A three-dimensional conductive structure construction method and system for smart packaging

Abstract

This application relates to the field of smart packaging technology, and in particular to a method and system for constructing a three-dimensional conductive structure for smart packaging. The method includes: S1, selecting paper-based, fiber-based, or composite packaging material as the packaging substrate, and pre-treating the surface of the area to be constructed on the packaging substrate; S2, dispersing lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion; S3, dispersing reduced graphene oxide in the lignocellulose nanofiber dispersion to obtain an rGO / LCNF composite dispersion; S4, mixing acrylic monomers, a crosslinking agent, and a photoinitiator to obtain a photocurable system, based on which a conductive construction medium is obtained; S5, depositing the conductive construction medium layer by layer onto the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor; S6, photocuring the wet three-dimensional conductive structure precursor to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate.

Description

Technical Field

[0001] This application relates to the field of smart packaging technology, and in particular to a method and system for constructing a three-dimensional conductive structure for smart packaging. Background Technology

[0002] As the packaging industry upgrades towards digitalization, networking, and low carbonization, the demand for intelligent packaging integrating anti-counterfeiting identification, status monitoring, and information interaction functions is growing. Traditional packaging mainly undertakes basic functions such as carrying, protection, and display, making it difficult to provide real-time feedback on conditions such as transportation compression, stacking deformation, opening damage, and environmental changes. It also struggles to meet the application requirements of full-process product traceability and highly reliable anti-counterfeiting. Therefore, how to construct stable, mass-producible, and readable functional structures on paper-based, fiber-based, and composite packaging materials has become one of the key issues in the development of intelligent packaging technology.

[0003] Current methods for constructing electrical functions in smart packaging often employ conductive ink printing, coating, or the application of conductive labels. For example, two-dimensional conductive patterns are formed on the packaging surface using processes such as screen printing, inkjet printing, and gravure / flexographic printing, and identification and sensing are achieved through resistance, capacitance, or radio frequency signals. However, these two-dimensional conductive patterns typically have limited thickness and a single dimensional shape, making it difficult to maintain stable conductivity and repeatable response under complex mechanical conditions such as pressure, bending, crumpling, or stacking. Furthermore, the rough, porous, and highly absorbent surfaces of paper-based and fiber-based materials make the conductive coating prone to penetration, diffusion, boundary distortion, and circuit breakage, resulting in poor electrical consistency. For metal-based conductive inks (such as silver and copper), post-treatment such as thermal sintering or chemical reduction is often required to achieve lower resistance. However, high-temperature / strong reduction treatments conflict with the heat resistance, environmental friendliness, and cost control of paper-based packaging, and are prone to cracking and peeling under long-term folding and friction conditions.

[0004] Furthermore, for packaging condition monitoring applications, two-dimensional thin-layer structures exhibit limited electrical changes and low signal-to-noise ratios during pressure and bending processes. They are also significantly affected by factors such as humidity, temperature, and substrate deformation, leading to increased risks of threshold drift and misjudgment. In summary, existing technologies still have shortcomings in terms of the adhesion reliability, morphological dimensional adjustability, electrical stability under complex operating conditions, and distinguishable response characteristics of conductive structures on packaging substrate surfaces. There is an urgent need for a structural construction method suitable for packaging substrates, capable of rapid low-temperature shaping, and able to construct three-dimensional interconnected conductive paths to meet the comprehensive performance requirements of smart packaging in scenarios such as condition monitoring and information interaction. Summary of the Invention

[0005] This application provides a method and system for constructing a three-dimensional conductive structure for smart packaging to solve the above-mentioned problems.

[0006] In a first aspect, this application provides a method for constructing a three-dimensional conductive structure for smart packaging, the method comprising:

[0007] S1. Select paper-based, fiber-based, or composite packaging materials as packaging substrates, and perform surface pretreatment on the area to be constructed of the packaging substrate.

[0008] S2. Disperse the lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion.

[0009] S3. Reduced graphene oxide is added to the lignocellulose nanofiber dispersion for dispersion treatment to obtain rGO / LCNF composite dispersion;

[0010] S4. Mix acrylic monomer, crosslinking agent and photoinitiator to obtain photocurable system, and add the photocurable system to the rGO / LCNF composite dispersion for mixing. After homogenization and degassing, a conductive building medium is obtained.

[0011] S5. The conductive building medium is deposited layer by layer on the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor with height, thickness and spatial connectivity characteristics.

[0012] S6. The wet three-dimensional conductive structure precursor is subjected to photocuring treatment to cause the photocuring system to undergo polymerization and cross-linking, and the rGO / LCNF composite network is cured to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate.

[0013] The reduced graphene oxide forms the conductive pathway in the three-dimensional conductive structure, and the lignocellulose nanofibers form the supporting framework in the three-dimensional conductive structure and regulate the forming rheological properties of the conductive building medium.

[0014] Through the above technical solution, LCNF is used as a bio-based nanoframework to endow the conductive building medium with shear-thinning rheological properties and yield stress, ensuring geometric fidelity and anti-collapse ability during the layer-by-layer deposition process. At the same time, the uniform anchoring and spatial overlap of rGO sheets in the entangled network of LCNF are used to construct percolation conductive pathways. Then, the AA / MBAA / DMPA photocuring system is used to form a cross-linked polyacrylic acid network in situ under UV irradiation, which simultaneously locks the rGO conductive path and the LCNF support structure, and strengthens its physical anchoring and chemical bonding with the interface of the pretreated substrate. The three work together to achieve a closed-loop manufacturing of "extrudable-stackable-curable-conductive-responsive" on porous and rough packaging materials such as paper, thereby solving the technical problems of poor adhesion, easy breakage under pressure, small response amplitude and inability to be calibrated of two-dimensional conductive structures on packaging substrates in the prior art.

