JP2008119665A - Manufacturing method of exhaust gas purification filter - Google Patents

Abstract

An object of the present invention is to provide a method for producing an exhaust gas purification filter capable of reducing the firing time to improve productivity and suppressing the occurrence of problems during firing.
A method for manufacturing an exhaust gas purification filter 1 in which a plug portion 13 is provided in a honeycomb structure 10 made of cordierite in which porous partition walls 11 are arranged in a honeycomb shape and a large number of cells 12 are provided. Extrusion molding of the material to produce a honeycomb molded body, a drying process for drying the honeycomb molded body, a firing process for firing the honeycomb molded body, and an end face of the honeycomb molded body before the firing step A plugging step of disposing a plugging slurry in a portion to be plugged by the plug portion 13 in the opening of the cell, and in the first firing in the firing step, the organic component contained in the honeycomb formed body From the start of the decomposition until the completion, the amount of oxygen supplied to the furnace is suppressed.
[Selection] Figure 1

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 as a base material for the exhaust gas purification filter, a ceramic material added with carbon as a pore former is extruded to produce a honeycomb formed body, dried, and then fired. And the porous partition which has a desired porosity is formed by burning off carbon at the time of baking.

  However, when a honeycomb formed body containing an organic component such as carbon or a binder as a pore former is fired, reaction heat (combustion heat) is generated due to the reaction of the organic component. In particular, when the rate of temperature rise is increased, the organic component reacts abruptly to generate large combustion heat. And local temperature rise etc. arise in a honeycomb fabrication object. As a result, thermal stress is generated in the honeycomb molded body, and defects such as cracks occur.

  Therefore, conventionally, in the temperature range where organic components such as carbon and binder are combusted, the temperature in the furnace is temporarily maintained or the temperature is slowly raised to gradually combust these organic components. However, in such a method, the firing time becomes long and the productivity is lowered.

  Therefore, there is a demand for a method for manufacturing an exhaust gas purification filter that can shorten the firing time to improve productivity and suppress the occurrence of defects during firing.

JP-A-8-73274

  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 suppressing the occurrence of defects during firing. 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 an introduction passage for introducing exhaust gas among the cells of the honeycomb structure. In a method for producing an exhaust gas purification filter comprising a plug portion closing a downstream end of a cell and an upstream end of a cell serving as a discharge passage for discharging exhaust gas that has passed through the porous partition wall,
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 firing step of firing the honeycomb formed body one or more times;
Before or during the firing step, the plugging step of placing 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 molded body,
In the first firing in the firing step, the exhaust gas purification is characterized in that the amount of oxygen supplied into the furnace is suppressed at least from the start to the completion of the decomposition of the organic component contained in the honeycomb formed body. It exists in the manufacturing method of a filter (Claim 1).

  As described above, the method for producing an exhaust gas purification filter of the present invention includes an extrusion molding process, a drying process, a firing process, and a plugging process. In the first firing in the firing step, the amount of oxygen supplied to the furnace is suppressed at least from the start of decomposition of the organic component contained in the honeycomb formed body until the completion. That is, in the first firing of the honeycomb formed body, oxygen in the atmosphere in the furnace is depleted more than usual during at least the burning of the organic component.

  Here, in the first firing of the honeycomb molded body, for example, the honeycomb molded body containing the organic component such as carbon as a binder or a pore former is fired, and the organic component is burned. Remove. At this time, as in the present invention, by firing in a state in which the oxygen in the furnace atmosphere is deficient, the organic content is smaller than when firing in a normal oxygen state without suppressing the oxygen supply amount. The reaction heat (combustion heat) due to the decomposition reaction when burned is reduced. In addition, since the supply amount of oxygen necessary for the decomposition reaction is reduced, the decomposition reaction itself proceeds slowly.

Thereby, in the first firing of the honeycomb formed body, the organic component contained in the honeycomb formed body can be stably removed by combustion. Therefore, it is possible to suppress the rapid combustion of the organic component and the generation of large combustion heat associated therewith, and further suppress the occurrence of cracks and the like due to the generation of large thermal stress in the honeycomb formed body.
Moreover, since the said organic component can be burned stably, a temperature increase rate can be made faster than before. Thereby, baking time can be shortened and productivity can be improved.

  Thus, according to the method for manufacturing an exhaust gas purification filter of the present invention, the firing time can be shortened to improve productivity, and the occurrence of defects during firing can be suppressed.

In the present invention, in the first firing in the firing step, the oxygen concentration in the firing furnace is set to 8% or less from the start to the completion of the decomposition of the organic component contained in the honeycomb formed body. (Claim 2).
When the oxygen concentration in the firing furnace exceeds 8%, the organic component contained in the honeycomb formed body may not be stably burned in the first firing of the honeycomb formed body. .

