JP3520600B2 - Aerogel manufacturing method - 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 an airgel having a porous skeleton of silica, and more specifically, for example, sunlight which is required to have daylighting properties, light transmission properties, transparency and high heat insulation properties. It can be used for various applications such as light-transmitting heat insulating material useful for heat collection, housing opening heat insulating material, peep window for high temperature equipment typified by furnaces, etc. Small refractive index not obtained (specifically 1.001
˜1.17), it relates to a method for producing an airgel which is also a useful material in the field of high energy physics as a medium of a Cherenkov detector for analyzing quarks.

[0002]

2. Description of the Related Art Conventionally, an airgel made of silica has been known as a material having extremely low refractive index, density, thermal conductivity and the like and having light transmittance. This airgel is obtained by hydrolyzing and polymerizing alkoxysilane (also referred to as silicon alkoxide, alkyl silicate, etc.) to obtain a gel compound in a wet state composed of a silica skeleton.
It can be produced by drying in the presence of a solvent (dispersion medium) such as alcohol or liquefied carbon dioxide in a supercritical state above the critical point of this solvent. It can also be produced by similarly obtaining a gel-like compound from sodium silicate as a raw material and supercritically drying this gel-like compound. The airgel obtained by such a manufacturing method is a material useful as, for example, a heat insulating material having light transmittance.

However, 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 manufacturing process thereof, and therefore, as in the above method. A so-called supercritical drying method is used to remove the solvent in a supercritical state. However, since the silica airgel as described above has excellent hygroscopicity, it tends to adsorb moisture over time, causing deterioration of performance and shrinkage. Further, since such an airgel has a very low density and a low strength, it has a drawback that it is very difficult to handle and is easily broken or broken. For the purpose of improving the strength of the airgel or for increasing the analysis range in the Cherenkov detection device, it has been considered to increase the density of the airgel, but in the conventional method, the density is 0.3 g /
The limit was about cc and the refractive index was about 1.06. Further, in the airgel production stage, it was also studied to produce a high-density silica xerogel by gently air-drying the gel-like compound to cause contraction, but this method requires a very long time. In addition, there are many problems such as difficulty in product design due to shrinkage and cracking.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object thereof is to produce an airgel having a high density and a high refractive index while maintaining transparency, heat insulation and the like. To provide.

[0005]

A method for producing an airgel according to claim 1 of the present invention is to prepare a gel compound by gelling a sol obtained by hydrolyzing an alkoxysilane oligomer having polycondensation property by a polycondensation reaction. In the method for producing an airgel by subjecting this gel-like compound to supercritical drying, the amount of water mixed when preparing the sol is less than the theoretical amount required for hydrolysis and polycondensation reaction. It is characterized by doing.

In the method for producing an airgel according to claim 2 of the present invention, the amount of water mixed when preparing the sol is 0.3 to 1 times the theoretical amount required for the hydrolysis and polycondensation reaction. It is characterized in that it is less than.

The method for producing an airgel according to claim 3 of the present invention is characterized in that the alkoxysilane oligomer is a tetramethoxysilane oligomer having an average molecular weight of 250 to 700.

The method for producing an airgel according to a fourth aspect of the present invention is characterized in that the alkoxysilane oligomer is a tetraethoxysilane oligomer having an average molecular weight of 300 to 900.

The method for producing an airgel according to a fifth aspect of the present invention is characterized in that the gel compound is also subjected to a hydrophobizing treatment using a hydrophobizing agent.

In the method for producing an airgel according to claim 6 of the present invention, the hydrophobizing agent is at least selected from the group consisting of trialkoxysilane, dialkoxysilane, trichlorosilane and dichlorosilane having an alkyl group or a phenyl group. It is characterized in that it is a single type of polymerizable organic silane.

The present invention will be described in detail below. The alkoxysilane used in the present invention is an oligomer of alkoxysilane represented by the following general formula.

