JP2017179063A - Aerogel composite - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an airgel excellent in toughness and flexibility by having high compression rupture strength, tensile rupture strength, and low tensile elastic modulus while maintaining heat insulation. In a solid-state 29Si-NMR spectrum containing an airgel component and silica particles and measured by a DD/MAS method, a silicon-containing bond unit Q (one oxygen atom bonded to one silicon atom is 4 A silicon-containing bond unit) and a signal area ratio derived from T (three oxygen atoms bonded to one silicon atom and one hydrogen atom or one monovalent organic group). Ratio (signal area ratio) Q+T:D is 1:0 of two oxygen atoms bonded to one silicon atom and a signal area derived from two hydrogen atoms or two monovalent organic groups). An airgel composite that is between 10 and 1:0.35. [Selection diagram] Figure 2

Description

  The present invention relates to an airgel composite excellent in toughness and flexibility.

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

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

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

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

  In this way, while various problems have been studied regarding the problems of conventional manufacturing processes, the airgel obtained has difficulty in toughness even if any of the above processes is adopted. There is a problem with sex. For example, the agglomerated airgel obtained by the above process may be broken simply by trying to lift it by hand. This is presumably due to the fact that the density of the airgel is low and that the airgel has a pore structure in which fine particles of about 10 nm are weakly connected.

  The present invention has been made in view of the above circumstances, and has an airgel excellent in toughness and flexibility by having high compressive breaking strength, tensile breaking strength, and low tensile elastic modulus while maintaining heat insulation. The object is to provide a complex.

As a result of intensive studies to achieve the above object, the present inventor has obtained signal areas derived from silicon-containing binding units Q and T in a solid ²⁹ Si-NMR spectrum measured using a DD / MAS method. It is found that the airgel composite having a ratio Q + T: D within a specific range with respect to the signal area derived from D has excellent compression rupture strength and tensile rupture strength, and excellent tensile elastic modulus. Completed.

That is, the present invention contains an airgel component and silica particles, and in a solid ²⁹ Si-NMR spectrum measured using a DD / MAS method, when silicon-containing binding units Q, T, and D are defined as follows: Provided is an airgel complex in which the ratio of the signal area derived from Q and T to the signal area derived from D (signal area ratio) Q + T: D is from 1: 0.10 to 1: 0.35.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
However, the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom.

In the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method, or when the silicon-containing binding units Q, T, and D are defined as follows, the present invention provides a signal area derived from Q and T The ratio of the signal area derived from D (signal area ratio) Q + T: D can be provided as an airgel complex having a ratio of 1: 0.10 to 1: 0.35.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
However, the signal area derived from Q is more than 0, and the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom.

  In the present invention, the average primary particle diameter of the silica particles can be 1 to 500 nm.

The present invention can have a structure represented by the following general formula (1).

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

The present invention can have a ladder structure including a support portion and a bridge portion, and the bridge portion can have a structure represented by the following general formula (2).

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

The present invention can have a structure represented by the following general formula (3).

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

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the airgel composite excellent in toughness and a softness | flexibility by having high compression fracture strength, tensile fracture strength, and low tensile elastic modulus, maintaining heat insulation. As shown in the examples described later, for example, an airgel composite having a compressive breaking strength of 0.3 MPa or more and a tensile breaking strength of 10 kPa or more and a tensile elastic modulus of less than 20 kPa can be provided. .

It is a figure which shows the calculation method of the biaxial average primary particle diameter of particle | grains. It is a figure which shows the solid ²⁹ Si-NMR spectrum with respect to the airgel composite of Example 1 obtained using DD / MAS method.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In this specification, the numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively. “A or B” only needs to include one of A and B, and may include both. The materials exemplified in this embodiment can be used singly or in combination of two or more unless otherwise specified.

<Airgel composite>
In a narrow sense, dry gel obtained by using supercritical drying method for wet gel is aerogel, dry gel obtained by drying under atmospheric pressure is xerogel, dry gel obtained by freeze-drying is cryogel and However, in the present embodiment, the obtained low-density dried gel is referred to as an aerogel regardless of the drying method of the wet gel. In other words, in the present embodiment, the airgel means “a gel composed of a microporous solid whose dispersed phase is a gas”, which is an aerogel in a broad sense, that is, “gel resolved of a microporous solid in which the dispersed phase is a gas”. To do. In general, the inside of an airgel has a network-like fine structure, and has a cluster structure in which airgel particles of about 2 to 20 nm are combined. Between the skeletons formed by the clusters, there are pores less than 100 nm, and a three-dimensionally fine porous structure is formed. In addition, the airgel in this embodiment is a silica airgel which has a silica as a main component. Examples of the silica airgel include so-called organic-inorganic hybrid silica airgel into which an organic group such as a methyl group or an organic chain is introduced. In addition, the airgel composite of the present embodiment has a cluster structure that is a feature of the above airgel while silica particles are composited 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. Although not necessarily meaning the same concept as this, the airgel composite of the present embodiment can also be expressed as containing 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 an airgel composite is improved and the size can be increased, so that the productivity can be increased. In addition, such an airgel composite is obtained by making silica particles exist in the airgel production environment. And the merit by the presence of silica particles is not only that the heat insulation and flexibility of the composite itself can be improved, but also shortening the time of the wet gel generation process described later, or simplifying the drying process from the washing and solvent replacement process. Is also possible. In addition, shortening of the time of this process and simplification of a process are not necessarily calculated | required when producing the airgel composite which is excellent in a softness | flexibility.

