JPH03257027A - Production of transparent porous body - Google Patents

Abstract

PURPOSE:To obtain a transparent porous body hardly adsorbing moisture, etc., and hardly undergoing deterioration with the lapse of time by successively subjecting bi- or terfunctional alkoxysilane to hydrolysis, condensation polymn. and supercritical drying. CONSTITUTION:At least one of bifunctional alkoxysilane represented by formula I (where each of R, R<1> and R<2> is 1-5C alkyl or phenyl) and terfunctional alkoxysilane represented by formula II (where each of R<3> and R<4> is 1-5C alkyl or phenyl) is successively subjected to hydrolysis, condensation polymn. and supercritical drying with one or more kinds of media such as CO2, ethanol, methanol, water and dichlorodifluoromethane to obtain a desired transparent porous body. A catalyst is preferably added to a reaction system contg. the alkoxysilane so as to perform efficient hydrolysis and condensation polymn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a porous body having optical transparency.

[Conventional technology]

Conventionally, as a method for manufacturing a porous body having optical transparency, a method of drying a gel-like compound obtained by condensation polymerization of a metal hydroxide at or above the critical point (U, S,
P, 2,093,454). In addition, as a method using alkoxysilane, a method of using tetramethylorthosilicate (7MO3) and drying it in a supercritical state (U, S, P, 4,327.065; U, S, P,
4.432.956), or a method of drying in a supercritical state using tetraethyl orthosilicate (U
, S, P, 4,610,863).

[Problem to be solved by the invention]

However, the porous material obtained in this way adsorbs moisture etc. over time, resulting in a decrease in light transmittance and a decrease in the function as a porous material (for example, heat insulation). It became.

In view of these circumstances, it is an object of the present invention to provide a method that can obtain a light-transmitting porous body that adsorbs moisture and the like and has little deterioration over time.

[Means to solve the problem]

In order to solve the above problems, a method for manufacturing a light-transmitting porous body according to the present invention includes 2 represented by the following general formula (I):
After hydrolyzing the functional alkoxysilane and at least one of the trifunctional alkoxysilanes represented by the following general formula (■): R''-3i (OR')= (II) and performing condensation polymerization,
The first gist is to perform supercritical drying, and at least one of a bifunctional alkoxysilane represented by the above general formula (1) and a trifunctional alkoxysilane represented by the above general formula (II). The second step is to hydrolyze the seed and a tetrafunctional alkoxysilane represented by the following general formula (■): S i (OR' ) 4 (III), perform condensation polymerization, and then perform supercritical drying. The summary is as follows.

The formulas (1), (II) and (
The difunctional, trifunctional and tetrafunctional alkoxysilanes represented by 1) are not particularly limited. To give specific examples thereof, examples of the bifunctional alkoxysilane include dimethyldimethoxysilane, dimethyljethoxysilane, diphenyljethoxysilane, diphenyldimethoxysilane, methylphenyldiethoxysilane, methylphenyldimethoxysilane, and diethyldimethoxysilane. Silane, diethyljethoxysilane, etc. are used. Examples of the trifunctional alkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, and phenyltrimethoxysilane. As a tetrafunctional alkoxysilane,
For example, tetraethoxysilane, tetramethoxysilane, etc. are used.

In order to efficiently hydrolyze the alkoxysilane and perform condensation polymerization in the present invention, it is preferable to add a catalyst in advance to the reaction system containing the alkoxysilane.

Such catalysts include, but are not particularly limited to, acid catalysts, base catalysts, and the like. Specifically, as acid catalysts, hydrochloric acid, citric acid, nitric acid, sulfuric acid, ammonium fluoride, etc. are used, and as base catalysts, ammonia, piperidine, etc. are used, but are not limited to these. .

The medium used in supercritical drying in this invention is not particularly limited, but examples include carbon dioxide, ethanol, methanol, water, dichlorodifluoromethane, etc. alone or in combination of two or more. can.

Although the method for producing a light-transmitting porous body according to the present invention is not particularly limited, it may be carried out, for example, as follows.

First, a mixture of alcohol, water, and the catalyst is added to the alkoxysilane, mixed, and the alkoxysilane is hydrolyzed and polycondensed.

Note that the alcohol used at this time may be, for example, methanol, ethanol, isopropanol, butanol, etc., and is not particularly limited.

When the polycondensation reaction progresses sufficiently, the reaction mixture turns into a gel.

Next, alcohol is added to this gelled product and heated.
After so-called aging, it is supercritically dried. Note that at this time, the aging step may be omitted if necessary.

The method of performing supercritical drying is not particularly limited, but
For example, a method in which the alkoxysilane gel obtained as described above is immersed in liquefied carbonic acid (approximately 50 to 60 atm) and then dried by bringing the carbon dioxide to a supercritical state;
Alternatively, a method of drying in a supercritical state of alcohol used as a solvent may be used, but is not particularly limited.

By performing such supercritical drying and removing the fluid contained in the gelled product, a light-transmitting porous body can be obtained.

[For production]

When the gelled product obtained by hydrolyzing and polycondensing alkoxysilane is subjected to supercritical drying, the solvent is removed when the solvent changes from a liquid to a gas and is removed from the structure of the gelled product. Since the surface tension is weakened and destruction and aggregation of the structure is prevented, the resulting porous body has light transparency.

