Hollow silica sol, method for producing the same, coating composition, and article

Abstract

The present invention relates to a hollow silica sol, a method for producing the same, a coating composition, and an article. The hollow silica sol of the present invention contains hollow silica particles and a dispersion medium, the hollow silica particles being produced by 29 The hollow silica sol of the present invention has a viscosity of 1 to 100 mPa-s, and a stability of 0.01 to 0.1. The hollow silica sol of the present invention has a resonance peak area Q1 of a chemical shift corresponding to a peak of -78 to -88 ppm, a resonance peak area Q2 of a chemical shift of -88 to -98 ppm, a resonance peak area Q3 of a chemical shift of -98 to -108 ppm, and a resonance peak area Q4 of a chemical shift of -108 to -117 ppm, as measured by Si nuclear magnetic resonance spectroscopy, wherein Q1 / (Q1+Q2+Q3+Q4) is substantially 0, Q2 / (Q1+Q2+Q3+Q4) is 0.01 to 0.2, Q3 / (Q1+Q2+Q3+Q4) is 0.01 to 0.6, and Q4 / (Q1+Q2+Q3+Q4) is 0.2 to 0.98. The dispersion medium is water, an organic solvent, or a combination of both. The hollow silica sol of the present invention has a low viscosity and a good stability, and when a coating layer is formed on a substrate, the coating layer has a high hardness, a good wear resistance, and an improved adhesion to the substrate.

Description

Technical Field

[0001] This invention relates to hollow silica sol, its preparation method, coating compositions and products. Background Technology

[0002] Hollow silica particles have the characteristics of high porosity, low refractive index, low dielectric constant, and non-toxicity to organisms, and are therefore widely used in lightweight materials, low-refractive-index materials, anti-reflective coatings, semiconductor materials, and active molecule loading and sustained release.

[0003] In applications such as low-refractive-index materials and anti-reflective coatings, there are requirements for the size of hollow silica particles, which are generally between tens and hundreds of nanometers. If the particle size is too large, it will lead to a decrease in optical transparency and make it difficult to apply. In addition to the size of the particles themselves, they are also required to have good dispersion stability during use and not to agglomerate. Therefore, sols with stable dispersion make subsequent use more convenient and avoid the dispersion difficulties caused by the use of powdered particles.

[0004] The inventors disclosed a method for preparing hollow silica particles in CN110128855A. This method involves first preparing an amphiphilic polyalkoxysiloxane through the hydrolysis and condensation of a silane monomer in water, and then utilizing its self-assembly behavior in an aqueous medium to obtain hollow silica particles. These hollow silica particles exhibit excellent dispersibility and controllable size, making them suitable for antireflection applications. However, when using these hollow particles to prepare antireflection coatings, the coatings suffer from low hardness, poor total light transmittance, and high reflectivity. Furthermore, they exhibit poor resistance to damp heat, insufficient adhesion, and poor abrasion resistance. Additionally, the sol prepared using these hollow silica particles has high viscosity, poor stability, and poor storage durability.

[0005] Patent Document 1: CN110128855A Summary of the Invention

[0006] After conducting in-depth research into the problems existing in the prior art, the inventors discovered that surface defects in the hollow silica particles contained in hollow silica sol lead to low hardness and poor wear resistance in coatings obtained using these particles. Surface defects also make the cavities inside the hollow particles easily filled by adhesives, solvents, etc., resulting in a less significant reduction in refractive index and poorer antireflective performance when preparing antireflective coatings, as well as reduced resistance to damp heat. Furthermore, the presence of surface defects indicates that the particle surface contains abundant hydroxyl groups, leading to instability, high viscosity, and easy gelation when stored in sol form.

[0007] This invention was made to solve at least some of the aforementioned problems, and its purpose is to provide a hollow silica sol with reduced viscosity, good stability, and, when formed as a coating on a substrate, high hardness, good wear resistance, and improved adhesion to the substrate. Furthermore, when formed as a transparent coating as an antireflective layer, it reduces refractive index, improves antireflective performance, and enhances resistance to damp heat.

[0008] The present invention also aims to provide a method for preparing hollow silica sol. The hollow silica sol prepared by this method exhibits reduced viscosity, improved stability, and, when forming a coating on a substrate, increased hardness, abrasion resistance, and adhesion to the substrate. Furthermore, when forming a transparent antireflective layer, it reduces refractive index, improves antireflective performance, and enhances resistance to damp heat.

[0009] Another objective of this invention is to provide a coating composition comprising hollow silica sol and an adhesive, wherein the hollow silica sol is the hollow silica sol described above, or is prepared according to the hollow silica sol preparation method described above.

[0010] Another object of the present invention is to provide an article having a coating formed by curing the coating composition of the present invention on the surface of a substrate. This coating has high hardness, good abrasion resistance, and improved adhesion to the substrate. Furthermore, when a transparent coating is formed as an antireflective layer, the refractive index decreases, and the antireflective performance and resistance to damp heat are improved.

[0011] This invention provides the following technical solution:

[0012] [1] A hollow silica sol containing hollow silica particles and a dispersion medium.

[0013] The aforementioned hollow silica particles, through 29 The resonance peak areas Q1, Q2, Q3, Q4, and Q4 corresponding to the peak values ​​with chemical shifts between -78 and -88 ppm, -88 and -98 ppm, -98 and -108 ppm, and -108 and -117 ppm, respectively, as measured by Si NMR spectroscopy, satisfy the following:

[0014] Q1 / (Q1+Q2+Q3+Q4) is essentially 0.

[0015] Q2 / (Q1+Q2+Q3+Q4) is 0.01 to 0.2.

[0016] Q3 / (Q1+Q2+Q3+Q4) is 0.01 to 0.6, and,

[0017] Q4 / (Q1+Q2+Q3+Q4) ranges from 0.2 to 0.98.

[0018] The aforementioned dispersion medium is water, an organic solvent, or a combination of both.

[0019] [2] According to the hollow silica sol described in [1], the thickness of the shell of the aforementioned hollow silica particles is 3 to 100 nm, and the pore size distribution of the aforementioned shell is in the range of 0.5 to 4 nanometers.

[0020] [3] Hollow silica sol as described in [1] or [2], wherein the pore volume of the aforementioned hollow silica particles is 0.15 to 1 cm. 3 / g, porosity 10%–90%, refractive index 1.10–1.45.

[0021] [4] The hollow silica sol described in any of [1] to [3] has a relative permittivity of 1.6 to 2.2.

[0022] [5] The hollow silica sol described in any of [1] to [4] has a particle size of 15 to 1000 nm and a polydispersity index of 0.05 to 0.3 as measured by dynamic light scattering.

[0023] The method for preparing hollow silica sol as described in any one of [6], [1] to [5] is characterized by comprising the following steps:

[0024] Intermediate product generation steps: The silicon source, the first solvent, the first catalyst and the active compound are mixed and reacted in the range of 0 to 150°C. Then, the substance with a boiling point of less than 300°C is removed to obtain the liquid organosilicon intermediate product P1.

[0025] Hollow silica generation steps: The aforementioned organosilicon intermediate P1 is dispersed in a second solvent, and a second catalyst is added. The reaction is carried out in the range of 0 to 95°C to obtain hollow silica sol.

[0026] Hydrothermal treatment steps: Hydrothermal treatment is carried out in the range of 30 to 300℃.

[0027] [7] According to the method for preparing hollow silica sol described in [6], in the aforementioned intermediate product generation step, the aforementioned silicon source is one or more silane monomers selected from the following Formula I, or a polyalkoxysiloxane oligomer with the simplest formula shown in the following Formula II.

[0028] R 1 4-n Si(OR 2 ) n Formula I

[0029] In Formula I, n = 1, 2, 3, or 4, and R 1 is alkyl, vinylalkyl, vinyl, epoxyalkyl, phenyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, ureidoalkyl, chloroalkyl, mercaptoalkyl, isocyanatealkyl, or hydroxyalkyl. When there are multiple Rs 1 each R 1 is optionally the same as or different from each other; R 2 is alkyl having 1 to 6 carbon atoms. When there are multiple Rs 2 each R 2 is optionally the same as or different from each other;

[0030] SiO m (OR 3 ) 4-2m Formula II

[0031] In Formula II, 0 < m < 2, m is an integer or a non-integer, and R 3 is alkyl having 1 to 6 carbon atoms. When there are multiple Rs 3 each R 3 is optionally the same as or different from each other.

[0032] [8]. The method for preparing hollow silica sol according to [6] or [7], wherein in the foregoing intermediate product formation step, the foregoing first solvent is water or a water-containing organic solvent, and the weight ratio of water to the foregoing silicon source is 0.001:1 or more and less than 0.5:1.

[0033] [9]. The method for preparing hollow silica sol according to any one of [6] to [8], wherein in the foregoing intermediate product formation step, the foregoing first catalyst is an acid or a base, and the weight ratio of the foregoing first catalyst to the foregoing silicon source is (0.001 to 0.5):1.

[0034]

[10] . The method for preparing hollow silica sol according to any one of [6] to [9], wherein in the foregoing intermediate product formation step, the foregoing active compound contains at least one OH group and has a molecular weight greater than 150, and the HLB value of the foregoing active compound calculated by the following Formula III is greater than 5,

[0035] HLB = 20 × M h / M Formula III

[0036] In Formula III, M h is the molecular weight of the hydrophilic part in the foregoing active compound, and M is the molecular weight of the foregoing active compound,

[0037] the weight ratio of the foregoing active compound to the foregoing silicon source is (0.05 to 0.5):1, and the foregoing active compound can be one or a mixture of two or more.

