TW201602054A - Method for producing porous ceramics and porous ceramics - Google Patents

Abstract

An embodiment of a method for producing porous ceramics of this invention comprises a formation step, a freezing step, a drying step and a calcining step. In the formation step, a compact is formed by discharging a raw material. In the freezing step, a frozen article containing ice is formed by freezing the compact. In the drying step, an ice-removed dried article is formed by drying the frozen article. In the calcining step, the dried article is calcined. The raw materia is produced by mixing and kneading a raw ceramics material comprising ceramics particles, a binder and water.

Description

Porous ceramic manufacturing method and porous ceramic

The embodiment disclosed in the present invention relates to a method for producing a porous ceramic and a porous ceramic.

Conventionally, a porous ceramic body in which a large number of pores are formed in a ceramic is used in various aspects such as a filter for removing impurities from a gas or a liquid, an adsorbent, a baking bracket for small parts, a heat exchanger, and the like.

As a method for producing such a porous ceramic, a method in which an organic pore-forming agent is added to ceramic particles and then formed to be removed during firing is used. However, in particular, in the production of a porous ceramic having a high porosity, it is necessary to add a large amount of a pore former. Therefore, it is necessary to add a degreasing process, and cracks are likely to occur at the time of degreasing, which is disadvantageous in terms of productivity.

Moreover, as a method of producing a porous ceramic, it is known to apply a method in which a slurry in which ceramic particles are dispersed in an aqueous solution of a water-soluble polymer is added to a mold to be gelated, and then the gel is frozen. The freezing method (for example, refer to Patent Document 1).

(previous technical literature) Patent literature

[Patent Document 1] Japanese Patent No. 5176198

In the porous ceramic which can stably produce a high porosity, the method is epoch-making. However, in the manufacturing method described in Patent Document 1, various shapes can be obtained according to the shape of the mold which gels the slurry. Porous ceramics of various shapes, but on the other hand, the steps of casting the slurry in the mold require labor and are not suitable for mass production of the same shape. Further, it is necessary to have a large number of molds for casting the slurry, gelating, etc., and it is easy to cost a lot. Further, in the production method described in Patent Document 1, it is necessary to have a gelation step by freezing, which takes time. That is, for example, when gelatinized using gelatin, it is necessary to stand still in the refrigerator for one day in order to sufficiently gel, and it is not preferable in terms of lead time.

In addition, for example, in order to produce a porous ceramic which can continuously produce a molded body by using the gelation freezing method disclosed in Patent Document 1, it is necessary to use a large amount of water in the raw material to produce a porous ceramic having a high porosity. The slurry, and the slurry must have the fluidity, water retention, and shape retention necessary for extrusion molding. However, in the prior method described in Patent Document 1, since the raw material mixture does not have sufficient fluidity, it cannot be deformed into a desired shape, and since it does not have sufficient water retention property, a water scatter phenomenon occurs. And because there is not enough conformal Sex, so it is impossible to maintain the desired shape after forming. Therefore, a porous ceramic having a target shape cannot be obtained.

As described above, in the production method described in Patent Document 1, the productivity of the porous ceramic is improved.

An aspect of the embodiment of the present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a porous ceramic having high productivity and a porous ceramic.

A method for producing a porous ceramic according to an embodiment of the present invention includes a molding step, a freezing step, a drying step, and a calcination step. In the forming step, a green body is discharged to form a molded body. In the freezing step, the formed body is frozen to form a frozen body containing ice. In the drying step, the frozen body is dried to form a dried body after removing ice. The aforementioned dried body is calcined in a calcination step. Further, the green body is obtained by mixing and kneading ceramic materials containing ceramic particles, a binder, and water.

According to an aspect of the embodiment of the present invention, a method for producing a porous ceramic having high productivity and a porous ceramic can be provided.

1‧‧‧ceramic particles

2‧‧‧Binder

3‧‧‧ water

4‧‧‧Ceramic materials

5‧‧‧Formed body

6‧‧‧Ice

7‧‧‧Freezing body

8‧‧‧Ceramic skeleton

9‧‧‧ stomata

10‧‧‧Porous ceramics

11‧‧‧Cellular ceramics

12‧‧‧ hole

13‧‧‧ hole wall

14‧‧‧Wall

15, 16‧‧‧ end face

20‧‧‧ Feeding hopper

21‧‧‧mixer

22‧‧‧Squeezing machine

23‧‧‧Nozzles

30‧‧‧Cooling device

40‧‧‧calcining unit

S101 to S106‧‧‧ steps

T1, t2‧‧‧ thickness

T3, t4‧‧‧ interval

Fig. 1A is an explanatory view showing an outline of a method for producing a porous ceramic according to an embodiment.

Fig. 1B is a view showing a method of manufacturing a porous ceramic according to an embodiment; An explanatory diagram of the outline.

Fig. 1C is an explanatory view showing an outline of a method for producing a porous ceramic according to an embodiment.

Fig. 2A is a schematic view showing an example of a honeycomb ceramic.

Fig. 2B is an illustration of the honeycomb ceramic viewed from the end face side in the extrusion direction.

Fig. 2C is a cross-sectional view taken along line A-A' of Fig. 2B.

Fig. 3 is a flow chart showing an example of a method for producing a porous ceramic according to an embodiment.

Fig. 4 is a partial cross-sectional view showing a porous ceramic produced in Example 2-1.

Fig. 5A is a partial cross-sectional view showing the honeycomb ceramic produced in Example 2-3.

Fig. 5B is a partial enlarged view of Fig. 5A.

