JP4980864B2 - Method for producing porous ceramics - Google Patents

Description

  The present invention relates to a porous ceramic and a manufacturing method thereof, and more particularly to a porous ceramic having macropores and mesopores and a manufacturing method thereof.

  Conventionally, in the field of adsorbent materials or reaction catalyst materials, porous bodies having a wide reaction field (area) within a small volume have been developed. However, when flowing a fluid through the porous body, increasing the specific surface area of the porous body decreases the pore diameter and increases the pressure loss. In this case, some holes will not function. In order to reduce the pressure loss, it is necessary to increase the pore diameter. In this case, however, the proportion of the surface area that becomes the reaction field decreases. Therefore, when designing a porous body, it was necessary to balance the specific surface area and the pore diameter according to the intended use. Under such a background, a porous body having macropores (through pores) for flowing a fluid and mesopores (mesopores) functioning as a reaction field has been proposed. .

  Japanese Patent Application Laid-Open No. 11-287791 discloses a capillary column in which a silica gel having a double pore structure is formed in a capillary having an inner diameter of 1000 μm or less. This silica gel has pores (through pores) having a pore diameter of 0.5 to 5 μm and pores (mesopores) having a pore diameter of 2 to 50 nm.

  The capillary column is manufactured as follows. First, a compound that can be thermally decomposed is dissolved in the reaction solution in advance. Then, a gel composed of a solvent-rich phase rich in a solvent and a skeleton phase rich in an inorganic substance and having pores on the surface is prepared in a capillary having an inner diameter of 1 mm or less by a sol-gel method. Next, the gel in a wet state is heated to thermally decompose the compound, and then the gel is dried and then heated to produce a capillary column.

In Japanese Patent Application Laid-Open No. 11-287791, it is preferable to use silica (SiO ₂ ) as an inorganic substance and to use an amide-based compound such as urea whose liquidity is changed to basic by thermal decomposition as a compound to be thermally decomposed. The effect is described.

  Japanese Patent Laid-Open No. 11-287791 discloses the following method as another method for producing a capillary column. First, a water-soluble polymer and a thermally decomposable compound (low molecular compound) are dissolved in an acidic aqueous solution, and then a metal compound having a hydrolyzable functional group is added to the acidic aqueous solution. Thereby, a hydrolysis reaction is performed in an acidic aqueous solution, and the product is solidified in a capillary having an inner diameter of 1 mm or less. Next, the low molecular weight compound previously dissolved in the acidic aqueous solution at the time of gel preparation is thermally decomposed by heating the wet gel. Next, after the gel is dried, it is heated to produce a capillary column.

Japanese Patent Application Laid-Open No. 2005-290032 discloses a method for producing an inorganic porous body having macropores in addition to mesopores. In this method for producing an inorganic porous material, first, an amphiphile as a template component is dissolved in an aqueous solution containing a sol-gel reaction catalyst component, and an inorganic low molecular compound having a hydrolyzable functional group is added to the above-mentioned method. Add to aqueous solution to cause sol-gel reaction. By this reaction, a gel composed of a solvent-rich phase rich in a solvent and a skeleton phase rich in an inorganic oxide polymer produced from the inorganic low molecular weight compound is formed. The inorganic oxide polymer is fixed to the surface of an amphiphilic substance that is a template component. Next, the solvent is removed from the gel by drying to form macropores, and the template component is removed from the dried gel by thermal decomposition or extraction to form mesopores in the skeleton phase.
JP-A-11-287791 JP 2005-290032 A

  According to the methods described in JP-A-11-287791 and JP-A-2005-290032, a porous material having pressure loss reduced by the presence of macropores and a wide reaction field due to the presence of mesopores is obtained. can get.

  However, in the method described in JP-A-11-287791, a porous body is obtained by filling a reaction solution into a capillary tube having an inner diameter of 1 mm or less, so that the degree of freedom of the form of the porous body is small.

  In the method described in Japanese Patent Application Laid-Open No. 2005-290032, mesopores are formed by removing a template component from a gel having a relatively brittle structure, so the degree of freedom of the form of the inorganic porous material is small.

  As described above, a method for easily producing a porous body having two types of hole groups having a large degree of freedom in form and different pore diameters has not yet been disclosed.

  Therefore, the present invention provides a production method and a porous ceramic that can easily produce a porous ceramic having two types of hole groups having a large degree of freedom in form and different pore diameters.

  The method for producing porous ceramics according to the present invention includes forming a mixture obtained by mixing particles containing at least silica, a flammable resin, and a plasticizer into a predetermined shape, and then from the mixture. The plasticizer is extracted to obtain a porous green molded body, and then the porous green molded body is impregnated with a sintering aid-containing liquid containing a sintering aid, and the sintering assistant-containing liquid is impregnated. A porous substrate comprising a porous substrate forming step of firing the porous green molded body to obtain a porous substrate by burning out the resin, and a porous film comprising a metal alkoxide, a catalyst, a surfactant, and water After impregnating the porous base material with a forming solution to form a coating film partially entering the pores of the porous base material on the porous base material, baking the coating film Forming a porous film by a porous film forming step No.

