WO2020012553A1

WO2020012553A1 - Coating liquid and coating film

Info

Publication number: WO2020012553A1
Application number: PCT/JP2018/026010
Authority: WO
Inventors: 寛之泉; 竜也牧野; 智彦小竹; 慧高安; 直義佐藤
Original assignee: 日立化成株式会社
Priority date: 2018-07-10
Filing date: 2018-07-10
Publication date: 2020-01-16
Also published as: JPWO2020012553A1; JP7230914B2

Abstract

The present invention pertains to a coating liquid which contains aerogel particles, a binder resin and a liquid medium, wherein the aerogel particle content is at least 20 mass%. The present invention also pertains to a coating film which contains aerogel particles and a binder resin, wherein the aerogel particle content is at least 80 mass% and the density thereof is 0.4 g/cm³ or less.

Description

Coating liquids and coatings

The present invention relates to a coating liquid and a coating film.

エア Aerogel is known as a material having excellent heat insulating properties and transparency. A method has been proposed in which aerogel having such properties is processed into particles and used as a constituent material of a heat insulating material (for example, Patent Document 1). Patent Literature 1 proposes using particulate aerogel as a filler between resin plates and the like constituting a heat insulating window.

JP 2012-91943 A

取り扱う When handling airgel particles as particles as a filler, a configuration other than the airgel particles is indispensable as described above. On the other hand, if the layer of the airgel particles can be formed directly on the surface of the object, the configuration can be made simpler, and the layer shape is hardly restricted by the surface shape of the object.

The present invention has been made in view of the above circumstances, and has an object to provide a novel airgel particle-containing coating liquid. Another object of the present invention is to provide a coating film obtained by using the coating liquid.

The present invention provides a coating liquid containing airgel particles, a binder resin and a liquid medium, wherein the content of the airgel particles is 20% by mass or more. In the coating liquid of the present invention, a larger amount of airgel particles than in the prior art is present in a dispersed state. Therefore, a coating film containing airgel particles densely can be formed on the target surface. One reason that a large amount of airgel particles could be dispersed in the coating liquid is that the dispersion method was appropriately adjusted.

液状 In the coating liquid of the present invention, the liquid medium can contain water. In addition, the liquid medium can further include an organic solvent.

In the coating liquid of the present invention, the binder resin is an epoxy resin, a silicone resin, a phenol resin, a urea resin, a melamine resin, a polyurethane resin, a polyethylene resin, a polypropylene resin, a polystyrene resin, a polyester resin, an acrylic resin, a polyvinyl chloride resin, At least one selected from the group consisting of vinyl acetate resin, polyamide resin, polyimide resin, cellulose resin, and polyvinyl resin can be included. Thereby, the film formability can be further improved.

比 The specific gravity of the coating liquid of the present invention can be 0.8 or less.

The present invention also provides a coating film containing airgel particles and a binder resin, wherein the content of the airgel particles is 80% by mass or more and the density is 0.4 g / cm ³ or less. Conventionally, it has been very difficult to obtain a light coating film (aerogel coating film) in which airgel particles are highly filled as described above. However, this can be realized by using the coating liquid of the present invention.

In the coating film of the present invention, the binder resin is an epoxy resin, silicone resin, phenol resin, urea resin, melamine resin, polyurethane resin, polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, acrylic resin, polyvinyl chloride resin, poly At least one selected from the group consisting of vinyl acetate resin, polyamide resin, polyimide resin, cellulose resin, and polyvinyl resin can be included. Thereby, the film quality can be further improved.

According to the present invention, a novel airgel particle-containing coating liquid can be provided. Further, according to the present invention, a coating film (airgel coating film) obtained by using the coating liquid can be provided.

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

<Aerogel particles>
In a narrow sense, a dry gel obtained by using a supercritical drying method for a wet gel is aerogel, a dry gel obtained by drying under atmospheric pressure is a xerogel, and a dry gel obtained by freeze-drying is a cryogel. In this embodiment, the obtained low-density dried gel is referred to as “aerogel” regardless of the method for drying the wet gel. That is, in the present embodiment, “aerogel” is a broadly defined aerogel, “Gel-complied of a microporous solid in which the dispersed phase is a gas (a gel composed of a microporous solid whose dispersed phase is a gas). Means. Generally, the inside of the airgel has a network-like fine structure, and has a cluster structure in which a particulate airgel component of about 2 to 20 nm is bonded. There are pores smaller than 100 nm between the skeletons formed by the clusters. Thereby, the airgel has a three-dimensionally fine porous structure. The aerogel according to the present embodiment is, for example, a silica aerogel containing silica as a main component. Examples of the silica airgel include a so-called organic-inorganic hybridized silica airgel into which an organic group (eg, a methyl group) or an organic chain is introduced.

は The airgel particles in the present embodiment are not particularly limited, and airgel particles manufactured by various known manufacturing methods can be used. As an example, an airgel that can constitute the airgel particles of the present embodiment will be described. The airgel 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 a silicon compound having a hydrolyzable functional group, as described below. It is a dried product of a wet gel which is a condensate of a sol containing at least one (a product obtained by drying a wet gel generated from a sol: a dried product of a wet gel derived from a sol).

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

In the formulas (1) and (1a), R ¹ and R ² each independently represent an alkyl group or an aryl group, and R ³ and R ⁴ each independently represent an alkylene group. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. In addition, 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 may be the same or different, and similarly, two or more R ² may be the same or different. In the formula (1a), two R ³ may be the same or different, and similarly, two R ⁴ may be the same or different.

By introducing the structure represented by the above formula (1) or (1a) into the skeleton of the aerogel as an aerogel component, a flexible aerogel with 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 1 to 6 carbon atoms, a phenyl group, and the like. And the like. In Formulas (1) and (1a), R ³ and R ⁴ each independently include an alkylene group having 1 to 6 carbon atoms, and the alkylene group includes an ethylene group, a propylene group, and the like. Can be In the formula (1a), p may be 2 to 30, and may be 5 to 20.

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

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. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In the formula (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 may be the same. May also be different.

By introducing the above structure as an airgel component into the skeleton of the airgel, for example, it has a structure derived from a conventional ladder-type silsesquioxane (that is, has a structure represented by the following general formula (X)) It becomes an aerogel having better flexibility than airgel. 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 by the following general formula (X), in the conventional aerogel having a structure derived from ladder-type silsesquioxane, the structure of the crosslinked portion is -O-, but the aerogel according to the present embodiment In the above, the structure of the crosslinked portion is a structure (polysiloxane structure) represented by the above general formula (2). However, the airgel of this embodiment may have a structure derived from silsesquioxane in addition to the structure represented by the general formula (2).

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

There is no particular limitation on the structure serving as the support portion, its chain length, and the interval between the structures serving as the bridge portions. 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 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 represents 1 to 50 Indicates an integer. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In addition, in Formula (3), 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 may be 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 may be the same or different, and similarly, when c is an integer of 2 or more, two or more R ⁸ may be the same or different.

From the viewpoint of obtaining more excellent flexibility, R ⁵ , R ⁶ , R ⁷ and R ^{8 in} the formulas (2) and (3) (where R ⁷ and R ⁸ are only in the formula (3)) Each independently represents an alkyl group having 1 to 6 carbon atoms, a phenyl group or the like, and the alkyl group includes a methyl group or the like. In the formula (3), a and c can each independently be 6 to 2000, but may be 10 to 1000. In the formulas (2) and (3), b may be 2 to 30, but may be 5 to 20.

構造 In addition, by using a silane monomer described below as a raw material of the airgel, the structure represented by the following general formulas (4) to (6) can be introduced into the skeleton of the airgel. The airgel according to the present embodiment can have one of these structures alone or two or more of them.

In the 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.

