JP2017043708A - Aerogel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aerogel that is excellent in heat insulating property and productivity.SOLUTION: An aerogel has a thermal conductivity of 0.03 W/m K or less and a tensile elastic modulus of 20 kPa or less at atmospheric pressure and 25°C. In the aerosol, in the solid-state 29Si-NMR spectrum measured by using DD/MAS method and when the silicon-containing bond units Q, T and D are defined under a specific condition, the ratio of a signal area derived from Q and T to a signal area derived from D, Q+T:D, is 1:0.01 to 1:0.5. The aerosol has a structure represented by the formula (1). The aerosol further has a ladder structure including a strut portion and a bridging portion.SELECTED DRAWING: None

Description

  The present invention relates to an airgel excellent in heat insulation and productivity.

  Silica airgel is known as a material having low thermal conductivity and heat insulation. Silica airgel is useful as a functional material having excellent functionality (thermal insulation, etc.), unique optical properties, and unique electrical properties. For example, an electronic substrate utilizing the ultra-low dielectric constant properties of silica airgel It is used as a material, a heat insulating material using the high heat insulating property of silica airgel, a light reflecting material using the ultra-low refractive index of silica airgel, and the like.

  As a method for producing such a silica airgel, a supercritical drying method is known in which a gel-like compound (alcogel) obtained by hydrolyzing and polymerizing alkoxysilane is dried under supercritical conditions of a dispersion medium. (For example, refer to Patent Document 1). In the supercritical drying method, an alcogel and a dispersion medium (solvent used for drying) are introduced into a high-pressure vessel, and the dispersion medium is applied to the supercritical fluid by applying a temperature and pressure above its critical point to form a supercritical fluid. It is a method of removing the solvent. However, since the supercritical drying method requires a high-pressure process, capital investment is required for a special apparatus that can withstand supercriticality, and much labor and time are required.

  Therefore, a technique for drying alcogel using a general-purpose method that does not require a high-pressure process has been proposed. As such a method, for example, a method of improving the strength of the resulting alcogel by using a monoalkyltrialkoxysilane and a tetraalkoxysilane in combination at a specific ratio as a gel material and drying at normal pressure is known. (See, for example, Patent Document 2). However, when such atmospheric pressure drying is employed, the gel tends to contract due to stress caused by the capillary force inside the alcogel.

U.S. Pat. No. 4,402,927 JP 2011-93744 A

  As described above, while the problems of the conventional manufacturing process have been studied from various viewpoints, even if any of the above processes is adopted, the obtained airgel is poor in handling and large in size. Because it was difficult, there was a problem in productivity. For example, the agglomerated airgel obtained by the above process may be broken simply by trying to lift it by hand. This is presumably due to the fact that the density of the airgel is low and that the airgel has a pore structure in which fine particles of about 10 nm are weakly connected.

  As a technique for improving such problems of conventional aerogels, a method of imparting flexibility to the gel by increasing the pore diameter of the gel to a micrometer scale is conceivable. However, the airgel thus obtained has a problem that the thermal conductivity is greatly increased, and the excellent heat insulating property of the airgel is lost.

  This invention is made | formed in view of said situation, and it aims at providing the airgel which is excellent in heat insulation and productivity.

  As a result of intensive studies to achieve the above object, the present inventor achieved excellent heat insulating properties and handling as long as it is an airgel having a specific range of thermal conductivity and a specific range of tensile modulus. Therefore, it has been found that productivity can be increased because the productivity is improved and the size can be increased, and the present invention has been completed.

  The present invention provides an airgel having a thermal conductivity of 0.03 W / m · K or less and a tensile elastic modulus of 20 kPa or less at 25 ° C. under atmospheric pressure. That is, unlike the airgel obtained by the prior art, the airgel of the present invention has a specific range of thermal conductivity and a specific range of tensile elastic modulus, and thus has excellent heat insulation and productivity. Thereby, while exhibiting the outstanding heat insulation, the handleability of an airgel improves and the enlargement is also possible, Therefore Productivity can be improved.

The airgel of the present invention has a signal area derived from Q and T when the silicon-containing binding units Q, T and D are defined as follows in the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method. The ratio Q + T: D with the signal area derived from D is preferably 1: 0.01 to 1: 0.5. However, in the following, the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.

The airgel of the present invention can have a structure represented by the following general formula (1). The airgel having such a structure is excellent in heat insulation and productivity. By introducing the structure represented by the following general formula (1) into the skeleton of the airgel, it is easy to control to a specific range of thermal conductivity and a specific range of tensile modulus.

In formula (1), R ₁ and R ₂ each independently represent an alkyl group or an aryl group, and R ₃ and R ₄ each independently represent an alkylene group.

The airgel of the present invention can have a ladder-type structure including a column part and a bridge part, and the bridge part is represented by the following general formula (2). Such an airgel has excellent flexibility resulting from the ladder structure while maintaining the heat insulating property of the airgel itself. By introducing such a structure into the skeleton of the airgel, it is easy to control to a specific range of thermal conductivity and a specific range of tensile modulus.

In formula (2), R ₆ and R ₇ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50.

Note that the airgel having a ladder structure preferably has a structure represented by the following general formula (3). Thereby, more excellent heat insulation and flexibility can be achieved.

In formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b is 1 to 50 Indicates an integer.

  The airgel of the present invention is obtained by drying a wet gel generated from a sol containing at least one selected from the group consisting of a polysiloxane compound having a reactive group in the molecule and a hydrolysis product of the polysiloxane compound. It may be.

  At this time, it is preferable that the said reactive group is a hydroxyalkyl group, and it is more preferable that carbon number of a hydroxyalkyl group is 1-6. Thereby, it becomes the airgel which has the more excellent heat insulation and a softness | flexibility.

In addition, when a reactive group is a hydroxyalkyl group, it is preferable that the said polysiloxane compound is what is represented by following General formula (4). Thereby, more excellent heat insulation and flexibility can be achieved.

In formula (4), R ₉ represents a hydroxyalkyl group, R ₁₀ represents an alkylene group, R ₁₁ and R ₁₂ each independently represents an alkyl group or an aryl group, and n represents an integer of 1 to 50.

  In the present invention, it is also preferable that the reactive group is an alkoxy group, and it is more preferable that the alkoxy group has 1 to 6 carbon atoms. Thereby, it becomes the airgel which has the more excellent heat insulation and a softness | flexibility.

In addition, when a reactive group is an alkoxy group, it is preferable that the said polysiloxane compound is what is represented by following General formula (5). Thereby, more excellent heat insulation and flexibility can be achieved.

In the formula (5), R ₁₄ represents an alkyl group or an alkoxy group, R ₁₅ and R ₁₆ each independently represent an alkoxy group, R ₁₇ and R ₁₈ each independently represent an alkyl group or an aryl group, and m is An integer of 1 to 50 is shown.

  In the present invention, the sol preferably further contains at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group in the molecule and a hydrolysis product of the silicon compound. Thereby, the further outstanding heat insulation and productivity can be achieved.

  Moreover, it is preferable that the said drying is performed under the temperature and atmospheric pressure below the critical point of the solvent used for drying, or it is supercritical drying. Thereby, it becomes easier to obtain an airgel excellent in heat insulation and productivity.

  ADVANTAGE OF THE INVENTION According to this invention, the airgel which is excellent in heat insulation and productivity can be provided. That is, an airgel having a specific range of thermal conductivity and a specific range of tensile modulus exhibits excellent heat insulating properties, improves handling, increases size, and increases productivity. No airgel having a specific range of thermal conductivity and a specific range of tensile modulus as defined above has ever been reported, and the present invention has the potential to be used in a variety of applications. .

It is a measurement chart at the time of measuring the thermal conductivity of the airgel of this embodiment under atmospheric pressure using a stationary method thermal conductivity measuring device. It is a stress-strain curve at the time of measuring the airgel of this invention whose tensile elasticity modulus is 7.1 kPa. It is a figure which shows the solid ²⁹ Si-NMR spectrum of the 3- (trimethoxysilyl) propyl methacrylate surface treatment silica measured using DD / MAS method. It was measured using the DD / MAS method is a diagram showing a solid ²⁹ Si-NMR spectrum of the silicone rubber.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. However, the present invention is not limited to the following embodiments.

<Aerogel>
In a narrow sense, dry gel obtained by using supercritical drying method for wet gel is aerogel, dry gel obtained by drying under atmospheric pressure is xerogel, dry gel obtained by freeze-drying is cryogel and However, in the present embodiment, the obtained low-density dried gel is referred to as an aerogel regardless of the drying method of the wet gel. That is, in the present embodiment, the airgel means “Gel composed of a microporous solid in which the dispersed phase is a gas”. To do. In general, the inside of an airgel has a network-like fine structure, and has a cluster structure in which airgel particles of about 2 to 20 nm are combined. Between the skeletons formed by the clusters, there are pores less than 100 nm, and a three-dimensionally fine porous structure is formed. In addition, the airgel in this embodiment is a silica airgel which has a silica as a main component. The silica airgel is preferably a so-called organic-inorganic hybrid silica airgel into which an organic group such as a methyl group or an organic chain is introduced. The airgel of this embodiment is excellent in heat insulation and productivity (flexibility) as described below.

