JP6745075B2 - Foamable resin composition, foam, and coaxial cable - Google Patents

Description

The present invention relates to a foamable resin composition, a foam, and a coaxial cable. More specifically, it relates to a foamable resin composition which is highly foamed, has independent cells, and is fine and uniform, and a foam thereof. Further, the present invention relates to a coaxial cable having excellent transmission characteristics, good kink resistance, and good solder resistance.

The coaxial cable generally includes an inner conductor provided in the center of the cable, an insulator covered on the outer periphery of the inner conductor, an outer conductor provided outside the insulator, and an outer side of the outer conductor. This is a cable having a structure having a sheath provided as the outermost layer. In recent years, coaxial cables have been particularly required to improve transmission characteristics such as transmission speed and transmission accuracy. As one of means for improving these transmission characteristics, there is a method of lowering the relative dielectric constant of the insulator. Since the relative permittivity of air is 1.0, which is lower than that of a material normally used for an insulator, foaming the insulator is one of the effective means for lowering the relative permittivity of the insulator. .. It is effective to use a higher expansion ratio for foaming. However, when foamed at a high magnification, the shape of the foam cells becomes non-uniform, and there is a problem that the mechanical properties of the cable and the kink resistance are reduced.

In addition, there is a further demand for heat resistance, and a coaxial cable having particularly excellent solder resistance is demanded.

JP, 2006-045268, A JP, 2011-090920, A JP, 2014-084341, A

An object of the present invention is to provide a foamable resin composition suitable as an insulator for a coaxial cable, a foam, and a coaxial cable using the foamed resin composition as a covering material.

As a result of earnest research, the present inventor has found that the above problems can be achieved by a specific resin composition.

That is, the present invention includes (α) 100 parts by mass of polyolefin resin; and (β) 0.1 to 2.0 parts by mass of chemical foaming agent;
It is a foamable resin composition containing.
The above (α) polyolefin resin is
(A) Propylene polymer satisfying the following characteristics (a) and (b): 10 to 50% by mass;
(B) A propylene-based polymer that satisfies the following characteristics (a) and (c): 30 to 70% by mass; and (C) a low-density polyethylene-based polymer: 5 to 40% by mass.
Here, the total of the components (A), (B), and (C) is 100% by mass,
The total of the above components (A) and (B) is 60 to 95 mass %.
(A) The melt mass flow rate is 1 to 15 g/10 minutes.
(B) The following formula (1) is satisfied.
Formula (1) MT×MFR ≧20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.
(C) The following formula (2) is satisfied.
Formula (2) MT×MFR<20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.

A second invention is the expandable resin composition according to the first invention for a coaxial cable.

A third invention is a foam of the foamable resin composition according to the first invention or the second invention, which has an expansion ratio of 30 to 60%.

A fourth invention is a foam of the foamable resin composition according to the first invention or the second invention, wherein the foam cells have an average diameter of 20 to 50 μm.

A fifth invention is a coaxial cable including the foam according to the third invention or the fourth invention.

The foamable resin composition of the present invention can provide a fine and uniform foam having independent foam cells even when foamed at a high ratio. Therefore, it can be suitably used as an insulator of a coaxial cable. Further, the coaxial cable containing the foamable resin composition of the present invention is excellent in transmission characteristics, kink resistance, and solder resistance.

The foamable resin composition of the present invention contains (α) 100 parts by mass of polyolefin resin; and (β) 0.1 to 2.0 parts by mass of chemical foaming agent. The (α) polyolefin resin is composed of (A) a high melt tension propylene polymer, (B) a propylene polymer and (C) a low density polyethylene.

(A) High melt tension propylene-based polymer:
The component (A) is a propylene-based polymer having a high melt tension and satisfies the following characteristics (a) and (b). The component (A) being a propylene-based polymer having a high melt tension means that the following property (B) is satisfied.
(A) The melt flow rate is 1 to 15 g/10 minutes.
(B) The following formula (1) is satisfied.
Formula (1) MT×MFR ≧20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.

The above component (A) functions to make the foam cells independent, fine and uniform even when foamed at a high magnification. It also functions to improve the extrusion moldability and solder resistance of the expandable resin composition of the present invention.

The above (a) melt mass flow rate of the above component (A) is a value measured according to JIS K7210-1999 under the conditions of a temperature of 230° C. and a load of 21.18 N. The unit is g/10 minutes. The (a) melt mass flow rate of the component (A) is preferably 2 to 13 g/10 minutes.

