JP2000003622A - Polyolefin resin composition for power cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the water content generated in reheating at the time of operation or connection of a cable, and provide satisfactory electric characteristic by using a specified resin composition as the constituting materials of the insulator layer of a power cable and an insulator layer to be formed on the conductor of a connecting part. SOLUTION: In this polyolefin resin composition for power cable, 0.01-0.1 pts.wt. of calcium stearate is blended to 100 pts.wt. of polyolefin of resin component in order to reduce the water content in the resin after reheating and prevent the reduction in electric characteristic. Further, to 100 pts.wt. of the resin component, 0.5-3 pts.wt. of an organic peroxide not particularly limited is added to provide sufficient cross-linking degree and prevent the reduction in electric characteristic by seizure in the early cross-linking in extrusion. As the polyolefin, any one for cable insulator can be used, but a copolymer of ethylene and unsaturated hydrocarbon synthesized by use of a single site catalyst is preferably used because of satisfactory cross-linking efficiency, so that the addition quantity of the organic peroxide can be minimized, and the quantity of decomposition product of moisture generating source can be also minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin resin composition suitably used for an insulation layer of a power cable.

[0002]

2. Description of the Related Art A conventional rubber / plastic insulated power cable (hereinafter simply referred to as a power cable) is usually a cable core having an inner semiconductive layer and an insulator layer provided on the outer periphery of a conductor, or an inner semiconductive layer. , A cable core provided with an insulator layer and an external semiconductive layer. Each of these layers was formed by extrusion-coating a polyolefin-based resin composition based on polyolefin containing an organic peroxide as a cross-linking agent on the outer periphery of a conductor by an extruder, and then heated under pressure and blended into the base resin. It is formed by decomposing a crosslinking agent and crosslinking by generated radicals.

[0003] Conventionally, connection of a power cable is performed by a mold joint method as follows. First, the conductors at the ends of the two power cables are exposed, and the inner semiconductive layer, the insulator layer, and the outer semiconductive layer near the exposed conductor are cut into a substantially conical shape to obtain a desired shape. Thereafter, the exposed conductors are joined to each other, and an inner semiconductive layer is formed by winding a semiconductive tape made of a polyolefin-based resin composition containing a cross-linking agent around the conductor joint and the periphery thereof. Next, an insulating tape made of a polyolefin-based resin composition containing a cross-linking agent is wound on the inner semiconductive layer (tape molding method), or the cross-linking agent is compounded in a mold installed at a connection site of both cables. The insulator layer is formed by injecting and extruding the extruded polyolefin resin composition (extrusion molding method). Then, the outer semiconductive layer is formed on the insulator layer by winding the semiconductive tape in the same manner as the inner semiconductive layer. After forming each layer in this way, these are heated under pressure, crosslinked and integrated, and a power cable is connected.

Hitherto, dicumyl peroxide has been generally used as a crosslinking agent when a power cable and a polyolefin resin composition forming an insulator layer at a connection portion of the power cable are crosslinked. Decomposition products formed by the decomposition of dicumyl peroxide at the time of crosslinking include cumyl alcohol. The cumyl alcohol decomposes when heated to produce water. The generated water increases the moisture content of the power cable, which may cause a decrease in the dielectric breakdown characteristics such as a reduction in the dielectric breakdown voltage of the cable. That is, when heated by the heat generated during cable operation, or when the cable is connected, and the vicinity of the connection portion is heated during extrusion or cross-linking of the molten resin, and heated again after cross-linking, cumyl alcohol in the insulator may be heated. However, it is necessary to pay close attention to the fact that water may be decomposed to generate water and increase the water content of the cable, which may cause voids and water trie.

Therefore, in order to reduce the amount of water generated from cumyl alcohol generated by heating during cable operation or cable connection, a power cable using a polyolefin-based resin to which an aromatic amide is added as an insulating layer (Japanese Patent Laid-Open Publication No. 2-2
No. 04910) and power cable insulating compositions containing two specific anti-aging agents (Japanese Patent Application Laid-Open No. 2-204912), and power cables and power cable insulating compositions containing specific additives have been proposed. I have. However, there were problems that the electrical properties of the cable were reduced due to the effects of the added additives, and the generation of moisture was insufficiently suppressed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a problem, and reduces the amount of water generated when the cable is reheated at the time of operation or connection of the cable. An object of the present invention is to provide a polyolefin-based resin composition for a power cable having characteristics.

[0007]

Means for Solving the Problems As a result of investigations to achieve the above object, the present inventors have found that the constituent materials of the insulator layer of the power cable and the insulator layer formed on the conductor at the connection part of the power cable are formed. By using a resin composition in which calcium stearate is blended with a polyolefin, it has been found that when a cross-linking agent such as dicumyl peroxide that generates water upon reheating is used as a cross-linking agent, the amount of water generated can be suppressed. The invention has been completed.

