JP5725395B2 - Cordierite ceramic honeycomb filter and manufacturing method thereof - Google Patents

Description

  The present invention relates to a ceramic honeycomb filter including a cordierite base material in which a predetermined channel is plugged with a plugging material, and a method for manufacturing the same.

PM (Particulate) mainly composed of black smoke in exhaust gas from diesel engines
Matter (particulate matter) is contained in large quantities, and if it is released into the atmosphere, it will adversely affect the human body and the environment. For this reason, an exhaust gas system such as a diesel engine is equipped with a filter for collecting and purifying PM. FIG. 1 shows an example of a ceramic honeycomb filter (hereinafter referred to as “honeycomb filter”) 10 made of a ceramic base material that collects and purifies PM in automobile exhaust gas, where (a) is a front view and (b) one. It is the side view which cut the section. In FIG. 1, the honeycomb structure 11 has a large number of flow paths 15a and 15b partitioned by partition walls 14 inside the outer peripheral wall 11a. Then, predetermined flow paths 15 a and 15 b on both end faces 12 a and 12 b of the honeycomb structure 11 are alternately plugged with plugging materials 13 a and 13 b, thereby forming a honeycomb filter 10. Although not shown, the honeycomb filter 10 is gripped so that the outer periphery of the outer peripheral wall 11a of the honeycomb structure 11 is not moved during use by a gripping member formed of a metal mesh or a ceramic mat or the like. Arranged in the storage container.

  In the honeycomb filter 10 as shown in FIG. 1, exhaust gas purification is performed as follows. Exhaust gas (indicated by a dotted arrow) flows from the cell 15b that opens to the end face 12a. The PM contained in the exhaust gas is collected when passing through the partition wall 14, and the purified exhaust gas flows out from the flow path 15a opened in the end face 12b and is released into the atmosphere.

  A honeycomb filter 10 as shown in FIG. 1 has been manufactured by the following process. First, a ceramic raw material for forming a cordierite ceramic honeycomb structure and a raw material other than a binder are weighed, mixed and kneaded to form a clay. Next, the kneaded material is extruded from, for example, a honeycomb-shaped die of a screw extruder, and at the same time, deformation that occurs in the drying or firing process is anticipated, and is cut longer than the target dimension to obtain a formed body having a honeycomb structure. Then, the formed body is dried and fired to obtain a cordierite ceramic honeycomb structure. Next, the end faces 12a and 12b are processed with a grinding tool such as a diamond cutter or a diamond saw to obtain a honeycomb structure 31 having a predetermined length. Furthermore, in the plugging step, the flow paths 15a and 15b on both end faces 12a and 12b of the honeycomb structure 11 are sealed with plugging materials 13a and 13b, respectively. 2A to 2C are schematic views of this plugging process. In FIG. 2 (a), a plugging film 21 is attached to one end face 12a of the honeycomb structure 11, and the through-holes 22 are aligned with the cells 15a by using a laser or the like on the plugging film 21, for example. Forms in a staggered pattern. Next, in FIG. 2B, the honeycomb structure 11 is inverted and immersed in a slurry 23 containing a plugging material having a cordierite composition, and the slurry 23 is inserted into the through holes 22 of the plugging film 21. The flow path 15a is filled to a predetermined depth. Next, in FIG. 2C, the filled slurry 23 is cured and dried to obtain a honeycomb structure 11 in which one end face 12a side is alternately plugged with the plugging material 13a. Similarly, the other end face 12b side is alternately sealed with the plugging material 13b, the plugging film 21 is removed, the plugging material is dried and baked, and the cord shown in FIG. A honeycomb filter 10 made of an elite base material is used.

  When the honeycomb filter made of such a cordierite base material is dried and fired, the plugging material shrinks and its volume decreases, so that the volume between the plugged portion and the partition wall is reduced. A gap is created. In that case, there is a problem that the PM collection rate is reduced, or cracks are generated between the plugged portions and the partition walls, and the plugged portions are dropped. In order to solve this, Patent Document 1 discloses that the plugging material is composed of a pulverized ceramic material of the same material as the ceramic raw material for forming the ceramic honeycomb structure, and preferably 70 to 80% by weight of the fired pulverized material of the ceramic substrate. A honeycomb filter composed of 20 to 30% by weight of an unfired pulverized product and a manufacturing method thereof have been proposed. According to Patent Document 1, the volume of the plugging material is reduced due to shrinkage caused by drying of the plugging material, cracks are generated in the plugged portion, or the plugged portion is dropped. The problem is solved, the bonding strength between the partition wall and the plugging portion is ensured, and the plugging portion can be made difficult to peel off or drop off.

