A flexible high-end packaging material based on an electroluminescent layer and a method for producing the same

Abstract

The application discloses a flexible high-end packaging material based on an electroluminescent layer and a preparation method thereof. The material forms a three-dimensional network matrix by paper pulp fibers, and a plurality of micro-electroluminescent bodies with single fibers as structural units are dispersed in the matrix. The structure is as follows: a dielectric layer formed by parallel orientation and stacking of kaolin sheet layers modified by amino silane is adsorbed on the surface of the paper pulp fibers, and a luminescent layer formed by compounding of sulfonic acid type waterborne polyurethane and ZnS:Cu fluorescent powder with surface grafting of polyacrylic acid is filled in the gap between adjacent fibers; wherein the Zeta potential of the kaolin is +15mV to +40mV, and the Zeta potential of the fluorescent powder is -25mV to -50mV. The application builds the electroluminescent structure in the paper fiber network, maintains the inherent hand feeling and post-printing processing suitability of the paper, and simultaneously obtains uniform light emission and excellent bending resistance and moisture and heat aging resistance.

Description

Technical Field

[0001] This invention relates to the field of functional packaging materials technology, specifically to a flexible packaging material with an integrated electroluminescent structure within a paper-based fiber network and its preparation method in the wet end of papermaking. This material can be applied to decorative luminescence and security anti-counterfeiting labels on high-end packaging for tobacco, alcohol, cosmetics, and cultural and creative gifts. Background Technology

[0002] In the packaging industry, enhancing product shelf appeal or achieving high-level anti-counterfeiting measures by adding dynamic visual effects such as luminescence and color changing has become a clear requirement for high-end brands. Compared to traditional decorative methods such as hot stamping and laser engraving that rely solely on ambient light, electroluminescent (EL) technology can actively emit light on the packaging surface, offering greater visual impact and recognizability.

[0003] Attaching thin-film EL devices to the surface of packaging materials is a common integration method. A typical approach involves sequentially printing a transparent conductive layer, a ZnS:Cu phosphor emitting layer, a barium titanate dielectric layer, and a carbon paste back electrode layer onto a PET base film. This is then processed using a roll-to-roll process to form a complete EL functional film, which is subsequently laminated to the packaging paper base surface using an adhesive layer. This type of solution addresses, to some extent, the problem of rigid EL devices being unable to bend with the packaging.

[0004] However, when applied to high-end packaging materials, the above solutions still reveal several structural shortcomings. Firstly, the increased thickness leads to a distorted feel. High-end packaging paper typically has a thickness between 100 and 300 μm, while a single EL functional film, along with necessary adhesive and protective layers, often exceeds 60 μm in total thickness, sometimes even reaching over 100 μm. This accumulation of thickness noticeably alters the stiffness, bending resilience, and surface feel of the packaging paper, causing the final product to lose the original high-end texture of the paper. Secondly, when the EL functional film is laminated with the paper base, the difference in deformation capacity between the film layer and the paper base during subsequent post-printing processes such as die-cutting, creasing, and folding can easily lead to delamination and bubbling at stressed areas, or breakage and failure of the luminescent layer at creases.

[0005] CN101289822A discloses a scheme for directly coating EL functional paste on the surface of paper, but its specification clearly points out that the roughness and porosity of the paper lead to uneven thickness and poor uniformity of the light-emitting layer.

[0006] In recent years, some studies have attempted to directly incorporate functional fibers such as conductive and luminescent fibers into paper pulp during wet papermaking, aiming to fundamentally eliminate the thickness of the functional layer. This approach aims to break down EL devices into fiber-level units and embed them into the three-dimensional network of paper, allowing the final paper to retain its inherent thickness and feel. However, this path faces unique technological challenges: how to construct a continuous and complete insulating dielectric layer on the surface of a single pulp fiber, while simultaneously ensuring that the luminescent material effectively fills the gaps between fibers and forms an electric field pathway. Pre-fabricated core-sheath structure functional fibers only have physical contact with the pulp fibers, making it difficult to form a stable electrical interface. Furthermore, attempting to generate the insulating and luminescent layers on-site during the wet papermaking stage requires addressing disturbances from multiple dynamic factors such as dehydration, flow, and diffusion, making the precise positioning of the functional components almost uncontrollable.

[0007] Therefore, there is a need for a solution that can spontaneously complete the structural differentiation and orderly arrangement of the dielectric layer and the light-emitting layer at the scale of a single fiber by utilizing the fiber template effect and the charge interaction between components in the wet end of the papermaking process. This would allow for the achievement of integrated electroluminescent function on the paper base without substantially affecting the feel, thickness, and post-printing processing suitability of the paper. Summary of the Invention

[0008] In view of this, the present invention proposes a flexible high-end packaging material based on an electroluminescent layer and its preparation method, aiming to establish an ordered electroluminescent structure inside the fiber network while retaining the feel and processing suitability of the paper base.

[0009] The technical solution of this invention is implemented as follows: This invention provides a flexible high-end packaging material based on an electroluminescent layer, comprising a three-dimensional network matrix formed of pulp fibers. Multiple micro-electroluminescent units, each with a single fiber as a structural unit, are dispersed within the three-dimensional network matrix. Each micro-electroluminescent unit has the following structure: a dielectric layer is adsorbed onto the surface of the pulp fibers, the dielectric layer being formed by stacking two-dimensional nanosheet materials in an orientation parallel to the fiber surface; a light-emitting layer is filled in the gaps between adjacent pulp fibers, the light-emitting layer being composed of an ionic polymeric electrolyte and an electroluminescent phosphor.

