Water-based ink with barrier property and preparation process thereof

Abstract

The invention discloses water-based ink with barrier property and a preparation process thereof, and relates to the technical field of water-based ink. Comprising the following components: modified acrylic resin, pigment, montmorillonite, a polyester type dispersant, an alkynediol wetting agent, an organic silicon composite defoaming agent, a low-viscosity modified siloxane flatting agent, an aziridine cross-linking agent and the balance of deionized water. Wherein perfluorobutyl, glycidyl ether oxygroup and hydroxyl are grafted on a molecular chain of the modified acrylic resin, the particle size of the montmorillonite is smaller than 500nm, and the radius-thickness ratio is larger than 50. The preparation process comprises the steps of nano clay pre-activation and pigment dispersion, reactive dispersion and resin grafting, low-temperature grinding and directional curing. According to the ink formula, the high-activity aziridine cross-linking agent and the flaky nano-clay filler are used in a matched mode in the modified acrylic resin, synergistic interaction is achieved through a specific formula proportion, the comprehensive barrier property of the ink is remarkably improved, and the OTR is reduced to 4.2 cc / m.day.

Description

Technical Field

[0001] The present invention relates to the field of inks, and in particular to a water-based ink with barrier properties and a preparation process thereof. Background Art

[0002] With growing environmental awareness, water-based inks are gradually replacing solvent-based inks in packaging for food, pharmaceuticals, and other applications. However, traditional water-based inks have the following shortcomings in barrier performance: Food packaging standards require an oxygen transmission rate (OTR) of less than 5 cc / m²·day and a water vapor transmission rate (WVTR) of less than 5 g / m²·day, and grease barrier properties must remain zero for 72 hours. Traditional water-based inks, however, have an OTR of 15-20 cc / m²·day and a WVTR of 8-12 g / m²·day. These inks experience grease penetration within 24 hours, making them difficult to meet the high barrier performance requirements of food and pharmaceutical packaging.

[0003] The main reasons for the weak barrier properties of traditional water-based inks are: poor film density, with water as a dispersion medium causing the entanglement of resin molecular chains to decrease by 30%-40%; weak interfacial bonding: adhesion on PE / PP substrates is only 3-4B (cross-hatch test), lower than the 5B of solvent-based inks; and insufficient weather resistance: after accelerated aging at 60°C / 75%RH, the barrier properties degrade by 50%.

[0004] In the existing technology, the methods for improving the barrier properties of water-based inks mainly include: adding inorganic nanomaterials, such as nano-silica and nano-alumina, but there are problems such as poor dispersibility and easy agglomeration, which affect the ink performance; adding organic barrier agents: such as polyvinyl alcohol and polyvinylidene chloride, but there are problems such as poor compatibility with water-based resins and affecting the printability of inks; multi-layer composite structure: improving the barrier properties by coating multiple layers of inks with different functions, but the process is complex and the cost is high. Summary of the Invention

[0005] The purpose of the present invention is to provide a water-based ink with barrier properties and a preparation process thereof, which improves the problem of insufficient barrier properties of existing water-based inks through a process of branch stripping-pre-crosslinking protection-directional final curing.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A water-based ink with barrier properties, comprising the following components by weight:

[0008] Modified acrylic resin: 30-50%; pigment: 10-20%; montmorillonite: 5-15%; polyester dispersant: 1-3%; acetylenic diol wetting agent: 0.5-2%; silicone composite defoamer: 0.1-0.5%; low-viscosity modified siloxane leveling agent: 0.1-0.5%; aziridine crosslinker: 2-5%; the balance is deionized water.

[0009] The modified acrylic resin has perfluorobutyl, glycidyl ether oxygen and hydroxyl grafted on its molecular chain. The particle size of the montmorillonite is less than 500 nm, and the aspect ratio is greater than 50.

[0010] The modified acrylic resin of this invention is grafted with perfluorobutyl groups, providing excellent low surface energy. This creates a fluorine brush structure on the acrylic resin surface with a contact angle greater than 110°, making the coating water- and oil-repellent, reducing the adsorption and penetration of water, oil, and other substances. The grafted glycidyl ether oxygen groups provide reactive sites, enhancing adhesion to the substrate. More importantly, they react efficiently with aziridine crosslinkers, enabling efficient and rapid crosslinking and curing, forming a high-density three-dimensional network structure. This high crosslink density effectively reduces free volume, hindering the diffusion and penetration of small molecules (such as water vapor and oxygen). The grafted hydroxyl groups enhance water dispersibility and prevent demulsification during compounding. This solution combines both functional groups within the same resin chain. This dual-functionality creates a synergistic effect: the fluorinated segments tend to migrate and accumulate toward the coating surface, providing a durable low-surface-energy barrier, while the epoxy groups primarily participate in crosslinking within the coating, building a dense network. The combination of these two groups creates a barrier layer both on the coating surface and within the coating, overcoming the limitations of single-modification methods.

[0011] Montmorillonite particles have a particle size of less than 500 nm and an aspect ratio greater than 50. Nanosheets are formed through an exfoliation-recombination technique, resulting in directional alignment during ink film formation, extending the oxygen permeation path. Conventional water-based inks have an OTR greater than 15 cc / m²·day, failing to meet packaging requirements for products like milk powder (which require less than 5 cc / m²·day). The montmorillonite nanosheets in this invention block oxygen and, in conjunction with fluorine brushes, block water, reducing the OTR to 4.2 cc / m²·day, a 300% improvement in barrier performance compared to pure resin coatings. Solvent-based inks offer excellent barrier properties but have a VOC greater than 300 g / L. Conventional water-based inks have a VOC less than 50 g / L but poor barrier properties. This invention, however, has a VOC less than 30 g / L and comparable barrier performance to solvent-based inks. High-barrier inks require high-temperature baking (greater than 120°C), making them unsuitable for heat-sensitive substrates like PET. This invention utilizes an aziridine crosslinker for room-temperature crosslinking, enabling room-temperature curing. The present invention solves the contradiction between barrier properties and water-based properties through ternary grafting of fluorine / silicon / hydroxyl groups; and adopts high-diameter-thickness montmorillonite to achieve directional arrangement during ink film formation, thus breaking through the permeation threshold of nanofillers.

[0012] The content ranges of each component in this invention are carefully considered. The resin content (30-50%) ensures sufficient continuous film-forming properties; the filler content (5-15%) provides barrier properties while avoiding excessive amounts that may lead to poor rheological properties and reduced gloss; and the crosslinker content (2-5%) needs to be sufficient to allow the epoxy groups to react effectively to form a network; excessive amounts may increase costs or affect flexibility.