[0015] Optionally, the surface pretreatment in step S1 includes one or more of cleaning and degreasing, plasma activation, surface roughening, applying a base coat, and applying an interface bonding layer.

[0016] Through the above technical solutions, the multi-stage pretreatment synergistically enhances the van der Waals forces, hydrogen bonds, and covalent bonds between the conductive building medium and the substrate, thereby solving the technical bottleneck that a single treatment method cannot simultaneously achieve cleanliness, active site density, and mechanical anchoring strength.

[0017] Optionally, in step S2, the solid content of the lignocellulose nanofiber dispersion is 0.5 to 3.0 wt%, and a uniform dispersion system is formed by stirring and / or ultrasonic dispersion.

[0018] In step S3, the mass ratio of the reduced graphene oxide to the lignocellulose nanofibers is (1-3):1, and the dispersion treatment includes shearing and / or ultrasonic dispersion.

[0019] By controlling the liquid-solid content of LCNF dispersion within the range of 0.5–3.0 wt%, its zero-shear viscosity is maintained at 50–2000 Pa·s and its yield stress reaches 100–500 Pa. This ensures that the shear thinning behavior meets the flowability requirements of direct writing extrusion, while also ensuring sufficient structural strength in a static state to suppress excessive interlayer fusion. At the same time, the rGO:LCNF mass ratio is limited to (1–3):1, so that the rGO sheets are effectively spaced and physically anchored by LCNF nanofibers, avoiding the conductive island effect caused by agglomeration, and also preventing the LCNF network from being excessively shielded and losing its supporting rigidity. The two synergistically regulate the rheological window of the conductive building medium and the construction efficiency of the conductive network, thereby solving key technical obstacles such as line collapse caused by low concentration of LCNF, blockage caused by high concentration, and large resistance dispersion caused by rGO ratio imbalance.

[0020] Optionally, in step S4, the crosslinking agent is N,N′-methylenebisacrylamide, and the mass ratio of N,N′-methylenebisacrylamide to acrylic acid monomer is 1:20.

[0021] The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone and / or Irgacure 2959, and the amount of the photoinitiator is 0.1 wt% of the acrylic acid monomer.

[0022] The degassing is performed using vacuum degassing with a vacuum degree of -0.10 MPa and a degassing time of 10 to 30 minutes.

[0023] Using the above technical solution, the mass ratio of MBAA to AA is precisely set to 1:20, forming a polyacrylic acid network with a moderate crosslinking density under UV irradiation. This ensures that the network rigidity is sufficient to lock the three-dimensional morphology (gel fraction > 92%), while retaining sufficient chain segment mobility to withstand bending deformation (Young's modulus 1.2–2.5 MPa). DMPA / Irgacure 2959 with a high molar absorptivity at 365 nm (ε > 200 L·mol⁻¹) is selected. - ¹·cm - ¹) With a dosage of 0.1 wt%, the monomer conversion rate is ensured to be >95% within 1-2 min, with few byproducts and no residual toxicity; combined with vacuum degassing at -0.10 MPa for 10-30 min, bubbles with a diameter >50μm are completely eliminated, avoiding printing interruption and interlayer voids; the three factors synergistically optimize the matching relationship between photopolymerization kinetics and the 3D forming process window, thereby solving process risks such as structural creep caused by under-curing, brittleness caused by over-curing, and bubble interference with forming continuity.

[0024] Optionally, the layer-by-layer deposition in step S5 may be carried out using one or more three-dimensional shaping methods, such as direct writing extrusion, dispensing deposition, micro-extrusion deposition, or jet deposition.

[0025] The three-dimensional forming parameters include nozzle inner diameter, printing speed and layer height, wherein the nozzle inner diameter is 0.20-0.80 mm, the printing speed is 10-120 mm / s, and the layer height is 0.10-0.60 mm.

[0026] Through the above technical solutions, by defining a universal parameter window covering macro to micro scales, the conductive building medium can be adapted to various three-dimensional forming paths: 0.20mm nozzle + 30mm / s is suitable for micro-extrusion to prepare 200 μm linewidth anti-counterfeiting circuits, relying on the high shear dispersion of LCNF to ensure fine resolution; 0.80mm nozzle + 100mm / s is suitable for direct-write extrusion to build 2mm wide load-bearing grids, relying on LCNF skeleton support to suppress collapse; 10mm / s low speed ensures sufficient spreading when depositing thick layers (0.60mm), while 120mm / s high speed matches the stringent requirements of jet deposition for low viscosity; this broad parameter combination can maintain interlayer fusion rate >98% and height error ≤±0.03 mm, thus solving the technical limitations of a single forming method that cannot simultaneously consider structural complexity, production cycle and resolution.

[0027] Optionally, the conductive building medium is deposited layer by layer along a grid path using a direct-write extrusion printing method to form the wet three-dimensional conductive structure precursor. The nozzle inner diameter is 0.30mm to 0.60mm, the printing speed is 60mm / s to 80mm / s, and the layer height is 0.15mm to 0.30mm.

[0028] By defining a dedicated parameter window for direct-write extrusion and employing a periodic grid path, the optimal coupling between LCNF support rigidity, rGO conductive path density, and AA curing rate is achieved: a 0.30mm nozzle with a speed of 60mm / s and a layer height of 0.15mm forms a "short and stout" cross-sectional structure with an aspect ratio of ≈2.3, exhibiting high lateral stability and suitability for low pressure sensitivity monitoring (10–50 kPa); a 0.60mm nozzle with a speed of 80mm / s and a layer height of 0.30mm forms a "tall and thin" cross-section with an aspect ratio of ≈1.7, exhibiting strong longitudinal compression sensitivity and suitability for high pressure sensitivity discrimination (100–200 kPa); the grid nodes undergo multiple coupling deformations of compression, bending, and contact under pressure, significantly amplifying the changes in electron tunneling probability and the total number of conductive paths, thereby solving the technical defects of discrete response characteristics and uncontrollable threshold under general parameters.

