Silica aerogel powder, production method for same, filler for heat insulation material, and heat insulation material

Abstract

A silica aerogel powder according to the present invention is characterized by comprising a hydrophobic spherical silica aerogel and by having a) a volume-based cumulative 50% diameter (D50) of 200–2000 μm on a particle size distribution measured by laser diffraction / scattering and b) a BET specific surface area of 400–1000 m2 / g, and a production method according to the present invention is characterized by spraying a silica sol that comprises an acid and an alkali silicate into a gas phase toward a liquid phase to produce a gelled body.

Description

Silica aerogel powder and method for producing the same, as well as fillers for thermal insulation materials and thermal insulation materials

[0001] The present invention relates to silica aerogel powder and a method for producing the same.

[0002] Aerogels are materials with high porosity and excellent oil absorption. Here, aerogel refers to a solid material with a porous structure and containing gas as a dispersion medium, and in particular, a solid material with a porosity of 60% or more. Porosity is the amount of gas contained in the apparent volume, expressed as a volume percentage. Silica aerogel is useful as an insulating filler. Heat conduction inside an object is contributed by solid conduction (propagation of thermal vibrations), convection, and radiation, and in materials with high porosity, convection generally contributes the most. In contrast, silica aerogel has a very small pore size of about 10 to 100 nm, so the movement of gas in the pores is greatly restricted, and heat conduction by convection is greatly inhibited. For this reason, silica aerogel has excellent insulating properties. Generally, the insulating performance depends on the amount of filler added to the substrate, so in order to increase the filling rate of silica aerogel and improve the insulating performance, it is desirable for silica aerogel to be spherical.

[0003] As a method for producing such spherical silica aerogels having an appropriate particle size, the following method has been proposed. Patent Document 1 discloses a method for producing spherical silica aerogels, comprising the steps of preparing an aqueous silica sol, dispersing the aqueous silica sol in a hydrophobic solvent to form a W / O emulsion, gelling the silica sol to convert the W / O emulsion into a dispersion of the gelled body, replacing the water in the gelled body with a solvent having a surface tension of 30 mN / m or less at 20°C, hydrophobizing (silylation treatment) the gelled body with a hydrophobic agent (silylation agent), and removing the substituted solvent, in the order described above. Patent Document 2 discloses a method for producing spherical silica aerogel, comprising the steps of: separating the dispersion of the gelled substance obtained in the step of converting the W / O type emulsion into a dispersion of the gelled substance into two layers, an O phase and a W phase; adding a basic substance to the W phase to mature the gelled substance dispersed in the W phase; silylation treatment of the gelled substance dispersed in the W phase; extracting the gelled substance with a hydrophobic organic solvent; and recovering the gelled substance to obtain a powder consisting of hydrophobic spherical silica aerogel. Patent Document 3 further discloses a method for obtaining spherical silica aerogel with a size of 20 to 200 μm by adjusting the size of the droplets in the W / O emulsion by the shear force used when creating the emulsion.

[0004] International Publication No. 2012 / 057086, Japanese Patent Publication No. 2018-177620, Japanese Patent Publication No. 2019-019017

[0005] While the spherical silica aerogels obtained by the conventional techniques described above exhibit excellent packing properties, when used as fillers for thermal insulation materials, those with a particle size of 200 μm or larger may be more effective. For example, when dispersed in a liquid as a thermal insulation filler, larger particle sizes allow for a reduction in the amount of dispersant used to disperse the spherical silica aerogel in water, and also reduce the amount of binder used during molding. As a result, the organic content can be reduced, improving thermal insulation and non-flammability. In conventional methods of creating silica sol droplets by emulsion, it was difficult to obtain large spherical silica aerogels of 200 μm or larger because larger particle sizes cause the droplets to settle and coalesce.

[0006] The inventors of the present invention have diligently studied to solve the aforementioned problems and have found that spherical silica with a particle size of 200 μm or more can be obtained by spraying silica sol into the gas phase using a spray, gelling the droplets of sprayed silica sol to create a spherical gel, and then recovering the gel after silylation treatment, thereby completing the present invention. Specifically, the present invention consists of a hydrophobic spherical silica aerogel, a) the volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by laser diffraction and scattering is 200 to 2000 μm, and b) the specific surface area by BET method is 400 to 1000 m². ２ This silica aerogel powder is characterized by having a concentration of / g.

[0007] The present invention also provides a method for producing silica aerogel powder consisting of hydrophobic spherical silica aerogel, characterized by comprising the following steps (1) to (4) in order. Specifically, (1) a step of mixing an acid and an alkali silicate to obtain a silica sol with a pH of 5 to 8, (2) a step of spraying the silica sol into the gas phase toward the liquid phase to obtain a gelled body, (3) a step of silylation treatment of the gelled body to obtain a silylated body, and (4) a step of recovering the silylated body to obtain a powder consisting of hydrophobic spherical silica aerogel. Furthermore, the present invention provides a filler for thermal insulation materials consisting of the silica aerogel powder obtained in the above invention, and a thermal insulation material containing the silica aerogel powder obtained in the above invention.

[0008] The spherical silica aerogel of the present invention has a particle size of 200 μm or more. When used as a filler for thermal insulation materials, it is possible to reduce organic components such as dispersants and binders. Furthermore, because it is spherical, it is possible to increase the packing density, making it possible to obtain thermal insulation materials with high thermal insulation performance.

[0009] The silica aerogel powder of the present invention is described below. <Silica Aerogel Powder> The powder of the present invention is composed of hydrophobic spherical silica aerogel. Here, silica refers to silicon dioxide, and is a general term for substances composed of silicon dioxide, SiO ２ This is how it is expressed.

[0010] Here, the term "spherical" for silica aerogel means that the average circularity of the silica aerogel particles is 0.7 or higher. Preferably, the average circularity is 0.8 or higher, and more preferably 0.85 or higher. Because the powder of the present invention consists of such spherical silica aerogel, it exhibits excellent packing properties when used as a filler for thermal insulation materials. The "average circularity" is calculated by obtaining an SEM image using a scanning electron microscope (SEM), analyzing the image to determine the value C (circularity) for each individual particle, defined by the following formula (1). This circularity C is then calculated as the arithmetic mean of 2000 or more particles. Note that a group of particles forming a single aggregated particle is counted as one particle. C = 4πS / L ２ (1) [In equation (1), S represents the area (projected area) occupied by the particle in the image. L represents the length of the outer circumference of the particle in the image.] The closer the average circularity is to 1, the closer the particle is to a perfect sphere. Generally, an average circularity of 0.7 or higher can be considered spherical, while a value less than 0.7 makes it difficult to consider it spherical.

[0011] In the present invention, the spherical silica aerogel is hydrophobic. Being hydrophobic reduces the adsorption of moisture, which causes degradation over time, and improves compatibility with hydrophobic resins, making it extremely useful when dispersed in hydrophobic resins. Furthermore, the hydrophobic nature of the aerogel is significant from the viewpoint that it can be manufactured without supercritical drying and solvent substitution. Specifically, hydrophobicity of the spherical silica aerogel can be achieved by treating the spherical silica aerogel with a silylation agent, thereby introducing organic silyl groups to its surface. Here, 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 it is hydrophobic, the powder will not disperse in the water, and when left to stand, it will return to a state where it separates into two layers, with water as the lower layer and the powder as the upper layer. Furthermore, hydrophobicity and its degree can also be evaluated using the M value. The M value is the value measured according to the measurement method described in the examples. The M value of the silica aerogel powder, which consists of hydrophobic spherical silica aerogel according to the present invention, is preferably 30 to 60 Vol%, more preferably 35 to 60 Vol%, and particularly preferably 40 to 60 Vol%. A higher M value makes it possible to suppress the adsorption of moisture to the silica aerogel powder and to suppress changes in electrical conductivity due to changes in temperature and humidity, but it is difficult to obtain an M value higher than this range.

[0012] Furthermore, the carbon content can be cited as one indicator of the hydrophobicity of the silica aerogel powder comprising the hydrophobic spherical silica aerogel of the present invention. The carbon content contained in the silica aerogel powder originates from the surface treatment agent and can be measured by quantifying the amount of carbon dioxide generated when the silica aerogel powder is oxidized in air or oxygen at a temperature of about 1000 to 1500°C. The carbon content of the silica aerogel powder comprising the hydrophobic spherical silica aerogel of the present invention is preferably 5 to 12%, more preferably 6 to 11%, and particularly preferably 7 to 10%.

[0013] The spherical silica aerogel of the present invention has a volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by the laser diffraction / scattering method of 200 to 2000 μm. Since it has a D50 value larger than 200 μm, when used as a filler for a heat insulating material, when dispersed in an aqueous system, it is possible to reduce the dispersant, and it is also possible to reduce the binder used for molding. As a result, a composition exhibiting excellent heat insulating performance can be obtained. For those with a particle size larger than 2000 μm, the sedimentation rate of the silica sol becomes too high during production, making it difficult to obtain a spherical gelated body. Therefore, it is difficult to produce a spherical silica aerogel larger than 2000 μm. Generally, as the particle size increases, the particles themselves become more likely to crack. Therefore, the D50 value is preferably 200 to 1000 μm, and more preferably 200 to 800 μm.

