JP2005302412A - High-frequency coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-frequency coaxial cable including an insulating layer of a two-layer structure in which a foam layer and an outer layer consisting of a solid material are formed in order on an internal conductor, wherein the insulating layer of a high foaming degree is securely formed preventing a huge air bubble, an appearance is better without a change in outer diameter of the insulating layer, and an attenuation amount at a high-frequency band (1GHz or more) is constituted to be smaller, by specifying the outer layer consisting of polyolefin family resin. <P>SOLUTION: In the high-frequency coaxial cable in which the insulating layer of the two-layer structure comprising the foam layer and the outer layer is formed on the internal conductor, the outer layer is constituted by the polyolefin family resin of which melt breaking tensile force is 6 to 20g when measured using a capillary rheometer of 9.55mm in furnace diameter, on condition of 10mm/min in piston speed and 400m/min<SP>2</SP>in take-off acceleration at 190°C, using a flat capillary of 2.095mm in inner diameter and 8.03mm in length. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-frequency coaxial cable having an insulating layer composed of two layers, a foam layer and an outer layer.

A high-frequency foamed coaxial cable is composed of a central conductor made of copper, a foamed insulator layer provided thereon, an outer conductor provided on the outer periphery thereof, and the like. Recently, a foamed coaxial cable with a small attenuation is required even in the frequency range of GHz, and therefore an insulator layer with a high foaming degree is desired. For example, in Patent Document 1, in order to obtain a coaxial cable having a fine cell, uniform, high foaming degree, and good appearance, it contains a polyolefin resin that can be hot melt extruded and a fluorine resin powder as a nucleating agent. A coaxial cable is described in which the composition is foam-extruded in the presence of a foaming agent. However, even in such a coaxial cable, when the degree of foaming is increased, huge air bubbles are formed in the foam layer, which is sufficiently high. There was a problem that a foam layer having a foaming degree was not formed. In addition, as the foamed insulator, an inner layer made of a solid body is formed on a conductor, and then a foam layer of a polyolefin resin is formed. A three-layered coaxial cable is disclosed in Patent Document 2 in order to increase the frequency. However, even in such a method for producing a highly foamed coaxial cable, there has been a problem in stably obtaining a highly foamed coaxial cable. That is, in the conventional outer layer material, gas is easily released from the outer layer at the time of foaming, and huge air bubbles are formed, and it is difficult to stably obtain a highly foamed insulator layer. And the foam insulation layer which consists of such a big air bubble had the problem that an outer diameter fluctuation | variation arises and an external appearance worsens.
Japanese Patent No. 3227091 Japanese Patent No. 2508128

  Therefore, the problem to be solved by the present invention is a high-frequency coaxial cable having an insulating layer having a two-layer structure in which an outer layer composed of a foam layer and a solid body is sequentially formed on an inner conductor. By identifying the outer layer to be formed, it is possible to reliably form an insulating layer having a high foaming degree by preventing giant air bubbles, and to have a good appearance without fluctuation of the outer diameter of the insulating layer, and in a high frequency band (1 GHz or more) Is to provide a high-frequency coaxial cable with a small attenuation.

The problem to be solved is a high-frequency coaxial cable in which an insulating layer having a two-layer structure composed of a foam layer and an outer layer is formed on an inner conductor, as described in claim 1, Measured using a capillary rheometer with a furnace diameter of 9.55 mm using a flat capillary with an inner diameter of 2.095 mm and a length of 8.03 mm at 190 ° C. with a piston speed of 10 mm / min and a take-up acceleration of 400 m / min ² This is solved by using a high-frequency coaxial cable made of a polyolefin resin having a melt breaking tension of 6 to 20 g.

  Further, as described in claim 2, the problem is solved by using the high-frequency coaxial cable according to claim 1, wherein the outer layer made of the polyolefin-based resin has a thickness of 0.3 mm or less.

  Further, as described in claim 3, the polyolefin resin constituting the outer layer is at least one selected from high density polyethylene, medium density polyethylene, low density polyethylene, polypropylene alone or a mixture. This is solved by using the high-frequency coaxial cable described in 1 or 2.

  And as described in Claim 4, the said insulator layer is solved by setting it as the high frequency coaxial cable in any one of Claims 1-3 which made foaming degree 78% or more by inert gas. The

  And as described in Claim 5, in the high frequency coaxial cable in any one of Claims 1-4, it is solved by making it a high frequency coaxial cable whose outer conductor is a copper corrugated structure.