  The porous ceramic of the present invention comprises at least silica and comprises a porous substrate having pores and an inorganic oxide, and is formed on the porous substrate, a part of which is the porous substrate. And a porous film having a hole smaller in diameter than the hole of the porous substrate.

  In the method for producing porous silica ceramics according to the present invention, porous ceramics having two types of hole groups having a large degree of freedom in form and different pore diameters can be easily produced. The porous ceramic of the present invention includes a porous substrate and a porous film having pores (for example, mesopores) having a diameter smaller than the pores (for example, macropores) of the porous substrate. . For this reason, in the holes of the porous base material having a relatively large pore diameter, a fluid such as liquid or gas can easily pass through, and the pores of the porous film having a relatively small pore diameter have a large specific surface area, which can be a wide reaction field. Therefore, the porous ceramic of the present invention can be used as, for example, a column filler for a chromatograph, a sensor, or a carrier.

  The present inventors have prepared a porous substrate that can be impregnated with a solution for forming a porous film (so-called sol-gel solution) containing a metal alkoxide, a catalyst, a surfactant, and water and that has pores (for example, macropores). Then, using the above-mentioned solution for forming a porous film, after forming a coating film partially entering the pores of the porous substrate on the porous substrate, the coating film is baked to make the porous By forming a porous film having pores (for example, mesopores) having a pore diameter smaller than the above-mentioned pores of the base material, a porous ceramic having two types of hole groups having a large degree of freedom and different pore diameters is obtained. I found out that

  That is, in the method for producing porous ceramics of the present invention, first, a porous green molded body is obtained. Next, the porous green molded body is impregnated with a sintering auxiliary agent-containing liquid, and the porous green molded body impregnated with the sintering auxiliary agent-containing liquid is fired to burn out the resin, To obtain (porous substrate forming step). The surface of the porous substrate is easily impregnated with the solution for forming a porous film by using a sintering aid-containing liquid containing a predetermined sintering aid.

  Thereafter, a coating film is formed on the surface of the porous substrate using a porous film forming solution containing a metal alkoxide, a catalyst, a surfactant, and water. Next, the coating film is baked to form a porous film, part of which has entered the pores of the porous substrate, on the porous substrate (porous film forming step).

  In the present invention, “macropores” and “mesopores” are defined by IUPAC. That is, macropores are pores having a diameter of 50 nm or more, and mesopores are pores having a diameter of more than 2 nm and less than 50 nm.

  The form of the porous ceramic of the present invention is not particularly limited. That is, the porous ceramics may be a powder or a sheet. If the porous ceramic is a powder, it can be used by filling the column with a porous ceramic, and if the porous ceramic is a sheet, it can be used as a filter or a separator. The porous membrane may be formed, for example, so as to completely cover the porous substrate. For example, when the porous substrate is in the form of a sheet, It may be formed only on one main surface and / or on both main surfaces.

  Next, the porous substrate forming step, which is the first step constituting the method for producing porous ceramics, will be described.

[Porous green compact]
The porous green molded body is obtained by molding a mixture obtained by mixing particles containing at least silica, a flammable resin, and a plasticizer into a predetermined shape, and then, for example, It can be obtained by extracting a plasticizer using an organic solvent or the like. Examples of the organic solvent include trichloroethylene and tribromoethylene. Only one type of organic solvent may be used, or two or more types may be used. Examples of extraction methods include immersion extraction, boiling extraction, and reduced pressure extraction.

  It is preferable that the porous green molded body has thermoplasticity because it can be easily processed into various shapes such as a sheet shape, a fiber shape or a bead shape. For example, when the shape of the porous green molded body is a sheet shape, it can be freely shaped by folding or stacking as in the case of ceramic paper used for ceramics. Further, by pressing a sheet-like porous green molded body, it can be embossed or three-dimensionally molded as well as being corrugated.

(Silica particles)
The silica particles constituting the porous green molded body may be particles composed solely of silica or particles comprising silica as a main component. In the present specification, both may be collectively referred to as silica particles. Since silica easily forms a network structure, it is suitable for forming a porous green molded body. The average secondary particle diameter of the silica particles is not particularly limited as long as the mixing with the plasticizer and the resin is performed well.

(resin)
Examples of the resin include polyethylene, polypropylene, polystyrene, methacrylic resin, vinyl chloride resin, polyamide, polyacetal, polybutylene terephthalate, glass fiber reinforced polyethylene terephthalate, polymethylpentene, polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyether ether ketone. , Thermoplastic resins such as polytetrafluoroethylene, polyetherimide, polyarylate, polysulfone, polyethersulfone, and polyamideimide. These resins may be used alone or in combination of two or more. Moreover, if the shape is powder and a pellet, it will be used preferably.

  Among the above resins, those having a molecular weight exceeding several hundreds of thousands are preferable because they facilitate molding into a sheet shape, for example. In particular, polyethylene having a molecular weight of 1,000,000 or more is preferable because moldability is better.

(Plasticizer)
As the plasticizer, turbine oil, paraffinic mineral oil (petroleum hydrocarbon), or the like can be used. In particular, when the mixture is molded by an extrusion method, heating is involved, and therefore, heavy oils that are less likely to volatilize or ignite are preferred. Paraffin mineral oil is preferable because it easily dissolves the resin. In addition, phthalic acid esters (butyl phthalate, dioctyl phthalate), adipic acid esters, phosphoric acid esters, trimellitic acid esters, citric acid esters, and the like can also be used as plasticizers.

