A waterborne polyurethane-based printing ink and a preparation method thereof

Abstract

The present application relates to the technical field of new ink, and particularly relates to a water-based polyurethane-based printing ink and a preparation method thereof. The ink comprises an epoxy silane cross-linking latent phosphorus-containing water-based polyurethane dispersion, a wear-resistant anti-blocking additive, a thickening agent, deionized water, a water-based carbon black grinding color paste and ammonia water for adjusting the pH to 8.2-9.0. The epoxy silane cross-linking latent phosphorus-containing water-based polyurethane dispersion is prepared by pre-polymerization, neutralization and chain extension of raw materials such as polycarbonate diol, isophorone diisocyanate, dimethylol propionic acid and phosphorus-containing diol, and then introducing an epoxy silane pre-hydrolysis solution. The present application enhances the interface anchoring by the phosphorus-containing structure, realizes latent cross-linking by using acidic pre-hydrolyzed silane, and adopts the process of adding ammonia water to trigger the cross-linking before printing, which significantly improves the water resistance, alcohol resistance, wear resistance, initial dryness and anti-blocking property of the ink film on the polypropylene substrate, effectively reduces the migration risk, and is suitable for high-speed printing of food packaging.

Description

Technical Field

[0001] This invention relates to the field of novel ink technology, and in particular to a water-based polyurethane-based printing ink and its preparation method. Background Technology

[0002] Waterborne polyurethane-based printing inks, as environmentally friendly inks, are increasingly used in flexographic / gravure printing for food packaging. However, their overall performance still has significant shortcomings. In existing technologies, waterborne polyurethane inks typically use polycarbonate diols, diisocyanates, and hydrophilic chain extenders to construct dispersions. While they offer the advantage of low VOCs, the film's resistance to media and mechanical durability after film formation are often difficult to balance. Especially in high-speed printing scenarios, the ink film on non-polar substrates such as polypropylene is prone to poor water and alcohol resistance due to insufficient cohesive strength. Upon contact with water or ethanol solvents, it is prone to whitening, swelling, or even peeling, affecting packaging safety and aesthetics.

[0003] More notably, slow drying speed and insufficient anti-blocking properties have become key factors restricting production efficiency. Existing water-based inks often rely on increasing drying temperature or extending the drying tunnel to promote film formation, but this not only increases energy consumption but also easily leads to premature sealing of the ink layer surface, with residual internal moisture causing later adhesion. Simultaneously, low rubbing fastness makes printed materials prone to fading during stacking and transportation, limiting their application in high-end packaging. The root cause of these performance defects lies in the lack of efficient cross-linking mechanisms and interfacial anchoring structures in polyurethane molecular chains; traditional single neutralizing agents and chain extenders struggle to achieve a balance between storage stability and rapid curing.

[0004] Migration risk is another core issue for food packaging inks. In existing waterborne polyurethane systems, small molecule components that can migrate (such as unreacted monomers and additive residues) are prone to precipitation upon contact with oils or ethanol-based food simulants, posing a safety hazard. Although adding wax emulsions or leveling agents can partially improve anti-blocking and leveling properties, this often comes at the cost of sacrificing resistance to media or increasing migration, creating a trade-off between performance characteristics. Furthermore, while the introduction of silane crosslinking agents can enhance network density, the direct addition of unhydrolyzed silanes can easily lead to localized phase separation, and strong catalytic conditions can shorten shelf life, exacerbating the risk of gelation.

[0005] Overall, existing technologies lack a comprehensive solution that can simultaneously improve water and alcohol resistance, abrasion resistance, drying speed, and inhibit migration. The fundamental problem lies in the failure of molecular structure design to achieve synergistic regulation of polar sites and crosslinking reactions, and the lack of precise control over the reaction path via process timing, resulting in bottlenecks in performance improvement. Therefore, developing a waterborne polyurethane ink that combines high-speed printing applicability, low migration safety, and excellent durability has become a key focus for technological breakthroughs. Summary of the Invention

[0006] In view of this, the purpose of this invention is to propose a water-based polyurethane-based printing ink and its preparation method, so as to solve the problems of insufficient water and alcohol resistance, low rubbing fastness, slow drying and easy migration of existing water-based polyurethane printing inks on polypropylene films, making it difficult to balance the efficiency of high-speed printing and the safety requirements of food packaging.

