Waterborne polyurethane paper printing ink and preparation method thereof

Abstract

The invention discloses waterborne polyurethane paper printing ink and a preparation method thereof, and relates to the technical field of novel ink. The preparation method comprises the following steps: firstly, nano cellulose and a silane coupling agent KH-560 are grafted and then dispersed in water, then the mixture is added into a waterborne polyurethane emulsion for crosslinking, and a modified emulsion is obtained; the preparation method comprises the following steps: activating nano titanium dioxide with hydrogen peroxide, coating with dopamine, and reacting with a silane coupling agent KH-550 to obtain composite modified nano titanium dioxide; dispersing organic pigment, a dispersing agent and water at a high speed to obtain color paste; and finally, mixing the modified emulsion with an acrylic emulsion, ethanol and PEG-1000, adding the color paste, the composite modified nano titanium dioxide, the amino modified nano silicon dioxide and an auxiliary agent, dispersing at a high speed, grinding and filtering. The prepared ink is high in adhesive force and good in printability.

Description

A water-based polyurethane paper printing ink and its preparation method Technical Field

[0001] This invention relates to the field of novel ink technology, specifically to a water-based polyurethane paper printing ink and its preparation method. Background Technology

[0002] The printing industry, traditionally a high-VOC (volatile organic compound) emission sector, is facing an urgent need for transformation and upgrading. Developing environmentally friendly printing materials has become a core trend in the industry's development. Waterborne polyurethane inks, as a new type of environmentally friendly ink, use water as the main dispersion medium. Compared to traditional solvent-based polyurethane inks, their VOC emissions are significantly reduced, effectively minimizing atmospheric pollution. They also possess significant advantages such as being environmentally friendly, non-toxic, odorless, and non-flammable and non-explosive, meeting the needs of fields with high environmental requirements, such as food packaging, children's product packaging, and book printing. Therefore, they show extremely broad application prospects in the field of green printing and have become a research hotspot and key development direction in the ink industry in recent years. However, despite the irreplaceable advantages of waterborne polyurethane inks in terms of environmental performance, the problem of insufficient adhesion to paper substrates has not been effectively solved in practical applications, becoming a key bottleneck restricting their large-scale promotion and application, and severely limiting their industrialization in the printing industry. Paper, as one of the most widely used substrates in the printing industry, has surface characteristics that directly affect the interfacial bonding effect between ink and substrate. The insufficient adhesion between waterborne polyurethane inks and paper substrates mainly stems from the limitations of the surface characteristics of the paper fibers themselves. Specifically, paper is mainly composed of plant fibers. The density of polar groups (such as hydroxyl and carboxyl groups) on the surface of plant fibers is relatively low, while water-based polyurethane ink molecules contain a large number of polar groups. According to the principle of "like dissolves like," it is difficult for the low-polarity paper fiber surface and the high-polarity ink molecules to form an effective polar interaction. At the same time, the paper fiber surface has a significant uneven structure and uneven surface energy distribution, with some areas having lower surface energy. This results in poor wetting and spreading of the ink on the paper surface, preventing it from fully penetrating into the gaps between the paper fibers. Furthermore, the paper fibers have a certain porous structure. During the ink drying process, rapid evaporation of moisture easily leads to ink film shrinkage, further weakening the interfacial adhesion between the ink and the paper substrate. Ultimately, this makes the printed ink film prone to peeling, scratching, and abrasion, seriously affecting the quality and lifespan of the printed products and failing to meet the requirements of actual printing production. Summary of the Invention

[0003] The purpose of this invention is to provide a water-based polyurethane paper printing ink and its preparation method, so as to solve the technical problem of insufficient adhesion between water-based polyurethane ink and paper mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0006] (1) The nanocellulose crystals were ultrasonically dispersed in water, and the acid-hydrolyzed silane coupling agent KH-560 was added to carry out the grafting reaction. After purification, the nanocellulose was dispersed again to obtain a silane-grafted nanocellulose dispersion.

[0007] (2) Add the silane-grafted nanocellulose dispersion to the neutralized emulsified and stabilized waterborne polyurethane emulsion, mix and then heat to crosslink to obtain the modified waterborne polyurethane emulsion.

[0008] (3) The nano-titanium dioxide was activated with hydrogen peroxide, then reacted with dopamine hydrochloride in tris(hydroxymethyl)aminomethane-hydrochloric acid buffer to form polydopamine coating, and then reacted with silane coupling agent KH-550, separated and dried to obtain composite modified nano-titanium dioxide.

[0009] (4) Mix and disperse organic pigment, sodium polycarboxylate dispersant and water at high speed to obtain pigment paste;

[0010] (5) Mix modified waterborne polyurethane emulsion, acrylic emulsion, ethanol and PEG-1000, then add pigment paste and mix well, then add composite modified nano titanium dioxide, amino modified nano silica, organosilicon defoamer, acrylate leveling agent and waterborne aziridine crosslinking agent, disperse at high speed and grind and filter to obtain waterborne polyurethane paper printing ink.

