A hydrophobic self-erasing anti-counterfeiting special paper and its preparation method and anti-counterfeiting application

Abstract

The present invention discloses a hydrophobic self-erasing anti-counterfeiting special paper, a preparation method thereof, and an anti-counterfeiting application. The hydrophobic self-erasing anti-counterfeiting special paper is prepared by using hydrophobic nanofibers formed by grafting octadecylamine onto carboxylated cellulose nanofibers through an amidation reaction as a base material, and then self-assembling spiropyran and amino-modified phosphors. The self-erasing anti-counterfeiting special paper combines the physical barrier properties of the hydrophobic substrate with the dynamic optical response of the fluorescent material. Under the specific action of ultraviolet light, the paper exhibits a time-ordered fluorescence behavior pattern: the phosphor lights up instantly, while the spiropyran emits light with a lag; on the contrary, when the ultraviolet light is removed, the phosphor emits light gradually fades, and the spiropyran is quickly extinguished, thereby realizing controllable self-erasing of information display. It demonstrates the multi-level, multi-dimensional and reusable anti-counterfeiting functions of the hydrophobic self-erasing anti-counterfeiting special paper.

Description

Technical Field

[0001] The present invention belongs to the technical field of biomass fiber modification, and in particular relates to a hydrophobic self-erasing anti-counterfeiting special paper, a preparation method thereof, and anti-counterfeiting applications. Background Art

[0002] Counterfeiting valuable items such as banknotes, passports, certificates, and confidential documents poses a significant threat to a country's national security, economic stability, and social credibility. With the continuous advancement of counterfeiting and decryption technologies, traditional anti-counterfeiting techniques are becoming increasingly inadequate and unable to effectively protect against modern security threats. This has led to a strong demand for the development of multi-layered anti-counterfeiting materials and advanced anti-counterfeiting strategies and technologies. Optical anti-counterfeiting technologies based on fluorescent materials have become a research hotspot due to their high difficulty in replicating and high concealment. However, widely used fluorescent materials have a single color change mode and are difficult to achieve multi-layered dynamic changes, which to some extent restricts their application in increasingly complex anti-counterfeiting scenarios.

[0003] Fluorescent materials that erase anti-counterfeiting information over time have become effective competitors in the development of anti-counterfeiting materials due to their dynamic optical properties and high rewritability in the time dimension. The uniqueness of this material lies in its ability to perform the writing, clearing, recycling and concealment of anti-counterfeiting information, which highlights its broad prospects for application in anti-counterfeiting technology. However, in existing self-erasing material systems, changes in fluorescence intensity mostly appear as simple binary state transitions (i.e., existence and disappearance), and dynamic changes in fluorescence color cannot be achieved, which in turn constitutes a major constraint on the construction of higher-level complex anti-counterfeiting mechanisms. Therefore, the development of self-erasing materials with higher security is encouraged. Summary of the Invention

[0004] The present invention provides a hydrophobic self-erasing anti-counterfeiting special paper, a preparation method thereof, and anti-counterfeiting applications. The material is not only hydrophobic, but also exhibits continuous fluorescent color switching over time and can achieve self-erasure of anti-counterfeiting information within 30 minutes.

[0005] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A method for preparing hydrophobic self-erasing anti-counterfeiting special paper comprises the following steps:

[0007] S1. Preparation of hydrophobic nanofiber material: Octadecylamine was grafted onto carboxylated cellulose nanofibers via an amidation reaction in the presence of a catalyst to prepare a hydrophobic nanofiber material;

[0008] S2. Preparation of amino-modified phosphor: After the phosphor was ball-milled, the ground phosphor was added to a mixed solution of tetraethyl silicate, deionized water and ethanol and stirred. After centrifugation and washing, the reacted phosphor was added to a mixed solution of 3-aminopropyltriethoxysilane and ethanol and stirred to obtain an amino-modified phosphor;

[0009] S3. Preparation of hydrophobic self-erasing anti-counterfeiting special paper: stir the hydrophobic nanofiber material and amino-modified phosphor, then add 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran and stir, and then dry the mixed solution to obtain the hydrophobic self-erasing anti-counterfeiting special paper.

[0010] Furthermore, the specific operation of preparing the hydrophobic nanofiber material in step S1 is: ultrasonically dispersing the carboxylated cellulose nanofibers in deionized water, adding N-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to the carboxylated cellulose nanofiber suspension in sequence to activate the carboxyl group, stirring at room temperature for 30 to 60 minutes, and then adding an octadecylamine solution dissolved in an ethanol solution to the solution, stirring at 50 to 60°C for 4 to 6 hours, and centrifuging the reacted solution with a mixed solution of ethanol and water.

