A flexible conductive film and a preparation method and application thereof

Abstract

The application provides a flexible conductive film and a preparation method and application thereof, and the preparation method comprises the following steps: step S1, dispersing nanoparticles in a solvent to prepare a nanometer ink; the nanoparticles are one of Cu, Cu@Ag or Cu@Ni nanoparticles, or a mixture of two or more thereof; step S2, using screen printing or ultrasonic printing to print the nanometer ink on a flexible substrate to obtain a conductive film pattern; step S3, performing heat sintering on the obtained conductive film pattern under a nitrogen atmosphere, the heat sintering is performed at a heating temperature of 200-300 DEG C for 10-30 min; and step S4, placing the conductive film pattern after heat sintering in air, and performing laser sintering treatment by using an ultraviolet nanosecond pulse laser. The technical scheme of the application can effectively improve the comprehensive performance of the conductive film, can realize low-temperature rapid sintering, and is stable in process, and can be compatible with fine forming and large-scale production.

Description

Technical Field

[0001] This invention relates to the field of flexible printing technology, and in particular to a flexible conductive film, its preparation method, and its application. Background Technology

[0002] Conductive nano-inks based on Ag and Cu nanoparticles are widely used in flexible electronics printing for commercial production due to their excellent electrical and thermal conductivity and high diffusion activity. However, traditional molding processes mainly rely on a single thermal sintering process, which typically requires prolonged processing at high temperatures (above 250°C). Common substrate materials for flexible electronics, such as polyimide (PI) and polyethylene terephthalate (PET), have poor heat resistance and are prone to deformation, aging, and even degradation during high-temperature sintering. This not only damages the mechanical properties of the substrate but also affects the adhesion between the conductive film and the substrate, leading to a shortened device lifespan. Furthermore, the thermal sintering of copper-based nano-inks requires high vacuum or a reducing atmosphere to prevent oxidation of the copper nanoparticles, resulting in high process costs and hindering large-scale production. These problems severely limit their further development and application in the field of flexible electronics.

[0003] Laser sintering, as a novel low-temperature sintering technology, has gradually become a research hotspot in flexible conductive film forming processes due to its advantages such as concentrated energy, rapid heating speed, and selective local sintering. Compared with traditional thermal sintering, laser sintering can precisely control the energy input range, heating only the patterned area of ​​the conductive film, effectively avoiding damage to the flexible substrate due to overall heating. Simultaneously, the short-duration high-temperature treatment can reduce the oxidation of nanoparticles, helping to improve the conductivity and structural density of the film. However, existing laser sintering technologies still have some shortcomings in practical applications: on the one hand, the laser sintering process parameters lack systematic optimization, making it difficult to accurately match the optimal power, frequency, energy density, and other parameters for different types of nano-inks and different flexible substrates. This often results in insufficient sintering leading to inadequate conductivity, or excessive energy causing film cracking and localized substrate damage. On the other hand, existing technologies mostly employ a single laser sintering process, without effectively combining it with processes such as thermal sintering. This makes it difficult to balance the adhesion, density, and conductivity of the conductive film, and it is also challenging to control the sintering uniformity of large-size, high-precision conductive patterns.

[0004] Furthermore, in the patterning process of conductive films, traditional screen printing is limited by the screen mesh size, resulting in low pattern precision and insufficient line spacing to meet the requirements of flexible micro / nano electronic devices. Ultrasonic printing, on the other hand, is a printing method with high-precision patterning capabilities. By rationally controlling process parameters such as ultrasonic power, dispersion intensity, and jetting intensity, and using nano-inks with appropriate viscosity and high dispersibility, the quality and consistency of pattern formation can be effectively ensured.

[0005] Therefore, developing a method for preparing flexible conductive films that features low-temperature rapid sintering, stable process, and the ability to balance precision molding and large-scale production, while effectively improving the overall performance of conductive films, has become a key technical problem that urgently needs to be solved in the field of flexible electronics. Summary of the Invention

[0006] To address the above technical problems, this invention discloses a flexible conductive film, its preparation method, and its application. It can achieve low-temperature rapid sintering, has a stable process, and can balance fine molding with large-scale production. It can also effectively improve the overall performance of the conductive film, solving problems such as high-temperature / long-time / vacuum sintering, poor microstructure density, and poor conductivity in the prior art.