  In addition, the present inventor disclosed in Patent Document 2 that the ceramic raw material of the plugging material is composed of an unfired pulverized product of the ceramic base material and a fired pulverized product of the ceramic base material. It was disclosed that the product was 40 to 80%, and the fired and pulverized product was 20 to 60%. According to Patent Document 2, a ceramic honeycomb filter in which the bonding strength between the partition walls and the plugging portions is stable can be manufactured.

JP 2002-136817 A JP 2008-136919 A

  However, in the plugging material proposed in Patent Document 1, the phenomenon that the volume of the plugging material is reduced due to shrinkage that occurs when the plugging material is dried and fired is alleviated, but further, In some cases, the bonding strength between the partition walls and the plugging portions is not stable and sufficient strength cannot be ensured. Then, a gap is generated between the plugged portion and the partition wall, and the PM collection rate is reduced, or a crack is generated between the plugged portion and the partition wall so that the plugged portion is dropped. Had a problem. Moreover, it was difficult to stabilize the length of the plugged portion.

  Further, in the plugging material proposed in Patent Document 2, the phenomenon that the volume of the plugging material is reduced due to the shrinkage that occurs when the plugging material is dried and fired is difficult to be mitigated. In some cases, the bonding strength with the sealing portion is not stable and sufficient strength cannot be ensured. Then, a gap is generated between the plugged portion and the partition wall, and the PM collection rate is reduced, or a crack is generated between the plugged portion and the partition wall so that the plugged portion is dropped. Had a problem. Moreover, it was difficult to stabilize the length of the plugged portion.

  The problem of the present invention is that the gap generated between the plugged portion and the partition wall is less likely to be generated due to the shrinkage that occurs when the plugging material is dried and fired, and the PM collection rate is improved. Is to obtain a honeycomb filter comprising a cordierite base material having a good plug strength and a stable plugged portion, and a method for manufacturing the honeycomb filter.

  The inventors of the present invention have described that the ceramic raw material used as the plugging material is a phenomenon in which the volume of the plugging material decreases due to shrinkage that occurs when the plugging material is dried and fired, and the partition wall and the plugging material. As a result of intensive studies on how it affects the bond strength, the following findings were obtained. That is, it is composed of a cordierite blended raw material blended to become cordierite after firing as a plugging material, and a cordierite fired powder fired in advance, having a predetermined sphericity, Obtaining knowledge that the above problems can be solved, the present invention has been conceived.

That is, the cordierite ceramic honeycomb filter of the present invention is a cordierite ceramic honeycomb filter in which predetermined channels of a ceramic honeycomb structure made of a cordierite base material are plugged with a plugging material. The ceramic raw material of the plugging material is composed of a cordierite blended raw material blended to become cordierite after firing, and a cordierite fired powder fired in advance, and the cordierite The fired powder has a sphericity of 0.5 or more , an average particle size of 70 to 230 μm , and a mass ratio of 30 to 70% with respect to the ceramic raw material.

Next, the function and effect of the present invention will be described.
The cordierite ceramic honeycomb filter of the present invention is a cordierite ceramic honeycomb filter in which a predetermined flow path of a ceramic honeycomb structure made of a cordierite base material is plugged with a plugging material, The ceramic raw material of the plugging material is composed of a cordierite blended raw material blended so as to become cordierite after firing, and a cordierite fired powder fired in advance, and the cordierite fired powder Has a sphericity of 0.5 or more and a mass ratio of 30 to 70% with respect to the ceramic raw material, so that the plugging material shrinks when the plugging material is dried and fired. A decrease in volume is suppressed, a gap is hardly formed between the plugged portion and the partition wall, and the PM collection rate is improved. Furthermore, a honeycomb filter made of a cordierite base material having a good plug strength between the partition walls and the plugged portions and having a stable length of the plugged portions can be obtained.