[0011] In the technical solution of this invention, the adhesion performance of waterborne polyurethane ink on paper is improved synergistically from the following aspects: (1) By grafting nanocellulose with a silane coupling agent, the adhesion of waterborne polyurethane to paper is enhanced from the resin matrix phase level. Paper and nanocellulose belong to the same cellulose homologous structure and are rich in free hydroxyl groups. They are very easy to spontaneously form high-density intermolecular hydrogen bonds at the interface. In order to solve the problem of easy detachment of nanocellulose under force in physical blending, this solution uses KH-560 to graft it on the surface: the silanol groups of KH-560 form Si-OC covalent bonds with nanocellulose, and the epoxy groups retained therein react with the active groups of waterborne polyurethane segments when crosslinking at elevated temperature. As the coating film is formed, a ternary covalent network with nanocellulose as crosslinking nodes, silane as bridging arms, and polyurethane as continuous phase is finally formed. This structure firmly anchors nanocellulose in the resin skeleton, and at the same time releases a large number of ungrafted free hydroxyl groups to the interface, which is equivalent to implanting a large number of anchor points with natural affinity to paper inside the resin, which greatly improves the overall chemical affinity and bonding strength of the ink system. (2) A composite modification of nano-titanium dioxide with dopamine biomimetic coating and aminosilane grafting is adopted to form a core-shell-crown structure of nano-rivets at the ink-paper interface, achieving synergistic enhancement at the interface level. The core is high-hardness TiO2, which, after dispersion, is embedded in the micropores and textures of the paper to provide a physical anchoring (pinning) effect and resist tangential slippage of the coating; the middle shell is polydopamine, which utilizes its rich catechol and amino groups to generate hydrogen bonds and coordination with the polar sites of the paper, giving the filler biomimetic adhesion and improving interfacial compatibility; the outermost crown layer introduces free primary amino groups by grafting KH-550, forming multiple chemical bonds at the interface: not only forming hydrogen bonds with cellulose, but also forming covalent bonds with the residual aldehyde groups generated by hemicellulose degradation through Schiff base condensation, and forming ionic bonds with the carboxyl groups on the paper surface through protonated amino groups. These three mechanisms are superimposed layer by layer from the inside out, which significantly improves the anti-peeling performance of the coating at the interface, and synergistically improves the adhesion performance of waterborne polyurethane inks on paper with the first aspect.

[0012] This invention discovered in experiments that the high cross-linking density of the cellulose-polyurethane network restricts the movement of matrix chain segments, and the modulus of the nano-TiO2 introduced into the system differs significantly from that of the polyurethane matrix. This makes the ink film prone to microcracks due to interfacial stress concentration under dynamic stresses such as bending and friction, resulting in decreased adhesion. To further address this technical problem, this invention synergistically introduces PEG-1000 and amino-functionalized nano-SiO2 during the ink formulation stage. After PEG-1000 is directly dissolved in the aqueous system, it covalently embeds itself between adjacent cross-linking nodes in the form of flexible buffer arms, dissipating strain energy through chain segment extension, thus improving the overall brittleness of the network while maintaining the cross-linking density. The amino-modified SiO2 is chemically anchored in the resin network, transforming the original rigid-flexible bipolar transition into a three-level transition of matrix-SiO2-TiO2, allowing external forces to be transmitted gradually and smoothly within the film. The synergistic effect of the two lies in the fact that PEG-1000 solves the "surface" problem of the overall flexibility of the cross-linked network, while SiO2 eliminates the local modulus abrupt change. The former provides the basis for deformation, while the latter prevents local stress concentration. Both are indispensable. Ultimately, the ink film maintains high static adhesion while also having excellent dynamic bending resistance and abrasion resistance, avoiding the decrease in adhesion caused by microcracks due to interfacial stress concentration when the ink film is subjected to dynamic forces such as bending and friction.

[0013] Preferably, in step (1), the mass ratio of nanocellulose crystals to silane coupling agent KH-560 is 1:(1.5~2.5).

[0014] Preferably, in step (1), the grafting reaction temperature is 60-75°C and the reaction time is 2-4 hours.

[0015] Preferably, in step (3), the mass ratio of nano-titanium dioxide to dopamine hydrochloride is 1:(0.3-0.5).

[0016] Preferably, in step (4), the mass ratio of organic pigment to sodium polycarboxylate dispersant is (6-10):1.

[0017] Preferably, in step (5), the mass ratio of modified waterborne polyurethane emulsion to acrylic emulsion is 214:(3-5).

[0018] Preferably, in step (5), the mass ratio of modified waterborne polyurethane emulsion to PEG-1000 is 214:(2-4).

[0019] Preferably, in step (5), the mass ratio of the modified waterborne polyurethane emulsion to the composite modified nano-titanium dioxide is 214:(2-4).

[0020] Preferably, in step (5), the mass ratio of modified waterborne polyurethane emulsion to amino-modified nano silica is 214:(1-3).

[0021] A water-based polyurethane paper printing ink is prepared by the method described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] 1. Nanocellulose is covalently anchored in an aqueous polyurethane network using the silane coupling agent KH-560, forming a ternary cross-linked structure. Utilizing the affinity of nanocellulose for the hydroxyl groups common to paper, dense hydrogen bonds are formed at the interface, significantly enhancing the overall chemical affinity and bonding strength of the ink system to the paper.

[0024] 2. A core-shell-crown structure was constructed by modifying nano-titanium dioxide with dopamine and aminosilane. These nano-rivets significantly improve the coating's anti-peeling properties at the interface through multiple interactions, including physical anchoring, hydrogen bonding, Schiff base covalent bonds, and ionic bonds.

[0025] 3. The synergistic introduction of PEG-1000 flexible chains and amino-modified nano-SiO2 improves overall flexibility by embedding the cross-linked network to dissipate strain energy, while the latter eliminates the modulus abrupt change between the matrix and TiO2, enabling stress to be transferred stepwise. Together, these two components enable the film to maintain high static adhesion while possessing excellent flexural and abrasion resistance, preventing microcracks from forming under dynamic stress. Attached Figure Description

[0026] Figure 1 is a low-magnification SEM image of the composite modified nano-titanium dioxide prepared in Example 1 of the present invention.

[0027] Figure 2 is a medium-magnification SEM image of the composite modified nano-titanium dioxide prepared in Example 1 of this invention.

[0028] Figure 3 is a high-magnification SEM image of the composite modified nano-titanium dioxide prepared in Example 1 of the present invention.