[Thermal conductivity]
The airgel of this embodiment has a thermal conductivity of 0.03 W / m · K or less at 25 ° C. under atmospheric pressure. The thermal conductivity is preferably 0.025 W / m · K or less, more preferably 0.02 W / m · K or less. When the thermal conductivity is 0.03 W / m · K or less, it is possible to obtain a heat insulating property higher than that of the polyurethane foam which is a high performance heat insulating material. The lower limit value of the thermal conductivity is not particularly limited, but can be set to 0.01 W / m · K, for example.

  The thermal conductivity can be measured by a steady method. Specifically, it can be measured using, for example, a steady-state thermal conductivity measuring device “HFM436 Lambda” (manufactured by NETZSCH, product name, HFM436 Lambda is a registered trademark). FIG. 1 is a diagram showing a measurement chart when the thermal conductivity of an airgel of Example 10, which will be described later, is measured under atmospheric pressure using the steady-state thermal conductivity measurement device. According to FIG. 1, it can be seen that the airgel according to the present example actually measured has a thermal conductivity of 0.020 W / m · K at 25 ° C.

  The outline of the thermal conductivity measurement method using the steady method thermal conductivity measuring apparatus is as follows.

(Preparation of measurement sample)
Using a blade with a blade angle of about 20 to 25 degrees, the airgel is processed into a size of 150 mm × 150 mm × 100 mm to obtain a measurement sample. In addition, although the recommended sample size in HFM436Lambda is 300 mm × 300 mm × 100 mm, the thermal conductivity when measured with the above sample size is the same value as the thermal conductivity when measured with the recommended sample size. Confirmed. Next, in order to ensure parallelism of the surface, the measurement sample is shaped with a sandpaper of # 1500 or more as necessary. Then, before the thermal conductivity measurement, the measurement sample is dried at 100 ° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd., product name). The measurement sample is then transferred into a desiccator and cooled to 25 ° C. Thereby, the measurement sample for thermal conductivity measurement is obtained.

(Measuring method)
The measurement conditions are an atmospheric pressure and an average temperature of 25 ° C. The measurement sample obtained as described above is sandwiched between the upper and lower heaters with a load of 0.3 MPa, the temperature difference ΔT is set to 20 ° C., and the guard sample is adjusted so as to obtain a one-dimensional heat flow. Measure upper surface temperature, lower surface temperature, etc. And the thermal resistance _RS of a measurement sample is calculated | required from following Formula.
R _S = N ((T _U −T _L ) / Q) −R _O
Wherein, T _U represents a measurement sample top surface temperature, T _L represents the measurement sample lower surface temperature, R _O represents the thermal contact resistance of the upper and lower interfaces, Q is shows the heat flux meter output. N is a proportionality coefficient, and is obtained in advance using a calibration sample.

From the obtained thermal resistance _RS , the thermal conductivity λ of the measurement sample is obtained from the following equation.
λ = d / R _S
In formula, d shows the thickness of a measurement sample.

[Tensile modulus]
The airgel of this embodiment has a tensile elastic modulus at 25 ° C. of 20 kPa or less. The tensile elastic modulus is preferably 15 kPa or less, more preferably 10 kPa or less. When the tensile modulus is 20 kPa or less, an airgel having excellent handleability can be obtained. The lower limit value of the tensile elastic modulus is not particularly limited, but can be set to 0.1 kPa, for example.

  The tensile elastic modulus can be measured using a small desktop testing machine “EZTest” (manufactured by Shimadzu Corporation, product name). The outline of the measuring method of the tensile elastic modulus using a small desktop testing machine is as follows.

(Preparation of measurement sample)
Using a blade having a blade angle of about 20 to 25 degrees, the airgel is processed into a thickness of 3 mm, a width of 6 mm, and a length of 30 mm to obtain a measurement sample. Next, the measurement sample is shaped with sandpaper of # 1500 or more as necessary. Before measurement, the measurement sample is dried at 100 ° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd., product name). The measurement sample is then transferred into a desiccator and cooled to 25 ° C. Thereby, a measurement sample of the tensile elastic modulus is obtained.

(Measuring method)
A 500N load cell is used. In addition, the specimen gripping tool is attached so that the main axis of the measurement sample coincides with the tensile direction passing through the center line of the specimen gripping tool. A measurement sample is set on a test piece gripping tool mounted on the upper and lower sides, is pulled at a speed of 0.5 mm / min, and the displacement of the measurement sample size at 25 ° C. is measured. The measurement is terminated when a load exceeding 500 N is applied or when the measurement sample is destroyed. Here, the tensile strain ε can be obtained from the following equation.
ε = Δd / d1
In the equation, Δd represents the displacement (mm) of the tensile force of the measurement sample due to the load, and d1 represents the distance (mm) between the clamps of the measurement sample before applying the load.
Further, the tensile stress σ (kPa) can be obtained from the following equation.
σ = F / A
In the formula, F represents the tensile force (N), and A represents the cross-sectional area (mm ² ) of the measurement sample before applying a load.

FIG. 2 is a diagram showing a tensile stress-tensile strain curve of an airgel of Example 5 described later. In addition, the tensile elasticity modulus E (kPa) can be calculated | required from following Formula, for example in the tensile force range of 0.1-0.2N.
E = (σ ₂ −σ ₁ ) / (ε ₂ −ε ₁ )
In the formula, σ ₁ represents a tensile stress (kPa) measured at a tensile force of 0.1 N, σ ₂ represents a tensile stress (kPa) measured at a tensile force of 0.2 N, and ε ₁ represents a tensile stress. The tensile strain measured at σ ₁ is shown, and ε ₂ shows the tensile strain measured at the tensile stress σ ₂ .

  According to FIG. 2 and the above equation, it can be seen that the airgel according to the present example actually measured has a tensile elastic modulus of 7.1 kPa at 25 ° C.

  These thermal conductivity and tensile elastic modulus can be appropriately adjusted by changing the airgel production conditions, raw materials, etc. described later.

[Signal area according to silicon-containing bonding units Q, T and D]
The airgel of the present embodiment has a signal area derived from Q and T when the silicon-containing binding units Q, T and D are defined as follows in the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method. And the ratio of the signal area derived from D (signal area ratio) Q + T: D is preferably 1: 0.01 to 1: 0.5. The signal area ratio is preferably 1: 0.01 to 1: 0.3, more preferably 1: 0.02 to 1: 0.2, and even more preferably 1: 0.03 to 1: 0. .1. When the signal area ratio is 1: 0.01 or more, there is a tendency that it is easy to obtain more excellent flexibility, and when it is 1: 0.5 or less, there is a tendency that a lower thermal conductivity is easily obtained.

The “oxygen atom” in the following Q, T, and D is an oxygen atom that mainly bonds between two silicon atoms, but may be an oxygen atom that has a hydroxyl group bonded to a silicon atom, for example. The “organic group” is a monovalent organic group in which the atom bonded to the silicon atom is a carbon atom, and examples thereof include an unsubstituted or substituted monovalent organic group having 1 to 10 carbon atoms. Examples of the unsubstituted monovalent organic group include hydrocarbon groups such as an alkyl group, an alkenyl group, an alkynyl group, a cycloalkyl group, an aryl group, and an aralkyl group. The substituted monovalent organic group includes a hydrocarbon group in which the hydrogen atom of these hydrocarbon groups is substituted with a halogen atom, a predetermined functional group, a predetermined functional group-containing organic group, or the like, or In particular, a hydrocarbon group in which a ring hydrogen atom such as a cycloalkyl group, an aryl group, and an aralkyl group is substituted with an alkyl group, and the like can be given. The halogen atom is a chlorine atom, a fluorine atom or the like (that is, a halogen atom-substituted organic group such as a chloroalkyl group or a polyfluoroalkyl group), and the functional group is a hydroxyl group, a mercapto group, a carboxyl group, An epoxy group, an amino group, a cyano group, an acryloyloxy group, a methacryloyloxy group, etc. The functional group-containing organic group includes an alkoxy group, an acyl group, an acyloxy group, an alkoxycarbonyl group, a glycidyl group, an epoxycyclohexyl group, an alkylamino group. Group, dialkylamino group, arylamino group, N-aminoalkyl-substituted aminoalkyl group and the like.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.

  When the signal area ratio Q + T: D is included in this range, the heat insulation and productivity can be further improved.

