JP7163967B2 - airgel composite - Google Patents

Description

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

In recent years, amid increasing demand for comfort in living spaces and energy saving, the shapes of objects to be insulated have become more complex, and the space where heat insulating materials are installed tends to become narrower. Therefore, heat insulating materials used for such devices are required to have further improved heat insulating performance and to be thinner.

Foamed heat insulating materials such as urethane foam and phenol foam are known as conventional heat insulating materials. However, since these materials have a higher thermal conductivity than air, in order to further improve the thermal insulation properties, it is necessary to develop materials that are superior in thermal insulation properties to air.

As a heat insulating material that has better heat insulating properties than air, there is a heat insulating material in which the voids forming the foam are filled with low thermal conductivity gas by using Freon or Freon substitute foaming agents, etc. However, due to deterioration over time, leakage of low heat conductive gas There is a possibility of this, and there is a concern that the heat insulation performance will be lowered (for example, Patent Document 1 below).

A vacuum heat insulating material having a core material using inorganic fibers and a phenol resin binder is also known (for example, Patent Document 2 below). However, with vacuum insulation materials, there are problems such as deterioration over time and damage to the packaging bag, resulting in a significant decrease in insulation performance. Furthermore, there is a problem that the insulation cannot be applied to curved surfaces due to the lack of flexibility of vacuum packaging.

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

Airgel is currently known as a material with the lowest thermal conductivity at normal pressure (for example, Patent Document 3 above). Airgel has a microporous structure, which suppresses the movement of gases such as air, thereby reducing heat conduction. However, general airgel has a problem in productivity.

For example, as a method for producing airgel, a supercritical drying method is known in which alkoxysilane is hydrolyzed and a gel compound (alcogel) obtained by polymerization is dried under the supercritical conditions of the dispersion medium ( For example, see Patent Document 3). In the supercritical drying method, the alcogel and the dispersion medium (solvent used for drying) are introduced into a high-pressure vessel, and the temperature and pressure above the critical point are applied to the dispersion medium to make it a supercritical fluid. It is a method of removing the solvent that is However, since the supercritical drying method requires a high-pressure process, it requires investment in special equipment that can withstand supercriticality, and much labor and time.

Therefore, a technique for drying the 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 is known in which monoalkyltrialkoxysilane and tetraalkoxysilane are used together in a specific ratio as gel raw materials to improve the strength of the resulting alcogel, followed by drying at normal pressure. (see Patent Document 4, for example). However, when such normal pressure drying is employed, the gel tends to shrink due to the stress caused by the capillary force inside the alcogel.

In addition, there is also the problem that general airgel is very fragile and difficult to handle. An airgel sheet using airgel and a reinforcing material has been devised as a method for solving such problems of conventional heat insulating materials. However, since the airgel itself is fragile, there is a workability problem that the airgel (airgel powder, etc.) 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 insulation by attaching an airgel with suppressed volume shrinkage 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.

The present inventors have made intensive studies to achieve the above object, and have found that a wet gel, which is a condensate of a sol containing a hydrolysis product of a specific silane oligomer, can suppress drying shrinkage during drying. In addition, since the airgel has excellent heat insulation and flexibility, it can be attached to a substrate having a porous structure to form a composite material with less airgel falling off. and completed the present invention.

The present disclosure comprises a substrate having a porous structure and an airgel attached to the substrate, wherein the airgel is a dried wet gel that is a condensate of a sol containing a hydrolysis product of a silane oligomer. and wherein 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 silane oligomer may have a weight average molecular weight of 200 or more and 10,000 or less. This further suppresses volumetric shrinkage during drying of the wet gel. In addition, in this 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. This further suppresses volumetric shrinkage of the airgel during drying.

In the airgel composite material of the present disclosure, the sol may further contain silica particles. This provides even better insulation and flexibility.

In the airgel composite material of the present disclosure, the silica particles may have an average primary particle size of 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 continuous pores, and the total volume of the pores may be 50-99% by volume of the total volume of the substrate. This makes it easier to further improve the heat insulation.

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

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

The airgel composite material of the present disclosure may have a mode in which the airgel is attached to the fibrous substance. In this case, the airgel present at the intersections of the fibrous substances can suppress the heat conduction between the fibrous substances, further facilitating the improvement of the heat insulating properties.

According to the present invention, it is easy to manufacture, has excellent heat insulation by attaching an airgel with suppressed volume shrinkage during drying, and can suppress the falling off of the airgel composite material. can be provided.

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

Preferred embodiments of the present invention are described below. I will explain in detail. However, the present invention is not limited to the following embodiments. In this specification, a numerical range indicated using "to" indicates a range including the numerical values before and after "to" as the minimum and maximum values, respectively. "A or B" may include either one of A and B, and may include both. The materials exemplified in this embodiment can be used singly or in combination of two or more unless otherwise specified. As used herein, the content of each component in the composition refers to the total amount of the multiple substances present in the composition unless otherwise specified when there are multiple substances corresponding to each component 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) that is a condensate of a sol containing hydrolysis products of silane oligomers. That is, the airgel is obtained by drying a wet gel produced from a sol containing hydrolysis products of silane oligomers. In this embodiment, 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 of this embodiment may have, for example, a porous substrate and an airgel layer covering at least a portion of the porous substrate. 1(a), 1(b) and 1(c) are cross-sectional views illustrating embodiments of airgel composites. 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. ing. In FIG. 1( a ), the inside of the porous substrate 10 is filled with airgel, and the entire porous substrate 10 is covered with the airgel layer 20 . In FIG. 1(b), an airgel layer 20 is arranged on the surface of the porous substrate 10. In FIG. In FIG. 1( c ), the inside of the porous substrate 10 is filled with airgel, and the airgel forms an airgel layer 20 inside the porous substrate 10 .

The airgel composite material of the present embodiment uses an airgel that is a dry product of a wet gel that is a condensate of a sol containing a hydrolysis product of a specific silane oligomer, so that both heat insulation and flexibility are achieved. be able to. In particular, conventional airgel has excellent heat insulation but is brittle, so handling is difficult, whereas in the airgel composite material of the present embodiment, flexibility is improved by using the above-mentioned specific airgel. can be improved.