[0014] The spherical silica aerogel of the present invention has a specific surface area by the BET method of 400 to 1000 m ２ / g. The larger the specific surface area of the spherical silica aerogel, the smaller the particle size of the primary particles constituting the porous structure (mesh structure) of the independent particles (secondary particles) of the spherical silica aerogel, and having a more complex mesh structure improves the particle strength, which is preferable for preventing pore destruction when added to and dispersed in a base material. On the other hand, if the specific surface area of the spherical silica aerogel becomes too large, the pore volume becomes small and the oil absorption amount becomes small. Therefore, it is preferably 850 m ２ / g or less, and more preferably 700 m ２ / g or less. Usually, it is difficult to obtain an aerogel with a specific surface area larger than 1000 m ２ / g. Conversely, if the specific surface area of the spherical silica aerogel becomes too small, the pore volume becomes small and the oil absorption amount becomes small. Therefore, it is more preferably 450 m ２ / g or more. In the present invention, the specific surface area by the BET method is a value obtained by drying the sample to be measured under a vacuum of 1 kPa or less at a temperature of 150 °C for 2 hours or more, and then obtaining an adsorption isotherm only on the nitrogen adsorption side at the liquid nitrogen temperature and analyzing it by the BET method. The partial pressure (P / P ０The range of ) is 0.1 to 0.25.

[0015] The silica aerogel powder of the present invention preferably has a D10 / D90 of 0.1 to 0.3 or less, and more preferably 0.1 to 0.2 or less. Generally, a larger D10 / D90 value means a sharper particle size distribution, and a smaller D10 / D90 value means a broader particle size distribution. That is, a smaller D10 / D90 value results in better packing performance, but it is difficult to obtain spherical silica aerogel with a D10 / D90 smaller than the above lower limit range. Even if it is obtained, the average roundness of the spherical silica aerogel decreases and does not fall within the range, or crushed silica aerogel is mixed in with the spherical silica aerogel, which usually reduces the yield of spherical silica aerogel.

[0016] The silica aerogel powder of the present invention preferably has peaks of pore volume and pore radius measured by the BJH method of 2 to 8 ml / g and 10 to 50 nm, respectively. The size of the pore volume indicates the porosity of the silica aerogel; therefore, a larger pore volume means that the silica aerogel has excellent heat insulation and oil absorption properties. 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 of the pore radius measured by the BJH method is usually preferably in the range of 10 to 50 nm. When the pore radius peak is within the above range, convective heat transfer of gas can be suppressed, and the heat insulation effect is greatly increased. Furthermore, if the pore radius peak is smaller than the above range, it is difficult to obtain spherical silica aerogel. The BJH pore volume is obtained by acquiring adsorption isotherms in the same manner as in the BET specific surface area measurement and analyzing them using 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 radii of 1 to 100 nm, and the cumulative volume of pores in this range is the pore volume in this invention. The peak of the pore radius is obtained by acquiring adsorption isotherms in the same manner as in the BET specific surface area measurement and analyzing them using the BJH method. It is the pore radius value at which the cumulative pore volume (volume distribution curve) on the logarithm of the pore radius takes its maximum peak value.

[0017] Furthermore, in the powder of the present invention, the thermal conductivity of the hydrophobic silica aerogel at room temperature (23°C) determined by the hot-wire method is preferably 30 mW / m·K or less, and more preferably 27 mW / m·K or less. Thermal conductivity is a physical quantity that represents the ability of a substance to conduct heat, and specifically, it is the value obtained by dividing the amount of heat passing through a unit area per unit time by the temperature gradient (temperature change per unit distance). A smaller value of thermal conductivity means that the amount of heat passing through the sample is low, and that the insulation is high. The hot-wire method is a method of calculating the thermal conductivity of a sample from the relationship between the temperature rise of the heater and time when a linear heater is placed inside the sample and a constant current is passed through it.

[0018] The silica aerogel powder of the present invention preferably has a fracture strength of 0.3 to 3.0 MPa, a compressibility of 10 to 60%, and a recovery rate of 5 to 30% as measured by a microcompression tester. The fracture strength indicates the strength of the silica aerogel and can be measured by performing a compression test on each individual silica aerogel particle. A load is applied to one silica aerogel particle with an indenter, and the strength at which the silica aerogel breaks is defined as the fracture strength. The fracture strength is calculated in accordance with JIS R1639-5. The fracture strength is more preferably 0.4 to 2.0 MPa, and particularly preferably 0.5 to 1.5 MPa. The compressibility indicates how much the silica aerogel could be compressed and can be measured by performing a load-unload test on each individual silica aerogel particle. It is calculated by dividing the displacement from a minimum test force of 0.49 mN to a maximum test force of 9.81 mN by the particle diameter of the measured silica aerogel. The compressibility is more preferably 15 to 60%, and particularly preferably 20 to 60%. The recovery rate can be measured by performing a load-unload test on silica aerogel, where the load is applied to the silica aerogel up to the maximum test force and then unloaded to the minimum test force. It is calculated by subtracting the displacement at the minimum test force from the displacement at the maximum test force and dividing the result by the measured particle size of the silica aerogel. A higher recovery rate indicates that the shape is closer to the shape before the load was applied. A recovery rate of 10-30% is more preferable, and 15-30% is particularly preferable.

[0019] The method for producing the silica aerogel powder of the present invention will be described below. <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 powder consisting of hydrophobic spherical silica aerogel having the properties defined in the present invention as described above.

[0020] According to the inventors' studies, the product can be preferably manufactured by the method described below. The method for producing the hydrophobic spherical silica aerogel powder of the present invention comprises the following four steps in order: (1) a step of mixing an acid and an alkali silicate to obtain a silica sol with a pH of 5 to 8; (2) a step of spraying the silica sol into the gas phase toward the liquid phase to obtain a gelled product; (3) a step of silylation treatment of the gelled product to obtain a silylated product; (4) a step of recovering the silylated product to obtain a powder consisting of hydrophobic spherical silica aerogel.

[0021] These steps will be explained below in order. (1) Step of mixing acid and alkali silicate to obtain silica sol with a pH of 5 to 8. Examples of alkali silicate include alkali metal silicates such as potassium silicate and sodium silicate, and the composition formula is shown in the following formula (2). m(M ２ O)・n(SiO ２ (2) [In formula (2), m and n each represent independently positive integers, and M represents an alkali metal atom.]

[0022] Among the raw materials for preparing silica sol as described above, sodium silicate is particularly preferred because it is readily available. The following explanation will use alkali silicate as a raw material as an example. When alkali silicate is used as a raw material for preparing silica sol according to 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, and the pH after neutralization should be adjusted to 5 to 8. In particular, it is preferable to adjust it to 5.5 to 7.6, and more preferably to 5.5 to 6.5. Within this range, the higher the pH, the faster the gelation rate, making the subsequent step of preparing the gelled product easier. If the pH is lower than 5.0, gelation will be slow, making it difficult to obtain spherical products. Also, if the pH is higher than 8.0, gelation will be fast, causing the nozzle to clog with gel, making it difficult to spray the silica sol. When neutralizing alkali silicate with a mineral acid as described above, it is preferable to mix the mixture in the piping and use it as is in the next step, as the sol gels immediately after mixing. If mixing within the piping is insufficient, localized gel formation may occur, potentially leading to blockage of the piping. Therefore, it is preferable to use an appropriate mixing method. Specifically, when the flow rates for alkali metal silicate and mineral acid are 2 L / min or more, it is preferable to mix using a stationary line mixer. When the flow rates are less than 2 L / min, it is preferable to mix using a Y-shaped pipe with a diameter of approximately 1 to 2 mm. As a stationary line mixer, the OHR mixer (manufactured by OHR Fluid Engineering Research Institute) can be suitably used.

[0023] The silica sol prepared by the above method has a concentration of silica (SiO₂) that allows gelation to be completed in a relatively short time, sufficiently forms a skeletal structure of silica particles to suppress shrinkage during drying, and easily yields a large pore capacity. ２It is preferable to have a density of 20 g / L or more (converted), more preferably 40 g / L or more, and particularly preferable 50 g / L or more. On the other hand, by relatively reducing the density of silica particles to obtain a good pore volume and reducing thermal conductivity (solid conduction) by the silica framework itself, it is preferable to have a density of 160 g / L or less, more preferably 120 g / L or less, and particularly preferable 100 g / L or less, as this makes it easier to obtain good thermal insulation performance.

