Silica hollow particles, method for producing the same, coating composition, and article

Abstract

The present invention relates to silica hollow particles, a method for preparing the same, a coating composition, and an article. The silica hollow particles of the present invention are formed by a shell mainly composed of silica. The thickness of the shell is 5 to 100 nm, and mesopores with a size of 4 to 10 nanometers are present on the shell. The pore volume of the silica hollow particles is 0.35 to 0.65 cm<supgt;3< / supgt> / g, the porosity is 40% to 60%, and the refractive index is 1.15 to 1.35. The method for preparing the silica hollow particles of the present invention can directly obtain a hollow structure without using a template. Pores exist simultaneously inside the particles and in the spherical shell, ensuring mechanical strength while increasing the porosity. A high-concentration particle dispersion can be obtained without adding any dispersing aids. It is widely used in transparent antireflection coatings, and no metal or non-metal ions are introduced during the preparation process, having excellent low dielectric properties. The spherical shell contains mesoporous channels and can be used for encapsulation and slow release.

Description

Technical Field

[0001] The present invention relates to silica hollow particles, and particularly to silica hollow particles and a preparation method thereof. Background Art

[0002] Silica hollow particles have characteristics such as high porosity, low refractive index, low dielectric constant, and biotoxicity, and thus are widely used in fields such as lightweight, low-refractive-index materials, antireflection coatings, semiconductor materials, and active molecule loading.

[0003] In fields such as low-refractive-index materials and antireflection coatings that require silica hollow particles to have a low refractive index, too large particle size will lead to enhanced light scattering, so the particle size is required to be in the range of dozens of nanometers to several micrometers.

[0004] The applicant disclosed a preparation method of silica hollow particles in CN110128855A, that is, first using the hydrolysis and condensation of silane monomers in water to prepare an amphiphilic polyalkoxysiloxane, and then using its self-assembly behavior in an aqueous medium to obtain silica hollow particles. The silica hollow particles have excellent dispersibility and controllable size, and have good applications in the field of antireflection. However, the silica shell layer of the hollow particles does not have an obvious mesoporous structure, resulting in a low porosity. If the porosity needs to be further improved, only the internal cavity volume can be increased, which leads to poor hardness of the hollow particles. When using the particles to prepare an antireflection coating, there are problems such as low coating hardness and poor wear resistance. At the same time, considering the enhanced light scattering of large particles, simply increasing the cavity does not result in better antireflection.

[0005] Therefore, in order to obtain a low refractive index and control the particle size at the same time, it has been reported that on the premise of a certain hollow particle size, the wall of the silica hollow particle is made thinner. However, if the wall of the silica hollow particle is too thin, it will also lead to a decrease in the mechanical strength of the particle. For example, CN102196996A discloses using zinc oxide particles as a template to prepare nanocomposite particles with a core-shell structure, and then obtaining thin-walled silica hollow particles after removing the zinc oxide used as a template. However, it is found that only by densifying the silica shell layer can sufficient mechanical strength be obtained. But densification will also lead to a decrease in the pore volume of the silica hollow particles, making the antireflection effect of the antireflection coating prepared using the hollow particles worse.

[0006] Therefore, how to obtain hollow particles with good pore volume without sacrificing mechanical strength, and when used in an antireflection coating, can maintain excellent antireflection performance, hardness and wear resistance is an urgent problem to be solved.

[0007] Patent Documents:

[0008] Patent Document 1: CN110128855A

[0009] Patent Document 2: CN102196996A SUMMARY OF THE INVENTION

[0010] The present invention provides silica hollow particles having both good particle strength and good pore volume, a method for producing the same, a coating composition capable of forming a coating film having a high antireflection effect and good abrasion resistance, and a coating having a high antireflection effect and good abrasion resistance.

[0011] The present invention provides the following technical solutions:

[0012] [1] A silica hollow particle formed of a shell mainly composed of silica, the thickness of the shell being 5 to 100 nm,

[0013] having mesopores of 4 to 10 nm on the shell, the pore volume of the silica hollow particle being 0.35 to 0.65 cm 3 / g, the porosity being 40% to 60%, and the refractive index being 1.15 to 1.35.

[0014] [2] The silica hollow particle according to [1], having a relative dielectric constant of 1.6 to 2.2.

[0015] [3] The silica hollow particle according to [1] or [2], the particle size of the silica hollow particle being 15 to 1000 nm, and its polydispersity index being 0.05 to 0.2.

[0016] [4] A method for producing the silica hollow particle according to any one of [1] to [3], comprising the following steps:

[0017] (1) Organosilicon intermediate generation step: mixing a silicon precursor, an acid anhydride, and a first catalyst, heating for reaction, and removing a first reaction by-product to obtain an organosilicon intermediate;

[0018] (2) Organosilicon intermediate generation step having surface activity: mixing the organosilicon intermediate obtained in the step (1) with a hydroxyl group-containing hydrophilic compound, heating for reaction, and removing a second reaction by-product to obtain an organosilicon intermediate having surface activity;

[0019] (3) Silica hollow particle generation step: mixing the organosilicon intermediate having surface activity obtained in the step (2) with an aqueous solvent and a second catalyst for reaction to obtain a dispersion containing silica hollow particles.

[0020] [5] The method for producing the silica hollow particle according to [4], the conductivity of the silica hollow particle dispersion obtained in the step (3) being 50 to 1000 μs / cm, and the pH of the dispersion being 4 to 10.

[0021] The method for preparing silica hollow particles according to [6][4] or [5], wherein the silicon precursor is a silane monomer represented by the following formula I or a polyalkoxysiloxane oligomer with a silica mass percentage of 80% or less,

[0022] R 1 4-n Si(OR 2 ) n Formula I

[0023] where n = 2 to 4;

[0024] R 1 is alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, ureidoalkyl, chloropropylalkyl, thioalkyl, isocyanatealkyl, or hydroxyalkyl. When there are multiple Rs, 1 each R 1 is optionally the same as or different from each other;

[0025] R 2 is alkyl with 1 to 6 carbon atoms. When there are multiple Rs, 2 each R 2 is optionally the same as or different from each other.

[0026] The method for preparing silica hollow particles according to any one of [7][4] to [6], wherein the acid anhydride in the aforementioned step (1) is at least one selected from phthalic anhydride, acetic anhydride, formic anhydride, propionic anhydride, maleic anhydride, and chromic anhydride, and the molar ratio of the acid anhydride to the silicon precursor is 0.01:1 or more and less than 2:1.

[0027] The method for preparing silica hollow particles according to any one of [8][4] to [7], wherein the first catalyst in the aforementioned step (1) is at least one selected from metal alkoxides and metal carboxylates, and the molar ratio of the first catalyst to the silicon precursor is (0.01 to 10):100.

[0028] The method for preparing silica hollow particles according to any one of [9][4] to [8], wherein in the aforementioned step (2), the hydroxy-containing hydrophilic compound is at least one selected from the group consisting of polyacrylic acid, polyethylene glycol, polyethylene glycol monoether, polyvinyl alcohol, polyglycerol, and a copolymer of ethylene oxide and propylene oxide, and the mass ratio of the hydroxy-containing hydrophilic compound to the organosilicon intermediate is (0.05 to 0.5):1.

[0029] The method for preparing silica hollow particles according to any one of

[10] [4] to [9], wherein,

[0030] In the foregoing step (3), the foregoing aqueous solvent is water, a mixture of water and a hydrophilic solvent, or a mixture of water and a hydrophobic solvent; the foregoing second catalyst is selected from acids or bases; the mass percentage of the foregoing surfactant-containing organosilicon intermediate relative to the solvent is 1 to 60%; the mass ratio of the foregoing second catalyst to the solvent is (0.01 to 0.5):1.