[0029] Figure 4 shows the XRD pattern of the composite modified nano-titanium dioxide prepared in Example 1 of this invention. Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1

[0032] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0033] Step 1: Weigh 6.0 g of cellulose nanocrystals (approximately 10 nm in diameter and 200 nm in length) and add them to 194.0 g of deionized water. Disperse the nanocrystals using pulsed ultrasonication at 400 W for 30 min to obtain a cellulose nanocrystal suspension. Mix 14 g of silane coupling agent KH-560 with 72.0 g of anhydrous ethanol, add 2% glacial acetic acid aqueous solution to adjust the pH to 4.0, and hydrolyze at room temperature for 45 min to obtain a hydrolyzed silane solution. Add the hydrolyzed silane solution dropwise to the cellulose nanocrystal suspension at a rate of 2 mL / min, react at 70 °C and 800 rpm for 3 h, and cool to room temperature. Centrifuge the reaction solution at 10,000 rpm, wash three times with anhydrous ethanol and twice with deionized water, and vacuum dry at 60 °C for 2 h to constant weight to obtain silane-grafted cellulose nanocrystals. Add the silane-grafted cellulose nanocrystals to 133.0 g of deionized water and ultrasonically redisperse to obtain a silane-grafted cellulose nanocrystal dispersion.

[0034] Step 2: Take 250.0g of a neutralized, emulsified, stabilized waterborne polyurethane emulsion with a solid content of 40% (soft segment is polycarbonate diol, hard segment is isophorone diisocyanate, chain extender is dimethylolpropionic acid, neutralized with triethylamine, pH 7.2) into a four-necked flask, stir at 600rpm under nitrogen protection, and add the silane-grafted nanocellulose dispersion obtained in step (1) dropwise at a rate of 1.5mL / min. After the addition is complete, continue stirring for 1.5h. Adjust the pH to 7.2 with triethylamine, raise the temperature to 50℃ and react at a constant temperature for 2h, cool to room temperature to obtain the modified waterborne polyurethane emulsion.

[0035] Step 3: Weigh 5.0 g of anatase nano-titanium dioxide (particle size approximately 20 nm) and add it in batches to 90.0 g of 30% hydrogen peroxide solution. Stir and react at 85 °C for 2.5 h. Centrifuge and wash until neutral, then vacuum dry at 60 °C for 10 h to obtain hydroxylated nano-titanium dioxide. Weigh 6.06 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Adjust the pH to 8.5 with 1.0 mol / L hydrochloric acid and bring the volume to 1000 mL to obtain Tris-HCl buffer. Add the above hydroxylated nano-titanium dioxide to 625 mL of buffer, sonicate and disperse for 20 min, then add 2.3 g of dopamine hydrochloride. Stir magnetically with an open container and react at 25 °C for 18 h. Monitor the pH every 4 h and adjust it to 8.5 with 0.1 mol / L NaOH. Centrifuge, wash, and freeze-dry for 24 h to obtain PDA@TiO2. The above PDA@TiO2 was dispersed in 200 mL of anhydrous ethanol, and 2.5 g of silane coupling agent KH-550 was added. The mixture was refluxed and stirred at 75 °C for 6 h under nitrogen protection. After centrifugation, the mixture was washed three times each with anhydrous ethanol and deionized water, dried under vacuum at 60 °C for 12 h, and ground through a 200-mesh sieve to obtain composite modified nano-titanium dioxide.

[0036] Step 4: Weigh 9g of organic pigment phthalocyanine blue and 1.0g of sodium polycarboxylate dispersant, add them to 18.0g of deionized water, first stir and wet at 1000rpm for 5min, then disperse at 2500rpm for 45min, and control the water bath temperature to not exceed 40℃ to obtain pigment paste.

[0037] Step 5: Take 214g of the modified waterborne polyurethane emulsion obtained in step (2), add 4.5g of acrylic emulsion (50% solid content), 7.0g of ethanol and 3.5g of PEG-1000 in sequence, stir at 600rpm for 30min to mix evenly, then add all the pigment paste from step (4) and stir for 30min. Take another 3.5g of the composite modified nano-titanium dioxide obtained in step (3) and 2.5g of amino modified nano-silica (particle size 12nm, KH-550 grafted fumed silica), add them to 3.5g of deionized water and ultrasonically disperse for 18min. Add the two suspensions to the above mixture, and add 0.5g of silicone defoamer, 0.6g of acrylate leveling agent and 2.8g of trifunctional waterborne aziridine crosslinking agent (pre-dissolved in 5.0g of deionized water), and disperse at 1000rpm for 50min. The dispersed material is ground by a three-roll mill and passed through a 200-mesh filter to obtain water-based polyurethane paper printing ink.

[0038] Example 2

[0039] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0040] Step 1: Weigh 6.0 g of cellulose nanocrystals (approximately 10 nm in diameter and 200 nm in length) and add them to 194.0 g of deionized water. Disperse the nanocrystals using pulsed ultrasonication at 400 W for 30 min to obtain a cellulose nanocrystal suspension. Mix 10 g of silane coupling agent KH-560 with 72.0 g of anhydrous ethanol, add 2% glacial acetic acid aqueous solution to adjust the pH to 4.0, and hydrolyze at room temperature for 45 min to obtain a hydrolyzed silane solution. Add the hydrolyzed silane solution dropwise to the cellulose nanocrystal suspension at a rate of 2 mL / min, react at 70 °C and 800 rpm for 3 h, and cool to room temperature. Centrifuge the reaction solution at 10,000 rpm, wash three times with anhydrous ethanol and twice with deionized water, and vacuum dry at 60 °C for 2 h to constant weight to obtain silane-grafted cellulose nanocrystals. Add the silane-grafted cellulose nanocrystals to 133.0 g of deionized water and ultrasonically redisperse to obtain a silane-grafted cellulose nanocrystal dispersion.

[0041] Step 2: Take 250.0g of a neutralized, emulsified, stabilized waterborne polyurethane emulsion with a solid content of 40% (soft segment is polycarbonate diol, hard segment is isophorone diisocyanate, chain extender is dimethylolpropionic acid, neutralized with triethylamine, pH 7.2) into a four-necked flask, stir at 600rpm under nitrogen protection, and add the silane-grafted nanocellulose dispersion obtained in step (1) dropwise at a rate of 1.5mL / min. After the addition is complete, continue stirring for 1.5h. Adjust the pH to 7.2 with triethylamine, raise the temperature to 50℃ and react at a constant temperature for 2h, cool to room temperature to obtain the modified waterborne polyurethane emulsion.

