JP2003231754A - Porous body and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a porous body which comprises a metal oxide having organosilyl groups loses its hydrophobic nature at about 250°C though it is hydrophobic in essence. <P>SOLUTION: A wet gel is made by using a metal alkoxide being tetramethoxysilane as a starting material, and the wet gel is immersed in water- containing acetone to hydrolyze the methoxy groups and is made hydrophobic by treatment with a silylating agent being trimethylchlorosilane and is heat-dried to obtain the porous body. The obtained porous body has a methoxy content of at most 1 wt.%. The obtained porous body can be kept hydrophobic to a high temperature because the heat decomposition temperature of the organosilyl groups of the porous body obtained is 350°C. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat insulating material, a sound absorbing material,
The present invention relates to a catalyst carrier, an interlayer insulating material used for LSI, etc., a low-density porous body used for an acoustic matching layer of a transducer for ultrasonic waves such as ultrasonic waves, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A low-density porous material has a low density, a large specific surface area, and a fine pore structure, so that a heat insulating material, a sound absorbing material,
It is used as a catalyst carrier, an interlayer insulating material such as LSI, and an acoustic matching layer of an ultrasonic wave transmitter / receiver.

For example, as a heat insulating material, solid heat conduction is reduced due to its low density. Further, since it has a fine pore structure finer than that of the mean free path of gas, gas heat conduction is also suppressed, and excellent heat insulating performance is exhibited. Further, by enclosing in a depressurized container, higher heat insulation performance is exhibited. The heat insulating material is used, for example, for heat insulation of thermal home appliances and houses.

In addition to the above-mentioned heat insulating material, when it is used as an acoustic matching layer of an ultrasonic wave transmitter / receiver, a sound absorbing material, a catalyst carrier, an interlayer insulating material such as LSI, the form of use may be a component other than a porous body. As a block-shaped or film-shaped porous body that does not contain
It is used by inserting it into a required part or directly forming it. Further, it is used by filling it into a container or the like as a powder or granular porous body. It is also possible to use the powder or granules in a block shape by molding them with an organic or inorganic binder. Further, a filler such as a fibrous body may be added to the block body and the powder molded body to reinforce the strength.

The above heat insulating material, sound absorbing material, catalyst carrier, LSI
When applied to an interlayer insulating material such as, an acoustic matching layer of an ultrasonic wave transmitter / receiver, or the like, the corresponding performance may decrease due to moisture absorption. Therefore, in order to prevent moisture absorption, the porous body preferably has hydrophobicity. Conventionally, there is known a porous body having a skeleton made of a metal oxide, the surface of which is modified with an organic silyl group to make it hydrophobic so as to prevent moisture absorption.

Two examples are shown below.

In the first example, an alkoxysilane which is a metal alkoxide is used as a raw material. A wet gel containing an alcohol solvent is formed from this raw material by using the sol-gel method. Furthermore, the water remaining in the wet gel is removed by replacing it with alcohol. Next, in supercritical carbon dioxide, a silylating agent that is a hydrophobizing agent is allowed to act on the surface of the wet gel to introduce an organic silyl group, and a hydrophobizing treatment is performed. Finally, supercritical drying is carried out at a temperature above the critical temperature to remove carbon dioxide. The dried gel thus obtained is a porous body having a skeleton made of silicon oxide, which is a metal oxide, and having an organic silyl group on the surface (JP-A-7-1).
38375 publication).

In the second example, a wet gel is formed in the same manner as in the first example, and alcohol substitution removes water remaining in the wet gel. Hydrophobization is performed by causing a silylating agent to act on the surface of a wet gel in a hydrocarbon solvent to introduce an organic silyl group. Drying is performed by removing the solvent in the wet gel by heating and drying. Thus, a porous body having a skeleton made of silicon oxide, which is a metal oxide, and having an organic silyl group on the surface is obtained (Journal of Crystalline Solid, Vol. 186, 104-1).
P. 12, 1995).

On the surface of the porous body of the above example, in addition to the organic silyl group introduced by the hydrophobizing treatment, a metal alkoxyside used as a raw material or an alcohol solvent used for the treatment for obtaining the porous body is used. A quantity of alkoxy groups is present. The hydrophobicity of the porous body is lost at a temperature of about 250 ° C. or lower due to the thermal decomposition of the organic silyl group.

