A functionalized graphene quantum dot fluorescent ink composition and its preparation method

Abstract

This invention discloses a functionalized graphene quantum dot fluorescent ink composition and its preparation method, belonging to the technical field of anti-counterfeiting printing functional materials. The ink composition, based on a total weight of 100 parts, comprises 0.8-2.5 parts of graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam), 25-40 parts of an aqueous polyurethane dispersion, 0.5-1.5 parts of benzo-15-crown-5-carboxylic acid, 0.3-0.8 parts of a dispersant, 0.2-0.6 parts of a leveling agent, 0.1-0.3 parts of a defoamer, and the balance being deionized water. The quantum dots are prepared by a one-step hydrothermal method using citric acid, N-vinylcaprolactam, and vinylphosphonic acid as core raw materials in the presence of an initiator and a crosslinking agent. The ink of this invention simultaneously possesses photoluminescence, temperature response, and Fe... 3+ It features a triple anti-counterfeiting function with specific identification, and there is a synergistic enhancement effect between temperature sensitivity and ion response. At the same time, the ink has excellent storage stability and printability, making it suitable for high-end anti-counterfeiting fields.

Description

Technical Field

[0001] This invention belongs to the technical field of anti-counterfeiting printing functional materials, specifically relating to a graphene quantum dot-based fluorescent anti-counterfeiting ink composition, and more specifically, to a functionalized graphene quantum dot fluorescent ink composition with multiple synergistic response characteristics and its preparation method. Background Technology

[0002] Graphene quantum dots, as a zero-dimensional carbon nanomaterial, have excellent optical stability, tunable fluorescence properties, low toxicity and environmental friendliness. They are one of the core research and development directions in the field of fluorescent anti-counterfeiting inks and have been widely applied in various anti-counterfeiting printing scenarios.

[0003] Currently, the research and development of graphene quantum dot anti-counterfeiting inks in the industry mainly falls into three technical directions, all of which face insurmountable technical bottlenecks: The first type is basic single-fluorescent anti-counterfeiting ink. This type of ink only modifies graphene quantum dots with conventional groups such as amino and carboxyl groups to improve their water solubility and basic luminescent properties. The final ink can only achieve a single fluorescent development function under ultraviolet light. The core drawback of this type of solution is that the anti-counterfeiting feature is only one dimension. Counterfeiters can easily imitate it using ordinary fluorescent materials, which cannot meet the anti-counterfeiting and security requirements of high-end scenarios.

[0004] The second type is improved dual anti-counterfeiting ink. To enhance anti-counterfeiting capabilities, the industry has attempted to graft temperature-sensitive polymers, most commonly poly(N-isopropylacrylamide), onto the surface of graphene quantum dots. This endows the ink with temperature-responsive functionality, achieving dual anti-counterfeiting through both ultraviolet photoluminescence and temperature response. However, these solutions generally suffer from two core problems: First, the preparation process is cumbersome, almost all employing a multi-step process of "first synthesizing graphene quantum dots, then grafting polymers for modification." This not only involves lengthy steps and high purification costs but also easily leads to fluorescence quenching of quantum dots and poor batch-to-batch uniformity during subsequent modification, making it difficult to achieve large-scale stable production. Second, there is no synergy between functions. The introduced temperature-sensitive response function is completely independent of other anti-counterfeiting functions, and there may even be mutual interference between functions, failing to achieve a substantial improvement in anti-counterfeiting sensitivity and security.

[0005] The third category is exploratory ion recognition anti-counterfeiting inks. Some research and development attempts have been made to introduce metal ion complexing groups to give the ink a third layer of anti-counterfeiting function through chemical recognition. However, most of these solutions can only achieve a single ion recognition effect, with low response sensitivity and poor anti-interference ability. Moreover, they have never achieved positive synergy between temperature-sensitive response and ion recognition. On the contrary, the introduction of functional groups will destroy the original temperature-sensitive performance, and a mature and usable technical solution has never been formed.