In the 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.

In the formula (6), 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.

エア The airgel according to the present embodiment may further contain silica particles in addition to the airgel component from the viewpoint of further toughening and achieving even better heat insulation and flexibility. An airgel containing an airgel component and silica particles can also be referred to as an airgel composite. The airgel composite has a cluster structure, which is a characteristic of aerogel, even though the airgel component and silica particles are composited, and is considered to have a three-dimensionally fine porous structure. .

According to the above expression, the airgel containing the airgel component and the silica particles is a silicon compound having a hydrolyzable functional group or a condensable functional group, and hydrolysis of a silicon compound having a hydrolyzable functional group. It can be said that the product is a dried product of a wet gel that is a condensate of a sol containing at least one selected from the group consisting of products and silica particles.

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

形状 The shape of the silica particles is not particularly limited, and examples thereof include a spherical shape, a cocoon shape, and an association type. Among them, the use of spherical particles as the silica particles makes it easier to suppress aggregation in the sol. The average primary particle diameter of the silica particles is 1 nm or more, or 5 nm or more, from the viewpoint that it is easy to impart appropriate strength and flexibility to the aerogel, and to easily obtain an aerogel having excellent resistance to shrinkage during drying. And may be 20 nm or more. The average primary particle diameter of the silica particles is 500 nm or less, 300 nm or less, and 100 nm or less, from the viewpoint of easily suppressing the solid heat conduction of the silica particles and easily obtaining an aerogel having excellent heat insulating properties. The following may be used. From these viewpoints, the average primary particle diameter of the silica particles may be 1 to 500 nm, 5 to 300 nm, or 20 to 100 nm.

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

平均 The average particle size of the silica particles can also 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 concentration of about 5 to 40% by mass and dispersed in water as an example, a dispersion liquid of colloidal silica particles was obtained by cutting a wafer with patterned wiring into 2 cm square. After soaking the chip for about 30 seconds, the chip is rinsed with pure water for about 30 seconds and dried with nitrogen blow. Thereafter, the chip is placed on a sample stage for SEM observation, an acceleration voltage of 10 kV is applied, and 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 the particles is defined as the average particle diameter.

The number of silanol groups per 1 g of the silica particles may be 10 × 10 ¹⁸ / g or more, and may be 50 × 10 ¹⁸ / g or more from the viewpoint of easily obtaining an aerogel having excellent shrink resistance. , 100 × 10 ¹⁸ / g or more. The number of silanol groups per gram of the silica particles may be 1000 × 10 ¹⁸ / g or less, 800 × 10 ¹⁸ / g or less, and 700 × It may be 10 ¹⁸ / g or less. From these viewpoints, the number of silanol groups per 1 g of the silica particles may be 10 × 10 ¹⁸ to 1000 × 10 ¹⁸ / g, or may be 50 × 10 ¹⁸ to 800 × 10 ¹⁸ / g. , 100 × 10 ¹⁸ to 700 × 10 ¹⁸ particles / g.

The specific surface area of the airgel particles can be 1200 m ² / g or less, but may be 1000 m ² / g or less, 900 m ² / g or less, or 800 m ² / g or less. . This makes it easy to prepare a coating liquid having excellent film-forming properties. The lower limit of the specific surface area of the airgel particles is not particularly limited, but may be about 30 m ² / g from the viewpoint of suppressing aggregation in the coating liquid and improving the filling rate.

The specific surface area can be measured by the BET method. As a measuring device, a gas adsorption amount measuring device (Autosorb-iQ (Autosorb is a registered trademark) manufactured by Kantachrome Instruments Japan GK) can be used.

The average particle diameter D50 of the airgel particles may be 1 to 1000 μm, but may be 3 to 700 μm, 5 to 500 μm, 10 to 100 μm, or 10 to 50 μm. You may. When the average particle diameter D50 of the airgel particles is 1 μm or more, it becomes easy to obtain airgel particles excellent in dispersibility, handleability, and the like. On the other hand, when the average particle diameter D50 is 1000 μm or less, airgel particles having excellent dispersibility can be easily obtained. The average particle size of the airgel particles can be appropriately adjusted by a pulverizing method and pulverizing conditions, a sieving method, a classification method, and the like.

平均 The average particle diameter D50 of the airgel particles can be measured by a laser diffraction / scattering method. For example, the airgel particles are added to a solvent (ethanol) so that the content of the airgel particles becomes 0.05 to 5% by mass, and the airgel particles are dispersed by vibrating for 15 to 30 minutes with a 50 W ultrasonic homogenizer. Thereafter, about 10 mL of the dispersion is injected into a laser diffraction / scattering type particle size distribution analyzer, and the particle size is measured at 25 ° C. with a refractive index of 1.3 and an absorption of 0. The particle diameter at an integrated value of 50% (by volume) in the particle diameter distribution is defined as an average particle diameter D50. As the measuring device, for example, Microtrac MT3000 (product name, manufactured by Nikkiso Co., Ltd.) can be used.

<Method for producing airgel particles>
The method for producing the airgel particles is not particularly limited, but for example, it can be produced by the following method.

The airgel particles of the present embodiment are formed by a sol generation step, a sol obtained in the sol generation step, and a wet gel generation step of aging to obtain a wet gel, and a wet gel obtained in the wet gel generation step. A manufacturing method mainly comprising a washing and solvent replacement step of washing and (if necessary) solvent replacement, a drying step of drying the washed and solvent-replaced wet gel, and a pulverization step of pulverizing the aerogel obtained by drying. Can be manufactured.

Also, a sol generating step, a wet gel generating step, a wet gel crushing step of crushing the wet gel obtained in the wet gel generating step, a washing and solvent replacement step, and a manufacturing method mainly comprising a drying step May be.

大き The size of the obtained airgel particles can be further uniformed by sieving, classification and the like. By adjusting the size of the particles, the dispersibility can be increased. Note that the “sol” is a state before a gelation reaction occurs, and in the present embodiment, means a state in which, for example, a silicon compound and optionally silica particles are dissolved or dispersed in a solvent. I do. In addition, the wet gel refers to a gel solid in a wet state that does not have fluidity while containing a liquid medium.

(Sol generation step)
The sol generation step is a step of mixing a silicon compound and, in some cases, silica particles (may be a solvent containing silica particles) in a solvent and performing a hydrolysis reaction as necessary. More specifically, the sol generation step includes a hydrolysis of a silicon compound having a hydrolyzable functional group, a silicon compound having a condensable functional group, and a silicon compound having a hydrolyzable functional group. This is a step of producing a sol containing a product or the like. The sol generation step includes a silicon compound having a hydrolyzable functional group or a condensable functional group, and at least one selected from the group consisting of hydrolysis products of the silicon compound having a hydrolyzable functional group. It can be said that this is a step of producing a sol to be contained. The aerogel exemplified above can be obtained by drying a wet gel generated from such a sol.

ポリ A polysiloxane compound can be used as the silicon compound. That is, the sol is at least selected from the group consisting of a polysiloxane compound having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of a polysiloxane compound having a hydrolyzable functional group. One kind of compound (hereinafter, sometimes referred to as “polysiloxane compound group”) may be contained.

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. 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. Note that a polysiloxane compound having a hydrolyzable functional group or a condensable functional group is a reactive group different from the hydrolyzable functional group and the condensable functional group (the hydrolyzable functional group and the condensable functional group). Functional group which does not correspond to a functional group). Examples of the reactive group include an epoxy group, a mercapto group, a glycidoxy group, a vinyl group, an acryloyl group, a methacryloyl group, 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 as a mixture of two or more. Among these functional groups and reactive groups, for example, groups that improve the flexibility of the airgel include alkoxy groups, silanol groups, hydroxyalkyl groups, and the like. Among these, alkoxy groups and hydroxyalkyl groups are: The compatibility of the sol can be further improved. Further, from the viewpoint of improving the reactivity of the polysiloxane compound and reducing the thermal conductivity of the aerogel, the number of carbon atoms of the alkoxy group and the hydroxyalkyl group can be 1 to 6, but the flexibility of the aerogel is further improved. From the viewpoint, it may be 2 to 4.