[0010]

In the porous body according to the prior art described above, since the organic silyl group is thermally decomposed at a temperature of about 250 ° C. or less to lose the hydrophobic property, a heat insulating material, a sound absorbing material, a catalyst carrier, When it is used as an interlayer insulating material such as an LSI or an acoustic matching layer of an ultrasonic wave transmitter / receiver, there is a problem that the corresponding characteristics deteriorate due to moisture absorption.

In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a porous body which maintains its hydrophobicity even at a temperature higher than the conventional one and a method for producing the same.

[0012]

In order to solve the above-mentioned problems, the porous body of the present invention is a porous body having a skeleton composed of a metal oxide and having an organic silyl group on at least a part of its surface. Therefore, the number of contained alkoxy groups is less than 5% with respect to the number of metal atoms of the metal oxide.

The above porous body has an apparent density of 50 to 500.
It is preferably in the range of kg / m ³ .

The metal atom of the metal oxide constituting the skeleton is preferably a silicon atom.

The organic silyl group is preferably a trimethylsilyl group. Further, the organic silyl group is preferably a dimethylsilyl group.

On the other hand, in the method for producing a porous body of the present invention, the skeleton is composed of a metal oxide, and at least a part of the surface of the porous body has an organic silyl group, and the number of alkoxy groups contained in the porous body is the metal oxide. A method for producing a porous body having less than 5% with respect to the number of metal atoms in the product, wherein the wet gel having an alkoxy group on the surface of (a) is immersed in a water-soluble solvent containing water. Hydrolyzing the group,
(B) a step of dissolving the hydrophobizing agent and subjecting the wet gel to a hydrophobic treatment in a solvent containing no alcohol, and (c) a drying step of removing the solvent remaining in the gel.

In the above manufacturing method, it is preferable that the wet gel having an alkoxy group on the surface is formed by a sol-gel method using a metal alkoxide as a raw material.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

First, the porous material of the present invention will be described.

As a result of intensive studies, the present inventors have surprisingly found that a porous material having an organic silyl group on the surface and having hydrophobicity has a small amount of alkoxy groups. It was found that it is possible to increase the heat resistance of the porous body with respect to hydrophobicity. The small amount of alkoxy groups means that the number of alkoxy groups is less than 5% with respect to the number of metal atoms of the metal oxide constituting the skeleton, and it is preferably less than 1%.

The reason why the hydrophobicity is maintained up to a high temperature when the amount of the alkoxy group is small is considered as follows.
When there are many alkoxy groups, the alkoxy groups burn at an ambient temperature of about 250 ° C. or lower. At that time, the organic silyl base also rises in temperature and burns due to a local temperature rise due to burning. On the other hand, when the number of alkoxy groups is small, it is considered that the combustion of the organic silyl groups induced by the combustion of the alkoxy groups does not occur and the atmosphere temperature is stable until the temperature reaches the temperature at which the organic silyl groups burn.

The skeleton of the porous body of the present invention is composed of a metal oxide, and as the metal oxide, silicon oxide, aluminum oxide, zirconium oxide, titanium oxide and the like are easily available as a gel raw material described later. Is preferred. Of these, silicon oxide is particularly preferable for the above reason.

The porous material of the present invention preferably has a low density in consideration of being used as a heat insulating material, an acoustic matching layer of an ultrasonic wave transmitter / receiver, a sound absorbing material, and the like, and the density thereof is 50-5.
It is 00 kg / m ³ . Due to its low density, heat and sound conduction by solids is reduced as a heat insulating material and sound absorbing material,
The acoustic impedance matching between the air and the piezoelectric body can be achieved as the acoustic matching layer of the ultrasonic wave transmitter / receiver, so that the efficiency of sound wave transmission / reception is increased.

As the organic silyl group which imparts hydrophobicity, there are an alkylsilyl group, an arylsilyl group and the like.
Strongly hydrophobic alkylsilyl is preferred. As the alkylsilyl, there are a trimethylsilyl group, a triethylsilyl group, a diethylmethylsilyl group, an ethyldimethylsilyl group, and also a long-chain alkylsilyl group, but since they have sufficient hydrophobicity and a small molecular weight, A trimethylsilyl group is particularly preferable because the increase in the density is small even when introduced into the surface of the porous body. For the same reason, a dimethylsilyl group having a smaller molecular weight is more preferable. On the other hand, of the arylsilyl groups, a phenylsilyl group is particularly preferable because it has high heat resistance.

