JP4540094B2 - Method for producing porous ceramic - Google Patents

Description

The present invention relates to a method for producing a porous ceramic (that is, a ceramic having many fine pores), and more particularly to a method for producing a porous ceramic having a high porosity and a high strength. Porous ceramics include: automobile exhaust gas purification ceramic filters, exhaust gas purification ceramic filters discharged from heat engines and combustion devices, etc., filtering materials such as water and other liquid filtration ceramic filters, exhaust gas purification catalysts Catalyst carriers such as automobile exhaust gas purification heat exchangers, heat accumulators, sintered substrates for batteries, heat insulating materials, and microbial carriers used for wastewater treatment.

  As a method for producing a porous ceramic, a method using a raw material in which the ceramic aggregate itself is porous and a method of mixing a foaming agent with the ceramic raw material are known. The former method has a low degree of freedom in design due to restrictions on raw materials, and the latter method has problems such as difficulty in controlling characteristics such as the amount of pores and pore diameter with good reproducibility. In order to solve these problems, there is also known a method of adding and kneading a water-absorbing polymer previously absorbed and swollen to a ceramic raw material as a pore-forming agent, and then molding the resulting mixture into a certain shape, followed by drying or firing ( For example, see Patent Documents 1 to 4.)

JP-A-62-212274 JP-A-8-73282 Japanese Patent Laid-Open No. 10-167856 JP-A-10-245278

In the method in which water-absorbing polymer swollen with water is mixed with a ceramic raw material as a pore-forming agent and molded and baked, the polymer that has absorbed and swollen absorbs not only its own volume but also the volume of water absorbed and retained inside the ceramic. It utilizes the fact that a pore-forming action is generated by generating voids between the raw material aggregates.
However, in the prior art disclosed in the above-mentioned patent documents, the pore size distribution of the ceramic fired body and the hardness of the kneaded material are controlled in the process for the reason that the water-absorbing polymer reverses water before firing. It was difficult. An object of the present invention is to provide a method for producing a porous ceramic, in which the pore size distribution of the ceramic fired body and the hardness of the kneaded product can be easily controlled in the process, and a ceramic fired body having a high porosity can be obtained. And

In order to solve the above-mentioned problem, a method for producing a porous ceramic according to claim 1 is a mixture comprising water-absorbing polymer particles having a water absorption of 5 to 30 ml / g at a pressure of 980 Pa, a ceramic raw material, and water. In the method for producing a porous ceramic including the step of forming a molded product and the step of heating and firing the obtained molded product, the water-absorbing polymer particles have a ratio of a water absorption amount Xml / g at a pressure of 980 Pa and a water absorption amount Yml / g at a pressure of 9800 Pa. X / Y is in the range of 1.0 to 1.6 .
According to a second aspect of the present invention, there is provided a method for producing a porous ceramic according to the first aspect of the present invention, wherein the water-absorbing polymer particles comprise a monofunctional vinyl monomer having one unsaturated bond and two unsaturated bonds. It is characterized by comprising a polymer obtained by radical polymerization of a monomer mixture containing 100 mol% and 0.1 to 10 mol% of polyfunctional vinyl monomers having at least one .
According to a third aspect of the present invention, there is provided a method for producing a porous ceramic according to the first or second aspect, wherein the water-absorbing polymer particles are obtained by polymerizing a vinyl monomer by a reverse phase suspension polymerization method. It is characterized by comprising a polymer.
The method for producing a porous ceramic according to a fourth aspect of the present invention is the method according to any one of the first to third aspects, wherein the water-absorbing polymer particles are 2-acrylamido-2-methylpropane as a constituent monomer unit. It consists of a polymer which has a sulfonic acid unit or an acrylamide unit.
According to a fifth aspect of the present invention, there is provided a method for producing a porous ceramic according to the first aspect of the present invention, wherein the mixture containing the water-absorbing polymer particles, the ceramic raw material and the water is powdered water-absorbing polymer particles and powder. Water is added to and mixed with a powdered mixture of water-absorbing polymer particles and ceramic raw material mixed with the ceramic raw material.

According to the present invention, the hardness and pore size distribution of the kneaded product with the porous ceramic can be easily controlled by using a hard water-absorbing resin that does not easily reverse water due to the share at the time of kneading as a pore-forming agent, In addition, a porous ceramic having high strength and high porosity can be obtained.

In this specification, acrylic and methacryl are referred to as (meth) acryl, and acrylate and methacrylate are referred to as (meth) acrylate.
The water-absorbing polymer particles used in the present invention function as a pore-forming agent, and the water absorption at a pressure of 980 Pa is 5 to 30 ml / g (the amount of ion-exchanged water absorbed per 1 g of the water-absorbing polymer in the dry state). Is in the range of 5 to 30 ml.).

  If the water absorption at a pressure of 980 Pa is smaller than 5 ml / g, it is necessary to add a large amount of pore-forming agent in order to obtain a sufficient porosity. Therefore, a large amount of organic gas is generated at the time of firing, exceeding the explosion limit, or firing. Problems such as long time may occur. On the other hand, if it is greater than 30 ml / g, it may be difficult to control the hardness of the kneaded product and the fired product. The reason is that when the mixture containing the water-absorbing polymer particles, the ceramic raw material and water is kneaded, the water contained in the water-absorbing polymer is easily reversed due to the share of the mixture, and as a result, the water absorption ratio of the water-absorbing polymer. This is probably because the particle diameter is likely to change. In addition, since the amount of water necessary for adjusting the hardness suitable for molding of the kneaded material (also known as kneaded clay) obtained by kneading increases, the amount of energy necessary for drying moisture increases significantly. It is not preferable.

