Method for producing hollow silica particles

Abstract

The present invention relates to a method for producing hollow silica particles. The object is to provide a hollow silica particle having a dense silica shell. A method for producing hollow silica particles, wherein the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is set to 3.0 or lower, a first silica raw material is added to the oil-in-water emulsion, a second silica raw material is added to the emulsion to which the first silica raw material is added in the presence of an alkali metal ion in such a manner that the pH of the emulsion is 8 or higher, a hollow silica precursor dispersion liquid is obtained, a hollow silica precursor is obtained from the hollow silica precursor dispersion liquid, and then a hollow silica particle is obtained from the hollow silica precursor.

Description

[0001] This application is a divisional application of Invention Patent Application No. 201880083744.0, filed on December 25, 2018, entitled "Method for Manufacturing Hollow Silica Particles". TECHNICAL FIELD

[0002] The present invention relates to a method for manufacturing hollow silica particles. BACKGROUND

[0003] Hollow silica particles are particles having a void inside a shell layer formed of silica. Hollow silica particles are widely used for catalysts, catalyst carriers, cosmetic pigments, resin fillers, adsorbents, drying agents, thermal insulating materials, paints, drug release, optical filters, and the like, due to the diversity of particle diameters, pore structures of the shell layer, and surface properties. In addition, they are also useful as anti-reflective coating materials due to the low refractive index based on the hollow shape.

[0004] One example of a method for manufacturing hollow silica particles is a method in which an oil-in-water emulsion in which an oil phase is dispersed in an aqueous phase is prepared, then silica raw material is attached to the oil droplets, oil core-silica shell particles are prepared, the oil droplet component is removed from the particles, and thus hollow silica particles are obtained. Since the particles are prepared from an emulsion, hollow silica particles having a particle diameter of several tens of nm to about 10 μm can be formed.

[0005] On the other hand, since the silica shell layer of a small particle diameter hollow silica particle is also thin, there is a problem that the particle strength is reduced and the particles are broken during use and storage. When the strength of the shell layer is low, there is a possibility that the particles are damaged when mixed with other raw materials such as ceramic raw materials. In addition, when the shell layer is porous, there is a possibility that the internal hollow structure cannot be maintained when mixed with a solvent or the like.

[0006] In Patent Literature 1, a method is proposed in which an initial container bottom charge containing water, sodium chloride, precipitated calcium carbonate, and sodium silicate is stirred at pH 9, then an aqueous sodium silicate solution and an aqueous sulfuric acid solution are added, and aging, filtration, and drying are performed, whereby dried particles are obtained, the dried particles are treated with concentrated hydrochloric acid to remove the calcium carbonate, and thus hollow silica particles are manufactured.

[0007] In Patent Literature 2, hollow silica microcapsules having an average pore diameter of 1.6 to 10 nm are proposed. In Patent Literature 2, a method is proposed in which a W / O type emulsion or an O / W / O type emulsion containing a silicate of an alkali metal in an aqueous phase is obtained, a precipitating agent is added to the emulsion to form hollow silica microcapsules, and prescribed water washing, drying, and firing are performed, and further the fired microcapsules are mesoporous, and thus hollow silica microcapsules are manufactured.

[0008] In Non-Patent Literature 1, the following method is proposed: an emulsion using a block copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) and sodium silicate are combined to synthesize hollow silica particles.

[0009] In Non-Patent Literature 1, in an aqueous solution to which a block copolymer is added, ethanol in which mesitylene is dissolved is added to obtain an emulsion, and an aqueous solution of sodium silicate is added to the emulsion, adjusted to pH 5.2 and aged, and a white powder is separated, dried, and fired to synthesize hollow silica particles. By this method, hollow silica particles having an average diameter of about 1 μm or less and a BET specific surface area of about 426 m2 / g can be obtained. 2 / g or less.

[0010] Prior Art Documents

[0011] Non-Patent Literature

[0012] Non-Patent Literature 1: Qianyao Sun et al, "The Formation of Well-Defined Hollow Silica Spheres with Multilamellar Shell Structure", Advanced Materials, 2003, 15, No. 13, July 4.

[0013] Patent Literature

[0014] Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No. 2000-500113

[0015] Patent Literature 2: Japanese Patent Application Laid-Open (JP-A) No. 2006-102592 SUMMARY

[0016] The invention addresses the problem

[0017] In Patent Literature 1, the core particles are calcium carbonate, and thus the emulsion is alkaline, and silica raw material is attached to the core particles. In this method, the particle diameter and shape of the hollow particles obtained are limited by the particle diameter and shape of the solid calcium carbonate particles serving as the core particles. In addition, when the calcium carbonate is removed by acid, pores are generated in the shell layer, and the shell layer cannot be sufficiently densified, and there is also a possibility that the strength of the shell layer is reduced by acid treatment.

[0018] In Patent Literature 1, as other examples of the core particles, liquid materials such as vegetable oil can be given, but there is a problem that the silica raw material cannot be sufficiently attached to the core particles formed of the liquid materials under alkaline conditions.

[0019] For the hollow silica obtained from the W / O type emulsion like Patent Literature 2, the water phase of the silicate containing alkali metal forms the hollow silica, and thus, not the particle in which the void is obviously present in the hollow portion, but the particle in which the silica density is smoothly reduced from the outermost shell to the center portion.

[0020] In addition, the hollow silica obtained from the W / O / W type emulsion is in the following manner: the oil droplet of the center portion becomes the hollow portion, and the silica raw material contained in the water phase of the intermediate layer forms the shell layer. The shell layer is formed from the water phase of the intermediate layer, and thus, it is difficult to densify.

[0021] In Non-Patent Literature 1, sodium silicate is attached to the oil droplet of the oil-in-water emulsion under acidic conditions and is cured, and then, a white powder is separated. In this method, there is a problem that the shell layer of the obtained hollow silica particle cannot be sufficiently densified, and the strength of the hollow silica particle is poor.

[0022] As one object of the present application, to provide a hollow silica particle having a dense silica shell layer.

[0023] The solution to the problem

[0024] The present application is directed to the following.

[0025] [1] A method for producing a hollow silica particle, wherein the pH of an oil-in-water emulsion containing a water phase, an oil phase, and a surfactant is set to 3.0 or less, and a first silica raw material is added to the oil-in-water emulsion, a second silica raw material is added to the emulsion to which the first silica raw material is added in the presence of alkali metal ions in such a manner that the pH of the emulsion is 8 or more, a hollow silica precursor dispersion liquid is obtained, a hollow silica precursor is obtained from the aforementioned hollow silica precursor dispersion liquid, and a hollow silica particle is obtained from the aforementioned hollow silica precursor.

