Insulated wire, communication cable, and method for manufacturing insulated wire

Abstract

To provide an insulated wire, a communication cable, and a method for manufacturing the insulated wire capable of easily manufacturing the insulated wire having high communication characteristics.SOLUTION: In the insulated electric wire 2, the insulator 22 covering the outer periphery of the stranded wire conductor 21 contains, as a base polymer, a first resin composition having a first crystallinity of more than 40% and a second resin composition having a second crystallinity of 40% or less at a predetermined ratio, and the first resin composition contains at least one resin selected from the group consisting of a polyethylene-based resin and a polypropylene-based resin, the second resin composition is a polyolefin-based resin, the content of the second resin composition is 5 mass% or more and 50 mass% or less when the total of the first resin composition and the second resin composition is 100 mass%, the thickness of the insulator 22 is 0.6 mm or less, and the standard deviation of the electrostatic capacitance is 0.10 pF / m or less in a range of 100 Ω ± 10 Ω of the characteristic impedance of the insulated wire 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an insulated wire, a communication cable, and a method for manufacturing an insulated wire. [Background technology]

[0002] In recent years, small-diameter multi-core cables have been proposed for use as in-vehicle communication cables installed in automobiles and other vehicles, and as communication cables for use within or between various devices. These cables reduce the gap between the central conductor and the insulator, thereby reducing the skew in signal transmission between pairs of cables (see, for example, Patent Document 1).

[0003] The multicore cable described in Patent Document 1 is composed of two coaxial wires, each with a central conductor covered with an insulator, twisted together, or a collection of multiple pairs of coaxial wires, each with two parallel wires, with the central conductor of each coaxial wire being a twisted wire made of 19 or more strands. With this configuration, by having 19 or more strands in the central conductor, the surface irregularities of the twisted wire are reduced compared to the usual case of seven strands, reducing gaps around the strands and gaps inside the strands. As a result, the variation in the dielectric constant of the coaxial wire in the longitudinal direction is reduced, making it possible to keep the propagation delay time difference (skew) of transmission signals between the two coaxial wires low. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-72806 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, polypropylene-based resins, which have a lower dielectric constant and a higher melting point than polyethylene-based resins and therefore do not have a cross-linked structure, have come to be used as the insulating material for covering the conductors of insulated wires that make up small-diameter multi-core cables for communication. However, insulated wires that use polypropylene-based resins as the insulating material have experienced high skew and reduced overall communication characteristics, even when the number of strands that make up the conductor is increased to reduce the surface irregularities of the stranded wires.

[0006] An object of the present invention is to provide an insulated wire, a communication cable, and a method for manufacturing an insulated wire, which can easily manufacture an insulated wire having high communication properties. [Means for solving the problem]

[0007] [1] An insulated wire comprising a stranded conductor formed by twisting together a plurality of wires and an insulator covering the outer periphery of the stranded conductor, the insulator includes, as a base polymer, a first resin composition having a first crystallinity and a second resin composition having a second crystallinity lower than the first crystallinity, in a predetermined ratio; the first crystallinity is greater than 40% and the second crystallinity is less than or equal to 40%; the first resin composition contains at least one resin selected from the group consisting of polyethylene-based resins and polypropylene-based resins, the second resin composition is a polyolefin-based resin, the content of the second resin composition is 5% by mass or more and 50% by mass or less when the total of the first resin composition and the second resin composition is 100% by mass; An insulated wire having an insulator thickness of 0.6 mm or less, and a standard deviation of capacitance of 0.10 pF / m or less when the characteristic impedance of the insulated wire is in the range of 100 Ω±10 Ω. [2] The insulated wire according to [1], wherein the difference between the maximum and minimum capacitances of the insulated wire is 0.33 pF / m or less. [3] The insulated wire according to [1], wherein the polypropylene-based resin constituting the first resin composition is a block copolymer polypropylene. [4] The insulated wire according to [1], wherein the polyolefin resin constituting the second resin composition is a low-crystalline polyolefin resin. [5] The insulated wire according to [1], wherein the wire is a round wire. [6] A pair of insulated wires according to any one of [1] to [5], A communication cable in which the difference in capacitance between the pair of insulated wires is 0.33 pF / m or less. [7] A method for producing an insulated wire according to the above [1], Preheating the stranded conductor to 130°C or less; The method for producing an insulated wire includes extrusion molding the outer periphery of the preheated stranded conductor with the resin composition to form the insulator having a thickness of 0.5 mm or less. [Effects of the Invention]

