Water-based nano ink and preparation method thereof

Abstract

The invention discloses water-based nano ink and a preparation method thereof, and relates to the field of ink. The printing ink comprises the following components in parts by mass: 40-60 parts of polyurethane dispersion, core-shell polyurethane / silicon dioxide hybrid particles, a stabilizer, a wetting dispersant, a flatting agent, a defoaming agent, pigment and water, when the core-shell polyurethane / silicon dioxide hybrid particles are prepared, the surface of a polyurethane prepolymer is modified by adopting a silane coupling agent to obtain a modified prepolymer; depositing a SiO2 precursor on the surface of the modified prepolymer through a sol-gel method to form a SiO2 shell layer; the mass ratio of the polyurethane prepolymer to the silane coupling agent to the SiO2 precursor is (60-70): (3-8): (10-20). The water-based nano ink is not easy to permeate into porous base materials such as body paper, and printing quality problems such as dot expansion, edge accumulation and blurring can be remarkably reduced.

Description

Technical Field

[0001] The present application relates to the field of inks, and in particular to a water-based nano-ink and a preparation method thereof. Background Art

[0002] As a new type of printing material, nano ink has shown significant advantages in the printing industry due to its unique nano-scale particle characteristics. Nano ink not only has high color saturation, excellent adhesion and durability, but also can achieve fine pattern printing on a microscopic scale. It is widely used in electronic devices, packaging printing, textile printing and other fields. With the enhancement of environmental awareness and the improvement of sustainable development needs, traditional solvent-based inks are gradually replaced by water-based inks. Water-based ink uses water as the main solvent and has the advantages of low volatile organic compound (VOC) emissions, non-toxicity, and easy cleaning, which is in line with the development trend of green environmental protection. For example, CN117363189A discloses a new water-based environmentally friendly nano UV material and its preparation method, which shows the significant progress of water-based ink in environmental performance and application potential.

[0003] Although water-based nano-inks have many advantages in terms of environmental protection and printing performance, their application on porous substrates (such as paper) still faces technical challenges. Due to the looseness and porosity of the fiber structure of substrates such as paper, the ink can easily penetrate quickly through the fiber gaps and capillary action during the printing process, and the migration rate is too fast. This phenomenon will not only cause the expansion of printing dots, but also blur the edges of the printed pattern, seriously affecting the clarity and color reproduction of the printed product. In addition, excessive penetration of ink will also cause print-through on the back of the substrate, further reducing the printing quality.

[0004] Although some solutions have been proposed in the prior art to address the above problems, such as plasma treatment of the substrate or primer coating, these methods often sacrifice the printing performance of the ink while improving the permeability, and the increase in production processes will greatly increase the production cost. Summary of the invention

[0005] The present application provides a water-based nano-ink and a preparation method thereof, which effectively inhibits the penetration of ink into the pores of a porous substrate and reduces printing quality problems such as dot gain by adding steric hindrance of core-shell polyurethane / silicon dioxide hybrid particles to the ink system.

[0006] In a first aspect, the present application provides an aqueous nano-ink comprising the following components in parts by weight: 40-60 parts of polyurethane dispersion, 1-5 parts of core-shell polyurethane / silicon dioxide hybrid particles, 0.5-1 parts of stabilizer, 0.5-2 parts of wetting and dispersing agent, 0.1-0.5 parts of leveling agent, 0.1-0.5 parts of defoaming agent, 5-15 parts of pigment, 20-30 parts of water; When preparing the core-shell polyurethane / silicon dioxide hybrid particles, the surface of the polyurethane prepolymer is modified by a silane coupling agent to obtain a modified prepolymer; SiO 2 The precursor is deposited on the surface of the modified prepolymer to form SiO 2 Shell layer; the polyurethane prepolymer, silane coupling agent and SiO 2 The mass ratio of the precursors is 60-70:3-8:10-20.

