Preparation process of silver nanowire transparent conductive film for ultrathin flexible touch screen

Abstract

The invention discloses a preparation process of a silver nanowire transparent conductive film for an ultrathin flexible touch screen, and belongs to the technical field of energy conservation and environmental protection. 3-mercaptopropyltrimethoxysilane is used for carrying out surface silane functionalization treatment, and the combining capacity of the silver nanowire and the substrate is enhanced; performing oxygen plasma treatment on the polyimide film to improve the surface energy; and coating the treated polyimide film with the functionalized silver nanowires, immersing the functionalized silver nanowires in a polyurethane solution to form a polyurethane-embedded silver nanowire film, and finally, carrying out annealing treatment under a vacuum condition to obtain the silver nanowire transparent conductive film. The resistance of the transparent conductive film is 20-50 omega / sq, the light transmittance is 85-95%, the resistance change is smaller than 5% when the bending radius is smaller than 5 mm, the resistance change is smaller than 3% after 1000 times of bending, and the transparent conductive film has excellent photoelectric performance and mechanical flexibility and is suitable for the fields of flexible display, wearable equipment and the like.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving and environmental protection technology. Specifically, it relates to a process for preparing a transparent conductive film with silver nanowires for ultra-thin flexible touch screens. Background Technology

[0002] With the rapid development of information technology and the electronics industry, touch display technology has become one of the main methods of human-computer interaction. Touchscreens are widely used in consumer electronics products such as smartphones, tablets, in-vehicle navigation systems, wearable devices, and smart home devices. According to market research data, the global flexible display market is projected to grow from US$15.46 billion in 2023 to US$35.49 billion in 2030, with a compound annual growth rate of 32-35.3%. This rapid growth is mainly driven by consumer demand for innovative product forms, including foldable smartphones, flexible wearable devices, curved car dashboards, and other new application scenarios. Flexible displays offer unique user experiences and entirely new product design possibilities, driving the transformation of electronic products from traditional rigid forms to flexible, foldable, and rollable forms.

[0003] As a core component of touch displays, transparent conductive films need to simultaneously possess high light transmittance, low resistance, and good mechanical flexibility. Currently, indium tin oxide (ITO) transparent conductive films are the most widely used transparent electrode material in the field of touch screens and displays. ITO films have excellent optoelectronic properties, with a light transmittance of 85-92% and good optical transparency in the visible light band. However, with the rise of flexible electronics and wearable devices, the inherent defects of ITO materials have become increasingly prominent, severely limiting their development in flexible display applications.

[0004] The main problems facing ITO materials include the following: First, ITO films are inherently brittle and lack flexibility. As a ceramic oxide material, ITO is prone to cracking and fracture under mechanical stress and cannot withstand bending, folding, or other deformations. When ITO films are deposited on flexible substrates, even small bending radii can cause the films to crack, resulting in a sharp increase in resistance and even complete loss of conductivity. This brittleness makes it difficult for ITO to meet the mechanical stability requirements of emerging applications such as foldable displays and flexible touchscreens. In applications such as wearable electronic devices and flexible OLED displays, transparent electrodes need to withstand thousands or even tens of thousands of bending cycles, which ITO materials clearly cannot meet. Second, the increasing scarcity of indium resources leads to a continuous increase in ITO costs. Indium is a rare metal element with limited and unevenly distributed global reserves. With the continued growth in demand for touch display devices, the supply of indium resources faces severe challenges. The large fluctuations in indium prices keep the cost of ITO materials high, which is detrimental to the large-scale, low-cost manufacturing of flexible electronic products. Against the backdrop of the rapid expansion of the touch screen and flat panel display market, finding alternatives to indium has become a consensus in both industry and academia. Third, the fabrication process of ITO thin films on flexible substrates is complex and presents numerous technical challenges. Commonly used flexible polymer substrates such as polyethylene terephthalate (PET) have poor high-temperature resistance, while ITO thin films typically require deposition or annealing at higher temperatures to achieve good crystallinity and electrical properties. Furthermore, there is a significant difference in the coefficients of thermal expansion between ITO and the polymer substrate, which can easily cause film expansion and cracking during processing, leading to decreased device reliability. ITO thin films also suffer from limited chemical stability, making them susceptible to corrosion under certain environmental conditions, affecting the long-term stability of devices. Fourth, ITO materials have a high refractive index and exhibit optical haze, which can affect display performance in some applications. For high-end displays and optoelectronic devices, transparent electrodes with lower refractive indices and higher optical quality are required to reduce optical losses and improve display clarity.

