Preparation method and application of cationic silica sol

Abstract

The invention discloses a preparation method and application of cationic silica sol, the cationic silica sol is obtained through reaction of acidic silica sol and organic aluminum salt hydrolysate, in the process, due to the fact that colloidal particle charges are reversely changed from negative to positive, Zeta potential is greatly increased compared with that of original acidic silica sol, and mutual repulsive force between colloidal particles is enhanced; according to the preparation method, the stability of silica sol with different particle sizes can be improved, the storage time of acidic silica sol is greatly prolonged, the organic compatibility of a system is also improved, meanwhile, good application in the fields of textiles, films, coatings, paper, printing ink and the like is met, and the problem that traditional anionic silica sol is poor in compounding property in the industries is solved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of silica gel preparation, in particular to a preparation method and application of cationic silica sol. BACKGROUND

[0002] Silica is a very important chemical substance, mainly in an amorphous state, with a typical size of 5-150 nm, and quasi-spherical or chain-like secondary agglomerates are shown by transmission electron microscopy. The pore size of mesoporous silica can reach 2-10 nm, and the specific surface area is 600-1500 m 2 / g, while the specific surface area of solid silica is generally 200-300 m 2 / g. Nanosilica has a rich chemical surface, with 4-5 -Si-OH per square nanometer, so the number of surface hydroxyl groups of a 20 nm particle is about 10 19 / g, giving other high hydrophilicity (water contact angle <20°) and modular modification (silane, phosphoric acid, polymer grafting, metal ion or non-metal ion modification). Optical properties, the visible region refractive index of silica is 1.46, close to that of polymers, so it can be filled in large quantities while maintaining transparency. In the ultraviolet light range of 200-360 nm, there is strong scattering / absorption, tests show that the addition of 2 wt% can reduce the ultraviolet light transmittance of PET film by 90%, while it does not yellow. The bulk melting point of silica is as high as 1723 K, which is a good high-temperature resistant material and has a wide application in casting and building materials. Nanosilica filling can significantly improve the tensile strength of epoxy resin and significantly reduce the wear rate. Under low shear, silica forms a three-dimensional silicon-oxygen spatial network, showing typical "shear thinning". A small amount of silica can increase the viscosity of aqueous solution by several times, while high shear is reduced to water-like, which is suitable for water-based paint, drilling fluid, etc. The surface energy of nanosilica is very high, and it is easy to soft aggregate, but in a liquid dispersion system, the Zeta potential is about -30--50 mV, and the colloidal dispersion system can exist stably for more than 6 months without aggregation and sedimentation. The liquid silica sol system solves the pain point of "the smaller the better". At room temperature, it is resistant to acid (except hydrofluoric acid) and most organic solvents, and at high temperature, it can form a eutectic phase with metal oxides, so it is widely used in catalyst carriers and ceramic sintering aids.

[0003] Therefore, the "trinity" of high specific surface, multiple hydroxyl groups and tailorable modification interface of nanosilica makes it a "stealth performance amplifier" in the fields of reinforcement, thickening, transparency, ultraviolet shielding, catalysis, drug loading, etc.

[0004] Although silica sol has the above-described rich uses, there are still bottlenecks in the application of some industries, such as the textile, film, coating, pigment aid, papermaking and other industries. After research, the Zeta potential of traditional silica sol, whether it is a single silicon synthesis method or a water glass synthesis method, or a mixed synthesis method of both, the surface of the synthesized silica sol colloidal particles is negatively charged, which is called anionic silica sol. For a period of time, people generally believe that after the alkaline silica sol is treated by acid resin ion exchange, the obtained acid silica sol is a cationic silica sol, but in fact it is not, the colloidal particles of the silica sol still have negative charges after resin treatment, and the counterions are changed from Na + to H + , and it is still essentially an anionic silica sol. In addition, the storage time of the acid silica sol after resin treatment will be shortened due to hydrogen bonding and the nature of the silica sol itself, which greatly limits the application of the acid silica sol and increases the loss cost of the finished product of the silica sol of the enterprise, and is not conducive to the application of some customers far away from the source of the manufacturer, so the development of cationic silica sol has great significance.

