Silica sol for inkjet printing paper and method for preparing the same

Abstract

The application discloses a kind of silica sol for ink-jet printing paper and a preparation method thereof, belonging to the technical field of silica sol material.The silica sol prepared by the application has improved coating firmness and durability in film-forming property by introducing composite silane to react with paper fibers, and uniform particle size distribution is formed by gradient hydrolysis and condensation to avoid local accumulation of holes, so that the uniformity and compactness of the film are significantly improved.In the ink-jet printing process, ink can be uniformly adsorbed and diffused, and the clarity and color uniformity of the printed image are significantly improved, the edges of the printed pattern are clearer, and the printing quality is effectively improved.In addition, the preparation method of the application has clear steps and controllable conditions, and is easy to industrialize.This new type of silica sol product has good application prospect and can meet the demand of ink-jet printing paper industry for high-performance coating, and promote the improvement of ink-jet printing paper quality and the development of the industry.

Description

Technical Field

[0001] This invention belongs to the field of silica sol technology, specifically relating to a silica sol for inkjet printing paper and its preparation method. Background Technology

[0002] To improve the clarity of printed images, high-grade inkjet paper requires a coating. One component of this coating is silica, which possesses excellent ink-fixing properties and can form a specific microporous network that inhibits ink diffusion in the X and Y directions. This microporous network not only ensures excellent color effects but also shortens drying time. Research on the application of nano-silica is very active both domestically and internationally, and its use in inkjet paper coatings is becoming increasingly widespread. Due to the high production cost and dispersion difficulties of powdered nano-silica, researchers have begun to explore methods for directly obtaining silica to prepare coating components, primarily using silica sol.

[0003] Silica sol, also known as silica water glass, is an inorganic polymeric polyvinylidene silicate colloidal solution with water as the dispersed phase. It is odorless and non-toxic, possesses a large specific surface area, and the particles themselves are colorless and transparent, not affecting the original color of the coated material. Silica sol particles typically range from 5 to 80 nm in size, much smaller than typical emulsions (0.1 to 10 μm), exhibiting excellent dispersibility and permeability when mixed with other substances. Silica sol molecules adhere to the surface of the substrate and filler particles; as water evaporates and dehydration occurs between the particles, a strong Si-O bonded cross-linked three-dimensional network coating is formed. Therefore, silica sol possesses certain film-forming properties.

[0004] However, currently used silica sol products do not meet the film-forming requirements of inkjet printing paper, mainly due to insufficient uniformity and density of the film. During inkjet printing, if the silica sol film is unevenly formed, the ink's adsorption and diffusion on the paper surface will be inconsistent, affecting the clarity and color uniformity of the printed image. Insufficient film density, on the other hand, cannot effectively prevent excessive ink penetration into the paper, resulting in blurred edges and reduced print quality.

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

[0006] This invention aims to provide a silica sol for inkjet printing paper and its preparation method, to solve the problems of insufficient film-forming properties and poor stability when mixed with other coating components in existing silica sols. The silica sol prepared by this invention has good film 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-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0009] (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.

[0010] (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;

[0011] (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.

[0012] (4) Surface modification:

[0013] a. Cool the solution obtained in step (3) to room temperature;

[0014] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0015] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0016] (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%.

[0017] Furthermore, in step (2), the molar ratio of the composite silane additive to tetraethyl orthosilicate (TEOS) is 1:4, and the composite silane additive contains γ-aminopropyltriethoxysilane KH550 and γ-glycidoxypropyltrimethoxysilane KH560, with a mass ratio of 1:0.5.

[0018] Furthermore, the aqueous dispersion system in step (3) 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%.

[0019] Furthermore, in step (3), the heating rate is 1℃ / min.

[0020] Furthermore, in step (4), the amount of titanium dioxide sol added is 2-4% of the solution mass, and the solid content of the titanium dioxide sol is 20-30%.

[0021] Furthermore, 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.

[0022] A method for preparing silica sol for inkjet printing paper.

[0023] Traditional silica sol generally presents the following problems in inkjet printing paper applications:

[0024] 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.

[0025] 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.

