JP2002234780A - Method for producing porous ceramic honeycomb structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for producing a honeycomb structure which has little generation of deformation and cracking after the drying or burning of the honey comb molded body even if a pore forming agent is largely added thereto for the purpose of increasing its porosity. SOLUTION: A raw material to become into a cordierite composition, a molding aid, a pore forming agent and water are mixed and kneaded. A honeycomb body is produced by an extrusion molding method therefrom, and, after that, the molded body is dried and burnt to produce the porous ceramic honeycomb structure. The production method contains (a) a first drying stage where 60 to 90 mass% of water contained in the molded body is evaporated by microwaves or dielectric drying, and (b) a second drying stage where the remaining of the water contained in the molded body is evaporated by hot-air drying, or further, (c) a first burning stage where the pore forming agent is burnt away by 50 to 70 mass% by a hot-air circulation furnace, and (d) a second burning stage where the remaining of the pore forming agent is burnt away by a single furnace, a tunnel furnace or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a porous ceramic honeycomb structure comprising a cordierite composition. In particular, the present invention relates to a method for manufacturing a porous ceramic honeycomb structure having a porosity of 50% or more.

[0002]

2. Description of the Related Art From the standpoint of preserving the local environment and the global environment, it is required to reduce harmful substances contained in exhaust gas emitted from engines of automobiles and the like. To meet this demand, catalytic converters for purifying exhaust gas have been used. I have. One of the catalytic converters is a ceramic honeycomb catalytic converter. Recently, a porous ceramic honeycomb structure made of cordierite (hereinafter referred to as a “porous ceramic honeycomb structure”) has been abbreviated to collect graphite particles and the like contained in exhaust gas from diesel engines. An exhaust gas purifying filter has been used in which both ends of a cell opening of the honeycomb structure are alternately plugged.

[0003] The exhaust gas purifying operation of the exhaust gas purifying filter 10 is performed as follows. Exhaust gas flows in (shown by 10a) from a cell 11c that is open on the inflow side 11d of the honeycomb structure 11, passes through pores formed in the cell wall 11b, and is discharged from an outflow side 11e (in 10b). Show)
Is done. Graphite fine particles and the like contained in the exhaust gas are filtered and collected when passing through adjacent pores in the cell wall 11b to the adjacent cells.

Next, a general method for manufacturing the honeycomb structure 11 will be described. First, as a cordierite composition is obtained, a raw material for forming a cordierite such as kaolin, talc, and alumina, a forming aid, a pore former for forming pores, and water are mixed and kneaded to obtain a ceramic clay. I have. Then, after the kneaded clay is degassed in vacuum, it is extruded through a special mold using an extrusion screw or a plunger to form a formed body having a honeycomb structure in which the outer peripheral wall 11a and the cell wall 11b are formed (hereinafter, “honeycomb”). The “formed body having a structure” is abbreviated to “formed body”. Then, it is dried and further decomposed and removed by a sintering furnace such as a tunnel furnace or a single furnace, a binder such as a molding aid in the molded body, water of crystallization, etc. To promote the reaction between them to form cordierite, and at the same time, shrink and densify by sintering to obtain a honeycomb structure 11 having a predetermined shape and strength and having fine pores penetrating the cell wall 11b. .

[0005] By the way, in the kneaded clay for obtaining a molded body, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, starch powder, and the like are generally used as the aforementioned molding aid.
An organic binder such as glycerin and a surfactant wax are included. Further, as the above-mentioned pore-forming agent, graphite, wheat flour, starch powder and the like are included.

For example, Japanese Patent Publication No. 27303/1988 discloses that a starch powder such as wheat flour or rice flour is used as a pore-forming agent.
There is a description that the mass% is added, the temperature of the kneaded material itself is set to 70 ° C. or lower, and the mixture is kneaded and burned during firing.

Further, Japanese Patent No. 2562186 discloses that
There is a description of using an easily combustible carbon powder having a mass reduction rate of 50% or more in a heat treatment held at 650 ° C. for one hour in an air atmosphere as a pore former.

[0008]

By the way, the exhaust gas purifying filter 10 shown in FIG. 3 not only collects the graphite fine particles and the like contained in the exhaust gas with high efficiency during use, but also forms the inside of the cell wall 11a. It is required to increase the porosity of the pores to be formed to reduce the pressure loss and reduce the load on the engine. Then, in order to increase the porosity of the honeycomb structure 11, it is necessary to increase the amount of a pore-forming agent that forms pores.

