JP6750626B2 - Airgel complex - Google Patents

Description

The present disclosure relates to airgel composites.

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

As a method for producing such a silica airgel, a supercritical drying method is known in which a gel-like compound (alcogel) obtained by hydrolyzing and polymerizing an alkoxysilane is dried under supercritical conditions of a dispersion medium. (For example, see Patent Document 1). In the supercritical drying method, the alcogel and the dispersion medium (solvent used for drying) are introduced into a high-pressure container, and the dispersion medium is heated to a temperature and pressure above its critical point to form a supercritical fluid. It is a method of removing the solvent. However, since the supercritical drying method requires a high-pressure process, it is necessary to invest in a special device that can withstand supercriticality, and also requires a lot of labor and time.

Therefore, a method of 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 of improving the strength of the obtained alcogel by using monoalkyltrialkoxysilane and tetraalkoxysilane together in a specific ratio as a gel raw material and drying at normal pressure is known. (For example, see Patent Document 2). However, when such atmospheric drying is adopted, the gel tends to contract due to the stress caused by the capillary force inside the alcogel.

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

As described above, while various problems have been investigated with respect to the problems of the conventional manufacturing process, even if any of the above processes is adopted, the obtained airgel is poor in handleability and large in size. Since it is difficult, there is a problem in productivity. For example, the agglomerated airgel obtained by the above process may be broken just by touching and lifting it by hand. It is speculated that this is due to the low density of the airgel and the fact that the airgel has a fine pore structure in which fine particles of about 10 nm are weakly connected.

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

The present disclosure has been made in view of the above circumstances, and an object thereof is to provide an airgel composite having excellent heat insulating properties and flexibility.

The present inventor has conducted extensive studies to achieve the above-mentioned object, and as a result, if it is an airgel composite produced using silica particles and a predetermined polysiloxane compound, it has excellent heat insulation and flexibility. Were found to be expressed.

The present disclosure condenses a sol containing silica particles, a polysiloxane compound represented by the following general formula (B), and at least one selected from the group consisting of hydrolysis products of the polysiloxane compound. The present invention provides an airgel composite which is a dried product of a wet gel which is a product. The airgel composite thus obtained is excellent in heat insulation and flexibility.
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 independently represent an alkyl group or aryl group. , M represents an integer of 1 to 50.

The airgel composite may have a ladder-type structure including a pillar and a bridge, and the bridge may have a structure represented by the following general formula (2).
In formula (2), R ⁵ and R ⁶ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50.

The airgel composite can have a ladder structure represented by the following general formula (3).
In formula (3), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b is 1 to 50. Indicates an integer.

The average primary particle diameter of the silica particles can be 1 to 200 nm. This makes it easier to improve heat insulation and flexibility.

At this time, the shape of the silica particles can be spherical. Further, the silica particles can be colloidal silica particles. Thereby, more excellent heat insulating property and flexibility can be achieved.

In the present disclosure, the sol is 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. At least one kind can be further contained. Thereby, more excellent heat insulating property and flexibility can be achieved.

The dried product can be obtained by drying at a temperature below the critical point of the solvent used for drying the wet gel and at atmospheric pressure. This makes it easier to obtain an airgel composite having excellent heat insulation and flexibility.

According to the present disclosure, it is possible to provide an airgel composite having excellent heat insulating properties and flexibility. That is, it is possible to provide an airgel composite that exhibits excellent heat insulation properties, has improved handleability and can be made larger, and can enhance productivity. As described above, the airgel composite having excellent heat insulation and flexibility has a possibility of being utilized in various applications. Here, an important point according to the present disclosure is that it is easier to control the heat insulating property and the flexibility than the conventional airgel. This cannot be achieved by the conventional airgel that needs to sacrifice the heat insulating property to obtain the flexibility or to sacrifice the flexibility to obtain the heat insulating property. The above "excellent in heat insulation and flexibility" does not necessarily mean that the numerical values representing both properties are both high, and for example, "excellent in flexibility while maintaining good heat insulation". , "Excellent heat insulation while maintaining good flexibility" and the like.

It is a figure which represents typically the microstructure of the airgel composite which concerns on one Embodiment of this indication. It is a figure which shows the calculation method of the biaxial average primary particle diameter of a particle. The surface of the airgel composite in the foil-shaped support member with the airgel composite obtained in Example 3 was (a) 10,000 times, (b) 50,000 times, (c) 200,000 times, and (d) 350,000 times. It is a SEM image observed at each magnification. SEM images of the surface of the airgel composite in the foil-like support member with the airgel composite obtained in Example 4, observed at (a) 10,000 times, (b) 50,000 times, and (c) 200,000 times, respectively. Is.

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

<Definition>
In the present specification, the numerical range indicated by using "to" indicates a range including the numerical values before and after "to" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value of the numerical range of a certain stage may be replaced with the upper limit value or the lower limit value of the numerical range of another stage. In the numerical range described in the present specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. “A or B” may include either one of A and B, or may include both. Unless otherwise specified, the materials exemplified in this specification can be used alone or in combination of two or more kinds. In the present specification, the content of each component in the composition is the total amount of the plurality of substances present in the composition, unless a plurality of substances corresponding to each component are present in the composition, unless otherwise specified. means.

<Airgel composite>
In a narrow sense, a dry gel obtained by using a supercritical drying method for a wet gel is an aerogel, a dry gel obtained by drying under atmospheric pressure is a xerogel, and a dry gel obtained by freeze-drying is a cryogel. However, in the present embodiment, the obtained low-density dry gel is referred to as “aerogel” regardless of these drying methods of the wet gel. That is, in the present embodiment, the aerogel means “a gel composed of a microporous solid in whithe the dispersed phase is a gas” that is an aerogel in a broad sense. To do. In general, the inside of an airgel has a mesh-like fine structure and has a cluster structure in which airgel particles of about 2 to 20 nm (particles forming the airgel) are bound. There are pores of less than 100 nm between the skeletons formed by this cluster. As a result, the airgel has a three-dimensionally fine porous structure. The airgel in the present embodiment is, for example, a silica airgel containing silica as a main component. Examples of silica aerogel include so-called organic-inorganic hybridized silica aerogel introduced with an organic group (such as a methyl group) or an organic chain. The airgel composite of the present embodiment has a cluster structure that is a feature of the airgel, even though silica particles are compounded in the airgel, and has a three-dimensionally fine porous structure. ing.

The airgel composite of this embodiment contains an airgel component and silica particles. It should be noted that although not necessarily meaning the same concept as this, it can be expressed that the airgel composite of the present embodiment contains silica particles as a component constituting the three-dimensional network skeleton. .. The airgel composite of this embodiment is excellent in heat insulation and flexibility as described later. In particular, since the flexibility is excellent, the handling property as the airgel composite is improved and the size can be increased, so that the productivity can be improved. In addition, such an airgel composite is obtained by allowing silica particles to exist in an airgel production environment. And the merit of the presence of the silica particles is not only to improve the heat insulating property and flexibility of the composite itself, but also to shorten the time of the wet gel formation step described later or to simplify the washing and solvent replacement steps to the drying step. It is also possible. It should be noted that shortening of the time of this step and simplification of the step are not always required for producing an airgel composite having excellent flexibility.

In this embodiment, there are various composite modes of the airgel component and the silica particles. For example, the airgel component may be in an amorphous form such as a film, or may be in the form of particles (airgel particles). In any of the embodiments, since the airgel component has various forms and exists between the silica particles, it is presumed that flexibility is imparted to the skeleton of the composite.

First, as an example of a composite mode of an airgel component and silica particles, a mode in which an amorphous airgel component is present between silica particles can be mentioned. As such an embodiment, specifically, for example, a mode in which silica particles are coated with a film-shaped airgel component (silicone component) (a mode in which the airgel component includes silica particles), the airgel component serves as a binder, and the silica particles are , A mode in which the airgel component fills a plurality of silica particle gaps, a mode in which these modes are combined (a mode in which silica particles arranged in clusters are covered with the airgel component), and the like. Aspects can be mentioned. As described above, in the present embodiment, the airgel composite can have a three-dimensional network skeleton composed of silica particles and an airgel component (silicone component), and there is no particular limitation on the specific mode (form) thereof.

On the other hand, as will be described later, in the present embodiment, the airgel component may be in the form of distinct particles as shown in FIG.

The mechanism by which such various aspects occur in the airgel composite of the present embodiment is not necessarily clear, but the present inventors presume that the generation rate of the airgel component in the gelation step is involved. For example, the production rate of the airgel component tends to vary by varying the number of silanol groups in the silica particles. Further, the production rate of the airgel component also tends to vary by varying the pH of the system.

This suggests that the mode (size, shape, etc. of the three-dimensional network skeleton) of the airgel composite can be controlled by adjusting the size, shape, number of silanol groups, pH of the system, etc. of the silica particles. Therefore, it is considered that the density, the porosity, etc. of the airgel composite can be controlled, and the heat insulating property and flexibility of the airgel composite can be controlled. The three-dimensional network skeleton of the airgel composite may be composed of only one kind of the various modes described above, or may be composed of two or more kinds of modes.

