JP2023146803A - Foamed electric wire - Google Patents

Abstract

To provide a foamed electric wire that has a foamed layer having highly independent foamed cells as an insulation covering.SOLUTION: Provided is a foamed electric wire 1 that has a conductor 2 and an insulation covering 3 covering the outer periphery of the conductor 2, and in which the insulation covering 3 has a foamed layer that has foam structure, and the constituent material of the foamed layer has a take-up speed at 220°C of 10 m/min or more.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD This disclosure relates to foamed wires.

In the field of automobiles and the like, foamed wires with foamed insulation coatings are sometimes used as insulated wires. In particular, in communication wires, foamed wires are used for the purpose of reducing the dielectric loss tangent of the insulation coating. By reducing the dielectric loss tangent of the insulating coating, it is possible to suppress attenuation of communication signals due to absorption of electrical energy. Furthermore, foaming of the insulation coating also lowers the dielectric constant, so in a pair of wires for transmitting differential signals, it is possible to maintain a predetermined characteristic impedance even if the diameter of the insulated wire is reduced.

By foaming the insulation coating of an insulated wire, a high effect can be obtained in reducing the dielectric loss tangent and dielectric constant. On the other hand, since the mechanical strength of the resin material decreases due to foaming, the mechanical strength of the insulation coating, including abrasion resistance and tensile strength, tends to decrease. Therefore, a non-foamed covering layer (skin layer) may be provided inside and/or outside of the foamed layer. The coating layer provides the insulation coating with properties different from those of the foam layer, including mechanical strength. For example, Patent Documents 1 to 4 disclose structures in which a non-foamed coating layer is provided inside and/or outside of a foamed layer in an insulating coating.

Japanese Patent Application Publication No. 6-267353 Japanese Patent Application Publication No. 2008-226772 International Publication No. 2011/118717 Utility Model Publication No. 4-127917

As described above, in the insulation coating of a foamed electric wire, it is possible to improve the strength of the insulation coating by providing a non-foamed coating layer inside and/or outside of the foam layer. However, when providing a non-foamed coating layer, a process for forming the coating layer is required in addition to the formation of the foamed layer, making the manufacturing process of the foamed electric wire complicated. In particular, when the covering layer is formed of a material different from that of the foam layer, it is necessary to arrange the material of the covering layer on the outer periphery of the conductor by extrusion molding or the like, separately from the material of the foam layer. Further, when a foamed electric wire is used as a communication wire, if a material different from the foam layer is used as the covering layer, the constituent material of the covering layer may affect the communication characteristics of the communication wire.

Therefore, in the insulating layer, it is preferable that high mechanical strength can be obtained as a characteristic of the foam layer itself without relying on the mechanical strength of the coating layer. The mechanical strength of the foam layer largely depends on the state of foam cells (bubbles) contained in the foam layer. When communication occurs between adjacent foam cells B, as indicated by reference numeral B1 in FIG. 3B, the mechanical strength of the foam layer tends to decrease. Therefore, it is desired to form a foam layer with highly independent foam cells.

In view of the above, it is an object of the present invention to provide a foamed electric wire having a foamed layer with highly independent foamed cells as an insulating coating.

The foamed electric wire of the present disclosure includes a conductor and an insulating coating that covers the outer periphery of the conductor, the insulating coating has a foamed layer having a foamed structure, and the constituent material of the foamed layer is heated to 220°C. The take-up speed is 10 m/min or more.

The foamed electric wire of the present disclosure has a foamed layer with highly independent foamed cells as an insulating coating.

FIG. 1 is a cross-sectional view schematically showing the configuration of a foamed electric wire according to an embodiment of the present disclosure. 2A to 2C are cross-sectional views showing a structure in which the foamed wire is applied to a communication wire, with FIG. 2A showing a coaxial wire, FIG. 2B showing a pair wire, and FIG. 2C showing a collectively coated wire. 3A and 3B are schematic diagrams showing enlarged foam layers. FIG. 3A shows the case where the foam cells maintain independence, and FIG. 3B shows the case where the foam cells communicate. 4A and 4B show cross-sectional images of the foamed wires of Sample A and Sample B, respectively.