[0008] According to the present invention, an insulated wire having high communication properties can be easily manufactured. Furthermore, according to the present invention, it is possible to provide a communication cable that can communicate differential signals with little skew. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a resin composition according to a first embodiment of the present invention and an insulated wire using the same. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a communication cable according to a second embodiment of the present invention. [Figure 3] FIG. 3(a) is a cross-sectional photograph of the insulated wire of Comparative Example 7, in which the insulation was not sufficiently filled and solidified due to the low preheating temperature of the conductor. FIG. 3(b) is a cross-sectional photograph of the insulated wire of Comparative Example 8, in which sink marks occurred in the insulation due to the high preheating temperature of the conductor. [Figure 4] FIG. 4 is a cross-sectional photograph of an insulated wire according to Example 2 of the present invention in which no sink marks are formed. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, components having substantially the same functions are designated by the same reference numerals, and redundant description thereof will be omitted.

[0011] [First embodiment] 1 is a cross-sectional view showing an example of a resin composition according to a first embodiment of the present invention and an insulated wire using the same. The insulated wire 2 includes a stranded conductor 21 formed by twisting together a plurality of wires 21a, and an insulator 22 covering the outer periphery of the stranded conductor 21.

[0012] As described above, insulated wires used in communication cables for in-vehicle and intra-device / inter-device communications use polypropylene-based resins as the insulating coating material because they have a lower dielectric constant and a higher melting point than polyethylene-based resins and therefore do not have a cross-linked structure. However, in actual multi-core cable products, even when the number of strands constituting the stranded conductor is increased (for example, by increasing the number to 19 or more without changing the conductor diameter) and the surface irregularities of the stranded conductor are reduced, high skew and reduced overall communication characteristics occur. After extensive research, the inventors discovered that when polypropylene-based resins are used as the insulator material for insulated wires, multiple voids (cavities) are likely to form between the stranded conductor and the insulator, even when the surface irregularities of the stranded wire are reduced.

[0013] Furthermore, the inventors have noted that, depending on the type of polypropylene-based resin, the volume change of the resin composition when it melts and solidifies can be significant, leading to the formation of voids (cavities) on the conductor surface or in the insulating layer, known as "sink marks." Homopolymer polypropylene and block copolymer polypropylene, in particular, have a high melting point and a high degree of crystallinity (high thermal shrinkage). Therefore, even if the temperature of the conductor is raised to fill the conductor with an insulating material made of a resin composition, sink marks are likely to occur around the conductor due to the temperature difference between the outside and inside when the resin composition cools and solidifies. If a portion of the insulator does not adhere to the conductor's outer periphery, multiple cavities are formed around the conductor, and the distribution of these cavities varies, resulting in changes in the capacitance along the longitudinal direction of the insulated wire, which in turn causes skew. However, highly precise control of manufacturing conditions is required to prevent sink marks. One aspect of the present invention is to provide a resin composition suitable for producing insulated wires and communication cables with excellent communication properties, without requiring the need for sophisticated control of manufacturing conditions for insulated wires.

[0014] Here, the propagation delay time Td of the insulated wire, which is a factor causing the skew, can be calculated from the following equations (1) and (2). Td=ε 0.5 ×0.33 (1) ε=C×log(D / d) / 24.1 (2) (ε: relative permittivity, C: capacitance, D: coating diameter, d: conductor diameter)

[0015] That is, the propagation delay time Td is determined by the relative dielectric constant ε of the insulated wire, and the relative dielectric constant ε can be calculated from the conductor diameter d of the insulated wire, the coating diameter (insulator diameter) D of the insulated wire, and the capacitance C of the insulated wire. Therefore, since changes in capacitance have an adverse effect on communication characteristics, in this embodiment, the material and manufacturing conditions of the insulator 22 are selected so as to prevent the occurrence of a gap between the outer periphery of the stranded conductor 21 and the insulator 22. Details of the material and manufacturing conditions of the insulator 22 will be described later.

