Honeycomb filter

Abstract

To provide a honeycomb filter configured so that pressure loss is low in the early stage of an exhaust gas treatment and hardly rises even if PMs accumulate.SOLUTION: In a honeycomb having a sealed portion, an exhaust gas introduction cell is constituted of a first exhaust gas introduction cell 12 and a second exhaust gas introduction cell 14 which is larger in cell cross sectional area than the first exhaust gas introduction cell, where cross sectional areas of an exhaust gas exhaust cell 11 are equal to or larger than cross sectional areas of the second exhaust gas introduction cell. Cross sections of the exhaust gas exhaust cell and the exhaust gas introduction cells are polygonal. A length L1 of a side at which the first exhaust gas introduction cell opposes to the exhaust gas exhaust cell is longer than a length L2 of a side at which the second exhaust gas introduction cell opposes to the exhaust gas exhaust cell. A cell bulkhead 13 includes: a first cell bulkhead 13a partitioning the first and second exhaust gas introduction cells; a second cell bulkhead 13b partitioning the first exhaust gas introduction cell and the exhaust gas exhaust cell; and a third cell bulkhead 13c partitioning the second exhaust gas exhaust cell and the exhaust gas exhaust cell, where a thickness Ta of the first cell bulkhead is smaller than thicknesses Tb and Tc of the second cell bulkhead and the third cell bulkhead.SELECTED DRAWING: Figure 2B

Description

Technical Field

[0001] The present invention relates to a honeycomb filter.

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as diesel engines contains particulate matter such as soot (hereinafter also referred to as PM). In recent years, there has been a problem that this PM harms the environment or the human body. In addition, since the exhaust gas also contains harmful gas components such as CO, HC, or NOx, there is also concern about the influence of these harmful gas components on the environment or the human body.

[0003] Therefore, as an exhaust gas purification device that collects PM in exhaust gas or purifies harmful gas components in exhaust gas such as CO, HC, or NOx by being connected to an internal combustion engine, honeycomb-structured filters (honeycomb filters) made of porous ceramics such as cordierite and silicon carbide have been variously proposed.

[0004] In addition, in these honeycomb filters, in order to improve the fuel consumption of the internal combustion engine and eliminate troubles during operation caused by an increase in pressure loss, honeycomb filters with a low initial pressure loss and honeycomb filters with a low rate of increase in pressure loss when a predetermined amount of PM accumulates have been variously proposed.

[0005] As an invention that discloses such a honeycomb filter, Patent Document 1 can be cited. FIG. 6 is an end view on the exhaust gas inlet side schematically showing the honeycomb filter according to Patent Document 1.

[0006] Patent Document 1 discloses a honeycomb fired body (honeycomb filter) 510 including exhaust gas introduction cells (12, 14) having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side, and an exhaust gas discharge cell 11 having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, as shown in FIG. 6. The exhaust gas discharge cell consists of a first exhaust gas introduction cell 12, the first of which has a square cross-sectional shape perpendicular to the longitudinal direction of the cell, and a second exhaust gas introduction cell 14, the second of which has an octagonal cross-sectional shape perpendicular to the longitudinal direction of the cell. Furthermore, the cross-sectional shape of the exhaust gas discharge cell perpendicular to its longitudinal direction is octagonal, which is the same shape as the cross-sectional shape of the second exhaust gas introduction cell 14 perpendicular to its longitudinal direction. In the honeycomb calcined body 510, the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14 are arranged alternately around the entire perimeter of the exhaust gas discharge cell 11. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2013 / 187444 [Overview of the project] [Problems that the invention aims to solve]

[0008] Patent Document 1 explains that by arranging the exhaust gas discharge cell and the exhaust gas introduction cell in this manner, the flow of exhaust gas is made uniform and smooth, resulting in low pressure loss in the initial stages and preventing the pressure loss from increasing even as PM accumulates. However, there was a demand to further reduce initial pressure loss in order to further improve the fuel efficiency of internal combustion engines.

[0009] This invention was made to solve the above problems, and the object of this invention is to provide a honeycomb filter that has even lower pressure loss in the initial stages of exhaust gas treatment and in which pressure loss does not easily increase even when PM accumulates. [Means for solving the problem]

[0010] In the honeycomb calcined body described in Patent Document 1, PM accumulates in the following order: on the cell partition between the first exhaust gas inlet cell and the exhaust gas discharge cell, on the cell partition between the second exhaust gas inlet cell and the exhaust gas discharge cell, and on the cell partition between the first exhaust gas inlet cell and the second exhaust gas inlet cell. In other words, the cell partition between the first and second exhaust gas inlet cells only becomes involved in PM collection after a certain amount of time has passed, and the cell partition between the first and second exhaust gas inlet cells is hardly involved in PM collection in the initial stages of exhaust gas treatment. The inventors estimated that by reducing the difference in gas flow velocity across each partition wall in the initial stages of exhaust gas treatment, PM would accumulate on the cell partition wall between the first and second exhaust gas introduction cells, thereby reducing the initial pressure loss. Based on this estimation, the inventors completed the present invention.

[0011] In other words, the honeycomb filter of the present invention comprises a porous cell partition wall that divides a plurality of cells that form a flow path for exhaust gas, an exhaust gas introduction cell having an open end on the exhaust gas inlet side and a sealed end on the exhaust gas outlet side, and an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, wherein the cross-sectional shape of the exhaust gas introduction cell and the exhaust gas discharge cell in the direction perpendicular to the longitudinal direction is the same in each cell from the end on the exhaust gas inlet side to the end on the exhaust gas outlet side, except for the sealed portion, and the exhaust gas introduction cells are adjacent to the exhaust gas discharge cell with porous cell partition walls separating them, and the exhaust gas introduction cell consists of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell whose cross-sectional area perpendicular to the longitudinal direction of the cell is larger than that of the first exhaust gas introduction cell, and the exhaust gas discharge cell in the longitudinal direction of the cell The cross-sectional area of ​​the vertical section is the same as or larger than the cross-sectional area of ​​the second exhaust gas introduction cell perpendicular to the longitudinal direction of the cell, and with respect to the cross-section perpendicular to the longitudinal direction of the cell, both the exhaust gas discharge cell and the exhaust gas introduction cell are made of polygons, and the length of the side of the first exhaust gas introduction cell that faces the exhaust gas discharge cell is longer than the length of the side of the second exhaust gas introduction cell that faces the exhaust gas discharge cell, and the cell partition wall includes a first cell partition wall separating the adjacent first exhaust gas introduction cell and the second exhaust gas introduction cell, a second cell partition wall separating the first exhaust gas introduction cell and the exhaust gas discharge cell, and a third cell partition wall separating the second exhaust gas discharge cell and the exhaust gas discharge cell, and the thickness of the first cell partition wall is thinner than the thickness of the second cell partition wall and the thickness of the third cell partition wall.

[0012] In the honeycomb filter of the present invention, the thickness of the first cell partition is thinner than the thickness of the second cell partition and the thickness of the third cell partition. Therefore, the resistance to exhaust gas passing through the second and third cell partitions becomes relatively large, making it difficult for exhaust gas to pass through the second and third cell partitions. Therefore, in the initial stages of exhaust gas treatment using the honeycomb filter, the exhaust gas passes through the first cell partition more easily compared to when the thickness of the first cell partition is the same as the thickness of the second and third cell partitions. As a result, the first cell partition can also function as a filter in the initial stages of exhaust gas treatment. As a result, it is estimated that the initial pressure loss can be reduced in the honeycomb filter of the present invention.

[0013] In the honeycomb filter of the present invention, with respect to the cross-section perpendicular to the longitudinal direction of the cell, it is desirable that the length of the side of the second exhaust gas introduction cell that faces the exhaust gas discharge cell is 0.8 times or less the length of the side of the first exhaust gas introduction cell that faces the exhaust gas discharge cell. With this ratio, the exhaust gas can more easily pass through the second cell partition separating the exhaust gas discharge cell and the first exhaust gas introduction cell, effectively suppressing pressure loss before PM accumulation. When the above ratio exceeds 0.8, the difference in the lengths of both sides becomes negligible, making it difficult to keep the initial pressure loss low.