[Description of embodiments of the present disclosure]
First, embodiments of the present disclosure will be described.
The foamed electric wire of the present disclosure includes a conductor and an insulating coating that covers the outer periphery of the conductor, the insulating coating has a foamed layer having a foamed structure, and the constituent material of the foamed layer is heated to 220°C. The take-up speed is 10 m/min or more.

In the foamed electric wire insulation coating of the present disclosure, the constituent material of the foamed layer has a high take-up speed of 10 m/min or more at 220° C. and exhibits high melt elongation. Therefore, when forming a foam layer by extrusion molding or the like, even if stress is generated due to contraction of the material during the solidification process and the inner walls of the foam cells are stretched, the foam layer is unlikely to break. As a result, communication between the foamed cells due to rupture of the inner walls of the foamed cells and the accompanying decrease in the mechanical strength of the foamed layer are less likely to occur, resulting in a foamed electric wire having an insulating coating with excellent mechanical strength.

Here, the foam layer preferably includes a polymer component having a take-up speed of 40 m/min or more at 220°C. This makes it easier to increase the take-up speed of the entire composition of the constituent materials of the foam layer to 10 m/min or more.

The constituent material of the foam layer preferably has a melt tension of 18 mN or more at 220°C. This makes it easier to increase the stability of the foam cells in the foam layer.

The foam layer preferably includes a polymer component having a melt tension of 30 mN or more at 220°C. This makes it easier to increase the melt tension of the entire constituent material of the foam layer to 18 mN or more. In particular, if a foam layer is formed by mixing a polymer component with high melt tension with a polymer component with high take-off speed, the composition of the constituent materials of the foam layer as a whole will have both high take-off speed and high melt tension. It becomes easier to obtain raw materials.

The foam layer preferably contains an olefin thermoplastic elastomer and polypropylene. Olefinic thermoplastic elastomers have excellent melt elongation and tend to exhibit high take-off speeds. Polypropylene, on the other hand, tends to exhibit high melt tension. By mixing these materials to form a foam layer, it becomes easier to obtain a material that has both a high take-up speed and a high melt tension as a whole of the constituent materials of the foam layer.

[Details of embodiments of the present disclosure]
Hereinafter, a foamed electric wire according to an embodiment of the present disclosure will be described in detail using the drawings. In the following, various properties are measured at room temperature and in the atmosphere unless otherwise specified. The organic polymer also includes polymers with a relatively low degree of polymerization, such as oligomers.

<Structure of foamed wire>
FIG. 1 schematically shows the structure of a cross section perpendicular to the axial direction of a foamed electric wire 1 according to an embodiment of the present disclosure. The foamed electric wire 1 includes a conductor 2 and an insulating coating 3 covering the outer periphery of the conductor 2.

The conductor 2 can be made of various metal materials, but it is preferable to use copper or a copper alloy because of its high conductivity. Although the conductor 2 may be configured as a single wire, it is preferably configured as a stranded wire in which a plurality of wires (for example, seven wires) are twisted together, from the viewpoint of increasing flexibility during bending. In this case, after the strands are twisted together, compression molding may be performed to obtain a compression stranded wire. When the conductor 2 is configured as a stranded wire, it may be composed of the same wire or may contain two or more types of wire. Even if the foamed wire 1 includes only one conductor 2, as in the foamed wire 1' included in FIG. It may be included in an insulated state.

The insulation coating 3 has a foam layer. The foam layer is configured as a layer having a foam structure, and has foam cells (bubbles) B within its structure. Even if the insulation coating 3 is composed of only a foam layer as shown in FIG. 1, it may include a non-foamed coating layer that covers the inner and/or outer periphery of the foam layer in addition to the foam layer. You may be prepared. When the insulation coating 3 includes a non-foamed coating layer, the coating layer may be formed of the same material as the foam layer or a different material from the foam layer, but depending on the structure of the insulation coating 3 and From the viewpoint of simplifying the manufacturing process, it is preferable not to provide a covering layer made of a material different from the foam layer. Furthermore, the covering layer formed from the same material as the foam layer is also formed by preferential cooling from the inner circumference and/or outer circumference by the conductor 2 and/or the external environment during the foam layer formation process. It is preferable not to provide any layer other than the non-foamed layer. In this specification, "non-foamed" includes not only a state in which the material does not have a foamed structure, but also a state in which the material is foamed at a foaming ratio lower than that of the foamed layer. As will be explained later, in this embodiment, the foam layer has high mechanical strength due to the high independence of the foam cells B, so for the purpose of improving the mechanical strength of the insulation coating 3, There is no need to provide a non-foamed coating layer other than that which occurs with cooling.

