JP5420662B2 - Foamed electric wire and transmission cable having the same - Google Patents

Description

  The present invention relates to a foamed electric wire and a transmission cable having the same.

  The foam insulation layer of foamed electric wires used for USB 3.0 cables, HDMI cables, Infiniband cables, micro USB cables, etc., has a small diameter, high heat resistance, and can be finely foamed. Is required.

  As such a foam insulating layer, there has heretofore been known one obtained by melting a polypropylene resin, supplying a chemical foaming agent such as azodicarbonamide, and kneading them uniformly (the following patents) Reference 1).

JP 2006-45268 A

  However, when the foamed insulating layer described in Patent Document 1 is obtained, the melting point of the propylene-based resin is high, so when the propylene-based resin and the chemical foaming agent are kneaded, the chemical foaming agent is decomposed before being uniformly kneaded. The chemical foaming agent cannot be directly kneaded into the propylene resin.

  Here, it is conceivable to knead a master batch containing a chemical foaming agent at a high concentration with a propylene-based resin. At this time, when polyethylene is used as the resin for the masterbatch, since polyethylene has a low melting point, melting of polyethylene occurs at a relatively low temperature. For this reason, a chemical foaming agent does not decompose | disassemble at the time of kneading | mixing a propylene-type resin and a masterbatch, and foaming does not occur easily. On the other hand, when a propylene-based resin is used as the masterbatch resin, the propylene-based resin generally has a higher melting point than polyethylene, and therefore it is necessary to give a high temperature to the masterbatch in order to melt the propylene-based resin. In this case, as in the case where the chemical foaming agent is directly kneaded into the propylene resin, the chemical foaming agent is decomposed and foaming occurs.

  Therefore, when a master batch containing a chemical foaming agent at a high concentration is kneaded with a propylene resin, it is considered that polyethylene, particularly low density polyethylene, must be used as the resin for the master batch.

  However, when polyethylene is used as the resin for the masterbatch, the foamed cells can be made sufficiently fine, but fluctuations in the outer diameter of the resulting foamed wire can still be sufficiently suppressed in order to achieve better high-frequency characteristics. I can't say that.

  This invention is made | formed in view of the said situation, and it aims at providing the foamed electric wire which can fully suppress an outer diameter fluctuation | variation, and the transmission cable which has this, implement | achieving sufficient refinement | miniaturization of a foam cell. .

  As a result of intensive studies to solve the above problems, the present inventor used a low melting point propylene resin having a low melting point as the resin of the masterbatch, and the blending ratio of the low melting point propylene resin in the entire resin was determined to be a predetermined value. The inventors have found that the above problem can be solved by specifying the range, and have completed the present invention.

  That is, the present invention is a foamed electric wire comprising a conductor and a foamed insulating layer covering the conductor, wherein the foamed insulating layer comprises a base resin composed of a high melting point propylene resin having a melting point of 150 ° C. or higher, and a heat A decomposable chemical foaming agent and a masterbatch containing a low melting point propylene resin having a melting point of 135 ° C. or lower are kneaded to melt the low melting point propylene resin, and then the pyrolyzable chemical foaming agent is thermally decomposed. It is obtained by foaming, characterized in that the blending ratio of the low melting point propylene resin in the whole resin composed of the high melting point propylene resin and the low melting point propylene resin is 20 to 70% by mass. It is a foamed electric wire.

  According to this foamed electric wire, fluctuations in the outer diameter can be sufficiently suppressed while realizing sufficient miniaturization of the foamed cell.

  In the foamed electric wire, the base resin is preferably a copolymer of propylene and an α-olefin other than propylene, and the copolymer preferably contains a block copolymer. In this case, compared with the case where a copolymer is comprised with the mixture of a block copolymer and a random copolymer, a foaming cell can be refined more fully and more excellent heat resistance can be acquired.

  Moreover, in the said foamed electric wire, it is preferable that the outer diameter of the said foaming insulation layer is 1.6 mm or less.

  Furthermore, in the said foamed electric wire, it is preferable that the compounding ratio of the said low melting point propylene resin in the whole resin consisting of the said high melting point propylene resin and the said low melting point propylene resin is 40-60 mass%.