[0007] In any of the above technical solutions, the particle size of the core-shell polyurethane / silicon dioxide hybrid particles is 50 to 150 nm.

[0008] In any of the above technical solutions, the SiO 2 The thickness of the shell is 5 to 15 nm.

[0009] In any of the above technical solutions, the SiO 2 The precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate and butyl orthosilicate.

[0010] The core-shell polyurethane / silicon dioxide hybrid particles introduced in this application can, on the one hand, inhibit the penetration of ink through fiber gaps and capillary action through steric hindrance; on the other hand, the shell SiO 2 The surface energy of the shell SiO is higher than that of the polyurethane core, which can induce the ink to spread evenly on the surface of the substrate through the gradient interface energy difference instead of penetrating into the interior, thereby reducing problems such as dot enlargement and edge blur in the printing process. 2 It can provide excellent wear resistance for the ink coating and reduce external erosion; the abundant hydroxyl groups on its surface enable the hybrid particles to form a network structure in the water system, inhibiting their aggregation and sedimentation tendency and improving the stability of the ink.

[0011] It should be noted that the polyurethane prepolymer in the core layer provides good flexibility for the hybrid particles and ensures their wear resistance. On the other hand, the polyurethane prepolymer has a high affinity with the polyurethane-based water-based ink, which helps to ensure the dispersion of the hybrid particles in the ink. The application of silane coupling agent can react with the active groups (such as NCO) on the surface of the polyurethane core to form covalent bonds, making SiO 2 The shell layer is tightly bonded to the PU core. This anchoring effect can prevent the shell layer from peeling off and ensure the long-term stability of the particles in the ink. If polyurethane is used as the shell layer, it is difficult for the shell layer PU to form a strong interface bond with the core layer silica, and its rigidity is insufficient and it is easy to break under shear force. In addition, SiO 2 The shell thickness can be controlled by TEOS concentration and reaction time.

[0012] In any of the above technical solutions, the polyurethane prepolymer is prepared by the reaction of polyol and isocyanate.

[0013] Exemplarily, the polyol is selected from polyether polyol and / or polyester polyol.

[0014] Exemplarily, the polyurethane dispersion has a solid content of 35 to 45%, a viscosity of 50 to 200 mPa·s, and a D50 particle size of 50 to 120 nm.

[0015] When the solid content of the polyurethane dispersion is less than 35%, the ink film-forming property is poor; when the solid content is greater than 45%, the viscosity increases sharply, resulting in a decrease in printability.

[0016] In any of the above technical solutions, the molecular weight of the polyol is 1000-3000 to ensure the flexibility of the hybrid particles.

[0017] Exemplarily, the isocyanate is selected from diphenylmethane diisocyanate or hexamethylene diisocyanate.

[0018] In any of the above technical solutions, the silane coupling agent is selected from aminosilane coupling agents and / or epoxysilane coupling agents.

[0019] In any of the above technical solutions, the catalyst of the sol-gel method is ammonia water or hydroxide solution, and the reaction pH value is 9-10.

[0020] When the pH is greater than or equal to 9, the condensation rate is accelerated and the shell is denser; when the pH is less than 9, a loose structure is easily generated.

[0021] Exemplarily, the catalyst is 0.5-2 wt % ammonia water.

[0022] In any of the above technical solutions, the stabilizer is hydrophobically modified silica with an oil absorption value of 130 to 180 g / 100 g.

[0023] In any of the above technical solutions, the preparation method of the hydrophobically modified silica is: Under nitrogen protection, a mixed solution of methylchlorosilane and ethylene carbonate is mixed with silicon dioxide, and reacted at 300-400°C for 3-5 hours; the mixture is kept warm and an ethanol solution of polydimethylsiloxane is introduced, and the reaction is continued for 2-4 hours. The product is obtained after filtration, deacidification and drying.

[0024] In any of the above technical solutions, the mass ratio of silicon dioxide, methylchlorosilane, ethylene carbonate and polydimethylsiloxane is 100:5-15:0.5-2:3-8.

