JP2008021585A - Foamed coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed coaxial cable applied with an outer skin layer (covered layer) having a collapse prevention function or the like in the outer periphery of a foamed insulator of a cable. <P>SOLUTION: In the foamed coaxial cable having the foamed insulator 2 coaxially covered on a conductor of which the extent of foaming is 80% or more, this is the foamed coaxial cable in which as the skin layer 5b, the covered layer of a polyolefin based resin having fracture tension in fusion of 6.0 to 20.0 g (190°C), MFRO of 0.4 g/10 min (190°C, 2.16 Kgf) or more, and type D durometer hardness of 55 or more is installed at the outer periphery, and improvement in collapse resistance can be obtained by this outer skin layer 5b. Moreover, by the confinement effect of gas in foaming, higher foaming and excellent cable appearance can be obtained, and improvement in VSWR or the like can be achieved. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a foamed coaxial cable in which an outer skin layer (coating layer) having a function of preventing crushing is provided on the outer periphery of a foamed insulation of a cable.

In recent years, high-frequency coaxial cables have used frequencies in the GHz order. In the GHz band, a coaxial cable having a smaller attenuation amount (dielectric characteristics such as tan δ) than that in the low frequency band is required, and therefore, an insulator covering the inner conductor (center conductor) is foamed. (Patent Documents 1 and 2).
Japanese Patent No. 3227091 Japanese Patent No. 2668198

  In such a foamed coaxial cable, it is possible to improve the mechanical properties such as crushability of the foamed insulator by miniaturizing the foam cell (bubble core), and excellent VSWR (Voltage Standing Wave Ratio). Further, it is known that cable production is stable and can be formed into a long shape.

  On the other hand, the foamed coaxial cable has a structure in which a foamed insulator such as polyethylene is coated directly on the inner conductor. Therefore, depending on the use in a high temperature environment, the insulator may be damaged by contact with the conductor (usually copper). It is known that deterioration such as receiving (copper damage) and molecular cutting of the resin is induced and the attenuation is deteriorated.

  In addition, a small amount of chemical foaming agents such as azodicarbonamide (ADCA) and 4,4′-oxybis (benzenesulfonylhydrazide) (OBSH) are added to the base resin for foaming such as polyethylene so far. It has been found that fine foam cells can be obtained.

  However, when such a chemical foaming agent is used as a nucleating agent that becomes the core of the foam cell, the foaming agent is thermally decomposed to generate a foaming gas, and at the same time, side reactions generally occur. Occurs and by-products such as decomposition residues are produced. Due to the water absorption effect of this by-product, it is known that even if the addition amount is small, the attenuation amount is adversely affected.

  Also, when trying to use the cable in a high temperature environment, copper damage is likely to occur as described above, so it is also possible to add an antioxidant, a metal deactivator of copper damage inhibitor, etc. as an anti-degradation agent. However, even in these additives, there is a concern that the amount of attenuation may be deteriorated by adding a large amount.

  Furthermore, it is said that fine foam cells can be obtained by adding polytetrafluoroethylene (PTFE) powder or boron nitride powder. However, boron nitride powder is expensive and has practical problems. In this case, there was a problem that the miniaturization was insufficient. Of course, even when these powders are used, when the cable is used in a high temperature environment, it is necessary to separately add the above-described antioxidant and copper damage inhibitor as a deterioration preventing agent.

Under such circumstances, the present inventor conducted various tests and found that the copper damage preventive agent was used without using the above chemical foaming agent such as ADCA, PTFE powder, boron nitride powder or the like. The present inventors have found and proposed that the above-described metal deactivator can be sufficiently miniaturized by appropriately adding the metal deactivator (Cited Document 3).
More specifically, the metal deactivator used is a triazole-based one such as 3- (N-salicyloyl) amino-1,2,4-triazole, or 2 ′, 3-bis [3- [3 Hydrazide series such as, 5-di-tert-butyl-4-hydroxyphenyl] propionyl] propionohydrazide was found to be good. In other words, the metal deactivator functions as a nucleating agent, and the foam cell can be made finer. Also, since the metal deactivator itself is a copper damage preventive agent, it is possible to prevent the foam insulation from being deteriorated. I found that there was. Furthermore, it has also been found that better results can be obtained if an antioxidant is used in combination.
Japanese Patent Application No. 2005-236290

  However, when the present inventor continued to test and research, when a polyolefin-based resin, particularly an ethylene-propylene copolymer-based resin having specific characteristics described later was used as the base resin, higher foaming (foaming degree of 80 It was found that a foaming resin composition having excellent electrical characteristics can be obtained. For example, when this foaming resin composition was extruded as a foam insulation of a coaxial cable, an excellent VSWR was obtained. It was also found that stable long objects can be formed (Cited Document 4).