[0026] 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.

[0027] Therefore, the present invention addresses the above problems by making the following improvements:

[0028] 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.

[0029] Subsequent gradient hydrolysis and condensation were achieved through a three-stage temperature control process (45℃→60℃→80℃, with a heating rate ≤1℃ / min) to promote hydrolysis and condensation stepwise. The gradient heating at a suitable rate controlled the reaction rate: slow hydrolysis at low temperatures ensured uniformity, hydrolysis deepened at medium temperatures, and condensation accelerated at high temperatures to form stable sol particles. The addition of polyvinylpyrrolidone (PVP) K30 and polyvinyl alcohol as an aqueous dispersion system effectively prevented particle agglomeration, ensuring the uniformity and stability of sol growth. PVA formed a hydrogen bond network with the SiO2 surface through hydroxyl groups on its molecular chain, synergistically enhancing the dispersion effect with the steric hindrance effect of PVP, resulting in a narrower particle size distribution and superior film-forming performance in the final silica sol. Simultaneously, the uniform particle size distribution ensured uniform capillary force during drying, avoiding localized accumulation of pores. Furthermore, the introduction of composite silanes optimized the silica particle growth process, and combined with the gradient hydrolysis process, made it easier to obtain a sol with uniform particle size and stable dispersion. After the sol-gel is formed, it creates a dense microporous layer with a uniform pore size distribution. This structure allows for precise control of ink absorption and fixation, effectively preventing lateral ink diffusion and excessive vertical penetration, thereby significantly reducing the "feathering" phenomenon in printed patterns and resulting in sharp text edges and clear images.

[0030] The added 5-10nm TiO2 particles are embedded in the gaps between SiO2 particles. The denser microporous network effectively blocks the longitudinal penetration of ink and reduces the feathering diffusion distance. The addition of titanium dioxide can improve the surface properties of the sol, enhance the weather resistance and UV resistance of the film, and also help to adjust the optical properties of the sol, thereby improving the color performance of inkjet printing paper.

[0031] By adding aluminum citrate and lanthanum nitrate, not only was the pH of the system adjusted, but a stable electric double layer structure was also formed on the surface of the sol particles. This electric double layer structure can effectively increase the zeta potential of the sol and enhance the electrostatic repulsion between particles, thereby preventing agglomeration. In addition, the introduction of a small amount of metallic lanthanum nitrate (La³⁺) also promotes the cross-linking reaction of the sol during the aging process, further improving the strength and quality of the subsequent film formation.

[0032] In summary, the beneficial effects of this invention are as follows:

[0033] The silica sol prepared by this invention effectively solves the problems existing in current silica sols. Regarding film-forming properties, the introduction of composite silanes to react with paper fibers improves the coating's strength and durability. Gradient hydrolysis and condensation form a uniform particle size distribution, avoiding localized accumulation of voids, thus significantly improving the uniformity and density of the film. During inkjet printing, the ink can be uniformly adsorbed and diffused, resulting in significantly improved clarity and color uniformity of the printed image, sharper edges, and effectively enhanced print quality.

[0034] Furthermore, the preparation method of this invention has clearly defined steps and controllable conditions, making it easy for industrial production. By precisely controlling the conditions of each reaction step, silica sol that meets the requirements can be stably prepared. This novel silica sol product has promising application prospects, meeting the inkjet printing paper industry's demand for high-performance coatings and promoting the improvement of inkjet printing paper quality and the industry's development. Attached Figure Description

[0035] Figure 1 This is a particle size distribution diagram of the silica sol obtained in Example 3 of the present invention;

[0036] Figure 2 This is a transmission electron microscope (TEM) image of the silica sol obtained in Example 3 of the present invention;

[0037] Figure 3 The text printing effect of the printing paper obtained by applying the silica sol in Example 3 and Comparative Examples 1-8 is shown. Detailed Implementation

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0039] Example 1

[0040] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0041] (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.

[0042] (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;

[0043] (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.

[0044] (4) Surface modification:

[0045] a. Cool the solution obtained in step (3) to room temperature;

[0046] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0047] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0048] (5) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (4), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 35%.

