JP7119292B2 - Package containing airgel and method for manufacturing package containing airgel - Google Patents

Description

TECHNICAL FIELD The present invention relates to an airgel-containing package and a method for manufacturing an airgel-containing package.

In recent years, due to the increasing demand for comfort and energy saving of living spaces, the shapes of objects requiring heat insulation tend to be complicated, and the space for installing heat insulating materials tends to be narrow. Therefore, there is a demand for a heat insulating material that not only has improved heat insulating performance but also has a reduced thickness.

As an attempt to improve the heat insulating performance of a heat insulating material using foamed resin, for example, Patent Document 1 proposes a plate-shaped foam containing polypropylene resin foam and/or at least one layer of metal thin film inside. there is

On the other hand, cryogenic substances such as liquid nitrogen and liquid helium are stored in a double-walled container consisting of an inner container and an outer container, and a vacuum is created between the inner container and the outer container. Filled with insulation. As a heat insulating material to be filled in a vacuum space, for example, Patent Document 2 discloses a laminated heat insulating material in which a reflective film having a metal layer formed on one or both sides of a polyimide film and a net-like spacer made of plastic yarn are laminated. It is Further, Patent Document 3 discloses a laminated heat insulating material obtained by laminating a reflective film having a metal layer formed on one or both sides of a thermoplastic liquid crystal polymer film or inside thereof, and a sheet-like spacer made of thermoplastic polymer fibers. there is

Japanese Patent Application Laid-Open No. 2001-179866 JP-A-9-109323 JP-A-11-70053

However, when the heat insulating material is used in a vacuum, the degree of vacuum deteriorates due to gas released from the heat insulating material, degrading the heat insulating performance. In addition, when the heat insulating material is stored for a long period of time, it is feared that moisture in the air will be adsorbed, further deteriorating the degree of vacuum. In addition, thermal insulation materials used in fields such as cryogenic technology and superconducting technology, which require cryogenic materials, are required to have a reduced thickness and further improved thermal insulation performance.

It should be noted that airgel may be used as a heat insulating material with a small thickness, but phenomena such as gas release and water adsorption may occur even in airgel.

The present invention has been made in view of the above circumstances, and provides an airgel-containing package that can suppress moisture absorption during long-term storage and outgassing during use, and a method for manufacturing the package. aim.

As a result of intensive research to achieve the above object, the inventors of the present invention have found that airgel with a water content of 10×10 ¹⁵ [pieces/cm ² ] or less can be used under vacuum for a long period of time. It has been found that the airgel does not deteriorate in temperature, and that the airgel absorbs less moisture if it is stored in a vacuumed state in the package.

The present invention comprises an airgel containing an airgel component and having a water content of 10×10 ¹⁵ [pieces/cm ² ] or less, and a package body formed by sealing the airgel under reduced pressure. Provide packaging. As a result, moisture absorption during long-term storage of the airgel and outgassing during use can be suppressed.

In the present invention, the airgel may be supported by a supporting member. Thereby, the flexibility of airgel can be improved more.

In the present invention, the package may be formed from a resin film having an aluminum layer. This makes it easier to take out the airgel from the package, and can further suppress the infiltration of moisture from the outside.

In the present invention, the airgel is at least selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of the silicon compound having the hydrolyzable functional group It may be a dried product of a wet gel that is a condensate of a sol containing one. The airgel thus obtained can achieve excellent thermal insulation and flexibility.

In the present invention, the airgel may further contain silica particles. As a result, the heat insulating properties, flexibility, etc. of the airgel can be further improved.

In the present invention, the silica particles may have an average primary particle size of 1 to 500 nm. This makes it easier to further improve the thermal insulation and flexibility of the airgel.

The present invention also provides at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of the silicon compound having the hydrolyzable functional group ^A step of drying the wet gel, which is a condensate of the ^sol containing and a sealing step. As a result, moisture absorption during long-term storage of the airgel and outgassing during use can be suppressed.

In the manufacturing method of the present invention, sealing may be performed by heat sealing.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the package containing an airgel which can suppress the moisture absorption at the time of long-term storage, and the outgassing at the time of use, and the said package can be provided. In addition, when the airgel contains silica particles, it is superior in handleability when used as a heat insulating material, and even when the thickness is reduced, it is possible to exhibit even better heat insulating performance.

FIG. 2 is a schematic representation of the microstructure of an airgel according to one embodiment of the present disclosure; It is a figure which shows the calculation method of the biaxial average primary particle diameter of particle|grains.

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

<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 particles (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-dimensional 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. The airgel of this embodiment can contain an airgel component composed of the airgel particles described above.

The airgel of the present embodiment may contain silica particles in addition to the airgel component. An airgel containing an airgel component and silica particles can also be referred to as an airgel composite. Although it does not necessarily mean the same concept as this, the airgel composite can also be expressed as containing silica particles as a component constituting a three-dimensional network skeleton. 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 composite is superior in heat insulation and flexibility as described below. In particular, the excellent flexibility improves the handleability and enables the size to be increased, so that the productivity can be improved. The airgel composite is obtained by allowing silica particles to exist in the airgel production environment. The advantage of the presence of silica particles is not only that the heat insulation properties and flexibility of the composite itself can be improved, but also that the time for the wet gel generation process described later can be shortened, or the drying process from the washing and solvent replacement process can be simplified. is possible. It should be noted that time reduction and simplification of this step are not necessarily required for producing an airgel composite with excellent flexibility.

There are various forms of composites between the airgel component and the silica particles. For example, the airgel component may be amorphous such as a film, or may be particulate (airgel particles). In any aspect, since the airgel components are present in various forms between the silica particles, it is presumed that flexibility is imparted to the skeleton of the airgel.

Examples of a composite mode of the airgel component and the silica particles include a mode in which the amorphous airgel component is interposed between the silica particles. Specifically, for example, the silica particles are coated with a film-like airgel component (silicone component) (the airgel component includes the silica particles), and the airgel component serves as a binder between the silica particles. is connected, a mode in which the airgel component fills the gaps between a plurality of silica particles, a combination of these modes (a mode in which silica particles arranged in a cluster are coated with an airgel component, etc.), etc. aspects. Thus, in the airgel composite, the three-dimensional network skeleton can be composed of silica particles and an airgel component (silicone component), and there is no particular limitation on the specific aspect (morphology).

On the other hand, as will be described later, the airgel component may be in the form of distinct particles as shown in FIG. 1 instead of being amorphous, and may be combined with silica particles in that state.

