Low-temperature developing anti-forgery ink composition based on acrylic acid water-based emulsion and preparation method of low-temperature developing anti-forgery ink composition

Abstract

The invention relates to a low-temperature developing anti-counterfeiting ink composition based on an acrylic water-based emulsion and a preparation method of the low-temperature developing anti-counterfeiting ink composition, and belongs to the technical field of water-based acrylic resin compositions and anti-counterfeiting printing. The composition comprises an acrylic acid water-based emulsion, a thermosensitive color-changing microcapsule, a ferric iron complexing agent, a hydroxyl polyurethane microemulsion, a cationic surface active agent, an anionic dispersing agent, a thickening agent and deionized water, wherein the core of the thermosensitive color-changing microcapsule is composed of a thermosensitive dye, a color developing agent and a hydrogen bond donor type solvent, a coating structure adopts a double-layer design, the inner layer is polymethyl methacrylate or a styrene-maleic anhydride copolymer, and the outer layer is a compound of hydroxyl polyurethane and chitosan-g-polyvinyl alcohol. The ink composition disclosed by the invention has the anti-counterfeiting performance of rapid color development at low temperature and color hiding at normal temperature, and is large in color development contrast and short in response time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water-based acrylic resin compositions, and in particular to a low-temperature color developing anti-counterfeiting ink composition based on an acrylic water-based emulsion and a preparation method thereof. BACKGROUND

[0002] Color-changing ink is a kind of functional ink with external response characteristics, and its color can change reversibly under changes in external conditions (such as temperature, light, etc.). It is widely used in anti-counterfeiting identification, commodity packaging, security paper, and other fields. In practical applications, heat-sensitive color-changing ink is widely used due to its good response to temperature changes, and is particularly suitable for temperature-sensitive anti-counterfeiting occasions such as identity verification, cold chain management, and security printing.

[0003] Most of the existing heat-sensitive color-changing inks are mainly high-temperature color developing, that is, they develop color under heating conditions, and present colorless or light-colored state at room temperature or low temperature environment. However, in some practical application scenarios, such as security paper, brand packaging authentication, or decorative paper labels, the ink needs to be in a stealth state at room temperature without affecting the appearance of the product, and only at a lower temperature can the color developing function be activated to achieve anti-counterfeiting identification. Compared with high-temperature color developing products, this type of low-temperature color developing ink has higher requirements for response temperature range, color developing condition, and use stability.

[0004] Existing low-temperature color developing inks generally have problems such as difficulty in controlling the color developing starting temperature, long response time, color unevenness, incomplete color developing / stealth conversion, and color developing effect decay after repeated use. In particular, in a water-based system, due to the influence of water-based resin on the solubility, compatibility, and environmental response behavior of the dye, traditional formulations cannot balance the color response sensitivity and film stability. In addition, the heat-sensitive color developing system often lacks effective control means, and the color developing starting point and color intensity are limited by the intrinsic properties of the material, which cannot flexibly meet the customized needs of different anti-counterfeiting levels for color developing conditions and color developing differences.

[0005] With the continuous improvement of anti-counterfeiting needs, how to construct a low-temperature color developing anti-counterfeiting ink system that does not develop color at room temperature, rapidly develops color at low temperature, has color developing reversibility, strong environmental adaptability, and high formulation stability has become a key problem that needs to be solved in this technical field. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide a low-temperature color developing anti-counterfeiting ink composition based on an acrylic water-based emulsion and a preparation method thereof.

[0007] A low-temperature color developing anti-counterfeiting ink composition based on an acrylic water-based emulsion, comprising the following components by weight: acrylic water-based emulsion 40-60 parts; Thermochromic microcapsule 5-15 parts; Ferric iron complexing agent 0.5-3 parts; Hydroxyl polyurethane microemulsion 5-20 parts; Cationic surfactant 0.2-1 part; Anionic dispersant 0.5-2 parts; Thickening agent 0.1-1 part; Deionized water 30-45 parts; The core part of the thermochromic microcapsule comprises a temperature-sensitive dye, a color developer and a hydrogen bond donor type solvent, wherein: The temperature-sensitive dye accounts for 3-10% of the core mass, which is crystal violet lactate or a benzothiazole electron donor dye; The color developer accounts for 5-15% of the core mass, which is bisphenol A or its sulfonate derivative; The ferric iron complexing agent is selected from one or both of ferric citrate or sodium phosphotungstate.

