An anti-counterfeiting digital invisible ink and its application

Abstract

The present invention discloses an anti-counterfeiting digital invisible ink and its application. The anti-counterfeiting label provided by the present invention is prepared by printing an anti-counterfeiting digital invisible ink on the label and drying it by heating. Each raw material component of the anti-counterfeiting digital invisible ink includes, by mass: 10-40 parts of an invisible anti-counterfeiting agent, 0.3-3 parts of a polymer, 0.05-1 part of a stabilizer, 5-30 parts of a solvent, and 0.05-5 parts of an auxiliary agent. The invisible anti-counterfeiting agent is selected from one of an invisible anti-counterfeiting core structure substance and a core-shell composite particle. The present invention obtains the anti-counterfeiting digital invisible ink by mixing and stirring each raw material component and performing a dispersion treatment. Compared with the prior art, the anti-counterfeiting label prepared by the present invention has the advantages of good invisibility effect, and the anti-counterfeiting digital invisible ink used has the advantages of high stability and good weather resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of printing inks, and in particular to an anti-counterfeiting digital invisible ink and its application. Background Art

[0002] "Anti-counterfeiting" mainly reflects prevention and can provide solutions to combat counterfeiting from the source; "anti-counterfeiting" is universal and can provide a way for people to identify the authenticity in daily life. With the rapid development of the social economy, various counterfeiting technologies have been continuously upgraded and iterated, and the phenomenon of counterfeiting in various manufacturing industries has become increasingly serious. This not only damages the interests of businesses but also those of the country. In this context, effective anti-counterfeiting technical means are needed to provide protection for the anti-counterfeiting of confidential documents, commodities, and currencies, such as digital information anti-counterfeiting, biometric anti-counterfeiting, and printing technology anti-counterfeiting. Among them, anti-counterfeiting inks in printing technology anti-counterfeiting play an important role.

[0003] CN116200075A discloses a high-resolution anti-counterfeiting electronic ink and its preparation method. By adding nano cadmium sulfide or nano titanium dioxide as nano anti-counterfeiting powder, the color purity is improved and the anti-counterfeiting performance of the ink is increased. However, the ink prepared by this method does not have a confidentiality effect when printed on a substrate and is easily counterfeited. CN114958092A discloses a temperature-changing anti-counterfeiting ink and its preparation method and application, which is composed of 5 - 20 parts of a color-changing material, 5 - 20 parts of acetic acid microcapsules, 30 - 50 parts of a water-based PUA emulsion, 15 - 30 parts of a styrene-acrylic resin, and 5 - 30 parts of water. The prepared ink can change color unidirectionally at 37 - 45°C. However, the ink prepared by this method has too low a color-changing temperature and is irreversible, and is prone to failure during natural storage. Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the present invention provides an anti-counterfeiting label prepared with an anti-counterfeiting digital invisible ink. The anti-counterfeiting label prepared by the present invention has the advantage of good invisibility effect, and the anti-counterfeiting digital invisible ink used has the advantages of high stability and good weather resistance.

[0005] To achieve the above object, the present invention provides a preparation method of an anti-counterfeiting digital invisible ink, comprising the following steps, by weight:

[0006] Disperse 10 - 40 parts of an invisible anti-counterfeiting agent, 0.3 - 3 parts of a polymer, 0.05 - 1 part of a stabilizer, 5 - 30 parts of a solvent, and 0.05 - 5 parts of an auxiliary agent uniformly through a high-speed disperser, then send them into a grinding machine for grinding, and then perform ultrasonic treatment to obtain the anti-counterfeiting digital invisible ink.

[0007] Further preferably, the grinding in the grinding machine is carried out until the particle size is less than 10 μm, and the ultrasonic treatment conditions are ultrasonic treatment at 40 - 100 kHz for 5 - 15 min.

[0008] Preferably, the polymer is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyoxyethylene, polyacrylamide, polyacrylic acid, polylactic acid, polyglycolic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, polyethylene-vinyl acetate, polydimethylsiloxane, and polyurethane.

[0009] The stabilizer is at least one of butanethiol, nonanethiol, dodecanethiol, hexadecanethiol, mercaptoacetic acid, mercaptopropionic acid, 4-mercaptobutyric acid, 8-mercaptoheptanoic acid, 1-mercapto-2-acetone, 4-mercapto-2-pentanone, 3-mercapto-2-butanone, mercaptoethylamine, 3-mercapto-1-propylamine, and 3-mercapto-N-nonylpropanamide.

