Water-based gravure ink and preparation method thereof

Abstract

The invention relates to the technical field of ink manufacturing, in particular to water-based gravure ink and a preparation method thereof. The ink is prepared from the following components according to solid content: epoxy-polyurethane-acrylic acid ternary hybrid emulsion, surface coating type high-color-concentration water-based color paste, citrate modified nano cellulose, an isosorbide diester coalescing agent, a polyoxyethylene-polyoxypropylene block wetting dispersant, a de-foaming agent, a preservative and de-ionized water. The ink has the advantages of low VOC (volatile organic compound), quick drying, excellent adhesive force and alcohol wiping resistance, is suitable for high-speed gravure of a 120-200L / cm anilox roller, and has excellent storage stability. The composition is green, environment-friendly and excellent in comprehensive performance.

Description

Technical Field

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

[0002] Gravure printing is renowned for its anilox roller metering, rich tonal range, and high-speed printing, and is widely used in flexible packaging, decorative paper, and metal foil. However, traditional gravure inks generally use ester and ketone solvents, with VOCs content reaching as high as 70%–80%, resulting in high emission costs and facing dual safety and environmental regulations. China has implemented GB38507-2020, "Limits for Volatile Organic Compounds (VOCs) Content in Inks," requiring low-VOC inks for gravure printing to have VOCs ≤10% (mass fraction) and encouraging the use of water-based systems; many provincial-level tiered control regulations also list "water-based gravure inks" as encouraged alternatives. Against this backdrop, water-based gravure inks have become a hot research topic in the industry.

[0003] The earliest water-based gravure inks mostly used pure acrylic emulsions, and the surface tension was reduced by adding hydrophilic solvents such as ethylene glycol butyl ether and isopropanol to improve transferability. For example, Chinese invention patent CN110760221A discloses a method for preparing water-based plastic gravure ink by mixing 10-15 parts by weight of acrylic resin liquid, 10-15 parts by weight of acrylic emulsion, and 10-15 parts by weight of polyurethane dispersion in a reactor at a temperature of 100-200°C to obtain a first mixture. Then, 20-30 parts by weight of water, 5-10 parts by weight of alcohol, 1-2 parts by weight of calcium carbonate, and 0.5-1 parts by weight of polyethylene wax are added to the first mixture, and the mixture is stirred in a reactor at a temperature of 30-50°C to obtain a second mixture. Finally, 10-12 parts by weight of pigment and 1-3 parts by weight of dispersant are added to the second mixture, followed by dispersion, grinding, and filtration to finally produce the water-based plastic gravure ink product. This patent still requires 5%-10% alcohol to ensure flow and drying; however, the large amount of volatile co-solvent not only weakens the "zero VOC" advantage but also leads to problems such as uneven drying and low film strength.

[0004] To improve adhesion to non-absorbent films such as PP and PE, researchers have attempted to introduce polyurethane soft segments into acrylic systems. For example, Chinese invention CN102086324A discloses a "water-based emulsion ink for non-absorbent substrates," which uses a PU-acrylic hybrid emulsion with an additional 5%-15% "water-soluble solvent" for foam suppression and wetting. However, it still relies on VOCs and has limited rub fastness due to the lack of cross-linking structures. Chinese invention CN104497699A reports a "high-performance water-based polyurethane ink" with a PU latex content as high as 60%-70%, supplemented with 30%-40% color paste, which achieves good adhesion on flexible packaging films. However, due to the lack of self-crosslinking sites, the dry film loses gloss or ink smudges after about 50 rubs with 96% ethanol, failing to meet the stringent solvent resistance requirements of high-speed gravure printing.

[0005] Lowering the minimum film-forming temperature (MFFT) relies on film-forming aids. While traditional alcohol ethers (DPnB, propylene glycol butyl ether) are effective, they have high VOC emissions and strong odors. European patent EP2531565A1 reports dianhydro-hexitol diester (DID), which has <20wt% VOC and >50% biochar content, and can lower the MFFT to 5°C while maintaining hardness. It has already been applied in waterborne wood coatings, providing a new approach for low-VOC co-film-forming agents. However, published literature has not yet verified its compatibility with highly reactive epoxy emulsions in waterborne gravure inks or its impact on the balance between drying speed and solvent resistance.

[0006] Traditional CMC and HEC thickeners tend to cause viscosity increases and slow drying during high-speed gravure printing. Cellulose nanofibers (CNF / CNC), with their high aspect ratio, can form reversible physical networks and exhibit significant thixotropy. Chinese invention patent CN111072786A discloses a method for preparing carboxylated cellulose nanofibers by hydrolyzing fibers under high pressure with citric acid. This material possesses abundant carboxyl groups, which can chemically couple with emulsion resins and improve water resistance. Current research focuses primarily on coatings and adhesives; publicly available data on the synergistic improvement of gravure inks' anti-settling and abrasion resistance using "cellulose nanofiber-epoxy emulsion" is still lacking.

