Low viscosity double security ink, its preparation method and application

Abstract

The application relates to the technical field of ink materials, in particular to a low-viscosity double anti-forgery ink as well as a preparation method and application thereof. The ink comprises, in percentage by mass, 0.5-1.5% of an Er / Yb / N-GQDs-BCNCs nanohybrid, 0.1-1.5% of a surfactant, 2-8% of polyvinyl alcohol, 0.5-1.5% of urea, 0.01-1% of a defoaming agent, and the balance of water; wherein the Er / Yb / N-GQDs-BCNCs nanohybrid is a bacterial cellulose nanocrystal and an Er / Yb / N co-modified graphene quantum dot nanohybrid. The prepared ink has relatively low viscosity and shear thinning characteristics, so that the flowability and extensibility of the ink are enhanced, the overflow amount during printing is reduced, and the printing effect is improved; meanwhile, the ink has photoluminescence (blue light) and up-conversion luminescence (green light) characteristics, can realize double anti-forgery, and therefore has excellent comprehensive performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ink materials, and particularly relates to a low-viscosity double anti-counterfeiting ink as well as a preparation method and application thereof. BACKGROUND

[0002] With the popularity of scalable technology and online open-source images, counterfeiters can manufacture identical replicas of food products and place them with the real products in any retail store. Counterfeit food includes fake brand identification (even exclusive anti-counterfeiting labels, quick response codes and barcodes, etc.), origin protection or geographical indication protection, etc. Ultimately, customers are deceived into purchasing counterfeit products, thereby posing a risk to health and brand reputation. Therefore, the food industry urgently needs an effective anti-counterfeiting technology. Concealed identification using photosensitive luminescent markers plays an important role in anti-counterfeiting technology because these materials have the advantages of high cost-effectiveness, high efficiency and easy detection with the naked eye under ultraviolet light. Currently, traditional luminescent materials, including lanthanide elements, CdS, ZnS, CdTe and other metal quantum dot type photochromic compounds, usually exhibit monochromatic luminescence properties under excitation of ultraviolet (UV) and near-infrared (NIR) light, and the anti-counterfeiting performance is relatively single, and has certain toxicity.

[0003] Graphene quantum dots (GQDs) have become a promising new type of fluorescent material due to their excellent optical stability, tunable photoluminescence properties and biocompatibility. Nitrogen atom modification of GQDs (N-GQDs) polarizes the material, affecting fluorescence emission, and N-doped GQDs have a high quantum yield. In addition, lanthanide-doped nanomaterials exhibit high spectral conversion capability and excellent luminescence properties through upconversion and downconversion processes, and under near-infrared radiation, visible light or ultraviolet illumination detection, they emit multicolor radiation across the entire visible and near-infrared spectral region. Lanthanide elements such as erbium (Er 3+ ) and ytterbium (Yb 3+ ) are usually mixed with GQDs to achieve anti-counterfeiting performance feasibility control. In addition, Yb 3+ ions are a good choice for co-doping with Er 3+ ions, and their absorption cross section matches the energy difference of Er 3+ near 980 nm. This matching promotes enhanced energy transfer between the activator and the sensitizer, amplifying upconversion photoluminescence (UCPL) while increasing the probability of energy transfer. Therefore, lanthanide elements can be considered for modifying GQDs to prepare advanced anti-counterfeiting measures with multi-color adjustment functions.

[0004] Patent CN111073393A discloses a kind of double anti-fake fluorescent ink and its preparation method and application.The method includes: with six hydrated citric acid, ethylenediamine, ytterbium chloride hexahydrate, erbium chloride hexahydrate and water reaction to obtain doped carbon quantum dots;Rare earth doped carbon dots, double aldehyde group nanofibrillar cellulose, 2-methylpyridine-N-methyl borane and sodium acetate-glacial acetic acid buffer solution are mixed to obtain Yb / Er-carbon dots-nanocellulose composite material;Yb / Er-carbon dots-nanocellulose composite material, polyvinyl alcohol, methylene blue, sodium stearate, urea and water are mixed to obtain double anti-fake fluorescent ink.Nanofibrillar cellulose has a great improvement on the rheological properties and thixotropic properties of water-based ink, but its comprehensive viscosity is relatively large, and the viscosity under high shear is also high, nearly 200 mPa.s, and the low shear viscosity is as high as 100000 mPa.s, so high viscosity and viscosity difference need to be printed quickly after shearing, otherwise it is easy to cause problems such as decline of printing quality and damage of equipment, and it will slow down the curing speed.