[0007] The technical solution adopted by this invention is as follows:

[0008] A method for preparing a flexible conductive thin film includes the following steps:

[0009] Step S1: Disperse the nanoparticles in a solvent to prepare nano-ink; the nanoparticles are one, two or more of Cu, Cu@Ag or Cu@Ni nanoparticles.

[0010] Step S2: The nano-ink is screen-printed or ultrasonically printed on a flexible substrate to obtain a conductive film pattern;

[0011] The ultrasonic printing process includes diluting nano-ink and loading it into a pre-positioned and calibrated ink cartridge, designing the required motion pattern using drawing software and generating corresponding printing instructions, using the capillary action of a ceramic needle to draw the nano-ink from the ink cartridge, and printing the required conductive film pattern sequentially on a flexible substrate according to the printing instructions and ink jetting state.

[0012] Step S3: The obtained conductive thin film pattern is thermally sintered in a nitrogen atmosphere. The heating temperature of the thermal sintering is 200~300℃, and the duration of the thermal sintering is 10~30 min.

[0013] Step S4: Place the thermally sintered conductive film pattern in the air and perform laser sintering using an ultraviolet nanosecond pulsed laser.

[0014] The ultrasonic printing described herein utilizes ultrasonic energy for on-demand ejection. Specifically, it uses energy pulses from ultrasonic vibrations to precisely drive ink from the nozzle in the form of droplets or streams directly onto designated locations on the substrate, completing the patterning of specified points, rather than atomization and dispersion, and without the assistance of a carrier gas. Ultrasonic printing is a precise direct-write process that can directly complete the "point-to-point" forming of circuits and patterns according to a preset path, without secondary processing. Its droplet ejection frequency, landing position, and the amount of ink per droplet can all be independently and precisely controlled, achieving micron-level pattern resolution and nanometer-level local thickness adjustment. The finished products of ultrasonic printing are high-precision discrete or continuous patterns (such as patterns for flexible interdigitated electrodes, flexible RFID, etc.), which can directly meet the circuit forming requirements of flexible electronic devices. Its core value lies in "direct patterning" and "low-damage processing of flexible substrates."

[0015] The laser sintering in step S4 uses ultraviolet nanosecond pulsed lasers, which have a single wavelength and are located in the ultraviolet band (Cu, Cu@Ag, and Cu@Ni nanoparticles all exhibit obvious single ultraviolet absorption characteristics). As a narrow-spectrum directional light source, it can achieve micron-level localized selective sintering through an optical system (especially suitable for thin film patterns with different shapes and curvatures). Furthermore, the instantaneous energy and peak power density of nanosecond pulses are far superior to xenon lamp pulses (accelerating the sintering rate and improving density). In terms of the sintering mechanism, ultraviolet light can be preferentially absorbed and photolyzed by the organic coating layer on the surface of metal nanoparticles. Simultaneously, the high energy density of nanosecond pulses can create transient high temperatures locally, which not only eliminates porosity defects from previous thermal sintering but also induces directional grain growth, achieving a secondary improvement in film structure densification and conductivity. This is a fine-tuning effect that xenon lamp pulses cannot achieve.

[0016] This technical solution involves first performing thermal sintering under a nitrogen atmosphere to remove most of the organic components and initially melt the particles, followed by laser sintering to optimize the conductivity and structural density of the flexible conductive film. Step S4, laser sintering, solves the problems of low sintering strength and high interfacial porosity inherent in thermal sintering, achieving a significant reduction in film resistivity and an improvement in structural density. This meets the performance requirements of high-precision flexible electronic devices (such as micro-sensors and flexible circuit boards), resulting in finished products with better conductivity stability and mechanical reliability. The obtained flexible conductive film pattern features low resistivity, narrow spacing, large area, and functionalization. The conductive film pattern obtained through the above preparation method can have a line spacing as low as 20 μm, exhibiting excellent precision forming capabilities; simultaneously, the printing area can reach 100 cm². 2 The above meets the needs of large-scale applications.

