Honeycomb structure

Abstract

To provide a honeycomb structure which satisfies all of excellent PM collecting performance, low pressure loss, excellent catalyst coating property at the time of catalyst carrying, prevention occurrence of ash clogging, and excellent mechanical strength.SOLUTION: A honeycomb structure is a columnar honeycomb structure having a plurality of introduction cells, and a plurality of discharge cells which are adjacent to each other while sandwiching a partition wall in at least one introduction cell, wherein a ratio of each opening area (Cin) of the plurality of introduction cells to each opening area (Cout) of the plurality of discharge cells, thickness (WT) of the partition wall, cell density (CD) based on the total number of the plurality of introduction cells and the plurality of discharge cells, depth (PD) of a plugged part, a distance (OF) of a middle point of a line segment connecting centers of gravity of the introduction cell and the discharge cell adjacent to each other while sandwiching the partition wall, and a center of the partition wall where the line segment crosses satisfy predetermined conditions, and satisfy 2≤OF×CD / (WT×PD)≤7.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a honeycomb structure. [Background technology]

[0002] Exhaust gases emitted from internal combustion engines, such as diesel engines, contain large amounts of particulate matter (PM), including carbon-based soot and ash (a type of residue left over from combustion of calcium and other elements), which cause environmental pollution. Because this particulate matter is known to be carcinogenic, preventing its release into the atmosphere is essential. Currently, strict regulations are being imposed, primarily in Europe, that restrict PM count in addition to the traditional weight-based restrictions. For this reason, diesel engines and other engines generally use a filter (Diesel Particulate Filter: DPF) to capture particulate matter. In recent years, particulate matter emitted from gasoline engines has also become a problem, and gasoline engines are increasingly being equipped with a filter (Gasoline Particulate Filter: GPF).

[0003] An effective filter is a wall-flow type filter, which is designed so that exhaust gas passes through porous partition walls. Specifically, a wall-flow type filter has a large number of inlet cells and a large number of outlet cells that are adjacent to each other via porous partition walls, and can be configured with a honeycomb structure that captures PM as the exhaust gas passes through the partition walls. A catalyst can also be supported on the surface of the partition walls depending on the purpose.

[0004] Wall-flow filters made of honeycomb structures are required to have various properties, such as excellent PM collection performance, low pressure loss, excellent catalytic performance when catalyst is loaded, low ash clogging, and excellent mechanical strength.

[0005] Japanese Patent Application Laid-Open No. 2023-147536 (Patent Document 1) describes that by controlling the cross-sectional shape of the inlet cells, the ratio of the cross-sectional area of ​​the outlet cells to the cross-sectional area of ​​the inlet cells, the thickness of the partition walls, the cell density, the shape of the plugging portions, the porosity of the partition walls, etc. within predetermined ranges, a honeycomb filter can be obtained that has low pressure loss, excellent erosion resistance of the plugging portions, and also excellent thermal shock resistance.

[0006] Japanese Patent No. 7353217 (Patent Document 2) describes that by controlling the porosity of the partition walls, the average pore size of the partition walls, the pore size distribution of the partition walls, the thickness of the partition walls, etc. within predetermined ranges, a honeycomb filter that has excellent collection performance and can reduce pressure loss can be obtained. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-147536 [Patent Document 2] Patent No. 7353217 Summary of the Invention [Problem to be solved by the invention]

[0008] However, conventional honeycomb structures have not been able to satisfy all of the requirements of excellent PM collection performance, low pressure loss, excellent catalytic performance when catalyst is loaded, low ash clogging, and excellent mechanical strength. Patent Document 1 describes a honeycomb filter that has excellent erosion resistance at the plugging portions and also excellent thermal shock resistance, but there is still room for improvement in terms of catalyst application. Patent Document 2 describes a honeycomb filter that has excellent collection performance and can reduce pressure loss by controlling the partition wall porosity, average pore size of the partition walls, pore size distribution of the partition walls, partition wall thickness, etc. within predetermined ranges, but there is still room for improvement in terms of catalyst application.

