JP2000264620A - Production of hydrophobic aerogel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for providing a hydrophobic aerogel by which a process time can be shortened to improve the efficiency of productivity, and the amount of a used solvent can be minimized to reduce the production cost. SOLUTION: An alkoxysilane compound is simultaneously hydrolyzed and polycondensed to prepare a gel compound, and the gel compound is subjected to a hydrophobizing treatment. The treated gel compound is supercritically dried to provide the objective hydrophobic aerogel. In this case, the gel compound is prepared in the presence of an alcohol, and the gel compound without washing the gel compound with a solvent and in a state of the gel compound including water is subjected to the hydrophobizing treatment in a hydrophobization-treating solution containing an organic silane compound having an alkyl group and an alkoxy group. The solvent included in the gel compound subjected to the hydrophobizing treatment is substituted with carbon dioxide, and the substituted gel compound is 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 an airgel having excellent heat insulating properties and light transmittance, a low refractive index of light, and excellent hydrophobicity.

[0002]

2. Description of the Related Art Silica airgel useful as a heat insulating material having a light-transmitting property has been conventionally provided. As a method for producing this airgel, US Pat. No. 4,402,927,
U.S. Pat. No. 4,432,956, U.S. Pat.
As disclosed in Japanese Patent No. 863, a gel-like compound obtained by hydrolyzing an alkoxysilane and subjecting it to polycondensation is treated in the presence of a dispersion medium in a supercritical condition at a temperature higher than the critical point of the dispersion medium. Is known.

[0003] In these methods, an organic solvent such as carbon dioxide or ethanol is used as a dispersion medium during supercritical drying. However, airgel obtained by supercritical drying using carbon dioxide as a dispersion medium,
Due to the silanol group on the surface, it exhibits hygroscopicity, easily adsorbs moisture in the atmosphere, and forms a highly hydrophilic silanol group by the adsorbed moisture, further adsorbing moisture in the atmosphere over time Easier to do. In addition, airgel obtained by supercritical drying using an organic solvent such as ethanol as a dispersion medium has an alkoxyl group on its surface, but has hydrophobicity immediately after supercritical drying, The alkoxyl group is hydrolyzed with the moisture in the atmosphere over time, and as a result, a silanol group is formed on the surface, and the moisture in the atmosphere is similarly adsorbed.

When the aerogel adsorbs moisture, optical and thermal characteristics such as light transmission and heat insulation are reduced, and further, dimensional changes and shrinkage due to shrinkage caused by the adsorption of moisture are caused. Cracks are generated, and as a result, there arises a problem that quality and performance are deteriorated and practicality is lost.

[0005] In order to overcome the drawbacks of the aerogel due to moisture adsorption, the present inventors have conducted hydrophobizing treatment of a gel-like compound obtained from alkoxysilane or sodium silicate in a liquid solvent, followed by supercritical drying. To obtain a hydrophobic airgel (see Japanese Patent Application Laid-Open No. 5-279011 and Japanese Patent Application No. 8-342176), or by adding a hydrophobizing agent to a supercritical drying vessel during supercritical drying. A method of obtaining a hydrophobic airgel by performing a hydrophobizing treatment in a supercritical state (Japanese Patent Application Laid-Open No. 7-138375, Japanese Patent Application No. 8-343282).
No.). By performing the hydrophobic treatment on the airgel in this manner, it is possible to obtain an airgel whose characteristics do not deteriorate with time due to adsorption of moisture.

Here, in producing a hydrophobic aerogel by subjecting a gel compound to a hydrophobic treatment as described above, conventionally, the gel compound is washed with a solvent before the hydrophobic treatment. I have. This is to prevent moisture contained in the gelled gelled compound from reacting with the hydrophobizing agent to lower the reaction efficiency of the hydrophobizing agent.

