A nano-dispersible pigment water-based ink for high frequency inkjet and a method for preparing the same

Abstract

The application belongs to the technical field of color paint and ink composition, and particularly relates to a nano self-dispersing pigment water-based ink for high-frequency inkjet and a preparation method thereof. The ink is composed of self-dispersing pigments with core-shell structure, deionized water, polyhydric alcohol-based cosolvent and environmentally-friendly biological killing agent. The self-dispersing pigments are composed of pigment primary particles and polyethylene glycol block copolymer with surface grafted phosphatidylcholine group. The preparation method comprises water phase free radical polymerization grafting coating on the surface of the pigment primary particles, removal of free substances through ultrafiltration centrifugation purification, and preparation of the ink through high-frequency shearing and ultrasonic cavitation treatment. The scheme utilizes the dynamic change of chain segment conformation of the block copolymer and the crosslinking network shell layer under extreme shearing, avoids chain segment collapse and detachment, maintains the dispersion state, and solves the problems of particle aggregation and ink breakage caused by the instability of the steric hindrance layer under high-frequency shearing circulation.

Description

Technical Field

[0001] This invention belongs to the technical field of paint and ink composition, specifically relating to a nano-self-dispersing pigment water-based ink for high-frequency inkjet printing and its preparation method. Background Technology

[0002] Existing high-frequency inkjet water-based inks using nano-self-dispersible pigments typically achieve self-dispersion by surface modification of primary pigment particles in an aqueous system. A common approach involves directly grafting small-molecule polyelectrolytes containing carboxylic acid or sulfonic acid groups onto the pigment particle surface. The system's suspension is maintained by the electrostatic repulsion generated after the ionization of these anionic groups and the steric hindrance of the short-chain molecules. These ink formulations usually include polyols such as glycerol or propylene glycol as moisturizing co-solvents and isothiazolinone compounds as biocides to meet the basic physical stability and anti-mildew requirements of conventional inkjet printing.

[0003] In actual high-frequency inkjet printing operations, the high-frequency opening and closing of piezoelectric inkjet valves exerts extreme shear forces on the ink. In the conventional solutions described above, the small-molecule polyelectrolyte chains grafted onto the pigment surface lack flexibility and dynamic adaptability. Under extreme high-frequency shear forces, these chains undergo irreversible collapse or detach directly from the surface of the primary pigment particles. This instability of the steric hindrance layer leads to irreversible aggregation of the originally isolated pigment particles. The size of the aggregated pigment particles exceeds the nozzle orifice diameter limit, resulting in nozzle clogging and ink interruption. Summary of the Invention

[0004] In response to the shortcomings of existing technologies, such as the irreversible collapse or desorption of small molecule polyelectrolyte chains grafted on the pigment surface during high-frequency inkjet printing, which leads to pigment particle aggregation, nozzle clogging and ink interruption, as well as the defects of free polymer-induced flocculation, residual microbubbles in the system, and the easy destruction of pigment dispersion interface structure by bactericides, this invention provides a nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing and its preparation method.

[0005] To address the aforementioned technical problems, this invention provides a nano-self-dispersible pigment aqueous ink for high-frequency inkjet printing. By mass percentage, the ink comprises the following components: 5%–15% core-shell self-dispersible pigment, 70%–85% deionized water, 5%–15% polyol co-solvent, and 0.1%–0.5% environmentally friendly biocidal agent. The core-shell self-dispersible pigment consists of primary pigment particles and a biomimetic phospholipid block copolymer grafted onto the surface of the primary pigment particles. The biomimetic phospholipid block copolymer is a polyethylene glycol block copolymer containing phosphocholine groups, which is grafted onto the surface of the primary pigment particles via an aqueous free radical polymerization system. The polyol co-solvent includes at least one of glycerol, 1,2-propanediol, and polyethylene glycol 200. The environmentally friendly biocidal agent includes isothiazolinone compounds.

[0006] The phosphocholine group, with its biomimetic hydrophilic phospholipid structure, possesses excellent hydration capabilities and resistance to non-specific adsorption. The polyethylene glycol block provides a long-range, stable steric hindrance effect. Through aqueous free radical polymerization, this block copolymer is covalently grafted onto the surface of primary pigment particles, forming a stable core-shell coating structure. This fundamentally avoids the defect of small-molecule polyelectrolytes easily desorbing from the pigment surface. Under the extreme shear force generated by the high-frequency opening and closing of piezoelectric inkjet valves, the grafted polymer segments can absorb and dissipate shear energy through reversible conformational adjustment, maintaining the stability of the steric barrier and preventing irreversible aggregation of pigment particles. Polyol cosolvents can precisely adjust the ink's moisturizing properties, viscosity, and surface tension, adapting to the dynamic opening and closing characteristics of high-frequency inkjet valves. Isothiazolinone biocides can broadly inhibit microbial growth within the system, preventing performance degradation and nozzle clogging caused by ink mold growth.