Moreover, when bifunctional alkoxysilane and/or trifunctional alkoxysilane are used as the alkoxysilane, water repellency is imparted to the resulting porous material, and adsorption of water, etc. is reduced, so that the porous material becomes more stable over time. Deterioration can be suppressed.

〔Example〕

Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following examples.

Example 1 - Methyltriethoxysilane (reagent manufactured by Toshi Dow Corning ■), ethanol (special grade reagent manufactured by Hanui Chemicals ■) and 0
．． A mixture of 0.01 mol/1 ammonia aqueous solution was gradually added. At this time, the reaction was carried out at room temperature, and the mixing ratio was methyltriethoxysilane:ethanol:ammonia water=1:5:4 (molar ratio). After stirring for about 2 hours, the mixture was allowed to stand still to form a gel. After gelation, add ethanol, heat at 40°C, and repeat the addition of ethanol to accelerate the polycondensation reaction to prevent the gel from drying out (
matured).

Next, this gelled product was placed in carbon dioxide at 18°C and 55 atmospheres, and an operation was performed for 2 to 3 hours to replace ethanol in the gelled product with carbon dioxide. Thereafter, the inside of the system was set to 40° C. and 80 atm, which are supercritical conditions for carbon dioxide, and supercritical drying was performed for about 24 hours to obtain a porous body.

Example 2 In Example 1, instead of using methyltriethoxysilane alone, tetraethoxysilane and methyltriethoxysilane (both reagents manufactured by Toshi Dow Corning ■) were used together in a 1:1 molar ratio. A porous body was obtained in the same manner as in Example 1, except that.

Example 3 In Example 1, instead of using methyltriethoxysilane alone, tetraethoxysilane and dimethyljethoxysilane (both reagents manufactured by Toshi Dow Corning ■) were used together at a molar ratio of 1=1. A porous body was obtained in the same manner as in Example 1 except for the following steps.

Example 4 In Example 1, instead of performing supercritical drying using carbon dioxide as a medium, ethanol was used under supercritical conditions (250°C, 8°C).
A porous body was obtained in the same manner as in Example 1, except that the supercritical drying was carried out under (0 atm).

Example 5 In Example 4, instead of using methyltriethoxysilane alone, diethyldimethoxysilane and ethyltriethoxysilane (both reagents manufactured by Toshi Dow Corning ■) were used together in a 1:1 molar ratio. A porous body was obtained in the same manner as in Example 4, except that.

Comparative Example 1 A porous body was obtained in the same manner as in Example 1 except that tetraethoxysilane (reagent manufactured by Toshi Dow Corning ■) was used instead of methyltriethoxysilane.

The porous bodies obtained in Examples 1 to 5 and Comparative Example 1 were examined for specific surface area, light transmittance, and deterioration over time. The specific surface area was determined using the BET method in the nitrogen adsorption method.

The light transmittance was visually inspected and evaluated as ◯ for transparent, △ for translucent, and × for opaque. Regarding deterioration over time, Table 1 shows the results of visually evaluating changes in light transmittance after leaving the porous body in air at room temperature and humidity 40-50R) 1% for 2 days.

As shown in Table 1, the porous bodies according to Examples are inferior to the porous bodies according to Comparative Examples in terms of specific surface area and light transmittance, but do not deteriorate over time. .

〔Effect of the invention〕

According to the method for manufacturing a light-transmitting porous body according to the present invention,
It is possible to obtain a porous body which has excellent functions specific to porous materials such as heat insulation, light transmittance, etc., and which exhibits little deterioration of the above-mentioned properties over time due to adsorption of moisture and the like.

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

Claims (1)

[Claims] 1 The following general formula (I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) [In the formula, R, R^1, R^2 are alkyl groups having 1 to 5 carbon atoms or represents a phenyl group] and the following general formula (II): R^3-Si(OR^4)_3(II) [In the formula, R^3 and R^4 are the number of carbon atoms 1 to 5 alkyl group or phenyl group] Production of a light-transmitting porous body in which at least one trifunctional alkoxysilane represented by the following is hydrolyzed, polycondensed, and then supercritically dried. Method. 2 The following general formula (I): ▲There are mathematical formulas, chemical formulas, tables, etc.▼(I) [In the formula, R, R^1, and R^2 represent an alkyl group or a phenyl group with 1 to 5 carbon layers] The difunctional alkoxysilane represented by the following general formula (II): R^3-Si(OR^4)_3(II) [In the formula, R^3 and R^4 are alkyl groups having 1 to 5 carbon atoms. or represents a phenyl group] and at least one trifunctional alkoxysilane represented by the following general formula (III): Si(OR^5)_4(III) [wherein R^5 is the number of carbon layers 1 ~5 represents an alkyl group or a phenyl group] A method for producing a light-transmitting porous body, which comprises hydrolyzing and polycondensing a tetrafunctional alkoxysilane represented by the following formula, followed by supercritical drying. 3. The method for producing a light-transmitting porous body according to claim 1 or 2, wherein the supercritical drying uses carbon dioxide.