  The mixture may contain a hydrophilicity imparting agent in order to impart hydrophilicity to the porous green molded body. It is preferable for the mixture to contain a hydrophilicity-imparting agent because the sintering aid-containing liquid is easily impregnated into the porous green molded body. Examples of the hydrophilicity-imparting agent include anionic hydrophilicity-imparting agents such as alkylsulfosuccinate and naphthalenesulfonate formalin condensate, and nonionic hydrophilicity-imparting agents such as polyoxyethylene alkyl ether. These hydrophilicity-imparting agents may be used alone or in combination of two or more.

  Instead of being added to the mixture or in addition to being added to the mixture, the hydrophilicity imparting agent is added to the porous green molded body obtained by extracting the plasticizer from the molded product of the mixture. It may be coated. Coating can be performed by methods such as dipping, spray coating, flow coating, and spin coating, for example.

  The pore diameter of the porous substrate can be controlled by adjusting the mass ratio of silica particles, combustible resin, and plasticizer, which is the main component of the mixture. A preferable range of each mass ratio of the silica particles, the combustible resin, and the plasticizer in the mixture varies depending on the size of the silica particles and / or the resin. For example, the mass ratio of silica particles in the mixture is preferably 20 to 50% by mass because the mixture can be kneaded more favorably and a porous substrate having more appropriate strength can be formed. Moreover, the mass ratio of the resin in the mixture is preferably 10 to 50% by mass because silica particles can be more suitably dispersed and a porous green molded body with better shape stability can be formed. Further, the content of the plasticizer in the mixture is preferably 15 to 60% by mass because the porous green molded body can be more favorably molded.

(Impregnation into porous green molded body of liquid containing sintering aid)
There are voids in the porous green molded body obtained by extracting the plasticizer from the molded product of the mixture. The porous green molded body is impregnated with the sintering aid-containing liquid so that the sintering aid-containing liquid enters the voids. When the porous green molded body impregnated with the sintering aid-containing liquid is fired, the sintering aid in contact with the silica particles acts as a flux, and the resin is burned out.

  Therefore, if the amount of impregnation of the sintering aid-containing liquid, that is, the amount of impregnation of the sintering aid is changed for each part of the porous green molded body, the diameter (pore diameter) of the pores (for example, macropores) It can be changed for each part. This change in hole diameter can be performed stepwise or continuously.

  Changing the amount of impregnation of the sintering aid-containing liquid means that, for example, when the sintering aid is supplied by water glass described later, water glass having a different dilution ratio is used as the sintering aid-containing liquid, and the porous green This can be realized by impregnating each part of the molded body.

(Sintering aid containing liquid)
The sintering aid used in the method for producing porous ceramics of the present invention has a function of lowering the melting point of silica particles. The sintering aid-containing liquid is selected from the group consisting of an alkali metal-containing compound, an alkaline earth metal-containing compound, a phosphorus-containing compound, and a boron-containing compound, for example, because the diffusion rate into the silica particles is fast. It is preferable that at least one inorganic material is included as a sintering aid. Among these sintering aids, the diffusion rate into the silica particles is faster and the effect as a sintering aid is high. When the alkali metal-containing compound is contained in the sintering aid-containing liquid, preferable.

  The pH of the surface of the porous substrate can be controlled by adjusting the type and amount of the sintering aid contained in the sintering aid-containing liquid.

  The pH of the surface of the porous substrate used in the method for producing porous ceramics of the present invention is preferably controlled to 8 or less. When controlled in this way, the speed of the sol-gel reaction is moderately suppressed, and not only on the surface of the porous substrate, but also on the surface of the pores communicating from the surface to the inside. This is preferred because the solution is impregnated. The lower limit of pH is not particularly limited as long as a coating film can be formed on the surface of the porous substrate.

  When an alkali metal-containing compound or an alkaline earth metal-containing compound is used as a sintering aid, the pH of the surface of the porous substrate changes to the alkaline side. On the other hand, when a phosphorus-containing compound or a boron-containing compound is used, the pH of the surface of the porous substrate changes to the acidic side. As the amount of sintering aid added increases, the change in surface pH also increases.

  When the sintering aid is a substance soluble in water, if the sintering aid-containing liquid is an aqueous solution containing a sintering aid and water, the sintering aid-containing liquid is a porous green molded body. It is preferable because it is easy to be impregnated. When the sintering aid is a compound soluble in alcohol, the sintering aid-containing liquid may be an alcohol solution.

  The alkali metal-containing compound serves as a network-modifying oxide for the network structure formed by the silica particles, and has a function of reducing the viscosity of the silica and promoting melting. Examples of the alkali metal include Na, K, and Li. Such an alkali metal-containing compound may be any compound of chloride, hydroxide, acetate, sulfate, carbonate or nitrate because it is easily dissolved in a solvent such as water and a solution is easily obtained. Preferably there is.