The signal area ratio can be confirmed by a solid ²⁹ Si-NMR spectrum. Generally, the measurement method of solid ²⁹ Si-NMR is not particularly limited, and examples thereof include CP / MAS method and DD / MAS method. In this embodiment, DD / MAS method is adopted from the viewpoint of quantitativeness. ing.

By the way, Roychen Joseph et al., Macromolecules, 1996, 29, pp. 1305-1312 reports the structural analysis of a composite of colloidal silica and polymethyl methacrylate using solid-state ²⁹ Si-NMR. Aramata et al., BUNSEKI KAGAKU, 1998, 47, pp. 971-978 reports a silica-siloxane interface analysis in silicone rubber using solid ²⁹ Si-NMR. In the measurement of the solid ²⁹ Si-NMR spectrum, these reports can be referred to as appropriate.

The chemical shifts of silicon-containing bond units Q, T, and D in the solid ²⁹ Si-NMR spectrum are in the ranges of Q units: -90 to -120 ppm, T units: -45 to -80 ppm, D units: 0 to -40 ppm, respectively. As observed, it is possible to separate the signals of silicon-containing binding units Q, T and D and calculate the signal area derived from each unit. In the spectrum analysis, it is preferable to use an exponential function as the window function and set the line broadcasting coefficient in the range of 0 to 50 Hz in order to improve the analysis accuracy.

For example, FIG. 3 is a diagram showing a solid ²⁹ Si-NMR spectrum of 3- (trimethoxysilyl) propyl methacrylate surface-treated silica, measured using the DD / MAS method. FIG. 4 is a diagram showing a solid ²⁹ Si-NMR spectrum of silicone rubber measured using the DD / MAS method. As shown in FIGS. 3 and 4, the signals of the silicon-containing binding units Q, T, and D can be separated by solid-state ²⁹ Si-NMR using the DD / MAS method.

  Here, a signal area ratio calculation method will be described with reference to FIGS. 3 and 4. For example, in FIG. 3, a Q unit signal derived from silica is observed in a chemical shift range of −90 to −120 ppm. Further, in the chemical shift range of −45 to −80 ppm, signals of T units derived from 3- (trimethoxysilyl) propyl methacrylate and the reaction product are observed. The signal area (integrated value) is obtained by integrating the signal in each chemical shift range. When the signal area of the Q unit is 1, the signal area ratio Q: T in FIG. 3 is calculated as 1: 0.32. The signal area is calculated using general spectrum analysis software (for example, NMR software “TopSpin” manufactured by Bruker (TopSpin is a registered trademark)).

  In FIG. 4, a Q unit signal in the silicone rubber filled with fumed silica is observed in the chemical shift range of -90 to -120 ppm. In addition, in the chemical shift range of 0 to −40 ppm, a signal of D unit in the silicone rubber filled with fumed silica is observed. The signal area (integrated value) is obtained by integrating the signal in each chemical shift range. When the signal area of the Q unit is 1, the signal area ratio Q: D in FIG. 4 is calculated as 1: 0.04.

[Density and porosity]
Airgel of the present embodiment, preferably the density at 25 ° C. is 0.05~0.25g / cm ^3, more preferably 0.1 to 0.2 g / cm ^3. When the density is 0.05 g / cm ³ or more, more excellent strength and flexibility can be obtained, and when it is 0.25 g / cm ³ or less, more excellent heat insulation can be obtained. it can.

  The airgel of the present embodiment preferably has a porosity at 25 ° C. of 85 to 95%, more preferably 87 to 93%. When the porosity is 85% or more, more excellent heat insulating properties can be obtained, and when it is 95% or less, more excellent strength and flexibility can be obtained.

  The center pore diameter, density and porosity of the airgel continuous pores (pores) in a three-dimensional network can be measured by mercury porosimetry according to DIN 66133.

<Specific embodiment of airgel>
The airgel of this embodiment includes the following first to third aspects. By adopting the first to third aspects, it becomes easy to control the thermal conductivity and tensile elastic modulus of the airgel within a specific range. However, adopting each of the first to third aspects is not necessarily intended to obtain an airgel having a specific range of thermal conductivity and a specific range of tensile modulus as defined in the present embodiment. By employing each aspect, an airgel having a thermal conductivity and a tensile elastic modulus according to each aspect can be obtained.

(First aspect)
The airgel of this embodiment can have a structure represented by the following general formula (1).

In formula (1), R ₁ and R ₂ each independently represent an alkyl group or an aryl group, and R ₃ and R ₄ each independently represent an alkylene group. Here, the aryl group is preferably a phenyl group or a substituted phenyl group. In addition, as a substituent of a substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group etc. are mentioned, for example.

By introducing the above structure into the skeleton of the airgel, a flexible airgel with low thermal conductivity is obtained. From such a viewpoint, in formula (1), R ₁ and R ₂ are each independently preferably an alkyl group having 1 to 6 carbon atoms or a phenyl group, and more preferably a methyl group. In Formula (1), R ₃ and R ₄ are each independently preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an ethylene group or a propylene group.

(Second embodiment)
The airgel of the present embodiment may be an airgel having a ladder type structure including a column part and a bridge part, and the airgel represented by the following general formula (2). By introducing such a ladder structure into the skeleton of the airgel, heat resistance and mechanical strength can be improved. In this embodiment, the “ladder structure” has two struts and bridges connecting the struts (having a so-called “ladder” form). It is. In this embodiment, the airgel skeleton may have a ladder structure, but the airgel may partially have a ladder structure.

In formula (2), R ₆ and R ₇ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. Here, the aryl group is preferably a phenyl group or a substituted phenyl group. Moreover, as a substituent of a substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group etc. are mentioned, for example. In formula (2), when b is an integer of 2 or more, two or more R _{6 s} may be the same or different, and similarly two or more R _{7 s} are each the same. May be different.

By introducing the above structure into the skeleton of the airgel, for example, the airgel has a structure derived from a conventional ladder-type silsesquioxane (that is, has a structure represented by the following general formula (X)). It becomes the airgel which has the outstanding softness | flexibility. In addition, as shown by the following general formula (X), in the airgel having a structure derived from the conventional ladder-type silsesquioxane, the structure of the bridge portion is -O-, but in the airgel of the present embodiment, The structure of the bridge portion is a structure (polysiloxane structure) represented by the general formula (2).

  In formula (X), R represents a hydroxy group, an alkyl group or an aryl group.

There are no particular limitations on the structure to be the strut portion and its chain length, and the interval between the structures to be the bridging portions, but from the viewpoint of further improving the heat resistance and mechanical strength, the ladder structure has the following general formula ( It is preferable to have the structure represented by 3).

In formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b is 1 to 50 Indicates an integer. Here, the aryl group is preferably a phenyl group or a substituted phenyl group. Moreover, as a substituent of a substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group etc. are mentioned, for example. In formula (3), when b is an integer of 2 or more, two or more R _{6 s} may be the same or different, and similarly two or more R _{7 s} are each the same. May be different. In Formula (3), when a is an integer of 2 or more, two or more R _{5 s} may be the same or different. Similarly, when c is an integer of 2 or more, 2 or more R ₈ may be the same or different.

From the viewpoint of obtaining more excellent flexibility, in formulas (2) and (3), R ₅ , R ₆ , R ₇ and R ₈ (however, R ₅ and R ₈ are only in formula (3)) are: It is preferably each independently an alkyl group having 1 to 6 carbon atoms or a phenyl group, and more preferably a methyl group. Moreover, in Formula (3), it is preferable that a and c are 6-2000 each independently, and it is more preferable that it is 10-1000. Moreover, in Formula (2) and (3), b is preferably 2 to 30, and more preferably 5 to 20.

(Third embodiment)
The aerogel of the present embodiment is obtained by drying a wet gel generated from a sol containing at least one selected from the group consisting of a polysiloxane compound having a reactive group in the molecule and a hydrolysis product of the polysiloxane compound. May be obtained. The airgel described so far is also produced from a sol containing at least one selected from the group consisting of a polysiloxane compound having a reactive group in the molecule and a hydrolysis product of the polysiloxane compound. It may be obtained by drying a wet gel.

  Although the reactive group in the polysiloxane compound having a reactive group in the molecule is not particularly limited, for example, alkoxy group, silanol group, hydroxyalkyl group, epoxy group, polyether group, mercapto group, carboxyl group, phenol group, etc. Is mentioned. These polysiloxane compounds having a reactive group may be used alone or in admixture of two or more. As the reactive group, for example, an alkoxy group, a silanol group, a hydroxyalkyl group or a polyether group is preferable from the viewpoint of improving the flexibility of the airgel, and from the viewpoint of improving the compatibility of the sol, an alkoxy group or a hydroxy group is preferable. An alkyl group is more preferred. However, from the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the airgel, the number of carbon atoms of the alkoxy group and hydroxyalkyl group is preferably 1 to 6, and the viewpoint of further improving the flexibility of the airgel 2 to 4 is more preferable.

