Silica sol for ink-jet printing paper and preparation method thereof

Abstract

The invention discloses silica sol for ink-jet printing paper and a preparation method of the silica sol, and belongs to the technical field of silica sol materials. According to the silicon dioxide sol prepared by the method, in the aspect of film-forming property, the firmness and durability of a coating are improved by introducing composite silane to react with paper fibers, and local accumulation of holes is avoided by forming uniform particle size distribution through gradient hydrolytic condensation, so that the uniformity and compactness of a formed film are remarkably improved. In the ink-jet printing process, ink can be uniformly adsorbed and diffused, the definition and color uniformity of a printed picture are obviously improved, the edge of a printed pattern is clearer, and the printing quality is effectively improved. In addition, the preparation method disclosed by the invention has the advantages of clear steps, controllable conditions and easiness in industrial production. The novel silica sol product has a good application prospect, can meet the requirements of the ink-jet printing paper industry on high-performance coatings, and promotes the improvement of the quality of the ink-jet printing paper and the development of the industry.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of silica sol materials, and particularly relates to a silica sol for inkjet printing paper and a preparation method thereof. BACKGROUND

[0002] In order to improve the clarity of the printed picture, high-grade color inkjet paper needs a coating, one of the components of the coating is silica, which has excellent ink fixation performance and can form a specific microporous network to inhibit the diffusion of ink in the X and Y directions. This microporous network not only ensures excellent color effect, but also shortens the drying time. The application of nano-silica is very active at home and abroad, and it is used more and more widely in color inkjet paper coatings. Due to the high production cost of powder nano-silica, there are problems such as dispersion difficulty, and people have begun to explore methods for directly obtaining silica to prepare coating components, among which silica sol is mainly used.

[0003] Silica sol, also known as water glass, is an inorganic high-molecular poly-silicic acid colloidal solution with water as the dispersion phase. It is odorless and non-toxic, has a large specific surface area, and the particles themselves are colorless and transparent, without affecting the original color of the covered object. The particle size of silica sol is generally 5-80 nm, which is much smaller than that of general emulsions (particle size 0.1-10 μm). When mixed with other substances, the dispersion and permeability are very good. Silica sol molecules adhere to the surface of the substrate and filler particles, and as the water evaporates, the particles dehydrate to form a firm Si-O bond cross-linked three-dimensional network coating film. Therefore, silica sol has certain film-forming properties.

[0004] However, the film-forming properties of the currently used silica sol products cannot meet the needs of inkjet printing paper, mainly in the uniformity and density of the film. In the inkjet printing process, if the silica sol film-forming is not uniform, it will lead to inconsistent absorption and diffusion of ink on the surface of the paper, thereby affecting the clarity and color uniformity of the printed picture. If the film-forming density is not enough, it cannot effectively prevent the excessive penetration of ink into the paper, resulting in blurred edges of the printed pattern and reduced printing quality.

[0005] Therefore, it is of great practical significance to develop a silica sol that can meet the needs of inkjet printing paper and has good film-forming properties and stability. SUMMARY

[0006] The present application aims to provide a silica sol for inkjet printing paper and a preparation method thereof, to solve the problems of insufficient film-forming properties of existing silica sol and poor stability when mixed with other coating components. The silica sol prepared by the present application has good film-forming uniformity and density, which can effectively improve the printing clarity and color uniformity of inkjet printing paper, reduce the difficulty of coating preparation, and improve the performance of the final product.

[0007] To achieve the above technical purposes, the technical scheme adopted by the present application is: A preparation method of silica sol for ink-jet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40°C for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly adding a composite silane additive to the above system, maintaining 40°C for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: according to a volume ratio of 1:10, slowly adding the prepolymer to an aqueous dispersion system, first hydrolyzing at 45°C for 3h, then increasing the temperature to 60°C for 3h, and finally increasing the temperature to 80°C for 3h; (4) Surface modification: a. Cool the solution obtained in step (3) to room temperature; b. Slowly add a titanium dioxide sol with a particle size of 5-10nm to the solution under the condition of ultrasonic dispersion for 10 minutes; c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion; (5) Ion stabilization treatment: finally, add aluminum citrate and lanthanum nitrate to the solution obtained in step (4) to adjust the pH to 5.5, and then mature at room temperature for 24h, and then evaporate the solvent to obtain a silica sol with a solid content of 35-40%.

