Film-coated stranded wire and composite film-coated stranded wire

Abstract

The utility model discloses a film-coated stranded wire and a composite film-coated stranded wire, and relates to the technical field of insulating wires. The film covered wire comprises a wire core and a polyimide film. The wire core comprises an inner core and a polyimide paint layer arranged on the peripheral surface of the inner core, and the polyimide film is sintered on the outer surface of the polyimide paint layer. Compared with a silicon pressure-sensitive adhesive type polyimide film covered wire, a fluorine 46 type polyimide film covered wire, a polyimide enameled wire and the like in the prior art, the film covered wire provided by the utility model has higher interlayer binding power in harsh environments such as high temperature, high pressure and the like, does not peel off, has higher reliability, and can be widely applied in the field of high frequency and high pressure.

Description

Technical Field

[0001] This utility model relates to the field of insulated cable technology, and in particular to a film-coated stranded wire and a composite film-coated stranded wire. Background Technology

[0002] With the rapid development of high-end industries such as new energy vehicles, aerospace, 5G communications, industrial automation, and medical equipment, the market demand for insulated cables is increasing, especially in the field of film-coated wires. Polyimide film-coated wires, due to their high temperature resistance, high voltage resistance, and impact resistance, are increasingly in demand for small or micro equipment and high-frequency equipment. Existing related wires include silicone varnish-type polyimide film-coated wires, fluorine-46 type polyimide film-coated wires, and polyimide enameled wires, each with the following shortcomings: Silicone varnish-type polyimide film-coated wires have a high risk of peeling due to the weak adhesion between the varnish layer and the polyimide film layer; fluorine-46 type polyimide film-coated wires have poor film uniformity due to fluorine content and are not heat-resistant, with an operating temperature limited to 200℃, where deformation occurs; polyimide enameled wires experience solvent evaporation of the polyimide varnish on the surface at high temperatures, are easily broken down under high voltage, and are not resistant to bending. Utility Model Content

[0003] The main purpose of this invention is to propose a membrane-coated wire, a membrane-coated stranded wire, and a composite membrane-coated stranded wire, aiming to develop a polyimide wire with good corona resistance, high temperature resistance, and high pressure resistance. The materials between the membrane layers are similar, and after sintering, the polyimide film and the polyimide varnish layer form a whole, thus the interlayer adhesion is strong and interlayer delamination is not easy to occur.

[0004] This utility model proposes a film-coated wire, which includes a wire core and a polyimide film; the wire core includes an inner core and a polyimide varnish layer disposed on the outer peripheral surface of the inner core, and the polyimide film is sintered on the outer surface of the polyimide varnish layer.

[0005] In one embodiment, in the film-coated wire, the polyimide film is wrapped around the outer surface of the wire core, and the polyimide film is arranged in at least multiple layers.

[0006] In one embodiment, the polyimide film overlap rate in the membrane wrapping wire is 10% to 75%.

[0007] In one embodiment, the width of the polyimide film in the membrane wrapping wire is 1 mm to 50 mm.

[0008] In one embodiment, the thickness of the polyimide film in the membrane wrapping wire is 1 μm to 50 μm.

[0009] In one embodiment, the thickness of the polyimide coating is less than 20 μm.

[0010] In one embodiment, the wire core includes a single-strand inner core, the polyimide varnish is coated on the outer surface of the inner core, and the polyimide film is sintered on the outer surface of the polyimide varnish.

[0011] In one embodiment, the inner core is a metal wire, and the cross-section of the metal wire is any one of a circle, an ellipse, or a polygon.

[0012] This utility model also proposes a film-coated stranded wire, which includes a wire core and a polyimide film; the wire core includes multiple strands of inner core twisted together, and the polyimide film is sintered on the outer surface of the wire core; wherein, the inner core is a metal conductor, and the outer peripheral surface of the metal conductor is coated with a polyimide varnish layer, or, the inner core is the film-coated wire.

[0013] This utility model also proposes a composite film-coated stranded wire, which includes a core and a polyimide film; the core includes multiple strands of inner core twisted together, and the polyimide film is sintered on the outer surface of the core; wherein, the inner core is the film-coated stranded wire.

