JP2912718B2 - Method for producing transparent inorganic porous material - Google Patents

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 a transparent inorganic porous material.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a light-permeable porous body, a method in which a gel compound obtained by condensation polymerization of a metal hydroxide is dried at a critical point or above (USP2, 093,454). Further, as a method using alkoxysilane, a method of drying in a supercritical state using tetramethyl orthosilicate (TMOS) (see US Pat. No. 4,327,065; US Pat. No. 4,432,956), or a method of using a supercritical state using tetraethyl orthosilicate (See USP 4,610,863).

[0003]

When a gel is obtained by the above condensation polymerization, the condensation polymerization of unreacted substances remaining in the solution after the solution has gelled further proceeds, and the fine structure changes with time. As a result, the transparency of the wet gel deteriorates. The transparency of this wet gel has a deep correlation with the transparency of the porous body after supercritical drying, and the higher the transparency of the wet gel, the better the transparency of the porous body after supercritical drying. .

In view of such circumstances, the present invention suppresses the hydrolysis and polycondensation reaction of unreacted alkoxysilane remaining after gelation to obtain a wet gel having excellent transparency, thereby obtaining excellent transparency. It is an object to obtain an inorganic porous body.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention hydrolyzes an alkoxysilane (also referred to as silicon alkoxide, alkyl silicate, etc.) and supercritically drys a wet gel obtained by condensation polymerization. In the method for producing a transparent inorganic porous body , immediately after gelation of unreacted alkoxysilane remaining in the wet gel body , that is,
The present invention provides a method for producing a transparent inorganic porous material, which comprises performing supercritical drying after removing it for about 0 to several minutes .

In the present invention, as the alkoxysilane,
For example, at least one of the alkoxysilanes represented by the following general formulas (I), (II) and (III) is used. The use ratio of these is not particularly limited, and may be appropriately set.

[0007]

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[0008]

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[0009]

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These polyfunctional (bifunctional or more) alkoxysilanes are preferable to monofunctional alkoxysilanes which do not polycondensate because they can undergo polycondensation. The bifunctional, trifunctional and tetrafunctional alkoxysilanes represented by the general formulas (I), (II) and (III) used in the present invention are not particularly limited. Specific examples thereof include bifunctional alkoxysilanes, for example, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldiethoxysilane, diphenyldimethoxysilane, methylphenyldiethoxysilane, methylphenyldimethoxysilane, diethyldimethoxysilane, Diethyldiethoxysilane or the like is used. As the trifunctional alkoxysilane, for example, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane and the like are used. As the tetrafunctional alkoxysilane, for example, tetraethoxysilane, tetramethoxysilane and the like are used.

In the present invention, in order to efficiently hydrolyze the alkoxysilane and carry out polycondensation, it is preferable to add a catalyst to a reaction system containing the alkoxysilane in advance. Such a catalyst is not particularly limited, and examples thereof include an acid catalyst and a base catalyst. Specifically, as the acid catalyst, hydrochloric acid, citric acid, nitric acid, sulfuric acid, ammonium fluoride and the like are used, and as the base catalyst, ammonia, piperidine and the like are used,
It is not limited to them.

The medium used for performing the supercritical drying in the present invention is not particularly limited. For example, a single system of carbon dioxide, ethanol, methanol, water, dichlorodifluoromethane or the like or a mixed system of two or more thereof may be used. Can be mentioned. The method for producing a transparent inorganic porous material according to the present invention is not particularly limited, for example,
This is performed as follows.

First, a mixture of alcohol, water and the catalyst is added to the alkoxysilane and mixed.
The alkoxysilane is hydrolyzed and polycondensed. In addition,
At this time, the alcohol is used as a solvent because, for example, the alkoxysilane and water are hardly mixed, or used to prevent a partial hydrolysis or polymerization reaction from occurring. The alcohol may be, for example, methanol, ethanol, isopropanol, butanol and the like, and is not particularly limited.

