Self-adhesive enameled stranded wire of pure gold conductor and preparation method of self-adhesive enameled stranded wire

Abstract

The invention relates to the technical field of electromagnetic medical treatment, and provides a self-adhesive enameled stranded wire of a pure gold conductor and a preparation method of the self-adhesive enameled stranded wire in order to enable a coil state to be more stable and soft when a pure gold coil is implanted into a human body and solve the technical problems that a pure gold wire cannot be formed in a self-adhesive mode and the reliability of subsequent dispensing is poor. Each single wire comprises a pure gold conductor core wire of which the purity is not lower than 99.99%, a first insulating layer formed by a high-temperature-resistant insulating paint film and a self-adhesive layer formed by a thermoplastic self-adhesive paint film, and a plurality of strands of single wires are stranded in a preset stranding pitch and stranding direction; the preparation method comprises the steps of wire drawing, cleaning, double-layer coating, baking and twisting. Through the collaborative design of the pure gold conductor and the double-layer coating structure, a stable coil structure can be formed without an additional adhesive, and the enameled stranded wire which has a self-adhesion function and is suitable for a miniature high-reliability coil is provided on the premise of keeping the excellent chemical stability, high conductivity and flexibility of the pure gold conductor.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic medical technology, specifically to a self-adhesive enameled stranded wire with a pure gold conductor and its preparation method. Background Technology

[0002] Enamelled stranded wire is an electromagnetic wire made by stranding multiple strands of enamelled wire coated with one or more layers of insulating varnish on the surface of a single conductive metal wire. It is a key basic material for manufacturing electromagnetic components such as inductors, transformers, and motors. As modern electronic equipment develops towards miniaturization, high frequency, and high reliability, extremely stringent requirements are placed on the performance of enamelled stranded wire.

[0003] In high-end applications, such as implantable coils in the medical field, pure gold, as one of the most stable materials, is an excellent choice. Combining pure gold wire with enameled wire technology to create specific pure gold self-adhesive enameled stranded wires significantly improves the coil's characteristics. Meanwhile, in aerospace, high-precision sensors, and ultra-high frequency communication components, coils often require low resistance, extremely high chemical stability, excellent flexibility and bending resistance, and long-term reliability. Traditional copper or silver enameled wires have the following limitations: 1. Copper wire: Although it has high conductivity, it is easily oxidized or sulfided in environments with high temperature, high humidity or corrosive media, which leads to increased contact resistance, insufficient long-term stability, and skin effect at high frequencies.

[0004] 2. Silver wire: It has the highest electrical conductivity, but it is prone to forming a non-conductive silver sulfide film in sulfur-containing environments, and the migration of silver ions may lead to short circuit risks.

[0005] 3. Alloy wire: Other elements are often added to improve performance, but this will reduce electrical conductivity.

[0006] 4. Currently, most high-end chips use pure gold, as non-pure gold materials cannot meet the process requirements.

[0007] Pure gold possesses the best chemical stability (resistance to oxidation and corrosion) among known metals, excellent ductility, and solderability, making it an ideal material for high-end micro-wires. However, in existing technologies, pure gold wires are mostly used as bonding wires, or only coated with a simple insulating layer (such as polyurethane or polyimide), without deep integration with the enameling process, and lack self-adhesive properties.

[0008] Some specific enameled wires require self-adhesive enameled wire to form coils that need to be implanted in the human body for nerve stimulation. In the winding process of miniature coils, traditional enameled wires require additional adhesives or soldering to fix the turns, which not only increases the complexity of the process but may also introduce contaminants and reduce insulation performance.

[0009] Therefore, there is an urgent need to develop a new type of enameled stranded wire that combines the excellent chemical stability, high conductivity, and flexibility of pure gold conductors with self-adhesive properties. Summary of the Invention

[0010] To address the technical problems of pure gold wire's inability to self-adhere and subsequent adhesive application reliability in implanting pure gold coils into the human body, and to ensure greater coil stability and flexibility, this invention provides a self-adhesive enameled stranded wire with a pure gold conductor and its preparation method. While maintaining the excellent chemical stability, high conductivity, and flexibility of pure gold conductors, this invention provides an enameled stranded wire with self-adhesive properties suitable for miniature, high-reliability coils (such as nerve stimulation coils for implantable medical devices). This avoids the pollution, insulation degradation, and process complexity issues associated with using additional adhesives in traditional winding processes. To achieve the above objectives, the technical solution of this invention is as follows: As one aspect of the present invention, a self-adhesive enameled stranded wire with a pure gold conductor is provided, which is formed by stranding multiple single wires. Each single wire includes, from the inside out, a conductor core, a first insulation layer, and a self-adhesive layer. The multiple single wires are stranded according to a predetermined stranding pitch and direction to form a stranded wire. The conductor core is made of pure gold with a purity of not less than 99.99% and has a wire diameter of 0.015 mm to 0.20 mm. The first insulation layer is a high-temperature resistant insulating varnish film coated on the outer surface of the conductor core, which provides basic electrical insulation strength, heat resistance, and adhesion to the pure gold conductor. The self-adhesive layer is a thermoplastic self-adhesive varnish film coated on the outer surface of the first insulation layer, which can achieve thermal fusion bonding between the turns after winding and heat treatment, thereby forming a stable coil structure.

