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 at the time when particulates accumulate.SOLUTION: A honeycomb filter comprises porous bulkheads 13 partitioning and forming a plurality of cells as passages of exhaust gas, and further comprises exhaust gas introduction cells whose inlet-side end parts are opened and whose outlet-side end parts are sealed, and exhaust gas exhaust cells 11 whose outlet-side end parts are opened and whose inlet-side end parts are sealed, where cross sectional shapes of passages of the exhaust gas introduction cells and of the exhaust gas exhaust cells are same, in spaces from the inlet sides to the outlet sides. The exhaust gas introduction cells are arranged adjacently to the circumferences of the exhaust gas exhaust cells. The exhaust gas introduction cells are constituted of a first exhaust gas introduction cell 12 and a second exhaust gas introduction cell 14 which is larger in cross sectional areas of the passage than the first exhaust gas introduction cell. Cross sectional areas of the passages of the exhaust gas exhaust cells are equal to or larger than cross sectional areas of the passages of the second exhaust gas introduction cell. A slit part 19 is formed in the bulkhead partitioning the first exhaust gas introduction cell and the second exhaust gas introduction cell.SELECTED DRAWING: Figure 2C

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), and 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 contained in exhaust gas 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. When a certain amount of PM is deposited on the honeycomb filter, it is burned by raising the temperature of the exhaust gas flowing into the honeycomb filter or heating it with an electric heater. Burning PM in this way is also called "regeneration of the honeycomb filter."

[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 is deposited have been variously proposed.

[0005] As an invention that discloses such a honeycomb filter, Patent Document 1 can be cited. FIG. 8 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, as shown in Figure 8, comprising exhaust gas introduction cells (12, 14) with 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 with an open end on the exhaust gas outlet side and a sealed end on the exhaust gas inlet side. The exhaust gas discharge cell consists of a first exhaust gas introduction cell 12, which has a square cross-sectional shape perpendicular to the longitudinal direction of the cell, and a second exhaust gas introduction cell 14, 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 Initiative] [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, the pressure loss is low in the initial stages, and the pressure loss does not increase easily even if 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 also has low pressure loss when PM accumulates. [Means for solving the problem]

[0010] 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 exhaust gas inlet side end to the exhaust gas outlet side end, except for the sealed portion, and the exhaust gas is distributed around the entire perimeter of the exhaust gas discharge cell, separated by a porous cell partition wall. The gas introduction cells are arranged adjacent to each other, 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 perpendicular to the longitudinal direction of the cell of the exhaust gas discharge cell is formed to be the same as or larger than the cross-sectional area perpendicular to the longitudinal direction of the cell of the second exhaust gas introduction cell, and a slit portion is formed in a cell partition wall separating the first exhaust gas introduction cell and the second exhaust gas introduction cell to connect the first exhaust gas introduction cell and the second exhaust gas introduction cell.

[0011] In the honeycomb filter of the present invention, a slit portion is formed in the cell partition wall separating some of the first exhaust gas introduction cells and the second exhaust gas introduction cells, allowing the first exhaust gas introduction cells and the second exhaust gas introduction cells to communicate with each other. If slits are formed in the honeycomb filter, the filtration area of ​​the honeycomb filter will decrease, but the opening area of ​​the end face can be increased. Increasing the opening area of ​​the end face of a honeycomb filter reduces pressure loss when exhaust gas flows into and out of the filter. Furthermore, in a honeycomb filter, when collecting PM, the cell partition separating the exhaust gas inlet cell (first exhaust gas inlet cell and second exhaust gas inlet cell) from the exhaust gas discharge cell functions primarily initially, while the cell partition separating the first exhaust gas inlet cell and the second exhaust gas inlet cell functions auxiliaryly. Therefore, if a slit is formed in the cell partition separating the first exhaust gas inlet cell and the second exhaust gas inlet cell, although the filtration area of ​​the honeycomb filter decreases, the increase in pressure loss due to PM accumulation can be suppressed. Based on the above, if a slit is formed in the cell partition separating some of the first exhaust gas introduction cells and the second exhaust gas introduction cells, connecting the first exhaust gas introduction cell and the second exhaust gas introduction cell, the initial pressure loss can be effectively reduced.

