JP3960050B2 - Method for producing dried gel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a low-density hydrophobized dry gel used for a heat insulating material, a sound absorbing material, a catalyst carrier, an acoustic sensor, and the like, and a heat insulating material using the method.
[0002]
[Prior art]
A dry gel used for obtaining a heat insulating material, a sound absorbing material, a catalyst carrier, an acoustic sensor and the like generally has a large specific surface area and a low density at the same time.
[0003]
In order to have a large specific surface area and low density, it is necessary to have a large number of fine pores, and in order to obtain such a dry gel, it is necessary to obtain a wet gel that satisfies the above conditions. .
[0004]
The wet gel is produced by a so-called sol-gel method, but shrinks due to the capillary force generated in the gel pores during drying, and the micropores are lost at that time. It is important to suppress this shrinkage in order to obtain a dry gel having a low density and a large specific surface area. For this purpose, two methods are mainly known.
[0005]
The first method is a supercritical drying method. This method is characterized in that a gas-liquid interface is not formed during drying because drying is performed at a pressure and temperature above the critical point. For this reason, it becomes possible to dry without causing capillary force and causing shrinkage of the gel. This method was developed as a method using supercritical drying of alcohol by Kistler (Journal of Physical Chemistry, 36, 52-64, 1932), and later by Hunt et al. To supercritical drying using carbon dioxide. Developed (US Pat. No. 4,610,863).
[0006]
As the second method, the wet gel surface is hydrophobized with a hydrophobizing agent to reduce the capillary force and dry it (Journal of Non-Crystaline Solid, 186, 104-112, 1995). Year) is known. Thus, when hydrophobizing the wet gel surface, the water in the gel was removed by solvent replacement with a water-soluble solvent such as alcohol in order to avoid the water contained in the gel reacting with the hydrophobizing agent. After that, further substitution is performed with a water-insoluble solvent, and a hydrophobic treatment is performed in the water-insoluble solvent. Thereafter, the solvent in the wet gel is heated and dried to obtain a dry gel. It is described that trimethylchlorosilane is used as the hydrophobizing agent.
[0007]
In addition, chlorosilane compounds represented by trimethylchlorosilane are likely to generate hydrogen chloride during hydrophobization and cause corrosion of the device, but silazane compounds are known as hydrophobizing agents that do not exhibit such strong corrosivity. Yes. As a method for hydrophobizing a wet gel surface to which this hydrophobizing agent can be applied, after the water in the wet gel is replaced and removed by a water-soluble solvent, the hydrophobizing agent is allowed to act on the gel in the water-soluble solvent. A method of performing a hydrophobization treatment is known. In addition, drying is performed by removing the solvent in the wet gel by heating after the hydrophobization as described above (Japanese Patent No. 3045411). Here, it does not describe the excellent effect of methanol as a solvent during hydrophobization.
[0008]
[Problems to be solved by the invention]
In the case where a wet gel surface is hydrophobized and dried using a silazane compound as a hydrophobizing agent, it is known that a water-soluble solvent is used as a solvent during the hydrophobizing treatment as described above. However, if a normal water-soluble solvent is used, it is not easy to proceed with efficient hydrophobization and obtain a dry gel with low density. Further, if a high-boiling water-soluble solvent is used, a low-density dry gel can be obtained. However, the solvent is limited to a small number of solvents such as dimethylformamide, and these solvents also have problems such as high price. It was.
[0009]
Therefore, the object of the present invention is to solve the above-mentioned problems, and in the case where a silazane compound is used as a hydrophobizing agent, a hydrophobized dry gel that enables highly efficient hydrophobizing treatment by using a general-purpose solvent. And a high-performance heat insulating material using the same.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, one means of the present invention includes a gelling step in which a wet gel is formed by mixing a solvent containing at least water and a gel raw material, and removal of water in the wet gel. A water step, a hydrophobizing step for hydrophobizing the surface of the wet gel using a silazane compound as a hydrophobizing agent, and a solvent remaining in the hydrophobized wet gel. And a drying step of obtaining a dry gel by removing under a condition less than the point, and in the hydrophobic step, a solvent containing at least methanol and a water-insoluble solvent is used as the solvent during the hydrophobic treatment. It is set as the manufacturing method of a dry gel. Thereby, a low-density dry gel is easily obtained.
