Honeycomb filter

Abstract

Provided is a honeycomb filter excellent in regeneration efficiency during continuous regeneration and capable of suppressing an increase in pressure loss due to accumulation of ash. The present invention comprises: a columnar honeycomb structure part 4 having a porous partition wall 1 arranged so as to surround a plurality of cells 2; and a sealing part 5 arranged so as to seal either one of an end part on the inflow end face 11 side or an end part on the outflow end face 12 side of the cells. The cross-sectional shape of an inflow cell 2a is an octagonal shape or a quadrangular shape, and the cross-sectional shape of an outflow cell 2b is a quadrangular shape. The cell density of the honeycomb structure part 4 is 49-70 cells / cm2, and the thickness of the partition wall 1 is 0.152 mm or more. The opening diameter L1 of the inflow cell 2a is 1.16-1.40 mm. The opening diameter L2 of the outflow cell 2b is 0.82 to 1.08 mm. The ratio (L1 / L2) of the opening diameter L1 to the opening diameter L2 is 1.30 to 1.53.

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter. More specifically, it relates to a honeycomb filter that is excellent in regeneration efficiency during continuous regeneration, in which particulate matter collected in the partition walls is burned and removed, and that can suppress the increase in pressure loss due to the accumulation of ash. [Background technology]

[0002] Internal combustion engines are used as a power source in various industries. However, the exhaust gas emitted by internal combustion engines during fuel combustion contains particulate matter such as soot and ash. Hereafter, particulate matter is sometimes referred to as "PM." "PM" is an abbreviation for "Particulate Matter." Regulations regarding the removal of harmful substances such as PM emitted from diesel engines are becoming stricter worldwide, and the installation of after-treatment systems to purify them is required.

[0003] In particular, filters used to remove PM (particulate matter) emitted from diesel engines are sometimes called diesel particulate filters (DPFs). Hereafter, diesel particulate filters will be referred to as "DPFs." As an example of such a DPF, a honeycomb filter using a honeycomb structure is known (see, for example, Patent Documents 1 and 2).

[0004] Exhaust gas purification using a honeycomb filter is performed as follows: First, the honeycomb filter is positioned so that its inlet end is located upstream of the exhaust system from which the exhaust gas is discharged. The exhaust gas flows into the inlet cell from the inlet end of the honeycomb filter. The exhaust gas that has entered the inlet cell then passes through the porous partition and flows to the outlet cell, where it is discharged from the outlet end of the honeycomb filter.

[0005] If PM (particulate matter) is continuously removed from exhaust gas using a DPF, soot and other PM accumulate inside the DPF, reducing the purification efficiency and increasing the pressure loss of the DPF. Therefore, in purification systems using DPFs, for example, a "regeneration process" is performed to burn the soot and other PM accumulated inside the DPF. If soot is burned when a large amount of soot has accumulated inside the DPF, the temperature inside the DPF will rise, which can lead to damage to the DPF. For this reason, it is important to perform soot combustion (in other words, the regeneration process) efficiently. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-000896 [Patent Document 2] Special Publication No. 2022-507651 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] DPF regeneration processes include, for example, "forced regeneration" and "continuous regeneration." Forced regeneration involves intentionally injecting fuel into the DPF to raise the gas temperature inside the DPF and forcibly burn the soot accumulated inside the DPF. In contrast, continuous regeneration sometimes involves converting NO in the exhaust gas to NO2 using an oxidation catalyst, and then using this as an oxidizer to continuously burn the soot accumulated inside the DPF. In continuous regeneration, an oxidation catalyst for exhaust gas purification is supported on the DPF, and continuous regeneration can be performed through the action of this catalyst. As mentioned above, forced regeneration uses fuel to burn soot, which can lead to a decrease in fuel efficiency. Continuous regeneration requires the application of relatively expensive precious metals as catalysts.

[0008] Due to recent stricter regulations, improving fuel efficiency is receiving more attention than ever before. Therefore, in DPF regeneration processes, continuous regeneration is gaining attention over forced regeneration, which can worsen fuel efficiency, and improvements in regeneration efficiency are expected. However, it has been unclear which aspects of the DPF need to be improved to enhance regeneration efficiency in continuous regeneration, and currently, improvements are being relied upon on the catalytic converter side.

[0009] Furthermore, when soot accumulated in the DPF is burned, ash is generated as unburned residue of calcium (Ca) and other materials. When this ash accumulates in the DPF, it increases the pressure loss in the DPF, leading to a decrease in fuel efficiency. For example, conventional measures to suppress the increase in pressure loss due to ash accumulation have included thinning the thickness of the partition walls. However, from the perspective of strength and heat capacity associated with thinning the walls, pursuing thinning alone is not practical, and there is a strong need for the development of technologies that suppress the increase in pressure loss due to ash accumulation using methods other than thinning the walls.