The thickness of the airgel layer may be, for example, 200 μm or less, may be 100 μm or less, may be 80 μm or less, may be 50 μm or less, or may be 30 μm or less. By setting the thickness of the airgel layer to 200 μm or less, there is a tendency that powder fall-off is easily suppressed and handleability is further improved. The thickness of the airgel layer may be, for example, 1 μm or more, may be 3 μm or more, may be 5 μm or more, or may be 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 workability is improved.

(aerogel)
In a narrow sense, a dry gel obtained by supercritical drying of a wet gel is called aerogel, a dry gel obtained by drying under atmospheric pressure is called xerogel, and a dry gel obtained by freeze-drying is called cryogel. However, in the present embodiment, the resulting low-density dried gel is referred to as an "aerogel" regardless of these drying techniques for wet gels. That is, in the present embodiment, airgel is aerogel in a broad sense, meaning "Gel comprised 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)". It is something to do. In general, the inside of an airgel has a network-like fine structure, and has a cluster structure in which airgel components (particles constituting the airgel) of about 2 to 20 nm are bonded. Between the frameworks formed by these clusters are pores less than 100 nm. As a result, the airgel has a three-dimensionally fine porous structure. In addition, the airgel in this embodiment is, for example, a silica airgel containing silica as a main component. Silica airgel includes, for example, so-called organic-inorganic hybridized silica airgel into which an organic group (such as a methyl group) or an organic chain is introduced. For example, the airgel layer in this embodiment is a layer made of airgel. The airgel layer may be a layer containing airgel having a structure derived from polysiloxane.

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

The airgel layer may be a layer composed of a dried wet gel that is a condensate of a sol containing hydrolysis products of silane oligomers. That is, the airgel layer may be composed of a layer obtained by drying a wet gel produced from a sol containing hydrolysis products of silane oligomers.

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. . A wet gel means a gel solid in a wet state that does not have fluidity even though it contains a liquid medium.

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

<Method for producing airgel>
The airgel of the present embodiment includes a sol-generating step of hydrolyzing a silane oligomer to generate a sol containing a hydrolysis product of the silane oligomer, and a wet-gel-generating step of gelling the sol to obtain a wet gel. , and a drying step of drying the 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 optionally replacing the solvent) the wet gel obtained in the wet gel production step. In addition, in the present embodiment, by using an appropriate catalyst and solvent in the sol generation step and the wet gel generation step, the airgel can be produced by omitting such a washing step. By omitting the cleaning step, process simplification and cost reduction can be achieved.

(Sol generation step)
The sol-generating step is a step of hydrolyzing the silane oligomer to generate a sol containing a hydrolysis product of the silane oligomer.

A silane oligomer is a polymer of silane monomers and has a structure in which a plurality of silicon atoms are linked via oxygen atoms. As used herein, a silane oligomer refers to a polymer having 2 to 100 silicon atoms per molecule. The silane oligomer may be, for example, a polymer of one or two or more silane monomers, which will be described later, and is preferably a polymer of silane monomers containing an alkyltrialkoxysilane.

The silicon atoms contained in the silane oligomer include a silicon atom bonded to one oxygen atom (M unit), a silicon atom bonded to two oxygen atoms (D unit), a silicon atom bonded to three oxygen atoms ( T units) and silicon atoms bonded to four oxygen atoms (Q units). The following formulas (M), (D), (T) and (Q) can be exemplified as M units, D units, T units and Q units, respectively.

In the above formula, R represents an atom other than an oxygen atom bonded to silicon (such as a hydrogen atom) or an atomic group (such as an alkyl group). 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 formulas (M), (D), (T) and (Q) above.

Examples of alkyl groups include alkyl groups having 1 to 6 carbon atoms. Specific examples of the alkyl group include methyl group, ethyl group, propyl group, butyl group, etc. Among these, methyl group and ethyl group are preferred, and methyl group is more preferred.

Aryl groups include phenyl groups, substituted phenyl groups, and the like. Substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups, cyano groups and the like. A phenyl group is preferred as the aryl group.

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

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. Also, 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. Such a silane oligomer can further suppress volumetric shrinkage during the drying process.

The weight average molecular weight of the silane oligomer may be, for example, 200 or more, preferably 400 or more, more preferably 600 or more. Also, 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. Such a silane oligomer can further suppress volumetric shrinkage during the drying process. In addition, in this 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 silane oligomers may be used, for example, XR31-B1410, XC96-B0446 (all manufactured by Momentive), KR-500, KR-515, X-40-9225, KC-89S (all , manufactured by Shin-Etsu Chemical Co., Ltd.), SR-2402, AY42-163 (both manufactured by Toray Dow Coating Co., Ltd.), and the like.

In the sol-forming step, silicon compounds other than the silane oligomer may be further subjected to hydrolysis. Other silicon compounds include, for example, silane monomers having hydrolyzable functional groups or condensable functional groups. As the hydrolyzable functional group, the same groups as those exemplified as the hydrolyzable functional group possessed by the silane oligomer can be exemplified. A silanol group is mentioned as a condensable functional group. The silane monomer can also be said to be a silicon compound that does not have a siloxane bond (Si--O--Si).

Silane monomers having a hydrolyzable functional group include, for example, monoalkyltrialkoxysilanes, monoaryltrialkoxysilanes, monoalkyldialkoxysilanes, monoaryldialkoxysilanes, dialkyldialkoxysilanes, diaryldialkoxysilanes, mono Examples include alkylmonoalkoxysilanes, monoarylmonoalkoxysilanes, dialkylmonoalkoxysilanes, diarylmonoalkoxysilanes, trialkylmonoalkoxysilanes, triarylmonoalkoxysilanes, tetraalkoxysilanes, and the like. Specifically, methyltrimethoxysilane, methyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, methyldimethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane, tetraethoxysilane. Silane etc. are mentioned.

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

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

Silane monomers having hydrolyzable functional groups and reactive groups include, for example, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltri methoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N -2-(aminoethyl)-3-aminopropylmethyldimethoxysilane and the like.

