Insulated wire

Abstract

Provided is an insulated wire in which a coating layer does not easily crack. An insulated wire (1) is provided with a conductor (2), and a coating layer (5) that covers the periphery of the conductor (2) and is formed on the outermost side, the coating layer (5) having a thickness of 0.04 mm or less and made of PFA, and in a Raman spectrum measured by irradiating the coating layer (5) with a laser beam in a polarization direction parallel to the longitudinal direction, a Raman spectrum measured by irradiating the coating layer (5) with laser light in a polarization direction perpendicular to the longitudinal direction, where Ip is the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributed to the A1 mode with the intensity of a peak of C-C stretching vibration attributed to the E2 mode. The degree of orientation (D) represented by Ip / (Ip + Ic) is less than 0.85, where Ic is the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributed to the A1 mode with the intensity of a peak of C-C stretching vibration attributed to the E2 mode.

Description

Technical Field

[0001] The present invention relates to insulated wires. Background Art

[0002] In recent years, the trend toward higher functionality in electronic devices like VR and wearables, as well as miniaturization and minimally invasive medical equipment, has led to a trend toward thinner insulated wires. For example, ultra-fine coaxial cables with outer diameters of 0.4 mm or less are used for signal transmission. To achieve these ultra-fine coaxial cables, efforts are underway to reduce the coating thickness to, for example, 40 μm or less.

[0003] It should be noted that Patent Document 1 is prior art document information related to the invention of the present application.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-192567 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] However, the coating is formed by extrusion molding. Raising the temperature during extrusion molding causes the resin to foam, making the coating susceptible to cracking. Furthermore, lowering the extrusion molding temperature to suppress resin foaming causes the molecular orientation of the resin constituting the coating to become uniform, making the coating more susceptible to cracking. Consequently, the coating is susceptible to unexpected cracking during terminal processing or use, and countermeasures are desired.

[0009] Therefore, an object of the present invention is to provide an insulated wire in which a coating layer is less likely to crack.

[0010] Means for solving problems

[0011] The present invention aims to solve the above-mentioned problems and provides an insulated wire comprising a conductor and a coating layer formed on the outermost side so as to cover the periphery of the conductor, wherein the coating layer has a thickness of 0.04 mm or less and is composed of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), wherein in a Raman spectrum measured by irradiating the coating layer with laser light having a polarization direction parallel to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributable to an A1 mode by the intensity of a peak of C-C stretching vibration attributable to an E2 mode is defined as Ip, and in a Raman spectrum measured by irradiating the coating layer with laser light having a polarization direction perpendicular to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributable to an A1 mode by the intensity of a peak of C-C stretching vibration attributable to an E2 mode is defined as Ic, and wherein the degree of orientation D represented by the following formula (1) is less than 0.85.

[0012] D=Ip / (Ip+Ic)···(1)

[0013] Effects of the Invention

[0014] According to the present invention, it is possible to provide an insulated electric wire in which the coating layer is less likely to crack.

[0015] Description of Reference Numerals

[0016] 1…insulated wire, 2…conductor, 3…insulator, 4…shield, 5…coating, 10…coaxial cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a cross-sectional view showing a cross section perpendicular to the longitudinal direction of an insulated wire 1 according to one embodiment of the present invention.

[0018] Figure 2 In the figure, (a) is an optical microscope image of the surface of the coating layer of sample A, (b) and (c) are Figure 2 (a) Mapping image of specimen A formed on an optical microscope image.

[0019] Figure 3 In the figure, (a) is an optical microscope image of the surface of the coating layer of sample B, and (b) and (c) are mapping images of sample B formed on the optical microscope image of (a).

[0020] Figure 4 In (a) and (b), the Figure 2 (b) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample A.

[0021] Figure 5 In (a) and (b), the Figure 2(c) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample A.

[0022] Figure 6 In (a) and (b), the Figure 3 (b) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample B.

[0023] Figure 7 In (a) and (b), the Figure 3 (c) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample B.

[0024] Figure 8 In (a), it is based on Figure 2 A histogram of the CC stretching vibration intensity ratios included in each pixel of the mapping image of sample A shown in (b) is created based on Figure 2 A histogram is created of the CC stretching vibration intensity ratio included in each pixel of the mapping image of sample A shown in (c).

