Methods for inspecting the quality of electric wires

Abstract

This invention provides a wire quality inspection method that allows for the examination of the properties of an insulating coating layer mainly composed of polyethylene or polypropylene using Raman mapping measurements. [Solution] A method for inspecting the quality of an electric wire 1 having an insulating coating layer 11 mainly composed of polyethylene, comprising: a measurement step of performing Raman mapping measurement on the surface of the insulating coating layer 11 to obtain a group of Raman spectra; and an evaluation step of evaluating the shrinkback deformation rate of the insulating coating layer 11 based on the intensity of a first peak in the group of Raman spectra that is attributed to the CH bending vibration of the polyethylene.

Description

[Technical Field]

[0001] The present invention relates to a method for inspecting the quality of electric wires. [Background technology]

[0002] Conventionally, methods for measuring the properties of polyethylene by Raman scattering are known (see Non-Patent Documents 1 and 2). Non-Patent Document 1 discloses a method for determining the crystallinity of polyethylene using the intensity of the peak attributed to the CH bending vibration of polyethylene contained in the Raman spectrum. Non-Patent Document 2 discloses a method for determining the amount of strain of polyethylene using the position of the peak of the CC symmetric stretching vibration of polyethylene contained in the Raman spectrum. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] AP Kotula et al., “The rheo-Raman microscope: Simultaneous chemical, conformational, mechanical, and microstructural measures of soft materials”, REVIEW OF SCIENTIFIC INSTRUMENTS 87 105105 (2016). [Non-Patent Document 2] PA Tarantili, AG Andreopoulos, and C. Galiotis, “Real-Time Micro-Raman Measurements on Stressed Polyethylene Fibers. 1. Strain Rate Effects and Molecular Stress Redistribution”, Macromolecules 1998, 31, 20, 6964-6976. [Overview of the Initiative]

Problems to be Solved by the Invention

[0004] Raman scattering measurement enables non-destructive and non-contact measurement of the object to be measured. Therefore, if the desired characteristics of the object to be measured can be measured by Raman scattering measurement, those characteristics can be measured without causing damage or contamination to the object to be measured.

[0005] An object of the present invention is to provide a method for inspecting the quality of an electric wire that can examine the characteristics of an insulating coating layer mainly composed of polyethylene or polypropylene using Raman mapping measurement.

Means for Solving the Problems

[0006] The present invention is a method for inspecting the quality of an electric wire provided with an insulating coating layer mainly composed of polyethylene or polypropylene, and aims to solve the above problems. The method includes a measurement step of performing Raman mapping measurement on the surface of the insulating coating layer to obtain a group of Raman spectra, and an evaluation step of evaluating the shrink-back deformation rate of the insulating coating layer based on the intensity of a first peak attributed to the C-H bending vibration of the polyethylene or the C-C stretching vibration of the polypropylene in the group of Raman spectra.

[0007] Further, the present invention is a method for inspecting the quality of an electric wire provided with an insulating coating layer mainly composed of polyethylene, and aims to solve the above problems. The method includes a measurement step of performing Raman mapping measurement at two locations on the surface of the insulating coating layer to obtain two groups of Raman spectra, and an evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in the positions of a third peak attributed to the C-C symmetric stretching vibration of the polyethylene in the two groups of Raman spectra.

[0008] Also, the present invention aims to solve the above problems, and provides a method for inspecting the quality of an electric wire provided with an insulating coating layer mainly composed of polyethylene or polypropylene, including a measurement step of performing Raman mapping measurement at two locations on the surface of the insulating coating layer to obtain two Raman spectrum groups, and an evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in the intensity of a first peak attributed to the C-H bending vibration of polyethylene or the C-C stretching vibration of polypropylene in the two Raman spectrum groups.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a method for inspecting the quality of an electric wire that can examine the characteristics of an insulating coating layer mainly composed of polyethylene or polypropylene using Raman mapping measurement.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a cross-sectional view in the radial direction of an insulated electric wire, which is an example of an electric wire according to the first embodiment of the present invention. [Figure 2] FIG. 2(a) is an optical microscope image of a part of the surface of the insulating coating layer of the first sample, and FIG. 2(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in FIG. 2(a) of the surface of the insulating coating layer. [Figure 3] FIG. 3(a) is an optical microscope image of a part of the surface of the insulating coating layer of the first sample, which is different from the portion shown in FIG. 2(a), and FIG. 3(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in FIG. 3(a) of the surface of the insulating coating layer. [Figure 4] FIG. 4(a) is an optical microscope image of a part of the surface of the insulating coating layer of the second sample, and FIG. 4(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in FIG. 4(a) of the surface of the insulating coating layer. [Figure 5]Figure 5(a) is an optical microscope image of a portion of the surface of the insulating coating layer of the second sample that differs from the portion shown in Figure 4(a), and Figure 5(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the surface of the insulating coating layer shown in Figure 5(a). [Figure 6] Figure 6(a) is a mapping image of the first sample formed on the optical microscope image of Figure 2(a). Figure 6(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the first sample shown in Figure 6(a). [Figure 7] Figure 7(a) is a mapping image of the first sample formed on the optical microscope image of Figure 3(a). Figure 7(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the first sample shown in Figure 7(a). [Figure 8] Figure 8(a) is a mapping image of the second sample formed on the optical microscope image of Figure 4(a). Figure 8(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the second sample shown in Figure 8(a). [Figure 9] Figure 9(a) is a mapping image of the second sample formed on the optical microscope image of Figure 5(a). Figure 9(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the second sample shown in Figure 9(a). [Figure 10] Figure 10 is a graph of the values ​​in Table 2. [Figure 11] Figure 11 is an optical microscope image of the surface of an insulating coating layer with cracks. [Figure 12] Figure 12(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the third sample, and Figure 12(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer shown in Figure 12(a). [Figure 13]Figure 13(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the third sample, showing the portion opposite to the portion shown in Figure 12(a) with respect to the central axis of the insulated wire. Figure 13(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in Figure 13(a) of the radial cross-section of the insulating coating layer. [Figure 14] Figure 14(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the fourth sample, and Figure 14(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer shown in Figure 14(a). [Figure 15] Figure 15(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the fourth sample, showing the portion opposite to the portion shown in Figure 14(a) with respect to the central axis of the insulated wire. Figure 15(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in Figure 15(a) of the radial cross-section of the insulating coating layer. [Figure 16] Figure 16(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the fifth sample, and Figure 16(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer shown in Figure 16(a). [Figure 17] Figure 17(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the fifth sample, showing the portion opposite to the portion shown in Figure 16(a) with respect to the central axis of the insulated wire. Figure 17(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion shown in Figure 17(a) of the radial cross-section of the insulating coating layer. [Figure 18] Figure 18(a) is a mapping image of the third sample formed on the optical microscope image of Figure 12(a). Figure 18(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the third sample shown in Figure 18(a). [Figure 19]Figure 19(a) is a mapping image of the third sample formed on the optical microscope image of Figure 13(a). Figure 19(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the third sample shown in Figure 19(a). [Figure 20] Figure 20(a) is a mapping image of the fourth sample formed on the optical microscope image of Figure 14(a). Figure 20(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the fourth sample shown in Figure 20(a). [Figure 21] Figure 21(a) is a mapping image of the fourth sample formed on the optical microscope image of Figure 15(a). Figure 21(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the fourth sample shown in Figure 21(a). [Figure 22] Figure 22(a) is a mapping image of the fifth sample formed on the optical microscope image of Figure 16(a). Figure 22(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the fifth sample shown in Figure 22(a). [Figure 23] Figure 23(a) is a mapping image of the fifth sample formed on the optical microscope image of Figure 17(a). Figure 23(b) is a histogram showing the frequency distribution of the position (cm-1) of the third peak P3 contained in each pixel of the mapping image of the fifth sample shown in Figure 23(a). [Figure 24] Figure 24 is a graph of the values ​​in Table 4. [Figure 25] Figure 25(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the third sample, and Figure 25(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer shown in Figure 25(a). [Figure 26]Figure 26(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the third sample, showing the portion opposite to the portion shown in Figure 25(a) with respect to the central axis of the insulated wire. Figure 26(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in Figure 26(a) of the radial cross-section of the insulating coating layer. [Figure 27] Figure 27(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the fourth sample, and Figure 27(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer shown in Figure 27(a). [Figure 28] Figure 28(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the fourth sample, showing the portion opposite to the portion shown in Figure 27(a) with respect to the central axis of the insulated wire. Figure 28(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in Figure 28(a) of the radial cross-section of the insulating coating layer. [Figure 29] Figure 29(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer of the fifth sample, and Figure 29(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer shown in Figure 29(a). [Figure 30] Figure 30(a) is an optical microscope image of the radial cross-section of the insulating coating layer of the fifth sample, showing the portion opposite to the portion shown in Figure 29(a) with respect to the central axis of the insulated wire. Figure 30(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion shown in Figure 30(a) of the radial cross-section of the insulating coating layer. [Figure 31] Figure 31(a) is a mapping image of the third sample formed on the optical microscope image of Figure 25(a). Figure 31(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the third sample shown in Figure 31(a). [Figure 32]Figure 32(a) is a mapping image of the third sample formed on the optical microscope image of Figure 26(a). Figure 32(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the third sample shown in Figure 32(a). [Figure 33] Figure 33(a) is a mapping image of the fourth sample formed on the optical microscope image of Figure 27(a). Figure 33(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the fourth sample shown in Figure 33(a). [Figure 34] Figure 34(a) is a mapping image of the fourth sample formed on the optical microscope image of Figure 28(a). Figure 34(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the fourth sample shown in Figure 34(a). [Figure 35] Figure 35(a) is a mapping image of the fifth sample formed on the optical microscope image of Figure 29(a). Figure 35(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the fifth sample shown in Figure 35(a). [Figure 36] Figure 36(a) is a mapping image of the fifth sample formed on the optical microscope image of Figure 30(a). Figure 36(b) is a histogram showing the frequency distribution of the degree of crystallinity αc contained in each pixel of the mapping image of the fifth sample shown in Figure 36(a). [Figure 37] Figure 37 is a graph of the values ​​in Table 5. [Modes for carrying out the invention]

