Environment-friendly water-based composite ink and preparation method thereof

Abstract

This application belongs to the field of ink technology and discloses an environmentally friendly water-based composite ink and its preparation method. The preparation method includes the following steps: adding polyurethane and metal salt to a solvent and mixing to obtain a mixture; then adding acrylate to the mixture, stirring, and adjusting the pH to alkaline to obtain a composite emulsion, wherein the acrylate contains acetyl groups, and the solvent is composed of a mixture of water and ethanol; adding a polyphenol compound and an acylhydrazine monomer sequentially to the composite emulsion, stirring evenly to obtain a dispersion solution; adding an adsorbent to the dispersion solution and stirring evenly to obtain a premixed ink; then adding a functional additive to the premixed ink and continuing stirring to obtain an environmentally friendly water-based composite ink, wherein the adsorbent contains hydroxyl or amide groups. The environmentally friendly water-based composite ink prepared by the above method can not only reduce the VOCs of the ink but also improve its adhesion.

Description

Technical Field

[0001] This application relates to the field of ink technology, specifically to an environmentally friendly water-based composite ink and its preparation method. Background Technology

[0002] Ink is a viscous dispersion system composed of pigments, binders, solvents, and additives, used to form graphic information on a substrate through printing processes. Traditional solvent-based inks use organic solvents such as toluene, methyl ethyl ketone (MEK), and ethyl acetate as the main diluents, with VOC content as high as 70% to 90%. During production and use, they release large amounts of harmful gases, causing air pollution and health risks, and are also flammable and explosive, posing safety hazards. Faced with increasingly stringent environmental regulations, water-based composite inks have emerged. These inks use deionized water to replace most organic solvents, reducing the VOC content and achieving low toxicity and low emissions from the source. They are widely used in the flexible packaging fields of food and pharmaceuticals.

[0003] Meanwhile, due to the high latent heat of vaporization and slow evaporation rate of water, the drying efficiency of ink is much lower than that of traditional solvent-based products, affecting production efficiency. Metal salt driers and other additives are often added to the system to accelerate ink film drying. However, ink drying is a gradual process from the surface inwards—the surface layer of the ink film first comes into contact with hot air and forms a film, while the inner layer gradually dries through heat transfer and solvent diffusion. The addition of fast-drying agents further accelerates surface evaporation, forming a dense polymer surface that seals in residual moisture and additives, leading to a problem of surface drying but internal incomplete drying. Simultaneously, premature surface curing hinders heat transfer to the inner layer, preventing the inner resin particles from reaching the glass transition temperature required for fusion, resulting in weak interfaces within the ink film. Furthermore, for systems relying on later chemical cross-linking, the rapid moisture loss caused by fast-drying agents leads to a sudden change in the system's pH value, locking the cross-linking agent before it fully reacts, reducing the cross-linking density, and ultimately resulting in a significant decrease in the adhesion strength of the ink on the plastic film, making it difficult to meet the high peel strength requirements of composite packaging. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an environmentally friendly water-based composite ink and its preparation method, which aims to solve the problem that the surface solvent in water-based composite ink evaporates too quickly, resulting in uneven cross-linking inside the ink film and a decrease in ink film adhesion.

[0005] To address the aforementioned technical problems, a method for preparing an environmentally friendly water-based composite ink is proposed, comprising the following steps: S1. Polyurethane and metal salt are added to a solvent and mixed to obtain a mixture. Then, acrylate is added to the mixture, and the pH is stirred and adjusted to alkaline to obtain a composite emulsion. The acrylate contains acetyl groups, and the solvent is a mixture of water and ethanol. S2. Add the polyphenol compound and hydrazide monomer to the composite emulsion in sequence, stir evenly to obtain a dispersion solution; S3. Add the adsorbent to the dispersion solution and stir evenly to obtain a premixed ink. Then add functional additives to the premixed ink and continue stirring to obtain an environmentally friendly water-based composite ink. The adsorbent contains hydroxyl or amide groups.

[0006] In some embodiments, step S1 includes: S1.1 Add polyurethane to a solvent, heat to 40-60℃ and stir until homogeneous. Then add to an aqueous solution containing a metal salt concentration of 5-10 wt%, and add over a period of 15-30 minutes, maintaining a stirring speed of 300-500 rpm during the addition process to obtain a mixture. The mass ratio of polyurethane to solvent is (20-40):(40-60), and the amount of metal salt added is 1-5 wt% of the mass of polyurethane. S1.2 The acetoacetyl compound and acrylate monomer are mixed at a mass ratio of 1:(10~20) to obtain a mixture. Then, a free radical initiator is added to the mixture, and the mixture is heated to 70~85℃ in an inert atmosphere and stirred for 2~4 hours to obtain an acrylate containing acetoacetyl groups. The amount of free radical initiator added is 0.5~2wt% of the mass of the mixture. S1.3 Add the acrylate containing acetoacetyl groups to the mixture within 10-20 min, stir for 20-30 min to obtain the initial emulsion, wherein the mass ratio of the acrylate containing acetoacetyl groups to the solvent is (15-30):(40-60); S1.4 Add a pH adjuster to the initial emulsion to adjust the pH of the initial emulsion to 8.0~9.5 to obtain a composite emulsion.

