AU2020101489A4

AU2020101489A4 - Preparation method and product of stress-sensitive paper anti-counterfeiting coating

Info

Publication number: AU2020101489A4
Application number: AU2020101489A
Authority: AU
Inventors: Zhengyin Duan; Guodong Li; Wenxia Liu; Zhaoping SONG; Huili Wang; Xiangyu Wang; Dehai Yu
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2020-07-24
Filing date: 2020-07-24
Publication date: 2020-09-03
Anticipated expiration: 2028-07-24

Abstract

The invention provides a preparation method of a stress-sensitive paper anti-counterfeiting coating. Including: (1) dissolving HAuCl4 and PVP-DADMAN in water, followed by boiling, adding into it a reducing agent, stirring and reacting in absence of light, centrifuging and vacuum drying of a supernatant, to obtain modified gold nanoparticles; and(2) diluting PEOS in ASA and using it as an oil phase; dissolving the modified gold nanoparticles prepared in step (1) in water, adjusting the pH to be acidic, and using it as an aqueous phase; and ultrasonically stirring the aqueous phase and the oil phase under heating conditions, and standing, to obtain a Pickering emulsion of oil-in-water ASA, that is, the stress-sensitive paper anti-counterfeiting coating.In the invention, a stable Pickering emulsion of oil-in-water ASA can be obtained, which can effectively reduce the coalescence between ASA oil droplets and significantly improve the stability of the emulsion. The emulsion is stable for several months without precipitation of the aqueous phase and the oil phase, and does not require the addition of any surfactants and other modifiers.

Description

Preparation Method and Product of Stress-Sensitive Paper Anti-Counterfeiting Coating

Technical Field The invention belongs to the application field of nanomaterials in papermaking, and in particular

relates to a preparation technology of a stress-sensitive alkenyl succinic anhydride (ASA) paper

anti-counterfeiting emulsion.

Background Art Anti-counterfeiting coatings can be applied to product packaging and trademark design, to prevent

products from being infringed by counterfeiting and to provide a powerful means for product

producers, consumers and distributors to judge the authenticity of products. The application of

anti-counterfeiting coatings generally has the following conditions: the anti-counterfeiting

coatings involve a color change that is reversible and can be triggered at room temperature and a

color change that is stable, accurate and vivid, and they generally do not contain heavy metals,

toxic substances and corrosive acid and alkaline substances. Anti-counterfeiting coatings cannot

be put on the market as general products. An enterprise generally should have a monopolistic

production right or use right for anti-counterfeiting coatings. This requires more varieties and

performance of anti-counterfeiting coatings to be developed to meet the needs of more different

commodities. Generally, anti-counterfeiting coatings developed based on color-changing pigments

can only provide their preliminary application and function. However, the development tendency

of anti-counterfeiting coatings and anti-counterfeiting agents should be to use anti-counterfeiting

inks that can cause sensitive features such as color change and temperature change as temperature

changes, changes of light intensity and pH, magnetic field changes, or other changing factors to

print product trademarks and instructions etc. At present, the change of the color of

anti-counterfeiting coatings is closely related to the environmental humidity. In the case of very

low humidity, the coatings may lose crystal water and become discolored even without heating.

Whereas when the environmental humidity is high, it may take a higher temperature for the

coatings to lose crystal water and to display a color change. At present, in order to prevent the

influence of the environmental humidity, generally the coating film is sealed during application.

This entails a hydrophobic anti-counterfeiting coating preparation technology to make up for this

limitation.

Summary of the Invention In view of the current problems of great impact of environmental humidity on anti-counterfeiting coatings, the invention provides a preparation method of a stress-sensitive alkenyl succinic anhydride (ASA) anti-counterfeiting coating, which method can obtain an anti-counterfeiting coating with good stability to humidity without the addition of other surfactants. To achieve the above objectives, the invention adopts the following technical solutions. A preparation method of a stress-sensitive paper anti-counterfeiting coating, comprising the following steps:

