Ultra-flat flexible electronic transfer paper and preparation method thereof

Abstract

The invention relates to the technical field of papermaking, and provides ultra-flat flexible electronic transfer paper and a preparation method thereof. The electronic transfer printing paper comprises a base material layer, wherein the base material layer comprises nano cellulose and graphene oxide; the middle layer covers at least part of the surface of the base material layer, and the middle layer comprises nano silicon dioxide particles and silica-based gel; the barrier layer covers at least part of the surface of the middle layer, and the barrier layer comprises an inorganic nanosheet and a polymer; wherein the surface roughness Ra of the electronic transfer paper ranges from 10 nm to 50 nm. According to the application, the base material layer provides flexible support and basic flatness; the middle layer inhibits microcosmic unevenness and can adjust surface adhesion; the blocking layer can effectively block solvents, oxygen and moisture; the three-layer structure has a synergistic effect, so that permeation, edge warping and breakage in pattern transfer printing can be reduced, and the pattern transfer printing precision, the yield and the bending reliability are improved.

Description

Technical Field

[0001] This application relates to the field of papermaking technology, and in particular to an ultra-flat flexible electronic transfer paper and its preparation method. Background Technology

[0002] With the rapid development of flexible electronics, wearable devices, flexible displays, RFID, and printed electronics, the demand for large-area, high-precision, and low-cost graphic transfer technology is increasing. As a crucial process for transferring intricate graphics from a substrate to a flexible target substrate, the transfer process must simultaneously meet the requirements of fidelity at the micron and submicron level, high-speed roll-to-roll processing, and the bending reliability of the finished product. Therefore, the surface morphology, interfacial adhesion, and barrier properties of the transfer paper, as the intermediate carrier and release layer, directly determine the transfer quality and yield, and have a critical impact on mass production applications.

[0003] Currently, the substrates and coating technologies used for transfer printing often present a trade-off between flatness, controllable adhesion / detachment, and barrier properties. On the one hand, calendering or thick coatings can improve surface flatness macroscopically, but it is difficult to eliminate microscopic undulations at the nanoscale, leading to defects such as penetration, edge lifting, breakage, or ink droplet diffusion during the transfer of micron- and sub-meter-level patterns. On the other hand, commonly used high-barrier films or multilayer coatings often sacrifice flexibility while improving barrier properties, or make adhesion / detachment behavior uncontrollable, which is detrimental to roll-to-roll high-speed transfer and subsequent thermal and chemical treatments. Therefore, how to achieve nanoscale surface ultra-flatness while maintaining high flexibility, and simultaneously ensure controllable adhesion / detachment and excellent barrier properties, has become a key challenge restricting the yield and reliability of flexible electronic transfer printing. Summary of the Invention

[0004] In view of the above-mentioned shortcomings in the prior art, the purpose of this application is to provide an ultra-flat flexible electronic transfer paper and its preparation method.

[0005] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows: The substrate layer provides flexible support, mechanical strength, and basic flatness, wherein graphene oxide can improve rigidity, enhance interlayer flatness, and improve gas and moisture barrier properties; the intermediate layer, filled with nano-silica particles and cross-linked with silicon-based gel, forms a dense nanoscale flat layer, which can suppress microscopic undulations and achieve controllable adhesion and detachment by adjusting surface energy; the barrier layer utilizes inorganic nanosheets and polymers to form tortuous diffusion pathways, significantly reducing the interference of solvents, oxygen, and moisture on the transfer layer; the three-layer structure works synergistically to form a tighter contact and a more stable interface energy match at the transfer interface, thereby reducing problems such as ink droplet penetration, edge lifting, and breakage, ultimately improving the transfer accuracy and consistency of micron and submicron level patterns, increasing product yield and bending reliability, while also taking into account the flexibility and thermal and chemical stability required for industrial roll-to-roll processing, and facilitating compatibility with various functional inks and post-processing processes.

[0006] In a first aspect, embodiments of this application provide an ultra-flat flexible electronic transfer paper, comprising: a substrate layer comprising nanocellulose and graphene oxide; an intermediate layer covering at least a portion of the surface of the substrate layer, comprising nanosilica particles and silicon-based gel; and a barrier layer covering at least a portion of the surface of the intermediate layer, comprising inorganic nanosheets and polymer; wherein the surface roughness Ra of the electronic transfer paper is in the range of 10~50 nm.

[0007] In one alternative embodiment, the substrate layer includes embossed microstructures with a depth of 2 to 6 μm.

[0008] In an optional embodiment, the electronic transfer paper further includes: a release layer covering at least a portion of the surface of the barrier layer, the release layer comprising a polydopamine adhesive layer and a thermosensitive polymer layer; wherein the thermosensitive polymer layer comprises a copolymer of acrylic acid and N-isopropylacrylamide.

