Method for manufacturing porous ceramics, clay for forming porous ceramics, and dried body

Abstract

The object of the present invention is to provide a method for producing porous ceramics, which can provide porous ceramics that maintain good formability and shape retention during production and have improved strength. [Solution] The method for producing porous ceramics disclosed herein includes a powder material preparation step of mixing a ceramic raw material with a pore-forming agent to obtain a powder material, a kneading step of kneading the powder material with an aqueous dispersion medium to obtain a clay, a clay forming step of forming the clay into a predetermined shape, a molded body drying step of drying the molded body obtained by the molding step, and a dried body firing step of firing the dried body after the drying step.The pore-forming agent is characterized by using two or more types of water-absorbent polymer powders with different average particle sizes.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing porous ceramics, a clay for forming porous ceramics, and a dried body. [Background technology]

[0002] Porous ceramics, which are primarily composed of inorganic materials such as ceramics, are widely used in various fields as filter materials, catalyst carriers, gas separation materials, etc. Porous ceramics, for example, have a skeleton with a three-dimensional network structure and pores formed between the skeletons.

[0003] Conventionally, porous ceramics are manufactured using a powder material containing ceramic raw materials and a pore-forming material made of combustible particles. This powder material is made into a clay-like form, molded into a desired shape, and then fired. This burns off the pore-forming material particles, forming pores, and sinters the ceramic raw materials to form a network structure skeleton. In recent years, water-absorbent polymer particles have been used as the pore-forming material to achieve decarbonization during firing. Patent Document 1 is an example of such prior art. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-245278 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the manufacturing method of porous ceramics using a water-absorbent polymer as a pore-forming material, the moldability and shape retention of the clay may be reduced, which may lead to a decrease in productivity. In addition, in the manufacturing of porous ceramics, the strength of the resulting sintered body (porous ceramics) is required.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a method for manufacturing porous ceramics that can maintain good formability and shape retention during manufacturing and produce porous ceramics with improved strength. [Means for solving the problem]

[0007] The manufacturing method disclosed herein is a method for manufacturing porous ceramics, and includes a powder material preparation step of mixing a ceramic raw material with a pore-forming agent to obtain a powder material, a kneading step of kneading the powder material with an aqueous dispersion medium to obtain a clay, a clay forming step of forming the clay into a predetermined shape, a molded body drying step of drying the molded body obtained by the molding step, and a dried body firing step of firing the dried body after the drying step.The manufacturing method is characterized in that two or more types of water-absorbent polymer powders having different average particle sizes are used as the pore-forming agent.

[0008] To achieve the above-mentioned object, the inventors focused on the particle size of the water-absorbent polymer. After extensive research, the inventors discovered that the larger the particle size of the water-absorbent polymer to be mixed, the lower the fluidity of the clay and the higher the yield point, which tends to improve shape retention. On the other hand, the inventors discovered that the smaller the particle size of the water-absorbent polymer, the higher the lubricity, which improves the moldability of the clay and the strength of the resulting fired body (porous ceramics). Therefore, in the manufacturing method according to this embodiment, two or more types of water-absorbent polymer powders with different average particle sizes are used as pore-forming materials. This allows for the production of porous ceramics that maintain good moldability and shape retention during manufacturing and have improved strength.

[0009] In a preferred embodiment of the manufacturing method disclosed herein, the pore-forming material comprises a first water-absorbent polymer powder and a second water-absorbent polymer powder having an average particle size relatively smaller than that of the first water-absorbent polymer powder.

[0010] In a preferred embodiment of the manufacturing method disclosed herein, when the weight of the entire pore-forming material is taken as 100 wt %, the weight ratio of the second water-absorbent polymer powder is 25 wt % or more and 80 wt % or less.

[0011] In a preferred embodiment of the production method disclosed herein, the ratio of the average particle size of the second water-absorbing polymer powder to the average particle size of the first water-absorbing polymer powder (average particle size of the second water-absorbing polymer powder / average particle size of the first water-absorbing polymer powder) is 1 / 20 or more and 1 / 5 or less.

[0012] In a preferred embodiment of the production method disclosed herein, the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

[0013] In a preferred embodiment of the production method disclosed herein, the water-absorbent polymer powder having the largest average particle size among the water-absorbent polymer powders has an average particle size of 25 μm or more and 600 μm or less, and the water-absorbent polymer powder having the smallest average particle size has an average particle size of 5 μm or more and 120 μm or less.

[0014] In one preferred embodiment of the manufacturing method disclosed herein, the drying step is carried out so that the moisture content of the dried body is greater than 0 wt% and less than 20 wt% when the total weight of the dried body is taken as 100 wt%.

[0015] Another aspect of the technology disclosed herein provides a clay for forming porous ceramics. The clay disclosed herein includes a pore-forming material, a ceramic raw material, and an aqueous dispersion medium. The pore-forming material is a granular water-absorbent polymer, and the granular water-absorbent polymer has a multimodal volume-based particle size distribution. By using a clay having such a configuration in the production of porous ceramics, it is possible to obtain porous ceramics that maintain good moldability and shape retention during production and have improved strength.

[0016] In one preferred embodiment of the clay disclosed herein, the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having an average particle size relatively smaller than that of the first water-absorbing polymer.

[0017] In a preferred embodiment of the clay disclosed herein, when the weight of the entire pore-forming material is taken as 100 wt %, the weight ratio of the second water-absorbent polymer is 25 wt % or more and 80 wt % or less.

[0018] In one preferred embodiment of the clay disclosed herein, the ratio of the average particle size of the second water-absorbing polymer to the average particle size of the first water-absorbing polymer (average particle size of the second water-absorbing polymer / average particle size of the first water-absorbing polymer) is 1 / 20 or more and 1 / 5 or less.

[0019] In a preferred embodiment of the clay disclosed herein, the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

[0020] In a preferred embodiment of the clay disclosed herein, in the particle size distribution of the granular water-absorbing polymer, the peak top of the peak with the largest particle size is 25 μm or more and 600 μm or less, and the peak top of the peak with the smallest particle size is 5 μm or more and 120 μm or less.

[0021] Another aspect of the technology disclosed herein provides a dried body for forming porous ceramics. The dried body disclosed herein includes a matrix made of ceramic raw materials and a pore-forming material dispersed in the matrix. The pore-forming material is composed of a granular water-absorbent polymer, and the granular water-absorbent polymer has a multimodal volume-based particle size distribution. By using a dried body having such a configuration in the production of porous ceramics, porous ceramics with improved strength can be obtained.

[0022] In one preferred embodiment of the dry body disclosed herein, the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having an average particle size relatively smaller than that of the first water-absorbing polymer.

[0023] In a preferred embodiment of the dried body disclosed herein, when the weight of the entire pore-forming material is taken as 100 wt %, the weight ratio of the second water-absorbing polymer is 25 wt % or more and 80 wt % or less.

[0024] In a preferred embodiment of the dried body disclosed herein, the ratio of the average particle size of the second water-absorbent polymer to the average particle size of the first water-absorbent polymer (average particle size of the second water-absorbent polymer / average particle size of the first water-absorbent polymer) is 1 / 20 or more and 1 / 5 or less.