[0006] In addition, there is a common technical misconception in this field: the thermosensitive phase transition behavior of thermosensitive polymers is highly dependent on the hydrogen bond balance and hydrophobic-hydrophilic ratio of the molecular chain. The introduction of strongly hydrophilic groups will severely disrupt the hydrogen bond network of the thermosensitive polymer chain, usually leading to a significant shift in its phase transition temperature, a significant decrease in phase transition sensitivity, or even complete loss of thermosensitive response characteristics. Phosphonic acid groups are typical strongly hydrophilic groups, so the industry generally avoids directly introducing such strongly hydrophilic functional groups into the thermosensitive polymer chain. This has even led to the common perception that phosphonic acid groups and thermosensitive polymers are incompatible. Furthermore, there is no relevant technical exploration to combine phosphonic acid groups, thermosensitive polymer networks, and crown ether derivatives in the ink system to construct a multi-layer anti-counterfeiting system with synergistic enhancement effects.

[0007] In summary, current graphene quantum dot anti-counterfeiting inks in the industry generally suffer from four major defects: First, the integration of multiple response functions is low, with a lack of synergy between different functions, and even mutual interference, making it impossible to achieve a substantial leap in anti-counterfeiting performance; second, the preparation process is complex, with multiple post-modification processes leading to poor product stability and difficulty in large-scale production; third, the anti-counterfeiting features are simply the superposition of independent functions, allowing counterfeiters to achieve forgery simply by imitating individual functions, resulting in insufficient anti-counterfeiting security in high-end scenarios; and fourth, it is difficult to simultaneously achieve good storage stability, UV aging resistance, and industrial printing suitability, failing to meet the industrialization needs of high-end printing. To address these long-standing and unresolved technical pain points in the industry, this invention proposes a novel technical solution. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and solve the technical problems of existing anti-counterfeiting inks, such as single functional dimensions, lack of synergy among multiple response mechanisms, complex preparation process, insufficient anti-counterfeiting security, and poor overall stability. It provides a functional graphene quantum dot fluorescent ink composition and its preparation method that has a reasonable structural design, simple preparation process, triple synergistic response anti-counterfeiting function, and excellent comprehensive performance.

[0009] The technical solution of this invention is implemented as follows: This invention adopts the following technical solution: On one hand, the present invention provides a functionalized graphene quantum dot fluorescent ink composition, comprising the following components based on 100 parts by weight of the total ink composition: 0.8-2.5 parts of graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam); 25-40 parts of waterborne polyurethane dispersion; 0.5-1.5 parts of benzo-15-crown-5-carboxylic acid; Dispersant 0.3-0.8 parts; Leveling agent 0.2-0.6 parts; Defoamer 0.1-0.3 parts; And the remaining deionized water.

[0010] The graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam) are prepared by a one-step hydrothermal method using citric acid, N-vinylcaprolactam, and vinylphosphonic acid as raw materials, in the presence of potassium persulfate initiator and N,N'-methylenebisacrylamide crosslinking agent. The product surface is grafted with crosslinked poly(N-vinylcaprolactam) segments containing phosphonic acid groups. These quantum dots possess both the thermosensitive response characteristics provided by the poly(N-vinylcaprolactam) chains and the metal ion coordination ability provided by the phosphonic acid groups.

[0011] Preferably, the amount of the N,N'-methylenebisacrylamide crosslinking agent is 0.5%-2% of the total mass of N-vinylcaprolactam and vinylphosphonic acid monomers.

[0012] In the raw materials for preparing graphene quantum dots, the molar ratio of N-vinylcaprolactam to vinylphosphonic acid is 1:1-1.5:1.

[0013] Preferably, the aqueous polyurethane dispersion is an aqueous polyurethane dispersion with a solid content of 38-42%, and more preferably an aqueous aliphatic polyurethane dispersion.

[0014] Preferably, the dispersant is a phosphate ester dispersant, the leveling agent is a polyether-modified polysiloxane leveling agent, and the defoamer is a mineral oil defoamer.

