JPS63313410A - Semiconducting composition for power cable - Google Patents

Abstract

PURPOSE:To obtain a semiconducting component to be used for power cables which is improved in water-tree-proof characteristic by adding at least 40 weight of conductive carbon black for 100 weight of specified ethylene propylene rubber or ethylene propylene diene rubber. CONSTITUTION:A semiconducting component is formed by adding conductive carbon black of at least 40pts.wt. to ethylene propylene rubber or ethylene propylene diene rubber of 100pts.wt.; the weight ratio between ethylene and propylene in these rubbers is 90:10 to 50:50, and each constituent shall have the viscosity of 1 to 10 in Mooney viscosity (ML1+4 100 deg.C). If ethylene is contained more than 90% water-tree-proof characteristic is degraded, and if propylene is contained more then 50% elasticity is lost. A semiconducting component to be used for power cables of which water-tree-proof characteristic is improved is thus obtained. Moreover it shows excellent characteristics for the problem of deterioration of conductivity and also for the workability when a common head extruder, a high efficiency machine for working, is used.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductive composition for an electric cable, and more particularly, to a semiconductive composition for use in a semiconductive composition provided on the outer periphery of a high-voltage conductor or the circumferential surface of an insulator of an electric cable. The present invention relates to improvements in compositions suitable for use in sexual layers.

[Prior Art] In general, the adhesion and smoothness between the semiconducting layer of an electrical cable such as cross-linked polyethylene insulation and the insulator interface are important for improving the reliability of the cable. A locally high electric field is formed, causing water tree deterioration during corona discharge and flooding, which deteriorates the electrical characteristics of the cable.

In response to this problem, studies were conducted from both the manufacturing and material aspects of the semiconductive layer, and an extruded semiconductive layer was developed in place of winding a semiconductive cloth tape that has a lot of fluff.

In this case, materials for the extruded semiconductive layer include polyethylene, ethylene-based copolymers such as ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-methyl methacrylate copolymer, and ethylene-based copolymer. Butene-1 copolymers, ethylene propylene rubber, styrene propylene rubber, and the like are added as base polymers or used as blends.

A crosslinked polyethylene insulating capeple having a semiconducting layer made of such a material has the advantage of significantly improved breakdown voltage.

[Problems to be Solved by the Invention] However, such conventional semiconductive compositions for electrical cables have the advantage that the breakdown voltage is significantly improved compared to the case where semiconductive cloth tape is wound. Although there is
Under severe environmental conditions where water intrudes into the cable, a problem arises in that water treeing occurs frequently and the breakdown voltage drops extremely when power is applied over a long period of time.

Therefore, this invention was made in view of the above circumstances.
The purpose is to provide a semiconductive composition for an electrical cable that has improved water resistance.

[Means and effects for solving the problems] The present invention provides an ethylene propylene rubber having a Mooney viscosity (ML 100°C) of 1+4 to 10 and a weight ratio of ethylene to propylene of 90:10 to 50:50. or at least 40 parts by weight of conductive carbon black per 100 parts by weight of ethylene propylene diene rubber.
By forming a semiconductive composition in which more than one part by weight is added, it is possible to obtain a semiconductive composition for power cables with significantly improved water resistance.

[Example] When we investigated the water resistance from the material aspect of extruded semiconductive layers, we found that materials with high rubber elasticity such as ethylene propylene rubber and ethylene propylene diene rubber have a high rubber elasticity such as polyethylene. It was found that the semiconductive composition has better water resistance than a polymer with almost no polymer.

However, when ethylene propylene rubber or ethylene propylene diene rubber is used as the base polymer, the viscosity of the semiconductive composition generally becomes extremely high, resulting in problems with the smoothness of the interface between the extruded semiconductive layer and the crosslinked polyethylene insulator. It is possible to adopt a common head extrusion method for the "inner semiconducting layer/insulator" and "inner semiconducting layer/insulator/outer semiconducting layer", which is an extremely effective cable manufacturing method for improving adhesion. Can not.

For this reason, we have no choice but to use a tandem head extrusion method in which each layer is extruded in sequence using a separate extruder, but with this method, the surface of each layer is scratched when it passes through the nipple of the extruder. Therefore, the water resistance that ethylene propylene rubber and ethylene propylene diene rubber originally have cannot be effectively exhibited.

Therefore, the molecular weight and chemical composition of ethylene propylene rubber (
After careful consideration of the composition ratio of ethylene and propylene, the Mooney viscosity (ML 100°C) was 1÷41 to 10, and the composition ratio of ethylene and propylene was in the range of 90:10 to 50:50 by weight. It has been found that semiconductive compositions using ethylene propylene rubber or ethylene propylene diene rubber as a paste trimer have excellent water resistance and can be molded by common head extrusion.

The Mooney viscosity (ML 100°C) 1+4 of this ethylene propylene rubber and ethylene propylene diene rubber is set to 1 to 10 because if it exceeds 10, the viscosity of the semiconductive composition increases and common head extrusion molding becomes difficult. It's for a reason. Moreover, if it is less than 1, it will not have rubber elasticity.

