JP7701028B2 - Aerogel Powder Composition - Google Patents

Description

The present invention relates to an aerogel powder composition containing an aerogel powder that has excellent flexibility and resistance to breakage against compressive force.

A dried gel having siloxane bonds, called aerogel, has been known for some time. Specifically, a sol is formed by hydrolyzing a monomer solution of a silane compound (solvent: water and/or organic solvent), and the sol is crosslinked to form a gel (condensation compound). The gel is then dried to obtain an aerogel (dried gel) having numerous pores (Patent Document 1).

This aerogel has excellent thermal insulation, optical properties, and electrical properties, and its use in various fields is being considered. Among them, aerogel powder is aerogel molded into a powder form, and due to its form, it is expected that its fields of use will expand (Patent Documents 2 and 3).

Patent No. 5250900 International Patent Publication No. 2014/024413 JP 2018-145331 A

However, aerogel powder is very brittle, and when it is processed into a form suitable for use, for example when packed at a high filling rate or when added to paint and mixed, it breaks down into smaller particles than the original powder particle size, posing the issue of not being able to achieve the level of breakage resistance (properties that make it difficult to break) that was initially expected.

Furthermore, in the case of surface-treated aerogel powder, there was also the issue that the untreated areas would be exposed when the powder was crushed into small pieces, thereby compromising the effectiveness of the surface treatment.
It is speculated that these issues are due to the aerogel powder not having sufficient flexibility, particularly its pliability (the ability to be elastic and bend easily against compressive forces).

The object of the present invention is to provide an aerogel powder composition containing an aerogel powder that is excellent in flexibility and resistance to breakage against compressive force.

The object of the present invention has been achieved by:

1. An aerogel powder composition containing at least an aerogel powder, the aerogel powder being made of an aerogel which is a hydrolysis condensation product of a silane compound, the silane compound being a tetrafunctional silane compound, a trifunctional silane compound and a bifunctional silane compound, the mass percentages of which are Qx, Tx and Dx, respectively, and 0≦Qx≦70, 30≦Tx≦100 and 0≦Dx<30 (where Qx+Tx+Dx=100), and the aerogel powder has a destruction rate of 10% or less as determined by the following formula (1):
Destruction rate (%) = (destruction amount (g) / mass (g) of aerogel powder before destruction) × 100 (1)
The term "destruction amount" used herein means the total mass (g) of the destroyed aerogel powder that has been adjusted to a particle size in the range of 250 μm to 1000 μm using a sieve, compressed in a universal testing machine under conditions of a compression cross-sectional area of 1.34 cm ² , a maximum load of 500 N, and a compression stress of 371.2 ^N /m 2 , and then passed through a sieve with a mesh size of 250 μm.
2. The aerogel powder composition according to 1 above, wherein the aerogel powder has a deformation rate determined by the following formula (2) of 15% or more.
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)
Here, the "deformation change amount" means the change in the filling height (mm) when the aerogel powder is filled to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 and compressed with a piston at 10 N, and the filling height of the aerogel before deformation is 16 mm.
3. The aerogel powder composition according to 1 above, wherein the silane compound satisfies 0<Qx≦50, 40≦Tx<100, and 0≦Dx<30 (where Qx+Tx+Dx=100), and the aerogel powder has a destruction rate of 6% or less.
4. The aerogel powder composition according to 3 above, wherein the aerogel powder has a deformation rate of 20% or more as determined by the following formula (2):
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)
Here, the "deformation change amount" means the change in the filling height (mm) when the aerogel powder is filled to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 and compressed with a piston at 10 N, and the filling height of the aerogel before deformation is 16 mm.
5. The aerogel powder composition according to any one of 1 to 4 above, wherein the aerogel powder is made of an aerogel dried by an atmospheric pressure drying method.
6. The aerogel powder composition according to any one of 1 to 5 above, wherein the aerogel powder composition is a mixture of the aerogel powder and other powder or granular material.
7. The aerogel powder composition according to any one of 1 to 5 above, wherein the aerogel powder composition is an aerogel powder dispersion in which the aerogel powder is dispersed as a dispersoid in a liquid dispersion medium.

The present invention provides an aerogel powder composition and aerogel powder thereof that are excellent in flexibility and resistance to breakage when subjected to compression force.

It is a triangular diagram showing the appropriate range (region I) and the preferred range (region II) of Qx, Tx, and Dx, which are the mass percentages of each of the tetrafunctional silane compound, trifunctional silane compound, and bifunctional silane compound, which are silane compounds used to form the aerogel powder contained in the aerogel composition of the present invention. FIG. 1 is a schematic diagram of a universal testing machine (compression testing machine) used to evaluate the fracture rate and deformation rate of aerogel powder.

Hereinafter, an embodiment of the present invention will be described.
(1) Aerogel Powder Composition (1-1) Aerogel The aerogel powder composition of the present invention is an aerogel powder composition containing at least an aerogel powder, the aerogel powder being composed of an aerogel which is a hydrolysis condensation product of a silane compound, the silane compound being such that, when the mass percentages of a tetrafunctional silane compound, a trifunctional silane compound and a bifunctional silane compound are Qx, Tx and Dx, respectively, 0≦Qx≦70, 30≦Tx≦100 and 0≦Dx<30 (where Qx+Tx+Dx=100), and the aerogel powder is an aerogel powder composition having a destruction rate of 10% or less as defined by the following formula (1):
Destruction rate (%) = (destruction amount (g) / mass (g) of aerogel powder before destruction) × 100 (1)

The term "destruction amount" used herein means the total mass (g) of the destroyed aerogel powder that has been adjusted to a particle size in the range of 250 μm to 1000 μm using a sieve, compressed in a universal testing machine under conditions of a compression cross-sectional area of 1.34 cm ² , a maximum load of 500 N, and a compression stress of 371.2 ^N /m 2 , and then passed through a sieve with a mesh size of 250 μm.