Silane monomers having condensable functional groups and reactive groups include, for example, vinylsilanetriol, 3-glycidoxypropylsilanetriol, 3-glycidoxypropylmethylsilanediol, 3-methacryloxypropylsilanetriol, 3- methacryloxypropylmethylsilanediol, 3-acryloxypropylsilanetriol, 3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilanediol, N-phenyl-3-aminopropylsilanetriol, N-2-(aminoethyl)- 3-aminopropylmethylsilanediol and the like.

Also, the silane monomers may have two or more silicon atoms, and such silane monomers include bistrimethoxysilylmethane, bistrimethoxysilylethane, bistrimethoxysilylhexane, and the like.

Other silicon compounds include polysiloxane compounds having hydrolyzable reactive groups or condensable functional groups (provided that the proportion of T units is less than 50%, or the number of silicon atoms exceeds 100). is 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 a polysiloxane compound having a 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 formula (A), R ^1a represents a hydroxyalkyl group, R ^2a represents an alkylene group, R ^3a and R ^4a each independently represent an alkyl group or an aryl group, and n represents an integer of 1-50. Here, the aryl group includes a phenyl group, a substituted phenyl group, and the like. Substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups, cyano groups and the like. In formula (A), two R ^1a may be the same or different, and two R ^2a may be the same or different. In formula (A), two or more R ^3a may be the same or different, and two or more R ^4a may be the same or different.

In 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. In 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. In formula (A), R ^3a and R ^4a each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like, and the alkyl group includes a methyl group and the like. In formula (A), n can range from 2 to 30, but may range from 5 to 20.

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

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 is formed in the skeleton of the airgel. can be introduced into

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 represents an integer from 1 to 50. Here, the aryl group includes a phenyl group, a substituted phenyl group, and the like. Substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups, cyano groups and the like. In formula (B), two R ^1b may be the same or different, two R ^2b may be the same or different, and similarly two R ^3b may be the same or different. In formula (B), when m is an integer of 2 or more, two or more R ^4b may be the same or different, and similarly two or more R ^5b may be the same. may also be different.

In formula (B), R ^1b includes an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like, and the alkyl group or alkoxy group includes a methyl group, a methoxy group, and an ethoxy group. etc. In formula (B), R ^2b and R ^3b each independently include an alkoxy group having 1 to 6 carbon atoms, and the alkoxy group includes a methoxy group, an ethoxy group, and the like. In formula (B), R ^4b and R ^5b each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like, and the alkyl group includes a methyl group and the like. In formula (B), m can range from 2 to 30, but may range from 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 and JP-A-2012-233110. .

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 also be used. Examples of such silicate oligomers include methyl silicate 51, methyl silicate 53A, ethyl silicate 40, and ethyl silicate 48 (all manufactured by Colcoat Co., Ltd.).

In addition, 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 its hydrolysis product are mixed. may be Moreover, in the polysiloxane compound having an alkoxy group, all the alkoxy groups in the molecule may be hydrolyzed or partially hydrolyzed.

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

In the sol generation step, when the above-mentioned silane monomer is further used as the silicon compound, the amount of the silane monomer may be 2000 parts by mass or less, preferably 1000 parts by mass or less, or more, relative to 100 parts by mass of the silane oligomer. Preferably, it is 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 during the drying process tends to be more easily suppressed.

In the sol-generating step, when the above polysiloxane compound is further used as the silicon compound, the amount of the polysiloxane compound may be 100 parts by mass or less, preferably 50 parts by mass or less, relative to 100 parts by mass of the silane oligomer. , more preferably 25 parts by mass or less. The addition of polysiloxane compounds may improve the flexibility and toughness of the airgel.

In the sol generation 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 alcohol include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol and the like. Among these, methanol, ethanol, 2-propanol, etc., which are alcohols having a low surface tension and a low boiling point, are preferable from the viewpoint 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. . Also, the volume ratio may be, for example, 100 or less, preferably 50 or less, and more preferably 10 or less.

A low surface tension solvent can also be added to the above mixed solvent. Low surface tension solvents 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 (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 ), 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) and diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2) ), isobutyl acetate (23.7), ethyl butyrate (24.6), and the like (surface tension at 20° C. is shown in parentheses, 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 solvents may be used alone or in combination of two or more.

In the sol-producing 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, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, and hypochlorous 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, an organic carboxylic acid can be mentioned as an acid catalyst that further improves the water resistance of the resulting airgel. The organic carboxylic acid includes acetic acid, but may also be formic acid, propionic acid, oxalic acid, malonic acid, or the like. From the viewpoint of omitting the washing step, it is preferable to use acetic acid, formic acid, or the like as the acid catalyst.

The amount of the acid catalyst to be 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 thermally hydrolyzable compound, etc. can be added to the solvent. However, from the viewpoint of omitting the washing step, it is desirable not to add the surfactant and the thermally hydrolyzable compound.

As surfactants, nonionic surfactants, ionic surfactants, 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 portion such as polyoxyethylene and a hydrophobic portion mainly composed of an alkyl group, a compound containing a hydrophilic portion such as polyoxypropylene, and the like can be used. Examples of compounds containing a hydrophilic portion such as polyoxyethylene and a hydrophobic portion mainly composed of alkyl groups include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether and the like. Compounds containing hydrophilic moieties such as polyoxypropylene include polyoxypropylene alkyl ethers, block copolymers of polyoxyethylene and polyoxypropylene, and the like.

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

These surfactants act to reduce the difference in chemical affinity between the solvent in the reaction system and the growing siloxane polymer in the wet gel formation step described later, thereby suppressing phase separation. It is believed that In the present embodiment, when a mixed solvent containing water and alcohol is used as a solvent, alcohol is considered to have the same effect as the above effect due to the surfactant, and even if the surfactant is not added, the wet gel can be preferably generated.

It is believed that the thermally hydrolyzable compound generates a base catalyst by thermal hydrolysis, makes the reaction solution basic, and promotes the sol-gel reaction in the wet gel formation step described later. Therefore, the thermohydrolyzable compound is not particularly limited as long as it is a compound capable of making the reaction solution basic after hydrolysis. Urea; formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N acid amides such as -methylacetamide and N,N-dimethylacetamide; and cyclic nitrogen compounds such as hexamethylenetetramine. Among these, urea is particularly easy to obtain the above promotion effect.