Hereinafter, the airgel composite of the present embodiment will be described with reference to FIG. 1 as an example, but the present disclosure is not limited to the aspect of FIG. 1 as described above. However, for matters common to any of the above aspects (type, size, content, etc. of silica particles), the following description can be appropriately referred to.

FIG. 1 is a diagram schematically showing a fine structure of an airgel composite according to an embodiment of the present disclosure. As shown in FIG. 1, the airgel composite 10 has a three-dimensional network skeleton formed by the airgel particles 1 constituting the airgel component being three-dimensionally randomly connected partially through the silica particles 2. And pores 3 surrounded by the skeleton. At this time, it is assumed that the silica particles 2 are present between the airgel particles 1 and function as a skeleton support that supports the three-dimensional network skeleton. Therefore, by having such a structure, it is considered that appropriate strength is imparted to the airgel while maintaining the heat insulating property and the flexibility as the airgel. That is, in the present embodiment, the airgel composite may have a three-dimensional network skeleton formed by silica particles being three-dimensionally and randomly connected through the airgel particles. Further, the silica particles may be covered 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 silica particles were successfully introduced into the three-dimensional network skeleton of the airgel in the present embodiment. In this respect, it is considered that the silanol groups of the silica particles also contribute to the affinity of both.

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

The silica particles 2 can be used without particular limitation, and examples thereof include amorphous silica particles. Further, 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, the colloidal silica particles have high monodispersibility, and it is easy to 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 examples thereof include a spherical shape, a cocoon shape, and an association type. Of these, the use of spherical particles as the silica particles 2 facilitates suppression of aggregation in the sol. The average primary particle diameter of the silica particles 2 may be 1 nm or more, and may be 5 nm or more, or 20 nm or more. Further, the average primary particle diameter can be 200 nm or less, and may be 100 nm or less. That is, the average primary particle diameter can be 1 to 200 nm, but may be 5 to 200 nm, or 20 to 100 nm. When the average primary particle diameter 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 composite having excellent shrinkage resistance during drying. On the other hand, when the average primary particle diameter is 200 nm or less, solid heat conduction of the silica particles is easily suppressed, and an airgel composite having excellent heat insulating properties is easily obtained.

It is presumed that the airgel particles 1 (airgel component) and the silica particles 2 are bound together in the form of hydrogen bonds and/or chemical bonds. At this time, it is considered that the hydrogen bond and/or the chemical bond is formed by the silanol group and/or the reactive group of the airgel particle 1 (airgel component) and the silanol group of the silica particle 2. Therefore, it is considered that when the bonding mode is a chemical bond, it is easy to impart appropriate strength to the airgel. Considering this, as the particles to be combined with the airgel component, not only silica particles but also inorganic particles or organic particles having a silanol group on the particle surface can be used.

The number of silanol groups per 1 g of the silica particles 2 may 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 pieces/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 to have excellent shrinkage resistance. It is easier to get a body. On the other hand, when the number of silanol groups is 1000×10 ¹⁸ /g or less, it is easy to suppress sudden gelation during sol preparation, and it is easy to obtain a homogeneous airgel composite.

In the present embodiment, the average particle size of particles (average secondary particle size of airgel particles, average primary particle size of silica particles, etc.) is determined by using a scanning electron microscope (hereinafter abbreviated as “SEM”). It can be obtained by directly observing the cross section of the body. 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 a diameter when the cross section of the skeleton forming the three-dimensional mesh skeleton is regarded as a circle. 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 with a circle having the same area. In calculating the average particle diameter, the diameter of a circle is calculated for 100 particles and the average thereof is calculated.

The average particle diameter of the silica particles can be measured from the raw material. For example, the biaxial average primary particle diameter is calculated as follows from the result of observing 20 arbitrary particles by SEM. That is, taking colloidal silica particles having a solid content concentration of 5 to 40% by mass, which are usually dispersed in water, as an example, a chip formed by cutting a 2 cm square wafer having a pattern wiring into a dispersion liquid of colloidal silica particles is immersed for about 30 seconds. After that, the chip is rinsed with pure water for about 30 seconds and dried by nitrogen blow. Then, the chip is placed on a sample stage for SEM observation, an accelerating voltage of 10 kV is applied, silica particles are observed at a magnification of 100,000 times, and an image is taken. Twenty silica particles are arbitrarily selected from the obtained image, and the average of the particle diameters of these particles is taken as the average particle diameter. At this time, when the selected silica particle has a shape as shown in FIG. 2, a rectangle (circumscribing rectangle L) circumscribing the silica particle 2 and having its longest side the longest is guided. Then, assuming that the long side of the circumscribed rectangle L is X and the short side is Y, the biaxial average primary particle diameter is calculated as (X+Y)/2, and is set as the particle diameter of the particle.

The size of the pores 3 in the airgel composite will be described in the section [Density and Porosity] below.

The content of the airgel component contained in the airgel composite can be 4 parts by mass or more based on 100 parts by mass of the total amount of the airgel composite, but may be 10 parts by mass or more. The content may be 25 parts by mass or less, but may be 20 parts by mass or less. That is, the content can be 4 to 25 parts by mass, but may be 10 to 20 parts by mass. When the content is 4 parts by mass or more, it is easy to impart appropriate strength, and when the content is 25 parts by mass or less, it is easy to obtain good heat insulating properties.

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

In addition to these airgel components and silica particles, the airgel composite 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 the other components is not particularly limited, but from the viewpoint of sufficiently ensuring the desired effect of the airgel composite, it can be 1 to 5 parts by mass with respect to 100 parts by mass of the total amount of the airgel composite.

The airgel composite of the present embodiment comprises silica particles, a polysiloxane compound represented by the following general formula (B), and at least one selected from the group consisting of hydrolysis products of the polysiloxane compound. It is a dried product of a wet gel which is a condensate of the contained sol (a wet gel produced from the sol is dried).
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 independently represent an alkyl group or aryl group. , M represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Moreover, examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In the formula (B), two R ^1b's may be the same or different, and two R ^2b's may be the same or different, and similarly two R ^1b's may be the same. ^3b may be the same or different. Further, in the formula (B), when m is an integer of 2 or more, the two or more R ^4b may be the same or different, and similarly, the two or more R ^5b are also the same. May also be different.

By using a wet gel (produced from a sol) which is a condensate of a sol containing the polysiloxane compound having the above structure or a hydrolysis product thereof, a flexible airgel composite having low thermal conductivity can be obtained more easily. From such a point of view, in the 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 as the alkyl group or the alkoxy group, Examples thereof include a methyl group, a methoxy group and an ethoxy group. Further, in the formula (B), R ^2b and R ^3b each independently include an alkoxy group having a carbon number of 1 to 6, 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. Further, in the formula (B), m can be 2 to 30, but may be 5 to 20.

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

Since the alkoxy group is hydrolyzed, the polysiloxane compound having an alkoxy group may be present as a hydrolysis product in the sol, and the polysiloxane compound having an alkoxy group and the hydrolysis product are mixed. You may have. Further, in the polysiloxane compound having an alkoxy group, all the alkoxy groups in the molecule may be hydrolyzed or may be partially hydrolyzed.

In producing the airgel composite of the present embodiment, the above-mentioned sol is composed of another polysiloxane compound having (in the molecule) a hydrolyzable functional group or a condensable functional group, and the hydrolyzable functional group. It may further contain at least one selected from the group consisting of hydrolysis products of other polysiloxane compounds having a group. Hereinafter, at least one selected from the group consisting of the polysiloxane compound represented by the general formula (B), and a hydrolysis product of the polysiloxane compound, and a hydrolyzable functional group (in the molecule) or At least one selected from the group consisting of the other polysiloxane compound having a condensable functional group and the hydrolysis product of the other polysiloxane compound having the hydrolyzable functional group, as the case may be. Siloxane compound group").

The functional group in the polysiloxane compound is not particularly limited, but may be a group that reacts with the same functional group or a group that reacts with another functional group. Examples of the hydrolyzable functional group include an alkoxy group contained in the polysiloxane compound having the structure represented by the general formula (B). Examples of the condensable functional group include a hydroxyl group, a silanol group, a carboxyl group and a phenolic hydroxyl group. The hydroxyl group may be contained in a hydroxyl group-containing group such as a hydroxyalkyl group. The other polysiloxane compound having a hydrolyzable functional group or a condensable functional group may be a reactive group different from the hydrolyzable functional group and the condensable functional group (the hydrolyzable functional group and the condensable functional group. It may further have a functional group which does not correspond to a functional group having a sex. Examples of the reactive group include an epoxy group, a mercapto group, a glycidoxy group, a vinyl group, an acryloyl group, a methacryloyl group and an amino group. The epoxy group may be contained in an epoxy group-containing group such as a glycidoxy group. These polysiloxane compounds having a functional group and a reactive group may be used alone or in combination of two or more. Among these functional groups and reactive groups, examples of the group that improves the flexibility of the airgel composite include an alkoxy group, a silanol group, and a hydroxyalkyl group. Among these, an alkoxy group and a hydroxyalkyl group Can further improve the compatibility of the sol. From the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the airgel composite, the alkoxy group and the hydroxyalkyl group can have 1 to 6 carbon atoms, but the flexibility of the airgel composite is high. It may be 2 to 4 from the viewpoint of further improving.

Examples of the polysiloxane compound having a hydroxyalkyl group include those having a structure represented by the following general formula (A).

