JP2003020218A - Method for manufacturing water-repellent dry gel, and heat insulating material using the gel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that it is difficult to enhance the heat insulating performance of a dry gel much more though the concentration of a raw material to be gelated is adjusted for enhancing the heat insulating performance when the dry gel is used as a heat insulating material. SOLUTION: The dry gel having optimum heat insulating performance and lower thermal conductivity is obtained by using an alkoxysilane as the raw material to be gelated and controlling the gelating temperature to be <=50 deg.C and the gel aging temperature to be 20-50 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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, and the like, and a heat insulating material using the dry gel obtained thereby.

[0002]

2. Description of the Related Art A dry gel used for obtaining a heat insulating material, a sound absorbing material and a catalyst carrier generally has a large specific surface area and, at the same time, preferably has a low density. In order to increase the specific surface area of the dry gel and reduce the density, it is necessary that the dry gel has a large number of fine pores. It is necessary to obtain a wet gel that fills. Such a wet gel can be produced by a so-called sol-gel method. To achieve a structure with low density and a large number of micropores,
It is common practice to optimize the concentration of raw materials.
When the raw material concentration is high, fine pores are formed, but the proportion of the portions where no pores are formed is high, resulting in high density. If the raw material concentration is low, the density will be low,
It is known that a small number of large holes are formed (for example, Journal of Non-Crystalline Solid, 145, 207-210, 1992).

Furthermore, the wet gel is liable to shrink when dried due to the capillary force in the micropores of the gel. Reducing this shrinkage is important for obtaining a dry gel with low density and micropores, and there are mainly two methods known for that purpose. The first method is the supercritical drying method. This method is characterized in that a gas-liquid interface is not formed during the drying because the drying is carried out at a pressure and temperature above the critical point. Therefore, it is possible to dry without causing a capillary force and causing shrinkage. This method was developed by Kistler as a method using supercritical drying of alcohol (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).

The second method is to dry the gel surface by hydrophobizing the gel surface to reduce the capillary force (US Pat. No. 3,015,645, Journal of Non-Crystalline Solid, 186, 104).
~ 112, 1995) is known. Further, in order to maintain the performance of the heat insulating material and the sound absorbing material made of the dry gel, it is necessary that the dry gel does not absorb moisture over time. In this regard, it is known that the above-mentioned hydrophobization of the gel surface is effective.

[0005]

As described above, as a method of forming a wet gel having a low density and a large number of fine pores, a method of adjusting the concentration of the raw material gel is known.
There was no other effective method. Further, when heat is generated during gelation, the gelation rapidly progresses due to heat generation, so that the physical properties of the obtained gel cannot be reproducible, or the physical properties of the gel are partially varied. was there.

Further, in order to obtain a dry gel having a low density and fine pores, or in order to prevent the dried gel from absorbing water, the method of making the surface of the gel hydrophobic as described above is effective. Target. However, when the gel raw material contains an alkaline component, the temperature at which the hydrophobicity can be maintained is not sufficiently high, and there is a problem that heat resistance cannot be ensured. Therefore, an object of the present invention is to provide a method for producing a sufficiently hydrophobized low-density dry gel, and a high-performance heat insulating material using the dry gel obtained thereby, in order to solve the above problems. It is in.

[0007]

The present invention comprises: (a) a step of mixing a gel raw material and a gelling catalyst to advance gelation and aging at a temperature of 50 ° C. or lower to obtain a gel; A step of hydrophobizing the surface of the gel obtained in step (a) with a hydrophobizing agent in an aqueous solvent to obtain a hydrophobized gel; (c) a non-aqueous solvent from the hydrophobized gel obtained in step (b) The present invention relates to a method for producing a hydrophobized dry gel, which comprises the step of removing the hydrophobized dry gel. It is effective that the hydrophobized dry gel has an apparent density of 50 to 300 kg / m ³ .

In this case, it is effective that the gel raw material is an aqueous solution or an aqueous colloid containing silicon oxide as a main component, and the aging temperature is 5 to 25 ° C. Further, the gel raw material is an aqueous solution or an aqueous colloid containing silicon oxide as a main component, and between the step (a) and the step (b),
It is effective to carry out the step of converting the alkali content in the gel obtained in the step (a) into a salt by bringing the gel into contact with an acid and further removing the salt. Further, it is effective that the gel raw material is alkoxysilane and the aging temperature is 20 to 50 ° C.

