JPWO2020084668A1 - Airgel composite material - Google Patents

Abstract

A dried product of a wet gel comprising a base material having a porous structure and an airgel attached to the base material, wherein the airgel is a condensate of a sol containing a hydrolysis product of a silane oligomer. An airgel composite material in which the ratio of silicon atoms bonded to three oxygen atoms to the total number of silicon atoms in the silane oligomer is 50% or more.

Description

The present invention relates to a novel airgel composite material, and more particularly to an airgel composite material suitably used as a heat insulating material for construction, cryogenic containers, high temperature containers, and the like.

In recent years, as the demand for comfort and energy saving in living spaces has increased, the shape of the heat insulating object has become complicated, and the installation space for the heat insulating material has tended to become narrow. Therefore, the heat insulating materials used for them are required to further improve the heat insulating performance and reduce the thickness.

As a conventional heat insulating material, a foamable heat insulating material such as urethane foam or phenol foam is known. However, since these materials have higher thermal conductivity than air, it is necessary to develop a material having better heat insulating property than air in order to further improve the heat insulating property.

As a heat insulating material having better heat insulating properties than air, there is a heat insulating material in which the voids forming the foam are filled with a low thermal conductive gas by using chlorofluorocarbon or a chlorofluorocarbon alternative foaming agent, but the low thermal conductive gas leaks due to deterioration over time. There is a possibility that the heat insulating performance may be deteriorated (for example, Patent Document 1 below).

Further, a vacuum heat insulating material having a core material using an inorganic fiber and a phenol resin binder is known (for example, Patent Document 2 below). However, the vacuum heat insulating material has a problem that the heat insulating performance is remarkably deteriorated due to problems such as deterioration over time or scratches on the packing bag, and further, the heat insulating material is not flexible from the viewpoint of vacuum packing and cannot be applied to a curved surface.

Japanese Patent No. 4084516 Japanese Patent No. 4898157 U.S. Pat. No. 4,402,927 Japanese Unexamined Patent Publication No. 2011-93744

Currently, airgel is known as a material having the lowest thermal conductivity at normal pressure (for example, Patent Document 3 above). Since the airgel has a finely porous structure, the movement of gas such as air is suppressed, so that the heat conduction is reduced. However, general airgel has a problem in productivity.

For example, as a method for producing airgel, a supercritical drying method is known in which a gel-like compound (alcogel) obtained by hydrolyzing alkoxysilane and polymerizing it is dried under supercritical conditions of a dispersion medium (supercritical drying method). For example, see Patent Document 3). In the supercritical drying method, an arcogel and a dispersion medium (solvent used for drying) are introduced into a high-pressure container, and the dispersion medium is made into a supercritical fluid by applying a temperature and pressure above the critical point to obtain a supercritical fluid, which is contained in the arcogel. It is a method of removing the solvent. However, since the supercritical drying method requires a high-pressure process, it requires capital investment in special equipment that can withstand supercriticality, and also requires a lot of labor and time.

Therefore, a method of drying the arcogel by 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 obtained arcogel by using monoalkyltrialkoxysilane and tetraalkoxysilane in a specific ratio as a gel raw material and drying at normal pressure is known. (See, for example, Patent Document 4). However, when such atmospheric drying is adopted, the gel tends to shrink due to the stress caused by the capillary force inside the arcogel.

In addition, general airgel has a problem that it is very brittle and difficult to handle. As a method for solving such a problem of the conventional heat insulating material, an airgel sheet using an airgel and a reinforcing material has been devised. However, since the airgel itself is brittle, there is a problem of workability such that the airgel (airgel powder or the like) falls off from the sheet due to impact or bending work.

The present invention has been made in view of the above circumstances, is easy to manufacture, has excellent heat insulating properties by adhering an airgel whose volume shrinkage is suppressed during drying, and prevents the airgel from falling off. It is an object of the present invention to provide an airgel composite material that can be suppressed.

As a result of intensive studies to achieve the above object, the present inventors have suppressed drying shrinkage during drying from a wet gel which is a condensate of a sol containing a hydrolysis product of a specific silane oligomer. It was found that the aerogel can be easily obtained, and since the aerogel has excellent heat insulating properties and flexibility, it is possible to form a composite material in which the aerogel is less likely to fall off by adhering to a substrate having a porous structure. Was found, and the present invention was completed.

The present disclosure comprises a substrate having a porous structure and an airgel attached to the substrate, and the airgel is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a silane oligomer. The present invention provides an airgel composite material in which the ratio of silicon atoms bonded to three oxygen atoms to the total number of silicon atoms in the silane oligomer is 50% or more.

In the airgel composite material of the present disclosure, the weight average molecular weight of the silane oligomer may be 200 or more and 10,000 or less. As a result, the volume shrinkage when the wet gel is dried is further suppressed. In the present specification, the weight average molecular weight of the silane oligomer indicates the weight average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC).

In the airgel composite material of the present disclosure, the silane oligomer may have an alkoxy group, and the content of the alkoxy group may be 2% by mass or more and 60% by mass or less based on the total amount of the silane oligomer. As a result, the volume shrinkage of the airgel during drying is further suppressed.

In the airgel composite material of the present disclosure, the sol may further contain silica particles. As a result, even better heat insulating properties and flexibility can be obtained.

In the airgel composite material of the present disclosure, the average primary particle size of the silica particles may be 1 to 500 nm. This makes it easier to further improve heat insulation and flexibility.

In the airgel composite material of the present disclosure, the pores in the porous structure may be communication holes, and the total volume of the pores may be 50 to 99% by volume of the total volume of the base material. This makes it easier to further improve the heat insulating property.

In the airgel composite material of the present disclosure, the airgel may be filled in the communication holes. As a result, heat conduction due to air is suppressed, and the heat insulating property is more likely to be improved.

In the airgel composite material of the present disclosure, the base material having the porous structure may be a sheet made of a fibrous substance having a diameter of 0.1 to 1000 μm. As a result, heat conduction by the fibers can be suppressed, and sufficient voids are secured, so that the impregnation property of the sol into the sheet is improved.

The airgel composite material of the present disclosure can be in a mode in which the airgel is attached to the fibrous substance. In this case, the airgel existing at the intersection of the fibrous substances can suppress the heat conduction between the fibrous substances, and the heat insulating property can be further improved.

According to the present invention, an airgel composite material that is easy to manufacture, has excellent heat insulating properties by adhering an airgel whose volume shrinkage is suppressed during drying, and can suppress the airgel from falling off. Can be provided.

1 (a), 1 (b) and 1 (c) are cross-sectional views showing embodiments of an airgel composite material, respectively.

Hereinafter, preferred embodiments of the present invention will be described. This will be described in detail. However, the present invention is not limited to the following embodiments. In the present specification, the numerical range indicated by using "~" indicates a range including the numerical values before and after "~" as the minimum value and the maximum value, respectively. "A or B" may include either A or B, and may include both. Unless otherwise specified, the materials exemplified in this embodiment may be used alone or in combination of two or more. In the present specification, the content of each component in the composition is the total amount of the plurality of substances present in the composition unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition. means.

<Airgel composite material>
The airgel composite material of the present embodiment includes a base material having a porous structure (porous base material) and airgel attached to the base material. The airgel is a dried product of a wet gel (wet gel derived from the sol) which is a condensate of a sol containing a hydrolysis product of a silane oligomer. That is, the airgel is obtained by drying a wet gel produced from a sol containing a hydrolysis product of a silane oligomer. Further, in the present embodiment, the ratio of the silicon atom bonded to the three oxygen atoms to the total number of silicon atoms in the silane oligomer is 50% or more.

The airgel composite material of the present embodiment may have, for example, a porous base material and an airgel layer that covers at least a part of the porous base material. 1 (a), 1 (b) and 1 (c) are cross-sectional views showing an embodiment of an airgel composite material. The airgel composite material 100 shown in FIG. 1 (a), the airgel composite material 200 shown in FIG. 1 (b), and the airgel composite material 300 shown in FIG. 1 (c) include a porous base material 10 and an airgel layer 20. ing. In FIG. 1A, the inside of the porous base material 10 is filled with airgel, and the entire porous base material 10 is covered with the airgel layer 20. In FIG. 1B, the airgel layer 20 is arranged on the surface of the porous base material 10. In FIG. 1 (c), the inside of the porous base material 10 is filled with airgel, and the airgel forms the airgel layer 20 inside the porous base material 10.

In the airgel composite material of the present embodiment, since airgel which is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a specific silane oligomer is used, both heat insulating properties and flexibility are compatible. be able to. In particular, the conventional airgel has excellent heat insulating properties but is brittle, so that it is difficult to handle. Can be improved.

