JPH02236912A - Semiconductive layer formation composite for power cable - Google Patents

Abstract

PURPOSE:To obtain a composite for a power cable having good heat resistance and a free-stripping property by uniformly blending a prescribed weight of conductive carbon black to a prescribed wt. of a resin member consisting of a prescribed amount of a polymer, in which a ethylene-alpha olefin copolymer is previously silane-grafted, and a prescribed weight of ethylene-alpha olefin copolymer. CONSTITUTION:Conductive carbon black 15 to 70 pts.wt. is uniformly blended to a resin raw mateiral 100 pts.wt. consisting of a copolymer 30 to 70wt.% in which an ethylene-alpha olefin copolymer is previously silane-grafted, and an ethylene-alpha olefin copolymer 70 to 30wt.%. Then, a composite for a semiconductive layer using no resin raw material such as a chlorine polymer and an ethylene vinyl acetate copolymer having poor thermostability, poor heat resistance and having carbon black not all over due to a high share at the time of kneading while having a freestripping property of a bridging polyethylene insulated power cable is obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a composition for forming a semiconducting layer for power cables, and particularly for forming an excellent semiconducting layer useful for forming an outer semiconducting layer of a crosslinked polyethylene insulated power cable. It concerns the composition. [Prior Art] In recent years, power cables made of cross-linked polyethylene have a so-called free-stripping property that allows the outer semiconducting layer to be easily peeled off and removed from the insulator, in order to simplify the unfinished end work and connection work and reduce the time required. Uta cables are starting to become popular. This outer semiconductive layer may be formed of a composition containing a chlorine polymer or an ethylene/vinyl acetate copolymer as a main component, as shown in Japanese Patent Publication No. 55-35806 and Japanese Patent Publication No. 63-32204. Many have been proposed. The above polymers have a good function in terms of free stripping properties, but on the other hand, chlorine-based polymers have poor extrusion processability and are chemically crosslinked and have poor thermal stability because they are passed through high-pressure steam pipes at about 200°C. It gets worse and deteriorates more easily. Similarly, ethylene-vinyl acetate copolymer has poor heat resistance (decomposes during the crosslinking process to generate acetic acid,
This reduces the strength and makes it more likely to break, or corrodes the copper tape that is the shielding layer on the cable. Furthermore, chemical crosslinking, which has been widely used in the past, requires a large amount of capital investment if crosslinking equipment is not available, and cannot be produced easily.

Furthermore, in conventional semiconductive compositions, carbon black particles are uniformly kneaded and not dispersed in the base polymer during the mixing process, resulting in a lot of carbon agglomeration.How can we improve dispersion and reduce carbon aggregation? has become an issue.

[Problem to be solved by the invention]

The purpose of the present invention is to eliminate the use of resin materials such as chlorine-based polymers and ethylene-vinyl acetate copolymers, which have poor thermal stability and heat resistance, and to eliminate carbon particles due to high shear during kneading. The object of the present invention is to provide a composition for a semiconducting layer that has free stripping properties for crosslinked polyethylene insulated power cables. [Means for Solving the Problems] The present invention provides a resin comprising 30 to 70% by weight of a polymer obtained by grafting an ethylene-α olefin copolymer with silane and 70 to 30% by weight of an ethylene-α olefin copolymer. This is a semiconductive layer forming composition for a power cable, characterized in that 15 to 70 parts by weight of conductive carbon black is uniformly blended with 100 parts by weight of the material. In the present invention, the α-olefin of the ethylene-α-olefin copolymer used after being silane-shifted is C
, ~C+Z, e.g., polypropylene, butene-1, pentene-1, hexene-1, hebutene-1, octene-1
14 methylpentene-1, 4 methylhexene-1, 4-
4-dimethylbentene-11 nonene-1, decene-1,
Examples include undecene-1 and dodecene-1.

Particularly desirable are butene-11 pentene-1,
Examples include hexene-1, heptene-1, and 4-methylpentene-1.

The silane graft tomer used in the present invention has the general formula RR' St Yz (R is a monovalent olefinically unsaturated hydrocarbon group, Y is a hydrolyzable organic group, and R' is an aliphatic unsaturated group) to the above-mentioned olefinic resin. It is obtained by reacting an organic silane represented by a monovalent hydrocarbon group other than a saturated hydrocarbon group (or the same group as Y) in the presence of a free radical-forming compound. This method uses a known method disclosed in Japanese Patent Publication No. 57-24373, Japanese Patent Publication No. 48-1711, Japanese Patent Application Laid-open No. 50-24342, etc. It is obtained by combining methoxysilane and other organic peroxides with a strong polymerization initiating effect, such as DCP (dicumyl peroxide). The amount of Silang Graftoma is 1 part resin.
It is preferable that the amount is 30% by weight or more based on the weight of the 00 weight product.If it is less than 30% by weight, the shape retention property at high temperature and the heat deformation rate will deteriorate.

In addition, the degree of crosslinking of the silane graftomer is expressed as a gel fraction of 2
0% to 80% by weight is preferred. Gel fraction 20% by weight
If the gel fraction is below 80% by weight, the shape retention property and heat deformation rate at high temperatures will be poor, and if the gel fraction is 80% by weight or more, the moldability will be poor.

The reason why the amount of conductive carbon black is limited to 15 to 70 parts by weight is that if it is less than 15 parts by weight, the conductivity is low and it cannot function as a semiconductive layer.
This is because if it exceeds 70 parts by weight, extrusion processability deteriorates, mechanical strength decreases, and cracking becomes more likely. As for the type of carbon black, any of Ketjen black, furnace black, acetylene black, etc. may be used, but carbon black with a large adsorption amount specific surface area is more effective. Of course, it goes without saying that antioxidants, lubricants, etc. can be added if necessary.

〔Example〕

A silane-grafted polymer was prepared with the composition shown in Table 1. The ethylene-butene-1 copolymer is CN2008, manufactured by Sumitomo Chemical, and has an MFR of 2.1 g/10 minutes.The ethylene-butene-1 copolymer shown in Table 2 is CN2002, also manufactured by Sumitomo Chemical, and has an MFR of 2.2 g/10 minutes. In order to prevent the temperature of the material from rising rapidly during kneading, water was poured into the jacket of a Banbury mixer, and the material was added all at once, and the material was kneaded until the temperature reached 150°C and pelletized. The granulated pellets were transferred to a 65sφ extruder (insulating material) and 40
A rod-shaped two-color molded product was molded using a 1IIIφ extruder (semi-conductive material). Regarding free stripping properties, a 1 inch wide test piece was taken from the molded product and the peel strength was measured using an autograph. The gel fraction was determined by treating the molded product with hot water at 80°C for 2 hours at 120°C.
The residual content was measured after immersion in xylene for 20 hours. The thermal deformation rate was measured in accordance with JIS K6723. - Thermal stability was evaluated using a Brabender Blast Graph when kneaded at 200°C, with an X if it started to decompose within 15 minutes, and a 0 if it lasted for more than 15 minutes. Table 1 [Effects of the Invention] From the above evaluations, a good semiconducting layer forming composition for power cables was obtained which had good heat resistance and free stripping properties.

Claims (1)

[Claims] (1) Conductive carbon based on 100 parts by weight of a resin material consisting of 30-70% by weight of a polymer prepared by silane grafting an ethylene-α-olefin copolymer and 70-30% by weight of an ethylene-α-olefin copolymer. black 1
1. A semiconductive layer forming composition for a power cable, characterized in that the composition is uniformly blended in an amount of 5 to 70 parts by weight.