The aerogel powder composition of the present invention that satisfies the above-mentioned requirements can increase the deformation rate of the aerogel powder contained therein, as determined by the following formula (2), and can make the deformation rate, for example, 15% or more.
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)
Here, the "deformation change amount" means the change in the filling height (mm) when the aerogel powder is filled to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 and compressed with a piston at 10 N, and the filling height of the aerogel before deformation is 16 mm.

By setting the composition of the silane compound to be hydrolyzed and condensed within the range of 0≦Qx≦70, 30≦Tx≦100, 0≦Dx<30, and setting the breakage rate to 10% or less, it is possible to obtain an aerogel powder that is both flexible and break-resistant.

The amount of deformation of the aerogel depends on the aerogel skeleton, and is therefore related to the ratio of Qx, Tx, and Dx, which determine the structure of the aerogel skeleton. As Qx increases, the aerogel loses flexibility and becomes less likely to deform. For this reason, when Qx exceeds 70%, the aerogel that constitutes the aerogel powder contained in the aerogel composition of the present invention loses its suppleness (flexibility), and the amount of deformation becomes smaller.

On the other hand, increasing the Dx content of the formulation increases flexibility and makes the material easier to deform, but if Dx is 30% or more, manufacturing problems arise, such as the material becoming difficult to gel.

In addition, the aerogel powder composition of a preferred embodiment of the present invention is an aerogel powder composition containing at least aerogel powder, the aerogel powder being made of aerogel which is a hydrolysis condensation product of a silane compound, the silane compound being a tetrafunctional silane compound, a trifunctional silane compound and a bifunctional silane compound in mass percentages of 0<Qx≦50, 40≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100), and the aerogel powder preferably has a breaking rate of 6% or less. By adopting this configuration, the aerogel powder has a breaking rate of 6% or less, which further improves the resistance to breaking, and the deformation rate is, for example, 20% or more, which further improves the flexibility.

Furthermore, in the aerogel powder composition of a preferred embodiment of the present invention, the silane compound is a tetrafunctional silane compound, a trifunctional silane compound, and a difunctional silane compound, and the mass percentage of the silane compound is preferably 0<Qx<50, 50≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100), and the aerogel powder has a break rate of 4% or less. By adopting this configuration, the aerogel powder has a break rate of 4% or less, which further improves the break resistance, and the deformation rate is, for example, 25% or more, which further improves the flexibility.

The present inventors have confirmed that the structure of the aerogel of the present invention can be identified by solid-state ^29Si -NMR (DD-MAS method), that is, the abundance ratios of the Q component, the T component and the D component calculated from the signal area integral values derived from the Q component, the T component and the D component measured by ^solid -state 29Si-NMR (DD-MAS method) are substantially consistent with the mass percentages Qx, Tx and Dx of the tetrafunctional silane compound, the trifunctional silane compound and the bifunctional silane compound, which are the main raw materials for producing the aerogel constituting the above-mentioned aerogel powder.

The measurement conditions for ²⁹ Si-NMR are as follows.
Equipment: Solid-state NMR device (JNM-ECA400 manufactured by JEOL Ltd.)
Conditions: Proton resonance frequency: 390 MHz, time: 750 seconds/time, number of integrations: 48 times, total measurement time: 10 hours: Magic angle spinning (DD) and dipolar decoupling (Magic Angle Spinning, Dipolar Dephasing) methods were used.

The aerogel powder composition of the present invention can be composed of only aerogel powder obtained by pulverizing aerogel, but can also be composed of a mixture or dispersion further containing additives intended to impart functionality, improve appearance, impart decorativeness, etc. The content of aerogel powder contained in the aerogel powder composition is preferably 80 volume % or more of the entire aerogel powder composition, more preferably 85 volume % or more, even more preferably 90 volume % or more, and even more preferably 95 volume % or more.

Additives to be contained in the aerogel powder composition are not particularly limited, but examples include inorganic fillers such as silica particles, antistatic agents, lubricants, inorganic pigments, organic pigments, inorganic dyes, organic dyes, etc.

Here, a tetrafunctional silane compound is a silane compound with four siloxane bonds (the number of oxygen atoms bonded to one silicon atom), a trifunctional silane compound is a silane compound with three siloxane bonds, and a bifunctional silane compound is a silane compound with two siloxane bonds.

Examples of tetrafunctional silane compounds include tetraalkoxysilane and tetraacetoxysilane. Preferred embodiments of tetraalkoxysilane include those in which the alkoxy group has 1 to 9 carbon atoms.

For example, tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, etc. can be mentioned. These silane compounds may be used alone or in combination. In the present invention, it is particularly preferable to use tetramethoxysilane (TMOS) as a tetrafunctional silane compound.

Examples of trifunctional silane compounds include trialkoxysilane and triacetoxysilane. A preferred embodiment of the trialkoxysilane is one in which the alkoxy group has 1 to 9 carbon atoms.

For example, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, propyltriethoxysilane, pentyltriethoxysilane, hexyltriethoxysilane, octyltriethoxysilane, etc.

These compounds may be used alone or in combination. In the present invention, it is particularly preferable to use methyltrimethoxysilane (MTMS) as the trifunctional silane compound.

Examples of bifunctional silane compounds include dialkoxysilane and diacetoxysilane. Preferred embodiments of dialkoxysilane include those in which the alkoxy group has 1 to 9 carbon atoms.

Specific examples include dimethyldimethoxysilane, diethyldimethoxysilane, and diisobutyldimethoxysilane. These compounds may be used alone or in combination. In the present invention, it is particularly preferable to use dimethyldimethoxysilane (DMDMS) as the bifunctional silane compound.

(1-2) Aerogel Powder The aerogel powder contained in the aerogel powder composition of the present invention is a powdered material obtained by mechanically pulverizing aerogel, and has a particle size of 5 nm to 10 mm. This pulverized aerogel powder can be classified using ordinary means such as a sieve or wind power.