[0010] In some embodiments, the aforementioned two-dimensional nanosheet material is kaolin modified with aminosilane, with a sheet thickness of 5-20 nm and a sheet diameter of 200-800 nm. The pulp fiber is bleached sulfate softwood pulp fiber, with a fiber diameter between 15-35 μm and a fiber length of 1.5-3.5 mm. Kaolin sheets naturally possess a high aspect ratio, and after aminosilane treatment, their surface carries a positive charge in a weakly acidic to neutral aqueous environment. When such a sheet material encounters pulp fibers, which typically have a negatively charged surface, in the wet end, electrostatic force drives the sheets to rapidly spread and stack on the fiber surface in an orientation parallel to the fiber surface, thereby forming a dense dielectric sheath layer with uniform thickness and consistent sheet orientation. It is estimated that, at the micrometer scale of the gaps between wet paper fibers, the time it takes for nanosheets to diffuse from the liquid phase to the fiber surface and be electrostatically captured is on the order of milliseconds to seconds. Within the 5-20 second vacuum suction window used in the example, the sheets have sufficient time to complete multilayer stacking.

[0011] In some embodiments, the aminosilane-modified kaolin in an aqueous dispersion at pH 6–8 has a surface zeta potential of +15 mV to +40 mV, preferably +18 mV to +30 mV. This potential range provides sufficient electrostatic attraction between the kaolin sheets and the pulp fibers (which typically carry a negative charge on their surface and have a zeta potential between -15 mV and -35 mV) to drive the sheets to migrate toward the fiber surface and complete directional coating.

[0012] In some embodiments, the aforementioned ionic polymeric electrolyte is a sulfonic acid-based aqueous polyurethane, with the sulfonic acid group content controlled within the range of 0.15~0.40 mmol / g. The electroluminescent phosphor is ZnS:Cu, with polyacrylic acid grafted onto its particle surface, and the grafting rate is preferably 3~8 wt%. When the grafting rate is below 3 wt%, the carboxyl group density on the phosphor surface is low, the absolute value of the Zeta potential may be insufficient, and the charge repulsion separation effect tends to weaken; when the grafting rate is above 8 wt%, the polyacrylic acid shell is too thick, which may provide some shielding for electric field excitation. The aforementioned range of 3~8 wt% is a balance range selected after comprehensively considering charge density and luminous efficiency. Both components carry a negative charge in the aqueous phase. In an aqueous dispersion with pH 6~8, the surface Zeta potential of the electroluminescent phosphor with polyacrylic acid grafted on its surface is -25mV to -50mV.

[0013] During the wet paper web forming stage, when negatively charged sulfonic acid-based waterborne polyurethane emulsion particles and phosphor particles grafted with polyacrylic acid encounter positively charged kaolin sheets already adsorbed on the fiber surface, the charge repulsion effect causes them to leave the fiber surface area and migrate and accumulate in the interfiber spaces. Subsequently, during the hot-pressing and drying process, the waterborne polyurethane solidifies into a film, bonding the phosphor particles within the fiber gaps to form a continuous luminescent layer. This luminescent layer, together with the kaolin dielectric layer coating the fiber surface, constitutes a complete micro-electroluminescent unit.

[0014] In some embodiments, the thickness of the dielectric layer is preferably controlled within the range of 50-150 nm, wherein the number of stacked layers of the two-dimensional nanosheet material is approximately 5-15. This thickness range provides insulation for the AC driving electric field required for electroluminescence. In terms of microstructure, the sheet material is stacked in an orientation parallel to the fiber axis along the fiber surface, and a certain amount of slippage can occur between adjacent sheets, which makes it less likely for the dielectric layer to develop through-cracks when the fiber is bent.

[0015] It should be noted that the determination of the dielectric layer thickness mentioned above takes into account both the dielectric strength of kaolin (typically 10~20 kV / mm) and the typical driving voltage range (50~150 V) of the electroluminescent phosphor ZnS:Cu. Taking a dielectric layer thickness of 100 nm as an example, at a driving voltage of 100 V, the electric field strength within the dielectric layer is approximately 1 MV / cm (i.e., 100 kV / mm). For nanoscale inorganic sheet stacked structures, due to the blocking effect of the sheet interfaces on charge transport during electron avalanche, their actual breakdown strength is often higher than that of bulk materials of the same material. An appropriate driving voltage can be selected accordingly during implementation.

[0016] In some embodiments, to further enhance the tolerance of phosphor particles during processing and use, silica nanoparticles with a particle size range of 15-30 nm can be distributed in the polyacrylic acid graft layer. The silica nanoparticles can be introduced by chemically bonding them to polyacrylic acid segments using γ-methacryloyloxypropyltrimethoxysilane (KH570). This inorganic-organic hybrid coating layer enhances the barrier effect against moisture and mechanical stress without significantly increasing the coating thickness.

[0017] In some embodiments, to enable the individual micro-electroluminescent elements dispersed within the fiber network to be uniformly driven, a transparent conductive layer is also permeated onto the upper and / or lower surfaces of the three-dimensional network substrate. The material of this transparent conductive layer can be PEDOT:PSS. Its penetration depth is preferably controlled within the range of 0.5 to 2 times the diameter of the pulp fibers. The penetration depth can be controlled by adjusting the solid content, viscosity, and coating method of the PEDOT:PSS aqueous dispersion. This structure allows a transparent electrode network electrically connected to the internal micro-electroluminescent elements to be formed on the paper surface without the need for an additional conductive film bonded to the entire sheet.

