Method for preparing flexible transparent electroluminescent film through solution method digital printing

Abstract

The invention provides a method for preparing a flexible transparent electroluminescent film through solution method digital printing, and relates to the field of displayers, and the method comprises the following steps: S1, preparing alternating current luminescent material ink; s2, preparing a viscoelastic substrate; s3, ink droplets of alternating current luminescent material ink are embedded and deposited through a liquid-liquid interface to form independent luminescent display units; and S4, digitally printing the flexible transparent alternating-current electroluminescent film. According to the method, orange, green and blue three-primary-color independent light emitting and mixed color matching are adopted, deposition is accurately controlled through ink droplet formula optimization and printing parameter adjustment and through systematic ink droplet refining and interaction Newtonian fluid dynamics analysis adjustment, and repeatable manufacturing of a multi-component structure is achieved; the problem that an alternating-current electroluminescent display is compatible with transparency, flexibility and color control is solved, high-precision and multi-color flexible transparent dynamic display is achieved, and the method can be widely applied to wearable equipment and vehicle-mounted navigation.

Description

Technical Field

[0001] The invention relates to the technical field of electroluminescent devices, and in particular to a method for preparing a flexible transparent electroluminescent film by digital printing using a solution method. Background Art

[0002] As flexible electronic display technology is widely used in wearable electronics, human-computer interaction and other fields, flexible transparent multi-color electroluminescent systems, as key components of wearable displays, still face challenges in achieving high transparency, flexibility and precise color control.

[0003] Among light-emitting diodes (LEDs), organic light-emitting diodes (OLEDs), electrochromic technologies (ECDs), and AC electroluminescence, LED / QLEDs: micro-μLEDs have high resolution, such as 1600PPI, but inorganic materials are rigid and complex to package. Organic materials (PeLED / OLEDs) have problems such as environmental sensitivity, efficiency-transparency trade-off, and short lifespan. Electrochromic technology: Relies on external light, has slow response speed, and has limited color control, such as Ni 2+ Active luminescence cannot be achieved in smart glass, ion gel electrode displays, etc. Traditional AC electroluminescence technology: ZnS-based materials are doped with luminescent centers, such as Cu and Mn, dispersed in dielectric prepolymers PDMS and PVDF, which have advantages such as uniform luminescence.

[0004] The existing technology has the following problems: (1) Material level: It is difficult to balance the dispersibility of luminescent particles and the dielectric properties of the matrix. High concentration doping easily leads to non-radiative recombination, while low concentration leads to insufficient brightness. (2) Preparation process: Patterning accuracy depends on complex pre-processing such as photolithography. Ink droplet spreading and agglomeration problems in inkjet printing lead to structural distortion, limiting high-resolution display to <200PPI. (3) Device performance: The existing method of multi-color integration is achieved by stacking multiple emission layers. It requires precise control of the electric field distribution of each luminescent layer, making it difficult to achieve uniform excitation and resulting in low transparency. Therefore, it is necessary to propose a preparation method for a flexible, transparent, multi-color AC electroluminescent display. Summary of the Invention

[0005] To address the shortcomings of the prior art, the present invention provides a method for preparing flexible, transparent electroluminescent films by solution-based digital printing. The solution-based printing method employs unique dynamic threshold-limited deposition behavior on a viscoelastic substrate. The dielectric prepolymer in the ink droplet acts both as a dispersion medium for the electroluminescent material and as an independent viscoelastic substrate for the droplet. The droplet as a whole depresses within the viscoelastic substrate, creating a threshold-limited wrapping effect at the liquid-liquid interface. By regulating and controlling deposition through Newtonian fluid dynamics analysis of droplet refinement and interaction, the method overcomes the problem of uneven electric field distribution during multi-color integration, a challenge encountered in conventional technologies.

