JP2652294B2 - Manufacturing method of foam insulated coaxial cable - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to a foam insulated coaxial cable comprising an aluminum pipe as an external conductor, in particular, internal
The present invention relates to a method for manufacturing a foamed insulated coaxial cable that can easily center a conductor and improve the adhesion between an insulator and an aluminum pipe.

[0002]

2. Description of the Related Art The establishment of the PCM communication system has made it possible to transmit clear images to various parts of the world by using communication geostationary satellites. In recent years, using this PCM communication system, it has been possible to launch a geostationary satellite for communication and simultaneously relay images to various parts of the world.
It has been remarkable. For this reason, with the development of communication for transmitting high-speed data, television images, and the like in addition to the conventional communication in the audio range, there is an increasing demand for cables for transmitting broadband signals.

Conventionally, coaxial cords, ITV cables connecting devices, and the like have been partially used as wiring for measuring instruments and the like. However, CCTV in specific premises, remote areas in mountains, or television sharing in buildings has become widespread. Accordingly, CATV for specific areas such as cities has been developed. This CATV
Services require a coaxial cable that can transmit up to VHF and UHF bands in order to transmit multi-channel television signals.

[0004] In addition, CATV facilities to which independent broadcasting and other functions are added in addition to retransmission for the purpose of countermeasures for difficult viewing are increasing. As a cable for CATV, since a specific trader has specified TC-10CAF, which is an outer conductor type of PEF insulated Al pipe of 10C size, the cable of this outer conductor type of PEF insulated Al pipe has been used. This CATV cable has a configuration as shown in FIG. That is, the foam insulated coaxial cable 100 is provided on the inner conductor 110 made of copper or copper alloy,
Insulator 1 foamed from synthetic resin (PE: polyethylene)
20 are coated. On the insulator 120, the insulator 120 is covered with a thin aluminum plate,
An outer conductor (aluminum pipe) 130 formed into a pipe shape and welded is covered. The outer conductor 130 is covered with a sheath 140 made of synthetic resin (PE: polyethylene).

[0005] Such a foamed insulated coaxial cable 100
Is manufactured by a method as shown in FIG. That is, the extruder 200 extrudes and foams a polyethylene resin on the copper or copper alloy internal conductor 110 to form an insulator 120, and then applies the aluminum tape 150 vertically by the aluminum pipe coating machine 210. Aluminum pipe 13
0, and the sheath 140 is extruded and coated thereon.

The insulator 120 is formed by foaming a synthetic resin (polyethylene). The foaming is performed by physical foaming by applying a physical change such as pressure release of a compressed gas or vaporization of an evaporative gas. Or a method of chemical foaming in which a foaming agent is added and foaming is performed using a gas generated in a polycondensation process of the material.

[0007]

It is necessary to attach an aluminum thin plate (aluminum tape 150) vertically on the insulator 120 so that the outer peripheral surface of the insulator 120 is in close contact with the inner wall of the aluminum pipe 130 formed into a pipe shape. Because there is insulator 1
In foaming 20, the foaming rate is required so that the outer diameter of the insulator 120 matches the inner diameter of the aluminum pipe 130.
However, the foaming state of the insulator 120 is caused by a subtle change in the pressure release of the compressed gas and a subtle change in the vaporization of the evaporative gas.
The outer diameter of the insulator 120 is changed
It is difficult to control the foaming state of the insulator 120 so as to fit the inner diameter of the insulator 30, and there is a problem that a gap is generated between the outer peripheral surface of the insulator 120 and the inner wall surface of the aluminum pipe 130. I have.

Therefore, the outer diameter of the insulator 120 is extruded to be slightly larger than the inner diameter of the aluminum pipe 130 to cover it. It is difficult to compress the insulator 120 to the same size as the inner diameter of the aluminum pipe 130, and the insulation 120 is insulated by heat generated when welding the aluminum pipe 130. There is a problem that the body 120 may be damaged.

