JP5126681B2 - Ceramic honeycomb filter and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ceramic honeycomb filter and a manufacturing method thereof. In particular, the present invention relates to a ceramic honeycomb filter suitable for use in a ceramic honeycomb filter used for purifying exhaust gas containing PM discharged from a diesel engine or the like, and a method for manufacturing the same.

  In order to remove fine particles contained in the exhaust gas discharged from the diesel engine, the partition walls 3 of the ceramic honeycomb structure 1 are formed of a porous ceramic body, and the flow path 2 surrounded by the partition walls is connected to the exhaust gas inflow side 7. For collecting particulates in the exhaust gas by forming the plugging portions 4 and 5 alternately with the plugging material on the outlet side 8 and allowing the exhaust gas to pass through the partition walls. A ceramic honeycomb filter 10 (hereinafter abbreviated as a honeycomb filter) has been put into practical use (FIG. 1). In this honeycomb filter, if the collected fine particles are accumulated, the pores of the partition walls are clogged and the pressure loss becomes high. Therefore, it is necessary to burn and remove the accumulated fine particles and regenerate the honeycomb filter. . For this reason, as a function of the honeycomb filter, it is required to endure a use environment in which the deposited fine particles are repeatedly exposed to a high temperature when burning. Therefore, the honeycomb filter needs high heat resistance and high thermal shock resistance, and cordierite has been mainly used as a ceramic body constituting the partition walls. When the fine particles burn, the temperature of the ceramic honeycomb filter sometimes exceeds 1450 ° C., which is the melting point of cordierite, due to the heat of combustion of the fine particles, and the partition wall may be melted and the filter function may not be performed. Therefore, studies have been made to use aluminum titanate having a melting point of about 1860 ° C.

Patent Document 1 discloses a ceramic honeycomb filter in which end portions of predetermined flow paths of a ceramic honeycomb structure are sealed with a plugging material, and the thermal expansion coefficient αA of the ceramic honeycomb structure from 40 ° C. to 800 ° C. is 0. The relationship between the thermal expansion coefficient αB from 40 ° C to 800 ° C of plugged parts made of ceramic powder of 149 µm or less in the range of 8.0 × 10 ^-6 / ° C | αA-αB | ≦ 3.5 × 10 ^-6 It is described that the plugged portion does not fall off when the reaction phase is not substantially interposed at the contact portion between the ceramic honeycomb structure and the plugged portion. In addition, in the examples, the ceramic honeycomb structure of mullite-aluminum titanate was fired at 1400 ° C., and plugged with a cordierite-mullite or non-oriented cordierite plugging material, and then 1400 ° C. It is described that it is fired.

  In Patent Document 2, for the purpose of improving the heat resistance of the plugged portion, it has a plurality of flow paths that serve as fluid flow paths partitioned by a partition wall, and one end portion of the predetermined flow path is A honeycomb structure plugged by a plugging member, wherein the material of the plugging member is aluminum titanate or a composite material thereof, and the material of the partition walls is cordierite or a composite material thereof. A ceramic honeycomb structure is described.

  In Patent Document 3, the cross-sectional aperture ratio in the vicinity of the partition wall of the sealing portion is smaller than the cross-sectional aperture ratio in the vicinity of the central axis of the plugged portion, and the difference is 10% or more. A ceramic honeycomb structure is described in which the partition walls are not in partial contact with each other and there are voids therebetween.

  Patent Document 4 discloses that a ceramic raw material obtained by kneading at least a raw material powder, water, and a binder is extruded to form an outer skin, partition walls arranged in a honeycomb shape in the outer skin, and partition walls in the partition walls. Extrusion molding process for forming a ceramic honeycomb formed body having a large number of flow paths formed along the direction, drying process for drying, main firing process for firing until cordierite, plugging (plugging) There is described a method for manufacturing a ceramic honeycomb formed body having a plugging (plugging) step of performing a plug and a plug firing step of firing at a firing temperature lower than the firing temperature in the main firing step.

Japanese Examined Patent Publication No. 2-53083 JP 2007-21484 A JP 2006-116483 A JP 2008-120656 A

  The ceramic honeycomb filter described in Patent Document 1 has a ceramic honeycomb structure and a plugged portion that are closely bonded to the partition walls, and therefore, the ceramic honeycomb of mullite-aluminum titanate described in the examples. When the ceramic honeycomb filter is plugged with cordierite-mullite or non-oriented cordierite plugging material, the heat of the partition walls of the ceramic honeycomb structure is plugged when used as a ceramic honeycomb filter. There is a problem that the temperature of the plugged portion is increased and the plugged portion breaks.

