Multicolor leuco dye developing ink composition and preparation method thereof

Abstract

According to the multicolor leuco dye developing ink composition and the preparation method thereof disclosed by the invention, by designing three types of leuco dyes of purple red, yellow and ink colors and optimizing the molecular structure and response mechanism of the three types of leuco dyes, multicolor synergistic developing is realized in a breakthrough manner, and the color gamut coverage of a developing system is enriched; dye combinations with structural complementarity and thermal / optical / acid-base response differentiation characteristics are selected, and a proper color developing agent and carrier system is matched, so that the dispersion stability and the color developing resolution of a multi-dye composite system are remarkably improved, and color developing cross interference is avoided; by optimizing the ratio of the dye to the color developing agent and finely adjusting the color developing trigger conditions (such as temperature, pH value and the like), the consistency control of the color developing intensity and the color tone is realized, and the reproducibility and the practicability of an ink printing pattern in different batches are remarkably improved; and a low-toxicity environment-friendly solvent or a water-based dispersion system is preferably selected as a carrier, so that the obtained ink is more suitable for environment-friendly requirements of green printing and special scenes.

Description

Technical Field

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

[0002] Leaky color-developing inks are functional inks that change from a colorless or light-colored state to a visible color under external stimuli (such as temperature, ultraviolet light, friction, moisture, or acidic / alkaline environments). They are widely used in areas such as product anti-counterfeiting, information concealment, document verification, and smart packaging. The core technology of this type of ink lies in the combined structure of leaky dyes and color developers. Their color-developing mechanisms typically include photochromism, thermochromism, water-induced color development, or pH response.

[0003] Currently, relevant research and industrial technologies have developed various color-developing mechanisms and dye types. For example, CN102898895A discloses a water-based color-developing ink that, by introducing a fluorescent colorant, produces yellow, red, or green fluorescent color-developing effects under the influence of water, for use in letterpress printing anti-counterfeiting patterns. CN107286753A proposes using coated nano-dyes in cigarette tipping paper, causing the pattern to change from transparent to one of red, green, or yellow upon contact with water, for visual switching in anti-counterfeiting. Furthermore, CN113817358B proposes a water-based color-developing ink that achieves irreversible color development through the combined use of a veil dye and a color-developing ink pen, offering both environmental friendliness and ease of operation. Regarding multi-color color development control, CN101760075A provides a dual-color-developing ink, which uses two colorants with different response mechanisms in combination, allowing the ink to display purple and green under different triggering conditions, thus increasing the complexity of anti-counterfeiting measures. CN103897493B proposes the combined use of invisible ink and color-developing stamp ink to achieve selective color development of images and text.

[0004] However, existing technologies still have significant limitations in the practical application of invisible color-developing inks:

[0005] (1) Limited color development and limited color spectrum coverage: Most existing luminescent inks mainly achieve single or dual color development such as red, blue, and black, which is difficult to meet the multi-color development requirements of highly complex patterns or information encoding. For example, medium-dark color development systems such as black and magenta are rarely involved in the existing technology.

[0006] (2) Difficulty in dye compounding and poor system stability: Different types of dyes (such as indophthalides, fluoranes, and aromatic amines) have different color development mechanisms and solvent compatibility, making it difficult for them to coexist in the same ink system, which can easily lead to problems such as uneven dispersion, color development interference, and poor storage stability.

[0007] (3) Poor color reproduction and insufficient color development control precision: It is difficult to control the ratio between compound dye and color developer. The color after development is easily affected by environmental and operating conditions, resulting in poor color consistency and failing to meet the needs of high-standard graphic output or batch application.

[0008] (4) Insufficient environmental protection and adaptability: Some traditional leuco dyes or color developers still require the use of toxic or highly volatile organic solvents, which makes it difficult to meet the environmental protection requirements of green printing, food packaging or children's products.

