Insulated wires and multi-core cables

Abstract

To provide insulated wires and multi-core cables that are small in diameter and have high adhesion between the conductor and the insulator. [Solution] The insulated wire 1 comprises a conductor 2 and an insulator 3 that surrounds the conductor 2. The insulator 3 is made of foamed resin, and the conductor 2 has a circular cross-sectional shape perpendicular to its longitudinal direction, with slits 6 formed on its surface along the radial direction, and the insulator 3 is inserted into at least a part of the slits 6.

Description

TECHNICAL FIELD

[0001] The present invention relates to an insulated wire and a multi-core cable.

BACKGROUND ART

[0002] A probe cable used in an ultrasonic diagnostic apparatus is configured by bundling a large number of coaxial wires, for example, several hundreds of coaxial wires. Therefore, the probe cable tends to be thick and heavy. Accordingly, there is a demand for a probe cable that is as thin and light as possible for easy handling, and the coaxial wires included in the probe cable are also required to be as thin and light as possible.

[0003] In an insulated wire including a coaxial wire, as a means for reducing the diameter while maintaining signal quality, forming an insulator from a foamed resin may be mentioned (for example, see Patent Document 1). Further, as a means for further reducing the diameter of the coaxial wire, using a single solid wire conductor as the conductor may be mentioned.

PRIOR ART DOCUMENTS

PATENT DOCUMENTS

[0004]

PATENT DOCUMENT 1

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] However, when an insulator made of a foamed resin is provided around a conductor formed of a single solid wire, there is a problem that the adhesion (bond strength) between the conductor and the insulator decreases. When the adhesion between the conductor and the insulator decreases, problems such as unintended protrusion of the conductor from the insulator occur, which makes handling difficult during terminal processing and the like.

[0006] Accordingly, an object of the present invention is to provide an insulated wire and a multi-core cable that have a small diameter and high adhesion between a conductor and an insulator.

MEANS FOR SOLVING THE PROBLEMS

[0007] The present invention aims to solve the above problems and provides an insulated wire comprising a conductor and an insulator covering the conductor, wherein the insulator is made of foamed resin, the conductor has a circular cross-sectional shape perpendicular to the longitudinal direction, and slits are formed on its surface along the radial direction, with the insulator fitting into at least a part of the slits.

[0008] Furthermore, the present invention aims to solve the above problems by providing a multi-core cable comprising a cable core containing a plurality of insulated wires and a sheath that covers the periphery of the cable core collectively. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide insulated wires and multi-core cables that are small in diameter and have high adhesion between the conductor and the insulator. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of an insulated electric wire according to one embodiment of the present invention. [Figure 2] This is a cross-sectional view showing a section perpendicular to the longitudinal direction of the conductor. [Figure 3] This is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of a multi-core cable according to one embodiment of the present invention. [Figure 4] (a) is a diagram showing the relationship between the outer diameter and conductor resistance of the examples and comparative examples, and (b) is a diagram showing the relationship between the outer diameter and attenuation of the examples and comparative examples. [Modes for carrying out the invention]

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

[0012] Figure 1 is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of an insulated wire 1 according to this embodiment. As shown in Figure 1, the insulated wire 1 is a coaxial wire comprising a conductor 2, an insulator 3 covering the conductor 2, a skin layer 7 covering the insulator 3, a shield layer 4 covering the skin layer 7, and a jacket layer 5 covering the shield layer 4.

[0013] (Request for reducing the diameter of insulated wire 1) Insulated wire 1 is used, for example, in medical probe cables. More specifically, insulated wire 1 is used as a probe cable for an ultrasound imaging device. In this case, each pixel element of the display device that shows the image of the ultrasound imaging device is connected to an insulated wire 1. Therefore, in order to increase the number of image elements and improve the image resolution, more insulated wires 1 are required, for example, a bundle of several hundred insulated wires 1 may be needed.

[0014] On the other hand, since the probe cable, which is composed of insulated wires 1, is applied to various parts of the patient's body by the examiner, for example, flexibility is also required of the insulated wires 1 that make up the probe cable. For this reason, there is a strong desire for the insulated wires 1 used in probe cables to be made thinner in order to increase both flexibility and wire density.

