Silica aerogel powder, production method therefor, and use thereof

Abstract

[Problem] To provide a spherical silica aerogel powder exhibiting a high oil absorption, and a production method therefor. [Solution] The silica aerogel powder is characterized by comprising hydrophobic spherical silica aerogel and having a) a volume-based cumulative 50% diameter (D50) value of 1-200 μm in terms of particle size distribution measured by a laser diffraction / scattering method, b) a specific surface area of 400-1,000 m2 / g based on the BET method, and c) an oil absorption of 850-1,300 ml / 100 g. The production method is characterized in that the moisture content of an undried gelled body is 10% or less.

Description

Silica aerogel powder, its manufacturing method and its uses

[0001] The present invention relates to a silica aerogel powder, more particularly to a powder made of hydrophobic spherical silica aerogel, a method for producing the same, and uses thereof.

[0002] Aerogel is a material with high porosity and excellent oil absorption. Here, aerogel refers to a solid material with a porous structure and gas as a dispersion medium, particularly a solid material with a porosity of 60% or more. Porosity is the amount of gas contained in an apparent volume, expressed as a volume percentage. Due to its high porosity, aerogel has excellent oil absorption. Silica aerogel has a variety of applications, including cosmetic additives, insulating fillers, matting agents for paints, and abrasive grains for semiconductor polishing agents. For example, when used as a cosmetic additive, in the case of foundation, it is used as an additive to improve the appearance durability of the foundation when applied to the skin. Specifically, the porous structure of silica aerogel effectively absorbs sebum, preventing the skin from becoming wet with sebum, which increases the specular reflectance of light and causes shine. Furthermore, if silica aerogel is produced by being hydrophobic, it has good affinity with organic components of cosmetic materials such as foundation, and disperses uniformly, further enhancing the above-mentioned shine-preventing effect for maintaining appearance.

[0003] These silica aerogels, when incorporated into cosmetics, preferably have a particle size of 1 to several tens of micrometers to achieve a smooth feel, and a spherical shape to improve rolling properties on the skin. Silica aerogels are also useful as insulating fillers. Solid conduction (propagation of thermal vibrations), convection, and radiation each contribute to heat conduction within an object, with convection generally contributing most significantly in materials with high porosity. In contrast, silica aerogels have extremely small pore sizes, on the order of 10 to 100 nm, which significantly restricts gas movement within the pores and significantly inhibits convective heat conduction. Therefore, silica aerogels have excellent insulating properties. Since insulating performance generally depends on the amount of filler added to the substrate, a spherical shape is desirable to increase the silica aerogel's packing ratio and improve its insulating performance.

[0004] For example, the following method has been proposed as a method for producing such spherical silica aerogel having an appropriate particle size: Patent Document 1 discloses a method for producing spherical silica aerogel, which includes, in this order, a step of preparing an aqueous silica sol, a step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion, a step of gelling the silica sol to convert the W / O emulsion into a dispersion of a gel, a step of substituting the water in the gel with a solvent having a surface tension of 30 mN / m or less at 20°C, a step of subjecting the gel to a hydrophobizing treatment (silylation treatment) with a hydrophobizing agent (silylating agent), and a step of removing the substituted solvent. Patent Document 2 discloses a method for producing spherical silica aerogel, which includes the steps of: separating the gel dispersion obtained in the step of converting the W / O emulsion into a gel dispersion into two layers, an O phase and a W phase; adding a basic substance to the W phase to age the gel dispersed in the W phase; silylating the gel dispersed in the W phase; extracting the gel with a hydrophobic organic solvent; and recovering the gel to obtain a powder of hydrophobic spherical silica aerogel. Patent Document 3 further discloses a method for producing spherical silica aerogel with a broad particle size distribution and excellent packing ability by broadening the particle size distribution of droplets in the W / O emulsion.

[0005] International Publication No. 2012 / 057086 JP 2018-177620 A JP 2019-019019 A

[0006] The thermal insulation performance of silica aerogel powder is due to convection suppression by the voids in the silica skeleton and solid-state heat transfer through the silica skeleton. The oil absorption, which is one indicator of the void ratio, is particularly important. The higher the oil absorption, the lower the convection suppression effect and the lower the solid-state heat transfer. Therefore, there is an optimal oil absorption value for maximizing thermal insulation performance. The existing methods described in Patent Documents 1 to 3 were unable to produce spherical silica aerogels with oil absorptions of 850 ml / 100 g or more, and the thermal insulation performance of spherical silica aerogels with even higher oil absorptions could not be verified. To increase oil absorption, the silica concentration in the aqueous silica sol must be reduced. However, when using aqueous silica sols with low silica concentrations in the methods described in the above patent documents, the silica skeleton weakens and shrinks upon drying, preventing the production of silica aerogel powders with high oil absorption. Given the above background, the objective of the present invention is to provide spherical silica aerogel powders with high oil absorption, methods for producing the same, and uses thereof.

[0007] The inventors conducted extensive research to solve the above-mentioned problems and found that gels prepared by conventional methods contained moisture before drying, which they speculated was the cause of drying shrinkage. They then found that removing the moisture from the gel before drying resulted in the production of silica aerogel powder with high oil absorption. Furthermore, they found that the spherical silica aerogel prepared by the present invention also had superior heat insulating properties compared to spherical silica aerogel prepared by existing methods.

[0008] That is, the present invention provides a hydrophobic spherical silica aerogel, which has a volume-based cumulative 50% diameter (D50) value of 1 to 200 μm in a particle size distribution measured by a laser diffraction / scattering method, and a specific surface area of ​​400 to 1000 m2 measured by a BET method. ２ / g, and c) an oil absorption of 850 to 1300 ml / 100 g.

[0009] The present invention also provides a method for producing silica aerogel powder comprising hydrophobic spherical silica aerogel, the method comprising the steps of (1) to (8) below in order: Specifically, the method for producing silica aerogel powder comprises, in the stated order, (1) preparing an aqueous silica sol, (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion, (3) gelling the silica sol in an acidic range by heating, thereby converting the W / O emulsion into a dispersion of a gel, (4) separating the dispersion into two layers, an O phase and a W phase, (5) adding a basic substance to the W phase to age the gel dispersed in the W phase, (6) silylating the gel dispersed in the W phase and extracting the gel into the O phase, (7) reducing the water content of the gel to 10% or less by azeotropic dehydration, and (8) recovering the gel to obtain a powder consisting of hydrophobic spherical silica aerogel. Furthermore, the present invention also provides a heat insulating material, a cosmetic additive, a cosmetic product, and a matting agent, each comprising the silica aerogel powder obtained by the above-mentioned invention.

[0010] The silica aerogel constituting the silica aerogel powder of the present invention has a high porosity, as represented by its oil absorption. Therefore, the powder itself has excellent heat insulating properties. Furthermore, because of its spherical shape, it has excellent packing properties, and a sheet made of the powder has excellent heat insulating properties.

[0011] The silica aerogel powder of the present invention will be described below. <Silica aerogel powder> The powder of the present invention is composed of hydrophobic spherical silica aerogel. Silica here refers to silicon dioxide, a general term for materials composed of silicon dioxide, and SiO ２Here, the spherical shape of silica aerogel means that the silica aerogel particles have an average circularity of 0.8 or more. Preferably, the average circularity is 0.85 or more. Since the powder of the present invention is composed of spherical silica aerogel, when used in cosmetics, it has excellent rolling properties on the skin. The "average circularity" is a value obtained by obtaining SEM images observed using a scanning electron microscope (SEM), determining the value C (circularity) defined by the following formula (1) for each particle through image analysis, and calculating the arithmetic mean value of this circularity C for 2,000 or more particles. In this case, a group of particles forming a single aggregate particle is counted as one particle. C = 4πS / L ２ (1) [In formula (1), S represents the area (projected area) occupied by the particle in the image, and L represents the length (perimeter) of the outer periphery of the particle in the image.] The closer the average circularity is to 1, the closer the particle is to a perfect sphere.