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

  First, the composite mode of the airgel component and the silica particles includes a mode in which an amorphous airgel component is interposed between the silica particles. Specifically, as such an embodiment, for example, an embodiment in which silica particles are coated with a film-like airgel component (silicone) (an embodiment in which the airgel component includes silica particles), the airgel component serves as a binder and the silica particles , A mode in which the airgel component is filled with a plurality of silica particle gaps, a mode of a combination of these modes (a mode in which silica particles arranged in a cluster are coated with the airgel component, etc.) An embodiment is mentioned. Thus, in this embodiment, the airgel composite can have a three-dimensional network skeleton composed of silica particles and an airgel component (silicone), and there is no particular limitation on the specific mode (form).

  On the other hand, in the present embodiment, the airgel component may be in the form of a clear particle, not an indefinite shape, and may be combined with silica particles.

  Although the mechanism by which such various aspects occur in the airgel composite of the present embodiment is not necessarily clear, the present inventor presumes that the generation rate of the airgel component in the gelation process is involved. For example, the production speed 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 fluctuate by changing the pH of the system.

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

  The silica particles can be used without any 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, colloidal silica particles have high monodispersibility and are easy to suppress aggregation in the sol. In addition, as a silica particle, the silica particle which has a hollow structure, a porous structure, etc. may be sufficient.

  The shape of the silica particles is not particularly limited, and examples thereof include a spherical shape, a cage shape, and an association type. Among these, by using spherical particles as silica particles, it becomes easy to suppress aggregation in the sol. The average primary particle diameter of the silica particles can be 1 to 500 nm, but may be 5 to 300 nm, or 20 to 100 nm. When the average primary particle diameter of the silica particles is 1 nm or more, it becomes easy to impart an appropriate strength to the airgel, and an airgel composite having excellent shrinkage resistance during drying is easily obtained. On the other hand, when the average primary particle diameter is 500 nm or less, it becomes easy to suppress the solid heat conduction of the silica particles, and it becomes easy to obtain an airgel composite excellent in heat insulation.

  It is presumed that the airgel particles (aerogel component) and the silica particles are bonded by taking a hydrogen bond, a chemical bond, or a combination of these bonds. At this time, hydrogen bonds, chemical bonds, or combinations of these bonds are considered to be formed by silanol groups, reactive groups, or both of the airgel particles (aerogel component) and the silanol groups of the silica particles. Therefore, it is thought that moderate strength is easily imparted to the airgel when the bonding mode is chemical bonding. Considering this, the particles to be combined with the airgel component are not limited to silica particles, and inorganic particles or organic particles having a silanol group on the particle surface can also be used.

The number of silanol groups per gram of silica particles can be 10 × 10 ^{18 to} 1000 × 10 ¹⁸ pcs / g, but may be 50 × 10 ^{18 to} 800 × 10 ¹⁸ pcs / g, or 100 × 10 10 ^18-700 may be a × ^{10 18} cells / g. When the number of silanol groups per gram of silica particles is 10 × 10 ¹⁸ pieces / g or more, an airgel composite that can have better reactivity with airgel particles (aerogel component) and has excellent shrinkage resistance. It becomes easy to obtain. On the other hand, when the number of silanol groups is 1000 × 10 ¹⁸ / g or less, it is easy to suppress abrupt gelation at the time of sol preparation, and it becomes easy to obtain a homogeneous airgel composite.

  In the present embodiment, the average particle size of the particles (the average secondary particle size of the airgel particles and the average primary particle size of the silica particles) is measured using a scanning electron microscope (hereinafter abbreviated as “SEM”). It can be obtained by directly observing the cross section of. For example, the particle diameter of each airgel particle or silica particle can be obtained from the three-dimensional network skeleton based on the diameter of the cross section. The diameter here means the diameter when the cross section of the skeleton forming the three-dimensional network 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 obtained for 100 particles, and the average is taken.

  In addition, about a silica particle, it is possible to measure an average particle diameter from a 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, when colloidal silica particles having a solid content concentration of 5 to 40% by mass, which is usually dispersed in water, are taken as an example, a chip obtained by cutting a 2 cm square wafer with a pattern wiring into a dispersion of colloidal silica particles for about 30 seconds After soaking, the chip is rinsed with pure water for about 30 seconds and blown with nitrogen. Thereafter, the chip is placed on a sample stage for SEM observation, an acceleration voltage of 10 kV is applied, the silica particles are observed at a magnification of 100,000, and an image is taken. 20 silica particles are arbitrarily selected from the obtained image, and the average of the particle diameters of these particles is defined as the average particle diameter. At this time, when the selected silica particles have a shape as shown in FIG. 1, a rectangle (circumscribed rectangle L) circumscribing the silica particles 1 and arranged so that the long side is the longest is led. And the long side of the circumscribed rectangle L is X, the short side is Y, and the biaxial average primary particle diameter is calculated as (X + Y) / 2, and is defined as the particle diameter of the particle.