In the sol-forming step, components such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound may be added to the solvent for the purpose of suppressing heat radiation. Further, in the sol-generating step, silica particles, which will be described later, may be added to the solvent.

The hydrolysis in the sol generation step depends on the types and amounts of the silicon compound, acid catalyst, etc. in the mixed liquid, but may be carried out, for example, in a temperature environment of 20 to 80° C. for 10 minutes to 24 hours. It may be carried out in a temperature environment of ~60°C for 5 minutes to 8 hours. As a result, the hydrolyzable functional groups in the silicon compound are sufficiently hydrolyzed, and the hydrolysis product of the silicon compound can be obtained more reliably.

However, when the thermally hydrolyzable compound is added to the solvent, the temperature environment in the sol formation step may be adjusted to a temperature that suppresses hydrolysis of the thermally hydrolyzable compound and gelation of the sol. . 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 thermally hydrolyzable compound, the temperature environment in the sol formation step can be 0 to 40°C, but may be 10 to 30°C.

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

(Wet gel generation step)
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 it to obtain a wet gel. In this step, a base catalyst can be used to promote gelation.

Basic catalysts 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 carbonate (I); Hydrogen carbonates such as calcium, potassium hydrogen carbonate, sodium hydrogen carbonate and ammonium hydrogen carbonate; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide; ammonium hydroxide, ammonium fluoride, Ammonium compounds such as ammonium chloride and ammonium bromide; basic sodium phosphate salts such as sodium metaphosphate, 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-butylamine, propyl Aliphatic amines such as amine, 3-(methylamino)propylamine, 3-(dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine; morpholine, N-methylmorpholine , 2-methylmorpholine, piperazine and its derivatives, piperidine and its derivatives, imidazole and its derivatives, and other nitrogen-containing heterocyclic compounds. Among these, ammonium hydroxide (aqueous ammonia) is highly volatile and hardly remains in the airgel after drying. Also from the viewpoint of omitting the washing step, ammonium hydroxide (ammonia water) is preferable as the basic catalyst. The above basic catalysts may be used alone or in combination of two or more.

By using a basic catalyst, the dehydration-condensation reaction or the dealcoholization-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 with higher strength (rigidity). In particular, ammonia is highly volatile and does not easily remain in the airgel. Therefore, by using ammonium hydroxide as a basic catalyst, an airgel with more excellent water resistance can be obtained.

The amount of the basic catalyst to be added may be 0.1 to 10 parts by mass, but may be 1 to 4 parts by mass, per 100 parts by mass of the silicon compound used in the sol-forming step. When the amount is 0.1 part by mass or more, gelation can be performed in a shorter time, and when the amount is 10 parts by mass or less, deterioration of water resistance can be further suppressed.

Gelation of the sol in the wet gel formation step may be performed in a sealed container so that the solvent and base catalyst do not volatilize. The gelation temperature can be 30-90°C, but may be 40-80°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. In addition, by setting the gelation temperature to 90° C. or lower, volatilization of the solvent (especially alcohol) can be easily suppressed, so that gelation can be performed while suppressing volume shrinkage.

Aging in the wet gel formation step may be performed in a closed container so that the solvent and basic catalyst do not volatilize. Aging strengthens the bonding of the components constituting the wet gel, and as a result, a wet gel having sufficient strength (rigidity) to suppress shrinkage during drying can be obtained. The aging temperature can be 30-90°C, but may be 40-80°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 alcohol) can be easily suppressed. , it is possible to gel while suppressing volumetric shrinkage.

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

The gelation time and aging time can be appropriately set depending on the gelation temperature and aging temperature. The gelling time can be 10-120 minutes, but can also be 20-90 minutes. A gelation time of 10 minutes or more makes it easier to obtain a homogeneous wet gel, and a gelation time of 120 minutes or less makes it possible to simplify the washing and drying steps, which will be described later. In addition, the total time of the gelling and aging steps can be 4 to 480 hours, but may be 6 to 120 hours. A wet gel with higher strength (rigidity) can be obtained by setting the total time of gelling time and aging time to 4 hours or more, and the effect of aging can be more easily maintained by setting the total time to 480 hours or less.

In order to reduce the density of the resulting airgel and increase the average pore size, the gelation temperature and aging temperature are increased within the above range, or the total time of gelation time and aging time is increased within the above range. good. In addition, in order to increase the density of the resulting airgel and reduce the average pore size, the gelation temperature and aging temperature are lowered within the above range, and the total time of gelation time and 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 replacement may be further performed to replace the washing liquid in the wet gel with a solvent suitable for the drying conditions (drying step described later).

In the washing step, the wet gel obtained in 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 the like can be used. The above organic solvents may be used alone or in combination of two or more.

In the solvent replacement, a low surface tension solvent can be used in order to suppress shrinkage of the gel due to drying. However, low surface tension solvents generally have very low mutual solubility with water. Therefore, when a low surface tension solvent is used for solvent replacement, the organic solvent used for washing includes hydrophilic organic solvents having high mutual solubility in both water and low surface tension solvents. In addition, the hydrophilic organic solvent used in washing can play a role of pre-replacement for solvent replacement. Among the above organic solvents, hydrophilic organic solvents include methanol, ethanol, 2-propanol, acetone, methyl ethyl ketone and the like. In addition, methanol, ethanol, methyl ethyl ketone, etc. are excellent in terms of economy.

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

The temperature environment for washing can be a temperature below the boiling point of the solvent used for washing.

In the solvent replacement, the solvent in the washed wet gel is replaced with a predetermined replacement solvent in order to suppress the shrinkage of the airgel during the drying process. At this time, the replacement efficiency can be improved by heating. Specific examples of the replacement solvent include low surface tension solvents described below when drying is performed 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, the replacement solvent includes, for example, ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide, or a mixture of two or more thereof.