[0005] Based on the limitations of ITO materials, researchers have proposed various alternatives, including novel transparent conductive materials such as carbon nanotubes, graphene, metal meshes, conductive polymers, and silver nanowires. Among these, silver nanowire transparent conductive films have attracted widespread attention due to their unique performance advantages. Silver nanowires possess excellent conductivity; silver's conductivity ranks among the highest of metals, and a silver nanowire network can form a highly efficient three-dimensional conductive pathway. Compared to ITO, silver nanowire transparent conductive films have the following significant advantages: excellent flexibility, capable of withstanding large-angle bending and multiple folds without failure; light transmittance reaching 85-95%, comparable to or even higher than ITO; furthermore, the preparation cost of silver nanowires is relatively low, raw materials are readily available, and the process can be carried out at room temperature and pressure, making it suitable for large-scale production.

[0006] However, transparent conductive films made of silver nanowires still face some challenges in practical applications: the interfacial bonding between silver nanowires and flexible substrates is weak, making them prone to detachment under mechanical stress; the contact resistance between silver nanowires is high, affecting overall conductivity; silver nanowires are easily oxidized when exposed to air, reducing conductivity and stability; and the surface roughness of the silver nanowire network is relatively large, affecting the touch feel and wear resistance of touchscreens. To overcome these problems, researchers have developed various surface modification and encapsulation technologies, including plasma treatment, silane coupling agent functionalization, polymer coating, and metal oxide protective layers.

[0007] Despite significant progress in silver nanowire transparent conductive film technology, existing techniques still suffer from complex processes, poor performance consistency, and insufficient long-term stability. Achieving a harmonious balance of high conductivity, high transmittance, excellent flexibility, and long-term stability through systematic optimization of key steps such as silver nanowire synthesis, surface functionalization, substrate treatment, coating processes, and encapsulation technologies is a pressing technical challenge. Developing a simple, efficient, environmentally friendly, and mass-production-ready process for silver nanowire transparent conductive films is of significant scientific and practical value for promoting the development of emerging industries such as flexible electronics, wearable devices, and flexible displays. Summary of the Invention