[0025] In a preferred embodiment of the dried body disclosed herein, the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

[0026] In a preferred embodiment of the dried body disclosed herein, in the particle size distribution of the granular water-absorbing polymer, the peak top of the peak with the largest particle size is 25 μm or more and 600 μm or less, and the peak top of the peak with the smallest particle size is 5 μm or more and 120 μm or less.

[0027] In a preferred embodiment of the dried material disclosed herein, the moisture content of the dried material is more than 0 wt% and 20 wt% or less when the weight of the entire dried material is taken as 100 wt%. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a flow diagram showing the method for producing the porous ceramics of this embodiment. [Figure 2] FIG. 2 shows the particle size distribution on a volume basis of the pore-forming materials according to Examples 2, 4 and 6. [Figure 3] FIG. 3 is a graph showing the porosity of the porous ceramics according to each of the test examples. [Figure 4] FIG. 4 is a graph showing the pore size distribution of the porous ceramics according to Reference Example, Example 2 and Example 4. [Figure 5] FIG. 5 is a graph showing an enlarged view of the pore size distribution in FIG. 4, covering the pore size range of 10 to 1000 μm (horizontal axis). [Figure 6] FIG. 6 is a graph showing the crushing strength of the porous ceramics according to each of the test examples. [Figure 7] FIG. 7 is a graph showing the wear rate of the porous ceramics according to each of the test examples. DETAILED DESCRIPTION OF THE INVENTION

[0029] An embodiment of the technology disclosed herein will be described below. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. In this specification, when a numerical range is indicated as "A to B," it means "greater than or equal to A and less than or equal to B."

[0030] <Method for manufacturing porous ceramics> First, a method for manufacturing porous ceramics according to this embodiment will be described. FIG. 1 is a flow diagram showing the method for manufacturing porous ceramics according to this embodiment. As shown in FIG. 1, the method for manufacturing porous ceramics according to this embodiment includes a powder material preparation step S110, a kneading step S120, a clay molding step S130, a molded body drying step S140, and a dried body firing step S150. Note that the manufacturing method disclosed herein may further include other steps at any stage. Each step will be described below.

[0031] (Powder material adjustment process S110) In the powder material preparation step S110, the ceramic raw material and the pore-forming material particles are mixed to obtain a powder material. Each material constituting the powder material will be described below.

[0032] 1. Ceramic raw materials The ceramic raw material is an inorganic material that forms ceramics by firing. Any ceramic raw material that has been conventionally used to produce porous ceramics by sintering can be used without particular limitation. The ceramic raw material includes, for example, an aggregate that is the main raw material and a secondary raw material.

[0033] (1)Main raw materials As described above, aggregate is included as the main raw material of the ceramic raw materials. The aggregate constitutes the skeleton of the porous ceramic after firing. As the aggregate, various ceramic powders such as metal oxides, carbides, and nitrides can be used. For example, α-alumina, γ-alumina, fused alumina, silica, zirconia, mullite, silicon nitride, silicon carbide, titania, calcia, various zeolites, etc. can be preferably used. Furthermore, the aggregate may be composed of a composite or mixture of these.

[0034] The average particle size of the main raw material constituting the ceramic raw material is, for example, about 0.1 μm or more, preferably 1 μm or more, and more preferably 10 μm or more. The larger the average particle size of the main raw material, the more effectively the gaps between the powder particles can remain as pores even after firing. On the other hand, from the viewpoint of maintaining mechanical strength, the average particle size of the main raw material is, for example, about 1000 μm or less, preferably 100 μm or less, and more preferably 10 μm or less. In this specification, unless otherwise specified, "average particle size" refers to the particle size at 50% of the cumulative value in the particle size distribution measured using a particle size distribution measuring device based on the laser scattering / diffraction method, i.e., the 50% volume average particle size (D50 diameter).

[0035] (2) Auxiliary raw materials The ceramic raw material may contain auxiliary materials, such as bond materials, slip materials, etc. Examples of such auxiliary materials include kaolin, talc, clay, clay minerals, chamotte, silica sand, pottery stone, feldspar, shirasu, and bentonite.

[0036] The shape (external shape) of the ceramic raw material is not particularly limited, and not only spherical or nearly spherical shapes but also powders that are aggregates of irregularly shaped particles prepared by, for example, roll milling or stamp milling can be suitably used. From the viewpoint of suppressing densification (movement of ceramic particles) during firing, ceramic powders having irregular shapes (for example, crushed, needle-like, or plate-like) can be preferably used.

[0037] The weight ratio of the main raw material to the auxiliary raw material (main raw material:auxiliary raw material) in the ceramic raw material is not particularly limited, but is, for example, 90:10 or more, preferably 80:20 or more, and more preferably 70:30 or more. As a result, even if the main raw material has a large particle size, for example, an average particle size of 100 μm or more (low sinterability), the auxiliary raw material forms necks and has sufficient strength to function as a porous body. On the other hand, from the viewpoint of forming a high porosity, the weight ratio of the main raw material to the auxiliary raw material (main raw material:auxiliary raw material) is, for example, 50:50 or less, preferably 60:40 or less, and more preferably 70:30 or less.

[0038] 2. Pore forming material The pore-forming material has the property of being burned away at a temperature above a certain level. This embodiment is characterized in that two or more types of water-absorbent polymer powders having different average particle diameters are used as the pore-forming material. Such water-absorbent polymer powder may be one in which the particle diameter has been reduced by processing such as pulverization of a water-absorbent polymer, or one in which the particle diameter has been reduced in a manufacturing process of the water-absorbent polymer (for example, a granulation process). Note that the term "powder" in this specification refers to a group of fine particles. In other words, "water-absorbent polymer powder" refers to a group of granular water-absorbent polymers.

[0039] The content of the pore-forming material (water-absorbent polymer powder) contained in the powder material is appropriately adjusted taking into consideration the shape and porosity of the porous ceramic (molded body), the water absorption capacity of the pore-forming material, etc. For example, when the total weight of the ceramic raw materials is 100 parts by weight, the content of the water-absorbent polymer powder is preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and particularly preferably 4 parts by mass or more. As the content of the water-absorbent polymer powder increases, the porosity of the resulting porous ceramic increases, and the moisture content of the clay also tends to increase. On the other hand, the upper limit of the content of the water-absorbent polymer powder is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 6 parts by mass or less. As the content of the water-absorbent polymer powder decreases, the strength of the porous ceramic tends to improve.

[0040] Among two or more types of water-absorbent polymer powders used as pore-forming materials, the average particle size of the water-absorbent polymer powder having the largest average particle size is preferably 600 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less, from the viewpoint of moldability of the clay. On the other hand, from the viewpoint of shape retention of the clay, the average particle size of the water-absorbent polymer powder having the largest average particle size is preferably 25 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. In addition, when the pore-forming material is composed of a first water-absorbent polymer powder and a second water-absorbent polymer powder, the "average particle size of the water-absorbent polymer powder having the largest average particle size" corresponds to the average particle size of the first water-absorbent polymer powder.

