JP2012046574A - Resin composition and high-frequency coaxial cable - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin composition which can stabilize the bubble shape of an expandable resin insulating layer as closed cells; and to provide a high-frequency coaxial cable which has satisfactory transmission characteristics.SOLUTION: The high-frequency coaxial cable 1 is obtained by providing, on the outer circumference of an internal conductor 2, an internal solid layer 3, an expandable resin insulating layer 4 and an external conductor 6 in this order. The expandable resin insulating layer 4 is made of a resin composition whose melt viscosity at a density of ≥950 [kg/m] and at a shear rate of 4.86×10[1/s] is ≤1×10[Pa s] at 140°C and ≥5×10[Pa s] at 132°C.

Description

  The present invention relates to a resin composition that can suppress the generation of open cells during the bubble growth process of a foamed resin insulating layer, and a high-frequency coaxial cable that reduces the voltage standing wave ratio and reduces the attenuation.

  High frequency coaxial cables are used in mobile communication facilities for mobile phone line relays and microwave communication facilities for TV line relays. A high-frequency coaxial cable tends to use a higher frequency for the purpose of improving communication speed and communication capacity.

  Along with this, it has been required to reduce the attenuation (signal attenuation). The attenuation amount of the coaxial cable is a value obtained by adding the conductor loss due to the conductor diameter and the dielectric loss due to the insulating layer material. Since the conductor loss is determined by the shape of the high-frequency coaxial cable, it cannot be changed. Therefore, it is desired to reduce the attenuation by reducing the dielectric loss.

  The dielectric loss is expressed by a relationship such as the equation (1).

Dielectric loss ∝√ε × tanδ × f (1)
ε is dielectric constant
tan δ is the dielectric loss tangent
f is frequency

  That is, dielectric loss is proportional to the square root of dielectric constant, dielectric loss tangent, and frequency. Therefore, it is important to reduce the dielectric constant and the dielectric loss tangent in a high-frequency coaxial cable having a high operating frequency.

  Considering a foamed resin material such as polyethylene with a low dielectric constant as the insulating layer, if the polyethylene has a high fluidity during the bubble growth process of the polyethylene foamed resin insulating layer discharged from the die of the extruder, bubbles are caused by the flow of the bubble wall. Are united, and there is a problem that independent bubbles tend to become continuous bubbles without growing. Such coarsening of bubbles occurs at any location within the foamed insulating layer, but is particularly likely to occur near the internal solid layer that is difficult to cool.

  This open cell causes non-uniformity as a dielectric, and increases the voltage standing wave ratio (VSWR) of the coaxial cable.

  For example, Patent Document 1 describes a method of forming a foam layer made of an olefin resin and an outer layer made of a polyolefin resin having a melt breaking tension of 6 to 20 g on the conductor. No internal enhancement layer is formed between the two. When there is no internal enhancement layer, the exhaust gas of the foaming agent when the foamed resin insulating layer is foamed may be mixed into the conductor side or abnormal foaming (nest-like giant bubbles may be formed) may occur. Further, since the foamed resin insulating layer expands toward the outside when foaming, a large gap is generated between the conductor and the foamed resin insulating layer, and the voltage standing wave ratio of the cable is increased.

Japanese Patent Application Laid-Open No. 2005-30212

  The voltage standing wave ratio means an error when a current is passed through the high-frequency coaxial cable, and this error is generated by the generation of open bubbles. Therefore, in order to improve the characteristics of the high-frequency coaxial cable, it is necessary to prevent the generation of continuous bubbles and reduce the voltage standing wave ratio.

  An object of the present invention is to solve the above-mentioned problems, to provide a resin composition capable of stabilizing the foam shape of a foamed resin insulating layer as closed cells, and to provide a high-frequency coaxial cable having good transmission characteristics. .

  The inventors have intensively studied such a resin composition that suppresses the generation of open cells, and as a result, have reached the following invention.

In the first aspect of the present invention, the melt viscosity at a density of 950 [kg / m ³ ] or more and a shear rate of 4.86 × 10 ² [1 / second] is 1 × 10 ³ [Pa · s] or less at 140 ° C., 132 The resin composition which is 5 × 10 ³ [Pa · s] or more at ° C.