[0009] Secondly, embodiments of this application provide a method for preparing ultra-flat flexible electronic transfer paper, comprising the following steps: S100, dispersing nanocellulose and graphene oxide in an aqueous solution containing surfactant and retention agent to form a composite suspension; coating the composite suspension into a wet film, and subjecting it to drying and hot pressing to form a substrate layer; S200, coating a sol-gel precursor on the surface of the substrate layer, and sequentially performing densification and curing treatments to form an intermediate layer; S300, depositing a composite layer of inorganic nanosheets and polymer on the surface of the intermediate layer through continuous coating or rapid layer-by-layer self-assembly process to form a barrier layer, thereby obtaining ultra-flat flexible electronic transfer paper; wherein, the sol-gel precursor comprises a silicon source, nano-silica particles, and a surface energy modifier.

[0010] In an optional embodiment, in step S100, the mass fraction of graphene oxide in the composite suspension is 0.05~0.20wt%; and / or the mass fraction of nanocellulose in the composite suspension is 0.8~1.2wt%; and / or the surfactant includes a nonionic surfactant; and / or the retaining agent includes at least one of polyacrylamide derivatives and sodium carboxymethyl cellulose; and / or the hot pressing treatment temperature is 100~130℃, the pressure is 5~15MPa, and the time is 1~3min.

[0011] In an optional implementation, step S100, the drying process includes a first stage, a second stage, and a third stage; the temperature of the first stage is 55~65℃ and the relative humidity is 55~65%; the temperature of the second stage is 65~75℃ and the relative humidity is 35~45%; the temperature of the third stage is 85~95℃ and the relative humidity is 10~25%; wherein, vacuum-assisted drying is applied in the third stage, and the vacuum degree is -0.05~-0.09MPa.

[0012] In an optional implementation, in step S100, when the solid content of the wet film reaches 12-18%, the wet film is subjected to micro-embossing treatment with a pressure of 0.3-1.5 MPa to form an embossed microstructure.

[0013] In an optional embodiment, in step S200, the silicon source includes tetraethyl orthosilicate; and / or the content of the silicon source is 15~25 vol%; and / or the content of nano-silica particles is 10~15 wt%; and / or the surface energy modifier includes fluorosilane; and / or the densification treatment pressure is 10~30 MPa and the time is 3~8 min; and / or the curing treatment includes ultraviolet curing and thermal curing.

[0014] In an alternative embodiment, in step S300, the inorganic nanosheets include montmorillonite nanosheets; and / or the polymer includes chitosan; and / or the rapid layer-by-layer self-assembly process includes spray-type layer-by-layer self-assembly.

[0015] In an optional embodiment, after step S300, the method further includes: S410, depositing a polydopamine adhesive layer on at least a portion of the surface of the barrier layer by oxidative self-polymerization; S420, coating the polydopamine adhesive layer with a thermosensitive polymer precursor liquid and performing a crosslinking treatment to form a thermosensitive polymer layer; wherein the thermosensitive polymer precursor liquid contains photothermal conversion nanomaterials, including antioxidant-treated MXene nanosheets.

[0016] The beneficial effects of this application include at least the following: (1) The intermediate layer of this application smooths out the micro-unevenness of the substrate, so that the surface roughness is controlled at 10~50nm, thereby reducing ink droplet penetration, edge lifting and breakage, and improving the fidelity and transfer yield of micron and submicron level patterns; The barrier layer of this application includes inorganic nanosheets and polymer composites to form a tortuous diffusion path, which greatly reduces water vapor transmission rate and oxygen transmission rate, reduces the impact of solvent, water and oxygen on patterns and subsequent processes, and enhances storage and process tolerance. Detailed Implementation

[0017] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are only for explaining this application, but the implementation of this application is not limited thereto.

[0018] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this application pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; the amounts of experimental reagents used are, unless otherwise specified, the amounts used in conventional experimental operations; and the experimental methods used are, unless otherwise specified, conventional methods.

[0019] With the rapid development of flexible electronics, wearable devices, and printed electronics, the market urgently needs graphic transfer technology with large-area, high-precision, and low-cost characteristics. As a key process for transferring intricate graphics to flexible substrates, transfer printing requires simultaneous achievement of fidelity at the micro-nano scale, efficient roll-to-roll manufacturing, and product bending reliability. The surface morphology, interfacial adhesion, and barrier properties of the transfer paper directly determine the transfer quality and yield, and are core factors affecting mass production applications. Current substrate and coating technologies often struggle to balance flatness, controllable adhesion / detachment, and barrier properties: macroscopic flattening cannot eliminate nanoscale undulations, easily leading to defects such as pattern penetration and edge curling; while high-barrier solutions often sacrifice flexibility or make adhesion / detachment uncontrollable, restricting high-speed processing and subsequent treatments.

[0020] Therefore, how to achieve a nanoscale ultra-flat surface while maintaining high flexibility, and how to synergistically optimize controllable adhesion and detachment with excellent barrier properties, has become a key challenge in improving the yield and reliability of flexible electronic transfer printing.

[0021] In view of the above-mentioned shortcomings in the prior art, the purpose of this application is to provide an ultra-flat flexible electronic transfer paper and its preparation method.

[0022] In a first aspect, embodiments of this application provide an ultra-flat flexible electronic transfer paper, the electronic transfer paper comprising: The substrate layer comprises nanocellulose and graphene oxide; An intermediate layer, which covers at least a portion of the surface of the substrate layer, includes nano-silica particles and a silicone-based gel. A barrier layer, which covers at least a portion of the surface of the intermediate layer, comprising inorganic nanosheets and polymers; The surface roughness Ra of the electronic transfer paper is between 10 and 50 nm.