[0011] To ensure the stability of the metal while making the 0.22mm diameter wire more flexible and bend-resistant, the desired effect can be achieved by using 5 strands of pure gold self-adhesive enameled wire with a diameter of 0.10mm twisted together.

[0012] In one alternative embodiment, the thickness of the first insulating layer is 3 μm to 25 μm.

[0013] In one alternative embodiment, the first insulating layer is one or more of modified polyimide varnish, polyamide-imide varnish, and high-temperature resistant polyesterimide varnish.

[0014] In one alternative embodiment, the first insulating layer is a polyurethane insulating varnish layer with direct soldering properties.

[0015] In one alternative embodiment, the self-adhesive layer comprises a thermoplastic resin, a latent curing agent, and a tackifier.

[0016] In one alternative embodiment, the thermoplastic resin is selected from one or more of polyester resin, polyvinyl acetal resin, or polyamide resin.

[0017] In another aspect of the present invention, a method for preparing a self-adhesive enameled stranded wire with a pure gold conductor is provided, comprising the following steps: Step S1, Wire Drawing: High-purity gold ingots with a purity of not less than 99.99% are drawn through multiple precision wire drawing dies to obtain pure gold conductor cores with a diameter of 0.015mm to 0.20mm. The pure gold conductor cores are then subjected to online or offline annealing to eliminate internal stress and improve ductility. Step S2, Surface Cleaning: The pure gold conductor cores are cleaned to remove surface oil and impurities to improve the adhesion of subsequent coatings. Step S3, Coating the First Insulation Layer: The cleaned pure gold conductor cores are passed through a coating device containing high-temperature resistant insulating varnish, and multiple coating and baking processes are performed. The process involves forming a first insulating layer on the outer surface of the wire; step S4, coating a self-adhesive layer: after the first insulating layer has fully cured, a self-adhesive varnish is coated on its outer surface and then baked at a medium temperature to allow the solvent to evaporate and form a self-adhesive layer that maintains thermoplasticity and the activity of the latent curing agent; step S5, cooling and winding: after the coated self-adhesive enameled gold wire has been cooled to room temperature, it is wound up under constant tension control; step S6, stranding: under the condition of maintaining uniform tension, multiple self-adhesive enameled gold wires are spirally and concentrically stranded by a stranding machine with a predetermined stranding pitch and direction to obtain a pure gold conductor self-adhesive enameled stranded wire.

[0018] In an optional embodiment, the cleaning process in step S2 is performed using ultrasonic cleaning.

[0019] In one optional embodiment, after each application of insulating varnish in step S3, the pure gold conductor core wire is sent into a vertical or horizontal oven for curing at a temperature range of 300°C to 450°C until the first insulating layer reaches a predetermined thickness.

[0020] In an optional embodiment, the medium-temperature baking process in step S4 is performed in a temperature range of 180°C to 250°C.

[0021] The beneficial effects of implementing this invention are: This invention provides a self-adhesive enameled stranded wire with a pure gold conductor and its preparation method, effectively solving the technical problem of achieving strong self-adhesion of the coil without additional adhesives during the winding process while maintaining the excellent chemical stability, high conductivity, and flexibility of pure gold conductors. Specifically, the stranded wire uses high-purity (≥99.99%) pure gold as the conductor core, ensuring long-term non-oxidation, non-corrosion, and stable contact resistance under harsh environments such as those for human implantation. By sequentially setting a high-temperature resistant first insulation layer and a thermoplastic self-adhesive layer on the outside of the conductor, the wire can achieve reliable thermal fusion bonding between the turns after winding only requires heating, completely avoiding the pollution risks, reduced insulation performance, and complex processes caused by the use of external adhesives in traditional processes. At the same time, the multi-strand micro-fine single-wire stranded structure significantly improves the overall flexibility and resistance to bending fatigue, meeting the stringent requirements of implantable devices such as micro-nerve stimulation coils for high reliability, high-precision winding, and long-term biocompatibility. Attached Figure Description

[0022] Figure 1 A cross-sectional structural diagram of a self-adhesive enameled stranded wire with a pure gold conductor provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the preparation method of pure gold conductor self-adhesive enameled stranded wire provided in an embodiment of the present invention.

[0023] In the diagram: 1. Conductor core wire; 2. First insulation layer; 3. Self-adhesive layer. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Example

[0025] Existing enameled stranded wires commonly suffer from insufficient chemical stability of conductor materials, susceptibility to oxidation or sulfidation, and performance degradation at high frequencies in high-end applications. This is particularly true in implantable medical devices, aerospace precision instruments, and high-Q miniature RF inductors, where extremely high requirements are placed on conductor purity, long-term biocompatibility, corrosion resistance, low contact resistance, and structural stability after winding. Traditional copper, silver, or alloy wires struggle to simultaneously meet the demands for electrical stability, mechanical flexibility, and process adaptability under extreme conditions. Existing pure gold wires are mostly limited to bonding wire applications and lack a fully functional, self-adhesive, strandable enameled wire structure. Furthermore, there is a lack of stable coating and stranding processes suitable for micro-diameter wires (≤0.20 mm).

