transmission cable

Abstract

The present invention provides a transmission cable that can improve transmission characteristics in a configuration in which two insulated wires of different colors are twisted together. [Solution] The device comprises two twisted insulated wires 11, each of which has a conductor 21 and an insulating coating 23 made of a polyolefin resin with added pigment that covers the conductor 21. The insulating coating 23 of the two insulated wires 11 is colored with pigment in two colors selected from white, pink, orange, light green, sky blue, and yellow.

Description

Technical Field

[0001] The present invention relates to a transmission cable.

Background Art

[0002] Conventionally, as a transmission cable, there is one that incorporates two insulated electric wires twisted together (for example, see Patent Document 1). This transmission cable (communication wire) includes two insulated electric wires twisted together and a sheath that covers the two insulated electric wires. The two insulated electric wires each have a conductor formed of a Su-Cu alloy and an insulation coating that covers the outer periphery of the conductor and is formed of a polypropylene resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the conventional transmission cable, when a pigment is added to the polypropylene resin to color the insulation coatings of the two insulated electric wires in different colors, a difference in dielectric constant occurs between the two insulated electric wires, resulting in a problem that the transmission characteristics deteriorate.

[0005] Therefore, an object of the present invention is to provide a transmission cable capable of improving transmission characteristics in a configuration where two insulated electric wires colored in different colors are twisted together.

Means for Solving the Problems

[0006] To achieve the above objective, the present invention comprises two twisted insulated wires, each of which has a conductor and an insulating coating made of a polyolefin resin to which a pigment has been added, covering the conductor, and the insulating coatings of the two insulated wires are colored with the pigment in two colors selected from white, pink, orange, light green, sky blue, and yellow. Furthermore, the two colors of the insulating coating in the two insulated wires are determined by the pigments, and the titanium content in the insulating coating is 200,000 cps or more in terms of integrated intensity, and the integrated intensity of the titanium content and heavy metals (density of 5 g / cm³) 3 The above metals.) are two colors in which the ratio of the integrated intensity of the total content of heavy metals to the sum of the integrated intensity of the total content of heavy metals is 5% or less. The total content of heavy metals is evaluated excluding antimony, zinc, and nickel. The integrated intensity of the titanium element content and the integrated intensity of the total content of heavy metals are both the integrated intensity of the characteristic X-ray peak after background correction, measured using an energy-dispersive X-ray fluorescence analyzer by the bulk FP method (tube voltage 50kV, optimized counting rate 60,000cps, counting time 60sec, collimator diameter 2.0mm, vacuum atmosphere). The difference in dielectric constant due to the pigment in the insulating coating of the two insulated wires is 0.010 or less. To provide a transmission cable characterized by [this feature]. [Effects of the Invention]

[0009] According to the transmission cable of the present invention, in a configuration in which two insulated wires of different colors are twisted together, the transmission characteristics can be improved. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1(a) shows a side view (a) and a cross-sectional view (b) of a transmission cable according to one embodiment of the present invention. [Figure 2] This is a flowchart illustrating the manufacturing method of insulated wires. [Figure 3] This is an explanatory diagram showing a method for manufacturing insulated electric wires. [Modes for carrying out the invention]

[0011] The following describes a transmission cable according to one embodiment of the present invention, with reference to the attached drawings. This transmission cable is a twisted-pair cable that incorporates two twisted-pair insulated wires and transmits electricity or electrical signals through the two insulated wires. This transmission cable is intended for use, for example, as a wire harness for automobiles. In particular, this transmission cable improves its transmission characteristics by devising a way to color the two twisted-pair insulated wires.

[0012] (Transmission cable configuration) As shown in Figure 1, the transmission cable 1 comprises two twisted insulated wires 11, 11 (paired wires) and a sheath 12 (jacket) that directly covers the two insulated wires 11, 11. In other words, the transmission cable 1 is a two-core shieldless cable with an internal twisted wire.