  Although content of the airgel component contained in an airgel composite can be 4-25 mass parts with respect to 100 mass parts of total amounts of an airgel composite, 10-20 mass parts may be sufficient. When the content is 4 parts by mass or more, an appropriate strength is easily imparted, and when the content is 25 parts by mass or less, good heat insulating properties are easily obtained.

  Although content of the silica particle contained in an airgel composite can be 1-25 mass parts with respect to 100 mass parts of total amounts of an airgel composite, 3-15 mass parts may be sufficient. When the content is 1 part by mass or more, an appropriate strength is easily imparted 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, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound for the purpose of suppressing heat radiation. The content of other components is not particularly limited, but may be 1 to 5 parts by mass with respect to 100 parts by mass of the total amount of the airgel complex from the viewpoint of sufficiently ensuring the desired effect of the airgel complex.

<Signal area according to silicon-containing bonding units Q, T and D>
From the viewpoint of toughness and flexibility, the airgel composite of this embodiment defines silicon-containing bonding units Q, T, and D as follows in a solid ²⁹ Si-NMR spectrum measured using the DD / MAS method. The ratio of the signal area derived from Q and T to the signal area derived from D (signal area ratio) Q + T: D is 1: 0.10 to 1: 0.35, but 1: 0. More than 10 may be 1: 0.35 or less, and may be 1: 0.15 to 1: 0.25.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
(However, the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom.)

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

The signal area ratio can be confirmed by a solid ²⁹ Si-NMR spectrum. Specifically, for example, a spectrum as shown in FIG. 2 is obtained by performing ²⁹ Si-NMR measurement using the DD / MAS method on the airgel composite. FIG. 2 is a diagram showing a solid-state ²⁹ Si-NMR spectrum for the airgel composite of Example 1 obtained by using the DD / MAS method. As seen in this figure, the chemical shifts of the silicon-containing bond units Q, T and D are in the range of Q units: -90 to -135 ppm, T units: -45 to -85 ppm, D units: 0 to -40 ppm. Since each is observed, it is possible to separate the signals of the silicon-containing binding units Q, T and D and calculate the signal area derived from each unit.

  Here, a signal area ratio calculation method will be described with reference to FIG. For example, in FIG. 2, a Q unit signal derived from silica is observed in a chemical shift range of −90 to −135 ppm. In addition, a signal of T unit is observed in the chemical shift range of −45 to −85 ppm, and a signal of D unit is observed in the chemical shift range of 0 to −40 ppm. The signal area (integrated value) is obtained by integrating the signal in each chemical shift range. When the signal areas of the Q unit and the T unit are added to 1, the signal area ratio Q + T: D in FIG. 2 is calculated as 1: 0.21. The signal area is calculated using general spectrum analysis software (for example, NMR software “TopSpin” manufactured by Bruker (TopSpin is a registered trademark)). For spectrum analysis, use the software attached to "FT-NMR data processing by personal computer (2nd edition) (by Windows with CD-ROM): Hiroshi Nakamura: Sankyo Publishing" (Windows is a registered trademark). You can also.

In the airgel composite of the present embodiment, a predetermined amount of silicon-containing bonding units Q can be observed in the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method. Specifically, the signal area (integrated value) of the Q unit signal is more than zero. The presence of the silica particles described so far can be defined by the signal area of the Q unit signal. Therefore, when the air-gel composite of this embodiment is defined as described above in the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method, the silicon-containing binding units Q, T, and D are defined as Q and T. Ratio of signal area derived from signal area derived from D (signal area ratio) Q + T: D is 1: 0.10 to 1: 0.35 Airgel complex (however, signal area derived from Q Is greater than 0).

  Note that such a signal area ratio can be appropriately adjusted by changing the airgel production conditions described later, particularly the amount of acid catalyst added.

<Specific embodiment of airgel component>
The following aspects are mentioned as an airgel component in the airgel composite of this embodiment. By adopting these aspects, it becomes easy to control the heat insulating property and flexibility of the airgel composite to a desired level. However, adopting each of these aspects is not necessarily the purpose of obtaining the airgel composite defined in the present embodiment. By employ | adopting each aspect, the airgel composite which has the heat conductivity and compression elastic modulus according to each aspect can be obtained. Therefore, the airgel composite which has the heat insulation according to a use and a softness | flexibility can be provided.

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

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

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

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

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

By introducing the above structure as an airgel component into the skeleton of the airgel complex, for example, it has a structure derived from a conventional ladder-type silsesquioxane (that is, a structure represented by the following general formula (X) An airgel composite having flexibility superior to that of the airgel. In addition, as shown by the following general formula (X), in the airgel having a structure derived from the conventional ladder-type silsesquioxane, the structure of the bridge portion is —O—, but the airgel composite of this embodiment In the body, the structure of the bridging portion is a structure (polysiloxane structure) represented by the general formula (2).

