Electric wire for communication

Abstract

Provided is a communication wire which is a communication wire having a compact sheath on the outer periphery of a signal wire including a plurality of insulated wires, and is less likely to cause a deterioration in transmission characteristics due to the influence of pressure when the sheath is extrusion-molded. The communication wire (1) includes: a signal wire (10) including a plurality of insulated wires (11), the insulated wire (11) having a conductor (12) and an insulating covering portion (13) covering the outer periphery of the conductor (12); and a compact sheath (20) covering the outer periphery of the signal wire (10), the constituent material of the sheath (20) having a melt flow rate measured at a load of 2.16 kg at 200 °C of 0.25 g / 10 min or more.

Description

Technical Field

[0001] The present disclosure relates to a wire for communication. Background Art

[0002] In the field of automobiles and the like, the need for high-speed communication has increased. As an example of a wire for communication used in high-speed communication, Patent Documents 1 and 2 disclose a wire for communication having a twisted pair formed by twisting a pair of insulated wires and a sheath made of an insulating material covering the outer periphery of the twisted pair, and the insulated wire has a conductor and an insulating covering portion covering the outer periphery of the conductor. In Patent Documents 1 and 2, a so-called loose sheath type in which a gap is provided between the sheath and the insulated wire constituting the twisted pair is mainly used.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: International Publication No. 2017 / 168842

[0006] Patent Document 2: International Publication No. 2018 / 117204 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] As a wire for communication having a sheath on the outer periphery of a signal line including a plurality of insulated wires, in addition to the loose sheath type wire for communication having a gap between the sheath and the signal line as disclosed in Patent Documents 1 and 2, there is also a tight sheath type wire for communication in which substantially no gap is provided between the sheath and the signal line, and the constituent material of the sheath is in close contact with the surface of the insulated wire constituting the signal line. The loose sheath type and the tight sheath type each have advantages. As a major advantage of a wire for communication having a tight sheath, the following aspects can be cited: by pressing the signal line from the outside with the sheath, the relaxation of the stranded structure and the deviation of the relative position can be suppressed in the insulated wire constituting the signal line. By stably maintaining the relative position of the insulated wires of the signal line, a stable characteristic impedance can be obtained in the wire for communication, and communication characteristics such as mode conversion characteristics are improved.

[0009] However, in the case where the sheath is of a tight structure, compared with the case of the loose sheath type, when the sheath is formed by extrusion molding, a large pressure is applied to the insulated wire constituting the signal line by the molten polymer material. As a result, it is possible that those insulated wires deviate and deform in relative position, thereby reducing the balance of the signal line. For example, Figure 2The state where the insulating coating portions 13, 13 that constitute a pair of insulated electric wires 11, 11 are flattened at positions adjacent to each other is shown. A decrease in the balance of the signal line can lead to a decrease in the transmission characteristics of the communication electric wire such as deterioration of the mode conversion characteristics.

[0010] In view of the above, it is an object to provide a communication electric wire that is a communication electric wire having a compact sheath on the outer periphery of a signal line including a plurality of insulated electric wires, and is not easily caused to have a decrease in transmission characteristics due to the influence of the pressure when the sheath is extrusion-molded.

[0011] Solution to the problem

[0012] The communication electric wire of the present disclosure includes: a signal line including a plurality of insulated electric wires, the insulated electric wires having a conductor and an insulating coating portion covering the outer periphery of the conductor; and a compact sheath covering the outer periphery of the signal line, and the constituent material of the sheath has a melt flow rate measured at a load of 2.16 kg at 200 °C of 0.25 g / 10 min or more.

[0013] Advantageous effects of the invention

[0014] The communication electric wire of the present disclosure is a communication electric wire having a compact sheath on the outer periphery of a signal line including a plurality of insulated electric wires, and becomes a communication electric wire that is not easily caused to have a decrease in transmission characteristics due to the influence of the pressure when the sheath is extrusion-molded. Description of the drawings

[0015] Figure 1 It is a cross-sectional view showing the structure of a communication electric wire constituting an embodiment of the present disclosure. Figure 1 And in the following Figure 2 For easy viewing, it is shown in such a way that small gaps are also provided at the contact portions between the members.

[0016] Figure 2 It is a cross-sectional view showing a communication electric wire in which the deformation of the insulating coating portion becomes large.

