JPS6012723B2 - How to manufacture power cables - Google Patents

Description

[Detailed Description of the Invention] Conventionally, crosslinked polyolefin power cables such as crosslinked polyethylene power cables are made by coating a conductor with a mixture of polyethylene and a crosslinking agent such as an organic peroxide, and then heating the conductor with pressurized steam or the like. It is cross-linked.

However, such a method has disadvantages such as scorch formation when extruding the acid mixture onto the conductor and the possibility that voids may be present in the manufactured cable. Furthermore, when water vapor is used for crosslinking, the cable is heated from the outside, so if the coating layer is thick, the heat transfer is limited, which is not suitable for industrial production. As an alternative to these methods, a method has been developed in which polyolefins are crosslinked by cross-linking silane-grafted polyolefins.

That is, the silane-grafted polyolefin undergoes a crosslinking reaction even at room temperature in the presence of water, so crosslinking equipment using a chemical crosslinking agent as described above is not required at all, and the crosslinked polyolefin has the characteristic that there are no voids. , which was considered suitable as an insulating layer for crosslinked polyolefin power cables. However, the rate at which water permeates into polyolefin is extremely slow.
For this reason, crosslinking takes a long time; for example, when silane-grafted polyolefin is immersed in water at room temperature for crosslinking, several weeks are required.

Therefore, it is possible to promote crosslinking by heating the water, but it takes several hours even when silane-grafted polyolefin is soaked in 80 gallons of hot water, and the conventional chemical crosslinking method cannot be used. In comparison, it was very slow to become a commercial enterprise, and there was a need for a method that could crosslink this in a short time. As a result of intensive research in response to such demands, the present invention has discovered a method for crosslinking silane-grafted polyolefin in a short time without generating bubbles.
This is applied to the insulation layer of power cables, and the conductor is coated with silane-grafted polyolefin alone or with a mixture of silane-grafted polyolefin and a silanol catalyst such as dibutyltin dilaurate, and then a small amount of water is removed. It is characterized by thermal crosslinking in any heating medium selected from the group of pressurized inert gas, silicone oil, or mineral oil.

That is, the present invention provides polyolefins such as polyethylene with the general formula RR'SiY, Y2 (where R is an olefinically unsaturated monovalent hydrocarbon or a hydrocarbonoxy group, Y,
, Y2 is a hydrolyzable organic group, and R' is an R group or Y, group) in the presence of a compound capable of generating a free radical site in the polyolefin. After coating the grafted polyolefin as an insulator on a conductor, the polyolefin is heated to a high temperature in a heating medium selected from the group of inert gas under pressure containing a small amount of water, silicone oil, or mineral oil. A method for producing a cross-linked polyolefin power cable obtained by cross-linking by heating to a temperature.

In this case, the crosslinking reaction may be further promoted by mixing a small amount of a silanol catalyst such as dibutyltin dilaurylate with the silane-grafted polyolefin. In the method of the present invention, the heating method for crosslinking the silane-grafted polyolefin is preferably carried out by the following method.

'1} Heating in a high-pressure inert gas containing a small amount of water that does not oxidize the polyolefin, such as carbon dioxide gas, nitrogen gas, or sulfur hexafluoride gas. ■ In silicone oil or mineral oil containing a small amount of water. Heat it up.

Note that the above heating method may also use dielectric heating using microwaves.

As described above, the heating step in the method of the present invention is performed at a high temperature, for example, 2
By carrying out the process in a heating medium containing a small amount of water at a temperature of 0,000 or higher, a crosslinking reaction occurs in a short period of time, ie, several minutes, and it is possible to form an insulating layer of polyolefin with a sufficient degree of crosslinking without generation of voids. It is possible.

Note that it is necessary that the heating medium contains a small amount of water in advance, or that the silane-grafted polyolefin contains a small amount of water, and in this case, the water content in the heating medium is 0.1%. % or more, preferably 1.0-2
0%, and 0.0% in silane-grafted polyolefins.
5 to 5.0% is preferred.