[0026] [2] The method for producing a hollow silica particle according to [1], wherein the aforementioned first silica raw material and the aforementioned second silica raw material each independently contain one or more selected from the group consisting of alkali metal silicate, active silicic acid, and silicic acid ester.

[0027] [3] The method for producing a hollow silica particle according to [2], wherein the aforementioned alkali metal silicate is sodium silicate.

[0028] [4] The method for producing a hollow silica particle according to any one of [1] to [3], wherein an aqueous alkali metal silicate solution is used as the aforementioned first silica raw material.

[0029] [5] The method for producing hollow silica particles according to any one of [1] to [4], wherein at least one of an aqueous alkali metal silicate solution and an active aqueous silicic acid solution is used as the second silica raw material.

[0030] [6] The method for producing hollow silica particles according to any one of [1] to [5], wherein the second silica raw material is added to the emulsion heated,

[0031] [7] The method for producing hollow silica particles according to any one of [1] to [6], wherein an acid is added to the oil-in-water emulsion so that the pH is 3 or more, and then an aqueous alkali metal silicate solution is added as the first silica raw material.

[0032] [8] The method for producing hollow silica particles according to any one of [1] to [7], wherein an alkali is added to the emulsion after the addition of the first silica raw material, and then the second silica raw material is added.

[0033] [9] The method for producing hollow silica particles according to any one of [1] to [8], wherein the hollow silica precursor is fired to obtain the hollow silica particles.

[0034]

[10] The method for producing hollow silica particles according to [9], wherein the firing temperature is 300°C to 800°C.

[0035]

[11] The method for producing hollow silica particles according to any one of [1] to

[10] , wherein the surfactant is a polyoxyethylene-polyoxypropylene copolymer.

[0036]

[12] The method for producing hollow silica particles according to any one of [1] to

[11] , wherein the average primary particle diameter of the obtained hollow silica particles is 10 nm to 10 μm, and the BET specific surface area is 300 m 2 / g or less.

[0037]

[13] Hollow silica particles having an average primary particle diameter of 10 nm to 10 μm, a BET specific surface area of 150 m 2 / g or less, and a shell layer containing 500 mass ppm or more of an alkali metal component.

[0038] Effects of the invention

[0039] By the present application, it is possible to provide hollow silica particles having a dense silica shell layer. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1A transmission electron microscope image (TEM image) of the hollow silica particles obtained in Example 1 is shown.

[0041] Figure 2 A transmission electron microscope image (TEM image) of the hollow silica particles obtained in Example 1 is shown.

[0042] Figure 3 A scanning electron microscope image (SEM image) of the hollow silica particles obtained in Example 1 after crushing is shown.

[0043] Figure 4 A transmission electron microscope image (TEM image) of the hollow silica particles obtained in Example 21 is shown.

[0044] Figure 5 A scanning electron microscope image (SEM image) of the hollow silica particles obtained in Example 21 after crushing is shown. DETAILED DESCRIPTION

[0045] Hereinafter, the present application will be described, but the present application is not limited by the following examples.

[0046] As a method for producing the hollow silica particles of the present application, the pH of an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is set to 3.0 or less, a first silica raw material is added to the oil-in-water emulsion, a second silica raw material is added to the emulsion to which the first silica raw material has been added in the presence of an alkali metal ion in such a manner that the pH of the emulsion becomes 8 or more, a hollow silica precursor dispersion liquid is obtained, a hollow silica precursor is obtained from the hollow silica precursor dispersion liquid, and then the hollow silica particles are obtained from the hollow silica precursor.

[0047] Thus, the hollow silica particles having a dense silica shell layer can be obtained. By making the shell layer dense, the strength of the particles is improved, and the shape can be maintained even when mixed with other materials. In addition, by making the shell layer dense, it is difficult for foreign matter from the solvent or the outside to intrude into the hollow portion inside.

[0048] Further, there is no limitation on the silica raw material, and for example, even when an alkali metal silicate is used, the hollow silica particles having a dense silica shell layer can be provided.

[0049] In the present method, an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is used. The oil-in-water emulsion is an emulsion in which the oil phase is dispersed in water, and when a silica raw material is added to the emulsion, the silica raw material adheres to the oil droplets, and thus oil core-silica shell particles can be formed. Hereinafter, the oil-in-water emulsion will be simply referred to as an emulsion.

[0050] Note that the following two dispersions are sometimes also referred to as emulsions: a dispersion of the oil core-silica shell particles generated by adding the first silica raw material and before adding the second silica raw material, and a dispersion of the oil core-silica shell particles after adding the second silica raw material. The latter dispersion of the oil core-silica shell particles after adding the second silica raw material can be equivalent to the hollow silica precursor dispersion.

[0051] The water phase of the emulsion mainly contains water as a solvent. Further additives such as a water-soluble organic liquid, a water-soluble resin, and the like can be further added to the water phase. The proportion of water in the water phase is preferably 50 to 100% by mass, and more preferably 90 to 100% by mass.

[0052] The oil phase of the emulsion preferably contains a non-water-soluble organic liquid that is not compatible with the water phase components. This organic liquid is in the form of droplets in the emulsion, forming the oil-core portion of the hollow silica precursor.

[0053] As the organic liquid, aliphatic hydrocarbons such as n-hexane, isohexane, n-heptane, isohexane, n-octane, isooctane, n-nonane, isononane, n-pentane, isopentane, n-decane, isodecane, n-dodecane, isododecane, pentadecane, or paraffin-based base oils as a mixture thereof, alicyclic hydrocarbons such as cyclopentane, cyclohexane, cyclohexene, or naphthene-based base oils as a mixture thereof, aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, propylbenzene, cumene, mesitylene, tetralin, styrene, ethers such as propyl ether, isopropyl ether, esters such as ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, butyl lactate, methyl propionate, ethyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, butyl butyrate, vegetable oils such as palm oil, soybean oil, rapeseed oil, fluorine-based solvents such as hydrofluorocarbon, perfluorocarbon, perfluoropolyether, and the like can be given. In addition, a polyoxyalkylene glycol that is a hydrophobic liquid at the shell formation reaction temperature can also be used. Examples include polypropylene glycol (molecular weight 1000 or more), a polyoxyethylene-polyoxypropylene block copolymer in which the proportion of the oxyethylene unit is less than 20% by mass and the cloud point (1% by mass aqueous solution) is 40°C or lower, preferably 20°C or lower, and the like. Among these, a block copolymer of the polyoxypropylene-polyoxyethylene-polyoxypropylene type is preferably used.

[0054] These can be used alone or in combination with two or more within the range of forming a single phase of the oil phase.