The average particle size of the classified aerogel powder can be adjusted and selected as appropriate depending on the purpose of use, but for example, when used as a filler, it is preferably 20 μm to 3 mm, and more preferably 50 μm to 1 mm. Furthermore, when the aerogel powder is used as a dispersoid and dispersed in a liquid dispersion medium such as paint to produce an aerogel powder dispersion, the average particle size of the aerogel powder is preferably 5 to 100 μm, and more preferably 5 to 50 μm.

Here, the average particle size refers to the average particle size measured using a laser diffraction particle size distribution analyzer SALD-2300 (manufactured by Shimadzu Corporation).

For example, to increase the filling rate, aerogel powder can be used by mixing multiple types of classified aerogel powder with different average particle sizes.

The shape of aerogel powder is usually amorphous due to the grinding process, but it can be made into specific shapes such as spheres, plates, flakes, and fibers. The shape can be directly observed using a SEM.

The elastic modulus of the aerogel powder is preferably 2.00 to 15.00 MPa, and more preferably 3.00 to 10.00 MPa. The elastic modulus here refers to the elastic modulus measured in an atmosphere of 23°C and 50% RH using a microcompression tester (manufactured by Shimadzu Corporation).

Since the aerogel powder has an elastic modulus within the above range, it can be highly packed into a specified container without being excessively crushed due to the pressure or high shear during processing, and when mixed into insulating paint, etc., it can achieve the designed insulating properties.

(1-3) Characteristics of Aerogel Powder The aerogel powder composition of the present invention is an aerogel powder composition containing at least an aerogel powder, and has a destruction rate of 10% or less, preferably 6% or less, and more preferably 4% or less. Furthermore, the aerogel powder composition of the present invention is preferably a homogeneous mixture or dispersion with low turbidity when mixed with, for example, the same volume of polyethylene glycol having a number average molecular weight of 200.

When the structure of aerogel, which is the material of the aerogel powder of the present invention, is observed microscopically, it is mainly composed of a bulk portion (skeleton portion) filled with solid matter and pores that run through the bulk portion in the form of a three-dimensional network.

It is believed that this structure has a significant effect on the compressibility of the powder. It is also believed that it is involved in the compatibility with polyethylene glycol with a number-average molecular weight of 200.

The bulk portion is composed of a continuum of solids that form a three-dimensional network through siloxane bonds. When the lattice, the smallest unit of the three-dimensional network, is approximated by a cube, the average length of one side is 2 nm or more and 25 nm or less.

It is preferable that the average length of one side is 2 nm or more, 5 nm or more, 7 nm or more, or 10 nm or more, and 25 nm or less, 20 nm or less, or 15 nm or less.

The pores are tubular and penetrate the bulk portion. When the pores are approximated by tubes and the inner diameter of the tubes is approximated by a circle, the average inner diameter is 5 nm or more and 100 nm or less. It is preferable that the average inner diameter of the pores is 5 nm or more, 7 nm or more, 10 nm or more, 20 nm or more, 30 nm or more, 50 nm or more, and 100 nm or less, 90 nm or less, 80 nm or less, 70 nm or less.

Here, the inner diameter of the tube is less than the mean free path (MFP) of the elemental molecules that make up air at atmospheric pressure.

The porosity of the aerogel, i.e., the ratio of the volume of the pores to the total volume of the aerogel, is 70% or more. Examples of the porosity include 75% or more, 80% or more, 85% or more, and 90% or more.

The aerogel of the present invention may contain structures other than the bulk and pores described above, so long as the physical properties are satisfied. As an example, it may contain voids other than the pores described above.

As another example, the material may contain water, organic solvents, surfactants, catalysts, and decomposition products thereof that remain as unavoidable components in the manufacturing process, so long as the material satisfies the physical properties described below. As yet another example, the material may contain dust that is mixed in from the manufacturing space or manufacturing equipment as unavoidable components in the manufacturing process.

The aerogel of the present invention preferably has a density of 0.15 g/cm3 or ^less . Here, the density is determined by mercury intrusion porosimetry. Since the aerogel of the present invention has a density of 0.15 g/cm3 or ^less , the thermal conductivity is small, at 0.015 W/m·K or less, and the aerogel has excellent heat insulation properties.

The aerogel powder composition of the present invention is a mixture of aerogel powder and other powder particles (e.g., pigments, dyes, etc.), and the aerogel powder dispersion of the present invention may be in a uniform dispersion state. In addition, the aerogel powder composition of the present invention can be an aerogel powder dispersion in which the aerogel powder is dispersed in a liquid dispersion medium as a dispersant (hereinafter, sometimes simply referred to as "aerogel powder dispersion"). As the liquid to be used as the dispersion medium, solvents used in ordinary paints, adhesives, etc., such as water, ethyl alcohol, ethylene glycol, ethyl acetate, and toluene, can be used. The aerogel powder can also be dispersed in paint in which pigments, dyes, etc. are already dispersed.

The aerogel powder dispersion of the present invention can stably maintain a uniform dispersion state. For example, when an aerogel powder is mixed and dispersed in an equal volume of polyethylene glycol having a number average molecular weight of 200 to prepare an aerogel powder dispersion, and then the aerogel powder dispersion is allowed to stand for 30 minutes, the aerogel powder dispersion, which is the aerogel powder composition of the present invention, maintains a uniform dispersion state and has a turbidity of 300 degrees or less.

Here, in the aerogel powder dispersion, "uniform dispersion state" means a state in which the aerogel powder is uniformly dispersed in the dispersion medium and does not settle to the bottom of the container that holds the aerogel powder dispersion.

The "turbidity" referred to here can be easily determined by comparing the sample liquid (aerogel powder dispersion) for which turbidity is to be measured with a formazin turbidity standard liquid, either visually or with a turbidimeter using the transmission scattering method. When the turbidity is close to 300, it can be compared with a turbidimeter. As the polyethylene glycol with a number average molecular weight of 200, which is the dispersion medium for the sample liquid, a commercially available product with a number average molecular weight of 180 to 220 can be used.