Further, in a foaming resin composition based on this polyolefin resin, particularly an ethylene propylene copolymer resin, in a normal resin molding, a molding machine such as an extruder is used, and its molding temperature (resin temperature in the molding machine). ) Was set to about 140 to 230 ° C., but the present inventor studied the molding temperature in consideration of the melting point of the metal deactivator to be used. It has been found that a better result can be obtained when the temperature is set above the moldable temperature of the resin composition and below the melting point of the metal deactivator.
Japanese Patent Application No. 2006-065340

  After that, when the present inventor further tested and researched, it was found that when the foaming degree of the foamed coaxial cable is increased, the cable tends to be extremely easily crushed. For example, a corrugated outer conductor such as a tube or an entrainment has an appropriate strength, so that it is difficult to be crushed, but in the case of an outer conductor made of a metal braid, since the self-shape holding force is small, an external lateral pressure is applied. Upon receipt, it was found that the metal braid of the outer conductor, the foamed insulator inside, the sheath of the exterior, etc. are likely to be crushed. For this reason, it was necessary to take measures to prevent side pressure as much as possible during use and manufacturing. Further, even if the corrugated type outer conductor is used, it may be crushed before the corrugated coating during the production winding, so that it is necessary to avoid the side pressure as much as possible.

Therefore, the present inventor can prevent crushing and the like even with a high-foaming insulator by applying an outer skin layer (coating layer) having excellent melting characteristics and high surface hardness to the outer periphery of the foamed insulating material. Invented that it can be done, and found that good results were obtained when the test described later was conducted.
Incidentally, the outer skin layer is also disclosed in the above-mentioned existing application as being provided as needed together with the inner skin layer. In particular, when there is an outer skin layer, the effect of confining gas during foaming can be expected, so that higher foaming can be obtained, a good cable appearance (surface) can be obtained, and VSWR can be improved. There is also an effect.

The present invention has been made based on the idea of such an outer skin layer, and provides a foamed coaxial cable in which an outer skin layer (coating layer) having a function of preventing crushing is applied to the outer periphery of a foamed insulator having a high foaming degree. Is.

  The present invention according to claim 1 is a foamed coaxial cable having a foamed insulator coated coaxially on a conductor having a foaming degree of 80% or more. -20.0 g (190 ° C), MFR 0.4 g / 10 min (190 ° C, 2.16 Kgf) or more and a foamed coaxial cable provided with a polyolefin resin coating layer having a type D durometer hardness of 55 or more It is in.

  The present invention according to claim 2 is the foamed coaxial cable according to claim 1, wherein the type D durometer hardness is 60 or more.

  The invention according to claim 3 is characterized in that the foamed insulator on the conductor is a foaming resin composition comprising a heat-meltable resin and a metal deactivator as a nucleating agent. Or it exists in the foaming coaxial cable of 2 description.

  According to a fourth aspect of the present invention, the foamed insulator is the heat-meltable resin, and has a breaking tension of 5.0 g or more (190 ° C.) when melted, MFR 1.0 g / 10 min (190 ° C., 2.16 Kgf) It consists of a resin composition for foaming formed by adding 0.01 to 1.0 part by mass of a metal deactivator as a nucleating agent for foaming with respect to 100 parts by mass of the base resin of polyolefin resin as described above. The foamed coaxial cable according to claim 3.

  According to a fifth aspect of the present invention, in the foamed coaxial cable according to the first, second, third, or fourth aspect, the outer conductor covered with the foamed insulator is made of a metal braid.

  The invention according to claim 6 is characterized in that the polyolefin resin of the skin layer is an ethylene propylene copolymer resin, polypropylene, polyethylene, or a mixture thereof. 5. Foamed coaxial cable according to item 5.

  The foamed coaxial cable according to claim 7, wherein an inner skin layer is coated between the conductor and the foamed insulator.

  The present invention according to claim 8 is characterized in that the foamed insulator uses the foaming resin composition, the molding temperature of the molding machine during foaming is equal to or higher than the moldable temperature of the foaming resin composition, and the metal. 8. The foamed coaxial cable according to claim 3, wherein the foamed coaxial cable is foam-molded at a melting point or less of an inert agent.

  According to the foamed coaxial cable of the present invention, in a foamed coaxial cable having a foamed insulator coated coaxially on a conductor having a foaming degree of 80% or more, a breaking tension at melting 6.0 as a skin layer on the outer periphery. ˜20.0 g (190 ° C.), MFR 0.4 g / 10 min (190 ° C., 2.16 Kgf) or more, and a coating layer of polyolefin resin having a type D durometer hardness of 55 or more is provided. Depending on the characteristics, crushing due to the side pressure of the cable can be improved. That is, improvement in crush resistance can be obtained. Of course, it is possible to further improve the foaming due to the gas confinement effect at the time of foaming, improve the cable appearance, and improve the VSWR.

  This improvement in crush resistance is particularly effective when the outer conductor is a metal braid. In addition, the improvement in the crush resistance can result in the production of a coaxial cable having a foamed insulator with a higher foaming degree, so that a lower attenuation of the cable can be realized. In addition, because of improved crushing resistance against side pressure, there is no need to take special measures during production or use (no special production equipment, equipment used, etc.), and the same measures as before can be used. . Furthermore, an inner skin layer can be provided together with the outer skin layer.