[0026] See Figure 1This invention provides a self-adhesive enameled stranded wire with a pure gold conductor, which is composed of multiple strands of single wires twisted together. Each single wire, from the inside out, includes: a conductor core wire 1, a first insulation layer 2, and a self-adhesive layer 3. The multiple strands of single wires are twisted together according to a predetermined stranding pitch and direction to form a stranded wire. The conductor core wire 1 is made of pure gold with a purity of not less than 99.99% and has a wire diameter of 0.015mm to 0.20mm. The first insulation layer 2 is a high-temperature resistant insulating varnish film coated on the outer surface of the conductor core wire 1, which provides basic electrical insulation strength, heat resistance, and adhesion to the pure gold conductor. The self-adhesive layer 3 is a thermoplastic self-adhesive varnish film coated on the outer surface of the first insulation layer 2, which can achieve thermal fusion bonding between the turns after winding and heat treatment, thereby forming a stable coil structure.

[0027] The conductor core 1 is made of pure gold with a purity of not less than 99.99%; the wire diameter is 0.015mm to 0.20mm, which can be selected according to the actual application scenario; after the pure gold conductor core 1 is drawn, it undergoes online continuous annealing treatment at an annealing temperature of 200℃ to 300℃ and a holding time of 0.5s to 3s to eliminate processing stress, improve ductility and bending life, and avoid winding cracks.

[0028] The first insulating layer 2 is a high-temperature resistant insulating varnish film coated on the outer surface of the conductor core wire 1. The varnish film is applied by dip coating or felt coating and is formed by multiple coatings and step-by-step thermal curing. Its composition is selected from one or more mixtures of modified polyimide, polyamide-imide or high-temperature resistant polyesterimide insulating varnish to meet the uniform film formation requirements of fine gold wires. The thickness of the varnish film is 3μm to 25μm (9μm in this embodiment). The thickness can be adjusted according to the target breakdown voltage and heat resistance level. For example, in applications that need to withstand short-term thermal shock of 400℃, the thickness can be selected as 10μm to 12μm. The insulating varnish film is finally cured in an oven at 300℃ to 450℃ to form a dense, pinhole-free insulating layer with strong interfacial bonding with the pure gold surface.

[0029] The self-adhesive layer 3 is a thermoplastic self-adhesive coating film applied to the outer surface of the first insulating layer 2. This coating film is formulated using a solvent system with good compatibility with the first insulating layer 2 and applied through a two-stage dip coating or micro-gap mold coating. Its components include a thermoplastic resin, a latent curing agent, and a tackifier. The thermoplastic resin is selected from one or more of polyester resin, polyvinyl acetal resin (such as polyvinyl formal), or polyamide resin (see Examples 5 and 6), with a glass transition temperature (Tg) of 60°C to 110°C to ensure non-sticking at room temperature and smooth winding operation, while allowing sufficient softening and flow during heat treatment at 150°C to 180°C. The latent curing agent is a microencapsulated isocyanate or a blocked epoxy curing agent, with an unsealing temperature of 140°C to 170°C. At ℃, under hot-pressing conditions, it releases active groups to participate in cross-linking; the tackifier is a rosin derivative or hydrogenated hydrocarbon resin, added at 3% to 8% of the resin solid content, to enhance initial contact tack and interfacial wettability; after being baked at a medium temperature of 180 ℃ to 250 ℃, the solvent completely evaporates, the resin is in a semi-plasticized state, maintaining thermoplasticity and latent curing agent activity, and the surface exhibits a slightly tacky or nearly non-sticky nature, facilitating automated winding; its dry film thickness can be adjusted according to wire diameter and winding density to balance adhesion and flexibility.

[0030] Multiple strands of single wires are twisted together according to a predetermined pitch and direction to form a stranded wire. The pitch is the distance that the single wire axis advances when rotating one revolution around the center axis of the twisting, and its value ranges from 10 to 30 times the outer diameter of the single wire. For example, when the outer diameter of the single wire is 0.08 mm (including conductor + double-layer enamel film), the pitch is set to 0.8 mm to 2.4 mm. The twisting direction can be left (S direction) or right (Z direction), and the twisting direction of each single wire in the same stranded wire is consistent to ensure structural symmetry and tension balance. The twisting process is carried out under a constant tension control system, and the tension fluctuation is controlled within ±0.5 cN to prevent enamel film scratches or single wire deformation.

[0031] Through the above technical solution, this invention achieves a double-layer functional structure based on a pure gold conductor core wire 1 with a purity of not less than 99.99%, combined with a high-temperature resistant first insulation layer 2 and a thermoplastic self-adhesive layer 3. By twisting multiple single wires together under strictly controlled pitch and twist direction, the resulting stranded wire possesses the inherent ultra-high chemical stability, low contact resistance, and excellent biocompatibility of pure gold. Furthermore, it can achieve thermal fusion bonding between the turns after simple heat treatment after winding, without the need for external adhesives. The stranded structure significantly improves the flexibility and resistance to bending fatigue of the wire, enabling the coil to maintain geometric integrity and electrical consistency even under repeated deformation or dynamic implantation environments. This effectively solves the key technical bottlenecks of poor conductor material stability, complex processes, and unreliable structures in high-end microelectronic components. Example

[0032] In one optional embodiment, the present invention also provides a self-adhesive enameled stranded wire with a pure gold conductor, wherein the thickness of the first insulation layer 2 is 3μm to 25μm.

