JP2023136732A - honeycomb filter - Google Patents

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

The present invention relates to a honeycomb filter.

Exhaust gas emitted from internal combustion engines such as diesel engines contains particulates (hereinafter also referred to as PM) such as soot, and in recent years, it has become a problem that this PM is harmful to the environment or the human body. ing. Moreover, since the exhaust gas also contains harmful gas components such as CO, HC, or NOx, there are concerns about the effects of these harmful gas components on the environment or the human body.

Therefore, cordierite is used as an exhaust gas purification device that is connected to an internal combustion engine to collect PM in exhaust gas and purify harmful gas components in exhaust gas such as CO, HC, or NOx contained in exhaust gas. Various honeycomb filters (honeycomb filters) made of porous ceramics such as silicon carbide and silicon carbide have been proposed.

In addition, these honeycomb filters are designed to improve the fuel efficiency of internal combustion engines and eliminate operational troubles caused by increased pressure loss. Various honeycomb filters have been proposed in which the rate of increase in pressure loss is low.

An example of an invention that discloses such a honeycomb filter is Patent Document 1.
FIG. 6 is an end view schematically showing the honeycomb filter according to Patent Document 1 on the exhaust gas inlet side.

As shown in FIG. 6, Patent Document 1 describes an exhaust gas introduction cell (12, 14) whose end on the exhaust gas inlet side is open and whose end on the exhaust gas outlet side is plugged, and an end on the exhaust gas outlet side. A honeycomb fired body (honeycomb filter) 510 is disclosed that includes an exhaust gas discharge cell 11 whose end is open and whose end on the exhaust gas inlet side is plugged.
The exhaust gas exhaust cell includes a first exhaust gas introduction cell 12 whose cross-sectional shape perpendicular to the longitudinal direction of the cell is a square, and a second exhaust gas introduction cell 14 whose cross-sectional shape perpendicular to the longitudinal direction of the cell is an octagon. Become.
Further, the cross-sectional shape of the exhaust gas exhaust cell perpendicular to the longitudinal direction is octagonal, and is the same shape as the cross-sectional shape of the second exhaust gas introduction cell 14 perpendicular to the longitudinal direction.
In the honeycomb fired body 510, the first exhaust gas introduction cells 12 and the second exhaust gas introduction cells 14 are alternately arranged around the exhaust gas discharge cells 11.

International Publication No. 2013/187444

Patent Document 1 discloses that by arranging the exhaust gas discharge cell and the exhaust gas introduction cell in this way, the flow of the exhaust gas is made uniform and smooth, the pressure loss is low in the initial stage, and the pressure loss is difficult to increase even if PM accumulates. It teaches you what to do.
However, in order to further improve the fuel efficiency of internal combustion engines, there has been a desire to further reduce the initial pressure loss.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a honeycomb filter that has even lower pressure loss in the initial stage of exhaust gas treatment and that does not easily increase pressure loss even when PM accumulates. It is to be.

In the honeycomb fired body described in Patent Document 1, the PM is included in the cell partition between the first exhaust gas introduction cell and the exhaust gas discharge cell, the cell partition between the second exhaust gas introduction cell and the exhaust gas discharge cell, and the first PM is deposited on the cell partition wall between the exhaust gas introduction cell and the second exhaust gas introduction cell. In other words, the cell partition wall between the first exhaust gas introduction cell and the second exhaust gas introduction cell becomes involved in collecting PM after a certain amount of time has passed, and the cell partition between the first exhaust gas introduction cell and the second exhaust gas introduction cell The cell partition wall between the two can hardly participate in PM collection in the early stage of exhaust gas treatment.
The present inventor has discovered that PM is also deposited on the cell partition wall between the first exhaust gas introduction cell and the second exhaust gas introduction cell by reducing the difference in gas passing flow rate between the respective partition walls in the early stage of exhaust gas treatment. It was estimated that this would reduce the initial pressure loss. Based on this assumption, the present inventor completed the present invention.

That is, the honeycomb filter of the present invention includes a porous cell partition wall that partitions and forms a plurality of cells that serve as flow paths for exhaust gas, and the end on the exhaust gas inlet side is open and the end on the exhaust gas outlet side is open. It comprises a sealed exhaust gas introduction cell, and an exhaust gas discharge cell whose end on the exhaust gas outlet side is open and whose end on the exhaust gas inlet side is plugged, and the exhaust gas introduction cell and the exhaust gas discharge The honeycomb filter has the same cross-sectional shape in a direction perpendicular to the longitudinal direction of each cell from the end on the exhaust gas inlet side to the end on the exhaust gas outlet side except for the plugged portion, and The exhaust gas introduction cell is adjacent to the entire periphery of the exhaust cell with a porous cell partition in between, and the exhaust gas introduction cell has a cross section perpendicular to the longitudinal direction of the cell with the first exhaust gas introduction cell. There are two types of second exhaust gas introduction cells, each of which has a larger area than the first exhaust gas introduction cell, and the cross-sectional area of the cross section perpendicular to the longitudinal direction of the cell of the second exhaust gas introduction cell is larger than that of the second exhaust gas introduction cell. The cross-sectional area of the cross-section perpendicular to the longitudinal direction of the cell is the same as or larger than the cross-sectional area of the cross-section perpendicular to the longitudinal direction of the cell, and the exhaust gas discharge cell and the exhaust gas introduction cell are All of them are polygonal, and among the sides forming the cross-sectional shape of the first exhaust gas introduction cell, the length of the side facing the exhaust gas discharge cell forms the cross-sectional shape of the second exhaust gas introduction cell. Among the sides, the cell partition wall is longer than the side facing the exhaust gas discharge cell, and the cell partition wall is connected to a first cell partition wall that separates the adjacent first exhaust gas introduction cell and the second exhaust gas introduction cell; a second cell partition that separates the first exhaust gas introduction cell and the exhaust gas discharge cell; and a third cell partition that separates the second exhaust gas discharge cell and the exhaust gas discharge cell, and the thickness of the first cell partition is equal to It is characterized by being thinner than the thickness of the second cell partition wall and the thickness of the third cell partition wall.

In the honeycomb filter of the present invention, 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.
Therefore, the resistance when the exhaust gas passes through the second cell partition wall and the third cell partition wall becomes relatively large, making it difficult for the exhaust gas to pass through the second cell partition wall and the third cell partition wall.
Therefore, at the initial stage of exhaust gas treatment using the honeycomb filter, compared to the case where the thickness of the first cell partition is the same as the thickness of the second cell partition and the thickness of the third cell partition, the exhaust gas It becomes easier to pass through the first cell partition. Therefore, in the initial stage of exhaust gas treatment, the first cell partition wall can also function as a filter.
As a result, it is estimated that the initial pressure loss can be reduced in the honeycomb filter of the present invention.

In the honeycomb filter of the present invention, regarding the cross section perpendicular to the longitudinal direction of the cell, the length of the side facing the exhaust gas discharge cell among the sides forming the cross-sectional shape of the second exhaust gas introduction cell is the same as the length of the side facing the exhaust gas discharge cell. Among the sides constituting the cross-sectional shape of the exhaust gas introduction cell, the length is preferably 0.8 times or less as long as the side facing the exhaust gas discharge cell.
With such a ratio, the exhaust gas can more easily pass through the second cell partition wall that separates the exhaust gas exhaust cell and the first exhaust gas introduction cell, and pressure loss before PM deposition can be effectively suppressed.
If the ratio exceeds 0.8, there will be no significant difference in length between the two sides, making it difficult to keep the initial pressure loss low.

