A water-based ink, and a method for preparing and using the same

Abstract

This invention discloses a water-based ink and its preparation and application methods, relating to the field of ink preparation. The method includes the following steps: Modified nano-alumina, a portion of water-based acrylic resin emulsion, a portion of APEO-free wetting and dispersing agent, and a portion of deionized water are dispersed evenly, then milled until the fineness is ≤5μm to obtain a slurry; a water-based blocked isocyanate crosslinking agent, a leveling agent, and a portion of ATBC are mixed evenly to obtain a pre-dispersion; a water-based polyurethane dispersion, a defoamer, and the remaining deionized water, water-based acrylic resin emulsion, ATBC, and APEO-free wetting and dispersing agent are dispersed evenly to obtain a main resin emulsion phase; the slurry is slowly added to the main resin emulsion phase and dispersed evenly; the pre-dispersion is then slowly added and dispersed evenly; a thickener is added to adjust the system viscosity; the mixture is filtered to obtain the target product. The ink of this invention exhibits ultra-low VOC emissions and excellent initial adhesion, anti-blocking properties, and long-term durability.

Description

Technical Field

[0001] This invention relates to the field of ink preparation technology, specifically to a water-based ink and its preparation and application methods. Background Technology

[0002] The green development of the printing and packaging industry has placed higher demands on the environmental performance of inks. While traditional solvent-based inks offer excellent adhesion, drying speed, and durability, their high emissions of volatile organic compounds (VOCs) pose significant risks to the environment and human health, leading to increasingly stringent regulations. Water-based inks, as an environmentally friendly alternative, have low VOC content; however, when applied to non-absorbent plastic substrates (such as BOPP and PET), they generally suffer from poor initial adhesion, slow drying speed, and insufficient water resistance, solvent resistance, and abrasion resistance, severely impacting product quality.

[0003] Current improvements to water-based inks often focus on optimizing a single property. However, such single-method approaches often fail to achieve a comprehensive balance of performance, frequently resulting in some aspects being neglected while others are improved. Furthermore, they may introduce new harmful substances such as organic amines and alkylphenol polyoxyethylene ethers (APEO), failing to fundamentally resolve the contradiction between environmental protection and high performance.

[0004] Therefore, the industry urgently needs a technical solution that can systematically address the multiple challenges faced by water-based inks in the printing and packaging industry, such as adhesion, anti-blocking properties, durability, and environmental friendliness. Summary of the Invention

[0005] The purpose of this invention is to provide a water-based ink and its preparation and application methods, which achieves ultra-low VOC emissions while also possessing excellent initial adhesion, anti-blocking properties and long-term durability, thus meeting the printing requirements of mid-to-high-end plastic packaging products.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing a water-based ink includes the following steps:

[0008] S100: Modified nano-alumina, a portion of water-based acrylic resin emulsion, a portion of APEO-free wetting and dispersing agent, and a portion of deionized water are uniformly dispersed under high shear, and then dispersed by sand milling until the fineness is ≤5μm to obtain a slurry.

[0009] S200. A water-based blocked isocyanate crosslinking agent, leveling agent and part of acetylated tributyl citrate are mixed evenly to obtain a pre-dispersion.

[0010] S300: Disperse the waterborne polyurethane dispersion, defoamer, remaining deionized water, waterborne acrylic resin emulsion, tributyl acetyl citrate, and APEO-free wetting and dispersing agent evenly to obtain the main resin emulsion phase.

[0011] Under low-speed stirring (S400), the above slurry is slowly added to the main resin emulsion phase. After being dispersed evenly at medium speed, the pre-dispersed body is slowly added under low-speed stirring and dispersed evenly. Thickener is added to adjust the viscosity of the system, and the mixture is filtered to obtain the target product.

[0012] The ink preparation method of this invention proactively controls the combination mode and introduction sequence of key components, pre-constructing and strengthening the microscopic basis of the final ink performance during the preparation stage. First, in the slurry preparation stage, modified nano-alumina is pre-encapsulated in situ using a portion of aqueous acrylic resin emulsion, pre-anchoring the resin molecular chains to the nanoparticle surface. This not only solves the process problem of uniform dispersion and easy re-agglomeration of nanomaterials in high-viscosity resin phases but also ensures that its reinforcing and anchoring effects are fully realized in the final product from the source. Second, in the pre-dispersion preparation stage, aqueous blocked isocyanate crosslinking agent and a portion of bio-based film-forming aids are pre-mixed and homogenized, achieving an extremely uniform distribution of the crosslinking agent in the system. The film-forming aids also act as physical isolation agents, significantly improving the ink's storage stability and ensuring that the crosslinking reaction proceeds efficiently and uniformly during subsequent baking. Finally, in the mixing process, the sequence of "first constructing a continuous phase, then introducing composite units, and finally locking the reaction sites" is followed. That is, a uniform and stable main resin emulsion phase is first formed, then the pre-encapsulated nanocomposite slurry is slowly added, and finally the crosslinking agent pre-dispersion is introduced under mild conditions. The preparation method of this invention ensures that each functional unit is precisely placed, laying a decisive foundation for the formation of a dense, robust, and synergistic microstructure during film formation.