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

In the 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. 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 may be the same or different, and similarly, two R ^2a may be the same or different. In the formula (A), two or more R ^3a may be the same or different, and similarly, two or more R ^4a may be the same or different.

By using a wet gel (formed from the sol) which is a condensate of a sol containing the polysiloxane compound having the above structure, it becomes easier to obtain a flexible aerogel having low thermal conductivity. From such a viewpoint, in the formula (A), R ^1a includes a hydroxyalkyl group having 1 to 6 carbon atoms and the like, and the hydroxyalkyl group includes a hydroxyethyl group and a hydroxypropyl group. In Formula (A), R ^2a includes an alkylene group having 1 to 6 carbon atoms, and the alkylene group includes an ethylene group, a propylene group, and the like. In the formula (A), R ^3a and R ^4a each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and the alkyl group includes a methyl group and the like. In the formula (A), n can be 2 to 30, but may be 5 to 20.

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

Examples of the polysiloxane compound having an alkoxy group in a molecule include those having a structure represented by the following general formula (B). By using a polysiloxane compound having a structure represented by the following general formula (B), a ladder-type structure having a crosslinked portion represented by the general formula (2) or (3) is introduced into the skeleton of the airgel. can do.

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 each independently represent an alkyl group or an 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. 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 may be the same or different, and two R ^2b may be the same or different, respectively. ^3b may be the same or different. In the formula (B), when m is an integer of 2 or more, two or more R ^4b may be the same or different, and similarly, two or more R ^5b may be the same. May also be different.

By using a wet gel (generated from the sol), which is a condensate of a sol containing the polysiloxane compound having the above structure or a hydrolysis product thereof, a soft aerogel having a low thermal conductivity and a low thermal conductivity can be more easily obtained. From such a viewpoint, 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 the alkyl group or the alkoxy group is a methyl group. Methoxy group, ethoxy group and the like. In the formula (B), R ^2b and R ^3b each independently include an alkoxy group having 1 to 6 carbon atoms, and the alkoxy group includes a methoxy group and an ethoxy group. In formula (B), R ^4b and R ^5b each independently include an alkyl group having 1 to 6 carbon atoms, a phenyl group and the like, and the alkyl group includes a methyl group and the like. In the formula (B), m can be 2 to 30, but may be 5 to 20.

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

Since the alkoxy group hydrolyzes, the polysiloxane compound having the alkoxy group may be present as a hydrolysis product in the sol, and the polysiloxane compound having the alkoxy group and the hydrolysis product are mixed. May be. In the polysiloxane compound having an alkoxy group, all of the alkoxy groups in the molecule may be hydrolyzed or partially hydrolyzed.

These polysiloxane compounds having a hydrolyzable functional group or a condensable functional group, and hydrolysis products of a polysiloxane compound having a hydrolyzable functional group may be used alone or as a mixture of two or more. May be used.

作製 In producing the airgel according to the present embodiment, a silicon compound other than the above-described polysiloxane compound can be used as the silicon compound. Such silicon compounds include silane monomers. That is, the sol containing the silicon compound is a group consisting of a silane monomer having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of the silane monomer having a hydrolyzable functional group. At least one selected from the following (hereinafter sometimes referred to as “silane monomer group”) may be contained in addition to the above-mentioned polysiloxane compound group or in place of the above-mentioned polysiloxane compound group. The number of silicon atoms in the molecule of the silane monomer can be 1 to 6.

シラン The silane monomer having a hydrolyzable functional group is not particularly limited, and examples thereof include an alkyl silicon alkoxide. Alkyl silicon alkoxides can reduce the number of hydrolyzable functional groups to three or less from the viewpoint of improving water resistance. Examples of such an alkyl silicon alkoxide include monoalkyl trialkoxy silane, monoalkyl dialkoxy silane, dialkyl dialkoxy silane, monoalkyl monoalkoxy silane, dialkyl monoalkoxy silane, and trialkyl monoalkoxy silane. Examples thereof include methyltrimethoxysilane, methyldimethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, ethyltrimethoxysilane, hexyltrimethoxysilane and the like. Here, examples of the hydrolyzable functional group include an alkoxy group such as a methoxy group and an ethoxy group.

The silane monomer having a condensable functional group is not particularly limited, but includes silanetetraol, methylsilanetriol, dimethylsilanediol, phenylsilanetriol, phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol, hexylsilane Triol, octylsilanetriol, decylsilanetriol, trifluoropropylsilanetriol and the like can be mentioned.

Even if the silane monomer further has the above-mentioned reactive group (functional group which does not correspond to the hydrolyzable functional group and the condensable functional group) different from the hydrolyzable functional group and the condensable functional group, Good.

Examples of the silane monomer having a hydrolyzable functional group and a reactive group include vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 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.

Examples of silane monomers having a condensable functional group and a reactive group include vinyl silane triol, 3-glycidoxypropyl silane triol, 3-glycidoxy propyl methyl silane diol, 3-methacryloxy propyl silane triol, and 3-methacryloxy propyl Methylsilanediol, 3-acryloxypropylsilanetriol, 3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilanediol, N-phenyl-3-aminopropylsilanetriol, N-2- (aminoethyl) -3-amino Propylmethylsilanediol and the like can also be used.

The silane monomer may have two or more silicon atoms, and bistrimethoxysilylmethane, bistrimethoxysilylethane, bistrimethoxysilylhexane and the like can also be used.

A silane monomer having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of the silane monomer having a hydrolyzable functional group may be used alone or as a mixture of two or more. Is also good.

When the airgel further contains silica particles, the sol generation step is a silicon compound having a hydrolyzable functional group or a condensable functional group, and a hydrolysis product of a silicon compound having a hydrolyzable functional group. It can be said that this is a step of generating a sol containing at least one selected from the group and silica particles.

The content of the polysiloxane compound group contained in the sol (the content of the polysiloxane compound having a hydrolyzable functional group or a condensable functional group, and the hydrolysis of the polysiloxane compound having a hydrolyzable functional group) The sum of the contents of the products) may be 5 parts by mass or more, or 10 parts by mass or more with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of more easily obtaining good reactivity. . The content of the polysiloxane compound group contained in the sol may be 50 parts by mass or less with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of making it easier to obtain good compatibility. There may be. From these viewpoints, the content of the polysiloxane compound group contained in the sol may be 5 to 50 parts by mass or 10 to 30 parts by mass based on 100 parts by mass of the total amount of the sol.

When the sol contains a silane monomer, the content of the silane monomer group (the content of the silane monomer having a hydrolyzable functional group or a condensable functional group, and the content of the silane monomer having a hydrolyzable functional group) The sum of the contents of the hydrolysis products) may be 5 parts by mass or more, or 10 parts by mass or more with respect to 100 parts by mass of the total amount of the sol, from the viewpoint of further obtaining good reactivity. Is also good. The content of the silane monomer group contained in the sol may be 50 parts by mass or less, or 30 parts by mass or less, based on 100 parts by mass of the total amount of the sol, from the viewpoint of further obtaining good compatibility. May be. From these viewpoints, the content of the silane monomer group contained in the sol may be 5 to 50 parts by mass, or may be 10 to 30 parts by mass.

