Insulated electric wire and cable

Abstract

To provide an insulated electric wire and a cable that allow reduction of deterioration in insulation of a covering layer and also make the covering layer resistant to tearing.SOLUTION: An insulated electric wire 1 comprising: a conductor 2; and a covering layer 5 formed outermost so as to cover around the conductor 2, the covering layer 5 having a thickness of 0.08 mm or less, the covering layer 5 being composed of a resin composition whose main component is PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), the covering layer 5 containing no titanium oxide and containing zinc oxide as a colorant.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to insulated wires and cables. [Background technology]

[0002] In recent years, insulated wires have become thinner due to the increasing functionality of electronic devices such as virtual reality (VR) devices and wearable devices, as well as the miniaturization and minimal invasiveness of medical devices. For example, ultra-thin coaxial cables with an outer diameter of 0.4 mm or less are used as insulated wires for signal transmission. To realize such ultra-thin coaxial cables, efforts are being made to make the coating thickness extremely thin, for example, to 80 μm or less.

[0003] Prior art document information related to the invention of this application includes Patent Document 1. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-164841 Summary of the Invention [Problem to be solved by the invention]

[0005] The coating layer is formed by extrusion molding, but if the coating layer is very thin, the screw rotation speed during extrusion molding will be low, causing the resin to stagnate in the extruder and decompose and foam due to excessive heat, which can reduce the insulating properties of the coating layer. Furthermore, if the temperature during extrusion molding is lowered to suppress the decomposition and foaming of the resin, the strain during extrusion molding can cause the orientation of the resin molecules that make up the coating layer to become uniform, making the coating layer more susceptible to tearing.

[0006] Therefore, an object of the present invention is to provide an insulated wire and cable in which the insulation properties of the coating layer are prevented from decreasing and the coating layer is less likely to tear. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides an insulated wire comprising a conductor and a coating layer formed on the outermost side so as to surround the conductor, the coating layer having a thickness of 0.08 mm or less, the coating layer being made of a resin composition containing PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) as a main component, and the coating layer not containing titanium oxide but containing zinc oxide as a colorant.

[0008] Furthermore, in order to solve the above-mentioned problems, the present invention provides a cable comprising an assembly made up of a plurality of insulated electric wires and a sheath that collectively covers the assembly, wherein at least one of the insulated electric wires that make up the assembly is the insulated electric wire described in any one of claims 1 to 4. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an insulated wire and a cable in which the insulation properties of the coating layer are prevented from decreasing and the coating layer is less likely to tear. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of an insulated wire according to an embodiment of the present invention. [Figure 2] (a) is an optical microscope image of the surface of the coating layer of sample A. (b) and (c) are mapping images of sample A formed on the optical microscope image of Figure 2(a). [Figure 3] (a) is an optical microscope image of the surface of the coating layer of sample B. (b) and (c) are mapping images of sample B formed on the optical microscope image of (a). [Figure 4] (a) and (b) show examples of Raman spectra measured in a mapping measurement that obtained a mapping image of sample A shown in FIG. 2(b). [Figure 5](a) and (b) show examples of Raman spectra measured in a mapping measurement to obtain a mapping image of sample A shown in FIG. 2(c). [Figure 6] (a) and (b) show examples of Raman spectra measured in a mapping measurement that obtained a mapping image of sample B shown in FIG. 3(b). [Figure 7] (a) and (b) show examples of Raman spectra measured in a mapping measurement that obtained the mapping image of sample B shown in FIG. 3(c). [Figure 8] (a) is a histogram created from the C-C stretching vibration intensity ratios contained in each pixel of the mapping image of sample A shown in Figure 2(b). (b) is a histogram created from the C-C stretching vibration intensity ratios contained in each pixel of the mapping image of sample A shown in Figure 2(c). [Figure 9] (a) is a histogram created from the C-C stretching vibration intensity ratios included in each pixel of the mapping image of sample B shown in Fig. 3(b). (b) is a histogram created from the C-C stretching vibration intensity ratios included in each pixel of the mapping image of sample B shown in Fig. 3(c). [Figure 10] 1(a) to 1(e) are diagrams illustrating a cracking test. [Figure 11] 1 is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of a cable according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment Mode] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0012] 1 is a cross-sectional view perpendicular to the longitudinal direction of an insulated wire 1 according to this embodiment. The insulated wire 1 includes a conductor 2 and a coating layer 5 formed on the outermost side so as to surround the conductor 2. In this embodiment, the insulated wire 1 is a coaxial wire 10 further including, between the conductor 2 and the coating layer 5, an insulator 3 that surrounds the conductor 2 and a shield layer 4 that surrounds the insulator 3.