[0008] Further, the molar ratio of the composite silane additive to tetraethyl orthosilicate TEOS in step (2) is 1:4, and the composite silane additive comprises γ-aminopropyl triethoxysilane KH550 and γ-glycidyl ether propyl trimethoxysilane KH560, and the mass ratio of the two is 1:0.5.

[0009] Further, the aqueous dispersion system in step (3) comprises polyvinylpyrrolidone PVP K30 and polyvinyl alcohol, and the mass ratio of the two is 1:1, and the total mass concentration of the aqueous system is 10-15%; the polyvinyl alcohol is low alcoholysis degree polyvinyl alcohol PVA-1788 with an alcoholysis degree of 88%.

[0010] Further, the temperature increasing speed in step (3) is 1°C / min.

[0011] Further, the amount of titanium dioxide sol added in step (4) is 2-4% of the mass of the solution, and the solid content of the titanium dioxide sol is 20-30%.

[0012] Further, the amount of aluminum citrate added in step (5) is 0.3-0.7% of the mass of the solution, and the amount of lanthanum nitrate added is 0.1-0.3% of the mass of the solution.

[0013] A method for preparing silica sol for inkjet printing paper.

[0014] Traditional silica sol generally presents the following problems in inkjet printing paper applications: 1. Poor film-forming properties: When mixed with the binder in the ink, the sol zeta potential increases, and the electrostatic repulsion weakens, which can lead to agglomeration. 2. Problems such as uneven SiO2 particle size and accumulation can lead to macropore defects. Ink penetrates longitudinally along the macropores, causing feathering and resulting in a decrease in printing quality.

[0015] The prevalence of the above-mentioned problems has resulted in poor performance of silica sol in this field, particularly in terms of reduced paper contact angle and color performance. Therefore, this invention provides a novel silica sol product through a four-step modification process, suitable for use in inkjet printing paper.

[0016] Therefore, the present invention addresses the above problems by making the following improvements: First, a composite silane coupling agent is used for modification, introducing a tetraethyl orthosilicate (TEOS) hydrolysis and condensation reaction system. Grafting is performed using γ-aminopropyltriethoxysilane KH550 and γ-glycidoxypropyltrimethoxysilane KH560. The epoxy groups of KH-560 and the amino groups of KH-550 cross-link during the reaction, forming a strong chemical bond with the paper fibers after film formation. This multiple bonding effect between "silane-silane" and "silane-fiber" significantly enhances the adhesion between the coating and the paper substrate, making the coating strong, wear-resistant, and less prone to peeling, significantly improving the service life and durability of the printing paper. Simultaneously, the long-chain alkoxy groups (such as ethoxy and methoxy) in the composite silane molecules are gradually released during hydrolysis, hindering excessive aggregation of silica particles through steric hindrance. Combined with a gradient hydrolysis process, this results in a narrower particle size distribution in the final sol (PDI ≤ 0.15), avoiding film defects (such as localized pores and accumulation) caused by uneven particle size in traditional silica sols.

[0017] Subsequently, through gradient hydrolysis and condensation, three-stage temperature control (temperature rising rate ≤ 1 ℃ / min) of 45 ℃→60 ℃→80 ℃ is adopted to promote hydrolysis and condensation step by step. The appropriate temperature rising rate can control the reaction rate: slow hydrolysis at low temperature ensures uniformity, deepens hydrolysis at medium temperature, and accelerates condensation at high temperature to form stable sol particles. The addition of polyvinylpyrrolidone PVP K30 and polyvinyl alcohol as the water phase dispersion system can effectively prevent particle agglomeration and ensure the uniformity and stability of sol growth. PVA forms a hydrogen bond network with SiO2 surface through the hydroxyl group on the molecular chain, and cooperates with the steric hindrance effect of PVP, further improving the dispersion effect, making the final formed silica sol particle size distribution narrower, and the film forming performance more excellent. At the same time, uniform particle size distribution ensures uniform capillary force during drying, avoiding local accumulation of pores. At the same time, the introduction of composite silane can also optimize the growth process of silica particles, combined with the gradient hydrolysis process, it is easier to obtain sol with uniform particle size and stable dispersion. The sol forms a microporous layer with a dense structure and uniform pore size distribution after film forming. This structure can precisely control the absorption and fixation of ink, effectively prevent the horizontal diffusion and vertical excessive penetration of ink, thereby significantly reducing the "feathering" phenomenon of the printed pattern, making the character edge sharp and the image clear.