[0041] Among two or more types of water-absorbent polymer powders used as the pore-forming material, the average particle size of the water-absorbent polymer powder having the smallest average particle size is preferably 120 μm or less, more preferably 80 μm or less, and even more preferably 30 μm or less, from the viewpoint of the fluidity of the clay. By improving the fluidity of the clay, defects (such as cracks) in the molded body can be further suppressed, and the strength of the porous ceramic can be suitably obtained. On the other hand, from the viewpoint of pore formation as a pore-forming material, the average particle size of the water-absorbent polymer powder having the smallest average particle size is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Note that when the pore-forming material is composed of a first water-absorbent polymer powder and a second water-absorbent polymer powder, the "average particle size of the water-absorbent polymer powder having the smallest average particle size" corresponds to the average particle size of the second water-absorbent polymer powder.

[0042] In some preferred embodiments, the pore-forming material preferably comprises a first water-absorbent polymer powder and a second water-absorbent polymer powder having a relatively smaller average particle size than the first water-absorbent polymer powder. This configuration allows for favorable control of both moldability and strength of the porous ceramics after production. The compositions of the first water-absorbent polymer powder and the second water-absorbent polymer powder may be the same or different. In addition, in this configuration, the volumetric particle size distribution of the pore-forming material (granular water-absorbent polymer) exhibits a so-called bimodal distribution, which has two peaks.

[0043] When the pore-forming material is composed of a first water-absorbent polymer powder and a second water-absorbent polymer powder, the weight ratio of the second water-absorbent polymer powder is preferably 25 wt% or more, more preferably 35 wt% or more, and even more preferably 45 wt% or more, when the weight of the entire pore-forming material is taken as 100 wt%. As the weight ratio of the second water-absorbent polymer powder (i.e., small particle size water-absorbent polymer powder) increases, the moldability improves and the strength of the manufactured porous ceramics improves. On the other hand, if the weight ratio of the second water-absorbent polymer powder is too high, the shape retention of the molded body may deteriorate. From this perspective, when the weight of the entire pore-forming material is taken as 100 wt%, the weight ratio of the second water-absorbent polymer powder is preferably 80 wt% or less, more preferably 70 wt% or less, and even more preferably 60 wt% or less.

[0044] When the pore-forming material is composed of a first water-absorbent polymer powder and a second water-absorbent polymer powder, the ratio of the average particle size of the second water-absorbent polymer powder to the average particle size of the first water-absorbent polymer powder (average particle size of the second water-absorbent polymer powder / average particle size of the first water-absorbent polymer powder) is preferably 1 / 5 or less, more preferably 1 / 8 or less, and even more preferably 1 / 10 or less. The smaller the average particle size of the second water-absorbent polymer powder is relative to the average particle size of the first water-absorbent polymer powder, the more improved the shape retention of the puddle. On the other hand, from the viewpoint of improving the fluidity of the puddle, the ratio of the average particle size of the second water-absorbent polymer powder to the average particle size of the first water-absorbent polymer powder (average particle size of the second water-absorbent polymer powder / average particle size of the first water-absorbent polymer powder) is preferably 1 / 20 or more, more preferably 1 / 17 or more, and even more preferably 1 / 15 or more.

[0045] When the volumetric particle size distribution of the pore-forming material of this embodiment is obtained, the particle size distribution shows a so-called multimodality, including a plurality of (two or more) peaks (mountains). "Particle size distribution of granular water-absorbent polymer" is a particle size volume distribution of the granular water-absorbent polymer (whole water-absorbent polymer powder) constituting the pore-forming material obtained by a dry laser diffraction particle size distribution measuring device, and specifically, is a graph obtained in which the horizontal axis represents the particle size of the water-absorbent polymer and the vertical axis represents the occupied volume (%).

[0046] In the volumetric particle size distribution of the pore-forming material of this embodiment, the peak top of the peak with the largest particle size (large particle size) is preferably 600 μm or less, more preferably 400 μm or less, and even more preferably 300 μm or less, from the viewpoint of the moldability of the clay. On the other hand, from the viewpoint of the shape retention of the clay, the peak top of the peak with the largest particle size is preferably 25 μm or more, more preferably 100 μm or more, and even more preferably 200 μm or more. Note that when the particle size distribution shows a bimodal distribution, the "peak top of the peak with the largest particle size" corresponds to the peak top of the first peak.

[0047] In the volumetric particle size distribution of the pore-forming material of this embodiment, the peak top of the peak with the smallest particle size (small particle size) is preferably 120 μm or less, more preferably 80 μm or less, and even more preferably 30 μm or less, from the viewpoint of improving the fluidity of the clay. On the other hand, from the viewpoint of pore formation as a pore-forming material, the peak top of the peak with the smallest particle size is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more. Note that when the particle size distribution exhibits bimodalities, the "peak top of the peak with the smallest particle size" corresponds to the peak top of the second peak.

[0048] The water absorption capacity of the pore-forming material (water-absorbent polymer powder) for pure water is preferably 100 g / g or more, more preferably 200 g / g or more, and even more preferably 400 g / g or more. The greater the water absorption capacity of the water-absorbent polymer powder, the softer the water-absorbent polymer powder tends to be after absorbing water. The softer the water-absorbent polymer powder after absorbing water, the better the lubricity of the moldable clay, and thus the better the moldability. On the other hand, from the viewpoint of maintaining the shape of the water-absorbent polymer, the water absorption capacity of the pore-forming material (water-absorbent polymer powder) for pure water is preferably 1000 g / g or less, more preferably 800 g / g or less, and even more preferably 600 g / g or less. The water absorption capacities of two or more types of water-absorbent polymer powders with different average particle sizes used in the pore-forming material may be the same or different from each other. When the water absorption capacities are made different from each other, it is preferable that the water absorption capacities of each water-absorbent polymer powder satisfy the above-mentioned numerical range. The "absorption amount of pure water of the pore-forming material" can be obtained by measuring using pure water as the test liquid in accordance with JIS K7223:1996.

[0049] The water-absorbing polymer powder used in the manufacturing method according to this embodiment may be a polyacrylate-based or polysulfonate-based polymer. Among them, a polyacrylate-based resin is preferably used because of its easy availability. Examples of commercially available polyacrylate-based resins include Sunfresh ST (Sanyo Chemical Industries, Ltd.), Aqualic CA (Nippon Shokubai Co., Ltd.), and Aqua Keep (Sumitomo Seika Chemicals Co., Ltd.).

[0050] The pore-forming material in the powder material preparation step S110 is preferably in a dry state (before absorbing water). By using a dry pore-forming material, a powder material in which the ceramic raw materials and the pore-forming material are more uniformly dispersed can be obtained. Then, in the subsequent kneading step S120, a clay in which the ceramic raw materials and the pore-forming material are more uniformly dispersed can be obtained. This makes it possible to more suitably improve the strength and porosity of the porous ceramic after production.

[0051] The powder material may also contain additives as long as they do not significantly impair the effects of the technology disclosed herein. An example of such an additive is a binder. The binder acts as a molding aid. In other words, adding a binder makes it easier to maintain the shape of the compact from the drying process to the firing process. Examples of binders that can be used include polyvinyl alcohol, ethyl cellulose, and methyl cellulose. The binder content is preferably adjusted taking into account the content of the ceramic raw materials. This makes it easier to maintain the shape of the dried body after the drying step S103. Specifically, when the content of the ceramic raw materials in the powder material is 100 parts by weight, the binder content is preferably 1 part by weight or more, more preferably 2 parts by weight or more, and particularly preferably 3 parts by weight or more. This allows the shape of the dried body to be favorably maintained. On the other hand, the upper limit of the binder content is preferably 13 parts by weight or less, more preferably 10 parts by weight or less, and particularly preferably 7 parts by weight or less. This prevents the viscosity of the porous ceramic clay from increasing excessively.