[0014] This invention includes film-coated wires with single-strand polyimide enameled wire as the core, film-coated stranded wires with multi-strand polyimide enameled wire as the core, film-coated stranded wires with multi-strand film-coated wire as the core, and composite film-coated stranded wires with multi-strand film-coated wire as the core. The polyimide enamel layer and polyimide film in the film-coated wires, film-coated stranded wires, and composite film-coated stranded wires of this invention use polyimide with a specific formulation, exhibiting good temperature resistance and insulation properties. This prevents the polyimide enamel layer from breaking or peeling off due to excessively high temperatures during sintering. Furthermore, the polyimide enamel layer and polyimide film can form a uniform whole during sintering, thereby significantly increasing the interlayer strength of the film-coated wire and preventing peeling and detachment under extreme environments such as high temperatures and strong vibrations. This results in higher reliability and insulation for the film-coated wires, film-coated stranded wires, and composite film-coated stranded wires of this invention under harsh environments such as high temperature and high pressure. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1This is a schematic diagram of the cross-sectional structure of the membrane envelope according to an embodiment of the present invention;

[0017] Figure 2 This is a schematic diagram of the cross-sectional structure of a membrane-covered stranded wire according to an embodiment of the present invention;

[0018] Figure 3 This is a schematic diagram of the cross-sectional structure of a membrane-wrapped stranded wire according to an embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the cross-sectional structure of a composite film-wrapped stranded wire according to an embodiment of the present invention.

[0020] Figure descriptions: 1. Film-coated wire; 11. Polyimide film layer; 12. Wire core; 121. Inner core; 122. Polyimide enamel layer.

[0021] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0022] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present utility model.

[0023] It should be noted that if the embodiments of this utility model involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0024] Furthermore, if the embodiments of this utility model involve descriptions such as "first" or "second," such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0025] Furthermore, the technical solutions of the various embodiments can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0026] The technical problem solved by this utility model is that there are some problems with polyimide wires in the prior art, mainly including: (1) the pressure-sensitive adhesive layer in the silicone pressure-sensitive adhesive type polyimide film-coated wire has a high risk of peeling due to the weak viscosity between the pressure-sensitive adhesive layer and the polyimide film layer; (2) the fluorine 46 type polyimide film-coated wire has poor film uniformity due to the presence of fluorine, is not resistant to high temperature, and its working temperature is limited to 200℃. It will deform if the temperature is higher than this; (3) the polyimide varnish on the surface of the polyimide enameled wire will evaporate at high temperature, and it is easily broken down under high pressure. Moreover, the polyimide enameled wire is not resistant to bending.

[0027] To address the aforementioned problems, this invention proposes a membrane-covered wire, a membrane-covered stranded wire, and a composite membrane-covered stranded wire.

[0028] This utility model proposes a membrane-covered wire, which includes a wire core and a polyimide film;

[0029] The wire core includes an inner core and a polyimide varnish layer disposed on the outer peripheral surface of the inner core, and the polyimide film is sintered on the outer surface of the polyimide varnish layer.

[0030] It should be noted that conventional polyimide enamel coatings have poor high-temperature resistance. For example, the commonly used 220-type polyimide enameled wire can only withstand temperatures up to 220°C. Above 220°C, the polyimide will decompose. However, the temperature during the sintering and curing process of film-coated wire typically reaches 400°C. Therefore, in existing film-coated wire technologies, a heat-resistant material is used to protect the polyimide enamel layer from the polyimide film layer, or other high-temperature resistant polymer materials are used as the coating for the wire core. The polyimide varnish layer and polyimide film in this invention both use polyimide with a specific formulation (see invention patent with publication number CN118027402A), which enhances the high temperature resistance of the polyimide. This prevents the polyimide varnish layer from breaking or falling off due to excessive temperature during the sintering process. Furthermore, the polyimide varnish layer and polyimide film can form a uniform whole during the sintering process, thereby significantly increasing the interlayer strength of the membrane wire and preventing the membrane wire from peeling off under extreme environments of high temperature and strong vibration.