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

By using a wet gel (produced from a sol) which is a condensate of a sol containing the polysiloxane compound having the above structure, a flexible airgel composite having low thermal conductivity can be obtained more easily. From such a viewpoint, in the formula (A), examples of R ^1a include a hydroxyalkyl group having a carbon number of 1 to 6 and the like, and examples of the hydroxyalkyl group include a hydroxyethyl group and a hydroxypropyl group. Further, in the formula (A), R ^2a includes an alkylene group having 1 to 6 carbon atoms, and the alkylene group includes an ethylene group and a propylene group. Further, in the formula (A), R ^3a and R ^4a each independently include an alkyl group having a carbon number of 1 to 6, a phenyl group, and the like, and the alkyl group includes a methyl group and the like. Further, in the formula (A), n may be 2 to 30, but may be 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, and KF-6003 (all are available). , Shin-Etsu Chemical Co., Ltd.), compounds such as XF42-B0970 and Fluid OFOH 702-4% (all are manufactured by Momentive Co.).

These other polysiloxane compounds having a hydrolyzable functional group or a condensable functional group, and hydrolysis products of other polysiloxane compounds having a hydrolyzable functional group may be used alone or in two kinds. The above may be mixed and used.

In producing the airgel composite of the present embodiment, the sol containing the above polysiloxane compound group may further contain a silicon compound (silicon compound) other than the polysiloxane compound. That is, the sol is a silicon compound (excluding a polysiloxane compound) having a hydrolyzable functional group or a condensable functional group (in the molecule), and a hydrolyzable silicon compound having the hydrolyzable functional group. At least one selected from the group consisting of decomposition products (hereinafter, sometimes referred to as "silicon compound group") can be further contained. The number of silicon atoms in the molecule of the silicon compound can be 1 or 2.

The silicon compound having a hydrolyzable functional group is not particularly limited, and examples thereof include alkyl silicon alkoxide. The alkyl silicon alkoxide can have the number of hydrolyzable functional groups of 3 or less from the viewpoint of improving water resistance. Examples of such alkyl silicon alkoxides include monoalkyl trialkoxy silanes, monoalkyl dialkoxy silanes, dialkyl dialkoxy silanes, monoalkyl monoalkoxy silanes, dialkyl monoalkoxy silanes, and trialkyl monoalkoxy silanes. Examples include methyltrimethoxysilane, methyldimethoxysilane, dimethyldimethoxysilane, and ethyltrimethoxysilane. Examples of the hydrolyzable functional group include alkoxy groups such as methoxy group and ethoxy group.

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

The silicon compound having a hydrolyzable functional group or a condensable functional group is a reactive group (hydrolyzable functional group and a condensable functional group) different from the above-mentioned reactive group and a condensable functional group. It may further have a functional group which does not correspond to a group).

The number of hydrolyzable functional groups is 3 or less, and as the silicon compound having a reactive group, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysisilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-amino Propyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane and the like can also be used.

Further, as a silicon compound 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 can also be used.

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

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 may be used alone or in combination of two or more kinds. Good.

Content of the polysiloxane compound group contained in the sol (content of the polysiloxane compound having a hydrolyzable functional group or a condensable functional group, and hydrolysis of the polysiloxane compound having a hydrolyzable functional group The total content of the products) may be 5 parts by mass or more, and may be 10 parts by mass or more based on 100 parts by mass of the total amount of the sol. The content can be 50 parts by mass or less, and may be 30 parts by mass or less, based on 100 parts by mass of the total amount of the sol. That is, the content of the polysiloxane compound group 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 it is 5 parts by mass or more, good reactivity is easily obtained, and when it is 50 parts by mass or less, good compatibility is easily obtained.

Further, when the sol further contains a silicon compound, the content of the polysiloxane compound group and the content of the silicon compound group (content of the silicon compound having a hydrolyzable functional group or a condensable functional group, and, , The total content of the hydrolysis products of the silicon compound having a hydrolyzable functional group) can be 5 parts by mass or more based on 100 parts by mass of the total amount of the sol, and 10 parts by mass or more. It may be. The total amount of the contents can be 50 parts by mass or less, and may be 30 parts by mass or less, based on 100 parts by mass of the total amount of the sol. That is, the sum of the contents 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 total content is 5 parts by mass or more, it becomes easier to obtain good reactivity, and when it is 50 parts by mass or less, it becomes easier to obtain good compatibility. At this time, the ratio of the content of the polysiloxane compound group to the content of the silicon compound group can be 1:0.5 to 1:4, but may be 1:1 to 1:2. .. When the content ratio of these compounds is 1:0.5 or more, good compatibility is more easily obtained, and when it is 1:4 or less, shrinkage of the gel is more easily suppressed.

The content of silica particles contained in the sol may be 1 part by mass or more, and may be 4 parts by mass or more, based on 100 parts by mass of the total amount of the sol. The content can be 20 parts by mass or less, and may be 15 parts by mass or less, based on 100 parts by mass of the total amount of the sol. That is, the content of the silica particles can be 1 to 20 parts by mass with respect to 100 parts by mass of the total amount of the sol, but may be 4 to 15 parts by mass. By setting the content to 1 part by mass or more, it becomes easy to impart appropriate strength to the airgel, and it becomes easy to obtain an airgel composite having excellent shrinkage resistance during drying. Further, when the content is 20 parts by mass or less, solid heat conduction of the silica particles is easily suppressed, and an airgel composite having excellent heat insulating properties is easily obtained. The mode of the silica particles contained in the sol is as described in the section of the airgel composite.

<Specific embodiment of airgel composite>
The airgel composite of the present embodiment comprises silica particles, at least one selected from the group consisting of the polysiloxane compound represented by the general formula (B), and a hydrolysis product of the polysiloxane compound. It is a dried product of a wet gel which is a condensate of the contained sol (obtained by drying the wet gel produced from the above sol). In addition, as described above, the condensate is obtained by a condensation reaction of a hydrolysis product obtained by hydrolysis of the polysiloxane compound represented by the general formula (B) having a hydrolyzable functional group. However, the condensate is not a condensation reaction of a hydrolysis product obtained by hydrolysis of another polysiloxane compound or a silicon compound having a hydrolyzable functional group, or a functional group obtained by hydrolysis. It may be obtained with a condensation reaction of another polysiloxane compound having a condensable functional group or a silicon compound. The other polysiloxane compound and the silicon compound may have at least one of a hydrolyzable functional group and a condensable functional group, and have both a hydrolyzable functional group and a condensable functional group. May be.

The airgel composite of the present embodiment can contain polysiloxane having a main chain containing a siloxane bond (Si-O-Si). The airgel composite may have the following M unit, D unit, T unit or Q unit as a structural unit.

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. The M unit is a unit composed of a monovalent group in which a silicon atom is bonded to one oxygen atom. The D unit is a unit composed of a divalent group in which a silicon atom is bonded to two oxygen atoms. The T unit is a unit composed of a trivalent group in which a silicon atom is bonded to three oxygen atoms. The Q unit is a unit composed 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 airgel composite of the present embodiment can have a ladder-type structure including a column and a bridge, and the bridge can have a structure represented by the following general formula (2). By introducing such a ladder type structure into the skeleton of the airgel composite as an airgel component, heat resistance and mechanical strength can be improved. By using a polysiloxane compound having a structure represented by the general formula (B), a ladder type structure having a bridging portion represented by the general formula (2) is introduced into the skeleton of the airgel composite. You can In the present embodiment, the “ladder structure” has two strut portions and bridge portions that connect the strut portions to each other (a so-called “ladder” form). Is. In this embodiment, the skeleton of the airgel composite may have a ladder type structure, but the airgel composite may partially have a ladder type structure.

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

By introducing the above structure into the skeleton of the airgel composite as an airgel component, for example, it has a structure derived from a conventional ladder-type silsesquioxane (that is, a structure represented by the following general formula (X) To have an aerogel composite having flexibility superior to that of the aerogel. Silsesquioxane is a polysiloxane having a composition formula: (RSiO _1.5 ) _n and can have various skeleton structures such as a cage type, a ladder type, and a random type. As shown in the following general formula (X), in the conventional airgel having a structure derived from ladder-type silsesquioxane, the structure of the bridging part is -O- (having the above-mentioned T unit as a structural unit). In the airgel composite of this embodiment, the structure of the crosslinked portion is the structure represented by the general formula (2) (polysiloxane structure). However, the airgel of the present embodiment may have a structure derived from silsesquioxane, in addition to the structure represented by the general formula (2).

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

The structure of the strut and its chain length, and the interval of the structure serving as the bridge are not particularly limited, but from the viewpoint of further improving heat resistance and mechanical strength, the ladder-type structure has the following general formula ( It may have a ladder structure represented by 3).

In formula (3), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b is 1 to 50. Indicates an integer. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Moreover, examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In the formula (3), when b is an integer of 2 or more, two or more R ⁵ may be the same or different, and similarly, the two or more R ⁶ are also the same. May also be different. Further, in the formula (3), when a is an integer of 2 or more, two or more R ^7's may be the same or different, and similarly, when c is an integer of 2 or more, 2 or more. R ^{8 s} in each may be the same or different.