[0038]

[11] A method for preparing hollow silica sol according to any one of [6] to

[10] , wherein,

[0039] In the aforementioned hollow silica generation step, the aforementioned second solvent is water, a mixture of water and a hydrophilic organic solvent, or a mixture of water and a hydrophobic organic solvent;

[0040] The aforementioned second catalyst is an acid or a base;

[0041] The aforementioned organosilicon intermediate P1 has a weight percentage of 1 to 60% relative to the aforementioned second solvent;

[0042] The weight ratio of the aforementioned second catalyst to the aforementioned organosilicon intermediate P1 is (0.05~2):1.

[0043]

[12] The method for preparing hollow silica sol according to any one of [6] to

[11] further includes: a solvent replacement step of replacing the solvent of the aforementioned hollow silica sol.

[0044] In the aforementioned solvent replacement step, all or part of the solvent in the aforementioned hollow silica sol is replaced by centrifugation, heating azeotropically, or ultrafiltration.

[0045]

[13] The method for preparing hollow silica sol according to any one of [6] to

[11] further comprises the following steps:

[0046] Surface modification step: Add one or more substances selected from the group consisting of silanes and / or their partial hydrolysates represented by Formula IV, hexamethyldisiloxane, and hexamethyldisilazane to the hollow silica sol to modify the surface of the hollow silica particles.

[0047] R 4 p -Si-X 4-p Formula IV

[0048] In equation IV, p = 0, 1, 2, or 3, R 4 Selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 4 At that time, each R 4 Whether they are the same or different, R 4 The hydrogen atoms in the fluorine atom can be partially or completely replaced by fluorine atoms.

[0049] X is selected from alkoxy groups with 1-6 carbon atoms, halogens, or hydrogen. When there are multiple Xs, each X may be the same or different from the others.

[0050] The aforementioned surface modification step is performed after the aforementioned hollow silica generation step and / or after the aforementioned hydrothermal treatment step.

[0051]

[14] The method for preparing hollow silica sol as described in

[12] further includes the following steps:

[0052] Surface modification step: Add one or more substances selected from the group consisting of silanes and / or their partial hydrolysates represented by Formula IV, hexamethyldisiloxane, and hexamethyldisilazane to the hollow silica sol to modify the surface of the hollow silica particles.

[0053] R 4 p -Si-X 4-p Formula IV

[0054] In equation IV, p = 0, 1, 2, or 3, R 4 Selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 4 At that time, each R 4 Whether they are the same or different, R 4 The hydrogen atoms in the fluorine atom can be partially or completely replaced by fluorine atoms.

[0055] X is selected from alkoxy groups with 1-6 carbon atoms, halogens, or hydrogen. When there are multiple Xs, each X may be the same or different from the others.

[0056] The aforementioned surface modification step is performed after the aforementioned hollow silica generation step, and / or after the aforementioned hydrothermal treatment step, and / or after the aforementioned solvent replacement step.

[0057]

[15] The method for preparing hollow silica sol according to

[14] , wherein the aforementioned hydrothermal treatment step or / and the aforementioned solvent replacement step are performed again after the aforementioned surface modification step.

[0058]

[16] A coating composition comprising hollow silica sol and an adhesive, wherein the hollow silica sol is any of the sols described in [1] to [5] or is prepared according to any of the hollow silica sol preparation methods described in [6] to

[15] .

[0059]

[17] An article having a coating on a substrate surface, wherein the coating is one or more layers, and at least one of the coatings is formed by curing the coating composition described in

[16] .

[0060] Invention Effects

[0061] The hollow silica sol of the present invention, by ensuring that the proportions of Q4 (the ratio of Si atoms with 4 -OSi- groups), Q3 (the ratio of Si atoms with 3 -OSi- groups and 1 hydroxyl group), Q2 (the ratio of silicon atoms with 2 -OSi- groups and 2 hydroxyl groups), and Q1 (the ratio of silicon atoms with 1 -OSi- group and 3 hydroxyl groups) of the hollow silica particles satisfy the following: Q1 / (Q1+Q2+Q3+Q4) is substantially 0, Q2 / (Q1+Q2+Q3+Q4) is 0.01 to 0.2, Q3 / (Q1+Q2+Q3+Q4) is 0.01 to 0.6, and Q4 / (Q1+Q2+Q3+Q4) is 0.2 to 0.98, the pore size of the shell of the hollow silica particles is small, thin, and dense, thereby the hollow silica sol of the present invention has low viscosity and excellent thermal and dispersion stability. Furthermore, the hollow particles in the hollow silica sol of the present invention have a good shell structure, resulting in high hardness, good wear resistance, and strong adhesion to the substrate when formed into a coating. Because it prevents the cavity from being filled with other substances, the coating also has a reduced refractive index. Additionally, when the formed coating is used as an antireflective layer, its antireflective performance and resistance to damp heat are improved.

[0062] According to the method for preparing hollow silica sol of the present invention, the hollow silica sol is subjected to hydrothermal treatment, which further condenses the hydroxyl groups on the surface of the hollow silica particles, thereby preparing a hollow silica sol with small pore size, thin and dense hollow silica particles containing a shell and low viscosity.

[0063] The coating composition of the present invention can form a coating film with significant anti-reflection effect, good wear resistance, high hardness, and strong adhesion to the substrate.

[0064] The products of this invention have excellent anti-reflective properties, good hardness, wear resistance, adhesion to the substrate, and excellent weather resistance such as resistance to damp heat. Attached Figure Description

[0065] Figure 1 This is a transmission electron microscope image of the hollow silica particles obtained in Example 1.

[0066] Figure 2 This is a transmission electron microscope image of the hollow silica particles obtained in Example 2.

[0067] Figure 3 This is a transmission electron microscope image of the hollow silica particles obtained in Example 3.

[0068] Figure 4 Transmission electron microscope images of hollow silica particles obtained in Comparative Example 1.

[0069] Figure 5 Transmission electron microscope images of hollow silica particles obtained in Comparative Example 2.

[0070] Figure 6 Transmission electron microscope images of hollow silica particles obtained in Comparative Example 3. Detailed Implementation

[0071] Hollow silica sol

[0072] The hollow silica sol of this invention contains hollow silica particles and a dispersion medium.

[0073] The above-mentioned hollow silica particles are passed through 29 The resonance peak areas Q1, Q2, Q3, Q4, and Q4 corresponding to the peak values ​​with chemical shifts between -78 and -88 ppm, -88 and -98 ppm, -98 and -108 ppm, and -108 and -117 ppm, respectively, as measured by Si NMR spectroscopy, satisfy the following:

[0074] Q1 / (Q1+Q2+Q3+Q4) is essentially 0.

[0075] Q2 / (Q1+Q2+Q3+Q4) is 0.01 to 0.2.

[0076] Q3 / (Q1+Q2+Q3+Q4) is 0.01 to 0.6, and,

[0077] Q4 / (Q1+Q2+Q3+Q4) ranges from 0.2 to 0.98.

[0078] Among them, the peak belonging to Q1 is related to the structure of silicon atoms with 1 -OSi- group and 3 hydroxyl groups bonded to the Si atom; the peak belonging to Q2 is related to the structure of silicon atoms with 2 -OSi- groups and 2 hydroxyl groups bonded to the Si atom; the peak belonging to Q3 is related to the structure of silicon atoms with 3 -OSi- groups and 1 hydroxyl group bonded to the Si atom; and the peak belonging to Q4 is related to the structure of silicon atoms with 4 -OSi- groups bonded to the Si atom.

[0079] "Q1 / (Q1+Q2+Q3+Q4) is substantially 0" means that it does not actually contain peaks related to the structure of silicon atoms with one -OSi- group and three hydroxyl groups bonded to the Si atom. However, it does not exclude the possibility that there are unavoidable peaks due to detection limits and noise, which may cause Q1 / (Q1+Q2+Q3+Q4) to be below, for example, 0.0001. In this case, Q1 / (Q1+Q2+Q3+Q4) is also considered to be substantially 0.

[0080] The aforementioned Q2 / (Q1+Q2+Q3+Q4) is 0.2 or less. Considering that the hydroxyl groups on the surface of hollow silica can meet the requirements of subsequent solvent replacement and / or surface modification, and the adhesion after coating formation, the aforementioned Q2 / (Q1+Q2+Q3+Q4) is preferably 0.01 or more, more preferably 0.03 or more, and even more preferably 0.05 or more.

[0081] The aforementioned Q3 / (Q1+Q2+Q3+Q4) is 0.6 or less. Considering that the hydroxyl groups on the surface of hollow silica can meet the requirements for subsequent solvent replacement and / or surface modification, and considering the adhesion after coating formation, the aforementioned Q3 / (Q1+Q2+Q3+Q4) is preferably 0.01 or more, more preferably 0.1 or more, further preferably 0.2 or more, even more preferably 0.3 or more, and more preferably 0.4 or more.

