Preparation methods and applications of photochromic inks

Abstract

This invention provides a method for preparing and applying a photoluminescent ink. The method involves adding a small amount of polyvinyl alcohol to a sodium tungstate dihydrate solution, then adding an appropriate amount of sulfuric acid to adjust the pH to 1.2-2.0 to obtain a tungstic acid solution. Further reaction and decomposition yield WO3, with the WO3 particles being kept small within the acidic range. Nickel sulfate hexahydrate is then added for reaction, and finally, a small amount of cuprous chloride is added to the solution and stirred to obtain the photoluminescent ink. This invention does not produce any toxic or harmful substances during the preparation of the photoluminescent ink, making it environmentally friendly and pollution-free. Furthermore, the process can be completed at room temperature, without any energy loss. The prepared photoluminescent ink can be used for writing and drawing on hydrophilic substrates such as paper and cotton cloth. Additionally, by adding an adhesive to the photoluminescent ink, patterns can be quickly printed using a stamp. After drying, the pattern becomes invisible, but it becomes visible under ultraviolet light. This method offers significant advantages in intelligent anti-counterfeiting and instant display applications.

Description

Technical Field

[0001] This invention relates to the field of photochromic technology, and more particularly to a method for preparing and applying a photochromic ink. Background Technology

[0002] In recent years, smart materials capable of responding to external stimuli such as heat, light, electricity, magnetism, force, humidity, and chemical input have attracted increasing attention. Among these stimuli, light, especially sunlight, has advantages such as easy control over parameters like precise location, wavelength, intensity, and duration of illumination, as well as unique advantages like versatility, renewability, and availability. Photochromic materials, which change color reversibly under light stimulation, have been widely developed.

[0003] Generally, photochromism requires a certain intensity of ultraviolet radiation to be activated. Ink solutions prepared using photochromic materials can become completely invisible after being dried, and only require a very low-power ultraviolet lamp to develop color. They have good applications in anti-counterfeiting and instant color development. Summary of the Invention

[0004] The purpose of this invention is to provide a simple, low-cost, and fast-responding method for preparing photochromic inks and their applications. This preparation method does not generate toxic or harmful substances, is environmentally friendly and pollution-free, and is simple to operate; moreover, it can be completed at room temperature, without energy loss through heating or heating, and is low in cost.

[0005] To achieve the above objectives, the present invention provides a method for preparing a photoluminescent ink, comprising the following steps:

[0006] S1, Prepare a sodium tungstate dihydrate solution of a predetermined concentration;

[0007] S2, add polyvinyl alcohol to the sodium tungstate dihydrate solution and stir until homogeneous to obtain a mixed solution;

[0008] S3, Add sulfuric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.2-2.0;

[0009] S4. Add nickel sulfate hexahydrate to the solution obtained in step S3 and stir to react.

[0010] S5. Add cuprous chloride to the solution obtained in step S4 and stir to react, thus obtaining the photoluminescent ink.

[0011] Further, in step S5, the mass fraction of cuprous chloride is 1-4%, and the stirring reaction time is 5-10 min.

[0012] Further, in step S2, the amount of polyvinyl alcohol added is 2-10 wt%.

[0013] Further, in step S1, the concentration of the sodium tungstate dihydrate solution is 0.1–0.2 mol / L, and the solvent used is ethylene glycol.

[0014] Furthermore, in step S3, the concentration of the added sulfuric acid is 2-3 mol / L.

[0015] Further, in step S4, the mass fraction of the nickel sulfate hexahydrate is 10-20 wt%, and the stirring reaction time is 20-30 min.

[0016] To achieve the above objectives, the present invention also provides an application of a photoluminescent ink, which is prepared by the preparation method described in any of the foregoing technical solutions; the photoluminescent ink is applied to the surface of a hydrophilic substrate by dipping a brush in the ink; the pattern becomes invisible after drying and becomes visible after being irradiated with ultraviolet light.

[0017] Furthermore, the hydrophilic substrate is a material such as paper or cotton cloth.

[0018] To achieve the above objectives, the present invention also provides an application of a photoluminescent ink, which is prepared by the preparation method described in any of the foregoing technical solutions; after adding an adhesive to the photoluminescent ink, a pattern is quickly printed using a stamp; after drying, the pattern becomes invisible, and after being irradiated with ultraviolet light, the pattern becomes visible.

[0019] Furthermore, the adhesive is polyvinyl alcohol (PVA), acrylic resin, epoxy resin, etc.

