Water-based low-voc high-concentration composite ink, preparation method and application thereof

Abstract

The application discloses a kind of water-based low VOCs high concentration composite ink and its preparation method and application, it is related to water-based printing ink field.Composite ink includes the following components: water-based polyurethane resin, water-based acrylic resin, water-based chlorinated polypropylene emulsion, pigment, deionized water, cosolvent, hyperbranched polymer wetting dispersant, water-based adhesion promoter, citrate modified nanocellulose, nitrogen-doped TiO2 / ZnO composite nanodispersion, phosphate-based modified zeolite, polysaccharide natural high molecular thickening / suspending agent.Preparation method includes the following steps: preparation of high concentration pigment pre-dispersion, preparation of high concentration color paste, base compound and total ink modulation, filtration to obtain product.Composite ink is suitable for intaglio printing on BOPP film, PET film or nylon film.The composite ink of the application achieves the comprehensive performance of solid content ≥56.8%, VOCs ≤3.2%, BOPP / PET / nylon adhesion ≥90%, 60 ℃ hot air drying ≤2.5 seconds, storage sedimentation grade 9~10 grade.

Description

Technical Field

[0001] This invention relates to the field of water-based printing ink technology, specifically to a water-based low-VOCs high-concentration composite ink, its preparation method, and its application. Background Technology

[0002] Gravure composite inks are widely used in the reverse printing of flexible packaging plastic films for food, pharmaceuticals, and cosmetics due to their advantages such as rich printing layers, uniform ink layers, and stable operation. Traditional gravure composite inks are mostly solvent-based, with volatile organic compound (VOC) content typically as high as 60% to 80%. During production, large quantities of organic solvents such as ethyl acetate, n-propyl acetate, and isopropanol are used as dilution and dispersion media, resulting in annual VOC emissions in the tens of thousands of tons.

[0003] Water-based inks, using water as the primary solvent, significantly reduce VOC emissions at the source, making them a mainstream technology for the environmental transformation of the printing industry. However, existing water-based composite inks still face several long-standing technical bottlenecks when applied to gravure printing on plastic films.

[0004] First, the solid content is generally low. Because water's wetting properties for pigments are weaker than organic solvents, a large amount of water must be added during pigment dispersion to reduce the system viscosity, resulting in most water-based inks maintaining a solid content of only 30% to 40%. This means that more water needs to be transferred for the same printing area, increasing drying energy consumption and overall operating costs. Second, the drying speed is slow. Water has a high boiling point and a large latent heat of vaporization, and its evaporation rate is far lower than that of organic solvents. Under high-speed gravure printing conditions of 150-250 m / min, water-based inks often cannot dry completely in a short time, easily causing printed materials to stick together, become tacky, and even blister during the lamination process due to residual moisture. Third, the adhesion to different plastic substrates varies significantly. BOPP, PE, and other polyolefin films have low surface energy, while water-based inks have relatively high surface tension, making spreading and wetting difficult. Furthermore, existing water-based resin systems lack specific adhesion to polyolefin materials, resulting in unstable ink adhesion and difficulty in meeting the peel strength requirements of flexible packaging.

[0005] Furthermore, there is a significant contradiction between high concentration and storage stability. When the pigment concentration increases, aqueous systems are prone to thickening, flocculation, and sedimentation, while conventional dispersants often cannot simultaneously meet the requirements of low viscosity and long-term anti-settling performance under high pigment loads. Summary of the Invention

[0006] The purpose of this invention is to provide a water-based low-VOCs high-concentration composite ink, its preparation method, and its application. By combining a ternary resin system with a multifunctional synergistic system, this invention solves the technical problems of existing water-based composite inks, such as low solid content, high VOCs content, unstable adhesion on different plastic film substrates, slow drying speed, and poor storage stability at high concentrations.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A water-based, low-VOCs, high-concentration composite ink, comprising the following components by weight:

[0009] Waterborne polyurethane resin 25-40 parts; waterborne acrylic resin 15-30 parts; waterborne chlorinated polypropylene emulsion 5-15 parts; pigment 20-35 parts; deionized water 8-20 parts; cosolvent 1-5 parts; hyperbranched polymer wetting and dispersing agent 1.5-4 parts; waterborne adhesion promoter 0.5-2.5 parts; citrate-modified nanocellulose 0.5-4.0 parts; nitrogen-doped TiO2 / ZnO composite nanodispersion 0.5-3.0 parts; phosphate-modified zeolite 1.0-5.0 parts; polysaccharide natural polymer thickener / suspending agent 0.2-1.5 parts; defoamer 0.1-0.6 parts; leveling agent 0.2-1.0 parts; waterborne wax emulsion 1-3 parts;

[0010] Among them, the solid content of waterborne polyurethane resin is 40%~50%, the solid content of waterborne acrylic resin is 45%~50%, and the chlorine content of waterborne chlorinated polypropylene emulsion is 20%~35%, with a solid content of 30%~40%.

[0011] In existing technologies, a single type of resin cannot simultaneously meet the adhesion requirements of various plastic substrates such as BOPP, PET, and nylon; conventional dispersants are prone to thickening and flocculation under high pigment loads; and the contradiction between high solids content and storage stability is even more difficult to reconcile. This invention addresses the issue from three levels simultaneously: resin skeleton, dispersion mechanism, and suspension network, constructing a complete solution.

[0012] This invention combines waterborne polyurethane, waterborne acrylic acid, and waterborne chlorinated polypropylene to form a film-forming framework with complementary functions. Waterborne polyurethane imparts excellent flexibility and basic adhesion to PET and nylon; waterborne acrylic acid provides fast drying and high hardness, ensuring the ink layer resists reverse tack; and waterborne chlorinated polypropylene exhibits a specific anchoring and bonding effect on low surface energy polyolefins such as BOPP. The synergistic effect of these three components results in an ink adhesion rate of ≥90% on corona-treated BOPP, PET, and nylon films using adhesive tape, and a composite peel strength with PE film reaching 2.20 N / 15 mm.

[0013] This invention overcomes the limitations of conventional dispersants by employing a hyperbranched polymer wetting and dispersing agent. Its three-dimensional dendritic structure can form multi-point anchoring and strong steric hindrance on the pigment surface, significantly reducing the viscosity of the grinding slurry and enabling pigments to be smoothly ground to a fineness ≤5μm even at high addition levels.

[0014] Simultaneously, this invention constructs a triple anti-settling synergistic mechanism of polysaccharide natural polymers, inorganic nanoparticles, and modified zeolite, achieving a balance between high concentration and long-term storage stability. Long chains of natural polymers such as xanthan gum or sodium carboxymethyl cellulose extend within the system, forming a three-dimensional network through hydrogen bonding adsorption and physical entanglement, uniformly supporting pigment particles. The nitrogen-doped TiO2 / ZnO composite nanodispersion surface is rich in hydroxyl groups and nitrogen-doped active sites, which on one hand strengthen the network through multi-point binding with polymer chains, and on the other hand, the nano-size effect of ZnO generates steric hindrance, preventing direct collision and aggregation of pigment particles. Phosphate-modified zeolite (type A), after hydrothermal treatment with phosphoric acid and grafting with phosphate groups, possesses both microporous adsorption and organic compatibility. Its micropores with a diameter of 0.3~0.8 nm can physically capture free pigments and resin particles, while simultaneously forming coordination between the phosphate groups and nanoparticles to jointly construct a stable suspension network.

