JPH04198238A - Preparation of hydrophobic aerogel - Google Patents

Abstract

PURPOSE:To prepare the title aerogel excellent in thermal insulating and light transmission properties and free from degradation with time in those properties due to adsorption of water, etc., by hydrolyzing and polycondensing a specific alkoxysilane, surface-treating the resulting gel in a specific way, and drying it in a supercritical state. CONSTITUTION:An alkoxysilane of the formula: SiR<1>n(OR<2>)4-n (wherein R<1> and R<2> are each 1-5C alkyl or phenyl; and n is 0-2) is hydrolyzed and polycondensed. The resulting gel is made hydrphobic by treating with a surface-treating agent (e.g. trimethylchlorosilane) and then dried in a supercritical state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for producing an airgel having excellent heat insulation properties and hydrophobicity.

[Conventional technology]

One method for producing a light-transmitting inorganic porous material is to dry a gel-like compound obtained by hydrolyzing and polycondensing alkoxysilane (also called silicon alkoxide, alkyl silicate, etc.) in a supercritical state. (U.S. Pat. No. 443'2956, U.S. Pat. No. 4,610,863, etc.).

[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 for producing a hydrophobic airgel that can adsorb moisture, etc., obtain a porous body that exhibits little deterioration over time and has optical transparency. Take it as a challenge.

[Means to solve the problem]

In order to solve the above problems, this invention solves the following general formula (
I) S i R'n (OR”)a-n
...(I) [In the formula, R1 and R2 each independently represent an alkyl group having 1 to 5 carbon atoms or a phenyl group.

When there are two or more R1s and two or more R8s, the two or more R1s and the two or more R2s may be the same or different.

n=o, ■ or 2] A hydrophobic aerogel is obtained by hydrolyzing an alkoxysilane represented by the formula and polycondensation to make the gelled product hydrophobically treated with a surface treatment agent, followed by supercritical drying. Provided is a method for producing a synthetic airgel.

The hydrophobic airgel obtained by the production method of the present invention is a porous body having optical transparency. Here, hydrophobicity means
For example, it is synonymous with water repellency, and moisture adsorption does not occur, so there is no performance deterioration due to moisture. Airgel generally refers to a porous material obtained by removing solvent from a gel body containing a solvent before drying, such as a wet alcogel, and is obtained by removing the solvent by supercritical extraction. Also included are dry porous gels.

The alkoxysilane used in this invention has the above general formula (
I), more specifically, the following general formula (II) [wherein R", R' and R' are each independently an alkyl group having 1 to 5 carbon atoms or phenyl represents a group. Two R%s may be the same or different. ] A bifunctional alkoxysilane represented by the following general formula (II[) R' S i (OR')s・・・
-(IIt) [In the formula, R- and R'' each independently represent an alkyl group having 1 to 5 carbon atoms or a phenyl group.

The three R7s may be the same or different. ] Trifunctional alkoxysilane represented by the following general formula (IV) S i (OR”)4...
(rV) [In the formula, R1 represents an alkyl group having 1 to 5 carbon atoms or a phenyl group. The four R@s may be the same or different. ] refers to a tetrafunctional alkoxysilane represented by, and at least one of these is hydrolyzed,
A gel body (for example, a wet alcogel) is obtained by condensation polymerization.

Bifunctional, trifunctional and tetrafunctional compounds represented by the formulas (II), (III) and (IV) used in this invention, respectively.
Each functional alkoxysilane is not particularly limited. To give specific examples thereof, examples of difunctional alkoxysilane include dimethyldimethoxysilane, dimethyljethoxysilane, diphenyljethoxysilane,
Diphenyldimethoxysilane, methylphenyldiethoxysilane, methylphenyldimethoxysilane, diethyldimethoxysilane, diethyljethoxysilane, etc. are used. Examples of trifunctional alkoxysilane include:
Methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltriethoxysilane, phenyltrimethoxysilane, etc. are used. As the 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. .