Further, the gel raw material is an alkoxysilane, and the solvent in the gel obtained in the step (a) is replaced with a non-alcoholic water-soluble solvent between the steps (a) and (b). It is effective to perform the step of replacing with a mixed solvent of water and water. Furthermore, the present invention comprises a hydrophobized dry gel produced by the method for producing a hydrophobized dry gel described above, wherein
Provided is a heat insulating material having hydrophobicity at the following temperatures.
Also in this case, the hydrophobized dry gel is 50 to 300 kg /
It is useful to have an apparent density of m ³ .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a hydrophobized dry gel of the present invention mainly comprises the following three steps. (A) Gelation and gel aging step (formation of wet gel) (b) Hydrophobicization step (hydrophobicization of wet gel surface) (c) Drying step (solvent removal from wet gel) These steps are described below. To do.

(A) Gelation and gel aging step (formation of wet gel) In the present invention, a wet gel is first produced by a so-called sol-gel method. In many cases, heat is generated when the gel and the gelling catalyst are mixed to allow the gelation to proceed. Due to this heat generation, gelation progresses rapidly, which causes a problem that the physical properties of the obtained gel cannot be reproducible, a problem that the physical properties of the gel are partially varied, and the like.

In order to solve such a problem, the inventors of the present invention have conducted extensive studies and as a result, have found that the temperature at the time of gelation is 50.
It was found that by controlling the temperature to be not higher than 0 ° C, gelation proceeds uniformly and reproducible gel properties can be obtained. Also,
It was also found that when the temperature during gelation is lowered, reproducible results are obtained, but the gelation time becomes too long, so the temperature should be controlled to 0 ° C or higher. In order to avoid a rapid temperature rise, for example, cooling, reducing the amount of the gelling catalyst mixed, or adding the gelling catalyst little by little is effective. Of course, it is also possible to use these methods together.

As the gel raw material used in the production method of the present invention, a general raw material used in the sol-gel method is used. For example, there are compounds such as oxides of silicon, aluminum, zirconium and titanium and their corresponding alkoxides. Among these, compounds containing silicon as a metal are preferable because of easy availability. For example, tetramethoxysilane, tetraalkoxysilane such as tetraethoxysilane, silicon alkoxide such as trialkoxysilane and dialkoxysilane and its oligomer, colloidal silica, water glass, and an aqueous solution of silicic acid obtained by electrodialysis from water glass are used. To be The shape of the gel raw material may be fine particles.

As the gelling catalyst, general organic acids, inorganic acids, organic bases and inorganic bases can be used. Examples of the organic acid include acetic acid and citric acid, and examples of the inorganic acid include sulfuric acid, hydrochloric acid and nitric acid. Examples of the organic base include piperidine and the like, and examples of the inorganic base include ammonia and the like.

When an alkoxysilane is used as a raw material, an acid or alkali and water are added to an alcohol solution as a gelling catalyst to cause hydrolysis and polycondensation of the alkoxysilane to form a wet gel. At this time, since gelation proceeds with heat generation, it is effective to control the temperature during gelation according to the production method of the present invention.
Further, when water glass is used as a gel raw material, an acid such as hydrochloric acid is mixed as a catalyst with the gel raw material to promote gelation. In this case as well, neutralization proceeds by the addition of acid and heat is generated by the heat of neutralization, and therefore it is effective to control the temperature during gelation according to the production method of the present invention.

Further, as the gel raw material, the aqueous silicic acid solution obtained by electrodialyzing water glass does not generate heat during gelation, and therefore it is easy to control the temperature during gelation according to the present invention. More preferable. This is because most of the alkali content in the water glass is removed by the electrodialysis treatment, and heat generation during neutralization is less likely to occur. Colloidal silica is also preferable in that it generates less heat during gelation, but it has the drawback that it is difficult to obtain the strength of the gel and shrinkage during drying tends to occur.

On the other hand, as a result of earnest studies, the present inventors found that
It was found that controlling the temperature for aging the gel to 50 ° C. or lower improves the heat insulating performance of the finally obtained dry gel. During the aging of the gel, the bond between the fine particles forming the gel is formed by the condensation of the hydroxyl groups, thereby increasing the strength of the gel. It is considered that this is because although the condensation progresses faster at a higher temperature, rearrangement of atoms occurs from the surface to form larger particles and the pores formed by the particles become larger. On the other hand, if the temperature is too low during gel aging, bonds between the fine particles forming the gel are formed, and it takes time to increase the gel strength. This is disadvantageous for suppressing shrinkage during drying, so the aging temperature must be adjusted to 0 ° C or higher.

Further, it has been clarified by the present inventors that the temperature suitable for aging the gel varies depending on the kind of the gel raw material. In particular, when alkoxysilane is used as a gel raw material from the viewpoint of enhancing the heat insulating performance of the obtained dry gel, the temperature is slightly higher than room temperature,
-50 degreeC, especially 35-50 degreeC are preferable. On the other hand, when a raw material such as an aqueous solution containing silicon oxide as a main component or an aqueous colloid, specifically water glass, an aqueous solution of silicic acid obtained by electrodialyzing water glass, colloidal silica or the like is used, the temperature is higher than room temperature. Low, 5-25 ° C, especially 10-2
It has been found that 0 ° C is preferred.