[0007] Furthermore, in the above technical solution, the polyethylene glycol block copolymer containing phosphocholine groups includes hydrophilic polyethylene glycol blocks, hydrophobic methacrylate blocks, and reactive blocks with phosphocholine groups at the ends. The hydrophilic polyethylene glycol blocks and the hydrophobic methacrylate blocks are arranged alternately to form a multi-block structure. The reactive blocks with phosphocholine groups at the ends are connected to the active groups on the surface of the pigment primary particles through chemical bonds.

[0008] In practice, the multi-block structure with alternating hydrophilic polyethylene glycol blocks and hydrophobic methacrylate blocks can form a flexible segmental network with dynamic response capabilities through hydrophilic-hydrophobic microphase separation. Under high-frequency shear force, the hydrophobic blocks can undergo reversible aggregation-depolymerization behavior, which, combined with the conformational expansion-contraction of the hydrophilic blocks, achieves efficient dissipation of shear energy and avoids the irreversible collapse of rigid segments. The terminal reactive blocks are connected to pigment particles through chemical bonds, which greatly improves the binding force between the polymer shell and the pigment core, fundamentally avoiding the polymer desorption problem under shear.

[0009] Furthermore, in the above technical solution, the active groups on the surface of the pigment primary particles are hydroxyl, carboxyl, or sulfonic acid groups, and the reactive blocks with terminal phosphocholine groups contain double bond structures. The double bond structures undergo graft copolymerization with the active groups on the surface of the pigment primary particles under the initiation of the aqueous free radical polymerization system to form carbon-carbon single bonds.

[0010] In practice, the hydroxyl, carboxyl, or sulfonic acid groups on the surface of the primary pigment particles can form active reaction sites in the aqueous polymerization system, and undergo free radical graft copolymerization with the double bond structure of the reactive block to form a carbon-carbon single bond covalent connection with high bond energy and strong chemical stability. Compared with physical adsorption or electrostatic adsorption, this covalent grafting method can ensure that the polymer shell remains stably bound to the pigment core during extreme shearing and long-term storage, without the risk of desorption.

[0011] Furthermore, in the above technical solution, in the core-shell structured self-dispersible pigment, the biomimetic phospholipid block copolymer forms a cross-linked network shell on the surface of the pigment primary particles. The cross-linked network shell is composed of linear polyethylene glycol block copolymer molecular chains containing phosphocholine groups that are entangled with each other and form hydrogen bonds between the chains. The cross-linked network shell covers 90% to 100% of the pigment primary particles.

[0012] In practice, the polar groups in the polyethylene glycol blocks and phosphocholine groups can form a large number of hydrogen bonds between molecular chains. Combined with the physical entanglement of molecular chains, a cross-linked network shell with dynamic and reversible characteristics is constructed. This cross-linked network not only retains the dynamic conformation adjustment ability of the chain segments to adapt to the high-frequency shear environment, but also forms a continuous and complete coating barrier. The high coating rate of 90% to 100% can completely isolate the pigment core from the direct contact between the pigment core and the aqueous medium, avoid direct collision and aggregation between pigment particles, and at the same time greatly improve the pigment's anti-settling stability and hydration ability.

[0013] Furthermore, in the above technical solution, the polyol cosolvent is a compound system composed of glycerol and polyethylene glycol 200 in a mass ratio of 1:1 to 3:1. In the compound system, glycerol molecules are inserted into the molecular gaps of the phosphocholine groups on the surface of the core-shell structured self-dispersing pigment, and polyethylene glycol 200 in the compound system is soluble with the deionized water.

[0014] In practice, glycerol molecules have a polyhydroxy structure, which can form hydrogen bonds with the polar sites of phosphocholine groups and insert into the intermolecular gaps of phosphocholine groups, thus plasticizing and stabilizing the polymer shell on the pigment surface, further enhancing the dynamic response and shear resistance of the chain segments. Polyethylene glycol 200 and deionized water have excellent compatibility, which can adjust the viscosity, surface tension and moisturizing properties of the ink system, preventing the ink from drying rapidly at the nozzle and adapting to the continuous operation requirements of high-frequency inkjet printing. When the two are compounded in a specific ratio, the stabilization of the pigment interface and the precise control of the overall rheological properties of the ink can be achieved simultaneously.