Further, even after the hydrophobizing treatment, the gel-like compound is similarly washed using a solvent in order to remove the hydrophobizing agent remaining in the gel-like compound and the reaction by-product generated by the hydrophobizing treatment. I am trying to do it. This is because, for example, when hexamethyldisilazane is used as a hydrophobizing agent, the concentration of hexamethyldisilazane remaining in the gel-like compound after the hydrophobizing treatment is reduced to carbon dioxide in a dispersion medium of supercritical drying. If the solubility is higher than or equal to, the gas-liquid interface occurs in the drying vessel in the supercritical drying step after the hydrophobizing treatment, resulting in the problem that the structure of the gel compound is destroyed, or the hydrophobizing treatment occurs This is to prevent ammonia generated as a reaction by-product from reacting with carbon dioxide during supercritical drying to precipitate ammonium carbonate, which prevents the problem of clogging the piping of the supercritical drying apparatus.

In the conventional method for producing a hydrophobic aerogel, when the hydrophobized gel-like compound is set in a drying vessel in a supercritical drying step, a solvent such as alcohol is previously filled in the drying vessel. I have to.
This is to prevent the generation of cracks due to drying of the gel compound when setting the gel compound in the drying container.

[0009]

As described above, in the conventional method for producing a hydrophobic airgel, the gel-like compound is washed with a solvent before and after the hydrophobizing treatment. The process time is required, the production efficiency is extremely low, and the amount of the solvent used is large, so that there is a problem in the production cost. In addition, since the gelled compound is set by filling the solvent in a supercritical drying container, the time required for filling the solvent is also required, which lowers the production efficiency and raises the problem of the production cost due to the use of the solvent. When the gel-like compound is set by filling the solvent in the supercritical drying container in this way, the solvent is also filled around the gel-like compound in the supercritical drying container. The time required to replace the solvent in the supercritical drying vessel with carbon dioxide during critical drying becomes longer, and the production efficiency is further reduced.

[0010] The present invention has been made in view of the above points, and it is possible to shorten the process time to increase the efficiency of productivity, and to minimize the amount of solvent used to reduce the production cost. It is an object of the present invention to provide a method for producing a hydrophobic aerogel that can be used.

[0011]

According to a first aspect of the present invention, there is provided a method for producing a hydrophobic airgel, which comprises hydrolyzing an alkoxysilane compound and polycondensing to prepare a gel-like compound. After producing the hydrophobic aerogel by supercritical drying after the gelation treatment, the gel compound is prepared in the presence of alcohol, and then the gel compound is washed with a solvent without washing the gel compound with water. Then, the gelled compound is hydrophobized in a hydrophobizing solution containing an organic silane compound having an alkyl group and an alkoxyl group, and then the solvent contained in the hydrophobized gelled compound is removed. It is characterized by substituting with carbon, and then supercritically drying the gel-like compound.

The invention of claim 2 is characterized in that, in the above-mentioned claim 1, after the gel compound is subjected to a hydrophobic treatment, the gel compound is supercritically dried without washing the gel compound with a solvent. Is what you do.

According to a third aspect of the present invention, there is provided a method for producing a hydrophobic aerogel, wherein a gel-like compound is prepared by gelling sodium silicate, and the gel-like compound is subjected to a hydrophobizing treatment, followed by supercritical drying. Thereby, in producing a hydrophobic airgel, the gel compound is subjected to a hydrophobic treatment in a hydrophobic treatment solution containing an organic silane compound having an alkyl group and an alkoxyl group, and then the gel compound is washed with a solvent. Instead, the solvent contained in the gel compound is replaced with carbon dioxide, and thereafter, the gel compound is supercritically dried.

According to a fourth aspect of the present invention, in the first to third aspects, the hydrophobized gel-like compound is set in the supercritical drying vessel without filling the solvent in the supercritical drying vessel, It is characterized in that the gel compound is supercritically dried.

The invention of claim 5 is characterized in that, in the above-mentioned claims 1 to 4, the hydrophobizing solution is made acidic, and the gel-like compound is hydrophobized under acidic conditions.

A sixth aspect of the present invention is characterized in that, in the first to fifth aspects, dimethyldimethoxysilane is used as the organic silane compound.

[0017]

Embodiments of the present invention will be described below.