(1) dissolving HAuCl 4 (tetrachloroauric acid) and PVP-DADMAN (poly(diallyldimethyl-ammonium nitrate) vinylpyrrolidone) in water, followed by boiling, adding into it a reducing agent, stirring and reacting in absence of light, centrifuging and vacuum drying of supernatant, to obtain modified gold nanoparticles; (2) diluting PEOS (polyethoxysiloxane) in ASA (alkenyl succinic anhydride) and using it as an oil phase; dissolving the modified gold nanoparticles prepared in step (1) in water, adjusting the pH to be acidic, and using it as an aqueous phase; and ultrasonically stirring the aqueous phase and the oil phase under heating conditions, and standing, to obtain a Pickering emulsion of oil-in-water ASA, that is, the stress-sensitive paper anti-counterfeiting coating. The PVP-DADMAN has a weight-average molecular weight Mw of 55-68 kg/mol, more preferably 60 kg/mol. The mass ratio of the HAuCl 4 to the PVP-DADMAN is 60:1-20:1, more preferably 35:1. The HAuCl4 preferably has a concentration of lx10-2 to lx10-4 M, more preferably 3x10-3 M. The

PVP-DADMAN preferably has a concentration of 1x 10-7 to 1x 10-5 M, more preferably 6x 10-6 M.

The reducing agent is selected from ascorbic acid or thiourea; preferably ascorbic acid. The mass ratio of the HAuCl 4 to the reducing agent is 3:1-1:5, preferably 1:2. In step (1), the time of the boiling is 1 h; the temperature of the reduction reaction is 98°C and the time of the reaction is 1 h; the speed of the centrifugation is 5000-20000 rpm and the time of the centrifugation is 5-30 min. In step (1), the modified gold nanoparticles are subhexagonal, and have an average particle size of 15-65 nm, preferably 30-45 nm. The PEOS has a weight-average molecular weight Mw of 1-3 kg/mol, more preferably 1.3 kg/mol. In step (2), the mass ratio of the PEOS to the ASA is 1:3-1:10, more preferably 1:6. In step (2), the mass ratio of the PEOS to the modified gold nanoparticles is 1:2-5:1, preferably 2:1. In step (2), a modified gold nanoparticle solution has a mass percentage concentration of 0.4-1.2%.

In step (2), the pH is 1-4, preferably 2. The acid to adjust the pH is inorganic or organic acid,

preferably selected from hydrochloric acid or citric acid. In step (2), the volume ratio of the oil phase to the aqueous phase is 1:5-1:1, preferably 1:2. The mixing of the oil phase and the aqueous phase may involve adding the aqueous phase into the oil phase or adding the oil phase into the aqueous phase, preferably adding the aqueous phase into the oil phase. In step (2), the temperature of the heating is 65-80°C, preferably 70°C. The time of the standing is 2-5 days. A paper prepared with the stress-sensitive paper anti-counterfeiting coating described above. In the invention, through the reduction reaction of PVP-DADMAN and HAuCl 4, the diallyldimethyl-ammonium nitrate long skeleton is grafted on the surfaces of the gold nanoparticles to modify the gold nanoparticles and to improve the lipophilicity thereof Then the modified gold nanoparticles are embedded by PEOS to further improve the lipophilicity thereof and to enable further affinity thereof with ASA. By adjusting the pH value to reduce the charge repulsion of the modified gold nanoparticles embedded by PEOS, dense and stable lumpy emulsifier particles are formed which wrap the ASA, and thus a stable Pickering emulsion is formed. The invention has the following advantages: In the invention, the lipophilicity of the gold nanoparticles can be effectively improved through the grafting of the diallyldimethyl-ammonium nitrate long-skeleton in the PVP-DADMAN and the PEOS embedding. The Pickering emulsion obtained has a three-phase contact angle close to 90 and a zeta potential of about 0. A stable Pickering emulsion of oil-in-water ASA is obtained, which can effectively reduce the coalescence between ASA oil droplets and significantly improve the stability of the emulsion. The emulsion is stable for several months without precipitation of the aqueous phase and the oil phase, and does not require the addition of any surfactants and other modifiers. Thus it involves steps that are simple and easy to operate.

Brief Description of the Drawings Figure 1 is a transmission electron microscopy picture of modified gold nanoparticles. Figure 2 is a microscopic picture of a Pickering emulsion of ASA. Detailed Description of the Invention The invention will be further described below with reference to examples and drawings, however, the invention is not limited to the following examples.

