JP6794731B2 - coaxial cable - Google Patents

Description

The present invention relates to a coaxial cable.

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.

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 (see, for example, Patent Document 1 for the heat resistance test of the leaky coaxial cable). However, the insulator formed of the foamed resin has an aspect that it is vulnerable to high temperature.

Japanese Unexamined Patent Publication No. 3-82204

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
An insulator arranged on the outer circumference of the inner conductor and
With the outer conductor arranged on the outer circumference of the insulator,
Have,
The insulator is
A foamed insulating layer made of foamed resin and
A reinforcing tape layer arranged on the outer periphery of the foamed insulating layer and formed by wrapping a reinforcing tape made of a crosslinked polyolefin resin,
Coaxial cable with is provided.

By arranging the reinforcing tape 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.

1 (a) and 1 (b) are an overall schematic side view and schematic sectional view of a coaxial cable according to an embodiment of the present invention, respectively. 2 (a) and 2 (b) are schematic side views and schematic cross-sectional views showing the parts of the inner conductor, the foamed insulating layer, and the reinforcing tape layer of the coaxial cable according to the embodiment, respectively. 3A and 3B are schematic views showing a process of forming a foamed insulating layer and a schematic diagram showing a process of manufacturing a reinforcing tape of the coaxial cable according to the embodiment, respectively. FIG. 4 is a schematic view showing from the step of forming the foamed insulating layer to the step of completing the coaxial cable according to the embodiment. FIG. 5A is a schematic view showing a heat resistance test method, and FIG. 5B is a graph showing a temperature rise curve in the heat resistance test. 6 (a) and 6 (b) are schematic cross-sectional views showing a state before the start of the heat resistance test and a state after the start of the heat resistance test (after the end of the heat resistance test), respectively, of the coaxial cable according to the embodiment. It is a schematic sectional view.

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), 1 (b), 2 (a), and 2 (b).

FIG. 1A is an overall schematic side view of the coaxial cable 100, showing a state in which the end portion is stripped. FIG. 1B is an overall schematic cross-sectional view of the coaxial cable 100.

FIG. 2A is a schematic side view showing the portions of the inner conductor 10, the foamed insulating layer 20, and the reinforcing tape layer 30 of the coaxial cable 100, and shows a state in which the ends are stripped. FIG. 2B is a schematic cross-sectional view showing a portion of the inner conductor 10, the foamed insulating layer 20, and the reinforcing tape layer 30 of the coaxial cable 100.

The coaxial cable 100 includes an inner conductor 10, a foam insulating layer 20, a reinforcing tape layer 30, a tightening tape layer (heat resistant tape layer) 40, an outer conductor 50, a presser foot tape layer 60, a sheath 70, and a messenger wire 80. It is configured.

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 made of foamed resin. As the resin constituting the foamed insulating layer 20, a polyolefin-based resin is preferably used, and more preferably polyethylene is used. The thickness of the foamed insulating layer 20 is, for example, a thickness in the range of 12 mm or more and 14 mm or less.

The foamed insulating layer 20 is preferably foamed and preferably not crosslinked in order to suppress the dielectric loss due to the foamed insulating layer 20.

A reinforcing tape 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 reinforcing tape layer 30. That is, the insulator 90 is arranged on the outer circumference of the inner conductor 10.

The reinforcing tape layer 30 is formed by wrapping a reinforcing tape 31 made of resin on the outer periphery of the foamed insulating layer 20. As the resin constituting the reinforcing tape 31, a crosslinked polyolefin resin is preferably used, and more preferably, a crosslinked polyethylene having a gel fraction in the range of 70% or more and 90% or less is used. The overall thickness T1 of the reinforcing tape layer 30 is preferably a thickness within the range of 0.4 mm or more and 0.8 mm or less, and the thickness T2 of the reinforcing tape 31 is 0.1 mm or more and 0.2 mm or less. The thickness is preferably within the range.

The resin constituting the reinforcing tape 31 is preferably not foamed in order to increase the strength, and is preferably crosslinked so as to be hard to melt when a high temperature is applied and to easily maintain the outer shape.

The reinforcing tape 31 can be formed, for example, by extruding a resin (for example, polyethylene) that is a base of the reinforcing tape 31 into a tape shape and then cross-linking the tape-shaped extruded product. The cross-linking method is not particularly limited, and irradiation cross-linking or chemical cross-linking may be used in addition to the silane cross-linking exemplified later.