[0014] In the honeycomb filter of the present invention, with respect to the cross-section perpendicular to the longitudinal direction of the cell, it is desirable that the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, and the second exhaust gas introduction cell is octagonal. The honeycomb filter with the above configuration can effectively suppress the initial pressure loss during exhaust gas treatment, and it is possible to increase the surface area on which PM accumulates, thereby keeping the pressure loss low.

[0015] In the honeycomb filter of the present invention, with respect to a cross-section perpendicular to the longitudinal direction of the cell, the cross-sectional area of ​​the second exhaust gas introduction cell is the same as the cross-sectional area of ​​the exhaust gas discharge cell, and it is desirable that the cross-sectional area of ​​the first exhaust gas introduction cell is 20 to 50% of the cross-sectional area of ​​the second exhaust gas introduction cell. In the honeycomb filter with the above configuration, the volume of the exhaust gas discharge cell does not become too small, which reduces the gas passage resistance from the exhaust gas introduction cell to the exhaust gas discharge cell and the resistance when passing through the exhaust gas discharge cell, thereby effectively suppressing pressure loss. If the cross-sectional area of ​​the first exhaust gas inlet cell is less than 20% of the cross-sectional area of ​​the second exhaust gas inlet cell, the cross-sectional area of ​​the first exhaust gas inlet cell becomes too small, resulting in a small filtration area and a tendency for high pressure loss. On the other hand, if the cross-sectional area of ​​the first exhaust gas inlet cell exceeds 50% of the cross-sectional area of ​​the second exhaust gas inlet cell, the volume of the exhaust gas discharge cell becomes too small, making it difficult to reduce pressure loss.

[0016] In the honeycomb filter of the present invention, with respect to the cross-section perpendicular to the longitudinal direction of the cell, the cross-sectional shape of the exhaust gas discharge cell is octagonal, the cross-sectional shape of the first exhaust gas introduction cell is square, the cross-sectional shape of the second exhaust gas introduction cell is octagonal, the cross-sectional shapes of the second exhaust gas introduction cell and the exhaust gas discharge cell are congruent to each other, and four first exhaust gas introduction cells and four second exhaust gas introduction cells are alternately arranged around the exhaust gas discharge cell, separated by cell partitions, and the exhaust gas discharge cell Of the imaginary line segments connecting the geometric centroids of the octagons that make up the cross-sectional shape of the four second exhaust gas introduction cells surrounding the exhaust gas, the intersection point of the two line segments that pass through the geometric region made up of the cross-sectional shape of the exhaust gas discharge cell coincides with the geometric centroid of the octagon that makes up the cross-sectional shape of the exhaust gas discharge cell. Furthermore, of the imaginary line segments connecting the geometric centroids of the octagons that make up the four second exhaust gas introduction cells, the four lines that do not pass through the geometric region made up of the cross-sectional shape of the exhaust gas discharge cell form a quadrilateral, and the midpoint of each side of this quadrilateral is the exhaust gas discharge cell. The exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell are arranged so as to coincide with the geometric centroid of each rectangle, which is the cross-sectional shape of the four first exhaust gas introduction cells surrounding the discharge cell, and the sides constituting the cross-sectional shape of the exhaust gas discharge cell that face the first exhaust gas introduction cell across the second cell partition wall are parallel to the sides constituting the cross-sectional shape of the first exhaust gas introduction cell that face the exhaust gas discharge cell across the second cell partition wall, and the cross-sectional shape of the exhaust gas discharge cell In the edges constituting the cross-sectional shape of the first exhaust gas introduction cell, it is desirable that the edge facing the second exhaust gas introduction cell across the third cell partition is parallel to the edge constituting the cross-sectional shape of the second exhaust gas introduction cell, and that the edge facing the exhaust gas discharge cell across the third cell partition is parallel to the edge constituting the cross-sectional shape of the first exhaust gas introduction cell, and that the edge facing the first exhaust gas introduction cell across the first cell partition is parallel to the edge constituting the cross-sectional shape of the second exhaust gas introduction cell. When the honeycomb filter has such a configuration, the effects of the present invention described above can be suitably exhibited.

[0017] In the honeycomb filter of the present invention, it is desirable that the exhaust gas introduction cell consists of only a first exhaust gas introduction cell and a second exhaust gas introduction cell. Such a honeycomb filter has a large effective area as an exhaust gas introduction cell, and can deposit PM thinly and widely.

[0018] The honeycomb filter of the present invention has the exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell, and it is desirable that it is formed by bonding a plurality of honeycomb fired bodies having an outer peripheral wall on the outer periphery through an adhesive layer. When the honeycomb filter has such a configuration, even when stress occurs in one honeycomb fired body, the stress is relaxed by the adhesive layer and is less likely to be transmitted to other honeycomb fired bodies. That is, the stress generated in the honeycomb filter can be relaxed. As a result, damage to the honeycomb filter can be prevented.

[0019] The honeycomb filter of the present invention is composed of honeycomb fired bodies, and it is desirable that the honeycomb fired bodies are made of silicon carbide or silicon-containing silicon carbide. Silicon carbide and silicon-containing silicon carbide are materials with excellent heat resistance. Therefore, the honeycomb filter with the above configuration becomes a honeycomb filter with excellent heat resistance.

[0020] In the honeycomb filter of the present invention, it is desirable that the thickness of the first cell partition wall is 0.05 to 0.25 mm. When the thickness of the first cell partition wall is within such a range, at the initial stage of exhaust gas treatment, the exhaust gas easily passes through the first cell partition wall, and the pressure loss can be reduced. When the thickness of the first cell partition wall is less than 0.05 mm, the strength becomes low and it is easily damaged. When the thickness of the first cell partition wall is 0.25 mm or more, it becomes difficult for the exhaust gas to pass through the first cell partition wall, and it becomes difficult to reduce the pressure loss at the initial stage of exhaust gas treatment.

[0021] In the honeycomb filter of the present invention, the thickness of the second cell partition is preferably 0.15 to 0.46 mm. Furthermore, in the honeycomb filter of the present invention, the thickness of the third cell partition is preferably 0.15 to 0.46 mm. Cell partitions of this thickness possess sufficient mechanical strength while effectively suppressing the increase in pressure loss.

[0022] In the honeycomb filter of the present invention, the ratio of the thickness of the second cell partition to the thickness of the first cell partition is preferably 1.2 to 6.0. Furthermore, in the honeycomb filter of the present invention, the ratio of the thickness of the third cell partition to the thickness of the first cell partition is preferably 1.2 to 6.0. If the above ratio is less than 1.2, the difference between the resistance of the exhaust gas as it passes through the first cell partition and the resistance of the exhaust gas as it passes through the second or third cell partition becomes small, making it difficult for the exhaust gas to pass through the first cell partition in the initial stages of exhaust gas treatment. As a result, it becomes difficult to reduce the pressure loss in the initial stages of exhaust gas treatment. If the above ratio exceeds 6.0, the first cell septum will become too thin, or the second or third cell septum will become too thick. If the first cell partition becomes too thin, its strength will decrease, making the honeycomb filter more susceptible to damage. If the second or third cell bulkhead is too thick, exhaust gas will have difficulty passing through it, resulting in increased pressure loss.

[0023] In the honeycomb filter of the present invention, the porosity of the cell partitions is preferably 30 to 65%. By setting the porosity in this way, the cell partitions can effectively capture PM in the exhaust gas, and the increase in pressure loss caused by the cell partitions can be suppressed. If the porosity of the cell partition is less than 30%, the proportion of pores in the cell partition is too small, making it difficult for exhaust gas to pass through the cell partition, resulting in a large pressure loss when the exhaust gas passes through the cell partition. If the porosity of the cell septum exceeds 65%, the mechanical properties of the cell septum will decrease, making it more susceptible to cracking during regeneration, etc.