[0011]
It is effective that the solvent during the hydrophobization treatment contains at least methanol and a water-insoluble solvent.
[0012]
It is effective that the main component of the inorganic porous material is silicon dioxide.
[0013]
It is effective that the gel raw material is alkoxysilane or an oligomer thereof.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The manufacturing method of the hydrophobized dry gel of this invention consists of the following four processes.
(1) Gelation step (formation of wet gel)
(2) Water removal step (removal of water in wet gel)
(3) Hydrophobization step (hydrophobization of wet gel surface)
(4) Drying process (drying of wet gel)
Hereinafter, each process will be described.
[0015]
(1) Gelation step (formation of wet gel)
In the present invention, a wet gel is first prepared by a sol-gel method. Specifically, by mixing a gel material, a solvent, and a gelling catalyst as necessary, the gel material is polymerized in the solvent to form a wet gel.
[0016]
As the gel material used in the production method of the present invention, general materials used in the sol-gel method are used. For example, there are oxide fine particles such as silicon, aluminum, zirconium and titanium, and corresponding alkoxides. Among these, a compound containing silicon as a metal is preferable from the viewpoint of availability. For example, tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane, silicon alkoxides such as trialkoxysilane, dialkoxysilane and oligomers thereof, colloidal silica, water glass, aqueous silicate solution obtained by electrodialysis from water glass, and the like Mixtures of these are used.
[0017]
As the gelation catalyst, a general organic acid, inorganic acid, organic base, or inorganic base is used. Examples of the organic acid include acetic acid, citric acid, inorganic acid, sulfuric acid, hydrochloric acid, nitric acid, organic base, piperidine, inorganic base, ammonia, and the like.
[0018]
The various gel raw materials described above can be used for forming the wet gel. However, when a typical gel raw material is used as will be described later, the formed wet gel contains water.
[0019]
When alkoxysilane is used as a raw material, a wet gel is formed through hydrolysis and polycondensation of alkoxysilane by adding alkoxysilane, alcohol as solvent, acid or base as gelling catalyst and water. Thus, when using alkoxysilane as a raw material in order to use water, the wet gel obtained will contain water.
[0020]
When water glass, which is an aqueous solution of a metal silicate salt, is used as a gel raw material, after removing metal ions from the water glass through a cation exchange resin, gelation is promoted by adding a base catalyst. In addition, there is a method in which gelation proceeds by directly mixing water glass with an acid such as hydrochloric acid as a catalyst. In the latter case, a metal salt is formed in the gel. If this metal salt is present, the efficiency of progress of the hydrophobizing treatment in the hydrophobizing step described later is lowered, so that it is removed by a method such as washing with water after gel aging described later. Even when such a water glass is used as the gel raw material, the resulting wet gel contains water because the solvent is water.
[0021]
Moreover, as a gel raw material, the silicic acid aqueous solution obtained by electrodialyzing water glass is used more suitably. Since most of the metal ions in the water glass are removed by the electrodialysis treatment, the water washing treatment after the gel ripening is greatly reduced as compared with the case of directly using the water glass. Moreover, since the viscosity is lower than that of water glass, it is easy to handle. Again, the resulting wet gel will contain water.
[0022]
After all, colloidal silica using water as a solvent is also used as a gel raw material, and gelation proceeds by the addition of an acid catalyst. However, there is a drawback in that it is difficult to obtain gel strength and shrinkage during drying tends to occur. Again, the resulting wet gel will contain water.
[0023]
In the case of the present invention, among the gel materials as described above, it is preferable to use alkoxysilane or its oligomer. This is due to the following reason. Water is a solvent used to produce a gel from other gel raw materials such as water glass, an aqueous silicic acid solution obtained by electrodialysis of water glass, and colloidal silica. On the other hand, when alkoxysilane is used as the gel raw material, a considerable amount of alcohol is used as the solvent, so that the proportion of water in the gel is reduced, and the effect of simplifying the water removal step described later is produced. It is.