[0011] [First Embodiment] (Method for inspecting the quality of electric wires) According to the wire quality inspection method of the first embodiment of the present invention, the shrink-back deformation rate of the insulating coating layer, which is mainly composed of polyethylene (for example, containing 50% or more by mass of the total), provided on the wire can be evaluated using Raman scattering measurement. Here, the insulating coating layer is the outermost layer provided on the wire and is formed, for example, by extrusion using an extruder.

[0012] The term "electric wire" according to the present invention includes not only an electric wire in which a single conductor, consisting of one linear conductor or twisted linear conductors, is covered with an insulating coating layer (hereinafter referred to as an insulated electric wire), but also a so-called cable in which multiple insulated electric wires are covered with a sheath. That is, if the electric wire according to the present invention is a cable, its sheath corresponds to the insulating coating layer of the present invention.

[0013] Shrinkback is a phenomenon in which the insulating coating layer shrinks when the temperature rises, due to residual stress generated in the insulating coating layer during the manufacturing of electric wires. The shrinkback deformation rate of the insulating coating layer refers to the rate of shrinkage of the insulating coating layer in the longitudinal direction of the electric wire due to shrinkback.

[0014] Raman scattering measurements allow for non-destructive evaluation of the shrinkback deformation rate of the insulating coating layer on electric wires. Furthermore, since Raman scattering measurements can be performed non-contact, contamination of the insulating coating layer during measurement can be avoided.

[0015] Furthermore, in Raman scattering measurements, the measurement area is determined by the spot diameter of the laser irradiated onto the surface of the resin material, making it possible to perform measurements within minute areas with a diameter of 1 μm or less. Therefore, it is possible to evaluate the shrink-back deformation rate of the insulating coating layer in thin-diameter wires (for example, wires with an outer diameter of 200 μm or less), where measurements within minute areas are required. For example, FT-IR is another measurement method that can perform measurements non-destructively and non-contact, similar to Raman scattering measurements, but with FT-IR, measurements in minute areas of several tens of μm or less are difficult.

[0016] Furthermore, while point measurements make it difficult to obtain information about localized alterations in the insulating coating layer, Raman mapping measurements, described later, allow us to obtain information about alterations within the range of the Raman mapping measurement. Therefore, the shrinkback deformation rate of the insulating coating layer can be evaluated with high accuracy. In addition, this allows us to accurately determine the difference in the shrinkback deformation rate of the insulating coating layer for each sample.

[0017] As a result of diligent research, the inventors have found a correlation between the intensity of the peak (referred to as the first peak) attributed to the CH bending vibration of polyethylene in the Raman spectrum group obtained by Raman mapping measurement of the insulating coating layer, and the shrink-back deformation rate of the insulating coating layer (the higher the intensity of the first peak in the Raman spectrum group, the greater the shrink-back deformation rate). Based on this correlation, the wire quality inspection method according to this embodiment allows for the evaluation of the shrink-back deformation rate of the insulating coating layer using the intensity of the first peak in the Raman spectrum group obtained by Raman mapping measurement of the insulating coating layer.

[0018] In other words, the wire quality inspection method according to this embodiment is a wire quality inspection method comprising an insulating coating layer mainly composed of polyethylene, and includes a measurement step of performing Raman mapping measurement on the surface of the insulating coating layer to obtain a group of Raman spectra, and an evaluation step of evaluating the shrinkback deformation rate of the insulating coating layer based on the intensity of a first peak in the group of Raman spectra that is attributed to the CH bending vibration of the polyethylene. The position of the first peak in the Raman spectrum (the position where the maximum intensity is obtained) is typically 1240 cm⁻¹. -1 Above, 1360cm -1 It falls within the following range. The position of each peak in the Raman spectrum can be read from the position of the peak's apex in the fitting curve obtained by fitting analysis of the Raman spectrum.

[0019] In the evaluation process described above, the shrink-back deformation rate of the insulating coating layer can be determined by using the correlation between the intensity of the first peak in the Raman spectrum group, which has been determined in advance by experiment, and the shrink-back deformation rate of the insulating coating layer. This correlation can be obtained, for example, from the results of Raman mapping measurements of the insulating coating layer of an electric wire and thermal shock tests on the electric wire.

[0020] In the evaluation process described above, for example, the shrinkback deformation rate of the insulating coating layer can be evaluated based on the mean value of the frequency distribution of the intensity of the first peak in the Raman spectrum. In this case, the shrinkback deformation rate of the insulating coating layer can be determined using the correlation between the mean value of the frequency distribution of the intensity of the first peak in the Raman spectrum, which has been determined in advance by experiment, and the shrinkback deformation rate of the insulating coating layer (for example, a formula that expresses the shrinkback deformation rate of the insulating coating layer as a function of the mean value of the frequency distribution of the intensity of the first peak in the Raman spectrum).

