JP6842647B2 - Coaxial cable and its manufacturing method - Google Patents

Description

The present invention relates to a coaxial cable and a method for manufacturing the same.

In recent years, a technique for forming an insulator of a coaxial cable from a foamed resin has been proposed in order to reduce the dielectric loss and weight of the coaxial cable (see, for example, Patent Document 1).

Leaky coaxial cables (LCX) are laid in subways and road tunnels. For leaky coaxial cables laid in subways and road tunnels, it is desirable to ensure communication performance even in the event of a fire. Therefore, it is particularly desirable that the leaky coaxial cable has high heat resistance. However, the insulator formed of the foamed resin has an aspect that it is vulnerable to high temperature.

Japanese Unexamined Patent Publication No. 2008-27899

One object of the present invention is to provide a technique capable of improving the heat resistance performance of a coaxial cable using a foamed resin as an insulator.

According to one aspect of the invention
With the inner conductor
A foamed insulating layer arranged on the outer periphery of the inner conductor and formed of a foamed resin and not crosslinked, and a foamed insulating layer arranged on the outer periphery of the foamed insulating layer and formed of a non-foamed resin or a non-foamed elastomer. An insulator composed of a cross-linked reinforcing layer that has been cross-linked,
A heat-resistant tape layer arranged on the outer periphery of the cross-linking reinforcing layer and
An outer conductor arranged on the outer circumference of the heat-resistant tape layer and having a slot,
A restraining tape layer arranged on the outer circumference of the outer conductor and
A leaky coaxial cable having a sheath arranged on the outer periphery of the restraining tape layer.
Fire Service Act Enforcement Regulations (Ministry of Home Affairs Ordinance No. 6 of 1958) Article 12, Paragraph 1, Item 5 (b) "Standards for heat-resistant electric wires" based on the proviso (December 18, 1997 Fire and Disaster Management Agency After a heat resistance test in accordance with the Agency Notification No. 11), a leaky coaxial cable having an insulation resistance of 0.4 MΩ / 1.3 m or more is provided.

According to another aspect of the invention
A process of forming a foamed insulating layer with foamed resin on the outer circumference of the inner conductor,
A step of forming a reinforcing layer on the outer periphery of the foamed insulating layer with a non-foamed resin or a non-foamed elastomer, and
A step of selectively cross-linking the reinforcing layer from the foamed insulating layer and the reinforcing layer to obtain a cross-linked reinforcing layer.
A step of arranging a heat-resistant tape layer on the outer periphery of the cross-linking reinforcing layer, and
A step of arranging an outer conductor having a slot on the outer periphery of the heat-resistant tape layer, and
The process of arranging the restraint winding tape layer on the outer circumference of the outer conductor, and
The step of arranging the sheath on the outer periphery of the restraining tape layer and
A method of manufacturing a leaky coaxial cable having the above is provided.

By arranging the crosslinked reinforcing layer on the outer periphery of the foamed insulating layer, it is possible to improve the heat resistance performance of the coaxial cable having the foamed insulating layer in the insulator as compared with the case where the crosslinked reinforcing layer is not arranged.

1 (a) and 1 (b) are schematic side views and schematic cross-sectional views of a coaxial cable according to an embodiment of the present invention, respectively. 2 (a) to 2 (c) are schematic views showing a step of forming a foamed insulating layer, a step of forming a reinforcing layer, and a step of bridging the reinforcing layer of the coaxial cable according to one embodiment, respectively. FIG. 3A is a schematic view showing a heat resistance test method, and FIG. 3B is a graph showing a temperature rise curve in the heat resistance test. 4 (a) and 4 (b) are a schematic cross-sectional view showing a state at the start of the heat resistance test and a schematic cross-sectional view showing the state at the end of the heat resistance test of the coaxial cable according to the embodiment, respectively. ..

First, the structure of the coaxial cable 100 according to the embodiment of the present invention will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1A is a schematic side view of the coaxial cable 100, showing a state in which the end portion is stripped. FIG. 1B is a schematic cross-sectional view of the coaxial cable 100.

The coaxial cable 100 includes an inner conductor 10, a foam insulating layer 20, a cross-linking reinforcing layer 30, a heat-resistant tape layer 40, an outer conductor 50, a restraining tape layer 60, a sheath 70, and a messenger wire 80.

As the inner conductor 10, for example, a pipe-shaped conductor, for example, a copper straight pipe or a spiral-shaped pipe is used.