  In addition, the ceramic honeycomb structure described in Patent Document 2 improves heat resistance by using aluminum titanate as the material of the plugging member, but the partition wall material is cordierite. In order to fire the plugged portion of aluminum titanate, it is necessary to fire at 1500 ° C. or higher, which exceeds the melting point of cordierite of 1450 ° C., and the partition wall melts and the firing cost of the plugged portion is reduced. There was a problem that it took.

  In the ceramic honeycomb structure described in Patent Document 3, since the partition wall portion and the plugging portion are formed of the same material, when aluminum titanate is used for the partition wall portion and the plugging portion, The sealing part must be fired at 1500 ° C. or higher as in the case of the partition part, and the cost of the plugging part is a problem.

  In addition, the method for manufacturing a ceramic honeycomb formed body described in Patent Document 4 is a plug firing in which the firing temperature in the main firing step for firing the ceramic honeycomb structure is in the range of 1430 ° C. ± 20 ° C., and the plugging material is fired. Since the firing temperature in the process is in the range of 1400 ± 20 ° C, since the temperature for firing the plugging material is low, the plugged portion may not be sufficiently cordierite, There was a problem that the strength was not ensured, the plugging portion dropped off, and the collection rate of the fine particles decreased.

  Accordingly, an object of the present invention is to provide a ceramic honeycomb filter that can be obtained at a low firing cost while ensuring the heat resistance as a ceramic honeycomb filter and the strength of the plugged portions and the partition walls, and a method for manufacturing the same. It is in.

That is, the ceramic honeycomb filter of the present invention is a ceramic honeycomb filter in which plugging portions are formed in a predetermined flow path of a ceramic honeycomb structure having flow paths partitioned by partition walls, wherein the ceramic honeycomb structure is It comprises a main crystal phase of at least aluminum titanate and a glass phase containing at least MgO and SiO _2, and the plugging portion has cordierite as the main crystal phase, and the partition walls of the ceramic honeycomb structure and the plugging The fusion part and the non-fusion part exist at the boundary part with the stop part, and the fusion part is a part integrated at the boundary between the partition wall and the plugging part of the ceramic honeycomb structure. Features.

  In the ceramic honeycomb filter of the present invention, it is preferable that a length ratio of the fused portion and the non-fused portion is 5/95 to 70/30.

  The method for manufacturing a ceramic honeycomb filter according to the present invention includes mixing and kneading ceramic raw material powder containing at least a titania source, an alumina source, a silica source, and a magnesia source, and extruding, drying, and firing into a honeycomb shape. A method for manufacturing a ceramic honeycomb filter, comprising: a fired body, plugging predetermined flow paths of the ceramic honeycomb fired body with a plugging material, firing the plugging material to obtain a ceramic honeycomb filter. The plugging material has cordierite or a composition that can be converted into cordierite, and the temperature at which the plugging material is fired is 100 ° C. or more lower than the firing temperature of the ceramic honeycomb fired body. The temperature raising rate from 800 ° C. to the maximum temperature in the process of firing the plugging material is 70 to 500 ° C./hr.

  In the method for manufacturing a ceramic honeycomb filter of the present invention, it is preferable that a holding time when firing the plugging material is 3 hours or more.

Next, the function and effect of the present invention will be described.
The ceramic honeycomb filter of the present invention is a ceramic honeycomb filter in which plugging portions are formed in a predetermined flow path of a ceramic honeycomb structure having flow paths partitioned by partition walls, wherein the ceramic honeycomb structure is at least titanium. The main crystal phase of aluminum oxide and a glass phase containing at least MgO and SiO ₂ , wherein the plugging portion has cordierite as the main crystal phase, and the partition walls of the ceramic honeycomb structure and the plugging portion The presence of the fused portion and the non-fused portion at the boundary between and has the following effects. That is, the presence of the fused portion and the non-fused portion at the boundary portion between the partition walls of the ceramic honeycomb structure and the plugged portions, the heat of the partition walls of the ceramic honeycomb structure when used as a ceramic honeycomb filter. Propagation to the plugged portion can be prevented, temperature rise of the plugged portion can be prevented, and cracking of the plugged portion can be prevented. Furthermore, since the partition walls and the plugging portions of the fired ceramic honeycomb fired body are firmly fixed, the plugging portions are removed, and a ceramic honeycomb filter is obtained in which the collection rate of fine particles does not decrease. is there. In the present invention, the fusion part refers to a part integrated at the boundary between the aluminum titanate containing the glass phase of the partition walls of the ceramic honeycomb structure and the cordierite of the plugged part.