[0029] Optionally, the photocuring process in step S6 uses ultraviolet light irradiation, the wavelength of which is 365nm and the irradiation time is 1-2min.

[0030] The above technical solution uses 365nm ultraviolet light as the excitation source, matched with the DMPA / Irgacure 2959 main absorption peak, to achieve efficient penetration of the LCNF / rGO composite medium (penetration depth > 350μm), avoiding over-curing of the surface layer and under-curing of the deep layer caused by strong absorption of rGO from short-wavelength light sources. The irradiation time is strictly controlled within 1-2 minutes, corresponding to the kinetic equilibrium window under light intensity of 10-50 mW / cm², ensuring that the monomer conversion rate gradient from the surface to the bottom layer of the 300μm thick structure is <5% and the gel content is >94%. This solves the production line-level reliability problems such as uneven curing, insufficient depth, or chain breakage and embrittlement caused by light intensity fluctuations or equipment aging.

[0031] Optionally, after step S6, an electrical parameter calibration step is further included, which includes:

[0032] Electrodes are led out from both ends of the three-dimensional conductive structure, the initial resistance is measured, and the resistance change is recorded under pressure to establish the electrical response parameters of the three-dimensional conductive structure.

[0033] Using the above technical solution, electrodes with low contact resistance (<0.5Ω) are prepared by silver paste screen printing followed by hot pressing at 80℃ for 30s. The initial resistance R0 is accurately measured to characterize the intrinsic conductivity and geometric dimensions of the structure. Subsequently, a gradient pressure of 0–200kPa is applied under a standard pressure testing platform (accuracy ±0.5kPa), and the change of ΔR / R0 is recorded in real time. The nonlinear response function R=a·P^b+c (R²>0.99) is fitted to obtain the nonlinear response function, and the response threshold, hysteresis rate (<5%) and repeatability index are extracted. This calibration process upgrades the three-dimensional conductive structure from a passive component to an active sensing unit, thereby solving the technical shortcomings of existing technologies that lack standardized mechanical-electrical mapping relationships and cannot support digital state recognition.

[0034] Optionally, the three-dimensional conductive structure is disposed in the pressure-bearing area, opening area, or functional interaction area of ​​the packaging.

[0035] Through the above technical solution, the three-dimensional conductive structure is precisely deployed according to functional logic in specific mechanical response areas of the packaging: at the four corners of the box and the stacking contact surface (pressure area), it withstands periodic compressive loads during logistics transportation, enabling real-time monitoring of stacking height and compression damage; at the sealing tear line and the edge of the easy-open lid (opening area), it utilizes the drastic deformation and material separation at the moment of opening to trigger a step-like irreversible resistance change of ΔR / R0 > 1000%, achieving one-time anti-counterfeiting indication; and at the touch sensing area and the RFID antenna coupling area (functional interaction area), it achieves a response time of <100ms and >10ms through finger pressure. 5 Multi-touch interaction with a short lifespan; three deployment strategies enable the same structural technology to serve three core scenarios: logistics monitoring, anti-counterfeiting and traceability, and user experience, thereby solving the technical pain points of random location of general-purpose structures and low coupling efficiency of mechanical excitation and electrical response.

[0036] Secondly, this application provides a three-dimensional conductive structure construction system for smart packaging, the system comprising:

[0037] The pretreatment module is used to select paper-based, fiber-based, or composite packaging materials as packaging substrates and perform surface pretreatment on the areas of the packaging substrates to be constructed.

[0038] The fiber dispersion module is used to disperse lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion.

[0039] A composite dispersion module is used to add reduced graphene oxide into the lignocellulose nanofiber dispersion for dispersion, to obtain an rGO / LCNF composite dispersion.

[0040] The medium preparation module is used to mix acrylic monomers, crosslinking agents and photoinitiators to obtain a photocurable system, and add the photocurable system to the rGO / LCNF composite dispersion for mixing. After homogenization and degassing, a conductive building medium is obtained.

[0041] The structural deposition module is used to deposit the conductive building medium layer by layer onto the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor with height, thickness and spatial connectivity characteristics;

[0042] The structure curing module is used to perform photocuring treatment on the wet three-dimensional conductive structure precursor, so that the photocuring system undergoes polymerization and cross-linking, and the rGO / LCNF composite network is cured to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate.

[0043] Optionally, in the pretreatment module, the surface pretreatment includes one or more of the following: cleaning and degreasing, plasma activation, surface roughening, applying a base coating, and applying an interface bonding layer.

[0044] Optionally, in the fiber dispersion module, the solid content of the lignocellulose nanofiber dispersion is 0.5-3.0 wt%, and a uniform dispersion system is formed by stirring and / or ultrasonic dispersion.

[0045] Optionally, in the composite dispersion module, the mass ratio of the reduced graphene oxide to the lignocellulose nanofibers is (1-3):1, and the dispersion treatment includes shear stirring and / or ultrasonic dispersion.

[0046] Optionally, in the media preparation module, the crosslinking agent is N,N′-methylenebisacrylamide, and the mass ratio of N,N′-methylenebisacrylamide to acrylic acid monomer is 1:20;

[0047] The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone and / or Irgacure 2959, and the amount of the photoinitiator is 0.1 wt% of the acrylic acid monomer.

[0048] The degassing is performed using vacuum degassing with a vacuum degree of -0.10 MPa and a degassing time of 10 to 30 minutes.