[0017] Figure 3 It is a photograph of the cross-section of the communication electric wire of Specimen 3 in the examples. Detailed description of the invention

[0018] [Description of the embodiment of the present disclosure]

[0019] First, the embodiment of the present disclosure will be described.

[0020] The communication wire of the present disclosure includes: a signal wire including a plurality of insulated wires, the insulated wire having a conductor and an insulating coating portion covering the outer periphery of the conductor; and a compact sheath covering the outer periphery of the signal wire, the constituent material of the sheath having a melt flow rate of 0.25 g / 10 min or more measured at a load of 2.16 kg at 200°C.

[0021] In the above communication wire, the sheath has a compact structure, and the constituent material of the sheath is in close contact with the surface of the insulated wire constituting the signal wire. However, the constituent material of the sheath has a melt flow rate above a predetermined lower limit. Therefore, when forming the sheath by extrusion molding, the constituent material easily fills the surrounding area of the insulated wire, and the pressure applied to the insulated wire can be small. As a result, it is not easy to occur that due to the pressure during extrusion molding, the relative position of the insulated wire changes or deforms, and the balance of the signal wire deteriorates. As a result, in the communication wire, transmission characteristics such as mode conversion characteristics are maintained at a high level.

[0022] Here, the signal wire may be configured as a twisted pair in which a pair of the insulated wires are twisted together. By configuring the signal wire as a twisted pair, it is easier to stably maintain the relative position of a pair of insulated wires compared to the case where a pair of insulated wires are arranged side by side without being twisted together. Therefore, in combination with the effect of increasing the melt flow rate of the constituent material of the sheath, when manufacturing the sheath by extrusion molding, it is particularly unlikely to cause a change in the relative position of the insulated wire. As a result, it is easy to maintain the transmission characteristics of the communication wire particularly well.

[0023] Preferably, no other layered member is provided between the sheath and the signal wire. When a member such as a tape is arranged on the outer periphery of the signal wire, it is easy to stably maintain the relative position of the insulated wires constituting the signal wire. In the communication wire of the present disclosure, since the melt flow rate of the constituent material of the sheath is sufficiently increased, even if a member such as a tape is not arranged on the outer periphery of the signal wire, the relative position of the insulated wires can be sufficiently stably maintained. By not arranging a member such as a tape on the outer periphery of the signal wire, the manufacturing cost of the communication wire can be suppressed.

[0024] Preferably, regarding the thickness of the insulating coating portion in the insulated wire, the thickness of the thinnest part is defined as the short thickness, and the thickness in the direction orthogonal to the direction of the short thickness is defined as the long thickness. The coating portion thickness ratio defined as the ratio of the short thickness to the long thickness is 65% or more. It shows that the larger the coating portion thickness ratio, the smaller the change or deformation in the relative position of the insulated wires constituting the signal wire, which becomes a good index for obtaining high transmission characteristics. When the coating portion thickness ratio is 65% or more, a sufficiently high mode conversion characteristic can be obtained as a communication wire.

[0025] In this case, it is preferable that the sheath thickness ratio is 95% or less. The larger the sheath thickness ratio, the better the transmission characteristics, such as the mode conversion characteristics, in the communication wire. However, even if the sheath thickness ratio is increased beyond 95%, the effect of improving the transmission characteristics saturates. There is a tendency that the higher the melt flow rate of the material constituting the sheath, the larger the sheath thickness ratio. However, by not excessively increasing the sheath thickness ratio, a variety of materials can be used as the constituent material of the sheath. In addition, the manufacturing cost of the communication wire can be suppressed.

[0026] [Details of the Embodiment of the Present Disclosure]

[0027] Hereinafter, a communication wire according to an embodiment of the present disclosure will be described in detail with reference to the drawings. In this specification, the melt flow rate (MFR) refers to the value measured at 200°C under a load of 2.16 kg. Regarding other characteristics, unless otherwise specified, the values are assumed to be measured at room temperature and in the atmosphere. In addition, in this specification, regarding the material composition, when a certain component is the main component, it means that the component accounts for 50% by mass or more in the total mass of the material. It is assumed that the organic polymer also includes substances with relatively low degrees of polymerization such as oligomers. Terms such as parallel, perpendicular, orthogonal, and circular indicating the shape and arrangement of components are not only strict geometric concepts but also include errors within the range allowed for communication wires.