(to implement the form of the invention)

Hereinafter, an embodiment of the method for producing a porous ceramic and a porous ceramic disclosed in the present invention will be described in detail with reference to the accompanying drawings. Further, the present invention is not limited to the embodiments shown below.

The prior method for producing a porous ceramic using a gelation freezing method includes various steps of gelation, freezing, drying, degreasing, and calcination. On the other hand, in the method for producing a porous ceramic according to the embodiment of the present invention, the composition and properties of the ceramic raw material are different from those of the conventional porous ceramic. Moreover, by performing a green body which is pressurized and kneaded Instead of the previous gelation step in which the ceramic raw material is added to the mold to be gelated, the step of forming the porous ceramic can be continuously produced. Hereinafter, a method for producing a porous ceramic according to an embodiment will be described using Figs. 1A to 1C.

1A to 1C are explanatory views for explaining an outline of a method for producing a porous ceramic according to an embodiment. The method for producing a porous ceramic according to an embodiment includes each step of kneading, molding, freezing, drying, degreasing, and calcination. Further, in the above-described manufacturing steps, in the above-described manufacturing steps, the respective steps of kneading, molding, freezing, and calcination are illustrated, and the respective steps corresponding to drying and degreasing are omitted.

First, the kneading step will be described using FIG. 1A. The kneading step is a step of preparing a green body from a raw material for producing a porous ceramic of an embodiment, that is, a ceramic raw material. Specifically, the ceramic raw material 4 containing the ceramic particles 1, the binder 2, and the water 3, which are supplied from the feed hopper 20, is kneaded while being degassed.

When the ceramic raw material 4 is kneaded, the binder 2 is swollen by the action of the water 3 to form a clay-like green body having fluidity and shape retention property suitable for molding and having fluidity. Further, the ceramic particles 1 in the green body are dispersed by sandwiching the adhesive 2 which is swollen by the water 3 therebetween and leaving a space therebetween. The green body thus prepared is transferred from the kneader 21 to the extrusion molding machine 22.

Next, the forming step will be described using FIG. 1A. The forming step is a step of forming the molded body 5 by applying pressure to the green body described above and discharging it. Specifically, it is transferred from the mixer 21 to the extrusion molding machine. The green body after 22 is subjected to a predetermined pressure, and the green body is continuously extruded from the nozzle 23 provided at the end of the extrusion molding machine 22.

The nozzle 23 is provided with an opening having a predetermined shape, and the green body extruded from the extrusion molding machine 22 can pass through the nozzle 23 to form a molded body 5 having a shape corresponding to the opening. Moreover, the shape of the formed molded body 5 is, for example, a tubular shape, a plate shape, a sheet shape, or the like. Further, a plurality of through holes may be formed in a columnar shape in a columnar shape in the extrusion direction via a partition wall, and the shape of the molded body 5 is not limited. Each time the molded body 5 is extruded to a predetermined width, it is cut by a cutter (not shown) and transferred to the next step.

Next, the freezing step will be described using FIG. 1B. The freezing step is a step of cooling the above-described formed body 5 to form a frozen body 7. When the molded body 5 is cooled and frozen by the cooling device 30, the state of the water 3 separated from the molded body 5 containing the ceramic particles 1 and the binder 2 is changed to ice 6 and crystal growth is performed. As a result, it is possible to obtain a portion (not shown) including the ceramic particles 1 in which the binder 2 formed around the ceramic particles 1 is concentrated in the water 3, and a frozen body 7 in the portion of the crystallized ice 6 .

Next, the drying step will be explained. The drying step is a step of removing the ice 6 grown in the above-described frozen body 7 to form a dried body. For example, when the frozen body 7 after the ice 6 has grown by freeze-drying is dried, the crystal of the ice 6 is sublimated and disappears, and the pores 9 are formed instead. That is, the drying step is a step of replacing the ice 6 into the pores 9.

Next, the degreasing step will be explained. The degreasing step is an organic formation of the binder 2 or the like from the dried body in which the pores 9 are formed in the drying step described above. The step of removing the points. Specifically, the organic component such as the binder 2 is decomposed and removed under the predetermined temperature conditions in accordance with the type of the ceramic particles 1 .

Finally, the calcination step is illustrated using Figure 1C. In the calcination step, the dried body obtained by removing the organic component such as the binder 2 in the degreasing step described above is calcined in the calcining apparatus 40 to produce a calcined body (porous ceramic) 10. The porous ceramics 10 obtained by the calcination have the pores 9 formed in the above-described drying step, and the ceramic skeleton 8 in which the ceramic particles 1 are bonded and densified so as to surround the pores 9.

As described above, according to the method for producing the porous ceramics 10 of the embodiment, the porous ceramics 10 in which the ceramic skeleton 8 is formed around the pores 9 are formed based on the shape of the ice 6 formed in the frozen body 7.

In the method for producing the porous ceramic 10 of the embodiment, the ceramic particles 1 are not particularly limited as long as they can be appropriately calcined in the calcination step. Specifically, for example, zirconia, alumina, cerium oxide, titanium oxide, magnesium oxide, cerium carbide, boron carbide, cerium nitride, boron nitride, cordierite, hydroxyapatite, or the like can be applied. One or more of samarium oxynitride (Sialon), zircon, aluminum titanate, kaolin, aluminum hydroxide, and mullite are used as the ceramic particles 1, but are not limited thereto. Further, for example, alumina or cerium oxide can be used to produce mullite, or zirconia and alumina can be used to produce a composite, and a plurality of ceramic particles 1 can be used in combination according to the required characteristics.