[0005] It can be seen that the existing technology still has the problems of poor rheological properties of the prepared anti-fake ink, which cannot be effectively printed on various material products, and poor printing effect.In addition, the existing anti-fake technology and measures are relatively single, mostly single-color anti-fake fluorescent, and the anti-fake technology is not enough hidden, which is easy to be imitated and counterfeited.

[0006] Therefore, it is necessary to provide an improved low-viscosity double anti-fake ink to solve the above problems. SUMMARY

[0007] The purpose of the present application is to provide a low-viscosity double anti-fake ink and its preparation method and application, by using bacterial cellulose nanocrystals and Er / Yb / N co-modified graphene quantum dot nanohybrids, a double fluorescent emission anti-fake ink with low viscosity and non-Newtonian fluid characteristics is obtained, and the printing performance and anti-fake ability are significantly improved.

[0008] To achieve the above purpose, the present application provides a low-viscosity double anti-fake ink, which comprises, by mass percentage: Er / Yb / N-GQDs-BCNCs nanohybrid 0.5-1.5%, surfactant 0.1-1.5%, polyvinyl alcohol 2-8%, urea 0.5-1.5% and defoaming agent 0.01-1%, and the balance is water.

[0009] The Er / Yb / N-GQDs-BCNCs nanohybrid is a bacterial cellulose nanocrystal and an Er / Yb / N co-modified graphene quantum dot nanohybrid.

[0010] Further, the crystallinity of the bacterial cellulose nanocrystal is 91±2%, and the average size is 600-750 nm; the bacterial cellulose nanocrystal used in the present application has the following characteristics:

[0011] High crystallinity: Bacterial cellulose nanocrystals (BCNCs) have very high crystallinity, which makes them exhibit extremely strong mechanical stability and rigidity when under stress, thus improving the wear resistance, scratch resistance, and other properties of the ink.

[0012] High specific surface area: Due to their nanoscale size, BCNCs have a very high specific surface area, which helps to enhance the interaction of the Er / Yb / N-GQDs-BCNCs nanohybrid with the ink matrix, thus improving the mechanical properties of the ink after printing.

[0013] Excellent reinforcement effect: The modulus and strength of the ink can be significantly improved while maintaining good rheological behavior.

[0014] Unique rheological properties: BCNCs can form stable suspensions in fluids that exhibit non-Newtonian fluid properties, such as shear thinning, which is very important for the manufacture of industrial coatings and adhesives, etc., i.e., it can effectively improve the rheological properties of the ink to enhance the printing quality while preventing overflow to the surrounding area.

[0015] Thermal stability: BCNCs exhibit good thermal stability, which is more suitable for high-temperature processing.

[0016] The viscosity of the low-viscosity dual-prevention ink is 100-400 mPa.s. When the shear rate is less than 2 / s, the viscosity is 300-400 mPa.s, and when the shear rate is greater than or equal to 1000 / s, the viscosity decreases to below 120 mPa.s. The thixotropic properties of the ink show a trend of first increasing and then gradually decreasing, i.e., significant shear thinning properties. Its characteristics are to enhance the flowability and ductility of the ink. Based on the above characteristics, when the ink is applied to the substrate, the amount of overflow to the surrounding area is minimized, thus producing clear marks on the printing medium.

[0017] Further, the preparation method of the Er / Yb / N-GQDs-BCNCs nanohybrid includes the following steps:

[0018] Dissolve citric acid, urea, erbium chloride, and ytterbium chloride in deionized water, and perform a hydrothermal reaction to obtain Er / Yb / N-GQDs;

[0019] Add the Er / Yb / N-GQDs to a bacterial cellulose suspension, and obtain the Er / Yb / N-GQDs-BCNCs nanohybrid through electrostatic self-assembly.

[0020] The nitrogen-doped graphene quantum dots are synthesized using citric acid and urea, and have higher quantum yield and nitrogen doping rate. The electrostatic self-assembly modification of BCNCs enhances the solvent resistance and information encryption capability of the nanohybrid. Then, the BCNCs with high strength, rigidity and high specific surface area are integrated into the water-based ink to establish a stable three-dimensional network structure. This enhancement leads to the improvement of the thixotropic performance and yield stress, thereby improving the printability and practicability of the water-based fluorescent dual security ink.