The present invention as described above is a high-frequency coaxial cable in which an insulating layer having a two-layer structure including a foam layer and an outer layer is formed on an inner conductor, and the outer layer has an inner diameter of 2.095 mm and a length of 8. The melt fracture tension measured using a capillary rheometer with a furnace diameter of 9.55 mm under the conditions of a flat capillary of 03 mm, a piston speed of 10 mm / min at 190 ° C., and a take-up acceleration of 400 m / min ² is 6 to 20 g. Since the high-frequency coaxial cable is composed of a certain polyolefin-based resin, an insulator layer having a high foaming degree of 78% or more can be reliably formed so as not to generate giant air bubbles. This is a high-frequency coaxial cable that has a good external appearance and has a small amount of attenuation in a high-frequency band (1 GHz or more).

  Further, by setting the thickness of the outer layer made of the polyolefin-based resin to preferably 0.3 mm or less, the polyolefin-based resin constituting the outer layer is made of high-density polyethylene, medium-density polyethylene, low-density polyethylene, polypropylene alone or By selecting from these mixtures, it is possible to select a polyolefin resin having a melt breaking tension of 6 to 20 g, a high-frequency coaxial cable having a high foaming degree and a low attenuation in a high-frequency band (1 GHz or more) can do.

  Furthermore, by making the insulator layer a high-frequency coaxial cable having a foaming degree of 78% or more using an inert gas, it is possible to reliably form an insulating layer having a high foaming degree without giant air bubbles. In addition, there is no problem that the dielectric properties are deteriorated by the foam decomposition residue as in the case of using a chemical foaming agent. In addition, the obtained insulating layer can be a high-frequency coaxial cable having a good appearance with no variation in outer diameter and a small attenuation in a high-frequency band (1 GHz or more).

  In the high-frequency coaxial cable as described above, by using a copper corrugated structure as the outer conductor, a high-frequency coaxial cable having the above-described characteristics and excellent in flexibility can be obtained.

The present invention is described in detail below. The invention described in claim 1 is a high-frequency coaxial cable in which an insulating layer having a two-layer structure including a foam layer and an outer layer is formed on an inner conductor, the outer layer having an inner diameter of 2.095 mm and a length. The melt fracture tension measured using a capillary rheometer with a furnace body diameter of 9.55 mm under the conditions of a flat capillary of 8.03 mm, a piston speed of 10 mm / min at 190 ° C., and a take-up acceleration of 400 m / min ² is 6 to This is a high-frequency coaxial cable composed of a polyolefin resin of 20 g.

  This will be described with reference to FIG. The high-frequency coaxial cable of the present invention is composed of an inner conductor 1 made of oxygen-free copper or the like and an insulator layer 2 provided thereon, and the insulator layer 2 is made of a foam layer 2a on the inner conductor 1 and a solid body. The outer layer 2b has a two-layer structure. As the inner conductor 1, one having a conductor diameter of about 0.5 to 15 mm is usually used. The foam layer 2a is selected from a mixture of high-density polyethylene and low-density polyethylene, or an olefin-based resin such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, or polypropylene. Furthermore, the outer layer 2b functions as a layer for suppressing gas when the foam layer 2a is foamed so as not to escape to the outside. In this way, by suppressing the foaming gas with the outer layer 2b having an appropriate melt breaking tension, the foaming degree of the insulator layer 2 can be made high. In addition, as a material of the outer layer 2b, various types of polyethylene and polypropylene are used alone, or a polyolefin-based material using a mixture thereof is used. Reference numeral 3 denotes an external conductor, which is usually formed of a thin plate such as copper, and a sheath (not shown) made of a plastic material is provided outside the external conductor.

  The polyolefin resin constituting the outer layer 2b preferably has a melt breaking tension of 6 to 20 g. This is because the foaming degree of the insulator layer 2 is kept high as described above. That is, when the melt breaking tension is less than 6 g, the strength at the time of melting to make the foaming degree of the insulator layer 2 high 78% or more is not sufficient, and when the melt breaking tension exceeds 20 g This is because the coating becomes too hard to swell during foaming and does not have a high foaming degree. Specific examples of the polyolefin resin having such a melt breaking tension include 2070 from Ube Industries, 6944NT from Nihon Unicar Co., Ltd., Hexex 539TE from Mitsui Chemicals, and ZM007 from Ube Industries as medium density polyethylene. Ube Industries, Ltd. B028 and Z463, Nippon Unicar Corporation 1253NT, etc. which are low density polyethylene are used individually or as a mixture.