The alkoxy group on the surface of the porous body is a methoxy group or an ethoxy group, which is introduced on the surface of the porous body by the remaining alkoxy group of the gel raw material described later or the alcohol solvent used in the treatment of the manufacturing process. , Propyl group, isopropyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group and the like. The presence of a large alkoxy group reduces the introduction efficiency of the organic silyl group due to a steric effect. Therefore, the alkoxy on the surface is preferably a small alkoxy group such as methoxy group and ethoxy group.

Further, since the porous body of the present invention has a very small amount of alkoxy, it has the effect of easily developing three-dimensional bonds in the porous body and increasing the strength. Further, since there is no alkoxy group, the introduction of the organic silyl group is easy, so that it also has the effect of having stronger hydrophobicity.

Next, the method for producing the porous body of the present invention will be described.

Although it has been described that the skeleton of the porous body of the present invention is made of a metal oxide, this porous body can be manufactured by a method including the following steps, for example.

(A) Hydrolysis step A step of hydrolyzing the alkoxy group by washing a wet gel formed by the sol-gel method and having an alkoxy group on the surface in a water-soluble solvent containing water, (b) hydrophobic Step of dissolving the hydrophobizing agent and subjecting the wet gel to a hydrophobic treatment in a solvent containing no alcohol (c) drying step removing the solvent remaining in the gel; The most characteristic step of the invention is the step a), in which the alkoxy group is hydrolyzed and converted into a hydroxyl group. Since this hydroxyl group is converted into an organic silyl group in the hydrophobizing step of b), the porous body of the present invention having an organic silyl group and containing very few alkoxy groups can be obtained.

In the following, the above steps will be sequentially described in detail, focusing on the case where a metal alkoxide is used, which is the most preferable because it is easy to control gelation as a gel raw material.

(A) Hydrolysis Step In this step, first, a wet gel is prepared by the so-called sol-gel method, and the alkoxy groups present in the wet gel are removed by hydrolysis.

When an alkoxysilane which is a metal alkoxide is used as a gel raw material, first, an acid or an alkali and water are added as a gelling catalyst in an alcohol solution,
A wet gel is formed through hydrolysis and polycondensation of alkoxysilane. This wet gel has about 10% to 40% of an alkoxy group derived from the metal alkoxide as the gel raw material or the alcohol of the solvent used, with respect to the number of metal oxide metal atoms constituting the skeleton.

Next, the wet gel is immersed in a mixed solvent of a water-soluble solvent and water to hydrolyze the alkoxy group contained in the wet gel. In this way, it is possible to form a wet gel containing almost no alkoxy groups. At this time, the water-soluble solvent in the mixed solvent for immersing the wet gel is acetone, tetrahydrofuran, dioxolane,
In addition to dioxane, formamide, dimethylformamide and the like, alcohols such as methanol, ethanol and propanol may be used, but the amount of water is preferably about 30 wt% or more in order to sufficiently promote hydrolysis.

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 oxide fine particles of silicon, aluminum, zirconium, titanium and the like, and corresponding alkoxides. Among these, compounds containing silicon as a metal are preferable because of easy availability. For example, tetraalkoxysilanes such as tetramethoxysilane and tetraethoxysilane, trialkoxysilanes, silicon alkoxides such as dialkoxysilanes and oligomers thereof, colloidal silica, water glass, and an aqueous solution of silicic acid obtained by electrodialysis from water glass are used. To be

As described above, the metal alkoxide, which is easy to control gelation and has excellent reproducibility of the wet gel to be formed, is preferable, and the above-mentioned silicon alkoxide is particularly preferable because of easy availability and handling.

As the gelling catalyst, general organic acids, inorganic acids, organic bases and inorganic bases are used. Organic acids include acetic acid, citric acid, inorganic acids, sulfuric acid, hydrochloric acid, nitric acid, organic bases such as piperidine, and inorganic bases such as ammonia.