Although the mechanism by which such various aspects occur in the airgel composite is not necessarily clear, the present inventors speculate that the generation rate of the airgel components in the gelation process is involved. For example, changing the number of silanol groups of silica particles tends to change the production rate of the airgel component. In addition, the production rate of the airgel component also tends to fluctuate by fluctuating the pH of the system.

This suggests that by adjusting the size and shape of silica particles, the number of silanol groups, the pH of the system, and the like, it is possible to control the aspect of the airgel (size, shape, etc. of the three-dimensional network skeleton). Therefore, it is possible to control the density, porosity, etc. of the airgel, and it is thought that the heat insulation and flexibility of the airgel can be controlled. In addition, the three-dimensional network skeleton of the airgel may be composed of only one of the various aspects described above, or may be composed of two or more aspects.

Hereinafter, taking FIG. 1 as an example, the airgel (airgel composite) will be described, but as described above, the airgel may not necessarily contain silica particles, and the present disclosure is not limited to the embodiment of FIG. . However, the following description can be appropriately referred to for matters common to all of the above embodiments (type, size, content, etc. of silica particles).

FIG. 1 is a diagram schematically showing the microstructure of an airgel (airgel composite) according to one embodiment of the present disclosure. As shown in FIG. 1, the airgel 10 includes a three-dimensional mesh skeleton formed by randomly connecting airgel particles 1 constituting the airgel component in three dimensions partially through silica particles 2, and the skeleton and a pore 3 surrounded by At this time, the silica particles 2 are interposed between the airgel particles 1, and are presumed to function as a skeleton support that supports the three-dimensional network skeleton. Therefore, by having such a structure, it is considered that moderate strength is imparted to the airgel while maintaining the heat insulating properties and flexibility of the airgel. That is, the airgel may have a three-dimensional network skeleton formed by randomly connecting silica particles three-dimensionally via airgel particles. Also, the silica particles may be coated with airgel particles. Since the airgel particles (airgel component) are composed of a silicon compound, it is presumed that they have a high affinity for silica particles. Therefore, it is considered that the present embodiment succeeded in introducing silica particles into the three-dimensional network framework of the airgel. In this respect, the silanol groups of the silica particles are also considered to contribute to the affinity between the two.

The airgel particles 1 are considered to take the form of secondary particles composed of a plurality of primary particles, and are generally spherical. The average particle size (ie, secondary particle size) of the airgel particles 1 can be 2 nm to 50 μm, but may be 5 nm to 2 μm, or 10 nm to 200 nm. When the average particle size of the airgel particles 1 is 2 nm or more, it becomes easy to obtain an airgel having excellent flexibility, while when the average particle size is 50 μm or less, it becomes easy to obtain an airgel having excellent heat insulating properties. In addition, the average particle diameter of the primary particles constituting the airgel particles 1 can be 0.1 nm to 5 μm from the viewpoint of easy formation of secondary particles with a low density porous structure, but 0.5 nm to It may be 200 nm, or it may be between 1 nm and 20 nm.

The silica particles 2 can be used without any particular limitation, and examples thereof include amorphous silica particles. Furthermore, the amorphous silica particles include at least one selected from the group consisting of fused silica particles, fumed silica particles and colloidal silica particles. Among these, colloidal silica particles have high monodispersity and easily suppress aggregation in the sol. The silica particles 2 may be silica particles having a hollow structure, a porous structure, or the like.

The shape of the silica particles 2 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 2, aggregation in the sol can be easily suppressed. The average primary particle size of the silica particles 2 can be 1 to 500 nm, but may be 5 to 300 nm, or may be 20 to 100 nm. When the average primary particle size of the silica particles 2 is 1 nm or more, it becomes easy to impart appropriate strength to the airgel, and it becomes easy to obtain an airgel excellent in shrinkage resistance during drying. On the other hand, when the average primary particle size is 500 nm or less, 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 is presumed that the airgel particles 1 (airgel component) and the silica particles 2 are bonded by hydrogen bonding and/or chemical bonding. At this time, hydrogen bonds and/or chemical bonds are considered to be formed by the silanol groups and/or reactive groups of the airgel particles 1 (airgel component) and the silanol groups of the silica particles 2 . Therefore, it is considered that appropriate strength can be easily imparted to the airgel when the bonding mode is a chemical bond. Considering this, the particles to be combined with the airgel component are not limited to silica particles, and inorganic or organic particles having silanol groups on the particle surface can also be used.

The number of silanol groups per 1 g of the silica particles 2 can be 10×10 ¹⁸ to 1000×10 ¹⁸ /g, but may be 50×10 ¹⁸ to 800×10 ¹⁸ /g, or 100 It may be ×10 ¹⁸ to 700×10 ¹⁸ /g. Since the number of silanol groups per 1 g of the silica particles 2 is 10 × 10 ¹⁸ / g or more, it is possible to have better reactivity with the airgel particles 1 (airgel component), and the airgel is excellent in shrinkage resistance. become easier to obtain. On the other hand, when the number of silanol groups is 1000×10 ¹⁸ /g or less, it becomes easier to suppress rapid gelation during sol production, and it becomes easier to obtain a homogeneous airgel.

In the present embodiment, the average particle size of the particles (average secondary particle size of airgel particles, average primary particle size of silica particles, etc.) is determined using a scanning electron microscope (hereinafter abbreviated as “SEM”). It can be obtained by directly observing the cross section. For example, from the three-dimensional network skeleton, the particle size of each airgel particle or silica particle can be obtained based on the diameter of its cross section. The diameter here means the diameter when the cross section of the skeleton forming the three-dimensional mesh skeleton is regarded as a circle. Further, the diameter when the cross section is regarded as a circle is the diameter of the circle when the area of the cross section is replaced by a 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.

As for the silica particles, it is possible to measure the average particle size 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 with a solid content concentration of 5 to 40% by mass, which are usually dispersed in water, as an example, a chip obtained by cutting a wafer with pattern wiring into 2 cm squares is immersed in the dispersion liquid of colloidal silica particles for about 30 seconds. After that, 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. At this time, if the selected silica particles have a shape as shown in FIG. 2, a rectangle (circumscribing rectangle L) that circumscribes the silica particles 2 and is arranged so that its long sides are the longest is derived. Then, the long side of the circumscribing rectangle L is X, the short side is Y, and the biaxial average primary particle size is calculated as (X+Y)/2, and is defined as the particle size of the particle.

