JP2007242589A - Foamed coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamed coaxial cable having as an insulator a foaming resin composition using a metal deactivator as a nucleant at foaming. <P>SOLUTION: With polyolefin-based resin with a break tension at fusion of 5.0 g or more (at 190°C), and an MFR of 1.0g/10min. or more (at 190°C, 2.16 Kgf) as base resin, a foaming resin composition has 0.01 to 1.0 parts by mass of metal deactivator added to 100 parts by mass of the base resin as a nucleant at the time of foaming, and is expansion molded at a molding temperature of the molding machine at foaming at which the foaming resin composition can be molded and below a melting point of the metal deactivator to be coated on an inner conductor to make up a foamed insulator. With this, foamed cells are made finer with a higher foaming degree and a cable of excellent characteristics is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a foamed coaxial cable for foaming a foaming resin composition using a metal deactivator as a nucleating agent during foaming.

In recent years, high-frequency coaxial cables have reached the GHz order in the frequency band used for the cables. 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 the collapse property of the foamed insulator by miniaturizing the foam cell (bubble core), and it is excellent in 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, PTFE powder and boron nitride powder are expensive and have practical problems. In the case of both powders, there was also a problem that 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 has also been found that a stable long product can be formed.

  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.

  The present invention has been made from this point of view. A metal deactivator is added as a nucleating agent to a polyolefin resin as a base resin, for example, a resin capable of hot melt molding using an ethylene propylene copolymer resin. The foaming resin in which the molding temperature of the molding machine is equal to or higher than the moldable temperature of the foaming resin composition and below the melting point of the metal deactivator when foaming the resulting foaming resin composition. A foamed coaxial cable using the composition is provided.

  The present invention according to claim 1 is based on a polyolefin resin having a breaking tension at melting of 5.0 g or more (190 ° C.) and MFR of 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more as a base resin. Using a foaming resin composition obtained by adding 0.01 to 1.0 part by mass of a metal deactivator as a nucleating agent at the time of foaming to 100 parts by mass, the molding temperature of the molding machine at the time of foaming is set as the foaming resin. The foamed coaxial cable is characterized in that it is foam-molded at a temperature equal to or higher than the moldable temperature of the composition and below the melting point of the metal deactivator and coated on the inner conductor to form a foamed insulator.

  According to a second aspect of the present invention, there is provided the foamed coaxial cable according to the second aspect, wherein the polyolefin resin is an ethylene-propylene copolymer resin.

  According to the foamed coaxial cable of the present invention, the resin composition for foaming is a resin that can be hot-melt molded as the base resin, and has a breaking tension at melting of 5.0 g or more (190 ° C.), MFR 1.0 g / 10 min (190 ° C.). , 2.16 Kgf) or more polyolefin resin, for example, ethylene propylene copolymer resin, to which a metal deactivator as a nucleating agent and a copper harm preventing agent is added as a nucleating agent, In order to control the temperature at the time, the molding temperature of the molding machine is equal to or higher than the moldable temperature of the foaming resin composition and equal to or lower than the melting point of the metal deactivator. The cell can be further miniaturized and have a high foaming degree (expansion degree of about 80% to about 90%), and a cable excellent in mechanical properties such as crush resistance can be obtained.

  At the time of foaming, the added metal deactivator functions as a nucleating agent and copper damage prevention agent. Therefore, it is necessary to add chemical foaming agents such as ADCA, PTFE powder, boron nitride powder, etc., which are ordinary nucleating agents. Absent. Therefore, in the case of the foamed insulation of the above-described foamed coaxial cable, there is no generation of decomposition residues as in the case of adding a chemical foaming agent, and there is no need to add a copper damage prevention agent. From the degree of foaming, the attenuation of transmission characteristics can be further reduced. In addition, mechanical properties such as the collapsibility of the obtained foamed insulator are improved, an excellent VSWR is obtained, the cable production is also stable, and long molding becomes possible. Furthermore, if an antioxidant is added together with the metal deactivator, a better effect in heat aging characteristics and the like can be obtained.