[0008] To address the problems existing in the prior art, such as weak interfacial adhesion between the transparent conductive film of silver nanowires and the flexible substrate, high contact resistance between silver nanowires, easy oxidation of silver nanowires, large surface roughness, high optical haze, poor mechanical stability, and insufficient long-term environmental stability, this invention provides a process for preparing a transparent conductive film of silver nanowires for ultra-thin flexible touch screens. By systematically optimizing key steps such as surface functionalization of silver nanowires, substrate plasma treatment, polymer encapsulation, and annealing, a unified approach is achieved that combines high conductivity, high transmittance, low haze, excellent flexibility, and long-term stability. Specifically, the existing transparent conductive film technology of silver nanowires has the following main defects: (1) The interfacial bonding force between silver nanowires and the flexible substrate is weak, which easily leads to desorption and slippage. Especially on low surface energy polymer substrates such as PDMS, the silver nanowire network is prone to peeling under mechanical stress, resulting in a sharp increase in resistance or even complete failure. Poor interfacial adhesion severely limits the long-term reliability of the transparent conductive film of silver nanowires in applications that require frequent deformation, such as wearable devices and flexible displays. (2) The contact resistance between silver nanowires is high, affecting the overall conductivity. The nano-silver wire network forms a conductive path through physical contact, but the contact between nano-silver wires is often a point contact with a small contact area and a large contact resistance. In addition, the residual polymer protective agent (such as PVP) on the surface of the nano-silver wire will further increase the contact resistance and reduce the conductivity of the transparent conductive film. How to effectively reduce the contact resistance between nano-silver wires is a key technical problem to improve the film resistance. (3) Nano-silver wires are easy to oxidize and sulfide, resulting in poor long-term stability. Silver is a metal with relatively high chemical activity. Due to its high specific surface area, nano-silver wires are easily corroded by oxygen, water vapor, hydrogen sulfide, etc. in the air. Studies have shown that the sheet resistance of unprotected nano-silver wire transparent conductive film can increase by more than 50% after aging in the air for 60 days. Under high temperature environment, nano-silver wires are more prone to oxidation and agglomeration, which leads to the destruction of the conductive network. Oxidation and chemical corrosion problems seriously limit the actual application life of nano-silver wire transparent conductive film. (4) Large surface roughness affects touch performance and device life. The nano-silver wire network presents a three-dimensional random distribution, and the surface of the film formed is uneven, with a surface roughness usually reaching tens of nanometers or even higher. High surface roughness affects the touch feel and wear resistance of touch screens, and can easily cause short circuits in applications such as OLEDs, reducing device yield and stability. Surface roughness issues need to be addressed through reasonable packaging technology. (5) High optical haze affects display clarity. The diameter of silver nanowires is usually between tens of nanometers and more than one hundred nanometers, which is comparable to the wavelength of visible light, resulting in a significant light scattering effect and high film haze. High haze will cause the displayed image to be blurry, which does not meet the requirements of high-end display applications. Although using thinner and longer silver nanowires can reduce haze, it will also increase the difficulty and cost of synthesis. How to reduce haze to the ITO level (1-3%) while ensuring conductivity and transmittance is an important challenge.(6) Insufficient mechanical stability and bending durability need to be improved. Although silver nanowires themselves have good flexibility, due to weak interfacial adhesion and unstable contact points, transparent conductive films made of silver nanowires are prone to nanowire breakage, desorption, and network recombination during repeated bending, resulting in a gradual increase in resistance. Under shear stress, silver nanowires are more prone to breakage failure. Improving the mechanical stability of transparent conductive films made of silver nanowires, enabling them to withstand thousands or even tens of thousands of bending cycles without significant performance degradation, is a necessary condition for the long-term reliable operation of flexible electronic devices. (7) Existing preparation processes are complex and difficult to achieve performance consistency and large-scale production. The performance of transparent conductive films made of silver nanowires is affected by a variety of factors, including the size distribution of silver nanowires, surface treatment, coating uniformity, annealing conditions, etc. Existing technologies often require multiple independent process steps, have narrow process windows, poor reproducibility, and are difficult to achieve large-area uniform coating and mass production. Developing a simple, efficient, green, and environmentally friendly integrated preparation process suitable for large-scale production has important industrial application value.

[0009] The present invention adopts the following technical solution: a process for preparing a transparent conductive film of silver nanowires for ultrathin flexible touch screens, comprising the following steps by weight: (1) taking 50-70 parts of silver nitrate (CAS No.: 7761-88-8) and 200-300 parts of ethylene glycol (CAS No.: 107-21-1) and mixing them, then adding 10-20 parts of polyvinylpyrrolidone (weight average molecular weight of 1300000g / mol, CAS No.: 9003-39-8) and 0.1-0.5 parts of copper chloride (CAS No.: 10125-13-0), stirring and reacting, and centrifuging to obtain a silver nanowire dispersion; (2) adding 2-8 parts of 3-mercaptopropyltriazine to the silver nanowire dispersion obtained in step (1). Methoxysilane (CAS No.: 14814-09-6) was ultrasonically dispersed and heated to obtain silane-functionalized silver nanowires; (3) 100-150 parts of a polyimide film with a thickness of 50-100 μm were subjected to oxygen plasma treatment to obtain the treated polyimide film; (4) The silane-functionalized silver nanowires obtained in step (2) were coated onto the treated polyimide film obtained in step (3) with a coating thickness of 100-200 nm, and then immersed in 20-40 parts of polyurethane solution, and dried to form a polyurethane-embedded silver nanowire film; (5) The polyurethane-embedded silver nanowire film obtained in step (4) was annealed to obtain a transparent conductive film of silver nanowires.

