JPH03122915A - Semiconductive resin composite - Google Patents

Abstract

PURPOSE:To improve water tree resistance by blending more than a fixed wt.% of conductive carbon black with a resin composite mainly composed of a linear ethylene - acrylic acid ester copolymer having a melting point above 115 deg.C. CONSTITUTION:As a semiconductive composite to be used at the time of extrusion coating the periphery of a conductor with a semiconductive layer and of extrusion coating thereon with an insulating layer to form a power cable, a semiconductive resin composite, in which more than 40wt.% of conductive carbon black is blended with 100wt.% of a resin composite mainly composed of a linear ethylene - acrylic acid ester copolymer having a melting point above 115 deg.C, is used. Water tree resistance can be thereby improved while improving reliability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is useful in the case where a semiconducting layer is first extruded coated on a conductor, and then an insulating layer is extruded coated thereon to produce a ring capeple. The present invention relates to a semiconductive resin composition.

[Prior Art] One method for obtaining a crosslinked polyethylene insulating capeple having an extruded semiconductive layer is to use an internal semiconductive layer extruder, an insulating layer extruder, and an external semiconductive layer extruder as necessary in tandem. There is a method in which each layer is successively extruded and coated on the cable conductor, and then cross-linked in a high-temperature and high-pressure cross-linked pipe.

In this method, an internal semiconducting layer is first extruded onto the conductor, and the conductor coated with the internal semiconducting layer is passed through the nipple of the next insulation layer extruder. During passage, the internal semiconducting layer is susceptible to trauma and deformation.

[Problems to be Solved by the Invention] As described above, if there is an irregularity due to trauma or deformation at the interface between the semiconducting layer and the insulating layer, a local high electric field is formed at the irregularity, and corona This can cause water tree deterioration during discharge or cable flooding.

Currently, the base polymers of semiconductive resin compositions mainly include:
Ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, etc. are used.

However, because these polymers have a low melting point, they do not solidify sufficiently and deform before entering the nipple of the insulator layer extruder after being extruded to cover the circumference of the gaple conductor, resulting in irregularities at the interface with the insulator. Therefore, there is a problem in that water trees occur when a long-term energization test is conducted.

The purpose of the present invention is to solve the problems of the prior art described above,
The object of the present invention is to provide a semiconductive resin composition for power cables that has excellent water resistance.

[Means for Solving the Problems] The present invention provides a semiconductive composition that is used when extrusion coating a semiconductive layer around the outer periphery of a conductor and extrusion coating an insulating layer thereon to form a salt capeple. A semiconductive resin composition is prepared by blending 40 parts by weight or more of conductive carbon black with 100 parts by weight of a resin composition mainly composed of a linear ethylene-acrylic acid ester copolymer with a melting point of 115°C or higher. It is used.

If a composition with such a high melting point is used, the risk of damage or deformation at the nipple of the extruder described above can be greatly reduced, and the water resistance can be significantly improved.

Linear ethylene-acrylic ester copolymers with a melting point of 115°C or higher are produced by a low-pressure ionic polymerization method, which is different from the conventional high-pressure radical method, and unlike conventional ethylene-acrylic esters, , has a linear molecular structure without long chain branches.

Ethylene-acrylic acid ester copolymers having such a molecular structure have a melting point that is about 20 to 30°C higher than conventional copolymers.

Examples of acrylic esters include methyl acrylate, ethyl acrylate, propyl acrylate, and pugil acrylate, but are not particularly specified in the present invention.
A typical example thereof is ethyl acrylate.

Linear ethylene-acrylic acid ester copolymer may be blended with polymers such as polyolefins such as polyethylene, polypropylene, and polybutene as compounding agents, and necessary additions such as antioxidants and lubricants may be added as appropriate. agents may be mixed.

Examples of conductive carbon black include channel black, furnace black, and acetylene black.
In order to obtain the desired conductivity, it is necessary to mix 40 parts by weight or more of conductive carbon black with respect to 100 parts by weight of the resin composition.

Cross-linked polyethylene is generally used as the insulator layer of the power cable in the present invention;
Crosslinked products such as vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-propylene rubber, etc. may also be used, and a crosslinked product obtained by mixing polyethylene and ethylene copolymer may also be used. .

[Example] The present invention will be described below with reference to Examples.

Various semiconductive compositions containing the components shown in Examples 1 to 4 and Comparative Example 1.2 in Table 1 were prepared and used as test materials.

These semiconducting compositions are extrusion coated onto a stranded copper conductor having a cross-sectional area of 150a+" and then coated with low density polyethylene (
Density 0.920g/am3MI=1.0) 2.0 parts by weight of dicumyl peroxide in the overlapping part, 0 antioxidants
, 2 parts by weight was extrusion coated, and the same semiconductive composition as above was further extrusion coated, followed by thermal crosslinking to obtain a salt capeple.

Note that the inner semiconducting layer, the insulating layer, and the outer semiconducting layer were formed by a tandem system in which respective extruders were arranged in series.

The measurement results of the water tree occurrence rate of the power cable thus obtained are shown in the lower column of Table 1.

In addition, the incidence of water trees was measured as follows.

After injecting water into the conductor of the cable to immerse the cable in water, a 50 Hz, 15 kV AC voltage was applied between the conductor and the water electrode for 18 months while maintaining the water temperature at 90°C.

After the voltage application was completed, the insulator was spirally cut to a thickness of 0.5 mm and dyed by boiling with a methylene blue aqueous solution, and then the number of water trees coming out from the interface between the insulator and the internal semiconducting layer was observed.

Examples 1 to 4 are based on the ethylene-ethyl acrylate copolymer with a high melting point according to the present invention, and Comparative Example 1. Compared to Example 2, the incidence of water trees was significantly reduced, and it can be said that the usefulness of the present invention is clearly demonstrated.

[Effects of the Invention] As described above, with the semiconductive resin composition of the present invention, water resistance can be greatly improved compared to conventional examples, and reliability can be improved. .

Claims (1)

[Claims] (1) A semiconductive composition used when forming a power cable by extruding a semiconductive layer around the outer circumference of a conductor and extruding an insulating layer thereon, the composition having a melting point of 115°C or higher. A semiconductive resin composition comprising 40 parts by weight or more of conductive carbon black added to 100 parts by weight of a resin composition mainly composed of a linear ethylene-acrylic acid ester copolymer.