[0021] Further, the temperature of the hydrothermal reaction is 140-160℃, and the time is 4-6 hours; after the reaction is completed, the Er / Yb / N-GQDs are obtained by dialysis for 24-36 hours using a dialysis bag.

[0022] Further, the electrostatic self-assembly time is 1-5 hours, followed by centrifugation, washing and freeze-drying to obtain the Er / Yb / N-GQDs-BCNCs nanohybrid.

[0023] Further, the molar ratio of citric acid to urea is 1:(3-4).

[0024] Further, the molar ratio of Er 3+ and Yb Yb 3+ in the chloroerbia and chloroerbium is 1:(5-10).

[0025] Further, the molar ratio of citric acid to Er 3+ in the chloroerbia is (70-80):1.

[0026] Further, the mass ratio of citric acid to deionized water is (1-3):10.

[0027] Further, the mass-volume ratio of the Er / Yb / N-GQDs and the bacterial cellulose suspension is (0.25-4) mg:1 mL; the concentration of the bacterial cellulose suspension is 0.5-1.5 mg / mL, preferably 0.8-1.2 mg / mL.

[0028] Further, the preparation method of the bacterial cellulose suspension comprises: crushing and homogenizing the bacterial cellulose membrane, then soaking it in 60±5 wt% sulfuric acid, continuously stirring at 40-45℃ for 1-2 hours, then centrifuging with water, obtaining a white precipitate, washing with water until neutral, preferably diluting with water to obtain the bacterial cellulose suspension.

[0029] The mass ratio of the BC membrane to 60% (w / w) sulfuric acid is 1:10-15; the volume ratio of the mixture solution to the deionized water required to stop the reaction is 1:15-17; the molecular weight cut-off of the dialysis bag is 10-15 kDa, and the cut-off time is 48-72 hours.

[0030] Further, the surface active agent includes one or more of sodium octadecyl sulfate, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfonate; and the defoaming agent includes one or more of a silicone oil defoaming agent, a polymer defoaming agent, and a mineral oil defoaming agent

[0031] In some preferred embodiments, the low-viscosity dual anti-counterfeiting ink includes, by mass percentage, 0.5-1.5% of the Er / Yb / N-GQDs-BCNCs nanohybrid, 0.5-1.5% of the surface active agent, 2-6% of the polyvinyl alcohol, 0.5-1.5% of the urea, and 0.1-1% of the defoaming agent, with the balance being water.

[0032] The low-viscosity dual anti-counterfeiting ink provided by the application is a dual-fluorescent emission anti-counterfeiting ink with dual anti-counterfeiting functions, specifically a lanthanide and nitrogen element doped graphene quantum dot grafted bacterial cellulose nanocrystal aqueous fluorescent ink.

[0033] A method for preparing the low-viscosity dual anti-counterfeiting ink according to any one of the preceding items, including the following steps:

[0034] Dissolve citric acid, urea, erbium chloride, and ytterbium chloride in deionized water, and perform a hydrothermal reaction at 140-160°C to obtain Er / Yb / N-GQDs;

[0035] Add the Er / Yb / N-GQDs to a bacterial cellulose suspension, and obtain an Er / Yb / N-GQDs-BCNCs nanohybrid through electrostatic self-assembly;

[0036] Weigh the Er / Yb / N-GQDs-BCNCs nanohybrid, the surface active agent, the polyvinyl alcohol, the urea, the defoaming agent, and the water according to the mass percentage, mix them uniformly, and obtain the low-viscosity dual anti-counterfeiting ink.

[0037] The low-viscosity dual anti-counterfeiting ink according to any one of the preceding items is used in the fields of packaging, information transmission, and identity authentication, for example, a dual-fluorescent emission anti-counterfeiting ink for food packaging.

[0038] The low-viscosity dual anti-counterfeiting ink exhibits photoluminescence (blue light) and upconversion luminescence (green light) characteristics under excitation at 370 nm and 980 nm wavelengths, and information extraction is only possible when two different excitation light sources are simultaneously irradiated, thereby increasing the complexity of illegal copying and improving the anti-counterfeiting capability.