[0005] Cationic silica sol is a colloidal dispersion system of silica particles with positive charges. Due to its unique charge characteristics and nano structure, it has advantages in many industrial fields. Cationic silica sol is widely used in the textile industry, mainly for enhancing the bonding force of fibers, penetrating the interstitial space of fibers, forming a -Si-O-Si- network structure, improving tensile strength, tear resistance and wear resistance, reducing yarn breakage rate, and improving dyeing and printing effect. When mixed with anionic dyes, strong electrostatic adsorption enhances color fastness and prevents dye pattern blurring. Cationic silica sol can endow fabrics with wrinkle resistance, antibacterial, antistatic, hydrophobic and stain-resistant properties, and is suitable for underwear, home textiles, medical textiles and other products, improving hand feeling and appearance. In the coating industry, it can be used as an aid to significantly improve coating performance and adhesion, firmly bond with negative substrates such as metal and concrete through electrostatic action, solve the problem of coating peeling, and improve physical properties. It can form a dense nanometer network to improve scrub resistance, hardness and scratch resistance. As a dispersant and viscosity regulator, it can prevent pigment precipitation, sagging and pinholes, and is suitable for various construction methods. Cationic silica sol can also be used as a wet aid to improve paper quality and increase filler retention. Through charge neutralization and flocculation, it quickly captures negative fibers and fillers, forms a dense flocculation, reduces loss, enhances paper strength, and improves printing quality. Cationic silica sol, with its positive compatibility, nanoscale particle size and high specific surface area, has achieved multiple values of performance enhancement, process optimization and function expansion in the fields of textiles, coatings and papermaking, and is a high-efficiency and environmentally-friendly nanofunctional material.

[0006] Patent document CN112041267A reports a method for producing charge-modified silica sol, but the method has a relatively low cationic silica sol solid content. After increasing the solid content, the system becomes unstable and cannot be stored for a long time. The process is also complicated. Patent document CN113135573A reports a method for preparing charge-modified silica sol, which uses a direct acidification method. The final product has a high ion content and is too acidic, which limits its application in some metal coatings and investment casting. At the same time, the cationic silica sol prepared by the above two methods uses a large amount of inorganic materials, which has poor compatibility with organic systems, limiting its application in some high-organic-content application fields such as pigments, textiles, and inks.

[0007] Therefore, it is necessary to optimize the existing preparation method of cationic silica sol. While successfully achieving a larger Zeta potential charge modification, the problem of poor stability of acidic cationic silica sol is solved. The content of impurity ions in the cationic silica sol is reduced, and the organic compatibility of the acidic silica sol is improved. SUMMARY

[0008] The present application provides a method for preparing cationic silica sol to improve Zeta potential, improve the organic compatibility and stability of acidic silica sol.

[0009] Therefore, the present application provides the following solutions: The first aspect of the present application provides a method for preparing cationic silica sol, comprising the following steps: Obtaining or preparing acidic anionic silica sol; Adding a cationic surfactant to the acidic anionic silica sol, and stirring to obtain solution one; Hydrolyzing an organic aluminum salt under acidic conditions to obtain solution two, wherein the organic aluminum salt contains an imidazole group or an organic group that generates a hydroxyl group after hydrolysis; Under stirring, drop solution one into solution two to obtain cationic silica sol.

[0010] The above preparation method uses organic aluminum salt, which greatly improves the positive Zeta potential of the system, thereby increasing the solid content. The introduced organic groups, such as hydroxyl or imidazole groups, can form hydrogen bonds with the surface silicon hydroxyl groups of the silica sol particles, thereby reducing the surface energy and providing steric hindrance to prevent the agglomeration of nanoparticles. In addition, some organic groups are adsorbed on the surface of the silica sol particles, physically isolating the particles and preventing agglomeration and sedimentation. The hydroxyl groups containing carbon chains can significantly improve the storage stability of the acidic silica sol. In application, the low molecular organic part can act as an internal plasticizer to improve the flexibility of the coating, and as a diluent to enhance the permeability of the porous substrate and promote chemical bonding. Imidazole ionic liquids can also be partially fixed on the surface of the silica sol through covalent bonds, hydrogen bonds, or electrostatic interactions, introducing multiple interaction sites (electrostatic, π-π stacking, hydrogen bonding) to achieve functional modification of the material. The weak basicity of the imidazole ring can also act as a buffer in the acidic silica sol system, maintaining a stable pH, which is beneficial to the stability of the entire system. The nitrogen heterocyclic structure of imidazole gives it unique pH response and coordination ability, which is more advantageous in scenarios where precise control of the surface chemistry of silica sol is required. By the above process, some organic components are introduced into the originally pure inorganic silica sol system, which enhances the organic compatibility of the silica sol system, thereby expanding its application in coatings, pigments, inks, textiles, films, and other fields.