[0013] The sheath 12 is, for example, a single sheath made of a highly heat-resistant and halogen-free polyolefin resin. In this embodiment, the sheath 12 is a solid sheath in which the two insulated wires 11, 11 are covered and the resin material is filled in the gaps between the two insulated wires 11, 11.

[0014] (Insulated wire configuration) Each insulated wire 11, 11 comprises a conductor 21 (core wire), a plating layer 22 covering the outer circumference of the conductor 21, an insulating coating 23 covering the outer circumference of the plating layer 22, and a silicone coating 24 covering the outer circumference of the insulating coating 23. In other words, each insulated wire 11, 11 has a three-layer structure in which the plating layer 22 is formed on the outer surface of the conductor 21, the insulating coating 23 is formed on the outer surface of the plating layer 22, and the silicone coating 24 is formed on the outer surface of the insulating coating 23. The insulating coating 23 covers the conductor 21 via the plating layer 22.

[0015] The conductor 21 is made of a copper-tin alloy and consists of a single wire or a stranded wire made by twisting together multiple strands. The material of the conductor 21 is not limited to a copper-tin alloy; any copper-based metal may be used, for example, soft copper.

[0016] (Composition of the plating layer) The plating layer 22 is formed by hot-dip tin (Sn) plating (plating treatment) over the entire outer surface of the conductor 21 and is interposed between the conductor 21 and the insulating coating 23. The material of the plating layer 22 is not limited to tin; for example, silver may also be used. The plating thickness of the plating layer 22 is approximately 1 μm (0.1 μm to 2 μm).

[0017] Thus, by interposing a tin plating layer 22 between the conductor 21 and the insulating coating 23, it is possible to suppress the copper damage of the insulating coating 23 caused by the conductor 21 (deterioration due to copper ion diffusion from the conductor 21), and the temperature at which the transmission characteristics (attenuation) can be maintained up to 10,000 hours, calculated by an Arrhenius plot using the time when the transmission characteristics deteriorate at three levels of temperature (150 °C, 140 °C, 130 °C), can be increased by 4 °C, improving the heat resistance.

[0018] (Configuration of Insulating Coating) The insulating coating 23 is formed in a cylindrical shape surrounding the conductor 21, and is formed of a crosslinked polyolefin resin (for example, high-density polyethylene resin) added with an antioxidant, a crosslinking aid, and a metal deactivator. Specifically, the insulating coating 23 is obtained by adding an antioxidant of 0.05 PHR or more and 0.5 PHR or less, a crosslinking aid of 0.1 PHR or more and 2 PHR or less, and a metal deactivator of 0.1 PHR or more and 0.5 PHR or less to 100 PHR of the polyolefin resin, and then molding the resin material 23a (see FIG. 3(b)) into a cylindrical shape by extrusion molding, and then irradiating the resin material 23a with an electron beam to crosslink the resin material 23a. The crosslinking aid is, for example, trimethallyl isocyanurate. Also, the remaining amount of the antioxidant after crosslinking in the insulating coating 23 is 25% or more of that before crosslinking.

[0019] Thus, by adding an antioxidant to the insulating coating 23, the oxidation of the insulating coating 23 is suppressed, so that the heat resistance of the insulating coating 23 can be improved. And by adding a crosslinking aid in addition to the antioxidant, the crosslinking efficiency can be improved, the consumption amount of the antioxidant by the crosslinking treatment can be reduced, and the remaining amount of the antioxidant can be increased. Thereby, the addition amount of the antioxidant can be made small, and the deterioration of the dielectric tangent due to the excessive addition of the antioxidant can be suppressed.