[0039] The beneficial effects of the application are as follows:

[0040] 1. The application prepares BC nanocrystals (BCNCs) and Er / Yb / N modified GQDs nanohybrids by electrostatic self-assembly, which exhibit photoluminescence (blue light) and upconversion luminescence (green light) characteristics under 370nm and 980nm wavelength excitation, respectively, and can enhance the solvent resistance and information encryption capability of the nanohybrid. By utilizing the unique rheological properties of BCNCs, the nanohybrid can be integrated into water-based ink to establish a stable three-dimensional network structure, which helps to improve the thixotropic properties and yield stress of the ink, thereby improving the printing performance.

[0041] 2. The low-viscosity double anti-counterfeiting ink provided by the application has moderate overall viscosity and reduced viscosity under high shear rate, facilitating printing and preventing the problems of printing difficulty and image blurring caused by excessive viscosity. After printing, the viscosity increases, which can prevent the ink from spreading and overflowing around, thereby improving the clarity and color saturation of the printed pattern.

[0042] 3. The low-viscosity double anti-counterfeiting ink provided by the application can be used as a powerful, sustainable and promising technology to combat today's escalating counterfeiting activities. In addition, the ultraviolet and near-infrared dual excitation anti-counterfeiting technology has broad application prospects in the field of printed packaging. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to more clearly illustrate the technical solutions in the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below are some embodiments of the application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0044] Figure 1 is a transmission electron microscope morphology diagram and a high-magnification transmission electron microscope diagram of Er / Yb / N-GQDs;

[0045] Figure 2 is an atomic force microscope diagram of Er / Yb / N-GQDs and a height diagram of the selected area;

[0046] Figure 3 is a size distribution diagram of Er / Yb / N-GQDs;

[0047] Figure 4 is an atomic force microscope diagram of BCNCs;

[0048] Figure 5 is a size distribution diagram of BCNCs;

[0049] Figure 6 is a transmission electron microscope diagram of Er / Yb / N-GQDs-BCNCs;

[0050] Figure 7 are the UV absorption spectra of N-GQDs (solid line) and Er / Yb / N-GQDs (dashed line) and the emission spectra at 370 nm and 980 nm wavelength;

[0051] Figure 8 are the fluorescence intensity of Er / Yb / N-GQDs-BCNCs nanohybrids with different amounts of Er / Yb / N-GQDs added;

[0052] Figure 9 are the thixotropic properties of the ink without the addition of Er / Yb / N-GQDs-BCNCs nanohybrids;

[0053] Figure 10 are the thixotropic property curves of the ink with the addition of Er / Yb / N-GQDs-BCNCs nanohybrids;

[0054] Figure 11 are the strain sweep curves of the ink of the Er / Yb / N-GQDs-BCNCs nanohybrids; the lower graph is the low-frequency amplitude sweep curve;

[0055] Figure 12 are the anti-counterfeiting fluorescent ink stamp seal and the writing effect on different packaging materials. DETAILED DESCRIPTION

[0056] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0057] Example 1

[0058] The preparation method of the Er / Yb / N-GQDs-BCNCs nanohybrids and the low-viscosity dual anti-counterfeiting water-based ink comprises the following steps:

[0059] (1) Dissolve the monohydrate citric acid, urea, erbium chloride hexahydrate and ytterbium chloride hexahydrate in deionized water and stir with a magnetic stirrer to form a precursor solution. Then transfer the precursor solution to a stainless steel autoclave lined with polytetrafluoroethylene, and heat in a high-temperature vacuum box at 140-160°C for 4-6 hours. The yellow-brown liquid obtained by reaction is then placed in a dialysis bag (with a molecular weight cut-off of 100-500 Da) and dialyzed for 24 hours, with water changed every 12 hours. The light green liquid obtained is freeze-dried to obtain Er / Yb / N-GQDs.

