A resistively controllable conductive flat wire and a preparation method thereof

Abstract

This invention relates to the field of conductive functional material preparation technology, specifically to a conductive flat wire with controllable micrometer resistance and its preparation method, comprising a substrate and a conductive layer composited inside and on the surface of the substrate. The conductive layer is formed by composite film formation of impregnated conductive slurry and coated conductive slurry, followed by sequential hot pressing and cold pressing for synergistic densification. The conductive flat wire with controllable micrometer resistance and its preparation method provided by this invention effectively solve the technical problems of low micrometer resistance control accuracy, poor overall performance, and insufficient stability in use in the prior art through the organic integration of gradient slurry formulation design, composite film formation process of impregnation and double-sided coating, and synergistic densification technology of hot pressing and cold pressing, and has significant technical advantages.

Description

Technical Field

[0001] This invention relates to the field of conductive functional material preparation technology, specifically to a conductive flat wire with controllable micrometer resistance and its preparation method. Background Technology

[0002] As a core basic material in the field of electrothermal applications, conductive flat wires are widely used in many scenarios such as thermotherapy clothing, home heating, industrial heat tracing, and precision electronic temperature control. With the technological development of various application fields, higher requirements are placed on the precise control capability of the micrometer resistance and the comprehensive performance of conductive flat wires.

[0003] In existing technologies for preparing conductive flat wires, the film-forming process often employs a single coating or impregnation method. The slurry formulation lacks a gradient design, failing to construct a uniform and hierarchical conductive network within and on the substrate. This results in low precision in microresistance control, large performance variations between product batches, and difficulty in accurately matching the application requirements of low, medium, and high voltages. Furthermore, existing densification processes often involve a single hot-pressing operation without subsequent locking treatment of the conductive layer structure. This makes it difficult to eliminate internal stress in the conductive layer, leading to resistance drift during long-term use, insufficient temperature resistance, and unsuitability for medium- and high-temperature applications.

[0004] Meanwhile, some technologies use a single conductive filler to construct the conductive network, resulting in low conductive path density. This not only leads to poor electrothermal conversion efficiency but also makes it difficult to guarantee far-infrared radiation performance even after adding functional fillers. In addition, conductive flat wires prepared by existing technologies generally suffer from weak adhesion between the conductive layer and the substrate, poor coating adhesion, and insufficient flexibility. They are prone to cracking and powdering after bending, which seriously affects the product's service life.

[0005] Furthermore, existing technologies struggle to balance precise microresistance control with comprehensive performance characteristics such as temperature resistance, flexibility, and heat generation. Different application scenarios require separate development of manufacturing processes, resulting in poor versatility. Some processes also suffer from issues such as special raw materials and cumbersome steps, hindering large-scale continuous production and failing to meet the diverse and high-performance application needs of conductive flat wires in various fields. Summary of the Invention

[0006] The primary objective of this invention is to provide a conductive flat wire with controllable resistance per meter and its preparation method.

[0007] A further objective of this invention is to provide a conductive flat filament with controllable micrometer resistance, comprising a substrate and a conductive layer composited within and on the surface of the substrate. The conductive layer is formed by combining an impregnating conductive slurry and a coating conductive slurry into a film, followed by sequential hot pressing and cold pressing for densification. The impregnating conductive slurry and the coating conductive slurry are designed with a gradient formulation, wherein the conductive filler has a higher mass percentage in the coating conductive slurry than in the impregnating conductive slurry. The conductive filler has a mass percentage of 5-25% in the impregnating conductive slurry and 8-48% in the coating conductive slurry. The conductive layer forms a gradient conductive network within and on the surface of the substrate.

[0008] Preferably, the substrate is one of flame-retardant aramid spunlace nonwoven fabric, modified glass fiber cloth, basalt fiber cloth, and high-basis-weight basalt fiber cloth, with a basis weight of 50-80 grams per square meter; the impregnating conductive slurry is composed of conductive filler, 18-38% by weight of resin binder, 0.5-1.5% by weight of dispersant and solvent; the coating conductive slurry is composed of conductive filler, 18-38% by weight of resin binder, 0.5-1.5% by weight of dispersant, solvent, and 0.2-0.6% by weight of hydroxyethyl cellulose thickener, and 5-20% by weight of functional far-infrared filler may be added to the coating conductive slurry; the solvent is deionized water or a mixture of deionized water and ethanol.

[0009] Preferably, the conductive filler is based on superconducting carbon black, and is compounded with one or more of carbon nanotubes, graphene, and ultrafine carbon fiber powder; the resin binder is one of waterborne acrylic resin, waterborne polyurethane resin, waterborne epoxy resin, and modified epoxy silicone resin.

[0010] Preferably, the dispersant is one of polycarboxylate dispersant, sodium lignosulfonate dispersant, and alkylphenol polyoxyethylene ether dispersant; the functional far-infrared filler is one or more of barium titanate-based far-infrared powder, zircon-based far-infrared powder, and barium titanate-zircon composite far-infrared powder.

[0011] A method for preparing the conductive flat wire with controllable micrometer resistance includes the following steps: (1) Substrate pretreatment: The substrate is soaked in room temperature deionized water and then dried by low temperature infrared drying after being rolled up; (2) Impregnation film formation: The pretreated substrate is impregnated by a two-roll impregnation mill under an impregnation pressure of 0.1-0.5 MPa. After the conductive slurry is adsorbed, it is dried to form a preliminary conductive substrate with a preliminary conductive network. (3) Double-sided coating film formation: The preliminary conductive substrate is coated on both sides using a doctor blade coater. The wet film thickness is 50-200 micrometers. After coating with conductive slurry, it is dried to form a composite conductive substrate. (4) Hot and cold pressing synergistic densification: The composite conductive substrate is continuously densified by passing it through hot and cold pressing rollers in sequence. The hot pressing pressure of the hot pressing roller is 2-10 MPa, and the cold pressing pressure of the cold pressing roller is 2-8 MPa. (5) Slitting and forming: The densified composite conductive substrate is slitting by a slitting machine to obtain conductive flat wires with controllable resistance per meter.