[0007] In summary, for waterborne gravure inks to replace traditional solvent-based products, breakthroughs are needed in several dimensions, including (1) rapid film formation at room temperature or low temperature, (2) adhesion and abrasion resistance on non-absorbent substrates, (3) long-term storage stability and low foaming, and (4) bio-based content and low VOC compliance. Existing technologies have not yet reported the use of RAFT microemulsion polymerization to introduce epoxy monomers into the PU-acrylic backbone in a single step and couple them with CNF thixotropic networks and DID bio-based film-forming aids to obtain high-performance waterborne gravure inks that dry for ≤15s and withstand 100 rubs with 96% ethanol without gloss loss. Therefore, there is still an urgent need to develop a waterborne gravure ink and its preparation method that comprehensively utilizes epoxy active self-crosslinking, nanocellulose synergistic toughening-rheological regulation, and bio-based low-VOC film-forming aids to meet increasingly stringent environmental regulations and the process window of high-speed gravure printing production lines. Summary of the Invention

[0008] To address the aforementioned technical problems, the present invention aims to provide a water-based gravure ink that solves the issues of existing water-based inks having a narrow drying-flow window in high-speed gravure printing, insufficient adhesion to non-absorbent films and alcohol rub fastness, and limited bio-based content. This results in a comprehensive performance improvement that includes rapid film formation at room temperature, high resistance to wet / alcohol rubbing, stable transfer on high-line-count anilox rollers, and regulatory compliance.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A water-based gravure ink, comprising the following components based on 100% by weight solid content: Epoxy-reactive polyurethane-acrylic-epoxy ternary hybrid emulsions, 28%-42%. Surface-coated high-concentration water-based pigments, 12%-25%. Citrate-modified nanocellulose 0.5%-3% Isosorbide diester film-forming aid 4%-12% Polyoxyethylene-polyoxypropylene block wetting and dispersing agent 1%-5% Defoamer 0.1%-0.8% Preservative 0.1%-0.5% Deionized water balance.

[0010] Preferably, the water-based gravure ink comprises the following components based on a 100% weight solids content: 30%-35% polyurethane-acrylic-epoxy ternary hybrid emulsion containing epoxy reactive polyurethane-acrylic-epoxy resin Surface-coated high-concentration water-based color pastes, 15%-20%. Citrate-modified nanocellulose 1.0%-2.0% Isosorbide diester film-forming aid 6%-10% Polyoxyethylene-polyoxypropylene block wetting and dispersing agent 2%-4% Defoamer 0.3%-0.6% Preservative 0.2%-0.4% Deionized water balance.

[0011] Preferably, the epoxy-reactive polyurethane-acrylic-epoxy ternary hybrid emulsion is obtained by RAFT microemulsion polymerization of an aqueous polyurethane prepolymer with hydroxyl-terminated groups and acrylic monomers including glycidyl methacrylate, with a solid content of 35%±2% and a particle size D50 of 90-150 nm. Based on the equivalent amount of active -NCO / hydroxyl groups in the prepolymer, the molar ratio of the aqueous polyurethane prepolymer to all acrylic monomers is 1:2.5-5.0; more preferably 1:3.0-4.5.

[0012] Preferably, the waterborne polyurethane prepolymer is obtained by reacting polytetrahydrofuran diol (PTMG), polycarbonate diol (PCDL), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI).

[0013] Preferably, the acrylic monomer also includes one or more of hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and butyl acrylate (BA).

[0014] Preferably, the molar ratio of polytetrahydrofuran diol (PTMG), polycarbonate diol (PCDL), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) is controlled at PTMG:PCDL:DMPA:IPDI = 1:0.2-0.6:0.4-0.9:2.2-3.2; wherein: PTMG and PCDL together provide soft segment binary hydroxyl groups, and the hard segment / soft segment ratio can be achieved by adjusting the PCDL / PTMG ratio in the range of 0.2-0.6; DMPA provides hydrophilic carboxyl groups and additional hydroxyl groups, and its dosage is limited to 0.4-0.9 times the PTMG molar ratio to ensure emulsion stability and subsequent neutralization ability; The amount of IPDI is maintained at 2.2-3.2 times the hydroxyl equivalent of PTMG, so that the overall NCO / Hydroxyl molar ratio of the system is between 1.2-1.4:1, thereby ensuring that the prepolymer is fully capped while avoiding excessive free NCO that could lead to gelation.

[0015] Preferably, the acrylic monomer is composed of glycidyl methacrylate (GMA), hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and butyl acrylate (BA), and their molar ratio satisfies GMA∶HEMA∶MMA∶BA=1∶(0.4-0.8)∶(1.2-2.0)∶(0.6-1.4).

[0016] Preferably, isosorbide diester contains ≥85% C8-C10 branched fatty acid esters; and / or, the modified nanocellulose is monoesterified with citric acid, with a carboxyl substitution degree of 0.15-0.30 mmol / g. -1 Length ≤ 500nm, aspect ratio ≥ 50.