Since the foamed insulating layer 20 is made of foamed resin and is not crosslinked and has a low melting point of, for example, about 115 ° C., it melts and shrinks when a high temperature (for example, 420 ° C. added in the test described later) is applied. Therefore, the outer shape cannot be maintained. Along with this, the molten resin of the foamed insulating layer 20 and its decomposition gas leak to the outside (if the reinforcing tape layer 30 is not provided) and ignite, and the foamed insulating layer 20 is sandwiched and arranged. The inner conductor 10 and the outer conductor 50 are electrically connected to each other.

The reinforcing tape layer 30 is a confinement layer that prevents the molten resin of the foamed insulating layer 20 and its decomposition gas from leaking to the outside and igniting by maintaining the outer shape without melting when a high temperature is applied. In addition, it is provided so as to be an intervening layer that suppresses the conduction between the inner conductor 10 and the outer conductor 50 arranged so as to sandwich the reinforcing tape layer 30. By providing the reinforcing tape layer 30, the coaxial cable 100 can pass the heat resistance test as described later.

The degree of cross-linking of the resin constituting the reinforcing tape 31 is preferably 70% or more, more preferably 75% or more as a gel fraction in order to increase the strength of the reinforcing tape layer 30. The degree of cross-linking of the resin constituting the reinforcing tape 31 is 90 as a gel fraction in order to suppress the dielectric loss due to the reinforcing tape layer 30 and to improve the smoothness of the surface of the reinforcing tape 31. % Or less, more preferably 85% or less. The gel fraction of the resin constituting the reinforcing tape 31 may be referred to as the gel fraction of the reinforcing tape 31, or may be referred to as the gel fraction of the reinforcing tape layer 30.

The thickness T1 of the reinforcing tape layer 30 is preferably 0.4 mm or more in order to increase the strength of the reinforcing tape layer 30. Further, the thickness T1 of the reinforcing tape layer 30 suppresses the dielectric loss due to the reinforcing tape layer 30 made of the crosslinked resin, and also suppresses the degree of foaming of the insulator 90 from being excessively lowered. Therefore, it is preferably 0.8 mm or less.

The thickness T2 of the reinforcing tape 31 is preferably 0.1 mm or more in order to increase the strength of the reinforcing tape 31. Further, the thickness T2 of the reinforcing tape 31 is preferably 0.2 mm or less in order to prevent the reinforcing tape layer 30 around which the reinforcing tape 31 is wrapped from becoming excessively thick.

The reinforcing tape layer 30 is formed by wrapping the reinforcing tape 31 on the outer periphery of the foamed insulating layer 20, that is, by winding the reinforcing tape 31 spirally so that a part of the tape width overlaps. Is preferable. By wrapping the reinforcing tape 31 in a wrap, the reinforcing tape layer 30 is formed with high strength without gaps, and good performance as the above-mentioned confinement layer or intervening layer can be obtained.

In order to make the thickness of the reinforcing tape layer 30 uniform, the reinforcing tape layer 30 is preferably formed of, for example, a 1/2 wrap winding in which the reinforcing tape 31 is wound so that 1/2 of the tape width overlaps. .. Since the winding operation involves an error, the overlap of the tape widths does not have to be exactly 1/2 in the 1/2 lap winding, and for example, a deviation within ± 0.5% of the tape width is allowed. .. In FIG. 2A, the tape width of the reinforcing tape 31 is shown as a width between a solid line or a width between a broken line and a broken line for ease of illustration.

It is more preferable that the reinforcing tape layer 30 has a structure in which a plurality of tape layers formed by wrapping the reinforcing tape 31 are laminated in order to enhance the performance as a confinement layer or an intervening layer. FIG. 2B shows an example in which the reinforcing tape layer 30 is formed by laminating the tape layers 30a and 30b formed by winding each of the reinforcing tapes 31a and 31b by 1/2 wrap. In the lamination, the lap stitch (boundary line between the overlapping reinforcing tapes 31a) 32a on the upper surface of the lower tape layer 30a and the wrap stitch (boundary line between the overlapping reinforcing tapes 31b) 32b on the lower surface of the upper tape layer 30b are formed. , It is preferable that they do not overlap (do not match, do not intersect). This is to improve the closing performance of the reinforcing tape layer 30.