[0007] To achieve the above objectives, the present invention provides a water-based polyurethane-based printing ink, comprising, by weight parts: 600-800 parts of an epoxy silane crosslinked latent phosphorus-containing water-based polyurethane dispersion, 100-140 parts of an abrasion-resistant and anti-blocking agent, 50-70 parts of a thickener, 250-350 parts of deionized water, 700-900 parts of water-based carbon black grinding paste, and ammonia, wherein the ammonia is used to adjust the pH of the water-based polyurethane-based printing ink to 8.2-9.0.

[0008] Furthermore, the water-based carbon black grinding paste comprises, by weight parts: 180-220 parts of an epoxy silane crosslinked latent phosphorus-containing water-based polyurethane dispersion, 70-90 parts of a dispersant, 5-20 parts of a wetting agent, 2-10 parts of a defoamer, 350-550 parts of deionized water, and 100-140 parts of carbon black.

[0009] Preferably, the ammonia solution has a mass fraction of 28%.

[0010] Preferably, the dispersant is an aqueous anionic polycarboxylate dispersant, the wetting agent is a polyether-modified siloxane copolymer, the defoamer is a polyether-modified siloxane copolymer containing fumed silica, the wear-resistant and anti-blocking aid is a wax emulsion, and the thickener is a nonionic HEUR rheology modifier.

[0011] Furthermore, the epoxy silane crosslinked latent phosphorus-containing aqueous polyurethane dispersion is prepared by reacting a prepolymer obtained from polycarbonate diol, isophorone diisocyanate, dimethylolpropionic acid, and diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate, neutralizing it with N,N-dimethylethanolamine, dispersing it in an aqueous phase, chain-extending it with ethylenediamine, and then introducing it into a pre-hydrolyzed solution containing γ-glycidyl etherpropyltrimethoxysilane; wherein, by mass parts, the dimethylolpropionic acid is 40-80 parts, the diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate is 20-60 parts, the N,N-dimethylethanolamine is 30-60 parts, the ethylenediamine is 25-37 parts, and the γ-glycidyl etherpropyltrimethoxysilane is 15-45 parts; and the final isocyanate group mass fraction of the prepolymer is controlled to be 4%-5%.

[0012] Preferably, the pre-hydrolyzed solution containing γ-glycidyl etherpropyltrimethoxysilane is composed of 15-45 parts by mass of γ-glycidyl etherpropyltrimethoxysilane, 15-45 parts of anhydrous ethanol, 7.5-22.5 parts of deionized water, and 0.1-0.5 parts of citric acid monohydrate.

[0013] Furthermore, the present invention also provides a method for preparing a water-based polyurethane-based printing ink, comprising the following steps: A) Preparation of phosphorus-containing aqueous polyurethane dispersions with latent epoxy silane crosslinking; B) Preparation of water-based carbon black grinding paste; C) A phosphorus-containing aqueous polyurethane dispersion with epoxy silane crosslinking potential, a wear-resistant and anti-blocking agent, a thickener and deionized water are mixed to obtain a binder. A water-based carbon black grinding paste is added to the binder and mixed to obtain a basic water-based ink. D) Let the base ink stand for 120 minutes before printing. Add ammonia 1-10 minutes before printing to adjust the pH to 8.2-9.0 to obtain water-based polyurethane printing ink.

[0014] Preferably, in step B), a horizontal sand mill is used for grinding, the grinding beads have a particle size of 0.6 mm, the cooling water temperature is controlled at ≤35℃, the grinding time is 60 min, and the fineness of the scraper after grinding is ≤10 μm.

[0015] The beneficial effects of this invention are: This invention modifies a polyurethane prepolymer with a phosphorus-containing diol, introducing a synergistic polar structure of phosphonate esters and tertiary amines into the molecular chain, significantly enhancing the interfacial adsorption between polymer particles and the substrate. This design allows the ink film to form a denser cohesive network during film formation, thereby simultaneously improving water resistance, alcohol resistance, and abrasion resistance without increasing the drying temperature. The ink layer exhibits more stable adhesion to the polypropylene film, effectively resisting friction and media erosion, and reducing the risk of color fading.