[0010] Preferably, the parameters for the stirring reaction in step (1) are as follows: react at 120-160 rpm at 160-180℃ for 30-60 min.

[0011] Preferably, the diameter of the silver nanowires in the silver nanowire dispersion in step (1) is 20-50 nm and the length is 10-20 μm; the centrifugation parameters in step (1) are as follows: centrifuge at 8000-12000 rpm for 10-20 min.

[0012] Preferably, the ultrasonic dispersion parameters in step (2) are as follows: ultrasonication at 200-400W power for 20-40 minutes under pH 4-6 conditions.

[0013] Preferably, the parameters for the heating reaction in step (2) are as follows: 80-100℃ for 2-6 hours.

[0014] Preferably, the parameters for oxygen plasma treatment in step (3) are as follows: treatment power 50-100W, treatment time 2-10min, oxygen flow rate 60-100sccm; the polyimide film in step (3) is as follows: 4,4'-diaminodiphenyl ether (CAS No.: 101-80-4) and 3,3',4,4'-biphenyltetracarboxylic anhydride (CAS No.: 2420-87-3) are reacted in DMAc (CAS No.: 127-19-5) solvent at a mass ratio of 1:1, and 0.2-0.4 times the mass of 4,4'-diaminodiphenyl ether is added to form a polyamic acid solution, which is spin-coated onto a glass substrate and cured at 250-300℃ for 2-3h to remove the solvent and obtain the film. Introducing 2,7-diamino-9,9'-spirofluorene (2,7-DASBF) into polyimide film formulations significantly impacts the material's structure and properties, primarily in the following ways: It inhibits charge-transfer complexes (CTCs), improving transparency; the rigid, non-coplanar structure of 2,7-DASBF effectively hinders intermolecular stacking, reducing the formation of intermolecular charge-transfer complexes, thus significantly reducing the intrinsic coloration of the polyimide film, making it more transparent and colorless, suitable for optical and display applications. It improves thermal stability and glass transition temperature (Tg); the high rigidity and steric hindrance of the spirofluorene structure make the polyimide backbone more rigid, restricting molecular chain movement and significantly improving the film's thermal stability and Tg, meeting the heat resistance requirements of high-end electronics and flexible displays. It increases free volume, improving solubility and film-forming properties; the steric hindrance of the spirofluorene units increases the intermolecular distance, increasing the free volume of the polyimide, which helps improve solubility and film flexibility, facilitating the preparation of high-quality films using solution methods. The water absorption rate is reduced by introducing 2,7-DASBF, which is beneficial for the low dielectric and high reliability requirements of fields such as microelectronics and communications.

[0015] Preferably, the parameters of the polyurethane solution in step (4) are as follows: the solvent is N,N-dimethylformamide (CAS No.: 68-12-2), the solution concentration is 10-20wt%, the viscosity is 50-200cP, and the CAS No. of the polyurethane is 9009-54-5; the coating speed in step (4) is 5-15cm / s.

[0016] Preferably, the soaking time in step (4) is 10-20 min and the soaking temperature is 40-60℃; the drying parameters in step (4) are as follows: 80-120℃, 40-60 min.

[0017] Preferably, the annealing parameters in step (5) are as follows: annealing at 150-200℃ for 10-20 min under a vacuum of 0.01-0.1MPa.