[0018] The present invention also provides a method for preparing the above-mentioned flexible high-end packaging material, the method comprising the following steps: The pulp fiber suspension with a freeness controlled at 35-50°SR is dewatered and shaped in the papermaking wire section until a wet paper web with a moisture content of 40-60% is obtained. At this point, the paper web has been initially shaped, and a physical network of overlap has been established between the fibers. However, a continuous water film still exists on the fiber surface, and the gaps between fibers are also filled with water, preserving channels for the subsequent penetration and directional migration of functional pulps.

[0019] A functional slurry is prepared, comprising at least an aqueous dispersion of aminosilane-modified kaolin, a sulfonic acid-based aqueous polyurethane emulsion, an aqueous dispersion of ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid, and a photoinitiator. The aminosilane-modified kaolin exhibits a surface zeta potential of +15mV to +40mV in the aqueous dispersion at pH 6–8, and the ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid exhibits a surface zeta potential of -25mV to -50mV in the same aqueous dispersion.

[0020] The functional slurry is sprayed onto at least one surface of the wet paper web.

[0021] Vacuum suction is applied to the wet paper web after spraying, with a vacuum level of -0.02 to -0.06 MPa and a suction time of 5 to 20 seconds. The water flow generated by the vacuum suction, perpendicular to the paper web plane, drives the components of the functional pulp to penetrate into the fiber network along the thickness direction of the paper web. During this process, positively charged kaolin sheets are electrostatically captured and spread and stacked along the fiber surface when flowing over the negatively charged pulp fiber surface; while negatively charged sulfonic acid-based waterborne polyurethane emulsion particles and phosphor particles are pushed into the depth of the fiber gaps due to charge repulsion when they encounter the fiber surface that has adsorbed kaolin. Thus, spatial differentiation of dielectric layer components and light-emitting layer components is achieved at the scale of a single fiber.

[0022] The wet paper web after vacuum suction is hot-pressed and cured at a temperature of 80~120℃ and a pressure of 0.1~0.5MPa. During the hot-pressing process, sulfonic acid-based waterborne polyurethane cures and forms a film, locking the phosphor particles within the fiber gaps, while the paper web is compacted to the target thickness.

[0023] It should be noted that the matching relationship between the vacuum suction time window and adsorption kinetics can be verified through the following experimental observation: Under the preparation conditions of Example 1 below (vacuum degree -0.04 MPa), samples after different suction times (2 seconds, 5 seconds, 8 seconds, 12 seconds, and 20 seconds) were taken, freeze-dried, and the fiber cross-section was observed by scanning electron microscopy. When the suction time was 2 seconds, the coverage of kaolin sheets on the fiber surface was about 60%, and there were some exposed areas; when the suction time reached 5 seconds, the coverage increased to about 90%; when the suction time reached 8 seconds or more, a continuous and complete sheet coating was formed on the fiber surface, with 8 to 12 stacked layers. It can be seen that under the vacuum conditions, a suction time of 5 to 20 seconds is sufficient to complete the directional assembly of the dielectric layer.

[0024] In some embodiments, the functional slurry also contains a multifunctional acrylate crosslinking agent, such as trimethylolpropane triacrylate (TMPTA). During hot pressing, the paper web is irradiated with ultraviolet light, causing the sulfonic acid-based waterborne polyurethane to undergo dual crosslinking through both thermo-curing and photo-curing. This dual curing helps increase the crosslinking density and cohesive strength of the luminescent layer, reducing the risk of cohesive failure during subsequent bending and indentation processes.

[0025] In some embodiments, the components of the functional slurry, by weight, are: 100 parts aminosilane-modified kaolin, 60-90 parts sulfonic acid-based waterborne polyurethane, and 100-130 parts ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid. The total solid content of the functional slurry is 20-30 wt%. The spraying rate is preferably 20-30 g / m³ (wet weight). 2 .

[0026] In some embodiments, the functional slurry also contains 2 to 10 parts by weight of silane coupling agent-modified nano-silica, the nano-silica having a particle size of 15 to 30 nm, based on the solid content.

[0027] In some embodiments, after the hot pressing step, the material is further further subjected to a step of coating at least one surface with a PEDOT:PSS aqueous dispersion and drying at a low temperature of 40-60°C to form a transparent conductive layer. The PEDOT:PSS may be of a grade with a solid content of 0.8%-1.5%, and after coating and drying, it forms a transparent conductive network with a surface sheet resistivity of 200-500 Ω / sq.

[0028] It should be noted that the aforementioned wet paper web moisture content window of 40-60% was determined through experimental screening. When the moisture content is above 60%, excessive free water occupies the interfiber spaces, diluting the functional pulp after spraying and reducing component concentration, which is detrimental to subsequent electrostatic adsorption and spatial differentiation. When the moisture content is below 40%, the water film on the fiber surface begins to rupture, and the capillary channels between fibers partially close, making it difficult for the functional pulp to effectively penetrate into the paper web. The 40-60% range balances pulp permeability with the maintenance of component concentration, providing a suitable medium environment for the self-assembly process.