Solvents with low surface tension include solvents with 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 (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 ), 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) and diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2) ), isobutyl acetate (23.7), ethyl butyrate (24.6), and the like (surface tension at 20° C. is shown in parentheses, and the unit is [mN/m]). Among these, aliphatic hydrocarbons (hexane, heptane, etc.) have low surface tension and are excellent in working environment. Among these, hydrophilic organic solvents such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane can also be used as organic solvents for washing. Among these, a solvent having a boiling point of 100° C. or lower under normal pressure may be used because it can be easily dried in the drying step to be described later. The above solvents may be used alone or in combination of two or more.

The amount of solvent used for solvent replacement can be an amount sufficient to 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 replacement can be a temperature below the boiling point of the solvent used for replacement.

In the present embodiment, for example, an organic carboxylic acid selected from the group consisting of acetic acid, formic acid, and propionic acid as an acid catalyst, water and an alcohol (e.g., methanol, ethanol, 2-propanol, n-propanol, t-butanol) as a solvent etc.) and ammonium hydroxide as the basic 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 production step in the drying step.

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

The method of drying is not particularly limited, and known normal pressure 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 aerogels. Moreover, normal pressure drying can be used from the viewpoint of low-cost production. In addition, in this embodiment, normal pressure means 0.1 MPa (atmospheric pressure).

Aerogels can be obtained by drying a wet gel under atmospheric pressure at a temperature below the critical point of the solvent in the wet gel. The drying temperature varies depending on the type of solvent in the wet gel, but it should be 20 to 180 ° C., especially considering that drying at high temperatures accelerates the evaporation rate of the solvent and may cause large cracks in the gel. can be done. Incidentally, the drying temperature may be 60 to 120°C. Also, 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 speeding up drying by applying a pressure below the critical point within a range that does not impede productivity.

Aerogels can also be obtained by supercritical drying of wet gels. 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 above 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 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 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 the solvent is removed.

The airgel obtained by such normal pressure drying or supercritical drying may be additionally dried at 105 to 200° C. for about 0.5 to 2 hours under normal pressure. This makes it easier to obtain aerogels with low densities 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 wet gel that is a condensate of a sol containing hydrolysis products of silane oligomers. Examples of the airgel of the present embodiment include the following aspects. By adopting these aspects, it becomes easier to obtain an airgel that is even more excellent in heat insulation and flexibility. By adopting each aspect, it is possible to obtain an airgel having thermal insulation 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 this embodiment can have a structure represented by the following general formula (1a) as a structure containing the structure represented by formula (1).

In formulas (1) and (1a), 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 includes a phenyl group, a substituted phenyl group, and the like. Substituents for the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group and the like. p represents an integer from 1 to 50; In formula (1a), two or more R ¹ 's may be the same or different, and two or more R ² 's may be the same or different. In formula (1a), two R ³ may be the same or different, and similarly, two R ⁴ may be the same or different.

By introducing the structure represented by the above formula (1) or formula (1a) as an airgel component into the skeleton of the airgel, a low thermal conductivity and flexible airgel can be obtained. From this point of view, in formulas (1) and (1a), R ¹ and R ² each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like. and the like. In formulas (1) and (1a), R ³ and R ⁴ each 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 2-30, and may be 5-20.

(Second aspect)
The airgel according to the present embodiment can have a ladder-type structure comprising a strut portion and a bridging portion, and the bridging portion can have a structure represented by the following general formula (2). Heat resistance and mechanical strength can be improved by introducing such a ladder structure as an airgel component into the skeleton of the airgel. In the present embodiment, the “ladder structure” refers to a structure having two struts and bridges that connect the struts (having a so-called “ladder” form) is. In this embodiment, the skeleton of the airgel may have a ladder-type structure, or 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 1-50. Here, the aryl group includes a phenyl group, a substituted phenyl group, and the like. Substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups, cyano groups and the like. In formula (2), when b is an integer of 2 or more, two or more R ⁵ may be the same or different, and two or more R ⁶ may also be the same. may also be different.

By introducing the above structure into the skeleton of the airgel, for example, having a structure derived from a conventional ladder-type silsesquioxane (i.e., having a structure represented by the following general formula (X)) airgel than It becomes an airgel with excellent flexibility. Silsesquioxane is a polysiloxane having a compositional formula: (RSiO _1.5 ) _n and can have various skeleton structures such as a cage type, ladder type and random type. In addition, as shown by the following general formula (X), in the airgel having a structure derived from a 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 the structure (polysiloxane structure) represented by the general formula (2). However, the airgel of this aspect may have a structure derived from silsesquioxane in addition to the structure represented by general formula (2).

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

The structure and chain length of the struts, and the spacing of the structure that serves as the bridging portion are not particularly limited. 3) may have a ladder-type structure.

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, b is 1 to 50 Indicates an integer. Here, the aryl group includes a phenyl group, a substituted phenyl group, and the like. Substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups, cyano groups and the like. In formula (3), when b is an integer of 2 or more, two or more R ⁵ may be the same or different, and two or more R ⁶ may also be the same. may also be different. In formula (3), when a is an integer of 2 or more, two or more R ⁷ may be the same or different, and similarly when c is an integer of 2 or more, two or more each R ⁸ may be the same or different.

From the viewpoint of obtaining better flexibility, in formulas (2) and (3), R ⁵ , R ⁶ , R ⁷ and R ⁸ (wherein R ⁷ and R ⁸ are only in formula (3)) each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and the alkyl group includes a methyl group and the like. Further, in formula (3), a and c can be independently 6 to 2,000, but may be 10 to 1,000. In 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 the viewpoint of achieving even better heat insulation and flexibility. An airgel containing an airgel component and silica particles can also be referred to as an airgel composite. The airgel composite has a cluster structure, which is a characteristic of airgel, even though the airgel component and silica particles are composited, and is considered to have a three-dimensionally fine porous structure. .