[0017] As a further improvement of the present invention, in step S1, the size of the nanoparticles is 50~200 nm. When the nanoparticle size is less than 50 nm, the particle specific surface area is too large and the surface energy is extremely high. It is easy to agglomerate into micron-sized aggregates due to van der Waals forces. During ultrasonic printing, this can easily block the capillary channel, leading to uneven ink jetting and needle failure. When the particle size is greater than 200 nm, the particle inertia increases. During ultrasonic printing, it is difficult to achieve stable droplet formation through the adsorption-jet kinetic balance of the capillary. Furthermore, the particles are prone to settling during ink delivery, which can damage ink uniformity and cause defects such as pinholes and broken lines in the printed pattern.

[0018] As a further improvement of the present invention, in step S1, the viscosity of the nano-ink is 2200~6400 mPa·s. This technical solution maintains good dispersibility and spreadability on flexible substrate surfaces, meeting the precise jetting requirements of ultrasonic printing.

[0019] As a further improvement of the present invention, in step S1, nanoparticles with good dispersibility and uniform size and morphology are prepared by liquid phase reduction method, and dispersed in solvent to prepare nano ink with appropriate viscosity to meet the molding requirements of subsequent printing process.

[0020] As a further improvement of the present invention, in step S2, during the ultrasonic printing process, when the nano-ink is dispersed, the voltage of the ultrasonic generator is 0.8~1.5 V. This range can both break the problem of easy agglomeration of nanoparticles through ultrasonic vibration and avoid the situation where the particle structure is damaged due to excessively high voltage, or the situation where the dispersion is insufficient and the ceramic needle capillary is blocked due to excessively low voltage. When the nano-ink is jetted, the voltage of the ultrasonic generator is 10~14 V. This range can both break the problem of easy agglomeration of nanoparticles through ultrasonic vibration and avoid the situation where the particle structure is damaged due to excessively high voltage, or the situation where the dispersion is insufficient and the ceramic needle capillary is blocked due to excessively low voltage.

[0021] As a further improvement of the present invention, in step S2, the screen printing includes: placing nano-ink on a screen; using a rubber squeegee to scrape along a preset direction, and using the pressure of the squeegee to make the nano-ink leak from the mesh of the screen onto the surface of the flexible substrate to form a conductive thin film pattern, wherein the mesh size of the screen used is 200~500 mesh.

[0022] As a further improvement of the present invention, the voltage of the ultrasonic generator is 1 V when the nano-ink is dispersed, and 12 V when it is sprayed.

[0023] As a further improvement of the present invention, in step S3, the hot sintering process is carried out in a vacuum eutectic reflow oven under nitrogen atmosphere protection, and the optical coating heating plate in the oven is used to achieve precise temperature control, with an actual temperature error of ≤±1~2%.

[0024] As a further improvement of the present invention, in step S4, the power of the laser is 4.5~6 W, the frequency is 50~80 kHz, the spot size is approximately 30 μm, the overlap rate of the spot in two directions is 25~35% and 50~90% respectively, and the cumulative energy density is 4.8~9.6 J / cm². 2 .

[0025] As a further improvement of the present invention, the cumulative energy density is 7.2~9.6 J / cm³. 2 The energy density achieved using this technology allows for the formation of a denser conductive network in the thin film, further enhancing its conductivity. If the energy density exceeds 9.6 J / cm², the conductivity will be significantly improved. 2 This can easily lead to localized ablation and cracking of the thin film, and even carbonization of the substrate surface, thus damaging the overall performance of the device.

[0026] As a further improvement of the present invention, the flexible substrate is a polyimide film or a polyethylene terephthalate film.

[0027] As a further improvement of the present invention, in step S3, the heating temperature for thermal sintering is 200°C. This technical solution ensures the sintering effect while preventing damage such as deformation and aging of the flexible substrate due to high temperatures.

[0028] This invention discloses a flexible conductive film, which is prepared by the method described above.

