JP3461610B2 - Sealing material, ceramic honeycomb structure using the same, and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for sealing an end face of a ceramic molded body having a honeycomb structure, and particularly for a diesel particulate filter for collecting fine particles discharged from a diesel engine. The present invention relates to a sealing material for an end face of a ceramic honeycomb structure.

[0002]

2. Description of the Related Art Conventionally, it has been known to use a honeycomb filter made of porous ceramics as a method for collecting fine particles in exhaust gas of a diesel engine. Generally, such a honeycomb structure has a plurality of through-holes parallel to the traveling direction of the exhaust gas, and seals the through-holes on one end face at intervals to seal in a checkered pattern and the other end face. In the above, the remaining through holes are sealed to form a structure in which one of the end faces of the through holes is alternately sealed.

Therefore, various methods for sealing the end faces of the ceramic honeycomb structure have been proposed. For example, in JP-A-57-7215 and JP-A-58-37481, the end faces of the honeycomb structure are made of a film or the like. After masking, a hole is made in the part corresponding to the through hole that is selectively sealed, and a sealing material prepared in the form of slurry or paste is introduced through this hole to form a molded body with the end face sealed as described above. A method has been proposed.

However, when a slurry or paste material is used as the sealing material, shrinkage of the sealing portion due to the drying process and the sintering process becomes a problem. As a means for solving such a problem, JP-A-5-85865 proposes a method of adjusting the particle size of the sealing material. However, if many sealing materials with a small particle size are used,
In addition to increasing the solvent content in the slurry and causing drying shrinkage, the sintering shrinkage in the sintering step is promoted, which impedes tight sealing in the sintered body. On the other hand, when a material having a coarse particle size is used as the sealing material, the content of the solvent in the slurry is reduced, but the adhesion between the sealing material and the ceramic honeycomb structure wall is poor, resulting in When made into a sintered body, the adhesive strength between the sealing material and the ceramic honeycomb structure wall portion becomes low.

As a means for preventing cracks in the sealed portion, Japanese Patent Laid-Open No. 1-297114 proposes a method of preparing a paste using an organic solvent-based dispersion medium. However, even with this method, it is difficult to say that it is sufficiently effective against cracks due to shrinkage in the drying and sintering steps, and the cost of raw materials and production equipment is high because an organic solvent is used. There was a problem that led to.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to reliably and closely seal the end surface of a ceramic molded body having a honeycomb structure. It is to provide a sealing material for stopping. In particular, a sealing material suitable for sealing the end face of a ceramic honeycomb molded body containing silicon carbide as a main component, and a ceramic honeycomb structure whose end face is sealed by the sealing material,
Another object of the present invention is to provide a method for manufacturing the ceramic honeycomb structure.

[0007]

That is, the features of the present invention are that the carbonaceous material, the silicon compound and the average particle size are 10 to 10.
It is a sealing material composed of a mixture of silicon carbide powder having a size of 0 μm, and of each stoichiometric amount (the number of moles) necessary for reacting the carbonaceous substance and the silicon compound to generate silicon carbide. , The theoretical amount of silicon carbide produced when all of the equal or lesser amount of material reacts is 10% of the mixture.
It is a sealing material for the end face of the ceramic honeycomb structure which is ˜50 wt%. A ceramic honeycomb structure containing silicon carbide as a main component is characterized in that its end surface is sealed with the sealing material. Further, a solvent is added to this sealing material to prepare a slurry, and the end surface of the ceramic honeycomb molded body containing silicon carbide as a main component is sealed and dried using the slurry, and then 170
A method for manufacturing a ceramic honeycomb structure having silicon carbide as a main component, the end surface of which is sealed, characterized by firing at 0 ° C to 2300 ° C.

The present invention will be described in more detail below.

The sealing material in the present invention is introduced into a desired position on the end face of a ceramic molded body having a honeycomb structure and then fired together with the ceramic molded body to seal the end face of the ceramic molded body having a honeycomb structure. To form a part.

Since this sealing material is a mixture of a carbonaceous substance, a silicon-containing compound and silicon carbide powder, the sealing portion obtained by firing is mainly composed of reaction sintered silicon carbide. As the carbonaceous substance used in the present invention, in addition to solid fine powders such as carbon black and acetylene black, organic resins such as phenol, furan and polyimide can be used. The silicon-containing compound may be any compound as long as it reacts with the carbonaceous material to generate silicon carbide in the firing step, and for example, metal silicon powder, silicon nitride powder, silica powder or the like can be used. The carbonaceous substance and the silicon-containing compound are preferably compounded at a stoichiometric ratio (molar ratio) required for the reaction of the carbonaceous substance and the silicon compound to generate silicon carbide. It can be used within a range of ± 20% of the stoichiometric ratio in consideration of composition deviation due to melting and vaporization of raw material components in the process. When deviating from the stoichiometric ratio, the carbonaceous material and the silicon compound react with each other to produce the silicon carbide. The theoretical amount of silicon carbide produced when all the components react is taken as the theoretical amount of silicon carbide obtained by the reaction.