  By forming the outer layer 2b having a high melt fracture tension as described above on the foam layer 2a, even if the foam layer 2a is expanded to form an insulating layer having a high foaming degree of 78% or more, formation of giant air bubbles In addition, the outer appearance of the insulator layer is not changed and the appearance is improved. Furthermore, a high-frequency coaxial cable with a small attenuation in a high-frequency band (1 GHz or more) can be obtained. And preferably, as described in claim 2, by using a high-frequency coaxial cable in which the outer layer made of the polyolefin-based resin has a thickness of 0.3 mm or less, as further described in claim 3. In addition, the polyolefin resin having a melt breaking tension of 6 to 20 g constituting the outer layer is a high density polyethylene, a medium density polyethylene, a low density polyethylene, or a polypropylene alone, or by making them a mixture, Is preferably a high-frequency coaxial cable using a polyolefin-based resin adjusted so as to be 6 to 20 g.

  That is, by setting the thickness of the outer layer 2b to 0.3 mm or less, this can provide an insulating layer with a high foaming degree and lower dielectric characteristics (dielectric constant and dielectric loss tangent) in a high frequency band (1 GHz or more). There is nothing. More preferably, it is about 0.05 to 0.2 mm. Also, as the polyolefin resin of the outer layer 2b, low density polyethylene, medium density polyethylene, high density polyethylene or polypropylene having a melt breaking tension of 6 to 20 g alone or a mixture of polyolefin resins having various melting breaking tensions. The melt breaking tension can be in the range of 6 to 20 g. The thus configured high-frequency coaxial cable becomes a layer that can sufficiently prevent gas release from the foam layer 2a during foaming, and can reliably form an insulating layer having a high foaming degree. In addition, this makes it possible to obtain a high-frequency coaxial cable that has a good external appearance without fluctuations in the outer diameter of the insulator layer 2 and has a small attenuation in the high-frequency band (1 GHz or more).

  Then, in order to obtain a high-frequency coaxial cable having a high foaming degree and a small attenuation in a high-frequency band (1 GHz or more), an insulating gas having a foaming degree of 78% or more by an inert gas as described in claim 4 It is better to have a body layer. As a result, it is possible to obtain an excellent high-frequency coaxial cable in which the outer layer fluctuation of the insulator layer is small and the attenuation in the high-frequency band (1 GHz or more) is small. That is, by foaming with an inert gas such as nitrogen gas, argon gas, Freon gas, carbon dioxide gas, and the like, when foamed with a chemical foaming agent, the foam residue has an adverse effect on the dielectric properties, and the foaming degree is low. Problems such as not enough are eliminated. In the foaming treatment, it is preferable to add a foam nucleating agent.

  Examples of such foam nucleating agents include fine powders of talc, boron nitride, silica, etc., fine powders of fluororesin such as polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymer, tetrafluoroethylene. -0.05-3 weight part of fine powders of fluorine-type rubbers, such as a propylene copolymer, are added with respect to 100 weight part of polyolefin resin. As a result, it is possible to obtain an insulator layer which has a high degree of foaming, uniform air bubbles, and a small increase in attenuation. Furthermore, for example, an antioxidant, a pigment, a lubricant, a processing aid and the like such as Irganox 1010 manufactured by Ciba Specialty Chemicals can be added to the insulator layer of the high-frequency coaxial cable of the present invention. The high-frequency coaxial cable having the insulator layer as described above is a high-frequency coaxial cable having a small attenuation in a high-frequency band (1 GHz or more) and excellent dielectric characteristics. Specifically, the attenuation at @ 2.2 GHz and 20D is 65 dB / km or less.

  The high-frequency coaxial cable described above is the high-frequency coaxial cable according to any one of claims 1 to 4 as described in claim 5, wherein the outer conductor 3 has a copper corrugated structure. In addition to having characteristics, sufficient flexibility can be imparted to the high-frequency coaxial cable. As this flexibility, it is possible to bend up to Φ200 mm. Further, corrugation processing of such corrugated irregularities may be formed by a usual method. For example, a corrugated shape is formed in a spiral shape using a copper thin plate, and flexibility (or flexibility) can be imparted even to a coaxial cable having a relatively large outer diameter. A sheath made of a plastic material is usually applied to the outside as a protective layer.