[0024] (2) Step of spraying the silica sol into the gas phase toward the liquid phase to obtain a gelled product In the manufacturing method of the present invention, the silica sol obtained by the method described above is sprayed into the gas phase. Known methods can be used for spraying, including methods using an atomizer or a spray nozzle. Of these, a spray nozzle can be preferably used, and spray nozzles are generally available in one-fluid and two-fluid types, but a one-fluid spray nozzle can be preferably used to obtain a particle size of 200 to 2000 μm. Generally, the particle size of droplets sprayed from a one-fluid nozzle tends to decrease as the liquid delivery pressure increases, provided the flow rate is constant. Therefore, to obtain a desired particle size, adjustments should be made to the nozzle inner diameter, such as the foreign matter passage diameter, and the liquid delivery pressure. For example, a nozzle with a foreign matter passage diameter of 0.1 to 15 mm (preferably 0.3 mm to 5 mm) can be used. The foreign matter passage diameter refers to the minimum dimension of the fluid flow path inside the nozzle. As such a nozzle, for example, the full cone nozzle "JJXP series" manufactured by Ikeuchi Co., Ltd. can be used. As the nozzle inner diameter, such as the diameter through which foreign matter passes, increases, the liquid delivery pressure decreases under the same flow rate conditions. Therefore, the droplets ejected from the nozzle can be made larger, and the particle size of the silica aerosol can be increased. On the other hand, as the nozzle inner diameter decreases, the liquid delivery pressure increases under the same flow rate conditions. Therefore, the droplets from the nozzle can be made smaller, and the particle size of the silica aerosol can be reduced. It is presumed that some of the sprayed silica sol gels in the gas phase, but most of it gels as it settles in the liquid phase. It is preferable to use a liquid that does not mix with silica sol in the liquid phase, and for example, aliphatic hydrocarbons such as heptane, octane, and decane, or silicone oils such as hexamethyldisiloxane (HMDSO) can be suitably used. Of these, silicone oils with a kinematic viscosity of 30 cSt or less can be suitably used. If the kinematic viscosity of the silicone oil is too high, separation from the gelled body tends to become difficult, and if the kinematic viscosity of the silicone oil is low, the settling speed increases, so it is necessary to increase the height of the liquid phase in order to gel.

[0025] Here, regarding the viscosity of the liquid used in the liquid phase, a higher viscosity results in a slower sedimentation rate and a longer residence time for the silica sol in the liquid phase, which is advantageous for the purpose of gelation. However, if the kinematic viscosity is high, separation of the gelled body and the liquid phase tends to be difficult, so it is preferable to use a viscosity within an appropriate range. For example, if the pH of the silica sol is set in the range of 5 to 8 (particularly 5 to 6.5), the time required for gelation becomes longer, so it is preferable to use a liquid with high kinematic viscosity as the liquid phase. In this case, silicone oil is preferred as the liquid used in the liquid phase. The lower limit of the kinematic viscosity range is preferably 1 cSt or higher, and more preferably 10 cSt or higher, at 25°C. The upper limit is preferably 50 cSt or lower, and more preferably 30 cSt or lower. On the other hand, if the pH of the silica sol is set in the range of 6.5 to 8, the time required for gelation becomes shorter, so it is preferable to use a liquid with low kinematic viscosity as the liquid phase. In this case, the liquid used in the liquid phase is preferably an aliphatic hydrocarbon with a boiling point of 90°C or higher, or hexamethyldisiloxane. The upper limit of its kinematic viscosity is preferably 30 cSt or less, and more preferably 5 cSt or less, at 25°C. The lower limit is preferably 0.1 cSt or more, and more preferably 0.5 cSt or more. The temperature of the liquid phase is preferably heated to speed up the gelation rate, and can be 50 to 100°C, preferably 50 to 80°C. To prevent aggregation of the settled gelled body, it is also preferable to prepare an aqueous phase (W phase) below the oil phase (O phase), such as a silicone oil phase. That is, it is preferable to use a liquid phase with an oil phase on top and an aqueous phase on the bottom. The height of the oil phase is preferably 5 cm or more in order to obtain a spherical gelled body, and although there is no particular upper limit to the height, it can be 30 cm or less for economic reasons. There is no limit to the height of the aqueous phase, but it is preferable to set the amount of aqueous phase to be at least 0.5 times the volume of the resulting gelled product. The upper limit is arbitrary, but from an economic standpoint, it is preferable to set the amount of aqueous phase to be 1 time or less.

[0026] (3) Step of obtaining a silylated product by subjecting the gelled product to silylation treatment. In the method for producing a powder composed of hydrophobic spherical silica aerogel of the present invention, it is necessary to subject the gelled product obtained in the above step to silylation treatment. The spherical silica aerogel obtained by the silylation treatment becomes hydrophobic, and in the subsequent step (4) of recovering the silylated product to obtain a powder composed of hydrophobic spherical silica aerogel, shrinkage is suppressed when the gelled product is dried, making it possible to obtain a powder that retains a porous structure as an aerogel. As a silylating agent that can be used in the present invention, a hydroxy group present on the surface of a metal oxide (here, silica): M-OH (3) [In formula (3), M represents a metal atom. In formula (3), the remaining valence of M is omitted.] reacts with this to form (M-O-) （４－ｎ） SiR ｎ (4) [In formula (4), n is an integer from 1 to 3, R is a hydrocarbon group, and when n is 2 or more, a plurality of Rs may be the same or different from each other.] As an example, a silylating agent capable of converting to can be cited. By performing silylation treatment using such a silylating agent, the hydroxy groups on the surface of the aerogel powder are end-capped and inactivated with hydrophobic silyl groups, so that the dehydration condensation reaction between the surface hydroxy groups can be suppressed. Therefore, even when drying is performed under conditions below the critical point, drying shrinkage can be suppressed, making it possible to obtain a metal oxide powder having a BJH pore volume of 2 mL / g or more.

[0027] As the above silylating agent, compounds represented by the following general formulas (5) to (7) are known. R ｎ SiX （４－ｎ） (5) [In formula (5), n represents an integer from 1 to 3; R represents a hydrophobic group such as a hydrocarbon group; X represents a group (detachable group) that can cleave the bond with the Si atom and detach from the molecule in the reaction with a compound having a hydroxy group. When n is 2 or more, a plurality of Rs may be the same or different. Also, when n is 2 or less, a plurality of Xs may be the same or different.]

[0028]

[0029] [In formula (6), R１ represents an alkylene group; R ２ and R ３ each independently represent a hydrocarbon group; R4 and R5 each independently represent a hydrogen atom or a hydrocarbon group. ]

[0030]

[0031] [In formula (7), R ６ and R ７ each independently represent a hydrocarbon group, and m represents an integer of 3 to 6. A plurality of R ６ may be the same or different. Also, a plurality of R ７ may be the same or different. ]

[0032] In the above formula (5), R is 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 group and ethoxy group; a group represented by -NH-SiR ３ (wherein R has the same meaning as R in formula (6)), etc. Specific examples of the silylating agent represented by the above formula (5) include chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, monomethyltrimethoxysilane, monomethyltriethoxysilane, hexamethyldisilazane, and hexamethyldisiloxane. In terms of good reactivity, chlorotrimethylsilane, dichlorodimethylsilane, trichloromethylsilane, octamethylcyclotetrasiloxane and / or hexamethyldisilazane, hexamethyldisiloxane are particularly preferred. Depending on the number (4 - n) of the leaving group X, the number of bonds to the hydroxy group on the aerogel powder skeleton changes. For example, for example, if n is 2: (M - O - ) ２ SiR ２ (8) such a bond will occur. Also, if n is 3: M - O - SiR ３ (9) such a bond will occur. Thus, by silylating the hydroxy group, the silylation treatment is carried out.

[0033] In formula (6) above, 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 formula (6) above, R2 and R3 are each independently hydrocarbon groups, and preferred groups include those similar to R in formula (5). R4 represents a hydrogen atom or a hydrocarbon group, and if it is a hydrocarbon group, preferred groups include those similar to R in formula (5). When the gelled product is treated with the compound represented by formula (6) (cyclic silazane), the Si-N bond is cleaved by reaction with the hydroxyl group, so (M-O-) is present on the surface of the aerogel powder skeleton in the gelled product. ２ SiR ２ R ３ (10) This results in the formation of a bond. Thus, the hydroxyl group is silylated and a silylation treatment is performed by the cyclic silazanes of formula (6) above.Specific examples of the cyclic silazanes represented by formula (6) above include hexamethylcyclotrisilazane and octamethylcyclotetrasilazane.

[0034] In formula (7) above, R6 and R7 are each independently hydrocarbon groups, and preferred groups include those similar to R in formula (5). m represents an integer from 3 to 6. When a gelled body is treated with the compound represented by formula (7) (cyclic siloxane), the following is formed on the surface of the aerogel powder skeleton in the gelled body: (M-O-) ２ SiR ６ R ７ (11) This results in the formation of a bond. Thus, the hydroxyl group is silylated and a silylation treatment is performed by the cyclic siloxanes of formula (7) above.Specific examples of cyclic siloxanes represented by formula (7) above include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and the like.