[0023] Preferably, this application provides an ultra-flat flexible electronic transfer paper comprising a substrate layer, an intermediate layer, and a barrier layer, wherein each layer works synergistically to achieve nanoscale surface flatness, controllable adhesion, and excellent barrier properties.

[0024] Specifically, the substrate layer of this application is constructed with nanocellulose as the main component to form a dense and flexible framework, with a small amount of graphene oxide added. Nanocellulose provides a continuous nanoscale fiber network structure, giving the substrate high elongation at break and mechanical flexibility. Graphene oxide, as a sheet-like nano-reinforcing phase, is dispersed between the fiber networks. Through the mechanical constraints between the sheets, it improves the flatness and tensile strength of the substrate. At the same time, its interstitial filling and interfacial steric hindrance effects can suppress the formation of large-scale pores, thereby reducing local protrusions and wrinkles during drying or hot pressing. The nano-dispersion and self-assembly characteristics of graphene oxide can effectively fill microscopic pores and form a stable network with nanocellulose through hydrogen bonds.

[0025] Furthermore, the substrate layer contains pre-stress-absorbing embossed microstructures with a depth of 2-6 μm. When the transfer paper undergoes large-area coating, drying, heat treatment, or subsequent bending, external forces can easily cause stress concentration, leading to microcracks or macroscopic ripples on the surface. By pre-setting controlled geometric deformation sites within the substrate, external stress can be dispersed and strain energy absorbed at the microscale, thereby reducing the tendency for uneven deformation of the continuous functional film layer on the surface and maintaining surface smoothness and film integrity macroscopically. If the depth is less than 2 μm, the stress relief capacity of the microstructure is insufficient, making it difficult to provide effective deformation buffering during large bending or drying shrinkage. If the depth is greater than 6 μm, the embossing itself may introduce significant morphological undulations or form visible traces during coating and post-processing, which is not conducive to smoothing. In a semi-dry state, the embossed area withstands shrinkage and stress concentration through microplastic flow or local fiber rearrangement. In subsequent processes, the smoothed intermediate layer can form a stress-compatible thickness gradient at the embossed valleys, thereby achieving a synergistic effect of microstructure buffering and nanolayer smoothing.

[0026] Preferably, the intermediate layer covers the surface of the substrate layer and is a composite dense layer with a silica-based sol-gel system as the matrix and incorporating nano-silica particles. The nano-silica particles fill in the micropores and micro-protrusions on the substrate surface, while the silica-based sol-gel undergoes hydrolysis and condensation to form a continuous inorganic-organic interpenetrating network, further smoothing the surface morphology at the nanoscale, thereby controlling the surface roughness Ra of the transfer paper within the range of 10-50 nm. Combining rigid fillers with a flexible gel matrix achieves nanoscale smoothing while dynamically controlling the adhesion and detachment behavior of the interface by adjusting the surface energy.

[0027] Preferably, the barrier layer covers the surface of the intermediate layer and comprises an inorganic nanosheet and a flexible polymer to form a composite system. The inorganic nanosheet, with its high aspect ratio, is oriented in the polymer matrix to form a multilayer staggered structure. This structure extends the diffusion path, forcing water vapor, oxygen, and solvents to migrate around it, thereby reducing water vapor permeability and oxygen permeability and achieving efficient barrier. The synergy between the inorganic nanosheet and the polymer cross-linking network constructs an incompressible thin-walled barrier, significantly improving barrier performance without sacrificing overall flexibility.

[0028] In summary, the three-layer structure works synergistically: the substrate layer provides mechanical support and dimensional stability, the middle layer achieves nanoscale surface smoothing and interfacial energy regulation, and the barrier layer provides reliable environmental isolation and protection. This allows the transfer paper to withstand the mechanical and thermal cycles required for subsequent manufacturing processes such as printing, vapor deposition, or photolithography, while maintaining a low-humidity, low-oxygen local environment during device storage and manufacturing. By organically integrating the structured substrate of nanocellulose and graphene oxide, the sol-gel-assisted nano-smoothing layer, and the inorganic nanosheet polymer composite barrier layer, the paper successfully achieves both a nanoscale ultra-smooth surface and high barrier properties in a flexible, large-area roll-to-roll process. This overcomes the technical bottleneck of traditional transfer carriers in balancing flatness, processability, and gas barrier properties, ultimately significantly reducing defects such as ink droplet penetration, edge curling, and breakage in pattern transfer, and improving transfer accuracy, yield, and device reliability.

[0029] Secondly, embodiments of this application provide a method for preparing ultra-flat flexible electronic transfer paper, comprising the following steps: S100. Nanocellulose and graphene oxide are dispersed in an aqueous solution containing surfactant and retention agent to form a composite suspension; the composite suspension is coated into a wet film, and then dried and hot-pressed to form a substrate layer. S200: A sol-gel precursor is coated on the surface of the substrate layer, and densification and curing processes are performed sequentially to form an intermediate layer. S300. On the surface of the intermediate layer, an inorganic nanosheet and polymer composite layer is deposited through continuous coating or rapid layer-by-layer self-assembly process to form a barrier layer, thus obtaining an ultra-flat flexible electronic transfer paper. The sol-gel precursor contains a silicon source, nano-silica particles, and a surface energy modifier.