[0016] Acidic pre-hydrolysis of epoxy silanes forms a stable, storage-ready crosslinking latent system. The pre-hydrolysis process improves the dispersibility of silanes in the aqueous phase, preventing localized phase separation and protecting the activity of epoxy groups. During film formation, the rapid silanol condensation and epoxy ring-opening reaction triggered by ammonia achieve a balance between storage stability and efficient crosslinking during film formation, significantly improving initial drying properties and inhibiting adhesion.

[0017] The timing of ethylenediamine chain extension and epoxy silane addition is strictly controlled to avoid premature reaction between the primary amine and epoxy groups. After chain extension, the cohesive strength of the molecular chain increases, causing subsequent crosslinking to be more concentrated at the particle interface, thus enhancing the early anti-blocking and abrasion resistance of the ink film. This timing design ensures the storage stability of the dispersion while optimizing film formation kinetics.

[0018] A two-stage strategy of neutral storage and pre-print alkaline triggering is adopted. A tertiary amine neutralizer is used to maintain pH stability during storage, and ammonia is added just before printing to create an alkaline environment. This mechanism promotes the rapid initiation of the silane condensation reaction in the drying stage, enabling the simultaneous completion of surface drying and internal cross-linking of the ink film under low temperature and short time conditions, effectively reducing the risk of migration.

[0019] Based on the interfacial enrichment effect between carboxylate sites and phosphorus-containing polar structures, epoxy silanes preferentially locate at the particle interface, forming a highly efficient bridging network. This crosslinking method achieves high-density crosslinking with low dosage, reduces the residue of migratable small molecules, and synergistically improves water resistance, alcohol resistance, and abrasion resistance, rather than at the expense of each other, thus broadening the overall performance window. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0021] Example 1: All raw materials used in this embodiment are commercially available and can be found on the official websites of various suppliers by product name / item number: The polycarbonate diol used is Covestro Desmophen C 1100 (number-average molecular weight approximately 1000, hydroxyl value approximately 112 mgKOH / g, bifunctional diol); the isophorone diisocyanate used is Evonik VESTANAT IPDI (isocyanate group content approximately 37.8%, viscosity at 23°C approximately 12 mPa·s); the pigment used is Cabot REGAL 660R carbon black (powder type, suitable for water-based liquid inks, low-structure, high-blackness); the dispersant used is Dow TAMOL 731A dispersant (solid content 25%, pH approximately 10.4, water-based anionic polycarboxylate dispersion system); and the wetting agent used is Evonik TEGO Wet. 270 (100% active ingredient, polyether-modified siloxane copolymer); Evonik TEGO Foamex 810 (100% active ingredient, polyether-modified siloxane copolymer containing fumed silica) was selected as the defoamer; Michelman Michem Lube 156 PFP (wax emulsion, 24.5%-25.5% non-volatile content, pH 4.5-7.5, used to improve wear resistance and anti-blocking) was selected as the abrasion-resistant and anti-blocking agent; Dow ACRYSOL RM-8W (17.5% solids content, nonionic HEUR rheology modifier) ​​was selected as the thickener.