  Specific examples of the alkali metal-containing compound include sodium oxide, sodium chloride, sodium hydroxide, sodium acetate, sodium sulfate, sodium carbonate, sodium hydrogen carbonate, sodium nitrate, potassium chloride, potassium hydroxide, potassium acetate, and potassium sulfate. , Potassium carbonate, potassium nitrate, lithium chloride, lithium hydroxide, lithium acetate, lithium sulfate, lithium carbonate, lithium nitrate and the like. As a supply source of the alkali metal-containing compound, for example, water glass containing sodium oxide may be used.

  The alkaline earth metal-containing compound becomes a network-modified oxide with respect to the network structure formed by the silica particles, and has a function of reducing the viscosity of silica and promoting melting. Examples of the alkaline earth metal include Mg, Ca, Sr, and Ba. As such an alkaline earth metal-containing compound, any one of chloride, hydroxide, acetate, sulfate, carbonate or nitrate can be obtained because it is easily dissolved in a solvent such as water and a solution is easily obtained. A compound is preferred.

  Specific examples of the alkaline earth metal-containing compound include magnesium chloride, magnesium hydroxide, magnesium acetate, magnesium sulfate, magnesium carbonate, magnesium nitrate, calcium chloride, calcium hydroxide, calcium acetate, calcium sulfate, calcium carbonate (limestone ), Calcium nitrate, strontium chloride, strontium hydroxide, strontium acetate, strontium sulfate, strontium carbonate, strontium nitrate, barium chloride, barium hydroxide, barium acetate, barium sulfate, barium carbonate, barium nitrate.

  The boron-containing compound and the phosphorus-containing compound also serve as a network-modified oxide with respect to the network structure formed by the silica particles, and have a function of reducing the viscosity of the silica and promoting melting. As the boron-containing compound, boric acid and / or borax are preferable because they are easily dissolved in a solvent such as water and easily formed into a solution. As the phosphorus-containing compound, at least one selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid and peroxophosphoric acid is preferable because it is easily dissolved in a solvent such as water and is easy to form a solution.

  As described above, according to the porous substrate forming step described above, it is possible to manufacture a mesh-like porous substrate with a small variation in pore diameter. The thickness of the network skeleton, the pore diameter, the pH of the porous substrate surface, and the like can be controlled by the type and amount of the sintering aid impregnated in the porous green molded body.

  In addition to the sintering aid, the sintering aid-containing liquid preferably further contains a surfactant in order to improve the permeability of the sintering aid-containing liquid into the porous green molded body. . Although there is no restriction | limiting in particular about the specific example of surfactant, For example, polyoxylene alkyl ether, polyoxylene ethylene distyrenated phenyl ether, acetylene glycol, polyoxyethylene polyoxypropylene glycol etc. are mentioned.

(Baking temperature)
The firing temperature (firing temperature) performed in the porous substrate forming step is slightly different depending on the concentration of the sintering aid, but is preferably 1000 ° C. or less, more preferably 700 ° C. to 1000 ° C., and still more preferably 700. ° C to 900 ° C. The firing temperature is the temperature of the atmosphere in which the porous green molded body is fired. The firing time is appropriately selected according to the firing temperature.

  The specific surface area of the porous substrate can be controlled by changing the firing conditions such as the firing temperature and the firing time.

  Next, the porous film forming step, which is the second step constituting the method for producing porous ceramics, will be described.

(Preparation of a solution for forming a porous film)
A solution for forming a porous film is obtained by dissolving a surfactant in a catalyst-containing solvent obtained by mixing water, a catalyst, and, if necessary, an alcohol solvent (a solvent containing alcohol as a main component). Thereafter, it is obtained by adding a metal alkoxide.

  The mass ratio of each component varies depending on the type of metal alkoxide and the like. For example, when the metal alkoxide is a silicon alkoxide, for example, silicon alkoxide: water: alcohol solvent: catalyst: surfactant = 1: (0 .3 to 1): (0.5 to 5): (0.02 to 0.1): (0.05 to 0.5). With such a solution for forming a porous film, the micelle diameter of the surfactant, the rate of hydrolysis reaction of the silicon alkoxide, the drying rate and the firing rate of the coating film can be controlled within a predetermined range.

  By changing the mass ratio of the metal alkoxide and the surfactant in the solution for forming the porous film, the porosity of the porous film can be changed. For example, the porosity is increased by increasing the surfactant (pore forming component) relative to the metal alkoxide (skeleton component).

  By changing the ratio of the total mass of the metal alkoxide and the surfactant to the total mass of the porous film forming solution, the viscosity of the porous film forming solution is changed, and the thickness of the coating film is changed. Can do.

  Examples of the metal alkoxide include silicon alkoxide, aluminum alkoxide, titanium alkoxide, and zirconium alkoxide. These metal alkoxides may be used alone or in combination of two or more. Also, the smaller the difference in the expansion coefficient between the porous membrane and the porous substrate, the better the adhesion between the porous membrane and the porous substrate, so that the metal alkoxide constitutes the silica of the porous substrate. A silicon alkoxide containing Si element is preferable.

  Examples of the silicon alkoxide include tetramethoxysilane, tetraethoxysilane, tetrabutoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltributoxysilane, tetrachlorosilane, and methyltrichlorosilane. These silicon alkoxides may be used alone or in combination of two or more.