[0012]

[Chemical 1]

The alkoxysilane oligomer represented by the above general formula preferably has a degree of polymerization of 10 (hereinafter, a monomer having a degree of polymerization of n is referred to as an n-mer) or less, but is a colorless transparent liquid. If so, it is not limited to this. The above-mentioned alkoxysilane oligomer does not need to be a compound having a uniform degree of polymerization, and may have a distribution of the degree of polymerization or have a mixed molecular structure in the form of chain, branch or ring. Considering the stability as a substance and the reaction time for producing a gel-like compound, those having 2 to 6 mers are preferable. R in the alkoxysilane oligomer represents an alkyl group or a phenyl group, and among them, a methyl group (—CH
_3), ethyl group (-C ₂ H ₅₎ are preferred. Specifically, in the case of an oligomer of methoxysilane, the average molecular weight is 2
In the case of an oligomer of ethoxysilane of 50 to 700, an oligomer having an average molecular weight of 300 to 900 is preferable.

In the present invention, in order to efficiently hydrolyze the alkoxysilane to carry out polycondensation, it is preferable to add a catalyst to the reaction solution containing the alkoxysilane in advance. 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 an alcohol, in order to uniformly dissolve and mix the starting alkoxysilane and water.
Acetone or the like is used, but the solvent is not limited to these and may be any solvent in which both alkoxysilane and water are easily dissolved. However, considering that alcohol is produced by the hydrolysis reaction in the production process of the gel-like compound and that supercritical drying is performed, alcohol is preferable as the solvent.

The manufacturing method of the airgel panel according to the present invention is as follows.
The amount of water to be mixed when preparing the sol is less than the theoretical amount required for the hydrolysis and polycondensation reaction. That is,
Water is mixed in an amount of less than (2n + 2) with respect to 1 mol of the alkoxysilane oligomer represented by the above general formula, and a minimum amount of a solvent that dissolves the oligomer and water is further mixed to mix the oligomer with water. A gel compound is obtained by decomposition and polymerization.

The mixing ratio of the oligomer, water and solvent in the preparation of the sol is appropriately selected according to the required properties such as the density, refractive index and transparency of the airgel. In general,
In order to produce an airgel excellent in transparency as intended in the present invention, it is preferable to add a little more water than the theoretical molar amount corresponding to the amount of the alkoxyl group of the oligomer to be hydrolyzed. However, in order to dissolve the water and the oligomer, an amount of solvent corresponding to the mixing ratio of the both is indispensable, and there is a limit to the high density, which is a major object of the present invention. Specifically, the density was 0.3 g / cc, and the refractive index was about 1.07, which was the limit of production. In the method for producing an airgel according to the present invention, the amount of water added to the oligomer is less than the theoretical amount, and the amount of the solvent added is the minimum amount necessary to dissolve the oligomer and water. Further, the amount of the catalyst to be added is adjusted according to the finally required transparency of the airgel. Here, the amount of water added to the oligomer is not particularly limited as long as it is less than the theoretical amount, but preferably about 0.3 times or more and less than 1.0 times the theoretical amount is effective.

The gel compound is obtained by leaving the sol prepared as described above. Next, it is desirable that the gel compound is subjected to a hydrophobizing treatment using a hydrophobizing agent. The hydrophobizing agent is an organic silane compound having a polymerizing property, and a hydrophobizing agent having a functional group that reacts with the silanol group of the gel-like compound and a hydrophobic group is used. Examples of the functional group that reacts with the silanol group include halogen, an alkoxyl group, and a hydroxyl group. Examples of the hydrophobic group include an alkyl group, a phenyl group, and their fluorides. An airgel is obtained by performing a hydrophobizing treatment with an organic silane compound represented by the following general formula and then drying in the presence of a dispersion medium under supercritical conditions at or above the critical point of the dispersion medium.