Further, it is preferable that the ceramic particles 1 have a practical average particle diameter of 100 μm or less. When the average particle diameter of the ceramic particles 1 exceeds 100 μm, The ceramic particles 1 are fired in accordance with the shape and size of the porous ceramic 10 required, and it is difficult to obtain the strength of the calcined body (porous ceramic) 10 for a combined use. Here, the "average particle diameter" refers to a median diameter (d50) obtained by a laser diffraction type particle size distribution measuring apparatus (wet method) based on a volume distribution based on a volume equivalent of a sphere equivalent. Further, as long as the same result can be obtained, the measurement method is not limited.

The ceramic particles 1 in the ceramic raw material 4 are preferably blended so as to be in the range of 1 to 30 vol% when the total of the water 3 is set to 100 vol%. When the amount of the ceramic particles 1 is less than 1 vol%, for example, there is a concern that the shape cannot be maintained in the drying step, and it is difficult to produce the porous ceramic 10 having the required strength. In addition, when the amount of the ceramic particles 1 is more than 30 vol%, the porosity of the obtained porous ceramics 10 is lowered, and the characteristics required as a porous body may not be sufficiently exhibited. Here, the "porosity" refers to a value obtained by the Archimedes method based on the method specified in JISR1634:2008. This measurement is also called "appearance porosity" because it does not consider closed pores. Further, in the present embodiment, since the air vent is hardly formed, the "appearance porosity" can be handled as the "porosity".

Further, the binder 2 can be appropriately held until the shape of the green body can be extruded from the extrusion molding machine 22, and the shape of the molded body 5 extruded from the extrusion molding machine 22 can be appropriately maintained. There is no limitation on the type of the drying step. Specifically, for example, methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl fiber can be used. Prime, Cellulose derivatives such as carboxymethylethylcellulose and carboxyethylcellulose are used as the binder 2, but are not limited thereto. Further, one type of the binder 2 may be used alone, or two or more types may be used in combination. Moreover, it is also possible to add a network structure to the binder 2 to maintain water retention. The third component of conformality.

Further, the weight average molecular weight (Mw) of the binder 2 is preferably 150,000 or more, preferably 150,000 to 2,000,000. When the binder 2 having a weight average molecular weight (Mw) as appropriately controlled is used as the ceramic raw material 4, it becomes easy to maintain the hardness of the green body to such an extent that it can be extruded from the extrusion molding machine 22, and The shape of the molded body 5 to be extruded by the molding machine 22 is appropriately maintained until the drying step.

Further, as the water 3, it is preferred to use deionized water containing less impurities.

Further, in order to appropriately calcine the ceramic particles 1, a calcining aid may be blended in the ceramic raw material 4 in accordance with the type of the ceramic particles 1. Further, in order to produce a green body having an appropriate shape, various additives such as a lubricant, a plasticizer, and a release agent may be added as necessary.

Further, the content of the nonvolatile matter in 100 vol% of the ceramic raw material 4 is preferably from 9 to 45 vol%. When the content of the non-volatile component is less than 9 vol%, for example, the shape retaining property of the molded body 5 may be insufficient and the green body may not be properly extruded from the extrusion molding machine 22, and it may be difficult to produce a porous material having a desired shape. Ceramic 10. On the other hand, when the content of the nonvolatile component exceeds 45 vol%, the green body is not appropriately deformed, and as a result, it is difficult to produce the porous ceramic 10 having a desired shape. Here, the so-called pottery The non-volatile component in the ceramic raw material 4 is the sum of the components obtained by removing the water 3 from the ceramic raw material 4, and mainly contains the ceramic particles 1 and the binder 2. Further, it is also possible to include various additives such as the above-mentioned calcining aid and tackifier in the nonvolatile matter.

Further, the green body obtained by kneading the ceramic raw material 4 contains a relatively large amount of water. However, by optimizing the type and addition conditions of the binder 2, it also has water retention and shape retention suitable for molding. . Specifically, the hardness of the green body obtained by kneading the ceramic raw material 4 is preferably from 1 to 12, preferably from 6 to 12, measured by a durometer. When the hardness of the green body is less than 1, the operation of the extrusion molding machine 22 to be described later becomes difficult, and the molding becomes difficult depending on the desired shape. Further, when the hardness of the green body exceeds 12, the load on the extrusion molding machine 22 and other equipment becomes too large, causing a molding defect or a design in which a pressure-resistant structure such as a device must be changed. Practically not suitable.

The hardness of the above green body was measured as follows. The surface of the green body taken out from the kneading machine 21 was arbitrarily selected, and the front end of the probe of the NGK type hardness tester (manufactured by Nippon Insulator Co., Ltd.) was vertically pressurized and contacted to measure the hardness. The same measurement was repeated by setting the measurement position to ten points, and the arithmetic mean of each measurement value was defined as the hardness of the green body. Further, as long as the same result can be obtained, there is no limitation on the measurement apparatus and the number of measurements.

Here, the hardness of the green body described above has a correlation with the content of the nonvolatile component blended in the ceramic raw material 4 and the weight average molecular weight (Mw) of the binder 2. That is, when the content of non-volatile components increases, The content of water 3 is relatively low and the green body tends to become hard. Moreover, when the compounding amount is constant, when the weight average molecular weight (Mw) of the binder 2 becomes large, the green body tends to be hardened in the same manner. Therefore, in order to manufacture a green body suitable for forming, it is preferable to prepare the ceramic raw material 4 while paying attention to such a situation.