When the sol contains both the polysiloxane compound group and the silane monomer group, the ratio between the content of the polysiloxane compound group and the content of the silane monomer group is preferably 1: from the viewpoint that good compatibility is more easily obtained. It may be 0.5 or more, or 1: 1 or more. The ratio between the content of the polysiloxane compound group and the content of the silane monomer group may be 1: 4 or less, or 1: 2 or less, from the viewpoint of further suppressing gel shrinkage. Good. From these viewpoints, the ratio of the content of the polysiloxane compound group to the content of the silane monomer group may be from 1: 0.5 to 1: 4, and may be from 1: 1 to 1: 2. Is also good.

When silica particles are contained in the sol, the content of the silica particles makes it easy to impart appropriate strength to the aerogel, and from the viewpoint of easily obtaining an aerogel having excellent shrink resistance during drying, the total amount of the sol is 100 parts by mass. On the other hand, it may be 1 part by mass or more, or 4 parts by mass or more. The content of the silica particles is easy to suppress the solid heat conduction of the silica particles, and from the viewpoint of easily obtaining an aerogel having excellent heat insulating properties, the total amount of the sol may be 20 parts by mass or less based on 100 parts by mass of the sol, It may be 15 parts by mass or less. From these viewpoints, the content of the silica particles may be 1 to 20 parts by mass or 4 to 15 parts by mass with respect to 100 parts by mass of the total amount of the sol.

溶媒 In the sol generation step, a solvent is used for mixing and possibly hydrolyzing the silicon compound. As the solvent, for example, water or a mixture of water and alcohol can be used. Examples of the alcohol include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, t-butanol and the like. Among these, examples of the alcohol having a low surface tension and a low boiling point in terms of reducing the interfacial tension with the gel wall include methanol, ethanol, and 2-propanol. These may be used alone or as a mixture of two or more.

For example, when an alcohol is used as the solvent, the amount of the alcohol can be 4 to 8 mol, or 4 to 6.5 mol per 1 mol of the total amount of the polysiloxane compound group and the silane monomer group. Alternatively, it may be 4.5 to 6 mol. By setting the amount of the alcohol to 4 mol or more, it becomes easier to obtain good compatibility, and to set the amount to 8 mol or less, the shrinkage of the gel is more easily suppressed.

Also, the solvent may contain an acid catalyst for promoting the hydrolysis reaction. Examples of the acid catalyst include inorganic acids such as hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, and hypochlorous acid; Acid phosphates such as aluminum, magnesium acid phosphate and zinc acid 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 And the like. Among these, an organic carboxylic acid is mentioned as an acid catalyst for further improving the water resistance of the obtained airgel. Examples of the organic carboxylic acid include acetic acid, and may be formic acid, propionic acid, oxalic acid, malonic acid, and the like. These may be used alone or as a mixture of two or more.

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

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

界面 Also, as disclosed in Japanese Patent No. 5250900, a surfactant, a thermally hydrolyzable compound, and the like can be added to a solvent.

非 As the surfactant, a nonionic surfactant, an ionic surfactant or the like can be used. These may be used alone or as a mixture of two or more.

As the nonionic surfactant, for example, a compound containing a hydrophilic part such as polyoxyethylene and a hydrophobic part mainly composed of an alkyl group, a compound containing a hydrophilic part such as polyoxypropylene and the like can be used. Examples of the compound containing a hydrophilic 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. Examples of the compound containing a hydrophilic portion, such as polyoxypropylene, include polyoxypropylene alkyl ether, a block copolymer 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 and cetyltrimethylammonium chloride, and examples of the anionic surfactant include sodium dodecylsulfonate. In addition, examples of the amphoteric surfactant include an amino acid-based surfactant, a betaine-based surfactant, and an amine oxide-based surfactant. Examples of the amino acid surfactant include acylglutamic acid and the like. Examples of the betaine-based surfactant include betaine lauryldimethylaminoacetate and betaine stearyldimethylaminoacetate. Examples of the amine oxide-based surfactant include 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 in the wet gel formation step described below, and suppressing phase separation. It is believed that.

The amount of the surfactant added depends on the type of the surfactant or the type and amount of the silicon compound. For example, 1 to 100 parts by mass relative to 100 parts by mass of the total of the polysiloxane compound group and the silane monomer group. It can be. Incidentally, the addition amount may be 5 to 60 parts by mass.

(4) It is considered that the thermally hydrolyzable compound generates a basic catalyst by thermal hydrolysis, makes the reaction solution basic, and promotes the sol-gel reaction in the wet gel formation step described later. Accordingly, the thermohydrolyzable compound is not particularly limited as long as it can make the reaction solution basic after hydrolysis, and urea; formamide, N-methylformamide, N, N-dimethylformamide, acetamide, N Acid amides such as -methylacetamide and N, N-dimethylacetamide; and cyclic nitrogen compounds such as hexamethylenetetramine. Among these, urea is particularly easy to obtain the above-mentioned promoting effect.

添加 The amount of the thermally hydrolyzable compound to be added is not particularly limited as long as it can sufficiently promote the sol-gel reaction in the wet gel forming step described below. For example, when urea is used as the thermally hydrolyzable compound, the amount of addition can be 1 to 200 parts by mass based on 100 parts by mass of the total of the polysiloxane compound group and the silane monomer group. The amount may be 2 to 150 parts by mass. By setting the addition amount to 1 part by mass or more, it becomes easier to obtain good reactivity, and by setting the addition amount to 200 parts by mass or less, it becomes easier to further suppress precipitation of crystals and reduction in gel density.

In the sol generation step, components such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound may be added to a solvent for the purpose of suppressing heat radiation.

The hydrolysis in the sol generation step depends on the type and amount of the silicon compound, silica particles, acid catalyst, surfactant and the like in the mixed solution, but for example, in a temperature environment of 20 to 60 ° C. for 10 minutes to 24 hours. The heat treatment may be performed for a period of time, or for 5 minutes to 8 hours in a temperature environment of 50 to 60 ° C. Thereby, the hydrolyzable functional group in the silicon compound is sufficiently hydrolyzed, and a hydrolysis product of the silicon compound can be obtained more reliably.

However, when the heat-hydrolyzable compound is added to the solvent, the temperature environment of the sol generation step may be adjusted to a temperature at which the hydrolysis of the heat-hydrolyzable compound is suppressed and the gelation of the sol is suppressed. . The temperature at this time may be any temperature as long as it can suppress hydrolysis of the thermally hydrolyzable 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 step)
The wet gel generation step is a step of gelling the sol obtained in the sol generation step and then aging to obtain a wet gel. In this step, a base catalyst can be used to promote gelation.

Examples of the base catalyst include carbonates such as calcium carbonate, potassium carbonate, sodium carbonate, barium carbonate, magnesium carbonate, lithium carbonate, ammonium carbonate, copper (II) carbonate, iron (II) carbonate and silver (I) carbonate; hydrogen carbonate Hydrogen carbonates such as calcium, potassium hydrogen carbonate, sodium hydrogen carbonate and ammonium hydrogen carbonate; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide and cesium hydroxide; ammonium hydroxide, ammonium fluoride; Ammonium compounds such as ammonium chloride and ammonium bromide; basic sodium phosphates such as sodium metaphosphate, sodium pyrophosphate and sodium polyphosphate; allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine Ruamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3- (diethylamino) propylamine, di-2-ethylhexylamine, 3- (dibutylamino) propylamine, tetramethylethylenediamine, t-butylamine, aliphatic amines such as sec-butylamine, propylamine, 3- (methylamino) propylamine, 3- (dimethylamino) propylamine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine and triethanolamine; morpholine Heterocyclic compounds such as N-methylmorpholine, 2-methylmorpholine, piperazine and its derivatives, piperidine and its derivatives, imidazole and its derivatives, etc. And the like. Among them, ammonium hydroxide (aqueous ammonia) is excellent in that it has high volatility and hardly remains in the airgel particles after drying, so that it does not easily impair water resistance, and furthermore, it is economical. The above base catalysts may be used alone or in combination of two or more.