  In the foamed electric wire, the low melting point propylene-based resin is preferably a random copolymer of propylene and an α-olefin. In this case, there exists an advantage that heat resistance and hardness are high compared with the case where low melting point propylene-type resin is not the random copolymer of a propylene and an alpha olefin.

  Moreover, this invention is a transmission cable which has the said foamed electric wire. According to this transmission cable, transmission loss can be reduced and good high-frequency characteristics can be obtained.

In the present invention, “melt tension at break” is a melt tension measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.), and specifically, an inner diameter of 1.0 mm and a length of 10 mm. After filling the flat capillary with resin, set the piston speed 5mm / min, barrel inner diameter 9.55mm, take-up acceleration 400m / min ² , barrel, capillary and thermostat just after the barrel to 200 ° C conditions The barrel is filled with resin, and after 5 minutes preheating, piston extrusion is started at the above-mentioned piston speed, accelerated at the above-mentioned take-up acceleration, taken up, and measured for the tension at the time of breaking. It shall mean the average value of measured values. The “resin” filled in the flat capillary or barrel means a mixed resin of the base resin and the resin in the master batch.

  ADVANTAGE OF THE INVENTION According to this invention, the foamed electric wire which can fully suppress an outer diameter fluctuation | variation, implement | achieving sufficient refinement | miniaturization of a foam cell, and a transmission cable which has this are provided.

It is a partial side view which shows one Embodiment of the foamed electric wire of this invention. It is sectional drawing along the II-II line of FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1 is a partial side view showing an embodiment of a foamed electric wire according to the present invention, and shows an example in which the foamed electric wire is applied to a coaxial cable as a transmission cable. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. As shown in FIG. 1, the transmission cable 10 is a coaxial cable, and includes a foamed electric wire 5, an outer conductor 3 that surrounds the foamed electric wire 5, and a sheath 4 that covers the outer conductor 3. The foamed electric wire 5 includes an inner conductor 1 and a foamed insulating layer 2 that covers the inner conductor 1.

  Here, the foamed insulating layer 2 is a master batch including a base resin made of a high melting point propylene resin having a melting point of 150 ° C. or higher, a pyrolytic chemical foaming agent, and a low melting point propylene resin having a melting point of 135 ° C. or lower. And the low melting point propylene-based resin is melted, and then the pyrolytic chemical foaming agent is thermally decomposed and foamed. Here, the blending ratio of the low melting point propylene resin in the whole resin composed of the high melting point propylene resin and the low melting point propylene resin is 20 to 70% by mass.

  According to the foamed electric wire 5 having such a configuration, fluctuations in the outer diameter can be sufficiently suppressed while sufficiently miniaturizing the foamed cells. Therefore, according to the transmission cable 10 having the foamed electric wire 5, it is possible to reduce transmission loss and obtain good high frequency characteristics.

  Next, a method for manufacturing the transmission cable 10 will be described.

  First, a method for manufacturing the foamed electric wire 5 will be described.

(Inner conductor)
First, the inner conductor 1 is prepared. Examples of the internal conductor 1 include metal wires such as copper wires, copper alloy wires, and aluminum wires. In addition, a material obtained by plating the surface of the metal wire with tin, silver or the like can be used as the internal conductor 1. The inner conductor 1 can be a single wire or a stranded wire.

(Foam insulation layer)
Next, the foamed insulating layer 2 is formed on the inner conductor 1.

  In order to form the foamed insulating layer 2, a base resin made of a high melting point propylene resin having a melting point of 150 ° C. or higher, a pyrolytic chemical foaming agent, and a low melting point propylene resin having a melting point of 135 ° C. or lower is included. Prepare a masterbatch.

  Here, the base resin will be described.

  The high melting point propylene resin means a propylene resin having a melting point of 150 ° C. or higher. Here, when the melting point is less than 150 ° C., the heat resistance of the foamed electric wire 5 is significantly reduced. The melting point of the high melting point propylene-based resin is preferably 155 ° C. or higher, and more preferably 160 ° C. or higher. However, the melting point of the high-melting-point propylene-based resin is preferably 170 ° C. or less because the balance between the heat resistance and the low-temperature embrittlement resistance and the bending resistance can be favorably maintained.

  Propylene-type resin means resin containing the structural unit derived from propylene. Therefore, such propylene-based resins include homopolypropylene obtained by homopolymerization of propylene, copolymers of olefins other than propylene and propylene, and mixtures of two or more thereof. Examples of olefins other than propylene include ethylene, 1-butene, 2-butene, 1-hexene and 2-hexene. Among these, α-olefins such as ethylene, 1-butene, and 1-hexene are preferably used from the viewpoint of realizing more sufficient refinement of the foamed cell and obtaining better heat resistance, and more preferably ethylene. .

  When the propylene-based resin is a copolymer of olefin other than propylene and propylene, the copolymer may include a block copolymer or a random copolymer. However, it is preferred that the copolymer comprises a block copolymer. When the copolymer contains a block copolymer, the foamed cells can be more sufficiently miniaturized and better heat resistance can be obtained as compared with the case where the block copolymer is not contained.

  Here, the copolymer may be composed only of a block copolymer, or may be composed of a mixture of a block copolymer and a random copolymer, but only composed of a block copolymer. Is preferred. In this case, compared with the case where a copolymer is comprised with the mixture of a block copolymer and a random copolymer, a foaming cell can be refined more fully and more excellent heat resistance can be acquired.

  Next, the master batch will be described.

  The masterbatch contains a low melting point propylene-based resin and a pyrolytic chemical foaming agent. The low melting point propylene resin refers to a propylene resin having a melting point of 135 ° C. or lower. Here, when the melting point exceeds 135 ° C., it is necessary to melt the propylene-based resin at a high temperature in the process of producing the master batch, and the chemical foaming agent is thermally decomposed. As a result, foaming unevenness occurs in the resulting foamed insulating layer 2 and the high-frequency characteristics are greatly deteriorated. Further, the melting point of the low melting point propylene-based resin is preferably 130 ° C. or less, and more preferably 127 ° C. or less. However, the melting point of the low-melting-point propylene-based resin is preferably 120 ° C. or higher from the viewpoint of ease of handling in production.

  Such low melting point propylene resins include homopolypropylene obtained by homopolymerization of propylene and copolymers of olefins other than propylene and propylene, as with the high melting point propylene resins. The low melting point propylene-based resin includes a mixture of two or more of these. Examples of olefins other than propylene include ethylene, 1-butene, 2-butene, 1-hexene and 2-hexene. Among these, α-olefins such as ethylene, 1-butene and 1-hexene are preferably used from the viewpoints of fine foaming and heat resistance, and more preferably ethylene.

  When the low-melting-point propylene-based resin is a copolymer of olefin other than propylene and propylene, the copolymer may include a block copolymer or a random copolymer. However, the copolymer preferably includes a random copolymer. When the copolymer contains a random copolymer, the melting point of the copolymer can be lowered more than when the random copolymer is not included, and the master batch without thermally decomposing the pyrolytic chemical foaming agent Can be easily obtained. Further, excellent low temperature embrittlement resistance and bending resistance can be obtained.

  Here, the copolymer may be composed only of a random copolymer or may be composed of a mixture of a random copolymer and a block copolymer, but only composed of a random copolymer. Is preferred. In this case, compared with the case where the copolymer is composed of a mixture of a random copolymer and a block copolymer, the melting point of the copolymer can be further lowered, and the foamed cell can be made sufficiently finer. And more excellent heat resistance can be obtained. Here, it is more preferable that the low-melting-point propylene-based resin is a random copolymer of α-olefin and propylene in terms of maintaining a better balance between heat resistance, low-temperature embrittlement characteristics, and flex resistance. .

  The low-melting-point propylene-based resin can be usually obtained by using a metallocene catalyst as a catalyst in homopolymerization of propylene or copolymerization of propylene and another olefin.

The pyrolytic chemical foaming agent is not particularly limited as long as it thermally decomposes to generate a gas such as NH ₃ , N ₂ , and CO _2. For example, azodicarbonamide (hereinafter referred to as “ADCA”), 4, Examples thereof include 4′-oxybisbenzenesulfonyl hydrazide, N, N′-dinitrosopentamethylenetetramine, azobisisobutyronitrile and the like. Among them, azodicarbonamide has a high thermal decomposition temperature, the difference between the melting point of the low melting point propylene resin and the thermal decomposition temperature becomes larger, and the thermal decomposition of the chemical blowing agent can be sufficiently suppressed in the process of producing the masterbatch. Therefore, it is preferable.

  The content of the pyrolytic chemical foaming agent in the masterbatch is usually 0.5 to 7% by mass, preferably 0.6 to 5% by mass, more preferably 0.7 to 4% by mass. .

  In order to obtain a master batch, a low melting point propylene resin and a pyrolytic chemical foaming agent may be introduced into an extruder and kneaded. For this purpose, the low-melting-point propylene resin and the pyrolytic chemical foaming agent may be heated and kneaded at a temperature equal to or higher than the melting point of the low-melting-point propylene resin. However, if the pyrolytic chemical foaming agent is thermally decomposed during kneading, foaming unevenness may occur in the foamed insulating layer 2. Therefore, kneading is preferably performed at a temperature of 150 ° C. or lower. For example, when ADCA is used as the pyrolytic chemical foaming agent, the kneading is preferably performed at a temperature of 130 ° C to 145 ° C.

  After preparing the base resin and the master batch as described above, the master batch and the high melting point propylene resin are kneaded. At this time, the blending ratio of the low melting point propylene resin in the entire resin composed of the high melting point propylene resin and the low melting point propylene resin is set to 20 to 70% by mass. This is because when the blending ratio is within the above range, the outer diameter fluctuation can be sufficiently suppressed as compared with the case where the blending ratio is less than 20% by mass, and when the blending ratio exceeds 70% by mass. This is because sufficiently fine foaming can be generated.

  Here, it is preferable that the compounding ratio of the low melting point propylene resin in the whole resin composed of the high melting point propylene resin and the low melting point propylene resin is 40 to 60% by mass.

  When the master batch and the base resin are kneaded, first, the low melting point propylene resin in the master batch is melted. At this time, the pyrolytic foaming agent is not thermally decomposed. In this way, after the thermal decomposition type chemical foaming agent is uniformly dispersed in the resin, the thermal decomposition type chemical foaming agent is heated to a temperature equal to or higher than the thermal decomposition temperature to be thermally decomposed to generate a decomposition gas. Then, the resin containing the decomposition gas is foamed while being extruded, and the inner conductor 1 is covered with the extrudate. Thus, the foamed insulating layer 2 is obtained on the inner conductor 1.

  In the foamed electric wire 5, it is preferable that the melt tension at the time of rupture of the resin in the foamed insulating layer 2 is 13 mN or more because the foamed cells can be more sufficiently miniaturized, and is preferably 17 mN or more. More preferred. However, if the melt tension at the time of rupture of the resin is too large, the degree of foaming tends to be low at the time of extrusion of the resin, so the melt tension is preferably 50 mN or less, more preferably 35 mN or less.

  The melt tension of the resin at the time of breaking can be adjusted, for example, by adjusting the temperature of the resin at the die outlet of the extruder.

  When the foamed electric wire 10 is used for a high-frequency cable, the outer diameter of the foamed insulating layer 2 is preferably 1.6 mm or less, and more preferably 1.0 mm or less.

  The average particle size of the base resin pellets is usually 0.2 to 3 mm, preferably 0.5 to 1.5 mm, more preferably 0.8 to 1.3 mm. The particle size of the pyrolytic chemical foaming agent The distribution is preferably a sharper particle size distribution, and the average particle size of the pyrolytic chemical foaming agent is preferably 3 to 10 μm. In this case, when the base resin and the master batch are kneaded, the foaming agent is uniformly dispersed in the base resin, and as a result, the outer diameter fluctuation of the resulting foamed insulating layer 2 can be more sufficiently suppressed. This is particularly useful when the foamed insulating layer 2 of the foamed electric wire 5 has a small diameter of 1.6 mm or less.

(Outer conductor)
Next, the outer conductor 3 is formed so as to surround the foamed electric wire 5 obtained as described above. As the external conductor 3, a known one that has been conventionally used can be used. For example, the external conductor 3 can be formed by winding a conductive wire or a tape formed by sandwiching a conductive sheet between resin sheets along the outer periphery of the insulating layer 2. Further, the outer conductor 3 can be constituted by a corrugated metal tube, that is, a corrugated metal tube. In this case, the flexibility of the foamed electric wire 5 can be improved.

(sheath)
Finally, the sheath 4 is formed. The sheath 4 protects the outer conductor 3 from physical or chemical damage. Examples of the material constituting the sheath 4 include resins such as fluororesin, polyethylene, and polyvinyl chloride. From the viewpoint of the above, a halogen-free material such as polyethylene resin is preferably used.

  The transmission cable 10 is obtained as described above.

  The present invention is not limited to the above embodiment. For example, it is preferable that the average particle size of the master batch pellets is approximately the same as the average particle size of the base resin pellets. Here, in this case, when the base resin pellets and the master batch are kneaded, the foaming agent is uniformly dispersed in the base resin, and as a result, the fluctuation in the outer diameter of the resulting foamed insulating layer 2 is sufficiently suppressed. be able to. This is particularly useful when the foamed insulating layer 2 of the foamed electric wire 5 has a small diameter of 1.6 mm or less. At this time, when the average particle size of the master batch pellets and the base resin pellets is 0.8 to 1.3 mm, it is more effective for suppressing fluctuations in the outer diameter.

  Moreover, although the example in which the foamed electric wire 5 is applied to a coaxial cable as a transmission cable is shown in the above embodiment, the foamed electric wire 5 is a USB 3.0 cable, an HDMI cable, an Infiniband cable, a micro USB cable, or the like. It can also be applied to high-speed transmission cables.

  Hereinafter, the content of the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples. The unit of numerical values in Table 1 is “% by mass” unless otherwise specified.

Example 1
First, an ethylene-propylene copolymer having a melting point of 165 ° C. (trade name: FB5100, manufactured by Nippon Polypro Co., Ltd., hereinafter referred to as “EP copolymer”) was prepared as a base resin.

On the other hand, a random copolymer (trade name: WFX4TC, manufactured by Nippon Polypro Co., Ltd.) having a melting point of 125 ° C. as a master batch resin (MB resin), and azodicarbonamide (ADCA) as a pyrolytic chemical foaming agent Was introduced into an extruder (product name: Labo Plast Mill D2020, screw diameter (D): φ20 mm, effective screw length (L): 400 mm, manufactured by Toyo Seiki Seisakusho Co., Ltd.). At this time, ADCA added 3 mass parts with respect to 100 mass parts of random copolymers. And melt extrusion was performed on condition of the following, the melt extrudate was cut with the pelletizer, and the pellet-shaped masterbatch was obtained. In addition, WFX4TC which is MB resin is a random copolymer of ethylene and propylene.
Kneading temperature: 140 ° C
Screw speed: 20rpm

  Then, the base copolymer EP copolymer and the masterbatch are put into an extruder (screw diameter (D): φ25 mm, effective screw length (L): 800 mm, manufactured by St. Seisakusho) different from the above extruder. Extrusion molding was performed. At this time, an 80 mm portion (hereinafter referred to as a “first portion”) from the inlet of the extruder toward the downstream side is set at 160 ° C., and a further 160 mm downstream portion (hereinafter referred to as a “second portion”). Was set at 190 ° C., the MB resin in the masterbatch was melted in the first part, and then the ADCA was pyrolyzed in the second part. In addition, when the base resin and the master batch are introduced into the extruder, the blending ratio of the MB resin is as shown in Table 1 with respect to the entire resin composed of the base resin and the MB resin in the master batch. did.

  Then, the extrudate was extruded into a tube shape from an extruder, and a conductor having a diameter of 0.32 mm was covered with the tube-shaped extrudate. Thus, a foamed electric wire comprising a conductor and a foamed insulating layer having an outer diameter of 0.92 mm and a thickness of 0.3 mm covering the conductor was produced.

(Example 2)
A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio of the base resin and the MB resin was changed as shown in Table 1.

(Example 3)
The MB resin was changed from WFX4TC to WFW4 (trade name, manufactured by Nippon Polypro Co., Ltd.), and a master batch was obtained in the same manner as in Example 2 except that it was obtained by melt-extruding MB resin and ADCA under the following conditions. Thus, a foamed electric wire was produced.
Kneading temperature: 150 ° C
Screw speed: 20rpm

Example 4
A foamed electric wire was produced in the same manner as in Example 2 except that the base resin was changed from FB5100 to FB3312 (trade name, mp: 165 ° C., manufactured by Nippon Polypro Co., Ltd.) which is an EP block copolymer.

(Example 5)
The base resin is changed from FB5100 to a mixture of FB5100 and EP random copolymer F227D (trade name, mp: 150 ° C., manufactured by Prime Polypro Co., Ltd.), and the blending ratio of FB5100, F227D and MB resin is changed. Changes were made as shown in Table 1, and a foamed electric wire was prepared in the same manner as in Example 1 except that the base resin and the master batch were kneaded as follows. That is, in the kneading of the base resin and the master batch, the first part of the extruder is set to 145 ° C., and the second part downstream thereof is set to 180 ° C. After the resin was melted, ADCA was pyrolyzed in the second part.

(Example 6)
The base resin was changed from FB5100 to a mixture of FB5100 and F113G which is a homopolypropylene (trade name, mp: 165 ° C., manufactured by Prime Polypro Co., Ltd.), and the mixing ratio of FB5100, F113G and MB resin is shown in Table 1. A foamed electric wire was produced in the same manner as in Example 1 except that the changes were made as shown.

(Example 7)
A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio of the base resin and the MB resin was changed as shown in Table 1.

(Example 8)
A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio of the base resin and the MB resin was changed as shown in Table 1.

(Comparative Example 1)
The MB resin was changed from WFX4TC to F522N (trade name, mp: 110 ° C., manufactured by Ube Industries, Ltd.) which is a low density polyethylene (LDPE), and the blending ratio of the base resin and the MB resin is shown in Table 1. A foamed electric wire was produced in the same manner as in Example 1 except that the change was made.

(Comparative Example 2)
The MB resin was changed from WFX4TC to Hi-Zex (registered trademark) 5305E (trade name, mp: 130 ° C., manufactured by Mitsui Chemicals, Inc.), which is a high-density polyethylene (HDPE). A foamed electric wire was produced in the same manner as in Example 1 except that it was obtained by melt extrusion under the following conditions.
Kneading temperature: 150 ° C
Screw speed: 20rpm

(Comparative Example 3)
As shown in Table 1, the base resin is changed from FB5100 to FB3312 (trade name, mp: 165 ° C., manufactured by Nippon Polypro Co., Ltd.), which is an EP block copolymer. A foamed electric wire was produced in the same manner as in Example 1 except that the change was made.

(Comparative Example 4)
A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio of the base resin and the MB resin was changed as shown in Table 1.

(Comparative Example 5)
The master batch was prepared in the same manner as in Example 1 except that the MB resin was changed to FB5100 used as the base resin of Example 1 and the kneading temperature of MB resin and ADCA was changed to 180 ° C. However, ADCA in the masterbatch is thermally decomposed and foamed in the process of producing the masterbatch, and the masterbatch cannot be produced. As a result, the foamed electric wire cannot be produced.

[Characteristic evaluation]
The following characteristics were evaluated about the foamed electric wire obtained in Examples 1-8 and Comparative Examples 1-4. In Comparative Example 5, a foamed insulating layer could not be formed, and thus was not subjected to characteristic evaluation.

(1) Melt tension at break The melt tension at break was measured for the foamed electric wires obtained in Examples 1 to 8 and Comparative Examples 1 to 4 as follows.

That is, the melt tension was measured using a capillary rheometer (Capillograph 1D, manufactured by Toyo Seiki Seisakusho Co., Ltd.). Specifically, a flat capillary with an inner diameter of 1.0 mm and a length of 10 mm is filled with resin, the piston speed is 5 mm / min, the barrel inner diameter is 9.55 mm, the take-up acceleration is 400 m / min ² , the barrel, the capillary, and the thermostat immediately after the barrel. After setting the temperature to 200 ° C., the barrel was filled with resin, and after preheating for 5 minutes, piston extrusion was started at the piston speed, accelerated by the take-up acceleration and taken up, and the tension when it was broken was measured. An average value of measured values of tension obtained by performing this 10 times was calculated. The results are shown in Table 1. The “resin” filled in the flat capillary or the barrel is a mixed resin of the base resin and the resin in the master batch.

に基づいて測定した。そして、１００個の発泡セルのセル径の平均値を「平均発泡セル径」として算出した。結果を表２に示す。なお、表２において、平均発泡セル径が５０μｍ未満である発泡絶縁層を有する発泡電線を合格とし、平均発泡セル径が５０μｍ以上である発泡絶縁層を有する発泡電線を不合格とした。(2) Average foamed cell diameter A part of the foam insulation layer was cut out from the foamed electric wires obtained in Examples 1 to 8 and Comparative Examples 1 to 4, and the cross section of the foam insulation layer was observed using a scanning electron microscope. did. And the cell diameter for each of 100 randomly selected foam cells is given by the following formula:

Measured based on And the average value of the cell diameter of 100 foam cells was computed as "average foam cell diameter." The results are shown in Table 2. In Table 2, a foamed electric wire having a foamed insulating layer having an average foamed cell diameter of less than 50 μm was accepted, and a foamed electric wire having a foamed insulating layer having an average foamed cell diameter of 50 μm or more was rejected.

（式中、Ｔｂは加熱変形試験前の発泡絶縁層の厚さ、Ｔａは加熱変形試験後の発泡絶縁層の厚さを示す）
に従って算出した。結果を表２に示す。(3) Heat resistance Heat resistance was evaluated by conducting a heat deformation test on the foamed electric wires of Examples 1 to 8 and Comparative Examples 1 to 4. The heat deformation test was performed by using a heat deformation tester of “three-piece heat deformation tester model number W-3” manufactured by Toyo Seiki Seisakusho Co., Ltd. Specifically, a foamed electric wire cut to a length of 5 cm is placed on a cylindrical jig having a diameter of 9 mm and a length of 5.0 mm, preheated for 1 hour, and then heated to 121 ° C. while pressing the foamed electric wire against the cylindrical jig. Then, a load of 250 g was applied for 1 hour. And the heating deformation rate is the following formula:

(In the formula, Tb represents the thickness of the foamed insulating layer before the heat deformation test, and Ta represents the thickness of the foamed insulating layer after the heat deformation test)
Calculated according to The results are shown in Table 2.

に基づいて外径変動幅を算出した。ここで、外径変動幅の合格基準は２５μｍとした。即ち外径変動幅が２５μｍ以下である発泡電線については外径変動幅の合格基準達成率が１００％以上となり、外径変動幅が抑制されたことになるので合格とした。また外径変動幅が２５μｍを超える発泡電線については外径変動幅の合格基準達成率が１００％未満となり、外径変動幅が十分抑制されていないことになるので不合格とした。結果を表２に示す。(4) Outer diameter fluctuation range For the foamed electric wires having a length of 2000 m obtained in Examples 1 to 8 and Comparative Examples 1 to 4, the maximum value and the minimum value of the outer diameter were measured using an outer diameter measuring instrument (high speed and high speed manufactured by Keyence Corporation). Accuracy digital measuring instrument LS-7000 series)

Based on the above, the outer diameter fluctuation range was calculated. Here, the acceptance standard of the outer diameter fluctuation range was 25 μm. That is, for the foamed electric wire having an outer diameter fluctuation width of 25 μm or less, the acceptance standard achievement rate of the outer diameter fluctuation width was 100% or more, and the outer diameter fluctuation width was suppressed. Moreover, about the foamed electric wire whose outer diameter fluctuation width exceeds 25 micrometers, the acceptance standard achievement rate of the outer diameter fluctuation width was less than 100%, and the outer diameter fluctuation width was not sufficiently suppressed. The results are shown in Table 2.

(5) VSWR (Voltage Standing Wave Ratio)
After covering the foamed electric wires obtained in Examples 1 to 8 and Comparative Examples 1 to 4 with an outer conductor made of a tin-plated braid, the outer conductor was coated with an olefin-based non-halogen material ANA9897N (trade name, manufactured by Riken Technos). A coaxial cable was produced by extrusion coating with a sheath made of The coaxial cable thus obtained was cut to prepare 10 3 m coaxial cables. And about these 10 coaxial cables, VSWR was measured using the network analyzer 8722ES (brand name, Agilent Technologies, Inc. make), and the average value of the measured value was computed. At this time, the frequency range was 100 MHz to 5 GHz. The results are shown in Table 2.

(6) Skew Two foamed electric wires obtained in Examples 1 to 8 and Comparative Examples 1 to 4 are arranged in parallel, and these are 22 μm in thickness composed of a laminate of an aluminum layer and a polyethylene terephthalate layer together with a drain wire. Wrapped with laminate tape. Next, this was wound with an aluminum tape layer having a thickness of 25 μm together with two power lines having an outer diameter of 0.8 mm, and then covered with a braided layer, and further olefin-based non-halo material ANA9897N (trade name, manufactured by Riken Technos) Covered with a sheath consisting of In this way, a Twinax type transmission cable was produced. The transmission cable thus obtained was cut to prepare 10 2 m transmission cables. And about these 10 transmission cables, the skew was measured using TDR TDS8000 (brand name, Nippon Tektronix Co., Ltd. product), and the average value was computed. The results are shown in Table 2.

に基づいて算出した。その結果、実施例１〜８及び比較例１〜４で得られた発泡電線の発泡絶縁層における発泡度はすべて４０％であった。ここで、「発泡前の樹脂」とは、押出機に投入する前のベース樹脂及びＭＢ樹脂の混合樹脂、又は、ベース樹脂のことを言う。

(7) Degree of foaming The degree of foaming is the following formula:

Calculated based on As a result, the foaming degree in the foam insulation layer of the foamed electric wires obtained in Examples 1 to 8 and Comparative Examples 1 to 4 was 40%. Here, the “resin before foaming” refers to a mixed resin of the base resin and the MB resin before being introduced into the extruder, or a base resin.

  From the results shown in Table 2, all of the foamed electric wires of Examples 1 to 8 had an average foamed cell diameter of 45 μm or less. On the other hand, the foamed electric wire of Comparative Example 3 had a large average foamed cell diameter of 50 μm. From this, it was found that the foamed electric wires of Examples 1 to 8 were able to realize sufficient miniaturization of the foamed cells as compared with the foamed electric wires of Comparative Example 3.

  Moreover, all the foamed electric wires of Examples 1-8 showed the acceptance standard achievement rate of the outer diameter fluctuation width of 25 micrometers or less, ie, the outer diameter fluctuation width of 100% or more. On the other hand, each of the foamed electric wires of Comparative Examples 1, 2, and 4 showed an acceptance standard achievement rate of an outer diameter fluctuation width exceeding 25 μm, that is, an outer diameter fluctuation width of less than 100%. From this, it was found that the foamed electric wires of Examples 1 to 8 were sufficiently suppressed in the outer diameter fluctuation range as compared with the foamed electric wires of Comparative Examples 1, 2, and 4. In addition, regarding the VSWR measured for the coaxial cable and the skew measured for the two-core parallel line, the foamed electric wires of Examples 1 to 8 showed better results than the foamed electric wires of Comparative Examples 1, 2, and 4. I found out.

  From the above, it was found that the foamed electric wires of Examples 1 to 8 can sufficiently suppress the outer diameter variation while realizing sufficient miniaturization of the foamed cells as compared with the foamed electric wires of Comparative Examples 1 to 4.

  Therefore, according to the foamed electric wire of the present invention, it was confirmed that fluctuations in the outer diameter can be sufficiently suppressed while realizing sufficient miniaturization of the foamed cell.

DESCRIPTION OF SYMBOLS 1 ... Internal conductor (conductor), 2 ... Foam insulation layer, 5 ... Foam electric wire.

Claims (5)

  A foamed electric wire comprising a conductor and a foamed insulating layer covering the conductor, wherein the foamed insulating layer is a base resin made of a high melting point propylene resin having a melting point of 150 ° C. or higher, and a pyrolytic chemical foaming agent And kneading with a masterbatch containing a low melting point propylene resin having a melting point of 135 ° C. or lower, melting the low melting point propylene resin, and then thermally decomposing and foaming the pyrolytic chemical foaming agent. The foamed electric wire obtained by the above process, wherein the blending ratio of the low-melting-point propylene-based resin in the entire resin composed of the high-melting-point propylene-based resin and the low-melting-point propylene-based resin is 20 to 70% by mass.   The foamed electric wire according to claim 1, wherein the high melting point propylene-based resin of the base resin is a copolymer of propylene and an α-olefin other than propylene, and the copolymer includes a block copolymer.   The foamed electric wire according to claim 1 or 2, wherein an outer diameter of the foamed insulating layer is 1.6 mm or less.   The foamed electric wire according to any one of claims 1 to 3, wherein a blending ratio of the low-melting-point propylene-based resin in the entire resin including the high-melting-point propylene-based resin and the low-melting-point propylene-based resin is 40 to 60% by mass. .   The transmission cable which has a foamed electric wire as described in any one of Claims 1-4.

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