[0020] The beneficial effects of this invention are:

[0021] 1. The method for preparing photoluminescent ink provided by this invention involves adding a small amount of polyvinyl alcohol (PVA) to a sodium tungstate dihydrate solution, followed by adding an appropriate amount of sulfuric acid to adjust the pH to 1.2-2.0. Sodium tungstate (Na₂WO₄) reacts with sulfuric acid (H₂SO₄) to generate tungstic acid (H₂WO₄) and sodium sulfate (Na₂SO₄). During this process, the sulfuric acid provides an acidic environment, allowing the tungstate ions in the sodium tungstate to combine with hydrogen ions, forming tungstic acid precipitate. Further reaction decomposes the tungstate to obtain WO₃. Controlling the solution within this acidic range results in smaller WO₃ particles, enhancing their absorption of ultraviolet light energy and improving the uniformity of the resulting ink. Nickel sulfate hexahydrate is then added for further reaction, and finally, a small amount of cuprous chloride is added to the solution and stirred to obtain the photoluminescent ink. This invention does not produce toxic or harmful substances during the preparation of the photoluminescent ink, is environmentally friendly and pollution-free, and is simple to operate. Furthermore, it can be completed at room temperature, without energy loss due to electrical or thermal processes, resulting in low cost.

[0022] 2. The photochromic ink prepared by this invention can be used to draw patterns on erasable substrates such as ordinary paper and cotton fabrics. The patterns become invisible after the ink dries, but instantly appear when exposed to ultraviolet light. These patterns remain invisible even after multiple switching cycles; experiments show that this display behavior can be repeated over a thousand times. It has significant advantages in intelligent anti-counterfeiting and instantaneous display applications.

[0023] 3. The photochromic ink prepared by this invention can not only instantly develop and fade colors, but also display patterns and retain them for a certain period of time under long-term ultraviolet light irradiation. This time is related to the duration of ultraviolet light irradiation. Furthermore, it can fade and become invisible under dark / indoor natural conditions, exhibiting excellent repeatability. Attached Figure Description

[0024] Figure 1 The image shows English letters written on paper using the photochromic ink prepared in Example 1, as displayed under a UV lamp.

[0025] Figure 2 A photograph of the photochromic ink prepared in Example 1 after a pattern was drawn on paper, displayed under a UV lamp.

[0026] Figure 3 This is a physical image of the instantaneous display cycle of ink in Example 1.

[0027] Figure 4 The image shows a physical representation of the ink-drawn pattern from Example 1 under strong ultraviolet light.

[0028] Figure 5 This is a real-world example of the effect of printing a pattern on paper using ink without PVA, as shown in Example 1.

[0029] Figure 6 The image shows the actual sample used in the stability test of ink without NiSO4·6H2O for Comparative Example 2.

[0030] Figure 7 This is a display image of the ink without CuCl in Comparative Example 3 after ultraviolet irradiation.

[0031] Figure 8 Photographs of the inks prepared in Example 1 (left) and Comparative Example 3 (right). Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0034] This invention provides a method for preparing a photoluminescent ink, comprising the following steps:

[0035] S1, Prepare a sodium tungstate dihydrate solution of a predetermined concentration;

[0036] The concentration of sodium tungstate dihydrate solution is 0.1–0.2 mol / L, the solvent used is ethylene glycol, and the mixture is stirred for 5–10 min.

[0037] S2, add a small amount of polyvinyl alcohol to sodium tungstate dihydrate solution and stir until homogeneous to obtain a mixed solution;

[0038] The amount of polyvinyl alcohol added is 2-10 wt%, and the mixture is stirred for 10-15 minutes.

[0039] S3, Add sulfuric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.2-2.0;

[0040] The concentration of the added sulfuric acid is 2-3 mol / L, and stirring is continued for 10-15 minutes.

[0041] S4. Add nickel sulfate hexahydrate to the solution obtained in step S3 and stir to react; the mass fraction of nickel sulfate hexahydrate is 10-20 wt%, and the stirring reaction time is 20-30 min.

[0042] S5. Add cuprous chloride to the solution obtained in step S4 and stir to react, thus obtaining the photoluminescent ink.

[0043] The mass fraction of cuprous chloride is 1-4%, and the stirring reaction time is 5-10 min.

[0044] This invention also provides the application of the photoluminescent ink prepared according to the aforementioned preparation method; writing and drawing on the surface of a hydrophilic substrate after dipping a brush in the photoluminescent ink; the pattern becomes invisible after drying, and the pattern appears after being irradiated with ultraviolet light, responding promptly and being able to be displayed repeatedly.

[0045] The hydrophilic substrate is made of materials such as paper or cotton cloth.

[0046] Furthermore, an adhesive can be added to the photochromic ink, and a pattern can be quickly printed using a stamp; the pattern becomes invisible after drying, but appears after being irradiated with ultraviolet light, providing a timely response and allowing for repeated display.

[0047] The adhesives include polyvinyl alcohol (PVA), acrylic resin, epoxy resin, etc.

[0048] The preparation method of the photoluminescent ink provided by the present invention will be described below with reference to specific embodiments.