[0082] The higher the aforementioned Q4 / (Q1+Q2+Q3+Q4), the more complete the spherical shell structure, the denser the surface, and the higher the mechanical strength. Considering that the hollow particles have sufficient mechanical properties, are not easily broken, and the internal cavities are not easily filled, resulting in excellent anti-reflective properties when formed into coatings or manufactured products, Q4 / (Q1+Q2+Q3+Q4) is 0.2 or higher. On the other hand, considering that the Si-O-Si structure with a non-completely hydrophobic surface has sufficient hydrophilicity to stabilize the hollow silica sol, is not prone to sedimentation, and the surface can be modified to facilitate dispersion in other solvent systems or coating systems, and considering that the resulting coating or product has poor adhesion and abrasion resistance, Q4 / (Q1+Q2+Q3+Q4) is preferably 0.98 or less, more preferably 0.8 or less, and even more preferably 0.6 or less.

[0083] In the hollow silica sol of the present invention, by adjusting the proportions of Q1, Q2, Q3, and Q4 in the hollow silica particles, sufficient hydroxyl groups on the surface of the hollow particles are made to facilitate dispersion in water and other solvents, forming a stable silica sol. This makes subsequent surface functionalization treatment easier, thus enabling its application in coating compositions of different systems. Furthermore, it ensures that the hydroxyl groups on the surface of the hollow particles are not excessive, resulting in a dense surface structure, excellent mechanical properties, low viscosity, and excellent storage stability.

[0084] In particular, while lower values ​​of Q2 / (Q1+Q2+Q3+Q4) and Q3 / (Q1+Q2+Q3+Q4) result in higher density and mechanical strength of the resulting hollow particle shells, excessively low values ​​of Q2 / (Q1+Q2+Q3+Q4) lead to insufficient hydroxyl groups on the surface of the hollow silica. This makes it difficult to meet the requirements for solvent replacement and / or surface modification needed for subsequent coating applications. Consequently, the solvent in the sol cannot be replaced with the required solvent, or the required amount of functional groups cannot be imparted through surface modification. Furthermore, insufficient adhesion occurs during subsequent coating formation. Therefore, in some embodiments of the hollow silica sol, it is preferable that (Q2+Q3) / (Q1+Q2+Q3+Q4) is 0.2 or higher, and more preferably 0.45 or higher.

[0085] The viscosity of the hollow silica sol of the present invention at 25°C and with a solid content of 20% is, for example, 5 to 200 mPa·sec. Considering good storage stability, it is preferably 5 to 100 mPa·sec, more preferably 5 to 50 mPa·sec, and even more preferably 5 to 20 mPa·sec.

[0086] In some embodiments of the hollow silica sol of the present invention, Q1, Q2, Q3, and Q4 satisfy the following conditions: Q1 / (Q1+Q2+Q3+Q4) is substantially 0, Q2 / (Q1+Q2+Q3+Q4) is 0.05 to 0.1, Q3 / (Q1+Q2+Q3+Q4) is 0.2 to 0.55, and Q4 / (Q1+Q2+Q3+Q4) is 0.35 to 0.75.

[0087] In some other embodiments of the hollow silica sol of the present invention, Q1, Q2, Q3, and Q4 satisfy the following conditions: Q1 / (Q1+Q2+Q3+Q4) is substantially 0, Q2 / (Q1+Q2+Q3+Q4) is 0.05 to 0.2, Q3 / (Q1+Q2+Q3+Q4) is 0.35 to 0.6, and Q4 / (Q1+Q2+Q3+Q4) is 0.3 to 0.65.

[0088] The determination methods for Q1, Q2, Q3, and Q4 described above are the same as those described in the examples below, and will not be repeated here.

[0089] The aforementioned hollow silica particles are particles whose shells are mainly composed of silica and whose interiors are hollow. The phrase "shells are mainly composed of silica" means that the shells of the hollow particles are primarily composed of silica, optionally containing small amounts of other oxides and / or organic groups.

[0090] In one embodiment of the hollow silica sol of the present invention, the thickness of the shell layer of the aforementioned hollow silica particles is preferably, for example, 3 to 100 nm. A shell layer thickness of 3 nm or more provides sufficient strength, and more preferably 4 nm or more. The aforementioned shell layer thickness is preferably, for example, 100 nm or less, more preferably 50 nm or less, and more preferably 10 nm or less, thereby facilitating the acquisition of a suitable refractive index, and more preferably 6 nm or less. The thickness of the aforementioned shell layer can be appropriately adjusted by the amount of reactants such as the silicon source and the reaction temperature in the manufacturing conditions of the hollow particles. From the perspective of obtaining an excellent refractive index, a shell thickness of 4 to 10 nm is more preferable.

[0091] The thickness of the shell was determined by the following method: hollow particles were observed by transmission electron microscopy (TEM), 100 particles were randomly selected, the thickness of the shell of each hollow particle was measured, and the measured values ​​were averaged.

[0092] In one embodiment of the hollow silica sol of the present invention, the shell of the aforementioned hollow silica particles has pores with a diameter distribution of, for example, 0.5 to 4 nanometers. By having pores larger than 0.5 nanometers, high pore volume, porosity, and low refractive index and relative permittivity can be obtained. If the pores of the hollow particle shell are less than 10 nanometers, the hollow particles have good particle strength, and when used as a coating composition to form a coating film, the internal pores are not easily filled, resulting in good abrasion resistance and antireflective properties. From the perspective of refractive index and relative permittivity, 0.5 to 4 nanometers is more preferable.

[0093] In one embodiment of the hollow silica sol of the present invention, the pore volume of the aforementioned hollow silica particles can be, for example, 0.15 to 1.0 cm³. 3 / g. The pore volume of the hollow silica particles is 0.15cm³. 3 A concentration of 1 g or higher allows the particles to have a low refractive index. The pore volume of hollow silica particles is 1.0 cm³. 3 If the particle strength is below a certain value (e.g.), then the particle has sufficient strength.

[0094] The aforementioned pore size and pore volume were determined by static adsorption measurements at 77 K using a Quadrasorb evo surface area and porosity analyzer (Quantachrome Instruments, USA). The pore size and pore volume on the hollow silica particle shell were determined using isothermal adsorption curves and the Barrett-Joyner-Halenda (BJH) model.

[0095] In one embodiment of the hollow silica sol of the present invention, the refractive index of the aforementioned hollow silica particles can be, for example, 1.10 to 1.45. A refractive index of 1.10 or higher results in the hollow silica particles exhibiting good hardness and strength. A refractive index of 1.45 or lower provides a lower refractive index, which performs excellently in antireflective coatings.

[0096] In one embodiment of the hollow silica sol of the present invention, the relative permittivity of the hollow silica particles is, for example, 1.6 to 2.2. When the relative permittivity of the hollow silica particles is 1.6 or higher, the particles have sufficient strength in the composite dielectric material. From the perspective of having excellent dielectric properties and low dielectric loss, the relative permittivity of the hollow silica particles is 2.2 or lower, more preferably 2.0 or lower.

[0097] In one embodiment of the hollow silica sol of the present invention, the particle size of the hollow silica particles is, for example, 15 to 1000 nm. From the perspective of the transparency of the formed optical coating, it is more preferably 20 to 500 nm, and even more preferably 20 to 100 nm.

[0098] In one embodiment of the hollow silica sol of the present invention, the polydispersity index (PDI) of the hollow silica particles is, for example, 0.05 to 0.3. The aforementioned polydispersity index is obtained through dynamic light scattering (DLS) test data of the hollow silica sol. A lower PDI indicates a more uniform size distribution of the hollow particles, and a greater tendency towards monodispersity. A PDI below 0.3 indicates a more uniform size distribution of the hollow silica particles, resulting in a lower surface roughness and superior abrasion resistance after coating preparation.

[0099] By setting appropriate pore sizes and shell thickness, sufficient porosity and a low refractive index are ensured, while preventing other substances from entering the internal cavity through the pores in the hollow particle shell. This ensures that the hollow particles always have excellent anti-reflective properties in coating compositions, coatings, and products containing coatings.

[0100] In one embodiment of the hollow silica sol of the present invention, the content of hollow silica particles is preferably in the range of 0.5% by mass to 70% by mass. When the content of hollow silica particles in the hollow silica sol is 0.5% by mass or more, it is preferred from the perspective of coating formation efficiency, more preferably 5% by mass or more, and even more preferably 10% by mass or more. When the content of hollow silica particles in the hollow silica sol is 70% by mass or less, it is preferred from the perspective of storage stability and suitable viscosity of the hollow silica sol, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0101] The dispersion medium in the aforementioned hollow silica sol is water, an organic solvent, or a combination of both. The aforementioned organic solvent refers to a free-flowing organic compound containing carbon atoms. The function of the dispersion medium is to ensure that the hollow silica particles exist as individual particles in the environment provided by the dispersion medium, preventing the aggregation of hollow silica particles in the dry state, which would affect the optical transparency of the final coating and product. Examples of the aforementioned organic solvents include, for instance, methanol, ethanol, isopropanol, butanol, ethyl acetate, butyl acetate, acetone, butanone, methyl isobutyl ketone, heptanone, hexane, cyclohexane, heptane, octane, nonane, ethylene glycol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, propylene glycol methyl ether, tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, etc., as long as they do not affect the properties of the hollow silica sol and the hollow silica particles, there are no particular limitations.