[0033] The thickness of the first insulating layer 2 is 3μm to 25μm, which refers to the range of dry film thickness formed on the outer surface of the conductor core 1 after the high-temperature resistant insulating varnish is fully cured and before the action of subsequent mechanical stress (such as stranding or winding). This thickness is achieved by controlling process parameters such as the number of coatings, solid content of the varnish, viscosity, baking temperature and time. For example, after each coating, hot air curing at 300°C–450°C can be used, and the thickness can be verified by online thickness gauge or cross-sectional electron microscope (SEM). This thickness range can be adaptively adjusted according to different emphases on dielectric strength, flexibility and winding accuracy in actual applications. For example, when used for ultra-fine wires with smaller diameters, the thickness can be reduced to 3μm to reduce the risk of bending stress concentration. When used for wires with a diameter of 0.15mm–0.20mm that require higher withstand voltage, the thickness can be increased to a maximum of 25μm. This embodiment of the invention does not impose any special limitations on this.

[0034] The minimum thickness of the first insulating layer 2 is 3μm, which is the minimum effective thickness to ensure basic electrical insulation performance, thermal shock resistance, and adhesion stability to the pure gold conductor surface. If it is less than 3μm, there is a risk of local pinholes, uneven film thickness, or cracking after thermal cycling, which will affect long-term reliability. The maximum thickness is 25μm, which is the critical value to avoid varnish wrinkles, cracking, or interlayer peeling during winding due to excessive film thickness, while maintaining the balance between the cohesion and interfacial adhesion of the varnish film. Especially in the multi-strand stranding and subsequent winding forming stages, an excessively thick insulating layer is prone to microcracks when the bending radius is <5mm, which will degrade the insulation resistance. The setting of this thickness range also takes into account the coating uniformity and process window stability under the extremely small wire diameter of the pure gold conductor core wire 1, so that the single wire still maintains structural integrity under stranding tension and winding tension.

[0035] Through the above technical solution, the present invention achieves, based on the pure gold conductor self-adhesive enameled stranded wire structure defined in the present invention, by applying a clear limitation of 3μm–25μm to the thickness of the first insulation layer 2, so that the insulation layer meets the basic electrical safety and heat resistance requirements while also possessing excellent flexibility, bending resistance and coating consistency; thereby effectively suppressing enamel film damage during the winding process under micro-diameter conditions, improving coil winding accuracy and yield, and supporting application scenarios with stringent requirements for dimensional accuracy and long-term stability, such as micro radio frequency inductors and implantable nerve stimulation coils. Example

[0036] In one optional embodiment, the present invention also provides a self-adhesive enameled stranded wire with a pure gold conductor, wherein the first insulation layer 2 is one or more of modified polyimide varnish, polyamide-imide varnish, and high-temperature resistant polyesterimide varnish.

[0037] Modified polyimide varnish refers to a modified resin system obtained by introducing flexible groups, fluorine-containing groups, or nano-reinforcing phases into the main chain or side chain of traditional polyimide molecules. Its glass transition temperature (Tg) is not lower than 380°C, and its thermal decomposition temperature (Td5%) is not lower than 520°C. After coating and film formation, it can form a dense, highly cross-linked insulating varnish film by thermal imidization treatment in the range of 300°C–450°C. This varnish film has excellent adhesion to the surface of pure gold conductor core wire 1.

[0038] Polyamide-imide paint is a heterocyclic copolymer high-temperature resistant resin solution made by condensation polymerization of aromatic diacid anhydrides, aromatic diamines and aliphatic diacids. It combines the toughness of polyamide with the heat resistance of polyimide. The resulting paint film has strong adhesion and good flexibility on pure gold surfaces. After bending tests (0.5 mm diameter mandrel, 180° repeated bending 5 times), it showed no cracking or delamination.

[0039] Through the above technical solution, the present invention achieves the following: under the premise that "the first insulating layer 2 is a high-temperature resistant insulating varnish film, used to provide basic electrical insulation strength, heat resistance and adhesion to pure gold conductors", the material system is further limited to one or more of modified polyimide varnish, polyamide-imide varnish or high-temperature resistant polyesterimide varnish. Since these three types of materials all have high thermal stability, strong polar functional group density and good interfacial interaction ability with gold surface, under the same thickness (7μm–12μm) and the same coating-curing process conditions, compared with conventional polyurethane or ordinary polyester varnish, they can more effectively suppress the softening, oxidation and interfacial debonding of the varnish film at high temperature, thereby improving the structural integrity and dielectric reliability of the insulating layer under long-term working conditions above 200°C, and thus ensuring the signal integrity and service life of the pure gold conductor in the miniature high-frequency coil. Example

[0040] In one optional embodiment, the present invention also provides a self-adhesive enameled stranded wire with a pure gold conductor, wherein the first insulation layer 2 is a polyurethane insulating varnish layer with direct soldering properties.

[0041] The first insulating layer 2 is a polyurethane insulating varnish film coated on the outer surface of the conductor core wire 1. This polyurethane insulating varnish layer has good electrical insulation, flexibility and adhesion to the pure gold conductor core wire 1 at room temperature. Its film is dense and uniform, and the thickness can be set according to actual process requirements, such as 7μm, 9μm or 12μm. This embodiment of the invention does not make any special limitation on this. The polyurethane insulating varnish layer has direct soldering performance. That is, under the conditions of soldering iron temperature of 300°C–400°C and contact time of 0.5–3 seconds, the varnish film can be locally pyrolyzed, carbonized and volatilized, exposing the surface of the pure gold conductor core wire 1 below, thereby realizing direct soldering operation without prior scraping or solvent removal of the insulating layer. The polyurethane insulating varnish layer and the outer self-adhesive layer 3 have good interfacial compatibility. There is no obvious delamination, blistering or interface peeling phenomenon between the two during heat treatment.