  The base resin used in the foaming resin composition of the foamed coaxial cable of the present invention is a resin that can be hot-melt molded, and has a melt breaking strength of 5.0 g or more (190 ° C.), MFR (melt flow ratio = melt flow ratio). ) A polyolefin-based resin, for example, an ethylene-propylene copolymer-based resin, of 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more is 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.

  As a single commercial product of an ethylene propylene copolymer resin that satisfies these conditions, FB3312 (manufactured by Nippon Polypro Co., Ltd., density 0.9, breaking tension at melting 10 g, MFR 2.0 g / 10 min) can be mentioned. 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) 2), MFR 3.0 g / 10 min), B701WB (Mitsui Chemicals, density 0.91, breaking strength 10 g at melting, MFR 0.4 g / 10 min). For example, in the case of the above mixed use, when the total resin amount is 100 parts by mass, it can be mixed in the range of 60 parts by mass as the upper limit for J703W with respect to FB3312, and in B701WB. Can be mixed in the range of 45 parts by mass as the upper limit. The reason is that if the mixing amount is too large, the above-mentioned breaking tension and MFR conditions at the time of melting cannot be satisfied.

  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, Hizex1300J (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 parts 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-tertiary-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 the heat aging characteristics cannot be obtained. This is because the adverse effect of the 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 case of the foamed coaxial cable of the present invention using the foaming resin composition having such a composition, if necessary, an inner skin layer is provided between the inner conductor and the foamed insulator, and an outer skin is provided between the metal layers of the foamed insulator and the outer conductor. The layers can be coated with both inner and outer skin layers, or both. As each of these skin layer materials, polyethylene (for example, low density polyethylene) is usually used. If the layer thickness is too thick, the foaming degree of the entire foamed insulation may be lowered. Since it becomes difficult, about 50 μm is preferable. These skin layers can be used alone or simultaneously with the extrusion coating of the foamed insulator.

  By providing such a skin layer, the following improvement in cable characteristics can be obtained. First, when the outer skin layer is coextruded with the foamed insulator, the appearance irregularities are eliminated, the VSWR is improved, the prevention of outgassing is obtained, and a higher foaming degree is obtained. Further, when the inner skin layer is provided, the adhesion between the inner conductor and the foamed insulator is improved, and the pulling force can be improved.

  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. A metal layer (outer conductor) made of a pipe or the like, 4 is a sheath made of polyethylene or the like, and 5a and 5b are an inner skin layer and an outer skin layer having a thickness of about 50 μm, which are provided as necessary. 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, when the inner skin layer is provided, copper damage is less likely to occur, and it becomes easier to form a long length, and a stable cable can be manufactured. 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.

  Further, as the base resin of the outer skin layer, when measured in the same manner as a base resin such as an ethylene propylene copolymer resin, a breaking tension at melting of 6.0 to 20 g or more (190 ° C.), MFR 0.4 g / It is desirable to use a polyolefin resin that is 10 min (190 ° C., 2.16 Kgf) or more, for example, low density polyethylene [UBE-C460 (trade name), manufactured by Ube Maruzen Polyethylene]. 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.

  FIG. 2 shows an example of an extrusion apparatus system for carrying out the method for producing a 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 the manufacturing method using this extrusion apparatus system, first, a master made of a base resin pellet, a nucleating agent, a metal deactivator, an antioxidant, and necessary additives from the resin supply port 11 of the first extruder 10. The batch is supplied by dry blending, and the foamed insulator is coated on the inner conductor 1 by the crosshead 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 in, for example, the cross head 12, and the outer skin layer 5b such as low-density polyethylene is coated 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.

  In the above description, the description has mainly focused on the foamed coaxial cable and the manufacturing method thereof, but the present invention is of course not limited to this foamed coaxial cable. For example, in the case of the foam molding, the resin coating layer material of a normal cable can be foamed by performing it under substantially the same conditions as described above.