The above-mentioned aerogel powder dispersion maintains a uniform dispersion state and has a turbidity of 300 degrees or less, which indicates that the aerogel powder as a dispersoid has a unique compatibility with polyethylene glycol having a number average molecular weight of 200. As a result, the aerogel powder contained in the aerogel powder composition of the present invention can exhibit good dispersibility in solvent-based paints, etc.

(2) Method for Producing Aerogel Powder Composition (2-1) Method for Producing Aerogel First, a method for producing aerogel, which is the material of the aerogel powder of the present invention, will be described.

The method for producing an aerogel of the present invention includes a sol production step of adding a silicon compound to an aqueous solution containing an acid catalyst and hydrolyzing the silicon compound to produce a sol, and the silicon compound includes at least a trifunctional silane compound among a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound.

A specific method for producing the aerogel powder of the present invention includes, for example, a sol production process, a wet gel production/molding process, a solvent exchange process, and a drying process, in that order. Each process will be described in detail below.

(2-2) Sol Formation Step The sol formation step includes a step of adding various raw materials including a silicon compound (main raw material) to a predetermined solution and stirring and mixing the raw materials, thereby forming a sol.

(2-2-1) Siloxane bond constituent material (main raw material)
The method for producing an aerogel of the present invention includes a sol generation step in which at least a trifunctional silane compound is mixed in a predetermined ratio (mass percentage) among a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound as a silicon compound that is a main raw material for producing an aerogel. More specifically, when the mass percentages of the tetrafunctional silane compound, the trifunctional silane compound, and the bifunctional silane compound are Qx, Tx, and Dx, respectively, the ratios satisfy 0≦Qx≦70, 30≦Tx≦100, 0≦Dx<30, preferably 0<Qx≦50, 40≦Tx<100, 0≦Dx<30, and more preferably 0<Qx<50, 50≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100).

(2-2-2) Mixing ratio of main raw materials (mass percentage)
In the sol generating process, the silicon compound serving as the main raw material includes a sol generating process in which at least a trifunctional silane compound is mixed in a predetermined ratio (mass percentage) among a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound; more specifically, when the mass percentages of the tetrafunctional silane compound, the trifunctional silane compound, and the bifunctional silane compound, respectively, are Qx, Tx, and Dx, the ratios satisfy 0≦Qx≦70, 30≦Tx≦100, 0≦Dx<30, preferably 0<Qx≦50, 40≦Tx<100, 0≦Dx<30, and more preferably 0<Qx<50, 50≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100).

Figure 1 shows the appropriate ranges of Qx, Tx, and Dx, which are the mass percentages of the preferred tetrafunctional silane compound, trifunctional silane compound, and bifunctional silane compound mixed in the mixing step of the aerogel manufacturing method of the present invention, in a triangular diagram with Qx, Tx, and Dx as the coordinate axes. Note that the line segment (0≦Qx≦40, 30≦Tx≦70, Dx=30%) connecting the two "○ (open circle)" shown in Figure 1 is shown as a dashed line, but this dashed line is not included in either the appropriate range (region I) or the preferred range (region II and region III) of the present invention.

Region I (hatched with an upward sloping slope) shown in FIG. 1 indicates the appropriate range of the present invention, that is, the region surrounded by 0≦Qx≦70, 30≦Tx≦100, 0≦Dx<30 (where Qx+Tx+Dx=100), and region II (hatched with a downward sloping slope) indicates the preferred range of the present invention, that is, the range surrounded by 0<Qx≦50, 40≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100). By mixing the silicon compound at a mass percentage that satisfies the ranges of region I and region II, it is possible to produce an aerogel that has few defects such as cracks and has a density of 0.15 g/cm3 or ^less . Aerogel powder produced at a mixing ratio of region I and region II and having a fracture rate of 10% or less has excellent flexibility and fracture resistance. In particular, the region I shown in Figure 1 is a region where aerogel powder with a destruction rate of 10% or less and a deformation rate of 15% or more can be obtained, and the region II is a region where aerogel powder with a destruction rate of 6% or less and a deformation rate of 20% or more can be obtained. Furthermore, the region III shown in Figure 1 (hatched with horizontal lines) is a further preferred range of the present invention, that is, the range surrounded by 0<Qx<50, 50≦Tx<100, 0≦Dx<30 (where Qx+Tx+Dx=100), if a silicon compound is mixed at a mass percentage that satisfies the range (where Qx+Tx+Dx=100) it is also possible to obtain aerogel powder with a destruction rate of 4% or less and a deformation rate of 25% or more.

(2-2-3) Sub-materials and sol generation conditions in the sol generation process In the sol generation process, a tetrafunctional silane compound, a trifunctional silane compound, and a bifunctional silane compound are mixed as main raw materials in the above-mentioned predetermined mixing ratio, and added to a solution containing water and a surfactant. This preparation causes the silane compound to hydrolyze and condense, generating a sol containing siloxane bonds. The solution to be prepared may contain an acid, a nitrogen compound, an organic solvent, an organic compound (e.g., sugars), and/or an inorganic compound (e.g., salt).

During the sol production process, the surfactant forms a microphase separation structure, which contributes to the formation of the bulk and pores that make up the aerogel described below. Surfactants that can be used to produce aerogel include nonionic surfactants and ionic surfactants.

Examples of ionic surfactants include cationic surfactants, anionic surfactants, and amphoteric surfactants. It is particularly preferable to use nonionic surfactants as the surfactant.

The amount of surfactant added to the solution to be prepared depends on the type and mixing ratio of the silane compound and the type of surfactant, but is preferably in the range of 0.001 to 100 parts by mass, more preferably in the range of 0.01 to 90 parts by mass, and even more preferably in the range of 0.1 to 80 parts by mass, per 100 parts by mass of the total amount of the silane compound, which is the main raw material.