The present invention, the outer diameter of the insulator can facilitate centering of the inner conductor without extrusion coating slightly larger diameter than the inner diameter of the aluminum pipe, the vertical served to aluminum
A foam-insulated coaxial cable that can improve the adhesion between the outer peripheral surface of the insulator and the inner wall surface of the aluminum pipe without damaging the insulator due to the heat generated when the thin plate is formed into a pipe and covered by welding . It is intended to provide a manufacturing method.

[0010]

In order to achieve the above object, in a method of manufacturing a foamed insulated coaxial cable according to the present invention, an insulator in which a foaming agent is mixed and dispersed in a synthetic resin around a running inner conductor is provided. the in the physical foaming Thus foamed outside
After continuously extruded coating to a smaller diameter than the inner diameter of the conductor, the aluminum sheet was continuously cover the outer conductor formed by molding in a pipe shape on the insulating body and thereafter, the external
The foaming agent mixed with the synthetic resin and dispersed by heating from the outside of the conductor is foamed by chemical foaming so that the insulator and the aluminum pipe are brought into close contact with each other.

Preferably, the synthetic resin is composed of high-density polyethylene or a mixed polyethylene of high-density polyethylene and low-density polyethylene.

Further, it is preferable to add a foaming aid to the insulator.

The compounding of the foaming agent and the foaming assistant is
For 100 parts by weight of high-density polyethylene or a mixed polyethylene of high-density polyethylene and low-density polyethylene, 1.5 to 0.7 parts by weight of a foaming agent and 1.5 parts by weight of a foaming aid
It is preferable that the amount is 0.3 parts by weight.

Preferably, the blowing agent is azodicarbonamide.

Preferably, the foaming aid is stearic acid.

[0016]

A foaming agent is mixed and dispersed in high-density polyethylene or a mixture of high-density polyethylene and low-density polyethylene to form a raw material for an insulator. This raw material is extruded and coated on an inner conductor composed of a copper wire while performing physical foaming. After extruding and covering the insulator onto the inner conductor, an aluminum thin plate is vertically attached on the insulator, and the vertically attached aluminum thin plate is formed into a pipe shape, covered so as to wrap the entire insulator, and vertically attached. The two ends of the combined aluminum sheet are welded to form an aluminum pipe. Thereafter, the insulator is expanded by heating from the outside of the aluminum pipe to chemically foam the foaming agent mixed and dispersed in the raw material of the insulator. Due to the expansion of the insulator, the insulator is brought into close contact with the aluminum pipe.

[0017]

Embodiments of the present invention will be described below. FIG. 1 shows an embodiment of a method of manufacturing a foam insulated coaxial cable according to the present invention.

In FIG. 1, reference numeral 1 denotes an inner conductor made of copper or a copper alloy, which transmits data signals such as high-speed data and television images in addition to communication in a voice range, and transmits broadband signals up to VHF and UHF bands. It is a possible signal line. 2 is an extruder,
FIG. 2 shows that the synthetic resin used as the material of the insulator 3 is foamed by applying physical changes such as decompression of a compressed gas and vaporization of an evaporative gas.
Extrusion coating as shown in (A). High-density polyethylene (HDPE) is suitable for this synthetic resin. A foaming agent is mixed and dispersed in the high-density polyethylene to form a raw material for the insulator 3. This foaming agent includes ADCA (azodicarbonamide).
This ADCA is a decomposition-type foaming agent, and mainly generates N ₂ gas by thermal decomposition. The foaming degree of this foaming agent is desirably 75 to 80%. The material in which ADCA is mixed and dispersed in the high-density polyethylene is extruded from the extruder 2 and coated on the inner conductor 1. The outer diameter of the insulator 3 covering the inner conductor 1 is formed smaller than the inner diameter of the aluminum pipe 6 formed by the aluminum tape 5 vertically covering the insulator 3.

