JP2000301516A - Manufacture of ceramic honeycomb structural body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high quality ceramic honeycomb structural body with a low heat capacity by a method wherein the cell wall is prevented from falling out at an extrusion molding when the thickness of the cell wall is made thinner. SOLUTION: After one or more kinds of ceramic stocks prepared so as to realize a desired ceramic composition is measured, before a kneading process is executed, the ceramic stocks forming agglutinated particles among the ceramic stocks are dispersed in advance in a solvent with either one or both of a chemical and a physical dispersing methods in order to realize the ceramics, which pass the slits of an extrusion mold. The resultant solution is added with other ceramic stock without drying so as to obtain a body, the re-agglutination of which is prevented from occurring, through kneading in order to allow to extrusion-mold under the state that stock particles are dispersed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion molding die having a narrow slit, which is used for a catalyst carrier in an exhaust gas purifying catalyst of an internal combustion engine such as an automobile engine or a filter for water purification. The present invention relates to a method for manufacturing a ceramic honeycomb structure formed by extruding soil into a honeycomb shape.

[0002]

2. Description of the Related Art In recent years, as exhaust gas regulations for automobiles have been tightened, early activation of exhaust gas purifying catalysts has been required in order to reduce the amount of hydrocarbon emissions immediately after engine start. One of the means corresponding to this is to reduce the heat capacity of the ceramic honeycomb structure constituting the catalyst carrier.
For this purpose, it has been studied to reduce the cell wall thickness. However, when trying to reduce the cell wall thickness, the cell walls may come off during extrusion molding of the honeycomb structure. This is due to coarse aggregated particles present in the raw material for forming the honeycomb structure, and the coarse aggregated particles are clogged in the lattice-shaped slits or at the entrance of the extrusion molding die, hindering the supply of the clay. It is thought to be.

[0003] Regarding the particle size of the raw material powder, for example, Japanese Patent Application Laid-Open No. HEI 8-112528 discloses that the ratio R / M of the maximum particle size R of the raw material powder to the slit width M of the extrusion die for molding should be 1/3 or less. Discloses that a molded body without lattice defects can be obtained. However, in a ceramic raw material that easily forms secondary particles by agglomeration, a raw material powder prepared to a predetermined size or less by classification or sieving or the like has a very small primary particle constituting the raw material powder,
The honeycomb structure is densified by molding and firing, and the porosity is reduced. For this reason, the heat capacity increases, and the thermal expansion coefficient also increases, and the thermal shock resistance decreases. Also, even if the raw material is smaller than the slit width as the primary particles, if care is not taken during the synthesis process before the raw material preparation and during the storage of the raw material, the apparent particle size increases due to re-aggregation due to moisture and the like. turn into. It is not easy to re-pulverize and re-disperse the once-agglomerated particles into lower-order particles, which is an obstacle to thinning the cell wall thickness.

[0004] When sieving or the like, in the case of a dry sieve, even if the agglomerated particles are sieved, the sieve mesh is immediately clogged, and the sieving yield is deteriorated and the cost is increased.
In addition, wet sieves have problems that they are re-agglomerated after drying even if they are sieved, or that the cost increases due to an increase in the number of steps.

[0005]

As described above, according to the conventional method, when trying to reduce the cell wall thickness of the honeycomb structure, clogging occurs at the time of extrusion molding due to coarse aggregated particles present in the kneaded clay, and the cell is clogged. There was a problem that the quality of the honeycomb structure deteriorated due to the removal of the wall. Accordingly, an object of the present invention is to obtain a high-quality ceramic honeycomb structure that can prevent the cell wall from coming off during extrusion molding, can reduce the thickness of the cell wall, and have a low heat capacity.