  The water-absorbing polymer particles preferably have a ratio X / Y of a water absorption amount Xml / g at a pressure of 980 Pa and a water absorption amount Yml / g at a pressure of 9800 Pa in the range of 1.0 to 1.6. When the ratio exceeds 1.6, it may be difficult to control the hardness of the kneaded product and the fired product. The reason for this is that when the mixture containing the water-absorbing polymer particles, the ceramic raw material and water is kneaded, if the share of the mixture is large, the water contained in the water-absorbing polymer is likely to be reversed. This is thought to be because the water absorption ratio and particle size are likely to change. Normally, this ratio is never less than 1.

  Water-absorbing polymer particles having a water absorption amount of 30 ml / g or less at a pressure of 980 Pa are simultaneously high in crosslinking density and high in polymer particle strength. In general, this means that “the amount of water absorption is larger as“ (ion osmotic pressure) + (affinity of polymer electrolyte) ”is larger,“ smaller as “crosslinking density of polymer particles” is larger ”and“ strength of polymer particles ”. Corresponds to “increasing in proportion to the crosslinking density of the polymer particles”.

  The water-absorbing polymer particles preferably have a spherical shape in the water-absorbed and swollen state, and the average particle diameter in the saturated water-absorbing state is in the range of 1/30 to 1/1 based on the thickness of the ceramic molded product. More preferably, it is in the range of 1/15 to 1/2, more preferably in the range of 1/15 to 1/3. If the particle diameter is too small, the ceramic fired product obtained has a low porosity, and for example, when using the ceramic fired product as a filter, the pressure loss of the gas or liquid that passes therethrough may increase. If the particle diameter is too large, the obtained ceramic fired product may have a low strength. The thickness of the ceramic molding means the thickness of the individual wall when the ceramic molding has a plurality of wall structures made of ceramic, and the thickness of the whole ceramic molding. Does not mean.

  As the water-absorbing polymer particles, a polymer obtained by aqueous polymerization of a vinyl monomer is pulverized to an appropriate size after drying (1), and a spherical shape obtained by reverse-phase suspension polymerization of a vinyl monomer. Polymer (2), spherical hydrophobic polymer particles obtained by suspension polymerization of a vinyl monomer to give a water-absorbing polymer by modification treatment such as saponification (3), and a polymer unit comprising starch (4) etc. which have as a main component the modified | denatured substance of the graft polymer containing polymer units other than styrene and starch.

Examples of vinyl monomers that can be used in the above (1) and (2) include water-soluble monomers having a hydrophilic group such as a sulfone group, a carboxyl group, an amide group, an amino group, and a hydroxyl group, that is, 2- Acrylamide-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, styrenesulfonic acid, (meth) acrylic acid, maleic acid, itaconic acid, crotonic acid, fumaric acid, and / or partially alkaline neutralized products thereof , (Meth) acrylamide, N, N-dimethylacrylamide, N-isopropylacrylamide, N-methylol (meth) acrylamide, N-alkoxymethyl (meth) acrylamide, diethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, N -Vinylpyrrolidone, acryloylmorpholine, etc. are mentioned. Two or more of these monomers may be used as a mixture. 2-acrylamido-2-methylpropanesulfonic acid, 2- (meth) acryloylethanesulfonic acid, (meth) acrylic acid, (meth) acrylamide, N, N-dimethyl due to easy control of polymerization and water absorption performance Acrylamide and N-methylol (meth) acrylamide are preferable, and 2-acrylamido-2-methylpropanesulfonic acid and acrylamide are particularly preferable.
Examples of the polymer (3) include a saponified product of vinyl acetate-methyl acrylate copolymer. Examples of the polymer (4) include polymer-modified products such as starch- (meth) acrylic acid graft resin, saponified starch-acrylonitrile copolymer, and saponified starch-acrylamide copolymer. In addition, a cross-linked product of a modified product of isobutylene-maleic anhydride copolymer may be used. Two or more water-absorbing polymers shown above may be used in combination.

  Among these, spherical water-absorbing polymer particles synthesized by reversed-phase suspension polymerization are most preferable because they have high miscibility with the ceramic component and the particle size and water absorption ratio can be easily controlled by selecting the polymerization conditions. Further, the shape of the water-absorbing polymer particles affects the pore shape of the porous ceramic obtained by firing. In general, when the pores of the porous ceramic fired body have a sharp shape, it is known that stress is easily concentrated at the tip of the sharp shape and is easily broken, and its strength is reduced. On the other hand, the use of spherical water-absorbing polymer particles is desirable because the pores are spherical and the ceramic strength is increased. Further, when a pulverized product of a water-absorbing polymer is used, it is preferable to classify after pulverization to make the particle diameters uniform.

The water-absorbing polymer may be cross-linked. Since the crosslinked water-absorbing polymer particles have high strength, the shape thereof is not easily lost in a process such as kneading with a ceramic raw material. Therefore, it is easy to obtain a porous ceramic as designed having pores of an intended shape and size. It becomes.
One means for introducing a cross-linked structure into the water-absorbing polymer is to use a cross-linking agent that is a polyfunctional vinyl monomer in producing the water-absorbing polymer. Examples of polyfunctional vinyl monomers used as crosslinking agents include polyols such as polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, glycerin tri (meth) acrylate, and trimethylolpropane tri (meth) acrylate. Bisamides such as di- or tri (meth) acrylate and methylene bis (meth) acrylamide may be mentioned. Of these, methylenebisacrylamide and polyethylene glycol diacrylate are particularly preferred.
The use amount of the polyfunctional vinyl monomer is preferably 0.1 to 10 mol%, and preferably 0.5 to 8 mol%, based on the use amount of 100 mol% of the monofunctional vinyl monomer. More preferably, it is 1.0-5 mol%. If the amount used is less than 0.1 mol%, the effect of increasing the strength of the kneaded material with the ceramic raw material may not be sufficiently exerted, and if it is greater than 10 mol%, it may be difficult to adjust to a preferable water absorption performance. is there.