[0008] The core component of the thermochromic microcapsule used in the application comprises a temperature-sensitive dye, a color developer and a hydrogen bond donor type solvent, and the mass ratio of the three is reasonably limited to 3-10% of the dye, 5-15% of the color developer and the remaining amount of the solvent. From the perspective of structural design, the thermal response efficiency and reversible stability of the color developing system are optimized. The proportioning can not only control the response starting temperature, but also ensure that the color developing / decoloring degree remains consistent under repeated heating-cooling cycle conditions, avoiding problems such as color distortion, response delay or incomplete color development, thereby improving the repeatability and system reliability of the color developing function.

[0009] The application introduces a ferric iron complexing agent into the thermochromic system, effectively interferes with the electron transfer reaction path between the dye and the color developer, significantly changes the trigger temperature range and color developing intensity of the color development, thereby constructing a response adjustment system with a "controllable color developing window". This mechanism not only makes the boundary of color developing / decoloring conversion clearer, but also realizes personalized anti-counterfeiting control under different security levels by adjusting the type and concentration of the complexing agent, thereby significantly improving the technical threshold and adjustability of the anti-counterfeiting system.

[0010] Preferably, the thermochromic microcapsule is 8-12 microns, the inner layer coating material of the thermochromic microcapsule is polymethyl methacrylate or styrene-maleic anhydride copolymer, and accounts for 5-15% of the total mass of the microcapsule; the outer layer coating material is composed of hydroxyl polyurethane and chitosan-g-polyvinyl alcohol, and the mass ratio of hydroxyl polyurethane to chitosan graft is 2:1-5:1, and the total mass of the outer layer accounts for 3-10% of the total mass of the microcapsule.

[0011] This invention significantly improves the thermal stability, dispersibility, and repeatability of color-changing materials by employing a double-layered encapsulation structure for thermosensitive color-changing microcapsules. Specifically, the inner encapsulation material is selected from polymethyl methacrylate or styrene-maleic anhydride copolymer, which have high glass transition temperatures, to effectively isolate external moisture and mechanical shear stress, enhancing the encapsulation stability of the thermosensitive dye. The outer encapsulation material is composed of hydroxyl polyurethane and chitosan-g-polyvinyl alcohol composites, which achieves good dispersibility and film-forming synergy in aqueous emulsion systems. Simultaneously, during the drying and film-forming process, hydrogen bonding enhances the interfacial bonding ability of the microcapsules within the polymer network. This structure significantly improves the integrity of the color-changing region and reduces color abnormalities or residual color caused by capsule breakage during use.

[0012] Preferably, the cationic surfactant is hexadecyltrimethylammonium bromide, the anionic dispersant is a polysulfonyl phenyl ether dispersant, and the mass ratio of the cationic surfactant to the anionic dispersant is 1:1.5 to 3.

[0013] This invention utilizes a compound of cationic surfactants and anionic dispersants, controlling their mass ratio between 1:1.5 and 3, to establish a stable electric double-layer structure in pigment particles during dispersion. During dry film formation, this structure induces segregation along the film thickness direction, resulting in a direction-dependent orientation structure. This structure exhibits significant color differences under different viewing angles, effectively enhancing the anti-counterfeiting identification effect of the ink. Simultaneously, this charge-bridging system improves pigment dispersion stability, inhibits agglomeration and sedimentation, and also has a positive synergistic effect on the density and color uniformity of the final film.

[0014] Preferably, the acrylic aqueous emulsion and the hydroxyl polyurethane microemulsion are blended at a mass ratio of 4 to 1:1.

[0015] Preferably, the thermochromic microcapsules and the complexing agent are compounded at a mass ratio of 3 to 5:1.