[0009] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a honeycomb structure that satisfies all of the following requirements: excellent PM collection performance, low pressure loss, excellent catalyst coating properties when catalyst is loaded, low ash clogging, and excellent mechanical strength. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which is exemplified below. [Aspect 1] A columnar honeycomb structure comprising: an outer peripheral side wall; a plurality of inlet cells arranged on an inner peripheral side of the outer peripheral side wall, extending from an inlet end face to an outlet end face, having openings at the inlet end faces and having plugging portions at the outlet end face; and a plurality of discharge cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet end face to the outlet end face, having plugging portions at the inlet end face and having openings at the outlet end face, and adjacent to at least one of the plurality of inlet cells with a partition wall interposed therebetween, The opening area (C out ) relative to the opening area (C in ) ratio is 1 <C in / C out ≦2.5, The thickness (WT) of the partition wall is 0.18 to 0.25 mm, A cell density (CD) based on the total number of the plurality of inlet cells and the plurality of outlet cells is 49 to 70 cells / cm 2 and The depth (PD) of the plugging portion is 4 to 7 mm, In a cross section of the honeycomb structure perpendicular to the extension direction of the plurality of inlet cells and the plurality of outlet cells, a distance (OF) between a midpoint of a line segment connecting centers of gravity of the inlet cell and the outlet cell adjacent to each other with the partition wall interposed therebetween and a center of the partition wall intersected by the line segment is 0.075 to 0.110 mm, 2≦OF×CD / (WT×PD)≦7 is satisfied. Honeycomb structure. [Aspect 2] 2. The honeycomb structure according to embodiment 1, wherein the partition walls have a porosity of 52 to 61%. [Aspect 3] 3. The honeycomb structure according to embodiment 1 or 2, wherein the partition walls have an average pore diameter of 6 to 10 μm. [Aspect 4] A honeycomb structure according to any one of Aspects 1 to 3, wherein the opening shapes of the plurality of introduction cells are all hexagonal or octagonal except for the one adjacent to the outer peripheral side wall. [Aspect 5] A honeycomb structure according to any one of Aspects 1 to 4, wherein the partition walls contain one or more materials selected from cordierite, silicon carbide, a silicon-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate. [Aspect 6] 6. The honeycomb structure according to any one of aspects 1 to 5, wherein a catalyst is supported on the partition walls. [Effects of the Invention]

[0011] The honeycomb structure according to one embodiment of the present invention satisfies all of the following requirements: excellent PM collection performance, low pressure loss, excellent catalyst coating properties when catalyst is loaded, low ash clogging, and excellent mechanical strength. Therefore, it can be said that one embodiment of the present invention can provide a practically excellent honeycomb structure that can be suitably used as a filter for exhaust gases emitted from internal combustion engines such as diesel engines. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective view schematically showing a wall-flow type honeycomb structure. [Figure 2] 1 is a schematic cross-sectional view of a wall-flow type honeycomb structure when observed from a cross section parallel to the cell extension direction. FIG. [Figure 3] FIG. 3 is a schematic partial enlarged view of a partition wall of a honeycomb structure when observed from a cross section perpendicular to the cell extension direction. [Figure 4] FIG. 10 is an explanatory diagram schematically illustrating an example of a method for forming plugging portions by a squeegee method. DETAILED DESCRIPTION OF THE INVENTION

[0013] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0014] (1. Honeycomb structure) 1 and 2 are a schematic perspective view and a cross-sectional view, respectively, of a cylindrical honeycomb structure 100 applicable as a wall-flow type automotive exhaust gas filter. The honeycomb structure 100 includes an outer peripheral sidewall 102, a plurality of inlet cells 108 arranged on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to each other from an inlet end face 104 to an outlet end face 106, having openings 107 at the inlet end face 104 and plugging portions 109 at the outlet end face 106, and a plurality of discharge cells 110 arranged on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to each other from an inlet end face 104 to an outlet end face 106, having plugging portions 109 at the inlet end face 104 and having openings 107 at the outlet end face 106, and being adjacent to at least one of the plurality of inlet cells with a partition wall 112 sandwiched therebetween.

[0015] For example, when exhaust gas containing particulate matter such as soot is supplied to the upstream inlet end face 104 of the honeycomb structure 100, the exhaust gas is introduced into the inlet cells 108 and travels downstream within the inlet cells 108. Because the downstream outlet end face 106 of the inlet cells 108 is plugged, the exhaust gas passes through the partition walls located between the adjacent inlet cells 108 and exhaust cells 110 and flows into the exhaust cells 110. Since the particulate matter cannot pass through the partition walls, it is captured and deposited within the inlet cells 108. After the particulate matter is removed, the clean exhaust gas that has flowed into the exhaust cells 110 travels downstream within the exhaust cells 110 and flows out from the downstream outlet end face 106.