[0015] Furthermore, in the above technical solution, the isothiazolinone compound is a mixture of methylchloroisothiazolinone and methylisothiazolinone, wherein the mass ratio of methylchloroisothiazolinone to methylisothiazolinone is 2.5:1 to 3:1, and the mixture of methylchloroisothiazolinone and methylisothiazolinone is pre-emulsified in the deionized water using a nonionic surfactant, polyoxyethylene sorbitan monooleate.

[0016] In practice, methylchloroisothiazolinone and methylisothiazolinone are compounded in a specific ratio to form a broad-spectrum and highly efficient antibacterial system, which has excellent killing and inhibition effects on various mold-causing microorganisms such as bacteria and fungi. Through pre-emulsification treatment with nonionic surfactants, the bactericide components can form a uniform and stable dispersion system in the aqueous phase, avoiding excessively high local concentrations caused by direct addition of bactericides, preventing high concentrations of bactericides from damaging the biomimetic phospholipid polymer interface structure on the pigment surface, and extending the action time of bactericides, thereby improving the long-term storage stability of inks.

[0017] To address the aforementioned technical problems, this invention also provides a method for preparing a nano-self-dispersible pigment aqueous ink for high-frequency inkjet printing, comprising the following steps: Step S1, dispersing primary pigment particles in deionized water to form a pigment dispersion, adding a polyethylene glycol block copolymer monomer containing phosphocholine groups and an aqueous free radical polymerization initiator to the pigment dispersion, and carrying out an aqueous free radical polymerization reaction under inert gas protection to obtain a core-shell structured self-dispersible pigment reaction solution containing free polymer; Step S2, purifying the core-shell structured self-dispersible pigment reaction solution using an ultrafiltration centrifuge device to remove ungrafted free polymer, collecting the retentate and freeze-drying it to obtain a core-shell structured self-dispersible pigment powder; Step S3, adding the core-shell structured self-dispersible pigment powder, deionized water, a polyol cosolvent, and an environmentally friendly biocidal agent to a dispersion vessel for physical mixing to obtain a primary mixture; Step S4, subjecting the primary mixture to high-frequency shearing treatment and ultrasonic cavitation treatment sequentially to obtain a nano-self-dispersible pigment aqueous ink for high-frequency inkjet printing.

[0018] Through aqueous free radical polymerization, in-situ grafting of polyethylene glycol block copolymers containing phosphocholine groups onto the surface of primary pigment particles can be achieved, constructing a core-shell structured self-dispersible pigment in one step. The reaction conditions are mild, the grafting efficiency is high, and the environmental and safety risks associated with organic solvents are avoided. Ultrafiltration and centrifugation purification can precisely remove ungrafted free polymers from the system, eliminating the risk of pigment flocculation caused by migration and bridging of free polymers during ink storage and use. Freeze-drying can prepare pigment powder at low temperatures, avoiding polymer shell denaturation and hard agglomeration of pigment particles caused by high-temperature drying. Through a combination of high-frequency shearing and ultrasonic cavitation, pigment particles can be uniformly dispersed at the nanoscale in the ink system, while effectively removing microbubbles encapsulated in the system. This avoids problems such as droplet breakage and ink interruption caused by microbubbles during high-frequency inkjet printing, ensuring the high-frequency inkjet printing stability of the ink.

[0019] Furthermore, in the above technical solution, the aqueous free radical polymerization initiator is a redox initiation system composed of ammonium persulfate and tetramethylethylenediamine, the molar ratio of ammonium persulfate to tetramethylethylenediamine is 1:1 to 1:1.5, the temperature of the aqueous free radical polymerization reaction in step S1 is controlled at 60°C to 70°C, the reaction time is 4 hours to 6 hours, and the inert gas is high-purity nitrogen.

[0020] In practice, the redox initiation system composed of ammonium persulfate and tetramethylethylenediamine can generate stable and continuous free radicals at a lower reaction temperature, avoiding monomer self-polymerization side reactions caused by high temperatures and improving the selectivity and efficiency of the graft copolymerization reaction. The specific molar ratio can ensure the smooth release of free radicals, so that the polymerization reaction proceeds at a uniform rate, forming polymer blocks with uniform molecular weight distribution and ensuring the uniformity of shell properties. The reaction temperature of 60°C to 70°C and the reaction time of 4 to 6 hours can ensure the full polymerization and grafting of monomers, while avoiding excessive polymer chain entanglement caused by over-reaction. High-purity nitrogen protection can isolate oxygen in the system, avoid the quenching effect of oxygen on free radicals, and ensure the smooth progress of the polymerization reaction.

