JPH04190503A - Semiconductive composition and power cable - Google Patents

Abstract

PURPOSE:To improve heat resistance, ease in extruding process, ease of dispersion, and safety by adding hydrotalsite to a blend composition made by mixing polymer (EVA-PVC) and ethylene vinyl acetate copolymer (EVA) together and further adding appropriate amount of conductivity producing agent. CONSTITUTION:A semiconductive composition is made by adding 0.5-20 parts by weight of hydrotalsite to 100 parts by weight of blend composition made by mixing a polymer of ethylelne vinyl acetate copolymer grafted with vinyl chloride (EVA-PVC) and ethylene acetate vinyl copolymer (EVA) by blending ratio of 90/10-20/80 further added with appropriate amount of conductivity producing agent. This improves heat resistance, ease in extruding process, ease of dispersion, and safety.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a semiconductive composition with excellent properties, particularly excellent heat resistance, and an electrical cable using the same in a semiconductive layer.

[Conventional technology]

For power cables such as cross-linked polyethylene insulated cables (C cables), insulating layers made of cross-linked polyethylene or cross-linked ethylene propylene rubber, etc. are It is necessary to make the semiconductive layer easy to peel off. At the same time, it is also necessary that the insulating layer and the semiconducting layer do not peel off at the interface when an external force such as bending is applied to the power cable. Therefore, the composition of the semiconducting layer is required to have both appropriate releasability and appropriate adhesion to the insulating layer. Conventionally, a polymer (E
VA-PVC) and ethylene vinyl acetate copolymer (EVA-PVC) and ethylene vinyl acetate copolymer (EVA-PVC)
) in a blend ratio of 90/10 to 20/80, and a composition in which a conductivity imparting agent such as carbon blank is added thereto has been proposed.

[Problem to be solved by the invention]

However, in the case of this semiconductive composition, there was room for improvement in terms of characteristics. That is, in addition to being particularly poor in heat resistance, it was also poor in other properties such as extrusion processability and dispersibility. In addition, this composition requires the addition of MgO or PbO as a stabilizer, but these substances are toxic and undesirable in terms of environmental hygiene, and there is also the problem of worsening dispersibility. Therefore, the present inventors conducted intensive research and found that EVA-pvc and EV with the above blend ratio of 90/10 to 20/80.
It has been found that the above-mentioned drawbacks can be overcome by further adding hydrotalcite to a composition in which a suitable amount of conductivity imparting agent is mixed with the blend with A. The present invention has been made from this viewpoint.

[Means for Solving the Problems and Their Effects] One of the aspects of the present invention is to blend EVA-PVC and EVA at a blend ratio of 90/10 to 20/80, and impart an appropriate amount of conductivity to this. 100 parts by weight of the blend composition to which the agent was added,
Hydrotalcite 0. Another aspect of the present invention is an electrical cable using this semiconductive composition in at least the outer semiconductive layer. In the present invention, the blend ratio of EVA-PVC and EVA is in the range of 90/10 to 20/80 because
This is because by setting the amount within this range, when a semiconducting layer is formed, appropriate releasability and adhesion to the insulating layer are maintained. Further, the amount of the conductivity imparting agent such as carbon black added in the present invention is 30 to 100 parts by weight per 100 parts by weight of the blend composition of EVA-PVC and EVA.
Parts by weight are preferred. In other words, if it is less than 30 parts by weight, the desired semiconductivity cannot be obtained, and if it exceeds 100 parts by weight, the conductivity is high (too much, and at the same time, extrudability and mechanical strength begin to deteriorate). Furthermore, the hydrotalcite used in the present invention has a composition formula of M g 4 , 5 A 122 (OH).
+3.5H20, etc., and its addition improves heat resistance, dispersibility, and extrusion processability. Moreover, when this substance is added, it is itself non-toxic, so the conventionally added stabilizers such as MgO and PbO are no longer necessary, and the problem of toxicity is solved. The type of hydrotalcite is not particularly limited, but membrane crystalline water type hydrotalcite is preferred in order to prevent water absorption and deterioration of the cable insulator. The blending amount was set at 0.5 to 20 parts by weight with respect to 100 parts by weight of the blend composition of EVA-PVC, EVA, and conductivity imparting agent, because if it is less than 0.5 parts by weight, the heat resistance This is because the improvement effect is small, and if it exceeds 20 parts by weight, extrusion processability and dispersibility deteriorate. In addition, other commonly added additives such as anti-aging agents, processing aids, crosslinking agents, etc. can be added to the semiconductive composition of the present invention, if necessary. Next, an example of an electric caple using the semiconductive composition of the present invention as a semiconductive layer is shown in the first illustration. In this figure, 1 is a conductor, and the outer periphery of this conductor 1 is coated with an internal semiconducting layer 2. This internal semiconductive layer 2 is a bond type semiconductive layer, and is of a different type from the semiconductive composition of the present invention. This internal semiconducting layer 2 is coated with an insulating layer 3 . This insulating layer 3
is composed of a resin composition obtained by extrusion coating a polyrefin resin such as crosslinked polyethylene or crosslinked ethylene propylene rubber, and then crosslinking it by heating. This insulating layer 3 is coated with an outer semiconducting layer 4 made of a semiconductive composition according to the present invention, and a shielding layer 5 and a sheath 6 are further coated in this order. The outer semiconducting layer 4 of the present invention has both appropriate releasability and adhesion to the insulating layer 3, so it is not necessary to peel off the outer semiconducting layer 4 from the insulating layer 3 during terminal processing. Although this can be done relatively easily, interfacial peeling does not easily occur between the insulating layer 3 and the external semiconducting layer N4 even if an external force such as bending is applied to the power cable. Furthermore, since the composition of the outer semiconducting layer 4 contains the above-mentioned hydrotalcite, the heat resistance is greatly improved, the dispersibility of the substance is good, and extrusion processing is also good. , the surface can be smoothed and extruded.