<Examples and comparative examples>
First, using the foaming resin composition having the composition shown in Tables 1 to 6, a foamed coaxial cable of each sample having substantially the same structure as in FIG. Examples 1-22, Comparative Examples 1-17). Each sample cable was manufactured under the above-described temperature setting by the extrusion apparatus system shown in FIG. Here, two types of cables were manufactured. For example, the outer diameter of the inner conductor is 9 mm, the outer diameter of the foamed insulator is 22 mm, and the outer diameter of the entire cable is 28 mm. In the other, the outer diameter of the inner conductor is 3 mm, the outer diameter of the foamed insulator is 8 mm, and the outer diameter of the entire cable is 11.1 mm. More specifically, after covering the foamed insulator by gas foaming with nitrogen gas, an outer conductor having a corrugated structure and a polyethylene sheath were applied. In some cases, an inner skin layer of low-density polyethylene is provided on the outer periphery of the inner conductor, or an outer skin layer of low-density polyethylene is provided on the outer periphery of the foamed insulator, and both the inner and outer skin layers are provided. It was. The low-density polyethylene for each of the inner and outer skin layers is UBE-C460 (manufactured by Ube Maruzen Polyethylene). Moreover, the pulling force test between the internal conductor mentioned later and a foaming insulator was done with the said small size type cable.

  The base resin ethylene propylene copolymer resin used was FB3312 (manufactured by Nippon Polypro, density 0.9, breaking tension at melting 10 g (190 ° C.), MFR (190 ° C.) 2.0 g / 10 min), J703W. [Mitsui Chemicals, density 0.91, breaking tension 2 g (190 ° C.), MFR (190 ° C.) 3.0 g / 10 min], B701WB [Mitsui Chemicals, density 0.91, breaking tension 10 g (190 ° C.) MFR (190 ° C.) 0.4 g / 10 min].

  The antioxidant is Irganox 1010 (hindered phenol-based antioxidant, manufactured by Ciba Specialty Chemicals), and the metal deactivator & nucleating agent (cumulative nucleating agent) is CDA-1M (manufactured by Asahi Denka Kogyo Co., Ltd.). , Triazole series = 3- (N-salicyloyl) amino-1,2,4-triazole, improved volatility during processing and dispersibility), Irganox MD1024 (hydrazide series = 2 ', 3 -Bis [3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl] propionohydrazide (manufactured by Ciba Specialty Chemicals), nucleating agent is vinylol AC # 3 (manufactured by Eiwa Chemical Industries, ADCA = Azodicarbonamide), HP-1 (manufactured by Mizushima Alloy Iron Co., Boron Nitride), KTL-500F (manufactured by Kitamura Co., Ltd., PTFE = Polytetraph) It is a Oroechiren). In addition, the compounding numerical value of Table 1-Table 4 shows a mass part.

  Each sample cable is subjected to a characteristic test as shown in Tables 5 to 6, and its characteristics [foaming degree, foaming magnification, attenuation, average foamed cell diameter, VSWR, heat aging property, pulling force (inner and outer conductors and foaming) (Between insulators), cost, crush resistance].

<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 82% 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 5.6 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 62 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, 0.25 mm or less is a pass level.

<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.

<Heat aging test>
The sample cable was put into a constant temperature bath at 90 ° C. for a predetermined time, and it was visually determined whether or not embrittlement or gelation occurred. The case where nothing occurs for more than 2 years is indicated by “◎”, the case where nothing occurs for less than 1 to 2 years is indicated by “◯”, and embrittlement or gel is observed within 0.5 to 1 year. The case where crystallization occurred was indicated by “Δ”, and the case where embrittlement or gelation occurred within less than 0.5 years was indicated by “x”. Here, “◎”, “◯”, “Δ” are acceptable, and “×” is unacceptable.