[0006]

According to the method of claim 1 of the present invention, a kneaded material obtained by mixing and kneading a solvent with one or more kinds of ceramic raw materials weighed to obtain a desired ceramic composition is obtained. In manufacturing a ceramic honeycomb structure by extrusion molding using an extrusion mold having a honeycomb-shaped narrow slit and firing, the above-mentioned ceramic raw materials are weighed, and prior to the step of kneading, the aggregated particles are dispersed. The step of causing the step to be performed. In the dispersing step, among the ceramic raw materials, the ceramic raw materials forming the aggregated particles are dispersed in advance in the solvent using a chemical or physical dispersion method or both of them, so that the aggregated particles are formed. After the extrusion mold has a size that passes through the slit, it is subjected to the subsequent kneading step without drying.

[0007] Ceramic raw materials are liable to aggregate to form secondary particles, and even if sieving or the like is performed at the time of mixing raw materials, the raw materials may re-agglomerate and cause cell loss during extrusion molding. On the other hand, according to the method of the present invention, in the dispersing step, the aggregated particles in the ceramic raw material are dispersed in the solvent in advance to obtain particles having a size that can pass through the slit of the extrusion die. In the subsequent kneading step, other ceramic raw materials, forming aids and the like are added and kneaded, so that the kneaded clay can be obtained with the raw material particles dispersed. Therefore, extrusion molding can be performed without causing clogging due to aggregated particles, and the cell can be prevented from coming off.Thus, the cell wall thickness can be reduced.
A high quality ceramic honeycomb structure having a low heat capacity can be obtained. Further, since no labor such as sieving the raw materials is required, the manufacturing process is simplified, and the cost can be reduced.

[0008] In the method of claim 2, the chemical dispersion method uses at least one selected from anionic, cationic, amphoteric and nonionic surfactants as a dispersant. Is added to the above-mentioned solvent together with the ceramic raw material containing the above-mentioned aggregated particles, and uniformly mixed to peptize and disperse the above-mentioned aggregated particles.

When the above-mentioned dispersing agent composed of a suitable surfactant is disposed around the ceramic raw material fine particles having formed the aggregated particles, the repelling force is generated due to the same polarity of the surfactant. It is easier to peptize and disperse into lower order particles, and prevents reaggregation.
If another ceramic raw material and a forming aid are added to this solution, it is possible to form a clay while maintaining a dispersed state.

According to a third aspect of the present invention, the physical dispersion method is characterized in that the aggregated particles are peptized and dispersed by applying vibration or rotation to a solution obtained by adding the ceramic raw material containing the aggregated particles to the solvent. Method.

By applying a physical force such as vibration or rotational force to the ceramic raw material fine particles having formed the aggregated particles, the aggregated particles are easily peptized and dispersed into lower order particles, and reagglomeration is prevented. can do.

[0012] In the method of claim 4, at least one selected from anionic, cationic, amphoteric and nonionic surfactants is added to the solution of claim 3 as a dispersant.

If the above-mentioned dispersant used in the above-mentioned chemical dispersion method is used in combination with the above-mentioned physical dispersion method, the dispersing effect can be further enhanced, and the above-mentioned aggregated particles can be peptized and dispersed efficiently.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a ceramic honeycomb structure of the present invention will be described in detail. In the present invention, examples of the ceramics constituting the honeycomb structure include cordierite. Cordierite theoretical composition 2MgO · 2Al ₂ O ₃ · 5
It is represented by SiO ₂ , and usually has 49.0 SiO _{2 in} the composition.
53.0 wt%, Al ₂ O ₃ 33.0~37.0 wt%, a proportion of MgO11.5~15.5 wt%. It is needless to say that the present invention can be applied not only to cordierite but also to a honeycomb structure made of other extrudable ceramics.

FIG. 1 is a view showing a process of manufacturing a ceramic honeycomb structure according to the method of the present invention. First, in the step shown in (1), one or more types of ceramic raw materials as starting materials are weighed so as to have a desired ceramic composition. As the ceramic raw material, an oxide, a nitride, a carbide, a boride, a hydroxide, a chloride and the like containing at least one of the metal elements constituting the target ceramics are usually used, and are appropriately selected as necessary. be able to. For example, when producing a cordierite honeycomb structure, talc (Mg ₃ S
i ₄ O ₁₀ (OH) ₂ ), kaolin (Al ₂ Si ₂ O)
₅ (OH) ₄ ), alumina (Al ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ), and the like are generally used. Good.