[0007] In some embodiments, the metal salt in step S1.1 includes at least one of calcium chloride, magnesium chloride, and magnesium sulfate, and the solvent is composed of water and ethanol mixed in a mass ratio of (65~75):(25~35). In step S1.2, the acetoacetyl compound includes at least one of diacetone acrylamide, ethyl acetoacetate methacrylate, and ethyl acetoacetate acrylate; the acrylate monomer includes at least one of methyl methacrylate, butyl acrylate, and isooctyl acrylate; and the free radical initiator includes at least one of potassium persulfate, ammonium persulfate, and azobisisobutyronitrile. The pH adjuster in step S1.4 includes one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine.

[0008] In some embodiments, step S2 includes: S2.1 Dissolve the polyphenol compound and the acylhydrazine monomer separately in deionized water to prepare aqueous solutions with concentrations of 5-15 wt% and 10-20 wt% respectively. Adjust the pH of the aqueous solution to 8.0-9.5 using a pH adjuster to obtain polyphenol aqueous solution and acylhydrazine aqueous solution. S2.2 Add the polyphenol aqueous solution dropwise to the composite emulsion. After the addition is complete, stir for 20-30 minutes. Then add the hydrazide aqueous solution dropwise and continue stirring for 10-20 minutes to obtain a dispersion solution. The amount of polyphenol compound added is 0.5-3 wt% of the total mass of polyurethane and acrylate. The molar ratio of hydrazide group in the hydrazide monomer to acetyl acetyl group in the acrylate is (0.8-1.2):1.

[0009] In some embodiments, the polyphenolic compound includes at least one of tannic acid, propyl gallate, epigallocatechin gallate, quercetin, and ellagic acid; the acylhydrazine monomer includes at least one of adipate dihydrazine, succinate dihydrazine, glutarate dihydrazine, and oxalate dihydrazine; and the pH adjuster includes one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine.

[0010] In some embodiments, step S3 includes: S3.1 Dissolve the adsorbent in deionized water to prepare an aqueous solution with a concentration of 5-15 wt%, and adjust the pH of the aqueous solution to 8.0-9.5 using a pH adjuster to obtain the adsorbed aqueous solution; S3.2 Add the adsorbent aqueous solution dropwise to the dispersion solution and stir for 15-30 minutes to obtain the premixed ink. The amount of adsorbent added is 0.3-2 wt% of the composite emulsion mass. S3.3 Add functional additives to the premixed ink, stir and disperse to obtain environmentally friendly composite ink, wherein the amount of functional additives added is 0.1~0.8wt% of the mass of the premixed ink.

[0011] In some embodiments, the adsorbent in step S3.1 is a hydroxyl adsorbent containing hydroxyl groups or an amide adsorbent containing amide groups, wherein the hydroxyl adsorbent is polyvinyl alcohol and / or polyethylene glycol, and the amide adsorbent is polyacrylamide and / or polyasparagine. The functional additive in step S3.3 includes at least one of wetting agent, defoamer, and thickener.

[0012] In some embodiments, the wetting agent includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and polyoxyethylene alkylamine; Defoamers include at least one of dimethyl silicone oil, polydimethylsiloxane, acetylenic diol, and mineral oil; Thickeners include at least one of hydroxyethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

[0013] In addition, an environmentally friendly water-based composite ink is provided, which is prepared by the method described above.