[0019]

[Chemical 2]

The organic silane compound is preferably at least one selected from the group consisting of trialkoxysilane, dialkoxysilane, trichlorosilane and dichlorosilane having an alkyl group or a phenyl group.
Further, as the structural formula of the hydrophobizing agent, a bifunctional or trifunctional organosilane compound as described in the above general formula is used.
Specifically, as the bifunctional one, dimethyldimethoxysilane, dimethyldichlorosilane, dimethyldiethoxysilane, diphenyldiethoxysilane, diphenyldichlorosilane, diphenyldimethoxysilane, phenylmethyldichlorosilane, phenylmethyldimethoxysilane, diphenylsilane. Examples of organic silane compounds such as diols include trifunctional compounds such as methyltrimethoxysilane, methyltriethoxysilane, methyltrichlorosilane, ethyltrichlorosilane, phenyltrichlorosilane, isobutyltrimethoxysilane, and n-hexyltrimethoxysilane. , Organic silane compounds such as n-decyltrimethoxysilane. Here, as the hydrophobizing agent, only one kind may be used, or two or more kinds may be used.

When the hydrophobizing agent is an organic silane compound having the above-described polymerizability, the hydrophobizing agent is finally obtained because the hydrophobizing agent polymerizes and grows on the silica surface while reacting with the silica surface in the gel-like compound. It further promotes high density and high refractive index of airgel. Further, there is an effect that a sufficient hydrophobic property is imparted to the airgel, and the airgel is obtained in which performance does not deteriorate with time due to humidity.

Here, the hydrophobization treatment is performed by using a liquid as a medium in advance before performing supercritical drying, or by using a supercritical fluid as a medium during supercritical drying which will be described later. The medium is not particularly limited as long as it has low reactivity with the hydrophobizing agent and dissolves the hydrophobizing agent. The reaction is heated if necessary.

The solvent used for the supercritical drying is not particularly limited, but for example, ethanol, methanol, isopropanol, dichlorodifluoromethane, carbon dioxide, water or the like alone or in combination of two or more. Mention may be made of mixed systems. When supercritical drying is performed using a single solvent instead of a mixed system, generally, the solvent and the gel compound obtained by solvent substitution in the same solvent are put together in an autoclave, and the solvent is used. After the temperature and pressure are raised to the critical point or higher, the solvent is gradually removed, and finally the temperature and temperature are returned to the normal temperature and normal pressure to complete the drying. When supercritical drying is carried out in a mixed 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 mixed system, There is a method in which the first solvent is replaced with a 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. Here in particular,
Carbon dioxide is useful as the second solvent. The gel compound thus obtained is dried in the presence of a dispersion medium under supercritical conditions at or above the critical point of the dispersion medium to obtain an airgel.

The high-density airgel produced by the method for producing an airgel according to the present invention is a structure composed of very fine silica particles, like the conventional airgel, and its particle diameter is much smaller than the wavelength of light and has a void structure. Since it is extremely homogeneous, it is transparent even though it is a porous body.
Here, the light transmissivity is, for example, visual transparency in the visible light wavelength region or the like, or transmissivity in the infrared region, but is not limited thereto. Moreover, since it is hydrophobic, it has excellent moisture resistance, and its performance and dimensions are stable over time.
Furthermore, according to the airgel manufacturing method of the present invention, a large density, which is difficult to manufacture in the past, specifically 0.3
A high density aerogel of ~ 0.7 g / cc can be produced.
This high-density airgel is excellent in strength and easy to handle, and is also a useful material as a medium for a Cherenkov detector in the field of high energy physics.

[0025]

The method for producing an airgel according to any one of claims 1 to 4 of the present invention is, for example, an oligomer of tetramethoxysilane having an average molecular weight of 250 to 700 or an average molecular weight of 30.
An alkoxysilane oligomer such as 0-900 tetraethoxysilane oligomer is used, and the amount of water to be mixed when preparing the sol is set to a theoretical amount required for the hydrolysis and polycondensation reaction, for example, 0. Since the amount is from 0.3 to less than 1 time, the amount of the solvent can be reduced and the airgel has a high density.

In the method for producing an airgel according to claims 5 and 6 of the present invention, the gel-like compound is also subjected to a hydrophobizing treatment using a hydrophobizing agent, and the hydrophobizing agent is an alkyl group or a phenyl group. Since it is a polymerizable organic silane that is at least one selected from the group consisting of trialkoxysilane, dialkoxysilane, trichlorosilane, and dichlorosilane, the airgel has hydrophobicity and further high density, It has a high refractive index.