[0013] The coaxial wire 10 is used as a medical insulated electric wire 1 that is inserted into the human body, for example, in an endoscope or catheter. The coaxial wire 10 is made extremely thin to reduce strain on the human body, with an outer diameter of 0.6 mm or less, more preferably 0.4 mm or less, and even more preferably 0.2 mm or less.

[0014] (Conductor 2) The conductor 2 is a stranded conductor formed by twisting together a plurality of metal wires 2a. The metal wires 2a may be made of copper or a copper alloy, and their surfaces may be plated. In this embodiment, the conductor 2 has an outer diameter of 0.039 mm and is formed by concentrically twisting seven metal wires 2a made of silver-plated copper alloy wires with an outer diameter of 0.013 mm. The twist pitch of the conductor 2 is 0.7 mm. The twist pitch of the conductor 2 is the distance along the longitudinal direction of the insulated wire 1 between points where the metal wires 2a are positioned at the same position in the circumferential direction of the insulated wire 1.

[0015] (Insulator 3) The insulator 3 is preferably made of fluororesin that can be molded into a thin wall. Here, the insulator 3 used was made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) with a thickness of 0.023 mm. The insulator 3 had an outer diameter of 0.085 mm.

[0016] (Shield layer 4) The shield layer 4 is a spirally wound shield in which multiple metal wires 4a are spirally wound around the insulator 3. The metal wires 4a may be made of copper or a copper alloy, and their surfaces may be plated. In this embodiment, the shield layer 4 is formed using 16 metal wires 4a made of silver-plated copper alloy wires with an outer diameter of 0.020 mm. The twisting direction of the shield layer 4 is preferably the same as the twisting direction of the conductor 2. This allows the twisting to loosen appropriately in response to bending or twisting when the coaxial cable 10 is bent or twisted, allowing stress to be released and improving resistance to bending or twisting. The twisting direction of the conductor 2 and the shield layer 4 refers to the direction in which the metal wires 2a and 4a rotate from one end to the other end of the coaxial cable 10, as viewed from one end of the coaxial cable 10.

[0017] (Coating layer 5) The coating layer 5 constitutes the outermost layer of the coaxial cable 10. Like the insulator 3, the coating layer 5 is preferably made of a fluororesin that can be molded into a thin wall. In this embodiment, a coating layer 5 made of a resin composition containing PFA as a main component is used. To reduce the diameter of the coaxial cable 10, the thickness of the coating layer 5 is preferably at least 0.08 mm or less, more preferably 0.04 mm or less, and even more preferably 0.02 mm or less. The outer diameter of the coating layer 5, i.e., the outer diameter of the coaxial cable 10, is set to a small diameter of at least 0.6 mm or less, more preferably 0.4 mm or less, and even more preferably 0.2 mm or less. In this embodiment, the thickness of the coating layer 5 is set to 0.02 mm, and the outer diameter of the entire coaxial cable 10 is set to 0.165 mm.

[0018] If the coating layer 5 is thin, such as 0.08 mm or less, the resin discharge rate during extrusion molding is reduced, causing the resin to stagnate in the extruder for a long time. Excessive heat in the extruder can cause the resin to decompose and foam, potentially resulting in pinholes in the molded coating layer 5 and reducing the insulating properties of the coating layer 5. The inventors' investigations revealed that, particularly when the coating layer 5 contains titanium oxide as a colorant, the titanium oxide acts as a catalyst and promotes resin decomposition. Titanium oxide is a white colorant commonly used to color the coating layer 5, for example, white or gray. Lowering the molding temperature to suppress foaming can cause strain during molding to align the molecular orientation of the resin constituting the coating layer 5, making the coating layer 5 more susceptible to longitudinal tearing. Therefore, the molding temperature must be maintained at a temperature that prevents tearing.