[0049] Example 1

[0050] This embodiment provides a method for preparing a photoluminescent ink, including the following steps:

[0051] S1, prepare a 0.1 mol / L sodium tungstate dihydrate solution with ethylene glycol and stir for 5 min;

[0052] S2, add 2wt% polyvinyl alcohol (PVA) to the sodium tungstate dihydrate solution prepared in step S1 and stir for 15 min to obtain a mixed solution;

[0053] S3, Add 2 mol / L sulfuric acid to the mixed solution obtained in step S2 to adjust the pH to 1.2;

[0054] S4. Add 20 wt% nickel sulfate hexahydrate (NiSO4·6H2O) to the solution obtained in step S3 and stir for 20 min.

[0055] S5. Add 2wt% cuprous chloride to the solution obtained in step S4 and stir for 5 minutes to obtain the photochromic ink.

[0056] A small amount of polyvinyl alcohol (PVA) is added to a sodium tungstate dihydrate solution, followed by the addition of sulfuric acid to adjust the pH to 1.2-2.0. Sodium tungstate (Na₂WO₄) reacts with sulfuric acid (H₂SO₄) to produce tungstic acid (H₂WO₄) and sodium sulfate (Na₂SO₄). During this process, the sulfuric acid provides an acidic environment, allowing the tungstate ions in the sodium tungstate to combine with hydrogen ions, forming tungstic acid precipitate. Further reaction decomposes the tungstate to produce WO₃. Controlling the solution within this acidic range results in smaller WO₃ particles, enhancing their absorption of ultraviolet light energy and improving the uniformity of the resulting ink. Nickel sulfate hexahydrate is then added to react, and finally, a small amount of cuprous chloride is added to the solution and stirred to produce the photochromic ink.

[0057] The prepared photochromic ink can be used for writing and drawing on hydrophilic substrates such as paper and cotton cloth; the pattern becomes invisible after drying and becomes visible after being exposed to ultraviolet light.

[0058] You can also add an adhesive to the photochromic ink and use a stamp to quickly print the pattern; the pattern becomes invisible after drying and becomes visible after being exposed to ultraviolet light.

[0059] Please see Figure 1 , Figure 2The image shows a photograph of English letters / patterns written on paper using the photoluminescent ink prepared in Example 1, displayed under ultraviolet light. As can be seen in the image, the letters / patterns are invisible after drying on the paper and only become visible after exposure to ultraviolet light.

[0060] Please see Figure 3 , Figure 4 The image shown is a physical representation of the ink-drawn pattern display / color retention from Example 1. Figure 3 It is known that the pattern drawn with the color-changing ink remains invisible even after repeated exposure to ultraviolet light, and the color display can be repeated more than a thousand times. This photochromic ink has significant advantages in intelligent anti-counterfeiting and instantaneous display applications.

[0061] Figure 4 It is known that after the pattern drawn with this ink is exposed to strong UV light, the pattern can be preserved for more than 72 hours, and the color will fade after 4-5 days. The pattern can still be displayed when exposed to light again.

[0062] Comparative Example 1

[0063] Comparative Example 1 provides a method for preparing a photoluminescent ink. The difference from Example 1 is that PVA is not added in step S2. The rest is roughly the same as Example 1 and will not be repeated here.

[0064] Experiments show that the absence of PVA has little effect on the stability of the solution; however, due to the high fluidity of the solution, it is prone to smudging when writing or drawing on fabric / paper surfaces. Figure 5 As shown.

[0065] Comparative Example 2

[0066] Comparative Example 2 provides a method for preparing a photoluminescent ink. The difference from Example 1 is that NiSO4·6H2O is not added in step S4. The rest is roughly the same as in Example 1, and will not be repeated here.

[0067] Experiments show that, compared with the photoluminescent ink prepared in Example 1, the stability of this solution system is reduced, and particles are prone to deposition after 12 hours of standing. Figure 6 As shown.

[0068] Comparative Example 3

[0069] Comparative Example 3 provides a method for preparing a photoluminescent ink. The difference from Example 1 is that CuCl is not added in step S5. The rest is roughly the same as in Example 1 and will not be described again here.

[0070] Experiments show that the solution has good stability, but if the ultraviolet light power is strong, it will directly retain the color and the recovery will be slow. Figure 7As shown.

[0071] Please see Figure 8 The image shows photographs of the inks prepared in Example 1 (left) and Comparative Example 3 (right). It can be seen from the image that the solution with CuCl added is bluish-black, while the solution without CuCl is cyan-green. This is due to the presence of CuCl. + After restoring WO3, WO3 was displayed in blue.

[0072] Comparative Example 4

[0073] Comparative Example 4 provides a method for preparing a photoluminescent ink. Compared with Example 1, the difference is that NiSO4·6H2O is not added in step d; CuCl is not added in step e. The rest is roughly the same as Example 1, and will not be repeated here.

