JPH10316414A - Production of aerogel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve light transmissibility and heat insulating properties without deterioration with time caused by water and moisture by carrying out suspension polymerization of a hydrosol obtained by ion exchange of a water glass solution with a specific ion exchange resin, conducting hydrophobic treatment of the resultant hydrogel and supercritically drying the hydrogel. SOLUTION: A water glass solution is passed through an ion exchange resin having >=1, preferably 1-2 ratio of number of mol of an alkali metal in the water glass solution to the number of ion exchangeable mol to carry out the ion exchange of the alkali metallic ions with hydrogen ions. Thereby, a hydrosol at pH 2-4 is obtained. A basic substance is added to the resultant hydrosol to provide a hydrosol at pH 5-7. The prepared hydrosol is dispersed in a poor solvent such as a silicone oil or xylene and stirred to carry out suspension polymerization. The resultant hydrogel is washed with water or acidic water and then hydrophobized with a hydrophobic treating agent having a functional group reactive with OH groups combined with silicon atom of the gel and a hydrophobic group and supercritically dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing aerogel using water glass as a raw material.

[0002]

2. Description of the Related Art Aerogels produced from water glass are used as heat insulators and the like. And as a method of producing aerogel using this water glass as a raw material,
Conventionally, JP-A-47-15398, JP-A-2-3
No. 04299, US Pat. No. 5,137,927 and the like.

[0003] In these methods, a gelling agent such as sulfuric acid is mixed with a water glass solution to prepare a sol just before gelation.
The sol immediately before the gelation is jetted from a nozzle, and the sol is gelled immediately after the jetting, thereby preparing a granular gel-like compound, and drying this to produce an airgel.

[0004]

However, in the above-mentioned method, the gelling agent is mixed so that the pH of the water glass solution becomes gel in a short time, and the gel is instantaneously formed when the water glass solution is ejected from the nozzle. As a result, the particle size and bonding structure of the silica particles in the gel compound become non-uniform, and the finally obtained aerogel has poor translucency. Aerogels also occur when alkali metal atoms such as sodium contained in the water glass solution are incorporated into the silica skeleton during gelation, or the presence of the alkali metal atoms prevents uniform silica skeleton formation. Had a reduced light transmittance. In addition, when the airgel absorbs water or absorbs moisture, there is a problem that dimensional shrinkage or the like occurs, and heat insulation and light transmission deteriorate over time.

The present invention has been made in view of the above points, and has as its object to provide a method for producing aerogel which is excellent in translucency and heat insulation and does not deteriorate with time due to water or moisture. It is.

[0006]

According to the present invention, there is provided a method for producing an aerogel, comprising the steps of: converting a water glass solution into an ion having an ion-exchangeable mole ratio of at least 1 with respect to the mole number of an alkali metal in the water glass solution; Using an exchange resin, ion exchange is performed to obtain a hydrosol, the hydrosol is subjected to suspension polymerization to prepare a hydrogel, and then the hydrogel is subjected to a hydrophobic treatment and supercritical drying. .

The invention of claim 2 is characterized in that the suspension polymerization is carried out by dropping the ion-exchanged hydrosol into a poor solvent in which the hydrosol is not dissolved while stirring the poor solvent. It is. The invention of claim 3 is characterized in that the poor solvent is selected from silicone oil, xylene, benzene, toluene, cyclohexane and castor oil.

The invention of claim 4 is characterized in that a basic substance is added to the hydrosol after ion exchange to neutralize the hydrosol. The invention of claim 5 is characterized in that a basic substance is added to the poor solvent. The invention according to claim 6 is characterized in that the basic substance is selected from ammonia, pyridine, hydrazine, and piperidine.

The invention of claim 7 is characterized in that the hydrogel hydrophobizing treatment is performed in a supercritical state. The invention according to claim 8 is characterized in that a dispersant is added to a poor solvent.