[0024]
In addition, after gelation, the formed wet gel is placed in a temperature-raising atmosphere as necessary, and the gel is aged by condensing unreacted hydroxyl groups in the gel. It is effective in suppressing shrinkage. Furthermore, it is known that the aging of the gel in the monomer by adding the gel raw material at the time of aging is more effective for ensuring the gel strength and reducing the shrinkage at the time of drying. (Journal of Non-Crystaline Solid, 186, 96, 1995).
[0025]
Further, adding a gelling catalyst after the gelation at the time of aging is also effective in increasing the gel strength. In particular, when the catalyst is added at the time of gelation and the gel acceleration becomes too fast, a method of adding the catalyst at the time of aging after gelation is effective.
[0026]
On the other hand, as a method for forming a wet gel, for example, as shown in JP-A-11-514324, the gel raw material may be formed into granules by dropping or stirring or spraying the gel raw material into a poor solvent. Is possible. By forming granules having a size of about mm, the penetration of the liquid containing the hydrophobizing agent is improved even in the hydrophobizing step described later, and there is an effect that the hydrophobization proceeds efficiently.
[0027]
The dry gel production method of the present invention can be applied to a wet gel formation method using a general gel material as described above or a gel formation method in which granulation is performed at the time of gel formation. If it is formed, it is not limited to the above method.
[0028]
(2) Water removal step (removal of water in wet gel)
In this step, water in the wet gel formed in (1) the gelation step is removed. As the method, the following two methods are preferable.
・ Solvent replacement
・ Evaporation by heating
First, solvent replacement will be described. The general solvent replacement is performed by immersing the formed wet gel in the solvent to be replaced and replacing the solvent with the solvent in the gel. The solvent used at this time is not particularly limited as long as it is a water-soluble solvent. For example, as water-soluble alcohols, lower alcohols such as methanol, ethanol, propanol and tertiary-butanol, ethylene glycol, glycerol, and other ketones such as acetone, 1,4-dioxane, tetrahydrofuran, 1,3-dioxolane, Ethers, formamides such as dimethylformamide, lower carboxylic acids such as formic acid, acetic acid and propionic acid, and mixtures thereof can be used. Among these, it is preferable to use methanol that is low in cost and has high hydrophobizing efficiency in the hydrophobizing step described later.
[0029]
The solvent replacement can be performed not only with the water-soluble solvent but also with a mixed solvent of the water-soluble solvent and another water-insoluble solvent. In this case, in order to increase the hydrophobizing efficiency in the hydrophobizing step described later, it is preferable that the water-soluble solvent is methanol. Similarly, in order to increase the above-described hydrophobization efficiency, a solvent having a boiling point of 80 ° C. or higher, particularly a solvent of 100 ° C. or higher is preferable as the water-insoluble solvent. The water-insoluble solvent satisfying this is not particularly limited as long as it is water-insoluble, and a very wide range of solvents such as alcohols, ketones, esters, aromatic and aliphatic hydrocarbons having other functional groups, and The hydrocarbon etc. which do not have a functional group are used. Specifically, the water-insoluble solvent having a boiling point of 80 ° C. or higher and a low surface tension includes decane, nonane, octane, heptane, octane, toluene, xylene, and the like. Of these, particularly preferred are octane, toluene, xylene and the like.
[0030]
Next, heating distillation will be described. When water is removed by distillation by heating, it is generally possible to distill water preferentially by adding and heating a water-insoluble solvent having a boiling point higher than that of water. By using a water-insoluble solvent, the organic solvent and water are naturally separated after distillation by heating, so that the solvent can be easily reused. Moreover, even if the boiling point of the water-insoluble solvent is lower than the boiling point of water, if it is added excessively, it is possible to remove water, but by further increasing the boiling point of the solvent, the selectivity of water distillation Can be increased. For this reason, compared with the case where water is removed by solvent substitution, the effect that the amount of solvent to be used can be reduced significantly is acquired. At the same time, a low-density dry gel can be easily obtained by using a water-insoluble solvent having a boiling point of 80 ° C. or higher, more preferably a water-insoluble solvent having a boiling point of 100 ° C. or higher. An effect is acquired and it is preferable.
