JP2008119666A - Manufacturing method of exhaust gas purifying filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an exhaust gas purifying filter capable of shortening a baking time to enhance productivity and capable of obtaining the exhaust gas purifying filter of high quality. <P>SOLUTION: The manufacturing method of the exhaust gas purifying filter 1 constituted by providing plug parts 13 to a honeycomb structure 10 comprising cordierite and having a large number of cells 12 by arranging porous partition walls 11 in a honeycomb state has an extrusion molding process for extruding a ceramics material containing a cordierite raw material to mold a honeycomb molded body, a drying process for drying the honeycomb molded body, a temporary baking process for baking the honeycomb molded body at a baking temperature T<SB>1</SB>, a plugging process for arranging plugging slurry to the parts to be plugged with the plug parts 13 among the opening parts of the cells of the end surface of the honeycomb molded body and a main baking process for baking the honeycomb molded body, to which the plugging slurry is arranged, at a baking temperature T<SB>2</SB>(≥T<SB>1</SB>) to form the honeycomb structure 10 having the plug parts 13 provided to its parts to be plugged. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine such as a diesel engine and purifies the exhaust gas.

2. Description of the Related Art Conventionally, exhaust gas purification filters that purify exhaust gas by collecting particulates discharged from an internal combustion engine such as a diesel engine are known.
This exhaust gas purification filter has a honeycomb structure as a base material provided with a large number of cells with porous partition walls arranged in a honeycomb shape (see Patent Document 1). Then, the downstream end of the cell serving as the introduction passage for introducing the exhaust gas and the upstream end of the cell serving as the discharge passage for discharging the exhaust gas that has passed through the porous partition walls are generally blocked by the plug portion. .

  When the exhaust gas is purified using the exhaust gas purification filter, the exhaust gas that has entered the cell serving as the introduction passage passes through the porous partition wall and moves to the exhaust passage composed of the adjacent cell. At this time, the particulates in the exhaust gas are collected in a large number of pores formed in the partition wall, and the exhaust gas is purified. Moreover, by collecting the catalyst on the partition wall, the collected particulate can be decomposed and removed by a catalytic reaction.

In producing a honeycomb structure that becomes a base material of the exhaust gas purification filter, a ceramic material is extruded to produce a honeycomb formed body and dried. Then, it is plugged and fired.
However, in the conventional manufacturing method in which firing is carried out after plugging, if a rapid firing is carried out at a high temperature rise rate, the binder or pore former contained in the honeycomb molded body due to plugging. As a result, organic components such as carbon are difficult to decompose (burn). For this reason, slowing the rate of temperature increase requires long-time firing, leading to a reduction in productivity.

  For this reason, there is a demand for a method for manufacturing an exhaust gas purification filter that can improve the productivity by shortening the firing time as much as possible and obtain a high quality exhaust gas purification filter.

JP 2003-145521 A

  The present invention has been made in view of such conventional problems, and is an exhaust gas purification filter capable of reducing the firing time to improve productivity and obtaining a high quality exhaust gas purification filter. A manufacturing method is to be provided.

The present invention has a honeycomb structure made of cordierite provided with a large number of cells with porous partition walls arranged in a honeycomb shape, and among the cells of the honeycomb structure, an introduction passage for introducing exhaust gas; In the method for producing an exhaust gas purification filter formed by closing the downstream end of the cell and the upstream end of the cell serving as a discharge passage for discharging the exhaust gas that has passed through the porous partition wall with a plug portion,
An extrusion process for producing a honeycomb formed body by extruding a ceramic material containing a cordierite forming raw material;
A drying step of drying the honeycomb formed body,
A temporary firing step of firing the honeycomb formed body at a firing temperature T ₁ ;
A plugging step of disposing a plugging slurry in a portion to be plugged by the plug portion of the opening of the cell in the end face of the honeycomb formed body,
A main firing step of firing the honeycomb formed body in which the plugging slurry is disposed at a firing temperature T ₂ (≧ T ₁ ) to produce the honeycomb structure in which the plug portion is provided in the portion to be plugged. The present invention resides in a method for manufacturing an exhaust gas purifying filter.

