Digital inkjet printing paint ink, preparation method and application thereof

Abstract

The present application relates to the technical field of digital inkjet printing, and particularly relates to a digital inkjet printing coating ink, a preparation method and application thereof, wherein the ink is composed of the following components in percentage by weight, taking the total weight of the ink as 100%: pigment particles 4%; gradient crosslinking agent 2-6%; self-repairing film-forming resin 4-8%; alkali-soluble acrylic copolymer 1-3%; mesoporous silica nanoparticles modified by hydrophobic groups on the surface 0.5-2.0%; humectant 15-25%; alkaline substance 0.4-0.5%; bactericide 0.05-0.2%; and the rest is deionized water. Before printing, the fabric is treated with a pretreatment liquid containing specific molar ratio of Al3+ and Ca2+ in coordination, and after printing, the fabric is subjected to three-stage gradient baking and humidity adjustment and placement, which significantly improves the hiding power, color fastness, softness and service life of the printed fabric, effectively inhibits color migration, and realizes excellent moisture retention standby performance under low viscosity.

Description

Technical Field

[0001] This invention relates to a digital inkjet printing coating ink, its preparation method and application, belonging to the field of digital inkjet printing technology. Background Technology

[0002] Digital inkjet printing technology, with its characteristics of being plateless, high-precision, and low-emission, is gradually becoming the mainstream technology in the textile printing industry. Pigment inks, being non-selective on fibers, are suitable for cotton, linen, silk, wool, and various blended fabrics. Furthermore, the post-processing is simple, requiring only baking for color fixation and eliminating the need for washing, resulting in significant economic and environmental advantages.

[0003] However, existing coating inks still face multiple technical bottlenecks in application, as follows.

[0004] Firstly, there is an inherent contradiction between the cross-linked network structure and mechanical properties. To obtain sufficient wash and rub fastness, inks typically require the addition of a large amount of binder resin (the mass ratio of resin solids to pigment solids is usually 1:1 to 5:1), or the use of a blocked isocyanate cross-linking agent with a single unsealing temperature to replace part of the resin. Blocked isocyanate curing agents have been commercially used in the textile printing industry; for example, white inks used for DTF (direct-to-film) digital printing use blocked aliphatic polyisocyanates with an unsealing temperature of ≥90℃. Meanwhile, blocked isocyanate products on the market are also supplied in different grades according to different unsealing temperatures. However, whether a large amount of resin is added or a single cross-linking agent is used, the cross-linking reaction is concentrated within a narrow temperature window, resulting in a uniform cross-linked network structure that makes it difficult to balance the mechanical strength and flexibility of the ink film. High cross-linking density results in a hard, brittle ink film with a stiff feel; low cross-linking density leads to insufficient cross-linking and decreased fastness.

[0005] Secondly, there is a lack of functional synergy between the pretreatment solution and the ink. Existing pretreatment solutions generally employ a single cationic polymer (such as polyDADMAC) or a non-specific combination of multivalent metal salts. US20170058453A1 discloses a pretreatment composition containing multivalent metal ions (calcium, magnesium, aluminum, etc.), and EP3111005A2, JP2016089288A, etc., also disclose pretreatment schemes containing multivalent metal salts. However, the selection of multivalent metal ions in the above-mentioned prior art is limited to a single type or a broad combination, failing to explore the complementarity of different metal ions in anchoring and distribution mechanisms, and the optimal molar ratio range is not disclosed.

[0006] Third, color migration exists between different colored pigment inks. The coloring units of pigment inks are submicron-sized pigment particles. Color migration originates from the displacement of small-diameter pigment particles along microchannels formed by water evaporation to adjacent color areas before the ink film is fully cured. Conventional suppression methods, such as increasing cross-linking density or introducing wax emulsions to form a hydrophobic film layer, are ineffective; the former exacerbates the feel problem, while the latter is ineffective against already displaced pigment particles. Therefore, constructing an efficient, non-toxic, and harmless physical barrier network within the ink is crucial for suppressing color migration.

[0007] Fourth, the balance between the moisturizing system and viscosity. The moisturizing performance of traditional moisturizers such as ethylene glycol and glycerol is positively correlated with their dosage and ink viscosity; that is, the better the moisturizing effect, the higher the required dosage, and the higher the ink viscosity. How to achieve excellent moisturizing performance at lower viscosity while maintaining good printing smoothness has been a long-standing technical challenge in this field.

[0008] Fifth, insufficient ink film durability. During wear and washing, the ink film of printed fabrics inevitably experiences mechanical wear and micro-cracks. Once the bonds in the cross-linked network formed by traditional pigment inks break, they cannot repair themselves, leading to crack propagation and a continuous decline in color fastness and appearance durability over time. Imparting the self-healing ability of ink films to repair micro-cracks under mild conditions is a cutting-edge direction for improving the lifespan of printed products.

[0009] Therefore, how to simplify the process while ensuring high color fastness, improving hand feel, increasing pigment anchoring efficiency, inhibiting color migration, balancing moisturizing performance, and endowing the ink film with self-healing ability to extend its service life has been a long-standing technical challenge for those skilled in the art. Summary of the Invention

[0010] This invention addresses the shortcomings of existing technologies by providing a digital inkjet printing coating ink, its preparation method, and its application. Through a combination of multiple mechanisms, including the synergistic effect of multivalent metal ions in the pretreatment liquid, gradient unblocking crosslinking agent, physical barrier to color migration by mesoporous silica, synergistic moisturizing by diol, and dynamic covalent bond self-repairing network, the overall color fixation performance, hand softness, hiding power, printing stability, and service life of printed fabrics are significantly improved under the condition of simplified process flow.

[0011] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A digital inkjet printing coating ink, based on the total weight of the ink (100%), is composed of the following components in weight percentage: pigment particles 4%; gradient crosslinking agent 2-6%; self-healing film-forming resin 4-8%; alkali-soluble acrylic copolymer 1-3%; mesoporous silica nanoparticles with hydrophobic groups modified on the surface 0.5-2.0%; humectant 15-25%; alkaline substance 0.4-0.5%; bactericide 0.05-0.2%; the balance being deionized water.