[0031]
In addition, when the solvent added with water forms an azeotrope, water and the solvent are distilled off at a constant rate, so that there is an effect that the control of water removal becomes easy. Furthermore, efficient water removal becomes possible by performing the heating and distillation under reduced pressure conditions as is done by drying an ordinary organic solvent. In particular, in the case where a gelling catalyst or the like is present, if the temperature is raised in a state containing water and then heat-dried, bonds in the gel skeleton may be broken. In such a case, it is effective to prevent the temperature from rising by distilling water off under reduced pressure.
[0032]
In addition, when the water-insoluble solvent at the time of distilling off the solvent is added as a poor solvent or the like at the time of gelation, as in the case of granulating at the time of gel formation described in (1) Gelation step Is preferable because the poor solvent can be used as it is.
[0033]
(3) Hydrophobization step (hydrophobization of wet gel surface)
Conventionally, when hydrolyzing a wet gel that has undergone a water removal step using silazane as a hydrophobizing agent, a water-soluble solvent has been used as a solvent for hydrophobization. However, it was not easy to obtain a dry gel having a low density by using a normal water-soluble solvent. Further, if a high-boiling water-soluble solvent is used, a dry gel having a low density can be obtained. However, as the water-soluble solvent, usable solvents such as dimethylformamide are limited, and the cost of the solvent is increased. there were.
[0034]
In order to solve this problem, the inventors of the present invention have intensively studied, and as a result, at the time of hydrophobization treatment. If you use a solvent containing methanol and a water-insoluble solvent, By mixing about 10 to 20% by weight of methanol, it becomes possible to perform a good hydrophobizing treatment in the same way as when hydrophobizing in methanol, and low density dry gel by drying according to the drying process described below. I found out that
[0035]
By the way, as described in the drying step described later, it was difficult to dry a wet gel containing methanol because shrinkage easily occurred. However, according to the present invention, a mixed solvent containing only a small amount of methanol can be used as the solvent during the hydrophobization treatment. In this case, a small amount of methanol having a low boiling point is selectively distilled off at the beginning of the drying step, and the gel can be dried from a solvent substantially free of methanol. Also, Solvent used with methanol is a water-insoluble solvent So Since it becomes easy to select a solvent having a smaller surface tension, it is preferable to suppress shrinkage during drying, thereby obtaining a low-density dried gel. In this way, the hydrophobization treatment in a mixed solvent of methanol and a water-insoluble solvent enables both efficient progress of hydrophobization and drying with low surface tension and reduced capillary force. The effect of obtaining a gel is provided.
[0036]
Thus, as the solvent during the hydrophobization treatment of the present invention,
·methanol And water-insoluble solvent Mixed solvent
Is used. Therefore, as a specific operation in the hydrophobization step, (2) when the solvent contained in the wet gel that has undergone the water removal step is not the above solvent, the solvent is replaced by the corresponding solvent replacement. It is necessary to. Thereafter, a silazane compound as a hydrophobizing agent is added, or a wet gel is immersed in the solvent containing the silazane compound as a hydrophobizing agent, and then the hydrophobizing treatment is performed by heating. At this time, during the above solvent replacement, Mixed solution containing methanol and water-insoluble solvent It is also possible to omit the above solvent substitution by adding a hydrophobizing agent.
[0037]
The silazane compound, which is a specific hydrophobizing agent used in the present invention, is not particularly limited, and examples thereof include hexamethyldisilazane, dimethyltrimethylsilylamine, diethyltrimethylsilylamine, and bis (dimethylamino) dimethylsilane. . Among these, hexamethyldisilazane is preferable from the viewpoint of availability.
[0038]
In addition, as a water-soluble solvent used in the hydrophobization treatment, which can be used in combination with methanol, the water-soluble solvent described above, specifically, water-soluble alcohols such as ethanol, propanol and tertiary-butanol, ethylene glycol, glycerol, etc. In addition to lower alcohols, ketones and ethers such as acetone, 1,4-dioxane, tetrahydrofuran and 1,3-dioxolane, lower carboxylic acids such as formic acid, acetic acid and propionic acid, and mixtures thereof can also be used. . Since acetic acid and the like also act as a catalyst for hydrophobization, it is more preferable to use it together.