[0021] Raman mapping is a measurement method that involves repeatedly scanning a measurement point (the laser irradiation point) within a predetermined measurement area on the surface of an object to be measured. The two-dimensional measurement data obtained by Raman mapping, known as the mapping image, contains data for the intensity of the first peak included in the Raman spectrum obtained from a single Raman scattering measurement (for example, the intensity of the first peak, or the intensity of the first peak normalized by the intensity of the second peak, which will be described later) for each pixel. In other words, the group of Raman spectra obtained by Raman mapping is a group of Raman spectra equal to the number of pixels in the mapping image.

[0022] Furthermore, the method of using a group of Raman spectra obtained by Raman mapping, which is a multi-point measurement (mapping) using a laser with a small spot diameter, can suppress the influence of fluorescence in the Raman spectrum compared to the method of using a single Raman spectrum obtained by irradiating the surface of an insulating coating layer with a laser with a large spot diameter (for example, equivalent to the measurement range of Raman mapping). This is because the increase in reflectivity with increasing laser irradiation area is significantly greater for fluorescence than for Raman light. As a result, the intensity of the Raman peak relative to the background (fluorescence) intensity in the Raman spectrum becomes larger, and the intensity and position of peaks used for analysis, such as the first peak, can be accurately measured.

[0023] It is known that the intensity of the first peak attributed to the CH bending vibration of polyethylene increases with increasing crystallinity of polyethylene (see Non-Patent Document 1 above). Therefore, the intensity of the first peak in the Raman spectrum obtained by Raman mapping measurements of the insulating coating layer represents the crystallinity of the insulating coating layer within the measurement range of the Raman mapping measurement. In the insulating coating layer, the higher the intensity of the first peak in the Raman spectrum, the greater the shrinkback deformation rate, which is thought to be because higher crystallinity makes it easier to shrink when heat is applied.

[0024] The intensity of the first peak is preferably normalized by the intensity of the peak attributable to the CH torsional vibration of polyethylene (referred to as the second peak), which is largely unaffected by the degree of polyethylene crystallinity, in order to minimize the influence of measurement conditions. The position of the second peak in the Raman spectrum (the position where the maximum intensity is obtained) is typically 1375 cm⁻¹. -1 The above is 1455cm. -1 It is within the following range.

[0025] In the evaluation process described above, for example, the degree of crystallinity α is determined using the intensity of the first peak in the Raman spectrum group. cBased on the average value of the frequency distribution (referred to as the average crystallinity), the shrink-back deformation rate of the insulating coating layer can be evaluated. The crystallinity α c is a physical property value proportional to the intensity of the first peak normalized by the intensity of the second peak in the Raman spectrum of the insulating coating layer, and is represented by the following formula (1).

[0026] [Number]

[0027] I in formula (1) b is the intensity of the first peak attributed to the C-H bending vibration of polyethylene, and I t is the intensity of the second peak attributed to the C-H torsional vibration of polyethylene. Also, N in formula (1) c is a scale factor. For example, in high-density polyethylene (HDPE), N c takes a value of 0.80 ± 0.03.

[0028] As the intensity of the first peak and the second peak, the peak height or the integrated intensity of the peak can be used. The integrated intensity of the peak can be calculated, for example, using the Covell method.

[0029] (Configuration of the electric wire) FIG. 1 is a cross-sectional view in the radial direction of an insulated electric wire 1, which is an example of an electric wire according to the first embodiment of the present invention. The insulated electric wire 1 includes a conductor 10 and an insulating coating layer 11 that covers the periphery of the conductor 10.

[0030] The conductor 10 is a stranded wire formed by twisting a plurality of strands 101 made of copper wires or copper alloy wires. The insulating coating layer 11 is a layer mainly composed of polyethylene, and is composed of an inner layer 111 that covers the periphery of the conductor 10 and an outer layer 112 that covers the periphery of the inner layer 111.

[0031] (Example of the quality inspection method of the electric wire) The following describes an example of the wire quality inspection method according to this embodiment. In this embodiment, first, using two insulated wires 1 with different shrinkback deformation rates, the average crystallinity is measured by Raman mapping and the shrinkback deformation rate is measured by thermal shock testing, demonstrating that there is a correlation between the average crystallinity of the insulating coating layer and the shrinkback deformation rate.

[0032] Here, of the two insulated wires 1 according to this embodiment, the insulated wire 1 with a low shrink-back deformation rate is referred to as the first sample, and the insulated wire 1 with a high shrink-back deformation rate is referred to as the second sample. Both the first and second samples had an outer diameter of approximately 1.4 mm, and the polyethylene concentration of the insulating coating layer 11 was approximately 99% by mass of the total.

[0033] In this embodiment, the integrated intensities of the first peak P1 and the second peak P2 are respectively defined as the intensity I of the first peak P1. b , the intensity of the second peak P2 t In addition, in this embodiment, the same polyethylene is used (i.e., N in Equation 1). c (The values ​​of are equal) In order to compare the average crystallinity between the insulating coating layer 11 of the first sample and the insulating coating layer 11 of the second sample, for convenience, N c Treat it as 1.

[0034] Table 1 shows the measurement conditions for Raman mapping of the insulating coating layer 11. The theoretical value of the laser irradiation diameter, calculated using the laser excitation wavelength (532.06 nm) and objective lens numerical aperture (NA 0.80) shown in Table 1, based on Abbe's definition, is 0.41 μm.

[0035] [Table 1]

[0036] Figure 2(a) is an optical microscope image of a portion of the surface of the insulating coating layer 11 of the first sample, and Figure 2(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the surface of the insulating coating layer 11 shown in Figure 2(a). The two Raman spectra shown in Figure 2(b) were measured at measurement positions A1 and A2, indicated by cross marks in Figure 2(a).

[0037] Figure 3(a) is an optical microscope image of a portion of the surface of the insulating coating layer 11 of the first sample that differs from the portion shown in Figure 2(a), and Figure 3(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the surface of the insulating coating layer 11 shown in Figure 3(a). The two Raman spectra shown in Figure 3(b) were measured at measurement positions B1 and B2, indicated by cross marks in Figure 3(a).

[0038] Figure 4(a) is an optical microscope image of a portion of the surface of the insulating coating layer 11 of the second sample, and Figure 4(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the surface of the insulating coating layer 11 shown in Figure 4(a). The two Raman spectra shown in Figure 4(b) were measured at measurement positions C1 and C2, indicated by cross marks in Figure 4(a).

[0039] Figure 5(a) is an optical microscope image of a portion of the surface of the insulating coating layer 11 of the second sample that differs from the portion shown in Figure 4(a), and Figure 5(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the surface of the insulating coating layer 11 shown in Figure 5(a). The two Raman spectra shown in Figure 5(b) were measured at measurement positions D1 and D2, indicated by cross marks in Figure 5(a).

[0040] The Raman spectra shown in Figures 2(b), 3(b), 4(b), and 5(b) include a first peak P1 attributed to the CH bending vibration of polyethylene and a second peak P2 attributed to the CH torsional vibration of polyethylene.