  Further, when a foamable resin composition comprising a heat-meltable resin and a metal deactivator as a nucleating agent is used as the foam insulator, for example, a breaking tension at the time of melting of 5.0 g or more (190 ° C.), Addition of 0.01 to 1.0 parts by mass of a metal deactivator as a nucleating agent during foaming with respect to 100 parts by mass of a polyolefin resin base resin having an MFR of 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more When a foamed resin composition is used, a finer foam with a high foaming degree is obtained. That is, an excellent foamed coaxial cable can be obtained by the combination with the outer skin layer.

  Further, when the foaming resin composition is used, when the molding temperature of the molding machine at the time of foaming is not less than the moldable temperature of the foaming resin composition and not more than the melting point of the metal inert agent, Therefore, it is possible to further reduce the size and increase the degree of foaming (foaming degree is about 80% to about 90%), and a more excellent foamed coaxial cable can be obtained.

  In the foamed coaxial cable of the present invention, the base resin used in the foaming resin composition that forms the foamed insulator coated on the conductor (inner conductor) is not particularly limited, but is preferably a resin that can be hot melt molded, Polyolefin resin such as ethylene propylene copolymer having a breaking tension at melting of 5.0 g or more (190 ° C.) and MFR (melt flow ratio) of 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more. System resin shall be used. As long as this resin has the said characteristic, it may be used independently or may be used in mixture of multiple types.

Here, with respect to the property of breaking tension at the time of melting of 5.0 g or more (190 ° C.), more specifically, a capillary rheometer with a capillary of φ2.095 × 8.03 mm is used at 190 ° C., and the piston speed is 10 mm / min. It is a value measured under a furnace body diameter: 9.55 mm and a take-up acceleration of 400 m / min ² . This is because if the breaking tension at the time of melting is less than 5.0 g, the breaking tension is insufficient, so that open cells tend to be generated during foaming and a high foaming degree cannot be obtained. The reason why the MFR is set to 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more is that when the MFR is less than 1.0 g / 10 min, the elongation at the time of melting is insufficient and a high foaming degree cannot be obtained.

  FB3312 (Nippon Polypro Co., Ltd., density 0.9, breaking tension at melting 10 g, MFR 2.0 g / 10 min) can be mentioned as a single commercial product of an ethylene propylene copolymer-based resin that satisfies these conditions. Although these conditions cannot be satisfied alone, for example, as a commercial product of an ethylene propylene copolymer-based resin that satisfies the conditions by mixing with FB3312, J703W (Mitsui Chemicals, density 0.91, when melted) And B101WAT (manufactured by Mitsui Chemicals, density 0.91, breaking tension at melting 10 g, MFR 0.4 g / 10 min). The ratio at the time of mixing shall be performed within the range which can satisfy | fill the conditions of the above-mentioned breaking tension at the time of melting and MFR.

  In addition, the base resin of the ethylene-propylene copolymer-based resin may be used in an appropriate amount as necessary, for example, in order to improve cold resistance and buckling property during bending, as long as the breaking tension and MFR of the above characteristics are not lost. The polyethylene resin can be mixed. As this resin, it is preferable to use high density polyethylene (HDPE) or low density polyethylene (LDPE). These can be used alone or as a mixture. As these commercial products, Hizex 1300J (HDPE, manufactured by Mitsui Chemicals), 2070 (HDPE, manufactured by Ube Maruzen Polyethylene), C180 (LDPE, manufactured by Ube Maruzen Polyethylene), B028 (LDPE, manufactured by Ube Maruzen Polyethylene) Etc.

  Furthermore, as polyolefin-based resins other than ethylene-propylene copolymer-based resins, polyethylene (PE), polypropylene (PP), etc., adjusted to the above-mentioned breaking tension and MFR by blending with other resins and additives, etc. Can be mentioned. Particularly in the case of polyethylene, it is preferable to use high density polyethylene (HDPE) or low density polyethylene (LDPE). These may be used alone or in combination. It is also possible to use polyethylene and polypropylene as a mixture.

  In addition, as described above, the metal deactivator used in the present invention functions as a nucleating agent, and the addition of the metal deactivator can make the foam cell finer. Examples of the metal deactivator include triazole type or hydrazide type. Specifically, 3- (N-salicyloyl) amino-1,2,4-triazole is used as the triazole type, and 2 ′, 3-bis [3- [3,5-di-tert-butyl is used as the hydrazide type. The use of -4-hydroxyphenyl] propionyl] propionohydrazide is preferred. Since these metal deactivators usually have a function as a copper damage preventing agent, the addition of the metal deactivator also provides a copper damage preventing function in a cable or the like.

  The addition amount of this metal deactivator shall be 0.01-1.0 mass part with respect to 100 mass parts of base resins. The reason is that if it is less than 0.01 part by mass, a sufficient function and effect as a nucleating agent cannot be obtained. On the contrary, the upper limit of 1.0 part by mass is that even if an amount exceeding this is added, the particle diameter of the foamed cell does not change, the amount of attenuation increases as the amount added increases, and the cost increases. This is because a problem such as becomes. However, a more desirable addition amount is 0.1 to 0.7 parts by mass.