In the insulation coating 3, the foam layer serves to increase the flexibility of the electric wire 1 and reduce the dielectric loss tangent and dielectric constant by enclosing the foam cells B occupied by air. Furthermore, as will be described later, in this embodiment, the independence of the foamed cells B in the foamed layer is high, so that even if it has a foamed structure, it exhibits high mechanical strength. The thickness of the foam layer is not particularly limited, but from the viewpoint of sufficiently obtaining these functions, a range of 200 μm or more and 400 μm or less can be suitably exemplified.

When manufacturing the foamed electric wire 1, a material constituting the foam layer of the insulating coating 3 is placed around the outer periphery of the conductor 2 to form a coating by extrusion molding or the like. A foaming agent that foams when heated is added to the material constituting the foam layer, and foaming is caused by the heat applied during extrusion molding. Alternatively, after the material is placed around the outer periphery of the conductor 2 by extrusion molding or the like, the covering is separately heated and foamed. The material placed around the outer periphery of the conductor 2 solidifies by being cooled and becomes a foam layer. Cooling occurs by removing heat through the conductor 2 and dissipating the heat to the outside environment. The sheathing may be immersed in a coolant, such as water, to facilitate cooling by the external environment. When the conductor 2 is not preheated during cooling, the coating is preferentially cooled on the inner circumference side, and the non-foamed coating layer reaches the inner circumference of the foam layer before foaming progresses. It may be formed on the side. In addition, when the cooling rate by the refrigerant is fast, the outer periphery of the coating is preferentially cooled, and a non-foamed coating layer is formed on the outer periphery of the foam layer before foaming progresses. There may be cases where

<Communication wires including foamed wires>
The foamed electric wire 1 according to the embodiment of the present disclosure may be used as an electric wire for any purpose. A particularly preferred use of the foamed wire 1 is as a communication wire. In communication wires, if the insulation coating of the signal line has a high dielectric loss tangent, the absorption of electrical energy by the insulation coating increases, resulting in signal loss, which is undesirable. Therefore, by using the foamed wire 1 according to the present embodiment as a signal line of a communication wire, the effect of the foamed cells B occupied by gas reduces the dielectric loss tangent of the insulation coating 3 and suppresses signal attenuation. be able to. By using the foamed electric wire 1 according to this embodiment, high mechanical strength can also be ensured in the communication electric wire. The communication wire including the foamed wire 1 according to this embodiment can be particularly suitably used for communication within a vehicle. Demand for high-speed communication is increasing in the automobile field, and the present foamed electric wire 1 is highly effective in reducing electrical signal loss. Further, since electric wires placed in a car are exposed to harsh environments such as vibrations and high temperatures, it is advantageous for the insulation coating 3 to have high mechanical strength. Since the foamed wire 1 according to the present embodiment is highly effective in reducing dielectric loss tangent, it can be particularly suitably used for high-speed communications at frequencies of 1 to 10 GHz.

The specific type and structure of the communication wire is not particularly limited as long as it includes the foamed wire 1 according to the present embodiment as a signal wire, but a coaxial wire can be cited as an example. As shown in FIG. 2A, in the coaxial line 1A, a metal shield layer made of at least one of a metal foil 5 and a metal braided layer 6, preferably both, is provided around the outer periphery of one foamed electric wire 1 as a signal line. provided. Further, a sheath 7 made of an insulating material is formed around the outer periphery of the metal shield layer. Note that the metal foil 5 also includes a form in which a metal layer is formed on the surface of a polymer base material.

Another suitable example of the communication wire is a pair of wires 1B that transmits differential signals. As shown in FIG. 2B, in the pair wire 1B, a pair of foamed electric wires 1, 1 according to the present embodiment are arranged in parallel or twisted together to form a signal line. A metal shield layer composed of at least one of the metal foil 5 and the metal braided layer 6, preferably both, is provided on the outer periphery of the signal line. Furthermore, a sheath 7 made of an insulating material is formed on the outermost periphery. Since the insulation coating 3 has a foam layer, in addition to the dielectric loss tangent, the dielectric constant is kept low, and even if the diameter of the wires 1, 1 is made small, the required characteristic impedance can be secured in the pair wire 1B. I can do it.