[0052] From the viewpoint of sintering porous ceramics, the sodium content of the powder material may be, but is not limited to, approximately 5 wt% or less, preferably 2 wt% or less, based on the total powder material. The lower the sodium content of the powder material, the more effectively the sinterability of the ceramic raw material can be controlled (more specifically, the more effectively the densification of the sintered body can be suppressed). The sodium content can be controlled by appropriately changing the ceramic raw material in accordance with the pore-forming agent prepared. The sodium content of the powder material can be measured, for example, by X-ray fluorescence analysis (XRF).

[0053] <Kneading process S120> In the kneading step S120, the powder material and the aqueous dispersion medium are kneaded. This produces a clay in which the pore-forming material and the ceramic raw material are dispersed in the aqueous dispersion medium. Note that the term "clay" in this specification refers to a mixture of solid particles and liquid, and includes not only granular but also clay-like and mud-like forms.

[0054] In this embodiment, an aqueous dispersion medium is used as the dispersion medium. This allows the powder material to be uniformly dispersed, and the water-absorbing polymer to absorb water and swell. Examples of such aqueous dispersion mediums include tap water, ion-exchanged water (deionized water), distilled water, and pure water. The aqueous dispersion medium may also be a mixed solvent of water and an organic solvent. The organic solvent used is an organic solvent that can be uniformly mixed with water. Specific examples of such organic solvents include lower alcohols having 1 to 4 carbon atoms (e.g., methanol, ethanol), and lower ketones. When preparing a mixed dispersion medium, it is preferable that the proportion of water be 80% by mass or more (more preferably 90% by mass or more, and even more preferably 95% by mass or more) when the total amount of the dispersion medium is 100% by mass.

[0055] The content of the aqueous dispersion medium in the clay is adjusted appropriately, taking into consideration the shape of the porous ceramic (molded body), the moldability of the clay, the water absorption and addition amount of the pore-forming material, etc. For example, when the total weight of the ceramic raw materials is 100 parts by weight, the content of the aqueous dispersion medium is preferably 15 parts by mass or more, more preferably 30 parts by mass or more, even more preferably 50 parts by mass or more, and particularly preferably 70 parts by mass or more. As the content of the aqueous dispersion medium in the clay increases, the fluidity of the clay tends to improve, making it easier to mold the molded body. On the other hand, the upper limit of the content of the aqueous dispersion medium is preferably 200 parts by mass or less, more preferably 160 parts by mass or less, even more preferably 110 parts by mass or less, and particularly preferably 90 parts by mass or less. As the content of the aqueous dispersion medium in the clay decreases, the shape retention of the molded body tends to improve.

[0056] The kneading of these various components can be carried out using a general kneading means such as a kneader, a planetary mixer, etc. Although not particularly limited, when the water contained in the water-absorbing polymer is returned back due to the shear applied during kneading, the mixture may be stirred with a mixer that is less susceptible to shear, such as a Henschel mixer or an intensive mixer, to form a granular kneaded product (clay).

[0057] Furthermore, in the kneading step S120, additives may be further added and kneaded as long as they do not significantly impair the effects of the technology disclosed herein. An example of such an additive is a lubricant. Adding a lubricant improves the slipperiness of the ceramic raw materials during the extrusion molding process, thereby enabling the production of a molded body with more effectively suppressed defects (e.g., cracks). Examples of lubricants that can be used include wax, olefin wax, stearic acid, and glycerin. The lubricant content is preferably adjusted taking into account the content of the ceramic raw materials. This reduces the friction of the ceramic raw materials, making molding easier in the clay molding step S130. Specifically, when the content of the ceramic raw materials in the powder material is 100 parts by weight, the content of the lubricant is preferably 1 part by weight or more, more preferably 2 parts by weight or more, and particularly preferably 4 parts by weight or more. This improves the slipperiness of the ceramic raw materials and enables the production of a molded body with more effectively suppressed defects. On the other hand, if the amount of lubricant is too large, there is a risk that the excess lubricant will separate from the clay during the clay molding step S130. Therefore, the upper limit of the amount of the lubricant is preferably 8 parts by weight or less, more preferably 6 parts by weight or less, and particularly preferably 5 parts by weight or less.

[0058] In the kneading step S120, the water-absorbent polymer contained in the powder material absorbs water and becomes swollen. Here, the inventors focused on the particle size of the water-absorbent polymer. The larger the particle size of the water-absorbent polymer to be mixed, the lower the fluidity of the clay and the higher the yield point, which tends to improve shape retention. On the other hand, the smaller the particle size of the water-absorbent polymer, the higher the lubricity in the swollen state (water-absorbed state). Therefore, the moldability of the clay (e.g., suppression of cracking) improves. Therefore, in the manufacturing method according to this embodiment, two or more types of water-absorbent polymer powders with different average particle sizes are used as pore-forming materials. That is, the clay according to this embodiment includes an aqueous dispersion medium, a ceramic raw material, and a granular water-absorbent polymer as a pore-forming material. The volume-based particle size distribution of the granular water-absorbent polymer exhibits multimodality. This achieves both improved moldability and shape retention.

[0059] <Kneaded clay forming process S130> In the clay molding step S130, the clay is molded into a predetermined shape. The molding method for the composition is not particularly limited, and any conventionally known molding method can be used. Examples of molding methods include extrusion molding, press molding, and molded molding, and pressure molding using a floating die or a press is preferred.

[0060] The shape of the product formed in the clay forming step S130 is not particularly limited and can be changed appropriately depending on the application. For example, the product can be formed into a cylindrical shape, a flat plate shape, a columnar shape, a ring shape, etc., but is not limited thereto.

[0061] <Molded object drying process S140> In the compact drying step S140, the compact obtained in the clay molding step S130 is dried at a predetermined temperature. This removes moisture from the compact, and a dried body of the desired shape is produced. Note that the term "dried body" in this specification refers to the compact after the drying process in the compact drying step S140 has been performed. In other words, it is not limited to a form in which moisture has been completely removed from the compact.

[0062] Although not limited thereto, it is preferable to perform the compact drying step S140 so that the moisture content of the dried body is greater than 0 wt% (more preferably, 1 wt% or more, even more preferably, 4 wt% or more) and 20 wt% or less (more preferably, 18 wt% or less, even more preferably, 15 wt% or less) when the weight of the entire dried body is taken as 100 wt%. The lower the moisture content in the dried body, the more likely it is that deformation of the dried body and adhesion between dried bodies will be suppressed. Therefore, from the viewpoint of handleability, a lower moisture content in the dried body is preferable. On the other hand, the higher the moisture content in the dried body, the more the time required for the compact drying step S140 can be shortened. Therefore, from the viewpoint of energy saving, a higher moisture content in the dried body is preferable. Therefore, by controlling the moisture content of the dried body within the above range, both handleability and energy saving can be achieved. The moisture content of the dried body can be measured, for example, using a heat-drying moisture meter.