[0009] Therefore, there is an urgent need to develop a new type of veil color developing ink composition that has multi-color development capability, strong dye structure complementarity, stable and controllable color development, and meets environmental protection requirements, so as to solve the core problems of existing technologies in multi-color synergy, color development stability, and application adaptability. Summary of the Invention

[0010] To address the shortcomings of existing leucochromic ink compositions in terms of color variety, formulation synergy, color development stability, and environmental performance, this invention provides a multi-color leucochromic dye ink composition and its preparation method. By designing three types of leucochromic dyes—purple-red, yellow, and black—and optimizing their molecular structure and response mechanism, a breakthrough is achieved in multi-color synergistic color development, enriching the color gamut coverage of the color development system. By selecting dye combinations with complementary structures and differentiated thermal / light / acid-base responses, and matching suitable color developers and carrier systems, the dispersion stability and color resolution of the multi-dye composite system are significantly improved, avoiding cross-interference in color development. By optimizing the dye-to-color developer ratio and fine-tuning the color development triggering conditions (such as temperature and pH), consistent control of color intensity and hue is achieved, significantly improving the reproducibility and practicality of ink printing patterns across different batches. The preferred carrier is a low-toxicity, environmentally friendly solvent or aqueous dispersion system, making the resulting ink more suitable for green printing and environmentally friendly requirements in special scenarios (such as food packaging and security anti-counterfeiting labels). This invention solves a series of key technical problems in traditional technologies, such as "limited types of color development, difficulty in dye synergy, poor color development stability, and insufficient environmental friendliness," by systematically constructing a multi-color leuco dye composition and a synergistic color development system. It provides reliable technical support for scenarios such as complex information labeling, anti-counterfeiting verification, and customized printing. It can be applied to fields such as anti-counterfeiting printing, carbonless copying, children's drawing, and information interaction labels, and has good practicality and promotional value.

[0011] The objective of this invention is achieved through the following technical solution:

[0012] A multicolor leuco dye developing ink composition comprises the following components (by weight): 0.01-15 parts of leuco dye, 10-40 parts of film-forming resin, 20-60 parts of solvent system, and 0.5-5 parts of additives, wherein:

[0013] The leuco dye is two or three of the following: yellow dye, magenta dye, and black dye;

[0014] When the leuco dye is a yellow dye, a magenta dye, or a black dye, the mass ratio of the yellow dye, the magenta dye, and the black dye is 0.01~5:0.02~8:0.01~5;

[0015] The yellow dye is N,N-dimethyl-4-(2-(2-(octyloxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline;

[0016] The purple-red dye is one, two, or three of the following: 3,3-bis(2-ethyl-1-decyl-1H-indole-3-yl)phthalide, 3,3-bis(2-methyl-1-octyl-1H-indole-3-yl)-4,5-dimethylphthalide, 3,3-bis(2-methyl-1-octyl-7-methoxy-1H-indole-3-yl)phthalide, 3,3-bis(2-methyl-1-octyl-1H-quinolin-3-yl)phthalide, and 3,3-bis(2-methyl-1-octyl-1H-indole-3-yl)naphthylphthalide.

[0017] The black dye is one or two of the following: 3-N-isohexyl-N-ethylamino-6-methyl-7-phenylaminofluorane, 3-N-isopentyl-N-ethylamino-6-methyl-7-(4-methoxyphenylamino)fluorane, 3-N-isopentyl-N-ethylamino-6-methyl-7-quinolineaminofluorane, 3-N-isopentyl-N-ethylamino-6-ethyl-7-phenylaminofluorane, and 3-N-isopentyl-N-ethylamino-6-methyl-7-(3,4-dimethoxyphenylamino)fluorane.

[0018] The film-forming resin is used as the ink skeleton and film-forming medium, and is one of alkyd resin, phenolic resin, acrylate, polyurethane emulsion, waterborne acrylic emulsion, etc.