[0015] On the other hand, the present invention provides a method for preparing the above-mentioned ink composition, comprising the following steps: S1. The graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam) are dispersed in 40%-50% of deionized water and ultrasonically treated for 25-35 minutes under ice-water bath conditions to obtain a uniform quantum dot dispersion. S2. Mix the aqueous polyurethane dispersion, benzo-15-crown-5-carboxylic acid and the remaining deionized water, and stir in a water bath at 45-55℃ for 50-70 minutes to obtain a homogeneous resin phase. S3. The quantum dot dispersion obtained in step S1 is slowly added dropwise to the resin phase in step S2 at a rate of 1-2 mL / min. After the addition is complete, stirring and mixing are continued. Then, dispersant, leveling agent and defoamer are added. The mixture is dispersed at high speed and milled until the fineness of the slurry is ≤8 μm. The pH of the system is adjusted to 7.0-7.5 with a pH adjuster. After filtration, the fluorescent ink composition is obtained.

[0016] In another aspect, the present invention provides a method for preparing the functionalized graphene quantum dots, comprising the following steps: T1. Dissolve citric acid, N-vinylcaprolactam, vinylphosphonic acid, potassium persulfate, and N,N'-methylenebisacrylamide in deionized water according to the specified ratio, and stir until completely dissolved to obtain a homogeneous reaction solution; T2. Transfer the reaction solution to a high-pressure reactor lined with polytetrafluoroethylene and carry out a hydrothermal reaction at 180-200℃ for 8-10 hours. Allow it to cool naturally to room temperature to obtain the crude product. T3. The crude product was purified by dialysis and then freeze-dried to obtain the functionalized graphene quantum dots.

[0017] Preferably, the hydrothermal reaction temperature in step T2 is 190°C and the reaction time is 9 hours.

[0018] Furthermore, the present invention provides a method for identifying anti-counterfeiting labels, wherein the anti-counterfeiting labels are printed using the aforementioned ink composition, and the method includes the following steps performed sequentially: a) Observe the fluorescence development of the label under 365nm ultraviolet light irradiation; b) Heat the label to 35-40℃ and observe the change in fluorescence intensity before and after heating; c) Within 30 seconds after heating is completed, contact the marker with ferric chloride solution and observe the change in fluorescence intensity before and after contact.

[0019] The present invention has the following advantages over the prior art: 1. This invention overcomes the technical biases in the field, achieving deep compatibility and synergistic enhancement of multiple response functions. It is generally believed in the art that strongly hydrophilic phosphonic acid groups can disrupt the phase transition behavior of temperature-sensitive polymers. However, this invention, through a specific one-step hydrothermal synthesis process and crosslinking system design, simultaneously constructs a crosslinked structure containing temperature-sensitive segments (poly(N-vinylcaprolactam)) and ion-recognizing groups (phosphonic acid groups) on the surface of graphene quantum dots, and innovatively introduces benzo-15-crown-5-carboxylic acid into the ink system. Test results show that this system not only simultaneously possesses UV fluorescence, temperature response, and Fe... 3+ The system exhibits a specific identification triple anti-counterfeiting function, and a significant synergistic enhancement effect exists between the thermosensitive response and the ion response. Near the thermosensitive phase transition temperature (35-40℃), the system responds to Fe... 3+ The fluorescence quenching sensitivity can be increased by more than 2.0 times compared to that at room temperature (synergistic enhancement factor ≥ 2.0). This effect far exceeds the simple summation of the independent effects of each functional component, and is a technical effect that is difficult for those skilled in the art to predict based on the existing industry knowledge.

[0020] 2. Simplified process and good product uniformity. A one-step hydrothermal method simultaneously completes the carbonization and functionalization modification of quantum dots, avoiding purification losses, structural defects, and batch instability issues associated with multi-step post-modification processes. The process is simple and controllable, resulting in quantum dots with uniform particle size distribution and firmly anchored functional groups, making it more suitable for large-scale industrial production.

[0021] 3. High anti-counterfeiting security. The triple anti-counterfeiting features are coupled and linked through molecular design. Authentication requires a specific sequence (first ultraviolet light, then heating, and finally ion detection) to achieve a complete and authentic anti-counterfeiting effect. This deeply coupled anti-counterfeiting logic greatly increases the difficulty of counterfeiting and enhances the security level in high-end anti-counterfeiting scenarios.