[0018] Compared with existing technologies, this invention has the following advantages: significantly improved interfacial adhesion and excellent mechanical stability. This invention uses 3-mercaptopropyltrimethoxysilane to functionalize the surface of silver nanowires with silane, utilizing the bifunctional group properties of the silane coupling agent to establish a strong chemical bridge between the silver nanowires and the flexible substrate, solving the problem of weak interfacial bonding between the silver nanowires and the substrate. Combined with oxygen plasma surface treatment of the polyimide substrate, the number of hydroxyl groups and surface energy on the substrate surface are further increased, significantly enhancing the bonding strength between the silver nanowire network and the substrate. According to test data from the examples, the resistance change is less than 5% when the bending radius is less than 5 mm, and less than 3% after 1000 bends, with mechanical stability far superior to the unfunctionalized control (resistance change reaches 8.4-9.5% after 1000 bends). This excellent mechanical durability allows the transparent conductive film prepared by this invention to meet the application requirements of flexible displays, wearable devices, and other applications requiring frequent deformation. It also exhibits excellent electrical properties and low sheet resistance. This invention improves the contact quality between silver nanowires and effectively reduces contact resistance by annealing under vacuum conditions, utilizing thermally induced atomic diffusion and sintering effects. According to test results from the examples, the sheet resistance is 32.5-38.7 Ω / sq, reaching an excellent level of 20-50 Ω / sq, far lower than the comparative example's 65.9-74.8 Ω / sq. This electrical performance is comparable to or even better than ITO, meeting the high conductivity requirements of transparent electrodes for touchscreens and displays. The high conductivity of the silver nanowires stems from the excellent metallic conductivity of silver and the efficient three-dimensional conductive pathways formed by the silver nanowire network. Excellent optical performance is also achieved, with high transmittance and low haze. This invention uses silver nanowires with a diameter of 20-50 nm and a length of 10-20 μm. The optimized aspect ratio allows for a lower density of silver nanowires required for the same resistance, thereby improving transmittance and reducing optical haze. Polyurethane encapsulation fills the pores of the silver nanowire network, further reducing surface roughness and light scattering. According to the test data of the embodiments, the light transmittance reaches 88.9-91.8%, and the haze is less than 3%, which is significantly better than the 75.3-79.4% light transmittance of the comparative example. The high light transmittance and low haze enable the transparent conductive film prepared by this invention to provide a clear display effect in display devices, reaching or even exceeding the optical performance of ITO. It also exhibits excellent flexibility, making it suitable for flexible electronics applications. Due to its nanoscale diameter and good metallic ductility, the silver nanowires can effectively disperse stress when subjected to mechanical stresses such as bending, folding, or stretching, avoiding brittle fracture. The silver nanowire network is interconnected by van der Waals forces; when subjected to bending or stretching, the relative movement of the contact nodes between the silver nanowires does not affect electron transport, therefore the conductivity of the film is not significantly affected. The transparent conductive film made of silver nanowires prepared by this invention can still maintain stable electrical properties under extreme conditions with a bending radius of less than 5 mm, and its flexibility is far superior to brittle oxide materials such as ITO.This excellent flexibility makes it particularly suitable for emerging applications such as foldable displays, flexible touchscreens, and wearable electronic devices. It exhibits excellent long-term stability and strong oxidation resistance. This invention utilizes polyurethane encapsulation technology to form a protective layer on the surface of the silver nanowire network, effectively isolating it from air and moisture and protecting the silver nanowires from oxidation and chemical corrosion. The polyurethane encapsulation layer not only provides a physical barrier but also enhances the overall structural stability by filling the gaps in the silver nanowire network. According to literature reports, the transparent conductive film of silver nanowires encapsulated with the protective layer can maintain stability in air for more than two months and shows no significant