Further, in the present invention, among the respective stoichiometric amounts (molar numbers) necessary for the above-mentioned carbonaceous substance or the silicon-containing compound to react with each other to produce silicon carbide, a substance equal to or less than The theoretical amount of silicon carbide produced when all the components react with each other is 10 to 5 with respect to the mixture of the carbonaceous material as the sealing material, the silicon-containing compound and the silicon carbide powder.
It is necessary to adjust the content to be in the range of 0% by weight. The reason for being 10 to 50% by weight here is 50% by weight
If the amount is larger, the ratio of the theoretical amount of silicon carbide generated by the reaction between the carbonaceous substance and the silicon-containing compound by firing increases, and the porosity of the sealing portion increases, which is not preferable as a sealing material. As a result, the adhesiveness between the sealing material and the through-hole portion deteriorates, so that a gap is created in the sealing portion of the sintered body or the sealing material is lost. On the other hand, if the amount is less than 10% by weight, the ratio of the theoretical amount of silicon carbide produced by the reaction between the carbonaceous substance and the silicon-containing compound decreases, so that sufficient bonding strength between the sealing material and the ceramic honeycomb molded body is obtained. I will not be able to.

The silicon carbide powder contained in the mixture as the sealing material is used as an aggregate, and its crystal system is one of α type, β type and amorphous ones, Or a mixture thereof may be used,
This average particle size must be in the range of 10 to 100 μm. Here, the reason that the average particle diameter of the silicon carbide powder is within the above range is that when the thickness is 100 μm or more, it causes the generation of cracks by hindering the sinterability of the sealing portion. This is because the viscosity of the material slurry becomes high, so that a gap is created between the sealing material and the wall portion of the ceramic honeycomb structure, so that tight sealing cannot be performed.

That is, in the present invention, the sealing material is a so-called reaction-bonded silicon carbide material in which a silicon carbide aggregate existing from the beginning of silicon carbide produced by the reaction of a carbonaceous substance and a silicon compound is bonded. In order to form a porous sealing part having appropriate closed pores in the reaction process, and to reduce shrinkage of the sealing material in the subsequent sintering process, a tight sealing state during drying can be maintained. It becomes possible to fire as it is. In addition, after the silicon vapor generated in the firing process is taken into the minute holes in the wall of the honeycomb formed body, silicon carbide activated by reacting with the carbonaceous material is generated in the contact portion with the wall of the honeycomb formed body. Therefore, a sealed portion having excellent adhesion is formed. However, according to the sealing material of the present invention, it is possible to seal the end face of the ceramic honeycomb molded body with high reliability and tightness. At this time, it is preferable that the material of the ceramic honeycomb molded body contains silicon carbide as a main component because the bonding strength with the sealing material becomes strong.

A method for manufacturing a ceramic honeycomb structure containing silicon carbide as a main component, the end faces of which are sealed with the sealing material of the present invention, will be described below. First, a binder, a dispersant, and a solvent such as water or an organic solvent are added to the above-mentioned sealing material of the present invention to prepare a slurry (the solvent here may be referred to as a dispersion medium). For example, the end face of the ceramic honeycomb formed body containing silicon carbide as a main component produced by the above method is
It is immersed in the slurry and sealed. In addition, as a sealing method, a method such as coating or filling may be used. After drying it, degreasing it if necessary, and then applying 1 in a non-oxidizing atmosphere.
Baking is performed at 700 to 2300 ° C. As the non-oxidizing atmosphere, an atmosphere of an inert gas such as argon or helium, nitrogen, hydrogen, a hydrocarbon gas, or the like is used, but a mixed gas atmosphere of these may be used. Firing temperature is 1700
˜2300 ° C. is preferable, but 190 is more preferable.
0 ° C to 2200 ° C is preferable. At 1700 ° C. or lower, the reaction and sintering of the ceramic honeycomb molded body containing silicon carbide as a main component are insufficient, sufficient strength as a structure cannot be obtained, and the composition of each composition in the encapsulating material cannot be obtained. Since the reaction and sintering are also insufficient, the strength of the sealing portion is not sufficient, and further, the bonding strength between the sealing material and the ceramic honeycomb molded body is insufficient, and the desired structure cannot be obtained. The sealing portion of the end face is formed by masking the through holes other than the portion to be sealed with, for example, a plastic film or the like and filling the slurry into only the through holes to be sealed.

EXAMPLE An example in which a ceramic honeycomb molded body having a desired end surface sealed by sealing the open end surface of the ceramic honeycomb molded body with the sealing material of the present invention was prepared is compared with a comparative example. However, the present invention is not limited to these examples.