Acids act as catalysts during hydrolysis and can accelerate the reaction rate of hydrolysis. Specific examples of acids include inorganic acids, organic acids, and organic acid salts.

Inorganic acids include hydrochloric acid, sulfuric acid, sulfurous acid, nitric acid, hydrofluoric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, hypochlorous acid, etc.

Organic acids include carboxylic acids such as acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid, and azelaic acid.

Examples of organic acid salts include acid aluminum phosphate, acid magnesium phosphate, and acid zinc phosphate. These acids may be used alone or in combination of two or more. In the present invention, it is preferable to use acetic acid, which is an organic acid, as the acid.

The concentration of acid added to the entire solution to be prepared is preferably in the range of 0.0001 mol/L to 0.1 mol/L, more preferably in the range of 0.0005 mol/L to 0.05 mol/L, and even more preferably in the range of 0.001 mol/L to 0.01 mol/L.

Nitrogen compounds can also be used as compounds that generate basic catalysts when heated in the wet gel production and molding process. Specific examples include amide compounds such as urea, formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, and N,N-dimethylacetamide, and heterocyclic compounds such as hexamethylenetetramine. Urea in particular is suitable for use in that it contributes to the formation of the fine spatial structure of the aerogel and achieves homogeneous gelation.

The amount of nitrogen compound added is not particularly limited, but for example, it is preferable to add 1 to 200 parts by mass of the nitrogen compound, and more preferably 2 to 150 parts by mass, per 100 parts by mass of the total amount of the silane compound, which is the main raw material.

As the organic solvent, alcohols such as methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol can be used. These may be used alone or in combination of two or more. From the viewpoint of compatibility, the amount of organic solvent added to the solution to be prepared is preferably in the range of 0 to 10 mol, more preferably 0 to 9 mol, and even more preferably 0 to 8 mol, per 1 mol of the total amount of the silicon compound, which is the main raw material.

The solution temperature and time required for the sol generation process depend on the types and amounts of silane compounds, surfactants, water, acids, nitrogen compounds, organic solvents, etc. in the mixed solution, but may be in the range of 0.05 hours to 48 hours in a temperature environment of 0°C to 70°C, for example, and preferably in a temperature environment of 20°C to 50°C for 0.1 hours to 24 hours.

When urea has already been added as a nitrogen compound, in order to allow the urea to act as a gelling catalyst, it is preferable to keep the solution temperature in the sol generation process below 40°C in order to suppress the hydrolysis of urea (a reaction that releases ammonia and carbon dioxide proceeds at temperatures above approximately 50°C).

By carrying out the sol generation process under these conditions, the silane compound is hydrolyzed, and as a whole, a liquid sol can be generated. Note that the auxiliary materials and/or decomposition products of the auxiliary materials used in the sol generation process may be mixed as unavoidable components in the manufactured aerogel.

(2-3) Wet Gel Forming and Molding Process The wet gel forming and molding process can be roughly divided into a process of adding a basic catalyst to the liquid sol produced in the above-mentioned sol forming process, a process of pouring the liquid sol into a mold to obtain a desired shape, and a process of curing the poured liquid sol inside the mold to produce a wet gel. Note that, if a nitrogen compound has already been added as a compound that generates a basic catalyst in the sol forming process, the process of adding a basic catalyst to the liquid sol can be omitted.

Examples of basic catalysts include ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, ammonium bromide, tetramethylammonium, tetraethylammonium, tetrapropylammonium (including isomers), and tetrabutylammonium (including isomers); alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; basic sodium phosphates such as sodium metaphosphate, sodium pyrophosphate, and sodium polyphosphate; allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, and the like. Examples of the basic catalyst include aliphatic amines such as propylamine, diisobutylamine, 3-(diethylamino)propylamine, di-2-ethylhexylamine, 3-(dibutylamino)propylamine, tetramethylethylenediamine, t-butylamine, sec-butylamine, propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, and triethanolamine; and nitrogen-containing heterocyclic compounds such as morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and its derivatives, piperidine and its derivatives, and imidazole and its derivatives. The basic catalyst may be used alone or in combination of two or more kinds.

The amount of basic catalyst added is preferably 0.001 to 5 parts by mass, and particularly preferably 0.01 to 4 parts by mass, per 100 parts by mass of the total amount of the main raw materials. If the amount added is less than 0.001 parts by mass, the reaction from the sol to the wet gel tends not to be sufficiently promoted, and if it exceeds 5 parts by mass, the formed siloxane bond may be broken, causing a delay in the gelation time and heterogeneity. In particular, an aqueous tetramethylammonium solution is preferred in that it has a high reaction promotion effect as a catalyst and can form a reaction from the sol to a wet gel in a short time with few defects.

The process of pouring the solution containing the basic catalyst into the mold is a process for obtaining the desired shape of the aerogel product. The mold can be made of metal, synthetic resin, wood, or paper, but it is preferable to use synthetic resin because it combines flatness of the shape with ease of releasability. Examples of synthetic resins include polystyrene, polyethylene, polypropylene, polyethylene terephthalate (PET), polycarbonate (PC), silicone, and polytetrafluoroethylene (PTFE).

The mold is used to obtain the desired shape of the aerogel product, and therefore has a concave and convex shape that corresponds to the concave and convex shapes of the desired aerogel product. For example, if the desired shape of the aerogel product is a plate (rectangular parallelepiped), a concave tray with an opening at one end can be used as the mold. The mold may also be a combination mold consisting of multiple molds, such as a so-called injection molding die.

As an example, a two-piece combination mold may be used in which a concave mold and a convex mold are used opposite each other, and the inner surface of the concave mold and the outer surface of the convex mold are spaced apart at a predetermined distance. As a result, a solution (a solution consisting of a sol and a basic catalyst) may be poured into the internal space of the combination mold and sealed for a predetermined period of time.