  The effects of the present invention were confirmed by the examples and comparative examples described in Table 1. A high-frequency coaxial cable having a two-layer structure composed of a foam layer and an outer layer shown in the table was produced, and the state of the outer layer was examined in order to observe the degree of foaming and the foamed state. The attenuation of the high-frequency coaxial cable was measured. First, the temperature of the first extruder of the two-stage extruder is adjusted to 180 to 220 ° C, and the temperature of the second extruder is adjusted to 140 to 180 ° C. Next, the dry blended pellet material is supplied to the first extruder, nitrogen gas is injected from the middle of the first extruder, melted and mixed, and after adjusting the temperature in the second extruder, the inside of the copper having an outer diameter of 9 mm is provided. While extruding onto the conductor, various polyolefin resin outer layer materials were simultaneously extruded and coated from another extruder, and foamed to produce a high-frequency coaxial cable having an outer diameter of the insulator layer of Φ22 mm. As the foam nucleating agent, talc fine powder (PKP-80) manufactured by Fuji Talc Kogyo Co., Ltd. was added. As a comparative example, a high-frequency coaxial cable having a crosslinked polyethylene outer layer crosslinked with a chemical crosslinking agent was also prepared.

  About these samples, the foaming degree (%) of the insulator layer (the foam layer and the outer layer is combined) is [(specific gravity of polyolefin resin−specific gravity after foaming) / (specific gravity of polyolefin resin)] × 100 Calculated. A foam having a foaming degree of 78% or more was regarded as acceptable. In addition, the outer conductor of the high-frequency coaxial cable was removed, and the state of whether or not the outer layer was torn was observed. The case where the outer layer is not torn is indicated by a circle, and the case where the tear is observed is indicated by an x. When the outer layer is broken, it is known that many large bubbles are generated in the foam layer. Furthermore, the attenuation amount (dB / km) of the insulator layer at 2.2 GHz was measured using a network analyzer. 65 dB / km or less was accepted. Table 1 shows the results.

  As is clear from Table 1, the high-frequency coaxial cables of the present invention described in Examples 1 to 7 have a highly foamed insulator layer with a foaming degree of 78% or more and an attenuation of 65 dB / km or less. It turns out that it is a thing. That is, as the polyolefin resin forming the outer layer, the melt breaking tension is in the range of 6 to 20 g, the coating thickness is 0.3 mm or less, and foaming with an inert gas does not cause the outer layer to break. , A high foam having a foaming degree of 78% or more can be obtained. A high-frequency coaxial cable having such an insulator layer is practical in a sufficiently high-frequency band (1 GHz or more) with little variation in the outer diameter of the dielectric layer and good appearance, and with an attenuation of 65 dB / km or less. It will be something like that.

  On the other hand, the high-frequency coaxial cable outside the scope of the present invention shown in Comparative Examples 1 to 4 has a problem in either the degree of foaming, the amount of attenuation, or the state of the outer layer. That is, when the melt breaking tension of the outer layer polyethylene resin is as small as 1 g as in Comparative Example 1, the degree of foaming is 74% and the attenuation is as large as 68 dB / km. Further, as in Comparative Example 4, when the melt fracture tension of the outer layer polyethylene resin is as large as 30 g, the foaming degree is not as high as 68%, and the attenuation is as large as 74 dB / km. Further, even when the melt breaking tension of the outer layer polyethylene resin is within the range of the present invention as in Comparative Examples 2 and 3, when the thickness is increased to 0.5 mm, the foaming degree is 72% and 69%, respectively. It is low and the attenuation is increased to 70 dB / km or more, which is not preferable.

  As described above, the high-frequency coaxial cable of the present invention is an insulator layer having a high foaming degree of 78% or more, and has a low attenuation in a high-frequency band (1 GHz or more) and excellent flexibility. Therefore, it can be used as a high-frequency coaxial cable for various applications.

It is a schematic sectional drawing of the high frequency coaxial cable of this invention.

Explanation of symbols

1 Inner conductor 2 Insulator layer 2a Foam layer 2b Outer layer 3 Outer conductor

Claims (5)

A high-frequency coaxial cable in which an insulating layer having a two-layer structure including a foam layer and an outer layer is formed on an inner conductor. The outer layer uses a flat capillary having an inner diameter of 2.095 mm and a length of 8.03 mm. It was composed of a polyolefin resin having a melt fracture tension measured using a capillary rheometer with a furnace body diameter of 9.55 mm under conditions of a piston speed of 10 mm / min and a take-up acceleration of 400 m / min ² at 6 ° C. High frequency coaxial cable characterized by   The high-frequency coaxial cable according to claim 1, wherein a thickness of the outer layer made of the polyolefin-based resin is 0.3 mm or less.   The polyolefin resin constituting the outer layer is at least one selected from high density polyethylene, medium density polyethylene, low density polyethylene, polypropylene alone, or a mixture thereof. High frequency coaxial cable.   The high-frequency coaxial cable according to any one of claims 1 to 3, wherein the insulating layer is formed by an inert gas so as to have a foaming degree of 78% or more.   5. The high frequency coaxial cable according to claim 1, wherein the outer conductor has a copper corrugated structure.

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