[0055] As the organic liquid, a hydrocarbon having a carbon number of 8 to 16, particularly a carbon number of 9 to 12 is preferred. The organic liquid is selected in consideration of the operability, the safety against fire, the separability of the hollow silica precursor from the organic liquid, the shape characteristics of the hollow silica particles, the solubility of the organic liquid in water, and the like. The hydrocarbon having a carbon number of 8 to 16 can be a straight-chain, branched-chain or cyclic hydrocarbon as long as it has good chemical stability, and hydrocarbons having different carbon numbers can be mixed and used. As the hydrocarbon, a saturated hydrocarbon is preferred, and a straight-chain saturated hydrocarbon is more preferred.

[0056] The flash point of the organic liquid is preferably 20 to 90°C, and more preferably 30 to 80°C. When an organic liquid having a flash point of less than 20°C is used, countermeasures against fire and the working environment are required because the flash point is too low. In addition, an organic liquid having a flash point of more than 90°C is less volatile, and thus there is a concern that the amount of the organic liquid adhering to the obtained hollow silica particles increases.

[0057] In order to improve the emulsion stability, the emulsion contains a surfactant. The surfactant is preferably water-soluble or water-dispersible, and is preferably added to the water phase for use. A nonionic surfactant is preferred.

[0058] As the nonionic surfactant, for example, the following surfactants can be mentioned.

[0059] Polyoxyethylene-polyoxypropylene copolymer-based surfactants

[0060] Polyoxyethylene sorbitan fatty acid ester-based surfactants: polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate

[0061] Polyoxyethylene higher alcohol ether-based surfactants: polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene nonylphenyl ether

[0062] Polyoxyethylene fatty acid ester-based surfactants: polyoxyethylene glycol monolaurate, polyoxyethylene glycol monostearate, polyoxyethylene glycol monooleate

[0063] Glycerin fatty acid ester-based surfactants: glycerin monostearate, glycerin monooleate

[0064] Further, polyoxyethylene sorbitol fatty acid ester-based surfactants, sucrose fatty acid ester surfactants, polyglycerin fatty acid ester surfactants, polyoxyethylene hydrogenated castor oil-based surfactants, and the like can also be used.

[0065] These can be used alone or in combination of two or more.

[0066] Among the above nonionic surfactants, a polyoxyethylene-polyoxypropylene copolymer-based surfactant can be preferably used. The polyoxyethylene-polyoxypropylene copolymer is a block copolymer in which a polyoxyethylene block (EO) and a polyoxypropylene block (PO) are bonded. As the block copolymer, an EO-PO-EO block copolymer, an EO-PO block copolymer, or the like can be given, with the EO-PO-EO block copolymer being preferred. The proportion of the oxyethylene units of the EO-PO-EO block copolymer is preferably 20% by mass or more, more preferably 30% by mass or more.

[0067] The weight average molecular weight of the polyoxyethylene-polyoxypropylene copolymer is preferably 3000 to 27000, more preferably 6000 to 19000.

[0068] The total amount of the polyoxyethylene blocks is preferably 40 to 90% by mass, and the total amount of the polyoxypropylene blocks is preferably 10 to 60% by mass, relative to the entire polyoxyethylene-polyoxypropylene copolymer.

[0069] The amount of the surfactant used varies depending on the type of the surfactant, an index indicating the degree of hydrophilicity or hydrophobicity of the surfactant, i.e., HLB (Hydrophile-lipophile balance), the particle diameter of the target silica particles, and the like, but the content in the aqueous phase is preferably 500 to 20000 ppm by mass, more preferably 1000 to 10000 ppm by mass. When it is 500 ppm by mass or more, the emulsion can be more stabilized. When it is 20000 ppm by mass or less, the amount of the surfactant remaining in the hollow silica particles as a product can be reduced.

[0070] The aqueous phase and the oil phase can be compounded in a mass ratio of 200: 1 to 5: 1, preferably 100: 1 to 9: 1.

[0071] The method of producing the oil-in-water emulsion is not limited to the following. It can be produced by the following method: the aqueous phase and the oil phase are prepared separately in advance, the oil phase is added to the aqueous phase, and they are mixed and / or stirred sufficiently. Further, methods such as ultrasonic emulsification, stirring type emulsification, and high pressure emulsification, which physically impart strong shearing force, can be applied. In addition, there are methods such as a membrane emulsification method in which an oil phase that has been micronized by a membrane having fine pores is dispersed in an aqueous phase, a phase inversion emulsification method in which a surfactant is dissolved in an oil phase, an aqueous phase is added, and emulsification is performed, a phase inversion temperature emulsification method in which a surfactant is used to change from water solubility to oil solubility at a temperature near the cloud point. These emulsification methods can be appropriately selected depending on the specific target particle diameter, particle size distribution, and the like.

[0072] To make the resulting hollow silica particles small in particle size and narrow in particle size distribution, it is preferable that the oil phase be sufficiently dispersed in the water phase and emulsified. For example, a high-pressure homogenizer can be used to emulsify the mixture at a pressure of 100 bar, preferably 400 bar or more.

[0073] In the present method, a first silica raw material is added to an oil-in-water emulsion.

[0074] As the first silica raw material, for example, an aqueous solution in which water-soluble silica is dissolved, an aqueous dispersion in which solid silica is dispersed, a mixture thereof, and one or more selected from the group consisting of alkali metal silicate, active silicic acid, and silicic acid ester, or an aqueous solution or aqueous dispersion thereof can be mentioned. Among these, from the viewpoint of high ease of acquisition, one or more selected from the group consisting of alkali metal silicate, active silicic acid, and silicic acid ester, or an aqueous solution or aqueous dispersion thereof is preferable.

[0075] As the solid silica, for example, a silica sol obtained by hydrolysis of an organosilicon compound, a commercially available silica sol can be mentioned.

[0076] As the alkali metal of the alkali metal silicate, lithium, sodium, potassium, rubidium, and the like can be mentioned, and among these, from the viewpoint of ease of acquisition and economy, sodium is preferable. That is, as the alkali metal silicate, sodium silicate is preferable. The sodium silicate has a composition represented by Na2O-nSiO2-mH2O. The ratio of sodium to silicic acid, in terms of the molar ratio n of Na2O / SiO2, is preferably 1.0 to 4.0, and further preferably 2.0 to 3.5.

[0077] The active silicic acid is obtained by subjecting an alkali metal silicate to a cation exchange treatment to replace the alkali metal with hydrogen, and an aqueous solution of the active silicic acid exhibits weak acidity. In the cation exchange, a hydrogen-type cation exchange resin can be used.