[0041] Measurement positions A1, B1, C1, and D1 are examples of locations where the intensity of the first peak P1 on the surface of the insulating coating layer 11 of the first or second sample is relatively high (relatively high degree of polyethylene crystallinity). On the other hand, measurement positions A2, B2, C2, and D2 are examples of locations where the intensity of the first peak P1 on the surface of the insulating coating layer 11 of the first or second sample is relatively low (relatively low degree of polyethylene crystallinity).

[0042] Figures 6(a) and 7(a) are mapping images of the first sample formed on the optical microscope images of Figure 2(a) and Figure 3(a), respectively. Figures 8(a) and 9(a) are mapping images of the second sample formed on the optical microscope images of Figure 4(a) and Figure 5(a), respectively.

[0043] Each pixel in the mapping images in Figures 6(a), 7(a), 8(a), and 9(a) represents the degree of crystallinity α obtained from the Raman spectrum measured at that location. c (Intensity of the first peak P1 I b / Intensity of the second peak P2 I t ) contains data, and each pixel has a crystallinity α c Each has a corresponding color.

[0044] Figures 6(b) and 7(b) show the degree of crystallinity α contained in each pixel of the mapping image of the first sample shown in Figures 6(a) and 7(a), respectively. c This is a histogram showing the frequency distribution. Figures 8(b) and 9(b) show the degree of crystallinity α contained in each pixel of the mapping image of the second sample shown in Figures 8(a) and 9(a), respectively. c This is a histogram showing the frequency distribution.

[0045] In the histograms shown in Figures 6(b), 7(b), 8(b), and 9(b), the degree of crystallinity α c The horizontal axis represents the 256 classes that divide the range from the minimum to the maximum value, and the vertical axis represents the frequency, which is the number of pixels in each class.

[0046] The average crystallinity of the insulating coating layer 11 in the first sample, calculated from the histograms shown in Figures 6(b) and 7(b), is 0.1000 and 0.1110, respectively. Similarly, the average crystallinity of the insulating coating layer 11 in the second sample, calculated from the histograms shown in Figures 8(b) and 9(b), is 0.1286 and 0.1207, respectively. Note that the average crystallinity may also be determined from the frequency distribution table on which the histograms are based, rather than from the histograms themselves.

[0047] Next, an example of a thermal shock test to measure the shrinkback deformation rate will be described. First, the conductor 10 was removed from the first and second samples, which are insulated wires 1, and the remaining insulating coating layer 11 was cut to a length L of 100 mm, which was used as the test piece for the thermal shock test. That is, the length L of this test piece before the test was 100 mm. Five of these test pieces were cut from the insulating coating layer 11 of the first sample and five from the second sample.

[0048] Next, a simple thermal shock test was performed by moving these specimens from room temperature to an environment of 150°C, holding them for 15 minutes, and then returning them to room temperature. The length L of the specimens after the test was measured, and the shrinkback deformation rate of the specimens was calculated as (L before test - L after test) / (L before test).

[0049] The average shrink-back deformation rate of five test pieces cut from the insulating coating layer 11 of the first sample was defined as the average shrink-back deformation rate of the insulating coating layer 11 of the first sample, and the average shrink-back deformation rate of five test pieces cut from the insulating coating layer 11 of the second sample was defined as the average shrink-back deformation rate of the insulating coating layer 11 of the second sample. The resulting average shrink-back deformation rates of the insulating coating layer 11 of the first sample and the insulating coating layer 11 of the second sample were 5.8% and 7.5%, respectively.

[0050] Table 2 below shows the average crystallinity of the insulating coating layer 11 in the first and second samples obtained by the Raman mapping measurement described above, and the average shrinkback deformation rate of the insulating coating layer 11 in the first and second samples obtained by the thermal shock test described above.

[0051] [Table 2]

[0052] Figure 10 is a graph of the values ​​in Table 2. The bar graph in Figure 10 shows the average crystallinity value, and the line graph shows the average shrinkback deformation rate. Table 2 and Figure 10 show that there is a correlation between the average crystallinity and the average shrinkback deformation rate in the insulating coating layer 11 of the insulated wire 1.

[0053] If the correlation between the intensity of the first peak in the Raman spectrum group (e.g., average crystallinity) and the shrinkback deformation rate in the insulating coating layer of an insulated wire is obtained in advance, as shown in Table 2 and Figure 10, the shrinkback deformation rate of the insulating coating layer can be evaluated from the intensity of the first peak in the Raman spectrum group obtained by Raman mapping measurement.

[0054] (Effects of the first embodiment) According to the wire quality inspection method of the first embodiment, the shrink-back deformation rate of the insulating coating layer can be evaluated from the intensity of the first peak in the Raman spectrum group obtained by Raman mapping measurement of the surface of the insulating coating layer. Therefore, the shrink-back deformation rate of an insulating coating layer mainly composed of polyethylene can be measured without causing damage or contamination.

[0055] [Second Embodiment] The second embodiment of the present invention differs in the content of the wire quality inspection method and the characteristics of the wire to be evaluated. The same aspects as those of the first embodiment will be omitted or simplified in the explanation.

[0056] (Method for inspecting the quality of electric wires) According to the wire quality inspection method of the second embodiment of the present invention, the fracture resistance of the polyethylene-based insulating coating layer provided on the wire can be evaluated using Raman scattering measurement.

[0057] As a result of diligent research, the inventors have found that when Raman mapping measurements are performed at two locations on the insulating coating layer (for example, two locations on the surface or two locations on the cross-section) to obtain two sets of Raman spectra, there is a correlation between the difference in the position of the peak attributed to the CC symmetric stretching vibration of polyethylene (referred to as the third peak) in the two Raman spectrum sets and the fracture resistance of the insulating coating layer (the larger the difference in the position of the third peak in the two Raman spectrum sets, the lower the fracture resistance of the insulating coating layer). Based on this correlation, according to the wire quality inspection method of this embodiment, the fracture resistance of the insulating coating layer can be evaluated using the position of the third peak in the two spectrum sets obtained by Raman mapping measurements of the insulating coating layer.

[0058] The wire quality inspection method according to this embodiment is a wire quality inspection method comprising an insulating coating layer mainly composed of polyethylene, and includes a measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer to obtain two Raman spectrum groups, and an evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in the position of the third peak in the two Raman spectrum groups that is attributed to the CC symmetric stretching vibration of the polyethylene. The position of the third peak in the Raman spectrum (the position where the maximum intensity is obtained) is typically 1115 cm⁻¹. -1 Over 1150cm -1 It is within the following range.

[0059] In the evaluation process described above, the fracture resistance of the insulating coating layer can be evaluated using the correlation between the difference in the position of the third peak of two Raman spectral groups, which has been determined in advance by experiment, and the presence or absence of cracks on the surface of the insulating coating layer, which serves as an indicator of the fracture resistance of the insulating coating layer (for example, a threshold for the difference in the position of the third peak of two Raman spectral groups that can effectively suppress the occurrence of cracks in the insulating coating layer under specific usage conditions). This correlation can be obtained, for example, from the results of Raman mapping measurements performed on electric wires with cracks on the surface of the insulating coating layer and electric wires without cracks on the surface of the insulating coating layer.

