JPS59217906A - Method of producing high foamable plastic cable - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for producing a highly foamed plastic cable with a foaming rate of 75% or more by a gas foaming method using a low boiling point liquid foaming agent.

[Technical RM of invention! In recent years, in coaxial cables, etc., the development of so-called highly foamed coaxial cables has been progressing, which aims to increase the foaming rate of the insulator, thereby reducing dielectric constant, tan δ, and leakage attenuation. It is being Freon (Freon) has traditionally been used as a method of manufacturing coaxial cable cores with high expansion ratio
A plastic composition containing a low boiling point liquid foaming agent such as (trade name) is fed to an extruder under pressure and extrusion coated onto a conductor.
Next, after foaming this in the air, it is cooled to 7JJ and solidified 1-
A gas foaming method is known, and foaming ratios of 60% or more have already been obtained.

However, 75% or more by gas foaming method? If you try to obtain an insulating layer with a foaming rate of 3, the problem of rotation will occur.

In other words, methods for obtaining a high foaming rate are (a) increasing the conductor temperature and (b) increasing the foaming agent mixture Φ, but in method (a), the first As shown in the figure, the foaming agent that has become scum tends to collect on the conductor 1, connects, and forms large cells 2, causing a problem of poor adhesion between the foam insulation layer 3 and the conductor 1. .

In order to solve this problem, as shown in Figure 2, it is possible to provide a solid insulating layer 4 made of, for example, a polyethylene composition on the conductor, but if you try to obtain a high foaming rate of 75% with that, , large cells 2 are formed around the solid insulating layer 4, resulting in a problem of reduced mechanical strength and elongation. On the other hand, even in the 11th method of formulating the blowing agent in (b), it is not only uneconomical because it uses an expensive blowing agent inefficiently, but also 75% With the above a1 foaming rate, the middle layer of the foamed insulation layer 3 has large cells 2.
This is a problem in terms of strength. Furthermore, even if method (a) is used in combination, the situation shown in FIGS. 1 and 2 will occur, and the above-mentioned problem will not be solved.

[Object of the Invention J The present invention has been made in response to such conventional circumstances,
We aim to provide a manufacturing method that uses gas foaming to produce highly foamed plastic cables with a foaming ratio of 75% or more that has excellent electrical properties and no mechanical strength problems.
It is something that

[Summary of the Invention 1] In other words, the plastic method for manufacturing a highly foamed plastic cable of the present invention is to provide a solid insulating layer around the outer periphery of the conductor. The product is made of an extruded plate W, which is characterized by 5) foaming in a high temperature atmosphere of 0 to 100°C.

The I\-subolimer of the plastic tank composition used in the present invention includes polyethylene, polypropylene 11-ethylene, silyl-modified polyethylene 14-ethylene, etc. Ru.

Among low-boiling point liquid blowing agents, such as low boiling point liquid blowing agents, for example, low: J1 point hydrocarbon cost liquid Freon (trade name) is known as low-boiling point liquid blowing agent. J1 Point When using a liquid blowing agent, the amount of the blowing agent to be mixed depends on the type of foaming agent used and the desired foaming rate, but in general, There are 15 small hanging parts or less C per 100 small broken parts of the polymer.

In the present invention, the foaming atmosphere after extrusion;
The range of 100°C was chosen because at a temperature of 50°C, there is no heating effect, and if the temperature exceeds 100°C, problems such as tearing of the cell coating in the foam and unevenness on the surface occur. j. It's because it's not good.

In order to obtain such an ambient temperature, for example, a temperature-adjustable heating cylinder having an infrared ray as a heating edge may be disposed on the passage 717 in front of the extrusion head.

[Embodiment J of the invention Next, examples of the present invention will be described.

Example 1 Ml3. O1 density 0.924g/CI+' (7) As shown in Fig. 3, a thin solid insulating layer 4 is formed by extrusion coating low-density polyethylene onto a conductor 1 having a diameter of 2.1mm to a thickness of 0.2iII. This polyethylene 10 is then added to the above low density polyethylene by an extruder onto this core.
A composition prepared by mixing 10 parts by weight of liquid Freon 114 (trade name) per 0 parts by weight is extruded and coated, and this is guided into a heating cylinder at an ambient temperature of 70°C placed in the foaming region of the core to form foam insulation. Forming layer 3, the outer diameter of the insulating layer is 8.0 to 8.
．． Two coaxial cable cores were manufactured.

Next, the capacitance of the obtained coaxial cable core was measured by wrapping aluminum foil around the outer periphery of the foamed insulating layer, and the compressive strength and elongation of the foamed insulating layer were also measured.

The capacitance of this coaxial cable core is /l 9 +) F
/m, and cell 2 had uniformly formed fins C around the outer periphery.

Here, for comparison, the capacitance of the above example is 771/1
A coaxial chip 17 was also manufactured according to Comparative Examples 1 and 2 below, aiming at ±2PF/m of 9PF/m.

Comparative Example 1 Liquid Freon 114 was added to the same low density polyethylene as in the example.
A coaxial cable core was produced in the same manner as in Example 1, using a composition obtained by mixing 3=JL30 parts by weight with 100 parts of the above polyethylene, and setting the foaming atmosphere temperature to air temperature.

Comparative Example 2 A coaxial cable core was manufactured in the same manner as in Example 1 except that the temperature of the foaming atmosphere was set to air temperature.

Ii J axis cable of the above examples and each comparative example -, 1
The measurement results of the characteristics of a are shown in the table below.

*The foaming rate was calculated using the following formula.

Foaming ratio - 1 - Density of foam / Density of solid polyethylene (
-0,920> **Compressive strength is measured by compressing a cylindrical test piece (made by cutting a foamed polyethylene insulation core into a predetermined length) in the radial direction, and compressing the foamed insulation layer twice. Expressed as load.

"Effects of the Invention" As is clear from the above examples, according to the method of the present invention, the foaming of the insulating layer is carried out at a high ambient temperature, so that cells are uniformly formed on the outer periphery of the insulating layer. It is possible to manufacture a plastic cable with a high foaming rate that has excellent not only electrical properties but also mechanical properties.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a foamed coaxial cable core made by a conventional method, FIG. 2 is a cross-sectional view of a foamed coaxial cable core made by another conventional method, and FIG. 3 is a cross-sectional view of a foamed coaxial cable core made by another conventional method. FIG. 3 is a cross-sectional view of the formed coaxial cage luer. 1......Conductor 2...Cell 3...Foam insulation layer 4...・・・
...Full Insulation Layer Patent Attorney Suyama Buddha - (1 other person)

Claims (1)

[Claims] (1) A solid insulating layer is provided on the outer periphery of the conductor, and a plastic phase composition in which a low boiling point liquid foaming agent is dissolved and mixed is extruded and coated on the outer periphery of the solid insulating layer, and this is C-foamed in a ^4 atmosphere at 50 to 100°C. A manufacturing method for highly foamed plastic cables that is characterized by: