JP5426948B2 - 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 insulation layer, what is conventionally obtained by melting a polypropylene resin, supplying a chemical foaming agent such as azodicarbonamide directly thereto, and kneading them uniformly is known (see below). Patent Document 1).

  However, the base resin used in Patent Document 1 is a propylene resin and has a high melting point. Therefore, in practice, when the propylene resin and the chemical foaming agent are kneaded, the chemical foaming agent decomposes and foams before being uniformly kneaded, and the chemical foaming agent is directly kneaded into the propylene resin. That is generally difficult.

Therefore, a method is known in which a foamed insulating layer is produced by kneading a master batch containing a chemical foaming agent at a high concentration with a propylene resin (see Patent Document 2 below). In Patent Document 2, low density polyethylene (LDPE) is used as a resin for the masterbatch. As described above, the reason why LDPE is used as the resin for the master batch is as follows.
(1) In order to obtain a master batch, the temperature when kneading LDPE and a chemical foaming agent can be lowered, and foaming is less likely to occur.
(2) The chemical foaming agent does not decompose during foaming of the masterbatch and the propylene-based resin, and foaming hardly occurs.
(3) It is generally considered that LDPE is closer in density than HDPE and has better compatibility with polypropylene resins.

JP 2006-45268 A JP-A-6-080787

  By the way, there is a possibility that the transmission cable is used in various environments, and such environments include extremely cold regions and extremely hot regions. For this reason, it is desirable that the foamed electric wire included in the transmission cable has not only heat resistance but also cold resistance at the same time from the viewpoint of enhancing the versatility of the transmission cable.

  However, when LDPE is used as the resin for the masterbatch, the heat resistance of the resulting foamed wire is insufficient from the viewpoint of the versatility of the transmission cable. Was difficult.

  Therefore, a transmission cable that can achieve both heat resistance and cold resistance has been demanded.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a foamed electric wire capable of achieving both excellent heat resistance and cold resistance and a transmission cable having the same.

  As a result of intensive studies to solve the above problems, the present inventor used HDPE as a masterbatch resin, and this HDPE was determined based on the entire propylene resin and HDPE contained in the foamed insulating layer. The present inventors have found that the above-mentioned problems can be solved by containing them in a proportion, 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 includes a base resin containing a propylene-based resin having a melting point of 150 ° C. or higher, and a thermal decomposition type It is obtained by kneading a chemical foaming agent and a masterbatch containing polyethylene and melting the polyethylene, and then thermally decomposing and foaming the pyrolyzable chemical foaming agent. High-density polyethylene (HDPE) having a melting point of 135 ° C. and a specific gravity of 0.94 or more, and the ratio of the polyethylene to the base resin and the polyethylene in the foamed insulating layer is 70% by mass or less. It is a foamed electric wire characterized by this.

  According to this foamed electric wire, both excellent heat resistance and cold resistance can be achieved.

  In the said foamed electric wire, it is preferable that the ratio of the said polyethylene to the said base resin and the said polyethylene in the said foaming insulation layer is 20 mass% or more.

  In this case, compared with the case where the ratio of the polyethylene to the base resin and the polyethylene in the foamed insulating layer is less than 20% by mass, fluctuations in the outer diameter of the obtained foamed electric wire can be further suppressed.

  In the said foamed electric wire, it is preferable that the melt tension at the time of the fracture | rupture of the resin in the said foaming insulation layer is 13-50 mN. When the melt tension at the time of rupture of the resin in the foamed insulating layer is 13 mN or more, the foamed cell can be further sufficiently miniaturized. On the other hand, when the melt tension at the time of rupture of the resin in the foamed insulating layer is 50 mN or less, the degree of foaming tends to be difficult to decrease during the extrusion of the resin.

  Moreover, this invention is a transmission cable which has the said foamed electric wire. According to this transmission cable, since both excellent heat resistance and cold resistance can be achieved, it can be used in both a high temperature environment and a low temperature environment, and high versatility can be realized.

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.

  According to the present invention, a foamed electric wire that can achieve both excellent heat resistance and cold resistance and a transmission cable having the same are provided.

It is a partial section side view showing one embodiment of a foamed electric wire of the present 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 prepared by kneading a base resin containing a propylene-based resin having a melting point of 150 ° C. or higher and a masterbatch containing a pyrolytic chemical foaming agent and polyethylene, It is obtained by thermally decomposing a decomposable chemical foaming agent to cause foaming. Here, the polyethylene is a high-density polyethylene having a melting point of 125 to 135 ° C. and a specific gravity of 0.94 or more, and the ratio of the high-density polyethylene to the base resin and the high-density polyethylene in the foamed insulating layer 2 Is 70% by mass or less.

  According to the foamed electric wire 5 having such a configuration, both excellent heat resistance and cold resistance can be achieved. Therefore, according to the transmission cable 10 having the foamed electric wire 5, it can be used in both a high temperature environment and a low temperature environment, and high versatility can be realized.

  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 containing a propylene resin having a melting point of 150 ° C. or higher and a master batch are prepared. Here, the masterbatch contains a pyrolytic chemical foaming agent and polyethylene.

  Here, the base resin will be described first.

  The propylene-based resin refers to a propylene-based 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 propylene-based resin is preferably 155 ° C. or higher, and more preferably 160 ° C. or higher. However, the melting point of the propylene-based resin is preferably 170 ° C. or lower because the good balance between heat resistance and resistance to low temperature embrittlement and bending resistance can be 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, ethylene, 1-butene, 1-hexene and other α-olefins are preferably used from the viewpoint of obtaining a sufficiently finer foam cell and better heat resistance, and more preferably ethylene.

  When the propylene-based resin is a copolymer of olefin other than propylene and propylene, the copolymer includes a random copolymer in addition to the block copolymer, but the copolymer includes a block copolymer. It is preferable. 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 foamed cell can be refined more fully.

  Next, the master batch will be described.

  As described above, the master batch contains polyethylene and a pyrolytic chemical foaming agent. Polyethylene is a high-density polyethylene having a melting point of 125 to 135 ° C. and a specific gravity of 0.94 or more. Here, when the melting point exceeds 135 ° C., it is necessary to melt the master batch resin at a high temperature in the process of producing the master batch, and the chemical foaming agent is thermally decomposed to cause foaming. As a result, foaming unevenness occurs in the resulting foamed insulating layer 2 and the high-frequency characteristics are greatly deteriorated. On the other hand, if the melting point is less than 125 ° C., the heat resistance is significantly reduced. Moreover, if specific gravity is less than 0.94, heat resistance will fall remarkably. The specific gravity of the high density polyethylene is preferably 0.965 or less from the viewpoint of cold resistance.

  As such high-density polyethylene, for example, Hizex 5305E (trade name, mp: 130 ° C., specific gravity: 0.951, manufactured by Prime Polymer Co., Ltd.) can be used.

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, high-density polyethylene and a pyrolytic chemical foaming agent may be introduced into an extruder and kneaded. For this purpose, the high-density polyethylene and the pyrolytic chemical foaming agent may be heated and kneaded at a temperature equal to or higher than the melting point of the high-density polyethylene. 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, kneading is preferably performed at a temperature of 145 ° C. or lower.

  After preparing the base resin and the master batch as described above, the master batch and the base resin are kneaded.

  Here, the ratio of the high density polyethylene to the base resin and the high density polyethylene is set to 70% by mass or less. Here, it is preferable that the ratio of the high-density polyethylene is 20% by mass or more. In this case, fluctuations in the outer diameter of the obtained foamed electric wire 5 can be further suppressed as compared with the case where the ratio is out of the above range.

  When kneading the master batch and the base resin, first, the high-density polyethylene in the master batch is melted. At this time, the pyrolyzable 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, the melt tension at the time of rupture of the resin in the foamed insulating layer 2, that is, the mixed resin of the base resin and the high-density polyethylene, is 13 mN or more, so that the foamed cell can be further sufficiently miniaturized. It is preferable from the reason of becoming, and it is more preferable that it is 20 mN or more. 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.

Example 1
First, as a base resin, an ethylene-propylene copolymer (trade name: FB5100, melting point (hereinafter abbreviated as “mp”): 165 ° C., MFR: 1 g / 10 min, manufactured by Nippon Polypro Co., Ltd. Called “union”).

On the other hand, Hizex 5305E (trade name, mp: 130 ° C., specific gravity: 0.951, manufactured by Mitsui Chemicals) as HDPE as a master batch resin (MB resin), and azodicarbonamide (ADCA) as a thermal decomposition type chemical blowing 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). At this time, ADCA added 3 mass parts with respect to 100 mass parts of MB resin. 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.

Kneading temperature: 150 ° 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 master batch was melted in the first part, and then ADCA was thermally decomposed in the second part. In addition, when the base resin and the master batch are put 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)
Foaming was performed in the same manner as in Example 1 except that the base resin was changed from FB5100 to FB3312 (trade name, mp: 165 ° C., MFR: 2 g / 10 min, manufactured by Nippon Polypro Co., Ltd.), which is an EP block copolymer. An electric wire was produced.

Example 4
The base resin was changed from FB5100 to a mixture of FB5100 and EP random copolymer F227D (trade name, mp: 150 ° C., MFR: 6 g / 10 min, manufactured by Prime Polypro Co., Ltd.), and FB5100, F227D and MB A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio with the resin was as shown in Table 1, and 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., so that the MB in the master batch at the first part is set. After the resin was melted, ADCA was thermally decomposed in the second part.

(Example 5)
The base resin was changed from FB5100 to a mixture of FB5100 and homopolypropylene F113G (trade name, mp: 165 ° C., MFR: 2 g / 10 min, manufactured by Prime Polypro Co., Ltd.), and FB5100, F113G, and MB resin A foamed electric wire was produced in the same manner as in Example 1 except that the blending ratio was changed as shown in Table 1.

(Example 6)
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)
A foamed electric wire was produced in the same manner as in Example 1 except that the MB resin was changed from HDPE to WFX4TC (trade name, mp: 125 ° C., manufactured by Nippon Polypro Co., Ltd.), which is a random copolymer.

(Comparative Example 2)
MB resin was changed from HDPE to WFX4TC (trade name, mp: 125 ° C., manufactured by Nippon Polypro Co., Ltd.), which is a random copolymer, and the mixing ratio of base resin and MB resin was changed as shown in Table 1. A foamed electric wire was produced in the same manner as in Example 1 except that.

(Comparative Example 3)
A foamed electric wire was produced in the same manner as in Example 1 except that the MB resin was changed from HDPE to F522N (trade name, mp: 110 ° C., manufactured by Ube Industries, Ltd.), which is a low density polyethylene (LDPE).

(Comparative Example 4)
A foamed electric wire was produced in the same manner as in Example 2 except that the MB resin was changed from HDPE to F522N, which is low density polyethylene (LDPE).

(Comparative Example 5)
The base resin was changed from FB5100 to Hizex5305E (trade name, mp: 130 ° C., manufactured by Nippon Polypro Co., Ltd.), which is a high-density polyethylene (HDPE). Was added at a ratio of 0.6 parts by mass, and a foamed electric wire was produced in the same manner as in Example 1 except that the base resin and ADCA were kneaded as follows. That is, in the kneading of the base resin and ADCA, the base resin was melted in the first part by setting the first part of the extruder to 145 ° C. and setting the second part downstream thereof to 180 ° C. Thereafter, ADCA was thermally decomposed in the second part.

(Comparative Example 6)
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 7)
MB resin was changed to FB5100 used as the base resin of Example 1, the mixing ratio of base resin and MB resin was changed as shown in Table 1, and the kneading temperature of MB resin and ADCA was changed to 180 ° C. A master batch was prepared in the same manner as in Example 1 except that. 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]
About the foamed electric wire obtained in Examples 1-6 and Comparative Examples 1-6, the following characteristics were evaluated.

(1) Melt tension at break The melt tension of the foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6 was measured 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 MB resin in the master batch.

(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 6 and Comparative Examples 1 to 6, and the cross section of the foam insulation layer was observed using a scanning electron microscope. The cell diameter for each of 100 randomly selected foam cells is given by the following formula:

Cell diameter = (longest cell diameter + shortest cell diameter) / 2

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 1. In Table 1, a foamed electric wire having a foamed insulating layer having an average foamed cell diameter of 45 μm or less was accepted, and a foamed electric wire having a foamed insulating layer having an average foamed cell diameter exceeding 45 μm was rejected.

(3) Outer diameter fluctuation range For the 2000 m long foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6, the maximum value and the minimum value of the outer diameter were measured using an outer diameter measuring instrument (high speed manufactured by Keyence Corporation). Measured using a precision digital measuring instrument LS-7000 series), the following formula:

Outer diameter fluctuation range = maximum value-minimum value

Was used to calculate the outer diameter fluctuation range. The results are shown in Table 1.

により算出した。ここで、加熱変形率の合格基準は２４％とした。即ち加熱変形率が２４％以下である発泡電線については加熱変形率の合格基準達成率が１００％以上となり、耐熱性が向上したことになるので合格とした。また加熱変形率が２４％を超える発泡電線については加熱変形率の合格基準達成率が１００％未満となり、耐熱性が十分向上していないことになるので不合格とした。結果を表１に示す。なお、加熱変形率は、下記式：

に従って算出した。 (4) Heat resistance The heat resistance was evaluated by conducting a heat deformation test on the foamed electric wires of Examples 1 to 6 and Comparative Examples 1 to 6. 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 the foamed electric wire is pressed to 121 ° C. so as to press the foamed electric wire against the cylindrical jig. The heating was performed by applying a load of 250 g for 1 hour while heating. Thus, the heat deformation rate is measured, and based on this heat deformation rate, the acceptance standard achievement rate of the heat deformation rate is expressed by the following formula:

Calculated by Here, the acceptance criterion of the heat deformation rate was 24%. That is, a foamed electric wire having a heat deformation rate of 24% or less was accepted because the heat distortion rate passed standard achievement rate was 100% or more and the heat resistance was improved. Moreover, about the foamed electric wire with a heat deformation rate exceeding 24%, the acceptance standard achievement rate of the heat deformation rate became less than 100%, and since heat resistance was not fully improved, it was set as the rejection. The results are shown in Table 1. The heating deformation rate is expressed by the following formula:

Calculated according to

(5) Cold resistance Cold resistance was evaluated by conducting a low temperature embrittlement test on the foamed electric wires of Examples 1 to 6 and Comparative Examples 1 to 6. The low temperature embrittlement test was performed as follows.

That is, for the foamed electric wires of Examples 1 to 6 and Comparative Examples 1 to 6, the embrittlement temperature was measured using an embrittlement temperature tester (product name: embrittlement tester TM-2110, manufactured by Ueshima Seisakusho). At this time, the test conditions followed ASTM D746. The results are shown in Table 1. In Table 1, the criteria for “◎”, “◯”, and “×” were as follows.
◎ ・ ・ ・ Embrittlement temperature is -50 ℃ or less ○ ・ ・ ・ Ebrittlement temperature is higher than -50 ℃ and -40 ℃ or less × ・ ・ ・ Ebrittlement temperature is higher than -40 ℃

(6) Flexibility Flexibility was evaluated for the foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6 as follows.
That is, the flexibility of the foamed electric wire of Example 1 was performed by forming a mixed resin of the MB resin of Example 1 and the base resin of Example 1 and evaluating the flexibility of the resin sheet. The mixed resin did not contain a foaming agent. The flexibility of the foamed electric wires of Examples 2 to 6 and Comparative Examples 1 to 6 was similarly evaluated. At this time, the flexibility of the resin sheet was evaluated using hardness (Shore D) as an index. The hardness was measured according to JIS standard K7215. At this time, the hardness was measured on a resin sheet prepared according to the ASTM D2240 standard (results are shown in Table 1. In Table 1, the acceptance criteria for hardness is 68 and the hardness is 68 or less. Since the sheet is highly flexible, it is indicated as “◯”, and the resin sheet having a hardness exceeding 68 is indicated as “Δ” because the flexibility is low.

(7) VSWR (Voltage Standing Wave Ratio)
After coating the foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6 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 2 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 1.

(8) Skew Two foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6 are arranged in parallel, and these are 22 μm in thickness composed of a stack 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 1.

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

Degree of foaming (%) = [1− (specific gravity of foamed insulating layer after foaming / specific gravity of resin before foaming)] × 100

Calculated based on As a result, all the foaming degrees in the foam insulation layer of the foamed electric wires obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were 40%. Here, “resin before foaming” refers to a mixed resin of base resin and MB resin before being introduced into an extruder, or a base resin.

  From the results shown in Table 1, the heat deformation rates of the foamed electric wires of Examples 1 to 6 were all less than 25%. On the other hand, the heat deformation rate of the foamed electric wires of Comparative Examples 3 to 6 was as large as 25% or more.

  Moreover, the cold resistance of the foamed electric wires of Examples 1-6 reached the acceptance standard. On the other hand, although the cold resistance of the foamed electric wires of Comparative Examples 3 to 6 reached the acceptance standard, the cold resistance of the foamed electric wires of Comparative Examples 1 to 2 did not reach the acceptance standard.

  Therefore, it is understood that the foamed electric wires of Examples 1 to 6 can achieve both excellent heat resistance and cold resistance, whereas the foamed electric wires of Comparative Examples 1 to 6 cannot achieve both excellent heat resistance and cold resistance. It was.

  Therefore, according to the foamed electric wire of the present invention, it was confirmed that both excellent heat resistance and cold resistance can be achieved.

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

Claims (4)

Conductors,
A foamed electric wire comprising a foamed insulating layer covering the conductor,
The foam insulation layer is
A base resin containing a propylene-based resin having a melting point of 150 ° C. or higher;
Kneading a pyrolytic chemical foaming agent and a masterbatch containing polyethylene,
After melting the polyethylene, the pyrolytic chemical foaming agent is obtained by thermally decomposing and foaming,
The polyethylene is a high density polyethylene having a melting point of 125 to 135 ° C. and a density of 0.94 or more,
The ratio of the polyethylene to the base resin and the polyethylene in the foamed insulating layer is 70% by mass or less,
Foamed wire characterized by   The foamed electric wire according to claim 1, wherein a ratio of the polyethylene to the base resin and the polyethylene in the foamed insulating layer is 20% by mass or more. The melt tension at break of the resin in the foamed insulating layer is 13 to 50 mN;
The foamed electric wire according to claim 1 or 2.   The transmission cable which has a foamed electric wire as described in any one of Claims 1-3.

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