[0012] In the present invention, the spherical silica aerogel is hydrophobic. Being hydrophobic reduces water adsorption, which causes deterioration over time, and improves compatibility with hydrophobic resins, making it extremely useful when dispersed in hydrophobic resins. The hydrophobic nature of the aerogel is also significant from the viewpoint that it can be produced without supercritical drying or solvent substitution. Specifically, hydrophobicity of the spherical silica aerogel can be achieved by treating the spherical silica aerogel with a silylating agent to introduce organic silyl groups onto the surface. Whether or not a silica aerogel is hydrophobic can be easily confirmed by placing the powder in a container with pure water and stirring. If the powder is hydrophobic, it will not disperse in water and, upon standing, will regain its two-layer structure, with the water layer below and the powder layer above. The hydrophobicity and its degree can also be evaluated using the M value. The M value was measured according to the measurement method described in the examples. The M value of the silica aerogel powder made of the hydrophobic spherical silica aerogel of the present invention is preferably 30 to 50 vol% , more preferably 35 to 50 vol% , and particularly preferably 40 to 50 vol% . Furthermore, the carbon content can be cited as an indicator of the hydrophobicity of the silica aerogel powder made of the hydrophobic spherical silica aerogel of the present invention. The carbon content in the silica aerogel powder is derived from the surface treatment agent and can be measured by quantifying the amount of carbon dioxide generated during oxidation treatment in air or oxygen at temperatures of approximately 1000 to 1500°C.

[0013] The powder of the present invention is characterized in that the hydrophobic spherical silica aerogel satisfies the following properties a) to c): a) a volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by a laser diffraction / scattering method is 1 to 200 μm, and b) a specific surface area measured by the BET method is 400 to 1000 m ２ / g, and c) the oil absorption is 850 to 1300 ml / 100 g.

[0014] a) The volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by a laser diffraction / scattering method is 1 to 200 μm. If this range is met, the particle is less likely to fall off or crack when blended as a filler in various base materials.

[0015] b) The specific surface area measured by the BET method is 400 to 1000 m ２ / g, and the larger the specific surface area of ​​the spherical silica aerogel, the smaller the particle diameter of the primary particles constituting the porous structure (network structure) of the independent particles (secondary particles) of the spherical silica aerogel, and the more complex the network structure, which improves the particle strength, is preferable in terms of preventing pore destruction when added to and dispersed in a substrate. On the other hand, if the specific surface area of ​​the spherical silica aerogel is too large, the pore volume becomes small and the oil absorption amount becomes low. ２ / g or less, and ２ / g or less. ２ On the other hand, if the specific surface area of ​​the spherical silica aerogel becomes too small, the pore volume becomes small and the oil absorption capacity becomes low. ２ In the present invention, the specific surface area measured by the BET method is a value determined by drying a sample to be measured at a temperature of 150°C for 2 hours or more under a vacuum of 1 kPa or less, obtaining an adsorption isotherm only on the nitrogen adsorption side at liquid nitrogen temperature, and analyzing the resulting adsorption isotherm by the BET method, with the partial pressure (P / P0) range during the analysis being 0.1 to 0.25.

[0016] c) The oil absorption is 850 to 1300 ml / 100 g. The higher this value, the higher the proportion of voids, making this range preferable because it can suppress gas convection. On the other hand, if this range is exceeded, the pore radius (described below) also increases, increasing gas convection, making it impossible to expect improved insulation performance. In addition, mechanical strength decreases, and the voids may be destroyed when added to a substrate. In this invention, the oil absorption is measured using a method in accordance with JIS K5101-13-1 "Oil Absorption - Section 1: Refined Linseed Oil Method." Specifically, the measurement procedure involves weighing 0.4 g of aerogel powder and placing it on a glass plate. Oleic acid is added dropwise using a Pasteur pipette and mixed with a spatula. The aerogel powder absorbs the oleic acid, forming a paste. The end point is when this paste reaches a smooth consistency. This paste should be able to be spread without breaking or crumbling, and should lightly adhere to a glass plate. The oil absorption is calculated from the amounts of aerogel powder and oleic acid added in the above procedure using the following formula: Oil absorption (mL / 100g) = Amount of oleic acid added (g) x 100 / Amount of Aerica added (g) / 0.895

[0017] In the silica aerogel powder of the present invention, the hydrophobic silica aerogel preferably has d) peak pore volume and peak pore radius measured by the BJH method of 2 to 8 ml / g and 10 to 50 nm, respectively. The pore volume indicates the porosity of the silica aerogel, and a larger pore volume indicates a silica aerogel with better heat insulating properties and oil absorption. The lower limit is more preferably 2.5 ml / g or more, and particularly preferably 4 ml / g or more. The upper limit is more preferably 6 ml / g or less. When the pore volume is within the above range, the peak pore radius measured by the BJH method is preferably typically in the range of 10 to 50 nm. Having the peak pore radius in the above range suppresses gas convection heat transfer and enhances the heat insulating effect. Furthermore, when the peak pore radius is smaller than the above range, it is difficult to obtain spherical silica aerogel. The BJH pore volume is obtained by obtaining an adsorption isotherm in the same manner as in the BET specific surface area measurement and analyzing it by the BJH method (Barrett, EP; Joyner, LG; Halenda, PP, J. Am. Chem. Soc. 73, 373 (1951)). The pores measured by this method are pores with a radius of 1 to 100 nm, and the integrated value of the volume of pores in this range is the pore volume in the present invention. The pore radius peak is obtained by obtaining an adsorption isotherm in the same manner as in the BET specific surface area measurement and analyzing it by the BJH method. It is the value of the pore radius at which the cumulative pore volume (volume distribution curve) based on the logarithm of the pore radius takes the maximum peak value.

[0018] Furthermore, in the powder of the present invention, it is preferable that the hydrophobic silica aerogel has a thermal conductivity of 25 mW / m·K or less at room temperature (23±2°C) as measured by a hot wire method. Thermal conductivity is a physical quantity that indicates a material's ability to transfer heat. Specifically, it is the amount of heat passing through a unit area per unit time divided by the temperature gradient (temperature change per unit distance). A smaller thermal conductivity value indicates a lower amount of heat passing through the sample, indicating higher thermal insulation. The hot wire method is a method in which a linear heater is placed inside the sample and a constant current is passed through it, and the thermal conductivity of the sample is calculated from the relationship between the temperature rise of the heater and time. Compared to measurements using a heat flow meter, this value is approximately 5 to 10 mW / mK higher.

[0019] <Method for producing silica aerogel powder> The method for producing the hydrophobic spherical silica aerogel powder of the present invention is not particularly limited as long as it can produce a hydrophobic spherical silica aerogel powder having the properties specified in the present invention. According to the studies of the present inventors, the powder can be preferably produced by the method described below.

[0020] The method for producing a powder of hydrophobic spherical silica aerogel of the present invention comprises the following eight steps in order: (1) preparing an aqueous silica sol, (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion, (3) gelling the silica sol in an acidic range by heating to convert the W / O emulsion into a dispersion of a gel, (4) separating the dispersion into two layers, an O phase and a W phase, (5) adding a basic substance to the W phase to age the gel dispersed in the W phase, (6) silylating the gel dispersed in the W phase and extracting the gel into the O phase, (7) reducing the water content of the gel to 10% or less by azeotropic dehydration, and (8) recovering the gel to obtain a powder of hydrophobic spherical silica aerogel.

[0021] These steps will be explained in order. (1) Step of preparing aqueous silica sol As a raw material for silica sol, a method using alkali metal silicate or the like can be suitably adopted because it is inexpensive. Examples of the alkali metal silicate include potassium silicate and sodium silicate, and the composition formula is represented by the following formula (2). m(M ２ O) n(SiO ２ ) (2) [In formula (2), m and n each independently represent a positive integer, and M represents an alkali metal atom.] Among the raw materials for preparing the silica sol described above, sodium silicate, which is easily available, is particularly suitable.

