Method for preparing large-area structural chromogenic pattern by ink-jet printing and anti-counterfeiting method based on structural color change

Abstract

A method for preparing a large-area structural chromogenic pattern by ink-jet printing, a structural chromogenic pattern obtained by the method, and an anti-counterfeiting method based on a structural color change. A dispersion liquid containing mono-disperse colloidal microspheres with high index of refraction is printed onto a piece of paper by using an ink-jet printer, and nano-microspheres are arranged and assembled on the paper to obtain a micro-structure having the features of being ordered from a short distance and disordered from a long distance. A pretty structural color can be observed by means of the interaction of the structure with light, thus displaying a pattern, changing the angle of observation, changing the brightness of the structural color, and hiding and displaying the pattern. The method is simple and convenient, is widely applicable, and can achieve the preparation and anti-counterfeiting of a large-area structural color without external stimulation.

Claims

1. A method for preparing a structural chromogenic pattern by ink-jet printing, comprising: (1) preparing a plurality of inks including a first ink and a second ink, each ink containing mono-disperse colloidal microspheres having a refractive index greater than 2, wherein the first ink contains a first mono-disperse colloidal microspheres having a first average particle diameter, and the second ink contains a second mono-disperse colloidal microspheres having a second average particle diameter, and the first average particle diameter differs from the second average particle diameter, wherein the first mono-disperse colloidal microspheres and the second mono-disperse colloidal microspheres are made of a same material; (2) designing a pattern having two or more different colors through computer software; and (3) using the plurality of inks prepared in step (1) to print the pattern designed in step (2) on paper through ink-jet printing technology to obtain the structural chromogenic pattern.

2. The method according to claim 1, wherein the first mono-disperse colloidal microspheres and the second mono-disperse colloidal microspheres are made of cadmium sulfide, cuprous oxide, titanium dioxide, zinc sulfide, or zinc oxide, and the first average particle diameter and the second average particle diameter are in a range of 90 nm to 400 nm.

3. The method according to claim 1, wherein, in the first ink or the second ink, a content of the mono-disperse colloidal microspheres is 5 wt % to 20 wt %, a content of an additive is 5 wt % to 15 wt %, a content of ethanol is 8 wt % to 20 wt %, a content of the glycerol is 1 wt % to 5 wt %, a content of a surfactant is 2 wt % to 5 wt %, a content of a defoaming agent is 0.1 wt % to 0.2 wt %, a content of an adhesive is 1 wt % to 4 wt %, a content of a pH regulator is 2 wt % to 4 wt %, and the balance is the deionized water, wherein the additive is an organic solvent having a boiling point higher than 180° C.

4. The method according to claim 3, wherein the additive is ethylene glycol, diethylene glycol, or formamide.

5. The method according to claim 3, wherein the surfactant is OP-10 or polyvinylpyrrolidone.

6. The method according to claim 3, wherein the defoaming agent is tributyl phosphate.

7. The method according to claim 3, wherein the adhesive is polyvinyl alcohol, polyurethane resin, or acrylic resin.

8. The method according to claim 3, wherein the pH regulator is triethanolamine, diethanolamine, or ethanolamine.

9. The method according to claim 3, wherein the paper is coated paper, resin coated photo paper, and high gloss photographic paper.

10. The large-area structural chromogenic pattern on paper obtained by the method according to claim 1.

11. A method for anti-counterfeiting, comprising: printing the structural chromogenic pattern according to the method of claim 1; and viewing the structural chromogenic pattern with a vertical incident angle of less than or equal to 30°.

12. The method for anti-counterfeiting according to claim 11, wherein the structural chromogenic pattern is a matrix code and the observing step is carrying out using a scanning device.

13. The method according to claim 1, wherein the first ink is prepared by: mixing the first mono-disperse colloidal microspheres, an additive that is an organic solvent with a boiling point greater than 180° C., ethanol, glycerol, surfactant, a defoaming agent, an adhesive, a pH regulator and deionized water to form a mixture; and performing ultrasonic dispersion on the mixture to obtain a stable solution as the first ink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1a, 1b and 1c illustrate respectively a digital photo, a scanning electron microscope image and a reflection spectrum image of a large-area red structural color pattern printed by ink-jet printing in example 1;

(2) FIGS. 2a, 2b and 2c illustrate respectively a digital photo, a scanning electron microscope image and a reflection spectrum image of a large-area green structural color pattern printed by ink-jet printing in example 2;

(3) FIG. 3a illustrates a hidden digital photo of a pattern in example 3, and the whole pattern is all yellow;

(4) FIG. 3b illustrates a displayed digital photo of the pattern in example 3, the butterfly in the upper left corner is red, the butterfly in the lower right corner is green, and the rest is yellow;

(5) FIG. 4 panel a and panel b illustrate digital photos of a quick-response matrix code when being hidden in example 4, the whole pattern is all yellow; and

(6) FIG. 4 panel c and panel d illustrate digital photos of the quick-response matrix code when being displayed in example 4, a red QR code can be observed in FIG. 4 panel c, the rest is yellow; and a green QR code is observed in FIG. 4 panel d, and the rest is yellow.