[0027]

EXAMPLES The present invention will be specifically described below with reference to 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 An oligomer of tetramethoxysilane having an average molecular weight of 470, an average degree of polymerization of 4 and an average of 10 methoxy groups per molecule [made by Colcoat Co., Ltd .; trade name Methylsilicate 51], ethanol,
And 0.075N ammonia water at room temperature, and a molar ratio of the oligomer: ethanol: water = 1: 3: 5,
A reaction solution having a mixing ratio (hereinafter referred to as sol) was obtained.

The sol was poured into a circular container having a diameter of 51 mm. Then, it was allowed to stand at room temperature for about 10 minutes and waited for the sol to gel. After leaving it at room temperature for another day,
This gel compound was taken out of the container and had a diameter of 51 mm.
A discotic gel compound having a thickness of 10 mm was obtained.

Next, the gel compound was placed in a high-pressure container,
Filled with ethanol. 18 ℃, 55kg in this container
/ Cm ² of carbon dioxide was added to replace the ethanol in the gel and in the container with carbon dioxide. After that, the inside of the container is under supercritical conditions of carbon dioxide, 80 ° C., 160 kg /
cm ² and supercritical drying (solvent removal) was performed for 2 hours.
Then, after passing carbon dioxide in a supercritical state, the pressure was reduced to remove ethanol contained in the gel-like compound to obtain a hydrophobic airgel sample composed of a porous skeleton having a diameter of 51 mm and a thickness of 10 mm.

Using the obtained airgel sample, the bulk density, light refractive index and visible light transmittance of the airgel were measured,
The results are shown in Table 1.

Here, the visible light transmittance is measured by measuring the light transmittance distribution in the visible light region, and the visible light transmittance is measured according to JIS-R3106.
The optical refractive index was measured with a laser beam having a wavelength of 534 nm.

(Example 2) In Example 1, the diameter 51
mm to obtain a discotic gel compound having a thickness of 10 mm,
1. As the hydrophobizing solution, methyltrimethoxysilane [made by Toray Dow Corning Silicone Co., Ltd .; trade name AY43-043] in which the hydrophobizing agent treatment medium is ethanol is 2.
A 4 mol / liter ethanol solution was prepared, and the above gel compound was immersed in this hydrophobizing solution and allowed to stand at room temperature for 1 week. Further, the gel compound was taken out from the hydrophobizing solution and washed with ethanol. An airgel sample having a diameter of 51 mm and a thickness of 10 mm was obtained in the same manner as in Example 1 except that the gelled compound was placed in a high-pressure container and filled with ethanol, and the bulk density, light refractive index and visible light transmittance of the airgel were measured. The measurement was performed, and the results are shown in Table 1.

(Example 3) In the same manner as in Example 2 except that n-hexyltrimethoxysilane was used as the hydrophobizing agent instead of methyltrimethoxysilane, a diameter of 51 mm and a thickness of 10 mm were obtained. The airgel sample was obtained, and the bulk density, light refractive index, and visible light transmittance of the airgel were measured, and the results are shown in Table 1.

Example 4 An oligomer of tetramethoxysilane having an average molecular weight of 470, an average degree of polymerization of 4 and an average of 10 methoxy groups per molecule [Colcoat Co., Ltd .; trade name: methyl silicate 51], ethanol,
And 0.015N aqueous ammonia are mixed at room temperature, and the oligomer: ethanol: water = 1: 5: 10 in molar ratio.
A sol having a mixing ratio of

The sol was poured into a circular container having a diameter of 51 mm. Then, it was allowed to stand at room temperature for about 40 minutes and waited for the sol to gel. After leaving it at room temperature for another day,
This gel compound was taken out of the container and had a diameter of 51 mm.
A discotic gel compound having a thickness of 10 mm was obtained.