[0014] The beneficial effects of this invention are as follows: Firstly, in terms of controlling solvent evaporation rate and improving adhesion, in step S1, metal ions coordinate and crosslink with polyurethane carboxyl groups, causing the polyurethane to shrink and become hydrophobic. Simultaneously, the salting-out effect forces acrylate to nucleate independently, forming a two-droplet dispersion system where polyurethane and acrylate are immiscible, thus avoiding internal stress caused by the difference in shrinkage rates between the two phases from the outset. In step S2, the polyphenol compound forms multiple hydrogen bonds and coordinate anchors with the surfaces of the two droplets through phenolic hydroxyl groups, constructing stable molecular bridges at the interface. Subsequently, during the drying process, the hydrazide monomer undergoes hydrazone crosslinking with acetoacetyl groups (-CO-CH2-CO-) as the pH decreases. Simultaneously, the polyphenol, after being oxidized to quinone, undergoes Michael addition with the polyurethane amino group, forming a complementary double-crosslinked network. Because the polyphenol is pre-anchored at the interface, the crosslinking reaction proceeds uniformly inward from the interface between the two phases, avoiding microcracks and internal stress concentration caused by the rapid evaporation of the surface solvent, which leads to the surface layer solidifying first and the inner layer shrinking later. This results in a uniform crosslinking density of the ink film and significantly improved adhesion. Secondly, regarding the reduction of VOCs volatilization, in step three, the adsorbent captures ethanol through hydroxyl-ethanol hydrogen bonds and amide-ethanol hydrogen bonds. In step two, the polyphenol compound preferentially captures free metal ions through competitive chelation, forming a stable chelated ring complex that completely encapsulates the metal ions. This avoids both the deactivation of the adsorbent due to coordination cross-linking between the metal ions and the active sites such as the amide and carbonyl groups, and the catalytic acceleration effect of metal ions on ethanol volatilization. The synergistic effect of these two processes significantly reduces VOCs emissions. Furthermore, the small amount of ethanol remaining in the membrane acts as a plasticizer, improving the flexibility of the ink film. This allows the ink film to release internal stress through deformation when the substrate deforms, preventing stress concentration at the interface and subsequent film detachment, thereby indirectly enhancing adhesion. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a method for preparing an environmentally friendly water-based composite ink in one embodiment. Detailed Implementation

[0016] In the description of this application, it should be noted that, unless specific conditions are specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0017] Please refer to Figure 1This invention proposes a method for preparing an environmentally friendly water-based composite ink, the method comprising the following steps: S1. Polyurethane and metal salt are added to a solvent and mixed to obtain a mixture. Then, acrylate is added to the mixture, and the pH is stirred and adjusted to alkaline to obtain a composite emulsion. The acrylate contains acetyl groups, and the solvent is a mixture of water and ethanol.

[0018] Metal ions coordinate and crosslink with the carboxyl groups of polyurethane, causing the polyurethane to shrink and become hydrophobic. At the same time, the salting-out effect forces the acrylate to nucleate independently, forming a two-droplet dispersion system in which the polyurethane and acrylate are immiscible, thus avoiding the internal stress caused by the difference in shrinkage rates between the two phases from the source.

[0019] Step S1 includes: S1.1 Add polyurethane to the solvent, heat to 40~60℃ and stir evenly, then add to an aqueous solution containing 5~10wt% metal salt. The addition time is 15~30min, and the stirring speed is maintained at 300~500rpm during the addition process to obtain a mixture. The mass ratio of polyurethane to solvent is (20~40):(40~60), and the amount of metal salt added is 1~5wt% of the mass of polyurethane.

[0020] In step S1.1, the metal salt includes at least one of calcium chloride, magnesium chloride, and magnesium sulfate, and the mass ratio of water to ethanol in the solvent is (65~75):(25~35).

[0021] The metal salt was prepared as a 5-10 wt% dilute solution and slowly added dropwise over 15-30 minutes. This avoided excessive local metal ion concentrations that could lead to over-crosslinking of the polyurethane, resulting in precipitation or gelation. It ensured that the metal ions uniformly coordinated and crosslinked with the carboxyl groups on the polyurethane molecular chains, allowing the polyurethane segments to shrink gently and controllably into fine, uniformly sized hydrophobic droplets. Secondly, the amount of metal salt added was controlled within the range of 1-5 wt% of the polyurethane mass. This was sufficient to induce sufficient hydrophobicity in the polyurethane and create conditions for subsequent phase separation of the acrylate, without causing excessive... The excessive crosslinking leads to system instability; secondly, the mass ratio of water to ethanol in the solvent is controlled at (65~75):(25~35). This ratio can ensure the initial stable dispersion of the polyurethane emulsion and reserve sufficient space for the polarity adjustment of the continuous phase for the subsequent salting-out effect. At the same time, an appropriate amount of ethanol helps to reduce the viscosity of the system and promote the uniform mixing of the metal salt solution; finally, heating to 40~60℃ and maintaining a stirring speed of 300~500rpm can accelerate the diffusion and coordination reaction rate of metal ions and avoid excessive shearing that could damage the integrity of the polyurethane droplets.

[0022] S1.2 Mix the acetoacetyl compound and acrylate monomer at a mass ratio of 1:(10~20) to obtain a mixture. Then add a free radical initiator to the mixture and heat it to 70~85℃ in an inert atmosphere. Stir the reaction for 2~4h to obtain an acrylate containing acetoacetyl groups. The amount of free radical initiator added is 0.5~2wt% of the mass of the mixture.

[0023] Meanwhile, in step S1.2, the acetoacetyl compound includes at least one of diacetone acrylamide, ethyl acetoacetate methacrylate, and ethyl acetoacetate acrylate; the acrylate monomer includes at least one of methyl methacrylate, butyl acrylate, and isooctyl acrylate; and the free radical initiator includes at least one of potassium persulfate, ammonium persulfate, and azobisisobutyronitrile.