[0015] In order to reduce the diameter of the insulated wire 1, it has been considered to change the structure of the conductor 2 from a stranded wire structure to a single-wire structure. Furthermore, in order to improve the transmission characteristics of the insulated wire 1, it has been required to reduce the dielectric constant by constructing the insulator 3 from foamed resin and thereby reduce the capacitance of the insulated wire 1. However, when the conductor 2 is made into a single-wire structure, there is a problem that the adhesion between the single-wire conductor 2 and the insulator 3 is reduced when the insulator 3 is made from foamed resin.

[0016] In particular, when the outer diameter of the conductor 2 is extremely thin at 0.127 mm or less, the size of the bubbles 3a relative to the conductor 2 becomes relatively large, so that large voids are generated between the conductor 2 and the insulator 3, and adhesion tends to decrease. As described above, when the conductor 2 has a single-wire structure, there is a problem that it is difficult to achieve both reduction of electrostatic capacitance and improvement of adhesion between the conductor 2 and the insulator 3. Note that if the adhesion between the conductor 2 and the insulator 3 is low, the possibility of occurrence of a defect called "protrusion" in which only the conductor 2 protrudes from the terminal during terminal processing or when the insulated wire 1 is bent increases, making the insulated wire 1 difficult to handle.

[0017] The present invention has been made in view of the above circumstances, and aims to realize an insulated wire 1 that can be made as thin as in the case where the conductor 2 has a single-wire structure, and that has high adhesion between the conductor 2 and the insulator 3 even when the insulator 3 is made of a foamed resin. Hereinafter, each part of the insulated wire 1 will be described in detail.

[0018] (Conductor 2) The conductor 2 is composed of a compressed conductor 100 obtained by compressing a stranded wire formed by stranding a plurality of (here, 7) metal element wires 2a to have a substantially circular cross-sectional shape. Details of the compressed conductor 100 will be described later. By using the compressed conductor 100 for the conductor 2, the outer diameter of the conductor can be reduced to the same level as that of a single-wire structure while maintaining a large conductor cross-sectional area, which contributes to reducing the diameter of the insulated wire 1. The outer diameter of the conductor 2 is extremely thin at 0.127 mm or less (that is, thinner than 36 AWG). More preferably, the outer diameter of the conductor 2 is 0.080 mm or less.

[0019] Further, by using the compressed conductor 100 for the conductor 2, the contact area between adjacent metal element wires 2a increases and the contact resistance decreases, so that the conductivity of the conductor 2 can be improved, and transmission characteristics can be enhanced. Furthermore, by using the compressed conductor 100 for the conductor 2, it is also possible to allow the insulator 3 to enter between the metal element wires 2a, thereby increasing the adhesion between the conductor 2 and the insulator 3. Details on this point will be described later.

[0020] (Insulator 3) The insulator 3 is made of a foamed resin. The foamed resin used for the insulator 3 is preferably made of any one of foamed PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), foamed FEP (tetrafluoroethylene-hexafluoropropylene copolymer), foamed PE (polyethylene), and foamed PP (polypropylene). In particular, it is more desirable to use foamed PFA, which is excellent in heat resistance and chemical resistance and can withstand sterilization treatment at high temperatures, as the foamed resin.

[0021] Bubbles 3a are formed inside the insulator 3. The presence of the bubbles 3a reduces the dielectric constant of the insulator 3, so that the electrostatic capacitance of the insulated wire 1 can be reduced. Relatively large bubbles 3a are formed around the conductor 2, and fine bubbles 3a are formed in the periphery thereof.

[0022] (Skin Layer 7) Around the insulator 3, a skin layer 7 is formed by spirally winding a resin tape. As the resin tape, for example, a polyester tape can be used.

[0023] (Shield Layer 4) The shield layer 4 is composed of a horizontally wound shield in which a plurality of metal element wires 4a are spirally wound around the skin layer 7. With this configuration, the horizontally wound shield deforms in response to an operation such as bending, so that the resistance to mechanical stress such as bending can be improved. In addition, compared with the case where a braided shield or the like is used as the shield layer 4, the shield layer 4 can be made thin to reduce the diameter of the insulated wire 1. As the metal element wires 4a constituting the shield layer 4, it is preferable to use silver-plated copper alloy wires having high conductivity and high mechanical strength.