Next, the kneading machine 21 in which the ceramic raw material 4 is kneaded can be, for example, a kneader, a three-roll mill, or a kneader. Further, the kneader 21 can be a batch type or a continuous type. In the embodiment, the kneading temperature of the kneaded ceramic raw material 4 is preferably from 1 to 30 °C. When the kneading temperature is less than 1 ° C, the ceramic raw material 4 is locally frozen and there is a concern that workability is lowered during kneading. On the other hand, when the kneading temperature exceeds 30 ° C, volatilization during moisture kneading may cause stable production.

Further, as the extrusion molding machine 22 for extruding the green body, for example, various extrusion molding machines such as a single shaft type or a double shaft type can be used. Further, the extrusion direction of the molded body 5 extruded from the extrusion molding machine 22 may be substantially horizontal or vertical as shown in Fig. 1A. Further, the extrusion molding machine 22 can be of a batch type or a continuous type, and is preferably a continuous type from the viewpoint of productivity improvement. In the embodiment, the extrusion temperature at which the green body is extruded is preferably the same as the above-described kneading temperature.

Moreover, in the freezing step, the well-known cooling device 30 can be utilized. Specifically, a cooling device 30 that applies a variety of cooling methods such as a lower side of the molded body 5 to a solid such as a cooled metal plate, and a freezer or the like can be used. Further, the freezing temperature of the molded body 5 in the freezing step is not limited as long as the water 3 in the molded body 5 can be frozen to form the ice 6. However, depending on the type of the bonding agent 2, There is a case where the molded body 5 is not frozen when the interaction between the binder 2 and the water 3 exceeds -10 ° C, so the freezing temperature of -10 ° C or lower is preferable.

Further, in the drying step, it is possible to prevent the crack from drying by gradually replacing the ice 6 with the pores 9 while suppressing the difference in the drying speed between the inside and the outside of the frozen body 7. Specifically, the frozen body 7 is freeze-dried or immersed in a water-soluble organic solvent and a water-soluble organic solvent aqueous solution, and air-dried to replace the ice 6 into the pores 9.

For example, when the frozen body 7 is immersed in a water-soluble organic solvent and an aqueous solution of a water-soluble organic solvent, the ice 6 in the frozen body 7 is melted and mixed with a water-soluble organic solvent. By performing such an operation one or more times, first, the portion of the ice 6 in the frozen body 7 is substituted into a water-soluble organic solvent. Subsequently, when the frozen body 7 in which the inside of the frozen body 7 is replaced with a water-soluble organic solvent is dried in the air or under reduced pressure, the portion which is ice 6 in the freezing step is substituted into the pores 9.

In the drying step using a water-soluble organic solvent, as the water-soluble organic solvent, it is possible to apply a catalyst which does not erode the binder 2 and has a higher volatility than water 3. Specific examples thereof include methanol, ethanol, isopropanol, acetone, and ethyl acetate, but are not limited thereto. The pores 9 are formed in the portion of the ice 6 in the frozen body 7 by using the water-soluble organic solvents alone or in combination with a plurality of types and performing one or more drying.

Further, in the degreasing step, for example, a degreasing temperature of 300 ° C to 900 ° C can be applied. Here, for example, when a non-oxide ceramic such as tantalum carbide or tantalum nitride is degreased, it is preferable to perform degreasing in an inert gas atmosphere such as argon or nitrogen. In contrast, for example, alumina, zirconia, apatite When an oxide ceramic such as (apatite) is used as a raw material, it is preferred to perform degreasing in an atmospheric environment.

Then, in the calcination step, the calcination temperature, the calcination time, and the calcination environment of the calcining apparatus 40 are appropriately adjusted in accordance with the kind and the amount of the ceramic particles 1 to be used, the hardness of the target, and the like, and the production is required. Porous ceramic 10 of shape and characteristics.

The average pore diameter of the porous ceramics 10 thus obtained is preferably from 1 μm to 500 μm in practice. Here, the "average pore diameter" means a median diameter (d50) obtained by using a mercury intrusion method at a contact angle of 140 degrees and based on a pore distribution when the pores 9 are approximated by a cylinder.

Further, the porosity of the porous ceramic 10 of the embodiment is preferably in the range of 50% to 99%, preferably 70% to 99%. When the porosity of the porous ceramic 10 is less than 50%, the necessity of using the method for producing the porous ceramic 10 of the embodiment is reduced. When the porosity of the porous ceramics 10 exceeds 99%, for example, it may be difficult to maintain the shape in the drying step, and it is difficult to produce the porous ceramics 10 having the required strength. In addition, in order to clearly distinguish from the "total porosity" which will be described later, the porosity of the porous ceramic 10 may be referred to as "material porosity".

As described above, the porous ceramics 10 having various shapes can be produced based on the molded body 5 extruded from the extrusion molding machine 22. In the following, the porous ceramics 10 produced by the method for producing the porous ceramics 10 of the embodiment will be described as an example, and the honeycomb-shaped porous ceramics will be described using FIGS. 2A to 2C (hereinafter referred to as "Honeycomb pottery porcelain".

Fig. 2A is a schematic view showing an example of the honeycomb ceramic 11 produced by the method for producing the porous ceramic 10 of the embodiment. Further, Fig. 2B is a schematic view of the honeycomb ceramic 11 shown in Fig. 2A viewed from the end face 15 side, and Fig. 2C is a cross-sectional view taken along line A-A' of the honeycomb ceramic 11 shown in Fig. 2B.