[0031]

[11] A coating composition containing the hollow particles described in any one of [1] to [3] and a dispersion medium.

[0032]

[12] An article having a coating formed from the coating composition described in

[11] on a substrate, the hardness of the coating being 1H to 3H, and the average reflectance of the coating being less than 1.0% in the wavelength range of 380 to 760 nm.

[0033] Advantages of the Invention

[0034] The oxide hollow particles of the present invention have high particle strength and high pore volume.

[0035] By the method for preparing oxide hollow particles of the present invention, oxide hollow microparticles having high particle strength and high pore volume can be prepared.

[0036] The coating composition of the present invention can form a coating film having a high antireflection effect and good abrasion resistance.

[0037] The article of the present invention has a high antireflection effect and good abrasion resistance. Brief Description of the Drawings

[0038] Figure 1 Transmission electron microscope (TEM) photograph of the silica hollow particles obtained in Example 1;

[0039] Figure 2 Dynamic light scattering (DLS) diagram of the silica hollow particles obtained in Example 1 in water;

[0040] Figure 3 Pore size distribution diagram of the silica hollow particles obtained in Example 1;

[0041] Figure 4 Transmission electron microscope (TEM) photograph of the silica hollow particles obtained in Example 2;

[0042] Figure 5 Dynamic light scattering (DLS) diagram of the silica hollow particles obtained in Example 2 in water;

[0043] Figure 6 Pore size distribution diagram of the silica hollow particles obtained in Example 2;

[0044] Figure 7 Transmission electron microscope (TEM) photograph of the silica hollow particles obtained in Example 3;

[0045] Figure 8 Dynamic light scattering (DLS) diagram of the silica hollow particles obtained in Example 3 in water;

[0046] Figure 9 Pore size distribution diagram of the silica hollow particles obtained in Example 3;

[0047] Figure 10 Transmission electron microscope (TEM) photograph of the silica hollow particles obtained in Example 4;

[0048] Figure 11 Dynamic light scattering (DLS) diagram of the silica hollow particles obtained in Example 4 in ethyl acetate;

[0049] Figure 12 Transmission electron microscope (TEM) photograph of the white emulsion obtained in Comparative Example 1;

[0050] Figure 13 Transmission electron microscope (TEM) photograph of the white suspension obtained in Comparative Example 2; Detailed implementation mode

[0051] [Silica hollow particles]

[0052] The silica hollow particles are fine particles with a shell mainly composed of silica and a void inside the shell.

[0053] The aforementioned "shell mainly composed of silica" means that the proportion of silica in the hollow particles is 90% by mass or more. Considering the reduction of the refractive index of the hollow particles, it is preferably 95% by mass or more, and more preferably substantially 100% silica.

[0054] The thickness of the shell of the hollow particles is 5 - 100 nm. When the thickness of the shell is 5 nm or more, it has sufficient strength, and when the thickness of the shell is 100 nm or less, it is beneficial to obtain an appropriate refractive index. The thickness of the shell can be appropriately adjusted by the amount of reaction raw materials such as organosilicon intermediates and the reaction temperature in the manufacturing conditions of the hollow particles. Considering the perspective of obtaining an excellent refractive index, the thickness of the shell is more preferably 6 - 20 nm.

[0055] The thickness of the shell is measured by the following method: observing the hollow particles through a transmission electron microscope (TEM), randomly selecting 100 particles, measuring the thickness of the shell of each hollow particle, and averaging the measured values.

[0056] The shell of the silica hollow particles has mesopores with a size of 4 to 10 nm. By having mesopores with a size of more than 4 nm, a high pore volume, porosity, and low refractive index and relative dielectric constant can be obtained. If the mesopores of the shell of the hollow particles are 10 nm or less, the hollow particles have good particle strength, and when used as a coating composition to form a coating film, good abrasion resistance can be obtained. From the perspective of refractive index and relative dielectric constant, it is more preferably 4 to 6 nm.

[0057] The pore volume of the silica hollow particles is 0.35 to 0.65 cm 3 / g. When the pore volume of the silica hollow particles is 0.35 cm 3 / g or more, the particles can have a lower refractive index. When the pore volume of the silica hollow particles is 0.65 cm 3 / g or less, the particles have sufficient strength.

[0058] The size and pore volume of the aforementioned mesopores can be measured by the following method: static adsorption measurement is carried out at 77K using a Quadrasorb evo specific surface area and porosity analyzer (Quantachrome Instruments, USA). The mesopore size and pore volume of the silica hollow particles are measured using an isothermal adsorption curve and the Barrett-Joyner-Halenda (BJH) model.

[0059] The refractive index of the silica hollow particles is 1.15 to 1.35. When the refractive index of the silica hollow particles is 1.15 or more, the hollow particles have better hardness and strength. When the refractive index of the silica hollow particles is 1.35 or less, they have a lower refractive index and show excellent performance in an antireflection coating.

[0060] Preferably, the relative dielectric constant of the silica hollow particles is 1.6 to 2.2. When the relative dielectric constant of the silica hollow particles is 1.6 or more, the particles have sufficient strength in a composite dielectric material. When the relative dielectric constant is 2.2 or less, they have excellent dielectric properties and low dielectric loss.

[0061] Preferably, the particle size of the silica hollow particles is 15 to 1000 nm. From the perspective of the transparency of the formed optical coating, it is more preferably 20 to 500 nm, and further preferably 20 to 100 nm.

[0062] Preferably, the polydispersity index (PDI) of the silica hollow particles is 0.05 to 0.2. The aforementioned polydispersity index is obtained from the dynamic light scattering (DLS) test data of the hollow particle dispersion. The lower the PDI index, the more uniform the size distribution of the hollow particles, and the more inclined to monodispersity. A PDI below 0.2 means that the silica hollow particles have a relatively uniform size distribution. After being formed into a coating, the coating surface has a lower roughness and more excellent mechanical properties.

[0063] For the silica hollow particles of the present invention described above, by setting the mesopores and wall thickness of appropriate sizes, defects such as the reduction of particle strength caused by the reduction of wall thickness due to the pursuit of high porosity in traditional silica hollow particles, resulting in the collapse of hollow particles and poor wear resistance when forming a coating, are avoided. On the one hand, by having an appropriate mesoporous structure on the shell, compared with the hollow particles with a dense shell layer, it has a higher pore volume and a higher overall porosity, and has excellent antireflection performance when formed into a coating. On the other hand, compared with the hollow particles with a small shell thickness, by increasing the shell thickness and setting the mesopores of appropriate sizes, the particles have good mechanical strength, and thus have good hardness and wear resistance when formed into a coating.

[0064] [Preparation method of silica hollow particles]

[0065] As the preparation method of the silica hollow particles of the present invention, the following preparation method can be adopted.

[0066] This preparation method includes the following steps:

[0067] (1) Organosilicon intermediate generation step: A step of mixing a silicon precursor, an acid anhydride, and a first catalyst, heating for reaction, and removing the first reaction by-product to obtain an organosilicon intermediate;

[0068] (2) Generation step of organosilicon intermediate with interfacial activity: A step of mixing the organosilicon intermediate obtained in the previous step (1) with a hydroxyl-containing hydrophilic compound, heating for reaction, and removing the second reaction by-product to obtain an organosilicon intermediate with interfacial activity;

[0069] (3) Silica hollow particle generation step: A step of mixing the organosilicon intermediate with interfacial activity obtained in the previous step (2) with an aqueous solvent and a second catalyst for reaction to obtain a dispersion containing silica hollow particles.