[0035] The amount of treatment agent used in the silylation treatment described above depends on the type of treatment agent, but when hexamethyldisiloxane is used as the treatment agent, 10 parts by mass or more per 100 parts by weight of silica is preferable. When the extraction of the gelled product into the O phase, described later, is performed simultaneously with silylation, 1500 to 2000 parts by mass is preferable. Using an amount of treatment agent exceeding 2000 parts by mass will not have any effect and may even worsen the volumetric efficiency.

[0036] The above silylation treatment conditions can be met by adding a silylation agent to the W phase of the aforementioned step and allowing it to react for a certain period of time. For example, if dimethyldichlorosilane is used as the silylation agent and the treatment temperature is 50°C, the treatment can be carried out by holding it for 4 to 12 hours or more. If octamethylcyclotetrasiloxane is used and the treatment temperature is 70°C, the treatment can be carried out by holding it for 6 to 12 hours or more. Furthermore, when using cyclic siloxanes such as octamethylsiloctetrasiloxane as the silylation agent, it is preferable to add hydrochloric acid to adjust the pH of the solution to 0.3 to 1.0 in order to improve the efficiency of the reaction. Furthermore, when using hexamethyldisiloxane as the silylation agent, it is preferable to add hydrochloric acid to adjust the pH of the solution to 0.1 to 1.0 in order to improve the efficiency of the reaction. In addition, setting the treatment temperature to 60°C is preferable because it can suppress gel scaling in the reaction vessel.

[0037] In the silylation treatment step, it is preferable to add a water-soluble organic solvent to increase the solubility of the treatment agent in the W phase and thereby improve the efficiency of the reaction. Examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol. Of these, isopropyl alcohol can be suitably used. It is preferable to add the water-soluble organic solvent so that its concentration in the W phase is about 20 to 80 wt%.

[0038] After the silylation treatment, a hydrophobic organic solvent is added to extract the silylated gel into the O phase, and then the resulting W phase is removed (this step can be omitted if the gel is extracted to the silylation agent during silylation and the solution forms a two-phase state). The selection criteria for the hydrophobic organic solvent used for gel extraction include low surface tension to prevent drying shrinkage during the subsequent drying process. Specifically, hexane, heptane, nonane, decane, dichloromethane, methyl ethyl ketone, toluene, etc. can be used, with hexane, heptane, decane, and toluene being preferred. After the above extraction into the O phase, it is preferable to wash the O phase with an aqueous solution of alcohol to remove acids and salts contained in the gel. This washing operation can be carried out by known methods. To improve washing efficiency, it is preferable to use an aqueous solution of alcohol at a concentration of several tens of wt%. During washing, it is preferable to raise the temperature to a range that does not exceed the boiling point of the hydrophobic organic solvent in order to improve washing efficiency. This can usually be done 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 described later of reducing the water content in the gel to 10% or less by azeotropy. Ethanol, isopropyl alcohol, n-propanol, butyl alcohol, isobutyl alcohol, secondary butyl alcohol, and tertiary butyl alcohol can be used, with ethanol and isopropyl alcohol being preferred.

[0039] It is also possible to remove the water contained in the gelled material in the O phase by azeotropic distillation with alcohol. The water content in the gelled material is positively correlated with the stress generated during drying, and removing it before drying is effective in suppressing drying shrinkage. The above water removal can be achieved by installing condensing equipment such as a condenser and heating the O phase to perform azeotropic distillation. It is preferable to continue the distillation operation until the water content of the gelled material is 10% or less. As a method for measuring the water content in the gelled material, the gelled material contained in the O phase can be filtered off, the gelled material can be mixed with a hydrophilic organic solvent such as isopropyl alcohol or ethanol, and then the solution can be quantified using a Karl Fischer type water meter. 1 g of gelled material and 10 g of ethanol can be added to a 20 mL screw tube, stirred with a magnetic stirrer at 25°C for 30 minutes, and the water content in the gelled material can be calculated from the amount of water contained in the filtrate.

[0040] (4) Steps to recover the gelled product and obtain a powder consisting of hydrophobic spherical silica aerogel By drying the silylated product obtained in step (3) Step to prepare the silylated product, the silica aerogel powder consisting of the hydrophobic spherical silica aerogel of the present invention can be obtained. Filtration may be performed before drying. Drying can be carried out by known methods, but it is preferable to dry under reduced pressure at a temperature above the boiling point of the solvent at that reduced pressure. Also, since applying shear force to the gelled product by stirring or the like during drying may reduce its circularity, it is preferable to use a dryer that does not apply shear force to the gelled product, such as a vibrating dryer. When the silica aerogel powder consisting of the hydrophobic spherical silica aerogel of the present invention is produced by the above method, it exhibits hydrophobicity, but it is also possible to change it to hydrophilicity by thermal decomposition of the hydrophobic groups on the surface. For example, it is possible to thermally decompose the hydrophobic groups on the surface by holding it at a temperature of 400 to 700°C, preferably 500 to 600°C, for about 1 to 8 hours under a non-oxidizing atmosphere (such as a nitrogen atmosphere). The above description of the present invention mainly illustrates silica aerogel powder consisting of hydrophobic spherical silica aerogel and a method for producing silica aerogel powder, but the present invention is not limited to these embodiments.

[0041] <Applications of Silica Aerogel Powder> The silica aerogel powder of the present invention can be used as an insulating material. This will be explained in detail below. (Insulating Material) Because the spherical silica aerogel of the present invention is spherical, it has good packing properties and, due to its low porosity, has very low thermal conductivity, making it suitable for use as an insulating material. When used as an insulating material, forms such as paint or sheets are preferred. When forming a paint, the insulating properties will be impaired if the resin penetrates into the pores of the silica aerogel, so the substrate is preferably an aqueous emulsion resin or aqueous resin. Examples of these substrates include vinyl acetate homopolymer dispersion, vinyl acetate copolymer dispersion, ethylene-vinyl acetate dispersion, styrene-acrylate copolymer dispersion, styrene-butadiene copolymer dispersion, acrylate dispersion, water glass (sodium silicate), and polyvinyl alcohol aqueous solution. 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, degassing may be done under reduced pressure or by centrifugal degassing.

[0042] Furthermore, when formed into a sheet, it can be used by inserting it between the cells of a lithium-ion battery to suppress thermal runaway of the lithium-ion battery. When used for this purpose, it must be non-flammable, and it is preferable to use inorganic fibers as the main fibers. The method for manufacturing the insulating material made of the spherical silica aerogel of the present invention is not limited, and examples include a dry pressing method and a wet molding method. In the dry pressing method described above, the spherical silica aerogel of the present invention and other components such as fibers, binders, and heat shielding agents are mixed using a V-type blender or the like, and the material can be molded by pressing it at a pressure of about 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 described above, a slurry is created by dispersing the spherical silica aerogel of the present invention and sheet components such as fibers and binders, and optionally paper strength agents, flocculants, dispersants, radiation suppressants, etc., in water, and a wet sheet is created by dewatering through a filtration mesh, and a molded sheet can be obtained by heating to remove the moisture.

[0043] 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 fibers, vinylon fibers, polyolefin fibers, polyurethane fibers, aramid fibers, acrylic fibers, polylactic acid fibers, polyvinyl chloride fibers, vinylidene fibers, polyphenylene sulfide fibers, ceramic fibers, alumina fibers, glass fibers, carbon fibers, and rock wool. When heat resistance is required for the sheet, it is preferable to use inorganic fibers such as ceramic fibers, alumina fibers, glass fibers, carbon fibers, and rock wool. The fiber length of the above fibers is not particularly limited, but is preferably about 0.1 to 20 mm. The fiber diameter is also not particularly limited, but is preferably about 1 to 10 μm. The thickness of the sheet of the present invention is not particularly limited, but is preferably 1 to 5 mm.

[0044] The binder used in the sheet of the present invention is not particularly limited, but 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 can be used. The amount of binder added can be about 1 to 20% of the solid content of the sheet, and a preferred range to avoid deteriorating the heat insulation properties is 1 to 10%, and more preferably 1 to 5%.

[0045] The paper 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 copolymer polymers consisting of two or more of the above resins; starch and modified starch; carboxymethylcellulose, guar gum, urea resin, etc. Preferably, polyacrylamide can be used, and more preferably, polyacrylamide containing a large amount of cations can be used. The amount of paper strength agent added is preferably about 0.05 to 2% relative to the solid content of the sheet, and more preferably about 0.1 to 0.5%. If the amount of paper strength agent added is low, the strength of the sheet tends to decrease, and if the amount added is high, the sheet tends to become hard and the heat insulation properties tend to deteriorate.

[0046] The flocculant used in the sheet of the present invention is not particularly limited, but polyethyleneimine, polyalkyleneimine, dicyandiamide polymer, polyamine, polyacrylamide, etc. can be used, and inorganic substances such as aluminum sulfate and polyaluminum chloride can also be used. The amount of flocculant added can be about 10 to 1000 ppm relative to the solid content 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 worsen the yield.

