JPH06191822A - Production of aerogel composite material - Google Patents

Abstract

PURPOSE:To provide a method for obtaining an aerogel composite material capable of making the best use of the light transmissivity and heat insulation of the aerogel, hardly causing crack or breaking in usual transportation or handling working and having the strength for preventing breaking due to vibration. CONSTITUTION:This aerogel composite material is obtained by integrating a gel like compound obtained by hydrolyzing and condensation polymerizing alkoxysilane expressed by the general formula SiR<1>n(OR<2>)4-n (in the formula, R<1> and R<2> may mutually be different and are alkyl group or phenyl group. When each of R<1> and R<2> is >=2, each of >=2 R<1> and >=2 R<2> can be mutually same or different (n) is 0-2) with a transparent reinforcing material and supercritically drying the integrated material.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a composite material containing an airgel. The airgel composite material obtained by this production method has excellent heat insulation properties, light transmission properties, sufficient strength, and is not easily broken. Therefore, for example, it is useful as a material that is required to have daylighting properties, translucency, heat insulating properties and sufficient strength at the same time.

[0002]

2. Description of the Related Art An airgel made of silica is known as a material having low thermal conductivity and optical transparency. This airgel is described in US Pat. No. 4,402,92.
No. 7, No. 4,432,956, No. 4,610,863
As disclosed in each specification, etc., SiO obtained by hydrolyzing and polycondensing alkoxysilane (also referred to as silicon alkoxide, alkyl silicate, etc.)
_In the presence of a solvent (dispersion medium) such as alcohol or liquefied carbon dioxide, a gel compound in a wet state consisting of _two skeletons,
It can be produced by drying in a supercritical state above the critical point of this solvent. The airgel obtained by such a manufacturing method is useful, for example, as a light-transmitting heat insulating material. In order to obtain such an airgel, it is necessary to remove the solvent therein without destroying the structure of the gel-like compound in the production process thereof, and therefore, as in the above method, the supercritical solvent is used. A so-called supercritical drying method is used to remove this in a state.

[0003]

However, the airgel obtained by the above-mentioned conventional method is very lightweight, and since it is weak in strength and brittle, it is easily broken or broken, so that it is very difficult to handle. In addition, it has a drawback that it is significantly deteriorated due to cracking. In view of such circumstances, the present invention makes full use of airgel's optical transparency and heat insulation properties, and is hard to crack or break during normal transportation or handling work, and has a strength not to be destroyed by vibration or the like. An object of the present invention is to provide a method capable of obtaining an airgel composite material having the same.

[0004]

In order to solve the above-mentioned problems, a method for manufacturing an airgel composite material according to the present invention is described by the following general formula (I): SiR ¹ _n (OR ² ) _4-n ... (I ) [In the formula, R ¹ and R ² independently of each other,
5 represents an alkyl group or a phenyl group. R ¹ and R
^When each ² is 2 or more, 2 or more R ¹ , 2 or more R ² may be the same as each other,
It may be different. n = 0 to 2], the gelling compound obtained by hydrolyzing and subjecting the alkoxysilane to polycondensation is obtained in a state of being integrated with a transparent strength-retaining material, and then the integrated product is supercritically dried. Is a method of obtaining an airgel composite material.

The airgel contained in the airgel composite material obtained by the manufacturing method of the present invention is a light-transmitting porous body. Aerogel generally refers to a porous material obtained by removing a solvent from a gel-like compound containing a solvent before drying, such as wet alcogel, and removing the solvent by supercritical extraction. The dried porous gel obtained by the above is included.