Another suitable example of the communication wire is a collectively covered wire 1C. Here, the foamed electric wire 1' according to the present embodiment is configured to have an insulating coating 3 that collectively covers the outer periphery of two conductors 2, 2, and serves as a signal line. In other words, the foam electric wire 1' has an insulation coating 3 that covers the outer periphery of a pair of conductors 2, 2 arranged in parallel with an interval, including the area between these conductors 2, 2, which is capable of transmitting signals. It becomes a line. Even if the foamed electric wire 1' is used as a signal line with the pair of conductors 2, 2 arranged in parallel, after forming the insulation coating 3, from above the insulation coating 3, The two conductors 2, 2 covered with the insulating coating 3 may be twisted by crossing each other in a spiral manner. A metal shield layer composed of at least one of the metal foil 5 and the metal braided layer 6, preferably both, is provided on the outer periphery of the foamed electric wire 1'. Furthermore, a sheath 7 made of an insulating material is formed on the outermost periphery.

<Constituent material of foam layer>
In the foamed electric wire 1 according to the present embodiment, the constituent material of the foam layer constituting the insulation coating 3 has a take-up speed of 10 m/min or more at 220°C.

Here, the drawing speed and the melt tension described later will be explained. The take-off speed of the resin material is an indicator of melt elongation, and the higher the take-off speed, the higher the melt elongation of the resin material. The withdrawal rate can be evaluated by melt strand stretch measurements using a capillary rheometer. That is, the molten strand extruded from the capillary is withdrawn under the conditions of constant load and constant extrusion speed while increasing the withdrawal speed, and the withdrawal speed when the molten strand breaks is recorded. In this specification, the value evaluated at 220° C. is used as the take-up speed. In addition, regarding the constituent materials of the foam layer, the take-up speed is evaluated without adding a foaming agent. The withdrawal speed can be measured, for example, by using a capillary with a hole diameter of 1.0 mm and a length of 20 mm, and after preheating for 5 minutes after filling the cylinder with the material, the extrusion speed of the capillary is set to 10 mm/min. .

The melt tension of the resin material indicates the tension generated in the melted resin material. Melt tension can also be evaluated by melt strand stretch measurements using a capillary rheometer. That is, while extruding the molten strand extruded from the capillary at a constant speed, a load is applied to the molten strand and taken off, and the load when the molten strand breaks is recorded as the melt tension. In this specification, a value evaluated at 220° C. is used as the melt tension. Furthermore, for the constituent materials of the foam layer, the melt tension is evaluated without adding a foaming agent. As the conditions for measuring the melt tension, the same conditions as exemplified above for measuring the withdrawal speed can be suitably employed.

In the foamed electric wire 1 according to the present embodiment, as described above, the drawing speed of the constituent material of the foam layer of the insulation coating 3 is 10 m/min or more. Thereby, it is possible to suppress the communication of the foam cells B in the foam layer and the accompanying decrease in the mechanical strength of the foam layer. The mechanism will be explained below.

As explained above regarding the manufacturing method of the foamed electric wire 1, when the material to be the foamed layer is extruded around the outer periphery of the conductor 2 to form a covering, and the covering is solidified by cooling using a refrigerant, The material that becomes the foam layer shrinks. At this time, a force is applied to the foam layer to stretch the inner wall of the foam cell B, but if the constituent material of the foam layer does not have sufficient melt elongation, it will not be able to follow the stretching, and the foam cell The inner wall of B is broken. As a result, as in the insulation coating 3' shown in FIG. 3B, the foam cells B cannot maintain independence in the foam layer, and adjacent foam cells B communicate with each other, resulting in a large and distorted shape ( (Indicated by code B1). If such communication of the foamed cells B occurs during the solidification process of the foamed layer, the solidification proceeds in that state, and a foamed layer containing the connected foamed cells B is finally obtained. When communication between the foam cells B occurs, the mechanical strength of the insulating coating 3 decreases. This is because in the foamed cells B that are connected in an irregular shape, there are places where stress is concentrated, and these places tend to become starting points for breakage.