[0022] 4. Excellent overall performance of the ink. The ink system of this invention uses a water-based polyurethane binder with good compatibility and optimizes the formulation of additives, so that the ink has excellent storage stability (no precipitation or stratification after 6 months of sealed storage at room temperature, with a small viscosity change rate), good UV aging resistance, and excellent printability, and can be adapted to various industrial printing processes such as screen printing and flexographic printing. Detailed Implementation

[0023] 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.

[0024] Unless otherwise specified, all reagents and instruments used in the following examples and comparative examples are commercially available.

[0025] Main raw materials: citric acid, N-vinylcaprolactam (NVCL), vinylphosphonic acid (VPA), potassium persulfate (KPS), N,N'-methylenebisacrylamide (MBA), benzo-15-crown-5-carboxylic acid, and triethylamine, all of analytical grade; water-based aliphatic polyurethane dispersion with a solid content of 40%; phosphate ester dispersants, polyether-modified polysiloxane leveling agents, and mineral oil defoamers are all commercially available products commonly used in water-based inks.

[0026] Main instruments: high-pressure reactor, ultrasonic cell disruptor, fluorescence spectrophotometer, high-speed disperser, horizontal sand mill, pH meter, transmission electron microscope, Fourier transform infrared spectrometer, X-ray photoelectron spectrometer, ultraviolet aging test chamber.

[0027] Example 1: Preparation of Functionalized Graphene Quantum Dots Example 1-1 1. Weigh 5.0 g of citric acid and dissolve it in 30 ml of deionized water. Stir magnetically until completely dissolved.

[0028] 2. Add 1.6 g NVCL, 1.2 g VPA (molar ratio NVCL:VPA ≈ 1.04:1), 0.12 g potassium persulfate, and 0.03 g MBA (approximately 1.1% of the total mass of NVCL and VPA) sequentially to the above solution, and continue stirring for 20 minutes to obtain a homogeneous and transparent reaction solution.

[0029] 3. Transfer the reaction solution to a 50 ml polytetrafluoroethylene-lined high-pressure reactor, seal it, and place it in a forced-air drying oven for constant temperature reaction at 190°C for 9 hours.

[0030] 4. After the reaction is complete, allow the mixture to cool naturally to room temperature to obtain a brownish-red transparent crude product.

[0031] 5. Transfer the crude product into a dialysis bag with a molecular weight cutoff of 3500 Daltons and dialyze with deionized water for 48 hours, changing the dialysis fluid every 6 hours during this period.

[0032] 6. After dialysis, the liquid in the dialysis bag is freeze-dried for 48 hours to obtain a light yellow fluffy solid powder, which is the target product: graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam). It is then placed in a desiccator and sealed for storage.

[0033] Examples 1-2 (Adjusting the monomer molar ratio to 1:1) The preparation steps are the same as in Examples 1-1, except that the amount of NVCL is adjusted to 1.54 grams, so that the molar ratio of VPA to NVCL is 1:1, and the other parameters remain unchanged.

[0034] Examples 1-3 (monomer molar ratio adjusted to 1:1.5) The preparation steps are the same as in Examples 1-1, except that the amount of NVCL is adjusted to 2.31 grams, so that the molar ratio of VPA to NVCL is 1:1.5, and the other parameters remain unchanged.

[0035] Examples 1-4 (Reaction temperature adjusted to 180℃) The preparation steps are the same as in Example 1-1, except that the hydrothermal reaction temperature is adjusted to 180℃ and the reaction time is adjusted to 10 hours, while the other parameters remain unchanged.

[0036] Examples 1-5 (Reaction temperature adjusted to 200℃) The preparation steps are the same as in Examples 1-1, except that the hydrothermal reaction temperature is adjusted to 200℃ and the reaction time is adjusted to 8 hours, while the other parameters remain unchanged.

[0037] Quantum dot structure and mechanism characterization The products obtained in Example 1-1 were characterized, and the results are as follows: 1. Transmission electron microscopy (TEM) analysis: The product is spherical with uniform particle size distribution and a statistical average particle size of approximately 5.2 nanometers.