When the polycondensation reaction proceeds sufficiently, the reaction mixture gels. The usage ratio of the alkoxysilane, water, catalyst, alcohol, and the like may be appropriately set so that a gel is formed, and is not particularly limited. Incidentally, one of the indexes indicating the transparency of the gel body is the light scattering intensity. When the gelation process of the alkoxysilane is traced by measuring the light scattering intensity, as shown in FIG. 1, the light scattering intensity of the gel body continues to increase even after the gelation, and the transparency deteriorates. The light scattering intensity shown in FIG. 1 is, for example, a dynamic light scattering photometer DLS-700 (manufactured by Otsuka Electronics Co., Ltd.).
The measurement was performed at an angle of 90 ° with respect to the incident light using Ar laser light as the incident light. The vertical axis in FIG. 1 is the natural logarithm of light scattering intensity [LN (Light scattering intensity)].
And the abscissa represents the natural logarithm [LN (Time)] of the reaction time (the time during which the two reactions of condensation polymerization and hydrolysis are occurring). The gelation point is a point at which the prepared solution changes from a sol to a gel state, for example, a point at which the meniscus does not move even when the container containing the solution is tilted.

Therefore, immediately after the gelation, the unreacted alkoxysilane remaining in the gel is removed. This removal is preferably performed after the gelation is confirmed and before the transparency is deteriorated. For example, the removal is performed in about 0 to several minutes after the gelation. The removal of alkoxysilane does not mean only complete removal but also includes partial removal. Examples of a method for removing the gel include, for example, a method of taking out the gel body from the reaction solution immediately after gelation, immersing the gel body in a large amount of alcohol, and exchanging the alcohol several times, but is not particularly limited.

Next, the wet gel is subjected to supercritical drying. If necessary, the gel is heated in a state in which alcohol is added to the gelled material, that is, aging is performed, followed by supercritical drying. The method for performing the supercritical drying is not particularly limited. For example, after immersing the gelled product of the alkoxysilane obtained as described above in liquefied carbonic acid (about 50 to 60 atm), the carbon dioxide is supercritically dried. And drying in a supercritical state of the alcohol used as a solvent. In the present invention, the supercritical drying includes drying at a critical point.

By performing such supercritical drying and removing the contained fluid from the gelled product, a transparent inorganic porous material can be obtained.

[0018]

When the gelled product obtained by hydrolyzing the alkoxysilane and subjecting it to polycondensation is subjected to supercritical drying, the solvent changes from a liquid to a gas and is removed from the structure of the gelled product. The resulting surface tension of the solvent is weakened, and the destruction and agglomeration of the structure are prevented, so that the resulting porous body has light transmittance.

Moreover, by removing unreacted alkoxysilane remaining in the gel immediately after the gelation of the alkoxysilane, deterioration of the transparency of the wet gel due to polycondensation of the unreacted material can be prevented.

[0020]

EXAMPLES Specific examples and comparative examples of the present invention will be shown below, but the present invention is not limited to the following examples. -Example 1-A mixture of ethanol (special grade reagent manufactured by Hanui Chemicals Co., Ltd.) and an aqueous ammonia solution of 0.01 mol / l was gradually added to tetramethoxysilane (reagent manufactured by Toray Dow Corning Silicone Co., Ltd.). At this time, the reaction was carried out at room temperature, and the mixing ratio was tetramethoxysilane: ethanol: aqueous ammonia = 1: 5: 4 (molar ratio). After stirring for about 2 hours, the mixture was allowed to stand and gelled. Immediately after gelation, the gel body was taken out of the reaction solution, immersed in a large amount of ethanol, and exchanged for alcohol all day and night to remove unreacted alkoxysilane. Thereafter, the mixture was heated at 50 ° C., and the addition of ethanol was repeated to accelerate (ripen) the condensation polymerization reaction (dehydration reaction) so that the gel was not dried.