[0013] The present invention simultaneously introduces fluorine-containing groups (perfluorobutyl), epoxy groups (glycidyl ether oxygen groups) and hydroxyl groups to modify the acrylic resin, and matches it with highly active aziridine crosslinkers and flaky nanoclay fillers (montmorillonite). Through a specific formula ratio, synergistic enhancement is achieved, significantly improving the comprehensive barrier properties of the ink.

[0014] Furthermore, the pigment is selected from one of composite titanium red and resinized phthalocyanine blue; and the aziridine crosslinking agent is trimethylolpropane tris(2-methylaziridine) propionate.

[0015] A preparation process, applicable to the water-based ink having barrier properties, comprises the following steps:

[0016] S100, adding filler, 45-55% of a wetting agent, and 25-35% of a dispersant to 35-45% of deionized water, and ultrasonically treating at 55-65°C for 28-32 minutes to fully exfoliate the filler to form a pre-activated slurry with a fineness of less than 5 μm; in another container, mixing pigment, defoamer, and remaining dispersant with 15-25% of deionized water, and pre-dispersing by high-speed shearing to obtain a pigment concentrate;

[0017] S200, adding the modified acrylic resin to the pre-activated slurry of step S100, heating to 72-78°C, slowly adding 45-55% of a cross-linking agent, and reacting for 0.8-1.2 hours;

[0018] Cool the reaction system to 38-42°C at a cooling rate of ≤5°C / min, add 20-35% of deionized water, then add the pigment concentrate, leveling agent, and remaining wetting agent from step S100, stir evenly, add the remaining deionized water, stir at a low speed for 18-22 minutes, and mix evenly to obtain a mixed slurry;

[0019] S300, grinding the mixed slurry of step S200 at a temperature of ≤35°C to a fineness of <5μm; immediately adding the remaining cross-linking agent after grinding, and then adding ammonia water, adjusting the pH to 8.2-8.6, stirring at a low speed for 8-12 minutes, and filtering to obtain the target product.

[0020] In step S100, the montmorillonite is not ultrasonically treated simultaneously with the pigment to avoid pigment interference and prevent pigment decomposition. Hydraulic shear is used to exfoliate the layered structure, achieving an aspect ratio greater than 50, effectively improving exfoliation efficiency and enhancing barrier properties. High-speed shearing of the pigment effectively breaks up aggregates, reducing fineness to less than 5μm. In step S200, at an elevated temperature of 72-78°C, 45-55% of a crosslinker pre-reacts with the resin-clay composite to form anchor crosslinking points, preventing subsequent concentrated crosslinking that would cause a sudden increase in viscosity. The nanoclays become nodes in the crosslinked network, enhancing coating density and improving oxygen barrier properties by 30%. Glycidyl ether oxygen groups preferentially react with aziridine crosslinkers, forming a dense crosslinked shell on the resin surface, preventing subsequent filler incorporation from disrupting the network. In step S300, after the temperature is reduced to ≤35°C, the remaining cross-linking agent is added to avoid high-temperature migration of fluorine chains, reducing the attenuation rate of the contact angle from 118° to 105° to <3%. After pre-cross-linking of the filler / resin, grinding is performed, and shear force is used to orient the montmorillonite flakes in parallel. The fineness is <5μm to ensure that the montmorillonite has no stacking pores, the oxygen permeation path is extended to twice the traditional level, and the OTR is reduced from 8.5cc / m²·day to 4.2cc / m²·day. The pH is 8.2~8.6, which can inhibit the hydrolysis of aziridine, and the viscosity increase after storage at 50°C for 30 days is <10%.

[0021] The ink preparation process of the present invention uses separate treatment paths for montmorillonite exfoliation and pigment dispersion, which can achieve both a high aspect ratio and hue stability. A 45-55% crosslinker is pre-reacted at high temperature to construct a resin protective shell layer, providing a low-temperature, efficient mass production process for high-barrier water-based inks.

[0022] Furthermore, in step S100, the power of the ultrasonic wave is 40 kHz, the rotation speed of the high-speed shear is 4500-5500 rpm, and the time is 12-18 min; in step S200, the cooling rate is ≤5°C / min; and the rotation speed of the low-speed stirring is 200-300 rpm.

[0023] Furthermore, the preparation process of the modified acrylic resin comprises the following raw materials by weight:

[0024] MMA: 35~45 parts, BA: 25~35 parts, HEA: 10~15 parts; SDS: 1.0~1.5 parts, emulsifier OP-10: 0.8~1.2 parts; APS: 0.8~1.2 parts; inhibitor hydroquinone: 0.01~0.02 parts; sodium bicarbonate 0.1~0.3 parts; deionized water: 120~150 parts; KH-560: 6~8 parts; tetraisopropyl titanate: 0.1~0.3 parts; PFBMA, 20~25 parts; CuBr: 4~5 parts; PMDETA: 10~12 parts; perfluoropolyether surfactant: 7~8 parts; KH-570 modified nano-SiO2: 2–4 parts; E-513~5 parts.

[0025] Furthermore, the preparation process of the modified acrylic resin comprises the following steps:

[0026] Step 1: Dissolve 28-32% of SDS and buffer NaHCO3 in 20-25% of deionized water, heat to 78-82°C, and replace with nitrogen for 14-16 minutes; add 29-31% of initiator APS, stir at low speed; add 9-11% of pre-emulsion at a rate of 1 ml / min, keep warm at 79-81°C, and react for 28-32 minutes;

[0027] Step 2: Dissolve the remaining initiator APS in the remaining deionized water to prepare a solution, and add the remaining pre-emulsion and initiator APS solution dropwise to the solution obtained in step 2 at a rate of 2 mL / min, controlling the temperature at 78-82°C; 28-32 minutes before the remaining pre-emulsion is added, cool to 74-76°C, add HEA, and rapidly mix for 8-12 minutes;

[0028] Step 3: Cool the mixture to 60°C, add KH-560 in three batches, with an interval of 18 to 22 minutes between each batch, add sodium bicarbonate, adjust the pH to 6.5 to 7.5, then add a 5% ethanol solution of tetraisopropyl titanate, and keep the mixture warm for 2.8 to 3.2 hours; after post-treatment, obtain a dry resin intermediate product;

[0029] Step 4: Add the intermediate product obtained in step 3, 2-bromoisobutyryl bromide, and triethylamine to a mixed solvent of THF and water, and react at 58-62°C under N2 protection for 1.8-2.2 hours; cool to 48-52°C, add PFBMA, CuBr, and PMDETA, and react under N2 protection for 11.5-12.5 hours; allow air to terminate the reaction, and add a perfluoropolyether surfactant;

[0030] Step 5: Add the pre-dispersed KH-570 modified nano-SiO2 to the solution obtained in step 4 and stir evenly; heat to 74-76°C, add bisphenol A epoxy resin E-51, and stir for 1 hour; cool to 35-40°C, adjust the pH to 7.5-8.0 with ammonia water, and filter the material through a 180-200 mesh filter to obtain a modified acrylic resin.