On the other hand, when the constituent material of the foam layer has a high take-up speed of 10 m/min or more and exhibits high melt elongation, when the foam layer shrinks due to solidification, the inner wall of the foam cell B Even if a stretching force is applied, since the foam layer is made of a material with high melt elongation, the inner wall of the foam cell B can follow the force and stretch without causing breakage. Then, as shown in FIG. 3A, each foam cell B does not communicate with other foam cells B until the solidification of the foam layer is completed, and each foam cell B assumes an approximately spherical or approximately oblate shape. Able to remain independent. By maintaining high independence of the foamed cells B, the mechanical strength of the foamed layer is less likely to decrease. This is because stress is dispersed with high uniformity around the independent foam cells B, which are formed into a substantially spherical shape or a substantially oblate shape, and the foam layer becomes able to withstand a large load. As a result, the insulation coating 3 has high mechanical strength. For example, an insulating coating 3 that does not easily deform even when subjected to a mechanical load in a heated environment can be obtained. From the viewpoint of further enhancing the effect of improving mechanical strength, it is more preferable that the take-up speed of the constituent material of the foam layer is 20 m/min or more, and more preferably 30 m/min or more. Although there is no particular upper limit to the drawing speed of the constituent material of the foam layer, from the viewpoint of extrusion moldability, etc., the drawing speed is preferably approximately 60 m/min or less.

It is preferable that the constituent material of the foam layer has a high melt tension in addition to having a high take-up speed as described above. Then, when forming the foam layer, high workability is obtained and the foam cells B are stabilized. Preferably, the melt tension of the constituent material of the foam layer is 10 mN or more, more preferably 20 mN or more, or 24 mN or more. On the other hand, there is no particular upper limit to the melt tension of the constituent material of the foam layer, but from the viewpoint of extrusion moldability etc., it is preferably approximately 100 mN or less. Although it is difficult to achieve both high withdrawal speed and high melt tension when using a single organic polymer, it can be easily achieved by mixing a plurality of organic polymers as described below.

Here, specific examples will be given of component compositions that can provide a foamed layer having the above-mentioned physical properties. As mentioned above, the specific composition of the constituent material of the foam layer is not particularly limited as long as the take-up speed is 10 m/min or more.

The foam layer is made of a material that contains a foaming agent in addition to an organic polymer, and further contains additives as necessary. The foamed layer may consist of only one kind of polymer component or two or more kinds of polymer components, but from the viewpoint of realizing a high take-up speed as a whole of the composition of the constituent materials of the foamed layer, at least one kind of high polymer component may be used. Preferably, it contains a melt elongation component. The high melt elongation component is a component that exhibits high melt elongation by having a high take-off speed, and preferably has a take-off speed of 30 m/min or more, and further preferably 50 m/min or more. From the viewpoint of efficiently increasing the melt elongation of the composition of the constituent materials of the foam layer as a whole by the high melt elongation component, the content of the high melt elongation component should be 20% by mass or more of the total organic polymer constituting the foam layer. , and more preferably 30% by mass or more.

A preferred example is an embodiment in which a thermoplastic olefin elastomer (TPO) is used as the high melt elongation component having a take-up speed of 40 m/min or more. TPO has excellent melt elongation and relatively low dielectric loss tangent and dielectric constant among various organic polymers, and can be suitably applied to the insulation coating 3 of the foamed wire 1 constituting the communication wire. Examples of organic polymers other than TPO that can be suitably used as the high melt elongation component include block polypropylene (PP) and styrene-ethylene-butylene-styrene (SEBS) block copolymers.

As mentioned above, it is preferable that the constituent material of the foam layer has a high take-off speed and high melt tension, but it is difficult to achieve both high take-off speed and high melt tension using a single organic polymer. Therefore, it is preferable to use a mixture of two or more organic polymers in the foam layer. As mentioned above, when using a high melt elongation component, it is preferable to mix the high melt elongation component with a high melt tension component. As the high melt tension component, it is preferable to use an organic polymer having a melt tension of 30 mN or more, more preferably 40 mN or more. From the viewpoint of efficiently increasing the melt tension of the entire composition of the constituent materials of the foam layer, the content of the high melt tension component should be 20% by mass or more, more preferably 30% by mass, of the total organic polymers constituting the foam layer. It is preferable to set it as above. Further, the mixing ratio of the high melt elongation component and the high melt tension component is preferably in the range of 1:3 to 3:1 in terms of mass ratio of [high melt elongation component]:[high melt tension component].