[0063] Typically, from the viewpoint of energy conservation, a shorter drying time for the compact is preferable. On the other hand, in the case of compacts produced by conventional porous ceramic manufacturing methods, if the moisture in the dried body is not completely removed, the dried body may deform or stick together. Therefore, it is necessary to dry the compact until it is substantially free of moisture. In the manufacturing method according to the present embodiment, a water-absorbent polymer is used as the pore-forming material. Compacts containing water-absorbent polymers have high shape retention and low adhesion. Therefore, even if the dried body contains moisture (e.g., a moisture content of approximately 20 wt% or less), the dried body is less likely to deform and stick together. Therefore, in the manufacturing method according to the present embodiment, it is not necessary to dry the compact until it is substantially free of moisture in the compact drying step S140. However, this is not limited thereto, and the compact may be dried until it is substantially free of moisture in the compact drying step S140. Note that, in this specification, the term "substantially free of moisture" refers to a state in which the moisture content in the dried body is approximately 1% or less.

[0064] The means used in the compact drying step S140 may be any known means. Examples of such means include hot air drying, far-infrared drying, and microwave drying. Among these, far-infrared drying and microwave drying are preferred in terms of accelerating the drying of the interior of the compact. Furthermore, the means used in the compact drying step S140 may include humidified drying and humidity-controlled drying, in which water vapor is added to the drying furnace. Furthermore, in the compact drying step S140, the drying means and drying temperature may be switched multiple times.

[0065] The drying temperature in the compact drying step S140 is set to a temperature at which the moisture in the compact evaporates but the pore-forming material particles are not burned away. From the viewpoint of preventing microcracks, when drying with a general hot air dryer or the like, gentle drying is preferred, and the drying temperature may be 120°C or lower, preferably 100°C or lower, and more preferably 90°C or lower. On the other hand, when drying with a general hot air dryer or the like, the drying temperature may be, for example, 70°C or higher, preferably 80°C or higher, and more preferably 85°C or higher. Furthermore, when drying with a far-infrared dryer, microwave dryer, or the like (in other words, a drying method that promotes drying of the interior of the compact), the drying temperature may be, for example, 170°C or lower, preferably 150°C or lower, and more preferably 120°C or lower. On the other hand, when drying with a far-infrared dryer, microwave dryer, or the like, the drying temperature may be, for example, 70°C or higher, preferably 80°C or higher, and more preferably 85°C or higher. The drying time is not particularly limited and can be adjusted appropriately depending on the size of the molded product.

[0066] Here, the dried body obtained by the manufacturing method according to this embodiment includes a matrix made of ceramic raw materials and two or more types of water-absorbent polymer powders having different average particle sizes dispersed in the matrix. More specifically, in the dried body, the granular water-absorbent polymer is uniformly arranged in the matrix made of ceramic raw materials. The volume-based particle size distribution of the granular water-absorbent polymer exhibits multimodality. By using a dried body having such a configuration, porous ceramics with good ceramic strength can be obtained.

[0067] <Dry body firing process S150> In the dried body firing step S150, the dried body obtained in the compact drying step S140 is fired, whereby the water-absorbing polymer and other organic substances (binder, wax, etc.) contained in the dried body are degreased (burned out).

[0068] As described above, in this embodiment, a water-absorbent polymer is used as the pore-forming material particles. Water-absorbent polymers have the property of expanding in volume upon absorbing water. Therefore, typically, the amount of organic component required to form the desired porosity is smaller than that of conventional pore-forming material particles made only of combustible substances (e.g., walnuts). This allows for firing in a short period of time. From this perspective, it is preferable to perform firing in a short period of time using a continuous furnace such as a roller hearth kiln (RHK). This configuration allows for reducing the energy input in the dried body firing step S150. However, the firing furnace is not limited to this, and any conventionally known firing furnace may also be used. For example, a batch-type firing furnace may be used as the firing furnace.

[0069] The maximum firing temperature in the dried body firing step S150 can be, for example, about 1100°C or higher, preferably 1200°C or higher, and more preferably 1300°C or higher, from the viewpoint of thoroughly degreasing the water-absorbent polymer and other organic matter contained in the dried body. This allows for the production of porous ceramics that are free of organic residue and have sufficient strength. On the other hand, from the viewpoint of the heat resistance of the firing furnace and the input energy, the maximum firing temperature in the dried body firing step S150 can be, for example, about 1700°C or lower, preferably 1600°C or lower, and more preferably 1400°C or lower.

[0070] The time for maintaining the calcination temperature (maximum calcination temperature) in the dried body calcination step S150 depends on the calcination temperature, but is generally about 0.5 to 4 hours, preferably about 1 to 2 hours. The atmosphere in the dried body calcination step S150 is not limited to air atmosphere, and can also be an oxygen atmosphere, etc., as necessary.

[0071] In the dried body firing step S150, pores are formed by burning out the water-absorbent polymer. Furthermore, a ceramic skeleton is formed by sintering the ceramic raw materials that form the matrix of the dried body. This allows for the production of porous ceramics with a skeleton having a three-dimensional network structure and pores surrounded by the skeleton as a fired body. The porous ceramics obtained by the manufacturing method according to this embodiment have good ceramic strength. The inventors speculate on this effect as follows: First, in the manufacturing method according to this embodiment, two or more types of water-absorbent polymer powders with different average particle sizes are used as pore-forming materials. This improves the fluidity of the clay and improves its moldability. More specifically, this improves the appearance of minute cracks that are not visible to the naked eye, and also homogenizes the pores in the porous ceramic. It is speculated that this leads to improved ceramic strength.

[0072] The shape and size of the pores in the porous ceramic according to this embodiment can be adjusted as needed by changing the shape and size of the pore-forming material. The porosity can be adjusted as needed by changing the content of the pore-forming material and the water content in the clay. The pore size and porosity of the porous ceramic can be determined as needed depending on the application, but the porosity measured by mercury intrusion porosimetry is generally in the range of 30% to 70%, preferably 50% to 70%. The average pore size measured by mercury intrusion porosimetry is not particularly limited, but can be, for example, in the range of approximately 0.05 μm to 500 μm.

[0073] The porous ceramics obtained by the manufacturing method disclosed herein can be used in a variety of applications, including ceramic structural materials (e.g., grinding wheels, industrial ceramic molds, refractories, firing setters, etc.) and functional ceramics (e.g., ceramic filters, porous substrates for fuel cells, catalyst carriers, etc.).

[0074] [Test example] Test examples relating to the technology disclosed herein will be described below, but these test examples are not intended to limit the technology disclosed herein.