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

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

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

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

(Third embodiment)
The airgel composite of the present embodiment includes at least one selected from the group consisting of silica particles, a silicon compound having a hydrolyzable functional group in the molecule, and a hydrolysis product of the silicon compound (hereinafter, these silicons). And may be a product obtained by drying a wet gel produced from a sol containing (a dried product of a wet gel derived from a sol). . The airgel composite described so far may also be obtained by drying a wet gel generated from a sol containing silica particles and silicon compounds.

  The number of silicon atoms in the molecule of the silicon compound can be 1 or 2. Although it does not specifically limit as a silicon compound which has a hydrolyzable functional group in a molecule | numerator, For example, an alkyl silicon alkoxide is mentioned. Alkyl silicon alkoxides can have a hydrolyzable functional group number of 3 or less from the viewpoint of improving water resistance. Specifically, for example, methyltrimethoxysilane, dimethyldimethoxysilane, and ethyltrimethoxy Examples include silane. Here, examples of the hydrolyzable functional group include alkoxy groups such as a methoxy group and an ethoxy group.

  Further, the number of hydrolyzable functional groups is 3 or less, and vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyl which are silicon compounds having a reactive group in the molecule. Methyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl -3-Aminopropyltrimethoxysilane, N-2- (aminoethyl) -3-aminopropylmethyldimethoxysilane, and the like can also be used.

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

  These silicon compounds may be used alone or in admixture of two or more.

  In producing the airgel composite of this embodiment, the sol containing the silicon compounds is selected from the group consisting of a polysiloxane compound having a reactive group in the molecule and a hydrolysis product of the polysiloxane compound. (Hereinafter, these polysiloxane compounds and the like may be collectively referred to as “polysiloxane compounds”).

  The reactive group in the polysiloxane compounds is not particularly limited, but may be a group that reacts with the same reactive group or a group that reacts with another reactive group, for example, an alkoxy group, a silanol group, a hydroxy group. Examples thereof include an alkyl group, an epoxy group, a polyether group, a mercapto group, a carboxyl group, and a phenol group. You may use the polysiloxane compound which has these reactive groups individually or in mixture of 2 or more types. Examples of the reactive group include an alkoxy group, a silanol group, a hydroxyalkyl group, and a polyether group from the viewpoint of improving the flexibility of the airgel composite. Among these, the alkoxy group or the hydroxyalkyl group is a sol. The compatibility can be further improved. In addition, from the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the airgel composite, the number of carbon atoms of the alkoxy group and hydroxyalkyl group can be 1 to 6, but the flexibility of the airgel composite is not limited. 2-4 may be sufficient from a viewpoint of improving more.

Examples of the polysiloxane compound having a hydroxyalkyl group in the molecule include those having a structure represented by the following general formula (4). By using a polysiloxane compound having a structure represented by the following general formula (4), the structure represented by the general formula (1) can be introduced into the skeleton of the airgel composite.

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

By using a wet gel generated from a sol containing polysiloxane compounds having the above structure, it becomes easier to obtain a flexible airgel composite with low thermal conductivity. From such a viewpoint, in formula (4), R ₉ includes a hydroxyalkyl group having 1 to 6 carbon atoms, and the hydroxyalkyl group includes a hydroxyethyl group, a hydroxypropyl group, and the like. In Formula (4), R ₁₀ includes an alkylene group having 1 to 6 carbon atoms, and examples of the alkylene group include an ethylene group and a propylene group. In formula (4), R ₁₁ and R ₁₂ each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like, and examples of the alkyl group include a methyl group. Moreover, in Formula (4), although n can be set to 2-30, 5-20 may be sufficient.

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

Examples of the polysiloxane compound having an alkoxy group in the molecule include those having a structure represented by the following general formula (5). By using a polysiloxane compound having a structure represented by the following general formula (5), a ladder structure having a bridge portion represented by the general formula (2) is introduced into the skeleton of the airgel composite. be able to.

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

By using a wet gel generated from a sol containing polysiloxane compounds having the above structure, it becomes easier to obtain a flexible airgel composite with low thermal conductivity. From such a viewpoint, in formula (5), R ₁₄ includes an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, and the like, and the alkyl group or alkoxy group includes a methyl group. , A methoxy group, an ethoxy group, and the like. In formula (5), R ₁₅ and R ₁₆ each independently include an alkoxy group having 1 to 6 carbon atoms, and examples of the alkoxy group include a methoxy group and an ethoxy group. In formula (5), R ₁₇ and R ₁₈ each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group, and the like, and examples of the alkyl group include a methyl group. Moreover, in Formula (5), m can be 2-30, but 5-20 may be sufficient.

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

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

  These polysiloxane compounds may be used alone or in admixture of two or more.

  Although content of the silicon compound contained in the said sol can be 5-50 mass parts with respect to 100 mass parts of total amounts of sol, 10-30 mass parts may be sufficient. By making it 5 parts by mass or more, it becomes easy to obtain good reactivity, and by making it 50 parts by mass or less, it becomes easy to obtain good compatibility.