[0013] The ink produced by this invention achieves a breakthrough in performance, exhibiting not only superior initial adhesion, high hardness, and abrasion resistance, but also demonstrating a synergistic enhancement effect far exceeding traditional simple blending techniques in key indicators such as resistance to chemical solvent wiping, resistance to thermal adhesion, and long-term weather resistance. Most importantly, all these high-performance characteristics are achieved simultaneously under environmentally friendly conditions with extremely low VOC emissions, successfully solving a core problem that has long been a challenge in the field of high-end water-based inks.

[0014] Further, by mass percentage, the composite resin film-forming system comprises 45-62%, acetylacetic tributyl citrate (ATBC) 3-7%, modified nano-alumina 0.8-3.5%, waterborne blocked isocyanate crosslinking agent (W-BIC) 1.5-5.0%, dispersant 0.5-1.5%, defoamer 0.1-0.5%, leveling agent 0.1-0.8%, thickener 0.2-1.0%, and the balance being deionized water;

[0015] The composite resin film-forming system consists of an aqueous acrylic resin emulsion with an effective solid mass ratio of 1.6~2.0:1 and an aqueous polyurethane dispersion; the modified nano alumina is nano alumina that has been surface modified with a silane coupling agent.

[0016] This invention abandons the traditional approach of relying on single-component improvement and instead constructs a multi-level, orderly, and synergistic system. Starting from the material source, this system systematically solves the industry problems of poor adhesion, insufficient durability, and difficulty in meeting environmental protection requirements of water-based inks on non-absorbent plastic substrates through a synergistic path of physical interpenetrating network foundation, nano-interface anchoring enhancement, and thermally triggered chemical cross-linking locking.

[0017] First, by compounding waterborne acrylic resin emulsion and waterborne polyurethane dispersion at a specific mass ratio, a rigid-flexible interpenetrating network structure spontaneously forms during film formation, constituting the initial skeleton of the ink film. This effectively balances the contradictions between hardness and elasticity, adhesion and cohesion, laying the structural foundation for high performance. Second, the introduction of nano-alumina modified with a silane coupling agent achieves secondary reinforcement at the nanoscale. Its surface active groups can form strong chemical bonds with the substrate and also act as hard particles dispersed within the network skeleton, physically pinning cracks and improving wear resistance and density. Furthermore, this invention introduces a waterborne blocked isocyanate crosslinking agent. During the drying stage after printing, this crosslinking agent undergoes a deblocking reaction upon heating. The active groups released by the crosslinking agent react rapidly with the functional groups on the resin network, forming a three-dimensional thermosetting crosslinked network. This permanently locks in the aforementioned physical and nano-reinforcement structure, giving the ink film excellent solvent resistance, heat resistance, and anti-blocking properties. By using environmentally friendly raw materials such as bio-based film-forming agents throughout the process, extremely low VOC emissions are ensured from the source, and the entire technical solution is compatible with existing printing processes.

[0018] This invention selects ATBC as a bio-based film-forming aid, whose main function is to promote the fusion of resin particles and the formation of a dense coating.

[0019] The composite resin film-forming system consists of an aqueous acrylic resin emulsion and an aqueous polyurethane dispersion with an effective solids mass ratio of 1.6 to 2.0:1. The effective solids mass ratio mentioned in this invention refers to the mass ratio of the two resin solid components after deducting water and volatile matter.

[0020] Furthermore, the preparation method of the modified nano-alumina includes the following:

[0021] Nano-alumina was dispersed in a mixed solvent of ethanol and deionized water to obtain a suspension; γ-aminopropyltriethoxysilane was pre-hydrolyzed under acidic conditions with a pH of 4.0-5.0 to obtain a hydrolysate; the hydrolysate was slowly added dropwise to the suspension at 60-65°C with stirring, and the reaction was carried out for 4-6 hours; after the reaction was completed, the nano-alumina was obtained by centrifugation, washing, vacuum drying and pulverization.

[0022] The method for preparing modified nano-alumina of this invention achieves active regulation of the modification process at the molecular level by precisely controlling the reaction conditions and the order of addition, decomposing the modification process into two independent and continuous stages: pre-hydrolysis and in-situ grafting. In the pre-hydrolysis stage, γ-aminopropyltriethoxysilane is hydrolyzed first in a specific weakly acidic environment, promoting the conversion of the ethoxy group at the terminal of the silane molecule into a highly reactive silanol group, preparing for subsequent bonding with nanoparticles, while effectively suppressing the self-condensation side reaction of the silane molecule. Subsequently, under strictly temperature-controlled stirring conditions, the resulting hydrolysate is slowly added dropwise to the nano-alumina suspension. This slow dropwise addition ensures that the highly reactive silane hydrolysate can fully contact the nanoparticle surface at a controllable rate, and that a directional dehydration condensation reaction occurs at the interface, thereby forming a strong Al-O-Si covalent bond. The entire reaction is carried out at 60-65°C for several hours, providing sufficient thermodynamic driving force and time for the grafting reaction, ensuring the integrity and stability of the modified layer.

[0023] Modification allows silane coupling agent molecules to be uniformly and densely anchored on the surface of nano-alumina particles through chemical bonds. The resulting modified nano-alumina changes its surface properties from hydrophilic to hydrophobic and contains reactive amino groups, which greatly improves its compatibility and interfacial bonding with organic resin matrices.