[0070] The above steps will be described in sequence below.

[0071] [Organosilicon intermediate generation step]

[0072] In the above-mentioned step of forming the silicone intermediate, under the catalysis of the first catalyst and heating conditions, the silicon precursor reacts with the anhydride through an esterification condensation reaction to form a silicone intermediate and small molecule ester compounds as by-products.

[0073] The above-mentioned silicon precursor is a silicon source for forming silicon dioxide hollow particles, and there is no limitation on the composition of the silicon precursor, as long as it contains an alkoxy group and can form a silicone intermediate through an esterification condensation reaction with the anhydride.

[0074] Preferably, the above-mentioned silicon precursor is a silane monomer having the structure shown in Formula I below, or a polyalkoxysiloxane oligomer with a silica mass content percentage of 80% or less.

[0075] R 1 4-n Si(OR 2 ) n Formula I

[0076] where n = 2 - 4;

[0077] In Formula I, R 1 is selected from alkyl, vinylalkyl, epoxyalkyl, styrylalkyl, methacryloxyalkyl, acryloxyalkyl, aminoalkyl, ureidoalkyl, chloropropylalkyl, thioalkyl, isocyanatealkyl, or hydroxyalkyl. When there are multiple Rs 1 , each R 1 is optionally the same or different from each other;

[0078] OR 2 is a hydrolyzable group, R 2 is an alkyl group with 1 - 6 carbon atoms. When there are multiple ORs 2 , each OR 2 is optionally the same or different from each other.

[0079] The silica mass percentage in the above-mentioned polyalkoxysiloxane oligomer is determined by the following method: Mix 25% concentrated ammonia water and absolute ethanol in equal volume and mix evenly. Take a certain mass of the polyalkoxysiloxane oligomer and place it in an alumina crucible. Add an equal mass of the mixed solution of concentrated ammonia water and ethanol, mix evenly, and place it in a fume hood overnight. Then place the crucible in a muffle furnace and calcine it at 800 °C for 2 hours. Measure the mass percentage of the residual solid in the crucible to the initially added polyalkoxysiloxane oligomer, and this mass percentage is the silica mass percentage in the above-mentioned polyalkoxysiloxane oligomer. Examples of such polyalkoxysiloxane oligomers include commercially available Silicone 40, Silicone 48, Silicone 53, Silicone 63, etc.

[0080] As the aforementioned silicon precursor, one of the silane monomers having the structure shown in the aforementioned Formula I or the aforementioned polyalkoxy siloxane oligomer can be used, or both can be used in combination. Preferably, the aforementioned silicon precursor is at least one selected from tetraethyl silicate, tetramethyl silicate, Si40, and Si48.

[0081] As the aforementioned acid anhydride, preferably, at least one selected from phthalic anhydride, acetic anhydride, formic anhydride, propionic anhydride, maleic anhydride, and chromic anhydride can be exemplified.

[0082] The molar ratio of the aforementioned acid anhydride to the silicon precursor is preferably 0.01:1 or more and less than 2:1. In the aforementioned step (1), the acid anhydride reacts with the alkoxy group in the silicon precursor to form an ester compound, and at the same time induces the condensation of the silicon precursor. When the molar ratio is 0.01:1 or more, the molecular weight of the obtained organosilicon intermediate is high enough, and the hydrophilicity is not too strong after reacting with the hydroxyl group-containing hydrophilic compound, and interfacial activity can be generated. When the molar ratio is less than 2:1, the molar equivalent of the acid anhydride relative to the silicon precursor is insufficient, so that there are still residual alkoxy groups on the organosilicon intermediate generated after the reaction, which is beneficial to the subsequent reaction with the hydroxyl group-containing hydrophilic compound.

[0083] In addition, the molar ratio of the acid anhydride to the silicon precursor is one of the factors affecting the wall thickness of the silica hollow particles as the final product, and the wall thickness of the silica hollow particles increases as the molar ratio of the acid anhydride to the silicon precursor increases. From the perspective of obtaining a sufficient wall thickness of the silica hollow particles so that the silica hollow particles have sufficient strength, the molar ratio of the acid anhydride to the silicon precursor is preferably 0.5:1 or more. From the perspective of the wall thickness of the silica hollow particles not being too thick so as to have a low refractive index, the molar ratio of the acid anhydride to the silicon precursor is preferably 1.5:1 or less.

[0084] Preferably, the aforementioned first catalyst is a metal alkoxide or a metal carboxylate. As such a metal alkoxide, for example, there are titanium alkoxides, aluminum alkoxides, zirconium alkoxides, etc. As such a metal carboxylate, for example, there are tin acetate, aluminum acetate, zirconium acetate, etc. From the perspective of reaction controllability, the aforementioned first catalyst is preferably a titanium alkoxide. As a titanium alkoxide, for example, tetramethoxy titanium, tetraethoxy titanium, tetrapropoxy titanium, etc. can be exemplified.

[0085] The molar ratio of the aforementioned first catalyst to the aforementioned silicon precursor is preferably 0.01-10:100. Controlling this molar ratio to be 10:100 or less is beneficial to preventing the formation of a gel-like solid caused by too fast reaction rate, and controlling this molar ratio to be 0.01:100 or more is beneficial to improving the catalytic efficiency and obtaining an appropriate reaction rate.

[0086] In the above-mentioned step of forming the silicone intermediate, the temperature of the above-mentioned heating reaction is 30 to 200 °C, preferably 60 to 150 °C. From the perspective of more fully removing reaction by-products and retaining the desired products, it is more preferably 125 to 140 °C.

[0087] In the above-mentioned step of forming the silicone intermediate, the heating reaction time is, for example, 1 to 24 hours, preferably 5 to 15 hours. From the perspective of balancing reaction sufficiency and reaction efficiency, it is more preferably 8 to 10 hours.

[0088] In the above-mentioned step of forming the silicone intermediate, the silicon precursor reacts with the acid anhydride under the action of the first catalyst by heating. The reaction of tetraethyl orthosilicate with acetic anhydride under the catalysis of tetraethoxytitanium is taken as an example for illustration. The ethoxy groups in tetraethyl orthosilicate react with acetic anhydride under the catalysis of tetraethoxytitanium to form ethyl acetate. In addition, tetraethyl orthosilicate undergoes condensation with each other. The presence of the first catalyst can accelerate the esterification reaction and further promote the condensation of tetraethyl orthosilicate to form a silicone intermediate.

[0089] During the above-mentioned reaction process, due to the esterification reaction between the acid anhydride and the alkoxy group and the condensation reaction of the silicon precursor, while forming a silicone intermediate with the target molecular weight, a part of by-products will also be generated. As the above-mentioned first by-products, for example, oligomeric silicone intermediates and low molecular weight ester compounds formed by the esterification of the above-mentioned acid anhydride and the alkoxy group in the silicon precursor can be listed.

[0090] The removal of the above-mentioned first reaction by-products has a crucial impact on the preparation of silica hollow particles. By removing the ester compounds as by-products therein, the polycondensation of the silicon precursor can proceed in a positive direction to obtain a silicone intermediate with a higher molecular weight, and finally form silica hollow particles. By removing the oligomeric silicone intermediates, the particle size of the silica hollow particles in the final product is more uniform and easier to control. The molecular weight range of the above-mentioned first reaction by-products is, for example, in the range of about 60 to 1000.