The melt tension in the above formula (1) is measured using Toyo Seiki Seisakusho's "Capirograph D1 (trade name)" and a cylindrical orifice with a length of 8 mm, a diameter of 2 mm, and an inflow angle of 190°C. , A piston speed of 20 mm/min, a take-up speed of 4 m/min, a preheating time of 5 min, and a charged sample amount of 8 g. Further, the sample was put in three times, and each time it was pushed in by using a push rod, the trapped air was released. The unit is g.

The value of MT × MFR in the formula (1), independent foam cells even by foaming at high magnification, from the viewpoint of fine and uniform ones, preferably 25 g ^2/10 minutes or more, more preferably 27 g ² /10 minutes or more. The value of MT×MFR in the above formula (1) may be preferably 60 g ² /10 minutes or less, more preferably 55 g ² /10 minutes or less from the viewpoint of extrusion moldability.

The melting point of the component (A) may be preferably 150° C. or higher, more preferably 160° C. or higher from the viewpoint of solder resistance. The upper limit of the melting point is not particularly limited from the viewpoint of solder resistance, and the higher the better. In the present specification, the melting point is, using a Diamond DSC type differential scanning calorimeter manufactured by Perkin Elmer Japan Co., Ltd., held at 230° C. for 5 minutes, cooled to −10° C. at 10° C./minute, and then 5 at −10° C. It is the peak-top melting point on the highest temperature side in the second melting curve (melting curve measured in the final heating process) measured by a program of holding for 10 minutes and heating up to 230°C at 10°C/minute.

The component (A) is not limited except that the above properties (a) and (b) are satisfied, and any propylene polymer can be used. Examples of the propylene-based polymer include propylene homopolymer; propylene and other small amounts of α-olefins (eg, ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene). ) And a copolymer (including a block copolymer and a random copolymer); and the like.

Examples of commercially available components (A) include "Newformer series FTS3000 (trade name)", "FTS6000 (trade name)" and "Weimax series (trade name)" manufactured by Nippon Polypropylene Corporation. be able to.

As the component (A), one kind or a mixture of two or more kinds thereof can be used. When a mixture is used as the component (A), the mixture may be made to satisfy the above characteristics (a) and (b).

(B) Propylene polymer:
The component (B) is a propylene-based polymer that satisfies the following characteristics (a) and (c). The component (B) functions to improve solder resistance and extrusion moldability.
(A) The melt mass flow rate is 1 to 15 g/10 minutes.
(C) The following formula (2) is satisfied.
Formula (2) MT×MFR<20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.

The (a) melt mass flow rate of the component (B) is a value measured in accordance with JIS K7210-1999 under the conditions of a temperature of 230° C. and a load of 21.18N. The unit is g/10 minutes. The (a) melt mass flow rate of the component (B) is preferably 0.5 to 13 g/10 minutes from the viewpoint of extrusion moldability.

The melt tension in the above formula (2) was measured using Toyo Seiki Seisakusho's "Capirograph D1 (trade name)" and a cylindrical orifice having a length of 8 mm, a diameter of 2 mm and no inflow angle, and a measurement temperature of 190°C. , A piston speed of 20 mm/min, a take-up speed of 4 m/min, a preheating time of 5 minutes, and a charged sample amount of 8 g. In addition, the sample was put in three times, and each time the sample was pushed in using a push rod, the trapped air was released. The unit is g.

The value of MT×MFR in the above formula (2) is preferably 5 to 15 g ² /10 minutes from the viewpoint of extrusion moldability.

The melting point of the component (B) may be preferably 150° C. or higher, more preferably 160° C. or higher from the viewpoint of solder resistance. The upper limit of the melting point is not particularly limited from the viewpoint of solder resistance, and the higher the better. The definition of the melting point and the measuring method are described above.

The component (B) is not limited as long as it satisfies the above characteristics (a) and (c), and any propylene-based polymer can be used. Examples of the propylene-based polymer include propylene homopolymer; propylene and other small amounts of α-olefins (eg, ethylene, 1-butene, 1-hexene, 1-octene, and 4-methyl-1-pentene). ) And a copolymer (including a block copolymer and a random copolymer); and the like.

