JP2020164336A - Method of producing honeycomb structure - Google Patents

Abstract

To provide a method of producing a honeycomb structure, not requiring high temperature calcination.SOLUTION: The method of producing a honeycomb structure, comprising a raw material composition preparation process of preparing a raw material composition by mixing raw materials including SiC powder, SiO2 and a carbon source, a molded body fabrication process of fabricating a molded body of a honeycomb by extrusion-molding the raw material composition, and a calcination process of calcining the molded body of a honeycomb, is characterized in that the raw material composition further comprises boron and sodium, and the calcination temperature in the calcination process is from 1620 to 1800°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a honeycomb structure.

Particulates such as soot (hereinafter sometimes referred to as PM) and other harmful components contained in the exhaust gas emitted from vehicles such as buses and trucks or internal combustion engines such as construction machinery are harmful to the environment and the human body. Has recently become a problem.

Therefore, as a honeycomb filter for purifying exhaust gas, a honeycomb filter composed of a plurality of bonded ceramic blocks in which a large number of cells are arranged side by side in the longitudinal direction across a porous cell partition wall has been proposed. ..

Patent Document 1 describes a method for producing a filter made of SiC, and describes that β-SiC is generated between α-SiC coarse particles and heated to be converted to α-SiC. ..

Patent Document 2 describes a method of mixing, molding, defatting, and firing a raw material composition containing silicon carbide powder, an organic additive, and silica to obtain a honeycomb filter.
In particular, the degreasing step is performed in a completely inert gas atmosphere.

International Publication No. 2003/024892 Japanese Unexamined Patent Publication No. 2016-67992

In Patent Document 1, the generated β-SiC is reheated to convert it to α-SiC, but the heating temperature for converting β-SiC to α-SiC and further sublimating α-SiC is 1900. It is described as ~ 2300 ° C.

In Patent Document 2, carbon remains in the degreasing step, and carbon and silica are reacted in the firing step to synthesize SiC. In order to proceed with the SiC synthesis reaction in the firing step, it is necessary to raise the firing temperature, and in the examples, firing is performed at 2200 ° C.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a honeycomb structure that does not require the use of firing at a high temperature.

The method for producing a honeycomb structure of the present invention includes a raw material composition preparation step of mixing raw materials containing SiC powder, SiO ₂ and a carbon source to prepare a raw material composition.
A molding body manufacturing step of manufacturing a honeycomb molded body by extrusion molding the above raw material composition, and
A method for producing a honeycomb structure, which comprises a firing step of firing the honeycomb molded body.
The raw material composition further contains boron and sodium.
The firing temperature in the firing step is 1620 to 1800 ° C.

In the method for producing a honeycomb structure of the present invention, the firing temperature in the firing step is 1620 to 1800 ° C., and firing is performed at a temperature lower than the firing temperature in the prior art.
The raw material composition used in the present invention contains boron and sodium, which act as an auxiliary agent for accelerating the synthesis reaction of SiC by the reaction of carbon and SiO ₂ .
Therefore, even if the firing temperature is lowered, the formation of the neck portion by the SiC synthesized between the particles of the SiC powder proceeds, and a honeycomb structure having sufficient strength can be manufactured.

In the method for producing a honeycomb structure of the present invention, in the raw material composition, the boron is preferably contained in an amount of 5 to 20% by weight with respect to the SiO _{2 in} terms of B ₂ O ₃ .
Further, in the method for producing a honeycomb structure of the present invention, it is preferable that the sodium is contained in the raw material composition in an amount of ₂ to 10% by weight with respect to the SiO _{2 in} terms of Na ₂ O.
Further, in the method for producing a honeycomb structure of the present invention, in the raw material composition, the sum of the B ₂ O ₃ equivalent amount of boron, the Na ₂ O equivalent amount of sodium, and the SiO ₂ content is , 2-7% by weight is preferable with respect to the above SiC powder.
By setting the amount of boron, the amount of sodium, and the total amount of boron, sodium, and SiO _{2 in} the above range, the strength, porosity, pore diameter, etc. of the honeycomb structure are adjusted to preferable ranges to manufacture the honeycomb structure. can do.