(B) Hydrophobizing step In this step, the wet gel obtained in (a) hydrolysis step is dissolved in a silylating agent which is a hydrophobizing agent and immersed in a solvent containing no alcohol. Then, the hydroxyl group in the wet gel is converted into an organic silyl group. By performing the hydrophobic treatment in a solution containing no alcohol, it is possible to prevent the conversion of the hydroxyl group into the alkoxy group. Here, the alcohol-free solution means that the number of alcohol molecules in the solution is
It is 1/10 or less of the number of molecules of the hydrophobizing agent contained in the solution.

At this time, if water is present in the solution in which the silylating agent is dissolved, the silylating agent reacts and is lost. Therefore, the water in the wet gel should be removed by washing with a non-alcoholic solvent. Is preferred.

The silylating agent used in the present invention includes:
Chlorosilane compounds and disilazane compounds are most suitable because they have high reactivity at the time of hydrophobization and are easily available, but alkoxysilane compounds can also be used.

Trimethylchlorosilane, methyltrichlorosilane and dimethyldichlorosilane, diethyldichlorosilane, ethylmethyldichlorosilane as the chlorosilane compound, hexamethyldisilazane as the silazane compound, methoxytrimethylsilane, ethoxytrimethylsilane, dimethoxydimethyl as the alkoxysilane. Examples include silane, dimethoxydiethylsilane and diethoxydimethylsilane. Among these, those in which the organic moiety bonded to the silicon atom is a methyl group are preferred. This is because the organic sites are small, so that the reactivity at the time of hydrophobization is high, and at the same time, the density increase due to hydrophobization of the obtained porous body is small.

As the water-soluble solvent used as the solvent for the hydrophobizing treatment liquid, water-soluble ketones, water-soluble ethers, water-soluble amides and the like are used. Specifically, acetone,
Examples include 1,4-dioxane, tetrahydrofuran, 1,3-dioxolane, dimethylformamide and the like.

(C) Drying step In this step, from the wet gel obtained in (b) having an organic silyl group and almost no alkoxy group,
By removing the solvent, the porous body of the present invention is obtained. As a solvent for drying, methanol or ethanol should be avoided in order to prevent conversion of an organic silyl group or a residual hydroxyl group into an alkoxy group. Further, in order to prevent conversion of the organic silyl group to a hydroxyl group, it is preferable to avoid mixing of water as a solvent during drying.

The solvent is usually removed by heating and drying. At that time, the capillary force generated in the pores of the wet gel during the drying causes the wet gel to shrink, resulting in an increase in the density of the obtained porous body. Sometimes. Therefore, it is preferable to reduce the capillary force generated by using a dry solvent having a low surface tension. Specifically, hydrocarbons such as heptane, hexane, pentane and the like and mixtures thereof are particularly preferably used.

Alternatively, a supercritical fluid can be used as the solvent in order to reduce the surface tension of the solvent during drying. Typical supercritical fluids used for drying are water, alcohol, and supercritical states such as carbon dioxide.
Alcohol is not preferable because it may cause hydrolysis of an organic silyl group or introduction of an alkoxy group. The supercritical state of carbon dioxide without these possibilities is preferably used.

Freeze-drying, in which the solvent in the wet gel is frozen and the solvent is removed by sublimation at a temperature below the melting point, is also effective in preventing the increase in the density of the porous body. This is because the solid state is dried and the capillary force does not work during the drying. For this method, t-butanol having a high melting point is preferably used.

In the above, a typical method for producing the porous body of the present invention has been described. In addition to this, after the hydrolysis step of (a), drying is carried out, and thereafter, a hydrophobizing treatment is carried out in the gas phase by exposing to the vapor of the silylating agent to introduce an organic silyl group, and the porous body of the present invention is obtained. It is also possible to obtain it.

The present invention is described below based on specific examples, but the present invention is not necessarily limited to the following contents.

[0048]

EXAMPLES << Example 1 and Comparative Example 1 >> In this example,
A wet gel was prepared using tetramethoxysilane as a metal alkoxide as a raw material, and the wet gel was immersed in hydrated acetone to hydrolyze the methoxy groups on the surface of the wet gel.
After that, trimethylchlorosilane was used as a silylating agent for hydrophobizing treatment, and drying was performed to obtain a porous body.