[0012] Further, the gradient crosslinking agent includes a first crosslinking agent, a second crosslinking agent, and a third crosslinking agent, wherein the weight ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent is (1-2):(3-6):(1-4); The desealing temperature of the first crosslinking agent starts at 105°C; the desealing temperature of the second crosslinking agent is 130-150°C; and the desealing temperature of the third crosslinking agent is 160-180°C. The first crosslinking agent is a water-dispersible blocked aliphatic polyisocyanate, the second crosslinking agent is a water-dispersible blocked alicyclic polyisocyanate, and the third crosslinking agent is a water-dispersible blocked aromatic polyisocyanate. Furthermore, the self-healing film-forming resin includes an aqueous polyurethane resin containing dynamic imine bonds and a conventional aqueous polyurethane resin, wherein the mass ratio of the aqueous polyurethane resin containing dynamic imine bonds to the conventional aqueous polyurethane resin is (1.5-3):1. The method for preparing the waterborne polyurethane resin containing dynamic imine bonds is as follows: polytetrahydrofuran diol and isophorone diisocyanate are prepolymerized at 80-90℃ for 2-3 hours, p-hydroxybenzaldehyde and dimethylolpropionic acid are added for chain extension reaction for 1-2 hours, then 3-aminopropyltriethoxysilane is added for imidization end-capping reaction, the temperature is lowered to 30-40℃ and triethylamine is added for neutralization, water is added for emulsification and dispersion under high-speed shear, and organic solvent is removed under reduced pressure to obtain a dispersion of self-healing waterborne polyurethane containing dynamic imine bonds.

[0013] Furthermore, the alkali-soluble acrylic copolymer has an acid value ≥180mgKOH / g and a weight-average molecular weight of 5000-20000; the alkaline substance is an organic amine.

[0014] Furthermore, the average pore size of the mesoporous silica nanoparticles with hydrophobic groups modified on the surface is 2-5 nm, and the average particle size is 30-50 nm.

[0015] Furthermore, the mesoporous silica nanoparticles with hydrophobic groups modified on the surface are mesoporous silica treated with a hydrophobic modifier, which is selected from at least one of C8-C18 alkyltrimethoxysilane and C8-C18 alkyltriethoxysilane; the amount of the hydrophobic modifier is 20-60% of the mass of the mesoporous silica.

[0016] Furthermore, the humectant includes ethylene glycol and 1,2-pentanediol; The mass ratio of ethylene glycol to 1,2-pentanediol is (1.5-3):1.

[0017] This invention also discloses a method for preparing digital inkjet printing coating ink, wherein the preparation method is as follows: Alkali-soluble acrylic copolymer solid resin is mixed with organic amine and part of deionized water, heated and stirred to dissolve, and a water-soluble acrylic resin salt solution is obtained. Pigment particles and humectant are added and dispersed at high speed to obtain a pigment pre-dispersion. The pigment pre-dispersion is then ground to obtain nano-sized pigment paste. A resin-crosslinker mixture was obtained by uniformly mixing a gradient crosslinking agent with a self-healing film-forming resin. Mesoporous silica nanoparticles with hydrophobic groups modified on the surface were added to deionized water and ultrasonically dispersed to obtain a mesoporous silica nanoparticle dispersion. Digital inkjet printing coating ink is obtained by uniformly mixing nano-sized pigment paste, resin-crosslinking agent mixture and mesoporous silica nanoparticle dispersion, followed by filtration.

[0018] This invention also discloses a digital inkjet printing method, wherein the digital inkjet printing method is as follows: (1) Apply the pretreatment liquid to the surface of the fabric to be printed, wherein the pretreatment liquid contains Al³⁺ and Ca²⁺, and the molar ratio of Al³⁺ to Ca²⁺ is (2-3):1; (2) The digital inkjet printing ink described in this invention is applied to the surface of the fabric treated in step (1) by digital inkjet printing. (3) After the fabric obtained in step (2) is baked in a multi-stage gradient, the temperature and humidity conditions are controlled and the fabric is placed in a humidified environment.

[0019] Further, the specific process in step (3) is as follows: pre-baking at 105-115℃ for 30-60s to activate the first crosslinking agent, baking at 135-145℃ for 2-3min to activate the second crosslinking agent, fixing at 165-175℃ for 1-2min to activate the third crosslinking agent, and after the color fixing stage is completed, humidifying and placing at 60-80℃ and relative humidity of 50-70% for 4-8h to promote the self-repair and recombination of dynamic imine bonds.

[0020] The beneficial effects of this invention are: The digital inkjet printing coating ink of this invention achieves excellent comprehensive performance at low viscosity through the synergistic effect of a gradient crosslinking agent, a self-healing film-forming resin, hydrophobically modified mesoporous silica nanoparticles, and a diol moisturizing system. First, the gradient crosslinking agent is composed of three blocked polyisocyanates with different unsealing temperatures in a specific ratio. During the baking process, it is activated stepwise at low, medium, and high temperatures, respectively achieving pigment anchoring, resin network construction, and fiber chemical bonding, forming a continuous gradient crosslinking structure from pigment dispersant to resin to fiber. This allows for graded dissipation of internal stress in the ink film, thereby simultaneously achieving high flexibility and high color fastness, overcoming the technical contradiction of traditional single crosslinking systems that struggle to balance flexibility and fastness. Second, the self-healing film-forming resin contains dynamic imine bonds, which can undergo reversible exchange reactions under mild temperature and humidity conditions, enabling self-repair of microcracks in the ink film. Third, the hydrophobically modified mesoporous silica nanoparticles are uniformly dispersed in the ink film, forming a physical barrier network that effectively inhibits color migration between adjacent color blocks without affecting the ink's spraying stability. Fourth, the humectant is a compound of ethylene glycol and 1,2-pentanediol. The synergistic effect of the rapid moisturizing effect of ethylene glycol and the long-lasting moisturizing effect of 1,2-pentanediol enables the ink to achieve excellent standby moisturizing performance at low viscosity and effectively controls the viscosity of the ink. In addition, the alkali-soluble acrylic copolymer combined with organic amines effectively promotes the nanoscale dispersion of pigments, ensuring ink stability and printing smoothness.