In this resin composition, an antioxidant is preferably added together with the metal deactivator. Although this antioxidant is not specifically limited, For example, the following can be mentioned. (1) In the monophenol type, 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-α-dimethylamino-p-cresol, 2,4,6-tri-tert-butylphenol, ortho-tert-butylphenol, etc.
(2) 2,2'methylene-bis- (4-methyl-6-tert-butylphenol), 2,2'methylene-bis- (4-ethyl-6-tert-butylphenol) for bis, tris and polyphenols ), 4,4′methylene-bis- (2,6-di-tert-butylphenol), 4,4′butylidene-bis-((4-methyl-6-tert-butylphenol), alkylated bisphenol, 1 , 3,5-trimethyl-2,4,6-tris (3,5-di-tert-4-hydroxybenzyl) benzene, etc.
(3) For hindered phenols, tetraxy- [methylene-3- (3 ′, 5′-di-tert-butyl-4-hydroxyphenyl) propionate] methane, n-octadecyl-3 (4′-hydroxy-3) ', 5'-di-tert-butylphenyl) propionate, hindered phenol, hinderbist phenol, etc.
(4) In the thiobisphenol series, 4,4′thiobis- (6-tert-butyl-3-methylphenol), 4,4′thiobis- (6-tert-butyl-o-cresol), bis (3 5-di-tert-butyl-4-hydroxybenzyl) sulfide, dialkyl phenol sulfide, etc.
(5) N, N′-di-2-naphthyl-p-phenylenediamine etc.
(6) Phosphorus-based tris (nonylphenol) phosphie, tris (mixture- and di-nonylphenol) phosphite,
(7) Others, dilauryl thiodibropionate, distearyl thiodibropionate, distearyl-β, β-thiobutyrate, lauryl stearyl thiodibropionate, dimyristyl-3,3′-thiodi With bropionate, ditridecyl-3,3′-thiodibropionate, sulfur-containing ester compound, amyl-thioglycolate, 1,1′-thiobis (2-naphthol), 2-mercaptobenzimidazole, hydrazine derivative, etc. These may be used alone or in combination in various forms.

  And the addition amount shall be 0.01-1.0 mass part with respect to 100 mass parts of base resins. The reason is that if the amount is less than 0.01 parts by mass, a sufficient addition effect, that is, an effect of improving heat aging characteristics cannot be obtained. This is because the adverse effect of an increase in attenuation increases as the amount increases.

  For the present resin composition, if necessary, other additives such as crosslinking aids, dispersants, inorganic fillers, and other nucleating agents such as ADCA and OBSH are decomposed. For example, an appropriate amount of talc, BN, fluororesin, azodicarbonamide, clay, or the like can be used in combination as a residue free from harmful effects.

  In the foamed coaxial cable of the present invention in which a foaming resin composition having such a composition is coated on a conductor as a foamed insulator, an outer skin layer having the following characteristics is provided on the outer periphery of the foamed insulator. And As the base resin for the outer skin layer, breaking tension at melting 6.0 to 20.0 g (190 ° C.), MFR 0.4 g / 10 min (190 ° C., 2.16 Kgf) or more, Type D durometer hardness 55 or more, More preferably, a polyolefin resin of 60 or more is used.

Here, as for the characteristic of breaking tension 6.0 to 20.0 g (190 ° C.) at the time of melting, as in the case described above, more specifically, a capillary of φ2.095 × 8.03 mm at 190 ° C. with a capillary rheometer. Is a value measured under a piston speed of 10 mm / min, a furnace body diameter: 9.55 mm, and a take-up acceleration of 400 m / min ² . The reason why the breaking tension at the time of melting is 6.0 to 20.0 g is that if it is less than 6.0 g, the breaking tension is insufficient. If it exceeds 0 g, it is difficult to swell and it becomes difficult to obtain a high degree of foaming. The reason why the MFR is set to 0.4 g / 10 min (190 ° C., 2.16 Kgf) or more is that when the MFR is less than 1.0 g / 10 min, the elongation at the time of melting is insufficient, and a high foaming degree cannot be obtained. Furthermore, the type D durometer hardness (Shore D, JIS-K7215) is 55 or more. If the hardness is less than 55, the surface hardness is too small, and the crushing prevention function on the foamed insulator side or the like is sufficient. It is because it is obtained. Since this crush resistance depends on the hardness of the outer skin layer, it is more preferably 60 or higher.

  Examples of the polyolefin resin having such characteristics include ethylene propylene copolymer resin, polypropylene, polyethylene, or a mixture thereof. For example, as a single commercial product of ethylene propylene copolymer-based resin, (1) FB3312 (manufactured by Nippon Polypro Co., Ltd., density 0.9, breaking tension at melting 10 g, MFR 2.0 g / 10 min, surface hardness 70), Although the above-mentioned characteristics cannot be satisfied alone, for example, (2) J703W (manufactured by Mitsui Chemicals, density 0) is available as a commercially available ethylene-propylene copolymer-based resin that satisfies the conditions by mixing with FB3312 or the like. .91, breaking tension at melting 2 g, MFR 3.0 g / 10 min, surface hardness 69). The base resin of these ethylene-propylene copolymer-based resins may be used in an appropriate amount as necessary, for example, in order to improve cold resistance and buckling properties when folded, as long as the above-mentioned breaking tension and MFR are not lost. The polyethylene resin can be mixed.

  Examples of polypropylene include VP103 (manufactured by Mitsui Chemicals, density 0.9, breaking tension at melting 10 g, MFR 2.0 g / 10 min, surface hardness 73).