[0017] Preferably, the surface-coated high-concentration water-based color paste is selected from one or more of the following: carbon black paste CAB-O-JET®200; cyan paste CAB-O-JET®450C; magenta paste CAB-O-JET®554B; and full-color high-concentration color paste Hostatint. TM AU series.

[0018] Preferably, the polyoxyethylene-polyoxypropylene block wetting and dispersing agent is a nonionic block copolymer with an HLB value of 10-14; selected from: Poloxamer 407, PEO-PPO-PEO structure, number average molecular weight ≈12600-18000; METOLAT® 390 modified polyether dispersant.

[0019] Preferably, the defoamer is selected from: polyether modified silicone BYK-024 and polyether siloxane TEGOFoamex810.

[0020] Preferably, the preservative is an isothiazolinone or benzisothiazolinone wet bactericide, selected from: KATHON™ LX 1.5%, Preventol® BIT 20N.

[0021] Preferably, the water-based gravure ink is used at 25°C and a shear rate of 10s. -1 The viscosity is 25-55 mPa·s, suitable for high-speed gravure printing with anilox rollers of 120L / cm-200L / cm; after a heat-humidity cycle of 50℃×30min, its resistance to alcohol rubbing test, 96% ethanol, 500g load, 100 cycles, no ink film peeling, and the gloss at 60° decrease ≤5GU.

[0022] Furthermore, the present invention also provides a method for preparing the water-based gravure ink, the method comprising the steps of: 1) Under N2 protection at 70-80℃, the aqueous polyurethane prepolymer with hydroxyl end groups was subjected to RAFT microemulsion polymerization with acrylic monomer and glycidyl methacrylate for 4-5 hours to obtain a ternary hybrid emulsion. 2) Cool the obtained emulsion to 25°C, and add the aqueous color paste and wetting and dispersing agent sequentially in a high-speed disperser at 1000-1400 rpm; 3) Add the modified nanocellulose dispersion and film-forming aid at 800-1200 rpm, and continue to disperse for 20-30 min; 4) Add defoamer, preservative and deionized water to dilute to the target viscosity, and adjust the pH to 7.0-8.0; 5) After being filtered through a 300-mesh stainless steel mesh, the finished product is bottled.

[0023] Preferably, step 1) includes the following steps in sequence: (a) Under nitrogen protection conditions at 70℃±5℃, polytetrahydrofuran diol (number average molecular weight 1000~1500g·mol⁻¹) was subjected to the following conditions: -1 The number-average molecular weight of polycarbonate diol is approximately 2000 g·mol⁻¹. -1 The NCO-terminated prepolymer with a residual -NCO mass fraction of 95% to 105% was prepared by reacting dimethylolpropionic acid and isophorone diisocyanate for 1.0 to 1.5 h under the catalysis of dibutyltin dilaurate. (b) Continue heating to 75–80°C, and add 0.3%–0.6% (by weight of emulsion) of potassium persulfate / ascorbic acid-Fe to the microemulsion system with a solid content of 25%–35%. 2+ The red oxygen initiation system was used, and the following monomer emulsions were uniformly added dropwise over 3 hours; after the addition was completed, the temperature was maintained for another 2-3 hours to complete the RAFT microemulsion copolymerization. (c) After the reaction is complete, cool the system to 35–45°C, add triethanolamine dropwise to adjust the pH to 7.2–7.8, and add deionized water to bring the solid content to 35% ± 2%. Then, rapidly cool the system to below 30°C, degas under vacuum, and filter through a 200-mesh filter to obtain particles with a number average size of 90–150 nm and an epoxy equivalent of not less than 3 mmol·g. -1 Self-crosslinking epoxy-polyurethane-acrylic ternary hybrid emulsion.

[0024] Preferably, the water-based pigment in step 2) is pre-processed using an integrated bead milling process, with a particle size D90 ≤ 0.5µm.

[0025] Preferably, in step 3), the modified nanocellulose is added in the form of a 1% solids content aqueous dispersion and premixed for 5 min in a high-shear mixer with a shear rate of 5000 s⁻¹ to avoid fiber agglomeration.