[0019] The solvent system is an environmentally friendly solvent or a water-based system, specifically one or more of propylene glycol methyl ether, ethanol, butanol, water, and water / ethanol mixtures.

[0020] The additives are used to enhance the stability and printability of the system, and are one or more of the following: dispersants, defoamers, leveling agents, antisettling agents, UV stabilizers, surfactants, preservatives, and water-based wetting agents.

[0021] A method for preparing the above-mentioned multicolor leuco dye color-developing ink composition includes the following steps:

[0022] Step 1, Pre-dispersion stage: Add the leuco dye to the solvent system and pre-disperse it for 10-30 minutes using a stirring device to ensure that the dye is completely wetted and dissolved;

[0023] Step 2: Add color developer, film-forming resin and additives: Add film-forming resin and additives in sequence, and keep stirring until the system viscosity is suitable and a stable dispersion system is formed;

[0024] Step 3, Filtration and Filling: Filter with 200-mesh filter cloth to remove impurities, and finally obtain transparent or light-colored ink. Pack and seal for storage.

[0025] The multicolor leuco dye color-developing ink composition of the present invention can be applied to the surface of paper, plastic film, labels, or packaging materials by means of screen printing, flexographic printing, gravure printing, or inkjet printing. The initial pattern is invisible. After treatment with an external color developer (such as one or more of bisphenol A, bisphenol F, phenol derivatives, organic acids (such as phthalic anhydride), metal ion complexes, specific acidic polymers, and proton donor type auxiliaries), the pattern appears as yellow, purplish-red, or black in different areas. The color development response can be controlled under different conditions according to the selected dye type. For example, purplish-red dyes are mainly thermo- or photo-induced (response temperature is 60~90℃ or 365 nm ultraviolet light irradiation); yellow dyes are more sensitive to friction, acids and alkalis, or local heating; black dyes are mainly acid-responsive, with the most obvious color development at pH 3~6.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] 1. Rich Color Variety and Wide Color Gamut: This invention utilizes a systematic design of three types of leuco dyes—purple-red, yellow, and black—and employs a compound structure and multi-response mechanism. This allows the ink to achieve independent or combined display of multiple colors within a single system, expanding the color range of traditional leuco inks, which are primarily red and blue. It is suitable for complex patterns and multi-channel information labeling scenarios. It can achieve high-contrast color output of at least three colors, with a color rendering ΔE... ab value > 50 ( Figures 1-5 ).

[0028] 2. Good compatibility between dyes and stable system: By selecting structurally complementary dye molecules (such as indophthalides and fluoranes) and rationally designing the solvent and auxiliary agent system, problems such as uneven dispersion, color interference, or sedimentation when multiple dyes coexist are effectively solved, achieving stability during long-term storage and use. The ink shows less than 5% sedimentation after aging at 40℃ for 7 days; there is no obvious stratification or visible particles.

[0029] 3. Sensitive color development and precise response: The dye structure used is optimized, with clearly defined response temperature or pH thresholds. The color development process is fast and the reaction is thorough, with good controllability and repeatability. Thermochromic response time is <10 seconds, photochromic response is visible within 3 seconds under UV365nm, and the pH response window can be controlled between 3 and 6.

[0030] 4. Green and environmentally friendly with a wide range of applications: Utilizing low-toxicity or water-based solvent systems, and employing environmentally friendly materials as color developers (such as bisphenol F replacing bisphenol A), significantly reducing volatile organic compound (VOC) emissions. Suitable for fields with high environmental requirements, such as food packaging and children's products. VOC emissions are controlled below 50 g / L, meeting the national standard for low-volatile inks.

[0031] 5. Strong processing adaptability and easy to use: The ink viscosity and surface tension of this invention are adjustable, making it suitable for various conventional printing methods such as screen printing, flexographic printing, gravure printing, and inkjet printing. The color development process does not rely on complex equipment; users can trigger color development simply by heating, rubbing, or irradiating with ultraviolet light. It can be used on conventional printing lines without equipment modification, and the color development control accuracy is ±3℃ or ±0.3 pH.