In addition, when a concave tray with an open end is used as a mold, a flat plate that covers the entire open (flat) surface of the concave tray may be prepared as a second mold, and two of the plates may be used as a combined mold so that the open surface of the concave tray faces the second mold. As a result, the solution (a solution consisting of the sol and the basic catalyst) may be poured into the combined mold and sealed for a predetermined period of time.

Following the process of filling the mold with a solution containing a basic catalyst, a cross-linking reaction of the solution takes place inside the mold, producing a wet gel, and then there is an aging process in which the gel is cured.

Curing involves applying a specified amount of energy over a specified period of time to promote the cross-linking reaction of the wet gel. One example of energy is heat (temperature), and heating to 30 to 90°C, preferably 40 to 80°C, is used. Heating may be by a heater or steam heating using water or an organic solvent.

Other examples of energy include application of electromagnetic waves such as infrared rays, ultraviolet rays, microwaves, and gamma rays, and application of electron beams. These energies may be used alone or in combination of multiple means.

The time required for curing varies depending on the composition of the silicon compound, the types and amounts of surfactants, water, acids, nitrogen compounds, organic solvents, and basic catalysts, as well as the type and density of energy, but ranges from 0.01 hours to 7 days. When the type of basic catalyst and the type of energy are optimized, gelation can be completed in 0.01 to 24 hours.

Curing may also be a process in which heat (temperature) and time are changed in multiple stages. Note that the materials used in the wet gel production and molding process and/or decomposition products of the materials may be mixed into the manufactured aerogel as unavoidable components.

(2-4) Gel Crushing Step In the gel crushing step, the gel obtained in the above step is crushed to a predetermined size. The gel can be crushed, for example, by a Henshall mixer under appropriate conditions (rotation speed and time).

The gel may be produced in a mixer and then crushed as is. Alternatively, the gel may be produced in a sealable container and a shaking device such as a shaker may be used. A jet mill, roller mill, or bead mill may be used to adjust the particle size. The crushed gel may be washed to reduce impurities such as unreacted materials and by-products.

(2-5) Solvent exchange step The solvent exchange step is an essential step in the method for producing an aerogel of the present invention, in which the water and/or organic solvent present on the surface and inside of the wet gel is exchanged with an organic solvent that can be dried at normal pressure to produce an aerogel, and is a step in which the water and/or organic solvent is replaced with an organic solvent (hydrocarbon solvent) with low surface energy in order to reduce the capillary force expressed by the Young-Laplace equation as much as possible and suppress shrinkage of the gel due to drying. The solvent exchange step may be performed after removal from the above-mentioned mold, or may be performed within the mold.

The hydrocarbon solvent used in the solvent exchange is not miscible with water, so in the solvent exchange process, the water and/or organic solvent present on the surface and inside of the wet gel is first exchanged for an intermediate solvent such as alcohol that is miscible with the hydrocarbon solvent, and then this intermediate solvent is exchanged for an organic solvent (hydrocarbon solvent) with low surface energy.

Examples of alcohols used as intermediate solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol (IPA), and butanol.

In the solvent exchange process, in order to prevent shrinkage damage to the gel during the subsequent drying process, the water (or organic solvent) on the surface and inside of the wet gel is replaced with an organic solvent with a surface tension of 45 mN/m or less at 20°C.

Examples include dimethyl sulfoxide (43.5 mN/m), cyclohexane (25.2 mN/m), isopropyl alcohol (21 mN/m), heptane (20.2 mN/m), and pentane (15.5 mN/m).

The organic solvent used in the solvent exchange process may have a surface tension at 20°C of 45 mN/m or less, 40 mN/m or less, 35 mN/m or less, 30 mN/m or less, 25 mN/m or less, 20 mN/m or less, or 15 mN/m or less, or 5 mN/m or more, 10 mN/m or more, 15 mN/m or more, or 20 mN/m or more.

Among these, it is particularly preferable to use organic solvents containing aliphatic hydrocarbons whose surface tension at 20°C is in the range of 18 to 40 mN/m. The organic solvents can be used alone or in combination of two or more types.

The amount of solvent used in the solvent exchange process depends on the temperature and the device (container) used for the solvent exchange, but it is desirable to use an amount that is 2 to 100 times the volume of the wet gel. The solvent exchange is not limited to one time, and may be performed multiple times. The solvent exchange method may be any of full replacement, partial replacement, and circulatory replacement.

In addition, when the solvent exchange is performed multiple times, the type of organic solvent, temperature, and processing time may be set independently for each time. Note that the materials used in the solvent exchange process and/or decomposition products of the materials may be mixed into the produced aerogel as unavoidable components.

As an example of a specific embodiment, the solvent exchange process can be performed according to the following procedure. First, the wet gel is immersed in a methanol (MeOH) solution equivalent to five times the volume of the wet gel, and the solvent is exchanged under conditions of 60°C for 8 hours. The solvent exchange using the MeOH solution is preferably repeated multiple times (e.g., five times). The purpose of the solvent exchange using the MeOH solution is to remove moisture, unreacted components of the raw materials, and by-products from side reactions from the wet gel.

Next, the wet gel after solvent exchange using the MeOH solution is immersed in an IPA/Hep mixed solution, which is a mixture of isopropyl alcohol (IPA) and heptane (Hep) in a volume ratio of 1:4 to 1:3, and is equivalent to five times the volume of the wet gel, and further solvent exchange is performed under conditions of 60°C for 8 hours. Since MeOH does not directly mix with Hep, the MeOH in the wet gel can be removed using the IPA/Hep mixed solution.

Then, the wet gel that has undergone solvent exchange using the IPA/Hep mixed solution is immersed in a Hep solution equivalent to five times the volume of the wet gel, and further solvent exchange is performed under conditions of 60°C for 8 hours. Solvent exchange using Hep solution is preferably repeated multiple times (e.g., twice). The purpose of solvent exchange using Hep solution is to replace all of the solvent in the wet gel with Hep solution, which is a dry solvent.