[0006] The present invention provides a method for preparing a flexible transparent electroluminescent film by solution-based digital printing, which comprises the following steps: S1. Preparing AC luminescent material ink: doping a dielectric material prepolymer with an AC electroluminescent material, and dispersing the AC electroluminescent material from the dielectric material prepolymer to obtain an AC luminescent material ink; S2. Preparing a viscoelastic substrate: selecting a prepolymer that is heterogeneous with the dielectric material prepolymer in step S1, uniformly adding an initiator to form a mixture, preparing a liquid prepolymer viscoelastic substrate from the mixture, and pre-curing and oxygen plasma treating the liquid prepolymer viscoelastic substrate; S3. Ink droplets of AC luminescent material ink are embedded and deposited at a liquid-liquid interface to form independent light-emitting display units: ink droplets formed by dispersing AC electroluminescent material from a dielectric material prepolymer are deposited on a liquid prepolymer viscoelastic substrate through a nozzle, and the deposition motion trajectory of the ink droplets at the interface of the liquid prepolymer viscoelastic substrate is regulated to form a structure in which the ink droplets are confinedly embedded within the liquid prepolymer viscoelastic substrate. After the ink droplets and the dielectric material of the liquid prepolymer viscoelastic substrate are solidified as a whole, the AC electroluminescent material in the ink droplets is dispersed in the dielectric material after the dielectric material prepolymer is solidified and is integrally embedded in the dielectric material substrate after the liquid prepolymer viscoelastic substrate is solidified, thereby forming an independent light-emitting display unit; S4. Digitally print a flexible transparent AC electroluminescent film: The prepared multi-color AC luminescent material ink is loaded into a digital printer cartridge, and the print head aperture size, inkjet pressure and speed, and printing parameters are adjusted. The ink droplets are sequentially inkjet-printed on the surface of the cured prepolymer viscoelastic substrate in step S2 according to a preset pattern through the nozzle using the method of step S3 to obtain a flexible transparent electroluminescent film.

[0007] Preferably, in step S1, the AC luminescent material ink includes 1.5 wt% Cu doped ZnS or SrS green ink, 0.3 wt% Cu doped ZnS or SrS blue ink, and Mn doped ZnS or SrS orange ink.

[0008] Preferably, in step S1 , by adjusting the doping concentration and the ratio of the dielectric material prepolymer, independent luminescence of the three primary colors and mixed color adjustment can be achieved.

[0009] Preferably, the dielectric material prepolymer is PDMS prepolymer, TPU prepolymer, PUA prepolymer, PVA prepolymer or PVDF prepolymer.

[0010] Preferably, in step S4, the nozzle diameter, extrusion pressure and interlayer spacing are adjusted so that the ink droplets are dynamically confined and deposited on the PDMS prepolymer substrate to form a light-emitting layer with uniform thickness.

[0011] Preferably, in step S3, the deposition trajectory of the electroluminescent ink on the interface of the viscoelastic substrate is controlled by utilizing capillary force, interfacial tension, interfacial wetting and interfacial adsorption force in the fluid.

[0012] Preferably, in step S4, the printing parameters include a nozzle diameter of 20-500 μm, an extrusion pressure of 2-12 psi, and a layer spacing of 20-200 μm.

[0013] Preferably, in step S3 , the thickness of the independent light-emitting display unit is 5-200 μm, and the distance between adjacent units is ≧10 μm.

[0014] Preferably, in step S1, ultrasonic dispersion is performed at a frequency of 40 kHz for 25 minutes, PDMS prepolymer is added at a curing mass ratio of 10:1, and stirring is performed at a speed of 500 rpm for 10 minutes, and vacuum degassing is performed at 0.1 MPa for 10 minutes to form a multi-color AC luminescent material ink.