[0015] This invention introduces citrate-modified nanocellulose, whose hydrophobic ester components reduce dependence on alcohol ether cosolvents, resulting in VOC content as low as 1.5-3.2%, far exceeding the national standard limit of ≤30%. Simultaneously, the free carboxyl groups of nanocellulose form hydrogen bonds with trace hydroxyl groups on the film surface, synergistically enhancing interfacial bonding with adhesion promoters. The micropores of phosphate-modified zeolite possess adsorption-slow-release functions for residual moisture and small-molecule solvents, effectively preventing surface-drying and internal-wet phenomena during printing. Combined with the fast-drying properties of acrylic resin, the 60℃ hot air drying time is shortened to 1.9-2.5 seconds, fully adaptable to high-speed gravure printing at 150-250 m / min.

[0016] Furthermore, the degree of esterification of the citrate-modified nanocellulose is 0.3~1.0, the carboxyl content is 0.2~0.8 mmol / g, and the aspect ratio is ≥50.

[0017] The degree of esterification determines the lipophilic / hydrophilic balance of nanocellulose. If it is below 0.3, the hydrophobicity is insufficient, and it cannot effectively replace the cosolvent, so the effect of reducing VOCs is not obvious. If it is above 1.0, excessive esterification will lead to a significant reduction in carboxyl groups, weakening its ability to form hydrogen bonds with the substrate (film), thereby losing its adhesion-promoting function.

[0018] Carboxyl groups are key to providing hydrogen bonding sites. Below 0.2 mmol / g, the interfacial adhesion between the ink and the plastic film cannot be effectively enhanced (adhesion improvement is not significant); above 0.8 mmol / g, the product is too water-soluble, leading to a decrease in the water resistance of the ink film and easily causing excessively high viscosity after reconstitution.

[0019] The aspect ratio determines the nano-network reinforcement effect of cellulose. Below 50, the network support capacity of cellulose nanofibers is insufficient, unable to effectively replace part of the co-solvent to maintain film density, and has a weak effect on improving the mechanical strength of the ink film.

[0020] Furthermore, the nitrogen-doped TiO2 / ZnO composite nanodispersion has a Ti to Zn atomic ratio of 10 to 1:1, a nitrogen doping content of 0.5 to 5%, and an average particle size of 20 to 100 nm.

[0021] Furthermore, the co-solvent is selected from one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether acetate, and diethylene glycol butyl ether; the water-based adhesion promoter is selected from one or more of water-based epoxy silane coupling agents, water-based amino silane coupling agents, or water-based titanate coupling agents.

[0022] Furthermore, the hyperbranched polymer wetting and dispersing agent is selected from hyperbranched polyester dispersants or hyperbranched polyether dispersants; the polysaccharide natural polymer thickener / suspending agent is selected from one or more of xanthan gum, sodium carboxymethyl cellulose, or microcrystalline cellulose.

[0023] Conventional water-based inks often use linear sodium polycarboxylate or ammonium polyacrylate dispersants. These dispersants maintain pigment stability through electrostatic repulsion. However, in high-concentration systems where the pigment content reaches 20-35 parts, their steric hindrance effect is insufficient, which can easily lead to a sharp increase in the viscosity of the pigment paste, a decrease in grinding efficiency, or even the inability to complete grinding.

[0024] The hyperbranched polyester or hyperbranched polyether dispersants selected in this invention have the advantage of a unique three-dimensional dendritic molecular structure. Compared with linear dispersants, hyperbranched dispersants have the following irreplaceable functions: Multiple terminal functional groups can be simultaneously adsorbed onto the surface of pigment particles, with adsorption strength far exceeding the single-point or double-point adsorption of linear dispersants, effectively preventing desorption during high-shear grinding; the dendritic structure forms a three-dimensional brush barrier on the pigment surface, and its steric hindrance effect is several times stronger than that of linear molecules, maintaining a stable physical isolation layer between pigment particles and preventing flocculation and thickening at high concentrations; the excellent solubilization ability of the hyperbranched structure can effectively reduce the viscosity of the grinding slurry, enabling high pigment additions of 20-35 parts to be successfully ground to a fineness ≤5μm. Hyperbranched polyester dispersants have a better affinity for inorganic pigments (such as titanium dioxide), while hyperbranched polyether dispersants have a better wetting and dispersing effect on organic pigments (such as phthalocyanine blue), and both can be flexibly selected according to the type of pigment.

[0025] The thickeners commonly used in conventional water-based inks are mostly alkali-swellable acrylic emulsions (ASE) or polyurethane associative thickeners. These synthetic thickeners mainly increase viscosity through hydrophobic association or swelling mechanisms. However, in the triple anti-settling synergistic mechanism constructed in this invention, the thickener needs to have three functions at the same time: forming physical network support, providing hydrogen bond binding sites, and interacting with inorganic nanoparticles.

[0026] The xanthan gum, sodium carboxymethyl cellulose, or microcrystalline cellulose selected in this invention are all polysaccharide-based natural polymers, rich in hydroxyl and carboxyl groups, possessing unique advantages. After these polymer chains fully extend in the system, they form a three-dimensional spatial network with certain strength and elasticity through inter-chain physical entanglement and adsorption with pigments and nanoparticles. This network can uniformly disperse and support pigment particles, significantly delaying sedimentation. The hydroxyl groups on the polysaccharide molecular chains can form strong hydrogen bonds with the hydroxyl groups on the surface of nitrogen-doped TiO2 / ZnO nanoparticles, anchoring the inorganic nanoparticles at network nodes and enhancing the stability of the entire suspension structure. The carboxyl groups of CMC-Na can also undergo weak coordination or electrostatic interaction with the phosphorus hydroxyl groups on the surface of phosphate-modified zeolite, further incorporating the zeolite particles into the three-dimensional network. In contrast, conventional synthetic thickeners lack a sufficient number of active functional groups to achieve the aforementioned multi-point hydrogen bond anchoring with nanoparticles and zeolite, thus making it difficult to construct the triple anti-sedimentation synergistic system required by this invention.

[0027] A method for preparing the aforementioned water-based low-VOCs high-concentration composite ink includes the following steps:

[0028] S100: Mix hyperbranched polymer wetting and dispersing agent, polysaccharide natural polymer thickener / suspending agent, part of defoamer and part of deionized water evenly, add pigment and disperse evenly at high speed to obtain pre-dispersed slurry;

[0029] S200. Nitrogen-doped TiO2 / ZnO composite nano-dispersion and phosphate-modified zeolite are added to the above pre-dispersed slurry. After mixing evenly, the mixture is ground to a fineness of ≤5μm to obtain a high-concentration color paste.

[0030] S300. Mix waterborne polyurethane resin, waterborne acrylic resin, and waterborne chlorinated polypropylene emulsion evenly. Add the above-mentioned high-concentration color paste, remaining deionized water, environmentally friendly co-solvent, citrate-modified nanocellulose, waterborne adhesion promoter, leveling agent, remaining defoamer, and waterborne wax emulsion. Stir evenly and filter to obtain the target composite ink.

[0031] In the S100 pre-dispersion stage, this invention adds hyperbranched polymer wetting and dispersing agents and polysaccharide-based natural polymers (such as xanthan gum and CMC-Na) in advance to perform high-speed dispersion together with the pigments. This timing arrangement has a dual effect: on the one hand, the hyperbranched dispersing agent, with its three-dimensional dendritic structure, forms a strong multi-point adsorption layer and a strong steric barrier on the pigment surface, ensuring that the high-concentration pigments maintain a stable dispersion state with low viscosity and anti-flocculation during subsequent grinding. On the other hand, the natural polymers fully dissolve in the early stage of dispersion, and their long-chain molecules rapidly extend, adsorbing onto the surface of pigment particles using their polyhydroxy structures, and initially constructing a three-dimensional spatial network framework. The process design of dispersion-network synergistic construction allows the natural polymers to participate in the stabilization of the pigment suspension system during the grinding stage, incorporating the pigment particles into the network support structure in advance.