[0016] The honeycomb structure 100 satisfies the following predetermined conditions (1) to (6), which makes it possible to satisfy all of the following requirements: excellent PM trapping performance, low pressure loss, excellent catalyst coating properties when catalyst is loaded, low ash clogging, and excellent mechanical strength. (1) The opening area (C out ) of the opening area (C in ) ratio (C in / C out ) (2) Thickness (WT) of the partition wall 112 (unit: mm) (3) Cell density (CD) based on the total number of the plurality of inlet cells 108 and the plurality of outlet cells 110 (unit: cells / cm 2 ) (4) Depth of plugging portion 109 (PD) (unit: mm) (5) In a cross section perpendicular to the extension direction of the plurality of inlet cells 108 and the plurality of outlet cells 110 of the honeycomb structure 100, the distance (OF) between the midpoint M of a line segment connecting the centers of gravity O of the inlet cells 108 and the outlet cells 110 adjacent to each other with a partition wall 112 in between, and the center C of the partition wall 112 that the line segment crosses (hereinafter also referred to as "offset") (unit: mm) (6) OF × CD / (WT × PD)

[0017] (1)C in / C out The opening area (C out ) of the opening area (C in ) ratio (C in / C out ) is 1 <C in / C out ≦2.5, and 1.5≦C in / C out It is more preferable that ≦2.5 is satisfied, and 1.5≦C in / C out It is even more preferable that ≦2.2 is satisfied. The opening area (C in) is defined as the average open area of ​​all the inlet cells excluding the cells adjacent to the peripheral sidewall 102. The opening area (C out ) is defined as the average open area of ​​all the exhaust cells excluding the cells adjacent to the peripheral sidewall 102.

[0018] The opening area (C in ) is, for example, 0.70 to 1.10 mm 2 It is preferable that the thickness is 0.70 to 1.00 mm. 2 More preferably, it is 0.75 to 0.90 mm 2 It is even more preferable that:

[0019] (2)WT The thickness (WT) of the partition walls 112 is preferably 0.18 to 0.25 mm, more preferably 0.18 to 0.24 mm, and even more preferably 0.18 to 0.23 mm. Here, the thickness (WT) of the partition walls 112 means the average value of the thicknesses (WT) of all the partition walls 112. Fig. 3 shows a schematic partial enlarged view of the partition walls 112 of a honeycomb structure 100 in which the opening shape of the inlet cells 108 is octagonal and the opening shape of the outlet cells 110 is rectangular, observed in a cross section perpendicular to the cell extension direction. The thickness (WT) of the partition walls 112 refers to the length D of a line segment that crosses the partition walls when the line segment connects the centers of gravity O of adjacent cells in a cross section perpendicular to the cell extension direction (height direction of the honeycomb structure 100). In addition, when two cells are adjacent across a partition wall, it means that when the partition wall of the honeycomb structure is observed from a cross section perpendicular to the cell extension direction, the two cells are adjacent across opposing wall surfaces of one partition wall (the sides of the polygon that defines the cell), and does not include cases where the two cells are adjacent across the vertices of the polygon that defines the two cells.

[0020] (3) CDs The cell density (CD) based on the total number of the inlet cells 108 and the outlet cells 110 is 49 to 70 cells / cm 2It is preferable that the density is 49 to 68 particles / cm. 2 More preferably, it is 50 to 66 particles / cm 2 Here, the cell density is calculated by dividing the total number of cells (including plugged cells, discharge cells 110 adjacent to the outer peripheral side wall 102, and inlet cells 108 adjacent to the outer peripheral side wall 102) by the area of ​​one end face of the honeycomb structure excluding the outer peripheral side wall.

[0021] (4)PD The depth (PD) of the plugging portions 109 is preferably 4 to 7 mm, more preferably 4 to 6.5 mm, and even more preferably 5 to 6.5 mm. Here, the depth (PD) of the plugging portions 109 means the average value of the depths (PD) of all the plugging portions 109. The depth (PD) of each plugging portion 109 is measured by cutting the honeycomb structure along a cross section parallel to the height direction (cell extension direction) of the honeycomb structure to obtain a cross section of the plugging portion. In the cross section, the length in the cell extension direction from the position of the inlet end face or outlet end face where the plugging portion is formed to the deepest position where the plugging portion exists is measured, and this is defined as the depth of the plugging portion 109.