[0016] This invention further achieves effective regulation of the color development equilibrium reaction pathway by controlling the compounding ratio of thermosensitive color-changing microcapsules to ferric complexing agent within the range of 3 to 5:1. This results in a more sensitive color development response and clearer color difference changes in the thermosensitive system, while maintaining good consistency across different batches of production. This compounding strategy, together with the aforementioned color development system and complexing mechanism, creates a synergistic effect, not only broadening the adjustment window for temperature-controlled color development but also enhancing the system's resistance to environmental disturbances, ensuring that the ink maintains stable anti-counterfeiting effects even after long-term use or multiple start-stop cycles.

[0017] Preferably, the solid content of the hydroxyl polyurethane microemulsion is 15-25%.

[0018] Preferably, the thickener is hydroxyethyl cellulose, and the amount added is 0.3 to 1.0 parts by weight.

[0019] A method for preparing a low-temperature color-developing anti-counterfeiting ink composition based on an acrylic aqueous emulsion includes the following steps: S1) Add the thermosensitive color-changing microcapsules to a portion of deionized water and pre-emulsify for 10 minutes while stirring at 400-600 rpm to obtain a microcapsule pre-dispersion. S2) At room temperature, add dispersant, cationic surfactant and thickener to acrylic aqueous emulsion in sequence, stir evenly and then slowly add microcapsule predispersant, continue stirring for 15 minutes to obtain uniform initial mixture; S3) Slowly add the hydroxyl polyurethane microemulsion to the initial mixture obtained in step S2, and shear at 1500-2500 rpm for 10 minutes in a high-speed shearing device. S4) Place the sheared mixture in an ultrasonic treatment device and treat it at a frequency of 20 kHz for 10 minutes to further uniformly disperse the heat-sensitive components; S5) Add a ferric complexing agent to the above system, stir evenly, pre-dry at 30°C for 15 minutes, and then dry at 80°C for 15 minutes to obtain a stable film-forming ink composition.

[0020] Preferably, during the ultrasonic treatment described in step S4, the system temperature is maintained at 20–25°C to avoid damage to the heat-sensitive capsule.

[0021] This invention incorporates an ultrasonic dispersion step in the preparation process, controlling the processing frequency and time to 20 kHz and 10 minutes, while limiting the system temperature to the range of 20–25°C. This ensures thorough and uniform dispersion of the heat-sensitive capsules while effectively preventing capsule structure damage or leakage caused by high temperatures. This process, combined with a high-shear dispersion process, achieves particle size reduction and uniform distribution without damaging the microcapsule membrane structure, ultimately improving the color consistency and optical uniformity of the ink film and ensuring long-term stability of low-temperature color development performance.

[0022] Preferably, the drying process is divided into two stages: the first stage is low-temperature drying at 30°C to form a film, and the second stage is high-temperature curing at 80°C to promote cross-linking.

[0023] Compared with the prior art, the beneficial effects of the present invention are mainly reflected in the following aspects: This invention provides a low-temperature color-changing anti-counterfeiting ink composition based on an aqueous acrylic emulsion and its preparation method, solving the technical problems of incomplete color development, large color difference after repeated use, and poor capsule stability in existing low-temperature color-changing ink systems. This composition uses an aqueous acrylic emulsion as the main component, combined with thermosensitive color-changing microcapsules with a double-layer coating structure, achieving excellent water dispersibility and thermo-responsive characteristics. It can rapidly develop color at low temperatures of 5–15°C, while exhibiting a stable invisibility at room temperature, making it particularly suitable for anti-counterfeiting scenarios requiring both visual concealment and low-temperature activation.

[0024] By introducing a ferric complexing agent as an auxiliary color development regulator, the color development temperature range of the thermosensitive dye is significantly expanded, constructing an adjustable "color development trigger window." This allows for flexible adjustment of the color response range for different anti-counterfeiting levels or usage environments, enhancing the technical threshold and differentiated identification capabilities of the anti-counterfeiting system. Simultaneously, the complexing agent forms a synergistic pathway with the dye-color developer, optimizing the electron migration mechanism of the color development process and effectively improving color intensity and color contrast.