The size of the pores 3 in the airgel will be explained later in the section [Density and porosity].

The content of the airgel component contained in the airgel can be 4 to 25 parts by mass with respect to 100 parts by mass of the total airgel, but may be 10 to 20 parts by mass. When the content is 4 parts by mass or more, it becomes easy to impart appropriate strength to the airgel, and when it is 25 parts by mass or less, it becomes easy to obtain good heat insulation.

When the airgel contains silica particles, the content of the silica particles contained in the airgel can be 1 to 25 parts by weight with respect to the total amount of 100 parts by weight of the airgel, but may be 3 to 15 parts by weight. . When the content is 1 part by mass or more, it becomes easy to impart appropriate strength to the airgel, and when it is 25 parts by mass or less, it becomes easy to suppress the solid heat conduction of the silica particles.

In addition to these airgel components and silica particles, the airgel may further contain other components such as carbon graphite, aluminum compounds, magnesium compounds, silver compounds, and titanium compounds for the purpose of suppressing heat radiation. The content of other components is not particularly limited, but from the viewpoint of sufficiently ensuring the desired effect of the airgel, it can be 1 to 5 parts by mass with respect to 100 parts by mass of the total amount of the airgel.

[Density and porosity]
In the airgel of the present embodiment, the size of the pores 3, that is, the average pore diameter can be 5 to 1000 nm, but may be 25 to 500 nm. When the average pore diameter is 5 nm or more, it becomes easy to obtain an airgel with excellent flexibility, and when it is 1000 nm or less, it becomes easy to obtain an airgel with excellent heat insulation.

In the airgel of this embodiment, the density at 25° C. can be 0.05-0.25 g/cm ³ , but it may be 0.1-0.2 g/cm ³ . When the density is 0.05 g/cm ³ or more, better strength and flexibility can be obtained, and when it is 0.25 g/cm ³ or less, better heat insulating properties can be obtained. can.

In the airgel of the present embodiment, the porosity at 25° C. can be 85-95%, but it may be 87-93%. When the porosity is 85% or more, better heat insulating properties can be obtained, and when it is 95% or less, better strength and flexibility can be obtained.

The average pore diameter, density, and porosity of pores (through pores) that are continuous in a three-dimensional network shape in an airgel can be measured by a mercury intrusion method according to DIN66133. As a measuring device, for example, Autopore IV9520 (manufactured by Shimadzu Corporation, product name) can be used.

<Specific aspects of the airgel component>
The airgel of this embodiment can contain polysiloxane having a backbone containing siloxane bonds (Si—O—Si). The airgel can have the following M units, D units, T units or Q units as structural units.

In the above formula, R represents an atom (such as a hydrogen atom) or an atomic group (such as an alkyl group) bonded to a silicon atom. An M unit is a unit consisting of a monovalent group in which a silicon atom is bonded to one oxygen atom. A D unit is a unit consisting of a divalent group in which a silicon atom is bonded to two oxygen atoms. A T unit is a unit consisting of a trivalent group in which a silicon atom is bonded to three oxygen atoms. A Q unit is a unit consisting of a tetravalent group in which a silicon atom is bonded to four oxygen atoms. Information on the content of these units can be obtained by Si-NMR.

The following aspects are mentioned as an airgel component in the airgel of this embodiment. By adopting these aspects, it becomes easy to control the thermal insulation and flexibility of the airgel to a desired level. However, the purpose of adopting each of these aspects is not necessarily to obtain the airgel defined in the present embodiment. By adopting each aspect, it is possible to obtain an airgel having thermal conductivity and compression elastic modulus according to each aspect. Therefore, it is possible to provide an airgel having thermal insulation and flexibility depending on the application.

(First aspect)
The airgel of this embodiment can have a structure represented by the following general formula (1). The airgel of 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. Examples of substituents for the substituted phenyl group include alkyl groups, vinyl groups, mercapto groups, amino groups, nitro groups and cyano groups. 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 of the present embodiment can have a ladder-type structure comprising struts and bridging portions, and the bridging portions 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, for example, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group 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 airgel skeleton as an airgel component, for example, it has a structure derived from a conventional ladder-type silsesquioxane (i.e., has a structure represented by the following general formula (X)) It becomes an airgel having flexibility superior to that of an airgel. 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 an airgel having a structure derived from a conventional ladder-type silsesquioxane, the structure of the bridging portion is -O- (having the above T unit as a structural unit). However, in the airgel of the present embodiment, 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, for example, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group 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 of the present embodiment is a silicon compound having a hydrolyzable functional group or a condensable functional group (in the molecule), and a hydrolysis product of a silicon compound having a hydrolyzable functional group. Dried wet gel that is a condensate of sol containing at least one selected and optionally silica particles (obtained by drying wet gel produced from sol: dried wet gel derived from sol object). The airgel described so far may also be obtained by drying a wet gel produced from a sol containing a silicon compound or the like.

As the silicon compound having a hydrolyzable functional group or a condensable functional group, a silicon compound (silicon compound) other than the polysiloxane compound described later can be used. That is, the sol is a group consisting of silicon compounds (excluding polysiloxane compounds) having hydrolyzable functional groups or condensable functional groups, and hydrolysis products of silicon compounds having hydrolyzable functional groups. It can contain at least one more selected compound (hereinafter sometimes referred to as "silicon compound group"). The number of silicon molecules in the silicon compound can be one or two.

Examples of the silicon compound having a hydrolyzable functional group in the molecule include, but are not particularly limited to, alkyl silicon alkoxides. From the viewpoint of improving water resistance, the alkyl silicon alkoxide can have 3 or less hydrolyzable functional groups. Examples of such alkyl silicon alkoxides include monoalkyltrialkoxysilanes, monoalkyldialkoxysilanes, dialkyldialkoxysilanes, monoalkylmonoalkoxysilanes, dialkylmonoalkoxysilanes, and trialkylmonoalkoxysilanes. are, for example, methyltrimethoxysilane, methyldimethoxysilane, dimethyldimethoxysilane and ethyltrimethoxysilane. Here, examples of the hydrolyzable functional group include alkoxy groups such as a methoxy group and an ethoxy group.

The silicon compound having a condensable functional group is not particularly limited, but examples include silanetetraol, methylsilanetriol, dimethylsilanediol, phenylsilanetriol, phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol, hexylsilanetriol, octylsilanetriol, decylsilanetriol, trifluoropropylsilanetriol, and the like.

