Honeycomb Filter

Abstract

To provide a honeycomb filter which has pressure loss reduced and is excellent in erosion resistance of a sealing part arranged to seal an opening part of a cell and further is excellent in thermal shock resistance.SOLUTION: The honeycomb filter comprises columnar honeycomb structure parts 4 having porous bulkheads 1 arranged to surround a plurality of cells 2 and sealing parts 5. A cross sectional shape of an inflow-side cell 2a is octagonal, and a cross sectional shape of an outflow-side cell 2b is quadrangular. An area ratio (S1 / S2) of cross sectional areas S2 of the outflow-side cell 2b to cross sectional areas S1 of the inflow-side cell 2a is 1.40-2.20. The sealing parts 5 have protruding parts 6 protruding from end faces of the honeycomb structure parts 4 on which the sealing parts 5 are arranged to the outside in an extending direction of the cells 2. Protrusion heights H of the protruding parts 6 with the end faces as bottom parts are 0.3-3.0 mm and sealing depths L from the end faces of the sealing parts 5 having the protruding parts 6 are 4.0-9.0 mm.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a honeycomb filter. More specifically, the present invention relates to a honeycomb filter that has low pressure loss, excellent erosion resistance at plugging portions arranged to plug openings of cells, and excellent thermal shock resistance. [Background technology]

[0002] Conventionally, honeycomb filters using a honeycomb structure have been known as filters for capturing particulate matter in exhaust gases emitted from internal combustion engines such as automobile engines, or as devices for purifying toxic gas components such as CO, HC, and NOx (see Patent Document 1). The honeycomb structure has partition walls made of porous ceramics such as cordierite, and these partition walls define a plurality of cells. A honeycomb filter is a honeycomb structure in which plugging portions are provided so that openings on the inflow end faces and openings on the outflow end faces of a plurality of cells are alternately plugged. That is, the honeycomb filter has a structure in which inflow cells that are open on the inflow end face and plugged on the outflow end face, and outflow cells that are plugged on the inflow end face and open on the outflow end face are alternately arranged with the partition walls sandwiched between them. In the honeycomb filter, the porous partition walls function as a filter for capturing particulate matter in exhaust gases. Hereinafter, particulate matter contained in exhaust gases may be referred to as "PM." "PM" stands for "particulate matter."

[0003] Exhaust gas purification using a honeycomb filter is performed as follows. First, the honeycomb filter is placed so that its inlet end face is located upstream of the exhaust system from which the exhaust gas is discharged. The exhaust gas flows into the inlet cells from the inlet end face of the honeycomb filter. The exhaust gas that has flowed into the inlet cells then passes through the porous partition walls, flows into the outlet cells, and is discharged from the outlet end face of the honeycomb filter.

[0004] When PM is continuously removed from exhaust gas using a honeycomb filter, PM such as soot accumulates inside the honeycomb filter, reducing the purification efficiency and increasing the pressure loss of the honeycomb filter. Therefore, for example, in purification devices using honeycomb filters, a "regeneration process" is carried out in which the PM accumulated inside the honeycomb filter is burned. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-309922 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, honeycomb filters used to purify exhaust gases emitted from engines of automobiles and the like are required to have reduced pressure loss in order to improve the fuel efficiency of automobiles. As one measure to reduce pressure loss, studies are being conducted on "increasing the porosity" of honeycomb filters, which would further increase the porosity of honeycomb filters compared to conventional methods. However, as the porosity of honeycomb filters increases, the plugging material that constitutes the plugging portions also has a high porosity. This reduces the heat capacity of the entire honeycomb filter, which poses a problem of increased susceptibility to damage to the honeycomb filter during the regeneration process described above.

[0007] Furthermore, honeycomb filters have a problem in that when foreign matter such as metal particles generated from the engine or exhaust pipe is carried along with the flow of exhaust gas, the foreign matter collides with the plugging portions of the honeycomb filter, causing the plugging portions to be worn away. In particular, plugging portions that correspond to the recent trend toward higher porosity are more susceptible to wear due to the collision of foreign matter, making the above-mentioned problem more pronounced. Hereinafter, the wear and scraping of plugging portions, etc. caused by foreign matter carried along with the flow of exhaust gas may be referred to as "erosion."

[0008] The present invention has been made in view of the problems of the prior art. The present invention provides a honeycomb filter that has low pressure loss, excellent erosion resistance at plugging portions, and excellent thermal shock resistance. [Means for solving the problem]

[0009] According to the present invention, there is provided the following honeycomb filter.