[0078] The alkali metal silicate and the active silicic acid are preferably dissolved and / or dispersed in water and then added to the emulsion. The concentration of the aqueous solution of the alkali metal silicate and the active silicic acid is preferably 3 to 30% by mass in terms of SiO2 concentration, and further preferably 5 to 25% by mass.

[0079] As the silicic acid ester, for example, tetraalkylsilane such as tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane can be preferably used.

[0080] In addition, a composite particle can also be obtained by mixing another metal oxide or the like together with the silica raw material. As the other metal oxide, titanium dioxide, zinc oxide, cerium oxide, copper oxide, iron oxide, tin oxide, and the like can be mentioned.

[0081] As the first silica raw material, the above-mentioned silica raw materials can be used alone or two or more kinds thereof can be used in combination. Among them, as the first silica raw material, an aqueous alkali metal silicate solution, particularly an aqueous sodium silicate solution, is preferably used.

[0082] In the present method, the addition of the first silica raw material to the oil-in-water emulsion is performed at a pH of 3.0 or less. It is preferable to set the pH of the oil-in-water emulsion including an aqueous phase, an oil phase, and a surfactant to 3.0 or less by adding an acid thereto.

[0083] One example of the addition of the first silica raw material is as follows: an acid is added to the emulsion, and then an aqueous sodium silicate solution is added.

[0084] Since the neutral emulsion is temporarily made acidic and then the aqueous sodium silicate solution as the base component is added, the entire emulsion can be kept acidic during the addition of the first silica raw material.

[0085] In the addition of the first silica raw material, it is preferable to set the pH of the emulsion after the addition of the acid to the emulsion to 2 or less, and then set the pH to 3.0 or less after the addition of the aqueous sodium silicate solution.

[0086] The pH at the time of the addition of the first silica raw material to the emulsion is preferably 3.0 or less, and more preferably 2.4 or less. Thereby, when a first layer of the coating film based on the silica raw material is formed on the oil droplets in the emulsion with the aid of the surfactant, the thickness of the coating film can be made more uniform, and the silica shell layer of the resulting hollow silica can be made denser.

[0087] The pH at the time of the addition of the first silica raw material to the emulsion can be 1 or more.

[0088] As the acid, for example, hydrochloric acid, nitric acid, sulfuric acid, acetic acid, perchloric acid, hydrobromic acid, trichloroacetic acid, dichloroacetic acid, methanesulfonic acid, and benzenesulfonic acid can be mentioned.

[0089] In the addition of the first silica raw material, with respect to the amount of the first silica raw material, SiO2 in the first silica raw material is preferably 1 to 50 parts by mass, and more preferably 3 to 30 parts by mass, relative to 100 parts by mass of the oil phase contained in the emulsion.

[0090] In the addition of the first silica raw material, it is preferable to maintain the pH of the emulsion after the addition of the first silica raw material to 3.0 or less for 1 minute or more, more preferably for 5 minutes or more, and further preferably for 10 minutes or more.

[0091] Next, it is preferable to maintain the pH of the emulsion to which the first silica raw material has been added to 5 or more. Thereby, the first silica raw material can be fixed to the surface of the oil droplets.

[0092] For example, there is a method of setting the pH of the emulsion to 5 or more by adding a base to the emulsion to which the first silica raw material has been added.

[0093] As the base, for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, ammonia, amines, and the like can be given.

[0094] Alternatively, a method of exchanging anions such as halide ions to hydroxide ions by anion exchange treatment can also be used.

[0095] When the base is added, it is preferable to slowly add the base while stirring the emulsion to which the silica raw material has been added, so that the pH of the emulsion slowly increases. When the stirring is weak or a large amount of base is added at once, the pH of the emulsion can sometimes become non-uniform, and the thickness of the first layer coating can become non-uniform.

[0096] It is preferable to maintain the emulsion while stirring, in a state where the pH of the emulsion is set to 5 or more. The maintenance time can be 10 minutes or more, preferably 1 hour or more, and can also be 4 hours or more.

[0097] During the maintenance, the pH of the emulsion is preferably 7 or less.

[0098] Next, a second silica raw material is added so that the pH of the emulsion becomes 8 or more in the presence of alkali metal ions. Thereby, a hollow silica precursor dispersion liquid is obtained. Here, the hollow silica precursor is an oil core-silica shell particle.

[0099] As the second silica raw material, the same raw materials as the first silica raw material described above can be used alone or in a mixture of two or more. Among them, at least one of a sodium silicate aqueous solution and an active silicic acid aqueous solution can be preferably used in the addition of the second silica raw material.

[0100] When the second silica raw material is added so that the pH of the emulsion becomes 8 or more, a method of simultaneously adding the second silica raw material and an alkali metal hydroxide can also be used. In addition, a method of using sodium silicate as an alkali metal silicate in the second silica raw material can also be used. At this time, since the sodium silicate component as a base component is added to the emulsion which is weakly acidic with the pH set to 5 or more after the addition of the first silica raw material, the pH of the emulsion can be maintained to be alkaline at 8 or more while the second silica raw material is added. In addition, alkali metal ions become present in the emulsion.

[0101] The pH of the emulsion at the time of adding the second silica raw material to the emulsion is preferably 8 or more, and can also be 9 or more. Thereby, a more dense second layer coating can be formed on the first layer coating based on the first silica raw material.

[0102] In the addition of the first silica raw material, in order to make the attachment of the first silica raw material to the oil droplets more uniform, a method of temporarily adjusting the emulsion to be acidic and then making the pH 5 or more is used. The first silica layer obtained by this method is porous, and the density is insufficient, so the strength becomes low. In the addition of the second silica raw material, by making the emulsion alkaline, a high-density second silica layer can be formed on the first silica layer obtained previously. By the silica layer formed by these two stages, a dense silica shell layer can be formed.

[0103] The pH of the emulsion at the time of the addition of the second silica raw material to the emulsion is not particularly limited, but can be 13 or less, and can also be 11 or less. In the case where an aqueous sodium silicate solution is used as the second silica raw material, and the like, when the pH excessively rises, an acid can also be added in order to adjust the pH. Among the acids used here, the same acid as that used at the time of the addition of the first silica raw material can also be used.

[0104] The addition of the second silica raw material is performed in the presence of an alkali metal ion. This alkali metal ion can be derived from the first silica raw material, derived from the second silica raw material, derived from an alkali added for pH adjustment, or can also be compounded by an additive added to the emulsion, and the like. For example, in the case where an alkali metal silicate is used in at least one of the first silica raw material and the second silica raw material. In addition, in the case where a halide, a sulfate, a nitrate, a fatty acid salt, or the like of an alkali metal is used in an additive of the emulsion.

