Special encrypted anti-counterfeiting ink based on rare earth up-conversion material, which is resistant to friction and has strong adhesion

Abstract

The present application relates to a kind of special encrypted anti-counterfeiting ink based on rare earth up-conversion material, which is friction-resistant and strongly attached.The ink is composed of copolymer-modified rare earth up-conversion material and solvent, and can be connected to the surface of cellulose paper through the covalent interaction between benzophenone and cellulose.The printed pattern shows no color under visible light, but shows strong green fluorescence under 980 nm excitation light.The benzophenone functional group in the copolymer-modified rare earth up-conversion material forms a covalent bond with cellulose, which enables printing on various cellulose paper surfaces (filter paper, sketch paper, kraft paper, rice paper, ordinary A4 paper).High-content cellulose paper cannot fade the printed pattern after soaking in water for 15 days.The special encrypted anti-counterfeiting ink described in the present application has good adhesion, friction resistance, water resistance, ultraviolet resistance and anti-interference on cellulose paper.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of encryption anti-counterfeiting, and relates to a special encryption anti-counterfeiting ink based on a rare earth upconversion material, which is resistant to friction and has strong adhesion. The ink is colorless under visible light, but shows bright green fluorescence under 980 nm excitation light. It can form covalent action with cellulose under ultraviolet light irradiation, and has good adhesion, resistance to friction, water washing, ultraviolet light and anti-interference on cellulose paper. BACKGROUND

[0002] Counterfeiting of currency, documents, food and branded goods has caused huge economic losses and safety impacts to governments, consumers and industrial sectors. With the continuous development of science and technology, counterfeiters use more advanced technology and tools to crack traditional anti-counterfeiting technology and implement product counterfeiting. Due to the significant growth of the anti-counterfeiting market, the demand for anti-counterfeiting technology has also increased significantly in recent years. Traditional fluorescent anti-counterfeiting mainly uses ultraviolet fluorescent ink, which adds ultraviolet fluorescent materials in the ink. Under ultraviolet light irradiation, the fluorescent color is shown, and the true and false discrimination is realized through color change. Traditional ultraviolet fluorescent materials generally show color under visible light, do not have concealment, and have the disadvantages of short fluorescent lifetime, fast photobleaching rate, and fluorescent color easily disturbed by environment.

[0003] At present, many luminescent materials have been explored for the manufacture of anti-counterfeiting ink, among which upconversion nanomaterials have the advantages of high fluorescent stability, no background fluorescence, long luminescence lifetime and low toxicity, and are potential materials for the preparation of anti-counterfeiting ink. Patent CN 105885845A reports a kind of β-NaYF4:Yb,Tm rare earth upconversion luminescent material, which realizes the printing of different anti-counterfeiting patterns on PET substrate and A4 paper through silk screen, proving that the upconversion nanomaterials have difficult-to-reproduce anti-counterfeiting performance. Patent CN107641375A reports an upconversion red, green and blue anti-counterfeiting material based on lanthanide NaYF4, using polyacrylic acid resin (PAA) as a connecting resin, and using the carboxyl groups contained in the PAA polymer to achieve good PET substrate adhesion and invisible anti-counterfeiting. However, the surface of the upconversion nanoparticles is not modified, and the durability effect is not tested, which limits the application effect of the upconversion luminescent ink. Patent CN105196722A reports a method for improving the adhesion of ink on the surface of paper by adding a photosensitizer. A layer of acrylic emulsion needs to be coated on the surface of the paper first, and then a layer of cellulose solution is coated to form intermolecular forces with the polar groups in the ink, making the printing process more complex. A space-controlled thiol-yne linked diphenylthiophene photochromic compound has been reported to be covalently linked to cellulose paper, which has better resistance to washing than non-covalent adsorption connection (ACS Appl. Polym. Mater. 2019, 1, 1240-1250).