According to a second aspect of the present invention, in the high-frequency coaxial cable in which an inner solid layer, a foamed resin insulating layer, and an outer conductor are sequentially provided on the outer periphery of the inner conductor, the foamed resin insulating layer has a density of 950 [kg / m ³ ] or more and A resin composition having a melt viscosity at a shear rate of 4.86 × 10 ² [1 / second] of 1 × 10 ³ [Pa · s] or less at 140 ° C. and 5 × 10 ³ [Pa · s] or more at 132 ° C. A high-frequency coaxial cable comprising a foamed material.

  In addition, the following invention has been reached from the study of the structure of the coaxial cable that gives good transmission characteristics.

  The outer conductor has a corrugated shape, and the outer diameter a of the foamed resin insulating layer is preferably in the following relationship with the inner diameter c at the top of the corrugated wave type and the inner diameter b at the trough.

      1.05 × b ≦ a ≦ 0.98 × c

  The foamed resin insulation layer preferably uses an inert gas such as nitrogen or carbon dioxide alone or a mixed gas as a foaming agent.

  The foaming resin insulating layer preferably has a foaming degree of 70% or more.

  According to the present invention, it is possible to reduce the transmission loss and voltage standing wave ratio of a high-frequency coaxial cable.

It is a figure of the high frequency coaxial cable which shows one Embodiment of this invention, (a) is sectional drawing, (b) is a terminal part side part. It is a graph which shows the temperature dependence of the melt viscosity of the resin composition of this invention. It is a principal part block diagram of the manufacturing apparatus which manufactures the high frequency coaxial cable of this invention. It is a figure of the high frequency coaxial cable which shows other embodiment of this invention, (a) is sectional drawing, (b) is a terminal part side part. It is a longitudinal cross-sectional view of the high frequency coaxial cable which shows one Embodiment of this invention. It is an internal structure figure of the extruder head of the manufacturing apparatus at the time of manufacturing the high frequency coaxial cable of other embodiment of this invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG.

The high-frequency coaxial cable 1 of the present invention is the high-frequency coaxial cable 1 in which the inner solid layer 3, the foamed resin insulating layer 4, the outer conductor 6, and the outer skin 8 are sequentially provided on the outer periphery of the inner conductor 2 made of a copper pipe. When the insulating layer 4 has a density of 950 [kg / m ³ ] or more, the melt viscosity at a shear rate of 4.86 × 10 ² [1 / second] is 1 × 10 ³ [Pa · s] or less at 140 ° C., and 5 at 132 ° C. × 10 ³ [Pa · s] or more of the foamed resin composition.

  The outer conductor 6 is formed in a ring shape using a copper corrugate, and the outer diameter a of the foamed resin insulating layer 4 and the inner diameter c at the top of the corrugated wave type of the outer conductor 6 and the inner diameter b at the trough are as follows. It is characterized by being in a relationship.

      1.05 × b ≦ a ≦ 0.98 × c

  In forming the foamed resin insulating layer 4, an inert gas such as nitrogen or carbon dioxide or a mixed gas is used as a foaming agent, and the degree of foaming is 70% or more.

  The degree of foaming is determined by equation (2).

  Foaming degree (%) = 100− (specific gravity after foaming / specific gravity before foaming) × 100 (2)

  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.

The density of the resin composition of the present invention is desirably 950 [kg / m ³ ] or more.

In order to obtain a good foam without generation of nests, the melt viscosity at a shear rate of 4.86 × 10 ¹² [1 / second] of the resin composition is 1 × 10 ³ [Pa · s] or less at 140 ° C. It is preferably 5 × 10 ³ [Pa · s] or more at 132 ° C.

When the melt viscosity at the shear rate of 4.86 × 10 ² [1 / sec] of the resin composition is 1 × 10 ³ [Pa · s] or more at 140 ° C., shear heat generation in the second extruder 22 increases. Therefore, the resin temperature cannot be effectively lowered, and a nest is generated in the foamed resin insulating layer.

Further, when the melt viscosity at a shear rate of 4.86 × 10 ² [1 / second] of the resin composition is less than 5 × 10 ³ [Pa · s] at 132 ° C., bubble growth immediately after extrusion from the extrusion head 25 is achieved. Since the melt viscosity of the resin composition in the process is lowered, the grown bubbles are united, and a nest is generated in the foamed resin insulating layer.