From the viewpoint of obtaining better flexibility, as R ⁵ , R ⁶ , R ^7, and R ⁸ in formulas (2) and (3) (provided that R ⁷ and R ⁸ are only in formula (3)). Are independently an alkyl group having a carbon number of 1 to 6, a phenyl group and the like, and the alkyl group includes a methyl group and the like. In addition, in the formula (3), a and c can independently be 6 to 2000, but may be 10 to 1000. Further, in the formulas (2) and (3), b can be 2 to 30, but may be 5 to 20.

The airgel composite of this embodiment may have a structure represented by the following general formula (1). The airgel composite of the present embodiment can have a structure represented by the following general formula (1a) as a structure including the structure represented by the formula (1). By using the polysiloxane compound having the structure represented by the general formula (A), the structures represented by the formulas (1) and (1a) can be introduced into the skeleton of the airgel composite.

In Formula (1) and Formula (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, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group and a cyano group. p represents an integer of 1 to 50. In formula (1a), two or more R ^1's may be the same or different, and similarly, two or more R ² 's may be the same or different. In formula (1a), two R ^{3 s} may be the same or different, and similarly two R ^{4 s} may be the same or different.

By introducing the structure represented by the above formula (1) or formula (1a) into the skeleton of the airgel composite as an airgel component, a flexible airgel composite having low thermal conductivity is obtained. From such a viewpoint, in the formulas (1) and (1a), R ¹ and R ² each independently include an alkyl group having a carbon number of 1 to 6, a phenyl group, and the like. , A methyl group and the like. Further, in the formulas (1) and (1a), R ³ and R ⁴ each independently include an alkylene group having 1 to 6 carbon atoms, and the alkylene group includes an ethylene group and a propylene group. Can be mentioned. In the formula (1a), p can be 2 to 30, and may be 5 to 20.

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

In formula (4), R ⁹ represents an alkyl group. Here, examples of the alkyl group include an alkyl group having 1 to 6 carbon atoms, and examples of the alkyl group include a methyl group.

The airgel composite 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, examples of the alkyl group include an alkyl group having 1 to 6 carbon atoms, and examples of the alkyl group include a methyl group.

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

In formula (8), R ¹² represents an alkylene group. Here, examples of the alkylene group include an alkylene group having 1 to 10 carbon atoms, and examples of the alkylene group include an ethylene group and a hexylene group.

<Physical properties of airgel composite>
[Thermal conductivity]
In the airgel composite of the present embodiment, the thermal conductivity at 25° C. under atmospheric pressure can be 0.03 W/m·K or less, but may be 0.025 W/m·K or less, or It may be 0.02 W/m·K or less. When the thermal conductivity is 0.03 W/m·K or less, it is possible to obtain heat insulation properties higher than that of polyurethane foam which is a high performance heat insulation material. The lower limit of the thermal conductivity is not particularly limited, but may be 0.01 W/m·K, for example.

The thermal conductivity can be measured by a stationary method. Specifically, for example, it can be measured using a steady-state method thermal conductivity measuring device “HFM436 Lambda” (product name, HFM436 Lambda is a registered trademark, manufactured by NETZSCH). The outline of the method for measuring the thermal conductivity using the steady-state thermal conductivity measuring device is as follows.

(Preparation of measurement sample)
Using a blade having a blade angle of about 20 to 25 degrees, the airgel composite is processed into a size of 150 mm×150 mm×100 mm to obtain a measurement sample. The recommended sample size for HFM436 Lambda is 300 mm×300 mm×100 mm, but the thermal conductivity when measured with the above sample size is similar to the thermal conductivity when measured with the recommended sample size. It has been confirmed. Next, in order to ensure the parallelism of the surfaces, the measurement sample is shaped with sandpaper of #1500 or more as needed. Then, before measuring the thermal conductivity, a constant temperature dryer "DVS402" (manufactured by Yamato Scientific Co., Ltd., product name) is used to dry the measurement sample under atmospheric pressure at 100°C for 30 minutes. Then, the measurement sample is transferred into a desiccator and cooled to 25°C. As a result, a measurement sample for measuring thermal conductivity is obtained.

(Measuring method)
The measurement conditions are atmospheric pressure and an average temperature of 25°C. The measurement sample obtained as described above was sandwiched between the upper and lower heaters with a load of 0.3 MPa, the temperature difference ΔT was set to 20° C., and a guard heater was used to adjust the heat flow to a one-dimensional heat flow. Measure the upper surface temperature, lower surface temperature, etc. Then, the thermal resistance R _S of the measurement sample is obtained from the following equation.
R _S =N((T _U −T _L )/Q)−R _O
In the formula, T _U represents the upper surface temperature of the measurement sample, T _L represents the lower surface temperature of the measurement sample, R _O represents the contact thermal resistance at the upper and lower interfaces, and Q represents the heat flux meter output. It should be noted that N is a proportional coefficient and is obtained in advance using a calibration sample.

From the obtained thermal resistance R _S , the thermal conductivity λ of the measurement sample is calculated by the following equation.
λ=d/R _S
In the formula, d represents the thickness of the measurement sample.

[Compression modulus]
In the airgel composite of the present embodiment, the compressive elastic modulus at 25° C. can be 3 MPa or less, but may be 2 MPa or less, 1 MPa or less, or 0.5 MPa or less. Good. When the compressive elastic modulus is 3 MPa or less, it becomes easy to form an airgel composite having excellent handleability. The lower limit of the compression elastic modulus is not particularly limited, but may be 0.05 MPa, for example.

[Deformation recovery rate]
In the airgel composite of the present embodiment, the deformation recovery rate at 25° C. can be 90% or more, but may be 94% or more, or 98% or more. When the deformation recovery rate is 90% or more, it becomes easier to obtain excellent strength, excellent flexibility with respect to deformation and the like. The upper limit of the deformation recovery rate is not particularly limited, but can be 100% or 99%, for example.

[Maximum compression deformation rate]
In the airgel composite of the present embodiment, the maximum compressive deformation rate at 25° C. can be 80% or more, but may be 83% or more, or 86% or more. When the maximum compression deformation rate is 80% or more, it becomes easier to obtain excellent strength, excellent flexibility with respect to deformation, and the like. The upper limit of the maximum compressive deformation rate is not particularly limited, but may be 90%, for example.

The compressive elastic modulus, the deformation recovery rate and the maximum compressive deformation rate can be measured using a small tabletop tester “EZTest” (manufactured by Shimadzu Corporation, product name). The outline of the method for measuring the compressive elastic modulus and the like using a small bench tester is as follows.

(Preparation of measurement sample)
The airgel composite is processed into a cube (dice shape) of 7.0 mm square by using a blade having a blade angle of about 20 to 25 degrees to obtain a measurement sample. Next, in order to ensure the parallelism of the surfaces, the measurement sample is shaped with sandpaper of #1500 or more as needed. Then, before measurement, a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd., product name) is used to dry the measurement sample at 100° C. for 30 minutes under atmospheric pressure. Then, the measurement sample is transferred into a desiccator and cooled to 25°C. Thereby, a measurement sample for measuring the compression elastic modulus, the deformation recovery rate, and the maximum compression deformation rate is obtained.

(Measuring method)
A 500 N load cell is used. Further, an upper platen (φ20 mm) and a lower platen (φ118 mm) made of stainless steel are used as a jig for compression measurement. The measurement sample is set between these jigs, compressed at a speed of 1 mm/min, and the displacement of the measurement sample size at 25° C. is measured. The measurement ends when a load of over 500 N is applied or when the measurement sample breaks. Here, the compressive strain ε can be obtained from the following equation.
ε=Δd/d1
In the formula, Δd represents the displacement (mm) of the thickness of the measurement sample due to the load, and d1 represents the thickness (mm) of the measurement sample before applying the load.
The compressive stress σ (MPa) can be obtained from the following equation.
σ=F/A
In the formula, F represents the compressive force (N), and A represents the cross-sectional area (mm ² ) of the measurement sample before applying a load.

The compressive elastic modulus E (MPa) can be obtained from the following equation in the compressive force range of 0.1 to 0.2 N, for example.
E=(σ ₂ −σ ₁ )/(ε ₂ −ε ₁ ).
In the formula, σ ₁ indicates a compressive stress (MPa) measured at a compressive force of 0.1 N, σ ₂ indicates a compressive stress (MPa) measured at a compressive force of 0.2 N, and ε ₁ indicates a compressive stress. The compressive strain measured at σ ₁ is shown, and ε ₂ is the compressive strain measured at compressive stress σ ₂ .

On the other hand, the deformation recovery rate and the maximum compressive deformation rate are the thickness of the measurement sample before applying the load d1, the thickness of the measurement sample at the time when the maximum load of 500 N is applied or the measurement sample is broken, and the load is removed. It can be calculated according to the following equation, where d3 is the thickness of the measured sample after the measurement.
Deformation recovery rate=(d3-d2)/(d1-d2)×100
Maximum compression deformation rate=(d1−d2)/d1×100

The thermal conductivity, compressive elastic modulus, deformation recovery rate, and maximum compressive deformation rate can be appropriately adjusted by changing the production conditions, raw materials, and the like of the airgel composite described later.

[Density and porosity]
In the airgel composite 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 composite having excellent flexibility, and when it is 1000 nm or less, it becomes easy to obtain an airgel composite having excellent heat insulating properties.