[0012] Furthermore, prolonged use of the honeycomb filter of the present invention can lead to the accumulation of PM (particulate matter), which can clog the slits. In this case, the pressure loss increases sharply. This rapid increase in pressure loss signals the burning of the PM. In other words, by using the honeycomb filter of the present invention, it is possible to easily determine the regeneration time of the honeycomb filter (the time when PM is burned).

[0013] In the honeycomb filter of the present invention, 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 may be longer than the length of the side of the second exhaust gas introduction cell that faces the exhaust gas discharge cell. Furthermore, in the honeycomb filter of the present invention, the exhaust gas introduction cell may consist only of the first exhaust gas introduction cell and the second exhaust gas introduction cell. Furthermore, 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. Furthermore, the honeycomb filter of the present invention, with respect to the cross section perpendicular to the longitudinal direction of the cell, has an octagonal cross-sectional shape for the exhaust gas discharge cell, a square cross-sectional shape for the first exhaust gas introduction cell, an octagonal cross-sectional shape for the second exhaust gas introduction cell, and the cross-sectional shapes of the second exhaust gas introduction cell and the exhaust gas discharge cell are congruent to each other. In addition, 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 is surrounded by... 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, the intersection 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, and 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, the four that do not pass through the geometric region made up of the cross-sectional shape of the exhaust gas discharge cell form a square, and the midpoints of each side of this square surround the four exhaust gas discharge cells. 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 square which is the cross-sectional shape of the first exhaust gas introduction 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 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 cell partition wall, and the sides constituting the cross-sectional shape of the exhaust gas discharge cell that face the second exhaust gas introduction cell across the cell partition wall are parallel to each other. 2. The side facing the exhaust gas introduction cell and the side constituting the cross-sectional shape of the second exhaust gas introduction cell are parallel to the side facing the exhaust gas discharge cell across the cell partition, and the side constituting the cross-sectional shape of the first exhaust gas introduction cell and the side facing the second exhaust gas introduction cell across the cell partition are parallel to the side constituting the cross-sectional shape of the second exhaust gas introduction cell and the side facing the first exhaust gas introduction cell across the cell partition, and it is more desirable that the distances between the parallel sides are equal in any combination. If the honeycomb filter has such a configuration, the effects of the present invention can be preferably exerted.

[0014] In the honeycomb filter of the present invention, regarding a cross section perpendicular to the longitudinal direction of the cell, among the sides constituting the cross-sectional shape of the second exhaust gas introduction cell, the length of the side facing the exhaust gas discharge cell is preferably 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. With such a ratio, the exhaust gas becomes more likely to pass through the partition wall separating the exhaust gas discharge cell and the first exhaust gas introduction cell, and the initial pressure loss before PM deposition can be effectively suppressed. If the above ratio exceeds 0.8, there is no large difference in the lengths of both sides, making it difficult to keep the initial pressure loss of the exhaust gas treatment low.

[0015] In the honeycomb filter of the present invention, the width of the slit portion is preferably 20 to 70% of the length of the side facing the second exhaust gas introduction cell among the sides constituting the cross-sectional shape of the first exhaust gas introduction cell. When the width of the slit portion is within the above range, the opening area of the end face of the honeycomb filter becomes preferably large, so that the pressure loss can be preferably reduced.

[0016] In the honeycomb filter of the present invention, it is desirable that the slit portion is formed on two sides among the sides constituting the cross-sectional shape of each second exhaust gas introduction cell. When the slit portion is formed in this way, the opening area of the end face of the honeycomb filter becomes preferably large. Also, the exhaust gas easily moves between the first exhaust gas introduction cell and the second exhaust gas introduction cell. Therefore, the pressure loss can be preferably reduced.