By using a base catalyst, a dehydration condensation reaction or a dealcoholization condensation reaction of the silicon compound and silica particles in the sol can be promoted, and the sol can be gelled in a shorter time. In addition, thereby, a wet gel having higher strength (rigidity) can be obtained. In particular, ammonia has high volatility and hardly remains in the airgel particles. Therefore, by using ammonia as the base catalyst, airgel particles having more excellent water resistance can be obtained.

The amount of the base catalyst added can be 0.5 to 5 parts by mass, or 1 to 4 parts by mass, based on 100 parts by mass of the total of the polysiloxane compound group and the silane monomer group. When the amount is 0.5 parts by mass or more, gelation can be performed in a shorter time, and when the amount is 5 parts by mass or less, a decrease in water resistance can be further suppressed.

ゲル 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 can be between 30 and 90 ° C, but may be between 40 and 80 ° C. By setting the gelation temperature to 30 ° C. or higher, gelation can be performed in a shorter time, and a wet gel having higher strength (rigidity) can be obtained. Further, by setting the gelling temperature to 90 ° C. or lower, the volatilization of the solvent (particularly, alcohol) is easily suppressed, so that gelation can be performed while suppressing 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. The aging strengthens the binding of the components constituting the wet gel, and as a result, a wet gel having high strength (rigidity) enough to suppress shrinkage during drying can be obtained. The aging temperature can be 30 to 90 ° C, but may be 40 to 80 ° C. By setting the aging temperature to 30 ° C. or higher, a wet gel having higher strength (rigidity) can be obtained, and by setting the aging temperature to 90 ° C. or lower, the volatilization of the solvent (particularly alcohol) is easily suppressed. Gelation can be performed while suppressing volume shrinkage.

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

The gelation time and the aging time can be appropriately set according to the gelation temperature and the aging temperature. When silica particles are contained in the sol, the gelation time can be particularly shortened as compared with the case where silica particles are not contained. This is presumed to be because the silanol group or the reactive group of the silicon compound in the sol forms a hydrogen bond or a chemical bond with the silanol group of the silica particles. The gelation time can be 10 to 120 minutes, but may be 20 to 90 minutes. By setting the gelling time to 10 minutes or more, it becomes easy to obtain a uniform wet gel, and by setting the gelling time to 120 minutes or less, the washing and solvent replacement steps to be described later can be simplified from the drying step. The total time of the gelation time and the aging time in the entire gelation and aging step can be 4 to 480 hours, but may be 6 to 120 hours. By setting the total of the gelation time and the aging time to 4 hours or more, a wet gel having higher strength (rigidity) can be obtained, and by setting the total time to 480 hours or less, the effect of the aging can be more easily maintained.

To lower the density of the obtained airgel particles, or to increase the average pore size, increase the gelation temperature and aging temperature within the above range, or increase the total time of the gelation time and the aging time within the above range. Is also good. Also, to increase the density of the obtained airgel particles, to reduce the average pore diameter, to lower the gelation temperature and aging temperature in the above range, or to set the total time of gelation time and aging time in the above range. It may be shorter.

(Wet gel crushing process)
When performing the wet gel pulverizing step, the wet gel obtained in the wet gel generating step is pulverized. The pulverization can be performed, for example, by putting the wet gel in a Henshall type mixer, or by performing a wet gel generation step in the mixer, and operating the mixer under appropriate conditions (number of rotations and time). In addition, more simply, a wet gel is placed in a sealable container, or a wet gel generation step is performed in a sealable container, and shaking is performed by using a shaking device or the like for an appropriate time. Can be. Note that the particle size of the wet gel can be adjusted using a jet mill, a roller mill, a bead mill, or the like, if necessary.

(Washing and solvent replacement process)
The washing and solvent replacement step includes a step of washing the wet gel obtained in the wet gel generation step or the wet gel pulverizing step (washing step) and a step of washing the washing liquid in the wet gel with a solvent suitable for drying conditions (a drying step described later). (A solvent replacement step). The washing and solvent replacement step can be performed in a form in which only the solvent replacement step is performed without performing the step of washing the wet gel, but it is possible to reduce impurities such as unreacted substances and by-products in the wet gel. The wet gel may be washed from the viewpoint of enabling the production of highly pure airgel particles.

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

Examples of the organic solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, methyl ethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, and methylene chloride. , N, N-dimethylformamide, dimethylsulfoxide, acetic acid, formic acid and the like can be used. The above organic solvents may be used alone or in combination of two or more.

では In the solvent replacement step described below, a solvent having a low surface tension can be used to suppress shrinkage of the gel due to drying. However, low surface tension solvents generally have very low mutual solubility with water. Therefore, when a low surface tension solvent is used in the solvent replacement step, the organic solvent used in the washing step includes a hydrophilic organic solvent having high mutual solubility in both water and the low surface tension solvent. 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, and methyl ethyl ketone. In addition, methanol, ethanol, methyl ethyl ketone, etc. are excellent in terms of economy.

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

温度 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. For example, when methanol is used, the temperature can be raised 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 of the airgel in the drying step. At this time, the replacement efficiency can be improved by heating. As the substitution solvent, specifically, in the drying step, when drying at a temperature lower than the critical point of the solvent used for drying under atmospheric pressure, a solvent having a low surface tension, which will be described later, may be mentioned. On the other hand, in the case of supercritical drying, examples of the replacement solvent include ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide, and the like, or a solvent obtained by mixing two or more of these.

溶媒 Examples of the solvent having a low surface tension include a solvent having a surface tension at 30C of 30 mN / m or less. The surface tension may be 25 mN / m or less, or 20 mN / m or less. Examples of low surface tension solvents include pentane (15.5), hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4), Aliphatic hydrocarbons such as methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2) and 1-pentene (16.0); benzene Aromatic hydrocarbons such as (28.9), toluene (28.5), m-xylene (28.7) and p-xylene (28.3); dichloromethane (27.9), chloroform (27.2) ), Carbon tetrachloride (26.9), 1-chloropropane (21.8), 2-chloropropane (18.1) and other halogenated hydrocarbons; ethyl ether (17.1), propyl ether (20.5) ), Isop Ethers such as pill ether (17.7), butyl ethyl ether (20.8) and 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), Esters such as isobutyl acetate (23.7) and ethyl butyrate (24.6) are exemplified (the values in parentheses indicate the surface tension at 20 ° C., and the unit is [mN / m]). Among them, aliphatic hydrocarbons (hexane, heptane, etc.) have low surface tension and excellent work environment. Among these, by using a hydrophilic organic solvent such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane, the organic solvent can also be used as the organic solvent in the washing step. Among these, a solvent having a boiling point at normal pressure of 100 ° C. or lower may be used because drying in a drying step described later is easy. The above solvents may be used alone or in combination of two or more.

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

温度 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 replacement. For example, when heptane is used, the temperature can be raised to about 30 to 60 ° C.

場合 When silica particles are contained in the gel, the solvent replacement step is not essential. The inferred mechanism is as follows. That is, since the silica particles function as a support for the three-dimensional network skeleton, the skeleton is supported, and 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, the use of the silica particles makes it possible to simplify the washing and solvent replacement steps to the drying step.

(Drying process)
In the drying step, the wet gel that has been washed and (if necessary) replaced with a solvent is dried as described above. Thereby, an airgel (an airgel block or an airgel particle) can be obtained. That is, an aerogel obtained by drying the wet gel generated from the sol can be obtained.