As a silica raw material for obtaining an airgel, alkoxysilane and sodium silicate (water glass) are generally used. Alkoxysilanes include bifunctional alkoxysilanes, trifunctional alkoxysilanes and tetrafunctional alkoxysilanes. Bifunctional alkoxysilanes include dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldiethoxysilane, diphenyldimethoxysilane, and methylphenyldiethoxysilane And trifunctional alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, and phenyltrimethoxysilane. Toshiki silane and the like, and tetrafunctional silane and tetramethoxy silane and tetraethoxy silane and the like can be mentioned respectively.

The alkoxysilane is mixed with water and a solvent that is compatible with water and dissolves the alkoxysilane. By mixing this mixed solution, hydrolysis and polycondensation proceed to form a gel. A compound can be obtained. In the present invention, an alcohol such as methanol, ethanol, isopropanol, or butanol is used as the solvent.

As for sodium silicate, the pH of the sodium silicate solution (water glass solution) is adjusted to near neutrality to bring the solution into a supersaturated state, thereby precipitating and gelling silicon oxide. A gel compound can be obtained.

Next, the hydrophobizing process for hydrophobizing the gel compound prepared as described above will be described.
The hydrophobizing treatment is performed to make the hydroxyl group of the silanol group of the gel compound react with the functional group of the hydrophobizing agent to hydrophobize. The method of performing the hydrophobizing treatment is not particularly limited.For example, the gelling compound is immersed in a hydrophobizing solution in which a hydrophobizing agent is dissolved in a solvent, and the hydrophobizing agent is hydrophobized in the gel compound by stirring or the like. After infiltrating the treating agent, a method of heating and, if necessary, performing a hydrophobizing treatment reaction may be mentioned.

In the present invention, as the hydrophobizing agent, an organic silane compound having an alkyl group and an alkoxyl group is used. In addition, the agent can be easily dissolved in carbon dioxide used as a solvent during supercritical drying. In addition, it is preferable to use a by-product generated in the hydrophobizing treatment reaction that dissolves in carbon dioxide. As such a hydrophobizing agent, for example, trimethylmethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, trimethylethoxysilane,
Examples thereof include dimethyldiethoxysilane and methyltriethoxysilane.

As described above, the hydrophobizing agent comprises an alkyl group and an alkoxyl group. When water is present in the gel compound before the hydrophobizing treatment, the hydrophobizing agent is hydrolyzed to form the alkoxyl group. Groups are replaced by hydroxyl groups,
It becomes easy to react with the hydroxyl groups on the surface of the pores of the gel compound. The above-mentioned hydrophobizing agent has a lower reactivity than hexamethyldisilazane or the like which is generally used as a hydrophobizing agent, but increases the reactivity due to the presence of water in the gel compound. It is.

Here, when sodium silicate is used as the silica raw material, the gelled compound after gelation is obtained in a state where water is filled therein, that is, in a hydrogel state. Since the above-mentioned hydrophobizing agent is hardly soluble in water, in this case, prior to the hydrophobizing treatment, the gel-like compound should be washed with a solvent such as alcohol that mutually dissolves the water and the hydrophobizing agent. Is preferred.

On the other hand, when alkoxysilane is used as a raw material for silica, the gelling treatment is carried out using alcohol as a solvent, so that the interior of the gel-like compound is filled with alcohol together with water. The agent can be dissolved in the alcohol. Therefore, when gelling in alcohol using alkoxysilane as a silica raw material, it is not necessary to wash the gel-like compound with a solvent, and the hydrophobizing treatment should be performed with the gel-like compound still containing water. Can be done.

In this hydrophobizing treatment step, an acid may be added to the hydrophobizing treatment solution to make it acidic, thereby increasing the reactivity of the hydrophobizing agent under acidic conditions. Here, examples of the acid to be added include inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as acetic acid and oxalic acid, and are added to an acidic state so that the pH value is in the range of 4 to 6. Is preferred.

Examples of the solvent used to dissolve the above-mentioned hydrophobizing agent include alcohols such as methanol, ethanol and isopropanol, xylene, toluene, benzene and N, N-dimethylformamide. However, it is not limited to these as long as the hydrophobizing agent easily dissolves and can be replaced with the solvent contained in the gel compound before the hydrophobizing treatment.