[0010] This invention has been made in view of the problems of the prior art. This invention provides a honeycomb filter that is excellent in regeneration efficiency during continuous regeneration and can suppress the increase in pressure loss due to the accumulation of ash. [Means for solving the problem]

[0011] According to the present invention, a honeycomb filter as shown below is provided.

[0012] [1] A columnar honeycomb structure having porous partition walls arranged to surround a plurality of cells that form a fluid flow path extending from an inlet end face to an outlet end face, and an opening sealing portion disposed to seal either the inlet end face side or the outlet end face side of the cell, The cell in which the sealing portion is provided at the end on the outflow end face side and the inflow end face side is open is designated as an inflow cell. The eye-sealing portion is disposed at the end portion on the inflow end face side, and the cell having the outflow end face side opened is used as an outflow cell. In a cross section orthogonal to the extending direction of the cells of the honeycomb structure, except for the cells disposed on the outermost periphery of the honeycomb structure, the cross-sectional shape of the inflow cell is octagonal or square, and the cross-sectional shape of the outflow cell is square. The cell density of the honeycomb structure is 49 to 70 cells / cm 2 and the thickness of the partition wall is 0.152 mm or more. The opening diameter L1 of the inflow cell is 1.16 to 1.40 mm. The opening diameter L2 of the outflow cell is 0.82 to 1.08 mm. A honeycomb filter in which the ratio (L1 / L2) of the opening diameter L1 to the opening diameter L2 is 1.30 to 1.53.

[0013] [2] The geometric surface area of the inflow cell is 1.23 to 1.50 mm 2 / mm 3 The honeycomb filter according to [1] above.

[0014] [3] The porosity of the partition wall is 35 to 65%, and the honeycomb filter according to [1] or [2] above.

[0015] [4] The honeycomb filter according to any one of [1] to [3] above, which is used as a diesel particulate filter.

Advantages of the Invention

[0016] The honeycomb filter of the present invention is excellent in regeneration efficiency during continuous regeneration for burning and removing PM such as soot, and can effectively suppress an increase in pressure loss due to ash deposition.

Brief Description of the Drawings

[0017] [Figure 1] It is a perspective view seen from the inflow end face side, schematically showing one embodiment of the honeycomb filter of the present invention. [Figure 2] Figure 1 is a plan view of the honeycomb filter as seen from the inlet end face. [Figure 3] Figure 1 is a plan view of the honeycomb filter as seen from the outlet end face. [Figure 4] This is a schematic cross-sectional view of the A-A' section in Figure 2. [Figure 5] Figure 2 is an enlarged plan view showing a portion of the inlet end face of the honeycomb filter. [Modes for carrying out the invention]

[0018] The embodiments of the present invention will be described below, but the present invention is not limited to the embodiments described below. Therefore, it should be understood that any modifications, improvements, etc., made to the embodiments described below, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the present invention, also fall within the scope of the present invention.

[0019] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figures 1 to 5. Here, Figure 1 is a schematic perspective view of one embodiment of the honeycomb filter of the present invention, viewed from the inlet end face side. Figure 2 is a plan view of the honeycomb filter shown in Figure 1, viewed from the inlet end face side, and Figure 3 is a plan view of the honeycomb filter shown in Figure 1, viewed from the outlet end face side. Figure 4 is a schematic cross-sectional view showing the section A-A' in Figure 2. Figure 5 is an enlarged plan view of a part of the inlet end face of the honeycomb filter shown in Figure 2.

[0020] As shown in Figures 1 to 5, the honeycomb filter 100 comprises a honeycomb structure 4 and a sealing portion 5. The honeycomb structure 4 has porous partition walls 1 arranged to surround a plurality of cells 2 that form fluid flow paths extending from an inlet end face 11 to an outlet end face 12. The honeycomb structure 4 is a columnar structure with the inlet end face 11 and the outlet end face 12 as its end faces. In the present invention, a cell 2 means a space surrounded by partition walls 1. The honeycomb structure 4 constituting the honeycomb filter 100 further has outer peripheral walls 3 arranged on its outer peripheral side surface so as to surround the partition walls 1.