  Further, in the ceramic honeycomb filter of the present invention, the length ratio of the fused portion and the non-fused portion is 5/95 to 70/30, and the following effects are obtained. That is, when the length ratio of the fused portion and the non-fused portion is 5/95 to 70/30, the fused portion and the non-fused portion are mixed at the boundary between the partition wall and the plugged portion of the ceramic honeycomb structure. When used as a ceramic honeycomb filter, the heat of the partition walls of the ceramic honeycomb structure is prevented from being transmitted to the plugging portion, the temperature rise of the plugging portion is prevented, and the plugging portion is prevented from cracking. Can do. Furthermore, a ceramic honeycomb filter in which partition walls and plugging portions are firmly fixed is obtained, and a ceramic honeycomb filter in which the plugging portions are not dropped and the collection rate of fine particles is not reduced is obtained. When the length ratio of the fused part and the non-fused part is less than 5/95, the fixing strength between the partition wall and the plugged part is weak, the plugged part falls off, and the particulate collection rate decreases. This is not preferable. On the other hand, when the length ratio of the fused part and the non-fused part exceeds 70/30, when used as a ceramic honeycomb filter, the heat of the partition walls of the ceramic honeycomb structure is transferred to the plugged part, and the temperature of the plugged part An increase is caused, and the plugged portion may be broken, which is not preferable. Preferably, it is 10 to 60%. Note that the length of the fusion part is the value obtained by observing the surface of the plugged part parallel to the flow path direction with an electron microscope and measuring the length of the fusion part excluding the voids linearly. It is expressed as a percentage divided by the total length. In the present invention, the fusion part does not need to be formed continuously at the boundary between the partition wall and the plugging part, and has a gap discontinuously at the boundary part between the partition wall and the plugging part. Also good.

Further, in the method for producing a ceramic honeycomb filter of the present invention, a ceramic raw material powder containing at least a titania source, an alumina source, a silica source, and a magnesia source is mixed, kneaded, extruded into a honeycomb shape, dried, and fired to obtain a ceramic honeycomb. A method for manufacturing a ceramic honeycomb filter, comprising: a fired body, plugging predetermined flow paths of the ceramic honeycomb fired body with a plugging material, firing the plugging material to obtain a ceramic honeycomb filter. The plugging material has cordierite or a composition that can be converted into cordierite, and the temperature at which the plugging material is fired is 100 ° C. or more lower than the firing temperature of the ceramic honeycomb fired body. In the process of firing the plugging material, the heating rate from 800 ° C. to the maximum temperature is 70 to 500 ° C./hr. With the results. That is, when a ceramic raw material powder containing at least a titania source, an alumina source, a silica source, and a magnesia source is mixed, kneaded, extruded into a honeycomb shape, dried, and fired to obtain a ceramic honeycomb fired body, the firing temperature is In order to synthesize aluminum titanate, it must be performed at 1500 ° C. or higher. The fired ceramic honeycomb structure includes a main crystal phase of aluminum titanate and a glass phase containing at least MgO and SiO2, and has a composition that can be converted into cordierite or cordierite. Is fired at a temperature 100 ° C. or more lower than the firing temperature of the ceramic honeycomb fired body, so that the alumina titanate containing the glass phase of the partition walls of the fired ceramic honeycomb fired body and the cordier of the plugging portion are obtained. A fusion part is formed at the boundary of the light. Furthermore, the temperature increase rate from 800 ° C. to the maximum temperature in the process of firing the plugging material is 70 to 500 ° C./hr, so that the plugging material is quickly heated to the cordierite synthesis temperature range. For this reason, the thermal shrinkage of the plugging material is suppressed to be small, and a part of the plugging material and the partition wall come into contact with each other. And since the plugging material has a larger capacity than the thin wall partition wall, the plugging material in the vicinity of the partition wall heats faster than the inside of the plugging material away from the partition wall due to the difference in heat capacity between them. Then, a part of the plugging material in the vicinity of the partition wall and the partition wall are fused, and a fusion part and a non-fusion part are formed at the boundary part between the partition wall and the plugging part. As a result, when the fused portion and the non-fused portion are mixed at the boundary portion between the partition wall and the plugging portion of the ceramic honeycomb structure, and the ceramic honeycomb filter is used as a ceramic honeycomb filter, the heat of the partition wall of the ceramic honeycomb structure is It is possible to prevent the temperature of the plugged portion from rising and prevent the plugged portion from cracking. Furthermore, the partition walls and the plugging portions of the ceramic honeycomb fired body are firmly fixed. Therefore, it is possible to provide a method for manufacturing a ceramic honeycomb filter in which the plugged portion does not fall off and the collection rate of the fine particles does not decrease. The temperature at which the plugged portion is fired is preferably 150 ° C. or more lower than the firing temperature at which the ceramic honeycomb fired body is obtained. Therefore, the firing temperature of the ceramic honeycomb fired body is preferably 1550 ° C. or higher for sufficient synthesis of aluminum titanate, and the plugged portions are sufficiently cordierite. Is preferably 1400 ° C. or higher.
Here, if the rate of temperature increase is too slow, less than 70 ° C./hr, the plugging material is not quickly heated to the cordierite synthesis temperature range, so that the entire plugged portion tends to heat shrink uniformly. Thus, the ratio of the non-fused portion is increased at the boundary portion between the plugged portion and the partition wall, and the plugged portion falls off, so that the collection rate of the fine particles is not preferable. On the other hand, if the rate of temperature rise exceeds 500 ° C./hr, it is not preferable because the temperature distribution in the honeycomb structure becomes too large and cracks are generated in the honeycomb structure due to thermal stress. Preferably, it is 80-400 degreeC / hr.
If necessary, the ceramic raw material may contain a pore former, a binder or the like.