As shown in FIGS. 2A to 2C, the honeycomb ceramic 11 has an outer cylindrical shape having a peripheral wall 14 and end faces 15 and 16. Further, the honeycomb ceramic 11 is provided with a hole wall 13 which is formed to be substantially perpendicular to the mutually facing end faces 15, 16; a plurality of holes which are partitioned by the hole wall 13 and which have the end faces 15 and end faces Between 16 runs through. The hole 12, the hole wall 13 and the peripheral wall 14 are formed from the extrusion molding machine 22 in the direction in which it is extruded.

The honeycomb ceramic 11 having such a configuration preferably has a total porosity of 85 to 99%. When the total porosity of the honeycomb ceramics 11 is less than 85%, for example, when a heat exchanger is used, the time required to reach the temperature for improving the heat exchange efficiency is increased due to the heat capacity, so that it is practically disadvantageous. On the other hand, when the total porosity of the honeycomb ceramics 11 exceeds 99%, for example, it becomes difficult to manufacture the honeycomb ceramics 11 having mechanical strength that can withstand practical use. Here, the "total porosity" means the outer shape of the honeycomb ceramic 11, that is, the total volume of the substantially cylindrical shape partitioned by the peripheral wall 14 and the end faces 15 and 16, and the holes 12 and the pores 9 are occupied. The ratio.

Further, the number of holes 12 per square inch (1 in ² , about 6.45 × 10 ^-4 m ² ) of the honeycomb ceramic 11 (hereinafter referred to as "the number of holes") is preferably from 250 to 2,000. When the number of holes per 1 in ² is less than 250, for example, when it is used as a heat exchanger, the effective specific surface area is small, and there is a concern that heat exchange efficiency is lowered. On the other hand, when the number of holes per 1 in ² exceeds 2,000, for example, when a heat exchanger is used, there is a concern that pores or the like in the heat exchange medium may cause clogging in the holes 12. Further, the "number of holes per 1 in ² " is obtained by dividing the number of holes 12 penetrating the end face 15 (or 16) by the area of the end face 15 (or 16) including the hole 12 and the air hole 9 (converted to in ² units) to calculate.

Further, the average thickness t1 of the hole walls 13 of the honeycomb ceramics 11 is preferably 10 to 200 μm. When the thickness t1 of the hole wall 13 is less than 10 μm, for example, the strength of the hole wall 13 may be difficult to maintain due to the pores 9 formed in the hole wall 13. On the other hand, when the thickness t1 of the hole wall 13 exceeds 200 μm, for example, when a filter is used, the pressure loss greatly increases the energy loss, and there is a concern that the energy efficiency of the entire system is lowered. Further, the "average thickness" of the hole walls 13 is obtained by observing the honeycomb ceramics 11 by SEM, and measuring the thickness of the hole walls 13 at an arbitrary twenty points and calculating the average value thereof.

Further, the interval t4 between the opposing hole walls 13 of the honeycomb ceramic 11 sandwiching the holes 12 is preferably 300 to 2000 μm. When the interval t4 between the hole walls 13 is less than 300 μm, for example, the pressure loss of the fluid flowing through the honeycomb ceramic 11 increases, and as a result, there is a concern that the energy efficiency is lowered. On the other hand, when the interval t4 between the hole walls 13 exceeds 2000 μm, for example, when the filter is used as a filter, the effective effective area of the filter per unit volume may be insufficient, and the characteristics of the filter may not be sufficiently exhibited.

Moreover, the peripheral wall of the outermost casing constituting the honeycomb ceramic 11 The thickness t2 of 14 can be set in such a manner as to ensure appropriate strength in accordance with the shape and use of the honeycomb ceramic 11. Specifically, the thickness t2 of the peripheral wall 14 can be made equal to the average thickness t1 of the above-described hole wall 13, but is not limited thereto. Further, the interval t3 between the hole wall 13 and the peripheral wall 14 can be made equal to the interval t4 between the hole walls 13 and the like, but the present invention is not limited thereto and can be appropriately set in accordance with the use of the honeycomb ceramic 11.

Further, in the above-described embodiment, the outer shape of the honeycomb ceramic 11 is described as being substantially cylindrical, but the invention is not limited thereto. Specifically, for example, it may be an elliptical cylinder, or may be a corner pillar including a regular triangular prism, a square pillar, a regular hexagonal column, a regular octagonal column, and other positive polygonal columns.

Further, in the above-described embodiment, the cross-sectional shape of the hole 12 is illustrated in a square manner, but is not limited thereto. Specifically, for example, it may be a polygonal shape such as a rectangle, a triangle, a hexagon, or an octagon, or may be a circle or an ellipse. Further, a plurality of holes 12 having different sizes and cross-sectional shapes from each other may be doped.

Next, a method of manufacturing the porous ceramic 10 of the embodiment will be described in detail using FIG. Fig. 3 is a flow chart showing a processing procedure of the porous ceramic 10 manufactured as an embodiment.

As shown in Fig. 3, first, the ceramic raw material 4 containing the ceramic particles 1, the binder 2, and the water 3 is kneaded to prepare a green body (step S101). Various additives such as a calcining aid may be added at this timing. Further, the binder 2 may be previously mixed with the ceramic particles 1 before being mixed with the water 3, and may be added to the kneader 21 by wet mixing with the water 3, and kneaded. Can directly cast ceramic raw materials 4 It enters the feed hopper 20 and is kneaded.