In the step shown in (2), among these ceramic raw materials, at least the ceramic raw material which forms coarse aggregated particles which do not pass through the slit of the extrusion die is used.
It is dispersed in a solvent in advance using a chemical or physical dispersion method or both. In this step, the effect can be obtained by pulverizing and dispersing at least the ceramic raw material forming the aggregated particles. When only a part of the ceramic raw material is aggregated, only the aggregated particles are used (2).
Or the whole of the ceramic raw material including the aggregated particles may be dispersed.

The chemical dispersing method is a method of peptizing and dispersing aggregated particles into a size that can pass through a slit of an extrusion die by using a dispersing agent. Amphoteric and nonionic (ethers, esters,
At least one selected from surfactants other than ionic type such as amines, amides, and derivatives) is used, and the type and amount of the dispersant that are optimally selected are selected according to the type of aggregated particles to be dispersed. . At this time, it is more preferable to use a material which shows high dispersibility with a small amount of addition. As the solvent, in addition to water, organic solvents such as alcohols can be suitably used. In the case of dispersing by this method, a solution in which a dispersant is added to a solvent and mixed well,
The ceramic raw material forming the aggregated particles may be added and further mixed until the mixture becomes uniform. The action of the dispersant facilitates peptization and dispersion of the aggregated particles, and prevents reaggregation.

When there are a plurality of ceramic raw materials containing agglomerated particles, they may be dispersed one by one using an optimal dispersant, and then mixed in the subsequent kneading step of the kneaded clay. When an agent can be used, a plurality of ceramic raw materials containing aggregated particles can be simultaneously added and dispersed in a solution containing a dispersant. In this step, it is possible to add another ceramic raw material that does not contain aggregated particles. However, if the proportion is increased, the dispersing effect is reduced. Therefore, it is desirable that the dispersibility is not reduced.

The physical dispersion method is a method in which vibration or rotational force is applied to a solution obtained by adding a ceramic raw material containing aggregated particles to a solvent by using a known dispersing apparatus, thereby forming aggregated particles in the solution. Shear stress is applied to the ceramic raw material particles to be physically peptized and dispersed. As the solvent, water and organic solvents such as alcohols can be suitably used. As for the dispersing device, the dispersing effect is higher for high frequency (high rotational speed) and high output devices such as ultrasonic dispersing machines that use ultrasonic waves. It is economically advantageous if glue and dispersion are possible. Also in this method, when there are a plurality of ceramic raw materials containing aggregated particles, they can be dispersed separately one by one or simultaneously in the same solution.

The above-mentioned chemical dispersion method can be used in combination with the physical dispersion method. In this case, at least one of the above-described anionic, cationic, amphoteric, and nonionic surfactants is used as a dispersant, and a solution obtained by uniformly mixing the same with a solvent contains a ceramic containing aggregated particles. The raw materials are added, and the aggregated particles are peptized and dispersed using a dispersion device. This is preferable because the dispersing effect is enhanced and the aggregated particles can be peptized and dispersed efficiently.

In the step (3), deflocculation,
To the solution containing the dispersed ceramic raw materials, add other ceramic raw materials, humectants, lubricants, binders, etc., which are usually used as molding aids, add an appropriate amount of solvent, knead, and extrude It should be possible clay. Examples of the humectant and the humectant include wax, a water-soluble polyhydric alcohol derivative, a surfactant, and the like, and examples of the binder include methyl cellulose, polyvinyl alcohol, and the like. As long as these molding aids do not affect the dispersibility,
It can be added in the dispersing step (2).
Here, the step (3) is performed subsequent to the dispersion step (2) to prevent re-aggregation due to drying.
At the time of kneading, a large amount of energy is required for the particles to move, so that agglomeration is unlikely to occur. By doing so, the clay can be produced while the raw material particles are dispersed.