[0060] wherein the molar ratio of monohydrated citric acid to urea is 0.3:1; the Er in the erbium chloride hexahydrate and ytterbium chloride hexahydrate 3+ and ytterbium Yb 3+ the molar ratio of monohydrated citric acid to the Er in the erbium chloride hexahydrate is 0.1:1; the molar ratio of monohydrated citric acid to urea is 0.3:1; the molar ratio of the Er in the erbium chloride hexahydrate and ytterbium chloride hexahydrate 3+ to urea is 75.0; the mass ratio of monohydrated citric acid to deionized water is 0.14:1;

[0061] (2) The dried BC membrane was broken and homogenized, then immersed in 60% (w / w) sulfuric acid and continuously stirred at 40-45°C for 1-2 hours. Then, deionized water was added to the mixture solution to stop the reaction. The excess acid in the BCNCs suspension was removed by centrifugation at 15000 rpm for 5 minutes. The collected white precipitate was redispersed in pure water. This process was repeated several times until the suspension was neutral. Further, the BCNCs suspension was treated with a dialysis bag for a long time, and the excess sulfate ions were eluted with water. Finally, the suspension was diluted to 0.1% (w / v), i.e. 0.1 mg / mL, and stored at 4°C.

[0062] wherein the mass ratio of the BC membrane to 60% (w / w) sulfuric acid is 0.08:1; the volume ratio of the mixture solution to the deionized water required to stop the reaction is 0.066:1; the molecular weight cut-off of the dialysis bag is 10-15 kDa, and the cut-off time is 60 h.

[0063] (3) The Er / Yb / N-GQDs were added to the BCNCs suspension. Then the solution was diluted to a specific volume with deionized water and stirred at room temperature for 1-2 hours to obtain the nanohybrid. Subsequently, the mixture was centrifuged to remove any excess unreacted Er / Yb / N-GQDs until the washing supernatant showed no fluorescence under ultraviolet light. The obtained precipitate was subjected to freeze-drying treatment to obtain the Er / Yb / N-GQDs-BCNCs nanohybrid.

[0064] wherein the mass-to-volume ratio (w / v) of the Er / Yb / N-GQDs to the BCNCs suspension is 0.25, 0.50, 0.75, 1.00, 1.50, 2.00, 2.50, 3.00, 4.00 mg:1 mL.

[0065] (4) The Er / Yb / N-GQDs-BCNCs nanohybrid, sodium octadecyl sulfate, polyvinyl alcohol, urea, antifoaming agent and deionized water were mixed uniformly in a mass ratio of 1:1:4:1:0.5:92.5 to obtain a low-viscosity double anti-counterfeiting water-based ink.

[0066] Figure 1 The TEM image of the Er / Yb modified N-GQD shows a morphology close to a sphere, and the high-magnification transmission electron microscopy image (Figure 1 The upper right corner) indicates the crystal nature of N-GQDs, showing a lattice spacing of 0.21 nm, corresponding to sp 2 the (102) crystal plane of graphite carbon structure.

[0067] Figure 2 Atomic force microscopy images provide further characterization of the quasi-spherical morphology of N-GQDs, with characteristic topography heights ranging from 1.0 to 3.0 nm. From Figure 3 It can be seen that the average size of Er / Yb modified N-GQDs is 4.32 nm.

[0068] Figure 4 、 5 Atomic force microscopy images of BCNCs and corresponding size distribution plots are shown, showing characteristic nanostructures with lengths ranging from 350 to 1000 nm and widths ranging from 30 to 60 nm. The average size of BCNCs is 681.82 nm.

[0069] Figure 6 It shows that many approximately spherical GQDs are uniformly dispersed on the surface of BCNCs, indicating that Er / Yb / N-GQDs are successfully grafted onto BCNCs.

[0070] Figure 7 The lower subgraph shows the optical absorption spectra of N-GQD and Er / Yb / N-GQD, with a main absorption peak at 242 nm, attributed to the π→π* transition (C=C) of aromatic sp 2 domains in the N-GQD structure. In addition, the absorption peaks in the range of 300-400 nm are attributed to the n→π* transition of the oxidized groups (such as C=O, epoxy groups and C-O) located at the edge of N-GQDs. The absorption peaks of Er / Yb / N-GQDs in the range of 300-400 nm are significantly enhanced, indicating that the generation of oxygen-containing functional groups along the edge of N-GQDs increases under the influence of Er / Yb. From Figure 7 It can be seen from the upper graph that Er / Yb / N-GQDs exhibit significantly enhanced fluorescence intensity at an emission wavelength of 440 nm and emit blue fluorescence after 370 nm excitation, and the emission spectrum of Er / Yb / N-GQDs reaches a peak at 556 nm and emits green fluorescence under 980 nm infrared radiation excitation, indicating that it has both photoluminescence and upconversion photoluminescence properties.