In the method for producing a honeycomb structure of the present invention, the SiO ₂ is preferably balloon-shaped. When SiO ₂ has a balloon shape, SiO ₂ can also function as a pore-forming agent.

FIG. 1 is a perspective view schematically showing an example of a honeycomb structure. FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb structure shown in FIG. 1, and FIG. 2B is a honeycomb fired body shown in FIG. 2A. FIG. 5 is a cross-sectional view taken along the line AA of the body.

(Detailed description of the invention)
Hereinafter, a method for producing the honeycomb structure of the present invention will be described. Prior to the description of the present invention, an example of the honeycomb structure, which is an object to be manufactured by the method for manufacturing the honeycomb structure of the present invention, will be described.

FIG. 1 is a perspective view schematically showing an example of a honeycomb structure.
FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb structure shown in FIG. 1, and FIG. 2B is a honeycomb fired body shown in FIG. 2A. It is sectional drawing of the body AA line.

As shown in FIG. 1, in the honeycomb structure 10 of the present invention, a plurality of honeycomb fired bodies 20 made of porous SiC are combined via an adhesive layer 11 to form a columnar ceramic block 15. A coat layer 12 is formed around the ceramic block 15.

In the honeycomb structure 10 shown in FIG. 1, the shape of the ceramic block is columnar, but in the present invention, the ceramic block is not limited to columnar as long as it is columnar, for example, elliptical columnar or angular. It may have any shape such as a columnar shape.

In the honeycomb fired body 20 shown in FIGS. 2 (a) and 2 (b), a large number of cells 21 are arranged side by side in the longitudinal direction, and any end of the cells 21 is sealed. The cell partition wall 23 that separates the cells functions as a filter. That is, in the cell 21 formed in the honeycomb fired body 20, as shown in FIG. 2B, either the inlet side or the outlet side end of the exhaust gas is sealed with the sealing material 22. The exhaust gas that has flowed into the cell 21 always passes through the cell partition wall 23 that separates the cell 21, and then flows out from the other cells 21.

In the honeycomb structure configured in this way, the exhaust gas can be purified by collecting PM such as soot contained in the exhaust gas discharged from the internal combustion engine.

The method for producing a honeycomb structure of the present invention includes a raw material composition preparation step of mixing raw materials containing SiC powder, SiO ₂ and a carbon source to prepare a raw material composition.
A molding body manufacturing step of manufacturing a honeycomb molded body by extrusion molding the above raw material composition, and
A method for producing a honeycomb structure, which comprises a firing step of firing the honeycomb molded body.
The raw material composition further contains boron and sodium.
The firing temperature in the firing step is 1620 to 1800 ° C.

(Raw material composition preparation process)
In this raw material composition preparation step, a raw material containing SiC powder, SiO _2, and a carbon source is mixed to prepare a raw material composition.

The particle size of the SiC powder is not particularly limited, but it is preferable to use two types of SiC powder having different average particle sizes. Examples of the two types of SiC powders having different average particle sizes include a combination of a SiC coarse powder having an average particle size of 5 to 15 μm and a SiC fine powder having an average particle size of 0.1 to 1.0 μm. ..

The content of the SiC powder in the raw material composition is preferably 85 to 95% by weight based on the inorganic solid content contained in the raw material composition.
Further, the content of the coarse SiC powder is preferably 55 to 65% by weight in the inorganic solid content contained in the raw material composition.

SiO ₂ is contained in the raw material composition.
Silica powder can be used as the material containing SiO ₂ . The silica powder is not particularly limited, and for example, various commercially available silica powders can be used. The average particle size of the silica powder is preferably 0.5 to 40 μm.
If the average particle size of the silica powder is smaller than 0.5 μm, the contact probability with carbon may decrease during the SiC synthesis described later. On the other hand, if the average particle size of the silica powder is larger than 40 μm, the inside of the silica particles may not come into contact with carbon during the SiC synthesis described later.