[0022] The following describes an example of a method using an alkali metal silicate or the like as a raw material. When an alkali metal silicate is used as a raw material for preparing the aqueous silica sol of the present invention, it is preferable to prepare the silica sol by neutralizing it with a mineral acid such as hydrochloric acid or sulfuric acid. Specific examples include a method in which an aqueous solution of an alkali metal silicate is added to an aqueous solution of an acid while stirring the aqueous solution, or a method in which the aqueous solution of an acid and the aqueous solution of an alkali metal silicate are impinged and mixed in a pipe (see, for example, Japanese Patent Publication No. 4-54619). In the present invention, the pH of the prepared silica sol is set to be in the acidic range. Specifically, the amount of acid used in preparing the aqueous silica sol is preferably 1.05 to 1.2, in terms of the molar ratio of hydrogen ions to the alkali metal content of the alkali metal silicate. When the amount of acid is within this range, the pH of the prepared silica sol will be approximately 1 to 5. More preferably, the amount of acid is adjusted so that the pH of the prepared silica sol is 2.5 to 3.5. The silica concentration of the aqueous silica sol prepared by the above method is preferably 50 to 80 g / L, in order to stably obtain silica aerogel powder with an oil absorption of 850 to 1300 mL / 100 g. The oil absorption relative to the silica concentration is approximately 1100 mL / 100 g when the silica concentration is 54 g / L, and approximately 850 mL when the silica concentration is 80 g / L. The silica concentration in the silica sol can be adjusted by any method. For example, a silica sol with a high silica concentration may be prepared and then water may be added to adjust the silica concentration, or the concentration of the acid or alkali metal silicate may be adjusted to achieve the desired concentration during the preparation of the silica sol.

[0023] (2) Step of dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion. In the manufacturing method of the present invention, the aqueous silica sol obtained by the above method is dispersed in a hydrophobic solvent to form a W / O emulsion. By forming such a W / O emulsion, the silica sol becomes spherical due to surface tension, etc., and the silica sol dispersed in the hydrophobic solvent in this spherical shape can be gelled to obtain a spherical gel. In this way, through the emulsion formation step of forming a W / O emulsion, it is possible to produce aerogels with a high circularity, typically 0.8 or higher. The hydrophobic solvent may be any solvent that is hydrophobic enough to form a W / O emulsion with the aqueous silica sol. Examples of such solvents include organic solvents such as hydrocarbons and halogenated hydrocarbons. More specifically, examples include hexane, heptane, octane, nonane, decane, dichloromethane, chloroform, carbon tetrachloride, and dichloropropane. Among these, heptane, which has a moderate viscosity, is particularly suitable. If necessary, a mixture of multiple solvents may be used. Furthermore, it is also possible to use a water-soluble solvent such as a lower alcohol in combination (as a mixed solvent) as long as it is possible to form a W / O emulsion with the aqueous silica sol. The amount of the hydrophobic solvent used is not particularly limited as long as it is an amount that results in a W / O emulsion. However, typically, the amount of the hydrophobic solvent used is about 1 to 10 parts by volume per part by volume of the aqueous silica sol.

[0024] When forming the W / O emulsion, it is preferable to add a surfactant. Anionic surfactants, cationic surfactants, and nonionic surfactants can be used as the surfactant. Among these, nonionic surfactants are preferred because they facilitate the formation of a W / O emulsion. In the present invention, since the silica sol is aqueous, surfactants with an HLB value of 3 to 6, which indicates the degree of water solubility and hydrophobicity of the surfactant, can be preferably used. In the present invention, the "HLB value" refers to the HLB value determined by the Griffin method. As described above, in the present invention, the shape of the aerogel particles is largely determined by the shape of the droplets in the W / O emulsion. The shape of the droplets is influenced by the surfactant used. As mentioned above, the shape of the aerogel particles is preferably spherical. Specific examples of surfactants that can be used from this perspective include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate. The amount of surfactant used is the same as that typically used when forming a W / O emulsion. Specifically, a suitable amount of surfactant is 0.05 g to 10 g per 100 ml of aqueous silica sol. A large amount of surfactant tends to result in finer droplets in the W / O emulsion, whereas a small amount of surfactant tends to result in larger droplets. Therefore, the average particle size of the aerogel can be adjusted by increasing or decreasing the amount of surfactant used.

[0025] When forming a W / O emulsion, known methods for forming W / O emulsions can be used to disperse the aqueous silica sol in a hydrophobic solvent. From the perspective of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specific examples include methods using a mixer, homogenizer, etc. Since the average particle size of the silica sol droplets in the W / O emulsion and the average particle size of the aerogel generally correspond to each other, the average particle size of the aerogel can be controlled by controlling the droplet size here. Note that by sufficiently reducing the particle size of the silica sol droplets in the emulsion, the shape of the silica sol droplets is less likely to be disturbed, making it easier to obtain spherical aerogels with a higher circularity (although the average particle size of the aerogel will also be reduced).

[0026] (3) A step of gelling the silica sol in an acidic range by heating to convert the W / O emulsion into a gelled dispersion. In this step, after forming an emulsion by the above-mentioned procedure, the aqueous silica sol is gelled. Any known gelling method can be used for this gelation, as long as the emulsion state is not disrupted. A first preferred method is to adjust the pH during the formation of the aqueous silica sol so that the time until gelation is relatively long. That is, this method involves adjusting the pH to a level at which gelation does not occur during emulsion formation, but occurs by maintaining the pH at a certain temperature for a certain period of time. The time until gelation begins after adjusting to the gelation temperature depends on the pH, gelation temperature, and silica sol concentration. However, the lower the pH, the lower the gelation temperature, and the lower the silica sol concentration, the longer this time tends to be. For example, at pH 5, a temperature of 50°C, and a silica concentration of 80 g / L in the silica sol, the time is approximately several minutes. When the pH is 3, the temperature is 70° C., and the silica concentration in the silica sol is 80 g / L, the time is about 60 minutes.

[0027] A second preferred method involves adding a basic substance to the emulsion to increase the pH of the W phase and make it weakly acidic or basic. In this case, it is preferable to prepare the metal oxide sol at a low pH (approximately 0.5 to 2.5) at which the sol is relatively stable. A specific method for increasing the pH of the W phase is to predetermine the amount of base required to achieve the desired pH in the W phase and then add that amount of base to the emulsion. The amount of base required to achieve the desired pH can be determined by taking a fixed amount of the metal oxide sol to be used in the emulsion, measuring the pH of the taken metal oxide sol with a pH meter, adding the base used for gelation to the taken metal oxide sol, and measuring the amount of base required to achieve the desired pH. When adding a basic substance to the emulsion, it is preferable to agitate the mixture using a mixer or the like to prevent a localized increase in pH (local pH increase) as much as possible. Examples of basic substances include ammonia, caustic soda, and alkali metal silicates.

[0028] (4) Step of Separating the Dispersion into Two Layers, O and W Phases In the manufacturing method of the present invention, the dispersion of the gel prepared as described above is separated into O and W phases. After separation, the gel obtained in the above step is dispersed in the W phase. This separation method can be performed using known emulsion demulsification methods. Specifically, this method can be performed using one or a combination of methods selected from the following: addition of a water-soluble organic solvent, addition of salt, application of centrifugal force, addition of acid, and change in volume ratio (addition of water or a hydrophobic solvent). Preferably, a certain amount of water-soluble organic solvent can be added to the emulsion, along with water as needed, to separate the emulsion into O and W phases. After the separation step, the upper layer generally becomes the O phase (organic layer), and the lower layer becomes the W phase (aqueous layer). Examples of the water-soluble organic solvent include acetone, methanol, ethanol, and isopropyl alcohol. Among these, isopropyl alcohol is preferably used because it is effective in improving the efficiency of the hydrophobization treatment described below.