The average degree of foaming of the insulator 90 including the foamed insulating layer 20 and the reinforcing tape layer 30 is preferably, for example, 60% or more, preferably 65%, in order to suppress the dielectric loss due to the insulator 90. The above is more preferable. Further, the average degree of foaming of the insulator 90 is preferably 80% or less, for example, in order to prevent the strength of the insulator 90 (particularly the portion of the foamed insulating layer 20) from being excessively lowered. , 75% or less is more preferable.

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 reinforcing tape layer 30 with the thickness a of the foamed insulating layer 20 and the thickness b of the reinforcing tape layer 30. By that, that is,
Average degree of foaming (%) = (aA + bB) / (a + b)
It is calculated by the formula.

The degree of foaming of the foamed insulating layer 20 is preferably in the range of, for example, 65% or more and 85% or less, for example, about 75%, and the degree of foaming of the reinforcing tape layer 30 is 0%. The average degree of foaming of the insulator 90 can be increased by not making the reinforcing tape layer 30 excessively thick, preferably 0.8 mm or less.

Both the resin constituting the foamed insulating layer 20 and the resin constituting the reinforcing tape layer 30 are non-halogen ones containing no halogen elements such as fluorine and chlorine in order to suppress the generation of toxic gas during combustion, for example. It is preferable to do so.

Additives such as an antioxidant may be added to the resin constituting the foamed insulating layer 20 and the resin constituting the reinforcing tape layer 30, if necessary.

A tightening tape layer (heat-resistant tape layer) 40 formed by wrapping a heat-resistant tape is arranged on the outer periphery of the reinforcing tape layer 30. Examples of the heat-resistant tape used for the tightening tape layer 40 include polyimide tape (for example, Kapton (registered trademark) tape). The thickness of the tightening tape layer 40 is, for example, a thickness in the range of 0.01 mm or more and 0.05 mm or less.

The heat-resistant tape of the tightening tape layer 40 is preferably one that does not soften even at a high temperature (for example, 420 ° C.) and does not spread fire. Further, if there is an adhesive layer, the adhesive layer melts, decomposes, and spreads fire at such a high temperature, so it is preferable that the adhesive layer does not have an adhesive layer.

By suppressing (tightening) the reinforcing tape layer 30 that the tightening tape layer 40 tends to expand from the inside due to the decomposition gas of the foamed insulating layer 20 generated by the high temperature, that is, by suppressing the loosening of the reinforcing tape layer 30. The performance of the reinforcing tape layer 30 as a confining layer or an intervening layer can be further improved. In order to suppress the reinforcing tape layer 30, the heat-resistant tape of the tightening tape layer 40 is preferably wrapped with an overlapping width of, for example, 1/4 wrap to 1/2 wrap, and is about 5N or more and 10N or less. It is preferably wound with tension.

The thickness of the tightening tape layer 40 is preferably 0.01 mm or more so that the strength for suppressing the reinforcing tape layer 30 can be obtained. Further, the thickness of the tightening tape layer 40 is preferably 0.05 mm or less in order to suppress the dielectric loss due to the tightening tape layer 40.

An outer conductor 50 is arranged on the outer periphery of the tightening tape layer 40. That is, the outer conductor 50 is arranged on the outer circumference of the insulator 90 (via the tightening 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 by winding a conductor tape such as a copper tape with a slot or an aluminum tape with a slot, for example. A tape having a pleated shape may be used.

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

A sheath 70 is arranged on the outer periphery of the presser foot 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, a method of manufacturing the coaxial cable 100 will be exemplarily described with reference to FIGS. 3 (a), 3 (b), and 4. FIG. 3A is a schematic view showing up to the process of forming the foamed insulating layer 20. FIG. 3B is a schematic view showing a manufacturing process of the reinforcing tape 31 constituting the reinforcing tape layer 30. FIG. 4 is a schematic view showing a process from the process of forming the foamed insulating layer 20 to the process of completing the coaxial cable 100.

See FIG. 3 (a). The transmitter, wire drawing machine, and core wire heater of the inner conductor (core wire) 10 are collectively referred to as a core wire preparing device 200. The inner conductor 10 is sent out from the core wire preparation device 200.