  Moreover, when the said sol further contains polysiloxane compounds, the sum total of content of a silicon compound and polysiloxane compounds can be 5-50 mass parts with respect to 100 mass parts of total amounts of sol. However, 10-30 mass parts may be sufficient. When the total content is 5 parts by mass or more, good reactivity is further easily obtained, and when it is 50 parts by mass or less, good compatibility is further easily obtained. At this time, the ratio of the content of the silicon compounds and the content of the hydrolysis product of the polysiloxane compounds can be 0.5: 1 to 4: 1, but is 1: 1 to 2: 1. It may be. When the ratio of the content of these compounds is 0.5: 1 or more, good compatibility is further easily obtained, and when the ratio is 4: 1 or less, gel shrinkage is further easily suppressed.

  Although content of the silica particle contained in the said sol can be 1-20 mass parts with respect to 100 mass parts of total amounts of sol, 4-15 mass parts may be sufficient. By setting the content to 1 part by mass or more, it becomes easy to impart an appropriate strength to the airgel, and it becomes easy to obtain an airgel composite having excellent shrinkage resistance during drying. Moreover, it becomes easy to suppress the solid heat conduction of a silica particle by making content 20 mass parts or less, and it becomes easy to obtain the airgel composite excellent in heat insulation.

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

In the formula (6), R ₁₉ 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 (7).

In formula (7), R ₂₀ and R ₂₁ each independently 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 (8).

In formula (8), R ₂₂ 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.

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

  That is, the airgel composite of the present embodiment is obtained in a sol generation step, a wet gel generation step in which the sol obtained in the sol generation step is gelled and then aged to obtain a wet gel, and the wet gel generation step. The wet gel is washed and (if necessary) solvent-replaced, and the washing and solvent-substituted wet gel is dried by a production method mainly comprising a drying process. The sol is a state before the gelation reaction occurs, and in the present embodiment, the silicon compounds, in some cases polysiloxane compounds, and silica particles are dissolved or dispersed in a solvent. Means state. The wet gel means a gel solid in a wet state that contains a liquid medium but does not have fluidity.

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

(Sol generation process)
The sol production step is a step of producing a sol by mixing the above-described silicon compound, optionally a polysiloxane compound, silica particles, and a solvent and hydrolyzing them. Silica particles may be mixed in the state of a dispersion dispersed in a solvent. In this step, an acid catalyst may be further added to the solvent in order to promote the hydrolysis reaction. Further, as shown in Japanese Patent No. 5250900, a surfactant, a thermally hydrolyzable compound, and the like can be added to the solvent. Furthermore, components such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound may be added to the solvent for the purpose of suppressing heat radiation.

  As the solvent, for example, water or a mixed solution of water and alcohols can be used. Examples of alcohols include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol. Among these, methanol, ethanol, 2-propanol etc. are mentioned as alcohol with a low surface tension and a low boiling point at the point which reduces the interfacial tension with a gel wall. You may use these individually or in mixture of 2 or more types.

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

  Acid catalysts include hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, odorous acid, chloric acid, chlorous acid, hypochlorous acid and other inorganic acids; acidic phosphoric acid Acidic phosphates such as aluminum, acidic magnesium phosphate and acidic zinc phosphate; organic carboxylic acids such as acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid and azelaic acid Etc. Among these, an organic carboxylic acid is mentioned as an acid catalyst which improves the water resistance of the airgel composite obtained more. 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 an acid catalyst, the hydrolysis reaction of the silicon compound and the polysiloxane compound is promoted, and a sol can be obtained in a shorter time.

  Although the addition amount of an acid catalyst can be 0.01-50.0 mass parts with respect to 100 mass parts of total amounts of a silicon compound and a polysiloxane compound, it is good also as 0.5-30 mass parts. It is good also as 0-10.0 mass parts. The silicon-containing bond units Q, T, and D can be controlled by appropriately adjusting the addition amount of the acid catalyst.

  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.

  Examples of the nonionic surfactant include those containing a hydrophilic part such as polyoxyethylene and a hydrophobic part mainly composed of an alkyl group, and those containing a hydrophilic part such as polyoxypropylene. Examples of those containing a hydrophilic part such as polyoxyethylene and a hydrophobic part mainly composed of an alkyl group include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene alkyl ether and the like. As what contains hydrophilic parts, such as polyoxypropylene, the polyoxypropylene alkyl ether, the block copolymer of polyoxyethylene and polyoxypropylene, etc. are mentioned.

  Examples of the ionic surfactant include a cationic surfactant, an anionic surfactant, and an amphoteric surfactant. Examples of the cationic surfactant include cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, and examples of the anionic surfactant include sodium dodecylsulfonate. Examples of amphoteric surfactants include amino acid surfactants, betaine surfactants, amine oxide surfactants, and the like. Examples of amino acid surfactants include acyl glutamic acid. Examples of betaine surfactants include lauryldimethylaminoacetic acid betaine, stearyldimethylaminoacetic acid betaine, and the like. Examples of the amine oxide surfactant include lauryl dimethylamine oxide.

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

  The addition amount of the surfactant depends on the type of the surfactant, or the type and amount of the silicon compound and the polysiloxane compound, but for example, 1 to 1 part by mass with respect to 100 parts by mass of the total amount of the silicon compound and the polysiloxane compound. The amount can be 100 parts by mass. In addition, 5-60 mass parts may be sufficient as the addition amount.