[0011] Furthermore, in step S1, the mass ratio of carboxylated cellulose nanofibers to N-hydroxysuccinimide is 1:1; the mass ratio of carboxylated cellulose nanofibers to 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is 1:1; and the mass ratio of carboxylated cellulose nanofibers to octadecylamine is 1:0.5-1.

[0012] Furthermore, the specific operation of preparing the amino-modified phosphor in step S2 is as follows: placing the phosphor in a ball mill and grinding for 20 to 28 hours, preparing a mixture of tetraethyl silicate, deionized water and ethanol, adjusting the pH value of the mixture to 2 to 3 with oxalic acid, stirring at 50 to 70°C for 1 to 2 hours, then adding the ground phosphor, stirring at 50 to 60°C for 4 to 6 hours, centrifuging and washing the reacted solution, and drying it in an oven at 70 to 80°C, then adding the reacted phosphor to a mixture of ethanol and 3-aminopropyltriethoxysilane, stirring at room temperature for 7 to 9 hours, centrifuging and washing, and drying at 70 to 80°C.

[0013] Furthermore, the volume ratio of tetraethyl silicate, deionized water and ethanol in the mixture of tetraethyl silicate, deionized water and ethanol in step S2 is 1:20:30, the volume ratio of ethanol to 3-aminopropyltriethoxysilane in the mixture of ethanol and 3-aminopropyltriethoxysilane is 100:1, the mass volume ratio of the ground phosphor to tetraethyl silicate is 1 g:1~3 mL, and the mass volume ratio of the reacted phosphor to 3-aminopropyltriethoxysilane is 1~3 g:1 mL.

[0014] Furthermore, the specific operation of preparing the hydrophobic self-erasing anti-counterfeiting special paper in step S3 is: adding the hydrophobic nanofiber material to the dimethylformamide solution, stirring at 40-50°C for 30-40 minutes, then adding the amino-modified phosphor, stirring at 40-50°C for 2-3 hours, and then adding 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, stirring at room temperature for 30-60 minutes, ultrasonic defoaming, adding the mixed solution to a polytetrafluoroethylene mold, and standing in an oven at 40-50°C for 20-24 hours.

[0015] Furthermore, in step S3, the mass ratio of the hydrophobic nanofiber material, the amino-modified phosphor, and 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran is 1:0.5 to 2:0.05.

[0016] The hydrophobic self-erasing anti-counterfeiting special paper exhibits the characteristics of gradual on and off fluorescence on the time axis and is hydrophobic; it exhibits continuous color switching over time and can achieve self-erasure of anti-counterfeiting information within 30 minutes.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The hydrophobic self-erasing anti-counterfeiting special paper prepared by the present invention has good hydrophobicity and can effectively avoid the interference of external factors on the anti-counterfeiting information.

[0019] (2) The hydrophobic self-erasing anti-counterfeiting specialty paper prepared by the present invention cleverly assembles interfacially incompatible phosphors and spiropyran. Furthermore, the nanofibers successfully suppress the aggregation effect between spiropyran molecules and the associated fluorescence quenching problem, significantly improving the optical properties of the material. This allows the hydrophobic self-erasing anti-counterfeiting specialty paper to achieve not only significant changes in fluorescent color but also a unique afterglow effect.

[0020] (3) The hydrophobic self-erasing anti-counterfeiting specialty paper prepared by the present invention changes its fluorescence from cyan to red with continuous exposure to ultraviolet light; after the ultraviolet light irradiation stops, it exhibits a persistent cyan afterglow fluorescence; when the afterglow disappears, it turns purple; after being stored in sunlight for a period of time, the purple fades and the original yellow color is revealed; the hydrophobic self-erasing anti-counterfeiting specialty paper at different color stages has different hydrophobic angles, embodying a multi-level, multi-dimensional and reusable anti-counterfeiting function. DETAILED DESCRIPTION

[0021] Example 1

[0022] The hydrophobic self-erasing anti-counterfeiting special paper of the present invention is prepared by the following steps:

[0023] S1. Preparation of hydrophobic nanofiber material: 20 g of carboxylated cellulose nanofibers (solid content: 1 wt%) were ultrasonically dispersed in 100 mL of deionized water. 0.2 g of N-hydroxysuccinimide and 0.2 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added to the carboxylated cellulose nanofiber suspension to activate the carboxyl groups. The mixture was stirred at room temperature for 30 min. 0.2 g of octadecylamine was dissolved in 100 mL of ethanol. The octadecylamine solution was then added to the reaction solution. The mixture was stirred at 60° C. for 4 h. The reaction solution was washed by centrifugation with a mixed solution of ethanol and water. The resulting precipitate was a hydrophobic nanofiber material.