[0042] Step 3: Weigh 5.0 g of anatase nano-titanium dioxide (particle size approximately 20 nm) and add it in batches to 90.0 g of 30% hydrogen peroxide solution. Stir and react at 85 °C for 2.5 h. Centrifuge and wash until neutral, then vacuum dry at 60 °C for 10 h to obtain hydroxylated nano-titanium dioxide. Weigh 6.06 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Adjust the pH to 8.5 with 1.0 mol / L hydrochloric acid and bring the volume to 1000 mL to obtain Tris-HCl buffer. Add the above hydroxylated nano-titanium dioxide to 625 mL of buffer, sonicate and disperse for 20 min, then add 1.8 g of dopamine hydrochloride. Stir magnetically with an open container and react at 25 °C for 18 h. Monitor the pH every 4 h and adjust it to 8.5 with 0.1 mol / L NaOH. Centrifuge, wash, and freeze-dry for 24 h to obtain PDA@TiO2. The above PDA@TiO2 was dispersed in 200 mL of anhydrous ethanol, and 2.5 g of silane coupling agent KH-550 was added. The mixture was refluxed and stirred at 75 °C for 6 h under nitrogen protection. After centrifugation, the mixture was washed three times each with anhydrous ethanol and deionized water, dried under vacuum at 60 °C for 12 h, and ground through a 200-mesh sieve to obtain composite modified nano-titanium dioxide.

[0043] Step 4: Weigh 7g of organic pigment phthalocyanine blue and 1.0g of sodium polycarboxylate dispersant, add them to 18.0g of deionized water, first stir and wet at 1000rpm for 5min, then disperse at 2500rpm for 45min, and control the water bath temperature to not exceed 40℃ to obtain pigment paste.

[0044] Step 5: Take 214g of the modified waterborne polyurethane emulsion obtained in step (2), add 3.5g of acrylic emulsion (50% solid content), 7.0g of ethanol and 2.5g of PEG-1000 in sequence, stir at 600rpm for 30min to mix evenly, then add all the pigment paste from step (4) and stir for 30min. Take another 2.5g of the composite modified nano-titanium dioxide obtained in step (3) and 2.5g of amino modified nano-silica (particle size 12nm, KH-550 grafted fumed silica), add them to 3.5g of deionized water and ultrasonically disperse for 18min. Add the two suspensions to the above mixture, and add 0.5g of silicone defoamer, 0.6g of acrylate leveling agent and 2.8g of trifunctional waterborne aziridine crosslinking agent (pre-dissolved in 5.0g of deionized water), and disperse at 1000rpm for 50min. The dispersed material is ground by a three-roll mill and passed through a 200-mesh filter to obtain water-based polyurethane paper printing ink.

[0045] Example 3

[0046] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0047] Step 1: Weigh 6.0 g of cellulose nanocrystals (approximately 10 nm in diameter and 200 nm in length) and add them to 194.0 g of deionized water. Disperse the nanocrystals using pulsed ultrasonication at 400 W for 30 min to obtain a cellulose nanocrystal suspension. Mix 12 g of silane coupling agent KH-560 with 72.0 g of anhydrous ethanol, add 2% glacial acetic acid aqueous solution to adjust the pH to 4.0, and hydrolyze at room temperature for 45 min to obtain a hydrolyzed silane solution. Add the hydrolyzed silane solution dropwise to the cellulose nanocrystal suspension at a rate of 2 mL / min, react at 70 °C and 800 rpm for 3 h, and cool to room temperature. Centrifuge the reaction solution at 10,000 rpm, wash three times with anhydrous ethanol and twice with deionized water, and vacuum dry at 60 °C for 2 h to constant weight to obtain silane-grafted cellulose nanocrystals. Add the silane-grafted cellulose nanocrystals to 133.0 g of deionized water and ultrasonically redisperse to obtain a silane-grafted cellulose nanocrystal dispersion.

[0048] Step 2: Take 250.0g of a neutralized, emulsified, stabilized waterborne polyurethane emulsion with a solid content of 40% (soft segment is polycarbonate diol, hard segment is isophorone diisocyanate, chain extender is dimethylolpropionic acid, neutralized with triethylamine, pH=7.2) into a four-necked flask, stir at 600rpm under nitrogen protection, and add the silane-grafted nanocellulose dispersion obtained in step (1) dropwise at a rate of 1.5mL / min. After the addition is complete, continue stirring for 1.5h. Adjust the pH to 7.2 with triethylamine, raise the temperature to 50℃ and react at a constant temperature for 2h, cool to room temperature to obtain the modified waterborne polyurethane emulsion.

[0049] Step 3: Weigh 5.0 g of anatase nano-titanium dioxide (particle size approximately 20 nm) and add it in batches to 90.0 g of 30% hydrogen peroxide solution. Stir and react at 85 °C for 2.5 h. Centrifuge and wash until neutral, then vacuum dry at 60 °C for 10 h to obtain hydroxylated nano-titanium dioxide. Weigh 6.06 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Adjust the pH to 8.5 with 1.0 mol / L hydrochloric acid and bring the volume to 1000 mL to obtain Tris-HCl buffer. Add the above hydroxylated nano-titanium dioxide to 625 mL of buffer, sonicate and disperse for 20 min, then add 2.0 g of dopamine hydrochloride. Stir magnetically with an open container and react at 25 °C for 18 h. Monitor the pH every 4 h and adjust it to 8.5 with 0.1 mol / L NaOH. Centrifuge, wash, and freeze-dry for 24 h to obtain PDA@TiO2. The above PDA@TiO2 was dispersed in 200 mL of anhydrous ethanol, and 2.5 g of silane coupling agent KH-550 was added. The mixture was refluxed and stirred at 75 °C for 6 h under nitrogen protection. After centrifugation, the mixture was washed three times each with anhydrous ethanol and deionized water, dried under vacuum at 60 °C for 12 h, and ground through a 200-mesh sieve to obtain composite modified nano-titanium dioxide.