Reference numeral 4 denotes an aluminum pipe coating machine for coating a thin plate of aluminum on the insulator 3. That is, the aluminum pipe coating machine 4 continuously applies the aluminum tape 5 wound in a tape shape on the insulator 3 vertically, forms it into a pipe shape, and covers the entire insulator 3. Further, this aluminum pipe coating machine 4 forms an aluminum pipe 6 by welding both ends of an aluminum tape 5 which is vertically attached and joined together as shown in FIG. 2 (B). This aluminum pipe 6
Constitutes a shield material. Further, the inner diameter of the aluminum pipe 6 is slightly larger than the outer diameter of the insulator 3, and as shown in FIG.
A gap 9 is formed between the inner wall and the inner wall.

Reference numeral 7 denotes a heater for heating the insulator 3 covered with the aluminum pipe 6 at a predetermined temperature from outside the aluminum pipe 6. That is, the heater 7 welds the insulator 3 extruded and coated on the inner conductor 1 by physical foaming by vertically attaching the aluminum tape 5 to the insulator 3 and then mixing it into the high-density polyethylene. A dispersed foaming agent (A
DCA) for chemical foaming. The heating temperature of the insulator 3 by the heater 7 is suitably set to 180 ° C. to 215 ° C., which is the decomposition temperature (foaming temperature) of ADCA. The chemical foaming by the heater 7 is performed by heating the insulator 3 from the outside of the aluminum pipe 6 to a predetermined temperature (180 ° C. to 21 ° C.).
When heated at 5 ° C.), the foaming agent (ADCA) is decomposed and foamed (secondarily foamed), so that the insulator 3 expands and the insulator 3 and the aluminum pipe 6 adhere to each other. Therefore, the foaming agent (ADCA) mixed and dispersed in the high-density polyethylene is
Secondary foaming (chemical foaming) and insulator 3 into aluminum pipe 6
Add an appropriate amount sufficient to make it adhere to.

Reference numeral 8 denotes a coaxial cable in which an aluminum pipe 6 is coated on the inner conductor 1 via an insulator 3 as shown in FIG. 2C, and is extruded onto the inner conductor 1 by physical foaming (primary foaming). After the aluminum tape 5 is vertically attached on the coated insulator 3 and welded, a foaming agent (ADCA) mixed and dispersed in high-density polyethylene is chemically foamed (secondarily foamed) to form the insulator 3. In this state, the gap 9 between the insulator 3 and the inner wall of the aluminum pipe 6 is eliminated, and the insulator 3 and the aluminum pipe 6 are brought into close contact with each other.

In this embodiment, high-density polyethylene (HDPE) is used as a synthetic resin as a raw material of the insulator 3. However, as a raw material of the insulator 3, high-density polyethylene (HDPE) and low-density polyethylene are used. Polyethylene mixed with (LDPE) may be used. This high density polyethylene and low density polyethylene mixed polyethylene,
Compared to high-density polyethylene alone, the melting point is reduced by the amount of low-density polyethylene mixed. Therefore, mixed polyethylene of high-density polyethylene and low-density polyethylene can be used, but considering the secondary foaming of the insulator 3 by heating, it is preferable to use only high-density polyethylene that can cope with higher temperatures.