As a wet gel to which the present invention is applied, a wet gel having a strong skeletal strength is preferable because it makes it easy to suppress shrinkage, particularly when drying under a condition below the critical point described later. . Generally, when the gel is aged, it is possible to improve the skeletal strength by placing the wet gel in a solution containing a high concentration of a monomer together with a catalyst for a certain period of time. For example, in the case of a silica wet gel, alkoxysilane or silicic acid is added to age the gel.

(B) Hydrophobizing Step (Hydrophobic Surface Hydrophobicization) In the method for producing a hydrophobized dry gel of the present invention, after the wet gel is formed in the gelation and gel aging steps, the wet gel is The surface is hydrophobized. This is the hydrophobization process described here. As described above, by performing the hydrophobizing treatment, the dried gel does not absorb water, so that the heat insulating performance and the sound absorbing performance do not deteriorate. Further, when drying under subcritical conditions, the pores in the gel are easily crushed by the capillary force to increase the density, but by hydrophobizing, the effect of the capillary force can be substantially reduced, There is an effect that contraction can be suppressed.

The above-mentioned hydrophobizing treatment can be carried out by directly immersing the wet gel obtained in the gelation and gel aging step (a) in a hydrophobizing treatment solution in which a hydrophobizing agent is dissolved. In addition, since hydrophobizing agents such as chlorosilane compounds and disilazane compounds described later react with water in the wet gel to reduce the hydrophobizing ability, solvent replacement with a solvent containing a water-soluble solvent is performed before the hydrophobizing step. Therefore, it is preferable to remove the water in the gel.

Further, as a solvent to be used for the solvent substitution before the hydrophobization and the hydrophobization, in order to suppress the reaction between the chlorosilane compound or the disilazane compound, which is a hydrophobizing agent having high reactivity, and water, a water-soluble solvent is used. It is preferable to use a mixed solvent with a non-water-soluble solvent. Further, it is preferable not to use the water-soluble solvent, particularly when a chlorosilane compound is used as a hydrophobizing agent, because it may reduce the hydrophobicity of the gel from which alcohol is obtained.

When the hydrophobizing treatment is performed, if a gel raw material containing an alkaline component such as sodium or potassium such as water glass is used, the alkaline component may remain in the wet gel. At that time, the progress of the hydrophobization reaction on the gel surface may be hindered. Among the hydrophobizing agents described later, in the case of a chlorosilane compound or the like, the inhibition of hydrophobization tends to be particularly remarkable.

Usually, the above-mentioned alkaline component is removed by washing with water after forming a salt with an acid as a gelling catalyst added at the time of gelation. But a lot of water is needed,
Especially when the thickness of the wet gel is large, it is difficult to remove the alkaline component. Therefore, a preferred embodiment of the production method of the present invention is that after the gelation and aging step (a) of the gel, the gel is brought into contact with a solution containing an acid to make the alkali content into a salt, and the salt is further removed. Is characterized by.

Specifically, an alkaline salt is formed by immersing the wet gel in a solution of an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid, or an organic acid such as formic acid, acetic acid or propionic acid, or exposing it to steam. This is washed and removed in an organic solvent that dissolves water or the salt. If the gel is particles and the particle size is large, or if the gel is block-shaped and the thickness is thick, it takes a long time to remove the alkaline component by washing with water only. Therefore, the method of the present invention becomes effective. Specifically, it is particularly effective for particles having a particle size or thickness of 1 to 5 mm or more.

Regarding the removal of the alkali content, an aqueous solution of silicic acid obtained by subjecting water glass to electrodialysis treatment is preferable because it originally has less alkali content and the time required for alkali removal is short. Regarding the removal, the method of forming a salt with an acid and the removal thereof in the present invention is still preferably used. The reason why stable hydrophobicity cannot be obtained by the hydrophobizing treatment is that, in addition to the above-mentioned residual alkali component, a large number of alkoxy groups which easily decompose on the surface are present. The phenomenon is
For example, this is remarkable for a gel obtained by using a metal alkoxide such as alkoxysilane as a gel raw material, and as a result, the heat resistance temperature at which the hydrophobicity is retained is lowered.