Examples of the foamed resin composition material of the present invention include high density polyethylene (HDPE) (density 942 kg / m ³ or more), medium density polyethylene (MDPE) (density 930 to 942 kg / m ³ ), linear low density polyethylene (LLDPE). ) (Density 910 to 929 kg / m ³ ), polyethylene such as low density polyethylene (LDPE) (density 910 to 929 kg / m ³ ), very low density polyethylene (VLDPE) (density 880 to 910 kg / m ³ ), or ethylene Examples thereof include ethylene-based copolymers such as α-olefin copolymers, ethylene-vinyl acetate copolymers, and ethylene- (meth) acrylic acid ester copolymers. These can be used alone or in combination of two or more. From the viewpoint of dielectric properties and moldability, a blend of high-density polyethylene and low-density polyethylene is preferred.

When polyethylene is lowered from the melted state to near the crystallization temperature, polyethylene crystals are partially formed and the fluidity of molecular chains is lost, so the melt viscosity increases rapidly. High density polyethylene (density 945 kg / m ³ or more), each crystalline melting point of the low-density polyethylene (density below 910 kg / m ³ or more 930 kg / m ³⁾ is approximately 125 to 140 ° C. and 100-125 ° C., both polyethylene However, the higher the density, the higher the crystalline melting point. When high density polyethylene and low density polyethylene are blended, the crystalline melting point changes depending on the blend ratio.

That the melt viscosity of the resin composition at a shear rate of 4.86 × 10 ² [1 / sec] and 140 ° C. is 1 × 10 ³ [Pa · s] or less is sufficient fluidity at 140 ° C. That is.

  In order to obtain such a composition, the resin composition comprises a blend of high-density polyethylene and low-density polyethylene, and the blend preferably contains 10% by mass or more of low-density polyethylene, and The melt index (MI), which is an index of resin fluidity, is preferably 0.2 [g / 10 min] or more.

  In particular, low density polyethylene produced by a high-pressure method is most preferred because it can prevent coalescence of bubbles.

In order to set the melt viscosity of a resin composition comprising a blend of high-density polyethylene and low-density polyethylene to 5 × 10 ³ [Pa · s] or higher at 132 ° C., the crystal melting point of the blended polyethylene composition is set to high density. It is effective to keep it at the same level as polyethylene, and it is preferable that 70% by mass or more of high-density polyethylene is contained in the blend.

  When the melt viscosity satisfies a specified value, the resin temperature is cooled from the process temperature to 132 ° C. to crystallize and solidify. Therefore, for example, by controlling the temperature of the extrusion head 25 of the second extruder 22 to about 135 ° C. and the die temperature to about 130 ° C., the resin composition is solidified immediately after the bubble growth, and the coalescence and abnormal growth of the bubbles. It is possible to effectively suppress the occurrence of nests caused by

In addition, since the higher the density of polyethylene, the lower the molecular chain branching, the resin composition comprising a blend of high-density polyethylene and low-density polyethylene has a resin composition of 950 [kg / m ³ ] or more. The tan δ of the object is reduced.

Melt viscosity is applied to a capillary flow meter having a furnace body diameter of 9.55 mm (for example, a Capillograph manufactured by Toyo Seiki Co., Ltd.) with a flat capillary having an inner diameter of 0.5 mm and a length of 2.5 mm, and a resin shear rate of 4.86 × 10 at the capillary portion. ² Measure at the piston push-in speed giving 1 / second.

  As the foam nucleating agent used in the present invention, inorganic compounds such as talc, clay, silica, boron nitride, metal oxide, zeolite, and organic foaming agents can be used. As the organic foaming agent, 4,4'-oxybisbenzenesulfonyl hydrazide (OBSH) or azodicarbonamide (ADCA) can be used.

  The content of the foam nucleating agent that can be highly foamed is not particularly specified, but 0.001 to 0.2 parts by weight is preferable with respect to 100 parts by weight of the resin composition material. Within this range, an appropriate degree of foaming can be obtained, and the dielectric loss tangent of the resin composition can be kept low.

  The method of adding the foam nucleating agent can knead the specified amount directly to the resin. More preferably, first, a nucleating agent master batch in which the concentration of the foam nucleating agent is 10 to 100 times the concentration in the foaming compound is prepared, and this nucleating agent master batch is added to the resin composition by a dry blend method. This is a method for obtaining a foaming compound. Use of this method improves the dispersion of the foam nucleating agent.