  That is, the ceramic raw material of the plugging material is composed of a cordierite blended raw material blended so as to become cordierite after firing, and a cordierite fired powder fired in advance, and the cordierite fired powder When the sphericity is 0.5 or more, the surface area of the cordierite calcined powder is reduced, the cordierite compounding raw material becomes easy to adhere to the cordierite calcined powder, and the bonding strength of the plugging material is good Thus, the bonding strength between the plugging material and the partition wall is also improved. In addition, the fluidity of the plugging material is improved, an increase in viscosity when the plugging material is filled in the flow path is suppressed, and a plugged portion having a stable length can be obtained. Further, when the plugging material is fired by having 30 to 70% by mass ratio of the pre-fired cordierite fired powder having a sphericity of 0.5 or more with respect to the ceramic raw material, Since the erite baked powder has been baked, it does not shrink during firing, and therefore, as a whole plugging material, shrinkage during the cordierite-forming reaction is suppressed, and a decrease in the volume of the plugging material is suppressed. it can. Furthermore, since the sphericity is 0.5 or more as described above, the bonding strength of the plugging material is good, and a gap is hardly formed between the plugged portion and the partition wall, and the PM collection rate is high. It becomes good. When the cordierite fired powder is less than 30%, the effect of suppressing shrinkage of the plugging material as a whole when the plugging material is fired is reduced, and the effect of suppressing the volume reduction of the plugging material is reduced. Thus, a gap is easily generated between the plugged portion and the partition wall, and the PM collection rate is lowered. On the other hand, when it exceeds 70%, the amount of the cordierite blending raw material fixed by firing becomes relatively small, so when the plugging material is fired, the bonding of the plugging material becomes weak, and further, The bonding strength between the sealing material and the partition wall also becomes weak, and the plugging portion may drop off. The sphericity is preferably 0.6 or more, and the cordierite fired powder is preferably 35 to 65% by mass ratio with respect to the ceramic raw material.

  Here, the sphericity of the cordierite calcined powder is calculated from the projected area and the straight line passing through the center of gravity obtained for each projected image of 20 particles obtained from an electron micrograph using an image analyzer. This is the average value of the ratio of the area of the circle with the maximum value of the length between the two points as the diameter.

  A cordierite fired powder having a sphericity of 0.5 or more can be obtained, for example, as follows. Cordierite raw material powder is prepared, water is added to this to prepare a cordierite raw material slurry, and then the moisture is evaporated by a spray dryer, so that cordierite has a sphericity of 0.5 or more To obtain granulated granules. By firing the cordierite-formed granules at a temperature of 1300 ° C. or higher, a powder having a cordierite composition with a sphericity of 0.5 or higher can be obtained.

  In the cordierite ceramic honeycomb filter of the present invention, the average particle size of the cordierite fired powder is preferably 50 to 250 μm for the following reason. When the average particle size of the cordierite fired powder is 50 to 250 μm, when the plugging material is dried, the cordierite blended raw material is filled between the cordierite fired powder of 50 to 250 μm and Even if the sealing material is dried, it is difficult to reduce the volume of the plugging material, and it is difficult to form a gap between the plugging portion and the partition wall, which improves the PM collection rate. Preferably, it is 70-230 micrometers.

  Next, a method for producing a cordierite ceramic honeycomb filter of the present invention includes cordierite that is plugged with a plugging slurry in a predetermined flow path of a ceramic honeycomb structure made of a cordierite base material and fired. A method for producing a porous ceramic honeycomb filter, wherein the plugging slurry comprises a cordierite blended raw material blended to be cordierite after firing and a cordierite fired powder fired in advance When the cordierite fired powder has a sphericity of 0.5 or more and contains 30 to 70% by mass with respect to the ceramic raw material, the plugging material is dried and fired. It is suppressed that the volume of the plugging material is reduced due to the shrinkage that occurs, and a gap is hardly generated between the plugged portion and the partition wall, and the PM collection rate is improved. . Furthermore, a honeycomb filter made of a cordierite base material having a good plug strength between the partition walls and the plugged portions and having a stable length of the plugged portions can be obtained.

  In the method for producing a cordierite ceramic honeycomb filter of the present invention, the sealing slurry preferably has a moisture content of 35 to 60% by mass with respect to the ceramic raw material for the following reason. By having a moisture content of 35 to 60% with respect to the ceramic raw material, the fluidity of the plugging material is improved, and a plugged portion having a stable plugging length can be obtained. When it is less than 35%, it becomes difficult to obtain the fluidity of the plugging material, and it becomes difficult to fill the flow path with the plugging material. On the other hand, if it exceeds 60%, shrinkage increases when the plugging material dries, and a gap is likely to be formed between the plugged portion and the partition wall, which is not preferable because the PM collection rate decreases. Preferably, it is 40 to 55%.