The firing step includes a first firing step of temporarily firing the honeycomb formed body before the plugging step;
After the plugging step, the honeycomb formed body is subjected to main firing at a firing temperature higher than the firing temperature of the temporary firing, and a second firing step of forming the plug portion at the portion to be plugged. (Claim 3).

In this case, the honeycomb formed body has a certain degree of strength by being temporarily fired in the first firing step. Therefore, in the subsequent plugging process, the handling property of the honeycomb formed body can be sufficiently ensured, and the plugging slurry can be easily arranged.
Further, in the second firing step, by performing the main firing at a firing temperature higher than the preliminary firing, for example, characteristics such as a thermal expansion coefficient and an average pore diameter can be adjusted to a desired value.

The firing step includes a first firing step of firing the honeycomb formed body before the plugging step;
After the plugging step, the honeycomb formed body is temporarily fired at a firing temperature lower than the firing temperature of the main firing, and has a second firing step of forming the plug portion at the portion to be plugged. (Claim 4).

In this case, the honeycomb formed body has a certain degree of strength by performing the main firing in the first firing step. Therefore, in the subsequent plugging process, the handling property of the honeycomb formed body can be sufficiently ensured, and the plugging slurry can be easily arranged.
Moreover, the dimensional change by baking can be substantially completed by the main baking in the said 1st baking process. Therefore, the plug portion can be formed with high precision in the second firing step.

In addition, the firing step may include a first firing step in which the honeycomb formed body is subjected to main firing after the plugging step and the plug portion is formed in a portion to be plugged. (Claim 5).
In this case, the honeycomb formed body and the plugging slurry can be fired simultaneously by only one firing in the first firing step. Thereby, the said honeycomb structure and the said plug part can be provided integrally.

Moreover, it is preferable that the baking temperature of the said temporary baking in the said baking process is 1300-1400 degreeC (Claim 6).
When the calcining temperature of the temporary calcining 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 increased only for the time required to raise the temperature, and the productivity may be reduced.
Therefore, it is more preferable that the calcining temperature of the preliminary calcining in the calcining step is 1380 to 1400 ° C. (Claim 7).

Moreover, it is preferable that the baking temperature of the said baking in the said baking process is 1400-1450 degreeC (Claim 8).
When the firing temperature of the main firing is less than 1400 ° C., the honeycomb formed body may not be completely cordierite. On the other hand, when the temperature exceeds 1450 ° C., the melting point of cordierite which is the main component of the honeycomb formed body may be exceeded, and there is a risk of melting.

(Example 1)
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 every other vertical and horizontal directions.

The exhaust gas purification filter of this example extrudes a clay-like ceramic material (extrusion molding process), and dries the obtained honeycomb molded body (drying process). Thereafter, the plugging slurry is disposed on the honeycomb formed body (plugging step), and the honeycomb formed body is subjected to main firing to produce a honeycomb structure provided with plug portions (first firing step). .
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 so as 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 addition amount of the organic binder was 3 to 10% by weight with respect to 100% by weight of the cordierite forming raw material. 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, plugging slurries serving as plug portions were arranged in a so-called checkered pattern at every other opening in the longitudinal direction and the lateral direction at the cell opening on the end face of the honeycomb formed body.

Next, main firing was performed in a firing furnace.
As shown in FIG. 3, the firing furnace 2 used in this example is composed of a plurality of zones, and is a continuous furnace (tunnel) capable of firing a workpiece (honeycomb molded body 100) on a carriage 29 while being conveyed. Furnace). The firing furnace 2 has a degreasing zone 21, a firing zone 22, and a cooling zone 23, and each zone is configured so that the temperature can be adjusted.

Moreover, as shown in FIG. 4, the degreasing zone 21 has a secondary combustion furnace 31 and a burner 32, and is configured so that the oxygen concentration in the furnace can be adjusted.
Specifically, exhaust gas containing unburned organic matter is recovered from the furnace. The recovered exhaust gas is adjusted to a predetermined temperature by a burner 32 that has been adjusted to an air-fuel ratio. Then, the exhaust gas adjusted in temperature and the low oxygen concentration exhaust gas supplied from the secondary combustion furnace 31 are mixed, and a predetermined amount is supplied into the furnace by a fan. Then, hot air whose temperature and oxygen concentration are adjusted is sent into the degreasing zone 21. The remaining amount of hot air supplied into the furnace is returned to the secondary combustion furnace 31, processed at 650 ° C., and then sent to a predetermined amount for mixing with the furnace exhaust. The oxygen concentration in the furnace is constantly monitored, and the oxygen concentration in the degreasing zone 21 is adjusted while feeding back the mixing ratio and the air-fuel ratio.