[0010] The solvent is selected from at least one of water, methanol, ethanol, isopropanol, n-propanol, ethylene glycol, propylene glycol, glycerol, n-butanol, n-octanol, n-nonanol, n-decanol, N-methylpyrrolidone, binary acid ester mixture, dimethylformamide, diacetone alcohol, 1,3-dimethyl-imidazolinone, dimethyl sulfoxide, diethylene glycol monobutyl ether, diethylene glycol acetate, ethylene glycol carbonate, propylene glycol carbonate, 1,4-butyrolactone, toluene, chlorobenzene, dichloromethane, and tetrahydrofuran.

[0011] The auxiliary agent is selected from at least one of perfluorinated surfactants BOK-B-100, BOK-B-101, BOK-B-102, and BOK-B-103.

[0012] More preferably, the solvent is a mixture of isopropanol and water in a mass ratio of 1-5:1-5.

[0013] Preferably, the invisible anti-counterfeiting agent is selected from an invisible anti-counterfeiting core structure material and core-shell composite particles.

[0014] Preferably, the preparation method of the invisible anti-counterfeiting core structure material comprises the following steps, by weight:

[0015] Mix 1-5 parts of 1,3-dimethylbarbituric acid, 0.1-1.5 parts of furfural, and 10-30 parts of water evenly, react at 20-40 °C and 800-1000 rpm for 1-3 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. Remove the solvent with a rotary evaporator to obtain Compound 1; mix 1-5 parts of Compound 1, 0.1-1.5 parts of diethylamine, and 10-30 parts of water evenly, react at 20-40 °C and 800-1000 rpm for 1-3 h, and then remove the solvent with a rotary evaporator to obtain DASA, that is, donor-acceptor Stenhouse adduct molecules.

[0016] As a further illustration of the present invention, the donor-acceptor Steinhaus adduct molecule DASA can be mainly divided into two states, namely linear and cyclic, and these two states can transform into each other. The donor-acceptor Steinhaus adduct molecule DASA will transform from the initial colored state into a colorless closed-loop isomer under visible light, showing a colorless state under visible light and coloring under specific ultraviolet light; DASA can combine with water molecules and transform into a colorless and structurally stable cyclic donor-acceptor Steinhaus adduct hydrate. The cyclic donor-acceptor Steinhaus adduct hydrate will lose the bound water molecules when heated to about 160 °C and rapidly transform into purple linear DASA in about 5 s.

[0017] Preferably, the preparation method of the core-shell composite particles comprises the following steps, by weight:

[0018] Step 1: Mix 1-5 parts of 1,3-dimethylbarbituric acid, 0.1-1.5 parts of furfural and 10-30 parts of water evenly, react at 20-40 °C and 800-1000 rpm for 1-3 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. After removing the solvent with a rotary evaporator, compound 1 is obtained; mix 1-5 parts of compound 1, 0.1-1.5 parts of diethylamine and 10-30 parts of water evenly, react at 20-40 °C and 800-1000 rpm for 1-3 h, and then obtain DASA after removing the solvent with a rotary evaporator; add 5-15 parts of PAMAM dendrimer and 1-5 parts of DASA to 30-60 parts of tetrahydrofuran and mix evenly, then react at 60-100 °C and 800-1000 rpm for 2-4 h; then centrifuge at 2000-4000 rpm, collect the solid, and dry it at 60-100 °C for 4-8 h to obtain core-structured DASA dendrimer microspheres;

[0019] Step 2: Mix 1-5 parts of silica with 5-10 parts of 5-15 wt% HCl and stir for 1-3 h, then centrifuge at 2000-4000 rpm, collect the solid, wash the solid with water until the supernatant is neutral, and dry the washed solid at 60-100 °C for 4-8 h to obtain activated silica; mix 1-5 parts of activated silica with 5-10 parts of ethanol evenly, add 0.1-1 part of ammonia water and 0.1-1 part of silane coupling agent, react at 50-70 °C and 800-1000 rpm for 16-48 h, then centrifuge at 2000-4000 rpm, collect the solid, wash the solid with ethanol until the supernatant is neutral, and dry the washed solid at 60-100 °C for 4-8 h to obtain modified silica;

[0020] Step 3: Mix 1 - 10 parts of modified silica evenly in 10 - 50 parts of tetrahydrofuran, then add 5 - 10 parts of core - structured DASA dendritic polymer microspheres, react at 20 - 60°C and 800 - 1000 rpm for 2 - 4 h, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry at 60 - 100°C for 4 - 8 h to obtain composite - modified silica, i.e., core - shell composite particles.