[0091] The methods for removing the above-mentioned first reaction by-products can include, for example, one or a combination selected from atmospheric distillation, vacuum distillation, thin-film evaporation, or rotary evaporation. The removal of the above-mentioned first reaction by-products can be carried out together with the heating reaction. During the reaction process, when it is observed that a liquid is distilled out, it indicates that the first reaction by-products are being removed. After the heating reaction is completed, the removal of the above-mentioned first reaction by-products can be further carried out to fully remove the first reaction by-products. During the removal process, when it is observed that no liquid is distilled out or the mass of the liquid in the collection bottle no longer changes for a certain period of time, it is considered that the first reaction by-products have been completely removed.

[0092] [Step for Generating Organosilicon Intermediate with Surface Activity]

[0093] In the step for generating an organosilicon intermediate with surface activity, the organosilicon intermediate obtained in the aforementioned step for generating an organosilicon intermediate is mixed with a hydroxyl group-containing hydrophilic compound, heated for reaction, and the second reaction by-product is removed to obtain an organosilicon intermediate with surface activity.

[0094] In the step for generating an organosilicon intermediate with surface activity, the temperature for the heating reaction can be, for example, 30 to 200 °C, preferably 60 to 180 °C. From the perspective of more fully removing the reaction by-products and retaining the desired product, it is more preferably 125 to 150 °C.

[0095] The time for the heating reaction can be, for example, 1 to 24 hours, preferably 5 to 15 hours, and more preferably 8 to 10 hours.

[0096] In this step, the alkoxy group that was not reacted in the aforementioned step (1) in the organosilicon intermediate and the hydroxyl group in the hydroxyl group-containing hydrophilic compound undergo a transesterification reaction under heating conditions. While generating small molecule alcohols, the hydroxyl group-containing hydrophilic compound is grafted onto the organosilicon intermediate to form an organosilicon intermediate with a certain hydrophilicity, which is called an organosilicon intermediate with surface activity.

[0097] During the aforementioned heating reaction, in addition to generating the aforementioned organosilicon intermediate with surface activity, low molecular weight second reaction by-products such as alcohols are also generated.

[0098] The removal of the aforementioned second reaction by-product can be carried out during the heating reaction. By continuously removing the second reaction by-product, the aforementioned transesterification reaction continuously proceeds in the forward direction, improving the efficiency of grafting the hydroxyl group-containing hydrophilic compound onto the organosilicon intermediate. The removal of the aforementioned second reaction by-product can be carried out by, for example, atmospheric distillation, vacuum distillation, thin film evaporation, or rotary evaporation, etc., without particular limitation, and these methods can also be combined for carrying out. In addition, after the aforementioned heating reaction is completed, the removal of the aforementioned second reaction by-product can be continued until the aforementioned second reaction by-product is basically completely removed.

[0099] Examples of the aforementioned hydroxyl group-containing hydrophilic compound include one or a combination of those selected from polyacrylic acid, polyethylene glycol, polyethylene glycol monoether, polyvinyl alcohol, polyglycerol, and copolymers of ethylene oxide and propylene oxide.

[0100] The mass ratio of the aforementioned hydroxyl-containing hydrophilic compound to the aforementioned silicone intermediate can be, for example, (0.05 to 0.5):1. By controlling this mass ratio to be 0.05:1 or more, the resulting silicone intermediate can have sufficient hydrophilicity, so that it is not likely to agglomerate in the aqueous solvent and can form particles with a hollow structure. By controlling this mass ratio to be 0.5:1 or less, the resulting silicone intermediate has partial hydrophobicity, thus having appropriate surface activity and being able to form hollow particles in the subsequent step (3).

[0101] In addition, the ratio of the hydroxyl-containing hydrophilic compound to the silicone intermediate is one of the factors affecting the particle size of the silica hollow particles as the final product. The larger the ratio of the hydroxyl-containing hydrophilic compound to the silicone intermediate, the smaller the particle size of the obtained silica hollow particles. From the perspective of obtaining an appropriate particle size, the ratio of the hydroxyl-containing hydrophilic compound to the silicone intermediate is preferably (0.1 to 0.5):1.

[0102] [Silica hollow particle generation step]

[0103] In the silica hollow particle generation step, when the aforementioned surface-active silicone intermediate is dispersed in the aqueous solvent, it assembles into a structure similar to a vesicle. Both the inside and outside of the vesicle are aqueous solvents, and the silicone intermediate is enriched at the interface. Under the action of the second catalyst, the surface-active silicone intermediate rapidly hydrolyzes and condenses to form a relatively dense silica shell layer, thereby obtaining a dispersion containing monodisperse silica hollow particles.

[0104] Under the action of the second catalyst, the surface-active silicone intermediate further hydrolyzes and condenses. While it transforms into silica, small-molecule alcohols are released. Without significant change in the vesicle size, the loss of small-molecule alcohols will introduce a sufficient number of mesopores on the silica spherical shell. By adjusting the type and dosage of the second catalyst, the mesopore size, pore volume, and refractive index of the hollow particles can be controlled. Generally, acid catalysts form mesopores with small size, low pore volume, and high refractive index, while base catalysts form mesopores with large size, high pore volume, and low refractive index.

[0105] The aforementioned aqueous solvent refers to water, or a combination of water and a hydrophilic solvent, or a combination of water and a hydrophobic solvent. As such a hydrophilic solvent, organic solvents miscible with water such as alcohols, ketones, and ethers can be listed. As such a hydrophobic solvent, organic solvents such as alkanes, aromatic hydrocarbons, and esters can be listed.

[0106] The aforementioned second catalyst may be, for example, an acid or a base. As the acid, it may be an organic acid or an inorganic acid. As the inorganic acid, for example, hydrochloric acid, nitric acid, sulfuric acid, etc. may be cited. As the organic acid, formic acid, acetic acid, acrylic acid, etc. may be cited. As the base, it may be an inorganic base or an organic base. As the aforementioned inorganic base, sodium hydroxide, potassium hydroxide, ammonia water, etc. may be cited. As the aforementioned organic base, triethylamine, etc. may be cited. In addition, when acid salts, basic salts, etc. are in the form of salts but exhibit acidity or basicity, as long as they can act as the aforementioned second catalyst to cause the interfacially active organosilicon intermediate to react to form silica hollow particles, they are considered to belong to the category of the aforementioned second catalyst.

[0107] In the aforementioned silica hollow particle forming step, from the perspective of obtaining an appropriate dispersion viscosity and production efficiency, the mass percentage of the interfacially active organosilicon intermediate relative to the aqueous solvent is 1 to 60%, and the mass ratio of the second catalyst relative to the aqueous solvent is (0.01 to 0.5):1.

[0108] Through the aforementioned silica hollow particle forming step, a dispersion containing silica hollow particles with good dispersibility can be obtained. The conductivity of the aforementioned dispersion is preferably 50 to 1000 μs / cm. By setting the conductivity of the dispersion to 50 μs / cm or more, the silica hollow particles can be kept in good stability in the dispersion and gelation can be avoided. By setting the conductivity of the dispersion to 1000 μs / cm or less, the subsequent modification treatment of the silica hollow particles can be more easily carried out. At the same time, when the silica hollow particles are used as a low dielectric material, the lower conductivity results in a lower relative dielectric constant and lower dielectric loss. The conductivity of the aforementioned dispersion can be adjusted to the aforementioned range through an ion exchange resin.

[0109] The pH of the aforementioned dispersion may be, for example, in the range of 4 to 10.