[0011] Further, the solid content of the acidic anionic silica sol is 5-40%; and / or, the pH of the acidic anionic silica sol is 1.8-2.8; and / or, the particle size of the acidic anionic silica sol is 3-200 nm; and / or, the total content of metal cations in the acidic anionic silica sol is less than 800 ppm, including but not limited to Na, K, Ca, Mg, Fe, Al, and other cations.

[0012] Further, the cationic surfactant is selected from at least one of cetyltrimethylammonium chloride, cetyltrimethylammonium bromide, dodecyltrimethylammonium chloride, benzalkonium chloride, and cetylpyridinium chloride. The addition amount of the cationic surfactant is 0.01-0.05% of the mass of the acidic silica sol. The cationic surfactant prevents the solution from gelling due to charge neutralization when it is added to solution two, thereby stabilizing the system.

[0013] Further, the organic aluminum metal salt is selected from one of imidazole aluminum chloride salt, organic acid aluminum salt and aluminum alcoholate; wherein the imidazole aluminum chloride salt includes but is not limited to 1-ethyl-3-methylimidazolium tetrachloroaluminate, 1-butyl-3-methylimidazolium tetrachloroaluminate; the organic acid aluminum salt includes but is not limited to aluminum citrate, aluminum lactate, aluminum malate, aluminum tartrate, etc.; the aluminum alcoholate includes but is not limited to isopropyl aluminum alcoholate, sec-butyl aluminum alcoholate.

[0014] Further, the organic aluminum salt hydrolysis process controls the pH to be 2-4, preferably 2-2.5, and ammonia or citric acid is used for adjustment; the hydrolysis process continues stirring for 0.5-2h, preferably 0.8-1.5h.

[0015] Further, the organic aluminum salt hydrolysis process uses organic aluminum salt and purified water, and the addition amount of the organic aluminum salt accounts for 5-15% of the total mass.

[0016] Further, the solution one is added dropwise into the solution two process: The mass ratio of the solution one to the solution two is (0.2-1):1, preferably (0.5-0.8):1; And / or, the stirring speed is >400 rpm, preferably 500-700 rpm; And / or, the dropwise addition speed is 10-35 mL / min; And / or, after the dropwise addition is completed, the stirring is continued for 1-3h; And / or, the dropwise addition process and the reaction process temperature is 15-35℃, preferably room temperature of 20-25℃.

[0017] Further, the preparation method of the acidic silica sol is that a cation exchange resin is added into a proper amount of acid solution and stirred, washed, drained, added into a basic silica sol and stirred to obtain an acidic silica sol. The acidic anionic silica sol is prepared by adding the cation exchange resin after acid washing into the basic silica sol.

[0018] Preferably, the cation exchange resin is a general-purpose cation resin, which is selected from one of AMBERLITE IRC120 Na of Rohm & Haas, Tulsimer@T-42H of KHS, and D001 cation resin of Lanxiao. The basic silica sol is a common commercially available basic silica sol, preferably with a pH value of 8.0-11.5, and the particle size is selected according to the particle size requirement of the acidic silica sol, such as in some embodiments, the basic silica sols of Whilte HS-1440B, S-1440B are selected as small particle size, HSD-5040B, SD-5040B are selected as medium particle size, and HSD-10055B, SD-10055B are selected as large particle size.

[0019] Preferably, the acid is hydrochloric acid or sulfuric acid, the concentration is 3-7 Be, and the addition amount is 0.5-1.6 times the volume of the cation exchange resin, which can reduce the cations such as Na, K, Ca, Mg, Fe and Al to below the target value.

[0020] Preferably, the process of adding to the basic silica sol has a stirring time of 20-50 min.

[0021] The second aspect of the present application is to provide a cationic silica sol prepared by the preparation method of the first aspect.