[0021] Furthermore, in the above technical solution, the ultrafiltration centrifuge device in step S2 is filled with an ultrafiltration membrane with a molecular weight cutoff of 10,000 Daltons, and the centrifugation speed of the ultrafiltration centrifuge device is 3,000 rpm to 5,000 rpm. During the ultrafiltration centrifugation purification process, after each centrifugation, an equal volume of deionized water is added for resuspension and washing, and the resuspension and washing is repeated 3 to 5 times.

[0022] In practice, an ultrafiltration membrane with a molecular weight cutoff of 10,000 Daltons can precisely retain polymer-grafted pigment particles while allowing ungrafted free polymers and small molecule reaction byproducts to pass through the membrane and be removed. A centrifugal speed of 3,000 to 5,000 rpm ensures the flux and efficiency of the ultrafiltration process while avoiding pigment particle aggregation and membrane damage caused by excessive speed. Three to five equal-volume resuspension washes with deionized water can thoroughly remove free polymers and impurities from the system, ensuring the purity of self-dispersing pigments and eliminating the risk of ink flocculation caused by free polymers at the source.

[0023] Furthermore, in the above technical solution, the high-frequency shearing treatment in step S4 uses a high-speed disperser with a rotor speed of 8000 rpm to 12000 rpm and a high-frequency shearing treatment time of 30 to 60 minutes. The ultrasonic cavitation treatment uses an ultrasonic cell disruptor with an ultrasonic frequency of 20 kHz to 25 kHz and an ultrasonic power of 600 watts to 800 watts. The total ultrasonic cavitation treatment time is 15 to 30 minutes and an intermittent ultrasonic mode is used.

[0024] In practice, high-frequency shearing at 8000 to 12000 rpm can fully disperse the soft pigment agglomerates in the primary mixture, achieving initial uniform dispersion of pigment particles. Ultrasonic cavitation with specific parameters can further open up the tiny pigment agglomerates through the microjets and shock waves generated by the collapse of cavitation bubbles, achieving nanoscale uniform dispersion. At the same time, it can effectively break down and remove microbubbles encapsulated in the system, avoiding interference from microbubbles on the morphology of high-frequency inkjet droplets. Intermittent ultrasonic mode can avoid excessive temperature rise in the system during ultrasonication, preventing thermal deformation of the polymer shell and volatilization and deterioration of ink components, and ensuring the stability of ink performance.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention grafts a polyethylene glycol block copolymer containing phosphocholine groups onto the surface of primary pigment particles to form a cross-linked network shell. This copolymer has a multi-block structure with alternating hydrophilic polyethylene glycol blocks and hydrophobic methacrylate blocks. Under the extreme high-frequency shear force generated by the high-frequency opening and closing of piezoelectric inkjet valves, this multi-block structure and cross-linked network shell can undergo dynamic changes in chain segment conformation to absorb shear energy, preventing the collapse and desorption of rigid chains, maintaining the dispersed state of pigment particles, and solving the problem of particle aggregation, nozzle clogging, and ink interruption caused by the instability of the steric hindrance layer on the pigment surface under high-frequency shear cycles.

[0026] 2. This invention removes ungrafted free polymers from the reaction solution through ultrafiltration and centrifugation purification with a specific molecular weight cutoff, eliminating the flocculation risk caused by the free migration of free polymers in the system. The glycerol-polyethylene glycol compound system inserts into the molecular gaps of the phosphocholine groups on the pigment surface, and combined with ultrasonic cavitation treatment, eliminates microbubbles within the system. The biocidal agent is pre-emulsified with the nonionic surfactant polyoxyethylene sorbitan monooleate and then dispersed in deionized water, avoiding the destruction of the pigment dispersion interface structure constructed by the biomimetic phospholipid block copolymer by localized high concentrations of bactericide. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto. All technologies implemented based on the above-described contents of the present invention fall within the scope of the present invention. Those skilled in the art should understand that experimental methods in the following embodiments, unless otherwise specified, were performed according to conventional experimental conditions and operating procedures in the art.

[0028] Example 1: 1. Ink Formulation The formulation, by weight percentage, consists of: 10% core-shell self-dispersible pigment, 78% deionized water, 11.7% polyol cosolvent, and 0.3% environmentally friendly biocide. The polyol cosolvent is a compound system of glycerol and polyethylene glycol 200 in a mass ratio of 2:1; the environmentally friendly biocidal agent is a mixture of methylchloroisothiazolinone (CIT) and methylisothiazolinone (MIT) in a mass ratio of 3:1, which is used after being pre-emulsified with nonionic surfactant polyoxyethylene sorbitan monooleate.