[0029] It should also be noted that there is a correlation between the vacuum level and the suction time. When the vacuum level is -0.02 MPa, the suction time should be 15-20 seconds; when the vacuum level is -0.06 MPa, the suction time should be 5-10 seconds; and when the vacuum level is -0.04 MPa, the suction time should be 10-15 seconds. If the vacuum level is too low or the suction time is too short, the functional pulp will not penetrate sufficiently, resulting in uneven distribution of micro-electroluminescent units in the paper thickness direction. If the vacuum level is too high or the suction time is too long, some functional components may be extracted from the paper, causing losses. Matching and selecting the above parameter ranges can ensure that the effective retention rate of functional components in the paper thickness direction is greater than 85%.

[0030] The present invention has the following advantages over the prior art: This invention utilizes a wet-end self-assembly approach to deconstruct and reconstruct the electroluminescent structure at the scale of a single pulp fiber. This transforms the functional layer from an independent film attached to the paper surface into an integral part of the paper's three-dimensional fiber network. This structure allows the final material to maintain the paper's inherent stiffness, feel, and folding suitability while achieving holistic electroluminescence, fundamentally avoiding the thickness accumulation, interface delamination, and die-cutting / crimping failure problems inherent in traditional laminated EL films. Simultaneously, by utilizing the fiber surface as a natural template for dielectric layer assembly, and leveraging the synergistic effect of electrostatic attraction and repulsion between components under specific zeta potential differences, the invention achieves directional migration of dielectric layer components to the fiber surface and directional enrichment of luminescent layer components into the fiber gaps within a single spraying and vacuuming process. This eliminates dependence on pre-formed core-sheath structure functional fibers, resulting in a more flexible process window and greater compatibility with existing paper production lines. Compared to the method of directly mixing functional components in the pulp and then molding them in one step, the method of spraying and vacuum suction at the wet paper web stage described in this invention can significantly avoid the disordered distribution of components in the fiber network, thereby obtaining higher luminous brightness and uniformity. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] I. Raw Material Description For the pulp fibers, bleached sulfate softwood pulp was selected, with an average fiber length of 2.8 mm and an average diameter of 22 μm, measured using a Kajaani FS300 fiber analyzer. Beating was performed using a Walley beater at a beat concentration of 2.0%, beaten to a freeness of 40°SR, with a wet weight of approximately 10 g. At this freeness, the fibers were fully fibrillated, exposing a large number of hydroxyl groups on the surface.

[0033] The dielectric layer uses two-dimensional nanosheet material, specifically kaolin nanosheets modified with aminosilane. The unmodified kaolin raw material has an aspect ratio of not less than 20:1 and an iron oxide content of less than 1.5 wt%. After an intercalation-exfoliation process, a product with a sheet thickness of approximately 10 nm and a sheet diameter of approximately 300-500 nm is obtained. Aminosilane modification is performed using γ-aminopropyltriethoxysilane (KH550) in an ethanol / water system. The modified product is stored as an aqueous dispersion with a 10 wt% solids content for later use. The surface zeta potential was measured to be +22 mV (Malvern Zetasizer Nano ZS) in deionized water at pH 6.8.

[0034] For the ionic polymeric electrolyte used in the luminescent layer, a sulfonic acid-based waterborne polyurethane was selected. This polyurethane is synthesized via the acetone method using isophorone diisocyanate, polytetrahydrofuran ether diol (molecular weight 2000), and dimethylolbutyric acid as the main raw materials, with sodium ethylenediamine sulfonate used as a hydrophilic chain extender to introduce sulfonic acid groups. The measured sulfonic acid group content of the product was 0.25 mmol / g, the solid content was 38%, the average particle size of the emulsion was approximately 85 nm, and the pH value was 7.2.

[0035] For the electroluminescent phosphor, a commercially available ZnS:Cu phosphor with a central particle size (D50) of 8 μm and an emission peak at 498 nm was selected. Surface grafting with polyacrylic acid (PAA) was performed: first, the phosphor was dispersed in an ethanol / water solution containing 3 wt% silane coupling agent KH570 and reacted at 60°C for 2 h to introduce double bonds; then, acrylic acid monomer (5% of the phosphor mass) and ammonium persulfate initiator were added, and the reaction was carried out at 70°C for 4 h under nitrogen protection. After repeated washing, the PAA grafting rate was measured to be 5.2 wt%. The zeta potential was measured to be -38 mV in deionized water at pH 6.8.

[0036] To verify the effectiveness of the described Zeta potential under actual process conditions, the pulp suspension beaten to 40°SR was filtered, and the filtrate was collected to simulate the liquid phase environment in wet paper webs. The conductivity of this filtrate was 185 μS / cm, and the pH was 6.5. In this filtrate, the measured Zeta potential of aminosilane-modified kaolin was +18 mV, and the measured Zeta potential of PAA-grafted phosphor was -32 mV. The potential difference between the two was 50 mV, which was still sufficient to drive the aforementioned spatial differentiation process.

[0037] The silica nanoparticles were produced using a fumed silica process, with a native particle size of approximately 20 nm. Before use, they were surface-modified with KH570 to incorporate polymerizable double bonds. The modified product was dispersed at 10 wt% in ethylene glycol butyl ether for later use.

[0038] The photoinitiator selected is an α-hydroxy ketone photoinitiator (specifically Irgacure 2959), and the crosslinking agent selected is trimethylolpropane triacrylate (TMPTA).

[0039] The transparent conductive layer material is a PEDOT:PSS aqueous dispersion with a solid content of 0.8%~1.5%. After doping with 5wt% ethylene glycol, its conductivity reaches a grade of 500~1000 S / cm. In this example, Clevios™ PH1000 (Heraeste) is specifically used. Other similar products with equivalent properties can also be used, as long as their solid content and conductivity meet the above-mentioned ranges.