In the honeycomb filter of the present invention, in terms of a cross section perpendicular to the longitudinal direction of the cells, the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, and the second exhaust gas introduction cell is octagonal. It is desirable that there be.
With the honeycomb filter having the above configuration, it is possible to effectively suppress the pressure loss at the initial stage of exhaust gas treatment, and it is also possible to increase the surface area on which PM is deposited, so that the pressure loss can be kept low.

In the honeycomb filter of the present invention, regarding the cross section perpendicular to the longitudinal direction of the cells, 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 , is preferably 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 is not too small, so the resistance of gas passing 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, resulting in 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 will become too small, and the filtration area will become small, resulting in high pressure loss. easy. 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 reduce pressure loss.

In the honeycomb filter of the present invention, with respect to a cross section perpendicular to the longitudinal direction of the cells, 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 square. has an octagonal cross-sectional shape, and the cross-sectional shapes of the second exhaust gas introduction cell and the exhaust gas discharge cell are congruent with each other, and the first exhaust gas introduction cell and the first exhaust gas introduction cell are arranged around the exhaust gas discharge cell with a cell partition between them. The four second exhaust gas introduction cells are arranged alternately to surround the exhaust gas discharge cell, and the four second exhaust gas introduction cells surrounding the exhaust gas discharge cell have a cross-sectional shape. Among the virtual line segments connecting the geometric center of gravity of each octagon, the intersection of two line segments that pass through a graphical area consisting of the cross-sectional shape of the exhaust gas exhaust cell is the cross-sectional shape of the exhaust gas exhaust cell. Among the hypothetical line segments that coincide with the geometric center of gravity of the octagon and connect the geometric center of gravity of each octagon that is the cross-sectional shape of the four second exhaust gas introduction cells. , the four lines that do not pass through the graphic area formed by the cross-sectional shape of the exhaust gas discharge cell constitute a quadrilateral, and the midpoint of each side of the square forms a cross section 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 so as to coincide with the geometric center of gravity of each rectangular shape, and the cross-sectional shape of the exhaust gas discharge cell is A side that faces the first exhaust gas introduction cell across the second cell partition, and a side that forms the cross-sectional shape of the first exhaust gas introduction cell across the second cell partition. The side facing the exhaust cell is parallel, and in the side constituting the cross-sectional shape of the exhaust gas exhaust cell, the side facing the second exhaust gas introduction cell across the third cell partition wall and the second exhaust gas introduction cell are parallel to each other. The side forming the cross-sectional shape of the cell is parallel to the side facing the exhaust gas discharge cell across the third cell partition, and the side forming the cross-sectional shape of the first exhaust gas introduction cell is parallel to the side facing the exhaust gas discharge cell across the third cell partition wall. A side that faces the second exhaust gas introduction cell across one cell partition, and a side forming the cross-sectional shape of the second exhaust gas introduction cell, faces the first exhaust gas introduction cell across the first cell partition. It is desirable to be parallel to the sides.
When the honeycomb filter has such a configuration, the effects of the present invention described above can be suitably exhibited.

In the honeycomb filter of the present invention, it is desirable that the exhaust gas introduction cell consists of only the first exhaust gas introduction cell and the 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.

The honeycomb filter of the present invention includes the exhaust gas discharge cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell, and a plurality of honeycomb fired bodies each having an outer peripheral wall are bonded together via an adhesive layer. It is desirable that it be formed by
When the honeycomb filter has such a configuration, even if stress occurs in one honeycomb fired body, the stress is relaxed by the adhesive layer and is difficult to be transmitted to other honeycomb fired bodies. In other words, the stress generated in the honeycomb filter can be alleviated. As a result, damage to the honeycomb filter can be prevented.

The honeycomb filter of the present invention is composed of a honeycomb fired body, and the honeycomb fired body is preferably 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 having the above structure has excellent heat resistance.

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

In the honeycomb filter of the present invention, the thickness of the second cell partition wall is preferably 0.15 to 0.46 mm.
Further, in the honeycomb filter of the present invention, the thickness of the third cell partition wall is preferably 0.15 to 0.46 mm.
A cell partition wall having such a thickness has sufficient mechanical strength and can effectively suppress an increase in pressure loss.

In the honeycomb filter of the present invention, the ratio of the thickness of the second cell partition wall to the thickness of the first cell partition wall is preferably 1.2 to 6.0.
Further, in the honeycomb filter of the present invention, the ratio of the thickness of the third cell partition wall to the thickness of the first cell partition wall is preferably 1.2 to 6.0.
When the above ratio is less than 1.2, the difference between the resistance when the exhaust gas passes through the first cell partition wall and the resistance when the exhaust gas passes through the second cell partition wall or the third cell partition wall becomes small, and the exhaust gas At the beginning of the process, it becomes difficult for exhaust gas to pass through the first cell partition. As a result, it becomes difficult to reduce pressure loss in the initial stage of exhaust gas treatment.
When the ratio exceeds 6.0, the first cell partition wall becomes too thin, or the second cell partition wall or the third cell partition wall becomes too thick.
If the first cell partition walls become too thin, the strength will decrease and the honeycomb filter will be easily damaged.
If the second cell partition wall or the third cell partition wall is too thick, it becomes difficult for exhaust gas to pass through the second cell partition wall or the third cell partition wall, resulting in a large pressure loss.

In the honeycomb filter of the present invention, the cell partition walls preferably have a porosity of 30 to 65%.
By setting the porosity in this manner, the cell partition wall can effectively trap PM in the exhaust gas, and can suppress an increase in pressure loss caused by the cell partition wall.
When the porosity of the cell partition wall is less than 30%, the proportion of pores in the cell partition wall is too small, making it difficult for exhaust gas to pass through the cell partition wall, and resulting in a large pressure loss when the exhaust gas passes through the cell partition wall.
When the porosity of the cell partition wall exceeds 65%, the mechanical properties of the cell partition wall become low, and cracks are likely to occur during playback or the like.

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

In the honeycomb filter of the present invention, it is desirable that an outer periphery coat layer is formed on the outer periphery.
The outer peripheral coating layer serves to mechanically protect the internal cells. Therefore, the honeycomb filter has excellent mechanical properties such as compressive strength.

FIG. 1 is a perspective view schematically showing an example of a honeycomb filter according to a first embodiment of the present invention. FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb filter according to the first embodiment of the present invention. FIG. 2B is an end view of the honeycomb fired body shown in FIG. 2A on the exhaust gas inlet side. FIG. 2C is a cross-sectional view taken along line AA of the honeycomb fired body shown in FIG. 2A. FIG. 3A is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas at the initial stage of purifying exhaust gas using a conventional honeycomb filter. FIG. 3B is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the middle stage of purifying exhaust gas using a conventional honeycomb filter. FIG. 3C is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the latter stage of purifying exhaust gas using a conventional honeycomb filter. FIG. 4A is a partially enlarged view of the end face of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas at an initial stage when exhaust gas is purified using the honeycomb filter according to the first embodiment of the present invention. It is. FIG. 4B is a part of the end face of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the middle and later stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention. This is an enlarged view. FIG. 5 is a graph showing the flow velocity simulation results when the inflow gas passes through the cell partition. FIG. 6 is an end view schematically showing the honeycomb filter according to Patent Document 1 on the exhaust gas inlet side.