[0024] (Jacket Layer 5) The jacket layer 5 is configured by spirally winding a resin tape around the shield layer 4. Here, a polyester tape having a thickness of 0.015 mm was used as the resin tape. The outer diameter of the jacket layer 5, that is, the outer diameter of the insulated wire 1, is 0.30 mm or less.

[0025] (Compressed Conductor 100) Figure 2 is a cross-sectional view showing a section perpendicular to the longitudinal direction of the compression conductor 100 (conductor 2). As shown in Figure 2, the compression conductor 100 comprises a first metal part 101 and a second metal part 102, which are made of different metallic materials. The second metal part 102 is made of a metal with higher conductivity than the first metal part 101. In this embodiment, the first metal part 101 is made of a copper alloy, and the second metal part 102 is made of silver.

[0026] This configuration ensures high adhesion between the copper alloy and silver, making delamination less likely during compression and reducing the likelihood of wire breakage caused by delamination. Furthermore, because silver has high conductivity, using it as the second metal part 102 offers the advantage of significantly improving the transmission characteristics (attenuation characteristics) of the compressed conductor 100.

[0027] In this embodiment, a copper alloy containing silver was used as the first metal part 101. In this case, a copper alloy containing 2 mass% silver was used.

[0028] This configuration makes it less prone to breakage even when the diameter is reduced, while also maintaining a sufficiently high conductivity (for example, around 80%).

[0029] Furthermore, in this embodiment, the copper that forms the base of the copper alloy constituting the first metal part 101 is pure copper such as oxygen-free copper with a purity of 99.99% or higher.

[0030] This configuration reduces the amount of impurities in the copper alloy, making it less likely for the first metal part 101 to break when stretched during compression, thus reducing the chance of breakage caused by impurities. As a result, even when using a hard copper alloy, breakage during compression is less likely, making it possible to form a very thin compression conductor 100 using a hard copper alloy. Consequently, a compression conductor 100 with high tensile strength despite its very small diameter can be realized, improving resistance to mechanical stress.

[0031] The first metal part 101 has a central part 101a located at the center of the conductor, and a plurality of peripheral parts 101b twisted spirally around the central part 101a. Here, six peripheral parts 101b are arranged around one central part 101a. The central part 101a has a roughly hexagonal shape in a cross-sectional view perpendicular to the longitudinal direction (hereinafter simply referred to as a cross-sectional view), and each peripheral part 101b is formed in a roughly fan shape extending radially outward from the six sides of the central part 101a. The central part 101a and each peripheral part 101b are fitted together to form a circular cross-section as a whole.

[0032] The second metal part 102 covers the central part 101a and each of the multiple (in this case, six) peripheral parts 101b. The central part 101a and the multiple peripheral parts 101b, as well as adjacent peripheral parts 101b in the circumferential direction, are in contact with each other with the second metal part 102 in between.

[0033] This configuration results in a structure where the second metal part 102, which has higher conductivity, is filled in a slit-like manner between the first metal parts 101. As a result, the overall conductivity of the compressed conductor 100 is improved, and the transmission characteristics are enhanced. For example, even when transmitting high-frequency signals where the skin effect is present, the transmission characteristics are less likely to deteriorate due to the presence of the highly conductive second metal part 102. Furthermore, because the first metal part 101 is covered by the second metal part 102, wire breakage is less likely to occur during the compression process described later, making it easier to manufacture even when the diameter is reduced.

[0034] The compressed conductor 100 is constructed using seven metal strands 103 (metal strands 2a) in which a second metal part 102 covers a first metal part 101. In other words, the second metal part 102 is a plating layer that covers the periphery of the first metal part 101. In this embodiment, a silver-plated copper alloy wire is used as the metal strand 103 (metal strand 2a), in which a second metal part 102 made of silver plating is provided around a first metal part 101 made of copper alloy.

[0035] When manufacturing the compressed conductor 100, first, seven metal strands 103 are concentrically twisted together, and the resulting strand is subjected to a very short heat treatment (for example, at a temperature of 300°C and a wire speed of 80 m / min). Then, the strand is passed through a die and compressed. The heat treatment before compression is performed to make the metal strands 103 more flexible and to reduce the likelihood of breakage during the compression process. The heat treatment is performed for a very short time so as not to reduce the tensile strength too much. In this embodiment, no heat treatment is performed after the compression process. As a result, the metal strands 103 (metal strands 2a) of the compressed conductor 100 (conductor 2) become more likely to unravel during the extrusion molding of the insulator 3, and resin can easily get between the unraveled metal strands 103 (metal strands 2a), improving the adhesion between the compressed conductor 100 (conductor 2) and the insulator 3.