[0012] Preferably, the substrate in step (1) is soaked in deionized water at room temperature for 10 minutes to remove impurities on the substrate surface and improve the bonding force between the slurry and the substrate.

[0013] Preferably, the operating speed of the twin-roll impregnation mill in step (2) is 2-6 meters per minute, and the impregnation and immersion allow the conductive filler to penetrate evenly into the gaps between the substrate fibers; the drying temperature is 100-140 degrees Celsius, and after drying, the conductive filler inside the substrate forms an interconnected preliminary conductive network.

[0014] Preferably, the operating speed of the doctor blade coating machine in step (3) is 1.5-5 meters per minute, forming a uniform coating slurry on both sides of the preliminary conductive substrate; the drying temperature is 115-135 degrees Celsius, and after drying, the preliminary conductive network inside the substrate merges with the conductive network of the surface coating to form a complete gradient conductive network.

[0015] Preferably, the temperature of the hot pressing roller in step (4) is 130-170 degrees Celsius, and the running speed of both the hot pressing roller and the cold pressing roller is 3-6 meters per minute; hot pressing is high temperature and high pressure treatment, cold pressing is normal temperature and pressure treatment, and the sheet resistance of the conductive flat wire after cold pressing is 0.8-18.8 ohms per square.

[0016] Preferably, the slitting width of the slitting machine in step (5) is 0.5-4.0 mm and the running speed is 2-8 meters per minute. The slitting width is adjusted according to the application scenario. By adjusting one or more process parameters among the conductive filler mass ratio in the conductive slurry, the wet film thickness of the doctor blade coating, the hot pressing pressure of the hot pressing roller, and the cold pressing pressure of the cold pressing roller, the precise control of the resistance per meter of the conductive flat wire is achieved, which is 155-9200 ohms per meter.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The conductive flat wire with controllable micrometer resistance and its preparation method provided by this invention effectively solves the technical problems of low micrometer resistance control accuracy, poor overall performance, and insufficient stability in the prior art by organically integrating gradient slurry formulation design, composite film formation process of impregnation and double-sided coating, and synergistic densification technology of hot pressing and cold pressing. This invention possesses significant technical advantages. It enables wide-range precise control of the micrometer resistance of the conductive flat wire, and the batch performance of the product is highly consistent. It can adapt to a full range of application scenarios from low voltage and high power to ultra-high voltage and low power, greatly improving the product's versatility.

[0018] 2. By selecting suitable high-temperature resistant resins and substrates and combining them with a synergistic densification process, this invention significantly improves the temperature resistance of the product, effectively suppresses resistance drift during long-term use, and ensures the stability and service life of the product under different temperature environments.

[0019] 3. The composite film-forming process enables the conductive layer to be tightly bonded to the substrate, resulting in excellent coating adhesion, good flexibility, no cracking or powdering after repeated bending, and stable resistance performance, making it suitable for complex application scenarios such as flexible heating.

[0020] 4. This invention constructs a high-density conductive network through the synergistic design of multiple conductive fillers and the scientific addition of functional fillers. While improving conductivity, it also significantly improves the electrothermal conversion efficiency and far-infrared radiation performance of the product, and optimizes the heating effect.

[0021] 5. The preparation process of this invention is continuous and the parameters are clear. All raw materials used are conventional commercial products, which do not require special customization. It is easy to achieve continuous and large-scale production and has good industrial application value and market promotion prospects. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1:

[0024] This embodiment presents a basic low-resistivity solution suitable for low-voltage, high-power applications ranging from 12 to 48V. Typical applications include wearable far-infrared thermotherapy clothing, car seat heating, and small flexible heating pads. The conductive flat filament in this embodiment comprises a flame-retardant aramid spunlace nonwoven fabric substrate and a conductive layer laminated to the substrate surface. The conductive layer is formed by combining impregnated and coated conductive slurries into a film, followed by a combined hot and cold pressing densification process. The impregnated and coated conductive slurries are designed with a gradient formulation, with the conductive filler content of the coated conductive slurry being higher than that of the impregnated conductive slurry. By precisely controlling the coating thickness and densification degree, precise preparation of low-resistivity materials is achieved.

[0025] (1) Slurry preparation Conductive slurry for impregnation: 25g superconducting carbon black, 5g carbon nanotubes, 18g waterborne acrylic resin, 1.5g polycarboxylate dispersant, 49.5g deionized water, viscosity 280cP. Among these, the waterborne acrylic resin, as a high-temperature resistant resin, ensures the adhesion between the conductive layer and the substrate; the superconducting carbon black and carbon nanotubes, as multi-element conductive fillers, synergistically construct a high-density conductive network; the polycarboxylate dispersant ensures uniform dispersion of the fillers and avoids agglomeration; and the deionized water, as a solvent, ensures the slurry's fluidity and suitability for the padding process.

[0026] Conductive coating paste: 30g superconducting carbon black, 8g graphene, 10g ultrafine carbon fiber powder, 22g water-based acrylic resin, 0.6g hydroxyethyl cellulose thickener, 1.5g polycarboxylate dispersant, 27.9g deionized water, viscosity 4000cP. Compared to the conductive paste for impregnation, this coating paste increases the amount of graphene and ultrafine carbon fiber powder to further improve conductivity. The addition of hydroxyethyl cellulose thickener adjusts the paste viscosity to suit the doctor blade coating process, ensuring uniform coating thickness.