(First embodiment)
EMBODIMENT OF THE INVENTION Hereinafter, 1st Embodiment which is an example of the honeycomb filter of this invention will be described in detail using drawings.
FIG. 1 is a perspective view schematically showing an example of a honeycomb filter according to a first embodiment of the present invention.
FIG. 2A is a perspective view schematically showing an example of a honeycomb fired body constituting the honeycomb filter according to the first embodiment of the present invention.
FIG. 2B is an end view of the honeycomb fired body shown in FIG. 2A on the exhaust gas inlet side.
FIG. 2C is a cross-sectional view taken along line AA of the honeycomb fired body shown in FIG. 2A.

In the honeycomb filter 20 shown in FIG. 1, a plurality of honeycomb fired bodies 10 are bound together via an adhesive layer 15 to form a ceramic block 18, and the outer periphery of the ceramic block 18 has a structure for preventing leakage of exhaust gas. An outer peripheral coating layer 16 is formed. Note that the outer peripheral coat layer 16 may be formed as necessary.

In the honeycomb filter 20, a plurality of honeycomb fired bodies 10 are bound together via an adhesive layer 15. Therefore, even if stress occurs in one honeycomb fired body 10, the stress is alleviated by the adhesive layer 15 and becomes difficult to be transmitted to other honeycomb fired bodies 10. In other words, the stress generated in the honeycomb filter 20 can be alleviated. As a result, damage to the honeycomb filter 20 can be prevented.
The adhesive layer 15 is obtained 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 is preferably 0.5 to 2.0 mm.

The outer peripheral coating layer 16 serves to mechanically protect the internal cells. Therefore, the honeycomb filter 20 has excellent mechanical properties such as compressive strength.
Note that it is desirable that the material of the outer peripheral coat layer 16 is the same as the material of the adhesive layer 15. The thickness of the outer peripheral coating layer 16 is preferably 0.1 to 3.0 mm.

The honeycomb fired body 10 has a square prism shape, but as shown in FIG. 2A, the corners of the end faces are chamfered so that they have a curved shape, which prevents thermal stress from concentrating on the corners. This prevents damage such as cracks from occurring. The corner portion may be chamfered so as to have a linear shape.

The honeycomb fired body 10 shown in FIG. 2A includes porous cell partition walls 13 that define a plurality of cells that serve as flow paths for exhaust gas, and has an open end 10a on the exhaust gas inlet side and an open end 10a on the exhaust gas outlet side. An exhaust gas introduction cell (cells indicated by reference numerals 12 and 14) in which the portion 10b is plugged, and an exhaust gas discharge cell in which the end 10b on the exhaust gas outlet side is open and the end 10a on the exhaust gas inlet side is plugged. It is equipped with a cell 11.

In addition, in the honeycomb filter of the present invention, it is desirable that the plugging material for plugging the exhaust gas introduction cells and the exhaust gas discharge cells is the same material as the honeycomb fired body.

In the honeycomb filter 20, the cross-sectional shape of the exhaust gas introduction cells (cells indicated by reference numerals 12 and 14) and the exhaust gas discharge cell 11 in the longitudinal direction perpendicular to the end 10a on the exhaust gas inlet side to the exhaust gas outlet side, excluding the plugged portions. is the same in each cell up to the end 10b.

As shown in FIG. 2B, in the honeycomb fired body 10, a first exhaust gas introduction cell 12 having a rectangular cross section and a second exhaust gas introducing cell 14 having an octagonal cross section are arranged all around the exhaust gas discharge cell 11 having an octagonal cross section. is adjacent.
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, and the cross-sectional area of the second exhaust gas introduction cell 14 is larger than the cross-sectional area of the first exhaust gas introduction cell 12. Largely, the cross-sectional area of the exhaust gas discharge cell 11 is the same as the cross-sectional area of the second exhaust gas introduction cell 14.
Further, 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 a square, and the cross-sectional shapes of the second exhaust gas introduction cell 14 and the exhaust gas discharge cell 11 are both octagonal and congruent with each other.

That is, in the honeycomb fired body 10, regarding the cross section perpendicular to the longitudinal direction of the cells, the cross-sectional shape of the exhaust gas discharge cells 11 is octagonal, the cross-sectional shape of the first exhaust gas introduction cells 12 is square, and the cross-sectional shape of the first exhaust gas introduction cells 12 is square. The cross-sectional shape of 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 with each other.
Four first exhaust gas introduction cells 12 and four second exhaust gas introduction cells 14 are alternately arranged around the exhaust gas discharge cell 11 with cell partition walls 13 in between to surround the exhaust gas discharge cell 11.
Also, among the virtual line segments connecting the geometric centers of gravity of each octagon, which is the cross-sectional shape of the four second exhaust gas introduction cells 14 surrounding the exhaust gas exhaust cell 11, the cross-sectional shape of the exhaust gas exhaust cell 11 is The intersection of the two line segments passing through the graphical area made up of coincides with the geometric center of gravity of the octagonal cross-sectional shape of the exhaust gas exhaust cell 11, and the intersection of the four second exhaust gas introduction cells 14. Of the virtual line segments connecting the geometric center of gravity of each octagonal cross-sectional shape, the four that do not pass through the graphic area consisting of the cross-sectional shape of the exhaust gas discharge cell 11 constitute a quadrilateral, and the The midpoint coincides with the geometric center of gravity of each rectangle that is the cross-sectional shape of the four first exhaust gas introduction cells 12 surrounding the exhaust gas exhaust cell 11.

In addition, in the honeycomb fired body 10, in order to make the thickness of the outer peripheral wall 17 other than the corner portions uniform, the side that is in contact with the outer peripheral wall of the exhaust gas introduction cell adjacent to the outer peripheral wall 17 in the cross section perpendicular to the longitudinal direction of the cell is , are formed straight and parallel to the sides forming 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 peripheral wall 17 is changed from an octagon to a hexagon because a portion thereof is cut. The cross-sectional shape of the first exhaust gas introduction cell 12A may be partially cut, but it is desirable that the cross-sectional shape of the first exhaust gas introduction cell 12A is congruent with the cross-sectional shape of the first exhaust gas introduction cell 12.

The second exhaust gas introduction cell 14B located at the corner of the honeycomb fired body 10 has changed from an octagonal shape to a substantially pentagonal shape having a chamfered portion 40 formed of a curve. Although the chamfered portion 40 of the second exhaust gas introduction cell 14B shown in FIG. 2B is chamfered so that the chamfered portion has a curve, it may be chamfered so that the chamfered portion becomes a straight line.

The exhaust gas discharge cell 11 and the second exhaust gas introduction cell 14 have the same octagonal shape, but this octagon is point symmetrical with respect to the center of gravity, and has four long sides and four short sides. are arranged alternately, and the angle between the long side and the short side is 135°.