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

The aerogel can be obtained by drying the wet gel after washing and (if necessary) solvent replacement 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 solvent that has been replaced (the solvent used for washing if solvent replacement is not performed), especially when drying at high temperatures increases the evaporation rate of the solvent and causes large cracks in the gel. In view of the above, the temperature can be set to 20 to 150 ° C. Incidentally, the drying temperature may be 60 to 120 ° C. The drying time varies depending on the volume of the wet gel and the drying temperature, but can be 4 to 120 hours. It should be noted that the drying under a normal pressure includes applying a pressure lower than the critical point within a range not impairing the productivity to accelerate the drying.

Airgel can also be obtained by supercritical drying of a wet gel that has been washed and (if necessary) replaced with a solvent. Supercritical drying can be performed by a known method. As a method of supercritical drying, for example, a method of removing the solvent at a temperature and a pressure higher than the critical point of the solvent contained in the wet gel may be mentioned. Alternatively, as a method of supercritical drying, the wet gel is immersed in liquefied carbon dioxide, for example, at a temperature of about 20 to 25 ° C. and about 5 to 20 MPa, so that all or a part of the solvent contained in the wet gel is dried. Is replaced with carbon dioxide having a lower critical point than the solvent, and then carbon dioxide alone or a mixture of carbon dioxide and a solvent is removed.

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

(Crushing process)
When the wet gel pulverizing step is not performed, the airgel (aerogel block) obtained by drying is pulverized to obtain airgel particles. For example, it can be carried out by putting aerogel into a jet mill, roller mill, bead mill, hammer mill or the like and operating at an appropriate rotation speed and time.

<Coating liquid and method for preparing coating liquid>
The coating liquid contains the airgel particles, the binder resin, and the liquid medium described above.

The binder resin has a function of binding the airgel particles after forming the coating film. As the binder resin, for example, epoxy resin, silicone resin, phenol resin, urea resin, melamine resin, polyurethane resin, polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, Examples thereof include a polyamide resin, a polyimide resin, a cellulose resin, and a polyvinyl resin. Among them, from the viewpoint of heat resistance and toughness, silicone resin, acrylic resin, phenol resin and polyester resin can be preferably used.

セルロース As the cellulose resin, for example, hydroxypropylmethylcellulose, carboxymethylcellulose ammonium, hydroxyethylmethylcellulose and the like can be mentioned. Examples of the polyvinyl resin include polyvinyl alcohol and polyvinyl pyrrolidone.

とき When the binder resin is a thermosetting resin, the coating liquid may further contain a curing agent. The curing agent is not particularly limited, and may be appropriately changed according to the type of the thermosetting resin. For example, when the thermosetting resin is an epoxy resin, a known epoxy resin curing agent can be used as the curing agent. Examples of the epoxy resin curing agent include, for example, an amine curing agent, an acid anhydride curing agent, a polyamide curing agent, and the like. From the viewpoint of reactivity, preferably use an amine curing agent and a polyamide curing agent. Can be.

Liquid media include water and organic solvents. The organic solvent is not particularly limited as long as it can disperse the airgel particles. Examples thereof include aromatic hydrocarbons such as toluene, xylene, mesitylene, cumene and p-cymene; and aliphatic hydrocarbons such as hexane, heptane and pentane. Hydrocarbons; ethers such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; alcohols such as methanol, ethanol, isopropanol (isopropyl alcohol), butanol, ethylene glycol and propylene glycol; acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone And ketones such as 4-hydroxy-4-methyl-2-pentanone; esters such as methyl acetate, ethyl acetate and butyl acetate; N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolid An amide such as emissions and the like. Among these, alcohols and ketones can be used from the viewpoints of volatility, boiling point, and the like, and alcohols can be particularly preferably used. Since alcohols and ketones can be easily mixed with water, an aqueous resin or the like, they are also suitable when used in combination with those components.

The coating liquid may contain a thickener, a fibrous substance, a pigment, a leveling agent and the like as other components.

(4) The thickener can improve the viscosity of the coating liquid and improve the coating property for the object. Examples of the thickener include fine particles such as fumed silica and clay mineral.

The fibrous substance can exhibit an anchor function between the airgel particles after the formation of the coating film, and can further improve the coating film strength. The fibrous substance is not particularly limited, and includes organic fibers and inorganic fibers. Examples of the organic fiber include polyamide fiber, polyimide fiber, polyvinyl alcohol fiber, polyvinylidene chloride fiber, polyvinyl chloride fiber, polyester fiber, polyacrylonitrile fiber, polyethylene fiber, polypropylene fiber, and polyurethane fiber. Fiber, phenolic fiber, polyetherester fiber, polylactic acid fiber, polycarbonate fiber and the like. Examples of the inorganic fibers include glass fibers, carbon fibers, ceramic fibers, and metal fibers.

塗 The coating liquid of the present embodiment contains a larger amount of airgel particles than in the past, and the content of airgel particles in the coating liquid is 20% by mass or more. From the viewpoint of obtaining a lower-density coating film, the content can be 25% by mass or more, may be 30% by mass or more, or may be more than 30% by mass. The upper limit of the content is not particularly limited, but may be 50% by mass from the viewpoint of the dispersibility of the airgel particles, good coating properties, and the like.

The content of the binder resin in the coating liquid may be 1% by mass or more, and may be 2% by mass or more from the viewpoints of the binding property between the airgel particles and the heat insulating property of the coating film. It may be not less than mass%. Further, the content can be 10% by mass or less, but may be 7% by mass or less, or may be 5% by mass or less.

The content of the binder resin in the coating liquid can be, for example, 5 parts by mass or more with respect to 100 parts by mass of the airgel particles, but may be 7 parts by mass or more, or 10 parts by mass or more. And may be 12 parts by mass or more. This makes it easier for the airgel particles to be firmly bound by the binder resin, further improving the strength of the coating film.

Further, the content of the binder resin can be, for example, 20 parts by mass or less with respect to 100 parts by mass of the airgel particles, but may be 18 parts by mass or less, or may be 15 parts by mass or less. . Thereby, the ratio of the airgel particles in the coating film is increased, the density of the coating film can be reduced, and the heat insulating property of the coating film is further improved.

The content of the fibrous substance in the coating liquid can be 0.01 to 30% by mass from the viewpoints of dispersibility in the coating liquid, good anchor function, and the like. It may be 10% by mass.

The content of the fibrous substance in the coating liquid can be, for example, 5 parts by mass or more with respect to 100 parts by mass of the airgel particles, but may be 7 parts by mass or more, or 9 parts by mass or more. You may. Thereby, the anchor effect by the fibrous substance is easily obtained, and the coating film strength is further improved.

Further, the content of the fibrous substance can be, for example, 50 parts by mass or less based on 100 parts by mass of the airgel particles, but may be 35 parts by mass or less, or 25 parts by mass or less. The amount may be 20 parts by mass or less, or 15 parts by mass or less. Thereby, the ratio of the airgel particles in the coating film is increased, and the heat insulating property of the coating film is further improved.

含有 The content of the thickener can be appropriately adjusted so as to have a desired coating liquid viscosity (for example, 1000 mPa · s or more). Since the viscosity of the coating liquid can be improved by blending a binder resin, in such a case, it is not always necessary to blend a thickener.

割合 The ratio of the airgel particles to the entire solid content in the coating liquid can be 90% by volume or more, but may be 95% by volume or more, or may be 98% by volume or more. In addition, the ratio of the binder resin to the entire solid content in the coating liquid can be 3% by volume or less, but may be 2.5% by volume or less, or may be 2% by volume or less.

The liquid medium may contain water as a main component (for example, 90% by mass or more). Water is less likely to penetrate into the porous structure of the water-repellent airgel particles, so that the application of the liquid becomes easier. However, the liquid medium may contain an organic solvent in order to further improve the kneading properties of the airgel particles and the binder resin. The content of the organic solvent in the liquid medium may be 1% by mass or more, may be 3% by mass or more, and may be 5% by mass or more.