[0027] (2) Preparation process Substrate pretreatment: Flame-retardant aramid spunlace nonwoven fabric (substrate basis weight 50 g / m²) is selected, soaked in room temperature deionized water for 10 minutes, taken out and wound together at low temperature infrared drying. The purpose is to remove impurities on the substrate surface, improve the bonding force between the slurry and the substrate, and lay the foundation for subsequent impregnation and film formation.

[0028] Impregnation and drying: The pretreated substrate is impregnated through a two-roll impregnation mill with an impregnation pressure of 0.5 MPa and an equipment operating speed of 2 meters per minute to ensure that the substrate fully absorbs the impregnation slurry and that the conductive filler is evenly penetrated into the fiber gaps of the substrate. After impregnation, the substrate is dried in a drying oven at a temperature of 140 degrees Celsius. After drying, the sheet resistance is measured to be 42 ohms per square, indicating that a preliminary conductive network has been formed inside the substrate.

[0029] Double-sided coating and drying: A doctor blade coater is used to coat the preliminary conductive substrate on both sides. The wet film thickness is 200 micrometers, and the equipment runs at a speed of 1.5 meters per minute, forming a uniform conductive coating on the substrate surface, further improving the conductivity. After coating, the substrate is dried in a drying oven at a temperature of 135 degrees Celsius. After drying, the sheet resistance is measured to be 1.0 ohms per square. At this point, a complete gradient conductive network has been formed on the surface and inside of the substrate.

[0030] Synergistic densification by hot and cold pressing: The composite conductive substrate is densified by sequentially passing it through hot and cold pressing rollers. The hot pressing roller temperature is 170 degrees Celsius, the hot pressing pressure is 10 MPa, and the equipment running speed is 3 meters per minute. The high temperature and high pressure make the conductive layer and the substrate tightly bonded, while improving the density of the conductive layer. The cold pressing is performed at room temperature, with a cold pressing pressure of 8 MPa and an equipment running speed of 3 meters per minute. The purpose is to lock the structure of the conductive layer after hot pressing, eliminate thermal stress, and avoid resistance drift during subsequent use. The final sheet resistance after calendering is measured to be 0.8 ohms per square.

[0031] Slitting: The conductive fabric is slitted into conductive flat wires with a width of 0.5 mm using a slitting machine at a slitting speed of 2 meters per minute, resulting in low-resistance conductive flat wires. Narrow-width slitting further matches the application requirements of low-voltage and high-power applications.

[0032] Example 2:

[0033] Based on the low resistance technology of Example 1, this method achieves precise preparation of medium resistance by reducing the proportion of conductive filler, thinning the coating thickness, lowering the calendering pressure, replacing the high-temperature resistant resin with water-based polyurethane resin, and adding barium titanate-based far-infrared powder to enhance the heating radiation effect. This is suitable for standard voltage and power applications from 110 to 220V, with typical applications including household electric blankets, baseboard heaters, and flexible indoor heating wall coverings. The conductive flat filament in this example includes a modified glass fiber cloth substrate and a conductive layer composited on the substrate surface. The conductive layer is formed by composite film formation of impregnated conductive slurry and coated conductive slurry, followed by hot and cold pressing for densification. The impregnating and coating slurries have a gradient formulation, with the conductive filler proportion in the coating slurry being higher than that in the impregnating slurry. Precise control of medium resistance is achieved by adjusting process parameters.

[0034] (1) Slurry preparation: The conductive slurry for impregnation consists of 18 parts superconducting carbon black, 3 parts graphene, 2 parts carbon nanotubes, 20 parts waterborne polyurethane resin, 1 part sodium lignosulfonate dispersant, and 56 parts deionized water, with a viscosity of 250 cP. Waterborne polyurethane resin was chosen to replace the waterborne acrylic resin of Example 1 to further improve the flexibility of the conductive layer; the sodium lignosulfonate dispersant is compatible with the waterborne polyurethane system to ensure uniform dispersion of the conductive filler; and the reduced total proportion of conductive filler lays the foundation for medium-voltage control.

[0035] Conductive coating slurry: 20g superconducting carbon black, 5g graphene, 5g ultrafine carbon fiber powder, 5g barium titanate-based far-infrared powder, 25g waterborne polyurethane resin, 0.4g hydroxyethyl cellulose thickener, 1g sodium lignosulfonate dispersant, 38.6g deionized water, viscosity 3000cP. Compared to impregnation slurry, coating slurry maintains a higher proportion of conductive fillers, forming a gradient conductive structure; the addition of barium titanate-based far-infrared powder makes the heating mainly through far-infrared radiation, improving the heating comfort in home settings; the amount of hydroxyethyl cellulose is adjusted to match the required wet film thickness.

[0036] (2) Preparation process Substrate pretreatment: Modified glass fiber cloth (substrate basis weight 60 grams per square meter) is selected, soaked in room temperature deionized water for 10 minutes, taken out and dried at low temperature infrared after being rolled up to remove surface impurities, improve the bonding force between the slurry and the substrate, and at the same time the strength of the modified glass fiber cloth is suitable for the use needs of household scenarios.

[0037] Impregnation and drying: The double-roller impregnation pressure is 0.3 MPa (lower than in Example 1), and the equipment operating speed is 2.5 meters per minute. Reducing the impregnation pressure reduces the amount of slurry absorbed by the substrate and further controls the resistance. The drying temperature is 120 degrees Celsius. After drying, the sheet resistance is measured to be 39 ohms per square, forming a preliminary conductive network inside the substrate.

[0038] Double-sided coating and drying: The wet film thickness is 120 micrometers (thinner than in Example 1), the equipment runs at a speed of 2 meters per minute, and the coating thickness is reduced to increase the resistance value; the drying temperature is 125 degrees Celsius, and the sheet resistance is measured to be 3.2 ohms per square after drying, forming a gradient conductive structure.