[0020] Although the addition amount of the antioxidant was described as 0.05 PHR or more and 0.5 PHR or less, it is more preferable that the addition amount of the antioxidant is 0.05 PHR or more and 0.25 PHR or less. Also, although the addition amount of the crosslinking aid was described as 0.1 PHR or more and 2 PHR or less, it is more preferable that the addition amount of the crosslinking aid is 0.5 PHR or more and 1 PHR or less. Further, although the remaining amount of the antioxidant after crosslinking in the insulating coating 23 was described as 25% or more of that before crosslinking, it is more preferable that the remaining amount of the antioxidant after crosslinking in the insulating coating 23 is 50% or more of that before crosslinking.

[0021] Also, the insulating coating 23 contains a color masterbatch which is low-density polyethylene containing a pigment added to the above polyolefin resin, and the insulating coatings 23 of the two insulated electric wires 11, 11 are colored in different colors by the color masterbatch. Specifically, the insulating coatings 23 of the two insulated electric wires 11, 11 are colored in two colors selected from white, pink, orange, light green, sky blue and yellow by the color masterbatch. For example, the insulating coating 23 of one insulated electric wire 11 is colored white, and the insulating coating 23 of the other insulated electric wire 11 is colored pink. Note that the addition rate of the color masterbatch is the same for the two insulated electric wires 11, 11, and is, for example, 2% or less.

[0022] The insulating coatings 23 of the two insulated electric wires 11, 11 colored in this way contain a color masterbatch (pigment) containing titanium oxide, and the content of titanium element becomes 200,000 cps or more in integral intensity, and the ratio of the total content of heavy metals to the total of the content of titanium element and the total content of heavy metals is 5% or less. Also, the insulating coatings 23 of the two insulated electric wires 11, 11 colored in this way have a difference in dielectric constant of 0.010 or less due to the color masterbatch (pigment). Here, the "integral intensity" is the so-called integrated count number, which is the total count number of X-rays detected within the energy range corresponding to the characteristic X-ray peak of the measured element after background correction. Also, the "heavy metals" mentioned here are metals with a density of 5 g / cm 3 as described above.

[0023] In this way, by coloring the insulating coating 23 of the two twisted insulated wires 11, 11 with two colors selected from white, pink, orange, light green, sky blue, and yellow, the difference in dielectric constant of the insulating coating 23 between the two insulated wires 11, 11 can be reduced, thereby improving the transmission characteristics.

[0024] Although it was stated that the insulating coatings 23 of the two insulated wires 11, 11 are colored in two colors selected from white, pink, orange, light green, sky blue, and yellow, it is preferable that the insulating coatings 23 of the two insulated wires 11, 11 are colored in two colors selected from white, pink, orange, and light green using a color masterbatch, in order to make the difference in dielectric constant of the insulating coatings 23 of the two insulated wires 11, 11 0.005 or less. Furthermore, it is preferable that the insulating coatings 23 of the two insulated wires 11, 11 have a titanium content of 400,000 cps or more in integral intensity, and that the ratio of the total heavy metal content to the sum of the titanium content and the total heavy metal content is 3% or less.

[0025] (Composition of the silicone coating) The silicone coating 24 is a silicone coating layer formed by a silicone coating on the outer surface of the insulating coating 23. Specifically, the silicone coating 24 is formed by applying aqueous silicone to the entire outer surface of the insulating coating 23 and vaporizing the water in the aqueous silicone by the heat generated during electron beam irradiation in the crosslinking process. As the aqueous silicone, an aqueous silicone solution obtained by diluting an oil-in-water type silicone emulsion with water is used. The silicone concentration of the aqueous silicone used for the silicone coating is 0.38% to 1.90%. Furthermore, the silicone coating 24 has an adhesion force of 15N to 30N to the sheath 12. The silicone coating 24 is transparent or translucent, and is configured to allow the coloring of the insulating coating 23 to be visible.