[0021] The sealing portion 5 is disposed at either the end of the cell 2 on the inlet end face 11 side or the end on the outlet end face 12 side, sealing the opening of the cell 2. The sealing portion 5 is made of a porous material (i.e., a porous body). In the honeycomb filter 100 shown in Figures 1 to 5, predetermined cells 2, each having a sealing portion 5 (inlet end face side sealing portion 5a) disposed at the end on the inlet end face 11 side, and the remaining cells 2, each having a sealing portion 5 (outlet end face side sealing portion 5b) disposed at the end on the outlet end face 12 side, are alternately arranged with a partition wall 1 in between. Hereinafter, a cell 2 with a sealing portion 5 disposed at the end on the inlet end face 11 side may be referred to as an "outlet cell 2b". A cell 2 with a sealing portion 5 disposed at the end on the outlet end face 12 side may be referred to as an "inlet cell 2a".

[0022] In the honeycomb filter 100, in a cross-section perpendicular to the direction in which the cells 2 of the honeycomb structure 4 extend, the cross-sectional shape of the inlet cells 2a is octagonal or quadrilateral, and the cross-sectional shape of the outlet cells 2b is quadrilateral, except for the cell 2 located on the outermost periphery of the honeycomb structure 4. Hereinafter, a cell 2 whose periphery is surrounded only by the partition wall 1 may be referred to as a "complete cell". On the other hand, when an outer periphery wall 3 is provided on the outer periphery side of the honeycomb structure 4, the cell 2 located on the outermost periphery of the honeycomb structure 4 (hereinafter also simply referred to as the "outermost cell 2") becomes a cell 2 surrounded by the partition wall 1 and the outer periphery wall 3. In such an outermost cell 2, a part of the periphery of the cell 2 is partitioned by the outer periphery wall 3, making it an incomplete cell 2, as if a part of a complete cell is missing. A cell 2 in which the periphery is surrounded by a partition wall 1 and an outer wall 3 is sometimes called an "incomplete cell," and such incomplete cells are not included in the cells 2 that make up the inflow cell 2a and outflow cell 2b described above. Therefore, unless otherwise specified, when simply referring to "inflow cell 2a" and "outflow cell 2b," it refers to the complete cells "inflow cell 2a" and "outflow cell 2b."

[0023] The honeycomb filter 100 of this embodiment has particularly important characteristics in the cell density of the honeycomb structure 4, the thickness of the partition wall 1, and the configuration of the inlet cell 2a and outlet cell 2b. Specifically, the honeycomb structure 4 has a cell density of 49 to 70 cells / cm³ of cells 2 partitioned by the partition wall 1. 2 Furthermore, the thickness of the partition wall 1 constituting the honeycomb structure 4 is 0.152 mm or more. The upper limit of the thickness of the partition wall 1 is determined by the cell density value of the honeycomb structure 4 and the opening diameter L1 of the inlet cell 2a and the opening diameter L2 of the outlet cell 2b, which will be described later.

[0024] Furthermore, in the honeycomb filter 100 of this embodiment, the opening diameter L1 of the inlet cell 2a is 1.16 to 1.40 mm, and the opening diameter L2 of the outlet cell 2b is 0.82 to 1.08 mm. The ratio of the opening diameter L1 of the inlet cell 2a to the opening diameter L2 of the outlet cell 2b (L1 / L2) is 1.30 to 1.53. Hereinafter, the "ratio of the opening diameter L1 of the inlet cell 2a to the opening diameter L2 of the outlet cell 2b (L1 / L2)" may be referred to as the "opening diameter ratio (L1 / L2)" of the outlet cell 2b and the inlet cell 2a.

[0025] The honeycomb filter 100 configured as described above exhibits excellent regeneration efficiency during continuous regeneration, which burns and removes PM such as soot, and effectively suppresses the increase in pressure loss due to ash accumulation. In particular, by setting the ratio of the opening diameters (L1 / L2) of the outflow cell 2b and the inflow cell 2a within the above numerical range, the honeycomb filter 100 can improve regeneration efficiency during continuous regeneration while effectively suppressing the increase in pressure loss due to ash accumulation. For example, during continuous regeneration, soot is burned by reacting it with NO2 on the oxidation catalyst (hereinafter also simply referred to as "catalyst") supported on the partition wall 1. Therefore, by adjusting the opening diameters L1 and L2 to achieve the above-mentioned ratio of opening diameters (L1 / L2), the geometric surface area of ​​the inflow cell 2a is made relatively larger. This configuration increases the contact between the catalyst and soot, improving the regeneration efficiency during continuous regeneration. In addition, the oxidation catalyst supported on the DPF removes NO2 emitted from the engine. x For example, NO can be oxidized to NO2, and here too, the oxidation function of the oxidation catalyst can be increased by increasing the geometric surface area of ​​the inflow cell 2a. As a result, the generation of NO2, which functions as an oxidizer during soot combustion, is promoted, contributing to improved regeneration efficiency.