[0049] Optionally, in the structure deposition module, the layer-by-layer deposition is implemented using one or more three-dimensional shaping methods selected from direct writing extrusion, dispensing deposition, micro-extrusion deposition, or jet deposition;

[0050] The three-dimensional forming parameters include nozzle inner diameter, printing speed and layer height, wherein the nozzle inner diameter is 0.20-0.80 mm, the printing speed is 10-120 mm / s, and the layer height is 0.10-0.60 mm.

[0051] Optionally, in the structure deposition module, the conductive building medium is deposited layer by layer along a grid path using a direct-write extrusion printing method to form the wet three-dimensional conductive structure precursor. The nozzle inner diameter is 0.30mm to 0.60mm, the printing speed is 60mm / s to 80mm / s, and the layer height is 0.15mm to 0.30mm.

[0052] Optionally, in the structure curing module, the photocuring process uses ultraviolet light irradiation, the wavelength of the ultraviolet light is 365nm, and the irradiation time is 1-2 minutes.

[0053] Optionally, the system further includes an electrical parameter calibration module, specifically used to: lead out electrodes from both ends of the three-dimensional conductive structure, measure the initial resistance, and record the resistance change under pressure conditions, so as to establish the electrical response parameters of the three-dimensional conductive structure.

[0054] Optionally, in the electrical parameter calibration module, the three-dimensional conductive structure is disposed in the pressure-bearing area, opening area, or functional interaction area of ​​the packaging. Attached Figure Description

[0055] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 A flowchart illustrating a method for constructing a three-dimensional conductive structure for smart packaging, as provided in an embodiment of this application;

[0057] Figure 2 A physical image of a wet three-dimensional conductive structure provided in an embodiment of this application;

[0058] Figure 3 This is a physical image of a three-dimensional conductive structure after photocuring, provided in an embodiment of this application.

[0059] Figure 4 An electrical response curve under pressure conditions of a three-dimensional conductive structure obtained by photocuring and stably adhering to the surface of a packaging substrate, as provided in an embodiment of this application;

[0060] Figure 5 This is a schematic diagram of a three-dimensional conductive structure construction system for smart packaging, provided as an embodiment of this application. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0062] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0063] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0064] Example 1

[0065] This embodiment provides a representative three-dimensional conductive structure construction scheme, aiming to verify the feasibility and core performance indicators of the technical solution of the present invention. (Refer to...) Figure 1 As shown, the specific implementation process is as follows:

[0066] Weigh 1.5g of lignocellulose nanofibers (LCNF) and add them to 298.5g of deionized water. Place the LCNF in an ultrasonic cell disruptor and ultrasonically disperse it for 20min at 600W to obtain an LCNF dispersion with a solid content of 0.5wt%. Separately weigh 1.5g of reduced graphene oxide (rGO) and add it to the above LCNF dispersion. Stir the mixture in a shear disperser at 600rpm for 20min to obtain an rGO / LCNF composite dispersion (solution A) with a mass ratio of rGO:LCNF of 1:1. Measure 10g of acrylic acid monomer (AA), add 0.5g of N,N′-methylenebisacrylamide (MBAA), stir to dissolve at room temperature, and then add 0.01g of acrylic acid monomer (AA). 2,2-Dimethoxy-2-phenylacetophenone (DMPA) was stirred for 10 min to obtain a photocurable system (solution B). Solution B was slowly added to solution A and magnetically stirred for 30 min. Then, it was placed in a vacuum degassing machine and degassed at -0.10 MPa for 20 min to obtain a homogeneous, bubble-free conductive building medium. This medium was loaded into the barrel of a direct-write extruder printer. Using a 0.45 mm inner diameter stainless steel nozzle, the printing speed was 70 mm / s, the layer height was 0.20 mm, and the medium was deposited layer by layer on the surface of kraft paper pretreated with plasma activation (air, 80 W, 60 s) and a KH-560 interfacial bonding layer (0.8 μm) in a 5 mm × 5 mm square grid pattern. A total of 8 layers were printed to form a wet three-dimensional conductive structure precursor with dimensions of 20 mm × 20 mm × 1.6 mm. The actual product is shown below. Figure 2 As shown; the obtained precursor was placed in a UV curing system and irradiated for 90 seconds with a 365nm LED light source (irradiance 30 mW / cm²) to obtain a firmly attached three-dimensional conductive structure, as shown in the figure. Figure 3 As shown.

[0067] SEM observation showed that the structure exhibited a clear mesh topology, with tight interlayer fusion and no collapse or fracture. XPS analysis confirmed that the C–O / C=O peak intensity ratio increased from 0.82 in the rGO raw material to 1.35 in the cured structure, indicating that DMPA successfully induced AA polymerization and slight esterification with oxygen-containing groups on the rGO surface. The initial resistance R0 was measured to be 24.6 Ω. Under 50 kPa pressure, ΔR / R0 was 286%. After 1000 cycles of bending with a radius of 5 mm, the resistance change rate was 2.3%. After being placed in a 95% RH environment for 72 h, the resistance drift was 4.2%.

[0068] The results show that this embodiment successfully constructed a conductive structure with a clear three-dimensional morphology, excellent adhesion, high-sensitivity electrical response, and good environmental stability, verifying the feasibility and core effects of the technical solution of this invention.

[0069] Example 2

[0070] This embodiment is intended to verify the feasibility of the lower limit of the liquid-solid content (0.5wt%) of the LCNF dispersion in this application.

[0071] With all other preparation conditions the same as in Example 1, only the solid content of the LCNF dispersion in step S2 was adjusted from 0.5 wt% to 0.5 wt% (i.e., kept unchanged as a control baseline), and the product was obtained. The results show that the product can still achieve the technical effects of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability in the range of 0.5 to 3.0 wt%.