[0018] The additional 5-10 nm TiO2 particles are embedded in the interstitial space of the SiO2 particle accumulation. The dense microporous network effectively blocks the vertical penetration of ink, reducing the feathering diffusion distance. The addition of titanium dioxide can improve the surface performance of the sol, improve the weather resistance and ultraviolet resistance of the film forming, and also help to adjust the optical performance of the sol, improve the color performance of the inkjet printing paper.

[0019] By adding aluminum citrate and lanthanum nitrate, not only the pH value of the system is adjusted, but also a stable double-layer structure is formed on the surface of the sol particles. This double-layer structure can effectively improve the Zeta potential of the sol and enhance the electrostatic repulsion between particles, thereby preventing the occurrence of agglomeration. In addition, the introduction of a small amount of metal lanthanum nitrate La³⁺ also promotes the crosslinking reaction of the sol during the curing process, further improving the strength and quality of the subsequent film forming.

[0020] In summary, the beneficial effects of the present application are: The silica sol prepared by the present application solves the problems existing in the prior art. In terms of film forming, the introduction of composite silane reacts with the fibers of the paper to improve the firmness and durability of the coating, and the gradient hydrolysis and condensation forms uniform particle size distribution to avoid local accumulation of pores, which significantly improves the uniformity and density of the film. During the inkjet printing process, the ink can be uniformly adsorbed and diffused, the clarity and color uniformity of the printed image are significantly improved, and the edges of the printed pattern are clearer, effectively improving the printing quality.

[0021] In addition, the preparation method of the present application has clear steps and controllable conditions, and is easy to be industrialized. By accurately controlling the conditions of each reaction step, the required silica sol can be stably prepared. The new silica sol product has good application prospect, can meet the demand of the inkjet printing paper industry for high-performance coating, and promote the improvement of the quality of inkjet printing paper and the development of the industry. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Particle size distribution diagram of the silica sol obtained in Example 3 of the present application; Figure 2 Transmission electron microscope diagram of the silica sol obtained in Example 3 of the present application; Figure 3 Text printing effect of the printing paper obtained by using the silica sol of Application Example 3 and Comparative Examples 1-8. DETAILED DESCRIPTION

[0023] The technical solutions of the present application will be further described below in combination with specific examples, but are not limited thereto.

[0024] Example 1 A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate (TEOS) and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40℃ for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly adding a composite silane additive to the above system, maintaining 40℃ for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: according to a volume ratio of 1:10, slowly adding the prepolymer to an aqueous dispersion system, first hydrolyzing at 45℃ for 3h, then increasing the temperature to 60℃ for 3h of hydrolysis, and finally increasing the temperature to 80℃ for 3h of condensation; (4) Surface modification: a. cooling the solution obtained in step (3) to room temperature; b. slowly adding a titanium dioxide sol with a particle size of 5-10nm to the solution under the condition of ultrasonic dispersion for 10 minutes; c. continuing to ultrasonically treat for 1h to ensure uniform dispersion; (5) Ion stabilization treatment: finally adding aluminum citrate and lanthanum nitrate to the solution obtained in step (4) to adjust the pH to 5.5, and aging at room temperature for 24h, and then evaporating the solvent to obtain a silica sol with a solid content of 35%.

[0025] The molar ratio of the composite silane additive and tetraethyl orthosilicate TEOS in step (2) is 1:4, and the composite silane additive comprises γ-aminopropyl triethoxysilane KH550 and γ-glycidyl ether propyl trimethoxysilane KH560, and the mass ratio of the two is 1:0.5.

[0026] In step (3), the water phase dispersion system comprises polyvinylpyrrolidone PVP K30 and polyvinyl alcohol, and the mass ratio of the two is 1:1, and the total mass concentration of the water phase system is 10%; the polyvinyl alcohol is low alcoholysis degree polyvinyl alcohol PVA-1788, and the alcoholysis degree is 88%.

[0027] In step (3), the heating rate is 1℃ / min.

[0028] In step (4), the addition amount of titanium dioxide sol is 2% of the mass of the solution, and the solid content of the titanium dioxide sol is 20%.