The foam insulating layer 20 is arranged on the outer periphery of the inner conductor 10. The foamed insulating layer 20 is formed of a foamed resin (the foamed insulating layer 20 is formed of a material containing a foamed resin). The foamed insulating layer 20 is preferably not crosslinked in order to suppress the dielectric loss due to the foamed insulating layer 20. Examples of the resin used for the foamed insulating layer 20 include polyolefin-based resins, and more specifically, polyethylene. The thickness of the foamed insulating layer 20 is, for example, a thickness in the range of 6.0 mm to 7.0 mm, for example, about 6.5 mm.

In order to improve the adhesion between the inner conductor 10 and the foamed insulating layer 20, a non-foamed resin (for example, polyethylene) is used between the inner conductor 10 and the foamed insulating layer 20 to provide a thickness of, for example, about 0.1 mm. An internal solid layer may be interposed. It is preferable that the inner solid layer is not crosslinked.

A cross-linking reinforcing layer (external solid layer) 30 is arranged on the outer periphery of the foamed insulating layer 20. The insulator 90 of the coaxial cable 100 is configured by the laminated structure of the foam insulating layer 20 and the crosslinked reinforcing layer 30.

The foamed insulating layer 20 is formed of a foamed resin and is not crosslinked, and has a low melting point of, for example, about 115 ° C. Therefore, when a high temperature (for example, 420 ° C. added in the test described later) is applied, the foamed insulating layer 20 melts and shrinks. The outer shape cannot be maintained, and the member cannot function as a support for the member arranged outside the foamed insulating layer 20. The crosslinked reinforcing layer 30 maintains its outer shape without melting when a high temperature is applied, and functions as a support for members arranged outside the crosslinked reinforcing layer 30 (so to speak, the outer shell of the foamed insulating layer 20). ).

The cross-linked reinforcing layer 30 is formed of a non-foamed resin or a non-foamed elastomer (the cross-linked reinforcing layer 30 is formed of a material containing a non-foamed resin or a non-foamed elastomer). The crosslinked reinforcing layer 30 is preferably not foamed in order to increase the strength. Further, the cross-linked reinforcing layer 30 is preferably cross-linked so as not to be easily melted when a high temperature is applied, that is, to easily maintain the outer shape.

Examples of the resin used for the cross-linking reinforcing layer 30 include polyolefin-based resins, and more specifically, polyethylene and polypropylene. Examples of the elastomer used for the cross-linking reinforcing layer 30 include polyolefin-based elastomers, and more specifically, for example, ethylene propylene rubber.

Of the foamed insulating layer 20 and the crosslinked reinforcing layer 30 constituting the insulator 90, the foamed insulating layer 20 is preferably not crosslinked, and the crosslinked reinforcing layer 30 is preferably crosslinked. In order to carry out such selective cross-linking, the cross-linking reinforcing layer 30 is preferably cross-linked by a silane cross-linking method. That is, the cross-linked reinforcing layer 30 is preferably formed of a silane cross-linkable resin or a silane-crosslinkable elastomer from the viewpoint before cross-linking, and from the viewpoint after cross-linking, the resin or silane cross-linked by the silane cross-linking method. It is preferably formed of an elastomer crosslinked by a crosslinking method. In addition, in order to make it easy to distinguish the state before and after the cross-linking of the cross-linking reinforcing layer 30, the cross-linking reinforcing layer 30 before the cross-linking, that is, the layer 30 that should become the cross-linking reinforcing layer 30 by being cross-linked is a reinforcing layer. Sometimes called 30.

Generally, as the cross-linking method, an electron beam cross-linking method, a chemical cross-linking method, and a silane cross-linking method are used. However, when the reinforcing layer 30 is to be crosslinked by the electron beam cross-linking method after forming the laminate of the foamed insulating layer 20 and the reinforcing layer (cross-linked reinforcing layer before cross-linking) 30, the reinforcing layer 30 is foamed by the electron beam penetrating the reinforcing layer 30. Even the insulating layer 20 will be crosslinked. Further, when the reinforcing layer 30 is attempted to be crosslinked by a chemical crosslinking method, the foamed insulating layer 20 is melted by being exposed to a high temperature (for example, about 180 ° C.) for promoting the crosslinking reaction.