[0029] 2. Preparation method Step S1: Disperse 100g of primary carbon black pigment particles (average particle size 50nm) with carboxyl active groups on the surface in 900g of deionized water and disperse at 3000rpm for 30min to obtain a uniform and stable pigment dispersion. Add 2-methacryloyloxyethyl phosphocholine (MPC) monomer, polyethylene glycol methacrylate (PEGMA, number average molecular weight 2000) monomer, and methyl methacrylate (MMA) monomer to the pigment dispersion, with a monomer molar ratio of MPC:PEGMA:MMA=1:3:2. Then add an aqueous free radical polymerization redox initiation system, with ammonium persulfate (APS) and tetramethylethylenediamine (TEMED) as initiators, with a molar ratio of APS to TEMED of 1:1.2, and the amount of APS added is 1.5% of the total monomer mass. After purging the system with high-purity nitrogen for 30min, seal the system, heat to 65℃, and stir for 5h to obtain a self-dispersed pigment reaction solution with a core-shell structure containing free polymer.

[0030] Step S2: Transfer the above reaction solution to an ultrafiltration centrifuge device, which is filled with a regenerated cellulose ultrafiltration membrane with a molecular weight cutoff of 10,000 Daltons. Set the centrifugation speed to 4,000 rpm. After each centrifugation for 20 min, discard the permeate and add an equal volume of deionized water to resuspend the solution. Repeat the resuspension and washing process 4 times to thoroughly remove ungrafted free polymers and unreacted monomers. Collect the final retentate and freeze-dry it in a -40℃ freeze dryer for 24 h to obtain a core-shell structured self-dispersible pigment powder.

[0031] Step S3: According to the above formula ratio, add 100g of core-shell structured self-dispersible pigment powder, 780g of deionized water, 117g of polyol cosolvent, and 3g of pre-emulsified environmentally friendly biocidal agent to the dispersion vessel, and stir at 300rpm for 30min at room temperature to obtain the primary mixture.

[0032] Step S4: Transfer the primary mixture to a high-speed disperser, set the rotor speed to 10,000 rpm, and perform high-frequency shearing for 45 minutes; then transfer the sheared mixture to an ultrasonic cell disruptor, set the ultrasonic frequency to 22 kHz, the ultrasonic power to 700 W, and use an intermittent ultrasonic mode (ultrasound for 2 seconds, pause for 3 seconds), with a total ultrasonic time of 20 minutes; after ultrasonic treatment, filter and sterilize using a 0.22 μm microporous membrane to obtain nano-self-dispersing pigment water-based ink for high-frequency inkjet printing.

[0033] Example 2: The formulation of this example is adjusted as follows: 5% core-shell self-dispersing pigment, 83% deionized water, 11.7% polyol cosolvent, and 0.3% environmentally friendly biocidal agent; the remaining formulation composition and preparation method are exactly the same as in Example 1.

[0034] Example 3: The formulation of this example is adjusted as follows: 15% core-shell self-dispersing pigment, 73% deionized water, 11.7% polyol cosolvent, and 0.3% environmentally friendly biocidal agent; the remaining formulation composition and preparation method are exactly the same as those in Example 1.

[0035] Example 4: In this example, the polyol cosolvent was replaced with an equal mass of 1,2-propanediol; the rest of the formulation and preparation method were exactly the same as in Example 1.

[0036] Example 5: In this example, the polyol cosolvent was replaced with a compound system of glycerol and 1,2-propanediol of equal mass (mass ratio 1:1); the rest of the formulation and preparation method were exactly the same as in Example 1.

[0037] Example 6: In this example, the amount of environmentally friendly biocidal agent added is adjusted to 0.1%, and the deionized water content is adjusted to 78.2% accordingly; the rest of the formulation and preparation method are exactly the same as in Example 1.

[0038] Example 7: In this example, the amount of environmentally friendly biocidal agent added is adjusted to 0.5%, and the deionized water content is adjusted to 77.8% accordingly; the rest of the formulation and preparation method are exactly the same as in Example 1.

[0039] Example 8: In this example, the mass ratio of glycerol to polyethylene glycol 200 in the polyol cosolvent was adjusted to 1:1 (the total added mass remained unchanged); the rest of the formulation and preparation method were exactly the same as in Example 1.

[0040] Example 9: In this example, the mass ratio of glycerol to polyethylene glycol 200 in the polyol cosolvent was adjusted to 3:1 (the total added mass remained unchanged); the rest of the formulation and preparation method were exactly the same as in Example 1.