[0036] Furthermore, by not performing heat treatment after the compression process, a decrease in tensile strength due to annealing does not occur, resulting in a high-strength compressed conductor 100 with a tensile strength of 800 MPa or more, more preferably 900 MPa or more. As a result, an insulated wire 1 is obtained that is small in diameter yet highly resistant to mechanical stress such as bending.

[0037] Furthermore, if a metal wire 103 consisting only of the first metal part 101 without the second metal part 102 is used, an oxide film will form on the surface of the first metal part 101 during the heat treatment before compression. This oxide film will reduce the conductivity of the compressed conductor 100 and also degrade its appearance. In addition, if a metal wire 103 consisting only of the first metal part 101 is used, scratches may occur on the surface of the metal wire 103 due to friction with the die during the compression process, making it easier for the wire to break starting from these scratches. In contrast, in this embodiment, a metal wire 103 with the second metal part 102 covering the first metal part 101 is used, so there is no risk of an oxide film forming during heat treatment, and a good appearance can be maintained. Also, during the compression process, the second metal part 102 acts as a protective layer to protect the surface of the first metal part 101, making it less likely for the wire to break.

[0038] Furthermore, in the compressed conductor 100, the ratio of the cross-sectional area occupied by the second metal part 102 to the total cross-sectional area in a cross-section perpendicular to the longitudinal direction should be 10% or more. This increases the proportion of the second metal part 102, which has high conductivity, thereby improving the overall conductivity of the compressed conductor 100 and enhancing its transmission characteristics.

[0039] In this embodiment, when forming a very small diameter compressible conductor 100, the ratio of the cross-sectional areas of the first metal part 101 and the second metal part 102 changes before and after the compression process. Specifically, the ratio of the cross-sectional area occupied by the second metal part 102 to the total cross-sectional area becomes larger after the compression process than before the compression process (i.e., the ratio of the cross-sectional area occupied by the first metal part 101 to the total cross-sectional area becomes smaller). This is thought to be because, during the compression process, when the conductor is stretched and compressed through the die, the relatively hard first metal part 101, where stress is more concentrated, is stretched more than the relatively soft second metal part 102.

[0040] Furthermore, in the compression conductor 100, the cross-sectional area of ​​the central part 101a in the first metal part 101 is smaller than the average value of the cross-sectional areas of the multiple surrounding parts 101b. This is thought to be because the compressive stress is concentrated in the central part 101a. The cross-sectional area of ​​the central part 101a should be between 92% and 95% of the average value of the cross-sectional areas of the multiple surrounding parts 101b.

[0041] Furthermore, if the proportion of the second metal part 102, which is the plating layer, becomes too large, it may lead to a decrease in mechanical strength. Therefore, in a cross-section perpendicular to the longitudinal direction, the ratio of the cross-sectional area occupied by the second metal part 102 to the total cross-sectional area should be 15% or less.

[0042] Furthermore, in this embodiment, the thickness of the second metal portion 102 is greater than the thickness of the outer surface of the compression conductor 100 (conductor outer surface) at least between the multiple peripheral portions 101b. This is because there are two layers of the second metal portion 102 between the peripheral portions 101b, while there is only one layer of the second metal portion 102 on the outer surface of the compression conductor 100.

[0043] (Regarding improving the adhesion between conductor 2 and insulator 3) In the insulated wire 1 according to this embodiment, the conductor 2 has a substantially circular cross-sectional shape perpendicular to its longitudinal direction, and a slit 6 is formed on its surface along the radial direction, with the insulator 3 entering into at least a portion of the slit 6. The length of the slit 6 along the radial direction should be 30% or more, more preferably 50% or more, of the radius of the conductor 2, because if it is too short, it may be difficult for the resin to enter.

[0044] The insulator 3 entering the slit 6 improves the adhesion between the conductor 2 and the insulator 3, even when foamed resin is used as the insulator 3. The entry of the insulator 3 into the slit 6 does not need to be continuous along the longitudinal direction of the insulated wire 1; for example, entry of the insulator 3 into the slit 6 may occur at multiple spaced positions along the longitudinal direction of the insulated wire 1. However, to improve the adhesion between the conductor 2 and the insulator 3, it is desirable that the insulator 3 enters the slit 6 as continuously as possible along the longitudinal direction of the insulated wire 1.