Next, the step of supercritically drying the gelled compound subjected to the hydrophobic treatment as described above will be described. The supercritical drying is a drying method in which a solvent (dispersion medium) is gradually removed in a supercritical atmosphere at a higher temperature and a higher pressure than the critical point of the solvent contained in the gel compound. Using methanol or ethanol as this solvent,
There is also a method of drying under these supercritical conditions, but in this case, the critical temperature is extremely high, so that it is not preferable to carry out the process industrially from the viewpoint of safety and the like. For this reason, in the present invention, carbon dioxide having a low critical temperature is used as a solvent (dispersion medium).

In the present invention, for supercritical drying of the hydrophobized gel-like compound, for example, the gel-like compound is immersed in liquefied carbon dioxide at about 50 to 60 atm. After replacing all or part of the solvent containing liquefied carbon dioxide with a lower critical point than this solvent, drying under supercritical conditions of a single system of carbon dioxide or a mixed system of carbon dioxide and a solvent Can be.

The hydrophobizing agent used in the present invention is easily soluble in supercritical carbon dioxide.
Furthermore, in the supercritical drying step, the gas is dissolved indefinitely at a predetermined temperature and pressure condition or higher, so that a gas-liquid interface does not occur in the supercritical drying vessel. In addition, in the hydrophobizing treatment reaction using the above-mentioned hydrophobizing agent, the reaction by-product generated is also an alcohol, and thus is similarly dissolved in supercritical carbon dioxide. Therefore, even if the step of washing the gel-like compound after the hydrophobizing treatment with a solvent is omitted, the hydrophobizing agent and reaction by-products remaining in the gel-like compound adversely affect the gel-like compound during supercritical drying. And it is not necessary to wash the gelled compound after the hydrophobic treatment with a solvent.

In the supercritical drying step, when setting the gel compound in the supercritical drying container, the gel compound can be set in a state in which the solvent is not filled in the supercritical drying container in advance. .
In this case, cracks may occur due to drying of the gel-like compound, but when it is not particularly necessary to consider quality deterioration due to the occurrence of cracks, a state in which the solvent is not previously filled in the supercritical drying container is used. The setting of the gel-like compound may be performed by using. Therefore, there is no need to replace a large amount of solvent and carbon dioxide in the supercritical drying container during supercritical drying, as in the case of setting a gel compound by filling a solvent in the supercritical drying container, The supercritical drying can be performed only by setting the gel-like compound in the supercritical drying container, and the supercritical drying can be efficiently performed.

The shape of the gel-like compound to be subjected to the hydrophobizing treatment or the supercritical drying is not particularly limited, but the gel-like compound may be formed in a bead-like or pulverized form rather than a plate-like form. It is possible to increase the drying efficiency of the gel-like compound and to reduce the particle size of the gel-like compound, so that cracks due to drying when setting the gel-like compound in a supercritical drying vessel are more unlikely to occur. Things.

By subjecting the gel-like compound to a hydrophobizing treatment as described above and further performing supercritical drying, silica aerogel having excellent hydrophobicity and high translucency can be obtained. That is, the hydroxyl groups of the silanol groups present on the silica surface of the aerogel are replaced by the hydrophobic group of the hydrophobizing agent by the hydrophobizing treatment, and the resulting aerogel does not adsorb moisture in the atmosphere,
The deterioration of the characteristics over time due to water absorption is eliminated.
By supercritical drying, drying can be performed without phase transition of the solvent in the gel compound, that is, so-called vaporization / condensation, and when the solvent is removed, the structure of the gel compound is broken or agglomerated. The aerogel obtained by supercritical drying becomes porous. And this airgel is a structure composed of very fine silica particles, the particle size of which is much smaller than the wavelength of light,
In addition, the space between the particles is smaller than the mean free path of air, is uniform, has a low thermal conductivity, and has translucency despite being a porous body.

The aerogel according to the present invention obtained as described above is useful, for example, for applications such as a heat insulating material at an opening, an acoustic material, a Cherenkov element, and a catalyst carrier.

[0035]

Next, the present invention will be described specifically with reference to examples.