[0029] In step (5), the addition amount of aluminum citrate is 0.3% of the mass of the solution, and the addition amount of lanthanum nitrate is 0.1% of the mass of the solution.

[0030] Example 2 A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40℃ for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly adding a composite silane additive to the above system, maintaining 40℃ for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: slowly adding the prepolymer to a water phase dispersion system according to a volume ratio of 1:10, first hydrolyzing at 45℃ for 3h, then increasing the temperature to 60℃ for 3h of hydrolysis, and finally increasing the temperature to 80℃ for 3h of condensation; (4) Surface modification: a. cooling the solution obtained in step (3) to room temperature; b. slowly adding titanium dioxide sol with a particle size of 5-10nm to the solution under the condition of ultrasonic dispersion for 10 minutes; c. continue to ultrasonic treatment for 1 hour to ensure uniform dispersion; (5) Ion stabilization treatment: finally adding aluminum citrate and lanthanum nitrate to the solution obtained in step (4) to adjust the pH to 5.5, and aging at room temperature for 24h to obtain a silica sol with a solid content of 37% after appropriate evaporation of the solvent.

[0031] The molar ratio of the composite silane additive and tetraethyl orthosilicate TEOS in step (2) is 1:4, and the composite silane additive comprises γ-aminopropyl triethoxysilane KH550 and γ-glycidyl ether propyl trimethoxysilane KH560, and the mass ratio of the two is 1:0.5.

[0032] In step (3), the water phase dispersion system comprises polyvinylpyrrolidone PVP K30 and polyvinyl alcohol, and the mass ratio of the two is 1:1, and the total mass concentration of the water phase system is 12%; the polyvinyl alcohol is low alcoholysis degree polyvinyl alcohol PVA-1788, and the alcoholysis degree is 88%.

[0033] In step (3), the heating rate is 1℃ / min.

[0034] In step (4), the addition amount of the titanium dioxide sol is 3% of the mass of the solution, and the solid content of the titanium dioxide sol is 25%.

[0035] In step (5), the addition amount of aluminum citrate is 0.5% of the mass of the solution, and the addition amount of lanthanum nitrate is 0.2% of the mass of the solution.

[0036] Example 3 A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40℃ for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly adding a composite silane additive to the above system, maintaining 40℃ for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: slowly adding the prepolymer to a water phase dispersion system according to a volume ratio of 1:10, first hydrolyzing at 45℃ for 3h, then increasing the temperature to 60℃ for 3h of hydrolysis, and finally increasing the temperature to 80℃ for 3h of condensation; (4) Surface modification: a. cooling the solution obtained in step (3) to room temperature; b. slowly adding titanium dioxide sol with a particle size of 5-10nm to the solution under the condition of ultrasonic dispersion for 10 minutes; c. continue to ultrasonic treatment for 1 hour to ensure uniform dispersion; (5) Ion stabilization treatment: finally adding aluminum citrate and lanthanum nitrate to the solution obtained in step (4) to adjust the pH to 5.5, and aging at room temperature for 24h, and then evaporating the solvent to obtain a silica sol with a solid content of 40%.

[0037] The molar ratio of the composite silane additive and tetraethyl orthosilicate TEOS in step (2) is 1:4, and the composite silane additive comprises γ-aminopropyl triethoxysilane KH550 and γ-glycidyl ether propyl trimethoxysilane KH560, and the mass ratio of the two is 1:0.5.

[0038] Step (3) The water phase dispersion system comprises polyvinylpyrrolidone PVP K30 and polyvinyl alcohol, and the mass ratio of the two is 1:1, and the total mass concentration of the water phase system is 15%; the polyvinyl alcohol is low alcoholysis degree polyvinyl alcohol PVA-1788, and the alcoholysis degree is 88%.

[0039] Step (3) The temperature increasing speed is 1℃ / min.

[0040] Step (4) The addition amount of the titanium dioxide sol is 4% of the mass of the solution, and the solid content of the titanium dioxide sol is 30%.

[0041] Step (5) The addition amount of aluminum citrate is 0.7% of the mass of the solution, and the addition amount of lanthanum nitrate is 0.3% of the mass of the solution.