As described above, the method for producing an exhaust gas purifying filter of the present invention includes an extrusion molding process, a drying process, a temporary baking process, a plugging process, and a main baking process. That is, in the present invention, the above-mentioned honeycomb formed body after extrusion molding is temporarily fired at the firing temperature T ₁ , and the honeycomb formed body in which the plugging slurry is disposed after the temporary firing is fired at the firing temperature T ₂ . Baking is performed twice with the main baking step for main baking.

  Here, the pre-firing in the pre-firing step is intended to burn and remove organic components such as carbon as a binder and pore former contained in the ceramic material. In the present invention, since the honeycomb formed body is fired at a stage before the plugging slurry is disposed, the above-described plugging slurry is disposed after the plugging slurry is disposed and fired at a higher temperature rise rate than the case where the heating is performed Organic components can be stably removed by combustion. Thereby, the time required for burning the organic component can be greatly shortened, and productivity can be improved.

  The provisional firing in the provisional firing step is intended to fire the honeycomb formed body to be cordierite, to almost complete the dimensional change by firing and to obtain a certain degree of strength. This facilitates handling of the honeycomb formed body in the subsequent plugging step and arrangement of the plugging slurry on the honeycomb formed body.

  Moreover, the main baking in the main baking step is intended to form the plug portion by baking the plugging slurry. In the present invention, since the plugging slurry is disposed and fired on the honeycomb formed body after calcination, in which the dimensional change due to firing is almost completed, the plug portion can be formed with high dimensional accuracy. Moreover, the strength of the plug portion is sufficiently high.

Further, in the main firing in the main firing step, the honeycomb formed body after the temporary firing is fired at the firing temperature T ₂ higher than the firing temperature T ₁ in the temporary firing, the cordierite is further oriented, and exhaust gas purification is performed. The purpose is to improve the characteristics of the filter. Thereby, characteristics, such as a thermal expansion coefficient and an average pore diameter, of an exhaust gas purification filter can be improved. A high-quality exhaust gas purification filter having a desired thermal expansion coefficient, average pore diameter, and the like can be obtained.

  In addition, as described above, in the present invention, the firing is performed twice, that is, the preliminary firing in the preliminary firing step and the main firing in the main firing step. That is, substantial initial firing of the honeycomb formed body and firing of the plugging slurry are performed in separate steps. As a result, the number of times of firing is increased by one as compared with the case where the plugging slurry is disposed in the honeycomb formed body before firing and both are fired simultaneously. However, since the time required for burning the organic component contained in the honeycomb formed body can be greatly reduced, the time required for the entire firing can be reduced. Therefore, productivity can be improved.

  Thus, according to the manufacturing method of the present invention, it is possible to improve the productivity by shortening the firing time, and it is possible to obtain a high quality exhaust gas purification filter.

In the present invention, in the pre-baking step, it is preferable that the sintering temperature T ₁ is a 1300-1400 ° C. (Claim 2).
When the firing temperature T ₁ is less than 1300 ° C., the honeycomb formed body may not be sufficiently cordierite. On the other hand, when the temperature exceeds 1400 ° C., the firing time is only prolonged, and the productivity may be lowered.

Therefore, in the temporary firing step, the firing temperature T ₁ is more preferably 1380 to 1400 ° C. (Claim 3).
In this case, the honeycomb formed body can be sufficiently cordierite, the dimensional change by firing can be almost completed, and a certain degree of strength can be obtained. Therefore, the handleability of the honeycomb formed body in the plugging step can be sufficiently ensured, and the plugging slurry can be easily arranged.

In the main firing step, the firing temperature T ₂ is preferably 1400 to 1450 ° C. (Claim 4).
When the firing temperature T ₂ is less than 1400 ° C., there is a possibility that further orientation of cordierite constituting the honeycomb formed body cannot be achieved. As a result, desired characteristics (thermal expansion coefficient, average pore diameter, etc.) may not be obtained. On the other hand, when the temperature exceeds 1450 ° C., the melting point of cordierite constituting the honeycomb formed body is exceeded, and the honeycomb formed body may be melted.

In the preliminary firing step, in the process of raising the temperature of the honeycomb formed body to the firing temperature T ₁ , the temperature raising rate is set to 100 until the completion of the decomposition of the organic component contained in the ceramic material. It is preferable to set it as below ℃ / h (Claim 5).
When the temperature increase rate exceeds 100 ° C., the organic component contained in the honeycomb formed body may be burnt rapidly. Due to this combustion, a local temperature rise occurs in the honeycomb formed body, and there is a possibility that thermal stress is generated in the honeycomb formed body and cracks or the like occur.