The silica powder can be added as a pore-forming agent in the raw material composition.
Examples of the pore-forming agent include balloons that are microhollow spheres, and specific balloons include silica balloons, glass microballoons, silas balloons, fly ash balloons (FA balloons), and mullite balloons. By using such a pore-forming agent, it becomes easy to control the porosity of the produced honeycomb structure.
The reason why SiO ₂ is contained in the raw material composition is that SiC is synthesized by reacting with carbon remaining in the honeycomb molded body after the subsequent degreasing step.

From the above circumstances, SiO ₂ is preferably balloon-shaped. When SiO ₂ has a balloon shape, SiO ₂ can also function as a pore-forming agent.

The content of SiO _{2 in} the raw material composition is preferably 1 to 7% by weight of the inorganic solid content contained in the raw material composition.

Examples of the carbon source include carbon powder and organic additives containing carbon.
Examples of the organic additive include an organic binder, a dispersion medium, a plasticizer, a lubricant and the like. Carbon can be obtained by thermally decomposing these organic additives during production.
Examples of the organic binder include methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol resin, epoxy resin and the like. Of these, methyl cellulose is preferred.

Examples of the dispersion medium include alcohols such as methanol and organic solvents such as benzene. Further, water may be contained as a dispersion medium other than the organic additive.
The plasticizer is not particularly limited, and examples thereof include glycerin and the like.

The lubricant is not particularly limited, and examples thereof include polyoxyalkylene compounds such as polyoxyethylene alkyl ether and polyoxypropylene alkyl ether. Specific examples of the lubricant include polyoxyethylene monobutyl ether and polyoxypropylene monobutyl ether.

The content of the carbon source in the raw material composition is preferably 1 to 7% by weight after thermal decomposition as the total amount.

The raw material composition further comprises boron and sodium.
Boron and sodium are contained in the raw material composition in the form of a boron-containing compound containing boron and a sodium-containing compound containing sodium.
The boron-containing compound and the sodium-containing compound may be added to the raw material composition by themselves, or may be components contained in other components.
For example, when SiO ₂ in the raw material composition is a silica balloon, a boron-containing compound or a sodium-containing compound that may be contained in the silica balloon can also be used.

The raw material composition contains boron and sodium, which act as an auxiliary agent for accelerating the synthesis reaction of SiC by the reaction of carbon and SiO ₂ .
Therefore, even if the firing temperature is lowered, the formation of the neck portion by the SiC synthesized between the particles of the SiC powder proceeds, and a honeycomb structure having sufficient strength can be manufactured.

In the raw material composition, boron is preferably contained in an amount of 5 to 20% by weight based on SiO _{2 in} terms of B ₂ O ₃ .
Further, in the raw material composition, sodium is preferably contained in an amount of ₂ to 10% by weight based on SiO _{2 in} terms of Na ₂ O.
Further, in the raw material composition, the total of the B ₂ O ₃ conversion amount of boron, the Na ₂ O conversion amount of sodium, and the content of SiO ₂ is 2 to 7% by weight with respect to the SiC powder. preferable.
By setting the amount of boron, the amount of sodium, and the total amount of boron, sodium, and SiO _{2 in} the above range, the strength, porosity, pore diameter, etc. of the honeycomb structure are adjusted to preferable ranges to manufacture the honeycomb structure. can do.

When preparing the raw material composition, the raw material composition is prepared by mixing SiC powder, SiO ₂ , carbon source, boron-containing compound, sodium-containing compound, and water as a dispersion medium using a wet mixer. It is preferable to prepare.

(Molded body manufacturing process)
In this molded body manufacturing step, a honeycomb molded body is manufactured by extrusion molding the raw material composition.
In this step, the obtained raw material composition is put into an extrusion molding machine, extrusion molding is performed to produce a prismatic continuous body, and then the composition is cut to a predetermined length to penetrate a large number in the longitudinal direction. A honeycomb molded body in which holes are arranged side by side is produced. This honeycomb molded body is dried by a dryer to obtain a dried body of the honeycomb molded body.