[0009] However, the above-mentioned JP-B-63-2730.
When the amount of starch powder, which is a pore-forming agent in JP-A-3, is increased, the starch powder swells due to a liquid such as water added at the time of kneading, and the shrinkage is large in the drying step after extrusion molding. Not only causes problems such as deformation and cracking,
Drying unevenness easily occurs, and as a result, the dimensional accuracy of the finished honeycomb structure is deteriorated. If the amount of the starch powder is increased to further increase the porosity, the honeycomb structure 11 tends to crack as the starch powder is thermally decomposed at about 300 ° C. at the time of firing.

On the other hand, if the amount of the easily combustible carbon powder, which is the pore-forming agent described in Japanese Patent No. 2562186, is increased, cracks may occur during drying. That is, when the whole of the molded body is uniformly evaporated and dried by microwaves, if a large amount of carbon powder is added to the inside of the molded body, the carbon powder absorbs the microwaves and generates heat, thereby generating heat. When the particle size becomes large, the carbon powder may burn and cracks may occur in the molded body. In addition, when the amount of the easily combustible carbon powder is increased, the easily combustible carbon powder is thermally decomposed at about 800 ° C. at the time of firing.
Cracks may occur in the honeycomb structure. Further, even in the firing process, the combustion of carbon does not proceed simultaneously inside and outside the honeycomb structure, and as a result, cracks may occur in the honeycomb structure.

In order to increase the porosity of the honeycomb structure 11, it is necessary to increase the amount of a pore-forming agent for forming pores. However, as described above, deformation and cracking are likely to occur after drying or firing. . Therefore, an object of the present invention is to provide a method for manufacturing a honeycomb structure having less deformation and cracking after drying or firing of a molded article even when a large amount of a pore forming agent is added to increase the porosity. It is in.

[0012]

Means for Solving the Problems The present inventors have made intensive studies on the relationship between drying and firing conditions and cracks generated in a molded article containing a large amount of a pore-forming agent. As a result, in the drying step, after the water added to the molded body is appropriately evaporated by microwave or dielectric drying, the remaining portion is further evaporated by hot air drying, or further added to the molded body in the firing step. It was found that, after the pore forming agent was burned out by circulating hot air and burned out properly, the remainder was burned off in a single furnace or a tunnel furnace to reduce the occurrence of cracks and lower the production cost. The inventors have arrived at the present invention.

Specifically, the present invention is to mix and knead a raw material for forming a cordierite composition, a molding aid, a pore former, and water.
A method for producing a porous ceramic honeycomb structure, in which a molded body is formed by an extrusion molding method, and then dried and fired, wherein in the drying step, (a) 60 to 90% by mass of the water content of the molded body In a microwave drying furnace or a dielectric drying furnace, (b) a second drying step in which the remaining moisture contained in the molded body is evaporated in a hot-air oven,
It is characterized by having. In the firing step,
(C) 50 to 70% by mass of the pore former in a hot air circulating furnace.
It is characterized by having a first firing step for burning out and (d) a second firing step for burning off the remaining part of the pore-forming agent in a single furnace or a tunnel furnace or the like. In the drying step,
(A) a first drying step of evaporating 60 to 90% by mass of the water content of the compact in a microwave drying furnace or a dielectric drying furnace, and (b) the remaining moisture content of the compact in a hot air oven. In the second drying step of evaporating and then in the baking step,
(C) 50 to 70% by mass of the pore former in a hot air circulating furnace.
It is characterized by having a first firing step for burning out and (d) a second firing step for burning off the remaining part of the pore-forming agent in a single furnace or a tunnel furnace or the like. At this time, the pore-forming agent is preferably starch powder.

Next, the reason for the configuration according to the present invention will be described. (First drying step) In order to reduce deformation and cracking after drying of the compact, as a first drying step, 60% by mass or more of the water content of the compact is evaporated in a microwave drying furnace or a dielectric drying furnace. Need to be done. On the other hand, when evaporating more than 90% by mass of the water content of the molded body in the first drying step,
In the first drying step, the molded body is likely to be deformed or cracked. Therefore, in the first drying step, 6% of the water content
0-90% by weight is evaporated. Preferably it is 70-80 mass%. Further, when performing microwave drying or dielectric drying, it is preferable to perform the drying with an output corresponding to the size of the molded body.

(Second Drying Step) The second drying step following the first drying step
In the drying step, the remaining water content of the molded body is evaporated.
In the second drying step, the molded body is heated in a hot-air drying oven at 100 to 1 mm.
It is preferred to heat to around 20 ° C.