[0032] If the natural polymer is added only in the S300 ink mixing stage, its long chains cannot fully interact with the pigment during the grinding process. Later, relying solely on low-speed stirring makes it difficult to form the same dense and stable three-dimensional network, resulting in a significant decrease in the ink's anti-settling properties. Similarly, if the hyperbranched dispersant is not added in the S100 stage, the pigment surface cannot obtain sufficient steric hindrance protection, leading to a substantial reduction in both grinding efficiency and dispersion stability.

[0033] Nitrogen-doped TiO2 / ZnO composite nanodispersion and phosphate-modified zeolite are added simultaneously in the S200 grinding step, rather than in the S300 ink mixing stage. This timing has dual technical benefits. First, the nanoparticles and zeolite undergo high shear forces with the pigment particles during grinding, resulting in close interfacial contact and physical interlocking, which creates conditions for the establishment of interparticle interactions (hydrogen bonds, coordination) in the subsequent triple anti-settling mechanism. Second, the zeolite and nanoparticles act as auxiliary grinding media in the grinding stage, utilizing their nanoscale effect to improve grinding efficiency and help to quickly reduce the fineness to ≤5μm. If the above components are added only in the ink mixing stage, they cannot play their auxiliary role in grinding, and it is difficult to achieve the same degree of uniform mixing by stirring alone.

[0034] This method achieves viscosity control through stepwise water addition and viscosity adjustment. In the S100 stage, only 60%~80% deionized water is added to maintain a high solids concentration, placing the grinding process within a favorable window of high solids content and low viscosity, thus preventing a decrease in grinding efficiency due to excessive water. In the S300 stage, the remaining water is added to adjust the ink to the target viscosity. This process route of first grinding a concentrated ink and then thinning it is a key technological guarantee for achieving a fineness of ≤5μm for high-concentration pigments.

[0035] Furthermore, in S100, high-speed dispersion at 1200~1800r / min for 40~60 minutes is obtained to obtain pre-dispersed slurry; the amount of defoamer added accounts for 16.7~50% of the total mass of defoamer, and the amount of deionized water added accounts for 60~80% of the total mass of deionized water.

[0036] In S100, the defoamer is used to suppress bubbles generated by mechanical shearing during high-speed dispersion, preventing foam from hindering pigment wetting and dispersion; in S300, the defoamer is used to suppress bubbles entrained during subsequent ink mixing and stirring, ensuring that the finished coating film is free of defects such as pinholes and craters.

[0037] Further, in S200, the preparation of the phosphate-modified zeolite includes the following: after washing and drying the type A zeolite with deionized water, it is mixed with a phosphoric acid solution with a concentration of 60% to 85%, and hydrothermally treated at 100 to 150°C for 2 to 6 hours. After washing and drying, the zeolite is obtained.

[0038] The present invention preferably uses type A zeolite. When its pore size, silica-alumina ratio, negative charge density and other parameters are best matched with other components (natural polymers and nanoparticles) in the ink system of the present invention, the synergistic effect is most significant, and it can achieve a comprehensive performance of 9-10 sedimentation level after 7 days of accelerated storage at 50°C and ≤3 seconds of hot air drying at 60°C.

[0039] Further, in S300, stir at 400~600 r / min for 20~30 minutes until homogeneous; then, adjust the pH of the ink to 8.0~9.5, and at room temperature, the viscosity of the Forecast-4 cup is 30~50 seconds.

[0040] The S300 segmented water addition viscosity adjustment strategy precisely controls the final ink viscosity within the target range of 30~50 seconds (25℃) using a Forte 4 cup, while adjusting the pH value to 8.0~9.5. This ensures that the ink has good transferability, leveling and resolubility on gravure printing presses, providing process assurance for high-speed printing at 150~250m / min.

[0041] An application of the aforementioned water-based low-VOCs high-concentration composite ink, which is suitable for gravure printing on BOPP film, PET film or nylon film.

[0042] Compared with the prior art, the beneficial effects of the present invention are:

[0043] 1. This invention systematically combines a ternary resin system, a hyperbranched dispersant, a triple anti-settling synergistic mechanism, and functional nanomaterials. The components produce a significant synergistic effect, with complementary adhesion between resins, synergistic anti-settling effect between dispersion and natural polymers, VOC reduction and enhanced adhesion of nanocellulose, and the joint construction of a suspension network by zeolite and nanoparticles. At the same time, it achieves comprehensive performance with solid content ≥56.8%, VOCs ≤3.2%, BOPP / PET / nylon adhesion ≥90%, 60℃ hot air drying time ≤2.5 seconds, and storage sedimentation level of 9~10. Detailed Implementation

[0044] Example 1

[0045] The preparation method of citrate-modified nanocellulose includes the following steps:

[0046] Step 1, Pretreatment and Dispersion: Take 10g of microcrystalline cellulose powder (Ashland, degree of polymerization 200-300), add it to 500mL of deionized water, and use ultrasonic treatment at 300W power, 40kHz frequency, and 30 minutes to fully disperse the cellulose and form a uniform suspension.

[0047] Step 2, Preparation of citric acid / catalyst solution: Add 10g of citric acid (1:1 ratio) and 2g of sodium hypophosphite (0.2:1 ratio) to 100mL of deionized water and stir until completely dissolved.

[0048] Step 3, Mixing and Low-Temperature Dehydration: Slowly add the above solution to the microcrystalline cellulose suspension and stir until homogeneous. Stir at 80°C for 60 minutes to allow the cellulose to fully swell.

[0049] Step 4, High-temperature esterification reaction: Transfer the mixture to a three-necked flask equipped with a reflux condenser, heat to 110°C, and carry out the esterification reaction for 2 hours under stirring.

[0050] Step 5, Product Purification: After the reaction is complete, cool to room temperature. Wash three times with anhydrous ethanol / deionized water (volume ratio 1:1), then wash once with anhydrous ethanol. After filtration, dry the filter cake in a vacuum drying oven at 60℃ for 24 hours.

[0051] Step 6, Grinding and Sieving: After drying, grind and pass through a 200-mesh sieve to obtain citrate-modified nanocellulose powder.

[0052] Example 2

[0053] In step 2, 20g of citric acid (2:1 ratio) and 4g of sodium hypophosphite (0.4:1 ratio) were added sequentially to 100mL of deionized water and stirred until completely dissolved. In step 4, the temperature was raised to 120℃, and the esterification reaction was carried out for 4 hours under stirring. The rest was the same as in Example 1.

[0054] Example 3

[0055] In step 2, 30g of citric acid (3:1 ratio) and 6g of sodium hypophosphite (0.6:1 ratio) were added sequentially to 110mL of deionized water and stirred until completely dissolved. In step 4, the temperature was raised to 130℃ and the esterification reaction was carried out for 6 hours under stirring.

[0056] In step 5, the volume ratio of anhydrous ethanol to deionized water is 2:1.

[0057] The properties of the citrate-modified nanocellulose prepared by the methods in Examples 1-3 are shown in Table 1.

