JPS5846261B2 - Rubber composition for electric field relaxation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in rubber compositions for mitigating electric fields.

Conventionally, in electric cables, electrical equipment, etc., insulating layers are formed of insulating materials such as polyethylene and cross-linked polyethylene, but in order to further alleviate the electric field between this insulating layer and electrodes, A semiconductive layer made of a semiconductive composition is provided on the inside.

This semiconductive composition is usually made of a mixture of rubber and carbon black, but this mixture cannot sufficiently alleviate the electric field. .

As an alternative to this, it is known that an excellent electric field relaxation effect can be achieved by using a material whose conductive properties are nonlinear, that is, a material whose volume resistivity decreases as the electric field strength increases. ing.

Attempts have been made to blend silicon carbide and carbon black into rubber in order to maintain such electrical properties, but in this case, unless a large amount of silicon carbide is blended, the above-mentioned mixture becomes conductive and non-linear. It was something I couldn't give away.

On the other hand, when a large amount of silicon carbide is blended, the mixture becomes hard and crumbly, making it extremely difficult to coat by extrusion processing, for example, in the manufacture of electric cables.

Therefore, in order to improve processing properties, a softening agent such as polybutene or polyisobutylene processing oil is blended into the above-mentioned mixture to facilitate extrusion processing.

However, when a softening agent is added to the extent that the processing properties are sufficiently maintained and the softening agent remains stable, a bleed-out phenomenon occurs.

In other words, the amount of the softening agent b in the rubber exceeds its solubility limit, so that the softener oozes out onto the surface of the mixture.

Therefore, when the softener that has oozed out comes into contact with other substances, the softener may migrate or the leached softener may significantly impede the adhesion of the mixture, and the amount of softener in the mixture may inevitably decrease. It became impossible to process it again.

As a result of extensive research in view of the current situation, the present invention has been made to discover a composition for mitigating electric fields that has excellent nonlinearity, conductive properties, and inductive properties, and can be easily coated during extrusion molding. be.

That is, the present invention uses 100 to 450 parts by weight of silicon carbide powder per 100 parts by weight of natural or synthetic rubber, and 10 to 20 parts of conductive carbon black having an oil absorption amount of 17,100 g or more per 300 m.
It is characterized in that it contains 40 to 80 parts by weight of a softener.

The composition of the present invention is characterized in that, among carbon blacks classified as conductive carbon blacks, carbon blacks having an oil absorption of 300 m 17,100 g or more are selected and used.

Incidentally, the oil absorption amount is usually a numerical value called DBP oil absorption amount.

By using such carbon black,
At high temperatures such as in extrusion processing, the solubility of the softener increases and a sufficient softening effect can be achieved, and the softener can be added in an amount sufficient to fulfill its role as a softener.

Moreover, since the softening agent, which should be insoluble at room temperature or a temperature close to it, is absorbed into the above-mentioned carbon black having a large oil absorption capacity, no bleed-out phenomenon occurs.

Therefore, the composition of the present invention does not cause migration due to adhesiveness or migration as described above.

The reason why the amount of carbon black is limited to 10 to 20 parts by weight is that if it is less than 10 parts by weight, sufficient nonlinearity cannot be imparted to the conductive properties of the composition of the present invention.

If it exceeds 20 parts by weight, it will harden and cannot be subjected to extrusion processing or other operations.

The reason for limiting the silicon carbide powder to 100 to 450 parts by weight in the composition of the present invention is that if it is less than 100 parts by weight, a non-linear product cannot be obtained, and if it exceeds 450 parts by weight, it is difficult to process. Characteristics deteriorate.

It is preferable to add 300 parts by weight or more.

The reason why the amount of the softener in the composition of the present invention is limited to 40 to 80 parts by weight is that if it is less than 40 parts by weight, the composition will harden and cannot be subjected to extrusion processing or the like.

Moreover, if the amount exceeds 80 parts by weight, a bleed-out phenomenon occurs.

Further, as the rubber to be applied to the composition of the present invention, a wide range of rubbers such as 5BR1 synthetic rubber and synthetic natural rubber can be used, but in particular, EPM, ethylene propylene copolymer rubber,
Butyl rubber is preferred.

In addition to the above-mentioned compounding agents, the composition of the present invention may contain auxiliary agents such as a vulcanizing agent, a crosslinking agent, and an anti-aging agent, which are commonly compounded in rubber.

The composition of the present invention can also be used, for example, by extrusion coating on the conductor of an electric cable or by wrapping it in the form of a tape.

Next, examples of the present invention will be described.

Examples (1) to (4) and Comparative Examples J) to (3) The compositions shown in Table 1 were kneaded at room temperature to produce electric field mitigation compositions of the present invention (products of the present invention) and comparative examples. A relaxing composition (comparative example product) was obtained.

All numerical values indicate parts by weight.

Non-linearity,
Inductivity, processability, bleed-out phenomenon, etc. were measured.

The results are shown in Table 2.

As is clear from the above table, according to the composition of the present invention, the volume resistivity decreases as a high voltage is applied, so the voltage applied to the conductive layer decreases, making it possible to prevent electrical breakdown on the conductor surface.

Moreover, it has remarkable effects as a semiconductive composition, such as easy processability and no fleet-out phenomenon.

Claims (1)

[Claims] 1 1 silicon carbide powder per 100 parts by weight of natural or synthetic rubber
00-450 parts by weight, 10-20 parts by weight of conductive carbon black having an oil absorption of 300 m17100.9' or more, and 40-80 parts by weight of a softener. .