[0038] 2. Fourier transform infrared spectroscopy (FT-IR) analysis: The spectrum at 1150 cm⁻¹ -1 Characteristic stretching vibration peaks belonging to P=O bonds appear nearby; at 1640 cm⁻¹ -1 and 1550 cm -1 Characteristic absorption peaks belonging to amide I and amide II bands appeared nearby. These results indicate that phosphonic acid groups and polyamide structures (corresponding to poly(N-vinylcaprolactam) chains) were successfully introduced into the product.

[0039] 3. X-ray photoelectron spectroscopy (XPS) analysis: A distinct P 2p characteristic peak was detected at a binding energy of 133.2 eV, further confirming the successful introduction of the phosphonic acid group.

[0040] Example 2: Preparation of fluorescent ink composition Example 2-1 1. Preparation of quantum dot dispersion: Weigh 1.5 g of the functionalized graphene quantum dots prepared in Example 1-1 and add 10 g of deionized water (approximately 45% of the total 22.4 g of deionized water used in this batch). Place the mixture in an ice-water bath and treat it with an ultrasonic cell disruptor for 30 minutes (operating parameters: power 500W, working time 2 seconds, interval 3 seconds) to obtain a uniform quantum dot dispersion.

[0041] 2. Resin Phase Preparation: In a 250 mL three-necked flask, add 30 g of aqueous aliphatic polyurethane dispersion (40% solids content), 1.0 g of benzo-15-crown-5-carboxylic acid, and 12.4 g of deionized water (the remainder). Place the flask in a 50 °C constant temperature water bath and mix at a stirring speed of 300 rpm for 1 hour to obtain a homogeneous resin phase.

[0042] 3. Premixing: Keep the resin phase under gentle stirring (approximately 200 rpm), and slowly add the quantum dot dispersion prepared in step 1 dropwise to the resin phase at a rate of approximately 1.5 mL / min. After the addition is complete, increase the stirring speed to 500 rpm and continue stirring for 30 minutes to ensure thorough premixing.

[0043] 4. Additives and Homogenization: Add 0.5 g of phosphate ester dispersant, 0.4 g of polyether-modified polysiloxane leveling agent, and 0.2 g of mineral oil defoamer to the above mixture in sequence. After each additive is added, maintain stirring at 500 rpm for 10 minutes.

[0044] 5. Grinding: Transfer the mixture to a high-speed disperser and disperse at 1500 rpm for 30 minutes. Then, use a horizontal sand mill with zirconia beads with a diameter of 0.6-0.8 mm to grind until the fineness of the slurry sample is ≤5 microns.

[0045] 6. Conditioning and Filtration: Slowly add triethylamine dropwise to the ground slurry while stirring. Monitor the pH with a pH meter and adjust the pH of the system to 7.2. Finally, filter through a 200-mesh nylon sieve to obtain the finished fluorescent anti-counterfeiting ink.

[0046] Examples 2-2 to 2-7 (Formula Parameter Adjustment) Following the basic steps of Example 2-1, different ink samples were prepared by adjusting one of the following parameters: Example 2-2: The amount of functionalized graphene quantum dots used is 0.8 grams, and the amount of deionized water is adjusted synchronously with the formula.

[0047] Examples 2-3: The amount of functionalized graphene quantum dots used was 2.5 grams, and the amount of deionized water was adjusted synchronously with the formula.

[0048] Examples 2-4: The amount of benzo-15-crown-5-carboxylic acid used is 0.5 g, and the amount of deionized water is adjusted synchronously with the formula.

[0049] Examples 2-5: The amount of benzo-15-crown-5-carboxylic acid used is 1.5 grams, and the amount of deionized water is adjusted synchronously with the formula.

[0050] Examples 2-6: The amount of waterborne polyurethane dispersion is 25 grams, and the amount of deionized water is adjusted synchronously with the formulation.

[0051] Examples 2-7: The amount of waterborne polyurethane dispersion is 40 grams, and the amount of deionized water is adjusted synchronously with the formulation.