  As the catalyst contained in the porous film forming solution, hydrochloric acid, sulfuric acid, catalytic nitric acid, formic acid, acetic acid, citric acid, phosphoric acid, methacrylic acid, and the like can be used. These catalysts may be used alone or in combination of two or more.

  The solution for forming a porous film contains water, and may further contain an alcohol solvent as described above. Examples of the alcohol contained in the alcohol solvent include primary alcohols such as ethanol, methanol, and propanol, cyclic alcohols such as benzyl alcohol, furfuryl alcohol, and tetrahydroxyfurfuryl alcohol, diethylene glycol, triethylene glycol, propylene glycol, and ethylene. Glycols such as glycol ethyl ether can be used. These alcohols may be used alone or in combination of two or more.

  As the surfactant contained in the porous film forming solution, aliphatic quaternary ammonium salts, aliphatic amine salts, alkyl sulfates, nonionic surfactants, and the like can be used. These surfactants may be used alone or in combination of two or more. With such a surfactant, it is possible to produce a porous thin film having mesopores having a pore diameter of more than 2 nm and less than 50 nm and a small variation in pore diameter.

  Aliphatic quaternary ammonium salts include long-chain alkylammonium halides such as hexadecyltrimethylammonium bromide, octadecyltrimethylammonium bromide, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, hexadecylmethylethylammonium bromide, etc. Examples include salt. Examples of the aliphatic amine salt include hexadecylamine, and examples of the alkyl sulfate include sodium dodecyl sulfate.

  Examples of the nonionic surfactant include a triblock polymer type nonionic surfactant having a structure having a propylene oxide (PO) chain or a butylene oxide (BO) chain between two ethylene oxide (EO) chains. It is preferable because the uniformity of the mesopore diameter is increased. Specifically, a triblock polymer having the following EO-PO-EO structure sold by BASF or ADEKA is preferable as the surfactant.

As a triblock polymer type nonionic surfactant,
"Pluronic" (registered trademark) L series: L31 (EO ₂ PO ₁₅ EO ₂ ), L34 (EO ₇ PO ₁₅ EO ₇ ), L44 (EO ₁₀ PO ₂₀ EO ₁₀ ), L61 (EO ₃ PO ₃₀ EO ₃ ) , L44 (EO ₁₀ PO ₂₀ EO ₁₀ ), L62 (EO ₆ PO ₃₀ EO ₆ ), L64 (EO ₁₃ PO ₃₀ EO ₁₃ ), L71 (EO ₃ PO ₃₅ EO ₃ ), L72 (EO ₉ PO ₃₅ EO ₉ ) , L101 (EO ₆ PO ₅₀ EO ₆ ), L121 (EO ₇ PO ₆₀ EO ₇ ),
"Pluronic" (registered trademark) P series: P65 (EO ₂₀ PO ₃₀ EO ₂₀ ), P84 (EO ₂₀ PO ₄₀ EO ₂₀ ), P85 (EO ₂₅ PO ₄₀ EO ₂₅ ), P103 (EO ₂₀ PO ₅₀ EO ₂₀ ) , P105 (EO ₃₇ PO ₄₀ EO ₃₇ ), P65 (EO ₂₀ PO ₃₀ EO ₂₀ ), P123 (EO ₂₀ PO ₇₀ EO ₂₀ ),
"Pluronic" (registered trademark) F series: F68 (EO ₈₀ PO ₃₀ EO ₈₀ ) P65 (EO ₂₀ PO ₃₀ EO ₂₀ ), F108 (EO ₁₄₁ PO ₁₀₆ EO ₁₄₁ ), F127 (EO ₁₀₆ PO ₇₀ EO ₁₀₆ ), Etc.

  The solid content (silica component) content in the solution for forming a porous film is preferably 3 to 30% by mass in order to form a coating film in which the occurrence of cracks during drying is suppressed.

  The content ratio of the surfactant in the solution for forming the porous film is 30 with respect to 100 parts by mass of the inorganic component derived from the metal alkoxide because it suppresses the occurrence of lamellar cracks when the coating film is dried. It is preferable that it is -300 mass parts.

  The solution for forming a porous film is preferably used after being made into a liquid containing a partial polymer of metal alkoxide, for example, by stirring at a predetermined temperature for a predetermined time. In this case, the coating property of the solution for forming a porous film becomes good, and a coating film can be formed on the porous substrate with good uniformity. When the metal alkoxide is, for example, silicon alkoxide, it is stirred at 25 ° C. to 60 ° C. for 30 minutes to 24 hours. In addition, the partial polymer of a metal alkoxide is a polymer obtained by a hydrolysis reaction and a condensation reaction, and a part of the alkoxyl group (—O—R) and / or hydroxyl group (—OH) remains unreacted. It means the remaining polymer.

(Formation of porous film)
In order to obtain a porous film, first, a coating film is formed on a porous substrate using a porous film forming solution. The method for forming the coating film is not particularly limited, and a spin coating method, a flow coating method, a dip method, a spray method, or the like can be employed.

  Subsequently, the water | moisture content and alcohol solvent in a coating film are volatilized. For the purpose of promoting the dehydration condensation reaction in the coating film, the coating film may be dried before firing the coating film. Although there is no restriction | limiting in particular about the drying method, For example, what is necessary is just to leave 5 minutes-48 hours for the porous base material with which the coating film was formed in the atmosphere of 25 to 60 degreeC.