[0019] Therefore, in this embodiment, the coating layer 5 does not contain titanium oxide, and zinc oxide is used as a white colorant. The absence of titanium oxide in the coating layer 5 can suppress decomposition and foaming of the resin during extrusion molding, thereby preventing a decrease in insulating properties. Furthermore, since extrusion molding can be performed at relatively high temperatures while suppressing foaming, it is possible to prevent the coating layer 5 from becoming easily torn. Furthermore, it has been confirmed that the inclusion of zinc oxide as a colorant in the coating layer 5 can prevent a decrease in insulating properties and a decrease in the coating layer 5 from becoming easily torn, compared to a case where the coating layer 5 is uncolored and does not contain zinc oxide. It is acceptable for the coating layer 5 to contain a trace amount of titanium as an unavoidable impurity.

[0020] The amount of zinc oxide added to the coating layer 5 is preferably set so that the zinc element is contained in the coating layer 5 at 0.4 mass% or more and 5.0 mass% or less. If the zinc oxide element in the coating layer 5 is less than 0.4 mass%, sufficient coloring cannot be expected, and if it exceeds 5.0 mass%, the mechanical strength and insulating properties of the coating layer 5 may be reduced.

[0021] When the thickness of the coating layer 5 is set to 0.04 mm or less (particularly when it is set to 0.02 mm or less), the coating layer 5 is likely to tear during terminal processing or the like due to the influence of the orientation of the resin. Therefore, in this embodiment, the orientation degree D of the coating layer 5 is set to be less than 0.85, and more preferably, the orientation degree D is set to be 0.75 or less. The orientation degree will be described in detail below.

[0022] (Regarding the degree of orientation D) Generally, the coating layer 5 is formed by extrusion molding, and therefore the coating layer 5 is likely to be oriented along the longitudinal direction of the insulated wire 1. The present inventors have found that the higher the orientation degree D of the coating layer 5 in the longitudinal direction of the insulated wire 1, the more likely cracks are to occur in the coating layer 5 along the longitudinal direction of the insulated wire 1.

[0023] In this embodiment, the degree of orientation D of the coating layer 5 (the degree of orientation of the resin molecules that make up the coating layer 5) is evaluated using Raman scattering measurement. Raman scattering measurement allows the degree of orientation D of the resin material to be evaluated non-destructively, and therefore does not cause problems such as deterioration of the coating layer 5 due to electron beam irradiation, which occurs when SEM-EDS is used for evaluation. Furthermore, in Raman scattering measurement, the measurement area is the spot diameter of the laser irradiated on the surface of the coating layer 5, so evaluation can be performed within a microscopic area with a diameter of 1 μm or less. This makes it possible to measure the degree of orientation D with high spatial resolution, which is difficult to achieve with, for example, FT-IR.

[0024] In this embodiment, first, a polarized laser is irradiated onto the coating layer 5 to measure its Raman spectrum. Then, the degree of orientation D of the coating layer 5 is determined based on the relationship between the polarization direction and the intensity of the polarization-dependent peak in the measured Raman spectrum, whose intensity depends on the polarization direction of the laser. Here, the polarization direction refers to the polarization direction on the surface of the coating layer 5 irradiated with the laser. When the surface of the coating layer 5 is irradiated with a polarized laser, Raman scattering occurs due to scattering by chemical bond species bonded in a direction close to the polarization direction, while scattering by chemical bond species bonded in a direction not close to the polarization direction generates almost no Raman scattering. Using this phenomenon, the degree of orientation D of the coating layer 5 can be evaluated based on the relationship between the intensity of the polarization-dependent peak in the Raman spectrum, whose intensity depends on the polarization direction of the laser, and the polarization direction. The laser irradiated onto the coating layer 5 can be polarized using a polarized Raman optical system using a polarizing filter such as a half-wave plate or a polarizer.

[0025] More specifically, in this embodiment, the degree of orientation D of the coating layer 5 is evaluated using the intensity of the polarization-dependent peak measured when the polarization direction is parallel to the longitudinal direction of the insulated wire 1 and the intensity of the polarization-dependent peak measured when the polarization direction is perpendicular to the longitudinal direction of the insulated wire 1 (parallel to the radial direction of the insulated wire 1). This is because the coating layer 5 is generally most strongly oriented in a direction close to the longitudinal direction of the insulated wire 1. Therefore, the difference between the intensity of the polarization-dependent peak measured when the polarization direction is parallel to the longitudinal direction of the insulated wire 1 and the intensity of the polarization-dependent peak measured when the polarization direction is perpendicular to the longitudinal direction of the insulated wire 1 is large, making it easy to compare them. The intensity of a peak, such as a polarization-dependent peak, in a Raman spectrum can be measured using the integrated intensity or peak height of the peak. The integrated intensity of the peak can be calculated, for example, using the Covell method.