[0029] This invention discloses the application of the flexible conductive film described above, for the preparation of flexible interdigitated electrodes, unfoldable bedside lamps, or flexible radio frequency identification tags.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] First, the technical solution of this invention improves upon the traditional single thermal sintering method by utilizing thermal sintering and ultraviolet nanosecond pulsed laser sintering technology to prepare high-performance flexible conductive films. The low-temperature thermal sintering process ensures that nanoparticles initially form a continuous conductive framework on the flexible substrate surface and avoids substrate damage. Subsequent ultraviolet nanosecond pulsed laser sintering allows for precise control of energy input and the sintering area, effectively removing the oxide layer on the nanoparticle surface, promoting full fusion between particles, filling the pores remaining after thermal sintering, forming a denser conductive network, and significantly improving the film's conductivity (resistivity can be reduced to approximately 20 μΩ·cm). The conductive film thickness can be as low as 300 nm, with a thickness uniformity error ≤5%.

[0032] Secondly, compared with traditional screen printing, this invention can utilize ultrasonic printing technology, resulting in higher forming accuracy and material utilization. By precisely controlling the adsorption and jetting of nano-ink through capillary action, stable forming of micron-sized droplets (diameter 10~50μm) can be achieved, with pattern line spacing reduced to 20μm and material utilization exceeding 95%. By optimizing ink viscosity (2200–6400 mPa·s) and printing parameters (dispersion intensity 0.8–1.5 V, jetting intensity 10–14 V), needle clogging and uneven jetting problems are effectively avoided, significantly improving process stability.

[0033] Third, this invention supports flexible switching between ultrasonic printing and screen printing, satisfying both the needs of high-precision, small-area device fabrication and large-scale printing of areas exceeding 100 cm², thus balancing high precision and large-scale requirements. Combined with a multi-axis drive system, it can also fabricate conductive patterns on various complex curved surfaces. The operation is simple, providing a practical and feasible technical solution for high-volume, highly integrated, and highly reliable 3D flexible electronic devices and packaging structures.

[0034] Fourth, at the application level, the flexible conductive film prepared by this invention possesses excellent mechanical flexibility and environmental stability, and can be widely used in the fabrication of flexible interdigitated electrodes, unfoldable bedside lamps, and flexible RFID tags. When used in flexible interdigitated electrodes, the 20μm line spacing can improve the electrode's capacitive response speed and detection sensitivity; when used in unfoldable bedside lamps, its large-area printing capability enables the integrated fabrication of the flexible conductive layer of the entire lamp body, and the ultra-thin thickness (300nm) does not affect the folding and unfolding performance of the lamp body; when used in flexible RFID tags, the excellent conductivity and flexibility ensure that the tag maintains stable signal transmission efficiency even when bent or folded. Compared with flexible conductive devices prepared by existing technologies, this invention has the advantages of superior performance, lower cost, and wider applicability, effectively overcoming the technical bottlenecks and cost limitations in the industrialization of flexible electronics. Attached Figure Description

[0035] Figure 1 This is a scanning electron microscope (SEM) image of nanoparticles in the conductive ink in Example 1 of the present invention;

[0036] Figure 2 These are schematic diagrams of the laser sintering process in Embodiments 1-3 of the present invention.

[0037] Figure 3 The images show the microstructure of Cu@Ni core-shell nanoparticles obtained by laser sintering at different cumulative energy densities in Example 2 of this invention; where (a) represents 4.8 J / cm³. 2 (b) is 7.2 J / cm 2(c) is 9.6 J / cm 2 ;

[0038] Figure 4 The conductive films obtained by thermal sintering and subsequent laser sintering of nanoparticles in Examples 1 and 2 of the present invention are compared. Among them, (a) is an appearance picture of the conductive film of Example 1, and (b) is a comparison of the resistivity of Cu nanoparticles of Example 1 and Cu@Ni core-shell nanoparticles of Example 2.

[0039] Figure 5 The results show the surface roughness test results of the conductive films obtained after laser sintering of nanoparticles in Examples 1 and 2 of the present invention; wherein, (a) is Cu nanoparticles of Example 1, and (b) is Cu@Ni core-shell nanoparticles of Example 2.

[0040] Figure 6 The results show the hydrophilicity test results of the conductive films obtained by laser sintering of nanoparticles in Examples 1 and 2 of the present invention; wherein, (a) is Cu nanoparticles of Example 1, and (b) is Cu@Ni core-shell nanoparticles of Example 2.