The alkoxysilane used in the present invention is
More specifically, it is represented by the above general formula (I).
Is the following general formula (II):[In the formula, R³, R^FourAnd R^FiveAre, independently of one another, carbon
It represents an alkyl group or a phenyl group of the numbers 1 to 5. Two
R^FiveMay be the same as or different from each other
Yes. ] A bifunctional alkoxysilane represented by the following general formula
(III): R⁶-Si (OR⁷)₃ (III) [wherein R⁶And R⁷Independently of one another have 1 to 1 carbon atoms.
5 represents an alkyl group or a phenyl group. 3 R⁷Is
They may be the same or different from each other. 〕so
Trifunctional alkoxysilane represented and the following general formula
(IV): Si (OR⁸)_Four (IV) [wherein R⁸Is an alkyl group having 1 to 5 carbon atoms or
Represents a nyl group. 4 R ⁸May be the same as each other
And may be different. ] Functional tetraalkoxy represented by
Refers to silane, for example, general formulas (III) and (IV)
At least one of the alkoxysilanes represented by
Or one of the general formulas (III) and (IV)
At least one of the alkoxysilanes represented
A mixture of alkoxysilanes represented by general formula (II) is added.
A gel body (for example, by water-decomposing and polycondensing)
A wet alcogel) is obtained.

The above formulas (II) and (II
The bifunctional, trifunctional and tetrafunctional alkoxysilanes represented by I) and (IV) are not particularly limited, but specific examples thereof include, for example, dimethyldimethoxy. Silane, dimethyldiethoxysilane, diphenyldiethoxysilane, diphenyldimethoxysilane, methylphenyldiethoxysilane, methylphenyldimethoxysilane,
Diethyldiethoxysilane, diethyldimethoxysilane and the like are used. As the trifunctional alkoxysilane, for example, methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane and the like are used. As the tetrafunctional alkoxysilane, for example, tetramethoxysilane, tetraethoxysilane or the like is used.

In order to efficiently hydrolyze the alkoxysilane and perform polycondensation in the present invention, it is preferable to add a catalyst in advance to the reaction system containing the alkoxysilane. Examples of such catalysts include acidic catalysts and basic catalysts. Specifically, as the acidic catalyst, hydrochloric acid, citric acid, nitric acid, sulfuric acid, ammonium fluoride or the like is used, and as the basic catalyst, ammonia, piperidine or the like is used, but is not limited to these. Absent.

The solvent used for the hydrolysis and polycondensation of the alkoxysilane is usually alcohol, in order to uniformly dissolve and mix the starting alkoxysilane and water.
Acetone or the like is used, but not limited to these, and any substance in which both alkoxysilane and water are easily dissolved may be used. However, alcohol is the most preferable in consideration of the fact that alcohol is produced by the hydrolysis reaction in the gel-like compound production process and the supercritical drying described later.

In the present invention, the gel compound obtained by hydrolyzing the alkoxysilane and polycondensation is obtained in a state of being integrated with the transparent strength-retaining material. The method for obtaining the gel-like compound in a state of being integrated with the transparent strength-retaining material (the method for obtaining an integrated product of the gel-like compound and the transparent strength-retaining material) is not particularly limited,
For example, there may be mentioned a method of gelling a reaction solution containing an alkoxysilane, a solvent and water (hereinafter, this reaction solution may be referred to as “sol”) in the state of coexisting with a strength retaining material. The method of gelling the sol in the state of coexisting with the strength-retaining material is not particularly limited, but, for example, a strength-retaining material is preliminarily laid on the bottom of a container used to put the sol and gelate. Place (Method A) or float the strength holding material on the upper surface of the sol placed in the container before the sol gels (Method B)
A method of coexisting a strength retaining material on the surface of the sol by doing so can be mentioned. In addition, in this method in which a strength maintaining material is allowed to coexist on the surface of the sol, in this method A or B,
Only one of them may be performed, or both may be used together. However, the method for obtaining an integrated product of the gel-like compound and the transparent strength-retaining material is not limited to the above-mentioned method, and for example, a plurality of sheets obtained by impregnating the sol with a porous sheet described below are laminated on the sol. It may be a method of gelling.