[0102] [Preparation method of hollow silica sol]

[0103] The preparation method of hollow silica sol includes the following steps:

[0104] Intermediate product generation steps: The silicon source, the first solvent, the first catalyst and the active compound are mixed and reacted in the range of 0 to 150°C. Then, the substance with a boiling point of less than 300°C is removed to obtain the liquid organosilicon intermediate product P1.

[0105] Hollow silica generation steps: The organosilicon intermediate P1 is dispersed in a second solvent and a second catalyst is added. The reaction is carried out in the range of 0 to 95°C to obtain hollow silica sol.

[0106] Hydrothermal treatment steps: After cleaning as needed, perform hydrothermal treatment within the range of 30 to 300℃.

[0107] The steps described above will be explained in the following sections.

[0108] [Intermediate product formation steps]

[0109] In the aforementioned intermediate product generation step, the alkoxy group in the silicon source undergoes hydrolysis in the presence of the first solvent under the catalysis of the first catalyst to generate silanol groups. The generated silanol groups can further undergo condensation reactions or react with hydroxyl groups in the active compound to generate high-boiling-point liquid organosilicon intermediate products and low-boiling-point substances (substances with boiling points less than 300°C) as byproducts. By removing the low-boiling-point substances, the intermediate products are purified, resulting in a narrower molecular weight distribution and more uniform chemical properties.

[0110] There are no restrictions on the composition of the aforementioned silicon source, as long as it contains alkoxy groups that can be hydrolyzed into silanol groups and further condensed to form a flowable intermediate product.

[0111] Preferably, the foregoing silicon source is one or more of the silane monomers represented by the following formula I, or is a polyalkoxysiloxane oligomer having the simplest formula represented by the following formula II.

[0112] R 1 4-n Si(OR 2 ) n Formula I

[0113] In formula I, n = 1, 2, 3, or 4, and R 1 is an alkyl group, a vinylalkyl group, a vinyl group, an epoxyalkyl group, a phenyl group, a styrylalkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureidoalkyl group, a chloroalkyl group, a mercaptoalkyl group, an isocyanatealkyl group, or a hydroxyalkyl group. When there are multiple Rs 1 , each R 1 is optionally the same or different from each other; R 2 is an alkyl group having 1 to 6 carbon atoms. When there are multiple Rs 2 , each R 2 is optionally the same or different from each other;

[0114] SiO m (OR 3 ) 4-2m Formula II

[0115] In formula II, 0 < m < 2, m is an integer or a non-integer, and R 3 is an alkyl group having 1 to 6 carbon atoms. When there are multiple Rs 3 , each R 3 is optionally the same or different from each other.

[0116] In the foregoing formula I, as the "alkyl group" in the alkyl group, vinylalkyl group, vinyl group, epoxyalkyl group, phenyl group, styrylalkyl group, methacryloxyalkyl group, acryloxyalkyl group, aminoalkyl group, ureidoalkyl group, chloroalkyl group, mercaptoalkyl group, isocyanatealkyl group, or hydroxyalkyl group represented by R 1 , for example, an alkyl group having 1 to 22 carbon atoms can be cited. It can be an alkyl group having 1 to 10 carbon atoms, and further can be an alkyl group having 1 to 8 carbon atoms.

[0117] As the foregoing "alkyl group having 1 to 8 carbon atoms", for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, hexyl, n-heptyl, n-octyl, etc. can be cited, and there is no particular limitation.

[0118] Examples of polyalkoxysiloxane oligomers with the simplest formula shown above (Formula II) include commercially available silicon 40, silicon 48, silicon 51, silicon 53, and silicon 63.

[0119] As the aforementioned silicon source, one or more of the silane monomers with the structure shown in Formula I or one or more of the polyalkoxysiloxane oligomers shown in Formula II can be used, or a combination of both can be used. Preferably, the aforementioned silicon source is at least one selected from tetraethyl silicate, tetramethyl silicate, vinyltriethoxysilane, methyltriethoxysilane, 3-(methacryloyloxy)propyltriethoxysilane, silicon 40, silicon 48, and silicon 51.

[0120] The first solvent mentioned above is preferably water, or a mixture of water and an organic solvent, and more preferably a mixture of water and an organic solvent. Examples of such solvents include at least one of aqueous methanol, aqueous ethanol, aqueous isopropanol, aqueous butanol, aqueous ethylene glycol, aqueous ethylene glycol butyl ether, aqueous propylene glycol, and aqueous propylene glycol methyl ether.

[0121] The weight ratio of water in the first solvent to the silicon source is preferably 0.001:1 or higher and less than 0.5:1. In the intermediate product formation step, the alkoxy groups in the silicon source hydrolyze upon contact with water, further condensing to form an intermediate product containing a Si-O-Si structure. When the weight ratio is 0.001:1 or higher, the resulting intermediate product has a sufficiently high molecular weight, and its hydrophilicity after reacting with the active compound is not too strong, thus enabling interfacial activity. When the weight ratio is less than 0.5:1, some of the alkoxy groups in the silicon source remain unreacted, which is beneficial for the subsequent reaction of the active compound with it.

[0122] Furthermore, the aforementioned weight ratio of water to silicon source is one of the factors affecting the shell thickness of the hollow silica particles, which are the final product. The shell thickness of the hollow silica particles increases with the increase of the weight ratio of water to silicon source. From the perspective of obtaining sufficient shell thickness of hollow silica particles to ensure sufficient strength, the aforementioned weight ratio of water to silicon source is preferably 0.01:1 or higher. From the perspective of ensuring that the shell thickness of the hollow silica particles is not too thick and thus has a low refractive index, the aforementioned weight ratio of water to silicon source is preferably 0.25:1 or lower.

[0123] The purpose of using solvents other than water in the aforementioned first solvent is to enable water and silicon source to mix quickly and uniformly. There is no particular limitation on the amount added. From the perspective of saving preparation costs, the preferred amount is the amount used to ensure that water and silicon source can be mixed evenly.

[0124] The aforementioned first catalyst is an acid, a base, or a metal alkoxide or metal carboxylate. Examples of such acids include hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid, oxalic acid, and acidic cation exchange resins, but are not limited to these. Examples of such bases include ammonia, organic amines, sodium hydroxide, potassium hydroxide, sodium bicarbonate, and sodium carbonate, but are not limited to these. Examples of such metal alkoxides include titanium alkoxides, aluminum alkoxides, and zirconium alkoxides, but are not limited to these. Examples of such metal carboxylates include tin acetate, aluminum acetate, and zirconium acetate, but are not limited to these. From the perspective of reaction controllability, the aforementioned first catalyst is preferably an acid or a titanium alkoxide. Examples of titanium alkoxides include tetramethoxytitanium, tetraethoxytitanium, and tetrapropoxytitanium.

[0125] The weight ratio of the aforementioned first catalyst to the aforementioned silicon source is preferably 0.001 to 0.5:1. Controlling this weight ratio to below 0.5:1 helps prevent the formation of gel-like solids due to excessively fast reaction rates, while controlling this weight ratio to above 0.001:1 helps improve catalytic efficiency and obtain a suitable reaction rate.

[0126] The aforementioned active compound refers to a compound that enhances the hydrophilicity of organosilicon intermediates. Such an active compound may, for example, be a substance containing at least one OH group, having a molecular weight greater than 150, and an HLB value greater than 5 calculated using Formula III below.

[0127] HLB = 20 × M h / M Type III

[0128] In Equation III, M h denoted as , where is the molecular weight of the hydrophilic portion of the active compound, and M is the molecular weight of the active compound.

[0129] The aforementioned active compound can be a single substance or a mixture of two or more substances. Examples of such active compounds include, for instance, one or more combinations selected from polyacrylic acid, polyethylene glycol, polyethylene glycol monoether, polyvinyl alcohol, polyglycerol, and copolymers of ethylene oxide and propylene oxide. When the HLB value of the active compound calculated using Formula III is less than 5, the active compound cannot impart adequate hydrophilicity to the organosilicon intermediate, and hollow silica particles cannot be obtained in subsequent steps.

[0130] The weight ratio of the aforementioned active compound to the aforementioned silicon source can be, for example, (0.05 to 0.5):1. By controlling this mass ratio to 0.05:1 or higher, the resulting organosilicon intermediate can have sufficient hydrophilicity, thus preventing it from easily agglomerating in aqueous solvents and enabling the formation of particles with hollow structures. By controlling this mass ratio to 0.5:1 or lower, the resulting organosilicon intermediate has partial hydrophobicity, thereby possessing suitable interfacial activity and enabling the formation of hollow particles in subsequent steps.

[0131] The reaction temperature for the aforementioned intermediate product formation step is 0–150°C, preferably 60–100°C. The reaction time is, for example, 1–24 hours, preferably 5–15 hours. From the perspective of balancing complete reaction and reaction efficiency, 8–10 hours is more preferable.

[0132] During the aforementioned intermediate product formation step, due to the hydrolysis and condensation reaction of alkoxy groups in the silicon source, a portion of byproducts with boiling points below 300°C are generated simultaneously with the organosilicon intermediate P1. Examples of such byproducts with boiling points below 300°C include intermediates with molecular weights below 500 and small molecule alcohols formed by the hydrolysis and condensation of alkoxy groups.