  Further, in the method for manufacturing a ceramic honeycomb filter of the present invention, when the plugging material is fired for a holding time of 3 hours or more, the following effects are obtained. That is, when the plugging material is fired for a holding time of 3 hours or more, formation of a fusion portion proceeds at the boundary between the partition walls and the plugging portion of the fired ceramic honeycomb fired body, and firing is performed. The partition walls and plugging portions of the fired ceramic honeycomb fired body are more firmly fixed. Even if the holding time is lengthened, the energy required for firing increases and the production cost increases. Therefore, the time is preferably 4 to 10 hours.

  According to the present invention, it is possible to provide a ceramic honeycomb filter that can be obtained at a low firing cost while ensuring the heat resistance as a ceramic honeycomb filter and the strength of the plugged portions and the partition walls, and a method for manufacturing the ceramic honeycomb filter. .

Next, the present invention will be described based on embodiments.
As a ceramic raw material powder so as to have an aluminum titanate composition, titania powder 44% by mass, alumina powder 56% by mass, and a total of 100% by mass of these, silica powder 3% by mass, magnesia powder 1.0% by mass, 14% Mixing, kneading, extruding, and drying a mass% foamed resin and 6 mass% methylcellulose to obtain a raw honeycomb structure having an outer diameter of 50 mm, a length of 90 mm, a partition wall thickness of 0.25 mm, and a partition wall pitch of 1.4 mm It was. The honeycomb structure of the green body is heated at an average speed of 50 ° C./hr in a temperature range from 1300 ° C. to 1350 ° C. and fired at the maximum holding temperature shown in Table 1 to obtain an aluminum titanate honeycomb fired body. did. A plugging film was affixed to one end face of the obtained honeycomb fired body, and a hole was formed with a laser in a predetermined flow path portion where a plugging portion of the plugging film was to be formed. Then, cordierite-producing raw material powder containing 50% by mass of SiO ₂ , 35% by mass of Al ₂ O ₃ and 15% by mass of MgO by adjusting kaolin, talc, silica, and alumina powder, methyl cellulose, lubricant Then, water was added to prepare a plugging portion forming slurry, and the plugging portion was formed to have a length of 10 mm by dipping the slurry on one end face portion of the honeycomb fired body. The other end surface portion was formed in the same manner. The ceramic honeycomb filters of Examples 1 to 12 and Comparative Examples 1 to 2 were fired at the temperature rising rate from 800 ° C. to the maximum temperature, the maximum holding temperature, and the holding time under the conditions shown in Table 1. Got. Further, in the ceramic honeycomb filter of Comparative Example 3, the plugged portions were made of aluminum titanate as in the ceramic honeycomb structure.
After firing, the plugged portion was cut to confirm the state of the partition wall and the fused portion of the plugged portion. The length ratio of the fusion part and the non-fusion part was measured as follows. The surface of the plugged portion cut in parallel to the flow path direction, the boundary between the plugged portion and the partition wall was observed with the electron microscope over the entire length of the plugged portion, and the length of the fused portion was determined from the microphotographs in each field of view. The values obtained by linearly measuring the thickness in the flow path direction are summed, and the value is divided by the length of the non-fused portion subtracted from the total length of the plugged portion, and measured in the same manner at five arbitrary plugged portions. And that was the average.