[0024] Further, in step S100, the amount of waterborne acrylic resin emulsion added accounts for 30-40% of the total mass of the waterborne acrylic resin emulsion; the amount of APEO-free wetting and dispersing agent added accounts for 45-55% of the total mass of APEO-free wetting and dispersing agent; deionized water accounts for 30-50% of the total mass of deionized water; and pre-disperse at 2000-3000 rpm for 15-20 minutes.

[0025] Further, in step S200, acetylated tributyl citrate accounts for 47-52% of the total mass of acetylated tributyl citrate; the mixture is stirred at 500-800 rpm for 20-30 minutes to obtain a pre-dispersion.

[0026] Furthermore, in step S300, stir at 300~500 rpm for 30~40 minutes.

[0027] Further, in step S400, the above slurry is slowly added to the main resin emulsion phase under stirring at 300-500 rpm, and the process is completed in 15-20 minutes; the mixture is dispersed at 800-1000 rpm for 18-25 minutes; under stirring at 300-500 rpm, the system temperature is kept below 35°C, and the pre-dispersion is slowly added, and the process is completed in 25-35 minutes. After uniform dispersion, a thickener is added to adjust the system viscosity; the mixture is then filtered through a 200-mesh or finer screen to obtain the target product.

[0028] Furthermore, in step S100, an environmentally friendly colorant is added, with the amount of the environmentally friendly colorant accounting for 8-12% of the total mass of the formula.

[0029] Environmentally friendly colorants can be selected from inorganic pigments that are free of heavy metals, such as cobalt-based or titanium-based pigments.

[0030] A water-based ink prepared by the preparation method described above.

[0031] A method for using the water-based ink, wherein the drying temperature after printing with the water-based ink is 80~100℃.

[0032] The water-based ink of this invention introduces a water-based blocked isocyanate crosslinking agent. During the drying stage after printing, this crosslinking agent undergoes a deblocking reaction upon heating, releasing highly reactive isocyanate groups (-NCO). These precisely released -NCO groups react rapidly and efficiently with functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups widely present on the molecular chains of water-based acrylic resins and polyurethanes. -NCO reacts with -OH to form urethane bonds (-NH-CO-O-), and reacts with -COOH to generate amide bonds and release carbon dioxide, thereby constructing a strong covalent bridge between molecular chains. This process is not a local or linear repair, but rather a dense generation of three-dimensional chemical crosslinking points within the preliminarily formed "physical interpenetrating network-nano-reinforced" composite framework. This transforms the originally plastic film layer, which mainly relies on physical entanglement and secondary bond interactions, into a highly crosslinked thermosetting network, greatly improving the ink film's solvent resistance (especially resistance to alcohol solvents), heat resistance, and anti-tack properties.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. The water-based ink prepared by this invention solves the industry problem of weak initial adhesion of water-based inks on non-absorbent substrates such as BOPP and PET. Through the chemical anchoring effect of nano-alumina surface, an initial adhesion of ≥95% is achieved. At the same time, the synergistic effect of the interpenetrating network formed by specific resin ratio and the three-dimensional network constructed by thermally triggered cross-linking enables the ink film to achieve high hardness and excellent wear resistance, while possessing chemical resistance and high-temperature adhesion resistance that surpasses conventional products. It can withstand 200 ethanol wiping cycles and retains an adhesion of over 95% after boiling in water, meeting the stringent requirements of high-end application scenarios such as automotive wiring harness tapes.

[0035] 2. This invention, by using entirely bio-based film-forming aids and being APEO-free, ensures extremely low VOC content in the final product from the source, with VOC content <15g / L, fully complying with stringent environmental regulations. More importantly, this superior performance is achieved without sacrificing process adaptability. This ink can be adapted to existing gravure or flexographic printing production lines, requiring only conventional drying tunnels to complete the entire process from drying to cross-linking and curing. The industrialization transition has low barriers to entry and possesses strong market application potential. Detailed Implementation

[0036] Example 1

[0037] 10 kg of nano-alumina;

[0038] Silane coupling agent: γ-aminopropyltriethoxysilane (KH-550), used at 6% of the mass of nano-alumina.

[0039] Solvent: A mixed solution of ethanol and deionized water. The volume ratio of ethanol to water is 7:1, and the total amount used is to achieve a nano-alumina solid content of 15wt%.

[0040] The preparation method of modified nano-alumina includes the following steps:

[0041] Step 1: Add nano-alumina to an ethanol / water mixed solvent and disperse it at 45°C and 2500 rpm for 45 minutes to obtain a uniform suspension.

[0042] Step 2: Mix KH-550 with a portion of the ethanol / water mixture, adjust the pH to 4.5 with acetic acid, and pre-hydrolyze for 40 minutes at 35°C and 400 rpm to obtain a clear and transparent hydrolysate.

[0043] Step 3: Stabilize the temperature of the suspension at 60℃ and maintain a medium-speed stirring at 1000 rpm. Using a constant-pressure dropping funnel, slowly and evenly add the hydrolysate to the suspension at a rate of 1 drop / second. After the addition is complete, continue the reaction at this temperature for 5 hours.