[0075] <Adjusting the clay> (Reference example) Here, a porous ceramic clay for the Reference Example was prepared using only one type of water-absorbent polymer powder (only the first water-absorbent polymer powder) as a pore-forming material. First, a ceramic raw material was prepared by blending electrofused alumina (average particle size 212-250 μm) as an aggregate as the main raw material with kaolin, clay, and pottery stone as the bond raw materials as the auxiliary raw materials in a weight ratio of 73:8:16:3 (total amount 100 parts by weight). Four parts by weight (based on 100 parts by weight of ceramic raw material) of Sunfresh ST-500D (manufactured by Sanyo Chemical Industries, Ltd., average particle size 380 μm, water absorption capacity 400 g / g, acrylic acid polymer partially cross-linked with sodium salt) in a pre-absorbed state was prepared as the first water-absorbent polymer powder. This was mixed with the ceramic raw material for 10 minutes using an intensive mixer to obtain a powder material. The resulting powder material was mixed with 70 parts by weight of water (based on 100 parts by weight of the ceramic raw material) and 1 part by weight of wax (based on 100 parts by weight of the ceramic raw material) as a lubricant in an intensive mixer for 15 minutes, resulting in a granular clay with a moisture content of approximately 38 wt%.

[0076] (Examples 1 to 7) In Examples 1 to 7, two types of water-absorbent polymer powders (first water-absorbent polymer powder and second water-absorbent polymer powder) having different average particle sizes were used as pore-forming materials to prepare porous ceramic clays. Specifically, the same water-absorbent polymer powder as in the Reference Example was prepared as the first water-absorbent polymer powder, and further, Sunfresh ST-500MPSA (manufactured by Sanyo Chemical Industries, Ltd., average particle size 30 μm, water absorption capacity 600 g / g, acrylic acid polymer partially cross-linked with sodium salt) in a state before water absorption was prepared as the second water-absorbent polymer powder. Then, the first water-absorbent polymer powder and the second water-absorbent polymer powder were mixed with the ceramic raw material at the weight ratio (relative to 100 parts by weight of the ceramic raw material) shown in Table 1. The rest of the procedure was the same as in the Reference Example. As a result, a granular clay with a moisture content of approximately 38 wt% was obtained.

[0077] The pore-forming materials (first water-absorbent polymer powder and second water-absorbent polymer powder) of Examples 2, 4, and 6 were measured using a dry laser diffraction particle size distribution analyzer to obtain particle size distributions. The results are shown in Figure 2. The horizontal axis represents the particle size (µm) of the water-absorbent polymer, and the vertical axis represents the occupied volume (%). As shown in Figure 2, the particle size distributions of the pore-forming materials of Examples 2, 4, and 6 were multimodal with multiple peaks (here, bimodal with two peaks). In addition, the peak top of the peak with the largest particle size of the pore-forming materials of Examples 2, 4, and 6 was 400 µm in all examples. In addition, the peak top of the peak with the smallest particle size of the pore-forming materials of Examples 2, 4, and 6 was 31 µm in all examples.

[0078] (Example 8) In Example 8, instead of using the first water-absorbing polymer powder (Sunfresh ST-500D), 4 parts by weight (based on 100 parts by weight of the ceramic raw material) of the second water-absorbing polymer powder (Sunfresh ST-500MPSA) used in Examples 1 to 7 was mixed with the ceramic raw material. The rest of the procedure was the same as in the Reference Example. As a result, a granular clay with a moisture content of approximately 38 wt% was obtained.

[0079] (Example 9) In Example 9, instead of Sunfresh ST-500D, AQUALIC CA QX-A-9001 (manufactured by Nippon Shokubai Co., Ltd., average particle size 380 μm, water absorption capacity 470 g / g, acrylic acid polymer partially cross-linked with sodium salt) was prepared as the first water-absorbent polymer powder. Then, the first water-absorbent polymer powder and the second water-absorbent polymer powder were each mixed with the ceramic raw material in a ratio of 2 parts by weight (relative to 100 parts by weight of the ceramic raw material). Except for this, the same procedure as in Example 1 was carried out. In this way, a granular clay having a moisture content of approximately 38 wt% was obtained.

[0080] (Example 10) In Example 10, the weight ratio of kaolin and clay in the ceramic raw materials was adjusted to match the sodium content of the prepared powder material with that of other examples (Reference Example and Examples 1-9). Specifically, the ceramic raw material of Example 10 was obtained by blending fused alumina, kaolin, clay, and pottery stone in a weight ratio of 73:19:5:3 (total amount 100 parts by weight). Next, 3 parts by weight of a first water-absorbing polymer powder (Sunfresh ST-500D) (relative to 100 parts by weight of the ceramic raw material) and 2 parts by weight of a second water-absorbing polymer powder (Sunfresh ST-500MPSA) (relative to 100 parts by weight of the ceramic raw material) were mixed with the ceramic raw material to obtain a powder material. The obtained powder material was kneaded with 85 parts by weight of water (relative to 100 parts by weight of the ceramic raw material) and 1 part by weight of wax (relative to 100 parts by weight of the ceramic raw material). Other than this, the same procedure as in Example 1 was followed. This resulted in a granular clay with a moisture content of approximately 45 wt%.

[0081] <Preparation of molded body> (Reference Examples, Examples 1 to 10) The clay was extruded into a cylindrical (pipe) shape using an extrusion molding machine. The extrusion conditions were adjusted for each example so that the molding pressure during extrusion was about 2 MPa. The cylindrical molded body was then cut to a certain length. As a result, a ring-shaped molded body was obtained.

[0082] <Evaluation of formability and shape retention> Here, the moldability and shape retention of the molded bodies of each example obtained above were evaluated. First, molded bodies in which cracks were observed upon visual inspection were judged to have poor moldability and marked with "X". On the other hand, molded bodies in which cracks were not visually observed were judged to have good moldability and marked with "O". The results are shown in the "Moldability" section of Table 1.

[0083] Furthermore, when the molded body was left standing with the ring hole of the molded body facing horizontally, if the molded body could not maintain its ring shape, it was deemed to have poor shape retention and was marked with "X". On the other hand, if the molded body could maintain its ring shape when left standing, it was deemed to have good shape retention and was marked with "O". The results are shown in the "Shape Retention" section of Table 1.

[0084] [Table 1]

[0085] As shown in Table 1, no cracks were observed in any of Examples 1 to 6, and the molded bodies were able to maintain their ring shape when left standing. On the other hand, in Examples 7 and 8, where the ratio (wt%) of the second water-absorbing polymer (small particle size) to the entire pore-forming material was 90% and 100% (i.e., only the second water-absorbing polymer), the ring shape could not be maintained.

[0086] <Preparation of dried body> (Reference Examples, Examples 1 to 10) The molded body of each example was placed in a far-infrared dryer and dried at 150°C for 20 minutes. After removing the molded body from the far-infrared dryer, it was placed in a hot air dryer and dried at 80°C for 20 minutes. This resulted in a dried body of each example with a moisture content of 15 wt%. The moisture content of the dried body was measured using a heat-drying moisture meter.

[0087] <Preparation of porous ceramics> (Reference Examples, Examples 1 to 9) The dried bodies according to each example were placed in a firing furnace and fired for 1.5 hours at a maximum firing temperature of 1250° C. This resulted in ring-shaped porous ceramics with an outer diameter of 8 to 9 mm, an inner diameter of 3 to 4 mm, and a length (width) of 8 to 9 mm.