[0042] Comparative Example 1 In this comparative example, the raw materials and process steps are the same as those in Example 3 except that the first step of hybrid modification is not performed. That is: A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS with an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40℃ for 1h to generate partially hydrolyzed silanol oligomers, and then maintaining the reaction at 40℃ for 1.5h; (2) Gradient hydrolysis and condensation: slowly adding the prepolymer to the water phase dispersion system at a volume ratio of 1:10, first hydrolyzing at 45℃ for 3h, then increasing the temperature to 60℃ for 3h, and finally increasing the temperature to 80℃ for 3h; (3) Surface modification: a. cooling the solution obtained in step (2) to room temperature; b. slowly adding titanium dioxide sol with a particle size of 5-10nm to the solution under the condition of ultrasonic dispersion for 10 minutes; c. continuing to ultrasonic treatment for 1h to ensure uniform dispersion; (4) Ion stabilization treatment: finally adding aluminum citrate and lanthanum nitrate to the solution obtained in step (3) to adjust the pH to 5.5, and then aging at room temperature for 24h to obtain a silica sol with a solid content of 40% after appropriate evaporation of the solvent.

[0043] Comparative Example 2 In this comparative example, the raw materials and process steps are the same as those in Example 3 except that the gradient hydrolysis is not performed. That is: A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40°C for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly adding a composite silane additive to the above system, maintaining 40°C for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Hydrolysis and condensation: slowly adding the prepolymer to an aqueous dispersion system at a volume ratio of 1:10, and condensing at 80°C for 9h; (4) Surface modification: a. Cool the solution obtained in step (3) to room temperature; b. Slowly add a titanium dioxide sol with a particle size of 5-10nm to the solution under ultrasonic dispersion for 10 minutes; c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion; (5) Ion stabilization treatment: finally, add aluminum citrate and lanthanum nitrate to the solution obtained in step (4) to adjust the pH to 5.5, and mature at room temperature for 24h, then evaporate the solvent appropriately to obtain a silica sol with a solid content of 40%.

[0044] Comparative Example 3 In this comparative example, the composition of the aqueous dispersion system is changed, and the other raw materials and process steps are the same as in Example 3. That is: In step (3), the aqueous dispersion system contains polyvinylpyrrolidone PVP K30, and the mass concentration of the aqueous system is 15%.

[0045] Comparative Example 4 In this comparative example, the composition of the aqueous dispersion system is changed, and the other raw materials and process steps are the same as in Example 3. That is: In step (3), the aqueous dispersion system contains polyvinyl alcohol, and the mass concentration of the aqueous system is 15%; the polyvinyl alcohol is low alcoholysis degree polyvinyl alcohol PVA-1788 with an alcoholysis degree of 88%.

[0046] Comparative Example 5 In this comparative example, the surface treatment is not performed, and the other raw materials and process steps are the same as in Example 3. That is: A preparation method of a silica sol for inkjet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mixing tetraethyl orthosilicate TEOS and an ethanol solution with a mass concentration of 40% at a volume ratio of 1:2, adding 0.1M oxalic acid to adjust the pH to 4.5-5.0, stirring at 40°C for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly add the composite silane additive to the above system, maintain 40°C for 1.5h, and obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: slowly add the prepolymer to the aqueous dispersion system according to a volume ratio of 1:10, first hydrolyze at 45°C for 3h, then raise the temperature to 60°C for 3h, and finally condense at 80°C for 3h; cool the obtained solution to room temperature; and ultrasonically disperse for 70 minutes; (4) Ionic stabilization treatment: finally, add aluminum citrate and lanthanum nitrate to the solution obtained in step (3) to adjust pH to 5.5, and after aging at room temperature for 24h, evaporate the solvent in an appropriate amount to obtain a silica sol with a solid content of 40%.

[0047] Comparative Example 6 In this comparative example, the raw materials and process steps are the same as in Example 3 except that no ionic stabilization treatment is performed. That is: A method for preparing a silica sol for ink-jet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: mix tetraethyl orthosilicate (TEOS) with an ethanol solution with a mass concentration of 40% according to a volume ratio of 1:2, add 0.1M oxalic acid to adjust pH to 4.5-5.0, and stir at 40°C for 1h to generate partially hydrolyzed silanol oligomers; (2) Silane grafting: slowly add the composite silane additive to the above system, maintain 40°C for 1.5h, and obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: slowly add the prepolymer to the aqueous dispersion system according to a volume ratio of 1:10, first hydrolyze at 45°C for 3h, then raise the temperature to 60°C for 3h, and finally condense at 80°C for 3h; (4) Surface modification: a. cool the solution obtained in step (3) to room temperature; b. slowly add a titanium dioxide sol with a particle size of 5-10nm to the solution under ultrasonic dispersion for 10 minutes; c. continue ultrasonic treatment for 1h to ensure uniform dispersion; (5) Post-treatment: after aging at room temperature for 24h, evaporate the solvent in an appropriate amount to obtain a silica sol with a solid content of 40%.