When a high melt elongation component and a high melt tension component are mixed, sufficient melt elongation and melt tension in the foamed layer can be ensured by each component. Therefore, the high melt tension component does not need to have a high take-off speed, and may have a take-off speed of less than 40 m/min. On the other hand, the high melt elongation component does not need to have high melt tension, and may have a melt tension of less than 30 mN. In particular, when the take-up speed of the high melt elongation component is 10 times or more that of the high melt tension component, or when the melt tension of the high melt tension component is twice or more that of the high melt elongation component, the respective Contribution becomes clear. The high melt elongation component and the high melt tension component are preferably organic polymers of the same type, that is, organic polymers containing the same type of monomer units, from the viewpoint of increasing their mutual affinity.

As a high melt tension component having a melt tension of 30 mN or more, polyolefins such as polypropylene (PP) can be exemplified. Polyolefin has excellent melt tension and has a lower dielectric loss tangent and dielectric constant among various organic polymers, and can be suitably applied to the insulation coating 3 of the foamed wire 1 constituting the communication wire. Furthermore, when TPO is employed as the high melt elongation component, high affinity can be obtained between the two. As the high melt tension component, polyolefins other than polypropylene such as polyethylene, and various organic polymers having a long chain branched structure such as TPO can also be suitably used.

The constituent material of the foamed layer may contain appropriate additives in addition to the organic polymer and the foaming agent. Examples of additives include copper damage inhibitors, hindered phenol type antioxidants, sulfur type antioxidants, and the like. Note that from the viewpoint of keeping the dielectric loss tangent of the foam layer low, it is preferable not to contain an inorganic filler.

Although the foaming ratio of the foam layer is not particularly limited, in the foamed electric wire 1 according to the present embodiment, the foam layer exhibits high melt elongation, so even if the foaming ratio is increased, sufficient mechanical strength cannot be maintained. can be kept. Increasing the foaming ratio increases the effect of reducing the dielectric loss tangent and dielectric constant in the foam layer. For example, the foaming ratio of the foam layer can be increased to more than 50%, and even more than 60%, in terms of cell ratio (volume ratio occupied by foamed cells B).

Examples are shown below. Here, we examined the relationship between the composition of the foam layer, the foam structure, and the mechanical strength of the foam wire. Note that the present invention is not limited to these Examples.

[Preparation of sample]
Each component shown in Table 1 was mixed in the stated content ratio to prepare material A and material B, which are constituent materials of the insulation coating. At this time, the components other than the blowing agent were mixed by melt kneading, and then the blowing agent was added by dry blending.

An insulating coating was formed around the outer periphery of a conductor configured as a twisted copper wire. At this time, a covering was formed by extruding material A for sample A and material B for sample B onto the outer periphery of the conductor. Foaming was progressing during extrusion molding. Next, the coated body was cooled and solidified by immersing it in a water bath. In this way, foamed wires of Samples A and B were formed. For all samples, the conductor cross-sectional area was 0.23 mm ² and the thickness of the insulation coating was about 300 μm. Further, the foam layer had a cell ratio of 66%.

The materials used to prepare the constituent materials of the insulation coating are as follows.
(organic polymer)
・PP1: Homo PP - "Novatec EA9FTD" manufactured by Nippon Polypro Co., Ltd.
・PP2: Metallocene-based high melt tension PP - “WAYMAX MFX6” manufactured by Nippon Polypro Co., Ltd.
・PP3: Homo PP - "Novatec MA3U" manufactured by Nippon Polypro Co., Ltd.
・TPO: Lyondell Bassell TPO “Adflex Q200F”

(Additive)
・Copper damage inhibitor: “CDA-10” manufactured by ADEKA
・Antioxidant 1: “Irganox 1010FF” manufactured by BASF
・Antioxidant 2: “Irgafos 168” manufactured by BASF
・Antioxidant 3: “ADEKA STAB AO-412S” manufactured by ADEKA
・Antioxidant 4: “ADEKA STAB LA-57” manufactured by ADEKA
・Foaming agent: “Cellmic MB1023” manufactured by Sankyo Kasei Co., Ltd.