[0133] The removal of byproducts with boiling points below 300℃ has a crucial impact on the preparation of hollow silica particles. By removing alcohol compounds, which are byproducts, the hydrolysis and condensation of the silicon source and its condensation with hydroxyl-containing active compounds can proceed in the forward direction, yielding intermediate products with higher molecular weights, ultimately forming hollow silica particles. Removing intermediate products with molecular weights below 500 results in more uniform particle size and easier size control in the prepared hollow silica particles.

[0134] The aforementioned methods for removing low-boiling-point byproducts can include, for example, one or a combination of atmospheric distillation, vacuum distillation, thin-film evaporation, or rotary evaporation. The removal of these low-boiling-point byproducts can be carried out simultaneously with hydrolysis and condensation reactions. During the reaction, the observation of liquid distillation indicates that the byproducts are being removed. After the heating reaction is complete, the removal of the first reaction byproducts can be further carried out to ensure complete removal. During the removal process, when no liquid is observed distilling or the liquid mass in the collection bottle remains unchanged for a certain period, the byproducts are considered to have been completely removed, and the remaining product is the organosilicon intermediate P1.

[0135] [Steps for forming hollow silica]

[0136] In the hollow silica generation step, the aforementioned organosilicon intermediate P1 is dispersed in a second solvent, and a second catalyst is added. The reaction is carried out in the range of 0 to 95°C to obtain hollow silica sol.

[0137] The aforementioned second solvent is water, or a combination of water and a hydrophilic solvent, or a combination of water and a hydrophobic solvent. Examples of such hydrophilic solvents include organic solvents miscible with water, such as alcohols, ketones, and ethers. Examples of such hydrophobic solvents include organic solvents such as alkanes, aromatic hydrocarbons, and esters.

[0138] When the aforementioned organosilicon intermediate P1 is dispersed in the second solvent, the organosilicon intermediate P1 and the second solvent assemble into a vesicle-like structure. The interior and exterior of the vesicle are both aqueous solvents. The organosilicon intermediate P1 is enriched at the interface. Under the action of the second catalyst, the organosilicon intermediate P1 is rapidly hydrolyzed and condensed to form hollow silica particles with a dense silica shell, thereby obtaining a sol containing monodisperse hollow silica particles.

[0139] On the other hand, under the action of the second catalyst, the organosilicon intermediate is hydrolyzed and condensed into silica, and small molecule alcohols are also released. With the vesicle size remaining basically unchanged, the release of small molecule alcohols will introduce a sufficient number of fine pores on the silica spherical shell.

[0140] The pore size, pore volume, and refractive index of the hollow particles can be adjusted by changing the type and amount of the second catalyst. Generally, compared with the use of acid catalysts, the use of base catalysts results in larger pore sizes, higher pore volumes, and lower refractive indices.

[0141] The aforementioned second catalyst can be, for example, an acid or a base. As an acid, it can be an organic or inorganic acid. Examples of inorganic acids include hydrochloric acid, nitric acid, and sulfuric acid; examples of organic acids include formic acid, acetic acid, and acrylic acid. As a base, it can be an inorganic or organic base. Examples of inorganic bases include sodium hydroxide, potassium hydroxide, and ammonia; examples of organic bases include triethylamine. Furthermore, if an acidic salt or basic salt is in salt form but exhibits acidic or basic properties, it is considered to fall within the category of a second catalyst as long as it can function as a second catalyst to react the organosilicon intermediate to generate hollow silica particles. The aforementioned second catalyst can be the same as or different from the first catalyst.

[0142] The weight ratio of the aforementioned second catalyst to the organosilicon intermediate can be, for example, (0.05–2):1.

[0143] In the aforementioned hollow silica particle generation step, from the perspective of obtaining a suitable dispersion viscosity and production efficiency, the weight percentage of organosilicon intermediate P1 relative to the second solvent is preferably 1 to 60%.

[0144] The aforementioned hollow silica particle generation steps yield well-dispersed hollow silica sol. However, since it has not undergone surface densification treatment, it contains excessive hydroxyl groups and defects. This causes the viscosity of this primary hollow silica sol to increase over time under high solids content conditions, and it may even gel, affecting subsequent use. In addition, the silica spheres are relatively soft and have many surface defects. When used in subsequent coating compositions or coating products, they may exhibit poor wear resistance, and the hollow structure may be easily filled, thus affecting antireflective properties and dielectric properties.

[0145] [Hydrothermal treatment steps]

[0146] The hydrothermal treatment process is carried out at temperatures ranging from 30 to 300°C. Through hydrothermal treatment, the shells of the hollow silica particles become more uniform and denser. Due to surface tension, the particles become closer to a spherical shape, and their mechanical strength is significantly improved. Compared to untreated hollow silica sol, the hydrothermally treated sol maintains a lower viscosity even at higher solid content, improving thermal and storage stability. Furthermore, the denser shells of the hollow silica particles reduce surface defects, resulting in increased hardness and abrasion resistance when forming the coating. Additionally, when used in antireflective coatings, relatively high-refractive-index resins cannot penetrate the interior of the hollow particles, thus yielding a coating with better antireflective properties.

[0147] By adjusting the proportion of hydroxyl and other groups on the surface of the hollow silica particles through the aforementioned hydrothermal treatment, the resulting hollow silica sol meets the Q1, Q2, Q3, and Q4 ranges of the hollow silica sol of the present invention. This results in hollow silica sol containing fewer defects in the hollow silica particles, a dense surface structure, excellent mechanical properties, and low sol viscosity. At the same time, it ensures that the surface of the hollow silica particles has sufficient hydroxyl groups to facilitate dispersion in water and other solvents, forming a stable silica sol. This makes subsequent surface functionalization treatment easier and allows it to be applied to coating compositions of different systems.

[0148] The hydrothermal temperature of the aforementioned hydrothermal step is between 30℃ and 300℃. At temperatures above 30℃, the silica spherical shells can be effectively densified, resulting in improved film properties, antireflective properties, and coating strength when used in coatings and platings. However, at temperatures exceeding 300℃, the surface of the hollow particles cannot be further densified, hindering further improvement in the performance of the resulting coatings and platings. Furthermore, it may cause the hollow particles to agglomerate and precipitate from the sol, affecting further use. Considering the water resistance, weather resistance, and abrasion resistance of the formed coating, the preferred hydrothermal treatment temperature is between 100℃ and 200℃.

[0149] Prior to the aforementioned hydrothermal treatment steps, depending on the circumstances, known cleaning steps such as ultrafiltration, centrifugation, and ion exchange resin can be performed to remove other substances or ions besides silica that may be present in the hollow silica sol. Through the cleaning steps, the hollow silica sol has higher purity and better stability.

[0150] The method for preparing hollow silica sol of the present invention can obtain a hollow particle dispersion with excellent monodispersity and no secondary agglomeration without the need for traditional methods such as high-temperature calcination, solvent etching or acid-base dissolution to remove the internal template.

[0151] In addition, the method for preparing hollow silica sol of the present invention can prepare hollow silica particles with high mechanical strength, uniform shell and dense structure through hydrothermal treatment. When these particles are used in coating compositions and coatings, they can impart excellent water resistance, wear resistance, weather resistance and anti-reflection properties to the coating.

[0152] The hollow silica sol obtained above can be used in combination with binders to form coating compositions, widely used to form antireflective coatings. Alternatively, various additives can be added to the coating composition according to the performance requirements of the formed coating. Furthermore, the hollow silica sol can also be dried and stored as a powder of hollow silica particles for later use.

[0153] Furthermore, the method for preparing hollow silica sol in this invention does not introduce any metal ions and has excellent low dielectric properties.

[0154] The hollow silica sol obtained by the aforementioned method contains hollow particles with fine porous channels in its shell, which can be used for encapsulation and sustained release.

[0155] Optionally, the method for preparing hollow silica sol of the present invention may further include the following steps:

[0156] Solvent replacement step

[0157] In the solvent replacement step, equipment such as ultrafiltration membranes, rotary evaporators, and centrifuges are used to replace all or part of the original solvent in the obtained hollow silica sol with an organic solvent, thereby obtaining a hollow silica organic sol. The aforementioned "part" can be, for example, more than 20%, more than 40%, more than 60%, more than 80%, more than 90%, or more than 99%.

[0158] The solvent used for displacement can be one or a mixture of two or more solvents. Hollow silica sol obtained after solvent displacement is suitable for most coating systems, exhibits excellent dispersion properties in the resulting coating composition, does not agglomerate in the prepared coating and product, imparts good optical transparency to the coating, and avoids whitening of the coating.

[0159] For example, if the solvent of the hollow silica sol before replacement is water, methanol can be used to replace the water to obtain hollow silica methanol sol.

[0160] In another embodiment, for example, if the solvent of the hollow silica sol before replacement is methanol, acetone can be used to replace a portion of the methanol to obtain a methanol / acetone sol of hollow silica.

[0161] Surface finishing steps

[0162] The surface of hollow silica particles is modified by adding one or more of the following ingredients to a hollow silica sol: silane and / or its partial hydrolysate as shown in Formula IV below, hexamethyldisiloxane, and hexamethyldisilazine (amine) alkane.

[0163] R 4 p -Si-X 4-p Formula IV

[0164] In equation IV, p = 0, 1, 2, or 3, R 4 Selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 4 At that time, each R 4 Whether they are the same or different, R 4 In this process, some or all of the hydrogen atoms may be replaced by fluorine atoms.