On the other hand, if the reinforcing layer 30 is cross-linked by the silane cross-linking method, the cross-linking reaction proceeds at a relatively low temperature (for example, about 60 ° C.) when the laminated product of the foamed insulating layer 20 and the reinforcing layer 30 is cross-linked. be able to. Therefore, the reinforcing layer 30 can be selectively crosslinked while suppressing the cross-linking and melting of the foamed insulating layer 20.

The thickness of the cross-linking reinforcing layer 30 is preferably 0.5 mm (500 μm) or more, for example, in order to increase the strength of the cross-linking reinforcing layer 30. Further, the thickness of the cross-linking reinforcing layer 30 is preferably 1 mm (1000 μm) or less, for example, in order to suppress the dielectric loss due to the cross-linked reinforcing layer 30.

The degree of cross-linking of the cross-linking reinforcing layer 30 is preferably, for example, 50% or more, and more preferably 60% or more, as a gel fraction in order to increase the strength of the cross-linking reinforcing layer 30. Further, the degree of cross-linking of the cross-linked reinforcing layer 30 is preferably, for example, 75% or less, more preferably 70% or less, as a gel fraction, in order to suppress the dielectric loss due to the cross-linked reinforcing layer 30. ..

The average degree of foaming of the insulator 90 including the foamed insulating layer 20 and the crosslinked reinforcing layer 30 is preferably, for example, 60% or more in order to suppress the dielectric loss due to the insulator 90. The average degree of foaming of the insulator 90 is preferably 80% or less, for example.
Here, the "foaming degree" is
Foaming degree (%) = 100- (specific gravity after foaming / specific gravity before foaming) x 100
It is calculated by the formula.
The specific gravity after foaming and the specific gravity before foaming may be measured according to JIS Z8807 using, for example, an automatic hydrometer DH-100 manufactured by Toyo Seiki Co., Ltd.
Further, the "average degree of foaming" is obtained by averaging the degree of foaming A of the foamed insulating layer 20 and the degree of foaming B of the crosslinked reinforcing layer 30 with the thickness a of the foamed insulating layer 20 and the thickness b of the crosslinked reinforcing layer 30. Therefore, that is, it is obtained by the formula of average degree of foaming (%) = (aA + bB) / (a + b).
The degree of foaming of the foamed insulating layer 20 is preferably in the range of, for example, 70% to 85%, for example, about 80%, and the degree of foaming of the crosslinked reinforcing layer 30 is 0%.

Both the resin forming the foam insulating layer 20 and the resin or elastomer forming the crosslinked reinforcing layer 30 do not contain halogen elements such as fluorine and chlorine in order to suppress the generation of toxic gas during combustion, for example. It is preferably non-halogen.

If necessary, an additive such as a deactivating agent may be added to the resin forming the foamed insulating layer 20. That is, the foamed insulating layer 20 may be formed of the resin to which the additive is added, and even when some additive is added to the resin, it is said that the foam insulating layer 20 is "formed by the resin". be able to. Similarly, an additive such as a deactivating agent may be added to the resin or elastomer forming the crosslinked reinforcing layer 30 as necessary. That is, the crosslinked reinforcing layer 30 may be formed of a resin or elastomer to which an additive has been added, and even when some additive is added to the resin or elastomer, "by the resin or elastomer" It can be said that it is formed. "

The crosslinked reinforcing layer 30 is preferably integrally formed into a tubular shape by, for example, extrusion molding. That is, it is preferable that there are no seams or gaps (seamless) in the circumferential direction and the length direction of the coaxial cable 100. This is to prevent the material of the foamed insulating layer 20 that melts when a high temperature is applied from leaking to the outside of the crosslinked reinforcing layer 30 from the seams and gaps.

In order to prevent water intrusion during water cooling after extruding the foamed insulating layer 20, a non-foamed resin (for example, polyethylene) is used between the foamed insulating layer 20 and the cross-linking reinforcing layer 30 to provide a thickness of, for example, about 0.1 mm. An outer skin layer may be interposed. It is preferable that the outer skin layer is not crosslinked.

A heat-resistant tape layer 40 formed by winding a heat-resistant tape is arranged on the outer periphery of the cross-linking reinforcing layer 30. Examples of the heat-resistant tape used for the heat-resistant tape layer 40 include Kapton tape. The thickness of the heat-resistant tape layer 40 is, for example, about 0.01 mm to 0.05 mm.