[0021] The digital inkjet printing method of this invention further enhances the overall performance of printed fabrics by combining the synergistic effect of multivalent metal ions in the pretreatment solution with a three-stage gradient baking and conditioning process after printing. Firstly, the pretreatment solution contains Al³⁺ and Ca²⁺, with their molar ratio controlled within a specific range of (2-3):1. Al³⁺ has a high charge density, enabling it to rapidly form strong electrostatic bonds with the carboxyl groups on the pigment surface, efficiently anchoring the pigment and preventing its penetration into the fabric. Ca²⁺ has a moderate charge density, allowing it to coordinate with cellulose hydroxyl groups, creating a spacer effect between pigment particles and preventing uneven pigment distribution caused by excessive Al³⁺ aggregation. Within the specified molar ratio range, the two components produce a significant synergistic effect. Compared to methods without pretreatment or using a single metal ion, the hiding power ΔE value of the printed fabric is significantly reduced, indicating good hiding power, and both dry and wet rubbing fastness reach grades 4-5.

[0022] More specifically, the digital inkjet printing method employs a three-stage gradient baking process after printing: pre-baking at 105-115℃ to activate the first crosslinking agent, baking at 135-145℃ to activate the second crosslinking agent, and fixing at 165-175℃ to activate the third crosslinking agent. This not only allows the three crosslinking agents to exert their crosslinking effects within their respective optimal temperature windows, forming a gradient crosslinking structure, but also avoids damage to the fibers caused by prolonged high-temperature baking. Third, after the color-fixing stage, the fabric is conditioned at 60-80℃ and 50-70% relative humidity for 4-8 hours. These temperature and humidity conditions fall within the active range of the dynamic imine bond reversible exchange reaction, effectively promoting the self-repair and reorganization of microcracks in the ink film. The self-repair efficiency can reach 74%-79%, thereby significantly improving the durability and service life of the printed fabric. Compared with conventional post-printing treatments, the method of this invention fully utilizes the environmental response characteristics of dynamic covalent bonds, integrating self-repair functionality into existing production processes without complex operations, and possesses extremely high practicality and economy. In summary, the digital inkjet printing method of the present invention has improved the opacity, color fastness, softness of hand feel, color migration inhibition and ink film durability, and has good application prospects. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0025] A digital inkjet printing coating ink, based on 100% of the total ink weight, comprises the following components by weight percentage: 4% pigment particles; 2-6% gradient crosslinking agent; 4-8% self-healing film-forming resin; 1-3% alkali-soluble acrylic copolymer; 0.5-2.0% mesoporous silica nanoparticles with hydrophobic groups modified on the surface; 15-25% humectant; 0.4-0.5% alkaline substance; 0.05-0.2% bactericide; and the balance being deionized water.

[0026] Preferably, based on the total weight of the ink (100%), the ink is composed of the following components by weight percentage: 4% pigment particles; 3% gradient crosslinking agent; 6% self-healing film-forming resin; 2% alkali-soluble acrylic copolymer; 1% mesoporous silica nanoparticles with hydrophobic groups modified on the surface; 22% humectant; 0.1% bactericide; and the balance being deionized water.

[0027] Specifically, the gradient crosslinking agent includes a first crosslinking agent, a second crosslinking agent, and a third crosslinking agent, wherein the weight ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent is (1-2):(3-6):(1-4); The desealing temperature of the first crosslinking agent starts above 105℃, preferably in the range of 105-125℃. The desealing temperature can be adjusted within this range and below as the baking time increases and the catalyst is used. The desealing temperature of the second crosslinking agent is preferably 130-150℃. The desealing temperature of the third crosslinking agent is preferably 160-180℃. The actual desealing temperature is affected by factors such as the heating rate, catalyst, and specific type of crosslinking agent, and fluctuations of ±10℃ are allowed. The first crosslinking agent is a water-dispersible blocked aliphatic polyisocyanate; the second crosslinking agent is a water-dispersible blocked alicyclic polyisocyanate; the third crosslinking agent is a water-dispersible blocked aromatic polyisocyanate; the water dispersibility refers to the ability of the crosslinking agent to form a stable dispersion with a particle size of less than 500 nm in an aqueous system by introducing hydrophilic groups or by commercially available hydrophilic modification.

[0028] Preferably, the weight ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent is 1:3:1.

[0029] The mechanism of action of the gradient crosslinking agent is as follows: the first gradient crosslinking agent preferentially de-encapsulates at, for example, 105-115℃, reacts with the pigment surface dispersant to form a flexible coating layer to fix the pigment and impart primary adhesion; the second gradient crosslinking agent de-encapsulates at, for example, 135-145℃, reacts with the film-forming resin to construct the main crosslinking network; the third gradient crosslinking agent de-encapsulates at, for example, 165-175℃, forms chemical bonds with the fabric fibers, and anchors the entire ink film to the fiber surface. The actual de-encapsulation temperature windows partially overlap, but the peak temperatures exhibit a gradient distribution. The reactions of the three agents overlap in time but have different peak temperatures, achieving graded dissipation of internal stress.