[0031] The present invention pre-emulsifies 65-75% of HEA and then adds the remaining 25-35% of HEA in a later stage. Hydroxyl groups are enriched on the surface of the latex particles, which can increase the surface hydroxyl density by 40% and the KH-560 grafting rate to 92%. Glycidyl ether oxygen groups are grafted first and then perfluorobutyl groups to avoid siloxane hydrolysis interfering with ATRP, and the fluorine grafting rate is increased to 94.1%, solving the phase separation problem. Nano-SiO2 is added in the post-crosslinking stage. SiO2 is anchored by the reaction of Si-OH and epoxy groups, and the barrier property is improved by 50%. Anionic emulsifier SDS is used in the seed stage to accurately control the particle size. Non-ionic emulsifier OP-10 is added in the main polymerization stage to improve the tolerance to fluorine / silicon monomers and avoid gel formation. The present invention solves the phase separation problem in the synthesis of multi-functional resins by delayed addition of functional monomers and coordinated regulation of temperature / emulsifier, while meeting the operability requirements of industrial production.

[0032] Furthermore, in step 1, the preparation process of the pre-emulsion includes the following: premixing MMA, BA, and 65-75% of HEA, and then adding them together with 68-72% of SDS, emulsifier OP-10, and hydroquinone to 55-65% of deionized water, stirring at a low speed for 30 minutes at 15-25° C. to obtain a pre-emulsion; in step 2, the mass of the additional HEA is 25-35% of the total mass of HEA.

[0033] Furthermore, in step 3, the post-treatment method includes the following: cooling to below 25°C, adding 5% CaCl2 solution and stirring for 15 minutes, centrifuging for 8-12 minutes to obtain a middle-layer resin flocculent; washing the resin flocculent with an acetone-water mixed solvent 2-3 times at a temperature of 60°C, and vacuum drying at 60-62°C for 23-24 hours, with a water content of less than 0.1% after drying; the volume ratio of acetone to water is 1-2:1; the mass of the added 5% CaCl2 accounts for 4.9-5.1% of the total mass of the emulsion after the reaction in step 3 is completed.

[0034] Precise control of CaCl2 demulsification (4.9-5.1%): compresses the double electrical layer without destroying the fluorine chain, resulting in a resin yield of >98%.

[0035] Furthermore, in step 4, the mass ratio of the intermediate product, 2-bromoisobutyryl bromide, and triethylamine is 1:0.28~0.32:0.50~0.55; the resin intermediate product and THF are prepared at a solid content of 10%, and the volume ratio of THF to water is 2.2~2.5:1.

[0036] The aqueous phase promotes the Cu⁺ / Cu²⁺ cycle, and THF dissolves the fluorinated monomer, resulting in a grafting efficiency of 92%.

[0037] Furthermore, it is characterized in that the pre-dispersion method of KH-570 modified nano-SiO2 includes: controlling the temperature of an ice-water bath to ≤30°C, ultrasonically dispersing the KH-570 modified nano-SiO2 in propylene glycol methyl ether for 20 to 30 minutes, the ultrasonic dispersion power is 300 to 400 W, and the mass ratio of KH-570 modified nano-SiO2 to propylene glycol methyl ether is 1:8 to 12.

[0038] Advantageous Effects of the Invention

[0039] 1. This ink formulation simultaneously introduces fluorinated groups (perfluorobutyl), epoxy groups (glycidyloxy), and hydroxyl groups into the acrylic resin. It also uses a highly active aziridine crosslinker and a flaky nanoclay filler (montmorillonite). Through a specific formulation ratio, this synergistic effect significantly improves the ink's overall barrier properties and significantly reduces its OTR. This invention provides a water-based ink solution for food and pharmaceutical packaging with a VOC of less than 30 g / L and an OTR of less than 4.2 cc / m²·day, promoting green development in the packaging industry.

[0040] 2. The ink preparation process of the present invention utilizes separate treatment paths for montmorillonite exfoliation and pigment dispersion, achieving a high aspect ratio while maintaining hue stability. A high-temperature pre-reaction of 45-55% crosslinker forms a protective resin shell, providing a low-temperature, efficient mass production process for high-barrier water-based inks.

[0041] 3. The preparation process of the modified acrylic resin of this invention breaks through the fluorine-silicon compatibility barrier, achieving a grafting rate of >92%. It also achieves efficient ATRP in a water-based system, with a fluorine grafting rate of 93.5% and a VOC of <28 g / L. This provides a resin synthesis solution for food packaging inks that combines ultra-barrier properties with extreme environmental friendliness.

[0042] MMA: methyl methacrylate;

[0043] BA: butyl acrylate;

[0044] HEA: hydroxyethyl acrylate;

[0045] SDS: sodium dodecyl sulfate;

[0046] E-51: bisphenol A epoxy resin;

[0047] KH-560: γ-glycidyloxypropyltrimethoxysilane;

[0048] PFBMA: perfluorobutyl methacrylate;

[0049] PMDETA: pentamethyldiethylenetriamine;

[0050] APS: ammonium persulfate;

[0051] THF: tetrahydrofuran. DETAILED DESCRIPTION

[0052] Example 1

[0053] The preparation process of the modified acrylic resin comprises the following raw materials:

[0054] MMA: 400g; BA: 300g; HEA: 120g; SDS: 12g; emulsifier OP-10: 10g; APS: 10g; inhibitor hydroquinone: 0.15g; sodium bicarbonate 2g; deionized water: 1350g; KH-560: 70g; tetraisopropyl titanate: 2g; PFBMA, 230g; CuBr: 45g; PMDETA: 110g; surfactant Capstone FS-3100: 75g; KH-570 modified nano-SiO2: 30g; E-5140g.

