JP2007090787A - Foaming method, foamed coaxial cable and manufacturing method of the foamed coaxial cable - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a forming method of a foaming resin composition, using a metal deactivator as nucleation agent at foaming. <P>SOLUTION: The method comprises the foaming method of the foaming resin composition made of the mixture of resin, capable of heat melting forming and the metal deactivator as the nucleation agent and enables foaming, at a temperature that is not lower than a temperature where the forming temperature of the forming apparatus is not lower than the temperature sufficient for forming the foaming resin composition described and at a temperature not higher than the melting point of the metal deactivator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a foam molding method, a foamed coaxial cable, and a foamed coaxial cable manufacturing method of 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 these circumstances, the present inventors conducted various tests and found that it was possible to prevent copper damage without using the above-mentioned chemical foaming agent such as ADCA, PTFE powder, boron nitride powder or the like. The present inventors have found and proposed that the foamed cell can be sufficiently miniaturized by appropriately adding the above-described metal deactivator, which is an agent (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

  In resin molding using the foaming resin composition, a molding machine such as an extruder is usually used, and the molding temperature (resin temperature in the molding machine) is set to about 140 to 230 ° C. In consideration of the melting point of the metal deactivator to be used, etc., the inventors have examined the molding temperature. As a result, the molding temperature of the molding machine is equal to or higher than the moldable temperature of the foaming resin composition, and the metal It has been found that better results are obtained when it is set below the melting point of the inert agent. That is, it was found that the foamed cell can be further miniaturized, and as a result, mechanical properties such as crush resistance are improved. 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. Moreover, it has been found that these characteristics can be obtained not only for the foamed insulator of the coaxial cable but also for a general foamed resin molded product.

  The present invention has been made from this point of view. When a foaming resin composition obtained by adding a metal deactivator as a nucleating agent to a resin capable of hot melt molding is subjected to foam molding, the molding temperature of a molding machine. Foam molding method of foaming resin composition, foamed coaxial cable, and production of foamed coaxial cable at a temperature equal to or higher than the moldable temperature of foaming resin composition and below melting point of metal deactivator A method is provided.

  The present invention according to claim 1 is a method of foam-molding a foamable resin composition comprising a heat-melt moldable resin and a metal deactivator as a nucleating agent, wherein the molding temperature of the molding machine is the above-mentioned In the foam molding method, foam molding is performed at a temperature equal to or higher than a moldable temperature of the foaming resin composition and equal to or lower than a melting point of the metal deactivator.

  The present invention according to claim 2 is that the foaming resin composition is obtained by adding 0.01 to 1.0 part by mass of a metal deactivator to 100 parts by mass of a resin that can be hot-melt molded. The foam molding method according to claim 1.

  The present invention according to claim 3 is a composition in which the foaming resin composition is obtained by adding 0.1 to 0.7 parts by mass of a metal deactivator to 100 parts by mass of a resin that can be hot-melt molded. It exists in the foam molding method of Claim 1 characterized by the above-mentioned.

  The present invention according to claim 4 is characterized in that the heat-melt moldable resin is a polyolefin resin and is a high density polyethylene, a low density polyethylene, a polypropylene, an ethylene propylene copolymer, or a mixture thereof. It exists in the foam molding method of Claim 1, 2 or 3.

  The fifth aspect of the present invention is the foam molding method according to the first, second, or fourth aspect, wherein the metal deactivator is a triazole-based or hydrazide-based metal deactivator.

  The present invention according to claim 6 resides in a foam molding method, wherein an antioxidant is added to the foaming resin composition selected from claims 1 to 5.

  The present invention according to claim 7 is a foam characterized in that the foamed resin composition used in the foam molding method selected from claims 1 to 6 is foam-coated on an internal conductor to form a foam insulator. Located on coaxial cable.

  In the eighth aspect of the present invention, the foamed resin composition used in the foam molding method selected from the first to sixth aspects is foam-coated on an internal conductor by an extruder in the presence of a foaming agent, and foamed. It is in the manufacturing method of the foaming coaxial cable characterized by making it a body.

  The present invention according to claim 9 is the method for producing a foamed coaxial cable according to claim 8, wherein the foaming agent is a gas foaming agent, a chemical foaming agent, or a combination thereof.