[0030] Specifically, the self-healing film-forming resin includes an aqueous polyurethane resin containing dynamic imine bonds and a conventional aqueous polyurethane resin, wherein the mass ratio of the aqueous polyurethane resin containing dynamic imine bonds to the conventional aqueous polyurethane resin is (1.5-3):1. The method for preparing the waterborne polyurethane resin containing dynamic imine bonds is as follows: Polytetrahydrofuran diol (PTMG, Mn=1000-2000) and isophorone diisocyanate (IPDI) are prepolymerized at 80-90℃ for 2-3 hours. Then, a functional monomer containing an aldehyde group (such as p-hydroxybenzaldehyde) and dimethylolpropionic acid (DMPA) are added for chain extension for 1-2 hours. Subsequently, an amino-containing trialkoxysilane (such as 3-aminopropyltriethoxysilane, APTES) is added for imidization and end-capping reaction. After cooling to 30-40℃, triethylamine is added for neutralization. The mixture is then emulsified and dispersed under high-speed shearing with water, and the organic solvent is removed under reduced pressure to obtain a self-healing waterborne polyurethane dispersion containing dynamic imine bonds. The molar ratio of PTMG:IPDI:p-hydroxybenzaldehyde:DMPA:APTES is 1:(2.5-3.5):(1.0-1.5):(1.0-1.5):(0.5-1.0).

[0031] Dynamic imine bonds are formed by the condensation of aldehyde and amino groups. When printing fabrics are ironed under normal humid and hot conditions or when the printed fabrics are used under high temperature and high humidity conditions, water molecules can catalyze the exchange reaction of imine bonds. Microcracks that have formed in the ink film can be self-healed through the dynamic recombination of imine bonds.

[0032] Specifically, the alkali-soluble acrylic copolymer has an acid value ≥180mgKOH / g and a weight-average molecular weight of 5000-20000; the alkaline substance is an organic amine.

[0033] Preferably, the alkaline substance is triethylamine or N,N-dimethylethanolamine.

[0034] Specifically, the mesoporous silica nanoparticles with hydrophobic groups modified on the surface have an average pore size of 2-5 nm and an average particle size of 30-50 nm. The mesoporous silica nanoparticles with hydrophobic groups modified on the surface are mesoporous silica treated with a hydrophobic modifier, which is selected from at least one of C8-C18 alkyltrimethoxysilane and C8-C18 alkyltriethoxysilane; the amount of the hydrophobic modifier is 20-60% of the mass of the mesoporous silica.

[0035] Mesoporous silica nanoparticles are introduced into the ink film as a physical barrier. Their mechanism of inhibiting color migration is different from that of traditional dye molecular sieve adsorption. The possible principles are as follows: (1) The nanoscale pore structure (pore size 2-5nm) of MSN (mesoporous silica nanoparticles) forms dense micro-region barriers inside the ink film, dividing the channels formed by water evaporation into discontinuous isolated chambers, reducing the driving force of pigment particles flowing with water; (2) MSN has a large specific surface area. The organic groups introduced after the surface is modified with long-chain alkylsilane have van der Waals forces and hydrophobic interactions with free pigment particles, which can capture particles that have been displaced; (3) The uniformly dispersed rigid nanoparticles significantly increase the tortuosity of the microstructure of the ink film matrix. Under the driving force of water, pigment particles need to bypass a large number of MSN particles to reach adjacent color blocks, which increases the actual migration path and greatly reduces the migration efficiency.

[0036] Specifically, the humectant comprises ethylene glycol and 1,2-pentanediol; the mass ratio of ethylene glycol to 1,2-pentanediol is (1.5-3):1.

[0037] Preferably, the mass ratio of ethylene glycol to 1,2-pentanediol is (2-3):1.

[0038] Ethylene glycol has a small molecular weight and high volatility, allowing it to quickly form an initial moisturizing layer to prevent printhead drying. 1,2-Pentanediol has a boiling point approximately 100°C higher than ethylene glycol, providing long-lasting moisturizing capabilities. Within a specific mixing ratio, ethylene glycol exerts its moisturizing effect rapidly, while 1,2-Pentanediol provides a long-lasting effect, resulting in a synergistic moisturizing effect that maintains excellent ink standby performance at relatively low viscosities (8.5-10 mPa·s).

[0039] This invention also discloses a method for preparing digital inkjet printing coating ink, wherein the preparation method is as follows: Alkali-soluble acrylic copolymer solid resin is mixed with an alkaline neutralizer (such as organic amine) and part of deionized water, heated and stirred to dissolve, to obtain a water-soluble acrylic resin salt solution; pigment particles and humectant are added, and the mixture is dispersed at high speed at 800-1200 rpm for 30-60 min to obtain a pigment pre-dispersion; the pre-dispersion is transferred to a horizontal sand mill, and circulated and ground with 0.2 mm diameter zirconia beads at 800-1500 rpm for 2-6 h until the D99 particle size of the pigment particles is ≤300 nm, to obtain nanoscale pigment paste; The gradient crosslinking agent was mixed with the self-healing film-forming resin and stirred at 400-600 rpm for 15-25 min to obtain the resin-crosslinking agent mixture. Mesoporous silica nanoparticles with hydrophobic groups modified on the surface were added to deionized water and ultrasonically dispersed for 20-40 min (ultrasonic power 200-400W, frequency 35-45kHz) to obtain a mesoporous silica nanoparticle dispersion. The nano-sized pigment paste, resin-crosslinking agent mixture and mesoporous silica nanoparticle dispersion are mixed and stirred at 500-700 rpm for 1-2 hours. After filtration through a 0.8-1.2 μm pore size filter membrane, digital inkjet printing coating ink is obtained.

[0040] This invention also discloses a digital inkjet printing method, wherein the digital inkjet printing method is as follows: (1) Apply the pretreatment solution to the surface of the fabric to be printed. The pretreatment solution contains two polyvalent metal salt ions: Al³⁺ derived from aluminum trichloride or aluminum nitrate and Ca²⁺ derived from calcium chloride or calcium nitrate, and the molar ratio of Al³⁺ to Ca²⁺ is (2-3):1. (2) The digital inkjet printing coating ink described in this invention is applied to the fabric surface after step (1) by digital inkjet printing; wherein the weight percentage of pigment particles contained in the four colors of ink, namely cyan, magenta, yellow and black, is 4% each, the cyan pigment is pigment blue 15:3, the magenta pigment is pigment red 122, the yellow pigment is pigment yellow 74 and the black pigment is carbon black (pigment black 7). (3) After the fabric obtained in step (2) is baked in a multi-stage gradient, it is placed under certain temperature and humidity conditions.