[0025] Figure 9 In (a), it is based on Figure 3 The histogram of the CC stretching vibration intensity ratio included in each pixel of the mapping image of sample B shown in (b) is created based on Figure 3 A histogram is created of the CC stretching vibration intensity ratio included in each pixel of the mapping image of sample B shown in (c).

[0026] Figure 10 In the figure, (a) to (e) are figures illustrating the crack test. DETAILED DESCRIPTION

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0028] Figure 1 This is a cross-sectional view showing a section 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 5 formed on the outermost side to cover the conductor 2. In this embodiment, the insulated wire 1 comprises a coaxial wire 10, which further includes an insulator 3 covering the conductor 2 and a shield 4 covering the insulator 3 between the conductor 2 and the coating 5. The coaxial wire 10 is used in medical equipment such as endoscopes and ultrasonic diagnostic equipment, or in small electronic devices. Its outer diameter is very small, 0.4 mm or less, and more preferably 0.2 mm or less.

[0029] (Conductor 2)

[0030] The conductor 2 is composed of a stranded conductor formed by twisting together multiple metal wires 2a. The metal wires 2a can be made of copper or a copper alloy, and their surfaces may also be plated. In this embodiment, seven silver-plated copper alloy wires 2a with an outer diameter of 0.013 mm are concentrically twisted together to form a conductor 2 with an outer diameter of 0.039 mm. The twist pitch of the conductor 2 is 0.7 mm. The twist pitch of the conductor 2 refers to the spacing along the length of the insulated wire 1 between points where the metal wires 2a are positioned uniformly along the circumference of the insulated wire 1.

[0031] (Insulator 3)

[0032] The insulator 3 can be made of a thin-walled fluororesin. Here, an insulator 3 made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer) with a thickness of 0.023 mm was used. The outer diameter of the insulator 3 was 0.085 mm.

[0033] (Shield 4)

[0034] The shielding layer 4 is composed of a transversely wound shielding member in which a plurality of metal wires 4a are wound into a spiral shape around the insulator 3. As the metal wire 4a, a wire made of copper or a copper alloy can be used, and a plating can also be applied to its surface. In this embodiment, the shielding layer 4 is composed of 16 metal wires 4a made of silver-plated copper alloy wires with an outer diameter of 0.020 mm. The twisting direction of the shielding layer 4 can be set to the same direction as the twisting direction of the conductor 2. Therefore, when bending or twisting is applied to the coaxial cable 10, the twisting will appropriately relax and release stress according to the bending or twisting, and the resistance to bending and twisting will be improved. It should be noted that when viewed from one end of the coaxial cable 10, the twisting direction of the conductor 2 and the shielding layer 4 is the direction in which the metal wires 2a and 4a rotate from one end to the other end.

[0035] (Coating layer 5)

[0036] The coating layer 5 constitutes the outermost layer of the coaxial cable 10. As the coating layer 5, similarly to the insulator 3, it can be made of a fluororesin that can be formed into a thin wall. In this embodiment, a coating layer 5 made of PFA is used. In order to reduce the diameter of the coaxial cable 10, the thickness of the coating layer 5 is preferably at least 0.04 mm or less, and more preferably 0.02 mm or less. The outer diameter of the coating layer 5, that is, the outer diameter of the coaxial cable 10, is a thin diameter of at least 0.4 mm or less, and 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 coaxial cable 10 as a whole is set to 0.165 mm.

[0037] In this embodiment, since the coating layer 5 is thinly formed to a thickness of 0.04 mm or less (preferably 0.02 mm or less), the coating layer 5 is susceptible to cracking during terminal processing. It should be noted that if the coating layer 5 is thicker than 0.04 mm, the issue of the coating layer 5 being susceptible to cracking does not arise. In other words, the issue of the coating layer 5 being susceptible to cracking is a problem unique to reducing the thickness of the coating layer 5 to 0.04 mm or less (preferably 0.02 mm or less).

[0038] In contrast, in this embodiment, the coating layer 5 is prevented from cracking easily by adjusting the orientation degree D of the coating layer 5. More specifically, in this embodiment, the orientation degree D is set to less than 0.85, and more preferably, to 0.75 or less. The orientation degree is described in detail below.