According to the foam molding method of the present invention, the foaming resin composition is obtained by adding a metal deactivator of a nucleating agent and a copper harm preventing agent as a nucleating agent to a resin that can be hot-melt molded, Since the molding temperature is controlled so that the molding temperature of the molding machine is higher than the moldable temperature of the foaming resin composition and lower than the melting point of the metal deactivator, the foam cell can be made even finer. Thus, a foamed molded article having excellent mechanical properties such as crush resistance can be obtained.
Since the metal deactivator functions as a nucleating agent and copper damage prevention agent, it is not necessary to add chemical foaming agents such as ADCA, PTFE powder, boron nitride powder, etc., which are normal nucleating agents, and it is sufficient when foaming Finer foaming can be obtained. Therefore, for example, if this is used for a foam insulation of a 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 separately. Can be reduced. Further, by making the foam finer, mechanical properties such as the crushability of the obtained foamed insulator are improved, an excellent VSWR is obtained, cable production is also stable, and long molding is possible. Furthermore, if an antioxidant is added together with the metal deactivator, a better effect can be obtained. These effects are not limited to the insulator of the foamed coaxial cable, but can be obtained in the same way for general foamed resin molded products.

  According to the foamed coaxial cable of the present invention, when the foaming resin composition is foam-coated on the inner conductor as a foamed insulation, the temperature control during molding is controlled, and the molding temperature of the molding machine is molding of the foaming resin composition. Since foam molding is performed at a temperature higher than the possible temperature and lower than the melting point of the metal deactivator, a cable with finer foam can be obtained. Of course, finer foaming improves the above-described effects, that is, the amount of attenuation, improves mechanical properties such as crushability, and provides an excellent VSWR. Manufacturing is stable and a cable that can be formed into a long shape is obtained.

  According to the method for producing a foamed coaxial cable of the present invention, when a foamed insulator is foam-coated on an internal conductor by an ordinary extruder, no special device is required, and the temperature control during molding is controlled by the molding temperature of the molding machine. However, since it is only necessary to perform foam molding at a temperature above the moldable temperature of the resin composition for foaming and below the melting point of the metal deactivator, good productivity can be obtained. At this time, similarly to normal foaming, a gas foaming agent, a chemical foaming agent, or a combination thereof can be used.

  The base resin of the foaming resin composition used in the foam molding method of the present invention is not particularly limited as long as it is a resin that can be hot melt molded. For example, in the case of a polyolefin resin, although not particularly limited, preferred resins include polyethylene (PE), polypropylene (PP), ethylene propylene copolymer, and the like. Particularly in the case of polyethylene, high-density polyethylene (HDPE) and low-density polyethylene (LDPE) are preferably used, and these can be used alone or as a mixture. Further, it is possible to use polyethylene and polypropylene as a mixture.

  In addition, examples of the metal deactivator added to the resin that can be hot-melt molded in the present invention include triazole-based or hydrazide-based ones. 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.

  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, and the adverse effect of increasing the amount of attenuation increases as the amount added increases. is there. However, a more desirable addition amount is 0.1 to 0.7 parts by mass.

In this foaming 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. Yes, these may be used alone or in combination.

  And the addition amount shall be 0.01-1.0 mass part with respect to 100 mass parts of base resins. The reason for this is that if the amount is less than 0.01 parts by mass, a sufficient addition effect cannot be obtained. Conversely, if the amount exceeds 1.0 parts by mass, the addition effect is not particularly improved, and the addition amount is increased. This is because the adverse effect of the increase in the amount becomes large.

  Further, for this foaming resin composition, if necessary, other additives such as crosslinking aids, dispersants, inorganic fillers, and other nucleating agents such as ADCA and OBSH are used. For example, an appropriate amount of talc, BN, fluororesin, azodicarbonamide, clay, or the like can be used in combination as a substance having no harmful effects of decomposition residues.

  In the foam molding method of the present invention using the foaming resin composition having such a composition, the molding temperature of the molding machine (resin temperature in the molding machine) is equal to or higher than the moldable temperature of the foaming resin composition, and It shall be foam-molded below the melting point of the metal deactivator. Here, the reason why the melting point of the metal deactivator is not higher than the melting point is that when the metal deactivator is melted in a molding machine such as an extruder, the foaming nucleating agent effect is lowered.

  Therefore, when the melting point of the metal deactivator is, for example, triazole type 3- (N-salicyloyl) amino-1,2,4-triazole (Asahi Denka Co., Adekastap, CDA-1M) having a temperature of about 220 ° C. And hydrazide-based 2 ′, 3-bis [3- [3,5-ditert-butyl-4-hydroxyphenyl] propionyl] propionohydrazide (Ciba Specialty Chemicals, Irganox MD1024) at about 225 ° C. In this case, it is necessary to control the molding temperature in a molding machine such as an extruder at a temperature not higher than these melting points, and, of course, not less than the temperature at which the foaming resin composition can be molded.

  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 under the above temperature control, and 3 is a metal braid or corrugate. A metal layer (outer conductor) made of a copper 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 applied 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.