The polysiloxane compound having a hydroxyalkyl group in the molecule is preferably one having a structure represented by the following general formula (4). By using a polysiloxane compound having a structure represented by the following general formula (4), the structure represented by the general formula (1) can be introduced into the skeleton of the airgel.

In formula (4), R ₉ represents a hydroxyalkyl group, R ₁₀ represents an alkylene group, R ₁₁ and R ₁₂ each independently represents an alkyl group or an aryl group, and n represents an integer of 1 to 50. Here, the aryl group is preferably a phenyl group or a substituted phenyl group. Moreover, as a substituent of a substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group etc. are mentioned, for example. In the formula (4), two R _{9 s} may be the same or different from each other, and similarly two R _{10 s} may be the same or different from each other. In formula (4), two or more R _{11 s} may be the same or different, and similarly two or more R _{12 s} may be the same or different.

By using a wet gel generated from a sol containing the polysiloxane compound or the like having the above structure, it becomes easier to obtain a flexible airgel having low thermal conductivity. From such a viewpoint, in formula (4), R ₉ is preferably a hydroxyalkyl group having 1 to 6 carbon atoms, and more preferably a hydroxyethyl group or a hydroxypropyl group. In formula (4), R ₁₀ is preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an ethylene group or a propylene group. In the formula (4), it is preferable that R ₁₁ and R ₁₂ carbon atoms each independently is an alkyl group or a phenyl group having 1 to 6, and more preferably a methyl group. Moreover, in Formula (4), it is preferable that n is 2-30, and it is more preferable that it is 5-20.

  As the polysiloxane compound having the structure represented by the general formula (4), commercially available products can be used, and compounds such as X-22-160AS, KF-6001, KF-6002, KF-6003, etc. , Manufactured by Shin-Etsu Chemical Co., Ltd.), XF42-B0970, Fluid OFOH 702-4%, etc. (all manufactured by Momentive).

The polysiloxane compound having an alkoxy group in the molecule preferably has a structure represented by the following general formula (5). By using a polysiloxane compound having a structure represented by the following general formula (5), it is possible to introduce a ladder structure having a bridge portion represented by the general formula (2) into the skeleton of the airgel. it can.

In the formula (5), R ₁₄ represents an alkyl group or an alkoxy group, R ₁₅ and R ₁₆ each independently represent an alkoxy group, R ₁₇ and R ₁₈ each independently represent an alkyl group or an aryl group, and m is An integer of 1 to 50 is shown. Here, the aryl group is preferably a phenyl group or a substituted phenyl group. Moreover, as a substituent of a substituted phenyl group, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group etc. are mentioned, for example. In the formula (5), two R _{14 s} may be the same or different, and two R _{15 s} may be the same or different. Similarly, two R 14 Each ₁₆ may be the same or different. In the formula (5), when m is an integer of 2 or more, two or more R _{17 s} may be the same or different, and similarly two or more R ₁₈ are each the same. May be different.

By using a wet gel generated from a sol containing the polysiloxane compound or the like having the above structure, it becomes easier to obtain a flexible airgel having low thermal conductivity. From such a viewpoint, in the formula (5), R ₁₄ is preferably an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and is a methyl group, a methoxy group or an ethoxy group. It is more preferable. In the formula (5), it is preferable that R ₁₅ and R ₁₆ carbon atoms each independently are 1-6 alkoxy group, more preferably a methoxy group or an ethoxy group. Moreover, in Formula (5), it is preferable that R <_17> and R < ₁₈ > are respectively independently a C1-C6 alkyl group or a phenyl group, and it is more preferable that it is a methyl group. In Formula (5), m is preferably 2 to 30, and more preferably 5 to 20.

  The polysiloxane compound having the structure represented by the general formula (5) can be obtained by appropriately referring to the production methods reported in, for example, JP-A Nos. 2000-26609 and 2012-233110. Can do.

  Since the alkoxy group is hydrolyzed, the polysiloxane compound having an alkoxy group in the molecule may exist as a hydrolysis product in the sol. The polysiloxane compound having an alkoxy group in the molecule and Decomposition products may be mixed. Further, in the polysiloxane compound having an alkoxy group in the molecule, all of the alkoxy groups in the molecule may be hydrolyzed or partially hydrolyzed.

  These polysiloxane compounds having a reactive group in the molecule and hydrolysis products of the polysiloxane compounds may be used alone or in admixture of two or more.

  In producing the airgel of this embodiment, the sol containing the polysiloxane compound or the like is selected from the group consisting of a silicon compound having a hydrolyzable functional group in the molecule and a hydrolysis product of the silicon compound. At least one of the above can be further contained. The number of silicon atoms in the molecule of the silicon compound is preferably 1 or 2. Although it does not specifically limit as a silicon compound which has a hydrolyzable functional group in a molecule | numerator, For example, an alkyl silicon alkoxide is mentioned. Among alkyl silicon alkoxides, those having 3 or less hydrolyzable functional groups are more preferable from the viewpoint of improving water resistance, and specific examples include methyltrimethoxysilane and dimethyldimethoxysilane. In addition, bistrimethoxysilylmethane, bistrimethoxysilylethane, bistrimethoxysilylhexane, ethyltrimethoxysilane, vinyltrimethoxysilane, etc., which are silicon compounds having 3 or less hydrolyzable functional groups at the molecular ends, are also preferably used. Can do. These silicon compounds may be used alone or in admixture of two or more.

  In addition, it is preferable that content of the polysiloxane compound contained in the said sol and the hydrolysis product of this polysiloxane compound is 5-50 mass parts with respect to 100 mass parts of total amounts of sol, 10-30 mass parts It is more preferable that By making it 5 parts by mass or more, it becomes easier to obtain good reactivity, and by making it 50 parts by mass or less, it becomes easier to obtain good compatibility.

  Further, when the sol further contains the silicon compound, the ratio between the content of the polysiloxane compound and the hydrolysis product of the polysiloxane compound and the content of the silicon compound and the hydrolysis product of the silicon compound is 1: 0.5 to 1: 4 is preferable, and 1: 1 to 1: 2 is more preferable. When the ratio of the content of these compounds is 1: 0.5 or more, good compatibility is further easily obtained, and when the ratio is 1: 4 or less, gel shrinkage is further easily suppressed.

  The total content of the polysiloxane compound, the hydrolysis product of the polysiloxane compound, the silicon compound and the hydrolysis product of the silicon compound is 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of the sol. Preferably, it is 10-30 mass parts. By making it 5 parts by mass or more, it becomes easier to obtain good reactivity, and by making it 50 parts by mass or less, it becomes easier to obtain good compatibility. At this time, it is preferable that the ratio of the content of the polysiloxane compound, the hydrolysis product of the polysiloxane compound, the silicon compound, and the hydrolysis product of the silicon compound is within the above range.

<Method for producing airgel>
Next, the manufacturing method of an airgel is demonstrated. Although the manufacturing method of an airgel is not specifically limited, For example, it can manufacture with the following method.

  That is, the airgel of this embodiment includes a sol generation step, a wet gel generation step in which the sol obtained in the sol generation step is gelled and then aged to obtain a wet gel, and the wet gel obtained in the wet gel generation step. Can be produced by a production method mainly comprising a step of washing and solvent substitution, and a drying step of drying the wet gel after washing and solvent substitution. The sol is a state before the gelation reaction occurs, and in this embodiment, the polysiloxane compound and / or the hydrolysis product of the polysiloxane compound, and in some cases, the silicon compound and / or the silicon compound. It means a state in which the hydrolysis product is dissolved or dispersed in a solvent. The wet gel means a gel solid in a wet state that contains a liquid medium but does not have fluidity.

  Hereinafter, each process of the manufacturing method of the airgel of this embodiment is demonstrated.

(Sol generation process)
The sol generation step is a step of mixing the above-described polysiloxane compound and / or silicon compound and a solvent and hydrolyzing them to generate a sol. In this step, it is preferable to further add an acid catalyst in the solvent in order to promote the hydrolysis reaction. Further, as shown in Japanese Patent No. 5250900, a surfactant, a thermally hydrolyzable compound, and the like can be added to the solvent.

  As the solvent, for example, water or a mixed solution of water and alcohols can be used. Examples of alcohols include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol. Among these, methanol, ethanol, or 2-propanol, which is an alcohol having a low surface tension and a low boiling point, is preferable in terms of reducing the interfacial tension with the gel wall. These may be used alone or in admixture of two or more.

  For example, when alcohol is used as the solvent, the amount of alcohol is preferably 4 to 8 mol, more preferably 4 to 6.5 mol, and more preferably 4.5 to 6 with respect to 1 mol of the total amount of the polysiloxane compound and the silicon compound. Mole is more preferred. By making the amount of alcohols 4 mol or more, it becomes easier to obtain good compatibility, and by making it 8 mol or less, it becomes easier to suppress gel shrinkage.