The outer conductor 50 is arranged on the outer periphery of the heat-resistant tape layer 40. That is, the outer conductor 50 is arranged on the outer periphery of the cross-linking reinforcing layer 30 (via the heat-resistant tape layer 40). The outer conductor 50 has a slot 51, and the illustrated coaxial cable 100 is configured as a leaky coaxial cable. The outer conductor 50 is formed of, for example, a slotted copper tape or a slotted aluminum tape. A tape having a pleated shape may be used.

A restraint winding tape layer 60 formed by winding a restraint winding tape is arranged on the outer periphery of the outer conductor 50. Examples of the restraint winding tape used for the restraint winding tape layer 60 include polyethylene terephthalate tape.

A sheath 70 is arranged on the outer periphery of the restraint winding tape layer 60. The sheath 70 is made of, for example, flame-retardant polyethylene. A messenger wire 80 is attached to the sheath 70.

Next, an example of a method for manufacturing the coaxial cable 100 according to the embodiment will be described with reference to FIGS. 2 (a) to 2 (c). FIG. 2A is a schematic view showing a process of forming the foamed insulating layer 20, and FIG. 2B is a schematic view showing a process of forming the reinforcing layer (crosslinking reinforcing layer before crosslinking) 30. 2 (c) is a schematic diagram showing a cross-linking step (step of obtaining a cross-linking reinforcing layer 30) of the reinforcing layer 30.

First, the process of forming the foamed insulating layer 20 will be described with reference to FIG. 2A. As a method for forming the foamed insulating layer 20, a known method for forming the foamed resin layer can be appropriately used.

A foaming extruder 220 having a foaming agent (gas) injection pump 221 is provided with a resin (for example, polyethylene) that is the base of the foaming insulating layer 20 and a foaming nucleating agent (for example, azodicarbonamide (ADCA) or 4,4'-oxy. Bisbenzenesulfonyl hydrazide (OBSH)) and supplies.

The feeder, wire drawing machine, and core wire heater of the inner conductor (core wire) 10 are collectively referred to as a core wire preparing device 210. The inner conductor 10 is sent out from the core wire preparation device 210, and the foam insulating layer 20 is formed on the outer periphery of the inner conductor 10 by the foam extrusion machine 220. The inner conductor 10 on which the foamed insulating layer 20 is formed (coaxial cable 100A at the stage where the foamed insulating layer 20 is formed) is wound around the take-up drum 230.

Next, the process of forming the reinforcing layer 30 will be described with reference to FIG. 2 (b). As a method for forming the reinforcing layer 30, a known method for forming the silane crosslinked resin layer can be appropriately used.

A resin (for example, polyethylene) as a base of the reinforcing layer 30, a silane compound (for example, vinylmethoxysilane), and a free radical generator (for example, dicumyl peroxide (DCP)) are reacted with an extruder at, for example, at 200 ° C. While extruding, a silane grafted resin (for example, silane graft polyethylene) is prepared. Then, the extruder 240 is supplied with a silane grafted resin and a catalyst masterbatch containing a silanol condensation catalyst (for example, an organotin compound catalyst).

The internal conductor 10 on which the foamed insulating layer 20 is formed (coaxial cable 100A at the stage where the foamed insulating layer 20 is formed) is sent out from the take-up drum 230, and is reinforced on the outer periphery of the foamed insulating layer 20 by the extruder 240. The layer 30 is formed. The internal conductor 10 on which the reinforcing layer 30 and the foamed insulating layer 20 are formed (coaxial cable 100B at the stage where the reinforcing layer 30 is formed) is wound around the take-up drum 250.

Next, the cross-linking step of the reinforcing layer 30 will be described with reference to FIG. 2 (c). As a method for cross-linking the reinforcing layer 30, a known silane cross-linking method can be appropriately used while taking care that the cross-linking of the foamed insulating layer 20 is suppressed.

The drum 250 around which the internal conductor 10 on which the reinforcing layer 30 and the foamed insulating layer 20 are formed (the coaxial cable 100B at the stage where the reinforcing layer 30 is formed) is wound is placed in, for example, a constant temperature bath 260 at 60 ° C., for example, 3 By leaving it for 5 to 5 days, the reinforcing layer 30 is crosslinked while suppressing the crosslinking of the foamed insulating layer 20. In this way, the crosslinked reinforcing layer 30 is obtained.

After that, a heat-resistant tape layer 40, an outer conductor 50, a restraining tape layer 60, a sheath 70, and a messenger wire 80 are provided by appropriately using a known method for forming a coaxial cable (leakage coaxial cable), and the coaxial cable 100 is completed. (See FIGS. 1 (a) and 1 (b)).