[0071] Figure 8 It is shown that the peak of fluorescence intensity increases with the increase of the amount of Er / Yb / N-GQD added in step (3), reaches a maximum when 2 mg is added, and then decreases to a relatively stable level with further increase of mass.

[0072] From Figure 9 and10 It can be seen that the thixotropic properties of inks without Er / Yb / N-GQDs-BCNCs nanohybrids remain almost unchanged, and their viscosity is extremely insensitive to changes in shear rate. However, the thixotropic properties of inks with Er / Yb / N-GQDs-BCNCs nanohybrids exhibit a trend of first increasing and then gradually decreasing, indicating significant shear thinning characteristics. The introduction of BCNCs endows water-based inks with excellent thixotropic properties, characterized by enhanced flowability and extensibility. Based on these characteristics, when the ink is applied to the substrate, the amount of spillage into the surrounding area is minimized, thus producing a clear imprint on the printing medium. It is worth noting that... Figure 10 During the transition from high shear to low shear, the viscosity of the composite ink rapidly recovers to its original level within a short time (approximately 15 seconds), indicating that the internal rheological properties of the water-based ink change during the high shear process. Furthermore, the incorporation of Er / Yb / N-GQDs-BCNCs accelerates the recovery of the ink's structural properties after the change, endowing the fluorescent ink with excellent thixotropic properties.

[0073] Figure 11 The figure above depicts the strain scanning test of the Er / Yb / N-GQDs-BCNCs-PVA composite ink. The relatively wide area to the left of the red dashed line corresponds to the linear viscoelastic region of the ink system, indicating strong intermolecular interactions between polymer chains in the composite ink, leading to the formation of a homogeneous solution system. Low-frequency amplitude scanning results are shown below. Figure 11 The figure below shows that the solution exhibits shear-thinning ability within the linear viscoelastic region throughout the test. As the angular frequency increases from 0.1 rad / s to 300 rad / s, the storage modulus and loss modulus of the system increase accordingly, leading to a linear decrease in complex viscosity and enhanced shear-thinning ability. In summary, the storage modulus of the composite ink shows low frequency dependence, while the loss modulus increases significantly with increasing frequency. The complex viscosity of the composite ink system exhibits a gradual transition from a solid to a gel-like state, highlighting its viscoelastic properties beneficial for large-scale continuous inkjet printing.

[0074] The low-viscosity dual anti-counterfeiting water-based ink obtained when the amount of Er / Yb / N-GQD added in step (3) was 2 mg was tested for its application effect.

[0075] Application Effect 1: The Stamping Effect of Ink Stamps

[0076] like Figure 12As shown, the aqueous ink doped with Er / Yb / N-GQDs-BCNCs was added to the inkable stamp (including various elements such as English letters, Chinese characters, numbers and artistic patterns). The ink-loaded stamp was stamped on the non-fluorescent paper, which did not show any pattern under daylight. Under the irradiation of 370 nm ultraviolet lamp and 980 nm laser lamp respectively, the irradiated area at the stamped stamp showed blue light and green light respectively, presenting stable and bright coloring effect, indicating that information encryption and double anti-counterfeiting can be achieved.

[0077] Application effect two: the writing effect of whiteboard pen on different packaging materials

[0078] The aqueous ink doped with Er / Yb / N-GQDs-BCNCs was added to the inkable whiteboard pen. The ink-loaded whiteboard pen was written on kraft paper, fresh-keeping box (polypropylene), aluminized plastic film, plastic bottle (polyethylene terephthalate), soda can (aluminum), fresh-keeping film (polyethylene or low-density polyethylene) and glass bottle. Under the irradiation of 370 nm ultraviolet lamp and 980 nm laser lamp respectively, the irradiated area at the written area showed blue light and green light respectively, achieving information encryption and double anti-counterfeiting. Each substrate showed obvious effect, therefore, the fluorescent ink has excellent anti-counterfeiting properties, making it widely applicable in various fields in terms of information transmission and anti-counterfeiting. However, when the viscosity is too large, it is difficult to present in the form of writing.