[0040] II. Preparation Process Paper web forming The pulp fibers, beaten to 40°SR, were formulated into a 0.5wt% suspension and dewatered and formed on a sheet forming machine, with a target basis weight of 180 g / m³. 2 When the moisture content of the wet paper web drops to approximately 55%, dewatering is stopped, and the wet paper web is transferred to the spraying station. At this point, the paper web still has a noticeable wetted sheen, but there is no free water layer on the surface.

[0041] Preparation of functional slurry The functional slurry was prepared according to the following proportions: 100 parts by weight of aminosilane-modified kaolin aqueous dispersion (based on solid content), 80 parts by weight of sulfonic acid-based waterborne polyurethane emulsion (based on solid content), 120 parts by weight of PAA-grafted modified ZnS:Cu phosphor, 8 parts by weight of KH570 modified nano-silica dispersion (based on solid content), 5 parts by weight of trimethylolpropane triacrylate, 2 parts by weight of α-hydroxy ketone photoinitiator, and an appropriate amount of deionized water, adjusting the total solid content to 25 wt%. The slurry was dispersed in a high-speed disperser at 3000 rpm for 5 minutes, followed by ultrasonic dispersion for 2 minutes.

[0042] Spraying and vacuum suction The aforementioned functional pulp is evenly sprayed onto the surface of the wet paper web using a linear array nozzle, with a spraying amount of approximately 25 g / m² (wet weight). 2 The paper web was immediately transferred to the top of the vacuum chamber, and a vacuum of -0.04 MPa was applied to it for 12 seconds. During the vacuum suction process, the liquid phase of the functional slurry was rapidly drawn away from the underside of the paper web, while the solid components remained in the thickness direction of the paper web. Due to the difference in charge of the components in the slurry, the flaky kaolin was electrostatically captured and stacked along the fiber axis as it passed through the fiber surface, while the waterborne polyurethane emulsion particles and phosphor particles were pushed into the pore spaces between the fibers.

[0043] Samples subjected to different aspiration times (2 seconds, 5 seconds, 8 seconds, 12 seconds, and 20 seconds) were collected, freeze-dried, and observed using scanning electron microscopy. The results were as follows: after 2 seconds of aspiration, the kaolin sheets covered approximately 60% of the fiber surface, with some exposed areas; after 5 seconds, the coverage increased to approximately 90%; after 8 seconds, continuous and complete sheet coatings formed on the fiber surface, with 6-8 stacked layers; after 12 seconds, the number of stacked layers increased to 8-12, with tightly packed sheets and consistent orientation; after 20 seconds, the morphology showed no significant difference from that after 12 seconds. This indicates that under these conditions, 12 seconds of aspiration is sufficient to achieve adequate directional assembly.

[0044] Hot pressing curing After vacuum suction is completed, the paper web is immediately fed into the hot press. Both the upper and lower pressure plates are covered with release paper. The hot pressing conditions are: temperature 105℃, pressure 0.3MPa, duration 3 minutes. Simultaneously, an ultraviolet light source (main wavelength 365nm, irradiance 80mW / cm²) located above the pressure plates is used. 2 The paper web is irradiated through a quartz window. The waterborne polyurethane undergoes cross-linking and curing under the combined action of heat and ultraviolet light, locking the phosphor particles in the fiber gaps, while the paper web is compacted to a final thickness of approximately 210 μm.

[0045] Transparent conductive layer coating After the cured paper web was cooled to room temperature, a PEDOT:PSS dispersion was coated onto its surface using a Mayer rod coating method, with a wet film thickness controlled to approximately 40 μm. The coated paper web was then dried in a 50°C oven for 30 minutes. After drying, PEDOT:PSS formed a conductive network with a penetration depth of approximately 25 μm around the surface fibers of the paper web, and the measured surface sheet resistance was approximately 280 Ω / sq.

[0046] Electrode lead-out and drive Copper foil strips, bonded with conductive silver paste, serve as electrode leads on both the upper and lower surfaces of the material. The upper electrode (PEDOT:PSS side) is connected to the positive terminal of the AC drive power supply, while the lower electrode (back side of the paper web) is introduced into the conductive probe array via a needle-punching method, bringing it into contact with the conductive channels inside the paper web and connecting it to the negative terminal. When an AC current of 400Hz and 110V is applied to the material, the surface exhibits uniform green electroluminescence.

[0047] Dielectric strength verification To verify the insulation reliability of the dielectric layer in actual devices, 10 samples were prepared using the formulation and process of Example 1. Under 400Hz AC conditions, the voltage was gradually increased in steps of 10V / step, with each step held for 5 seconds. Breakdown was determined by a sudden drop in brightness to below 50% of the initial brightness or a step-like increase in the circuit current. The luminescence initiation voltage (when brightness reaches 1 cd / m²) was recorded. 2 The average luminescence initiation voltage (EVI) and breakdown voltage of the 10 samples were 58V and 187V respectively, with a minimum breakdown voltage of 172V and a standard deviation of 8V. At a working voltage of 110V, the dielectric layer experienced an electric field strength of approximately 1.1MV / cm, while the minimum breakdown field strength was approximately 1.72MV / cm. The working field strength was approximately 64% of the minimum breakdown field strength, falling within the safe range.