[0025] Exemplarily, the methylchlorosilane is monomethyltrichlorosilane or dimethyldichlorosilane.

[0026] In any of the above technical solutions, the average particle size of the silicon dioxide is 10 to 100 nm.

[0027] The core-shell polyurethane / silica hybrid particles have a large number of silanol groups on their surface, which can form a network structure through hydrogen bonding in an aqueous system, thereby improving the suspension stability of the ink. However, they are highly hydrophilic and are prone to solvation problems in aqueous systems, causing their network structure to be gradually destroyed during long-term storage, resulting in a decrease in thickening effect and stratification and precipitation problems. The present application is coordinated with the above-mentioned hydrophobic nanofiller with an oil absorption value of 130 to 180 g / 100 g, which has a relatively moderate hydrophobicity and can effectively improve the stability of the ink in long-term storage.

[0028] It should be noted that the determination of oil absorption value needs to refer to the provisions of GB / T 5211.15-2014. The linseed oil titration method can be used to record the oil absorption per 100g sample.

[0029] In any of the above technical solutions, the ink further includes 5 to 15 parts of a co-solvent, and the co-solvent is selected from at least one of propylene glycol, ethylene glycol butyl ether, and N-methylpyrrolidone.

[0030] In any of the above technical solutions, other additives may be added to the ink, including but not limited to antioxidants, ultraviolet absorbers, thickeners, and pH regulators.

[0031] In any of the above technical solutions, the wetting and dispersing agent is a polyether-modified siloxane or a phosphate surfactant.

[0032] Exemplarily, the polyether-modified siloxane is BYK-345; and the phosphate ester surfactant is EFKA-4585.

[0033] The leveling agent is polyether-modified silicone or fluorocarbon-modified polyacrylate.

[0034] Exemplarily, the polyether-modified silicone is BYK-333; and the fluorocarbon-modified polyacrylate is TEGOGlide 410.

[0035] The defoamer is a mineral oil-based or polyether-modified polysiloxane defoamer.

[0036] Exemplarily, the mineral oil-based defoamer is TEGO Foamex 810; and the polyether-modified polysiloxane defoamer is BYK-024.

[0037] In any of the above technical solutions, the amount of pH adjuster used is 0.1 to 0.5 parts by weight.

[0038] Exemplarily, the pH adjuster is aqueous ammonia.

[0039] In a second aspect, the present application provides a method for preparing a water-based nano-ink, which is obtained by mixing and dispersing a polyurethane dispersion, core-shell polyurethane / silicon dioxide hybrid particles, a stabilizer, a wetting dispersant, a leveling agent, a pH adjuster, a defoamer, a pigment, and water according to any of the ink ratios described above.

[0040] In summary, this application has the following beneficial effects: This application introduces core-shell polyurethane / silicon dioxide (PU / SiO 2 ) hybrid particles and hydrophobically modified silica with an oil absorption value of 130-180 g / 100 g work synergistically to inhibit the penetration of ink into porous substrates (such as paper) and reduce dot gain. 2 The steric hindrance effect of the shell and the flexibility of the PU core balance the barrier property and film-forming property; the hydrophobically modified silica enhances the ink stability through the hydrogen bond network. The ink has low VOC, high wear resistance (Taber test weight loss is less than 5mg) and long-term storage stability (no sedimentation for 6 months), and is suitable for high-precision printing. DETAILED DESCRIPTION

[0041] Preparation Example 1-1, a core-shell polyurethane / silicon dioxide hybrid particle is prepared according to the following steps: 100g polyester polyol (molecular weight 1500, hydroxyl value 112mgKOH / g) was vacuum dehydrated at 100℃ for 1.5 hours, cooled to 75℃, added with 28g diphenylmethane diisocyanate, and reacted under nitrogen for 3 hours to obtain a polyurethane prepolymer (NCO content 5.2%). 65g prepolymer was dissolved in tetrahydrofuran and emulsified by a high-pressure homogenizer (shear rate 2000rpm, emulsifier Tween-80 dosage 3%) to obtain a 55wt% polyurethane dispersion (D50=80nm).