(2-6) Drying Step The drying step is a step of drying the above-mentioned solvent-exchanged wet gel to obtain an aerogel with a predetermined property. Although there is no particular limitation on the drying method, the supercritical drying method has a problem that the equipment becomes large, the manufacturing cost is extremely high, and mass production is difficult. Therefore, in the drying step of the present invention, the supercritical drying method is not applied, and the atmospheric pressure drying method or the freeze drying method is used, and the atmospheric pressure drying method is particularly preferable. By using this drying method, it is possible to obtain an aerogel powder with a lower compression failure rate than the supercritical drying method.

Note that atmospheric pressure refers to the surface pressure of 300 hPa to 1100 hPa, and there is no limit to the altitude at which the present invention can be carried out as long as it is on the surface of the earth. In other words, drying at a reduced pressure of around 300 hPa is also included in the present invention.

From the above, by going through each of the steps (2-1) to (2-6) described above, the aerogel of the present invention can be produced with a high elastic modulus and a low density (0.15 g/ ^cm3 or less).

(2-7) Final pulverization step In order to adjust the average particle size of the aerogel powder, a final pulverization step can be provided. The pulverization in the final pulverization step can be performed by using the device used in the (2-4) step and by appropriately determining the pulverization conditions. It is preferable to also classify the powder using a sieve or wind force. The (2-4) gel pulverization step may be omitted and pulverization may be performed only in this step.

(2-8) Aerogel Powder Composition Preparation Step An aerogel powder composition can be produced by appropriately adding necessary additives to the aerogel powder obtained in the previous step.

(2-9) Uses of Aerogel Powder Composition The aerogel powder composition of the present invention can be used for a variety of purposes, for example, by filling it into insulating windows, insulating building materials (paints, insulating boards), etc.

The above is merely an example of an embodiment of the present invention, and various modifications can be made within the scope of the claims.

Examples of the present invention are described in detail below. Unless otherwise specified, the evaluation was carried out in an atmosphere of 23°C and 50% RH.

<Examples 1 to 11>
3.28 g of a nonionic surfactant (Pluronic PE9400, manufactured by BASF) was dissolved in 28.96 g of a 0.005 mol/L aqueous solution of acetic acid, and then 4.00 g of urea (manufactured by Nacalai Tesque) was further added as a hydrolyzable compound and dissolved. 10.00 g of a silicon compound, which is a main raw material, was added to this aqueous solution, and the mixture was stirred and mixed at room temperature for 60 minutes to carry out a hydrolysis reaction of the silicon compound and generate a sol (sol generation process).

The silicon compound was selected from tetramethoxysilane (methyl orthosilicate manufactured by Tama Chemical Industry Co., Ltd., hereafter sometimes abbreviated as "TMOS"), which is a tetrafunctional silane compound, methyltrimethoxysilane (DOWSIL Z-6366 Silane manufactured by Dow Corning Toray Co., Ltd., hereafter sometimes abbreviated as "MTMS"), which is a trifunctional silane compound, and dimethyldimethoxysilane (Tokyo Chemical Industry Co., Ltd., product code: D1052, hereafter sometimes abbreviated as "DMDMS"), which is a bifunctional silane compound, and was added at the mass percentage Qx of the tetrafunctional silane compound, the mass percentage Tx of the trifunctional silane compound, and the mass percentage Dx of the bifunctional silane compound shown in Table 1.

Both TMOS and MTMS were purified by vacuum distillation before use. The sol was then left to stand in a sealed container at 60°C to gel. It was then allowed to stand for 96 hours to mature the wet gel (wet gel production and molding process).

The wet gel was immersed in a methanol (MeOH) solution equivalent to five times its volume, and solvent exchange was repeated five times at 60°C for eight hours. The wet gel was then immersed in an IPA/Hep mixed solution, which was a mixture of isopropyl alcohol (IPA) and heptane (Hep) in a volume ratio of 1:4 to 1:3, equivalent to five times the wet gel volume, and solvent exchange was further performed at 60°C for eight hours. After that, the wet gel was immersed in a Hep solution equivalent to five times the wet gel volume, and solvent exchange was further repeated two times at 60°C for eight hours.

The methanol and isopropanol used for the solvent exchange were both manufactured by Nacalai Tesque.

The wet gel was dried under atmospheric pressure (atmospheric pressure drying) by the following method.
Heptane (manufactured by Nacalai Tesque) was used as the low surface tension solvent, and the solvent in the wet gel was exchanged (substituted) with the low surface tension solvent.

The wet gel was placed in a volume of low surface tension solvent sufficient to fully immerse the wet gel, heated to near the boiling point of 55°C, and refluxed for 8 hours. After refluxing, the container was cooled to room temperature, and the low surface tension solvent was removed and replaced with fresh low surface tension solvent, followed by further refluxing. This process was repeated three times to complete the solvent exchange to the low surface tension solvent (solvent exchange process).

Next, the solvent in the wet gel was replaced with a low surface tension solvent, and then it was placed in a container (dryer) that can control the evaporation rate, and drying began. When the gel mass became constant, drying was stopped, and an aerogel was produced (drying process).

The aerogel powders of Examples 1 to 11 were obtained by pulverizing the obtained aerogel in a Henschel mixer. In this case, the powder particle size was more uniform when visually observed when Dx was not 0. In addition, the elastic modulus of the aerogel powders of Examples 1 to 11 was in the range of 2.00 to 15.00 MPa for all of them (final pulverization process).

For reference, in Comparative Example 1, aerogel powder was produced by using a main raw material consisting of a tetrafunctional silane compound and a bifunctional silane compound in a mass percentage outside the appropriate range of the present invention (area I in Figure 1) and by the same manufacturing method as in Example 1, and in Comparative Example 2, aerogel powder was produced by drying using the supercritical method.