The thickness of the airgel layer can be, for example, 200 μm or less, 100 μm or less, 80 μm or less, 50 μm or less, or 30 μm or less. By setting the thickness of the airgel layer to 200 μm or less, powder falling is easily suppressed and the handleability tends to be further improved. The thickness of the airgel layer can be, for example, 1 μm or more, 3 μm or more, 5 μm or more, or 10 μm or more.

The thickness of the airgel composite material of the present embodiment may be, for example, 100 mm or less, 10 mm or less, or 1 mm or less. By setting the thickness of the airgel composite material to 100 mm or less, the airgel composite material is easily cut and the workability is improved.

(Airgel)
In a narrow sense, airgel is a dry gel obtained by using the supercritical drying method for wet gel, xerogel is a dry gel obtained by drying under atmospheric pressure, and cryogel is a dry gel obtained by freeze-drying. However, in the present embodiment, the obtained low-density dry gel is referred to as "airgel" regardless of these drying methods of the wet gel. That is, in the present embodiment, the airgel means "Gel compressed of a microporous solid in which the dispersed phase is a gas" (a gel composed of a microporous solid in which the dispersed phase is a gas), which is an airgel in a broad sense. Is what you do. Generally, the inside of an airgel has a mesh-like fine structure, and has a cluster structure in which airgel components (particles constituting the airgel) of about 2 to 20 nm are bonded. There are pores of less than 100 nm between the skeletons formed by these clusters. As a result, the airgel has a three-dimensionally fine porous structure. The airgel in the present embodiment is, for example, a silica airgel containing silica as a main component. Examples of the silica airgel include a so-called organic-inorganic hybridized silica airgel in which an organic group (methyl group or the like) or an organic chain is introduced. For example, the airgel layer in this embodiment is a layer composed of airgel. The airgel layer may be a layer containing an airgel having a structure derived from polysiloxane.

The airgel of the present embodiment is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a silane oligomer. That is, the airgel of the present embodiment is obtained by drying a wet gel produced from a sol containing a hydrolysis product of a silane oligomer. The condensate may be obtained by a condensation reaction of a hydrolysis product.

The airgel layer may be a layer composed of a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a silane oligomer. That is, the airgel layer may be composed of a layer formed by drying a wet gel produced from a sol containing a hydrolysis product of a silane oligomer.

The sol is a state before the gelation reaction occurs, and in the present embodiment, it means a state in which a silicon compound containing a hydrolysis product of a silane oligomer is dissolved or dispersed in a liquid medium. .. The wet gel means a wet gel solid that contains a liquid medium but does not have fluidity.

The airgel of the present embodiment may be produced, for example, by the production method shown below.

<Manufacturing method of airgel>
The airgel of the present embodiment has a sol generation step of hydrolyzing a silane oligomer to produce a sol containing a hydrolysis product of the silane oligomer, and a wet gel production step of gelling the sol to obtain a wet gel. , It may be manufactured by a manufacturing method including a drying step of drying a wet gel to obtain an airgel. In this production method, the ratio of silicon atoms bonded to three oxygen atoms to the total number of silicon atoms in the silane oligomer is 50% or more.

The method for producing an airgel of the present embodiment may further include a washing step of washing (and, if necessary, solvent substitution) the wet gel obtained in the wet gel forming step. In the present embodiment, by using an appropriate catalyst and solvent in the sol formation step and the wet gel formation step, such a washing step can be omitted and the airgel can be manufactured. By omitting the cleaning process, process simplification and cost reduction can be achieved.

(Sol generation process)
The sol formation step is a step of hydrolyzing a silane oligomer to form a sol containing a hydrolysis product of the silane oligomer.

A silane oligomer is a polymer of a silane monomer and has a structure in which a plurality of silicon atoms are linked via oxygen atoms. In the present specification, the silane oligomer represents a polymer having 2 to 100 silicon atoms in one molecule. The silane oligomer may be, for example, one or more polymers of the silane monomer described later, and is preferably a polymer of the silane monomer containing an alkyltrialkoxysilane.

The silicon atom contained in the silane oligomer is a silicon atom bonded to one oxygen atom (M unit), a silicon atom bonded to two oxygen atoms (D unit), and a silicon atom bonded to three oxygen atoms (M unit). It can be distinguished into a silicon atom (Q unit) bonded to four oxygen atoms (T unit). Examples of the M unit, the D unit, the T unit, and the Q unit include the following equations (M), (D), (T), and (Q), respectively.

In the above formula, R represents an atom (hydrogen atom or the like) or an atomic group (alkyl group or the like) other than the oxygen atom bonded to silicon. Information on the content of these units can be obtained by Si-NMR.

In the silane oligomer, the ratio of T units to the total number of silicon atoms is 50% or more, preferably 60% or more, more preferably 70% or more, and may be 100%.

The silane oligomer preferably has an alkyl group or an aryl group as R in the above formulas (M), (D), (T) and (Q).

Examples of the alkyl group include an alkyl group having 1 to 6 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group and the like, of which a methyl group and an ethyl group are preferable, and a methyl group is more preferable.

Examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. As the aryl group, a phenyl group is preferable.

The silane oligomer has a hydrolyzable functional group, and it is considered that this hydrolyzable functional group is hydrolyzed to generate a silanol group in the sol formation step. Examples of the hydrolyzable functional group include an alkoxy group. Specific examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group and the like, and a methyl group and an ethoxy group are preferable from the viewpoint of the reaction rate of the hydrolysis reaction.

The content of the hydrolyzable functional group may be, for example, 2% by mass or more, preferably 10% by mass or more, and more preferably 20% by mass or more based on the total amount of the silane oligomer. The content of the hydrolyzable functional group may be, for example, 60% by mass or less, preferably 50% by mass or less, and more preferably 45% by mass or less, based on the total amount of the silane oligomer. According to such a silane oligomer, volume shrinkage in the drying step can be further suppressed.

The weight average molecular weight of the silane oligomer may be, for example, 200 or more, preferably 400 or more, and more preferably 600 or more. The weight average molecular weight of the silane oligomer may be, for example, 10,000 or less, preferably 7,000 or less, and more preferably 5,000 or less. According to such a silane oligomer, volume shrinkage in the drying step can be further suppressed. In the present specification, the weight average molecular weight of the silane oligomer indicates the weight average molecular weight in terms of standard polystyrene measured by gel permeation chromatography (GPC).

Commercially available products may be used as the silane oligomer, and for example, XR31-B1410, XC96-B0446 (all manufactured by Momentive), KR-500, KR-515, X-40-9225, KC-89S (all are manufactured by Momentive). , Shin-Etsu Chemical Co., Ltd.), SR-2402, AY42-163 (all manufactured by Toray Dow Coating Co., Ltd.) and the like.

In the sol formation step, silicon compounds other than the silane oligomer may be further subjected to hydrolysis. Examples of other silicon compounds include silane monomers having a hydrolyzable functional group or a condensable functional group. Examples of the hydrolyzable functional group include the same groups as those exemplified as the hydrolyzable functional groups of the silane oligomer. Examples of the condensable functional group include a silanol group. The silane monomer can also be said to be a silicon compound having no siloxane bond (Si—O—Si).

Examples of the silane monomer having a hydrolyzable functional group include monoalkyltrialkoxysilane, monoaryltrialkoxysilane, monoalkyldialkoxysilane, monoaryldialkoxysilane, dialkyldialkoxysilane, diaryldialkoxysilane, and mono. Examples thereof include alkyl monoalkoxysilanes, monoarylmonoalkoxysilanes, dialkylmonoalkoxysilanes, diarylmonoalkoxysilanes, trialkylmonoalkoxysilanes, triarylmonoalkoxysilanes, and tetraalkoxysilanes. Specifically, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltrietoshisisilane, methyldimethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, tetraethoxy. Examples include silane.

Examples of the silane monomer having a condensable functional group include silanetetraol, methylsilanetriol, dimethylsilanediol, phenylsilanetriol, phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol, hexylsilanetriol and octyl. Examples thereof include silanetriol, decylsilanetriol, trifluoropropylsilanetriol and the like.

The silane monomer may further have a reactive group different from the hydrolyzable functional group and the condensing functional group. Examples of the reactive group include an epoxy group, a mercapto group, a glycidoxy group, a vinyl group, an acryloyl group, a methacryloyl group, an amino group and the like. The epoxy group may be contained in an epoxy group-containing group such as a glycidoxy group.

Examples of the silane monomer having a hydrolyzable functional group and a reactive group include vinyl trimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, and 3-methacryloxypropyltri. Methoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N -2- (Aminoethyl) -3-aminopropylmethyldimethoxysilane and the like can be mentioned.