[0055] The preparation process of the modified acrylic resin comprises the following steps:

[0056] Step 1: Dissolve 3.6g of SDS and buffer NaHCO3 in 310g of deionized water, heat to 80°C, and replace with nitrogen for 15 minutes; add 3g of initiator APS, stir at low speed; add 10% of the total amount of pre-emulsion at a rate of 1ml / min, keep warm at 80°C, and react for 30 minutes;

[0057] The pre-emulsion preparation process includes the following steps: 400 g of MMA, 300 g of BA, and 84 g of HEA are pre-mixed, and then added to 810 g of deionized water together with 8.4 g of SDS, 10 g of emulsifier OP-10, and 0.15 g of hydroquinone, and stirred at low speed for 30 minutes at 20° C. to obtain a pre-emulsion;

[0058] Step 2: Dissolve the remaining initiator APS in the remaining deionized water to prepare a solution, and add the remaining pre-emulsion and initiator APS solution dropwise to the solution obtained in step 2 at a rate of 2 mL / min, controlling the temperature to 80°C; 30 minutes before the remaining pre-emulsion is added, cool to 75°C, add 36g of HEA, and rapidly mix for 10 minutes;

[0059] Step 3: Cool to 60°C, add KH-560 in three batches, with an interval of 20 minutes between each batch, add sodium bicarbonate, adjust the pH to 7, then add a 5% ethanol solution of tetraisopropyl titanate, and keep the temperature for reaction for 3 hours; after post-treatment, obtain a dry resin intermediate product;

[0060] The post-treatment method includes the following: cooling to below 25°C, adding a 5% CaCl2 solution and stirring for 15 minutes, and centrifuging for 10 minutes to obtain a middle-layer resin floc; washing the resin floc three times with a mixed solvent of 15L acetone and 10L water at 60°C, and vacuum drying at 61°C for 24 hours; the mass of the added 5% CaCl2 accounts for 5.0% of the total mass of the emulsion after the reaction in step 3 is completed.

[0061] Step 4: 500 g of the intermediate product obtained in step 3, 150 g of 2-bromoisobutyryl bromide, and 260 g of triethylamine were added to 6457 mL of a mixed solvent of THF and water, and the mixture was reacted at 60 ° C. under N2 protection for 2 h; the temperature was lowered to 50 ° C., 230 g of PFBMA, 45 g of CuBr, and 110 g of PMDETA were added under N2 protection and the reaction was continued for 12 h; air was introduced to terminate the reaction, and 75 g of a perfluoropolyether surfactant was added;

[0062] The resin intermediate product was prepared with THF at a solid content of 10%, and the volume ratio of THF to water was 2.3:1.

[0063] Step 5: Add the pre-dispersed KH-570 modified nano-SiO2 to the solution obtained in step 4 and stir evenly; heat to 75°C, add 40g of bisphenol A epoxy resin E-51, and stir for 1 hour; cool to 38°C, adjust the pH to 7.6 with ammonia water, and filter the material through a 200-mesh filter to obtain a modified acrylic resin;

[0064] The pre-dispersion method of KH-570 modified nano-SiO2 includes: controlling the temperature at 30°C in an ice-water bath, ultrasonically dispersing 30g of KH-570 modified nano-SiO2 in 300g of propylene glycol methyl ether for 25 minutes, and the ultrasonic dispersion power is 350W.

[0065] Example 2

[0066] The preparation process of the modified acrylic resin comprises the following raw materials:

[0067] MMA: 350g; BA: 250g; HEA: 100g; SDS: 10g; emulsifier OP-10: 8g; APS: 8g; polymerization inhibitor hydroquinone: 0.1g; sodium bicarbonate: 1g; deionized water: 1200g; KH-560: 60g; tetraisopropyl titanate: 1g; PFBMA, 200g; CuBr: 40g; PMDETA: 100g; surfactant Capstone FS-3100: 70g; KH-570 modified nano-SiO2:

[0068] 20g; E-5130g.

[0069] The preparation process of the modified acrylic resin comprises the following steps:

[0070] Step 1: Dissolve 2.8 g of SDS and buffer NaHCO3 in 300 g of deionized water, heat to 78°C, and replace with nitrogen for 14 minutes; add 2.3 g of initiator APS, stir at low speed; add 9% of the total amount of pre-emulsion at a rate of 1 ml / min, keep warm at 79°C, and react for 28 minutes;

[0071] The preparation process of the pre-emulsion includes the following: 350g of MMA, 250g of BA and 65g of HEA are pre-mixed, and then added together with 7.2g of SDS, 8g of emulsifier OP-10 and 0.1g of hydroquinone into 780g of deionized water, and stirred at low speed for 30 minutes at 15°C to obtain a pre-emulsion.

[0072] Step 2: Dissolve the remaining initiator APS in the remaining deionized water to prepare a solution, and add the remaining pre-emulsion and initiator APS solution dropwise to the solution obtained in step 2 at a rate of 2 mL / min, controlling the temperature to 78°C; 28 minutes before the remaining pre-emulsion is added, cool to 74°C, add 35g of HEA, and rapidly mix for 8 minutes;

[0073] Step 3: Cool to 60°C, add KH-560 in three batches, with an interval of 18 minutes between each batch, add sodium bicarbonate, adjust the pH to 6.5, then add a 5% ethanol solution of tetraisopropyl titanate, and keep the reaction warm for 2.8 hours; after post-treatment, obtain a dry resin intermediate product;

[0074] The post-treatment method includes the following: cooling to below 25°C, adding 5% CaCl2 solution and stirring for 15 minutes, and centrifuging for 8 minutes to obtain a middle-layer resin floc; washing the resin floc twice with a 12L acetone-12L water mixed solvent at 60°C, and vacuum drying at 60°C for 23 hours; the mass of the added 5% CaCl2 accounts for 4.9% of the total mass of the emulsion after the reaction in step 3 is completed.

[0075] Step 4: 500 g of the intermediate product obtained in step 3, 140 g of 2-bromoisobutyryl bromide, and 250 g of triethylamine were added to a mixed solvent of 6928 mL of THF and water, and the mixture was reacted at 58 ° C. under N2 protection for 1.8 h; the temperature was lowered to 48 ° C., 200 g of PFBMA, 40 g of CuBr, and 100 g of PMDETA were added under N2 protection and the reaction was continued for 11.5 h; air was introduced to terminate the reaction, and 70 g of a perfluoropolyether surfactant was added;

[0076] The resin intermediate product was prepared with THF at a solid content of 9.5%, and the volume ratio of THF to water was 2.2:1.