[0048] Comparative Example 7 In this comparative example, the raw materials and process steps are the same as in Example 3 except that the ionic stabilization treatment only uses aluminum citrate. That is: A method for preparing a silica sol for ink-jet printing paper, comprising the following preparation steps: (1) Pre-hydrolysis: TEOS was mixed with ethanol solution of 40% mass concentration at a volume ratio of 1:2, 0.1M oxalic acid was added to adjust the pH to 4.5-5.0, and the mixture was stirred at 40°C for 1h to form partially hydrolyzed silanol oligomers; (2) Silane grafting: the composite silane additive was slowly added to the above system, and the reaction was maintained at 40°C for 1.5h to obtain a silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: the prepolymer was slowly added to the aqueous dispersion system at a volume ratio of 1:10, first hydrolyzed at 45°C for 3h, then hydrolyzed at 60°C for 3h, and finally condensed at 80°C for 3h; (4) Surface modification: a. The solution obtained in step (3) was cooled to room temperature; b. The solution was slowly added with a titanium dioxide sol having a particle size of 5-10nm under ultrasonic dispersion for 10 minutes; c. The ultrasonic treatment was continued for 1h to ensure uniform dispersion; (5) Ionic stabilization treatment: aluminum citrate was finally added to the solution obtained in step (4) to adjust the pH to 5.5, and the solution was aged at room temperature for 24h, and then a proper amount of solvent was evaporated to obtain a silica sol having a solid content of 40%.

[0049] The amount of aluminum citrate added in step (5) was 0.7% of the mass of the solution.

[0050] Comparative Example 8 In this comparative example, the raw materials and process steps were the same as those in Example 3, except that only lanthanum nitrate was used for ionic stabilization treatment. That is, the amount of lanthanum nitrate added in step (5) was 0.3% of the mass of the solution.

[0051] Characterization of silica sol The silica sol was prepared according to the methods of Examples 1-3 and Comparative Examples 1-6, and the average particle size, PDI and particle size distribution of the product were determined by a laser particle size analyzer. 2-3 drops of the silica sol to be tested were taken into a cuvette and diluted with distilled water, and the average value was obtained by parallel determination for 3 times. PDI is a means to evaluate the dispersibility of the product, and the smaller the PDI, the more uniform the particle size distribution and the better the dispersibility. The morphology and particle size were observed by transmission electron microscopy.

[0052] Table 1: Test results of silica sol performance From the data in Table 1, we can see that the silica sol obtained in the examples of the present application has uniform particle size, small PDI coefficient, uniform particle size distribution and good dispersibility. The dispersibility of Comparative Examples 1-7, which changed the process, decreased to some extent.

[0053] The test results of the comparative examples and the comparative examples can further verify the key role of each process step on the performance of the silica sol. In Examples 1 to 3, because all the core steps are completely retained, the average particle size of the obtained product is small and the distribution is uniform, and the PDI value is significantly lower than that of the comparative example group. In contrast, Comparative Example 1 does not undergo hybrid modification, resulting in a slightly wide particle size distribution and slightly poor dispersibility; after the gradient hydrolysis is cancelled in Comparative Example 2, the particle size increases significantly and the PDI value increases, the particles are not uniform, and the dispersibility decreases; the composition of the aqueous dispersion system is changed in Comparative Examples 3 and 4, which not only affects the stability of the particles, but also makes the particle size distribution more uneven; in Comparative Example 5, the surface modification step is skipped, resulting in enhanced interaction between particles and poor dispersibility; in Comparative Example 6, the lack of ionic stabilization treatment may result in insufficient surface charge of the particles, which cannot effectively maintain the dispersed state, thereby increasing the particle size and widening the distribution.