Examples of the silane monomer having a condensable functional group and a reactive group include vinylsilanetriol, 3-glycidoxypropylsilanetriol, 3-glycidoxypropylmethylsilanediol, 3-methacryloxypropylsilanetriol, 3-. Methacryloxypropylmethylsilanediol, 3-acryloxypropylsilanetriol, 3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilanediol, N-phenyl-3-aminopropylsilanetriol, N-2- (aminoethyl)- Examples thereof include 3-aminopropylmethylsilanediol.

Further, the silane monomer may have two or more silicon atoms, and examples of such a silane monomer include bistrimethoxysilylmethane, bistrimethoxysilylethane, and bistrimethoxysilylhexane.

Other silicon compounds include polysiloxane compounds having a hydrolyzable reactive group or a condensable functional group (provided that the ratio of T units is less than 50% or the number of silicon atoms exceeds 100). Can be mentioned. Examples of the hydrolyzable reactive group and the condensable functional group include the same groups as described above.

Among the above polysiloxane compounds, examples of the polysiloxane compound having a hydroxyalkyl group include those having a structure represented by the following general formula (A). By using the polysiloxane compound having the structure represented by the following general formula (A), the structures represented by the general formulas (1) and (1a) described later can be introduced into the skeleton of the airgel. ..

In the formula (A), R ^1a represents a hydroxyalkyl group, R ^2a represents an alkylene group, R ^3a and R ^4a independently represent an alkyl group or an aryl group, and n represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. In the formula (A), the two R ^1a may be the same or different, and similarly, the two R ^2a may be the same or different. Further, in the formula (A), two or more R ^3a may be the same or different, and similarly, two or more R ^4a may be the same or different.

In the formula (A), R ^1a includes a hydroxyalkyl group having 1 to 6 carbon atoms, and examples of the hydroxyalkyl group include a hydroxyethyl group and a hydroxypropyl group. Further, in the formula (A), R ^2a includes an alkylene group having 1 to 6 carbon atoms, and examples of the alkylene group include an ethylene group and a propylene group. Further, in the formula (A), R ^3a and R ^4a independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and examples of the alkyl group include a methyl group and the like. Further, in the formula (A), n can be 2 to 30, but may be 5 to 20.

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

Among the above polysiloxane compounds, examples of the polysiloxane compound having an alkoxy group include those having a structure represented by the following general formula (B). By using a polysiloxane compound having a structure represented by the following general formula (B), a ladder-type structure having a bridging portion represented by the general formula (2) or (3) described later can be formed in the airgel skeleton. Can be introduced in.

In formula (B), R ^1b represents an alkyl group, an alkoxy group or an aryl group, R ^2b and R ^3b each independently represent an alkoxy group, and R ^4b and R ^5b each independently represent an alkyl group or an aryl group. , M represent an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. In the formula (B), the two R ^1bs may be the same or different, and the two R 2 ^bs may be the same or different, and similarly, the two Rs may be different. ^{Each of 3b} may be the same or different. Further, in the equation (B), when m is an integer of 2 or more, the two or more R ^4b may be the same or different, and similarly, the two or more R ^5b are also the same. May be different.

In the formula (B), ^{examples of R 1b} include an alkyl group having 1 to 6 carbon atoms and an alkoxy group having 1 to 6 carbon atoms, and examples of the alkyl group or alkoxy group include a methyl group, a methoxy group and an ethoxy group. And so on. Further, in the formula (B), R ^2b and R ^3b independently include an alkoxy group having 1 to 6 carbon atoms, and examples of the alkoxy group include a methoxy group and an ethoxy group. Further, in the formula (B), R ^4b and R ^5b independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and examples of the alkyl group include a methyl group and the like. Further, in the formula (B), m can be 2 to 30, but may be 5 to 20.

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

Further, as the polysiloxane compound having an alkoxy group, for example, a silicate oligomer such as a methyl silicate oligomer or an ethyl silicate oligomer can be used. Examples of such a silicate oligomer include methyl silicate 51, methyl silicate 53A, ethyl silicate 40, and ethyl silicate 48 (all manufactured by Corcote Co., Ltd.).

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

The proportion of the above-mentioned silane oligomer among the silicon compounds subjected to hydrolysis in the sol formation step may be, for example, 5% by mass or more, preferably 10% by mass or more, and more preferably 20% by mass or more.

When the above-mentioned silane monomer is further used as the silicon compound in the sol formation step, the amount of the silane monomer may be 2000 parts by mass or less, preferably 1000 parts by mass or less, based on 100 parts by mass of the silane oligomer. It is preferably 500 parts by mass or less. The amount of the silane monomer may be, for example, 1 part by mass or more, preferably 10 parts by mass or more, and more preferably 50 parts by mass or more with respect to 100 parts by mass of the silane oligomer. By using such an amount of silane monomer, the flexibility and toughness of the airgel are improved, and the volume shrinkage in the drying step tends to be more easily suppressed.

When the above-mentioned polysiloxane compound is further used as the silicon compound in the sol formation step, the amount of the polysiloxane compound may be 100 parts by mass or less, preferably 50 parts by mass or less, based on 100 parts by mass of the silane oligomer. , More preferably 25 parts by mass or less. The addition of the polysiloxane compound may improve the flexibility and toughness of the airgel.

In the sol formation step, for example, a silicon compound containing a silane oligomer can be hydrolyzed in a solvent. As the solvent, for example, water or a mixed solvent containing water and alcohol can be used. Examples of the alcohol include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol and the like. Among these, methanol, ethanol, 2-propanol and the like, which are alcohols having a low surface tension and a low boiling point, are preferable in terms of reducing the interfacial tension with the gel wall. These may be used alone or in combination of two or more.

From the viewpoint of omitting the washing step, the solvent is preferably a mixed solvent containing water and alcohol. At this time, the mixing ratio of water and alcohol is not particularly limited, but for example, the volume ratio of alcohol to water (alcohol / water) may be 1 or more, preferably 1.5 or more, and more preferably 2 or more. .. The volume ratio may be, for example, 100 or less, preferably 50 or less, and more preferably 10 or less.

Further, a solvent having a low surface tension can be further added to the above-mentioned mixed solvent. Examples of the solvent having a low surface tension include those having a surface tension of 30 mN / m or less at 20 ° C. The surface tension may be 25 mN / m or less, or 20 mN / m or less. Examples of low surface tension solvents 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); benzene Aromatic hydrocarbons such as (28.9), toluene (28.5), m-xylene (28.7), p-xylene (28.3); 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) ), Isopropyl ether (17.7), butyl ethyl ether (20.8), 1,2-dimethoxyethane (24.6) and other ethers; acetone (23.3), methyl ethyl ketone (24.6), methyl Ketones such as propyl ketone (25.1), diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2) ), Ethers such as isobutyl acetate (23.7) and ethyl butyrate (24.6) (the values in parentheses indicate the surface tension at 20 ° C., and the unit is [mN / m]). Among these, aliphatic hydrocarbons (hexane, heptane, etc.) have low surface tension and are excellent in working environment. The above solvent may be used alone or in combination of two or more.

In the sol formation step, an acid catalyst may be further added to the solvent in order to promote the hydrolysis reaction.

Acid catalysts include inorganic acids such as hydrofluoric acid, hydrochloric acid, nitrate, sulfuric acid, sulfite, phosphoric acid, phosphite, hypophosphoric acid, bromic acid, chloric acid, chloric acid, hypochlorous acid; acidic phosphoric acid. Acidic phosphates such as aluminum, acidic magnesium phosphate, 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, azelaic acid, etc. And so on. Among these, an organic carboxylic acid can be mentioned as an acid catalyst in which the water resistance of the obtained airgel is further improved. Examples of the organic carboxylic acid include acetic acid, but formic acid, propionic acid, oxalic acid, malonic acid and the like may be used. Further, from the viewpoint of omitting the cleaning step, it is preferable to use acetic acid, formic acid or the like as the acid catalyst.

The amount of the acid catalyst added is not particularly limited, but can be, for example, 0.001 to 10 parts by mass with respect to 100 parts by mass of the total amount of the silicon compound.

In the sol formation step, as shown in Japanese Patent No. 5250900, a surfactant, a thermohydrolyzable compound and the like can be added to the solvent. However, from the viewpoint of omitting the cleaning step, it is desirable not to add the surfactant and the thermohydrolyzable compound.

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

As the nonionic surfactant, for example, a compound containing a hydrophilic part such as polyoxyethylene and a hydrophobic part mainly composed of an alkyl group, a compound containing a hydrophilic part such as polyoxypropylene, and the like can be used. Examples of the compound containing a hydrophilic portion such as polyoxyethylene and a hydrophobic portion mainly composed of an alkyl group include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether and the like. Examples of the compound containing a hydrophilic portion such as polyoxypropylene include polyoxypropylene alkyl ether and block copolymers of polyoxyethylene and polyoxypropylene.