[0032] 6. Enhanced Anti-counterfeiting Complexity and Security: The multi-color collaborative concealment and display capability achieved by this invention significantly increases the technical barriers and anti-counterfeiting difficulty of the product. Through color combinations, response condition settings, and printing position encoding, customized anti-counterfeiting patterns can be realized, which are difficult to imitate and copy, achieving a triple information security structure of "multi-color display + condition triggering + position encryption". Attached Figure Description

[0033] Figure 1 The inks are different colors of occult ink, from left to right: magenta, yellow, and black.

[0034] Figure 2 The color development effect of yellow leuco dye;

[0035] Figure 3 The color development effect of the purplish-red leuco dye;

[0036] Figure 4 To achieve the color rendering effect of ink-colored elliptical dyes;

[0037] Figure 5 The effect is shown after both purplish-red and yellow leuco dyes are used to develop color. Detailed Implementation

[0038] 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.

[0039] Example 1: Multicolor Ink Composition Suitable for Screen Printing

[0040]

[0041] Preparation steps:

[0042] (1) Pre-disperse the three leuco dyes in propylene glycol methyl ether and stir for 30 minutes;

[0043] (2) Add alkyd resin, ethanol and various additives in sequence, and mix well;

[0044] (3) After filtration, the ink is filled to form ink suitable for screen printing (viscosity is about 3000~5000 mPa·s, surface tension is about 35~40 mN / m).

[0045] Instructions for use: Use a 200-mesh screen to print the ink onto coated paper, label paper, or plastic sheet; the initial pattern is invisible; after treatment with an external developer (such as a developer pen, spray, or stamp), the pattern will appear in yellow, magenta, or black by area.

[0046] Example 2: A Leaky Ink Composition Suitable for Flexographic Printing

[0047]

[0048] Preparation steps:

[0049] (1) Disperse the leuco dye in deionized water using a high-shear apparatus;

[0050] (2) Add water-based acrylic emulsion and additives;

[0051] (3) After stirring evenly, filter to obtain low viscosity water-based flexographic printing ink (viscosity is about 150~180 mPa·s, surface tension is 28~33 mN / m).

[0052] Application method: Flexographic printing on film or food packaging materials; the pattern is invisible to the naked eye; specific areas are triggered by the developer stamp, resulting in bright color contrast, suitable for high-speed roll-to-roll printing.

[0053] Example 3: A Leaky Ink Composition Suitable for Inkjet Printing

[0054]

[0055] Preparation steps:

[0056] (1) The dye was added to ethylene glycol and deionized water and dispersed using ultrasound;

[0057] (2) Add the polyurethane dispersion and additives, and mix thoroughly;

[0058] (3) After filtering (0.45 µm), inject into the inkjet printing cartridge (viscosity is about 10~30 mPa·s, surface tension is 22~30 mN / m).

[0059] How to use:

[0060] Using modified inkjet printers, ink is printed onto porous paper or label materials; the output image and text are indistinct; subsequently, the image is revealed in color by spraying with a color developer or by handwriting a color developer pen, making it suitable for anti-counterfeiting of customized documents.

[0061] In the above embodiments, the color developer is used as follows:

[0062] (1) Color developer pen: The color developer is prepared into a writing pen, and the color appears after the user writes in the designated area;

[0063] (2) Color developing stamp: Mix the color developer with the ink and apply it to the stamp to trigger the pattern to appear;

[0064] (3) Color developing spray: The color developing agent is made into a low-concentration spray and sprayed on the surface to show the pattern.

[0065] Color type matching:

[0066] (1) Yellow dyes: Bisphenol-based color developers (e.g., bisphenol F);

[0067] (2) Purple-red dyes: acid anhydride color developers (e.g., phthalic anhydride);

[0068] (3) Ink-colored dyes: phenols or acidic conditions (e.g., 4-methylphenol or polystyrene sulfonate).