[0010]

Embodiments of the present invention will be described below. Water glass has a molecular formula of m (M ₂ O) · n (SiO
₂ ) [m, n are positive integers, M is an alkali metal atom), and is specified in JIS K1408. In the present invention, among these, it is preferable to use an aqueous solution of sodium silicate or potassium silicate as the water glass, and a colloidal solution of silica sol can be used as the water glass. The silica concentration of the water glass solution is the bulk density,
It is appropriately adjusted according to the physical properties required for the hydrogel, such as the refractive index, heat insulation, and light transmission.

In the present invention, as the ion exchange resin, a cation exchange resin such as a styrene type, an acrylic type, and a methacrylic type can be used. By performing ion exchange using such an ion exchange resin, an alkali metal atom such as a sodium atom in a water glass solution is removed. Here, the amount of the ion exchange resin needs to be set to an amount capable of exchanging all the alkali metal atoms contained in the water glass solution to be ion exchanged with hydrogen. That is, the number of moles that the ion exchange resin can exchange hydrogen ions with respect to the number of moles of alkali metal atoms in the water glass solution to be ion-exchanged (total exchange capacity)
It is necessary to set the amount of the ion exchange resin so that the ratio is 1 or more. Here, the upper limit of the ratio of the ion-exchangeable moles of the ion-exchange resin to the moles of the alkali metal atoms in the water glass solution is not particularly set, but becomes economically disadvantageous as the amount of the ion-exchange resin increases. Therefore, the upper limit of the molar ratio is 3. The preferred range of the molar ratio is 1 to 2.

As a method of ion-exchanging a water glass solution with an ion exchange resin, a method of passing an aqueous glass solution through a packed bed filled with the ion exchange resin to replace alkali metal ions with hydrogen ions, or a method of ion exchange resin Is mixed with a water glass solution, and the mixture is stirred to replace the alkali metal ions with hydrogen ions, and then the ion exchange resin is separated by filtration or the like. The water-glass solution thus ion-exchanged becomes a hydrosol in which the alkali metal atoms in the solution are replaced with hydrogen atoms, and the solution becomes an acidic solution.

Since the pH of the hydrogel after ion exchange as described above drops to about 2 to 4, a basic substance is added to the hydrogel in order to facilitate gelation of the hydrosol. Examples of the basic substance include ammonia, pyridine, hydrazine, piperidine, and the like. Among these, one kind can be used alone, or two or more kinds can be used in combination. By adding these basic substances, the pH value of the hydrosol is brought to near neutrality so that the hydrosol gels when a predetermined time has elapsed, and the pH of the hydrosol is in the range of 5 to 7. It is preferable to adjust the amount of the basic substance to be added.

Next, this hydrosol is subjected to suspension polymerization.
Suspension polymerization uses a poor solvent that does not dissolve the hydrosol after the above-mentioned ion exchange, and drops the hydrosol after the ion exchange into the poor solvent while stirring the poor solvent, so that the hydrosol gels. This can be performed by stirring until the required predetermined time has elapsed. Examples of such poor solvents include silicone oil, xylene, benzene, toluene, cyclohexane, castor oil and the like, and of these, one type can be used alone, or two or more types can be used in combination. In this way, the hydrosol is dropped into the poor solvent and gelled by stirring, so that the hydrosol is dispersed and gelled while being dispersed in the poor solvent, thereby obtaining a substantially spherical bead-like hydrogel. It should be noted that such a method can be applied even when a long time is required for gelation, and is useful, for example, when producing a low-density gel.

The bead diameter of the hydrogel varies depending on the stirring conditions during the suspension polymerization, that is, the shape and size of the vessel, the shape and size of the stirrer, the stirring speed, the mixing ratio of the hydrosol and the poor solvent, and the like. I do. Therefore, a hydrogel having an arbitrary bead diameter can be obtained by changing the stirring conditions. In addition, when the suspension polymerization is performed as described above, the hydrosol can be efficiently dispersed in the poor solvent by adding a dispersant in advance to the poor solvent. As the dispersant, heavy metal soap, lanolin, rosin, cholesterin, lecithin, fatty acid esters of polyhydric alcohols among nonionic surfactants such as sorbitan monooleate, and the like can be used. Is preferably added in the range of 1 to 20% by weight, more preferably 5 to 10% by weight.
It is.