In the temporary firing step, the honeycomb formed body is preferably fired while circulating the furnace atmosphere at least 8 times / minute.
When the number of circulations of the furnace atmosphere is less than 8 times / minute, the furnace atmosphere cannot be made uniform, and there is a concern that temperature variation becomes large. Therefore, there is a possibility that the organic component contained in the honeycomb formed body cannot be stably burned.

In the temporary firing step, the honeycomb formed body is preferably fired in an atmosphere having a variation in furnace temperature within ± 5 ° C. (Claim 7).
When the variation in the furnace temperature exceeds ± 5 ° C., there is a possibility that the organic component contained in the honeycomb formed body cannot be stably burned.

Moreover, in the said temporary baking process, it is preferable that the oxygen concentration in a furnace shall be 17% or less.
When the oxygen concentration in the furnace exceeds 17%, there is a possibility that the organic component contained in the honeycomb formed body cannot be stably burned.
Therefore, the oxygen concentration in the furnace is more preferably 12% or less.

Embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the exhaust gas purification filter 1 manufactured in this example has a honeycomb structure 10 in which porous partition walls 11 are arranged in a honeycomb shape and a large number of cells 12 having a quadrangular cross section are provided. The honeycomb structure 10 is made of ceramic mainly composed of cordierite, and has a cylindrical shape.

  Further, as shown in the figure, among the cells 12 of the honeycomb structure 10, the downstream end of the cell 12 serving as the introduction passage 121 for introducing the exhaust gas G and the exhaust passage for discharging the exhaust gas G that has passed through the porous partition wall 11 are used. The upstream end of the cell 12 that becomes 122 is closed by the plug portion 13. In this example, the plug portions 13 are arranged so that the adjacent cells 12 alternately become the introduction passage 121 and the discharge passage 122. When viewed from both end surfaces, the plug portions 13 are arranged in a so-called checkered pattern alternately in the vertical and horizontal directions.

The exhaust gas purification filter of this example is formed by extruding a clay-like ceramic material (extrusion molding process), drying the obtained honeycomb formed body (drying process), and pre-firing at a firing temperature T ₁ (pre-firing process). . Thereafter, a plugging slurry is disposed on the temporarily fired honeycomb formed body (plugging process), and main firing is performed at a firing temperature T ₂ (≧ T ₁ ) to produce a honeycomb structure provided with a plug portion (main firing). Process).
Hereinafter, the manufacturing method of this example will be described.

First, it contains kaolin, fused silica, aluminum hydroxide, alumina, talc, etc., and the chemical composition finally has a weight ratio of SiO ₂ : 45 to 55%, Al ₂ O ₃ : 33 to 42%, MgO: 12 A cordierite-forming raw material adjusted to have a composition mainly composed of ˜18% cordierite was mixed with water, and methylcellulose as an organic binder was added. At this time, the content of the organic binder was 3 to 10% by weight. Further, organic components such as carbon and pore forming lubricant were added and kneaded to obtain a clay-like ceramic material.

  Next, the clay-like ceramic material was extruded using an extruder and cut to a desired length to produce a honeycomb molded body. This honeycomb formed body has substantially the same shape as the final honeycomb structure, and has partition walls provided in a honeycomb shape, and a plurality of cells partitioned by this and penetrating in the axial direction. In this example, a viscous ceramic material was formed into a honeycomb formed body having a diameter of 160 mm, a length of 100 mm, a partition wall thickness of 0.3 mm, and a cell count of 300 mesh. Note that the size and the like of the honeycomb formed body can be changed according to the application.

Next, after the honeycomb formed body was dried, temporary firing was performed in a firing furnace.
The preliminary firing in this example was performed with a firing pattern P ₁ as shown in FIG. That is, the temperature is raised from room temperature to 600 ° C. at a temperature raising rate of 25 to 50 ° C./h. At this time, organic components such as an organic binder and a pore former contained in the honeycomb formed body are slowly burned and removed. Then, the firing temperature T _1: 1400 after Atsushi Nobori at a rate of temperature rise of 70 to 100 ° C. / h until ° C., held for 4 hours. At this time, the honeycomb formed body is converted into cordierite, and the dimensional change due to firing is almost completed, and a strength sufficient to provide sufficient handling properties is obtained. Then, it cools to room temperature and complete | finishes temporary baking. The time required for calcination was 57 hours.