  As another means for introducing a crosslinked structure into the water-absorbing polymer, the reactivity with the carboxyl group contained in the unsaturated carboxylic acid monomer that is a constituent monomer of the water-absorbing polymer and its partially neutralized salt is used. There is also a method of using a utilized cross-linking agent. Examples of such crosslinking agents include (poly) ethylene glycol diglycidyl ether, (poly) propylene glycol diglycidyl ether, (poly) glycerol diglycidyl ether, (poly) glycerol triglycidyl ether, sorbitol diglycidyl ether, sorbitol triglycidyl Polyglycidyl compounds such as ether, pentaerythritol diglycidyl ether, pentaerythritol triglycidyl ether, pentaerythritol tetraglycidyl ether, haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and 2,4-tolylene diisocyanate And isocyanate compounds such as hexamethylene diisocyanate. Of these, ethylene glycol diglycidyl ether is particularly preferred.

  When a cordierite forming raw material is used as the ceramic raw material, the water-absorbing polymer is preferably free of alkali metals or alkaline earth metals. This is because, when a polymer containing a large amount of the above metal is used, physical properties such as a cordierite formation reaction may be hindered and a thermal expansion coefficient may be increased. Therefore, in the water-absorbing polymer containing a sulfone group or a carboxyl group, it is desirable that these functional groups are not in a state such as sodium salt or potassium salt but in an unneutralized state or an ammonium salt. In addition, a water-absorbing polymer containing a nonionic hydrophilic functional group is also desirable. Examples of nonionic hydrophilic functional groups include hydroxyl groups, oxyalkylene groups such as oxyethylene groups and oxypropylene groups, and amide groups.

  Ceramic materials used in the present invention include ceramic materials such as clay, clay minerals, chamotte, silica, quartz sand, diatomaceous earth, porcelain stone, feldspar, blast furnace slag, shirasu, shirasu balloon, fly ash, and other special ceramic materials. For example, cordierite, talc, alumina, kaolin, aluminum hydroxide, magnesia, ferrite, zeolite, mullite, apatite, slag, silicon carbide, zirconia, aluminum nitride, aluminum titanate, etc., and battery electrode raw materials such as nickel powder , Cobalt powder, lanthanum / manganite, lanthanum / strontium / manganite and the like.

  The method for producing a porous ceramic comprises a step of kneading and molding the above-mentioned ceramic raw material, water-absorbing polymer particles and water, and optionally a mixture containing a binder such as methylcellulose and a lubricant such as olefin wax. Including. The kneading may be performed by a known method, for example, using a kneader, a pony mixer, a screw extruder, a vacuum kneader or the like. Ceramic materials are usually used in powder form.

  Moreover, the process of drying and baking the obtained molded object is included. Drying and firing may be performed by a known method, and devices such as a high frequency dielectric heating type heating device, a hot air dryer, a heated floor dryer, a mangle dryer, and a tunnel dryer can be used. Drying is usually performed at a temperature of 150 ° C. or lower, and it is preferable to dry to a state that does not substantially contain moisture. Firing is performed by heating to a temperature exceeding 150 ° C, preferably 800 ° C or higher. The firing temperature and firing time are set so that organic substances such as water-absorbing polymer particles and binder are sufficiently combusted and the ceramic raw material is sufficiently fired.

  As for the ratio of the usage-amount of a ceramic raw material and a water-absorbing polymer particle, 0.1-20 mass parts of water-absorbing polymer particles are preferable on the basis of 100 mass parts of ceramic raw materials in a dry state (state which does not contain water), 0.5-10 mass parts is more preferable. If the amount of water-absorbing polymer used is less than 0.1 parts by mass, sufficient porosity may not be obtained. When the amount exceeds 20 parts by mass, a large amount of organic gas is generated during firing, and the gas composition in the firing device exceeds the explosion limit, the firing time becomes too long, or the volume change during firing is large. May cause problems such as being likely to have distortion or cracks.

  The mixture containing the water-absorbing polymer particles, the ceramic raw material and water is obtained by mixing these raw materials by an arbitrary method. The amount of water used is adjusted so as to obtain a preferable hardness and formability of the kneaded material, depending on the water-absorbing polymer particles, the type of ceramic raw material, and the formulation. When the amount of water used is 100 parts by mass or less based on 100 parts by mass of the ceramic raw material, it is preferable because the time and energy cost required for drying the kneaded product do not become excessive.

The method for adding the water-absorbing polymer particles in the raw material mixing may be either a method of adding a water-containing state (water-absorbing state) or a method of adding a dry state. The appearance of the water-containing water-absorbing polymer particles may be in the form of a powder or a paste.
When using water-absorbing polymer particles in a water-containing state, the water content is not particularly limited, but the water-absorbing polymer can be handled as a powder, that is, the water content in a range where the water-absorbing polymer powder has fluidity. Is preferred. The reason for this is that polymer particles that have a high water content and are in a gel state are difficult to handle, and mixing and dispersion with ceramic raw materials become insufficient, resulting in insufficient strength and porosity of the fired ceramic molded product. This is because there are cases.
The water-absorbing polymer particles in a dried powder state or a powder state in which the moisture content is adjusted are easy to mix with the ceramic raw material powder, and the resulting mixture of the water-absorbing polymer particles and the ceramic raw material powder has a high uniform dispersibility. It becomes easy to have. That is, a method in which water is added to and mixed with a powdery mixture of water-absorbing polymer particles and ceramic raw material in which powdered water-absorbing polymer particles and powdered ceramic raw material are mixed and dispersed in advance. This is a preferable method because a ceramic molded product obtained by drying and firing the molded raw material kneaded product tends to be uniform and the pore distribution tends to be uniform. On the other hand, in the method in which the water-absorbing polymer particles, the ceramic raw material and the water are mixed substantially simultaneously without the powdery water-absorbing polymer particles and the powdered ceramic raw material being mixed in advance, the obtained material kneading The product may be non-uniform, and the ceramic molded product obtained by drying and firing the molded raw material kneaded product may have insufficient strength and uniformity of pore distribution.