[0021] Further preferably, Step 3 can also be:

[0022] Mix 1 - 10 parts of modified silica evenly in 10 - 50 parts of tetrahydrofuran, then add 5 - 10 parts of core - structured DASA dendritic polymer microspheres, react at 20 - 60°C and 800 - 1000 rpm for 2 - 4 h, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry at 60 - 100°C for 4 - 8 h to obtain composite - modified silica; mix 1 - 5 parts of composite - modified silica and 1 - 50 parts of isopropanol evenly, then add 1 - 5 parts of phenolic resin, and react at 80 - 120°C and 800 - 1000 rpm for 2 - 4 h, cool to room temperature, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry the solid at 60 - 100°C for 4 - 8 h to obtain core - shell composite particles.

[0023] Further preferably, the silane coupling agent in Step 2 is selected from at least one of trimethoxy[2 - (7 - oxabicyclo[4.1.0]hept - 3 - yl)ethyl]silane.

[0024] As a further illustration of the present invention, the core - shell structure is a special composite material, composed of an inner core (core) and one or more outer shells (shells) surrounding the outer part of the inner core. PAMAM dendritic polymer has a unique topological structure and excellent thermosensitive properties, and can self - assemble with DASA into microspheres as the core structure in the core - shell structure. The shell structure is a composition of modified silica, phenolic resin, or modified silica and phenolic resin, and is assembled into core - shell composite particles through adsorption and / or chemical action. The use of the silane coupling agent in the core - shell composite particles can promote the chemical bonding between the modified silica and the DASA dendritic polymer microspheres, forming a stable core - shell structure. The modified silica and phenolic resin may form a physical network structure in the particles. The outer shell of the core - shell structure can improve the dispersion of the inner core in the ink, reduce particle aggregation, thereby improving the stability of the ink, and can also effectively limit the aggregation and sedimentation of the particles. In addition, the outer shell of the core - shell structure may also form a protective layer on the particle surface, and this protective layer can slow down the influence of external factors such as temperature, humidity, acidity, and alkalinity on the inner core, thereby improving the weather resistance and stability of the ink.

[0025] The present invention also provides the application of the above anti-counterfeiting digital invisible ink on anti-counterfeiting labels. The specific application is as follows: The anti-counterfeiting label is prepared by printing the anti-counterfeiting digital invisible ink on the label and drying it at a temperature of 80 - 100 °C for 1 - 3 h. At this time, the printed content is invisible, and the printed content appears purple after heating.

[0026] Advantages of the present invention:

[0027] 1. Compared with the prior art, through reasonable proportioning and utilizing the interaction between various substances, the present invention prepares an anti-counterfeiting digital invisible ink, and the anti-counterfeiting digital invisible ink is printed on a label to obtain an anti-counterfeiting label. The anti-counterfeiting digital invisible ink provided by the present invention not only has an invisible effect and can display graphic information under specific light conditions, endowing traditional wearable labels with anti-counterfeiting characteristics, but also has good stability and acid and alkali resistance. The present invention introduces core-shell composite particles to prepare the anti-counterfeiting digital invisible ink, improving the stability of the ink. The anti-counterfeiting digital invisible ink prepared by the present invention has a sedimentation rate of only 0.99% after being placed at 42 ± 1 °C for 21 d.

[0028] 2. Compared with the prior art, core-shell composite particles are added during the preparation process of the anti-counterfeiting digital invisible ink of the present invention. Modified silica and phenolic resin are simultaneously added to the core-shell composite particles, and a physical network structure may be formed in the core-shell composite particles, which can effectively limit the aggregation and sedimentation of particles. The sedimentation rate of the anti-counterfeiting digital invisible ink of the present invention is only 0.99% after being placed at 42 ± 1 °C for 21 days, indicating that the ink of the present invention has better stability during storage and use.

[0029] 3. Compared with the prior art, the label prepared from the anti-counterfeiting digital invisible ink of the present invention has a color development temperature of 210 °C and a color development time of 35 seconds, which is higher than the color development temperature of ordinary DASA and takes longer for color development. This means that the anti-counterfeiting label of the present invention is more difficult to be illegally copied because higher temperature and more precise conditions are required to display the printed content. Specific embodiments

[0030] The parameters and sources of some raw materials in the embodiments of the present invention are as follows:

[0031] Silica, particle size: < 150 μm;

[0032] Perfluorinated surfactant BOK-B-100, sourced from Guangzhou Xinrui Chemical Materials Co., Ltd.;