[0029] The addition of water is not necessarily required to form the W phase in this step. A method can be employed in which the water used as a raw material is expelled from the gel in an amount sufficient to disperse the gel. Specifically, this method can be achieved by selecting a water-soluble organic solvent that penetrates the pores of the gel and expels water. The amount of water-soluble organic solvent added is preferably adjusted depending on the type and amount of surfactant used during emulsion formation. For example, when sorbitan monooleate is used as the surfactant for a W / O emulsion, separation into the O phase and the W phase can be achieved by adding a water-soluble organic solvent in an amount approximately 0.1 to 0.4 times by mass relative to the O phase, stirring as necessary, and then allowing to stand. However, in this case, it is preferable to add water in an amount approximately 0.6 to 0.9 times by mass relative to the O phase along with the water-soluble organic solvent. The temperature during the separation process is not particularly limited, but it can typically be performed at approximately 20 to 70°C. It is preferable to remove the O phase that results from the process of separating the O phase and the W phase. This is to improve the efficiency of the subsequent hydrophobic treatment of the gelled body. While the removal method is not particularly limited, it can be easily achieved by, for example, removing the O phase by decantation or the like and recovering the W phase, which is separated into two phases. While it is not necessary to completely separate and remove the O phase, in order to efficiently perform the hydrophobic treatment of the gelled body contained in the W phase (described later), the proportion of the O phase that remains unremoved should be as small as possible, preferably 20% by mass or less of the amount of the W phase (including the mass of the gelled body), and more preferably 10% by mass or less.

[0030] (5) A step of adding a basic substance to the W phase to age the gelled bodies dispersed in the W phase. This step is carried out by adding a basic substance to the W phase (in which the gelled bodies are dispersed) to adjust the pH of the W phase to a weakly acidic or basic state. In this production method, aging the gel using this technique is important. While the gelled bodies dispersed in the W phase are uniformly formed by heating in the step (3) of gelling the silica sol in the acidic range by heating and converting the W / O emulsion into a dispersion of gelled bodies, heating alone is not sufficient to fully develop the three-dimensional network structure. Therefore, a basic substance is added to the separated W phase to uniformly adjust the pH throughout the dispersed gelled bodies. This further advances the gelation reaction (dehydration condensation reaction) in each gelled body, resulting in a fully aged aerogel. By adding a basic substance, the pH of the W phase, which is in the acidic range, increases to a weakly acidic or basic state. Specifically, the pH of the W phase is preferably 4.5 to 10, more preferably 5.5 to 8.5, and particularly preferably 6.0 to 8.0. In the present invention, a basic substance containing sodium is used as the basic substance. Examples of the basic substance include inorganic bases such as sodium hydroxide, sodium bicarbonate, and sodium carbonate, and sodium salts of organic acids such as sodium acetate. However, inorganic bases are preferred because organic acids may potentially become undesirable impurities. Among these, sodium hydroxide is preferred because it allows for easy pH adjustment. Furthermore, the gelled body can be aged by maintaining the aging temperature at room temperature to approximately 80°C. The aging time can be appropriately set depending on the pH of the W phase and the aging temperature, but is approximately 0.1 to 12 hours. The basic substance to be added in step (5) can be added simultaneously with the water-soluble organic solvent to be added in step (4) for separating the dispersion into two layers, an O phase and a W phase. In this case, steps (4) and (5) can be carried out simultaneously.

[0031] (6) A step of silylating the gelled body dispersed in the W phase and extracting the gelled body into the O phase. In the method for producing a powder consisting of hydrophobic spherical silica aerogel of the present invention, it is necessary to silylate the gelled body using a silylating agent after the W phase recovery step. The spherical silica aerogel obtained by the silylation treatment exhibits hydrophobic properties. In the subsequent step (8) of recovering the gelled body and obtaining a powder consisting of hydrophobic spherical silica aerogel, shrinkage is suppressed when the gelled body is dried, making it possible to obtain a powder that retains the porous structure of an aerogel. A silylating agent that can be used in the present invention reacts with a hydroxy group present on the surface of a metal oxide (here, silica): M-OH (3) [in formula (3), M represents a metal atom. The remaining valence of M is omitted in formula (3)] to form (M-O-) （４－ｎ） SiR ｎ (4) [In formula (4), n is an integer of 1 to 3, R is a hydrocarbon group, and when n is 2 or greater, the multiple Rs may be the same or different from one another.] By performing a silylation treatment using such a silylating agent, the hydroxy groups on the surface of the aerogel powder are end-capped with hydrophobic silyl groups and inactivated, thereby suppressing dehydration condensation reactions between the surface hydroxy groups. Therefore, drying shrinkage can be suppressed even when drying is performed under conditions below the critical point, making it possible to obtain a metal oxide powder having a BJH pore volume of 2 mL / g or more.

[0032] Known silylating agents include compounds represented by the following general formulas (5) to (7): RnSiX （４－ｎ） (5) [In formula (5), n represents an integer of 1 to 3; R represents a hydrophobic group such as a hydrocarbon group; and X represents a group (leaving group) that can be released from the molecule by cleaving the bond to the Si atom in a reaction with a compound having a hydroxy group. When n is 2 or more, multiple Rs may be the same or different. Also, when n is 2 or less, multiple Xs may be the same or different.]

[0033]

[0034] [In formula (6), R1 represents an alkylene group; R2 and R3 each independently represent a hydrocarbon group; and R4 and R5 each independently represent a hydrogen atom or a hydrocarbon group.]

[0035]

[0036] [In formula (7), R6 and R7 each independently represent a hydrocarbon group, and m represents an integer of 3 to 6. Multiple R6s may be the same or different. Also, multiple R7s may be the same or different.]

[0037] In the above formula (5), R represents a hydrocarbon group, preferably a hydrocarbon group having 1 to 10 carbon atoms, more preferably a hydrocarbon group having 1 to 4 carbon atoms, and particularly preferably a methyl group. Examples of the leaving group represented by X include halogen atoms such as chlorine and bromine; alkoxy groups such as methoxy and ethoxy; and groups represented by -NH-SiR3 (wherein R has the same meaning as R in formula (6)). Specific examples of the silylating agent represented by formula (5) include chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, monomethyltrimethoxysilane, monomethyltriethoxysilane, hexamethyldisilazane, and hexamethyldisiloxane. In terms of favorable reactivity, chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, octamethylcyclotetrasiloxane, and / or hexamethyldisilazane and hexamethyldisiloxane are particularly preferred. The number of bonds with hydroxy groups on the aerogel powder skeleton varies depending on the number of leaving groups X (4-n). For example, if n is 2, then: (M-O-) ２ SiR ２ (8) If n is 3, the bond is: MO-SiR ３ The following bond (9) is formed. By silylating the hydroxy group in this way, the silylation treatment is carried out.

[0038] In the above formula (6), R1 is an alkylene group, preferably an alkylene group having 2 to 8 carbon atoms, and particularly preferably an alkylene group having 2 to 3 carbon atoms. In the above formula (6), R2 and R3 are each independently a hydrocarbon group, and preferred groups include the same groups as R in formula (5). R4 represents a hydrogen atom or a hydrocarbon group, and in the case of a hydrocarbon group, preferred groups include the same groups as R in formula (5). When a gelled body is treated with this compound (cyclic silazane) represented by formula (6), the Si-N bond is cleaved by reaction with the hydroxy group, and thus (M-O-) is formed on the surface of the aerogel powder skeleton in the gelled body. ２ A bond of the form SiR2R3 (10) is generated. In this way, the cyclic silazanes of formula (6) also silylate hydroxy groups, resulting in a silylation treatment. Specific examples of cyclic silazanes represented by formula (6) include hexamethylcyclotrisilazane and octamethylcyclotetrasilazane. In formula (7), R6 and R7 each independently represent a hydrocarbon group, and preferred groups include the same groups as R in formula (5). m represents an integer of 3 to 6. When a gelled body is treated with this compound (cyclic siloxane) represented by formula (7), the following bond (M-O-) appears on the surface of the aerogel powder skeleton in the gelled body: ２ The bond SiR6R7 (11) is thus generated. In this way, the cyclic siloxane of the above formula (7) also silylates the hydroxy group, thereby carrying out a silylation treatment.