[0058] The detection method is as follows:

[0059] Degree of esterification (DS): An acid-base titration method was used. Accurately weigh 0.5 g of the modified product into an Erlenmeyer flask, add 50 mL of 0.1 mol / L NaOH standard solution, and saponify by shaking at room temperature for 4 hours. Using phenolphthalein as an indicator, back-titrate with 0.1 mol / L HCl standard solution, and calculate the degree of esterification using the following formula: DS = (V1 × C1 – V2 × C2) × M / (m × 1000).

[0060] Carboxyl content determination: Conductivity titration was used. 0.5 g of the modified product was weighed and dispersed in 50 mL of deionized water. Conductivity titration was performed using 0.01 mol / L NaOH standard solution. The conductivity change curve with the amount of NaOH added was recorded, and the carboxyl content was calculated.

[0061] Aspect ratio determination: The modified product was diluted to a concentration of 0.01%, dropped onto a mica sheet and allowed to dry naturally. The aspect ratio of at least 50 fibers was observed and counted using an atomic force microscope (AFM) or a transmission electron microscope (TEM).

[0062] Table 1. Performance of citrate-modified nanocellulose prepared by the methods in Examples 1-3

[0063]

[0064] Example 4

[0065] A method for preparing nitrogen-doped TiO2 / ZnO composite nanodispersions includes the following steps:

[0066] Step 1, Preparation of Solution A: Measure 30 mL of anhydrous ethanol into a 250 mL three-necked flask, slowly add 15 mL of tetrabutyl titanate under ice-water bath conditions, and stir at 300 r / min to form a uniform, transparent, pale yellow solution.

[0067] Step 2, Preparation of Solution B: Add 6 mL of glacial acetic acid and 4 mL of deionized water to 30 mL of anhydrous ethanol, mix well and transfer to a constant pressure dropping funnel.

[0068] Step 3, TiO2 sol preparation: Stir solution A in a 25℃ water bath, and slowly add solution B dropwise (approximately 2 mL / min). After the addition is complete, continue stirring for 30 minutes to obtain a transparent TiO2 sol.

[0069] Step 4: Preparation of ZnO precursor solution: Weigh 0.58g of zinc acetate dihydrate, dissolve it in 30mL of deionized water, and stir to dissolve.

[0070] Step 5: Preparation of composite doped sol: Mix TiO2 sol with ZnO precursor solution, add 0.085g urea, and stir thoroughly. Transfer to a microwave synthesizer and heat at 60℃, 600W for 30 minutes.

[0071] Step 6, Gelation and Drying: Pour the sol solution into a petri dish and let it stand at 40°C for 12 hours to form a gel. Dry under vacuum at 80°C for 12 hours to obtain a pale yellow dry gel.

[0072] Step 7, calcination treatment: After grinding the dry gel, heat it in a muffle furnace to 450°C at a rate of 5°C / min, hold it at that temperature for 2 hours, and then let it cool naturally.

[0073] Step 8: Preparation of aqueous dispersion: Take 5g of calcined powder, add 45g of deionized water, add 0.25g of hyperbranched wetting and dispersing agent, and ultrasonically disperse (600W, 20kHz) for 20 minutes to obtain a stable dispersion.

[0074] Example 5

[0075] The amount of zinc acetate was adjusted to 1.16g, and the amount of urea was adjusted to 0.51g. The calcination temperature was 500℃, and the temperature was maintained for 3 hours. The rest was the same as in Example 4.

[0076] Example 6

[0077] The amount of zinc acetate was increased to 5.80 g, and the amount of urea was increased to 0.85 g. Note: The ZnO precursor solution concentration is high, so complete dissolution must be ensured; the microwave-assisted time can be extended to 40 minutes to promote uniform compounding. Calcination treatment: The temperature was increased to 600°C at 5°C / min, held for 5 hours, and then naturally cooled. The rest was the same as in Example 4.

[0078] The performance parameters of the nitrogen-doped TiO2 / ZnO composite nanodispersions prepared by the methods in Examples 4-6 are shown in Table 2.

[0079] Performance testing methods:

[0080] Ti / Zn atomic ratio determination: determined using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0081] Nitrogen doping content was determined using an elemental analyzer.

[0082] Particle size determination: The particle size distribution of the aqueous dispersion was determined using a dynamic light scattering particle size analyzer (DLS).

[0083] Table 2 Performance parameters of nitrogen-doped TiO2 / ZnO composite nanodispersions prepared by the methods in Examples 4-6

[0084]

[0085] Example 7

[0086] A method for preparing phosphate-modified zeolites includes the following steps:

[0087] Step 1: Zeolite pretreatment: Take 50g of type A zeolite (4A, passed through a 200-mesh sieve) powder, add it to 500mL of deionized water, and stir and wash at 80℃ for 1 hour. After filtration, wash with deionized water until neutral, and dry at 120℃ for 6 hours to activate.

[0088] Step 2, Preparation of Phosphoric Acid Solution: Calculate the amount of phosphoric acid solution needed to prepare a 60% phosphoric acid solution. Take 70.6 mL of 85% phosphoric acid, dilute with deionized water to 100 mL (total volume), and stir well before use.

[0089] Step 3, Phosphoric acid esterification hydrothermal treatment: Add 100 mL of 60% phosphoric acid solution to a 250 mL polytetrafluoroethylene-lined hydrothermal reactor, then add 30 g of pretreated zeolite powder and stir to disperse evenly. After sealing, place in an oven and hydrothermally treat at 100℃ for 2 hours.

[0090] Step 4, Cooling and Washing: Allow to cool naturally to room temperature. Filter by suction, wash 4 times with deionized water until the washing solution is neutral, and then wash once with anhydrous ethanol.

[0091] Step 5, Drying and Activation: Dry in an oven at 120℃ for 12 hours to obtain the phosphate-modified zeolite product.

[0092] Example 8

[0093] Step 1 is the same as in Example 7;

[0094] Step 2, Preparation of phosphoric acid solution: Mix 85% phosphoric acid and water at a volume ratio of 4:1, that is, take 80mL of 85% phosphoric acid and add 20mL of deionized water, mix well to obtain about 100mL of 68% phosphoric acid solution.

[0095] Step 3, Phosphoric acid esterification hydrothermal treatment: Add the above phosphoric acid solution and 30g of zeolite to the reactor, and treat at 120°C for 4 hours. The rest is the same as in Example 7.

[0096] Example 9

[0097] Step 1 is the same as in Example 7;

[0098] Step 2, Preparation of phosphoric acid solution: Take 100 mL of 85% phosphoric acid directly, without dilution.

[0099] Step 3, Phosphoric acid esterification hydrothermal treatment: Add 100 mL of 85% phosphoric acid and 30 g of pretreated zeolite to a 250 mL hydrothermal reactor, and stir to disperse. After sealing, perform hydrothermal treatment at 150 °C for 6 hours.

[0100] Step 4, Cooling and Washing: Allow to cool naturally to room temperature. Filter by suction, and wash repeatedly with deionized water until neutral, repeating 7 times to remove high concentrations of free phosphoric acid. Finally, wash once with anhydrous ethanol.

[0101] Step 5, Drying and Activation: Dry at 120℃ for 12 hours. Calcine at 300℃ for 2 hours to solidify the phosphate groups.

[0102] Comparative Example 1

[0103] Replace step 3 with stirring zeolite and 68% phosphoric acid at 80°C and atmospheric pressure for 4 hours, and the rest is the same as in Example 8.

[0104] Comparative Example 2

[0105] Replace the 68% phosphoric acid in step 3 with 30% phosphoric acid, and the rest is the same as in Example 8.