[0049] 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.

[0050] 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%; the polyvinyl alcohol is low-hydrolysis polyvinyl alcohol PVA-1788 with a degree of hydrolysis of 88%.

[0051] Step (3) The heating rate is 1℃ / min.

[0052] In step (4), the amount of titanium dioxide sol added is 2% of the solution mass, and the solid content of titanium dioxide sol is 20%.

[0053] In step (5), the amount of aluminum citrate added is 0.3% of the solution mass, and the amount of lanthanum nitrate added is 0.1% of the solution mass.

[0054] Example 2

[0055] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0056] (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.

[0057] (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;

[0058] (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.

[0059] (4) Surface modification:

[0060] a. Cool the solution obtained in step (3) to room temperature;

[0061] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0062] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0063] (5) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (4), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 37%.

[0064] 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.

[0065] 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 12%; the polyvinyl alcohol is low-hydrolysis polyvinyl alcohol PVA-1788 with a degree of hydrolysis of 88%.

[0066] Step (3) The heating rate is 1℃ / min.

[0067] In step (4), the amount of titanium dioxide sol added is 3% of the solution mass, and the solid content of titanium dioxide sol is 25%.

[0068] In step (5), the amount of aluminum citrate added is 0.5% of the solution mass, and the amount of lanthanum nitrate added is 0.2% of the solution mass.

[0069] Example 3

[0070] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0071] (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.

[0072] (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;

[0073] (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.

[0074] (4) Surface modification:

[0075] a. Cool the solution obtained in step (3) to room temperature;

[0076] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0077] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0078] (5) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (4), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 40%.

[0079] 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.

[0080] 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 15%; the polyvinyl alcohol is low-hydrolysis polyvinyl alcohol PVA-1788 with a degree of hydrolysis of 88%.

[0081] Step (3) The heating rate is 1℃ / min.

[0082] In step (4), the amount of titanium dioxide sol added is 4% of the solution mass, and the solid content of titanium dioxide sol is 30%.

[0083] In step (5), the amount of aluminum citrate added is 0.7% of the solution mass, and the amount of lanthanum nitrate added is 0.3% of the solution mass.

[0084] Comparative Example 1

[0085] In this comparative example, except for omitting the first-step hybridization modification, the raw materials and process steps are the same as in Example 3. That is:

[0086] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0087] (1) Pre-hydrolysis: Tetraethyl orthosilicate (TEOS) and a 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. The reaction was then maintained at 40°C for another 1.5 hours.

[0088] (2) 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.

[0089] (3) Surface modification:

[0090] a. Cool the solution obtained in step (2) to room temperature;

[0091] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0092] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0093] (4) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (3), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 40%.

[0094] Comparative Example 2

[0095] In this comparative example, except for the absence of gradient hydrolysis, the raw materials and process steps are the same as in Example 3. That is:

[0096] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0097] (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.

[0098] (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;

[0099] (3) Hydrolysis and condensation: The prepolymer was slowly added to the aqueous dispersion system at a volume ratio of 1:10, and the temperature was raised to 80℃ for condensation for 9 hours.

[0100] (4) Surface modification:

[0101] a. Cool the solution obtained in step (3) to room temperature;

[0102] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0103] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0104] (5) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (4), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 40%.

[0105] Comparative Example 3

[0106] In this comparative example, except for the change in the composition of the aqueous dispersion system, the raw materials and process steps are the same as in Example 3. That is:

[0107] Step (3) The aqueous dispersion system contains polyvinylpyrrolidone (PVP) K30, and the mass concentration of the aqueous system is 15%.

[0108] Comparative Example 4

[0109] In this comparative example, except for the change in the composition of the aqueous dispersion system, the raw materials and process steps are the same as in Example 3. That is:

[0110] Step (3) The aqueous dispersion system contains polyvinyl alcohol, and the mass concentration of the aqueous system is 15%; the polyvinyl alcohol is low-hydrolysis polyvinyl alcohol PVA-1788, with a degree of hydrolysis of 88%.