A silicon compound having a hydrolyzable functional group or a condensable functional group has a reactive group different from the hydrolyzable functional group and the condensable functional group (hydrolyzable functional group and condensable functional group It may further have a non-applicable 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.

In addition, the number of hydrolyzable functional groups is 3 or less and the silicon compound having a reactive group includes vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane. Silane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3 -aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and the like can also be used.

Further, as silicon compounds having a condensable functional group and a reactive group, 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 can also be used.

Furthermore, bistrimethoxysilylmethane, bistrimethoxysilylethane, bistrimethoxysilylhexane, ethyltrimethoxysilane, vinyltrimethoxysilane, etc., which are silicon compounds having 3 or less hydrolyzable functional groups at the molecular terminals, can also be used. .

A silicon compound having a hydrolyzable functional group or a condensable functional group (excluding polysiloxane compounds), and a hydrolysis product of a silicon compound having a hydrolyzable functional group may be used alone or in combination of two or more. may be mixed and used.

In producing the airgel of this embodiment, the silicon compound can contain a polysiloxane compound having a hydrolyzable functional group or a condensable functional group. That is, the sol containing the silicon compound is composed of a polysiloxane compound having a hydrolyzable functional group or a condensable functional group (inside the molecule), and a hydrolyzable polysiloxane compound having a hydrolyzable functional group. At least one selected from the group consisting of decomposition products (hereinafter sometimes referred to as "polysiloxane compound group") can be further contained.

The functional groups in the polysiloxane compound and the like are not particularly limited, but may be groups that react with the same functional groups or groups that react with other functional groups. Hydrolyzable functional groups include, for example, alkoxy groups. Examples of condensable functional groups include hydroxyl groups, silanol groups, carboxyl groups, and phenolic hydroxyl groups. A hydroxyl group may be contained in a hydroxyl group-containing group such as a hydroxyalkyl group. In addition, the polysiloxane compound having a hydrolyzable functional group or a condensable functional group is a reactive group different from the hydrolyzable functional group and the condensable functional group (hydrolyzable functional group and condensable functional group). may further have a functional group that does not correspond to a functional group of Polysiloxane compounds having these functional groups and reactive groups may be used alone or in combination of two or more. Among these functional groups and reactive groups, for example, groups that improve the flexibility of the airgel include alkoxy groups, silanol groups, hydroxyalkyl groups, etc. Among these, the alkoxy groups and hydroxyalkyl groups are The compatibility of the sol can be further improved. In addition, from the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the airgel, the number of carbon atoms of the alkoxy group and the hydroxyalkyl group can be 1 to 6, but the flexibility of the airgel is further improved. It may be 2 to 4 from the point of view.

Polysiloxane compounds having a hydroxyalkyl group in the molecule 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) 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, for example, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group 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.

By using a wet gel (produced from the sol), which is a condensate of the sol containing the polysiloxane compound having the above structure, it becomes easier to obtain a low thermal conductivity and flexible airgel. From this point of view, R ^1a in formula (A) 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).

Polysiloxane compounds having an alkoxy group in the molecule 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) can be introduced into the skeleton of the airgel. can.

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, for example, an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, a cyano group 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.

By using a wet gel (produced from the sol), which is a condensate of the sol containing the polysiloxane compound having the above structure or a hydrolysis product thereof, it becomes easier to obtain a low thermal conductivity and flexible airgel. From such a viewpoint, 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 is a methyl group. , methoxy group, ethoxy group and the like. 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, for example, JP-A-2000-26609 and JP-A-2012-233110. can be done.

In addition, since the alkoxy group is hydrolyzed, the polysiloxane compound having an alkoxy group may exist as a hydrolysis product in the sol. may be Moreover, in the polysiloxane compound having an alkoxy group, all the alkoxy groups in the molecule may be hydrolyzed or partially hydrolyzed.

These polysiloxane compounds having a hydrolyzable functional group or a condensable functional group, and the hydrolysis products of the polysiloxane compounds having a hydrolyzable functional group may be used alone or in combination of two or more. may be used.

The content of the silicon compound group contained in the sol (the content of the silicon compound having a hydrolyzable functional group or a condensable functional group, and the hydrolysis product of the silicon compound having a hydrolyzable functional group The total content) can be 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of the sol, but may be 10 to 30 parts by mass. When the amount is 5 parts by mass or more, good reactivity can be easily obtained, and when the amount is 50 parts by mass or less, good compatibility can be easily obtained.

In addition, when the sol further contains a polysiloxane compound, the content of the silicon compound group and the content of the polysiloxane compound group (the content of the polysiloxane compound having a hydrolyzable functional group or a condensable functional group , and the sum of the contents of the hydrolysis products of the polysiloxane compound having a hydrolyzable functional group) can be 5 to 50 parts by mass with respect to 100 parts by mass of the total amount of the sol, It may be 10 to 30 parts by mass. A total content of 5 parts by mass or more makes it easier to obtain good reactivity, and a total content of 50 parts by mass or less makes it easier to obtain good compatibility. At this time, the ratio of the content of the silicon compound group and the content of the polysiloxane compound group can be 0.5:1 to 4:1, but may be 1:1 to 2:1. . A content ratio of these compounds of 0.5:1 or more makes it easier to obtain good compatibility, and a content ratio of 4:1 or less makes it easier to suppress gel shrinkage.

When silica particles are contained in the sol, the content of the silica particles may be 1 to 20 parts by mass, but may be 4 to 15 parts by mass, with respect to 100 parts by mass of the total amount of the sol. By setting the content to 1 part by mass or more, it becomes easier to impart appropriate strength to the airgel, and it becomes easier to obtain an airgel that is excellent in shrinkage resistance during drying. In addition, by setting the content to 20 parts by mass or less, 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.

(Other aspects)
The airgel of this embodiment can have a structure represented by the following general formula (4).

In formula ( ⁴ ), R9 represents an alkyl group. Here, the alkyl group includes an alkyl group having 1 to 6 carbon atoms and the like, and the alkyl group includes a methyl group and the like.

The airgel of this embodiment can have a structure represented by the following general formula (5).

In formula (5), R ¹⁰ and R ¹¹ each independently represent an alkyl group. Here, the alkyl group includes an alkyl group having 1 to 6 carbon atoms and the like, and the alkyl group includes a methyl group and the like.

The airgel of this embodiment can have a structure represented by the following general formula (6).

In formula (6), R ¹² represents an alkylene group. Here, the alkylene group includes an alkylene group having 1 to 10 carbon atoms and the like, and the alkylene group includes an ethylene group, a hexylene group and the like.