[0039] Co-dense densification by hot and cold pressing: hot press roller temperature 150 degrees Celsius (lower than Example 1), hot press pressure 7 MPa (lower than Example 1), equipment running speed 4 m / min; cold press pressure 5 MPa (lower than Example 1), equipment running speed 4 m / min. By reducing the hot and cold press pressures, the degree of densification of the conductive layer is reduced, matching the medium resistance requirement. The final sheet resistance after calendering is measured to be 2.6 ohms per square.

[0040] Slitting: The slitting width is 2.0 mm (wider than in Example 1), and the slitting speed is 4 meters per minute. The wide slitting adapts to the power requirements of household standard voltage, resulting in medium-sized resistive conductive flat wires.

[0041] Example 3:

[0042] Based on the medium-meter resistance technology solution in Example 2, the proportion of conductive filler is further reduced, the coating thickness is thinned, the calendering pressure is lowered, the high-temperature resistant resin is replaced with water-based epoxy resin, the content of zircon-based far-infrared powder is increased, and basalt fiber cloth with better temperature resistance is selected as the substrate to achieve precise preparation of high-meter resistance. It is suitable for 380V industrial medium-high voltage and low-power applications, with typical applications including agricultural product baking equipment, small industrial pipeline heating, and medical precision physiotherapy instruments. The conductive flat wire in this embodiment includes a basalt fiber cloth substrate and a conductive layer composited on the surface of the substrate. The conductive layer is formed by composite film formation of impregnated conductive slurry and coated conductive slurry, followed by hot and cold pressing for densification. The impregnating and coating slurries are gradient formulations, with the proportion of conductive filler in the coating slurry being higher than that in the impregnating slurry, which is suitable for the resistance requirements of high-voltage industrial scenarios.

[0043] (1) Slurry preparation Conductive slurry for impregnation: 10g superconducting carbon black, 2g graphene, 28g waterborne epoxy resin, 0.8g alkylphenol polyoxyethylene ether dispersant, 20g ethanol, 39.2g deionized water, viscosity 230cP. Waterborne epoxy resin is used instead of waterborne polyurethane resin to improve the product's temperature resistance, making it suitable for high-temperature industrial applications. The proportion of conductive filler is further reduced. Ethanol and deionized water are mixed as a solvent to improve the slurry's wettability to the basalt fiber cloth. The alkylphenol polyoxyethylene ether dispersant is compatible with the epoxy resin system, ensuring uniform dispersion of the conductive filler.

[0044] Conductive coating slurry: 12g superconducting carbon black, 10g zircon-based far-infrared powder, 32g waterborne epoxy resin, 0.3g hydroxyethyl cellulose thickener, 0.8g alkylphenol polyoxyethylene ether dispersant, 20g ethanol, 24g deionized water, viscosity 2500cP. Compared to impregnation slurry, coating slurry maintains a higher proportion of conductive fillers, forming a gradient conductive structure; increases the content of zircon-based far-infrared powder to improve heating efficiency in industrial applications; and adjusts the amount of hydroxyethyl cellulose to match the viscosity requirements of ultra-thin coating layers.

[0045] (2) Preparation process Substrate pretreatment: Basalt fiber cloth (substrate basis weight 70 grams per square meter) is selected, soaked in room temperature deionized water for 10 minutes, taken out and dried at low temperature infrared by warp-to-wound. The temperature resistance and mechanical strength of basalt fiber cloth are better than those of modified glass fiber cloth, making it suitable for high temperature and high requirements in industrial settings. Pretreatment can improve the wettability of slurry.

[0046] Impregnation and drying: The double-roller impregnation pressure is 0.2 MPa (lower than in Example 2), and the equipment operating speed is 3 meters per minute to further reduce the impregnation pressure, reduce the amount of slurry absorbed by the substrate, and increase the resistance value; the drying temperature is 110 degrees Celsius, and the sheet resistance is measured to be 45 ohms per square after drying, forming a preliminary conductive network inside the substrate.

[0047] Double-sided coating and drying: The wet film thickness is 80 micrometers (thinner than in Example 2), the equipment runs at a speed of 3 meters per minute to further reduce the coating thickness and precisely control the resistance; the drying temperature is 120 degrees Celsius, and the sheet resistance is measured to be 11.5 ohms per square after drying, forming a gradient conductive structure.

[0048] Co-dense densification by hot and cold pressing: hot pressing roller temperature 140 degrees Celsius (lower than Example 2), hot pressing pressure 4 MPa (lower than Example 2), equipment running speed 5 m / min; cold pressing pressure 3 MPa (lower than Example 2), equipment running speed 5 m / min, further reducing the calendering pressure to reduce the density of the conductive layer and match the high resistance requirement. The final sheet resistance after calendering is measured to be 10.2 ohms per square.

[0049] Slitting: The slitting width is 4.0 mm (wider than in Example 2), and the slitting speed is 6 meters per minute. The wide slitting is suitable for high voltage and low power scenarios in industry, resulting in high-resistance conductive flat wires.

[0050] Example 4:

[0051] Based on the high-resistance technology solution of Example 3, the proportion of conductive filler is further reduced, the coating thickness is thinned, the calendering pressure is lowered, the high-temperature resistant resin is replaced with modified epoxy silicone resin, high-quantity basalt fiber cloth is selected as the substrate, and barium titanate zircon composite far-infrared powder is added to achieve precise preparation of ultra-high resistance, while simultaneously improving both temperature resistance and insulation. It is suitable for ultra-high voltage micro-power applications above 1000V, with typical applications including large oil pipeline heating, anti-condensation heating of high-altitude equipment, and constant temperature protection of precision electronic devices. The conductive flat wire of this embodiment includes a high-quantity basalt fiber cloth substrate and a conductive layer composited on the surface of the substrate. The conductive layer is formed by composite film formation of impregnated conductive slurry and coated conductive slurry, followed by densification treatment through hot and cold pressing. The impregnating and coating slurries are gradient formulations, with the proportion of conductive filler in the coating slurry being higher than that in the impregnating slurry, adapting to the resistance requirements of ultra-high voltage micro-power scenarios.