[0039] (About orientation degree D)

[0040] Typically, the coating layer 5 is formed by extrusion molding, and therefore the coating layer 5 is easily oriented along the longitudinal direction of the insulated wire 1. The present inventors have discovered that the higher the degree of orientation D of the coating layer 5 in the longitudinal direction of the insulated wire 1, the more likely cracks are to form in the coating layer 5 along the longitudinal direction of the insulated wire 1.

[0041] In this embodiment, Raman scattering measurement is used to evaluate the orientation degree D of the coating layer 5 (the degree of molecular orientation of the resin constituting the coating layer 5). Raman scattering measurement allows for non-destructive evaluation of the orientation degree D of the resin material, thus eliminating the problem of degradation of the coating layer 5 caused by electron beam irradiation, as occurs with SEM-EDS. Furthermore, in Raman scattering measurement, the spot diameter of the laser beam irradiating the surface of the coating layer 5 serves as the measurement area, enabling evaluation within a microscopic area with a diameter of 1 μm or less. This enables measurement of the orientation degree D with high spatial resolution, which is difficult to achieve with FT-IR or other methods.

[0042] In this embodiment, the coating layer 5 is first irradiated with polarized laser light to measure a Raman spectrum. The degree of orientation D of the coating layer 5 is then determined based on the relationship between the intensity of the polarization-dependent peak in the measured Raman spectrum, whose intensity depends on the polarization direction of the laser light, and the polarization direction. Here, the polarization direction refers to the polarization direction of the surface of the coating layer 5 irradiated with the laser light. When the surface of the coating layer 5 is irradiated with polarized laser light, Raman scattered light is generated due to scattering by chemically bonded species that are bonded in a direction close to the polarization direction. On the other hand, scattering by chemically bonded species that are bonded in a direction not close to the polarization direction generates almost no Raman scattered light. This phenomenon is exploited to evaluate the degree of orientation D of the coating layer 5 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 light, and the polarization direction. Polarization of the laser light irradiated on the coating layer 5 can be performed using a polarization Raman optical system that utilizes polarization filters such as a half-wave plate or a polarimeter.

[0043] 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 comparison easier. The intensity of a peak such as the polarization-dependent peak in a Raman spectrum can be measured using the integrated intensity or peak height. The integrated peak intensity can be calculated using, for example, the Covell method.

[0044] In this embodiment, the coating layer 5 is made of PFA. In this case, as the polarization-dependent peak whose intensity depends on the polarization direction of the laser light, the peak at 1340 cm-1 in the Raman spectrum belonging to the CC stretching vibration of the A1 mode can be used. -1 Above 1425cm -1The peak with the highest peak height within the following range (referred to as Peak P1) is the peak with the highest peak height. It should be noted that the wavenumbers at the peaks' maximum heights in the Raman spectrum may shift due to factors such as the ambient temperature during measurement. However, since the magnitude relationship between the wavenumbers at the peaks' maximum heights remains constant, peak misidentification is avoided. When the degree of orientation D of the coating 5 in the longitudinal direction of the insulated wire 1 is high, the difference in peak P1 intensity between when the polarization direction is close to (nearly parallel to) the longitudinal direction of the insulated wire 1 and when it is not (nearly perpendicular to) the longitudinal direction becomes larger. Conversely, when the degree of orientation D of the coating 5 in the longitudinal direction of the insulated wire 1 is low, the difference in peak P1 intensity between when the polarization direction is close to and when it is not close to the longitudinal direction of the insulated wire 1 becomes smaller. Therefore, by comparing the intensities of Peak P1 when the polarization direction is close to and when it is not close to the longitudinal direction of the insulated wire 1, the degree of orientation D of the coating 5 can be evaluated.