[0010] [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 inflow end face to an outflow end face, and plugging portions arranged to plug either the inflow end face side or the outflow end face side of the cells, The plugging portion is disposed at the end portion on the outflow end surface side, and the cell having an opening on the inflow end surface side is defined as an inflow cell, The plugged portion is disposed at an end portion on the inflow end face side, and the cell having an open outflow end face side is defined as an outflow cell, In a cross section of the honeycomb structure section perpendicular to the cell extension direction, the cross-sectional shape of the inlet cells is octagonal and the cross-sectional shape of the outlet cells is quadrangular, except for the cells arranged on the outermost periphery of the honeycomb structure section, an area ratio (S1 / S2) of a cross-sectional area S2 of the outflow cell having a rectangular cross-sectional shape to a cross-sectional area S1 of the inflow cell having an octagonal cross-sectional shape is 1.40 to 2.20; the plugging portions that plug the ends of the inflow cells having an octagonal cross-sectional shape and the outflow cells having a rectangular cross-sectional shape have convex portions that protrude outward in the extension direction of the cells from the end face on the side where the plugging portions are disposed, A honeycomb filter, wherein the protrusion height H from the end face of the convex portion as a base is 0.3 to 3.0 mm, and the plugging depth L from the end face of the plugging portion having the convex portion is 4.0 to 9.0 mm.

[0011] [2] The honeycomb filter according to the above [1], wherein the partition walls have a thickness of 0.17 to 0.32 mm.

[0012] [3] The cell density of the honeycomb structure part is 30 to 62 cells / cm 2 The honeycomb filter according to the above [1] or [2],

[0013] [4] The honeycomb filter according to any one of the above [1] to [3], wherein the porosity of the partition walls is 50 to 60%. [Effects of the Invention]

[0014] The honeycomb filter of the present invention has the effects of low pressure loss, excellent erosion resistance at the plugged portions, and excellent thermal shock resistance. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a perspective view schematically showing one embodiment of a honeycomb filter of the present invention. [Figure 2] FIG. 2 is a plan view showing the inlet end face side of the honeycomb filter shown in FIG. [Figure 3] FIG. 2 is a plan view showing the outflow end face side of the honeycomb filter shown in FIG. [Figure 4] FIG. 3 is an enlarged plan view showing a part of the inlet end face side of the honeycomb filter shown in FIG. 2. [Figure 5] FIG. 3 is a cross-sectional view schematically showing the AA' cross section of FIG. [Figure 6] FIG. 6 is an enlarged cross-sectional view showing a part of the inlet end face side of the honeycomb filter shown in FIG. 5. DETAILED DESCRIPTION OF THE INVENTION

[0016] While the present invention will be described below with reference to exemplary embodiments, it should be understood that the present invention is not limited to the following exemplary embodiments. Therefore, it should be understood that modifications and improvements to the following exemplary embodiments, based on the ordinary knowledge of those skilled in the art, are also within the scope of the present invention, provided that they do not deviate from the spirit of the present invention.

[0017] (1) Honeycomb filter: One embodiment of the honeycomb filter of the present invention is a honeycomb filter 100 as shown in Figs. 1 to 6. Here, Fig. 1 is a perspective view schematically showing one embodiment of the honeycomb filter of the present invention. Fig. 2 is a plan view showing the inflow end face side of the honeycomb filter shown in Fig. 1. Fig. 3 is a plan view showing the outflow end face side of the honeycomb filter shown in Fig. 1. Fig. 4 is an enlarged plan view showing a part of the inflow end face side of the honeycomb filter shown in Fig. 2. Fig. 5 is a cross-sectional view schematically showing the A-A' cross section of Fig. 2. Fig. 6 is an enlarged cross-sectional view showing a part of the inflow end face side of the honeycomb filter shown in Fig. 5.

[0018] As shown in FIGS. 1 to 6, the honeycomb filter 100 includes a honeycomb structure portion 4 and plugging portions 5. The honeycomb structure portion 4 has porous partition walls 1 arranged to surround a plurality of cells 2 that serve as fluid flow paths extending from an inflow end face 11 to an outflow end face 12. The honeycomb structure portion 4 is a columnar structure having the inflow end face 11 and the outflow end face 12 as its end faces. In the present invention, the cell 2 means a space surrounded by the partition walls 1. The honeycomb structure portion 4 constituting the honeycomb filter 100 further has an outer peripheral wall 3 arranged on its outer peripheral side surface so as to surround the partition walls 1.