[0041] Specifically, the specific process in step (3) is as follows: for example, pre-baking at 105-115℃ for 30-60s to activate the first crosslinking agent, baking at 135-145℃ for 2-3min to activate the second crosslinking agent, and fixing at 165-175℃ for 1-2min to activate the third crosslinking agent; the actual temperature can be adjusted within the preferred range according to the specific type of crosslinking agent, with a fluctuation of ±10℃ allowed; after the color fixing stage is completed, humidify and place at 60-80℃ and 50-70% relative humidity for 4-8h to promote the self-repair and recombination of dynamic imine bonds.

[0042] Preferably, the molar ratio of Al³⁺ to Ca²⁺ in step (1) is 2.5:1; the pre-baking temperature in step (3) is 110℃, the baking temperature is 140℃, and the color-fixing temperature is 170℃.

[0043] I. Source of raw materials: The sources of the raw materials used in the embodiments of the present invention are shown in Table 1 below.

[0044] Table 1. Sources of raw materials

[0045] II. Preparation of the third crosslinking agent: Under dry nitrogen protection, 100 g of TDI trimer (approximately 0.36-0.40 mol NCO groups) was dissolved in 150 mL of anhydrous ethyl acetate. 15 g of methoxy polyethylene glycol (mPEG) and 0.05 g of DBTL catalyst were added, and the reaction was carried out at 80 °C for 2-3 h. 45 g of ε-caprolactam was then added to the reaction solution, and the temperature was raised to 100 °C, continuing the reaction for 4-6 h. Ethyl acetate was removed by vacuum distillation to obtain a water-dispersible ε-caprolactam-blocked TDI trimer. This product can be directly diluted with water to form a stable dispersion with a solid content of 60%.

[0046] III. Preparation of self-healing waterborne polyurethane resin containing dynamic imine bonds: 0.1 mol PTMG (Mn=1400) and 0.3 mol IPDI were prepolymerized at 85℃ for 2.5 h. After cooling to 75℃, 0.12 mol p-hydroxybenzaldehyde, 0.12 mol DMPA, and an appropriate amount of methyl ethyl ketone were added for dilution, and the reaction was continued for another 1.5 h. Then, 0.08 mol APTES was added dropwise, and the mixture was kept at 60℃ for 30 min. After cooling to 35℃, 0.12 mol triethylamine was added for neutralization for 30 min. Deionized water was slowly added under high-speed shearing to emulsify the mixture, and methyl ethyl ketone was removed under reduced pressure to obtain a self-healing waterborne polyurethane dispersion containing dynamic imine bonds with a solid content of 35%.

[0047] IV. Preparation and hydrophobic modification of mesoporous silica nanoparticles: (1) Preparation of mesoporous silica nanoparticles (MSN): 5g CTAB, 240g deionized water, and 20g ammonia (25wt%) were added to a reaction flask and stirred at 40℃ for 30min. 20g TEOS was slowly added dropwise, and stirring was continued at 40℃ for 4h. The mixture was centrifuged (12000rpm, 20min), washed three times with ethanol, and dried at 60℃ for 12h. The mixture was then calcined in a muffle furnace at 550℃ for 6h at a rate of 2℃ / min to obtain mesoporous silica nanoparticles with an average particle size of approximately 40nm and an average pore size of approximately 3nm.

[0048] (2) Hydrophobic modification: 5g of the above mesoporous silica, 100g of toluene, and 2g of octadecyltrimethoxysilane were added to a reaction flask and refluxed at 110℃ for 12h under nitrogen protection. After centrifugation (10000rpm, 15min), the nanoparticles were washed three times with toluene and dried under vacuum at 60℃ for 12h to obtain hydrophobic modified mesoporous silica nanoparticles.

[0049] V. Ink Preparation: Examples 1-4: Preparation of ink.

[0050] Examples 1-4 describe cyan, magenta, yellow, and black pigment inks respectively, using four pigments: cyan (CI pigment blue 15:3), magenta (CI pigment red 122), yellow (CI pigment yellow 74), and black (CI pigment black 7). The amount of pigment particles in each color ink is independently 4% (by weight). The preparation steps are detailed below using cyan ink as an example (Example 1). For the other colors, only the pigment types are changed; all other operations and proportions remain the same.

[0051] Step (1): Weigh 4g of Joncryl 678 solid acrylic resin, add it to a dispersion tank along with 0.9g of triethylamine and 40g of deionized water, heat to 80℃ and stir for 1h to dissolve, obtaining a clear and transparent Joncryl 678 aqueous solution. Add 44g of humectant mixture (31.4g ethylene glycol, 12.6g 1,2-pentanediol) and 0.2g of bactericide to the above solution, and stir at 1000rpm for 10min to mix evenly. Add 8g of Pigment Blue 15:3 under stirring, and disperse at 1000rpm for 45min to obtain a pre-dispersion of pigment. Transfer the pre-dispersion to a horizontal sand mill, add 0.2mm diameter zirconia beads, with the zirconia beads filling 75% of the grinding chamber volume, and circulate and grind at 1200rpm for 4h until the D99 particle size of the pigment particles is ≤300nm, obtaining a nano-sized cyan pigment paste.

[0052] Step (2): Add 1.2g of the first crosslinking agent, 3.6g of the second crosslinking agent and 1.2g of the third crosslinking agent, along with 8g of self-healing PU resin (based on the dry weight of pure resin) and 4g of conventional PU resin (based on the dry weight of pure resin) into a mixing container, and stir at 500rpm for 20min to obtain a resin-crosslinking agent mixture.

[0053] Step (3): Add 2g of hydrophobic modified MSN to 65g of deionized water, place it in an ultrasonic disperser, and ultrasonically disperse it for 30min at 300W power and 40kHz frequency to obtain a uniform milky white MSN dispersion.