Examples of the surface treatment agent for treating the surface of the gel body include silane compounds such as methyldisilazane, trimethylchlorosilane, trimethylmethoxysilane, dimethyldichlorosilane, diethyljethoxysilane, and methyltrichlorosilane. It will be done. Such silane compounds easily react with and bond to the silanol groups on the surface of the silica particles (e.g., -C1, -0
R1-NH-, etc.) and an alkyl group having 1 to 5 carbon atoms, it is not limited to the above.

Examples of the solvent used during surface treatment include toluene, benzene, ethanol, methanol, etc., but the above solvents may be used as long as the surface treatment agent is easily dissolved and the resulting wet gel can be replaced with the solvent. It is not limited.

In addition, since supercritical drying will be performed later, a solvent that can be easily used for supercritical drying, such as a solvent that can be easily replaced with alcohol, is preferred.

The amount of the surface treatment agent added is not particularly limited, but it is preferably added in an amount equal to or more than the number of silanol groups on the surface of the silica particles. For example, the weight ratio is (silica)/(
surface treatment agent)=approximately 0.5 to 1O. The amount of the solvent used is not particularly limited.

The solvent to be finally substituted is used when performing supercritical drying and is not particularly limited, but examples include carbon dioxide, ethanol, methanol, water, dichlorodifluoromethane, etc. alone or in combination of two or more. be able to.

The method for producing the hydrophobic airgel of the present invention is not particularly limited, but 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.
This is called maturing. In addition, at this time, if necessary,
The aging step may be omitted. If alcohol is added, a wet alcogel is obtained.

A gelled product such as a wet alcogel is hydrophobized using a surface treatment agent. The surface treatment reaction for this hydrophobization treatment is carried out, for example, by replacing the alcohol contained in the gelled product with a solvent in which the surface treatment agent is dispersed, and heating the mixture. After the reaction, for example, the solvent is replaced with alcohol again, and then supercritical drying is performed.

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 porous body having excellent hydrophobicity and light transmittance can be obtained.

[For production]

The gelled product obtained by hydrolyzing and polycondensing alkoxysilane is surface-treated and supercritically dried.

Supercritical drying refers to removing a solvent contained in a gel in an atmosphere at a critical point or at a higher temperature and pressure than the critical point. In such an atmosphere, phase transition (vaporization, condensation) of the solvent does not occur, so the surface tension of the solvent does not become weaker, so that destruction and aggregation of the gelled product structure are prevented. Therefore, the inorganic porous body obtained by this invention is extremely porous. On the other hand, in normal heat drying, the solvent changes from a liquid to a gas, so the surface tension of the solvent weakens when it is removed from the gelled structure, causing the structure to be destroyed or aggregated. or

Furthermore, the porous body obtained by the manufacturing method of the present invention is
It is a structure made of extremely fine silica particles, and its particle size and interparticle voids are much smaller than the wavelength of light, so it has light transparency even though it is porous.

In addition, by surface-treating the silica particles of the gelled product (gel body) so that the particle surface has water repellency, the resulting aerogel exhibits excellent hydrophobicity, so it is possible to prevent heat insulating properties due to moisture etc. , it is possible to prevent performance deterioration such as transparency. Transparency here refers to, for example, visual transparency to visible light, but is not limited thereto.

〔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 - A mixture of ethanol (special grade reagent manufactured by Hanui Chemicals ■) and 0.01 mol/It ammonia aqueous solution was gradually added to tetramethoxysilane (reagent manufactured by Dow Corning Silicone ■). . At this time, the reaction was carried out at room temperature, and the mixing ratio was: tetramethoxysilane:ethanol:
Ammonia water = 175:4 (molar ratio). After stirring for about 2 hours, the mixture was allowed to stand still to form a gel. After gelation, ethanol was added and heated at 50° C., and the addition of ethanol was repeated to accelerate (ripen) the polycondensation reaction so as not to dry the gel.

Next, add this gel to 0.2@ol, which is 5 times the volume of the gel.
/ 1-trimethylchlorosilane (reagent manufactured by Dow Corning Silicone @ 1) in toluene solution, and this solvent exchange was repeated day and night to perform solvent replacement.

After that, the alcogel was heated at 110°C for about 2 hours to perform a surface treatment reaction, and then the alcogel was transferred to ethanol again.
The solvent was replaced by exchanging alcohols day and night.