[0024] S2. Preparation of amino-modified phosphor: 3 g of phosphor was placed in a ball mill and milled for 20 h. A mixture of 9 mL of tetraethyl silicate, 180 mL of deionized water, and 270 mL of ethanol was prepared. The pH of the mixture was adjusted to 2 with oxalic acid and stirred at 50°C for 2 h. Subsequently, 3 g of the ground phosphor was added and stirred at 50°C for 6 h. The reacted solution was centrifuged and washed and dried in a 70°C oven. 3 g of the reacted phosphor was then added to a mixture of 300 mL of ethanol and 3 mL of 3-aminopropyltriethoxysilane. The mixture was stirred at room temperature for 7 h, centrifuged and washed, and dried at 70°C. The resulting powder was an amino-modified phosphor.

[0025] S3. Preparation of hydrophobic self-erasing anti-counterfeiting special paper: add 0.2g of hydrophobic nanofiber material to 20mL of dimethylformamide solution, stir at 40℃ for 40min, then add 0.4g of amino-modified phosphor, stir at 40℃ for 3h, then add 0.01g of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, stir at room temperature for 30min, ultrasonically defoam, add the mixed solution into a 5cm*5cm*1cm polytetrafluoroethylene mold, let it stand in an oven at 40℃ for 24h, and dry the obtained product to obtain hydrophobic self-erasing anti-counterfeiting special paper.

[0026] An example of the application of the hydrophobic self-erasing anti-counterfeiting special paper prepared in Example 1 in anti-counterfeiting: the special paper appears light yellow under visible light; when it is placed under 365nm ultraviolet light, the special paper exhibits cyan fluorescence; then a black mask is covered on the special paper, leaving only the "gold" pattern exposed, and then it is placed under ultraviolet light for 1 minute. During this period, the fluorescence of the "gold" pattern can be seen to slowly change from cyan to red; then, the mask is removed, and it is observed that a red fluorescent pattern is formed on the special paper in contrast to the cyan fluorescent background; then, the ultraviolet light is turned off and the special paper is placed in a dark environment, and a "gold" pattern with a cyan afterglow can be observed (the afterglow can last for 16 minutes); then, the special paper is exposed to visible light again, and the purple "gold" pattern can be clearly seen on it; finally, the contact angles of different color areas of the special paper are measured, and it is found that the contact angle at the yellow part is 135°, while the contact angle at the purple part is 121°. Expose the specialty paper to sunlight for 30 minutes, and all previous changes will gradually disappear and eventually return to their original state.

[0027] Example 2

[0028] The hydrophobic self-erasing anti-counterfeiting special paper of the present invention is prepared by the following steps:

[0029] S1. Preparation of hydrophobic nanofiber material: 20 g of carboxylated cellulose nanofibers (solid content: 1 wt%) were ultrasonically dispersed in 100 mL of deionized water. 0.2 g of N-hydroxysuccinimide and 0.2 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added to the carboxylated cellulose nanofiber suspension to activate the carboxyl groups. The mixture was stirred at room temperature for 60 min. 0.1 g of octadecylamine was dissolved in 100 mL of ethanol. The octadecylamine solution was then added to the reaction solution. The mixture was stirred at 50° C. for 6 h. The reaction solution was washed by centrifugation with a mixed solution of ethanol and water. The resulting precipitate was a hydrophobic nanofiber material.

[0030] S2. Preparation of amino-modified phosphor: 3 g of phosphor was placed in a ball mill and milled for 28 h. A mixture of 3 mL of tetraethyl silicate, 60 mL of deionized water, and 90 mL of ethanol was prepared. The pH of the mixture was adjusted to 3 with oxalic acid and stirred at 70°C for 1 h. Subsequently, 3 g of the ground phosphor was added and stirred at 60°C for 4 h. The reacted solution was centrifuged and washed and dried in an oven at 80°C. 3 g of the reacted phosphor was then added to a mixture of 100 mL of ethanol and 1 mL of 3-aminopropyltriethoxysilane. The mixture was stirred at room temperature for 9 h, centrifuged and washed, and dried at 80°C. The resulting powder was an amino-modified phosphor.

[0031] S3. Preparation of hydrophobic self-erasing anti-counterfeiting special paper: add 0.2g of hydrophobic nanofiber material to 20mL of dimethylformamide solution, stir at 50℃ for 30min, then add 0.1g of amino-modified phosphor, stir at 50℃ for 2h, then add 0.01g of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, stir at room temperature for 60min, ultrasonically defoam, add the mixed solution into a 5cm*5cm*1cm polytetrafluoroethylene mold, let it stand in an oven at 50℃ for 20h, and dry the obtained product to obtain hydrophobic self-erasing anti-counterfeiting special paper.