In order to solve the above problems, alkoxysilane is used as a gel raw material, and a non-alcoholic water-soluble solvent is added between the gelation and gel aging step (a) and the hydrophobizing step (b). It is preferable to carry out the step of replacing the solvent in the wet gel with a mixed solvent with water. The alkoxy group on the surface is hydrolyzed in an alcohol-free aqueous solution to form a hydroxyl group, which is converted into a stable hydrophobic group such as an organic silyl group in the hydrophobizing step. Therefore, it is considered that good hydrophobicity can be obtained and the temperature at which the hydrophobicity can be maintained, that is, the heat resistance is also increased. Further, when replacing the solvent in the wet gel with a mixed solvent of a non-alcoholic water-soluble solvent and water, it is also effective to add an acid or a base as a catalyst for promoting the hydrolysis of the alkoxy group. Target.

The alkoxysilane as the gel raw material includes alkoxysilane monomers such as tetramethoxysilane and tetraethoxysilane, and oligomers thereof. Examples of the non-alcoholic water-soluble solvent include water-soluble ketones, ethers, carboxylic acids, and amides. Specifically, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane,
Formic acid, acetic acid, propionic acid, N, N-dimethylformamide and the like can be used.

The hydrophobizing agent used in the hydrophobizing step of the present invention is preferably a silylating agent from the viewpoint of high reactivity,
Examples thereof include silazane compounds, chlorosilane compounds, alkylsilanol compounds and alkoxysilane compounds. Among these, silazane compounds and chlorosilane compounds having high reactivity are preferably used. The silylating agent is
By reacting with the hydroxyl group on the gel surface, an organosilyl group is introduced to impart hydrophobicity to the gel. In the case of a silazane compound, a chlorosilane compound, and an alkoxysilane compound, they react with the hydroxyl group even after they are hydrolyzed by reaction with water to form the corresponding alkylsilanol, but the reactivity before hydrolysis is higher. It is preferably used under the condition that hydrolysis does not proceed.

Specific examples of the silylating agent include chlorosilane compounds such as trimethylchlorosilane, methyltrichlorosilane and dimethyldichlorosilane, silazane compounds such as hexamethyldisilazane, methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethylsilane and dimethoxydiethyl. Examples include alkoxysilanes such as silane, diethoxydimethylsilane, trimethoxymethylsilane and triethoxymethylsilane. Further, when a fluorinated silylating agent is used as the hydrophobizing agent, excellent hydrophobicity is obtained, which is very effective.
For example, chlorosilanes having a perfluoroalkyl group can be preferably used.

Other hydrophobizing agents include alcohols such as ethanol, propanol, butanol, hexanol, heptanol, octanol, ethylene glycol and glycerol, as well as carboxylic acids such as formic acid, acetic acid, propionic acid and succinic acid, and acetic acid. Acid chlorides such as chlorides can also be used. These react with hydroxyl groups on the gel surface to form an ether or an ester to promote hydrophobicity, but the reaction is relatively slow, so high temperature conditions are required.

As the water-soluble solvent which serves as a solvent for the hydrophobizing agent during the hydrophobizing treatment, acetone, 1,4-dioxane, tetrahydrofuran, ketones such as 1,3-dioxolane and ether, as well as methanol, ethanol and propanol. Also, lower alcohols such as tert-butanol, lower carboxylic acids such as formic acid, acetic acid and propionic acid can be used. The alcohols and acids mentioned above also act as hydrophobizing agents, as already mentioned.

However, although the lower alcohol acts as a water-soluble solvent and promotes hydrophobicity, it may react with a hydrophobizing agent such as chlorosilane or deteriorate the hydrophobic performance achieved by a hydrophobizing agent such as a silylating agent. Therefore, it is more preferable to use a water-soluble ketone or a water-soluble ether as the water-soluble solvent. Specifically, the above-mentioned acetone, 1,4-dioxane, tetrahydrofuran, 1,3
-Dioxolane or the like is used.

(C) Drying Step (Solvent Removal from Wet Gel) Finally, the drying step will be described. In this step, the solvent is removed from the wet gel to obtain a dry gel. The method can be divided into a supercritical drying method and a drying method under conditions below the critical point. As a supercritical drying method, a non-aqueous gel is installed, the non-aqueous solvent in the gel is put into a supercritical state, and then the pressure is gradually released at a constant temperature to remove the solvent and dry the gel. The method of extracting and removing the non-aqueous solvent of the above with the solvent used for the supercritical fluid, replacing the solvent, releasing the pressure at a constant temperature and removing the fluid in the supercritical state to the atmospheric pressure gas state, and drying. is there. In both cases, since the supercritical state is dried without passing through the liquid phase, a gas-liquid interface does not occur,
The feature is that the gel does not contract due to capillary force.

The solvent used for supercritical drying is
Wet gel solvents can be used. In particular, it is preferable to replace with a solvent that is easy to handle in supercritical drying. Specific solvents include alcohols such as methanol, ethanol, propanol, isopropanol, butanol, and tert-butanol, which can be directly used as a supercritical fluid, and liquefied carbon dioxide. Further, it may be replaced with a general organic solvent such as acetone, isoamyl acetate or hexane, which is easily eluted with these supercritical fluids. The solvent is not limited to these as long as the gel can be dried to a low density without shrinking well.

