JPS59196512A - 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 manufacturing a highly foamed plastic cable, and particularly to a highly foamed plastic cable that improves deterioration in electrical properties and discoloration of conductors caused by decomposition residues of chemical foaming agents. This invention relates to a method for manufacturing a table.

[Technical background of the invention and its problems]

Conventionally, in manufacturing foamed plastic insulated cables such as foamed polyethylene, plastic mixed with a chemical foaming agent is fed into an extruder, extruded and coated onto a conductor at a temperature above the decomposition temperature of the foaming agent, and then this is coated onto a conductor. It is carried out to foam in the air and then cool and solidify.

On the other hand, in recent years, in the field of coaxial cables and the like, progress has been made in the development of so-called highly foamed plastic cables in which the foaming rate of the insulator is increased, thereby reducing the dielectric constant, tan δ range, and leakage attenuation.

In addition, highly foamed cables have the advantage that even if the cable size is the same in terms of design, the conductor diameter can be made larger to reduce the amount of resistance attenuation, thereby eliminating the need for cables and reducing material costs.

However, it is clear from various technical documents that a high foaming rate cannot be obtained immediately by simply increasing the amount of foaming agent blended. For this reason, cables having high foaming ratio insulators are often manufactured using gas foaming. However, the gas foaming method requires large equipment costs, and the economic efficiency of the chemical foaming method cannot be overlooked.

The present inventors have conducted various studies to solve the problems of the chemical foaming method as described above, and as a result, it has become possible to obtain a high foaming rate by selecting a base resin and improving extrusion conditions.

However, when the amount of foaming agent blended into the insulator is increased, a large amount of decomposed residue of the foaming agent is generated, which causes deterioration of electrical properties such as an increase in tan δ and an increase in attenuation in the high frequency region, and
．． A problem arose in that the internal conductor became discolored.

It is also believed that the discoloration of the conductor causes an increase in the conductor resistance, which is a contributing factor to further increasing the amount of attenuation.

Therefore, the present inventors attempted a method of heat-treating such a highly foamed plastic insulator in air or under reduced pressure to quickly volatilize the decomposition residue of the foaming agent from within the insulator. However, although a decrease in tan δ and attenuation is observed in both methods, the method of heating in air has the disadvantage that it must be heated at a high temperature or at low humidity for a long time, and the decomposition residue that evaporates when heated Since it comes into contact with the conductor in the coexistence with 02, there is a problem in that discoloration of the conductor cannot be sufficiently prevented.

In addition, in the method of heating in a vacuum or under reduced pressure, it takes time to reach the specified humidity, and after that the temperature of objects in contact with the cable insulation, such as the drum around which the cable is wound, increases and the insulation There was a risk that the body would become soft and deformed.

[Purpose of the invention]

It is an object of the present invention to overcome these difficulties and to provide a manufacturing method for obtaining a high foaming rate plastic cable that has excellent electrical properties and does not cause discoloration of the conductor using a chemical foaming agent.

[Summary of the invention]

In the present invention, a plastic composition such as polyethylene mixed with a chemical foaming agent is extruded onto a conductor at a temperature higher than the decomposition temperature of the foaming agent and foamed, and then □ At a temperature higher than 60°C in an inert gas. By applying heat treatment to the insulation coating, the residue from the decomposition of the foaming agent is quickly volatilized and removed from the insulation coating, and O7, which causes discoloration of the conductor, is removed to prevent it from coexisting with the residue. Regarding the manufacturing method.

Here, the highly foamed cable in the present invention refers to a foaming ratio of 60
% or more of polyethylene, polypropylene, silyl-modified polyethylene, etc., coated on a copper conductor.

Examples of the chemical blowing agent in the present invention include azodicarbonamide (hereinafter referred to as ADOA) and P.

Y-oxybis(benzenesulfonylhydrazide) (hereinafter referred to as 0BSH) and other known chemical blowing agents can be used.

The amount of the blowing agent to be added varies depending on the type of plastic used, the type of blowing agent, and the foaming rate to be manufactured, but is preferably in the range of about 1 to 5 parts by weight per 100 parts by weight of the plastic.

In addition, in the present invention, the heat treatment humidity is 60°C or higher,
In addition, the reason why we limited the temperature to below the softening point of the plastic that makes up the insulator is that temperatures below 60°C have little effect on improving electrical properties, and conversely, temperatures above the softening point of the plastic cause the insulator to deteriorate. This is because there are disadvantages such as the shape becoming unstable, which is not preferable.

Furthermore, Nt, Ar, or the like is suitable as the inert gas. Since heat treatment greatly contributes to the convection of this gas, it is also good to circulate the gas.

The treatment time can be shortened if the treatment temperature is as close as possible to the insulator softening temperature.

[Embodiments of the invention]

Next, examples of the present invention will be described.

Example 1 A masterbatch containing low density polyethylene with a melt index of 3 and a density of 0.92 and containing ADOA and 0BSR,
ADOA and 0B per 100 parts by weight of polyethylene
The amounts of 8H were mixed to be 1.5 parts by weight and 0.8 parts by weight, respectively, and the mixture was fed to an extruder and the extrusion temperature was set to 18 parts by weight.
At 0° C., the insulator was overlaid on a mild steel wire with a diameter of 1.8 m with an outer diameter of 7.3 mm (inner diameter of the die) and allowed to foam naturally.

Next, the obtained foamed polyethylene insulated wire core (foaming ratio 75
%) under nitrogen gas at 60°C, 70°C1 and 80″C
The dielectric loss tangent (t
and (δ) was measured.

The measurement results are shown in the graph of the drawing.

For comparison, changes in tan δ after heat treatment in air under the same temperature conditions were measured.

The measurement results are shown as dashed lines in the same graph.

At this time, when compared with the one heat-treated under reduced pressure, the tan
The effect of improving δ is slightly better when treated under reduced pressure, but in the case of the method of the present invention, the time it takes to reach the specified temperature (although an absolute comparison cannot be made because it varies depending on the size of the container) is very fast. The total treatment time was ultimately shorter with the method of the invention. Example 2 The same highly expanded polyethylene insulated wire core as obtained in Example 1 was heated at a temperature of 70"C in the presence of nitrogen gas. After the treatment, the amount of attenuation at 200 MHz was measured.

In addition, the insulator of this insulated wire core was peeled off, and the condition of the conductor surface was observed with the naked eye.

For comparison, attenuation was measured and the conductor surface was observed for cables that were not heat-treated and were heat-treated under the conditions shown in the table.

The results of the above measurements and observations are shown in the table below.

Table [Effects of the Invention] As is clear from the above examples, the method of the present invention can produce a high foaming rate plastic cable that does not discolor the conductor surface, has excellent electrical properties, and has particularly low attenuation at high frequencies. can be manufactured.

[Brief explanation of the drawing]

The drawing is a graph showing differences in tan δ changes over time due to differences in heating temperature and atmosphere for the insulated wire core obtained in Example 1. =9− →− 4 Craftsmanship

Claims (1)

[Claims] 1. After extrusion coating a conductor with a plastic composition containing a chemical foaming agent and foaming it, it is heated in an inert gas for 6 hours.
1. A method for producing a highly foamed plastic cable, which comprises performing heat treatment to a temperature of 0° C. or higher. 2. The method for manufacturing a highly foamed plastic cable according to claim 1, wherein the foaming rate of the insulator is 60% or more.