Example

The invention is further explained in combination with the embodiment and the drawings, but the invention is not limited by the embodiment. Embodiment 1 (1) 60 parts by weight of HAuCl 4 and 1 part by weight of PVP-DADMAN with a Mw of 68 kg/mol were each dissovled in water to obtain a HAuCl 4 solution with a concentration of 1x 10- M and a solution of PVP-DADMAN with a concentration of 5x10- M, respectively. The solutions were mixed followed by boiling for 1 h. Then 50 parts by weight of ascorbic acid were added into it, followed by stirring and reacting in absence of light for 1 h at 98 °C, and centrifuging at 10000 rpm for 15 minutes, to obtain a supernatant. The TEM picture of the supernatant was shown in Figure 1. The supernatant was vacuum dried to obtain modified gold nanoparticles with an average particle size of 65 nm. (2) 1 parts by weight of PEOS with a Mw of1 kg/mol were dissolved in 3 parts by weight of ASA and used as an oil phase. 2 parts by weight of the modified gold nanoparticles prepared in step (1) were taken and dispersed in water to formulate a solution with a mass percentage concentration of 0.4%, into which dilute hydrochloric acid was dropwise added to adjust the pH to 1, and used as an aqueous phase. The aqueous phase was added into the oil phase at a volume ratio of the oil phase to the aqueous phase of 1:5. The phases were ultrasonically stirred at room temperature for 15 minutes followed by standing for 2 days, to obtain a Pickering emulsion of oil-in-water ASA, that is, the ASA paper anti-counterfeiting coating. The sizing agent emulsion had an average particle size of 1.8 tm, and the emulsion remained unchanged for 24 h and thus had good stability. Anti-counterfeiting performance test of paper sized by ASA paper anti-counterfeiting coatings: Hydrophobic anti-counterfeiting performance: The paper tested was first surface sized by the ASA paper anti-counterfeiting coatings, with an amount of sizing agent of 8%o. As a result, the surface of the sized paper showed a color of baby blue, a surface sizing degree of 1427 seconds, and a contact angle with water of 1620. Therefore, it presented to be a superhydrophobic surface with hydrophobicity. Strain sensing anti-counterfeiting performance: Stretch sensing, in which a sized paper was put on the surface of transparent glass, and the paper was clamped by a plier and was dragged slowly by it. When observed the color change of the sized paper with an optical microscope, it could be seen that as the paper was stretched, the film changed color from baby blue to light pink, to lavender, and finally to red. Mechanical force impact sensing, in which the sized paper was spreaded horizontally with the sized side facing up. A 200 g of iron block was taken and hung over the sized paper. Then the iron block was freely fell from different heights and onto the sized paper. When observed and recorded with an optical microscope the color change of the sized paper which was impacted by the iron block, it could be seen that with the gradual increase of the falling height of the iron block, the impact points on the sized paper respectively impacted by the iron block showed a tendacy of change from blue to light pink and to red. Perforation sensing, in which the sized paper was punched (round holes) with a paper puncher. When observed the holes with naked eyes, it could be seen that the perforation edges of the sized paper showed different colors. Wherein the areas from far to near the hole edges showed a color change from light blue, to light pink, to pink, to mauveand to red. Therefore, the paper sized by the ASA paper anti-counterfeiting coatings had obvious hydrophobicity and strain-sensing properties, obvious color changes that could be distinguished with naked eyes, and thus good anti-counterfeiting performance. Embodiment 2 (1) 55 parts by weight of HAuCl 4 and 1 part by weight of PVP-DADMAN with a Mw of 68 kg/mol were each dissovled in water to obtain a HAuCl4 solution with a concentration of 1x 102 M and a solution of PVP-DADMAN with a concentration of 5x10- M, respectively. The solutions were mixed followed by boiling for 1 h. Then 70 parts by weight of ascorbic acid were added into it, followed by stirring and reacting in absence of light for 1 h at 98 °C, and centrifuging at 10000 rpm for 15 minutes, to obtain a supernatant. The TEM picture of the supernatant was shown in Figure 1. The supernatant was vacuum dried to obtain modified gold nanoparticles with an average particle size of 40 nm. (2) 2 parts by weight of PEOS with a Mw of1 kg/mol were dissolved in 12 parts by weight of ASA and used as an oil phase. 2 parts by weight of the modified gold nanoparticles prepared in step (1) were taken and dispersed in water to formulate a solution with a mass percentage concentration of 0.8%, into which dilute hydrochloric acid was dropwise added to adjust the pH to 2, and used as an aqueous phase. The aqueous phase was added into the oil phase at a volume ratio of the oil phase to the aqueous phase of 1:2. The phases were ultrasonically stirred at room temperature for 15 minutes followed by standing for 5 days, to obtain a Pickering emulsion of oil-in-water ASA, that is, the ASA paper anti-counterfeiting coating, the microscopic picture of which was shown in Figure 2. The sizing agent emulsion had an average particle size of 2 tm, and the emulsion remained unchanged for 24 h and thus had good stability. Anti-counterfeiting performance test of paper sized by ASA paper anti-counterfeiting coatings: Hydrophobic anti-counterfeiting performance: The paper tested was first surface sized by the ASA paper