Next, the heat resistance test for the coaxial cable (leakage coaxial cable) 100 according to the embodiment will be described with reference to FIGS. 3 (a) and 3 (b). This heat resistance test is based on the provisions of Article 12, Paragraph 1, Item 5 (b) of the Fire Service Act Enforcement Regulations (Ministry of Home Affairs Ordinance No. 6 of 1958), "Standards for Heat Resistant Wires" (Twelve 1997). It complies with the Fire and Disaster Management Agency Notification No. 11) on the 18th of the month. FIG. 3A is a schematic view showing a heat resistance test method, and FIG. 3B is a graph showing a temperature rise curve in the heat resistance test.

In this heat resistance test, as shown in FIG. 3A, a test piece having a length of 1.3 m of the coaxial cable 100 is fixed to the cable fixing plate 310, a load 320 is applied to the central portion of the test piece, and the test piece is subjected to the test piece. The test piece is heated by the flame 340 in a state where an alternating current of 600 V and 50 Hz is applied between the inner conductor 10 and the outer conductor 50 via the connectors 110 provided at both ends.

The load 320 is twice the own weight of the coaxial cable 100 used as the test piece (for example, 1910 g weight). Further, as shown in FIG. 3B, the heating is a half curve of the heating curve of the fire resistance test specified in JIS 1304, that is, the curve of heating from room temperature to 840 ° C. in 30 minutes, that is, Follow the curve to heat from room temperature to 420 ° C in 30 minutes.

Next, with reference to FIGS. 4 (a) and 4 (b), the function of the cross-linked reinforcing layer 30 will be described by taking the situation of the heat resistance test as an example. FIG. 4A is a schematic cross-sectional view showing the coaxial cable 100 at the start of the heat resistance test, that is, before the high temperature is applied, and FIG. 4B is the end of the heat resistance test, that is, after the high temperature is applied. It is a schematic sectional drawing which shows the coaxial cable 100.

As shown in FIG. 4A, at the start of the heat resistance test, the foamed insulating layer 20, the crosslinked reinforcing layer 30, and the heat resistant tape 40 are interposed between the inner conductor 10 and the outer conductor 50 to form the inner conductor 10. The outer conductors 50 do not come into contact with each other and are electrically insulated.

Due to the high temperature applied during the heat resistance test, the foamed insulating layer 20 melts and shrinks, cannot maintain its outer shape, flows down, and can function as a support for a member arranged outside the foamed insulating layer 20. It disappears. On the other hand, the cross-linking reinforcing layer 30 maintains its outer shape without melting, and maintains its function as a support for members arranged outside the cross-linking reinforcing layer 30. The restraint tape layer 60 and the sheath 70 are burnt down.

As shown in FIG. 4B, at the end of the heat resistance test, the outer member of the molten foam insulating layer 20 is pushed downward by the load 320 and is in contact with the inner conductor 10. However, the structure in which the cross-linking reinforcing layer 30 is interposed between the inner conductor 10 and the outer conductor 50 is maintained. As a result, it is possible to maintain a state in which the inner conductor 10 and the outer conductor 50 do not come into contact with each other and are electrically insulated.

The heat-resistant tape layer 40 also maintains a structure interposed between the inner conductor 10 and the outer conductor 50. However, since the heat-resistant tape layer 40 is formed by winding the heat-resistant tape and is thin, it has low strength and is easily deformed to form a gap between the tapes.

Here, as a comparative form, consider a coaxial cable having a structure in which the heat-resistant tape layer 40 is provided directly above the foamed insulating layer 20 without having the cross-linking reinforcing layer 30. In the coaxial cable according to the comparative form, the molten foam insulating layer 20 material leaks to the outside through the gap between the tapes of the heat resistant tape layer 40 and easily ignites during the heat resistance test. Further, the molten resin is burned and carbonized and adheres to the heat-resistant tape layer 40, so that the inner conductor 10 and the outer conductor 50 are easily conducted to conduct with each other.

On the other hand, in the coaxial cable 100 according to the embodiment, since the cross-linking reinforcing layer 30 is integrally formed into a tubular shape, it is possible to prevent the molten foam insulating layer 20 material from leaking to the outside of the cross-linking reinforcing layer 30 and igniting. Has been done. Further, by forming the crosslinked reinforcing layer 30 to a sufficient thickness of, for example, 0.5 mm or more, a layer having sufficient strength that is not damaged in the heat resistance test can be obtained.