performance degradation after 10,000 bending cycles. This excellent environmental stability and long-term reliability are key to the practical application of transparent conductive films of silver nanowires. High surface flatness is suitable for device integration. This invention utilizes polyurethane encapsulation technology, where polyurethane fills the pores of the silver nanowire network, significantly reducing surface roughness. The flat surface not only improves the touch feel and wear resistance of touchscreens but also avoids short-circuit problems caused by excessive surface roughness in applications such as OLEDs, improving device yield and stability. Improved surface smoothness also facilitates uniform deposition and good interfacial contact of subsequent device layers, which is of great significance for the fabrication of multilayer optoelectronic devices. The fabrication process is simple and efficient, suitable for large-scale production. This invention uses a polyol method to synthesize silver nanowires, a process that is simple, has high yield, and allows for controllable dimensions. The coating process can be carried out at room temperature and pressure, with an annealing temperature of only 150-200℃, far lower than the high-temperature deposition requirements of ITO films, and exhibits good compatibility with flexible polymer substrate processing. The entire fabrication process does not require complex vacuum equipment or expensive targets, resulting in relatively low raw material costs, making it suitable for large-area coating and mass production. Laser etching or photolithography can be used to precisely fabricate touch patterns with a patterned linewidth of 50-100μm and a resolution greater than 1000dpi, meeting the requirements of high-resolution touch screens. It is environmentally friendly and meets green manufacturing requirements. The polyol method used in this invention for synthesizing silver nanowires is relatively environmentally friendly, without involving toxic or harmful reagents. Compared to ITO, it avoids the use of the rare metal indium, alleviating resource scarcity. The preparation process has low energy consumption, aligning with the technological development trend of energy conservation and environmental protection. It exhibits good performance stability and reproducibility. This invention establishes a complete preparation process system by systematically optimizing the process parameters of key steps such as the synthesis of silver nanowires, surface functionalization, substrate treatment, coating process, and encapsulation technology, achieving consistent performance and batch stability. According to the test results of Examples 1-8, the transparent conductive films prepared under different process parameters all exhibit excellent performance (sheet resistance 32.5-38.7 Ω / sq, transmittance 88.9-91.8%, resistance change 1.8-2.4% after 1000 bends), demonstrating good process window and reproducibility. With excellent overall performance, it has broad application prospects.The transparent conductive film made of silver nanowires prepared in this invention achieves a harmonious balance of high conductivity, high transmittance, low haze, excellent flexibility, and long-term stability, with overall performance reaching or even exceeding that of ITO, while overcoming the drawbacks of ITO such as poor flexibility, resource scarcity, and high cost. This superior overall performance makes it a promising candidate for applications in flexible displays, flexible touchscreens, wearable electronic devices, flexible solar cells, transparent heaters, and electromagnetic shielding. Particularly in emerging applications such as foldable smartphones, flexible OLED displays, electronic skin, and smart textiles, the transparent conductive film made of silver nanowires is considered the most promising transparent electrode material. In summary, this invention, through innovative surface functionalization, substrate treatment, polymer encapsulation, and annealing processes, successfully solves the problems of weak interfacial adhesion, high contact resistance, easy oxidation, large surface roughness, and high optical haze in existing transparent conductive film technologies using silver nanowires. It achieves excellent performance with a sheet resistance of 20-50 Ω / sq, light transmittance of 85-95%, haze below 3%, resistance change of less than 5% at a bending radius of less than 5 mm, and resistance change of less than 3% after 1000 bends. This provides a high-performance, high-reliability, and low-cost transparent conductive film solution for emerging applications such as ultra-thin flexible touchscreens, flexible OLED displays, and wearable electronic devices, and has significant scientific value and broad application potential. Attached Figure Description