(First firing step) In order to reduce cracks after firing the compact, it is necessary to burn out at least 50% by mass of the pore former in a hot air circulation furnace as a first firing step. On the other hand, if the loss of the pore-forming agent in the first baking step exceeds 70% by mass, the strength of the formed body during or after the first baking step is reduced, and cracking by hot air or the first baking step is performed. In the case where the transfer operation of the molded body at the time of shifting to the firing step 2 occurs, a crack may be generated due to mechanical external force. Therefore, in the first firing step, 50 to 70% by mass of the pore former is burned off. Preferably it is 55-65 mass%.

(Second firing step) In the second firing step following the first firing step, the remaining part of the added pore-forming agent is burned off. This second firing step can be performed in a single furnace, a tunnel furnace, or a firing furnace such as a roller hearth kiln.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to examples. FIG. 1 is a diagram illustrating a manufacturing process of the honeycomb structure according to the embodiment. The honeycomb structure 11 shown in FIGS. 2 and 3 was manufactured as follows.

(Example 1) Kaolin, talc, silica,
A powder of aluminum hydroxide, alumina or the like is prepared to obtain a cordierite ceramic raw material.
% By mass, and 30 to 50% by mass ratio of hydroxypropyl methylcellulose to methylcellulose. And, as a pore-forming agent, starch powder 3
0% by weight is added. Then, after thoroughly mixing in a dry system,
A specified amount of water was injected to perform further sufficient kneading to purify the clay. Next, extrusion molding is performed using an extrusion molding die.
A molded body having a honeycomb structure of 150 mm × length 160 mm was obtained. Next, the formed body is subjected to dielectric drying to perform first drying while changing the amount of moisture contained in the formed body, and then the formed body after the first drying step is heated to 120 ° C. in a hot air drying furnace. To perform a second drying.

Then, the evaporation rate of the moisture contained in the compact in the first drying step, (A): deformation or cracking after the first drying step in dielectric drying, and (B): after the drying step Deformation or cracking was evaluated. In addition, the evaporation rate of water in the first drying step is based on the difference in mass of the molded body before and after the first drying step, and
The total amount of evaporation was determined from the difference between the masses before and after the first and second drying steps, and was calculated as the ratio of the amount of evaporation during the first drying step. In addition, the occurrence of deformation or cracking was judged as excellent (○) when 5% or less per lot was good (○), good (５〜) when 5 to 10% per lot, and defective (）) when more than 10% per lot. . Table 1 shows the results.

(Table 1) In the first drying stepEvaluation of deformation or crack  Division Water evaporation rate (% by mass) (A) After the first drying (B) After the drying step Comparative Example 1 47 ○ × Comparative Example 2 51 ○ × Comparative Example 3 58 ○ × Invention Example 1 63 ○ △ Invention Example 2 67 ○ △ Invention Example 3 72 ○ ○ Invention Example 4 75 ○ ○ Invention Example 5 77 ○ ○ Invention Example 6 80 ○ ○ Invention 7 87 △ △ Comparative 4 94 × × Comparative 5 100 × ×

As shown in Inventive Examples 1 to 7 in Table 1, if 60 to 90% by mass of the contained water is evaporated in the first drying step, deformation or deformation occurs after the first drying step or after the drying step. It can be seen that the occurrence of cracks is small. Further, when the amount of moisture contained in the molded body in the first drying step was 70 to 80% by mass, favorable results were obtained in which deformation and cracking were less likely to occur.

Example 2 Kaolin, talc, silica,
A powder of aluminum hydroxide, alumina or the like is prepared to obtain a cordierite ceramic raw material.
% By mass, and 30 to 50% by mass ratio of hydroxypropyl methylcellulose to methylcellulose. Then, starch powder 30 is used as a pore-forming agent for the ceramic raw material.
% By weight is added. Next, after sufficient mixing in a dry system, a specified amount of water was poured and further sufficient kneading was performed to purify the clay. Next, extrusion molding is performed using an extrusion molding die.
A molded body having a honeycomb structure of 50 mm × length 160 mm was obtained. Next, after drying this molded body, the first baking was performed in a hot-air circulating furnace while circulating hot air and changing the burnout amount of starch powder, which was the added pore-forming agent. Further, the molded body subjected to the first calcination is subjected to a batch-type calcination furnace without circulating hot air.
A second firing up to 00 ° C. is performed, φ145 mm × length 1
55 mm, cell wall thickness 0.30 mm, cell pitch 1.80
mm and a porosity of 50 to 80%.