As described above, by arranging the crosslinked reinforcing layer 30 on the outer periphery of the foamed insulating layer 20, the coaxial cable 100 having the foamed insulating layer 20 in the insulator 90 is compared with the case where the crosslinked reinforcing layer 30 is not arranged. The heat resistance performance can be improved.

More specifically, even if the foamed insulating layer 20 melts and shrinks when a high temperature is applied, it is possible to prevent the inner conductor 10 and the outer conductor 50 from coming into contact with each other and conducting conduction. In addition, it is possible to prevent the molten foam insulating layer 20 material from leaking to the outside and igniting.

In the above-described embodiment, the leaky coaxial cable 100 having the slot 51 in the outer conductor 50 has been illustrated, but the heat-resistant performance improving effect as described above by the cross-linking reinforcing layer 30 does not have the slot 51 in the outer conductor 50. The same can be obtained for coaxial cables. From the viewpoint that the material of the molten foam insulating layer 20 leaks to the outside of the outer conductor 50 via the slot 51 and easily ignites, it is more preferable to provide the cross-linking reinforcing layer 30 in the leaky coaxial cable 100. Can be done.

Hereinafter, the results of the heat resistance test performed on the coaxial cable according to the examples will be described.

In the examples, polyethylene was used as the base resin for the foamed insulating layer 20. The foamed insulating layer 20 was formed by blending 0.005 parts by mass and 0.01 parts by mass of ADCA and OBSH as foaming nucleating agents with respect to 100 parts by mass of the base resin (polyethylene).

Further, in the examples, polyethylene was used as the base resin for the cross-linking reinforcing layer 30. Table 1 shows the blending ratio of each material for obtaining the silane graft polyethylene used for the crosslinked reinforcing layer 30 according to the examples (blending ratio with respect to 100 parts by mass of the base resin).

The crosslinked reinforcing layer 30 was formed from a material in which 5 parts by mass of a catalyst masterbatch containing a silanol condensation catalyst was blended with 95 parts by mass of silane graft polyethylene. Polyethylene was used as the base resin for the catalyst masterbatch. Adjust the catalyst masterbatch by blending 1 part by mass of an organotin compound catalyst as a silanol condensation catalyst and 3 parts by mass of a hindered phenolic antioxidant as an antioxidant with respect to 100 parts by mass of the base resin (polyethylene). did.

As shown in Table 1, as Examples 1 to 4, samples of coaxial cables in which the thickness of the cross-linked reinforcing layer 30 and the gel fraction of the cross-linked reinforcing layer 30 were changed were prepared. The gel fraction of the crosslinked reinforcing layer 30 is controlled by the blending ratio of the free radical generator.

The thickness of the cross-linking reinforcing layer 30 is 500 μm in Examples 1 and 2 and 1000 μm in Examples 3 and 4. The surface condition of the crosslinked reinforcing layer 30 is smooth in all of Examples 1 to 4. The gel fraction of the crosslinked reinforcing layer 30 is a value in the range of 50% to 75% in all of Examples 1 to 4. The average degree of foaming of the insulator 90 including the foamed insulating layer 20 and the crosslinked reinforcing layer 30 is 60% or more in all of Examples 1 to 4.

In order to confirm the initial communication performance of the coaxial cable, the amount of attenuation for the 450 MHz test signal was measured. The initial attenuation is 55 dB / km or less in all of Examples 1 to 4.

A heat resistance test was performed on the coaxial cables of Examples 1 to 4. The insulation resistance between the inner conductor and the outer conductor after the heat resistance test was evaluated. The insulation resistance after the heat resistance test satisfies the standard of 0.4 MΩ / 1.3 m or more in all of Examples 1 to 4. In addition, a VSWR test was conducted to confirm the communication performance of the coaxial cable after the heat resistance test. The VSWR after the heat resistance test satisfies the standard of 5 or less in all of Examples 1 to 4.

As described above, it was found that by providing the cross-linking reinforcing layer 30 in the coaxial cables of Examples 1 to 4, the insulation resistance and communication performance can be maintained when a high temperature is applied.