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

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

  Hydrolysis in the sol production step depends on the type and amount of silicon compound, polysiloxane compound, silica particles, acid catalyst, surfactant, etc. in the mixed solution, but for example, in a temperature environment of 20 to 60 ° C. May be performed for 10 minutes to 24 hours, or may be performed at a temperature environment of 50 to 60 ° C. for 5 minutes to 8 hours. Thereby, the hydrolyzable functional group in a silicon compound and a polysiloxane compound is fully hydrolyzed, and the hydrolysis product of a silicon compound and the hydrolysis product of a polysiloxane compound can be obtained more reliably.

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

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

  Base catalysts include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, and ammonium bromide; sodium metaphosphate Basic sodium phosphates such as sodium pyrophosphate and sodium polyphosphate; allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3 -(Diethylamino) propylamine, di-2-ethylhexylamine, 3- (dibutylamino) propylamine, tetramethylethylenediamine, t-butylamine, sec- Aliphatic amines such as tilamine, propylamine, 3- (methylamino) propylamine, 3- (dimethylamino) propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, triethanolamine; morpholine, N -Nitrogen-containing heterocyclic compounds such as methylmorpholine, 2-methylmorpholine, piperazine and derivatives thereof, piperidine and derivatives thereof, imidazole and derivatives thereof, and the like. Among these, ammonium hydroxide (ammonia water) is excellent in that it has high volatility and does not remain in the airgel composite after drying, and thus does not impair water resistance, and is economical. You may use said base catalyst individually or in mixture of 2 or more types.

  By using a base catalyst, the dehydration condensation reaction, dealcoholization condensation reaction, or both of the silicon compounds, polysiloxane compounds, and silica particles in the sol can be promoted, and the gelation of the sol It can be performed in a shorter time. Thereby, a wet gel with higher strength (rigidity) can be obtained. In particular, ammonia has high volatility and hardly remains in the airgel composite. Therefore, by using ammonia as a base catalyst, an airgel composite having better water resistance can be obtained.

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

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

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

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

  Although the gelation time and the aging time differ depending on the gelation temperature and the aging temperature, in the present embodiment, since the sol contains silica particles, the gelation time is particularly compared with the conventional method for producing an airgel. Can be shortened. This is because the silanol groups, reactive groups, or both of the silicon compounds and polysiloxane compounds in the sol form hydrogen bonds, chemical bonds, or a combination of these bonds with the silanol groups of the silica particles. I guess that is to do. The gelation time can be 10 to 120 minutes, but may be 20 to 90 minutes. By setting the gelation time to 10 minutes or more, it becomes easy to obtain a homogeneous wet gel, and by setting it to 120 minutes or less, the drying process can be simplified from the washing and solvent replacement process described later. In addition, as a whole process of gelation and aging, the total time of the gelation time and the aging time can be 4 to 480 hours, but may be 6 to 120 hours. By setting the total gelation time and aging time to 4 hours or more, a wet gel with higher strength (rigidity) can be obtained, and by setting it to 480 hours or less, the effect of aging can be more easily maintained.

  In order to decrease the density of the obtained airgel composite or increase the average pore diameter, the gelation temperature and the aging temperature are increased within the above range, or 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 diameter, the gelation temperature and the aging temperature are reduced within the above range, or the total time of the gelation time and the aging time is within the above range. It can be shortened.

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

  In the washing step, the wet gel obtained in the wet gel production step is washed. The said washing | cleaning can be repeatedly performed using water or an organic solvent, for example. At this time, washing efficiency can be improved by heating.

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

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

  The amount of water or organic solvent used in the washing step can be set to an amount that can sufficiently wash the solvent in the wet gel and wash it. The amount can be 3 to 10 times the amount of wet gel volume. The washing can be repeated until the moisture content in the wet gel after washing is 10% by mass or less with respect to the silica mass.

  The temperature environment in the washing step can be set to a temperature equal to or lower than the boiling point of the solvent used for washing. 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 replacement efficiency can be improved by heating. Specific examples of the solvent for substitution include a low surface tension solvent described later in the drying step when drying is performed under atmospheric pressure at a temperature lower than the critical point of the solvent used for drying. On the other hand, when performing supercritical drying, examples of the substitution solvent include ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide, and the like, or a solvent obtained by mixing two or more of these.

  Examples of the low surface tension solvent include those having a surface tension at 20 ° C. of 30 mN / m or less. 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); (28.9), toluene (28.5), m-xylene (28.7), p-xylene (28.3) and other aromatic hydrocarbons; dichloromethane (27.9), chloroform (27.2) ), Carbon tetrachloride (26.9), 1-chloropropane (21.8), 2-chloropropane (18.1) and other halogenated hydrocarbons; ethyl ether (17.1), propyl ether (20.5) ), Isop Ethers such as pyrether (17.7), butyl ethyl ether (20.8), 1,2-dimethoxyethane (24.6); acetone (23.3), methyl ethyl ketone (24.6), methyl propyl ketone (25.1), ketones such as diethyl ketone (25.3); methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2), Examples include esters such as isobutyl acetate (23.7), ethyl butyrate (24.6), etc. (in parentheses indicate surface tension at 20 ° C., and the unit is [mN / m]). Among these, aliphatic hydrocarbons (hexane, heptane, etc.) have a low surface tension and an excellent working environment. Among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, or 1,2-dimethoxyethane, it can be used as the organic solvent in the washing step. Among these, those having a boiling point of 100 ° C. or less at normal pressure may be used because they can be easily dried in the drying step described later. You may use 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 that can sufficiently replace the solvent in the wet gel after washing. The amount can be 3 to 10 times the amount of wet gel volume.