  In the kneading and molding processes, it is necessary to make the hardness of the kneaded material in an appropriate range in order to improve the moldability. In general, the hardness of the kneaded product is likely to change depending on the type of ceramic raw material, the amount of water-absorbing polymer particles added, the amount of water and the kneading method, and reproducible hardness may not be obtained even when carried out under the same conditions. Many. When the water-absorbing polymer particles of the present invention are used, the hardness of the kneaded material is easily reproduced as intended under the preset conditions, so that the process can be easily controlled and molding can be performed stably. About other conditions, a well-known method is employable.

(Production Example 1 Production of water-absorbing polymer particles A to E by reverse phase suspension polymerization)
In a 3 liter separable flask, 1603 g of n-hexane and 10 g of sorbitan monolaurate (HLB 4.3) were added and dissolved. On the other hand, 96 g of acrylic acid, 224 g of 2-acrylamido-2-methylpropanesulfonic acid, 14.9 g of methylenebisacrylamide (4 mol% based on 100 mol% of monomers other than the cross-linking agent) in 286.4 g of ion-exchanged water in a separate container A monomer aqueous solution that was partially neutralized (75 mol% neutralized) was prepared by adding 124.67 g of 25% aqueous ammonia solution while cooling with ice. While stirring the contents of the separable flask at a stirring speed of 400 rpm (rotation / min), the aqueous monomer solution was added, and then the atmosphere was purged with nitrogen at a flow rate of 200 ml / min for 2 hours until the dissolved oxygen concentration was sufficiently low. . When the temperature of the flask contents was stabilized by controlling the external temperature to 30 ° C., 0.58 g of a 6.9% aqueous solution of t-butylhydroxyperoxide was added. Next, 0.90 g of 5% sodium bisulfite aqueous solution was divided into five portions, and one portion of them was added to initiate polymerization. A temperature rise of the reaction solution due to the heat of polymerization was observed. When the temperature of the reaction solution decreased to the same temperature as the external temperature controlled at 30 ° C., one portion of the remaining four sodium bisulfite aqueous solutions was added. The operation of adding once a sodium bisulfite aqueous solution was repeated three more times when the temperature of the reaction solution once increased and then decreased to reach the same temperature as the external temperature. After the fifth addition of the sodium bisulfite aqueous solution, the temperature was once aged for about 1 hour after the temperature rose to almost the same as the external temperature. Nitrogen substitution was continued while the external temperature was controlled at 30 ° C. even after the start of polymerization, and the reaction was stirred at the rotation speed of 400 rpm until the reaction was completed. After allowing to stand to separate into two phases, the supernatant was discarded. Thereafter, the lower layer precipitate was dried at 120 ° C. for 6 hours and then pulverized by a crusher to obtain spherical water-absorbing polymer particles A.
The water-absorbing polymer particles B and C were produced in the same manner as the water-absorbing polymer particle A except that the amount of methylenebisacrylamide used was changed to 3 mol% and 2 mol%, respectively.
In the production of the water-absorbing polymer particles D, the monomers other than the cross-linking agent were changed to 224 g of 2-acrylamido-2-methylpropanesulfonic acid and 192 g of 50% acrylamide aqueous solution, and the usage amounts of 25% ammonia aqueous solution and ion-exchanged water were 55.1 respectively. The same procedure as in the production of the water-absorbing polymer particles A was carried out except that g and 261.8 g were changed. The use of 4 mol% of methylene bisacrylamide as a crosslinking agent based on 100 mol% of a monomer other than the crosslinking agent is the same as the production conditions for the water-absorbing polymer particles A.
For the production of water-absorbing polymer particles E, the monomers other than the crosslinking agent are changed to 480 g of 50% acrylamide aqueous solution and 80.0 g of acrylic acid, and the usage amounts of 25% aqueous ammonia solution and ion-exchanged water are changed to 56.6 g and 114.7 g, respectively. Except for this, the production was performed in the same manner as in the production of the water-absorbing polymer particles A. The use of 4 mol% of methylene bisacrylamide as a crosslinking agent based on 100 mol% of a monomer other than the crosslinking agent is the same as the production conditions for the water-absorbing polymer particles A.
All of the water-absorbing polymer particles B to E had a spherical shape.

(Production Example 2 Production of water-absorbing polymer particles F and G)
After mixing 100 g of acrylic acid and ion-exchanged water, an aqueous solution with an acrylic acid concentration of 35% by mass was prepared by adding a 25% aqueous ammonia solution while cooling with ice to partially neutralize (75 mol% neutralization). 20 g of Aronix M-245 (polyethylene glycol diacrylate, the number of repeating oxyethylene units n is about 9) manufactured by Synthetic Co., Ltd. was added. To this aqueous monomer solution, 0.01 g of 2,2-dimethoxy-2-phenylacetophenone and 0.1 g of ammonium persulfate were added as a photoinitiator and charged into a cylindrical glass container (reactor) having an inner diameter of 146 mm. Was kept under nitrogen bubbling for 30 minutes. Then, ultraviolet rays were irradiated from the top of the reactor for 3 minutes using a 100 W black light (trade name “H100BL”, manufactured by Toshiba Corporation) with an irradiation intensity of 5.0 mW / cm ² to create a sheet-like water-containing crosslinked polymer gel. (Integrated light intensity: 900 mJ / cm ² ). This gel was dried and pulverized to obtain coarse particles of a water absorbent resin. Next, after pulverizing with a ball mill, the particles passed through a 330 mesh (45 μm) sieve were collected to obtain water-absorbing polymer particles F.
The water-absorbing polymer particles G are produced by mixing 200 g of a 50% aqueous acrylamide solution and ion-exchanged water to prepare an aqueous solution having an acrylamide concentration of 30% by mass, and using Aronix M-240 (polyethylene glycol diacrylate) manufactured by Toagosei Co., Ltd. The number of repeating oxyethylene units n was the same as that for polymer particles F except that the monomer aqueous solution was added with 10 g of about 4).