[0026] In addition, the increase in the pressure loss during ash deposition is attributed to the fact that ash accumulates on the inner wall surface of the inflow cell 2a and the end portion on the outflow end face 12 side, narrowing the flow path through which the exhaust gas flowing into the inflow cell 2a can pass. Therefore, by setting the cell density of the honeycomb structure 4 and the geometric surface area of the inflow cell 2a to appropriate values, the amount of ash deposited per inflow cell 2a and the ash deposition thickness can be reduced, and the increase in the pressure loss caused by ash deposition can be effectively suppressed. Hereinafter, each component of the honeycomb filter 100 of the present embodiment will be described in more detail.

[0027] The cell density of the honeycomb structure 4 is 49 to 70 cells / cm 2 . When the cell density is less than 49 cells / cm 2 , both the opening diameter L1 of the inflow cell and the opening diameter L2 of the outflow cell become large, making it difficult to sufficiently improve the regeneration efficiency during continuous regeneration. On the other hand, when the cell density exceeds 70 cells / cm 2 , for example, when the opening diameter L1 of the inflow cell is unreasonably increased, the cell structure of the honeycomb structure 4 becomes distorted, and the isostatic strength of the honeycomb filter 100 decreases. The cell density is preferably 50 to 70 cells / cm 2 , more preferably 50 to 69 cells / cm 2 , and particularly preferably 52 to 68 cells / cm 2 .

[0028] The thickness of the partition wall 1 is 0.152 mm or more. When the thickness of the partition wall 1 is less than 0.152 mm, the isostatic strength of the honeycomb filter 100 decreases. The upper limit value of the thickness of the partition wall 1 is specified by the value of the cell density of the honeycomb structure 4 and the values of the opening diameter L1 of the inflow cell 2a and the opening diameter L2 of the outflow cell 2b as described above. For example, the thickness of the partition wall 1 is preferably 0.152 to 0.198 mm, more preferably 0.173 to 0.196 mm, and particularly preferably 0.178 to 0.193 mm. The thickness of the partition wall 1 can be measured using, for example, a scanning electron microscope or a microscope.

[0029] The opening diameter L1 of the inlet cell 2a is 1.16 to 1.40 mm, and the opening diameter L2 of the outlet cell 2b is 0.82 to 1.08 mm. The ratio of the opening diameters of the outlet cell 2b to the inlet cell 2a (L1 / L2) is 1.30 to 1.53. If the opening diameter L1 of the inlet cell 2a is less than 1.16 mm, the opening diameter L1 of the inlet cell 2a is too small, and the increase in pressure loss during ash accumulation increases. On the other hand, if the opening diameter L1 of the inlet cell 2a exceeds 1.40 mm, and the cell structure is designed to satisfy the above opening diameter ratio (L1 / L2), the cell structure becomes distorted, and the isostatic strength decreases. Furthermore, even if the opening diameter L2 of the outlet cell 2b is outside the above numerical range, the above-mentioned problems may occur if the cell structure is designed to satisfy the numerical range of the opening diameter L1 and the opening diameter ratio (L1 / L2) of the inlet cell 2a.

[0030] The opening diameter L1 of the inlet cell 2a may be 1.16 to 1.40 mm, but is preferably 1.17 to 1.39 mm. The opening diameter L2 of the outlet cell 2b may be 0.82 to 1.08 mm, but is preferably 0.83 to 1.08 mm. The ratio of the opening diameters of the outlet cell 2b to the inlet cell 2a (L1 / L2) may be 1.30 to 1.53, but is preferably 1.32 to 1.49.

[0031] Furthermore, in a cross-section perpendicular to the direction in which the cells 2 of the honeycomb structure 4 extend, except for the cell 2 located on the outermost periphery of the honeycomb structure 4, the cross-sectional shape of the inlet cell 2a is octagonal or quadrilateral, and the cross-sectional shape of the outlet cell 2b is quadrilateral. Hereinafter, for example, the "cross-sectional shape of cell 2" in a cross-section perpendicular to the direction in which the cells 2 of the honeycomb structure 4 extend may be referred to as the "cross-sectional shape of cell 2" or simply the "shape of cell 2". In the cross-sectional shape of the inlet cell 2a, "octagonal" includes an octagon, a shape in which at least one corner of the octagon is formed in a curved manner, and a shape in which at least one corner of the octagon is chamfered in a straight line. Similarly, in the cross-sectional shapes of the inlet cell 2a and the outlet cell 2b, "quadrilateral" includes a quadrilateral, a shape in which at least one corner of the quadrilateral is formed in a curved manner, and a shape in which at least one corner of the quadrilateral is chamfered in a straight line.