[0030] Preferably, in step S100, nanocellulose (CNF) and graphene oxide (GO) are dispersed in an aqueous solution containing surfactants and retention agents to prepare a composite suspension, which is then coated into a wet film, dried, and hot-pressed to form a substrate layer. The fundamental purpose of this step is to construct a nanoscale composite substrate framework that is both dense and flexible, thereby providing a dimensionally stable, mechanically reliable, and uniform bearing surface for subsequent nano-smoothing and barrier layers. CNF forms a continuous, interpenetrating network structure in the form of nanofibers, giving the dry film good toughness and excellent flexural fatigue life. GO is dispersed in the cellulose network in the form of high aspect ratio layered nanosheets, transferring and bearing stress through frictional locking and interfacial shearing between the sheets, thereby improving the tensile modulus and smoothness retention of the substrate. Furthermore, in the wet film stage, GO can effectively suppress the formation of large-scale surface roughness by hindering the expansion of capillary channels.

[0031] Furthermore, the mass fraction of GO is controlled between 0.05% and 0.20%. Within this range, the mechanical reinforcement and leveling effects can be fully utilized, while avoiding side effects such as sheet aggregation, excessive increase in system viscosity, or introduction of unnecessary conductivity due to excessive content. The mass fraction of CNF is controlled between 0.8% and 1.2% to obtain a rheological window during film coating that allows for entanglement without excessive viscosity, thus facilitating the smooth implementation of doctor blade or slot coating in roll-to-roll processes. Nonionic surfactants are preferred, specifically including polyoxyethylene esters, polyoxyethylene-polyoxypropylene block copolymers, and fatty alcohol polyoxyethylene ethers. The role of nonionic surfactants is to effectively improve the wettability and leveling of the wet film at low concentrations and reduce the surface tension of the system. This is beneficial for the continuous and uniform formation of the film and also facilitates its removal or stable storage in subsequent high-temperature hot pressing processes. The retaining agents selected include polyacrylamide derivatives and sodium carboxymethyl cellulose. Through charge neutralization and bridging adsorption, they firmly fix the fine fibers, fillers, and nanoparticles in the slurry during the wet end stage, preventing them from being lost with moisture during coating. This significantly improves the uniformity of film formation and the final strength of the dry film. Specifically, polyacrylamide derivatives can strongly bind to the negatively charged nanocellulose and graphene oxide interfaces, forming adsorption bridges and enhancing the cohesion of the fiber network. Sodium carboxymethyl cellulose, as an anionic retaining agent and viscosity modifier, can increase the viscoelasticity of the wet film even at low concentrations, effectively suppressing sagging and flow lines during coating.

[0032] Furthermore, when the solid content of the wet film reaches 12-18%, a micro-embossing treatment with a pressure of 0.3-1.5 MPa is applied to the wet film. This solid content range corresponds to the semi-dry state of the film. At this state, the wet film retains sufficient plastic deformation capacity and fluidity, without sticking to the mold or undergoing severe backflow deformation due to excessive moisture, nor cracking or peeling under pressure due to excessive dryness. Embossing under this state allows for local rearrangement of cellulose nanofibers and the formation of a controlled thickness gradient at the embossing grooves, thereby pre-constructing microscale stress buffer zones and geometric deformation sites within the substrate. This enables the effective dispersion of stress during subsequent drying shrinkage, hot pressing densification, device fabrication, or bending stress, significantly reducing the probability of film cracks and macroscopic ripples.

[0033] Preferably, in step S100, the drying process includes a first stage, a second stage, and a third stage, with vacuum extraction supplemented in the final stage. This is to reduce the capillary tension gradient and internal vapor pressure generated during the drying process, thereby avoiding stress concentration, cracking, and curling. The temperature of the first stage is 55~65℃ and the relative humidity is 55~65%. Free water is slowly removed at a lower temperature and higher relative humidity, controlling the surface drying rate so that internal moisture has time to migrate to the surface gradient, reducing the formation of a shell on the surface that could lead to internal shrinkage. The temperature of the second stage is 65~75℃ and the relative humidity is 35~45%, accelerating moisture migration and promoting the initial hydrogen bond rearrangement between fibers. The temperature of the third stage is 85~95℃ and the relative humidity is 10~25%, combined with a vacuum degree of -0.05~-0.09MPa, to remove residual bound water and solvent molecules, thereby reducing the risk of bubble and pore formation during the hot pressing densification process. The segmented drying process can significantly reduce the stress gradient within the film layer, thereby ensuring the hot pressing densification effect and surface smoothness. The hot-pressing process involves temperatures of 100–130°C, pressures of 5–15 MPa, and durations of 1–3 minutes. This is based on the material's thermal stability, the manufacturing equipment's capacity, and the plastic flow required for film densification. Temperatures should not be too high to avoid thermal decomposition of the CNF or sol-gel matrix or irreversible volume changes. The pressure and time must be sufficient to allow for localized rearrangement of the fiber network and fillers within the substrate, increase the interfacial contact area, compress pores, and promote bonding and consolidation of the binder phase, thereby obtaining a substrate layer with uniform thickness, a smooth surface, and high mechanical strength. The hot-pressing process can be performed continuously in a flat press or hot rollers, with a short-term vacuum pre-evacuation performed before hot pressing to remove residual gases and improve the consistency of the finished product.