[0047] Examples of radiation suppressants used in the sheet of the present invention include metal particles (aluminum particles, silver particles, gold particles, etc.) and inorganic particles (graphite, carbon black, silicon carbide, titanium dioxide, tin oxide, potassium titanate, etc.). Preferably, titanium dioxide can be used. The amount of radiation suppressant added can be about 1 to 30% of the solid content of the sheet, and preferably about 1 to 10%. When used for heat insulation at high temperatures of several hundred degrees Celsius or higher, it is preferable to increase the amount of radiation suppressant in order to suppress radiative heat transfer.

[0048] The hydrophobic spherical silica aerogel powders produced in Examples 1 and 2 and Comparative Examples 1 to 3 were tested for the following items: (oil absorption, specific surface area, and pore volume) The BET specific surface area and BJH pore volume were measured using a BELSORP-max manufactured by Nippon Bell Co., Ltd., according to the definitions described above. The oil absorption was measured according to JIS K6217-4 "Method for determining oil absorption". (D50, D10 / 90) 0.3 g of silica aerogel powder and 40 mL of ethanol (99.5 Vol%) were added to a 50 mL screw-cap bottle, and the container was placed in an ultrasonic cleaner and dispersed at 90 W for 30 minutes. The resulting dispersion was measured for volume-based particle size distribution using a laser diffraction / scattering particle size distribution analyzer LS 13 320 manufactured by Beckman Coulter, Inc. The volume-based cumulative 50% diameter (D50) was calculated from the particle size distribution curve. D10 / 90 was calculated from the cumulative 10th and 90th percentile diameters based on volume.

[0049] (M-value) Hydrophobic silica aerogel floats in water but completely suspends in methanol. Utilizing this property, the M-value, measured by the following method, was used as an indicator of the hydrophobic treatment by the 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 then added using a burette, dropping until the entire amount of silica aerogel powder was wet and suspended in the solvent in the beaker. During this process, methanol was guided into the solution via a tube to prevent direct contact with the sample. The volume percentage of methanol in the methanol-water mixture at the endpoint was defined as the hydrophobicity (M-value). M-value = Methanol drop volume / (Methanol drop volume + 50 ml)

[0050] (Average Circularity) Silica aerogel powder was observed using a Hitachi High-Technologies SEM (S-5500) with an acceleration voltage of 3.0 kV, secondary electron detection, and a magnification of 1000x. The circularity of the silica aerogel particles was calculated by image analysis of the obtained SEM images using the above formula (1). The average circularity was calculated by averaging the circularity of more than 2000 silica aerogel particles.

[0051] (Carbon content) The carbon content was measured by oxidizing the material at 1150°C while flowing oxygen and helium using an elemental analyzer (vario MICRO cube) manufactured by Elementary Japan Co., Ltd., and quantifying the amount of carbon dioxide generated. The carbon content was calculated as a mass percentage with the total amount of metal oxide powder as the standard (100 mass%). (Thermal conductivity) The thermal conductivity of the powder at room temperature (23°C) was measured using a rapid thermal conductivity meter QTM-500 manufactured by Kyoto Electronics Manufacturing Co., Ltd. A powder case QTM-PA1 filled with 150 mL of silica aerogel powder and a box-type probe PD-11 were used. (Insulation test) An insulating 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 mm) were placed on top of it. The temperature of the underside of the insulating sheet was evaluated 5 minutes after it was placed on the hot plate.

[0052] (Fracture Strength) Compression tests were conducted using a micro-compression testing machine MCT-510 manufactured by Shimadzu Corporation. The strength at which the silica aerogel particles broke was defined as the fracture strength. The loading speed was measured at 0.0446 mN / s. (Compressibility, Recovery Rate) Load-unload tests were conducted using a micro-compression testing machine MCT-510 manufactured by Shimadzu Corporation. The maximum test force was measured at 9.81 mN, the minimum test force at 0.49 mN, and the loading speed at 0.0446 mN / s.

[0053] [Example 1] (Production of silica aerogel powder) Two smooth-flow pumps (Takumina Q-100) were connected in parallel to deliver 9% sulfuric acid and sodium silicate, respectively. 180 mL / min of 9% sulfuric acid and 180 mL / min of sodium silicate were delivered into a Y-shaped tube with an inner diameter of 1 mm. The pH of the silica sol produced by the neutralization of these two liquids was 5.6, and the silica concentration was 9.0 g / L. This was continuously flowed through a full-cone nozzle (Ikeuchi Co., Ltd., 1 / 8 MJJXP005S303, foreign matter passage diameter 0.4 mm), and the silica sol was sprayed for 2 minutes and 40 seconds towards a two-layer liquid of 20 cSt silicone oil (Shin-Etsu Chemical Co., Ltd., KF-96-20cs, kinematic viscosity at 25°C 20 cSt) and water in a 3 L flask (silicone oil: 1398 g, silicone oil layer thickness: 6.5 cm, water: 490 g, liquid temperature: 70°C), thereby obtaining a slurry in which the gelled material was dispersed in the W phase. After removing the silicone oil layer by decantation, 768 g of 55% IPA (Fujifilm Wako Pure Chemical Industries, Ltd., 2-propanol), 341 g of 35% hydrochloric acid, and 1058 g of HMDSO (Shin-Etsu Chemical Co., Ltd., KF-96L-0.65cs) were added to the W phase, and the gelled material was silylated at 60°C for 2 hours. After silylation, the W phase was removed and washed twice with 910 g of 55% isopropanol. After the second wash, the O phase was heated under reflux using the Dean-Stark method to remove water from the gel. The process was terminated when no water was detected in the condensate. After washing, the lower layer was removed, and the obtained silylated gel was filtered off by suction filtration. The gel was dried under vacuum pressure and heated at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. The physical properties of the obtained silica aerogel powder are shown in Table 2.

[0054] (Manufacturing of Insulation Sheet) 4.93 g of the obtained spherical silica aerogel, 0.14 g of dispersant (Meisei Chemical Industry, Meika Surf MK-37), 21.46 g of alumina fiber (Almedio, Alumina Fiber Bulk), 0.87 g of polyester fiber (Kuraray, N721), 1.45 g of sepiolite (Showa KDE, Milcon SP), and 800 g of water were mixed in a juice mixer for 1 minute and 30 seconds. Further, 1300 g of water was added, and while stirring with a three-one motor, 3.63 g of paper strength agent (Seiko PMC, DS4812) and 1.81 g of yield agent (Arakawa Chemical Industry, Polytension 2000) were added to create a slurry. The solid content of the prepared slurry was filtered off using a paper machine to create a wet sheet, which was then dewatered using a press and dried at 150°C for 30 minutes or more to create an insulation sheet. The thickness of the insulation sheet was 1.7 to 1.9 mm. The temperature of the back surface of the insulation sheet is shown in Table 3.

[0055] [Example 2] Silica aerogel powder was produced in the same manner as in Example 1, except that the kinematic viscosity of the silicone oil in the 3L flask was set to 10 cSt (Shin-Etsu Chemical Co., Ltd., KF-96-10cs). The physical properties of the obtained silica aerogel powder are shown in Table 1. In addition, an insulating sheet was produced in the same manner as in Example 1, and the results of its insulating properties test are shown in Table 3. [Example 3] Silica aerogel powder was produced in the same manner as in Example 1, except that the flow rate of the liquid supplied during silica sol production was 160 ml / min of 9% sulfuric acid and 168 ml / min of sodium silicate No. 3, the pH of the silica sol was set to 5.5, and the nozzle used for spraying the silica sol was a full cone nozzle 010 (Ikeuchi Co., Ltd., 1 / 8MJJXP010S303, foreign matter passage diameter 0.8 mm). The physical properties of the obtained silica aerogel powder are shown in Table 2.

[0056] [Example 4] A mono pump (Hyoshin Equipment Co., Ltd., sulfuric acid transfer pump 3NY10 type) was prepared to deliver 9% sulfuric acid, and a mono pump (Hyoshin Equipment Co., Ltd., alkali transfer pump 3NY10 type) was prepared to deliver sodium silicate. 1.9 L / min of 9% sulfuric acid and 1.95 L / min of sodium silicate were delivered to a Y-shaped joint and then mixed with an OHR mixer (OHR Fluid Engineering Laboratory Co., Ltd., MX-F6 type). The pH of the silica sol produced by the neutralization of these two liquids was 6.4, and the silica concentration was 9.0 g / L. This was continuously flowed through a full-cone nozzle 070 (Ikeuchi Co., Ltd., 3 / 8MJJXP070S303, foreign matter passage diameter 1.9 mm), and 45 L of silica sol was sprayed onto a two-layer liquid of hexamethyldisiloxane and water in a 200 L reaction group (hexamethyldisiloxane: 54 kg, thickness of hexamethyldisiloxane layer: 24.9 cm, water: 23 kg, liquid temperature: 70°C) to obtain a slurry in which the gelled material was dispersed. The gelled material was silylated with 55% IPA (Fujifilm Wako Pure Chemical Industries, Ltd., 2-propanol), 36 kg of water, and 20 kg of 35% hydrochloric acid at 60°C for 6 hours. After the silylation treatment, the W phase was removed and washed twice with 13 kg of 55% isopropanol. After the second wash, the O phase was heated under reflux using the Dean-Stark method to remove water from the gelled material. At this point, the operation was terminated when no more water was detected in the condensate. After washing, the lower layer was removed, and the resulting gel was heated in a dryer under vacuum pressure at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. The physical properties of the obtained silica aerogel powder are shown in Table 2. [Example 5] Silica aerogel powder was produced in the same manner as in Example 4, except that the flow rate of the liquid supplied during silica sol production was 2.8 L / min of 9% sulfuric acid and 2.85 L / min of sodium silicate No. 3, the pH of the silica sol was 5.8, and the nozzle used for spraying the silica sol was a full cone nozzle 14 (Ikeuchi Co., Ltd., 1 / 2 MJJXP14S303, foreign matter passage diameter 3.5 mm). The physical properties of the obtained silica aerogel powder are shown in Table 2.