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

Silica particles can be used without any particular limitation, and include amorphous silica particles and the like. Amorphous silica particles include fused silica particles, fumed silica particles, colloidal silica particles, and the like. Among these, colloidal silica particles have high monodispersity and easily suppress aggregation 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 may be spherical, cocoon-shaped, association-shaped, or the like. Among these, by using spherical particles as the silica particles, aggregation in the sol can be easily suppressed. The average primary particle size of the silica particles may be 1 nm or more, and may be 5 nm or more, from the viewpoint of easily imparting appropriate strength and flexibility to the airgel and easily obtaining an airgel having excellent shrinkage resistance during drying. 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 insulation properties. It may be below. From these viewpoints, the average primary particle size of 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 silica particles can be obtained by directly observing the airgel using a scanning electron microscope (hereinafter abbreviated as "SEM"). The "diameter" as used herein means the diameter when the cross section of the particles exposed in 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 a perfect circle when the area of the cross section is replaced by a perfect circle having the same area. In addition, in calculating the average particle size, the diameters of circles of 100 particles are obtained and the average is taken.

The average particle size of silica particles can also be measured from raw materials. 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 with a normal solid content concentration of about 5 to 40% by mass as an example, a wafer with pattern wiring was cut into 2 cm squares in a dispersion liquid of colloidal silica particles. After dipping the chip for about 30 seconds, the chip is rinsed with pure water for about 30 seconds and dried by blowing nitrogen. After that, the chip is placed on a sample table for SEM observation, an acceleration voltage of 10 kV is applied, the silica particles are observed at a magnification of 100,000 times, and an image is taken. 20 silica particles are arbitrarily selected from the obtained image, and the average particle size of those particles is taken as the average particle size.

The number of silanol groups per 1 g of silica particles may be 10×10 ¹⁸ /g or more, or may be 50×10 ¹⁸ /g or more, from the viewpoint of easily obtaining an airgel having excellent shrinkage resistance. , 100×10 ¹⁸ pieces/g or more. The number of silanol groups per 1 g of silica particles may be 1000 × 10 ¹⁸ / g or less, 800 × 10 ¹⁸ / g or less, from the viewpoint of easily obtaining a homogeneous airgel. It may be 10 ¹⁸ pieces/g or less. From these viewpoints, the number of silanol groups per gram of silica particles may be 10×10 ¹⁸ to 1000×10 ¹⁸ /g, and may be 50×10 ¹⁸ to 800×10 ¹⁸ /g. , 100×10 ¹⁸ to 700×10 ¹⁸ /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 with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of making it easier to obtain good reactivity. good too. 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 with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of making it easier to obtain good compatibility. good too. From these points of view, 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 silica particles are contained in the sol, the content of silica particles makes it easier to impart appropriate strength to the airgel, and from the viewpoint of making it easier to obtain an airgel with 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 may be 4 parts by mass or more. The content of the silica particles is 20 parts by mass or less with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of easily suppressing the solid heat conduction of the silica particles and easily obtaining an airgel with excellent heat insulation. It may be 15 parts by mass or less. From these points of view, the content of 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 substrate" is generally a generic term for materials containing many pores (micropores), and is classified into microporous materials, mesoporous materials and macroporous materials depending on the size of the pores. In terms of morphology, the term "porous substrate" is used regardless of the size of the pores. Examples of porous substrates include substrates made of fibrous substances and substrates forming a three-dimensional and complex skeleton. Specifically, porous substrates include nonwoven fabrics, porous sheets having a porous structure, and the like. The pores in the porous structure (pores forming the porous structure) may be communicating pores. Communicating pores refer to a state in which the pores (voids) inside the porous substrate and the pores (voids) on the surface of the porous substrate are connected, forming a two-dimensional or three-dimensional void network. means that the The communication holes may be filled with airgel.

The above hole size indicates the maximum linear distance of the shape formed by the holes on the observation surface when observing arbitrary 10 cross sections of the substrate along the surface direction of the substrate (direction perpendicular to the thickness direction). . The pore size can be from 0.1 to 1000 μm. If the size is 0.1 μm or more, it can be easily impregnated with the sol coating liquid. If the size is 1000 μm or less, it is possible to easily prevent the airgel from falling out of the pores.

The total volume of the pores (porosity, porosity) can be 50 to 99% by volume of the total volume of the substrate, may be 60 to 99% by volume, and can be 70 to 99% by volume. There may be. This makes it easier to further improve the heat insulation. When the pores in the porous structure are communicating pores, the total volume of the pores may satisfy the above range. The pore volume can be obtained based on the following formula.
Porosity (volume%) = (1 - true volume of substrate / apparent volume of substrate) x 100
True volume of base material: Volume calculated from the density and mass of the base material (material constituting the base material) Apparent volume of 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, phenolic resin, polyurethane, polyamide, polyimide, and carbon; glass, metal (eg, nickel), and metal oxide. (for example, alumina) and other inorganic porous materials. Vinyl polymers include polyolefins (eg, polyethylene and polypropylene), cellulose acetate, nitrocellulose, polytetrafluoroethylene, polycarbonate, polystyrene, polyvinyl alcohol, polyacrylate, polyvinyl acetate, and the like. As the material constituting the porous substrate, 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 thermal conductivity. can be used.

In the airgel composite material of the present embodiment, for example, the airgel is present in the void portions of the base material made of fibrous substances or the base material forming a three-dimensional and complex skeleton. By adopting such a structure, movement of air in the thickness direction is suppressed, and heat insulation is easily improved. Furthermore, the thermal conduction path of the solid is highly complicated by filling the airgel, which is effective in reducing the thermal conductivity.

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

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. , metal fibers such as aluminum, and the like. As the fibrous substance, inorganic fibers can be used from the viewpoint of further excellent heat resistance, and glass, rock wool or ceramics can be used from the viewpoint of further reducing thermal conductivity.

The fibrous substance may have a diameter (fiber diameter) of 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 ensured, so that the impregnating property of the sol into the sheet is improved. The diameter of the fibrous material can be observed under a microscope and measured as the average diameter of 10 arbitrarily selected fibers.

<Method for producing 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 production method can also be said to be a method in which an impregnation step is provided between the sol formation step and the wet gel formation step in the airgel production method described above. That is, the production method comprises a sol-generating step of hydrolyzing a silane oligomer to generate a sol containing a hydrolysis product of the silane oligomer, an impregnating step of impregnating a porous substrate with the sol, and a step of impregnating the sol. It may comprise a wet gel producing step of gelling to obtain a wet gel and a drying step of drying the wet gel to obtain an aerogel.