[0072] Example 3

[0073] This embodiment is intended to verify the feasibility of the upper limit of the liquid-solid content (3.0 wt%) of the LCNF dispersion in this application.

[0074] With all other preparation conditions the same as in Example 1, only the solid content of the LCNF dispersion in step S2 was adjusted from 0.5 wt% to 3.0 wt%, while other parameters remained unchanged, to obtain a conductive building medium. This medium did not experience nozzle clogging during direct-write extrusion, with a printed linewidth of 0.42 ± 0.015 mm and a layer height of 0.21 ± 0.022 mm. SEM observation of the obtained three-dimensional structure showed full mesh nodes without collapse; the initial resistance R0 was measured to be 18.3 Ω; under 50 kPa pressure, ΔR / R0 was 257%; and the resistance change rate after 1000 bends was 2.6%. The results indicate that even with a high solid content of 3.0 wt%, the LCNF framework still provides sufficient support, and the rGO conductive network maintains efficient percolation, verifying the rationality and robustness of the solid content range in this application.

[0075] Example 4

[0076] This embodiment is intended to verify the feasibility of the lower limit (1:1) of the rGO to LCNF mass ratio in this application.

[0077] With all other preparation conditions the same as in Example 1, only the mass ratio of rGO to LCNF in step S3 was adjusted from 1:1 to 1:1 (i.e., kept unchanged as a control baseline), and the product was obtained. The results show that the product can still achieve the technical effect of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability within the range of (1 to 3):1.

[0078] Example 5

[0079] This embodiment is intended to verify the feasibility of the upper limit of the rGO to LCNF mass ratio (3:1) in this application.

[0080] With all other preparation conditions the same as in Example 1, only the mass ratio of rGO to LCNF in step S3 was adjusted from 1:1 to 3:1 to obtain a conductive building medium. This medium printed smoothly, and the resulting three-dimensional structure was uniformly black. SEM showed that the rGO sheets were densely distributed in the LCNF network but without significant aggregation. The initial resistance R0 was measured to be 12.7 Ω. At 50 kPa pressure, ΔR / R0 was 231%. A 30-day sedimentation experiment showed that the transmittance of the supernatant decreased by <3%, indicating good dispersion stability. The results show that a 3:1 ratio can still maintain the integrity and structural stability of the conductive network, supporting the full disclosure of the ratio range in this application.

[0081] Example 6

[0082] This embodiment is intended to verify the feasibility of the lower limit of the mass ratio of crosslinking agent MBAA to acrylic monomer (1:20) in this application.

[0083] With all other preparation conditions the same as in Example 1, only the mass ratio of MBAA to AA in step S4 was adjusted from 1:20 to 1:20 (i.e., remained unchanged as a control baseline), and the product was obtained. The results show that the product can still achieve the technical effect of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability at a ratio of 1:20.

[0084] Example 7

[0085] This embodiment is intended to verify the feasibility of the maximum mass ratio (1:20) of crosslinking agent MBAA to acrylic monomer in this application.

[0086] With all other preparation conditions the same as in Example 1, only the mass ratio of MBAA to AA in step S4 was adjusted from 1:20 to 1:20 (i.e., remained unchanged as a control baseline), and the product was obtained. The results show that the product can still achieve the technical effect of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability at a ratio of 1:20.

[0087] Example 8

[0088] This embodiment is intended to verify the feasibility of the lower limit of the nozzle inner diameter (0.20 mm) in this application.

[0089] With all other preparation conditions the same as in Example 1, only the nozzle inner diameter in step S5 was adjusted from 0.45 mm to 0.20 mm, and the printing speed was adjusted accordingly to 30 mm / s to ensure extrusion continuity. The layer height was maintained at 0.20 mm, resulting in a microscale mesh structure (single line width ≈ 220 μm). Optical microscopy showed continuous lines and sharp edges; the initial resistance R0 was measured to be 89.4 Ω; under a pressure of 20 kPa, ΔR / R0 was 192%; and the structural height error was ±0.019 mm. The results indicate that a 0.20 mm nozzle can achieve microstructure manufacturing while ensuring forming accuracy, supporting the comprehensive coverage of the parameter range in this application.

[0090] Example 9

[0091] This embodiment is intended to verify the feasibility of the upper limit of the nozzle inner diameter (0.80 mm) in this application.

[0092] With all other preparation conditions the same as in Example 1, only the nozzle inner diameter in step S5 was adjusted from 0.45 mm to 0.80 mm, the printing speed was adjusted accordingly to 100 mm / s, and the layer height was kept at 0.20 mm, resulting in a wide-width load-bearing grid (single line width ≈ 0.85 mm). Macroscopic observation showed no collapse or burrs; the initial resistance R0 was measured to be 8.2 Ω; under 150 kPa pressure, ΔR / R0 was 315%; and the interlayer fusion rate was >98.5%. The results indicate that the 0.80 mm nozzle can still maintain the structural geometric fidelity and electrical performance, verifying the rationality of the nozzle size range in this application.

[0093] Example 10

[0094] This embodiment is intended to verify the feasibility of the lower limit of printing speed (10mm / s) in this application.

[0095] With all other preparation conditions the same as in Example 1, only the printing speed in step S5 was adjusted from 70 mm / s to 10 mm / s, while the nozzle inner diameter and layer height remained unchanged, resulting in a high packing density structure. SEM showed uniform layer thickness and no overflow; the initial resistance R0 was measured to be 22.1 Ω; at a pressure of 50 kPa, ΔR / R0 was 263%; and the structure height error was ±0.023 mm. The results indicate that a high-quality three-dimensional structure can still be obtained at a low speed of 10 mm / s, supporting the wide adaptability of the speed range in this application.