  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 the first extruder, 11 is the resin supply port of the first extruder, 20 is the second extruder, 21 is the crosshead of the second extruder, 30 is the cooling unit, and 40 is the gas foam to the first extruder The agent supply unit 50 is a third extruder for the inner skin layer.

  In the manufacturing method using this extrusion apparatus system, first, a master composed of a base resin pellet, a nucleating agent, a metal deactivator, an antioxidant, a necessary additive and the like from a resin supply port 11 of the first extruder 10. The batch is supplied by dry blending and is fed to the second extruder 20, and the foamed insulator is coated on the inner conductor 1 by the crosshead 21. Before this, the inner skin layer 5a such as low density polyethylene is preferably coated on the inner conductor 1 by the third extruder 50 for inner skin layer. The extrusion temperature of the 1st extruder 10 or the 2nd extruder 20 is set below in melting | fusing point of the metal deactivator to be used, for example, about 140-230 degreeC. The extrusion temperature of the third extruder is set in the range of about 140 to 200 ° C. for the inner skin layer. Nitrogen gas or the like is supplied as a foaming agent from the gas foaming agent supply unit 40 to the first extruder 10. Thereby, as above-mentioned, a metal deactivator functions as a nucleating agent and a foaming cell is refined | miniaturized.

  The foamed insulation covered with the cross head 21 of the second extruder 20 is cooled by the cooling unit 30. At this time, preferably, the extruded portion of a fourth extruder (not shown) is incorporated in, for example, the cross head 21 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 fourth extruder is set in the range of about 140 to 200 ° C. for the outer skin layer. 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. As the gas as the foaming agent, in addition to nitrogen gas, for example, an inert gas such as argon gas, chlorofluorocarbon gas, or carbon dioxide gas 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. Examples of such a chemical foaming agent include azodicarbonamide, 4,4′oxybis (benzenesulfonylhydrazide), N, N′-dinitrosopentamethylenetetramine and the like.

<Examples and comparative examples>
First, using the foaming resin compositions (Examples 1 to 14 and Comparative Examples 1 to 15) having the composition shown in Tables 1 and 2, foamed coaxial cables of the respective samples having the same structure as FIG. 1 were produced. . Each sample cable was manufactured by an extrusion apparatus system shown in FIG.
Here, the setting of the molding temperature is based on the melting point of the metal deactivator used below, and the measured maximum temperature of the cylinder part of the first extruder or the second extruder in FIG. The measured maximum temperature of the die part was set to 150 ° C or 230 ° C. 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. More specifically, an inner skin layer of low density polyethylene is provided on the outer periphery of the inner conductor, and the foamed insulator is covered with gas foaming with nitrogen gas, and an outer skin layer of low density polyethylene is applied on the outer periphery of the foamed insulator. After that, a corrugated outer conductor and a polyethylene sheath were applied. In addition, the low density polyethylene of each said inner and outer skin layer is UBE-C460 (made by Ube Industries).

  The HDPE of the base resin used was 2070 (manufactured by Ube Maruzen Polyethylene, density 0.963, high density polyethylene with MI = 8), and LDPE was B028 (manufactured by Ube Maruzen Polyethylene, density 0.928, MI = 0.20). No. 4 low density polyethylene), PP is J703W (Mitsui Chemicals, block copolymer having a density of 0.91). The antioxidant is Irganox 1010 (hindered phenol antioxidant, manufactured by Ciba Specialty Chemicals), and the metal deactivator & nucleating agent (combined nucleating agent) is CDA-1M (manufactured by Asahi Denka Kogyo Co., Ltd., Triazole). System thing = 3- (N-salicyloyl) amino-1,2,4-triazole, volatile during processing, improved dispersibility, melting point = 220 ° C., Irganox MD1024 (Ciba Specialty Chemicals, Hydrazide series = 2 ′, 3-bis [3- [3,5-ditert-butyl-4-hydroxyphenyl] propionyl] propionohydrazide, melting point = 225 ° C.), nucleating agent is vinylol AC # 3 ( Eiwa Kasei Kogyo Co., Ltd., ADCA = Azodicarbonamide), HP-1 (Mizushima Alloy Iron Co., Boron Nitride), KTL-500F (Kitamura Co., Ltd.) A PTFE = polytetrafluoroethylene). In addition, the compounding numerical value of Table 1-Table 2 shows a mass part.

  About each sample cable, the characteristic test as shown in Table 3-Table 4 was done, and the characteristic (heat aging property, crushing resistance, average foamed cell diameter, VSWR, foaming degree, attenuation amount) was calculated | required.