  Examples of polyethylene include, for example, (1) DGDN3364 (manufactured by Nihon Unicar Company, medium density PE, density 0.945, breaking tension 6.0 g at melting, MFR 0.8 g / 10 min, surface hardness 58) and the like. be able to. In the case of a blended mixture, for example, the above DGDN3364, (2) Hizex5305E (Mitsui Chemicals, high density PE, density 0.951, breaking tension at melting 5 g, MFR 0.8 g / 10 min, surface hardness 62) (3) Hizex5000SR (Mitsui Chemicals, high density PE, density 0.955, breaking tension at melting 7 g, MFR 0.37 g / 10 min, surface hardness 64), (4) Hizex5100B (Mitsui Chemicals, high density) PE, density 0.944, breaking tension at melting 8 g, MFR 0.27 g / 10 min, surface hardness 61), (5) 2070 (manufactured by Ube Maruzen Polyethylene Co., Ltd., high density PE, density 0.962, breaking tension at melting) 0.6 g, MFR 8.0 g / 10 min, surface hardness 66), (6) Z463 (manufactured by Ube Maruzen Polyethylene, low Degrees PE, density 0.918, mixed fracture tension 7.0g upon melting, MFR3.0g / 10min, surface hardness 52) or the like as appropriate, may be mentioned those to satisfy the above characteristics.

  If necessary, these polyolefin-based resins can be added with the above-mentioned antioxidant and a metal deactivator for obtaining the original copper damage prevention effect. And in the case of the outer skin layer which consists of these polyolefin resin, the thickness is desirable about 20-50 micrometers. If the thickness is less than 20 μm, the processing (coating) itself becomes difficult because it is too thin, and the desired crush resistance cannot be improved. On the other hand, when the thickness exceeds about 50 μm and becomes too thick, the foaming degree of the foamed layer becomes larger than the limit, and the foaming is continuously connected to the foamed foam, so that the foaming degree of the entire foamed insulator may be lowered. Because.

  The coating of the outer skin layer can be carried out independently, but is preferably coextruded with the foamed insulator. In the case of this simultaneous extrusion, there are no irregularities in appearance, VSWR is improved, prevention of outgassing is obtained, and a higher foaming degree is obtained.

  In addition to the outer skin layer, an inner skin layer may be provided between the inner conductor and the foamed insulator as necessary. As the material for the inner skin layer, polyethylene (for example, low density polyethylene) is usually used. When the inner skin layer is provided, the adhesion between the inner conductor and the foamed insulation is improved, the pull-out force can be improved, copper damage is less likely to occur, long lengths are easier to form, and stable cable Manufacture is possible. The inner skin layer can be used alone or by coextrusion with the foamed insulator and the outer skin layer. The thickness of the inner skin layer is preferably about 20 to 50 μm.

  In the foamed coaxial cable of the present invention, the foaming resin composition is extruded and foamed by injecting a desired foaming agent into a molding apparatus such as an extruder. As this foaming agent, a physical foaming agent or a chemical foaming agent can be mentioned, for example. Here, as the physical foaming agent, for example, a gas foaming agent of an inert gas such as nitrogen gas, argon gas, alternative chlorofluorocarbon gas or carbon dioxide gas can be used. In addition, a supercritical fluid (SCF: Super Critical Fluid) can be used as the physical foaming agent. As the chemical foaming agent, azodicarbonamide, 4,4'-oxybis (benzenesulfonylhydrazide), N, N'-dinitrosopentamethylenetetramine and the like can be used. Mixtures of these can also be used. Furthermore, a physical foaming agent and a chemical foaming agent can be used in combination as appropriate.

  FIG. 1 shows an example of a foamed coaxial cable according to the present invention. In the figure, 1 is an internal conductor such as a stranded wire conductor, 2 is a foamed insulator coated on the conductor 1 by extrusion molding, and 3 is a metal braid or corrugated copper. Metal layer (outer conductor) made of a pipe or the like, 4 is a sheath made of polyethylene or the like, 5a is applied if necessary, an inner skin layer having a thickness of about 50 μm, and 5b is a thickness of 50 μm applied to the outer periphery of the foam insulator 2 The outer skin layer of the degree. The outer diameter of the cable is not particularly limited, but is formed as about 3 to 50 mm. In addition, an aluminum tape etc. can also be put between the insulator 2 and the metal layer 3 as needed.

  Here, as the base resin of the outer skin layer, as described above, the breaking tension at melting is 5.0 to 20.0 g (190 ° C.), MFR 0.4 g / 10 min (190 ° C., 2.16 Kgf) or more, type A polyolefin resin having a D durometer hardness of 55 or more is used. When this outer skin layer is provided, the appearance of the cable is improved and the gas confinement effect at the time of foaming can be obtained, so that a higher degree of foaming can be obtained and a low attenuation can be achieved.

  In addition, when the inner skin layer is provided, as described above, the adhesion between the inner conductor and the foamed insulator is improved, the pulling force can be improved, copper damage is less likely to occur, and a long length is formed. This makes it easier to manufacture a stable cable. As the resin for the inner skin layer, it is possible to use an ethylene-propylene copolymer resin or polypropylene, but from the viewpoint of electrical characteristics and copper damage deterioration characteristics, it is desirable to use polyethylene.