[0088] (Example 10) In Example 10, the dried body was placed in a firing furnace and fired for 1.5 hours at a maximum firing temperature of 1350°C. Other than this, the procedure was the same as in the Reference Example. As a result, a ring-shaped porous ceramic with an outer diameter of 8-9 mm, an inner diameter of 3-4 mm, and a length (width) of 8-9 mm was obtained.

[0089] <Measurement of porous ceramics> (1) Porosity measurement In this test, the porosity of the porous ceramic samples according to each example was measured. Specifically, the porosity (%) was measured using a mercury porosimeter (AutoPore IV 9500, a pore size distribution measuring device manufactured by Shimadzu Science East Japan Co., Ltd.). The results are shown in Table 1. In addition, a graph in which the porosity (%) is plotted on the vertical axis and the proportion (wt%) of the second water-absorbing polymer (small particle size) for each example is plotted on the horizontal axis is shown in Figure 3.

[0090] As shown in Table 1 and Figure 3, the porosity was almost the same between the Reference Example and Examples 1 to 9, where the weight part of the pore-forming material (4 parts by weight) and the moisture content of the clay (approximately 38 wt%) were the same. This shows that the ratio (wt%) of the second water-absorbing polymer (small particle size) to the total pore-forming material does not affect the porosity. On the other hand, in Example 10, where the weight part of the pore-forming material and the moisture content of the clay were higher than in the other examples, the porosity was 69%. This shows that the porosity of porous ceramics can be increased by increasing the weight part of the pore-forming material and the moisture content of the clay.

[0091] (2) Measurement of pore size distribution In this test, the pore size distribution of the porous ceramic samples of each example was measured. Specifically, the pore size distribution was measured using a mercury porosimeter (AutoPore IV 9500, a pore size distribution measuring device manufactured by Shimadzu Science East Japan Co., Ltd.). Graphs of the pore size distributions of the Reference Example, Example 2, and Example 4 are shown in Figure 4. Furthermore, a graph of the pore size distribution of Figure 4, enlarged over the pore size range of 10 to 1000 μm (horizontal axis), is shown in Figure 5.

[0092] As shown in Figures 4 and 5, when comparing the Reference Example, Example 2, and Example 4, in which the proportions of the second water-absorbent polymer (small particle diameter) are 0 wt%, 25 wt%, and 50 wt%, respectively, it was found that as the proportion of the second water-absorbent polymer (small particle diameter) increases, the curve of the main pore peak becomes smoother (on the larger diameter side of the main peak) and the half-value width tends to become smaller. This is presumed to be due to the following: First, by increasing the proportion (wt%) of the second water-absorbent polymer (small particle diameter) relative to the entire pore-forming material, the fluidity of the clay improves. It is presumed that this leads to the homogenization of the pores in the porous ceramics.

[0093] <Evaluation test> (1) Measurement of crushing strength In this test, the crushing strength of the porous ceramic samples according to each example was measured. The crushing strength was measured using a digital hardness tester (KHT-40N, Fujiwara Seisakusho Co., Ltd.). Specifically, each example was placed on a set table (φ25 mm) so that the ring hole was facing horizontally. Then, the sample was pressed vertically using a pressure head (φ20 mm), and the strength at which the sample broke was measured and defined as the crushing strength (N). The crushing strength was measured for 20 samples (n=20) for each example, and the average value was calculated for each example. The results are shown in Table 1. Figure 6 shows a graph plotting the crushing strength (N) on the vertical axis and the proportion (wt%) of the second water-absorbent polymer powder (small particle size) on the horizontal axis.

[0094] (2) Measurement of wear rate In this test, the wear rate of the porous ceramic samples of each example was measured in accordance with ASTM D4058. Specifically, 100 g of each porous ceramic sample was placed in a cylindrical abrasion drum with an inner dimension of 254 mm, a length of 152 mm, and a height of 51 mm and equipped with one baffle. The drum was rotated at 60 rpm for 30 minutes. After the rotation was completed, the sample was recovered from the drum. Powder adhering to the sample was removed using a sieve (mesh opening 850 μm), and the sample weight was measured. The wear rate (%) was calculated using the following formula (I), where X (g) is the weight of the sample placed in the abrasion drum and Y (g) is the weight of the recovered sample. The lower the wear rate (%), the better the wear resistance. A wear rate of approximately 50% or less can be considered to be particularly excellent. Figure 7 shows a graph plotting the wear rate (%) on the vertical axis and the proportion (wt%) of the second water-absorbent polymer (small particle size) for each example on the horizontal axis. Wear rate (%)=(XY) / X×100...(I)

[0095] As shown in Table 1, Figures 6 and 7, as the ratio (wt%) of the second water-absorbent polymer (small particle size) to the entire pore-forming material increased, the crushing strength of the porous ceramic improved and the wear rate decreased. This is presumably due to the following: First, increasing the ratio (wt%) of the second water-absorbent polymer (small particle size) to the entire pore-forming material improves the fluidity of the clay. This is presumably improving the moldability of the clay and reducing microscopic cracks that are not visible to the naked eye. It is also presumed that the homogenization of the pores in the porous ceramic contributes to the improvement of the crushing strength and wear rate.

[0096] The technology disclosed herein has been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. In other words, the technology disclosed herein encompasses the aspects described in the following paragraphs.

[0097] <Section 1> A method for producing porous ceramics, comprising: a powder material preparation step of mixing a ceramic raw material with a pore-forming agent to obtain a powder material; a kneading step of kneading the powder material with an aqueous dispersion medium to obtain a clay; a clay molding step of molding the clay into a predetermined shape; a compact drying step of drying the compact obtained by the molding step; A dried body firing step of firing the dried body after the drying step, As the pore-forming material, two or more types of water-absorbing polymer powders having different average particle sizes are used. A method for producing porous ceramics.

[0098] <Section 2> Item 1. A method for producing porous ceramics according to Item 1, wherein the pore-forming material comprises a first water-absorbing polymer powder and a second water-absorbing polymer powder having an average particle size relatively smaller than that of the first water-absorbing polymer powder.

[0099] <Section 3> Item 3. The method for producing porous ceramics according to Item 2, wherein the weight ratio of the second water-absorbing polymer powder is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

[0100] <Section 4> Item 2 or 3, wherein the ratio of the average particle size of the second water-absorbing polymer powder to the average particle size of the first water-absorbing polymer powder (average particle size of the second water-absorbing polymer powder / average particle size of the first water-absorbing polymer powder) is 1 / 20 or more and 1 / 5 or less.

[0101] <Section 5> 5. The method for producing a porous ceramic according to any one of items 1 to 4, wherein the pore-forming material has a pure water absorption of 100 g / g or more and 1000 g / g or less.

[0102] <Section 6> Item 6. The method for producing porous ceramics according to any one of items 1 to 5, wherein the water-absorbing polymer powder having the largest average particle size has an average particle size of 25 μm or more and 600 μm or less, and the water-absorbing polymer powder having the smallest average particle size has an average particle size of 5 μm or more and 120 μm or less.

[0103] <Section 7> Item 7. The method for producing a porous ceramic according to any one of Items 1 to 6, wherein the drying step is carried out so that the moisture content of the dried body is more than 0 wt% and not more than 20 wt% when the total weight of the dried body is taken as 100 wt%.