A foam extruder 210 having a foaming agent (gas) injection pump 211 is provided with a resin (for example, polyethylene) that is the base of the foam insulation layer 20 and a foaming nucleating agent (for example, azodicarbonamide (ADCA)) or 4,4'-oxy. Bisbenzenesulfonyl hydrazide (OBSH)) is supplied, and a foam insulating layer 20 is formed on the outer periphery of the inner conductor 10 by a foam extruder 210. The coaxial cable 100A in which the foamed insulating layer 20 is formed on the inner conductor 10 is wound around the winding drum 220.

See FIG. 3 (b). First, a resin (for example, polyethylene) as a base of the reinforcing tape 31, a silane compound (for example, vinylmethoxysilane), a free radical generator (for example, dicumyl peroxide), and an antioxidant are put into an extruder. For example, a silane grafted resin (for example, silane graft polyethylene) is prepared by causing a graft reaction at an extrusion temperature of 200 ° C. A silane grafted resin and a catalyst masterbatch containing a silanol condensation catalyst (for example, an organotin compound catalyst) are put into a single-screw extruder 300, and a slit-shaped mouthpiece having a height of 0.1 mm and a width of 20 mm is formed. A tape-shaped extruded product is extruded from the extruded head T-die 301 having the extruded head, and is wound around the take-up drum 320 via the water tank 310. After that, the take-up drum 320 is placed in the constant temperature bath 330 and placed in a steam atmosphere at 80 ° C. for about 12 to 15 hours to crosslink the tape-shaped extruded product and obtain the reinforcing tape 31. To make.

See FIG. The coaxial cable 100A is sent out from the take-up drum 220 around which the coaxial cable 100A in which the foam insulating layer 20 is formed is wound.

The reinforcing tape 31a is wound around the outer periphery of the foamed insulating layer 20 by the first reinforcing tape winding machine 230a to form the first tape layer 30a of the reinforcing tape layer 30. Further, the reinforcing tape winding machine 230b winds the reinforcing tape 31b on the outer periphery of the tape layer 30a of the first layer to form the tape layer 30b of the second layer of the reinforcing tape layer 30. In this way, the reinforcing tape layer 30 is formed.

The heat-resistant tape winding machine 240 winds the heat-resistant tape on the outer periphery of the reinforcing tape layer 30 to form the tightening tape layer 40. A conductor tape is wound around the outer periphery of the tightening tape layer 40 by the outer conductor vertical attachment machine 250 to form the outer conductor 50. The presser foot roll tape winding machine 260 winds the presser foot roll tape on the outer circumference of the outer conductor 50 to form the presser foot roll tape layer 60.

A material containing a base resin and a flame retardant is supplied to the sheath extruder 270, and the sheath 70 is formed on the outer periphery of the presser foot tape layer 60 by the sheath extruder 270. At this time, the messenger wires 80 sent out from the messenger wire transmitter 280 in front of the sheath extruder 270 are arranged in parallel, and the messenger wires 80 are simultaneously covered to complete the coaxial cable 100. The coaxial cable 100 is wound around the take-up drum 290. In this way, the coaxial cable 100 is manufactured.

Next, the heat resistance test for the coaxial cable (leakage coaxial cable) 100 according to the embodiment will be described with reference to FIGS. 5 (a) and 5 (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. 5A is a schematic view showing a heat resistance test method, and FIG. 5B is a graph showing a temperature rise curve in the heat resistance test.

In this heat resistance test, as shown in FIG. 5A, a test piece having a length of 1.3 m of the coaxial cable 100 is fixed to the cable fixing plate 400, a load 410 is applied to the center of the test piece, and the test piece is subjected to. The test piece is heated by the flame 430 in a state where an alternating current of power supply 420 to 600 V, 50 Hz is applied between the inner conductor 10 and the outer conductor 50 via the connectors 110 provided at both ends.

The load 410 is twice the weight of the coaxial cable 100 used as the test piece. Further, as shown in FIG. 5 (b), 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. 6 (a) and 6 (b), the function of the reinforcing tape layer 30 will be described by taking the situation of the heat resistance test as an example. FIG. 6A is a schematic cross-sectional view showing the coaxial cable 100 before the start of the heat resistance test, that is, before the high temperature is applied, and FIG. 6B is after the start of the heat resistance test or the end of the heat resistance test, that is, It is a schematic sectional drawing which shows the coaxial cable 100 after a high temperature is applied.