[0026] In this way, by forming a silicone coating 24 on the outer surface of the insulating coating 23 and making the outermost layer of the insulated wire 11 the silicone coating 24, the adhesion force of the insulated wire 11 to the sheath 12 can be reduced, and the processability of processing the end of the transmission cable 1 (removal of the sheath 12) can be improved. Furthermore, by using aqueous silicone, the adhesion force of the insulated wire 11 to the sheath 12 can be precisely adjusted by adjusting the silicone concentration of the aqueous silicone. In addition, by vaporizing the water in the aqueous silicone due to the heat generated during electron beam irradiation, the silicone coating 24 does not peel off easily, thus ensuring stable adhesion even in subsequent processes.

[0027] (Explanation of the manufacturing method of insulated wires) Next, the manufacturing method of the insulated wire 11 will be described with reference to Figures 2 and 3. As shown in Figure 2, in the manufacturing method of the insulated wire 11, the insulated wire 11 is manufactured by performing a resin material molding step S1, an aqueous silicone coating step S2, and a crosslinking treatment step S3 on a conductor 21 (see Figure 3(a)) on which a tin plating layer 22 has been formed. Note that the resin material molding step S1 and the crosslinking treatment step S3 are examples of insulation coating formation steps.

[0028] As shown in Figure 2, a resin material 23a is obtained by adding an antioxidant, a crosslinking aid, and a metal deactivator to a polyolefin resin, along with a color masterbatch, to a conductor 21 on which a plating layer 22 has been formed. This resin material 23a is then extruded to form a cylindrical shape that covers the outer circumference of the plating layer 22 (S1: Resin material molding process) (see Figure 3(b)). At this time, the amount of antioxidant added to the resin material 23a is 0.05 PHR or more and 0.5 PHR or less, the amount of crosslinking aid added is 0.1 PHR or more and 2 PHR or less, and the amount of metal deactivator added is 0.1 PHR or more and 0.5 PHR or less.

[0029] Subsequently, an aqueous silicone with a silicone concentration of 0.38% to 1.90% is applied to the outer surface of the molded resin material 23a (insulating coating 23 before crosslinking) (S2: aqueous silicone application step). Then, the resin material 23a and the aqueous silicone are irradiated with an electron beam using an electron beam irradiation device 101 to perform a crosslinking treatment on the resin material 23a (S3: crosslinking treatment step) (see Figure 3(c)). In this crosslinking treatment, for example, an electron beam with an acceleration voltage of 500 keV to 1500 keV is irradiated. As a result, the resin material 23a is crosslinked, forming a crosslinked insulating coating 23 on the outer surface of the plating layer 22, and the water in the aqueous silicone vaporizes due to the heat from the electron beam irradiation, forming a silicone coating 24 on the outer surface of the insulating coating 23. This forms an insulating coating 23 in which 25% or more of the antioxidant remains before crosslinking. This is how the insulated wire 11 is manufactured.