比 The specific gravity of the coating liquid can be 0.8 or less, but may be 0.77 or less, or 0.75 or less. The lower limit of the specific gravity can be set to 0.35, and may be set to 0.6, from the viewpoint of easily forming a coating film while suppressing the occurrence of cracks. The specific gravity of the coating solution can be measured at room temperature (10 to 30 ° C.) using a disposable syringe. Specifically, a 2.5 mL disposable syringe is filled with 1.5 mL or more of the coating liquid, and after evacuating the air in the syringe, the total weight (A) of the syringe and the coating liquid is measured. Subsequently, the total weight (B) of the syringe and the coating liquid in the syringe after extruding 1.0 mL of the coating liquid from the syringe is measured. The specific gravity of the coating liquid can be calculated by setting the weight difference between (A) and (B) as the weight per 1.0 mL of the coating liquid. However, the specific gravity of the coating liquid can be measured by a laser volume meter, a float, a specific gravity meter, or the like, in addition to the above-described method using a syringe.

The coating liquid according to the present embodiment can be referred to as an airgel particle-containing coating liquid, but may be in a paste form depending on the viscosity, and can be referred to as an airgel particle-containing paste.

The coating liquid can be prepared by stirring (mixing) a raw material containing at least airgel particles, a binder resin and a liquid medium using one or more commercially available mixers. Examples of such a mixer include a shear stirrer such as a rotation-revolving mixer, a low-speed shear stirrer such as a planetary mixer (planetary mixer), and a high-speed shear stirrer such as a homomixer.

撹拌 As for the stirring conditions when using a rotation and revolution type mixer, the stirring speed can be 500 to 1500 rpm, and the stirring time can be 1 to 60 minutes. The stirring conditions when using a planetary mixer can be a stirring speed of 8 to 200 rpm and a stirring time of 1 to 120 minutes. The homomixer is preferably used in combination with the main stirring by these mixers, and particularly preferably used as a preliminary stirring means for the main stirring. For example, the stirring of the present embodiment can include a high-speed shearing and stirring step of stirring the raw material by a high-speed shearing stirrer and a subsequent low-speed shearing and stirring step of stirring by a low-speed shearing stirrer. When a homomixer is used as the preliminary stirring means, the stirring conditions may be a stirring speed of 1000 to 3000 rpm and a stirring time of 1 to 20 minutes.

Examples of the rotation-revolution type mixer include the Awatori Rentaro series (Shinky Co., Ltd., product name), ME-N300BR (Beat Sensing Co., Ltd., product name), Hi-Maja (AS-ONE Co., Ltd., product name) and the like. Can be Planetary mixers series include Planetary Mixer Series (product name, Inoue Manufacturing Co., Ltd.), PD Mixer Series (product name, Inoue Manufacturing Co., Ltd.), Hibis Mix Series (product name, manufactured by Primix Co., Ltd.), Hibis Dispermix series (product name, manufactured by Primix Corporation) and the like. Examples of the homomixer include an L5 series (manufactured by SILVERSON, product name) and a homomixer MARKII series (manufactured by Primix, product name).

多く If a lot of liquid components (binder resin, liquid medium, etc.) enter the pores of the airgel particles, the specific gravity of the coating liquid increases, and as a result, the density of the coating film increases. In order to suppress this, when preparing the coating liquid, adjust the stirring conditions according to the characteristics of the airgel particles to be used (do not perform stirring under excessive conditions), or change the type of binder resin. (It is preferable to increase the viscosity of the liquid component and to select a binder resin having low affinity for the airgel particles).

<Production method and coating film>
The coating film can be formed by removing the liquid medium from the coating liquid containing the airgel particles, the binder resin, and the liquid medium. More specifically, a method for producing a coating film (a method for forming a coating film) includes a step of applying the above-described coating liquid on an object, and a step of removing a liquid medium from the coating liquid applied on the object. , Can be provided.

方法 The method of applying the coating liquid on the object is not particularly limited, and examples thereof include dip coating, spray coating, spin coating, and roll coating. When forming a coating film, the applied coating liquid is subjected to a heating (for example, 40 to 150 ° C.) treatment, a reduced pressure (for example, 10,000 Pa or less) treatment, or both of these treatments, so that the coating liquid is converted to a liquid medium. May be removed.

により By the above steps, a coating film containing the airgel particles and the binder resin can be obtained.

含有 The content of the airgel particles in the coating film can be, for example, 80% by mass or more, but may be 85% by mass or more, or 90% by mass or more. As a result, the coating film density is reduced, and the heat insulating properties of the coating film are further improved. The content of the airgel particles in the coating film can be, for example, 95% by mass or less, but may be 93% by mass or less. Thereby, a coating film tends to be easily formed.

割合 The proportion of the airgel particles in the coating film can be 90% by volume or more, but may be 95% by volume or more, or 98% by volume or more. Further, the ratio of the binder resin in the coating film can be 3% by volume or less, but may be 2.5% by volume or less, or may be 2% by volume or less.

By using the coating liquid of the present embodiment, a very light coating film (airgel coating film) can be obtained. The density of the coating may be 0.4 g / cm ³ or less, but may be 0.37 g / cm ³ or less, or 0.35 g / cm ³ or less. Although the lower limit of the density of the coating film is not particularly limited, it may be 0.1 g / cm ³ or may be 0.2 g / cm ³ from the viewpoint of easily obtaining good coating strength. The density of the coating film can be measured by the “method of measuring density and specific gravity by weighing in liquid” or “the measuring method of density and specific gravity by geometrical measurement” described in JIS Z 8827: 2012.

The thickness of the coating film is not particularly limited, and may be, for example, 0.01 to 5 mm.

材料 The material constituting the object is not particularly limited, and examples thereof include metal, ceramic, glass, resin, and composite materials thereof. The form of the target object can be appropriately selected according to the purpose or material used, and includes a block shape, a sheet shape, a powder shape, a fiber shape, and the like.

The coating film has excellent heat insulation, heat resistance, flame retardancy, etc. derived from aerogel. Due to such advantages, the coating film can be applied to a cryogenic container, a space field, an architectural field, an automobile field, a home appliance field, a semiconductor field, a heat insulating material in industrial equipment, and the like. The coating film can be used not only as a heat insulating material but also as a water repellent material, a sound absorbing material, a vibration damping material, a catalyst supporting material, and the like.

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.

(Preparation of airgel particles A)
100.0 parts by mass of PL-2L (product name, manufactured by Fuso Chemical Industry Co., Ltd.) as a silica particle-containing raw material, 80.0 parts by mass of water, 0.5 parts by mass of acetic acid as an acid catalyst, a cationic surfactant 1.0 part by mass of cetyltrimethylammonium bromide (manufactured by Wako Pure Chemical Industries, Ltd.) and 150.0 parts by mass of urea as a thermally hydrolyzable compound, and methyltrimethoxysilane (Shin-Etsu) as a silicon compound 60.0 parts by mass of Chemical Industry Co., Ltd., product name: KBM-13), 20.0 parts by mass of dimethyldimethoxysilane (Shin-Etsu Chemical Co., Ltd., product name: KBM-22), and the above-mentioned general formula (B) 20.0 parts by mass of a bifunctional alkoxy-modified polysiloxane compound having a structure represented by the formula (hereinafter referred to as “polysiloxane compound X”), Obtain a sol by. After gelling the obtained sol at 60 ° C., it was aged at 60 ° C. for 48 hours to obtain a wet gel.