[0110] The preparation method of the silica hollow particles described above can obtain silica hollow particles with excellent monodispersity and no agglomeration without performing steps such as removing the core of the hollow particles by high-temperature calcination, solvent etching, or acid-base dissolution.

[0111] In addition, in the preparation method of the oxide hollow particles described above, by removing the first reaction by-product and the second reaction by-product, controlling the mesopore size, wall thickness, particle size, and monodispersity, oxide hollow microparticles with high particle strength and high pore volume can be prepared.

[0112] The dispersion liquid containing silica hollow particles obtained in the above-mentioned silica hollow particle generation step can be directly used as a component of the coating composition. A high-concentration particle dispersion liquid can be obtained without adding any dispersion aids and is widely used in transparent antireflection coatings. In addition, it can also be stored as a concentrated liquid after concentration, or further dried and stored in the form of a powder of silica hollow particles for later use.

[0113] In addition, no metal or non-metal ions are introduced in the preparation process of the oxide hollow particles, and they have excellent low dielectric properties.

[0114] The shell layer of the hollow particles obtained by the above-mentioned preparation method of the oxide hollow particles contains mesoporous channels and can be used for coating and slow release.

[0115] Optionally, in the preparation method of the silica hollow particles of the present invention, the following post-treatment step and modification step can be further included:

[0116] Post-processing step

[0117] The dispersion liquid containing silica hollow particles obtained in the above-mentioned silica hollow particle generation step is separated, washed and concentrated to obtain a concentrated liquid of silica hollow particles; or further dried to obtain a powder of silica hollow particles.

[0118] The above-mentioned separation can be, for example, centrifugal separation, ultrafiltration separation, or dialysis separation, etc.

[0119] The type of solvent used for the above-mentioned washing can be appropriately selected according to the solution environment required for subsequent use. The amount of the solvent used for the above-mentioned washing can also be appropriately selected according to the concentration of the silica hollow particles required for subsequent use, etc., and there is no particular limitation.

[0120] The above-mentioned separation and washing can be repeated.

[0121] The above-mentioned drying can be carried out under heating and / or vacuum conditions and can be heating drying, freeze drying or spray drying, etc.

[0122] Modification step

[0123] The concentrated liquid of silica hollow particles obtained in the above-mentioned post-treatment step is mixed with a non-aqueous solvent and a silane coupling agent for reaction, and the water brought by the above-mentioned concentrated liquid is removed to obtain a non-aqueous solvent dispersion liquid of silica hollow particles; or the powder of silica hollow particles obtained in the above-mentioned post-treatment step is dispersed in a non-aqueous solvent, and a silane coupling agent is added for reaction to obtain a non-aqueous solvent dispersion liquid of silica hollow particles.

[0124] The aforementioned non-aqueous solvents are, for example, methanol, ethanol, isopropanol, propylene glycol ethyl ether, propylene glycol methyl ether, ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, benzene, toluene, xylene, cyclohexane, n-hexane, etc.

[0125] Preferably, the aforementioned silane coupling agent has the following chemical formula,

[0126] R 3 4-m SiR 4 m or R 5 3Si-O-Si-R 5 3 or R 5 3Si-NH-Si-R 5 3

[0127] wherein, m = 1 to 3, R 3 、R 5 are each independently selected from alkyl, vinyl alkyl, epoxy alkyl, styryl alkyl, methacryloxy alkyl, acryloxy alkyl, amino alkyl, ureido alkyl, chloropropyl alkyl, thioalkyl, isocyanate alkyl, or hydroxy alkyl; R 4 is selected from alkoxy groups having 1 to 6 carbon atoms, chlorine, bromine, or iodine, and when there are multiple R 3 each R 3 may be the same or different from each other optionally, and when there are multiple R 4 each R 4 may be the same or different from each other optionally, and when there are multiple R 5 each R 5 may be the same or different from each other optionally.

[0128] The aforementioned silane coupling agent can be used in an amount of, for example, 1 to 60% by mass relative to the mass of the aforementioned silica hollow particles.

[0129] Through the aforementioned modification step, the silica hollow microparticles can be better compatible with other solvent-based coating compositions and can meet the requirements of different dispersion systems.

[0130] The method for preparing the silica hollow particles of the present invention does not use any hard template or soft template, and utilizes the self-assembly behavior of an organosilicon intermediate with interfacial activity in water to generate an aqueous dispersion of silica hollow particles. In the later stage, there is no need to remove the template by means of high-temperature calcination, solvent etching, acid-base dissolution, etc., avoiding the aggregation of the hollow particles, and being able to perform surface treatment on the silica hollow particles in the state of aqueous dispersion or powder state, so that they can be dispersed in water and most organic solvents without a dispersion aid, achieving a dispersion concentration of more than 20% by mass percentage without aggregation, and avoiding the negative impact brought by the use of a dispersion aid to the backend product.

[0131] Furthermore, the method for preparing silica hollow particles of the present invention enables the silica hollow particles to have a mesoporous structure with a pore size of 4 to 10 nanometers on the spherical shell in addition to the internal cavity, which further increases the pore volume of the hollow particles and makes the low dielectric and low refractive properties more excellent. In addition, the mesoporous structure on the spherical shell contributes greatly to the overall porosity of the particles, avoiding the defect that the mechanical properties of traditional silica hollow particles deteriorate due to continuously reducing the wall thickness in the pursuit of high porosity. On the other hand, the mesoporous structure present in the spherical shell enables the silica hollow particles to be used for the loading and slow release of active molecules.

[0132] [Coating composition]

[0133] The coating composition of the present invention comprises the silica hollow particles of the present invention, a dispersion medium, and a binder used as required.

[0134] Examples of the dispersion medium include water, alcohols, ketones, ethers, esters, nitrogen-containing compounds, sulfur-containing compounds, etc. Examples of the alcohols include methanol, ethanol, isopropyl alcohol, etc. Examples of the ketones include acetone, methyl ethyl ketone, etc. Examples of the ethers include tetrahydrofuran, 1,4-dioxane, etc. Examples of the esters include ethyl acetate, methyl acetate, etc. Examples of the nitrogen-containing compounds include N,N-dimethylacetamide, N,N-dimethylformamide, etc. Examples of the sulfur-containing compounds include dimethyl sulfoxide, etc.

[0135] Examples of the binder include inorganic binders, including those precursor compounds well-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. Organic adhesives can also be used, including various different polymers well-known to those skilled in the art and monomers and oligomers that can be thermally cured or radiation (e.g., UV) cured, including acrylate monomers, methacrylate monomers, and various oligomers derived therefrom, 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 free-radically cured in acrylates and methacrylates.

[0136] In the coating composition of the present invention, other hollow particles or solid particles other than the hollow particles of the present invention can be included within the scope that does not impair the effects of the present invention.

[0137] Furthermore, other functional materials can also be contained in the coating composition of the present invention, such as conductive particles, pigments, dyes, surfactants, ultraviolet shielding agents, infrared shielding agents, antistatic agents, photocatalysts, lubricants, etc.

[0138] In the coating composition of the present invention, the content of the silica hollow particles contained may be, for example, 0.1 to 80% by mass, preferably 1 to 60% by mass, and more preferably 5 to 40% by mass.

[0139] The coating composition of the present invention described above contains the hollow particles of the present invention having a low refractive index and high particle strength. Therefore, a coating film having excellent antireflection effect and high abrasion resistance and hardness can be formed.

[0140] [Article]

[0141] The article of the present invention is an article formed with a coating formed from the coating composition of the present invention.

[0142] The aforementioned coating can be formed by coating the coating composition of the present invention on a substrate and drying it. In addition, the coating can be further heated or calcined or irradiated.