In airgel composite of this embodiment, the density can be 0.05~0.25g / cm ³ at 25 ° C., may be 0.1 to 0.2 g / cm ^3. When the density is 0.05 g/cm ³ or more, more excellent strength and flexibility can be obtained, and when the density is 0.25 g/cm ³ or less, more excellent heat insulating property can be obtained. it can.

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

The average pore diameter, the density and the porosity of the three-dimensional mesh-shaped continuous pores (through holes) in the airgel composite can be measured by the mercury porosimetry according to DIN66133. As the measuring device, for example, Autopore IV9520 (manufactured by Shimadzu Corporation, product name) can be used.

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

That is, the airgel composite of the present embodiment was obtained in the sol-forming step, the wet gel-forming step of gelling the sol obtained in the sol-forming step, and then aging to obtain the wet gel, and the wet-gel forming step. It can be manufactured by a manufacturing method mainly including a step of washing and replacing the wet gel with a solvent (if necessary) and a drying step of drying the washed and solvent-replaced wet gel. The "sol" is a state before the gelation reaction occurs, and in the present embodiment, the polysiloxane compound group, and optionally the silicon compound group, and the silica particles are dissolved or dispersed in a solvent. Means that The wet gel means a gel solid in a wet state which does not have fluidity even though it contains a liquid medium.

Hereinafter, each step of the method for producing an airgel composite according to this embodiment will be described.

(Sol generation process)
The sol generation step is a step of mixing the above-mentioned polysiloxane compound, a silicon compound, and optionally silica particles and/or a solvent containing silica particles, and hydrolyzing them to generate a sol. In this step, an acid catalyst may be further added to the solvent in order to accelerate the hydrolysis reaction. Further, as shown in Japanese Patent No. 5250900, a surfactant, a thermohydrolyzable compound, etc. can be added to the solvent. Further, 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 mixed liquid of water and alcohols can be used. Examples of alcohols include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol and t-butanol. Among these, methanol, ethanol, 2-propanol, etc. are mentioned as an alcohol with a low surface tension and a low boiling point in order to reduce the interfacial tension with a gel wall. You may use these individually or in mixture of 2 or more types.

For example, when alcohols are used as the solvent, the amount of the alcohols can be 4 to 8 mol per 1 mol of the total amount of the polysiloxane compound group and the silicon compound group, but it is 4 to 6.5 mol. Well, it may be 4.5 to 6 moles. When the amount of alcohols is 4 mol or more, good compatibility is more easily obtained, and when it is 8 mol or less, shrinkage of the gel is more easily suppressed.

As the acid catalyst, 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 phosphoric acid Acidic phosphates such as aluminum, acidic magnesium phosphate, acidic zinc phosphate; acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid, azelaic acid and other organic carboxylic acids And so on. Among these, organic carboxylic acids are mentioned as the acid catalyst which further improves the water resistance of the obtained airgel composite. Examples of the organic carboxylic acids include acetic acid, but may be formic acid, propionic acid, oxalic acid, malonic acid and the like. You may use these individually or in mixture of 2 or more types.

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

The addition amount of the acid catalyst can be 0.001 to 0.1 parts by mass based on 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group.

As the surfactant, a nonionic surfactant, an ionic surfactant or the like can be used. You may use these individually or in mixture of 2 or more types.

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

Examples of the ionic surfactant include a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. Examples of the cationic surfactant include cetyltrimethylammonium bromide, cetyltrimethylammonium chloride and the like, and examples of the anionic surfactant include sodium dodecylsulfonate and the like. Examples of the zwitterionic surfactant include amino acid surfactants, betaine surfactants, amine oxide surfactants and the like. Examples of the amino acid-based surfactant include acylglutamic acid and the like. Examples of betaine-based surfactants include lauryldimethylaminoacetic acid betaine and stearyldimethylaminoacetic acid betaine. Examples of the amine oxide-based surfactant include lauryl dimethyl amine oxide.

These surfactants reduce the difference in chemical affinity between the solvent in the reaction system and the growing siloxane polymer and suppress the phase separation in the wet gel formation step described later. Is believed to be.

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

It is considered that the thermohydrolyzable compound generates a basic catalyst by thermal hydrolysis to make the reaction solution basic and promotes the sol-gel reaction in the wet gel forming step described later. Therefore, the thermohydrolyzable compound is not particularly limited as long as it is a compound that can make the reaction solution basic after hydrolysis, and urea; formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N Examples thereof include acid amides such as -methylacetamide and N,N-dimethylacetamide; cyclic nitrogen compounds such as hexamethylenetetramine. Among these, urea is particularly likely to obtain the above-mentioned promoting effect.

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

The hydrolysis in the sol formation step depends on the type and amount of the polysiloxane compound, silicon compound, silica particles, acid catalyst, surfactant, etc. in the mixed solution, but is, for example, under a temperature environment of 20 to 60°C. It may be carried out for 10 minutes to 24 hours, or may be carried out for 5 minutes to 8 hours under a temperature environment of 50 to 60°C. Thereby, the hydrolyzable functional groups in the polysiloxane compound and the silicon compound are sufficiently hydrolyzed, and the hydrolysis product of the polysiloxane compound and the hydrolysis product of the silicon compound can be more reliably obtained.

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

(Wet gel formation process)
The wet gel forming step is a step of gelating 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.

As the base catalyst, alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride and ammonium bromide; sodium metaphosphate. , Basic sodium phosphates such as sodium pyrophosphate, 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-( Aliphatic amines such as dimethylamino)propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine; morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and its derivatives, piperidine and its Examples thereof include nitrogen-containing heterocyclic compounds such as derivatives, imidazole, and their derivatives. Among these, ammonium hydroxide (ammonia water) has high volatility and is unlikely to remain in the airgel composite after drying, so that it is difficult to impair the water resistance, and is further excellent in economical efficiency. The above base catalysts may be used alone or in combination of two or more.

By using the base catalyst, the dehydration condensation reaction and/or dealcoholization condensation reaction of the polysiloxane compound group, the silicon compound group, and the silica particles in the sol can be promoted, and gelation of the sol can be performed in a shorter time. It can be carried out. Further, this makes it possible to obtain a wet gel having higher strength (rigidity). In particular, ammonia has high volatility and is unlikely to remain in the airgel composite. Therefore, by using ammonia as the base catalyst, an airgel composite having more excellent water resistance can be obtained.

The addition amount of the base catalyst can be 0.5 to 5 parts by mass with respect to 100 parts by mass of the total amount of the polysiloxane compound group and the silicon compound group, but may be 1 to 4 parts by mass. 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, a decrease in water resistance can be further suppressed.

The gelation of the sol in the wet gel formation step may be performed in a closed container so that the solvent and the base catalyst do not volatilize. The gelling temperature may be 30 to 90°C, but may be 40 to 80°C. By setting the gelling temperature to 30° C. or higher, gelation can be performed in a shorter time, and a wet gel having higher strength (rigidity) can be obtained. Further, by setting the gelling temperature to 90° C. or lower, it is easy to suppress the volatilization of the solvent (particularly alcohols), and thus it is possible to gel while suppressing the volume shrinkage.

The aging in the wet gel forming step may be performed in a closed container so that the solvent and the base catalyst do not volatilize. By aging, the binding of the components that make up the wet gel is strengthened, and as a result, a wet gel having high strength (rigidity) sufficient to suppress shrinkage during drying can be obtained. The aging temperature may be 30 to 90°C, but may be 40 to 80°C. By setting the aging temperature to 30°C or higher, a wet gel having higher strength (rigidity) can be obtained, and by setting the aging temperature to 90°C or lower, it becomes easy to suppress the volatilization of the solvent (especially alcohols). Therefore, gelation can be achieved while suppressing volume shrinkage.

Since it is often difficult to determine the end point of gelation of the sol, gelation of the sol and subsequent aging may be carried out continuously by a series of operations.

The gelation time and the aging time differ depending on the gelation temperature and the aging temperature, but in the present embodiment, since silica particles are contained in the sol, the gelation time is particularly longer than that of the conventional airgel production method. Can be shortened. The reason for this is presumed to be that the silanol groups and/or reactive groups contained in the polysiloxane compound, silicon compound, etc. in the sol form hydrogen bonds and/or chemical bonds with the silanol groups of the silica particles. The gelling time may be 10 to 120 minutes, but may be 20 to 90 minutes. By setting the gelling time to 10 minutes or longer, it is easy to obtain a homogeneous wet gel, and by setting it to 120 minutes or shorter, the washing and solvent replacement steps to be described later and the drying step can be simplified. The total time of gelation time and aging time can be 4 to 480 hours in the entire steps of gelation and aging, but it may be 6 to 120 hours. By setting the total of the gelling time and the aging time to 4 hours or more, a wet gel having higher strength (rigidity) can be obtained, and by setting it to 480 hours or less, the effect of aging can be more easily maintained.