(Example 1) Tetramethoxysilane oligomer ("Methylsilicate 5" manufactured by Colcoat Co., Ltd.)
1 ", an average molecular weight of about 470), a sol obtained by mixing 47 parts by weight of methanol, 163 parts by weight of methanol, 50 parts by weight of water and 1 part by weight of 15N aqueous ammonia and stirring for about 30 seconds. Was poured into a container to gel the sol, and then left at room temperature for 1 day to obtain a gel compound. The gel compound thus obtained is pulverized to an average particle size of about 3
mm particles were produced.

Next, a solution having a concentration of 0.6
An isopropanol solution of dimethyldimethoxysilane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) at a concentration of 1 mol / L was prepared. Hydrophobization treatment was applied for one day. At this time, the volume of the hydrophobizing solution was set to be equal to the volume of the gel compound, and the hydrophobizing solution was stirred several times a day.

Next, the gel-like compound thus hydrophobized is placed in a supercritical vessel, and carbon dioxide is dissolved in a solvent (dispersion medium).
The inside of the supercritical drying container was set to 80 ° C. and 160 atm, which are the supercritical conditions of carbon dioxide, and supercritical drying was performed for 5 hours to obtain a hydrophobic airgel.

(Example 2) A hydrophobizing solution was prepared in the same manner as in Example 1, except that methanol was used instead of isopropanol as a solvent for dissolving the hydrophobizing agent. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained.

Example 3 In Example 1, 2% by volume of dilute hydrochloric acid was added to the hydrophobizing solution. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained.

Example 4 A hydrophobizing solution was prepared in the same manner as in Example 1, except that methyltrimethoxysilane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was used instead of dimethyldimethoxysilane as the hydrophobizing agent. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained.

Example 5 In Example 1, when the hydrophobized gel compound was set in a supercritical drying container, the supercritical drying container was previously filled with isopropanol. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained.

(Example 6) An aqueous solution of sodium silicate ("Sodium silicate No. 3" manufactured by Nippon Chemical Industry Co., Ltd.) was added to 10
The hydrosol solution prepared by mixing 32 parts by weight of ion-exchanged water and 32 parts by weight of ion-exchanged water was passed through a column filled with an 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 hydrosol solution to the number of exchangeable moles of the ion exchange resin was 0.5. The p of the hydrosol solution obtained by passing through an ion exchange resin
H was 3. Next, 1 part by weight of 2.8% by weight aqueous ammonia was added to 200 parts by weight of the hydrosol solution, and the mixture was rapidly stirred. PH of the hydrosol solution at this time
Was 6. This hydrosol solution was allowed to stand at room temperature for one day to obtain a hydrogel. The obtained gel compound was pulverized to produce particles having an average particle size of 3 mm.

The obtained gel compound particles were immersed in an equal volume of isopropanol to replace water in the gel compound. This replacement operation was performed four times in total. After that, a hydrophobic treatment was performed in the same manner as in Example 1, and further, supercritical drying was performed to obtain a hydrophobic airgel.

Comparative Example 1 In Example 1, the gel-like compound was washed twice with isopropanol before the hydrophobizing treatment, and the gel-like compound was washed twice with isopropanol after the hydrophobizing treatment. Washed. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained. At this time, the washing of the gel compound required one day for each washing.

(Comparative Example 2) A hydrophobizing solution was prepared in the same manner as in Comparative Example 1, except that hexamethyldisilazane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was used instead of dimethyldimethoxysilane as the hydrophobizing agent. Others were carried out similarly to the comparative example 1, and obtained the hydrophobic airgel.

Comparative Example 3 A hydrophobizing solution was prepared in the same manner as in Example 1 except that hexamethyldisilazane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was used as the hydrophobizing agent instead of dimethyldimethoxysilane. Otherwise in the same manner as in Example 1, a hydrophobic airgel was obtained.

Comparative Example 4 An airgel was obtained in the same manner as in Example 1, except that the hydrophobic treatment was not performed.