[0025] This invention uses high glass transition temperature materials such as polymethyl methacrylate as the inner coating material of microcapsules, which effectively improves the structural stability and shear resistance of thermosensitive dyes in emulsion environments. The outer composite coating structure is composed of hydroxyl polyurethane and chitosan-g-polyvinyl alcohol, which has both good film-forming properties and capsule network interface bonding performance, effectively reducing the capsule breakage rate during the color development process and improving the integrity of the color development area and the consistency of repeated use.

[0026] Furthermore, the optimized ratio of cationic surfactants and anionic dispersants forms a charged bilayer structure, enhancing the orientation and alignment of pigment particles. This results in noticeable color differences in the ink when viewed from different angles, further improving its anti-counterfeiting effect. The preparation process employs ultrasonic-assisted dispersion and segmented drying techniques to achieve uniform distribution of the thermosensitive capsules and protect the thermosensitive structure during film formation and curing. This ensures that the ink maintains stable low-temperature color development and long-term reliability even under repeated cold-heat cycling conditions. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the embodiments.

[0028] Example 1: This example discloses a low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion and its preparation method, which is suitable for the construction of printed temperature-sensitive anti-counterfeiting labels.

[0029] The preparation method of thermosensitive color-changing microcapsules is as follows: M1: At 80°C, 6 parts of crystal purple lactate, 10 parts of bisphenol A-4,4′-disulfonic acid diphenyl ester and 84 parts of decylphenol ether are mixed and magnetically stirred for 10 minutes to form a transparent homogeneous oil phase.

[0030] M2: Dissolve 5 parts gelatin and 2 parts gum arabic in deionized water at 60°C to form an aqueous phase with a concentration of 10%.

[0031] M3: Slowly add the oil phase to the aqueous phase and shear emulsify at 800 rpm for 15 minutes to obtain an O / W type emulsion.

[0032] M4: Add 3 parts of 10% glutaraldehyde solution to the emulsion, adjust the pH to 5.0, and continue stirring for 2 hours to carry out the initial cross-linking reaction.

[0033] M5: Cool the system to 10°C and keep stirring for 30 minutes to complete the shell curing.

[0034] M6: After microporous filtration, washing with cold water three times, and vacuum drying at 40°C, thermosensitive color-changing microcapsules with a particle size of 3-5 μm were obtained.

[0035] The raw materials and parameters of each component are as follows: The acrylic waterborne emulsion is a terpolymer emulsion of ethylene-methyl acrylate-butyl acrylate with a solid content of 48%, a glass transition temperature of about 5°C, and a mass fraction of 50 parts.

[0036] Hydroxyl polyurethane microemulsion is a polyether-type aqueous polyurethane emulsion with a solid content of 20%, a particle size of approximately 70 nm, and a mass fraction of 12 parts. It is used to adjust the flexibility and interfacial adhesion of the film layer.

[0037] The thermosensitive color-changing microcapsules are 10 parts by weight, and the core components are crystal violet lactate (thermosensitive dye), bisphenol A-4,4′-disulfonic acid diphenyl ester (color developer) and decylphenol ether (co-solvent), which exhibit a reversible color development / leuco response between 20 and 25°C.

[0038] The ferric complexing agent is prepared by mixing ferric ammonium citrate and sodium phosphotungsten at a mass ratio of 1:1, with a mass fraction of 1.5 parts. It is used to form a reversible complex with the dye to control the color development window.

[0039] The cationic surfactant was hexadecyltrimethylammonium bromide, with a mass fraction of 0.6 parts, used to adjust the zeta potential of the system.

[0040] The anionic dispersant is a polysulfonyl phenyl ether dispersant with an average molecular weight of approximately 8000 g / mol and a mass fraction of 1.2 parts, used to enhance the dispersion stability of capsules.

[0041] The thickener is hydroxyethyl cellulose (HEC), with a mass fraction of 0.6 parts, used to adjust the shear viscosity and scraping performance of the ink.