[0033] Phenolic resin, grade: S607, sourced from Jiangsu Senbo New Materials Co., Ltd.;

[0034] PAMAM dendrimer, product number: P475373, molecular weight 516.68, sourced from Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0035] Polyvinylpyrrolidone, product number: P110611, average molecular weight 10,000, sourced from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0036] Example 1

[0037] A method for preparing an anti-counterfeiting label using anti-counterfeiting digital invisible ink, comprising the following steps:

[0038] Step a: Disperse 200 g of the invisible anti-counterfeiting core structure material, 10 g of polyvinylpyrrolidone, 2 g of butanethiol, 200 g of isopropanol, 50 g of water, and 2 g of perfluorinated surfactant BOK-B-100 evenly through a high-speed disperser, then send it into a grinder and grind until the particle size is less than 10 μm, and then perform ultrasonic treatment at 50 kHz for 10 min to obtain the anti-counterfeiting digital invisible ink;

[0039] Step b: Print the anti-counterfeiting digital invisible ink obtained in step a on the label and dry it at a temperature of 90 °C for 2 h to obtain an anti-counterfeiting label with invisible printed content; the printed content of the anti-counterfeiting label appears purple after heating.

[0040] The preparation method of the invisible anti-counterfeiting core structure material comprises the following steps:

[0041] Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural, and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase and remove the solvent with a rotary evaporator to obtain compound 1; mix 30 g of compound 1, 10 g of diethylamine, and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; thus obtaining the invisible anti-counterfeiting core structure material.

[0042] Example 2

[0043] A method for preparing an anti-counterfeiting label using anti-counterfeiting digital invisible ink, comprising the following steps:

[0044] Step a: By mass, disperse 200 g of the core structure DASA dendritic polymer microspheres, 10 g of polyvinylpyrrolidone, 2 g of butanethiol, 200 g of isopropanol, 50 g of water, and 2 g of BOK-B-100 evenly through a high-speed disperser, then send it into a grinder and grind until the particle size is less than 10 μm, and then perform ultrasonic treatment at 50 kHz for 10 min to obtain the anti-counterfeiting digital invisible ink;

[0045] Step b: Print the anti-counterfeiting digital invisible ink obtained in step a on the label and dry it at 90°C for 2 hours to obtain an anti-counterfeiting label with invisible printed content; the printed content appears purple after the anti-counterfeiting label is heated.

[0046] The preparation method of the core-structured DASA dendritic polymer microspheres comprises the following steps:

[0047] Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30°C and 900 rpm for 2 hours, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. Remove the solvent with a rotary evaporator to obtain Compound 1; mix 30 g of Compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30°C and 900 rpm for 2 hours, and then remove the solvent with a rotary evaporator to obtain DASA; add 100 g of PAMAM dendritic polymer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80°C and 900 rpm for 3 hours; then centrifuge at 3000 rpm, collect the solid, and dry at 80°C for 6 hours to obtain core-structured DASA dendritic polymer microspheres.

[0048] Example 3

[0049] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink comprises the following steps:

[0050] Step a: Disperse 200 g of core-shell composite particles, 10 g of polyvinylpyrrolidone, 2 g of butanethiol, 200 g of isopropanol, 50 g of water, and 2 g of BOK-B-100 evenly with a high-speed disperser, then send them into a grinder and grind until the particle size is less than 10 μm, and then perform ultrasonic treatment at 50 kHz for 10 minutes to obtain anti-counterfeiting digital invisible ink;

[0051] Step b: Print the anti-counterfeiting digital invisible ink obtained in step a on the label and dry it at 90°C for 2 hours to obtain an anti-counterfeiting label with invisible printed content; the printed content appears purple after the anti-counterfeiting label is heated.

[0052] The preparation method of the core-shell composite particles comprises the following steps:

[0053] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. After removing the solvent with a rotary evaporator, compound 1 is obtained; mix 30 g of compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0054] Step 2: Mix 30 g of silica with 80 g of 10 wt% HCl and stir for 2 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with water until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain activated silica; mix 30 g of activated silica with 80 g of ethanol evenly, add 5 g of ammonia water and 5 g of trimethoxy[2-(7-oxabicyclo[4.1.0]hept-3-yl)ethyl]silane, react at 60 °C and 900 rpm for 24 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with ethanol until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain modified silica;

[0055] Step 3: Mix 50 g of modified silica evenly in 300 g of tetrahydrofuran, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 70 °C for 6 h to obtain composite modified silica, that is, core-shell composite particles.