  Acid catalysts include hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, odorous acid, chloric acid, chlorous acid, hypochlorous acid and other inorganic acids; acidic phosphoric acid Acidic phosphates such as aluminum, acidic magnesium phosphate and acidic zinc phosphate; organic 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 Etc. Among these, organic carboxylic acids are preferable, acetic acid, formic acid, propionic acid, oxalic acid or malonic acid are more preferable, and acetic acid is more preferable from the viewpoint of further improving the water resistance of the obtained airgel. These may be used alone or in admixture of two or more.

  By using an acid catalyst, the hydrolysis reaction of the polysiloxane compound and the silicon compound is promoted, and a sol can be obtained in a shorter time.

  It is preferable that the addition amount of an acid catalyst is 0.001-0.1 mass part with respect to 100 mass parts of total amounts of a polysiloxane compound and a silicon compound.

  As the surfactant, a nonionic surfactant, an ionic surfactant, or the like can be used. These may be used alone or in admixture of two or more.

  Examples of the nonionic surfactant include those containing a hydrophilic part such as polyoxyethylene and a hydrophobic part mainly composed of an alkyl group, and those containing a hydrophilic part such as polyoxypropylene. Polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene alkyl ether, and the like are preferably used as those containing a hydrophilic portion such as polyoxyethylene and a hydrophobic portion mainly composed of an alkyl group. As those containing a hydrophilic portion such as polyoxypropylene, polyoxypropylene alkyl ethers, block copolymers of polyoxyethylene and polyoxypropylene, and the like are preferably used.

  As the ionic surfactant, a cationic surfactant, an anionic surfactant, an amphoteric surfactant, and the like can be used. In particular, a cationic surfactant or an anionic surfactant is preferably used. It is done. As the cationic surfactant, cetyltrimethylammonium bromide or cetyltrimethylammonium chloride is preferable, and as the anionic surfactant, sodium dodecylsulfonate is preferable. As the amphoteric surfactant, an amino acid surfactant, a betaine surfactant, or an amine oxide surfactant can be used. As the amino acid surfactant, for example, acylglutamic acid is preferably used. As the betaine surfactant, for example, lauryldimethylaminoacetic acid betaine or stearyldimethylaminoacetic acid betaine is preferably used. As the amine oxide surfactant, for example, lauryl dimethylamine oxide is preferably used.

  These surfactants have the effect of reducing the difference in chemical affinity between the solvent in the reaction system and the growing siloxane polymer and suppressing phase separation in the wet gel formation process described later. To do.

  The amount of the surfactant to be added depends on the type of the surfactant, or the types and amounts of the polysiloxane compound and the silicon compound, but is preferably 1 with respect to 100 parts by mass of the total amount of the polysiloxane compound and the silicon compound. -100 mass parts, More preferably, it is 5-60 mass parts.

  The thermohydrolyzable compound generates a base catalyst by thermal hydrolysis, renders the reaction solution basic, and promotes a sol-gel reaction in a wet gel generation process described later. Therefore, the thermohydrolyzable compound is not particularly limited as long as it is a compound that can make the reaction solution basic after hydrolysis. Urea; formamide, N-methylformamide, N, N-dimethylformamide, acetamide, N -Acid amides such as methylacetamide and N, N-dimethylacetamide; cyclic nitrogen compounds such as hexamethylenetetramine, and the like. Among these, urea is particularly preferable.

  The amount of the thermally hydrolyzable compound added is not particularly limited as long as it is an amount that can sufficiently promote the sol-gel reaction in the wet gel generation step described later. For example, when urea is used as the thermally hydrolyzable compound, the amount added is preferably 1 to 200 parts by mass, and 2 to 150 parts by mass with respect to 100 parts by mass of the total amount of the polysiloxane compound and the silicon compound. It is more preferable that By making the addition amount 1 mass part or more, it becomes easier to obtain good reactivity, and by making it 200 mass parts or less, it becomes easier to further suppress the precipitation of crystals and the decrease in gel density.

  The hydrolysis in the sol production step depends on the types and amounts of the polysiloxane compound, silicon compound, acid catalyst, surfactant and the like in the mixed solution, but for example, 10 minutes under a temperature environment of 20 to 60 ° C. It is preferably performed for ˜24 hours, and more preferably performed for 5 minutes to 8 hours in a temperature environment of 50 to 60 ° C. Thereby, the hydrolyzable functional group in a polysiloxane compound and a silicon compound is fully hydrolyzed, and the hydrolysis product of a polysiloxane compound and the hydrolysis product of a silicon compound can be obtained more reliably.

  However, when adding a thermohydrolyzable compound in the solvent, it is preferable to adjust the temperature environment of the sol production step to a temperature that suppresses hydrolysis of the thermohydrolyzable compound and suppresses gelation of the sol. . The temperature at this time may be any temperature as long as the hydrolysis of the thermally hydrolyzable compound can be suppressed. For example, when urea is used as the thermally hydrolyzable compound, the temperature environment in the sol generation step is preferably 0 to 40 ° C, and more preferably 10 to 30 ° C.

(Wet gel production process)
The wet gel generation step is a step in which the sol obtained in the sol generation step is gelled and then aged to obtain a wet gel. In this step, a base catalyst is preferably used to promote gelation.

  Base catalysts include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, and ammonium bromide; sodium metaphosphate Basic sodium phosphates such as sodium pyrophosphate and sodium polyphosphate; allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3 -(Diethylamino) propylamine, di-2-ethylhexylamine, 3- (dibutylamino) propylamine, tetramethylethylenediamine, t-butylamine, sec- Aliphatic amines such as tilamine, propylamine, 3- (methylamino) propylamine, 3- (dimethylamino) propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine; morpholine, N -Nitrogen-containing heterocyclic compounds such as methylmorpholine, 2-methylmorpholine, piperazine and derivatives thereof, piperidine and derivatives thereof, imidazole and derivatives thereof, and the like. Among these, ammonium hydroxide (ammonia water) is preferable from the viewpoints of high volatility and difficulty in remaining in the airgel after drying without impairing water resistance, and economical efficiency. The above base catalysts may be used alone or in admixture of two or more.

  By using a base catalyst, the dehydration condensation reaction and dealcoholization condensation reaction of the polysiloxane compound and / or the hydrolysis product of the polysiloxane compound and the silicon compound and / or the hydrolysis product of the silicon compound in the sol are promoted. The sol can be gelled in a shorter time. Thereby, a wet gel with higher strength (rigidity) can be obtained. In particular, ammonia has high volatility and hardly remains in the airgel. Therefore, by using ammonia as a base catalyst, an airgel having better water resistance can be obtained.

  The addition amount of the base catalyst is preferably 0.5 to 5 parts by mass, and more preferably 1 to 4 parts by mass with respect to 100 parts by mass of the total amount of the polysiloxane compound and the silicon compound. By setting it as 0.5 mass part or more, gelatinization can be performed in a short time, and a water resistance fall can be suppressed more by setting it as 5 mass part or less.

  The gelation of the sol in the wet gel generation step is preferably performed in a sealed container so that the solvent and the base catalyst do not volatilize. The gelation temperature is preferably from 30 to 90 ° C, more preferably from 40 to 80 ° C. By setting the gelation temperature to 30 ° C. or higher, gelation can be performed in a shorter time, and a wet gel with higher strength (rigidity) can be obtained. Moreover, since it becomes easy to suppress volatilization of a solvent (especially alcohols) by making gelation temperature into 90 degrees C or less, it can gelatinize, suppressing volume shrinkage.

  The aging in the wet gel production step is preferably performed in a closed container so that the solvent and the base catalyst do not volatilize. By aging, the components of the wet gel are strongly bonded, and as a result, a wet gel having a high strength (rigidity) sufficient to suppress shrinkage during drying can be obtained. The aging temperature is preferably 30 to 90 ° C, more preferably 40 to 80 ° C. By setting the aging temperature to 30 ° C. or higher, a wet gel with higher strength (rigidity) can be obtained, and by setting the aging temperature to 90 ° C. or lower, volatilization of the solvent (especially alcohols) can be easily suppressed. Therefore, it can be gelled while suppressing volume shrinkage.

  Since it is often difficult to determine the sol gelation end point, sol gelation and subsequent aging may be performed in a series of operations.

  Although the gelation time and the aging time vary depending on the gelation temperature and the aging temperature, the total of the gelation time and the aging time is preferably 4 to 480 hours, more preferably 6 to 120 hours. By setting the total gelation time and aging time to 4 hours or more, a wet gel with higher strength (rigidity) can be obtained, and by setting it to 480 hours or less, the effect of aging can be more easily maintained.