[0028] (Overall Configuration of Communication Wire)

[0029] Figure 1 FIG. shows a cross-sectional view taken perpendicular to the axial direction of a communication wire 1 according to an embodiment of the present disclosure.

[0030] The communication wire 1 has a signal wire 10. The signal wire 10 includes a plurality of insulated wires 11. The communication wire 1 further has a sheath 20 that covers the outer periphery of the signal wire 10. In the present embodiment, the sheath 20 has a compact structure. Regarding the constituent material of the sheath 20, it will be described in detail later, but the MFR is 0.25 g / 10 min or more.

[0031] Each insulated wire 11 constituting the signal line 10 has a conductor 12 and an insulating coating portion 13 that coats the outer periphery of the conductor 12. The number of insulated wires 11 constituting the signal line 10 is not particularly limited, and can be set to 2, 4, etc. Here, a configuration including 2 (a pair) of insulated wires 11, 11 is used. As the communication wire 1 including a pair of insulated wires 11, 11 of the signal line 10, it can be used to transmit differential signals. The signal line 10 can also be configured as a parallel pair wire in which a pair of insulated wires 11, 11 are arranged in parallel and the axial directions are parallel and in contact with each other, but preferably a pair of insulated wires 11, 11 are configured as a twisted pair wire twisted together. Compared with the parallel pair wire, the twisted pair wire has an excellent effect of stably maintaining the relative positions of a pair of insulated wires 11, 11. Hereinafter, the case where the signal line 10 is configured as a twisted pair wire is mainly used. The applicable frequency of the communication wire 1 is not particularly limited, and it is preferably used in a frequency band of at least 1 MHz to 50 MHz.

[0032] As the material constituting the conductor 12, various metal materials can be used, but from the viewpoints of maintaining strength and improving transmission characteristics in the signal line 10, etc., a copper alloy is preferably used. The conductor 12 can also be composed of a single wire, but from the viewpoints of improving flexibility when bent, etc., it is preferably composed of a stranded wire formed by stranding a plurality of wire materials (for example, 7 wires). In this case, after stranding the wire materials, it can also be compression-molded to form a compressed stranded wire. When the conductor 12 is configured as a stranded wire, it can be composed of all the same wire materials or two or more types of wire materials.

[0033] The material constituting the insulating coating portion 13 is not particularly limited, but a material mainly composed of an organic polymer is preferably used. Examples of the organic polymer include polyolefins such as polyethylene and polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, polyphenylene sulfide, etc. In particular, as the organic polymer, a substance with low molecular polarity, especially a non-polar substance, is preferably used. Among the above, polyolefins, especially polypropylene, are preferably used. The organic polymer can be used by mixing multiple types from the substances listed above, or can be used by mixing the substances listed above and substances other than the substances listed above. The polymer material constituting the insulating coating portion 13 can be crosslinked, and can also be foamed. In addition, the insulating coating portion 13 can appropriately contain additives in addition to the organic polymer. As the additives, various additives that can usually be added to the coating material of the wire, such as flame retardants, stabilizers, extenders, anti-aging agents, pigments, lubricants, etc., can be listed.

[0034] The diameter of the conductor 12 and the thickness of the insulating coating portion 13 are not particularly limited, but from the viewpoint of making the insulated wire 11 thinner, etc., it is preferably that the cross-sectional area of the conductor is set to less than 0.22 mm 2 、especially 0.15 mm 2Next, it is preferable to set the thickness of the insulating coating portion 13 to 0.30 mm or less, particularly 0.20 mm or less in advance. When such a conductor cross-sectional area and coating portion thickness are adopted, the outer diameter of the insulated wire 11 can be set to 1.0 mm or less, and further to 0.90 mm or less. In addition, when such a conductor cross-sectional area and coating portion thickness are adopted, it is easy to control the characteristic impedance of the communication wire 1 within a range of, for example, 100 ± 10 Ω. As the twist pitch of the twisted pair formed by a pair of insulated wires 11, 11, an example is a method of setting it to 12 mm or more and further to 30 mm or less.