  The foaming method of the resin composition includes chemical foaming and physical foaming. Since chemical foaming is foamed with decomposition gas, a decomposition residue remains, and this decomposition residue causes deterioration of the electrical characteristics of the high-frequency coaxial cable. Physical foaming includes foaming with chlorofluorocarbon gas, foaming with hydrocarbon gas, and foaming with inert gas. However, chlorofluorocarbon gas cannot be used from the viewpoint of environmental protection, and hydrocarbon gas is not preferable because it is flammable. It is preferable to use an active gas.

  In the present invention, an inert gas such as nitrogen or carbon dioxide or a mixed gas is used as a foaming agent.

  The foaming degree of the foamed resin insulating layer is 70% or more. This has the effect of lowering the dielectric constant and dielectric loss tangent (tan δ), and can reduce the transmission loss of the coaxial cable. The degree of foaming can be adjusted by changing the amount of gas injected into the extruder and the basis weight of the resin when producing the foamed insulating layer.

  In foam molding, since the structure of the foam is fixed earlier as the resin temperature in the bubble growth process is closer to the melting point, it is necessary to fix the structure simultaneously with the bubble growth. In order to realize this, it is effective to lower the process temperature.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

  First, the manufacturing apparatus of the high frequency coaxial cable of this invention is demonstrated.

  FIG. 3 omits the step of providing the outer conductor 6 and the outer skin 8 from the high-frequency coaxial cable manufacturing apparatus of the present invention.

  The manufacturing apparatus of FIG. 3 includes a hopper 24 for introducing a foaming compound, a gas injection device 23 for injecting an inert gas, a first extruder 21 for kneading the foaming compound and an inert gas, and foaming the kneaded product. A second extruder 22 for lowering the temperature to a temperature suitable for the above, a delivery device 29 for sending out the inner conductor 2, a stretching machine 30 for extending the inner conductor 2 and adjusting it to a predetermined size, and an internal enhancement layer for the inner conductor 2 3, an internal solid layer extruder 27 that forms 3, an extrusion head 25 that forms a foamed resin insulating layer 4 for an intermediate product in which up to the internal solid layer 3 is formed, and an intermediate that is formed up to the foamed resin insulating layer 4 A cooling water tank 26 for cooling the product and a winder 31 for winding the high-frequency coaxial cable 1 are provided.

  Next, the manufacturing method of the high frequency coaxial cable of this invention is demonstrated.

In FIG. 1, sectional drawing and the terminal part side view of the high frequency coaxial cable of this invention are shown.
First, foam nucleating agent is kneaded into low-density polyethylene to produce a nucleating agent master batch, and then the nucleating agent master batch is added to a mixture of low-density polyethylene and high-density polyethylene and dry blended to produce a foaming compound. .

  This foaming compound is put into the first extruder 21 from the hopper 24 of FIG. Carbon dioxide gas is injected from the gas injection device 23 and kneaded. Thereafter, in the second extruder 22, the kneaded product is lowered to a temperature suitable for foaming.

  On the other hand, in the internal solid layer extruder 27, the internal solid layer 3 is coated on the outside of the internal conductor 2, and the intermediate product is supplied to the extrusion head 25.

  Thereafter, in the extrusion head 25, the foamed resin insulating layer 4 formed to have an outer diameter of 22.5 mm and a foaming degree of 73 ± 0.5% is extruded and coated on the outside of the inner solid layer 3.

  The intermediate product on which the insulating layer 7 discharged from the extrusion head 25 is formed can be shaped by a sizing die immediately after discharge. The sizing die can be provided between the extrusion head 25 and the cooling water tank 26 or in the cooling water tank 26.

  The intermediate product formed up to the insulating layer 7 is cooled in the cooling water tank 26, and the outer conductor 6 and the outer skin 8 are provided by a well-known and conventional method.

  The outer conductor 6 is composed of a copper or aluminum corrugated tube, and the corrugated shape includes a spiral type in which a groove is formed in a spiral shape and an annular corrugated type in which a groove is formed on a concentric circle. Since the transmission loss of the coaxial cable can be reduced, the annular corrugated type is more preferable.

  The cable structure uses a copper pipe with a conductor diameter of 9.0 mm and a thickness of 0.25 mm for the inner conductor 2, forms the inner solid layer 3, and the foamed resin insulating layer 4 and the outer conductor 6 are arranged according to & 3 described in Table 3. Formed with structure. The outer conductor 6 was formed by vertically attaching a copper tape having a thickness of 0.25 mm so as to wrap the foamed resin insulating layer 4, welding the tape edge, and then performing an annular corrugation process. The corrugated pitch was set to 6.90 mm.