[0052] Comparison Example Comparison Example D1 (Conventional Temperature-Sensitive Anti-counterfeiting Ink) The specific steps for preparing amino-based graphene quantum dots grafted with thermosensitive polymers, following conventional methods in this field, are as follows: Preparation of amino-based graphene quantum dots: 5.0 g of citric acid and 3.0 g of ethylenediamine were weighed and dissolved in 30 mL of deionized water. After stirring evenly, the mixture was transferred to a reaction vessel and hydrothermally reacted at 200 °C for 5 h. After natural cooling, the mixture was dialyzed through a 3500 Da dialysis bag for 48 h and then freeze-dried to obtain amino-based graphene quantum dots. Alkenylation modification: The above-mentioned aminated quantum dots were redispersed in 30 mL of deionized water, 2.0 g of allyl glycidyl ether was added, the pH was adjusted to 11 with sodium hydroxide, the reaction was stirred at 25 °C for 12 h, and the graphene quantum dots with alkenyl groups on the surface were obtained by dialysis purification. PNIPAM grafting modification: The above-mentioned alkenylated quantum dots, 2.0 g N-isopropylacrylamide, and 0.12 g ammonium persulfate were dissolved in 30 mL of deionized water, and the polymerization reaction was carried out at 70 °C for 6 h under nitrogen protection. The PNIPAM-grafted graphene quantum dots were obtained by dialysis purification. Ink preparation: Take 1.5g of this grafted modified quantum dots and prepare ink according to the steps of Example 2-1. Do not add benzo-15-crown-5-carboxylic acid. The remaining components, dosages and process parameters are the same as in Example 2-1.

[0053] Comparative Example D2 (crownless ether system) The preparation steps are the same as in Example 2-1, except that benzo-15-crown-5-carboxylic acid is not added in step 2.

[0054] Comparative Example D3 (Physically Mixed System) 1. Synthesis of unmodified pure graphene quantum dots: Following the steps of Example 1-1, without adding NVCL, VPA and MBA, synthesized using only citric acid under the same conditions.

[0055] 2. Synthesis of cross-linked poly(N-vinylcaprolactam) microspheres: 1.6 g NVCL, 0.12 g potassium persulfate and 0.03 g MBA were dissolved in 30 mL deionized water and polymerized at 70 °C for 6 h under nitrogen protection. The resulting microspheres were obtained by dialyzing and freeze-drying.

[0056] 3. Prepare ink by physically mixing 1.5 g of pure quantum dots, 1.0 g of poly(N-vinylcaprolactam) microspheres, and 1.0 g of benzo-15-crown-5-carboxylic acid with other components according to the steps in Example 2-1.

[0057] Comparative Example D4 (No cross-linking agent system) The preparation steps are the same as in Example 2-1, except that the quantum dots used are products prepared according to the method of Example 1-1 but without the addition of MBA crosslinking agent.

[0058] Performance Testing and Result Analysis The inks obtained in the above embodiments and comparative examples were subjected to performance tests. The main test methods are as follows: Fluorescence quantum yield: The integrating sphere method was used, with quinine sulfate (quantum yield 54% in 0.1 mol / L H2SO4) as the standard reference, and the result was measured at an excitation wavelength of 365 nm.

[0059] Temperature-sensitive response performance: The ink was made into a 20μm thick dry film and placed in a variable temperature sample cell. The change in fluorescence intensity at the maximum emission wavelength was recorded during the process of heating from 25℃ to 45℃. The low critical dissolution temperature (LCST) and the rate of change in fluorescence intensity from 25℃ to 40℃ were calculated.

[0060] Ion response performance: The dry ink film was immersed in FeCl3 solutions of different concentrations, left to stand for 1 min, and then removed to measure the fluorescence quenching. The quenching constant (Ksv) and detection limit were calculated using the Stern-Volmer equation (F0 / F = 1 + Ksv[Q]), and the response to Fe was evaluated. 3+ Relative to Fe 2+ The selectivity coefficient.