[0019] Figure 1 This is a transmission electron microscope image of the silver nanowire dispersion prepared in Example 1.

[0020] Figure 2 This is the infrared spectrum of the transparent conductive film made of silver nanowires prepared in Example 1. Detailed Implementation

[0021] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0022] Example 1 The preparation process of the transparent conductive film of silver nanowires for ultrathin flexible touch screen includes the following steps: (1) Take 60g of silver nitrate (CAS No.: 7761-88-8) and 250g of ethylene glycol (CAS No.: 107-21-1) and mix them. Then add 15g of polyvinylpyrrolidone (weight average molecular weight of 1300000g / mol, CAS No.: 9003-39-8) and 0.3g of copper chloride (CAS No.: 10125-13-0). Stir the mixture at 140rpm at 170℃ for 45min. After the reaction, centrifuge at 10000rpm for 15min to obtain a dispersion of silver nanowires, wherein the diameter of the silver nanowires is 35nm and the length is 15μm. Figure 1 As shown. (2) Add 5g of 3-mercaptopropyltrimethoxysilane (CAS No.: 14814-09-6) to the nanosilver wire dispersion obtained in step (1), and ultrasonically disperse at 300W power for 30min under pH 5 conditions, and then react at 90℃ for 4h to obtain surface silane-functionalized nanosilver wires. (3) Take 125g of polyimide film with a thickness of 75μm and perform oxygen plasma treatment. The treatment power is 75W, the treatment time is 6min, and the oxygen flow rate is 80sccm to obtain the treated polyimide film. The polyimide film is as follows: 4,4'-diaminodiphenyl ether (CAS No.: 101-80-4) and 3,3',4,4'-biphenyltetracarboxylic anhydride (CAS No.: 2420-87-3) are reacted in DMAc (CAS No.: 127-19-5) solvent at a mass ratio of 1:1. At the same time, 0.2-0.4 times the mass of 4,4'-diaminodiphenyl ether is added to 2,7-diamino-9,9'-spirofluorene to form a polyamic acid solution. The solution is spin-coated onto a glass substrate and cured at 275℃ for 2.5h to remove the solvent and obtain the film. (4) The surface-functionalized silver nanowires obtained in step (2) are coated onto the polyimide film obtained in step (3) at a coating speed of 10 cm / s and a coating thickness of 150 nm. Then, the film is immersed in 30 g of polyurethane solution for 15 min at a temperature of 50 °C. After removal, the film is dried at 100 °C for 50 min to form a polyurethane-embedded silver nanowire film. The solvent of the polyurethane solution is N,N-dimethylformamide (CAS No.: 68-12-2), the solution concentration is 15 wt%, the viscosity is 125 cP, and the CAS No. of the polyurethane is 9009-54-5. (5) The polyurethane-embedded silver nanowire film obtained in step (4) is annealed at 175 °C for 15 min under a vacuum of 0.05 MPa to obtain a transparent conductive film of silver nanowires, such as Figure 2As shown in the figure. Subsequently, a touch pattern was formed by laser etching using a picosecond laser with a wavelength of 1064nm and a power of 3W; the patterned linewidth was 75μm, and the resolution was greater than 1000dpi; the final film had a sheet resistance of 35Ω / sq, a transmittance of 90%, and a resistance change of less than 5% with a bending radius of less than 5mm. The mechanical properties were: a resistance change of less than 3% after 1000 bends.

[0023] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progress of the steps, and each table reflects different parameter values ​​for the examples / comparative examples, covering all endpoint values ​​and intermediate values. The remaining unlisted parameters are the same as in Example 1.

[0024] Table 1: Parameters of step (1)

[0025] Table 2: Parameters of step (1)

[0026] Table 3: Parameters of step (2)

[0027] Table 4: Parameters of step (3)

[0028] Table 5: Parameters of step (4)

[0029] Table 6: Parameter 2 of step (4)

[0030] Table 7: Parameters of step (5)

[0031] To verify the performance of the transparent conductive film made of silver nanowires described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included sheet resistance (Ω / sq), transmittance (%), and bending performance (resistance change %) after 1000 bends. The test methods are as follows: Sheet resistance test: The surface resistivity of the film was measured using a four-probe tester (model: Keithley 2400). Sample size: 5cm × 5cm. Transmittance test: The average transmittance of visible light (400-700nm) was measured using a UV-Vis spectrophotometer (model: UV-3600). Bending performance test: The rate of change of resistance was measured using a bending tester (radius <5mm, 1000 bends).