[0041] Example 10: This example keeps the formula completely consistent with Example 1, except that the temperature of the aqueous free radical polymerization reaction in step S1 is adjusted to 60°C and the reaction time is adjusted to 6h; the rest of the preparation method steps are exactly the same as in Example 1.

[0042] Example 11: This example keeps the formula completely consistent with Example 1, except that the centrifugation speed of the ultrafiltration centrifuge in step S2 is adjusted to 3000 rpm and the number of resuspension washings is adjusted to 3 times; the rest of the preparation method steps are exactly the same as in Example 1.

[0043] Example 12: This example keeps the formula completely consistent with Example 1, except that the rotor speed of the high-frequency shearing treatment in step S4 is adjusted to 8000 rpm and the treatment time is adjusted to 60 min. At the same time, the ultrasonic frequency of the ultrasonic cavitation treatment is adjusted to 20 kHz, the ultrasonic power is adjusted to 600 W, and the total ultrasonic time is adjusted to 30 min. All other preparation methods and steps are exactly the same as in Example 1.

[0044] Comparative Example 1: In this comparative example, the core-shell structured self-dispersing pigment in the formulation was replaced with an equal mass of unmodified carbon black pigment primary particles; the rest of the formulation composition and preparation method were exactly the same as in Example 1.

[0045] Comparative Example 2: This comparative example adopts the conventional existing technology described in the background art. The formula is as follows: 10% carbon black pigment grafted with polyacrylic acid small molecule polyelectrolyte, 79.7% deionized water, 10% glycerol, and 0.3% CIT / MIT mixture (mass ratio 3:1). The preparation method adopts the conventional small molecule polyelectrolyte free radical grafting process, omitting the ultrafiltration centrifugation purification step and the ultrasonic cavitation treatment step. The remaining operating environment is consistent with that of Example 1.

[0046] Comparative Example 3: This comparative example maintains the same formulation as Example 1, except that the temperature of the aqueous free radical polymerization reaction in step S1 is adjusted to 90°C; the rest of the preparation methods and steps are exactly the same as in Example 1.

[0047] Comparative Example 4: This comparative example maintains the same formulation as Example 1, except that step S2, ultrafiltration and centrifugation purification, is omitted. The reaction solution obtained in step S1 is directly freeze-dried and used for subsequent ink preparation. All other preparation steps are exactly the same as in Example 1.

[0048] Test method: Particle size and particle size distribution test: Malvern Zetasizer NanoZS90 dynamic light scattering particle size analyzer was used. The test temperature was 25℃ and the scattering angle was 90°. Each sample was tested in parallel 3 times, and the average value was recorded as the initial average particle size and particle size distribution coefficient (PDI).

[0049] High-frequency shear stability test: 50 mL of the ink to be tested was placed in a high-speed shearing apparatus and continuously sheared at 15,000 rpm for 2 hours to simulate the extreme shearing environment of high-frequency inkjet printing. After shearing, the average particle size of the ink was tested and the particle size change rate was calculated. The calculation formula is: Particle size change rate = (average particle size after shearing - initial average particle size) / initial average particle size × 100%.

[0050] Long-term storage stability test: The ink to be tested was sealed in a brown sample bottle and stored in a constant temperature and humidity chamber at 25°C and 60% relative humidity for 6 months. The average particle size after storage was tested and the particle size change rate was calculated. At the same time, the presence of precipitation, stratification, or flocculation was observed by visual inspection.

[0051] High-frequency inkjet continuous printing performance test: A 30kHz high-frequency piezoelectric inkjet printer with a nozzle orifice diameter of 20μm and a printing resolution of 600dpi was used. Standard test samples were printed continuously using the ink to be tested. The time when ink interruption and nozzle clogging first occurred was recorded. If there were no abnormalities after 72 hours of continuous printing, it was recorded as >72h.

[0052] Antibacterial performance test: The agar diffusion method was used. Escherichia coli (ATCC25922) and Aspergillus niger (ATCC16404) were used as test strains. Sterilized filter paper was soaked in the ink to be tested for 2 hours and then laid flat on the agar plate coated with the test bacteria. It was incubated at 37℃ for 24 hours (E. coli) and at 28℃ for 72 hours (Aspergillus niger). The diameter of the inhibition zone was measured. Each sample was tested in parallel for 3 times and the average value was taken.

[0053] Microbubble content test: Using a laser confocal microscope, 10 μL of the ink to be tested was placed on a glass slide. Ten fields of view were randomly selected under a 100x oil immersion microscope. The number of microbubbles per unit volume was counted and converted to cells / mL. The average value was then taken.