[0017] In the honeycomb filter of the present invention, regarding 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 the cross-sectional area of the first exhaust gas introduction cell is preferably 20 to 50% of the cross-sectional area of the second exhaust gas introduction cell. In the honeycomb filter having the above-described configuration, since the volume of the exhaust gas discharge cell does not become too small, 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 can be reduced, and the pressure loss can be effectively suppressed. If the cross-sectional area of the first exhaust gas introduction cell is less than 20% of the cross-sectional area of the second exhaust gas introduction cell, the cross-sectional area of the first exhaust gas introduction cell becomes too small, and the filtration area becomes small, so the pressure loss tends to increase. On the other hand, if the cross-sectional area of the first exhaust gas introduction cell exceeds 50% of the cross-sectional area of the second exhaust gas introduction cell, the volume of the exhaust gas discharge cell becomes too small, making it difficult to lower the pressure loss.

[0018] In the honeycomb filter of the present invention, it is desirable that the thickness of the cell partition walls separating the cells of the honeycomb filter be the same thickness. If there is variation in the thickness of the cell walls, when pressure such as stress is generated, damage is likely to occur in the thinner portions of the cell walls. However, if the thickness of the cell partition walls separating the cells is the same thickness, even when pressure is generated, it is uniformly dispersed, making the honeycomb filter less likely to be damaged.

[0019] In the honeycomb filter of the present invention, it is desirable that a plurality of honeycomb fired bodies having the exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell and having an outer peripheral wall on the outer periphery are bonded via 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.

[0020] The honeycomb filter of the present invention is composed of a honeycomb fired body, and it is desirable that the honeycomb fired body be 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 is a honeycomb filter with excellent heat resistance.

[0021] In the honeycomb filter of the present invention, the thickness of the cell partitions is preferably 0.10 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 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.

[0023] 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.

[0024] 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 serves to mechanically protect the internal cells. As a result, it creates a honeycomb filter with excellent mechanical properties such as compressive strength. [Brief explanation of the drawing]

[0025] [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 a cross-sectional view along line AA of the honeycomb-fired body shown in Figure 2A. [Figure 2C] Figure 2C is an end view of the exhaust gas inlet side of the honeycomb calcined body shown in Figure 2A. [Figure 3] Figure 3 is a schematic enlarged view of a portion of the exhaust gas inlet end face of a honeycomb filter, illustrating an example of a honeycomb filter according to a second embodiment of the present invention. [Figure 4] Figure 4 is a schematic enlarged view of a portion of the exhaust gas inlet side end face of a honeycomb filter, illustrating an example of a honeycomb filter according to the third embodiment of the present invention. [Figure 5] Figure 5 is a schematic enlarged view of a portion of the exhaust gas inlet side end face of a honeycomb filter, illustrating an example of a honeycomb filter according to the fourth embodiment of the present invention. [Figure 6] Figure 6 is a schematic cross-sectional view illustrating the pressure loss measurement method. [Figure 7] Figure 7 is a graph showing the relationship between PM collection amount and pressure loss measured in Example 1 and Comparative Example 1. [Figure 8] Figure 8 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]

[0026] (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 exhaust gas inlet side of the honeycomb calcined body shown in Figure 2A. Figure 2C is a cross-sectional view along line AA of the honeycomb firing body shown in Figure 2A.

[0027] 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.

[0028] 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.

[0029] The outer coating layer 16 serves to mechanically protect 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] Here, we will explain the case where exhaust gas flows into the honeycomb calcined body 10 and PM is collected. As shown in Figure 2B, exhaust gas G (in Figure 2B, 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 2B) 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.