[0060] In the evaluation process described above, for example, the fracture resistance of the insulating coating layer can be evaluated based on the difference in the mean values ​​of the frequency distributions of the third peak position of two Raman spectrum groups. In this case, the fracture resistance of the insulating coating layer can be evaluated using the correlation between the difference in the mean values ​​of the frequency distributions of the third peak position of two Raman spectrum groups, which has been determined in advance by experiment, and the fracture resistance of the insulating coating layer.

[0061] The difference in the position of the third peak of two Raman spectrum groups obtained by Raman mapping measurements at two locations on the surface of the insulating coating layer correlates with the difference in the amount of strain at those two locations (see Non-Patent Literature 2 above). For example, the difference in the position of the third peak of two Raman spectrum groups obtained by Raman mapping measurements at two locations on the surface of the insulating coating layer (cm -1 If we let ΔP be the value of the strain at the two points and ΔS be the difference (%) between the amounts of strain at those two points, then the relationship shown in Equation 2 below holds.

[0062]

number

[0063] In an insulating coating layer, the greater the difference in the position of the third peak of the two Raman spectral groups, the lower the fracture resistance of the insulating coating layer. This is thought to be because fracture is more likely to occur in the insulating coating layer when the above ΔS is large, i.e., when the uniformity of the amount of strain in the insulating coating layer is low.

[0064] Furthermore, in the measurement process described above, Raman mapping measurements may be performed at three or more locations on the surface of the insulating coating layer to obtain three or more Raman spectrum groups. In that case, in the evaluation process described above, for example, the difference in the position of the third peak in two of the three or more Raman spectrum groups can be determined, and the fracture resistance of the insulating coating layer can be evaluated based on the average value of these differences.

[0065] Figure 11 is an optical microscope image of the surface of the insulating coating layer 11 (surface of the outer layer 112) that has cracks. The cracks on the surface of the insulating coating layer illustrated in Figure 11 are caused by displacement between atoms and molecules due to the application of external force, and by intermolecular severance or reduction of intermolecular forces due to the penetration of attached solvents, etc., and are thought to be more likely to occur when the uniformity of strain and stress uniformity in the insulating coating layer is low.

[0066] (Examples of methods for inspecting the quality of electric wires) The following describes an example of the wire quality inspection method according to this embodiment. In this embodiment, first, using one insulated wire 1 having cracks on the surface of the insulating coating layer 11 and two insulated wires 1 without cracks on the surface of the insulating coating layer 11, the position of the third peak of the insulating coating layer 11 is measured by Raman mapping, and it is shown that there is a correlation between the difference in the average value of the frequency distribution of the position of the third peak of the insulating coating layer 11 and the break resistance.

[0067] Here, of the three insulated wires 1 according to this embodiment, the one insulated wire 1 having a crack on the surface of the insulating coating layer 11 is referred to as the third sample, and the two insulated wires 1 without cracks on the surface of the insulating coating layer 11 are referred to as the fourth sample and the fifth sample. The third sample, the fourth sample, and the fifth sample all had an outer diameter of approximately 2.2 mm, and the polyethylene concentration of the insulating coating layer 11 was approximately 99% by mass of the total.

[0068] Table 3 shows the measurement conditions for Raman mapping of the insulating coating layer 11 in this embodiment. The theoretical value of the laser irradiation diameter, which can be obtained by performing calculations based on Abbe's definition using the laser excitation wavelength (532.06 nm) and the numerical aperture of the objective lens (NA 0.80) shown in Table 3, is 0.41 μm. [Table 3]

[0069] Figure 12(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the third sample, and Figure 12(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 12(a). The two Raman spectra shown in Figure 12(b) were measured at measurement positions E1 and E2, indicated by cross marks in Figure 12(a).

[0070] Figure 13(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the third sample, showing the portion opposite to the portion shown in Figure 12(a) with respect to the central axis of the insulated wire 1. Figure 13(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 13(a). The two Raman spectra shown in Figure 13(b) were measured at measurement positions F1 and F2, indicated by cross marks in Figure 13(a).

[0071] Figure 14(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the fourth sample, and Figure 14(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 14(a). The two Raman spectra shown in Figure 14(b) were measured at measurement positions G1 and G2, indicated by cross marks in Figure 14(a).

[0072] Figure 15(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the fourth sample, showing the portion opposite to the portion shown in Figure 14(a) with respect to the central axis of the insulated wire 1. Figure 15(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 15(a). The two Raman spectra shown in Figure 15(b) were measured at measurement positions H1 and H2, indicated by cross marks in Figure 15(a).

[0073] Figure 16(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the fifth sample, and Figure 16(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 16(a). The two Raman spectra shown in Figure 16(b) were measured at measurement positions I1 and I2, indicated by cross marks in Figure 16(a).

[0074] Figure 17(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the fifth sample, showing the portion opposite to the portion shown in Figure 16(a) with respect to the central axis of the insulated wire 1. Figure 17(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 17(a). The two Raman spectra shown in Figure 17(b) were measured at measurement positions J1 and J2, indicated by cross marks in Figure 17(a).

[0075] The Raman spectra shown in Figures 12(b), 13(b), 14(b), 15(b), 16(b), and 17(b) include a third peak, P3, which is attributed to the CC symmetric stretching vibration of polyethylene.

[0076] Figures 18(a) and 19(a) are mapping images of the third sample formed on the optical microscope images of Figures 12(a) and 13(a), respectively. Figures 20(a) and 21(a) are mapping images of the fourth sample formed on the optical microscope images of Figures 14(a) and 15(a), respectively. Figures 22(a) and 23(a) are mapping images of the fifth sample formed on the optical microscope images of Figures 16(a) and 17(a), respectively.

[0077] Each pixel in the mapping images in Figures 18(a), 19(a), 20(a), 21(a), 22(a), and 23(a) shows the position of the third peak P3 obtained from the Raman spectrum measured at that location (cm²). -1 The data includes ), and each pixel has a color corresponding to the position of the third peak P3.

[0078] Figures 18(b) and 19(b) show the position (cm) of the third peak P3 contained in each pixel of the mapping image of the third sample shown in Figures 18(a) and 19(a), respectively. -1 This is a histogram showing the frequency distribution of ). Figures 20(b) and 21(b) show the position (cm) of the third peak P3 contained in each pixel of the mapping image of the fourth sample shown in Figures 20(a) and 21(a), respectively. -1 This is a histogram showing the frequency distribution of ). Figures 22(b) and 23(b) show the position (cm) of the third peak P3 contained in each pixel of the mapping image of the fifth sample shown in Figures 22(a) and 23(a), respectively. -1 This is a histogram showing the frequency distribution of ).

[0079] In the histograms shown in Figures 18(b), 19(b), 20(b), 21(b), 22(b), and 23(b), the horizontal axis represents the 256 classes that divide the range from the minimum to the maximum position of the third peak P3, and the vertical axis represents the frequency, which is the number of pixels in each class.

[0080] The mean value of the frequency distribution of the position of the third peak P3 in the insulating coating layer 11 of the third sample (referred to as the mean position of P3), calculated from the histograms shown in Figures 18(b) and 19(b), is 1133.9 cm². -1 1133.1cm -1 Furthermore, the average P3 position of the insulating coating layer 11 in the fourth sample, calculated from the histograms shown in Figures 20(b) and 21(b), is 1133.8 cm². -1 1133.3cm -1 Furthermore, the average P3 position of the insulating coating layer 11 in the fifth sample, calculated from the histograms shown in Figures 22(b) and 23(b), is 1133.1 cm². -1 1133.3cm -1 The P3 mean position can also be determined from the frequency distribution table on which the histogram is based, rather than from the histogram itself.