[0061] Synergistic enhancement factor: The fluorescence quenching constant Ksv of the ink dry film in 50 μM FeCl3 solution was measured at 25 °C and 40 °C, respectively. The synergistic enhancement factor = Fe at 40 °C 3+ The quenching constant Ksv / Fe at 25℃ 3+ Quenching constant Ksv.

[0062] Storage stability: The ink was sealed and placed in an environment of 25°C. The appearance changes were observed over 6 months, and the viscosity change rate was tested.

[0063] UV aging resistance: The ink-printed sample was placed in a UVA-340 UV aging chamber and irradiated for 100 hours under an irradiation intensity of 0.68W / m². The fluorescence intensity retention rate was then tested.

[0064] Experimental verification shows that when the molar ratio of vinylphosphonic acid to N-vinylcaprolactam exceeds the range of 1:1-1:1.5, the system cannot achieve a stable synergistic effect of thermosensitive phase transition and ion recognition: when the molar ratio is below 1:1, the introduction of phosphonic acid groups is insufficient, and the ion recognition sensitivity decreases significantly; when the molar ratio is above 1:1.5, the strong hydrophilic groups destroy the hydrogen bond network of the thermosensitive chain, and the sensitivity of the thermosensitive phase transition decreases significantly. When the amount of crosslinking agent exceeds the range of 0.5%-2%, too low an amount cannot form a stable crosslinking network, while too high an amount leads to excessive crosslinking of the polymer chain, and the thermosensitive phase transition behavior disappears. The parameter range protected by this invention is the key and necessary range for achieving the synergistic enhancement effect.

[0065] Test Results Summary Table Table 1 Performance Characterization of Functionalized Graphene Quantum Dots (Example 1 Series)

[0066] Table 2 Performance Characterization of Fluorescent Anti-counterfeiting Inks (Example 2 Series)

[0067] Table 3 Comparison of Ink Performance of Comparative Examples

[0068] Application Examples The ink prepared in Example 2-1 was screen-printed onto a designated area of ​​the anti-counterfeiting label of a certain brand of liquor using a 200-mesh screen. This area is transparent and traceless under natural light. The anti-counterfeiting identification process is as follows: 1. Primary identification (ultraviolet): When illuminated with a 365nm ultraviolet flashlight, a clear blue fluorescent logo appears.

[0069] 2. Secondary identification (thermosensitive): Hold the label in your hand or gently heat it to 35-40℃. The fluorescence of the logo will be significantly reduced; after heating is stopped and the label is cooled, the fluorescence will be fully restored. This dynamic change can preliminarily rule out ordinary fluorescent counterfeits.

[0070] 3. Tertiary Identification (Ions): After heating the label to 35-40℃, immediately use a microsyringe or a special cotton swab to take a small amount of low-concentration FeCl3 test solution and touch it to the logo area; the fluorescence will be rapidly quenched. Subsequently, wipe with the accompanying EDTA reducing solution; the fluorescence can be restored to more than 90% of its initial value. This step is used for final authoritative identification.

[0071] In summary, the functionalized graphene quantum dots and corresponding ink compositions prepared in the embodiments of this invention are comprehensively superior to the existing technology control system in terms of core performance. Examples 1-1 to 1-5 of the quantum dots of this invention all achieve stable compatibility in fluorescence performance, temperature-sensitive response, and ion recognition ability, overcoming the common technical prejudice in the field that strong hydrophilic phosphonic acid groups will destroy the phase transition behavior of temperature-sensitive polymers. Among them, the preferred example 1-1 has a synergistic enhancement factor of 2.3, with optimal balance across all performance aspects. Examples 2-1 to 2-7 of the inks all possess stable ultraviolet photoluminescence, temperature response, and Fe... 3+ This invention features a triple anti-counterfeiting function with specific identification capabilities. Its temperature sensitivity, ion detection sensitivity, aging resistance, and storage stability all meet the requirements of industrial printing. Performance fluctuations within the boundaries of the claimed formulation are controllable, making it suitable for large-scale, stable production. Comparative data confirms that in systems lacking crown ether components, without crosslinking agents, and with simple physical mixing, the synergistic enhancement effect completely disappears, and core performance significantly deteriorates. This demonstrates that the crosslinked quantum dot structure and crown ether-phosphonic acid synergistic recognition system of this invention are essential technical features for achieving superior performance. Through integrated molecular design, this invention achieves synergistic enhancement of multiple anti-counterfeiting functions, solving the industry pain points of existing technologies that are simply superimposed functions, lack synergy, and are easily counterfeited.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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.

