JP3431197B2 - Method for producing porous silica body by sol-gel method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous silica material by a sol-gel method, and more particularly, to a method for producing a porous material having a simple drying step and having cracks. The present invention relates to a method for producing a porous silica material which hardly occurs. 2. Description of the Related Art Conventionally, there is a sol-gel method as one of the methods for producing a glass capable of producing a high-purity product and capable of being synthesized at a low temperature. In order to produce a bulk body of silica glass (plate or bar) by the sol-gel method, first, a porous silica body is produced by the sol-gel method, and this is heated to produce a bulk body of nonporous silica glass. It has gained. In a method for producing a porous silica material by a sol-gel method, generally, alkoxysilane is hydrolyzed, and the generated silica sol is polycondensed to form a wet gel, which is dried to obtain a porous silica material. In this method for producing a porous silica material by the sol-gel method, in the step of drying a wet gel after gelation, volumetric shrinkage of the porous material occurs due to evaporation of a solvent, and cracks occur in the obtained porous material. There was a big problem that it was easy to do. For this reason, it was difficult to manufacture products having large dimensions. In order to solve such a problem, several methods have been proposed in recent years. As a typical method,
Slow drying by spending several weeks to several months while suppressing the evaporation rate of the solvent, adding silica fine powder to the raw material solution, widening the distribution range of the pore size of the gel, and reducing the shrinkage of the gel Method, a method of adding a drying inhibitor such as formamide, eliminating the gas-liquid interface existing in the wet gel, weakening the surface tension at the gas-liquid interface causing shrinkage and destruction of the gel network, and removing the solvent. There is a method of drying under supercritical conditions to remove them. Of these methods, the method of drying under supercritical conditions is also used as a method of producing a transparent porous silica material having fine silica particles and an extremely small gel pore size. [0004] However, the above-mentioned conventional techniques and the above-mentioned methods require a long period of production and are extremely poor in productivity. In addition, the above-mentioned prior art method has a problem in that an autoclave must be used to achieve the supercritical condition, and a large capital investment is required. [0005] Accordingly, an object of the present invention is to provide a sol which is less likely to crack in the obtained porous body, can be dried in a simple and short time, and can produce a large-sized porous body at low cost. -To provide a method for producing a porous silica material by a gel method. Means for Solving the Problems In the process of drying a gel, the force for generating cracks in the gel is gas-liquid-
This is a capillary force generated at the solid interface, and this capillary force is represented by the following formula (I). ΔP = 2γ cos θ / r (I) where ΔP is the capillary force, r is the pore radius of the gel, γ is the surface tension of the liquid filling the pores, and θ is the surface tension of the liquid filling the pores. It is the wetting angle. In order to suppress the generation of cracks in the gel in the drying step, besides making the gel soft, in addition to increasing r, ie, increasing the pore radius of the gel, smaller, i.e., lower the surface tension of the liquid meets the pores, small and cosθ
To fence, that is, poor wetting of the liquid meets the gel and pores, it is considered effective. Therefore, as a result of diligent study of the above-described measures, trifunctional alkoxysilane or a polycondensate thereof (hereinafter, sometimes simply referred to as "alkoxysilane" including a polycondensate of alkoxysilane) is used as alkoxysilane. Has been found to be the most effective means for preventing the occurrence of cracks in the gel in the drying step. By using a trifunctional alkoxysilane or a polycondensate thereof, the development of a three-dimensional network structure is partially inhibited as compared with the case of using a conventionally used tetrafunctional alkoxysilane or a polycondensate thereof. It is considered that the gel can provide flexibility and increase the pore radius of the gel. That is, even when a trifunctional alkoxysilane or a polycondensate thereof is used, each functional group does not completely react, and partially gels in an unreacted state to form a chain portion in the gel. It is possible to impart flexibility to the gel. Furthermore, the gel can be made hydrophobic because an alkyl group is introduced into the gel skeleton. As described above, by using a trifunctional alkoxysilane or a polycondensate thereof which is extremely effective in preventing the occurrence of cracks in a gel, a conventional drying method which requires a long time or a drying method under supercritical drying conditions can be used. It is not necessary to use it, and a method by air drying or heat drying which can be performed in a short time with simple equipment as a method for drying a wet gel is extremely advantageous. Therefore, in order to solve the above-mentioned problems, a method for producing a porous silica material by a sol-gel method according to the present invention comprises:
A trifunctional alkoxysilane represented by the following general formula (I) or
Hydrolyzes the polycondensate of the trifunctional alkoxysilane
As a silica sol, the silica sol was allowed to stand and gelled
Then, dried by air drying or heat drying to obtain a porous silica material
Gaining . Embedded image (Wherein, R ¹ and R ² each represent the same or different alkyl group having 1 to 5 carbon atoms or phenyl group, and n represents 1 to 1