【Example】

Various semiconductive compositions were prepared according to the formulations shown in Table 1 (Examples 1 to 5, Comparative Examples 1 to 2), and characteristic tests were conducted on these compositions, and the test results are also shown in Table 1. Also listed. In addition, the property test of the composition was conducted as follows. First, a mixture having the formulation shown in Table 1 above was kneaded according to a conventional method, and then molded into a sheet having a thickness of about 1 mm. Then, this semiconductive sheet I was pressed onto both sides of the copper plate, which had been thoroughly removed from surface impurities and clarified.
After heating for 30 min at
was removed and the state of discoloration on the surface of the copper plate was observed. In addition, thermal stability, surface smoothness, and peeling force were investigated as other physical properties. Here, the surface smoothness was measured by extruding a tape using an 18 mm extruder and counting the protrusions on the surface. The evaluation at this time was: Good - less than 20 protrusions of 0.1 mm or more per 100 cm2, Fair - 0.1 per 100 cm2. mm
The number of protrusions above is 20 to less than 100, and the number of protrusions of 0.1 mm or more per 100 cm2 of defects is 100 or more. In addition, the peeling force was measured after stacking a 2mmmm sheet of polyethylene containing 2 parts of DCP and 0.2 parts of Tsukrac 3000 and the above 1mmmm sheet and pressing at 200°C for 30 minutes. , shows the results of a peel test conducted on a 0.5 inch width. From Table 1 above, the semiconductive compositions according to the present invention (Examples 1 to 5) have superior heat resistance compared to conventional products (Comparative Examples 1 to 2) in which hydrotalcite was not added. It can be seen that corrosion resistance is obtained, and the releasability and surface smoothness are on the same level as conventional products.

【Effect of the invention】

As is clear from the above description, the present invention provides an excellent semiconducting composition with improved properties, particularly heat resistance, extrusion processability, dispersibility, safety, etc. Excellent electrical cables such as CV cables can be obtained using this method.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an example of an electrical cable in which the semiconductive composition according to the present invention is used as an outer semiconductive layer. In the figure, ■...conductor, 2...inner semiconducting layer, 3...insulating layer, 4...outer semiconducting layer, 5...shielding layer, 6... ·sheath,

Claims (2)

[Claims] (1) A polymer obtained by grafting vinyl chloride onto an ethylene vinyl acetate copolymer (EVA-PVC) and an ethylene vinyl acetate copolymer (EVA) at a blend ratio of 90/10.
A semi-conductor characterized in that 0.5 to 20 parts by weight of hydrotalcite is blended to 100 parts by weight of a blend composition in which a suitable amount of conductivity imparting agent is added to the blended composition at a ratio of ~20/80. sexual composition. (2) A power cable characterized in that the semiconductive composition according to claim 1 is used for at least an outer semiconductive layer.