[0039] Specific examples of cyclic siloxanes represented by formula (7) include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane. The amount of treating agent used in the silylation treatment varies depending on the type of treating agent, but when hexamethyldisiloxane is used as the treating agent, 10 parts by mass or more per 100 parts by weight of silica is preferred. When extraction of the gelled body into the O phase (described below) is carried out simultaneously with silylation, 1500 to 2000 parts by mass is preferred. Using more than 2000 parts by mass of treating agent is ineffective and may even result in a deterioration in volumetric efficiency. The silylation treatment can be carried out by adding the silylation treating agent to the W phase in the previous step and allowing it to react for a certain period of time. For example, when dimethyldichlorosilane is used as the silylation treating agent and the treatment temperature is 50° C., the reaction can be carried out by holding the solution for about 4 to 12 hours or more, and when octamethylcyclotetrasiloxane is used and the treatment temperature is 70° C., the reaction can be carried out by holding the solution for about 6 to 12 hours or more. Furthermore, when a cyclic siloxane such as octamethylsiloctetrasiloxane is used as the silylation treating agent, it is preferable to add hydrochloric acid to adjust the pH of the solution to 0.3 to 1.0 in order to increase the efficiency of the reaction.

[0040] In the silylation treatment step, a water-soluble organic solvent is preferably added to increase the solubility of the treatment agent in the W phase and thereby improve reaction efficiency. Examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol. Among these, isopropyl alcohol is preferred. The water-soluble organic solvent is preferably added so that its concentration in the W phase is approximately 20 to 80 wt %. (4) If a water-soluble organic solvent was added during the separation of the W phase in the step of separating the dispersion into two layers, the O phase and the W phase, it can be used as is in this step. After the silylation treatment, a hydrophobic organic solvent is added to extract the silylated gel into the O phase, and the resulting W phase is then removed (this step can be omitted if the gel is extracted by the silylating agent during silylation and the solution forms a two-phase state). Criteria for selecting a hydrophobic organic solvent to be used for gel extraction include low surface tension to prevent drying shrinkage during the subsequent drying step. Specifically, hexane, heptane, nonane, decane, dichloromethane, methyl ethyl ketone, toluene, etc. can be used, and hexane, heptane, decane, and toluene are preferably used. When hexamethyldisiloxane is used as the silylation treatment agent, it is preferable to add the same amount of hexamethyldisiloxane as the hydrophobic organic solvent used for extraction into the O phase, thereby simultaneously performing the silylation treatment and extraction into the O phase, in order to shorten the treatment time. Generally, hexamethyldisiloxane is more expensive than the hydrophobic organic solvent, so it is preferable to recover it and reuse it.

[0041] After the extraction into the O phase, the O phase is preferably washed with an aqueous alcohol solution to remove the acid and salt contained in the gel. This washing procedure can be performed by a known method. To improve washing efficiency, it is preferable to use an aqueous alcohol solution with a concentration of approximately several tens of wt %. During washing, it is preferable to raise the temperature within a range that does not exceed the boiling point of the hydrophobic organic solvent in order to improve washing efficiency. Washing can usually be performed at a temperature in the range of 45 to 70°C. The alcohol used must be azeotropic with water and have a low boiling point, in order to perform the step (7) of reducing the water content in the gel to 10% or less by azeotropic dehydration, as described below. Ethanol, isopropyl alcohol, normal propanol, butyl alcohol, isobutyl alcohol, secondary butyl alcohol, and tertiary butyl alcohol can be used, with ethanol and isopropyl alcohol being preferred.

[0042] (7) Azeotropic dehydration process to reduce the water content of the gel to 10% or less. Residual water remains in the gel in the O phase, which is removed by azeotropic distillation with a hydrophobic organic solvent and alcohol. The water content in the gel is positively correlated with the stress generated during drying, making this process of removing water before drying particularly important for preventing drying shrinkage. Water is removed by azeotropic distillation using a condensing device such as a cooling tube and heating the O phase. The distillation process is continued until the water content of the gel is reduced to 10% or less. If the solvent continues to evaporate and drying of the gel begins while the gel still contains more than 10% water, drying shrinkage of the gel will occur, preventing the production of a high-oil-absorption aerogel powder. Therefore, it is necessary to maintain the gel in a slurry state in which it is dispersed in a hydrophobic organic solvent. This can be achieved by returning only the O phase of the two-phase liquid condensed during azeotropic distillation to the heating vessel, or by adding a separately prepared hydrophobic organic solvent while performing the distillation process. Furthermore, the use of a Dean-Stark apparatus to remove water while heating and refluxing can also prevent solvent loss, making this apparatus preferable (note that the removal of water from the gel by the Dean-Stark method described in the Examples refers to heating and refluxing using a Dean-Stark apparatus). The water content of the gel can be measured by filtering the gel contained in the O phase, soaking the gel in a hydrophilic organic solvent such as isopropyl alcohol or ethanol, and then quantifying the solution with a Karl Fischer moisture meter. 1 g of the gel and 10 g of ethanol are added to a 20 mL screw tube and stirred with a magnetic stirrer at 25°C for 30 minutes. The water content of the gel can then be calculated from the water content in the filtrate.

[0043] (8) Step of recovering the gelled body and obtaining a powder consisting of hydrophobic spherical silica aerogel. The gelled body dispersed in the O phase obtained in the step (7) of reducing the water content of the gelled body to 10% or less by azeotropic dehydration is filtered, and the hydrophobic organic solvent is removed (i.e., dried). The drying temperature is preferably above the boiling point of the solvent and below the decomposition temperature of the surface treatment agent, and the pressure is preferably normal pressure or reduced pressure. When the silica aerogel powder consisting of the hydrophobic spherical silica aerogel of the present invention is produced by the above-mentioned method, it exhibits hydrophobicity, but it can also be converted to hydrophilicity by thermal decomposition of the hydrophobic groups on the surface. For example, the hydrophobic groups on the surface can be thermally decomposed by holding the powder at a temperature of 400 to 700°C, preferably 500 to 600°C, for about 1 to 8 hours in a non-oxidizing atmosphere (such as a nitrogen atmosphere). The above description of the present invention mainly exemplified silica aerogel powder consisting of hydrophobic spherical silica aerogel and a method for producing the silica aerogel powder, but the present invention is not limited to this embodiment.

[0044] <Uses of Silica Aerogel Powder> The silica aerogel powder of the present invention can be used as a heat insulating material, a cosmetic additive, a cosmetic product, a matting agent, etc. These will be described in detail below.

[0045] The spherical silica aerogel of the present invention has good packing properties due to its spherical shape, and has very low thermal conductivity due to its low porosity, so it can be suitably used as a thermal insulating material. When used as a thermal insulating material, it is suitable to form it into a paint, a sheet, or the like.

[0046] When forming a paint, the resin penetrates into the pores of the silica aerogel, impairing its heat insulating properties. Therefore, an aqueous emulsion resin or aqueous resin is preferred as the substrate. Examples of such substrates include vinyl acetate homopolymer dispersions, vinyl acetate copolymer dispersions, ethylene-vinyl acetate dispersions, styrene-acrylate copolymer dispersions, styrene-butadiene copolymer dispersions, acrylate dispersions, water glass (sodium silicate), and aqueous polyvinyl alcohol solutions. Furthermore, if bubbles are generated when the spherical silica aerogel of the present invention is added to the substrate, they can be degassed using known methods. For example, the mixture may be placed in a reduced pressure environment or centrifugal degassing may be used.

[0047] The heat insulating sheet of the present invention can be inserted between the cells of a lithium-ion battery to suppress thermal runaway in the battery. When used for this purpose, it must be nonflammable, and inorganic fibers are preferably used as the main fiber. The manufacturing method for the heat insulating sheet made from the spherical silica aerogel of the present invention is not limited, and examples include dry press molding and wet molding. In the dry press molding method, the spherical silica aerogel of the present invention and other components such as fibers, binders, and heat-shielding agents are mixed in a V-type blender or the like, and molded by pressing at a pressure of approximately 1 to 10 MPa. If necessary, it is also preferable to apply heat above the melting point of the binder. In the wet molding method, the spherical silica aerogel of the present invention and sheet components such as fibers and binders, as well as, if necessary, strength agents, flocculants, dispersants, radiation suppressants, etc., are dispersed in water to prepare a slurry, which is then dehydrated through a filtration mesh to form a wet sheet, and the molded sheet is obtained by heating to remove the moisture. The thickness of the sheet is not particularly limited, but is, for example, 0.8 to 4.0 mm, and a suitable range is 1.0 to 3.0 mm.