[0015] Preferably, step S5 is also included, in which a flexible transparent multi-color AC electroluminescent display is prepared using a flexible transparent electroluminescent film. The specific process is: after the flexible transparent electroluminescent film is treated with oxygen plasma, a single-walled carbon nanotube electrode is printed on the flexible transparent electroluminescent film, a current limiting resistor is connected to the transistor, and a prepolymer protective layer is spin-coated, and the edges are sealed to obtain a flexible transparent multi-color AC electroluminescent display. The flexible transparent multi-color AC electroluminescent display is a multi-layer structure including a bottom ITO / PET transparent electrode, a middle patterned electroluminescent layer and a top SWCNT conductive network, and a dielectric material layer is provided between each layer of the multi-layer structure.

[0016] Compared with the prior art, the beneficial effects of the present invention are embodied in: (1) The method of the present invention obtains the rheological characteristics of the viscoelastic substrate through quantitative analysis of functional group molecular bonds. The solution-printed ink droplets of the present invention will form a special dynamic threshold-limited deposition behavior on the viscoelastic substrate. The dielectric material prepolymer in the ink droplet acts as both a dispersion medium for the electroluminescent material in the ink and a viscoelastic substrate. The ink droplet is sunken in the viscoelastic substrate area in contact, thereby forming a liquid-liquid interface threshold-limited wrapping effect. During the printing process, by regulating the interfacial tension, interfacial wetting, and interfacial adsorption forces during the liquid-liquid interface contact between the ink droplet and the viscoelastic substrate, the ink droplet is embedded in the viscoelastic substrate in a controllable confined area.

[0017] (2) This invention uses the three primary colors of orange, green, and blue to emit light independently and mix them for color matching. By analyzing and controlling the deposition of ink droplets through Newtonian fluid dynamics analysis and regulation, while ensuring the transparency and flexibility of the device, it overcomes the problem of uneven electric field distribution during multi-color integration in traditional technologies. Its innovative liquid-liquid interface embedded deposition process constructs a sandwich structure consisting of a bottom ITO / PET transparent conductive film, a middle patterned light-emitting layer, and a top SWCNT transparent conductive network. This ultimately achieves high-precision dynamic display and wide color gamut coverage, demonstrating significant application advantages in scenarios such as wearable device heart rate monitoring and in-vehicle navigation symbol projection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart for preparing the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 2 Schematic diagram of the ink droplet deposition process in the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 3 This is a scanning electron microscope image of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 4 This is a graph showing the visible light transmittance of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 5 Schematic diagram of the structure of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 6 This is a diagram of the printing structure mechanism of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 7 This is a test chart of the luminous performance of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 8 A diagram showing the color gamut achievable by the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 9 This is a mechanical performance test diagram of the flexible transparent multi-color AC electroluminescent display of the present invention; Figure 10 The flexible transparent multi-color AC electroluminescent display of the present invention is applied to wearable devices and vehicle-mounted dynamic displays; Figure 11 Schematic diagram of the preparation of a flexible transparent multi-color AC electroluminescent display according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0019] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0020] The present invention provides a method for preparing a flexible transparent electroluminescent film by digital printing using a solution method, such as Figure 1 As shown, it includes the following steps: S1. Preparation of AC Luminescent Material Ink: An AC electroluminescent material is doped with a dielectric prepolymer, and the AC electroluminescent material is dispersed from the dielectric prepolymer to produce an AC luminescent material ink. By adjusting the doping concentration and the ratio of the dielectric prepolymer, independent emission of the three primary colors and mixed color adjustment can be achieved. AC electroluminescent materials can be obtained by doping luminescent centers such as copper (Cu), manganese (Mn), and cerium (Ce) into semiconductor dielectric materials such as zinc sulfide (ZnS) and strontium sulfide (SrS). Subsequently, embedding the AC electroluminescent material into the dielectric material can produce stable AC electroluminescence. The target color can be configured as needed in specific applications. In this example, a ZnS-based phosphor-doped PDMS prepolymer was used, including 1.5wt% Cu-doped ZnS green ink, 0.3wt% Cu-doped ZnS blue ink, and Mn-doped ZnS orange ink. By adjusting the doping concentration and ratio, independent emission of the three primary colors of red, green, and blue and mixed color adjustment can be achieved. 10~50wt% ZnS phosphor and PDMS prepolymer were ultrasonically dispersed at 40kHz for 25min, PDMS curing agent was added at a curing mass ratio of 10:1, and stirred at 500rpm for 10min. The mixture was vacuum degassed at 0.1MPa for 10min to form a multi-color AC luminescent material ink.