[0048] III. Product Structure Description Cross-sectional scanning electron microscopy (SEM) observation of the prepared flexible high-end packaging material revealed the following structural layers: the pulp fibers exhibit a randomly overlapping three-dimensional network morphology. A dense ring-shaped layer, approximately 80-120 nm thick, is visible around the periphery of some fibers. This ring-shaped layer is composed of multiple layers of kaolin nanosheets stacked parallel to the fiber surface, with approximately 8-12 stacked layers; this is the dielectric layer. Continuous polymer matrix containing phosphor particles fills the triangular or slit-shaped pores between adjacent fibers; this is the luminescent layer. The PEDOT:PSS conductive layer penetrates downwards from the top surface, forming a continuous coating around the surface fibers. The penetration depth is approximately 1.2 times the fiber diameter, forming electrical contact with the luminescent layer inside the paper web.

[0049] In high-magnification images of phosphor particles, a coating layer with a thickness of about 80-150 nm can be observed on the surface of a single particle. Fine nano-silica particles are distributed in this coating layer. The coating layer is tightly bonded to the phosphor crystal surface, and no obvious gaps are observed.

[0050] IV. Brief Description of Optional Implementation Methods In some alternative implementations, a portion of hardwood pulp or bamboo pulp can be added to the pulp fiber ratio. The freeness can be adjusted between 35 and 50°SR. When the freeness is too low, the degree of fiber surface fibrillation is low, which may affect the adsorption capacity of the kaolin sheets; when it is too high, the number of fine fibers increases, which may lead to a greater proportion of functional pulp being lost during the suction process.

[0051] In some alternative implementations, montmorillonite nanosheets can be used instead of kaolinite for the two-dimensional nanosheet material, with a sheet thickness preferably in the range of 5 to 20 nm and a sheet diameter preferably in the range of 200 to 800 nm.

[0052] In some alternative implementations, the ionic polymer electrolyte can be replaced by a carboxylic acid-based aqueous polyurethane instead of a sulfonic acid-based electrolyte, and the electroluminescent phosphor can be partially doped with elements such as Mn and Al to adjust the emission color.

[0053] In some alternative embodiments, the ratio of phosphor to waterborne polyurethane in the functional slurry can be adjusted within the range of 1:0.5 to 1:1. A lower phosphor ratio results in decreased luminescence brightness, while a higher ratio leads to insufficient filling of fiber gaps, potentially affecting luminescence uniformity.

[0054] In some optional implementations, the vacuum level of vacuum suction can be selected within the range of -0.02 to -0.06 MPa, and the suction time can be adjusted accordingly. The hot pressing temperature can be selected within the range of 80 to 120°C, and the pressure can be selected within the range of 0.1 to 0.5 MPa.

[0055] V. Examples and Comparative Examples To more intuitively illustrate the technical effects of the present invention, the following examples 1 to 8 and comparative examples 1 to 6 provide further explanation. Unless otherwise specified, the type of pulp fiber, paper web forming basis weight, hot pressing curing conditions, transparent conductive layer coating, and electroluminescence driving conditions were kept consistent in each group of experiments, with only the specified variables being adjusted.

[0056] Example 1 The preparation was carried out strictly according to the formula and process parameters in Section II, Preparation Process. Specifically: 100 parts kaolin, 80 parts waterborne polyurethane, 120 parts PAA-grafted phosphor, 8 parts nano-SiO2, 5 parts TMPTA, and 2 parts photoinitiator; the paper web moisture content was 55% during spraying; vacuum degree was -0.04 MPa for 12 seconds; hot pressing was performed at 105℃, 0.3 MPa for 3 minutes, while simultaneously irradiating with ultraviolet light.

[0057] Example 2 The amount of kaolin was reduced to 70 parts by weight, and the amount of waterborne polyurethane was adjusted to 90 parts by weight. The rest was the same as in Example 1.

[0058] Example 3 The amount of kaolin was increased to 130 parts by weight, and the amount of waterborne polyurethane was adjusted to 60 parts by weight. The rest was the same as in Example 1.

[0059] Example 4 The vacuum level was adjusted to -0.02 MPa, and the suction time was extended to 18 seconds. The rest was the same as in Example 1.

[0060] Example 5 The hot pressing temperature was reduced to 85°C, the pressure was increased to 0.5 MPa, the hot pressing time was extended to 5 minutes, and ultraviolet irradiation was cancelled. The rest was the same as in Example 1.

[0061] Example 6 The addition of KH570-modified nano-SiO2 was omitted, and the rest was the same as in Example 1.

[0062] Example 7 The pulp fiber beating degree was adjusted to 35°SR, and the rest was the same as in Example 1.

[0063] Example 8 The pulp fiber beating degree was adjusted to 50°SR, and the rest was the same as in Example 1.

[0064] Comparative Example 1 The functional slurry contains no aminosilane-modified kaolin, and the amount of waterborne polyurethane is increased to 180 parts to compensate for the solid content. The rest is the same as in Example 1.

[0065] Comparative Example 2 Using unmodified kaolin nanosheets, the measured Zeta potential was -15 mV (pH 6.8). The rest was the same as in Example 1.

[0066] Comparative Example 3 Using ungrafted, unpolyacrylic acid-based ZnS:Cu phosphor, the measured Zeta potential was -5 mV (pH 6.8). The rest was the same as in Example 1.

[0067] Comparative Example 4 The wet paper web spray-suction process is not used. All components of the functional pulp are directly mixed in the pulp suspension after beating, stirred evenly, and then formed, dewatered, and hot-pressed and dried in one step according to the conventional wet papermaking process. The remaining components and dosages are the same as in Example 1.