[0054] Test results: Table 1 Performance test results of each embodiment and comparative example

[0055] The samples in Examples 1-12 of this invention all exhibit excellent nano-dispersion and shear stability: the initial average particle size is less than 81 nm, the PDI is less than 0.085, and after 2 hours of extreme high-frequency shearing at 15,000 rpm, the particle size change rate is less than 5%, far superior to all comparative examples. The core reason is that the polyethylene glycol block copolymer containing phosphocholine groups covalently grafted onto the surface of the pigment primary particles forms a complete cross-linked network shell. Under high-frequency shearing, the multi-block structure can efficiently dissipate shear energy through dynamic and reversible adjustment of the chain segment conformation, fundamentally avoiding the defects of irreversible collapse and desorption of small molecule polyelectrolyte chains in the prior art, and solving the core technical problems of pigment aggregation and nozzle clogging in high-frequency inkjet scenarios.

[0056] After 6 months of long-term storage, the samples in Examples 1-12 all showed a particle size change rate of less than 6%, with no precipitation, stratification, or flocculation. They also exhibited excellent long-term storage stability and continuous operation performance, with no ink interruption or nozzle clogging after 72 hours of continuous high-frequency inkjet printing. Comparative Example 4, which omitted the ultrafiltration and centrifugation purification step, showed a particle size change rate as high as 65.8% after storage and ink interruption after only 36 hours. This directly proves that the ultrafiltration purification step of this invention can completely remove ungrafted free polymers from the system, eliminating the flocculation risk caused by free polymer migration and bridging, and is a key process for ensuring the long-term stability of the ink.

[0057] Comparative Example 1 uses unmodified primary pigment particles with a large initial particle size and wide distribution. After high-frequency shearing, the particle size change rate exceeds 280%, and severe clogging occurs within 0.5 hours. This proves that the biomimetic phospholipid block copolymer graft modification of the present invention is a core and essential technical feature for achieving stable pigment dispersion and shear resistance. Comparative Example 2 uses the existing small molecule polyelectrolyte modification scheme described in the background art. After high-frequency shearing, the particle size change rate reaches 124.8%, and ink breakage occurs within 12 hours. This directly proves that the technical solution of the present invention has unexpected technical effects compared with the prior art, and has outstanding substantive features and significant progress.

[0058] Comparative Example 3 adjusted the polymerization temperature to 90°C, which is outside the range defined in this invention. This resulted in an intensification of monomer self-polymerization side reactions, uneven polymer shells grafted onto the pigment surface, a significant decrease in grafting rate, and a substantial deterioration in shear resistance and storage performance. This demonstrates that the polymerization process parameters defined in this invention are the key guarantee for constructing a stable core-shell structure and achieving excellent ink performance.

[0059] The samples in Examples 1-12 all exhibited excellent antibacterial properties and low bubble content. The compound cosolvent system of glycerol and polyethylene glycol 200 can insert into the molecular gaps of the phosphocholine groups on the pigment surface. Combined with ultrasonic cavitation treatment, it effectively eliminates microbubbles in the system. The pre-emulsified biocides can be uniformly dispersed in the aqueous phase, avoiding the damage to the pigment dispersion interface caused by local high concentrations of bactericides. At the same time, it achieves a broad-spectrum and highly efficient antibacterial effect, comprehensively ensuring the long-term storage of ink and the performance of high-frequency inkjet printing.

Claims

1. A nano-self-dispersing pigment water-based ink for high-frequency inkjet printing, characterized in that, The ink, by weight percentage, consists of the following components: The composition includes 5%–15% core-shell self-dispersible pigments, 70%–85% deionized water, 5%–15% polyol co-solvents, and 0.1%–0.5% environmentally friendly biocides. The core-shell structured self-dispersible pigment is composed of primary pigment particles and biomimetic phospholipid block copolymers grafted onto the surface of the primary pigment particles. The biomimetic phospholipid block copolymer is a polyethylene glycol block copolymer containing phosphocholine groups, and the polyethylene glycol block copolymer containing phosphocholine groups is grafted onto the surface of the pigment primary particles through an aqueous free radical polymerization system. The polyol cosolvent includes at least one of glycerol, 1,2-propanediol, and polyethylene glycol 200; The environmentally friendly biocides include isothiazolinone compounds.

2. The nano-self-dispersing pigment water-based ink for high-frequency inkjet printing according to claim 1, characterized in that, The polyethylene glycol block copolymer containing phosphocholine groups includes hydrophilic polyethylene glycol blocks, hydrophobic methacrylate blocks, and reactive blocks with phosphocholine groups at the ends. The hydrophilic polyethylene glycol blocks and the hydrophobic methacrylate blocks are arranged alternately to form a multi-block structure. The reactive blocks with phosphocholine groups at the ends are connected to the active groups on the surface of the pigment primary particles by chemical bonds.