  FIG. 2 shows an example of an extrusion apparatus system for producing the foamed coaxial cable according to the present invention. 10 is a first extruder, 11 is a resin supply port of the first extruder, 12 is a crosshead of the first extruder, 20 is a cooling unit, and 30 is a gas foaming agent supply unit (physical foaming agent) to the first extruder (Supply unit) 40 is a second extruder for the inner skin layer.

  In this extrusion apparatus system, first, from a resin supply port 11 of the first extruder 10, a base resin pellet and a master batch composed of a nucleating agent, a metal deactivator, an antioxidant, a necessary additive, and the like. The dry conductor is supplied after being dry blended, and the foamed insulator is coated on the inner conductor 1 by the cross head 12. Before this, the inner skin layer 5a such as low density polyethylene is preferably coated on the inner conductor 1 by the second extruder 40 for inner skin layer. Here, the extrusion temperature of the first extruder 10 is set as a temperature such as 225 ° C. so as to be equal to or lower than the melting point of the metal deactivator used. The extrusion temperature of the second extruder is set to about 140 to 200 ° C. Nitrogen gas or the like is supplied as a foaming agent from the gas foaming agent supply unit 30 to the first extruder 10. Thereby, as above-mentioned, a metal deactivator functions as a nucleating agent and a foaming cell is refined | miniaturized. Further, the degree of foaming is increased by the ethylene-propylene copolymer-based resin used as the base resin. The first extruder 10 may have a two-stage extruder structure in which another kneading extruder having a resin supply port and a gas foaming agent supply unit is connected.

  The foamed insulation covered with the cross head 12 of the first extruder 10 is cooled by the cooling unit 20. At this time, preferably, an extruding portion of a third extruder (not shown) is incorporated into, for example, the cross head 12, and the outer skin layer 5b described above is covered on the outer periphery of the foamed insulator. The extrusion temperature of the third extruder is set to about 140 to 200 ° C. Thereafter, the above-described foamed coaxial cable is obtained by applying necessary external conductors and sheaths.

  These extrusion moldings can be performed by a normal extruder and can be performed with good productivity. The extrusion method may be performed in tandem (sequentially) for each coating layer, or may be simultaneous extrusion. Further, the extrusion temperature in each extruder is the actually measured resin temperature, and as described above, the extrusion temperature is higher than the moldable temperature of the foaming resin composition and lower than the melting point of the metal deactivator. . In particular, in the 1st extruder 10 which is a main extruder for foam insulation, the temperature of a cylinder part is set to the highest temperature (extruder highest temperature). As the blowing agent, in addition to nitrogen gas, as described above, for example, a gas blowing agent of an inert gas such as argon gas, alternative chlorofluorocarbon gas, carbon dioxide gas, supercritical fluid, or the like can be used. In addition, as described above, the chemical foaming agent has a problem of generation of decomposition residues, but it can be added in an extremely small amount and can be used in combination with the gas foaming. As such a chemical foaming agent, as described above, azodicarbonamide, 4,4′oxybis (benzenesulfonylhydrazide), N, N′-dinitrosopentamethylenetetramine and the like can be used.

<Examples and comparative examples>
First, a foamed coaxial cable having substantially the same structure as that of FIG. 1 and having a foamed insulator and an outer skin layer (thickness: 50 μm) having the composition shown in Tables 1 to 6 was produced as a sample cable (Examples 1 to 12, Comparative Examples 1 to 8, except that the comparative row 7 has a structure without an outer skin layer). A 50 μm thick inner skin layer (manufactured by Ube Maruzen Polyethylene Co., Ltd., low density PE, C460: trade name) was provided. Each sample cable was manufactured under the above-described temperature setting by the extrusion apparatus system shown in FIG.
The outer diameter of the inner conductor of the obtained cable is 9 mm, the outer diameter of the foamed insulator is 22 mm, and the outer diameter of the entire cable (after sheath coating) is 28 mm. More specifically, after covering the foamed insulator by gas foaming with nitrogen gas, an outer conductor of a metal braid and a polyethylene sheath were applied.