[0024] The acetoacetyl compound has carbon-carbon double bonds at its molecular end, and the acrylate monomer also has carbon-carbon double bonds. Under the attack of free radicals generated by the thermal decomposition of the free radical initiator, the carbon-carbon double bonds are opened and a chain-growth polymerization reaction occurs. The acetoacetyl compound is covalently embedded in the acrylate polymer backbone, so that the acetoacetyl group is suspended on the polymer chain as a side group, thereby obtaining a functionalized acrylate copolymer containing acetoacetyl groups.

[0025] S1.3 Add the acrylate containing acetoacetyl groups to the mixture within 10-20 minutes, stir for 20-30 minutes to obtain the initial emulsion.

[0026] When acrylates containing acetoacetyl groups are added to the mixture, the pre-added metal ions dissociate in the continuous phase into positively charged metal ions and negatively charged anions. These ions undergo strong hydration with water and ethanol molecules, and a large number of free water molecules are attracted by the ions to form a hydration layer. This reduces the number of free water molecules available to dissolve the acrylate in the continuous phase. At the same time, the presence of ions disrupts the hydrogen bond network between the acrylate monomer and the solvent molecules. This salting-out effect significantly reduces the solubility of acrylate in the water-alcohol mixed solvent, causing it to precipitate from the continuous phase and be forced to nucleate independently. In addition, the metal ions preferentially coordinate and crosslink with the carboxyl groups on the polyurethane molecular chain, causing the polyurethane chain segments to shrink, fold, and hydrophobize, forming stable hydrophobic polyurethane droplets. The acrylate cannot enter the interior of the hydrophobic polyurethane droplets and therefore exists as an independent droplet, ultimately resulting in a two-droplet system in which polyurethane and acrylate are independently dispersed.

[0027] S1.4 Add a pH adjuster to the initial emulsion to adjust the pH of the initial emulsion to 8.0~9.5 to obtain a composite emulsion.

[0028] The pH adjuster includes one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine. The pH is adjusted to 8.0-9.5, causing the carboxyl groups on the surface of the polyurethane droplets to ionize into carboxylate anions, which enhances the electrostatic repulsion between the droplets. This prevents the polyurethane droplets from aggregating or merging with the acrylate droplets, maintaining their independent and dispersed two-droplet structure. This ensures that the composite emulsion obtained in step one has a stable phase separation morphology. At the same time, the selected pH adjusters such as ammonia and triethylamine gradually escape with the solvent during the ink drying process, causing the pH of the system to slowly decrease from alkaline to neutral or weakly acidic, creating conditions for the smooth triggering of the subsequent hydrazone crosslinking reaction.

[0029] S2. Add the polyphenol compound and hydrazide monomer to the composite emulsion in sequence, stir evenly, and obtain a dispersion solution.

[0030] Polyphenolic compounds form multiple hydrogen bonds and coordinate anchors with the surfaces of the two droplets through phenolic hydroxyl groups, constructing stable molecular bridges at the interface. Subsequently, during the drying process, the hydrazide monomer undergoes hydrazone crosslinking with acetoacetyl groups as the pH decreases. Simultaneously, the polyphenols are oxidized to quinones and undergo Michael addition with polyurethane amino groups, forming a complementary double crosslinked network. Because the polyphenols are pre-anchored at the interface, the crosslinking reaction proceeds uniformly inward from the interface between the two phases, avoiding microcracks and internal stress concentrations caused by the rapid evaporation of the surface solvent, which leads to the surface layer solidifying first and the inner layer shrinking later. This results in a uniform crosslinking density of the ink film and significantly improved adhesion.

[0031] Step S2 includes: S2.1 Dissolve the polyphenol compound and the acylhydrazine monomer separately in deionized water to prepare aqueous solutions with concentrations of 5~15wt% and 10~20wt% respectively. Adjust the pH of the aqueous solution to 8.0~9.5 using a pH adjuster to obtain polyphenol aqueous solution and acylhydrazine aqueous solution.

[0032] The polyphenolic compounds include at least one of tannic acid, propyl gallate, epigallocatechin gallate, quercetin, and ellagic acid; the acylhydrazide monomers include at least one of adipic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, and dioxalate dihydrazide; and the pH adjuster includes one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine.

[0033] Polyphenolic compounds are prone to intermolecular aggregation in the solid state or at high concentrations. Direct addition may lead to excessively high local concentrations, resulting in precipitation or uneven dispersion. Although acylhydrazide monomers have good water solubility, their dissolution rate is slow when added directly in solid state, easily resulting in undissolved particles. Through pre-dissolution, polyphenols and acylhydrazides are uniformly dispersed in the aqueous phase at the molecular level, avoiding the problems of uneven dispersion and excessive local concentration caused by direct addition in solid state. At the same time, pre-adjusting the pH to 8.0~9.5 allows the phenolic hydroxyl groups of polyphenols to partially ionize, enhancing their water solubility, and keeps the acylhydrazides in a stable and inert state under alkaline conditions. This ensures that both can be rapidly and uniformly dispersed in the system after being added to the composite emulsion, laying the foundation for subsequent interfacial anchoring of polyphenols and uniform distribution of acylhydrazides.

