Yellow leuco dye developing ink and preparation method thereof

Abstract

According to the yellow leuco dye developing ink and the preparation method thereof disclosed by the invention, by optimizing the molecular structure of the yellow leuco dye and the matching relationship between the yellow leuco dye and a color developing agent, the ink can quickly develop under the conditions of low temperature, slight pressure or low-concentration acid / metal salt, the developing effect is distinct, and handwriting or patterns are clear and visible; by selecting a yellow leuco dye with better photostability of a color body after color development and introducing an antioxidant component, the color fading of a color development product under the irradiation of ultraviolet and visible light is effectively delayed, and the storage period of color development images and texts is prolonged; by improving an ink formula and a packaging process, the ink can keep good leuco stability in different environments such as high temperature, high humidity, low temperature and the like, and the phenomena of self color development, non-uniform color development and the like are prevented. The ink is colorless or light in color under normal conditions, can show bright yellow after being stimulated by acid, metal salt or heat, and has the characteristics of high color developing sensitivity, clean background and wide application range, and the comprehensive performance of the ink is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of ink material technology, and relates to a color-developing ink, specifically a color-developing ink containing a yellow leuco dye and its preparation method. Background Technology

[0002] Leuco dye developing inks are widely used in anti-counterfeiting printing, carbonless copy paper, thermal labels, and children's drawing supplies. These inks typically contain leuco dyes, which are initially colorless or light-colored. Under specific conditions (such as heat, pressure, or contact with acids or metal salts), their molecular structure changes, forming a conjugated system and revealing the desired color. Yellow leuco dye developing inks, with their vibrant color development and excellent invisibility, have significant application prospects in areas such as document anti-counterfeiting, packaging labeling, and educational supplies.

[0003] In the existing technology, there are various veil-color developing inks and their preparation methods in China. For example, CN1542065A discloses an anti-counterfeiting printing ink in which pigment particles are coated with a thin film containing veil-color dye and color developer. After heating, the veil-color dye reacts with the color developer to develop color, which is used for anti-counterfeiting labels. However, this technology is mainly used for heat-sensitive coatings, and its application in inks suffers from problems such as complex formulations, poor ink stability, and insufficient environmental adaptability. CN103897493A discloses an invisible color-developing printing ink and a color-developing stamp ink, which achieves anti-counterfeiting color development through the reaction of the stamp ink with the color developer in the ink. However, this solution is mainly used for anti-counterfeiting of invoices and is not suitable for flexographic printing and high-requirement anti-counterfeiting packaging. Furthermore, the color developer is prone to migration, resulting in uneven color development. In addition, carbonless copy paper technology has been developed and matured. For example, CN101722753A discloses a carbonless copy paper color development system containing zinc salicylate and terpene phenolic resin color developer. Although it improves the color development speed and antioxidant properties, the compatibility between the color developer and leuco dye is limited, and there are still shortcomings in background pollution, color development sensitivity and lightfastness.

[0004] Existing yellow leuco dye color-developing ink technologies generally suffer from the following problems:

[0005] (1) Insufficient color development sensitivity: color development requires high temperature or pressure, the color development speed is slow, and the writing is faint;

[0006] (2) Poor lightfastness: The chromophores after color development are easily faded by light exposure, affecting the durability of information;

[0007] (3) Poor environmental adaptability: The color development performance of ink is unstable due to changes in humidity and temperature. It is prone to self-coloring in high humidity and aging in high temperature.

[0008] (4) Obvious background pollution: The ink has poor color hiding effect, and there is residual background color in the pattern or text area after printing, which affects the anti-counterfeiting effect and aesthetics;

[0009] (5) Insufficient environmental friendliness of the formula: Some inks contain high VOC solvents, which do not meet the requirements of environmental protection regulations.