[0031] In one embodiment, during the preparation of the film-coated wire, when the wire core is wrapped with a polyimide film, the polyimide film is wrapped around the outer surface of the wire core, and the polyimide film is wrapped in at least multiple layers; wherein, the number of overlapping strands of the polyimide film is 2 to 3 strands; it can be understood that the number of overlapping strands of the polyimide film in this embodiment can be 2 or 3 strands.

[0032] In one embodiment, during the preparation of the film-coated wire, when the polyimide film is used to wrap the wire core, the overlap rate of the polyimide film is 10% to 75%. It is understood that the overlap rate of the polyimide film in this embodiment can be any one of 10%, 20%, 50%, 60%, 65%, and 75%, including but not limited to any value within the above range, as long as it matches other parameters of the polyimide film.

[0033] It should also be noted that, in special application scenarios, the overlap rate of the polyimide film in this embodiment can be less than 10%. The overlap rate of the polyimide film in this embodiment can be any one of 1%, 2%, or 9%, including but not limited to any value within the above range, as long as it matches the other parameters of the polyimide film. Alternatively, the overlap rate of the polyimide film in this embodiment can be greater than 75%. The overlap rate of the polyimide film in this embodiment can be any one of 76%, 79%, or 99%, including but not limited to any value within the above range, as long as it matches the other parameters of the polyimide film.

[0034] In one embodiment, during the preparation of the film-coated wire, when the polyimide film is used to wrap the wire core, the width of the polyimide film is 1mm to 50mm. It can be understood that the width of the polyimide film in this embodiment is any one of 1mm, 5mm, 8mm, 14mm, 16mm, 24mm, and 50mm, including but not limited to any value within the above range, as long as it matches other parameters of the polyimide film.

[0035] In one embodiment, during the preparation of the film-coated wire, when the polyimide film is used to wrap the wire core, the single-strand thickness of the polyimide film is 1μm to 50μm. It is understood that the single-strand thickness of the polyimide film in this embodiment can be any one of 1μm, 5μm, 20μm, 25μm, 30μm, and 50μm, including but not limited to any value within the above range, as long as it matches other parameters of the polyimide film.

[0036] In one embodiment, the thickness of the polyimide enamel layer in the polyimide enameled wire is less than 20 μm. It should be noted that the thickness of the polyimide enamel layer refers to the thickness of the cured polyimide enamel layer; in ultra-precision applications, the thickness of the polyimide enamel layer can reach the nanometer level.

[0037] In one embodiment, reference is made to Figure 1The enameled wire 1 includes a wire core 12 and a polyimide film 11; the polyimide film 11 is sintered on the outer surface of the wire core 12; the wire core 12 includes a single-strand inner core 121, and the polyimide enamel layer 122 is coated on the outer surface of the inner core 121. It is understood that in this embodiment, the wire core 12 can be a polyimide enameled wire.

[0038] In one embodiment, the inner core is a metal wire, and the cross-section of the metal wire is any one of a circle, an ellipse, or a polygon.

[0039] This utility model also proposes a membrane-covered stranded wire, as shown in the reference. Figure 2 The film-coated stranded wire includes a core and a polyimide film 11; the core includes multiple strands twisted together, and the polyimide film is sintered onto the outer surface of the core; wherein, the inner core is a metal conductor, and the outer peripheral surface of the metal conductor is coated with a polyimide enamel layer; it can be understood that, in this embodiment, the inner core can be a polyimide enameled wire. It should be noted that the number of strands in the twisted wire is not limited in this embodiment.

[0040] This utility model also proposes a membrane-covered stranded wire 3, as shown in the reference. Figure 3 The film-coated stranded wire 3 includes a wire core and a polyimide film 11; the wire core includes multiple strands twisted together, and the polyimide film 11 is sintered on the outer surface of the wire core; wherein, the inner core is the film-coated wire 1. It should be noted that the number of strands of the twisted wire in this embodiment is not limited.

[0041] This utility model also proposes a composite film-coated stranded wire 4, as shown in the reference. Figure 4 The composite film-coated stranded wire 4 includes a wire core and a polyimide film 11; the wire core includes multiple strands twisted together, and the polyimide film is sintered on the outer surface of the wire core; wherein, the inner core is the film-coated stranded wire 3. It should be noted that the number of strands of the multiple twisted wires is not limited in this embodiment.