Then, the burnout ratio of the pore-forming agent in the first firing step, and (C): deformation or cracking after the first firing step;
(D): The deformation or crack after the completion of the firing step was evaluated. The burn-out rate of the pore-forming agent in the first baking step was determined based on the difference in mass of the product before and after the first baking step.
The theoretical mass of crystallization water contained in the ceramic raw material was subtracted to obtain the mass of the pore-forming agent, and the ratio to the amount of the pore-forming agent added was defined as the proportion of the burning-off. In addition, the occurrence of deformation or cracking was determined as excellent (○) when 1% or less per lot was good (○), 1-2% per lot was good (△), and that exceeding 2% per lot was defective (×). . Table 2 shows the results.

[0025] (Table 2) first modification or cracking evaluation Classification pore former burn off ratio of at firing step (wt%) (C) after the first calcination (D) firing step after completion of Comparative Example 6 41 ○ × Comparative Example 7 47 ○ × Comparative Example 8 49 ○ × Invention Example 8 52 ○ △ Invention Example 9 55 ○ ○ Invention Example 10 57 ○ ○ Invention Example 11 60 ○ ○ Invention Example 12 63 ○ ○ Invention Example 13 68 △ △ Invention Example 14 70 △ △ Comparative Example 9 80 × × Comparative Example 10 100 × ×

As shown in Invention Examples 8 to 14 in Table 2, if 50 to 70% by mass of the starch powder added in the first baking step is burned off, after the first baking step or after the completion of the baking step, It can be seen that the occurrence of deformation and cracking is small. Preferably 55 to
65% by mass.

The honeycomb structure, which has not been deformed or cracked, supports a catalyst in the cell walls 11b and in the pores as necessary. The honeycomb structure 11 plugs every other cell on the exhaust gas inflow side 11d, and plugs only cells not sealed on the inflow side 11d on the exhaust gas outflow side 11e. By storing the filter, the exhaust gas purifying filter 10 can reduce the pressure loss and efficiently collect the fine particles in the exhaust gas, or can further enhance the purifying function immediately after the engine is started.

Example 3 Kaolin, talc, silica,
A powder of aluminum hydroxide, alumina or the like is prepared to obtain a cordierite ceramic raw material.
% By mass, and 30 to 50% by mass ratio of hydroxypropyl methylcellulose to methylcellulose. Then, starch powder 30 is used as a pore-forming agent for the ceramic raw material.
% By weight is added. Next, after sufficient mixing in a dry system, a specified amount of water was poured and further sufficient kneading was performed to purify the clay. Next, extrusion molding is performed using an extrusion molding die.
A molded body having a honeycomb structure of 50 mm × length 160 mm was obtained. Next, the formed body is subjected to dielectric drying to perform first drying while changing the amount of moisture contained in the formed body, and then the formed body after the first drying step is heated to 120 ° C. in a hot air drying furnace. To perform a second drying. Next, the first baking was performed in a hot-air circulating furnace while changing the burnout amount of the starch powder as a pore-forming agent added. Further, the molded body subjected to the first calcination is not subjected to hot air circulation, and is heated to 1400 ° C. in a batch-type calcination furnace.
The second firing is performed until φ145 mm x length 155 m
m, cell wall thickness 0.30 mm, cell pitch 1.80 mm,
The honeycomb structure had a porosity of 50 to 80%.

Then, in the drying step, the evaporation rate of the moisture contained in the compact in the first drying step, (A): deformation or cracking after the first drying step in dielectric drying, and (B): drying Deformation or cracking after the end of the process was evaluated. In addition, the evaporation rate of water in the first drying step is obtained by calculating the total evaporation amount from the difference in mass between the molded bodies before and after the first drying step and the difference in mass between before and after the first and second drying steps. In the first drying step. In addition, the occurrence of deformation or cracking was judged as excellent (○) when 5% or less per lot was good (○), good (５〜) when 5 to 10% per lot, and defective (）) when more than 10% per lot. . Table 3 shows the results.
Shown in Further, the burnout ratio of the pore-forming agent in the first firing step, and (C): deformation or cracking after the first firing step,
(D): The deformation or crack after the completion of the firing step was evaluated. The burn-out rate of the pore-forming agent in the first baking step was determined based on the difference in mass of the product before and after the first baking step.
The theoretical mass of crystallization water contained in the ceramic raw material was subtracted to obtain the mass of the pore-forming agent, and the ratio with the amount of the pore-forming material added was taken as the mass-burning ratio. In addition, the occurrence of deformation or cracking was determined as excellent (○) when 1% or less per lot was good (○), 1-2% per lot was good (△), and that exceeding 2% per lot was defective (×). . Table 4 shows the results.