[0039]
The water-insoluble solvent used for hydrophobization is not particularly limited as long as it does not dissolve in water. However, the smaller surface tension is advantageous because the capillary force acting at the time of drying becomes small and shrinkage hardly occurs.
[0040]
Examples of the water-insoluble solvent suitably used in the present invention include aliphatic and aromatic hydrocarbons that do not contain a functional group, fluorinated hydrocarbons, ethers, alcohols, alkylsilanes, dimethylpolysiloxanes, and the like. Silicon compounds are preferred because of their low surface tension at the boiling point.
[0041]
Specifically, as the surface tension, if the value at the boiling point is about 0.02 N / m or less, it can be suitably used because it is suitable for drying in the drying step described later. The tension is preferably 0.016 N / m or less. Solvents that satisfy this and are easily available include decane, nonane, octane, heptane, hexane and pentane, butane and the like, aliphatic hydrocarbons having no cyclic structure, isomers thereof, and mixtures thereof.
[0042]
Among these, as the water-insoluble solvent having a boiling point of 80 ° C. or less and a low surface tension, hexane, pentane, or petroleum ether mainly composed of a mixture thereof is particularly preferable.
[0043]
Among these, decane, nonane, octane, heptane, octane, toluene, xylene and the like are examples of the water-insoluble solvent having a boiling point of 80 ° C. or higher and a low surface tension.
[0044]
Of these, octane, toluene, xylene and the like are particularly preferable when the boiling point is 100 ° C. or higher.
[0045]
(4) Drying process
Finally, the drying method will be described.
[0046]
A hydrophobized wet gel is obtained through the above-mentioned (1) gelation step, (2) water removal step, and (3) hydrophobization step. In the drying step, the solvent that increases the capillary force during drying is selectively removed, and then the solvent remaining in the gel is removed by heating to obtain a hydrophobized dry gel. Methanol is the most important solvent for increasing the capillary force during drying. Therefore, for example, when hydrophobization treatment is performed in methanol, the capillary force during drying is reduced by replacing methanol in the gel with another solvent or adding another solvent before or during drying. It is preferable to do.
[0047]
As already mentioned, when the hydrophobizing solvent is a mixed solvent of methanol and a water-insoluble solvent, by leaving the water-insoluble solvent in excess, before the substantial drying of the wet gel begins, It is preferable because methanol can be selectively distilled off. Furthermore, it is preferable to increase the boiling point of the water-insoluble solvent, so that methanol can be more selectively distilled off. However, since the boiling point of methanol itself is as low as 64.1 ° C., the water-insoluble solvent The solvent can be easily selected, and the methanol can be selectively distilled off easily. The water-insoluble solvent is not particularly limited as long as it has a boiling point higher than that of methanol. However, it is preferable to use a solvent that forms an azeotrope with methanol because stable removal of methanol is possible. Examples of the solvent include ethyl methyl ketone, toluene, and cyclohexane. Xan Etc.
[0048]
As a method for preferentially removing methanol during drying, it is preferable to dry in a vapor atmosphere of an organic solvent other than methanol contained in the wet gel. For example, when the wet gel contains hexane and methanol, the methanol is preferentially vaporized by drying while blowing heated steam of hexane, and finally the wet gel containing almost no methanol is obtained. By doing so, a good low density dry gel can be obtained.
[0049]
On the other hand, drying can be performed at atmospheric pressure or lower as described in JP-A-7-257918. At this time, it is preferable to select a solvent having a low surface tension in order to reduce the capillary force at the drying temperature, particularly as the drying solvent. Moreover, drying under reduced pressure also has the effect of reducing the risk of drying the organic solvent. As such a solvent, it is particularly preferable to use pentane, hexane, petroleum ether, which is a mixture containing these as main components, in view of availability.
[0050]
Moreover, the low density of a dry gel becomes easy by applying the manufacturing method of the hydrophobized dry gel of the present invention described above. Specifically, it becomes easy to produce a hydrophobized dry gel with a low density of 50 to 500 kg / m3, and in particular, it is possible to produce a hydrophobized dry gel with a low density of 50 to 300 kg / m3 which is preferable as a heat insulating material. There is an effect that becomes easy.