[0052] (1) Slurry preparation Conductive slurry for impregnation: 5g superconducting carbon black, 35g water-based modified epoxy silicone resin, 0.5g alkylphenol polyoxyethylene ether dispersant, 40g ethanol, 19.5g deionized water, viscosity 200cP. Modified epoxy silicone resin is used instead of water-based epoxy resin to further improve the product's temperature resistance and insulation, making it suitable for ultra-high voltage applications. An extremely low proportion of conductive filler lays the foundation for ultra-high resistance control. The increased ethanol content further enhances the slurry's wettability to high-weight basalt fiber cloth. The alkylphenol polyoxyethylene ether dispersant ensures uniform dispersion of the low-content conductive filler, preventing agglomeration.

[0053] Conductive coating slurry: 8g superconducting carbon black, 20g barium titanate zircon composite far-infrared powder, 38g water-based modified epoxy silicone resin, 0.2g hydroxyethyl cellulose thickener, 0.5g alkylphenol polyoxyethylene ether dispersant, 40g ethanol, 13.3g deionized water, viscosity 2000cP. Compared to impregnation slurry, coating slurry maintains a higher proportion of conductive fillers, forming a gradient conductive structure; the addition of barium titanate zircon composite far-infrared powder balances heating efficiency and temperature resistance; and the significantly reduced amount of hydroxyethyl cellulose matches the viscosity requirements of ultra-thin coating layers, ensuring uniform coating.

[0054] (2) Preparation process Substrate pretreatment: Basalt fiber cloth (substrate basis weight 80 grams per square meter, higher than Example 3) is selected, soaked in room temperature deionized water for 10 minutes, taken out and dried at low temperature infrared after being rolled up and rolled back together. The high basis weight basalt fiber cloth has better mechanical strength and insulation performance, which is suitable for the use requirements of ultra-high voltage scenarios. Pretreatment improves the wettability of slurry.

[0055] Impregnation and drying: The double-roller impregnation pressure is 0.1 MPa (lower than in Example 3), the equipment operating speed is 6 meters per minute, the minimum impregnation pressure reduces the amount of slurry absorbed by the substrate and maximizes the increase in resistance value; the drying temperature is 100 degrees Celsius, and the sheet resistance is measured to be 55 ohms per square after drying, forming a preliminary conductive network inside the substrate.

[0056] Double-sided coating and drying: The wet film thickness is 50 micrometers (thinner than in Example 3, which is the minimum coating thickness), the equipment operating speed is 5 meters per minute, and the ultra-thin coating layer further increases the resistance value; the drying temperature is 115 degrees Celsius, and the sheet resistance is measured to be 20.5 ohms per square after drying, forming a gradient conductive structure.

[0057] Co-dense densification by hot and cold pressing: hot pressing roller temperature 130 degrees Celsius (lower than Example 3), hot pressing pressure 2 MPa (lower than Example 3, the lowest hot pressing pressure), equipment running speed 6 meters per minute; cold pressing pressure 2 MPa (lower than Example 3, the lowest cold pressing pressure), equipment running speed 6 meters per minute. The minimum calendering pressure reduces the density of the conductive layer, precisely matching the ultra-high meter resistance requirements. The final sheet resistance after calendering is measured to be 18.8 ohms per square.

[0058] Slitting: Slitting width 2.0 mm, slitting speed 8 m / min, matching the usage requirements of ultra-high voltage micro-power scenarios, to obtain ultra-high resistance conductive flat wire.

[0059] Comparative Example 1: Corresponding to Example 2, the existing traditional single-coating process is used, without impregnation or hot / cold pressing. Only one conductive paste is prepared for single-coating, which is a single process application of the prior art. The remaining parameters are the same as in Example 2. Its process design does not use the impregnation double-sided coating composite film formation process of the present invention, and does not construct a gradient conductive network. Only a conductive layer is formed through a single coating.

[0060] (1) Slurry preparation: 20g superconducting carbon black, 5g graphene, 25g waterborne polyurethane resin, 1g sodium lignosulfonate dispersant, 4g deionized water, viscosity 3500cP.

[0061] (2) Preparation process: The substrate pretreatment is the same as in Example 2. The thickness of the wet film in a single coating is 120 micrometers, the drying temperature is 125 degrees Celsius, and the film is directly slit with a slit width of 2.0 mm.

[0062] (3) Preparation process: The substrate pretreatment is the same as in Example 2. The thickness of the wet film in a single coating is 120 micrometers, the drying temperature is 125 degrees Celsius, and the film is directly slit with a slit width of 2.0 mm.

[0063] Comparative Example 2: In Example 2, a single impregnation process using existing technology is employed, without a double-sided coating step. This represents a single application of existing technology, and the remaining process parameters are consistent with Example 2. However, the process design does not utilize the impregnation-double-sided coating composite film-forming process of this invention. Instead, it only distributes the conductive filler into the gaps between the substrate fibers through impregnation, without forming a conductive coating layer on the substrate surface.

[0064] (1) Slurry preparation: consistent with the conductive slurry used for impregnation in Example 2.

[0065] (2) Preparation process: The substrate pretreatment, impregnation and drying steps are the same as in Example 2. There is no coating step. Hot pressing and cold pressing and slitting are performed directly, and the slitting width is 2.0 mm.

[0066] Comparative Example 3: Corresponding to Example 2, the hot-pressing step of double-sided coating is retained, while the cold-pressing step is removed. This is a simple combination of existing processes, and the remaining process parameters are the same as in Example 2. However, its process design does not employ the hot-pressing and cold-pressing synergistic densification technology of this invention; it only processes the conductive layer through a single hot-pressing process and does not perform cold-pressing to lock the structure.