[0105] For the addition of the second silica raw material, for example, in the emulsion after the addition of the first silica raw material, one of an aqueous sodium silicate solution and an active aqueous silicic acid solution can be added, or both can be added. In the case where both are added, the aqueous sodium silicate solution and the active aqueous silicic acid solution can be added at once, or can be added sequentially.

[0106] For example, for the addition of the second silica raw material, in order to adjust the pH and promote the attachment of the silica raw material to the first silica layer, the process of adding the aqueous sodium silicate solution and the process of adding the active aqueous silicic acid solution can be repeated one or two or more times.

[0107] In order to promote the attachment of the silica raw material to the first silica layer, the second silica raw material is preferably added to the emulsion that is heated. The heating temperature is preferably 30 to 100°C, and more preferably 50 to 80°C. In the case where the emulsion is used that is heated, it is preferable to slowly cool the generated emulsion to room temperature (23°C) after the addition of the second silica raw material.

[0108] In the addition of the second silica raw material, the amount of the second silica raw material added is preferably adjusted so that the SiO2in the second silica raw material becomes 20 to 500 parts by mass with respect to 100 parts by mass of the oil phase, and more preferably adjusted so that it becomes 40 to 300 parts by mass.

[0109] In the addition of the second silica raw material, it is preferable to maintain the pH of the emulsion at 8 or higher for 10 minutes or more after the addition of the second silica raw material.

[0110] It is preferable that the total amount of the first silica raw material and the second silica raw material be adjusted so that the total of the SiO2in the first silica raw material and the SiO2in the second silica raw material becomes 30 to 500 parts by mass with respect to 100 parts by mass of the oil phase, and more preferably adjusted so that it becomes 50 to 300 parts by mass, by the addition of the first silica raw material and the addition of the second silica raw material.

[0111] The silica shell layer of the present application is mainly composed of silica, but depending on the need for adjustment of the refractive index or the like, it can also contain other metal components such as Ti and Zr. The method of making it contain other metal components is not particularly limited, and for example, a method of simultaneously adding a metal sol solution, an aqueous metal salt solution or the like in the process of adding the silica raw material can be used.

[0112] Next, the process of obtaining the hollow silica precursor from the hollow silica precursor dispersion liquid, and then obtaining the hollow silica particle from the hollow silica precursor will be described.

[0113] As a method of obtaining the hollow silica precursor from the hollow silica precursor dispersion liquid, for example, there are a method of filtering the dispersion liquid, a method of removing the aqueous phase by heating, a method of separating the precursor by precipitation separation or centrifugal separation, and the like.

[0114] As one example, there is a method of filtering the dispersion liquid using a filter of about 0.1 μm to 5 μm, and drying the filtered hollow silica precursor.

[0115] In addition, the obtained hollow silica precursor can also be washed with water, acid, alkali, organic solvent or the like as needed.

[0116] As a method of removing the oil core from the hollow silica precursor to obtain the hollow silica particle, for example, there are a method of firing the hollow silica precursor to thereby combust and decompose the oil, a method of volatilizing the oil by drying, a method of adding an appropriate additive to decompose the oil, a method of extracting the oil using an organic solvent or the like, and the like.

[0117] As an example, the hollow silica precursor is preferably heated at a heating temperature of 300°C to 800°C, particularly 400°C to 600°C, for a heating time of 1 to 8 hours, particularly 3 to 6 hours. In this case, the temperature increase rate is preferably 1 to 20°C / minute, particularly 2 to 10°C / minute.

[0118] The obtained hollow silica particles are aggregated by the processes of drying and firing, and thus can be crushed in order to make the aggregation diameter easy to handle. As a method of crushing, for example, there are a method using a mortar, a method using a dry or wet ball mill, a method using a vibrating sieve, a method using a pin mill, a cutter mill, a hammer mill, a shredder, a roll mill, and the like.

[0119] It can be confirmed by TEM observation that the obtained hollow silica particles have voids inside the shell layer. A spherical particle having voids inside that can be confirmed by TEM observation is defined as a "primary particle". By the processes of firing and drying, primary particles are partially combined with each other, and thus the obtained hollow silica is mostly a collection of secondary particles in which primary particles are aggregated.

[0120] The size of the primary particles can be directly observed by measuring the particle diameter using TEM observation. Specifically, for a part in which the distribution of the primary particle diameters in the observation range is considered to be the same degree as the distribution of the primary particle diameters of the entire obtained hollow silica particles, magnified observation is performed, the size of each primary particle is measured, and the distribution of the sizes of the primary particles obtained by statistically processing these is assumed to be the distribution of the sizes of the primary particles of the entire obtained hollow silica particles.

[0121] The average value of the sizes of the primary particles is preferably 10 nm to 10 μm, more preferably 50 nm to 2 μm, and further preferably 100 nm to 1 μm.

[0122] The BET specific surface area of the hollow silica particles is preferably 300 m 2 / g or less, more preferably 200 m 2 / g or less, further preferably 150 m 2 / g or less.

[0123] Here, the BET specific surface area is measured using a specific surface area measuring device "Tristar II 3020" manufactured by Shimadzu Corporation, and is measured by a multipoint method using liquid nitrogen after drying at 230°C to 50 mTorr as a pretreatment.

[0124] The shell thickness of the hollow silica particles relative to the size of the primary particles is preferably 0.01 to 0.3, more preferably 0.02 to 0.2, and further preferably 0.03 to 0.1.

[0125] When the shell thickness is less than 0.01 relative to the size of the primary particles, the strength of the hollow silica particles sometimes decreases. When the ratio is greater than 0.3, the internal voids become small and cannot exhibit the characteristics based on the hollow shape.

[0126] Here, the shell thickness is measured in the same manner as the primary particle diameter by TEM observation to measure the shell thickness of each particle.

[0127] The hollow silica particles are formed with oil droplets of an oil-in-water emulsion as the core particles, and thus the shape of the hollow silica particles is spherical, and preferably a regular spherical shape.

[0128] In the present application, the obtained hollow silica particles have an alkali metal component in the shell layer. When a silicon alkoxide is used as the silica raw material, the alkali metal component is hardly observed.

[0129] For example, when an aqueous sodium silicate solution is used as the silica raw material, the mass concentration of the Na component in the shell of the obtained hollow silica particles is 500 mass ppm or more, and more often 1000 mass ppm or more. On the other hand, the mass concentration of the Na component in the shell of a conventional hollow silica particle produced using tetraethyl orthosilicate as the silica raw material is 100 mass ppm or less.