[0016] (Stranded conductor configuration) The stranded conductor 21 has an outer diameter equivalent to, for example, 20 to 30 AWG (American Wire Gauge). This allows for a small-diameter communication cable suitable for high-speed digital signal transmission. One example of the stranded conductor 21 may be one in which seven round wires 21a, each having a diameter of 0.16 mm, are twisted together, resulting in an outer diameter equivalent to 26 AWG (approximately 0.48 mm). The number of wires 21a constituting the stranded conductor 21 is not limited to seven, and may be six or less, or eight or more. Furthermore, a solid wire may be used instead of the stranded conductor 21.

[0017] The wire 21a is, for example, a round wire having a circular cross section. However, the wire 21a may also be a rectangular wire having a square cross section or a flat wire having a rectangular cross section. The wire 21a may be made of, for example, a tin-plated soft steel wire or a tin-plated copper alloy wire.

[0018] (Insulator composition) The insulator 22 is made of a resin composition containing a first resin composition having a first crystallinity and a second resin composition having a second crystallinity lower than the first crystallinity, in a predetermined ratio, as a base polymer. Specifically, the base polymer for the insulator 22 is made by mixing a first resin composition having a high crystallinity with a second resin composition having a low crystallinity, thereby reducing the crystallinity of the entire resin composition. By extruding this resin composition to coat the stranded conductor 21, the occurrence of sink marks due to cooling shrinkage of the insulator 22 can be reduced. This stabilizes the shape of the insulator 22 after cooling, ensuring that the insulator 22 adheres closely to the outer periphery of the stranded conductor 21 throughout its entire length. This minimizes voids between the stranded conductor 21 and the insulator 22, and even if voids exist, minimizes variation in their distribution. As a result, an insulated electric wire 2 is obtained with minimal change in capacitance along the length. The content of the base polymer in the resin composition does not include fillers or flame retardants that change the dielectric constant of the insulator 22, and the content of antioxidants and heavy metal deactivators is kept to the minimum necessary to obtain heat resistance, preferably 95% by mass or more, and even more preferably 98% by mass or more.

[0019] The first crystallinity of the first resin composition is preferably more than 40%, and the second crystallinity of the second resin composition is preferably 40% or less. Furthermore, the content of the second resin composition is preferably 5% by mass or more and 50% by mass or less, and more preferably more than 10% by mass and 40% by mass or less, when the total of the first resin composition and the second resin composition is taken as 100% by mass. This allows the crystallinity of the entire resin composition to be lowered by mixing the first resin composition with the second resin composition having a lower crystallinity to form a base polymer, even when the first resin composition has a high crystallinity.

[0020] The first resin composition contains at least one resin selected from the group consisting of polyethylene-based resins and polypropylene-based resins. Examples of polypropylene-based resins that can be used include homopolymer polypropylene, random copolymer polypropylene, and block copolymer polypropylene (e.g., ethylene-propylene copolymer). Among these, block copolymer polypropylene, which has a high melting point and good impact properties, may be used.

[0021] The second resin composition may be, for example, a polyolefin resin. Examples of polyolefin resins that can be used include homopolymer polypropylene, propylene-α-olefin copolymer elastomer, ethylene / octene copolymer, and but-1-ene-ethene polymer. Note that propylene resins may also be used in consideration of compatibility with the polypropylene resin of the first resin composition.

[0022] The thickness of the insulator 22 may be determined by the content of the second resin composition. When the insulator 22 is thin, the temperature difference between the outside and inside when solidifying by cooling is small, so the content of the second resin composition can be reduced. Conversely, when the insulator 22 is thick, the content of the second resin composition is increased. When the total of the first resin composition and the second resin composition is 100% by mass, and the content of the second resin composition is in the range of 5% by mass or more and 50% by mass or less, or more than 10% by mass and 40% by mass or less, the thickness of the insulator 22 is preferably 0.2 mm or more and 0.6 mm or less, and more preferably 0.3 mm or more and 0.5 mm or less, when the characteristic impedance is 100±10 Ω.

[0023] The polyolefin resin composition used as the material for the insulator 22 may contain additives such as stabilizers (e.g., antioxidants, heavy metal deactivators, etc.) to improve heat resistance. Examples of antioxidants include 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diyl bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoate] (ADEKA: ADK STAB AO-80). Examples of heavy metal deactivators include N'1,N'12-bis(2-hydroxybenzoyl)dodecane dihydrazide (ADEKA: ADK STAB CDA-6S).