[0032] The honeycomb structure 4 preferably has repeating units in which inlet cells 2a with an octagonal or square cross-sectional shape and outlet cells 2b with a square cross-sectional shape are alternately arranged in a grid pattern with a partition wall 1 in between. The cross-sectional shape of the outlet cells 2b is preferably square. The cross-sectional shape of the inlet cells 2a is preferably an octagon with chamfered corners or a square. For example, as shown in Figure 5, if there is a cell structure in which a plurality of cells 2 are arranged along the left-right and up-down directions of the paper in Figure 5, it is preferable that inlet cells 2a and outlet cells 2b are alternately arranged with a partition wall 1 in between in the arrangement of cells in each direction. In the honeycomb filter 100, the inlet cells 2a preferably have one type of cross-sectional shape that satisfies an opening diameter L1 of 1.16 to 1.40 mm, and the outlet cells 2b preferably have one type of cross-sectional shape that satisfies an opening diameter L2 of 0.82 to 1.08 mm.

[0033] The aperture diameter L1 of the inlet cell 2a shall be the value measured by the following method: In the opening shape of the inlet cell 2a, the distance between two opposing sides of the four sides adjacent to the outlet cell 2b across the partition wall 1 shall be defined as the "aperture diameter L1 of the inlet cell 2a". The aperture diameter L2 of the outlet cell 2b shall be defined as the distance between two opposing sides of the four sides of the rectangular opening shape of the outlet cell 2b, defined as the "aperture diameter L2 of the outlet cell 2b". The aperture diameters L1 and L2 can be measured, for example, using a scanning electron microscope or a microscope.

[0034] The honeycomb filter 100 has a geometric surface area of ​​the inlet cell 2a of 1.23 to 1.50 mm². 2 / mm 3 Preferably, it is 1.25 to 1.49 mm 2 / mm 3 It is even more preferable that the size be 1.27 to 1.48 mm. 2 / mm 3 It is particularly preferable that this be the case. Here, the geometric surface area of ​​the inflow cell 2a refers to the geometric surface area of ​​the partition wall 1 arranged to surround the inflow cell 2a. The "geometric surface area" of the inflow cell 2a is the total internal surface area of ​​the inflow cell 2a (S: unit mm). 2 ) is the total volume of the honeycomb structure 4 (V: unit mm 3 The value obtained by dividing by (S / V: unit mm) 2 / mm 3 It can be calculated as follows. Note that the total internal surface area (S) of the inlet cell 2a is the sum of the surface areas of the partition walls 1 arranged to surround the inlet cell 2a (however, the surface area of ​​the area where the outlet end face side sealing portion 5b is arranged is excluded). Geometric surface area is sometimes called, for example, "GSA" or "geometric surface area GSA". GSA is an abbreviation for "Geometric Surface Area". The geometric surface area of ​​the inlet cell 2a is 1.23 mm². 2 / mm 3 If it is less than 1.50 mm², sufficient improvement in playback efficiency during continuous playback may not be expected. On the other hand, if the geometric surface area of ​​the inflow cell 2a is 1.50 mm² 2 / mm 3If the value exceeds a certain limit, the isostatic strength of the honeycomb filter 100 may decrease if the cell structure of the honeycomb structure 4 becomes distorted.

[0035] There are no particular restrictions on the porosity of the partition wall 1, but it is preferably 35-65%, and more preferably 40-60%. The porosity of the partition wall 1 is a value measured by the mercury intrusion method. The porosity of the partition wall 1 can be measured using, for example, the Autopore 9500 (product name) manufactured by Micromeritics. The porosity can be measured by cutting out a part of the partition wall 1 from the honeycomb structure 4 to make a test piece, and using the test piece obtained in this way. By setting the porosity of the partition wall 1 within the above numerical range, the honeycomb filter 100 can be used particularly suitably as an exhaust gas purification filter, especially as a diesel particulate filter (DPF).

[0036] There are no particular restrictions on the material of partition wall 1. For example, the material of partition wall 1 may include at least one material selected from the group consisting of silicon carbide, cordierite, silicon-silicon carbide composite material, cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate. A silicon-silicon carbide composite material is a composite material formed using silicon carbide as the aggregate and silicon as the binder. A cordierite-silicon carbide composite material is a composite material formed using silicon carbide as the aggregate and cordierite as the binder.

[0037] The outer periphery wall 3 of the honeycomb structure 4 may be integrally formed with the partition wall 1, or it may be an outer periphery coating layer formed by applying an outer periphery coating material to the outer periphery side of the partition wall 1. For example, although not shown in the figures, the outer periphery coating layer can be provided on the outer periphery side of the partition wall after the partition wall and the outer periphery wall have been integrally formed during manufacturing, and the formed outer periphery wall has been removed by a known method such as grinding.