[0022] Step S1: In a four-necked reactor (mechanical stirrer, thermometer, reflux condenser, nitrogen inlet), add 600g of polycarbonate diol, 60g of dimethylolpropionic acid, and 40g of N,N-bis(2-hydroxyethyl)aminomethylenephosphonate diethyl ester sequentially. Heat to 110℃ and dehydrate under reduced pressure at -0.09MPa for 60min, then purge with nitrogen to restore atmospheric pressure. Cool to 80℃; subsequently add 250g of acetone and stir at 400r / min until the system is clear and homogeneous. Add 382g of isophorone diisocyanate and 2g of bismuth neodecanoate. Maintain the reaction at 80℃ for 180min, taking samples every 30min for isocyanate group content using dibutylamine-hydrochloric acid back titration. Control the endpoint isocyanate group mass fraction to 4.5%, obtaining an acetone solution of phosphorus-containing diol-modified polyurethane prepolymer. Cool to 50℃ and maintain nitrogen protection, then add 40g of... After stirring with N,N-dimethylethanolamine for 300 r / min for 30 min, a carboxyl-neutralized prepolymer solution was obtained. Step S2: Add 1600g of deionized water to the dispersion vessel and control the temperature at 25℃. Turn on the high-speed disperser and adjust the speed to 1500r / min. Add the carboxyl-neutralized prepolymer solution obtained in step S1 to the deionized water in a thin stream over 30min. After the addition is complete, continue to disperse for 30min. Then, raise the temperature to 45℃ and remove acetone under reduced pressure at -0.08MPa until the system mass is stable (mass change ≤1g over 15min) to obtain a phosphorus-containing aqueous polyurethane dispersion. Step S3: Cool the aqueous polyurethane dispersion obtained in step S2 to 30°C and stir at 500 r / min; separately, add 200 g of deionized water to a beaker and cool it to 10°C in an ice-water bath, then add 31 g of ethylenediamine and stir until clear; add the ethylenediamine aqueous solution to the dispersion dropwise over 20 min at 30°C, controlling the system temperature not to exceed 35°C during the dropwise addition, and continue stirring for 30 min after the dropwise addition is complete to obtain the chain-extended modified phosphorus-containing aqueous polyurethane dispersion; Step S4: Add 30g of γ-glycidyl ether propyltrimethoxysilane, 30g of anhydrous ethanol, 15g of deionized water and 200mg of citric acid monohydrate to a glass beaker in sequence. Stir at 600r / min for 30min at 25℃ to obtain epoxy silane pre-hydrolyzed solution. Control the temperature of the chain-extended modified waterborne polyurethane dispersion obtained in step S3 at 25℃ and stir at 400r / min. Then add the epoxy silane pre-hydrolyzed solution to the dispersion in one go and continue stirring for 60min. Then seal the system and mature for 12h to obtain a phosphorus-containing waterborne polyurethane dispersion with latent epoxy silane crosslinking. Step S5: In a grinding kettle, add 200g of epoxy silane cross-linked latent phosphorus-containing waterborne polyurethane dispersion, 80g of dispersant, 10g of wetting agent, 6g of defoamer and 400g of deionized water in sequence. After stirring for 5 minutes, add 120g of carbon black. Then, use a horizontal sand mill (zirconia grinding beads with a particle size of 0.6mm) to grind for 60 minutes under the condition of cooling water temperature control ≤35℃, so that the scraper fineness is ≤10μm, and obtain waterborne carbon black grinding paste. Step S6: Add 700g of epoxy silane crosslinking latent phosphorus-containing waterborne polyurethane dispersion, 120g of abrasion-resistant and anti-blocking agent, 60g of thickener, and 292g of deionized water to the ink mixing tank, and stir at 300r / min for 20min to obtain a binder; then add 800g of waterborne carbon black grinding paste and stir for 15min to obtain the base ink; let the base ink stand for 120min before printing, and add 28% ammonia water to adjust the pH to 8.5 5min before printing to obtain waterborne polyurethane-based printing ink. Step S7: Use water-based polyurethane printing ink for gravure printing on polypropylene film substrate. Set the printing line speed to 150m / min, the hot air drying temperature to 55℃, and the hot air dwell time for single color segment to 3s. After printing, place at 25℃ for 24h to complete cross-linking and curing.

[0023] Example 2: The difference from Example 1 is as follows: In step S1, the amount of diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate was adjusted to 20g; in step S1, the amount of N,N-dimethylethanolamine was adjusted to 30g; in step S3, the amount of ethylenediamine was adjusted to 25g; in step S4, the amounts of γ-glycidyl etherpropyltrimethoxysilane, anhydrous ethanol, deionized water, and citric acid monohydrate were adjusted to 100mg, and the mixture was stirred at 600r / min for 15min at 25℃ to obtain an epoxysilane pre-hydrolyzed solution, and after the dispersion was added once, the mixture was stirred for another 30min and then aged in a sealed container for 4h; in step S6, 10min before printing, 28% ammonia was added to adjust the pH to 8.2. All other conditions were the same as in Example 1.

[0024] Example 3: The difference from Example 1 is as follows: In step S1, the amount of N,N-bis(2-hydroxyethyl)aminomethylenephosphonic acid diethyl ester was adjusted to 60g; in step S1, the amount of N,N-dimethylethanolamine was adjusted to 60g; in step S3, the amount of ethylenediamine was adjusted to 37g; in step S4, the amounts of γ-glycidyl etherpropyltrimethoxysilane, anhydrous ethanol, deionized water, and citric acid monohydrate were adjusted to 45g, 45g, 22.5g, and 300mg, respectively. The mixture was stirred at 600r / min for 45min at 25°C to obtain an epoxysilane pre-hydrolyzed solution, and after the dispersion was added once, stirring continued for 90min, followed by sealed maturation for 24h; in step S6, 28% ammonia was added 2min before printing to adjust the pH to 9.0. All other conditions were the same as in Example 1.