[0030] (Effects and workings of the embodiment) As described above, according to the configuration of the above embodiment, by coloring the insulating coating 23 of the two twisted insulated wires 11, 11 with two colors selected from white, pink, orange, light green, sky blue, and yellow, the difference in dielectric constant of the insulating coating 23 of the two insulated wires 11, 11 can be reduced, and the transmission characteristics can be improved. In detail, Table 1 shows the titanium content in each color of insulating coating 23, with a density of 5 g / cm³ as a general definition. 3The table above shows the total content, percentage of heavy metals, dielectric constant, and dielectric loss tangent of the heavy metals. The dielectric constant and dielectric loss tangent in Table 1 were measured in the insulating coating 23 of the insulating wire 11, which was prepared by coloring each color using a color masterbatch based on the above embodiment. The color masterbatches for each color were "TET Color" manufactured by Toyo Color Co., Ltd., and the polyolefin resin that forms the base of the insulating coating 23 was low-density polyethylene resin, which is easy to extrude and provides a stable shape. In detail, Table 1 evaluates the "titanium element content," "total heavy metal content," "percentage of heavy metals," "dielectric constant," and "dielectric loss tangent" of the insulating coating 23 made from low-density polyethylene resin with 2% of each color of TET Color added. The "titanium element content" and "total heavy metal content" were measured using the bulk FP method (tube voltage 50kV, optimized) with an energy-dispersive X-ray fluorescence analyzer (XRF) of JSX-1000S (JEOL Ltd). Total Counting rate 60,000 cps (counts per second), counting time 60 sec, collimator diameter 2.0 mm The integrated intensity (total count of X-rays detected within the energy range corresponding to the characteristic X-ray peak of the measured element after background correction) measured in a vacuum atmosphere was used for evaluation. The "heavy metal content" was calculated as the content of the titanium element, the total content of heavy metals, and the percentage of the total heavy metal content relative to the total. The "total heavy metal content" was evaluated excluding antimony (Sb), zinc (Zn), and nickel (Ni). In addition, the "dielectric constant" and "dielectric loss tangent" were evaluated by measuring them in a 2.45 GHz frequency band using a cavity resonator. [Table 1] As shown in Table 1, by coloring the insulating coating 23 of the two insulated wires 11, 11 with two colors selected from white, pink, orange, light green, sky blue, and yellow, the difference in dielectric constant of the insulating coating 23 of the two insulated wires 11, 11 due to the color masterbatch (pigment) can be reduced to 0.010 or less. This reduces the propagation delay time difference (phase difference in signal transmission, SKEW) and improves the transmission characteristics. Based on Table 1, it can be inferred that this difference in dielectric constant is strongly influenced by the titanium element content (mainly titanium oxide) and the proportion of heavy metals. More specifically, as shown in Table 1, by using two colors for the insulating coating 23 of the two insulated wires 11, 11, where the titanium element content in the insulating coating 23 is 200,000 cps or more and the proportion of heavy metals is 5% or less, it can be said that the difference in dielectric constant of the insulating coating 23 of the two insulated wires 11, 11 can be reduced to 0.010 or less.

[0031] Furthermore, by coloring the insulating coatings 23 of the two insulated wires 11, 11 with different colors (colors that workers can recognize as different colors), identification during the manufacturing and assembly processes can be improved, and incorrect connections during terminal processing can be prevented. In addition, during cable maintenance and inspection, it becomes easier to distinguish each insulated wire 11, 11, thereby improving work efficiency and reliability.

[0032] Furthermore, by including a predetermined amount or more of titanium dioxide in the color masterbatch added to the insulating coating 23 of each insulated wire 11, 11, the color distinguishability and opacity of each insulated wire 11, 11 can be improved. In other words, by mixing titanium dioxide, which has excellent whiteness and high opacity, into the color masterbatch (pigment) and using it in the insulating coating 23, the color distinguishability and opacity of each insulated wire 11, 11 can be improved.

[0033] In other words, according to the configuration of the above embodiment, by coloring the insulating coating 23 of the two twisted insulated wires 11, 11 with two colors selected from white, pink, orange, light green, sky blue, and yellow, it is possible to improve transmission characteristics while obtaining the advantages of color discrimination due to coloring with different colors, and the advantages of opacity and color discrimination due to the inclusion of titanium dioxide in the color masterbatch (pigment). In particular, titanium dioxide has a relatively high dielectric constant, and when dispersed in resin, it tends to increase the dielectric constant of the entire insulator in proportion to its content. Therefore, when using color masterbatches (pigments) of different colors, a difference in dielectric constant occurs due to the difference in titanium dioxide content, which may affect the characteristic impedance and propagation delay time in signal transmission. Also, heavy metals have a higher conductivity than titanium (especially copper), and even a small difference in content has a large effect on the dielectric constant, which may affect the characteristic impedance and propagation delay time in signal transmission, similar to the effect of the difference in titanium dioxide content. In contrast to this, the effect of titanium dioxide content and the density, which is generally defined as 5 g / cm³, 3 By selecting a color that takes into account the influence of the heavy metal content ratio described above, the transmission characteristics of the two insulated wires 11, 11 can be made uniform.