[0019] The plugging portions 5 are disposed at either the end of the cell 2 on the inflow end face 11 side or the end of the cell 2 on the outflow end face 12 side, and plug the openings of the cell 2. The plugging portions 5 are porous and made of a porous material (i.e., a porous body). In the honeycomb filter 100 shown in FIGS. 1 to 6, predetermined cells 2 having plugging portions 5 disposed at their end on the inflow end face 11 side and the remaining cells 2 having plugging portions 5 disposed at their end on the outflow end face 12 side are alternately arranged with the partition wall 1 in between. Hereinafter, the cells 2 having plugging portions 5 disposed at their end on the inflow end face 11 side may be referred to as "outflow cells 2b." The cells 2 having plugging portions 5 disposed at their end on the outflow end face 12 side may be referred to as "inflow cells 2a."

[0020] In the honeycomb filter 100, in a cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure section 4, the cross-sectional shape of the inlet cells 2a is octagonal and the cross-sectional shape of the outlet cells 2b is quadrangular, except for the cells 2 arranged on the outermost periphery of the honeycomb structure section 4. Hereinafter, a cell 2 whose periphery is surrounded only by partition walls 1 may be referred to as a "complete cell." On the other hand, when an outer peripheral wall 3 is arranged on the outer peripheral side surface of the honeycomb structure section 4, the cell 2 arranged on the outermost periphery of the honeycomb structure section 4 (hereinafter simply referred to as the "outermost cell 2") is a cell 2 surrounded by the partition walls 1 and the outer peripheral wall 3. Part of the periphery of such an outermost cell 2 is partitioned by the outer peripheral wall 3, making it an incomplete cell 2 in which part of the complete cell is missing. Such cells 2 whose peripheries are surrounded by the partition walls 1 and the outer peripheral wall 3 are sometimes called "incomplete cells," and such incomplete cells are not included in the cells 2 that make up the inflow cells 2a and outflow cells 2b described above. Therefore, unless otherwise specified, when simply referring to "inflow cells 2a" and "outflow cells 2b," they refer to the "inflow cells 2a" and "outflow cells 2b," which are complete cells.

[0021] The honeycomb filter 100 of this embodiment has particularly important characteristics in the shapes and cross-sectional areas of the inflow cells 2a and outflow cells 2b, and the configuration of the plugging portions 5 disposed at either end of these cells 2. That is, the honeycomb filter 100 of this embodiment has an area ratio (S1 / S2) of 1.40 to 2.20 of the cross-sectional area S2 of the outflow cells 2b having a rectangular cross-sectional shape to the cross-sectional area S1 of the inflow cells 2a having an octagonal cross-sectional shape. The plugging portions 5 that plug the ends of these inflow cells 2a and outflow cells 2b have protrusions 6 that protrude outward in the extension direction of the cells 2 from the end face on the side where the plugging portions 5 are disposed. Here, "the end face on the side where the plugging portions 5 are disposed" refers to the outflow end face 12 of the honeycomb structure portion 4 in the plugging portions 5 disposed at the ends of the inflow cells 2a, and refers to the inflow end face 11 of the honeycomb structure portion 4 in the plugging portions 5 disposed at the ends of the outflow cells 2b. The protruding height H of the convex portions 6 of the plugging portions 5 is 0.3 to 3.0 mm, and the plugging depth L of the plugging portions 5 having the convex portions 6 is 4.0 to 9.0 mm. Here, the protruding height H of the convex portions 6 refers to the height to the top of the convex portions 6 when the end face (i.e., the inflow end face 11 or the outflow end face 12) of the honeycomb structure portion 4 on which the convex portions 6 are disposed is taken as the bottom. The plugging depth L of the plugging portion 5 refers to the length (length in the direction in which the cell extends) of the plugging portion 5 filled in the cell 2, starting from the end face (i.e., the inlet end face 11 or the outlet end face 12) of the honeycomb structure portion 4 on which the convex portion 6 is arranged.

[0022] The honeycomb filter 100 of this embodiment configured as described above has the effects of low pressure loss, excellent erosion resistance of the plugging portions 5, and excellent thermal shock resistance. In particular, by providing the plugging portions 5 with the above-described convex portions 6, an inclination is formed at the end of the plugging portions 5 on the inlet end face 11 side, and exhaust gas flowing in from the inlet end face 11 side flows smoothly into the inlet cells 2a, thereby reducing the pressure loss of the honeycomb filter 100. Furthermore, as a result of studying the process of wear (erosion) of the plugging portions 5 due to foreign matter carried by the flow of exhaust gas for the plugging portions 5 having the convex portions 6, the following new findings were obtained. When the cross-sectional area S1 of the inlet cells 2a is made larger relative to the cross-sectional area S2 of the outflow cells 2b, the plugging portions 5 having the convex portions 6 have a lower probability of contact with the foreign matter, and the erosion resistance of the plugging portions 5 is improved. In particular, by making the cross-sectional shape of the inlet cells 2a an octagon and the cross-sectional shape of the outlet cells 2b a rectangle and setting the area ratio (S1 / S2) therebetween to 1.40 to 2.20, the erosion resistance of the plugging portion 5 is extremely excellent. Furthermore, by setting the cross-sectional shapes and area ratio (S1 / S2) of the inlet cells 2a and the outlet cells 2b to such shapes, the smooth inflow of exhaust gases by the convex portions 6 is promoted, and the pressure loss of the honeycomb filter 100 can be further reduced.