[0050] Step 4: Weigh 8g of organic pigment phthalocyanine blue and 1.0g of sodium polycarboxylate dispersant, add them to 18.0g of deionized water, first stir and wet at 1000rpm for 5min, then disperse at 2500rpm for 45min, and control the water bath temperature to not exceed 40℃ to obtain pigment paste.

[0051] Step 5: Take 214g of the modified waterborne polyurethane emulsion obtained in step (2), add 4g of acrylic emulsion (50% solid content), 7.0g of ethanol and 3g of PEG-1000 in sequence, stir at 600rpm for 30min to mix evenly, then add all the pigment paste from step (4) and stir for 30min. Take another 3g of the composite modified nano-titanium dioxide and 2g of amino modified nano-silica (particle size 12nm, KH-550 grafted fumed silica) obtained in step (3), add them to 3.5g of deionized water and ultrasonically disperse for 18min. Add the two suspensions to the above mixture, and add 0.5g of silicone defoamer, 0.6g of acrylate leveling agent and 2.8g of trifunctional waterborne aziridine crosslinking agent (pre-dissolved in 5.0g of deionized water), and disperse at 1000rpm for 50min. Grind the dispersed material through a three-roll mill and filter through a 200-mesh screen to obtain waterborne polyurethane paper printing ink.

[0052] Example 4

[0053] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0054] Step 1: Weigh 6.0 g of cellulose nanocrystals (approximately 10 nm in diameter and 200 nm in length) and add them to 194.0 g of deionized water. Disperse the nanocrystals using pulsed ultrasonication at 400 W for 30 min to obtain a cellulose nanocrystal suspension. Mix 15 g of silane coupling agent KH-560 with 72.0 g of anhydrous ethanol, add 2% glacial acetic acid aqueous solution to adjust the pH to 4.0, and hydrolyze at room temperature for 45 min to obtain a hydrolyzed silane solution. Add the hydrolyzed silane solution dropwise to the cellulose nanocrystal suspension at a rate of 2 mL / min, react at 75 °C and 800 rpm for 4 h, and cool to room temperature. Centrifuge the reaction solution at 10,000 rpm, wash three times with anhydrous ethanol and twice with deionized water, and vacuum dry at 60 °C for 2 h to constant weight to obtain silane-grafted cellulose nanocrystals. Add the silane-grafted cellulose nanocrystals to 133.0 g of deionized water and ultrasonically redisperse to obtain a silane-grafted cellulose nanocrystal dispersion.

[0055] Step 2: Take 250.0g of a neutralized, emulsified, stabilized waterborne polyurethane emulsion with a solid content of 40% (soft segment is polycarbonate diol, hard segment is isophorone diisocyanate, chain extender is dimethylolpropionic acid, neutralized with triethylamine, pH 7.2) into a four-necked flask, stir at 600rpm under nitrogen protection, and add the silane-grafted nanocellulose dispersion obtained in step (1) dropwise at a rate of 1.5mL / min. After the addition is complete, continue stirring for 1.5h. Adjust the pH to 7.2 with triethylamine, raise the temperature to 50℃ and react at a constant temperature for 2h, cool to room temperature to obtain the modified waterborne polyurethane emulsion.

[0056] Step 3: Weigh 5.0 g of anatase nano-titanium dioxide (particle size approximately 20 nm) and add it in batches to 90.0 g of 30% hydrogen peroxide solution. Stir and react at 85 °C for 2.5 h. Centrifuge and wash until neutral, then vacuum dry at 60 °C for 10 h to obtain hydroxylated nano-titanium dioxide. Weigh 6.06 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Adjust the pH to 8.5 with 1.0 mol / L hydrochloric acid and bring the volume to 1000 mL to obtain Tris-HCl buffer. Add the above hydroxylated nano-titanium dioxide to 625 mL of buffer, sonicate and disperse for 20 min, then add 2.5 g of dopamine hydrochloride. Stir magnetically with an open container and react at 25 °C for 18 h. Monitor the pH every 4 h and adjust it to 8.5 with 0.1 mol / L NaOH. Centrifuge, wash, and freeze-dry for 24 h to obtain PDA@TiO2. The above PDA@TiO2 was dispersed in 200 mL of anhydrous ethanol, and 2.5 g of silane coupling agent KH-550 was added. The mixture was refluxed and stirred at 75 °C for 6 h under nitrogen protection. After centrifugation, the mixture was washed three times each with anhydrous ethanol and deionized water, dried under vacuum at 60 °C for 12 h, and ground through a 200-mesh sieve to obtain composite modified nano-titanium dioxide.

[0057] Step 4: Weigh 10g of organic pigment phthalocyanine blue and 1.0g of sodium polycarboxylate dispersant, add them to 18.0g of deionized water, first stir and wet at 1000rpm for 5min, then disperse at 2500rpm for 45min, and control the water bath temperature to not exceed 40℃ to obtain pigment paste.

[0058] Step 5: Take 214g of the modified waterborne polyurethane emulsion obtained in step (2), add 5g of acrylic emulsion (50% solid content), 7.0g of ethanol and 4g of PEG-1000 in sequence, stir at 600rpm for 30min to mix evenly, then add all the pigment paste from step (4) and stir for 30min. Take another 4g of the composite modified nano-titanium dioxide and 3g of amino modified nano-silica (particle size 12nm, KH-550 grafted fumed silica) obtained in step (3), add them to 3.5g of deionized water and ultrasonically disperse for 18min. Add the two suspensions to the above mixture, and add 0.5g of silicone defoamer, 0.6g of acrylate leveling agent and 2.8g of trifunctional waterborne aziridine crosslinking agent (pre-dissolved in 5.0g of deionized water), and disperse at 1000rpm for 50min. Grind the dispersed material through a three-roll mill and filter through a 200-mesh screen to obtain waterborne polyurethane paper printing ink.