Examples of the ionic surfactant include a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. Examples of the cationic surfactant include cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, and examples of the anionic surfactant include sodium dodecylsulfonate and the like. Examples of the amphoteric surfactant include amino acid-based surfactants, betaine-based surfactants, amine oxide-based surfactants, and the like. Examples of the amino acid-based surfactant include acylglutamic acid and the like. Examples of the betaine-based surfactant include betaine lauryldimethylaminoacetate and betaine stearyldimethylaminoacetate. Examples of the amine oxide-based surfactant include lauryldimethylamine oxide.

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 step described later. It is believed that. In the present embodiment, when a mixed solvent containing water and alcohol is used as the solvent, it is considered that the alcohol has the same effect as the above-mentioned effect of the surfactant, and the wet gel is not added with the surfactant. Can be suitably produced.

It is believed that the thermally hydrolyzable compound generates a base catalyst by thermal hydrolysis to make the reaction solution basic and promote the sol-gel reaction in the wet gel formation step described later. Therefore, the thermally hydrolyzable compound is not particularly limited as long as it is a compound capable of making the reaction solution basic after hydrolysis, and 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 can be mentioned. Among these, urea is particularly likely to obtain the above-mentioned promoting effect.

In the sol generation step, components such as carbon graphite, aluminum compound, magnesium compound, silver compound, and titanium compound may be added to the solvent for the purpose of suppressing heat ray radiation. Further, in the sol formation step, silica particles described later may be added to the solvent.

Hydrolysis in the sol formation step depends on the type and amount of the silicon compound, acid catalyst, etc. in the mixed solution, but may be carried out, for example, in a temperature environment of 20 to 80 ° C. for 10 minutes to 24 hours, 50. It may be carried out for 5 minutes to 8 hours in a temperature environment of about 60 ° C. As a result, the hydrolyzable functional groups in the silicon compound are sufficiently hydrolyzed, and the hydrolyzed product of the silicon compound can be obtained more reliably.

However, when the thermally hydrolyzable compound is added to the solvent, the temperature environment of the sol formation step may be adjusted to a temperature at which the hydrolysis of the thermally hydrolyzable compound is suppressed and the gelation of the sol is suppressed. .. The temperature at this time may be any temperature as long as it can suppress the hydrolysis of the thermally hydrolyzable compound. For example, when urea is used as the thermohydrolyzable compound, the temperature environment in the sol formation step can be 0 to 40 ° C, but it may be 10 to 30 ° C.

In the sol formation step, the silicon compound containing the silane oligomer is hydrolyzed to produce a sol containing the hydrolysis product of the silicon compound. It can also be said that the hydrolyzed product is obtained by hydrolyzing a part or all of the hydrolyzable functional groups of the silicon compound.

(Wet gel formation process)
The wet gel forming step is a step of gelling the sol obtained in the sol forming step to obtain a wet gel. This step may be a step of gelling the sol and then aging to obtain a wet gel. In this step, a base catalyst can be used to promote gelation.

Examples of the base catalyst include carbonates such as calcium carbonate, potassium carbonate, sodium carbonate, barium carbonate, magnesium carbonate, lithium carbonate, ammonium carbonate, copper (II) carbonate, iron (II) carbonate, and silver (I) carbonate; hydrogen carbonate. Hydrogen carbonates such as calcium, potassium hydrogen carbonate, sodium hydrogen carbonate, ammonium hydrogen carbonate; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide; ammonium hydroxide, ammonium fluoride, etc. Ammonium compounds such as ammonium chloride and ammonium bromide; basic sodium phosphate salts such as sodium metaphosphate, sodium pyrophosphate, 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-butylamine, propyl Aliphatic amines such as amines, 3- (methylamino) propylamines, 3- (dimethylamino) propylamines, 3-methoxyamines, dimethylethanolamines, methyldiethanolamines, diethanolamines, triethanolamines; morpholine, N-methylmorpholine , 2-Methylmorpholin, piperazine and its derivatives, piperidine and its derivatives, nitrogen-containing heterocyclic compounds such as imidazole and its derivatives. Among these, ammonium hydroxide (ammonia water) is highly volatile and does not easily remain in the airgel after drying, so that it does not easily impair water resistance, and is excellent in terms of economy. Further, from the viewpoint of omitting the washing step, ammonium hydroxide (water ammonia) is preferable as the base catalyst. The above-mentioned base catalyst may be used alone or in combination of two or more.

By using a base catalyst, the dehydration condensation reaction or the dealcohol condensation reaction of the silicon compound in the sol can be promoted, and the sol can be gelled in a shorter time. In addition, this makes it possible to obtain a wet gel having higher strength (rigidity). In particular, ammonia is highly volatile and does not easily remain in the airgel. Therefore, by using ammonium hydroxide as a base catalyst, an airgel having more excellent water resistance can be obtained.

The amount of the base catalyst added can be 0.1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the silicon compounds used in the sol generation step, but may be 1 to 4 parts by mass. When the amount is 0.1 parts by mass or more, gelation can be performed in a shorter time, and when the amount is 10 parts by mass or less, a decrease in water resistance can be further suppressed.

The gelation of the sol in the wet gel formation step may be carried out in a closed container so that the solvent and the base catalyst do not volatilize. The gelation temperature can be 30 to 90 ° C, but may be 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 having higher strength (rigidity) can be obtained. Further, by setting the gelation temperature to 90 ° C. or lower, volatilization of the solvent (particularly alcohol) can be easily suppressed, so that gelation can be performed while suppressing volume shrinkage.

The aging in the wet gel formation step may be carried out in a closed container so that the solvent and the base catalyst do not volatilize. By aging, the bonds of the components constituting the wet gel are strengthened, and as a result, a wet gel having high strength (rigidity) sufficient to suppress shrinkage during drying can be obtained. The aging temperature can be 30 to 90 ° C, but may be 40 to 80 ° C. By setting the aging temperature to 30 ° C. or higher, a wet gel having higher strength (rigidity) can be obtained, and by setting the aging temperature to 90 ° C. or lower, volatilization of the solvent (particularly alcohol) can be easily suppressed. , It can be gelled while suppressing volume shrinkage.

Since it is often difficult to determine the time when the gelation of the sol is completed, the gelation of the sol and the subsequent aging may be continuously performed in a series of operations.

The gelling time and the aging time can be appropriately set depending on the gelling temperature and the aging temperature. The gelation time can be 10 to 120 minutes, but may be 20 to 90 minutes. By setting the gelation time to 10 minutes or more, it becomes easy to obtain a homogeneous wet gel, and by setting it to 120 minutes or less, the drying step can be simplified from the washing step described later. The total time of the gelling time and the aging time can be 4 to 480 hours as a whole of the gelling and aging steps, but it may be 6 to 120 hours. When the total of the gelling time and the aging time is 4 hours or more, a wet gel having higher strength (rigidity) can be obtained, and when it is 480 hours or less, the aging effect can be more easily maintained.

In order to reduce the density of the obtained airgel or increase the average pore size, the gelation temperature and aging temperature may be increased within the above range, or the total time of gelation time and aging time may be increased within the above range. good. Further, in order to increase the density of the obtained airgel and reduce the average pore diameter, the gelation temperature and the aging temperature are lowered within the above range, and the total time of the gelation time and the aging time is shortened within the above range. You may.

(Washing process)
The washing step is a step of washing the wet gel obtained in the wet gel forming step. In the washing step, solvent substitution may be further carried out in which the washing liquid in the wet gel is replaced with a solvent suitable for the drying conditions (drying step described later).

In the washing step, the wet gel obtained by the wet gel forming step is washed. The washing can be repeated using, for example, water or an organic solvent. At this time, the cleaning efficiency can be improved by heating.

Organic solvents include 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, dimethylsulfoxide, acetic acid, formic acid and various other organic solvents can be used. The above organic solvent may be used alone or in combination of two or more.

In solvent substitution, a solvent having a low surface tension can be used in order to suppress the shrinkage of the gel due to drying. However, low surface tension solvents generally have extremely low mutual solubility in water. Therefore, when a solvent having a low surface tension is used in solvent substitution, examples of the organic solvent used for cleaning include a hydrophilic organic solvent having high intersolubility in both water and a solvent having a low surface tension. The hydrophilic organic solvent used in washing can play a role of preliminary substitution for solvent substitution. Among the above organic solvents, examples of the hydrophilic organic solvent include methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone and the like. Methanol, ethanol, methyl ethyl ketone and the like are excellent in terms of economy.

The amount of water or organic solvent used for washing can be an amount that can be washed by sufficiently substituting the solvent in the wet gel. The amount can be 3 to 10 times the volume of the wet gel.

