JP2008119664A - 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 reducing the number of pores with respect to the total pore volume of a partition wall. <P>SOLUTION: The manufacturing method of an exhaust gas purifying filter 1, which is constituted by providing plug parts 13 to a honeycomb structure 10 comprising cordierite and having a large number of cells 12 provided by arranging porous partition walls 11 in a honeycomb state, has an extrusion molding process for extruding a ceramic material to mold a honeycomb molded member, a drying process for drying the honeycomb molded member, a baking process for baking the honeycomb molded member a plurality of times and a plugging process for arranging a plugging slurry to the parts to be plugged among the opening parts of the cells provided to the edge surface of the honeycomb molded member on the way of the baking process. In the first baking in the baking process, baking is performed at the highest temperature of 1,300-1,450°C, and in a case that the temperature rising speed to the highest temperature from 1,000°C is set to 50-A°C/hr. (in a case that the mass of the honeycomb molded member after the drying process is set to B kg, A is A=150/B). <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, an exhaust gas purification filter that collects particulates in exhaust gas discharged from an internal combustion engine and purifies the exhaust gas is 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 that serves as the introduction passage passes through the porous partition wall and moves to the exhaust passage that is formed by 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 the honeycomb structure that becomes the base material of the exhaust gas purification filter, a ceramic material is extruded to produce a honeycomb formed body, dried, and then fired.
As described above, the performance of the exhaust gas purification filter is required to collect particulates and efficiently purify the exhaust gas, and to have a low pressure loss. Therefore, for example, a pore-forming material is added to a ceramic material to produce a honeycomb structure having a predetermined porosity and pore diameter.

  However, the pores formed in the partition walls of the honeycomb structure are never uniform, and pores with a pore diameter of 10 μm or less that cannot sufficiently capture particulates in the exhaust gas (hereinafter, appropriately, (Referred to as micropores). Further, when the catalyst is supported on the partition walls, the catalyst closes the fine holes, and the particulate collection function is further deteriorated. In addition, there is a problem that pressure loss increases due to clogging of the fine holes by the catalyst.

  For this reason, there is a demand for a method for manufacturing an exhaust gas purification filter that can reduce the amount of fine pores that cannot sufficiently collect particulates with respect to the total pore volume of the partition walls.

JP 2003-145521 A

  The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a method for manufacturing an exhaust gas purification filter capable of reducing the amount of fine pores with respect to the total pore volume of a partition wall.

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,
Extrusion molding of a ceramic material containing a cordierite forming raw material, and forming a honeycomb molded body provided with a large number of cells by arranging porous partition walls in a honeycomb shape; and
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, 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,
In the first firing in the firing step, firing is performed at a maximum temperature of 1300 to 1450 ° C., and a rate of temperature increase from 1000 ° C. to the maximum temperature is 50 to A ° C./hr (however, after the drying step) In the manufacturing method of the exhaust gas purification filter, A = 150 / B when the mass of the honeycomb formed body is set to Bkg (Claim 1).

  The manufacturing method of the exhaust gas purification filter of the present invention performs the extrusion molding step, the drying step, the firing step, and the plugging step. In the firing step, the honeycomb formed body is fired one or more times. In the first firing in the firing step, firing is performed at a maximum temperature of 1300 to 1450 ° C., and a temperature increase rate from 1000 ° C. to the maximum temperature is set to 50 to A ° C./hr.

  That is, in the present invention, in the first firing in which the honeycomb formed body is fired for the first time, the temperature range (about 1200 ° C. or higher) where pores are formed as the cordierite of the honeycomb formed body progresses. In a specific temperature range from 1000 ° C. to the maximum temperature (1300 to 1450 ° C.), the rate of temperature rise is defined in a specific range of 50 to A ° C./hr.

  In this way, in the specific temperature range, by setting the rate of temperature rise to the specific range, the volume of the formed pores remains substantially constant, while pores with a small pore diameter, particularly particulates, are used. It is possible to suppress the formation of fine pores having a pore diameter of 10 μm or less that cannot be sufficiently collected. As a result, the obtained exhaust gas purification filter has a reduced proportion of fine pores with respect to the total pore volume of the porous partition wall in which the pores are formed. Therefore, the particulates can be collected sufficiently and the pressure loss is low.