<Method for producing airgel>
Next, a method for producing an airgel will be described. Although the method for producing an airgel is not particularly limited, it can be produced, for example, by the following method.

That is, the airgel of the present embodiment includes a sol generation step, a wet gel generation step in which the sol obtained in the sol generation step is gelled and then aged to obtain a wet gel, and a wet gel obtained in the wet gel generation step. It can be produced by a production method mainly comprising a step of washing and (if necessary) solvent replacement, and a drying step of drying the wet gel after washing and solvent replacement. In addition, the "sol" is a state before the gelation reaction occurs, and in the present embodiment, the silicon compound group, optionally the polysiloxane compound group, and optionally silica particles are dissolved in a solvent. Or it means a dispersed state. A wet gel means a gel solid in a wet state that does not have fluidity even though it contains a liquid medium.

Each step of the method for producing an airgel according to the present embodiment will be described below.

(Sol generation step)
The sol-producing step is a step of mixing the silicon compound described above, optionally a polysiloxane compound, and optionally silica particles and/or a solvent containing silica particles, followed by hydrolysis to produce a sol. In this step, an acid catalyst may be further added to the solvent in order to promote the hydrolysis reaction. Further, as shown in Japanese Patent No. 5250900, a surfactant, a thermally hydrolyzable compound, etc. can be added to the solvent. Furthermore, components such as carbon graphite, aluminum compounds, magnesium compounds, silver compounds, and titanium compounds may be added to the solvent for the purpose of suppressing heat radiation.

As the solvent, for example, water or a mixture of water and alcohols can be used. Alcohols include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol and the like. Among these alcohols, methanol, ethanol, 2-propanol, and the like are listed as alcohols having a low surface tension and a low boiling point in terms of reducing the interfacial tension with the gel wall. These may be used alone or in combination of two or more.

For example, when alcohol is used as a solvent, the amount of alcohol can be 4 to 8 mol per 1 mol of the total amount of silicon compound group and polysiloxane compound group, but 4 to 6.5. , or 4.5 to 6 mol. When the amount of alcohol is 4 mol or more, it becomes easier to obtain good compatibility, and when it is 8 mol or less, it becomes easier to suppress gel shrinkage.

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, organic carboxylic acids are exemplified as acid catalysts that further improve the water resistance of the resulting airgel. The organic carboxylic acids include acetic acid, but may also be formic acid, propionic acid, oxalic acid, malonic acid, and the like. These may be used alone or in combination of two or more.

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

The amount of the acid catalyst added can be 0.001 to 0.1 part by mass with respect to 100 parts by mass as the total amount of the silicon compound group and the polysiloxane compound group.

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

Examples of nonionic surfactants that can be used include those containing a hydrophilic portion such as polyoxyethylene and a hydrophobic portion mainly composed of alkyl groups, and those containing a hydrophilic portion such as polyoxypropylene. Those 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. Polyoxypropylene alkyl ethers, block copolymers of polyoxyethylene and polyoxypropylene, and the like are examples of those containing hydrophilic moieties such as polyoxypropylene.

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

The amount of surfactant to be added depends on the type of surfactant, or the type and amount of silicon compound group and polysiloxane compound group, but for example, the total amount of silicon compound group and polysiloxane compound group is 100 parts by mass. , 1 to 100 parts by mass. The amount of addition may be 5 to 60 parts by mass.

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.

The amount of the thermally hydrolyzable compound to be added is not particularly limited as long as it is an amount capable of sufficiently promoting the sol-gel reaction in the wet gel forming step described below. For example, when urea is used as the thermohydrolyzable compound, the amount added can be 1 to 200 parts by mass with respect to 100 parts by mass as the total amount of the silicon compound group and the polysiloxane compound group. The addition amount may be 2 to 150 parts by mass. When the amount added is 1 part by mass or more, it becomes easier to obtain good reactivity, and when it is 200 parts by mass or less, it becomes easier to suppress precipitation of crystals and decrease in gel density.

Hydrolysis in the sol generation step depends on the types and amounts of silicon compounds, polysiloxane compounds, silica particles, acid catalysts, surfactants, etc. in the mixed liquid, but is carried out in a temperature environment of, for example, 20 to 60°C. It may be carried out for 10 minutes to 24 hours, or may be carried out in a temperature environment of 50 to 60° C. for 5 minutes to 8 hours. As a result, the hydrolyzable functional groups in the silicon compound and the polysiloxane compound are sufficiently hydrolyzed, and a hydrolysis product of the silicon compound and a hydrolysis product of the polysiloxane 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.

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

Base catalysts include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride and ammonium bromide; sodium metaphosphate. , 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, propylamine, 3-(methylamino)propylamine, 3-( dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine and other aliphatic amines; morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and its derivatives, piperidine and its nitrogen-containing heterocyclic compounds such as derivatives, imidazole and derivatives thereof; Among these, ammonium hydroxide (aqueous ammonia) has high volatility and is less likely to remain in the airgel after drying, so it is less likely to impair water resistance. The above basic catalysts may be used alone or in combination of two or more.

By using a basic catalyst, the dehydration condensation reaction and/or dealcoholization condensation reaction of the silicon compound, polysiloxane compound, and silica particles in the sol can be promoted, and the sol can be gelled in a shorter time. can. In addition, this makes it possible to obtain a wet gel with higher strength (rigidity). In particular, since ammonia is highly volatile and hardly remains in the airgel, using ammonia as the basic catalyst makes it possible to obtain an airgel with more excellent water resistance.