Next, in step (4), the kneaded clay is formed into a round bar by extrusion using a die having a honeycomb-shaped narrow slit. At this time, since the raw material particles constituting the round bar are all large enough to pass through the slits, it is possible to prevent the occurrence of defects such as detachment on the cell walls of the obtained molded body. This is dried in the step (5), and then cut to a predetermined length in the step (6).
In the step (7), a honeycomb structure is obtained by firing under predetermined conditions according to the type of ceramics.

As described above, according to the method of the present invention, by introducing the step of dispersing the agglomerated particles before the kneading step, the raw material particles can be passed through the slit of the extrusion mold in the kneaded material. Can be dispersed. Therefore, it is possible to prevent the aggregated particles from being clogged at the time of the extrusion molding and hinder the supply of the clay, and it is possible to obtain a ceramic honeycomb structure in which the cell wall does not come off and the cell wall is thin. In addition, since the raw material containing coarse aggregated particles can be used without sieving or the like, the process is simplified,
Manufacturing costs can be reduced.

[0024]

EXAMPLE A cordierite honeycomb structure was manufactured based on the method of the present invention. Powders of talc, kaolin, alumina, and aluminum hydroxide were used as cordierite-forming raw materials, and were prepared such that the composition after firing was close to the theoretical composition of cordierite. Among these cordierite-forming raw materials, kaolin (halloysite) whose primary particles were needle-like crystals formed aggregated particles, and the other cordierite-forming raw materials did not contain aggregated particles. Therefore, next, a process of dispersing kaolin forming aggregated particles using a chemical and physical dispersion method was performed. At this time, as a solvent, an amount of water necessary for kneading the kneaded material for extrusion molding, ammonium polycarboxylate, which is an anionic surfactant and an aqueous dispersant, as a dispersant, and 0.1 to kaolin. 4% by weight were added and mixed until uniform. Kaolin was added to this solution, and the mixture was further mixed using an ultrasonic disperser as a dispersing device until the mixture became uniform to pulverize and disperse the aggregated particles in order to disperse the aggregated particles in a short time.

FIG. 2 shows the results of measuring the particle size distribution of the wet method by the laser scattering method before peptizing and dispersing kaolin. FIG. 3 shows the results after pulverizing and dispersing the aggregated particles as described above. Of the particle size distribution measurement results. As is clear from the comparison of the figures, before the treatment, the peak of the particle size distribution is several tens of μm.
In the vicinity, there are a lot of coarse aggregated particles exceeding 100 μm, but it can be seen that the particle size is reduced to about 1 μm or less by peptization and dispersion treatment.

Next, a lubricant and a lubricant were added to the dispersion solution obtained in this manner, with talc, alumina and aluminum hydroxide, which are other cordierite-forming raw materials, and 100% by weight of the cordierite-forming raw materials. 2.8 humectant
5.5% by weight of a binder and 5.5% by weight of a binder are added, and water is further added to an adjusted amount of a clay state (viscosity, shape retention, fluidity, hardness, etc.) and kneaded to produce a clay. did. Here, a 5% solution of a polyalkylene glycol was used as a lubricant and a humectant, and methyl cellulose as a water-soluble binder was used as a binder. The kneaded material was further formed into a round bar having a size suitable for an extruder, and extruded using an extrusion die having a slit width of 50 μm. Next, the obtained molded body was dried, cut into a predetermined length, and fired at a firing temperature of cordierite or higher to produce a cordierite honeycomb structure.

FIG. 4 shows the state of the end face of the obtained cordierite honeycomb structure. For comparison, FIG. 5 shows a state of an end face of a honeycomb structure manufactured without performing pulverization and dispersion of kaolin after preparation. As is clear from FIG. 4, according to the method of the present invention, a cordierite honeycomb structure having a thin cell wall can be manufactured without cell loss. On the other hand, in FIG. 5, many cells are missing, and it can be seen that clogging occurs during extrusion molding due to the aggregated particles present in the clay.