[0051]
Finally, the heat insulating material using the hydrophobized dry gel of the present invention will be described. This heat insulating material is mainly composed of a dry gel produced by the method for producing a hydrophobized dry gel of the present invention. The dried gel is in the form of blocks, granules, powders, and the like, and can be used as a heat insulating material by filling them into necessary parts such as equipment to be insulated. Moreover, what was shape | molded by adding a binder, a filler, etc. is used suitably as a heat insulating material.
[0052]
Further, the apparent density is 50 to 500 kg / m 3. Since it has a low density, low thermal conductivity can be realized, and it has moisture resistance because it is mainly composed of a hydrophobized gel.
[0053]
Hereinafter, the present invention will be described based on specific examples, but the present invention is not limited thereto.
[0054]
【Example】
《 reference Example 1 and Comparative Examples 1, 2, 3, 4 >>
Book reference In the example, a wet gel is formed using alkoxysilane as a gel raw material, and after removing the solvent containing water in the wet gel by solvent replacement with methanol, bis (dimethylamino) dimethylsilane is used as a hydrophobizing agent. Hydrophobization treatment was performed in methanol. Finally, in the drying step, solvent substitution was performed and then dried to prepare a dried gel.
[0055]
Specifically, a wet gel was obtained by first mixing tetramethoxysilane / methanol / water = 100/90/47 (weight ratio). As the water, 0.1N ammonia water was used. Subsequently, the obtained wet gel was immersed in methanol 10 times the gel volume, so that the solvent containing water in the wet gel was replaced with methanol. This solvent substitution was repeated once more. Subsequently, the wet gel was immersed in a 10 wt% methanol solution of 0.5 mol of bis (dimethylamino) dimethylsilane with respect to 1 mol of tetramethoxysilane used for gel formation. After the immersion was continued at 60 ° C. for 3 hours, the solvent substitution was performed by immersing the wet gel in 10 times the gel volume of hexane. Furthermore, this solvent substitution was repeated once. Finally, the wet gel was dried under a nitrogen stream at 100 ° C. to obtain a dry gel. The density of the obtained dried gel was calculated by determining the volume by measuring the weight of the gel piece and substituting in water. The obtained dried gel was pulverized and filled into a non-woven bag to produce a heat insulating material, and the thermal conductivity was measured by a parallel plate method. ( reference Example 1)
For comparison, except for solvent replacement before hydrophobization and changing the solvent at the time of hydrophobization to ethanol, reference Dry gel preparation and density and thermal conductivity measurements were performed under the same conditions as in the examples. (Comparative Example 1)
Similarly, except for solvent substitution before hydrophobization, and the solvent at hydrophobization changed to isopropanol, reference A dried gel was prepared and the density and thermal conductivity were measured under the same conditions as in the examples. (Comparative Example 2)
Similarly, the solvent substitution before hydrophobization, except that the solvent at the time of hydrophobization was changed to tertiary butanol, reference A dried gel was prepared and the density and thermal conductivity were measured under the same conditions as in the examples. (Comparative Example 3)
Similarly, solvent replacement before hydrophobization, except that the solvent at hydrophobization was changed to acetone, reference A dried gel was prepared and the density and thermal conductivity were measured under the same conditions as in the examples. (Comparative Example 4)
The density of the obtained dried gel was 260 kg / m 3 ( reference Example 1), 350 kg / m3 (Comparative Example 1), 360 kg / m3 (Comparative Example 2), 340 kg / m3 (Comparative Example 3), and 330 kg / m3 (Comparative Example 4). Among water-soluble solvents, it has been found that methanol gives a remarkably low density dry gel. This is presumably because the hydrophobization efficiency in methanol is high.
[0056]
Moreover, the heat conductivity of the obtained heat insulating material is 20.5 mW / mK (in order) reference Example 1), 28.4 mW / mK (Comparative Example 1), 29.0 mW / mK (Comparative Example 2), 27.6 mW / mK (Comparative Example 3), 27.0 mW / mK3 (Comparative Example 4), It was found that those obtained with a low density gel by using methanol showed excellent thermal conductivity.