In the above description, the basic substance is added to the ion-exchanged hydrogel before the suspension polymerization step. However, the basic substance may be added to the poor solvent. The basic substance may be added to the poor solvent by adding the hydrosol to the poor solvent and then adding the basic substance to the suspension while stirring, or by adding the basic substance to the poor solvent in advance. Alternatively, the hydrosol may be added dropwise while stirring.

Next, the gel thus obtained is washed with water or acidic water, and then subjected to a hydrophobizing treatment by reacting the gel with a hydrophobizing agent. It is preferable to remove water in advance from the gel in order to efficiently perform the hydrophobic treatment.
The method for removing water from the gel is not particularly limited, but a method of washing the gel using a solvent for dissolving a hydrophobizing agent described below is preferable.

The hydrophobizing agent has a functional group that reacts with an OH group (silanol group) bonded to a silicon atom of a gel and a hydrophobic group. The functional group that reacts with a silanol group includes: Examples include a halogen, an amino group, an imino group, a carboxyl group, and an alkoxyl group. Examples of the hydrophobic group include an alkyl group, a phenyl group, and a fluoride thereof. The hydrophobizing agent may have only one of the above functional groups and hydrophobic groups, or may have two or more thereof. Specific examples of the hydrophobizing agent include hexamethyldisilazane, hexamethyldisiloxane, trimethylchlorosilane, trimethylmethoxysilane, trimethylethoxysilane, triethylethoxysilane, triethylmethoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, dimethyl Organic silane compounds such as dimethoxysilane, methyltrichlorosilane, and ethyltrichlorosilane.In addition to these, carboxylic acids such as acetic acid, formic acid, and succinic acid, and organic compounds such as alkyl halides such as methyl chloride. it can. As the hydrophobizing agent, only one kind may be used, or two or more kinds may be used.

The method for performing the hydrophobizing treatment is not particularly limited. For example, the hydrophobizing agent is immersed in a solution in which the hydrophobizing agent is dissolved in a solvent and mixed, and the hydrophobizing agent is added to the gel. After infiltration, a method of performing a hydrophobizing treatment reaction by heating as necessary is exemplified. Examples of the solvent used in the hydrophobizing treatment include methanol, ethanol, isopropanol, toluene, benzene, N, N-dimethylformamide and the like. It is not limited to the above as long as the hydrophobizing agent can be easily dissolved and can be replaced with the solvent (the poor solvent described above) contained in the gel. For this purpose, a medium that can be easily supercritically dried, for example, the same type as methanol, ethanol, liquid carbon dioxide, or the like, or a medium that can be easily replaced with the same is preferable.

The hydrophobizing treatment is performed in order to introduce the hydrophobic group of the hydrophobizing agent into the gel by reacting the hydroxyl group of the silanol group of the gel with the functional group of the hydrophobizing agent to hydrophobize the gel. It is. Therefore, the amount of the hydrophobizing agent used is preferably set to be sufficient for the number of silanol groups on the particle surface of the gel. For example, the weight ratio of (gel) / (hydrophobizing agent) is preferably in the range of about 0.5 to 10, but this is because the amount of the solvent, the temperature, the time, etc., when performing the hydrophobizing reaction, and the cost It is appropriately selected from the balance between performance and the like, and is not limited to this range. Also, the amount of the solvent used is not particularly limited. The gel hydrophobized as described above is
It is obtained by substituting a hydroxyl group in a silanol group of a gel with a hydrophobic group and hydrophobizing the gel, and comprises two phases of a solid content of the gel and a solvent used in suspension polymerization or hydrophobic treatment.