[0023] Furthermore, in the honeycomb filter 100 of this embodiment, the protrusion height H of the convex portions 6 is set to 0.3 to 3.0 mm, and the plugging depth L of the plugging portions 5 having the convex portions 6 is set to 4.0 to 9.0 mm, thereby increasing the heat capacity of the honeycomb filter 100, including the increase in volume due to the convex portions 6. Therefore, in the regeneration process in which PM accumulated inside the honeycomb filter 100 is burned, the honeycomb filter 100 is less likely to be damaged, and it also has excellent thermal shock resistance.

[0024] The inflow cells 2a have an octagonal cross-sectional shape, and the outflow cells 2b have a rectangular cross-sectional shape. Hereinafter, the "cross-sectional shapes" of the inflow cells 2a and the outflow cells 2b may be referred to as "cell shapes." The cell shapes of the inflow cells 2a and the outflow cells 2b may be polygonal (octagonal and rectangular) shapes with curved corners, for example, a substantially rectangular shape with curved corners. Furthermore, when the cell shape of the outflow cells 2b is a "rectangle" and the cell shape of the inflow cells 2a is an "octagon," it is preferable that the cell shape of the inflow cells 2a be an "octagon" configured as follows. That is, it is preferable that the cell shape of the inflow cells 2a be an "octagon" configured by expanding the length of one side of the rectangular cell shape of the outflow cells 2b by a predetermined length and chamfering the four corners of the expanded rectangle.

[0025] The area ratio (S1 / S2) of the cross-sectional area S2 of the outflow cells 2b to the cross-sectional area S1 of the inflow cells 2a is 1.40 to 2.20. If the area ratio (S1 / S2) is less than 1.40, the effect of reducing pressure loss is low, and sufficient improvement in erosion resistance cannot be expected. If the area ratio (S1 / S2) exceeds 2.20, the pressure loss increases. The area ratio (S1 / S2) is preferably 1.50 to 2.10, and more preferably 1.70 to 2.10.

[0026] The cross-sectional area S1 of the inlet cell 2a and the cross-sectional area S2 of the outlet cell 2b can be measured by analyzing images obtained by observation using a scanning electron microscope (SEM) or a microscope. The cross-sectional area S1 of the inlet cell 2a and the cross-sectional area S2 of the outlet cell 2b are measured at 10 arbitrarily selected locations and the average values ​​are calculated.

[0027] In the plugging portion 5, the protrusion height H of the convex portion 6 is 0.3 to 3.0 mm, and the plugging depth L is 4.0 to 9.0 mm. If the protrusion height H of the convex portion 6 is less than 0.3 mm, it is not preferable in terms of erosion resistance. If the protrusion height H of the convex portion 6 exceeds 3.0 mm, it is not preferable in terms of purification performance. The protrusion height H of the convex portion 6 is preferably 0.5 to 3.0 mm, and more preferably 0.5 to 2.0 mm. Furthermore, if the plugging depth L is less than 4.0 mm, it is not preferable in terms of thermal shock resistance. If the plugging depth L exceeds 9.0 mm, it is not preferable in terms of pressure loss. The plugging depth L is preferably 4.0 to 9.0 mm, and more preferably 4.5 to 9.0 mm.

[0028] The protrusion height H and plugging depth L of the convex portions 6 can be measured by the following method. The protrusion height H can be measured from the end face of the honeycomb filter 100 using a scale. The plugging depth L is measured by inserting a rod of known length that is longer than the overall length of the honeycomb filter 100 into the cell 2, and calculating the length of the plugged portion 5 (i.e., plugging depth L) from the difference between the length of the rod exposed from the honeycomb filter 100 and the length of the rod itself. In addition, the protrusion height H and plugging depth L are measured at 10 arbitrarily selected locations, and the respective average values ​​are calculated.