[0042] Through the above technical solution, the present invention achieves the replacement of the first insulation layer 2 with a polyurethane insulating varnish layer with direct soldering performance while retaining all the technical features such as the pure gold conductor core 1, the self-adhesive layer 3, and the stranded structure. Because the polyurethane insulating varnish layer can be controllably decomposed under the action of the soldering heat source, the pure gold conductor core 1 is partially exposed, thereby achieving direct soldering without pretreatment at the ends or intermediate taps of the wound coil. This feature significantly simplifies the electronic assembly process, avoids conductor damage and insulation layer edge burrs caused by mechanical paint scraping, reduces human operation errors and automated soldering failure rate, and is particularly suitable for high-reliability application scenarios that require high-frequency soldering debugging, miniature coil terminal lead-out, or flying probe testing before SMT mounting. Example

[0043] In an optional embodiment, the present invention also provides that the self-adhesive layer 3 is composed of a thermoplastic resin, a latent curing agent, and a tackifier.

[0044] Thermoplastic resins are used to soften and melt during heating, providing initial flowability and interfacial spreading ability, enabling physical interlocking and surface wetting of adjacent coil contact surfaces under pressure; their glass transition temperature (Tg) ranges from 80°C to 130°C, and can be adjusted according to the actual heat treatment process window and coil forming temperature requirements; for example, it can be one or more of polyester resin, polyvinyl acetal resin (such as polyvinyl formal), or polyamide resin, or a blend or modified derivative of the above resins.

[0045] The latent curing agent is activated after heating to a predetermined temperature, initiating a partial cross-linking reaction of the thermoplastic resin, thereby improving the bonding strength, heat resistance and long-term dimensional stability; it is chemically inert at room temperature and does not react significantly with the thermoplastic resin, so as to ensure that the self-adhesive layer 3 does not cure prematurely or stick during the winding operation.

[0046] The tackifier is used to improve the interfacial compatibility and adhesion between the self-adhesive layer 3 and the first insulating layer 2, and to enhance the wetting and penetration ability of the adjacent wire turns in the hot-melt state.

[0047] Through the above technical solution, the present invention achieves a controllable micro-adhesive or non-adhesive state on the surface of the self-adhesive layer 3 during the winding operation stage, which facilitates wire laying and tension control. After the coil is wound, it is heat-treated at 150°C–180°C, which softens and flows the thermoplastic resin, activates the latent curing agent and initiates slow cross-linking, and simultaneously migrates and enriches the coil contact interface. The three work together to form a composite adhesive structure with both physical interlocking and partial chemical bonding under pressure between adjacent coils. After cooling, the structure remains stable and does not rebound, significantly improving the overall rigidity, shock resistance and inter-turn displacement resistance of the coil, while not sacrificing the flexibility and electrical insulation performance of the winding. Example

[0048] In one optional embodiment, the present invention also provides a thermoplastic resin selected from one or more of polyester resin, polyvinyl acetal resin, or polyamide resin.

[0049] Through the above technical solution, the present invention achieves the following: within the framework of the self-adhesive layer 3 composed of "thermoplastic resin, latent curing agent and tackifier" as defined in the present invention, one or more of polyester resin, polyvinyl acetal resin or polyamide resin are selected as the thermoplastic matrix. This allows the self-adhesive layer 3 to have sufficient hot melt fluidity to fill the gaps between the turns during the heat treatment at 150°C–180°C, and to form a moderately cross-linked network after activation by the latent curing agent. Thus, after cooling, a coil structure with mechanical strength, dimensional stability and strong inter-turn adhesion is obtained. The selection of different resin types can be adaptively matched according to the target application scenario for flexibility (e.g., implanted coils require high bending fatigue life), thermal response speed (e.g., high frequency winding cycle requirements), and chemical resistance (e.g., the presence of specific solvents in the encapsulation environment). Example

[0050] The technical problem to be solved by this invention is the lack of a complete, controllable, and applicable process for the preparation of self-adhesive enameled stranded wires for high-purity gold micro-wires, especially the coordinated control of key steps such as wire drawing, cleaning, double coating, baking, and stranding.

[0051] See Figure 2 To address the aforementioned problems, this invention provides a method for preparing a pure gold conductor self-adhesive enameled stranded wire, the method comprising the following steps: Step S1, drawing: A high-purity gold ingot with a purity of not less than 99.99% is drawn through multiple precision drawing dies to obtain a pure gold conductor core wire 1 with a wire diameter of 0.015mm to 0.20mm. The pure gold conductor core wire 1 is then subjected to online or offline annealing treatment to eliminate internal stress and improve ductility. In one alternative implementation, the wire drawing method can employ a diamond die in conjunction with a constant tension closed-loop control system to monitor and adjust the tensile force of each pass in real time to ensure wire diameter consistency. In another alternative implementation, the wire drawing method includes adding an ultrasonic vibration-assisted lubrication module after the final wire drawing to reduce die wear and suppress surface scratches; Furthermore, this wire drawing method can also employ a segmented temperature-controlled wire drawing process, completing rough drawing in the initial low-temperature zone (≤100 °C) and fine drawing in the subsequent temperature-controlled zone (200 °C–300 °C), thus balancing forming accuracy and the ductility of the metal material.