Next, the gel hydrophobized as described above is supercritically dried. Here, the supercritical drying is a drying method in which the solvent is gradually removed in a critical point of the solvent contained in the gel or in an atmosphere at a higher temperature and a higher pressure than the critical point. When performing supercritical drying, the solvent in the gel is replaced in advance with a solvent used as a medium for supercritical drying, if necessary. At that time, it is preferable to use a solvent composed of a compound having a lower critical point than the solvent in the gel, as a solvent used as a medium for supercritical drying. For example, the solvent used in the hydrophobizing treatment may be used as it is as a medium for supercritical drying, and in this case, it is not necessary to perform a solvent replacement operation. The solvent used as the medium for the supercritical drying is preferably one in which the temperature and pressure at or above the critical point can be easily set. Specifically, for example, methanol, ethanol, propanol, isopropanol,
A single system such as alcohol such as butanol, dichlorodifluoromethane, liquefied carbon dioxide, and water, or a mixed system of two or more thereof can be used. The solvent used as the medium for the supercritical drying may be the same type as the solvent used in the above-described hydrophobic treatment, or may be a different type.

As a method for supercritically drying the hydrophobized gel, for example, when liquefied carbon dioxide is used as a medium for supercritical drying, the gel is liquefied with carbon dioxide (50%).
(About 60 atm), and substituting all or part of the solvent contained in the gel with liquefied carbon dioxide having a lower critical point than this solvent, and then singly using carbon dioxide, or carbon dioxide and gel Under a supercritical condition of a mixed system with the solvent contained in the above. Further, a method in which the solvent contained in the gel is dried under supercritical conditions without performing the replacement with the liquefied carbon dioxide is also possible.

When the solvent used for the hydrophobizing treatment of the gel and the solvent used for the supercritical drying are of the same type, if the hydrophobizing treatment is performed in a supercritical state, the hydrophobic treatment and the supercritical Drying can be performed in a series of continuous steps. By removing the solvent contained in the gel by performing supercritical drying in this way, an aerogel can be obtained. In such supercritical drying, the phase transition of the solvent, that is, vaporization and condensation do not occur. Therefore, when the solvent is removed, the gel structure can be prevented from destruction and aggregation, and the obtained airgel becomes porous and has high heat insulating performance. In addition, since alkali metal atoms are removed by ion exchange with an ion exchange resin, it is possible to obtain an airgel having a structure composed of very fine silica particles, and the diameter of the silica particles is larger than the wavelength of light. Is much smaller, and the particle space of the silica particles is smaller than the mean free path of air, and is uniform, and has high translucency despite being porous. Furthermore, since the aerogel is hydrophobized by replacing the hydroxyl group of the silanol group on the surface with the hydrophobic group of the hydrophobizing agent, moisture in the atmosphere does not adsorb to the aerogel, and the dimensions due to water absorption and moisture absorption are eliminated. It is possible to prevent the properties of the airgel, such as heat insulation and light transmission, from changing over time due to shrinkage or the like.

The aerogel produced as described above can be used for applications such as a heat insulating material at the opening, an acoustic material, a Cherenkov element, a catalyst carrier and the like. Here, aerogel is obtained in the form of beads, and when using aerogel as a heat insulating material, the diameter of the beads can be appropriately selected depending on the thickness and required performance of the heat insulating material to be used, but higher heat insulating performance is required. In this case, it is preferable to mix a plurality of types of aerogels having different bead diameters to increase the packing density.

[0025]

Next, the present invention will be described specifically with reference to examples. (Example 1) An aqueous solution of sodium silicate ("Sodium J Silicate No. 3" manufactured by Nippon Chemical Industry Co., Ltd .: 29% by weight of silicon dioxide, 9.5% by weight of sodium oxide, pH 11) was added to 10
A water glass solution containing 32 parts by weight of ion-exchanged water and 32 parts by weight of ion-exchanged water was subjected to ion exchange by passing through a column filled with a styrene-based ion exchange resin (“Amberlite IR-120B” manufactured by Organo Corporation). . At this time, the ratio of the number of moles of sodium atoms in the water glass solution to the number of exchangeable moles of the ion exchange resin was 1: 2.
The pH of the hydrosol solution obtained by passing through the ion exchange resin was 3.