[0029] The convex portions 6 of the plugging portions 5 may protrude outward in the extension direction of the cells 2 from the end face on the side where the plugging portions 5 are arranged, and the shape of the convex portions 6 may be any shape, such as a hemisphere or a pyramid. It is preferable that the convex portions 6 have one apex, and it is more preferable that the perpendicular line drawn from the apex to the bottom of the convex portion 6 is close to the cross-sectional center (cross-sectional center of gravity) of the cell 2 in which the plugging portions 5 are arranged. The protruding height H and plugging depth L of the convex portions 6 may be the same or different between the plugging portions 5 arranged on the inlet end face 11 side and the plugging portions 5 arranged on the outlet end face 12 side. However, the protruding height H1 and plugging depth L1 of the plugging portion 5 arranged on the inlet end face 11 side of the honeycomb structure portion 4, and the protruding height H2 and plugging depth L2 of the plugging portion 5 arranged on the outlet end face 12 side of the honeycomb structure portion 4, must satisfy the numerical ranges explained above.

[0030] In the honeycomb filter 100, there are no particular limitations on the configuration of the honeycomb structure part 4 having the porous partition walls 1. However, the preferred embodiments of the honeycomb structure part 4 are as follows.

[0031] In the honeycomb structure portion 4, the thickness of the partition walls 1 is preferably 0.17 to 0.32 mm, and more preferably 0.20 to 0.30 mm. The thickness L2 of the partition walls 1 can be measured using, for example, a scanning electron microscope or a microscope. If the thickness L2 of the partition walls 1 is less than 0.17 mm, sufficient strength may not be obtained. On the other hand, if the thickness L2 of the partition walls 1 exceeds 0.32 mm, the pressure loss of the honeycomb filter 100 may increase.

[0032] In the honeycomb structure section 4, the porosity of the partition walls 1 is preferably 50 to 60%, and more preferably 52 to 58%. The porosity of the partition walls 1 is a value measured by mercury intrusion porosimetry. The porosity of the partition walls 1 can be measured using, for example, an Autopore 9500 (trade name) manufactured by Micromeritics. The porosity of the partition walls 1 can be measured using a sample piece obtained by cutting out a part of the partition walls 1 from the honeycomb structure section 4. It is preferable that the porosity of the partition walls 1 is a constant value throughout the entire honeycomb structure section 4.

[0033] The honeycomb structure portion 4 has a cell density of the cells 2 partitioned and formed by the partition walls 1 of 30 to 62 cells / cm. 2 It is preferable that the density is 31 to 62 particles / cm. 2 With this configuration, the collection performance of the honeycomb filter 100 can be maintained while suppressing an increase in pressure loss.

[0034] The outer peripheral wall 3 of the honeycomb structure portion 4 may be configured integrally with the partition walls 1, or may be an outer peripheral coating layer formed by applying an outer peripheral coating material to the outer peripheral side of the partition walls 1. For example, although not shown in the drawings, the outer peripheral coating layer can be provided on the outer peripheral side of the partition walls after the partition walls and the outer peripheral wall are integrally formed during production and then the formed outer peripheral wall is removed by a known method such as grinding.

[0035] There is no particular limitation on the shape of the honeycomb structure 4. Examples of the shape of the honeycomb structure 4 include a columnar shape in which the inlet end face 11 and the outlet end face 12 are circular, elliptical, polygonal, or the like.

[0036] There are no particular limitations on the size of the honeycomb structure part 4, for example, the length from the inflow end face 11 to the outflow end face 12 and the size of the cross section perpendicular to the extension direction of the cells 2 of the honeycomb structure part 4. When the honeycomb filter 100 is used as a filter for purifying exhaust gases, each size may be selected appropriately so as to obtain optimal purification performance.

[0037] The material of the partition walls 1 is not particularly limited. For example, the material of the partition walls 1 can be a material containing at least one selected from the group consisting of silicon carbide, cordierite, a silicon-silicon carbide composite material, a cordierite-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate. The material constituting the partition walls 1 is preferably a material containing 90 mass% or more of the materials listed in the above group, more preferably a material containing 92 mass% or more, and particularly preferably a material containing 95 mass% or more. The silicon-silicon carbide composite material is a composite material formed using silicon carbide as an aggregate and silicon as a binder. The cordierite-silicon carbide composite material is a composite material formed using silicon carbide as an aggregate and cordierite as a binder.

[0038] The material of the plugging portions 5 is preferably a material that is considered to be preferable as the material of the partition walls 1. The material of the plugging portions 5 and the material of the partition walls 1 may be the same material or different materials.