In addition, as the base resin for the foamed insulator and the base resin for the outer skin layer, the following resins were used alone or in a blended manner.
1: FB3312 [manufactured by Nippon Polypro Co., Ltd., ethylene propylene copolymer, density 0.9, breaking tension at melting 10 g (190 ° C.), MFR (190 ° C.) 2.0 g / 10 min]
2: J703W [Mitsui Chemicals Co., Ltd., ethylene propylene copolymer, density 0.91, breaking tension at melting 2 g (190 ° C.), MFR (190 ° C.) 3.0 g / 10 min]
3: B101WAT [Mitsui Chemicals, ethylene propylene copolymer, density 0.91, breaking tension at melting 10 g (190 ° C.), MFR (190 ° C.) 0.4 g / 10 min]
4: VP103 (manufactured by Mitsui Chemicals, PP, density 0.9, breaking tension at melting (190 ° C.) 10 g, MFR (190 ° C.) 2.0 g / 10 min, surface hardness 73)
5: Hizex 5305E (Mitsui Chemicals, high density PE, density 0.951, breaking tension at melting (190 ° C.) 5 g, MFR (190 ° C.) 0.8 g / 10 min, surface hardness 62)
6: Hizex 5000SR (Mitsui Chemicals, high density PE, density 0.955, breaking tension at melting (190 ° C.) 7 g, MFR (190 ° C.) 0.37 g / 10 min, surface hardness 64)
7: 2070 (manufactured by Ube Maruzen Polyethylene Co., Ltd., high density PE, density 0.962, breaking tension at melting (190 ° C.) 0.6 g, MFR (190 ° C.) 8.0 g / 10 min, surface hardness 66)
8: DGDN3364 (manufactured by Nippon Unicar Co., Ltd., medium density PE, density 0.945, breaking tension at melting (190 ° C.) 6.0 g, MFR (190 ° C.) 0.8 g / 10 min, surface hardness 58)
9: Z463 (manufactured by Ube Maruzen Polyethylene Co., Ltd., low density PE, density 0.918, breaking tension at melting (190 ° C.) 7.0 g, MFR (190 ° C.) 3.0 g / 10 min, surface hardness 52)
10: R300 (manufactured by Ube Maruzen Polyethylene, low density PE, density 0.920, breaking tension at melting (190 ° C.) 20.0 g, MFR (190 ° C.) 0.4 g / 10 min, surface hardness 52)
11: Hizex 5100B [Mitsui Chemicals, high density PE, density 0.944, breaking tension at melting 8 g (190 ° C.), MFR (190 ° C.) 0.27 / 10 min, surface hardness 61

12: Blend 1 (mixture of Hizex 5305E and Hizex 5100B, mixing ratio 60:40, density 0.952, breaking tension at melting 6.0 g, MFR 0.6 g / 10 min, surface hardness 62)
13: Blend 2 (mixture of DGDN3364 and Z463, mixing ratio 70:30, density 0.937, breaking tension at melting 6.0 g, MFR 1.2 g / 10 min, surface hardness 55)
14: Blend 3 (mixture of DGDN3364 and Z463, mixing ratio 50:50, density 0.932, breaking tension at melting 6.0 g, MFR 1.4 g / 10 min, surface hardness 54)
15: Blend 4 (mixture of 2070 and Hizex5000SR, mixing ratio 20:80, density 0.957, breaking tension at melting 5.0 g, MFR 4.0 g / 10 min, surface hardness 64)
16: Blend 5 (mixture of FB3312 and J703W, mixing ratio 50:50, density 0.91, breaking tension at melting 6.0 g, MFR 2.3 g / 10 min, surface hardness 70)
17: Blend 6 (mixture of FB3312 and J703W, mixing ratio 35:65, density 0.91, breaking tension at melting 4.0 g, MFR 2.8 g / 10 min, surface hardness 70)
18: Blend 7 (mixture of FB3312 and J703W, mixing ratio 40:60, density 0.91, breaking tension at melting 5.0 g, MFR 2.4 g / 10 min, surface hardness 70)
19: Blend 8 (mixture of FB3312 and B101WAT, mixing ratio 55:45, density 0.90, breaking tension at melting 10.0 g, MFR 1.0 g / 10 min, surface hardness 70) 20: Blend 9 (of FB3312 and B101WAT Mixture, mixing ratio 50:50, density 0.91, breaking tension at melting 10.0 g, MFR 0.9 g / 10 min, surface hardness 70) 21: Cross-linked PE (R300 cross-linked with DCP 0.05 wt%, density) 0.92, melting breaking tension (190 ° C.) 25.0 g, MFR (190 ° C.) 0.2 g / 10 min, surface hardness 55)

  Further, the metal deactivator & nucleating agent (combining nucleating agent) is CDA-1M (manufactured by Asahi Denka Kogyo Co., Ltd., triazole type = 3- (N-salicyloyl) amino-1,2,4-triazole, during processing Volatile and dispersible, melting point: 220 ° C.), nucleating agent is KTL-500F (Kitamura Co., Ltd., PTFE powder). In addition, the compounding numerical value in a table | surface shows a mass part.

  About each sample cable, the characteristic test as shown in Table 3 and Table 6 was performed, and the characteristic [foaming degree, foaming magnification, attenuation, average foamed cell diameter, crush resistance, appearance, VSWR, cost] was obtained. .

<Foaming degree test>
The foam insulation of the sample cable was taken out, and the foaming degree was determined by the formula: foaming degree = (1-specific gravity after foaming / specific gravity before foaming) × 100. Here, a foaming degree of 80% or more is an acceptable level.

<Foaming ratio test>
The foam insulation of the sample cable was taken out, and the foaming ratio was determined by the formula: foaming ratio = 1 / (100−foaming degree) × 100. Here, an expansion ratio of 5.0 or more is an acceptable level.

<Attenuation test>
The attenuation amount under 2.2 GHz was calculated for the sample cable using a network analyzer (manufactured by Agilent Technologies, 8722ES). Here, the pass level is less than 64 dB / Km.