<Heat aging test>
The sample cable was put into a constant temperature bath at 80 ° C. for a predetermined time, and it was visually determined whether or not embrittlement or gelation occurred. The case where nothing occurs for 2 years or more is indicated by “◎”, and the case where it does not occur for less than 1 to 2 years is indicated by “◯”, and embrittlement or gelation occurs in less than 1 year. “×” is shown.

<Crush resistance test>
Evaluation was made based on the deformation rate of the outer diameter of the insulator with conductor when a load of 3 kg was applied to the sample cable. The deformation rate was determined at 23 ° C. as 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”.

<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). .

<VSWR test>
The sample cable was measured using a network analyzer (manufactured by Agilent Technologies, 8722ES). Here, less than 1.20 is an acceptable level, and the closer to 1.00, the better. Here, the case where the VSWR value is less than 1.10 is indicated by “◎”, the case where the VSWR value is less than 1.10 to 1.15 is indicated by “◯”, and the VSWR value is 1.15 to 1.. The case of less than 20 is indicated by “Δ”, and the case where the VSWR value is 1.20 or more is indicated by “x”.

<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.

<Attenuation test>
The attenuation amount under 2.2 GHz was calculated for the sample cable using a network analyzer. Here, the pass level is less than 62 dB / Km.

  As is apparent from Tables 1 to 4 above, in the case of the foamed coaxial cable of the present invention (Examples 1 to 14), 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 15), it can be seen that there is a problem in any point.
That is, in Comparative Examples 1 to 3, since the molding temperature exceeds the melting point of the metal deactivator and nucleating agent, the average foamed cell diameter is large, and a sufficient nucleating agent function is not obtained. I understand. In Comparative Examples 4 to 10, since the metal deactivator and nucleating agent is not added, it can be seen that the heat aging property is insufficient. In Comparative Examples 11 and 13, although the metal deactivator / nucleating agent was added, the amount thereof was too small, so that it was found that sufficient foamed cells were not miniaturized and there was a problem in characteristics. In Comparative Examples 12 and 14, since the addition amount of the metal deactivator and nucleating agent is too large, it can be seen that the attenuation amount is increased by this addition amount. In Comparative Example 15, since neither a metal deactivator / nucleating agent nor a conventional nucleating agent is added, foaming cannot be controlled, huge air bubbles are generated, and cable production itself is impossible. I understand.

  In the above description, as the foam molding method of the present invention, the foamed coaxial cable and the manufacturing method thereof have been described focusing on the case where the foaming resin composition is used for the foamed coaxial cable. Of course, it is not limited to this, but can also be used as a resin cover layer material for ordinary cable positives, or as a foam for electronic and electrical equipment parts having the same problems as those of the present invention. Furthermore, the foam molding method of the present invention can also be applied to general foamed resin molded products.

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 ... Inner conductor, 2 ... Foam insulator, 3 ... Metal layer (outer conductor), 4 ... Sheath, 10 ... 1st extruder, 20 ... 2nd extruder, 21 ... Cross head of second extruder, 30 ... Cooling unit, 40 ... Gas blowing agent supply unit, 50 ... Third extruder

Claims (9)

A method of foam-molding a foamable resin composition comprising a heat-melt-moldable resin and a metal deactivator as a nucleating agent, wherein the molding temperature of the molding machine is capable of molding the foamable resin composition A foam molding method comprising foam molding at a temperature above the melting point of the metal deactivator. The foaming resin composition is a composition obtained by adding 0.01 to 1.0 parts by mass of a metal deactivator to 100 parts by mass of a resin that can be hot-melt molded. Foam molding method. The foaming resin composition is a composition obtained by adding 0.1 to 0.7 parts by mass of a metal deactivator to 100 parts by mass of a resin that can be hot-melt molded. The foam molding method described. 4. The heat-melt moldable resin is a polyolefin-based resin, and is a high-density polyethylene, low-density polyethylene, polypropylene, an ethylene-propylene copolymer, or a mixture thereof. Foam molding method. 5. The foam molding method according to claim 1, wherein the metal deactivator is a triazole-based or hydrazide-based metal deactivator. 6. A foam molding method, comprising adding an antioxidant to the foaming resin composition selected from claims 1-5. A foamed coaxial cable, wherein the foamed resin composition used in the foam molding method selected from claims 1 to 6 is foam-coated on an internal conductor to form a foamed insulator. Foam, wherein the foaming resin composition used in the foam molding method selected from claims 1 to 6 is foam-coated on an internal conductor by an extruder in the presence of a foaming agent to form a foam insulator. Coaxial cable manufacturing method. 9. The method for producing a foamed coaxial cable according to claim 8, wherein the foaming agent comprises a gas foaming agent, a chemical foaming agent, or a combination thereof.

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