(Measurement of water absorption under pressure of water-absorbing polymer particles)
The amount of water absorption under pressure of the water-absorbing polymer particles, that is, the amount of water absorption at pressures of 980 Pa and 9800 Pa, was measured using the measuring apparatus shown in FIG. As shown in FIG. 1, the measuring device is composed of (1) to (3). (1) consists of a burette 1 with a branch pipe for venting air, a pinch cock 2, a silicon tube 3 and a polytetrafluoroethylene tube 4. In (2), a support cylinder 8 having a large number of holes on the bottom surface is provided on the funnel 5, and a filter paper 10 for the apparatus is further provided thereon. As shown in (3), a sample 6 of water-absorbing polymer particles is sandwiched between two sample fixing filter papers 7 and fixed to a cylindrical weight 11 by an adhesive tape 9. There are two types of cylindrical weights, one that gives a load of 980 Pa to sample 6 and one that gives a load of 9800 Pa. (1) and (2) are connected by a silicon tube 3. The height of the funnel 5 and the support cylinder 8 is fixed with respect to the burette 1, and the lower end of the polytetrafluoroethylene tube 4 installed inside the buret branch pipe and the bottom of the support cylinder 8 are the same height. It is set to become. (Dotted line in Fig. 1)

The amount of water absorption under pressure was measured using the measuring apparatus having the above configuration. The measurement method will be described below. The pinch cock 2 in (1) was removed, and ion exchange water was poured from the upper part of the burette 1 through the silicon tube 3 so that the burette 1 to the filter paper 10 for apparatus were filled with the ion exchange water 12. Next, the pinch cock 2 was closed to maintain the pressure inside the burette 1, and air was removed from the polytetrafluoroethylene tube 4 connected to the buret branch pipe with a rubber stopper. Thus, the ion exchange water 12 was continuously supplied from the burette 1 to the filter paper 10 for the apparatus. Next, after removing the excess ion-exchanged water 12 oozing out from the filter paper for apparatus 10, the reading (a) on the scale of the burette 1 was recorded. Weigh out 0.05g of water-absorbing polymer particle sample and place it evenly on the center of the filter paper 7 for sample fixing as shown in (3), and stick the dry water-absorbing polymer particle sample with another filter paper. The bottom of the weight 11 was fixed with a tape 9. The weight 11 on which the sample was fixed was placed on the filter paper 10 for apparatus shown in (2). Next, the reading (b) of the scale of the bullet 1 after 30 minutes from the time when the weight 11 was placed on the filter paper 10 for apparatus was recorded. The sum (c) of the water absorption amount of the water-absorbing polymer particles and the water absorption amount of the two filter papers 7 is obtained by (ab). By the same operation, the water absorption of the two filter papers 7 not containing the water absorbent polymer particle sample was measured (d). The amount of water absorption under pressure was determined from the following equation.
Water absorption under pressure (ml / g) = (cd) / (Water-absorbing polymer particle amount (g))

  As described above, the amount of water absorption under pressure was measured for each sample under the respective conditions of 980 Pa and 9800 Pa.

(Measurement of kneaded material hardness)
The hardness of the kneaded material (before molding and firing) obtained in the examples and comparative examples was measured by the following method. The kneaded material was collected in a 50 ml screw vial, packed tightly so that there was almost no void, and the surface was flattened. The kneaded product was kept at 23 ° C., and the kneaded product hardness was measured using a card meter (ME-303, manufactured by Iio Electric Co., Ltd.) under the following conditions.
Load: 400g
Diameter of pressure sensitive shaft: 3mmφ
Decrease speed of pressure-sensitive axis: 0.36 cm / sec. The hardness of the kneaded material having good moldability under the conditions used in the examples and comparative examples was in the range of 1.5 × 10 ^{4 to} 6.0 × 10 ⁴ N / m ² . .

(Evaluation of formability)
The appearance of the kneaded product formed into a cylindrical shape by extrusion molding (before firing) was visually evaluated. Those with cracks in the molded product or those that cannot maintain the cylindrical shape when the molded product is left standing (poor shape retention) are all marked with “x”, and have no cracks and good shape retention Was marked as “◯”.

Example 1
The polymer particle A produced in Production Example 1 was used as the water-absorbing polymer particle. The water absorption amount of the polymer particles A at a pressure of 980 Pa is 9 ml / g, the ratio X / Y of the water absorption amount Xml / g at a pressure of 980 Pa and the water absorption amount Yml / g at a pressure of 9800 Pa is 1.32. The weight of the water-absorbing polymer in a dry state at normal pressure is 10 g / g in mass (including the mass of the polymer itself) when ion-exchanged water is saturated and absorbed, and the average in the saturated water-absorbing state. The particle size was 40 μm. The normal-pressure water absorption amount of the polymer particles A means the water absorption amount measured in a state where the “weight 11” is not used in the “measurement of water absorption amount under pressure of the water-absorbing polymer particles” and is lightly pressed. The same applies to the atmospheric water absorption amount of water-absorbing polymer particles B, C, D and E described later.
As a ceramic raw material, the cordierite forming raw materials kaolin, calcined kaolin, talc, alumina, aluminum hydroxide, and silica are mixed in a mass ratio of 21: 13: 39: 9: 13: 5 (100 parts by mass in total). 4 parts by weight of methylcellulose as a binder, 1 part by weight of an olefin wax as a lubricant, and 5 parts by weight of dry water-absorbing polymer particles A as a pore-forming agent were added and mixed, and then 80 parts by weight of ion-exchanged water. Immediately after adding the part, the mixture was kneaded with a σ type kneader for 30 minutes. Thereafter, it was molded into a cylindrical shape by an extrusion molding method and dried at 120 ° C. to remove moisture. Drying was performed at 120 ° C. until the weight was almost constant. Next, after raising the temperature to 1000 ° C., the temperature was raised between 1000 ° C. and 1400 ° C. at a rate of temperature rise of 50 ° C./hour, and after reaching 1420 ° C., the temperature was maintained and firing was performed for 4 hours. The porosity of the fired body was measured with a mercury porosimeter.