[0056] Example 4

[0057] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink, which is different from Example 2 in that the preparation method of the core-shell composite particles includes the following steps:

[0058] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. After removing the solvent with a rotary evaporator, Compound 1 is obtained; Mix 30 g of Compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; Add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; Then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0059] Step 2: Mix 30 g of silica with 80 g of 10 wt% HCl and stir for 2 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with water until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain activated silica; Mix 30 g of activated silica with 80 g of ethanol evenly, add 5 g of ammonia water and 5 g of N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, react at 60 °C and 900 rpm for 24 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with ethanol until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain modified silica;

[0060] Step 3: Mix 50 g of modified silica evenly in 300 g of tetrahydrofuran, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 70 °C for 6 h to obtain composite modified silica, that is, core-shell composite particles.

[0061] Example 5

[0062] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink, which is different from Example 2 in that the preparation method of the core-shell composite particles includes the following steps:

[0063] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. After removing the solvent with a rotary evaporator, compound 1 is obtained; Mix 30 g of compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; Add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; Then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0064] Step 2: Mix 30 g of silica with 80 g of 10 wt% HCl and stir for 2 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with water until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain activated silica; Mix 30 g of activated silica with 80 g of ethanol evenly, add 5 g of ammonia water and 5 g of γ-mercaptopropyltrimethoxysilane, react at 60 °C and 900 rpm for 24 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with ethanol until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain modified silica.

[0065] Step 3: Mix 50 g of modified silica evenly in 300 g of tetrahydrofuran, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 70 °C for 6 h to obtain composite modified silica, that is, core-shell composite particles.

[0066] Example 6

[0067] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink, which is different from Example 2 in that the preparation method of the core-shell composite particles includes the following steps:

[0068] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. Remove the solvent with a rotary evaporator to obtain Compound 1; Mix 30 g of Compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; Add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; Then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0069] Step 2: Mix 30 g of silica with 80 g of 10 wt% HCl and stir for 2 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with water until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain activated silica; Mix 30 g of activated silica with 80 g of ethanol evenly, add 5 g of ammonia water and 5 g of trimethoxy[2-(7-oxabicyclo[4.1.0]hept-3-yl)ethyl]silane, react at 60 °C and 900 rpm for 24 h, then centrifuge at 3000 rpm, collect the solid, wash the solid with ethanol until the supernatant is neutral, and dry the washed solid at 80 °C for 6 h to obtain modified silica;

[0070] Step 3: Mix 50 g of modified silica evenly in 300 g of tetrahydrofuran, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain composite modified silica; Mix 25 g of composite modified silica and 300 g of isopropanol evenly, then add 25 g of phenolic resin, and react at 100 °C and 900 rpm for 3 h, cool to room temperature, then centrifuge at 3000 rpm, collect the solid, and dry the solid at 80 °C for 6 h to obtain core-shell composite particles.

[0071] Comparative Example 1

[0072] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink, which is different from Example 2 in that the preparation method of the core-shell composite particles includes the following steps:

[0073] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. Remove the solvent with a rotary evaporator to obtain Compound 1; Mix 30 g of Compound 1, 10 g of diethylamine and 200 g of water evenly, react at 30 °C and 900 rpm for 2 h, and then remove the solvent with a rotary evaporator to obtain DASA; Add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; Then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0074] Step 2: Mix 50 g of silica evenly in 300 g of tetrahydrofuran, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 70 °C for 6 h to obtain core-shell composite particles.

[0075] Comparative Example 2

[0076] A preparation method of an anti-counterfeiting label prepared with anti-counterfeiting digital invisible ink, which is different from Example 2 in that the preparation method of the core-shell composite particles includes the following steps:

[0077] Step 1: Mix 30 g of 1,3-dimethylbarbituric acid, 10 g of furfural and 200 g of water evenly, react at 30 °C and 800 - 1000 rpm for 1 - 3 h, then collect the precipitate, dissolve it in dichloromethane, extract with water and saturated sodium chloride, and collect the organic phase. Remove the solvent with a rotary evaporator to obtain Compound 1; Mix 1 - 5 parts of Compound 1, 0.1 - 1.5 parts of diethylamine and 10 - 30 parts of water evenly, react at 20 - 40 °C and 800 - 1000 rpm for 1 - 3 h, and then remove the solvent with a rotary evaporator to obtain DASA; Add 100 g of PAMAM dendrimer and 30 g of DASA to 450 g of tetrahydrofuran and mix evenly, then react at 80 °C and 900 rpm for 3 h; Then centrifuge at 3000 rpm, collect the solid, and dry at 80 °C for 6 h to obtain core-structured DASA dendrimer microspheres;

[0078] Step 2: Mix 50 g of phenolic resin and 300 g of tetrahydrofuran evenly, then add 80 g of core-structured DASA dendrimer microspheres, react at 40 °C and 900 rpm for 3 h, then centrifuge at 3000 rpm, collect the solid, and dry at 70 °C for 6 h to obtain core-shell composite particles.