[0026] This invention, by employing the above-mentioned technical solution, achieves multiple technical effects by synergistically introducing epoxy-polyurethane-acrylic ternary self-crosslinking emulsion, citric acid esterified nanocellulose, and isosorbide diester film-forming aid into the same formulation: Firstly, the average concentration of the emulsion is ≥3 mmol / g. -1 After the printing and drying process, the epoxy groups of the nanofiber undergo room-temperature ring-opening crosslinking with the hydroxyl groups of the resin and the carboxyl groups of the nanofiber cellulose, forming a dense network. This ensures that the ink film maintains a 96% ethanol rub fastness (500g load, 100 cycles) without ink fading and a 60° gloss decay of ≤5GU. Compared with the traditional PU-acrylic system, the alcohol rub fastness is increased by approximately 2.5 times. Secondly, the citrate-esterified nanofiber cellulose with an aspect ratio ≥50 constructs a reversible thixotropic mesh when stationary, significantly inhibiting pigment sedimentation. Under high-speed doctor blade shearing, it instantly "unwinds," ensuring that the ink maintains a viscosity of 120-200 Lcm. -1 Anilox roller, 150-200 mmin -1 Maintaining a low shear viscosity of 25-55 mPa·s even at high speeds, this invention solves the problems of screen clogging and knife line defects in high-speed gravure printing. Furthermore, isosorbide diester containing ≥85% C8-C10 branched fatty acid esters lowers the minimum film-forming temperature to below 5°C. Combined with epoxy post-curing, this reduces the surface drying time to 12-15 seconds, meeting the requirements for short drying tunnels or room temperature curing. Simultaneously, the overall VOC content is controlled to <3%, and the biochar content is increased to over 25%, fully complying with GB38507-2020 and the EU's dual regulations on VOCs and NIAS for packaging and printing. Further testing shows that the ink exhibits a cross-cut adhesion grade of 0 on BOPP, PET, and aluminized films. After 72 hours of high humidity aging at 45°C / 95%RH, there is no re-tackiness. After standing at 40°C for 90 days, the viscosity increase is <8%, with no foaming or gelation, demonstrating excellent storage and transportation stability. In summary, this invention achieves significant improvements in key indicators such as rapid low-temperature film formation, moisture / solvent resistance, thixotropic anti-settling properties, and low VOC and high bio-based properties, providing a new high-performance water-based ink solution for green high-speed gravure printing. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present invention.

[0028] I. Raw materials and their sources

[0029] Unless otherwise specified, the other materials are conventional raw materials in this field.

[0030] II. Preparation of Ternary (Epoxy-Polyurethane-Acrylic) Hybrid Emulsions 1. Equipment and Preparation In a 5L stainless steel reactor equipped with a jacketed thermostat, anchored stirring, dropping funnel, nitrogen protection, and vacuum interface, a trace amount of nitrogen (approximately 0.2L / min) was introduced beforehand. -1 15 minutes to remove dissolved oxygen, and set the jacket temperature to 70°C.

[0031] 2. Prepolymer Synthesis Polytetrahydrofuran diol (Mn≈1000gmol) was added sequentially. -1 200g, polycarbonate diol (Mn≈2000gmol) -1 50g of isophorone diisocyanate, 111g of isophorone diisocyanate, and 22g of dimethylolpropionic acid were added. 0.08g of dibutyltin dilaurate was added as a catalyst, and the reaction temperature was maintained at 70℃±3℃ with stirring for 1.5h. Samples were taken and NCO was determined by tert-butanol-dibutylamine titration. The stage was ended after confirming that the free NCO mass fraction had decreased to the theoretical value (approximately 4.5wt%), yielding an NCO-terminated polyurethane prepolymer.

[0032] 3. Constructing the RAFT microemulsion system Raise the reactor temperature to 75°C, add 600g of deionized water, 3g of RAFT crosslinking agent CPADB, and 2g of sodium dodecyl sulfate. Perform high-speed shearing (3000rpm) for 10 minutes to uniformly disperse the prepolymer into a transparent orange microemulsion.

[0033] 4. Monomer addition and graft copolymerization Prepare the monomer emulsion: 100g glycidyl methacrylate, 50g hydroxyethyl methacrylate, 110g methyl methacrylate, 80g butyl acrylate, and 100g deionized water. Add the monomer emulsion to the microemulsion system dropwise over 3 hours, maintaining the reactor temperature at 75-78℃. Simultaneously add the red oxygen initiation system: 5g 5wt% potassium persulfate solution, 3g 5wt% ascorbic acid solution, and 0.05wt% FeSO4. 7H₂O solution. Continuously monitor the redox potential, maintaining it at 270-300 mV. After the monomer is added, continue to incubate for 30 minutes to ensure conversion.

[0034] 5. Neutralization and dilution Cool the system to 40°C, and slowly add 14g of triethanolamine dropwise to neutralize the residual carboxyl groups until the pH is approximately 7.4. While stirring, add 400g of deionized water to adjust the final solid content to 34% ± 1%. At this point, the emulsion is light milky white and semi-transparent, with a viscosity of approximately 120 mPa·s (25°C, 60 rpm).

[0035] 6. Post-ripening, defoaming and cooling Continue stirring for 30 minutes and check that the residual monomer (GC) is below 500 ppm, then cool to ≤30℃. Apply a vacuum of 0.08 MPa for 5 minutes to remove microbubbles and ensure low-foaming properties for subsequent inks.

[0036] 7. Filtration and Packaging The emulsion is filtered through a 200-mesh stainless steel filter, then filled into HDPE food-grade drums and labeled with batch number and inspection label. Typical quality indicators: solid content 34.2%, D 50 ≈115nm, epoxy equivalent ≈3.1mmolg -1 Glass transition temperature Tg≈6℃. No gelation or stratification occurred after 12 months of storage in a light-protected environment at 25℃.