[0067] (1) Slurry preparation: Same as in Example 2.

[0068] (2) Preparation process: The substrate pretreatment, impregnation and drying, double-sided coating and drying, and hot pressing steps are the same as in Example 2. There is no cold pressing step. The substrate is directly cut with a cutting width of 2.0 mm.

[0069] Comparative Example 4: Corresponding to Example 1, this example uses a single conductive filler formulation from the prior art, employing only superconducting carbon black as the conductive filler, without graphene, carbon nanotubes, or ultrafine carbon fiber powder. It represents a single formulation application of existing technology, with the remaining process parameters consistent with Example 1. However, its formulation design does not utilize the multi-component conductive filler synergistic design of this invention; it only constructs a conductive network through a single conductive filler, failing to form a multi-component synergistic conductive structure.

[0070] (1) Slurry preparation: The conductive slurry for impregnation contains 30g of superconducting carbon black, 18g of waterborne acrylic resin, 1.5g of polycarboxylate dispersant, 50.5g of deionized water, and a viscosity of 280cP; the conductive slurry for coating contains 48g of superconducting carbon black, 22g of waterborne acrylic resin, 0.6g of hydroxyethyl cellulose thickener, 1.5g of polycarboxylate dispersant, 27.9g of deionized water, and a viscosity of 4000cP.

[0071] (2) Preparation process: Same as in Example 1.

[0072] Comparative Example 5: Corresponding to Example 3, a single slurry formulation from the prior art is used. The same conductive slurry formulation is used for both impregnation and coating, without a gradient design. This is a simple combination of existing formulations and processes, and the remaining process parameters are the same as in Example 3. However, its formulation design does not employ the gradient slurry formulation design of this invention. There is no difference in the proportion of conductive filler between the impregnation and coating slurries, and a gradient conductive network from the interior to the surface of the substrate is not constructed.

[0073] (1) Slurry preparation: The same slurry is used for both impregnation and coating. The slurry consists of 12g of superconducting carbon black, 10g of zircon-based far-infrared powder, 32g of waterborne epoxy resin, 0.3g of hydroxyethyl cellulose thickener, 0.8g of alkylphenol polyoxyethylene ether dispersant, 20g of ethanol, 24.9g of deionized water, and a viscosity of 2500 cP.

[0074] (2) Preparation process: Same as in Example 3.

[0075] Performance testing and results analysis Comprehensive performance tests were conducted on the conductive flat wires of Examples 1 to 4 and the samples of Comparative Examples 1 to 5. The tests covered resistivity per meter, batch-to-batch resistance per meter, long-term operating temperature, flexibility, electrothermal conversion efficiency, far-infrared emissivity, and coating adhesion. All tests were performed according to national standards. Specific test methods and conditions are as follows to ensure repeatability by those skilled in the art and to avoid insufficient disclosure. The test results are shown in the table below. Performance testing methods and conditions: (1) Meter resistance test: A digital multimeter (model: FLUKE8846A) was used. The ambient temperature was 25±2℃ and the relative humidity was 50±5%. A 1-meter-long conductive flat wire sample was selected. The two probes of the multimeter were fixed at both ends of the sample. After the reading stabilized, the value was recorded. Each sample was tested 3 times and the average value was taken. After 50 samples of the same specification were tested, the average meter resistance and batch deviation of all samples were calculated.

[0076] (2) Meter resistance batch deviation test: Based on the above meter resistance test data, calculate the standard deviation of meter resistance of 50 samples, and then divide it by the average meter resistance of 50 samples to obtain the batch deviation, expressed as a percentage and retained to one decimal place.

[0077] (3) Long-term use temperature test: A high-temperature aging test chamber (model: BINDERFD260) was used. The sample was placed in the test chamber and the test temperature was set (200℃, 250℃, and 300℃ respectively). The temperature was kept constant and heated for 1000 hours. The sample was taken out every 200 hours and the resistance value was measured according to the meter resistance test method. The sample was observed to see if it was damaged or the coating was peeled off. If there was no damage or the resistance drift was ≤10% within 1000 hours, the temperature was the long-term use temperature of the sample. If the sample was damaged, the coating was peeled off or the resistance drift was >10% during the test, the failure temperature was recorded.

[0078] (4) Flexibility test: A bending tester (model: GT-7010-A) was used. The ambient temperature was 25±2℃ and the relative humidity was 50±5%. The sample was fixed on the tester, the bending angle was set to 180°, the bending speed was 10 times / minute, and the sample was bent continuously for 1000 times. After the bending was completed, the resistance value of the sample was measured according to the meter resistance test method, and the resistance change rate before and after bending was calculated and expressed as a percentage. If the coating cracks or powder falls off during the bending process, the number of bends when the phenomenon first occurs was recorded.

[0079] (5) Electrothermal conversion efficiency test: The electrothermal performance tester (model: DRT-1000) was used. The test environment temperature was 25±2℃ and the relative humidity was 50±5%. The sample was connected to the rated voltage (corresponding to the voltage of each embodiment / comparative example). After working stably for 30 minutes, the input power and output heat of the sample were measured. Electrothermal conversion efficiency = (output heat / input power) × 100%, rounded to the nearest integer.

[0080] (6) Far-infrared emissivity test: Use a far-infrared emissivity tester (model: IR-2000), test ambient temperature 25±2℃, test wavelength range 8-14μm, lay the sample flat on the test platform, and record the far-infrared emissivity value after the tester reading stabilizes, retaining two decimal places.