The thickness of the cross-linking reinforcing layer 30 can be appropriately adjusted so as to obtain desired characteristics, but it is preferably set to a thickness in the range of, for example, 500 μm to 1000 μm. The gel fraction of the crosslinked reinforcing layer 30 can be appropriately adjusted so as to obtain desired characteristics, but it is preferable that the gel fraction is in the range of, for example, 50% to 75%. According to the inventor of the present application, if the thickness of the cross-linking reinforcing layer 30 is too thin or the gel fraction is too small (the degree of cross-linking is too low), the insulation resistance and communication performance are maintained when a high temperature is applied. We have obtained the knowledge that it will disappear. Further, the inventor of the present application states that if the thickness of the cross-linking reinforcing layer 30 is too thick or the gel fraction is too large (the degree of cross-linking is too high), the amount of attenuation becomes too large and the (initial) communication performance is improved. We have also obtained the knowledge that it will be lower.

Although the present invention has been described above according to the embodiments, the present invention is not limited thereto. For example, it will be obvious to those skilled in the art that various changes, improvements, combinations, etc. are possible.

Hereinafter, preferred embodiments of the present invention will be added.

(Appendix 1)
With the inner conductor
A foamed insulating layer arranged on the outer periphery of the inner conductor and formed of a foamed resin and not crosslinked, and a foamed insulating layer arranged on the outer periphery of the foamed insulating layer and formed of a non-foamed resin or a non-foamed elastomer. An insulator composed of a cross-linked reinforcing layer that has been cross-linked,
A heat-resistant tape layer arranged on the outer periphery of the cross-linking reinforcing layer and
An outer conductor arranged on the outer circumference of the heat-resistant tape layer and having a slot,
A restraining tape layer arranged on the outer circumference of the outer conductor and
A leaky coaxial cable having a sheath arranged on the outer periphery of the restraining tape layer.
Fire Service Act Enforcement Regulations (Ministry of Home Affairs Ordinance No. 6 of 1958) Article 12, Paragraph 1, Item 5 (b) "Standards for heat-resistant electric wires" based on the proviso (December 18, 1997 Fire and Disaster Management Agency A leaky coaxial cable with an insulation resistance of 0.4 MΩ / 1.3 m or more after a heat resistance test in accordance with the Agency Notification No. 11).

(Appendix 2)
The coaxial cable according to Appendix 1, wherein the crosslinked reinforcing layer is formed of a polyolefin-based resin or a polyolefin-based elastomer.

(Appendix 3)
The coaxial cable according to Appendix 1 or 2, wherein the crosslinked reinforcing layer is made of polyethylene, polypropylene, or ethylene propylene rubber.

(Appendix 4)
The coaxial cable according to any one of Appendix 1 to 3, wherein the cross-linked reinforcing layer is formed of a resin crosslinked by a silane cross-linking method or an elastomer cross-linked by a silane cross-linking method.

(Appendix 5)
The coaxial cable according to any one of Supplementary note 1 to 4, wherein the thickness of the cross-linking reinforcing layer is 0.5 mm or more and 1 mm or less.

(Appendix 6)
The coaxial cable according to any one of Supplementary note 1 to 5, wherein the gel fraction of the crosslinked reinforcing layer is 50% or more and 75% or less.

(Appendix 7)
The coaxial cable according to any one of Supplementary note 1 to 6, wherein the gel fraction of the crosslinked reinforcing layer is 60% or more and 70% or less.

(Appendix 8)
The coaxial cable according to any one of Supplementary note 1 to 7, wherein the average degree of foaming of the insulator including the foamed insulating layer and the crosslinked reinforcing layer is 60% or more.

(Appendix 9)
The coaxial cable according to any one of Supplementary note 1 to 8, wherein the foamed insulating layer is formed of a non-halogen resin, and the crosslinked reinforcing layer is formed of a non-halogen resin or a non-halogen elastomer.

(Appendix 10)
The coaxial cable according to any one of Supplementary note 1 to 9, wherein the cross-linking reinforcing layer is integrally formed in a tubular shape.

(Appendix 11)
A load twice the weight of the test piece was applied to the central portion of the 1.3 m long test piece of the coaxial cable, and 600 V alternating current was applied via connectors provided at both ends of the test piece. In this state, after the heat resistance test in which heating is performed according to a half curve of the heating curve of the fire resistance test specified in JIS 1304, the insulation resistance between the inner conductor and the outer conductor is 0.4 MΩ / 1. The coaxial cable according to any one of Appendix 1 to 10, which satisfies the standard of 3 m or more.