[0024] In the honeycomb filter of the present invention, the average pore diameter of the pores contained in the cell partitions is preferably 5 to 25 μm. When the average pore size is within the above range, PM can be collected with high collection efficiency while suppressing an increase in pressure loss. If the average pore size of the pores in the cell partition is less than 5 μm, the pores are too small, resulting in a large pressure loss when the exhaust gas passes through the cell partition. If the average pore diameter of the pores contained in the cell septum exceeds 25 μm, the pore diameter becomes too large, which reduces the PM collection efficiency.

[0025] In the honeycomb filter of the present invention, it is desirable that an outer periphery coating layer be formed on the outer periphery. The outer coating layer mechanically protects the internal cells. Therefore, it results in a honeycomb filter with excellent mechanical properties such as compressive strength. [Brief explanation of the drawing]

[0026] [Figure 1] Figure 1 is a schematic perspective view showing an example of a honeycomb filter according to the first embodiment of the present invention. [Figure 2A] Figure 2A is a schematic perspective view showing an example of a honeycomb firing body constituting a honeycomb filter according to the first embodiment of the present invention. [Figure 2B] Figure 2B is an end view of the honeycomb calcined body shown in Figure 2A, on the exhaust gas inlet side. [Figure 2C] Figure 2C is a cross-sectional view along line AA of the honeycomb firing body shown in Figure 2A. [Figure 3A] Figure 3A is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of the exhaust gas flow in the initial stages when purifying exhaust gas using a conventional honeycomb filter. [Figure 3B]Figure 3B is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of exhaust gas flow during the medium term when purifying exhaust gas using a conventional honeycomb filter. [Figure 3C] Figure 3C is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of exhaust gas flow in the later stages of exhaust gas purification using a conventional honeycomb filter. [Figure 4A] Figure 4A is a schematic enlarged view of a portion of the end face on the exhaust gas inlet side of the honeycomb filter, illustrating an example of the exhaust gas flow in the initial stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention. [Figure 4B] Figure 4B is a schematic enlarged view of a portion of the end face on the exhaust gas inlet side of the honeycomb filter, illustrating an example of the exhaust gas flow during the mid- and late-stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention. [Figure 5] Figure 5 is a graph showing the simulation results of the flow velocity as the incoming gas passes through the cell partition. [Figure 6] Figure 6 is a schematic end view of the exhaust gas inlet side of the honeycomb filter according to Patent Document 1. [Modes for carrying out the invention]

[0027] (First Embodiment) A first embodiment, which is an example of the honeycomb filter of the present invention, will be described in detail below with reference to the drawings. Figure 1 is a schematic perspective view showing an example of a honeycomb filter according to the first embodiment of the present invention. Figure 2A is a schematic perspective view showing an example of a honeycomb firing body constituting a honeycomb filter according to the first embodiment of the present invention. Figure 2B is an end view of the honeycomb calcined body shown in Figure 2A, on the exhaust gas inlet side. Figure 2C is a cross-sectional view along line AA of the honeycomb firing body shown in Figure 2A.

[0028] In the honeycomb filter 20 shown in Figure 1, multiple honeycomb fired bodies 10 are bound together via an adhesive layer 15 to form a ceramic block 18, and an outer periphery coating layer 16 is formed on the outer circumference of this ceramic block 18 to prevent exhaust gas leakage. Note that the outer periphery coating layer 16 may be formed only if necessary.

[0029] In the honeycomb filter 20, multiple honeycomb firing bodies 10 are bound together via an adhesive layer 15. Therefore, even if stress occurs in one honeycomb firing body 10, that stress is relieved by the adhesive layer 15 and is less likely to be transmitted to other honeycomb firing bodies 10. In other words, the stress generated in the honeycomb filter 20 can be relieved. As a result, damage to the honeycomb filter 20 can be prevented. The adhesive layer 15 is formed by applying and drying an adhesive paste containing an inorganic binder and inorganic particles. The adhesive layer 15 may further contain inorganic fibers and / or whiskers. The thickness of the adhesive layer 15 should preferably be 0.5 to 2.0 mm.

[0030] The outer coating layer 16 plays a role in mechanically protecting the internal cells. As a result, the honeycomb filter 20 has excellent mechanical properties such as compressive strength. Furthermore, it is desirable that the material of the outer coating layer 16 be the same as the material of the adhesive layer 15. The thickness of the outer coating layer 16 is preferably 0.1 to 3.0 mm.

[0031] Although the honeycomb-fired body 10 has a rectangular prism shape, as shown in Figure 2A, the corners at the end faces are chamfered to have a curved shape, thereby preventing thermal stress from concentrating at the corners and causing damage such as cracks. The corners may also be chamfered to have a straight shape.

[0032] The honeycomb calcined body 10 shown in Figure 2A comprises a porous cell partition wall 13 that divides a plurality of cells that serve as exhaust gas flow paths, and includes exhaust gas introduction cells (cells indicated by reference numerals 12 and 14) with an open end 10a on the exhaust gas inlet side and a sealed end 10b on the exhaust gas outlet side, and an exhaust gas discharge cell 11 with an open end 10b on the exhaust gas outlet side and a sealed end 10a on the exhaust gas inlet side.

[0033] In the honeycomb filter of the present invention, it is desirable that the sealing material used to seal the exhaust gas introduction cell and the exhaust gas discharge cell be made of the same material as the honeycomb firing body.

[0034] In the honeycomb filter 20, the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas introduction cells (cells indicated by reference numerals 12 and 14) and the exhaust gas discharge cells 11 is the same in each cell from the end 10a on the exhaust gas inlet side to the end 10b on the exhaust gas outlet side, except for the sealing portion.

[0035] As shown in Figure 2B, in the honeycomb calcined body 10, a first exhaust gas introduction cell 12 with a square cross-section and a second exhaust gas introduction cell 14 with an octagonal cross-section are adjacent to the entire perimeter of the exhaust gas discharge cell 11, which has an octagonal cross-section. The first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14 are arranged alternately around the exhaust gas discharge cell 11, with the cross-sectional area of ​​the second exhaust gas introduction cell 14 being larger than that of the first exhaust gas introduction cell 12, and the cross-sectional area of ​​the exhaust gas discharge cell 11 being the same as that of the second exhaust gas introduction cell 14. Furthermore, an outer peripheral wall 17 is formed on the outer periphery of this honeycomb-fired body 10. The cross-sectional shape of the first exhaust gas introduction cell 12 is rectangular, while the cross-sectional shapes of the second exhaust gas introduction cell 14 and the exhaust gas discharge cell 11 are both octagonal and congruent to each other.

[0036] In other words, in the honeycomb calcined body 10, with respect to the cross-section perpendicular to the longitudinal direction of the cells, the cross-sectional shape of the exhaust gas discharge cell 11 is octagonal, the cross-sectional shape of the first exhaust gas introduction cell 12 is square, the cross-sectional shape of the second exhaust gas introduction cell 14 is octagonal, and the cross-sectional shapes of the second exhaust gas introduction cell 14 and the exhaust gas discharge cell 11 are congruent to each other. Then, surrounding the exhaust gas discharge cell 11, four first exhaust gas introduction cells 12 and four second exhaust gas introduction cells 14 are arranged alternately, separated by cell partitions 13, thus enclosing the exhaust gas discharge cell 11. Furthermore, of the imaginary line segments connecting the geometric centroids of the octagonal cross-sectional shapes of the four second exhaust gas introduction cells 14 surrounding the exhaust gas discharge cell 11, the intersection of the two line segments that pass through the geometric region formed by the cross-sectional shape of the exhaust gas discharge cell 11 coincides with the geometric centroid of the octagonal cross-sectional shape of the exhaust gas discharge cell 11. Additionally, of the imaginary line segments connecting the geometric centroids of the octagonal cross-sectional shapes of the four second exhaust gas introduction cells 14, the four lines that do not pass through the geometric region formed by the cross-sectional shape of the exhaust gas discharge cell 11 form a quadrilateral, and the midpoint of each side of this quadrilateral coincides with the geometric centroid of the quadrilateral cross-sectional shapes of the four first exhaust gas introduction cells 12 surrounding the exhaust gas discharge cell 11.