As supercritical drying conditions, it is carried out in a pressure vessel such as an autoclave. For example, in methanol, the critical conditions are critical pressure of 8.09 MPa and critical temperature of 23.
The temperature is kept at 9.4 ° C. or higher, and the pressure is gradually released while drying at a constant temperature. Further, in the case of carbon dioxide, the critical pressure is set to 7.38 MPa and the critical temperature is set to 31.1 ° C. or higher.

Next, the drying method performed under the condition below the critical point will be described. This method can use various conditions for pressure, from reduced pressure to increased pressure, but unlike the supercritical drying method, it is a general heating method in which a solvent in a liquid state is dried while forming a gas-liquid interface during drying. It is a drying method. And, since this method does not require high pressure, it can be implemented with low equipment cost.

Since the gas-liquid interface is formed, shrinkage due to the capillary force easily occurs during drying. Since the hydrophobic treatment is performed in the hydrophobic step (b), shrinkage is less likely to occur, but in order to further reduce the shrinkage,
It is preferable to lower the surface tension of the solvent retained in the wet gel. Therefore, the solvent in the wet gel may be replaced with a solvent having a low surface tension, if necessary. Alternatively, it is preferable to use a solvent having a low surface tension at the time of hydrophobization. As the solvent used for drying in the present invention, a liquid having a surface tension of 0.016 N / m or less at the boiling point is particularly preferable. Liquids that meet this include decane, nonane, octane, heptane, hexane and pentane,
There are hydrocarbons having no cyclic structure such as butane, and isomers thereof.

In addition, HFC-134a, HFC-1
52a and hydrofluorocarbon compounds (HFC) such as octafluorocyclopentane, hydrofluoroether compounds such as nonafluorobutyl methyl ether and nonafluorobutyl ethyl ether (HF
E), fluoroalcohols such as hexafluoroisopropanol, alkylsilanes such as tetramethylsilane, dimethylpolysiloxanes such as hexamethyldisiloxane, hexamethylcyclotrisiloxane and octamethyltrisiloxane.

Further, in order to reduce the surface tension and the capillary force in the drying step, it is effective and preferable to add a surfactant. Surfactants include silicon-based and hydrocarbon-based surfactants, and fluorine-based surfactants obtained by fluorinating the above-mentioned surfactants, and there are anionic, cationic and nonionic surfactants, respectively. On the other hand, among the hydrophobizing agents used for hydrophobizing, those that did not react with the hydroxyl groups on the gel surface remain in the pores of the gel at the beginning of the drying process. However, most of these vaporize and are removed from the pores as the drying progresses.

Further, in order to remove a very small amount of the hydrophobizing agent, the temperature can be further raised after the drying to decompose. However, if the temperature cannot be raised for some reason, it is also possible to dry under a liquid vapor that dissolves the hydrophobizing agent after the hydrophobizing step, and further dry the solvent. At this time, if the washing solvent used is one that dissolves the hydrophobizing agent,
It goes without saying that the one having a low surface tension is preferable.

In the drying step, the drying is carried out under the condition below the critical point, but if the drying is carried out under pressure, the boiling point of the liquid held in the pores will rise. In this case, since the surface tension is lowered by the temperature rise, the contraction is effectively suppressed by reducing the capillary force, which is preferable. For example, when ethanol is dried under pressure, if the boiling point is raised by about 80 ° C. to about 150 ° C., the surface tension becomes 0.006.
N / m can be reduced to about 0.012 N / m, and drying under pressure is effective for suppressing shrinkage.

Finally, a heat insulating material using the hydrophobized dry gel of the present invention will be described. This heat insulating material is manufactured by the method for manufacturing a hydrophobized dry gel of the present invention, and is characterized by having an apparent density of 50 to 300 kg / m ³ and maintaining hydrophobicity at 350 ° C. Since the density is low, low thermal conductivity can be realized, and since the temperature at which the hydrophobicity is maintained is high, it can be used as a heat insulating material in a high temperature range.

As described above, a low density of 50 to 300 kg / m ³ can be realized even under the condition below the critical point by carrying out the hydrophobization by the method for producing a hydrophobized wet gel of the present invention. Moreover, as a result of diligent study, the present inventors have found that
Even when alkoxysilane is used as a gel raw material, the solvent in the wet gel is replaced with a mixed solvent of a non-alcoholic water-soluble solvent and water before the hydrophobic treatment.
It was found that a hydrophobic property with heat resistance is imparted up to ℃. Hereinafter, the present invention will be described based on specific examples, but the present invention is not limited thereto.