[0042] Deionized water has a conductivity of less than 1 μS / cm and is present in 38 parts by mass. It is used to adjust the viscosity and stability of the system.

[0043] The preparation method of the ink composition is as follows: S1: Disperse 10 parts of microcapsules in 12 parts of deionized water, stir at 500 rpm at room temperature for 10 minutes to obtain a microcapsule predispersion.

[0044] S2: Add 1.2 parts of anionic dispersant, 0.6 parts of cationic surfactant and 0.6 parts of hydroxyethyl cellulose to 50 parts of acrylic emulsion in sequence, and stir until homogeneous.

[0045] S3: Slowly add the microcapsule dispersion from S1 and continue stirring for 15 minutes to obtain a homogeneous initial mixture.

[0046] S4: Add 12 parts of hydroxyl polyurethane microemulsion and shear at 2000 rpm for 10 minutes.

[0047] S5: Treat the shear system in a 20 kHz ultrasonic device for 10 minutes, keeping the system temperature at 23°C to prevent capsule rupture.

[0048] S6: Add 1.5 parts of trivalent iron complexing agent, stir evenly, then apply the ink to the surface of the PET substrate, dry at 30°C for 15 minutes, and then dry at 80°C for 15 minutes.

[0049] Example 2: This example discloses a low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion and its preparation method.

[0050] The ink composition consists of the following components in parts by weight: 60 parts of acrylic aqueous emulsion, 15 parts of thermochromic microcapsules, 3 parts of ferric complexing agent, 20 parts of hydroxyl polyurethane microemulsion, 1 part of cationic surfactant, 2 parts of anionic dispersant, 1 part of thickener, and 45 parts of deionized water.

[0051] The core components of the thermochromic microcapsule include a thermosensitive dye, a color developer, and a hydrogen bond donor solvent. The thermosensitive dye has a mass fraction of 10%, using crystal violet lactate as the electron donor dye. The color developer has a mass fraction of 15%, using bisphenol A-4,4′-disulfonic acid diphenyl ester. The solvent is decylphenol ether. The mass ratio of the microcapsule to the ferric complexing agent is 5:1, and the ferric complexing agent is a mixture of ferric ammonium citrate and sodium phosphotungstenate in equal mass proportions.

[0052] An acrylic aqueous emulsion and a hydroxyl polyurethane microemulsion were blended at a mass ratio of 3:1, with the hydroxyl polyurethane microemulsion having a solid content of 25%. The cationic surfactant was hexadecyltrimethylammonium bromide, and the anionic dispersant was a polysulfonyl phenyl ether dispersant at a mass ratio of 1:2, used to stabilize the capsule dispersion. Hydroxyethyl cellulose was added at a rate of 1 part to control the system's application rheology.

[0053] The method for preparing the ink composition includes the following steps: S1 Disperse 15 parts of thermosensitive color-changing microcapsules in 15 parts of deionized water and stir at 500 rpm for 10 minutes at room temperature to form a stable suspension of microcapsule pre-dispersion.

[0054] S2 At room temperature, 2 parts of anionic dispersant, 1 part of cationic surfactant and 1 part of hydroxyethyl cellulose are added sequentially to 60 parts of acrylic aqueous emulsion. The mixture is stirred for 5 minutes to form a homogeneous initial liquid. Then, the microcapsule pre-dispersion is slowly introduced and stirred for another 15 minutes to obtain a uniform initial mixture.

[0055] S3. Slowly inject 20 parts of hydroxyl polyurethane microemulsion into the above initial mixture and place it in a high-speed shearing device to shear at 2500 rpm for 10 minutes to enhance the mixing uniformity and particle size distribution consistency of the multiphase system.

[0056] S4 The sheared mixture is transferred into an ultrasonic treatment device and ultrasonically treated at a frequency of 20 kHz for 10 minutes. At the same time, the system temperature is maintained at 25°C by a cooling jacket to prevent thermal rupture of the heat-sensitive microcapsules during the treatment process.

