JPH04106B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a semiconductive resin composition suitable for forming an internal semiconductive layer of a crosslinked polyethylene insulated power cable. Generally, a crosslinked polyethylene insulated power cable is obtained by forming an inner semiconducting layer, an insulating layer, an outer semiconducting layer and a sheath as necessary on a conductor by extrusion coating. Among these layers, the electric field is highest especially on the upper surface of the internal semiconducting layer, and if there are protrusions at this interface due to poor dispersion of carbon black, etc., electric field concentration will occur, reducing the dielectric breakdown strength of the cable. Ta. Therefore, it is necessary to make the surface of the internal semiconducting layer as smooth as possible without any protrusions. Furthermore, if the internal semiconductive layer has heat resistance equal to or higher than that of the insulating layer, crosslinking can be carried out at high temperature in the crosslinking step, so crosslinking time can be shortened and productivity can be improved. Furthermore, by providing an internal semiconducting layer with good oil resistance and flexibility, the characteristics of the cable can be improved. The composition of the conventional internal semiconductive layer is one in which conductive carbon black is added to an ethylene copolymer such as ethylene ethyl acrylate copolymer (A) or ethylene vinyl acetate copolymer (B). However, compared to polyethylene, which is used as an insulating material for cables, (A) was inferior in oil resistance, and (B) was inferior in heat resistance. Therefore, the characteristics of the cable were significantly influenced by the material constituting the internal semiconducting layer. Under these circumstances, it is desirable to use polyethylene as the internal semiconductive material, but when polyethylene (high-pressure low-density polyethylene) is blended with a large amount of carbon black, it loses its flexibility and the internal semiconductive layer deteriorates. It could not be used because of the problem of generating protrusions at the interface. In view of the current situation, the present invention has been made to discover a semiconductive resin composition for power cables that has improved heat resistance and oil resistance and is capable of forming an internal semiconductive layer with a smooth surface. That is, the present invention uses 50 to 95% by weight of linear low density polyethylene and 50% by weight of ethylene copolymer.
5% by weight of conductive carbon black. In the present invention, linear low-density polyethylene is a copolymer of ethylene and α-olefin having 3 or more carbon atoms, and refers to polyethylene without long chain branches. The manufacturing method may be either a gas phase method or a liquid phase method, and the density is determined to facilitate workability.
It is desirable that the weight is 0.930g/cm ³ or less. Examples of the ethylene copolymer include ethylene ethyl acrylate copolymer, ethylene vinyl acetate copolymer, and ethylene propylene rubber. In the present invention, the content of ethylene copolymer is 50
The reason why it is limited to ~5% by weight is that oil resistance decreases when it is blended in excess of 50% by weight.
If the amount is less than 5% by weight, the interface of the semiconductive layer formed using the composition becomes rough and protrusions are formed. The preferred blending range of the ethylene copolymer is
It is 30-50% by weight. Further, as the carbon black for imparting conductivity, any of furnace black, acetylene black, butthorn black, etc. may be used. Next, examples of the present invention will be described. Examples 1 to 5 and Comparative Examples 1 to 4 60 parts by weight of acetylene black, 0.3 parts by weight of antioxidant, and 1.0 parts by weight of dicumyl peroxide per 100 parts by weight of the base polymer having the composition shown in Table 1.
Parts by weight of each were added and kneaded to obtain a semiconductive resin composition of the present invention and a comparative semiconductive resin composition. In order to test the performance of the semiconductive resin composition thus obtained, it was press-crosslinked at 180°C for 10 minutes and then subjected to an oil resistance test (tensile strength retention %) in accordance with JISK-6723.The results are as follows. is shown in Table 1. In addition, an internal semiconductive layer is formed by extruding the above semiconductive resin composition on the outside of the conductor, and a polyethylene insulating layer is provided on the outside to manufacture a 6.6 KV 250 mm ² polyethylene insulated power cable. The electrical properties as well as the interfacial conditions of the layers were tested. The results are shown in Table 1. Note that all numerical values in the base polymer column of Table 1 are parts by weight.

【table】

[Table] As is clear from the above table, the semiconductive composition for power cables of the present invention has excellent oil resistance and AC breakdown voltage value, and no protrusions are formed at the interface of the internal semiconductive layer extruded onto the conductor. On the other hand, in the case of the comparative semiconductive composition, when the interface of the internal semiconductive layer is good, the oil resistance decreases, and when the oil resistance is good, the interface of the internal semiconductive layer becomes rough and becomes poor. It had its advantages and disadvantages. As detailed above, the semiconductive resin composition for power cables of the present invention has excellent oil resistance, flexibility, and electrical properties. The present invention is extremely useful as a power cable with electrical properties can be obtained.

Claims (1)

[Claims] 1. A semiconductive material for power cables, which is made by blending a predetermined amount of conductive carbon black into a mixture of 50 to 95% by weight of linear low-density polyethylene and 50 to 5% by weight of ethylene copolymer. Resin composition.