  Further, in the obtained exhaust gas purification filter, even if the catalyst is supported on the partition wall, the amount of fine pores is reduced, so that the catalyst closes the fine pores and the particulate collection function is reduced. It is possible to suppress an increase in pressure loss due to clogging of fine holes due to. Thereby, even when a catalyst is supported and used, an excellent particulate collection function and low pressure loss can be maintained.

  In the present invention, the rate of temperature increase in the first firing is specified. As for this, by performing the first firing at the maximum temperature of 1300 to 1450 ° C., the formation of cordierite of the honeycomb formed body is almost completed. For this reason, when firing a plurality of times, the first and subsequent firings may complete cordierite formation of the honeycomb formed body, improve characteristics (for example, thermal expansion coefficient), or from the plugging slurry. Firing to form the plug portion. Accordingly, the pores formed by the first firing are maintained with little influence from the subsequent firing. Also, new pores are hardly formed by the first and subsequent firings. That is, the volume of fine pores and the amount of fine pores finally formed are determined by the first firing. For this reason, the rate of temperature increase in the first firing is specified, and the amount of micropores is controlled.

  Further, as described above, when the rate of temperature rise in the above temperature range is defined in the above range, the fact that the amount of micropores can be reduced has been confirmed in Examples described later, but the details This mechanism has not been clarified yet. However, it is estimated as follows.

  That is, when the above honeycomb formed body made of a ceramic material containing a cordierite forming raw material is fired, fine pores are generated by the volume shrinkage of the contained aluminum hydroxide, and the molten talc and fused silica are dispersed by the diffusion reaction. While filling the micropores, the honeycomb formed body is made into cordierite. Therefore, when the temperature rising rate is high, the diffusion reaction is also promoted, and the fine holes can be sufficiently filled with molten talc or fused silica, and the amount of fine holes can be reduced. On the other hand, when the rate of temperature rise is slow, the diffusion reaction becomes dull, and the fine holes cannot be filled sufficiently, and many fine holes remain.

  As described above, the exhaust gas purification filter obtained by the production method of the present invention has a reduced amount of fine pores with respect to the total pore volume of the partition walls.

  In the present invention, when the maximum temperature of the first firing in the firing step is less than 1300 ° C., the honeycomb formed body may not be sufficiently 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.

  Moreover, when the said temperature increase rate of the 1st baking in the said baking process is less than 50 degreeC / hr, there exists a possibility that formation of a micropore cannot fully be suppressed. Moreover, there is a possibility that the firing time becomes long and the productivity is lowered. On the other hand, when it exceeds A ° C./hr, the temperature difference in the honeycomb formed body becomes large due to rapid heating, and there is a possibility that thermal stress occurs and cracks occur.

The firing step includes a first firing step of temporarily firing the honeycomb formed body at a maximum temperature T ₁ before the plugging step;
After the plugging step, the honeycomb formed body is subjected to main firing at a maximum temperature T ₂ (≧ T ₁ ) and a second firing step of forming the plug portion at the portion to be plugged. (Claim 2).

In this case, in the first firing step, the honeycomb formed body is fired (temporarily fired) so that the fired honeycomb formed body has a certain degree of strength. Therefore, the plugging slurry can be easily arranged in the subsequent plugging process.
In addition, since the preliminary firing is performed at a temperature equal to or lower than the maximum temperature T ₂ of the subsequent main firing, the confirmation work is performed in a short cycle by confirming cracks of the honeycomb formed body in the stage after the temporary firing. Can do. Thereby, work efficiency can be improved and productivity can be improved.

Further, the firing step includes a first firing step of subjecting the honeycomb formed body to main firing at a maximum temperature T ₂ before the plugging step;
After the plugging step, the honeycomb formed body is temporarily fired at a maximum temperature T ₁ (≦ T ₂ ) and has a second firing step of forming the plug portion in the portion to be plugged. (Claim 3).