The cordierite honeycomb structure manufactured as described above has almost no cell loss, and has a small cell wall thickness. Therefore, the cordierite honeycomb structure is suitable as a catalyst carrier for an exhaust gas purifying catalyst of an internal combustion engine, and has a low heat capacity. Since it can be reduced, the catalyst can be activated early. Further, in the above embodiment, a production example of a cordierite honeycomb structure was described. For example, a ceramic honeycomb structure formed into a honeycomb shape by extrusion molding, such as a ceramic honeycomb structure used for a filtration filter for water purification, and the like. Of course, any body can be suitably applied.

In the above embodiment, water was used as a solvent, halloysite (kaolin) having needle-like crystals was used as a cordierite-forming raw material containing agglomerated particles, and an ultrasonic disperser was used as a dispersing device. And the pH of the solution
Is desirable to be more neutral, etc.
Although the above dispersant, which is an anionic surfactant, is used, the type of the solvent or the ceramic material, the particle shape, the molding aid, the dispersing device, etc. are taken into account, and the anionic type, the cationic type,
From the amphoteric and nonionic surfactants, any suitable surfactant can be used as needed.

Although an ultrasonic dispersing machine is used as the dispersing device, it is to be noted that the so-called stirrer (mixer) for applying a rotational force to the solution can be similarly used to obtain the peptizing and dispersing effects of the aggregated particles. confirmed. However, the rotor blade and the ceramic raw material may contact and wear at high speed, and the rotor blade material may be mixed as impurities. In this case, an ultrasonic dispersing machine using vibration that does not have the possibility of mixing impurities is used. More desirable.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of a ceramic honeycomb structure according to a method of the present invention.

FIG. 2 is a diagram showing the particle size distribution of kaolin before peptization and dispersion treatment in an example.

FIG. 3 is a diagram showing the particle size distribution of kaolin after peptization and dispersion treatment in an example.

FIG. 4 is a view showing a state of an end face of a ceramic honeycomb structure manufactured by the method of the present invention.

FIG. 5 is a diagram showing a state of an end face of a ceramic honeycomb structure manufactured without performing peptization and dispersion treatment.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tomohiko Nakanishi 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Inside Japan Automotive Parts Research Institute Co., Ltd. (72) Masakazu Murata 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture F term in DENSO Corporation (reference) 4G030 BA34 GA03 GA04 GA16 GA17 GA18 GA21 4G054 AA05 AB09 BD19 DA01 4G056 AA03 BA07 CB11

Claims (4)

[Claims] 1. A kneaded material obtained by mixing and kneading a solvent with one or more kinds of ceramic raw materials weighed so as to obtain a desired ceramic composition by using an extrusion mold having a honeycomb-shaped narrow slit. In a method of manufacturing a ceramic honeycomb structure by extrusion molding and firing, after weighing the ceramic raw material, prior to the step of kneading, the ceramic raw material forming aggregated particles among the ceramic raw materials is previously By dispersing in the solvent using a chemical or physical dispersion method or both, the aggregated particles are converted into particles having a size that passes through the slits of the extrusion mold, and are dried without drying. A method for producing a ceramic honeycomb structure, which is provided in the kneading step. 2. The chemical dispersion method according to claim 1, wherein at least one selected from anionic, cationic, amphoteric, and nonionic surfactants is used as the dispersant, and the dispersant is used to disperse the aggregated particles. 2. The method for producing a ceramic honeycomb structure according to claim 1, wherein the method is a method of pulverizing and dispersing the agglomerated particles by adding to the solvent and uniformly mixing the same with the ceramic raw material to be contained. 3. The physical dispersion method according to claim 1, wherein the aggregated particles are peptized and dispersed by applying vibration or rotation to a solution obtained by adding the ceramic raw material containing the aggregated particles to the solvent. Item 3. A method for producing a ceramic honeycomb structure according to Item 1. 4. An anionic type, a cationic type,
4. The method for producing a ceramic honeycomb structure according to claim 3, wherein at least one selected from amphoteric and nonionic surfactants is added as a dispersant.