[0035] The sheath 20 functions to protect the signal wire 10 and stabilize the relative positions of the insulated wires 11 in the signal wire 10 in the communication wire 1. As described above, the sheath 20 has a compact structure. That is, except for inevitable gaps, no gaps are provided between the sheath 20 and the insulated wires 11, 11 constituting the signal wire 10, and the constituent material of the sheath 20 closely adheres to substantially the entire area of the surfaces of the insulated wires 11, 11 that is exposed on the outer side of the entire signal wire 10. In addition, as the inevitable gaps generated between the sheath 20 and the insulated wires 11, 11 constituting the signal wire 10, the void ratio is defined as being substantially less than 5%. Here, the void ratio refers to the ratio of the area occupied by the voids in the area surrounded by the outer peripheral surface of the sheath 20 in a cross-section perpendicular to the axial direction of the communication wire 1.

[0036] The constituent material of the sheath 20 is mainly composed of an organic polymer and is not particularly limited as long as it has an MFR of 0.25 g / 10 min or more. However, materials similar to those of the insulating coating portion 13 can be cited, that is, materials containing organic polymers such as polyolefins including polyethylene and polypropylene, polyvinyl chloride, polystyrene, polytetrafluoroethylene, polyphenylene sulfide, etc. Among these, polyolefins, particularly polypropylene, are preferably used. The organic polymer can be used by mixing multiple types from the substances listed above, or by mixing the substances listed above and substances other than those listed above. The polymer material constituting the sheath 20 can be cross-linked or foamed. In addition, the sheath 20 can appropriately contain additives in addition to the organic polymer. As additives, various additives that can usually be added to the coating material of the wire, such as flame retardants, stabilizers, extenders, anti-aging agents, pigments, lubricants, etc., can be cited. The constituent material of the sheath 20 can be the same material or a different material from that of the insulating coating portion 13, but from the viewpoint of simplifying the overall structure and manufacturing process of the communication wire 1, it is preferably composed of the same material.

[0037] The thickness of the sheath 20 only needs to be appropriately set so that the protection of the signal wire 10 is sufficiently obtained, the relative positions of the insulated wires 11, 11 in the signal wire 10 are maintained, etc., and the desired characteristic impedance is obtained. As long as the thickness of the thinnest part is 0.2 mm or more, and more preferably 0.3 mm or more. On the other hand, when considering suppressing the effective dielectric constant to be small, ensuring the characteristic impedance within a predetermined range, and making the overall diameter of the communication wire 1 thinner, as long as the thickness of the thinnest part of the thickness of the sheath 20 is set to 1.0 mm or less, and more preferably 0.8 mm or less. In addition, as long as the outer diameter of the entire communication wire 1 defined by the outer peripheral surface of the sheath 20 is made 4.0 mm or less, and further 3.5 mm or less.

[0038] In the communication wire 1, a method of providing other layered members between the sheath 20 and the signal wire 10 is not prohibited, but it is preferable not to provide such layered members. Here, the so-called layered member refers to a member mainly composed of an organic polymer, etc., a member that surrounds the outer periphery of the signal wire 10 with a layered continuous solid material, and examples thereof include a tape body wound in a spiral shape around the outer periphery of the signal wire 10. In addition, other substances other than the layered member may be interposed between the sheath 20 and the signal wire 10. As a preferred method, for example, a release agent containing an inorganic powder material such as talc is disposed on the outer periphery of the signal wire 10, and on this basis, the sheath 20 is provided.

[0039] (Constituent material of the sheath and transmission characteristics)

[0040] In the communication wire 1 of the present embodiment, since the sheath 20 has a compact structure, the signal wire 10 can be pressed from the outside to stably maintain the structure of the signal wire 10. As a result, in the communication wire 1, a predetermined characteristic impedance can be stably obtained, and transmission characteristics such as mode conversion characteristics are also improved. In particular, when the signal wire 1 is configured as a twisted pair in which a pair of insulated wires 11, 11 are twisted together, together with the effect of stabilizing the mutual arrangement of the insulated wires 11, 11 by using this twisted structure, the stabilization of the characteristic impedance and the improvement of the transmission characteristics are highly effective. In this case, the compact sheath 20 functions to maintain the twisted structure of the twisted pair without loosening.