The temperature environment in washing can be a temperature equal to or lower than the boiling point of the solvent used for washing. For example, when methanol is used, the temperature can be set to about 30 to 60 ° C.

In solvent replacement, the solvent of the washed wet gel is replaced with a predetermined replacement solvent in order to suppress the shrinkage of the airgel in the drying step. At this time, the replacement efficiency can be improved by heating. Specific examples of the replacement solvent include low surface tension solvents, which will be described later, when drying under atmospheric pressure at a temperature below the critical point of the solvent used for drying in the drying step. On the other hand, in the case of supercritical drying, examples of the replacement solvent include ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide and the like, or a solvent obtained by mixing two or more of these.

Examples of the solvent having a low surface tension include a solvent having a surface tension of 30 mN / m or less at 20 ° C. The surface tension may be 25 mN / m or less, or 20 mN / m or less. Examples of low surface tension solvents 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); benzene Aromatic hydrocarbons such as (28.9), toluene (28.5), m-xylene (28.7), p-xylene (28.3); 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) ), Isopropyl ether (17.7), butyl ethyl ether (20.8), 1,2-dimethoxyethane (24.6) and other ethers; acetone (23.3), methyl ethyl ketone (24.6), methyl Ketones such as propyl ketone (25.1), diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2) ), Ethers such as isobutyl acetate (23.7) and ethyl butyrate (24.6) (the values in parentheses indicate the surface tension at 20 ° C., and the unit is [mN / m]). Among these, aliphatic hydrocarbons (hexane, heptane, etc.) have low surface tension and are excellent in working environment. Further, among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, 1,2-dimethoxyethane, etc., it can also be used as an organic solvent at the time of washing. Among these, a solvent having a boiling point of 100 ° C. or lower at normal pressure may be used because it is easy to dry in the drying step described later. The above solvent may be used alone or in combination of two or more.

The amount of the solvent used for the solvent replacement can be an amount that can sufficiently replace the solvent in the wet gel after washing. The amount can be 3 to 10 times the volume of the wet gel.

The temperature environment in the solvent substitution can be a temperature equal to or lower than the boiling point of the solvent used for the substitution. For example, when heptane is used, the temperature can be about 30 to 60 ° C.

In this embodiment, for example, the acid catalyst is an organic carboxylic acid selected from the group consisting of acetic acid, formic acid, and propionic acid, and the solvents are water and alcohol (for example, methanol, ethanol, 2-propanol, n-propanol, t-butanol). By selecting a mixed solvent containing (etc.) and ammonium hydroxide as the base catalyst, the washing step can be omitted. When the washing step is omitted, for example, the airgel is produced by removing the solvent in the wet gel obtained in the wet gel forming step in the drying step.

(Drying process)
In the drying step, the airgel can be obtained by drying the wet gel (which has undergone a washing step if necessary). That is, an airgel obtained by drying a wet gel produced from the above sol can be obtained.

The drying method is not particularly limited, and known atmospheric drying, supercritical drying or freeze-drying can be used. Among these, freeze-drying or supercritical drying can be used from the viewpoint of easy production of low-density airgel. Further, from the viewpoint of low cost production, atmospheric drying can be used. In this embodiment, normal pressure means 0.1 MPa (atmospheric pressure).

The airgel can be obtained by drying the wet gel at a temperature below the critical point of the solvent in the wet gel under atmospheric pressure. The drying temperature varies depending on the type of solvent in the wet gel, but it should be 20 to 180 ° C. in view of the fact that drying at a high temperature accelerates the evaporation rate of the solvent and may cause large cracks in the gel. Can be done. The drying temperature may be 60 to 120 ° C. The drying time varies depending on the volume of the wet gel and the drying temperature, but can be 4 to 120 hours. It should be noted that normal pressure drying also includes accelerating drying by applying a pressure below the critical point within a range that does not impair productivity.

Airgels can also be obtained by supercritical drying of wet gels. Supercritical drying can be performed by a known method. Examples of the method of supercritical drying include a method of removing the solvent at a temperature and pressure equal to or higher than the critical point of the solvent contained in the wet gel. Alternatively, as a method of supercritical drying, the wet gel is immersed in liquefied carbon dioxide under the conditions of, for example, 20 to 25 ° C. and 5 to 20 MPa, so that all or part of the solvent contained in the wet gel is used. Is replaced with carbon dioxide having a lower critical point than the solvent, and then carbon dioxide alone or a mixture of carbon dioxide and a solvent is removed.

The airgel obtained by such atmospheric drying or supercritical drying may be further dried under atmospheric pressure at 105 to 200 ° C. for about 0.5 to 2 hours. This makes it easier to obtain airgels with low density and small pores. Additional drying may be performed at 150 to 200 ° C. under normal pressure.

<Aerogel>
The airgel of the present embodiment is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a silane oligomer. Examples of the airgel of the present embodiment include the following aspects. By adopting these aspects, it becomes easy to obtain an airgel having further excellent heat insulating properties and flexibility. By adopting each aspect, it is possible to obtain an airgel having heat insulating properties and flexibility according to each aspect.

(First aspect)
The airgel according to this embodiment can have a structure represented by the following general formula (1). The airgel according to the present embodiment can have a structure represented by the following general formula (1a) as a structure including a structure represented by the formula (1).

In formulas (1) and (1a), R ¹ and R ² independently represent an alkyl group or an aryl group, and R ³ and R ⁴ each independently represent an alkylene group. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. p represents an integer of 1 to 50. Wherein (1a), two or more of R ¹ may be the or different than a respectively identical, likewise, two or more R ² may be each independently selected from the same. Wherein (1a), two R ³ may be each independently selected from the same, likewise, the two R ⁴ may be each independently selected from the same.

By introducing the structure represented by the above formula (1) or the formula (1a) into the skeleton of the airgel as an airgel component, an airgel having low thermal conductivity and flexibility can be obtained. From this point of view, in the formulas (1) and (1a), R ¹ and R ² independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and the alkyl group is methyl. The group etc. can be mentioned. Further, in the formulas (1) and (1a), R ³ and R ⁴ independently include an alkylene group having 1 to 6 carbon atoms, and examples of the alkylene group include an ethylene group and a propylene group. Be done. In formula (1a), p can be 2 to 30, and may be 5 to 20.

(Second aspect)
The airgel according to the present embodiment can have a ladder type structure including a strut portion and a bridging portion, and the bridging portion can have a structure represented by the following general formula (2). By introducing such a ladder type structure into the skeleton of the airgel as an airgel component, heat resistance and mechanical strength can be improved. In the present embodiment, the "ladder type structure" has two struts and bridges connecting the struts (those having a so-called "ladder" form). Is. In this embodiment, the skeleton of the airgel may have a ladder-type structure, but the airgel may partially have a ladder-type structure.

In formula (2), R ⁵ and R ⁶ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. In the equation (2), when b is an integer of 2 or more, the two or more R ^5s may be the same or different, and similarly, the two or more R ^6s are also the same. May be different.

By introducing the above structure into the skeleton of the airgel, for example, it is more than an airgel having a structure derived from the conventional ladder type silsesquioxane (that is, having a structure represented by the following general formula (X)). It becomes an airgel with excellent flexibility. The silsesquioxane is a polysiloxane having a composition formula: (RSiO _1.5 ) _n , and can have various skeletal structures such as a basket type, a ladder type, and a random type. 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 bridging portion is −O−, but the airgel according to the present embodiment. Then, the structure of the bridging portion is a structure (polysiloxane structure) represented by the above general formula (2). However, the airgel of this embodiment may have a structure derived from silsesquioxane in addition to the structure represented by the general formula (2).

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

The interval between the structure to be the support column and its chain length and the structure to be the bridging part is not particularly limited, but from the viewpoint of further improving heat resistance and mechanical strength, the ladder type structure is described by the following general formula ( It may have a ladder type 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, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. In the equation (3), when b is an integer of 2 or more, the two or more R ^5s may be the same or different, and similarly, the two or more R ^6s are also the same. May be different. Further, in the equation (3), when a is an integer of 2 or more, two or more R ^7s may be the same or different, and similarly, when c is an integer of 2 or more, two or more. R ⁸ may be the same or different.

From the viewpoint of obtaining more excellent flexibility, R ⁵ , R ⁶ , R ⁷ and R ⁸ (however, R ⁷ and R ⁸ are only in the formula (3)) are used in the formulas (2) and (3). Each independently includes an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like, and examples of the alkyl group include a methyl group and the like. Further, in the formula (3), a and c can be independently set to 6 to 2000, respectively, but may be 10 to 1000. Further, in the formulas (2) and (3), b can be 2 to 30, but may be 5 to 20.