  Although there is no particular limitation on the thickness of the coating film, it suppresses the generation of cracks during drying of the coating film, and the pores of the porous substrate on which the coating film is formed are completely filled with the porous film forming solution. In order to suppress this, it is preferably 1 μm or less.

(Firing coating)
Subsequently, the coating film is baked. During the firing process, the surfactant contained in the coating film is decomposed. Due to the decomposition of the surfactant, pores (for example, mesopores) whose pore diameter is smaller than the pores of the porous substrate are formed at the locations where the surfactant was present. As a result, a porous membrane having periodicity, made of silica and having a high uniformity of pore diameter can be obtained. Firing is preferably performed, for example, in an atmosphere of 350 ° C. to 600 ° C. for 5 minutes to 2 hours. When the firing temperature is 350 ° C. or higher, the surfactant can be completely decomposed, so that a porous film having a high porosity can be formed.

  As described above, on the porous substrate having pores (for example, macropores), a part of the pores enter the pores of the porous substrate, and the pores having a smaller diameter than the pores of the porous substrate ( For example, a porous film having mesopores) can be formed. Thereby, porous ceramics with a small pressure loss and a high surface area can be easily produced. Moreover, the hole (for example, macropore) of a porous base material penetrates in the thickness direction of a base material, and is formed in the base material with sufficient uniformity. The pores (for example, mesopores) of the porous membrane also penetrate in the thickness direction of the membrane and are formed with good uniformity in the membrane. For this reason, the macro hole and the meso hole communicate with each other. Therefore, the porous ceramic of the present invention is suitably used for applications that require a wide reaction field while minimizing the pressure loss when a fluid is flowed.

  Next, an example of the method for producing the porous ceramic of the present invention will be described in detail using examples.

[Example 1]
(Preparation of porous substrate)
The porous substrate used in Example 1 was produced as follows. The following amount of silica particles (average secondary particle size 6.1 μm, specific surface area 200 m ² / g) was prepared. As the combustible resin, the following amount of powdered polyethylene (weight average molecular weight: 2 million) was prepared. The following amount of mineral oil was prepared as a plasticizer. As a surfactant, the following amount of alkylsulfosuccinate was prepared.

Silica particles 27 parts by weight Polyethylene 15 parts by weight Mineral oil 57 parts by weight Alkylsulfosuccinate 1 part by weight

  The above components were mixed and then kneaded while being heated and melted with an extruder, and then the obtained kneaded product was pressure-molded with a molding roll to obtain a sheet-like product having a thickness of 400 μm.

Subsequently, the plasticizer in the sheet-like material is extracted and removed using an organic solvent (normal propyl bromide), and then the sheet-like material from which the plasticizer has been removed is dried by heating to have a thickness of 400 μm and a basis weight of 250 ( g / m ² ) porous green molded body was obtained. In this porous green molded body, voids were formed where the extracted plasticizer was present. The porosity calculated from the specific gravity was 60% when the ratio of the pore volume to the apparent volume in the porous green molded body was defined as the porosity. This porous green molded body was also used in the following Examples 2 to 6 and Comparative Example 1. The average thickness and basis weight of the porous green molded body and the like are values obtained as follows.

(Average thickness of porous green compact)
One point was measured per 300 mm ² with a digimatic standard outer micrometer (manufactured by Mitutoyo Corporation), and five points were averaged.

(Weight)
Three test pieces of 20 cm × 20 cm are collected, and the mass in each standard state (temperature 25 ° C., 10 ⁵ Pa) is measured. The mass per 1 m ² is obtained from the mass, and the average value is measured on the sample. It was.

Next, JIS No. 3 water glass was prepared. JIS No. 3 water glass is composed of SiO ₂ (28-30% by mass), Na ₂ O (9-10% by mass), and water (remainder), and the molar ratio (SiO ₂ / Na ₂ O) is 2.8- 3.33. By adding 1% by mass of acetylene glycol to a solution obtained by diluting this JIS No. 3 water glass 100 times with water, a sintering aid-containing liquid (abbreviated as WG × 100 in Table 1) was obtained. . The porous green molded body was impregnated with the sintering aid-containing liquid by dipping the porous green molded body into the sintering auxiliary-containing liquid.

  Next, the porous green molded body was pulled up from the sintering auxiliary agent-containing liquid, and after removing the excess sintering auxiliary agent-containing liquid adhering to the surface of the porous green molded body, the sintering auxiliary agent-containing liquid was impregnated. The porous green molded body was dried in an atmosphere of 50 ° C. for 1 hour, and subsequently fired at 900 ° C. for 1 hour to obtain a porous substrate.

(Preparation of porous membrane)
The porous film forming solution was prepared as follows. First, 5.9 g of a solvent AP-7 (Nippon Alcohol Sales Co., Ltd.), which is an alcoholic solvent, the main agent of ethanol, 0.2 g of HCl (catalyst) (1 mol / L) and 6.0 g of water. The catalyst-containing solvent is prepared by adding 1.0 g of “Pluronic” (registered trademark) P105 as a surfactant, and 6.9 g of tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ ) is dissolved therein. Was added. Next, the catalyst-containing solvent to which the surfactant and tetraethoxysilane were added was stirred at 50 ° C. for 2 hours to obtain a porous film forming solution containing a partial polymer of tetraethoxysilane.