Commercially available examples of the component (B) include, for example, "MA3 (trade name)" of Nippon Polypropylene Co., Ltd., "Y400GP (trade name)" of Prime Polymer Co., Ltd., and "VS700A (trade name)" of Sun Allomer Co., Ltd. And so on.

As the component (B), one kind or a mixture of two or more kinds thereof can be used. When a mixture is used as the component (B), the mixture may be made to satisfy the above characteristics (a) and (c).

(C) Low density polyethylene polymer:
The above component (C) has a density (measured by an underwater substitution method according to JIS K7112:1999) of usually 945 Kg/m ³ or less, preferably 940 Kg/m ³ or less, and more preferably 860 to 930 Kg/m ³ , And more preferably a polyethylene polymer having a weight of 860 to 925 Kg/m ³ . The component (C) functions to improve kink resistance, extrusion moldability, and appearance of the molded product.

The component (C) is not limited except that the density is within the above range. Examples of the component (C) include high-pressure low-density polyethylene, low-density polyethylene, linear low-density polyethylene, ethylene/α-olefin copolymer, ethylene/vinyl acetate copolymer, ethylene/(meth)acrylic. Examples thereof include acid alkyl copolymers and ethylene/unsaturated carboxylic acid copolymers.

Examples of the α-olefin include propylene, 1-butene, 1-hexene, 1-octene, 1-decene, and 4-methyl-1-pentene.

Examples of the alkyl (meth)acrylate include methyl acrylate, ethyl acrylate, methyl methacrylate, and ethyl methacrylate.

Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid.

As the component (C), one kind or a mixture of two or more kinds thereof can be used. When a mixture is used as the component (C), the mixture may have a density within the above range.

From the viewpoint of kink resistance, the density of the component (C) may be more preferably 930 Kg/m ³ or less, further preferably 925 Kg/m ³ or less.

According to JIS K7210:1999 of the above component (C), the melt mass flow rate measured under the conditions of a temperature of 190° C. and a load of 21.18 N is preferably 0.1 to 50 g/10 minutes, more preferably from the viewpoint of extrudability. It is preferably 0.5 to 10 g/10 minutes.

Examples of commercially available components (C) include "UBEC450 (trade name)" by Ube Maruzen Polyethylene Co., Ltd., "C215 (trade name)" by Sumitomo Chemical Co., Ltd., and "DOWLEX2645G (trade name)" by Dow Chemical Co., Ltd. )”, and “DFDJ-7540 (trade name)” by NUC Co., Ltd., and the like.

The ratio of the component (A) in the (α) polyolefin resin is 100% by mass of the components (A), (B), and (C), and the foamability (even when foamed at a high magnification). From the viewpoint of making it possible to obtain a foamed cell having independent, fine and uniform foamed cells), the content is usually 10% by mass or more, preferably 15% by mass or more, and more preferably 20% by mass or more. On the other hand, from the viewpoint of extrusion moldability, it is usually 50% by mass or less, preferably 45% by mass or less, and more preferably 40% by mass or less.

The ratio of the component (B) in the (α) polyolefin-based resin is 100% by mass of the components (A), (B), and (C) in terms of the balance between foamability and extrudability. , Usually 30 to 70% by mass, preferably 35 to 65% by mass, more preferably 40 to 60% by mass.

The ratio of the total of the above components (A) and (B) in the above (α) polyolefin resin is 100% by mass of the above components (A), (B), and (C), and the foaming property and the From the viewpoint of solderability, it is usually 60% by mass or more, preferably 65% by mass or more, and more preferably 70% by mass or more. On the other hand, from the viewpoint of kink resistance, it is usually 95 mass% or less, preferably 90 mass% or less, more preferably 85 mass% or less.

The proportion of the component (C) in the (α) polyolefin resin is 5% by mass or more from the viewpoint of kink resistance, with the total amount of the components (A), (B), and (C) being 100% by mass. , Preferably 10 mass% or more, more preferably 15 mass% or more. On the other hand, from the viewpoint of solder resistance, it is 40% by mass or less, preferably 35% by mass or less, more preferably 30% by mass or less.

(Β) Chemical blowing agent:
The component (β) is a chemical foaming agent, which is a liquid or solid at room temperature and decomposes by heating to generate a gas. The component (β) is preferably a chemical foaming agent whose decomposition temperature is higher than the melting points of the components (A) and (B).

The decomposition temperature of the component (β) is preferably 170 to 220°C, more preferably 190 to 210°C.