  In order to reduce the density of the resulting airgel or increase the average pore diameter, increase the gelation temperature and aging temperature within the above range, or increase the total time of the gelation time and aging time within the above range. Is preferred. In order to increase the density of the obtained airgel or reduce the average pore diameter, the gelation temperature and the aging temperature are lowered within the above range, or the total time of the gelation time and the aging time is within the above range. It is preferable to shorten it.

(Washing and solvent replacement process)
The washing and solvent replacement step is a step of washing the wet gel obtained by the wet gel generation step (washing step), and a step of replacing the washing liquid in the wet gel with a solvent suitable for the drying conditions (the drying step described later). It is a process which has (solvent substitution process). The washing and solvent replacement step can be performed in a form in which only the solvent replacement step is performed without performing the step of washing the wet gel, but the impurities such as unreacted substances and by-products in the wet gel are reduced, and more From the viewpoint of enabling the production of a highly pure airgel, it is preferable to wash the wet gel.

  In the washing step, it is preferable to repeatedly wash the wet gel obtained in the wet gel production step with water or an organic solvent. At this time, washing efficiency can be improved by heating.

  As organic solvents, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, methyl ethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, methylene chloride , N, N-dimethylformamide, dimethyl sulfoxide, acetic acid, formic acid, and other various organic solvents can be used. You may use said organic solvent individually or in mixture of 2 or more types.

  In the solvent replacement step described later, a low surface tension solvent may be suitably used in order to suppress gel shrinkage due to drying. However, low surface tension solvents generally have very low mutual solubility with water. Therefore, when using a low surface tension solvent in the solvent replacement step, the organic solvent used in the washing step is preferably a hydrophilic organic solvent having high mutual solubility in both water and a low surface tension solvent. . Note that the hydrophilic organic solvent used in the washing step can serve as a preliminary replacement for the solvent replacement step. From this, methanol, ethanol, 2-propanol, acetone, or methyl ethyl ketone is preferable from the viewpoint of being a hydrophilic organic solvent among the above organic solvents, and methanol, ethanol, or methyl ethyl ketone is more preferable from the viewpoint of economy.

  The amount of water or organic solvent used in the washing step is preferably such that the solvent in the wet gel can be sufficiently substituted and washed, and the amount of the solvent is 3 to 10 times the volume of the wet gel. Can be used. The washing is preferably repeated until the water content in the wet gel after washing is 10% by mass or less based on the mass of silica.

  The temperature environment in the washing step is preferably a temperature not higher than the boiling point of the solvent used for washing. For example, when methanol is used, heating at about 30 to 60 ° C. is preferred.

  In the solvent replacement step, it is preferable to replace the solvent of the washed wet gel with a predetermined replacement solvent in order to suppress shrinkage in the drying step described later. At this time, the replacement efficiency can be improved by heating. As the replacement solvent, specifically, in the drying step, when drying under atmospheric pressure at a temperature below the critical point of the solvent used for drying, a low surface tension solvent described later is preferable, In the case of performing supercritical drying, for example, it is preferable to use a solvent such as ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide or the like alone or a mixture of two or more thereof.

  The low surface tension solvent preferably has a surface tension at 20 ° C. of 30 mN / m or less, more preferably 25 mN / m or less, and even more preferably 20 mN / m or less. Examples of the low surface tension solvent include pentane (15.5), hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4), 3- Aliphatic hydrocarbons such as methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2), 1-pentene (16.0); (28.9), toluene (28.5), m-xylene (28.7), p-xylene (28.3) and other aromatic hydrocarbons; dichloromethane (27.9), chloroform (27.2) ), Carbon tetrachloride (26.9), 1-chloropropane (21.8), 2-chloropropane (18.1) and other halogenated hydrocarbons; ethyl ether (17.1), propyl ether (20.5) ), Isop Ethers such as pyrether (17.7), butyl ethyl ether (20.8), 1,2-dimethoxyethane (24.6); acetone (23.3), methyl ethyl ketone (24.6), methyl propyl ketone (25.1), ketones such as diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2), Examples include esters such as isobutyl acetate (23.7), ethyl butyrate (24.6), etc. (in parentheses indicate surface tension at 20 ° C., and the unit is [mN / m]). Among these, from the viewpoint of low surface tension and work environment, aliphatic hydrocarbons are preferable, and hexane or heptane is more preferable. Among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, or 1,2-dimethoxyethane, it can be used as the organic solvent in the washing step. Of these, those having a boiling point of 100 ° C. or less at normal pressure are preferred in that they can be easily dried in the drying step described later. You may use said organic solvent individually or in mixture of 2 or more types.

  The amount of the solvent used in the solvent replacement step is preferably an amount that can sufficiently replace the solvent in the wet gel after washing, and the amount of the solvent is 3 to 10 times the volume of the wet gel. be able to.

  The temperature environment in the solvent substitution step is preferably a temperature below the boiling point of the solvent used for substitution. For example, when heptane is used, heating at about 30 to 60 ° C. is preferred.

(Drying process)
In the drying step, the wet gel washed and solvent-substituted as described above is dried. Thereby, an airgel can be finally obtained.

  The drying method is not particularly limited, and known atmospheric pressure drying, supercritical drying or freeze drying can be used. Among these, from the viewpoint of easy production of a low density airgel, atmospheric pressure drying or Supercritical drying is preferred. Moreover, it is preferable that it is normal pressure drying from a viewpoint that it can produce at low cost. In the present embodiment, the normal pressure means 0.1 MPa (atmospheric pressure).

  The airgel of this embodiment can be obtained by drying a wet gel that has been washed and solvent-substituted at a temperature below the critical point of the solvent used for drying under atmospheric pressure. The drying temperature varies depending on the type of the substituted solvent, but is preferably 20 to 80 ° C. in view of the fact that drying at a high temperature increases the evaporation rate of the solvent and may cause a large crack in the gel. -60 degreeC is more preferable. Moreover, although drying time changes with the volume and drying temperature of a wet gel, 4-120 hours are preferable. In the present embodiment, drying can be accelerated by applying pressure within a range that does not impair productivity.

  The airgel of this embodiment can also be obtained by supercritically drying a wet gel that has been washed and solvent-substituted. Supercritical drying can be performed by a known method. Examples of the supercritical drying method include a method of removing the solvent at a temperature and pressure higher than the critical point of the solvent contained in the wet gel. Alternatively, as a method of supercritical drying, all or part of the solvent contained in the wet gel is obtained by immersing the wet gel in liquefied carbon dioxide, for example, under conditions of about 20 to 25 ° C. and about 5 to 20 MPa. And carbon dioxide having a lower critical point than that of the solvent, and then removing carbon dioxide alone or a mixture of carbon dioxide and the solvent.

  The airgel obtained by such atmospheric pressure drying or supercritical drying is preferably further dried at 105 to 200 ° C. for about 0.5 to 2 hours under normal pressure. This makes it easier to obtain an airgel having a low density and small pores. The additional drying is more preferably performed at 150 to 200 ° C. under normal pressure.

  The airgel of the present embodiment obtained through the above steps has a thermal conductivity of 0.03 W / m · K or less at 25 ° C. under atmospheric pressure, a tensile modulus of 20 kPa or less, and a conventional aerogel It has excellent heat insulation and productivity that were difficult to achieve. Because of such advantages, it can be preferably applied to applications as a heat insulating material in the construction field, automobile field, home appliances, semiconductor field, industrial equipment, and the like. Moreover, the airgel of this embodiment can be utilized as a coating additive, a cosmetic, an antiblocking agent, a catalyst carrier, etc. besides the use as a heat insulating material.

  Next, the present invention will be described in more detail with reference to the following examples, but these examples do not limit the present invention.

[Production of airgel]
Example 1
40.0 parts by mass of carbinol-modified siloxane “X-22-160AS” (manufactured by Shin-Etsu Chemical Co., Ltd., product name) represented by the above general formula (4) as a polysiloxane compound, and methyltrimethoxysilane as a silicon compound 60.0 parts by mass of “LS-530” (manufactured by Shin-Etsu Chemical Co., Ltd., product name: hereinafter abbreviated as “MTMS”), 120.0 parts by mass of water and 80.0 parts by mass of methanol were mixed. As an acid catalyst, 0.10 parts by mass of acetic acid was added and reacted at 25 ° C. for 8 hours to obtain a sol. To the obtained sol, 40.0 parts by mass of 5% aqueous ammonia as a base catalyst was added, gelled at 60 ° C. for 8 hours, and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, the obtained wet gel was immersed in 2500.0 parts by mass of methanol and washed at 60 ° C. for 12 hours. This washing operation was performed 3 times while exchanging with fresh methanol. Next, the washed wet gel was immersed in 2500.0 parts by mass of heptane, which is a low surface tension solvent, and solvent substitution was performed at 60 ° C. for 12 hours. This solvent replacement operation was performed three times while exchanging with new heptane. The airgel 1 having the structure represented by the above general formula (1) is obtained by drying the washed and solvent-substituted wet gel at normal pressure for 96 hours at 40 ° C. and then further drying at 150 ° C. for 2 hours. Got.