Next, this gel was put into carbon dioxide at 18 ° C. and 55 atm, and the operation of replacing ethanol in the gel with carbon dioxide was performed for 2 to 3 hours. After that, the system is heated to 40 ° C. and 80 atm, which are the supercritical conditions of carbon dioxide in the system, and supercritical drying is performed for about 24 hours to obtain a 5 mm thick, 50 mm diameter
mm porous body was obtained. Example 2 In Example 1, tetraethoxysilane was used instead of tetramethoxysilane, and 0.001 mol / l ammonium fluoride water was used instead of 0.01 mol / l ammonia water. :methanol:
A porous body was obtained in the same manner as in Example 1 except that the mixture was mixed at a molar ratio of aqueous ammonium fluoride = 1: 5.5: 5.

Example 3 Except that, in Example 1, the gel was taken out of the reaction solution instead of exchanging ethanol immediately after gelation, immersed in a large amount of ethanol and ultrasonically washed at a temperature of 5 ° C. for 2 hours. Was obtained in the same manner as in Example 1. Example 4 Instead of performing supercritical drying using carbon dioxide as a medium in Example 1, supercritical conditions of ethanol (250 ° C., 8
A porous body was obtained in the same manner as in Example 1 except that the supercritical drying was performed under 0 atm.

Example 5 A porous material was prepared in the same manner as in Example 1, except that tetramethoxysilane was used instead of methyltrimethoxysilane: tetramethoxysilane at a molar ratio of 1: 9. I got In the above example, immediately after gelation is within several minutes after gelation.

Comparative Example 1 A porous body was obtained in the same manner as in Example 1, except that the mixture was left for a day and night without alcohol exchange immediately after gelation, followed by aging. -Comparative Example 2- A porous body was obtained in the same manner as in Example 2 except that aging was performed after standing for a day and night without alcohol exchange immediately after gelation.

Comparative Example 3 A porous body was obtained in the same manner as in Example 3, except that the mixture was left for a day and a night without alcohol exchange immediately after gelation, followed by aging. -Comparative Example 4- A porous body was obtained in the same manner as in Example 4, except that aging was performed after standing for a day and a night without alcohol exchange immediately after gelation.

Comparative Example 5 A porous material was obtained in the same manner as in Example 5, except that the mixture was left for a day and a night without alcohol exchange immediately after gelation, followed by aging. Examples 1 to 5 and Comparative Example 1
About the porous body obtained in ~ 5, specific surface area, light transmittance,
The thermal conductivity was examined. The specific surface area is B in the nitrogen adsorption method.
It was determined using the ET method. The light transmittance was obtained by measuring the spectral distribution in the visible light range, and determining the visible light transmittance based on JIS-R3106. The results are shown in Tables 1 and 2.

[0027]

[Table 1]

[0028]

[Table 2]

As shown in Tables 1 and 2, the microporous bodies of the examples were superior in light transmittance to those of the corresponding comparative examples.

[0030]

According to the method for producing a transparent inorganic porous material of the present invention, the unreacted alkoxysilane remaining in the wet gel formed by hydrolysis and condensation polymerization of alkoxysilane is immediately gelled, Since the supercritical drying of the wet gel body is performed after the removal within several minutes , deterioration of transparency due to polycondensation of unreacted alkoxysilane is prevented. ADVANTAGE OF THE INVENTION According to the manufacturing method of this invention, the porous body excellent in the function peculiar to a porous material, such as heat insulation, and a light transmittance can be obtained.

The obtained light-transmitting porous body can be used for various purposes such as a heat insulating material, an acoustic material, a Cherenkov element, and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing a change in light scattering intensity during a gelation process of an alkoxysilane.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Hiroshi Yokokawa 1048 Odakadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works, Ltd. (56) References JP-A-61-46237 (JP, A) (58) Fields investigated ( Int.Cl. ⁶ , DB name) C01B 33/00-33/193

Claims (2)

(57) [Claims] 1. A method for producing a transparent inorganic porous material, comprising supercritically drying a wet gel obtained by hydrolyzing an alkoxysilane and subjecting it to polycondensation, wherein unreacted alkoxysilane remaining in the wet gel is subjected to gelation. Immediately, that is, 0 to several minutes
A method for producing a transparent inorganic porous material, wherein supercritical drying is carried out after removal during a certain period . 2. The method for producing a transparent inorganic porous material according to claim 1, wherein supercritical drying is performed using carbon dioxide.