[0035] As shown in Figure 2C, in the honeycomb calcined body 10, the exhaust gas discharge cell 11, which has an octagonal cross-section, is surrounded by 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. 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 the honeycomb-fired body 10. 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 square, and the midpoint of each side of this square coincides with the geometric centroid of the square formed by the cross-sectional shape 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 walls 17 is uniform except at the corners, the edges of cells 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] In the honeycomb calcined body 10, a slit portion 19 is formed in the cell partition wall 13b separating some of the first exhaust gas introduction cells 12 and the second exhaust gas introduction cells 14, allowing the first exhaust gas introduction cells 12 and the second exhaust gas introduction cells 14 to communicate with each other. If slit portions 19 are formed in the honeycomb calcined body 10, the filtration area of ​​the honeycomb calcined body 10 will decrease, but the opening area of ​​the end face can be increased. If the end face opening area of ​​the honeycomb-fired body 10 is increased, the pressure loss can be reduced. Furthermore, in the honeycomb calcined body 10, when collecting PM, initially the cell partition wall 13a separating the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14 from the exhaust gas discharge cell 11 functions primarily, while the cell partition wall 13b separating the first exhaust gas introduction cell 12 from the second exhaust gas introduction cell 14 functions auxiliaryly. Therefore, if a slit portion 19 is formed in the cell partition wall 13b separating the first exhaust gas introduction cell 12 from the second exhaust gas introduction cell 14, although the filtration area of ​​the honeycomb filter decreases, the increase in pressure loss due to PM accumulation can be suppressed. Based on the above, if a slit portion 19 is formed in the cell partition wall 13b separating the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14, the initial pressure loss can be effectively reduced.

[0042] Furthermore, prolonged use of the honeycomb calcined body 10 can lead to the accumulation of PM, which can clog the slit sections 19. In this case, the pressure loss increases sharply. This rapid increase in pressure loss signals the burning of the PM. In other words, by using the honeycomb calcined body 10, the regeneration timing of the honeycomb calcined body 10 (the combustion timing of PM) can be easily determined.

[0043] Furthermore, as shown in Figure 2C, in the honeycomb calcined body 10, the slit portions 19 are formed on two of the sides that constitute the cross-sectional shape of each second exhaust gas introduction cell 14. In addition, the slit portions 19 are formed on one of the sides that constitute the cross-sectional shape of the first exhaust gas introduction cell 12. When the slit portion 19 is formed in this manner, the opening area of ​​the end face of the honeycomb firing body 10 is suitably increased. In addition, exhaust gas can move more easily between the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14. Therefore, pressure loss can be suitably reduced.

[0044] As will be described later, the honeycomb-fired body is fired after the raw material composition is extruded. In the honeycomb-fired body, the position where the slits are formed is not particularly limited as long as each cell is formed without interruption during extrusion, but it is desirable to design it so that the slits are evenly distributed throughout.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] In the honeycomb fired body 10, the width of the slit portion 19 (in Figure 2C, L s The length indicated by (L) is preferably 20-70% of the length of the side of the cross-sectional shape of the first exhaust gas introduction cell 12 that faces the second exhaust gas introduction cell 14 (the length indicated by L3 in Figure 2C), and more preferably 25-65%. When the width of the slit portion 19 is within the above range, the opening area of ​​the end face of the honeycomb fired body 10 becomes suitably large, thus suitably reducing pressure loss. If the above percentage is less than 20%, the slit is too narrow, making it prone to blockage by PM, and the pressure loss reduction effect may not be fully achieved. If the above percentage exceeds 70%, the strength of the honeycomb-fired body tends to decrease.

[0049] In the honeycomb fired body 10, the width of the slit portion 19 (in Figure 2C, indicated by the symbol L) s The distance indicated by is preferably 0.1 to 0.7 mm, and more preferably 0.15 to 0.65 mm.

[0050] In the honeycomb calcined body 10 shown in Figure 2C, the slit portion 19 is formed in the center of the edge that forms the outline of the cross-sectional shape of the first exhaust gas introduction cell 12. However, in the honeycomb filter of the present invention, the slit portion may be formed closer to one end of the edge. Alternatively, the slit portion may be formed at the end of the edge.

[0051] 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 the initial 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.

[0052] 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, the volume of the exhaust gas discharge cell does not become too small, which reduces 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, 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.

[0053] In the honeycomb sintered body 10, it is desirable that the thickness of the cell partitions 13 separating the cells of the honeycomb sintered body 10 be the same. If there are variations in the thickness of the cell walls, when pressure such as stress is applied, the thinner parts of the cell walls are more prone to damage. However, if the cell partitions 13 separating the cells are all the same thickness, the pressure will be evenly distributed even when pressure is generated, making the honeycomb filter less likely to be damaged.