[0042] In one embodiment, another composite film-coated stranded wire is also included, the composite film-coated stranded wire comprising a core and a polyimide film 11; the core comprises multiple strands twisted together, and the polyimide film is sintered onto the outer surface of the core; wherein, the core is the film-coated stranded wire 2. It should be noted that the number of strands of the multiple strands twisted together is not limited in this embodiment.

[0043] The present invention will be further described below through specific embodiments:

[0044] It should be noted that the synthesis process and raw materials of polyimide in this utility model are directly referenced from the invention patent with publication number CN118027402A.

[0045] Example 1

[0046] Example 1 is a film-coated wire, comprising polyimide enameled wire and a polyimide film; the polyimide enameled wire includes a copper flat wire and a polyimide enamel layer, and the copper flat wire has a diameter of 0.3 mm. 0.7mm; The polyimide enamel layer and polyimide film in the polyimide enameled wire use the same polyimide precursor resin.

[0047] The preparation process of the polyimide precursor resin in Example 1 includes the following steps:

[0048] S1. Dissolve 50 mL (0.251 mol) methyltriethoxysilane in 250 mL (0.42375 mol) anhydrous ethanol, stir continuously until well mixed, then add 24 mL (1.6625 mol) deionized water and concentrated hydrochloric acid in sequence, adjust the pH value to 2, and react at a constant temperature of 80℃ for 42 h to obtain a white powder. Heat the white powder to 150℃ under a pressure of 0.06 kPa to obtain a pure trapezoidal organosilicon intermediate. At 150℃, in an oxygen atmosphere of 0.8 MPa, add 8 mg of cobalt-nickel-selenium catalyst and 1 mol of acetic acid to carry out a redox reaction and dehydrate to obtain a high molecular weight silicic anhydride.

[0049] S2, under room temperature and N2 atmosphere protection, 0.961 g of 4,4' Diaminodiphenyl ether and 1.569 g of p-aminophenyltrimethoxysilane were dissolved by stirring in 73.26 g of N,N Completely dissolve the polyimide in dimethylformamide, cool to -5°C, and add 1.7914g of pyromellitic dianhydride and 32.63g of the high molecular weight silicate anhydride with a ladder structure obtained in step S1 in small batches over 3 hours for copolymerization. Stir the reaction for 10 hours, then add 0.4965g of phenylacetylene phthalic anhydride for end-capping and react for 1 hour to obtain the polyimide precursor resin.

[0050] The preparation process of the polyimide enameled wire in Example 1 includes:

[0051] Under a nitrogen protective atmosphere, the prepared polyimide precursor resin and NMP were stirred and mixed at a weight ratio of 1:5 until completely dissolved to obtain a polyimide varnish. An appropriate amount of polyimide varnish was weighed and placed into the fixed container of a dip-coating machine. The copper flat wire was immersed at a speed of 50 mm / min and then lifted at a speed of 20 mm / min. The coated copper wire was placed in a tube furnace and subjected to the following heat treatments in sequence: 80℃ for 3 hours, 120℃ for 50 minutes, 160℃ for 50 minutes, 200℃ for 50 minutes, 250℃ for 35 minutes, and 280℃ for 35 minutes to obtain a polyimide enameled wire. The thickness of the polyimide varnish layer in the polyimide enameled wire after curing is approximately 3 μm.

[0052] The preparation process of the membrane envelope in Example 1 includes:

[0053] Under a nitrogen protective atmosphere, the prepared polyimide precursor resin and pyridine were mixed at a weight ratio of 1:20 and stirred for 15 hours (for imidization). After the reaction was complete, the mixture was filtered under reduced pressure and degassed under vacuum to obtain the resin. The resin was then cast onto a steel strip through a 5-layer co-casting die and biaxially stretched to obtain a 25 μm thick polyimide film. The polyimide film was cut into 12 mm wide strips and wrapped around the surface of a polyimide enameled wire. The film overlapped by 3 strands, with an overlap rate of 54%, a wrapping angle of 60°, and a wrapping pitch of 25 mm. The tension force applied to the polyimide film by the wrapping head was 4 kgf, and the traction speed of the wrapping wire was 15 m / min. The flat wire was then heated to 400°C and sintered for 5 seconds using a spiral high-frequency induction coil to obtain the film-coated wire.