[0106] Comparative Example 3

[0107] Replace type A zeolite in step 1 with type Y zeolite, and the rest is the same as in Example 8.

[0108] The properties of the phosphate-modified zeolites prepared by the methods of Examples 7-9 and Comparative Examples 1-3 are shown in Table 3.

[0109] The testing method is as follows:

[0110] Phosphorus content determination: The determination was performed according to the molybdenum-antimony spectrophotometric method in GB / T8573-2017 "Determination of Available Phosphorus Content in Compound Fertilizers", with pretreatment of the zeolite samples before digestion.

[0111] Accurately weigh 0.2000 g of the dried modified zeolite sample, place it in a polytetrafluoroethylene digestion vessel, add 5 mL of hydrofluoric acid and 3 mL of perchloric acid, cover and digest on a 160℃ hot plate for 2 hours until the solution is clear and transparent.

[0112] Transfer the digestion solution to a 50 mL volumetric flask and dilute to volume with deionized water. Pipette 5.00 mL of the above solution into a 50 mL volumetric flask, add 10 mL of molybdenum antimony colorimetric reagent, dilute to volume with deionized water, and let stand at room temperature for 15 minutes.

[0113] The absorbance was measured at a wavelength of 700 nm, and the mass fraction (%) of phosphorus in the sample was calculated based on the phosphorus standard curve.

[0114] XRD relative crystallinity: X-ray diffractometer (XRD, CuKα radiation, λ=0.15406nm, tube voltage 40kV, tube current 40mA, scanning range 2θ=5°~50°, scanning speed 2° / min).

[0115] The corresponding strongest peak integral intensity of the modified zeolite sample was measured under the same conditions, and the relative crystallinity (%) was calculated as (peak intensity after modification / peak intensity of original zeolite) × 100%.

[0116] Table 3. Performance of phosphate-modified zeolites prepared by the methods of Examples 7-9 and Comparative Examples 1-3

[0117]

[0118] As shown in Table 3, in Examples 7 to 9, the phosphorus content increased with the gradual increase of phosphoric acid concentration, reaction temperature, and time, indicating that the degree of esterification grafting gradually improved. At the same time, the relative crystallinity of XRD showed a slight decreasing trend, indicating that the zeolite skeleton underwent a certain degree of dealuminization under more severe acidic conditions, but all remained above 85%, proving that the hydrothermal treatment conditions defined by the present invention can effectively balance grafting efficiency and structural stability.

[0119] In Comparative Example 1, phosphoric acid could not effectively penetrate the zeolite channels at atmospheric pressure and 80°C, and the reaction only occurred on the outer surface of the particles. Furthermore, the low liquid phase temperature resulted in slow esterification kinetics, and the phosphorus content was only 0.4%. The low degree of reaction caused no damage to the framework, and the crystallinity was the highest. In Comparative Example 2, the phosphoric acid concentration was too low, resulting in a severely insufficient equilibrium driving force for the esterification reaction. Even under hydrothermal conditions, the grafting rate was far below the 68% concentration, and the phosphorus content was only 0.6%. In Comparative Example 3, although the Y-type zeolite had a high silica-to-alumina ratio, the use of 85% high-concentration phosphoric acid and harsh conditions at 150°C resulted in a higher degree of grafting, but this was accompanied by some dealuminization of the framework.

[0120] Example 10

[0121] Waterborne polyurethane resin (Huajinsi HD1188, solid content 40%~45%) 35g; waterborne acrylic resin (Dibang B-178, solid content 47±1%) 20g; waterborne chlorinated polypropylene emulsion (Xinhua Chemical X-PU696, chlorine content 26%, solid content ≥35%) 10g; pigment (titanium dioxide R996) 28g; deionized water 12g; propylene glycol methyl ether 2g; dipropylene glycol methyl ether 1g; hyperbranched polyester dispersant (DISPERBYK®-2152) 2g; epoxy trimethoxysilane (Dow Chemical) 1g of Z-6040; 1.5g of citrate-modified nanocellulose (prepared by the method of Example 2); 1.2g of nitrogen-doped TiO2 / ZnO composite nanodispersion (prepared by the method of Example 5); 2.5g of phosphate-modified zeolite (prepared by the method of Example 8); 0.6g of xanthan gum; 0.3g of defoamer (BYK-024); 0.4g of leveling agent (TEGO® Glide450); and 2g of polyethylene wax emulsion (30% solid content).

[0122] A method for preparing the aforementioned water-based low-VOCs high-concentration composite ink includes the following steps:

[0123] S100: Mix hyperbranched polyester dispersant, xanthan gum, part of defoamer and part of deionized water evenly, add pigment and disperse at high speed of 1500r / min for 50 minutes to obtain pre-dispersed slurry;

[0124] The amount of defoamer added accounts for 35% of the total mass of defoamer, and the amount of deionized water added accounts for 70% of the total mass of deionized water.

[0125] S200. Add nitrogen-doped TiO2 / ZnO composite nano-dispersion and phosphate-modified zeolite to the above pre-dispersed slurry, mix evenly, and pump into a horizontal sand mill. Use 0.8mm zirconia beads with a filling rate of 75%, control the grinding temperature to ≤45℃, and circulate and grind until the fineness is ≤5μm to obtain a high-concentration color paste.

[0126] S300: Mix waterborne polyurethane resin, waterborne acrylic resin, and waterborne chlorinated polypropylene emulsion evenly. Add the above-mentioned high-concentration color paste, remaining deionized water, propylene glycol methyl ether, dipropylene glycol methyl ether, citrate-modified nanocellulose, epoxy trimethoxysilane, leveling agent, remaining defoamer, and polyethylene wax emulsion. Stir evenly at 500 rpm for 20-30 minutes until uniform. Adjust the pH of the ink to 9.0. At room temperature, the viscosity of the Forecast-4 cup is 25 seconds. Filter through a 300-mesh filter to obtain the target composite ink.

[0127] Example 11

[0128] Waterborne polyurethane resin (Huajinsi HD1188, solid content 40%~45%) 25g; waterborne acrylic resin (Dibang B-178, solid content 47±1%) 15g; waterborne chlorinated polypropylene emulsion (Xinhua Chemical X-PU696, chlorine content 26%, solid content ≥35%) 5g; phthalocyanine blue BGS 20g; deionized water 8g; propylene glycol methyl ether acetate 1g; hyperbranched polyether dispersant (HyPerC100) 1.5g; aminopropyltriethoxysilane ( Dow Chemical Z-6011) 0.5g; Citrate-modified nanocellulose (prepared by the method of Example 3) 0.5g; Nitrogen-doped TiO2 / ZnO composite nanodispersion (prepared by the method of Example 6) 0.5g; Phosphate-modified zeolite (prepared by the method of Example 9) 1.0g; Sodium carboxymethyl cellulose 0.2g; Defoamer (BYK-024) 0.1g; Leveling agent (TEGO® Glide450) 0.2g; Polyethylene wax emulsion (30% solid content) 1g.

[0129] A method for preparing the aforementioned water-based low-VOCs high-concentration composite ink includes the following steps:

[0130] S100: Mix hyperbranched polymer wetting and dispersing agent, polysaccharide natural polymer thickener / suspending agent, part of defoamer and part of deionized water evenly, add pigment and disperse at high speed of 1200r / min for 40 minutes to obtain pre-dispersed slurry;

[0131] The amount of defoamer added accounts for 16.7% of the total mass of defoamer, and the amount of deionized water added accounts for 60% of the total mass of deionized water.