In this case, in the first firing step, the honeycomb formed body is fired (main fired) so that the honeycomb formed body after firing has a certain degree of strength. Therefore, the plugging slurry can be easily arranged in the subsequent plugging process.
In addition, by performing the main firing at a temperature equal to or higher than the maximum temperature T ₁ of the subsequent preliminary firing prior to the preliminary firing, the honeycomb formed body is completely cordierite, and dimensional changes such as shrinkage and expansion due to the firing. Is almost complete. Therefore, the dimensions of the honeycomb formed body after the main firing are maintained until after the preliminary firing. Thereby, it can be confirmed whether it becomes a desired dimension in the stage after this baking. Further, this confirmation work can be performed in a short cycle, so that the work efficiency can be improved and the productivity can be improved.

Moreover, the firing step is configured to have after the plugged step, as well as the firing the honeycomb molded body at a maximum temperature T _2, only the first firing step of forming the plug portion in a portion to be the plugged (Claim 4).
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 plug portion can be integrally provided in the honeycomb structure.

Further, the maximum temperature T ₁ of the calcination in the calcination step is preferably 1300-1400 ° C. (Claim 5).
When the maximum 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 increased only for the time required to raise the temperature, and the productivity may be reduced.

Moreover, the highest temperature T ₂ of the main firing in the firing step is preferably 1400-1,450 ° C. (Claim 6).
When the maximum temperature T ₂ is less than 1400 ° C., the honeycomb formed body may not be completely cordierite, and shrinkage or expansion due to firing may occur. 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.

In the obtained exhaust gas purification filter, the porous partition wall preferably has a porosity of 55 to 75%. The porous partition wall preferably has an average pore diameter of 15 to 35 μm.
In this case, the exhaust gas purification filter has an excellent particulate collection function and a low pressure loss.

The partition wall preferably has a ratio of fine pores having a pore diameter of 10 μm or less to the total pore volume (hereinafter, appropriately referred to as “fine pore amount”) of 6% or less.
In this case, the particulate collection function of the exhaust gas purification filter can be improved and the pressure loss can be reduced.

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 an extrusion process for extruding a clay-like ceramic material, a drying process for drying the obtained honeycomb molded body, a firing process for firing the honeycomb molded body after drying a plurality of times, In the middle of the firing process, a plugging process is performed in which a plugging slurry serving as a plug part is disposed.
As the firing step of the present example, the first firing step of temporarily firing the honeycomb formed body is performed before the plugging step, and the second firing step of firing the honeycomb formed body at a temperature higher than the temporary firing is the plugging step. After that. That is, after the drying process, the first baking process, the plugging process, and the second baking process are performed in this order.

In this example, first, exhaust gas purification filters (sample 11 to sample 17) were prepared by changing the temperature increase rate (temperature increase rate V described later) of the first firing in the firing step (temporary firing in the first firing step). , Evaluate.
Hereinafter, a method for manufacturing each sample will be described.

First, containing kaolin, fused silica, aluminum hydroxide, alumina, talc, pore former (graphite), finally SiO ₂ Chemical composition in _{weight: 45~55%, Al 2 O 3} : 33~ By mixing a cordierite forming raw material adjusted to have a cordierite composition consisting mainly of 42% and MgO: 12-18% with water, adding an organic binder and kneading, A ceramic material was obtained. In addition, the compounding quantity of the graphite as a pore making material in the cordierite forming raw material was 10 to 30% by weight, and the compounding quantity of the foaming material was 4 to 7% by weight.

  Next, the clay-like ceramic material was extruded by an extruder and cut to a desired length to prepare a honeycomb formed body. This honeycomb formed body has the same shape as the final honeycomb structure, and has partition walls provided in a honeycomb shape, and a plurality of cells that are partitioned by this and penetrate the longitudinal direction of the formed body. 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. The size of the honeycomb formed body can be changed according to the application.