The transparent strength-retaining material used in the present invention is, for example, a fiber cloth or non-woven fabric made of glass fiber, or a porous sheet typified by a fiber cloth or non-woven fabric made of an organic polymer compound such as polyester. Sheet material: A plate material such as a glass plate can be used. When a porous sheet is used, the sol permeates into the sheet and gels, whereby an integrated product of the sheet and the gel compound is obtained. When using a glass plate, it is preferable to use a glass plate which has been surface-treated in advance with hydrofluoric acid, a strong alkali or the like. The glass plate that has been subjected to such surface treatment,
The surface of the glass plate is rough, and therefore, a gel compound physically adheres to the surface, or silanol groups (-SiOH), which are often present on the glass surface, bond with alkoxysilane. And the gel compound are integrated. However, the strength-retaining material is not particularly limited as long as it has the effect of integrating with the gel-like compound and has a light-transmitting property to the extent necessary.

The integrated product of the gel-like compound and the transparent strength-retaining material (hereinafter sometimes simply referred to as "integral product") obtained by the above-mentioned method is prepared by the method described below. The desired airgel composite material is obtained by supercritical drying. The solvent used for supercritical drying is not particularly limited, and examples thereof include ethanol, methanol, dichlorodifluoromethane, carbon dioxide, water and the like alone or in combination of two or more.

When supercritical drying is performed using a single solvent rather than a combined system, the solvent and the same solvent as that in a high-pressure container (or pressure container or drying container) such as an autoclave are generally used. Put the integrated product that has been subjected to solvent replacement together with, and after gradually raising the temperature and pressure above the critical point of the solvent, gradually removing the solvent, and finally returning to the state of normal temperature and normal pressure to finish the drying. To do.

When supercritical drying is carried out in a combination system of two or more kinds, a method of raising the temperature and pressure set in the drying container to a supercritical state in the combination system, an integrated product in the drying container The contained solvent (first solvent) is replaced with a solvent (second solvent) desired to be in a supercritical state, the solvent replacement is almost completed, and then the solvent is removed in a supercritical state of the second solvent. The method etc. are made.

The method for producing the airgel composite material of the present invention is not particularly limited, but is carried out as follows, for example. First, alcohol, water, and the catalyst are added to and mixed with the alkoxysilane to hydrolyze the alkoxysilane to cause polycondensation. The alcohol used at this time is, for example, methanol,
It can be ethanol, isopropanol, butanol, etc.,
There is no particular limitation.

This reaction solution (sol) is placed in a container, and the strength-retaining material is allowed to coexist by the above method. When the polycondensation reaction proceeds sufficiently, the sol gels, and a gel-like compound integrated with the strength-retaining material is obtained. Next, so-called aging is performed by adding alcohol to the integrated product of the gel-like compound and the strength-retaining material and heating. At this time, the aging step may be omitted if necessary. The gel-like compound contained in this integrated product has water and unreacted substances removed,
It is preferable that the solvent portion is completely replaced with alcohol (also referred to as alcogel).

Next, the integrated product of the gel-like compound and the strength retaining material in this state is supercritically dried to remove the solvent (mainly alcohol). Examples of the method for performing supercritical drying include the following methods. That is, the integrated product of the gel-like compound and the strength-retaining material obtained as described above is heated up to a temperature pressure above the critical point of alcohol, and the method of drying alcohol in that state is also integrated. Examples of the method include immersing the compound in liquefied carbonic acid (about 50 to 60 atm), and then setting carbon dioxide to a supercritical state and drying.

By carrying out such supercritical drying to remove the solvent contained in the gel compound in the integrated product, the desired airgel composite material is obtained.

[0019]

In the present invention, a gel-like compound obtained by hydrolyzing an alkoxysilane and polycondensation is obtained in a state of being integrated with a transparent strength-retaining material, and then the integrated product is supercritically dried. , To obtain an airgel composite material. Here, the supercritical drying is to remove the solvent contained in the gel-like compound in the integrated product in a critical point or in an atmosphere at a temperature and pressure higher than the critical point. Since the phase transition (vaporization, condensation) of the solvent does not occur in such an atmosphere, it is possible to suppress the destruction and aggregation of the structure of the gel compound when removing the solvent. Therefore, the airgel in the airgel composite material obtained by supercritical drying becomes porous. In contrast,
If normal heating and drying are performed, the solvent changes from liquid to gas, so when the solvent is removed from the structure of the gel compound, the surface energy of the solvent destroys the structure. Or aggregate.