[0034] S2.2 Add the polyphenol aqueous solution dropwise to the composite emulsion. After the addition is complete, stir for 20-30 minutes. Then add the hydrazide aqueous solution dropwise and continue stirring for 10-20 minutes to obtain a dispersion solution. The amount of polyphenol compound added is 0.5-3 wt% of the total mass of polyurethane and acrylate. The molar ratio of hydrazide group in the hydrazide monomer to acetyl acetyl group in the acrylate is (0.8-1.2):1.

[0035] First, add an aqueous polyphenol solution and stir for 20-30 minutes to fully anchor the polyphenol compound to the surfaces of the polyurethane and acrylate droplets. The phenolic hydroxyl groups of the polyphenol form multiple hydrogen bonds and coordination interactions with the urethane bonds and ester carbonyl groups on the surfaces of the two droplets, constructing stable molecular bridges at the interface and providing uniform initiation sites for subsequent crosslinking reactions. The amount of polyphenol added is controlled at 0.5-3 wt% of the total mass of polyurethane and acrylate to form a complete interfacial anchoring layer without causing excessive crosslinking or thickening of the system. After the polyphenol anchoring is complete, add an aqueous hydrazide solution and continue stirring for 10-20 minutes. At this point, the hydrazide is uniformly dispersed in the continuous phase, but because the system pH is maintained at an alkaline condition of 8.0-9.5, the hydrazide groups remain inert and will not prematurely crosslink with the acetoacetyl groups. The molar ratio of hydrazide groups to acetoacetyl groups is controlled at 0.8-1.2:1 to ensure that the crosslinking reaction proceeds fully during the subsequent drying process. The order of adding polyphenols first and then acylhydrazides avoids the competitive reaction that may occur when polyphenols and acylhydrazides come into direct contact in the solution phase. This ensures that polyphenols preferentially complete interfacial anchoring and that acylhydrazides are uniformly dispersed in the continuous phase, resulting in a dispersion solution with controllable interfacial structure, stable two-phase dispersion, and a clear reaction sequence.

[0036] S3. Add the adsorbent to the dispersion solution and stir evenly to obtain a premixed ink. Then add functional additives to the premixed ink and continue stirring to obtain an environmentally friendly water-based composite ink. The adsorbent contains hydroxyl or amide groups.

[0037] The adsorbent captures ethanol through hydroxyl-ethanol hydrogen bonds and amide-ethanol hydrogen bonds, while the polyphenolic compound preferentially captures free metal ions through competitive chelation, forming a stable chelate ring complex that completely encapsulates the metal ions. This avoids both the deactivation of the adsorbent due to coordination cross-linking between the metal ions and the active sites such as the amide and carbonyl groups, and the catalytic acceleration effect of metal ions on ethanol volatilization. The synergistic effect of these two mechanisms significantly reduces VOC emissions.

[0038] Step S3 includes: S3.1 Dissolve the adsorbent in deionized water to prepare an aqueous solution with a concentration of 5~15wt%, and adjust the pH of the aqueous solution to 8.0~9.5 using a pH adjuster to obtain the adsorbed aqueous solution.

[0039] The adsorbent is either a hydroxyl adsorbent containing hydroxyl groups or an amide adsorbent containing amide groups, wherein the hydroxyl adsorbent is polyvinyl alcohol and / or polyethylene glycol, and the amide adsorbent is polyacrylamide and / or polyasparagine.

[0040] Polyvinyl alcohol, polyethylene glycol, polyacrylamide, and polyasparagine are all high molecular weight compounds. When added directly in solid form, they can form undissolved micelles or particles due to excessively high local concentrations, resulting in uneven dispersion of the adsorbent in the system and hindering its effective hydrogen bond capture of ethanol. Pre-dissolving ensures that the adsorbent is uniformly dispersed at the molecular level in the aqueous phase, allowing the polymer chains to fully extend and expose more hydroxyl or amide group active sites. Simultaneously, the pH is pre-adjusted to 8.0–9.5 to maintain consistency between the pH of the adsorbent aqueous solution and the dispersion solution obtained in step S2, preventing local pH fluctuations during addition that could affect system stability.

[0041] S3.2 Add the adsorbent aqueous solution dropwise to the dispersion solution and stir for 15-30 min to obtain the premixed ink, wherein the amount of adsorbent added is 0.3-2 wt% of the composite emulsion mass.