[0024] (Insulated Wire Manufacturing Method) Next, an example of a method for manufacturing the insulated wire 2 will be described. First, a plurality of wires 21a (e.g., seven in this embodiment) are twisted together to form the stranded conductor 21. Next, the stranded conductor 21 is preheated to a predetermined temperature (e.g., 100°C or higher and 130°C or lower), and a polyolefin resin composition constituting the insulator 22 is extruded at a predetermined linear speed (e.g., 200 m / min) to coat the outer periphery of the stranded conductor 21 with the insulator 22. Generally, when using polypropylene resin with a melting point of 160°C, the conductor preheating temperature must be set high, around 140°C, in order for the insulator 22 to fill around the stranded conductor 21. On the other hand, a high conductor preheating temperature of 140°C can cause sink marks. Even if it were possible to address this issue by adjusting the extrusion temperature and cooling conditions, other problems would arise, such as a decrease in tensile elongation due to distortion during cooling and a flattened (oval) shape, and advanced control has been required to obtain a stable insulated wire 2. However, by using a polyolefin resin as the second resin composition, it is possible to provide flexibility in the conditions for conductor preheating, extrusion temperature, and cooling, so the advanced control required in the past is no longer necessary.

[0025] (Effects of this embodiment) The resin composition according to the present embodiment provides the following effects. (a) By using a resin composition as the material for the insulator 22 covering the stranded conductor 21, in which a polypropylene-based resin (e.g., block copolymer polypropylene) as an example of a first resin composition having a high degree of crystallinity is mixed with a polyolefin-based resin (e.g., low-crystalline polyolefin resin or low-crystalline olefin elastomer) as an example of a second resin composition having a low degree of crystallinity, the crystallinity of the entire resin composition can be reduced. As a result, cooling shrinkage of the insulator 22 when the resin composition is extruded to cover the stranded conductor 21 can be suppressed. This stabilizes the shape of the insulator 22, ensures that the insulator 22 adheres closely to the outer periphery of the stranded conductor 21 throughout its entire length, and virtually eliminates voids between the stranded conductor 21 and the insulator 22. As a result, an insulated electric wire 2 is obtained that exhibits little change in longitudinal capacitance and excellent communication characteristics. (b) The occurrence of voids between the stranded conductor 21 and the insulator 22 can be suppressed not only when the number of strands constituting the stranded conductor is large (e.g., 19 or more) and the surface irregularities of the stranded conductor are small, but also when the number of strands is small (e.g., 7 or less) and the surface irregularities of the stranded conductor are large. (c) The resin composition according to the present embodiment makes it extremely easy to control the manufacturing conditions when manufacturing the insulated wire 2.

[0026] [Second embodiment] Fig. 2 is a cross-sectional view showing an example of a communication cable according to a second embodiment of the present invention. This communication cable 1 uses the insulated wire 2 shown in Fig. 1 as signal wires 2a to 2d. The following describes this embodiment, focusing on the differences from the first embodiment. Here, the signal wires 2a to 2d are an example of insulated wires.

[0027] The communication cable 1 includes a pair of signal wires 2a, 2b for transmitting differential signals, a pair of signal wires 2c, 2d for receiving differential signals, a shielding layer 3 that twists these signal wires 2a to 2d together to cover the entire cable, and a sheath 4 that covers the outer periphery of the shielding layer 3. Note that the pair of signal wires 2a, 2b for transmitting differential signals may be twisted together, and the pair of signal wires 2c, 2d for receiving differential signals may be twisted together. Alternatively, the signal wires 2a to 2d may be arranged in parallel without being twisted together.

[0028] The shield layer 3 includes an inner shield layer 3a provided on the inside and formed by winding a resin tape (for example, polyester tape), an outer shield layer 3b provided outside the inner shield layer 3a and formed by winding a conductive tape (for example, a tape in which aluminum and polyester are laminated), and a metal shield layer 3c provided outside the outer shield layer 3b and formed from a metal braid (for example, a tin-plated annealed copper wire braid). Note that the configuration of the shield layer 3 is not limited to the above.

[0029] The sheath 4 is made of, for example, a polyolefin such as polyethylene or polypropylene. However, the resin constituting the sheath 4 is not limited to polyolefin.