[0037] III. Preparation method of water-based gravure ink of the present invention 1. Resin pre-loading The qualified ternary hybrid emulsion is pre-poured into a stainless steel mixing tank, accounting for 30%–35% of the planned solid content of the finished product. It is slowly stirred at room temperature of 25°C (about 300 rpm) while continuously introducing a low flow of nitrogen to avoid resin oxidation or foam accumulation caused by dissolved oxygen.

[0038] 2. High-concentration water-based pigment dispersion Start the high-speed disperser and add the pigment paste in two batches according to the formulation ratio (usually 15%–20% solid content): add 70% at once and quickly disperse for 10 minutes at 1000–1200 rpm; after the system is homogeneous, add the remaining 30% and disperse for another 15 minutes at the same speed. Do not add other additives at this stage to avoid competitive adsorption of surfactants that could cause the pigment to coarsen.

[0039] 3. Wetting and dispersing agents and thixotropic agents are introduced simultaneously. Reduce the speed to 800 rpm and slowly add the polyoxyethylene-polyoxypropylene block wetting and dispersing agent (Pluronic F-127 or METOLAT 390), followed by a one-time addition of a 1% solids content citrate-esterified nanocellulose dispersion (0.5%-3% solids content). Continue dispersing for 20-25 minutes to allow the dispersant to fully protect the pigment and for the thixotropic network to be initially established. Record the power changes and observe the viscosity plateau in real time during this period; if the torque increases too quickly, the speed can be appropriately reduced to 700 rpm.

[0040] 4. Addition and fine-tuning of bio-based film-forming aids Maintain 600 rpm and add isosorbide diester in three portions (total amount 4%-12% of solid content). Stir for 5 minutes after each addition to ensure complete dissolution and penetration into the emulsion particles. Once all emulsion particles have been added, the apparent viscosity of the system will decrease slightly. At this point, measure the minimum film-forming temperature. If it is higher than 5°C, increase the film-forming aid by 0.5%-1%.

[0041] 5. Post-addition of functional additives Reduce the stirring speed to 400 rpm, and add the polyether-modified silicone defoamer (0.3%-0.6% solids) and the CMIT / MIT-BIT compound preservative (0.2%-0.4% solids) sequentially. Add the defoamer dropwise while continuing low-speed stirring for 10 minutes to break up any microbubbles that have formed. After adding the preservative, check the pH again to confirm it is within the 7.0-8.0 range.

[0042] 6. Viscosity and Solid Content Adjustment Add deionized water to the target solid content in one go, slowly increase the speed to 600 rpm and homogenize for 5 minutes, then take a sample and use a rotational viscometer (25℃, 10s) -1 The viscosity should be controlled between 25-55 mPa·s. If the viscosity is too high, it can be adjusted by adding water in two stages; if it is too low, a small amount of ternary emulsion or thixotropic agent can be added to raise it.

[0043] 7. Degassing and Filtration Reduce the stirring speed to 200 rpm and maintain a vacuum of 0.06-0.08 MPa for 3-5 minutes to release microbubbles. Immediately afterwards, filter through a 300-mesh stainless steel wire mesh or a 5µm microporous membrane to remove any possible gel particles and impurities, preventing the gravure printing screen from clogging.

[0044] 8. Final inspection and filling The filtered ink must be tested individually according to the following items: solid content, pH, Brookfield viscosity, particle size D90 (≤5µm), surface drying time, adhesion pre-test, and alcohol swab pre-test. After all indicators meet the design values, while the temperature is still below 30℃, pour the ink into dry and clean PE or PP containers, seal and label them. Store at room temperature and away from light for 6 months without stratification or thickening exceeding 10%.

[0045] IV. Formulation of the Examples (mass fraction, solids content)

[0046] V. Comparative formulation (solid content percentage, balance made up with deionized water)

[0047] Note: All comparative examples maintained the same pigment type (CAB-O-JET series) and preservative (KATHONLX 1.5% + BIT20N), deviating only from the formulation of this invention in the key factors listed in the table, in order to compare performance differences. The main differences among the 8 comparative examples are as follows: Comparative Example 1: Removing epoxy activity → alcohol resistance and adhesion decreased significantly.

[0048] Comparative Example 2: Replacing bio-based film-forming agents with high-VOC solvents → VOC levels exceed standards, drying becomes slower.

[0049] Comparative Example 3: No CNF → Sedimentation and viscosity drift occur.

[0050] Comparative Example 4: CNF excess → excessive static viscosity and knife line defects.

[0051] Comparative Example 5: No film-forming aid → Failure to form film at room temperature, resulting in foggy white printing.

[0052] Comparative Example 6: Using a high-foaming anionic dispersant → foaming, pinholes, and flocculation during storage.

[0053] Comparative Example 7: Using unmodified CNF → insufficient thixotropy and decreased alcohol resistance.

[0054] Comparative Example 8: Conventional NPE dispersant → high foaming and roughening, adhesion degradation.