[0041] In the communication wire 1 of the present embodiment, the material constituting the compact sheath 20 mainly consists of an organic polymer and has an MFR of 0.25 g / 10 min or more at 200°C under a load of 2.16 kg. The sheath 20 is formed by extruding a molten polymer material around the signal wire 10. Generally, as a sheath provided for a communication wire including a plurality of insulated wires, in addition to the compact type in which there is substantially no gap between the sheath and the signal wire, there is also a loose sheath type in which a gap is provided between the sheath and the signal wire. In the case of forming the compact sheath 20 among these, since it is necessary to make the constituent material of the molten sheath 20 closely adhere to the insulating covering portion 13 constituting the signal wire 10, a relatively large pressure is applied to the insulated wires 11, 11 from the constituent material of the molten sheath 20 as compared with the case of the loose sheath type.

[0042] When a relatively large pressure is applied to the insulated wires 11, 11 by the molten polymer material, there is a possibility that the relative positions of the pair of insulated wires 11, 11 deviate and a possibility that the insulated wires 11, 11 are deformed. Typically, as in the communication wire 1' shown in Figure 2 the central portion C where the pair of insulated wires 11, 11 are adjacent to each other, the insulating covering portion 13 is liable to be extruded. When the relative positions of the insulated wires 11, 11 constituting the signal wire 10 deviate or are deformed, the balance of the signal wire 10 is reduced. The reduction in balance can be related to the deterioration of the transmission characteristics of the communication wire 1 such as the deterioration of the mode conversion characteristics.

[0043] However, in the communication wire 1 of the present embodiment, since the constituent material of the sheath 20 has an MFR of 0.25 g / 10 min or more and is a material with excellent fluidity, even without applying a high pressure, when extrusion forming is performed, the molten polymer material easily fills the surrounding area of the insulated wires 11, 11 until it becomes a state of closely adhering to the surfaces of the insulated wires 11, 11 constituting the signal wire 10. Therefore, when the sheath 20 is extrusion formed, it is not easy to apply a large pressure to the insulated wires 11, 11 by the molten polymer material, and it is not easy for the insulated wires 11, 11 to deviate or be deformed in relative positions. As shown in Figure 1 the central portion C where the pair of insulated wires 11, 11 are adjacent to each other, it is also not easy for the insulating covering portion 13 to be extruded, and each of the insulated wires 11, 11 is liable to maintain a highly symmetric shape.

[0044] By suppressing the deviation and deformation of the relative positions of the insulated wires 11, 11, the balance of the signal wire 10 is maintained at a high level, and the transmission characteristics of the communication wire 1 such as the mode conversion characteristics can be maintained at a high level. In particular, when the signal wire 10 is configured as a twisted pair, when the sheath 20 is extrusion-molded, it is easy to stably maintain the relative arrangement of the pair of insulated wires 11, 11 by using the stranded structure of the insulated wires 11, 11, and the effect of suppressing the reduction of the balance of the signal wire 10 is excellent. For example, when the signal wire 10 is a twisted pair, the through-mode conversion (LCTL) in the communication frequency range of 1 MHz to 50 MHz can be set to -50 dB or less (LCTL ≤ -50 dB), and further to -55 dB or less (LCTL ≤ -55 dB).

[0045] From the viewpoint of further effectively suppressing the influence of the pressure applied during the extrusion molding of the sheath 20 on the transmission characteristics, it is particularly preferable that the MFR of the constituent material is 0.3 g / 10 min or more, further 0.5 g / 10 min or more, and 0.8 g / 10 min or more. On the other hand, no particular upper limit is set for the MFR of the constituent material of the sheath 20. When the MFR is too high, the manufacturability of the extrusion-molded sheath 20 decreases, so it is preferably approximately 7.0 g / 10 min or less, and further 5.0 g / 10 min or less. The MFR of the constituent material of the sheath 20 can be adjusted by the type of organic polymer used (type of monomer unit and repeating pattern), degree of polymerization, type of additive, amount of additive, etc. The MFR can also be adjusted by mixing multiple organic polymers with different degrees of polymerization, etc.

[0046] As described above, by having an MFR of 0.25 g / 10 min or more for the constituent material of the sheath 20, the deviation and deformation of the positions of the insulated wires 11, 11 during the extrusion molding of the sheath 20 can be sufficiently suppressed. Therefore, there is no need to dispose other layered members such as a tape body between the sheath 20 and the signal wire 10 for the purpose of suppressing the deviation and deformation. By not disposing other layered members, the number of components constituting the communication wire 1 decreases, and the manufacturing process of the communication wire 1 is also simplified, so the manufacturing cost of the communication wire 1 can be suppressed to a low level.