Next, a predetermined amount of a sealing material paste is filled in any end of the through holes constituting the dried body of the honeycomb molded product, and the cells are sealed. When sealing cells, for example, a mask for cell sealing is applied to the end surface of the honeycomb molded body (that is, the cut surface after cutting both ends), and the sealing material is applied only to the cells that need to be sealed. Fill the paste and allow the encapsulant paste to dry. Through such a process, a honeycomb molded body in which one end of the cell is sealed is produced.

(Baking process)
Next, a degreasing step is performed in which the produced honeycomb molded body is heated to oxidatively decompose and remove organic substances.
The degreasing step is not an essential step and may be continuously performed in combination with the firing step described later.
In addition, the degreasing conditions in the degreasing step are adjusted to proceed with degreasing to the extent that carbon remains on the cell partition wall.

After the degreasing step, in the firing step, the degreased honeycomb molded body is fired.
The firing temperature is 1620 to 1800 ° C.
The firing time (holding time at the firing temperature) is preferably 0.5 to 5 hours.
By leaving carbon in the cell partition and further allowing boron and sodium to exist, even if the firing temperature is lowered to 1620 to 1800 ° C., the reaction sintered SiC by the reaction of carbon and SiO ₂ between the particles of the SiC powder The synthetic reaction is promoted.
Further, the reaction sintered SiC and carbon form composite particles at the neck portion, and a honeycomb structure having sufficient strength can be manufactured.

A honeycomb structure having sufficient strength can be produced by the above steps.
The obtained honeycomb structure is regarded as a honeycomb fired body, and when a honeycomb structure in which a plurality of honeycomb fired bodies are combined is manufactured, a sealing material paste is applied to the side surface of the honeycomb fired body to apply a sealing material paste. A layer is formed, and another honeycomb fired body is sequentially laminated via the sealant paste layer. This procedure is repeated to prepare an aggregate of the honeycomb fired bodies in which a predetermined number of honeycomb fired bodies are bound. As the sealing material paste, for example, a paste composed of an inorganic binder, an organic binder, an inorganic fiber and / or an inorganic particle can be used.

Next, the aggregate of the honeycomb fired bodies is heated to dry and solidify the sealing material paste layer to obtain a sealing material layer (adhesive material layer). After that, the aggregate of the honeycomb fired bodies is cut using a diamond cutter or the like to form a ceramic block, and a sealant paste is applied to the outer peripheral surface of the ceramic block and dried and solidified to form a coat layer. A honeycomb structure can be manufactured.

(Example)
Hereinafter, examples in which the embodiments of the present invention are disclosed more specifically will be shown. The present invention is not limited to these examples.

(Example 1)
(Raw material composition preparation process)
First, as a raw material composition preparation step, 52.0% by weight of a coarse SiC powder having an average particle size of 11 μm and 22.2% by weight of a fine powder of SiC having an average particle size of 0.5 μm were mixed and obtained. A pore-forming agent consisting of 3.9% by weight of organic binder (methyl cellulose), 2.3% by weight of lubricant (Unilube manufactured by Nichiyu Co., Ltd.), 1.0% by weight of glycerin, and silica balloon (average particle size 40 μm) with respect to the mixture. ) 3.5% by weight, 2.1% by weight of carbon particles having an average particle diameter of 5 μm, and 13.0% by weight of water were added and kneaded to obtain a raw material composition.

The silica balloon used here is a silica balloon having a composition containing boron and sodium. The content of boron in the silica balloon is 10% by weight with respect to SiO _{2 in} terms of B ₂ O ₃ , and the content of sodium in the silica balloon is 4% by weight with respect to SiO _{2 in} terms of Na ₂ O. Is.

(Molded body manufacturing process)
Then, as a molding body manufacturing step, extrusion molding was performed using the obtained raw material composition to obtain a raw honeycomb molded body. Next, the raw honeycomb molded body was dried using a microwave dryer to prepare a dried honeycomb molded body.