anti-counterfeiting coatings, with an amount of sizing agent of 8o. As a result, the surface of the sized paper showed a color of baby blue, a surface sizing degree of 1227 seconds, and a contact angle with water of 159°. Therefore, it presented to be a superhydrophobic surface with hydrophobicity. Strain sensing anti-counterfeiting performance: Stretch sensing, in which a sized paper was put on the surface of transparent glass, and the paper was clamped by a plier and was dragged slowly by it. When observed the color change of the sized paper with an optical microscope, it could be seen that as the paper was stretched, the film changed color from baby blue to light pink, to lavender, and finally to red. Mechanical force impact sensing, in which the sized paper was spreaded horizontally with the sized side facing up. A 200 g of iron block was taken and hung over the sized paper. Then the iron block was freely fell from different heights and onto the sized paper. When observed and recorded with an optical microscope the color change of the sized paper which was impacted by the iron block, it could be seen that with the gradual increase of the falling height of the iron block, the impact points on the sized paper respectively impacted by the iron block showed a tendacy of change from blue to light pink and to red. Perforation sensing, in which the sized paper was punched (round holes) with a paper puncher. When observed the holes with naked eyes, it could be seen that the perforation edges of the sized paper showed different colors. Wherein the areas from far to near the hole edges showed a color change from blue to light blue, to pink, to mauve and to red. Therefore, the paper sized by the ASA paper anti-counterfeiting coatings had obvious hydrophobicity and strain-sensing properties, obvious color changes that could be distinguished with naked eyes, and thus good anti-counterfeiting performance. Embodiment 3 (1) 20 parts by weight of HAuCl 4 and 1 part by weight of PVP-DADMAN with a Mw of 68 kg/mol were each dissovled in water to obtain a HAuCl 4 solution with a concentration of 1x 10- M and a solution of PVP-DADMAN with a concentration of 5x10- M, respectively. The solutions were mixed followed by boiling for 1 h. Then 100 parts by weight of ascorbic acid were added into it, followed by stirring and reacting in absence of light for 1 h at 98 °C, and centrifuging at 10000 rpm for 25 minutes, to obtain a supernatant. The TEM picture of the supernatant was shown in Figure 1. The supernatant was vacuum dried to obtain modified gold nanoparticles with an average particle size of 18 nm. (2) 5 parts by weight of PEOS with a Mw of 1 kg/mol were dissolved in 100 parts by weight of ASA and used as an oil phase. 1 parts by weight of the modified gold nanoparticles prepared in step (1) were taken and dispersed in water to formulate a solution with a mass percentage concentration of 1.2%, into which dilute hydrochloric acid was dropwise added to adjust the pH to 4, and used as an aqueous phase. The aqueous phase was added into the oil phase at a volume ratio of the oil phase to the aqueous phase of 1:1. The phases were ultrasonically stirred at room temperature for 15 minutes followed by standing for 4 days, to obtain a Pickering emulsion of oil-in-water ASA , that is, the ASA paper anti-counterfeiting coating, the microscopic picture of which was shown in Figure 2. The sizing agent emulsion had an average particle size of 3tm, and the emulsion remained unchanged for 24 h and thus had good stability. Anti-counterfeiting performance test of paper sized by ASA paper anti-counterfeiting coatings: Hydrophobic anti-counterfeiting performance: The paper tested was first surface sized by the ASA paper anti-counterfeiting coatings, with an amount of sizing agent of 8%o. As a result, the surface of the sized paper showed a color of baby blue, a surface sizing degree of 1379 seconds, and a contact angle with water of 1630. Therefore, it presented to be a superhydrophobic surface with hydrophobicity. Strain sensing anti-counterfeiting performance: Stretch sensing, in which a sized paper was put on the surface of transparent glass, and the paper was clamped by a plier and was dragged slowly by it. When observed the color change of the sized paper with an optical microscope, it could be seen that as the paper was stretched, the film changed color from baby blue to light pink, to lavender, and finally to red. Mechanical force impact sensing, in which the sized paper was spreaded horizontally with the sized side facing up. A 200 g of iron block was taken and hung over the sized paper. Then the iron block was freely fell from different heights and onto the sized paper. When observed and recorded with an optical microscope the color change of the sized paper which was impacted by the iron block, it could be seen that with the gradual increase of the falling height of the iron block, the impact points on the sized paper respectively impacted by the iron block showed a tendacy of change from blue to light pink and to red. Perforation sensing, in which the sized paper was punched (round holes) with a paper puncher. When observed the holes with naked eyes, it could be seen that the perforation edges of the sized paper showed different colors. Wherein the areas from far to near the hole edges showed a color change from blue to light blue, to pink and to red. Therefore, the paper sized by the ASA paper anti-counterfeiting coatings had obvious hydrophobicity and strain-sensing properties, obvious color changes that could be distinguished with naked eyes, and thus good anti-counterfeiting performance.