[0045]

EXAMPLES << Example 1 and Comparative Example 1 >> In this example,
A wet gel was formed by adjusting the gelling temperature to 50 ° C. or lower using water glass as a gel raw material, and the thermal conductivity of the obtained dry gel was examined. The wet gel was dried by the supercritical drying method. Wet silica gel, the Na ₂ 0 and SiO ₂ 1: water glass containing 3 (molar ratio), SiO ₂
The mixture was diluted with water to a concentration of 10% by weight, and 2N sulfuric acid was added little by little to the diluted water glass so that the pH became 7, while the gelation was allowed to proceed. The temperature during gelation was controlled at 25-40 ° C. The wet gel formed was aged for 3 days at 25 ° C. Subsequently, after adding ion-exchanged water to the wet gel, it was pulverized with a stirrer to a particle size of about several mm or less, and further washed 3 times with ion-exchanged water having a volume 10 times the gel volume.

Next, the water in the gel is replaced with ethanol by immersing the above-mentioned wet gel in ethanol having a volume five times the gel volume, replacing the water in each operation with fresh ethanol. did. Similarly, the solvent, ethanol, in the wet gel was replaced with hexane. Thereafter, the gel was immersed in a 10 volume% hexane solution of trimethylchlorosilane having a volume 5 times the volume of the gel at 45 ° C. for 1 day to perform a hydrophobic treatment. Furthermore, in the same manner, the solution in the gel was replaced with pure hexane. The hydrophobized wet gel obtained was placed in an autoclave, and hexane in the gel was replaced with liquefied carbon dioxide.
From the conditions of ° C and 12 MPa, the temperature was maintained and the pressure was released to perform drying. Further, the same experiment was repeatedly carried out (Example 1).

For comparison, 2N sulfuric acid was added to the same gel raw material as in Example 1 at a time so that the pH became 7.
During the process leading to gelation, the temperature increased, and the temperature near the surface exceeded 50 ° C and rose to about 60 ° C. After that, the gel was aged, hydrophobized, and supercritically dried under the same conditions as in Example 1. Further, the same experiment was repeated (Comparative Example 1). The hydrophobized dry gel obtained in Example 1 had an average density of about 240 kg / m ³ and a thermal conductivity of 0.021 W / mK at an average temperature of 24 ° C. Further, the variation in the density of each part was within 5%, and the variation in the thermal conductivity due to repeated experiments was within 1%.

On the other hand, in Comparative Example 1, the density of the dry gel was 230 kg / m ³ , but the variation in each part was 2
The thermal conductivity was about 0%, the thermal conductivity was 0.023 W / mK, and the variation due to repeated experiments was about 10%. in this way,
The variation in the thermal conductivity and the density in Example 1 is smaller than that in Comparative Example 1 because the uniform gelation reaction progresses partially with time by controlling the temperature during gelation. Conceivable.

<< Example 2 and Comparative Example 2 >> In this example, tetramethoxysilane, which is an alkoxysilane, is used as a gel raw material, and the gelling temperature is adjusted to 50 ° C. or lower to form a wet gel, which is obtained. The thermal conductivity of the gel was investigated. The wet gel was dried by a supercritical drying method. When tetramethoxysilane, ethanol, and 0.1N ammonia water are mixed at a ratio of 1: 1: 4 (molar ratio), the ammonia water is gradually added to the mixture of tetramethoxysilane and ethanol while cooling. And the temperature is 4
Gelation was allowed to proceed while adjusting the temperature to 0 ° C or lower. Although no water washing was carried out, solvent replacement, hydrophobization and supercritical drying were carried out in the same manner as in Example 1 thereafter. However, the wet gel was pulverized in the same manner as in Example 1 at the time of the first solvent replacement (Example 2).

For comparison, when the same raw materials as in Example 2 were mixed to form a gel, 0.1N ammonia water was added at once to promote gelation. At this time, a rapid temperature rise occurred, reaching a temperature of 50 ° C. or higher near the gel surface. Thereafter, a dry gel was prepared in the same manner as in Example 2 (Comparative Example 2). The hydrophobized dry gel obtained in Example 2 was
The density was about 280 kg / m ³ on average, and the thermal conductivity was 0.020 W / mK on average at an average temperature of 24 ° C.
Further, the variation of the density due to each part was within 5%, and the variation of the thermal conductivity due to repeated experiments was within 1%.

On the other hand, in Comparative Example 2, the density of the dry gel was 270 kg / m ³ , but the dispersion of each part was about 15%, the thermal conductivity was 0.022 W / mK, and the dispersion was found by repeated experiments. Was about 10%. As described above, the variation in the thermal conductivity and the density in Example 2 is smaller than that in Comparative Example 2 because the temperature control during gelation causes a partial gelation reaction to progress partially over time. I think that is because.