[0034] Furthermore, according to the configuration of the above embodiment, by coloring the insulating coating 23 of the two insulated wires 11, 11 with two colors selected from white, pink, orange, and light green, the difference in dielectric constant of the insulating coating 23 of the two insulated wires 11, 11 due to the color masterbatch (pigment) can be made 0.005 or less, as shown in Table 1. This makes it possible to further reduce the propagation delay time difference and further improve the transmission characteristics. It can also be said that, as shown in Table 1, by coloring the insulating coating 23 of the two insulated wires 11, 11 with two colors such that the titanium element content in the insulating coating 23 has an integrated intensity of 400,000 cps or more, and the ratio of the total heavy metal content to the sum of the titanium element content and the total heavy metal content is 3% or less, the difference in dielectric constant of the insulating coating 23 of the two insulated wires 11, 11 can be made 0.005 or less.

[0035] (Regarding other embodiments) Although embodiments of the present invention have been described above, these embodiments do not limit the invention as defined in the claims. Furthermore, it should be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention. The present invention can be implemented with appropriate modifications without departing from its spirit.

[0036] For example, in the above embodiment, the insulating coating 23 of the two insulated wires 11 was colored with two colors selected from white, pink, orange, light green, sky blue, and yellow, or two colors selected from white, pink, orange, and light green. However, the configuration is not limited to this, as long as the dielectric constants of the insulating coatings 23 are close, the color combinations are not limited. For example, considering that the titanium dioxide content and the total heavy metal content strongly affect the dielectric constant, there are no restrictions on the color combinations as long as the difference between them is small. For example, based on Table 1, the insulating coating 23 of the two insulated wires 11 may be colored with two colors selected from red, green, blue, and purple using a color masterbatch (pigment). Even in such cases, it is preferable to exclude black and gray, which contain highly conductive carbon, from the coloring.

[0037] Furthermore, in the above embodiment, the configuration selected a color combination that minimizes the difference in dielectric constant, but a configuration that minimizes the difference in dielectric loss tangent may also be used.

[0038] Furthermore, in the above embodiment, high-density polyethylene resin was exemplified as the base resin (polyolefin resin) of the insulating coating 23, but it is not limited to this. For example, a low-density polyethylene resin may be used as the base resin of the insulating coating 23, or a polyethylene resin containing polypropylene resin may be used. In other words, a low-density polyethylene resin or polypropylene resin may be used as the base resin of the insulating coating 23.

[0039] Furthermore, in the above embodiment, the conductor 21 was formed of a copper-tin alloy, and the surrounding material was a tin-plated copper-tin alloy (Sn-plated Cu-Sn alloy), but this is not the only option. For example, the conductor 21 may be formed of soft copper, and the surrounding material may be tin-plated soft copper.

[0040] Furthermore, in the above embodiment, the outer surface of the copper-tin alloy conductor 21 was plated with tin to form a tin plating layer 22, but the configuration is not limited to this. For example, the outer surface of the copper-tin alloy conductor 21 may be plated with silver to form a silver plating layer 22. With such a configuration, due to the skin effect, when a high-frequency current flows through the conductor 21, the current concentrates on the surface portion of the conductor 21, thereby improving the transmission characteristics.

[0041] (Summary of the embodiments) Next, the technical concept understood from the embodiments described above will be described using the reference numerals, etc., from the embodiments. However, the reference numerals, etc., in the following description are not limited to the components in the claims that are specifically shown in the embodiments.