[0032] An application example of the hydrophobic self-erasing anti-counterfeiting special paper prepared in Example 2 in anti-counterfeiting: the special paper appears light yellow under visible light; when it is placed under 365nm ultraviolet light, the special paper exhibits cyan fluorescence; then a black mask is covered on the special paper, leaving only the "gold" pattern exposed, and then it is placed under ultraviolet light for 1 minute. During this period, the fluorescence of the "gold" pattern can be seen to slowly change from cyan to red; then, the mask is removed, and it is observed that a red fluorescent pattern is formed on the special paper in contrast to the cyan fluorescent background; then, the ultraviolet light is turned off and the special paper is placed in a dark environment, and a "gold" pattern with a cyan afterglow can be observed (the afterglow can last for 4 minutes); then, the special paper is exposed to visible light again, and the purple "gold" pattern can be clearly seen on it; finally, the contact angles of different color areas of the special paper are measured, and it is found that the contact angle at the yellow part is 112°, while the contact angle at the purple part is 96°. Expose the specialty paper to sunlight for 30 minutes, and all previous changes will gradually disappear and eventually return to their original state.

[0033] Example 3

[0034] The hydrophobic self-erasing anti-counterfeiting special paper of the present invention is prepared by the following steps:

[0035] S1. Preparation of hydrophobic nanofiber material: 20 g of carboxylated cellulose nanofibers (solid content: 1 wt%) were ultrasonically dispersed in 100 mL of deionized water. 0.2 g of N-hydroxysuccinimide and 0.2 g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride were added to the carboxylated cellulose nanofiber suspension to activate the carboxyl groups. The mixture was stirred at room temperature for 45 min. 0.15 g of octadecylamine was dissolved in 100 mL of ethanol. The octadecylamine solution was then added to the reaction solution. The mixture was stirred at 55° C. for 5.5 h. The reaction solution was washed by centrifugation with a mixed solution of ethanol and water. The resulting precipitate was a hydrophobic nanofiber material.

[0036] S2. Preparation of amino-modified phosphor: 3 g of phosphor was placed in a ball mill and milled for 24 h. A mixture of 6 mL of tetraethyl silicate, 120 mL of deionized water, and 180 mL of ethanol was prepared. The pH of the mixture was adjusted to 2.5 with oxalic acid and stirred at 60°C for 1.5 h. Subsequently, 3 g of the ground phosphor was added and stirred at 55°C for 5 h. The reacted solution was centrifuged and washed and dried in a 75°C oven. 3 g of the reacted phosphor was then added to a mixture of 150 mL of ethanol and 1.5 mL of 3-aminopropyltriethoxysilane. The mixture was stirred at room temperature for 8 h, centrifuged and washed, and dried at 75°C. The resulting powder was an amino-modified phosphor.

[0037] S3. Preparation of hydrophobic self-erasing anti-counterfeiting special paper: add 0.2g of hydrophobic nanofiber material to 20mL of dimethylformamide solution, stir at 45℃ for 35min, then add 0.2g of amino-modified phosphor, stir at 45℃ for 2.5h, then add 0.01g of 1-(2-hydroxyethyl)-3,3-dimethylindoline-6'-nitrobenzospiropyran, stir at room temperature for 45min, ultrasonically defoam, add the mixed solution into a 5cm*5cm*1cm polytetrafluoroethylene mold, let it stand in a 45℃ oven for 22h, and dry the obtained product to obtain hydrophobic self-erasing anti-counterfeiting special paper.

[0038] An example of the application of the hydrophobic self-erasing anti-counterfeiting special paper prepared in Example 3 in anti-counterfeiting: the special paper appears light yellow under visible light; when it is placed under 365nm ultraviolet light, the special paper exhibits cyan fluorescence; then a black mask is covered on the special paper, leaving only the "gold" pattern exposed, and then it is placed under ultraviolet light for 1 minute. During this period, the fluorescence of the "gold" pattern can be seen to slowly change from cyan to red; then, the mask is removed, and it is observed that a red fluorescent pattern is formed on the special paper in contrast to the cyan fluorescent background; then, the ultraviolet light is turned off and the special paper is placed in a dark environment, and a "gold" pattern with a cyan afterglow can be observed (the afterglow can last for 10 minutes); then, the special paper is exposed to visible light again, and the purple "gold" pattern can be clearly seen on it; finally, the contact angles of different color areas of the special paper are measured, and it is found that the contact angle at the yellow part is 129°, while the contact angle at the purple part is 117°. Expose the specialty paper to sunlight for 30 minutes, and all previous changes will gradually disappear and eventually return to their original state.