(Example 2)
40.0 parts by mass of X-22-160AS represented by the above general formula (4) as a polysiloxane compound, 60.0 parts by mass of MTMS as a silicon compound, 120.0 parts by mass of water, and 80 parts by mass of methanol 0.10 parts by mass of acetic acid as an acid catalyst and 20.0 parts by mass of cetyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd .: hereinafter abbreviated as “CTAB”) as a cationic surfactant were added to the mixture. , And reacted at 25 ° C. for 8 hours to obtain a sol. Thereafter, in the same manner as in Example 1, an airgel 2 having a structure represented by the general formula (1) was obtained.

(Example 3)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 40.0 parts by mass of X-22-160AS represented by the above general formula (4) as a polysiloxane compound and 60.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. It was. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 3 having a structure represented by the general formula (1) was obtained.

Example 4
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, and “F-127” (BASF Corporation) which is a block copolymer of polyoxyethylene and polyoxypropylene as a nonionic surfactant Manufactured product name) 20.0 parts by mass and 120.0 parts by mass of urea as a thermohydrolyzable compound, and X-22-160AS represented by the above general formula (4) as a polysiloxane compound 40.0 parts by mass and 60.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, the airgel 4 having the structure represented by the general formula (1) was obtained in the same manner as in Example 1.

(Example 5)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 20.0 parts by mass of X-22-160AS represented by the above general formula (4) as a polysiloxane compound and 80.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. It was. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 5 having a structure represented by the general formula (1) was obtained.

(Example 6)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 40.0 parts by mass of a bifunctional alkoxy-modified polysiloxane compound (hereinafter referred to as “polysiloxane compound A”) represented by the above general formula (5) as a polysiloxane compound and MTMS of 60. 0 parts by mass was added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 6 having a ladder type structure including the structures represented by the general formulas (2) and (3) was obtained.

  The “polysiloxane compound A” was synthesized as follows. First, in a 1 liter three-necked flask equipped with a stirrer, a thermometer, and a Dimroth condenser, 100.0 parts by mass of hydroxy-terminated dimethylpolysiloxane “XC96-723” (product name, manufactured by Momentive), methyl 181.3 parts by mass of trimethoxysilane and 0.50 parts by mass of t-butylamine were mixed and reacted at 30 ° C. for 5 hours. Thereafter, this reaction solution was heated at 140 ° C. for 2 hours under reduced pressure of 1.3 kPa to remove volatile components, thereby obtaining a bifunctional alkoxy-modified polysiloxane compound (polysiloxane compound A) at both ends.

(Example 7)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 20.0 parts by mass of polysiloxane compound A represented by the above general formula (5) as a polysiloxane compound and 80.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. . The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 7 having a ladder structure represented by the general formulas (2) and (3) was obtained.

(Example 8)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 20.0 parts by mass of X-22-160AS represented by the above general formula (4) as a polysiloxane compound and 60.0 parts by mass of MTMS and 20.0 parts by mass of bistrimethoxysilylhexane as a silicon compound, A sol was obtained by reacting at 25 ° C. for 2 hours. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 8 having a structure represented by the general formula (1) was obtained.

Example 9
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 20.0 parts by mass of the polysiloxane compound A represented by the above general formula (5) as a polysiloxane compound and 60.0 parts by mass of MTMS and 20.0 parts by mass of bistrimethoxysilylhexane as a silicon compound were added. A sol was obtained by reacting at 2 ° C. for 2 hours. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 9 having a ladder structure represented by the general formulas (2) and (3) was obtained.

(Example 10)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. As a polysiloxane compound, 20.0 parts by mass of X-22-160AS represented by the above general formula (4), 20.0 parts by mass of a polysiloxane compound A represented by the above general formula (5), and a silicon compound As a result, 60.0 parts by mass of MTMS was added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 1, an airgel 10 having a structure represented by the general formula (1) and a ladder structure represented by the general formulas (2) and (3) was obtained.

(Example 11)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 40.0 parts by mass of X-22-160AS represented by the above general formula (4) as a polysiloxane compound and 60.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. It was. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, the obtained wet gel was immersed in 2500.0 parts by mass of methanol and washed at 60 ° C. for 12 hours. This washing operation was performed 3 times while exchanging with fresh methanol. Next, the washed wet gel was immersed in 2500.0 parts by mass of 2-propanol, and solvent substitution was performed at 60 ° C. for 12 hours. This solvent replacement operation was performed three times while exchanging with new 2-propanol.

  Next, supercritical drying of the solvent-substituted wet gel was performed. The inside of the autoclave was filled with 2-propanol, and a wet gel substituted with a solvent was added. And the liquefied carbon dioxide gas was sent in the autoclave, and the inside of the autoclave was filled with the mixture of 2-propanol and carbon dioxide which is a dispersion medium. Then, after heating and pressurizing so that the environment in the autoclave becomes 80 ° C. and 14 MPa and sufficiently flowing carbon dioxide in the supercritical state through the autoclave, the pressure is reduced and 2-propanol and dioxide contained in the gel are added. Carbon was removed. Thus, the airgel 11 which has a structure represented by the said General formula (1) was obtained.

(Example 12)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 40.0 parts by mass of the polysiloxane compound A represented by the above general formula (5) as a polysiloxane compound and 60.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. . The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, in the same manner as in Example 11, an airgel 12 having a ladder structure represented by the general formulas (2) and (3) was obtained.

(Example 13)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 40.0 parts by mass of trifunctional alkoxy-modified polysiloxane compound at both ends represented by the above general formula (5) as a polysiloxane compound (hereinafter referred to as “polysiloxane compound B”) and MTMS of 60. 0 parts by mass was added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, airgel 13 was obtained in the same manner as in Example 1.

  The “polysiloxane compound B” was synthesized as follows. First, 100.0 parts by mass of XC96-723, 202.6 parts by mass of tetramethoxysilane and 0. 2 parts of t-butylamine in a 1 liter three-necked flask equipped with a stirrer, a thermometer and a Dimroth condenser. 50 parts by mass was mixed and reacted at 30 ° C. for 5 hours. Thereafter, this reaction solution was heated at 140 ° C. for 2 hours under a reduced pressure of 1.3 kPa to remove volatile components, thereby obtaining a trifunctional alkoxy-modified polysiloxane compound (polysiloxane compound B) at both ends.

(Example 14)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 20.0 parts by mass of polysiloxane compound B represented by the above general formula (5) as a polysiloxane compound and 80.0 parts by mass of MTMS as a silicon compound were added and reacted at 25 ° C. for 2 hours to obtain a sol. . The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, airgel 14 was obtained in the same manner as in Example 1.

(Comparative Example 1)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 100.0 parts by mass of MTMS as a silicon compound was added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, the airgel 15 was obtained in the same manner as in Example 1.

(Comparative Example 2)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 70.0 parts by mass of MTMS as a silicon compound and 30.0 parts by mass of dimethyldimethoxysilane “LS-520” (manufactured by Shin-Etsu Chemical Co., Ltd., product name: hereinafter abbreviated as “DMDMS”) were added at 25 ° C. The reaction was performed for a time to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, the airgel 16 was obtained in the same manner as in Example 1.

(Comparative Example 3)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. As a silicon compound, 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS were added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, airgel 17 was obtained in the same manner as in Example 1.

(Comparative Example 4)
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermohydrolyzable compound were mixed. 100.0 parts by mass of MTMS as a silicon compound was added and reacted at 25 ° C. for 2 hours to obtain a sol. The obtained sol was gelled at 60 ° C. for 8 hours and then aged at 80 ° C. for 48 hours to obtain a wet gel. Thereafter, an airgel 18 was obtained in the same manner as in Example 11.

  Table 1 summarizes the drying methods and Si raw materials (polysiloxane compounds and silicon compounds) in each Example and Comparative Example.

[Various evaluations]
For the airgels 1 to 18 obtained in each Example and Comparative Example, the thermal conductivity, the tensile modulus, the signal area ratio of the silicon-containing bonding units Q, T and D, the density and the porosity are measured according to the following conditions. evaluated. The evaluation results are summarized in Table 2.

(1) Measurement of thermal conductivity Using a blade with a blade angle of about 20 to 25 degrees, the airgel was processed into a size of 150 mm x 150 mm x 100 mm to obtain a measurement sample. Next, in order to ensure parallelism of the surface, shaping was performed with sandpaper of # 1500 or more as necessary. The obtained measurement sample was dried at 100 ° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd., product name) before measuring the thermal conductivity. The measurement sample was then transferred into a desiccator and cooled to 25 ° C.