[0048] The fibers used in the sheet of the present invention are not limited and can be appropriately selected from known fibers depending on the intended use of the sheet. Examples include pulp, polyester fiber, vinylon fiber, polyolefin fiber, polyurethane fiber, aramid fiber, acrylic fiber, polylactic acid fiber, polyvinyl chloride fiber, vinylidene fiber, polyphenylene sulfide fiber, ceramic fiber, alumina fiber, glass fiber, carbon fiber, and rock wool. When heat resistance is required for the sheet, inorganic fibers such as ceramic fiber, alumina fiber, glass fiber, carbon fiber, and rock wool are preferably used. The fiber length of the above fibers is not particularly limited, but is preferably approximately 0.1 to 20 mm. The fiber diameter is also not particularly limited, but is preferably approximately 1 to 10 μm.

[0049] The binder used in the sheet of the present invention is not particularly limited, but examples thereof include organic binders such as acrylic resin, acrylic emulsion resin, methacrylic resin, styrene resin, acrylic-styrene resin, vinyl acetate resin, vinyl acetate-acrylic resin, styrene-butadiene rubber, acrylonitrile-butadiene rubber, chloroprene rubber, ethylene-vinyl acetate resin, vinyl chloride-vinyl acetate resin, vinyl chloride resin, vinyl chloride-ethylene resin, vinylidene chloride resin, vinylidene chloride acrylic resin, acrylic-urethane resin, urethane resin, polyvinyl alcohol, starch, polyester fiber, aramid fiber, and vinylon fiber, as well as inorganic binders such as sodium silicate, silica sol, sepiolite, kaolinite, and amorphous silica. The amount of binder added can be about 1 to 20% of the solid content of the sheet, and a preferred range to avoid deterioration of heat insulation is 1 to 10%, or even 1 to 5%.

[0050] The strength agent used in the sheet of the present invention is not particularly limited, but includes resins such as urea-formaldehyde resin, melamine-formaldehyde resin, polyamide, polyamine, epichlorohydrin resin, vegetable gum, latex, polyethyleneimine, glyoxal, gum, mannogalactan polyethyleneimine, polyacrylamide, polyvinylamine, acrylic resin, and polyvinyl alcohol; composite polymers or copolymers composed of two or more selected from the above resins; starch and modified starch; carboxymethyl cellulose, guar gum, and urea resin. Polyacrylamide is preferred, and polyacrylamide containing a large amount of cations is even more preferred. The amount of strength agent added is preferably about 0.05 to 2% of the solids content of the sheet, and even more preferably about 0.1 to 0.5%. If the amount of strength agent added is low, the strength of the sheet tends to decrease, while if the amount added is high, the sheet tends to become hard and its insulation properties tend to deteriorate.

[0051] The flocculant used in the sheet of the present invention is not particularly limited, but may be polyethyleneimine, polyalkyleneimine, dicyandiamide polymer, polyamine, polyacrylamide, or the like. Furthermore, inorganic substances such as aluminum sulfate and polyaluminum chloride may also be used. The amount of flocculant added may be approximately 10 to 1000 ppm relative to the solids concentration of the sheet, with a preferred range being 10 to 100 ppm. Increasing the amount of flocculant added tends to cause unevenness in the sheet, while decreasing the amount of flocculant added tends to result in poor yield.

[0052] Examples of radiation inhibitors used in the sheet of the present invention include metal particles (aluminum particles, silver particles, gold particles, etc.), inorganic particles (graphite, carbon black, silicon carbide, titanium oxide, tin oxide, potassium titanate, etc.), etc. Titanium oxide can be preferably used. The amount of radiation inhibitor added can be about 1 to 30% of the solid content of the sheet, and preferably about 1 to 10%. When used for the purpose of high-temperature insulation at or above several hundred degrees Celsius, it is preferable to increase the amount of radiation inhibitor in order to suppress radiation heat transfer.

[0053] (Cosmetic Additives, Cosmetics) The spherical silica aerogel of the present invention can be suitably used as a cosmetic additive. For example, when used as an additive in foundation, its spherical shape and high specific surface area ensure excellent appearance retention and a smooth feel. In addition, its extremely high oil absorption capacity efficiently absorbs oil from the skin and scalp surface, providing excellent shine prevention. Furthermore, because it exhibits hydrophobicity and sweat-repelling properties, it can be suitably used in cosmetics other than the foundation, such as paste and cream-type makeup and skin care cosmetics, as well as deodorants and hair styling products.

[0054] (Matting Agent) When used as a matting agent, the spherical silica aerogel of the present invention has a very high porosity and low particle density, making it possible to create unevenness on the surface of a coating film even with a small amount added. When a large amount of silica is added, the coating film tends to lose its transparency, but when the spherical silica aerogel of the present invention is used, a matting effect can be obtained while maintaining transparency. The preferred D50 value range for use as a matting agent is 1 to 20 μm, more preferably 1 to 5 μm. The smaller the D50 value, the finer the coating film texture. When used as a matting agent, the spherical silica aerogel of the present invention is usually dispersed in an organic resin. In the matting paint containing the matting agent and organic resin of the present invention, any organic resin can be used. In terms of the type of resin, examples include conventional paints known per se, such as oil-based paints, nitrocellulose paints, alkyd resin paints, aminoalkyd paints, vinyl resin paints, acrylic resin paints, epoxy resin paints, polyester resin paints, and chlorinated rubber-based paints, as well as paints containing one or more of rosin, ester gum, pentaresin, coumarone-indene resin, phenolic resins, modified phenolic resins, maleic resins, alkyd resins, amino resins, vinyl resins, petroleum resins, epoxy resins, polyester resins, styrene resins, acrylic resins, silicone resins, rubber-based resins, chlorinated resins, urethane resins, polyamide resins, polyimide resins, fluorine-based resins, and natural or synthetic lacquers. Furthermore, the paint used may be any type, such as a solvent-based paint, an ultraviolet-curable paint, or a powder paint, depending on how it is used.

[0055] Examples of organic solvents that can be used in this solvent-based paint include aromatic hydrocarbon solvents such as toluene and xylene; aliphatic hydrocarbon solvents such as n-heptane, n-hexane, and Isopar; alicyclic hydrocarbon solvents such as cyclohexane; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcohol solvents such as ethanol, propanol, butanol, and diacetone alcohol; ether solvents such as tetrahydrofuran and dioxane; cellosolve solvents such as ethyl cellosolve and butyl cellosolve; ester solvents such as ethyl acetate and butyl acetate; and aprotic polar solvents such as dimethylformamide, dimethylacetamide, and dimethyl sulfoxide. Examples of ultraviolet (UV)-curable paints include high-solid resins, such as UV-curable acrylic resins, epoxy resins, vinyl urethane resins, acrylic urethane resins, and polyester resins, which can be used alone or in combination of two or more. Examples of powder coatings include thermoplastic resins such as polyamide, polyester, acrylic resin, olefin resin, cellulose derivative, polyether, and vinyl chloride resin, as well as epoxy resin, epoxy / novolac resin, isocyanate, or epoxy-cured polyester resin. The amount of matting agent added to the resin in this invention can be any ratio, but a suitable amount is 1 to 10 parts by mass, preferably 1 to 5 parts by mass, per 100 parts by mass of organic resin. This allows a high degree of matting effect to be imparted to the coating surface with a small amount of the agent. It is also expected that the scratch resistance of the coating surface will be improved at the same time.