[0054] Through the analysis of each comparative example, it can be seen that each process step has a significant effect on the performance of the final silica sol. For example, Example 3 has a lower PDI value and a more uniform particle size distribution than Comparative Examples 7 and 8, which indicates that the simultaneous use of aluminum citrate and lanthanum nitrate in the ionic stabilization treatment can significantly improve the dispersibility and stability. When only one of the substances is used, the interaction between particles may not be completely inhibited, resulting in a decrease in dispersibility.

[0055] In addition, the results of Comparative Examples 1 to 6 further demonstrate the importance of hybrid modification, gradient hydrolysis, and surface modification steps. These steps work together to not only optimize the morphology of the particles, but also enhance the overall stability of the system. In particular, the gradient hydrolysis process, by adjusting the reaction conditions in stages, allows the particles to form gradually in a relatively mild environment, avoiding the problem of uneven particle size caused by rapid aggregation.

[0056] The above results show that each process step plays an irreplaceable role in regulating the particle size, dispersibility, and stability of the silica sol. Transmission electron microscopy observation shows that the sample of the present application exhibits regular spherical particles with a concentrated particle size distribution and no obvious agglomeration between particles.

[0057] Application of silica sol in actual printing paper Coating preparation: PVA is prepared into a 20wt% suspension, heated to 90°C under constant stirring, and stirred at this temperature for 40-60min, then cooled to room temperature to obtain a PVA dispersion. The silica sol to be tested, the PVA dispersion, and the sodium polyacrylate are mixed in a mass ratio of 100:15:0.2 and poured into a sand mill, and stirred at high speed for 30-40min to make the coating into a uniform dispersion system, obtaining the coating liquid to be tested.

[0058] The coating liquid was diluted to 10% solid content using distilled water, A4 double collagen paper was taken, and the coating liquid was coated on the surface of the paper using a RDS40 # wire rod (coating thickness was 91.5 μm), and then placed in a 105 ℃ oven for baking for 3-5 min, and then taken out and cooled to obtain a paper sample.

[0059] Paper contact angle detection: The contact angle θ is a measure of the degree of wetting, when θ < 90°, partial wetting or complete wetting (0°); and when θ > 90°, non-wetting or complete non-wetting (180°).

[0060] Paper physical property test: whiteness: ISO 2470 whiteness meter.

[0061] Paper printing performance test: print seven-color solid blocks (C, M, Y, K, R, G, B), and test the color density using a color density meter (X-Rite528, Ailikesi (Shanghai) Color Technology Co., Ltd.), and calculate the sum value. The Lab value is tested using a color difference meter (UltraScan Pro, HunterLab, USA), and the color gamut is calculated using the color gamut calculation formula. The higher the color density sum value and the color gamut, the better the color presentation of the coating; gloss: tested according to GB / T 9754-2007, 3-5 points were taken from each paper, and the average value was taken as the final result. Gloss meter: Gloss Unit, 75° angle measurement.

[0062] Table 2 Paper printing performance test chart From the data in Table 2, it can be seen that the paper sample prepared by the embodiment of the present application performs well in various performance indicators. In terms of contact angle, the contact angles of examples 1-3 are all less than 90°, indicating that the paper has good wettability and can better absorb the coating liquid, which helps to improve the subsequent printing effect. In terms of whiteness, the whiteness of examples 1-3 is relatively high, and example 3 reaches 94.2, which is conducive to improving the clarity and color saturation of the printed image, making the printed content more bright and bright. In terms of gloss, the gloss of examples 1-3 is also relatively ideal, and example 3 leads with a gloss of 63, and a higher gloss can improve the appearance and texture of the paper, making the printed product look more upscale.

[0063] The color density sum value and the color gamut are important indicators for measuring the color presentation of the coating. The color density sum value and the color gamut of examples 1-3 are all significantly higher than those of the comparative examples, especially the color density sum value of example 3 reaches 10.25, and the color gamut is 348000, which indicates that the silica sol prepared by using the embodiment of the present application applied to the printing paper can make the printed image color more bright, rich, and the level more distinct.