[0042] When the adsorbent aqueous solution is added dropwise to the dispersion solution, the hydroxyl or amide groups in the adsorbent capture ethanol molecules through hydrogen bonding, binding them within the adsorbent network and thus reducing the total amount of ethanol volatilized during ink drying. Simultaneously, stirring ensures the adsorbent is uniformly dispersed in the system, guaranteeing sufficient contact with the ethanol and enabling stable capture.

[0043] S3.3 Add functional additives to the premixed ink, stir and disperse to obtain environmentally friendly composite ink, wherein the amount of functional additives added is 0.1~0.8wt% of the mass of the premixed ink.

[0044] The aforementioned functional additives include at least one of wetting agents, defoamers, and thickeners. The wetting agents are used to reduce the surface tension of the ink and improve its spreading and wetting ability on the substrate, and include at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and polyoxyethylene alkylamine. The defoamers are used to suppress and eliminate foam generated during production and printing, and to avoid surface defects such as pinholes, and include at least one of dimethyl silicone oil, polydimethylsiloxane, acetylsyl glycol, and mineral oil. The thickeners are used to adjust the viscosity of the ink and improve its printability and leveling properties, and include at least one of hydroxyethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

[0045] In addition, this application also provides an environmentally friendly water-based composite ink, which is prepared by the above-described method for preparing an environmentally friendly water-based composite ink.

[0046] For example, the present invention provides the following specific embodiments to illustrate the specific preparation method: Example 1 S1.1. Add polyurethane to a solvent composed of water and ethanol in a mass ratio of 70:30, stir evenly, and then add it to an aqueous solution containing 8 wt% calcium chloride. The addition time is 20 min, and the stirring speed is maintained at 400 rpm during the addition process to obtain a mixture. The mass ratio of polyurethane to solvent is 30:50, and the amount of calcium chloride added is 3 wt% of the mass of polyurethane. S1.2. Diacetone acrylamide and butyl acrylate are mixed at a mass ratio of 1:15 to obtain a mixture. Then, azobisisobutyronitrile (AIBN) is added to the mixture, and the mixture is heated to 80°C under an inert atmosphere and stirred for 3 hours to obtain an acrylate containing acetoacetyl groups. The amount of AIBN added is 0.5~2 wt% of the mass of the mixture. S1.3 Add the acrylate containing acetoacetyl groups to the mixture within 15 min and stir for 25 min to obtain the initial emulsion, wherein the mass ratio of the acrylate containing acetoacetyl groups to the solvent is 20:50. S1.4 Add ammonia water dropwise to the initial emulsion to adjust the pH of the initial emulsion to 9.0, and obtain a composite emulsion; S2.1. Epigallocatechin gallate and adipic acid dihydrazide are dissolved in deionized water to prepare aqueous solutions with concentrations of 10wt% and 15wt% respectively. The pH of the aqueous solution is adjusted to 9.0 using ammonia water to obtain polyphenol aqueous solution and hydrazide aqueous solution. S2.2 Add polyphenol aqueous solution dropwise to composite emulsion. After the addition is complete, stir for 25 min. Then add hydrazide aqueous solution dropwise and continue stirring for 15 min to obtain a dispersion solution. The amount of epigallocatechin gallate added is 2 wt% of the total mass of polyurethane and acrylate. The molar ratio of hydrazide group in adipic acid dihydrazide to acetyl acetyl group in acrylate is 1:1. S3.1 Dissolve polyvinyl alcohol in deionized water to prepare an aqueous solution with a concentration of 10 wt%, and adjust the pH of the aqueous solution to 9.0 using ammonia water to obtain an adsorption aqueous solution; S3.2 Add the adsorbed aqueous solution dropwise to the dispersion solution and stir for 20 min to obtain the premixed ink, wherein the amount of polyvinyl alcohol added is 1 wt% of the mass of the composite emulsion; S3.3 Add polydimethylsiloxane to the premixed ink, stir and disperse, let stand, and obtain environmentally friendly composite ink, wherein the amount of polydimethylsiloxane added is 0.2wt% of the mass of the premixed ink.

[0047] Example 2 It is basically the same as Example 1, except that the metal salt used in step S1.1 is magnesium chloride.

[0048] Example 3 It is basically the same as Example 1, except that the adsorbent used in step S3.1 is polyacrylamide, i.e. amide adsorbent.

[0049] Comparative Example 1 It is basically the same as Example 1, except that calcium chloride was not added in step S1.1, that is, no metal salt was added.

[0050] Comparative Example 2 It is basically the same as Example 1, except that no acetoacetyl compound is added in step S1.2, that is, the acrylate in step S1 does not contain acetoacetyl groups.

[0051] Comparative Example 3 The process is basically the same as in Example 1, except that the acetoacetyl compound used in step S1.2 is directly mixed with the acrylate monomer and then added to the mixture in step S1.3. That is, the acetoacetyl group in step S1 is not in the acrylate, but is added in the form of a separate acetoacetyl compound.