[0004] Therefore, aiming at the technical problems of the existing anti-counterfeiting ink, the present application is based on the covalent action of benzophenone and cellulose, takes the rare earth upconversion nanomaterial NaYF4:Yb,Ho as the main body luminescent material, modifies the rare earth upconversion nanomaterial through the copolymer of vinyl pyrrolidone and benzophenone, and obtains the special encrypted anti-counterfeiting ink based on the rare earth upconversion material, which is resistant to friction and has strong adhesion, and has good adhesion, friction resistance, water resistance, ultraviolet resistance and anti-interference on the cellulose paper. SUMMARY

[0005] The present application aims to provide a special encrypted anti-counterfeiting ink based on the rare earth upconversion material, which is resistant to friction and has strong adhesion. The ink is mainly composed of the rare earth upconversion material NaYF4:Yb,Ho modified by the copolymer and a solvent. After being printed on the surface of paper by silk screen printing, the anti-counterfeiting mark is invisible and colorless under visible light and cannot be detected by naked eyes. The encrypted anti-counterfeiting mark displays strong green fluorescence under 980nm excitation light and can form covalent action with cellulose under ultraviolet light, thus having good adhesion, friction resistance, water resistance, ultraviolet resistance and anti-interference on the cellulose paper. The defects of the traditional ultraviolet anti-counterfeiting material, such as easy imitation, poor invisible effect, poor water resistance and poor anti-interference, are effectively overcome. The special encrypted anti-counterfeiting ink has good adhesion, friction resistance, ultraviolet resistance, water resistance, anti-interference and fluorescence stability.

[0006] The special encrypted anti-counterfeiting ink based on the rare earth upconversion material is composed of the rare earth upconversion material NaYF4:Yb,Ho modified by the copolymer and a solvent. The copolymer is the copolymer of vinyl pyrrolidone and benzophenone, the solvent is the mixed solution of ethanol, dimethyl sulfoxide and glycerol, and the concentration of the rare earth upconversion material in the solvent is 1.8mg / mL. The specific operation is performed according to the following steps:

[0007] a. At room temperature, yttrium nitrate, ytterbium nitrate, holmium nitrate, sodium hydroxide, ethanol and oleic acid are added in sequence, stirred for 20min, and then ammonium fluoride solution is added dropwise under stirring for 30min. The temperature is heated to 200℃ for 8h, and then naturally cooled to room temperature. After centrifugal washing and drying, the oil acid-coated yttrium, ytterbium and holmium doped sodium yttrium fluoride rare earth upconversion material NaYF4:Yb,Ho is obtained.

[0008] b. Under nitrogen atmosphere, 4-methacryloyloxybenzophenone, vinyl pyrrolidone and azobisisobutyronitrile are dissolved in dioxane, and then stirred and heated at a temperature of 60℃ for 16h. Then the product is precipitated with diethyl ether, and then centrifugal washing and drying are performed to obtain the copolymer of vinyl pyrrolidone and benzophenone.

[0009] c. The copolymer modified rare earth upconversion material is obtained by dispersing the rare earth upconversion material obtained in step a and the copolymer of vinyl pyrrolidone and benzophenone obtained in step b in dimethyl sulfoxide respectively, then slowly dropping the copolymer solution of vinyl pyrrolidone and benzophenone into the rare earth upconversion material solution, heating at 95°C for 8 hours, precipitating with anhydrous ethanol, centrifuging, washing with chloroform for 3 times, and drying;

[0010] d. The copolymer modified rare earth upconversion material obtained in step c is dissolved in dimethyl sulfoxide at room temperature, and then glycerol and anhydrous ethanol are added in a volume ratio of 3:2 after ultrasonic dissolution. After stirring for 24 hours, the rare earth upconversion material based anti-friction and strong adhesion special encryption anti-counterfeiting ink is obtained.

[0011] The rare earth upconversion material based anti-friction and strong adhesion special encryption anti-counterfeiting ink is used in silk screen printing, inkjet printing, pen type brush writing or seal.

[0012] The anti-counterfeiting ink shows no color under visible light.

[0013] The anti-counterfeiting ink shows green fluorescence under 980 nm excitation light.