  FIG. 5 shows the longitudinal cross-sectional structure of the cable.

  The outer conductor 6 has a corrugated shape, and the outer diameter a of the foamed resin insulating layer 4, the inner diameter c at the top of the corrugated wave type of the outer conductor 6, and the inner diameter b at the trough have the following relationship: is required.

      1.05 × b ≦ a ≦ 0.98 × c

  This relationship brings about an improvement in transmission characteristics by keeping an appropriate air layer between the outer conductor 6 and the insulating layer 7 at the top of the corrugated wave type, and an insulating layer by the outer conductor 6 at the trough of the corrugated wave type. 7 gives the cable bending resistance. When the outer diameter a of the foamed resin insulating layer 4 is smaller than 1.05 × b, the fixing of the insulating layer 7 by the outer conductor 6 becomes weak, and the transmission characteristic is deteriorated by the displacement of the insulating layer 7 when the cable is bent. Getting worse.

  When the outer diameter a of the foamed resin insulating layer 4 is larger than 0.98 × c, it becomes impossible to maintain an appropriate air layer between the outer conductor 6 and the insulating layer 7, and the transmission characteristics are deteriorated.

  FIG. 4 shows another embodiment of the high-frequency coaxial cable of the present invention. An external enhancement layer 45 is provided between the foamed resin insulation layer 44 and the external conductor 46, and this can be prevented when water enters the foamed resin insulation layer 44 during cooling to deteriorate electrical characteristics. is there. An example of the material of the external enhancement layer 45 is HDPE.

  FIG. 6 shows an internal structure of the extrusion head 33 of the manufacturing apparatus when the high frequency coaxial cable 41 is manufactured. When manufacturing the high frequency coaxial cable 41, since the process of forming the external enhancement layer 45 is required, the external enhancement layer extruder 35 is added to a manufacturing apparatus. An internal solid layer extruder 34 for forming the internal solid layer 43 with respect to the internal conductor 42, a second extruder 32 for forming the foamed resin insulating layer 44, and an external solid layer extruder 35 for extruding the external solid layer 45. With.

  In this manufacturing apparatus, the internal conductor 42 is fed into the extrusion head 33, and the internal solid layer 43, the foamed resin insulating layer 44, and the external solid layer 45 are simultaneously extruded by the extrusion head 33 to form the insulating layer 47 in a lump.

  The thickness of the external enhancement layer 45 is not particularly limited, but is preferably 0.01 to 0.3 mm. When the thickness is 0.01 mm or less, there is a possibility that the cooling water partially enters. When the thickness exceeds 0.3 mm, the proportion of the non-foamed layer increases, resulting in an increase in attenuation.

  Using the materials of Examples # 1 to # 10 and Comparative Examples $ 1 to $ 6, high-frequency coaxial cables were manufactured by the above method and evaluated. Examples # 1 to # 10 satisfy all the conditions of the present invention, and Comparative Examples $ 1 to $ 6 are materials that do not partially satisfy the conditions of the present invention.

The characteristics of each cable were evaluated, and the results are shown in Tables 1 and 2.
Further, the temperature dependence of the melt viscosity at the shear rate of 4.86 × 10 ² [1 / second] of the materials of Examples # 1 to # 10 and Comparative Examples $ 1 to $ 6 was measured, and an example is shown in FIG. Show.

  The evaluation method will be described below.

  The transmission loss and VSWR of the cable are measured using an Agilent network analyzer 8757D. The transmission loss at 2.2 GHz is less than 6.10 dB / 100 m, ◎, less than 6.14 dB / 100 m, and 6.14 dB. / 100 m or more was taken as x. ◎ and ○ are acceptable. The VSWR was determined to be 1.10 or less at 2.2 GHz.

  In the cable bending test, a mandrel having a radius of 350 mm was fixed to both sides of the cable, and 90 ° left / right bending was performed 10 times. Thereafter, VSWR was measured. A value of 1.10 or less at 2.2 GHz was accepted, ◎ when there was no change in VSWR before and after bending, and ◯ when increased by bending but 1.10 or less.