[0079] Test Example 1

[0080] Stability test

[0081] Take 100 mL (V1) of the anti-counterfeiting digital invisible inks prepared in Examples 1-6 and Comparative Examples 1-2 as test samples, and place them at 42 ± 1 °C for 21 d. Observe the sedimentation of the inks in each test sample, record the non-sedimented volume (V2), and calculate the ink sedimentation rate (S) based on the change in the ink sedimentation volume; the smaller the sedimentation rate, the better the stability of the ink; the calculation formula for the ink sedimentation rate is shown in the following formula:

[0082] S = (V1 - V2) / V1 × 100%;

[0083] In the formula, V1 is the initial volume, unit mL; V2 is the non-sedimented volume, unit mL; S is the sedimentation rate, %; the results are shown in Table 1.

[0084] Table 1 Sedimentation rate

[0085] Item / Number Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Comparative Example 1 Comparative Example 2 Sedimentation Rate (%) 3.36 3.13 2.26 2.67 2.43 0.99 2.95 2.24

[0086] It can be found from the comparison between Examples 1-6 and Comparative Examples 1-2 that the sedimentation rates of Examples 2-6 and Comparative Examples 1-2 are significantly lower than that of Example 1. Among them, the sedimentation rate of Example 6 is the lowest at 0.99%. The reason may be that the core-shell composite particles added in Example 6 have better dispersibility and stability.

[0087] It can be found from the comparison between Examples 2-5 that the sedimentation rate of Example 3 is lower than that of Examples 4 and 5. The reason may be that Example 2 is DASA dendritic polymer microspheres, and in Example 3, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane is used to modify silica to obtain modified silica. The silica surface-modified by β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane can undergo ring-opening reactions with the hydroxyl or amino groups in DASA dendritic polymer microspheres and polymers to form covalent bonds, enhancing the interaction between the polymer and silica, thereby improving the stability of the system; Examples 4 and 5 use N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane and γ-mercaptopropyltrimethoxysilane, which contain amino and mercapto groups respectively. They can form hydrogen bonds or coordination bonds with the hydroxyl groups on the silica surface, enhancing the interaction between silica and the polymer and also improving the stability of the system. Although the stability can be improved, the effect is lower than that of Example 3.

[0088] By comparing Examples 2-3, Example 6, and Comparative Examples 1-2, it can be found that compared with Example 2 where a stealth ink was prepared by introducing a core structure DASA dendritic polymer microsphere, Comparative Example 1 with an ink of a core-shell composite particle obtained by introducing a core structure DASA dendritic polymer microsphere and silica, and Comparative Example 2 with an ink of a core-shell composite particle prepared by introducing a core structure DASA dendritic polymer microsphere and phenolic resin, the sedimentation rate of the stealth ink prepared by simultaneously introducing a core structure DASA dendritic polymer microsphere, modified silica, and phenolic resin in Example 6 is the lowest, only 0.99%. Its stability is significantly higher than that of Comparative Example 1 and Comparative Example 2. The reason may be that the modified silica and phenolic resin may form a physical network structure in the core-shell composite particles, which can effectively limit the aggregation and sedimentation of the particles. The cross-linking points in the network structure can capture and fix the particles, reducing their free movement in the ink. At the same time, it can improve the overall chemical stability of the core-shell composite particles, reduce degradation during storage and use, thereby improving the stability of the ink. Adding silica or phenolic resin alone can improve the stability of the ink to a certain extent, but the effect is not as good as that of Example 6.

[0089] Test Example 2

[0090] Test on the Color Development Temperature and Time of the Ink

[0091] The anti-counterfeiting digital stealth inks prepared in Examples 1-3, Example 6, and Comparative Examples 1-2 were respectively printed on labels, and the prepared labels were respectively recorded as the Example 1-3 group, the Example 5 group, and the Comparative Examples 1-2 group. Then, each group of labels was heated to test the color development temperature and color development time of the labels. Among them, the color development temperature refers to the temperature when the label color changes, and the color development time refers to the time required for the label to develop color. The specific test results are shown in Table 2 below.