[0096] Example 11

[0097] This embodiment is intended to verify the feasibility of the upper limit of printing speed (120 mm / s) in this application.

[0098] With all other preparation conditions the same as in Example 1, only the printing speed in step S5 was adjusted from 70 mm / s to 120 mm / s, while the nozzle inner diameter and layer height remained unchanged, resulting in a high-speed prototyping structure. High-speed imaging observation showed that the ink spread sufficiently and without discontinuity on the substrate surface; the initial resistance R0 was measured to be 26.8 Ω; under a pressure of 50 kPa, ΔR / R0 was 274%; and the standard deviation of resistance was 1.9 Ω (n=50). The results indicate that high-speed printing at 120 mm / s did not compromise the structural integrity and electrical consistency, verifying the feasibility of the upper speed limit in this application.

[0099] Example 12

[0100] This embodiment is intended to verify the feasibility of the lower limit of the layer height (0.10 mm) in this application.

[0101] With all other preparation conditions the same as in Example 1, only the layer height in step S5 was adjusted from 0.20 mm to 0.10 mm, while the nozzle inner diameter and printing speed remained unchanged, resulting in a thin-layer structure. Profilometer measurements showed a layer height accuracy of 0.102 ± 0.008 mm; the initial resistance R0 was measured to be 28.4 Ω; under 30 kPa pressure, ΔR / R0 was 215%; and no delamination occurred in the structure at a bending radius of 3 mm. The results demonstrate that a layer height of 0.10 mm can still achieve reliable 3D construction and effective electrical response, supporting the full disclosure of the layer height range in this application.

[0102] Example 13

[0103] This embodiment is intended to verify the feasibility of the upper limit of the floor height (0.60mm) in this application.

[0104] With all other preparation conditions the same as in Example 1, only the layer height in step S5 was adjusted from 0.20 mm to 0.60 mm, while the nozzle inner diameter and printing speed remained unchanged, resulting in a thick-layer structure. Optical microscopy showed that the single-layer profile was full and without collapse; the initial resistance R0 was measured to be 19.7 Ω; under 100 kPa pressure, ΔR / R0 was 348%; and the height error was ±0.029 mm. The results indicate that a layer height of 0.60 mm can still maintain structural stability and response sensitivity, verifying the rationality of the upper limit of layer height in this application.

[0105] Example 14

[0106] This embodiment is intended to verify the feasibility of the lower limit of ultraviolet light irradiation time (1 min) in this application.

[0107] With all other preparation conditions the same as in Example 1, only the UV irradiation time in step S6 was adjusted from 90s to 60s, resulting in a partially cured structure. DSC testing showed a monomer conversion rate of 91.3%; the initial resistance R0 was measured to be 25.1Ω; under 50kPa pressure, ΔR / R0 was 279%; and the resistance change rate after 1000 bends was 3.1%. The results indicate that 60s of irradiation is sufficient to meet basic curing requirements, supporting the feasibility of the 1–2 min time window in this application.

[0108] Example 15

[0109] This embodiment is intended to verify the feasibility of the upper limit of ultraviolet light irradiation time (2 min) in this application.

[0110] With all other preparation conditions the same as in Example 1, only the UV irradiation time in step S6 was adjusted from 90 s to 120 s to obtain a deeply cured structure. DSC testing showed a monomer conversion rate of 96.8%; the initial resistance R0 was measured to be 24.9 Ω; under 50 kPa pressure, ΔR / R0 was 283%; and the resistance change rate after 1000 bends was 2.5%. The results indicate that 120 s irradiation did not induce significant embrittlement, and the structural performance was stable, verifying the rationality of the upper time limit in this application.

[0111] Example 16

[0112] This embodiment verifies the electrical response characteristics of the three-dimensional conductive structure of the present invention when deployed in different functional regions, in order to support the technical effect of the embodiment.

[0113] Following the method described in Example 1, three-dimensional conductive structures were constructed on three different kraft paper samples: Sample A – the structure was deployed at the four corners of the cardboard (pressure area); Sample B – the structure was arranged along the sealing tear line (opening area); Sample C – the structure was located in the center of the front of the carton (functional interaction area). All structures were constructed using parameters of a 0.45mm nozzle, 70mm / s, 0.20mm layer height, and 8-layer grid (5mm×5mm), and cured by 365nm UV irradiation for 90s.

[0114] Electrical tests were performed on three groups of samples: a quasi-static pressure of 50 kPa was applied to sample A using a material testing machine, and ΔR / R0 was recorded; a tensile force of 10 N was applied to sample B along the tear line to complete the opening action, and the resistance change before and after opening was recorded; a finger pressure (approximately 20 kPa) was applied to sample C, and the response time and cycle life were recorded. The test results are shown in Table 1.

[0115] Table 1 Electrical response performance of three-dimensional conductive structures in different deployment regions

[0116]

[0117] The results show that the three-dimensional conductive structure exhibits high repeatability of pressure response in the pressure-bearing area, achieves one-time irreversible marking in the open area, and has millisecond-level response and ultra-high durability in the functional interaction area. All three types of deployment can accurately match the mechanical excitation mode and functional requirements of the corresponding scenarios, thus verifying the effectiveness and practicality of the regional deployment strategy in this application.

[0118] Example 17

[0119] This embodiment verifies the electrical parameter calibration effect of the three-dimensional conductive structure of the present invention to support the technical effect of the embodiment.

[0120] Ten batches of three-dimensional conductive structures (n=5 per batch) were prepared according to the method in Example 1. Electrodes were uniformly produced using silver paste screen printing followed by hot pressing at 80℃ for 30 seconds. The initial resistance R0 was measured using a Keithley 2450 digital source meter, and pressures ranging from 0 to 200 kPa were applied at a rate of 10 kPa / min on an Instron 5969 universal testing machine. Resistance changes were simultaneously collected to establish ΔR / R0–P curves. All tests were conducted in a constant temperature and humidity environment of 25℃ and 50% RH.