[0037] Furthermore, in the honeycomb-fired body 10, in order to ensure that the thickness of the outer peripheral wall 17 is uniform except at the corners, the edges of the exhaust gas introduction cell adjacent to the outer peripheral wall 17 in a cross section perpendicular to the longitudinal direction of the cell are formed parallel and linearly to the edges that form the outer wall of the outer peripheral wall 17. Therefore, the cross-section of the second exhaust gas introduction cell 14A adjacent to the outer perimeter wall 17 changes from octagonal to hexagonal because a portion of it has been cut away. The cross-sectional shape of the first exhaust gas introduction cell 12A may also be partially cut away, but it is desirable that it be congruent to the cross-sectional shape of the first exhaust gas introduction cell 12.

[0038] The second exhaust gas introduction cell 14B located at the corner of the honeycomb calcined body 10 changes from an octagon to a roughly pentagonal shape having a curved chamfered portion 40. In Figure 2B, the chamfered portion 40 of the second exhaust gas introduction cell 14B is chamfered so that the chamfered portion has a curve, but it may also be chamfered so that the chamfered portion is a straight line.

[0039] The exhaust gas discharge cell 11 and the second exhaust gas introduction cell 14 have the same octagonal shape, but this octagon is point-symmetric with respect to its centroid, with four long sides and four short sides arranged alternately, and the angle between the long sides and short sides is 135°.

[0040] In the honeycomb calcined body 10, the length L1 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell 12 is longer than the length L2 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell 14.

[0041] Furthermore, in the honeycomb calcined body 10, the cell partitions 13 include a first cell partition 13a separating the adjacent first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14, a second cell partition 13b separating the first exhaust gas introduction cell 12 and the exhaust gas discharge cell 11, and a third cell partition 13c separating the second exhaust gas introduction cell 14 and the exhaust gas discharge cell 11.

[0042] In other words, the sides constituting the cross-sectional shape of the first exhaust gas introduction cell 12 and the sides constituting the cross-sectional shape of the exhaust gas discharge cell 11, which face each other across the second cell partition 13b, are parallel. Also, the sides constituting the cross-sectional shape of the exhaust gas discharge cell 11 and the sides constituting the cross-sectional shape of the second exhaust gas introduction cell 14, which face each other across the third cell partition 13c, are parallel. Furthermore, the sides constituting the cross-sectional shape of the first exhaust gas introduction cell 12 and the sides constituting the cross-sectional shape of the second exhaust gas introduction cell 14, which face each other across the first cell partition 13a, are parallel.

[0043] In the honeycomb calcined body 10, the thickness Ta of the first cell partition 13a is thinner than the thickness Tb of the second cell partition 13b and the thickness Tc of the third cell partition 13c.

[0044] Here, we will explain the case where exhaust gas flows into the honeycomb calcined body 10 and PM is collected. As shown in Figure 2C, exhaust gas G (in Figure 2C, exhaust gas is indicated by G and the flow of exhaust gas is indicated by arrows) that flows into the first exhaust gas inlet cell 12 and the second exhaust gas inlet cell 14 (not shown in Figure 2C) passes through the cell partition wall 13 separating the exhaust gas discharge cell 11 from the first exhaust gas inlet cell 12 or the second exhaust gas inlet cell 14, and then flows out from the exhaust gas discharge cell 11. As the exhaust gas G passes through the cell partition wall 13, PM and other particles in the exhaust gas are captured, so the cell partition wall 13 functions as a filter.

[0045] In the honeycomb calcined body 10, the cross-sectional shape perpendicular to the longitudinal direction of the first exhaust gas introduction cell 12 is different from the cross-sectional shape perpendicular to the longitudinal direction of the second exhaust gas introduction cell 14. Therefore, the resistance when exhaust gas passes from the first exhaust gas introduction cell 12 to the exhaust gas discharge cell 11 is different from the resistance when exhaust gas passes from the second exhaust gas introduction cell 14 to the exhaust gas discharge cell 11. In other words, the ease with which exhaust gas passes from the first exhaust gas introduction cell 12 to the exhaust gas discharge cell 11 is different from the ease with which exhaust gas passes from the second exhaust gas introduction cell 14 to the exhaust gas discharge cell 11.

[0046] Furthermore, PM and other particles accumulated on the cell partition wall 13 create resistance as the exhaust gas G passes through the cell partition wall 13. Therefore, the amount of PM accumulation also affects how easily the exhaust gas passes from the first exhaust gas introduction cell 12 or the second exhaust gas introduction cell 14 to the exhaust gas discharge cell 11. In other words, the accumulation of PM over time changes the ease with which exhaust gas can pass from the first exhaust gas introduction cell 12 or the second exhaust gas introduction cell 14 to the exhaust gas discharge cell 11.

[0047] Here, we will explain the flow of exhaust gas passing through the cell partitions in a conventional honeycomb filter where the thickness of the cell partitions is uniform. Figure 3A is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of the exhaust gas flow in the initial stages when purifying exhaust gas using a conventional honeycomb filter. Figure 3B is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of exhaust gas flow during the medium term when purifying exhaust gas using a conventional honeycomb filter. Figure 3C is a schematic, enlarged view of a portion of the end face on the exhaust gas inlet side of a honeycomb filter, illustrating an example of exhaust gas flow in the later stages of exhaust gas purification using a conventional honeycomb filter.

[0048] The conventional honeycomb sintered body 510 shown in Figures 3A to 3C has the same configuration as the honeycomb sintered body 10 described above, except that the cell partitions 513, consisting of the first cell partition 513a, the second cell partition 513b, and the third cell partition 513c, have a uniform thickness.

[0049] As shown in Figure 3A, when exhaust gas flows into the honeycomb calcined body 510, it flows into the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14, both of which have open ends 10a on the inlet side. The exhaust gas flows from the part of the filter where it flows most easily. In the honeycomb calcined body 510, the length L1 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell 12 is longer than the length L2 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell 14. Therefore, the surface area of ​​the second cell partition wall 513b separating the exhaust gas discharge cell 11 and the first exhaust gas introduction cell 12 is larger than the surface area of ​​the third cell partition wall 513c separating the exhaust gas discharge cell 11 and the second exhaust gas introduction cell 14. As a result, the exhaust gas passes through the second cell partition wall 513b more easily, and PM accumulates on the surface of the first cell partition wall 513b in the initial stages of exhaust gas treatment.

[0050] Next, as shown in Figure 3B, when a certain amount of PM accumulates on the inner wall surface of the first exhaust gas introduction cell 12 in the second cell partition 513b, the PM accumulates thickly because the cross-sectional area of ​​the first exhaust gas introduction cell 12 is small. As a result, the resistance caused by the accumulation of PM increases, making it difficult for the exhaust gas to pass through the second cell partition 513b. In this situation, as described above, the exhaust gas passes through the third cell partition wall 513c separating the exhaust gas discharge cell 11 and the second exhaust gas introduction cell 14 (switching the main flow path), and PM also accumulates on the surface of the third cell partition wall 513c.

[0051] Next, since the exhaust gas can pass through the cell partition fairly freely, as shown in Figure 3C, it also passes through the inside of the first cell partition 513a separating the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14, and flows to the exhaust gas discharge cell 11. In this case, the exhaust gas enters the first cell partition 513a from the second exhaust gas introduction cell 14 side, and also enters the first cell partition 513a from the first exhaust gas introduction cell 12 side.