(Examples 1 to 10 and Comparative Examples 1 to 6) 100 α-silicon carbide powder having an average particle size of 10 μm (manufactured by Yakushima Denko)
Methylcellulose 15 parts by weight binder parts, 25 parts by weight of water, mixed with stearic acid emulsion 2 parts by weight were uniformly mixed in a Henschel mixer,
A honeycomb molded ceramic molded body was molded using an auger type vacuum extrusion molding machine. The end face of the ceramic molded body having the honeycomb structure has a side of 100 mm and a length of 15 mm.
0 mm, cell wall thickness 0.45 mm, cell pitch 2.5
It is 4 mm and the number of cells is 100 cells / square inch. Also,
After the molded body is dried, the end surface is sealed with the sealing material slurry, and then the molded body is degreased and fired.

The sealing material slurry is compounded with metallic silicon, silicon nitride, and silica powder as the silicon-containing compound, carbon black as the carbonaceous substance, and an average particle size of 5 to 150 μm.
The compounding ratio shown in Table 1 was adjusted using m type α-type silicon carbide powder. 100 parts by weight of these raw material powders were dry mixed by a ball mill for 1 hour, and then 2 parts by weight of methyl cellulose as a binder, 0.8 parts by weight of a cationic dispersant, and 25 parts of water.
A sealing material slurry was prepared by adding parts by weight and wet mixing with a ball mill for 2 hours.

[0017]

[Table 1]

Next, the opening end face of the dried ceramic molded body having a honeycomb structure was masked in a checkered pattern with through holes not sealed with a film, and then immersed in the sealing material slurry prepared as described above for 5 minutes. . As a result, after the sealing material slurry has entered a predetermined amount through the unmasked through holes, it is solidified on the end face of the ceramic honeycomb structure to seal the through holes over a sealing depth of 5 mm. Thereafter, the other end surface of the ceramic honeycomb structure was also sealed in a checkered pattern by the same procedure.

Next, one of the numerous through holes opened on both end faces is sealed, and the alternately sealed ceramic molded bodies are dried with hot air at 60 ° C. for 5 hours and then dried. The sealing state of the sealing portion of the end face was investigated. The investigation method is to check the presence or absence of cracks in the sealed part using an optical microscope.
Moreover, the presence or absence of a gap in the sealed portion was observed by examining the light leakage by passing a light beam parallel to the through hole. The survey results are shown in Table 2. For those without cracks and gaps, a degreasing step is performed at 500 ° C. for 1 hour, and then a main firing is performed at 2100 ° C. for 2 hours in an inert atmosphere to sinter the ceramic molded body having a honeycomb structure. At the same time, the sealing material on the end face was sintered to form a sealing portion.

Regarding the ceramic honeycomb structure manufactured as described above, the sealed state was examined by inspecting the presence or absence of cracks or gaps in the sealed portion in the same manner as in the dried body. In addition, the sealed portion of the sealed through hole has a diameter of 1 mm in the through hole direction.
The adhesive strength of the sealing material was measured by pushing out with a round bar. However, the punching speed at this time is 0.5 mm / min
It was evaluated by the average value which measured the adhesive strength of 10 sealing parts about each sample. The results are shown in Table 2. As is clear from the results in Table 2, in Comparative Examples 1 to 6, cracks or gaps were generated in the sealed portion, which resulted in a decrease in adhesive strength, whereas in Examples 1 to 8, the drying and sintering steps were performed. After that, generation of cracks and gaps was not observed, and it was confirmed that a sealed portion having high adhesive strength was formed and the end face was sealed in a state of good adhesion.

[0021]

[Table 2]

[0022]

As described above, according to the encapsulating material and the manufacturing method of the present invention, the desired portion of the end face can be encapsulated without cracks or gaps, so that the adhesiveness is excellent. It is possible to easily obtain a ceramic honeycomb structure having a sealing portion whose end surface is tightly sealed with high reliability. Then, the ceramic honeycomb structure is
In particular, it is preferably used for a diesel particulate filter that collects fine particles discharged from a diesel engine.

Claims (3)

(57) [Claims] 1. A sealing material comprising a mixture of a carbonaceous material, a silicon compound, and silicon carbide powder having an average particle size of 10 to 100 μm, and the carbonaceous material reacts with the silicon compound to produce silicon carbide. Of the respective stoichiometric amounts (number of moles) required to produce, the theoretical amount of silicon carbide produced when all the equal or smaller amount of substances react is 10 to 50% by weight of the mixture. A sealing material for an end face of a ceramic honeycomb structure, which is characterized by being present. 2. A ceramic honeycomb structure containing silicon carbide as a main component, the end surface of which is sealed with the sealing material according to claim 1. 3. A solvent is added to the sealing material according to claim 1 to prepare a slurry, the slurry is used to seal an end surface of a ceramic honeycomb molded body containing silicon carbide as a main component, and the slurry is dried. A method for manufacturing a ceramic honeycomb structure having silicon carbide as a main component whose end faces are sealed, characterized by firing at 1700 ° C to 2300 ° C in an oxidizing atmosphere.