Claims

1. A stress-sensitive paper anti-counterfeiting coating, characterized in that the preparation method thereof comprising the following steps: (1) dissolving HAuCl4 and PVP-DADMAN in water, followed by boiling, adding into it a reducing agent, stirring and reacting in absence of light, centrifuging and vacuum drying of a supernatant, to obtain modified gold nanoparticles; and (2) diluting PEOS in ASA and using it as an oil phase; dissolving the modified gold nanoparticles prepared in step (1) in water, adjusting the pH to be acidic, and using it as an aqueous phase; and ultrasonically stirring the aqueous phase and the oil phase under heating conditions, and standing, to obtain a Pickering emulsion of oil-in-water ASA, that is, the stress-sensitive paper anti-counterfeiting coating.

2. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that the PVP-DADMAN has a weight-average molecular weight Mw of 55-68 kg/mol; the PVP-DADMAN has a concentration of 1x10-7 to xi10-5 M; the mass ratio of the HAuCl 4 to the

PVP-DADMAN is 60:1-20:1; and the HAuCl4 has a concentration of 1x10-2 to 1x10-4 M.

3. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that the reducing agent is selected from ascorbic acid or thiourea; and the mass ratio of the HAuCl 4 to the reducing agent is 3:1-1:5.

4. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that, in step (1), the modified gold nanoparticles are subhexagonal and have an average particle size of 15-65 nm.

5. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that the PEOS has a weight-average molecular weight Mw of 1-3 kg/mol; the mass ratio of the PEOS to the ASA is 1:3-1:10; the mass ratio of the PEOS to the modified gold nanoparticles is 1:2-5:1; and a modified gold nanoparticle solution has a mass percentage concentration of 0.4-1.2%.

6. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that, in step (2), the pH is 1-4; and the volume ratio of the oil phase to the aqueous phase is 1:5-1:1.

7. The stress-sensitive paper anti-counterfeiting coating of claim 1, characterized in that, in step (1), the time of the boiling is 1 h; the temperature of the reduction reaction is 98°C and the time of the reaction is 1 h; the speed of the centrifugation is 5000-20000 rpm and the time of the centrifugation is 5-30 min; in step (2), the temperature of the heating is 65-80°C; and the time of the standing is 2-5 days.

8. A paper prepared with the stress-sensitive paper anti-counterfeiting coating of claim 1.