[0045] In this embodiment, the conductor 2 is made of a compressed conductor 100, and the slit 6 is formed between the second metal parts 102 that cover the peripheral portion 101b of the compressed conductor 100. In other words, the slit 6 consists of a gap formed between the metal strands 2a (metal strands 103). Since the metal strands 2a are twisted together, the slit 6 is formed spirally along the longitudinal direction of the insulated wire 1. As a result, the insulator 3 is less likely to move longitudinally relative to the conductor 2, and thus the adhesion between the conductor 2 and the insulator 3 can be further improved compared to, for example, the case where the slit 6 is formed linearly along the longitudinal direction of the conductor 2.

[0046] In this embodiment, slits 6 are formed by separating some of the metal strands 2a of the conductor 2 from other metal strands 2a. More specifically, some of the metal strands 2a constituting the conductor 2 protrude slightly radially outward. Therefore, the conductor 2 is slightly deformed from a perfect circular shape, but maintains a circular shape overall. The number of slits 6 formed in the conductor 2 should be between two and four. If there is only one slit 6, sufficient adhesion between the conductor 2 and the insulator 3 may not be obtained, and if there are five or more slits 6, the metal strands 2a may spread out too much, reducing the contact area between the metal strands 2a, which may degrade the transmission characteristics.

[0047] More specifically, during the extrusion molding of the insulator 3, the flow of the resin slightly unravels the twist of the metal wires 2a, and the resin enters the resulting slits 6. At this time, by using a compressed conductor 100 that has not undergone heat treatment after compression as the conductor 2, the twist of the conductor 2 becomes easier to unravel, and the resin enters the slits 6 more easily. If the twist of the conductor 2 unravels too much, that is, if the conductor 2 becomes too scattered (if the number of slits 6 becomes too large), the twist pitch of the conductor 2 can be adjusted to be smaller. The twist pitch of the conductor 2 is the distance that the metal wires 2a travel along the longitudinal direction of the insulated wire 1 while making one rotation in the circumferential direction of the insulated wire 1.

[0048] It is not necessary for the entire slit 6 to be filled with the insulator 3; there may be parts of the slit 6 that are not filled with the insulator 3. When a seven-strand compressed conductor 100 is used as the conductor 2 as in this embodiment, it is desirable that the insulator 3 does not come into contact with the metal strands 2a located in the center (the central part 101a and the second metal part 102 surrounding it). This is because if the insulator 3 penetrates to the point of contacting the metal strands 2a located in the center, the metal strands 2a will be too scattered, which may lead to a deterioration of the transmission characteristics.

[0049] (modified version) In this embodiment, the case in which a compressed conductor 100 is used as conductor 2 has been described, but it is not limited to this, and for example, a single-wire conductor with slits 6 formed by laser processing or the like may be used as the conductor. However, in this case, the mechanical strength of the single-wire conductor used as conductor 2 may decrease, so it is more desirable to use a compressed conductor 100 as conductor 2.

[0050] Furthermore, the shield layer 4 and jacket layer 5 are not mandatory and can be omitted.

[0051] (Multi-core cable 10) Figure 3 is a cross-sectional view showing a cross-section perpendicular to the longitudinal direction of the multi-core cable 10 according to this embodiment. The multi-core cable 10 is, for example, a probe cable for an ultrasonic imaging device.

[0052] As shown in Figure 3, the multi-core cable 10 comprises a cable core 11 containing multiple insulated wires 1, a single shield layer 12 covering the cable core 11, and a sheath 13 covering the single shield layer 12. The number of insulated wires 1 contained in the cable core 11 is preferably four or more. More specifically, the number of insulated wires 1 contained in the cable core 11 is, for example, 10 to 300. The single shield layer 12 consists of, for example, a braided shield made of braided metal wires. The sheath 13 is made of, for example, PVC (polyvinyl chloride).

[0053] Because the multi-core cable 10 uses a small-diameter insulated wire 1, it is small in diameter, lightweight, and easy to handle. In addition, because the adhesion between the conductor 2 and the insulator 3 in the insulated wire 1 is high, unintended protrusion of the conductor 2 is less likely to occur, making terminal processing and connection work easy.