[0111] Comparative Example 5

[0112] In this comparative example, except for the absence of surface treatment, the raw materials and process steps are the same as in Example 3. That is:

[0113] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0114] (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.

[0115] (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;

[0116] (3) Gradient hydrolysis and condensation: The prepolymer was slowly added to the aqueous dispersion system at a volume ratio of 1:10. First, it was hydrolyzed at 45℃ for 3 hours, then heated to 60℃ for 3 hours, and finally heated to 80℃ for condensation for 3 hours. The resulting solution was cooled to room temperature and ultrasonically dispersed for 70 minutes.

[0117] (4) Ion stabilization treatment: Finally, aluminum citrate and lanthanum nitrate were added to the solution obtained in step (3), the pH was adjusted to 5.5, and after aging at room temperature for 24 hours, an appropriate amount of solvent was evaporated to obtain silica sol with a solid content of 40%.

[0118] Comparative Example 6

[0119] In this comparative example, except for the absence of ion stabilization treatment, the raw materials and process steps are the same as in Example 3. That is:

[0120] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0121] (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.

[0122] (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;

[0123] (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.

[0124] (4) Surface modification:

[0125] a. Cool the solution obtained in step (3) to room temperature;

[0126] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0127] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0128] (5) Post-treatment: After aging at room temperature for 24 hours, the solvent is evaporated in appropriate amount to obtain silica sol with a solid content of 40%.

[0129] Comparative Example 7

[0130] In this comparative example, except that only aluminum citrate was used for the ion stabilization treatment, all other raw materials and process steps were the same as in Example 3. That is:

[0131] A method for preparing silica sol for inkjet printing paper includes the following preparation steps:

[0132] (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.

[0133] (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;

[0134] (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.

[0135] (4) Surface modification:

[0136] a. Cool the solution obtained in step (3) to room temperature;

[0137] b. Under ultrasonic dispersion for 10 minutes, slowly add titanium dioxide sol with a particle size of 5-10 nm into the solution;

[0138] c. Continue ultrasonic treatment for 1 hour to ensure uniform dispersion;

[0139] (5) Ion stabilization treatment: Finally, aluminum citrate is added to the solution obtained in step (4) to adjust the pH to 5.5. After aging at room temperature for 24 hours, an appropriate amount of solvent is evaporated to obtain silica sol with a solid content of 40%.

[0140] Step (5) The amount of aluminum citrate added is 0.7% of the solution mass.

[0141] Comparative Example 8

[0142] In this comparative example, except that only lanthanum nitrate was used for the ion stabilization treatment, all other raw materials and process steps were the same as in Example 3. That is, in step (5), the amount of lanthanum nitrate added was 0.3% of the solution mass.

[0143] Characterization of silica sol

[0144] Silica sol was prepared according to the methods of Examples 1-3 and Comparative Examples 1-6 of this invention. The average particle size, PDI, and particle size distribution of the product were measured using a laser particle size analyzer. Two to three drops of the silica sol to be tested were placed in a cuvette, diluted with distilled water, and measured in triplicate, with the average value taken. PDI is a means of evaluating the dispersibility of the product; the smaller the PDI, the more uniform the particle size distribution and the better the dispersibility. The morphology and particle size were observed using a transmission electron microscope.

[0145] Table 1. Test results of silica sol performance

[0146]

[0147] As can be seen from the data in Table 1, the silica sol particles obtained in the embodiments of the present invention have uniform particle size, small PDI coefficient, uniform particle size distribution, and good dispersibility. In contrast, comparative examples 1-7, which changed the process, all showed a certain degree of decrease in dispersion stability.

[0148] By comparing the test results of the examples and comparative examples, the key role of each process step in the performance of silica sol can be further verified. In Examples 1 to 3, since all core steps were fully retained, the average particle size of the resulting products was smaller and more uniformly distributed, and the PDI value was significantly lower than that of the comparative example group. In contrast, Comparative Example 1, due to the lack of hybridization modification, resulted in a slightly wider particle size distribution and slightly poorer dispersibility; Comparative Example 2, after eliminating gradient hydrolysis, showed a significant increase in particle size and PDI value, with uneven particle formation and reduced dispersibility; Comparative Examples 3 and 4 changed the composition of the aqueous dispersion system, which not only affected the stability of the particles but also made the particle size distribution more uneven; Comparative Example 5 skipped the surface modification step, resulting in enhanced interparticle interactions and poorer dispersibility; Comparative Example 6 lacked ion stabilization treatment, which may have led to insufficient surface charge on the particles, making it impossible to effectively maintain the dispersed state, thereby increasing the particle size and widening the distribution.