Next, the honeycomb formed body was dried, and then pre-fired by holding at a maximum temperature of 1390 ° C. for 5 hours. At this time, as shown in Table 1, for each sample, the rate of temperature increase from 1000 ° C. to the maximum temperature of 1390 ° C. (hereinafter referred to as temperature increase rate V) was changed in the range of 10 to 150 ° C./hr.
Thereafter, a plugging slurry serving as a plug portion in a so-called checkered pattern was disposed in an opening of a predetermined cell on the end face of the honeycomb formed body.

Next, the main calcination was performed by maintaining the maximum temperature at 1440 ° C. for 30 hours. The main firing was performed under the same conditions for each sample.
In this way, exhaust gas purification filters (samples 11 to 17) having a honeycomb structure provided with plug portions were produced.

  With respect to the exhaust gas purification filters (Samples 11 to 17) thus obtained, the porosity of the partition walls and the amount of micropores of 10 μm or less were measured. Furthermore, pressure loss was also measured.

  The porosity and the amount of fine pores of 10 μm or less were measured by mercury porosimetry using a mercury intrusion porosimeter, and the total volume of all pores existing in the partition walls (total pore volume) and the pore diameter was 10 μm or less. The total volume of micropores (micropore volume) was determined. The porosity (%) was calculated based on the formula {total pore volume / (total pore volume + 1 / 2.52)} × 100. Moreover, the micropore amount (%), which is the ratio of micropores of 10 μm or less to the total pore volume, was calculated based on the formula (micropore volume / total pore volume) × 100. The results are shown in Table 1.

For the pressure loss, room temperature air is introduced at a flow rate of 9 m ³ / min into an exhaust gas purification filter having a catalyst such as platinum supported on the partition wall, and the pressure difference before and after the exhaust gas purification filter is obtained using a manometer. It was. And pressure loss (kPa) was computed from this pressure difference. The results are shown in Table 1.

Further, based on the results of Table 1, FIG. 3 shows the relationship between the heating rate V (° C./hr) and the amount of micropores (%) of 10 μm or less, and FIG. 4 shows the amount of micropores (%) of 10 μm or less. And the pressure loss (kPa).
As is known from FIG. 3, the faster the heating rate V, the smaller the amount of fine pores of 10 μm or less. Further, as is known from FIG. 4, the pressure loss becomes lower as the amount of fine pores of 10 μm or less decreases. That is, as is known from FIGS. 3 and 4, the faster the heating rate V, the smaller the amount of fine pores of 10 μm or less, and the lower the pressure loss. In addition, as shown in Table 1, the porosity of each sample was substantially constant and was 65%.

  For example, when this exhaust gas purification filter is mounted on the exhaust pipe of an automobile engine, it is desired to reduce the pressure loss in order to suppress a decrease in engine output. In practice, it is desirable that the pressure loss be 2.5 kPa or less in order to minimize the engine output reduction. Therefore, from the results of FIGS. 3 and 4, it is understood that the temperature rising rate V is preferably 50 ° C./hr or more in order to make the pressure loss 2.5 kPa or less.

Next, the exhaust gas purification filters (Samples 21 to 27, Sample 31) were changed by changing the mass of the honeycomb formed body after drying and the temperature increase rate V of the first firing in the firing step (temporary firing in the first firing step). Sample 35) is prepared and evaluated.
Hereinafter, a method for manufacturing each sample will be described. In addition, it is basically the same as the manufacturing method described above.

First, a clay-like ceramic material was extruded and the obtained honeycomb formed body was dried. Table 2 shows the mass (dry mass Bkg) of each sample after drying.
Subsequently, temporary baking was performed by holding at a maximum temperature of 1390 ° C. for 5 hours. At this time, as shown in Table 2, with respect to Samples 21 to 27, the heating rate V was set to A ° C./hr or less. Moreover, about the samples 31-35, the temperature increase rate V was similarly made faster than A degree C / hr. However, A = 150 / B.

Next, after the plugging slurry was placed on the honeycomb formed body, main firing was performed by maintaining the slurry at a maximum temperature of 1440 ° C. for 30 hours. The main firing was performed under the same conditions for each sample.
Thus, exhaust gas purification filters (sample 21 to sample 27, sample 31 to sample 35) having a honeycomb structure provided with plug portions were produced.