[0056] (Moisture Content in Gel Mass) In Examples 1 to 5 and Comparative Examples 1 to 3 shown below, the moisture content of the gel mass obtained during production before drying was measured using the following procedure. 1 g of the gel mass and 7.8 g of ethanol were weighed into a 20 mL screw tube and stirred using a magnetic stirrer at 25°C for 30 minutes. The moisture content of the filtrate obtained by filtration from the dispersion was measured using a Karl Fischer Trace Moisture Analyzer CA-200 manufactured by Mitsubishi Chemical Analytech Co., Ltd. From the obtained moisture content, the moisture content w (%) of the gel mass was calculated using the following formula: w = {(a - b) (c + d - de / 100)} / c (In the above formula, a is the measured trace moisture value of the filtrate (%), b is the measured trace moisture value of ethanol, i.e., the blank value (%), c is the amount of ethanol (g) added to the screw tube, d is the amount of gel mass (g) added to the screw tube, and e is the solids concentration of the gel mass (%). The hydrophobic spherical silica aerogel powders produced in Examples 1 to 5 and Comparative Examples 1 to 3 were tested for the following items.

[0057] (Oil absorption, specific surface area, and pore volume) The BET specific surface area and BJH pore volume were measured according to the above definitions using a BELSORP-max manufactured by Japan BEL Co., Ltd. The oil absorption was measured according to JIS K6217-4 "Determination of oil absorption."

[0058] (D50) 0.3 g of silica aerogel powder and 40 mL of ethanol (99.5 vol% %) were added to a 50 mL screw cap, and the container was placed in an ultrasonic cleaner and dispersed at 90 W for 30 minutes. The volume-based particle size distribution of the resulting dispersion was measured using a Beckman Coulter Laser Diffraction / Scattering Particle Size Distribution Analyzer LS 13 320. The volume-based cumulative 50% diameter (D50) was calculated from the particle size distribution curve.

[0059] (M Value) Hydrophobic silica aerogel floats in water but completely dissolves in methanol. Taking advantage of this, the M value measured by the following method was used as an index of hydrophobic treatment by hydrophobic groups on the silica aerogel surface. 0.2 g of silica aerogel powder was added to 50 ml of water in a 200 mL beaker and stirred with a magnetic stirrer. Methanol was added dropwise using a burette, and the end point was the point at which the entire silica aerogel powder was wetted and suspended in the solvent in the beaker. During this process, the methanol was introduced into the solution using a tube to prevent direct contact with the sample. The volume percent of methanol in the methanol-water mixed solvent at the end point was taken as the hydrophobicity (M value). M value = amount of methanol added / (amount of methanol added + 50 ml)

[0060] (Average circularity) The silica aerogel powder was observed using a Hitachi High-Technologies SEM (S-5500) at an acceleration voltage of 3.0 kV, secondary electron detection, and a magnification of 1000 times. The obtained SEM image was analyzed to calculate the circularity of the silica aerogel particles using the above formula (1). The average circularity was calculated by averaging the circularities of 2000 or more silica aerogel particles.

[0061] (Carbon Content) The carbon content was measured using an elemental analyzer (vario MICRO cube) manufactured by Elementor Japan Co., Ltd.

[0062] (Thermal Conductivity) The thermal conductivity of the powder was measured at room temperature using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0063] Example 1: While stirring 200 g of 4% sulfuric acid with a stirring blade, 100 g of sodium silicate (silica concentration 15%) was gradually added to prepare an aqueous silica sol with a silica concentration of 54 g / L. The pH was 3.0. 139 g of the prepared aqueous silica sol was separated and added to 130.5 g of heptane in which 1.5 g of sorbitan monooleate had been dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. The resulting emulsion was gelled at 70°C for 1 hour while stirring with a stirring blade. 71.0 g of isopropyl alcohol and 58.0 g of ion-exchanged water were added, and the O and W phases were separated while stirring with a stirring blade. The O phase was removed by decantation, and the W phase was recovered. Subsequently, 8.0 g of 0.5 mol / L aqueous sodium hydroxide solution was added. The pH of the W phase was 7.8. The gel was aged at 70°C for 20 minutes. 24 g of 35% hydrochloric acid and 150 g of hexamethyldisiloxane were added to the resulting W phase, and the mixture was stirred in a 60°C water bath for 2 hours to carry out a silylation treatment. After silylation, the W phase was removed and washed twice with 129 g of 55% isopropanol. After the second wash, the O phase was heated under reflux using a Dean-Stark system to remove the water from the gel. The end point of the operation was the point at which no water phase was detected in the condensate. The resulting silylated gel was filtered using a suction filter and dried under vacuum at 150°C for at least 16 hours to obtain a powder of hydrophobic spherical silica aerogel of the present invention. The water content of the gel before drying and the physical properties of the resulting silica aerogel powder are shown in Table 1.

[0064] Example 2 The same procedure as in Example 1 was carried out, except that an aqueous silica sol with a silica concentration of 63 g / L was prepared. The moisture content of the gelled body before drying and the physical properties of the obtained silica aerogel powder are shown in Table 1. Example 3 The same procedure as in Example 1 was carried out, except that an aqueous silica sol with a silica concentration of 76 g / L was prepared. Table 1 shows the moisture content of the gelled body before drying and the physical properties of the obtained silica aerogel powder.

[0065] Example 4: While stirring 200 g of 4% sulfuric acid with a stirring blade, 100 g of sodium silicate (silica concentration 15%) was gradually added to prepare an aqueous silica sol with a silica concentration of 54 g / L. The pH was 3.0. 139 g of the prepared aqueous silica sol was taken and added to 130.5 g of heptane in which 1.5 g of sorbitan monooleate had been dissolved. This solution was transferred to a 0.5 L apparatus equipped with four inclined paddle blades and stirred at a peripheral speed of 57 m / s for 60 minutes to form a W / O emulsion. The emulsification process and subsequent steps were carried out in the same manner as in Example 1. The moisture content of the gel before drying and the physical properties of the resulting silica aerogel powder are shown in Table 1.

[0066] Example 5: While stirring 200 g of 4% sulfuric acid with a stirring blade, 100 g of sodium silicate (silica concentration 15%) was gradually added to prepare an aqueous silica sol with a silica concentration of 54 g / L. The pH was 3.0. 139 g of the prepared aqueous silica sol was separated and added to 130.5 g of heptane in which 1.5 g of sorbitan monooleate had been dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. The resulting emulsion was gelled at 70°C for 1 hour while stirring with a stirring blade. 71 g of isopropyl alcohol and 58 g of ion-exchanged water were added, and the O and W phases were separated while stirring with a stirring blade. The O phase was removed by decantation, and the W phase was recovered. Subsequently, 8.0 g of a 0.5 mol / L aqueous sodium hydroxide solution was added. At this time, the pH of the W phase was 7.8. The gel was aged at 70°C for 20 minutes. 48.3 g of 35% hydrochloric acid and 7.7 g of hexamethyldisiloxane were added to the resulting W phase, and the mixture was stirred in a water bath at 60°C for 4 hours to carry out a silylation treatment. After silylation, 90 g of heptane was added to extract the gel, and the W phase was removed by decantation, recovering the O phase. The O phase was washed twice with 129 g of 55% isopropyl alcohol. After the second wash, the O phase was heated under reflux using a Dean-Stark system to remove the water from the gel. The end point of the operation was the point at which no water phase was detected in the condensate. The resulting silylated gel was filtered using a suction filter. The moisture content of the gel was measured and found to be 3.5%. The gel was dried under vacuum pressure at 150°C for 16 hours or more to obtain a powder of hydrophobic spherical silica aerogel of the present invention. The moisture content of the gel before drying and the physical properties of the obtained silica aerogel powder are shown in Table 1.

[0067] Comparative Example 1: While stirring 200 g of 4% sulfuric acid with a stirring blade, 100 g of sodium silicate (silica concentration 15%) was gradually added to prepare an aqueous silica sol with a silica concentration of 54 g / L. The pH was 3.0. 139 g of the prepared aqueous silica sol was separated and added to 130.5 g of heptane in which 1.5 g of sorbitan monooleate had been dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. The resulting emulsion was gelled at 70°C for 1 hour while stirring with a stirring blade. 71.0 g of isopropyl alcohol and 58.0 g of ion-exchanged water were added, and the O and W phases were separated while stirring with a stirring blade. The O phase was removed by decantation, and the W phase was recovered. Subsequently, 8.0 g of 0.5 mol / L aqueous sodium hydroxide solution was added. The pH of the W phase was 7.8. The gel was aged at 70°C for 20 minutes. 24 g of 35% hydrochloric acid and 150 g of hexamethyldisiloxane were added to the resulting W phase, and the mixture was stirred in a water bath at 60°C for 2 hours to carry out a silylation treatment. After the silylation treatment, the W phase was removed and washed twice with 129 g of 55% isopropanol. The resulting silylated gel was filtered using a suction filter. The gel was dried under vacuum pressure at 150°C for 16 hours or more to obtain a powder of the hydrophobic spherical silica aerogel of the present invention. The moisture content of the gel before drying and the physical properties of the resulting silica aerogel powder are shown in Table 1.