[0057]
《 reference Example 2
Book reference In the example, the hydrophobizing agent was changed to dimethyltrimethylsilylamine reference A dry gel was prepared in the same manner as in Example 1, and the density was measured.
[0058]
The density of the resulting dried gel is 270 kg / m3, reference It was found that the density was low as in Example 1. This is presumably because the hydrophobization progressed with high efficiency because methanol was used as the hydrophobizing solvent.
[0059]
《 reference Examples 3, 4, 5 and Comparative Examples 5, 6, 7 >>
Book reference In the example, a wet gel was formed using alkoxysilane as a gel raw material. The solvent containing water in the wet gel was removed by solvent replacement using methanol, and then solvent replacement was further performed using toluene. Hydrophobization was performed in toluene using hexamethyldisilazane as a hydrophobizing agent, and a dry gel was prepared by performing a drying treatment as it was.
[0060]
In particular, reference A wet gel was prepared in the same manner as in Example 1, and after methanol substitution, toluene substitution was carried out in the same manner as methanol substitution. Subsequently, the wet gel was immersed in a 10 wt% toluene solution of hexamethyldisilazane at a ratio of 0.25 mol to 1 mol of tetramethoxysilane used for gel formation. The soaking was continued at 80 ° C. for 3 hours. Finally, the wet gel subjected to the hydrophobization treatment was dried as it was in a pressure-resistant container under a nitrogen stream of 0.2 MPa and 150 ° C. to obtain a dry gel. The density of the obtained dried gel reference Determined in the same manner as in Example 1. ( reference Example 3)
Furthermore, except that the hydrophobization temperature was set to 100 ° C. reference A dry gel was produced in the same manner as in Example 3, and density measurement was performed. ( reference Example 4) Also, reference After gelation and methanol substitution in the same manner as in Example 3, 0.5 mol of hexamethyldisilazane was made into a 10 wt% methanol solution with respect to 1 mol of tetramethoxysilane used for gel formation. The wet gel was immersed at 60 ° C. for 3 hours. Thereafter, as in the case of methanol substitution, toluene substitution is performed, and drying is performed under a nitrogen stream at 150 ° C. under a pressure of 0.2 MPa, reference The density of the dried gel was measured in the same manner as in Example 3. ( reference Example 5)
For comparison, except that the hydrophobization temperature was 40 ° C. reference A dry gel was produced in the same manner as in Example 4, and the density was measured. (Comparative Example 5)
For comparison, except that the hydrophobization temperature was set to 60 ° C. reference A dry gel was produced in the same manner as in Example 4, and the density was measured. (Comparative Example 6)
For comparison, the toluene in the wet gel was replaced with liquefied carbon dioxide gas in a high-pressure vessel, and then heated to 70 ° C. and 10 MPa to obtain a supercritical state, and then the pressure was gradually released. A dry gel was obtained. reference Density measurement was performed in the same manner as in Example 4. (Comparative Example 7)
The density of the obtained dried gel was 460 kg / m 3 (toluene, 40 ° C., comparative example 5), 360 kg / m 3 (toluene, 60 ° C., comparative example 6), 260 kg / m 3 (toluene, 80 ° C., reference Example 3), 260 kg / m 3 (methanol, 60 ° C., reference Example 5), 220 kg / m 3 (toluene, 100 ° C., reference Example 4). At a temperature lower than about 60 ° C., the density of the dried gel increased, but when hydrophobized at 80 ° C., a low density comparable to that obtained when hydrophobized in methanol was realized even in toluene, which is a water-insoluble solvent. Also, by drying at 100 ° C., shrinkage was almost completely suppressed even under conditions below the critical pressure, and a low density equivalent to that during supercritical drying was realized.
[0061]
"Example 1, 2 , Reference Example 6 And Comparative Example 8 >>
Example Reference examples Then, after substitution with methanol, hexane was added to hydrophobize in a mixed solvent of methanol / hexane, and the dried gel was prepared by heating and drying as it was. Hexamethyldisilazane was used as the hydrophobizing agent.