Next, the gel compound was placed in a high-pressure container,
Filled with ethanol. 18 ℃, 55kg in this container
/ Cm ² of carbon dioxide was added to replace the ethanol in the gel and in the container with carbon dioxide. After that, the inside of the container is at a supercritical condition of carbon dioxide, 80 ° C., 160 kg /
cm ² and supercritical drying (solvent removal) was performed for 2 hours.
Then, dimethyldimethoxysilane [Toray Dow Corning Silicone Co., Ltd .; trade name AY43-004] was injected into this high-pressure container at 160 kg / cm ² , and the temperature was 80 ° C.
It was left as it was for one night. Then, after passing carbon dioxide in a supercritical state, the pressure was reduced to remove ethanol contained in the gel-like compound to obtain a hydrophobic airgel sample composed of a porous skeleton having a diameter of 51 mm and a thickness of 10 mm.

Using the obtained airgel sample, the bulk density, light refractive index and visible light transmittance of the airgel were measured,
The results are shown in Table 1.

(Comparative Example 1) A diameter of 51 mm and a thickness of 10 mm were obtained in the same manner as in Example 1 except that the molar ratio of oligomer: ethanol: water was 1: 9: 20.
Was obtained, and the bulk density, light refractive index and visible light transmittance of the airgel were measured, and the results are shown in Table 1.

The main contents of the sample and the measurement results are shown in Table 1.

[0042]

[Table 1]

From the results shown in Table 1, it was confirmed that the airgel of the example has light transmittance and has a larger optical refractive index and density as compared with the comparative example.

The aerogel obtained by the method for producing an aerogel according to the present invention retains the characteristic of an aerogel that it has a light-transmitting property while having functions peculiar to a porous material such as heat insulation. It has a large density never before seen. This densification can improve the handling difficulty, which is one of the drawbacks of conventional airgel. In particular, the increase in the refractive index due to the higher density can expand the range of application as a medium for Cherenkov detector in the field of high energy physics.

[0045]

EFFECTS OF THE INVENTION According to the method for producing an airgel according to claims 1 to 4 of the present invention, the average molecular weight is 250 to 700.
Of tetramethoxysilane or an oligomer of alkoxysilane such as tetraethoxysilane having an average molecular weight of 300 to 900, and the amount of water mixed when preparing a sol is determined by hydrolysis and polycondensation. Since it is 0.3 to less than 1 time the theoretical amount required for the reaction, the amount of solvent can be reduced and a high density airgel can be obtained.

According to the method for producing an airgel according to claims 5 and 6 of the present invention, the gel compound is also subjected to a hydrophobizing treatment using a hydrophobizing agent, and the hydrophobizing agent is an alkyl group or a phenyl group. Since it is a polymerizable organic silane that is at least one selected from the group consisting of trialkoxysilane, dialkoxysilane, trichlorosilane and dichlorosilane, it has hydrophobicity, high density and high refractive index. A rate of airgel is obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-6-135712 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 83/00-83/16 C08G 77 / 00-77/62

Claims (6)

(57) [Claims] 1. An aerogel is produced by subjecting a sol obtained by hydrolyzing an alkoxysilane oligomer having polycondensation property to a gel compound by gelation by a polycondensation reaction, and subjecting this gel compound to supercritical drying. In the method for producing an airgel, the amount of water mixed when preparing the sol is set to be less than the theoretical amount required for hydrolysis and polycondensation reaction. 2. The amount of water mixed when preparing the sol is set to 0.3 of the theoretical amount necessary for hydrolysis and polycondensation reaction.
The method for producing an airgel according to claim 1, wherein the airgel is made to be twice to less than one time. 3. The oligomer of tetramethoxysilane having an average molecular weight of 250 to 700, wherein the alkoxysilane oligomer is an oligomer of tetramethoxysilane.
The method for producing the airgel described. 4. The method according to claim 1, wherein the alkoxysilane oligomer is a tetraethoxysilane oligomer having an average molecular weight of 300 to 900.
The method for producing the airgel described. 5. The method for producing an airgel according to claim 1, wherein the gel compound is also subjected to a hydrophobizing treatment using a hydrophobizing agent. 6. The organic silane having a polymerizable property, wherein the hydrophobizing agent is at least one selected from the group consisting of trialkoxysilane having an alkyl group or a phenyl group, dialkoxysilane, trichlorosilane and dichlorosilane. The method for producing an airgel according to claim 5, wherein