[0052] This invention, through the synergistic effect of multiple precision wire drawing dies and matching online / offline annealing processes, not only ensures the dimensional accuracy and surface quality of the pure gold conductor core wire 1, but also endows it with sufficient plastic deformation capacity, laying the foundation for the uniform coating of the insulation layer and self-adhesive layer 3 and the deformation adaptability during the stranding process.

[0053] Step S2, Surface cleaning: The pure gold conductor core wire 1 is cleaned to remove oil and impurities from its surface in order to improve the adhesion of subsequent coatings. In one alternative implementation, the cleaning method may employ an ultrasonic cleaning tank containing a mixture of deionized water and nonionic surfactant, with a cleaning time of 2 to 5 minutes. This invention effectively removes surface contaminants from the pure gold conductor core wire 1 through cleaning treatment, significantly improves the spreadability and adhesion of high-temperature resistant insulating varnish and self-adhesive varnish on its surface, and avoids blistering, peeling or local breakdown of the varnish film caused by interface defects.

[0054] Step S3, Coating the first insulation layer 2: The cleaned pure gold conductor core wire 1 is passed through a coating device containing high-temperature resistant insulating varnish, and a first insulation layer 2 is formed on its outer surface by a process combining multiple coatings and baking. The "coating device" can be a dip-coating felt type, a mold-coating type, or a spray-coating head, and its structure is adapted to stably guide the fine gold wires (0.015mm–0.20mm) and control the paint film thickness. "Multi-pass coating combined with baking" means that after each coat of paint is completed, it is immediately put into an independent temperature-controlled oven for staged heat treatment before the next coat is applied. This cycle continues until the target thickness is achieved. This process can avoid sagging, pinholes, or internal stress accumulation caused by a single thick coat, ensuring that the insulation layer is dense, uniform, and defect-free.

[0055] In one alternative implementation, the coating method may employ a vertical oven; In another alternative implementation, the coating method includes using a horizontal multi-segment oven, with the temperature gradient of each zone set as follows: for example, an inlet preheating zone (150 °C–200 °C), a main curing zone (320 °C–420 °C), and a slow cooling zone (100 °C–150 °C), so as to achieve full control of the coating film from solvent evaporation → resin crosslinking → stress release; This invention achieves controllable film formation of high-temperature resistant insulating varnish on the surface of pure gold conductor through a process combining multi-pass coating and baking, resulting in a bottom insulating structure with uniform thickness, strong adhesion, and stable electrical performance, providing a reliable support platform for the subsequent self-adhesive layer 3.

[0056] Step S4, applying self-adhesive layer 3: After the first insulating layer 2 is completely cured, self-adhesive paint is applied to its outer surface and then baked at a medium temperature to evaporate the solvent and form self-adhesive layer 3 that maintains the thermoplasticity and activity of the latent curing agent. "The first insulation layer 2 is fully cured" means that it has passed all coating-baking cycles. The self-adhesive layer 3 is slightly sticky or non-sticky at room temperature, and the winding operation is smooth. The bonding reaction is only triggered in the subsequent coil heat treatment stage.

[0057] This invention precisely controls the physical state of the self-adhesive layer 3 through medium-temperature baking, ensuring its operability during the winding stage and reliable thermal bonding and partial cross-linking during the final heat treatment stage, thus balancing processability and functionality.

[0058] Step S5, Cooling and winding: After the coated self-adhesive enameled gold wire has been cooled to room temperature, it is wound up under constant tension control. Among them, "cooling" refers to passing the self-adhesive enameled gold wire, which has been baked at a medium temperature, through an air-cooled or water-cooled cooling channel to reduce its surface temperature, thereby preventing the enameled film from creeping, indenting, or interlayer adhesion caused by hot winding; "constant tension control conditions" refers to controlling the fluctuation range of the winding tension within a set value to prevent the thin wire from breaking or the enameled film from being scratched.

[0059] This invention ensures the integrity of the enamel film and the stability of the geometric shape of the self-adhesive enameled gold wire during the winding process through the coordinated control of cooling and constant tension winding, providing high-quality raw materials for subsequent unwinding and stranding.

[0060] Step S6, stranding: Multiple self-adhesive enameled gold wires are spirally and concentrically stranded by a stranding machine with a predetermined stranding pitch and direction while maintaining uniform tension, to obtain a pure gold conductor self-adhesive enameled stranded wire. This invention obtains a pure gold conductor self-adhesive enameled stranded wire with a regular structure and excellent mechanical properties through uniform tension control. Its multi-strand synergistic deformation capability is improved compared with single wire, meeting the requirements of repeated bending and long-term service of micro coils.