(Table 3) In the first drying stepEvaluation of deformation or crack  Division Water evaporation rate (% by mass) (A) After the first drying (B) After the drying step Comparative Example 11 60 ○ △ Invention Example 15 69 ○ △ Invention Example 16 74 ○ ○ Invention Example 17 79 ○ ○ Comparative Example 12 89 ○ △

[0031] (Table 4) the first variant or cracking evaluation Classification pore former burn off ratio of at firing step (wt%) (C) first after firing (D) firing step after completion of Comparative Example 11 46 ○ × Invention Example 15 54 ○ △ Invention Example 16 58 ○ ○ Invention Example 17 64 ○ ○ Comparative Example 12 75 × ×

As shown in Inventive Examples 15 to 17 in Tables 3 and 4, if 60 to 90% by mass of the water content of the molded body is evaporated in the first drying step, after or after the first drying step. After the completion, deformation or cracking is less likely to occur, and if 50 to 70% by mass of the starch powder added in the first baking step is burned off, deformation or cracking will occur after the first baking step or after the baking step. It can be seen that the occurrence of is small. Preferably 55 to 65
What is necessary is just to burn out by mass%.

The honeycomb structure, which has not been deformed or cracked, supports a catalyst in the cell walls 11b and in the pores as needed. The honeycomb structure 11 plugs every other cell on the exhaust gas inflow side 11d, and plugs only cells not sealed on the inflow side 11d on the exhaust gas outflow side 11e. By storing the filter, the exhaust gas purifying filter 10 can reduce the pressure loss and efficiently collect the fine particles in the exhaust gas, or can further enhance the purifying function immediately after the engine is started.

[0034]

As described in detail above, according to the method for manufacturing a honeycomb structure of the present invention, even if a large amount of a pore-forming agent is added to increase the porosity, the honeycomb structure is deformed after drying or firing. A honeycomb structure with less occurrence of cracks and cracks can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a manufacturing process of a honeycomb structure according to an embodiment.

FIG. 2 is a perspective view of a honeycomb structure.

FIG. 3 is a schematic cross-sectional view of an example of an exhaust gas purification filter 10 using the honeycomb structure of FIG.

[Explanation of symbols]

 10a: gas inflow 10b: gas discharge 11: honeycomb structure 11a: outer peripheral wall 11b: cell wall 11c: cell 11d: inflow side 11e: outflow side 12: storage container 23a, 23b: gripping member 31a, 31b: sealing material 31d: Through hole

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B01J 32/00 ZAB B01J 35/04 301N 35/04 301 B28B 3/20 K B28B 3/20 B01D 53/36 CF term (reference) 4D019 AA01 BA05 BB06 CB06 4D048 AA14 BB02 BB17 CC41 4G054 AA06 AB09 BD01 BD19 DA03 4G069 AA01 AA08 BA13A BA13B BA29C DA05 EA19 FB30 FB57 FB58 FB67 FC03

Claims (4)

[Claims] 1. A porous ceramic obtained by mixing and kneading a raw material for forming a cordierite composition, a molding aid, a pore-forming agent, and water, forming a molded body by an extrusion molding method, and drying and firing the molded body. A method for manufacturing a honeycomb structure, wherein in a drying step, (a) a first drying step of evaporating 60 to 90% by mass of the water content of the molded body in a microwave drying furnace or a dielectric drying furnace, (b) A) a second drying step of evaporating a remaining portion of the water content of the molded body in a hot-air drying oven. 2. A method for producing a porous ceramic honeycomb structure, comprising mixing and kneading a raw material for forming a cordierite composition, a molding aid, a pore-forming agent, and water, extruding, drying, and firing. In the firing step, (c) a first firing step in which the pore-forming agent is burned out by 50 to 70% by mass in a hot-air circulation furnace, and (d) the remaining part of the hole-forming agent is burned out in a single furnace or a tunnel furnace. A method for producing a porous ceramic honeycomb structure, comprising a second firing step. 3. A porous ceramic obtained by mixing and kneading a raw material having a cordierite composition, a molding aid, a pore-forming agent, and water, forming a molded body by an extrusion molding method, and drying and firing the molded body. A method for manufacturing a honeycomb structure, comprising: (a) 60 to 90% by mass of water content of the molded body in a drying step;
First in a microwave drying oven or a dielectric drying oven
(B) a second drying step of evaporating the remaining moisture content of the compact in a hot-air drying furnace, and then a baking step (c) the pore-forming agent is heated to 50 to 70 in a hot-air circulating furnace.
A porous ceramic honeycomb structure, comprising: a first firing step of burning out the mass% by mass; and (d) a second firing step of burning out the remainder of the pore-forming agent in a single furnace or a tunnel furnace. Production method. 4. The method for producing a porous ceramic honeycomb structure according to claim 1, wherein the pore-forming agent is starch powder.