[0030] (Effects of this embodiment) According to the communication cable 1 of this embodiment, there is almost no gap between the stranded conductor 21 and the insulator 22, and by using signal lines 2a to 2d with little change in capacitance in the longitudinal direction, differential signals with little skew can be communicated. [Example]

[0031] Table 1 shows the materials, configurations, manufacturing conditions, and properties of Examples 1 to 14. Table 2 shows the materials, configurations, manufacturing conditions, and properties of Examples 15 to 17 and Comparative Examples 1 to 6. Table 3 shows the variations in capacitance of Examples 1 to 5 and Comparative Examples 2 and 6 to 9. Examples 1 to 17 correspond to the first embodiment.

[0032] A 50 mm single-screw extruder was used for extrusion molding of the insulator 22. Round wires made of tin-plated mild steel wires were used as the stranded conductor 21. The extrusion temperature was a maximum of 210 to 230°C, the conductor preheating was in the range of 100 to 130°C, and the screw rotation speed was in the range of 30 to 50 rpm.

[0033] [Table 1]

[0034] [Table 2]

[0035] [Table 3]

[0036] In Tables 1 and 2, material A is manufactured by LCY Chemical under the trade name "Globalene 7633," material B is manufactured by Mitsui Chemicals under the trade name "Tafmer PN2060N," material C is manufactured by Idemitsu Kosan under the trade name "L-Modu S901," and material D is manufactured by Mitsui Chemicals under the trade name "Tafmer XM7090."

[0037] In Tables 1 and 2, the characteristic "Contraction around the conductor / stable cross-sectional shape" means that the propagation delay time difference (skew) of the transmission signal between two pairs of insulated wires in a multi-core cable can be kept low. "Characteristics 2" and "Characteristics 3" in Table 3 show the capacitance measured at 10 points within a 1m length of wire, and the standard deviation and range (maximum and minimum values) from the measurement results are listed in Table 3.

[0038] (Results of investigation into materials and conductor preheating temperature) As shown in "Characteristic 1" in Tables 1 and 2, stable (◯) results were obtained in Examples 1 to 17, and unstable (×) results were obtained in Comparative Examples 1 to 6. From this, it can be said that the ratio of material A to other materials (materials B, C, or D) is preferably 50% by mass or more and 90% by mass or less for material A, and 10% by mass or more and 50% by mass or less for other materials.

[0039] When the thickness of the insulator 22 is 0.3 mm, it was found that the amount of other materials could be reduced to 10% by mass if the conductor preheating temperature was set to 130°C, as shown in Example 15. When the thickness of the insulator 22 is 0.5 mm, it was found that the amount of other materials could be reduced to 20% by mass if the conductor preheating temperature was set to 130°C, as shown in Example 1 and Comparative Example 3. When the thickness of the insulator 22 is 0.5 mm, it was found that the conductor preheating temperature could be reduced to 100°C if the amount of other materials was set to 30% by mass or more, as shown in Examples 2, 4, 8-10, 12-14 and Comparative Example 6.

[0040] (Study results of capacitance variation) The capacitance variation was measured for n = 10 samples, and as shown in Table 3, the standard deviation was 0.06 to 0.10 pF / m in Examples 1 to 5, and the difference (range) between the maximum and minimum values ​​was 0.14 to 0.33 pF / m. On the other hand, the standard deviation was 0.15 to 0.34 pF / m in Comparative Examples 2 and 6 to 9, and the range was 0.36 to 0.99 pF / m. Since the relative dielectric constant ε of air is approximately 1, the capacitance variation is thought to reflect the voids inside the stranded conductor 21 and the multiple voids formed between the stranded conductor 21 and the insulator 22. Therefore, compared to Comparative Examples 2 and 6 to 9, it is thought that in Examples 1 to 5, the insulator 22 is in close contact with the outer periphery of the stranded conductor 21 throughout its entire length, resulting in smaller void distribution variation (or almost no voids at all) between the stranded conductor 21 and the insulator 22.