Represents an integer of 0. In the general formula (I), R ¹ and R ² may be the same or different and specific examples include a methyl group, an ethyl group, a propyl group, a butyl group and a phenyl group. Since it is considered that the reaction tends to be slow when the number of carbon atoms is large, a methyl group or an ethyl group is preferable. Further, a preferable range of n is an integer of 1 to 6. Specific examples of the trifunctional alkoxysilane of the general formula (I) or a polycondensate of the trifunctional alkoxysilane include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, Examples include, but are not limited to, phenyltrimethoxysilane, phenyltriethoxysilane, or polycondensates thereof. In addition, it is easy to obtain the desired three-dimensional network structure by controlling the hydrolysis and the polycondensation reaction when these trifunctional alkoxysilanes or polycondensates of the trifunctional alkoxysilanes are used alone. However, in some cases, a mixture of different types can be used. When a bifunctional alkoxysilane or a polycondensate thereof is used in place of a trifunctional alkoxysilane or a polycondensate thereof as the alkoxysilane, a three-dimensional network structure is not formed, so that it is difficult to gel, while When an alkoxysilane or a polycondensate thereof is used, a three-dimensional network structure is formed too densely, so that it is difficult to impart flexibility to the gel, and cracks are easily generated in the gel. In addition, it is also possible to arbitrarily combine two or more selected from bifunctional alkoxysilanes or polycondensates thereof, trifunctional alkoxysilanes or polycondensates thereof, and tetrafunctional alkoxysilanes or polycondensates thereof. However, as the reaction rate tends to increase as the number of functional groups increases, when using a mixture of alkoxysilanes having different numbers of functional groups, the alkoxysilane having a smaller number of functional groups remains in the gel without reacting, It is difficult to obtain a desired three-dimensional network structure because the effect of mixing the alkoxysilane hardly appears, or reaction conditions and the like must be strictly controlled to obtain a desired three-dimensional network structure. Therefore, it is extremely important to use a trifunctional alkoxysilane or a polycondensate thereof, which does not have such a problem and can easily control the reaction conditions. In the hydrolysis and polycondensation of the alkoxysilane of the general formula (I) or the polycondensate thereof, the hydrolysis is represented by the following reaction formula (II), and the polycondensation is represented by the following reaction formula (III). Embedded image Embedded image In the above reaction formulas (II) and (III), R ¹ , R ²
And n are the same as described above. These reaction equations are based on the case where the stoichiometric reaction is completed, but in practice, S
Each functional group attached to i does not completely react,
The gel grows in a partially unreacted state. An alcohol is used as a solvent in the hydrolysis and polycondensation reaction of the alkoxysilane or the polycondensate thereof, and a catalyst for the hydrolysis and polycondensation reaction is
An acid catalyst and a base catalyst are used. Examples of the acid catalyst include hydrochloric acid and ammonium fluoride, and examples of the base catalyst include ammonia and piperidine, but are not particularly limited thereto. The ratio of the alkoxysilane or its polycondensate, water, solvent, catalyst and the like is not particularly limited, and may be appropriately set so as to obtain a porous body having a desired network structure. In the present invention, air drying or heat drying is used as a method for drying a gel obtained by hydrolyzing the above alkoxysilane or its polycondensate to form a silica sol, gelling the silica sol and then drying the gel. The heat drying method is preferable because the drying step is completed in a shorter time than air drying. As the drying conditions by heating and drying, it is preferable to employ a method of removing excess water after drying at a temperature equal to or lower than the boiling point of the solvent. As other drying methods, a freeze drying method, a vacuum drying method, a supercritical drying method, or the like can be considered, but it is not preferable because the equipment required for drying becomes large-scale. In the method for producing a porous silica material by a sol-gel method, the alkoxysilane is represented by the above general formula (I)
By using a trifunctional alkoxysilane represented by or a polycondensate thereof and performing air drying or heat drying as a method for drying the gel, the porous body obtained is hardly cracked, and the drying step is simple and short. Time
An inexpensive porous silica material can be manufactured. The following examples are provided to further illustrate the present invention. These examples illustrate the present invention by way of example and do not limit the present invention. Example 1 In a 1- liter beaker, 132 g of methyltrimethoxysilane (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 384 g of methanol (special-grade reagent manufactured by Kanto Chemical Co., Ltd.) and 108 g of a 3 mol / l aqueous ammonia solution were added. The molar ratio of methyltrimethoxysilane: methanol: aqueous ammonia solution is
1: 12: 6) and stirred at room temperature for 10 minutes. The obtained sol solution was poured into a glass container having an inner diameter of 200 mm and a depth of 50 mm, and allowed to stand in a sealed state for 24 hours to obtain a white wet gel body having a diameter of 194 mm and a thickness of 23 mm. Remove the lid and set at 60 ° C for 2
After drying for 4 hours, drying at 105 ° C. for 24 hours, a diameter of 188
mm, thickness 22 mm, density 0.11 g / cm ³ , porosity 95
%, And a white porous body having a thermal conductivity of 0.026 kcal / mh ° C. Example 2 In a 1-liter beaker, 178 g of methyltriethoxysilane (reagent manufactured by Tokyo Chemical Industry Co., Ltd.), 368 g of ethanol (special-grade reagent manufactured by Kanto Chemical Co., Ltd.), 0.5 mol / l hydrochloric acid 1
08 g (in this case, methyltriethoxysilane:
The molar ratio of ethanol: hydrochloric acid is 1: 8: 6) and 1 at room temperature.