The airgel in the airgel composite material obtained by the present invention is a structure composed of very fine silica particles, and since its particle diameter and interparticle voids are much smaller than the wavelength of light, it is a porous body. It has transparency despite its existence. If only this airgel is used, as described above, the strength is very weak and brittle, and it easily breaks or breaks, which makes it extremely difficult to handle, and has a drawback such as significant deterioration due to cracking. . However, if the airgel is obtained in a form integrated with the strength-retaining material, it will not easily break or be broken during normal transportation and handling work while making full use of the heat insulating properties of the airgel, and will not be destroyed by vibration. In addition, the strength is improved, and performance deterioration due to breakage such as cracking is less likely to occur. Further, as the strength-retaining material, a material having a light-transmitting property is used, so that the light-transmitting property of the airgel is sufficiently utilized. Therefore, the obtained airgel composite material has transparency.

Here, the transparency is, for example, visual transparency in the visible light wavelength region, but is not limited thereto.

[0022]

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-Tetramethoxysilane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was mixed with ethanol (Nacalai Tesque Co., Ltd.).
(Special grade reagent manufactured by Mitsui Chemicals Co., Ltd.) and a 0.01 mol / l aqueous ammonia solution are gradually added at room temperature to give tetramethoxysilane: ethanol: aqueous ammonia = 1: 1.
A reaction solution having a mixing ratio of 5: 4 (molar ratio) was obtained.

The reaction solution was poured into a container having a hydrofluoric acid-treated glass plate (thickness: 2 mm) laid on the bottom in advance, and then allowed to stand at room temperature for gelation. After gelation, ethanol was added and heated at 50 ° C., and the addition of ethanol was repeated to accelerate (age) the polycondensation reaction so that the gel compound was not dried. Next, the operation of replacing the ethanol in the gel-like compound with carbon dioxide is carried out for 2 to 3 hours by putting the obtained gel-like compound and the glass plate integrated product into carbon dioxide of 55 kg / cm ² at 18 ° C. It was After that, the inside of the container is supercritical condition of carbon dioxide, 80 ° C, 160 kg / cm
² and supercritical drying (solvent removal) was performed for 48 hours. Then, the inside of the container was lowered to room temperature and atmospheric pressure, and a sample of the airgel composite material was taken out from the container. The thickness of the sample was about 7 mm.

Example 2 In Example 1, instead of performing supercritical drying using carbon dioxide as an extraction solvent, ethanol was supercritical for 24 hours under supercritical conditions of ethanol (250 ° C., 80 kg / cm ² ). An airgel composite material sample was obtained in the same manner as in Example 1 except that the airgel composite material sample was taken out after being dried and then cooled to room temperature and atmospheric pressure.

Example 3 Tetraethoxysilane (a reagent manufactured by Toray Dow Corning Silicone Co., Ltd.) was mixed with ethanol (Nacalai Tesque Co., Ltd.).
Production grade reagent) and 0.04 mol / l ammonium fluoride aqueous solution are gradually added to obtain tetraethoxysilane: ethanol: ammonium fluoride aqueous solution = 1:
A reaction solution having a mixing ratio of 5.5: 5 (molar ratio) was obtained.

The reaction solution was poured into a container in which a polyester non-woven fabric was previously laid on the bottom, and left standing for 2 hours.
After the viscosity of the reaction solution increased, another polyester non-woven fabric was floated on the liquid surface of the reaction solution and allowed to stand still for gelation. Thereafter, in the same manner as in Example 1, aging and supercritical drying were performed to obtain a sample of airgel composite material.

Example 4-In Example 1, instead of tetramethoxysilane,
An airgel composite material sample was obtained in the same manner as in Example 1 except that a mixture of dimethyldimethoxysilane which was a bifunctional alkoxysilane and tetramethoxysilane was used in a ratio of 1: 9 (molar ratio).