[0044] Step 4: After the reaction is complete, allow it to cool naturally to room temperature. Centrifuge at 9000 rpm using a high-speed centrifuge and wash the precipitate three times with ethanol to remove the physically adsorbed coupling agent. Dry the washed product in a vacuum drying oven at 75°C for 10 hours. Finally, gently depolymerize the dried powder using an air jet mill to obtain surface-modified nano-alumina powder.

[0045] Example 2

[0046] 10 kg of nano-alumina; KH-550 dosage is 3.0% of the mass of nano-alumina.

[0047] The solvent is a mixed solution of ethanol and deionized water. The volume ratio of ethanol to water is 4:1, and the total amount used is to achieve a nano-alumina solid content of 10 wt%.

[0048] The preparation method of modified nano-alumina includes the following steps:

[0049] Step 1: Add nano-alumina to an ethanol / water mixed solvent and disperse it at 40°C and 2000 rpm for 30 minutes to obtain a uniform suspension.

[0050] Step 2: Mix KH-550 with a portion of the ethanol / water mixture, adjust the pH to 4.0 with acetic acid, and pre-hydrolyze for 30 minutes at 30°C and 300 rpm to obtain a clear and transparent hydrolysate.

[0051] Step 3: Stabilize the temperature of the suspension at 58℃ and maintain a medium-speed stirring at 800 rpm. Using a constant-pressure dropping funnel, slowly and evenly add the hydrolysate to the suspension at a rate of 1 drop / second. After the addition is complete, continue the reaction at this temperature for 4 hours.

[0052] Step 4: After the reaction is complete, allow it to cool naturally to room temperature. Centrifuge at 8000 rpm using a high-speed centrifuge and wash the precipitate twice with ethanol to remove physically adsorbed coupling agents. Dry the washed product in a vacuum drying oven at 70°C for 8 hours. Finally, gently depolymerize the dried powder using an air jet mill to obtain surface-modified nano-alumina powder.

[0053] Example 3

[0054] 10 kg of nano-alumina; KH-550 dosage is 8.0% of the nano-alumina mass. The solvent is a mixed solution of ethanol and deionized water. The volume ratio of ethanol to water is 9:1, and the total dosage is used to make the solid content of nano-alumina 20 wt%.

[0055] The preparation method of modified nano-alumina includes the following steps:

[0056] Step 1: Add nano-alumina to an ethanol / water mixed solvent and disperse it at 3000 rpm for 60 minutes at 50°C to obtain a uniform suspension.

[0057] Step 2: Mix KH-550 with a portion of the ethanol / water mixture, adjust the pH to 5.0 with acetic acid, and pre-hydrolyze for 45 minutes at 40°C and 500 rpm to obtain a clear and transparent hydrolysate.

[0058] Step 3: Stabilize the temperature of suspension A at 62℃ and maintain a medium-speed stirring at 1200 rpm. Using a constant-pressure dropping funnel, slowly and evenly add the hydrolysate to the suspension at a rate of 2 drops / second. After the addition is complete, continue the reaction at this temperature for 6 hours.

[0059] Step 4: After the reaction is complete, allow it to cool naturally to room temperature. Centrifuge at 10,000 rpm using a high-speed centrifuge, and wash the precipitate three times with ethanol to remove the physically adsorbed coupling agent. Dry the washed product in a vacuum drying oven at 80°C for 12 hours. Finally, gently depolymerize the dried powder using an air jet mill to obtain surface-modified nano-alumina powder.

[0060] Comparative Example 1

[0061] The preparation method of modified nano-alumina includes the following steps:

[0062] 10 kg of nano-alumina with an average particle size of 32 nm was dispersed in an ethanol / water mixed solvent of the same ratio (solid content 15 wt%), and dispersed under high shear at 45 °C and 2500 rpm for 45 minutes to obtain a suspension. 0.6 kg of KH-550 was directly added to the suspension, and the mixture was stirred at 60 °C and 1000 rpm for 5 hours. Subsequent centrifugation, washing, drying, and pulverization steps were exactly the same as in Example 1.

[0063] In Comparative Example 2, step 3, the suspension temperature was stabilized at 60°C, and stirring was maintained at 1000 rpm. All the hydrolysate was quickly poured into the suspension at once, and the reaction was continued at this temperature for 5 hours. Steps 1-3 were the same as in Example 1.

[0064] The performance parameters of the modified nano-alumina prepared by the methods of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0065] Table 1. Performance parameters of modified nano-alumina prepared by the methods of Examples 1-3 and Comparative Examples 1-2

[0066]

[0067] As shown in Table 1, the sedimentation volumes of Examples 1-3 were significantly lower than those of Comparative Examples 1-2, especially in toluene where no visible sedimentation was observed after 30 days, demonstrating good dispersion stability. This proves that the modified nanoparticles changed from hydrophilic to hydrophobic, effectively preventing aggregation. The larger sedimentation volumes of Comparative Examples 1 and 2 indicate uneven modification or the presence of more physically adsorbed silane oligomers, leading to interparticle bridging and aggregation.

[0068] The contact angles of Examples 1-3 were all greater than 100°, indicating the formation of a dense organic molecular layer. Comparative Example 1 had the lowest contact angle, proving that the lack of pre-hydrolysis resulted in the ineffective grafting of silanes; Comparative Example 2 had a acceptable contact angle, but its poor dispersibility indicated that the modified layer was not uniform.

