslinked to form a crosslinked polyolefin insulation coating, and then heated and dried to reduce the decomposition residue of DCP remaining in the crosslinked polyolefin insulation coating. In the method for producing a crosslinked polyolefin insulated cable, the heating drying of the crosslinked polyolefin insulation coating is a two-step drying process of heating in an oxygen atmosphere and then heating while vacuuming. be. In the present invention, the polyolefin composition containing DCP as a crosslinking agent is based on polyolefins such as ethylene copolymers such as polyethylene, polypropylene, ethylene/propylene copolymers, and ethylene/vinyl acetate copolymers (EVA). Examples include those in which DCP is blended with the base, and if necessary, inorganic fillers, anti-aging agents, and other additives are mixed.

[0010] In the present invention, after extrusion coating such a polyolefin composition onto a conductor and crosslinking it, the method of heating and drying this crosslinked polyolefin insulation coating includes heating drying in an oxygen atmosphere, and then Two-stage drying is used: heating and drying while applying a vacuum.

The oxygen atmosphere may be in the air, but
In order to prevent cable oxidation, the oxygen concentration should be 2 to 2.
A mixed gas atmosphere of nitrogen and oxygen (approximately atmospheric pressure) adjusted to be in the range of 0% is more preferable. Heating temperature is 60
~90°C is suitable. By heating and drying in such an oxygen atmosphere, secondary decomposition of cumyl alcohol into α-methylstyrene and water is promoted. In other words, cumyl alcohol has a large molecular weight and is difficult to be removed by diffusion.
The drying time can be shortened by decomposing the molecule into α-methylstyrene and water, which are relatively easy to diffuse. Further, by heating and drying in an oxygen atmosphere, the cable can be raised to the drying temperature in a short time, and from this point as well, the drying time can be shortened. By the way, cables that took more than 200 hours to reach drying temperature in a vacuum atmosphere
In the oxygen atmosphere mentioned above, approximately 1/16 to 1/17 of that, 12
It is possible to do it before or after the hour.

However, heating in an oxygen atmosphere
As mentioned above, although it is possible to promote the decomposition of cumyl alcohol and shorten the cable temperature rise time, as drying progresses and the concentration of the residue decreases, the diffusion rate decreases and eventually equilibrium is reached. state and the spread stops. Therefore, by first heating in an oxygen atmosphere and then heating while vacuuming, the product of the decomposition reaction of cumyl alcohol promoted in the oxygen atmosphere, that is, α-
This is intended to quickly and more completely diffuse and remove methylstyrene and water. Note that the heating temperature under vacuum is also suitably 60 to 90°C, as in the case under oxygen atmosphere. Further, as a guideline for the heating time, it is appropriate to set the heating time in an oxygen atmosphere until the amount of cumyl alcohol becomes approximately 20% of the initial amount. Specifically, it varies depending on the cable size, insulation coating thickness, etc., but it is usually 100 to 300 hours in an oxygen atmosphere and 50 to 4 hours in a vacuum.
00 hours, the drying time can be reduced by approximately 100 hours or more compared to conventional methods.

[0013]

[Function] In the method of the present invention, after forming the crosslinked polyolefin insulation coating, first, by heating in an oxygen atmosphere, the cable temperature is quickly raised to the drying temperature, and the cumyl alcohol, which is difficult to be removed by diffusion, is decomposed. promote. Next, by switching to heating under vacuum, diffusion removal of α-methylstyrene and water, which are decomposition products of cumyl alcohol, and other decomposition residues that remain are completed. By performing such two-stage drying, the decomposition residue of DCP used as a crosslinking agent can be quickly removed, and a crosslinked polyolefin insulated cable with excellent long-term reliability can be manufactured.

The present invention is particularly useful for producing high-voltage crosslinked polyolefin insulated cables of 110K or higher, which have thick insulation coatings and require an extremely long time to dry using conventional methods.

[0015]

[Example] Next, an example of the present invention will be described.

[0016] A crosslinkable insulating polyethylene composition containing DCP as a crosslinking agent was extruded and coated onto a conductor having an outer diameter of 29.5 mm to a thickness of 27 mm, and the insulation was crosslinked by heating in a conventional manner. After forming the body, it was rolled up into a drum. Subsequently, this was placed in a heating chamber and held at a temperature of 90° C. for 120 hours under atmospheric pressure, and then the pressure inside the heating chamber was reduced to create a vacuum atmosphere of approximately 10 mmHg, and heat drying was continued while vacuuming. After 100 hours had elapsed, the coated conductor was taken out from the heating chamber, and the outer periphery was coated with an aluminum sheath to produce a 275 KV class crosslinked polyolefin insulated cable (Example 1).

[0017] Furthermore, the drying conditions described above were the same as those described above, except that the drying conditions in the first stage were heating and drying at a temperature of 90°C for 120 hours while flowing a mixed gas of oxygen and nitrogen (oxygen concentration 5%) into the heating chamber. A crosslinked polyolefin insulated cable was produced in the same manner as in the example (Example 2).

In each of these Examples, the content of DCP decomposition residue in the insulator after heat drying was cumyl alcohol.
0.1 to 0.2 Wt%, water 20 to 150 ppm
Met.

[0019] In an example in which a cable was manufactured in the same manner as in the above example except that the drying condition was only drying in the air at a temperature of 50°C, DCP was maintained even after heating drying for a total of 220 hours or more. The content of decomposition residues did not decrease to the above extent. In addition, the drying conditions were changed to 90°C.
In an example in which a cable was manufactured in the same manner as in the above example except that only drying was carried out under vacuum at a temperature of
A heating time of 0 hours or more was required.

[0020]

Effects of the Invention As is clear from the above examples, according to the method of the present invention, after forming the crosslinked polyolefin insulation coating, heating was performed in an oxygen atmosphere, and then heating was performed while being evacuated. Cumyl alcohol, which is difficult to diffuse and remove, can be removed in a short time, and high-quality cross-linked polyolefin insulated cables with excellent long-term reliability can be manufactured with high productivity.

[0021]

Claims (1)

[Claims] 1. A polyolefin composition containing dicumyl peroxide as a crosslinking agent is extrusion coated onto a conductor, crosslinked to form a crosslinked polyolefin insulation coating, and then heated and dried to form the crosslinked polyolefin insulation coating. In the method for manufacturing a crosslinked polyolefin insulated cable, which comprises reducing the decomposition residue of dicumyl peroxide remaining in the cable, the heating drying of the crosslinked polyolefin insulation coating includes heating in an oxygen atmosphere, and then while vacuuming. 1. A method for producing a crosslinked polyolefin insulated cable, comprising two steps of heating and drying.