[0130] The Na component can be measured by adding perchloric acid and hydrofluoric acid to the obtained hollow silica and applying strong heat to remove the main component silicon, and then measuring by ICP emission spectroscopy.

[0131] In addition, when an alkali metal silicate is used as the silica raw material, the carbon (C) component derived from the raw material in the shell layer of the obtained hollow silica particles is less than when a silicon alkoxide is used as the silica raw material.

[0132] The hollow silica particles produced by the method of the present application are characterized by the density of the shell layer, and for example, can have the property of precipitating in water but floating in an oil component.

[0133] A part of the hollow silica particles produced by the method of the present application can be a hollow silica having a single hole (hollow silica having one hole). The hole can be observed by an electron microscope (SEM), and the hole diameter is preferably 5 nm to 3 μm and 1 / 3 or less of the particle diameter of the hollow silica particles, and more preferably 10 nm to 1 μm and 1 / 5 or less of the particle diameter of the hollow silica particles.

[0134] Such a hollow silica having a single hole can be used as a sustained-release agent for a perfume, a medicament, or the like. That is, a prescribed medicament or the like (preferably a liquid or a solution) is absorbed into the particles under reduced pressure. The medicament or the like is sustained-released by the single hole under normal pressure.

[0135] The hollow silica particles having a single hole can be selected from the particle group of the present application, for example, by the following method. First, the particles are put into a liquid medium under atmospheric pressure and the particles that float are recovered. At this time, when a fluorine-based solvent is used as the liquid medium, the particle group having a lower apparent specific gravity than the liquid medium is easily recovered. After that, the recovered particle group is put into a liquid medium under reduced pressure. The hollow silica particles having a single hole sink in the liquid medium because the liquid medium enters the hollow portion. Therefore, if the particles that sink in the liquid medium are recovered and dried, the particle group of the hollow silica having a single hole can be recovered.

[0136] The hollow silica particles of the present application are characterized in that the average primary particle diameter is 10 nm to 10 μm, the BET specific surface area is 300 m 2 / g or less, and the shell layer contains an alkali metal component.

[0137] The mass concentration of the alkali metal component in the shell of the hollow silica particles of the present application is preferably 500 mass ppm or more, and more preferably 1000 mass ppm or more. When the alkali metal component is small, the shell becomes porous and becomes unable to obtain a dense and high-strength shell.

[0138] The hollow silica particles of the present application can be produced by the production method described above, but are not limited to the hollow silica particles produced by the production method described above.

[0139] The average primary particle diameter, the BET specific surface area, and the like of the hollow silica particles are as described above.

[0140] Examples

[0141] Hereinafter, the present application will be described in detail by examples, but the present application is not limited to these. In the following description, the same substances are used for common components. In addition, unless otherwise specified, "%" means "mass %". Examples 1 to 17 are examples, and Example 21 is a comparative example.

[0142] (Example 1)

[0143] "Preparation of Emulsion"

[0144] EO-PO-EO block copolymer (Kolliphor P188 manufactured by BASF) 3.6 g was added to 1778 g of pure water and stirred until dissolved.

[0145] To this aqueous solution, 18 g of n-dodecane (reagent special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was added, and the liquid was stirred uniformly as a whole using a homogenizer (manufactured by IKA) to produce a coarse emulsion.

[0146] This coarse emulsion was subjected to three times of emulsification at a pressure of 400 bar using a high-pressure emulsifier (LAB 1000 manufactured by SMT company) to produce a fine emulsion.

[0147] "First-stage shell formation"

[0148] To 1600 g of the obtained fine emulsion, 3.4 g of 35% hydrochloric acid (reagent special grade, manufactured by Wako Pure Chemical Industries, Ltd.) was added to set the pH to 1.7.

[0149] Next, 34.8 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 6.9 mass%, Na2O concentration: 2.3 mass%) was added and stirred sufficiently, and the pH was set to 2.4 and maintained for 15 minutes.

[0150] While the liquid was stirred sufficiently, 46.1 g of a 0.1 M aqueous sodium hydroxide solution was slowly added dropwise, and after the stirred state was maintained for 4 hours, an oil core-silica shell particle dispersion liquid having a pH of 5.2 was obtained.

[0151] "Active silicic acid preparation"

[0152] To 270 g of a well-washed hydrogen-type cation exchange resin (SK1BH manufactured by Mitsubishi Rayon Co., Ltd.), 380 g of pure water was added, and the temperature was cooled to 5°C.

[0153] While the above resin dispersion liquid was stirred sufficiently, 360 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 10.3 mass%, Na2O concentration: 3.5 mass%) was added dropwise in small amounts and multiple times while the temperature was maintained at 5°C.

[0154] After the addition was completed, the resin was removed by filtration to obtain a 5 mass% aqueous active silicic acid solution.

[0155] "Second-stage shell formation"

[0156] 1300 g of the oil core-silica shell particle dispersion liquid obtained by the first-stage shell formation was heated to 70°C, and while stirring, 35.2 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 3.5 mass%, Na2O concentration: 1.2 mass%) was added to set the pH to 9.6.

[0157] While stirring, 200 g of the previously prepared 5 mass% aqueous active silicic acid solution was slowly added dropwise while the suspension was maintained at 70°C to set the pH to 9.2.

[0158] Next, add 1.4g of diluted sodium silicate aqueous solution (SiO2 concentration 3.5% by mass, Na2O concentration 1.2% by mass) and set the pH to 9.5.

[0159] Slowly add 200g of 5% (w / w) active silicic acid aqueous solution to set the pH to 9.2.

[0160] Next, add another 5.2g of diluted sodium silicate aqueous solution (SiO2 concentration 3.5% by mass, Na2O concentration 1.2% by mass) to set the pH to 9.4.

[0161] Add 195g of a 5% (w / w) aqueous solution of active silicic acid dropwise again, and set the pH to 8.9. Slowly cool the solution to room temperature to obtain a hollow silica precursor dispersion.

[0162] "Filtering, drying, firing"

[0163] The hollow silica precursor dispersion was filtered by pressure filtration (0.28 MPa) using a 0.45 μm hydrophilic PTFE membrane filter and then dried at 80 °C for 8 hours to obtain the hollow silica precursor.

[0164] The precursor was calcined at 550℃ for 4 hours (heating rate 10℃ / min) to obtain 6g of hollow silica particles.

[0165] "evaluate"

[0166] The BET specific surface area of ​​the hollow silica obtained in Example 1, based on the nitrogen adsorption method, is 118 m². 2 / g.

[0167] Transmission electron microscope (TEM) images of the hollow silica particles obtained in Example 1 are shown below. Figure 1 and Figure 2 .