In Examples # 1 to # 10 in which the physical properties of the materials satisfy the specified values, the transmission loss, the voltage standing wave ratio (VSWR), and the bending resistance were all good. In Examples # 1 to # 7 and Examples # 9 and # 10, the melt viscosity at 132 ° C. and 4.86 × 10 ² [1 / second] is 5 × 10 ³ Pa · s or more, which is favorable. A foam that provides transmission characteristics is formed, which is more preferable.

Comparative example $ 1 to $ 4 material having a melt viscosity of less than 5 × 10 ³ Pa · s at 132 ° C. and a shear rate of 4.86 × 10 ² [1 / second], and 140 ° C. and a shear rate of 4.86 × In Comparative Example $ 5, in which the melt viscosity at 10 ² [1 / sec] is 1 × 10 ³ Pa · s or more, nests were observed in the foam, and the voltage standing wave ratio (VSWR) increased due to this effect. . Further, Comparative Example $ 6 having a density equal to or less than the specified value has a large transmission loss. It can be inferred that this is because the tan δ of the polyethylene material is large.

  Next, the resin composition material was fixed to the material of Example # 2, a cable having the configuration shown in Table 3 was produced, and the influence of the outer conductor shape of the cable was evaluated.

  In & 1 to & 7 in which the inner diameter b of the corrugated valley portion of the outer conductor 6 is changed, the value of b is small and a / b ≧ 1.05. In & 1 to & 5, the VSWR before and after bending does not change and is particularly good. The bending resistance was confirmed.

  In & 8 to & 13 in which the inner diameter c of the top portion of the corrugated outer conductor 6 was changed, it was found that the transmission loss can be reduced in & 10 to & 13 where the value of c is large and a / c ≦ 0.98.

Therefore, as the foamed resin insulating layer, the melt viscosity at a shear rate of 4.86 × 10 ² [1 / sec] is 1 × 10 ³ [Pa · s] or less at 140 ° C., and 5 × 10 ³ [Pa · s at 132 ° C. By using the resin composition as described above, the nest in the layer can be suppressed and the voltage standing wave ratio can be reduced, and the corrugated wave type of the outer diameter a of the foamed resin insulation layer and the outer conductor 6 can be reduced. It can be seen that good transmission characteristics can be obtained when the inner diameter c at the top and the inner diameter b at the trough have a relationship of 1.05 × b ≦ a ≦ 0.98 × c.

DESCRIPTION OF SYMBOLS 1 High frequency coaxial cable 2 Inner conductor 3 Inner solid layer 4 Foamed resin insulation layer 6 Outer conductor 7 Insulation layer 8 Outer skin 9 Annular corrugate 21 First extruder 22 Second extruder 23 Gas injection device 24 Hopper 25 Extrusion head 26 Cooling water tank 27 Internal solid layer extruder 28 External solid layer extruder 29 Sending machine 30 Stretcher 31 Winder 32 Second extruder 33 Extrusion head 34 Internal solid layer extruder 35 External solid layer extruder 41 High-frequency coaxial cable 42 Internal conductor 43 Internal Solid layer 44 Foamed resin insulating layer 45 External solid layer 46 External conductor 47 Insulating layer 48 Skin

Claims (5)

The melt viscosity at a density of 950 [kg / m ³ ] or more and a shear rate of 4.86 × 10 ² [1 / second] is 1 × 10 ³ [Pa · s] or less at 140 ° C., and 5 × 10 ³ [132 ° C.] Pa · s] or more. In the high-frequency coaxial cable in which an inner solid layer, a foamed resin insulating layer, and an outer conductor are sequentially provided on the outer periphery of the inner conductor, the foamed resin insulating layer has a density of 950 [kg / m ³ ] or more and a shear rate of 4.86 × The melt viscosity at 10 ² [1 / second] is 1 × 10 ³ [Pa · s] or less at 140 ° C. and 5 × 10 ³ [Pa · s] or more at 132 ° C. A high-frequency coaxial cable characterized by that. The outer conductor has a corrugated shape, and the outer diameter a of the foamed resin insulating layer has the following relationship with the inner diameter c at the top and the inner diameter b at the trough of the corrugated wave type. Item 5. A high-frequency coaxial cable according to Item 2.
1.05 × b ≦ a ≦ 0.98 × c   The high-frequency coaxial cable according to claim 2 or 3, wherein the foamed resin insulating layer uses an inert gas such as nitrogen or carbon dioxide alone or a mixed gas as a foaming agent.   The high-frequency coaxial cable according to claim 4, wherein the foamed resin insulating layer has a foaming degree of 70% or more.

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