[0165] X is selected from alkoxy groups, halogens, or hydrogen atoms with 1-6 carbon atoms. When there are multiple Xs, each X may be the same or different from the others.

[0166] The aforementioned R 4 The "alkyl" in "alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloyloxyalkyl, acryloyloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanatealkyl, or hydroxyalkyl" can be, for example, alkyl with 1 to 22 carbon atoms, alkyl with 1 to 10 carbon atoms, and further alkyl with 1 to 8 carbon atoms.

[0167] The aforementioned "alkyl groups having 1 to 8 carbon atoms" can include, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, 1-methylbutyl, 2-methylbutyl, 1-ethylpropyl, 1,2-dimethylpropyl, hexyl, n-heptyl, n-octyl, etc., without particular limitation.

[0168] By adding one or more of the aforementioned silanes selected from the group consisting of silanes and / or their partial hydrolysates as shown in Formula IV, hexamethyldisiloxane, and hexamethyldisilazine, the surface of hollow silica particles is modified. This allows organic groups to be added to the surface of the hollow silica particles, resulting in better dispersion stability of the hollow silica in certain organic solvents. Consequently, it exhibits stronger affinity with the adhesive in the coating and stronger interaction with the adhesive during the coating curing process, thus imparting better adhesion, hardness, and abrasion resistance to the coating.

[0169] In the aforementioned equation IV, by using R 4 The hydrogen atoms in the hollow silica particles are partially or completely replaced by fluorine atoms, which can further reduce the refractive index of the particles. In addition, the surface of the hollow particles is more hydrophobic, which can impart excellent anti-fingerprint, slip and stain resistance to the coating when used in coating compositions, thereby providing better wear resistance.

[0170] The surface modification steps described above can be performed after the aforementioned hollow silica generation step, and / or after the aforementioned hydrothermal treatment step, and / or after the aforementioned solvent replacement step.

[0171] The order of the aforementioned hydrothermal treatment step, solvent replacement step, and surface modification step can be randomly selected, or any one or more steps can be repeated, as long as the stability of the hollow silica sol and its dispersion in the coating composition are not impaired.

[0172] Alternatively, in the method for preparing hollow silica sol of the present invention, drying or sintering can be performed after one of the steps of hollow silica generation, hydrothermal treatment, solvent replacement, and surface modification to obtain hollow silica powder.

[0173] The hollow silica sol preparation method of this invention does not employ any hard or soft templates, but utilizes the self-assembly behavior of organosilicon intermediates in water to generate an aqueous dispersion of hollow silica particles. Subsequent template removal through high-temperature calcination, solvent etching, or acid-base dissolution is unnecessary, avoiding particle agglomeration. Hydrothermal treatment further densifies the surface of the hollow particles, resulting in a more uniform shell, higher mechanical strength, and better weather resistance. Solvent displacement yields hollow silica organosilicon sols with different dispersion systems. Surface modification further enhances the dispersion stability of the hollow particles in organic solvents and their affinity for organic resins, endowing the coating composition and coating with excellent optical, mechanical, and weather-resistant properties.

[0174] Furthermore, the hollow silica sol preparation method of the present invention, in addition to possessing excellent low refractive index suitable for antireflective coatings, also exhibits superior low dielectric properties due to the absence of metal ions. Additionally, the fine porous structure on the spherical shell allows the hollow silica particles to be used for loading and sustained release of active molecules.

[0175] [Coating Composition]

[0176] The coating composition of the present invention comprises the hollow silica sol of the present invention, a binder, and solvents and additives as needed.

[0177] As adhesives, examples include inorganic adhesives, including precursor compounds known to those skilled in the art that can form corresponding inorganic oxides through hydrolysis and condensation reactions, such as metal alkoxides, metal salts, siloxanes, silicates, and mixtures thereof. Examples also include organic adhesives, including various polymers known to those skilled in the art and monomers and oligomers that can be cured by heat or radiation (e.g., UV, electron radiation), including acrylate monomers, methacrylate monomers, and various oligomers derived from both, such as (meth)acrylate oligomers, polyurethane (meth)acrylate oligomers, epoxy (meth)acrylate oligomers, polyester (meth)acrylate oligomers, and unsaturated polyesters or polyurethanes that can be cured by free radicals in acrylates and methacrylates.

[0178] Examples of solvents include water, alcohols, ketones, ethers, esters, nitrogen-containing compounds, and sulfur-containing compounds. Examples of alcohols include methanol, ethanol, and isopropanol. Examples of ketones include acetone and methyl ethyl ketone. Examples of ethers include tetrahydrofuran and 1,4-dioxane. Examples of esters include ethyl acetate and methyl acetate. Examples of nitrogen-containing compounds include N,N-dimethylacetamide and N,N-dimethylformamide. Examples of sulfur-containing compounds include dimethyl sulfoxide.

[0179] The coating composition of the present invention may contain hollow particles or solid particles other than the hollow particles of the present invention, without impairing the effects of the present invention.

[0180] Furthermore, the coating composition of the present invention may also contain other additives, such as thermal initiators, photoinitiators, antistatic agents, leveling agents, wetting agents, defoamers, pigments, dyes, ultraviolet shielding agents, infrared shielding agents, antioxidants, anti-fingerprint agents, etc.

[0181] In the coating composition of the present invention, the weight ratio of hollow silica particles to binder can be, for example, 0.1:1 to 5:1, preferably 0.5:1 to 3:1, and more preferably 0.8:1 to 2:1. If the hollow particle / binder ratio is too low, the antireflective properties of the coating are not significant; if the ratio is too high, it cannot further improve the antireflective properties and can easily reduce the mechanical properties and weather resistance of the coating.

[0182] The coating composition of the present invention described above contains hollow particles of the present invention with low refractive index and high particle strength, thus forming a coating film with excellent anti-reflection effect and high wear resistance and hardness.

[0183] [Products]

[0184] The article of the present invention comprises a substrate and a coating on the surface of the substrate. The coating consists of one or more layers, at least one of which is formed by curing the coating composition described in the present invention.

[0185] The aforementioned coating can be formed by applying the coating composition of the present invention onto a substrate and drying it. Alternatively, the coating can be further subjected to heating, baking, or irradiation.

[0186] Examples of suitable substrates include glass, transparent polymers, and metals; there are no particular limitations.

[0187] As for coating methods, examples include bar coating, blade coating, spin coating, dip coating, roller coating, curtain coating, spray coating, slot coating, and gravure coating, etc., without any particular limitation.

[0188] The articles of the present invention described above have good anti-reflection effect, good wear resistance, and high hardness because they have a coating formed by the coating composition of the present invention.

[0189] Example

[0190] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0191] In this invention, the preparation methods are all conventional unless otherwise specified, and the raw materials used can be obtained from publicly available commercial sources unless otherwise specified. All percentages refer to mass percentages, and the temperature is in degrees Celsius (°C).

[0192] The specific meanings of the symbols involved in each embodiment and the test conditions are as follows:

[0193] Solid content: Obtained by a Precisa, XM60 solid content analyzer, after baking at 150°C until constant weight is achieved, indicating the solid content.

[0194] Viscosity: Measured by a rotational viscometer at a temperature of 25°C, with the solid content of the hollow silica sol fixed at 20%.

[0195] Average particle size: In the corresponding TEM image, 100 particles are randomly selected, and the particle size of each particle is measured. The average value of the measured particle sizes is taken as the average particle size.

[0196] Shell thickness: In the corresponding TEM image, 100 particles are randomly selected, and the wall thickness of each particle is measured. The average value of the measured shell thickness is taken as the shell thickness.

[0197] Determination of the proportions of Q1, Q2, Q3, and Q4: After drying the hollow silica sol into powder, the proportions were determined using a nuclear magnetic resonance spectrometer (Bruker AVIII HD 500 spectrometer). 29 The Si NMR spectrum was analyzed, and then the resonance peak areas Q1, Q2, Q3, and Q4 with chemical shifts of -78 to -88 ppm, -88 to -98 ppm, -98 to -108 ppm, and -108 to -117 ppm were integrated to calculate the values ​​of Q1, Q2, Q3, and Q4.

[0198] Polydispersity determination: The dispersion was measured using a dynamic light scattering instrument (Malven, Zetasizer Nano, ZS90-2027) to obtain size distribution curves and polydispersity results.

[0199] Pore ​​size distribution, pore volume, and porosity: BET was measured by static adsorption at 77 K using a Quadrasorb evo surface area and porosity analyzer (Quantachrome Instruments, USA) through N2 adsorption testing. Pore size distribution, pore volume, and porosity were determined using isothermal adsorption curves and the Barrett-Joyner-Halenda (BJH) model, and the refractive index RI was calculated using the following formula.