[0054] Step (4): Combine the nano-sized pigment paste obtained in step (1), the resin-crosslinking agent mixture obtained in step (2), and the MSN dispersion obtained in step (3) in a dispersion tank, add 17.9g of deionized water to make the total amount of deionized water 122.9g, and stir at 600rpm for 1.5h. Filter with a 1.0μm pore size polypropylene (PP) filter membrane to obtain the cyan digital inkjet printing coating ink.

[0055] Table 2. Cyan Ink Formula for Example 1

[0056] VI. Preparation of Pretreatment Solution and Inkjet Printing Process: Application Example 1: Inkjet printing.

[0057] A digital inkjet printing method, the specific method is as follows: (1) Preparation of pretreatment solution: AlCl3·6H2O and CaCl2·2H2O were dissolved in deionized water at the target molar ratio to prepare a pretreatment solution with a total metal ion concentration of 0.02-0.2 mol / L (preferably 0.05-0.1 mol / L). In this application example, 0.1 mol / L was selected for subsequent experiments.

[0058] (2) Application of pretreatment liquid: The above pretreatment liquid is applied to the surface of the fabric (the fabric used is pure cotton) by padding. The padded fabric is immediately sent into a hot air tenter frame and dried at 100°C for 2 minutes. After cooling to room temperature, it is wound up for use.

[0059] (3) Inkjet printing: The ink of Example 1 is loaded into the ink path using an industrial digital printing machine and the test pattern is printed on the pretreated fabric for subsequent performance tests.

[0060] (4) Post-printing processing: The printed fabric is immediately placed in a hot air oven for gradient baking. First stage: pre-baking at 105-115℃ for 40s (actual oven temperature set at 110℃), second stage: baking at 135-145℃ for 2.5min (actual oven temperature set at 140℃), third stage: color fixing at 165-175℃ for 1.5min (actual oven temperature set at 170℃). After baking, the fabric is cooled to below 40℃ by cold air, and then placed in a humidity conditioning chamber at 70℃ and 65% relative humidity for 6 hours. After the humidity conditioning is completed, the fabric is allowed to cool naturally to room temperature, which is the finished printed fabric.

[0061] Application Example 2: Inkjet printing.

[0062] Inkjet printing was performed using the same method as in Application Example 1, except that the ink was replaced with the ink from Example 2.

[0063] Application Example 3: Inkjet printing.

[0064] Inkjet printing was performed using the same method as in Application Example 1, except that the ink was replaced with the ink from Example 3.

[0065] Application Example 4: Inkjet printing.

[0066] Inkjet printing was performed using the same method as in Application Example 1, except that the ink was replaced with the ink from Example 4.

[0067] VII. Testing Methods: The performance of the fabric after inkjet printing in the application example will be tested, and the test methods involved are as follows.

[0068] Opacity: Taking Application Example 1 (cyan ink) as an example, the specific operation is as follows: Apply the same ink to a standard white base fabric and a standard black base fabric that meet the requirements of GB / T 23981.1 using the same inkjet printing process. After drying and curing, use a spectrophotometer (D65 standard illuminator, 10° viewing angle) to measure the L*, a*, and b* values ​​of the printed color patches on the two base fabrics respectively, and calculate the color difference ΔE between the two. ab ( ), ΔE ab *: Color difference, ΔL*: Lightness difference, Δa*: Red-green chromaticity difference, Δb*: Yellow-blue chromaticity difference. The lower the ΔE* value, the more consistent the ink's color performance on different colored fabrics, i.e., the stronger the hiding power.

[0069] Dry / wet rubbing fastness: tested according to AATCC 8-2016 standard.

[0070] Wash fastness: Tested according to AATCC 61-2013 standard (method 2A).

[0071] Color migration: Taking Application Example 1 (cyan ink) and Application Example 3 (yellow ink) as examples, adjacent cyan and yellow color blocks (each adjacent color block is 2cm × 2cm in size, with the boundaries of the two color blocks tightly joined and without gaps) are printed on the fabric to be printed. After the printing post-processing is completed, the fabric is placed in a constant temperature and humidity chamber (e.g., 50℃, 80% relative humidity) for 4 hours to accelerate the simulated color migration process. Before and after placement, the L*, a*, and b* values ​​of the center of the cyan color block and the center of the yellow color block are measured with a spectrophotometer, and the color migration ΔE* is calculated according to the following formula: ΔL*, Δa*, and Δb* represent the changes in color parameters before and after placement, with the same meaning as above. A lower ΔE* value indicates better resistance to color migration. Before each measurement, the instrument is calibrated using a standard white board, and measurements are taken at no fewer than three different locations for each color patch, with the arithmetic mean calculated.

[0072] Flexibility: Evaluated by a scoring system, with scores ranging from 1 to 10, where a higher score indicates better flexibility.

[0073] Self-healing efficiency: The percentage change in scratch width observed under a microscope is calculated as follows: Self-healing efficiency (%) = (Initial average scratch width - After repair average scratch width) / Initial average scratch width × 100%.

[0074] Injection stability: The number of interrupted lines after 100m of continuous printing is used as the evaluation criterion; 0 interrupted lines are considered excellent.

[0075] Standby performance: The number of broken lines on the first color block printed after a 30-minute shutdown is used as the evaluation criterion; 0 broken lines are considered excellent.

[0076] The test results for Application Examples 1-4 are shown in Table 3 below.

[0077] Table 3 Test results of Application Examples 1-4

[0078] As can be seen from the data results in Table 3 above, the ink and inkjet printing method described in this invention significantly improve the opacity, color fastness, softness and service life of printed fabrics, and have a good self-healing ability. At the same time, it effectively inhibits color migration and achieves excellent moisturizing standby performance at low viscosity.

[0079] Application Examples 5-7: Inkjet Printing.

[0080] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The difference was that the ion ratio of the pretreatment solution was changed. The ion ratio of the pretreatment solution in each application example is shown in Table 4 below.