Stirred for 0 minutes. The obtained sol solution was poured into a glass container having an inner diameter of 200 mm and a depth of 50 mm, and was allowed to stand in a sealed state for 24 hours to obtain a white wet gel body having a diameter of 192 mm and a thickness of 24 mm. After taking off the lid and drying at 60 ° C. for 24 hours, drying at 105 ° C. for 24 hours, the diameter is 184 mm, the thickness is 23 mm, and the density is 0.
12g / cm ³ , porosity 94%, thermal conductivity 0.027kcal
A white porous body having a temperature of / mh ° C was obtained. Example 3 In a 1 l beaker, 102 g of a polycondensate of methyltrimethoxysilane (manufactured by Colcoat Co., Ltd., trade name: MTMSP-1, average degree of polymerization n = 4), methanol (special grade reagent manufactured by Kanto Chemical Co., Ltd.) 480 g of a 9 mol / l aqueous ammonia solution (54 g) was taken (in this case, the molar ratio of polycondensate of methyltrimethoxysilane: methanol: aqueous ammonia solution was 1:60:12), and the mixture was stirred at room temperature for 10 minutes. The obtained sol solution was poured into a glass container having an inner diameter of 200 mm and a depth of 50 mm, and was allowed to stand in a sealed state for 24 hours.
A white wet gel having a thickness of 23 mm and a thickness of 23 mm was obtained. Remove the lid 60
After drying at 105 ° C for 24 hours, drying at 105 ° C for 24 hours, a white porous material having a diameter of 180 mm, a thickness of 22 mm, a density of 0.12 g / cm ³ , a porosity of 94%, and a thermal conductivity of 0.027 kcal / mh ° C I got COMPARATIVE EXAMPLE 1 In Example 1, 152 g of tetramethoxysilane (a reagent manufactured by Tokyo Chemical Industry Co., Ltd.) was used instead of methyltrimethoxysilane, and 108 g of a 0.1 mol / l aqueous ammonia solution was used instead of a 3 mol / l aqueous ammonia solution. (In this case, the molar ratio of tetramethoxysilane: methanol: aqueous ammonia solution is 1: 8: 6) in the same manner as in Example 1 to obtain a colorless transparent wet gel having a diameter of 190 mm and a thickness of 21 mm. Was. When the lid was taken off and the gel body was air-dried, a crack was formed in a few hours, and after several days, it was crushed and fragmented. Comparative Example 2 In Example 3, 118 g of a polycondensate of tetramethoxysilane (trade name: methyl silicate 51, average polymerization degree n = 4, manufactured by Colcoat Co., Ltd.) instead of the polycondensate of methyltrimethoxysilane 54 g of a 0.3 mol / l aqueous ammonia solution was used instead of the 9 mol / l aqueous ammonia solution (in this case, the molar ratio of the polycondensate of tetramethoxysilane: methanol: aqueous ammonia solution was 1: 60: 1).
A colorless transparent wet gel having a diameter of 188 mm and a thickness of 23 mm was obtained in the same manner as in Example 3 except for 2). When the lid was taken off and the gel body was air-dried, a crack was formed in a few hours, and after several days, it was crushed and fragmented. According to the method for producing a porous silica material by the sol-gel method according to the present invention, a predetermined trifunctional alkoxysilane or a polycondensate thereof is used as an alkoxysilane, and a method for drying a gel is used. Since air drying or heat drying is performed as described above, cracks are less likely to occur in the obtained porous body, and a large-sized porous body can be manufactured with simple equipment in a short time. The obtained porous body is lightweight, has low thermal conductivity, is excellent in water resistance or moisture resistance, and can be used for various uses such as a heat insulating material and a sound absorbing material.

Continuation of the front page (56) References JP-A-2-172830 (JP, A) JP-A-62-279840 (JP, A) JP-A-62-223029 (JP, A) JP-A-62-278106 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 33/12 C03B 8/02

Claims (1)

(57) [Claims 1] Trifunctional alcohol represented by the following general formula (I)
Xysilane or a polycondensate of the trifunctional alkoxysilane
Hydrolyze to silica sol, and leave the silica sol to stand
After gelation, dry by air drying or heat drying
A method for producing a porous silica material by a sol-gel method, comprising obtaining a porous material. Embedded image (Wherein, R ¹ and R ² each represent the same or different alkyl group having 1 to 5 carbon atoms or phenyl group, and n represents 1 to 1
Represents an integer of 0. )