[0059] Example 5

[0060] A method for preparing a water-based polyurethane paper printing ink includes the following steps:

[0061] Step 1: Weigh 6.0 g of cellulose nanocrystals (approximately 10 nm in diameter and 200 nm in length) and add them to 194.0 g of deionized water. Disperse the nanocrystals using pulsed ultrasonication at 400 W for 30 min to obtain a cellulose nanocrystal suspension. Mix 9 g of silane coupling agent KH-560 with 72.0 g of anhydrous ethanol, add 2% glacial acetic acid aqueous solution to adjust the pH to 4.0, and hydrolyze at room temperature for 45 min to obtain a hydrolyzed silane solution. Add the hydrolyzed silane solution dropwise to the cellulose nanocrystal suspension at a rate of 2 mL / min, react at 60 °C and 800 rpm for 2 h, and cool to room temperature. Centrifuge the reaction solution at 10,000 rpm, wash three times with anhydrous ethanol and twice with deionized water, and vacuum dry at 60 °C for 2 h to constant weight to obtain silane-grafted cellulose nanocrystals. Add the silane-grafted cellulose nanocrystals to 133.0 g of deionized water and ultrasonically redisperse to obtain a silane-grafted cellulose nanocrystal dispersion.

[0062] Step 2: Take 250.0g of a neutralized, emulsified, stabilized waterborne polyurethane emulsion with a solid content of 40% (soft segment is polycarbonate diol, hard segment is isophorone diisocyanate, chain extender is dimethylolpropionic acid, neutralized with triethylamine, pH 7.2) into a four-necked flask, stir at 600rpm under nitrogen protection, and add the silane-grafted nanocellulose dispersion obtained in step (1) dropwise at a rate of 1.5mL / min. After the addition is complete, continue stirring for 1.5h. Adjust the pH to 7.2 with triethylamine, raise the temperature to 50℃ and react at a constant temperature for 2h, cool to room temperature to obtain the modified waterborne polyurethane emulsion.

[0063] Step 3: Weigh 5.0 g of anatase nano-titanium dioxide (particle size approximately 20 nm) and add it in batches to 90.0 g of 30% hydrogen peroxide solution. Stir and react at 85 °C for 2.5 h. Centrifuge and wash until neutral, then vacuum dry at 60 °C for 10 h to obtain hydroxylated nano-titanium dioxide. Weigh 6.06 g of tris(hydroxymethyl)aminomethane and dissolve it in deionized water. Adjust the pH to 8.5 with 1.0 mol / L hydrochloric acid and bring the volume to 1000 mL to obtain Tris-HCl buffer. Add the above hydroxylated nano-titanium dioxide to 625 mL of buffer, sonicate and disperse for 20 min, then add 1.5 g of dopamine hydrochloride. Stir magnetically with an open container and react at 25 °C for 18 h. Monitor the pH every 4 h and adjust it to 8.5 with 0.1 mol / L NaOH. Centrifuge, wash, and freeze-dry for 24 h to obtain PDA@TiO2. The above PDA@TiO2 was dispersed in 200 mL of anhydrous ethanol, and 2.5 g of silane coupling agent KH-550 was added. The mixture was refluxed and stirred at 75 °C for 6 h under nitrogen protection. After centrifugation, the mixture was washed three times each with anhydrous ethanol and deionized water, dried under vacuum at 60 °C for 12 h, and ground through a 200-mesh sieve to obtain composite modified nano-titanium dioxide.

[0064] Step 4: Weigh 6g of organic pigment phthalocyanine blue and 1.0g of sodium polycarboxylate dispersant, add them to 18.0g of deionized water, first stir and wet at 1000rpm for 5min, then disperse at 2500rpm for 45min, and control the water bath temperature to not exceed 40℃ to obtain pigment paste.

[0065] Step 5: Take 214g of the modified waterborne polyurethane emulsion obtained in step (2), add 3g of acrylic emulsion (50% solid content), 7.0g of ethanol and 2g of PEG-1000 in sequence, stir at 600rpm for 30min to mix evenly, then add all the pigment paste from step (4) and stir for 30min. Take another 2g of the composite modified nano-titanium dioxide and 1g of amino modified nano-silica (particle size 12nm, KH-550 grafted fumed silica) obtained in step (3), add them to 3.5g of deionized water and ultrasonically disperse for 18min. Add the two suspensions to the above mixture, and add 0.5g of silicone defoamer, 0.6g of acrylate leveling agent and 2.8g of trifunctional waterborne aziridine crosslinking agent (pre-dissolved in 5.0g of deionized water), and disperse at 1000rpm for 50min. Grind the dispersed material through a three-roll mill and filter through a 200-mesh screen to obtain waterborne polyurethane paper printing ink.

[0066] Comparative Example 1: The only difference from Example 1 is that the silane grafting nanocellulose modification operations in steps 1 and 2 are not performed. Unmodified aqueous polyurethane emulsion is used directly as the matrix resin. The remaining steps and component ratios are exactly the same as in Example 1.

[0067] Comparative Example 2: The only difference from Example 1 is that hydrogen peroxide activation, dopamine coating and KH-550 grafting are not performed in step 3. An equal amount of unmodified anatase nano-titanium dioxide is used to directly replace the composite modified nano-titanium dioxide. The remaining steps and component ratios are exactly the same as in Example 1.

[0068] Comparative Example 3: The difference from Example 1 is that the nanocellulose grafting modification in steps 1 and 2 and the nano titanium dioxide composite modification in step 3 are not performed simultaneously. Unmodified waterborne polyurethane emulsion and unmodified nano titanium dioxide are used directly. The remaining steps and component ratios are exactly the same as in Example 1.

[0069] Comparative Example 4: The only difference from Example 1 is that PEG-1000 is not added in step 5. The remaining steps and component ratios are exactly the same as in Example 1.