[0081] (7) Coating adhesion test: The test shall be conducted in accordance with GB / T9286-1998 "Cross-cut test for paints and varnishes". A cross-cut tester (model: QFH) shall be used, with a cross-cut size of 1mm×1mm. After the cross-cut is made, the debris at the cross-cut area shall be gently brushed away with a soft brush. Then, 3M 600 tape shall be applied to the cross-cut area. After pressing firmly, the tape shall be quickly removed. The coating peeling shall be observed and the grade shall be determined according to the standard. Grade 0 is the best (no coating peeling) and Grade 3 is the worst (large area of ​​coating peeling).

[0082] The test results are shown in Table 1 below: Table 1:

[0083] Test Result Analysis Based on the above test data and the preparation processes of each embodiment and comparative example, the following conclusions can be drawn: (1) Performance of resistance per meter (RTM): Examples 1 to 4 achieved precise control of RTM from 155 ohms per meter (low resistance) to 9200 ohms per meter (ultra-high resistance) by gradient adjustment of the proportion of conductive filler, coating thickness, and calendering process parameters. The batch deviation of RTM for all 50 samples was controlled within 7.1%, with the batch deviation of Example 2 being only 2.7%. This indicates that the gradient slurry formulation and composite film formation process of the present invention can effectively ensure the uniformity and control precision of RTM. In contrast, Comparative Example 1 (single coating), Comparative Example 2 (impregnation only), Comparative Example 4 (single conductive filler), and Comparative Example 5 (non-gradient slurry) all showed significant deviations from the design value in RTM, with batch deviations generally greater than 7.8%. The batch deviation of Comparative Example 2 was as high as 15.2%, which could not achieve precise control of RTM. Although the initial RTM deviation of Comparative Example 3 (hot pressing without cold pressing) was small, the resistance change rate after high-temperature aging was as high as 110%, indicating extremely poor stability and failing to meet the requirements for long-term use.

[0084] (2) Temperature resistance: Examples 3 and 4 use water-based epoxy resin, modified epoxy silicone resin, and basalt fiber cloth as substrates. The long-term operating temperature can reach 300 degrees Celsius, and there is no damage or significant resistance drift after continuous heating for 1000 hours. Examples 1 and 2 have a long-term operating temperature of 250 degrees Celsius, and also have excellent high-temperature stability. However, the long-term operating temperature of each comparative example does not exceed 250 degrees Celsius. Among them, comparative examples 1, 2, and 4 are only 200 degrees Celsius, and comparative example 3 fails directly after high-temperature aging at 200 degrees Celsius. This shows that the present invention effectively improves the temperature resistance of the product by selecting high-temperature resistant resin and substrate, combined with a synergistic densification process, and is suitable for medium and high temperature application scenarios.

[0085] (3) Flexibility and coating adhesion: After bending 180 degrees 1000 times in Examples 1 to 4, the resistance change rate was controlled within 4%, and the coating adhesion reached level 0 in the cross-cut adhesion test, with no cracking or powdering. This indicates that the gradient conductive layer of the present invention is tightly bonded to the substrate, and the synergistic densification process effectively improves the flexibility and adhesion of the conductive layer. In contrast, Comparative Example 1 showed coating cracking after 100 bends, Comparative Example 2 showed coating powdering after 50 bends, and the flexibility or adhesion of Comparative Examples 3, 4, and 5 were significantly inferior to the Examples. This proves that the impregnation and double-sided coating composite film-forming process of the present invention can significantly improve the bonding force between the conductive layer and the substrate, ensuring the flexibility of the product.

[0086] (4) Electrothermal conversion efficiency and far-infrared radiation performance: The electrothermal conversion efficiency of Examples 1 to 4 is not less than 90%, and the far-infrared emissivity is not less than 0.85. Among them, the far-infrared emissivity of Example 4 is as high as 0.93, indicating that the synergistic design of the multi-element conductive filler and the addition of functional fillers in this invention can effectively construct a high-density conductive network and improve the electrothermal conversion efficiency and far-infrared radiation effect. The electrothermal conversion efficiency of each comparative example is less than 88%, and the far-infrared emissivity is less than 0.88. Among them, the far-infrared emissivity of Comparative Example 2 is only 0.70, and the electrothermal conversion efficiency is only 75%, further proving the advantages of the technical solution of this invention in improving heating performance.

[0087] In summary, this invention achieves wide-range precise control of the resistance of conductive flat wire nanometers by organically integrating gradient slurry formulation design, a composite film-forming process of impregnation and double-sided coating, and a synergistic densification technology of hot pressing and cold pressing. Simultaneously, it improves the product's temperature resistance, flexibility, electrothermal conversion efficiency, far-infrared radiation performance, and long-term stability, solving the technical problem that existing technologies and simple combinations of existing technologies cannot simultaneously achieve both precise resistance control and comprehensive performance. The test results of each comparative example further demonstrate that the core technical features of this invention (gradient slurry formulation, composite film-forming process, and synergistic densification technology) are all necessary conditions for achieving the above-mentioned technical effects; none can be omitted, and they are not simply a superposition or parameter adjustment of existing technologies.

[0088] The preparation process of this invention is sequential and the parameters are clearly defined. All testing methods and conditions are disclosed in detail. The raw materials and equipment used are all conventional commercially available products. Those skilled in the art can repeatedly prepare the conductive flat wire of this invention based on the content disclosed in this specification, fully meeting the requirements of sufficient patent disclosure. Furthermore, the technical solution of this invention is adaptable to various applications ranging from low voltage to ultra-high voltage. The preparation process is easy to scale up for continuous production, demonstrating good practical application value.