[0055] VI. Test Methods According to standards such as GB / T38507-2020, GB / T9286-2021, and ASTM D5402-21, under the same equipment and the same process window (160Lcm) -1 Anilox roller, 150mmin -1 Five examples and eight comparative examples were prepared and continuously printed in a single batch under conditions of high speed and hot air temperature (60°C). The comprehensive contribution of the key technical features of this invention (epoxy self-crosslinking + citrate CNF + isosorbide diester + low-foaming block dispersant) was compared and verified by key indicators such as VOC, drying speed, minimum film-forming temperature (MFFT), adhesion, resistance to 96% ethanol rubbing, wet rubbing, cyclic ink viscosity drift, and static settling. All the following tests were conducted in a laboratory environment of 25±2°C and 50±5% relative humidity; all samples were taken from the same batch of ink after thorough stirring and defoaming.

[0056] 1. Volatile Organic Compounds (VOC) Content Standard basis: GB / T23985—2009 (Headspace Sampling-Gas Chromatography).

[0057] Reagents and Instruments: Gas chromatograph (with FID, capillary column 30m × 0.32mm × 1µm DB-624 or equivalent). High-purity helium (99.999%) carrier gas. Standard mixed solvents (toluene, butyl acetate, propylene glycol butyl ether, etc.) for quantitative calibration.

[0058] 1) Sample preparation: Weigh about 1.0g ± 0.05g of ink into a 20mL headspace vial, cap it with an aluminum cap, and seal it with a butyl septum.

[0059] 2) Headspace conditions: constant temperature 140℃×30min, headspace injection volume 1mL.

[0060] 3) Chromatographic conditions: Column temperature 40℃ for 5 min → 10℃ for 1 min -1 Heat to 220℃ and hold for 5 minutes; injection port 200℃; FID 250℃.

[0061] 4) Calculation: Convert the mass of each solvent according to the calibration curve, sum them, and divide by the sample mass to obtain the VOC mass fraction (%). The blank and repeatability tests should be performed in parallel twice, with a deviation ≤5%.

[0062] 2. Surface drying time Reference: NY / T380—1999 (Quick-drying ink), homemade touch-finger method. Coat a 30mm × 100mm ink film onto a 12µm PET film using a 12µm wire rod. Place in a 60℃ hot air duct (air velocity 2m / s). -1 Record the number of seconds from insertion to when the sample is no longer sticky when lightly touched with a finger. Take 3 parallel samples and take the average value.

[0063] 3. Minimum Film Formation Temperature (MFFT) Standard: ISO 2115—1981. Equipment: Aluminum alloy stepped plate (0-30℃ gradient), constant temperature cooling bath. Use a spatula to evenly coat the ink onto the stepped plate, covering each level. After placing it in a drying oven for 10 minutes, observe for cracks and chalking. The temperature at which a continuous film forms first without cracks is the MFFT (Medium-to-Flat Temperature). Repeat twice; error ≤ 1℃.

[0064] 4. Cross-hatching adhesion Standard: GB / T9286—2021. Gravure printing of ink onto 38µm BOPP sheets (160Lcm). -1 (Anilox roller). Let stand at room temperature for 24 hours; use a multi-blade crisscross cutter (1mm spacing, 6×6 blades) to score the grid. Apply 3M 610 tape (25mm) and peel it off quickly at 90°. Grades are classified from 0 to 5 according to standards; grade 0 is optimal.

[0065] 5. Abrasion resistance of 96% ethanol Standard: ASTM D5402-21 (revised). Mark a 50mm × 100mm area on the same substrate for the adhesion test. Load the apparatus with 500g; wrap the rubber head with cotton cloth, soaked in 96% ethanol but without dripping. Perform 60 ± 5 cycles per minute. -1 Wipe back and forth at a high speed, and record the number of times that visible ink loss or substrate exposure occurs. A pass is defined as wiping 100 times without failure.

[0066] 6. Water wiping (moisture-resistant wiping) Similar to step 5, but replace ethanol with deionized water and repeat 200 times; if discoloration, loss of gloss, or ink loss occurs, it is considered invalid.

[0067] 7. 60° gloss loss Standard: GB / T9754—2007. Using a BYK-Gardner miniature gloss meter, after calibration, the measurement was repeated three times at the same point. The gloss value was measured before and after the alcohol rub test, and the difference was taken as ΔGU.

[0068] 8. Viscosity drift during ink circulation (Δη) Method: Simulate actual printing ink return circulation. Place 300g of ink in an open cup, maintain a constant temperature of 25℃, and circulate at 600rpm for 4 hours using a blade stirrer. Measure the viscosity every hour using a Brookfield DV2T (Spindle3, 20rpm). The ratio of the initial viscosity to the viscosity is: Δη = (η_t – η0) / η0 × 100%. |Δη| ≤ ±10% is considered excellent.

[0069] 9. Settling under static conditions Reference: China Coatings Industry Association, "Evaluation Method for Sedimentation of Water-based Inks". Fill a 100mL graduated cylinder with ink and let it stand at 25℃ for 24 hours. Observe the height h (mm) of the sediment layer at the bottom of the bottle; expressed as h / mm / 100mL. ≤1mm is considered "good anti-settling".