The amount of the basic catalyst to be added may be 0.5 to 5 parts by mass, but may be 1 to 4 parts by mass, with respect to 100 parts by mass as the total amount of the silicon compound group and the polysiloxane compound group. When the amount is 0.5 parts by mass or more, gelation can be performed in a shorter time, and when the amount is 5 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. Further, by setting the gelation temperature to 90° C. or lower, volatilization of the solvent (especially alcohols) 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 alcohols) can be easily suppressed. Therefore, gelation can be achieved 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 according to the gelation temperature and aging temperature. When silica particles are contained in the sol, the gelation time can be particularly shortened compared to when they are not contained. The reason for this is presumed to be that the silanol groups and/or reactive groups of the silicon compound, polysiloxane compound, etc. in the sol form hydrogen bonds and/or chemical bonds with the silanol groups of the silica particles. The gelling time can be 10 to 120 minutes, but may be 20 to 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 solvent replacement steps and the 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 and solvent replacement step)
The washing and solvent replacement step includes a step of washing the wet gel obtained in the wet gel generation step (washing step) and a step of replacing the washing liquid in the wet gel with a solvent suitable for drying conditions (drying step described later). (solvent replacement step). The washing and solvent replacement step can be performed in a form in which only the solvent replacement step is performed without performing the step of washing the wet gel. The wet gel may be washed from the viewpoint of enabling production of airgel with high purity. In addition, when silica particles are contained in the gel, the solvent replacement step after the washing step is not necessarily essential, as will be 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, and 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 step, which will be described later, 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 in the solvent replacement step, the organic solvent used in the washing step includes a hydrophilic organic solvent having high mutual solubility in both water and the low surface tension solvent. It should be noted that the hydrophilic organic solvent used in the washing step can serve as preliminary replacement for the solvent replacement step. 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 in the washing step 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. Washing can be repeated until the water content in the wet gel after washing is 10% by mass or less relative to the mass of silica.

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

In the solvent replacement step, the solvent of the washed wet gel is replaced with a predetermined solvent for replacement in order to suppress shrinkage in the drying step described later. 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.

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. Among these, hydrophilic organic solvents such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane can be used as organic solvents in the washing step. Among these, those having a boiling point of 100° C. or lower under normal pressure may be used because they are easy to dry 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 in the solvent replacement step 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 step can be a temperature below the boiling point of the solvent used for replacement.

In addition, when silica particles are contained in the gel, the solvent replacement step is not necessarily essential as described above. The presumed mechanism is as follows. That is, in general, in order to suppress shrinkage in the drying process, the solvent of the wet gel is replaced with a predetermined replacement solvent (low surface tension solvent). By functioning as a support for the skeleton of , the skeleton is supported and shrinkage of the gel during the drying process is suppressed. Therefore, it is considered that the gel can be directly subjected to the drying process without replacing the solvent used for washing. Thus, when silica particles are contained in the gel, it is possible to simplify the drying process from the washing and solvent replacement process. However, this embodiment does not exclude performing the solvent replacement step.

(Drying process)
In the drying step, the wet gel that has been washed and (if necessary) solvent-substituted as described above is dried (baked). Thereby, an aerogel can be finally obtained. 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, normal pressure drying or supercritical drying can be used from the viewpoint of easy production of low-density airgel. 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).

The airgel of the present embodiment can be obtained by drying the washed and (optionally) solvent-substituted wet gel under atmospheric pressure at a temperature below the critical point of the solvent used for drying. The drying temperature depends on the type of solvent replaced (or the solvent used for washing if solvent replacement is not performed), especially if drying at high temperature accelerates the evaporation rate of the solvent and causes large cracks in the gel. In view of the fact that there is a 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. In the present embodiment, normal pressure drying also includes accelerating drying by applying a pressure below the critical point within a range that does not hinder productivity.

The airgel of this embodiment can also be obtained by supercritical drying of a washed and (optionally) solvent-exchanged wet gel. 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 airgel with low density and small pores. Additional drying may be performed at 150 to 200° C. under normal pressure.

<Insulation material>
A heat insulating material comprising the airgel of the present embodiment can have high heat insulating properties and excellent flexibility. In addition, the airgel obtained by the above airgel manufacturing method can be used as a heat insulating material as it is (processed into a predetermined shape as necessary).

From such advantages, the airgel and the airgel with a support member of the present embodiment can be applied to applications such as heat insulating materials in the construction field, the automobile field, home appliances, the semiconductor field, industrial equipment, and the like. Further, the airgel of the present embodiment can be used as an additive for paint, cosmetics, an anti-blocking agent, a catalyst carrier, etc., in addition to being used as a heat insulating material.

<Aerogel with support member>
The airgel of the present embodiment may be one supported by a supporting member (aerogel with a supporting member). The airgel with a support member includes the airgel described above and a support member that supports the airgel. Such an airgel with a support member can exhibit high heat insulation and excellent flexibility.

Examples of the supporting member include a film-like supporting member and a foil-like supporting member.

The film-like support member is formed by forming a polymer raw material into a thin film, and examples thereof include organic films such as PET and polyimide, and glass films (including metal-deposited films).

The foil-shaped support member is formed by forming a metal raw material into a thin film, and examples thereof include aluminum foil and copper foil.

An airgel with a support member can be produced, for example, as follows. First, a sol is prepared according to the sol generation process described above. After applying this to the support member using a film applicator or the like, or after impregnating the support member with this, according to the above-described wet gel production step, a wet gel carried on the film-like support member is obtained. Then, the wet gel supported by the support member is washed and (if necessary) solvent-substituted according to the above-described washing and solvent-substitution steps, and further dried according to the above-described drying step to obtain an airgel with a support member. can be done.

The thickness of the airgel formed on the film-like support member or foil-like support member can be 1-200 μm, but it may be 10-100 μm or 30-80 μm. A thickness of 1 μm or more makes it easy to obtain good heat insulation, and a thickness of 200 μm or less makes it easy to obtain flexibility.

<Package>
The airgel-containing package of the present embodiment includes an airgel and a package formed by sealing the airgel under reduced pressure. That is, it can be said that the airgel-containing package of the present embodiment is a package in which the airgel is sealed in the package under reduced pressure.

The amount of water contained in the airgel is 10×10 ¹⁵ [pieces/cm ² ] or less from the viewpoint of reducing the amount of outgassing under vacuum, but it is preferable that it is 7×10 ¹⁵ [pieces/cm ² ] or less. It is preferably 4×10 ¹⁵ [pieces/cm ² ] or less. The water content [number/cm ² ] can be calculated from the gas desorption strength [A·sec] from the airgel measured under the following conditions using thermal desorption spectrometry.
Airgel size: 9 mm × 8 mm × 40 μm (thickness)
Measurement initial pressure: 3.0 × 10 ^-7 Pa
Measurement time: 45 minutes Measurement temperature: 45°C from 0 to 8 minutes, temperature rising rate from 45°C: 80°C at 5°C/min, and maintained at 80°C until 45 minutes.

From the viewpoint of sufficiently suppressing moisture absorption by the airgel, the packaging body preferably has moisture resistance with sufficiently suppressed water vapor permeability. The moisture vapor permeability of the package is preferably 15 g/m ² /24 hours or less, more preferably 10 g/m ² /24 hours or less, and still more preferably 2 g/m ² /24 hours or less. When the water vapor transmission rate exceeds 15 g/m ² /24 hours, water is adsorbed to the airgel, and the heat insulating performance may deteriorate when the airgel is used under vacuum.