Next, 1 part by weight of 2.8% by weight aqueous ammonia was added to 200 parts by weight of this hydrosol solution, and the mixture was rapidly stirred. By adding the ammonia water in this way, the pH value of the hydrosol solution became 6. Next, 500 g of this hydrosol solution was applied to silicone oil (“SH” manufactured by Toray Dow Corning Silicone Co., Ltd.).
200 oil ": viscosity 20 CS (at 25 ° C.) 150
The resulting mixture was dropped into 0 g, and suspension polymerization was carried out by continuing stirring for 5 minutes to obtain a hydrogel. The container used here was a 2 liter tall beaker, and the shape of the stirring blade was 50 mm in diameter.
Was a marine type, and the number of revolutions was 1,050 rpm. The obtained hydrogel was washed with water, followed by washing the hydrogel with isopropanol to replace water in the hydrogel with isopropanol.

Next, the above gel was immersed in a hydrophobizing agent solution in which hexamethyldisilazane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was dissolved at a concentration of 1.2 mol / liter in an isopropanol solution, and the gel was immersed at 78 ° C. The mixture was reacted for 24 hours while stirring, and the gel was subjected to hydrophobic treatment. Thereafter, the hydrophobized gel is transferred into isopropanol,
While stirring, exchange isopropanol repeatedly,
The solvent was replaced for 4 hours. Next, the gel was heated at 18 ° C. for 5 hours.
An operation of placing the mixture in liquefied carbon dioxide at 5 atm and replacing isopropanol in the gel with liquefied carbon dioxide was performed for 3 hours. Next, in the system, the supercritical condition of carbon dioxide, 4
After the pressure was reduced to 0 ° C. and 80 atm and supercritical carbon dioxide was passed, the pressure was reduced to atmospheric pressure to obtain a beaded hydrophobic airgel. The time required for the supercritical drying step was 10 hours.

The average particle size of the thus obtained beaded aerogel was measured. Further, two transparent acrylic plates each having a thickness of 1 mm were arranged in parallel with an interval of 12 mm to produce a hollow panel, and the hollow panel was filled with the beaded airgel obtained as described above.
The filling factor was 70%. Then, the light transmittance and the thermal conductivity of the panel filled with the airgel were measured. The light transmittance is measured by using an illuminometer (illuminometer “Model No. 510-02” manufactured by Yokogawa Instruments Co., Ltd.) and measuring the illuminance before and after installation of a panel filled with airgel using a fluorescent lamp as a light source in an acrylic box. I asked. The thermal conductivity was measured using a thermal conductivity measuring device manufactured by Eiko Seiki Co., Ltd.
It was determined by measuring the thermal conductivity at 20 ° C to 40 ° C based on STM-C518.

Example 2 In the ion exchange of the water glass solution, the ion exchange was performed so that the ratio of the number of moles of sodium atoms in the water glass solution to the number of exchangeable moles of the ion exchange resin was 1: 1. A bead-like hydrophobic airgel was obtained in the same manner as in Example 1 except that the amount of the resin was set. And about this beaded aerogel,
As in Example 1, the average particle size was measured, and the light transmittance and the thermal conductivity were measured.

Example 3 A bead-like hydrophobic airgel was obtained in the same manner as in Example 1 except that a silicone oil having a viscosity of 10 CS was used as a poor solvent when performing suspension polymerization. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

Example 4 A bead-like hydrophobic aerogel was obtained in the same manner as in Example 1, except that castor oil was used in place of silicone oil as a poor solvent in performing suspension polymerization. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

Example 5 A hydrosol solution obtained by passing an aqueous solution of sodium silicate through an ion exchange resin in the same manner as in Example 1 was dropped into silicone oil in the same manner as in Example 1, and then stirred. 1. In a suspension of this silicone oil and hydrosol solution while continuing for 5 minutes;
8% by weight aqueous ammonia was added to the hydrosol solution 200
Suspension polymerization was carried out by adding 1 part by weight to 1 part by weight. Otherwise in the same manner as in Example 1, a bead-like hydrophobic airgel was obtained. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

Example 6 The procedure of Example 1 was repeated, except that sorbitan monooleate was added as a dispersant to the silicone oil at a ratio of 10% by weight to the silicone oil. Thus, a bead-like hydrophobic airgel was obtained. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