[0052] Furthermore, if the exhaust gas passes through the inside of the first cell partition wall 513a to reach the exhaust gas discharge cell 11, the distance the exhaust gas travels becomes longer, thus increasing the resistance the exhaust gas encounters as it passes through. Therefore, in the honeycomb calcined body 510, the exhaust gas passes through the inside of the first cell partition wall 513a only after PM has accumulated in the second cell partition wall 513b and the third cell partition wall 513c, and the resistance to the exhaust gas passing through these cell partition walls has increased. In other words, in the initial stages of exhaust gas purification, the amount of exhaust gas that passes through the first cell partition 513a and reaches the exhaust gas discharge cell 11 is small. Therefore, in the initial stages of exhaust gas purification, the first cell partition 513a does not function adequately as a filter for capturing PM.

[0053] Next, the flow of exhaust gas passing through the cell partitions in the honeycomb calcined body 10 described above will be explained. Figure 4A is a schematic enlarged view of a portion of the end face on the exhaust gas inlet side of the honeycomb filter, illustrating an example of the exhaust gas flow in the initial stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention. Figure 4B is a schematic enlarged view of a portion of the end face on the exhaust gas inlet side of the honeycomb filter, illustrating an example of the exhaust gas flow during the mid- and late-stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention.

[0054] In the honeycomb calcined body 10, the thickness Ta of the first cell partition 13a is thinner than the thickness Tb of the second cell partition 13b and the thickness Tc of the third cell partition 13c. Therefore, the resistance to the exhaust gas passing through the second cell partition 13b and the third cell partition 13c becomes relatively large, making it difficult for the exhaust gas to pass through the second cell partition 13b and the third cell partition 13c. Therefore, as shown in Figure 4A, the exhaust gas can pass through the inside of the first cell partition 13a and flow into the exhaust gas discharge cell 11 even in the initial stages of exhaust gas treatment. In addition, in the initial stages of exhaust gas treatment, the exhaust gas will pass through the second cell partition 13b and flow into the exhaust gas discharge cell 11. Therefore, PM accumulates on the first cell partition 13a and the second cell partition 13b.

[0055] Subsequently, once a certain amount of PM has accumulated on the first cell partition wall 13a and the second cell partition wall 13b, the exhaust gas flows through the third cell partition wall 13c into the exhaust gas discharge cell 11, as shown in Figure 4B.

[0056] Subsequently, the PM will accumulate uniformly on the first cell partition 13a, the second cell partition 13b, and the third cell partition 13c.

[0057] Thus, in the honeycomb calcined body 10, the first cell partition wall 13a can also function as a filter in the initial stages of exhaust gas treatment. As a result, it is estimated that the initial pressure loss can be reduced in the honeycomb calcined body 10.

[0058] In this specification, it is preferable to measure "length," "thickness," "cross-sectional area," etc., using electron microscope images. Electron microscope images can be taken, for example, with an electron microscope (FE-SEM: Hitachi High-Technologies Corporation's High-Resolution Field Emission Scanning Electron Microscope S-4800). Furthermore, the magnification of the electron microscope image must be such that the irregularities of particles and pores on the surface (inner wall) of the cell septa that make up the cell do not hinder the identification of the cell's cross-sectional shape, the measurement of the side length, the septum thickness, and the cell's cross-sectional area. At the same magnification, it is necessary to adopt a magnification that allows for the identification of the cell's cross-sectional shape, the measurement of the side length, the thickness of the cell septum, and the cell's cross-sectional area. Optimally, measurements should be taken using an electron microscope image with a magnification of 30x. Specifically, based on the definitions of cell length and cell wall thickness mentioned above, the length of each side of the cell is measured using the scale of the electron microscope image, and the value is determined. The cross-sectional area is then calculated arithmetically based on the obtained values ​​such as the cell length. If arithmetically measuring the cross-sectional area is cumbersome, a square corresponding to the unit area (a square with sides equal to the scale length) is cut from the scale of the electron microscope image, and its weight is measured. Meanwhile, a cell cross-section is cut along the cross-sectional shape of the cell (if the vertices are curved in the case of a polygon, it is cut along the curve), and the weight of the cut-out portion is measured. The cross-sectional area of ​​the cell can then be calculated from the weight ratio.

[0059] In addition to manual measurements, it is also possible to capture electron microscope images as image data, or to use image data directly captured from an electron microscope, inputting the scale of the image, and replacing it with electronic measurements. Of course, both manual and electronic measurement methods are based on the same principle, as they rely on the scale of the electron microscope image, and therefore there should be no discrepancies in the measurement results of the two methods.

[0060] For electronic measurement, the MAC-View (Version 3.5) image analysis particle size distribution software (manufactured by Mountech Co., Ltd.) can be used. This software allows measurement of cross-sectional area by scanning electron microscope images or directly acquiring image data from an electron microscope, inputting the scale of the image, and specifying a range along the inner wall of the cell. In addition, the distance between any points in the image can also be measured based on the scale of the electron microscope image. When photographing cell cross-sections with an electron microscope, a filter is cut perpendicular to the longitudinal direction of the cell, and a 1cm × 1cm × 1cm sample is prepared so that the cut surface is included. The sample is then ultrasonically cleaned or embedded in resin, and an electron microscope image is taken. Resin embedding does not affect the measurement of the cell side length or the thickness of the cell septa.

[0061] In the honeycomb calcined body 10, with respect to the cross-section perpendicular to the longitudinal direction of the cell, the length L2 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell 14 is preferably 0.8 times or less, and more preferably 0.1 to 0.7 times, the length L1 of the side facing the exhaust gas discharge cell 11 among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell 12. With this ratio, the exhaust gas can more easily pass through the second cell partition separating the exhaust gas discharge cell 11 and the first exhaust gas introduction cell 12, effectively suppressing pressure loss before PM accumulation. When the above ratio exceeds 0.8, the difference in the lengths of both sides becomes negligible, making it difficult to keep the initial pressure loss in exhaust gas treatment low.

[0062] In the honeycomb calcined body 10, with respect to the cross-section perpendicular to the longitudinal direction of the cells, the cross-sectional area of ​​the first exhaust gas introduction cell 12 is preferably 20-50% of the cross-sectional area of ​​the second exhaust gas introduction cell 14, and more preferably 25-45%. With this ratio, it is possible to create a difference between the resistance when the exhaust gas passes through the first exhaust gas introduction cell 12 and the resistance when it passes through the second exhaust gas introduction cell 14, thereby effectively suppressing pressure loss. Because the volume of the exhaust gas discharge cell does not become too small, the gas flow resistance from the exhaust gas introduction cell to the exhaust gas discharge cell and the resistance when passing through the exhaust gas discharge cell can be reduced, thereby effectively suppressing pressure loss. If the cross-sectional area of ​​the first exhaust gas inlet cell is less than 20% of the cross-sectional area of ​​the second exhaust gas inlet cell, the cross-sectional area of ​​the first exhaust gas inlet cell becomes too small, resulting in a small filtration area and a tendency for high pressure loss. On the other hand, if the cross-sectional area of ​​the first exhaust gas inlet cell exceeds 50% of the cross-sectional area of ​​the second exhaust gas inlet cell, the volume of the exhaust gas discharge cell becomes too small, making it difficult to reduce pressure loss.

[0063] In the honeycomb calcined body 10, the thickness of the first cell partition wall 13a is preferably 0.05 to 0.25 mm. When the thickness of the first cell partition wall 13a is within this range, the exhaust gas can pass through the first cell partition wall 13a more easily in the initial stages of exhaust gas treatment, thereby reducing pressure loss. If the thickness of the first cell partition is less than 0.05 mm, its strength will be reduced and it will be more prone to breakage. If the thickness of the first cell partition is 0.25 mm or more, exhaust gas will have difficulty passing through the first cell partition, making it difficult to reduce the initial pressure loss during exhaust gas treatment.