[0054] (Evaluation of adhesion, etc.) Insulated wires 1 of four different examples with varying conductor cross-sectional areas were fabricated, and their bond strength and protrusion were evaluated. The conductor 2 used a compressed conductor 100, which was made by twisting together and compressing seven silver-plated copper alloy wires 2a. The insulator 3 was made of foamed PFA, and a skin layer 7 was formed by spirally wrapping polyester tape around it. The shield layer 4 was a horizontally wound shield, in which metal wires 4a made of silver-plated copper alloy wire were spirally wrapped around the skin layer 7. The jacket layer 5 was constructed by spirally wrapping polyester tape around the shield layer 4.

[0055] Bond strength was evaluated by removing the skin layer 7, shield layer 4, and jacket layer 5, then making a circumferential cut in the insulator 3 50 mm from the terminal, and measuring the load when the insulator 3 was pulled out longitudinally. A larger load indicates a higher adhesion between the conductor 2 and the insulator 3.

[0056] The protrusion was evaluated by removing the skin layer 7, shield layer 4, and jacket layer 5, then clean-cutting the terminal portion and checking whether the conductor 2 protruded from the end of the insulator 3. It should be noted that the absence of protrusion indicates a higher adhesion between the conductor 2 and the insulator 3.

[0057] Furthermore, for the insulated wire 1 of Examples 1 to 4, the conductor resistance of conductor 2, the characteristic impedance at a frequency of 10 MHz, the capacitance at a frequency of 1 kHz, and the attenuation at a frequency of 10 MHz were measured, respectively.

[0058] Furthermore, for comparison with Examples 1-4 of the present invention, Comparative Example 1, in which conductor 2 was a single-wire conductor, and Comparative Examples 2 and 3, in which conductor 2 was an uncompressed stranded conductor, were also evaluated in the same manner. The sizes of each part of Examples 1-4 and Comparative Examples 1-3, along with the various evaluation results and measurement results, are summarized in Table 1.

[0059] [Table 1]

[0060] As shown in Table 1, in Examples 1 to 4, the bond strength was sufficiently high at 0.3 N / 50 mm or more, and it was confirmed that sufficient adhesion was obtained between the conductor 2 and the insulator 3 without any protrusion. In contrast, in Comparative Example 1, which used a single-wire conductor, no bond strength was observed, and protrusion occurred, confirming that sufficient adhesion was not obtained between the conductor 2 and the insulator 3. In Comparative Examples 2 and 3, which used uncompressed stranded wire, sufficiently high bond strength was obtained, and no protrusion occurred.

[0061] Here, the relationship between outer diameter and conductor resistance is shown in Figure 4(a), and the relationship between outer diameter and attenuation is shown in Figure 4(b) for Examples 1-4 and Comparative Examples 2 and 3. As shown in Figures 4(a) and (b), when comparing the examples with the comparative examples, it can be seen that even with the same outer diameter, the conductor resistance and attenuation are smaller. More specifically, although Example 2 and Comparative Example 2 have the same outer diameter of 0.234 mm and the same AWG size of conductor 2, Comparative Example 2 has higher conductor resistance and greater attenuation than Example 2. In other words, it was confirmed that in Example 2, further reduction in diameter is possible when increasing the outer diameter and attenuation to the same extent as in Comparative Example 2.

[0062] Similarly, comparing Example 3 and Comparative Example 3, the AWG size of conductor 2 is the same, and the conductor resistance and attenuation are also similar, but it can be confirmed that the outer diameter of Example 3 is smaller than that of Comparative Example 3. Thus, Examples 1 to 4 of the present invention have a better balance between outer diameter and characteristics compared to Comparative Examples 2 and 3 (that is, good characteristics are obtained even with a small diameter).

[0063] (Operation and Effects of the Embodiment) As described above, in the insulated wire 1 according to this embodiment, the insulator 3 is made of foamed resin, the conductor 2 has a circular cross-sectional shape perpendicular to the longitudinal direction, and a slit 6 is formed on its surface along the radial direction, with the insulator 3 fitting into at least a part of the slit 6. With this configuration, an insulated wire 1 can be realized that is small in diameter yet has high adhesion between the conductor 2 and the insulator 3. As a result, unintended protrusion of the conductor 2 at the end of the insulated wire 1 is suppressed, and workability such as terminal processing is improved.