(Example 7) Using the gel obtained in Example 1 before the hydrophobizing treatment, this gel was placed in liquefied carbon dioxide at 18 ° C and 55 atm, and the isopropanol in the gel was replaced with carbon dioxide. Operation was performed for 3 hours. Next, the inside of the system was set at 80 ° C.
The pressure was adjusted to 60 atm. Hexamethyldisilazane as a hydrophobizing agent is added at a rate of 0.25 mol / l to the supercritical atmosphere, and the hydrophobizing agent is diffused into the supercritical fluid over 2 hours. Hydrophobization treatment was performed by leaving it for a while. Thereafter, the inside of the system was set to 40 ° C. and 80 atm, which are supercritical conditions of carbon dioxide, and carbon dioxide in a supercritical state was circulated, and then reduced to atmospheric pressure to perform supercritical drying. Here, diffusion of the hydrophobizing agent into the supercritical fluid,
The time required for the reaction after standing and the subsequent supercritical drying by flowing carbon dioxide was 6 hours. About the hydrophobic beaded airgel thus obtained, the average particle diameter was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

Example 8 A bead-like hydrophobic airgel was obtained in the same manner as in Example 1, except that the number of revolutions of the stirring blade during suspension polymerization was changed to 1200 rpm. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1. This beaded aerogel and the beaded aerogel obtained in Example 1 were mixed by an equal weight, and the mixture was filled in a hollow panel in the same manner as in Example 1. At this time, the filling rate was 75%. Then, the light transmittance and the thermal conductivity of the panel filled with the airgel were measured.

Example 9 A bead-like hydrophobic airgel was obtained in the same manner as in Example 1 except that the supercritical drying was carried out at 80 ° C. and 160 atm. Was. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1. This beaded aerogel and the beaded aerogel obtained in Example 1 were mixed by an equal weight, and the mixture was filled in a hollow panel in the same manner as in Example 1. At this time, the filling rate was 65%. Then, the light transmittance and the thermal conductivity of the panel filled with the airgel were measured. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

(Example 10) The gel obtained in Example 9 before the hydrophobizing treatment was used.
An operation of replacing isopropanol in the gel with carbon dioxide at 0 atm was performed for 3 hours. Hexamethyldisilazane as a hydrophobizing agent is added at a rate of 0.25 mol / l to the supercritical atmosphere, and the hydrophobizing agent is diffused into the supercritical fluid over 2 hours. Hydrophobization treatment was performed by leaving it for a while. Next, after passing carbon dioxide in a supercritical state, the pressure was reduced to atmospheric pressure to perform supercritical drying. Here, the time required for diffusion of the hydrophobizing agent into the supercritical fluid, reaction by standing, and subsequent supercritical drying by flowing carbon dioxide was 6 hours in total. About the hydrophobic beaded airgel thus obtained, the average particle diameter was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

(Example 11) In ion exchange of a water glass solution, the ratio of the number of moles of sodium atoms in the water glass solution to the number of exchangeable moles of the ion exchange resin was 1: 4.
A bead-like hydrophobic airgel was obtained in the same manner as in Example 9, except that the amount of the ion-exchange resin was set such that The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

Example 12 A bead-like hydrophobic airgel was obtained in the same manner as in Example 9 except that dimethyldimethoxysilane was used instead of hexamethyldisilazane as the hydrophobizing agent. The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

Example 13 In Example 9, ethanol was used instead of carbon dioxide as the dispersion medium during supercritical drying. That is, the gel after the hydrophobization treatment obtained in Example 9 was put in ethanol,
After forming an atmosphere at a temperature of 80 ° C. and a pressure of 80 atm, the pressure was reduced to atmospheric pressure to obtain a bead-shaped hydrophobic airgel. still,
The time required for the supercritical drying step was 6 hours. And about this beaded aerogel, like Example 9,
The average particle size was measured, and the light transmittance and thermal conductivity were measured.