Moreover, the baking of this example was performed by the baking pattern E as shown in FIG. That is, in the degreasing zone 21 of the firing furnace 2, the temperature is raised from room temperature to a firing temperature of 1400 ° C. at a heating rate of 100 ° C./h. At this time, the organic component contained in the honeycomb formed body 100 is removed by combustion. The oxygen concentration in the furnace in the degreasing zone 21 was adjusted to 2% or less, and oxygen in the atmosphere in the furnace was depleted more than usual. And in the baking zone 22, it hold | maintains at the baking temperature of 1400 degreeC for 4 hours. Then, in the cooling zone 23, it cools to room temperature and complete | finishes baking. The time required for the firing was 29 hours.
In this way, as shown in FIG. 1, the exhaust gas purification filter 1 having the honeycomb structure 10 provided with the plug portion 13 was produced.

Next, as a comparative example, an exhaust gas purification filter was produced by a conventional method.
The comparative example was fired with a firing pattern C as shown in FIG. That is, in the degreasing zone 21 of the firing furnace 2, the temperature is raised from room temperature to 160 ° C. over 3 hours, from 160 ° C. to 650 ° C. over 24 hours, and from 650 ° C. to 1400 ° C. over 15 hours. In addition, the oxygen concentration in the furnace in the degreasing zone 21 was not adjusted, and was in a normal state (oxygen concentration 16%). And in the baking zone 22, it hold | maintains at the baking temperature of 1400 degreeC for 4 hours. Then, in the cooling zone 23, it cools to room temperature and complete | finishes baking. The time required for firing was 57 hours.
Other steps are the same as above.

Next, the effect in the manufacturing method of the exhaust gas purification filter 1 of this example is demonstrated, comparing with a comparative example.
In the manufacturing method of the exhaust gas purification filter 1 of the present example, in the main firing step, the amount of oxygen supplied into the furnace is suppressed from the start to the completion of the decomposition of the organic component contained in the honeycomb formed body 100. . That is, in the first firing of the honeycomb formed body 100, in the degreasing zone 21 of the firing furnace 2 where the temperature is raised from room temperature to a firing temperature of 1400 ° C., oxygen in the atmosphere in the furnace is depleted more than usual. Yes.

  Here, in the main firing step, the honeycomb formed body 100 in a state where an organic component such as carbon as a binder or a pore forming material is contained is fired, and this organic component is burned and removed. At this time, as in this example, the organic content is burned and removed in a state where the oxygen in the furnace atmosphere is depleted, so that the organic content is combusted compared to the comparative example baked in a normal oxygen state. Reaction heat (combustion heat) due to the decomposition reaction is reduced. In addition, since the supply amount of oxygen necessary for the decomposition reaction is reduced, the decomposition reaction itself proceeds slowly.

Thereby, in the main firing step, organic components contained in the honeycomb formed body 100 can be stably removed by combustion. Therefore, it is possible to suppress the rapid combustion of the organic component and the generation of the large combustion heat associated therewith, and further suppress the occurrence of cracks and the like due to the large thermal stress generated in the honeycomb formed body 100.
Moreover, since the organic component contained in the honeycomb formed body 100 can be stably burned, the temperature rising rate can be increased as compared with the comparative example. Thereby, baking time can be shortened and productivity can be improved. The actual time required for firing is 57 hours for the comparative example with respect to 29 hours for this example, and the firing time can be greatly shortened.

  Thus, according to the manufacturing method of the exhaust gas purification filter of this example, the firing time can be shortened to improve the productivity, and the occurrence of defects during firing can be suppressed.

(Example 2)
In this example, the defect rate is examined for the exhaust gas purification filter 1 manufactured by changing the oxygen concentration in the degreasing zone 21 of the firing furnace 2.
In this example, the exhaust gas purification filter 1 was manufactured by changing the oxygen concentration in the degreasing zone 21 of the firing furnace 2 in the range of 2 to 16%. Specifically, using the honeycomb formed body 100 having the same size as that of Example 1, firing was performed with a firing pattern E similar to that of Example 1, and oxygen concentrations from room temperature to 500 ° C. were respectively 2% and 5%. , 8%, 12% and 16%. In addition, after 500 degreeC, all adjusted oxygen concentration to 9%. And the defects, such as a crack, were observed visually about the produced exhaust gas purification filter 1, and the defect rate was calculated | required from the generation | occurrence | production ratio. The result is shown in FIG.

In FIG. 6, the vertical axis represents the defect rate (%), and the horizontal axis represents the oxygen concentration (%) from room temperature to 500 ° C.
As can be seen from the figure, the failure rate at an oxygen concentration of 16% was 100%, but the failure rate at an oxygen concentration of 12% was about 10%, and the failure rate was greatly reduced. Furthermore, the defect rate at oxygen concentrations of 2%, 5%, and 8% was almost 0%, and no occurrence of defects was observed.