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 atmospheres, which are supercritical conditions for carbon dioxide, and supercritical drying was performed for about 24 hours to obtain a porous body with a thickness of 5 fl and a sample diameter of 50 mm.

Example 2 A porous body was obtained in the same manner as in Example 1, except that instead of using trimethylchlorosilane, Heki-No. methyldisilazane (reagent manufactured by Toshi Dow Corning Silicone ■) was used.

Example 3 In Example 2, 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 2, except that the supercritical drying was carried out under (0 atm).

Example 4 In Example 3, tetraethoxysilane (reagent manufactured by Toshi Dow Corning Silicone ■) was used instead of tetramethoxysilane, and the mixing ratio was set to tetraethoxysilane: ethanol: aqueous ammonia = 1:1112. A porous body was obtained in the same manner as in Example 3 except for the above.

Example 5 A porous body was obtained in the same manner as in Example 4, except that 0.1 mol/L hydrochloric acid was used instead of 0.01 mol/II ammonia aqueous solution. Example 6 - In Example 1, instead of supercritical drying at 40° C. and 80 atm for about 24 hours, the supercritical conditions were changed to 80 atm.
A porous body was obtained in the same manner as in Example 1, except that supercritical drying was performed at 0° C. and 160 atm for about 48 hours.

Example 7 - In Example 1, instead of tetramethoxysilane, 2
A porous body was obtained in the same manner as in Example 1, except that a 1:9 mixture of dimethyldimethoxysilane and tetramethoxysilane, which were functional alkoxysilanes, was used.

Example 8 In Example 1, instead of tetramethoxysilane, 3
A porous body was obtained in the same manner as in Example 1 except that methyltrimethoxysilane, which is a functional alkoxysilane, was used.

Comparative Example 1 Supercritical drying was carried out in the same manner as in Example 1, except that after aging of the gelled product, supercritical drying was carried out without replacing the solvent with a toluene solution of trimethylchlorosilane. A porous body was obtained.

The porous bodies obtained in Examples 1 to 8 and Comparative Example 1 were examined for specific surface area, light transmittance, and deterioration over time due to humidity. The specific surface area was determined using the BET method in the nitrogen adsorption method. The light transmittance was determined by measuring the spectral distribution in the visible light region and determining the visible light transmittance based on JIS-R3106. To determine changes over time due to humidity, we performed a humidity test by leaving the airgel (porous material) in a constant temperature and humidity chamber at 60°C and 90% relative humidity for 48 hours, and measured the light transmittance and thermal conductivity of the airgel before and after that. . The results are shown in Table 1.

As shown in Table 1, the microporous material of the example clearly has superior light transmittance compared to that of the comparative example, does not absorb water, etc., and has excellent light transmittance and heat insulation properties. There were no changes over time.

〔Effect of the invention〕

According to the method for producing a hydrophobic airgel of the present invention, a microporous material is produced which has excellent functions unique to porous materials such as heat insulation, light transmittance, etc., and which does not deteriorate over time in the above-mentioned properties due to adsorption of moisture, etc. Obtainable.

The hydrophobic airgel obtained by this production method can be used in various applications such as heat insulating materials, acoustic materials, Cerenkov elements, and the like.

Agent: Patent Attorney Takehiko Matsumoto Bow Ize Seisho Seisho Tears) February 25, 1991

Claims (1)

[Claims] 1 The following general formula (I) SiR^1_n, (OR^2)_4_-_n...(
I) [In the formula, R^1 and R^2 each independently represent an alkyl group having 1 to 5 carbon atoms or a phenyl group. When there are two or more R^1 and two or more R^2, the two or more R^1 and the two or more R^2 may be the same or different. n = 0, 1 or 2] A hydrophobic aerogel is obtained by hydrolyzing an alkoxysilane represented by the formula and polycondensation to make the gelled product hydrophobically treated with a surface treatment agent, followed by supercritical drying. Method for producing aerogel. 2. The method for producing a hydrophobic airgel according to claim 1, wherein the solvent contained in the gelled product is replaced with a solvent containing a surface treatment agent to perform a surface treatment reaction, and then the solvent is further replaced and then supercritically dried.