[0025] Example 4: The difference from Example 1 is as follows: In step S1, the amount of dimethylolpropionic acid was adjusted to 80g; in step S1, the amount of N,N-dimethylethanolamine added was adjusted to 60g; in step S4, the amount of γ-glycidyl ether propyltrimethoxysilane was 30g, the amount of anhydrous ethanol was 30g, the amount of deionized water was 15g, and the amount of citric acid monohydrate was 200mg. The mixture was stirred at 600r / min for 30min at 25℃ to obtain an epoxy silane pre-hydrolyzed solution, and after the dispersion was added once, stirring continued for 60min, followed by sealed aging for 12h; in step S6, 28% ammonia was added 1min before printing to adjust the pH to 8.8. All other conditions were the same as in Example 1.

[0026] Example 5: The difference from Example 1 is as follows: In step S1, the amount of dimethylolpropionic acid was adjusted to 40g; the amount of N,N-dimethylethanolamine added in step S1 was adjusted to 30g; in step S4, the amounts of γ-glycidyl etherpropyltrimethoxysilane, anhydrous ethanol, deionized water, and citric acid monohydrate were adjusted to 20g, 20g, 10g, and 500mg, respectively. The mixture was stirred at 600r / min for 20min at 25℃ to obtain an epoxy silane pre-hydrolyzed solution, and after the dispersion was added once, stirring continued for 60min, followed by sealed maturation for 8h; in step S6, 28% ammonia was added 3min before printing to adjust the pH to 8.5. All other conditions were the same as in Example 1.

[0027] Comparative Example 1 The difference from Example 1 is that 40g of N,N-bis(2-hydroxyethyl)aminomethylenephosphonic acid diethyl ester is not added in step S1, and the amount of polycarbonate diol is adjusted from 600g to 640g. The remaining conditions are the same as in Example 1.

[0028] Comparative Example 2 The difference from Example 1 is that 30g of γ-glycidyl ether propyltrimethoxysilane is not added in step S4. Instead, in step S4 of Example 1, 30g of anhydrous ethanol, 15g of deionized water, and 200mg of citric acid monohydrate are added sequentially to a glass beaker. The mixture is stirred at 600 rpm for 30 minutes at 25°C, then the dispersion is added all at once, and stirring continues for another 60 minutes. The system is then sealed and allowed to mature for 12 hours. All other conditions are the same as in Example 1.

[0029] Comparative Example 3 The difference from Example 1 is that in step S4, the time for obtaining the epoxy silane pre-hydrolyzed solution by stirring at 600 r / min at 25°C is adjusted from 30 min to 1 min. The remaining conditions are the same as in Example 1.

[0030] Comparative Example 4 The difference from Example 1 is as follows: First, the epoxy silane pre-hydrolyzed solution is added to the phosphorus-containing aqueous polyurethane dispersion obtained in step S2 according to step S4 of Example 1, and stirring is continued for 60 min, followed by sealed curing for 12 h; then, ethylenediamine aqueous solution is added dropwise to the dispersion according to step S3 of Example 1, and stirring is continued for 30 min. The remaining conditions are the same as in Example 1.

[0031] Comparative Example 5 The difference from Example 1 is that in step S6, 28% ammonia solution is not added to adjust the pH to 8.5. The remaining conditions are the same as in Example 1.

[0032] Comparative Example 6 The difference from Example 1 is that in step S6, the addition of 28% ammonia solution was changed from 5 minutes before printing to adding it immediately after the base ink had been left to stand for 30 minutes, adjusting the pH to 8.5, and then letting it stand for another 90 minutes before printing. All other conditions were the same as in Example 1.

[0033] Performance testing: To verify the comprehensive performance of the waterborne polyurethane-based printing inks obtained in the examples and comparative examples in terms of drying speed, anti-blocking, abrasion resistance, water and ethanol resistance, and low migration, the following standards were used for testing. Sample printing preparation: Each sample was gravure printed on the same polypropylene film substrate according to step S7 of its corresponding example or comparative example. The printing line speed was 150 m / min, the hot air drying temperature was 55℃, and the hot air residence time for a single color segment was 3 s. After printing, the samples were placed at 25℃ for 24 h to complete cross-linking and curing, thus obtaining printed samples for abrasion, anti-blocking, water and ethanol resistance, adhesion, and migration tests.