  In the preliminary firing of this example, firing is performed by adjusting the atmosphere in the furnace so that the temperature variation in the furnace is within ± 5 ° C. and the oxygen concentration in the furnace is 16%. It was. The atmosphere in the furnace was circulated at a rate of 10 times / minute.

Next, plugging slurries serving as plug portions were arranged in a so-called checkered pattern alternately in the vertical direction and the horizontal direction at the cell opening on the end face of the honeycomb formed body. Thereafter, main firing was performed in a firing furnace.
The main baking of this example was performed with a baking pattern P ₂ as shown in FIG. That is, the temperature is raised from room temperature to the firing temperature T ₂ : 1450 ° C. at a rate of temperature rise of 100 ° C./h, and then held for 36 hours. At this time, the plugging slurry is fired to form the plug portion, and the cordierite is further oriented to adjust to a desired thermal expansion coefficient, average pore diameter, and the like. Then, it cools to room temperature and complete | finishes this baking. The time required for the main firing was 65 hours.

  As described above, an exhaust gas purification filter having a honeycomb structure provided with a plug portion was produced. In this example, the time required for the firing was 122 hours, which was 57 hours for the preliminary firing and 65 hours for the final firing.

Next, as a comparative example, an exhaust gas purification filter was produced by a conventional method.
In the comparative example, the plugging slurry was placed on the manufactured honeycomb formed body, and then fired in a firing furnace. In the firing of the comparative example, the temperature is raised from room temperature to 450 ° C. over 70 hours, raised to 1450 ° C., which is the firing temperature, over 45 hours, and then held for 36 hours. Then, it cools to room temperature and complete | finishes this baking. The time required for firing was 165 hours.
Thus, an exhaust gas purification filter was produced.

Next, the effect in the manufacturing method of the exhaust gas purification filter of this example is demonstrated, comparing with a comparative example.
In the manufacturing method of the exhaust gas purification filter of this example, the honeycomb molded body after the extrusion molding is temporarily fired at the firing temperature T ₁ , and the honeycomb molded body in which the plugging slurry is disposed after the temporary firing is fired at the firing temperature T _2. Baking is performed twice with the main baking step of main baking.

  Here, the provisional firing in the provisional firing step is intended to burn and remove organic components such as an organic binder and a pore forming material contained in the ceramic material. In this example, since the honeycomb formed body is fired at the stage before the plugging slurry is arranged, the organic content is reduced even if the heating rate is increased as compared with the comparative example in which the firing is performed after the plugging slurry is arranged. It can be burned and removed stably. Thereby, the time required for burning the organic component can be greatly shortened, and the productivity can be improved.

  In addition, the provisional firing in the provisional firing step aims to obtain a certain degree of strength while firing the honeycomb formed body to make cordierite, almost completing dimensional changes due to firing. Thereby, the handling of the honeycomb formed body in the subsequent plugging process and the arrangement of the plugging slurry on the honeycomb formed body can be facilitated.

  Further, the main firing in the main firing step is intended to form the plug portion by firing the plugging slurry. In this example, since the plugging slurry is disposed and fired on the honeycomb formed body after calcination, in which the dimensional change due to firing is almost completed, the plug portion can be formed with high dimensional accuracy. Moreover, the strength of the plug portion is sufficiently high.

In the main firing in the main firing step, the honeycomb formed body after the temporary firing is fired at a firing temperature T ₂ higher than the firing temperature T ₁ in the temporary firing, the cordierite is further oriented, and the characteristics of the exhaust gas purification filter are improved. The purpose is to improve. Thereby, characteristics, such as a thermal expansion coefficient and an average pore diameter, of an exhaust gas purification filter can be improved. A high-quality exhaust gas purification filter having a desired thermal expansion coefficient, average pore diameter, and the like can be obtained.