[0010] Therefore, there is an urgent need to develop a yellow leuco dye coloring ink with high color development sensitivity, good lightfastness, strong environmental adaptability, excellent leuco effect, and environmentally friendly formula, in order to overcome the shortcomings of existing technologies and meet the application needs of multiple fields such as anti-counterfeiting printing, carbonless copying, and children's drawing. Summary of the Invention

[0011] To address the problems of insufficient color development sensitivity, poor lightfastness, poor environmental adaptability, significant background pollution, and poor environmental friendliness in existing yellow leuco dye color-developing ink technologies, this invention provides a yellow leuco dye color-developing ink and its preparation method. By optimizing the molecular structure of the yellow leuco dye and its matching relationship with the color developer, the ink can rapidly develop color under low temperature, slight pressure, or low concentration acid / metal salt conditions, resulting in a vivid color development effect and clear visibility of text or patterns. By selecting a yellow leuco dye with better photostability after color development and introducing antioxidant components, the fading of the color-developed product under ultraviolet and visible light irradiation is effectively delayed, extending the preservation period of the color-developed images and text. Through improvements to the ink formulation and packaging process, the ink can maintain good leuco stability under different environments such as high temperature, high humidity, and low temperature, preventing self-development and uneven color development. This ink is colorless or light-colored under normal conditions, but turns bright yellow when exposed to acid, metal salts, or heat. It features high color development sensitivity, clean background, and wide applicability, significantly improving the overall performance of the ink and meeting the needs of high-performance invisible color developing inks in fields such as anti-counterfeiting printing, carbonless copying, and children's drawing.

[0012] The objective of this invention is achieved through the following technical solution:

[0013] A yellow leuco dye developing ink, based on 100 parts by total mass, mainly consists of the components shown in Table 1:

[0014]

[0015] Yellow leuco dye 0.3–1.0 parts, main solvent 50–75 parts, auxiliary solvent 5–20 parts, film-forming agent 5–15 parts, wetting agent 1–5 parts, antioxidant 0.01–0.2 parts, nonionic surfactant 0.2–0.3 parts, deionized water 0–25 parts.

[0016] The yellow leuco dyes include N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline, N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline, N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline, N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline, and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate. These yellow leuco dyes can be used alone or in combination of two or more in a specific ratio to adjust the color hue, sensitivity, and lightfastness.

[0017] The main solvent is one of anhydrous ethanol and isopropanol;

[0018] The auxiliary solvent is one of the low-VOC environmentally friendly solvents such as ethyl acetate, butyl acetate, acetone, and DPM (propylene glycol methyl ether).

[0019] The film-forming agent is one of waterborne acrylic resin, polyvinyl alcohol (PVA), waterborne polyurethane, epoxy emulsion, etc.

[0020] The wetting agent is one of PEG-400, glycerin, etc.;

[0021] The nonionic surfactants are Triton X-100, Triton X-114 (alkylphenol polyoxyethylene ethers); Pluronic L61, Synperonic PE (polyethers), etc.

[0022] The antioxidants mentioned are BHT (Butylated HydroxyToluene), BHA (Butylated HydroxyAnisole), TBHQ (Tertiary Butyl Hydroquinone), PG (Propyl Gallate), etc.

[0023] A method for preparing the above-mentioned yellow leuco dye color-developing ink includes the following steps:

[0024] Step 1: Dissolving the dye: Add the yellow leuco dye to the mixture of the main solvent and the auxiliary solvent, stir and / or ultrasonically disperse for 15-30 minutes until fully dissolved or dispersed. The stirring speed is 300-800 rpm, the ambient temperature is 15-40℃, and the ambient humidity is ≤65%.

[0025] Step 2: Add film-forming agent and additives: Slowly add film-forming agent to the solution from Step 1, continue stirring until homogeneous, then add wetting agent, antioxidant, nonionic surfactant and deionized water in sequence, and mix until homogeneous and stable;

[0026] Step 3, Filtration: Filter the ink obtained in Step 2 through an 80-100 μm filter cloth to remove impurities or undissolved particles;

[0027] Step 4: Packaging and Storage: Fill the filtered ink from Step 3 into a light-proof, sealed container and store it in a cool, dry place. The ink viscosity should be 10–60 mPa·s (adjustable according to the intended use).

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. Significantly improved colorimetric sensitivity: The yellow leuco dye used in this invention has a good electron donor structure and a high reaction rate with the colorimetric reagent. It can rapidly develop color under slightly acidic conditions (pH < 6.5), slight heat (40–60°C), or light pressure (>50 g / cm²). The colorimetric time is ≤10 seconds, and the colorimetric concentration ΔE > 30 (CIE Lab 1976 colorimetric system). Figures 1-2 ).

[0030] 2. Excellent lightfastness after color development: The introduction of substituted pyridine or quinoline rings into the chromogen structure improves conjugation and molecular stability. After 72 hours of outdoor sunlight exposure, the yellow image remains unchanged. The lightfastness rating after color development is ≥ 6 (Blue Wool Standard ISO 105-B02), superior to existing similar inks (most are 4-5).