[0045] In this embodiment, in order to more accurately evaluate the orientation degree D of the coating layer 5 composed of PFA, the CC stretching vibration at 1255 cm in the Raman spectrum belonging to the E2 mode is used. -1 Over 1340cm -1 The intensity of the peak with the highest peak height within the following range (referred to as Peak P2) is normalized by the intensity of the polarization-dependent peak. The intensity of the CC stretching vibration peak attributed to the E2 mode is almost independent of the laser polarization direction. If the intensity of Peak P1 is I1 and the intensity of Peak P2 is I2, the intensity ratio of Peak P1 to Peak P2, I1 / I2 (hereinafter referred to as the CC stretching vibration intensity ratio), is the intensity of Peak P1 normalized by the intensity of Peak P2.

[0046] Hereinafter, in a Raman spectrum measured by irradiating the coating 5 with laser light having a polarization direction parallel to the longitudinal direction of the insulated wire 1, the intensity of the polarization-dependent peak (CC stretching vibration intensity ratio) obtained by normalizing the intensity I1 of the peak P1 of the C-C stretching vibration attributable to the A1 mode by the intensity I2 of the peak P2 of the C-C stretching vibration attributable to the E2 mode is referred to as Ip. Furthermore, in a Raman spectrum measured by irradiating the coating 5 with laser light having a polarization direction perpendicular to the longitudinal direction of the insulated wire 1, the intensity of the polarization-dependent peak (CC stretching vibration intensity ratio) obtained by normalizing the intensity I1 of the peak P1 of the C-C stretching vibration attributable to the A1 mode by the intensity I2 of the peak P2 of the C-C stretching vibration attributable to the E2 mode is referred to as Ic. In this case, in the present embodiment, the degree of orientation D is defined by the following formula (1).

[0047] D=Ip / (Ip+Ic)···(1)

[0048] It should be noted that regarding the polarization-dependent peak intensities Ip and Ic, it is preferable to use the average value of the intensities Ip and Ic of the polarization-dependent peaks obtained by measuring at multiple locations, taking into account the variations in each measurement position. In this case, for example, a method of mapping measurement of the Raman spectrum can be used. Mapping measurement refers to a measurement method in which measurement is repeatedly performed while scanning a measurement point (laser irradiation point) within a predetermined measurement area on the surface of the object being measured. For example, mapping measurement can be performed on the Raman spectrum, and a histogram of the intensities Ip and Ic of the polarization-dependent peaks contained in each pixel of the resulting mapping image can be created. The average value can then be calculated based on the created histogram.

[0049] (Specific Example of How to Determine the Orientation Degree D)

[0050] Hereinafter, a method for determining the orientation degree D will be described more specifically using 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 prone to cracking along the longitudinal direction of the insulated wire 1 .

[0051] Figure 2 (a) is an optical microscope image of the surface of the coating layer 5 in Sample A in which cracks are likely to occur along the longitudinal direction of the insulated wire 1 . Figure 2 (b) and (c) are in Figure 2 (a) Raman spectrum mapping image of sample A formed on an optical microscope image. Figure 2 The mapping image (b) is obtained by mapping measurement performed by making the polarization direction of the laser light parallel to the longitudinal direction of the insulated wire 1. Figure 2 The mapping image (c) is obtained by mapping measurement performed with the polarization direction of the laser light being perpendicular to the longitudinal direction of the insulated wire 1 (parallel to the circumferential direction).

[0052] Figure 3 (a) is an optical microscope image of the surface of the coating layer 5 of sample B in which cracks along the longitudinal direction of the insulated wire 1 are less likely to occur. Figure 3 (b) and (c) are in Figure 3 (a) Raman spectrum mapping image of sample B formed on the optical microscope image. Figure 3 The mapping image (b) is obtained by mapping measurement performed by making the polarization direction of the laser light parallel to the longitudinal direction of the insulated wire 1. Figure 3 The mapping image (c) is obtained by mapping measurement performed with the polarization direction of the laser light perpendicular to the longitudinal direction of the insulated wire 1 .