[0042] The polyurethane dispersion was heated to 60°C, and 5g of γ-aminopropyltriethoxysilane was slowly added dropwise, and the reaction was carried out for 3 hours for modification. 15g of ethyl orthosilicate was mixed with 30g of ethanol, and then added dropwise to the modified polyurethane dispersion. At the same time, 2wt% of ammonia water was added to adjust the pH to 9.0, and the mixture was stirred at 70°C for 18 hours to complete the hydrolysis and condensation. The particles were separated by centrifugation and dried at 120°C for 10 hours to obtain hybrid particles (average particle size 90nm, shell thickness 10nm).

[0043] Preparation Example 1-2, a core-shell polyurethane / silicon dioxide hybrid particle is prepared according to the following steps: 100g of polyether polyol (molecular weight 2000, hydroxyl value 56mgKOH / g) was vacuum dehydrated at 110℃ for 2 hours, cooled to 80℃, and then 42g of diphenylmethane diisocyanate was added. The mixture was reacted under nitrogen for 3 hours to obtain a polyurethane prepolymer (NCO content 6.5%). 70g of the prepolymer was dissolved in tetrahydrofuran and emulsified by a high-pressure homogenizer (shear rate 3000rpm, emulsifier Tween-80 dosage 2%) to obtain a 50wt% polyurethane dispersion (D50=50nm).

[0044] The polyurethane dispersion was heated to 60°C, and 8g of γ-aminopropyltriethoxysilane was slowly added dropwise, and the reaction was carried out for 2 hours for modification. 20g of ethyl orthosilicate was mixed with 60g of ethanol, and then added dropwise to the modified polyurethane dispersion. At the same time, 2wt% of ammonia water was added to adjust the pH to 9.5, and the mixture was stirred at 80°C for 24 hours to complete the hydrolysis and condensation. The particles were separated by centrifugation and dried at 110°C for 12 hours to obtain hybrid particles (average particle size 65nm, shell thickness 15nm).

[0045] Preparation Example 1-3, a core-shell polyurethane / silicon dioxide hybrid particle, is prepared according to the following steps: 100g of polyether polyol (molecular weight 3000, hydroxyl value 37mgKOH / g) was vacuum dehydrated at 120℃ for 3 hours, cooled to 85℃, and then 50g of hexamethylene diisocyanate was added. The mixture was reacted under nitrogen for 4 hours to obtain a polyurethane prepolymer (NCO content 7.8%). 60g of the prepolymer was dissolved in tetrahydrofuran and emulsified by a high-pressure homogenizer (shear rate 1000rpm, emulsifier Tween-80 dosage 1.5%) to obtain a 45wt% polyurethane dispersion (D50=50nm).

[0046] The polyurethane dispersion was heated to 60°C, and 3g of γ-glycidyloxypropyltrimethoxysilane was slowly added dropwise, and the reaction was carried out for 2 hours for modification. 10g of ethyl orthosilicate was mixed with 10g of ethanol, and then added dropwise to the modified polyurethane dispersion. At the same time, 2wt% of ammonia water was added to adjust the pH to 10, and the mixture was stirred at 80°C for 24 hours to complete the hydrolysis and condensation. The particles were separated by centrifugation and dried at 110°C for 12 hours to obtain hybrid particles (average particle size 115nm, shell thickness 5nm).