[0031] 3. Enhanced environmental adaptability: By optimizing the ink formulation (such as using a stable solvent system and film-forming aids), the ink maintains good colorfastness within a temperature range of 0–45℃ and a relative humidity range of 20–85%, without premature color development or ink precipitation. No self-coloring or component precipitation occurred after high-temperature storage (50℃ × 7 days) or high humidity (90% RH × 48h).

[0032] 4. Reduced background contamination and enhanced invisibility: After the improved formulation, the ink is completely colorless and transparent in its undeveloped state, allowing for seamless printing on light-colored materials such as white, yellow, and light pink. After development, it exhibits high contrast. Background color ΔE < 1.5 (imperceptible to the naked eye), while after development, ΔE > 30, resulting in clear images and text.

[0033] 5. Superior Environmental Friendliness: The ink of this invention uses a low-VOC or ethanol system, complies with RoHS and REACH regulations, and can be used in applications sensitive to odor and toxicity, such as children's drawing and food packaging labels. VOC content ≤10% (by mass), and does not contain harmful solvents such as toluene and benzene.

[0034] 6. Excellent printability, suitable for various printing methods: The ink viscosity and rheology are adjustable, suitable for various processes such as flexographic printing, screen printing, and inkjet printing, and it does not clog the screen or settle, with good storage stability. Viscosity 10~60 mPa·s (25℃), shelf life ≥6 months (protected from light and sealed).

[0035] In summary, this invention employs a pyridine / quinoline structured yellow leuco dye with functional group regulation, exhibiting good solubility, structural stability, and color development reactivity. The color development system has controllable triggering, capable of color development through acid-base, heat, and pressure methods, and possesses multi-scenario adaptability. The use of environmentally friendly solvents and auxiliary components complies with green printing and safe usage standards. The ink exhibits high leucotropy and high color contrast, making it highly suitable for security anti-counterfeiting and entertainment interactive scenarios. The main performance indicators are shown in Table 2.

[0036] Table 2

[0037] Attached Figure Description

[0038] Figure 1 The image shows a comparison of the yellow leuco dye before and after color development. From left to right, the dyes are N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline, N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline, and N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline. The color-developing agent used is zinc chloride solution.

[0039] Figure 2 The effect after color development of N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline. Detailed Implementation

[0040] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0041] Example 1:

[0042] This embodiment provides a yellow leuco ink based on N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline. The raw material composition (parts by weight) is as follows: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline: 0.5 g; anhydrous ethanol: 60 g; butyl acetate: 15 g; aqueous acrylic resin (30% aqueous dispersion): 10 g; PEG-400: 3 g; BHT antioxidant: 0.1 g; Triton X-100 (nonionic surfactant): 0.3 g; deionized water: appropriate amount, adjusted to a total of 100 g.

[0043] The preparation steps are as follows: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline is added to a mixture of anhydrous ethanol and butyl acetate, stirred and ultrasonically dispersed for 15 minutes until completely dissolved; acrylic resin, PEG-400, antioxidant, surfactant and deionized water are added in sequence and stirred evenly; the mixture is filtered (using 80 µm filter cloth) to remove impurities, dispensed, sealed and stored in the dark.

[0044] Results: The ink was applied to the surface of pretreated paper using flexographic printing and was colorless to the naked eye after drying. When written on with a transparent water-based developer containing gallic acid (1 wt%), the ink rapidly turned bright yellow within 10 seconds, with a ΔE value of approximately 33. The color remained stable after 24 hours of exposure to ultraviolet (UV-A) light. No premature color development was observed after 7 days of storage at 50°C.

[0045] Example 2:

[0046] This embodiment provides a mixed yellow veil ink based on N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline. The raw material composition (parts by weight) is as follows: N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline: 0.3 g; N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline: 0.2 g; isopropanol: 55 g; ethyl acetate: 12 g; aqueous acrylic resin (30% aqueous dispersion): 10 g; PEG-600: 2 g; BHT antioxidant: 0.1 g; Triton X-114 (nonionic surfactant): 0.3 g; deionized water: appropriate amount, adjusted to 100 g. g.