[0014] The rare earth upconversion material based anti-friction and strong adhesion special encryption anti-counterfeiting ink shows no color under visible light and shows green fluorescence under 980 nm excitation light. After ultraviolet irradiation, the benzophenone functional group of the copolymer modified rare earth upconversion material can form a covalent bond with cellulose. Through printing effect comparison on various paper surfaces (filter paper, sketch paper, parchment paper, rice paper, and ordinary A4 paper), the ink has good adhesion to paper bases with high cellulose content. The printed pattern cannot fade after being soaked in water for 15 days. The printed pattern shows no color under sunlight and shows characteristic green fluorescence under 980 nm excitation light. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The present application is used for printing different pattern fluorescence effect figures on various surfaces (filter paper, sketch paper, parchment paper, rice paper, and ordinary A4 paper) by silk screen printing. (a) is a filter paper silk screen printing different pattern fluorescence effect figure, (b) is a sketch paper silk screen printing different pattern fluorescence effect figure, (c) is a parchment paper silk screen printing different pattern fluorescence effect figure, (d) is a rice paper silk screen printing different pattern fluorescence effect figure, and (e) is an ordinary A4 paper silk screen printing different pattern fluorescence effect figure.

[0016] Figure 2 The present application is used for printing different pattern fluorescence effect figures on various surfaces (filter paper, sketch paper, parchment paper, rice paper, and ordinary A4 paper) by silk screen printing. (a) is a filter paper silk screen printing different pattern fluorescence effect figure, (b) is a sketch paper silk screen printing different pattern fluorescence effect figure, (c) is a parchment paper silk screen printing different pattern fluorescence effect figure, (d) is a rice paper silk screen printing different pattern fluorescence effect figure, and (e) is an ordinary A4 paper silk screen printing different pattern fluorescence effect figure. DETAILED DESCRIPTION

[0017] Example 1

[0018] Preparation of rare earth upconversion material NaYF4:Yb,Ho:

[0019] a, at room temperature, add yttrium nitrate 0.5M, ytterbium nitrate 0.5M, holmium nitrate 0.2M, sodium hydroxide, ethanol and oleic acid in turn, stir for 20 min to be uniform, add ammonium fluoride solution 0.4M dropwise under stirring, stir for 30 min, heat at 200℃ for 8h, naturally cool to room temperature, centrifugal wash and dry to obtain oleic acid coated yttrium, ytterbium, holmium doped sodium yttrium fluoride rare earth upconversion material NaYF4:Yb,Ho;

[0020] Preparation of copolymer:

[0021] b, under nitrogen atmosphere, dissolve 4-methacryloyloxybenzophenone 1mmol, vinyl pyrrolidone 10mmol, azobisisobutyronitrile 0.12mmol in dioxane, stir and heat at temperature 60℃ for 16h, then precipitate the product with diethyl ether, centrifugal, wash and dry to obtain the copolymer of vinyl pyrrolidone and benzophenone;

[0022] Preparation of copolymer modified rare earth upconversion material:

[0023] c, disperse the rare earth upconversion material NaYF4:Yb,Ho obtained in step a and the copolymer of vinyl pyrrolidone and benzophenone obtained in step b into dimethyl sulfoxide solvent respectively, then slowly add the copolymer solution of vinyl pyrrolidone and benzophenone into the rare earth upconversion material NaYF4:Yb,Ho solution, heat at 95℃ for 8h, precipitate with anhydrous ethanol, centrifugal, wash with chloroform for 3 times, dry to obtain the copolymer modified rare earth upconversion material;

[0024] Preparation of special encrypted anti-counterfeiting ink

[0025] d, at room temperature, weigh 20mg of the copolymer modified rare earth upconversion material of step c, dissolve in 1mL of dimethyl sulfoxide, ultrasonic dissolve, then add 6mL of glycerol and 4mL of ethanol according to the volume ratio of 3:2, stir for 24h to obtain the special encrypted anti-counterfeiting ink based on rare earth upconversion material with good dispersion, strong adhesion and resistance to friction.

[0026] Use different types of paper-based (filter paper, sketch paper, kraft paper, rice paper, ordinary A4 paper) on the market as printing substrate to test the anti-counterfeiting effect.