[0034] Ink viscosity and fineness: Viscosity was determined according to GB / T 13217.4-2020 "Ink Viscosity Test Method". After the sample was kept at 25℃ for 30 min, the outflow time was measured using a No. 4 cup. The viscosity was recorded as t(25℃, s / No. 4 cup). Each sample was tested 3 times and the arithmetic mean was taken. Fineness was determined according to GB / T 13217.3-2022 "Ink Fineness Test Method". The sample was placed on a scraper fineness meter and scraped once with a specified scraper. The fineness value was read and expressed as μm. Each sample was tested 3 times and the arithmetic mean was taken.

[0035] Drying performance (initial drying): The drying performance was tested according to GB / T 13217.5-2023 "Ink Drying Test Method". Under the conditions of 25℃ and 65% relative humidity, a uniform ink film with a width of 50 mm and a wet film thickness of 10 μm was prepared on a glass plate using a wire rod. The timing was started immediately after film preparation, and at 30s, a standard scraper was used to lightly touch the film along the coating direction. The length of the dry film that was not damaged after 30s was read as L30s (mm). The longer L30s, the better the initial drying performance. Each sample was tested 3 times and the arithmetic mean was taken.

[0036] Anti-blocking performance: According to GB / T 13217.8-2009 "Test method for anti-blocking of liquid inks", each sample was cut into 50mm×50mm pieces, with the ink side facing up and placed between two glass plates. A pressure of 0.02MPa was applied and the sample was kept at a constant temperature of 40℃ for 24 hours. After removal, the sample was allowed to stand at 25℃ for 30 minutes, and then separated at a uniform speed along a 180° direction to observe whether adhesion and transfer occurred. Adhesion grade B (0-5) was used for characterization, where 0 is no adhesion and no transfer, 1 is slight edge adhesion with transfer area ≤5%, 2 is slight adhesion with transfer area 5%-20%, 3 is obvious adhesion with transfer area 20%-50%, 4 is severe adhesion with transfer area 50%-80%, and 5 is complete adhesion or transfer area ≥80%.

[0037] Rubbing fastness: Tested according to QB / T 5345-2018 "Test Method for Rubbing Fastness of Ink". Each printed sample was cut to 100mm × 250mm and dry-rubbing was performed using a reciprocating rubbing tester. The rubbing head was covered with cotton cloth, the load was 9N, the stroke was 100mm, the reciprocating frequency was 60 times / min, and the number of rubbing cycles was 100. The optical density of the printed black ink was measured before and after rubbing using a reflective densitometer, and the density loss rate ΔOD% was calculated as follows: ΔOD% = [(OD0...] OD 100 [(OD0)]×100%; each sample was tested 3 times and the arithmetic mean was taken.

[0038] Water resistance and ethanol wiping resistance: Water resistance was tested according to GB / T 1733-1993 "Determination of Water Resistance of Paint Films". Each printed sample was immersed in deionized water at 25℃ for 24 hours. After removal, the surface moisture was blotted dry with filter paper and allowed to stand at 25℃ for 60 minutes. The appearance change was evaluated according to a grade W (0-5), where 0 represents no whitening, no blistering, and no peeling; 1 represents slight whitening that recovers within 60 minutes; 2 represents significant whitening but no blistering that recovers within 24 hours; 3 represents whitening that does not recover within 24 hours but has no blistering or peeling; 4 represents blistering or edge peeling area ≤5%; and 5 represents peeling area >5%. Ethanol wiping resistance was tested according to GB / T The test was conducted according to 23989-2009 "Determination of Solvent Resistance of Coatings by Wiping": A cotton cloth soaked in 95% ethanol was used, with a load of 9N, to wipe the printed ink layer repeatedly at a frequency of 1 sw. The number of swipes (NEtOH) at which the ink layer was exposed or the optical density decreased by 0.10 was recorded.