[0047] The preparation steps are as follows: N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline are added to a mixture of isopropanol and ethyl acetate, stirred and ultrasonically dispersed for 15 minutes until completely dissolved; acrylic resin, PEG-600, antioxidant, surfactant and deionized water are added in sequence and stirred evenly; the mixture is filtered (using 80 µm filter cloth) to remove impurities, dispensed, sealed and stored in the dark.

[0048] Results: The ink was applied to the surface of pretreated paper using flexographic printing and was colorless to the naked eye after drying. When written on with a transparent water-based developer containing sodium benzenesulfonate (0.1 wt%), the ink rapidly turned orange-yellow within 6 seconds, with a faster color development speed and a ΔE value of approximately 38. The color remained stable after 24 hours of exposure to ultraviolet (UV-A) light. No premature color development was observed after 7 days of storage at 50°C.

[0049] Example 3:

[0050] This embodiment provides a mixed yellow leuco ink based on N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline. The raw material composition (parts by weight) is as follows: N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline: 0.25 g; N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline: 0.25 g; anhydrous ethanol: 60 g; acetone: 8 g; aqueous polyurethane emulsion (35%): 10 g; PEG-200: 2 g; Irganox 1076 antioxidant: 0.05 g; Triton... X-114 (nonionic surfactant): 0.3 g; deionized water: appropriate amount, adjust the total amount to 100 g.

[0051] The preparation steps are as follows: N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline are added to a mixture of anhydrous ethanol and acetone, stirred and ultrasonically dispersed for 15 minutes until completely dissolved; aqueous polyurethane emulsion, PEG-200, antioxidant, surfactant and deionized water are added in sequence and stirred evenly; the mixture is filtered (using 80 µm filter cloth) to remove impurities, dispensed, sealed and stored in the dark.

[0052] Results: The ink was applied to the surface of pretreated paper using flexographic printing and was colorless to the naked eye after drying. When written on with a transparent water-based developer containing ferric nitrate (0.05 wt%), the ink quickly turned into a bright pale yellow within 10 seconds, with a ΔE value of approximately 37. After 24 hours of exposure to ultraviolet (UV-A) light, the color remained stable and the ΔE value before and after exposure was ≤0.8, indicating better lightfastness. No premature color development was observed after 7 days of storage at 50°C.

[0053] Example 4:

[0054] This embodiment provides a mixed yellow leuco ink based on N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline, N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate, and N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline. The raw material composition (parts by weight) is: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline: 0.2 g; N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate: 0.1 g. g; N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline: 0.1 g; isopropanol: 50 g; DPM: 15 g; aqueous acrylic resin (30% aqueous dispersion): 10 g; PEG-600: 2 g; Irganox 1076 antioxidant: 0.05 g; Pluronic L61 (nonionic surfactant): 0.2 g; deionized water: appropriate amount, adjust the total amount to 100 g.

[0055] The preparation steps are as follows: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline, N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate and N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline are added to a mixture of isopropanol and DPM, stirred and ultrasonically dispersed for 15 minutes until completely dissolved; water-based acrylic resin, PEG-600, antioxidant, surfactant and deionized water are added in sequence and stirred evenly; the mixture is filtered (using 80 µm filter cloth) to remove impurities, dispensed, sealed and stored in the dark.

[0056] Results: The ink was applied to the surface of pretreated paper using flexographic printing. After drying, it was colorless to the naked eye. When the writing area was written with a transparent water-based developer containing gallic acid (0.5 wt%), it rapidly turned into an orange-yellow color with a bright gold hue within 3-4 seconds. The color development speed was faster than that of the two leuco dyes mixed in Example 2, with a ΔE value of approximately 41. The color remained stable after 24 hours of irradiation under ultraviolet (UV-A) light. No premature color development was observed after 7 days of storage at 50°C, and the thermal stability was better with ΔE ≤ 1.2.

[0057] Example 5:

[0058] This embodiment provides a mixed yellow leuco ink based on N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate. The raw material composition (parts by weight) is as follows: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline: 0.4 g; N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate: 0.2 g; anhydrous ethanol: 52 g; butyl acetate: 13 g; aqueous acrylic resin (30% aqueous dispersion): 12 g; PEG-4000: 1.5 g; BHT antioxidant: 0.1 g. g; Triton X-114 (nonionic surfactant): 0.2 g; Deionized water: appropriate amount, adjust the total amount to 100 g.