[0074] Without any additives, pure tungstic acid solution has poor stability. After being left for 2-3 hours, the solution tends to deposit. When written with it as ink, it can be air-dried and become invisible. However, after being exposed to ultraviolet light, it will leave traces that take a long time to recover.

[0075] Examples 2-6 and Comparative Examples 5-7

[0076] The preparation methods of the photoluminescent inks provided in Examples 2-6 and Comparative Examples 5-7 differ from those in Example 1 in that the mass fraction of PVA in step S2, the pH value in step S3, the mass fraction of NiSO4·6H2O in step S4, and the mass fraction of cuprous chloride in step S5 are changed, as shown in the table below; the rest are roughly the same as in Example 1 and will not be repeated here.

[0077]

[0078] Comparative Examples 1-3 show that the stability of the ink increases with the increase of the mass fraction of PVA added. Compared with high-concentration PVA, low-concentration PVA is more beneficial in improving the writeability and printability of the ink. However, when the mass fraction is greater than 10 wt% (Comparative Example 5), the ink viscosity is high, which is not conducive to printing patterns, and the drying of the pattern after writing is prone to leaving marks.

[0079] Comparing Examples 1 and 6 with Comparative Examples 6-7, it can be seen that CuCl has good reducing properties and plays an important role in improving the color reduction of solution particles. However, when the CuCl content is too low, its improvement on fading ability is not significant, and when the content is too high, CuCl... + The reduction of W ions from WO3 in the system directly appears as blue-black ink. After a period of time, a large amount of Cu is released. 2+ The presence of ions has an adverse effect on the stability of the solution.

[0080] In summary, the method for preparing a photoluminescent ink provided by this invention involves adding a small amount of polyvinyl alcohol (PVA) to a sodium tungstate dihydrate solution, then adding an appropriate amount of sulfuric acid to adjust the pH to 1.2-2.0 to obtain tungstic acid. Tungstic acid readily decomposes to form WO3, and the WO3 particles obtained in this acidic range are smaller, thus enhancing their absorption of ultraviolet light energy and resulting in better ink uniformity. Nickel sulfate hexahydrate is then added to react, and finally, a small amount of cuprous chloride is added to the solution and stirred to obtain the photoluminescent ink. This invention does not produce any toxic or harmful substances during the preparation of the photoluminescent ink, is environmentally friendly and pollution-free, and is simple to operate. Furthermore, it can be completed at room temperature, without energy loss due to electrical or thermal processes, resulting in low cost. It has significant advantages in intelligent anti-counterfeiting and instantaneous display applications.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a photoluminescent ink, characterized in that, Includes the following steps: S1, prepare a sodium tungstate dihydrate solution with a concentration of 0.1~0.2 mol / L; S2, add polyvinyl alcohol to the sodium tungstate dihydrate solution and stir until homogeneous to obtain a mixed solution; the amount of polyvinyl alcohol added is 2-10 wt%. S3, Add sulfuric acid to the mixed solution obtained in step S2 to adjust the pH value to 1.2-2.0; S4. Add nickel sulfate hexahydrate to the solution obtained in step S3 and stir to react. S5. Add cuprous chloride with a mass fraction of 1-4% to the solution obtained in step S4, stir and react to obtain photochromic ink.

2. The method for preparing the photoluminescent ink according to claim 1, characterized in that: In step S5, the stirring reaction time is 5-10 min.

3. The method for preparing the photoluminescent ink according to claim 1, characterized in that: In step S1, the solvent used to prepare the sodium tungstate dihydrate solution is ethylene glycol.

4. The method for preparing the photoluminescent ink according to claim 1, characterized in that: In step S3, the concentration of the added sulfuric acid is 2-3 mol / L.

5. The method for preparing the photoluminescent ink according to claim 1, characterized in that: In step S4, the mass fraction of the nickel sulfate hexahydrate is 10-20 wt%, and the stirring reaction time is 20-30 min.

6. An application of a photochromic ink, characterized in that: The photoluminescent ink is prepared by the preparation method according to any one of claims 1-5; the photoluminescent ink is applied to the surface of a hydrophilic substrate by writing or drawing with a brush; the pattern becomes invisible after drying and becomes visible after being irradiated with ultraviolet light.

7. The application of the photoluminescent ink according to claim 6, characterized in that: The hydrophilic substrate is paper or cotton cloth.

8. An application of a photochromic ink, characterized in that: The photoluminescent ink is prepared by the preparation method according to any one of claims 1-5; after adding an adhesive to the photoluminescent ink, a pattern is quickly printed using a stamp; the pattern becomes invisible after drying and becomes visible after being irradiated with ultraviolet light.

9. The application of the photoluminescent ink according to claim 8, characterized in that: The adhesive is polyvinyl alcohol, acrylic resin, or epoxy resin.

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