[0069] Compared with Comparative Examples 1-2, it is evident that the pre-hydrolysis-slow drop-addition process used in Examples 1-3 of the present invention is the key to achieving uniform grafting of silane coupling agent onto the surface of nano-alumina in the form of a monolayer through strong Al-O-Si covalent bonds.

[0070] Example 4

[0071] By weight percentage, the composite resin film-forming system comprises 53%, ATBC 5%, modified nano-alumina (prepared by the method in Example 1) 2%, W-BIC (TSCA4000) 3%, APEO-free wetting and dispersing agent 1%, mineral oil / organic silicone composite defoamer 0.3%, polyether-modified siloxane leveling agent 0.4%, polyurethane associative thickener 0.6%, phthalocyanine blue pigment 10%, and the balance being deionized water.

[0072] The composite resin film-forming system consists of an aqueous acrylic resin emulsion with an effective solid mass ratio of 1.8:1 and an aqueous polyurethane dispersion.

[0073] A method for preparing a water-based ink includes the following steps:

[0074] S100: Modified nano-alumina, phthalocyanine blue pigment, part of water-based acrylic resin emulsion, part of APEO-free wetting and dispersing agent, and part of deionized water are pre-dispersed at 2400 rpm for 18 minutes, and then dispersed by sand milling until the fineness is ≤5μm to obtain a slurry.

[0075] The amount of waterborne acrylic resin emulsion added accounts for 36% of the total mass of waterborne acrylic resin emulsion; the amount of APEO-free wetting and dispersing agent added accounts for 50% of the total mass of APEO-free wetting and dispersing agent; and deionized water accounts for 40% of the total mass of deionized water.

[0076] S200, W-BIC, leveling agent and part of ATBC are mixed at 650 rpm for 25 minutes to obtain a pre-dispersion; ATBC accounts for 50% of the total mass of ATBC.

[0077] S300, the aqueous polyurethane dispersion, defoamer, remaining deionized water, aqueous acrylic resin emulsion, ATBC and APEO-free wetting and dispersing agent are stirred at 400 rpm for 35 minutes to obtain the main resin emulsion phase.

[0078] Under stirring at 400 rpm and 400 rpm, the above slurry is slowly added to the main resin emulsion phase, and the process is completed within 18 minutes; disperse at 920 rpm for 20 minutes; under stirring at 400 rpm, while keeping the system temperature <35℃, slowly add the above pre-dispersion, and the process is completed within 30 minutes. After uniform dispersion, add the thickener, and the system viscosity is 43 seconds (25℃) of a Forecast cup 4. Filter with a 240-mesh filter to obtain the target product.

[0079] Example 5

[0080] By weight percentage, the composite resin film-forming system comprises 45%, ATBC 3%, modified nano-alumina (prepared by the method in Example 1) 0.8%, W-BIC (TSCA4000) 1.5%, APEO-free wetting and dispersing agent 0.5%, mineral oil / organic silicone composite defoamer 0.1%, polyether-modified siloxane leveling agent 0.1%, polyurethane associative thickener 0.2%, cobalt green 8%, and the balance being deionized water.

[0081] The composite resin film-forming system consists of an aqueous acrylic resin emulsion with an effective solid mass ratio of 1.6:1 and an aqueous polyurethane dispersion; the modified nano-alumina is nano-alumina surface-modified with a silane coupling agent.

[0082] A method for preparing a water-based ink includes the following steps:

[0083] S100: Modified nano-alumina, environmentally friendly colorant, part of water-based acrylic resin emulsion, part of APEO-free wetting and dispersing agent, and part of deionized water are pre-dispersed at 2000 rpm for 15 minutes, and then dispersed by sand milling until the fineness is ≤5μm to obtain a slurry.

[0084] The amount of waterborne acrylic resin emulsion added accounts for 30% of the total mass of waterborne acrylic resin emulsion; the amount of APEO-free wetting and dispersing agent added accounts for 45% of the total mass of APEO-free wetting and dispersing agent; and deionized water accounts for 30% of the total mass of deionized water.

[0085] S200, W-BIC, leveling agent and part of ATBC are mixed at 500 rpm for 20 minutes to obtain a pre-dispersion; ATBC accounts for 47% of the total mass of ATBC.

[0086] S300, the aqueous polyurethane dispersion, defoamer, remaining deionized water, aqueous acrylic resin emulsion, ATBC and APEO-free wetting and dispersing agent are stirred at 300 rpm for 30 minutes to obtain the main resin emulsion phase.

[0087] Under stirring at 400 and 300 rpm, the above slurry is slowly added to the main resin emulsion phase, and the process is completed within 15 minutes; disperse at 800 rpm for 18 minutes; under stirring at 300 rpm, while keeping the system temperature <35℃, slowly add the above pre-dispersion, and the process is completed within 25 minutes. After uniform dispersion, add the thickener, and the system viscosity is 40 seconds (25℃) of a Forecast cup 4. Filter with a 220-mesh filter to obtain the target product.