[0047] The degree of deformation of the insulated wires 11, 11 during the extrusion molding of the sheath 20 can be evaluated using the coating thickness ratio R. As Figure 2As shown, in a cross-section orthogonal to the axial direction of the communication wire 1, the thickness of the thinnest part of the insulation coating 13 is defined as the short thickness a, and the thickness of the insulation coating 13 in the direction orthogonal to the direction corresponding to the short thickness a is defined as the long thickness b. Further, the ratio of the short thickness a to the long thickness b is defined as the coating thickness ratio R (R = a / b × 100%). The larger the value of the coating thickness ratio R, the smaller the difference between the short thickness a and the long thickness b, and the cross-section of the insulated wires 11, 11 is in a state of high symmetry, that is, close to a circular shape, and when the sheath 20 is extrusion-molded, it shows that no large deformation occurs. Also as described above, in the signal wire 10, at the central portion C where the pair of insulated wires 11, 11 are adjacent to each other, extrusion of the insulation coating 13 easily occurs, and the thickness of the insulation coating 13 at the portion where the pair of insulated wires 11, 11 are in contact with each other becomes the short thickness a. On the other hand, in the direction rotated 90° from the adjacent direction of the insulated wires 11, 11 in the direction of the short thickness a ( Figure 2 in the up-and-down direction), the long thickness b is defined. The thickness of the insulation coating 13 in the direction of the long thickness b and in the outer direction of the arrangement of the insulated wires 11, 11 further rotated 90° ( Figure 2 in the left-and-right outer direction) is maintained at a thickness that hardly changes compared to before the extrusion molding of the sheath 20.

[0048] In the communication wire 1 of the present embodiment, by sufficiently increasing the MFR of the sheath 20, the coating thickness ratio R of the insulation coatings 11, 11 is maintained at a large value even after the extrusion molding of the sheath 20. For example, the coating thickness ratio R can be set to 65% or more, further 70% or more, 80% or more. By the insulation coatings 11, 11 having such a high coating thickness ratio R, the effect of maintaining high transmission characteristics of the communication wire 1 is particularly excellent. The upper limit of the coating thickness ratio R is not particularly limited, but even if it is too large, the effect of improving the transmission characteristics saturates. In addition, when the coating thickness ratio R is limited to an overly large range, the materials used to form the sheath 20 are restricted, and the cost required for the extrusion molding of the sheath 20 and the like, the manufacture of the communication wire 1 also becomes large. Therefore, it is preferable that the coating thickness ratio R is previously limited to 95% or less, further 90% or less.

[0049] Examples

[0050] Examples are shown below. In addition, the present invention is not limited by these examples. Below, the relationship between the MFR of the constituent material of the sheath and the structure and transmission characteristics of the communication wire is verified.

[0051] [Production of Specimens]

[0052] Seven copper alloy wire rods having a wire diameter were stranded to produce a conductor cross-sectional area of 0.13 mm2 A wire conductor. Polypropylene resin was extruded onto the outer circumference of the obtained wire conductor to form an insulating coating portion with a thickness of 0.19 mm. The outer diameter of the insulated wire became 0.84 mm. Two such obtained insulated wires were stranded with a pitch of 20 mm to produce a signal wire.

[0053] Polypropylene resin was extruded onto the outer circumference of the above-produced signal wire to form a compact sheath, thereby producing a communication wire. The overall outer diameter of the communication wire was set to 3.2 mm, and the thickness of the sheath became approximately 0.74 mm at the thinnest part. When forming the sheath, as the polypropylene resin, substances having the MFR (value at 200 °C × 2.16 kg load) shown in Table 1 below were used respectively to produce communication wires of Samples 1 to 7. The control of MFR was carried out by combining polypropylene resins with different molecular weights.

[0054] [Evaluation]

[0055] (Coating portion thickness ratio)

[0056] The produced communication wires of Samples 1 to 7 were embedded in an acrylic resin and fixed, and then cut to obtain cross-sectional specimens. In the cross-sectional specimens, as Figure 2 shown, the thickness of the insulating coating portion was measured at the portion where a pair of insulated wires were adjacent to each other, and set as the short thickness a. In addition, the thickness of the insulating coating portion was measured in the direction orthogonal to the short thickness direction, and set as the long thickness b. And the ratio of the short thickness a to the obtained long thickness b was calculated and set as the coating portion thickness ratio R (R = a / b × 100%). The evaluation was carried out for four individual specimens (N = 4), and the values for the two insulated wires included in each specimen individual were averaged with a total of four individuals, and the average value was recorded.