[0022] Further, the cationic silica sol has at least one of the following properties: 1) PDI is 0.010-0.300; 2) Conductivity is 5-60 mS / cm; 3) Zeta potential is +10 to +70 mV; 4) Specific surface area is 10-2000 m 2 / g; 5) pH is 1.0-7.0.

[0023] Preferably, the cationic silica sol has all the above properties. It can be understood that the Zeta potential of the silica sol is greater than |30| mV, which will exhibit good stability. The Zeta potential of the cationic silica sol prepared by the present application is greater than +45 mV, indicating strong stability.

[0024] Compared with the prior art, the present application has the following beneficial effects: The cationic silica sol provided by the present application has a reversed charge from negative to positive, and the Zeta potential is greatly increased compared with the original acidic silica sol. The mutual repulsive force between the colloidal particles is enhanced, so that the storage stability is good. The original acidic silica sol, 3-30 nm acidic anionic silica sol has a stable period of about 7 days, and 30-150 nm acidic anionic silica sol has a stable period of about 3 months. The cationic silica sol prepared by the preparation method provided by the present application has a stable period of 6 months for 3-30 nm small particle size anionic silica sol (particle size <80 nm), and a stable period of more than 1 year for 30-150 nm medium and large particle size anionic silica sol (particle size 60-200 nm).

[0025] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0026] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0027] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0028] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0029] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0030] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation.

[0031] The cationic silica sol prepared by the method has the following advantages: the O, N and other electronegative atoms in the hydroxyl groups or imidazole groups in the system can form hydrogen bonds with the silicon hydroxyl groups on the surface of the silica sol particles, thereby reducing the surface energy and providing a steric hindrance effect to prevent the agglomeration of the nanoparticles; and some organic groups are adsorbed on the surface of the silica sol particles, thereby physically isolating the particles and preventing agglomeration and sedimentation. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The scanning electron microscope image of the small-particle-size overfinishing resin after the acid anion silica sol of Example 1.

[0033] Figure 2 Scanning electron micrograph of the cationic silica sol prepared for Example 1 small particle size.

[0034] Figure 3 Zeta potential plot of the acidic anionic silica sol after passing through the resin for Example 1 small particle size.

[0035] Figure 4 Zeta potential plot of the cationic silica sol prepared for Example 1 small particle size.

[0036] Figure 5 Malvern particle size distribution plot of the acidic anionic silica sol after passing through the resin for Example 1 small particle size.

[0037] Figure 6 Malvern particle size distribution plot of the cationic silica sol prepared for Example 1 small particle size.

[0038] Figure 7 Scanning electron micrograph of the acidic anionic silica sol after passing through the resin for Example 3 large particle size.

[0039] Figure 8 Scanning electron micrograph of the cationic silica sol prepared for Example 3 large particle size.

[0040] Figure 9 Zeta potential plot of the acidic anionic silica sol after passing through the resin for Example 3 large particle size.

[0041] Figure 10 Zeta potential plot of the cationic silica sol prepared for Example 3 large particle size.

[0042] Figure 11 Malvern particle size distribution plot of the acidic anionic silica sol after passing through the resin for Example 3 large particle size.

[0043] Figure 12 Malvern particle size distribution plot of the cationic silica sol prepared for Example 3 large particle size. DETAILED DESCRIPTION

[0044] The technical solutions of the present application will be described clearly and completely below in conjunction with preferred embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0045] Example 1

[0046] Preparation of cationic silica sol from small particle size basic silica sol: 1) In the AMBERLITE IRC120 Na cation resin, add 1.3 times the volume of 5 Be hydrochloric acid, stir for 6 min, then add tap water to wash the acid 3 times, the pH after washing the acid is >3.5, drain the water and wait for use. In 500 g of 40% content of 14 nm particle size basic silica sol (HS-1440B), add the above resin, adjust the amount of resin according to the size of the pH, control the pH to be 2.0, stir for 40 min, then detect the total content of metal cations such as Na, K, Ca, Mg, Fe and Al to be less than 800 ppm, the pH value is 2.0, filter to obtain an acidic silica sol; 2) Add 0.03% of dodecyltrimethylammonium chloride to the acidic silica sol prepared in step 1), stir for 5 min to obtain solution A. Take 180 g of distilled water, adjust the pH to 2.3 with citric acid, add 20 g of 1-ethyl-3-methylimidazolium tetrachloroaluminate, stir at 300 rpm at room temperature for 1 h to obtain solution B. Then, 200 g of solution A is added to solution B at a speed of 25 mL / min, the stirring speed is maintained at 600 rpm, after the addition is completed, continue to stir for 1.5 h for sufficient reaction to obtain a small particle size cationic silica sol.