[0068] Comparative Example 2: While stirring 200 g of 4% sulfuric acid with a stirring blade, 100 g of sodium silicate (silica concentration 15%) was gradually added to prepare an aqueous silica sol with a silica concentration of 54 g / L. The pH was 3.0. 139 g of the prepared aqueous silica sol was separated and added to 130.5 g of heptane in which 1.5 g of sorbitan monooleate had been dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. The resulting emulsion was gelled at 70°C for 1 hour while stirring with a stirring blade. 71 g of isopropyl alcohol and 58 g of ion-exchanged water were added, and the O and W phases were separated while stirring with a stirring blade. The O phase was removed by decantation, and the W phase was recovered. Subsequently, 8.0 g of a 0.5 mol / L aqueous sodium hydroxide solution was added. The pH of the W phase was 7.8. The gel was aged at 70°C for 20 minutes. 48.3 g of 35% hydrochloric acid and 7.7 g of hexamethyldisiloxane were added to the resulting W phase, and the mixture was stirred in a 60°C water bath for 4 hours to carry out a silylation treatment. After silylation, 90 g of heptane was added to extract the gel. The W phase was removed by decantation, and the O phase was recovered. The O phase was washed twice with 129 g of 55% isopropyl alcohol. The resulting silylated gel was filtered using a suction filter. The gel was dried under vacuum pressure at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic spherical silica aerogel of the present invention. The moisture content of the gel before drying and the physical properties of the resulting silica aerogel powder are shown in Table 1.

[0069] Comparative Example 3 The procedure was the same as in Comparative Example 1, except that an aqueous silica sol with a silica concentration of 76 g / L was prepared. The moisture content of the gelled body before drying and the physical properties of the obtained silica aerogel powder are shown in Table 1.

[0070]

[0071] When the silica concentration of the aqueous silica sol is 54 g / L, the oil absorption of Comparative Examples 1 and 2, which were dried in a state where the moisture content in the gel was 10% or more, was about 800 mL / 100 g due to drying shrinkage, but in Examples 1, 4, and 5, the moisture was removed by azeotropy, drying shrinkage was suppressed, and the oil absorption was 1000 mL / 100 g or more.

[0072] <Heat insulation sheet preparation example 1> 4.93 g of spherical silica aerogel of Example 1, 0.29 g of dispersant (manufactured by Meisei Chemical Industry Co., Ltd., Pascol HA-52), 21.46 g of alumina fiber (manufactured by Almedio Co., Ltd., alumina fiber bulk), 0.87 g of polyester fiber (manufactured by Kuraray, N720), 1.45 g of sepiolite (manufactured by Showa KDE Co., Ltd., Milcon SP), and 800 g of water were mixed in a juice mixer for 1 minute 30 seconds, and the fibers were crushed and mixed. Furthermore, 1300 g of water was added, and while stirring with a three-one motor, 3.63 g of paper strength agent (manufactured by Seiko PMC Co., Ltd., DS4424) was added to prepare a slurry. The solid content of the prepared slurry was filtered using a paper machine to prepare a wet sheet, which was then dehydrated using a press and dried at 150 ° C. to prepare a heat insulation sheet. The thermal conductivity of the prepared sheet was 50.1 mW / mK, and the back surface temperature when heated at 600° C. was 181° C. The non-combustibility was V0. The thickness of the sheet was 1.5 mm.

[0073] <Heat insulation sheet preparation example 2> 4.93 g of spherical silica aerogel of Comparative Example 1 and 0.29 g of dispersant (manufactured by Meisei Chemical Industry Co., Ltd., Pascol HA-52), 21.46 g of alumina fiber (manufactured by Almedio Co., Ltd., alumina fiber bulk), 0.87 g of polyester fiber (manufactured by Kuraray, N720), 1.45 g of sepiolite (manufactured by Showa KDE Co., Ltd., Milcon SP), and 800 g of water were mixed in a juice mixer for 1 minute 30 seconds, and the fibers were crushed and mixed. Furthermore, 1300 g of water was added, and while stirring with a three-one motor, 3.63 g of a paper strength agent (manufactured by Seiko PMC Co., Ltd., DS4424) was added to prepare a slurry. The solid content of the prepared slurry was filtered using a paper machine to prepare a wet sheet, which was then dehydrated using a press and dried at 150 ° C. to prepare a heat insulation sheet. The thermal conductivity of the prepared sheet was 67.0 mW / mK, and the back surface temperature when heated at 600° C. was 228° C. The non-combustibility was V0. The thickness of the sheet was 1.6 mm.

[0074] <Evaluation Method> The heat insulating sheets produced according to the Examples and Comparative Examples were evaluated by the following methods. (Measurement of Thermal Conductivity) The thermal conductivity of the heat insulating sheets was measured using a rapid thermal conductivity meter QTM-500 (manufactured by Kyoto Electronics Manufacturing Co., Ltd.) according to the "unsteady hot wire method" specified in JIS R2616.

[0075] (Insulation Test) An insulation sheet (50 x 80 mm) was placed on a hot plate heated to 600°C, and a thermocouple and a 370 g weight (stainless steel, 50 x 50 cm) were placed on top of it. The temperature of the backside of the insulation sheet was evaluated 5 minutes after placing it on the hot plate. (Non-flammability Test) This was performed using the UL94 vertical flame test in accordance with ASTM D3801. A test piece (125 x 13 x t mm) was held vertically and exposed to a 20 mm flame for 10 seconds twice, and the flame behavior was evaluated as V0, V1, V2, or Not. The UL94 rating criteria are shown below.

[0076]

Claims

1. Made of hydrophobic spherical silica aerogel, a) the volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by the laser diffraction / scattering method is 1 to 200 μm, and b) the specific surface area measured by the BET method is 400 to 1000 m ２ / g, and c) an oil absorption of 850 to 1300 ml / 100 g.

2. The silica aerogel powder according to claim 1, wherein the peak pore volume and peak pore radius measured by the BJH method are 2 to 8 ml / g and 10 to 50 nm, respectively.

3. e) The silica aerogel powder according to claim 1, wherein the thermal conductivity at room temperature measured by a hot wire method is 25 mW / m·K or less.

4. A method for producing silica aerogel powder, comprising, in the above order: (1) preparing an aqueous silica sol; (2) dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion; (3) gelling the silica sol in an acidic range by heating, thereby converting the W / O emulsion into a dispersion of a gelled material; (4) separating the dispersion into two layers, an O phase and a W phase; (5) adding a basic substance to the W phase to age the gelled material dispersed in the W phase; (6) silylating the gelled material dispersed in the W phase and extracting it into the O phase; (7) reducing the water content of the gelled material to 10% or less by azeotropic dehydration; and (8) recovering the gelled material to obtain a powder consisting of hydrophobic spherical silica aerogel.

5. The method for producing silica aerogel powder according to claim 4, further comprising the step of washing the gelled body after the step (6) of silylating the gelled body dispersed in the W phase and extracting the gelled body into the O phase.

6. The method for producing silica aerogel powder according to claim 4, wherein in the step (1) of preparing an aqueous silica sol, the silica concentration of the aqueous silica sol is set to 50 to 80 g / L.

7. A heat insulating material comprising the silica aerogel powder according to claim 1.

8. The heat insulating material according to claim 7, which is in the form of a sheet.

9. A cosmetic additive comprising the silica aerogel powder according to claim 1.

10. A cosmetic product containing the silica aerogel powder according to claim 1.

11. A matting agent comprising the silica aerogel powder according to claim 1.

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