When a porous substrate made of a fibrous substance is used, the fibrous substance is dispersed in the sol in advance, and then the wet gel forming step and the drying step described above are carried out to produce a fibrous substance to which the airgel is attached. Then, it can be made into an airgel composite material by making a paper and making it into a non-woven fabric.

In the above-mentioned fibrous substance with airgel attached, the bonding mode is limited, such as bonding due to chemical interaction between the functional group on the fiber surface and the functional group on the airgel surface, and bonding due to intermolecular interaction between the fiber surface and the airgel. not something to do. Airgel particles (particles constituting airgel) may adhere to part or all of the fiber surface.

The impregnation step may be, for example, a step of impregnating the porous substrate or attaching the sol to the material of the porous substrate (for example, the raw material fibers of the nonwoven fabric). The impregnation step includes, for example, a dipping method in which the porous substrate or its material is immersed in a sol, or a coating method in which a sol is applied to the porous substrate. The impregnation method is not limited, and a suitable method can be selected according to physical properties such as the size, shape, and elastic modulus of the porous substrate.

Regarding the method of treating the raw material fibers of the non-woven fabric with the sol, for example, a wet method in which the fibers are placed in a container containing the sol and heated and stirred for a predetermined time to treat the surface of the fibers, and the fibers are 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 of applying the sol to the fiber is not particularly limited, but a wet method can be used because the sol can be easily applied to the fiber surface uniformly.

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

A separator can be laminated on both sides of the porous substrate. By laminating the separator, it is possible to prevent transfer or contamination of the uncured sol during transportation of the porous substrate and other processes. As a method of laminating the separator in the impregnation step, for example, there is a method of laminating after impregnating with a sol. Examples of separators include inorganic fibers such as glass nonwoven fabric and glass cloth; organic fibers such as polyimide, polyamideimide, and polyester; base films made of polyolefin, polyester, polycarbonate, polyimide, and the like; release paper; copper foil, aluminum foil, and the like. can be mentioned. The separator may be subjected to release treatment in addition to matte treatment and corona treatment.

The airgel composite material of the present embodiment described above is an airgel that is a dry product of a wet gel that is a condensation product 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 dry airgel) and a substrate having a porous structure, and has excellent heat insulation properties, and can be made into sheets and boards of airgel, which has been difficult to handle in the past. Due to such advantages, the airgel composite material of the present embodiment can be applied to cryogenic containers, the space field, the construction field, the automobile field, the home appliance field, the semiconductor field, the use as a heat insulating material in industrial equipment, and the like. Further, the airgel composite material of the present embodiment can be used for water repellency, sound absorption, vibration damping, catalyst support, etc., in addition to use as a heat insulator.

(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 Co., Ltd., product name) as a silane monomer. , hereinafter abbreviated as “TEOS”), 300 parts by mass of 2-propanol, and 100 parts by mass of water are mixed. reacted. A sol coating liquid 1 was obtained by adding 80 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 1]
The sol coating liquid 1 is put in a vat, and a glass nonwoven fabric (manufactured by Nippon Sheet Glass Co., Ltd., product name: MGP BMS-5, fiber diameter: 1.5 μm, void ratio: 90% by volume) was placed on the sol coating liquid 1 and impregnated with the sol coating liquid 1. After confirming that the sol coating solution 1 was sufficiently impregnated into the glass nonwoven fabric and that the glass nonwoven fabric was submerged in the sol coating solution, gelling was performed at 60° C. for 30 minutes to obtain an airgel sheet. After that, the obtained airgel sheet (wet gel) was transferred to a closed container and aged at 60° C. for 12 hours. After that, the airgel sheet 1 was obtained by drying the aged airgel sheet at 120° C. for 6 hours under normal pressure.

(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 Dow Corning Toray Co., Ltd., product name) was used as the silane oligomer.
[Airgel sheet 2]
An airgel sheet 2 was obtained in the same manner as in Example 1 using the sol coating liquid 2 described above.

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

(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 added as an acid catalyst to this. 0.15 parts by mass was added and reacted at 25° C. for 4 hours. A sol coating liquid 4 was obtained by adding 60 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 4]
An airgel sheet 4 was obtained in the same manner as in Example 1 using the sol coating liquid 4 described above.

(Example 5)
[Sol coating liquid 5]
100 parts by mass of "KR-500" (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. ), 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. A sol coating liquid 5 was obtained by adding 90 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 5]
An airgel sheet 5 was formed in the same manner as in Example 1 except that the sol coating liquid 5 was used and glass nonwoven fabric Boroid GMU (manufactured by Orivest 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. abbreviated as), 20 parts by mass of dimethyldiethoxysilane “KBE-22” (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter abbreviated as “DMDES”), 300 parts by mass of 2-propanol, 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. A sol coating solution 6 was obtained by adding 90 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 6]
While using the sol coating liquid 6, a porous nickel sheet: Celmet (manufactured by Sumitomo Electric Industries, Ltd., product name, thickness: 1.4 mm, nickel basis weight: 420 g / m ² , porosity: 97 in place of the glass nonwoven fabric) %) was used, and an airgel sheet 6 was obtained in the same manner as in Example 1.