Claims

1. A multi-color leuco dye color developing ink composition characterized in that The composition comprises the following components in parts by mass: 0.01-15 parts of leuco dye, 10-40 parts of film-forming resin, 20-60 parts of solvent system and 0.5-5 parts of auxiliary agent, wherein: the leuco dye is two or three of yellow dye, purple red dye and black dye.

2. The multicolour leuco dye developer ink composition according to claim 1 characterised in that When the leuco dye is yellow dye, purple red dye and black dye, the mass ratio of yellow dye, purple red dye and black dye is 0.01-5:0.02-8:0.01-5.

3. The multicolour leuco dye developing ink composition according to claim 1 or 2, characterized in that The yellow dye is N,N-dimethyl-4-(2-(2-(octyloxy)phenyl)-6-(4-methoxyphenyl)pyridin-4-yl)aniline.

4. The multicolour leuco dye developing ink composition according to claim 1 or 2, characterized in that The purple red dye is one, two or three of 3,3-bis(2-ethyl-1-decyl-1H-indol-3-yl)phthalide, 3,3-bis(2-methyl-1-octyl-1H-indol-3-yl)-4,5-dimethylphthalide, 3,3-bis(2-methyl-1-octyl-7-methoxy-1H-indol-3-yl)phthalide, 3,3-bis(2-methyl-1-octyl-1H-quinolin-3-yl)phthalide and 3,3-bis(2-methyl-1-octyl-1H-indol-3-yl)naphthalophthalide.

5. The multicolour leuco dye developing ink composition according to claim 1 or 2, characterized in that The black dye is one or two of 3-N-isohexyl-N-ethylamino-6-methyl-7-anilino fluorophore, 3-N-isopentyl-N-ethylamino-6-methyl-7-(4-methoxyanilino) fluorophore, 3-N-isopentyl-N-ethylamino-6-methyl-7-quinolinylamino fluorophore, 3-N-isopentyl-N-ethylamino-6-ethyl-7-anilino fluorophore and 3-N-isopentyl-N-ethylamino-6-methyl-7-(3,4-dimethoxyanilino) fluorophore.

6. The multicolour leuco dye developer ink composition according to claim 1 characterised in that The film-forming resin is one of alkyd resin, phenolic resin, acrylate, polyurethane emulsion and water-based acrylic emulsion; the solvent system is environmentally friendly solvent or water-based system; and the auxiliary agent is one or more of dispersant, defoamer, leveling agent, anti-settling agent, ultraviolet stabilizer, surfactant, preservative and water-based wetting agent.

7. The multicolour leuco dye developer ink composition according to claim 1 characterised in that The solvent system is one or more of propylene glycol methyl ether, ethanol, butanol, water and water / ethanol mixture.

8. A process for the preparation of a multi-colour leuco dye developer ink composition according to any one of claims 1 to 7 characterised in that The method comprises the following steps: Step one, pre-dispersion stage: adding leuco dye into solvent system and pre-dispersing with stirring device to make the dye completely wet and dissolve; Step two, adding color developer, film-forming resin and auxiliary agent: adding film-forming resin and auxiliary agent in sequence and keeping stirring until a stable dispersion system is formed; Step three, filtering and filling: filtering with filter cloth to remove impurities and finally obtaining transparent or light-colored leuco ink which is packaged and stored.

9. Application of the multicolor leuco dye color developing ink composition of any one of claims 1-7 to the surface of paper, plastic film, label or packaging material.

10. Use of the multicolour leuco dye developer ink composition according to claim 9 on the surface of paper, plastic film, label or packaging material, characterised in that The multicolor leuco dye color developing ink composition is applied to the surface of paper, plastic film, label or packaging material by screen printing, flexographic printing, gravure printing or inkjet printing, and the initial pattern is invisible; after being treated with external color developer, the pattern appears as yellow, purple red or black by area.

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