[0054] Example 2

[0055] Example 2 is a film-coated wire, comprising polyimide enameled wire and a polyimide film; the polyimide enameled wire includes a round copper wire and a polyimide enamel layer, the round copper wire having a diameter of 0.5 mm. 0.5mm; The polyimide enamel layer and polyimide film in the polyimide enameled wire use the same polyimide precursor resin.

[0056] The polyimide precursor resin in Example 2 is the polyimide precursor resin prepared in Example 1.

[0057] The polyimide enameled wire in Example 2 is the polyimide enameled wire prepared in Example 1.

[0058] The preparation process of the membrane envelope in Example 2 includes:

[0059] Under a nitrogen protective atmosphere, the prepared polyimide precursor resin, acetic anhydride, and pyridine were stirred and reacted for 15 hours at a weight ratio of 1:0.01:10 (for imidization reaction). The mixture was then filtered under reduced pressure and degassed under vacuum to obtain the resin. The resin was cast onto a steel strip through a 5-layer co-casting die and then biaxially stretched to obtain a 20 μm thick polyimide film. The polyimide film was cut into 4 mm wide strips and wrapped around the surface of a polyimide enameled wire. The film overlapped by 3 strands, with an overlap rate of 67%, a wrapping angle of 45°, and a wrapping pitch of 15 mm. The tension force applied to the polyimide film by the wrapping head was 3 kgf, and the wrapping wire traction speed was 25 m / min. The flat wire was then heated to 420°C and sintered for 0.5 seconds using a spiral high-frequency induction coil to obtain the film-coated wire.

[0060] Example 3

[0061] Example 3 is a film-coated wire, comprising polyimide enameled wire and a polyimide film; the polyimide enameled wire includes a copper flat wire and a polyimide enamel layer, and the copper flat wire has a diameter of 0.95 mm. 0.22mm; The polyimide enamel layer and polyimide film in the polyimide enameled wire use the same polyimide precursor resin.

[0062] The polyimide precursor resin in Example 3 was the polyimide precursor resin prepared in Example 1.

[0063] The polyimide enameled wire in Example 3 is the polyimide enameled wire prepared in Example 1.

[0064] The preparation process of the membrane envelope in Example 3 includes:

[0065] Under a nitrogen protective atmosphere, the prepared polyimide precursor resin and pyridine were stirred and reacted at a weight ratio of 1:12 for 15 hours (for imidization reaction). The mixture was then filtered under reduced pressure and degassed under vacuum to obtain the resin. The resin was cast onto a steel strip through a 5-layer co-casting die and biaxially stretched to obtain a 15 μm thick polyimide film. The polyimide film was cut into 15 mm wide strips and wrapped around the surface of a polyimide enameled wire. The film overlapped by 2 strands, with an overlap rate of 66%, a wrapping angle of 30°, a tension force of 2 kgf applied to the polyimide film by the wrapping head, and a wrapping wire traction speed of 20 m / min. The flat wire was then heated to 420°C and sintered for 0.3 seconds using a spiral high-frequency induction coil to obtain the film-coated wire.

[0066] Comparative Example 1

[0067] Comparative Example 1 is the polyimide enameled wire prepared in Example 1.

[0068] Comparative Example 2

[0069] Comparative Example 2 is also a film-wrapped wire, but in Comparative Example 2, the film-wrapped wire is made by directly wrapping a polyimide film around a flat copper wire.

[0070] The preparation process of the membrane envelope in Comparative Example 2 includes:

[0071] The polyimide film is cut into 12mm wide strips and wrapped around the surface of a flat copper wire. The film overlaps by 3 strands, with an overlap rate of 54%. The wrapping angle is 60°, the wrapping pitch is 25mm, the tension force of the wrapping head on the polyimide film is 4Kgf, and the traction speed of the wrapping wire is 15m / min. Then, it is heated to 400℃ and sintered for 2 seconds by a spiral high-frequency induction coil to obtain the film-wrapped wire.