[0057] [Comparative Example 1] To deliver 9% sulfuric acid and sodium silicate, two smooth-flow pumps (Takumina Q-100) were connected in parallel to each other, and 180 mL / min of 9% sulfuric acid and 165 mL / min of sodium silicate were delivered into a Y-shaped tube with an inner diameter of 1 mm. The pH of the silica sol produced by the neutralization of these two liquids was 1.2. This was continuously flowed through a full-cone nozzle (Ikeuchi, 1 / 8MJJXP005S303) and sprayed for 2 minutes and 51 seconds towards a two-layer liquid of 20 cSt of silicone oil and water in a 3 L flask (silicone oil: 1398 g, thickness of silicone oil layer: 6.5 cm, water: 490 g, liquid temperature: 70°C). However, the pH of the silica sol was low, and no gel was obtained.

[0058] [Comparative Example 2] To deliver 9% sulfuric acid and sodium silicate, two smooth-flow pumps (Takumina Q-100) were connected in parallel to each other, and 180 mL / min of 9% sulfuric acid and 175 mL / min of sodium silicate were delivered into a Y-shaped tube with an inner diameter of 1 mm. The pH of the silica sol produced by the neutralization of these two liquids was 3.0. This was continuously flowed into a full-cone nozzle (Ikeuchi 1 / 8MJJXP005S303), and the silica sol was sprayed for 2 minutes and 46 seconds towards a two-layer liquid of 20 cSt of silicone oil and water in a 3 L flask (silicone oil: 1398 g, thickness of silicone oil layer: 6.5 cm, water: 490 g, liquid temperature: 70°C), thereby obtaining a slurry with a dispersed gel in the W phase. After removing the silicone oil layer by decantation, 768 g of 55% IPA water, 341 g of 35% hydrochloric acid, and 1058 g of HMDSO were added to the W phase, and the gelled body was silylated at 60°C for 2 hours. After the silylation treatment, the W phase was removed and washed twice with 910 g of 55% isopropanol. After the second wash, the O phase was heated under reflux using the Dean-Stark method to remove water from the gelled body. The procedure was terminated when no water was detected in the condensate. After the silylation treatment, the lower layer was removed, and the obtained silylated gelled body was filtered off by suction filtration. The gelled body was dried under vacuum pressure and heated at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. The physical properties of the obtained silica aerogel powder are shown in Table 2. Furthermore, an insulating sheet was manufactured in the same manner as in Example 1, except that the dispersant was 0.29 g, and the results of its insulating properties test are shown in Table 3.

[0059] [Comparative Example 3] An aqueous silica sol was prepared by gradually adding 100 g of sodium silicate to 100 g of sulfuric acid while stirring with a stirring blade. At this time, the pH was 3.0. 139 g of the prepared aqueous silica sol was taken and added to 129 g of heptane in which 1.5 g of sorbitan monooleate was dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. While stirring the obtained emulsion with a stirring blade, 71 g of isopropyl alcohol gelled at 70°C for 1 hour and 58 g of ion-exchanged water were added, and the O phase and W phase were separated while stirring with a stirring blade. The W phase was recovered by removing the O phase by decantation. Subsequently, 9.63 g of 0.5 mol / L sodium hydroxide aqueous solution was added. At this time, the pH of the W phase was 7.8. The gelled material was matured at 70°C for 20 minutes. 48.3 g of 35% hydrochloric acid and 3.6 g of hexamethyldisiloxane were added to the obtained W phase, and the mixture was held in a 60°C water bath for 2 hours while stirring to perform silylation. After silylation, 48.3 g of 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade to perform neutralization. Subsequently, 90 g of heptane was added to extract the gelled material, and after removing the W phase, 71 g of isopropyl alcohol and 58 g of deionized water were added, and the mixture was washed twice. After the second wash, the obtained gelled material was filtered using a suction filter. The gelled material was dried by heating 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 physical properties of the obtained silica aerogel powder are shown in Table 2. In addition, an insulating sheet was manufactured in the same manner as in Comparative Example 2, and the results of its insulating properties test are shown in Table 3.

[0060] [Example 6] Silica aerogel powder was produced in the same manner as in Example 1, except that the flow rate of the liquid supplied during silica sol production was 170 ml / min of 9% sulfuric acid and 175 ml / min of sodium silicate No. 3, the pH of the silica sol was 6.5, and the nozzle used for spraying the silica sol was a full cone nozzle 010 (Ikeuchi Co., Ltd., 1 / 8MJJXP010S303). The physical properties of the obtained silica aerogel powder are shown in Table 2. [Example 7] Silica aerogel powder was produced in the same manner as in Example 1, except that the flow rate of the liquid supplied during silica sol production was 160 ml / min of 9% sulfuric acid and 168 ml / min of sodium silicate No. 3, the pH of the silica sol was 6.3, and the nozzle used for spraying the silica sol was a full cone nozzle 010 (Ikeuchi Co., Ltd., 1 / 8MJJXP010S303). The physical properties of the obtained silica aerogel powder are shown in Table 2. [Example 8] Silica aerogel powder was produced in the same manner as in Example 4, except that the flow rate of the liquid supplied during silica sol production was 2.0 L / min of 9% sulfuric acid and 2.1 L / min of sodium silicate No. 3, the pH of the silica sol was 6.5, the nozzle used for spraying the silica sol was a full cone nozzle 070 (Ikeuchi Co., Ltd., 3 / 8MJJXP070S303), and the kinematic viscosity of the silicone oil was 10 cSt (Shin-Etsu Chemical Co., Ltd., KF-96-10cs). The physical properties of the obtained silica aerogel powder are shown in Table 2.

[0061] [Example 9] Silica aerogel powder was produced in the same manner as in Example 4, except that the flow rate of the liquid supplied during silica sol production was 1.9 L / min of 9% sulfuric acid and 1.95 L / min of sodium silicate No. 3, the pH of the silica sol was 6.3, the nozzle used for spraying the silica sol was a full cone nozzle 070 (Ikeuchi Co., Ltd., 3 / 8MJJXP070S303), and the kinematic viscosity of the silicone oil was 10 cSt (Shin-Etsu Chemical Co., Ltd., KF-96-10cs). The physical properties of the obtained silica aerogel powder are shown in Table 2. [Example 10] Silica aerogel powder was produced in the same manner as in Example 4, except that the flow rate of the liquid supplied during silica sol production was 1.8 L / min of 9% sulfuric acid and 1.83 L / min of sodium silicate No. 3, the pH of the silica sol was 5.9, the nozzle used for spraying the silica sol was a full cone nozzle 070 (Ikeuchi Co., Ltd., 3 / 8MJJXP070S303), and the kinematic viscosity of the silicone oil was 10 cSt (Shin-Etsu Chemical Co., Ltd., KF-96-10cs). The physical properties of the obtained silica aerogel powder are shown in Table 2. [Example 11] Silica aerogel powder was produced in the same manner as in Example 4, except that the flow rate of the liquids supplied during silica sol production was 2.8 L / min of 9% sulfuric acid and 2.85 L / min of sodium silicate No. 3, the pH of the silica sol was 6.2, the nozzle used for spraying the silica sol was a full cone nozzle 14 (Ikeuchi Co., Ltd., 1 / 2 MJJXP14S303), and the kinematic viscosity of the silicone oil was 10 cSt (Shin-Etsu Chemical Co., Ltd., KF-96-10cs). The physical properties of the obtained silica aerogel powder are shown in Table 2.