[0061] This invention constructs a complete, controllable, and adaptable self-adhesive enameled stranded wire preparation process system adapted to the characteristics of high-purity gold micro-wires through the orderly connection and parameter coordination of steps S1 to S6: S1 provides a high-precision, high-ductility core wire substrate; S2 ensures interface cleanliness and adhesion reliability; S3 and S4 respectively construct a double-layer enamel film structure with clear functions and complementary performance; S5 ensures the quality stability of intermediate products; and S6 finally forms a stranded product with excellent flexibility and structural stability. A strict input-output relationship is formed between each step—the annealed gold wire output from S1 is the object of cleaning in S2; the cleaned gold wire in S2 is the prerequisite for coating in S3; the cured insulation layer in S3 is the foundation for coating the self-adhesive layer 3 in S4; and the self-adhesive enameled wire obtained in S4 is the direct raw material for winding in S5 and stranding in S6. This method requires no additional adhesive or welding process, is fully compatible with existing enameled wire production lines, and can stably produce pure gold self-adhesive enameled stranded wires with diameters of 0.015mm–0.20mm, strand counts of 2–12, and strand pitches of 10mm–50mm. It fully supports the domestic manufacturing needs of high-end application scenarios such as miniature RF inductors, high-Q coils, and implantable medical device coils. Example

[0062] In an optional embodiment, the method further includes: In step S2, ultrasonic cleaning is used for the cleaning process.

[0063] Among them, ultrasonic cleaning refers to the use of high-frequency mechanical vibration with a frequency of 20 kHz to 100 kHz to generate cavitation effect in the cleaning fluid, causing a large number of instantaneous high-pressure microbubbles to form inside the cleaning fluid and violently break down, thereby generating local impact force and micro-jet on the surface of the pure gold conductor core wire 1, achieving efficient removal of adsorbed oil stains, wire drawing lubricant residues and micron-sized particulate impurities from the wire surface; this method is particularly suitable for fine pure gold conductor core wires 1 with a wire diameter of 0.015 mm to 0.20 mm, because of their large specific surface area, high surface energy and strong adhesion of contaminants, which are difficult to be fully removed by conventional soaking or spray cleaning.

[0064] This invention replaces conventional cleaning methods with ultrasonic cleaning, and significantly enhances the physical removal ability of stubborn contaminants on the surface of the fine pure gold conductor core wire 1 by utilizing the microscopic impact generated by cavitation effect. On this basis, the conductor surface achieves higher cleanliness and a better activation state, thereby providing a more reliable adhesion base for the subsequent first insulation layer 2 and self-adhesive layer 3, effectively suppressing blistering, pinholes or local peeling of the coating film after coating, and improving the overall coating bonding strength and process stability. Example

[0065] In an optional embodiment, the present invention further provides that after each application of insulating varnish in step S3, the pure gold conductor core wire 1 is sent into a vertical or horizontal oven for curing treatment in a temperature range of 300°C to 450°C until the first insulating layer 2 reaches a predetermined thickness.

[0066] This invention performs independent curing treatment within a temperature range of 300℃ to 450℃ after each coating, ensuring that each layer of insulating varnish completes molecular structure rearrangement and chemical bonding under controlled thermal conditions. This not only avoids surface drying but also prevents residual bubbles or shrinkage cracking caused by single thick coatings, but also ensures that each varnish film has similar crosslinking density and thermal expansion coefficient in the thickness direction. On this basis, the composite insulating layer formed by multiple layers exhibits excellent interlayer bonding, thermal shock resistance, and electrical insulation consistency, ultimately supporting the reliability and signal integrity of pure gold conductors in the long-term service of micro high-frequency coil winding.

[0067] Example 10: In an optional embodiment, the method further includes: The medium-temperature baking process in step S4 is carried out in a temperature range of 180°C to 250°C.

[0068] "Medium-temperature baking" refers to the temperature range of the heat treatment process applied to the coated self-adhesive layer 3. This temperature range is between the boiling point of the solvent, the glass transition temperature (Tg) of the thermoplastic resin, and the initial activation temperature of the latent curing agent. Its technical function is to allow the organic solvent in the self-adhesive paint to fully evaporate, while promoting the initial softening and molecular chain extension of the thermoplastic resin, forming an intermediate film layer with surface micro-adhesion, internal thermoplastic flowability, and no significant decomposition or reaction of the latent curing agent. This provides a process window for subsequent wire winding operations and ensures sufficient hot melt flowability and controllable crosslinking reaction kinetics in the final hot bonding stage.

[0069] This invention strictly limits the medium-temperature baking temperature to the range of 180℃ to 250℃. On the one hand, this ensures the effective evaporation of commonly used organic solvents in self-adhesive varnishes, preventing pinholes, bubbles, or decreased adhesion after film formation. On the other hand, it inhibits the premature desealing and cross-linking reaction of latent curing agents, allowing their activity to be fully preserved. Furthermore, the thermoplastic resin acquires appropriate chain segment mobility, preventing excessive melting and flow that could lead to uneven coating thickness, and also ensuring that molecular-level interfacial contact is achieved even at excessively low temperatures. The resulting self-adhesive layer 3 is stable and solid at room temperature, facilitating winding operations. During subsequent coil heat treatment, it can rapidly respond to temperature increases, achieving controllable thermal fusion bonding and progressive cross-linking curing of the coil contact surfaces, ultimately resulting in a dense, slip-free, and vibration-resistant stable coil.

[0070] The beneficial effects of implementing the self-adhesive enameled stranded wire with pure gold conductor and its preparation method provided by the present invention are as follows: 1. Superior conductor performance: Using ultra-high purity gold as the conductor, it has extremely high chemical stability, corrosion resistance, oxidation resistance and extremely low contact resistance, ensuring the long-term stability of the coil and the quality of signal transmission in extreme environments.