The "polysiloxane compound X" was synthesized as follows. First, in a 1-liter three-necked flask equipped with a stirrer, a thermometer and a Dimroth condenser, dimethylpolysiloxane XC96-723 having silanol groups at both ends (manufactured by Momentive Performance Materials Japan GK. (Product name), 101.3 parts by mass of methyltrimethoxysilane, and 0.50 parts by mass of t-butylamine were mixed and reacted at 30 ° C. for 5 hours. Thereafter, this reaction solution was heated at 140 ° C. for 2 hours under a reduced pressure of 1.3 kPa to remove volatile components, thereby obtaining a bifunctional alkoxy-modified polysiloxane compound at both ends (polysiloxane compound X).

Thereafter, the obtained wet gel was transferred to a plastic bottle, sealed, and then pulverized for 10 minutes at 27,000 rpm using an extreme mill (manufactured by As One Corporation, MX-1000XTS) to obtain a particulate wet gel. . The obtained particulate wet gel was immersed in 2500.0 parts by mass of methanol and washed at 25 ° C. for 24 hours. This washing operation was performed three times in total while exchanging with fresh methanol. Next, the washed particulate wet gel was immersed in 2500.0 parts by mass of heptane as a low surface tension solvent, and the solvent was replaced at 25 ° C. for 24 hours. This solvent replacement operation was performed a total of three times while exchanging for new heptane. The washed and solvent-substituted particulate wet gel was dried at 40 ° C. for 96 hours under normal pressure, and further dried at 150 ° C. for 2 hours. Finally, it was sieved (Tokyo Screen Co., Ltd., mesh size: 45 μm, wire diameter: 32 μm) to obtain the airgel particles A having the structures represented by the general formulas (3), (4) and (5).

(Preparation of airgel particles B)
JIOS AeroVa (registered trademark, manufactured by JIOS AEROGEL CORPORATION, product name) was prepared as the airgel particles B.

(Specific surface area measurement of airgel particles)
The BET specific surface area of the airgel particles was measured using a gas adsorption amount measurement device (Autosorb-iQ (Autosorb is a registered trademark) manufactured by Kantachrome Instruments Japan GK). The specific surface area of the airgel particles A was 125 m ² / g, and the specific surface area of the airgel particles B was 716 m ² / g.

(Average particle size measurement of airgel particles)
Ethanol was added so that the content of the airgel particles was 0.5% by mass, and this was vibrated with a 50 W ultrasonic homogenizer for 20 minutes to prepare a dispersion. 10 mL of the obtained dispersion was injected into Microtrac MT3000 (manufactured by Nikkiso Co., Ltd., product name), and the particle size was measured at 25 ° C. with a refractive index of 1.3 and an absorption of 0. The particle diameter at an integrated value of 50% (by volume) in the obtained particle diameter distribution was defined as an average particle diameter D50. The average particle diameter D50 of the airgel particles A was 20 μm, and the average particle diameter D50 of the airgel particles B was 17 μm.

(Example 1)
0.50 g of Marpolose MP30000 (manufactured by Matsumoto Yushi Co., Ltd., product name, specific gravity: 1.2) as hydroxypropyl methylcellulose in a dedicated container of Awatori Nerita ARV-310 (manufactured by Shinky Inc., product name), 1 g of specific gravity 0.78), 10 g of water, and 5.00 g of airgel particles A were added. Then, the lid of the container was closed, and the mixture was stirred at a stirring speed of 1000 rpm for 10 minutes to obtain a coating liquid of Example 1.

(Example 2)
5.00 g of Marpolose MP30000 and 10 g of isopropyl alcohol were placed in a 100 mL polycup, and stirred with a spoonful of scoop to prepare a dispersion of MP30000. Next, 100 g of pure water was placed in a 500 mL polycup, and the whole amount of the above dispersion was added while stirring the pure water at 2000 rpm using a homomixer L5R (manufactured by SILVERSON, product name). The stirring time was 3 minutes. Thus, a base solution was prepared.

Next, the entire amount of the above base liquid was put into a receiving container of Hibismix 2P-03 type (manufactured by Primix Co., Ltd.), and 50 g of airgel particles A was added while stirring at 100 rpm. The stirring time was 60 minutes. Thus, a coating liquid of Example 2 was obtained.

(Other Examples and Comparative Examples)
A coating liquid was prepared in the same manner as in Example 1, except that the raw materials and the stirring method of the coating liquid were changed as shown in Table 1 or 2.

In Tables 1 and 2, details of the stirring means A to C are as follows.
A: Awatori Naritaro ARV-310 (Shinky Co., Ltd., product name)
B: Homomixer L5R (SILVERSON, product name)
C: Planetary mixer Hibismix 2P-03 (Primix Corporation, product name)

(Various evaluations)
The following evaluation was performed on the coating liquid obtained in each example. Table 3 shows the evaluation results.

(Evaluation of coating liquid dispersibility)
The coating solution obtained in each case was placed in a vertically long glass container like a measuring cylinder, and the container was covered. After standing in that state for 60 minutes, the state of the coating liquid was visually observed. The evaluation criteria were as follows.
Good: A cloudy paste was formed.
Poor: The liquid component and the airgel particles were separated, and a supernatant of 1% by volume or more of the entire coating liquid was generated.

(Measurement of coating liquid specific gravity)
The specific gravity of the coating liquid obtained in each example was measured using a disposable syringe (manufactured by Terumo Corporation, capacity: 2.5 mL). Specifically, at room temperature (10 to 30 ° C), remove the plunger from the syringe, fill the syringe with a spoon using a spoon so that air bubbles do not enter the coating solution, and set the plunger again. To remove air bubbles at the tip of the syringe. Using an electronic balance, the difference between the weight of the entire syringe including the coating liquid and the weight after discharging 1 mL of the coating liquid was defined as the weight per 1 mL of the coating liquid, and the specific gravity of the coating liquid was calculated.

(Evaluation of film formability)
A coating film was formed using the coating liquid obtained in each example. Specifically, the coating liquid was applied on an aluminum foil using a metal spatula so as to have a thickness of 2 mm. Then, the liquid medium was removed from the coating liquid by heating at 120 ° C. for 1 hour to obtain a coating film. The obtained coating film was visually observed and evaluated according to the following evaluation criteria.
Good: had a good appearance without cracks.
Poor: cracks occurred.

(Measurement of coating film density)
The density of the coating film obtained in the above evaluation of the film forming property was measured. Specifically, the obtained coating film was cut into a size of 3 cm × 3 cm to obtain a measurement sample, and the measurement sample was measured using a hydrometer (MDS-300, manufactured by Alpha Mirage Co., Ltd.) equipped with a water tank having a water temperature of 20 ° C. The weight in the air and in the water was measured to obtain the specific gravity of the coating film.

Claims

(4) A coating liquid containing airgel particles, a binder resin, and a liquid medium, wherein the content of the airgel particles is 20% by mass or more.
The coating liquid according to claim 1, wherein the liquid medium contains water.
The coating liquid according to claim 2, wherein the liquid medium further contains an organic solvent.
The binder resin is an epoxy resin, silicone resin, phenol resin, urea resin, melamine resin, polyurethane resin, polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, polyamide resin 4. The coating liquid according to claim 1, comprising at least one selected from the group consisting of a polyimide resin, a cellulose resin, and a polyvinyl resin.
The coating liquid according to any one of claims 1 to 4, wherein the specific gravity is 0.8 or less.
A coating film containing airgel particles and a binder resin, wherein the content of the airgel particles is 80% by mass or more and the density is 0.4 g / cm 3 or less.
The binder resin is an epoxy resin, silicone resin, phenol resin, urea resin, melamine resin, polyurethane resin, polyethylene resin, polypropylene resin, polystyrene resin, polyester resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, polyamide resin The coating film according to claim 6, comprising at least one selected from the group consisting of a polyimide resin, a cellulose resin, and a polyvinyl resin.