Example 14 A bead-like hydrophobic airgel was obtained in the same manner as in Example 9, except that ethanol was used instead of isopropanol as the organic solvent. The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

(Comparative Example 1) In Example 1, after the airgel was hydrophobized, the hydrogel was not supercritically dried, but was gradually dried at 25 ° C under atmospheric pressure for 48 hours to obtain beads. Was obtained.
The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

(Comparative Example 2) In Example 1, a hydrogel was obtained by suspension polymerization, and then supercritically dried without performing a hydrophobizing treatment to obtain a beaded aerogel. The average particle diameter of the beaded airgel was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured.

(Comparative Example 3) In ion exchange of a water glass solution, the ratio of the number of moles of sodium atoms in the water glass solution to the number of exchangeable moles of the ion exchange resin was 1: 0.
A bead-like hydrophobic airgel was obtained in the same manner as in Example 9, except that the amount of the ion-exchange resin was set so as to be 5. The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

Comparative Example 4 A water glass solution in which 10 parts by weight of the same aqueous solution of sodium silicate as in Example 1 and 16 parts by weight of water were mixed, and an aqueous solution of sulfuric acid having a concentration of 0.95 mol / liter were prepared. Then, the water glass solution was dropped into the aqueous sulfuric acid solution with stirring, and when the amount of the water glass solution dropped to 26 parts by weight with respect to 16 parts by weight of the aqueous sulfuric acid solution, the stirring was stopped to obtain a hydrosol. This hydrosol was dropped into silicone oil, and thereafter suspension polymerization, hydrophobic treatment and supercritical drying were carried out in the same manner as in Example 9 to obtain a granular hydrophobic airgel. And about this airgel, similarly to Example 9, the average particle diameter was measured, and the light transmittance and the thermal conductivity were measured.

(Comparative Example 5) The gel before the hydrophobizing treatment obtained in Comparative Example 4 was used.
The operation of replacing isopropanol in the gel with carbon dioxide at atmospheric pressure was performed for 3 hours. Hexamethyldisilazane as a hydrophobizing agent is added at a rate of 0.25 mol / l to the supercritical atmosphere, and the hydrophobizing agent is diffused into the supercritical fluid over 2 hours. Hydrophobization treatment was performed by leaving it for a while. Next, after passing carbon dioxide in a supercritical state, the pressure was reduced to atmospheric pressure to perform supercritical drying. Here, the time required for diffusion of the hydrophobizing agent into the supercritical fluid, reaction by standing, and subsequent supercritical drying by flowing carbon dioxide was 6 hours in total. About the hydrophobic beaded airgel thus obtained, the average particle diameter was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

(Comparative Example 6) In Example 9, the suspension was subjected to suspension polymerization to obtain a hydrogel, followed by supercritical drying without hydrophobizing treatment to obtain a beaded airgel. The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

Comparative Example 7 In Comparative Example 4, a hydrogel was obtained by suspension polymerization, and then subjected to supercritical drying without hydrophobizing to obtain a beaded airgel. The average particle diameter of the beaded airgel was measured in the same manner as in Example 9, and the light transmittance and the thermal conductivity were measured.

Table 1 shows the measurement results of the average particle size, light transmittance and thermal conductivity of the aerogels of Examples 1 to 14 and Comparative Examples 1 to 7.
Shown in

[0050]

[Table 1]

As shown in Table 1, the light transmittance and the thermal conductivity of Comparative Example 1 in which supercritical drying was not performed were poor, and that of Comparative Example 3 in which the amount of the ion exchange resin used was small was sodium metal. The light transmittance is low due to insufficient removal of atoms and the hydrosol is gelled using sulfuric acid as the gelling agent. It was confirmed that the product had excellent light transmittance and thermal conductivity. Also, as seen in Examples 3 and 8, it was confirmed that the bead diameter can be adjusted by changing the stirring conditions for suspension polymerization.

Next, Examples 1, 9 to 14 and Comparative Examples 2 to
The beaded aerogel obtained in 7 was exposed to a high humidity atmosphere at 60 ° C. and 90% RH for 48 hours to perform a moisture absorption test. The average particle diameter of the airgel subjected to the moisture absorption test was measured in the same manner as in Example 1, and the light transmittance and the thermal conductivity were measured. Table 2 shows the results.