<Pullout force test>
In the sample cable (the small-sized cable described above), 50 mm of the foamed insulating layer was left, and the pulling force (N) at a pulling speed of 200 mm / min was determined. If this value is too large, the workability (stickiness) will deteriorate. Moreover, if it becomes too small, cable shrinkage (shrinkage) tends to occur. For this reason, here, when less than 50N or more than 200N, it was rejected and indicated by “x”. On the other hand, in the case of 50N to less than 100N, or 150N to 200N, it was passed and indicated as “◯”, and in the case of 100N to less than 150N, it was indicated as “◎” as a passed and better case.

<Cost test>
The evaluation was made based on the amount of additive, particularly metal deactivator & nucleating agent. A case where the cost is low is indicated by “◯”, and a case where the cost is high is indicated by “X”.

<Crush resistance test>
Using the same sample cable as the pull-out force test, the deformation rate at 23 ° C. of the outer diameter of the foamed insulator with the inner conductor when a load of 3 kgf was applied was 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 6% is indicated by “◎”, a case where the deformation rate is 6% to less than 8% is indicated by “◯”, and a case where the deformation rate is 8% or more 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 22), it can be seen that all the characteristics are good. In particular, it has been found that good results can be obtained by suppressing the maximum molding temperature in the extruder (cylinder part) to a temperature lower than the melting point of the metal deactivator such as 215 ° C. or 225 ° C., for example. It was.

On the other hand, in the case of the foamed coaxial cable lacking the conditions of the present invention (Comparative Examples 1 to 22), it can be seen that there is a problem in any point.
That is, in Comparative Examples 1 and 2, the molding temperature (230 ° C.) of the extruder (cylinder part) is higher than the melting point (220 ° C.) of the metal deactivator and nucleating agent. As a result, good cable production was impossible. In Comparative Example 3, the molding temperature (230 ° C.) of the extruder (die part) is higher than the melting point (225 ° C.) of the metal deactivator and nucleating agent. Cable manufacturing was impossible. In Comparative Examples 4 to 5, the mixing ratio of the base resin is inadequate, and the breaking tension or MFR at the time of melting is insufficient, so that open cells are likely to be formed. As a result, the expansion ratio is insufficient and the crush resistance is also a problem. was there. In Comparative Examples 6 to 7, since the metal deactivator and nucleating agent were not added, the foamed cell became huge, could not be controlled, and cable production was impossible. In Comparative Examples 8 and 10, since the addition amount of the metal deactivator and nucleating agent is too small, the nucleating agent effect becomes weak, the foaming degree becomes low, the average foamed cell diameter and VSWR fail, and heat aging It can be seen that the characteristics are slightly worse. In Comparative Examples 9 and 11, since the addition amount of the metal deactivator and nucleating agent is too large, it can be seen that the attenuation amount is slightly deteriorated and the cost is also increased. In Comparative Examples 12 to 17, since the conventional nucleating agent is used, there is a problem that the amount of attenuation is slightly large, the average foamed cell diameter is large, the heat aging characteristics are poor, and the cost is high. I understand.

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 enforcing the manufacturing method of 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 blowing agent supply unit, 40 ... Second extruder

Claims (2)

A polyolefin resin having a breaking tension of 5.0 g or more (190 ° C.) and MFR of 1.0 g / 10 min (190 ° C., 2.16 Kgf) or more when melted is used as a base resin, and nucleation during foaming is performed on 100 parts by mass of the base resin. Using a foaming resin composition obtained by adding 0.01 to 1.0 part by mass of a metal deactivator as an agent, the molding temperature of the molding machine during foaming is equal to or higher than the moldable temperature of the foaming resin composition. The foamed coaxial cable is formed by foam molding below the melting point of the metal deactivator and covering the inner conductor to form a foam insulation. 3. The foamed coaxial cable according to claim 2, wherein the polyolefin resin is an ethylene propylene copolymer resin.

Images