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

(Washing and solvent replacement steps)
The washing and solvent replacement steps include a step of washing the wet gel obtained in the wet gel generation step (washing step) and a step of replacing the washing solution in the wet gel with a solvent suitable for the drying conditions (drying step described below). It is a process including (solvent replacement process). The washing and solvent replacement steps can be performed in a form in which only the solvent replacement step is performed without performing the step of washing the wet gel, but impurities such as unreacted products and by-products in the wet gel are reduced, and The wet gel may be washed from the viewpoint of enabling production of a highly pure airgel composite. In addition, in this embodiment, since the silica particles are contained in the gel, the solvent substitution step is not always essential as described later.

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

As the organic solvent, 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. , Various organic solvents such as N,N-dimethylformamide, dimethylsulfoxide, acetic acid and formic acid can be used. The above organic solvents may be used alone or in combination of two or more.

In the solvent replacement step described below, a solvent having a low surface tension can be used in order to suppress the shrinkage of the gel due to drying. However, low surface tension solvents generally have very low mutual solubility with water. Therefore, when a low surface tension solvent is used in the solvent replacement step, examples of the organic solvent used in the washing step include hydrophilic organic solvents having high mutual solubility in both water and the low surface tension solvent. The hydrophilic organic solvent used in the washing step can serve as a preliminary replacement for the solvent replacement step. Among the above organic solvents, examples of the hydrophilic organic solvent include methanol, ethanol, 2-propanol, acetone and methyl ethyl ketone. In addition, methanol, ethanol, methyl ethyl ketone and the like are excellent in economical efficiency.

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

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

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

Examples of the solvent having a low surface tension include a solvent having a surface tension of 30 mN/m or less at 20°C. The surface tension may be 25 mN/m or less, or 20 mN/m or less. Examples of the low surface tension solvent include pentane (15.5), hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4), 3- Aliphatic hydrocarbons such as methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2), 1-pentene (16.0); 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 the like 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 (esters have surface tension at 20° C., and unit is [mN/m]). Of these, aliphatic hydrocarbons (hexane, heptane, etc.) have low surface tension and are excellent in work environment. Further, among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, or 1,2-dimethoxyethane, it can be used also as the organic solvent in the above-mentioned washing step. Note that among these, a solvent having a boiling point of 100° C. or less at normal pressure may be used because it is easy to dry in the drying step described later. You may use the said solvent individually or in mixture of 2 or more types.

The amount of the 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 equal to or lower than the boiling point of the solvent used for the replacement, and for example, when heptane is used, it can be heated at about 30 to 60°C.

In addition, in this embodiment, since the silica particles are contained in the gel, the solvent replacement step is not always essential as described above. The inferred mechanism is as follows. That is, in the past, in order to suppress shrinkage in the drying step, the solvent of the wet gel was replaced with a predetermined displacing solvent (a solvent having a low surface tension), but in the present embodiment, the silica particles have a three-dimensional network shape. By functioning as a support for the skeleton, the skeleton is supported and the shrinkage of the gel in the drying step is suppressed. Therefore, it is considered that the gel can be directly subjected to the drying step without replacing the solvent used for washing. As described above, in the present embodiment, the washing and solvent replacement steps to the drying step can be simplified. However, this embodiment does not exclude performing the solvent replacement step.

(Drying process)
In the drying step, the wet gel, which has been washed and solvent-substituted as described above, is dried. Thereby, the airgel composite can be finally obtained. That is, an airgel composite obtained by drying the wet gel produced from the sol can be obtained.

The drying method is not particularly limited, and known atmospheric drying, supercritical drying or freeze drying can be used. Among these, atmospheric pressure drying or supercritical drying can be used from the viewpoint of easily producing a low density airgel composite. From the viewpoint of being able to produce at low cost, atmospheric drying can be used. In the present embodiment, normal pressure means 0.1 MPa (atmospheric pressure).

The airgel composite of the present embodiment can be obtained by drying the washed and solvent-substituted wet gel (at need) at a temperature below the critical point of the solvent used for drying under atmospheric pressure. The drying temperature depends on the type of solvent that has been replaced (the solvent used for washing when solvent replacement is not performed), but especially when drying at high temperatures accelerates the evaporation rate of the solvent and causes large cracks in the gel. In view of the fact that there is, the temperature can be set to 20 to 150°C. The drying temperature may be 60 to 120°C. The drying time may vary depending on the volume of the wet gel and the drying temperature, but may be 4 to 120 hours. In addition, in the present embodiment, to accelerate the drying by applying a pressure below the critical point within a range that does not impair the productivity is also included in the atmospheric drying.

The airgel composite of the present embodiment can also be obtained by supercritically drying a washed and solvent-substituted wet gel (if necessary). Supercritical drying can be performed by a known method. Examples of the method of supercritical drying include a method of removing the solvent at a temperature and a pressure not lower than the critical point of the solvent contained in the wet gel. Alternatively, as a method of supercritical drying, by dipping the wet gel in liquefied carbon dioxide under conditions of, for example, 20 to 25° C. and 5 to 20 MPa, all or part of the solvent contained in the wet gel. After substituting the carbon dioxide with carbon dioxide having a lower critical point than the solvent, carbon dioxide may be used alone or a mixture of carbon dioxide and the solvent may be removed.

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

<Supporting member with airgel composite>
By forming the airgel composite of this embodiment on a predetermined support member, it can be used as a support member with an airgel composite. That is, the support member with the airgel composite includes the airgel composite described above and the support member carrying the airgel composite. With such a supporting member with an airgel composite, it is possible to exhibit high heat insulation and excellent flexibility.

Examples of the supporting member include a film-shaped supporting member, a sheet-shaped supporting member, a foil-shaped supporting member, and a porous supporting member.

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

The sheet-shaped support member is a member formed by molding a fibrous raw material of organic, inorganic and/or metal, and includes paper, non-woven fabric (including glass mat), organic fiber cloth, glass cloth and the like.

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

The porous support member is a member having a porous structure made of organic, inorganic and/or metal as a raw material, and includes a porous organic material (for example, polyurethane foam), a porous inorganic material (for example, a zeolite sheet), and a porous material. A metal material (for example, a porous metal sheet or a porous aluminum sheet) can be used.

The support member with the airgel composite can be produced, for example, as follows. First, a sol is prepared according to the sol generation process described above. After applying the sol to a support member using a film applicator or the like, or after impregnating the sol with the support member, a support member with a wet gel is obtained according to the above-described wet gel generating step. Then, the obtained supporting member with a wet gel is subjected to washing and solvent replacement (if necessary) according to the above-mentioned washing and solvent replacement steps, and further dried according to the above-mentioned drying step to obtain a supporting member with an airgel composite. be able to.

The thickness of the airgel composite formed on the film-shaped support member or the foil-shaped support member may be 1 to 200 μm, but may be 10 to 100 μm or 30 to 80 μm. When it is 1 μm or more, good heat insulating property is easily obtained, and when it is 200 μm or less, flexibility is easily obtained.

The airgel composite of the present embodiment as described above contains the airgel component and silica particles, and thus has excellent heat insulating properties and flexibility that are difficult to achieve with conventional airgel. Particularly excellent flexibility has made it possible to form a layer of an airgel composite on a film-shaped support member and a foil-shaped support member, which have heretofore been difficult to achieve. Therefore, the support member with the airgel composite of the present embodiment has high heat insulation and excellent flexibility. Even in the mode in which the sheet-shaped support member and the porous support member are impregnated with the sol, it is possible to suppress the powder drop of the airgel composite during handling after drying.

Due to such advantages, the airgel composite and the support member with the airgel composite of the present embodiment can be applied to applications such as a heat insulating material in the fields of construction, automobiles, home appliances, semiconductors, industrial equipment, and the like. Further, the airgel composite of the present embodiment can be used not only as a heat insulating material but also as an additive for paints, cosmetics, an anti-blocking agent, a catalyst carrier, and the like.

<Insulation material>
The airgel composite of this embodiment can be used as a heat insulating material. Such a heat insulating material has high heat insulating properties and excellent flexibility. The airgel composite obtained by the above-mentioned method for producing an airgel composite can be used as it is (processed into a predetermined shape as necessary) to serve as a heat insulating material.

Next, the present disclosure will be described in more detail by the following examples, but these examples do not limit the present disclosure.

(Example 1) [Wet gel, airgel composite]
200.0 parts by mass of PL-06L (details of PL-06L are shown in Table 1. The same applies to the silica particle-containing starting material) as a silica particle-containing raw material, 0.10 parts by mass of acetic acid as an acid catalyst, and a cation system. 20.0 parts by mass of cetyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.: hereinafter abbreviated as “CTAB”) as a surfactant and 120.0 parts by mass of urea as a thermally hydrolyzable compound were mixed, and mixed with this. 80.0 parts by mass of methyltrimethoxysilane LS-530 (manufactured by Shin-Etsu Chemical Co., Ltd., product name: abbreviated as "MTMS" hereinafter) as a silicon compound, and a structure represented by the above general formula (B) as a polysiloxane compound. 20.0 parts by mass of a bifunctional alkoxy-modified polysiloxane compound having both ends (hereinafter referred to as “polysiloxane compound A”) was added and reacted at 25° C. for 2 hours to obtain Sol 1. The obtained sol 1 was gelated at 60° C. and then aged at 80° C. for 24 hours to obtain wet gel 1.