  The temperature environment in the solvent replacement step can be set to a temperature not higher than the boiling point of the solvent used for the replacement. For example, when heptane is used, the temperature can be set to about 30 to 60 ° C.

  In the present embodiment, since the silica particles are contained in the gel, the solvent replacement step is not necessarily essential as described above. The inferred mechanism is as follows. That is, conventionally, in order to suppress shrinkage in the drying process, the solvent of the wet gel is replaced with a predetermined replacement solvent (a low surface tension solvent), but in this embodiment, the silica particles are in a three-dimensional network shape. By functioning as a skeleton support, 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. Thus, in this embodiment, the drying process can be simplified from the washing and solvent replacement process. However, this embodiment does not exclude performing the solvent substitution step at all.

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

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

  The airgel composite of this embodiment can be obtained by drying a wet gel that has been washed and (if necessary) solvent-substituted at a temperature below the critical point of the solvent used for drying under atmospheric pressure. The drying temperature varies depending on the type of substituted solvent (the solvent used for washing if solvent substitution is not performed), but especially when drying at a high temperature increases the evaporation rate of the solvent and causes large cracks in the gel. In view of that there is, it can be 20-150 degreeC. The drying temperature may be 60 to 120 ° C. Moreover, although drying time changes with the capacity | capacitances and drying temperature of a wet gel, it can be 4 to 120 hours. In the present embodiment, it is also included in the atmospheric pressure drying that the drying is accelerated by applying a pressure less than the critical point within a range not inhibiting the productivity.

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

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

  The airgel composite of this embodiment has high heat insulation and excellent flexibility. The airgel composite obtained by the above method for producing an airgel composite can be used as it is (processed into a predetermined shape as needed) as a heat insulating material. Therefore, it can be applied to applications such as the construction field, automobile field, home appliances, semiconductor field, and industrial equipment.

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

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

Example 1
As a silica particle-containing raw material, PL-2L (manufactured by Fuso Chemical Industry Co., Ltd., product name, average primary particle size: 20 nm, solid content: 20% by mass) is 100.0 parts by mass, water is 99.0 parts by mass, acid catalyst 1.0 parts by mass of acetic acid, 20.0 parts by mass of hexadecyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter abbreviated as “CTAB”) as an ionic surfactant, and urea as a thermally hydrolyzable compound 120.0 parts by mass, 60.0 parts by mass of methylcitrimethoxylane (manufactured by Shin-Etsu Chemical Co., Ltd., hereinafter abbreviated as “MTMS”) and dimethoxydimethylsilane (manufactured by Tokyo Chemical Industry Co., Ltd.) as a silicon compound. , Hereinafter abbreviated as “DMDMS”) and 20.0 parts by mass of polysiloxane compound A as a polysiloxane compound, It was reacted for 30 minutes at 5 ° C.. The obtained sol was gelled at 60 ° C. for 4 hours and then aged at 60 ° C. for 60 hours to obtain a wet gel.

  Then, the obtained wet gel was immersed in a mixed solution of 1000.0 parts by mass of water and 1500.0 parts by mass of methanol, and washed at 60 ° C. for 3 hours. This washing operation was performed again by exchanging the mixed solution with 2500.0 parts by mass of methanol. Next, the washed wet gel was immersed in 2500.0 parts by mass of methyl ethyl ketone, which is a low surface tension solvent, and solvent substitution was performed at 60 ° C. for 3 hours. This solvent replacement operation was performed twice while exchanging with new methyl ethyl ketone. The washed and solvent-substituted wet gel is dried at 25 ° C. for 48 hours under normal pressure, and then further dried at 150 ° C. for 2 hours, so that the general formulas (3), (6) and (7) An airgel composite having the structure represented was obtained.

(Examples 2-3)
An airgel composite was obtained in the same manner as in Example 1 except that the amount of water added and the amount of acetic acid added during sol generation were as shown in Table 1.

[Various evaluations]
For the airgel composites obtained in each Example, the signal area ratio, compression rupture strength, tensile rupture strength, tensile elastic modulus, and thermal conductivity of silicon-containing bonding units Q, T, and D were measured and evaluated according to the following contents. did. The evaluation results are summarized in Table 2. For reference, a solid ²⁹ Si-NMR spectrum for the airgel composite of Example 1 obtained by using the DD / MAS method is shown in FIG.

(1) Measurement of signal area ratio concerning silicon-containing bonding units Q, T and D Measurement was performed using “FT-NMR AV400WB” (product name, manufactured by Bruker BioSpin Corporation) as a solid ²⁹ Si-NMR apparatus. It was. The measurement conditions were: measurement mode: DD / MAS method, probe: 7 mmφ CPMAS probe, magnetic field: 9.4 T, resonance frequency: 79 MHz, MAS rotation speed: 4 kHz, delay time: 150 seconds. As a reference substance for chemical shift, sodium 3-trimethylsilylpropionate was used, and the chemical shift was set to 1.259 ppm.