[0021] In other embodiments, the AC electroluminescent material may also be SrS, and the dielectric material prepolymer may be polydimethylsiloxane PDMS prepolymer, thermoplastic polyurethane TPU prepolymer, polyurethane acrylate PUA prepolymer, polyvinyl alcohol PVA prepolymer or polyvinylidene fluoride PVDF prepolymer.

[0022] S2, prepare viscoelastic substrate: select a prepolymer that is heterogeneous with the dielectric material prepolymer in step S1, uniformly add an initiator to form a mixture, spin coat or extrude the above mixture to prepare a liquid prepolymer viscoelastic substrate, and the liquid prepolymer viscoelastic substrate is cured to form a flexible transparent dielectric layer. The prepolymer in this step is heterogeneous with the dielectric material prepolymer in step S1, and can also be one of dimethylsiloxane PDMS prepolymer, thermoplastic polyurethane TPU prepolymer, polyurethane acrylate PUA prepolymer, polyvinyl alcohol PVA prepolymer or polyvinylidene fluoride PVDF prepolymer. In a specific embodiment, the liquid prepolymer viscoelastic substrate is partially cured by pre-curing the liquid prepolymer viscoelastic substrate at 80 degrees Celsius for 45 seconds to 90 seconds, preferably 45 seconds, to prevent the ink droplets from diffusing in the prepolymer substrate during printing, affecting the accuracy of the printed structure. Accurate pre-curing time can avoid the curing time being too long, which makes the prepolymer substrate polymerization degree high, resulting in the ink droplets not being completely wrapped and embedded. After pre-curing, the surface of the pre-cured prepolymer viscoelastic substrate is treated with oxygen plasma to increase the surface free energy of the prepolymer.

[0023] The viscoelastic base prepolymer and the dielectric material prepolymer of the ink in step S1 are heterogeneous and are different media, which can avoid the diffusion of ink droplets in the base due to diffusion when the two are the same medium, thereby causing AC electroluminescence diffusion to reduce printing accuracy.

[0024] S3. Ink droplets of AC luminescent material ink are embedded and deposited at the liquid-liquid interface to form independent light-emitting display units: ink droplets formed by dispersing AC electroluminescent materials from dielectric material prepolymers are deposited on a liquid prepolymer viscoelastic substrate through a nozzle, and the deposition motion trajectory of the ink droplets at the interface of the liquid prepolymer viscoelastic substrate is regulated to form a structure in which the ink droplets are confined and embedded inside the liquid prepolymer viscoelastic substrate. After the ink droplets and the dielectric material of the liquid prepolymer viscoelastic substrate are solidified as a whole, the AC electroluminescent material in the ink droplets is dispersed in the dielectric material after the dielectric material prepolymer is solidified and is embedded in the dielectric material substrate after the liquid prepolymer viscoelastic substrate is solidified, forming an independent light-emitting display unit. In a specific embodiment, the ink droplets are precisely deposited on the PDMS prepolymer by digital printing. After 30 seconds, the ink droplets are precisely sunk into the PDMS prepolymer and heated and cured at 80 degrees Celsius for 10 minutes. A multi-color AC electroluminescent film is obtained.

[0025] S4. Digitally print a flexible transparent AC electroluminescent film: The prepared multi-color AC luminescent material ink is loaded into a digital printer cartridge, and the print head aperture size, inkjet pressure and speed, and printing parameters are adjusted. The ink droplets are sequentially inkjet-printed on the surface of the cured prepolymer viscoelastic substrate in step S2 according to a preset pattern through the nozzle using the method of step S3 to obtain a flexible transparent electroluminescent film.