[0077] Step 5: Add the pre-dispersed KH-570 modified nano-SiO2 to the solution obtained in step 4 and stir evenly; heat to 74°C, add bisphenol A epoxy resin E-51, and stir for 0.9 h; cool to 35°C, adjust the pH to 7.5 with ammonia water, and filter the material with a 180-mesh filter to obtain a modified acrylic resin.

[0078] The pre-dispersion method of KH-570 modified nano-SiO2 includes: controlling the temperature of an ice water bath at 25°C, ultrasonically dispersing 20g of KH-570 modified nano-SiO2 in 160g of propylene glycol methyl ether for 20 minutes, and the ultrasonic dispersion power is 300W.

[0079] Example 3

[0080] The preparation process of the modified acrylic resin comprises the following raw materials:

[0081] MMA: 450g, BA: 350g, HEA: 150g; SDS: 15g, emulsifier OP-10: 12g; APS: 12g; inhibitor hydroquinone: 0.2g; sodium bicarbonate 3g; deionized water 1500g; KH-560: 80g; tetraisopropyl titanate: 3g; PFBMA, 250g; CuBr: 50g; PMDETA: 120g; surfactant Capstone FS-3100: 80g; KH-570 modified nano-SiO2: 40g; E-5150g.

[0082] The preparation process of the modified acrylic resin comprises the following steps:

[0083] Step 1: Dissolve 4.8 g of SDS and buffer NaHCO3 in 525 g of deionized water, heat to 82°C, and replace with nitrogen for 16 minutes; add 3.7 g of initiator APS, stir at low speed; add 11% of the total amount of pre-emulsion at a rate of 1 ml / min, keep warm at 81°C, and react for 32 minutes;

[0084] The preparation process of the pre-emulsion includes the following: MMA, BA and 112.5g HEA are premixed, and then 10.2g SDS, emulsifier OP-10 and hydroquinone are added to 825g deionized water. The mixture is stirred at a low speed for 30 minutes at 25°C to obtain a pre-emulsion.

[0085] Step 2: Dissolve the remaining initiator APS in the remaining deionized water to prepare a solution, and add the remaining pre-emulsion and the initiator APS solution dropwise to the solution obtained in step 2 at a rate of 2 mL / min, controlling the temperature at 82°C; 32 minutes before the remaining pre-emulsion is added, cool to 76°C, add HEA, and rapidly mix for 12 minutes;

[0086] Step 3: Cool to 60°C, add KH-560 in three batches, with an interval of 22 minutes between each batch, add sodium bicarbonate, adjust the pH to 7.5, then add a 5% ethanol solution of tetraisopropyl titanate, and keep the reaction warm for 3.2 hours; after post-treatment, a dry resin intermediate product is obtained;

[0087] The post-treatment method includes the following: cooling to below 25°C, adding a 5% CaCl2 solution and stirring for 15 minutes, and centrifuging for 12 minutes to obtain a middle-layer resin floc; washing the resin floc three times with a 16L acetone-8L water mixed solvent at 60°C, and vacuum drying at 60-62°C for 23.5 hours; the mass of the added 5% CaCl2 accounts for 5.1% of the total mass of the emulsion after the reaction in step 3 is completed.

[0088] Step 4: 500 g of the intermediate product obtained in step 3, 160 g of 2-bromoisobutyryl bromide, and 275 g of triethylamine were added to a mixed solvent of 6704 mL of THF and water, and the mixture was reacted at 62 ° C. under N2 protection for 2.2 h; the temperature was lowered to 52 ° C., PFBMA, CuBr, and PMDETA were added under N2 protection, and the reaction was continued for 12.5 h; air was introduced to terminate the reaction, and a perfluoropolyether surfactant was added;

[0089] The resin intermediate product was prepared with THF at a solid content of 10.5%, and the volume ratio of THF to water was 2.5:1.

[0090] Step 5: Add the pre-dispersed KH-570 modified nano-SiO2 to the solution obtained in step 4 and stir evenly; heat to 76°C, add bisphenol A epoxy resin E-51, and stir for 1.1 hours; cool to 40°C, adjust the pH to 8.0 with ammonia water, and filter the material with a 190-mesh filter to obtain a modified acrylic resin.

[0091] The pre-dispersion method of KH-570 modified nano-SiO2 includes: controlling the temperature of an ice water bath at 28°C, ultrasonically dispersing 40g of KH-570 modified nano-SiO2 in 480g of propylene glycol methyl ether for 30 minutes, and the ultrasonic dispersion power is 400W.

[0092] Comparative Example 1

[0093] The traditional preparation process of modified acrylic resin includes the following raw materials:

[0094] MMA: 400g, BA: 300g, HEA: 120g; PFBMA: 230g; KH-560: 65g; SDS: 12g; emulsifier OP-10: 10g; APS: 10g; nano-SiO2 (unmodified): 30g.

[0095] The preparation process of the modified acrylic resin comprises the following steps:

[0096] Step 1: Preparation of pre-emulsion: Mix all monomers of MMA, BA, HEA, PFBMA, and KH-560; add SDS, OP-10, and deionized water (total amount 60%), and stir at 25°C for 30 min to obtain a pre-emulsion.

[0097] Step 2: Emulsion polymerization: Add the remaining deionized water (40%) and 0.2 parts of NaHCO3 to the reactor and heat to 85°C;

[0098] Add 50% of the total amount of APS and stir for 10 minutes; add all the pre-emulsion at once at a rate of 4 mL / min (rapid addition);

[0099] The reaction was kept at 85°C for 3 h.

[0100] Step 3: Add nanofiller: cool to 70°C and add unmodified nano-SiO2; stir for 1 h (non-ultrasonic dispersion).

[0101] Step 4: Demulsification and post-treatment: Add 8% Al2(SO4)3 solution (dosage: total mass of emulsion × 0.08); centrifuge, wash the resin flocs with acetone: water = 1:1 (volume ratio); dry with hot air at 80℃ for 24 h to obtain solid resin.

[0102] The performance comparison data of Examples 1-3 and Comparative Example 1 are shown in Table 1.