[0062]

[0063] As shown in Table 1, spherical silica aerogels with high average circularity were obtained in Examples 1 and 2. On the other hand, in Comparative Example 1, the pH of the prepared aqueous silica sol was low at 1.2, and gelation did not proceed. In Comparative Example 2, the pH of the sprayed silica sol was 3, which is in the range of slow gelation rate. Therefore, it is thought that gelation occurred in the aqueous phase with sol diffusion rather than in the oil phase, resulting in an aerogel with low circularity and abnormally high oil absorption. In Comparative Example 3, gelation of the silica sol was performed in the W phase, which is a droplet in a W / O emulsion, and the particle size became very small, about 10 μm. In Examples 3 to 5, a silicone oil with a kinematic viscosity of 20 cSt was used in the oil phase to spray the silica sol, and spherical silica aerogels with high average circularity were obtained. By adjusting the flow rate of the pump when delivering sulfuric acid and sodium silicate, and by using different nozzles, spherical silica aerogels with the desired particle size were obtained. In Examples 6 to 11, a silicone oil with a kinematic viscosity of 10 cSt was used as the oil phase for spraying the silica sol, resulting in spherical silica aerogels with a high average circularity. Here too, by adjusting the flow rate of the pump when delivering sulfuric acid and sodium silicate, and by using different nozzles, spherical silica aerogels with the desired particle size were obtained.

[0064]

[0065]

[0066] As shown in Table 3, the thermal insulation sheets using the spherical silica aerogel obtained in Examples 1 and 2 showed excellent thermal insulation properties. This is thought to be because the wide particle size distribution and high packing density allowed for a reduction in the amount of dispersant used to make the silica aerogel compatible with water. On the other hand, the thermal insulation sheet using the silica aerogel in Comparative Example 2 showed reduced thermal insulation properties. This is presumed to be because, although the particle size distribution was wide, the shape was non-spherical, resulting in a low packing density. Furthermore, the thermal insulation sheet with added spherical silica aerogel in Comparative Example 3 also showed reduced thermal insulation properties. This is thought to be because the particle size was less than 200 μm, resulting in a low packing density.

[0067] [Example 12] (Production of silica aerogel powder) Two smooth-flow pumps (Takumina Q-100) were connected in parallel to deliver 9% sulfuric acid and sodium silicate. 180 mL / min of 9% sulfuric acid and 187 mL / min of sodium silicate No. 3 (silica concentration 14.6%, sodium oxide concentration 4.8%) were delivered into a Y-shaped tube with an inner diameter of 1 mm. The pH of the silica sol produced by the neutralization of these two liquids was 6.6, and the silica concentration was 9.0 g / L. This was continuously flowed into a full cone nozzle 010 (Ikeuchi Co., Ltd., 1 / 8MJJXP010S303), and 980 ml of silica sol was sprayed onto a two-layer liquid in a 5 L flask containing hexamethyldisiloxane (kinematic viscosity at 25°C: 0.65 cSt) (Shin-Etsu Chemical Co., Ltd., KF-96L-0.65cs) and water (hexamethyldisiloxane: 2246 g, thickness of hexamethyldisiloxane layer: 13.1 cm, water: 490 g, liquid temperature: 70°C), thereby obtaining a slurry in which the gelled material was dispersed as the W phase. After removing the hexamethyldisiloxane layer by decantation, 768 g of 55% IPA (manufactured by Fujifilm Wako Pure Chemical Industries, 2-propanol), 341 g of 35% hydrochloric acid, and 1058 g of hexamethyldisiloxane were added to the W phase, and the gelled body was silylated at 60°C for 2 hours. After the silylation treatment, the W phase was removed and washed twice with 910 g of 55% IPA. After the second wash, the O phase was heated under reflux using the Dean-Stark method to remove water from the gelled body. The procedure was terminated when no water was detected in the condensate. After washing, the lower layer was removed, and the obtained silylated gelled body was filtered off by suction filtration. The gelled body was dried under vacuum pressure and heated at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. Table 4 shows the flow rates of sulfuric acid and sodium silicate, the pH of the silica sol, and the properties of the oil phase, while Table 5 shows the physical properties of the obtained silica aerogel powder.

[0068] (Manufacturing of Insulation Sheets) Insulation sheets were prepared using the same method as in Example 1. The results of the insulation performance test of the obtained insulation sheets are shown in Table 6.

[0069] [Example 13] Silica aerogel powder was produced in the same manner as in Example 12, except that the flow rate of 9% sulfuric acid (170 ml / min) and sodium silicate (179 ml / min) during silica sol production was set to 7.1. The physical properties of the obtained silica aerogel powder are shown in Table 5. Furthermore, an insulating sheet was prepared using the same method as in Example 12, and the results of the insulating properties test are shown in Table 6. [Example 14] Silica aerogel powder was produced in the same manner as in Example 12, except that the flow rate of 9% sulfuric acid (160 ml / min) and sodium silicate (170 ml / min) during silica sol production was set to 7.4. The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 15] Silica aerogel powder was produced in the same manner as in Example 12, except that the flow rate of the liquid supplied during silica sol production was 150 ml / min of 9% sulfuric acid and 158 ml / min of sodium silicate No. 3, and the pH of the silica sol was 7.2. The physical properties of the obtained silica aerogel powder are shown in Table 5.

[0070] [Comparative Example 4] Silica aerogel powder was produced in the same manner as in Example 12, except that the flow rates of 9% sulfuric acid (180 ml / min) and sodium silicate (No. 3) (177 ml / min) were used during silica sol production, and the pH of the silica sol was set to 4.8. The physical properties of the obtained silica aerogel powder are shown in Table 4. Due to insufficient gelation, many fragments were obtained, resulting in a low average circularity. Furthermore, when attempting to produce an insulating sheet in the same manner as in Example 12, it was difficult to disperse the silica aerogel powder in the slurry. Therefore, the amount of dispersant added was increased from 0.14 g to 0.29 g to create the slurry, and an insulating sheet was produced by papermaking. The results of the insulating properties test of the prepared insulating sheet are shown in Table 6. [Comparative Example 5] Except for setting the flow rate of 9% sulfuric acid to be 180 ml / min and sodium silicate No. 3 to be 197 ml / min during silica sol production, and setting the pH of the silica sol to 8.5, the procedure was the same as in Example 12, and an attempt was made to continuously flow the silica sol into a full cone nozzle (Ikeuchi 1 / 8 MJJXP010S303). However, the silica sol immediately gelled, and the nozzle became clogged, so silica aerogel powder could not be obtained.

[0071] [Example 16] A mono pump (Hyoshin Equipment Co., Ltd., sulfuric acid transfer pump 3NY10 type) was prepared to deliver 9% sulfuric acid, and a mono pump (Hyoshin Equipment Co., Ltd., alkali transfer pump 3NY10 type) was prepared to deliver sodium silicate. 2.0 L / min of 9% sulfuric acid and 2.2 L / min of sodium silicate were delivered to a Y-shaped joint and then mixed with an OHR mixer (OHR Fluid Engineering Laboratory Co., Ltd., MX-F6 type). The pH of the silica sol produced by the neutralization of these two liquids was 7.2, and the silica concentration was 9.0 g / L. This was continuously flowed through a full-cone nozzle 070 (Ikeuchi, 3 / 8MJJXP070S303), and 45 L of silica sol was sprayed onto a two-layer liquid of hexamethyldisiloxane and water (hexamethyldisiloxane: 54 kg, thickness of hexamethyldisiloxane layer: 24.9 cm, water: 23 kg, liquid temperature: 70°C) in a 200 L reaction group, thereby obtaining a slurry in which the gelled material was dispersed as phase W. After removing the silicone oil layer by decantation, the gelled material was silylated with 55% IPA (Fujifilm Wako Pure Chemical Industries, 2-propanol), 36 kg of water, and 20 kg of 35% hydrochloric acid at 60°C for 6 hours. After the silylation treatment, phase W was removed and washed twice with 13 kg of 55% isopropanol. After the second wash, phase O was heated under reflux using the Dean-Stark method to remove water from the gelled material. At this point, the operation was terminated when no more water was detected in the condensate. After washing, the lower layer was removed, and the resulting gel was heated in a dryer under vacuum pressure at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 17] Silica aerogel powder was produced in the same manner as in Example 16, except that the flow rate of liquid supplied during silica sol production was 1.8 L / min of 9% sulfuric acid and 1.9 L / min of sodium silicate No. 3, and the pH of the silica sol was 7.0. The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 18] Silica aerogel powder was produced in the same manner as in Example 16, except that the flow rate of the liquid supplied during silica sol production was 2.8 L / min of 9% sulfuric acid and 2.9 L / min of sodium silicate No. 3, the pH of the silica sol was 6.7, and the nozzle used for spraying the silica sol was a full cone nozzle 14 (Ikeuchi Co., Ltd., 1 / 2 MJJXP14S303).The physical properties of the obtained silica aerogel powder are shown in Table 5.