In the honeycomb fired body 10, among the sides forming the cross-sectional shape of the first exhaust gas introduction cell 12, the length _L1 of the side facing the exhaust gas discharge cell 11 forms the cross-sectional shape of the second exhaust gas introduction cell 14. Among the sides facing the exhaust gas discharge cell 11, the length _L2 is longer than the side facing the exhaust gas discharge cell 11.

Further, in the honeycomb fired body 10, the cell partition wall 13 is a first cell partition wall 13a that separates the adjacent first exhaust gas introduction cell 12 and second exhaust gas introduction cell 14, and a first cell partition wall 13a that separates the first exhaust gas introduction cell 12 and the exhaust gas discharge cell 11. It includes a second cell partition 13b and a third cell partition 13c that separates the second exhaust gas introduction cell 14 and the exhaust gas discharge cell 11.

That is, the side forming the cross-sectional shape of the first exhaust gas introduction cell 12 and the side forming the cross-sectional shape of the exhaust gas discharge cell 11, which face each other across the second cell partition wall 13b, are parallel to each other. Further, the side forming the cross-sectional shape of the exhaust gas discharge cell 11 and the side forming the cross-sectional shape of the second exhaust gas introduction cell 14, which face each other across the third cell partition wall 13c, are parallel to each other. The side forming the cross-sectional shape of the first exhaust gas introduction cell 12 and the side forming the cross-sectional shape of the second exhaust gas introduction cell 14, which face each other across the first cell partition wall 13a, are parallel to each other.

In the honeycomb fired 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.

Here, a case where exhaust gas flows into the honeycomb fired body 10 and PM is collected will be described.
As shown in FIG. 2C, the exhaust gas G that has flowed into the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14 (not shown in FIG. 2C) (in FIG. 2C, the exhaust gas is indicated by G, and the flow of the exhaust gas is ) flows out from the exhaust gas exhaust cell 11 after passing through a cell partition 13 that separates the exhaust gas exhaust cell 11 from the first exhaust gas introduction cell 12 or the second exhaust gas introduction cell 14. When the exhaust gas G passes through the cell partition wall 13, PM and the like in the exhaust gas are collected, so the cell partition wall 13 functions as a filter.

In the honeycomb fired body 10, the shape of the cross section perpendicular to the longitudinal direction of the first exhaust gas introduction cell 12 is different from the shape of the cross section perpendicular to the longitudinal direction of the second exhaust gas introduction cell 14.
Therefore, the resistance when the exhaust gas passes from the first exhaust gas introduction cell 12 to the exhaust gas discharge cell 11 is different from the resistance when the 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.

Furthermore, PM and the like deposited on the cell partition walls 13 act as resistance when the exhaust gas G passes through the cell partition walls 13 . Therefore, the amount of PM deposited also affects the ease with which exhaust gas passes from the first exhaust gas introduction cell 12 or the second exhaust gas introduction cell 14 to the exhaust gas exhaust cell 11.
That is, the ease with which exhaust gas passes from the first exhaust gas introduction cell 12 or the second exhaust gas introduction cell 14 to the exhaust gas exhaust cell 11 changes due to the accumulation of PM over time.

Here, in a conventional honeycomb filter in which the cell partition walls have a uniform thickness, the flow of exhaust gas passing through the cell partition walls will be described.
FIG. 3A is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas at the initial stage of purifying exhaust gas using a conventional honeycomb filter.
FIG. 3B is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the middle stage of purifying exhaust gas using a conventional honeycomb filter.
FIG. 3C is a partially enlarged view of the end surface of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the latter stage of purifying exhaust gas using a conventional honeycomb filter.

The conventional honeycomb fired body 510 shown in FIGS. 3A to 3C is manufactured using the honeycomb fired body 510 shown in FIGS. It has the same configuration as the body 10.

As shown in FIG. 3A, when exhaust gas flows into the honeycomb fired body 510, it flows into the first exhaust gas introduction cell 12 and the second exhaust gas introduction cell 14, each of which has an open end 10a on the inlet side. Exhaust gas flows from the easy-flowing part within the filter.
In the honeycomb fired body 510, among the sides forming the cross-sectional shape of the first exhaust gas introduction cell 12, the length _L1 of the side facing the exhaust gas discharge cell 11 forms the cross-sectional shape of the second exhaust gas introduction cell 14. Among the sides facing the exhaust gas discharge cell 11, 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 longer than the length _L2 of the side facing the exhaust gas discharge cell 11. This is larger than the surface area of the third cell partition wall 513c that separates the cell 11 and the second exhaust gas introduction cell 14, and the exhaust gas can more easily pass through the second cell partition wall 513b. PM is deposited on the surface of 513b.

Next, as shown in FIG. 3B, when a certain amount of PM is deposited on the inner wall surface of the first exhaust gas introduction cell 12 of the second cell partition 513b, the PM becomes thicker because the cross-sectional area of the first exhaust gas introduction cell 12 is small. accumulate. As a result, resistance due to PM deposition increases, making it difficult for exhaust gas to pass through the second cell partition 513b.
In such a situation, as described above, the exhaust gas passes through the third cell partition wall 513c that separates the exhaust gas discharge cell 11 and the second exhaust gas introduction cell 14 (main channel switch), and PM also accumulates on the surface.

Next, since the exhaust gas can pass through the cell partition walls quite freely, as shown in FIG. It also passes through the interior and flows into 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.

Note that when the exhaust gas passes through the inside of the first cell partition wall 513a and reaches the exhaust gas discharge cell 11, the moving distance of the exhaust gas becomes longer, so the resistance when the exhaust gas passes becomes larger.
Therefore, in the honeycomb fired body 510, the exhaust gas passes through the inside of the first cell partition wall 513a because PM is deposited on the second cell partition wall 513b and the third cell partition wall 513c, and the resistance when the exhaust gas passes through these cell partition walls is increased. After rising.
In other words, in the initial stage of exhaust gas purification, the amount of exhaust gas that passes through the inside of the first cell partition wall 513a and reaches the exhaust gas exhaust cell 11 is small. Therefore, it can be said that the first cell partition wall 513a does not function sufficiently as a filter for collecting PM in the initial stage of purifying exhaust gas.

Next, the flow of exhaust gas passing through the cell partition walls in the honeycomb fired body 10 will be explained.
FIG. 4A is a partially enlarged view of the end face of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas at an initial stage when exhaust gas is purified using the honeycomb filter according to the first embodiment of the present invention. It is.
FIG. 4B is a part of the end face of the honeycomb filter on the exhaust gas inlet side, schematically showing an example of the flow of exhaust gas in the middle and later stages when purifying exhaust gas using the honeycomb filter according to the first embodiment of the present invention. This is an enlarged view.

In the honeycomb fired 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 when the exhaust gas passes through the second cell partition wall 13b and the third cell partition wall 13c becomes relatively large, making it difficult for the exhaust gas to pass through the second cell partition wall 13b and the third cell partition wall 13c.
Therefore, as shown in FIG. 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 stage of exhaust gas treatment. Further, in the initial stage of exhaust gas treatment, the exhaust gas passes through the second cell partition wall 13b and flows into the exhaust gas discharge cell 11.
Therefore, PM is deposited on the first cell partition wall 13a and the second cell partition wall 13b.