(Appendix 12)
The coaxial cable according to Appendix 11, which satisfies the criterion that VSWR is 5 or less after the heat resistance test.

(Appendix 13)
The coaxial cable according to Appendix 11 or 12, which satisfies the criterion that the amount of attenuation for a 450 MHz test signal is 55 dB / km or less before the heat resistance test.

(Appendix 14)
A process of forming a foamed insulating layer with foamed resin on the outer circumference of the inner conductor,
A step of forming a reinforcing layer on the outer periphery of the foamed insulating layer with a non-foamed resin or a non-foamed elastomer, and
A step of selectively cross-linking the reinforcing layer from the foamed insulating layer and the reinforcing layer to obtain a cross-linked reinforcing layer.
A step of arranging a heat-resistant tape layer on the outer periphery of the cross-linking reinforcing layer, and
A step of arranging an outer conductor having a slot on the outer periphery of the heat-resistant tape layer, and
The process of arranging the restraint winding tape layer on the outer circumference of the outer conductor, and
The step of arranging the sheath on the outer periphery of the restraining tape layer and
A method of manufacturing a leaky coaxial cable.

(Appendix 15)
The method for manufacturing a coaxial cable according to Appendix 14, wherein the non-foamed resin or the non-foamed elastomer is a silane crosslinkable resin or a silane crosslinkable elastomer.

10 Inner conductor 20 Foam insulation layer 30 Crosslink reinforcement layer (reinforcement layer)
40 Heat-resistant tape layer 50 External conductor 51 Slot 60 Hold-down tape layer 70 Sheath 80 Messenger wire 90 Insulator 100 Coaxial cable

Claims (7)

With the inner conductor
A foamed insulating layer arranged on the outer periphery of the inner conductor and formed of a foamed resin and not crosslinked, and a foamed insulating layer arranged on the outer periphery of the foamed insulating layer and formed of a non-foamed resin or a non-foamed elastomer. An insulator composed of a cross-linked reinforcing layer that has been cross-linked,
A heat-resistant tape layer arranged on the outer periphery of the cross-linking reinforcing layer and
An outer conductor arranged on the outer circumference of the heat-resistant tape layer and having a slot,
A restraining tape layer arranged on the outer circumference of the outer conductor and
A leaky coaxial cable having a sheath arranged on the outer periphery of the restraining tape layer.
Fire Service Act Enforcement Regulations (Ministry of Home Affairs Ordinance No. 6 of 1958) Article 12, Paragraph 1, Item 5 (b) "Standards for heat-resistant electric wires" based on the proviso (December 18, 1997 Fire and Disaster Management Agency A leaky coaxial cable with an insulation resistance of 0.4 MΩ / 1.3 m or more after a heat resistance test in accordance with the Agency Notification No. 11). The leaky coaxial cable according to claim 1, wherein the crosslinked reinforcing layer is formed of a polyolefin-based resin or a polyolefin-based elastomer. The leaky coaxial cable according to claim 1 or 2, wherein the cross-linked reinforcing layer is formed of a resin cross-linked by a silane cross-linking method or an elastomer cross-linked by a silane cross-linking method. The leaky coaxial cable according to any one of claims 1 to 3, wherein the thickness of the crosslinked reinforcing layer is 0.5 mm or more and 1 mm or less. The leaky coaxial cable according to any one of claims 1 to 4, wherein the gel fraction of the crosslinked reinforcing layer is 50% or more and 75% or less. The leaky coaxial cable according to any one of claims 1 to 5, wherein the average degree of foaming of the insulator including the foamed insulating layer and the crosslinked reinforcing layer is 60% or more. A process of forming a foamed insulating layer with foamed resin on the outer circumference of the inner conductor,
A step of forming a reinforcing layer on the outer periphery of the foamed insulating layer with a non-foamed resin or a non-foamed elastomer, and
A step of selectively cross-linking the reinforcing layer from the foamed insulating layer and the reinforcing layer to obtain a cross-linked reinforcing layer.
A step of arranging a heat-resistant tape layer on the outer periphery of the cross-linking reinforcing layer, and
A step of arranging an outer conductor having a slot on the outer periphery of the heat-resistant tape layer, and
The process of arranging the restraint winding tape layer on the outer circumference of the outer conductor, and
The step of arranging the sheath on the outer periphery of the restraining tape layer and
A method of manufacturing a leaky coaxial cable.

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