Then, the obtained wet gel 1 was immersed in 2500.0 parts by mass of methanol and washed at 60° C. for 12 hours. This washing operation was repeated three times while replacing with fresh methanol. Next, the washed wet gel was immersed in 2500.0 parts by mass of heptane, which is a low surface tension solvent, and the solvent was replaced at 60° C. for 12 hours. This solvent replacement operation was repeated 3 times while replacing with new heptane. The washed and solvent-substituted wet gel is dried under normal pressure at 40° C. for 96 hours, and then at 150° C. for 2 hours to obtain the structure represented by the general formulas (3) and (4). Airgel composite 1 having

The "polysiloxane compound A" was synthesized as follows. First, in a 1-liter three-necked flask equipped with a stirrer, a thermometer and a Dimroth condenser, 100.0 mass of dimethylpolysiloxane XC96-723 (manufactured by Momentive Co., Ltd.) having silanol groups at both ends was used. Parts, 181.3 parts by mass of methyltrimethoxysilane and 0.50 parts by mass of t-butylamine were mixed and reacted at 30° C. for 5 hours. Then, this reaction liquid was heated at 140° C. for 2 hours under a reduced pressure of 1.3 kPa to remove a volatile component, thereby obtaining a bifunctional alkoxy-modified polysiloxane compound having both ends (polysiloxane compound A).

(Example 2) [Wet gel, airgel composite]
10-20 parts by mass of PL-20 as a silica particle-containing raw material, 100.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and hot hydration. 120.0 parts by mass of urea is mixed as a decomposable compound, 60.0 parts by mass of MTMS is added as a silicon compound, and trifunctional alkoxy modified at both ends having a structure represented by the above general formula (B) as a polysiloxane compound. 40.0 parts by mass of a polysiloxane compound (hereinafter, referred to as “polysiloxane compound B”) was added and reacted at 25° C. for 2 hours to obtain Sol 2. The obtained sol 2 was gelled at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 2. Thereafter, the obtained wet gel 2 was used to obtain an airgel composite 2 having a structure represented by the general formulas (2) and (4) in the same manner as in Example 1.

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

(Example 3) [Wet gel, airgel composite]
PL-2L as a silica particle-containing raw material is 100.0 parts by mass, water is 100.0 parts by mass, acetic acid is 0.10 parts by mass as an acid catalyst, CTAB is 20.0 parts by mass as a cationic surfactant, and hot water is added thereto. 120.0 parts by mass of urea was mixed as a decomposable compound, and 60.0 parts by mass of MTMS as a silicon compound and dimethyldimethoxysilane LS-520 (manufactured by Shin-Etsu Chemical Co., Ltd., product name: hereinafter abbreviated as "DMDMS"). 20.0 parts by mass, and 20.0 parts by mass of the polysiloxane compound A as a polysiloxane compound were added and reacted at 25° C. for 2 hours to obtain Sol 3. The obtained sol 3 was gelated at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 3. Thereafter, the obtained wet gel 3 was used to obtain an airgel composite 3 having a structure represented by the general formulas (3), (4) and (5) in the same manner as in Example 1.

(Example 4) [Wet gel, airgel composite]
As a silica particle-containing raw material, 143.0 parts by mass of ST-OZL-35, 57.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea was mixed as a thermally hydrolyzable compound, 60.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as a silicon compound, and 20.0 parts of polysiloxane compound B as a polysiloxane compound were mixed with urea. Mass parts were added and the mixture was reacted at 25° C. for 2 hours to obtain Sol 4. The obtained sol 4 was gelled at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 4. Thereafter, the obtained wet gel 4 was used to obtain an airgel composite 4 having a structure represented by the general formulas (2), (4) and (5) in the same manner as in Example 1.

(Example 5)
PL-2L as a silica particle-containing raw material is 100.0 parts by mass, ST-OZL-35 is 50.0 parts by mass, water is 50.0 parts by mass, acetic acid is 0.10 parts by mass as an acid catalyst, and cationic surfactant. 20.0 parts by mass of CTAB as an agent and 120.0 parts by mass of urea as a thermally hydrolyzable compound are mixed, and 60.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as a silicon compound and a polysiloxane compound are mixed therein. 20.0 parts by mass of polysiloxane compound A was added and reacted at 25° C. for 2 hours to obtain Sol 5. The sol 5 thus obtained was gelated at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 5. Thereafter, the obtained wet gel 5 was used to obtain an airgel composite 5 having a structure represented by the general formulas (3), (4) and (5) in the same manner as in Example 1.

(Example 6) [Wet gel, airgel composite]
The wet gel 5 obtained above was immersed in 2500.0 parts by mass of methanol and washed at 60° C. for 12 hours. This washing operation was repeated three times while replacing with fresh methanol. Next, the washed wet gel was immersed in 2500.0 parts by mass of 2-propanol, and the solvent was replaced at 60° C. for 12 hours. This solvent replacement operation was performed 3 times while exchanging with fresh 2-propanol.

Next, the solvent-substituted wet gel was supercritically dried. The inside of the autoclave was filled with 2-propanol, and the wet gel whose solvent was replaced was put therein. Then, liquefied carbon dioxide gas was fed into the autoclave to fill the interior of the autoclave with a mixture of 2-propanol and carbon dioxide as a dispersion medium. Thereafter, the environment in the autoclave is heated and pressurized so that the environment is 80° C. and 14 MPa, and the carbon dioxide in the supercritical state is sufficiently circulated in the autoclave, and then the pressure is reduced to the 2-propanol and the dioxide contained in the gel. The carbon was removed. In this way, the airgel composite 6 having the structures represented by the general formulas (3), (4) and (5) was obtained.

(Example 7) [Wet gel, airgel composite]
The wet gel 3 obtained above was immersed in 2500.0 parts by mass of methanol and washed at 60° C. for 12 hours. This washing operation was repeated three times while replacing with fresh methanol. Next, the washed wet gel is dried at 60° C. for 2 hours and 100° C. for 3 hours under normal pressure without solvent substitution, and then further dried at 150° C. for 2 hours to obtain the above general formula. An airgel composite 7 having the structures represented by (3), (4) and (5) was obtained.

(Example 8) [Wet gel, airgel composite]
Using the wet gel 4 obtained above, an airgel composite 8 having a structure represented by the general formulas (2), (4) and (5) was obtained in the same manner as in Example 7.

(Comparative Example 1) [wet gel, aerogel]
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant and 120.0 parts by mass of urea as a thermally hydrolyzable compound are mixed, and 100.0 parts by mass of MTMS as a silicon compound was added thereto and reacted at 25° C. for 2 hours to obtain Sol 1C. The obtained sol 1C was gelled at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 1C. Then, using the obtained wet gel 1C, an airgel 1C was obtained in the same manner as in Example 1.

(Comparative Example 2) [wet gel, aerogel]
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant and 120.0 parts by mass of urea as a thermally hydrolyzable compound are mixed, and Then, 80.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as a silicon compound were added thereto and reacted at 25° C. for 2 hours to obtain Sol 2C. The obtained sol 2C was gelated at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 2C. Then, using the obtained wet gel 2C, an airgel 2C was obtained in the same manner as in Example 1.

(Comparative Example 3) [Wet gel, aerogel]
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant and 120.0 parts by mass of urea as a thermally hydrolyzable compound are mixed, and 70.0 parts by mass of MTMS and 30.0 parts by mass of DMDMS as a silicon compound were added thereto and reacted at 25° C. for 2 hours to obtain Sol 3C. The obtained sol 3C was gelled at 60° C. and then aged at 80° C. for 24 hours to obtain wet gel 3C. Then, using the obtained wet gel 3C, an airgel 3C was obtained in the same manner as in Example 1.

(Comparative Example 4) [Wet gel, aerogel]
200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant and 120.0 parts by mass of urea as a thermally hydrolyzable compound are mixed, and 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as a silicon compound were added thereto, and the mixture was reacted at 25° C. for 2 hours to obtain Sol 4C. The obtained sol 4C was gelated at 60° C. and then aged at 80° C. for 24 hours to obtain a wet gel 4C. Then, using the obtained wet gel 4C, a comparative example aerogel 4C was obtained in the same manner as in Example 1.

Table 1 shows the modes of the silica particle-containing raw materials in each example. In addition, Table 2 collectively shows the drying method, the type and addition amount of the Si raw material (silicon compound and polysiloxane compound), and the addition amount of the silica particle-containing raw material in each Example and Comparative Example.

[Various evaluations]
The wet gel and airgel composites obtained in each example and comparative example were measured or evaluated according to the following conditions. The gelation time in the wet gel formation step, the state of the airgel composite and the airgel in the atmospheric drying of the methanol-substituted gel, and the evaluation results of the thermal conductivity, the compressive elastic modulus, the density and the porosity of the airgel composite and the airgel are summarized. It shows in Table 3.

(1) Measurement of gelation time 30 mL of the sol obtained in each of the Examples and Comparative Examples was transferred to a 100 mL PP closed container to obtain a measurement sample. Next, a constant temperature dryer "DVS402" (manufactured by Yamato Scientific Co., Ltd., product name) set at 60°C was used to measure the time from the introduction of the measurement sample to the gelation.