[0034] Preferably, in step S200, the sol-gel precursor uses tetraethyl orthosilicate as the silicon source and undergoes controlled hydrolysis and polycondensation reactions in the presence of a solvent, water, and an acid catalyst to ultimately form an inorganic or organic-inorganic interpenetrating network that can be coated and cured into a dense film on the substrate surface. The content of tetraethyl orthosilicate is controlled within the range of 15-25% by volume. If the silicon source content is too low, it may be insufficient to construct a complete and continuous thin layer to effectively fill the nanopores of the substrate; conversely, if the content is too high, it will significantly accelerate the reaction rate of the sol and increase its viscosity, thereby increasing the risk of cracking and internal stress in the coating. Silica nanoparticles at a weight ratio of 10-15% are incorporated into the sol, and high surface density is achieved through particle rearrangement. Adding a small amount of surface energy modifier, such as fluorosilane compounds, typically at a weight ratio of 0.1–0.5%, is used to regulate the initial spreading behavior of the sol on the substrate surface and the surface free energy of the cured film. Appropriate hydrophobic modification can reduce coating collapse or localized adhesion, promoting the formation of a more uniform film and providing controllable adhesion and desorption properties for subsequent interface design with the release layer. Densification treatment employs a pressure of 10–30 MPa for 3–8 minutes. Applying pressure while the sol is in a gel or semi-gel state drives the rearrangement of silica nanoparticles and hydrolysis condensation products, reducing particle spacing and increasing the contact area between inorganic networks, thereby achieving high density of the thin layer at low temperatures. Subsequent curing combines UV curing and thermal curing. UV light initiates rapid cross-linking to form a framework, while thermal curing promotes deep condensation and strengthening of the siloxane network, ultimately forming a dense, hard, and surface-energy-tunable inorganic-organic composite planar layer.

[0035] Furthermore, the preparation method of the sol-gel precursor is as follows: tetraethyl orthosilicate is pre-hydrolyzed under the action of an acidic catalyst, followed by the addition of a dispersion of nano-silica particles and ultrasonic treatment to make it uniformly dispersed; finally, a surface energy modifier is added and stirred evenly to obtain a stable, homogeneous and coatable sol.

[0036] Preferably, in step S300, an inorganic nanosheet and polymer composite layer is deposited on the intermediate layer through continuous coating or rapid layer-by-layer self-assembly to form a barrier layer. The inorganic nanosheets are preferably montmorillonite, and the polymer is chitosan. Montmorillonite nanosheets have an extremely high aspect ratio and good barrier properties; chitosan, as a natural cationic polymer, not only firmly bonds with montmorillonite through electrostatic interactions but also possesses certain film-forming and barrier capabilities. Using rapid processes such as spray-type layer-by-layer self-assembly, the nanosheets and polymer molecules can be rapidly and orderly adsorbed onto the surface, stacking layer by layer to construct a dense structure. The highly oriented inorganic nanosheets form numerous tortuous diffusion paths in the polymer matrix, greatly extending and hindering the permeation channels of small molecules such as water vapor and oxygen, thereby endowing the transfer paper with excellent barrier properties without significantly increasing thickness or sacrificing flexibility.

[0037] Furthermore, after step S300, the method further includes: S410. A polydopamine adhesive layer is formed on at least a portion of the surface of the barrier layer by oxidative self-polymerization deposition. S420. A thermosensitive polymer precursor liquid is coated onto a polydopamine adhesive layer and cross-linked to form a thermosensitive polymer layer; wherein the thermosensitive polymer precursor liquid contains photothermal conversion nanomaterials, including MXene nanosheets treated with antioxidants.

[0038] Preferably, a polydopamine adhesive layer is deposited on the barrier layer surface through the oxidative self-polymerization of dopamine in a weakly alkaline environment. This layer has excellent adhesion and versatility, providing a strong adhesion point for subsequent layers. Subsequently, a thermosensitive polymer precursor liquid containing antioxidant-treated MXene nanosheets is coated onto the polydopamine layer and cross-linked to form a thermosensitive polymer layer. The thermosensitive polymer is copolymerized from acrylic acid and N-isopropylacrylamide, exhibiting temperature responsiveness. MXene nanosheets, as a highly efficient photothermal conversion material, can be rapidly converted into heat energy by near-infrared light irradiation when transfer is required. This triggers a phase transition in the local thermosensitive polymer, causing a sharp decrease in adhesion and achieving rapid, precise, and low-damage release of the pattern. Integrating the photothermal trigger release mechanism into the transfer interface enables non-contact, spatiotemporally controllable pattern transfer, greatly improving the flexibility and precision of the transfer process.