[0089] Based on the preparation process and test results of each embodiment, the core technical effect of the present invention is specifically manifested as follows: Example 1 achieves low resistivity per meter through a high proportion of multi-element conductive fillers, a thick coating, and a high-pressure hot-pressing process, laying the foundation for subsequent gradient control. Example 2 balances resistance and heating power by adjusting the conductive filler ratio and process parameters in a gradient manner, adapting to standard household voltage scenarios while improving product flexibility. Example 3 further optimizes the formula and process to improve product temperature resistance and strength, adapting to high-voltage, low-power industrial scenarios. Example 4 achieves precise preparation of ultra-high resistivity per meter through an extremely low proportion of conductive fillers and an ultra-thin coating design, while improving temperature resistance and insulation, adapting to extreme ultra-high voltage applications. Overall, this invention, through the organic integration of gradient slurry formulation, composite film formation process, and synergistic densification technology, achieves the technical goal of precise control of resistivity over a wide range and simultaneous improvement of comprehensive performance, solving the core defects of existing technologies.

[0090] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A conductive flat wire with controllable resistance per meter, characterized in that, The invention includes a substrate and a conductive layer composited inside and on the surface of the substrate. The conductive layer is formed by combining an impregnating conductive slurry and a coating conductive slurry into a film, followed by a co-densification process involving hot pressing and cold pressing. The impregnating conductive slurry and the coating conductive slurry are designed with a gradient formulation, with the conductive filler having a higher mass percentage in the coating conductive slurry than in the impregnating conductive slurry. The conductive filler has a mass percentage of 5-25% in the impregnating conductive slurry and 8-48% in the coating conductive slurry. The conductive layer forms a gradient conductive network inside and on the surface of the substrate.

2. The conductive flat wire with controllable resistance per meter according to claim 1, characterized in that, The substrate is one of flame-retardant aramid spunlace nonwoven fabric, modified glass fiber cloth, basalt fiber cloth, and high-basis-weight basalt fiber cloth, with a basis weight of 50-80 grams per square meter; the impregnating conductive slurry is composed of conductive filler, 18-38% by weight of resin binder, 0.5-1.5% by weight of dispersant and solvent; the coating conductive slurry is composed of conductive filler, 18-38% by weight of resin binder, 0.5-1.5% by weight of dispersant, solvent, and 0.2-0.6% by weight of hydroxyethyl cellulose thickener, and 5-20% by weight of functional far-infrared filler may be added to the coating conductive slurry; the solvent is deionized water or a mixture of deionized water and ethanol.

3. The conductive flat wire with controllable resistance per meter according to claim 2, characterized in that, The conductive filler is based on superconducting carbon black, and is compounded with one or more of carbon nanotubes, graphene, and ultrafine carbon fiber powder; the resin binder is one of waterborne acrylic resin, waterborne polyurethane resin, waterborne epoxy resin, and modified epoxy silicone resin.

4. The conductive flat wire with controllable resistance per meter according to claim 2, characterized in that, The dispersant is one of polycarboxylate dispersant, sodium lignosulfonate dispersant, and alkylphenol polyoxyethylene ether dispersant; the functional far-infrared filler is one or more of barium titanate-based far-infrared powder, zircon-based far-infrared powder, and barium titanate-zircon composite far-infrared powder.

5. A method for preparing a conductive flat wire with controllable micrometer resistance as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Substrate pretreatment: The substrate is soaked in room temperature deionized water and then dried by low temperature infrared drying after being rolled up; (2) Impregnation film formation: The pretreated substrate is impregnated by a two-roll impregnation mill under an impregnation pressure of 0.1-0.5 MPa. After the conductive slurry is adsorbed, it is dried to form a preliminary conductive substrate with a preliminary conductive network. (3) Double-sided coating film formation: The preliminary conductive substrate is coated on both sides using a doctor blade coater. The wet film thickness is 50-200 micrometers. After coating with conductive slurry, it is dried to form a composite conductive substrate. (4) Hot and cold pressing synergistic densification: The composite conductive substrate is continuously densified by passing it through hot and cold pressing rollers in sequence. The hot pressing pressure of the hot pressing roller is 2-10 MPa, and the cold pressing pressure of the cold pressing roller is 2-8 MPa. (5) Slitting and forming: The densified composite conductive substrate is slitting by a slitting machine to obtain conductive flat wires with controllable resistance per meter.

6. The preparation method according to claim 5, characterized in that, The substrate described in step (1) is soaked in deionized water at room temperature for 10 minutes to remove impurities on the surface of the substrate and improve the bonding force between the slurry and the substrate.

7. The preparation method according to claim 5, characterized in that, The operating speed of the twin-roll impregnation mill in step (2) is 2-6 meters per minute. The impregnation and immersion process allows the conductive filler to penetrate evenly into the gaps between the substrate fibers. The drying temperature is 100-140 degrees Celsius. After drying, the conductive filler inside the substrate forms an interconnected preliminary conductive network.

8. The preparation method according to claim 5, characterized in that, The operating speed of the doctor blade coating machine in step (3) is 1.5-5 meters per minute, forming a uniform coating slurry on both sides of the preliminary conductive substrate; the drying temperature is 115-135 degrees Celsius, and after drying, the preliminary conductive network inside the substrate merges with the conductive network of the surface coating to form a complete gradient conductive network.

9. The preparation method according to claim 5, characterized in that, The temperature of the hot pressing roller in step (4) is 130-170 degrees Celsius, and the running speed of both the hot pressing roller and the cold pressing roller is 3-6 meters per minute. Hot pressing is a high temperature and high pressure treatment, and cold pressing is a normal temperature and pressure treatment. After cold pressing, the sheet resistance of the conductive flat wire is 0.8-18.8 ohms per square.

10. The preparation method according to claim 5, characterized in that, The slitting width of the slitting machine in step (5) is 0.5-4.0 mm and the running speed is 2-8 meters per minute. The slitting width is adjusted according to the application scenario. By adjusting one or more process parameters such as the mass ratio of conductive filler in the conductive slurry, the wet film thickness of the doctor blade coating, the hot pressing pressure of the hot pressing roller, and the cold pressing pressure of the cold pressing roller, the meter resistance of the conductive flat wire is precisely controlled at 155-9200 ohms per meter.

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