[0104] <Section 8> A clay used to form a porous ceramic, a pore-forming material, a ceramic raw material, and an aqueous dispersion medium; The pore-forming material is made of a granular water-absorbent polymer, The particle size distribution of the granular water-absorbing polymer on a volume basis is characterized by being multimodal. Clay for forming porous ceramics.

[0105] <Section 9> Item 9. The clay according to Item 8, wherein the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having a relatively smaller average particle size than the first water-absorbing polymer.

[0106] <Section 10> Item 10. The clay according to Item 9, wherein the weight ratio of the second water-absorbing polymer is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

[0107] <Section 11> Item 9 or 10, wherein the average particle size ratio of the second water-absorbing polymer to the average particle size of the first water-absorbing polymer (average particle size of the second water-absorbing polymer / average particle size of the first water-absorbing polymer) is 1 / 20 or more and 1 / 5 or less.

[0108] <Section 12> Item 12. The clay according to any one of Items 8 to 11, wherein the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

[0109] <Section 13> Item 13. The clay according to any one of items 8 to 12, wherein in the particle size distribution of the granular water-absorbing polymer, the peak top of the largest particle size peak is 25 μm or more and 600 μm or less, and the peak top of the smallest particle size peak is 5 μm or more and 120 μm or less.

[0110] <Section 14> A dried body used to form a porous ceramic, A ceramic matrix is ​​formed from a ceramic material, and a pore-forming material is dispersed in the matrix. The pore-forming material is composed of a granular water-absorbing polymer, The particle size distribution of the granular water-absorbing polymer on a volume basis is characterized by being multimodal. dry body.

[0111] <Section 15> Item 15. The dried body according to Item 14, wherein the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having a relatively smaller average particle size than the first water-absorbing polymer.

[0112] <Section 16> Item 16. The dried body according to Item 15, wherein the weight ratio of the second water-absorbing polymer is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

[0113] <Section 17> Item 15 or 16, wherein the average particle size ratio of the second water-absorbing polymer to the average particle size of the first water-absorbing polymer (average particle size of the second water-absorbing polymer / average particle size of the first water-absorbing polymer) is 1 / 20 or more and 1 / 5 or less.

[0114] <Section 18> Item 18. The dried material according to any one of Items 14 to 17, wherein the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

[0115] <Section 19> Item 19. The dried body according to any one of items 14 to 18, wherein in the particle size distribution of the granular water-absorbing polymer, the peak top of the largest particle size peak is 25 μm or more and 600 μm or less, and the peak top of the smallest particle size peak is 5 μm or more and 120 μm or less.

[0116] <Section 20> 20. The dried product according to any one of items 14 to 19, wherein the moisture content of the dried product is more than 0 wt% and 20 wt% or less when the total weight of the dried product is taken as 100 wt%.

Claims

1. A method for producing porous ceramics, comprising: a powder material preparation step of mixing a ceramic raw material with a pore-forming agent to obtain a powder material; a kneading step of kneading the powder material and an aqueous dispersion medium to obtain a clay; a clay molding step of molding the clay into a predetermined shape; a compact drying step of drying the compact obtained by the molding step; A dried body firing step of firing the dried body after the drying step, As the pore-forming material, two or more types of water-absorbing polymer powders having different average particle sizes are used. A method for producing porous ceramics.

2. 2. The method for producing porous ceramics according to claim 1, wherein the pore-forming material comprises a first water-absorbing polymer powder and a second water-absorbing polymer powder having an average particle size relatively smaller than that of the first water-absorbing polymer powder.

3. 3. The method for producing porous ceramics according to claim 2, wherein the weight ratio of the second water-absorbing polymer powder is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

4. The method for producing porous ceramics according to claim 2 or 3, wherein the average particle size ratio of the second water-absorbing polymer powder to the average particle size of the first water-absorbing polymer powder (average particle size of the second water-absorbing polymer powder / average particle size of the first water-absorbing polymer powder) is 1 / 20 or more and 1 / 5 or less.

5. 3. The method for producing porous ceramics according to claim 1, wherein the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

6. The method for producing porous ceramics according to claim 1 or 2, wherein the water-absorbing polymer powder having the largest average particle size has an average particle size of 25 μm or more and 600 μm or less, and the water-absorbing polymer powder having the smallest average particle size has an average particle size of 5 μm or more and 120 μm or less.

7. 3. The method for producing porous ceramics according to claim 1, wherein the drying step is carried out so that the moisture content of the dried body is more than 0 wt% and not more than 20 wt% when the total weight of the dried body is taken as 100 wt%.

8. A clay used to form a porous ceramic, a pore-forming material, a ceramic raw material, and an aqueous dispersion medium; The pore-forming material is composed of a granular water-absorbent polymer, The particle size distribution of the granular water-absorbing polymer on a volume basis is multimodal, Clay for forming porous ceramics.

9. 9. The clay according to claim 8, wherein the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having an average particle size smaller than that of the first water-absorbing polymer.

10. 10. The clay according to claim 9, wherein the weight ratio of the second water-absorbing polymer is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

11. The average particle size ratio of the second water-absorbing polymer to the average particle size of the first water-absorbing polymer (average particle size of the second water-absorbing polymer / average particle size of the first water-absorbing polymer) is 1 / 20 or more and 1 / 5 or less, according to claim 9 or 10.

12. The clay according to claim 8 or 9, wherein the pore-forming material has a water absorption amount for pure water of 100 g / g or more and 1000 g / g or less.

13. The clay according to claim 8 or 9, wherein in the particle size distribution of the granular water-absorbing polymer, the peak top of the largest particle size peak is 25 μm or more and 600 μm or less, and the peak top of the smallest particle size peak is 5 μm or more and 120 μm or less.

14. A dried body used to form a porous ceramic, A ceramic matrix is ​​formed from a ceramic material, and a pore-forming material is dispersed in the matrix. the pore-forming material is composed of a granular water-absorbent polymer, The particle size distribution of the granular water-absorbing polymer on a volume basis is multimodal, dry body.

15. 15. The dry body according to claim 14, wherein the pore-forming material comprises a first water-absorbing polymer and a second water-absorbing polymer having an average particle size relatively smaller than that of the first water-absorbing polymer.

16. 16. The dried body according to claim 15, wherein the weight ratio of the second water-absorbing polymer is 25 wt% or more and 80 wt% or less when the weight of the entire pore-forming material is 100 wt%.

17. The average particle size ratio of the second water-absorbing polymer to the average particle size of the first water-absorbing polymer (average particle size of the second water-absorbing polymer / average particle size of the first water-absorbing polymer) is 1 / 20 or more and 1 / 5 or less, according to claim 15 or 16. The dried body.

18. The dried body according to claim 14 or 15, wherein the pore-forming material has a water absorption capacity for pure water of 100 g / g or more and 1000 g / g or less.

19. In the particle size distribution of the granular water-absorbing polymer, the peak top of the largest particle size peak is 25 μm or more and 600 μm or less, and the peak top of the smallest particle size peak is 5 μm or more and 120 μm or less. The dried body according to claim 14 or 15.

20. 16. The dried body according to claim 14, wherein the moisture content of the dried body is more than 0 wt% and 20 wt% or less when the weight of the entire dried body is 100 wt%.

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