[0200] RI = 1.5 * (1 - Vc) + 1.0 * Vc

[0201] (Where, 1.5 represents the refractive index of silicon dioxide, 1.0 represents the refractive index of air, and V...) c (porosity)

[0202] Relative permittivity: Relative permittivity e r The capacitance C0 of the capacitor was first measured using an electrostatic field under standard atmospheric pressure when the distance between the two plates was a vacuum. Then, the capacitance C was measured after a dielectric was added between the plates while maintaining the distance between them. x The result is obtained by calculation using the following formula:

[0203] e r =C x / C0

[0204] Example 1

[0205] 208 g of tetraethoxysilane, 20 g of water, 5 g of hydrochloric acid (concentration 37%), and 30 g of polyethylene glycol (molecular weight 500) were mixed evenly and stirred. The mixture was heated to 85°C and reacted for 8 hours. Then the temperature was increased to 135°C and a vacuum was drawn until no liquid was extracted, yielding 156 g of a transparent organosilicon intermediate with a certain viscosity.

[0206] The 156 g of organosilicon intermediate obtained above was mixed with 500 g of water, and stirring was started. At the same time, 20 g of ammonia (25% by mass) was quickly added, and the reaction was continued for 24 hours to obtain hollow silica sol with a solid content of 9.2% in the hollow silica particles.

[0207] The hollow silica sol was cleaned with an ultrafiltration membrane and then subjected to hydrothermal treatment at 200°C for 12 hours to obtain hollow silica sol 1.

[0208] Transmission electron microscopy (TEM) images of hollow silica particles in the obtained hollow silica sol 1 are shown in the appendix. Figure 1 The average particle size was measured to be 55 nanometers, and the shell thickness was 5.5 nanometers.

[0209] The results of dynamic light scattering (DLS) size, PDI, Q1-Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0210] Example 2

[0211] 120 grams of silicon 48 (Gelest Int., simplest formula: SiO) 1.12 (OCH2CH3) 1.7660 g of ethanol, 2.5 g of water, 1.0 g of ammonia (concentration 25%), and 25 g of polyethylene glycol monomethyl ether (molecular weight 500) were mixed evenly and stirred. The mixture was heated to 65°C and reacted for 8 hours. Then the temperature was increased to 135°C and a vacuum was drawn until no liquid was extracted, resulting in 150 g of a transparent organosilicon intermediate with a certain viscosity.

[0212] The 150g organosilicon intermediate obtained above was mixed with 1000g of water, and stirring was started. At the same time, 50g of ammonia (25% by mass) was quickly added, and the reaction was continued for 24 hours to obtain hollow silica sol with a solid content of 4.8% in the hollow silica particles.

[0213] After the aforementioned hollow silica sol was cleaned with an ultrafiltration membrane, it was subjected to hydrothermal treatment at 150°C for 24 hours to obtain hollow silica sol 2.

[0214] Transmission electron microscopy (TEM) images of the hollow silica particles in the obtained hollow silica sol 2 are shown in the appendix. Figure 2 The average particle size was measured to be 70 nanometers, and the shell thickness was 6.5 nanometers.

[0215] The results of dynamic light scattering (DLS) size, PDI, Q1-Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0216] Example 3

[0217] 145 g of tetramethoxysilane, 5 g of methyltriethoxysilane, 75 g of isopropanol, 25 g of water, 5 g of nitric acid (63% concentration), and 40 g of polyethylene glycol monomethyl ether (molecular weight 500) were mixed evenly and stirred. The mixture was heated to 85°C and reacted for 8 hours. Then, the temperature was increased to 135°C and a vacuum was applied until no liquid was extracted, yielding 160 g of a transparent organosilicon intermediate with a certain viscosity.

[0218] The 160g organosilicon intermediate obtained above was mixed with 500g of water, and then stirred while 20g of ammonia (25% by mass) was quickly added. The mixture was stirred and reacted for 24 hours to obtain hollow silica sol with a solid content of 8.6% in the hollow silica particles.

[0219] After the aforementioned hollow silica sol was cleaned with an ultrafiltration membrane, it was subjected to hydrothermal treatment at 120°C for 12 hours to obtain hollow silica sol 3.

[0220] Transmission electron microscopy (TEM) images of the hollow silica particles in the obtained hollow silica sol 3 are shown in the appendix. Figure 3 The average particle size was measured to be 40 nanometers, and the shell thickness was 4.5 nanometers.

[0221] The results of dynamic light scattering (DLS) size, PDI, Q1-Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0222] Comparative Example 1

[0223] Except for omitting the hydrothermal treatment in Example 1, the process was carried out in the same manner as in Example 1 to obtain hollow silica sol 4.

[0224] Transmission electron microscopy (TEM) images of the obtained hollow silica particles 4 are shown in the appendix. Figure 4 The results for dynamic light scattering (DLS) size, PDI, Q1–Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0225] Comparative Example 2

[0226] Except for omitting the hydrothermal treatment in Example 2, the process was carried out in the same manner as in Example 2 to obtain hollow silica sol 5.

[0227] Transmission electron microscopy (TEM) images of the obtained hollow silica particles 5 are shown in the appendix. Figure 5 The results for dynamic light scattering (DLS) size, PDI, Q1–Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0228] Comparative Example 3

[0229] Except for omitting the hydrothermal treatment as in Example 3, the process was carried out in the same manner as in Example 3 to obtain hollow silica sol 6.

[0230] Transmission electron microscopy (TEM) images of the obtained hollow silica particles 6 are shown in the appendix. Figure 6 The results for dynamic light scattering (DLS) size, PDI, Q1–Q4 ratio, aperture distribution, pore volume, dielectric constant, etc. are shown in Table 1.

[0231] Example 4

[0232] The solvent of hollow silica sol 1 prepared in Example 1 was replaced with isopropanol using an ultrafiltration membrane and then concentrated to obtain hollow silica isopropanol sol 7 with a solid content of 20%.

[0233] Take 50g of the above hollow silica isopropanol sol 7, add 2g of γ-methacryloxypropyltrimethoxysilane and 0.2g of water, heat to 80℃ and react for 12 hours, then add 2g of trimethyl orthoformate to obtain hollow silica modified isopropanol sol 8 with a solid content of 20.5%.

[0234] Example 5

[0235] Using an ultrafiltration membrane, the solvent of hollow silica sol 2 prepared in Example 2 was replaced with isopropanol and concentrated to obtain hollow silica isopropanol sol 9 with a solid content of 20%.

[0236] Take 50g of the above hollow silica isopropanol sol 9, add 2g of γ-methacryloxypropyltrimethoxysilane and 0.2g of water, heat to 80℃ and react for 12 hours, then add 2g of trimethyl orthoformate to obtain hollow silica modified isopropanol sol 10 with a solid content of 20.5%.

[0237] Example 6

[0238] Using an ultrafiltration membrane, the solvent of the hollow silica sol 3 prepared in Example 3 was replaced with isopropanol and concentrated to obtain hollow silica isopropanol sol 11 with a solid content of 20%.

[0239] Take 50g of the above hollow silica isopropanol sol 11, add 2g of γ-methacryloxypropyltrimethoxysilane and 0.2g of water, heat to 80℃ and react for 12 hours, then add 2g of trimethyl orthoformate to obtain hollow silica modified isopropanol sol 12 with a solid content of 20.5%.

[0240] Comparative Example 4

[0241] Hollow silica sol 4 obtained in Comparative Example 1 was used instead of hollow silica sol 1 in Example 4, and the rest was carried out in the same manner as in Example 4, to obtain hollow silica modified isopropanol sol 13 with a solid content of 20.5%.

[0242] Comparative Example 5

[0243] Hollow silica sol 5 obtained in Comparative Example 2 was used instead of hollow silica sol 2 in Example 5, and the rest was carried out in the same manner as in Example 5, to obtain hollow silica modified isopropanol sol 14 with a solid content of 20.5%.

[0244] Comparative Example 6

[0245] Hollow silica sol 6 obtained in Comparative Example 3 was used instead of hollow silica sol 3 in Example 6, and the rest was carried out in the same manner as in Example 6, to obtain hollow silica modified isopropanol sol 15 with a solid content of 20.5%.

[0246] Preparation Examples 1-12

[0247] Antireflective coating compositions and examples of antireflective coating preparation:

[0248] The sols prepared in Examples 1-6 and Comparative Examples 1-6 were diluted with methyl isobutyl ketone (MIBK) to a solid content of 10%. 10 g of the sol with a solid content of 10% was taken, and 1 g of dipentaerythritol hexaacrylate (DPHA), 0.05 g of photoinitiator (Irgacure-184), and 38.95 g of MIBK were added. The mixture was thoroughly mixed to obtain 50 g of a coating composition with a solid content of 4%.

[0249] The above coating composition was coated onto a PET film (Yihua Toray, Lumiere PY2, thickness 100 micrometers) using a No. 3 wire rod (3 micrometers), dried in an oven at 80°C for 2 minutes, and then UV cured (energy 800-1500 mJ / cm). 2 A PET product containing a 100-nanometer-thick antireflective coating was prepared. Its reflectivity, haze, resistance to damp heat, pencil hardness, adhesion, and abrasion resistance were characterized, and the results are shown in Table 2.

[0250] Reflectance: Spectral reflectance was measured using a spectrophotometer (UV-3150 manufactured by Shimadzu Corporation) in the wavelength range of 300–800 nm at an incident angle of 5 degrees. The average reflectance in the range of 380–760 nm was taken as the average reflectance.

[0251] Haze: The total light transmittance and haze are measured using a haze meter.

[0252] Moisture and heat resistance: The temperature and humidity of the constant temperature and humidity chamber were set to 85℃ and 85% for 1000 hours. The moisture and heat resistance was evaluated by testing the attenuation rate of the total light transmittance of the PET products. The moisture and heat resistance was divided into the following three levels:

[0253] ◎: Attenuation less than 0.5%

[0254] ○: Attenuation ranges from 0.5% to 1.0%.