That is, in the present invention, for a power cable, calcium stearate is incorporated in an amount of 0.01 to 0.1 part by weight and an organic peroxide in an amount of 0.5 to 3 parts by weight based on 100 parts by weight of a polyolefin. Provided is a polyolefin-based resin composition. It is preferable that the polyolefin is a copolymer of ethylene, an unsaturated hydrocarbon and ethylene produced using a single-site catalyst, from the viewpoint of reducing the amount of generated water.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polyolefin-based resin composition for power cables of the present invention contains calcium stearate and an organic peroxide in a polyolefin as a resin component. Calcium stearate is blended in an amount of 0.01 to 0.1 part by weight based on 100 parts by weight of polyolefin. When the amount is less than 0.01 part by weight, the effect of reducing the water content in the resin after reheating is small. On the other hand, if the compounding amount is too large, the electric characteristics are deteriorated.

The organic peroxide used in the present invention is not particularly restricted but includes dicumyl peroxide, t-butylcumyl peroxide, 1,3-bis- (t-butylperoxy-isopropyl) benzene, , 5-dimethyl2,5-di- (t-butylperoxy) -hexyne and the like. An appropriate amount of addition is 0.5 to 3 parts by weight based on 100 parts by weight of the resin component. If the amount is less than 0.5 part by weight, a sufficient degree of crosslinking cannot be obtained. If the amount exceeds 3 parts by weight, premature crosslinking (scorch) occurs at the time of extrusion, and "burn" occurs, resulting in a decrease in electrical characteristics.

The polyolefin used as the resin component is not particularly limited as long as it is a polyolefin used for a cable insulator, and examples thereof include low-density polyethylene, high-density polyethylene, linear low-density polyethylene, and ethylene-propylene copolymer. May be used alone or in combination of two or more.

[0012] Among polyolefins, a copolymer of ethylene and an unsaturated hydrocarbon synthesized using a single-site catalyst requires only a small amount of an organic peroxide because of its good crosslinking efficiency. Therefore, the amount of decomposition products that are decomposed to generate water is small, and the amount of water generated when heated after crosslinking can be suppressed to a very small amount.

The polyolefin resin composition of the present invention may contain an antioxidant, a lubricant, a coloring agent, a flame retardant,
An antistatic agent, a copper damage inhibitor and the like can be added.

The above-mentioned polyolefin resin composition for a power cable of the present invention can be applied to an insulating layer of a power cable and a connection portion thereof. That is, a semiconductive layer or an insulating layer of a power cable may be formed by extrusion molding and crosslinking, or may be formed as a semiconductive tape or an insulating tape and wound around the conductor to be used. You may.

[0015]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below.

Example 1 A polyolefin resin composition having the composition shown in Table 1 was kneaded in an extruder and then pressed at 120 ° C. for 10 minutes to produce a sheet. Then 170
Cross-linking was performed by pressing at 1 ° C. for 1 hour to obtain cross-linked sheets having a thickness of 5 mm and 0.2 mm.

After measuring the degree of crosslinking and the water content of the obtained crosslinked sheet having a thickness of 5 mm, the sheet was heated again at 190 ° C. for 2 hours to measure the water content. The tan δ of the 0.2 mm thick crosslinked sheet was measured at room temperature.

The crosslinking was carried out according to JIS C 3005, and the water content was measured by the Karl Fischer method. The tan δ was measured by applying 1 kV (50 Hz) to the sheet and using a sharing bridge. Table 1 shows the results
Shown in

[0019]

[Table 1]

As is clear from Table 1, in the crosslinked sheet prepared from the polyolefin resin composition of the present invention, the amount of increase in the water content of the crosslinked sheet before and after heating is extremely small, and tan δ is suppressed to a small value. I have. In particular, in Examples 4 and 5 using a copolymer of ethylene and an unsaturated hydrocarbon produced using a single-site catalyst, Examples 1 to 3 were used.
Only 70% of the organic peroxide used in Examples 1 to 3 was required to obtain the same degree of crosslinking as in Example 1, and the increase in the water content was suppressed to a very small value. On the other hand, in the crosslinked sheets of Comparative Examples 1 and 2 in which calcium stearate is not blended or the blending amount is too small, the moisture content of the crosslinked sheets after heating is significantly increased. The crosslinked sheet of Comparative Example 3 containing a large amount of calcium stearate has a small increase in the water content, but has a large tan δ and a low insulation performance.

[0021]

According to the polyolefin resin composition for power cables of the present invention, an increase in the water content in the resin can be suppressed even if the resin composition is heated again after crosslinking. When the polyolefin-based resin composition for a power cable of the present invention is used as a constituent material of an insulator layer of a power cable or an insulator layer of a power cable connection portion, water-induced dielectric breakdown caused by heating during cable operation or cable connection. A decrease in characteristics can be prevented, and a power cable having good electric characteristics and a connection portion thereof can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J002 BB031 BB051 BB151 EG036 EK037 EK047 FD068 FD147 GQ01 5G305 AA02 AA04 AB02 AB06 BA12 BA13 CA01 CA06 CA51 CB14 CB27 CD05

Claims (2)

[Claims] 1. A polyolefin for a power cable, comprising 0.01 to 0.1 part by weight of calcium stearate and 0.5 to 3 parts by weight of an organic peroxide based on 100 parts by weight of a polyolefin. -Based resin composition. 2. The polyolefin resin composition for an electric power cable according to claim 1, wherein the polyolefin is a copolymer of ethylene and an unsaturated hydrocarbon produced using a single-site catalyst. .