[0038] There are no particular restrictions on the shape of the honeycomb structure 4. Examples of the shape of the honeycomb structure 4 include the inlet end face 11 and the outlet end face 12 being columnar shapes such as circular, elliptical, or polygonal.

[0039] There are no particular restrictions on the size of the honeycomb structure 4, such as the length from the inlet end face 11 to the outlet end face 12, or the size of the cross-section perpendicular to the direction in which the cells 2 of the honeycomb structure 4 extend. The sizes should be appropriately selected to obtain optimal purification performance when the honeycomb filter 100 is used as a filter for exhaust gas purification.

[0040] In the honeycomb filter 100, it is preferable that a catalyst for exhaust gas purification is supported on partition walls 1 that divide multiple cells 2. Supporting the catalyst on the partition walls 1 means that the catalyst is coated on the surface of the partition walls 1 and on the inner walls of the pores formed in the partition walls 1. With this configuration, CO, NOx, HC, etc. in the exhaust gas can be converted into harmless substances through catalytic reactions.

[0041] There are no particular restrictions on the catalyst supported on the partition wall 1. For example, a catalyst containing platinum group elements, which includes an oxide of at least one element among aluminum, zirconium, and cerium, can be used.

[0042] (2) Method for manufacturing a honeycomb filter: There are no particular limitations on the method for manufacturing the honeycomb filter of the present invention, and for example, the following method can be given. First, a plastic clay for making the honeycomb filter is prepared. The clay for making the honeycomb filter can be prepared by adding additives such as binders, pore-forming materials, and water as appropriate to a material selected from the above-mentioned suitable materials for partitions as a raw material powder.

[0043] Next, the clay obtained in this manner is extruded to produce a columnar honeycomb molded body having partition walls that divide a plurality of cells, and an outer peripheral wall arranged to surround these partition walls. In the extrusion molding, a die can be used for extrusion molding, which has slits on the extrusion surface of the clay that form the inverted shape of the honeycomb molded body to be formed. In particular, when manufacturing the honeycomb filter of the present invention, it is preferable to use a die for extrusion molding which has slits for forming inlet cells and outlet cells of predetermined opening diameters in the honeycomb molded body to be extruded. Next, the obtained honeycomb molded body is dried, for example, with microwaves and hot air.

[0044] Next, a sealant is placed at the opening of the cells in the dried honeycomb molded body. Specifically, for example, first, a sealant containing raw materials for forming the sealant is prepared. Next, a mask is applied to the inlet end face of the honeycomb molded body so that the inlet cells are covered. Next, the previously prepared sealant is filled into the openings of the outlet cells on the inlet end face side of the honeycomb molded body that are not masked. After that, the sealant is also filled into the openings of the inlet cells on the outlet end face of the honeycomb molded body in the same manner as described above.

[0045] Next, a honeycomb molded body with a sealing portion placed at one of the cell openings is fired to produce a honeycomb filter. The firing temperature and firing atmosphere vary depending on the raw materials, and a person skilled in the art can select the optimal firing temperature and firing atmosphere for the selected material. [Examples]

[0046] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0047] (Example 1) To 100 parts by mass of cordierite raw material, 2 parts by mass of pore-forming agent, 1 part by mass of dispersion medium, and 6 parts by mass of organic binder were added, mixed, and kneaded to prepare a clay material. Methylcellulose was used as the organic binder. Potassium laurate was used as the dispersant. A water-absorbing polymer with an average particle size of 20 μm was used as the pore-forming agent.

[0048] Next, the clay was extruded using a die for honeycomb molding to obtain a honeycomb mold with an overall cylindrical shape. The cells of the honeycomb mold were octagonal and square in shape, and these octagonal and square cells were arranged alternately with partitions in between.

[0049] Next, the honeycomb molded body was dried in a microwave dryer, and then completely dried in a hot air dryer. After that, both ends of the honeycomb molded body were cut to the specified dimensions.

[0050] Next, a sealing material was prepared to form the sealing portions. Specifically, a slurry-like sealing material was prepared by adding water and a binder to ceramic raw materials. Then, using the sealing material, sealing portions were formed at the openings of predetermined cells on the inlet end face side and at the openings of the remaining cells on the outlet end face side of the dried honeycomb molded body. The sealing portions were formed such that octagonal cells became the inlet cells and square cells became the outlet cells.

[0051] Next, the honeycomb molded body with each pore sealed was degreased and fired to produce the honeycomb filter of Example 1.