[0255] ●: Attenuation exceeds 1%

[0256] Pencil Hardness: According to Japanese JIS K 5600, the pencil hardness of the obtained coating is determined using a pencil scratch tester. On the obtained coating, a pencil is held at a 45-degree angle and scratched from above for about 5 cm with a load of 750 grams. The hardness is expressed as the pencil that does not show scratches in 4 or more out of 5 scratches.

[0257] Adhesion: 100 squares are cut into the PET coated surface with a knife. Transparent tape is then applied to the surface and peeled off. The adhesion is evaluated by observing the number of remaining squares. The number of remaining squares is divided into the following three levels:

[0258] ◎:90~100

[0259] ○: 80~89

[0260] ●: Less than 80

[0261] Abrasion resistance: Apply 500g / cm of #0000 steel wool to a 2cm x 2cm abrasive. 2 The load was applied and repeated 100 times. The condition of the abrasions was visually observed, and the evaluation criteria were as follows.

[0262] Level 5: No scratches

[0263] Level 4: One or more but no more than ten abrasions occur.

[0264] Level 3: 10 to 30 abrasions

[0265] Grade 2: More than 30 abrasions

[0266] Level 1: The entire surface is scratched or peeled.

[0267] Table 1: Properties of Hollow Silica Sol and Hollow Silica Particles

[0268]

[0269] Table 2: Performance of Coated PET Products

[0270]

[0271] As shown in Table 1, compared with Comparative Examples 1-3, the sol viscosity of Examples 1-3 decreased significantly, the surface of the spherical shell became denser, the pore size of the micropores became smaller, and the wall thickness of the hollow particles became thinner. Correspondingly, the refractive index and relative permittivity both decreased, exhibiting excellent low refractive index and low permittivity characteristics.

[0272] As shown in Table 2, the comparison revealed that hollow particles that underwent hydrothermal treatment, when used in antireflective coating compositions and coated on PET substrates, showed significant improvements in transmittance, reflectance, resistance to damp heat, pencil hardness, adhesion, and abrasion resistance compared to hollow particles that did not undergo hydrothermal treatment.

[0273] Meanwhile, comparing preparation examples 1-3 with preparation examples 7-9, it was found that when surface-modified hollow particles were used to coat an antireflective coating composition onto a PET substrate, the transmittance, reflectance, haze, resistance to damp heat, pencil hardness, adhesion, and abrasion resistance were all improved compared to unmodified hollow particles, especially the improvements in haze and abrasion resistance were very significant.

[0274] Therefore, the present invention has both excellent anti-reflection performance and outstanding mechanical properties and weather resistance.

[0275] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A hollow silica sol, characterized in that: Contains hollow silica particles and a dispersion medium. The hollow silica particles pass through 29 The resonance peak areas Q1, Q2, Q3, and Q4 corresponding to the peak values ​​in the chemical shift range of -78 to -88 ppm, measured by Si NMR spectroscopy, satisfy the following conditions: Q1 / (Q1+Q2+Q3+Q4) is essentially 0. Q2 / (Q1+Q2+Q3+Q4) is 0.01~0.

2. Q3 / (Q1+Q2+Q3+Q4) is 0.01~0.6, and, Q4 / (Q1+Q2+Q3+Q4) is 0.2~0.

98. The dispersion medium is water, an organic solvent, or a combination of both. The thickness of the shell of the hollow silica particles is 3~100nm, and the pore size distribution of the pores on the shell is in the range of 0.5~4nm.

2. The hollow silica sol according to claim 1, wherein, The hollow silica particles have a pore volume of 0.15~1 cm. 3 / g, porosity 10%~90%, refractive index 1.10~1.

45.

3. The hollow silica sol according to claim 1, wherein the relative permittivity of the hollow silica particles is 1.6 to 2.

2.

4. The hollow silica sol according to claim 1, wherein the hollow silica particles have a particle size of 15~1000 nm as measured by dynamic light scattering and a polydispersity index of 0.05~0.

3.

5. A method for preparing hollow silica sol according to any one of claims 1 to 4, characterized in that, Includes the following steps: Intermediate product generation steps: The silicon source, the first solvent, the first catalyst and the active compound are mixed and reacted in the range of 0~150℃. Then, the substance with a boiling point of less than 300℃ is removed to obtain the liquid organosilicon intermediate product P1. Hollow silica generation steps: The organosilicon intermediate P1 is dispersed in a second solvent, and a second catalyst is added, at a temperature of 0~95°C. o The reaction is carried out within the range of C to obtain hollow silica sol; Hydrothermal treatment steps: at 30~300 o Hydrothermal treatment is carried out within range C; In the intermediate product generation step, the silicon source is one or more silane monomers selected from Formula I below, or a polyalkoxysiloxane oligomer with the simplest formula shown in Formula II below. R 1 4-n Si(OR 2 ) n Formula I In formula I, n = 1, 2, 3, or 4, R 1 It is an alkyl, vinylalkyl, vinyl, epoxyalkyl, phenyl, styrylalkyl, methacryloyloxyalkyl, acryloyloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 1 At that time, each R 1 They can be either the same or different from each other; R 2 It is an alkyl group with 1 to 6 carbon atoms and has multiple Rs. 2 Each R 2 They can choose to be the same or different from each other; SiO m (OR 3 ) 4-2m Formula II In formula II, 0 < m < 2, m is an integer or non-integer, and R 3 is an alkyl group having 1 to 6 carbon atoms, and when there are multiple Rs 3 each R 3 is optionally the same as or different from each other; In the intermediate product generation step, the first catalyst is an acid or a base, and the weight ratio of the first catalyst to the silicon source is (0.001~0.5):1; In the intermediate product generation step, the active compound contains at least one OH group and has a molecular weight greater than 150, and the HLB value of the active compound calculated using Formula III below is greater than 5. HLB=20×M h / M Type III In Equation III, M h Here, M represents the molecular weight of the hydrophilic portion of the active compound. The weight ratio of the active compound to the silicon source is (0.05~0.5):1, and the active compound is one or more of the same compounds. In the hollow silica generation step, the second solvent is water, a mixture of water and a hydrophilic organic solvent, or a mixture of water and a hydrophobic organic solvent. The second catalyst is an acid or a base; The organosilicon intermediate P1 has a weight percentage of 1-60% relative to the second solvent; The weight ratio of the second catalyst to the organosilicon intermediate P1 is (0.05~2):

1.

6. The method for preparing hollow silica sol according to claim 5, wherein, In the intermediate product generation step, the first solvent is water or an aqueous organic solvent, and the weight ratio of water to the silicon source is greater than or equal to 0.001:1 and less than 0.5:

1.

7. The method for preparing hollow silica sol according to claim 5, further comprising: The solvent replacement step involves replacing the solvent in the hollow silica sol. In the solvent replacement step, all or part of the solvent in the hollow silica sol is replaced by centrifugation, heating azeotropically, or ultrafiltration.

8. The method for preparing hollow silica sol according to claim 5, further comprising the following steps: Surface modification step: Add one or more substances selected from the group consisting of silanes and / or their partial hydrolysates represented by Formula IV, hexamethyldisiloxane, and hexamethyldisilazane to the hollow silica sol to modify the surface of the hollow silica particles. R 4 p -Si-X 4-p Formula IV In equation IV, p = 0, 1, 2, or 3, R 4 Selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 4 At that time, each R 4 Whether they are the same or different, R 4 The hydrogen atoms in the fluorine atom can be partially or completely replaced by fluorine atoms. X is selected from alkoxy groups with 1-6 carbon atoms, halogens, or hydrogen. When there are multiple Xs, each X may be the same or different from the others. The surface modification step is performed after the hollow silica generation step and / or after the hydrothermal treatment step.

9. The method for preparing hollow silica sol according to claim 7, further comprising the following steps: Surface modification step: Add one or more substances selected from the group consisting of silanes and / or their partial hydrolysates represented by Formula IV, hexamethyldisiloxane, and hexamethyldisilazane to the hollow silica sol to modify the surface of the hollow silica particles. R 4 p -Si-X 4-p Formula IV In equation IV, p = 0, 1, 2, or 3, R 4 Selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, urealkyl, chloroalkyl, mercaptoalkyl, isocyanate alkyl, or hydroxyalkyl, having multiple Rs. 4 At that time, each R 4 Whether they are the same or different, R 4 The hydrogen atoms in the fluorine atom can be partially or completely replaced by fluorine atoms. X is selected from alkoxy groups with 1-6 carbon atoms, halogens, or hydrogen. When there are multiple Xs, each X may be the same or different from the others. The surface modification step is performed after the hollow silica generation step, and / or after the hydrothermal treatment step, and / or after the solvent replacement step.

10. The method for preparing hollow silica sol according to claim 9, wherein the hydrothermal treatment step and / or the solvent replacement step are performed again after the surface modification step.

11. A coating composition comprising hollow silica sol and an adhesive, wherein the hollow silica sol is the sol according to any one of claims 1 to 4.

12. An article, characterized in that, The substrate surface has a coating, said coating having one or more layers, at least one of said coatings being formed by curing the coating composition of claim 11.

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