Next, the green body prepared in step S101 is extruded to form a molded body 5 (step S102). Next, the molded body 5 is frozen by the cooling device 30 to form a frozen body 7 in which crystals of the ice 6 are grown in one direction (step S103). Next, the frozen body 7 is dried to form a dried body in which the ice 6 having grown in the frozen body 7 has been removed and replaced with the pores 9 (step S104).

Then, the organic component such as the binder 2 is removed from the dried body in which the pores 9 have been formed (step S105), and then calcined (step S106). From the above steps, the production of the porous ceramic 10 of one of the embodiments is completed.

As described above, the method for producing a porous ceramic according to the embodiment includes a molding step, a freezing step, a drying step, and a calcination step. The forming step is a step of forming a molded body by discharging the green body. The freezing step is a step of freezing the formed body to form a frozen body containing ice. The drying step is a step of drying the frozen body to form a dried body after removing ice. The calcination step is a step of calcining the dried body. Further, the green body is obtained by mixing and kneading ceramic materials containing ceramic particles, a binder, and water.

Therefore, according to the method for producing a porous ceramic according to the embodiment, the productivity of the porous ceramic can be improved. That is, by mixing. The viscosity-increasing effect of the dissolution or swelling of the binder during mixing, without the need for an additional gelation step.

Further, in the above-described embodiment, the kneading machine 21 and the extrusion molding machine 22 are described as individual devices, but the configuration is not limited thereto. For example, the kneading function and the extrusion molding machine of the kneading machine 21 can also be applied. The kneading extruder in which the extrusion molding function is integrated is used instead of the kneading machine 21 and the extrusion molding machine 22.

Further, in the above-described embodiment, the honeycomb ceramic 11 is described as being integrally formed with the hole wall 13 and the peripheral wall 14, but the configuration is not limited thereto. For example, the honeycomb ceramics 11 may be produced by joining the respective pore walls 13 and the peripheral walls 14 which are separately formed before or after calcination. Further, a part of the hole wall 13 and the peripheral wall 14 may be manufactured according to the method for producing the porous ceramic 10 of the embodiment, and the honeycomb ceramic 11 may be produced simultaneously with one or a plurality of separately prepared members.

Further, in the above-described embodiment, the degreasing step (step S105) is described as a necessary step, but may be omitted depending on the type and amount of the binder 2. At this time, the binder 2 is decomposed and removed in the calcination step (step S106).

[Examples] [Kneading of ceramic raw materials (manufacturing of green bodies)]

(Example 1-1)

As the ceramic raw material 4, the amount of alumina (corresponding to ceramic particles 1, density 3.98 × 10 ³ kg / m ³ ) 9.2 vol%, hydroxypropyl methylcellulose (HPMC, weight average molecular weight Mw = 1 million) (corresponding to bonding) Agent 2) 7.9 vol%, and deionized water (corresponding to water 3) 82.9 vol%. These ceramic raw materials 4 were mixed for 30 minutes using a mixer, and then the green body was prepared by kneading twice using a three-roll mill (corresponding to the kneader 21). The resulting green body is suitable for extrusion. The hardness of the obtained green body and the composition of the ceramic raw material 4 in the green body are shown in Table 1.

Here, the "density of alumina" means the true specific gravity of the alumina raw material measured by the pycnometer method. Further, the density of the ceramic particles 1 other than alumina was also measured by the same method as the measurement of the "density of alumina".

(Example 1-2)

Cordierite (corresponding to ceramic particles 1, density 2.52 × 10 ³ kg / m ³ ) 8.7 vol%, HPMC (weight average molecular weight Mw = 1 million) (corresponding to binder 2) 12.6 vol formed of kaolin, talc and alumina %, deionized water (corresponding to water 3) 78.7 vol% was mixed to prepare ceramic raw material 4. This ceramic raw material 4 was kneaded in the same manner as in Example 1-1 to prepare a green body. The hardness of the obtained green body and the composition of the ceramic raw material 4 in the green body are shown in Table 1. Further, cordierite is obtained by calcining ceramic particles 1 containing kaolin, talc, and alumina mixed at an appropriate ratio.

(Example 1-3)

A green body was produced in the same manner as in Example 1-2, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-4)

A green body was produced in the same manner as in Example 1-2, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The resulting green body The hardness is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Example 1-5)

Manufactured with SiC (cerium carbide, corresponding ceramic particles 1, density 3.21 × 10 ³ kg / m ³ ) 4.2 vol%, HPMC (weight average molecular weight Mw = 1 million) (corresponding to binder 2) 16.5 vol%, deionized water ( Corresponding to water 3) 79.3 vol% of ceramic raw material 4. This ceramic raw material 4 was kneaded in the same manner as in Example 1-1 to prepare a green body. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-6)

A green body was produced in the same manner as in Example 1-5, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-7)

A green body was produced in the same manner as in Example 1-1, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-8)

A green body was produced in the same manner as in Example 1-1, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-9)

A green body was produced in the same manner as in Example 1-1, except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-10)

The green body was prepared in the same manner as in Example 1-7 except that HPMC (weight average molecular weight Mw = 750,000) was used as the binder 2, and the blending ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-11)

The green body was prepared in the same manner as in Example 1-10, except that HPMC (weight average molecular weight Mw = 290,000) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-12)

A green body was prepared in the same manner as in Example 1-10, except that hydroxyethyl methylcellulose (HEMC, weight average molecular weight Mw = 800,000) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-13)

The green body was prepared in the same manner as in Example 1-10, except that methyl cellulose (MC, weight average molecular weight Mw = 290,000) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-14)

The green body was prepared in the same manner as in Example 1-10 except that cordierite was used as the ceramic particles 1. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-15)