[0088] Example 6

[0089] By weight percentage, the composite resin film-forming system comprises 62%, ATBC 7%, modified nano-alumina (prepared by the method in Example 1) 3.5%, W-BIC (TSCA4000) 5.0%, APEO-free wetting and dispersing agent 1.5%, mineral oil / organic silicone composite defoamer 0.5%, polyether-modified siloxane leveling agent 0.8%, polyurethane associative thickener 1.0%, titanium nickel yellow 12%, and the balance being deionized water.

[0090] The composite resin film-forming system consists of an aqueous acrylic resin emulsion with an effective solid mass ratio of 2.0:1 and an aqueous polyurethane dispersion.

[0091] A method for preparing a water-based ink includes the following steps:

[0092] S100: Modified nano alumina, environmentally friendly colorant, part of water-based acrylic resin emulsion, part of APEO-free wetting and dispersing agent, and part of deionized water are pre-dispersed at 3000 rpm for 20 minutes, and then dispersed by sand milling until the fineness is ≤5μm to obtain a slurry.

[0093] The amount of waterborne acrylic resin emulsion added accounts for 40% of the total mass of waterborne acrylic resin emulsion; the amount of APEO-free wetting and dispersing agent added accounts for 55% of the total mass of APEO-free wetting and dispersing agent; and deionized water accounts for 50% of the total mass of deionized water.

[0094] S200, W-BIC, leveling agent and part of ATBC are mixed at 800 rpm for 30 minutes to obtain a pre-dispersion; ATBC accounts for 52% of the total mass of ATBC.

[0095] S300, the aqueous polyurethane dispersion, defoamer, remaining deionized water, aqueous acrylic resin emulsion, ATBC and APEO-free wetting and dispersing agent are stirred at 500 rpm for 40 minutes to obtain the main resin emulsion phase.

[0096] Under stirring at 400 and 500 rpm, the above slurry is slowly added to the main resin emulsion phase, and the process is completed within 20 minutes; disperse at 1000 rpm for 25 minutes; under stirring at 500 rpm, while keeping the system temperature <35℃, slowly add the above pre-dispersion, and the process is completed within 35 minutes. After uniform dispersion, add the thickener, and the system viscosity is 50 seconds (25℃) of a Forecast cup 4. Filter with a 250-mesh filter to obtain the target product.

[0097] Comparative Example 3

[0098] By mass percentage, the composition is 53% waterborne acrylic resin emulsion, 5% ATBC, 1% APEO-free wetting and dispersing agent, 0.3% mineral oil / organic silicone composite defoamer, 0.4% polyether-modified siloxane leveling agent, 0.6% polyurethane associative thickener, 10% phthalocyanine blue pigment, and the balance being deionized water; the preparation method is the same as in Example 4.

[0099] Comparative Example 4

[0100] By weight percentage, the composite resin film-forming system comprises 53% ATBC, 5% APEO-free wetting and dispersing agent, 1% mineral oil / organic silicone composite defoamer, 0.3% polyether-modified siloxane leveling agent, 0.4% polyurethane associative thickener, 10% phthalocyanine blue pigment, and the balance being deionized water. The composite resin film-forming system consists of an aqueous acrylic resin emulsion and an aqueous polyurethane dispersion with an effective solids mass ratio of 1.8:1. The preparation method is the same as in Example 4.

[0101] Comparative Example 5

[0102] By mass percentage, the composite resin film-forming system comprises 53% ATBC, 5% modified nano-alumina (prepared by the method in Example 1), 2% APEO-free wetting and dispersing agent, 0.3% mineral oil / organosilicone composite defoamer, 0.4% polyether-modified siloxane leveling agent, 0.6% polyurethane associative thickener, 10% phthalocyanine blue pigment, and the balance being deionized water. The composite resin film-forming system consists of an aqueous acrylic resin emulsion and an aqueous polyurethane dispersion with an effective solids mass ratio of 1.8:1. The preparation method is the same as in Example 4.

[0103] Comparative Example 6

[0104] By weight percentage, the composite resin film-forming system is 53%, ATBC is 5%, W-BIC (TSCA4000) is 3%, APEO-free wetting and dispersing agent is 1%, mineral oil / organic silicone composite defoamer is 0.3%, polyether modified siloxane leveling agent is 0.4%, polyurethane associative thickener is 0.6%, phthalocyanine blue pigment is 10%, and the balance is deionized water.

[0105] The composite resin film-forming system consists of an aqueous acrylic resin emulsion and an aqueous polyurethane dispersion with an effective solids mass ratio of 1.8:1. The preparation method is the same as in Example 4.

[0106] Comparative Example 7

[0107] The modified nano-alumina was replaced with ordinary nano-alumina, and its parameters and preparation method were the same as in Example 4.

[0108] Comparative Example 8

[0109] The raw materials are the same as in Example 4.

[0110] A method for preparing a water-based ink includes the following steps:

[0111] Step 1: Add all deionized water, waterborne acrylic resin emulsion, waterborne polyurethane dispersion, ATBC, modified nano-alumina, phthalocyanine blue pigment, APEO-free wetting and dispersing agent, mineral oil / silicone composite defoamer, W-BIC (TSCA4000), and polyether-modified siloxane leveling agent at once. Stir continuously at 1000 rpm for 60 minutes at room temperature to ensure all raw materials are initially and evenly mixed, resulting in a slurry.

[0112] Step 2: Grind and disperse the mixed slurry until the fineness is ≤5μm to obtain a ground slurry.