Example 5-In Example 3, instead of tetraethoxysilane,
An airgel composite material sample was obtained in the same manner as in Example 3 except that a 5: 5 (molar ratio) mixture of trifunctional alkoxysilane, methyltrimethoxysilane, and tetramethoxysilane was used.

-Comparative Example 1-In Example 1, after aging the integrated product of the gel-like compound and the glass plate, it was heated at 80 to 100 ° C under normal pressure to dry it, and a dried product sample was obtained. It was -Comparative Example 2-Aging and supercritical drying were performed in the same manner as in Example 1 except that a glass plate was not placed on the bottom of the container and only the reaction solution was added to obtain the gel compound. A sample was obtained by performing.

Comparative Example 3 In Example 3, after aging the integrated product of the gel-like compound and the non-woven fabric, it was heated at 80 to 100 ° C. under normal pressure and dried to obtain a dried product sample. . -Comparative Example 4-Example 3 except that the non-woven fabric was not used at all and the gel compound was obtained only from the reaction solution.
In the same manner as above, a sample was obtained by performing aging and supercritical drying.

The bulk density, specific surface area and thermal conductivity of the airgel portion of the samples obtained in the above-mentioned Examples and Comparative Examples were measured. The light transmittance and bending strength of the sample were also measured. The specific surface area was determined using the BET method based on the nitrogen adsorption method. The thermal conductivity was measured using a thermal conductivity measuring device manufactured by Hideko Seiki Co.
By the method based on ASTM-C518, the set temperature is 20 ° C.
And 40 ° C. were measured.

The light transmittance was measured by measuring the spectral distribution in the visible light region of the light transmitted through the sample, and the visible light transmittance was measured according to JIS-R3.
Based on 106. Table 1 shows the main contents of the samples of the above-mentioned Examples and Comparative Examples and the operating conditions for obtaining them, and Table 2 shows the measurement results.

[0033]

[Table 1]

[0034]

[Table 2]

In Tables 1 and 2 above, "-" indicates that measurement is impossible or not applicable. In addition, the samples of Comparative Examples 1 and 3 are
It shattered and shattered due to drying and fell apart. As can be seen from the above table, the samples of the airgel composite materials of the Examples are both aerogels excellent in heat insulation and light transmission due to excellent porosity retained by supercritical drying as compared with the samples of Comparative Examples. It is composed of a light-transmitting strength-retaining material, so it has a light-transmitting property according to the purpose depending on the type of strength-retaining material, has excellent heat insulation properties, and has sufficient strength that it is easy to handle and does not break easily. Was confirmed.

[0036]

EFFECTS OF THE INVENTION According to the present invention, the light-transmitting property and the heat insulating property of airgel are fully utilized, and the strength is such that the airgel is not easily cracked or broken during normal transportation and handling work and is not broken by vibration or the like. An airgel composite material having the same can be obtained. Since the obtained airgel composite material has the above-mentioned excellent performance, it can be used for various applications such as a heat insulating material, an acoustic material, a Cherenkov element, and a catalyst carrier.

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[Procedure amendment]

[Submission date] April 5, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction content]

[0034]

[Table 2]

Claims (2)

[Claims] 1. The following general formula (I): SiR ¹ _n (OR ² ) _4-n (I) [In the formula, R ¹ and R ² are independently of each other a carbon number of 1 to 1;
5 represents an alkyl group or a phenyl group. R ¹ and R
^When each ² is 2 or more, 2 or more R ¹ , 2 or more R ² may be the same as each other,
It may be different. n = 0 to 2], the gelling compound obtained by hydrolyzing and subjecting the alkoxysilane to polycondensation is obtained in a state of being integrated with a transparent strength-retaining material, and then the integrated product is supercritically dried. A method of manufacturing an airgel composite material, which comprises obtaining an airgel composite material by 2. The integrated product of the gel-like compound and the strength-retaining material is obtained by gelling a reaction solution containing an alkoxysilane, a solvent and water in the state of coexisting with the strength-retaining material. A method for manufacturing an airgel composite material.