[0041] Figure 7 The images show the appearance of various flexible electronic devices obtained in Embodiments 2-3 of the present invention; (a) is a flexible interdigital electrode with narrow spacing printed by ultrasound; (b) is a pattern of a Peashooter head with different curvatures printed; (c) is a pattern of printed straight lines; (d) is a printed unfoldable upright bedside lamp; and (e) is a large-area flexible radio frequency identification (RFID) tag obtained by screen printing.

[0042] Figure 8 The images show the microstructure of nanoparticles obtained after single thermal sintering in Comparative Examples 1 and 2; where (a) is Cu nanoparticles of Comparative Example 1 and (b) is Cu@Ni core-shell nanoparticles of Comparative Example 2. Detailed Implementation

[0043] The preferred embodiments of the present invention will be described in further detail below.

[0044] Example 1

[0045] A method for preparing a flexible conductive thin film includes the following steps:

[0046] (1) Preparation of nano-ink: Cu nanoparticles with good dispersibility and uniform size and morphology were prepared using the existing liquid-phase reduction method, with a particle size of 70–120 nm. The Cu nanoparticles were dispersed in a mixed solution of terpineol and ethanol to prepare Cu nano-ink with a viscosity of approximately 5000–6400 mPa·s to meet the molding requirements of subsequent printing processes. The scanning electron microscope image of the nanoparticles in the conductive ink is shown below. Figure 1 As shown.

[0047] (2) Using screen printing to achieve patterned forming of conductive film: Cu nano ink is placed on the screen; a rubber squeegee is used to uniformly scrape along the preset direction, and the pressure of the squeegee is used to make Cu nano ink leak from the mesh of the screen onto the surface of polyethylene terephthalate (PET) substrate to form a fine conductive film pattern, wherein the mesh size of the screen used is 200~500 mesh.

[0048] (3) Thermal sintering: The printed conductive film pattern is thermally sintered to improve the adhesion between the film and the flexible substrate and the conductivity of the film itself. The thermal sintering process is carried out in a vacuum eutectic reflow oven under nitrogen atmosphere protection. The optical coating heating plate in the oven is used to achieve precise temperature control, and the actual temperature error is ≤±1~2%. The specific sintering parameters are: heating temperature is 200℃, and the duration is 10~20 min.

[0049] (4) Laser sintering: The thermally sintered conductive film pattern is then placed in air and laser sintered using an ultraviolet nanosecond pulsed laser. The process diagram is shown below. Figure 2 As shown, the conductivity and structural compactness of the thin film were further optimized through precise laser energy input. Specific laser sintering parameters were: laser power of 4.5–6 W, frequency of 50–80 kHz, spot size of approximately 30 μm, overlap rates of 31% and 80% in the two directions, and cumulative energy density of 7.2–9.6 J / cm². 2 .

[0050] The application involves using the prepared flexible conductive film pattern to fabricate flexible electrodes and flexible radio frequency identification (RFID) tags.

[0051] The conductive thin film pattern obtained in this embodiment exhibits excellent conductivity, dense structure, and good adhesion to flexible substrates. The thickness of this conductive thin film can be as low as 300 nm, with a thickness uniformity error ≤5%. An image of the conductive thin film is shown below. Figure 4 As shown in (a), the resistivity is as follows Figure 4 As shown in (b), the resistivity of the flexible conductive electrode obtained after sintering Cu nanoparticles is as low as below 20 μΩ·cm. Further observation of the surface morphology of this conductive film reveals a surface roughness as low as 147 nm. Figure 5 As shown in (a), the conductive film exhibits good surface smoothness. The wetting angle test results are as follows: Figure 6 As shown in (a), the conductive film has good hydrophilicity and a wetting angle as low as 56.8±0.5°, which further proves the excellent structural compactness and good adhesion to the flexible substrate of the conductive film.

[0052] Example 2

[0053] Another method for preparing flexible conductive films, which differs from Example 1 in that:

[0054] This embodiment utilizes the existing dual-stabilizer system liquid-phase reduction method to prepare Cu@Ni core-shell nanoparticles with good dispersibility and uniform size and morphology. The particle morphology is as follows: Figure 1 As shown, its average particle size is 90 nm. These nanoparticles are then used in subsequent nano-ink preparation, printing, and sintering processes to obtain high-performance flexible conductive film patterns. Step (4) of this embodiment employs laser sintering with different cumulative energy densities.

