JPH07109730B2 - Highly foamed insulated wire manufacturing method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a high-foam insulated wire, which can improve the adhesion between a conductor and a high-foam insulating body.

[Prior Art] In a high-speed information circuit such as a computer and a telephone communication, an electric wire having a low dielectric constant is required, and a foamed polyolefin insulated electric wire is often used. As a method for producing a foamed polyolefin insulated wire, a method is generally known in which a polyolefin containing a chemical foaming agent is supplied to an extruder, melt-kneaded at a temperature equal to or higher than the decomposition temperature of the foaming agent, and extrusion-coated on the outer circumference of the conductor. However, in this method, the decomposition gas of the foaming agent is easily scattered, and it is difficult to obtain a high-foamed product of 50% or more.

As a measure to prevent the decomposition gas of the foaming agent from scattering,
53-4909 proposes a manufacturing method in which a plastic mixture containing a foaming agent is extrusion-coated on a conductor, continuously crosslinked by radiation and electron beams, and subsequently heated in a pressurized fluid atmosphere to foam. Has been done.

[Problems to be Solved by the Invention] According to this method, it is possible to obtain a highly foamed insulator having a foaming degree of 60% or more, but the adhesion between the conductor and the highly foamed insulator is still solved. I can't.

The present invention has been made based on the above, and provides a manufacturing method capable of achieving high foaming of an insulator and realizing a highly foamed insulated wire having excellent adhesion between a conductor and a highly foamed insulator. It is intended.

[Means for Solving Problems] A method for producing a highly foamed insulated electric wire according to the present invention is a polyolefin.
A resin composition containing 2 parts by weight or more of azodicarbonamide per 100 parts by weight is extrusion-coated on the outer circumference of the conductor at a temperature not higher than the decomposition temperature of azodicarbonamide, and then crosslinked by irradiation with ionizing radiation. It is characterized in that it is heated above the decomposition temperature of azodicarbonamide under pressure to form a highly foamed insulation.

That is, the inventors have found that the combination of the use of a specific foaming agent and heat foaming under normal pressure can significantly improve the adhesion between the conductor and the highly foamed insulating material, and have reached the present invention.

Examples of the polyolefin in the present invention include, but are not limited to, low density polyethylene, medium high density polyethylene, linear low density polyethylene, ultra low density polyethylene, polypropylene and the like.

Azodicarbonamide is a powder substance having a decomposition temperature of 200 to 210 ° C., and a gas generated by the decomposition forms a foam. The amount of azodicarbonamide added needs to be 2 parts by weight or more relative to 100 parts by weight of polyolefin, and if it is less than this, the adhesion between the conductor and the highly foamed insulator is insufficient, and the degree of foaming is high. I can't. The upper limit is not particularly specified, but it is preferably 15 parts by weight or less from the viewpoint of easy control of the foaming state.

The resin composition containing polyolefin and azodicarbonamide is melt-kneaded at a temperature not higher than the decomposition temperature of azodicarbonamide, for example at a temperature not higher than 160 ° C., and extrusion-coated on the outer periphery of the conductor. Subsequently, ionizing radiation such as an electron beam is irradiated in the range of 0.5 to 5 Mrad to crosslink, and heated at a temperature not lower than the decomposition temperature of azodicarbonamide under normal pressure to form a highly foamed insulator. This heating is preferably performed continuously using an electric furnace or the like, and the set temperature is preferably several tens of degrees higher than the decomposition temperature of azodicarbonamide. Of course, the high temperatures at which the polyolefin decomposes should be avoided.

[Examples of the Invention] Example 1 4 parts by weight of azodicarbonamide was added to 100 parts by weight of low-density polyethylene (UBEC-400 manufactured by Ube Industries, Ltd.), and this was heated to 135 ° C.
After mixing with an 8-inch roll set to No. 2, it was introduced into a 28mm extruder (set temperature 150 ° C) and melt-kneaded to give an outer diameter of 0.4.
A 0.12 mm thick extruded coating was applied to the outer circumference of a tin-plated copper wire of mm. Then, 2 Mrad irradiation was carried out by an electron beam irradiation device to perform cross-linking, and a high-foam insulated electric wire was produced by passing it through a cylindrical electric furnace having an inner diameter of 70 mmφ and a furnace length of 2.5 m set at 280 ° C. under normal pressure.

The degree of foaming of this insulated wire was 75%, and moreover, the conductor and the highly foamed insulating material were in close contact with each other.

Example 2 Low-density polyethylene (Mitsui Petrochemical Mirason 3530) 100
A high-foam insulated wire was produced in the same manner as in Example 1 except that the composition containing 3 parts by weight of azodicarbonamide was used.

The degree of foaming of this insulated wire was 70%, and moreover, the conductor and the highly foamed insulating material were in very good contact with each other.

Comparative Example 1 Low-density polyethylene (Mitsui Petrochemical Mirason 3530) 100
A high-foam insulated wire was produced in the same manner as in Example 1 except that the composition was added with 1.5 parts by weight of azodicarbonamide.

The adhesion between the conductor of the insulated wire and the high-foam insulation was weak.

Comparative Example 2 A high-foam insulated wire was produced in the same manner as in Example 1 except that the heating for foaming was performed in silicone oil set at 260 ° C.

A large gap was formed between the conductor of the insulated wire and the highly foamed insulation, and the adhesion was extremely weak.

Comparative Example 3 A high-foam insulated wire was produced in the same manner as in Example 1 except that dinitropentamethyl ether amine was used instead of azodicarbonamide as a foaming agent.

There is almost no adhesion between the conductor of the insulated wire and the high-foam insulation,
Foaming was also non-uniform.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize a highly foamed insulated electric wire having excellent adhesion between the conductor and the highly foamed insulator. As a result, it becomes possible to stably manufacture a high-foam insulated wire having a uniform outer diameter over a long length.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shiro Konishi 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Electric Cable Research Laboratory, Hitachi Cable Ltd. (72) Inventor Takayasu Asai 5-chome, Hidaka-cho, Hitachi-shi, Ibaraki 1-1 Hitachi Cable Co., Ltd. Hidaka Plant (72) Inventor Masami Maeda 5-1-1 Hidakacho, Hitachi City, Ibaraki Prefecture Hitachi Cable Co., Ltd. Hidaka Plant (72) Inventor Hideo Takano Hitachi, Ibaraki Prefecture 5-1-1 Hidaka-cho, Ichi, Hitachi, Ltd. Hidaka Factory (56) References JP-A-48-22559 (JP, A) JP-A-49-85583 (JP, A) JP-A-49- 93881 (JP, A)

Claims (1)

[Claims] 1. A resin composition containing 2 parts by weight or more of azodicarbonamide with respect to 100 parts by weight of polyolefin is extrusion-coated on the outer periphery of a conductor at a temperature not higher than the decomposition temperature of azodicarbonamide, and then irradiated with ionizing radiation. A method for producing a high-foam insulated wire, which comprises cross-linking, and then heating at a temperature not lower than the decomposition temperature of azodicarbonamide under normal pressure to form a high-foam insulated wire.