[0057] Add 3 parts of trivalent iron complexing agent to S5, stir thoroughly, spread the mixture on the surface of the printing substrate, perform the first stage pre-drying treatment at 30°C for 15 minutes, and then transfer to 80°C for drying for 15 minutes to complete the second stage of thermosetting process, and obtain a stable film-forming color-developing anti-counterfeiting ink.

[0058] Example 3: This example discloses a low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion and its preparation method.

[0059] The ink composition consists of the following components in parts by weight: 40 parts of acrylic aqueous emulsion, 5 parts of thermochromic microcapsules, 0.5 parts of ferric complexing agent, 5 parts of hydroxyl polyurethane microemulsion, 0.2 parts of cationic surfactant, 0.5 parts of anionic dispersant, 0.1 parts of thickener, and 30 parts of deionized water.

[0060] The core components of the thermochromic microcapsule include a thermosensitive dye, a color developer, and a hydrogen bond donor solvent. The thermosensitive dye has a mass fraction of 3%, using crystal violet lactate as the electron donor dye. The color developer has a mass fraction of 5%, using bisphenol A-4,4′-diphenyl sulfonate. The solvent is decylphenol ether. The mass ratio of the microcapsule to the ferric complexing agent is 10:1, with ferric ammonium citrate used alone as the complexing agent.

[0061] An acrylic aqueous emulsion and a hydroxyl polyurethane microemulsion were blended at a mass ratio of 8:1, with the hydroxyl polyurethane microemulsion having a solid content of 15%. The cationic surfactant was hexadecyltrimethylammonium bromide, and the anionic dispersant was a polysulfonyl phenyl ether dispersant at a mass ratio of 1:2.5. Hydroxyethyl cellulose was added as a thickener at a rate of 0.1 parts to control the rheology of the system.

[0062] The method for preparing the ink composition includes the following steps: S1 Disperse 5 parts of thermosensitive color-changing microcapsules in 8 parts of deionized water and stir at 500 rpm for 10 minutes at room temperature to form a microcapsule pre-dispersion.

[0063] S2 At room temperature, 0.5 parts of anionic dispersant, 0.2 parts of cationic surfactant and 0.1 parts of hydroxyethyl cellulose were added sequentially to 40 parts of acrylic aqueous emulsion. The mixture was stirred for 5 minutes to form a homogeneous initial liquid. Then, the microcapsule pre-dispersion was slowly introduced and stirred for another 15 minutes to obtain a uniform initial mixture.

[0064] S3. Slowly inject 5 parts of hydroxyl polyurethane microemulsion into the above initial mixture and place it in a high-speed shearing device to shear at 1500 rpm for 10 minutes to promote droplet interface stability.

[0065] S4 The sheared mixture is transferred to an ultrasonic treatment device and ultrasonically treated at a frequency of 20 kHz for 10 minutes, while the system temperature is controlled at 20°C to maintain the integrity of the capsule.

[0066] Add 0.5 parts of trivalent iron complexing agent to S5, stir thoroughly, apply the mixture to the surface of the printing substrate, pre-dry at 30°C for 15 minutes, and then dry at 80°C for 15 minutes to form a colored ink film.

[0067] Comparative Example 1 Compared with Example 1, the thermochromic microcapsules used in this comparative example have a single-layer PMMA coating structure and do not introduce gelatin / gum arabic to form a composite shell.

[0068] In the preparation of the thermosensitive capsules, 6 parts of crystal violet lactate, 10 parts of bisphenol A-4,4′-diphenyl sulfonate, 84 parts of decylphenol ether, and 10 parts of PMMA were blended, heated to 80°C to form an oil phase, and then rapidly condensed by spray drying to form capsules. No glutaraldehyde crosslinking or aqueous phase coating was performed.

[0069] The resulting capsules were added to the following formulation (parts by weight): 50 parts of acrylic aqueous emulsion, 10 parts of thermosensitive color-changing microcapsules, 1.5 parts of trivalent iron complexing agent, 12 parts of hydroxyl polyurethane microemulsion, 0.6 parts of cationic surfactant, 1.2 parts of anionic dispersant, 0.6 parts of thickener, and 38 parts of deionized water.

[0070] The preparation process is the same as in Example 1.