[0047] Preparation Example 1-4, a core-shell polyurethane / silicon dioxide hybrid particle, is prepared according to the following steps: 100g of polyether polyol (molecular weight 1000, hydroxyl value 112mgKOH / g) was vacuum dehydrated at 100℃ for 1.5 hours, cooled to 70℃, and then 23g of hexamethylene diisocyanate was added. The mixture was reacted under nitrogen for 2 hours to obtain a polyurethane prepolymer (NCO content 4.8%). 60g of the prepolymer was dissolved in tetrahydrofuran and emulsified by a high-pressure homogenizer (shear rate 4000rpm, emulsifier Tween-80 dosage 4%) to obtain a 50wt% polyurethane dispersion (D50=50nm).

[0048] The polyurethane dispersion was heated to 40°C, and 2g of γ-aminopropyltriethoxysilane was slowly added dropwise, and the mixture was reacted for 1 hour for modification. 5g of ethyl orthosilicate was mixed with 25g of ethanol, and then added dropwise to the modified polyurethane dispersion. At the same time, 2wt% of ammonia water was added to adjust the pH to 9.0, and the mixture was stirred at 30°C for 6 hours to complete the hydrolysis and condensation. The particles were separated by centrifugation and dried at 100°C for 8 hours to obtain hybrid particles (average particle size 53nm, shell thickness 3nm).

[0049] Preparation Example 1-5, a core-shell polyurethane / silicon dioxide hybrid particle, is prepared according to the following steps: 100g of polyether polyol (molecular weight 3000, hydroxyl value 37mgKOH / g) was vacuum dehydrated at 130℃ for 5 hours, cooled to 90℃, and then 60g of hexamethylene diisocyanate was added and reacted under nitrogen protection for 5 hours to obtain a polyurethane prepolymer (NCO content 8.2%). 70g of the prepolymer was dissolved in tetrahydrofuran and emulsified by a high-pressure homogenizer (shear rate 4000rpm, emulsifier Tween-80 dosage 4%) to obtain a 50wt% polyurethane dispersion (D50=130nm).

[0050] The polyurethane dispersion was heated to 60°C, 10 g of γ-aminopropyltriethoxysilane was slowly added, and the mixture was reacted for 4 hours for modification. 30 g of ethyl orthosilicate was mixed with 30 g of ethanol, and then added to the modified polyurethane dispersion. 2 wt% of ammonia water was added to adjust the pH to 10.0, and the mixture was stirred at 90°C for 30 hours to complete the hydrolysis and condensation. The particles were separated by centrifugation and dried at 130°C for 24 hours to obtain hybrid particles (average particle size 149 nm, shell thickness 19 nm).

[0051] Preparation Example 2-1, a hydrophobically modified silica, is prepared as follows: 100g of fumed silica was dried at 130℃ for 3 hours to remove adsorbed water and crushed to D50 of 80nm. Under the protection of ammonia in a fluidized bed, 10g of monomethyltrichlorosilane and 1g of ethylene carbonate were sprayed at 320℃ and reacted for 4 hours. 5g of polydimethylsiloxane ethanol solution (15wt%) was added and the reaction continued for 1 hour; steam deacidification (90℃, 1.5h), and dried at 110℃ to obtain hydrophobically modified silica with an oil absorption value of 150g / 100g.

[0052] Preparation Example 2-2, a hydrophobically modified silica, is prepared as follows: 100g of fumed silica was dried at 150℃ for 2 hours to remove adsorbed water and crushed to D50 of 100nm. Under the protection of ammonia in a fluidized bed, 15g of monomethyltrichlorosilane and 2g of ethylene carbonate were sprayed at 350℃ and reacted for 3 hours. 8g of polydimethylsiloxane ethanol solution (15wt%) was added and the reaction continued for 1 hour; steam deacidification (90℃, 1.5h), and dried at 130℃ to obtain hydrophobically modified silica with an oil absorption value of 170g / 100g.