[0168] from Figure 1 From the TEM images shown, 116 clearly defined primary particles were selected, their diameters were measured and statistically analyzed, and the average value was 278 nm. Additionally, from... Figure 2 The TEM image shown indicates that the shell thickness is 15 nm.

[0169] Scanning electron microscope (SEM) images of the hollow silica particles obtained in Example 1 after being crushed using an agate mortar are shown below. Figure 3 .Depend on Figure 3 It can be seen that the hollow silica particles in Example 1 can maintain their hollow particle shape even after being broken in the mortar.

[0170] The mass concentration of Na in the shell of the hollow silica obtained in Example 1 was 3800 mass ppm.

[0171] (Example 21)

[0172] "Preparation of Emulsion"

[0173] To 1765 g of pure water, 18 g of EO-PO-EO block copolymer (Kolliphor P188 manufactured by BASF) was added and stirred until dissolved.

[0174] To this aqueous solution, 18 g of n-dodecane was added, and the liquid was homogeneously stirred using a homogenizer (manufactured by IKA) to prepare a coarse emulsion.

[0175] This coarse emulsion was subjected to 3 times of emulsification using a high-pressure emulsifier (LAB1000 manufactured by SMT company) at a pressure of 400 bar to prepare a fine emulsion.

[0176] "Formation of Hollow Silica Precursor"

[0177] To 1700 g of the fine emulsion obtained, 9.2 g of 35% hydrochloric acid was added to set the pH to 1.5.

[0178] Next, 123.3 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 6.9 mass%, Na2O concentration: 2.3 mass%) was added and stirred well, and the pH was maintained at 2.2 for 15 minutes.

[0179] While the liquid was stirred well, 127.1 g of a 0.1 M aqueous sodium hydroxide solution was slowly added dropwise, and after the stirred liquid was maintained for 4 hours, a hollow silica precursor dispersion liquid having a pH of 5.2 was obtained.

[0180] "Filtering, Drying, and Calcination"

[0181] After the 600 g of the hollow silica precursor dispersion liquid was filtered by reduced pressure filtration using a 0.45 μm hydrophilic PTFE membrane filter, it was dried at 80°C for 8 hours to obtain a hollow silica precursor.

[0182] The obtained precursor was calcined at 550°C for 4 hours (temperature increase rate: 10°C / min) to obtain 3 g of hollow silica particles.

[0183] "Evaluation"

[0184] The BET specific surface area of the hollow silica obtained in Example 21 based on the nitrogen adsorption method was 554 m 2 / g.

[0185] A TEM image of the hollow silica particles obtained in Example 21 is shown in Figure 4 .

[0186] Figure 4 The TEM image of the shell layer is thinner than that shown in Figure 2 The TEM image of the shell layer is thinner than that shown in

[0187] The SEM image of the hollow silica particles obtained in Example 21 after crushing using an agate mortar is shown in Figure 5 It is understood from Figure 5 that the hollow silica particles of Example 21 collapsed due to insufficient strength of the silica shell, and there were a large number of fragments of the silica shell.

[0188] (Example 2)

[0189] "Preparation of the emulsion"

[0190] To 480 g of pure water, 2.4 g of an EO-PO-EO block copolymer (Kolliphor P188 manufactured by BASF) was added and stirred until dissolved. To this aqueous solution, 16 g of n-dodecane was added, and the entire liquid was stirred until uniform using a homogenizer (manufactured by IKA), thereby preparing a coarse emulsion.

[0191] To this coarse emulsion, a high-pressure emulsifier (LAB1000 manufactured by MST company) was used to perform emulsification three times at a pressure of 400 bar, thereby preparing a fine emulsion.

[0192] "First-stage shell formation"

[0193] To 442 g of the obtained fine emulsion, 9 g of 2M hydrochloric acid was added, and the pH was set to 1.5.

[0194] Next, 12.3 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 10.4 mass%, Na2O concentration: 3.6 mass%) was added and stirred sufficiently, and the pH was set to 2.1 and maintained for 15 minutes.

[0195] While stirring the liquid sufficiently, 4 g of 1M aqueous sodium hydroxide solution was slowly added dropwise, and after maintaining the state under stirring for 1 hour, an oil core-silica shell particle dispersion liquid having a pH of 5.8 was obtained.

[0196] "Second-stage shell formation"

[0197] The oil core-silica shell particle dispersion liquid obtained in the first-stage shell formation was heated to 30°C, and while stirring, 3 g of a diluted aqueous sodium silicate solution (SiO2 concentration: 10.4 mass%, Na2O concentration: 3.6 mass%) was slowly added, and the pH was set to 9.

[0198] Next, 127 g of the diluted aqueous sodium silicate solution (SiO2 concentration 10.4 mass%, Na2O concentration 3.6 mass%) and 0.5 M hydrochloric acid were added slowly so that the pH was 9.

[0199] After the suspension was kept at 30°C for 2 days, it was slowly cooled to room temperature to obtain a hollow silica precursor dispersion.

[0200] "filtration, drying, firing"

[0201] The 770 g of the hollow silica precursor dispersion was filtered by pressure filtration (pressure 0.28 MPa) using a 0.45 μm hydrophilic PTFE membrane filter.

[0202] The filtered filter cake was dried at 60°C for 1 hour and at 400°C for 4 hours (temperature increase time 5°C / min) under a nitrogen atmosphere to obtain a hollow silica precursor.

[0203] The obtained precursor was fired at 550°C for 4 hours (temperature increase time 5°C / min) to obtain 13.8 g of hollow silica particles.

[0204] The specific surface area of the hollow silica particles obtained in Example 2 is shown in Table 1.

[0205] (Examples 3 to 5)

[0206] Silica particles were produced in the same manner as in Example 2. Among them, the reaction temperature and the holding temperature at the time of the second-stage shell formation were changed.

[0207] The reaction temperature and the holding temperature at the time of the second-stage shell formation in Examples 3 to 5 and the specific surface area of the hollow silica particles obtained are shown in Table 1.

[0208] It is considered that the higher the reaction temperature and the holding temperature at the time of the second-stage shell formation, the smaller the specific surface area, and thus it is possible to produce hollow silica particles having a dense shell.

[0209] [Table 1]

[0210]

[0211] (Examples 6 to 13)

[0212] Silica particles were produced in the same manner as in Example 5. Among them, the kind of the EO-PO-EO block copolymer used in Examples 6 to 13 was changed. The EO-PO-EO block copolymer used in each example is shown in Table 2.

[0213] Hollow silica particles were obtained in each of Examples 6 to 13, but in Examples 6, 7, and 11, a large number of hollow silica particles having one hole were observed.