[0052] The honeycomb filter of Example 1 had an end face diameter of 228.6 mm and a cell length in the direction of cell extension of 184.2 mm. The honeycomb filter of Example 1 had a partition wall thickness of 0.185 mm and a cell density of 52 cells / cm³. 2The results for the partition wall thickness and cell density are shown in Table 1. Furthermore, the porosity of the partition wall of the honeycomb filter in Example 1 was 58%. The porosity of the partition wall was measured using an Autopore 9500 (product name) manufactured by Micromeritics.

[0053] For the honeycomb filter of Example 1, the opening diameter L1 of the inlet cell and the opening diameter L2 of the outlet cell were measured. The results are shown in Table 1. In Table 1, the "Opening Diameter Ratio (L1 / L2)" column shows the ratio of the opening diameter L1 of the inlet cell to the opening diameter L2 of the outlet cell. In addition, the honeycomb filter of Example 1 has a geometric surface area of ​​1.27 mm² of the inlet cell. 2 / mm 3 That was the case.

[0054] [Table 1]

[0055] For the honeycomb filter of Example 1, the regeneration efficiency (%) and isostatic strength (MPa) during continuous regeneration were measured using the following method. Furthermore, the pressure loss during ash accumulation (hereinafter referred to as "pressure loss evaluation during ash accumulation") was evaluated using the following method. The results are shown in Table 2.

[0056] [Playback efficiency during continuous playback (%)] First, an oxidation catalyst was supported on the partition wall of the honeycomb filter. The amount of catalyst supported was 10 g / L. Next, 3 g / L of soot was deposited on the partition wall of the honeycomb filter on which the catalyst was supported as described above. A total of 23 g of soot was deposited inside the honeycomb filter. In this state, another honeycomb structure (catalyst support) on which the oxidation catalyst was supported was installed upstream of the honeycomb filter. Then, high-temperature exhaust gas was flowed from the upstream side of the upstream honeycomb structure, and the exhaust gas that had passed through the upstream honeycomb structure was passed through the inlet end face of the honeycomb filter to perform continuous regeneration of the filter. The exhaust gas was assumed to be discharged from a 6.7 L diesel engine. The regeneration conditions were a gas temperature of 350°C at the inlet end face and a gas passage time of 60 minutes. After that, the honeycomb filter was removed from the device that had performed continuous regeneration, and the amount of soot remaining inside the honeycomb filter was measured. The regeneration efficiency (%) during continuous regeneration was calculated by dividing the mass of soot reduced by continuous regeneration by the mass of soot initially deposited. If the regeneration efficiency (%) during continuous regeneration calculated in this way exceeded the regeneration efficiency (50.8%) of the honeycomb filter in Comparative Example 1 described later, it was considered acceptable; otherwise, it was considered unacceptable.

[0057] [Evaluation of pressure loss during ash accumulation] First, the pressure loss of the honeycomb filter was measured, and the measured pressure loss was defined as the "initial pressure loss (kPa)". Next, the pressure loss was measured again with a predetermined amount of soot and ash deposited on the partition wall of the honeycomb filter, and the measured pressure loss was defined as the "pressure loss with ash deposition (kPa)". When measuring the pressure loss with ash deposition, the amount of soot deposited was set to 3 g / L and the amount of ash deposited to 60 g / L. Here, the amount of soot and ash deposited refers to the amount of soot and ash deposited (g) per unit volume (1 L) of the honeycomb filter. The value obtained by subtracting the "initial pressure loss (kPa)" from the "pressure loss with ash deposition (kPa)" was defined as the "pressure loss increase ΔP (kPa)" of the honeycomb filter being evaluated. Furthermore, using the pressure loss increase ΔP of the honeycomb filter in Comparative Example 1, described later, as the base, the pressure loss increase rate (%) for the pressure loss evaluation with ash deposition was calculated using the following formula (1). In formula (1) below, the pressure loss increase ΔP (kPa) of the honeycomb filter of Comparative Example 1, which serves as the standard, is defined as "standard pressure loss increase ΔP0," and the pressure loss increase ΔP (kPa) of the honeycomb filter under evaluation is defined as "target pressure loss increase ΔP1." In the evaluation of pressure loss during ash accumulation, a failure was deemed to occur if the pressure loss increase ΔP was greater than that of the honeycomb filter of Comparative Example 1, and the pressure loss increase rate (%) was positive. Pressure loss increase rate (%) = (Target pressure loss increase ΔP1 - Reference pressure loss increase ΔP0) × Reference pressure loss increase ΔP0 × 100% (1)

[0058] [Isostatic strength (MPa)] The isostatic strength was measured based on the isostatic fracture strength test specified in the Japanese Automotive Standard (JASO standard) M505-87, issued by the Society of Automotive Engineers of Japan. The isostatic fracture strength test involves placing a honeycomb filter in a cylindrical rubber container, covering it with an aluminum plate, and applying isotropic pressure compression in water. The isostatic strength measured by the isostatic fracture strength test is indicated by the pressure value (MPa) at which the honeycomb filter breaks. An isostatic strength of 1.0 MPa or higher was considered a pass, and an isostatic strength below 1.0 MPa was considered a fail.