[0081] Table 4 below shows the P3 average position of the insulating coating layer 11 in the third, fourth, and fifth samples obtained by the above Raman mapping measurements, as well as the difference in strain amounts at two locations in the insulating coating layer 11 calculated using Equation 2 above from the difference between the two P3 average positions of each sample.

[0082] [Table 4]

[0083] Figure 24 is a graph of the values ​​in Table 4. Table 4 and Figure 24 show that there is a correlation between the difference in the average P3 position at two different locations in the insulating coating layer 11 of the insulated wire 1 and the presence or absence of surface cracks due to fracture resistance. In the above example, Raman mapping measurements were performed on the radial cross-section of the insulating coating layer 11, but similar results can be obtained even if Raman mapping measurements are performed on the surface of the insulating coating layer 11. Raman mapping measurements on the surface of the insulating coating layer 11 can be performed non-destructively and non-contact on the insulating coating layer 11.

[0084] If the correlation between the difference in the position of the third peak of two Raman spectral groups in the insulating coating layer of an insulated wire (for example, the difference in the P3 average position of the two Raman spectral groups, i.e., the difference in the P3 average position at two locations) and the presence or absence of cracks on the surface is obtained in advance, as shown in Table 4 and Figure 24, then the fracture resistance of the insulating coating layer can be evaluated from the difference in the position of the third peak of the two Raman spectral groups obtained by Raman mapping measurements at two locations.

[0085] (Effects of the second embodiment) According to the wire quality inspection method of the second embodiment, the fracture resistance of the insulating coating layer can be evaluated from the difference in the position of the third peak of two Raman spectrum groups obtained by Raman mapping measurements of the surface of the insulating coating layer at two locations. Therefore, the fracture resistance of an insulating coating layer mainly composed of polyethylene can be evaluated without causing damage or contamination.

[0086] [Third Embodiment] The third embodiment of the present invention differs in the content of the wire quality inspection method and the characteristics of the wire to be evaluated. The same aspects as those of the first embodiment will be omitted or simplified in the explanation.

[0087] (Method for inspecting the quality of electric wires) According to the third embodiment of the present invention, the wire quality inspection method can be used to evaluate the fracture resistance of the polyethylene-based insulating coating layer provided on the wire using Raman scattering measurement.

[0088] As a result of diligent research, the inventors have found that when Raman mapping measurements are performed at two locations on the insulating coating layer (for example, two locations on the surface or two locations on the cross-section) to obtain two sets of Raman spectra, there is a correlation between the difference in intensity of the first peak attributed to the CH bending vibration of polyethylene in the two Raman spectrum sets and the fracture resistance of the insulating coating layer (the larger the difference in intensity of the first peak in the two Raman spectrum sets, the lower the fracture resistance of the insulating coating layer). Based on this correlation, according to the wire quality inspection method of this embodiment, the fracture resistance of the insulating coating layer can be evaluated using the intensity of the first peak in the two spectrum sets obtained by Raman mapping measurements of the insulating coating layer.

[0089] The wire quality inspection method according to this embodiment is a wire quality inspection method comprising an insulating coating layer mainly composed of polyethylene, and includes a measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer to obtain two Raman spectrum groups, and an evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in intensity of the first peak attributed to the CH bending vibration of the polyethylene in the two Raman spectrum groups (for example, the difference in average crystallinity). Note that the first peak in this embodiment is the same as the first peak in the first embodiment.

[0090] In the evaluation process described above, the fracture resistance of the insulating coating layer can be evaluated using the correlation between the difference in intensity of the first peak of two Raman spectral groups determined in advance by experiment (for example, the difference in average crystallinity of the two Raman spectral groups, i.e., the difference in average crystallinity at two locations) and the presence or absence of cracks on the surface of the insulating coating layer, which serves as an indicator of the fracture resistance of the insulating coating layer (for example, a threshold for the difference in intensity of the first peak of the two Raman spectral groups that can effectively suppress the occurrence of cracks in the insulating coating layer under specific usage conditions). This correlation can be obtained, for example, from the results of Raman mapping measurements performed on electric wires with cracks on the surface of the insulating coating layer and electric wires without cracks on the surface of the insulating coating layer.

[0091] In the evaluation process described above, for example, the fracture resistance of the insulating coating layer can be evaluated based on the difference in the mean values ​​of the frequency distributions of the first peak intensity of two Raman spectrum groups. In this case, the fracture resistance of the insulating coating layer can be evaluated using the correlation between the difference in the mean values ​​of the frequency distributions of the first peak intensity of two Raman spectrum groups, which has been determined in advance by experiment, and the fracture resistance of the insulating coating layer.

[0092] As described in the first embodiment above, the intensity of the first peak in the Raman spectrum group obtained by mapping measurement represents the degree of crystallinity of the insulating coating layer within the measurement range of the Raman mapping measurement. The greater the difference in intensity between the first peaks of the two Raman spectrum groups in the insulating coating layer, the lower the fracture resistance of the insulating coating layer is thought to be because fracture is more likely to occur in the insulating coating layer when the uniformity of the degree of crystallinity in the insulating coating layer is low.

[0093] The intensity of the first peak is preferably normalized by the intensity of the second peak, which is attributed to the CH torsional vibration of polyethylene and is hardly affected by the degree of crystallinity of polyethylene, in order to suppress the influence of measurement conditions and other factors. This second peak is the same as the second peak in the first embodiment.

[0094] In the evaluation process described above, for example, the degree of crystallinity α is determined using the intensity of the first peak in the Raman spectrum group. c The fracture resistance of the insulating coating layer can be evaluated based on the mean value (average degree of crystallinity) of the frequency distribution.

[0095] Furthermore, in the measurement process described above, Raman mapping measurements may be performed at three or more locations on the surface of the insulating coating layer to obtain three or more Raman spectrum groups. In that case, in the evaluation process described above, for example, the difference in intensity of the first peak in two of the three or more Raman spectrum groups can be determined, and the fracture resistance of the insulating coating layer can be evaluated based on the average value of these differences.

[0096] (Examples of methods for inspecting the quality of electric wires) The following describes an example of the wire quality inspection method according to this embodiment. In this embodiment, first, the average crystallinity is measured by Raman mapping using a third sample, which is an insulated wire 1 having cracks on the surface of the insulating coating layer 11, and a fourth and fifth sample, which are insulated wires 1 without cracks on the surface of the insulating coating layer 11, to show that there is a correlation between the average crystallinity of the insulating coating layer and its fracture resistance. The third, fourth, and fifth samples in this embodiment are the same as the third, fourth, and fifth samples in the second embodiment described above.

[0097] In this embodiment, the integrated intensities of the first peak P1 and the second peak P2 are respectively defined as the intensity I of the first peak P1. b , the intensity of the second peak P2 t In addition, in this embodiment, the same polyethylene is used (i.e., N in Equation 1). c To compare the average crystallinity between the insulating coating layers 11 of the third sample, the fourth sample, and the fifth sample (where the values ​​are equal), for convenience, N c Treat it as 1.

[0098] The measurement conditions for the Raman mapping measurement of the insulating coating layer 11 in this embodiment are the same as the measurement conditions for the Raman mapping measurement used in the embodiment of the second embodiment described above.