[0026] In this embodiment, the coating layer 5 is made of PFA. In this case, a polarization-dependent peak, the intensity of which depends on the polarization direction of the laser, is at 1340 cm in the Raman spectrum, which is attributed to the CC stretching vibration of the A1 mode. -1 Over, 1425cm-1 The peak with the maximum peak height (referred to as peak P1) within the following range can be used. The wavenumbers at which the heights of each peak in the Raman spectrum are maximized may shift depending on factors such as the ambient temperature during measurement. However, the relative magnitudes of the wavenumbers at which these peaks are maximized remain unchanged, preventing misidentification of the peaks. When the degree of orientation D of the coating layer 5 in the longitudinal direction of the insulated electric wire 1 is high, the difference in intensity of peak P1 increases when the polarization direction is close to (close to parallel with) the longitudinal direction of the insulated electric wire 1 and when it is not close to (close to perpendicular to) the longitudinal direction of the insulated electric wire 1. Conversely, when the degree of orientation D of the coating layer 5 in the longitudinal direction of the insulated electric wire 1 is low, the difference in intensity of peak P1 decreases when the polarization direction is close to (close to) the longitudinal direction of the insulated electric wire 1 and when it is not close to (close to perpendicular to) the longitudinal direction of the insulated electric wire 1. Therefore, the degree of orientation D of the coating layer 5 can be evaluated by comparing the intensities of peak P1 when the polarization direction is close to (close to) the longitudinal direction of the insulated electric wire 1 and when it is not close to (close to) the longitudinal direction of the insulated electric wire 1.

[0027] In this embodiment, in order to evaluate the degree of orientation D of the coating layer 5 made of PFA with higher accuracy, the peak at 1255 cm in the Raman spectrum, which is attributed to the CC stretching vibration of the E2 mode, is used. -1 Above, 1340cm -1 The intensity of the polarization-dependent peak was normalized by the intensity of the peak (called peak P2) with the largest peak height within the following range. The intensity of the peak attributed to the CC stretching vibration of the E2 mode is almost independent of the polarization direction of the laser. If the intensity of peak P1 is I1 and the intensity of peak P2 is I2, then the intensity ratio of peak P1 to peak P2, I1 / I2 (hereafter referred to as the CC stretching vibration intensity ratio), is the intensity of peak P1 normalized by the intensity of peak P2.

[0028] Hereinafter, Ip denotes the intensity of a polarization-dependent peak (CC stretching vibration intensity ratio) obtained by normalizing the intensity I1 of peak P1 attributed to CC stretching vibration in the A1 mode by the intensity I2 of peak P2 attributed to CC stretching vibration in the E2 mode in a Raman spectrum measured by irradiating the coating layer 5 with a laser beam polarized in a direction parallel to the longitudinal direction of the insulated wire 1. Also, Ic denotes the intensity of a polarization-dependent peak (CC stretching vibration intensity ratio) obtained by normalizing the intensity I1 of peak P1 attributed to CC stretching vibration in the A1 mode by the intensity I2 of peak P2 attributed to CC stretching vibration in the E2 mode in a Raman spectrum measured by irradiating the coating layer 5 with a laser beam polarized in a direction perpendicular to the longitudinal direction of the insulated wire 1. In this case, in this embodiment, Ic is calculated by the following formula (1): D = Ip / (Ip + Ic) (1) The degree of orientation D is defined as follows:

[0029] It is preferable to use the average values ​​of the intensities Ip and Ic of the polarization-dependent peaks obtained by performing measurements at multiple locations, taking into account variations at each measurement position. In this case, for example, a method of mapping measurement of the Raman spectrum can be used. Mapping measurement is a measurement method in which measurements are repeated while scanning a measurement point (a laser irradiation point) within a predetermined measurement area on the surface of the measurement object. For example, a Raman spectrum can be mapped, and a histogram of the intensities Ip and Ic of the polarization-dependent peaks contained in each pixel of the obtained mapping image can be created, and the average value can be calculated from the created histogram.