(Third aspect)
The airgel according to the present embodiment may further contain silica particles in addition to the airgel component from the viewpoint of further toughening and achieving further excellent heat insulating properties and flexibility. An airgel containing an airgel component and silica particles can also be referred to as an airgel complex. Although the airgel complex is a composite of an airgel component and silica particles, it has a cluster structure that is characteristic of airgel, and is considered to have a three-dimensionally fine porous structure. ..

The airgel containing the airgel component and the silica particles can be said to be a dried product of a wet gel which is a condensate of a sol containing the above-mentioned hydrolysis product of a silicon compound containing a silane oligomer and silica particles. Therefore, the description regarding the first aspect to the second aspect can be appropriately applied mutatis mutandis to the airgel according to this aspect.

The silica particles can be used without particular limitation, and examples thereof include amorphous silica particles. Examples of the amorphous silica particles include fused silica particles, fumed silica particles, colloidal silica particles and the like. Of these, colloidal silica particles have high monodispersity and easily suppress agglomeration in the sol. The silica particles may be silica particles having a hollow structure, a porous structure, or the like.

The shape of the silica particles is not particularly limited, and examples thereof include spherical, cocoon-shaped, and associative types. Of these, by using spherical particles as the silica particles, it becomes easier to suppress aggregation in the sol. The average primary particle size of the silica particles may be 1 nm or more, or 5 nm or more, from the viewpoint that it is easy to impart appropriate strength and flexibility to the airgel and it is easy to obtain an airgel having excellent shrinkage resistance during drying. It may be 20 nm or more. The average primary particle size of the silica particles may be 500 nm or less, 300 nm or less, or 100 nm from the viewpoint of easily suppressing the solid heat conduction of the silica particles and easily obtaining an airgel having excellent heat insulating properties. It may be as follows. From these viewpoints, the average primary particle size of the silica particles may be 1 to 500 nm, 5 to 300 nm, or 20 to 100 nm.

In the present embodiment, the average primary particle size of the silica particles can be obtained by directly observing the aerogel using a scanning electron microscope (hereinafter abbreviated as “SEM”). The "diameter" here means the diameter when the cross section of the particles exposed on the cross section of the airgel is regarded as a circle. Further, the "diameter when the cross section is regarded as a circle" is the diameter of the perfect circle when the area of the cross section is replaced with a perfect circle having the same area. In calculating the average particle size, the diameter of the circle is calculated for 100 particles and the average is taken.

The average particle size of the silica particles can also be measured from the raw material. For example, the biaxial average primary particle size is calculated as follows from the result of observing 20 arbitrary particles by SEM. That is, taking colloidal silica particles dispersed in water having a solid content concentration of about 5 to 40% by mass as an example, a wafer with a pattern wiring was cut into 2 cm squares in a dispersion liquid of colloidal silica particles. After soaking the chips for about 30 seconds, the chips are rinsed with pure water for about 30 seconds and blow-dried with nitrogen. After that, the chip is placed on a sample table for SEM observation, an acceleration voltage of 10 kV is applied, silica particles are observed at a magnification of 100,000 times, and an image is taken. Twenty silica particles are arbitrarily selected from the obtained image, and the average particle size of these particles is taken as the average particle size.

The number of silanol groups per gram of the silica particles may be 10 × 10 ¹⁸ / g or more, or 50 × 10 ¹⁸ / g or more, from the viewpoint of facilitating the acquisition of airgel having excellent shrinkage resistance. , 100 × 10 ¹⁸ pieces / g or more. The number of silanol groups per gram of the silica particles may be 1000 × 10 ¹⁸ / g or less, 800 × 10 ¹⁸ / g or less, or 700 × 10 from the viewpoint of facilitating the acquisition of a homogeneous airgel. It ^{may be 10 18} pieces / g or less. From these viewpoints, the number of silanol groups per gram of the silica particles may be 10 × 10 ^{18 to} 1000 × 10 ¹⁸ / g, or 50 × 10 ^{18 to} 800 × 10 ¹⁸ / g. , 100 × 10 ^{18 to} 700 × 10 ¹⁸ pieces / g.

The content of the silicon compound contained in the sol may be 5 parts by mass or more, or 10 parts by mass or more, based on 100 parts by mass of the total amount of the sol, from the viewpoint of further facilitating good reactivity. May be good. The content of the silicon compound contained in the sol may be 50 parts by mass or less, or 30 parts by mass or less, based on 100 parts by mass of the total amount of the sol, from the viewpoint of further facilitating good compatibility. May be good. From these viewpoints, the content of the silicon compound contained in the sol may be 5 to 50 parts by mass or 10 to 30 parts by mass with respect to 100 parts by mass of the total amount of the sol.

When the sol contains silica particles, the content of the silica particles makes it easy to impart appropriate strength to the airgel, and from the viewpoint of making it easy to obtain an airgel having excellent shrinkage resistance during drying, the total amount of the sol is 100 parts by mass. On the other hand, it may be 1 part by mass or more, or 4 parts by mass or more. The content of the silica particles may be 20 parts by mass or less with respect to 100 parts by mass of the total amount of the sol from the viewpoint that it becomes easy to suppress the solid heat conduction of the silica particles and it becomes easy to obtain an airgel having excellent heat insulating properties. It may be 15 parts by mass or less. From these viewpoints, the content of the silica particles may be 1 to 20 parts by mass or 4 to 15 parts by mass with respect to 100 parts by mass of the total amount of the sol.

(Porous substrate)
"Porous medium" is a general term for materials containing many pores (micropores), and is classified into microporous materials, mesoporous materials, and macroporous materials according to the size of the pores. In terms of form, it is referred to as a "porous substrate" regardless of the size of the pores. Examples of the porous base material include a base material made of a fibrous substance and a base material forming a three-dimensionally complicated skeleton. Specifically, examples of the porous substrate include a non-woven fabric, a porous sheet having a porous structure, and the like. The pores in the porous structure (pores constituting the porous structure) may be communication holes. The communication hole is a state in which the hole (void) inside the porous base material and the hole (void) on the surface of the porous base material are connected to form a network of voids two-dimensionally or three-dimensionally. Means the state of being. The communication holes may be filled with airgel.

The size of the hole indicates the maximum linear distance of the shape formed by the hole on the observation surface when observing a cross section of an arbitrary 10 points of the base material along the surface direction of the base material (direction orthogonal to the thickness direction). .. The hole size can be 0.1 to 1000 μm. When the size is 0.1 μm or more, the sol coating liquid can be easily impregnated. When the size is 1000 μm or less, the airgel can be easily suppressed from falling out from the pores.

The total volume of the pores (porosity, porosity) can be 50 to 99% by volume of the total volume of the base material, 60 to 99% by volume, or 70 to 99% by volume. There may be. This makes it easier to further improve the heat insulating property. When the holes in the porous structure are communication holes, the total volume of the holes may satisfy the above range. The volume of the hole can be obtained based on the following formula.
Porosity (% by volume) = (1-true volume of substrate / apparent volume of substrate) x 100
True volume of the base material: Volume calculated from the density and mass of the base material (materials constituting the base material) Apparent volume of the base material: Volume calculated from the dimensions of the base material

Materials constituting the porous substrate include organic porous materials such as vinyl polymer, polyester, polyacrylonitrile, polysulfone, phenol resin, polyurethane, polyamide, polyimide, and carbon; glass, metal (for example, nickel), and metal oxide. Examples thereof include an inorganic porous body such as (for example, alumina). Examples of the vinyl polymer include polyolefins (for example, polyethylene and polypropylene), cellulose acetate, nitrocellulose, polytetrafluoroethylene, polycarbonate, polystyrene, polyvinyl alcohol, polyacrylic acid ester, polyvinyl acetate and the like. As the material constituting the porous base material, glass, metal or metal oxide (for example, alumina) can be used from the viewpoint of further excellent heat resistance, and glass or alumina can be used from the viewpoint of further reducing the thermal conductivity. Can be used.

In the airgel composite material of the present embodiment, for example, the airgel is present in the void portion of the base material made of a fibrous substance or the base material forming a three-dimensionally complicated skeleton. By adopting such a structure, the movement of air in the thickness direction is suppressed, and the heat insulating property is easily improved. Further, the solid heat conduction path is highly complicated by filling with airgel, which is effective in reducing the heat conductivity.

The porous base material may be a sheet made of a fibrous substance (nonwoven fabric, fiber sheet, etc.). In such a porous substrate, for example, airgel is attached to a fibrous substance.

Fibrous substances include organic fibers such as nylon, polyester, polypropylene, polyacrylonitrile, vinylon, polyolefin, polyurethane, rayon, and carbon fibers; inorganic fibers such as glass, rock wool, and ceramics; copper, iron, stainless steel, gold, and silver. , Metallic fibers such as aluminum and the like. As the fibrous material, inorganic fibers can be used from the viewpoint of further excellent heat resistance, and glass, rock wool or ceramic can be used from the viewpoint of further reducing the thermal conductivity.