  Further, the strength of the plugged portion was evaluated as follows. A stainless steel round bar with a diameter of 1 mm is inserted into the flow path in which the plugged portion is formed, and the load when the plugged portion is damaged by applying a load to the round bar is measured. The average value was calculated. And the relative value which set the plugging part intensity | strength of the comparative example 1 to 1 exceeded 1.5, and (triangle | delta), and what exceeded 1.5 and 2.0 or less ((circle)). ), Those exceeding 2.0 were indicated by (◎), and those below 1.0 were indicated by (×).

Further, as an evaluation of the heat resistance of the ceramic honeycomb filter, the following evaluation was made. The cracking state of the honeycomb filter at high temperature was introduced from the exhaust gas inflow side end face side with an air flow rate of 2Nm ³ / min and carbon powder with a particle size of 0.042μm at 3g / h for 1 hour. Carbon powder is deposited on the partition walls. Next, air at 800 ° C. is allowed to flow at 0.1 Nm ³ / min for 5 minutes from the exhaust gas inflow side end face of the honeycomb filter to burn carbon powder. Next, air at 50 ° C. is flowed from the exhaust gas inflow side end face of the honeycomb filter at 0.1 nm ³ / min for 5 minutes to cool the honeycomb filter. After the above carbon powder is charged, burned, and cooled in the same manner 20 times, the presence or absence of cracks in the plugged portion of the honeycomb filter is confirmed. The results are shown in Table 1. In Table 1, the evaluation is indicated by ◎ for those in which cracks cannot be confirmed, ◯ for those in which cracks that do not affect actual use are confirmed, and × in which cracks that have an effect on actual use are confirmed.

As shown in Table 1, as shown in Table 1, the ceramic honeycomb filters of Examples 1 to 12 are excellent in the strength of the plugged portions, and when used as ceramic honeycomb filters, the plugged portions are cracked. It can be seen that it can be prevented. On the other hand, in the ceramic honeycomb filters of Comparative Examples 1 and 2, the temperature at which the plugging material is fired is the same as the firing temperature of the ceramic honeycomb fired body, or less than 100 ° C., in the process of firing the plugging material. Since the rate of temperature increase from 800 ° C to the maximum temperature is less than 70 ° C / hr, the entire plugged portion thermally shrinks uniformly, forming a fusion zone at the boundary between the plugged portion and the partition wall It can be seen that the plugged portion was not removed and the partition wall and the plugged portion were not firmly fixed.

It is a schematic cross section of the ceramic honeycomb filter according to the present invention.

Explanation of symbols

1: Ceramic honeycomb structure 2: Flow path 3: Partition wall 4, 5: Plugging portion 7: Exhaust gas inflow side 8: Exhaust gas outflow side 10: Ceramic honeycomb filter

Claims (4)

A ceramic honeycomb filter having a plugged portion formed in a predetermined flow path of a ceramic honeycomb structure having flow paths partitioned by partition walls, wherein the ceramic honeycomb structure has at least a main crystal phase of aluminum titanate, It consists of a glass phase containing MgO and SiO ₂ , the plugged portion has cordierite as the main crystal phase, and the fusion portion and the non-plugged portion at the boundary between the partition walls of the ceramic honeycomb structure and the plugged portion. A ceramic honeycomb filter, wherein a fusion part is present, and the fusion part is a part integrated at a boundary between a partition wall and a plugging part of the ceramic honeycomb structure . 2. The ceramic honeycomb filter according to claim 1, wherein a length ratio of the fused portion and the non-fused portion is 5/95 to 70/30. A ceramic raw material powder containing at least a titania source, an alumina source, a silica source, and a magnesia source is mixed and kneaded, extruded into a honeycomb shape, dried and fired to obtain a ceramic honeycomb fired body, and a predetermined flow of the ceramic honeycomb fired body is determined. The method for manufacturing a ceramic honeycomb filter according to claim 1, further comprising a step of plugging a path with a plugging material and firing the plugging material to form a ceramic honeycomb filter. In the process of firing the plugging material, the material has a composition capable of being cordierite, and the firing temperature of the plugging material is 100 ° C. lower than the firing temperature of the ceramic honeycomb fired body. A method for manufacturing a ceramic honeycomb filter, wherein a temperature rising rate from 800 ° C. to a maximum temperature is 70 to 500 ° C./hr. 4. The method for manufacturing a ceramic honeycomb filter according to claim 3, wherein a holding time when firing the plugging material is 3 hours or more.

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