Example 3 and Comparative Example 3 In this example, tetramethoxysilane, which is an alkoxysilane, was used as a gel raw material, the gel aging temperature was changed to form a wet gel, and the thermal conductivity obtained was examined. . Drying a wet gel
It was performed by the supercritical drying method. As the gel raw material, a mixture of tetramethoxysilane, ethanol and 0.1N ammonia water in a ratio of 1: 3: 4 (molar ratio) was used, and the gelation temperature was controlled in the same manner as in Example 2 to proceed the gelation. Let
Four gels were formed. Continue to 2 for each gel
Aging was carried out for 3 days in each of the constant temperature baths of 5 ° C, 35 ° C and 45 ° C. Thereafter, a dried gel was prepared in the same manner as in Example 2 (Example 3).

For comparison, three wet gels before aging were aged at 5 ° C., 10 ° C. and 60 ° C. for 3 days in the same manner as in Example 3. Thereafter, a dried gel was prepared in the same manner as in the example (Comparative example 3). The thermal conductivity of the dried gels obtained in Example 3 and Comparative Example 3 was 5 ° C, 10 ° C, 25 ° C, 35 ° C, 45.
C., 60.degree. C. in the order of 0.0242, 0.0221, 0.
0189, 0.0177, 0.0172, 0.0210
It was W / mK, and the thermal conductivity increased on the low temperature side and the constant temperature side.

Example 4 and Comparative Example 4 In this example, an aqueous solution of silicic acid obtained by electrodialyzing water glass was used as a gel raw material, and a aging temperature of the gel was changed to form a wet gel. The effect of aging temperature on thermal conductivity was investigated.
Drying of the wet gel was performed under conditions below the critical point. The gel raw material is obtained by passing a water glass solution of sodium silicate through an ion exchange membrane electrodialyzer, p
A silicic acid aqueous solution having H10.5, a silicic acid concentration of 14% by weight, and a sodium oxide concentration of 0.8% by weight was used.

2N sulfuric acid was added at once to the above silicic acid aqueous solution to promote gelation. However, heat was hardly generated, and gelation was performed at 30 ° C. or lower without cooling. I was able to proceed. 5mm thick in this way
A wet gel block with a diameter of 10 cm was formed. We made three such blocks, each at 10 ℃, 20 ℃, 4
The gel was aged for 5 days in each thermostat at 5 ° C.

Subsequently, washing was performed 3 times with ion-exchanged water having a volume 10 times the gel volume. Next, the above wet gel was mixed with 5 times the gel volume of acetone and hexane 4: 1.
(Volume ratio) The operation of immersing in the mixed solvent is carried out three times in total by replacing each operation with a new mixed solvent, so that the water in the gel is mixed with acetone and hexane in a 4: 1 (volume ratio) mixed solvent. Replaced. Thereafter, the gel was immersed in a mixed solvent of 10 volume% trimethylchlorosilane of 10 volume% of the gel volume of acetone and hexane 4: 1 (volume ratio) at 45 ° C. for 1 day to perform a hydrophobic treatment.

Finally, the hydrophobized wet gel described above is
After replacing the solvent contained in the gel with hexane by the same method as the above solvent replacement, 80 to 100 in a drying container.
Drying was performed by removing the solvent while flowing heated nitrogen at ℃ (Example 4). For comparison, three wet gel blocks before aging were formed in the same manner as in the example, and each of them was set to 0.
The gel was aged in each of the constant temperature baths at 60 ° C, 60 ° C and 80 ° C.
Thereafter, a dry gel was prepared in the same manner as in the example (Comparative example 4). The thermal conductivity of the dried gel block bodies obtained in Example 4 and Comparative Example 4 was 0 ° C, 10 ° C, 20 ° C, 45 ° C, 6
0 ℃, 80 ℃ in order of 0.0175, 0.0152,
0.0157, 0.0177, 0.0181, 0.01
It was 93 W / mK, and the lowest thermal conductivity was obtained in a temperature range slightly lower than room temperature.

Example 5 In this example, an aqueous solution of silicic acid obtained by electrodialyzing water glass was used as a gel raw material, and after aging the gel, a salt removing step by dipping in an acid solution and washing with water was performed. We examined the effects that were incorporated. Gelation was performed in the same manner as in Example 4, and aging was performed under the conditions of 20 ° C. in Example 4. After that, the obtained gel was immersed in 0.1N sulfuric acid having a volume 5 times the volume of the gel for 4 hours, and subsequently washed with ion-exchanged water having a volume 10 times the volume of the gel 3 times. Thereafter, a dried gel was prepared in the same manner as in Example 4. The thermal conductivity of the obtained dried gel block body is 0.0141 W.
/ MK, which is reduced by about 0.001 W / mK, as compared with Example 4 in which immersion in sulfuric acid was not performed. It is considered that this is because a slight amount of water was not adsorbed because the hydrophobization proceeded more completely by immersion in sulfuric acid.