[0027] The special encrypted security ink obtained from example 1 was evenly printed on different types of paper substrates by silk screen printing, and the security image was observed. Through experiments, under visible light, the security ink was invisible to the naked eye on the surface of the paper substrate, and under 980nm excitation light, the security pattern showed green fluorescence on different paper substrates. Figure 1 )。

[0028] Example 2

[0029] Preparation of rare earth upconversion material:

[0030] a. At room temperature, add yttrium nitrate 0.5M, ytterbium nitrate 0.5M, holmium nitrate 0.2M, sodium hydroxide, ethanol and oleic acid in sequence, stir for 12 min until uniform, add ammonium fluoride solution 0.4M dropwise under stirring, stir for 30 min, heat at 200℃ for 8h, naturally cool to room temperature, centrifuge, wash and dry to obtain oleic acid-coated yttrium, ytterbium and holmium-doped yttrium tetrafluoride sodium rare earth upconversion material NaYF4:Yb,Ho;

[0031] Preparation of copolymer:

[0032] b. Under nitrogen atmosphere, dissolve 4-methacryloyloxybenzophenone 1mmol, vinylpyrrolidone 10mmol and azobisisobutyronitrile 0.12mmol in dioxane, stir and heat at 60℃ for 16h, then precipitate the product with diethyl ether, centrifuge, wash and dry to obtain the copolymer of vinylpyrrolidone and benzophenone;

[0033] Preparation of copolymer-modified rare earth upconversion material:

[0034] c. Disperse the rare earth upconversion material NaYF4:Yb,Ho obtained in step a and the copolymer of vinylpyrrolidone and benzophenone obtained in step b into dimethyl sulfoxide solvent respectively, then slowly add the copolymer of vinylpyrrolidone and benzophenone solution into the rare earth upconversion material NaYF4:Yb,Ho solution, heat at 95℃ for 8h, precipitate with anhydrous ethanol, centrifuge, wash with chloroform for 3 times, and dry to obtain the copolymer-modified rare earth upconversion material;

[0035] Preparation of special encrypted security ink:

[0036] d. At room temperature, weigh 20mg of the copolymer-modified rare earth upconversion material of step c, dissolve in 1mL of dimethyl sulfoxide, ultrasonically dissolve, then add 6mL of glycerol and 4mL of ethanol according to the volume ratio of 3:2, stir for 24h to obtain the well-dispersed special encrypted security ink based on the rare earth upconversion material with good friction resistance and strong adhesion.

[0037] The special encrypted anti-counterfeiting ink obtained from example 2 is evenly printed on different types of paper bases by silk screen printing, and is irradiated in a UV light box for 15 min. Through comparative tests, the special encrypted anti-counterfeiting ink has better covalent action with high cellulose content paper bases. The pattern of the special encrypted anti-counterfeiting ink on the surface of the paper base is invisible under visible light, and still shows green fluorescence under 980 nm excitation light after being soaked in pure water for 15 days. Figure 2

[0038] Example 3

[0039] Preparation of rare earth upconversion material:

[0040] a. At room temperature, add yttrium nitrate 0.5M, ytterbium nitrate 0.5M, holmium nitrate 0.2M, sodium hydroxide, ethanol and oleic acid in sequence, stir for 20 min until uniform, add ammonium fluoride solution 0.4M dropwise under stirring, stir for 30 min, heat at 200℃ for 8h, naturally cool to room temperature, centrifuge, wash, dry to obtain oleic acid coated yttrium, ytterbium, holmium doped yttrium tetrafluoride sodium rare earth upconversion material NaYF4:Yb,Ho;

[0041] Preparation of copolymer:

[0042] b. Under nitrogen atmosphere, dissolve 4-methacryloyloxybenzophenone 1mmol, vinylpyrrolidone 10mmol, azobisisobutyronitrile 0.12mmol in dioxane, stir and heat at temperature 60℃ for 16h, then precipitate the product with diethyl ether, centrifuge, wash, dry to obtain copolymer of vinylpyrrolidone and benzophenone;

[0043] Preparation of copolymer modified rare earth upconversion material:

[0044] c. Disperse the rare earth upconversion material NaYF4:Yb,Ho obtained in step a and the copolymer of vinylpyrrolidone and benzophenone obtained in step b into dimethyl sulfoxide solvent respectively, then slowly add the copolymer of vinylpyrrolidone and benzophenone solution into the rare earth upconversion material NaYF4:Yb,Ho solution, heat at 95℃ for 8h, precipitate with anhydrous ethanol, centrifuge, wash with chloroform for 3 times, dry to obtain copolymer modified rare earth upconversion material;