[0149] Analysis of the comparative examples reveals that each process step significantly impacts the final silica sol performance. For instance, Example 3 exhibits a lower PDI value and more uniform particle size distribution compared to Comparative Examples 7 and 8, indicating that the simultaneous use of aluminum citrate and lanthanum nitrate during ion stabilization significantly improves dispersibility and stability. Conversely, using only one of these substances may not completely suppress interparticle interactions, leading to decreased dispersibility.

[0150] Furthermore, the results of Comparative Examples 1 to 6 further confirm the importance of steps such as hybridization modification, gradient hydrolysis, and surface modification. These steps work together to not only optimize particle morphology but also enhance the overall stability of the system. In particular, the gradient hydrolysis process, by controlling the reaction conditions in stages, allows particles to gradually form in a relatively mild environment, avoiding the particle size inhomogeneity problem caused by rapid aggregation.

[0151] The above results demonstrate that each process step plays an irreplaceable role in controlling the particle size, dispersibility, and stability of the silica sol. Transmission electron microscopy revealed that the samples from this embodiment exhibited regular spherical particles with a concentrated particle size distribution and no obvious agglomeration.

[0152] Application of silica sol in actual printing paper

[0153] Coating preparation: Prepare a 20wt% PVA suspension, heat it to 90℃ with continuous stirring, and continue stirring at this temperature for 40–60 min. Cool to room temperature to obtain a PVA dispersion. Mix the silica sol to be tested, the PVA dispersion, and sodium polyacrylate at a mass ratio of 100:15:0.2 and pour the mixture into a multi-purpose sand mill. Stir at high speed for 30–40 min to make the coating a uniform dispersion system, thus obtaining the coating solution to be tested.

[0154] Dilute the coating solution to 10% solids content using distilled water. Take A4 double-sided colloid paper and use an RDS40# wire rod to apply the coating solution to the paper surface (coating thickness is 91.5μm). Place it in a 105 ℃ oven and bake for 3-5 minutes. Remove and cool to obtain a paper sample.

[0155] Paper contact angle detection:

[0156] The contact angle θ is a measure of the degree of wetting. When θ < 90°, it is partially or completely wetted (0°); while when θ > 90°, it is not wetted or not wetted at all (180°).

[0157] Paper physical properties test: Whiteness: ISO 2470 whiteness meter.

[0158] Paper printing performance testing: Print seven pure color blocks (C, M, Y, K, R, G, B), and use a color density meter (X-Rite528, Ailise (Shanghai) Color Technology Co., Ltd.) to test the color density and calculate the sum value. Use a colorimeter (UltraScan Pro, Huntley Corporation, USA) to test the Lab value and calculate the color gamut using the color gamut calculation formula. The higher the color density sum value and color gamut, the better the coating's color rendering. Gloss: Tested according to GB / T 9754—2007, taking 3-5 points per sheet, and using the average value as the final result. Gloss meter: Gloss Unit, measured at a 75° angle.

[0159] Table 2. Paper Printing Performance Test Chart

[0160]

[0161] As can be seen from the data in Table 2, the paper samples obtained in the embodiments of the present invention exhibit excellent performance in all performance indicators. Regarding the 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 improve the subsequent printing effect. In terms of whiteness, Examples 1-3 all have high whiteness, with Example 3 reaching 94.2, which is beneficial for improving the clarity and color saturation of the printed image, making the printed content more vibrant and bright. Regarding gloss, Examples 1-3 also have relatively ideal gloss, with Example 3 leading with a gloss of 63. Higher gloss can enhance the appearance and texture of the paper, making the printed products look more upscale.