[0039] This application has undergone multiple experiments, and some of the test results are presented here for reference to further describe the invention in detail. The following is a detailed description in conjunction with specific embodiments.

[0040] Example 1 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, and a barrier layer. The preparation method includes the following steps: S100: 0.1 wt% graphene oxide and 1.0 wt% nanocellulose are co-dispersed in an aqueous solution containing 0.05 wt% fatty alcohol polyoxyethylene ether and 0.1 wt% polyacrylamide. The mixture is subjected to high-speed shearing and ultrasonic treatment to obtain a composite suspension. A slot coater is used to coat the suspension onto a stainless steel conveyor belt to form a wet film. The wet film undergoes three stages of drying: stage 1 at 65°C and 60% relative humidity; stage 2 at 70°C and 40% relative humidity; stage 3 at 90°C and 15% relative humidity with a vacuum of -0.07 MPa. After drying, the film is hot-pressed at 120°C and 10 MPa for 2 minutes to obtain the substrate layer. S200: 20 vol% tetraethyl orthosilicate is pre-hydrolyzed in an acidic ethanol aqueous solution, followed by the addition of 12 wt% nano-silica particle dispersion and 0.3 wt% heptadecafluorodecyltrimethoxysilane. The mixture is stirred until homogeneous, and the precursor is coated onto the surface of the substrate layer. The substrate is densified under 15 MPa pressure for 5 min. Then, it is photocured by 365 nm ultraviolet light for 3 min and then heat-cured at 80 °C for 40 min to complete the thermal curing, forming an intermediate layer. S300 employs a spray-type layer-by-layer self-assembly process, alternately spraying and depositing a positively charged chitosan solution and a negatively charged montmorillonite nanosheet dispersion onto the surface of the intermediate layer, repeating the process 20 times. After each layer is deposited, it is dried with hot air, ultimately forming a dense barrier layer with alternating inorganic nanosheets and polymers, thus producing an ultra-smooth flexible electronic transfer paper.

[0041] Example 2 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, a barrier layer, and a release layer. The release layer includes a polydopamine adhesive layer and a temperature-sensitive polymer layer. The preparation method is the same as that shown in Example 1, except that: In step S100, when the wet film is dried to a solid content of 15%, an embossing roller with micro-hexagonal protrusions is used to emboss the wet film under a pressure of 0.8MPa to form an embossed microstructure with a depth of about 4μm, and then the subsequent complete drying and hot pressing are carried out. Following step S300, the method further includes: S410. Immerse the barrier layer in Tris-HCl buffer containing 2 mg / mL dopamine and shake at room temperature for 12 h to form a polydopamine adhesive layer on its surface through oxidative self-polymerization. S420: A precursor liquid containing acrylic acid, N-isopropylacrylamide monomer, crosslinking agent and 1.0 wt% antioxidant-treated MXene nanosheets as photothermal conversion material is coated onto a polydopamine layer and then crosslinked and cured by ultraviolet light to form a film, thereby forming a temperature-sensitive polymer release layer.

[0042] Example 3 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, and a barrier layer. The preparation method includes the following steps: S100: 0.05 wt% graphene oxide and 0.8 wt% nanocellulose are co-dispersed in an aqueous solution of 0.1 wt% Surfynol 465 and 0.1 wt% sodium carboxymethyl cellulose. The mixture is then subjected to high-speed shearing and ultrasonic treatment to obtain a composite suspension. The suspension is coated onto a stainless steel conveyor belt using a slot coater to form a wet film. When the solid content of the wet film reaches 12%, it is subjected to micro-embossing at a pressure of 0.3 MPa, followed by three stages of drying: stage 1 at 55°C and 65% relative humidity; stage 2 at 65°C and 45% relative humidity; stage 3 at 85°C and 25% relative humidity with a vacuum of -0.05 MPa. After drying, the substrate layer is obtained by hot pressing at 100°C and 5 MPa for 3 minutes. S200: 15 vol% tetraethyl orthosilicate is pre-hydrolyzed, followed by the addition of 10 wt% nano-silica particle dispersion and heptadecafluorodecyltrimethoxysilane. The mixture is stirred until homogeneous to obtain a precursor, which is then coated onto the surface of the substrate layer and densified under 10 MPa pressure for 8 min. UV curing and thermal curing at 60°C for 60 min are then performed sequentially to form an intermediate layer. S300: Through a continuous coating process, a composite layer of montmorillonite nanosheets and chitosan is deposited on the surface of the intermediate layer to form a barrier layer, thus producing an ultra-smooth flexible electronic transfer paper.

[0043] Example 4 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, a barrier layer, and a release layer. The release layer includes a polydopamine adhesive layer and a temperature-sensitive polymer layer. The preparation method is the same as that shown in Embodiment 3, except that after obtaining the barrier layer in step S300, the method further includes: S410. Immerse the barrier layer in Tris-HCl buffer containing 2 mg / mL dopamine and shake at room temperature for 12 h to form a polydopamine adhesive layer on its surface through oxidative self-polymerization. S420: A precursor liquid containing acrylic acid, N-isopropylacrylamide monomer, crosslinking agent and 0.5 wt% antioxidant-treated MXene nanosheets as photothermal conversion material is coated onto a polydopamine layer and then crosslinked and cured by ultraviolet light to form a film, thereby forming a temperature-sensitive polymer release layer.