  From this result, it can be seen that firing is performed in a state where oxygen in the furnace atmosphere is deficient, and the organic component contained in the honeycomb formed body 100 is combusted and removed, whereby the organic component can be stably combusted and removed. In particular, by setting the oxygen concentration to 8% or less, it is possible to further suppress the rapid combustion of organic components and the accompanying generation of large combustion heat, and to prevent the occurrence of defects such as cracks in the honeycomb molded body 100. I understand.

(Example 3)
Next, the internal and external temperatures of the honeycomb formed body 100 when the oxygen concentration in the degreasing zone 21 of the firing furnace 2 was changed and fired were examined.
In this example, the honeycomb formed body 100 was fired by adjusting the oxygen concentration in the degreasing zone 21 of the firing furnace 2 to 2% or 16%. Specifically, using the honeycomb formed body 100 having the same size as that of Example 1, firing is performed with a firing pattern E similar to that of Example 1, and the oxygen concentration from room temperature to 500 ° C. is set to 2% and 16%. It was adjusted. And the center part of the honeycomb molded object 100, the outer peripheral part, and the furnace temperature were measured with the platinum thermocouple. The result is shown in FIG.

7A and 7B show temperature (° C.) on the vertical axis and time on the horizontal axis. Further, the temperature of the central part is shown as S ₁ , the temperature of the outer peripheral part is shown as S ₂ , and the temperature in the furnace is shown as S ₃ .
As can be seen from the figure, when the oxygen concentration is 16%, an internal / external temperature difference is generated in the honeycomb formed body 100, but when the oxygen concentration is 2%, the internal / external temperature difference is hardly observed.

  From this result, it can be seen that firing is performed in a state where oxygen in the furnace atmosphere is deficient, and the organic component contained in the honeycomb formed body 100 is combusted and removed, whereby the organic component can be stably combusted and removed. And it turns out that the rapid combustion of an organic part can be suppressed and it can suppress that the local temperature rise arises in the honeycomb molded object 100. FIG.

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. Explanatory drawing which shows the structure of the baking furnace in an Example. Explanatory drawing which shows the structure of the degreasing zone in an Example. Explanatory drawing which shows the baking pattern in an Example. Explanatory drawing which shows the relationship between the defect rate and oxygen concentration in an Example. Explanatory drawing which shows the relationship between the temperature of a honeycomb molded object, and time in an Example.

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 (8)

It has a honeycomb structure made of cordierite in which porous partition walls are arranged in a honeycomb shape and a large number of cells are provided. 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 firing step of firing the honeycomb formed body one or more times;
Before or during the firing step, the plugging step of placing 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 molded body,
In the first firing in the firing step, the exhaust gas purification is characterized in that the amount of oxygen supplied into the furnace is suppressed at least from the start to the completion of the decomposition of the organic component contained in the honeycomb formed body. A method for manufacturing a filter.   In claim 1, in the first firing in the firing step, the oxygen concentration in the furnace is set to 8% or less from the start to the completion of the decomposition of the organic component contained in the honeycomb molded body. An exhaust gas purification filter manufacturing method characterized by the above. In claim 1 or 2, the firing step includes a first firing step of temporarily firing the honeycomb formed body before the plugging step;
After the plugging step, the honeycomb formed body is subjected to main firing at a firing temperature higher than the firing temperature of the temporary firing, and a second firing step of forming the plug portion in the portion to be plugged. An exhaust gas purification filter manufacturing method characterized by the above. In claim 1 or 2, the firing step includes a first firing step of firing the honeycomb formed body before the plugging step;
After the plugging step, the honeycomb formed body is temporarily fired at a firing temperature lower than the firing temperature of the main firing, and has a second firing step of forming the plug portion in the portion to be plugged. An exhaust gas purification filter manufacturing method characterized by the above.   3. The firing process according to claim 1, wherein the firing step includes only a first firing step of firing the honeycomb formed body after the plugging step and forming the plug portion in the portion to be plugged. An exhaust gas purification filter manufacturing method characterized by the above.   5. The method for producing an exhaust gas purification filter according to claim 3, wherein a calcination temperature of the preliminary calcination in the calcination step is 1300 to 1400 ° C. 5.   The method for producing an exhaust gas purification filter according to claim 6, wherein the calcining temperature of the preliminary calcination in the calcination step is 1380 to 1400 ° C.   The method for producing an exhaust gas purification filter according to any one of claims 3 to 5, wherein a firing temperature of the main firing in the firing step is 1400 to 1450 ° C.

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