[0092] Test on the Acid and Alkali Resistance of the Ink

[0093] The anti-counterfeiting digital stealth inks prepared in Examples 1-3, Example 6, and Comparative Examples 1-2 were respectively made into ink samples according to the standard of "GB / T 18724-2008 Printing Technology - Determination of Resistance of Printed Matter and Printing Inks to Various Reagents", and were recorded as the Example 1-3 group, the Example 6 group, and the Comparative Examples 1-2 group. According to the standard method of "GB / T 18724-2008 Printing Technology - Determination of Resistance of Printed Matter and Printing Inks to Various Reagents", the acid and alkali resistance of each group of inks was respectively tested. The test samples were considered qualified if there were no phenomena such as peeling, foaming, and color change. The specific test results are shown in Table 2 below.

[0094] Table 2

[0095] Group Example 1 Example 2 Example 3 Example 6 Comparative Example 1 Comparative Example 2 Color Development Temperature (°C) 160 164 185 210 170 190 Color Development Time (s) 5 10 20 35 15 18 Acid Resistance Unqualified Qualified Qualified Qualified Qualified Qualified Alkali Resistance Unqualified Qualified Qualified Qualified Qualified Qualified

[0096] Through the comparison of Examples 1-3, Example 6 and Comparative Examples 1-2, it can be found that compared with Example 2 in which the core structure DASA dendrimer microspheres are introduced to prepare the invisible ink, Comparative Example 1 of the ink with the core-shell composite particles obtained by introducing the core structure DASA dendrimer microspheres and silica, and Comparative Example 2 of the ink with the core-shell composite particles prepared by introducing the core structure DASA dendrimer microspheres and phenolic resin, the color development temperature of the invisible ink with the core-shell composite particles prepared by simultaneously introducing the core structure DASA dendrimer microspheres, modified silica and phenolic resin in Example 6 is 210 °C, the color development time is 35 s, and the acid and alkali resistance performance is qualified. The reason may be that modified silica and phenolic resin are added simultaneously during the preparation of the core-shell composite particles. Modified silica and phenolic resin may crosslink with phenolic resin to form a physical network structure in the core-shell particles again and form a protective layer on the surface. This protective layer can slow down the speed of heat transfer to the DASA molecules, so higher temperature and longer time are required to achieve color development; at the same time, this protective layer can reduce the influence of external acid and alkali properties on the inner core and improve the acid and alkali resistance performance. The core-shell structures of Comparative Examples 1-2 can both form a protective layer to reduce the influence of external acid and alkali properties on the inner core, but they are weaker than Example 6 in increasing the color development temperature and color development time.

