JPH0824013B2 - Method for manufacturing foam insulated wire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a foam-insulated electric wire, which is capable of high foaming and which prevents adhesion between a conductor and a foam insulator.

[Background Art] In high-speed information circuits such as computers and telephone communications, low dielectric constant electric wires are required, and foamed polyolefin insulated electric wires are frequently used. As a method for producing a foamed polyolefin insulated wire, a method is generally known in which a polyolefin containing a chemical foaming material is supplied to an extruder, melted and kneaded at a temperature equal to or higher than the decomposition temperature of the foamed material, 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, in JP-B-53-4909, a plastic mixture containing a foaming agent is extrusion-coated on a conductor and then continuously crosslinked by radiation and electron beams, There has been proposed a manufacturing method in which foaming is performed by heating in a pressurized fluid atmosphere.

[Problems to be Solved by the Invention] However, this method lacks versatility due to the necessity of a fluid pressurizing facility, and has non-uniform outer diameter due to pressure fluctuation, and contamination of insulated wires due to fluid. There is such a problem.

For this reason, various studies were conducted on heat foaming under normal pressure. When the most suitable azodicarbonamide was used as a foaming agent, the conductor and foam insulation adhered, and the foam insulation using a wire stripper was peeled off. At this time, it has been pointed out that the foam insulation remains around the conductor and the workability of the terminal treatment is extremely deteriorated.

The present invention has been made on the basis of the above, and is a method for manufacturing a foam insulated wire, which is capable of high foaming, and which suppresses adhesion between a conductor and a foam insulating material and facilitates peeling of the foam insulating material. It is intended to be provided.

[Means for Solving the Problems] The method for producing a foamed insulated wire according to the present invention comprises a polyolefin
A resin composition containing 0.5 to 15 parts by weight of azodicarbonamide and 0.1 to 8 parts by weight of dibasic lead stearate per 100 parts by weight is extrusion-coated on the outer circumference of a conductor at a temperature not higher than the decomposition temperature of azodicarbonamide. It is characterized in that it is crosslinked by irradiation with ionizing radiation, and then heated above the decomposition temperature of azodicarbonamide to form a foamed insulator.

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 addition amount of azodicarbonamide must be in the range of 0.5 to 15 parts by weight per 100 parts by weight of polyolefin, and if it is less than 0.5 part by weight, foaming is insufficient, and if it exceeds 15 parts by weight, the foaming state is controlled. Becomes difficult.

The dibasic lead stearate is added to suppress the adhesion between the conductor and the foamed insulation. That is, the adhesion between the conductor and the foamed insulating material is due to the decomposition residue of azodicarbonamide, and the dibasic lead stearate suppresses the generation of this decomposition residue. The amount of the dibasic lead stearate added is in the range of 0.1 to 8 parts by weight with respect to 100 parts by weight of the polyolefin. If it is less than 0.1 parts by weight, the effect of preventing the adhesion between the conductor and the foamed insulating material is 8
If it exceeds the weight part, the decomposition temperature of azodicarbonamide is remarkably lowered, so that foaming occurs during extrusion molding.

A resin composition containing polyolefin, azodicarbonamide and dibasic lead stearate as essential components 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. To do. Next, 0.5 to 5 ionizing radiation such as an electron beam is applied.
Irradiation is carried out in the range of Mrad to crosslink, and the foamed insulator is formed under normal pressure by heating above the decomposition temperature of azodicarbonamide. This heating is preferably performed continuously using an electric furnace or the like, and the set temperature is preferably set to several tens of degrees higher than the decomposition temperature of azodicarbonamide. Of course, high temperatures at which the polyolefin decomposes should be avoided.