[0053]

[Table 2]

As shown in Table 2, in Comparative Examples 2, 6, and 7 which were not subjected to the hydrophobizing treatment, the average particle size was reduced due to moisture absorption, and the light transmittance and thermal conductivity were deteriorated. In the case of Examples 1 and 9 to 14 where the chemical treatment was performed, such a change with time was not observed.

[0055]

As described above, according to the present invention, a water glass solution is prepared by using an ion exchange resin having a ratio of at least one ion-exchangeable mole to a mole number of an alkali metal in the water glass solution. After obtaining a hydrosol by ion exchange, the hydrosol was subjected to suspension polymerization to prepare a hydrogel, and then the hydrogel was subjected to hydrophobic treatment and supercritical drying. Atoms can be removed and aerogels with high translucency can be obtained.In addition, supercritical drying enables drying without destruction and aggregation of hydrogel structures, and is porous. An aerogel having high heat insulation performance can be obtained. In addition, it is possible to reduce the adsorption of water to the airgel by the hydrophobic treatment, and to prevent the properties such as the heat insulating property and the light transmission property of the airgel from changing over time due to dimensional contraction due to water absorption or moisture absorption. You can do it.

According to a second aspect of the present invention, the suspension polymerization is performed by dropping the ion-exchanged hydrosol into a poor solvent in which the hydrosol is not dissolved while stirring the poor solvent. Is gelled while being dispersed in a poor solvent to form a substantially spherical hydrogel, and can obtain an aerogel having uniform spherical particles.

According to a third aspect of the present invention, the poor solvent is selected from silicone oil, xylene, benzene, toluene, cyclohexane and castor oil, and a spherical hydrogel can be easily obtained. Can be done. According to a fourth aspect of the present invention, a basic substance is added to the hydrosol after the ion exchange to neutralize the hydrosol. As a result, it can be easily gelled, and suspension polymerization is facilitated.

According to the fifth aspect of the present invention, since the basic substance is added to the poor solvent, the hydrosol can be gelled in a state of being sufficiently dispersed in the poor solvent, and spherical particles can be formed. It is easy to obtain a uniform aerogel. In the invention according to claim 6, a substance selected from ammonia, pyridine, hydrazine and piperidine is used as the basic substance, so that neutralization of the hydrosol is facilitated.

According to the seventh aspect of the present invention, since the hydrophobizing treatment of the hydrogel is performed in a supercritical state, the hydrophobizing treatment and the supercritical drying can be performed in a continuous process. According to the invention of claim 8, since the dispersant is added to the poor solvent, the suspension polymerization can be performed by dispersing the hydrosol in the poor solvent efficiently, and a spherical aerogel with uniform particles can be obtained. That makes things easier.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Tsubaki 1048 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Works, Ltd.

Claims (8)

[Claims] 1. A water sol is obtained by ion-exchanging a water glass solution using an ion exchange resin having a ratio of a mole number capable of ion exchange to a mole number of an alkali metal in the water glass solution of 1 or more. Thereafter, the hydrosol is subjected to suspension polymerization to prepare a hydrogel, and then the hydrogel is subjected to a hydrophobic treatment and supercritically dried. 2. The airgel according to claim 1, wherein the suspension polymerization is carried out by dropping the ion-exchanged hydrosol into a poor solvent in which the hydrosol is not dissolved while stirring the poor solvent. Manufacturing method. 3. The method for producing an airgel according to claim 2, wherein the poor solvent is selected from silicone oil, xylene, benzene, toluene, cyclohexane, and castor oil. 4. The method for producing an aerogel according to claim 1, wherein a basic substance is added to the hydrosol after the ion exchange to neutralize the hydrosol. 5. The method for producing an airgel according to claim 2, wherein a basic substance is added to the poor solvent. 6. The method for producing an airgel according to claim 4, wherein the basic substance is selected from ammonia, pyridine, hydrazine, and piperidine. 7. The method for producing an airgel according to claim 1, wherein the hydrogel is subjected to a hydrophobic treatment in a supercritical state. 8. The method for producing an airgel according to claim 2, wherein a dispersant is added to the poor solvent.