[0132] S200. Add nitrogen-doped TiO2 / ZnO composite nano-dispersion and phosphate-modified zeolite to the above pre-dispersed slurry. After mixing evenly, pump it into a horizontal sand mill, use 0.6mm zirconia beads, fill rate 70%, control the grinding temperature ≤45℃, circulate and mix evenly, and grind to fineness ≤5μm to obtain high-concentration color paste.

[0133] S300: Mix waterborne polyurethane resin, waterborne acrylic resin, and waterborne chlorinated polypropylene emulsion evenly. Add the above-mentioned high-concentration color paste, remaining deionized water, environmentally friendly co-solvent, citrate-modified nanocellulose, waterborne adhesion promoter, leveling agent, remaining defoamer, and waterborne wax emulsion. Stir evenly at 400 r / min for 20 minutes until uniform. Adjust the pH of the ink to 8.0. At room temperature, the viscosity of the Forecast-4 cup is 20 seconds. Filter through a 300-mesh filter to obtain the target composite ink.

[0134] Example 12

[0135] 40g of waterborne polyurethane resin (Huajinsi HD1188, solid content 40%~45%); 30g of waterborne acrylic resin (Dibang B-178, solid content 47±1%); and 30g of waterborne chlorinated polypropylene emulsion (Xinhua Chemical X-PU696, chlorine content 26%, solid content ≥35%). 15g; Phthalocyanine Green 35g; Deionized Water 20g; Diethylene Glycol Butyl Ether 5g; Hyperbranched Polyester Dispersant (DISPERBYK®-2152) 4g; Bis(dioctyloxypyrophosphate) ethylene titanate amine salt aqueous solution (Herun GR-311W) 2.5g; Citrate-modified nanocellulose (prepared by the method of Example 1) 4.0g; Nitrogen-doped TiO2 / ZnO composite nanodispersion (prepared by the method of Example 4) 3.0g; Phosphate-modified zeolite (prepared by the method of Example 7) 5.0g; Microcrystalline cellulose 1.5g; Defoamer (BYK-024) 0.6g; Leveling Agent (TEGO® Glide450) 1.0g; Polyethylene Wax Emulsion (30% solid content) 3g;

[0136] A method for preparing the aforementioned water-based low-VOCs high-concentration composite ink includes the following steps:

[0137] S100: Mix hyperbranched polymer wetting and dispersing agent, polysaccharide natural polymer thickener / suspending agent, part of defoamer and part of deionized water evenly, add pigment and disperse at high speed of 1800r / min for 60 minutes to obtain pre-dispersed slurry;

[0138] The amount of defoamer added accounts for 50% of the total mass of defoamer, and the amount of deionized water added accounts for 80% of the total mass of deionized water.

[0139] S200. Add nitrogen-doped TiO2 / ZnO composite nano-dispersion and phosphate-modified zeolite to the above pre-dispersed slurry. After mixing evenly, pump it into a horizontal sand mill, use 1.0mm zirconia beads, fill rate 80%, control the grinding temperature ≤45℃, circulate and mix evenly, and grind to fineness ≤5μm to obtain high-concentration color paste.

[0140] S300: Mix waterborne polyurethane resin, waterborne acrylic resin, and waterborne chlorinated polypropylene emulsion evenly. Add the above-mentioned high-concentration color paste, remaining deionized water, environmentally friendly co-solvent, citrate-modified nanocellulose, waterborne adhesion promoter, leveling agent, remaining defoamer, and waterborne wax emulsion. Stir evenly at 600 r / min for 30 minutes until uniform. Adjust the ink pH to 9.5. At room temperature, the viscosity of the Forecast-4 cup is 30 seconds. Filter through a 300-mesh filter to obtain the target composite ink.

[0141] Comparative Example 4

[0142] No aqueous chlorinated polypropylene emulsion (CPP) was added; otherwise, it was the same as in Example 10.

[0143] Comparative Example 5

[0144] The hyperbranched polyester dispersant was replaced with a conventional sodium polycarboxylate dispersant, and the rest was the same as in Example 10.

[0145] Comparative Example 6

[0146] The same as in Example 10 was used without adding nitrogen-doped TiO2 / ZnO composite nanodispersion, phosphate-modified zeolite, and xanthan gum.

[0147] Comparative Example 7

[0148] The nanocellulose was modified without adding citrate ester, and otherwise remained the same as in Example 10.

[0149] Comparative Example 8

[0150] The same as in Example 10 was used without adding nitrogen-doped TiO2 / ZnO composite nanodispersion.

[0151] Comparative Example 9

[0152] No phosphate-modified zeolite was added; otherwise, the same as in Example 10.

[0153] Comparative Example 10

[0154] No xanthan gum was added; otherwise, it was the same as in Example 10.

[0155] Comparative Example 11

[0156] Xanthan gum was added instead of S100, and the rest was the same as in Example 10.

[0157] Comparative Example 12

[0158] The nitrogen-doped TiO2 / ZnO composite nanodispersion and phosphate-modified zeolite S200 were replaced with S300, and the rest were the same as in Example 10.

[0159] Comparative Example 13

[0160] In the S100 stage, all deionized water is added, and the rest is the same as in Example 10.

[0161] Comparative Example 14

[0162] No pH adjustment was performed; otherwise, it was the same as in Example 10.

[0163] Comparative Example 15

[0164] All defoamers were added in step S300, and the rest was the same as in Example 10.

[0165] Comparative Example 16

[0166] The phosphate-modified zeolite was replaced with ordinary type A zeolite (average particle size 0.4 nm), and the rest was the same as in Example 10.

[0167] Comparative Example 17

[0168] Replace xanthan gum with polyurethane associative thickener (ZY-5220B), otherwise the same as in Example 10.

[0169] Comparative Example 18

[0170] The citrate-modified nanocellulose was replaced with an equal amount of ordinary unmodified nanocellulose (Cellulose Microcrystalline 101), and the rest was the same as in Example 10.

[0171] The performance parameters of the water-based low-VOCs high-concentration composite inks prepared by the methods of Examples 10-12 and Comparative Examples 4-18 are shown in Table 4.

[0172] Test method:

[0173] Solid content (%): GB / T1725, weigh 2.0±0.1g of sample, dry in an oven at 105±2℃ for 3h to constant weight, and calculate the mass fraction of residue;

[0174] VOCs content (%): GB / T38608-2020, Gas chromatography (FID detector), determination of total volatile organic compounds such as methanol, ethanol, isopropanol, and propylene glycol methyl ether;

[0175] Viscosity was determined according to the Forecast cup method in GB / T 13217.4.

[0176] Adhesion (%): GB / T13217.7, disc peeling method or manual peeling method, transparent tape is applied to the printed ink surface and then peeled off. Adhesion is expressed as a percentage, and the higher the value, the better the adhesion.

[0177] 60℃ hot air drying time (s): Gravure color explorer, printing speed 100m / min, 60℃ hot air from the moment the ink film leaves the doctor blade, until the ink film surface is no longer sticky when lightly touched with a finger.

[0178] Composite strength (N / 15mm): GB 8808, first print ink on BOPP (inner printing), after drying, laminate it with PE film through solvent-free lamination process, cure at 50℃ for 24h and then cut into 15mm wide strips, T-type peeling speed 300mm / min;

[0179] Water resistance: Immersion method, cut the printed film into 5cm×5cm squares, immerse them completely in deionized water, and take them out after 24 hours to observe the bubbling, whitening and peeling.

