JPS5917135B2 - semiconductive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconducting composition suitable as a constituent material of an outer semiconducting layer of a solid power cable such as a crosslinked polyethylene insulated power cable.

For the electrical performance of the cable, it is necessary for the external semiconductive layer to be in close contact with the insulating layer without any gaps during cable operation.
On the other hand, in cable connection work, it is required that the insulation layer be easily peeled off. Various types of releasable semiconducting compositions have been proposed in the past, but some have good releasability but are difficult to process into pellets or have high viscosity and are difficult to extrude. This is because some materials have the disadvantage of being too hot or prone to scorching due to the heat during extrusion, while others have disadvantages in terms of peelability even though they are excellent in pellet processability. However, it cannot be said that a satisfactory semiconductive composition has been proposed. In view of the above, the present invention has excellent pellet processability and scorch resistance, and is easy to extrude. The present invention proposes a novel semiconductive composition that can form an external semiconductive layer with excellent adhesion and easy peelability to an insulating layer made of an organic polymer or a crosslinked product thereof.

The present invention provides an ethylene-vinyl acetate copolymer (
It is characterized by consisting of 100 parts by weight of EVA), 20 to 70 parts by weight of polystyrene having a melt flow index (hereinafter MFI) of 5 or more, more preferably 10 or more, conductive carbon black, and an organic peroxide. It is something.

The reason why the vinyl acetate content of EVA is set to 25 parts by weight or more is that when the vinyl acetate content is less than 25% by weight, the semiconductive layer formed with this composition has a significantly increased adhesive strength with the insulating layer. This is because the connection workability is poor. Further, polystyrene was measured according to JIS K6870, and if the MFI was less than 5, the resulting composition would have a high melt viscosity and poor extrusion processability.

The reason why parts by weight of EVAIOO and polystyrene are 20 to 70 parts by weight is that pellet processability is insufficient in a composition containing less than 20 parts by weight of polystyrene;
If the amount exceeds 0 parts by weight, the composition will not be able to form a semiconducting layer with practically sufficient adhesive strength on the insulating layer, and the melt viscosity of the composition will be extremely high, making extrusion processing difficult. It is from.

In the end, the resin material used in the present invention is the above-mentioned specific E
Only when VA and polystyrene are adjusted within the above-mentioned limited blending range, an external semiconductive layer with excellent pellet processability and extrusion processability, excellent adhesion to the insulating layer, and easy peelability can be formed. The resulting composition is obtained. As conductive carbon blacks for imparting conductivity necessary for a semiconductive layer to such resin materials, well-known conductive carbon blacks such as furnace black, acetylene black, and ketten black ECl are used as semiconducting materials for power cables. It is used in an amount necessary to impart the electrical conductivity required for the composition.

For example, Furness Black, Channel Black,
In the case of conductive carbon black with a low to medium surface area such as acetylene black, the amount is about 40 to 70 parts by weight per 100 parts by weight of the total amount of resin material (that is, EVA and polystyrene), while Kettien Black (manufactured by Akzo Corporation) In the case of conductive carbon black having a high surface area, the amount is about 10 to 30 parts by weight per 100 parts by weight of the total amount of resin composite.

Anti-aging agents, stabilizers, etc. can be added to the composition of the present invention, if necessary.

Further, examples of the crosslinking agent (vulcanizing agent) used in the composition of the present invention include dicumyl peroxide, 1,3-bis(
t-butylperoxyisopropyl)benzene, 2,5
An organic peroxide crosslinking agent such as -dimethyl-2,5-di(t-butylbaroxy)hexyne-3 is preferably used.
Tables 1 and 2 show the compositions (parts by weight) and various properties of Examples of the compositions of the present invention, as well as those of Comparative Examples.

Each characteristic was evaluated by the method shown below.

Peelability: Each semiconducting composition is mixed and adjusted using an open roll, and press-molded to a thickness of 1 mm at a temperature below the decomposition temperature of the crosslinking agent.

On the other hand, a composition comprising 100 parts by weight of polyethylene (Ml; 1), 2.0 parts by weight of dicumyl peroxide, and 0.3 parts by weight of 4,45-thiobis-(6-t-butyl-3-methylphenol). Mix and adjust in the same manner as above,
Press molding to a thickness of 1 ml at a temperature below the decomposition temperature of the crosslinking agent. These two sheets were stacked and press vulcanized at 180° C. for 30 minutes at a pressure of 50 k9/cm2 to create a crosslinked bonded sample sheet (about 10 square meters in size). Next, an inch-wide cut is made only in the semiconductive composition layer, reaching all the way to the polyethylene layer. AE the inch-wide cut-out part
The polyethylene layer is peeled off perpendicularly to the polyethylene layer in accordance with the IC standard, and the average value of the force (Kg) required for the peeling is determined. Pellet processability: Two uncrosslinked sheets of 1m71L thickness were stacked and sandwiched between glass plates from both the top and bottom sides and heated at 40°C for 3 hours.
The presence or absence of adhesion between the two sheets was examined, and those with no adhesion at all were ◎, those with adhesion were rated as ×, those with some adhesion but the degree of adhesion were extremely light were 01, and those with relatively good adhesion were △.
It was shown in

The lower the adhesiveness between the sheets, the less the pellets will stick to each other when made into pellets, and when fed to the hopper of an extruder, the pellets will be less likely to stick together in the hopper. Easy to store, transport, etc. in pellet form 〇Using scorch-resistant rubber bender plasticator, the chamber temperature is 110℃.
The torque increase start time was measured under the conditions of ℃ and 25 RPM.

Claims (1)

[Claims] 1. 100 parts by weight of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 25% by weight or more, 20 to 70 parts by weight of polystyrene having a melt flow index of 5 or more, conductive carbon black, and organic peroxide. A semiconducting composition consisting of 2. The first semiconductive composition of claim 1, wherein the vinyl acetate content of the ethylene-vinyl acetate copolymer is 35% by weight or more. 3. The semiconductive composition according to claim 1 or 2, wherein the polystyrene has a melt flow index of 10 or more.