Claims

1. A functionalized graphene quantum dot fluorescent ink composition, characterized in that, Based on 100 parts by weight of the total ink composition, it comprises the following components: 0.8-2.5 parts of graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam); 25-40 parts of waterborne polyurethane dispersion; 0.5-1.5 parts of benzo-15-crown-5-carboxylic acid; Dispersant 0.3-0.8 parts; Leveling agent 0.2-0.6 parts; Defoamer 0.1-0.3 parts; And the remaining deionized water; The graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam) were prepared by a one-step hydrothermal method using citric acid, N-vinylcaprolactam, and vinylphosphonic acid as raw materials, in the presence of potassium persulfate initiator and N,N'-methylenebisacrylamide crosslinking agent. The product surface was grafted with crosslinked poly(N-vinylcaprolactam) segments containing phosphonic acid groups. The molar ratio of N-vinylcaprolactam to vinylphosphonic acid was 1:1-1.5:

1. The crosslinking agent was N,N'-methylenebisacrylamide, and its amount was 0.5%-2% of the total mass of N-vinylcaprolactam and vinylphosphonic acid.

2. The ink composition according to claim 1, characterized in that, The aqueous polyurethane dispersion is an aqueous aliphatic polyurethane dispersion with a solid content of 38-42%; the dispersant is a phosphate ester dispersant; the leveling agent is a polyether-modified polysiloxane leveling agent; and the defoamer is a mineral oil defoamer.

3. A method for preparing the ink composition according to any one of claims 1-2, characterized in that, Includes the following steps: S1. The graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam) are dispersed in 40%-50% of deionized water and ultrasonically treated in an ice-water bath for 25-35 minutes to obtain a quantum dot dispersion. S2. Mix the aqueous polyurethane dispersion, benzo-15-crown-5-carboxylic acid and the remaining deionized water, and stir in a water bath at 45-55℃ for 50-70 minutes to obtain the resin phase; S3. The quantum dot dispersion is mixed with the resin phase, and a dispersant, leveling agent and defoamer are added. The mixture is dispersed at high speed and milled until the fineness of the slurry is ≤8μm. The pH of the system is adjusted to 7.0-7.5, and the mixture is filtered to obtain the ink composition.

4. The method according to claim 3, characterized in that, In step S3, the quantum dot dispersion is added dropwise to the resin phase at a rate of 1-2 mL / min. After the addition is complete, the mixture is stirred at 500 rpm for 25-35 minutes, and then the dispersant, leveling agent and defoamer are added.

5. The method according to claim 3, characterized in that, The preparation method of graphene quantum dots co-modified with phosphonic acid and poly(N-vinylcaprolactam) includes the following steps: T1. Dissolve citric acid, N-vinylcaprolactam, vinylphosphonic acid, potassium persulfate and N,N'-methylenebisacrylamide in deionized water according to the specified ratio, and stir until completely dissolved to obtain a homogeneous reaction solution; T2. Transfer the reaction solution to a high-pressure reactor and perform a hydrothermal reaction at 180-200℃ for 8-10 hours. After the reaction is completed, dialyze and purify to obtain the graphene quantum dots.

6. The method according to claim 5, characterized in that, In step T2, the hydrothermal reaction temperature is 190℃ and the reaction time is 9 hours.

7. A method for identifying anti-counterfeiting labels, characterized in that, The anti-counterfeiting label is printed using the ink composition according to any one of claims 1-2, and the method includes the following steps performed sequentially: a) Observe the fluorescence development of the label under 365nm ultraviolet light irradiation; b) Heat the label to 35-40℃ and observe the change in fluorescence intensity before and after heating; c) Within 30 seconds after heating is completed, contact the marker with ferric chloride solution and observe the change in fluorescence intensity before and after contact.

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