[Evaluation method]
(1) Physical Properties of Constituent Components and Mixed Materials The withdrawal speed and melt tension of Materials A and B and each organic polymer used as a component constituting these materials were measured. All measurements were carried out at 220° C. by melt strand stretch measurements using a capillary rheometer. Regarding the withdrawal speed, the molten strand extruded from the capillary was withdrawn under the conditions of constant load and constant extrusion speed while increasing the withdrawal speed, and the withdrawal speed when the molten strand broke was recorded. Regarding the melt tension, a load was applied to the melt strand while extruding it from the capillary at a constant speed, and the load was taken off when the melt strand broke, and the load when the melt strand broke was recorded as the melt tension. Regarding Materials A and B, the drawing speed and melt tension were measured without adding any blowing agent. A capillary with a hole diameter of 1.0 mm and a length of 20 mm was used for the measurement, the material was filled into the cylinder, and the measurement was performed after preheating for 5 minutes. The extrusion speed of the capillary was the same at 10 mm/min for all materials.

(2) Evaluation of foamed structure The foamed electric wires of Samples A and B were cut perpendicularly to the axial direction to obtain cross-sectional samples. An optical microscope image of this cross-sectional sample was photographed, and the state of the foam cells was observed in the photographed image.

(3) Evaluation of mechanical strength The insulating coatings including the foamed layers of Samples A and B were subjected to a tensile test in accordance with JIS K 7161, and the tensile strength at break was measured.

[Evaluation results]
Table 1 shows the component compositions of materials A and B, and the evaluation results of the take-up speed and melt tension of each material in a state where each component is mixed, and the tensile rupture strength of the insulation coating. Regarding the component composition, the content of each component is expressed in parts by mass. The table also shows the withdrawal speed and melt tension of each polymer component. Further, FIGS. 4A and 4B show cross-sectional images of foamed wires of samples A and B in which foam layers were formed using material A and material B, respectively.

According to FIG. 4A, which is an observation of sample A, there are almost non-foamed inner and outer layers on the inner and outer periphery of the insulation coating, which were formed when the coating was cooled, but in the middle part between them, In this case, a foam layer having a large number of foam cells observed as white is formed. In this foam layer, most of the foam cells have a nearly circular or oval shape, and have a highly independent structure that does not communicate with adjacent foam cells. This is because the material A constituting the foam layer is made of a material with a high melting elongation that has a take-up speed of 10 m/min or more, and the inner walls of the foam cells are less likely to break when the foam layer solidifies. It is interpreted that there is.

On the other hand, according to FIG. 4B, which is an observation of sample B, a concavo-convex structure is formed in the middle part of the insulating coating, and these structures can be associated with foam cells. However, unlike the case in Figure A, these foam cells do not take the form of independent bubbles in a circular or oval shape, but are continuously distributed in an irregular shape. In other words, it can be said that highly independent foam cells were not generated. This is because the take-up speed of material B constituting the foam layer is less than 10 m/min and the melt elongation is low. It is thought that the cells are connected.

Furthermore, as shown in Table 1, the insulation coating of Sample A exhibited a higher tensile strength at break than that of Sample B. This is because the foam layer of Sample A has many circular or oval shapes, and the force is evenly distributed in the independent cells, so the insulation coating as a whole can withstand a large load. It is interpreted as On the other hand, in the bubbles contained in the foam layer of Sample B, which are connected in an irregular shape, there are places where force is concentrated, and it is thought that breakage is more likely to occur from those places.

Although the embodiments of the present disclosure have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

1, 1' Foamed electric wire 1A Coaxial wire 1B Pair wire 1C Collectively covered wire 2 Conductor 3, 3' Insulation coating 5 Metal foil 6 Metal braided layer 7 Sheath B Foamed cell B1 Connected foamed cell

Claims (5)

a conductor;
an insulating coating that covers the outer periphery of the conductor;
The insulation coating has a foam layer having a foam structure,
The constituent material of the foamed layer is a foamed electric wire whose take-up speed at 220° C. is 10 m/min or more. The foamed electric wire according to claim 1, wherein the foamed layer contains a polymer component having a take-up speed of 40 m/min or more at 220°C. The foamed electric wire according to claim 1 or 2, wherein the constituent material of the foamed layer has a melt tension of 18 mN or more at 220°C. The foamed electric wire according to any one of claims 1 to 3, wherein the foamed layer contains a polymer component having a melt tension of 30 mN or more at 220°C. The foamed electric wire according to any one of claims 1 to 4, wherein the foamed layer contains an olefinic thermoplastic elastomer and polypropylene.

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