[0070] Comparative Example 5: The only difference from Example 1 is that amino-modified nano-silica is not added in step 5. The remaining steps and component ratios are exactly the same as in Example 1.

[0071] Comparative Example 6: The difference from Example 1 is that PEG-1000 and amino-modified nano silica are not added in step 5. The remaining steps and component ratios are exactly the same as in Example 1.

[0072] Performance testing:

[0073] 1. Cross-cut adhesion test: Inks prepared in Examples 1-5 and Comparative Examples 1-6 were applied using a rod coater at a cross-cut adhesion rate of 80 g / m². 2 The coating was applied to double-sided offset paper (wet film thickness approximately 12 μm), dried in an oven at 80℃ for 5 minutes, and then left at room temperature for 24 hours to allow the film to fully cure. The test was conducted according to GB / T 9286-2021 "Cross-cut Test for Paints and Varnishes". An 11×11 grid pattern was drawn on the coating surface using a multi-blade cutter with 1 mm spacing. Debris was removed by gently sweeping along the diagonal five times with a soft brush. Then, 3M 610 transparent tape was firmly adhered to the grid area, and the tape was peeled off at a uniform speed of 0.5-1 second at approximately a 60° angle. The coating peeling was observed using a 4x magnifying glass. The rating criteria are as follows: Grade 0 indicates that the incision edge is completely smooth with no detachment; Grade 1 indicates that there is small detachment at the intersection of the incision, with a detachment area not exceeding 5%; Grade 2 indicates detachment at the incision edge and intersection, with a detachment area of ​​5%-15%; Grade 3 indicates large detachment along the incision edge, with a detachment area of ​​15%-35%; Grade 4 indicates large, whole detachments, with a detachment area of ​​35%-65%; Grade 5 indicates a detachment area exceeding 65%. Each group of samples is tested in parallel three times, and the worst grade is taken as the final result.

[0074] 2. Dry Friction Resistance Test: Coating and curing conditions are the same as above. The test is conducted using a friction testing machine according to the friction resistance test method specified in GB / T 7706-2008 "Relief Printing Materials". White standard cotton cloth is used as the friction medium, a normal load of 2.0 N is applied, the friction speed is 43 times / min, and the reciprocating friction stroke is approximately 100 mm. The number of friction cycles until the ink coating shows obvious discoloration or exposes the substrate (the paper's base color is visually visible) is taken as the dry friction resistance cycle. Each group of samples is tested in parallel for 3 times, and the average value is taken.

[0075] 3. Wet Friction Resistance Test: Coating and curing conditions are the same as above. The test method is the same as the dry friction resistance test, except that the standard cotton cloth is fully wetted with deionized water (moisture content approximately 100%) before friction, and a reciprocating friction test is performed in a wet state. The number of friction cycles until the ink coating shows obvious discoloration or exposes the substrate is taken as the wet friction resistance cycle. Each group of samples is tested in parallel for 3 times, and the average value is taken.

[0076] 4. Bending resistance test: Coating and curing conditions are the same as above. Cut the ink-coated paper into 50mm × 100mm sample strips. Fold the strip 180° along the center line of the sample with the ink side facing outward (the crease is parallel to the short side). Roll the strip back and forth along the crease once with a 2kg standard roller, then unfold it. Observe whether the ink coating at the crease cracks or peels off. If no damage occurs, continue to repeat the folding-unfolding operation at the same crease. Record the cumulative number of bends when visible cracks or peeling of the ink coating at the crease appear. Test 5 parallel samples in each group and take the average value.

[0077] 5. Gloss Test: Coating and curing conditions are the same as above. A gloss meter was used to test the specular gloss of the ink coating at a 60° incident angle according to GB / T 9754-2007 "Determination of 20°, 60° and 85° Specular Gloss of Paint Films Without Metallic Pigments". Five measurements were taken at different locations for each sample, and the average value was taken as the test result. The unit is GU (gloss unit).

[0078] 6. Water Resistance Test: Coating and curing conditions are the same as above. Cut the ink-coated paper into 50mm×50mm samples, completely immerse them in 25℃ deionized water, and soak for 24 hours. After soaking, remove them and gently blot the surface moisture with filter paper. Visually observe whether the ink coating shows any abnormalities such as whitening, blistering, wrinkling, or peeling. Retest the adhesion grade after soaking using the cross-cut adhesion test. Evaluation criteria: "Excellent" is recorded as no abnormalities in appearance and the adhesion grade is consistent with that before soaking; "Good" is recorded as no abnormalities in appearance but a decrease in adhesion grade of 1; "Average" is recorded as slight whitening or a decrease in adhesion grade of 2; "Poor" is recorded as blistering, peeling, or a decrease in adhesion grade of 3 or more.

[0079] Table 1:

[0080] Test Samples Adhesion (100-cross test) / Grade Dry Friction Resistance / Cycles Wet Friction Resistance / Cycles Bending Resistance / Cycles 60° Gloss / GU Water Resistance Example 1 0 2 3 5 6 2 4 8 7 5.3 Excellent Example 2 0 2 1 8 5 5 4 2 7 2.1 Excellent Example 3 0 2 2 6 5 8 4 5 7 3.8 Excellent Example 4 0 2 4 2 6 5 5 0 7 4.6 Excellent Example 5 1 2 0 5 4 8 3 8 7 0.5 Good Comparative Example 1 3 1 2 0 2 8 3 5 6 8.2 Average Comparative Example 2 2 1 5 5 3 5 4 0 7 1.4 Good Comparative Example 3 4 8 5 1 8 3 0 6 5.7 Poor Comparative Example 4 0 1 9 0 5 0 1 8 7 4.8 Good Comparative Example 5 0 1 8 5 4 6 2 2 7 4.2 Good Comparative Example 6 0 1 6 8 4 0 1 2 7 3.9 Average surface

[0081] Test data result analysis:

[0082] (1) Adhesion: The adhesion of Examples 1-4 reached the optimal level of 0 in the cross-cut adhesion test, Example 5 reached level 1, while Comparative Example 1 (without nanocellulose modification) dropped to level 3, Comparative Example 2 (without TiO2 composite modification) dropped to level 2, and Comparative Example 3 (without any of the above modifications) dropped to level 4. This shows that both modifications significantly contribute to the improvement of adhesion, and the synergistic effect of the two is far better than that of a single modification. Although Comparative Examples 4-6 retained both modifications (static adhesion was still level 0), the adhesion of Comparative Examples 4-6 decreased significantly in dynamic tests (friction, bending) after removing PEG-1000 and / or amino-modified SiO2.