[0054] In the honeycomb-fired body 10, the thickness of the cell partitions 13 is preferably 0.10 to 0.46 mm. Cell partitions 13 of this thickness have sufficient mechanical strength and can effectively suppress the increase in pressure loss.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] (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.

[0062] 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.

[0063] 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 2C.

[0064] (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.

[0065] (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.

[0066] (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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] (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.

[0071] (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.

[0072] (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.

[0073] 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.

[0074] In the honeycomb filter according to the first embodiment of the present application, in a cross-section perpendicular to the longitudinal direction of the honeycomb filter, the cross-sectional shape of the first exhaust gas introduction cell is square, and the cross-sectional shape of the second exhaust gas introduction cell and the cross-sectional shape of the exhaust gas discharge cell are octagonal. However, in the honeycomb filter of the present invention, the cross-sectional shape of the first exhaust gas introduction cell, the cross-sectional shape of the second exhaust gas introduction cell, and the cross-sectional shape of the exhaust gas discharge cell are not particularly limited, and may be, for example, the conventional shapes shown in the second to fourth embodiments of the present invention below.

[0075] (Second Embodiment) Next, a honeycomb filter according to a second embodiment of the present invention will be described. Figure 3 is a schematic enlarged view of a portion of the exhaust gas inlet end face of a honeycomb filter, illustrating an example of a honeycomb filter according to a second embodiment of the present invention. The honeycomb filter 120 shown in Figure 3 has a square-section exhaust gas discharge cell 111, surrounded by a porous cell partition wall 113, with a first exhaust gas introduction cell 112 and a second exhaust gas introduction cell 114 adjacent to it. The first exhaust gas introduction cell 112 and the second exhaust gas introduction cell 114 are arranged alternately around the exhaust gas discharge cell 111, with the cross-sectional area of ​​the second exhaust gas introduction cell 114 being larger than that of the first exhaust gas introduction cell 112, and the cross-sectional area of ​​the exhaust gas discharge cell 111 being the same as that of the second exhaust gas introduction cell 114. Furthermore, regarding the cross-sectional shapes of the three adjacent cells, namely the exhaust gas discharge cell 111, the first exhaust gas introduction cell 112, and the second exhaust gas introduction cell 114, the sides of the square exhaust gas discharge cell 111 that face the first exhaust gas introduction cell 112 across the cell partition wall 113 are parallel, and the sides of the square first exhaust gas introduction cell 112 that face the exhaust gas discharge cell 111 across the cell partition wall 113 are parallel. Furthermore, the edges of the first exhaust gas introduction cell 112 that face the second exhaust gas introduction cell 114 across the cell partition wall 113 are parallel, and the edges of the second exhaust gas introduction cell 114 that face the first exhaust gas introduction cell 112 across the cell partition wall 113 are parallel. Also, the distance between the parallel edges is equal in all combinations. Furthermore, in the vertical or horizontal direction of Figure 3, the center of gravity of the exhaust gas discharge cell 111 and the center of gravity of the first exhaust gas introduction cell 112 are aligned in a straight line. Furthermore, in the diagonal direction of Figure 3 (at a 45° or 135° angle to the horizontal direction of Figure 14), the center of gravity of the exhaust gas discharge cell 111 and the center of gravity of the second exhaust gas introduction cell 114 are aligned in a straight line.

[0076] Furthermore, a slit portion 119 is formed in the cell partition wall 113 separating some of the first exhaust gas introduction cells 112 and the second exhaust gas introduction cells 114, allowing the first exhaust gas introduction cells 112 and the second exhaust gas introduction cells 114 to communicate with each other.

[0077] In the honeycomb filter 120, since the slit portion 119 is formed, it is possible to effectively reduce pressure loss while suppressing a decrease in PM collection capacity.