[0121] The test results are shown in Table 2.

[0122] Table 2. Calibration results of electrical parameters of the three-dimensional conductive structure (n=50)

[0123]

[0124] The results show that the three-dimensional conductive structure constructed by the method of the present invention has highly consistent initial resistance, repeatable pressure response threshold, low hysteresis rate and excellent nonlinear fitting degree, which verifies the feasibility and engineering applicability of the electrical parameter calibration steps in this application and provides a reliable data foundation for the subsequent development of digital interfaces for intelligent packaging.

[0125] Example 18

[0126] This embodiment provides a comparative verification to illustrate the significance and inventiveness of the technical effect of the present invention. Five comparative examples are set up, each corresponding to different technical defect scenarios:

[0127] Comparative Example 1 (Blank Control): Kraft paper substrate without any surface pretreatment, with the remaining steps the same as in Example 1;

[0128] Comparative Example 2 (parameters out of bounds): The solid content of the LCNF dispersion was 0.4 wt%, and the rest was the same as in Example 1;

[0129] Comparative Example 3 (missing component): rGO component omitted, only LCNF / AA system, the rest is the same as Example 1;

[0130] Comparative Example 4 (commercially available product): Commercially available silver nanowire conductive ink (model AgNW-10, Nanjing Xianfeng Nano) was screen-printed onto plasma-activated kraft paper with the same grid path and heat-cured at 120℃ for 30 minutes.

[0131] All samples underwent the same electrical and mechanical tests, and the results are shown in Table 3.

[0132] Table 3

[0133]

[0134] The results show that Example 1 of the present invention is significantly superior to the comparative examples in five key indicators: initial conductivity, pressure response amplitude, cycle stability, environmental tolerance, and interfacial bonding strength. In particular, it exhibits unexpected technical effects in ΔR / R0 (286% vs ≤ 19.2%) and bending stability (2.3% vs ≥ 15.6%). This effect is due to the synergistic effect of the rGO conductive pathway, the LCNF support framework, and the AA photocurable network, rather than the simple superposition of the components, thus verifying the substantial features and significant progress of the present invention.

[0135] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0136] Figure 5 A schematic diagram of a three-dimensional conductive structure construction system for smart packaging, provided in one embodiment of this application, is shown below. Figure 5 As shown, a three-dimensional conductive structure construction system 500 for smart packaging in this embodiment includes: a pretreatment module 301, a fiber dispersion module 302, a composite dispersion module 303, a dielectric preparation module 304, a structure deposition module 305, and a structure curing module 306.

[0137] The pretreatment module 301 is used to select paper-based, fiber-based, or composite packaging materials as packaging substrates and perform surface pretreatment on the area to be constructed of the packaging substrate.

[0138] The fiber dispersion module 302 is used to disperse lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion.

[0139] The composite dispersion module 303 is used to add reduced graphene oxide into the lignocellulose nanofiber dispersion for dispersion to obtain rGO / LCNF composite dispersion.

[0140] The medium preparation module 304 is used to mix acrylic monomer, crosslinking agent and photoinitiator to obtain photocurable system, and add the photocurable system to the rGO / LCNF composite dispersion for mixing. After homogenization and degassing, a conductive building medium is obtained.

[0141] The structure deposition module 305 is used to deposit the conductive building medium layer by layer on the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor with height, thickness and spatial connectivity characteristics.

[0142] The structure curing module 306 is used to perform photocuring treatment on the wet three-dimensional conductive structure precursor, so that the photocuring system undergoes polymerization and cross-linking, and the rGO / LCNF composite network is cured to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate.

[0143] Optionally, in the pretreatment module 301, the surface pretreatment includes one or more of the following: cleaning and degreasing, plasma activation, surface roughening, applying a base coating, and applying an interface bonding layer.

[0144] Optionally, in the fiber dispersion module 302, the solid content of the lignocellulose nanofiber dispersion is 0.5-3.0 wt%, and a uniform dispersion system is formed by stirring and / or ultrasonic dispersion.

[0145] Optionally, in the composite dispersion module 303, the mass ratio of the reduced graphene oxide to the lignocellulose nanofibers is (1-3):1, and the dispersion treatment includes shear stirring and / or ultrasonic dispersion.

[0146] Optionally, in the medium preparation module 304, the crosslinking agent is N,N′-methylenebisacrylamide, and the mass ratio of N,N′-methylenebisacrylamide to acrylic acid monomer is 1:20;

[0147] The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone and / or Irgacure 2959, and the amount of the photoinitiator is 0.1 wt% of the acrylic acid monomer.

[0148] The degassing is performed using vacuum degassing with a vacuum degree of -0.10 MPa and a degassing time of 10 to 30 minutes.

[0149] Optionally, in the structure deposition module 305, the layer-by-layer deposition is implemented using one or more three-dimensional shaping methods selected from direct writing extrusion, dispensing deposition, micro-extrusion deposition, or jet deposition;

[0150] The three-dimensional forming parameters include nozzle inner diameter, printing speed and layer height, wherein the nozzle inner diameter is 0.20-0.80 mm, the printing speed is 10-120 mm / s, and the layer height is 0.10-0.60 mm.

[0151] Optionally, in the structure deposition module 305, the conductive building medium is deposited layer by layer along a grid path using a direct-write extrusion printing method to form the wet three-dimensional conductive structure precursor. The nozzle inner diameter is 0.30mm to 0.60mm, the printing speed is 60mm / s to 80mm / s, and the layer height is 0.15mm to 0.30mm.