Claims

1. A preparation method of an anti-counterfeiting digital invisible ink, characterized in that, It includes the following steps, by weight: dispersing 10 - 40 parts of invisible anti-counterfeiting agent, 0.3 - 3 parts of polymer, 0.05 - 1 part of stabilizer, 5 - 30 parts of solvent, and 0.05 - 5 parts of auxiliary agent evenly through a high-speed disperser, then sending it into a grinder for grinding, and then performing ultrasonic treatment to obtain anti-counterfeiting digital invisible ink; The invisible anti-counterfeiting agent is selected from one of core-structured DASA dendritic polymer microspheres and core-shell composite particles; The preparation method of the core-structured DASA dendritic polymer microspheres includes the following steps, by weight: mixing 1 - 5 parts of 1,3-dimethylbarbituric acid, 0.1 - 1.5 parts of furfural, and 10 - 30 parts of water evenly, reacting at 20 - 40 °C and 800 - 1000 rpm for 1 - 3 h, then collecting the precipitate, dissolving it in dichloromethane, extracting with water and saturated sodium chloride, and collecting the organic phase and removing the solvent with a rotary evaporator to obtain compound 1; mixing 1 - 5 parts of compound 1, 0.1 - 1.5 parts of diethylamine, and 10 - 30 parts of water evenly, reacting at 20 - 40 °C and 800 - 1000 rpm for 1 - 3 h, and then removing the solvent with a rotary evaporator to obtain DASA; adding 5 - 15 parts of PAMAM dendritic polymer and 1 - 5 parts of DASA to 30 - 60 parts of tetrahydrofuran and mixing evenly, then reacting at 60 - 100 °C and 800 - 1000 rpm for 2 - 4 h; then centrifuging at 2000 - 4000 rpm, collecting the solid, and drying at 60 - 100 °C for 4 - 8 h to obtain core-structured DASA dendritic polymer microspheres; The preparation method of the core-shell composite particles includes the following steps, by weight: Mixing 1 - 5 parts of silicon dioxide with 5 - 10 parts of 5 - 15 wt% HCl and stirring for 1 - 3 h, then centrifuging at 2000 - 4000 rpm, collecting the solid, washing the solid with water until the supernatant is neutral, and drying the washed solid at 60 - 100 °C for 4 - 8 h to obtain activated silicon dioxide; mixing 1 - 5 parts of activated silicon dioxide with 5 - 10 parts of ethanol evenly, adding 0.1 - 1 part of ammonia water and 0.1 - 1 part of silane coupling agent, reacting at 50 - 70 °C and 800 - 1000 rpm for 16 - 48 h, then centrifuging at 2000 - 4000 rpm, collecting the solid, washing the solid with ethanol until the supernatant is neutral, and drying the washed solid at 60 - 100 °C for 4 - 8 h to obtain modified silicon dioxide; Mix 1 - 10 parts of modified silica evenly in 10 - 50 parts of tetrahydrofuran, then add 5 - 10 parts of core - structured DASA dendritic polymer microspheres, react at 20 - 60 °C and 800 - 1000 rpm for 2 - 4 h, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry at 60 - 100 °C for 4 - 8 h to obtain composite - modified silica, that is, core - shell composite particles; or, mix 1 - 10 parts of modified silica evenly in 1 - 50 parts of tetrahydrofuran, then add 5 - 10 parts of DASA dendritic polymer microspheres, react at 20 - 60 °C and 800 - 1000 rpm for 2 - 4 h, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry at 60 - 100 °C for 4 - 8 h to obtain composite - modified silica; mix 1 - 5 parts of composite - modified silica and 1 - 50 parts of isopropanol evenly, then add 1 - 5 parts of phenolic resin, and react at 80 - 120 °C and 800 - 1000 rpm for 2 - 4 h, cool to room temperature, then centrifuge at 2000 - 4000 rpm, collect the solid, and dry the solid at 60 - 100 °C for 4 - 8 h to obtain core - shell composite particles.

2. The preparation method of the anti-counterfeiting digital invisible ink according to claim 1, characterized in that, The polymer is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene oxide, polyacrylamide, polyacrylic acid, polylactic acid, polyglycolic acid, polylactic - glycolic acid copolymer, polycaprolactone, polyethylene - vinyl acetate, polydimethylsiloxane, polyurethane; the stabilizer is selected from at least one of butanethiol, nonanethiol, dodecanethiol, hexadecanethiol, mercaptoacetic acid, mercaptopropionic acid, 4 - mercaptobutyric acid, 8 - mercaptoheptanoic acid, 1 - mercapto - 2 - acetone, 4 - mercapto - 2 - pentanone, 3 - mercapto - 2 - butanone, mercaptoethylamine, 3 - mercapto - 1 - propylamine, 3 - mercapto - N - nonylpropionamide; the solvent is selected from at least one of water, methanol, ethanol, isopropanol, n - propanol, ethylene glycol, propylene glycol, glycerol, n - butanol, n - octanol, n - nonanol, n - decanol, N - methylpyrrolidone, binary acid ester mixture, dimethylformamide, diacetone alcohol, 1,3 - dimethyl - imidazolinone, dimethyl sulfoxide, diethylene glycol monobutyl ether, diethylene glycol acetate, ethylene glycol carbonate, propylene glycol carbonate, 1,4 - butyrolactone, toluene, chlorobenzene, dichloromethane, tetrahydrofuran; the auxiliary agent is selected from at least one of perfluorinated surfactants BOK - B - 100, BOK - B - 101, BOK - B - 102, BOK - B - 103.

3. The preparation method of the anti-counterfeiting digital invisible ink according to claim 1, characterized in that: The silane coupling agent is selected from at least one of trimethoxy[2 - (7 - oxabicyclo[4.1.0]hept - 3 - yl)ethyl]silane, N - β - (aminoethyl)-γ - aminopropyltrimethoxysilane, γ - mercaptopropyltrimethoxysilane.

4. Anti - counterfeiting digital invisible ink, prepared by the method according to any one of claims 1 - 3.

5. The application of the anti-counterfeiting digital invisible ink in an anti-counterfeiting label according to claim 4, characterized in that: The anti - counterfeiting label is prepared by printing the anti - counterfeiting digital invisible ink on the label and drying at a temperature of 80 - 100 °C for 1 - 3 h. When printed, the content is invisible, and the printed content appears purple after heating.