JPH01100804A - Electric insulator for wire and cable - Google Patents

Abstract

PURPOSE:To restrain the occurrence of a water tree and in particular a cellular tree by adding the predetermined quantity of a neutral or antioxidant to polyethylene and ethylene polymer or a mixture thereof, and applying bridging treatment thereto. CONSTITUTION:0.05 to 3 weight parts of a neutral or basic antioxidant is added to 100pt.wt. of base resin comprising polyethylene and/or ethylene polymer. The acidity of the antioxidant is evaluated in such a way that the predetermined quantity of the antioxidant is added to ion exchange water having a known hydrogen exponent, filtrated after heating and cooling for the predetermined hours and then the hydrogen index is measured. If the hydrogen index is larger than in the original ion exchange water, the antioxidant is judged to be basic. If the index is unchanged, the antioxidant is judged to be neutral. The base resin added with the antioxidant is bridged via irradiation bridging, silane bridging and the like. The aforesaid constitution is free from the occurrence of a cellular tree, compared with other constitutions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrical insulator for electric wires and cables that can suppress water trees, particularly bow trees.

[Prior Art] Cross-linked polyethylene has a high degree of electrical insulation and is therefore frequently used as an insulator for electric wires and cables. However, when cross-linked polyethylene insulated electrical cables are used in a humid or waterlogged atmosphere, water trees occur in the insulator, significantly reducing electrical insulation performance.

Water trees occur when water condenses in local high electric field areas such as voids in crosslinked polyethylene insulators, foreign matter, and irregularities at the interface between the insulator and the semiconducting layer. Therefore, much effort has been made to eliminate these defects in wire and cable insulation, and several pieces of resin quality control and wire and cable manufacturing techniques have improved the effectiveness of water tree prevention. ing. In particular, water trees that occur due to irregularities at the interface between semiconducting layers can be solved by developing an extruded semiconducting composition that provides a smooth interface with fewer protrusions, and by using common extrusion, which extrudes the insulator and semiconducting layer using the same crosshead. It has decreased significantly. On the other hand, measures to prevent water trees generated from foreign objects and voids in insulators, so-called bow trees, are currently being considered from various angles.

[Problems to be Solved by the Invention] This invention has been made in view of the above-mentioned problems, and even if there are defects such as voids or foreign objects in the wire/cable insulation, water trees, especially bowtight saws, cannot be used. To provide an electrical insulator for electric wires and cables that can suppress

[Means for Solving the Problems] The electrical insulator of the present invention contains 100 fff of polyethylene, ethylene copolymer, or a mixture thereof, and a neutral or basic antioxidant is added to O, OS to H part.
It is constructed by crosslinking a composition in which 3 parts by weight are added.

[Function] By adding 0.05 to 3 parts by weight of a neutral or basic antioxidant, the precipitation of the antioxidant on the surface of the insulator can be prevented without impairing heat resistance, and water trees, especially ,
It can prevent the occurrence of bow-tied trees.

[Example] The inventors of the present application have so far conducted various studies and experiments regarding the relationship between the material composition of crosslinked polyethylene and the bow tie tree. A crosslinking agent, an antioxidant, a lubricant, a weather resistance imparting agent, etc. are added to the crosslinked polyethylene composition as necessary. I learned that it has a big impact on Bow Titley.

In other words, when a neutral or basic acid inhibitor is applied to crosslinked polyethylene, bow tree formation is suppressed.

However, even if it is initially modified or basic, if it is used as an antioxidant in crosslinked polyethylene, it may become acidic due to a chemical reaction.

For example, certain sulfur-based antioxidants with thioether groups generate acidic substances such as sulfene when heated in the presence of element IV.

Therefore, in the present invention, the acidity of the antioxidant is defined by the following method. Add 100 mJl of ion-exchanged water with a known hydrogen index to a 200-500 m airtight container, and add 10g of an antioxidant to this. This container is heated at a temperature of 180'C for 3 hours, and after cooling, it is filtered through a filter paper of about 5 L. If the measured value of the hydrogen index of the antioxidant-extracted water is equal to or larger than the hydrogen index of the ion-exchanged water used, the antioxidant is determined to be neutral or basic.

The hydrogen index was measured by a glass PH electrode at 1 atm, 2
The value is at 5°C.

In addition, as a method of using antioxidants, it is also possible to use two or more types of antioxidants having different mechanisms of action in combination, and to expect a synergistic effect between them.