[0047] Example 2

[0048] Preparation of a cationic silica sol from a medium particle size basic silica sol: 1) In the AMBERLITE IRC120 Na cation resin, add 1.2 times the volume of 6 Be hydrochloric acid, stir for 6 min, then add tap water to wash the acid 3 times, the pH after washing the acid is >3.5, drain the water and wait for use. In 500 g of 40% content of 50 nm particle size basic silica sol (HSD-5040B), add an appropriate amount of the above resin, adjust the amount of resin according to the size of the pH, control the pH to be 2.0, stir for 40 min, then detect the total content of metal cations such as Na, K, Ca, Mg, Fe and Al to be less than 800 ppm, the pH value is 2.0, filter to obtain an acidic silica sol; 2) Add 0.03% of dodecyltrimethylammonium chloride to the acidic silica sol prepared in step 1), stir for 5 min to obtain solution A. Take 180 g of distilled water, adjust the pH to 2.3 with citric acid, add 20 g of 1-ethyl-3-methylimidazolium tetrachloroaluminate, stir at 300 rpm at room temperature for 1 h to obtain solution B. Then, 200 g of solution A is added to solution B at a speed of 25 mL / min, the stirring speed is maintained at 700 rpm, after the addition is completed, continue to stir for 1.5 h for sufficient reaction to obtain a medium particle size cationic silica sol.

[0049] Example 3

[0050] Preparation of cationic silica sol from large-particle-size basic silica sol: 1) In AMBERLITE IRC120 Na, add 1.3 times the volume of 5 Be hydrochloric acid, stir for 6 min, then wash with tap water to remove the acid 3 times, and the pH after washing the acid is >3.5. Drain the water and reserve. In 500 g of 55% content, 100 nm particle size basic silica sol (HSD-10055B), add an appropriate amount of the above resin, and adjust the amount of resin according to the pH value to control the pH to 2.0. After stirring for 40 min, the total content of metal cations such as Na, K, Ca, Mg, Fe, and Al is less than 800 ppm, and the pH is 2.0. Filter to obtain an acidic silica sol; 2) To the acidic silica sol prepared in step 1), add 0.03% of dodecyltrimethylammonium chloride and stir for 5 min to obtain solution A. Take 180 g of distilled water, adjust the pH to 2.3 with citric acid, and add 20 g of 1-ethyl-3-methylimidazolium tetrachloroaluminate. Stir at 300 rpm at room temperature for 1 h to obtain solution B. Then, add 150 g of solution A to solution B at a rate of 15 mL / min, and maintain the stirring speed at 500 rpm. After the addition is complete, continue stirring for 1.5 h to ensure complete reaction, and obtain a large-particle-size cationic silica sol.

[0051] Example 4

[0052] Preparation of cationic silica sol from small-particle-size basic silica sol (aluminum lactate): The difference between this example and Example 1 is that in step 2), an equal amount of aluminum lactate is used to replace 1-ethyl-3-methylimidazolium tetrachloroaluminate, and the other conditions and steps remain unchanged.

[0053] Example 5

[0054] Preparation of cationic silica sol from small-particle-size basic silica sol (aluminum isopropoxide): The difference between this example and Example 1 is that in step 2), an equal amount of aluminum isopropoxide is used to replace 1-ethyl-3-methylimidazolium tetrachloroaluminate, and the other conditions and steps remain unchanged.

[0055] Comparative Example 1

[0056] Preparation of cationic silica sol from small-particle-size basic silica sol, which is different from Example 1 in that solution B is added to solution A at the same speed, and the other conditions and steps are the same.