[0044] Example 5 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, and a barrier layer. The preparation method includes the following steps: S100: 0.20 wt% graphene oxide and 1.2 wt% nanocellulose are co-dispersed in an aqueous solution containing 0.15 wt% fatty alcohol polyoxyethylene ether and 0.15 wt% polyacrylamide to obtain a composite suspension; this suspension is coated into a wet film, and when the solid content reaches 18%, it is subjected to micro-embossing treatment at a pressure of 1.5 MPa, followed by three stages of drying: the first stage is 65℃ and 55% relative humidity; the second stage is 75℃ and 35% relative humidity; and the third stage is 95℃ and 10% relative humidity with a vacuum of -0.09 MPa. After drying, it is hot-pressed at 130℃ and 15 MPa for 1 min to obtain the substrate layer. S200: 25 vol% tetraethyl orthosilicate is pre-hydrolyzed, followed by the addition of 15 wt% nano-silica particle dispersion and heptadecafluorodecyltrimethoxysilane to obtain a precursor; it is coated on the surface of the substrate layer, densified under 30 MPa pressure for 3 min, and then subjected to UV curing and thermal curing at 120℃ for 30 min to form an intermediate layer. S300 uses a spray-on, layer-by-layer self-assembly process to alternately deposit montmorillonite nanosheets and polymers on the surface of the intermediate layer to form a barrier layer, thus producing an ultra-smooth flexible electronic transfer paper.

[0045] Example 6 This embodiment provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer, a barrier layer, and a release layer. The release layer includes a polydopamine adhesive layer and a temperature-sensitive polymer layer. The preparation method is the same as that shown in Embodiment 5, except that after obtaining the barrier layer in step S300, the method further includes: S410. Using a spraying method, the barrier layer is sprayed into a Tris-HCl buffer solution containing 2 mg / mL dopamine and reacted in a humid environment at room temperature to form a polydopamine adhesive layer. S420: A precursor liquid containing acrylic acid, N-isopropylacrylamide monomer, crosslinking agent and 2.0 wt% antioxidant-treated MXene nanosheets is coated onto a polydopamine layer and then crosslinked and cured by ultraviolet light to form a film, thereby forming a temperature-sensitive polymer release layer.

[0046] Comparative Example 1 This comparative example provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer and a barrier layer. The preparation method is the same as that shown in Example 1, except that the substrate layer uses only 1.1 wt% nanocellulose and does not add graphene oxide.

[0047] Comparative Example 2 This comparative example provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer and a barrier layer. The preparation method is the same as that shown in Example 1, except that step S200 is omitted, that is, after the substrate layer is prepared, the barrier layer is directly deposited on the surface of the substrate layer.

[0048] Comparative Example 3 This comparative example provides an ultra-flat flexible electronic transfer paper and its preparation method. The electronic transfer paper includes a substrate layer, an intermediate layer and a barrier layer. The preparation method is the same as that shown in Example 1, except that in step S300, the barrier layer does not use inorganic nanosheets, but only a single coating of chitosan polymer in the same amount as in Example 1.

[0049] Test method: The flexible electronic transfer papers prepared in Examples 1-6 and Comparative Examples 1-6 were subjected to the following tests, and the test results are shown in Table 1: Surface roughness: The arithmetic mean roughness Ra value was determined by atomic force microscopy within a scanning range of 10μm×10μm according to GB / T 2523 standard; Tensile properties: According to GB / T 1040.3 standard, the samples were cut into standard dumbbell shapes, and the tensile strength and elongation at break were determined using a universal testing machine; Bending reliability: Using a self-made bending tester, the sample was bent 180° repeatedly with a curvature of R=3mm, and the number of cycles when visible cracks or a sudden increase in the resistance of the conductive layer was recorded. Water vapor transmission rate: The WVTR value was determined using a moisture permeability tester under the conditions of 38℃ and 90% relative humidity, according to GB / T 26253 standard. Oxygen transmission rate: The OTR value was determined using an oxygen transmission rate tester under the conditions of 23℃ and 0% relative humidity, according to GB / T 19789 standard. Pattern transfer fidelity and yield: Using a standard photolithography template, a silver nanowire mesh pattern with a linewidth of 10 μm was prepared on transfer paper and then transferred to a flexible PET substrate. The linewidth after transfer was measured using an optical microscope, and the deviation from the design value was calculated to evaluate fidelity. The percentage of pattern units without broken lines or bridging defects was counted as the transfer yield. For embodiments containing a release layer, release was triggered by an 808 nm near-infrared laser. Coefficient of thermal expansion: The CTE value was determined using a thermomechanical analyzer in the temperature range of 50~150℃ according to GB / T 4339 standard. Surface energy: The contact angles of water and diiodomethane on the sample surface were measured using a contact angle meter, and the surface energy was calculated according to the Owens-Wendt two-liquid method.