[0057] (Transmission characteristics)

[0058] For the communication wires of Samples 1 to 7, as the transmission characteristics, the through-mode conversion (LCTL) was measured. The measurement was carried out using a network analyzer in the frequency range of 1 MHz to 50 MHz, and the maximum value in this frequency range was recorded.

[0059] [Results]

[0060] In Table 1, for Samples 1 to 7, the evaluation results of the coating portion thickness ratio and LCTL are summarized together with the MFR of the constituent material of the sheath. In addition, Figure 3 a photograph of the cross-section of Sample 3 is published as an example.

[0061] [Table 1]

[0062]

[0063] In Samples 1 to 5, the MFR of the constituent material of the sheath became 0.25 g / 10 min or more. Correspondingly, the thickness ratio of the covering portion in the insulated wire constituting the communication wire took a larger value of 65% or more, and it was found that the deformation of the insulated wire was suppressed to a small extent. In Figure 3 In the cross-sectional photograph of Sample 3 of Figure 3 , it was also confirmed that the two insulated wires maintained a highly symmetric shape that approximated a substantially circular shape. Moreover, in Samples 1 to 5, the larger the MFR of the constituent material of the sheath, the larger the value of the thickness ratio of the covering portion. On the other hand, in Samples 6 and 7 where the MFR of the constituent material of the sheath was less than 0.25 g / 10 min, the thickness ratio of the covering portion became a smaller value of less than 65%, and it was found that the deformation of the insulated wire became larger.

[0064] Next, when looking at the measurement results of LCTL, in Samples 1 to 5 where the MFR of the constituent material of the sheath was 0.25 g / 10 min or more, LCTL became -50 dB or less (LCTL ≤ -50 dB). Moreover, it was generally found that the larger the MFR of the constituent material of the sheath, the smaller the LCTL. On the other hand, in Samples 6 and 7 where the MFR of the constituent material of the sheath was less than 0.25 g / 10 min, LCTL exceeded -50 dB (LCTL > -50 dB).

[0065] Based on the above experimental results, as the constituent material of the sheath, a material with a high MFR is used, and by improving the fluidity in the molten state, deformation of the insulated wire can be suppressed when extruded into a compact shape. And by suppressing the deformation of the insulated wire, the transmission characteristics of the communication wire represented by the mode conversion characteristics can be improved. Specifically, by setting the MFR of the constituent material of the sheath to 0.25 g / 10 min or more, the LCTL of the communication wire can be maintained at a level of -50 dB or less.

[0066] The embodiments of the present disclosure have been described in detail above, but the present invention is not limited to the above embodiments at all, and various changes can be made without departing from the spirit of the present invention.

[0067] Description of Reference Numerals

[0068] 1, 1' Communication wire

[0069] 10 Signal wire

[0070] 11 Insulated wire

[0071] 12 Conductor

[0072] 13 Insulating covering portion

[0073] 20 Sheath

[0074] a Short thickness

[0075] b long thickness

[0076] C central part

Claims

1. A communication wire having: A signal wire, configured as a twisted pair in which a pair of insulated wires are twisted together, the insulated wire having a conductor and an insulating coating portion covering the outer periphery of the conductor; and A compact sheath covering the outer periphery of the signal wire, The constituent material of the sheath includes polypropylene, and the melt flow rate of the constituent material of the sheath measured at a load of 2.16 kg at 200 °C is 0.25 g / 10 min or more, Regarding the thickness of the insulating coating portion in the insulated wire, The thickness of the thinnest part is set as the short thickness, The thickness in the direction orthogonal to the direction of the short thickness is set as the long thickness, The coating portion thickness ratio defined as the ratio of the short thickness to the long thickness is 65% or more and 95% or less, The short thickness is the thickness of the insulating coating portion at the portion where the pair of insulated wires are in contact with each other at the central portion of the signal wire.

2. The communication wire according to claim 1, wherein, No other layered member is provided between the sheath and the signal wire.

3. The communication wire according to claim 1 or claim 2, wherein, The melt flow rate of the constituent material of the sheath is controlled by combining a plurality of polypropylene resins having different molecular weights.

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