As a measurement sample, an airgel composite cut into small pieces was prepared, packed in a ZrO ₂ rotor, mounted on a probe, and measured. The signal area ratio (Q + T: D) relating to the obtained silicon-containing binding units Q, T and D was determined. In the spectrum analysis, the line broadcasting coefficient was set to 100 Hz.

(2) Measurement of compressive breaking strength The airgel composite was processed into a cube having a thickness of 7 mm, a width of 7 mm, and a length of 7 mm using a blade having a blade angle of about 20 to 25 degrees to obtain a measurement sample. Next, in order to ensure parallelism of the surfaces, the measurement sample was shaped with sandpaper of # 1500 or more as necessary.

  As a measuring apparatus, a small tabletop testing machine “EZTest” (manufactured by Shimadzu Corporation, product name) was used. In addition, 500N was used as a load cell. Further, a stainless upper platen (φ20 mm) and a lower platen (φ118 mm) were used as measuring jigs. A measurement sample was set between an upper platen and a lower platen arranged in parallel, and the sample was compressed at a speed of 1 mm / min. The measurement temperature was 25 ° C., and the compression strength at the time when the measurement sample was broken was defined as compression rupture strength.

Here, the compressive strength δ (MPa) was determined as follows.
δ = 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.

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

As a measuring apparatus, a small tabletop testing machine “EZTest” (manufactured by Shimadzu Corporation, product name) was used in the same manner as the measurement of compressive breaking strength. A measurement sample was set between an upper platen and a lower platen arranged in parallel, and tension was performed at a speed of 1 mm / min. The measurement temperature was 25 ° C., and the tensile stress at the time when a load exceeding 500 N was applied or when the measurement sample was broken was defined as the tensile strength at break. Here, the strain ε was obtained from the following equation.
ε = Δd / d1
In the equation, Δd represents the displacement (mm) of the tensile force of the measurement sample due to the load, and d1 represents the distance (mm) between the clamps of the measurement sample before applying the load.
The tensile stress σ (kPa) was obtained from the following formula.
σ = F / A
In the formula, F represents the tensile force (N), and A represents the cross-sectional area (mm ² ) of the measurement sample before applying a load.

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

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

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

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

  From Table 2, the airgel composite of this example in which the area ratio Q + T: D has a value in the range of 1: 0.10 to 1: 0.35 has a thermal conductivity of 0.2 at 25 ° C. under atmospheric pressure. Although it is 03 W / m · K or less, the compression breaking strength is 0.3 MPa or more and the tensile breaking strength is 10 kPa or more, and it has excellent toughness that was difficult to achieve with conventional airgel. Moreover, it turns out that a tensile elasticity modulus is less than 20 kPa and has the outstanding softness | flexibility. The airgel composite of this embodiment can be used as a coating additive, cosmetics, antiblocking agent, catalyst carrier, etc., in addition to its use as a heat insulating material.

  1 ... Silica particles, L ... circumscribed rectangle.

Claims (6)

Containing an airgel component and silica particles,
In the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method, when the silicon-containing binding units Q, T, and D are defined as follows, the signal area derived from Q and T, and the signal derived from D The airgel composite whose ratio to the area (signal area ratio) Q + T: D is 1: 0.10 to 1: 0.35.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
[However, the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom]. In the solid ²⁹ Si-NMR spectrum measured using the DD / MAS method, when the silicon-containing binding units Q, T, and D are defined as follows, the signal area derived from Q and T, and the signal derived from D The airgel composite whose ratio to the area (signal area ratio) Q + T: D is 1: 0.10 to 1: 0.35.
Q: A silicon-containing bond unit having four oxygen atoms bonded to one silicon atom.
T: A silicon-containing bond unit having three oxygen atoms bonded to one silicon atom and one hydrogen atom or monovalent organic group.
D: A silicon-containing bond unit having two oxygen atoms bonded to one silicon atom and two hydrogen atoms or two monovalent organic groups.
[However, the signal area derived from Q is more than 0, and the organic group is a monovalent organic group in which an atom bonded to a silicon atom is a carbon atom].   The airgel composite according to claim 1, wherein an average primary particle diameter of the silica particles is 1 to 500 nm. The airgel composite according to any one of claims 1 to 3, which has a structure represented by the following general formula (1).

[In Formula (1), R ₁ and R ₂ each independently represent an alkyl group or an aryl group, and R ₃ and R ₄ each independently represent an alkylene group. ] The airgel composite according to any one of claims 1 to 4, wherein the airgel composite has a ladder structure including a support portion and a bridge portion, and the bridge portion is represented by the following general formula (2).

[In Formula (2), R ₆ and R ₇ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. ] The airgel composite according to claim 5, which has a structure represented by the following general formula (3).

[In Formula (3), R < ₅ >, R < ₆ >, R < ₇ > and R < ₈ > show an alkyl group or an aryl group each independently, a, b, and c show the integer of 1-50 each independently. ]