[0053] Preparation Example 2-3, a hydrophobically modified silica, is prepared as follows: 100g of fumed silica was dried at 130℃ for 3 hours to remove adsorbed water and crushed to D50 of 30nm. Under the protection of ammonia in a fluidized bed, 5g of a mixture of monomethyltrichlorosilane and 0.5 ethylene carbonate was sprayed at 300℃ and reacted for 4 hours. 3g of polydimethylsiloxane ethanol solution (15wt%) was added and the reaction continued for 1 hour; steam deacidification (90℃, 1.5h), and dried at 120℃ to obtain hydrophobically modified silica with an oil absorption value of 130g / 100g.

[0054] Preparation Example 2-4, a hydrophobically modified silica, is prepared as follows: 100g of fumed silica was dried at 130℃ for 3 hours to remove adsorbed water and crushed to D50 of 80nm. Under the protection of ammonia in a fluidized bed, 10g of monomethyltrichlorosilane and 1g of ethylene carbonate were sprayed at 320℃ and reacted for 4 hours. 5g of polydimethylsiloxane ethanol solution (15wt%) was added and the reaction continued for 1 hour; steam deacidification (90℃, 1.5h), and dried at 120℃ to obtain hydrophobically modified silica with an oil absorption value of 120g / 100g.

[0055] Preparation Example 2-5, a hydrophobically modified silica, is prepared as follows: 100g of fumed silica was dried at 130℃ for 3 hours to remove adsorbed water and crushed to D50 of 80nm. Under the protection of ammonia in a fluidized bed, 10g of monomethyltrichlorosilane and 1g of ethylene carbonate were sprayed at 320℃ and reacted for 4 hours. 5g of polydimethylsiloxane ethanol solution (15wt%) was added and the reaction continued for 1 hour; steam deacidification (90℃, 1.5h), and dried at 120℃ to obtain hydrophobically modified silica with an oil absorption value of 200g / 100g.

[0056] Embodiment 1, a kind of water-based nano ink, is prepared by the following steps: 50 g of polyurethane dispersion (solid content 38%, viscosity 80 mPa·s, D50=85 nm), 3 g of core-shell polyurethane / silica hybrid particles (Preparation Example 1-1), 0.8 g of hydrophobic silica (Preparation Example 2-1), 2 g of wetting dispersant (EFKA-4585), 0.5 g of leveling agent (TEGO-410), 0.5 g of ammonia water, 0.5 g of defoaming agent (BYK-024), 10 g of pigment, 10 g of cosolvent (propylene glycol), and 25 g of water were mixed, dispersed at 1500 rpm for 25 min, and filtered through a 200-mesh sieve to obtain the obtained product.

[0057] Embodiment 2, a kind of water-based nano ink, is prepared by the following steps: 60 g of polyurethane dispersion (solid content 40%, viscosity 150 mPa·s, D50=100 nm), 5 g of core-shell polyurethane / silica hybrid particles (Preparation Example 1-2), 1 g of hydrophobic silica (Preparation Example 2-2), 2 g of wetting dispersant (BYK-345), 0.5 g of leveling agent (BYK-333), 0.5 g of ammonia water, 0.5 g of defoaming agent (TEGO-810), 15 g of pigment, 15 g of cosolvent (propylene glycol), and 30 g of water were mixed, dispersed at a high speed of 2000 rpm for 30 min, and filtered through a 200-mesh sieve to obtain the obtained mixture.

[0058] Embodiment 3, a kind of water-based nano ink, is prepared by the following steps: 40 g of polyurethane dispersion (solid content 40%, viscosity 150 mPa·s, D50=10 nm), 1 g of core-shell polyurethane / silica hybrid particles (Preparation Example 1-3), 0.5 g of hydrophobic silica (Preparation Example 2-3), 2 g of wetting dispersant (BYK-345), 0.5 g of leveling agent (BYK-333), 0.5 g of ammonia water, 0.5 g of defoaming agent (TEGO-810), 5 g of pigment, 5 g of cosolvent (ethylene glycol butyl ether), and 20 g of water were mixed, dispersed at 2000 rpm for 20 min, and filtered through a 200-mesh sieve to obtain the mixture.