Examples of the above component (β) include azo compounds such as diethylazocarboxylate, azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, barium azodicarboxylate; N,N′-dimethyl- Nitroso compounds such as N,N′-dinitrosoterephthalamide and N,N′-dinitrosopentamethylenetetramine; semicarbazide compounds such as p-toluenesulfonyl semicarbazide and 4,4′-oxybis(benzenesulfonylhydrazide); be able to. Among these, azo compounds are preferable, and azodicarbonamide is more preferable. Since the decomposition temperature is within the above range and the amount of heat generated during decomposition is small, deterioration of the resin during foam molding can be suppressed.

As the component (β), one kind or a mixture of two or more kinds thereof can be used.

The amount of the component (β) is usually 0.1 part by mass or more, from the viewpoint of increasing the expansion ratio and obtaining a coaxial cable having good transmission characteristics, relative to 100 parts by mass of the (α) polyolefin resin. It is preferably 0.5 part by mass or more, more preferably 0.7 part by mass or more. On the other hand, from the viewpoint of keeping the foam cells in an appropriate size and maintaining good extrusion moldability and kink resistance, it is usually 2 parts by mass or less, preferably 1.5 parts by mass or less, more preferably 1.2 parts by mass or less. Is.

In the expandable resin composition of the present invention, components other than the components (A) to (C) and (β), for example, the components (A) to Addition of thermoplastic resins other than (C); pigments, inorganic fillers, organic fillers, resin fillers; lubricants, antioxidants, weather resistance stabilizers, heat stabilizers, release agents, antistatic agents, surfactants, etc. Agents; and the like can be further included.

Method for producing foamable composition:
The expandable resin composition of the present invention is obtained by melt-kneading the above-mentioned components (A) to (C), (β), and optionally optional components using an arbitrary melt-kneading machine; preferably, From the viewpoint of suppressing thermal decomposition of the component (β) and uniformly dispersing the component (β) in the composition, the melting point of the component having the highest melting point among the components (A) to (C) is not less than By melt-kneading at a temperature lower than the decomposition temperature of the component (β); more preferably at a temperature of 5° C. or higher higher than the melting point and 5° C. or lower than the decomposition temperature of the component (β). It can be obtained by melt-kneading.

Examples of the melt-kneader include a single-screw extruder, a twin-screw extruder, a calender roll, a Banbury mixer, various kneaders, and an apparatus combining two or more of these.

Foam:
The foam of the present invention is obtained by molding and foaming the foamable resin composition of the present invention. The method for obtaining the foam of the present invention is not particularly limited. As a method for obtaining the foam of the present invention, for example, an apparatus equipped with any extruder and any die is used, and the foamable resin composition of the present invention is melted at a temperature equal to or higher than the decomposition temperature of the above component (β). -Extrusion methods can be mentioned. Moreover, you may perform the process of manufacturing a foamable resin composition and the process of molding a foam body continuously.

The foam of the present invention has an expansion ratio of preferably 30 to 60%, more preferably 35 to 55%, measured by the following test (1-1). When the expansion ratio is within the above range, the coaxial cable containing the foam of the present invention has excellent transmission characteristics, kink resistance, and solder resistance.

In the foam of the present invention, the average diameter of the foam cells measured by the following test (1-2) is preferably less than 50 μm, more preferably less than 45 μm, still more preferably less than 40 μm. When the average diameter of the foam cells is within the above range, the coaxial cable containing the foam of the present invention has excellent transmission characteristics, kink resistance, and solder resistance.

coaxial cable:
The coaxial cable of the present invention is a cable including the foam of the present invention. Typically, the present invention is not limited to the cable in which the conductor is insulation-coated with the foam of the present invention. It may be a cable including the foam of the present invention as a sheath or an interposer. The method of insulatingly coating the conductor with the foam of the present invention is not particularly limited. As a method for insulatingly coating a conductor with the foam of the present invention, for example, a cable molding apparatus including an arbitrary extruder and an arbitrary die is used, and the expandable resin composition of the present invention is applied to the periphery of an arbitrary conductor. A method of coating by melting and extruding at a temperature equal to or higher than the decomposition temperature of the above component (β) can be mentioned.

FIG. 1 is a conceptual diagram of a cross section showing an example of the coaxial cable of the present invention. An inner conductor 1 is provided at the center of the cable, the outer periphery of the inner conductor 1 is covered with a foamed insulator 2 made of the foamed material of the present invention, and an outer conductor 4 is provided on the outside through an interposition 3. Further, a sheath 5 is provided as an outermost layer on the outer circumference of the outer conductor 4.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.