Then, a predetermined cell of the dried body of the honeycomb molded product was filled with a sealing material paste to seal the cell, and a honeycomb molded product with a seal was obtained. The raw material composition was used as a sealing material paste. After sealing the cell, the dried body of the honeycomb molded product filled with the sealing material paste was dried again using a dryer.

(Baking process)
Subsequently, a plurality of dried honeycomb compacts were placed on a transport member, carried into a batch furnace, introduced with nitrogen, heated to 400 ° C. in a nitrogen atmosphere at normal pressure, and then heated. The degreasing treatment was performed by stopping. After that, the honeycomb molded body after the degreasing treatment was fired in the same batch furnace in a nitrogen atmosphere at normal pressure at 1650 ° C. for 1 hour, and the honeycomb fired body (honeycomb structure) was fired. Manufactured.

The obtained honeycomb structure is made of porous SiC, has a porosity of 62%, an average pore diameter of 11 μm, a size of 34.3 mm × 34.3 mm × 150 mm, and a number of cells (cell density) of 54.3. The number of pieces / cm ² (350 pieces / inch ² ), the thickness of the cell partition wall was 0.28 mm, and the thickness of the outer peripheral wall was 0.3 mm.

(Comparative Example 1)
A honeycomb fired body (honeycomb structure) was produced in the same manner as in Example 1 except that the firing temperature in the firing step of Example 1 was changed from 1650 ° C. to 2200 ° C. for 1 hour to 2 hours.

(Comparative Example 2)
A honeycomb fired body (honeycomb structure) was produced in the same manner as in Example 1 except that a silica balloon having a composition not containing boron and sodium was used as the silica balloon.

(Evaluation)
[Strength measurement]
As a sample for measuring the three-point bending strength, a member composed of a raw material composition mixed and kneaded with the same composition as in each example and comparative example was formed into a rectangular parallelepiped, degreased under the same conditions, and processed into 6 mm × 6 mm × 40 mm after firing. Ten samples were prepared and used as a sample for measuring the bending strength at three points (hereinafter referred to as a sample). A load was applied in a direction perpendicular to the main surface of the sample (the wider surface of the outer peripheral surface of the sample), and the breaking load (the load at which the sample was broken) was measured. The breaking load was measured for 10 samples for measuring the bending strength at three points, and the average value was taken as the bending strength. The three-point bending strength test was carried out using an Instron 5582 with reference to JIS R 1601 at a distance between spans of 30 mm and a speed of 1 mm / min.
The three-point bending strength was 12.0 MPa in Example 1, 12.0 MPa in Comparative Example 1, and 7.5 MPa in Comparative Example 2.

10 Honeycomb structure 11 Adhesive layer 12 Coat layer 15 Ceramic block 20 Honeycomb fired body 21 Cell 22 Encapsulant 23 Cell partition wall

Claims (5)

A raw material composition preparation step of mixing raw materials containing SiC powder, SiO ₂ and a carbon source to prepare a raw material composition, and
A molding body manufacturing step of manufacturing a honeycomb molded body by extrusion molding the raw material composition, and
A method for producing a honeycomb structure, which comprises a firing step of firing the honeycomb molded body.
The raw material composition further contains boron and sodium.
A method for producing a honeycomb structure, wherein the firing temperature in the firing step is 1620 to 1800 ° C. The method for producing a honeycomb structure according to claim 1, wherein in the raw material composition, the boron is contained in an amount of 5 to 20% by weight based on the SiO _{2 in} terms of B ₂ O ₃ . The method for producing a honeycomb structure according to claim 1 or 2, wherein in the raw material composition, the sodium is contained in an amount of ₂ to 10% by weight based on the SiO _{2 in} terms of Na ₂ O. In the raw material composition, the total of the B ₂ O ₃ conversion amount of boron, the Na ₂ O conversion amount of sodium, and the content of SiO ₂ is 2 to 7% by weight based on the SiC powder. The method for producing a honeycomb structure according to any one of claims 1 to 3. The method for manufacturing a honeycomb structure according to any one of claims 1 to 4, wherein the SiO ₂ is balloon-shaped.

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