As shown in FIG. 6A, before the start of the heat resistance test, the foamed insulating layer 20, the reinforcing tape layer 30, and the tightening tape layer (heat resistant tape layer) 40 are placed between the inner conductor 10 and the outer conductor 50. The inner conductor 10 and the outer conductor 50 do not come into contact with each other and are electrically insulated from each other.

As shown in FIG. 6B, due to the high temperature applied during the heat resistance test, the foamed insulating layer 20 melts and shrinks so that the outer shape cannot be maintained and flows downward. On the other hand, the reinforcing tape layer 30 maintains its outer shape without melting. The presser foot tape layer 60 and the sheath 70 arranged on the outside of the outer conductor 50 are burnt out.

The molten resin of the foamed insulating layer 20 accumulates on the inner surface of the reinforcing tape layer 30, and the molten resin of the foamed insulating layer 20 and its decomposition gas are confined inside the reinforcing tape layer 30. In this way, the reinforcing tape layer 30 functions as a confining layer, so that the molten resin of the foamed insulating layer 20 and its decomposition gas are prevented from leaking to the outside and igniting.

As the foamed insulating layer 20 melts and loses its outer shape, the outer member of the foamed insulating layer 20 is pushed downward by the load 410. However, since the reinforcing tape layer 30 maintains the outer shape, the structure in which the reinforcing tape layer 30 (and the tightening tape layer 40) is interposed between the inner conductor 10 and the outer conductor 50 is maintained. By functioning the reinforcing tape layer 30 as an intervening layer in this way, 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.

By making the reinforcing tape layer 30 function as the confinement layer and the intervening layer as described above, the coaxial cable 100 can pass the heat resistance test, that is, the coaxial cable (leakage coaxial cable) 100 can be used even after the heat resistance test. It is possible to maintain the communication performance above a predetermined level.

As described above, by arranging the reinforcing tape 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 reinforcing tape layer 30 is not arranged. The heat resistance performance can be improved.

The reinforcing tape layer 30 is formed by wrapping a reinforcing tape 31 made of a crosslinked polyolefin resin. Since the reinforcing tape 31 is crosslinked, the reinforcing tape layer 30 is less likely to melt when a high temperature is applied, and can maintain its outer shape.

Further, since the reinforcing tape 31 is wrapped around, the reinforcing tape layer 30 is formed with high strength without gaps. As a result, the reinforcing tape layer 30 functions as a confining layer that suppresses the molten resin of the foamed insulating layer 20 and its decomposition gas from leaking to the outside and igniting, and is arranged with the reinforcing tape layer 30 interposed therebetween. It functions as an intervening layer that suppresses the continuity between the inner conductor 10 and the outer conductor 50.

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

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

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 of the reinforcing tape 31. Table 1 shows the blending ratio of each material (blending ratio to 100 parts by mass of the base resin) for obtaining the silane graft polyethylene used for the reinforcing tape 31 according to the examples.

The reinforcing tape 31 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. A catalyst masterbatch is prepared 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 100 parts by mass of the base resin (polyethylene). did.

The reinforcing tape layer 30 is formed by laminating two tape layers in which the reinforcing tape 31 is wound in 1/2 wrap on the coaxial cable 100A (in a state where the foam insulating layer 20 is formed on the inner conductor 10). did.

As shown in Table 1, as Examples 1 to 4, the thickness of the reinforcing tape layer 30 (that is, the thickness of the reinforcing tape 31) and the gel fraction of the reinforcing tape layer 30 (that is, the gel content of the reinforcing tape 31). Samples of coaxial cables with different rates) were prepared. The gel fraction of the reinforcing tape layer 30 is controlled by the blending ratio of the free radical generator.

The thickness of the reinforcing tape layer 30 is 400 μm in Examples 1 and 2 and 8000 μm in Examples 3 and 4 (that is, the thickness of the reinforcing tape 31 is 100 μm in Examples 1 and 2). Examples 3 and 4 are 200 μm).

In all of Examples 1 to 4, the gel fraction (of the reinforcing tape 31) of the reinforcing tape layer 30 is a value within the range of 70% or more and 90% or less, and the gel fraction is 90% or less. As a result, the surface condition of the reinforcing tape 31 is smooth. Further, in all of Examples 1 to 4, the average degree of foaming of the insulator 90 including the foamed insulating layer 20 and the reinforcing tape layer 30 is a value of 60% or more.