[0039] Total migration: Tested according to GB 31604.1-2015 "National Food Safety Standard General Rules for Migration Testing of Food Contact Materials and Articles" and GB 31604.8-2016 "National Food Safety Standard Determination of Total Migration of Food Contact Materials and Articles". Each printed sample was cut to 10cm × 10cm, with only the printed surface remaining as the contact surface. A 10% (v / v) ethanol aqueous solution was used as the food simulant, calculated at 1mL / cm². 2 The contact ratio was adjusted by adding the simulant, and contact was carried out at 40℃ for 10 days. After contact, the extract was transferred to a pre-weighed evaporating dish and dried at 105℃ to constant weight (mass change ≤ 0.5 mg over 30 min). The total migration amount M (mg / dm³) was calculated. 2 Each sample was tested three times and the arithmetic mean was taken.

[0040] Table 1 Performance test results of the examples and comparative examples

[0041] Data Analysis: As can be seen from the data in Table 1, the waterborne polyurethane-based printing ink prepared by this invention exhibits a consistent synergistic improvement trend in indicators such as initial drying properties, anti-blocking properties, abrasion resistance, water resistance, and ethanol wiping resistance, while the total migration remains at a low level. Specifically, Example 3 is generally superior in terms of initial drying properties, anti-blocking properties, and media resistance; Example 1 achieves a balance between abrasion resistance and low migration; Examples 2 and 5 are slightly weaker in some media resistance and anti-blocking indicators; and Example 4 is slightly affected by the adjustment of the hydrophilicity of the formulation in terms of water resistance and migration, but still maintains stable performance. The reasons may be as follows: the aqueous polyurethane dispersion constructed from polycarbonate diol, isophorone diisocyanate, and dimethylolpropionic acid provides the basis for film formation and toughness; the phosphorus-containing polar structure introduced by diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate is beneficial to improving the interfacial interaction between carbon black and the polymer network, and enhancing the wetting and anchoring of the polypropylene film surface; after hydrolysis under acidic conditions, γ-glycidyl ether propyltrimethoxysilane forms a denser network structure with ethylenediamine through a reaction process triggered by ammonia, thereby improving anti-blocking, friction resistance, and media resistance without significantly sacrificing rheology and dispersion, and reducing the residue of migratable small molecules.

[0042] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, when diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonic acid is not added to the system, the initial drying properties, anti-blocking properties, abrasion resistance, water resistance, and ethanol wiping resistance all decrease to varying degrees, while the total migration increases. The main reason for this is that the lack of a phosphorus-containing polar structure weakens the interfacial interaction between carbon black and the polyurethane matrix, and results in insufficient wetting and anchoring of the polypropylene film. This makes the ink film more susceptible to microscopic damage and the release of migratable components under friction and media action. Therefore, the phosphorus-containing structure makes a crucial contribution to interfacial stability and low migration.

[0043] As can be seen from the data in Example 1 and Comparative Example 2 in Table 1, when γ-glycidyl ether propyltrimethoxysilane is not added to the system, the decrease in anti-adhesion, abrasion resistance, water resistance, and ethanol wiping resistance is more significant, while the total migration is also significantly increased. The main reason is that without this component, the system struggles to form a stable hydrolysis-reaction-densification network structure. The reaction process triggered by ethylenediamine and ammonia water is less likely to construct effective structural reinforcement points, making the ink film more prone to swelling and density decay under the influence of water and ethanol. Compared to the case where only the phosphorus-containing structure is missing, this change exhibits a stronger overall degradation, indicating that the network structure plays a fundamental supporting role in overall performance.

[0044] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 3 and 4, when the hydrolysis time of γ-glycidyl etherpropyltrimethoxysilane is insufficient or its addition order is changed, the fineness and rheological stability deteriorate, leading to a simultaneous deterioration in initial drying properties, anti-adhesion, and abrasion resistance, as well as a decrease in water resistance, ethanol wiping resistance, and an increase in migration. Among these, Comparative Example 4 shows a greater degree of deterioration, presumably related to the premature local reaction caused by the earlier addition of γ-glycidyl etherpropyltrimethoxysilane, which easily leads to uneven dispersion structure and micro-agglomeration, ultimately forming defective channels after film formation, making it easier for the medium to enter and amplify frictional damage. Therefore, sufficient hydrolysis and the order of addition jointly determine the controllability of the structural construction.