  In the method for producing a cordierite ceramic honeycomb filter of the present invention, the plugging slurry contains 0.5 to 3.0% by mass of a cellulose derivative having a viscosity of 4000 cP or less in a 2% aqueous solution with respect to the ceramic raw material. It is preferable for the following reason. By including 0.5 to 3.0% of a cellulose derivative having a viscosity of 4000 cP or less in a 2% aqueous solution with respect to the ceramic raw material, when the plugging material is dried and fired, the bonding between the ceramic raw materials becomes good. The bond strength between the partition wall and the plugged portion is improved. Furthermore, the fluidity of the plugging material is improved, and a plugged portion having a stable plugging length can be obtained. If it is less than 0.5%, shrinkage increases when the plugging material dries, and a gap is likely to be formed between the plugged portion and the partition wall, which is not preferable because the PM collection rate is reduced. On the other hand, if it exceeds 3.0%, it is difficult to obtain the fluidity of the plugging material, and it is difficult to fill the flow path with the plugging material. Preferably, it is 0.7 to 2.8%. As the cellulose derivative, methylcellulose, hydroxypropylmethylcellulose, and the like can be used.

  In the method for manufacturing a cordierite ceramic honeycomb filter of the present invention, the plugging slurry is preferably kneaded in an atmosphere reduced from atmospheric pressure by 80 kPa or more for the following reason. By kneading the plugging slurry in an atmosphere reduced from atmospheric pressure to 80 kPa or more, the air entrained during the kneading can be removed from the plugging slurry, and the generation of voids in the plugging portion is prevented. Can do.

  In the method for producing a cordierite ceramic honeycomb filter of the present invention, the plugging slurry preferably has an aluminum hydroxide content of not more than 10% by mass with respect to the cordierite-blended raw material for the following reason. by. Aluminum hydroxide promotes the shrinkage of the plugging material by diffusing the crystal water when the plugging material is fired. When the mass ratio is 10% or less, the shrinkage is alleviated and the plugging material is prevented from shrinking. If it exceeds 10%, the contribution to the shrinkage of the plugging material becomes remarkable, the plugging material shrinks, and a gap is easily formed between the plugged portion and the partition wall, and the PM collection rate is lowered. This is not preferable. Preferably, it is 8% or less.

In the method for producing a cordierite ceramic honeycomb filter according to the present invention, it is preferable that the end surface of the ceramic honeycomb structure is subjected to water content of 0.2 g / cm ² or more before plugging with the plugging slurry. Because of the reason. Before plugging with the plugging slurry, by performing water content of 0.2 g / cm ² or more on the end face of the ceramic honeycomb structure, when the plugging material dries, the boundary between the plugged portion and the partition wall The drying of the portion becomes slow, and it becomes difficult to form a gap between the plugged portion and the partition wall, and the PM collection rate is improved. A water content of less than 0.2 g / cm ² is not preferable because a gap is likely to be formed between the plugged portion and the partition wall, and the PM collection rate is reduced. Preferably it is 0.3 g / cm ² or more.

  According to the present invention, it is possible to suppress the volume of the plugging material from being reduced due to shrinkage that occurs when the plugging material is dried and fired, and it is difficult to generate a gap between the plugging portion and the partition wall. A honeycomb filter comprising a cordierite base material having a good plug strength and a good bond strength between the partition walls and the plugging portions and having a stable length of the plugging portions, and a method for producing the same. it can.

An example of the ceramic honeycomb filter 10 which collects and purifies PM in the exhaust gas which concerns on this invention is shown, (a) is a front view, (b) It is sectional drawing. It is the schematic diagram which showed the plugging process which concerns on this invention.

Embodiments of the present invention will be described below.
Cordierite-type ceramic honeycomb structure in which kaolin, talc, silica, and alumina powder are prepared and the mass ratio is SiO ₂ : 48 to 52%, Al ₂ O ₃ : 33 to 37%, MgO: 12 to 15% Prepare the body forming ceramic raw material, add graphite as a binder such as methylcellulose and hydroxypropylmethylcellulose, lubricant, pore forming material, mix thoroughly by dry process, add specified amount of water, and knead sufficiently A plasticized ceramic clay was produced. Next, the kneaded material was extruded using an extrusion molding die and cut into a predetermined length to obtain a molded body having a honeycomb structure. Next, the molded body was dried using a microwave drying apparatus, and then fired at a temperature of 1425 ° C., and a cordy having an outer diameter of 266.7 mm, an overall length of 304.8 mm, a partition wall thickness of 0.3 mm, and a partition wall pitch of 1.5 mm. A honeycomb structure made of an elite ceramic base material was obtained.