The silica raw material, the type of the hydrophobizing agent, the type of the solvent of the hydrophobizing solution, the pH of the hydrophobizing solution, the gel compound and the hydrophobizing process in Examples 1 to 6 and Comparative Examples 1 to 4 described above. The bath ratio of the solution, the number of washings before the hydrophobizing treatment, the number of washings after the hydrophobizing treatment, the presence or absence of filling of the solvent in the supercritical drying container during supercritical drying, and Table 1 shows the amount of the solvent used and the number of days required for the hydrophobic treatment step.

[0050]

[Table 1]

Next, the airgel obtained in Examples 1 to 5 and Comparative Examples 1 to 4 was subjected to the aerogel immediately after supercritical drying and in an atmosphere at a temperature of 60 ° C. and a humidity of 90% RH for 48 hours. After the exposure moisture resistance test, the bulk density, thermal conductivity and light transmittance of the airgel were measured. Here, the thermal conductivity was measured at a set temperature of 20 ° C. and 40 ° C. by a method based on ASTM-C518 using a thermal conductivity measuring device by a steady method manufactured by Eiko Seiki Co., Ltd. The light transmittance was measured using an illuminometer (illuminometer “Model No. 510-02” manufactured by Yokogawa Instruments Co., Ltd.) and a 12 mm thick sample made of aerogel using a fluorescent lamp as a light source in an acrylic box. It was determined by measuring the illuminance before and after. Table 2 shows the results.

[0052]

[Table 2]

As can be seen from Table 2, Examples 1 to 5 in which washing before and after the hydrophobizing treatment were not performed and those in Example 6 in which the washing after the hydrophobizing treatment was not performed were performed before the hydrophobizing treatment. And the same moisture resistance as those of Comparative Examples 1 and 2 in which washing after the hydrophobizing treatment is performed.

[0054]

As described above, in the method for producing a hydrophobic airgel according to the first aspect of the present invention, a gel-like compound is prepared by hydrolyzing and condensation-polymerizing an alkoxysilane compound. After producing the hydrophobic aerogel by supercritical drying after the gelation treatment, the gel compound is prepared in the presence of alcohol, and then the gel compound is washed with a solvent without washing the gel compound with water. Then, the gelled compound is hydrophobized in a hydrophobizing solution containing an organic silane compound having an alkyl group and an alkoxyl group, and then the solvent contained in the hydrophobized gelled compound is removed. Substituted with carbon and then supercritically dried the gel compound, so that the alcohol compound was contained in the gel compound of the alkoxysilane compound. Hydrophobic treatment can be performed by dissolving water and a hydrophobizing agent in this alcohol, and the hydrophobizing agent comprising an organic silane compound having an alkyl group and an alkoxyl group is contained in the gel-like compound. When the presence of moisture is hydrolyzed, the alkoxyl group is replaced by a hydroxyl group, and easily reacts with the hydroxyl group on the surface of the pores of the gel compound, and the gel compound can be subjected to a hydrophobic treatment. As a result, it is not necessary to wash the gel-like compound with a solvent, and it is possible to perform the hydrophobic treatment while the gel-like compound still contains water, and the step of washing the gel-like compound with a solvent becomes unnecessary. In addition to shortening the process time, the efficiency of productivity can be increased, and the amount of the solvent used can be minimized to reduce the production cost.

According to a second aspect of the present invention, in the first aspect, after the gel-like compound is subjected to a hydrophobic treatment, the gel-like compound is supercritically dried without washing the gel-like compound with a solvent. The above-mentioned hydrophobizing agent is easily dissolved in supercritical carbon dioxide, does not generate a gas-liquid interface in a supercritical drying vessel, and is produced by the hydrophobizing reaction using the above hydrophobizing agent. The reaction by-product is an alcohol which is also dissolved in supercritical carbon dioxide, and the hydrophobizing agent and reaction by-product remaining in the gel-like compound are converted into the gel-like compound during supercritical drying. The step of washing the gelled compound after the hydrophobizing treatment with a solvent can be omitted without adverse effects, and the process time can be shortened to improve the productivity and use of the solvent. The amount It is those that can be less expensive production costs and ginger.