[0045] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 5 and 6, when ammonia is not added or is added at an inappropriate time, initial drying properties and anti-blocking properties are affected, and water resistance, ethanol wiping resistance, and abrasion resistance also decrease synergistically, while the total migration increases accordingly. The main reason is that ammonia not only affects the reaction initiation rhythm of the system but also the formation window of the network structure in the early stage of film formation. Without ammonia, the structural enhancement process is insufficient, and the ink film is more likely to retain migratable components in the short film-forming stage, which are then released more rapidly under the action of the medium. Adding ammonia too early can easily cause local structural changes in the system and result in uneven dispersion and film formation, thereby simultaneously weakening anti-blocking and abrasion resistance. Therefore, there is a significant synergy between the timing of ammonia addition and γ-glycidyl etherpropyltrimethoxysilane and ethylenediamine, demonstrating a comprehensive gain greater than the sum of its parts.

[0046] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A water-based polyurethane-based printing ink, characterized in that, By weight, it comprises: 600-800 parts of an epoxy silane crosslinking latent phosphorus-containing aqueous polyurethane dispersion, 100-140 parts of abrasion-resistant and anti-blocking additive, 50-70 parts of thickener, 250-350 parts of deionized water, 700-900 parts of aqueous carbon black grinding paste, and ammonia, wherein the ammonia is used to adjust the pH of the aqueous polyurethane-based printing ink to 8.2-9.0; The epoxy silane crosslinked latent phosphorus-containing aqueous polyurethane dispersion is prepared by reacting a prepolymer obtained from polycarbonate diol, isophorone diisocyanate, dimethylolpropionic acid, and diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate, neutralizing it with N,N-dimethylethanolamine, dispersing it in an aqueous phase, chain-extending it with ethylenediamine, and then introducing it into a pre-hydrolyzed solution containing γ-glycidyl etherpropyltrimethoxysilane; wherein, by mass parts, the dimethylolpropionic acid is 40-80 parts, the diethyl N,N-bis(2-hydroxyethyl)aminomethylenephosphonate is 20-60 parts, the N,N-dimethylethanolamine is 30-60 parts, the ethylenediamine is 25-37 parts, and the γ-glycidyl etherpropyltrimethoxysilane is 15-45 parts; and the final isocyanate group mass fraction of the prepolymer is controlled to be 4%-5%.

2. The water-based polyurethane printing ink according to claim 1, characterized in that, The water-based carbon black grinding paste comprises, by weight parts: 180-220 parts of epoxy silane crosslinked latent phosphorus-containing water-based polyurethane dispersion, 70-90 parts of dispersant, 5-20 parts of wetting agent, 2-10 parts of defoamer, 350-550 parts of deionized water, and 100-140 parts of carbon black.

3. The water-based polyurethane printing ink according to claim 1, characterized in that, The ammonia solution has a mass fraction of 28%.

4. The water-based polyurethane printing ink according to claim 1, characterized in that, The dispersant is an aqueous anionic polycarboxylate dispersant, the wetting agent is a polyether-modified siloxane copolymer, the defoamer is a polyether-modified siloxane copolymer containing fumed silica, the wear-resistant and anti-blocking aid is a wax emulsion, and the thickener is a nonionic HEUR rheology modifier.

5. The water-based polyurethane printing ink according to claim 1, characterized in that, The pre-hydrolyzed solution containing γ-glycidyl etherpropyltrimethoxysilane is composed of 15-45 parts by mass of γ-glycidyl etherpropyltrimethoxysilane, 15-45 parts of anhydrous ethanol, 7.5-22.5 parts of deionized water, and 0.1-0.5 parts of citric acid monohydrate.

6. A method for preparing an aqueous polyurethane-based printing ink according to any one of claims 1-5, characterized in that, Includes the following steps: A) Preparation of phosphorus-containing aqueous polyurethane dispersions with latent epoxy silane crosslinking; B) Preparation of water-based carbon black grinding paste; C) A phosphorus-containing aqueous polyurethane dispersion with epoxy silane crosslinking potential, a wear-resistant and anti-blocking agent, a thickener and deionized water are mixed to obtain a binder. A water-based carbon black grinding paste is added to the binder and mixed to obtain a basic water-based ink. D) Let the base ink stand for 120 minutes before printing. Add ammonia 1-10 minutes before printing to adjust the pH to 8.2-9.0 to obtain water-based polyurethane printing ink.

7. The method for preparing waterborne polyurethane-based printing ink according to claim 6, characterized in that, In step B), a horizontal sand mill is used for grinding. The grinding beads have a particle size of 0.6 mm, the cooling water temperature is controlled at ≤35℃, the grinding time is 60 min, and the fineness of the scraper after grinding is ≤10 μm.

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