[0162] Color density and color gamut are important indicators for evaluating the color performance of a coating. The color density and color gamut of Examples 1-3 are significantly higher than those of the comparative examples, especially Example 3, which has a color density and color gamut of 10.25 and a color gamut of 348,000. This indicates that the silica sol prepared using the examples of this invention, when applied to printing paper, can make the printed images more vibrant, richer, and more distinct in color.

[0163] In contrast, Comparative Examples 1-6 showed inferior performance compared to the Example in all performance indicators. Through comparative analysis of the Comparative Examples and the Example, the impact of each process step on the final paper performance can be further clarified. Comparative Example 1, lacking silane hybrid modification, exhibited a decreased contact angle and improved wettability, but key indicators such as whiteness, gloss, and color gamut all declined, indicating that hybrid modification plays a crucial role in improving coating structural stability and color performance. Comparative Example 2, after eliminating gradient hydrolysis, saw an increased contact angle to 65.6°, worsened wettability, and significantly reduced whiteness and color density. This demonstrates that gradient hydrolysis effectively controls particle size and distribution, thereby optimizing the film-forming properties of the coating solution. Comparative Examples 3 and 4, by altering the composition of the aqueous dispersion system, showed varying degrees of decline in all paper properties, reflecting the critical importance of the choice of aqueous dispersion system for the stability of silica sol particles and coating quality. Comparative Example 5, lacking a surface modification step, exhibited an increased contact angle and significantly reduced color density and gamut. This indicates that surface modification helps improve the interaction between particles and the substrate, thereby enhancing coating uniformity and adhesion. Comparative Example 6, without ion stabilization treatment, resulted in a further increase in contact angle and a significant decrease in gloss and gamut, demonstrating that ion stabilization is indispensable for maintaining particle dispersion and improving coating performance. Comparative Examples 7-8, using only aluminum citrate or lanthanum nitrate, showed reduced synergistic effects and relatively lower stabilizing effects. In summary, the silica sol prepared through the complete process of this invention, when applied to printing paper, exhibits excellent performance in terms of contact angle, whiteness, gloss, color density, and gamut, fully validating the necessity and synergistic effects of each process step. These results not only demonstrate the scientific validity and practicality of the method of this invention but also provide important reference for the development of high-performance inkjet printing paper.

[0164] Text quality is also a crucial aspect of inkjet print quality. We analyze and evaluate text quality by comparing the area of ​​printed black text. We also use a Patriot Digital Observation King to photograph and observe the microscopic structure of lines.

[0165] from Figure 3 As we can see, the text area obtained in Embodiment 3 of the present invention is smaller and the text edges are clearer, while the comparative embodiment has a relatively larger area and a significant feathering effect.

[0166] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

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: A composite silane additive is slowly added dropwise to a partially hydrolyzed silanol oligomer system, and the reaction is maintained at 40°C for 1.5 h to obtain a silane-modified hybrid prepolymer; the molar ratio of the composite silane additive to tetraethyl orthosilicate (TEOS) is 1:4, and the composite silane additive contains γ-aminopropyltriethoxysilane KH550 and γ-glycidoxypropyltrimethoxysilane KH560, with a mass ratio of 1:0.5; (3) Gradient hydrolysis and condensation: The hybrid prepolymer was slowly added to the aqueous dispersion system at a volume ratio of 1:

10. First, it was hydrolyzed at 45℃ for 3 hours, then the temperature was raised to 60℃ for 3 hours, and finally the temperature was raised to 80℃ for condensation for 3 hours. The heating rate was 1℃ / min. The aqueous dispersion system contained polyvinylpyrrolidone (PVP K30) and polyvinyl alcohol (PVA) in a mass ratio of 1:

1. The PVA was low-hydrolysis polyvinyl alcohol PVA-1788 with a degree of hydrolysis of 88%. (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%; 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.

2. The method for preparing silica sol for inkjet printing paper according to claim 1, characterized in that, Step (3) The total mass concentration of the aqueous dispersion system is 10-15%.

3. 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%.

4. A silica sol prepared by the method for preparing silica sol for inkjet printing paper according to any one of claims 1-3.

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