[0072] [Example 19] Silica aerogel powder was produced in the same manner as in Example 12, except that decane (decane: 1465 g, layer thickness: 13.1 cm, kinematic viscosity at 25°C: 1.2 cSt) was used as the oil phase during silica sol spraying instead of hexamethyldisiloxane, the pH of the silica sol was set to 7.3, the flow rate of 9% sulfuric acid (180 ml / min) and sodium silicate (190 ml / min) during silica sol production was set to 9% sulfuric acid (180 ml / min) and sodium silicate (190 ml / min), and the nozzle used for spraying the silica sol was a full cone nozzle 010 (Ikeuchi Co., Ltd., 1 / 8 MJJXP010S303). The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 20] Silica aerogel powder was produced in the same manner as in Example 19, except that the flow rate of 9% sulfuric acid (170 ml / min) and sodium silicate (176 ml / min) during silica sol production was set to 9% sulfuric acid (170 ml / min) and sodium silicate (176 ml / min), and the pH of the silica sol was set to 6.7. Table 5 shows the physical properties of the obtained silica aerogel powder. [Example 21] Silica aerogel powder was produced in the same manner as in Example 19, except that the flow rate of 9% sulfuric acid (160 ml / min) and sodium silicate (No. 3) (166 ml / min) during silica sol production was set to 6.6. The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 22] Silica aerogel powder was produced in the same manner as in Example 19, except that the flow rate of 9% sulfuric acid (150 ml / min) and sodium silicate (No. 3) (158 ml / min) during silica sol production was set to 7.1. The physical properties of the obtained silica aerogel powder are shown in Table 5.

[0073] [Example 23] A mono pump (Hyoshin Equipment Co., Ltd., sulfuric acid transfer pump 3NY10 type) was prepared to transfer 9% sulfuric acid, and a mono pump (Hyoshin Equipment Co., Ltd., alkali transfer pump 3NY10 type) was prepared to transfer sodium silicate. 1.8 L / min of 9% sulfuric acid and 1.9 L / min of sodium silicate No. 3 were transferred to a Y-shaped joint and then mixed with an OHR mixer (OHR Fluid Engineering Laboratory Co., Ltd., MX-F6 type). The pH of the silica sol produced by the neutralization of these two liquids was 7.2, and the silica concentration was 9.0 g / L. This was continuously flowed through a full-cone nozzle 070 (Ikeuchi, 3 / 8MJJXP070S303), and 45 L of silica sol was sprayed onto a two-layer liquid of decane and water in a 200 L reaction group (decane: 29 kg, decane layer thickness: 13.1 cm, water: 23 kg, liquid temperature: 70°C), thereby obtaining a slurry in which the gelled material was dispersed as phase W. After removing the decane layer by decantation, the W phase was subjected to a silylation treatment of the gelled material with 54 kg of hexamethyldisiloxane, 55% IPA (Fujifilm Wako Pure Chemical Industries, 2-propanol), 36 kg of water, and 20 kg of 35% hydrochloric acid at 60°C for 6 hours. After the silylation treatment, the W phase was removed and washed twice with 13 kg of 55% IPA. After the second wash, the O phase was heated under reflux using the Dean-Stark method to remove water from the gelled material. At this point, the operation was terminated when no more water was detected in the condensate. After washing, the lower layer was removed, and the resulting gel was heated in a dryer under vacuum pressure at 150°C for 16 hours or more to obtain a powder consisting of the hydrophobic silica aerogel of the present invention. The physical properties of the obtained silica aerogel powder are shown in Table 5. [Example 24] Silica aerogel powder was produced in the same manner as in Example 23, except that the flow rate of liquid supplied during silica sol production was 2.8 L / min of 9% sulfuric acid and 2.9 L / min of sodium silicate No. 3, the pH of the silica sol was 7.6, and the nozzle used for spraying the silica sol was a full cone nozzle 14 (Ikeuchi Co., Ltd., 1 / 2 MJJXP14S303). The physical properties of the obtained silica aerogel powder are shown in Table 5.

[0074] [Comparative Example 6] An aqueous silica sol was prepared by gradually adding 100 g of sodium silicate to 100 g of sulfuric acid while stirring with a stirring blade. At this time, the pH was 3.0. 139 g of the prepared aqueous silica sol was taken and added to 129 g of heptane in which 1.5 g of sorbitan monooleate was dissolved. This solution was stirred for 2.5 minutes at 4600 rpm using a homogenizer (IKA, T25BS1) to form a W / O emulsion. While stirring the obtained emulsion with a stirring blade, 71 g of isopropyl alcohol gelled at 70°C for 1 hour and 58 g of ion-exchanged water were added, and the O phase and W phase were separated while stirring with a stirring blade. The W phase was recovered by removing the O phase by decantation. Subsequently, 9.63 g of 0.5 mol / L sodium hydroxide aqueous solution was added. At this time, the pH of the W phase was 7.8. The gelled material was matured at 70°C for 20 minutes. 48.3 g of 35% hydrochloric acid and 3.6 g of hexamethyldisiloxane were added to the obtained W phase, and the mixture was held in a 60°C water bath for 2 hours while stirring to perform silylation. After silylation, 48.3 g of 24% sodium hydroxide aqueous solution was added while stirring with a stirring blade to perform neutralization. Subsequently, 90 g of heptane was added to extract the gelled material, and after removing the W phase, 71 g of isopropyl alcohol and 58 g of deionized water were added, and the mixture was washed twice. After the second wash, the obtained gelled material was filtered using a suction filter. The gelled material was dried by heating under vacuum pressure at 150°C for more than 16 hours to obtain a powder consisting of hydrophobic spherical silica aerogel. The physical properties of the obtained silica aerogel powder are shown in Table 5. Furthermore, when attempting to manufacture an insulating sheet in the same manner as in Example 12, it was difficult to disperse the silica aerogel powder in the slurry. Therefore, the amount of dispersant added was increased from 0.14 g to 0.29 g to create the slurry, and the insulating sheet was manufactured by papermaking. The results of the insulating performance test of the manufactured insulating sheet are shown in Table 6.

[0075]

[0076]

[0077]

[0078] As shown in Tables 4 and 5, in Examples 12 to 18, spherical silica aerogels with high average circularity were obtained by using hexamethyldisiloxane in the oil phase for spraying the silica sol. By adjusting the flow rate of the pump when delivering sulfuric acid and sodium silicate, and by using different nozzles, spherical silica aerogels with the desired particle size were obtained. On the other hand, in Comparative Example 4, when the pH of the silica sol was set to 4.8, gelation was insufficient, resulting in a large amount of fragmented material and a low average circularity. In Comparative Example 5, when the pH of the silica sol was set to 8.5, the silica sol gelled immediately, clogging the nozzle, and it was not possible to obtain silica aerogel powder. In Examples 19 to 24, spherical silica aerogels with high average circularity were obtained by using decane in the oil phase for spraying the silica sol. Here too, by adjusting the flow rate of the pump when delivering sulfuric acid and sodium silicate, and by using different nozzles, spherical silica aerogels with the desired particle size were obtained.

[0079] As shown in Table 6, the thermal insulation sheets using spherical silica aerogel obtained in Examples 12 and 13 showed excellent thermal insulation properties. This is thought to be because the large particle size and spherical shape allowed for a reduction in the amount of dispersant used to make the silica aerogel compatible with water. On the other hand, in Comparative Example 4, the non-spherical shape of the aerogel particles resulted in poor packing efficiency and required a large amount of dispersant, resulting in poor thermal insulation performance. In the thermal insulation sheet using silica aerogel in Comparative Example 6, although the aerogel particles were spherical, the particle size was too small, which is thought to have necessitated a large amount of dispersant.

Claims

1. Consists of hydrophobic spherical silica aerogel with an average circularity of 0.7 or higher, a) having a volume-based cumulative 50% diameter (D50) value in the particle size distribution measured by laser diffraction / scattering method of 200 to 2000 μm, and b) having a specific surface area of ​​400 to 1000 m² as measured by the BET method. ２ A silica aerogel powder characterized by having a weight of / g.

2. c) The silica aerogel powder according to claim 1, wherein D10 / D90 is 0.1 to 0.

3.

3. d) The silica aerogel powder according to claim 1, wherein the peaks of pore volume and pore radius obtained by the BJH method are 2 to 8 ml / g and 10 to 50 nm, respectively.

4. e) The silica aerogel powder according to claim 1, wherein the fracture strength measured by a microcompression tester is 0.3 to 3.0 MPa, the compressibility is 10 to 60%, and the recovery rate is 5 to 30%.

5. A method for producing silica aerogel powder, comprising the steps of: (1) mixing an acid and an alkali silicate to obtain a silica sol with a pH of 5 to 8; (2) spraying the silica sol into the gas phase toward the liquid phase to obtain a gelled body; (3) silylation treatment of the gelled body to obtain a silylated body; and (4) recovering the silylated body to obtain a powder consisting of hydrophobic spherical silica aerogel, in the order described above.

6. The manufacturing method according to claim 5, characterized in that the liquid phase in step (2) contains a silicone oil having a kinematic viscosity of 1 cSt or more.

7. A filler for thermal insulation made of silica aerogel powder as described in claim 1.

8. A thermal insulation material characterized by containing the silica aerogel powder described in claim 1.

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