[0022] (5) OF (offset) 3, in a cross section perpendicular to the extension direction of the plurality of inlet cells 108 and the plurality of discharge cells 110 of the honeycomb structure 100, the distance between the midpoint M of a line segment connecting the centers of gravity O of the inlet cells 108 and the discharge cells 110 adjacent to each other with a partition wall 112 in between, and the center C of the partition wall 112 crossed by the line segment is called OF (offset). OF is preferably 0.075 to 0.110 mm, more preferably 0.075 to 0.105 mm, and even more preferably 0.080 to 0.105 mm. Here, OF means the average value of all calculable OFs.

[0023] (6) OF × CD / (WT × PD) It is desirable that the thickness (WT) of the partition walls 112, the cell density (CD), the depth (PD) of the plugged portions 109, and the OF (offset) each satisfy the above-mentioned conditions, and that OF×CD / (WT×PD) satisfy a predetermined condition. Specifically, it is preferable that 2≦OF×CD / (WT×PD)≦7, it is more preferable that 2.2≦OF×CD / (WT×PD)≦6.9, it is even more preferable that 2.4≦OF×CD / (WT×PD)≦6.9, it is even more preferable that 3.0≦OF×CD / (WT×PD)≦6.9, it is even more preferable that 4.0≦OF×CD / (WT×PD)≦6.5, and it is even more preferable that 5.0≦OF×CD / (WT×PD)≦6.0.

[0024] From the viewpoint of further reducing pressure loss, the lower limit of the porosity of the partition walls 112 is preferably 52% or more, more preferably 53% or more. Moreover, from the viewpoint of further increasing the mechanical strength of the honeycomb structure, the upper limit of the porosity of the partition walls is preferably 61% or less, more preferably 60% or less. Therefore, the porosity of the partition walls is preferably, for example, 52 to 61%, more preferably 53 to 60%. In this specification, the porosity is measured by the mercury intrusion method specified in JIS R1655:2003. Moreover, the porosity is measured by the average value of the porosity of partition wall samples (0.3 g each) taken evenly from six positions of the honeycomb structure.

[0025] From the viewpoint of further improving the particulate matter collection efficiency, the average pore diameter of the partition walls 112 is preferably 10 μm or less, and more preferably 9 μm or less. Furthermore, from the viewpoint of further reducing pressure loss, the average pore diameter of the partition walls 112 is preferably 6 μm or more, and more preferably 7 μm or more. Therefore, the average pore diameter of the partition walls 112 is preferably, for example, 6 to 10 μm, and more preferably 7 to 9 μm. The average pore diameter of the partition walls is measured by mercury intrusion porosimetry in accordance with JIS R1655:2003. Twenty test pieces of the partition walls are collected evenly from the center and outer periphery of the cylindrical honeycomb structure, and the average pore diameter of each is measured, and the average value is taken as the average pore diameter of the entire cylindrical honeycomb structure.

[0026] The opening shape of the inlet cells 108 is not particularly limited. For example, the cross section perpendicular to the cell extension direction of the honeycomb structure 100 may be polygonal (quadrilateral (rectangle, square), pentagon, hexagon, heptagon, octagon, etc.), round (circular, elliptical, oval, egg, oval, etc.), or the like. These shapes may be used alone or in combination of two or more. Among these, for the reason of reducing pressure loss, it is preferable that the opening shape of each of the multiple inlet cells 108, except for those adjacent to the outer peripheral side wall 102, is all hexagonal or octagonal, and more preferably octagonal. When the opening shape of the inlet cells 108 and the discharge cells 110 is polygonal, the corners may be rounded. Note that in this specification, even rounded corners are treated as polygonal.

[0027] The opening shape of the discharge cell 110 is not particularly limited, and may be set to match the opening shape of the inlet cell 108. For example, if the opening shape of the inlet cell 108 is octagonal, it is preferable to make it quadrangular.

[0028] There is no limitation on the end face shape of the honeycomb structure 100, and it may be, for example, a circular shape, an elliptical shape, a round shape such as a racetrack shape or an oval shape, a polygonal shape such as a triangular shape or a quadrangular shape, or any other irregular shape. The illustrated honeycomb structure 100 has a circular end face shape and is cylindrical as a whole.