[0078] (Third embodiment) Next, a honeycomb filter according to a third embodiment of the present invention will be described. Figure 4 is a schematic enlarged view of a portion of the exhaust gas inlet side end face of a honeycomb filter, illustrating an example of a honeycomb filter according to the third embodiment of the present invention. The honeycomb filter 220 shown in Figure 4 has the same configuration as the honeycomb filter 120 shown in Figure 3, except that in the cross-section of the honeycomb filter 220, the contours of the exhaust gas discharge cell 211 and the second exhaust gas introduction cell 214 are curved so as to be convex outwards in each cell, and the contour of the first exhaust gas introduction cell 212 is curved so as to be convex inwards in each cell.

[0079] In the honeycomb filter 220, a slit portion 219 is formed in the cell partition wall 213 separating some of the first exhaust gas introduction cells 212 and the second exhaust gas introduction cells 214, which connects the first exhaust gas introduction cells 212 and the second exhaust gas introduction cells 214.

[0080] In the honeycomb filter 220, since the slit portion 219 is formed, it is possible to effectively reduce pressure loss while suppressing a decrease in PM collection capacity.

[0081] (Fourth Embodiment) Next, a honeycomb filter according to a fourth embodiment of the present invention will be described. Figure 5 is a schematic enlarged view of a portion of the exhaust gas inlet side end face of a honeycomb filter, illustrating an example of a honeycomb filter according to the fourth embodiment of the present invention.

[0082] The honeycomb filter 320 shown in Figure 5 has a circular exhaust gas discharge cell 311, and around its entire perimeter are adjacent first exhaust gas introduction cells 312 and second exhaust gas introduction cells 314, both with circular cross-sections, separated by porous cell partitions 313. The first exhaust gas introduction cells 312 and second exhaust gas introduction cells 314 are arranged alternately around the exhaust gas discharge cell 311, with the cross-sectional area of ​​the second exhaust gas introduction cells 314 being larger than that of the first exhaust gas introduction cells 312, and the cross-sectional area of ​​the exhaust gas discharge cell 311 being the same as that of the second exhaust gas introduction cells 314. Furthermore, in the vertical or horizontal direction of Figure 5, the center of gravity of the exhaust gas discharge cell 311 and the center of gravity of the first exhaust gas introduction cell 312 are aligned in a straight line. Furthermore, in the diagonal direction of Figure 5 (at a 45° or 135° angle to the horizontal direction of Figure 5), the center of gravity of the exhaust gas discharge cell 311 and the center of gravity of the second exhaust gas introduction cell 314 are aligned in a straight line.

[0083] Furthermore, a slit portion 319 is formed in the cell partition wall 313 separating some of the first exhaust gas introduction cells 312 and the second exhaust gas introduction cells 314, allowing the first exhaust gas introduction cells 312 and the second exhaust gas introduction cells 314 to communicate with each other.

[0084] In the honeycomb filter 320, since the slit portion 319 is formed, it is possible to effectively reduce pressure loss while suppressing a decrease in PM collection capacity.

[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 54.2% by weight of coarse silicon carbide powder having an average particle size of 22 μm with 23.1% by weight of fine silicon carbide powder having 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, 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 2C. 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 square with four sides of length 1.00 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 1.10 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 1.10 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 cell partitions was 0.17 mm. In Example 1, the width of the slit portion was 0.50 mm. Furthermore, the honeycomb calcined material has a porosity of 38%, an average pore size of 13 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.

[0091] 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 φ266.7mm × 177.8mm.

[0092] (Comparative Example 1) A honeycomb filter according to Comparative Example 1 was manufactured in the same manner as in Example 1, except that a slit portion was not formed.

[0093] (Pressure loss measurement) For the honeycomb filters manufactured in Example 1 and Comparative Example 1, the relationship between gas flow rate and pressure loss was measured using the pressure loss measuring device shown in Figure 6. Figure 6 is a schematic cross-sectional view illustrating the pressure loss measurement method. This pressure loss measuring device 410 has a honeycomb filter 20 fixed inside a metal casing 413 and placed on the gas pipe 412 of the blower 411, and a pressure gauge 414 is attached so that the pressure before and after the honeycomb filter 20 can be detected. The honeycomb filter 20 is positioned so that its exhaust gas inlet end is closer to the gas pipe 412 of the blower 411. In other words, it is positioned so that exhaust gas flows into the cell with the exhaust gas inlet end open. The gas flow rate supplied from blower 411 is 0 to 2000 m³. 3 The system was operated while varying the pressure up to / hr, and the gas was passed through the honeycomb filter 20 to measure the pressure loss before and after the honeycomb filter.