Claims

1. A method for preparing a hydrophobic self-erasing anti-counterfeiting special paper, characterized in that: The method comprises the following preparation steps: S1. Preparation of hydrophobic nanofiber material: Octadecylamine was grafted onto carboxylated cellulose nanofibers via an amidation reaction in the presence of a catalyst to prepare a hydrophobic nanofiber material; S2. Preparation of amino-modified phosphor: After the phosphor was ball-milled, the ground phosphor was added to a mixed solution of tetraethyl silicate, deionized water and ethanol and stirred. After centrifugation and washing, the reacted phosphor was added to a mixed solution of 3-aminopropyltriethoxysilane and ethanol and stirred to obtain an amino-modified phosphor; S3. Preparation of hydrophobic self-erasing anti-counterfeiting special paper: stir the hydrophobic nanofiber material and amino-modified phosphor, and then add After stirring, the mixed solution is dried to prepare a hydrophobic self-erasing anti-counterfeiting special paper; The specific steps of preparing the hydrophobic self-erasing anti-counterfeiting special paper in step S3 are as follows: adding the hydrophobic nanofiber material to the dimethylformamide solution, stirring at 40-50°C for 30-40 minutes, then adding the amino-modified phosphor, stirring at 40-50°C for 2-3 hours, and then adding , stir at room temperature for 30-60 min, defoam with ultrasound, add the mixed solution into a polytetrafluoroethylene mold, and place it in an oven at 40-50°C for 20-24 h; In step S3, the hydrophobic nanofiber material, the amino-modified phosphor and The mass ratio is 1:0.5~2:0.

05.

2. The preparation method according to claim 1, characterized in that The specific operation of preparing the hydrophobic nanofiber material in step S1 is as follows: ultrasonically dispersing the carboxylated cellulose nanofibers in deionized water, sequentially adding N-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride to the carboxylated cellulose nanofiber suspension to activate the carboxyl group, stirring at room temperature for 30 to 60 minutes, then adding an octadecylamine solution dissolved in an ethanol solution to the solution, stirring at 50 to 60° C. for 4 to 6 hours, and centrifuging the reacted solution with a mixed solution of ethanol and water.

3. The preparation method according to claim 2, characterized in that In step S1, the mass ratio of carboxylated cellulose nanofibers to N-hydroxysuccinimide is 1:1; the mass ratio of carboxylated cellulose nanofibers to 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride is 1:1; and the mass ratio of carboxylated cellulose nanofibers to octadecylamine is 1:0.5~1.

4. The preparation method according to claim 1, characterized in that The specific operation of preparing the amino-modified phosphor in step S2 is as follows: placing the phosphor in a ball mill and grinding for 20-28 hours, preparing a mixture of tetraethyl silicate, deionized water and ethanol, adjusting the pH value of the mixture to 2-3 with oxalic acid, stirring at 50-70°C for 1-2 hours, then adding the ground phosphor, stirring at 50-60°C for 4-6 hours, centrifuging and washing the reacted solution, and drying it in an oven at 70-80°C, then adding the reacted phosphor to a mixture of ethanol and 3-aminopropyltriethoxysilane, stirring at room temperature for 7-9 hours, centrifuging and washing, and drying at 70-80°C.

5. The preparation method according to claim 4, characterized in that The volume ratio of tetraethyl silicate, deionized water and ethanol in the mixture of tetraethyl silicate, deionized water and ethanol in step S2 is 1:20:30, the volume ratio of ethanol to 3-aminopropyltriethoxysilane in the mixture of ethanol and 3-aminopropyltriethoxysilane is 100:1, the mass volume ratio of the ground phosphor to tetraethyl silicate is 1 g:1~3 mL, and the mass volume ratio of the reacted phosphor to 3-aminopropyltriethoxysilane is 1~3 g:1 mL.

6. A hydrophobic self-erasing anti-counterfeiting special paper prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the hydrophobic self-erasing anti-counterfeiting special paper prepared by the preparation method according to any one of claims 1 to 5 in anti-counterfeiting.

8. The use according to claim 7, characterized in that The hydrophobic self-erasing anti-counterfeiting special paper exhibits the characteristics of gradual on and off fluorescence on the time axis and is hydrophobic; it exhibits continuous color switching over time and can achieve self-erasure of anti-counterfeiting information within 30 minutes.