The package is preferably formed from a resin film having an aluminum layer. A specific example of the package includes an aluminum-coated plastic bag. By providing the package with an aluminum coating, the water vapor transmission rate of the package can be reduced. When the package is to be heat-sealed, which will be described later, the material of the exterior of the package is preferably one that can be welded by heat. Examples of such materials include plastics such as polyethylene, polyester, vinyl chloride, and polyethylene terephthalate. As the structure of the package that satisfies these conditions, for example, a three-layered film-like structure in which a polyester layer/AL (aluminum) layer/PE (polyethylene) layer are sequentially laminated is preferable, and PET (polyethylene terephthalate) is preferred. It is more preferable to have a five-layer film-like structure in which a layer/SPE (sand polyethylene) layer/AL (aluminum) layer/SPE layer/PE (polyethylene) layer are sequentially laminated.

When the airgel is housed in the package and sealed, the package should be made of a flexible material and have a bag shape in order to suck the gas in the package and reduce the gas in the package as much as possible. preferable. Moisture absorption of the airgel can be further suppressed by reducing the amount of gas in the package. Moreover, it is preferable that the package has a thickness sufficient to have excellent flexibility. The flexibility referred to here means the degree of softness that can be flexibly deformed according to the structure of the airgel. By having such flexibility, it becomes possible to flexibly deal with airgel having a complicated structure, and it becomes possible to sufficiently reduce the amount of air remaining in the package. Moreover, airgel can be easily taken out as a package is a bag shape. The size of the package is not limited as long as it is large enough to wrap the entire airgel.

However, the packaging does not necessarily have to be bag-like. That is, the airgel may be sandwiched between two packages and the ends of the package may be heat-sealed to accommodate the airgel, or one package may be folded in half so as to sandwich the airgel, and the ends of the package may be heat sealed to contain the airgel.

From the viewpoint of reducing the influence of moisture such as water and steam, the smaller the gas volume in the package, the better. The gas volume in the package is preferably 30% by volume or less of the total volume of the package, more preferably 20% by volume or less, even more preferably 10% by volume or less, and 5% by volume or less. It is most preferable to have

As a preferred aspect of the package of the present embodiment, the airgel supported by the support member and having a water content of 10×10 ¹⁵ [pieces/cm ² ] or less is contained in a bag-shaped package having an aluminum coating layer. Another example is an embodiment in which the opening is heat-sealed after evacuation. As a result, the airgel with a support member, which is excellent in heat insulation and handleability and hardly generates outgas, can be stored for a long period of time while suppressing moisture absorption.

<Manufacturing method of package>
The airgel-containing package of the present embodiment can be produced, for example, by the following method. That is, the method for producing an airgel-containing package of the present embodiment includes a silicon compound having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of the silicon compound having the hydrolyzable functional group Dry a wet gel that is a condensate of a sol containing at least one selected from the group consisting of and optionally silica particles to obtain an airgel having a water content of 10 × 10 ¹⁵ [pieces/cm ² ] or less A drying step of obtaining and a sealing step of sealing the airgel under reduced pressure using a package can be provided.

(Drying process)
Through this step, an airgel with a sufficiently reduced water content is obtained. The temperature and time are not limited, but the water content can be further reduced by treating at a higher temperature for a longer time. The details of the drying process are as described in the section on the airgel production method.

(Sealing process)
In this step, the airgel is sealed in the package so that the airgel obtained in the drying step does not re-adsorb water or the like. More specifically, this step includes a step of accommodating the airgel inside the package, a sealing step of sealing the opening of the package containing the airgel under reduced pressure to obtain an airgel-containing package, can have

As a method for depressurizing the inside of the package (package), for example, a method of vacuuming using a vacuum pump or the like to remove gas containing moisture in the package can be mentioned. At this time, the vacuum drawing condition is not particularly limited, and may be set so that the gas volume in the package is within the above desired range.

The opening of the package can be sealed, for example by heat sealing. Heat sealing means sealing the opening of the package by applying heat and pressure to a part of the package.

The present disclosure will now be described in more detail with the following examples, which are not intended to limit the disclosure.

(Synthesis example)
In a 1-liter three-necked flask equipped with a stirrer, a thermometer and a Dimroth condenser, 100.0 parts by mass of hydroxy-terminated dimethylpolysiloxane "XC96-723" (manufactured by Momentive, product name), methyltrimethoxy 181.3 parts by mass of silane and 0.50 parts by mass of t-butylamine were mixed and reacted at 30° C. for 5 hours. Thereafter, the reaction solution is heated at 140° C. for 2 hours under a reduced pressure of 1.3 kPa to remove volatile matter, thereby obtaining a bifunctional alkoxy-modified polysiloxane compound ( A polysiloxane compound A) was obtained.

[Preparation of airgel]
PL-2L as a raw material containing silica particles (manufactured by Fuso Chemical Industry Co., Ltd., product name, average primary particle size: 20 nm, solid content: 20% by mass) 100.0 parts by mass, water 100.0 parts by mass, acid catalyst 0.10 parts by weight of acetic acid as an ionic surfactant (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter abbreviated as "CTAB") 20.0 parts by weight of urea as a thermohydrolyzable compound 120.0 parts by mass of is mixed, and 60.0 parts by mass of methyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., hereinafter abbreviated as “MTMS”) as a silicon compound and dimethoxydimethylsilane (manufactured by Tokyo Chemical Industry Co., Ltd. , hereinafter abbreviated as "DMDMS") and 20.0 parts by mass of polysiloxane compound A as a polysiloxane compound were added and reacted at 25°C for 1 hour. After that, a sol-gel reaction was carried out at 80° C. for 15 minutes to obtain a sol coating liquid.

(Example 1)
The above sol coating liquid is applied to a base material (vertical) 1500 mm × (horizontal) 1000 mm × (thickness) 12 μm double-sided aluminum vapor deposition PET film (manufactured by Hitachi AIC Co., Ltd., product name: VM-PET). was applied using a film applicator (manufactured by Tester Sangyo Co., Ltd., product name: PI-1210) so that the thickness of the sol was 40 μm, dried at 90 ° C. for 1.5 minutes, and the sol coating liquid was gelled on the support member. turned into After that, the support member on which the gelled product of the sol coating liquid was formed was transferred to a closed container and aged at 60° C. for 3 hours to obtain a wet gel on the support member.