Example 6 In this example, a step of using alkoxysilane as a gel raw material and substituting the solvent in the wet gel with a mixed solvent of a non-alcoholic water-soluble solvent and water after gel aging The influence of the retention of hydrophobicity on the heat resistance when incorporated was examined. 45 ° C. as in Example 3
A wet gel aged in 1. was prepared. This is 5 of the gel
The solvent in the wet gel was replaced with a mixed solvent of double volume of acetone and water 4: 1 (volume ratio). Then, the solvent in the wet gel was replaced with acetone in the same manner as in Example 1, and the gel was added to a gel volume of 5 times the volume of trimethylchlorosilane in 10 vol% acetone.
A hydrophobizing treatment was performed by immersing at 1 ° C. for 1 day. Thereafter, a dried gel was prepared in the same manner as in Example 3.

Regarding the dried gel of the present invention and the dried gel of Example 3, whether or not the hydrophobicity is maintained by putting them in an electric furnace at 350 ° C. for 10 minutes and examining the ups and downs in water before and after that. I checked. As a result, it was confirmed that the dried gel of the present invention floated in water and maintained its hydrophobicity, but the gel of Example 3 was found to sink in water and lose its hydrophobicity.

[0061]

The method for producing a hydrophobized dry gel of the present invention is characterized by controlling the temperature during gelation and during gel aging. In particular, the water glass-based gel raw material and the alkoxysilane-based gel raw material have different preferable temperature ranges, and by performing gelation and gel aging in a certain temperature range, good reproducibility, uniform and high heat insulation performance is realized. effective. Further, in the production method of the present invention, when a gel is produced from a water-glass-based gel raw material, after the gelation, an alkali salt formation with an acid and a step of washing with water are added to increase the efficiency of hydrophobization. , Has the effect of achieving high heat insulation performance.

In the production method of the present invention, when alkoxysilane is used as the gel raw material, the solution in the wet gel is temporarily replaced with a mixed solvent of a non-alcoholic water-soluble solvent and water after gel aging. This has the effect of improving the heat resistant temperature for maintaining the hydrophobicity of the dried gel obtained through the hydrophobizing step and the drying step. Further, by configuring the heat insulating material composed of the hydrophobized dry gel obtained by the production method of the present invention, there is an effect that a heat insulating material having a high heat insulating property and having a hydrophobic property maintained at a high temperature can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G065 AA02 AA09 AB11X BA09                       BB01 BB02 BB08 CA14 CA30                       DA03 EA10 FA01                 4G072 AA25 CC10 EE01 GG03 HH19                       HH30 JJ13 MM01 MM31 PP06                       PP14 QQ07 RR01 UU17 UU30

Claims (7)

[Claims] 1. A step of (a) mixing a gel raw material and a gelling catalyst to proceed with gelation and aging at a temperature of 50 ° C. or lower to obtain a gel, and (b) a hydrophobizing agent in a non-aqueous solvent. A step of hydrophobizing the surface of the gel obtained in step (a) to obtain a hydrophobized gel; (c) a hydrophobized dry gel obtained by removing the non-aqueous solvent from the hydrophobized gel obtained in step (b); A method for producing a hydrophobized dry gel, which comprises the step of obtaining. 2. The hydrophobized dry gel is 50 to 300 kg.
The method for producing a hydrophobized dry gel according to claim 1, which has an apparent density of / m ³ . 3. The method for producing a hydrophobized dry gel according to claim 1, wherein the gel raw material is an aqueous solution or an aqueous colloid containing silicon oxide as a main component, and the aging temperature is 5 to 25 ° C. 4. The gel raw material is an aqueous solution or an aqueous colloid containing silicon oxide as a main component, and an alkali in the gel obtained in the step (a) between the step (a) and the step (b). The method for producing a hydrophobized dry gel according to claim 1, further comprising the step of converting a component into a salt by bringing the gel into contact with an acid, and further removing the salt. 5. The method for producing a hydrophobized dry gel according to claim 1, wherein the gel raw material is alkoxysilane, and the aging temperature is 20 to 50 ° C. 6. The gel raw material is an alkoxysilane, and the solvent in the gel obtained in the step (a) is a non-alcoholic water-soluble solvent between the steps (a) and (b). The method for producing a hydrophobized dry gel according to claim 1, further comprising the step of replacing with a mixed solvent of water and water. 7. A hydrophobized dry gel produced by the method for producing a hydrophobized dry gel according to claim 1, comprising 350 ° C.
A heat insulating material having hydrophobicity at the following temperatures.