(Example 2)
The same procedure as in Example 1 was performed except that the amount of ion-exchanged water was changed from 80 parts by mass to 90 parts by mass.

(Example 3)
The same procedure as in Example 1 was carried out except that the amount of the water-absorbing polymer particles A was changed from 5 parts by mass to 3.1 parts by mass.

Example 4
The same procedure as in Example 1 was performed except that the water absorbent polymer particles B produced in Production Example 1 were used in place of the water absorbent polymer particles A. The water absorption amount of the polymer particles B at a pressure of 980 Pa was 13 ml / g, the ratio X / Y was 1.33, the atmospheric water absorption amount was 15 g / g, and the average particle size in a saturated water absorption state was 53 μm. .

(Example 5)
The same procedure as in Example 1 was performed except that the water absorbent polymer particles C produced in Production Example 1 were used in place of the water absorbent polymer particles A. The water absorption amount of the polymer particles C at a pressure of 980 Pa was 20 ml / g, the ratio X / Y was 1.45, the normal pressure water absorption amount was 23 g / g, and the average particle size in a saturated water absorption state was 62 μm. .

(Example 6)
The same procedure as in Example 1 was performed except that the water absorbent polymer particles D produced in Production Example 1 were used in place of the water absorbent polymer particles A. The water absorption amount of the polymer particles D at a pressure of 980 Pa was 11 ml / g, the ratio X / Y was 1.13, the normal pressure water absorption amount was 13 g / g, and the average particle size in a saturated water absorption state was 49 μm. .

(Example 7)
The same procedure as in Example 1 was carried out except that the water absorbent polymer particles E produced in Production Example 1 were used in place of the water absorbent polymer particles A. The water absorption of the polymer particles E at a pressure of 980 Pa was 10 ml / g, the ratio X / Y was 1.36, the water absorption at normal pressure was 12 g / g, and the average particle diameter in a saturated water absorption state was 65 μm. .

(Example 8)
The same procedure as in Example 1 was carried out except that the water absorbent polymer particles F produced in Production Example 2 were used in place of the water absorbent polymer particles A. The water absorption amount of the polymer particles F at a pressure of 980 Pa was 27 ml / g, the ratio X / Y was 1.16, the normal water absorption amount was 29 g / g, and the average particle size in a saturated water absorption state was 42 μm. .

Example 9
The same procedure as in Example 1 was performed except that the water absorbent polymer particles G produced in Production Example 2 were used in place of the water absorbent polymer particles A. The water absorption amount of the polymer particles G at a pressure of 980 Pa was 19 ml / g, the ratio X / Y was 1.05, the normal pressure water absorption amount was 22 g / g, and the average particle size in a saturated water absorption state was 41 μm. .

(Example 10)
Instead of the water-absorbing polymer particles A, water-absorbing polymer particles H (manufactured by Kuraray Isoprene Chemical Co., Ltd., KI gel 201K, 330 mesh pass product, a crushed product of a crosslinked salt of a modified product of isobutylene-maleic anhydride copolymer). The same procedure as in Example 1 was performed except that it was used. The water absorption amount of the polymer particles H at a pressure of 980 Pa was 25 ml / g, the ratio X / Y was 1.32, the normal pressure water absorption amount was 32 g / g, and the average particle size in the saturated water absorption state was 60 μm. .

(Comparative Example 1)
Instead of 5 parts by mass of the water-absorbing polymer particles A, water-absorbing polymer particles I (Kuraray isoprene Chemical Co., Ltd., KI gel 201K, granular product, cross-linked salt of isobutylene-maleic anhydride copolymer modified product). An operation similar to that of Example 1 was attempted except that 5 parts by mass were used as they were without being pulverized. The water absorption of the polymer particles I at a pressure of 980 Pa is 35 ml / g, the ratio X / Y is 1.54, the normal water absorption is 200 g / g (catalog value), and the average particle diameter in the saturated water absorption state is 320 μm. An attempt was made to form the kneaded product, but the fluidity was insufficient and the product could not be formed well, and the molded product was cracked.
Separately, when the amount of water necessary for imparting appropriate fluidity to this kneaded material was searched, it was found that 120 parts by mass were necessary. When a large amount of water is used in this way, it takes much time and energy to dry, which is not practical.

(Comparative Example 2)
The same operation as in Example 1 was attempted except that 0.15 part by mass of the water-absorbing polymer particle I was used instead of 5 parts by mass of the water-absorbing polymer particle A. The obtained kneaded product had poor shape retention, and the molded product could not maintain its shape.

(Comparative Example 3)
The same operation as in Example 1 was performed except that 2 parts by mass of the water-absorbing polymer particles I were used in place of 5 parts by mass of the water-absorbing polymer particles A.

(Comparative Example 4)
Except that 5 parts by mass of the water-absorbing polymer particles A was used instead of 5 parts by mass of the water-absorbing polymer particles J (Sanfresh ST-500D pulverized product manufactured by Sanyo Chemical Industries, Ltd., polyacrylic crosslinked resin). The same operation as in Example 1 was attempted. The water absorption of the polymer particle J at a pressure of 980 Pa is 75 ml / g, the ratio X / Y is 1.09, the normal pressure water absorption is 400 g / g (catalog value), and the average particle diameter in the saturated water absorption state is It was 190 μm. An attempt was made to form the kneaded product, but the fluidity was insufficient and the product could not be formed well, and the molded product was cracked.
Separately, when the amount of water necessary for imparting appropriate fluidity to this kneaded material was searched, it was found that 140 parts by mass were necessary. When a large amount of water is used in this way, it takes much time and energy to dry, which is not practical.