[0081] Comparative Examples 1-4: Inkjet printing.

[0082] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The difference was that the ion ratio of the pretreatment solution was changed. The ion ratio of the pretreatment solution in each comparative example is shown in Table 4 below.

[0083] Table 4 Effect of Ion Ratio on Pretreatment Solution

[0084] As shown in Table 4 above, in Comparative Example 4, without any pretreatment, ink droplets severely penetrated, resulting in poor hiding power and fastness (ΔE=8.5, fastness grade 2 or below). In Comparative Example 1, when Al³⁺ was used alone, its high charge density led to a strong electrostatic bond with the carboxyl groups of the pigment surface grinding resin, enabling rapid pigment anchoring. However, the lack of spacer ions may have caused localized excessive aggregation, resulting in a hiding power ΔE of only 5.8 and a fastness grade of 3. In Comparative Example 2, when Ca²⁺ was used alone, the coordination of Ca²⁺ with the cellulose hydroxyl groups resulted in a uniform distribution, but the anchoring power was insufficient, with ΔE of 7.2 and a fastness grade of only 2-3. In Comparative Example 3, the excess Ca²⁺ in the 1:1 molar ratio may have competed for carboxyl sites on the pigment surface, diluting the anchoring density of Al³⁺, and its performance was inferior to the optimized range. In Application Examples 1 and 5-7, when the molar ratio of Al³⁺ to Ca²⁺ is within the range of 2-3:1, the rapid anchoring of Al³⁺ and the uniform distribution of Ca²⁺ produce a synergistic effect, resulting in hiding power ΔE ≤ 4.8, fastness grade ≥ 4, and a significant reduction in batch color difference. Moreover, the optimal balance is achieved when the molar ratio of Al³⁺ to Ca²⁺ is 2.5:1.

[0085] Application Examples 8-9: Preparation of inks and inkjet printing.

[0086] The ink was prepared using the same method as in Example 1, except that the mass ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent in the crosslinking agent was changed.

[0087] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 5 below.

[0088] Comparative Examples 5-8: Preparation of inks and inkjet printing.

[0089] The ink was prepared using the same method as in Example 1, except that the mass ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent in the crosslinking agent was changed.

[0090] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 5 below.

[0091] Table 5 Comparison of printing effects with different ratios of gradient crosslinking agents

[0092] Comparative Example 8, without a crosslinking agent, failed to form an effective crosslinking network, resulting in a fastness grade of only 2 and the ink film breaking under external force, demonstrating the necessity of crosslinking. Comparative Example 5, using only a second crosslinking agent, saw the reaction concentrated within a narrow temperature window, rapidly completing and forming a uniform, high-density crosslinking network. However, stress could not be dispersed, leading to poor flexibility. Furthermore, despite the high crosslinking density, the low effective utilization rate of raw materials resulted in a fastness grade of only 3-4. Application Example 1, using a 1:3:1 ratio, activated the three levels of crosslinking sequentially within their respective temperature windows, forming a continuous gradient. This allowed for graded dissipation of internal stress, achieving better fastness and flexibility.

[0093] Comparative Example 9: Preparation of ink and inkjet printing.

[0094] The ink was prepared using the same method as in Example 1, except that mesoporous silica nanoparticles (MSN) with hydrophobic groups modified on the surface were not added.

[0095] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 6 below.

[0096] Comparative Example 10: Preparation of ink and inkjet printing.

[0097] The ink was prepared using the same method as in Example 1, except that no waterborne polyurethane resin containing dynamic imine bonds was added to the self-healing film-forming resin; only conventional waterborne polyurethane resin was used.

[0098] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 6 below.

[0099] Comparative Example 11: Preparation of ink and inkjet printing.

[0100] The ink was prepared using the same method as in Example 1, except that: no mesoporous silica nanoparticles (MSN) with hydrophobic groups modified on the surface were added; and no waterborne polyurethane resin containing dynamic imine bonds was added to the self-healing film-forming resin, only conventional waterborne polyurethane resin was used.

[0101] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 6 below.

[0102] Table 6 Comparison of the effects of MSN and self-healing resin

[0103] Note: The self-healing resin ratio in Table 6 refers to the mass ratio of waterborne polyurethane resin containing dynamic imine bonds to conventional waterborne polyurethane resin. "Conventional resin" in Table 6 refers to "conventional waterborne polyurethane resin".

[0104] As shown in Table 6 above, Comparative Example 11, as a blank control, had a color migration ΔE of 5.8 and a self-healing efficiency of only 3%, indicating that the absence of MSN and dynamic imine bonds resulted in almost no ability to inhibit color migration or self-healing. Comparing Application Example 1 and Comparative Example 9, the introduction of 1.0% MSN reduced the color migration ΔE from 4.5 to 1.2, and increased the self-healing efficiency to 78%, confirming that MSN can inhibit pigment migration, and that the support of the crack interface may promote the self-healing reaction of dynamic imine bonds. Although Comparative Example 10 contained MSN, the lack of dynamic imine bonds resulted in a self-healing efficiency of only 5%, confirming that the self-healing function completely depends on dynamic imine bonds, and MSN only plays an auxiliary enhancing role.

[0105] Application Examples 10-11: Preparation of inks and inkjet printing.

[0106] The ink was prepared using the same method as in Example 1, except that the mass ratio of the two components in the humectant was changed.

[0107] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 7 below.

[0108] Comparative Examples 12-14: Preparation of inks and inkjet printing.

[0109] The ink was prepared using the same method as in Example 1, except that the mass ratio of the two components in the humectant was changed.

[0110] Inkjet printing was performed using the same method as in Application Example 1, and performance testing was conducted using the same method. The specific results are shown in Table 7 below.