The green body was prepared in the same manner as in Example 1-10, except that SiC was used as the ceramic particles 1. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-16)

A green body was produced in the same manner as in Example 1-7 except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-17)

A green body was produced in the same manner as in Example 1-7 except that the mixing ratio of the ceramic particles 1, the binder 2, and the water 3 was changed. Will get The hardness of the green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-18)

The green body was prepared in the same manner as in Example 1-10, except that polyvinyl alcohol (PVA, weight average molecular weight Mw = 500) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-19)

The green body was prepared in the same manner as in Example 1-10, except that polyethylene oxide (PEO, weight average molecular weight Mw = 3.5 million) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-20)

The green body was prepared in the same manner as in Example 1-10, except that polyethylene glycol (PEG, weight average molecular weight Mw = 4,000) was used as the binder 2. The hardness of the obtained green body is shown in Table 1 together with the composition of the ceramic raw material 4 in the green body.

(Examples 1-21)

The green body was prepared in the same manner as in Example 1-10, except that HPMC (weight average molecular weight Mw = 140,000) was used as the binder 2. The hardness of the obtained green body is displayed together with the composition of the ceramic raw material 4 in the green body. Table 1.

The hardness of the ceramic raw material 4 used in Examples 1-1 to 1-21 and the green body produced was summarized in Table 1.

As shown in Table 1, the hardness of the green body obtained according to Examples 1-16 to 1-21 was out of a certain range, and it became easy to become difficult to use the green body and to form a porous ceramic by extrusion molding. 10. On the other hand, in the green sheets obtained in accordance with Examples 1-1 to 1-15, the hardness measured by using a durometer is 1 to 12, and it is preferable to manufacture the porous ceramic 10 by extrusion molding. . Hereinafter, specific examples of the production of the porous ceramics 10 will be described by taking a few of the green sheets obtained in accordance with the respective examples as an example.

[Manufacture of porous ceramics]

(Example 2-1)

The green body obtained in Example 1-1 was extruded by using an extrusion molding machine (corresponding to the "squeezing machine 22") to which a sheet mold (corresponding to "nozzle 23") was attached, and the formed body 5 was produced. An opening having an inner dimension of 150 mm in width × 4 mm in height was formed by a mold. Next, the extruded molded body 5 was cooled in a freezer at -20 ° C to be frozen, and then dried by a freeze-drying apparatus for 24 hours. Further, after degreasing at 600 ° C for 1 hour in an air atmosphere using an electric furnace, it was calcined at 1600 ° C for 3 hours. After the completion of the calcination, it was naturally cooled to obtain a flaky ceramic having a width of 117 mm and a thickness of 3.1 mm. A partial cross-sectional view of the obtained flaky ceramic is shown in Fig. 4. Further, the porosity of the material of the obtained porous ceramic 10 is shown in Table 2.

(Example 2-2)

In place of the extrusion molding machine in which a cylindrical mold having a cylindrical opening having an inner circumferential diameter (hereinafter referred to as "inner circumferential diameter") of 40 mm is formed, the extrusion molding die of the sheet mold of the embodiment 2-1 is used. The green body obtained in Example 1-2 was extruded to produce a molded body 5. The honeycomb mold to be used has a number of holes of 650 per 1 in ² in the opening, and a width (hereinafter referred to as "slit width") of the slit from which the green body is extruded is 0.15 mm. Next, the extruded molded body 5 was cooled and frozen in a freezer at -20 ° C, and then dried in a freeze-drying apparatus for 24 hours. Further, after degreasing at 600 ° C for 1 hour in an air atmosphere using an electric furnace, it was calcined at 1400 ° C for 3 hours. After the completion of the calcination, natural cooling was carried out to obtain a honeycomb ceramic 11 having a pore number of 1060 per 1 in ² , an overall porosity of 93%, a material porosity of 64%, an aperture ratio of 80%, and an average thickness of the pore walls 13 of 156 μm. The physical properties of the obtained honeycomb ceramics 11 are summarized in Table 2. In addition, the "opening ratio" of the honeycomb ceramic 11 means the ratio of the hole 12 occupied by the total volume of the honeycomb ceramic 11.

(Example 2-3)

The honeycomb ceramic 11 was obtained in the same manner as in Example 2-2 except that the green body obtained in Example 1-3 was extruded instead of the green body obtained in Example 1-2. A partial cross-sectional view of the obtained honeycomb ceramic 11 is shown in Fig. 5A, and a partial enlarged view of Fig. 5A is shown in Fig. 5B. Further, the physical properties of the obtained honeycomb ceramics 11 are collectively shown in Table 2.

(Example 2-4)

The honeycomb ceramic 11 was obtained in the same manner as in Example 2-2 except that the green body obtained in Example 1-4 was extruded instead of the green body obtained in Example 1-2. The physical properties of the obtained honeycomb ceramics 11 are summarized in Table 2.

(Example 2-5)

The raw material obtained in Example 1-5 was used instead of the extrusion molding machine in which the honeycomb mold having the inner peripheral diameter of 40 mm was formed instead of the honeycomb mold of Example 2-2. The honeycomb ceramic 11 was obtained in the same manner as in Example 2-2 except for the extrusion of the blank. The honeycomb mold used had a number of holes per one in ² in the opening portion of 200 and a slit width of 0.3 mm. The physical properties of the obtained honeycomb ceramics 11 are summarized in Table 2.