[0180] Storage sedimentation rating: ASTM D869, accelerated 7-day at 50°C; Grade 10: No sedimentation at all, homogeneous system; Grade 8-9: Slightly loose sediment, which can be completely dispersed by shaking; Grade 6-7: Obvious sedimentation, with some hard lumps; Grade ≤5: Severely hardened lumps;

[0181] Table 4 Performance parameters of water-based low-VOCs high-concentration composite inks prepared by the methods of Examples 10-12 and Comparative Examples 4-18

[0182]

[0183] As shown in Table 4, Example 10 exhibits the best overall performance. It has a high solids content of 64.2%, VOCs of only 2.8%, adhesion to BOPP, PET, and nylon films of ≥90%, requires only 2.1 seconds for hot air drying at 60°C, achieves a composite strength of 2.15 N / 15 mm with PE film, and achieves the highest sedimentation level of 10 (completely no sedimentation) after 7 days of accelerated storage at 50°C. Example 11 uses lower amounts of resin and co-solvent, further reducing VOCs to 1.5% and shortening the drying time to 1.9 seconds. However, due to the lower total resin content, the composite strength is slightly lower (1.85 N / 15 mm), and the sedimentation level is 9. Example 12 uses a high-resin, high-pigment, and high-co-solvent formulation, achieving the highest composite strength of 2.20 N / 15 mm. However, due to the large amount of pigment and water, the solids content is 58.5%, VOCs are 3.2%, and the drying time is slightly longer (2.5 seconds). All three examples achieved solid content ≥56%, VOCs ≤4%, adhesion ≥90%, drying time ≤3 seconds, and sedimentation ≥9, demonstrating the good adaptability of the formulation to different pigment systems.

[0184] In Comparative Example 4, the BOPP adhesion plummeted from ≥90% to 53%, and the composite strength dropped drastically from 2.15 N / 15 mm to 0.42 N / 15 mm, a decrease of up to 80%. This is because the CPP segments in the waterborne chlorinated polypropylene emulsion migrate to the BOPP film surface during the ink drying and curing process, physically anchoring with the polyolefin substrate to form a compatible adhesive layer that other resins cannot achieve. Without CPP, the ink-BOPP interface relies solely on weak van der Waals forces, making it extremely easy to peel off. Simultaneously, the hydrophobicity of CPP helps prevent moisture penetration, and its removal also results in slight blistering of water resistance.

[0185] Comparative Example 5 resulted in a sharp drop in solid content from 64.2% to 46.2%, an increase in drying time from 2.1 seconds to 4.5 seconds, and a decrease in sedimentation grade from 10 to 5. Conventional linear dispersants cannot provide sufficient steric hindrance under high pigment loads, causing pigment particles to rapidly flocculate and thicken during grinding. This forces a reduction in the actual amount of pigment that can be ground, leading to a significant decrease in solid content. Insufficient dispersion also results in a loose ink layer structure, hindering moisture evaporation and doubling the drying time. Furthermore, pigment particles are highly prone to sedimentation and hardening during storage, resulting in a sedimentation grade of only 5.

[0186] Comparative Example 6 completely disrupted the triple anti-settling synergistic mechanism, causing the sedimentation level to drop from 10 to 3, resulting in severe hardening and clumping. The drying time was extended to 4.2 seconds, and significant whitening occurred in the water resistance. With the loss of the three-dimensional network framework of xanthan gum, the pigment particles lost their support; the steric hindrance and photocatalytic function of the nanoparticles were lost; and the microporous trapping and solvent slow-release effects of zeolite disappeared. The performance collapse caused by the simultaneous loss of all three was far greater than that caused by the loss of any single component, proving that the natural polymer network, the steric hindrance of inorganic nanoparticles, and the microporous physical trapping of zeolite are all indispensable, and their synergistic effect is not a simple additive one.

[0187] Although the amount of cosolvent used in Comparative Example 7 was the same as in Example 10, the VOCs increased from 2.8% to 3.6%. This is because the hydrophobic ester group component of the nanocellulose has a substitution effect on the alcohol ether cosolvent. Its hydrophobic surface reduces the system's dependence on the cosolvent, thus achieving a lower measured VOCs value with the same amount of cosolvent. After removing this component, the VOCs returned to the baseline level without the substitution effect. In addition, the hydrogen bonding between the free carboxyl groups of nanocellulose and the hydroxyl groups on the film surface disappeared, resulting in a slight decrease in the composite strength.

[0188] Comparative Example 8 reduced the sedimentation level from 10 to 7. ZnO nanoparticles adsorb through hydrogen bonds formed between their surface hydroxyl groups and natural polymer chains, and provide steric hindrance at the nanoscale, thus aiding in pigment suspension.

[0189] Comparative Example 9 showed that the drying time at 60℃ was increased from 2.1 seconds to 3.5 seconds, and the sedimentation grade decreased from 10 to 6. After phosphoesterification modification, the 0.3–0.8 nm micropores of the zeolite exhibit adsorption-slow release capabilities for residual moisture and co-solvents, effectively preventing the phenomenon of the ink film drying on the surface before the interior dries during printing, thus significantly shortening the time required for complete drying. Simultaneously, the phosphate groups form coordination and hydrogen bond networks with nanoparticles and natural polymer chains, enhancing suspension stability. Removing the zeolite resulted in the loss of slow-release and coordination functions, slower drying, and increased sedimentation.

[0190] Comparative Example 10 reduced the sedimentation level from 10 to 5. Xanthan gum, as a polysaccharide-based natural polymer, forms a three-dimensional network framework through interchain entanglement and adsorption with pigment particles after its long chains fully extend in the system. This framework is the first layer of the triple anti-sedimentation mechanism; without it, even with the retention of hyperbranched dispersants and nanoparticles, the pigment particles will still significantly settle due to gravity.

[0191] Comparative Example 11 reduced the sedimentation level from 10 to 6. This invention incorporates natural polymers during the S100 pre-dispersion stage, allowing them to fully extend and adsorb onto the pigment particle surface under high-speed shear, achieving a synergistic dispersion-network construction. If added later, during the S300 ink mixing stage (low-speed stirring), xanthan gum cannot be fully dispersed and adsorbed, resulting in a significantly reduced network strength, demonstrating the inventiveness of the material addition timing itself.

[0192] Comparative Example 12 extended the drying time to 3.8 seconds, reducing the sedimentation level to 6. Adding the two components during the grinding stage allows them to act as auxiliary grinding media, forming a tight interfacial bond with the pigment particles and laying the foundation for the subsequent synergistic network. If added later, during the ink mixing stage, grinding efficiency decreases, and subsequent low-speed stirring alone cannot achieve sufficient bonding between the three components, resulting in weakened anti-settling and slow-release effects.

[0193] Comparative Example 13 reduced the solids content from 64.2% to 57.2%, and the sedimentation grade to level 5. This invention employs a process strategy of first thickening and then thinning, adding only 60%–80% water to the S100 slurry. This keeps the grinding slurry within a favorable window of high solids content and low viscosity, resulting in high grinding efficiency and sufficient pigment dispersion. If all the water is added at once, the slurry becomes too thin, reducing the shear force of the zirconium beads on the pigment particles, significantly decreasing grinding efficiency, leading to insufficient pigment dispersion, ultimately reducing the solids content, and the poor dispersion directly exacerbating sedimentation.

[0194] Comparative Example 14 reduced the adhesion of BOPP, PET, and nylon to 76%, 78%, and 76%, respectively. Under weakly acidic conditions, the epoxy silane coupling agent hydrolyzed too rapidly, resulting in excessive self-polymerization in the ink and a significant decrease in the proportion of effective reactions with the hydroxyl groups on the substrate surface. Simultaneously, the carboxylate ionization degree of the hyperbranched dispersant decreased, leading to a drop in the zeta potential of the pigment surface and weakened dispersion stability. Both factors combined resulted in a comprehensive decrease in adhesion.