Specifically, tetramethoxysilane / methanol / water = 1: 3: 4 (molar ratio) was used as a raw material, and this was mixed to prepare a wet gel. Water was used in the form of 0.1N ammonia water as a catalyst.

Next, the obtained wet gel is mixed with acetone / water.
= 1/1 (weight ratio) was immersed for 1 day.

Further, the wet gel was immersed in acetone to replace the inside of the wet gel with acetone, and then the wet gel was immersed in a 6 vol% acetone solution of trimethylchlorosilane for 1 day.

Finally, acetone was removed by heating and drying under atmospheric pressure to obtain a porous body. The density of the porous body is 22
It was 0 g / cm ³ .

Further, the total amount of carbon due to the methoxy group and the trimethylsilyl group in the porous body was quantified by elemental analysis. Further, the total amount of silicon was quantified from the remaining silicon oxide by heat treatment at 900 ° C. in the presence of oxygen. Also,
By performing ¹³ C-NMR measurement in the solid state, the ratio of the methoxy group having carbon and the trimethylsilyl group in the porous body was determined. By doing so, the ratio of the number of methoxy groups and the number of trimethylsilyl groups to the number of silicon atoms was determined. The ratios were less than 1% and 11%, respectively.

Further, by thermogravimetric analysis, the temperature at which weight loss occurs when the temperature was raised to 500 ° C. was measured to determine the thermal decomposition temperature of the organic silyl group. At this time, the measurement was performed in the air. The thermal decomposition temperature of the organic silyl group of the obtained porous body was 350 ° C (Example 1).

For comparison, a wet gel was formed in the same manner as in the example and then immersed in methanol to replace the liquid in the wet gel with methanol. After that, in the same manner as in the example,
Acetone substitution, hydrophobization, and drying were performed.

The ratio of the number of methoxy groups and the number of trimethylsilyl groups in the obtained porous material to the number of silicon atoms was 13% and 10%, respectively. Also, the density is 230
kg / m ³ , and the thermal decomposition temperature of the organic silyl group was 260 ° C (Comparative Example 1).

As described above, in the example, the thermal decomposition temperature of the organic silyl group is higher than that of the comparative example, and the hydrophobicity can be maintained up to a high temperature because the alkoxy group is removed by hydrolysis during the production of the porous body, It is considered that the ratio of alkoxy groups in the porous body is decreased.

Example 2 In this example, a wet gel was prepared in the same manner as in Example 1, and then the obtained wet gel was immersed in methanol / water = 1/1 (weight ratio) for 1 day. After that, a porous body was prepared in the same manner as in Example 1. The density of the obtained porous body was 220 kg / m ³ , and the ratios of the number of methoxy groups and the number of trimethylsilyl groups to the number of silicon atoms were less than 1% and 11%, respectively. The thermal decomposition temperature of the organic silyl group was 340 ° C.

As described above, when the alkoxy group is hydrolyzed after the formation of the wet gel, even if the solvent used is methanol / water, the thermal decomposition temperature of the organic silyl group rises and the hydrophobicity is maintained up to a high temperature. I found out that This is considered to be because the hydrolysis of the methoxy group during the formation of the porous body favorably proceeded due to the large amount of water contained.

Example 3 and Comparative Example 2 In this example, a wet gel was prepared using tetraethoxysilane as a metal raw material as a metal alkoxide, and the wet gel was immersed in water-containing ethanol to obtain an ethoxy group on the surface of the wet gel. Was hydrolyzed. Next, acetone substitution and toluene substitution were carried out in that order, followed by hydrophobic treatment using hexamethyldisilazane as a silylating agent in toluene, followed by drying to obtain a porous body.

The specific operation is shown below.

As raw materials for the wet gel, tetraethoxysilane, water, ethanol, hydrogen chloride, and ammonia are used in a ratio of 1:
3.5: 4: 8 × 10 ⁻⁴ : 6 × 10 ⁻³ (molar ratio) was used. At this time, hydrogen chloride was used in the form of hydrochloric acid, and ammonia was used in the form of aqueous ammonia. First, tetraethoxysilane, water,
Ethanol and hydrochloric acid were mixed, and then aqueous ammonia and ethanol were added to cause gelation.