  Next, the porous substrate was immersed in the porous film forming solution for 5 minutes while stirring the porous film forming solution. After pulling up the porous substrate from the porous film-forming solution, the excess porous film-forming solution on the surface of the porous substrate is removed, dried in an atmosphere of 30 ° C. for 24 hours, and then at 500 ° C. By firing for 2 hours, a porous silica ceramic was obtained.

[Evaluation]
(SEM observation)
About the obtained porous substrate and porous silica ceramics, using a scanning electron microscope (manufactured by Keyence Corporation, model number: VE-7800), acceleration voltage: 5 kV, photographing magnification: 2,000 times, 5,000 times Observed. From the result of SEM observation by VE-7800, the possibility of forming a highly uniform porous film was evaluated.

(Measurement of pore diameter and specific surface area)
The most frequent pore diameter Dm of the porous substrate and the specific surface areas of the porous substrate and the porous silica ceramic were measured at 77K using a gas adsorption device (BELsorp-mini manufactured by Nippon Bell Co., Ltd.). . The measured most frequent pore diameter Dm and specific surface area are shown in Tables 1 and 2. The most frequent hole diameter Dm is the hole diameter at which the value on the vertical axis of the hole diameter distribution graph (the differential value of the hole solution) is maximized. In Examples 2 to 6 and Comparative Example 1 described later, the most frequent pore diameter Dm and the specific surface area were obtained in the same manner.

  Moreover, when SEM observation was performed, the macropore which a porous base material has penetrated in the thickness direction of the porous base material. A part of the porous film entered the macropores of the porous substrate. In addition, since the gas adsorption measurement described above is possible, it is considered that the pores of the porous membrane alone penetrate through the thickness direction of the porous membrane alone.

  Separately from the porous film formed on the porous substrate, a porous film was separately formed on the ash content determination dish to obtain a porous film alone. For this porous membrane alone, the most frequent pore diameter Dm and the specific surface area were measured by the method described above. The results are shown in Table 3.

(PH of porous substrate surface)
The pH of the surface of the porous substrate (silica ceramic) was measured as follows based on the method defined in JAPAN TAPPI paper pulp test method No. 49-2. First, the following six kinds of pH measurement indicator solutions were prepared.
-Cresol red (CR) Measurement pH range: 0.0-2.4, 6.8-9.2
Thymol blue (TB) Measurement pH range: 1.0 to 3.4, 7.6 to 10.0,
-Bromophenol blue (BPB) Measurement pH range: 2.2 to 4.8,
-Bromocresol green (BCG) Measurement pH range: 3.6-6.0,
-Methyl red (MR) Measurement pH range: 5.0 to 7.4
Bromothymol blue (BTB) Measurement pH range: 5.8 to 8.2

  The porous base material was pulverized to select small lumps having a size of about 5 to 10 mm and used as test pieces. Subsequently, an appropriate pH measurement indicator solution was dropped on the surface of the test piece. The dropped solution naturally spread on the surface of the test piece. When the solution was left to stand for 1 to 2 minutes after dropping and the solution became semi-dry and the color became uniform, the pH value was read to the first decimal place in comparison with the color tone of the pH standard color change table. . Two test pieces were tested, and the average value was defined as the surface pH. The measurement results are shown in Table 1.

  The SEM observation photograph (photographing magnification: 5,000 times) of the obtained porous substrate surface is shown in FIG. 1, and the SEM observation photograph (photographing magnification: 5,000 times) of the porous silica ceramic surface is shown in FIG. .

  As can be seen from the SEM observation photograph, the surface of the porous ceramic (the surface of the porous film) is not greatly different from that of the porous substrate. Moreover, as can be seen from Tables 1 and 2, the specific surface area is larger than that of the porous substrate. From these facts, it was confirmed that the porous film was formed uniformly on the porous substrate, that is, with good uniformity.

[Examples 2 to 4]
Also in Examples 2 to 4, the same porous substrate used in Example 1 was used. In Example 2, ethylene glycol monoethyl ether (“ethyl cellosolve”, abbreviated as EC in Table 4) was used as a solvent constituting the porous film forming solution, and each of the solutions in the porous film forming solution was used. The mass parts of the components were as shown in Table 4.

  The porous membrane forming solution used in Example 3 is the same as the porous membrane forming solution used in Example 2, except that the mass parts of each component are as described in Table 4.

  The porous membrane forming solution used in Example 4 is the same as the porous membrane forming solution used in Example 2, except that the mass parts of each component are as described in Table 4.

[Example 5]
In Example 5, 1% by mass of acetylene glycol was added to a calcium hydroxide 0.25 mol / L (0.5N) solution as a sintering aid-containing solution used for the production of the porous substrate (in Table 1). Then, Ca (OH) ₂ (abbreviated as 0.5N) was used. The same porous membrane forming solution as used in Example 4 was used as the porous membrane forming solution.