(2) State of Airgel Complex and Airgel in Drying Methanol-Displaced Gel under Normal Pressure 30.0 parts by mass of the wet gel obtained in each of Examples and Comparative Examples is immersed in 150.0 parts by mass of methanol, and then at 60° C. It was washed for 12 hours. This washing operation was repeated three times while replacing with fresh methanol. Next, the washed wet gel was processed into a size of 100 mm×100 mm×100 mm by using a blade having a blade angle of about 20 to 25 degrees to obtain a sample before drying. The obtained pre-drying sample was dried at 60° C. for 2 hours and 100° C. for 3 hours using a thermostat “SPH(H)-202” (manufactured by ESPEC Co., Ltd.) with a safety door, and further 150° C. After drying, a sample was obtained by drying for 2 hours (especially, the solvent evaporation rate and the like were not controlled). Here, the volumetric shrinkage rate SV of the sample before and after drying was obtained from the following equation. Then, when the volume shrinkage rate SV was 5% or less, it was evaluated as "no shrinkage", and when it was 5% or more, it was evaluated as "shrinkage".
SV=(V ₀ −V ₁ )/V ₀ ×100
In the formula, V ₀ represents the volume of the sample before drying, and V ₁ represents the volume of the sample after drying.

(3) Measurement of thermal conductivity Using a blade having a blade angle of about 20 to 25 degrees, the airgel composite and the airgel were processed into a size of 150 mm x 150 mm x 100 mm to obtain a measurement sample. Next, in order to ensure the parallelism of the surfaces, sanding of #1500 or more was performed as needed. The obtained measurement sample was dried at 100° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd.) before measuring the thermal conductivity. Then, the measurement sample was transferred into a desiccator and cooled to 25°C. As a result, a measurement sample for measuring thermal conductivity was obtained.

The thermal conductivity was measured using a stationary method thermal conductivity measuring device “HFM436 Lambda” (manufactured by NETZSCH, product name). The measurement conditions were an atmospheric pressure and an average temperature of 25°C. The measurement sample obtained as described above was sandwiched between the upper and lower heaters with a load of 0.3 MPa, the temperature difference ΔT was set to 20° C., and a guard heater was used to adjust the heat flow to a one-dimensional heat flow. The upper surface temperature and the lower surface temperature were measured. Then, the thermal resistance R _S of the measurement sample was obtained from the following equation.
R _S =N((T _U −T _L )/Q)−R _O
In the formula, T _U represents the upper surface temperature of the measurement sample, T _L represents the lower surface temperature of the measurement sample, R _O represents the contact thermal resistance at the upper and lower interfaces, and Q represents the heat flux meter output. It should be noted that N is a proportional coefficient and was obtained in advance using a calibration sample.

From the obtained thermal resistance R _S , the thermal conductivity λ of the measurement sample was obtained by the following formula.
λ=d/R _S
In the formula, d represents the thickness of the measurement sample.

(4) Measurement of compressive elastic modulus Using a blade having a blade angle of about 20 to 25 degrees, the airgel composite and the airgel were processed into a 7.0 mm square cube (dices) to obtain a measurement sample. Next, in order to ensure the parallelism of the surfaces, the measurement sample was shaped with sandpaper of #1500 or more as needed. Before measurement, the obtained measurement sample was dried at 100° C. for 30 minutes under atmospheric pressure using a constant temperature dryer “DVS402” (manufactured by Yamato Scientific Co., Ltd.). Then, the measurement sample was transferred into a desiccator and cooled to 25°C. Thus, a measurement sample for measuring the compression elastic modulus was obtained.

As the measuring device, a small tabletop tester "EZTest" (manufactured by Shimadzu Corporation, product name) was used. The load cell used was 500N. Further, an upper platen (φ20 mm) and a lower platen (φ118 mm) made of stainless steel were used as a jig for compression measurement. The measurement sample was set between the upper platen and the lower platen arranged in parallel, and compression was performed at a speed of 1 mm/min. The measurement temperature was 25° C., and the measurement was terminated when a load of more than 500 N was applied or when the measurement sample was destroyed. Here, the strain ε was obtained from the following equation.
ε=Δd/d1
In the formula, Δd represents the displacement (mm) of the thickness of the measurement sample due to the load, and d1 represents the thickness (mm) of the measurement sample before applying the load.
Further, the compressive stress σ (MPa) was obtained from the following equation.
σ=F/A
In the formula, F represents the compressive force (N), and A represents the cross-sectional area (mm ² ) of the measurement sample before applying a load.

The compression elastic modulus E (MPa) was obtained from the following equation in the compression force range of 0.1 to 0.2N.
E=(σ ₂ −σ ₁ )/(ε ₂ −ε ₁ ).
In the formula, σ ₁ indicates a compressive stress (MPa) measured at a compressive force of 0.1 N, σ ₂ indicates a compressive stress (MPa) measured at a compressive force of 0.2 N, and ε ₁ indicates a compressive stress. The compressive strain measured at σ ₁ is shown, and ε ₂ is the compressive strain measured at compressive stress σ ₂ .

(5) Measurement of Density and Porosity The density and porosity of the three-dimensional mesh-like continuous pores (pores) of the airgel composite and the airgel were measured by the mercury porosimetry according to DIN66133. The measurement temperature was room temperature (25° C.), and Autopore IV9520 (manufactured by Shimadzu Corporation, product name) was used as a measuring device.

From Table 3, the airgel composites of Examples had a short gelling time in the wet gel formation step and excellent reactivity, and had good shrink resistance in atmospheric drying using a methanol-substituted gel. In this evaluation, good shrinkage resistance was shown in any of the Examples, which means that a good quality airgel composite can be obtained without performing the solvent replacement step. ..

Further, it can be read that the airgel composites of Examples have small thermal conductivity and compressive elastic modulus and are excellent in both high heat insulation and high flexibility.

On the other hand, in Comparative Examples 1 to 3, the gelation time in the wet gel formation step was long, and the gel shrank and cracked on the surface in the normal pressure drying using the methanol-substituted gel. Further, either the thermal conductivity or the flexibility was poor. In Comparative Example 4, the shrinkage resistance, flexibility and bending resistance were sufficient, but the gelation time was long and the thermal conductivity was large.

(6) SEM Observation The surface of the airgel composite obtained in Example 3 and Example 4 was observed by SEM. FIG. 3 is a SEM obtained by observing the surface of the airgel composite obtained in Example 3 at (a) 10,000 times, (b) 50,000 times, (c) 200,000 times, and (d) 350,000 times. It is an image. FIG. 4 is SEM images of the surface of the airgel composite obtained in Example 4, observed at (a) 10,000 times, (b) 50,000 times, and (c) 200,000 times, respectively.

As shown in FIG. 3, it was observed that the airgel composite obtained in Example 3 had a three-dimensional network skeleton (three-dimensionally fine porous structure). The particle size of the observed particles was mainly about 20 nm derived from silica particles. Although it is possible to confirm a spherical airgel component having a smaller particle size than the silica particles (airgel particles), mainly the airgel component does not take a spherical form and does not cover the silica particles or functions as a binder between silica particles. It is observed that they appear to be. As described above, since some of the airgel components function as a binder between the silica particles, it is presumed that the strength of the airgel composite can be improved.

As shown in FIG. 4, it was observed that the airgel composite obtained in Example 4 also had a three-dimensional network skeleton. However, its cluster structure is unique. In the present example, unlike the ordinary airgel, it does not have a structure in which particles are connected in a beaded shape, and the connection between particles seems to be densely packed with an airgel component (silicone component). It is observed that there is. Moreover, since the particle size of the particles derived from the silica particles is significantly larger than the particle size of the silica particles themselves, it is presumed that the silica particles are thickly covered with the airgel component. As described above, in this example, since the airgel component not only functions as a binder between particles but also covers the entire cluster structure, it is presumed that the strength of the airgel composite can be further improved. To be done. In Example 4, since the ST-OZL-35 used was an acidic sol, the airgel composite was produced in a state where the pH in the system was low. Therefore, it is presumed that the generation rate of the airgel component was slowed down, and the airgel component in the obtained airgel composite was difficult to be particulate.

1... Airgel particles, 2... Silica particles, 3... Pores, 10... Airgel composite, L... Enclosing rectangle.

Claims (7)

Wet, which is a condensate of a sol, containing silica particles, a polysiloxane compound represented by the following general formula (B), and at least one selected from the group consisting of hydrolysis products of the polysiloxane compound. An airgel complex that is a dried product of gel.

[In the 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 independently represent an alkyl group or an aryl group. It shows and m shows the integer of 1-50. ] The airgel composite according to claim 1, wherein the airgel composite has a ladder-type structure including a column and a bridge, and the bridge has a structure represented by the following general formula (2).

[In the formula (2), R ⁵ and R ⁶ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. ] The airgel composite according to claim 2, having a ladder-type structure represented by the following general formula (3).

[In the formula (3), R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent an alkyl group or an aryl group, a and c each independently represent an integer of 1 to 3000, and b is 1 to 50. Indicates an integer of. ] The airgel composite according to any one of claims 1 to 3, wherein the average primary particle diameter of the silica particles is 1 to 200 nm. The airgel composite according to any one of claims 1 to 4, wherein the silica particles have a spherical shape. The airgel composite according to any one of claims 1 to 5, wherein the silica particles are colloidal silica particles. The sol further comprises 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. The airgel composite according to any one of claims 1 to 6, which is contained.