[0083] (2) In terms of abrasion resistance: Examples 1-4 all had more than 218 dry abrasion cycles and more than 55 wet abrasion cycles, which were significantly better than the comparative examples. Comparative Example 1 (unmodified resin matrix) had only 120 / 28 dry / wet abrasion cycles, while Comparative Example 3 (unmodified) was the worst with only 85 / 18 cycles. It is worth noting that Comparative Example 6 (removed PEG-1000 and amino-modified SiO2) had 168 / 40 dry / wet abrasion cycles, which was better than Comparative Examples 1-3 (because it retained the adhesion base provided by the two modifications), but significantly lower than Examples 1-4 with the complete formulation, indicating that the synergistic introduction of PEG-1000 and amino-modified SiO2 is indispensable for improving the abrasion resistance and durability of the film.

[0084] (3) Bending resistance: This indicator most directly reflects the dynamic flexibility and crack resistance of the film. The bending resistance of Examples 1-4 reached 42-50 times, while that of Comparative Example 4 (PEG-1000 removed) dropped sharply to 18 times, Comparative Example 5 (amino-modified SiO2 removed) dropped to 22 times, and Comparative Example 6 (both removed) only 12 times. The comparison between Comparative Example 4 and Comparative Example 5 shows that both PEG-1000 and amino-modified SiO2 contribute to the bending resistance, but the improvement when added alone is limited (18 times and 22 times), far less than the effect when they are present synergistically (48 times in Example 1), which fully demonstrates the necessity of the synergistic mechanism of matrix flexibility and modulus smoothing. Although Comparative Examples 1-3 had a lower crosslinking density and a softer film due to the lack of dual modification, resulting in a slightly higher number of bends than Comparative Examples 4-6, their adhesion level was very poor (level 3-4). Although they were not prone to cracking during the bending test, the coating had already peeled off severely, making them of little practical value.

[0085] (4) Regarding gloss and water resistance: The 60° gloss of Examples 1-4 were all between 72-76 GU, and the water resistance evaluation was excellent, indicating that the operation of the present invention did not have a negative impact on the optical properties and water resistance of the ink. Comparative Example 3 had the lowest gloss (65.7 GU) and poor water resistance because the uneven dispersion of nanofillers in the unmodified system led to increased surface roughness and decreased film density.

[0086] Based on the above test results, it can be concluded that this invention, through the synergistic effect of silane-grafted nanocellulose-modified waterborne polyurethane resin (bulk phase reinforcement) and dopamine biomimetic coating-aminosilane-grafted composite modified nano-titanium dioxide (interface reinforcement), combined with the synergistic combination of PEG-1000 flexibility modification and amino-modified nano-SiO2 modulus smoothing, enables the ink to achieve the optimal level of 0 adhesion on paper. At the same time, it also has excellent dry / wet rubbing resistance, bending resistance, gloss and water resistance. All performance indicators are superior to the comparative examples, meeting the requirements for high-quality paper printing.

[0087] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a water-based polyurethane paper printing ink, characterized in that, Includes the following steps: (1) Disperse nanocellulose crystals ultrasonically in water, add acid-hydrolyzed silane coupling agent KH-560 for grafting reaction, purify and then disperse to obtain silane-grafted nanocellulose dispersion; (2) Add silane-grafted nanocellulose dispersion to neutralized emulsion-stabilized waterborne polyurethane emulsion, mix and then heat to crosslink to obtain modified waterborne polyurethane emulsion; (3) Activate nano-titanium dioxide with hydrogen peroxide, then react with dopamine hydrochloride in tris(hydroxymethyl)aminomethane-hydrochloric acid buffer to form polydopamine coating, and then couple with silane. (3) React with agent KH-550, separate and dry to obtain composite modified nano titanium dioxide; (4) Mix organic pigment, sodium polycarboxylate dispersant and water and disperse at high speed to obtain pigment paste; (5) Mix modified waterborne polyurethane emulsion, acrylic emulsion, ethanol and PEG-1000, then add pigment paste and mix well, then add composite modified nano titanium dioxide, amino modified nano silica, organosilicon defoamer, acrylate leveling agent and waterborne aziridine crosslinking agent, disperse at high speed and grind and filter to obtain waterborne polyurethane paper printing ink.

2. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (1), the mass ratio of nanocellulose crystals to silane coupling agent KH-560 is 1:(1.5~2.5).

3. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (1), the grafting reaction temperature is 60-75℃ and the reaction time is 2-4h.

4. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (3), the mass ratio of nano-titanium dioxide to dopamine hydrochloride is 1:(0.3-0.5).

5. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (4), the mass ratio of organic pigment to sodium polycarboxylate dispersant is (6-10):

1.

6. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (5), the mass ratio of modified waterborne polyurethane emulsion to acrylic emulsion is 214:(3-5).

7. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (5), the mass ratio of modified waterborne polyurethane emulsion to PEG-1000 is 214:(2-4).

8. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (5), the mass ratio of modified waterborne polyurethane emulsion to composite modified nano-titanium dioxide is 214:(2-4).

9. The method for preparing a water-based polyurethane paper printing ink according to claim 1, characterized in that, In step (5), the mass ratio of modified waterborne polyurethane emulsion to amino-modified nano silica is 214:(1-3).

10. A water-based polyurethane paper printing ink, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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