[0103] Table 1 Performance comparison data of Examples 1-3 and Comparative Example 1

[0104] Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Fluorine grafting rate (%) 93.5% 92.8% 94.1% 78.2% Epoxy retention rate (%) 89.7% 90.2% 88.5% 61.3% OTR (cc / m²·day) 3.9 4.1 3.8 15.2 Water contact angle 117° 115° 118° 102° Adhesion (cross-hatch method) 5B 5B 5B 3B Gel rate (%) 0.2% 0.3% 0.1% 6.5% VOC emissions (g / L) 20 27 26 105 Wastewater COD (mg / L) 680 780 750 5000 Particle size uniformity (PDI) 0.08 0.12 0.10 0.43

[0105] As shown in Table 1, the fluorine grafting rates in Examples 1-3 are all greater than 92%, a 16% increase from 78.2% in Comparative Example 1; the epoxy retention rates are all greater than 88.5%, a 29% increase from 61.3% in Comparative Example 1; the oxygen transmission rate (OTR) can be controlled at ≤4.1cc / m²·day, a 75% decrease from 15.2cc / m²·day in Comparative Example 1; and the water contact angles are all greater than 115°, a 16° increase from 102° in Comparative Example 1. The adhesion is 5B, which is 2 levels higher than 3B in comparative example 1. The gel rate is lower than 0.3%, which is 95% lower than that in comparative example 1. The VOC emission can be controlled below 27g / L, which is 75% lower than that in comparative example 1 (105g / L). The COD of wastewater can be controlled at 780mg / L, which is 85% lower than that in comparative example 1 (5000mg / L). The particle size uniformity is less than 0.13, while that in comparative example 1 is 0.43.

[0106] In summary, the present invention utilizes HEA positioning, epoxy / fluorine stepwise grafting, and water / THF coordinated ATRP system to prepare modified acrylic resin, which has significant advantages over traditional preparation processes, among which Example 1 is the best example.

[0107] Example 4

[0108] A water-based ink with barrier properties, comprising the following components:

[0109] Modified acrylic resin (prepared in Example 1): 400g; composite titanium red 57DT4659: 150g; montmorillonite: 100g; polyester dispersant 1998: 20g; acetylene glycol wetting agent Dynol 960: 10g; silicone composite defoamer SXP-107-1: 3g; low-viscosity modified siloxane leveling agent BYK-347: 3g; trimethylolpropane tris(2-methylaziridine) propionate: 35g; deionized water 279g;

[0110] The modified acrylic resin has perfluorobutyl, glycidyl ether oxygen and hydroxyl grafted on its molecular chain. The montmorillonite has a particle size of 450 nm and an aspect ratio of 52.

[0111] A preparation process, applicable to the water-based ink having barrier properties, comprises the following steps:

[0112] S100, add the filler, 5g of wetting agent and 6g of dispersant to 40% of the total amount of deionized water, and perform ultrasonic treatment at 60°C for 30min with an ultrasonic power of 40kHz to fully peel the filler and form a pre-activated slurry with a fineness of 3μm; in another container, mix the pigment, defoamer and remaining dispersant with 55.8g of deionized water, and pre-disperse by high-speed shearing at a speed of 5000rpm for 15min to obtain a pigment concentrate;

[0113] S200, adding the modified acrylic resin to the pre-activated slurry of step S100, heating to 75°C at a heating rate of 3°C / min, slowly adding 17.5g of a cross-linking agent, and reacting for 1h;

[0114] The reaction system was cooled to 40°C at a cooling rate of 4°C / min, 83.7 g of deionized water was added, and then the pigment concentrate, leveling agent, and remaining wetting agent from step S100 were added, and the mixture was stirred evenly. The remaining deionized water was added, and the mixture was stirred at a low speed of 250 rpm for 20 min to obtain a mixed slurry.

[0115] S300, grinding the mixed slurry of step S200 at 30°C to a fineness of 3 μm; immediately adding the remaining cross-linking agent after grinding, then adding ammonia water, adjusting the pH to 8.5, stirring at a low speed of 200 rpm, after 10 minutes, filtering through a 4-μm pore size filter membrane to obtain the target product.

[0116] Example 5

[0117] A water-based ink with barrier properties, comprising the following components:

[0118] Modified acrylic resin (prepared in Example 1): 500g; resinized phthalocyanine blue B2G 131-CN: 100g; montmorillonite: 50g; polyester dispersant 1998: 10g; acetylene glycol wetting agent Dynol 960: 5g; silicone composite defoamer SXP-107-1: 1g; low-viscosity modified siloxane leveling agent BYK-347: 1g; trimethylolpropane tris(2-methylaziridine) propionate: 20g; 313g deionized water;

[0119] The modified acrylic resin has perfluorobutyl, glycidyl ether oxygen and hydroxyl grafted onto its molecular chain. The montmorillonite has a particle size of 400 nm and an aspect ratio of 58.

[0120] A preparation process, applicable to the water-based ink having barrier properties, comprises the following steps:

[0121] S100, add the filler, 2.25g of wetting agent, and 2.5g of dispersant to 109.6g of deionized water, and perform ultrasonic treatment at 55°C for 28min with an ultrasonic power of 40kHz to fully exfoliate the filler to form a pre-activated slurry with a fineness of 4μm; in another container, mix the pigment, defoamer, and remaining dispersant with 47g of deionized water, and pre-disperse by high-speed shearing at a speed of 4500rpm for 12min to obtain a pigment concentrate;

[0122] S200, adding the modified acrylic resin to the pre-activated slurry of step S100, heating to 72°C at a heating rate of 5°C / min, slowly adding 9g of a cross-linking agent, and reacting for 0.8h;

[0123] The reaction system was cooled to 38°C at a cooling rate of 3°C / min, 62.6 g of deionized water was added, and then the pigment concentrate, leveling agent, and remaining wetting agent from step S100 were added and stirred evenly. The remaining deionized water was added and stirred at a low speed of 200 rpm for 18 min to obtain a mixed slurry.

[0124] S300, grinding the mixed slurry of step S200 at 35°C to a fineness of 4 μm; immediately adding the remaining cross-linking agent after grinding, and then adding ammonia water, adjusting the pH to 8.2, stirring at a low speed of 280 rpm, after 8 minutes, filtering with a 3-μm pore size filter membrane to obtain the target product.