[0079] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A low viscosity dual security ink, characterized in that, The low viscosity double anti-counterfeiting ink comprises the following components in percentage by mass: 0.5-1.5% of the Er / Yb / N-GQDs-BCNCs nanohybrid, 0.1-1.5% of a surfactant, 2-8% of polyvinyl alcohol, 0.5-1.5% of urea, 0.01-1% of an antifoaming agent, and the balance of water; The Er / Yb / N-GQDs-BCNCs nanohybrid is a bacterial cellulose nanocrystal and an Er / Yb / N co-modified graphene quantum dot nanohybrid, The crystallinity of the bacterial cellulose nanocrystal is 91±2%, and the average size is 600-750 nm. The viscosity of the low viscosity double anti-counterfeiting ink is 100-400 mPa.s, The bacterial cellulose and the Er / Yb / N-GQDs in the Er / Yb / N-GQDs-BCNCs nanohybrid are electrostatically self-assembled to combine and establish a stable three-dimensional network structure.

2. The low viscosity dual security ink according to claim 1, characterized in that, The preparation method of the Er / Yb / N-GQDs-BCNCs nanohybrid comprises the following steps: Dissolve citric acid, urea, erbium chloride and ytterbium chloride in deionized water, and perform hydrothermal reaction to obtain Er / Yb / N-GQDs; Add the Er / Yb / N-GQDs to a bacterial cellulose suspension, and obtain the Er / Yb / N-GQDs-BCNCs nanohybrid through electrostatic self-assembly.

3. The low viscosity dual security ink according to claim 2, characterized in that, The temperature of the hydrothermal reaction is 140-160°C, and the time is 4-6 hours; after the reaction is completed, the Er / Yb / N-GQDs is obtained through dialysis for 24-36 hours using a dialysis bag; And / or, the time of the electrostatic self-assembly is 1-5 hours, followed by centrifugation, washing, and freeze-drying to obtain the Er / Yb / N-GQDs-BCNCs nanohybrid.

4. The low viscosity dual security ink according to claim 2, wherein, The molar ratio of the citric acid to the urea is 1:(3-4); and / or the molar ratio of Er in the erbium chloride and ytterbium chloride 3+ and ytterbium Yb 3+ is 1: (5-10); And / or, the citric acid reacts with Er in erbium chloride. 3+ The molar ratio is (70-80):1; And / or, the mass ratio of the citric acid to the deionized water is (1-3):

10.

5. The low viscosity dual security ink according to claim 2, wherein, The mass-volume ratio of the Er / Yb / N-GQDs to the bacterial cellulose suspension is (0.25-4) mg:1 mL; The concentration of the bacterial cellulose suspension is 0.5-1.5 mg / mL.

6. The low viscosity double security ink according to any one of claims 2 to 5, characterized in that, The preparation method of the bacterial cellulose suspension comprises the following steps: crushing and homogenizing a bacterial cellulose membrane, then soaking it in 60±5 wt% sulfuric acid, continuously stirring at 40-45°C for 1-2 hours, then centrifuging with water, washing the white precipitate to neutral, and diluting with water to obtain the bacterial cellulose suspension.

7. The low viscosity double security ink according to any one of claims 1 to 6, characterized in that, The surfactant comprises one or more of sodium octadecyl sulfate, sodium dodecyl benzene sulfonate, and sodium dodecyl sulfonate; and the antifoaming agent comprises one or more of a silicone oil antifoaming agent, a polymer antifoaming agent, and a mineral oil antifoaming agent.

8. A process for the preparation of the low viscosity dual security ink according to any one of claims 1 to 7, characterized in that, The preparation method of the low viscosity double anti-counterfeiting ink comprises the following steps: Dissolve citric acid, urea, erbium chloride and ytterbium chloride in deionized water, and perform hydrothermal reaction at 140-160°C to obtain Er / Yb / N-GQDs; Add the Er / Yb / N-GQDs to a bacterial cellulose suspension, and obtain the Er / Yb / N-GQDs-BCNCs nanohybrid through electrostatic self-assembly. The low viscosity double anti-counterfeiting ink is prepared by taking Er / Yb / N-GQDs-BCNCs nanohybrids, a surfactant, polyvinyl alcohol, urea, a defoaming agent and water by mass percentage, and mixing uniformly.

9. Use of the low viscosity double security ink according to any one of claims 1 to 7, characterized in that, The low viscosity double anti-counterfeiting ink is used in the fields of packaging, information transmission and identity authentication.

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