[Examples of the Invention] Example 1 To 100 parts by weight of low-density polyethylene (UBEC-400 manufactured by Ube Industries, Ltd.), 3 parts by weight of azodicarbonamide was added, and 135 parts of this was added.
The mixture was kneaded with an 8-inch roll set at 0 ° C., and then 0.5 part by weight of dibasic lead stearate was added and compounded. This compound was introduced into a 28 mm extruder (set temperature 130 ° C.), melt-kneaded, and extrusion-coated to a thickness of 1.0 mm on the outer circumference of a tin-plated copper wire having an outer diameter of 0.45 mm. Subsequently, 1.5 Mrad was irradiated by an electron beam irradiation device to perform cross-linking, and the foamed insulated wire was manufactured by passing through a cylindrical electric furnace having an inner diameter of 70 mmφ and a furnace length of 2.5 m set at 300 ° C. under normal pressure.

The foamed degree of this insulated wire was about 70%, and the foamed insulator was extremely easily peeled off by the wire stripper.

Example 2 Low-density polyethylene (Mitsui Petrochemical Mirason 3530) 10
Example 1 except that 4 parts by weight of azodicarbonamide and 0.8 parts by weight of dibasic lead stearate were added to 0 parts by weight.
A foam insulated wire was produced in the same manner as in.

The degree of foaming of this insulated wire was about 72%, and it was extremely easy to peel off the foamed insulation with a wire stripper.

Comparative Example 1 Low-density polyethylene (Mitsui Petrochemical Mirason 3530) 10
A foam insulated wire was produced in the same manner as in Example 1 except that the composition in which 3 parts by weight of azodicarbonamide was added to 0 parts by weight.

Although the degree of foaming of this insulated wire was about 70%, the conductor and the foamed insulator adhered to each other. When the foamed insulator was peeled off with a wire stripper, the foamed insulator remained on the conductor.

Comparative Example 2 Low Density Polyethylene (Mitsui Petrochemical Mirason 3530) 10
A foam insulated wire was produced in the same manner as in Example 1 except that the composition in which 4 parts by weight of azodicarbonamide was added to 0 parts by weight.

Although the foaming degree of this insulated wire was about 76%, the conductor and the foamed insulator adhered to each other. When the foamed insulator was peeled off with a wire stripper, the foamed insulator remained on the conductor.

Comparative Example 3 A foam insulated wire was produced in the same manner as in Example 1 except that the addition amount of dibasic lead stearate was changed to 10 parts by weight.

It was impossible to manufacture an insulated wire because foaming occurred in the step of extrusion-coating the outer circumference of the conductor.

Comparative Example 4 Low-density polyethylene (Mitsui Petrochemical Mirason 3530) 10
A foamed insulated wire was manufactured in the same manner as in Example 1 except that a compound obtained by adding 3 parts by weight of azodicarbonamide and 0.5 part by weight of stearic acid to 0 parts by weight was used.

The degree of foaming of this insulated wire was about 75%, but the conductor and the foamed insulation adhered to each other, and when the foamed insulation was stripped off with a wire stripper, the foamed insulation remained on the conductor.

[Effects of the Invention] As described above, according to the present invention, it is possible to realize a foamed insulated wire that can be highly foamed and that can prevent sticking between a conductor and a foamed insulator to improve workability of terminal treatment. become.

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Hirotoshi Okubo 5-1-1 Hidaka-cho, Hitachi-shi, Ibaraki Electric Cable Research Laboratory, Hitachi Cable, Ltd. (72) Inventor Takayasu Asai 5 Hidaka-cho, Hitachi-shi, Ibaraki 1-1-1 Hitachi Cable Co., Ltd. Electric Cable Research Laboratory (72) Inventor Norimoto Abe 5-1-1 Hidakacho, Hitachi City, Ibaraki Hitachi Cable Co., Ltd. Electric Cable Research Laboratory (56) Reference JP 48- 22559 (JP, A) JP 61-44933 (JP, A) JP 54-162190 (JP, A)

Claims (1)

[Claims] 1. A resin composition containing 0.5 to 15 parts by weight of azodicarbonamide and 0.1 to 8 parts by weight of dibasic lead stearate with respect to 100 parts by weight of polyolefin at a temperature below the decomposition temperature of azodicarbonamide. A method for producing a foam-insulated electric wire, comprising the steps of: extrusion-coating on the composition, cross-linking it by irradiation with ionizing radiation, and then heating it to a temperature not lower than the decomposition temperature of azodicarbonamide to form a foamed insulation.