In such a case, the total ffil O
g, and the acidity of the combined system is determined using the method described above.

That is, when an antioxidant is used in combination, it is sufficient that the antioxidant is neutral or basic as a whole.

The reason why the amount of antioxidant added was 0.05 to 3% by weight was because
This is because if it is less than 0.05 parts by weight, it has no effect as an antioxidant, and if it exceeds 3 parts by weight, so-called bloom or bleed phenomena, in which the antioxidant precipitates on the surface of crosslinked polyethylene, occurs.

In this invention, conventionally known polyethylene or ethylene copolymer is used as the base resin,
Depending on the case, a mixture of these may be used. Examples of the ethylene copolymer include ethylene-vinyl acetate copolymer,
Examples include ethylene/ethyl acrylate copolymer, ethylene/butene-1 copolymer, ethylene proprene rubber, etc., and these may be used alone or in combination of two or more.

The composition thus obtained is crosslinked by chemical crosslinking using an organic peroxide, irradiation crosslinking using ionizing radiation, or silane crosslinking using a silane compound. Although there is no stipulation regarding the addition of lubricants, resistance, and vc properties, it is preferable that these agents are also neutral or basic to produce better results.

Examples of the present invention will be described below in comparison with comparative examples.

Table 1 summarizes the formulations of the compositions of Examples 1 to 6, Comparative Examples 1 to 5, and Reference Examples, and the acidity of the antioxidants. Acidity was measured by the method described above. Since the hydrogen index of the ion-exchanged water used at this time was 6.6, this value was subtracted from the hydrogen index of the antioxidant extracted water for display. That is, if it is negative, the antioxidant is acidic, if it is zero, it is neutral, and if it is positive, it is basic.

A sheet was prepared by kneading the composition shown in Table 1 using an 8-inch mixing roll, and this sheet was pelletized using a pelletizer. The pellet was then introduced into an extruder and the outer diameter was 3 mm.
The copper conductor was extruded and coated with a 0.5 mm thick polyethylene semiconductive layer so that the insulator was 2 mm thick, and then cross-linked in a dry cross-linked pipe using nitrogen gas as a heating medium. Then, an insulated wire was obtained by cooling under pressure.

The thus obtained insulated wire was evaluated as follows. Heat resistance was determined by cross-linking a sheet kneaded with an 8-inch mixing roll into a 1 mm thick sheet using a heat press at a temperature of 180°C, punching it with a No. 3 dumbbell, and heat aging at 150°C for 2 hours using a gear oven aging tester. I let it happen. Measure the remaining percentage of tensile strength and elongation before and after the test: 75%~
Those between 125% and 125% were considered to be passed.

Observation of the occurrence of bowtery and the precipitation of antioxidants was carried out as follows.

An insulated wire is immersed in distilled water, and 3K is applied between the copper conductor and the water.
V, 50) An alternating current voltage of 1z was applied for 18 months at room temperature. After the zero voltage application, the insulator was sliced into thin rings, boiled and stained with a methylene blue aqueous solution, and the number of bow tit trees generated was observed using an optical microscope.

In addition, the surface of the wire after energization was visually observed and analyzed by infrared absorption spectroscopy to investigate the precipitation of antioxidants.

In Table 1, in Examples 1 to 6, neutral or salt-based antioxidants were added in the number prescribed in the present invention, and as can be seen from the evaluation results in Table 2, the occurrence of bow tit tree was was sufficiently suppressed, and the heat resistance and precipitation of antioxidant on the surface of the insulator were not observed.

On the other hand, Comparative Examples 1 to 5 are outside the scope of the present invention, and are insufficient in terms of the effect of inhibiting bow-tree tree, heat resistance, and precipitation of antioxidant on the surface of the insulator.

[Effect of invention] I! 7. As explained above, the gas insulator of the present invention contains 3 parts by weight of a neutral and basic antioxidant based on 100 parts by weight of polyethylene, ethylene copolymer or a mixture thereof. It is made by cross-linking a composition obtained by adding it, and has an excellent effect of inhibiting water tree, especially bow tree tree, and greatly contributes to improving the reliability of electric wires and cables.

Claims (1)

[Claims] A composition obtained by crosslinking a composition obtained by adding 0.05 to 3 parts by weight of a neutral or basic antioxidant to 100 parts by weight of polyethylene, an ethylene copolymer, or a mixture thereof. Characteristic electrical insulators for wires and cables.