[0064] In the honeycomb filter of the present invention, the thickness of the second cell partition is preferably 0.15 to 0.46 mm. Furthermore, in the honeycomb filter of the present invention, the thickness of the third cell partition is preferably 0.15 to 0.46 mm. Cell partitions of this thickness possess sufficient mechanical strength while effectively suppressing the increase in pressure loss.

[0065] In the honeycomb calcined body 10, the ratio of the thickness of the second cell partition wall 13b to the thickness of the first cell partition wall 13a is preferably 1.2 to 6.0, and more preferably 1.5 to 5.0. Furthermore, the ratio of the thickness of the third cell partition wall 13c to the thickness of the first cell partition wall 13a is preferably 1.2 to 6.0, and more preferably 1.5 to 5.0. If the above ratio is less than 1.2, the difference between the resistance of the exhaust gas as it passes through the first cell partition and the resistance of the exhaust gas as it passes through the second or third cell partition becomes small, making it difficult for the exhaust gas to pass through the first cell partition in the initial stages of exhaust gas treatment. As a result, it becomes difficult to reduce the pressure loss in the initial stages of exhaust gas treatment. If the above ratio exceeds 6.0, the first cell septum will become too thin, or the second or third cell septum will become too thick. If the first cell partition becomes too thin, its strength will decrease, making the honeycomb filter more susceptible to damage. If the second or third cell bulkhead is too thick, exhaust gas will have difficulty passing through it, resulting in increased pressure loss.

[0066] In the honeycomb calcined body 10, the porosity of the cell partitions 13 is preferably 30-65%. By setting the porosity in this way, the cell partition 13 can effectively capture PM in the exhaust gas, and the increase in pressure loss caused by the cell partition 13 can be suppressed. If the porosity of the cell partition is less than 30%, the proportion of pores in the cell partition is too small, making it difficult for exhaust gas to pass through the cell partition, resulting in a large pressure loss when the exhaust gas passes through the cell partition. If the porosity of the cell septum exceeds 65%, the mechanical properties of the cell septum will decrease, making it more susceptible to cracking during regeneration, etc.

[0067] In the honeycomb calcined body 10, the average pore diameter of the pores contained in the cell septa 13 is preferably 5 to 25 μm. When the average pore size is within the above range, PM can be collected with high collection efficiency while suppressing an increase in pressure loss. If the average pore size of the pores in the cell partition is less than 5 μm, the pores are too small, resulting in a large pressure loss when the exhaust gas passes through the cell partition. If the average pore diameter of the pores contained in the cell septum exceeds 25 μm, the pore diameter becomes too large, which reduces the PM collection efficiency.

[0068] In this specification, "pore diameter of cell partitions" and "porosity of cell partitions" refer to values ​​measured by the mercury intrusion method under conditions of a contact angle of 130° and a surface tension of 485 mN / m.

[0069] The material of the honeycomb sintered body 10 is not particularly limited as long as it is composed of a porous material, but examples of constituent materials for the honeycomb sintered body 10 include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide, nitride ceramics such as aluminum nitride, silicon nitride, boron nitride, and titanium nitride, oxide ceramics such as alumina, zirconia, cordierite, mullite, and aluminum titanate, and silicon-containing silicon carbide. Among these, silicon carbide or silicon-containing silicon carbide is preferred. Silicon carbide and silicon-containing silicon carbide are materials with excellent heat resistance. For this reason, the honeycomb sintered body 10 made of silicon carbide or silicon-containing silicon carbide has excellent heat resistance. Furthermore, silicon-containing silicon carbide is a material in which metallic silicon is blended with silicon carbide, and silicon-containing silicon carbide containing 60 wt% or more of silicon carbide is preferred.

[0070] The number of cells per unit area in the cross-section of the honeycomb calcined body 10 is 31 to 93 cells / cm². 2 (200~600 pieces / inch 2 ) is desirable.

[0071] Next, a method for manufacturing a honeycomb filter according to the first embodiment of the present invention will be described. In the following section, we will explain the case where silicon carbide is used as the ceramic powder.

[0072] (1) A molding process is performed to produce a honeycomb molded body by extruding a wet mixture containing ceramic powder and a binder. Specifically, first, a wet mixture for manufacturing honeycomb molded bodies is prepared by mixing silicon carbide powder with different average particle sizes as ceramic powder, an organic binder, a liquid plasticizer, a lubricant, and water.

[0073] The above wetted mixture may optionally contain pore-forming agents such as balloons, which are tiny hollow spheres made of oxide ceramics, spherical acrylic particles, or graphite. The type of balloon is not particularly limited; examples include alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), and mullite balloons. Among these, alumina balloons are preferred.

[0074] Next, the wet mixture is fed into an extrusion molding machine and extruded to produce a honeycomb molded body of a predetermined shape. In this process, a honeycomb molded body is produced using a mold that produces a cross-sectional shape having the cell structure (cell shape and cell arrangement) shown in Figure 2B.

[0075] (2) The honeycomb molded body is cut to a predetermined length, dried using a microwave dryer, hot air dryer, dielectric dryer, vacuum dryer, freeze dryer, etc., and then a sealing step is performed in which a sealing paste that will serve as a sealing material is filled into predetermined cells to seal the cells. Here, the above-mentioned wet mixture can be used as the sealing paste.

[0076] (3) The honeycomb molded body is heated in a degreasing furnace to 300-650°C to remove organic matter from the honeycomb molded body in a degreasing process. Then, the degreasing honeycomb molded body is transported to a firing furnace and heated to 2000-2200°C in a firing process to produce a honeycomb fired body as shown in Figures 2A to 2C. Furthermore, the sealing paste filled into the ends of the cell is fired by heating to become a sealant. Furthermore, the conditions for the cutting, drying, sealing, degreasing, and firing processes can be those that have been conventionally used when manufacturing honeycomb fired bodies.

[0077] (4) A binding process is performed in which multiple honeycomb fired bodies are sequentially stacked and bound together on a support base using an adhesive paste, thereby creating a honeycomb assembly made up of multiple stacked honeycomb fired bodies. As an adhesive paste, for example, one consisting of an inorganic binder, an organic binder, and inorganic particles may be used. Furthermore, the adhesive paste may also contain inorganic fibers and / or whiskers.

[0078] Examples of inorganic particles included in the above adhesive paste include carbide particles and nitride particles. Specifically, these include silicon carbide particles, silicon nitride particles, and boron nitride particles. These may be used individually or in combination of two or more. Among the inorganic particles, silicon carbide particles, which have excellent thermal conductivity, are preferable.

[0079] Examples of inorganic fibers and / or whiskers included in the above adhesive paste include silica-alumina, mullite, alumina, silica, and the like. These may be used individually or in combination of two or more. Among the inorganic fibers, alumina fibers are preferred. The inorganic fibers may also be biosoluble fibers.

[0080] Furthermore, the adhesive paste may contain, if necessary, balloons which are tiny hollow spheres made of oxide ceramics, spherical acrylic particles, graphite, etc. The balloons are not particularly limited and include, for example, alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), mullite balloons, etc.

[0081] (5) Next, the honeycomb assembly is heated to solidify the adhesive paste, forming an adhesive layer, and a rectangular prism-shaped ceramic block is produced. The conditions for heating and solidifying the adhesive paste can be those conventionally used when manufacturing honeycomb filters.

[0082] (6) A cutting process is performed on the ceramic block. Specifically, a ceramic block with a roughly cylindrical outer surface is produced by cutting its outer surface using a diamond cutter.