[0071] 2. Self-adhesive function: The unique double-layer structure design allows the self-adhesive layer to achieve reliable bonding between the turns after heat treatment, making the coil a whole structure with good shock resistance and no loosening between turns, which is especially suitable for precision winding of fine wire diameter.

[0072] 3. Stranded wire: The stranded structure makes the wire easier to bend and wind, and can withstand repeated bending, vibration or impact. This is crucial for coils that require precision winding or are used in dynamic environments (such as implantable medical devices), and can effectively prevent conductors from breaking due to fatigue.

[0073] 4. Excellent overall performance: The bottom insulation layer provides high dielectric strength, thermal shock resistance, and mechanical protection. The self-adhesive layer maintains good insulation and flexibility after bonding. The integral enameled wire exhibits excellent flexibility, scratch resistance, and solvent resistance.

[0074] 5. Good process compatibility: The preparation method is mature and reliable, with strong compatibility with existing enameled wire production processes, and is easy to scale up for production.

[0075] 6. High application value: This product is particularly suitable for fields with extremely high requirements for reliability, stability and miniaturization, such as high-end military electronics, spacecraft, implantable medical devices (such as neurostimulators), high-frequency communication modules, high-precision sensors, etc.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A self-adhesive enameled stranded wire with a pure gold conductor, composed of multiple strands of single wire twisted together, characterized in that, The single line, from the inside out, includes the following: The conductor core (1), the first insulation layer (2) and the self-adhesive layer (3) are formed by stranding multiple strands of the single wires together according to a predetermined stranding pitch and direction; The conductor core (1) is made of pure gold with a purity of not less than 99.99% and has a diameter of 0.015mm to 0.20mm. The first insulating layer (2) is a high-temperature resistant insulating varnish film coated on the outer surface of the conductor core (1) to provide basic electrical insulation strength, heat resistance and adhesion to pure gold conductors; The self-adhesive layer (3) is a thermoplastic self-adhesive paint film coated on the outer surface of the first insulating layer (2). After the winding is completed and heated, it can achieve thermal bonding between the coil turns, thereby forming a stable coil structure.

2. The self-adhesive enameled stranded wire with pure gold conductor according to claim 1, characterized in that, The thickness of the first insulating layer (2) is 3μm to 25μm.

3. The self-adhesive enameled stranded wire with a pure gold conductor according to claim 1 or 2, characterized in that, The first insulating layer (2) is made of one or more of the following: modified polyimide paint, polyamide-imide paint, and high-temperature resistant polyester-imide paint.

4. The self-adhesive enameled stranded wire with pure gold conductor according to claim 1, characterized in that, The first insulating layer (2) is a polyurethane insulating varnish layer with direct welding performance.

5. The self-adhesive enameled stranded wire with a pure gold conductor according to claim 1, characterized in that, The self-adhesive layer (3) is composed of thermoplastic resin, latent curing agent and tackifier.

6. The self-adhesive enameled stranded wire with a pure gold conductor according to claim 5, characterized in that, The thermoplastic resin is selected from one or more of polyester resin, polyvinyl acetal resin, or polyamide resin.

7. A method for preparing a pure gold conductor self-adhesive enameled stranded wire, characterized in that, Includes the following steps: Step S1, drawing: A high-purity gold ingot with a purity of not less than 99.99% is drawn through a multi-pass precision drawing die to obtain a pure gold conductor core wire (1) with a wire diameter of 0.015mm to 0.20mm. The pure gold conductor core wire (1) is then subjected to online or offline annealing treatment to eliminate internal stress and improve ductility. Step S2, Surface cleaning: The pure gold conductor core wire (1) is cleaned to remove oil and impurities from its surface in order to improve the adhesion of subsequent coatings; Step S3, coating the first insulating layer (2): the cleaned pure gold conductor core wire (1) is passed through a coating device containing high temperature resistant insulating varnish, and a first insulating layer (2) is formed on its outer surface by a process combining multiple coatings and baking. Step S4, applying self-adhesive layer (3): After the first insulating layer (2) is completely cured, self-adhesive paint is applied to its outer surface and then baked at a medium temperature to evaporate the solvent and form a self-adhesive layer (3) that maintains the thermoplasticity and the activity of the latent curing agent. Step S5, Cooling and winding: After the coated self-adhesive enameled gold wire is cooled to room temperature, it is wound up under constant tension control. Step S6, stranding: Under the condition of maintaining uniform tension, multiple self-adhesive enameled gold wires are spirally and concentrically stranded by a stranding machine with a predetermined stranding pitch and direction to obtain a pure gold conductor self-adhesive enameled stranded wire.

8. The preparation method according to claim 7, characterized in that, The cleaning process described in step S2 uses ultrasonic cleaning.

9. The preparation method according to claim 7, characterized in that, In step S3, after each application of insulating varnish, the pure gold conductor core wire (1) is sent into a vertical or horizontal oven for curing in a temperature range of 300℃ to 450℃ until the first insulating layer (2) reaches the predetermined thickness.

10. The preparation method according to claim 7 or 19, characterized in that, The medium-temperature baking process in step S4 is carried out in a temperature range of 180℃ to 250℃.

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