[0030] (Example of how to determine the degree of orientation D) Hereinafter, a method for determining the degree of orientation D will be described in more detail using the measurement results of sample A, which is prone to cracking along the longitudinal direction of the insulated wire 1, and sample B, which is less likely to crack along the longitudinal direction of the insulated wire 1.

[0031] Figure 2(a) is an optical microscope image of the surface of the coating layer 5 of sample A, which is prone to cracks along the longitudinal direction of the insulated wire 1. Figures 2(b) and 2(c) are Raman spectrum mapping images of sample A formed on top of the optical microscope image of Figure 2(a). The mapping image of Figure 2(b) was obtained by a mapping measurement performed with the laser polarization direction parallel to the longitudinal direction of the insulated wire 1, while the mapping image of Figure 2(c) was obtained by a mapping measurement performed with the laser polarization direction perpendicular to the longitudinal direction of the insulated wire 1 (parallel to the circumferential direction).

[0032] Figure 3(a) is an optical microscope image of the surface of the coating layer 5 of sample B, which is less likely to develop cracks along the longitudinal direction of the insulated wire 1. Figures 3(b) and 3(c) are Raman spectrum mapping images of sample B formed on top of the optical microscope image of Figure 3(a). The mapping image of Figure 3(b) was obtained by a mapping measurement performed with the laser polarization direction parallel to the longitudinal direction of the insulated wire 1, while the mapping image of Figure 3(c) was obtained by a mapping measurement performed with the laser polarization direction perpendicular to the longitudinal direction of the insulated wire 1.

[0033] Each pixel in the mapping images in Figures 2(b), 2(c), 3(b), and 3(c) contains the data of the C-C stretching vibration intensity ratio obtained from the Raman spectrum measured at that position, and each pixel has a color corresponding to the magnitude of the C-C stretching vibration intensity ratio (i.e., the intensities Ip and Ic of the polarization-dependent peaks). In calculating the C-C stretching vibration intensity ratio contained in each pixel of these mapping images, the peak areas of peaks P1 and P2 calculated using the Cobel method were used as the intensities of peaks P1 and P2. In calculating the peak areas using the Cobel method, the peak areas were calculated within ±21 cm from the wavenumber at which each peak had its maximum height. -1The range of wavenumbers used to measure the peak area was set to be 1. Comparing the mapping images in Figures 2(b), 2(c), 3(b), and 3(c), it can be seen that the difference in the C-C stretching vibration intensity ratio between the mapping images of sample A in Figures 2(b) and 2(c) is larger than the difference in the C-C stretching vibration intensity ratio between the mapping images of sample B in Figures 3(b) and 3(c). This result indicates that sample A, in which cracks are more likely to occur in the coating layer 5 along the longitudinal direction of the insulated wire 1, has a higher degree of orientation D of the coating layer 5 along the longitudinal direction of the insulated wire 1 than sample B, in which cracks are less likely to occur in the coating layer 5 along the longitudinal direction of the insulated wire 1.

[0034] Figures 4(a) and (b) show examples of Raman spectra measured in a mapping measurement that obtained a mapping image of sample A shown in Figure 2(b). The Raman spectrum shown in Figure 4(b) was measured at measurement positions A1 and A2, indicated by cross marks in Figure 4(a). Figures 5(a) and (b) show examples of Raman spectra measured in a mapping measurement that obtained a mapping image of sample A shown in Figure 2(c). The Raman spectrum shown in Figure 5(b) was measured at measurement positions A3 and A4, indicated by cross marks in Figure 5(a).

[0035] Figures 6(a) and 6(b) show examples of Raman spectra measured in a mapping measurement that acquired a mapping image of sample B shown in Figure 3(b). The Raman spectrum shown in Figure 6(b) was measured at measurement positions B1 and B2, indicated by cross marks in Figure 6(a). Figures 7(a) and 7(b) show examples of Raman spectra measured in a mapping measurement that acquired a mapping image of sample B shown in Figure 3(c). The Raman spectrum shown in Figure 7(b) was measured at measurement positions B3 and B4, indicated by cross marks in Figure 7(a). Note that in Figures 4(b), 5(b), 6(b), and 7(b), the position of peak P1, which is a polarization-dependent peak, and the position of peak P2, which is used to normalize the intensity I1 of peak P1, are indicated by dashed lines. Based on the intensity I1 of peak P1 and the intensity I2 of peak P2, the CC stretching vibration intensity ratio I1 / I2 (that is, the intensities Ip and Ic of the polarization-dependent peaks) can be determined.