[0057] Comparative Example 2

[0058] Small-particle-size alkaline silica sol can be directly added to B: Take 180 g of distilled water, adjust the pH to 2.3 with citric acid, add 20 g of 1-ethyl-3-methylimidazolium tetrachloroaluminate, and stir at 300 rpm for 1 h to obtain solution B. Add 0.06 g of dodecyltrimethylammonium chloride to 200 g of 40% alkaline silica sol (HS-1440B) with a particle size of 14 nm, and add it dropwise to solution B at a rate of 25 mL / min. Strengthen the stirring and maintain the stirring speed at 600 rpm. After the addition is complete, continue stirring for 1.5 h to ensure complete reaction and obtain small-particle-size cationic silica sol.

[0059] Comparative Example 3

[0060] Preparation of small-particle-size acidic silica sol: Add 1.3 times the volume of 5 Be hydrochloric acid to the cation exchange resin, stir and regenerate for 6 min, then wash with tap water 3 times until the pH after washing is >3.5, drain and set aside. Add an appropriate amount of the above resin to 500 g of 40% silica sol (HS-1440B) with a particle size of 14 nm, adjust the amount of resin according to the pH value, control the pH at 2.0, stir for 40 min, and filter to obtain small particle size acidic silica sol with pH 2.0.

[0061] Comparative Example 4

[0062] The preparation of medium-sized acidic silica sol differs from that in Example 2 in that step 2 is not included, and only step 1) is performed to prepare acidic silica sol.

[0063] Comparative Example 5

[0064] The preparation of large-particle-size acidic silica sol differs from that in Example 3 in that step 2 is not included, and only step 1) is performed to prepare acidic silica sol.

[0065] Comparative Example 6

[0066] The difference between this comparative example and Example 1 is that, in step 2), 1-ethyl-3-methylimidazolium tetrachloroaluminate was replaced with an equal mass of aluminum chloride hexahydrate, while other conditions and steps remained unchanged.

[0067] Comparative Example 7

[0068] The difference between this comparative example and Example 1 is that, in step 2), an equal mass of aluminum sulfate is used to replace 1-ethyl-3-methylimidazolium tetrachloroaluminate, while other conditions and steps remain unchanged.

[0069] Test case

[0070] 1. Characterization and detection

[0071] The SEM images, Zeta potential images and Malvern particle size distribution images of the small-particle-size prepared cationic silica sol after the resin in step 1) in Example 1 above are shown in Figure 1 、 Figure 3 、 Figure 5 ; the SEM images, Zeta potential images and Malvern particle size distribution images of the small-particle-size prepared cationic silica sol after the resin in step 2) are shown in Figure 2 、 Figure 4 、 Figure 6 .

[0072] The SEM images, Zeta potential images and Malvern particle size distribution images of the large-particle-size prepared cationic silica sol after the resin in step 1) in Example 3 above are shown in Figure 7 、 Figure 9 、 Figure 11 ; the SEM images, Zeta potential images and Malvern particle size distribution images of the large-particle-size prepared cationic silica sol after the resin in step 2) are shown in Figure 8 、 Figure 10 、 Figure 12 .

[0073] 2. Performance comparison and analysis

[0074] The relevant performance tests of the silica sols obtained in Examples 1-5 above and the original anionic silica sol, and Comparative Examples 1-7, are shown in Tables 1 and 2.

[0075] Table 1: Comparison of various indexes of the examples and the original anionic silica sol

[0076] As can be seen from the data in Table 1, the cationic silica sols prepared in Examples 1-5, compared with the original anionic silica sol, the Zeta potential changed from negative to positive, realizing charge modification, and the significant feature is that the cationic silica sol is an acidic silica sol, the conductivity is significantly increased, and the particle size volume is expanded.

[0077] Table 2: Comparison of various indexes of the examples and the comparative examples

[0078] Based on the data in Table 2, the cationic silica sol prepared in Examples 1-5 can change the surface charge of silica sol particles from negative to positive, and significantly increase the absolute value of the charge, which can enhance the charge repulsion between sol particles, thereby improving the storage stability of acidic silica sol. In particular, under the conditions of medium and large particle sizes, the storage time can be greatly improved. The preparation process of cationic silica sol can only add A liquid to B, not vice versa (Comparative Example 1), and can only use acidic silica sol to add to B liquid, adding basic silica sol to B liquid will cause gelation (Comparative Example 2). Compared with acidic silica sol (Zeta potential <│-6│mV) and the original basic silica sol (Zeta potential <│-40│mV), the absolute value of the charge of the prepared cationic silica sol is significantly increased (Zeta potential >│+46│mV), which can enhance the charge repulsion between sol particles, thereby improving the storage stability of acidic silica sol. In particular, the synthesized medium and large particle size acidic cationic silica sol can greatly improve the storage time (Examples 1 or 4 or 5, 2, 3 and Comparative Examples 3, 4, 5).