[0083] (7) An outer coating layer formation process is performed in which an outer coating paste is applied to the outer surface of a roughly cylindrical ceramic block and dried and solidified to form an outer coating layer. Here, the adhesive paste described above can be used as the outer perimeter coating paste. Alternatively, a paste with a different composition from the adhesive paste may be used as the outer perimeter coating paste. Furthermore, the outer coating layer is not necessarily required and can be added only if necessary. By applying an outer coating layer, the shape of the outer perimeter of the ceramic block can be adjusted to create a cylindrical honeycomb filter. By following the above steps, a honeycomb filter according to the first embodiment of the present invention, including a honeycomb calcined body, can be manufactured.

[0084] In the above process, a honeycomb filter of a predetermined shape was manufactured by a cutting process. However, in the process of manufacturing the honeycomb fired body, multiple shapes of honeycomb fired bodies having an outer wall around their entire circumference may be manufactured, and these multiple shapes of honeycomb fired bodies may be combined via an adhesive layer to form a predetermined shape such as a cylinder. In this case, the cutting process can be omitted.

[0085] (Other embodiments) In the honeycomb filter according to the first embodiment of the present invention, a so-called aggregated honeycomb filter was formed by assembling a plurality of honeycomb firing bodies. However, the honeycomb filter of the present invention may be a so-called integrated honeycomb filter consisting of a single honeycomb firing body.

[0086] In the honeycomb filter according to the first embodiment of the present invention, the outer wall of the honeycomb firing body has a constant thickness except at the corners, and the cross-sectional shape of the exhaust gas introduction cell at the outermost periphery of the honeycomb firing body is partially cut out. However, in the honeycomb filter of the present invention, the cross-sectional shape of the exhaust gas introduction cell at the outermost periphery of the honeycomb firing body is not cut, and the thickness of the outer wall does not have to be a constant thickness. [Examples]

[0087] (Example 1) A molding process was carried out by mixing 52.8% by weight of coarse silicon carbide powder with an average particle size of 22 μm and 22.6% by weight of fine silicon carbide powder with an average particle size of 0.5 μm. To the resulting mixture, 4.6% by weight of an organic binder (methylcellulose), 0.8% by weight of a lubricant (Unilube, manufactured by NOF Corporation), 1.3% by weight of glycerin, 1.9% by weight of a pore-forming agent (acrylic resin), 2.8% by weight of oleic acid, and 13.2% by weight of water were added and kneaded to obtain a wet mixture, after which it was extruded. In this process, a raw honeycomb molded body was produced that had the same shape as the honeycomb fired body 10 shown in Figures 2A to 2C, but without sealing the cell gaps.

[0088] Next, the raw honeycomb molded body was dried using a microwave dryer to produce a dried honeycomb molded body. After that, sealing paste was filled into predetermined cells of the dried honeycomb molded body to seal the cells. Specifically, the cells were sealed so that the ends on the exhaust gas inlet side and the exhaust gas outlet side were sealed at the positions shown in Figure 2B. The above-mentioned wet mixture was used as a sealing paste. After sealing the cells, the dried honeycomb molded body filled with the sealing paste was dried again using a dryer.

[0089] Next, the honeycomb molded body, with its cells sealed, underwent a degreasing treatment at 400°C, followed by a firing treatment at 2200°C for 3 hours under atmospheric pressure and an argon atmosphere. This allowed us to produce the honeycomb calcined body according to Example 1.

[0090] In Example 1, the cross-sectional shape of the first exhaust gas introduction cell perpendicular to the longitudinal direction was a rectangle with side lengths of 0.94 mm × 0.97 mm. In Example 1, the cross-sectional shape of the second exhaust gas introduction cell perpendicular to the longitudinal direction was an octagon, consisting of four long sides with a length of 1.04 mm and four short sides with a length of 0.30 mm arranged alternately. The angle between the long sides and the short sides was 135°. In Example 1, the cross-sectional shape of the exhaust gas discharge cell perpendicular to the longitudinal direction was an octagon, consisting of four long sides with a length of 1.01 mm and four short sides with a length of 0.30 mm arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Example 1, the thickness of the first cell partition was 0.15 mm, the thickness of the second cell partition was 0.18 mm, and the thickness of the third cell partition was 0.18 mm.

[0091] The honeycomb calcined body according to Example 1 has a porosity of 45%, an average pore size of 15 μm, dimensions of 36.4 mm × 36.4 mm × 177.8 mm, and a cell density of 300 cells / inch. 2 That was the case. Multiple honeycomb-fired bodies were bundled together using an adhesive paste consisting of a mixture of SiC particles, silica sol, and alumina fibers. The outer periphery was then processed, and a coating layer made of the same material as the adhesive paste was applied to the outer periphery to create a cylindrical honeycomb filter measuring φ330.2 mm × 177.8 mm.

[0092] (Example 2) A honeycomb filter according to Example 2 was manufactured in the same manner as in Example 1, except that the structure of the manufactured honeycomb calcined body was changed as follows. In the honeycomb calcined body according to Example 2, the cross-sectional shape perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a rectangle with side lengths of 0.91 mm × 1.02 mm. In the honeycomb-fired body according to Example 2, the cross-sectional shape perpendicular to the longitudinal direction of the second exhaust gas introduction cell was an octagon, consisting of four long sides with a length of 1.03 mm and four short sides with a length of 0.34 mm arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Example 2, the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas discharge cell was an octagon, with four long sides of 0.92 mm length and four short sides of 0.34 mm length arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Example 2, the thickness of the first cell partition was 0.10 mm, the thickness of the second cell partition was 0.21 mm, and the thickness of the third cell partition was 0.21 mm.

[0093] (Example 3) A honeycomb filter according to Example 3 was manufactured in the same manner as in Example 1, except that the structure of the manufactured honeycomb calcined body was changed as follows. In the honeycomb-fired body according to Example 3, the cross-sectional shape perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a rectangle with side lengths of 0.88 mm × 1.07 mm. In the honeycomb-fired body according to Example 3, the cross-sectional shape perpendicular to the longitudinal direction of the second exhaust gas introduction cell was an octagon, with four long sides of 0.82 mm length and four short sides of 0.52 mm length arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Example 3, the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas discharge cell was an octagon, with four long sides of 1.02 mm length and four short sides of 0.24 mm length arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Example 3, the thickness of the first cell partition was 0.05 mm, the thickness of the second cell partition was 0.24 mm, and the thickness of the third cell partition was 0.24 mm.

[0094] (Comparative Example 1) A honeycomb filter according to Comparative Example 1 was manufactured in the same manner as in Example 1, except that the structure of the manufactured honeycomb calcined body was changed as follows. In the honeycomb calcined body according to Comparative Example 1, the shape of the cross-section perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a square with side lengths of 0.95 mm. In the honeycomb calcined body according to Comparative Example 1, the cross-sectional shape perpendicular to the longitudinal direction of the second exhaust gas introduction cell was an octagon, consisting of four long sides with a length of 1.05 mm and four short sides with a length of 0.28 mm arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Comparative Example 1, the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas discharge cell was an octagon, consisting of four long sides with a length of 1.05 mm and four short sides with a length of 0.28 mm arranged alternately. The angle between the long sides and the short sides was 135°. In the honeycomb-fired body according to Comparative Example 1, the thickness of the first cell partition, the second cell partition, and the third cell partition were all uniformly 0.17 mm.

[0095] (Simulation of flow velocity as inflow waste passes through the cell partition) Using the honeycomb filters described in Examples 1-3 and Comparative Example 1, the gas flow velocity through the first, second, and third cell partitions at predetermined positions from the exhaust gas inlet end to the exhaust gas outlet end of each honeycomb filter was simulated. The software used for the simulation was "STAR-CCM+". The simulation conditions were set to an inflow gas temperature of 380°C and an inflow gas flow rate of 1700 kg / hr.