Therefore, in the heating process, a conductor coated with silane-grafted polyolefin is soaked in water or hot water (e.g. 70-80 pm) for a short period of time so that moisture is attached to the surface of the polyolefin. Subsequently, crosslinking may be carried out by heating in an inert gas such as high-pressure nitrogen gas as described above. In this case, the crosslinking reaction is further accelerated and the crosslinking time can be significantly shortened.

In the method of the present invention, polyolefins include polyethylene, polypropylene, polyisobutylene, ethylene vinyl acetate copolymer, ethylene acrylic acid copolymer, chlorinated polyethylene, ethylene propylene copolymer, and the like.

Further, in the method of the present invention, there is no problem even if an antioxidant, an ultraviolet absorber, a coloring agent, etc. are added to the silane-grafted polyethylene forming the coating layer.

Next, examples of the present invention will be described.

Example 1 A mixture of 0.05 parts by weight of dibutyltin dilaurylate mixed with 10 parts by weight of silane-grafted polyethylene based on polyethylene with a specific gravity of 0.92 was placed on a copper conductor with a cross-sectional area of 38 squares at 170 to 180 q0. Thickness approx. 2/
After extrusion coating on the skin, heating was performed for 5 minutes at 20,000°C under hydrous nitrogen gas (water content 15%) at a pressure of 3k9/cm to produce a power cable.

When the degree of crosslinking of the silane-grafted polyethylene coating layer was measured, the insoluble content due to 90q0 toluene was 7.
5% and no poids were observed. Example 2 On a copper conductor with a cross-sectional area of 100 squares, a mixture of 0.05 parts by weight of dibutyl tin dilaurilate mixed with 10 parts by weight of silane-grafted polyethylene based on polyethylene with a specific gravity of 0.92 was mixed at 170 to 180 parts by weight. Approximately 3cm thick at °C
After coating by extrusion, a power cable was manufactured by heating at 230 qC for 5 minutes in hydrous silicone oil (water content 10%) at a pressure of 5k9/kg.

When the silane-grafted polyethylene coating layer was measured for its thickness, the amount of insoluble matter due to toluene in 90q0 was 77%, and no voids were observed. Example 3 A conductor was coated with a silane-grafted polyethylene mixture at 170 to 180 qO in the same manner as in Example 1, and then heated at 10,000 C for 5 minutes under water-containing nitrogen gas (moisture content 10%) at a pressure of 3 kg/base, and then left at room temperature. A power cable was manufactured after being left unused for 2 hours.

When the degree of crosslinking of the silane-grafted polyethylene coating layer was measured, the amount not removed by 90q○ of toluene was 70%.
%, and no voids were observed. Comparative Example 1 In the same manner as in Example 1, a conductor was coated with a silane-grafted polyethylene mixture to produce a power cable.

When the degree of crosslinking of the silane-grafted polyethylene coating layer was measured, the amount of 90q0 that did not fall off due to toluene was 4.
It was 0%.

Furthermore, after leaving this product in the air at room temperature for 3 weeks, the degree of crosslinking was measured, and the insoluble content due to 9000 toluene was 72.
% has been reached.

As detailed above, according to the method of the present invention, the crosslinking of the silane-grafted polyolefin can be carried out extremely quickly, which makes it possible to continuously produce silane-crosslinked polyolefin cables, and also allows the silane-grafted polyolefin to be formed in a short period of time after extrusion molding. Since cross-linking occurs over time, there is no need to store the cable for a long time since it is cross-linked after molding.

Claims (1)

[Claims] 1. After coating a conductor with silane-grafted polyolefin alone or a mixture of silane-grafted polyolefin and a silanol catalyst such as dibutyltin dilaurate, the conductor is coated with an inert gas containing water under pressure, silicone oil, etc. A method for producing a power cable, characterized in that it is thermally crosslinked in any heating medium selected from the group of mineral oils. 2. The method of manufacturing a power cable according to claim 1, wherein the amount of water in the heating medium is within the range of 1.0 to 20%.