[0125] Example 6

[0126] A water-based ink with barrier properties, comprising the following components:

[0127] Modified acrylic resin (prepared in Example 1): 300g; composite titanium red 57DT4659: 200g; montmorillonite: 50g; polyester dispersant 1998: 30g; acetylene glycol wetting agent Dynol 960: 20g; silicone composite defoamer SXP-107-1: 5g; low-viscosity modified siloxane leveling agent BYK-347: 5g; trimethylolpropane tris(2-methylaziridine) propionate: 50g; 340g deionized water;

[0128] The modified acrylic resin has perfluorobutyl, glycidyl ether oxygen and hydroxyl grafted on its molecular chain. The montmorillonite has a particle size of 460 nm and an aspect ratio of 55.

[0129] A preparation process, applicable to the water-based ink having barrier properties, comprises the following steps:

[0130] S100, add the filler, 11g of wetting agent, and 10.5g of dispersant to 153g of deionized water, and perform ultrasonic treatment at 65°C for 32min with an ultrasonic power of 40kHz to fully peel the filler and form a pre-activated slurry with a fineness of 2μm; in another container, mix the pigment, defoamer, and remaining dispersant with 85g of deionized water, and pre-disperse by high-speed shearing at a speed of 5500rpm for 18min to obtain a pigment concentrate;

[0131] S200, adding the modified acrylic resin to the pre-activated slurry of step S100, heating to 78°C at a heating rate of 5°C / min, slowly adding 27.5g of a cross-linking agent, and reacting for 1.2h;

[0132] The reaction system was cooled to 42°C at a cooling rate of 4°C / min, 119 g of deionized water was added, and then the pigment concentrate, leveling agent, and remaining wetting agent from step S100 were added and stirred evenly. The remaining deionized water was added and stirred at a low speed of 300 rpm for 22 min to obtain a mixed slurry.

[0133] S300, grinding the mixed slurry of step S200 at 30°C to a fineness of 3 μm; immediately adding the remaining cross-linking agent after grinding, then adding ammonia water, adjusting the pH to 8.6, stirring at a low speed of 300 rpm, after 12 minutes, filtering through a 5-μm pore size filter membrane to obtain the target product.

[0134] Comparative Example 2

[0135] A water-based ink with barrier properties, comprising the following components:

[0136] Acrylic resin: 400g; titanium red: 150g; montmorillonite: 100g; polyester dispersant 1998: 20g; acetylene glycol wetting agent Dynol 960: 10g; silicone composite defoamer SXP-107-1: 3g; low viscosity modified siloxane leveling agent BYK-347: 3g; isocyanate crosslinker: 35g; 279g deionized water; montmorillonite particle size 450nm, aspect ratio 28.

[0137] A preparation process, applicable to the water-based ink having barrier properties, comprises the following steps:

[0138] S100, adding montmorillonite, wetting agent, pigment, defoamer, and dispersant to 167.4 g of deionized water, mechanically stirring at 25° C. for 15 min at a speed of 3000 rpm to form a pre-activated slurry with a fineness of 8.5 μm;

[0139] S200, adding acrylic resin to the pre-activated slurry of step S100, heating to 75°C, slowly adding a cross-linking agent, and reacting for 1 hour; cooling the reaction system to 40°C, adding 83.7g of deionized water, then adding a leveling agent, stirring evenly, adding the remaining deionized water, stirring at a low speed of 250 rpm for 20 minutes, mixing evenly, and obtaining a mixed slurry;

[0140] S300, grinding the mixed slurry of step S200 at 45°C to a fineness of 6.8 μm; then adding ammonia water, adjusting the pH to 8.5, stirring at a low speed of 200 rpm, after 10 minutes, filtering with a 4-μm pore size filter membrane to obtain the target product.

[0141] The performance comparison data of Examples 4-6 and Comparative Example 2 are shown in Table 2.

[0142] Table 2 Performance comparison data of Examples 4-6 and Comparative Example 2

[0143] Performance indicators Example 4 Example 5 Example 6 Comparative Example 2 <![CDATA[OTR (cc / m 2 ·day)]]> 4.1 4.2 3.9 15.6 WVTR (g / m²·day) 2.3 2.5 2.0 9.8 Drying speed (m / min) 150 145 155 80 VOC emissions (g / L) 28 30 26 105 Storage stability at 50°C Viscosity↑9% Viscosity↑11% Viscosity↑8% Turns into gel

[0144] As shown in Table 2, the oxygen transmission rates (OTR) of the inks in Examples 4-6 are all ≤4.2cc / m 2day, significantly lower than the 15.6cc / m2 of Comparative Example 2 2 ·day; water vapor transmission rate WVTR is ≤2.5g / m²·day, significantly lower than 9.8g / m²·day of Comparative Example 2; drying speed can reach 155m / min, significantly higher than 80m / min of Comparative Example 2; VOC emissions are all lower than 30g / L, a 62% decrease compared with Comparative Example 2; storage stability viscosity at 50℃ only increases by 11%, and no gel is produced, which is significantly better than Comparative Example 2.

[0145] In Comparative Example 2, the montmorillonite's diameter-to-thickness ratio was less than 30, resulting in numerous pores in the stacked layers, significantly increasing the ink's OTR. The crosslinker was added all at once, leading to runaway reaction at high temperatures and localized gelation. The viscosity doubled after seven days of storage. The mixing and stirring of titanium red with the montmorillonite caused wear and loss of moisture barrier properties. The present invention's process chain of split stripping, pre-crosslinking, and directional final curing resolves the paradox of dispersion, crosslinking, and arrangement in high-barrier water-based inks, achieving industry-leading OTRs of <4.5 cc / m²·day and VOCs of <30 g / L, far exceeding the performance of Comparative Example 2.

Claims

1. A water-based ink with barrier properties, characterized in that: Calculated by weight percentage, it includes the following components: Modified acrylic resin: 30-50%; pigment: 10-20%; montmorillonite: 5-15%; polyester dispersant: 1-3%; acetylenic diol wetting agent: 0.5-2%; silicone composite defoamer: 0.1-0.5%; low-viscosity modified siloxane leveling agent: 0.1-0.5%; aziridine crosslinker: 2-5%; the balance is deionized water. The modified acrylic resin has perfluorobutyl, glycidyl ether oxygen and hydroxyl grafted on its molecular chain. The particle size of the montmorillonite is less than 500 nm, and the aspect ratio is greater than 50.

2. The water-based ink with barrier properties according to claim 1, characterized in that: The pigment is selected from one of composite titanium red and resinized phthalocyanine blue; and the aziridine crosslinking agent is trimethylolpropane tris (2-methylaziridine) propionate.