3. The nano-self-dispersing pigment water-based ink for high-frequency inkjet printing according to claim 2, characterized in that, The active groups on the surface of the pigment primary particles are hydroxyl, carboxyl, or sulfonic acid groups. The reactive blocks with terminal phosphocholine groups contain double bond structures. The double bond structures undergo graft copolymerization with the active groups on the surface of the pigment primary particles under the initiation of the aqueous free radical polymerization system to form carbon-carbon single bonds.

4. The nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 1, characterized in that, In the core-shell structured self-dispersible pigment, the biomimetic phospholipid block copolymer forms a cross-linked network shell on the surface of the pigment primary particles. The cross-linked network shell is composed of linear polyethylene glycol block copolymer molecular chains containing phosphocholine groups that are entangled with each other and form hydrogen bonds between the chains. The cross-linked network shell covers 90% to 100% of the pigment primary particles.

5. The nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 1, characterized in that, The polyol cosolvent is a compound system composed of glycerol and polyethylene glycol 200 in a mass ratio of 1:1 to 3:

1. In the compound system, glycerol molecules are inserted into the intermolecular gaps of the phosphocholine groups on the surface of the core-shell structured self-dispersing pigment. In the compound system, polyethylene glycol 200 is soluble with the deionized water.

6. The nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 1, characterized in that, The isothiazolinone compound is a mixture of methylchloroisothiazolinone and methylisothiazolinone, wherein the mass ratio of methylchloroisothiazolinone to methylisothiazolinone is 2.5:1 to 3:1, and the mixture of methylchloroisothiazolinone and methylisothiazolinone is dispersed in the deionized water after being pre-emulsified with the nonionic surfactant polyoxyethylene sorbitan monooleate.

7. A method for preparing a nano-self-dispersing pigment water-based ink for high-frequency inkjet printing, characterized in that, Includes the following steps: Step S1: Disperse primary pigment particles in deionized water to form a pigment dispersion. Add polyethylene glycol block copolymer monomer containing phosphocholine groups and an aqueous free radical polymerization initiator to the pigment dispersion. Carry out an aqueous free radical polymerization reaction under inert gas protection to obtain a self-dispersed pigment reaction solution with a core-shell structure containing free polymer. Step S2: The core-shell structured self-dispersible pigment reaction solution is purified by ultrafiltration centrifugation to remove ungrafted free polymers, the retentate is collected and freeze-dried to obtain core-shell structured self-dispersible pigment powder. Step S3: The core-shell structured self-dispersible pigment powder is added to a dispersion vessel with deionized water, polyol cosolvent, and environmentally friendly biocidal agent for physical mixing to obtain a primary mixture. Step S4: The primary mixture is subjected to high-frequency shearing and ultrasonic cavitation treatments in sequence to obtain nano-self-dispersing pigment water-based ink for high-frequency inkjet printing.

8. The method for preparing nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 7, characterized in that, The aqueous free radical polymerization initiator is a redox initiation system composed of ammonium persulfate and tetramethylethylenediamine, wherein the molar ratio of ammonium persulfate to tetramethylethylenediamine is 1:1 to 1:1.5, the temperature of the aqueous free radical polymerization reaction in step S1 is controlled at 60°C to 70°C, the reaction time is 4 hours to 6 hours, and the inert gas is high-purity nitrogen.

9. The method for preparing nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 7, characterized in that, In step S2, the ultrafiltration centrifuge device is filled with an ultrafiltration membrane with a molecular weight cutoff of 10,000 Daltons. The centrifugation speed of the ultrafiltration centrifuge device is 3,000 to 5,000 rpm. During the purification process through the ultrafiltration centrifuge device, after each centrifugation, an equal volume of deionized water is added for resuspension and washing. The resuspension and washing is repeated 3 to 5 times.

10. The method for preparing nano-self-dispersing pigment aqueous ink for high-frequency inkjet printing according to claim 7, characterized in that, In step S4, the high-frequency shearing treatment uses a high-speed disperser with a rotor speed of 8000 rpm to 12000 rpm and a treatment time of 30 to 60 minutes. The ultrasonic cavitation treatment uses an ultrasonic cell disruptor with an ultrasonic frequency of 20 kHz to 25 kHz and an ultrasonic power of 600 watts to 800 watts. The total ultrasonic cavitation treatment time is 15 to 30 minutes and uses an intermittent ultrasonic mode.

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