[0079] Compared with inorganic aluminum salt (such as aluminum chloride or aluminum sulfate), the effect of preparing cationic silica sol is significant (Comparative Examples 6 and 7). Using inorganic aluminum salt by this operation will cause obvious viscosity. Using Malvern Zeta potential instrument for testing, the core index of particle charge reversal has not been achieved, the silica sol particle center still carries negative charge, which is still anionic silica sol. The reduction of the absolute value of Zeta potential means the decrease of the stability of anionic acidic silica sol. Therefore, under this operation condition, inorganic aluminum salt cannot be used.

[0080] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing cationic silica sol, characterized in that the steps include... include: Obtain or prepare acidic anionic silica sol; A cationic surfactant was added to an acidic anionic silica sol, and the mixture was stirred to obtain solution one. Solution 2 is obtained by hydrolyzing an organoaluminum salt under acidic conditions. The organoaluminum salt contains an imidazole group or an organic group that produces a hydroxyl group after hydrolysis. With stirring, solution one is added to solution two to react and obtain cationic silica sol.

2. The preparation method according to claim 1, characterized in that, The solid content of the acidic anionic silica sol is 5-40%. And / or, the pH of the acidic anionic silica sol is 1.8 to 2.8; And / or, the particle size of the acidic anionic silica sol is 3~200nm; And / or, the total content of metal cations in the acidic anionic silica sol is less than 800 ppm.

3. The preparation method according to claim 1, characterized in that, The cationic surfactant is selected from at least one of hexadecyltrimethylammonium chloride, hexadecyltrimethylammonium bromide, dodecyltrimethylammonium chloride, benzalkonium chloride, and hexadecylpyridine chloride; And / or, the amount of the cationic surfactant added is 0.01~0.05% of the mass of the acidic anionic silica sol.

4. The preparation method according to claim 1, characterized in that, The organoaluminum metal salt is selected from at least one of imidazole aluminum chloride salts, organic acid aluminum salts, and aluminum alkoxides; And / or, the hydrolysis process is controlled at pH 2-4, and stirring is continued for 0.5-2 hours; And / or, the hydrolysis process uses organoaluminum salts and purified water, with the amount of organoaluminum salts added accounting for 5-15% of the total mass.

5. The preparation method according to claim 1, characterized in that, During the process of adding solution one dropwise to solution two: The mass ratio of solution one to solution two is (0.2~1):1; And / or, stirring speed >400 rpm; And / or, the dropping rate is 10~35 mL / min; And / or, continue stirring for 1~3 hours after the addition is complete.

6. The preparation method according to claim 1, characterized in that, The method for preparing the acidic anionic silica sol is as follows: take a cation exchange resin, add an appropriate amount of acid solution, stir, wash and drain, add to alkaline silica sol and stir to obtain acidic anionic silica sol.

7. The preparation method according to claim 6, characterized in that, The cation exchange resin is a general-purpose cation exchange resin, selected from Rohm and Haas, Kohler, and Lanxiao cation exchange resins.

8. The preparation method according to claim 6, characterized in that, The acid is hydrochloric acid or sulfuric acid, with a concentration of 3-7 Be, and the amount added is 0.5-1.6 times the volume of the cation exchange resin; And / or, the process of adding to the alkaline silica sol involves stirring for 20 to 50 minutes.

9. A cationic silica sol, characterized in that, It is obtained by the preparation method described in any one of claims 1 to 8.

10. The cationic silica sol according to claim 9, characterized in that, The cationic silica sol has a PDI of 0.010~0.300; and / or a conductivity of 5~60 mS / cm; and / or a Zeta potential of +10~+70 mV; and / or a specific surface area of ​​10~2000 m². 2 / g.

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