[0055] The conductive film pattern obtained in this embodiment also exhibits excellent conductivity, dense structure, and good adhesion to flexible substrates. For example... Figure 3 As shown, the cumulative energy density reaches 7.2~9.6 J / cm². 2 During this process, the connection region between the sintering necks of Cu@Ni core-shell nanoparticles rapidly increases, forming a large-area, dense sintered network structure. The resulting conductive film has a good appearance and higher conductivity, with its resistivity still reaching below 20 μΩ·cm. Figure 4 As shown. Figure 5 (b) shows the surface roughness of the conductive film obtained after laser sintering of the nanoparticles, indicating that the conductive film has good surface smoothness. The wetting angle test results are as follows: Figure 6 As shown in (b), the conductive film has good hydrophilicity and a wetting angle as low as 61.9±0.7°, indicating that the conductive film has excellent structural compactness and good adhesion to the flexible substrate.

[0056] The preparation method described in this embodiment can be used to prepare materials with an area of ​​100 cm². 2 The above-mentioned large-area mass-printed flexible RFID devices, such as Figure 7 As shown in (e), the flexible RFID device has excellent conductivity and flexibility, which can ensure that the tag can maintain stable signal transmission efficiency even when it is bent or folded.

[0057] Example 3

[0058] This embodiment provides another method for preparing the aforementioned flexible conductive film and its application, which differs from Embodiments 1 and 2 in that:

[0059] The Cu@Ni core-shell nanoparticles from Example 2 were continued for the subsequent preparation, printing, and sintering of nano-inks, but the printing method was changed to ultrasonic printing. The specific printing steps were as follows: the nano-ink was diluted to a viscosity of 2000-2800 mPa·s and loaded into a pre-positioned and calibrated ink cartridge; the required pattern was designed using drawing software and corresponding printing instructions were generated; the nano-ink was drawn from the cartridge using the capillary action of a ceramic needle, and the desired conductive film pattern was sequentially printed on the flexible substrate according to the printing instructions and ink jetting state; during ultrasonic printing, the dispersion intensity of the nano-ink was controlled at 1 V, and the jetting intensity was controlled at 12 V to achieve stable jetting of micron-sized droplets. After sintering, a high-performance flexible conductive film pattern was obtained.

[0060] The flexible conductive film pattern prepared by the method of this embodiment can be used to prepare flexible interdigitated electrodes, curved patterns of different curvatures, straight lines, and unfoldable bedside lamps, such as... Figure 7 As shown in (a)-7(d), these conductive thin film patterns have a line spacing as low as 20 μm, possess excellent precision forming capabilities, and can meet the needs of large-scale applications.

[0061] Comparative Example 1

[0062] The difference between this comparative example and Examples 1-3 is that the nanoparticles used are the same Cu nanoparticles as in Example 1, and the printed Cu nanoparticle conductive film pattern is subjected to a single thermal sintering process instead of laser sintering. The microstructure obtained after thermal sintering is as follows. Figure 8 As shown in (a), the Cu nanoparticles still exhibit a relatively loose nanoparticle morphology. The magnified image shows that only a small number of Cu nanoparticles form a good sintering neck structure. At the same time, the Cu nanoparticles do not show obvious surface melting and pre-sintering phenomena such as particle rounding, indicating that under the single hot sintering condition, the Cu nanoparticles do not form a good dense sintering structure and cannot effectively guarantee the excellent conductivity of the conductive film pattern.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Examples 1-3 and Comparative Example 1 is that the nanoparticles used are Cu@Ni core-shell nanoparticles, and the printed Cu@Ni nanoparticle conductive film pattern is subjected to a single thermal sintering process instead of laser sintering. The microstructure obtained after thermal sintering in this comparative example is as follows. Figure 8As shown in (b), although the Cu@Ni core-shell nanoparticles exhibited obvious surface melting and pre-sintering phenomena such as particle rounding, and a clear sintering neck appeared, the particles still maintained a relatively loose nanoparticle distribution similar to Cu nanoparticles, without forming a dense sintered conductive film pattern. Therefore, laser sintering is particularly important and necessary for improving the structural density and conductivity of the nanoparticle conductive film pattern.