Measurement method (1) Foamability:
(1-1) Expansion ratio:
The specific gravity (D ₀ ) of the unfoamed expandable resin composition and the specific gravity (D ₁ ) of the round rod-shaped foam obtained in the following (4) Evaluation of extrusion moldability were calculated by the following formula (3). The average value of 5 samples was calculated and evaluated according to the following criteria. The specific gravity was measured according to JIS K7112:1999 by an underwater substitution method.
Formula (3) Foaming ratio (%)=(D ₀ −D ₁ )/D ₀ ×100
◯: Expansion ratio of 35% or more.
B: Expansion ratio is 30% or more and less than 35%.
X: Expansion ratio is less than 30%.
(1-2) Foam cell diameter:
The cross section of the round rod-shaped foam obtained in the following (4) Evaluation of extrusion moldability was observed with a scanning electron microscope at a magnification of 100 to obtain an image. From the above images, the diameters of 30 randomly selected foamed cells (long diameters when the cells were elliptical) were measured, average values were calculated, and evaluation was made according to the following criteria.
◯: Foam cell diameter less than 40 μm.
B: Foam cell diameter of 40 μm or more and less than 50 μm.
X: Foam cell diameter of 50 μm or more.

(2) Kink resistance:
A test piece with a length of 10 cm was sampled from the round bar-shaped foam obtained by the following (4) Evaluation of extrusion moldability and sandwiched between two plane-parallel flat plates in a U-shaped bent state (see FIG. 2). , Kink (the round rod-shaped foam is broken or buckled) is narrowed at a speed of 50 mm/min while maintaining the plane-parallel state of the flat plate, and the flatness of the flat plate when the kink occurs The distance (mm) was measured. The average value of five samples was calculated and evaluated according to the following criteria.
◯: Distance is less than 15 mm.
Δ: Distance is 15 mm or more and less than 20 mm.
X: Distance is 20 mm or more.

(3) Heat resistance:
A 10 cm long test piece was taken from the round bar-shaped foam obtained in the following (4) Evaluation of extrusion moldability, and was vertically hung in an oven at a temperature of 200°C. It was visually observed through the window of the oven whether it occurred within 20 seconds. Five samples were measured and evaluated according to the following criteria. Here, "dripping down due to its own weight" means that a part or all of the test piece has fallen to the floor of the oven. Those having excellent heat resistance in this test can be expected to have good solder resistance.
◯: There were 0 drops.
Δ: 1-2 drips.
×: Three or more dropped

(4) Extrudability:
Using a single screw extruder (φ20 mm, L/D=28) and a round die of φ3.0 mm, the screw rotation speed is 60 rpm, mesh size #60, and the cylinder temperature is 170 to 210° C. inclined from the raw material inlet side. , And a die temperature of 210° C. were used to extrude a round rod-shaped foam. The round rod-shaped foam obtained above was visually observed and evaluated according to the following criteria.
(4-1) Appearance of extrusion surface:
◯: The surface of the molded product has no rough surface or uneven melting, or the surface of the molded product has no rough surface or uneven melting.
Δ: Rough skin and uneven melting are observed on the surface of the molded product. However, there is no problem in practical use.
X: Remarkable skin roughness and melting unevenness are recognized on the surface of the molded body. This is a problematic level for practical use.
(4-2) Extruded shape:
◯: The cross section of the molded body substantially holds a perfect circle, and its diameter is 4 mm or more.
Δ: The cross section of the molded body is substantially circular, but its diameter is 3 mm or more and less than 4 mm, or the cross section of the molded body is slightly elliptical, but its major axis is 3 mm or more, which is practical. Is at a level without problems.
X: The cross-section of the molded body is largely broken, which is a problematic level for practical use.

Raw materials used Component (A):
(A-1) High melt tension propylene block copolymer "FTS3000 (trade name)" manufactured by Japan Polypro Co., Ltd. Melt mass flow rate (MFR) 10 g/10 minutes, melt tension (MT) 3 g, MT×MFR 30 g ² /10 minutes, melting point 161° C.
(A-2) A high melt tension propylene-based block copolymer “FTS6000 (trade name)” manufactured by Japan Polypro Co., Ltd. Melt mass flow rate (MFR) 3 g/10 minutes, melt tension (MT) 17 g, MT×MFR 51 g ² /10 minutes, melting point 161° C.