[0042] (1) A transmission cable (1) comprising two twisted insulated wires (11), each of the two insulated wires (11) having a conductor (21) and an insulating coating (23) made of a polyolefin resin to which a pigment has been added and covering the conductor (21), wherein the insulating coating (23) of the two insulated wires (11) is colored with the pigment in two colors selected from white, pink, orange, light green, sky blue and yellow. (2) The transmission cable (1) according to (1), characterized in that the insulating coating (23) of the two insulated wires (11) is colored with the pigment in two colors selected from white, pink, orange, and light green. (3) A transmission cable (1) comprising two twisted insulated wires (11), each of which comprises a conductor (21) and an insulating coating (23) formed of a polyolefin resin to which a color masterbatch has been added, covering the conductor (21), wherein the insulating coating (23) of the two insulated wires (11) is colored in different colors by the color masterbatch, and the colors of the insulating coating (23) of the two insulated wires (11) are selected by the color masterbatch to be two colors such that the titanium element content in the insulating coating (23) has an integrated intensity of 200,000 cps or more, and the ratio of the total content of heavy metals to the sum of the titanium element content and the total content of heavy metals is 5% or less. (4) The transmission cable (1) according to (3), characterized in that the color of the insulating coating (23) on the two insulated wires (11) is selected by the color masterbatch to be two colors such that the titanium element content in the insulating coating (23) has an integrated intensity of 400,000 cps or more, and the ratio of the total heavy metal content to the sum of the titanium element content and the total heavy metal content is 3% or less. (5) A transmission cable (1) comprising two twisted insulated wires (11), each of which comprises a conductor (21) and an insulating coating (23) made of a polyolefin resin to which a pigment has been added, covering the conductor (21), wherein the insulating coating (23) of the two insulated wires (11) is colored in different colors by the pigment, and the difference in dielectric constant due to the pigment of the insulating coating (23) of the two insulated wires (11) is 0.010 or less. (6) The transmission cable (1) according to (5), characterized in that the difference in dielectric constant due to the pigment in the insulating coating (23) of the two insulated wires (11) is 0.003 or less. [Explanation of Symbols]

[0043] 1: Transmission cable, 11: Insulated wire, 12: Sheath, 21: Conductor, 22: Plating layer, 23: Insulating coating, 24: Silicone coating

Claims

1. It has two insulated wires that are twisted together, The two insulated wires mentioned above are, A conductor and It is formed of a polyolefin resin to which pigment has been added, and has an insulating coating that covers the conductor, The insulating coating of the two insulated wires is colored with the pigment to two colors selected from white, pink, orange, light green, sky blue, and yellow. The two colors of the insulating coating in the two insulated wires are such that, by the pigment, the titanium content in the insulating coating is 200,000 cps or more in terms of integrated intensity, and the ratio of the integrated intensity of the total heavy metal content to the sum of the integrated intensity of the titanium content and the integrated intensity of the total heavy metal content (metals with a density of 5 g / cm³ or more) is 5% or less, and the total heavy metal content is evaluated excluding antimony, zinc, and nickel. The integrated intensity of the titanium element content and the integrated intensity of the total heavy metal content were both measured using an energy-dispersive X-ray fluorescence analyzer by the bulk FP method (tube voltage 50 kV, optimized counting rate 60,000 cps, counting time 60 sec, collimator diameter 2.0 mm, vacuum atmosphere), and are the integrated intensities of the characteristic X-ray peaks after background correction. A transmission cable characterized in that the difference in dielectric constant due to the pigment in the insulating coating of the two insulated wires is 0.010 or less.

2. The transmission cable according to claim 1, characterized in that the two colors of the insulating coating in the two insulated wires are selected from white, pink, orange, and light green.

3. The transmission cable according to claim 2, characterized in that the two colors of the insulating coating in the two insulated wires are such that the titanium element content in the insulating coating is 400,000 cps or more in terms of integrated intensity, and the ratio of the integrated intensity of the total heavy metal content to the sum of the integrated intensity of the titanium element content and the integrated intensity of the total heavy metal content is 3% or less.

4. The transmission cable according to claim 3, characterized in that the difference in dielectric constant due to the pigment in the insulating coating of the two insulated wires is 0.005 or less.

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