[0099] Figure 25(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the third sample, and Figure 25(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 25(a). The two Raman spectra shown in Figure 25(b) were measured at measurement positions K1 and K2, indicated by cross marks in Figure 25(a).

[0100] Figure 26(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the third sample, showing the portion opposite to the portion shown in Figure 25(a) with respect to the central axis of the insulated wire 1. Figure 26(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 26(a). The two Raman spectra shown in Figure 26(b) were measured at measurement positions L1 and L2, indicated by cross marks in Figure 26(a).

[0101] Figure 27(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the fourth sample, and Figure 27(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 27(a). The two Raman spectra shown in Figure 27(b) were measured at measurement positions M1 and M2, indicated by cross marks in Figure 27(a).

[0102] Figure 28(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the fourth sample, showing the portion opposite to the portion shown in Figure 27(a) with respect to the central axis of the insulated wire 1. Figure 28(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 28(a). The two Raman spectra shown in Figure 28(b) were measured at measurement positions N1 and N2, indicated by cross marks in Figure 28(a).

[0103] Figure 29(a) is an optical microscope image of a portion of the radial cross-section of the insulating coating layer 11 of the fifth sample, and Figure 29(b) shows an example of a Raman spectrum obtained by Raman scattering measurement of the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 29(a). The two Raman spectra shown in Figure 29(b) were measured at measurement positions O1 and O2, indicated by cross marks in Figure 29(a).

[0104] Figure 30(a) is an optical microscope image of the radial cross-section of the insulating coating layer 11 of the fifth sample, showing the portion opposite to the portion shown in Figure 29(a) with respect to the central axis of the insulated wire 1. Figure 30(b) shows an example of a Raman spectrum obtained by Raman scattering measurement on the portion of the radial cross-section of the insulating coating layer 11 shown in Figure 30(a). The two Raman spectra shown in Figure 30(b) were measured at measurement positions P1 and P2, indicated by cross marks in Figure 30(a).

[0105] The Raman spectra shown in Figures 25(b), 26(b), 27(b), 28(b), 29(b), and 30(b) include a first peak P1 attributed to the CH bending vibration of polyethylene and a second peak P2 attributed to the CH torsional vibration of polyethylene.

[0106] Measurement positions K1, L1, M1, N1, O1, and P1 are examples of positions where the intensity of the first peak P1 in the radial cross-section of the insulating coating layer 11 of the third, fourth, or fifth sample is relatively large (indicating a relatively high degree of polyethylene crystallinity). On the other hand, measurement positions K2, L2, M2, N2, O2, and P2 are examples of positions where the intensity of the first peak P1 in the radial cross-section of the insulating coating layer 11 of the third, fourth, or fifth sample is relatively small (indicating a relatively low degree of polyethylene crystallinity).

[0107] Figures 31(a) and 32(a) are mapping images of the third sample formed on the optical microscope images of Figures 25(a) and 26(a), respectively. Figures 33(a) and 34(a) are mapping images of the fourth sample formed on the optical microscope images of Figures 27(a) and 28(a), respectively. Figures 35(a) and 36(a) are mapping images of the fifth sample formed on the optical microscope images of Figures 29(a) and 30(a), respectively.

[0108] Each pixel in the mapping images in Figures 31(a), 32(a), 33(a), 34(a), 35(a), and 36(a) has a crystallinity α obtained from the Raman spectrum measured at that location. c(Intensity of the first peak P1 I b / Intensity of the second peak P2 I t ) contains data, and each pixel has a crystallinity α c Each has a corresponding color.

[0109] Figures 31(b) and 32(b) show the degree of crystallinity α contained in each pixel of the mapping image of the third sample shown in Figures 31(a) and 32(a), respectively. c This is a histogram showing the frequency distribution. Figures 33(b) and 34(b) show the degree of crystallinity α contained in each pixel of the mapping image of the fourth sample shown in Figures 33(a) and 34(a), respectively. c This is a histogram showing the frequency distribution. Figures 35(b) and 36(b) show the degree of crystallinity α contained in each pixel of the mapping image of the fifth sample shown in Figures 35(a) and 36(a), respectively. c This is a histogram showing the frequency distribution.

[0110] In the histograms shown in Figures 31(b), 32(b), 33(b), 34(b), 35(b), and 36(b), the degree of crystallinity α c The horizontal axis represents the 256 classes that divide the range from the minimum to the maximum value, and the vertical axis represents the frequency, which is the number of pixels in each class.

[0111] The average crystallinity of the insulating coating layer 11 in the third sample, calculated from the histograms shown in Figures 31(b) and 32(b), is 0.357 and 0.138, respectively. Similarly, the average crystallinity of the insulating coating layer 11 in the fourth sample, calculated from the histograms shown in Figures 33(b) and 34(b), is 0.054 and 0.126, respectively. Furthermore, the average crystallinity of the insulating coating layer 11 in the fifth sample, calculated from the histograms shown in Figures 35(b) and 36(b), is 0.127 and 0.224, respectively. Note that the average crystallinity may also be determined from the frequency distribution table on which the histograms are based, rather than from the histograms themselves.

[0112] Table 5 below shows the average crystallinity of the insulating coating layer 11 in the third, fourth, and fifth samples obtained by the Raman mapping measurements described above.

[0113] [Table 5]

[0114] Figure 37 is a graph of the values ​​in Table 5. Table 5 and Figure 37 show that there is a correlation between the difference in the average crystallinity of two different locations in the insulating coating layer 11 of the insulated wire 1 and the presence or absence of surface cracks due to fracture resistance. In the above example, Raman mapping measurements were performed on the radial cross-section of the insulating coating layer 11, but similar results can be obtained even if Raman mapping measurements are performed on the surface of the insulating coating layer 11. Raman mapping measurements on the surface of the insulating coating layer 11 can be performed non-destructively and non-contact on the insulating coating layer 11.

[0115] If the correlation between the difference in intensity of the first peak of two Raman spectral groups in the insulating coating layer of an insulated wire (for example, the difference in the average crystallinity of the two Raman spectral groups, i.e., the difference in the average crystallinity at two locations) and the presence or absence of cracks on the surface is obtained in advance, as shown in Table 5 and Figure 37, the fracture resistance of the insulating coating layer can be evaluated from the difference in intensity of the first peak of the two Raman spectral groups obtained by Raman mapping measurements at two locations.

[0116] (Effects of the third embodiment) According to the wire quality inspection method of the third embodiment, the fracture resistance of the insulating coating layer can be evaluated from the difference in intensity of the first peak of two Raman spectrum groups obtained by Raman mapping measurements of the surface of the insulating coating layer at two locations. Therefore, the fracture resistance of an insulating coating layer mainly composed of polyethylene can be evaluated without causing damage or contamination.

[0117] Although embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the wire quality inspection method according to the first and third embodiments described above can be applied to the quality inspection of wires equipped with an insulating coating layer mainly composed of polypropylene to evaluate the shrink-back deformation rate and break resistance of the insulating coating layer. In that case, in the evaluation step, instead of the peak attributed to the CH bending vibration of polyethylene, the peak attributed to the CC stretching vibration of polypropylene is used as the first peak. The peak attributed to the CC stretching vibration of polypropylene is the 808 cm⁻¹ peak of the Raman spectrum of the insulating coating layer. -1 This is a nearby peak. Furthermore, as a second peak for normalizing the first peak, instead of the peak attributed to the CH torsional vibration of polyethylene, the peak attributed to the CH lateral vibration of polypropylene can be used. The peak attributed to the CH lateral vibration of polypropylene is at 840 cm⁻¹ in the Raman spectrum of the insulating coating layer. -1 This is a peak located in the vicinity. Other specific means and effects are the same as those described in the first and third embodiments above.