[0036] Figure 8(a) is a histogram created from the C-C stretching vibration intensity ratio I1 / I2 (i.e., the intensity of the polarization-dependent peak Ip) included in each pixel of the mapping image of sample A shown in Figure 2(b) measured with the laser polarization direction parallel to the longitudinal direction of the insulated electric wire 1. Figure 8(b) is a histogram created from the C-C stretching vibration intensity ratio I1 / I2 (i.e., the intensity of the polarization-dependent peak Ic) included in each pixel of the mapping image of sample A shown in Figure 2(c) measured with the laser polarization direction perpendicular to the longitudinal direction of the insulated electric wire 1.

[0037] 9(a) is a histogram created from the C-C stretching vibration intensity ratio I1 / I2 (i.e., the intensity of the polarization-dependent peak Ip) included in each pixel of the mapping image of sample B shown in FIG. 3(b), which was measured with the laser polarization direction parallel to the longitudinal direction of the insulated electric wire 1. FIG. 9(b) is a histogram created from the C-C stretching vibration intensity ratio I1 / I2 (i.e., the intensity of the polarization-dependent peak Ic) included in each pixel of the mapping image of sample B shown in FIG. 3(c), which was measured with the laser polarization direction perpendicular to the longitudinal direction of the insulated electric wire 1. In the histograms shown in FIGS. 8(a) and 8(b) and 9(a) and 9(b), the horizontal axis represents the 256 classes obtained by dividing the range from the minimum to the maximum value of the C-C stretching vibration intensity ratio I1 / I2, and the vertical axis represents the frequency, which is the number of pixels in each class.

[0038] From the histograms in Figures 8(a), (b) and 9(a), (b), the following equation is obtained: {Total of (class value x frequency)} ÷ {Total of frequency} The average values ​​of the polarization dependent peak intensities Ip and Ic can be calculated by the above equation (1).

[0039] (Example) A 15 mm extruder with a full-flight screw of L / D ratio 20, a nozzle diameter of 4.0 mm, and a mandrel diameter of 2.5 mm was used to extrude PFA (335°C, melt viscosity of approximately 1.5 (1.0-2.0) × 10 at a shear rate of 121.6 (1 / s)). 3 A coating layer 5 was formed from a resin composition containing cellulose acetate (Pa / s) as a main component and zinc oxide as a colorant. In Example 1, the molding temperature (crosshead and die temperature) / screw rotation speed was 360°C / 0.9 rpm, in Example 2 it was 340°C / 0.8 rpm, and in Example 3 it was 345°C / 0.9 rpm. Regarding temperatures other than the die and crosshead, the cylinder temperature C1 (upstream section) / C2 (center section) / C3 (downstream section) was 265°C / 325°C / 330°C, and the nozzle temperature was 330°C. The time until foaming began in the molding machine was measured, and the resulting coating layer 5 was subjected to a spark test (to check for pinholes) using an in-line spark tester. Furthermore, the degree of orientation D of the coating layer 5 was measured. A component analysis of the resulting coating layer 5 confirmed that it contained no Ti and 1.9 mass% Zn.

[0040] A cracking test was also conducted on the resulting coating layer 5. In the cracking test, as shown in FIG. 10(a), a 20-30 mm slit 101 was made in the coating layer 5 along the longitudinal direction at the tip end of the coaxial cable 10 using a razor 100, and then the coating layer 5 was pulled toward the base end so as to peel off, as shown in FIG. 10(b). As a result, if the slit 101 easily propagated in the longitudinal direction of the coaxial cable 10 as shown in FIG. 10(c), the coating layer 5 was deemed to be prone to tearing and was therefore deemed to have failed. If the slit 101 did not propagate and the coating layer 5 broke as shown in FIG. 10(d), or if a crack propagated from the slit 101 but the crack propagated while the coating layer 5 underwent plastic deformation (necking) under load as the cracking progressed, the coating layer 5 was deemed to be resistant to tearing and was therefore deemed to have passed.