Next, as a plugging material, a cordierite blending raw material and a pre-fired cordierite fired powder are blended as shown in Table 1, and further, methylcellulose having a viscosity of 1500 cP in a 2% aqueous solution as an organic binder and Water was added and kneaded under reduced pressure from atmospheric pressure shown in Table 1 to prepare a slurry-like plugging material. The cordierite fired powder fired in advance was obtained as follows. A mass _{ratio, SiO 2: 48~52%, Al} 2 O 3: 33~37%, MgO: the cordierite raw material powder to be 12 to 15% formulated, cordierite-forming raw material slurry by adding water And changing the inlet temperature to the spray dryer to obtain cordierite-formed granules with different sphericity. The cordierite-formed granules are fired at a temperature of 1400 ° C. to obtain a pre-fired cordierite fired powder. Then, based on the plugging step of FIG. 2 described above, plugging was performed on the honeycomb structure so that the plugging portion length was 10 mm. Further, after the plugging material, the plugged honeycomb filter was heated to 1400 ° C., and the partition wall and the plugging material were fixed and integrated.

Next, the state of the gap between the plugged portion and the partition wall was evaluated by the PM collection rate. The collection rate is measured at a pressure loss test stand with an air flow rate of 10 Nm ³ / min and carbon powder with a particle size of 0.042 μm being charged at a rate of 3 g / h to the honeycomb filter every minute. The number of carbon powder particles flowing into the filter and the number of carbon powder particles flowing out of the honeycomb filter are measured by SMPS (Scanning
Measurement was performed using Mobility Particle Sizer. The number of carbon powder particles was measured using a model 3936 manufactured by TIS. From the number Nin of carbon powder particles flowing into the honeycomb filter from 3 to 4 minutes from the start of charging and the number Nout of carbon powder particles flowing out from the honeycomb filter, the collection efficiency is expressed by the formula: (Nin−Nout) / Nin
Determined by As a result, the collection rate is
98% or more (◎),
If it is 95% or more and less than 98% (○),
If less than 95% (×),
The collection efficiency was evaluated as

Next, the bonding strength between the plugged portions and the partition walls was evaluated. The bonding strength between the plugging part and the partition wall is calculated by calculating the average value of 10 locations by pressing a round bar-shaped indenter with a 1 mm diameter tip into the plugging material and measuring the load when the indenter is pushed through. Asked. Then, assuming that the bonding strength of Comparative Example 1 using 100% cordierite blending raw material as the plugging material is 1.0, the bonding strength between the plugging portion and the partition wall is relatively compared,
When the bonding strength of Comparative Example 1 exceeds 2.0 times (◎),
The case where the bond strength of Comparative Example 1 exceeds 1.0 times and is 2.0 times or less (O),
The case where the bonding strength of Comparative Example 1 is 1.0 times or less (×)
As evaluated.

Next, the length of the plugged portion was evaluated as follows. Insert a metal rod in the shape of a round bar with a 1 mm diameter tip from the opposite side of the plugged flow path, and plug it from the length of the metal bar inserted into the flow path when it reaches the plugged portion. The length of the stop was measured, and the average value at 10 locations was calculated. As a result, the length of the plugged portion is 10mm for the target,
When it is 8-12mm (◎),
When it is 6mm or more and less than 8mm or more than 12mm and 14mm or less (○),
Less than 6mm or more than 14mm (×)
As evaluated.
These results are shown in Table 1.

From Table 1, it can be seen that Examples 1 to 6 of the present invention are excellent in PM collection rate, bonding strength, and plugging portion length. On the other hand, it can be seen that Comparative Examples 1 to 5 have problems in any aspect of PM collection rate, bonding strength, and plugging portion length.

10: Ceramic honeycomb filter (honeycomb filter)
11: Ceramic honeycomb structure (honeycomb structure)
11a: outer peripheral walls 12a, 12b: end faces 13a, 13b: plugging materials 14: partition walls 15a, 15b: flow channels 21: plugging films 22: through holes 23: slurry

Claims (1)

A cordierite-type ceramic honeycomb filter in which a predetermined flow path of a ceramic honeycomb structure made of a cordierite base material is plugged with a plugging material, and the ceramic raw material of the plugging material is: It is composed of cordierite blended raw material blended to become cordierite after firing and cordierite fired powder pre-fired, the cordierite fired powder has a sphericity of 0.5 or more and an average particle size Is a cordierite ceramic honeycomb filter, characterized by having a mass ratio of 30 to 70% with respect to the ceramic raw material.

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