[0094] Figure 7 is a graph showing the relationship between the gas flow rate and pressure loss before PM deposition, as measured in Example 1 and Comparative Example 1. As shown in Figure 7, the honeycomb filter according to Example 1 had a lower pressure loss before PM deposition compared to the honeycomb filter according to Comparative Example 1. [Explanation of symbols]

[0095] 10, 510 Honeycomb fired body 10a End on the exhaust gas inlet side 10b End on the exhaust gas outlet side 11, 111, 211, 311 Exhaust Gas Emission Cells 12, 12A, 112, 212, 312 First exhaust gas introduction cell 13, 13a, 13b, 113, 213, 313 Cell partitions 14, 14A, 14B, 114, 214, 314 Second exhaust gas introduction cell 15 Adhesive layer 16 Outer coating layer 17 Peripheral wall 18 Ceramic Blocks 19, 119, 219, 319 Slit section 20, 120, 220, 320 honeycomb filters 410 Pressure loss measuring device 411 Blower 412 Exhaust pipe 413 Metal casing 414 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. A slit portion is formed in the cell partition wall separating some of the first exhaust gas introduction cells and the second exhaust gas introduction cells, which connects the first exhaust gas introduction cell and the second exhaust gas introduction cell. With respect to a 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, and 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, A honeycomb filter characterized in that 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, thereby surrounding the exhaust gas discharge cell.

2. The honeycomb filter according to claim 1, wherein, with respect to a cross-section perpendicular to the longitudinal direction of the cell, both the exhaust gas discharge cell and the exhaust gas introduction cell are polygonal, 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.

3. The honeycomb filter according to claim 1 or 2, wherein the exhaust gas introduction cell comprises only the first exhaust gas introduction cell and the second exhaust gas introduction cell.

4. Of the imaginary line segments connecting the geometric centroids of the octagons that are the cross-sectional shapes of the four second exhaust gas introduction cells surrounding the exhaust gas discharge cell, the intersection 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 is 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 square, and the midpoint of each side of the square coincides with the geometric centroid of each square that makes 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 cell partition wall is parallel to the side facing the exhaust gas discharge cell across the cell partition wall 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 sides constituting the cross-sectional shape of the exhaust gas discharge cell, the side facing the second exhaust gas introduction cell across the cell partition is parallel to the side constituting the cross-sectional shape of the second exhaust gas introduction cell across the cell partition, and the side facing the second exhaust gas introduction cell across the cell partition is parallel to the side constituting the cross-sectional shape of the first exhaust gas introduction cell across the cell partition, and the distance between the parallel sides is equal in any combination.

5. With respect to a cross-section perpendicular to the longitudinal direction of the cell, The honeycomb filter according to claim 4, 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.

6. The honeycomb filter according to claim 4 or 5, wherein the width of the slit portion is 20 to 70% of the length of the side of the cross-sectional shape of the first exhaust gas introduction cell that faces the second exhaust gas introduction cell.

7. The honeycomb filter according to any one of claims 4 to 6, wherein the slit portion is formed on two of the sides that constitute the cross-sectional shape of each of the second exhaust gas introduction cells.

8. 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 any one of claims 1 to 7, 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.

9. The honeycomb filter according to any one of claims 1 to 8, wherein the thickness of the cell partitions separating the cells of the honeycomb filter is the same.

10. The aforementioned honeycomb filter is A honeycomb filter according to any one of claims 1 to 9, 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.

11. The honeycomb filter according to any one of claims 1 to 10, 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.

12. The honeycomb filter according to any one of claims 1 to 11, wherein the thickness of the cell partition is 0.10 to 0.46 mm.

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 size 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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