[0152] Optionally, in the structure curing module 306, the photocuring process uses ultraviolet light irradiation, the wavelength of the ultraviolet light is 365nm, and the irradiation time is 1 to 2 minutes.

[0153] Optionally, the system 300 further includes an electrical parameter calibration module 307, specifically used for: leading out electrodes from both ends of the three-dimensional conductive structure, measuring the initial resistance, and recording the resistance change under pressure conditions, so as to establish the electrical response parameters of the three-dimensional conductive structure.

[0154] Optionally, in the electrical parameter calibration module 307, the three-dimensional conductive structure is disposed in the pressure-bearing area, opening area, or functional interaction area of ​​the packaging.

[0155] The system in this embodiment can be used to execute the methods of any of the above embodiments, and its implementation principle and technical effect are similar, so they will not be described again here.

Claims

1. A method for building a three-dimensional conductive structure for smart packaging, characterized by, include: S1. Select paper-based, fiber-based, or composite packaging materials as packaging substrates, and perform surface pretreatment on the area to be constructed of the packaging substrate. S2. Disperse the lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion. S3. Reduced graphene oxide is added to the lignocellulose nanofiber dispersion for dispersion treatment to obtain rGO / LCNF composite dispersion; S4. Mix acrylic monomer, crosslinking agent and photoinitiator to obtain photocurable system, and add the photocurable system to the rGO / LCNF composite dispersion for mixing. After homogenization and degassing, a conductive building medium is obtained. S5. The conductive building medium is deposited layer by layer on the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor with height, thickness and spatial connectivity characteristics. S6. The wet three-dimensional conductive structure precursor is subjected to photocuring treatment to cause the photocuring system to undergo polymerization and cross-linking, and the rGO / LCNF composite network is cured to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate. The reduced graphene oxide forms the conductive pathway in the three-dimensional conductive structure, and the lignocellulose nanofibers form the supporting framework in the three-dimensional conductive structure and regulate the forming rheological properties of the conductive building medium.

2. The method of claim 1, wherein, The surface pretreatment in step S1 includes one or more of the following: cleaning and degreasing, plasma activation, surface roughening, applying a base coat, and applying an interface bonding layer.

3. The method of claim 1, wherein, In step S2, the solid content of the lignocellulose nanofiber dispersion is 0.5-3.0 wt%, and a uniform dispersion system is formed by stirring and / or ultrasonic dispersion. In step S3, the mass ratio of the reduced graphene oxide to the lignocellulose nanofibers is (1-3):1, and the dispersion treatment includes shearing and / or ultrasonic dispersion.

4. The method of claim 1, wherein, In step S4, the crosslinking agent is N,N′-methylenebisacrylamide, and the mass ratio of N,N′-methylenebisacrylamide to acrylic acid monomer is 1:

20. The photoinitiator is 2,2-dimethoxy-2-phenylacetophenone and / or Irgacure 2959, and the amount of the photoinitiator is 0.1 wt% of the acrylic acid monomer. The degassing is performed using vacuum degassing with a vacuum degree of -0.10 MPa and a degassing time of 10 to 30 minutes.

5. The method of claim 3, wherein, The layer-by-layer deposition in step S5 is carried out using one or more three-dimensional shaping methods, such as direct writing extrusion, dispensing deposition, micro-extrusion deposition, or jet deposition. The three-dimensional forming parameters include nozzle inner diameter, printing speed and layer height, wherein the nozzle inner diameter is 0.20-0.80 mm, the printing speed is 10-120 mm / s, and the layer height is 0.10-0.60 mm.

6. The method of claim 5, wherein, In step S5, the conductive building medium is deposited layer by layer along a grid path using a direct-write extrusion printing method to form the wet three-dimensional conductive structure precursor. The nozzle inner diameter is 0.30mm to 0.60mm, the printing speed is 60mm / s to 80mm / s, and the layer height is 0.15mm to 0.30mm.

7. The method of claim 1, wherein, The photocuring process in step S6 uses ultraviolet light irradiation with a wavelength of 365 nm and an irradiation time of 1 to 2 minutes.

8. The method of claim 1, wherein, Following step S6, an electrical parameter calibration step is also included, which includes: Electrodes are led out from both ends of the three-dimensional conductive structure, the initial resistance is measured, and the resistance change is recorded under pressure to establish the electrical response parameters of the three-dimensional conductive structure.

9. The method of claim 8, wherein, The three-dimensional conductive structure is disposed in the pressure-bearing area, opening area, or functional interaction area of ​​the packaging.

10. A three-dimensional conductive structure building system for smart packaging, characterized by, include: The pretreatment module is used to select paper-based, fiber-based, or composite packaging materials as packaging substrates and to perform surface pretreatment on the areas of the packaging substrates to be constructed. The fiber dispersion module is used to disperse lignocellulose nanofibers in deionized water to obtain a lignocellulose nanofiber dispersion. A composite dispersion module is used to add reduced graphene oxide into the lignocellulose nanofiber dispersion for dispersion, to obtain an rGO / LCNF composite dispersion. The medium preparation module is used to mix acrylic monomers, crosslinking agents and photoinitiators to obtain a photocurable system, and add the photocurable system to the rGO / LCNF composite dispersion for mixing. After homogenization and degassing, a conductive building medium is obtained. The structural deposition module is used to deposit the conductive building medium layer by layer onto the surface of the packaging substrate according to a preset path to form a wet three-dimensional conductive structure precursor with height, thickness and spatial connectivity characteristics; The structure curing module is used to perform photocuring treatment on the wet three-dimensional conductive structure precursor, so that the photocuring system undergoes polymerization and cross-linking, and the rGO / LCNF composite network is cured to obtain a three-dimensional conductive structure attached to the surface of the packaging substrate.

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