[0070] 10. Data Processing and Repeatability All items should be tested in at least three parallel trials, and the average value should be used. If the relative deviation is >10%, remove one obvious outlier and retest. Use OriginLab to perform a t-test, and P<0.05 is considered statistically significant.

[0071] VII. Experimental Data and Results 1. Experimental Data The following lists the average experimental data obtained using the testing methods described in the previous section (n=5, standard deviation ≤5%). These results are sufficient to verify the comprehensive technical advantages of the embodiments of the present invention compared to the comparative examples from multiple dimensions (environmental protection, drying-film formation, adhesion-solvent resistance, rheology-storage and transportation).

[0072]

[0073] *Grade 0 = Best adhesion; Grade 2 or higher is considered significant peeling.

[0074] 2. Judgment Rules: Drying-film formation: Surface drying ≤15s, MFFT ≤5℃ is acceptable for high-speed gravure printing; Solvent resistance: No ink loss after 100 cycles of 96% ethanol is considered "pass"; ΔGU≤10 is considered to indicate no significant loss of gloss. Rheology-storage and transportation: |Δη|≤±10% and settlement≤1mm are considered excellent; >±20% or settlement≥2mm are considered rheological instability; Environmental protection: VOC ≤ 10%, meeting the limits for gravure printing inks in GB38507.

[0075] 3. Results Summary Examples 1-5 fully meet or exceed the judgment threshold: 1) VOC ≈ 3%, significantly lower than the 10% limit; 2) Surface drying for 13-16 seconds, MFFT at 4-5℃, ensuring high-speed film formation in a short drying tunnel at 60℃; 3) Alcohol wipe ≥100× No ink fading, adhesion level 0; 4) Rheologically stable (Δη≤±8%, no sedimentation).

[0076] Missing or out-of-bounds critical variables result in performance degradation. 1) Epoxy-free (Comparative Example 1): Alcohol wiping only 35×, adhesion reduced to level 2.

[0077] 2) High VOC replacing DID (Comparative Example 2): VOC exceeded the standard by 11.2%, and drying was slowed down by 2 times.

[0078] 3) No CNF or unmodified CNF (Comparative Example 3 / 7): Sedimentation, insufficient thixotropy, and decreased alcohol resistance occurred.

[0079] 4) CNF overdose (Comparative Example 4): Viscosity increased by 30%, resulting in severe cutter marks during production.

[0080] 5) No DID (Comparative Example 5): MFFT is raised to 18℃, and the production of fog white cracks occurs at 15℃.

[0081] 6) Mismatched dispersant (Comparative Example 6 / 8): Foaming and coarsening caused viscosity drift > ±20% and adhesion degradation.

[0082] The foregoing description of embodiments of the present invention, through which those skilled in the art are able to implement or use the present invention, will be readily apparent to those skilled in the art. Various modifications to these embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novelty disclosed herein.

Claims

1. A water-based gravure ink, characterized in that, This water-based gravure ink consists of the following components based on 100% by weight of solids content: 28%–42% polyurethane-acrylic-epoxy ternary hybrid emulsion containing epoxy reactive materials. Surface-coated high-concentration water-based pigments, 12%–25%, Citrate-modified nanocellulose 0.5%–3%, Isosorbide diester film-forming aid 4%–12%, Polyoxyethylene-polyoxypropylene block wetting and dispersing agent 1%–5%, Defoamer 0.1%–0.8%, Preservatives 0.1%–0.5%, Deionized water balance.

2. The water-based gravure ink according to claim 1, characterized in that, This water-based gravure ink consists of the following components based on 100% by weight of solids content: 30%–35% polyurethane-acrylic-epoxy ternary hybrid emulsion containing epoxy reactive polyurethane-acrylic-epoxy Surface-coated high-concentration water-based pigments, 15%–20%, Citrate-modified nanocellulose 1.0%–2.0%, Isosorbide diester film-forming aid 6%–10%, Polyoxyethylene-polyoxypropylene block wetting and dispersing agent 2%–4%, Defoamer 0.3%–0.6%, Preservatives 0.2%–0.4%, Deionized water balance.

3. A water-based gravure ink according to claim 1 or 2, characterized in that, The epoxy-reactive polyurethane-acrylic-epoxy ternary hybrid emulsion is obtained by RAFT microemulsion polymerization of a waterborne polyurethane prepolymer with hydroxyl-terminated groups and acrylic monomers including glycidyl methacrylate. The solid content is 35%±2%, and the particle size is D5090-150nm. Based on the equivalent amount of active -NCO / hydroxyl groups in the prepolymer, the molar ratio of the waterborne polyurethane prepolymer to all acrylic monomers is 1:2.5-5.

0. And / or, the aqueous polyurethane prepolymer is obtained by reacting polytetrahydrofuran diol (PTMG), polycarbonate diol (PCDL), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI). And / or, the acrylic monomers also include one or more of hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and butyl acrylate (BA).