[0062]
In particular, reference A wet gel was prepared in the same manner as in Example 1, and after replacement with methanol having a volume three times the gel volume, the wet gel was transferred into hexane so that the solvent contained in the wet gel was methanol. / Hexane = 10/90 (weight ratio). Furthermore, the hydrophobization process was advanced as a 10 wt% solution by adding hexamethyldisilazane to the solvent. The hydrophobization treatment was continued at 60 ° C. for 3 hours. Finally, the wet gel subjected to the hydrophobization treatment was dried as it was under a nitrogen stream at 100 ° C. to obtain a dry gel. In addition, the density of the obtained dry gel, reference Determined in the same manner as in Example 1. (Example 1 )
Examples except that the ratio of the mixed solvent contained in the wet gel before hydrophobization was methanol / hexane = 20/80 (weight ratio) 1 In the same manner as above, a dried gel was prepared, and the density was measured. (Example 2 )
In addition, the examples were the same except that the hydrophobization was performed in methanol after the methanol substitution and the hexane substitution was performed before the drying. 1 A dry gel was prepared in the same manner as described above, and the density was measured. ( reference Example 6 )
In addition, Example 1 was performed except that hexane replacement was performed after methanol replacement and hydrophobization was performed in hexane. 1 In the same manner as above, a dried gel was prepared, and the density was measured. (Comparative Example 8)
The density of the obtained dried gel was 260 kg / m3 in order (Example 1 ) 280 kg / m3 (Example) 2 ), 260 kg / m3 ( reference Example 6 ) 340 kg / m3 (Comparative Example 8).
[0063]
Thus, it has been found that the density of the resulting dried gel is reduced only by mixing a small amount of methanol with the hydrophobic solvent. This is thought to be because hydrophobic efficiency is improved by mixing a small amount of methanol, and during drying, the amount of methanol is small and the boiling point is low, so that it is selectively distilled off and the capillary force during drying does not increase.
[0064]
《 reference Example 7 》
Book reference In the example, a wet gel was formed using alkoxysilane as a gel raw material. Toluene was added to the solvent containing water in the wet gel, and water was distilled off by heating. Hydrophobization was performed in toluene using hexamethyldisilazane as a hydrophobizing agent, and a dry gel was prepared by performing a drying treatment as it was.
[0065]
In particular, reference A wet gel was prepared in the same manner as in Example 1, and toluene was added in a volume 5 times that of the gel. Then, half of all the solvents were distilled off by heating under reduced pressure. Furthermore, 0.5 mol of hexamethyldisilazane was added to 1 mol of tetramethoxysilane used at the time of gelation, and the mixture was held at 110 ° C. for 3 hours. Finally, the wet gel subjected to the hydrophobization treatment was dried as it was in a pressure-resistant container under a nitrogen stream of 0.2 MPa and 150 ° C. to obtain a dry gel. When the density of the obtained dry gel was determined in the same manner as in Example 1, it was 230 kg / m 3. Thus, by removing the water in the formed wet gel by heating distillation, the amount of the solvent can be greatly reduced as compared with the case of removing the water by solvent replacement. ( reference Example 3)
[0066]
【The invention's effect】
In the method for producing a hydrophobized dry gel of the present invention, after the formation of a wet gel, water contained in the gel is removed, and a silazane compound as a hydrophobizing agent is allowed to act to hydrophobize the gel. Is characterized in that a solvent containing at least methanol and a water-insoluble solvent is used as a solvent during the hydrophobization treatment. This produces an effect that a low-density dry gel can be easily obtained.

Claims (3)

  A gelling step in which a wet gel is formed by mixing a solvent containing at least water and a gel raw material, a dewatering step for removing water in the wet gel, and the surface of the wet gel as a hydrophobizing agent A hydrophobizing step of hydrophobizing using a silazane compound, and a drying step of obtaining a dry gel by removing the solvent remaining in the hydrophobized wet gel under conditions below the critical point of the solvent. In the hydrophobizing step, a solvent containing at least methanol and a water-insoluble solvent is used as the solvent during the hydrophobizing treatment.   The method for producing a dry gel according to claim 1, wherein the main component of the inorganic porous material is silicon dioxide.   The method for producing a dry gel according to claim 1, wherein the gel raw material is alkoxysilane or an oligomer thereof.