Ingredient (B):
(B-1) Propylene homopolymer “MA3 (trade name)” manufactured by Japan Polypro Co., Ltd. Melt mass flow rate (MFR) 11 g/10 minutes, melt tension (MT) 1 g, MT×MFR 11 g ² /10 minutes, melting point 161° C.
(B-2) Propylene homopolymer “Y400GP (trade name)” of Prime Polymer Co., Ltd. Melt mass flow rate (MFR) 4 g/10 minutes, melt tension (MT) 2 g, MT×MFR 8 g ² /10 minutes, melting point 161° C.

Ingredient (C):
(C-1) Linear low-density polyethylene "DOWLEX2645G (trade name)" manufactured by Dow Chemical Company. Density 919 Kg/m ³ , melt mass flow rate 0.9 g/10 minutes.
(C-2) Ube Maruzen Polyethylene Co., Ltd.'s high pressure low density polyethylene "UBEC450 (product name)". Density 921 Kg/m ³ , melt mass flow rate 1.0 g/10 minutes.

Reference component (C'):
(C'-1) High-density polyethylene "Hi-Zex 5100B (trade name)" manufactured by Mitsui Chemicals, Inc. Density 947 Kg/m ³ , melt mass flow rate 0.25 g/10 minutes

Ingredient (β):
(Β-1) Azodicarbonamide “Uniform AZ L-25I (trade name)” manufactured by Otsuka Chemical Co., Ltd. Decomposition temperature 198°C.

Optional component (E):
(E-1) A hindered phenolic antioxidant "Irganox 1010 (trade name)" manufactured by Ciba Specialty Chemicals Co., Ltd.

Examples 1-12, Examples 1S-7S
Using a twin-screw kneading extruder, a compound having a compounding ratio shown in any one of Tables 1 to 3 is melt-kneaded at a die outlet resin temperature of 170 to 190° C. to obtain an unfoamed foamable resin composition. It was The above tests (1) to (4) were performed. The results are shown in any one of Tables 1 to 3.

The foamable resin composition of the present invention can provide a fine and uniform foam having independent foam cells even when foamed at a high ratio. It also has excellent kink resistance and extrusion moldability. Further, it has excellent heat resistance, and good solder resistance can be expected. Therefore, the expandable resin composition of the present invention can be suitably used as an insulator for coaxial cables.

It is a conceptual diagram of a section showing an example of a coaxial cable of the present invention. It is a conceptual diagram explaining a kink resistance test.

1: Inner conductor 2: Foam insulation 3: Interposition 4: Outer conductor 5: Sheath 6: Round bar foam 7: Flat plate

Claims (4)

(Α) 100 parts by mass of polyolefin resin; and (β) 0.1 to 2.0 parts by mass of chemical foaming agent;
A foamable resin composition for a coaxial cable , comprising:
The above (α) polyolefin resin is
(A) Propylene polymer satisfying the following characteristics (a) and (b): 10 to 50% by mass;
(B) Propylene homopolymer satisfying the following characteristics (a) and (c): 30 to 70% by mass; and (C) Low density polyethylene-based polymer: 5 to 35% by mass.
Here, the total of the components (A), (B), and (C) is 100% by mass,
The total of the above components (A) and (B) is 65 to 95 mass %.
(A) The melt mass flow rate is 1 to 15 g/10 minutes.
(B) The following formula (1) is satisfied.
Formula (1) MT×MFR ≧20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.
(C) The following formula (2) is satisfied.
Formula (2) MT×MFR<20 g ² /10 min where MT is melt tension and MFR is melt mass flow rate.
Coaxial cable foam coaxial cable foamable resin composition of claim 1 expansion ratio is 30% to 60%:
Here, the expansion ratio is calculated by the following formula (3):
Formula (3) Foaming ratio (%)=(D ₀ −D ₁ )/D ₀ ×100
However, D ₀ is the specific gravity of the unfoamed foamable resin composition, D ₁ is the specific gravity of the foam,
The specific gravity is based on JIS K7112:1999 and measured by an underwater substitution method.
Coaxial cable foam coaxial cable foamable resin composition according to claim 1, wherein the average diameter of the foamed cell is 20 to 50 m.
A coaxial cable comprising the foam for coaxial cable according to claim 2 or 3 .