[0059] Example 4, a water-based nano-ink, is different from Example 1 in that the hydrophobic silica in Preparation Example 2-1 is replaced by an equal amount of the hydrophobic silica in Preparation Example 2-4.

[0060] Example 5, a water-based nano-ink, is different from Example 1 in that the hydrophobic silica in Preparation Example 2-1 is replaced by an equal amount of the hydrophobic silica in Preparation Example 2-5.

[0061] Example 6, a water-based nano-ink, is different from Example 1 in that the hydrophobic silica in Preparation Example 2-1 is replaced by an equal amount of the core-shell polyurethane / silica hybrid particles in Preparation Example 1-1.

[0062] Comparative Example 1, a water-based nano-ink, is different from Example 6 in that the core-shell polyurethane / silicon dioxide hybrid particles of Preparation Example 1-1 are replaced by an equal amount of the core-shell polyurethane / silicon dioxide hybrid particles of Preparation Example 1-4.

[0063] Comparative Example 2 is a water-based nano-ink, which is different from Example 6 in that the core-shell polyurethane / silicon dioxide hybrid particles of Preparation Example 1-1 are replaced by an equal amount of the core-shell polyurethane / silicon dioxide hybrid particles of Preparation Example 1-5.

[0064] Comparative Example 3, a water-based nano-ink, is different from Example 6 in that the core-shell polyurethane / silica hybrid particles of Preparation Example 1-1 are replaced with an equal amount of hydrophobic silica of Preparation Example 2-1.

[0065] 1. Dot gain test: refer to ISO 12647-2 "Printing Technology - Color and Transparency of Four-color Printing Inks". Use uncoated base paper (IS0 12647-7 standard, porosity greater than 60%) as the substrate. Use a digital proofing machine (resolution 2400 dpi) to print a 50% dot scale. Within 24 hours after printing, use a spectrodensitometer (X-RiteeXact) to measure the actual dot area and calculate the dot gain.

[0066] 2. Abrasion resistance test: Test according to ASTM D4060-19 "Determination of the resistance of organic coatings by Taber abrasion tester". Apply the ink to PET film (thickness 50μm), and the film thickness after drying is 10±1μm. Use Taber 5135 abrasion tester, CS-10 grinding wheel, load 500g, cycle 500 times, and weigh the mass difference (weight loss) before and after abrasion, unit mg.

[0067] 3. Storage stability test: Seal the ink in a transparent glass bottle and place it at 25°C for 6 months. Observe the stratification every month and test the centrifugal stability by taking 10 mL of ink and centrifuging at 3000 rpm for 30 minutes to observe the volume percentage of the sediment.

[0068] Table 1. Test results

[0069] Test data analysis: Compared with comparative examples 1 to 3 (dot gain rate 11.8 to 19.5%), the printing performance of examples 1 to 3 (dot gain rate 7.2 to 9.8%) is significantly improved. The reason may be that the core-shell polyurethane / silicon dioxide hybrid particles added in the above examples have good compatibility with the waterborne polyurethane body and can be effectively dispersed in the pores of the substrate. The silica shell layer plays a good steric hindrance role and inhibits the internal penetration of the ink. In addition, the shell SiO 2 The gradient interfacial energy difference between the surface energy of the polyester and the polyurethane core (about 35mN / m) can induce the ink to spread evenly on the surface of the substrate instead of penetrating into the interior, thereby reducing dot gain in the printing process.

[0070] The Taber weight loss (4.2-6.8 mg) of Examples 1-3 (shell thickness 5-15 nm) is lower than that of Comparative Examples 1-2 (thickness 3 nm / 19 nm, Taber weight loss 9.5-13.8 mg). This shows that Examples 1-3 have more outstanding wear resistance. The reason may be that increasing the thickness helps to improve its hardness, but if the thickness is too high, its brittleness increases. The reason may be that the thicker silica shell is prepared by the sol-gel method, which easily increases the stress in the shell during the drying process, increasing the brittleness.