[0026] like Figure 2 As shown in the figure, based on the Navier-Stokes equations and dimensionless analysis, the Pareto condition for droplet formation is obtained for an Ohnesorge value Z, 4 ≤ Z ≤ 14, with a 200 μm nozzle, 8 psi pressure, and 1.5 mm spacing for a 40 wt% ink. Dynamic confined deposition of ink droplets on the PDMS prepolymer substrate was achieved by adjusting the nozzle diameter, extrusion pressure, and interlayer spacing. The Ohnesorge value Z, also known as the Ohnesorge number, describes the balance between viscous forces, inertial forces, and surface tension during droplet formation.

[0027] like Figure 3 Scanning electron microscope images of the device's cross-section show clear edges in the device's heterostructure and uniform thickness of the light-emitting layer. Printing parameters range from a nozzle diameter of 20 to 500 μm, extrusion pressure of 2 to 12 psi, and interlayer spacing of 20 to 200 μm. The thickness of the independent light-emitting display units ranges from 5 to 200 μm, with spacing between adjacent units ≥10 μm.

[0028] The multi-color AC luminescent material ink was deposited onto a pre-cured viscoelastic substrate and, after printing, was vacuum-cured at 80°C for 30 min to form a cross-linked luminescent layer.

[0029] In a specific embodiment, the invention also includes preparing a flexible transparent multi-color AC electroluminescent display, which is specifically as follows: S5, forming pixelated light-emitting units by liquid-liquid interface embedding deposition: digitally printing single-walled carbon nanotube electrodes on the flexible transparent AC electroluminescent film, connecting a current limiting resistor and a transistor, and spin-coating a 400μm thick PDMS protective layer, sealing the edges, and forming a flexible transparent multi-color AC electroluminescent display. Figure 4 As shown, the visible light transmittance of the flexible transparent multi-color AC electroluminescent display is >45%.

[0030] like Figure 5 As shown in the figure, a multi-color flexible transparent display is designed by integrating orange / green / blue electroluminescent inks with different emission layers. The display has a three-layer structure, including a bottom ITO / PET transparent electrode, a middle patterned AC electroluminescent light-emitting layer and a top SWCNT conductive network, with a PDMS dielectric layer between each layer. The patterned AC electroluminescent light-emitting layer is sandwiched between two insulating layers, and a stable strong electric field of more than 200V / cm can be formed in the light-emitting layer. Moreover, due to the protection of the dense insulating layer, impurities and moisture can be prevented from damaging the light-emitting layer. Equivalent circuit analysis confirms the parallel capacitive coupling, as shown in Figure 5 Inset. Green emission (λ ≈ 500 nm) is generated by excited Cu 2+ The subsequent radiation of the ion t2→ e g The orange emission band (λ≈590nm) originates from the spin-gap Mn due to orbital transition. 2+ A2 electrons in ions (3d 5 configuration, high spin state S=5 / 2) transition 4 T1→ 6 A2, where the transition probability is enhanced by lattice distortion mediated by vibronic coupling, which partially relaxes the spin selection rule. In contrast, the blue emission centered at λ ≈ 470 nm comes from the 3d 9 Allowed parity 3 crystal field splitting under tetrahedrally coordinated Cu + Center of 3D 10 Intra-ion transitions.

[0031] like Figure 6 As shown in Figure 2, the luminance of the printed light-emitting unit decreases as the thickness increases, regarding the mechanism of digital printing structure and display performance. Figure 7As shown in Figure 1, the brightness of the electroluminescence increases with increasing voltage and frequency. Performance increases with increasing voltage (100-400 Vpp) at 1000 Hz. When 400 Vpp is applied, the brightness of the blue light is 22 cd / m 2 , the brightness of orange light is 14cd / m 2 The CIE1931 color gamut range of flexible transparent multicolor AC electroluminescent display is as follows: Figure 8 As shown. Figure 9 As shown, the display was bent back and forth using a dedicated flexible conductive film testing device at a fixed bend radius of 8 mm and a strain rate of 1 Hz. The electroluminescence intensity was measured with a luminance meter after every 2,000 cycles. After 20,000 cycles, the electroluminescence intensity remained at 89.4%.

