JPS6041402B2 - Crosslinked polyolefin insulated wire/cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to crosslinked polyolefin insulated wires and cables that can prevent copper damage deterioration and conductor discoloration.

A polyolefin resin is supplied into the extruder, and a crosslinking agent and an antioxidant are injected from the resin supply port or its vicinity.
A method has been proposed in which the three components are kneaded in an extruder, extruded and coated on the circumference of the conductor, and then crosslinked (so-called crosslinking agent monoxidant simultaneous injection extrusion method).

Electric wires and cables manufactured using this method have the following problems.

'1} If the conductor and insulator come into direct contact, the insulator will deteriorate, so it is necessary to wrap separator tape over the conductor.

■ A drying process is necessary because the conductor discolors due to the reaction between the decomposition products of the liquid crosslinking agent and the vapor.

As a method to improve these problems, (1) add a large amount of oxidizing agent to stabilize the insulator to a high degree; ■Two or more types of antioxidants act together to prevent oxidation through a synergistic effect. ■It has been proposed to add a steel sheeting inhibitor. However, according to method 1, the crosslinking speed is slow due to crosslinking inhibition, resulting in a decrease in productivity.

According to item (2), when the crosslinking agent monoxidant mixture is supplied from the injection port, the resin becomes slippery, resulting in uneven extrusion and fluctuations in the outer diameter of the cable. According to (2), copper damage inhibitors have a high melting point, so they have to be made into a master batch, or a kneading process such as banburi, rolls, etc. are required, making them expensive and not being put into practical use. It has not yet reached this point. An object of the present invention is to provide electric wires and cables having a novel polyolefin insulating layer that eliminates the drawbacks of the prior art described above and prevents deterioration of the copper wire and discoloration of the conductor. The gist of the present invention is to combine a polyolefin resin, a crosslinking agent that is liquid at room temperature, and 4,4'-thiobis(6-tertiarybutyl-methacrensol) in an extruder.
and tetrakis{methylene (dodecylthiopropionate)}methane, extrusion coating onto a conductor, and crosslinking treatment to form an insulating layer.

Representative examples of the polyolefin resin and crosslinking agent used in the present invention are listed below.

Examples of the polyolefin resin include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-propylene-gene terpolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid ester copolymer.

As a crosslinking agent, di-tert-butyl peroxide, t-tert-butyl cumyl peroxide, 2,
5-dimethyl 2,5 di(tert-butylberoxy)
Examples include hexane, 2,5-dimethyl 2,5-dihydroberoxyhexane, and the like.

As antioxidants, 4,4'-thiobis(6-tertiarybutylmetacresol) and tetrakis{methylene(dodecylthiopropionate)}methane are used in combination.

The reason why the antioxidant used in the present invention is limited is that the conventional drawbacks cannot be improved by using other combinations.

When an antioxidant is used alone, it must be added in a larger amount than in a combination system, and the stability of the antioxidant-crosslinking agent mixture deteriorates, leading to recrystallization of the antioxidant. formation, separation from the crosslinking agent, and precipitation.

In the present invention, the antioxidant is dissolved in the liquid crosslinking agent using tetrakis {methylene (dodecylthiopropionate).
}It has been found that the long-term stability of the solution increases when dissolved in a crosslinking agent at a temperature above the melting point of methane. Next, examples of the present invention will be shown together with comparative examples.

(The unit is parts by weight.

) Polyethylene (density 0.921, melting index 2) 100
Parts by weight and indicated parts by weight of the crosslinking agent monoxidant shown in Examples and Comparative Examples are kneaded in an extruder, and this is mixed with a cross-sectional area of 1
Extrusion coating was applied onto 50 squares of copper conductor, followed by steam crosslinking.

This was used as the test cable. To evaluate copper damage deterioration, the cable 135 with a conductor attached was heated for 07 days, and the deterioration of the insulator on the surface in contact with the conductor was determined with the naked eye, and the tensile properties were used as a measure of deterioration.

Discoloration of the conductor was determined by visually determining the discoloration of the conductor by leaving a cable with a length of 100 mm wrapped around a drum in a constant temperature room at 30° C. for 6 days.

As shown in the examples, a liquid crosslinking agent alone, a three-way mixture system, and a combination system of 4,4'-thiobis(6-t-butyl-metacresol) and tetrakis{(methylene(dodecylthiopropionate)}methane) No copper damage deterioration or conductor discoloration was observed in any of the combinations, and it was recognized that the combination was significantly superior to the combination system in the comparative example.

Copper damage deterioration is oxidative deterioration that uses copper as a catalyst, so it can be prevented by highly stabilizing the insulator.
Even when 4,4'-thiobis(6-obutyl-metacresol) is added alone in a large amount, the solubility of the copper damage deterioration inhibitor in the liquid crosslinking agent is 1'1 degree, and if the concentration is increased beyond this level, it will dissolve. Because of problems such as poor liquid stability, none of the previously proposed combinations of antioxidants could satisfy both properties.

The present invention has been able to overcome these drawbacks, and it has been confirmed that due to the synergistic effect of two specific antioxidants, a sufficient effect can be obtained with a smaller amount than when adding one antioxidant alone. .

It can be said that the crosslinked poly-IJ olefin insulated wire/cable manufactured by the crosslinking agent monoxidant simultaneous injection extrusion method is in an ideal state. In other words, unlike conventional kneading methods, there is no need to perform bundling or roll mixing operations to add antioxidants, crosslinking agents, etc. to the resin. It is expected that performance will improve as it has features such as being able to prevent a drop in dielectric breakdown voltage caused by such conditions and the occurrence of bow-tightness caused by water immersion.

Claims (1)

[Scope of Claims] 1. In a crosslinked polyolefin insulated wire/cable having a crosslinked polyolefin insulating layer on the circumference of the conductor, the crosslinked polyolefin insulating layer is made by kneading the following components (1) and (2) and applying this to the conductor circumference. A cross-linked polyolefin insulated wire/cable characterized by being made of an extrusion coated and cross-linked wire/cable. (1) Polyolefin resin (2) A crosslinking agent that is liquid at room temperature and an antioxidant 4,4'-thiobis(6-
A liquid mixture of tertiary butyl-metacresol) and tetrakis {methylene (dodecylthiopropionate)}methane.