[0053] exist Figure 2 (b) Figure 2 (c) Figure 3 (b) and Figure 3Each pixel of the mapping image (c) contains data on the CC stretching vibration intensity ratio obtained based on the Raman spectrum measured at that position, and each pixel has a color corresponding to the size of the CC stretching vibration intensity ratio (i.e., the intensity Ip, Ic of the polarization-dependent peak). It should be noted that in the calculation of the CC stretching vibration intensity ratio contained in each pixel of these mapping images, the peak areas of peaks P1 and P2 calculated using the Kolver method are used as the intensities of peaks P1 and P2. In the calculation of the peak area based on the Kolver method, the ±21 cm centering on the wave number when the height of each peak is the maximum is used. -1 The range of wave numbers for peak area measurement is as follows. Figure 2 (b) Figure 2 (c) Figure 3 (b) and Figure 3 Comparing the mapping image of (c), we can see that Figure 2 (b) and Figure 2 (c) The difference in the CC stretching vibration intensity ratio of the mapping image of sample A is greater than Figure 3 (b) and Figure 3 The difference in CC stretching vibration intensity ratio of the mapping image of sample B in (c) is shown. This result indicates that the orientation degree D of the coating layer 5 in the longitudinal direction of the insulated wire 1 is higher in sample A, where cracks are more likely to form in the coating layer 5 along the longitudinal direction of the insulated wire 1, than in sample B, where cracks are less likely to form in the coating layer 5 along the longitudinal direction of the insulated wire 1.

[0054] Figure 4 (a) and (b) indicate that Figure 2 (b) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample A. Figure 4 The Raman spectrum shown in (b) is Figure 4 The measurement positions A1 and A2 indicated by the cross marks in (a) are measured. Figure 5 (a) and (b) indicate that Figure 2 (c) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample A. Figure 5 The Raman spectrum shown in (b) is Figure 5 The measurement positions A3 and A4 indicated by cross marks in (a) were measured.

[0055] Figure 6 (a) and (b) indicate that Figure 3 (b) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample B. Figure 6 The Raman spectrum shown in (b) is Figure 6The measurement positions B1 and B2 indicated by the cross marks in (a) are measured. Figure 7 (a) and (b) indicate that Figure 3 (c) shows an example of a Raman spectrum measured in the mapping measurement of the mapping image of sample B. Figure 7 The Raman spectrum shown in (b) is Figure 7 The measurement positions B3 and B4 indicated by the cross marks in (a) are measured. Figure 4 (b) Figure 5 (b) Figure 6 (b) and Figure 7 In (b), the dotted lines indicate the position of peak P1, a polarization-dependent peak, and the position of peak P2, which is used to normalize the intensity I1 of peak P1. The CC stretching vibration intensity ratio I1 / I2 (i.e., the polarization-dependent peak intensities Ip and Ic) can be calculated based on the intensity I1 of peak P1 and the intensity I2 of peak P2.

[0056] Figure 8 (a) is measured by making the polarization direction of the laser parallel to the longitudinal direction of the insulated wire 1. Figure 2 A histogram is created of the CC stretching vibration intensity ratio I1 / I2 (ie, the intensity Ip of the polarization-dependent peak) contained in each pixel of the mapping image of sample A shown in (b). Figure 8 (b) is measured by making the polarization direction of the laser perpendicular to the longitudinal direction of the insulated wire 1. Figure 2 A histogram is created of the CC stretching vibration intensity ratio I1 / I2 (ie, the intensity Ic of the polarization-dependent peak) contained in each pixel of the mapping image of sample A shown in (c).

[0057] Figure 9 (a) is measured by making the polarization direction of the laser parallel to the longitudinal direction of the insulated wire 1. Figure 3 A histogram is created of the CC stretching vibration intensity ratio I1 / I2 (ie, the intensity Ip of the polarization-dependent peak) contained in each pixel of the mapping image of sample B shown in (b). Figure 9 (b) is measured by making the polarization direction of the laser perpendicular to the longitudinal direction of the insulated wire 1. Figure 3 A histogram is created of the CC stretching vibration intensity ratio I1 / I2 (i.e., the intensity Ic of the polarization-dependent peak) contained in each pixel of the mapping image of sample B shown in (c). Figure 8 (a), (b) and Figure 9 In the histograms shown in (a) and (b), the range of the CC stretching vibration intensity ratio I1 / I2 from the minimum value to the maximum value is divided into 256 levels as the horizontal axis, and the number of pixels in each level, that is, the frequency, is the vertical axis.