[0041] FIG. 3(a) is a cross-sectional photograph of the insulated wire of Comparative Example 7, in which the insulation was not sufficiently filled and solidified due to a low conductor preheating temperature. FIG. 3(b) is a cross-sectional photograph of the insulated wire of Comparative Example 8, in which sink marks occurred in the insulation due to a high conductor preheating temperature. FIG. 4 is a cross-sectional photograph of the insulated wire of Example 2 of the present invention, in which no sink marks occurred. Note that FIGS. 3 and 4 show cross-sectional photographs after the stranded conductor has been removed. The stranded conductors of Comparative Examples 7, 8, and Example 2 were all constructed by twisting together seven 0.18 mm diameter round bar wires, and the outer diameter of the insulated wire was 1.54 mm. As shown in Table 3, the insulators of Comparative Examples 7 and 8 contained 100% by mass of material A (ethylene-propylene copolymer) and did not contain the other materials B, C, or D. The conductor preheating temperature for Comparative Example 7 was 100°C, and that for Comparative Example 8 was 130°C. As shown in Table 3, the insulator of Example 2 contains 70 mass% of material A (ethylene-propylene copolymer) and 30 mass% of material B (propylene-1-butene-ethylene copolymer), and the conductor preheating temperature is 100°C.

[0042] As is clear from the cross-sectional photograph in Figure 3, in the insulated wire of Comparative Example 7, the conductor preheating temperature was low, so the insulation solidified without being sufficiently filled in, and in the insulated wire of Comparative Example 8, multiple voids occurred between the stranded conductor and the insulation even when the conductor preheating temperature was high. The inventors confirmed that the distribution of voids varied throughout the entire length of the insulated wire, and that when the conductor preheating temperature was low, there was little sink mark but the insulation was not filled around the stranded conductor, while when the conductor preheating temperature was high, the insulation was filled around the stranded conductor but there were many sink marks. This is thought to be due to the difficulty in controlling the manufacturing conditions, particularly the conductor preheating and cooling conditions.

[0043] On the other hand, as is clear from the cross-sectional photograph of Fig. 4, almost no voids were formed between the stranded conductor and the insulator in the insulated wire of Example 2. The inventors confirmed that there were no areas where voids were concentrated, and that there was no variation in the distribution of voids over the entire length of the insulated wire.

[0044] Although the embodiments of the present invention have been described above, the embodiments of the present invention are not limited to the above-described embodiments and various modifications and implementations are possible. For example, a twin-ax cable may be formed by a pair of insulated electric wires 2 that transmit differential signals, or a coaxial cable may be formed by a pair of coaxial wires that transmit differential signals. [Explanation of symbols]

[0045] 1...communication cable, 2...insulated wire, 2a to 2d...signal wire, 3...shield layer, 3a...inner shield layer, 3b...outer shield layer, 3c...metal shield layer, 4...sheath, 21...stranded conductor, 21a...stranded wire, 22...insulator

Claims

1. An insulated wire comprising a stranded conductor formed by stranding a plurality of wires together, and an insulator covering the outer periphery of the stranded conductor, the insulator includes, as a base polymer, a first resin composition having a first crystallinity and a second resin composition having a second crystallinity lower than the first crystallinity, in a predetermined ratio; the first crystallinity is greater than 40% and the second crystallinity is less than or equal to 40%; the first resin composition contains at least one resin selected from the group consisting of polyethylene-based resins and polypropylene-based resins, the second resin composition is a polyolefin-based resin, the content of the second resin composition is 5% by mass or more and 50% by mass or less when the total of the first resin composition and the second resin composition is 100% by mass; the thickness of the insulator is 0.6 mm or less, and the standard deviation of the capacitance of the insulated wire is 0.10 pF / m or less when the characteristic impedance of the insulated wire is in the range of 100 Ω±10 Ω; Insulated wire.

2. The difference between the maximum and minimum capacitance of the insulated wire is 0.33 pF / m or less. The insulated wire according to claim 1 .

3. The polypropylene-based resin constituting the first resin composition is a block copolymer polypropylene. The insulated wire according to claim 1 .

4. The polyolefin resin constituting the second resin composition is a low-crystalline polyolefin resin. The insulated wire according to claim 1 .

5. The wire is a round wire. The insulated wire according to claim 1 .

6. A pair of insulated wires according to any one of claims 1 to 5 is provided, The difference in capacitance between the pair of insulated wires is 0.33 pF / m or less. Communication cable.

7. The method for producing an insulated wire according to claim 1, Preheating the stranded conductor to 130°C or less; The outer periphery of the preheated stranded conductor is covered with the resin composition by extrusion molding to form the insulator having a thickness of 0.5 mm or less. Manufacturing method of insulated wire.

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