[0045] Preparation of special encrypted anti-counterfeiting ink:

[0046] d. At room temperature, weigh 20mg of copolymer modified rare earth upconversion material of step c, dissolve in 1mL of dimethyl sulfoxide, ultrasonic dissolve, then add 6mL of glycerol and 4mL of ethanol according to the volume ratio of 3:2, stir for 24h to obtain well dispersed rare earth upconversion material based special encrypted anti-counterfeiting ink with good friction resistance and strong adhesion.

[0047] ​The special encryption anti-counterfeiting ink in Example 3 is filled into a pen type brush ink cartridge for writing. After testing, the anti-counterfeiting ink is invisible on the paper surface under visible light, and shows green fluorescence under 980 nm excitation light.

[0048] Example 4

[0049] Preparation of rare earth upconversion material

[0050] a. At room temperature, add yttrium nitrate 0.5M, ytterbium nitrate 0.5M, holmium nitrate 0.2M, sodium hydroxide, ethanol and oleic acid in sequence, stir for 20 min until uniform, add ammonium fluoride solution 0.4M dropwise under stirring, stir for 30 min, heat at 200℃ for 8h, naturally cool to room temperature, centrifuge, wash, dry to obtain oleic acid coated yttrium, ytterbium, holmium doped yttrium tetrafluoride sodium rare earth upconversion material NaYF4:Yb,Ho;

[0051] Preparation of copolymer:

[0052] b. Under nitrogen atmosphere, dissolve 4-methacryloyloxybenzophenone 1mmol, vinylpyrrolidone 10mmol, azobisisobutyronitrile 0.12mmol in dioxane, stir and heat at temperature 60℃ for 16h, then precipitate the product with diethyl ether, centrifuge, wash, dry to obtain copolymer of vinylpyrrolidone and benzophenone;

[0053] Preparation of copolymer modified rare earth upconversion material:

[0054] c. Disperse the rare earth upconversion material NaYF4:Yb,Ho obtained in step a and the copolymer of vinylpyrrolidone and benzophenone obtained in step b into dimethyl sulfoxide solvent respectively, then slowly add the copolymer of vinylpyrrolidone and benzophenone solution into the rare earth upconversion material NaYF4:Yb,Ho solution, heat at 95℃ for 8h, precipitate with anhydrous ethanol, centrifuge, wash with chloroform for 3 times, dry to obtain copolymer modified rare earth upconversion material;

[0055] Preparation of special encryption anti-counterfeiting ink:

[0056] d. At room temperature, weigh 20mg of copolymer modified rare earth upconversion material in step c, dissolve in 1mL dimethyl sulfoxide, ultrasonic dissolve, then add 6mL glycerol and 4mL ethanol according to volume ratio 3:2, stir for 24h to obtain well dispersed rare earth upconversion material based special encryption anti-counterfeiting ink with good rubbing resistance and strong adhesion.

[0057] The special encryption anti-counterfeiting ink obtained in Example 4 is added to an ink cartridge of an inkjet printer for printing. After testing, the printed pattern of the anti-counterfeiting ink is invisible on the paper surface under visible light, and the pattern shows green fluorescence under 980 nm excitation light.

[0058] Example 5

[0059] Preparation of rare earth upconversion material:

[0060] a, at room temperature, add yttrium nitrate 0.5M, ytterbium nitrate 0.5M, holmium nitrate 0.2M, sodium hydroxide, ethanol and oleic acid in turn, stir for 20 min to be uniform, add ammonium fluoride solution 0.4M dropwise under stirring, stir for 30 min, heat at 200℃ for 8h, cool to room temperature naturally, centrifugal wash and dry to obtain oleic acid coated yttrium, ytterbium, holmium doped yttrium tetrafluoride sodium rare earth upconversion material NaYF4:Yb,Ho;

[0061] Preparation of copolymer:

[0062] b, under nitrogen atmosphere, dissolve 4-methacryloyloxybenzophenone 1mmol, vinyl pyrrolidone 10mmol, azobisisobutyronitrile 0.12mmol in dioxane, stir and heat at temperature 60℃ for 16h, then precipitate the product with diethyl ether, centrifugal, wash and dry to obtain copolymer of vinyl pyrrolidone and benzophenone;

[0063] Preparation of copolymer modified rare earth upconversion material:

[0064] c, disperse the rare earth upconversion material NaYF4:Yb,Ho obtained in step a and the copolymer of vinyl pyrrolidone and benzophenone obtained in step b into dimethyl sulfoxide solvent respectively, then slowly add the copolymer solution into the rare earth upconversion material NaYF4:Yb,Ho solution, heat at 95℃ for 8h, precipitate with anhydrous ethanol, centrifugal, wash with chloroform for 3 times, dry to obtain copolymer modified rare earth upconversion material;

[0065] Preparation of special encrypted security ink:

[0066] d, at room temperature, weigh 20mg of copolymer modified rare earth upconversion material of step c, dissolve in 1mL of dimethyl sulfoxide, ultrasonic dissolve, then add 6mL of glycerol and 4mL of ethanol according to the volume ratio of 3:2, stir for 24h to obtain well dispersed rare earth upconversion material based special encrypted security ink with good friction resistance and strong adhesion.

[0067] The special encrypted security ink obtained in example 5 is printed on cellulose paper by silk screen printing to form a security pattern, the pattern is rubbed 50 times with sandpaper and rubber respectively, under visible light, the security ink is invisible on the surface of the paper base, and still shows green fluorescence under 980nm excitation light.

Claims

1. A special encrypted anti-counterfeiting ink based on rare earth upconversion material, which is resistant to friction and has strong adhesion, characterized in that The ink is composed of copolymer modified rare earth upconversion material NaYF4:Yb, Ho and solvent, wherein the copolymer is a copolymer of vinyl pyrrolidone and benzophenone, the solvent is a mixed solution of ethanol, dimethyl sulfoxide and glycerol, the concentration of the rare earth upconversion material in the solvent is 1.8 mg / mL, and the specific operation is performed according to the following steps: a. At room temperature, yttrium nitrate, ytterbium nitrate, holmium nitrate, sodium hydroxide, ethanol and oleic acid are added in sequence, stirred for 20 min, and then ammonium fluoride solution is added dropwise under stirring, stirred for 30 min, heated at 200℃ for 8 h, naturally cooled to room temperature, and then centrifuged, washed and dried to obtain oleic acid-coated yttrium, ytterbium and holmium-doped sodium yttrium fluoride rare earth upconversion material NaYF4:Yb, Ho; b. Under a nitrogen atmosphere, 4-methacryloyloxybenzophenone, vinyl pyrrolidone and azobisisobutyronitrile are dissolved in dioxane, stirred and heated at a temperature of 60℃ for 16 h, and then the product is precipitated with diethyl ether, centrifuged, washed and dried to obtain a copolymer of vinyl pyrrolidone and benzophenone; c. The rare earth upconversion material obtained in step a and the copolymer of vinyl pyrrolidone and benzophenone obtained in step b are dispersed in dimethyl sulfoxide solvent respectively, then the copolymer of vinyl pyrrolidone and benzophenone solution is slowly added dropwise into the rare earth upconversion material solution, heated to 95℃ for refluxing for 8 h, precipitated with anhydrous ethanol, washed with chloroform for 3 times, and dried to obtain the copolymer modified rare earth upconversion material; d. At room temperature, the copolymer modified rare earth upconversion material obtained in step c is dissolved in dimethyl sulfoxide, ultrasonically dissolved, then glycerol and anhydrous ethanol are added in a volume ratio of 3:2, stirred for 24 h, and then a rare earth upconversion material-based special encryption anti-counterfeiting ink with good dispersion, strong adhesion and resistance to friction is obtained.

2. Use of the rare earth upconversion material-based special encryption anti-counterfeiting ink with strong adhesion and resistance to friction according to claim 1 in silk screen printing, inkjet printing, pen brush writing or seal making.

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