[0214] [Table 2]

[0215]

[0216] (Example 14)

[0217] Silica particles were produced in the same manner as in Example 5. Among them, the addition amount of the EO-PO-EO block copolymer (Kolliphor P188 manufactured by BASF) was set to an amount 10 times as much.

[0218] The specific surface area of the hollow silica particles obtained in Example 14 was 140 m 2 / / g.

[0219] (Example 15)

[0220] "Production of emulsion"

[0221] To 480 g of pure water, 2.4 g of the EO-PO-EO block copolymer (F-68 manufactured by ADEKA) was added and stirred until dissolved. To this aqueous solution, 16 g of n-dodecane was added, and the entire liquid was stirred to be uniform using a homogenizer manufactured by IKA, thereby producing a coarse emulsion.

[0222] To this coarse emulsion, an ultrasonic disperser (GSCVP-600 manufactured by Ginsen) was used, and ultrasonic irradiation was performed 2 times for 1 minute at a strength of V-Level 3.4, thereby producing a fine emulsion.

[0223] After the formation of the first shell, silica particles were produced in the same manner as in Example 5. Among them, after the formation of the first shell, instead of keeping the liquid to which the silica raw material was added at pH 5, a 1M aqueous sodium hydroxide solution was directly added to pH 9.

[0224] The specific surface area of the hollow silica particles obtained in Example 15 was 170 m 2 / g.

[0225] (Example 16)

[0226] "Production of emulsion"

[0227] To 462 g of pure water, 4.9 g of the EO-PO-EO block copolymer (Pluronic PE10400 manufactured by BASF) was added and stirred until dissolved.

[0228] To this aqueous solution, 33 g of the fluorine-based solvent ASAHIKLIN AC-6000 (1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane) manufactured by AGC COMPANY was added, and the entire liquid was stirred to be uniform using a homogenizer manufactured by IKA, thereby producing a coarse emulsion.

[0229] To the coarse emulsion, ultrasonic disperser (Ginsen Corporation, GSCVP-600) was used to irradiate ultrasonic wave for 2 times of 1 minute at the intensity of V-Level 3.4, thereby producing the fine emulsion.

[0230] "First shell formation" "Second shell formation" "Filtration"

[0231] For the first shell formation, the second shell formation and the filtration, the silica particles were produced in the same manner as in Example 5.

[0232] "Drying"

[0233] The filtered filter cake was dried at 60°C for 2 days to remove AC-6000, thereby obtaining 8 g of the hollow silica particles.

[0234] The specific surface area of the hollow silica particles obtained in Example 16 was 80 m 2 / g.

[0235] (Example 17)

[0236] "Production of emulsion"

[0237] To 174 g of pure water, 13 g of EO-PO-EO block copolymer (PE10500, BASF Corporation) was added and dissolved. The solution was kept at 5°C, 13 g of PO-EO-PO block copolymer (25R-1, ADEKA Corporation) was added and dissolved, thereby obtaining a transparent aqueous solution. 300 g of pure water was heated to 60°C, and the block copolymer mixed solution was added dropwise while stirring. Thereby, a fine emulsion having a droplet diameter of about 300 nm was obtained.

[0238] After the first shell formation, the silica particles were produced in the same manner as in Example 5. Among them, the first shell formation was performed at 60°C, and after that, instead of keeping the liquid to which the silica raw material was added at pH 5, 1M sodium hydroxide aqueous solution was directly added to pH 9.

[0239] The specific surface area of the hollow silica particles obtained in Example 17 was 160 m 2 / g.

[0240] Note that the specification, claims, abstract, and drawings of Japanese Patent Application No. 2017-248972 filed on December 26, 2017 are hereby incorporated by reference in their entirety and are incorporated into the present specification as a disclosure of the present application.

Claims

1. A method for producing hollow silica particles, wherein, The pH of an oil-in-water emulsion containing an aqueous phase, an oil phase, and a surfactant is set to 3.0 or less, and a first silica raw material is added to the oil-in-water emulsion, The surfactant is a polyoxyethylene-polyoxypropylene copolymer, In the presence of an alkali metal ion, a second silica raw material is added to the emulsion to which the first silica raw material is added, so that the pH of the emulsion is 8 or more, and the emulsion is heated to 30 to 100°C, to obtain a hollow silica precursor dispersion liquid, A hollow silica precursor is obtained from the hollow silica precursor dispersion liquid, and a hollow silica particle is obtained from the hollow silica precursor, the hollow silica precursor being an oil core-silica shell particle, The method of obtaining the hollow silica precursor from the hollow silica precursor dispersion liquid is selected from a method of filtering the dispersion liquid, a method of removing the aqueous phase by heating, or a method of separating the precursor by sedimentation or centrifugation, The method of removing the oil core from the hollow silica precursor to obtain the hollow silica particle is selected from a method of firing the hollow silica precursor to combust and decompose the oil, a method of volatilizing the oil by drying, a method of decomposing the oil by adding a suitable additive, or a method of extracting the oil; The first and second silica raw materials are each independently an aqueous solution in which a water-soluble silica is dissolved, an aqueous dispersion in which a solid silica is dispersed, a mixture thereof, or one or more selected from the group consisting of an alkali metal silicate, active silicic acid, and a silicon alkoxide, or an aqueous solution or an aqueous dispersion thereof.

2. The method for producing hollow silica particles according to claim 1, wherein, The first and second silica raw materials each independently contain one or more selected from the group consisting of an alkali metal silicate, active silicic acid, and a silicon alkoxide.

3. The method for producing hollow silica particles according to claim 2, wherein, The alkali metal silicate is sodium silicate.

4. The method for producing hollow silica particles according to any one of claims 1 to 3, wherein As the first silica raw material, an aqueous solution of an alkali metal silicate is used.

5. The method of producing hollow silica particles according to any one of claims 1 to 3, wherein, As the second silica raw material, at least one of an aqueous solution of an alkali metal silicate and an aqueous solution of active silicic acid is used.

6. The method for producing hollow silica particles according to any one of claims 1 to 3, wherein An alkali is added to the emulsion after the addition of the first silica raw material, and then the second silica raw material is added.

7. The method of producing hollow silica particles according to any one of claims 1 to 3, wherein, The hollow silica particle is obtained by firing the hollow silica precursor.

8. The method of producing hollow silica particles according to claim 7, wherein, The firing temperature is 300 to 800°C.

9. The method of producing hollow silica particles according to any one of claims 1 to 3, wherein, The average primary particle diameter of the obtained hollow silica particles is 10 nm to 10 μm, and the BET specific surface area is 300 m 2 / g or less.

Images