[0041] Similarly, similar tests were conducted on Comparative Examples 1 and 2, which used titanium oxide as a colorant, and Comparative Examples 3 and 4, which were uncolored. In Comparative Example 1, the molding temperature (crosshead and die temperature) / screw rotation speed was 335°C / 0.6 rpm, and in Comparative Example 2, it was 340°C / 0.8 rpm. In Comparative Example 3, the molding temperature (crosshead and die temperature) / screw rotation speed was 360°C / 0.9 rpm, the same as in Example 1, and in Comparative Example 4, it was 360°C / 1.2 rpm. Regarding temperatures other than the die and crosshead, the cylinder temperature C1 (upstream section) / C2 (center section) / C3 (downstream section) was 265°C / 325°C / 330°C, and the nozzle temperature was 330°C. The test results for Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1.

[0042] [Table 1]

[0043] As shown in Table 1, in Examples 1 to 3, in which the coating layer 5 contained zinc oxide but not titanium oxide, the foaming initiation time was sufficiently long, at 480 minutes or more, under all molding conditions, and it was confirmed that decomposition and foaming of the resin were less likely to occur during extrusion molding, even in Example 1, in which the molding temperature was as high as 360°C. All of Examples 1 to 3 passed the spark test, confirming that the insulating properties of the coating layer 5 were sufficient. Furthermore, all of Examples 1 to 3 had a degree of orientation D of less than 0.85 (more specifically, 0.75 or less), and passed the crack test.

[0044] In contrast, in Comparative Examples 1 and 2, in which titanium oxide was contained in the coating layer 5, the foaming start time was short, at 90 minutes or less, and pinholes were likely to occur in the coating layer 5, confirming the possibility that sufficient insulation properties could not be obtained. Furthermore, in Comparative Example 1, when the molding temperature was lowered to 335°C to suppress foaming, the degree of orientation D became 0.85 or more, and the cracking test was failed.

[0045] Furthermore, in the uncolored Comparative Examples 3 and 4, the foaming start time was 240 minutes in Comparative Example 3 under the same molding conditions as Example 1. This confirms that the inclusion of zinc oxide in the coating layer 5 can further suppress resin decomposition and foaming, and can also suppress a decrease in the insulating properties of the coating layer 5. These results confirm that when white or gray coloring is desired, it is preferable to use zinc oxide as a colorant rather than titanium oxide.

[0046] (cable) Next, a cable 110 using the insulated wire 1 according to this embodiment will be described. The cable 110 includes an assembly 111 made up of a plurality of insulated wires 1, and a sheath 113 that collectively covers the assembly 111. In this embodiment, a bind tape 112 is wound around the assembly 111, and a sheath 113 is provided around the bind tape 112.

[0047] In the cable 110, it is sufficient that at least one of the insulated wires 1 constituting the assembly 111 is the insulated wire 1 according to the present embodiment, and the assembly 110 may also include insulated wires of other configurations. In the illustrated example, the assembly 111 is constituted by twisting together four insulated wires 1 according to the present embodiment.

[0048] The bind tape 112 can be made of nonwoven fabric tape, paper tape, resin tape, or the like. In this embodiment, polyester tape with copper vapor-deposited on one side is used as the bind tape 112. The copper layer formed by vapor deposition serves as a shielding layer. This allows the outer diameter of the cable 110 to be smaller than when a shielding layer is provided separately from the bind tape 112. The thickness of the bind tape 112 is 0.01 mm, and the width is 2.0 mm. The bind tape 112 is wound spirally so that portions of the tape overlap in the width direction.

[0049] The twisting direction of the assembly 111 and the winding direction of the bind tape 112 are opposite to each other. This prevents the twisted wire cores from coming apart, improving durability against repeated bending and the like. The twisting direction of the assembly 111 is the direction in which the insulated wires 1 rotate from one end to the other when viewed from one end of the cable 110. The winding direction of the bind tape 112 is the direction in which the bind tape 112 rotates from one end to the other when viewed from the one end of the cable 110.

[0050] The sheath 113 is preferably made of a fluororesin that can be molded into a thin wall. Here, a sheath 113 made of PFA and having a thickness of 0.025 mm is used. The outer diameter of the entire cable 110 is approximately 0.47 mm.

[0051] (Actions and Effects of the Embodiments) As described above, in the insulated wire 1 according to this embodiment, the thickness of the coating layer 5 is 0.08 mm or less, the coating layer 5 is made of a resin composition containing PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) as a main component, and the coating layer 5 does not contain titanium oxide but contains zinc oxide as a colorant.