[0050] Table 1

[0051] As shown in Table 1, the ultra-flat flexible electronic transfer paper provided by this invention achieves a nanoscale ultra-flat surface, excellent mechanical and bending properties, high environmental barrier properties, and high-precision printing through the design of a multi-layer structure. The comparison of graphene oxide and its transfer capabilities demonstrates that the absence of graphene oxide leads to a deterioration in surface roughness and a significant decrease in mechanical strength and barrier properties, proving its crucial role in constructing strong and smooth substrates. Comparative Example 2 confirms that the absence of an intermediate layer results in an extremely uneven surface, making it impossible to transfer micron-level patterns. Comparative Example 3 confirms that the water and oxygen barrier properties deteriorate drastically when the barrier layer does not contain inorganic nanosheets. Furthermore, the introduction of embossed microstructures can greatly improve bending life, while the integrated photothermal response release layer enables higher precision, non-contact intelligent transfer, further expanding its application advantages.

[0052] In summary, the above embodiments and comparative data fully support the fact that this application effectively solves the technical problem of prior art in balancing flatness, flexibility, barrier properties, and controllable transfer. The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. An ultra-flat flexible electronic transfer paper, characterized in that, The electronic transfer paper includes: A substrate layer comprising nanocellulose and graphene oxide; An intermediate layer covering at least a portion of the surface of the substrate layer, the intermediate layer comprising nano-silica particles and a silicone-based gel; A barrier layer covering at least a portion of the surface of the intermediate layer, the barrier layer comprising inorganic nanosheets and a polymer; The surface roughness Ra of the electronic transfer paper is between 10 and 50 nm.

2. The electronic transfer paper according to claim 1, characterized in that, The substrate layer includes embossed microstructures with a depth of 2~6μm.

3. The electronic transfer paper according to claim 1, characterized in that, The electronic transfer paper also includes: A release layer, the release layer covering at least a portion of the surface of the barrier layer, the release layer comprising, in sequence, a polydopamine adhesive layer and a temperature-sensitive polymer layer; The temperature-sensitive polymer layer comprises a copolymer of acrylic acid and N-isopropylacrylamide.

4. A method for preparing the ultra-flat flexible electronic transfer paper as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S100. Nanocellulose and graphene oxide are dispersed in an aqueous solution containing surfactants and retention agents to form a composite suspension. The composite suspension is coated into a wet film, and then dried and hot-pressed to form the substrate layer. S200: A sol-gel precursor is coated on the surface of the substrate layer, and densification and curing processes are performed sequentially to form the intermediate layer. S300. On the surface of the intermediate layer, a composite layer of inorganic nanosheets and polymer is deposited by continuous coating or rapid layer-by-layer self-assembly process to form the barrier layer, thus obtaining the ultra-flat flexible electronic transfer paper. The sol-gel precursor comprises a silicon source, nano-silica particles, and a surface energy modifier.

5. The preparation method according to claim 4, characterized in that, In step S100, The graphene oxide in the composite suspension has a mass fraction of 0.05~0.20 wt%; and / or The nanocellulose in the composite suspension has a mass fraction of 0.8~1.2wt%; and / or The surfactant includes nonionic surfactants; and / or The retaining agent includes at least one of polyacrylamide derivatives and sodium carboxymethyl cellulose; and / or The hot pressing treatment is performed at a temperature of 100~130℃, a pressure of 5~15MPa, and a time of 1~3min.

6. The preparation method according to claim 4, characterized in that, In step S100, the drying process includes a first stage, a second stage, and a third stage; The temperature in the first stage is 55~65℃ and the relative humidity is 55~65%. The temperature in the second stage is 65~75℃, and the relative humidity is 35~45%. The temperature in the third stage is 85~95℃ and the relative humidity is 10~25%. In the third stage, vacuum-assisted drying is applied with a vacuum degree of -0.05 to -0.09 MPa.

7. The preparation method according to claim 4, characterized in that, In step S100, when the solid content of the wet film reaches 12-18%, the wet film is subjected to micro-embossing treatment with a pressure of 0.3-1.5 MPa to form the embossed microstructure.

8. The preparation method according to claim 4, characterized in that, In step S200, The silicon source includes tetraethyl orthosilicate; and / or The silicon source content is 15-25 vol%; and / or The content of the nano-silica particles is 10~15wt%; and / or The surface energy modifier includes fluorosilanes; and / or The densification treatment is performed at a pressure of 10-30 MPa for 3-8 minutes; and / or The curing process includes ultraviolet curing and thermal curing.

9. The preparation method according to claim 4, characterized in that, In step S300, The inorganic nanosheets include montmorillonite nanosheets; and / or The polymer includes chitosan; and / or The rapid layer-by-layer self-assembly process includes spray-type layer-by-layer self-assembly.

10. The preparation method according to claim 4, characterized in that, Following step S300, the following is also included: S410. A polydopamine adhesive layer is formed by oxidative self-polymerization deposition on at least a portion of the surface of the barrier layer; S420. A thermosensitive polymer precursor liquid is coated onto the polydopamine adhesive layer and crosslinked to form the thermosensitive polymer layer; wherein the thermosensitive polymer precursor liquid contains photothermal conversion nanomaterials, and the photothermal conversion nanomaterials include MXene nanosheets treated with antioxidants.

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