(Example 7)
[Sol coating liquid 7]
As a silane oligomer, 100 parts by mass of “XR31-B1410” (manufactured by Momentive Performance Materials Japan LLC, product name), dimethyldiethoxysilane “KBE-22” (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter 70 parts by mass of 2-propanol, 300 parts by mass of 2-propanol, and 80 parts by mass of water are mixed, 0.1 part by mass of acetic acid is added as an acid catalyst, and reacted at 25° C. for 4 hours. rice field. A sol coating liquid 7 was obtained by adding 80 parts by mass of 5% aqueous ammonia as a basic catalyst.
[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) was added to 100 parts by mass of the sol coating liquid 7, and the mixture was heated at 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. After that, the drying process was performed in the same manner as in Example 1 to obtain glass fibers to which airgel was attached.
40 L of a dispersion containing the obtained glass fiber, water, and 0.1% by mass of a surfactant (polyoxyethylene lauryl ether) was prepared, and the dispersion was put into a papermaking apparatus. As a papermaking apparatus, an apparatus comprising an upper papermaking tank (capacity 30 L) equipped with a stirrer with rotary blades and a lower water tank (capacity 10L) with a porous support provided between the papermaking tank and the water tank is used. board. First, using a stirrer, the dispersion was stirred until microbubbles of air were generated. After that, the glass fiber whose mass was adjusted so as to have the desired basis weight was put into a dispersion liquid in which air microbubbles were dispersed and stirred to obtain a slurry in which the glass fiber with the airgel attached was dispersed. Next, the slurry was sucked from the water tank and dehydrated through the porous support to obtain a fiber paper product. The paper product was dried in a hot air dryer at 150° C. for 2 hours to obtain an airgel sheet 7 having a basis weight of 100 g/m ² and a porosity of 90% by volume.

(Example 8)
[Sol coating liquid 8]
As a silane oligomer, 100 parts by mass of “XR31-B1410” (manufactured by Momentive Performance Materials Japan LLC, product name), methyltrimethoxysilane “KBM-13” (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter 200 parts by mass of tetraethoxysilane "KBE-04" (manufactured by Shin-Etsu Chemical Co., Ltd., product name, hereinafter abbreviated as "TEOS"), 50 parts by mass, 800 parts by mass of 2-propanol, Then, 200 parts by mass of water was mixed, 0.5 parts by mass of acetic acid was added as an acid catalyst, and the mixture was reacted at 25° C. for 4 hours. A sol coating liquid 8 was obtained by adding 200 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 8]
Same as Example 1 except that the sol coating liquid 8 was used and a porous alumina sheet: AZP60 (manufactured by Asuzac Co., Ltd., product name, average thickness: 700 μm, porosity: 60% by volume) was used instead of the glass nonwoven fabric. An airgel sheet 8 was obtained in the same manner.

(Comparative example 1)
[Sol coating liquid 11]
PL-2L as a raw material containing silica particles (Fuso Chemical Industry Co., Ltd., product name, average primary particle size: 20 nm, solid content: 20% by mass) 100.0 parts by mass, water 120.0 parts by mass, methanol 80.0 parts by mass of and 0.10 parts by mass of acetic acid as an acid catalyst, and methyltrimethoxysilane LS-530 as a silicon compound (manufactured by Shin-Etsu Chemical 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 Co., Ltd., product name; hereinafter abbreviated as “DMDMS”) were added and reacted at 25° C. for 2 hours. A sol coating liquid 11 was obtained by adding 40.0 parts by mass of 5% aqueous ammonia as a basic catalyst.
[Airgel sheet 11]
The sol coating liquid 11 is used, and a PET film having no porous structure: G2 (manufactured by Teijin DuPont Co., Ltd., product name) is used instead of the glass nonwoven fabric, and the sol coating liquid 11 is applied to the PET film by a bar coater. was applied so that the film thickness of the sol coating liquid was 80 μm. The obtained airgel sheet was transferred to a closed container and aged at 60° C. for 12 hours. After that, the aged airgel sheet was immersed in 2000 mL of water and washed over 30 minutes. Next, it was immersed in 2000 mL of methanol and washed at 60° C. for 30 minutes. The methanol wash was performed two more times with fresh methanol changes. Next, it was immersed in 2000 mL of methyl ethyl ketone, and the solvent was replaced at 60° C. over 30 minutes. Washing with methyl ethyl ketone was carried out two more times by replacing with fresh 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 nonwoven fabric, a thin sheet glass having no porous structure: OA-10G (manufactured by Nippon Electric Glass Co., Ltd., thickness: 150 μm) was used, and the sol coating liquid 11 was applied to the thin sheet 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 to a film thickness of 80 μm.

<Various evaluations>
(Thermal conductivity measurement)
The airgel composite materials obtained in each example and comparative example were measured or evaluated under the following conditions. The thermal conductivity was measured using a thermal conductivity measuring device HC-074 manufactured by Eiko Seiki Co., Ltd. A sample of 20 cm×20 cm was used as a measurement sample, and thermal conductivity was measured by setting the temperatures of the upper and lower heat plates to 30° C. and 10° C., respectively. Table 1 shows the results.

(Powder off property evaluation)
Powder falling property of the airgel composite material (airgel sheet) obtained in each example and comparative example was evaluated. Evaluation is performed by stacking multiple layers of the same type of airgel composite material so that the length is 30 cm × width 30 cm × height 10 to 15 mm thick, and the four sides of the laminated airgel composite material in the vertical and horizontal directions are each placed on the table. The amount of powder dropped when dropped five times was measured. The drop height was set to 5 cm from the table, and the test method for powder removal was to drop the powder vertically. Table 1 shows the results.

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

Claims (8)

A substrate having a porous structure and an airgel attached to the substrate,
The airgel is a dry wet gel that is a condensate of a sol containing a hydrolysis product of a silane oligomer,
the ratio of silicon atoms bonded to three oxygen atoms to the total number of silicon atoms in the silane oligomer is 70 % or more ;
The airgel composite material, wherein the silane oligomer has a weight average molecular weight of 200 or more and 10,000 or less . the silane oligomer has an alkoxy group,
The airgel composite material according to claim 1 , 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. 3. The airgel composite according to claim 1 or 2 , wherein the sol further contains silica particles. The airgel composite material according to claim 3 , wherein the silica particles have an average primary particle size of 1 to 500 nm. the pores in the porous structure are communicating pores,
The airgel composite according to any one of claims 1 to 4 , wherein the total volume of the pores is 50-99% by volume of the total volume of the substrate. The airgel composite material according to claim 5 , wherein the communication holes are filled with the airgel. The airgel composite material according to any one of claims 1 to 6 , wherein the substrate having a porous structure is a sheet made of a fibrous substance with a diameter of 0.1 to 1000 µm. 8. The airgel composite according to claim 7 , wherein the airgel is attached to the fibrous material.

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