[0059] The preparation steps are as follows: N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate were added to a mixture of anhydrous ethanol and ethyl acetate, stirred and ultrasonically dispersed for 15 minutes until completely dissolved; aqueous acrylic resin (30% aqueous dispersion), PEG-4000, antioxidant, surfactant and deionized water were added in sequence and stirred evenly; the mixture was filtered (using 80 µm filter cloth) to remove impurities, dispensed, sealed and stored in the dark.

[0060] Results: The ink was applied to the surface of pretreated paper using flexographic printing. After drying, it was colorless to the naked eye. When the writing pressure or scratching force was greater than 8 N / cm², it quickly turned into a bright yellow with a ΔE of approximately 42. The color remained stable after 24 hours of exposure to ultraviolet (UV-A) light. No premature color development was observed after 7 days of storage at 50°C.

[0061] Different colorimetric reagents (such as ZnCl2, bisphenol S, gallic acid, and ferric nitrate) can be used to develop the colorimetric response of each dye.

[0062] Application examples: children's drawing pens, anti-counterfeiting labels, and heavy metal detection.

[0063] (1) Children's graffiti pen: The ink is filled into a transparent water-based colorless watercolor pen and comes with a color-developing backing paper. It will immediately develop a yellow color when writing. It is non-toxic, odorless, safe and environmentally friendly.

[0064] (2) Variable information tickets: Invisible ink is printed by laser engraving or micro-pressure printing. After color development, it is used for temporary QR codes and ticket verification marks. It is light resistant, scratch resistant and has good anti-counterfeiting performance.

[0065] (3) Heavy metal test strips: for Fe³⁺ + Cu² + It exhibits selective colorimetric response to heavy metal ions, making it suitable for rapid and visual heavy metal ion detection scenarios.

Claims

1. A yellow leuco dye developing ink, characterized in that... The color-developing ink, by weight, comprises the following components: 0.3-1.0 parts of yellow leuco dye, 50-75 parts of main solvent, 5-20 parts of auxiliary solvent, 5-15 parts of film-forming agent, 1-5 parts of wetting agent, 0.01-0.2 parts of antioxidant, 0.2-0.3 parts of nonionic surfactant, and 0-25 parts of deionized water.

2. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The yellow leuco dye includes one or more of N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline, N,N-diethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline, N,N-dimethyl-4-(2-(2-(nonoxy)phenyl)-6-phenylpyridin-4-yl)aniline, N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylquinoline-4-yl)aniline, and N,N-dimethyl-4-(2-(2-(octoxy)phenyl)-6-phenylpyridin-4-yl)aniline-3'-sulfonate.

3. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The main solvent is one of anhydrous ethanol and isopropanol.

4. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The auxiliary solvent is one of ethyl acetate, butyl acetate, acetone, and DPM.

5. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The film-forming agent is one of waterborne acrylic resin, polyvinyl alcohol, waterborne polyurethane, and epoxy emulsion.

6. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The wetting agent is one of PEG-400 and glycerin.

7. The yellow leuco dye color-developing ink according to claim 1, characterized in that... The antioxidant is one of BHT, BHA, and TBHQ.

8. A method for preparing a yellow leuco dye color-developing ink according to any one of claims 1-7, characterized in that... The method includes the following steps: Step 1: Dissolve the dye: Add the yellow leuco dye to the mixture of the main solvent and the auxiliary solvent, stir and / or sonicate until fully dissolved or dispersed; Step 2: Add film-forming agent and additives: Slowly add film-forming agent to the solution from Step 1, continue stirring until homogeneous, then add wetting agent, antioxidant, nonionic surfactant and deionized water in sequence, and mix until homogeneous and stable; Step 3, Filtration: Filter the ink obtained in Step 2 to remove impurities or undissolved particles; Step 4: Dispensing and Storage: Fill the filtered ink from Step 3 into a light-proof, sealed container and store it in a cool, dry place.

9. The method for preparing the yellow leuco dye color-developing ink according to claim 8, characterized in that... In step one, the stirring and / or ultrasonic dispersion time is 15-30 minutes, the stirring speed is 300-800 rpm, the ambient temperature is 15-40℃, and the ambient humidity is ≤65%; in step three, the ink viscosity is 10-60 mPa·s.

10. The application of the yellow leuco dye developing ink according to any one of claims 1-7 in children's drawing pens, anti-counterfeiting labels, and heavy metal detection.

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