[0052] Comparative Example 4 The procedure is basically the same as in Example 1, except that no polyphenol aqueous solution was added in step S2.2, that is, no polyphenol compound was added in step S2.

[0053] Comparative Example 5 It is basically the same as Example 1, except that no aqueous solution of hydrazide was added in step S2.2, that is, no hydrazide monomer was added in step S2.

[0054] Comparative Example 6 It is basically the same as Example 1, except that no adsorption aqueous solution is added in step S3.2, that is, no adsorbent is added in step S3.

[0055] Comparative Example 7 Polyurethane was added to a solvent composed of water and ethanol in a mass ratio of 70:30 and mixed. After stirring evenly, butyl acrylate was added, and the mixture was stirred and ammonia was added dropwise to adjust the pH to 9.0 to obtain a composite emulsion. The mass ratio of polyurethane to solvent was 30:50, and the mass ratio of acrylate to solvent was 20:50. Then polydimethylsiloxane is added, stirred and dispersed, and allowed to stand to obtain environmentally friendly composite ink, wherein the amount of polydimethylsiloxane added is 0.2 wt% of the composite emulsion.

[0056] Performance testing: Adhesion test: conducted in accordance with GB / T 13217.7-2023 "Test Method for Ink Adhesion"; VOCs testing: The tests shall be conducted in accordance with the methods specified in GB 38507-2020 "Limits for the content of volatile organic compounds (VOCs) in inks" and GB / T 38608-2020.

[0057] The test results are shown in Table 1: Table 1 Performance Tests of Environmentally Friendly Water-Based Composite Inks According to the results in Table 1, compared with Comparative Example 7 (no metal salts, no acetyl acetyl groups, no polyphenols, no hydrazides, no adsorbents, only simple physical blending), the environmentally friendly water-based composite inks prepared in Examples 1-3 have good adhesion and low VOC content. Observations of Example 1 and Comparative Examples 1-6 show that the environmentally friendly water-based composite ink of Example 1 is significantly superior to the inks prepared in Comparative Examples 1-6. In Comparative Example 1, the lack of metal salt and the pre-mixing of polyurethane and acrylate raw materials led to internal stress caused by the difference in shrinkage rates between the two phases during drying, resulting in decreased adhesion. Furthermore, observations of Comparative Examples 2-3 show that when the acrylate lacks acetoacetyl groups or when acetoacetyl groups are added as a single acetoacetyl compound, the hydrazide monomer cannot form an effective hydrazone crosslinking network at the acrylate droplet interface, resulting in insufficient cohesive strength and uneven crosslinking density of the ink film, significantly reducing adhesion. The VOC content decreased; in Comparative Example 4, the lack of polyphenol compounds led to the direct poisoning of the adsorbent by metal ions, causing its deactivation. Simultaneously, the polyphenols lost their hydrogen bond fixation of ethanol and interfacial molecular bridge anchoring effects, resulting in an increase in VOCs content and a decrease in adhesion. In Comparative Example 5, the lack of hydrazide monomers resulted in a slight increase in VOCs content, but the inability of the acetylacetyl groups in the acrylate droplets to undergo hydrazone cross-linking led to insufficient cohesive strength of the ink film, resulting in a significant decrease in ink film adhesion. Similarly, in Comparative Example 6, the lack of adsorbent meant that the hydrogen bond fixation of ethanol by polyphenols alone was insufficient to adequately reduce VOCs, leading to a significant increase in the total ethanol volatilization.

[0058] The above embodiments are preferred embodiments of this application, but the implementation of this application is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of this application shall be considered equivalent substitutions and shall be included within the protection scope of this application.

Claims

1. A method for preparing an environmentally friendly water-based composite ink, characterized in that, The preparation method includes the following steps: S1. Polyurethane and metal salt are added to a solvent and mixed to obtain a mixture. Then, acrylate is added to the mixture, and the pH is stirred and adjusted to alkaline to obtain a composite emulsion. The acrylate contains acetyl groups, and the solvent is a mixture of water and ethanol. S2. Add the polyphenol compound and hydrazide monomer to the composite emulsion in sequence, stir evenly to obtain a dispersion solution; S3. Add the adsorbent to the dispersion solution and stir evenly to obtain a premixed ink. Then add functional additives to the premixed ink and continue stirring to obtain an environmentally friendly water-based composite ink. The adsorbent contains hydroxyl or amide groups.