The diameter (fiber diameter) of the fibrous substance can be 0.1 to 1000 μm, may be 0.1 to 100 μm, or may be 0.1 to 80 μm. As a result, heat conduction by the fibers can be easily suppressed, and sufficient voids are secured, so that the impregnation property of the sol into the sheet is improved. The diameter of the fibrous material can be observed with a microscope and measured as an average value of the diameters of 10 arbitrarily selected fibers.

<Manufacturing method of airgel composite material>
The method for producing the airgel composite material is not particularly limited, but may be, for example, the following method.

The airgel composite material can be produced, for example, by a production method including an impregnation step of impregnating the porous substrate or the material of the porous substrate with a sol containing a hydrolysis product of a silane oligomer. The manufacturing method can also be said to be a method in which an impregnation step is provided between the sol forming step and the wet gel forming step in the above-mentioned airgel manufacturing method. That is, the production method includes a sol generation step of hydrolyzing a silane oligomer to produce a sol containing a hydrolysis product of the silane oligomer, an impregnation step of impregnating a porous substrate with the sol, and a sol. It may include a wet gel producing step of gelling to obtain a wet gel, and a drying step of drying the wet gel to obtain an airgel.

When using a porous substrate made of a fibrous substance, the fibrous substance is prepared by dispersing the fibrous substance in a sol in advance and then performing the above-mentioned wet gel forming step and drying step to prepare a fibrous substance to which airgel is attached. Then, by making this into a non-woven fabric, it can be made into an airgel composite material.

In the fibrous substance to which the airgel is attached, the bonding mode such as the bond between the functional group on the fiber surface and the functional group on the airgel surface by chemical interaction and the bond between the fiber surface and the airgel by the molecular interaction is limited. It's not something to do. Airgel particles (particles constituting the airgel) may be attached to a part or the whole of the fiber surface.

The impregnation step may be, for example, a step of impregnating the porous base material with the sol or adhering the sol to the material of the porous base material (for example, the raw material fiber of the non-woven fabric). Examples of the impregnation step include a dipping method in which the porous base material or its material is immersed in the sol, or a coating method in which the sol is applied to the porous base material. The impregnation method is not limited, and a suitable method can be selected according to the physical properties such as the size, shape, and elastic modulus of the porous substrate.

Regarding the method of treating the sol into the raw material fiber of the non-woven fabric, for example, a wet method in which the fiber is placed in a container containing the sol and heated and stirred for a predetermined time to surface-treat the fiber, and a wet method in which the fiber is stirred at high speed with a stirrer. A dry method in which a sol is added to uniformly treat the fiber surface can be mentioned. The method for treating the sol on the fiber is not particularly limited, but a wet method can be used because the sol can be easily treated uniformly on the fiber surface.

As a coating method (coating machine), a die coater, a comma coater, a bar coater, a kiss coater, a roll coater, etc. can be used, and are appropriately used depending on the material or thickness of the porous base material, the viscosity of the sol coating liquid, the coating amount, and the like. ..

Separators can be laminated on both sides of the porous substrate. By laminating the separator, it is possible to prevent the transfer or contamination of the uncured sol in the transport of the porous base material and other steps. Examples of the method of laminating the separator in the impregnation step include a method of laminating after impregnating the sol. Examples of the separator include inorganic fibers such as glass non-woven fabric and glass cloth; organic fibers such as polyimide, polyamide-imide and polyester; base film made of polyolefin, polyester, polycarbonate, polyimide and the like; release paper; copper foil, aluminum foil and the like. Metal leaf can be mentioned. In addition to the matte treatment and the corona treatment, the separator may be subjected to a mold release treatment.

The airgel composite material of the present embodiment described above is an airgel which is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a specific silane oligomer (a wet gel produced from the above sol). It is provided with a dried airgel) and a base material having a porous structure, and has excellent heat insulating properties, and can be made into a sheet or board of airgel, which has been difficult to handle in the past. From such an advantage, the airgel composite material of the present embodiment can be applied to applications as a heat insulating material in an ultra-low temperature container, a space field, a building field, an automobile field, a home appliance field, a semiconductor field, an industrial facility, and the like. In addition to the use as a heat insulating material, the airgel composite material of the present embodiment can be used for water repellency, sound absorption, static vibration, catalyst support, and the like.

(Example 1)
[Sol coating liquid 1]
100 parts by mass of "XR31-B1410" (manufactured by Momentive Performance Materials Japan LLC, product name) as a silane oligomer, and tetraethoxysilane "KBE-04" (manufactured by Shin-Etsu Chemical Industry Co., Ltd., product name) as a silane monomer. , Hereinafter abbreviated as "TEOS") by 50 parts by mass, 2-propanol by 300 parts by mass, and water by 100 parts by mass, acetic acid as an acid catalyst was added by 0.1 parts by mass, and the temperature was 25 ° C. for 4 hours. It was reacted. To this, 80 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating solution 1.
[Aerogel sheet 1]
Put the above sol coating liquid 1 in a bat, and put a glass non-woven fabric (length) 300 mm x (width) 200 mm x (thickness) 3 mm (manufactured by Nippon Sheet Glass Co., Ltd., product name: MGP BMS-5, fiber diameter: 1.5 μm, voids). Rate: 90% by volume) was placed on the sol coating solution 1 and impregnated with the sol coating solution 1. After confirming that the sol coating liquid 1 was sufficiently impregnated into the glass non-woven fabric and the glass non-woven fabric was submerged in the sol coating liquid, gelation was performed at 60 ° C. for 30 minutes to obtain an aerogel sheet. Then, the obtained airgel sheet (wet gel) was transferred to a closed container and aged at 60 ° C. for 12 hours. Then, the aged airgel sheet was dried at 120 ° C. for 6 hours under normal pressure to obtain an airgel sheet 1.

(Example 2)
[Sol coating liquid 2]
A sol coating liquid 2 was obtained in the same manner as in Example 1 except that "SR-2402" (manufactured by Toray Dow Corning Co., Ltd., product name) was used as the silane oligomer.
[Airgel sheet 2]
Using the sol coating liquid 2, an airgel sheet 2 was obtained in the same manner as in Example 1.

(Example 3)
[Sol coating liquid 3]
A sol coating solution 3 was obtained in the same manner as in Example 1 except that "AY42-163" (manufactured by Toray Dow Corning Co., Ltd., product name) was used as the silane oligomer.
[Airgel sheet 3]
Using the sol coating liquid 3, an airgel sheet 3 was obtained in the same manner as in Example 1.

(Example 4)
[Sol coating liquid 4]
100 parts by mass of "KC-89S" (manufactured by Shin-Etsu Chemical Co., Ltd., product name) as a silane oligomer, 200 parts by mass of 2-propanol, and 50 parts by mass of water are mixed, and acetic acid is 0 as an acid catalyst. .15 parts by mass was added, and the mixture was reacted at 25 ° C. for 4 hours. To this, 60 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating liquid 4.
[Airgel sheet 4]
Using the sol coating liquid 4, an airgel sheet 4 was obtained in the same manner as in Example 1.

(Example 5)
[Sol coating liquid 5]
100 parts by mass of "KR-500" (manufactured by Shin-Etsu Chemical Industry Co., Ltd., product name) as a silane oligomer, and tetraethoxysilane "KBE-04" (manufactured by Shin-Etsu Chemical Industry Co., Ltd., product name, hereinafter "TEOS"" as a silane monomer. 100 parts by mass of (abbreviated as), 250 parts by mass of 2-propanol, and 80 parts by mass of water were mixed, 0.15 parts by mass of acetic acid was added as an acid catalyst, and the mixture was reacted at 25 ° C. for 4 hours. To this, 90 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating solution 5.
[Aerogel sheet 5]
The airgel sheet 5 was prepared in the same manner as in Example 1 except that the sol coating liquid 5 was used and the glass non-woven fabric Boroid GMU (manufactured by Olivest Co., Ltd., product name, fiber diameter: 13 μm, porosity: 95% by volume) was used. Obtained.

(Example 6)
[Sol coating liquid 6]
100 parts by mass of "KR-515" (manufactured by Shin-Etsu Chemical Co., Ltd., product name) as a silane oligomer, and tetraethoxysilane "KBE-04" (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter "TEOS") as a silane monomer. 20 parts by mass, dimethyldiethoxysilane "KBE-22" (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter abbreviated as "DMDES") by 20 parts by mass, 2-propanol by 300 parts by mass, and 80 parts by mass of water was mixed, 0.12 parts by mass of acetic acid was added as an acid catalyst, and the mixture was reacted at 25 ° C. for 4 hours. To this, 90 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating solution 6.
[Airgel sheet 6]
While using the above sol coating liquid 6, instead of the glass non-woven fabric, a porous nickel sheet: Celmet (manufactured by Sumitomo Electric Co., Ltd., product name, thickness: 1.4 mm, nickel grain amount: 420 g / m ² , porosity: 97 An airgel sheet 6 was obtained in the same manner as in Example 1 except that (% by volume) was used.