After aging, the supporting member on which the wet gel was formed was immersed in 100 mL of water to wash the wet gel for 1 minute. Next, it was immersed in 100 mL of methanol to replace the solvent for 1 minute. This solvent replacement operation was performed twice while replacing with new methanol. After drying the wet gel washed and solvent-substituted on the support member at 120° C. for 1 minute under normal pressure, a dryer heated to 120° C. (manufactured by Espec Co., Ltd., product name: Perfect Oven SPHH-301 mold) for 24 hours to obtain an airgel with a support member having a structure represented by the general formulas (3), (4) and (5).

Next, a PET (polyethylene terephthalate) layer, an SPE (sand polyethylene) layer, an AL (aluminum) layer, an SPE layer, and a PE (polyethylene) layer were sequentially laminated from the outer layer side of the obtained airgel with a support member. A bag-shaped package formed from a composite film (thickness: 0.14 mm, moisture permeability: 0.1 to 0.29 g/30 days = 0.01 to 0.03 g/m ² /24 hours (calculated value)) housed in the body. After the inside of the package was evacuated using a vacuum sealer (manufactured by Fuji Impulse Co., Ltd.), the opening of the package was sealed by heat sealing. Thus, an airgel-containing package (an airgel-containing package with a supporting member) was obtained.

(Example 2)
An airgel-containing package was obtained in the same manner as in Example 1 except that the wet gel was dried at 120 ° C. for 1 minute under normal pressure and then baked for 48 hours in a dryer heated to 120 ° C. .

(Example 3)
An airgel-containing package was obtained in the same manner as in Example 1 except that the wet gel was dried at 120 ° C. for 1 minute under normal pressure and then baked for 96 hours in a dryer heated to 120 ° C. .

(Comparative example 1)
An airgel-containing package was obtained in the same manner as in Example 1, except that the wet gel was dried at 120° C. for 1 minute under normal pressure and then not baked.

(Comparative example 2)
An airgel with a support member was obtained in the same manner as in Example 1. However, the obtained airgel was not packed using a packing material, and was left in the atmosphere.

Table 1 summarizes the drying method and storage method in each example and comparative example.

[evaluation]
(1) Preparation for Measurement of Released Moisture Amount The packages and the airgels with support members obtained in the respective Examples and Comparative Examples were stored for a predetermined period of time. The storage environment was room temperature. In addition, the storage period of 0 days means that the evaluation was performed immediately after the package was produced. The airgel with a support member was taken out from the package after being stored for a predetermined period of time, and processed into a size of 9 mm (vertical)×8 mm (horizontal). Next, the processed airgel with a support member was fixed on a silicon chip of (vertical) 10 mm × (horizontal) 10 mm × (thickness) 0.24 mm using Kapton tape to obtain a measurement sample. The same operation was performed on the airgel with a supporting member stored in the air atmosphere to obtain a measurement sample.

(2) Measurement of Released Moisture Amount The amount of released moisture of the measurement sample stored for 0 days and/or 4 days was measured using a thermal desorption gas analyzer (manufactured by Denshi Kagaku Co., Ltd., EMD-WA1000S). . In the measurement method, after the measurement sample is put into the measurement chamber, the pressure inside the measurement chamber is evacuated to 3.0 × 10 ^-7 Pa, and the pressure is 3.0 × 10 ^-7 Pa at 0 minutes. As a result, the desorption strength [A·sec] of released water for 45 minutes was measured. The temperature conditions at that time were 45° C. for 0 to 8 minutes, then increased by 5° C. per minute to 80° C., and maintained at 80° C. until 45 minutes. Then, the desorption strength [A·sec] obtained at each time was added up from 0 to 45 minutes, and this was defined as the released water content [pieces/cm ² ] of the measurement sample.
That is, the amount of released water [number/cm ² ] was calculated from the gas desorption strength [A·sec] from the sample measured under the following conditions using the thermal desorption spectrometry method.
Sample size: 9 mm x 8 mm x 40 µm (thickness)
Measurement initial pressure: 3.0 × 10 ^-7 Pa
Measurement time: 45 minutes Measurement temperature: 45°C from 0 to 8 minutes, temperature rising rate from 45°C: 80°C at 5°C/min, and maintained at 80°C until 45 minutes.

From Table 2, it can be seen that the amount of water released from the airgels with support members of Examples is 10×10 ¹⁵ [pieces/cm ² ] or less. Furthermore, it can be seen that there is almost no increase in the amount of released water even after storage for 4 days. Therefore, by sufficiently baking the wet gel to obtain an airgel, and then storing the obtained airgel in a sealed package under reduced pressure, an airgel that can withstand use under vacuum can be obtained. It was confirmed.

On the other hand, in Comparative Example 1, the amount of released water was very large. From this, it can be confirmed that the moisture is removed by sufficiently baking the wet gel.

In Comparative Example 2, the amount of released water increased compared to Example 2. From this, it can be confirmed that the airgel obtained by baking is sealed in a package under reduced pressure to prevent moisture absorption during storage.

1 airgel particles, 2 silica particles, 3 pores, 10 airgel, L circumscribing rectangle.

Claims (8)

an airgel containing an airgel component and having a water content of 10×10 ¹⁵ [pieces/cm ² ] or less;
A package formed by sealing the airgel under reduced pressure;
A package containing an airgel, wherein the airgel is silica airgel . The package according to claim 1, wherein the airgel is supported by a support member. The package according to claim 1 or 2, wherein the package is formed from a resin film having an aluminum layer. The airgel is a silicon compound having a hydrolyzable functional group or a condensable functional group, and at least one selected from the group consisting of a hydrolysis product of the silicon compound having the hydrolyzable functional group. The package according to any one of claims 1 to 3, which is a dried wet gel that is a condensate of the sol contained. The package according to any one of claims 1 to 4, wherein the airgel further contains silica particles. The package according to claim 5, wherein the silica particles have an average primary particle size of 1 to 500 nm. A sol containing at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having the hydrolyzable functional group. a step of drying the wet gel, which is a condensate, to obtain an airgel having a moisture content of 10×10 ¹⁵ [pieces/cm ² ] or less;
A step of sealing the airgel under reduced pressure using a packaging body;
A method for producing an airgel-containing package, wherein the airgel is silica airgel . 8. The manufacturing method according to claim 7, wherein said sealing is by heat sealing.

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