  In addition, as described above, in this example, the firing is performed twice, that is, the pre-baking in the pre-baking step and the main baking in the main baking step. That is, substantial initial firing of the honeycomb formed body and firing of the plugging slurry are performed in separate steps. Thereby, the number of times of firing is increased by one as compared with the comparative example in which the plugging slurry is arranged in the honeycomb formed body before firing and both are fired simultaneously. However, the time required for the entire firing is 165 hours in the comparative example and 122 hours in the present example. In other words, in this example, the time required for burning the organic component contained in the honeycomb formed body can be greatly shortened, so that the time required for the entire firing can be shortened. Therefore, productivity can be improved.

Further, in this example, in the preliminary firing step, the temperature rising rate is set to 100 ° C./h or less in the process of raising the temperature of the honeycomb formed body to the firing temperature T ₁ . Therefore, there is no possibility that the organic component contained in the honeycomb formed body burns rapidly. Thereby, the crack etc. of the honeycomb molded object which arise with the rapid combustion heat of an organic part can be suppressed.

Further, in the temporary firing step, the furnace atmosphere is circulated at least 8 times / minute, and the honeycomb formed body is fired in an atmosphere in which the temperature variation in the furnace is within ± 5 ° C. Therefore, the furnace atmosphere becomes more uniform, and the temperature variation becomes smaller. Thereby, the organic component contained in the honeycomb formed body can be stably burned.
In the pre-baking step, the oxygen concentration in the furnace is 16%. Therefore, there is no fear that the organic component contained in the honeycomb formed body burns rapidly, and the honeycomb formed body can be burned more stably.

  Thus, according to the manufacturing method of this example, the firing time can be shortened to improve productivity, and a high-quality exhaust gas purification filter can be obtained.

The perspective view which shows the exhaust gas purification filter in an Example. Cross-sectional explanatory drawing which shows the exhaust gas purification filter in an Example. In an Example, (a) Explanatory drawing which shows the baking pattern of a temporary baking process, (b) Explanatory drawing which shows the baking pattern of this baking process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification filter 10 Honeycomb structure 11 Partition 12 Cell 121 Introduction passage 122 Discharge passage 13 Plug part G Exhaust gas

Claims (7)

It has a honeycomb structure made of cordierite provided with a large number of cells with porous partition walls arranged in a honeycomb shape, and among the cells of the honeycomb structure, downstream of the cells serving as introduction passages for introducing exhaust gas In a method of manufacturing an exhaust gas purification filter in which an end and an upstream end of a cell serving as a discharge passage for discharging exhaust gas that has passed through the porous partition wall are closed by a plug portion,
An extrusion process for producing a honeycomb formed body by extruding a ceramic material containing a cordierite forming raw material;
A drying step of drying the honeycomb formed body,
A temporary firing step of firing the honeycomb formed body at a firing temperature T ₁ ;
A plugging step of disposing a plugging slurry in a portion to be plugged by the plug portion of the opening of the cell in the end face of the honeycomb formed body,
A main firing step of firing the honeycomb formed body in which the plugging slurry is disposed at a firing temperature T ₂ (≧ T ₁ ) to produce the honeycomb structure in which the plug portion is provided in the portion to be plugged. And a method for producing an exhaust gas purification filter. 2. The method for manufacturing an exhaust gas purification filter according to claim 1, wherein, in the temporary firing step, the firing temperature T ₁ is 1300 to 1400 ° C. 3. 3. The method for manufacturing an exhaust gas purification filter according to claim 2, wherein, in the temporary firing step, the firing temperature T ₁ is 1380 to 1400 ° C. 3. In any one of claims 1 to 3, the present sintering process, method of manufacturing an exhaust gas purifying filter, wherein said sintering temperature T ₂ is from 1400 to 1,450 ° C.. In any 1 paragraph of Claims 1-4, decomposition of at least organic content contained in the ceramic material is started in the process of raising the temperature of the honeycomb formed body to the firing temperature T _{1 in the} temporary firing step. The process for producing an exhaust gas purification filter is characterized in that the temperature rising rate is set to 100 ° C./h or less until the process is completed.   6. The method for manufacturing an exhaust gas purification filter according to any one of claims 1 to 5, wherein, in the temporary firing step, the honeycomb formed body is fired while the furnace atmosphere is circulated at least 8 times / minute.   7. The exhaust gas purification filter according to claim 1, wherein, in the temporary firing step, the honeycomb formed body is fired in an atmosphere having a variation in furnace temperature of within ± 5 ° C. 7. Method.

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