In order to make the foaming agent (ADCA) chemically foam (secondary foam), an aluminum pipe 6 is heated by a heater 7.
From the outside of the aluminum pipe 6
It is necessary to heat at a temperature between 0 ° C and 215 ° C. The lower the foaming temperature of the foaming agent is, the easier it is to control, and there is little adverse effect on the insulator 3 when heated. Therefore, when the foaming agent is mixed and dispersed in the high-density polyethylene or the mixed polyethylene of the high-density polyethylene and the low-density polyethylene in consideration of the secondary foaming temperature, a foaming aid may be appropriately added. This foaming aid aids foaming of the foaming agent, and specifically has an effect of lowering the foaming temperature of the foaming agent. As the foaming aid, for example,
There is calcium stearate. When calcium stearate, which is a foaming aid, is added together with a foaming agent (ADCA), the decomposition temperature (foaming temperature) is increased.
Decomposition temperature (foaming temperature) when mixing and dispersing only
The temperature can be significantly reduced to 150 ° C to 175 ° C as compared with 80 ° C to 215 ° C. The compounding of the foaming agent (ADCA) and the foaming assistant (calcium stearate) is, for example, as follows:
It is advisable to mix calcium stearate 5 with DCA1. The compounding of the foaming agent (ADCA) and the foaming assistant (calcium stearate) with respect to the high-density polyethylene, which is a raw material of the insulator 3, and the mixed polyethylene of the high-density polyethylene and the low-density polyethylene is performed by using a high-density polyethylene or a high-density polyethylene. For 100 parts by weight of polyethylene mixed with low-density polyethylene, the foaming agent is added in an amount of 1.
5 to 0.7 parts by weight, and the foaming aid is 1.5 to 0.3 parts by weight.

[0024]

According to the present invention, since the outer diameter of the insulator is slightly larger than the inner diameter of the aluminum pipe, the inner conductor can be centered without being covered. Because it can be easily performed, it is possible to reduce the outer diameter management when extruding the insulator.

According to the present invention, the gap between the insulator and the aluminum pipe is eliminated by secondary foaming to improve the adhesion between the outer peripheral surface of the insulator and the inner wall surface of the aluminum pipe.
The outer diameter of the insulator does not have to be extruded and coated to a diameter slightly larger than the inner diameter of the aluminum pipe, so that the insulator can be prevented from being damaged by heat generated by welding at the time of forming the aluminum pipe.

[Brief description of the drawings]

FIG. 1 is a schematic view of a manufacturing process showing an embodiment of a method of manufacturing a foam insulated coaxial cable according to the present invention.

FIG. 2 is a cross-sectional view at each stage of manufacturing a foam insulated coaxial cable.

FIG. 3 is a perspective view showing a structure of a foam insulated coaxial cable.

FIG. 4 is a schematic view of a manufacturing process showing a method for manufacturing a conventional foam insulated coaxial cable.

[Explanation of symbols]

1 ……………………………… Inner conductor 2 …………………………………………………………………………………………………………………………………… ……………………………… Insulator 4 ………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. ………………… Aluminum tape 6 ……………………………………… Aluminum pipe 7 ……………… ……………………………………………………………………………………………… Coaxial cable

Claims (6)

(57) [Claims] Around 1. A traveling inner conductor, thus foaming the foaming agent was mixed dispersed in the synthetic resin insulator physical foaming
After being continuously extruded and coated to a diameter smaller than the inner diameter of the outer conductor, the outer conductor formed by molding an aluminum thin plate into a pipe shape on the insulator is continuously coated, and then ,
A foamed insulated coaxial cable, characterized in that a foaming agent mixed and dispersed in the synthetic resin by heating from the outside of the outer conductor is foamed by chemical foaming so that the insulator and the aluminum pipe are brought into close contact with each other. Production method. 2. The method according to claim 1, wherein the synthetic resin is high-density polyethylene or a mixed polyethylene of high-density polyethylene and low-density polyethylene. 3. The method for producing a foamed insulated coaxial cable according to claim 1, wherein the insulator has a foaming aid added thereto. 4. The compounding of the foaming agent and the foaming assistant is such that the foaming agent is 1.5 to 0.7 parts by weight based on 100 parts by weight of high-density polyethylene or a mixture of high-density polyethylene and low-density polyethylene. 1.5 to 0.3 foaming aid
4. The method for producing a foamed insulated coaxial cable according to claim 3, wherein the amount is part by weight. 5. The method according to claim 1, wherein the foaming agent is azodicarbonamide. 6. The method according to claim 3, wherein the foaming aid is stearic acid.