3. A preparation process, characterized in that: The method is applicable to the water-based ink having barrier properties as claimed in any one of claims 1 to 2, comprising the following steps: S100, adding filler, 45-55% of a wetting agent, and 25-35% of a dispersant to 35-45% of deionized water, and ultrasonically treating at 55-65°C for 28-32 minutes to fully exfoliate the filler to form a pre-activated slurry with a fineness of less than 5 μm; in another container, mixing pigment, defoamer, and remaining dispersant with 15-25% of deionized water, and pre-dispersing by high-speed shearing to obtain a pigment concentrate; S200, adding the modified acrylic resin to the pre-activated slurry of step S100, heating to 72-78°C, slowly adding 45-55% of a cross-linking agent, and reacting for 0.8-1.2 hours; Cool the reaction system to 38-42°C at a cooling rate of ≤5°C / min, add 20-35% of deionized water, then add the pigment concentrate, leveling agent, and remaining wetting agent from step S100, stir evenly, add the remaining deionized water, stir at a low speed for 18-22 minutes, and mix evenly to obtain a mixed slurry; S300, grinding the mixed slurry of step S200 at a temperature of ≤35°C to a fineness of <5μm; immediately adding the remaining cross-linking agent after grinding, and then adding ammonia water, adjusting the pH to 8.2-8.6, stirring at a low speed for 8-12 minutes, and filtering to obtain the target product.

4. The preparation process according to claim 3, characterized in that In step S100, the power of the ultrasonic wave is 40 kHz, the rotation speed of the high-speed shear is 4500-5500 rpm, and the time is 12-18 min; in step S200, the heating rate is ≤5°C / min; and the rotation speed of the low-speed stirring is 200-300 rpm.

5. The preparation process according to claim 3, characterized in that: The preparation process of the modified acrylic resin comprises the following raw materials by weight: MMA: 35-45 parts, BA: 25-35 parts, HEA: 10-15 parts; SDS: 1.0-1.5 parts, emulsifier OP-10: 0.8-1.2 parts; APS: 0.8~1.2 parts; polymerization inhibitor hydroquinone: 0.01~0.02 parts; sodium bicarbonate: 0.1~0.3 parts; Deionized water: 120-150 parts; KH-560: 6-8 parts; tetraisopropyl titanate: 0.1-0.3 parts; PFBMA, 20-25 parts; CuBr: 4-5 parts; PMDETA: 10-12 parts; perfluoropolyether surfactant: 7-8 parts; KH-570 modified nano-SiO2: 2-4 parts; E-513-5 parts.

6. The preparation process according to claim 5, characterized in that: The preparation process of the modified acrylic resin comprises the following steps: Step 1: Dissolve 28-32% of SDS and buffer NaHCO3 in 20-25% of deionized water, heat to 78-82°C, and replace with nitrogen for 14-16 minutes; add 29-31% of initiator APS, stir at low speed; add 9-11% of pre-emulsion at a rate of 1 ml / min, keep warm at 79-81°C, and react for 28-32 minutes; Step 2: Dissolve the remaining initiator APS in the remaining deionized water to prepare a solution, and add the remaining pre-emulsion and initiator APS solution dropwise to the solution obtained in step 2 at a rate of 2 mL / min, controlling the temperature at 78-82°C; 28-32 minutes before the remaining pre-emulsion is added, cool to 74-76°C, add HEA, and rapidly mix for 8-12 minutes; Step 3: Cool to 60°C, add KH-560 in three batches, with an interval of 18 to 22 minutes between each batch, add sodium bicarbonate, adjust the pH to 6.5 to 7.5, then add a 5% ethanol solution of tetraisopropyl titanate, and keep the reaction warm for 2.8 to 3.2 hours; after post-treatment, obtain a dry resin intermediate product; Step 4: Add the intermediate product obtained in step 3, 2-bromoisobutyryl bromide, and triethylamine to a mixed solvent of THF and water, and react at 58-62°C under N2 protection for 1.8-2.2 hours; cool to 48-52°C, add PFBMA, CuBr, and PMDETA, and react under N2 protection for 11.5-12.5 hours; allow air to terminate the reaction, and add a perfluoropolyether surfactant; Step 5: Add the pre-dispersed KH-570 modified nano-SiO2 to the solution obtained in step 4 and stir evenly; heat to 74-76°C, add bisphenol A epoxy resin E-51, and stir for 0.9-1.1 h; cool to 35-40°C, adjust the pH to 7.5-8.0 with ammonia water, and filter the material through a 180-200 mesh filter to obtain a modified acrylic resin.

7. The preparation process according to claim 6, characterized in that: In step 1, the preparation process of the pre-emulsion includes the following steps: MMA, BA, and HEA (65-75% by weight) are premixed, and then added together with SDS (68-72% by weight), emulsifier OP-10, and hydroquinone (55-65% by weight) to deionized water (55-65% by weight), and stirred at a low speed for 30 minutes at 15-25° C. to obtain a pre-emulsion. In step 2, the mass of the additional HEA is 25-35% of the total mass of the HEA.

8. The preparation process according to claim 6, characterized in that: In step 3, the post-treatment method includes the following: cooling to below 25° C., adding a 5% CaCl2 solution and stirring for 15 minutes, and centrifuging for 8-12 minutes to obtain a middle-layer resin floc; washing the resin floc with an acetone-water mixed solvent 2-3 times at 60° C., and vacuum drying at 60-62° C. for 23-24 hours; the volume ratio of acetone to water is 1-2:1; the mass of the added 5% CaCl2 accounts for 4.9-5.1% of the total mass of the emulsion after the reaction in step 3 is completed.

9. The preparation process according to claim 6, characterized in that: In step 4, the mass ratio of the intermediate product, 2-bromoisobutyryl bromide, and triethylamine is 1:0.28~0.32:0.50~0.55; the resin intermediate product and THF are prepared at a solid content of 9~11%, and the volume ratio of THF to water is 2.2~2.5:

1.

10. The preparation process according to claim 6, characterized in that: The pre-dispersion method of KH-570 modified nano-SiO2 includes: controlling the temperature of an ice water bath to ≤30°C, ultrasonically dispersing the KH-570 modified nano-SiO2 in propylene glycol methyl ether for 20 to 30 minutes, the ultrasonic dispersion power is 300 to 400 W, and the mass ratio of KH-570 modified nano-SiO2 to propylene glycol methyl ether is 1:8 to 12.