[0118] Furthermore, for example, the Raman spectrometer used for Raman mapping measurement in the wire quality inspection method according to the first to third embodiments described above may be connected to an evaluation device for performing an evaluation step to evaluate the shrink-back deformation rate or fracture resistance of the insulating coating layer. This evaluation device is, for example, a personal computer that stores a program for performing the evaluation step (e.g., derivation of the shrink-back deformation rate or fracture resistance from the mapping image) in its storage. In other words, according to this embodiment, it is possible to provide an evaluation device that can be connected to a Raman spectrometer capable of performing the measurement step in the wire quality inspection method, and that can perform the evaluation step in the wire quality inspection method.

[0119] Furthermore, according to the first to third embodiments described above, the measurement process using a Raman spectrometer and the evaluation process using the evaluation device can be performed non-destructively and non-contactually on the insulating coating layer of the electric wire. Therefore, an extrusion molding system for insulating coating layers that enables in-line evaluation of the shrinkback deformation rate or break resistance of the insulating coating layer is provided, comprising an extruder that extrudes insulating material to form an insulating coating layer around a conductor or the like, and the above-described Raman spectrometer and evaluation device that perform inspections on the formed insulating coating layer according to the electric wire quality inspection method of this embodiment.

[0120] Furthermore, the embodiments described above do not limit the invention as defined in the claims. It should also be noted that not all combinations of features described in the embodiments are necessarily essential for solving the problem of the invention.

[0121] (Summary of the embodiments) Next, the technical concept understood from the embodiments described above will be described using the reference numerals and other symbols from the embodiments. However, the reference numerals and other symbols in the following description are not limited to the components in the claims that are specifically shown in the embodiments.

[0122] [1] A method for inspecting the quality of an electric wire (1) comprising an insulating coating layer (11) mainly composed of polyethylene or polypropylene, comprising: a measurement step of performing Raman mapping measurement on the surface of the insulating coating layer (11) to obtain a group of Raman spectra; and an evaluation step of evaluating the shrinkback deformation rate of the insulating coating layer (11) based on the intensity of a first peak in the group of Raman spectra that is attributed to the CH bending vibration of the polyethylene or the CC stretching vibration of the polypropylene.

[0123] [2] The method for inspecting the quality of an electric wire (1) according to [1] above, wherein in the evaluation step, the shrinkback deformation rate of the insulating coating layer (11) is evaluated based on the mean value of the frequency distribution of the intensity of the first peak in the Raman spectrum group.

[0124] [3] The method for inspecting the quality of an electric wire (1) as described in [1] or [2] above, wherein the intensity of the first peak is normalized by the intensity of a second peak attributed to the CH torsional vibration of the polyethylene or the CH lateral oscillation vibration of the polypropylene.

[0125] [4] A method for inspecting the quality of an electric wire (1) having an insulating coating layer (11) mainly composed of polyethylene, comprising: a measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer (11) to obtain two Raman spectrum groups; and an evaluation step of evaluating the fracture resistance of the insulating coating layer (11) based on the difference in the position of a third peak in the two Raman spectrum groups that is attributed to the CC symmetric stretching vibration of the polyethylene.

[0126] [5] The method for inspecting the quality of an electric wire (1) according to [4] above, wherein in the evaluation step, the fracture resistance of the insulating coating layer (11) is evaluated based on the difference in the mean values ​​of the frequency distribution of the positions of the third peak of the two Raman spectrum groups.

[0127] [6] A method for inspecting the quality of an electric wire (1) having an insulating coating layer (11) mainly composed of polyethylene or polypropylene, comprising: a measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer (11) to obtain two Raman spectrum groups; and an evaluation step of evaluating the fracture resistance of the insulating coating layer (11) based on the difference in intensity of a first peak attributed to the CH bending vibration of the polyethylene or the CC stretching vibration of the polypropylene in the two Raman spectrum groups.

[0128] [7] The method for inspecting the quality of an electric wire (1) according to [6] above, wherein in the evaluation step, the fracture resistance of the insulating coating layer (11) is evaluated based on the difference in the mean values ​​of the frequency distribution of the intensity of the first peak of the two Raman spectrum groups.

[0129] [8] The method for inspecting the quality of an electric wire (1) as described in [6] or [7] above, wherein the intensity of the first peak is normalized by the intensity of a second peak attributed to the CH torsional vibration of the polyethylene or the CH lateral oscillation vibration of the polypropylene. [Explanation of Symbols]

[0130] 1 electric wire 10 Conductors 11. Insulating coating layer

Claims

1. A method for inspecting the quality of electric wires having an insulating coating layer mainly composed of polyethylene or polypropylene, A measurement step of performing Raman mapping measurements on the surface of the insulating coating layer to obtain a group of Raman spectra, An evaluation step of evaluating the shrinkback deformation rate of the insulating coating layer based on the intensity of a first peak in the Raman spectrum group that is attributed to the C-H bending vibration of the polyethylene or the C-C stretching vibration of the polypropylene, A method for inspecting the quality of electric wires, including the method described above.

2. In the evaluation step, the shrinkback deformation rate of the insulating coating layer is evaluated based on the average value of the frequency distribution of the intensity of the first peak in the Raman spectrum group. The method for inspecting the quality of electric wires according to claim 1.

3. The intensity of the first peak is normalized by the intensity of the second peak, which is attributed to the C-H torsional vibration of the polyethylene or the C-H lateral oscillation vibration of the polypropylene. A method for inspecting the quality of electric wires according to claim 1 or 2.

4. A method for inspecting the quality of electric wires having an insulating coating layer mainly composed of polyethylene, A measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer to obtain two groups of Raman spectra, An evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in the position of the third peak attributed to the C-C symmetric stretching vibration of the polyethylene in the two Raman spectrum groups, A method for inspecting the quality of electric wires, including the method described above.

5. In the evaluation step, the fracture resistance of the insulating coating layer is evaluated based on the difference in the mean values ​​of the frequency distributions of the positions of the third peaks of the two Raman spectrum groups. The method for inspecting the quality of electric wires according to claim 4.

6. A method for inspecting the quality of electric wires having an insulating coating layer mainly composed of polyethylene or polypropylene, A measurement step of performing Raman mapping measurements at two locations on the surface of the insulating coating layer to obtain two groups of Raman spectra, An evaluation step of evaluating the fracture resistance of the insulating coating layer based on the difference in intensity of the first peaks in the two Raman spectrum groups that are attributed to the C-H bending vibration of the polyethylene or the C-C stretching vibration of the polypropylene, A method for inspecting the quality of electric wires, including the method described above.

7. In the evaluation step, the fracture resistance of the insulating coating layer is evaluated based on the difference in the mean values ​​of the frequency distributions of the intensity of the first peak of the two Raman spectrum groups. The method for inspecting the quality of electric wires according to claim 6.

8. The intensity of the first peak is normalized by the intensity of the second peak, which is attributed to the C-H torsional vibration of the polyethylene or the C-H lateral oscillation vibration of the polypropylene. The method for inspecting the quality of electric wires according to claim 6 or 7.

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