The thermal conductivity was measured using a steady-state thermal conductivity measuring device “HFM436 Lambda” (manufactured by NETZSCH, product name). The measurement conditions were an average temperature of 25 ° C. under atmospheric pressure. The measurement sample obtained as described above is sandwiched between the upper and lower heaters with a load of 0.3 MPa, the temperature difference ΔT is set to 20 ° C., and the guard sample is adjusted so as to obtain a one-dimensional heat flow. Upper surface temperature, lower surface temperature, etc. were measured. And thermal resistance _RS of the measurement sample was calculated | required from following Formula.
R _S = N ((T _U −T _L ) / Q) −R _O
Wherein, T _U represents a measurement sample top surface temperature, T _L represents the measurement sample lower surface temperature, R _O represents the thermal contact resistance of the upper and lower interfaces, Q is shows the heat flux meter output. Note that N is a proportionality coefficient, and is obtained in advance using a calibration sample.

From the obtained thermal resistance _RS , the thermal conductivity λ of the measurement sample was obtained from the following equation.
λ = d / R _S
In formula, d shows the thickness of a measurement sample.

(2) Measurement of tensile elastic modulus Using a blade having a blade angle of about 20 to 25 degrees, the airgel was processed into a thickness of 3 mm, a width of 6 mm, and a length of 30 mm to obtain a measurement sample. Next, in order to ensure parallelism of the surfaces, the measurement sample was shaped with sandpaper of # 1500 or more as necessary. The obtained measurement sample was dried at 100 ° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd., product name) before the tensile modulus. The measurement sample was then transferred into a desiccator and cooled to 25 ° C.

As a measuring apparatus, a small tabletop testing machine “EZTest” (manufactured by Shimadzu Corporation, product name) was used. In addition, 500N was used as a load cell. In addition, the specimen gripping tool was attached up and down so that the main axis of the measurement sample coincided with the tensile direction passing through the center line of the specimen gripping tool. A measurement sample was set on the test piece gripper and pulled at a speed of 0.5 mm / min. The measurement temperature was 25 ° C., and the measurement was terminated when a load exceeding 500 N was applied or when the measurement sample was destroyed. Here, the strain ε was obtained from the following equation.
ε = Δd / d1
In the equation, Δd represents the displacement (mm) of the tensile force of the measurement sample due to the load, and d1 represents the distance (mm) between the clamps of the measurement sample before applying the load.
The tensile stress σ (kPa) was obtained from the following formula.
σ = F / A
In the formula, F represents the tensile force (N), and A represents the cross-sectional area (mm ² ) of the measurement sample before applying a load.

The tensile elastic modulus E (kPa) was determined from the following formula in a tensile force range of 0.1 to 0.2N.
E = (σ ₂ −σ ₁ ) / (ε ₂ −ε ₁ )
In the formula, σ ₁ represents a tensile stress (kPa) measured at a tensile force of 0.1 N, σ ₂ represents a tensile stress (kPa) measured at a tensile force of 0.2 N, and ε ₁ represents a tensile stress. The tensile strain measured at σ ₁ is shown, and ε ₂ shows the tensile strain measured at the tensile stress σ ₂ .

(3) Measurement of signal area ratio concerning silicon-containing bonding units Q, T and D Measurement was performed using “FT-NMR AV400WB” (product name, manufactured by Bruker BioSpin Corporation) as a solid ²⁹ Si-NMR apparatus. It was. The measurement conditions were: measurement mode: DD / MAS method, probe: 4 mmφ CPMAS probe, magnetic field: 9.4 T, resonance frequency: 79 Hz, MAS rotation speed: 6 kHz, delay time: 150 seconds. As a standard sample, sodium 3-trimethylsilylpropionate was used.

As a measurement sample, an airgel finely cut was prepared, packed in a ZrO ₂ rotor, mounted on a probe, and measured. Further, in the spectrum analysis, the line broadening coefficient was set to 2 Hz, and the signal area ratio (Q + T: D) relating to the obtained silicon-containing binding units Q, T, and D was obtained.

(4) Measurement of density and porosity The center pore diameter, density and porosity of airgel continuous pores (pores) in airgel were measured by mercury porosimetry according to DIN 66133. The measurement temperature was room temperature (25 ° C.), and Autopore IV9520 (manufactured by Shimadzu Corporation, product name) was used as the measurement apparatus.

  In addition, FIG. 1 is a figure which shows the measurement chart at the time of measuring the thermal conductivity of the airgel of Example 10 under atmospheric pressure using a stationary method thermal conductivity measuring apparatus. According to FIG. 1, it can be seen that the airgel according to Example 10 has a thermal conductivity of 0.020 W / m · K at 25 ° C.

  Moreover, FIG. 2 is a figure which shows the stress-strain curve of the airgel of Example 1. FIG. From FIG. 2, it can be calculated that the tensile modulus at 25 ° C. of the airgel according to Example 5 is 7.1 kPa.

From Table 2, it can be read that each of the airgels of the examples has a heat conductivity of 0.03 W / m · K or less and a tensile modulus of 20 kPa or less, and has heat insulating properties and flexibility. Also, airgel embodiment, the measured solid ²⁹ Si-NMR spectrum using the DD / MAS method, the silicon-bonded unit Q, the signal area ratio according to the T and D Q + T: D is 1: 0.01 The range was 1: 0.5.

  On the other hand, Comparative Examples 1 and 4 have a thermal conductivity of 0.03 W / m · K or less, but they were easily broken because of their large tensile elastic modulus and brittleness against deformation. In Comparative Example 2, the thermal conductivity was large. Comparative Example 3 had sufficient flexibility but high thermal conductivity.

  The airgel of the present invention has an excellent heat insulation, which has a thermal conductivity of 0.03 W / m · K or less and a tensile elastic modulus of 20 kPa or less at 25 ° C. under atmospheric pressure, which is difficult to achieve with conventional aerogels. Has flexibility and flexibility. Because of such advantages, it can be preferably applied to applications as a heat insulating material in the construction field, automobile field, home appliances, semiconductor field, industrial equipment and the like. Moreover, the airgel of this invention can be utilized as a coating additive, cosmetics, an antiblocking agent, a catalyst support body etc. other than the use as a heat insulating material.

Claims (15)

  An airgel having a thermal conductivity of 0.03 W / m · K or less and a tensile elastic modulus of 20 kPa or less at 25 ° C. under atmospheric pressure. In the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method, when the silicon-containing binding units Q, T and D are defined as follows, the signal area derived from Q and T, and the signal derived from D The airgel according to claim 1, wherein a ratio Q + T: D to the area is 1: 0.01 to 1: 0.5.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
[However, the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom. ] The airgel of Claim 1 or 2 which has a structure represented by following General formula (1).

[In Formula (1), R ₁ and R ₂ each independently represent an alkyl group or an aryl group, and R ₃ and R ₄ each independently represent an alkylene group. ] The airgel of Claim 1 or 2 which has a ladder type structure provided with a support | pillar part and a bridge part, and the said bridge part is represented by following General formula (2).

[In Formula (2), R ₆ and R ₇ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. ] The airgel of Claim 4 which has a structure represented by following General formula (3).

[In Formula (3), R ₅ , R ₆ , R ₇ and R ₈ each independently represents an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b represents 1 to 50 Indicates an integer. ]   The wet gel produced from the sol containing at least one selected from the group consisting of a polysiloxane compound having a reactive group in the molecule and a hydrolysis product of the polysiloxane compound is dried. 2. The airgel according to 2.   The airgel according to claim 6, wherein the reactive group is a hydroxyalkyl group.   The airgel according to claim 7, wherein the hydroxyalkyl group has 1 to 6 carbon atoms. The airgel according to claim 7 or 8, wherein the polysiloxane compound is represented by the following general formula (4).

[In formula (4), R ₉ represents a hydroxyalkyl group, R ₁₀ represents an alkylene group, R ₁₁ and R ₁₂ each independently represents an alkyl group or an aryl group, and n represents an integer of 1 to 50. . ]   The airgel according to claim 6, wherein the reactive group is an alkoxy group.   The airgel of Claim 10 whose carbon number of the said alkoxy group is 1-6. The airgel according to claim 10 or 11, wherein the polysiloxane compound is a polysiloxane compound represented by the following general formula (5).

[In the formula (5), R ₁₄ represents an alkyl group or an alkoxy group, R ₁₅ and R ₁₆ each independently represents an alkoxy group, R ₁₇ and R ₁₈ each independently represent an alkyl group or an aryl group, m Represents an integer of 1 to 50. ]   The sol further contains at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group in the molecule and a hydrolysis product of the silicon compound. The airgel described.   The airgel according to any one of claims 6 to 13, wherein the drying is performed at a temperature lower than a critical point of a solvent used for drying and at atmospheric pressure.   The airgel according to any one of claims 6 to 13, wherein the drying is supercritical drying.