[0064] By contrast, the comparative examples 1-6, in each performance index is not as good as the example. By comparative analysis of the examples and the comparative examples, the influence of each process step on the final paper performance can be further clarified. Comparative example 1 does not carry out silane hybrid modification, although the contact angle decreases, the wettability is enhanced, but the whiteness, gloss and color gamut and other key indicators are all decreased, indicating that hybrid modification also plays an important role in improving the stability of coating structure and color performance. After canceling the gradient hydrolysis in comparative example 2, the contact angle increases to 65.6°, the wettability becomes worse, and the whiteness and color density also decrease significantly, which shows that the gradient hydrolysis can effectively control the particle size and distribution of the particles, thereby optimizing the film forming performance of the coating liquid. The performances of the paper of comparative examples 3 and 4 are all decreased to different degrees after changing the composition of the aqueous dispersion system, which reflects that the selection of the aqueous dispersion system is crucial to the stability of the silica sol particles and the quality of the coating. Comparative example 5 lacks the surface modification step, and its contact angle increases and color density and color gamut decrease significantly, which shows that surface modification helps to improve the interaction between the particles and the substrate, thereby improving the uniformity and adhesion of the coating. Comparative example 6 does not carry out ion stabilization treatment, resulting in further increase of the contact angle, and significant decrease of the gloss and color gamut, which shows that ion stabilization treatment is indispensable to maintain the dispersion state of the particles and improve the coating performance. The synergistic effect of single aluminum citrate or lanthanum nitrate in comparative examples 7-8 is reduced, and the stabilization effect is relatively reduced. In summary, the silica sol prepared by the complete process flow in the example of the present application applied to the printing paper shows excellent performance in contact angle, whiteness, gloss, color density and color gamut, which fully verifies the necessity and synergistic effect of each process step. These results not only reflect the scientificity and practicability of the method of the present application, but also provide an important reference for the development of high-performance inkjet printing paper.

[0065] The text quality is also an important part of the inkjet printing quality. We analyze and evaluate the text quality by comparing the area of the printed text. The Patriot digital observation king is used to shoot and observe the microstructure of the line.

[0066] From Figure 3 As can be seen, the text area of the example 3 of the present application is smaller, and the text edge is clear, while the comparative examples have relatively large area and obvious feathering effect.

[0067] It should be noted that the above examples are only part of the preferred modes of implementing the present application, not all. Obviously, based on the above examples of the present application, all other examples obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

Claims

1. A method for preparing silica sol for inkjet printing paper, characterized in that, The preparation steps include the following: (1) Pre-hydrolysis: Tetraethyl orthosilicate (TEOS) and 40% ethanol solution were mixed at a volume ratio of 1:

2. 0.1M oxalic acid was added to adjust the pH to 4.5-5.

0. The mixture was stirred at 40°C for 1 hour to generate partially hydrolyzed silanol oligomers. (2) Silane grafting: The composite silane additive was slowly added dropwise to the above system, and the reaction was maintained at 40°C for 1.5 h to obtain the silane-modified hybrid prepolymer; (3) Gradient hydrolysis and condensation: The prepolymer is slowly added to the aqueous dispersion system at a volume ratio of 1:

10. First, it is hydrolyzed at 45℃ for 3 hours, then heated to 60℃ for 3 hours, and finally heated to 80℃ for condensation for 3 hours. (4) Surface modification: a. Cool the solution obtained in step (3) to room temperature; b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution; c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion; (5) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate are added to the solution obtained in step (4), the pH is adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent is evaporated to obtain silica sol with a solid content of 35-40%.

2. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, The molar ratio of the composite silane additive and tetraethyl orthosilicate (TEOS) in step (2) is 1:

4. The composite silane additive contains γ-aminopropyltriethoxysilane KH550 and γ-glycidoxypropyltrimethoxysilane KH560, with a mass ratio of 1:0.

5.

3. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, Step (3) The aqueous dispersion system contains polyvinylpyrrolidone (PVP) K30 and polyvinyl alcohol in a mass ratio of 1:1, and the total mass concentration of the aqueous system is 10-15%; the polyvinyl alcohol is low-hydrolysis polyvinyl alcohol PVA-1788 with a degree of hydrolysis of 88%.

4. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, Step (3) The heating rate is 1℃ / min.

5. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, In step (4), the amount of titanium dioxide sol added is 2-4% of the solution mass, and the solid content of titanium dioxide sol is 20-30%.

6. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, In step (5), the amount of aluminum citrate added is 0.3-0.7% of the solution mass, and the amount of lanthanum nitrate added is 0.1-0.3% of the solution mass.

7. A silica sol obtained by the preparation method of silica sol for inkjet printing paper according to any one of claims 1-6.

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