[0071] Comparative Example 2 Compared with Example 1, this comparative example did not use microcapsules, but directly mixed the dye, color developer and solvent into the emulsion.

[0072] Six parts of crystal violet lactate, 10 parts of bisphenol A-4,4′-diphenyl sulfonate, and 84 parts of decylphenol ether were mixed evenly and used as a thermosensitive colorimetric component to be directly blended with acrylic emulsion.

[0073] The ink composition is formulated as follows: 50 parts of acrylic aqueous emulsion, 10 parts of thermosensitive color developer mixture, 1.5 parts of trivalent iron complexing agent, 12 parts of hydroxyl polyurethane microemulsion, 0.6 parts of cationic surfactant, 1.2 parts of anionic dispersant, 0.6 parts of thickener, and 38 parts of deionized water.

[0074] Comparative Example 3 Compared with Example 1, no complexing agent was added in this comparative example, and all other conditions were the same as in Example 1.

[0075] The thermosensitive color-changing microcapsules were prepared according to Example 1. The ink composition consisted of: 50 parts of acrylic aqueous emulsion, 10 parts of microcapsules, 12 parts of hydroxyl polyurethane microemulsion, 0.6 parts of cationic surfactant, 1.2 parts of anionic dispersant, 0.6 parts of thickener, and 38 parts of deionized water.

[0076] Comparative Example 4 Compared with Example 1, this comparative example uses NaCl and MgCl2 instead of ferric complexing agents.

[0077] The same formulation as in Example 1 was used, except that 1.5 parts of the ferric complexing agent were replaced by an equal mass mixture of NaCl and MgCl2.

[0078] Comparative Example 5 Compared with Example 1, the amount of colorimetric agent added in this comparative example is only 2% of the core mass of the thermosensitive capsule, which is far below the colorimetric reaction threshold.

[0079] When preparing the thermosensitive capsules, the content of the color developer bisphenol A-4,4′-disulfonic acid diphenyl ester was controlled at 2%, and the amount of dye and solvent used was kept consistent with that in Example 1.

[0080] Other components and ink formulations remain unchanged, and the preparation process is the same as in Example 1.

[0081] Comparative Example 6 Compared with Example 1, this comparative example uses decanol with a melting point higher than 50°C instead of decylphenol ether as a solvent.

[0082] The core components of the microcapsule are 6% crystal violet lactate, 10% bisphenol A derivative, and 84% decanol, with a melting point of approximately 52°C.

[0083] The microcapsule structure and ink system formulation are the same as in Example 1, and the preparation process is exactly the same.

[0084] Comparative Example 7 Compared with Example 1, in this comparative example, the temperature was not controlled during ultrasonic treatment, and the system temperature rose to about 40°C during the treatment process.

[0085] The other formulations, raw materials, and preparation steps are the same as in Example 1, but no cooling control is set during the ultrasonic treatment stage.

[0086] Comparative Example 8 Compared with Example 1, this comparative example omits the ultrasonic treatment step and retains only the shear dispersion.

[0087] The formulation is the same as in Example 1. The preparation process involves adding the complexing agent directly after shearing (2000 rpm) and drying, without ultrasonic treatment.

[0088] Comparative Example 9 Compared with Example 1, this comparative example uses only 1.2 parts of anionic dispersant and no cationic surfactant is added.

[0089] The rest of the formulation is the same as in Example 1. The preparation process is the same as in Example 1.

[0090] Comparative Example 10 Compared with Example 1, this comparative example replaces the cationic surfactant with the nonionic Tween-80.

[0091] Replace 0.6 parts of hexadecyltrimethylammonium bromide with 0.6 parts of Tween-80, and keep the other components and processes the same as in Example 1.

[0092] I. Color contrast ΔE and response time (t) 10-90 ) Detection method: Each ink composition was coated onto a PET substrate with a film thickness controlled at 10 μm. The substrate was placed on a temperature-controlled constant-temperature platform, and the temperature was increased in 2°C increments starting from 10°C until complete color development. The Lab* values ​​at 20°C (no color development) and 35°C (complete color development) were measured using a spectrophotometer, and the ΔE value was calculated. Simultaneously, the time required from initial color development to complete color development (t) was recorded using video image analysis. 10-90 ).