[0039] In the honeycomb filter 100, a catalyst for purifying exhaust gas is preferably supported on the partition walls 1 that define the plurality of cells 2. Supporting a catalyst on the partition walls 1 means that the catalyst is coated on the surfaces of the partition walls 1 and the inner walls of the pores formed in the partition walls 1. This configuration makes it possible to convert CO, NOx, HC, and other substances in the exhaust gas into harmless substances through a catalytic reaction. It also promotes the oxidation of PM, such as collected soot. In the honeycomb filter 100 of this embodiment, it is particularly preferable that the catalyst is supported inside the pores of the porous partition walls 1. This configuration makes it possible to achieve both improved collection performance and reduced pressure loss after catalyst loading when a low catalyst amount is used. Furthermore, since the gas flow becomes uniform after catalyst loading, improved purification performance can also be expected.

[0040] There is no particular limitation on the catalyst supported on the partition walls 1. For example, a catalyst containing a platinum group element, which contains an oxide of at least one element selected from aluminum, zirconium, and cerium, can be used.

[0041] (2) Honeycomb filter manufacturing method: The method for manufacturing the honeycomb filter of the present invention is not particularly limited, and examples thereof include the following method. First, a plastic clay for manufacturing the honeycomb structure part is prepared. The clay for manufacturing the honeycomb structure part can be prepared by adding, as raw material powder, a material selected from the above-mentioned suitable materials for the partition walls, as appropriate, additives such as a binder, a pore-forming material, and water.

[0042] Next, the thus obtained clay is extrusion-molded to produce a columnar honeycomb molded body having partition walls that define a plurality of cells and an outer peripheral wall that surrounds the partition walls. In the extrusion molding, a die having slits formed on the extrusion surface of the clay, which form the inverted shape of the honeycomb molded body to be molded, can be used. The extrusion die used has slits that allow octagonal cells and quadrangular cells to be alternately arranged with the partition walls sandwiched between them in the honeycomb molded body to be molded. The sizes of the octagonal cells and quadrangular cells are adjusted so that the area ratio (S1' / S2') of the area S1' of the octagonal cells to the area S2' of the quadrangular cells is 1.40 to 2.20. Next, the obtained honeycomb molded body is dried, for example, by microwaves and hot air.

[0043] Next, plugging portions are disposed in the openings of the cells of the dried honeycomb formed body. Specifically, for example, first, a plugging material containing raw materials for forming the plugging portions is prepared. Next, a mask is applied to the inlet end face of the honeycomb formed body so that the inlet cells are covered. Next, the previously prepared plugging material is filled into the openings of the outlet cells on the inlet end face side of the honeycomb formed body that are not covered with the mask. At this time, it is preferable to fill using a tool that allows the transfer of a predetermined amount of plugging material, such as a dropper. When filling the plugging material, the plugging material is poured until it overflows the inlet end face of the honeycomb formed body so that a protrusion is formed on the end face. In this way, a protrusion with a protrusion height H of 0.3 to 3.0 mm is formed. Thereafter, the plugging material is filled into the openings of the inlet cells on the outlet end face of the honeycomb formed body using the same method as above. Furthermore, when filling the plugging material, the filling depth of the plugging material is adjusted so that the resulting plugging depth L is 4.0 to 9.0 mm.

[0044] Next, the honeycomb formed body having the plugging portions disposed in either one of the openings of the cells 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 optimum firing temperature and firing atmosphere for the selected materials. [Example]

[0045] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0046] Example 1 To 100 parts by mass of the cordierite raw material, 2 parts by mass of a pore-forming material, 2 parts by mass of a dispersing medium, and 7 parts by mass of an organic binder were added, mixed, and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite raw materials. Water was used as the dispersing medium. Methylcellulose was used as the organic binder. Dextrin was used as the dispersing agent. A water-absorbing polymer with an average particle diameter of 20 μm was used as the pore-forming material. In this example, the average particle diameter of each raw material refers to the particle diameter (D50) at 50% of the integrated value in the particle size distribution determined by laser diffraction and scattering.

[0047] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having an overall cylindrical shape. The cell shapes of the honeycomb formed body were octagonal and quadrangular, and such octagonal and quadrangular cells were arranged alternately with partition walls sandwiched between them.

[0048] Next, the honeycomb formed body was dried in a microwave dryer and further completely dried in a hot air dryer, after which both end faces of the honeycomb formed body were cut and adjusted to a predetermined size.

[0049] Next, a plugging material for forming plugging portions was prepared. Specifically, a slurry plugging material was prepared by adding water, a binder, and the like to the ceramic raw material. The ceramic raw material may be, for example, the cordierite-forming raw material used in producing the honeycomb formed body. Thereafter, plugging portions were formed using the plugging material in the openings of predetermined cells on the inflow end face side of the dried honeycomb formed body and in the openings of the remaining cells on the outflow end face side. The plugging portions were formed so that cells with an octagonal cell shape became inflow cells and cells with a rectangular cell shape became outflow cells.