DETAILED DESCRIPTION OF THE INVENTION

(7) The examples in the invention are described with reference to the drawings, so that the invention can be better understood by those skilled in the art, and the protection scope of the invention can be defined.

Example 1

(8) A large-area red structural color pattern is obtained by ink-jet printing of CdS ink.

(9) Firstly, mono-disperse CdS colloidal microspheres were prepared, and the detailed preparation method was as follows:

(10) 5 g of polyvinylpyrrolidone (PVP) powder was added into 150 mL of diethylene glycol, then cadmium nitrate and thiourea powder with equal amount of substance were added, wherein the amount of substance of the cadmium nitrate and the thiourea was 20 mmol, and then the mixture was stirred until all the powder was completely dissolved. The above solution was heated to 160° C. and thermal reaction for 5 h, then naturally cooled to a room temperature, and a product was centrifuged and then dried after washing with ethanol and water for 3 times. Mono-disperse CdS nano-particles with an average particle diameter of 335 nm were obtained.

(11) A certain amount of the mono-disperse CdS microsphere powder obtained above was fully grinded, wherein a content of the mono-disperse CdS microspheres added was 12 wt %, a content of ethylene glycol was 5 wt %, a content of ethanol was 10 wt %, a content of glycerol was 5 wt %, a content of PVP was 2.7 wt %, a content of tributyl phosphate was 0.1 wt %, a content of polyvinyl alcohol was 1 wt %, a content of triethanolamine was 3 wt %, and the balance was deionized water. Ultrasonic processing was performed for 30 min to prepare uniformly dispersed ink.

(12) The prepared ink is fed into an ink box, and the designed pattern is printed by an ink-jet printer, so that CdS nano-particles in the ink are uniformly deposited on high-gloss photo paper to obtain a micro-structure ordered in short range and disordered in long range, as shown in FIG. 1a, a large-area red structural color pattern is obtained.

Example 2

(13) A large-area green structural color pattern is obtained by ink-jet printing of CdS ink.

(14) Firstly, mono-disperse CdS colloidal microspheres were prepared, and the detailed preparation method was as follows:

(15) 5 g of polyvinylpyrrolidone (PVP) powder was added into 150 mL of diethylene glycol, then cadmium nitrate and thiourea powder with equal amount of substance were added, wherein the amount of substance of the cadmium nitrate and the thiourea was 15 mmol, and then the mixture was stirred until all the powder was completely dissolved. The above solution was heated to 162° C. and thermal reaction for 6 h, then naturally cooled to a room temperature, and a product was centrifuged and then dried after washing with ethanol and water for 3 times. Mono-disperse CdS nano-particles with an average particle diameter of 270 nm were obtained.

(16) A certain amount of the mono-disperse CdS microsphere powder obtained above was fully grinded, wherein a content of the mono-disperse CdS colloidal microspheres added was 15 wt %, a content of ethylene glycol was 5 wt %, a content of ethanol was 10 wt %, a content of glycerol was 5 wt %, a content of PVP was 3 wt %, a content of tributyl phosphate was 0.1 wt %, a content of polyvinyl alcohol was 1.5 wt %, a content of triethanolamine was 3 wt %, and the balance was deionized water. Ultrasonic processing was performed for 30 min to prepare uniformly dispersed ink.

(17) The prepared ink is fed into an ink box, and the designed pattern is printed by an ink-jet printer, so that CdS nano-particles in the ink are uniformly deposited on high-gloss photo paper, as shown in FIGS. 2a-2c, a large-area green structural color pattern is obtained.

Example 3

(18) Preparation of a large-area structural color pattern, and its hide or display based on a structural color brightness change.

(19) Firstly, mono-disperse CdS colloidal microspheres with different particle diameters were prepared, and the detailed preparation method was as follows:

(20) 5 g of polyvinylpyrrolidone (PVP) powder was added into 150 mL of diethylene glycol solution, then cadmium nitrate and thiourea powder with a molar ratio of 1 were added, and stirring was performed until all the powder was completely dissolved. The above solution was heated to 150-160° C. and thermal reaction for 5 h, then naturally cooled to a room temperature, and a product was centrifuged and washed with ethanol and water for 3 times, then was dried and grinded to obtain CdS powder with particle diameter of 270 nm.

(21) 4.5 g of polyvinylpyrrolidone (PVP) powder was added into 150 mL of diethylene glycol solution, then cadmium nitrate and thiourea powder with a molar ratio of 1 were added, and stirring was performed until all the powder was completely dissolved. The above solution was heated to 150-160° C. and thermal reaction for 5 h, then naturally cooled to a room temperature, and a product was centrifuged and washed with ethanol and water for 3 times then was dried and grinded to obtain CdS powder with particle diameter of 290 nm.