(Example 2-6)

The honeycomb ceramic 11 was obtained in the same manner as in Example 2-5 except that the green body obtained in Example 1-6 was extruded instead of the green body obtained in Example 1-5. The physical properties of the obtained honeycomb ceramics 11 are shown in Table 2.

(Comparative Example 2-1)

A sheet-like shape was obtained in the same manner as in Example 2-1 except that hot air drying (60 ° C) was used instead of freezing and freeze drying of the molded body 5 . Porous ceramic 10. The porosity of the material of the obtained porous ceramic 10 is shown in Table 2.

(Comparative Example 2-2)

A sheet-like porous ceramic 10 was obtained in the same manner as in Example 2-1 except that the constant temperature and humidity drying (40 ° C, relative humidity: 80%) was used instead of freezing and freeze drying of the molded body 5. The porosity of the material of the obtained porous ceramic 10 is shown in Table 2.

(Comparative Example 2-3)

A sheet-like porous ceramic 10 was obtained in the same manner as in Example 2-1 except that the microwave drying was used instead of the freezing and lyophilization of the molded body 5. The porosity of the material of the obtained porous ceramic 10 is shown in Table 2.

(Comparative Example 2-4)

In addition to changing the blending ratio of the ceramic particles 1, the binder 2, and the water 3 to 56:12:32 (volume basis), the weight average molecular weight Mw of the binder 2 was changed to 290,000, and the ceramic particles 1 were blended. A starch corresponding to Example 1-5 was produced in the same manner as in Example 1-5 except that the starch corresponding to a volume ratio of 50% was used as a pore former. The obtained green body was extruded from the extrusion molding machine in which the honeycomb mold was used in Example 2-5 to produce a molded body 5. Subsequently, it was carried out in the same manner as in Example 2-5 except that microwave drying was used instead of freezing and freeze-drying of the molded body 5. To the honeycomb ceramic 11. The physical properties of the obtained honeycomb ceramics 11 are shown in Table 2.

The physical properties of the flaky porous ceramics 10 or the honeycomb ceramics 11 obtained in the examples 2-1 to 2-4 are collectively shown in Table 2.

As shown in Table 2, the porosity of the material and the overall porosity of any of the porous ceramics 10 obtained according to Examples 2-2 to 2-6 showed high values. Particularly in Examples 2-2 to 2-5, it was found that although the entire porosity was 90% or more, the average thickness of the pore walls 13 was 200 μm or less, for example, a honeycomb ceramic 11 having excellent characteristics as a filter, an adsorbent, a baking bracket for a small component, and a fluid permeation member.

Further, the porous ceramic 10 obtained in accordance with Example 2-1 showed a higher porosity value of the porous ceramic 10 obtained in comparison with Comparative Examples 2-1 to 2-3 which were different only in the drying method. . Similarly, the honeycomb ceramics 11 obtained in accordance with Comparative Examples 2 to 4 which were different from the formulation and drying methods of Examples 2 to 5, the honeycomb ceramics 11 obtained in accordance with Examples 2 to 5, the material porosity and The overall porosity ratio shows a higher value at the same time.

Further, in the above-described embodiment, the cordierite is described by being formed of kaolin, talc, and alumina, but may be formed, for example, of magnesium oxide, aluminum oxide, or cerium oxide.

Further, in the above-described embodiment, the molding machine for discharging the raw material is described by the extrusion molding machine 22 in the molding step. However, an injection molding machine for projecting a raw material in a mold based on a predetermined shape may be applied. .

Further effects and modifications can be easily derived by the manufacturer. Therefore, the invention in its broader aspects is not limited to Accordingly, various modifications may be made without departing from the spirit and scope of the inventions.

S101 to S106‧‧‧ steps

Claims (10)

A method for producing a porous ceramic, comprising: a molding step of producing a molded body by kneading a green body obtained by kneading a ceramic material containing ceramic particles, a binder, and water; and a freezing step of The molded body is frozen to form a frozen body containing ice; a drying step of drying the frozen body to form a dried body after removing the ice; and a calcining step of calcining the dried body to form a calcined body. The method for producing a porous ceramic according to claim 1, wherein the binder contains a cellulose derivative. The method for producing a porous ceramic according to the second aspect of the invention, wherein the cellulose derivative comprises methyl cellulose, ethyl cellulose, ethyl methyl cellulose, hydroxymethyl cellulose, hydroxypropyl One or more of methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, carboxymethyl ethyl cellulose, and carboxyethyl cellulose. The method for producing a porous ceramic according to the first aspect of the invention, wherein the weight average molecular weight Mw of the binder is 150,000 or more. The method for producing a porous ceramic according to the first aspect of the invention, wherein the ceramic raw material contains 1 to 30 vol% of the ceramic particles, 100 vol% when the total of the water and the ceramic particles is 100 vol%. The content of non-volatile components in the aforementioned ceramic raw materials It is 9 to 45 vol%. The method for producing a porous ceramic according to claim 1, wherein the forming step of forming the molded body by discharging the green body is performed by using a nozzle having an opening portion having a predetermined shape. Extrusion extrusion molding machine. A porous ceramics produced by the method for producing a porous ceramic according to any one of claims 1 to 6, wherein the porous ceramics have a total porosity of 85 to 99%. A honeycomb ceramic having a porosity of 50% or more. The porous ceramic according to claim 7, wherein the number of pores per square inch is from 250 to 2,000. The porous ceramic according to the seventh aspect of the invention, wherein the pore wall has an average thickness of 200 μm or less. The porous ceramic according to claim 7, wherein the honeycomb ceramics comprise alumina, cordierite or tantalum carbide.