[0050] Next, the honeycomb formed body with the plugged portions formed therein was degreased and fired to produce the honeycomb filter of Example 1.

[0051] The honeycomb filter of Example 1 was cylindrical with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 267 mm. The length of the honeycomb filter in the cell extension direction was 178 mm. In the honeycomb filter of Example 1, the cell shape (cross-sectional shape) of the inlet cells was octagonal, and the cell shape (cross-sectional shape) of the outlet cells was quadrangular. The partition wall thickness was 0.26 mm, and the cell density was 47 cells / cm. 2 The porosity of the partition walls was 55%. The porosity of the partition walls was measured using Autopore 9500 (trade name) manufactured by Micromeritics. Table 1 shows the results.

[0052] The cross-sectional area S1 of the inlet cell and the cross-sectional area S2 of the outlet cell were measured by observing them using a scanning electron microscope (SEM) or a microscope and analyzing the images obtained. Based on the measurement results, the area ratio (S1 / S2) of the inlet cell cross-sectional area S1 to the outlet cell cross-sectional area S2 was calculated. The calculated cell area ratio (S1 / S2) was 1.70. The results are shown in Table 1.

[0053] The plugging portions that plugged the ends of each cell had protrusions that protruded outward in the cell extension direction from the end face on the side where the plugging portion was disposed. The protrusion height H of the plugging portion was 2.0 mm. The plugging depth L of each plugging portion was 7.0 mm. The results are shown in Table 1.

[0054] [Table 1]

[0055] The honeycomb filter of Example 1 was evaluated for "pressure loss," "erosion resistance," and "thermal shock resistance" by the following methods. Table 2 shows the results.

[0056] [Pressure loss] Exhaust gas emitted from a 6.7 L diesel engine was made to flow into the honeycomb filters of each Example and Comparative Example, and soot in the exhaust gas was collected by the partition walls of the honeycomb filter. The soot collection was continued until the amount of soot deposited per unit volume (1 L) of the honeycomb filter reached 5 g / L. Then, when the amount of soot deposited reached 5 g / L, the engine exhaust gas at 200°C was passed through 12 m 3 / min, and the pressure at the inlet end face side and the outlet end face side of the honeycomb filter were measured. The pressure difference between the inlet end face side and the outlet end face side was calculated to determine the pressure loss (kPa) of the honeycomb filter. The pressure loss ratio (%) of each honeycomb filter was calculated, assuming that the pressure loss value of the honeycomb filter of Comparative Example 1 was 100%, and the honeycomb filters of each Example and Comparative Example were evaluated based on the following evaluation criteria. In the evaluation criteria below, the "pressure loss ratio (%)" refers to the pressure loss ratio (%) of each honeycomb filter, assuming that the pressure loss value of the honeycomb filter of Comparative Example 1 was 100%. Evaluation "Excellent": A pressure loss ratio (%) of 80% or less is considered "Excellent." Evaluation "Good": A pressure loss ratio (%) exceeding 80% and not exceeding 90% is evaluated as "Good". Evaluation: "Acceptable": The pressure loss ratio (%) is rated as "acceptable" if it is greater than 90% and less than or equal to 100%. Evaluation: "Fail": If the pressure loss ratio (%) exceeds 100%, it is rated as "Fail."

[0057] [Erosion resistance] First, the honeycomb filter was canned (stored) in a can and placed in a gas burner tester. Next, SiC abrasive grains were collided with the inlet end face of the honeycomb filter using the gas burner tester. The conditions for the abrasive grain collision were as follows: 5 g of abrasive grains were added. The temperature of the gas flowing into the honeycomb filter was 700°C. The flow rate of the gas flowing into the honeycomb filter was 120 m / s. The test lasted 10 minutes, during which the abrasive grains were added little by little. After that, the honeycomb filter was removed and photographed using computed tomography (CT). The depth of the honeycomb filter eroded by the abrasive grain collision (erosion depth (mm)) was calculated. In this erosion amount measurement test, abrasive grains with an average particle diameter of 50 μm were used. The "erosion resistance" of the honeycomb filter was evaluated according to the following evaluation criteria. Evaluation "OK": When the erosion depth of the evaluation object is smaller than the erosion depth of Comparative Example 1, it is judged as passing (OK). Evaluation "NG": When the erosion depth of the evaluation target is greater than the erosion depth of Comparative Example 1, it is judged as failing (NG).