The resulting aerogel powder was evaluated for the failure rate (%) in the compression failure test and the deformation rate (%) in the compression deformation test shown below. The evaluation was performed in an atmosphere of 23°C and 50% RH unless otherwise specified. The evaluation results are shown in Table 1.

(Evaluation method)

<Compression fracture test>
The prepared aerogel powder was sieved through sieves with 250 μm and 1000 μm openings, and only aerogel powders having particle sizes in the range of 250 μm to 1000 μm were collected. 3 ml of the collected aerogel powder was weighed out, and the weighed aerogel powder was compressed using a universal testing machine (compression fracture tester) shown in FIG. 2. The compression cross-sectional area was 1.34 cm ² , the maximum load was 500 N, and the compression stress was 371.2 N/m ^2. After compression, the powder was sieved through a sieve with 250 μm openings, and the amount of broken powder (broken amount) that passed through the sieve was measured, and the measured broken amount (g) was substituted into the following formula (1) to calculate the breakage rate (%). Then, the breakage resistance (characteristics that are difficult to break) was evaluated from the numerical value of this breakage rate (%).
Destruction rate (%) = (destruction amount (g) / mass (g) of aerogel powder before destruction) × 100 (1)

<Compression deformation test>
The prepared aerogel powder was filled up to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 , and compressed with a load of 10 N by a piston having an area almost the same as the bottom area to measure the change in filling height (mm). The filling height of the aerogel before deformation was 16 mm. The same universal testing machine used in the compression fracture test was used as the device. After the measurement, the deformation amount was measured by the following formula (2), and the measured deformation amount was substituted into the following formula to calculate the deformation rate. The flexibility was evaluated from the numerical value of this deformation rate.
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)

<Dispersibility evaluation: uniformity and turbidity>
The monolithic aerogel was crushed, and the aerogel powder was classified and adjusted with a sieve so that the average particle size was 50 to 60 μm. 5 ml of the aerogel powder thus prepared was added to 5 ml of polyethylene glycol 200 as a dispersion medium and stirred to prepare an aerogel powder dispersion. After that, the mixture was left to stand for 30 minutes, and the uniform state of the dispersion was visually confirmed, and the turbidity was visually compared with that of a formazin standard solution with a turbidity of 300. For the polyethylene glycol 200, a grade 1 product from Fujifilm Wako Pure Chemical Co., Ltd. was used.

The aerogel powder dispersions prepared using the aerogel powders of Examples 1 to 11 and Comparative Example 1 of the present invention were uniformly dispersed and had low turbidity, whereas the aerogel powder dispersion prepared using the aerogel powder of Comparative Example 2 was non-uniformly dispersed and had high turbidity. Furthermore, none of the aerogel powders of Examples 1 to 11 were destroyed when stirred in the dispersion medium.

As described above, the aerogel powder contained in the aerogel powder composition of the present invention has excellent flexibility and resistance to breakage against compressive force, and is uniformly and stably dispersed in a dispersion medium such as polyethylene glycol having an average molecular weight of 200. It is also found to have low turbidity and good compatibility.

1 Universal testing machine 2 Aerogel powder P Pressure

Claims (7)

An aerogel powder composition containing at least an aerogel powder,
The aerogel powder is made of an aerogel which is a hydrolysis condensation product of a silane compound, and the silane compound has a mass percentage of a tetrafunctional silane compound, a trifunctional silane compound and a bifunctional silane compound, respectively, Qx, Tx and Dx, and the mass percentages of the silane compound are 0≦Qx≦70, 30≦Tx≦100 and 0≦Dx<30 (where Qx+Tx+Dx=100);
The aerogel powder has a destruction rate of 10% or less as determined by the following formula (1):
The aerogel has a skeleton that forms a three-dimensional network by siloxane bonds, and pores that penetrate the skeleton in the form of a three-dimensional network .
Destruction rate (%) = (destruction amount (g) / mass (g) of aerogel powder before destruction) × 100 (1)
The term "destruction amount" used herein means the total mass (g) of the destroyed aerogel powder that has been adjusted to a particle size in the range of 250 μm to 1000 μm using a sieve, compressed in a universal testing machine under conditions of a compression cross-sectional area of 1.34 cm ² , a maximum load of 500 N, and a compression stress of 371.2 ^N /m 2 , and then passed through a sieve with a mesh size of 250 μm. 2. The aerogel powder composition according to claim 1, wherein the aerogel powder has a deformation rate defined by the following formula (2) of 15% or more.
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)
Here, the "deformation change amount" means the change in the filling height (mm) when the aerogel powder is filled to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 and compressed with a piston at 10 N, and the filling height of the aerogel before deformation is 16 mm. 2. The aerogel powder composition of claim 1, wherein the silane compound satisfies 0<Qx≦50, 40≦Tx<100, and 0≦Dx< 30 (where Qx+Tx+Dx=100), and the aerogel powder has a destruction rate of 6% or less. The aerogel powder composition according to claim 3, wherein the aerogel powder has a deformation rate defined by the following formula (2) of 20% or more.
Deformation rate (%) = {deformation change (mm) / aerogel filling height before deformation (mm)} × 100 (2)
Here, the "deformation change amount" means the change in the filling height (mm) when the aerogel powder is filled to a height of 16 mm in a cylindrical cylinder container having a bottom area of 1.34 ^cm2 and compressed with a piston at 10 N, and the filling height of the aerogel before deformation is 16 mm. 5. The aerogel powder composition according to claim 1 , wherein the aerogel powder is made of an aerogel dried by an atmospheric pressure drying method. 6. The aerogel powder composition according to claim 1 , wherein the aerogel powder composition is a mixture of the aerogel powder and other powder or granular material. The aerogel powder composition according to any one of claims 1 to 5 , wherein the aerogel powder composition is an aerogel powder dispersion in which the aerogel powder is dispersed as a dispersoid in a liquid dispersion medium.

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