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 has been found that by providing the reinforcing tape 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 reinforcing tape layer 30 can be appropriately adjusted so as to obtain desired characteristics, but is preferably in the range of, for example, 400 μm (0.4 mm) or more and 800 μm (0.8 mm) or less. .. The gel fraction of the reinforcing tape layer 30 can be appropriately adjusted so as to obtain desired characteristics, but for example, the gel fraction is preferably in the range of 70% or more and 90% or less, and is 75% or more. It is more preferable to set the gel fraction within the range of 85% or less. According to the inventor of the present application, if the thickness of the reinforcing tape 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 reinforcing tape 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 also have 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
An insulator arranged on the outer circumference of the inner conductor and
With the outer conductor arranged on the outer circumference of the insulator,
Have,
The insulator is
A foamed insulating layer made of foamed resin and
A reinforcing tape layer arranged on the outer periphery of the foamed insulating layer and formed by wrapping a reinforcing tape made of a crosslinked polyolefin resin,
Coaxial cable with.

(Appendix 2)
The reinforcing tape layer is wrapped with the reinforcing tape made of cross-linked polyethylene having a gel fraction preferably 70% or more and 90% or less, more preferably 75% or more and 85% or less. The coaxial cable according to Appendix 1, which is formed and has a thickness in the range of 0.4 mm or more and 0.8 mm or less.

(Appendix 3)
The coaxial cable according to Appendix 1 or 2, wherein the reinforcing tape has a thickness in the range of 0.1 mm or more and 0.2 mm or less.

(Appendix 4)
The coaxial cable according to any one of Appendix 1 to 3, wherein the reinforcing tape layer is formed by 1/2 wrap winding.

(Appendix 5)
The coaxial cable according to any one of Supplementary note 1 to 4, wherein the reinforcing tape layer has a structure in which a plurality of tape layers formed by wrapping the reinforcing tape are laminated.

(Appendix 6)
The coaxial cable according to any one of Supplementary note 1 to 5, which is arranged on the outer periphery of the reinforcing tape layer, is formed by winding a heat-resistant tape, and further has a tightening tape layer that suppresses loosening of the reinforcing tape layer.

(Appendix 7)
The coaxial cable according to any one of Supplementary note 1 to 6, wherein the foamed insulating layer is preferably made of an uncrosslinked polyolefin resin, more preferably an uncrosslinked polyethylene.

(Appendix 8)
The coaxial cable according to any one of Supplementary note 1 to 7, wherein the average degree of foaming of the insulator is preferably 60% or more, more preferably 65% or more.

(Appendix 9)
The coaxial cable according to any one of Appendix 1 to 8, wherein the outer conductor has a slot and is a leaky coaxial cable.

10 Inner conductor 20 Foam insulation layer 30 Reinforcing tape layer 40 Tightening tape layer (heat resistant tape layer)
50 External conductor 51 Slot 60 Presser-wrap tape layer 70 Sheath 80 Messenger wire 90 Insulator 100 Coaxial cable

Claims (5)

With the inner conductor
An insulator arranged on the outer circumference of the inner conductor and
With the outer conductor arranged on the outer circumference of the insulator,
Have,
The insulator is
A foamed insulating layer made of foamed resin and
A reinforcing tape layer arranged on the outer periphery of the foamed insulating layer and formed by wrapping a reinforcing tape made of a crosslinked polyolefin resin,
A tightening tape layer arranged on the outer periphery of the reinforcing tape layer, formed by winding a heat-resistant tape, and suppressing loosening of the reinforcing tape layer.
Coaxial cable with. The reinforcing tape layer is formed by wrapping the reinforcing tape made of cross-linked polyethylene having a degree of cross-linking having a gel content in the range of 70% or more and 90% or less, and is 0.4 mm or more and 0.8 mm or less. The coaxial cable according to claim 1, which has a thickness within the range of. The coaxial cable according to claim 1 or 2, wherein the reinforcing tape layer is formed of 1/2 wrap winding. The coaxial cable according to any one of claims 1 to 3, wherein the reinforcing tape layer has a structure in which a plurality of tape layers formed by wrapping the reinforcing tape are laminated. The coaxial cable according to any one of claims 1 to 4 , wherein the outer conductor has a slot and is a leaky coaxial cable.