[0096] Next, the difference between the maximum and minimum gas flow velocity was calculated at each measurement position (a predetermined distance from the exhaust gas inlet side of the honeycomb filter). The simulation results were then plotted on a coordinate system where the horizontal axis represented the distance from the exhaust gas inlet end of the honeycomb filter, and the vertical axis represented the difference between the maximum and minimum values ​​of the gas flow velocity, as shown in Figure 5. Figure 5 is a graph showing the simulation results of the flow velocity as the incoming gas passes through the cell partition.

[0097] As shown in Figure 5, the honeycomb filters in Examples 1 to 3 show a smaller difference in gas flow velocity at each measurement position compared to the honeycomb filter in Comparative Example 1. This indicates that the entire cell partition wall is effectively utilized as a filter from the initial stage before PM deposition, and therefore, pressure loss is thought to be reduced. [Explanation of symbols]

[0098] 10, 510 Honeycomb fired body 10a End on the exhaust gas inlet side 10b End on the exhaust gas outlet side 11 Exhaust gas emission cells 12, 12A First exhaust gas introduction cell 13 Cell partitions 13a Cell 1 partition 13b Second cell partition 13c Third cell partition 14, 14A, 14B Second exhaust gas injection cell 15 Adhesive layer 16 Outer coating layer 17 Peripheral wall 18 Ceramic Blocks 20 Honeycomb Filters 40 Chamfered section 210 Pressure loss measuring device 211 Diesel engine 212 Exhaust pipe 213 Metal casing 214 Pressure Gauge

Claims

1. An exhaust gas introduction cell is provided with porous cell partitions that divide multiple cells that form an exhaust gas flow path, with the end on the exhaust gas inlet side being open and the end on the exhaust gas outlet side being sealed, A honeycomb filter comprising an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side, wherein the cross-sectional shape perpendicular to the longitudinal direction of the exhaust gas introduction cell and the exhaust gas discharge cell is the same in each cell from the exhaust gas inlet side end to the exhaust gas outlet side end, except for the sealed portion, The exhaust gas introduction cells are arranged adjacent to the exhaust gas discharge cell, separated by porous cell partitions, and the exhaust gas introduction cells consist of two types: a first exhaust gas introduction cell and a second exhaust gas introduction cell whose cross-sectional area perpendicular to the longitudinal direction of the cell is larger than that of the first exhaust gas introduction cell, and The cross-sectional area of ​​the exhaust gas discharge cell in the direction perpendicular to the longitudinal direction of the cell is the same as or larger than the cross-sectional area of ​​the second exhaust gas introduction cell in the direction perpendicular to the longitudinal direction of the cell. With respect to a cross-section perpendicular to the longitudinal direction of the cell, the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, the second exhaust gas introduction cell is octagonal, and the length of the side of the cross-sectional shape of the first exhaust gas introduction cell that faces the exhaust gas discharge cell is longer than the length of the side of the cross-sectional shape of the second exhaust gas introduction cell that faces the exhaust gas discharge cell. The cell partition includes a first cell partition separating adjacent first exhaust gas introduction cells and second exhaust gas introduction cells, a second cell partition separating the first exhaust gas introduction cell and the exhaust gas discharge cell, and a third cell partition separating the second exhaust gas introduction cell and the exhaust gas discharge cell. A honeycomb filter characterized in that the thickness of the first cell partition is thinner than the thickness of the second cell partition and the thickness of the third cell partition.

2. With respect to a cross-section perpendicular to the longitudinal direction of the cell, The honeycomb filter according to claim 1, wherein the length of the side facing the exhaust gas discharge cell among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell is 0.8 times or less the length of the side facing the exhaust gas discharge cell among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell.

3. With respect to a cross-section perpendicular to the longitudinal direction of the cell, The cross-sectional area of ​​the second exhaust gas introduction cell is the same as the cross-sectional area of ​​the exhaust gas discharge cell. The honeycomb filter according to claim 1 or 2, wherein the cross-sectional area of ​​the first exhaust gas introduction cell is 20 to 50% of the cross-sectional area of ​​the second exhaust gas introduction cell.

4. With respect to a cross-section perpendicular to the longitudinal direction of the cell, The cross-sectional shapes of the second exhaust gas introduction cell and the exhaust gas discharge cell are congruent, Surrounding the exhaust gas discharge cell are four first exhaust gas introduction cells and four second exhaust gas introduction cells, each separated by a cell partition, arranged alternately. Furthermore, among the imaginary line segments connecting the geometric centroids of the octagons that make up the cross-sectional shape of the four second exhaust gas introduction cells surrounding the exhaust gas discharge cell, the intersection point of two line segments that pass through the geometric region consisting of the cross-sectional shape of the exhaust gas discharge cell coincides with the geometric centroid of the octagon that makes up the cross-sectional shape of the exhaust gas discharge cell. Furthermore, of the imaginary line segments connecting the geometric centroids of the octagons that make up the cross-sectional shape of the four second exhaust gas introduction cells, four that do not pass through the geometric region made up of the cross-sectional shape of the exhaust gas discharge cell form a quadrilateral, and the midpoint of each side of the quadrilateral coincides with the geometric centroid of the quadrilaterals that make up the cross-sectional shape of the four first exhaust gas introduction cells surrounding the exhaust gas discharge cell. The exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell are arranged accordingly. In the cross-sectional shape of the exhaust gas discharge cell, the side facing the first exhaust gas introduction cell across the second cell partition is parallel to the side facing the exhaust gas discharge cell across the second cell partition in the cross-sectional shape of the first exhaust gas introduction cell. The honeycomb filter according to any one of claims 1 to 3, wherein, in the edges constituting the cross-sectional shape of the exhaust gas discharge cell, the edge facing the second exhaust gas introduction cell across the third cell partition is parallel to the edge constituting the cross-sectional shape of the second exhaust gas introduction cell, and the edge facing the exhaust gas discharge cell across the third cell partition is parallel to the edge constituting the cross-sectional shape of the first exhaust gas introduction cell, and the edge facing the second exhaust gas introduction cell across the first cell partition is parallel to the edge constituting the cross-sectional shape of the second exhaust gas introduction cell, and the edge facing the first exhaust gas introduction cell across the first cell partition is parallel to the edge constituting the cross-sectional shape of the second exhaust gas introduction cell.

5. The honeycomb filter according to any one of claims 1 to 4, wherein the exhaust gas introduction cell consists only of a first exhaust gas introduction cell and a second exhaust gas introduction cell.

6. The aforementioned honeycomb filter is A honeycomb filter according to any one of claims 1 to 5, comprising the exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell, formed by bonding a plurality of honeycomb fired bodies having an outer peripheral wall on their outer periphery via an adhesive layer.

7. The honeycomb filter according to claim 6, wherein the honeycomb filter is composed of a honeycomb calcined body, and the honeycomb calcined body is composed of silicon carbide or silicon-containing silicon carbide.

8. The honeycomb filter according to any one of claims 1 to 7, wherein the thickness of the first cell partition is 0.05 to 0.25 mm.

9. The honeycomb filter according to any one of claims 1 to 8, wherein the thickness of the second cell partition is 0.15 to 0.46 mm.

10. The honeycomb filter according to any one of claims 1 to 9, wherein the thickness of the third cell partition is 0.15 to 0.46 mm.

11. The honeycomb filter according to any one of claims 1 to 10, wherein the ratio of the thickness of the second cell partition to the thickness of the first cell partition is 1.2 to 6.

0.

12. The honeycomb filter according to any one of claims 1 to 11, wherein the ratio of the thickness of the third cell partition to the thickness of the first cell partition is 1.2 to 6.

0.

13. The honeycomb filter according to any one of claims 1 to 12, wherein the porosity of the cell partitions is 30 to 65%.

14. The honeycomb filter according to any one of claims 1 to 13, wherein the average pore diameter of the pores contained in the cell partition is 5 to 25 μm.

15. A honeycomb filter according to any one of claims 1 to 14, wherein an outer periphery coating layer is formed on the outer periphery.

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