<Average foamed cell diameter test>
The foam insulation section of the sample cable was observed, and the average of “(long cell diameter + short cell diameter) / 2” of 100 cells randomly selected was defined as the average foam cell diameter (mm). . Here, less than 0.25 mm is an acceptable level.

<Crush resistance test>
Using a sample cable, the deformation ratio at 23 ° C. of the outer diameter of the foamed insulator with the inner conductor when a load of 3 kgf was applied as a side pressure to the insulator portion 1 cm was determined and determined. Here, deformation rate (%) = 100 − [(insulator outer diameter after test−inner conductor diameter) / (insulator outer diameter before test−inner conductor diameter) × 100]. A case where the deformation rate is less than 4% is indicated by “◎”, a case where the deformation rate is 4% to less than 6% is indicated by “◯”, and a case where the deformation rate is 6% to less than 8% is indicated by “△”. The case of 8% or more is indicated by “x”.

<Appearance test>
The surface of the sample cable was visually observed. Then, the cable surface was smooth and smooth (accepted product) with “◯” and the surface with irregularities in part (failed product) was indicated with “△”.

<VSWR test>
The sample cable was measured using a network analyzer (manufactured by Agilent Technologies, 8722ES). This measured value becomes smaller as the bubbles are finer and uniform. Here, less than 1.2 is an acceptable level, and the closer to 1.0, the better.

<Cost test>
Evaluation was made according to the additive used. A case where the cost is low is indicated by “◯”, and a case where the cost is high is indicated by “X”.

  As apparent from Tables 1 to 6 above, in the case of the foamed coaxial cable of the present invention (Examples 1 to 12), it can be seen that all the characteristics are good.

On the other hand, in the case of the foamed coaxial cable lacking the conditions of the present invention (Comparative Examples 1 to 8), it can be seen that there is a problem in any point.
In Comparative Example 1, the surface hardness of the outer skin layer is small (54), and it can be seen that the crush resistance is not good. In Comparative Example 2, since the breaking tension at the time of melting is small (5 g), and in Comparative Example 3, the MFR is small (0.37 g / 10 min), it can be seen that there is a problem in crush resistance, appearance, and VSWR. In Comparative Example 4, it can be seen that cable formation was impossible because neither the nucleating agent & metal deactivator nor the normal nucleating agent was added. In the comparative example 5, since the nucleating agent is expensive, it turns out that a cable becomes expensive. Since Comparative Example 6 is a normal cross-linked polyethylene, it can be seen that the average cell diameter is large, the crush resistance and the appearance are not good because the breaking tension at melting is too large and the MFR is too small. In Comparative Example 7, since there is no outer skin layer, it can be seen that there is a problem in crush resistance and appearance. In Comparative Example 8, the maximum temperature of the extruder was higher (230 ° C.) than the melting point (220 ° C.) of the nucleating agent & metal deactivator (CDA-1M).

1 is a longitudinal end view showing an example of a foamed coaxial cable according to the present invention. It is the schematic explanatory drawing which showed an example of the extrusion apparatus system for manufacturing the foaming coaxial cable which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal conductor, 2 ... Foam insulator, 3 ... Metal layer (outer conductor), 4 ... Sheath, 5a ... Inner skin layer, 5b ... Outer skin layer, 10 * .. First extruder, 12 ... Cross head of first extruder, 20 ... Cooling unit, 30 ... Gas foaming agent supply unit, 40 ... Second extruder,

Claims (8)

In a foamed coaxial cable having a foamed insulation coated coaxially on a conductor having a foaming degree of 80% or more, as a skin layer on the outer periphery, a breaking tension at melting of 6.0 to 20.0 g (190 ° C.), A foamed coaxial cable provided with a coating layer of polyolefin resin having an MFR of 0.4 g / 10 min (190 ° C., 2.16 Kgf) or more and a type D durometer hardness of 55 or more. The foamed coaxial cable according to claim 1, wherein the type D durometer has a hardness of 60 or more. The foamed coaxial cable according to claim 1 or 2, wherein the foamed insulator on the conductor is a foamable resin composition comprising a heat-meltable resin and a metal deactivator as a nucleating agent. Base resin of polyolefin resin in which the foamed insulator is the heat-meltable resin, and has a breaking tension at melting of 5.0 g or more (190 ° C.) and MFR 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more. 4. The foamed coaxial according to claim 3, comprising a resin composition for foaming formed by adding 0.01 to 1.0 part by weight of a metal deactivator as a nucleating agent for foaming with respect to 100 parts by weight. cable. 5. The foamed coaxial cable according to claim 1, wherein the outer conductor covered with the foamed insulator is made of a metal braid. The foamed coaxial cable according to claim 1, 2, 3, 4, or 5, wherein the polyolefin resin of the skin layer is an ethylene propylene copolymer resin, polypropylene, polyethylene, or a mixture thereof. 6. The foamed coaxial cable according to claim 1, wherein an inner skin layer is coated between the conductor and the foamed insulator. The foam insulator uses the foaming resin composition, and the molding temperature of the molding machine at the time of foaming is equal to or higher than the moldable temperature of the foaming resin composition and lower than the melting point of the metal deactivator. 8. The foamed coaxial cable according to claim 3, 4, 5, 6 or 7.

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