Further, the wet gel is mixed with 50 parts by weight of water.
%, The wet gel was first immersed in acetone to replace the liquid in the wet gel with acetone. Further, similarly, the liquid in the wet gel was replaced with toluene. Then, wet gel,
It was dipped in a 20 wt% toluene solution of hexamethyldisilazane and subjected to a hydrophobic treatment for 5 hours under reflux conditions. After that, the hydrogel-treated wet gel is immersed in liquefied carbon dioxide in a pressure vessel to replace the liquid in the wet gel with liquefied carbon dioxide, and then the temperature is raised to 50 ° C. and 10 MPa, and the pressure is increased to withstand pressure. The inside of the container was put into a supercritical state. Finally the temperature is 50 ℃
With the temperature kept at 1, the carbon dioxide was gradually released to reduce the pressure in the pressure vessel to the atmospheric pressure to complete the drying. The density of the obtained porous body was 130 kg / m ³ .

As a result of performing the same analysis as in Example 1, the ratio of the number of ethoxy groups and the number of trimethylsilyl groups in the obtained porous material to the number of silicon atoms was less than 1% in order,
It was 11%. The thermal decomposition temperature of the organic silyl group is 340
It was ℃. (Example 2) For comparison, a wet gel was formed in the same manner as in Example and then immersed in ethanol to replace the liquid in the wet gel with ethanol. After that, toluene replacement, hydrophobization, and drying were performed in the same manner as in the example. The ratio of the number of ethoxy groups and the number of trimethylsilyl groups in the obtained porous body to the number of silicon atoms is 10% in order,
It was 9%. The density of the porous body is 140 kg / m.
^3. The thermal decomposition temperature of the organic silyl group was 240 ° C. (Comparative Example 2).

As in the example, it was found that the thermal decomposition temperature of the organic silyl group rises irrespective of the gel raw material, the hydrophobizing agent and the drying method, and the hydrophobicity can be maintained at a high temperature.
It is considered that this is because the alkoxy groups in the porous body are reduced because the alkoxy groups are hydrolyzed during the production of the porous body.

[0066]

The porous material of the present invention is characterized by having an organic silyl group and almost no alkoxy group. Due to this structure, the hydrophobicity is maintained up to a high temperature.

The method for producing a porous body of the present invention is characterized by having a step of removing an alkoxy group in a wet gel by hydrolysis. Due to this constitution, a porous body having almost no alkoxy group is obtained. Therefore, there is an effect that it is possible to easily provide a porous body whose hydrophobicity can be maintained up to a high temperature.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazuhiko Hashimoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F term (reference) 4G072 AA28 BB15 CC10 GG01 GG03                       HH19 HH28 HH30 PP17 QQ07                       RR07 RR12                 4J030 CA02 CB17 CC16 CF02 CG16                       CG29                 4J035 AA01 AB01 AB02 AB06 LA03                       LB20

Claims (7)

[Claims] 1. A porous body having a skeleton composed of a metal oxide and having an organic silyl group on at least a part of the surface thereof, wherein the number of alkoxy groups contained is equal to that of the metal atoms of the metal oxide. A porous body characterized by being less than 5% with respect to the number. 2. The porous body according to claim 1, wherein the apparent density is in the range of 50 to 500 kg / m ³ . 3. The porous body according to claim 1, wherein the metal atom of the metal oxide forming the skeleton is a silicon atom. 4. The porous body according to claim 1, wherein the organic silyl group is a trimethylsilyl group. 5. The porous body according to claim 1, wherein the organic silyl group is a dimethylsilyl group. 6. The skeleton is composed of a metal oxide, has an organic silyl group on at least a part of the surface of the porous body, and the number of alkoxy groups contained is 5 with respect to the number of metal atoms of the metal oxide. % Of less than 100%, wherein (a) a step of hydrolyzing the alkoxy group by immersing a wet gel having an alkoxy group on the surface in a water-soluble solvent containing water, (b) A porous body comprising a step of dissolving a hydrophobizing agent and subjecting the wet gel to a hydrophobic treatment in a solvent containing no alcohol, and (c) a drying step of removing the solvent remaining in the gel. Manufacturing method. 7. The method for producing a porous body according to claim 6, wherein the wet gel having an alkoxy group on the surface is formed by a sol-gel method using a metal alkoxide as a raw material.