After that, when PM is deposited to some extent on the first cell partition wall 13a and the second cell partition wall 13b, the exhaust gas passes through the third cell partition wall 13c and flows into the exhaust gas exhaust cell 11, as shown in FIG. 4B.

Thereafter, PM will be uniformly deposited on the first cell partition wall 13a, the second cell partition wall 13b, and the third cell partition wall 13c.

In this manner, in the honeycomb fired body 10, the first cell partition walls 13a can also function as a filter at the initial stage of exhaust gas treatment.
As a result, it is estimated that the initial pressure loss can be reduced in the honeycomb fired body 10.

In this specification, measurements of "length", "thickness", "cross-sectional area", etc. are preferably performed using electron micrographs. The electron micrograph can be taken using, for example, an electron microscope (FE-SEM: high-resolution field emission scanning electron microscope S-4800 manufactured by Hitachi High-Technologies).
In addition, the magnification of the electron micrograph can be determined by determining the unevenness of particles and pores on the surface (inner wall) of the cell partition walls that make up the cell, identifying the cross-sectional shape of the cell, the length of the sides, the thickness of the partition wall, and the cross-sectional area of the cell. It is necessary to use a magnification that does not interfere with the measurement of the cells, and also allows the measurement of the cross-sectional shape of the cell, the length of the sides, the thickness of the cell partition wall, and the cross-sectional area of the cell. Therefore, it is best to measure using an electron micrograph with a magnification of 30 times.
That is, based on the definitions of cell length and cell partition thickness described above, the length of each side of the cell is measured using the scale of the electron micrograph, and its value is determined. Arithmetic calculation is performed based on the cell length and other values obtained. In addition, if it is troublesome to measure the cross-sectional area mathematically, you can cut out a square corresponding to the unit area from the scale of the electron micrograph (a square whose side is the length of the scale) and measure the weight. The cross section of the cell is cut along the cross-sectional shape of the cell (in the case of a polygon, if the apex portion is a curve, cut along the curve), and the weight of the cut portion is measured. The cross-sectional area of the cell can be calculated from the weight ratio.

In addition to such manual measurements, measurements can also be performed by importing electron micrographs as image data, or using image data directly imported from an electron microscope, inputting the scale of the photograph, and replacing it with electronic measurement. It is also possible. Of course, both the manual measurement method and the computerized measurement method are measurements based on the scale of the electron microscope image, and are based on the same principle, so it goes without saying that there will be no discrepancy in the measurement results of the two methods.

For electronic measurement, measurement software called image analysis particle size distribution software (manufactured by Mountech Co., Ltd.) MAC-View (Version 3.5) can be used. This software allows you to measure the cross-sectional area by scanning an electron micrograph or using image data directly from an electron microscope, inputting the scale of the photo, and specifying a range along the inner wall of the cell. Furthermore, the distance between arbitrary points in the image can be measured based on the scale of the electron micrograph.
When photographing a cross section of a cell using an electron microscope, cut a filter perpendicular to the longitudinal direction of the cell, prepare a 1 cm x 1 cm x 1 cm sample so that the cut surface is included, and then clean the sample with ultrasonic waves. Alternatively, embed it in resin and take an electron micrograph. Embedding with resin does not affect the measurement of cell side length and cell partition thickness.

In the honeycomb fired body 10, in a 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 forming the cross-sectional shape of the second exhaust gas introduction cell 14 is 1 Among the sides constituting the cross-sectional shape of the exhaust gas introduction cell 12, the length L1 of the side facing the exhaust gas discharge cell ₁₁ is desirably 0.8 times or less, and preferably 0.1 to 0.7 times. It is more desirable that
With such a ratio, the exhaust gas can more easily pass through the second cell partition wall that separates the exhaust gas exhaust cell 11 and the first exhaust gas introduction cell 12, and the pressure loss before PM deposition can be effectively suppressed. can.
If the ratio exceeds 0.8, there will be no large difference in length between the two sides, making it difficult to keep pressure loss low in the initial stage of exhaust gas treatment.

In the honeycomb fired body 10, the cross-sectional area of the first exhaust gas introduction cell 12 is desirably 20 to 50% of the cross-sectional area of the second exhaust gas introduction cell 14, and 25 to 45 % is more desirable.
With such a ratio, a difference can be created 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, and pressure loss can be effectively suppressed. can do.
Since the volume of the exhaust gas discharge cell does not become too small, the resistance of gas passing 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 pressure loss can be effectively suppressed. I can do it.
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, which tends to increase pressure loss. . 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 reduce pressure loss.

In the honeycomb fired body 10, the thickness of the first cell partition walls 13a is preferably 0.05 to 0.25 mm.
When the thickness of the first cell partition wall 13a is within such a range, the exhaust gas can easily pass through the first cell partition wall 13a at the initial stage of exhaust gas treatment, and pressure loss can be reduced.
If the thickness of the first cell partition is less than 0.05 mm, the strength will be low and it will be easily damaged.
When the thickness of the first cell partition wall is 0.25 mm or more, it becomes difficult for exhaust gas to pass through the first cell partition wall, and it becomes difficult to reduce pressure loss in the initial stage of exhaust gas treatment.

In the honeycomb filter of the present invention, the thickness of the second cell partition wall is preferably 0.15 to 0.46 mm.
Further, in the honeycomb filter of the present invention, the thickness of the third cell partition wall is preferably 0.15 to 0.46 mm.
A cell partition wall having such a thickness has sufficient mechanical strength and can effectively suppress an increase in pressure loss.

In the honeycomb fired 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 preferably 1.5 to 5.0. is more desirable.
Further, 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, more preferably 1.5 to 5.0.
When the above ratio is less than 1.2, the difference between the resistance when the exhaust gas passes through the first cell partition wall and the resistance when the exhaust gas passes through the second cell partition wall or the third cell partition wall becomes small, and the exhaust gas At the beginning of the process, it becomes difficult for exhaust gas to pass through the first cell partition. As a result, it becomes difficult to reduce pressure loss in the initial stage of exhaust gas treatment.
When the ratio exceeds 6.0, the first cell partition wall becomes too thin, or the second cell partition wall or the third cell partition wall becomes too thick.
If the first cell partition walls become too thin, the strength will decrease and the honeycomb filter will be easily damaged.
If the second cell partition wall or the third cell partition wall is too thick, it becomes difficult for exhaust gas to pass through the second cell partition wall or the third cell partition wall, resulting in a large pressure loss.

In the honeycomb fired body 10, the cell partition walls 13 preferably have a porosity of 30 to 65%.
By setting the porosity in this manner, the cell partition wall 13 can effectively trap PM in the exhaust gas, and can suppress an increase in pressure loss caused by the cell partition wall 13.
When the porosity of the cell partition wall is less than 30%, the proportion of pores in the cell partition wall is too small, making it difficult for exhaust gas to pass through the cell partition wall, and resulting in a large pressure loss when the exhaust gas passes through the cell partition wall.
When the porosity of the cell partition wall exceeds 65%, the mechanical properties of the cell partition wall become low, and cracks are likely to occur during playback or the like.