[0065] In summary, the technical solution of this invention improves upon the traditional single thermal sintering method, utilizing thermal sintering and ultraviolet nanosecond pulsed laser sintering technology to achieve the fabrication of high-performance flexible conductive films. Ultraviolet nanosecond pulsed laser sintering allows for precise control of energy input and the sintering area, effectively removing the oxide layer on the surface of nanoparticles and forming a denser conductive network, significantly improving the film's conductivity. Furthermore, by leveraging the capillary action of the ceramic needle and controlling ultrasonic printing parameters, stable jetting of micron-sized droplets can be achieved, avoiding ink waste. In addition, this technology can fabricate various complex curved conductive patterns and adapt to the structural needs of various complex 3D flexible electronic devices, and can be widely used in the fabrication of flexible interdigitated electrodes, unfoldable bedside lamps, and flexible RFID tags, among other applications.

[0066] The above description, in conjunction with specific preferred 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, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a flexible conductive thin film, characterized in that, Includes the following steps: Step S1: Disperse the nanoparticles in a solvent to prepare nano-ink; the nanoparticles are one, two or more of Cu, Cu@Ag or Cu@Ni nanoparticles. Step S2: The nano-ink is screen-printed or ultrasonically printed on a flexible substrate to obtain a conductive film pattern; The ultrasonic printing process includes diluting nano-ink and loading it into a pre-positioned and calibrated ink cartridge, designing the required motion pattern using drawing software and generating corresponding printing instructions, using the capillary action of a ceramic needle to draw the nano-ink from the ink cartridge, and printing the required conductive film pattern sequentially on a flexible substrate according to the printing instructions and ink jetting state. Step S3: The obtained conductive thin film pattern is thermally sintered in a nitrogen atmosphere. The heating temperature of the thermal sintering is 200~300℃ and the duration is 10~30 min. Step S4: Place the thermally sintered conductive film pattern in the air and perform laser sintering using an ultraviolet nanosecond pulsed laser.

2. The method for preparing a flexible conductive thin film according to claim 1, characterized in that: In step S1, the size of the nanoparticles is 50~200 nm; the viscosity of the nano-ink is 2200~6400 mPa·s.

3. The method for preparing a flexible conductive thin film according to claim 1, characterized in that: In step S2, during the ultrasonic printing process, the voltage of the ultrasonic generator is 0.8~1.5 V when the nano-ink is dispersed, and the voltage of the ultrasonic generator is 10~14 V when the nano-ink is ejected; the screen printing includes: placing the nano-ink on a screen; using a rubber squeegee to scrape along a preset direction, and using the pressure of the squeegee to make the nano-ink leak from the mesh of the screen onto the surface of the flexible substrate to form a conductive thin film pattern, wherein the mesh size of the screen used is 200~500 mesh.

4. The method for preparing the flexible conductive thin film according to claim 3, characterized in that: The dispersion intensity of the nano-ink is 1 V, and the jetting intensity is 12 V.

5. The method for preparing a flexible conductive thin film according to claim 1, characterized in that: In step S4, the laser power is 4.5~6 W, the frequency is 50~80 kHz, the spot size is approximately 30 μm, the overlap rate of the spot in two directions is 25~35% and 50~90%, respectively, and the cumulative energy density is 4.8~9.6 J / cm². 2 .

6. The method for preparing a flexible conductive thin film according to claim 5, characterized in that: The cumulative energy density is 7.2~9.6 J / cm³. 2 .

7. The method for preparing a flexible conductive thin film according to claim 1, characterized in that: The flexible substrate is a polyimide film or a polyethylene terephthalate film.

8. The method for preparing a flexible conductive thin film according to claim 1, characterized in that: Step S3, the heating temperature for hot sintering is 200°C.

9. A flexible conductive film, characterized in that: The flexible conductive film was prepared using the preparation method described in any one of claims 1 to 8.

10. The application of the flexible conductive film as described in claim 9, characterized in that: It can be used to prepare flexible interdigitated electrodes, deployable bedside lamps, or flexible radio frequency identification tags.

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