4. The water-based gravure ink according to claim 3, characterized in that, The molar ratio of polytetrahydrofuran diol (PTMG), polycarbonate diol (PCDL), dimethylolpropionic acid (DMPA), and isophorone diisocyanate (IPDI) is controlled at PTMG:PCDL:DMPA:IPDI = 1:0.2-0.6:0.4-0.9:2.2-3.2; And / or, the acrylic monomer is composed of glycidyl methacrylate (GMA), hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and butyl acrylate (BA), with a molar ratio satisfying GMA∶HEMA∶MMA∶BA=1∶(0.4–0.8)∶(1.2–2.0)∶(0.6–1.4).

5. A water-based gravure ink according to claim 1 or 2, characterized in that, The isosorbide diester contains ≥85% C8-C10 branched fatty acid esters; and / or, the modified nanocellulose is monoesterified with citric acid, with a carboxyl substitution degree of 0.15-0.30 mmol / g. -1 Length ≤ 500nm, aspect ratio ≥ 50.

6. A water-based gravure ink according to claim 1 or 2, characterized in that, The surface-coated high-concentration water-based color paste is selected from one or more of the following: carbon black paste CAB-O-JET®200; cyan paste CAB-O-JET®450C; magenta paste CAB-O-JET®554B; and full-color high-concentration color paste Hostatint. TM AU series; And / or, the polyoxyethylene-polyoxypropylene block wetting and dispersing agent is a nonionic block copolymer with an HLB value of 10-14; selected from: Poloxamer 407, PEO-PPO-PEO structure, number average molecular weight ≈12600-18000; METOLAT® 390 modified polyether dispersant; And / or, the defoamer is selected from: polyether modified silicone BYK-024, polyether siloxane TEGOFoamex810; And / or, the preservative is an isothiazolinone or benzisothiazolinone wet disinfectant, selected from: KATHON TM LX1.5%, Preventol® BIT20N.

7. A water-based gravure ink according to claim 1 or 2, characterized in that, The water-based gravure ink is used at 25°C and a shear rate of 10s. -1 The viscosity is 25-55 mPa·s, suitable for high-speed gravure printing with anilox rollers of 120L / cm-200L / cm; after a heat-humidity cycle of 50℃×30min, its resistance to alcohol rubbing test, 96% ethanol, 500g load, 100 cycles, no ink film peeling, and the gloss at 60° decrease ≤5GU.

8. A method for preparing the water-based gravure ink according to any one of claims 1-7, characterized in that, The method includes the following steps: 1) Under N2 protection at 70-80℃, the aqueous polyurethane prepolymer with hydroxyl end groups was subjected to RAFT microemulsion polymerization with acrylic monomer and glycidyl methacrylate for 4-5 hours to obtain a ternary hybrid emulsion. 2) Cool the obtained emulsion to 25°C, and add the aqueous color paste and wetting and dispersing agent sequentially in a high-speed disperser at 1000-1400 rpm; 3) Add the modified nanocellulose dispersion and film-forming aid at 800-1200 rpm, and continue to disperse for 20-30 min; 4) Add defoamer, preservative and deionized water to dilute to the target viscosity, and adjust the pH to 7.0-8.0; 5) After being filtered through a 300-mesh stainless steel mesh, the finished product is bottled.

9. The method according to claim 8, characterized in that, Step 1) Preparation includes the following steps in sequence: (a) Under nitrogen protection, polytetrahydrofuran diol, polycarbonate diol, dimethylolpropionic acid and isophorone diisocyanate were reacted for 1.0 to 1.5 h, and NCO-terminated prepolymer with a residual -NCO mass fraction of 95% to 105% of the theoretical value was obtained under dibutyltin dilaurate catalysis. (b) Continue heating to 75–80°C, and add 0.3%–0.6% (by weight of emulsion) of potassium persulfate / ascorbic acid-Fe to the microemulsion system with a solid content of 25%–35%. 2+ The red oxygen initiation system was used, and the following monomer emulsions were uniformly added dropwise over 3 hours; after the addition was completed, the temperature was maintained for another 2-3 hours to complete the RAFT microemulsion copolymerization. (c) After the reaction is complete, cool the system to 35–45°C, add triethanolamine dropwise to adjust the pH to 7.2–7.8, and add deionized water to bring the solid content to 35% ± 2%. Then, rapidly cool the system to below 30°C, degas under vacuum, and filter through a 200-mesh filter to obtain particles with a number average size of 90–150 nm and an epoxy equivalent of not less than 3 mmol·g. -1 Self-crosslinking epoxy-polyurethane-acrylic ternary hybrid emulsion.

10. The method according to claim 8, wherein the aqueous pigment in step 2) is pre-processed using an integrated bead milling process, with a particle size D90 ≤ 0.5 µm; and / or, in step 3), the modified nanocellulose is added in the form of a 1% solids content aqueous dispersion, and at a shear rate of 5000 s⁻¹. -1 Premix in a high-shear mixer for 5 minutes to avoid fiber agglomeration.

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