In the honeycomb fired body 10, the average pore diameter of the pores included in the cell partition walls 13 is preferably 5 to 25 μm.
When the average pore diameter is within the above range, PM can be collected with high collection efficiency while suppressing an increase in pressure loss.
If the average pore diameter of the pores included in the cell partition wall is less than 5 μm, the pores are too small, resulting in a large pressure loss when exhaust gas passes through the cell partition wall.
When the average pore diameter of the pores included in the cell partition walls exceeds 25 μm, the pore diameter becomes too large, resulting in a decrease in PM collection efficiency.

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

The material of the honeycomb fired body 10 is not particularly limited as long as it is made of a porous material, but examples of the constituent material of the honeycomb fired body 10 include carbide ceramics such as silicon carbide, titanium carbide, tantalum carbide, and tungsten carbide; Examples include 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. Therefore, the honeycomb fired body 10 made of silicon carbide or silicon-containing silicon carbide has excellent heat resistance.
Note that silicon-containing silicon carbide is silicon carbide mixed with metallic silicon, and silicon-containing silicon carbide containing 60 wt% or more of silicon carbide is preferable.

The number of cells per unit area in the cross section of the honeycomb fired body 10 is preferably 31 to 93 cells/cm ² (200 to 600 cells/inch ² ).

Next, a method for manufacturing a honeycomb filter according to the first embodiment of the present invention will be described.
In addition, below, the case where silicon carbide is used as a ceramic powder is demonstrated.

(1) A molding step is performed in which a honeycomb molded body is produced by extrusion molding a wet mixture containing ceramic powder and a binder.
Specifically, first, silicon carbide powders having different average particle sizes as ceramic powders, an organic binder, a liquid plasticizer, a lubricant, and water are mixed to create a wet mixture for manufacturing a honeycomb formed body. Prepare.

If necessary, a pore-forming agent such as balloons, which are microscopic hollow spheres made of oxide ceramic, spherical acrylic particles, or graphite, may be added to the above-mentioned wet mixture.
The balloon is not particularly limited, and examples thereof include alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), mullite balloons, and the like. Among these, alumina balloons are preferred.

Subsequently, the wet mixture is put into an extrusion molding machine and extrusion molded to produce a honeycomb molded body having a predetermined shape.
At this time, 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 FIG. 2B.

(2) Cut the honeycomb molded body into a predetermined length, dry it using a microwave dryer, hot air dryer, dielectric dryer, vacuum dryer, vacuum dryer, freeze dryer, etc., and then cut it into a predetermined length. A plugging step is performed in which the cells are filled with a sealant paste serving as a sealant to plug the cells.
Here, the above-mentioned wet mixture can be used as the sealant paste.

(3) After heating the honeycomb molded body to 300 to 650°C in a degreasing furnace and performing a degreasing process to remove organic matter in the honeycomb molded body, the degreased honeycomb molded body is transported to a firing furnace and heated to 300 to 650°C. By performing a firing step of heating to 2200° C., honeycomb fired bodies as shown in FIGS. 2A to 2C are produced.
Note that the sealing material paste filled in the end portions of the cells is fired by heating and becomes a plugging material.
Further, the conditions for the cutting step, drying step, plugging step, degreasing step, and firing step can be those conventionally used when producing a honeycomb fired body.

(4) A bundling step is performed in which a plurality of honeycomb fired bodies are sequentially piled up and bound using an adhesive paste on a support table, thereby producing a honeycomb aggregate formed by stacking a plurality of honeycomb fired bodies.
As the adhesive paste, for example, one made of an inorganic binder, an organic binder, and inorganic particles is used. Moreover, the adhesive paste may further contain inorganic fibers and/or whiskers.

Examples of the inorganic particles contained in the adhesive paste include carbide particles and nitride particles. Specifically, silicon carbide particles, silicon nitride particles, boron nitride particles, etc. may be mentioned. These may be used alone or in combination of two or more. Among inorganic particles, silicon carbide particles are preferable because of their excellent thermal conductivity.

Examples of the inorganic fibers and/or whiskers contained in the adhesive paste include inorganic fibers and/or whiskers made of silica-alumina, mullite, alumina, silica, and the like. These may be used alone or in combination of two or more. Among inorganic fibers, alumina fibers are preferred. Moreover, the inorganic fiber may be a biosoluble fiber.

Furthermore, balloons, which are minute hollow spheres made of oxide ceramic, spherical acrylic particles, graphite, etc. may be added to the adhesive paste, if necessary. The balloon is not particularly limited, and examples thereof include alumina balloons, glass microballoons, shirasu balloons, fly ash balloons (FA balloons), mullite balloons, and the like.

(5) Next, by heating the honeycomb aggregate, the adhesive paste is heated and solidified to form an adhesive layer, and a quadrangular prism-shaped ceramic block is produced.
As the conditions for heating and solidifying the adhesive paste, the conditions conventionally used for manufacturing honeycomb filters can be applied.

(6) Perform a cutting process of cutting the ceramic block.
Specifically, by cutting the outer periphery of the ceramic block using a diamond cutter, a ceramic block whose outer periphery is processed into a substantially cylindrical shape is produced.

(7) A peripheral coating layer forming step is performed in which a peripheral coating material paste is applied to the peripheral surface of a substantially cylindrical ceramic block and dried and solidified to form a peripheral coating layer.
Here, the adhesive paste described above can be used as the outer circumferential coating material paste. Note that a paste having a different composition from the adhesive paste described above may be used as the outer circumferential coating material paste.
Note that the outer peripheral coat layer does not necessarily need to be provided, and may be provided as necessary.
By providing the outer periphery coat layer, the outer periphery of the ceramic block can be shaped into a cylindrical honeycomb filter.
Through the above steps, the honeycomb filter according to the first embodiment of the present invention including the honeycomb fired body can be manufactured.

In the above process, a honeycomb filter of a predetermined shape was produced by performing a cutting process, but in the process of producing a honeycomb fired body, honeycomb fired bodies of multiple shapes having an outer peripheral wall on the entire outer periphery are produced, A predetermined shape such as a cylinder may be formed by combining shaped honeycomb fired bodies via an adhesive layer. In this case, the cutting process can be omitted.

(Other embodiments)
The honeycomb filter according to the first embodiment of the present invention is a so-called aggregate type honeycomb filter formed by aggregating a plurality of honeycomb fired bodies, but the honeycomb filter of the present invention is formed from one honeycomb fired body. It may be a so-called integrated honeycomb filter.

In the honeycomb filter according to the first embodiment of the present invention, the outer circumferential wall of the honeycomb fired 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 fired body is partially It had been cut.
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 fired body is not cut, and the thickness of the outer peripheral wall does not have to be constant.

(Example 1)
52.8% by weight of coarse silicon carbide powder having an average particle size of 22 μm and 22.6% by weight of fine silicon carbide powder having an average particle size of 0.5 μm are mixed, and an organic binder is added to the resulting mixture. (Methyl cellulose) 4.6% by weight, lubricant (Unilube manufactured by NOF Corporation) 0.8% by weight, glycerin 1.3% by weight, pore former (acrylic resin) 1.9% by weight, oleic acid 2.8% by weight % and 13.2% by weight of water were added and kneaded to obtain a wet mixture, followed by an extrusion molding step.
In this step, a raw honeycomb molded body having a shape similar to the honeycomb fired body 10 shown in FIGS. 2A to 2C and without cell plugging was produced.