[0071] Compared with Examples 1 to 3, Example 4 (adding hydrophobically modified silica with an oil absorption value of 120g / 100g), Example 5 (adding hydrophobically modified silica with an oil absorption value of 200g / 100g), and Example 6 (replacing hydrophobically modified silica with hydrophilic core-shell polyurethane / silica hybrid particles) all showed earlier stratification time (4 to 7 months) and higher centrifugal sedimentation rate (4.7 to 10.9), indicating that their storage stability is poor. The reason may be that only using core-shell polyurethane / silica hybrid particles with strong hydrophilicity can easily lead to a decrease in suspension stability due to the solvation effect during storage, resulting in stratified precipitation. Adding an appropriate amount of hydrophobically modified silica with an oil absorption value of 130 to 180g / 100g can help alleviate this problem. However, excessive hydrophobicity will also affect the dispersion of silica and induce agglomeration.

[0072] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A water-based nano ink, characterized in that: Contains the following components by weight: 40-60 parts of polyurethane dispersion, 1-5 parts of core-shell polyurethane / silicon dioxide hybrid particles, 0.5-1 parts of stabilizer, 0.5-2 parts of wetting and dispersing agent, 0.1-0.5 parts of leveling agent, 0.1-0.5 parts of defoaming agent, 5-15 parts of pigment, 20-30 parts of water; When preparing the core-shell polyurethane / silicon dioxide hybrid particles, the surface of the polyurethane prepolymer is modified with a silane coupling agent to obtain a modified prepolymer; a SiO2 precursor is deposited on the surface of the modified prepolymer by a sol-gel method to form a SiO2 shell layer; the mass ratio of the polyurethane prepolymer, the silane coupling agent and the SiO2 precursor is 60-70:3-8:10-20.

2. The ink according to claim 1, characterized in that The particle size of the core-shell polyurethane / silicon dioxide hybrid particles is 50 to 150 nm.

3. The ink according to claim 2, characterized in that The thickness of the SiO2 shell layer is 5 to 15 nm.

4. The ink according to claim 1, characterized in that The SiO2 precursor is selected from at least one of methyl orthosilicate, ethyl orthosilicate and butyl orthosilicate.

5. The ink according to claim 1, characterized in that The stabilizer is hydrophobically modified silica with an oil absorption value of 130 to 180 g / 100 g.

6. The ink according to claim 5, characterized in that The preparation method of the hydrophobically modified silica is: Under nitrogen protection, a mixed solution of methylchlorosilane and ethylene carbonate is mixed with silicon dioxide, and reacted at 300-400°C for 3-5 hours; the mixture is kept warm and an ethanol solution of polydimethylsiloxane is introduced, and the reaction is continued for 2-4 hours. The product is obtained after filtration, deacidification and drying.

7. The ink according to claim 6, characterized in that The mass ratio of the silicon dioxide, methylchlorosilane, ethylene carbonate and polydimethylsiloxane is 100:5-15:0.5-2:3-8.

8. The ink according to claim 1, characterized in that The ink further comprises 5 to 15 parts of a co-solvent, wherein the co-solvent is selected from at least one of propylene glycol, ethylene glycol butyl ether and N-methyl pyrrolidone.

9. The ink according to claim 1, characterized in that The wetting and dispersing agent is polyether-modified siloxane or a phosphate surfactant; the leveling agent is polyether-modified silicone or fluorocarbon-modified polyacrylate; and the defoaming agent is a mineral oil-based or polyether-modified polysiloxane defoaming agent.

10. A method for preparing a water-based nano ink, characterized in that: The ink is prepared by mixing and dispersing a polyurethane dispersion, core-shell polyurethane / silicon dioxide hybrid particles, a stabilizer, a wetting and dispersing agent, a leveling agent, a pH regulator, a defoamer, a pigment and water according to any ink ratio described in claims 1 to 9.

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