(Comparative Example 5)
The same operation as in Example 1 was tried except that 0.08 part by mass of the water-absorbing polymer particle J was used instead of 5 parts by mass of the water-absorbing polymer particle A. The obtained kneaded product had poor shape retention, and the molded product could not maintain its shape.

(Comparative Example 6)
The same operation as in Example 1 was performed except that 2 parts by mass of the water-absorbing polymer particles J were used instead of 5 parts by mass of the water-absorbing polymer particles A.

(Comparative Example 7)
Example except that 5 parts by mass of spherical water-absorbing polymer particles K (Aquakeep SA-60N manufactured by Sumitomo Seika Co., Ltd., polyacrylamide-based crosslinked resin) was used instead of 5 parts by mass of the water-absorbing polymer particles A. I tried the same operation as 1. The water absorption amount of the polymer particles K at a pressure of 980 Pa was 140 ml / g, the ratio X / Y was 1.93, the normal pressure water absorption amount was 480 g / g, and the average particle size in the saturated water absorption state was 710 μm. . An attempt was made to form the kneaded product, but the fluidity was insufficient and the product could not be formed well, and the molded product was cracked.
Separately, when an amount of water necessary for imparting appropriate fluidity to this kneaded material was searched, it was found that 150 parts by mass was necessary. When a large amount of water is used in this way, it takes much time and energy to dry, which is not practical.

(Comparative Example 8)
The same operation as in Example 1 was attempted except that 0.06 part by mass of the water-absorbing polymer particle K was used instead of 5 parts by mass of the water-absorbing polymer particle A. The obtained kneaded product had poor shape retention, and the molded product could not maintain its shape.

(Comparative Example 9)
The same operation as in Example 1 was performed except that 2 parts by mass of the water-absorbing polymer particles K was used instead of 5 parts by mass of the water-absorbing polymer particles A.

(Comparative Example 10)
Instead of 5 parts by mass of the water-absorbing polymer particles A, water-absorbing polymer particles L (Alonzap TS-U-1 manufactured by Toagosei Co., Ltd. Crosslinked polymer having acrylic acid units and 2-acrylamido-2-methylpropanesulfonic acid units.) The same operation as in Example 1 was attempted except that 5 parts by mass of the above was used. The water absorption amount of the polymer particles L at a pressure of 980 Pa was 98 ml / g, the ratio X / Y was 2.80, the normal water absorption amount was 150 g / g, and the average particle size in the saturated water absorption state was 450 μm. . An attempt was made to form the kneaded product, but the fluidity was insufficient and the product could not be formed well, and the molded product was cracked.
Separately, when an amount of water necessary for imparting appropriate fluidity to the kneaded product was searched, it was found that 120 parts by mass was necessary. When a large amount of water is used in this way, it takes much time and energy to dry, which is not practical.

(Comparative Example 11)
The same operation as in Example 1 was attempted except that 0.2 parts by mass of the water-absorbing polymer particles L was used instead of 5 parts by mass of the water-absorbing polymer particles A. The obtained kneaded product had poor shape retention, and the molded product could not maintain its shape.

(Comparative Example 12)
The same operation as in Example 1 was performed except that 2 parts by mass of the water-absorbing polymer particles L were used instead of 5 parts by mass of the water-absorbing polymer particles A.

(Comparative Example 13)
Instead of using 5 parts by mass of the water-absorbing polymer particles A, 5 parts by mass of spherical water-absorbing polymer particles M (Aronzap U manufactured by Toagosei Co., Ltd., a cross-linked polymer having an acrylic acid unit as a main constituent unit) were used. The same operation as in Example 1 was attempted. The water absorption amount of the polymer particles M at a pressure of 980 Pa was 112 ml / g, the ratio X / Y was 1.67, the normal pressure water absorption amount was 210 g / g, and the average particle size in a saturated water absorption state was 590 μm. . An attempt was made to form the kneaded product, but the fluidity was insufficient and the product could not be formed well, and the molded product was cracked.
Separately, when an amount of water necessary for imparting appropriate fluidity to the kneaded product was searched, it was found that 120 parts by mass was necessary. When a large amount of water is used in this way, it takes much time and energy to dry, which is not practical.

(Comparative Example 14)
The same operation as in Example 1 was attempted except that 0.14 parts by mass of the water-absorbing polymer particles M were used in place of 5 parts by mass of the water-absorbing polymer particles A. The obtained kneaded product had poor shape retention, and the molded product could not maintain its shape.

(Comparative Example 15)
The same operation as in Example 1 was performed except that 2 parts by mass of the water-absorbing polymer particles M were used in place of 5 parts by mass of the water-absorbing polymer particles A.

  Table 1 shows the evaluation results of the hardness and formability of the kneaded materials and the porosity data of the fired bodies in the examples and comparative examples.

In Comparative Examples 1, 4, 7, 10 and 13, as a result of using the same amount of water-absorbing polymer particles as in Examples 1, 2, 4, 5, 6, 7, 8, 9 and 10, the moldability of the kneaded product was However, the molded product had cracks.
The above results show that the known water-absorbing polymer particles used in the comparative examples and the water-absorbing polymer particles used in the examples within the technical scope of the present invention are significantly different in water absorption under normal pressure. It is also possible that Therefore, for each of the various water-absorbing polymer particles, 30 parts by mass of ions obtained by subtracting 50 parts by mass necessary for kneading the ceramic raw material powder in the absence of the water-absorbing polymer from the total amount of ion-exchanged water used of 80 parts by mass. Examples 3 and Comparative Examples 2, 5, 8, 11, and 14 are experiments in which the exchanged water is compared using an amount corresponding to the saturated water absorption. As a result, in Example 3, the kneaded material hardness was appropriate, and the kneaded material had good moldability, but in Comparative Examples 2, 5, 8, 11, and 14, the kneaded material hardness was small, and the moldability (retaining property) was maintained. (Formality) was bad.
Therefore, in Comparative Examples 3, 6, 9, 12, and 15, when the amount of water-absorbing polymer particles was adjusted to 2 parts by mass, conditions for having the necessary kneaded material hardness and moldability were also found. The obtained fired body had a porosity smaller than that of the example, such that the porosity was 46 to 54%.