[0059] [Table 2]

[0060] (Examples 2-14 and Comparative Examples 1-4) A honeycomb filter was fabricated in the same manner as in Example 1, except that the configuration of the honeycomb filter was changed as shown in Table 1.

[0061] For the honeycomb filters of Examples 2-14 and Comparative Examples 1-4, the regeneration efficiency (%) and isostatic strength (MPa) during continuous regeneration were measured using the same method as in Example 1, and the pressure loss during ash accumulation was evaluated. The results are shown in Table 2.

[0062] (result) The honeycomb filters of Examples 1 to 14 showed good measurement results in both regeneration efficiency (%) and isostatic strength (MPa) during continuous regeneration. Furthermore, in the evaluation of pressure loss during ash accumulation, the honeycomb filters of Examples 1 to 14 showed a smaller pressure loss increase ΔP and a negative pressure loss increase rate (%) compared to the reference honeycomb filter of Comparative Example 1.

[0063] On the other hand, the honeycomb filter in Comparative Example 2 was able to improve the regeneration efficiency (%) during continuous regeneration and reduce pressure loss during ash accumulation by reducing the thickness of the partition walls. However, because the thickness of the partition walls was made excessively thin, the isostatic strength was significantly reduced.

[0064] The honeycomb filter in Comparative Example 3 had a small opening diameter L1 of the inlet cell, and a small opening diameter ratio (L1 / L2) of 1.26. As a result, in the pressure loss evaluation during ash accumulation, the honeycomb filter in Comparative Example 3 was blocked in the middle section rather than the downstream section in the overall length direction by the ash accumulated inside the honeycomb filter, reducing the effective volume of the honeycomb filter. Consequently, the pressure loss increase ΔP was greater than that of the honeycomb filter in Comparative Example 1.

[0065] The honeycomb filter in Comparative Example 4 increased the cell density of the honeycomb structure to 71 cells / cm². 2 In this cell density, if we try to maintain a constant inflow cell opening diameter L1 and increase the geometric surface area of ​​the inflow cells, we are forced to decrease the outflow cell opening diameter L2, resulting in a distorted cell structure of the honeycomb structure and a deterioration of isostatic strength. [Industrial applicability]

[0066] The honeycomb filter of the present invention can be used as a filter for removing PM (particulate matter) emitted from a diesel engine. [Explanation of Symbols]

[0067] 1: Partition wall, 2: Cell, 2a: Inlet cell, 2b: Outlet cell, 3: Outer wall, 4: Honeycomb structure, 5: Eye seal, 5a: Eye seal on the inlet end face side, 5b: Eye seal on the outlet end face side, 11: Inlet end face, 12: Outlet end face, 100: Honeycomb filter, L1: Opening diameter of inlet cell, L2: Opening diameter of outlet cell.

Claims

1. The structure comprises a columnar honeycomb structure having porous partition walls arranged to surround a plurality of cells that form a fluid flow path extending from an inlet end face to an outlet end face, and an opening sealing portion disposed to seal either the inlet end face side or the outlet end face side of the cells, The cell in which the sealing portion is provided at the end on the outflow end face side and the inflow end face side is open is designated as an inflow cell. The cell in which the sealing portion is provided at the end on the inlet end face side and the outlet end face side is open is designated as an outlet cell. In a cross-section perpendicular to the direction in which the cells of the honeycomb structure extend, excluding the cells arranged on the outermost periphery of the honeycomb structure, the cross-sectional shape of the inflow cells is octagonal or quadrilateral, and the cross-sectional shape of the outflow cells is quadrilateral. The cell density of the aforementioned honeycomb structure is 49 to 70 cells / cm². ２ And, The thickness of the partition wall is 0.152 to 0.198 mm. The opening diameter L1 of the inflow cell is 1.16 to 1.40 mm. The opening diameter L2 of the outflow cell is 0.82 to 1.08 mm. A honeycomb filter in which the ratio of the aperture diameter L1 to the aperture diameter L2 (L1 / L2) is 1.30 to 1.

53.

2. The geometric surface area of ​​the inflow cell is 1.23 to 1.50 mm². ２ / mm ３ The honeycomb filter according to claim 1.

3. The honeycomb filter according to claim 1 or 2, wherein the porosity of the partition wall is 35 to 65%.

4. A honeycomb filter according to claim 1 or 2, used as a diesel particulate filter.

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