[Example 6]
Example 6 is a solution in which 1% by mass of acetylene glycol is added to a 0.33 mol / L (1N) phosphoric acid solution as a sintering aid-containing solution used for the production of a porous substrate (in Table 1, H ₃ PO ₄ (abbreviated as 1N)). The same porous membrane forming solution as that used in Example 4 was used as the porous membrane forming solution.

[Comparative Example 1]
In Comparative Example 1, a solution obtained by adding 1% by mass of each acetylene glycol to a solution obtained by diluting the water glass No. 3 with water 10 times with the sintering aid-containing liquid in Example 1 (in Table 1) , Abbreviated as WG × 10). Except for the above, a porous substrate and porous silica ceramics were obtained in the same manner as in Example 1.

The SEM observation photograph (photographing magnification: 5,000 times) of the surface of the porous substrate obtained in Comparative Example 1 is shown in FIG. The surface pH of the porous substrate was 9, and the specific surface area was less than 1 m ² / g.

An SEM observation photograph (photographing magnification: 2,000 times) of the surface of the porous silica ceramic obtained in Comparative Example 1 is shown in FIG. The specific surface area of the porous silica ceramics was smaller than 1 m ² / g.

  In the porous ceramic obtained in Comparative Example 1, as can be seen from the SEM observation photograph, the surface of the porous substrate is not partially covered with the porous film, and the porous film is formed on the porous substrate. It was confirmed that segregated. This is considered to be because the solution for forming a porous film was solidified before being uniformly applied onto the porous substrate.

  As described above, in Comparative Example 1, the porous film having mesopores could not be formed on the porous substrate with good uniformity. On the other hand, in Examples 1-6, the porous film | membrane which has a mesopore was able to be formed with sufficient uniformity on the porous base material. From these results, it was confirmed in the present invention that a porous body having two types of pore groups having different pore diameters can be easily produced.

Surface observation photograph by SEM of the porous substrate obtained in Example 1 SEM surface observation photograph of the porous ceramics obtained in Example 1 Surface observation photograph by SEM of the porous substrate obtained in Comparative Example 1 SEM surface observation photograph of the porous ceramic obtained in Comparative Example 1

Claims (15)

After forming a mixture obtained by mixing particles comprising at least silica, a combustible resin, and a plasticizer into a predetermined shape, the plasticizer is extracted from the mixture, and porous green Obtaining a molded body, and then impregnating the porous green molded body with a sintering aid-containing liquid containing a sintering aid, and firing the porous green molded body impregnated with the sintering auxiliary agent-containing liquid. The porous substrate forming step of burning the resin to obtain a porous substrate having a pH of 8.0 or less measured based on the method defined in JAPAN TAPPI paper pulp test method No. 49-2 When,
A porous film forming solution containing a metal alkoxide, a catalyst, a surfactant, and water is impregnated into the porous substrate, and a part of the solution is formed on the porous substrate having a pH of 8.0 or less. After forming the coating film that has entered the pores of the porous substrate, the coating film is baked to have holes having a smaller diameter than the pores of the porous substrate, and part of the porous substrate forming a porous membrane which has entered into the pores of the substrate, seen including a porous membrane forming step,
A method for producing porous ceramics, wherein the sintering aid is at least one selected from the group consisting of an alkali metal-containing compound, an alkaline earth metal-containing compound, a boron-containing compound, and a phosphorus-containing compound .   The method for producing porous ceramics according to claim 1, wherein the particles are silica particles. Wherein the metal alkoxide is silicon alkoxide method for producing a porous ceramic according to claim 1 or 2. 2. The porous ceramic according to claim 1 , wherein the alkali metal-containing compound and / or the alkaline earth metal-containing compound is any one of chloride, hydroxide, carbonate, acetate, sulfate, or nitrate. Production method. The method for producing a porous ceramic according to claim 1 , wherein the boron-containing compound is boric acid and / or borax. The method for producing porous ceramics according to claim 1 , wherein the phosphorus-containing compound is at least one selected from the group consisting of orthophosphoric acid, phosphonic acid, phosphinic acid and peroxophosphoric acid.   The method for producing porous ceramics according to claim 1, wherein the supply source of the alkali metal-containing compound is water glass containing sodium oxide.   The method for producing porous ceramics according to claim 1, wherein a sintering temperature of the porous green molded body impregnated with the sintering aid-containing liquid is 1000 ° C or lower.   The manufacturing method of the porous ceramics of Claim 1 whose content of solid content in the said solution for porous film formation is 3-30 mass%.   2. The production of porous ceramics according to claim 1, wherein the content of the surfactant in the solution for forming a porous film is 30 to 300 parts by mass with respect to 100 parts by mass of the inorganic component derived from the metal alkoxide. Method.   The said coating film is formed in the said porous film formation process, after the said porous base material is immersed in the said solution for porous film formation, it pulls up from the said solution for porous film formation. A method for producing the porous ceramics according to 1. The method for producing porous ceramics according to claim 11 , wherein the coating film is dried and then fired.   The method for producing porous ceramics according to claim 1, wherein the pores of the porous substrate are macropores.   The method for producing porous ceramics according to claim 1, wherein the pores of the porous membrane are mesopores.   The method for producing a porous ceramic according to any one of claims 1 to 14, wherein the porous ceramic is a column filler for a chromatograph.

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