2. The method for preparing an environmentally friendly water-based composite ink according to claim 1, characterized in that, Step S1 includes: S1.1 Add polyurethane to a solvent, heat to 40-60℃ and stir until homogeneous. Then add to an aqueous solution containing a metal salt concentration of 5-10 wt%, and add over a period of 15-30 minutes, maintaining a stirring speed of 300-500 rpm during the addition process to obtain a mixture. The mass ratio of polyurethane to solvent is (20-40):(40-60), and the amount of metal salt added is 1-5 wt% of the mass of polyurethane. S1.2 The acetoacetyl compound and acrylate monomer are mixed at a mass ratio of 1:(10~20) to obtain a mixture. Then, a free radical initiator is added to the mixture, and the mixture is heated to 70~85℃ in an inert atmosphere and stirred for 2~4 hours to obtain an acrylate containing acetoacetyl groups. The amount of free radical initiator added is 0.5~2wt% of the mass of the mixture. S1.3 Add the acrylate containing acetoacetyl groups to the mixture within 10-20 min, stir for 20-30 min to obtain the initial emulsion, wherein the mass ratio of the acrylate containing acetoacetyl groups to the solvent is (15-30):(40-60); S1.4 Add a pH adjuster to the initial emulsion to adjust the pH of the initial emulsion to 8.0~9.5 to obtain a composite emulsion.

3. The method for preparing an environmentally friendly water-based composite ink according to claim 2, characterized in that, In step S1.1, the metal salt includes at least one of calcium chloride, magnesium chloride, and magnesium sulfate, and the solvent is composed of water and ethanol in a mass ratio of (65~75):(25~35). In step S1.2, the acetoacetyl compound includes at least one of diacetone acrylamide, ethyl acetoacetate methacrylate, and ethyl acetoacetate acrylate; the acrylate monomer includes at least one of methyl methacrylate, butyl acrylate, and isooctyl acrylate; and the free radical initiator includes at least one of potassium persulfate, ammonium persulfate, and azobisisobutyronitrile. The pH adjuster in step S1.4 includes one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine.

4. The method for preparing an environmentally friendly water-based composite ink according to claim 1, characterized in that, Step S2 includes: S2.1 Dissolve the polyphenol compound and the acylhydrazine monomer separately in deionized water to prepare aqueous solutions with concentrations of 5-15 wt% and 10-20 wt% respectively. Adjust the pH of the aqueous solution to 8.0-9.5 using a pH adjuster to obtain polyphenol aqueous solution and acylhydrazine aqueous solution. S2.2 Add the polyphenol aqueous solution dropwise to the composite emulsion. After the addition is complete, stir for 20-30 minutes. Then add the hydrazide aqueous solution dropwise and continue stirring for 10-20 minutes to obtain a dispersion solution. The amount of polyphenol compound added is 0.5-3 wt% of the total mass of polyurethane and acrylate. The molar ratio of hydrazide group in the hydrazide monomer to acetyl acetyl group in the acrylate is (0.8-1.2):

1.

5. The method for preparing an environmentally friendly water-based composite ink according to claim 4, characterized in that, The polyphenolic compounds include at least one of tannic acid, propyl gallate, epigallocatechin gallate, quercetin, and ellagic acid; the acylhydrazide monomers include at least one of adipic acid dihydrazide, succinic acid dihydrazide, glutaric acid dihydrazide, and oxalate dihydrazide; and the pH adjusters include one of ammonia, triethylamine, sodium bicarbonate, and dimethylethanolamine.

6. The method for preparing an environmentally friendly water-based composite ink according to claim 1, characterized in that, Step S3 includes: S3.1 Dissolve the adsorbent in deionized water to prepare an aqueous solution with a concentration of 5-15 wt%, and adjust the pH of the aqueous solution to 8.0-9.5 using a pH adjuster to obtain the adsorbed aqueous solution; S3.2 Add the adsorbent aqueous solution dropwise to the dispersion solution and stir for 15-30 minutes to obtain the premixed ink. The amount of adsorbent added is 0.3-2 wt% of the composite emulsion mass. S3.3 Add functional additives to the premixed ink, stir and disperse to obtain environmentally friendly composite ink, wherein the amount of functional additives added is 0.1~0.8wt% of the mass of the premixed ink.

7. The method for preparing an environmentally friendly water-based composite ink according to claim 6, characterized in that, In step S3.1, the adsorbent is a hydroxyl adsorbent containing hydroxyl groups or an amide adsorbent containing amide groups, wherein the hydroxyl adsorbent is polyvinyl alcohol and / or polyethylene glycol, and the amide adsorbent is polyacrylamide and / or polyasparagine. In step S3.3, the functional additives include at least one of wetting agents, defoamers, and thickeners.

8. The method for preparing an environmentally friendly water-based composite ink according to claim 7, characterized in that, The wetting agent includes at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, and polyoxyethylene alkylamine; Defoamers include at least one of dimethyl silicone oil, polydimethylsiloxane, acetylenic diol, and mineral oil; Thickeners include at least one of hydroxyethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, and hydroxypropyl methyl cellulose.

9. An environmentally friendly water-based composite ink, characterized in that, The environmentally friendly water-based composite ink is prepared by any one of the preparation methods of environmentally friendly water-based composite ink according to claims 1-8.

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