[0058] according to Figure 8 (a), (b) and Figure 9 The histograms of (a) and (b) are given by the following formula:

[0059] {(level value × frequency) total} ÷ {total frequency}

[0060] The average value of the polarization-dependent peak intensities Ip and Ic can be calculated, and the obtained average value can be used to calculate the orientation degree D according to the above formula (1).

[0061] (Regarding the Relationship between the Orientation Degree D of the Coating Layer 5 and the Resistance to Crack)

[0062] [Example 1]

[0063] In Example 1, a 15 mm extruder using a full-flight screw with an L / D ratio of 20 was used. Under the conditions of barrel temperatures C1 (upstream portion) / C2 (center portion) / C3 (downstream portion) = 265°C / 325°C / 330°C, nozzle temperature 330°C, crosshead temperature 335°C, die temperature 335°C, die diameter 4.0 mm, mandrel diameter 2.5 mm, extrusion temperature 335°C, and screw speed 0.6 rpm, a PFA film with a melt viscosity of 1.5×10- 3 Pa / s) of the coating layer 5 is extruded and formed to produce multiple Figure 1 The coaxial line 10 was obtained. The orientation degree D of the coating layer 5 of the coaxial line 10 was measured and found to be 0.75.

[0064] In addition, a crack test was performed on the obtained coating layer 5. In the crack test, Figure 10 As shown in (a), a slit 101 of 20 mm to 30 mm in the longitudinal direction is formed on the coating layer 5 at the front end of the coaxial line 10 using a razor 100. Figure 10 As shown in (b), the coating layer 5 is pulled toward the base end side in a manner of peeling off. As a result, Figure 10 As shown in (c), if the cut 101 easily progresses in the longitudinal direction of the coaxial line 10, it is considered that the coating layer 5 is likely to be cracked and unqualified. Figure 10 As shown in (d), when the cut 101 does not progress and the coating 5 is broken, or as shown in Figure 10 As shown in (e), although cracking progresses from the slit 101, the coating 5 undergoes plastic deformation (necking) while cracking under load. Therefore, the coating 5 is considered to be less likely to crack and is considered acceptable. Crack testing of multiple coaxial cables 10 of Example 1 revealed no failures, resulting in a 100% pass rate.

[0065] [Example 2]

[0066] In Example 2, the same 15 mm extruder as in Example 1 was used, with the crosshead and die temperatures set to 340°C and the screw speed set to 0.8 rpm. Extrusion molding of the coating layer 5 was performed under the same conditions to produce a plurality of coaxial wires 10. The orientation degree D of the coating layer 5 of the coaxial wires 10 obtained in Example 2 was measured and found to be 0.62. Furthermore, a crack test was conducted on the coaxial wires 10 in Example 2, and the pass rate was 100%.

[0067] [Example 3]

[0068] In Example 3, a plurality of coaxial wires 10 were produced by extrusion molding the coating layer 5 using the same 15 mm extruder as in Examples 1 and 2, except that the crosshead and die temperatures were set to 345°C and the screw speed was set to 1.1 rpm. The coating layer 5 of the coaxial wires 10 obtained in Example 3 was measured for its orientation degree D, which was 0.68. Furthermore, a crack test was conducted on the coaxial wires 10 in Example 3, and the pass rate was 100%.

[0069] In contrast, a plurality of coaxial wires of the comparative example were produced using the same 15 mm extruder as in Examples 1 to 3, with the crosshead and die temperatures set to 335°C and the screw speed set to 0.8 rpm, except that the coating layer 5 was extruded under the same conditions. Aside from the changes in the extrusion conditions for the coating layer 5, the coaxial wires of the comparative example were identical to the coaxial wire 10 of the example. The orientation degree D of the coating layer 5 of the obtained coaxial wires of the comparative example was measured, and the result was 0.85. The plurality of coaxial wires 10 of the comparative example were subjected to a crack test in the same manner as in the example, and all failed, resulting in a pass rate of 0%.

[0070] The above results indicate that when forming the covering layer 5 by thin-wall molding of PFA, the orientation degree D must be at least less than 0.85 to prevent the covering layer 5 from cracking. By setting the orientation degree D to 0.75 or less, a covering layer 5 that is less likely to crack can be obtained more reliably. Furthermore, it was confirmed that the orientation degree D of the covering layer 5 can be adjusted by appropriately adjusting the extrusion molding conditions (extrusion temperature, screw speed) of the covering layer 5.