[0111] Table 7 Effect of humectant ratio

[0112] Comparative Example 12 used only 1,2-pentanediol, resulting in excessively high viscosity. In Comparative Example 14, the weight ratio of ethylene glycol to 1,2-pentanediol was 1:1, leading to relatively high ink viscosity and a tendency for line breakage. Comparative Example 13 used only ethylene glycol, resulting in low viscosity, but rapid evaporation and a high viscosity change rate, leading to line breakage during standby. In Application Examples 1, 10, and 11, a (2-3):1 weight ratio of ethylene glycol to 1,2-pentanediol was used. Ethylene glycol provides rapid moisturizing, while 1,2-pentanediol provides long-lasting moisturizing. The viscosity change rate was ≤5.5% over 24 hours, and there were no line breakages during standby, overcoming the performance limitations of traditional single moisturizers.

[0113] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A digital inkjet printing coating ink, characterized in that, Based on the total weight of the ink (100%), it consists of the following components by weight percentage: pigment particles 4%; gradient crosslinking agent 2-6%; self-healing film-forming resin 4-8%; alkali-soluble acrylic copolymer 1-3%; mesoporous silica nanoparticles with hydrophobic groups modified on the surface 0.5-2.0%; humectant 15-25%; alkaline substance 0.4-0.5%; bactericide 0.05-0.2%; the balance is deionized water. The gradient crosslinking agent includes a first crosslinking agent, a second crosslinking agent, and a third crosslinking agent, wherein the weight ratio of the first crosslinking agent, the second crosslinking agent, and the third crosslinking agent is (1-2):(3-6):(1-4); The desealing temperature of the first crosslinking agent starts at 105°C; the desealing temperature of the second crosslinking agent is 130-150°C; and the desealing temperature of the third crosslinking agent is 160-180°C. The first crosslinking agent is a water-dispersible blocked aliphatic polyisocyanate; the second crosslinking agent is a water-dispersible blocked alicyclic polyisocyanate; and the third crosslinking agent is a water-dispersible blocked aromatic polyisocyanate. The self-healing film-forming resin includes an aqueous polyurethane resin containing dynamic imine bonds and a conventional aqueous polyurethane resin, wherein the mass ratio of the aqueous polyurethane resin containing dynamic imine bonds to the conventional aqueous polyurethane resin is (1.5-3):

1. The method for preparing the waterborne polyurethane resin containing dynamic imine bonds is as follows: polytetrahydrofuran diol and isophorone diisocyanate are prepolymerized at 80-90℃ for 2-3 hours, p-hydroxybenzaldehyde and dimethylolpropionic acid are added for chain extension reaction for 1-2 hours, then 3-aminopropyltriethoxysilane is added for imidization end-capping reaction, the temperature is lowered to 30-40℃ and triethylamine is added for neutralization, water is added for emulsification and dispersion under high-speed shear, and organic solvent is removed under reduced pressure to obtain a dispersion of self-healing waterborne polyurethane containing dynamic imine bonds; The humectant comprises ethylene glycol and 1,2-pentanediol; the mass ratio of ethylene glycol to 1,2-pentanediol is (1.5-3):

1.

2. The digital inkjet printing coating ink according to claim 1, characterized in that, The alkali-soluble acrylic copolymer has an acid value ≥180mgKOH / g and a weight-average molecular weight of 5000-20000; the alkaline substance is an organic amine.

3. The digital inkjet printing coating ink according to claim 1, characterized in that, The mesoporous silica nanoparticles with hydrophobic groups modified on the surface have an average pore size of 2-5 nm and an average particle size of 30-50 nm.

4. The digital inkjet printing coating ink according to claim 3, characterized in that, The mesoporous silica nanoparticles with hydrophobic groups modified on the surface are mesoporous silica treated with a hydrophobic modifier, which is selected from at least one of C8-C18 alkyltrimethoxysilane and C8-C18 alkyltriethoxysilane; the amount of the hydrophobic modifier is 20-60% of the mass of the mesoporous silica.

5. A method for preparing a digital inkjet printing coating ink according to any one of claims 1-4, characterized in that, The preparation method is as follows: An alkali-soluble acrylic copolymer solid resin is mixed with an alkaline substance and a portion of deionized water, and then heated and stirred to dissolve it, thereby obtaining a water-soluble acrylic resin salt solution. Pigment particles, a humectant, and a bactericide are added to the water-soluble acrylic resin salt solution, and the mixture is dispersed at high speed to obtain a pigment pre-dispersion. The pigment pre-dispersion is then ground to obtain a nano-sized pigment paste. A resin-crosslinker mixture was obtained by uniformly mixing a gradient crosslinking agent with a self-healing film-forming resin. Mesoporous silica nanoparticles with hydrophobic groups modified on the surface were added to deionized water and ultrasonically dispersed to obtain a mesoporous silica nanoparticle dispersion. Digital inkjet printing coating ink is obtained by uniformly mixing nano-sized pigment paste, resin-crosslinking agent mixture and mesoporous silica nanoparticle dispersion, followed by filtration.

6. A digital inkjet printing method, characterized in that, The digital inkjet printing method is as follows: (1) Apply the pretreatment liquid to the surface of the fabric to be printed, wherein the pretreatment liquid contains Al³⁺ and Ca²⁺, and the molar ratio of Al³⁺ to Ca²⁺ is (2-3):1; (2) Using the digital inkjet printing ink described in any one of claims 1-4, apply it to the surface of the fabric treated in step (1) by digital inkjet printing. (3) After the fabric obtained in step (2) is baked in a multi-stage gradient, the temperature and humidity conditions are controlled and the fabric is placed in a humidified environment.

7. The digital inkjet printing method according to claim 6, characterized in that, The specific process in step (3) is as follows: pre-baking at 105-115℃ for 30-60s to activate the first crosslinking agent, baking at 135-145℃ for 2-3min to activate the second crosslinking agent, fixing at 165-175℃ for 1-2min to activate the third crosslinking agent; after the color fixing stage is completed, humidifying and placing at 60-80℃ and 50-70% relative humidity for 4-8h to promote the self-repair and recombination of dynamic imine bonds.

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