[0032] Materials, voltage, and frequency for achieving multi-color AC electroluminescent display color Material Voltage frequency Luminous intensity green ZnS:Cu(Cu: 1.5wt%) 60~400Vpp 100~4000Hz <![CDATA[1 cd / m 2 ~100cd / m 2 ]]> blue ZnS:Cu(Cu: 0.3wt%) 60~400Vpp 100~10000Hz <![CDATA[0.7 cd / m 2 ~85cd / m 2 ]]> orange color ZnS:Mn 60~400Vpp 100~10000Hz <![CDATA[0.3 cd / m 2 ~60cd / m 2 ]]> like Figure 10 and Figure 11 As shown, in a preferred embodiment, the flexible, transparent, multi-color AC electroluminescent display prepared by the present invention is used to display navigation symbols on vehicle smart windows and heart rate alarms on wearable devices. Under a power supply of 400 Vpp and 1000 Hz, a 10×10 addressable matrix architecture realizes a special-shaped display interface. The system uses a color signal protocol to achieve real-time cardiovascular status visualization: a green emission state of 60-100 bpm corresponds to heart condition, an orange state of >100 bpm indicates tachycardia, and a blue state of <60 bpm indicates bradycardia. The integrated alphanumeric display module enables continuous cardiovascular parameter tracking, establishing a collaborative platform for physiological monitoring.

[0033] The fabrication method of this invention demonstrates the feasibility of digitally printed multicolor AC electroluminescent displays for developing intelligent wearable diagnostic interfaces. Beyond wearable devices, the digital printing method also possesses multifunctional automotive integration capabilities. A high-definition 20×30 pixel array facilitates dynamic navigation symbology, projecting intersection guidance arrows with spatial precision, while a 10×10 pixel matrix replicates regulatory traffic signal patterns. The vehicle speed monitoring subsystem utilizes a color feedback mechanism: a green display between 30 and 80 km / h indicates optimal urban speed parameters, a blue indicator light <30 km / h indicates suboptimal operation, and an orange alert >80 km / h activates when the speed limit is exceeded. When integrated into an automotive glazing system, this adaptive display architecture provides dual-function navigation assistance and safety warnings while maintaining essential optical transmittance.

[0034] The replacement scheme for the materials used in the flexible transparent multi-color AC electroluminescent display of the present invention is as follows: 1. Dielectric material replacement: Flexible dielectric materials such as thermoplastic polyurethane (TPU) and polyvinylidene fluoride (PVDF) can be used. By adjusting the molecular weight and cross-linking degree, the rheological properties can be optimized to adapt to different printing parameters.

[0035] 2. Electrode material replacement: Silver nanowires (AgNWs), indium tin oxide (ITO) nanoparticles, etc. can replace SWCNTs to improve conductivity, but the surface needs to be hydrophilic treated to improve the interface bonding with PDMS.