[0064] (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.

[0065] [1] An insulated electric wire (1) comprising a conductor (2) and an insulator (3) covering the conductor (2), wherein the insulator (3) is made of foamed resin, the conductor (2) has a circular cross-sectional shape perpendicular to the longitudinal direction, and a slit (6) is formed on its surface along the radial direction, and the insulator (3) is inserted into at least a part of the slit (6).

[0066] [2] The conductor (2) has a central part (101a) and a plurality of peripheral parts (101b) twisted spirally around the central part (101a), and the central part (101a) and the plurality of peripheral parts (101b) are fitted together to form a first metal part (101) which has a circular cross-section as a whole, and the central part (101a) and the plurality of peripheral parts (1 The insulated wire (1) described in [1] has a second metal part (102) covering each of the 01b), and the central part (101a) and a plurality of the peripheral parts (101b), and adjacent peripheral parts (101b) are in contact with each other with the second metal part (102) in between, and the slit (6) is formed between the second metal parts (102) covering the peripheral parts (101b).

[0067] [3] The insulated wire (1) described in [1], wherein the outer diameter of the conductor (2) is 0.127 mm or less.

[0068] [4] The foamed resin is made of any of the following: foamed PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer), foamed FEP (tetrafluoroethylene-hexafluoropropylene copolymer), foamed PE (polyethylene), or foamed PP (polypropylene), as described in [1] (1).

[0069] [5] The insulated wire (1) according to [1], wherein the length of the slit (6) along the radial direction is 30% or more of the radius of the conductor (2).

[0070] [6] The insulated wire (1) according to [1], further comprising a shield layer (4) covering the periphery of the insulator (3), and a jacket layer (5) covering the periphery of the shield layer (4).

[0071] A multi-core cable (10) comprising a cable core (11) containing a plurality of insulated wires (1) as described in any one of items [7][1] to [6], and a sheath (13) that covers the cable core (11) collectively.

[0072] (Note) Although 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 essential for solving the problem of the invention. In addition, the present invention can be implemented with appropriate modifications without departing from its spirit. [Explanation of Symbols]

[0073] 1…Insulated wire 2... Conductor 2a…metal wire 3…Insulator 3a... air bubbles 4…Shield layer 4a…metal wire 5…Jacket layer 6…Slit 7…Skin layer 10… Multi-core cable 11… Cable core 12... Unified Shield Layer 13...Sheath 100... Compression conductor 101...First metal part 101a…center 101b... Peripheral area 102…Second metal part

Claims

1. A conductor and The conductor comprises an insulator covering the periphery of the conductor, The aforementioned insulator is made of foamed resin, The conductor has a circular cross-sectional shape perpendicular to its longitudinal direction, and a slit is formed on its surface along the radial direction. The insulator is inserted into at least a portion of the slit. Insulated wire.

2. The aforementioned conductor is A first metal part having a central part and a plurality of peripheral parts twisted spirally around the central part, wherein the central part and the plurality of peripheral parts are fitted together to form a circular cross-section as a whole, It has a second metal part made of a metal with higher conductivity than the first metal part, and covering the central part and each of the multiple surrounding parts, The central part and the plurality of surrounding parts, and adjacent surrounding parts, are made of compression conductors that are in contact with each other with the second metal part in between. The slit is formed between the second metal parts that cover the surrounding area. The insulated wire according to claim 1.

3. The outer diameter of the conductor is 0.127 mm or less. The insulated wire according to claim 1.

4. The foamed resin consists of one of the following: foamed PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer), foamed FEP (tetrafluoroethylene / hexafluoropropylene copolymer), foamed PE (polyethylene), or foamed PP (polypropylene). The insulated wire according to claim 1.

5. The length of the slit along the radial direction is 30% or more of the radius of the conductor. The insulated wire according to claim 1.

6. A shielding layer covering the periphery of the insulator, The shield layer further comprises a jacket layer covering the periphery of the shield layer, The insulated wire according to claim 1.

7. A cable core comprising a plurality of insulated wires as described in any one of claims 1 to 6, A sheath that covers the entire periphery of the cable core, Multi-core cable.

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