[0113] Step 3: Add all of the polyurethane associative thickener while stirring at low speed, adjust the viscosity of the system, and apply to the Fore-4 cup for 43 seconds (25°C).

[0114] Step 4: Filter using a 240-mesh filter to obtain the comparative sample ink.

[0115] The water-based inks prepared in Examples 4-6 and Comparative Examples 3-8 were printed on a plastic substrate (BOPP). The drying temperature after printing the water-based inks was 90°C. The relevant performance parameters are shown in Table 2.

[0116] Table 2 Performance parameters of the water-based inks prepared in Examples 4-6 and Comparative Examples 3-8

[0117]

[0118] As shown in Table 2, Examples 4-6 exhibited balanced and excellent comprehensive performance, excellent storage stability (viscosity change <8%), VOC content <15g / L, pencil hardness up to 3H, initial adhesion ≥95%, resistance to ethanol wiping up to 200 times, and adhesion retention of over 95% after boiling in water.

[0119] Comparative Example 3 uses a traditional single resin. A single resin system cannot construct an IPN framework, lacks nano-anchoring and chemical cross-linking, and completely fails in all aspects of performance. This shows that the present invention is not a simple improvement on the prior art, but a completely new systemic solution.

[0120] Comparative Example 4 only contains an interpenetrating polymer network formed by waterborne acrylic resin and waterborne polyurethane dispersion, but completely lacks modified nano-alumina and water-locked isocyanate crosslinking agent. As a result, the system only has a basic physical framework, without the reinforcement and anchoring of nanoparticles or the final locking of chemical crosslinking network, resulting in the weakest comprehensive performance in terms of hardness, adhesion and solvent resistance.

[0121] Comparative Example 5, based on a resin skeleton, introduced modified nano-alumina, achieving nano-reinforcement and partial anchoring effects, thus improving its initial hardness and adhesion. However, due to the lack of a water-based blocked isocyanate crosslinking agent, the system could not form a three-dimensional thermosetting network during drying. As a result, when the ink film is exposed to harsh conditions such as solvent erosion or boiling water, the physical network is prone to loosening or damage, thus exhibiting significant shortcomings in its resistance to ethanol wiping and boiling water.

[0122] Comparative Example 6 incorporated a composite resin film-forming system and an aqueous blocked isocyanate crosslinking agent, enabling the construction of a chemical crosslinking network, which resulted in good solvent resistance and anti-blocking properties. However, due to the absence of modified nano-alumina, the system lacked key nanoscale physical reinforcement points and deep interfacial chemical anchoring points, leading to limited improvement in the macroscopic hardness of the ink film, and significantly insufficient adhesion, especially adhesion durability after aging or damp heat testing.

[0123] The performance data of Comparative Examples 3 to 6 illustrate the indispensability and synergistic mechanism of each component in this invention.

[0124] Comparative Example 7 used ordinary nano-alumina. The interfacial bonding between the hydrophilic surface of ordinary nano-alumina and the hydrophobic resin matrix is ​​extremely weak, resulting in a large number of microscopic defects and stress concentration points inside the ink film. The initial adhesion was only 20-30%, and the adhesion after boiling water resistance was only 5-15%.

[0125] Comparative Example 8, prepared using a simple mixing process, showed inks that were significantly inferior to those prepared using the stepwise directional assembly process in Example 4 in terms of storage stability, ethanol wiping resistance, and anti-blocking properties. Simple mixing cannot achieve pre-encapsulation of nanoparticles and uniform pre-dispersion of the crosslinking agent, leading to uneven component dispersion, weak interfacial bonding, and even storage instability. This demonstrates that the preparation process of this invention is an indispensable part of achieving its performance.

[0126] The preferred waterborne acrylic resin emulsion is WE-306, with a solid content of 44.0~46.0%; the preferred waterborne polyurethane dispersion is UH2558, with a solid content of 35~39%. As long as the final effective solid ratio falls within the core range of 1.6~2.0:1 by adjusting the raw material addition ratio and selecting raw materials with different solid contents, it falls within the protection scope of this invention.

[0127] The water-based inks prepared by the method in Example 4 were printed on BOPP and PET respectively, and dried at temperatures of 80°C, 85°C, 90°C and 100°C respectively. The performance of the inks after drying is shown in Table 3.

[0128] Table 3. Performance of the water-based inks prepared by the method in Example 4 after printing on BOPP and PET and drying.

[0129]

[0130] The data in Table 3 reveals that the drying temperature directly determines the degree of completion of the thermally triggered crosslinking reaction in the ink, thus having a systematic impact on the final performance.

[0131] In the under-curing range of 80-85℃, insufficient temperature leads to incomplete desealing of the water-based blocked isocyanate crosslinking agent, resulting in a relatively loose three-dimensional chemical crosslinking network. Therefore, the ink's adhesion, ethanol resistance, and boiling water resistance all show significant but not optimal improvement with increasing temperature, and its anti-blocking properties are also imperfect.

[0132] 90℃ is the optimal curing point for this system. At this temperature, the crosslinking agent is fully unblocked and undergoes a rapid and complete crosslinking reaction with the active functional groups of the resin and the amino groups on the surface of the modified nano-alumina, forming a dense network. This chemical network efficiently locks in the physical interpenetrating framework and nano-anchor points, enabling the ink to achieve an optimal balance of overall performance on both substrates.