[0032] Table 8: Performance Test Results

[0033] Table 9: Performance Test Results II

[0034] The test results show that the sheet resistance of the products in the examples is 32.5-38.7 Ω / sq, the transmittance is 88.9-91.8%, and the bending change is 1.8-2.4%, demonstrating excellent performance. In contrast, the comparative examples showed a significant decrease in performance due to missing components or parameter deviations (e.g., sheet resistance increased to 65.9-74.8 Ω / sq, and transmittance decreased to 75.3-79.4%). This proves the superiority of the preparation process of this invention.

[0035] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A process for preparing a transparent conductive film of silver nanowires for ultrathin flexible touch screens, characterized in that: The process, by weight, includes the following steps: (1) Mix 50-70 parts silver nitrate with 200-300 parts ethylene glycol, then add 10-20 parts polyvinylpyrrolidone and 0.1-0.5 parts copper chloride, stir and react, and centrifuge to obtain a silver nanowire dispersion; (2) Add 2-8 parts 3-mercaptopropyltrimethoxysilane to the silver nanowire dispersion obtained in step (1), disperse ultrasonically and heat to react, and obtain silane-functionalized silver nanowires; (3) Take 100-150 parts of silver nanowires with a thickness of 50-100 mm (3) The polyimide film with a diameter of μm is subjected to oxygen plasma treatment to obtain the treated polyimide film; (4) The surface silane-functionalized silver nanowires obtained in step (2) are coated onto the treated polyimide film obtained in step (3) with a coating thickness of 100-200 nm. Then, it is immersed in 20-40 parts of polyurethane solution, taken out and dried to form a polyurethane-embedded silver nanowire film; (5) The polyurethane-embedded silver nanowire film obtained in step (4) is annealed to obtain a transparent conductive film of silver nanowires.

2. The fabrication process of the transparent conductive film with silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The parameters for the stirring reaction in step (1) are as follows: react at 120-160 rpm at 160-180℃ for 30-60 min.

3. The process for preparing the transparent conductive film of silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The diameter of the silver nanowires in the dispersion of the silver nanowires in step (1) is 20-50 nm and the length is 10-20 μm; the centrifugation parameters in step (1) are as follows: centrifuge at 8000-12000 rpm for 10-20 min.

4. The process for preparing the transparent conductive film of silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The parameters for ultrasonic dispersion in step (2) are as follows: ultrasonication at 200-400W power for 20-40 minutes under pH 4-6 conditions.

5. The process for preparing a transparent conductive film with silver nanowires for an ultrathin flexible touchscreen according to claim 1, characterized in that: The parameters for the heating reaction in step (2) are as follows: 80-100℃ for 2-6 hours.

6. The process for preparing the transparent conductive film of silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The parameters for oxygen plasma treatment in step (3) are as follows: treatment power 50-100W, treatment time 2-10min, oxygen flow rate 60-100sccm; the polyimide film in step (3) is as follows: 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic anhydride are reacted in DMAc solvent at a mass ratio of 1:1, and 0.2-0.4 times the mass of 4,4'-diaminodiphenyl ether and 2,7-diamino-9,9'-spirofluorene are added at the same time to form a polyamic acid solution, which is spin-coated onto a glass substrate and cured at 250-300℃ for 2-3h to remove solvent and obtain the film.

7. The process for preparing the transparent conductive film of silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The parameters of the polyurethane solution in step (4) are as follows: the solvent is N,N-dimethylformamide, the solution concentration is 10-20wt%, the viscosity is 50-200cP, and the CAS number of the polyurethane is 9009-54-5; the coating speed in step (4) is 5-15cm / s.

8. The process for preparing the transparent conductive film of silver nanowires for ultrathin flexible touch screens according to claim 1, characterized in that: The soaking time in step (4) is 10-20 min and the soaking temperature is 40-60℃; the drying parameters in step (4) are as follows: 80-120℃, 40-60 min.

9. The process for preparing a transparent conductive film with silver nanowires for an ultrathin flexible touchscreen according to claim 1, characterized in that: The parameters for annealing in step (5) are as follows: annealing at 150-200℃ for 10-20 min under a vacuum of 0.01-0.1MPa.

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