Next, the raw honeycomb molded body was dried using a microwave dryer to produce a dried honeycomb molded body. Thereafter, predetermined cells of the dried honeycomb molded body were filled with a sealing material paste to plug the cells.
Specifically, the cells were plugged so that the end on the exhaust gas inlet side and the end on the exhaust gas outlet side were plugged at the positions shown in FIG. 2B.
Note that the above wet mixture was used as a sealant paste. After plugging the cells, the dried honeycomb formed body filled with the sealing material paste was dried again using a dryer.

Subsequently, the dried body of the honeycomb molded body whose cells had been plugged was subjected to a degreasing treatment at 400° C., and further a firing treatment was performed at 2200° C. for 3 hours in an argon atmosphere at normal pressure.
In this way, a honeycomb fired body according to Example 1 was produced.

In Example 1, the shape of the cross section perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a rectangle with side lengths of 0.94 mm x 0.97 mm.
In Example 1, the shape of the cross section perpendicular to the longitudinal direction of the second exhaust gas introduction cell is such that four long sides each having a length of 1.04 mm and four short sides each having a length of 0.30 mm are arranged alternately. It was an octagon. Note that the angle between the long side and the short side was 135°.
In Example 1, the shape of the cross section perpendicular to the longitudinal direction of the exhaust gas discharge cell is such that four long sides each having a length of 1.01 mm and four short sides each having a length of 0.30 mm are arranged alternately. It was octagonal. Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Example 1, the thickness of the first cell partition wall is 0.15 mm, the thickness of the second cell partition wall is 0.18 mm, and the thickness of the third cell partition wall is 0.15 mm. It was .18 mm.

The honeycomb fired body according to Example 1 had a porosity of 45%, an average pore diameter of 15 μm, a size of 36.4 mm x 36.4 mm x 177.8 mm, and a number of cells (cell density) of 300 pieces/inch ^2. Met.
A plurality of the completed honeycomb fired bodies are bound together using an adhesive paste made of a mixture of SiC particles, silica sol, and alumina fibers, the outer periphery is processed, and a coating layer made of the same material as the adhesive paste is provided on the outer periphery. A cylindrical honeycomb filter measuring φ330.2 mm×177.8 mm was produced.

(Example 2)
A honeycomb filter according to Example 2 was manufactured in the same manner as Example 1, except that the structure of the honeycomb fired body to be manufactured was changed as follows.
In the honeycomb fired body according to Example 2, the shape of the cross section perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a rectangle with side lengths of 0.91 mm x 1.02 mm.
In the honeycomb fired body according to Example 2, the shape of the cross section perpendicular to the longitudinal direction of the second exhaust gas introduction cell has four long sides with a length of 1.03 mm and four short sides with a length of 0.34 mm. It was an octagon with alternating sections. Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Example 2, the shape of the cross section perpendicular to the longitudinal direction of the exhaust gas discharge cell is such that four long sides each having a length of 0.92 mm and four short sides each having a length of 0.34 mm alternate. It was an octagonal shape arranged in . Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Example 2, the thickness of the first cell partition wall is 0.10 mm, the thickness of the second cell partition wall is 0.21 mm, and the thickness of the third cell partition wall is 0.21 mm. there were.

(Example 3)
A honeycomb filter according to Example 3 was manufactured in the same manner as Example 1, except that the structure of the honeycomb fired body to be manufactured was changed as follows.
In the honeycomb fired body according to Example 3, the shape of the cross section perpendicular to the longitudinal direction of the first exhaust gas introduction cell was a rectangle with side lengths of 0.88 mm x 1.07 mm.
In the honeycomb fired body according to Example 3, the shape of the cross section perpendicular to the longitudinal direction of the second exhaust gas introduction cell has four long sides with a length of 0.82 mm and four short sides with a length of 0.52 mm. It was an octagon with alternating sections. Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Example 3, the shape of the cross section perpendicular to the longitudinal direction of the exhaust gas discharge cell is such that four long sides each having a length of 1.02 mm and four short sides each having a length of 0.24 mm alternate. It was an octagonal shape arranged in . Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Example 3, the thickness of the first cell partition wall is 0.05 mm, the thickness of the second cell partition wall is 0.24 mm, and the thickness of the third cell partition wall is 0.24 mm. there were.

(Comparative example 1)
A honeycomb filter according to Comparative Example 1 was manufactured in the same manner as Example 1, except that the structure of the manufactured honeycomb fired body was changed as follows.
In the honeycomb fired 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 a side length of 0.95 mm.
In the honeycomb fired body according to Comparative Example 1, the shape of the cross section perpendicular to the longitudinal direction of the second exhaust gas introduction cell has four long sides with a length of 1.05 mm and four short sides with a length of 0.28 mm. It was an octagon with alternating sections. Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Comparative Example 1, the shape of the cross section perpendicular to the longitudinal direction of the exhaust gas discharge cell is such that four long sides each having a length of 1.05 mm and four short sides each having a length of 0.28 mm alternate. It was an octagonal shape arranged in . Note that the angle between the long side and the short side was 135°.
In the honeycomb fired body according to Comparative Example 1, the thickness of the first cell partition wall, the thickness of the second cell partition wall, and the thickness of the third cell partition wall were uniformly 0.17 mm.

(Flow velocity simulation when inflowing scum passes through cell partition wall)
Using the honeycomb filters according to Examples 1 to 3 and Comparative Example 1, the first cell partition wall, the second cell partition wall, and the second cell partition wall were formed at predetermined positions from the end on the exhaust gas inlet side to the end on the exhaust gas outlet side of each honeycomb filter. The gas flow velocity in a three-cell partition was simulated. The software used for the simulation was "STAR-CCM+".
As conditions for the simulation, the temperature of the inflow gas was 380° C., and the flow rate of the inflow gas was 1700 kg/hr.

Next, the difference between the maximum value of the gas passing flow rate and the minimum value of the gas passing flow rate at each measurement position (a position at a predetermined distance from the exhaust gas inlet side of the honeycomb filter) was calculated.
Then, the simulation results were plotted in coordinates, with the horizontal axis representing the distance from the exhaust gas inlet side end of the honeycomb filter and the vertical axis representing the difference between the maximum value and the minimum value of the gas passing flow velocity, as shown in FIG. 5.
FIG. 5 is a graph showing the flow velocity simulation results when the inflow gas passes through the cell partition.

As shown in FIG. 5, it can be seen that in the honeycomb filters according to Examples 1 to 3, the difference in gas passing flow velocity at each measurement position is smaller than that in the honeycomb filter of Comparative Example 1. This indicates that the entire cell partition wall can be effectively used as a filter from the initial stage before PM deposition, and therefore it is thought that the pressure loss is reduced.