In the method for producing a hydrophobic airgel according to claim 3 of the present invention, a gel-like compound is prepared by gelling sodium silicate, and the gel-like compound is subjected to a hydrophobizing treatment, followed by supercritical drying. Thereby, in producing a hydrophobic airgel, the gel compound is subjected to a hydrophobic treatment in a hydrophobic treatment solution containing an organic silane compound having an alkyl group and an alkoxyl group, and then the gel compound is washed with a solvent. Without replacing the solvent contained in the gel-like compound with carbon dioxide, thereafter, the gel-like compound was supercritically dried, so the above hydrophobizing agent is easily dissolved in supercritical carbon dioxide, A gas-liquid interface does not occur in the supercritical drying vessel, and the reaction by-product produced in the hydrophobizing reaction using the above hydrophobizing agent is alcohol. It is also soluble in supercritical carbon dioxide, and the hydrophobizing agent and reaction by-products remaining in the gel compound do not adversely affect the gel compound during supercritical drying. , The step of washing the gelled compound after the hydrophobizing treatment with a solvent can be omitted, the process time can be shortened and the productivity can be increased, and the amount of solvent used can be minimized to reduce the production cost. Can be inexpensive.

According to a fourth aspect of the present invention, the hydrophobized gel-like compound is set in the supercritical drying vessel without filling the solvent into the supercritical drying vessel, and the gel-like compound is supercritically dried. Therefore, it is necessary to replace a large amount of solvent in the supercritical drying container with carbon dioxide during supercritical drying, as in the case of setting a gel compound by filling a solvent in the supercritical drying container. And supercritical drying can be performed efficiently.

According to the fifth aspect of the present invention, the hydrophobizing solution is made acidic, and the gel-like compound is hydrophobized under acidic conditions. Can be performed efficiently.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mikio Kiyo 1048 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Works, Ltd. 72) Inventor Kenji Tsubaki 1048, Kazuma Kadoma, Kadoma, Osaka Prefecture Inside the Matsushita Electric Works, Ltd. No. 1048 Kadoma, Kazuma, Kazuma, Osaka Prefecture F-term (reference) 4G072 AA25 BB15 GG03 HH21 HH30 JJ11 JJ23 LL04 LL11 MM02 MM26 MM31 PP05 PP14 QQ07 RR30 UU30

Claims (6)

[Claims] In producing a hydrophobic airgel, a gel-like compound is prepared by hydrolyzing and condensation-polymerizing an alkoxysilane compound, and then subjecting the gel-like compound to a hydrophobizing treatment and supercritical drying. After preparing the gel-like compound in the presence of alcohol, the gel-like compound contains water without washing the gel-like compound with a solvent, and is hydrophobized containing an organic silane compound having an alkyl group and an alkoxyl group. This gel compound is subjected to a hydrophobic treatment in a treatment solution, and then the solvent contained in the hydrophobic compound is replaced with carbon dioxide.
A method for producing a hydrophobic airgel, comprising supercritically drying a gel compound. 2. The method for producing a hydrophobic airgel according to claim 1, wherein the gel-like compound is subjected to a hydrophobic treatment, and then the gel-like compound is supercritically dried without washing the gel-like compound with a solvent. Method. 3. A gel-like compound is prepared by gelling sodium silicate, and the gel-like compound is subjected to a hydrophobizing treatment and then supercritically dried to produce a hydrophobic aerogel. The compound is subjected to a hydrophobic treatment in a hydrophobic treatment solution containing an organic silane compound having an alkyl group and an alkoxyl group, and then the solvent contained in the gel compound is removed without washing the gel compound with a solvent. And then supercritically drying the gel-like compound. 4. The method according to claim 1, wherein the hydrophobized gel-like compound is set in the supercritical drying vessel without filling the solvent into the supercritical drying vessel, and the gel-like compound is supercritically dried. Item 4. The method for producing a hydrophobic airgel according to any one of Items 1 to 3. 5. The method for producing a hydrophobic aerogel according to claim 1, wherein the hydrophobizing solution is made acidic, and the gel-like compound is hydrophobized under acidic conditions. 6. The method for producing a hydrophobic airgel according to claim 1, wherein dimethyldimethoxysilane is used as the organic silane compound.