[0143] Examples of the substrate include, for example, glass, transparent polymers, metals, etc., and there is no particular limitation.

[0144] Examples of the coating method include, for example, bar coating, knife coating, spin coating, dip coating, roll coating, curtain coating, spray coating, slot coating, etc., and there is no particular limitation.

[0145] The reflectance of the aforementioned coating is preferably less than 1%. If the reflectance of the coating is less than 1%, excellent optical effects can be obtained. More preferably, it is less than 0.5%.

[0146] The hardness of the aforementioned coating is preferably 1H to 3H. From the perspective of obtaining good abrasion resistance, the hardness is set to 1H or more. From the perspective of obtaining the flexibility of the coating, the hardness is set to 3H or less.

[0147] Since the article of the present invention described above has a coating formed from the coating composition of the present invention, it has a good antireflection effect, good abrasion resistance, and high hardness.

[0148] Examples

[0149] To more clearly illustrate the present invention, the present invention will be further described below in conjunction with preferred examples. Those skilled in the art should understand that the specific content described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0150] In the present invention, unless otherwise specified, the preparation methods are all conventional methods, the raw materials used can be obtained from public commercial channels unless otherwise specified, the percentages are all by mass percentage, and the temperature is in degrees Celsius (°C).

[0151] The specific meanings of the symbols involved in each example and the test conditions are as follows:

[0152] Solid content: Obtained by a solid content analyzer Precisa, XM60, baked at 150 °C until constant weight, and the solid content is shown.

[0153] Average particle size: In the corresponding TEM images, randomly select 100 particles, measure the particle size of each particle, and take the average value of the measured particle sizes as the average particle size of the particles.

[0154] Wall thickness: In the corresponding TEM images, randomly select 100 particles, measure the wall thickness of each particle, and take the average value of the measured wall thicknesses as the wall thickness.

[0155] Determination of polydispersity (PDI): The dispersion liquid is measured by a dynamic light scattering instrument (Malven, Zetasizer Nano series) to obtain the size distribution curve and the PDI result.

[0156] Mesopore size, pore volume and porosity: Through N2 adsorption test, static adsorption measurement of BET is carried out at 77K using a Quadrasorb evo specific surface area and porosity analyzer (Quantachrome Instruments, USA). The mesopore size, pore volume and the porosity required for calculating the refractive index described below are measured using the isothermal adsorption curve and the Barrett-Joyner-Halenda (BJH) model.

[0157] Refractive index: Calculated from the porosity, the refractive index of silica is 1.5, the refractive index of air is 1.0, assuming the porosity is V c , then the refractive index RI can be simply calculated by the following formula:

[0158] RI = 1.5*(1 - Vc) + 1.0*Vc

[0159] Relative dielectric constant: The relative dielectric constant ε r can be measured by an electrostatic field in the following way. Under standard atmospheric pressure, first measure the capacitance C0 of the capacitor when the space between two plates is vacuum, and then measure the capacitance C with the same distance between the capacitor plates but with a dielectric inserted between the plates. x . The relative dielectric constant can be calculated by the following formula:

[0160] ε r = C x / C0

[0161] Example 1

[0162] Mix 208 g (1 mol) of tetraethyl orthosilicate and 102 g (1 mol) of acetic anhydride evenly, add 0.228 g (0.001 mol) of tetraethoxytitanium, keep stirring, heat up to 135 °C, start timing from when liquid is observed to evaporate, react for 8 hours, then perform vacuum distillation, quickly extract the residual first reaction by-product until no liquid is extracted, and obtain 224 g of a light yellow transparent organosilicon intermediate with a certain viscosity.

[0163] After cooling the obtained 224 g of organosilicon intermediate to room temperature, add 42 g of polyethylene glycol (molecular weight 750) under stirring, gradually heat up to 150 °C, when no obvious liquid droplets are observed to evaporate, start vacuum distillation to further remove the generated second reaction by-product, and obtain 270 g of an organosilicon intermediate with surface activity.

[0164] Mix the previously obtained 270 g of organosilicon intermediate with surface activity with 2700 g of water, start stirring, and at the same time quickly add 200 g of ammonia water (mass concentration 25%), continue stirring and reacting for 24 hours to obtain a dispersion containing silica hollow particles, and the solid content of the silica hollow particles is 4%.

[0165] The transmission electron microscope (TEM) photograph of the obtained silica hollow particles is as Figure 1 shown. Measure its average particle size to be 40 nm and the wall thickness to be 5.5 nm. As Figure 1 can be seen, the internal cavity structure of the hollow particles is obvious and no agglomeration occurs.

[0166] As Figure 2 can be seen from the dynamic light scattering results of the shown dispersion, the particle size distribution is uniform, and the PDI of the hollow particles is 0.07.

[0167] The pore size distribution calculated and analyzed from the nitrogen adsorption experiment results is as Figure 3 shown, and there is a mesoporous structure of 4 - 5 nm on the spherical shell. Measure the pore volume of the hollow particles to be 0.392 cm 3 / g.

[0168] Example 2

[0169] The difference between Example 2 and Example 1 is that the amount of acetic anhydride used in the organosilicon intermediate generation step is increased to 153 g (1.5 mol), and the amount of tetraethoxytitanium is increased to 0.684 g (0.003 mol) to obtain 194 g of organosilicon intermediate. The amount of polyethylene glycol (molecular weight 750) used in the organosilicon intermediate generation step with surface activity is reduced to 30 g to obtain 175 g of organosilicon intermediate with surface activity. The finally obtained dispersion containing silica hollow particles has a solid content of 4% for the oxidized hollow particles.

[0170] The transmission electron microscopy (TEM) image of the obtained silica hollow particles is as Figure 4 shown. The average particle size is measured to be 75 nm, the wall thickness is 7.5 nm, the internal cavity structure is obvious, and no agglomeration occurs.

[0171] As Figure 5 shown by the dynamic light scattering result of the dispersion, the particle size distribution is uniform. The measured PDI is 0.08.

[0172] The pore size distribution calculated and analyzed from the nitrogen adsorption experiment result is as Figure 6 shown. Mesoporous structures of 4 - 6 nm exist on the spherical shell.

[0173] The measured pore volume of the hollow particles is 0.517 cm 3 / g.

[0174] Example 3

[0175] The difference between Example 3 and Example 1 is that 208 g (1 mol) of tetraethyl orthosilicate in the organosilicon intermediate formation step is replaced by 110 g of commercially available Si48 (Gelest Int., silica content is 48%), 102 g (1 mol) of acetic anhydride is replaced by 49 g (0.5 mol) of maleic anhydride, and the reaction temperature is increased to 200 °C. The polyethylene glycol (molecular weight 750) used in the organosilicon intermediate formation step with interfacial activity is replaced by methoxypolyethylene glycol (molecular weight 500). 2700 g of water used in the silica hollow particle formation step is replaced by a mixture of 2600 g of water and 100 g of cyclohexane, and a silica hollow particle dispersion (solid content 4%) is obtained.

[0176] Furthermore, the obtained silica hollow particle dispersion is separated, washed, and concentrated through an inorganic ceramic membrane ultrafiltration device, and finally a silica hollow particle dispersion with a solid content of 30% is obtained.

[0177] The transmission electron microscopy (TEM) image of the obtained silica hollow particles is as Figure 7 shown. The average particle size is measured to be 85 nm, the wall thickness is 8 nm, the internal cavity structure is obvious, and no agglomeration occurs even in a dispersion with a relatively high concentration.