[0133] When the temperature rises to 100℃, the crosslinking reaction is complete, which may lead to over-crosslinking. For PET substrates with good heat resistance, the performance remains excellent; however, for BOPP substrates with poor heat resistance, excessively high temperatures may cause slight changes on the substrate surface, potentially adversely affecting the durability of long-term adhesion.

[0134] Furthermore, the data in Table 3 show that, at the same temperature, the ink generally performs slightly better on PET substrates than on BOPP. This is because PET has a more polar surface, enabling it to form more physical interactions with ink components; while BOPP is a non-polar substrate, and its excellent adhesion relies more on the specific chemical anchoring provided by modified nano-alumina and the construction of a complete cross-linked network, thus making it more sensitive to under-curing.

[0135] In summary, the water-based ink of this invention is suitable for non-absorbent plastic substrates such as BOPP and PET, and its performance is highly dependent on a precise thermally triggered crosslinking process. 80~100℃ is the effective drying temperature range to ensure its superior performance, with 90℃ being the optimal process point.

Claims

1. A method for preparing a water-based ink, characterized in that, Includes the following steps: S100: Modified nano-alumina, a portion of water-based acrylic resin emulsion, a portion of APEO-free wetting and dispersing agent, and a portion of deionized water are dispersed evenly under high shear, and then dispersed by sand milling until the fineness is ≤5μm to obtain a slurry. S200. A water-based blocked isocyanate crosslinking agent, leveling agent and part of acetylated tributyl citrate are mixed evenly to obtain a pre-dispersion. S300: Disperse the waterborne polyurethane dispersion, defoamer, remaining deionized water, waterborne acrylic resin emulsion, tributyl acetyl citrate, and APEO-free wetting and dispersing agent evenly to obtain the main resin emulsion phase. S400, under low-speed stirring, the above slurry is slowly added to the above main resin emulsion phase. After being dispersed evenly at medium speed, the above pre-dispersion is slowly added under low-speed stirring and dispersed evenly. Then, a thickener is added to adjust the viscosity of the system. After filtration, the target product is obtained. A composite resin film-forming system is composed of an aqueous acrylic resin emulsion and an aqueous polyurethane dispersion with an effective solid mass ratio of 1.6~2.0:

1. The method for preparing the modified nano-alumina includes the following: Nano-alumina was dispersed in a mixed solvent of ethanol and deionized water to obtain a suspension; γ-aminopropyltriethoxysilane was pre-hydrolyzed under acidic conditions with a pH of 4.0-5.0 to obtain a hydrolysate; the hydrolysate was slowly added dropwise to the suspension at 60-65°C with stirring, and the reaction was carried out for 4-6 hours; after the reaction was completed, the nano-alumina was obtained by centrifugation, washing, vacuum drying and pulverization.

2. The preparation method according to claim 1, characterized in that, By weight percentage, the composite resin film-forming system comprises 45-62%, tributyl acetylacetonate 3-7%, modified nano-alumina 0.8-3.5%, waterborne blocked isocyanate crosslinking agent 1.5-5.0%, dispersant 0.5-1.5%, defoamer 0.1-0.5%, leveling agent 0.1-0.8%, thickener 0.2-1.0%, and the balance being deionized water; Among them, the modified nano-alumina is nano-alumina with a surface modified by a silane coupling agent.

3. The preparation method according to claim 1, characterized in that, In step S100, the amount of waterborne acrylic resin emulsion added accounts for 30-40% of the total mass of the waterborne acrylic resin emulsion; the amount of APEO-free wetting and dispersing agent added accounts for 45-55% of the total mass of APEO-free wetting and dispersing agent; deionized water accounts for 30-50% of the total mass of deionized water; and pre-disperse at 2000-3000 rpm for 15-20 minutes.

4. The preparation method according to claim 1, characterized in that, In step S200, acetylated tributyl citrate accounts for 47-52% of the total mass of acetylated tributyl citrate; the mixture is stirred at 500-800 rpm for 20-30 minutes to obtain a pre-dispersion.

5. The preparation method according to claim 1, characterized in that, In step S300, stir at 300-500 rpm for 30-40 minutes.

6. The preparation method according to claim 1, characterized in that, In step S400, the above slurry is slowly added to the main resin emulsion phase under stirring at 300-500 rpm, and the process is completed in 15-20 minutes; the mixture is then dispersed at 800-1000 rpm for 18-25 minutes; under stirring at 300-500 rpm, the system temperature is kept below 35°C, and the pre-dispersion is slowly added, and the process is completed in 25-35 minutes. After uniform dispersion, a thickener is added to adjust the system viscosity; the mixture is then filtered through a 200-mesh or finer screen to obtain the target product.

7. The preparation method according to claim 1, characterized in that, In step S100, an environmentally friendly colorant is also added, with the amount of the environmentally friendly colorant accounting for 8-12% of the total mass of the formula.

8. An aqueous ink prepared by the preparation method according to any one of claims 1 to 7.

9. A method of using the water-based ink as described in claim 8, characterized in that, The drying temperature after printing with the water-based ink is 80~100℃.

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