In the thus obtained exhaust gas purification filters (Samples 21 to 27, Samples 31 to 35), evaluation of cracks after temporary firing was performed.
For evaluation of cracks, light was transmitted through the honeycomb formed body after the temporary firing, and the presence or absence of cracks inside was visually confirmed. The results are shown in Table 2.

  As can be seen from Table 2, no cracks were observed in Samples 21 to 27 having a temperature increase rate V of A ° C./hr or less. On the other hand, all of the samples 31 to 35 having the heating rate V higher than A ° C./hr were cracked. It is considered that this is because the temperature difference is generated in the honeycomb formed body by increasing the temperature rising rate V, and cracks are generated due to the accompanying thermal stress. Therefore, it can be seen that the temperature increase rate V is preferably set to A ° C./hr or less in order to suppress the occurrence of cracks during firing.

  From the above, in the first firing in the firing step, the pores formed by setting the heating rate V from 1000 ° C. to the maximum temperature (1390 ° C. in this example) to 50 to A ° C./hr. Can be suppressed from forming pores having a small pore diameter, in particular, fine pores having a pore diameter of 10 μm or less that cannot sufficiently collect particulates. The obtained exhaust gas purification filter has a reduced amount of fine pores with respect to the total pore volume of the partition wall, and has an excellent particulate collection function and a low pressure loss. Furthermore, generation | occurrence | production of the crack at the time of baking can be suppressed.

As the firing step, the first firing step of firing the honeycomb formed body is performed before the plugging step, and the honeycomb formed body is temporarily fired at a lower temperature than the firing after the plugging step. It is good also as a structure which performs a baking process.
In addition, the firing process may be configured to perform only the first firing process for main firing the honeycomb formed body after the plugging process.
In any case, in the first firing in the firing step, the same effect as in this example can be obtained by setting the temperature rising rate V from 1000 ° C. to the maximum temperature to 50 to A ° C./hr. it can.

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. The diagram which shows the relationship between the temperature increase rate V and the amount of micropores of 10 micrometers or less in an Example. The diagram which shows the relationship between the amount of micropores of 10 micrometers or less and a pressure loss in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification filter 10 Honeycomb structure 11 Partition 12 Cell 13 Plug part

Claims (6)

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,
Extrusion molding of a ceramic material containing a cordierite forming raw material, and forming a honeycomb molded body provided with a large number of cells by arranging porous partition walls in a honeycomb shape; and
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, firing is performed at a maximum temperature of 1300 to 1450 ° C., and a temperature increase rate from 1000 ° C. to the maximum temperature is 50 to A ° C./hr (however, after the drying step) (A = 150 / B, where Bkg is the mass of the honeycomb formed body.) In claim 1, the firing step includes a first firing step in which the honeycomb formed body is temporarily fired at a maximum temperature T ₁ before the plugging step.
After the plugging step, the honeycomb formed body is subjected to a main firing at a maximum temperature T ₂ (≧ T ₁ ) and a second firing step of forming the plug portion at the portion to be plugged. A method for producing an exhaust gas purification filter. According to claim 1, said calcination step, prior to said plug inserting process, a first firing step of the sintering of the honeycomb molded body at a maximum temperature T _2,
After the plugging step, the honeycomb formed body is temporarily fired at a maximum temperature T ₁ (≦ T ₂ ), and a second firing step of forming the plug portion in the portion to be plugged is provided. A method for producing an exhaust gas purification filter. In claim 1, the firing step, after the plug inserting process, as well as the firing the honeycomb molded body at a maximum temperature T _2, the first firing step of forming the plug portion in a portion to be the plugged only A method for producing an exhaust gas purification filter comprising: 4. The method for manufacturing an exhaust gas purification filter according to claim 2, wherein the maximum temperature T ₁ for pre-baking in the baking step is 1300 to 1400 ° C. 5. 5. The method for producing an exhaust gas purification filter according to claim ₂ , wherein the maximum temperature T ₂ of the main firing in the firing step is 1400 to 1450 ° C. 6.

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