[0178] As Figure 8 shown by the dynamic light scattering result of the dispersion, the size distribution of the hollow particles is uniform. The measured PDI is 0.1.

[0179] As Figure 9 shown, the nitrogen adsorption test result calculation and analysis show that mesopores of 4.5 nm exist on the spherical shell.

[0180] The measured pore volume of the hollow particles is 0.581 cm3 / g.

[0181] Example 4

[0182] The difference between Example 4 and Example 1 is that 208 g (1 mol) of tetraethyl orthosilicate used in the generation step of the silicone intermediate is replaced with 156 g (0.75 mol) of tetraethyl orthosilicate and 34 g (0.25 mol) of methyltrimethoxysilane, and 200 g of ammonia water used in the generation step of the silica hollow particles is replaced with 30 g of triethylamine, to obtain a silica hollow particle dispersion (solid content 4%).

[0183] Furthermore, the obtained silica hollow particle dispersion (solid content 4%) is subjected to repeated centrifugation - redispersion processes, and finally 280 g of a silica hollow particle dispersion with a solid content of 20% is obtained.

[0184] 280 g of methyl isobutyl ketone (MIBK) is added to the obtained 280 g of silica hollow particle dispersion (solid content 20%), and 11.2 g of γ - methacryloxypropyltrimethoxysilane is added. After heating to 80 °C and reacting for 12 hours, water and MIBK are removed by rotary evaporation and redispersed in MIBK to obtain a silica hollow particle MIBK dispersion with a solid content of 40%.

[0185] The transmission electron microscope (TEM) photograph of the obtained silica hollow particles is as Figure 10 shown. The average particle size is measured to be 100 nm, the wall thickness is 8.5 nm, the internal cavity structure is obvious, and no agglomeration occurs even in a non - aqueous solvent dispersion with a relatively high concentration. Through nitrogen adsorption experiment analysis and calculation, the size of the mesopores on the shell of the particles is measured to be 5.5 nm. The pore volume of the obtained hollow particles is 0.623 cm 3 / g.

[0186] The dynamic light scattering result of the dispersion is as Figure 11 shown. It can be seen that the particle size distribution is uniform. The measured PDI is 0.11.

[0187] Comparative Example 1

[0188] 208 g (1 mol) of tetraethyl orthosilicate, 102 g (1 mol) of acetic anhydride, and 42 g of polyethylene glycol (molecular weight 750) are mixed evenly, 0.228 g (0.001 mol) of tetraethoxytitanium is added, and while maintaining the stirring state, the temperature is raised to 135 °C. Starting from the time when liquid evaporation is observed, the reaction is carried out for 8 hours to obtain 280 g of a silicone intermediate with a certain viscosity and light yellow transparency;

[0189] After mixing the previously obtained 280 g of silicone intermediate with 2700 g of water, start stirring, and at the same time quickly add 200 g of ammonia water (mass concentration 25%), and continue stirring and reacting for 24 hours to obtain a white emulsion.

[0190] The transmission electron microscope photograph of the obtained white emulsion is as Figure 12 shown. The particle shape is irregular, and serious agglomeration and adhesion occur, and no hollow structure is observed.

[0191] Comparative Example 2

[0192] Mix 208 g (1 mol) of tetraethyl orthosilicate, 102 g (1 mol) of acetic anhydride, and 42 g of polyethylene glycol (molecular weight 750) evenly, add 0.228 g (0.001 mol) of tetraethoxytitanium, keep stirring, heat up to 135 °C, start timing from when liquid evaporation is observed, react for 8 hours, then carry out vacuum distillation, and quickly extract the residual reaction by-products until no liquid is extracted to obtain 273 g of a silicone intermediate with a certain viscosity, light yellow and transparent;

[0193] After mixing the previously obtained 280 g of silicone intermediate with 2700 g of water, start stirring, and at the same time quickly add 200 g of ammonia water (mass concentration 25%), and continue stirring and reacting for 24 hours to obtain a suspension of white particles.

[0194] The transmission electron microscope photograph of the obtained suspended particles is as Figure 13 shown. The shape is irregular and the size is in the micron level, with serious agglomeration and adhesion, all of which are solid structures, and no hollow structure is observed.

[0195] Comparative Example 3

[0196] Repeat the preparation method of hollow particles in Patent Document CN110128855A "Example 2". 1) Mix 146 g of Silicon 40 (Gelest Int.), 50 g of ethanol, and 15 g of polyvinyl alcohol (average molecular weight 500) evenly until transparent, then add 7.5 g of concentrated hydrochloric acid (mass fraction 37%) and 5 g of deionized water and mix evenly. After stirring for 5 minutes, heat up to 80 °C and continue reacting for 2 hours. Rapidly rotate and distill off the solvents and low molecular weight compounds in the system under reduced pressure to obtain a polyalkoxysiloxane precursor with a certain viscosity, flowable, and transparent; 2) Take 100 g of the polyalkoxysiloxane precursor and add it to 350 g of deionized water, and stir quickly to obtain a white dispersion; 3) Add 25 g of concentrated ammonia water (mass fraction 25%) to the white dispersion, and continue stirring for 5 hours to obtain a semi-transparent dispersion; 4) Carry out dialysis operation on the dispersion (the molecular weight cut-off of the dialysis bag is 14000) until the pH is less than 10, and adjust the solid content of the dispersion to 15%.

[0197] The average size of the obtained silica hollow particles is 75 nm, the average wall thickness is 7.5 nm, the size distribution is relatively uniform, the PDI is 0.21, the spherical structure is complete, the cavity structure is obvious. Through nitrogen adsorption test, pore structure is only found above 10 nm, and no mesopore distribution is found below 10 nm. The pore volume is 0.324 cm 3 / g.

[0198] Comparative Example 4

[0199] Repeat the preparation process of the hollow particle dispersion liquid in Patent Document CN102196996A "Example 4" to obtain the hollow particles.

[0200] 1) Add 50.0 g of an aqueous dispersion of zinc oxide particles (size 70 nm, solid content 20%), 5.2 g of tetraethyl orthosilicate (TEOS), 44.4 g of ethanol, and 0.4 g of concentrated ammonia water (28%) into a 200 mL quartz pressure-resistant container to prepare a raw material liquid with a pH of 10.

[0201] 2) After sealing the pressure-resistant container, heat it in an oil bath (OB) at 60 °C for 60 minutes to hydrolyze TEOS, precipitate silica on the surface of the zinc oxide particles to form a shell, and obtain a dispersion of 100 g of core-shell particles.

[0202] 3) Heat the dispersion of core-shell particles in an oil bath at 120 °C for 30 minutes to densify the shell. Add 100 g of strongly acidic cation exchange resin (total exchange capacity above 2.0 meq / mL) into 100 g of the dispersion of core-shell particles, stir for 1 hour, and after the pH reaches 4, remove the strongly acidic cation exchange resin by filtration to obtain a dispersion of hollow particles. Concentrate this dispersion by ultrafiltration until the solid content reaches 20%.

[0203] The average size of the obtained silica hollow particles is 75 nm, the average wall thickness is 4 nm, the size distribution is uniform, the PDI is 0.15, the spherical structure is complete, the cavity structure is obvious. Through nitrogen adsorption test, fine pore structure with a size of 3 nm and below is found on the spherical shell, and the pore volume is 0.681 cm 3 / g.