On the other hand, the reason why the weight ratio of ethylene and propylene is set to 90:10 or 50:5.0 is that if the ethylene ratio is higher than 90, the water resistance will deteriorate, and conversely, if the propylene ratio is higher than 50, the water resistance will deteriorate. This is because rubber elasticity is lost.

In the case of ethylene propylene diene rubber, general-purpose non-conjugated dienes such as dicyclopentane and ethyral norbornene can be used as the diene component.

Furthermore, it is also possible to blend an ethylene-based polymer with ethylene propylene rubber or ethylene propylene diene rubber within a range that does not excessively increase the viscosity of the semiconductive composition. Examples of these ethylene-based polymers include polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-metal methacrylate copolymer, ethylene-butene-1 copolymer, and the like.

As the conductive carbon black, acetylene black, furnace black, Ketjen black, etc. can be used. In this case, the amount of carbon black to be mixed is set to 40 parts by weight or more, since conductivity is low if it is less than 40 parts by weight based on 100 parts by weight of the base polymer. However, since Ketjen black has extremely high conductivity, the amount to be mixed can be further reduced.

Further, as compounding agents, anti-aging agents, lubricants, process oils, etc. may be added as necessary. As anti-aging agents, amine type N,N'-diphenyl-Pphenylenediamine, phenyl-α-naphthylamine, N-phenyl-N'isopropyl-phenylenediamine, poly(2,
2,4-trimethyl-1,2-dihydroquinoline), etc.
Phenolic 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 2,6-sheet
ert-butyl-4-methylphenol, 4゜4'thiobis(6-tert-butyl-3-methylphenol)
etc., imidazole-based 2-mercaptobenzimidazole, 2-mercaptobenzimidazole zinc group, etc., sulfur-based distearyluboodipropionate, dilaurylthiopropionate, tetrakis(methyl-dodecylthiopropionate)methane, etc. and other anti-aging agents used for rubber can be used alone or in combination.

Such a semiconductive composition may be crosslinked, and the crosslinking method in this case includes dicumyl peroxide, 1
-Crosslinking with organic peroxides such as -3-bis-(teabutyl-peroxy-isopropyl)benzene, crosslinking with ionizing radiation, and crosslinking with water in the presence of a silanol condensation catalyst, etc. is applicable.

In order to demonstrate the effectiveness of such a semiconductive composition for power cables, experiments were conducted as detailed below.

That is, as shown in Table 1 on the next page, a total of 9 samples of Examples 1 to 4 and Comparative Examples 1 to 5 were prepared with various combinations of ingredients.

(Left below) Semiconductive compositions made from various samples prepared as shown in Table 1 were applied onto a stranded conductor with a cross-sectional area of 80 mm2 using a common head extruder to form an inner semiconducting layer and an outer semiconducting layer. It was extruded at the same time as the uncrosslinked polyethylene insulation layer. The thickness of each layer at this time is 1 mm for the inner and outer semiconducting layers.
The uncrosslinked polyethylene insulation layer is 4 mm.

Following such extrusion processing, heating crosslinking was performed to obtain a crosslinked polyethylene insulating capeple. The composition of crosslinked polyethylene is low density polyethylene (density ρ=0.9
To 100 parts by weight of MI=1.0 at 2g/Cm2, 2.5 parts by weight of dicumyl peroxide and 0.0 parts by weight of an antioxidant.
251 parts by weight.

After injecting water into the conductor of such a cable to immerse the cable in water, an AC voltage of 15 kV at 50 Hz is applied between the conductor and the water electrode, and the water temperature at that time is 90 ° C.
8 Power is applied monthly, and after this voltage is finished, the insulator is Q, 5
After spiral cutting to a thickness of mm and boiling and staining with a methylene blue aqueous solution, the number of water trees generated at the interface between the insulator and the internal semiconducting layer was observed using a microscope. The results are shown in Table 2.

The conductivity of the semiconductive composition is determined by measuring the volume resistivity of the external semiconductive layer of the cable, and is 5X103Ω.
- A value of cm or less was considered a pass.

In addition, the viscosity of the semiconductive composition is determined by the extruder head pressure during cable extrusion, and this pressure is 300 kCJ/
Those exceeding cm2 were judged to have poor workability. (
As is clear from Table 2, the semiconductive compositions according to the present invention shown in Examples 1 to 4 are the same as those in Comparative Examples 1 to 4.
Compared to No. 5, the number of water tree occurrences was significantly lower, and there were no problems with conductivity or common head extrusion processability, showing good results.

[Effects of the Invention] As is clear from the above explanation, the semiconductive composition for power cables according to the present invention has solved all the conventional problems, and has no problem with water when applying electricity for a long period of time. Since there is very little tree, it is possible to provide a semiconductive composition for electrical cables with improved water resistance, and it also solves the problem of deterioration of conductivity and the problem of efficient processing when using a common head extruder. It also has the remarkable effect of being extremely good in processability.

Claims (1)

[Claims] Mooni viscosity (ML_1_+_4100℃) is 1 to 1
The weight ratio of ethylene and propylene with 0 is 90:10
1. A semiconductive composition for a power cable, characterized in that at least 40 parts by weight or more of conductive carbon black is added to 100 parts by weight of ethylene propylene rubber or ethylene propylene diene rubber in a ratio of 50 to 50.