[0052] This suppresses decomposition and foaming of the resin during extrusion molding, making it possible to perform extrusion molding with suppressed foaming even at relatively high temperatures, thereby suppressing deterioration in the insulating properties of the coating layer 5 and realizing an insulated wire 1 in which the coating layer 5 is less likely to tear.

[0053] (Summary of the embodiment) Next, the technical ideas grasped from the above-described embodiments will be described by using the reference numerals and the like in the embodiments. However, the reference numerals and the like in the following description do not limit the components in the claims to the members and the like specifically shown in the embodiments.

[0054] [1] An insulated wire (1) comprising a conductor (2) and a coating layer (5) formed on the outermost surface of the conductor (2) so as to surround the conductor (2), the coating layer (5) having a thickness of 0.08 mm or less, the coating layer (5) being made of a resin composition containing PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) as a main component, and the coating layer (5) not containing titanium oxide but containing zinc oxide as a colorant.

[0055] [2] The insulated wire (1) according to [1], wherein the coating layer (5) contains 0.4 mass% or more and 5.0 mass% or less of zinc element.

[0056] [3] In a Raman spectrum measured by irradiating the coating layer (5) with a laser beam polarized in a direction parallel to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak attributed to the CC stretching vibration of the A1 mode with the intensity of a peak attributed to the CC stretching vibration of the E2 mode is defined as Ip, and in a Raman spectrum measured by irradiating the coating layer with a laser beam polarized in a direction perpendicular to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak attributed to the CC stretching vibration of the A1 mode with the intensity of a peak attributed to the CC stretching vibration of the E2 mode is defined as Ic, and the following formula (1) is obtained: D = Ip / (Ip + Ic) (1) The insulated wire (1) according to [1], wherein the degree of orientation D, expressed as:

[0057] [4] The insulated wire (1) according to [1], further comprising an insulator (3) that covers the conductor (2) and a shielding layer (4) that covers the insulator (3) between the conductor (2) and the coating layer (5), and the outer diameter of the coating layer (5) is 0.6 mm or less.

[0058] [5] A cable (110) comprising an assembly (111) consisting of a plurality of insulated electric wires and a sheath (113) that collectively covers the assembly (111), wherein at least one of the insulated electric wires that make up the assembly (111) is the insulated electric wire (1) described in any one of [1] to [4].

[0059] (Addendum) Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the above-described embodiments. It should be noted that not all of the combinations of features described in the embodiments are necessarily essential to the means for solving the problems of the invention. Furthermore, the present invention can be appropriately modified and implemented within the scope of its spirit. [Explanation of symbols]

[0060] 1...Insulated wire 10…Coaxial line 2...conductor 3...Insulator 4...Shield layer 5…Covering layer 110...Cable 111…Aggregation 112...Binding tape 113...Sheath

Claims

1. A conductor; a coating layer formed on the outermost surface of the conductor so as to cover the conductor, The thickness of the coating layer is 0.08 mm or less, the coating layer is made of a resin composition containing PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) as a main component, The coating layer does not contain titanium oxide but contains zinc oxide as a colorant. Insulated wire.

2. The coating layer contains zinc element in an amount of 0.4 mass% or more and 5.0 mass% or less. The insulated wire according to claim 1 .

3. In the Raman spectrum measured by irradiating the coating layer with a laser beam polarized in a direction parallel to the longitudinal direction, １ The intensity of the peak attributed to the C-C stretching vibration of the mode is defined as E ２ The intensity of the polarization-dependent peak normalized by the intensity of the peak assigned to the C-C stretching vibration of the mode is defined as Ip, In the Raman spectrum measured by irradiating the coating layer with a laser beam polarized in a direction perpendicular to the longitudinal direction, １ The intensity of the peak attributed to the C-C stretching vibration of the mode is defined as E ２ When the intensity of the polarization-dependent peak normalized by the intensity of the peak attributed to the C-C stretching vibration of the mode is Ic, Below formula (1) D=Ip / (Ip+Ic)...(1) The degree of orientation D represented by is less than 0.85; The insulated wire according to claim 1 .

4. The device further includes an insulator covering the conductor between the conductor and the covering layer, and a shield layer covering the insulator, The outer diameter of the coating layer is 0.6 mm or less. The insulated wire according to claim 1 .

5. an assembly consisting of a plurality of insulated wires; a sheath that covers the assembly as a whole; At least one of the insulated wires constituting the assembly is the insulated wire according to any one of claims 1 to 4. cable.

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