(22) 5 g of polyvinylpyrrolidone (PVP) powder was added into 150 mL of diethylene glycol solution, then cadmium nitrate and thiourea powder with a molar ratio of 1 were added, and stirring was performed until all the powder was completely dissolved. The above solution was heated to 150-160° C. and thermal reaction for 5 h, then naturally cooled to a room temperature, and a product was centrifuged and washed with ethanol and water for 3 times, then was dried and grinded to obtain CdS powder with particle diameter of 335 nm.

(23) A certain amount of mono-disperse CdS microsphere powder with the three particle diameters above was fully grinded respectively for preparing inks respectively to print different parts of the pattern. For the preparation of the ink, a content of mono-disperse colloidal microspheres added was 15 wt %, a content of ethylene glycol was 5 wt %, a content of ethanol was 10 wt %, a content of glycerol was 5 wt %, a content of PVP was 3 wt %, a content of tributyl phosphate was 0.1 wt %, a content of polyvinyl alcohol was 1.5 wt %, a content of triethanolamine was 3 wt %, and the balance was deionized water. Ultrasonic processing was performed for 30 min to prepare uniformly dispersed ink. Three inks were fed into three ink boxes respectively. A pattern with two butterflies was designed through computer software, and a computer was connected with a printer.

(24) The ink is printed on high-gloss photographic paper by using an ink-jet printer, an experimental condition is a room temperature, and a large-area structural color pattern with different colors is finally obtained. As shown in FIGS. 3a and 3b, (wherein a background color is printed with ink prepared by CdS nano-particles with a particle diameter of 290 nm, and an orange-yellow structural color can be obtained), when an angle of observation is closer to vertical incidence, a contrast ratio of structural colors of two butterflies to a structural color of a background is more obvious, and a pattern with three pretty structural colors can be observed; and when the angle of observation deviates from a vertical incident angle (>30), the structural colors of the butterflies and the background are covered by the body colors, while the body colors of the butterflies and the background are similar and are all yellow. At the moment, the contrast ratio of colors of the butterflies to the background is low, and the butterflies are hidden in a background pattern.

Example 4

(25) Anti-counterfeiting application of a quick-response matrix code based on a structural color brightness change is provided.

(26) The ink in the third example is used, a quick-response matrix code with a background is generated through computer software design, and the ink is printed on high-gloss photographic paper by using an ink-jet printer to obtain a large-area pattern with two structural colors. As shown in FIG. 4, when an angle of observation is closer to vertical incidence, a contrast of colors of a matrix code to a background is more obvious, two pretty structural colors can be observed, while the matrix code can be scanned and a link is obtained. A quick-response matrix code which can be hidden or displayed is obtained, and when the pretty structural color can be observed, the matrix code can be scanned and the link is obtained; and when the angle of observation deviates from the vertical incident angle (>30), the structural colors of the matrix code and the background are covered by the body colors of the matrix code and the background, while the body colors of the matrix code and the background are both yellow. At the moment, the matrix code is hidden in the background pattern and cannot be observed, and the matrix code cannot be scanned due to the low contrast of the matrix code and the background.

Example 5

(27) A large-area red structural color pattern is obtained by ink-jet printing of ZnS ink.

(28) Firstly, mono-disperse ZnS colloidal microspheres were prepared, and the specific preparation method was as follows:

(29) A certain amount of polyvinylpyrrolidone was placed in a 250 mL three-necked flask, 75 mL of deionized water was added, and slow stirring and heating were performed. When a temperature reached 80° C., 0.01 mol of thioacetamide was added into a system, and stirred for 10 min for even mixing, 100 μL of concentrated nitric acid was added, then 0.02 mol of Zn(NO.sub.3).6H.sub.2O was prepared into 5 mL of water solution after the reaction for 10 min, and added into a three-necked flask, a rotation speed was immediately increased to mix the mixture evenly, the rotation speed was reduced to 500 rpm after a few minutes, and a reflux reaction was performed for 3 h at 75° C. A product obtained was washed with deionized water for 3 times to 4 times to obtain mono-disperse ZnS nano-particles with an average particle diameter of 230 nm. Centrifugation and vacuum drying were performed for later use.

(30) A certain amount of the mono-disperse ZnS microsphere powder was fully grinded, wherein a content of mono-disperse colloidal microspheres added was 10 wt %, a content of formamide was 10 wt %, a content of ethanol was 10 wt %, a content of glycerol was 2 wt %, a content of PVP was 2 wt %, a content of tributyl phosphate was 0.1 wt %, a content of polyvinyl alcohol was 1 wt %, a content of triethanolamine was 2 wt %, and the balance was deionized water. Ultrasonic processing was performed for 30 min to prepare evenly dispersed ink.

(31) The prepared ink is fed into an ink box, and the designed pattern is printed by using an ink-jet printer, so that ZnS nano-particles in the ink are evenly deposited on RC photographic paper, and a large-area red structural color pattern is finally obtained.