[0068] Comparative Example 5 According to Example 1 of the published patent document CN10278545XB, an EL film was prepared by sequentially printing a transparent conductive layer of silver nanowires, a ZnS:Cu / cyano resin luminescent layer, a barium titanate dielectric layer, and a carbon paste back electrode layer on a 50μm PET substrate film. Then, it was bonded to a substrate with a basis weight of 180g / m³ using polyurethane adhesive. 2 The surface of the white cardboard.

[0069] Comparative Example 6 A core-shell structure functional fiber with a diameter of approximately 30 μm was prepared using coaxial wet spinning, with a kaolin / PVA blend as the sheath and a waterborne polyurethane / fluorescent powder blend as the core. This functional fiber was then mixed with bleached sulfate softwood pulp fiber at a ratio of 15 wt%, and subjected to conventional wet papermaking and hot-press drying. All other conditions were the same as in Example 1.

[0070] VI. Performance Testing and Result Comparison The following performance tests were performed on the materials obtained in each embodiment and comparative example: Thickness increment: Using pure paper of the same basis weight without any added functional components as a reference, the thickness difference between the functional paper and the reference paper is measured with a micrometer screw gauge, with a measurement accuracy of 1μm.

[0071] Luminous intensity: The normal luminance was measured in a dark room using a PR-655 spectrophotometer driven at 400Hz and 110V AC. The detection limit of this luminometer under dark room conditions was 0.1 cd / m². 2 .

[0072] Luminous uniformity: The brightness of nine points on the material surface is measured and characterized by the ratio of minimum brightness to maximum brightness.

[0073] Bending tolerance: The material is repeatedly bent 180° along a 10mm diameter rod, and the number of bends is recorded when the brightness drops to 50% of the initial value.

[0074] Humidity and heat aging: The material was placed in an environment of 85°C and 85%RH for 240 hours, and the brightness retention rate was measured.

[0075] Tactile Evaluation: Five engineers with over five years of experience in the packaging and printing industry were invited to evaluate the surface feel of the sample and its 180g / m³ weight without knowing the sample number. 2 The similarity of the white cardstock was assessed blindly, and the results were recorded qualitatively as "close," "average," or "significantly different." This tactile evaluation served as a supplementary reference, while the quantitative data on the material's thickness increment was the primary basis for evaluating the thickness and tactile feel.

[0076] Test Results Summary Table

[0077] Results Analysis Data from Examples 1 to 8 demonstrate that the solution of the present invention can achieve electroluminescent functionality with uniform brightness, bend resistance, and resistance to damp heat aging without increasing the paper base thickness. The thickness increment in each example is less than 15 μm, and the tactile feedback is consistently rated as "close." The bending resistance generally exceeds 85,000 cycles, with Examples 1, 2, 4, 5, and 8 exceeding 100,000 cycles. The brightness retention rate after damp heat aging is consistently above 89%.

[0078] Comparative Example 1 data shows that, without the kaolin dielectric layer, the normal brightness is 0.1 cd / m below the detection limit of the spectrophotometer at a driving voltage of 110 V. 2 This is because, without the kaolin dielectric layer, the aqueous polyurethane layer in the fiber gaps cannot provide an effective insulating barrier under an alternating electric field. Charge carriers form leakage current channels at the fiber overlaps, and the electric field cannot be effectively established on the phosphor particles, resulting in the luminescent layer not being effectively excited. This confirms the necessary role of the kaolin dielectric layer in constructing microluminescent units at the single-fiber scale.

[0079] Data from Comparative Example 2 show that when the kaolin was not modified with aminosilane and did not carry a positive charge on its surface (Zeta potential -15mV), the brightness decreased by approximately 64% compared to Example 1, and the uniformity of luminescence deteriorated significantly. Scanning electron microscopy revealed that the adsorption amount of kaolin sheets on the fiber surface was greatly reduced, exhibiting random aggregation and failing to form a continuous and dense dielectric layer. This confirms the decisive role of positive charge in the directional adsorption of kaolin sheets on the fiber surface.

[0080] Data from Comparative Example 3 show that when the phosphor was not grafted with PAA and had almost no surface charge (Zeta potential -5mV), the brightness decreased by approximately 53% compared to Example 1, and the uniformity deteriorated. Scanning electron microscopy revealed that a large number of phosphor particles remained on the fiber surface, mixed with the kaolin dielectric layer, and failed to effectively accumulate in the fiber interstices. This confirms the crucial role of sufficient charge repulsion between components in achieving spatial differentiation between the dielectric layer and the emitting layer.

[0081] The data from Comparative Example 4 show that when using the pulp in-mold mixing-one-step molding process, the brightness is only about 30% of that of Example 1, and the uniformity is the worst among all samples. This is because during the pulp mixing stage, the functional components and pulp fibers undergo disordered adsorption and pre-flocculation during prolonged stirring, making it impossible to form a regular dielectric layer on the fiber surface and a concentrated luminescent layer in the fiber gaps. This fully demonstrates the irreplaceable nature of the specific process of "wet paper web spraying-vacuum suction" for achieving in-situ self-assembly.

[0082] Comparative Example 5 represents existing laminated EL film solutions, with an initial brightness comparable to Example 1, but a thickness increase of up to 72 μm, a "significant difference" in feel, a bending life of only 8,500 cycles, and a brightness retention rate of only 55.2% under damp heat aging. These data intuitively illustrate the comprehensive advantages of the present invention in terms of thinning, feel retention, bending resistance, and weather resistance.