[0058] [Thermal shock resistance] First, a predetermined amount of soot was generated under constant operating conditions in an engine bench equipped with a 6.7L diesel engine, and the generated soot was deposited on the surface of the partition walls of the honeycomb filters of each Example and Comparative Example. Next, a regeneration process was performed using post-injection to increase the inlet gas temperature of the honeycomb filter. When the pressure loss before and after the honeycomb filter began to decrease, the post-injection was turned off and the engine was switched to an idle state. The predetermined amount of soot deposited before the regeneration process was gradually increased, and the above operation was repeated until cracks occurred in the honeycomb filter. The amount of soot deposited at which cracks occurred in the honeycomb filter was defined as the "soot deposition limit" for each honeycomb filter. The honeycomb filters of each Example and Comparative Example were evaluated based on the following evaluation criteria. Evaluation "Excellent": When the "soot accumulation limit amount" of Comparative Example 1 is taken as 100%, if the "soot accumulation limit amount" of the evaluated object is 110% or more, the evaluation is "Excellent". Evaluation "Good": If the "soot accumulation limit amount" of Comparative Example 1 is taken as 100%, when the "soot accumulation limit amount" of the evaluated object is 105% or more and less than 110%, the evaluation is "Good". Evaluation "Fair": If the "soot accumulation limit amount" of Comparative Example 1 is taken as 100%, and the "soot accumulation limit amount" of the evaluated object is 100% or more and less than 105%, the evaluation is "Fair". Evaluation "Fail": When the "soot accumulation limit amount" of Comparative Example 1 is taken as 100%, if the "soot accumulation limit amount" of the evaluation target is less than 100%, the evaluation is "Fail".

[0059] [Table 2]

[0060] (Examples 2 to 5 and Comparative Examples 1 to 5) Honeycomb filters were produced in the same manner as the honeycomb filter of Example 1, except that the configuration of the honeycomb filter was changed as shown in Table 1.

[0061] The honeycomb filters of Examples 2 to 5 and Comparative Examples 1 to 5 were also evaluated for "pressure loss," "erosion resistance," and "thermal shock resistance" in the same manner as in Example 1. Table 2 shows the results.

[0062] (result) It was confirmed that the honeycomb filters of Examples 1 to 5 had better performance in terms of pressure drop, erosion resistance, and thermal shock resistance than the honeycomb filter of Comparative Example 1, which served as the benchmark. On the other hand, the honeycomb filters of Comparative Examples 2 to 5 had inferior evaluation results for pressure drop, erosion resistance, or thermal shock resistance compared to the honeycomb filters of Examples 1 to 5. [Industrial Applicability]

[0063] The honeycomb filter of the present invention can be used as a filter for collecting particulate matter in exhaust gases. [Explanation of symbols]

[0064] 1: partition wall, 2: cell, 2a: inlet cell, 2b: outlet cell, 3: outer wall, 4: honeycomb structure portion, 5: plugging portion, 6: convex portion, 11: inlet end face, 12: outlet end face, 100: honeycomb filter, H, H1, H2: protrusion height, L, L1, L2: plugging depth, S1, S2: cross-sectional area (cross-sectional area of ​​cell).

Claims

1. The honeycomb structure includes a columnar honeycomb structure portion having porous partition walls arranged so as to surround a plurality of cells that form fluid flow paths extending from an inflow end face to an outflow end face, and plugging portions arranged so as to plug either an end portion of the cells on the inflow end face side or the outflow end face side, The plugging portion is disposed at the end portion on the outflow end surface side, and the cell having an opening on the inflow end surface side is defined as an inflow cell, The plugged portion is disposed at an end portion on the inflow end face side, and the cell having an open outflow end face side is defined as an outflow cell, In a cross section of the honeycomb structure section perpendicular to the cell extension direction, the cross-sectional shape of the inlet cells is octagonal and the cross-sectional shape of the outlet cells is quadrangular, except for the cells arranged on the outermost periphery of the honeycomb structure section, an area ratio (S1 / S2) of a cross-sectional area S1 of the inflow cell having an octagonal cross-sectional shape to a cross-sectional area S2 of the outflow cell having a rectangular cross-sectional shape is 1.70 to 1.74; the plugging portions that plug the ends of the inflow cells having an octagonal cross-sectional shape and the outflow cells having a rectangular cross-sectional shape have convex portions that protrude outward in the extension direction of the cells from the end face on the side where the plugging portions are disposed, a protrusion height H from the end face of the convex portion as a bottom is 0.3 to 3.0 mm, and a plugging depth L from the end face of the plugging portion having the convex portion is 4.0 to 9.0 mm, the porosity of the partition walls is 52 to 58%, The honeycomb filter has a cell density of 47 to 54 cells / cm 2 .

2. 2. The honeycomb filter according to claim 1, wherein the partition walls have a thickness of 0.17 to 0.32 mm.

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