[0036] The above embodiments are merely descriptions of preferred implementations of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A method for preparing a flexible transparent electroluminescent film by solution-based digital printing, characterized in that: It includes the following steps: S1. Preparing AC luminescent material ink: doping a dielectric material prepolymer with an AC electroluminescent material, and dispersing the AC electroluminescent material from the dielectric material prepolymer to obtain an AC luminescent material ink; S2. Preparing a viscoelastic substrate: selecting a prepolymer that is heterogeneous with the dielectric material prepolymer in step S1, uniformly adding an initiator to form a mixture, preparing a liquid prepolymer viscoelastic substrate from the mixture, and pre-curing and oxygen plasma treating the liquid prepolymer viscoelastic substrate; S3. Ink droplets of AC luminescent material ink are embedded and deposited at a liquid-liquid interface to form independent light-emitting display units: ink droplets formed by dispersing AC electroluminescent material from a dielectric material prepolymer are deposited on a liquid prepolymer viscoelastic substrate through a nozzle, and the deposition motion trajectory of the ink droplets at the interface of the liquid prepolymer viscoelastic substrate is regulated to form a structure in which the ink droplets are confinedly embedded within the liquid prepolymer viscoelastic substrate. After the ink droplets and the dielectric material of the liquid prepolymer viscoelastic substrate are solidified as a whole, the AC electroluminescent material in the ink droplets is dispersed in the dielectric material after the dielectric material prepolymer is solidified and is integrally embedded in the dielectric material substrate after the liquid prepolymer viscoelastic substrate is solidified, thereby forming an independent light-emitting display unit; S4. Digitally print a flexible transparent AC electroluminescent film: The prepared multi-color AC luminescent material ink is loaded into a digital printer cartridge, and the print head aperture size, inkjet pressure and speed, and printing parameters are adjusted. The ink droplets are sequentially inkjet-printed on the surface of the cured prepolymer viscoelastic substrate in step S2 according to a preset pattern through the nozzle using the method of step S3 to obtain a flexible transparent electroluminescent film.

2. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: In step S1 , the AC luminescent material ink includes 1.5 wt % Cu doped ZnS or SrS green ink, 0.3 wt % Cu doped ZnS or SrS blue ink, and Mn doped ZnS or SrS orange ink.

3. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 2, characterized in that: In step S1, by adjusting the doping concentration and the ratio of the dielectric material prepolymer, independent luminescence of the three primary colors and mixed color adjustment can be achieved.

4. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: The dielectric material prepolymer is PDMS prepolymer, TPU prepolymer, PUA prepolymer, PVA prepolymer or PVDF prepolymer.

5. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 4, characterized in that: In step S4, the nozzle diameter, extrusion pressure and interlayer spacing are adjusted so that the ink droplets are dynamically confined and deposited on the PDMS prepolymer substrate to form a light-emitting layer with uniform thickness.

6. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: In step S3, the deposition trajectory of the electroluminescent ink on the interface of the viscoelastic substrate is controlled by utilizing the capillary force, interfacial tension, interfacial wetting and interfacial adsorption force in the fluid.

7. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: In step S4 , the printing parameters include a nozzle diameter of 20 to 500 μm, an extrusion pressure of 2 to 12 psi, and a layer spacing of 20 to 200 μm.

8. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: In step S3 , the thickness of the independent light-emitting display unit is 5-200 μm, and the distance between adjacent units is ≧10 μm.

9. The method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: In step S1, ultrasonic dispersion at a frequency of 40 kHz was performed for 25 minutes, PDMS prepolymer was added at a curing mass ratio of 10:1, and stirring was performed at a speed of 500 rpm for 10 minutes. Degassing was performed at a vacuum of 0.1 MPa for 10 minutes to form a multi-color AC luminescent material ink.

10. A method for preparing a flexible transparent electroluminescent film by solution-based digital printing according to claim 1, characterized in that: The method further includes step S5, wherein a flexible transparent multi-color AC electroluminescent display is prepared using the flexible transparent electroluminescent film. The specific process is as follows: after the flexible transparent electroluminescent film is treated with oxygen plasma, a single-walled carbon nanotube electrode is printed on the flexible transparent electroluminescent film, a current limiting resistor is connected to the transistor, and a prepolymer protective layer is spin-coated. The edges are sealed to obtain a flexible transparent multi-color AC electroluminescent display. The flexible transparent multi-color AC electroluminescent display is a multi-layer structure including a bottom ITO / PET transparent electrode, a middle patterned electroluminescent layer, and a top SWCNT conductive network, and a dielectric material layer is provided between each layer of the multi-layer structure.

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