[0072] In Comparative Example 2, the flat copper wire specifications are the same as in Example 1, and the polyimide film in Comparative Example 2 is also the same as in Example 1.

[0073] Performance testing:

[0074] (1) Withstand voltage test: Refer to standard ASTM D-149, use 60Hz AC voltage as the test voltage, and the voltage rise rate is 500V / s; take 305mm of wire from each of Examples 1-3 and Comparative Examples 1-2, fold it into 12cm segments, twist it evenly 33 times, and measure the breakdown voltage.

[0075] (2) Thermal shock test: Take 305 mm of wire from Examples 1-3 and Comparative Examples 1-2, and wind it 1-3 turns around a 10 mm diameter round wooden rod for 10 turns. No damage or wire elongation should occur during winding. Place the above samples in an environment of 200℃ for 30 min, take them out, cool them and observe their appearance.

[0076] (3) Solderability test: Take 200 mm of wire from each of Examples 1-3 and Comparative Examples 1-2, immerse both ends of the sample in solder at a temperature of 375±5℃ for 3~6s and take them out. Observe the surface of the tin plating layer of the sample under a microscope with a magnification of 30X to see if it is smooth, whether there are pinholes or whether there are residues in the paint film.

[0077] (4) Elongation test: The elongation of the film wrapping in Examples 1-3 and Comparative Examples 1-2 was determined according to standard GB / T 2951.14—2008;

[0078] (5) Pinhole test: Take 6m of each of the wires in Examples 1-3 and Comparative Examples 1-2, heat them in a constant temperature oven at 125±3℃ for 10min, keep the shape unchanged, immerse them in 0.2% saline solution (immersion length is 5m), add an appropriate amount of phenolphthalein 3% alcohol solution, apply 12V DC current to the wire, energize for 1min, then stop energizing, and observe whether there are pinholes on the surface of the wire.

[0079] The test results are shown in Table 1.

[0080] Table 1

[0081]

[0082] The above description is merely an exemplary embodiment of the present utility model and does not limit the patent scope of the present utility model. Any equivalent structural transformations made based on the technical concept of the present utility model and the contents of the present utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present utility model.

Claims

1. A film wrapped stranded wire characterized by, The film-coated stranded wire includes a core and a polyimide film; The core comprises multiple strands of inner core twisted together, and the polyimide film is sintered onto the outer surface of the core. The inner core is a metal conductor, and the outer peripheral surface of the metal conductor is coated with a polyimide varnish layer. Alternatively, the inner core is a film-coated wire, which includes a wire core and a polyimide film. The wire core of the film-coated wire includes a metal conductor and a polyimide varnish layer disposed on the outer peripheral surface of the metal conductor. The polyimide film is sintered on the outer surface of the polyimide varnish layer.

2. The film-laced wire of claim 1, wherein, In the film-coated wire, the polyimide film is wrapped around the outer surface of the wire core, and the polyimide film is wrapped in at least multiple layers.

3. The film-laced wire of claim 1, wherein, The overlap ratio of the polyimide film is 10% to 75%.

4. The film-laced wire of claim 1, wherein, The width of the polyimide film is 1mm to 50mm; And / or, the thickness of a single layer of the polyimide film is 1 μm to 50 μm.

5. The film-coated stranded wire as described in claim 1, characterized in that, The thickness of the polyimide coating is 0.001 μm to 20 μm.

6. The membrane-covered stranded wire as described in claim 1, characterized in that, The wire core includes a single-strand inner core, the polyimide varnish is coated on the outer surface of the inner core, and the polyimide film is sintered on the outer surface of the polyimide varnish.

7. The membrane-covered stranded wire as described in claim 6, characterized in that, The cross-section of the metal wire is any one of a circle, an ellipse, or a polygon.

8. A composite film wrapped around a stranded wire, characterized by The composite film-coated stranded wire includes a core and a polyimide film; The core comprises multiple strands of inner core twisted together, and the polyimide film is sintered onto the outer surface of the core. Wherein, the inner core is the membrane-wrapped stranded wire as described in claim 1.

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