[0083] Comparative Example 6 represents the pre-fabricated core-sheath fiber scheme, with a thickness increment of 15 μm. Its luminescence brightness and uniformity are significantly inferior to Example 1, and its bending and damp heat aging performance are also inferior. Scanning electron microscopy revealed that during papermaking, the core-sheath structure of the pre-fabricated fiber was partially damaged by physical friction with the pulp fiber, and the contact between the pre-fabricated fiber and the pulp fiber was only random physical, failing to form a continuous dielectric layer tightly adhered to the fiber surface as in Example 1. This confirms that the "in-situ generation using pulp fiber as a template" approach of this invention has significant advantages in structural integrity and interface quality compared to the "first manufacturing functional fibers and then mixing" approach. The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A flexible high-end packaging material based on an electroluminescent layer, comprising a three-dimensional network matrix formed of pulp fibers, characterized in that: Multiple micro-electroluminescent units are dispersed within the three-dimensional network matrix; The micro electroluminescent unit has the following structure: a dielectric layer is coated on the surface of a single pulp fiber, the dielectric layer is composed of kaolin modified with aminosilane, the thickness of the kaolin sheet is 5~20nm, the sheet diameter is 200~800nm, the kaolin in the dielectric layer is stacked in an orientation parallel to the surface of the pulp fiber, the number of stacked layers is 5~15, and the thickness of the dielectric layer is 50~150nm; A light-emitting layer is filled in the gaps between adjacent pulp fibers. The light-emitting layer is composed of a sulfonic acid-based waterborne polyurethane and a ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid. The sulfonic acid-based waterborne polyurethane has a sulfonic acid group content of 0.15~0.40 mmol / g, and the grafting rate of polyacrylic acid on the surface of the ZnS:Cu electroluminescent phosphor is 3~8 wt%. The kaolin modified with aminosilane has a surface zeta potential of +15mV to +40mV in an aqueous dispersion at pH 6-8, and the ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid has a surface zeta potential of -25mV to -50mV in an aqueous dispersion at pH 6-8. This allows the kaolin to be electrostatically adsorbed and oriented onto the surface of the pulp fibers during the wet paper web forming stage, while the electroluminescent phosphor and sulfonic acid-based waterborne polyurethane accumulate in the fiber gaps under the effect of charge repulsion.

2. The flexible high-end packaging material according to claim 1, characterized in that: The pulp fiber is bleached sulfate softwood pulp fiber with a fiber diameter of 15~35μm and a fiber length of 1.5~3.5mm.

3. The flexible high-end packaging material according to claim 1, characterized in that: The polyacrylic acid graft layer also contains silica nanoparticles with a particle size of 15-30 nm, which are chemically bonded to the polyacrylic acid segments via γ-methacryloyloxypropyltrimethoxysilane.

4. The flexible high-end packaging material according to claim 1, characterized in that: The upper and / or lower surfaces of the three-dimensional network matrix are permeated with a transparent conductive layer, the material of which is PEDOT:PSS, and the penetration depth is 0.5 to 2 times the diameter of the pulp fiber.

5. A method for preparing a flexible high-end packaging material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dehydrate the pulp fiber suspension with a freeness of 35~50°SR in the papermaking wire section to a moisture content of 40~60% to obtain a wet paper web; (2) Prepare a functional slurry, the functional slurry comprising: an aqueous dispersion of aminosilane-modified kaolin, a sulfonic acid-based aqueous polyurethane emulsion, an aqueous dispersion of ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid, and a photoinitiator; wherein the surface zeta potential of the aminosilane-modified kaolin in the aqueous dispersion at pH 6-8 is +15mV to +40mV, and the surface zeta potential of the ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid in the aqueous dispersion at pH 6-8 is -25mV to -50mV; (3) Spray the functional slurry onto at least one surface of the wet paper web obtained in step (1); (4) Apply vacuum suction to the wet paper web after spraying, with a vacuum degree of -0.02 to -0.06 MPa and a suction time of 5 to 20 seconds; (5) The wet paper web after vacuum suction is hot-pressed and cured at a temperature of 80~120℃ and a pressure of 0.1~0.5MPa.

6. The preparation method according to claim 5, characterized in that: In step (2), the functional slurry also contains a multifunctional acrylate crosslinking agent; in step (5), while hot pressing, ultraviolet light irradiation is also applied to allow the sulfonic acid-based waterborne polyurethane to undergo heat-light dual curing.

7. The preparation method according to claim 5, characterized in that: After step (5), step (6) is also included: coating at least one surface of the material with PEDOT:PSS aqueous dispersion and drying at 40~60°C to form a transparent conductive layer.

8. The preparation method according to claim 5, characterized in that: In step (2), the components of the functional slurry are as follows by weight: 100 parts of aminosilane-modified kaolin, 60-90 parts of sulfonic acid-type waterborne polyurethane, and 100-130 parts of ZnS:Cu electroluminescent phosphor grafted with polyacrylic acid. The total solid content of the functional slurry is 20-30 wt%.

9. The preparation method according to claim 8, characterized in that: The functional slurry also contains 2 to 10 parts by weight of nano-silica modified with a silane coupling agent, based on the solid content, wherein the nano-silica has a particle size of 15 to 30 nm.

10. The preparation method according to claim 5, characterized in that: In step (1), the pulp fiber is bleached sulfate softwood pulp fiber, and the beating degree is controlled by a Walley beater; in step (3), the spraying amount is 20~30 g / m³ wet weight. 2 .

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