[0071] (Functions and Effects of Implementation Methods)

[0072] As described above, in the insulated wire 1 of this embodiment, the coating layer 5 is formed of PFA having a thickness of 0.04 mm or less, and the orientation degree D represented by the above formula (1) is less than 0.85. This makes it possible to realize an insulated wire 1 in which the coating layer 5 is less likely to crack.

[0073] (Summary of implementation methods)

[0074] Next, the technical ideas grasped from the above-described embodiments will be described with reference to the reference numerals in the embodiments. However, the reference numerals in the following description do not limit the constituent elements in the claims to those specifically shown in the embodiments.

[0075] [1] An insulated wire (1) comprising a conductor (2) and a coating layer (5) formed on the outermost side so as to cover the periphery of the conductor (2), wherein the thickness of the coating layer (5) is 0.04 mm or less, and the coating layer (5) is composed of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), and in a Raman spectrum measured by irradiating the coating layer (5) with a laser beam having a polarization direction parallel to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributable to the A1 mode by the intensity of a peak of C-C stretching vibration attributable to the E2 mode is set as Ip, and in a Raman spectrum measured by irradiating the coating layer (5) with a laser beam having a polarization direction perpendicular to the longitudinal direction, the intensity of a polarization-dependent peak obtained by normalizing the intensity of a peak of C-C stretching vibration attributable to the A1 mode by the intensity of a peak of C-C stretching vibration attributable to the E2 mode is set as Ic, in which case the orientation degree D represented by the following formula (1) is less than 0.85.

[0076] D=Ip / (Ip+Ic)···(1)

[0077] [2] The insulated wire (1) according to [1], wherein the orientation degree D is 0.75 or less.

[0078] [3] The insulated wire (1) according to [1], wherein the thickness of the coating layer (5) is 0.02 mm or less.

[0079] [4] The insulated wire (1) according to [1] further comprises an insulator (3) covering the periphery of the conductor (2) and a shielding layer (4) covering the periphery of the insulator (3) between the conductor (2) and the coating (5), and the outer diameter of the coating (5) is not more than 0.4 mm.

[0080] [5] The insulated wire (1) according to [4], wherein the outer diameter of the coating layer (5) is 0.2 mm or less.

[0081] (Note)

[0082] While the embodiments of the present invention have been described above, the embodiments described above 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 required to achieve the goals of the invention. Furthermore, the present invention can be implemented with appropriate modifications without departing from its spirit.

Claims

1. An insulated wire comprising a conductor and a coating layer formed on the outermost side so as to cover the periphery of the conductor. The thickness of the coating layer is less than 0.04 mm, The coating layer is composed of tetrafluoroethylene-perfluoroalkoxyethylene copolymer, namely PFA. In the Raman spectrum measured by irradiating the coating layer with laser light having a polarization direction parallel to the longitudinal direction, the intensity of the polarization-dependent peak obtained by normalizing the intensity of the peak of the C—C stretching vibration attributable to the A1 mode with the intensity of the peak of the C—C stretching vibration attributable to the E2 mode is defined as Ip. In the Raman spectrum measured by irradiating the coating layer with laser light having a polarization direction perpendicular to the longitudinal direction, the intensity of the polarization-dependent peak obtained by normalizing the intensity of the peak of the C—C stretching vibration attributable to the A1 mode by the intensity of the peak of the C—C stretching vibration attributable to the E2 mode is defined as Ic. At this time, the orientation degree D represented by the following formula (1) is less than 0.85, D=Ip / (Ip+Ic)···(1).

2. The insulated wire according to claim 1, wherein The orientation degree D is 0.75 or less.

3. The insulated wire according to claim 1, wherein The coating layer has a thickness of 0.02 mm or less.

4. The insulated wire according to claim 1, wherein An insulator covering the periphery of the conductor and a shield layer covering the periphery of the insulator are further provided between the conductor and the coating layer, and an outer diameter of the coating layer is 0.4 mm or less.

5. The insulated wire according to claim 4, wherein The outer diameter of the coating layer is 0.2 mm or less.

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