  The meaning of the requirements characterizing the invention described in the claims will be supplemented below. The essence of the present invention is to use water-absorbing polymer particles having a relatively small amount of water absorption (but not zero) near normal pressure as the pore-forming agent (the invention according to claim 1). If the water-absorbing polymer particles have an excessively small amount of water absorption near normal pressure, a sufficient porosity cannot be obtained because the amount of water retained by the polymer particles is small. If the water-absorbing polymer particles have an excessive amount of water absorption at around normal pressure, the water is reversed from the polymer particles absorbed when the shear is applied in the kneading process, and the particle diameter is likely to change. It may be difficult to control the hardness and pore size distribution of the fired product. However, the amount of water absorption at normal pressure varies depending on the measurement conditions, and when the particle size of the water-absorbing polymer is small, measurement is not easy, and the data on the amount of water absorption obtained may be poorly reproducible. Therefore, in claim 1 of the present invention, the amount of water absorption at a pressure of 980 Pa obtained by adding a slight load to the normal pressure is defined as a condition that represents normal pressure (close to normal pressure) and has good reproducibility of measurement. .

  The invention according to claim 2 stipulates that the amount of water absorption when shearing in kneading is not extremely reduced compared to the amount of water absorption near normal pressure. When the amount of water absorption at a pressure of 9800 Pa (equivalent to a share in kneading) is extremely smaller than the amount of water absorption at a pressure of 980 Pa (approximate to the amount of water absorption near normal pressure), when a share is applied in the kneading process Since the water reverts from the polymer particles that have absorbed water and the particle size is likely to change, it may be difficult to control the hardness and pore size distribution of the kneaded product and the fired product.

In Patent Document 3, deformation of the water-absorbing gel is suppressed by using water-absorbent resin particles having high gel strength as a pore-forming agent by saturated water absorption. However, in this case, it is gel strength against a water-absorbing polymer gel containing physiological saline, which is much less water-absorbing than pure water. A functional polymer was used. In paragraph 0012 of Patent Document 3, it is described that “the water absorption performance with respect to pure water is 50 g / g or more, preferably 100 to 1000 g / g”, and can be used suitably in the present invention. It can be seen that this is a technique that uses a water-absorbing resin larger than the water absorption amount of the polymer particles. Comparative Examples 4 to 6 using the water-absorbing polymer particles J, which are considered to be equivalent to or similar to the water-absorbing polymer used in the examples of Patent Document 3, are Comparative Examples 4 to 6 of the present application. The moldability was poor, or the porosity was small compared to the examples of the present application.
In the method of suppressing the amount of water absorption using a saline solution, there is a problem that the obtained porous ceramic fired body contains a large amount of salt.

According to the present invention, a porous ceramic having a high porosity and a high strength can be obtained. Porous ceramics include: automobile exhaust gas purification ceramic filters, exhaust gas purification ceramic filters discharged from heat engines and combustion devices, etc., filtering materials such as water and other liquid filtration ceramic filters, exhaust gas purification catalysts Catalyst carriers such as automobile exhaust gas purification heat exchangers, heat accumulators, sintered substrates for batteries, heat insulating materials, and microbial carriers used for wastewater treatment.

Measuring device for water absorption under pressure.

Explanation of symbols

1 Burette
2 Pinch cock
3 Silicon tube
4 Polytetrafluoroethylene tube
5 Funnel
6 samples (water-absorbing polymer particles)
7 Sample fixing filter paper
8-post cylinder (made of stainless steel, with many holes)
9 Adhesive tape
10 Filter paper for equipment
11 Weight (cylindrical, stainless steel)
12 Ion exchange water

Claims (5)

In a method for producing a porous ceramic comprising a step of forming a mixture containing water-absorbing polymer particles having a water absorption amount of 5 to 30 ml / g at a pressure of 980 Pa, a ceramic raw material and water, and a step of heating and firing the obtained molded product ,
The water-absorbing polymer particles have a ratio X / Y of a water absorption amount Xml / g at a pressure of 980 Pa and a water absorption amount Yml / g at a pressure of 9800 Pa in the range of 1.0 to 1.6. Manufacturing method. The water-absorbing polymer particles are composed of a monofunctional vinyl monomer having one unsaturated bond and a polyfunctional vinyl monomer having two or more unsaturated bonds in proportions of 100 mol% and 0.1 to 10 mol%, respectively. 2. The method for producing a porous ceramic according to claim 1, comprising a polymer obtained by radical polymerization of the monomer mixture to be contained . The method for producing a porous ceramic according to claim 1 or 2, wherein the water-absorbing polymer particles comprise a polymer obtained by polymerizing a vinyl monomer by a reverse phase suspension polymerization method. The porous polymer according to any one of claims 1 to 3, wherein the water-absorbing polymer particles are composed of a polymer having a 2-acrylamide-2-methylpropanesulfonic acid unit or an acrylamide unit as a constituent monomer unit. Manufacturing method of ceramic. The mixture containing water- absorbing polymer particles , ceramic raw material and water is a mixture of powdered water-absorbing polymer particles and powdered ceramic raw material. Water is added to and mixed with the powdered mixture of water-absorbing polymer particles and ceramic raw material. The method for producing a porous ceramic according to claim 1, wherein the method is obtained .

Images