[0093] The test results are shown in Table 1 below.

[0094] Table 1

[0095] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A low-temperature color-developing anti-counterfeiting ink composition based on an acrylic aqueous emulsion, characterized in that, Includes the following components in parts by weight: 40-60 parts of acrylic aqueous emulsion; 5-15 parts of thermosensitive color-changing microcapsules; 0.5–3 parts of ferric chelating agent; 5-20 parts of hydroxyl polyurethane microemulsion; 0.2 to 1 part of cationic surfactant; 0.5–2 parts of anionic dispersant; Thickener 0.1 to 1 part; 30-45 parts deionized water; The core components of the thermochromic microcapsule include a thermosensitive dye, a color developer, and a hydrogen bond donor solvent, wherein: Thermosensitive dyes account for 3-10% of the core mass and are crystal violet lactate or benzothiazole electron donor dyes; The color developer accounts for 5-15% of the core mass and is bisphenol A or its sulfonate derivatives; The ferric complexing agent is selected from one or both of ferric citrate or sodium phosphotungstenate.

2. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The thermochromic microcapsules are 8–12 μm in size. The inner coating material of the thermochromic microcapsules is polymethyl methacrylate or styrene-maleic anhydride copolymer, accounting for 5–15% of the total mass of the microcapsules. The outer coating material is composed of hydroxyl polyurethane and chitosan-g-polyvinyl alcohol composite, with a mass ratio of hydroxyl polyurethane to chitosan graft material of 2:1 to 5:

1. The total mass of the outer layer accounts for 3–10% of the total mass of the microcapsules.

3. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The cationic surfactant is hexadecyltrimethylammonium bromide, and the anionic dispersant is a polysulfonyl phenyl ether dispersant. The mass ratio of the cationic surfactant to the anionic dispersant is 1:1.5 to 3.

4. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The acrylic aqueous emulsion and the hydroxyl polyurethane microemulsion are blended at a mass ratio of 4 to 1:

1.

5. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The thermosensitive color-changing microcapsules are compounded with a complexing agent at a mass ratio of 3 to 5:

1.

6. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The hydroxyl polyurethane microemulsion has a solid content of 15-25%.

7. The low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 1, characterized in that, The thickener is hydroxyethyl cellulose, and its addition amount is 0.3 to 1.0 parts by weight.

8. A method for preparing a low-temperature color-developing anti-counterfeiting ink composition based on an acrylic aqueous emulsion according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1) Add the thermosensitive color-changing microcapsules to a portion of deionized water and pre-emulsify for 10 minutes while stirring at 400-600 rpm to obtain a microcapsule pre-dispersion. S2) At room temperature, add dispersant, cationic surfactant and thickener to acrylic aqueous emulsion in sequence, stir evenly and then slowly add microcapsule predispersant, continue stirring for 15 minutes to obtain uniform initial mixture; S3) Slowly add the hydroxyl polyurethane microemulsion to the initial mixture obtained in step S2, and shear at 1500-2500 rpm for 10 minutes in a high-speed shearing device. S4) Place the sheared mixture in an ultrasonic treatment device and treat it at a frequency of 20 kHz for 10 minutes to further uniformly disperse the heat-sensitive components; S5) Add a ferric complexing agent to the above system, stir evenly, pre-dry at 30°C for 15 minutes, and then dry at 80°C for 15 minutes to obtain a stable film-forming ink composition.

9. The method for preparing the low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 9, characterized in that, During the ultrasonic treatment described in step S4, the system temperature is maintained at 20–25°C to avoid damage to the heat-sensitive capsule.

10. The method for preparing the low-temperature color-developing anti-counterfeiting ink composition based on acrylic aqueous emulsion according to claim 9, characterized in that, The drying process is divided into two stages: the first stage is low-temperature drying at 30°C to form a film, and the second stage is high-temperature drying at 80°C to promote cross-linking and curing.

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