[0204] Coating composition and coating preparation example:

[0205] Dilute the hollow particle dispersions prepared in the above Examples 1-4 and Comparative Examples 3-4 with water to a solid content of 10%. Take 100 g of the dispersion, add 100 g of methyl isobutyl ketone (MIBK), and add 2 g of γ-methacryloxypropyltrimethoxysilane. After heating to 80 °C and reacting for 12 hours, remove water and MIBK by rotary evaporation and redisperse in MIBK to obtain a 10% solid content silica hollow particle MIBK dispersion.

[0206] Take 10 g of the MIBK dispersion of hollow particles, 1 g of dipentaerythritol hexaacrylate (DPHA), 0.05 g of photoinitiator (Irgacure-184), and 39 g of MIBK, mix them evenly to obtain 50 g of an antireflection coating with a solid content of 4%.

[0207] Coat the antireflection coating (4%) on a PET film with a #3 wire bar (3 μm), dry it in an oven at 80 °C for two minutes, and perform UV curing (energy 800 - 1500 mJ / cm 2 ), to obtain a PET product with an antireflection coating. Characterize its reflectance, pencil hardness, and steel wool resistance performance, and the results are shown in Table 1.

[0208] Reflectance: Measured using a spectrophotometer (UV-3150 manufactured by Shimadzu Corporation), in the wavelength range of 300 - 800 nm, the spectral reflectance is measured at an incident angle of 5 degrees. The average reflectance is represented by taking the average reflectance in the range of 380 - 760 nm.

[0209] Pencil hardness: According to Japanese JIS K 5600, use a pencil scratch tester to measure the pencil hardness of the obtained coating. On the obtained coating, make the pencil scratch at an angle of 45 degrees from above with a load of 750 g for about 5 cm, and represent it with the hardness of the pencil with no scratches in 4 or more times out of 5 times.

[0210] Abrasion resistance: Apply a load of 500 g / cm 2 on #0000 steel wool and reciprocate 100 times, and visually observe the abrasion condition. The evaluation criteria are as follows.

[0211] Grade 5: No abrasion

[0212] Grade 4: More than 1 and no more than 10 abrasions occur

[0213] Grade 3: More than 10 and no more than 30 abrasions occur

[0214] Grade 2: More than 30 abrasions occur

[0215] Grade 1: Abrasion or peeling occurs on the entire surface

[0216] Table 1: Measurement results of the reflectance, pencil hardness, and abrasion resistance of the coating

[0217]

[0218] In the manufacturing method of the above embodiments, the step of generating the silicone intermediate and the step of generating the surfactant-containing silicone intermediate are separated. The operation of removing the first by-product is carried out in the first step, and the operation of removing the second by-product is carried out in the second step. Thus, monodisperse silica hollow particles can be obtained. In Comparative Example 1 and Comparative Example 2, the step of generating the silicone intermediate and the step of generating the surfactant-containing silicone intermediate are combined into one step, resulting in the inability to obtain monodisperse silica hollow particles.

[0219] Example 2 and Comparative Example 3 have similar hollow particle sizes, but the hollow particle shell of Comparative Example 3 does not have an obvious mesoporous structure smaller than 10 nm. The coating hardness and wear resistance of Comparative Example 3 are comparable to those of Example 2, but the overall refractive index of the hollow particles in Comparative Example 3 is higher than that in Example 2, and the antireflection effect in the coating is worse than that in Example 2.

[0220] The particle size of Comparative Example 4 is the same as that of Example 2, but the wall thickness of its particles is reduced, and the overall refractive index of the particles is slightly lower than that of Example 2. The average reflectance of the obtained coating is also slightly lower than that of Example 2. Although the shell layer of the hollow particles in Comparative Example 4 was densified, the obtained coating still exhibited poor hardness (HB) and poor wear resistance.

[0221] Therefore, the solution of this application combines excellent antireflection performance and outstanding mechanical properties.

[0222] Those skilled in the art will readily conceive of other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include known common knowledge or conventional technical means in the technical field not disclosed by the present invention.

Claims

1. A method for preparing silica hollow particles, characterized in that, the silica hollow particles are formed by a shell mainly composed of silica, the thickness of the shell is 5-100 nm, and the shell has mesopores with a size of 4-10 nanometers. The statement that the shell is mainly composed of silica means that the proportion of silica is 90% by mass or more. The pore volume of the silica hollow particles is 0.35~0.65 cm 3 / g, the porosity is 40%~60%, and the refractive index is 1.15~1.35, The method for preparing the silica hollow particles comprises the following steps: (1) Organosilicon intermediate generation step: mixing a silicon precursor, an acid anhydride, and a first catalyst, heating for reaction, and removing a first reaction by-product to obtain an organosilicon intermediate; (2) Organosilicon intermediate with surface activity generation step: mixing the organosilicon intermediate obtained in the step (1) with a hydroxyl-containing hydrophilic compound, heating for reaction, and removing a second reaction by-product to obtain an organosilicon intermediate with surface activity; (3) Silica hollow particle generation step: mixing the organosilicon intermediate with surface activity obtained in the step (2) with an aqueous solvent and a second catalyst for reaction to obtain a dispersion containing silica hollow particles. The silicon precursor is a silane monomer represented by the following formula I, or a polyalkoxysiloxane oligomer with a silica mass percentage of 80% or less. R 1 4-n Si(OR 2 ) n Formula I where n = 2-4; R 1 is an alkyl group, a vinylalkyl group, an epoxyalkyl group, a styrylalkyl group, a methacryloxyalkyl group, an acryloxyalkyl group, an aminoalkyl group, a ureaalkyl group, a chloropropylalkyl group, a sulfanyl group, an isocyanatealkyl group, or a hydroxyalkyl group, and there are multiple R 1 When each R 1 can be the same or different from each other; R 2 is an alkyl group having 1 to 6 carbon atoms, and there are multiple Rs 2 When there are multiple Rs 2 they may be the same as or different from each other optionally; the acid anhydride in the step (1) is at least one selected from phthalic anhydride, acetic anhydride, formic anhydride, propionic anhydride, maleic anhydride, and chromic anhydride, and the molar ratio of the acid anhydride to the silicon precursor is 0.01:1 or more and less than 2:1; the first catalyst in the step (1) is at least one selected from metal alkoxides and metal carboxylates, and the molar ratio of the first catalyst to the silicon precursor is (0.01-10):

100.

2. The method for preparing silica hollow particles according to claim 1, wherein, The relative dielectric constant of the silica hollow particles is 1.6-2.

2.

3. The method for preparing silica hollow particles according to claim 1, wherein the particle size of the silica hollow particles is 15-1000 nm, and its polydispersity index is 0.05-0.

2.

4. The method for preparing silica hollow particles according to claim 1, wherein, The conductivity of the dispersion of silica hollow particles obtained in the step (3) is 50-1000 μs / cm, and the pH of the dispersion is 4-10.

5. The method for preparing silica hollow particles according to claim 1, wherein, In the step (2), the hydroxyl-containing hydrophilic compound is at least one selected from the group consisting of polyacrylic acid, polyethylene glycol, polyethylene glycol monoether, polyvinyl alcohol, polyglycerol, and a copolymer of ethylene oxide and propylene oxide, and the mass ratio of the hydroxyl-containing hydrophilic compound to the organosilicon intermediate is (0.05-0.5):

1.

6. The method for preparing silica hollow particles according to claim 1, wherein in the step (3), the aqueous solvent is water, a mixture of water and a hydrophilic solvent, or a mixture of water and a hydrophobic solvent; the second catalyst is selected from an acid or a base; the mass percentage of the organosilicon intermediate with surface activity relative to the solvent is 1-60%; and the mass ratio of the second catalyst to the solvent is (0.01-0.5):1.

Images