10, 510 Honeycomb fired body 10a Exhaust gas inlet side end 10b Exhaust gas outlet side end 11 Exhaust gas discharge cell 12, 12A First exhaust gas introduction cell 13 Cell partition 13a First cell partition 13b Second cell partition 13c Third cell partition 14, 14A, 14B Second exhaust gas introduction cell 15 Adhesive layer 16 Peripheral coat layer 17 Peripheral wall 18 Ceramic block 20 Honeycomb filter 40 Chamfered portion 210 Pressure loss measuring device 211 Diesel engine 212 Exhaust gas pipe 213 Metal casing 214 Pressure gauge

Claims (16)

an exhaust gas introduction cell that includes a porous cell partition wall that partitions a plurality of cells that serve as flow paths for exhaust gas, has an open end on the exhaust gas inlet side, and has a plugged end on the exhaust gas outlet side;
an exhaust gas discharge cell having an open end on the exhaust gas outlet side and a plugged end on the exhaust gas inlet side; A honeycomb filter whose shape 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 plugged portion,
The exhaust gas introduction cell is adjacent to the entire periphery of the exhaust gas discharge cell with a porous cell partition in between, and the exhaust gas introduction cell has a cross section perpendicular to the longitudinal direction of the first exhaust gas introduction cell and the cell. consisting of two types of second exhaust gas introduction cells having a larger cross-sectional area than the first exhaust gas introduction cell, and
The cross-sectional area of the cross-section perpendicular to the longitudinal direction of the cell of the exhaust gas exhaust cell is equal to or larger than the cross-sectional area of the cross-section perpendicular to the longitudinal direction of the cell of the second exhaust gas introduction cell. It is formed large,
Regarding the cross section perpendicular to the longitudinal direction of the cell, the exhaust gas discharge cell and the exhaust gas introduction cell are both polygonal, and of the sides forming the cross-sectional shape of the first exhaust gas introduction cell, the side facing the exhaust gas discharge cell The length of the side facing the exhaust gas exhaust cell is longer than the length of the side facing the exhaust gas exhaust cell among the sides forming the cross-sectional shape of the second exhaust gas introduction cell,
The cell partition includes a first cell partition that separates the first and second exhaust gas introduction cells that are adjacent to each other, a second cell partition that separates the first and second exhaust gas introduction cells, and a second cell partition that separates the first and second exhaust gas introduction cells. comprising an exhaust gas exhaust cell and a third cell partition that separates the exhaust gas exhaust cell,
The honeycomb filter is characterized in that the first cell partition wall is thinner than the second cell partition wall and the third cell partition wall. Regarding the cross section perpendicular to the longitudinal direction of the cell,
Among the sides forming the cross-sectional shape of the second exhaust gas introduction cell, the length of the side facing the exhaust gas discharge cell is equal to the length of the side facing the exhaust gas discharge cell among the sides forming the cross-sectional shape of the first exhaust gas introduction cell. The honeycomb filter according to claim 1, wherein the honeycomb filter is 0.8 times or less the length of the side facing the . Regarding the cross section perpendicular to the longitudinal direction of the cell,
The honeycomb filter according to claim 1 or 2, wherein the exhaust gas discharge cell is octagonal, the first exhaust gas introduction cell is square, and the second exhaust gas introduction cell is octagonal. Regarding the 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 3, 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. Regarding the cross section perpendicular to the longitudinal direction of the cell,
The cross-sectional shape of the exhaust gas exhaust cell is an octagon, the cross-sectional shape of the first exhaust gas introduction cell is a quadrangle, and the cross-sectional shape of the second exhaust gas introduction cell is an octagon,
The cross-sectional shapes of the second exhaust gas introduction cell and the exhaust gas discharge cell are congruent with each other, and
Around the exhaust gas exhaust cell, four of the first exhaust gas introduction cells and four of the second exhaust gas introduction cells are each arranged alternately with a cell partition wall in between, so as to surround the exhaust gas exhaust cell,
Also, the cross-sectional shape of the exhaust gas exhaust cell is selected from among the virtual line segments connecting the geometric centers of gravity of each octagon, which is the cross-sectional shape of the four second exhaust gas introduction cells surrounding the exhaust gas exhaust cell. The intersection of two line segments passing through a graphic area consisting of coincides with the geometric center of gravity of the octagon that is the cross-sectional shape of the exhaust gas discharge cell,
And, among the virtual line segments connecting the geometric centers of gravity of each octagon, which is the cross-sectional shape of the four second exhaust gas introduction cells, four lines do not pass through the graphic area formed by the cross-sectional shape of the exhaust gas discharge cell. constitutes a quadrilateral, and the midpoint of each side thereof coincides with the geometric center of gravity of each quadrilateral, which is the cross-sectional shape of the four first exhaust gas introduction cells surrounding the exhaust gas discharge cell,
The exhaust gas exhaust cell, the first exhaust gas introduction cell, and the second exhaust gas introduction cell are respectively arranged, and
In the side constituting the cross-sectional shape of the exhaust gas exhaust cell, the side facing the first exhaust gas introduction cell across the second cell partition, and the side constituting the cross-sectional shape of the first exhaust gas introduction cell, the second The side facing the exhaust gas discharge cell across the cell partition is parallel,
In the side forming the cross-sectional shape of the exhaust gas exhaust cell, the side facing the second exhaust gas introduction cell across the third cell partition, and the side forming the cross-sectional shape of the second exhaust gas introduction cell, the side forming the cross-sectional shape of the second exhaust gas introduction cell, The side facing the exhaust gas exhaust cell across the three-cell partition is parallel, and the side forming the cross-sectional shape of the first exhaust gas introduction cell is parallel to the second exhaust gas introduction cell across the first cell partition. According to claim 3 or 4, the side facing the first exhaust gas introduction cell and the side forming the cross-sectional shape of the second exhaust gas introduction cell are parallel to the side facing the first exhaust gas introduction cell across the first cell partition. Honeycomb filter as described. The honeycomb filter according to any one of claims 1 to 5, wherein the exhaust gas introduction cell comprises only a first exhaust gas introduction cell and a second exhaust gas introduction cell. The honeycomb filter is
A claim in which 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 are bonded together via an adhesive layer. The honeycomb filter according to any one of items 1 to 6. The honeycomb filter according to claim 7, wherein the honeycomb filter is made of a honeycomb fired body, and the honeycomb fired body is made of silicon carbide or silicon-containing silicon carbide. The honeycomb filter according to any one of claims 1 to 8, wherein the first cell partition wall has a thickness of 0.05 to 0.25 mm. The honeycomb filter according to any one of claims 1 to 9, wherein the second cell partition wall has a thickness of 0.15 to 0.46 mm. The honeycomb filter according to any one of claims 1 to 10, wherein the third cell partition wall has a thickness of 0.15 to 0.46 mm. The honeycomb filter according to any one of claims 1 to 11, wherein the ratio of the thickness of the second cell partition wall to the thickness of the first cell partition wall is 1.2 to 6.0. The honeycomb filter according to any one of claims 1 to 12, wherein the ratio of the thickness of the third cell partition wall to the thickness of the first cell partition wall is 1.2 to 6.0. The honeycomb filter according to any one of claims 1 to 13, wherein the cell partition wall has a porosity of 30 to 65%. The honeycomb filter according to any one of claims 1 to 14, wherein the average pore diameter of pores included in the cell partition walls is 5 to 25 μm. The honeycomb filter according to any one of claims 1 to 15, wherein an outer periphery coating layer is formed on the outer periphery.

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