[0195] Comparative Example 15 reduced the solid content to 60.5% and the sedimentation grade to level 4. No defoamer was added during the high-speed dispersion stage of S100. A large number of bubbles generated by mechanical shearing adhered to the surface of the pigment particles, hindering pigment wetting and dispersant adsorption, resulting in uneven dispersion, decreased grinding efficiency, and ultimately, a lower solid content. The pigment particles also experienced severe sedimentation during storage.

[0196] Comparative Example 16 extended the drying time to 4.0 seconds, reduced the settling grade to level 4, and showed slight whitening in water resistance. The unmodified zeolite surface is rich in hydrophilic silanol groups, exhibiting poor compatibility with ink resins. It cannot form an effective coordination network or provide sustained-release function; instead, its strong hydrophilicity absorbs moisture, exacerbating the surface-drying-internal-wet phenomenon and negatively impacting water resistance. This directly demonstrates the necessity of phosphate esterification modification.

[0197] In Comparative Example 17, replacing xanthan gum with a conventional polyurethane associative thickener reduced the sedimentation grade from 10 to 6, extended the drying time to 2.6 seconds, and decreased the composite strength to 1.95 N / 15 mm. This is because conventional thickener molecules lack active functional groups such as hydroxyl and carboxyl groups, and can only provide basic thickening through hydrophobic association, unable to form hydrogen bonds or coordination networks with nanoparticles and zeolites. Xanthan gum, on the other hand, is rich in active groups, and can simultaneously construct a three-dimensional network in the S100 stage, incorporating nanoparticles and zeolites into the synergistic system through multi-point anchoring. Conventional thickeners disrupt the triple anti-settling mechanism, leading to a reduced synergistic effect and significant performance degradation.

[0198] In Comparative Example 18, replacing citrate-modified nanocellulose with ordinary unmodified cellulose resulted in an increase in VOCs from 2.8% to 3.2%, a decrease in adhesion from ≥90% to <85%, an extension of drying time to 2.6 seconds, a decrease in composite strength to 1.65 N / 15 mm, whitening of water resistance, and a drop in sedimentation grade to level 8. The performance degradation is attributed to the lack of both ester and carboxyl functional groups in ordinary cellulose, which prevents it from reducing VOCs, hydrogen-bonded anchoring of the film, and dispersing pigments. Its degree of esterification is approximately 0, its aspect ratio is low, it is prone to aggregation, and its network reinforcement effect is weak. Compared to the complete removal of nanocellulose (VOCs 3.6%), ordinary cellulose shows a negligible effect in reducing VOCs (only to 3.2%), far less than the 2.8% reduction achieved by modified cellulose, demonstrating that only citrate esterification modification can simultaneously achieve low VOCs and high adhesion.

Claims

1. A water-based, low-VOCs, high-concentration composite ink, characterized in that, By weight, it includes the following components: Waterborne polyurethane resin 25-40 parts; waterborne acrylic resin 15-30 parts; waterborne chlorinated polypropylene emulsion 5-15 parts; pigment 20-35 parts; deionized water 8-20 parts; cosolvent 1-5 parts; hyperbranched polymer wetting and dispersing agent 1.5-4 parts; waterborne adhesion promoter 0.5-2.5 parts; citrate-modified nanocellulose 0.5-4.0 parts; nitrogen-doped TiO2 / ZnO composite nanodispersion 0.5-3.0 parts; phosphate-modified zeolite 1.0-5.0 parts; polysaccharide natural polymer thickener / suspending agent 0.2-1.5 parts; defoamer 0.1-0.6 parts; leveling agent 0.2-1.0 parts; waterborne wax emulsion 1-3 parts; Among them, the solid content of waterborne polyurethane resin is 40%~50%; the solid content of waterborne acrylic resin is 45%~50%; and the chlorine content of waterborne chlorinated polypropylene emulsion is 20%~35%, and the solid content is 30%~40%.

2. The water-based low-VOCs high-concentration composite ink according to claim 1, characterized in that, The citrate-modified nanocellulose has a degree of esterification of 0.3~1.0, a carboxyl content of 0.2~0.8 mmol / g, and an aspect ratio of ≥50.

3. The water-based low-VOCs high-concentration composite ink according to claim 1, characterized in that, The nitrogen-doped TiO2 / ZnO composite nanodispersion has a Ti to Zn atomic ratio of 10 to 1:1, a nitrogen doping content of 0.5 to 5%, and an average particle size of 20 to 100 nm.

4. The water-based low-VOCs high-concentration composite ink according to claim 1, characterized in that, The co-solvent is selected from one or more of propylene glycol methyl ether, dipropylene glycol methyl ether, propylene glycol methyl ether acetate, and diethylene glycol butyl ether; the water-based adhesion promoter is selected from one or more of water-based epoxy silane coupling agents, water-based amino silane coupling agents, or water-based titanate coupling agents.

5. The water-based low-VOCs high-concentration composite ink according to claim 1, characterized in that, The hyperbranched polymer wetting and dispersing agent is selected from hyperbranched polyester dispersants or hyperbranched polyether dispersants; the polysaccharide natural polymer thickener / suspending agent is selected from one or more of xanthan gum, sodium carboxymethyl cellulose, or microcrystalline cellulose.

6. A method for preparing a water-based low-VOCs high-concentration composite ink as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S100: Mix hyperbranched polymer wetting and dispersing agent, polysaccharide natural polymer thickener / suspending agent, part of defoamer and part of deionized water evenly, add pigment and disperse evenly at high speed to obtain pre-dispersed slurry; S200. Nitrogen-doped TiO2 / ZnO composite nano-dispersion and phosphate-modified zeolite are added to the above pre-dispersed slurry. After mixing evenly, the mixture is ground to a fineness of ≤5μm to obtain a high-concentration color paste. S300. Mix waterborne polyurethane resin, waterborne acrylic resin, and waterborne chlorinated polypropylene emulsion evenly. Add the above-mentioned high-concentration color paste, remaining deionized water, co-solvent, citrate-modified nanocellulose, waterborne adhesion promoter, leveling agent, remaining defoamer, and waterborne wax emulsion. Stir evenly and filter to obtain the target composite ink.

7. The preparation method according to claim 6, characterized in that, In S100, high-speed dispersion at 1200~1800r / min for 40~60 minutes is used to obtain pre-dispersed slurry; the amount of defoamer added accounts for 16.7~50% of the total mass of defoamer, and the amount of deionized water added accounts for 60~80% of the total mass of deionized water.

8. The preparation method according to claim 6, characterized in that, In S200, the preparation of the phosphate-modified zeolite includes the following steps: after washing and drying the type A zeolite with deionized water, it is mixed with a phosphoric acid solution with a concentration of 60% to 85%, and hydrothermally treated at 100 to 150°C for 2 to 6 hours. After washing and drying, the zeolite is obtained.

9. The preparation method according to claim 6, characterized in that, In S300, stir at 400~600 r / min for 20~30 minutes until homogeneous; then, adjust the pH of the ink to 8.0~9.5, and at room temperature, the viscosity of the Forecast-4 cup is 30~50 seconds.

10. The application of a water-based low-VOCs high-concentration composite ink as described in any one of claims 1 to 5, characterized in that, The ink is suitable for gravure printing on BOPP film, PET film or nylon film.

Images