(Example 7)
[Sol coating liquid 7]
100 parts by mass of "XR31-B1410" (manufactured by Momentive Performance Materials Japan GK, product name) as a silane oligomer, dimethyldiethoxysilane "KBE-22" (manufactured by Shin-Etsu Chemical Co., Ltd., product name, below) 70 parts by mass of "DMDES"), 300 parts by mass of 2-propanol, and 80 parts by mass of water were mixed, 0.1 part by mass of acetic acid was added as an acid catalyst, and the mixture was reacted at 25 ° C. for 4 hours. rice field. 80 parts by mass of aqueous ammonia having a concentration of 5% was added thereto as a base catalyst to obtain a sol coating solution 7.
[Airgel sheet 7]
In a flask, 100 parts by mass of glass fiber ECS03T-187 (manufactured by Nippon Electric Glass Co., Ltd., product name, fiber diameter: 13 μm) is added to 100 parts by mass of the sol coating solution 7, and the temperature is 25 ° C. for 10 minutes at 200 rpm. After stirring, the obtained glass fiber dispersion sol was transferred to a closed container and aged at 60 ° C. for 8 hours. Then, the drying step was carried out in the same manner as in Example 1 to obtain glass fibers to which airgel was attached.
40 L of a dispersion liquid consisting of the obtained glass fiber, water, and 0.1% by mass of a surfactant (polyoxyethylene lauryl ether) was prepared, and the dispersion liquid was put into a making apparatus. As a papermaking device, a device consisting of an upper papermaking tank (capacity 30 L) equipped with a rotor-equipped stirrer and a lower water storage tank (capacity 10 L), and a porous support provided between the papermaking tank and the water storage tank is used. board. First, the dispersion liquid was stirred using a stirrer until microbubbles of air were generated. Then, the glass fiber whose mass was adjusted so as to have a desired texture was put into a dispersion liquid in which air bubbles were dispersed and stirred to obtain a slurry in which the glass fiber to which the airgel was attached was dispersed. Next, the slurry was sucked from the water storage tank and dehydrated through the porous support to obtain a fiber papermaking product. The above-mentioned paper machine was dried in a hot air dryer under the conditions of 150 ° C. for 2 hours ^{to obtain an airgel sheet 7 having a grain size of 100 g / m 2} and a porosity of 90% by volume.

(Example 8)
[Sol coating liquid 8]
100 parts by mass of "XR31-B1410" (manufactured by Momentive Performance Materials Japan GK, product name) as a silane oligomer, methyltrimethoxysilane "KBM-13" (manufactured by Shin-Etsu Chemical Industry Co., Ltd., product name, below) 200 parts by mass of "MTMS"), 50 parts by mass of tetraethoxysilane "KBE-04" (manufactured by Shinetsu Chemical Industry Co., Ltd., product name, hereinafter abbreviated as "TEOS"), 800 parts by mass of 2-propanol, Then, 200 parts by mass of water was mixed, 0.5 part by mass of acetic acid was added as an acid catalyst, and the mixture was reacted at 25 ° C. for 4 hours. To this, 200 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating liquid 8.
[Airgel sheet 8]
In addition to using the sol coating liquid 8, a porous alumina sheet: AZP60 (manufactured by Aszac Co., Ltd., product name, average thickness: 700 μm, porosity: 60% by volume) was used instead of the glass non-woven fabric. Similarly, an airgel sheet 8 was obtained.

(Comparative Example 1)
[Sol coating liquid 11]
PL-2L (manufactured by Fuso Chemical Industry Co., Ltd., product name, average primary particle diameter: 20 nm, solid content: 20% by mass) is 100.0 parts by mass, water is 120.0 parts by mass, and methanol is used as a silica particle-containing raw material. 80.0 parts by mass and 0.10 parts by mass of acetic acid as an acid catalyst, and methyltrimethoxysilane LS-530 as a silicon compound (manufactured by Shinetsu Chemical Industry Co., Ltd., product name; hereinafter abbreviated as "MTMS"). 60.0 parts by mass and 40.0 parts by mass of dimethyldimethoxysilane LS-520 (manufactured by Shin-Etsu Chemical Industry Co., Ltd., product name; hereinafter abbreviated as "DMDMS") were added, and the mixture was reacted at 25 ° C. for 2 hours. To this, 40.0 parts by mass of aqueous ammonia having a concentration of 5% was added as a base catalyst to obtain a sol coating solution 11.
[Airgel sheet 11]
In addition to using the sol coating liquid 11, a PET film having no porous structure: G2 (manufactured by Teijin DuPont Co., Ltd., product name) is used instead of the glass non-woven fabric, and the sol coating liquid 11 is applied to the PET film by a bar coater. The sol coating liquid was applied so as to have a film thickness of 80 μm. The obtained airgel sheet was transferred to a closed container and aged at 60 ° C. for 12 hours. Then, the aged airgel sheet was immersed in 2000 mL of water and washed for 30 minutes. Next, it was immersed in 2000 mL of methanol and washed at 60 ° C. for 30 minutes. Washing with methanol was performed twice more, replacing with fresh methanol. Next, the mixture was immersed in 2000 mL of methyl ethyl ketone, and the solvent was replaced at 60 ° C. for 30 minutes. Washing with methyl ethyl ketone was performed twice more, replacing with new methyl ethyl ketone. The washed and solvent-substituted airgel sheet was dried at 120 ° C. for 2 hours under normal pressure to obtain a PET core airgel sheet (airgel sheet 11).

(Comparative Example 2)
Instead of the glass non-woven glass, thin plate glass having no porous structure: OA-10G (manufactured by Nippon Electric Glass Co., Ltd., thickness: 150 μm) is used, and the above sol coating liquid 11 is applied to the thin plate glass with a bar coater. A glass core airgel sheet (airgel sheet 12) was obtained in the same manner as in Comparative Example 1 except that the film was applied so as to have a film thickness of 80 μm.

<Various evaluations>
(Measurement of thermal conductivity)
The airgel composite materials obtained in each Example and Comparative Example were measured or evaluated according to the following conditions. The thermal conductivity was measured using a thermal conductivity measuring device HC-074 manufactured by Hideko Seiki Co., Ltd. Using a sample of 20 cm × 20 cm as a measurement sample, the temperature of the upper and lower heat plates was set to 30 ° C. and 10 ° C., respectively, and the thermal conductivity was measured. The results are shown in Table 1.

(Evaluation of powder removal property)
The powder removal property of the airgel composite material (airgel sheet) obtained in each Example and Comparative Example was evaluated. In the evaluation, a plurality of airgel composite materials of the same type were laminated so as to have a thickness of 30 cm in length × 30 cm in width × 10 to 15 mm in height, and the four sides of the laminated airgel composite material in the vertical direction and the horizontal direction were respectively laid on the table. The amount of powder dropped when dropped 5 times each was measured. The height of dropping was set to a height of 5 cm from the table, and dropping vertically was used as a test method for powder dropping property. The results are shown in Table 1.

10 ... Porous substrate, 20 ... Airgel layer, 100, 200, 300 ... Airgel composite material.

Claims (9)

A base material having a porous structure and an airgel attached to the base material are provided.
The airgel is a dried product of a wet gel which is a condensate of a sol containing a hydrolysis product of a silane oligomer.
An airgel composite material in which the ratio of silicon atoms bonded to three oxygen atoms to the total number of silicon atoms in the silane oligomer is 50% or more. The airgel composite material according to claim 1, wherein the weight average molecular weight of the silane oligomer is 200 or more and 10000 or less. The silane oligomer has an alkoxy group and
The airgel composite material according to claim 1 or 2, wherein the content of the alkoxy group is 2% by mass or more and 60% by mass or less based on the total amount of the silane oligomer. The airgel composite material according to any one of claims 1 to 3, wherein the sol further contains silica particles. The airgel composite material according to claim 4, wherein the silica particles have an average primary particle size of 1 to 500 nm. The pores in the porous structure are communication holes,
The airgel composite material according to any one of claims 1 to 5, wherein the total volume of the pores is 50 to 99% by volume of the total volume of the base material. The airgel composite material according to claim 6, wherein the communication holes are filled with the airgel. The airgel composite material according to any one of claims 1 to 7, wherein the base material having a porous structure is a sheet made of a fibrous substance having a diameter of 0.1 to 1000 μm. The airgel composite material according to claim 8, wherein the airgel is attached to the fibrous substance.

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