[0029] There are no particular restrictions on the height of the honeycomb structure (the length from the inlet end face to the outlet end face) and it may be set appropriately depending on the application and required performance. The height of the honeycomb structure may be, for example, 40 to 450 mm, preferably 60 to 400 mm, and more preferably 100 to 330 mm. There are also no particular restrictions on the relationship between the height of the honeycomb structure and the maximum diameter of each end face (the maximum length of the diameter passing through the center of gravity of each end face of the honeycomb structure). Therefore, the height of the honeycomb structure may be longer or shorter than the maximum diameter of each end face.

[0030] From the viewpoint of obtaining excellent thermal shock resistance, at least the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions contain one or more materials selected from cordierite, silicon carbide, silicon-silicon carbide composite material, silicon nitride, mullite, alumina and aluminum titanate.

[0031] The outer peripheral side walls, partition walls, and plugging portions of the honeycomb structure may contain ceramics other than those mentioned above. Examples of the other ceramics include zirconium phosphate, cordierite-silicon carbide composite, zirconia, spinel, indialite, sapphirine, corundum, titania, and ceria. These other ceramics may be contained singly or in combination of two or more.

[0032] The honeycomb structure can also be used as a catalyst carrier. A catalyst can be supported on the surface of the partition walls according to the purpose. Examples of catalysts include, but are not limited to, oxidation catalysts (DOCs) for oxidatively burning hydrocarbons (HC) and carbon monoxide (CO) to increase the exhaust gas temperature, PM combustion catalysts for assisting the combustion of PM such as soot, SCR catalysts and NSR catalysts for removing nitrogen oxides (NOx), and three-way catalysts capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst can appropriately contain, for example, noble metals (e.g., Pt, Pd, Rh), alkali metals (e.g., Li, Na, K, Cs), alkaline earth metals (e.g., Mg, Ca, Ba, Sr), rare earth elements (e.g., Ce, Sm, Gd, Nd, Y, La, Pr), transition metals (e.g., Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr), etc.

[0033] The honeycomb structure may be a honeycomb bonded body having a plurality of honeycomb segments and a bonding layer bonding the outer peripheral surfaces of the plurality of honeycomb segments together. The use of a honeycomb bonded body makes it possible to increase the total cross-sectional area of ​​the cells, which is important for ensuring air flow while suppressing the occurrence of cracks. The bonding layer can be formed using a bonding material. The bonding material is not particularly limited, but a paste-like material obtained by adding a solvent such as water to a ceramic material can be used. The bonding material may contain the same material as the partition walls. In addition to bonding the honeycomb segments together, the bonding material can also be used as an outer peripheral coating material after the honeycomb segments are bonded.

[0034] (2. Manufacturing method) A method for manufacturing a cylindrical honeycomb structure according to one embodiment of the present invention will be described below by way of example. First, a raw material composition containing a cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder is kneaded to form a puddle, and the puddle is then extrusion-molded to obtain a cylindrical honeycomb molded body having an outer peripheral sidewall and a cylindrical honeycomb molded body disposed on the inner peripheral side of the outer peripheral sidewall, extending from an inlet end face to an outlet end face, and having openings at both the inlet end face and the outlet end face. Additives such as a dispersant or other ceramic raw materials may be blended into the raw material composition as needed. During extrusion molding, a die having the desired overall shape, cell shape, cell arrangement, partition wall thickness, cell density, etc. can be used.

[0035] The cordierite-forming raw material is a raw material that becomes cordierite when fired, and can be provided, for example, in the form of powder. The cordierite-forming raw material preferably has a chemical composition of 30 to 45 mass% alumina (Al2O3) (including aluminum hydroxide converted to alumina), 11 to 17 mass% magnesia (MgO), and 42 to 57 mass% silica (SiO2).

[0036] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0037] The content of the dispersion medium in the honeycomb formed body before the drying step is preferably 20 to 110 parts by mass, more preferably 25 to 100 parts by mass, and even more preferably 30 to 90 parts by mass, relative to 100 parts by mass of the cordierite-forming raw material. When the content of the dispersion medium in the honeycomb formed body is 20 parts by mass or more relative to 100 parts by mass of the cordierite-forming raw material, the advantage of easily stabilizing the quality of the honeycomb structure is easily obtained. When the content of the dispersion medium in the honeycomb formed body is 110 parts by mass or less relative to 100 parts by mass of the cordierite-forming raw material, the amount of shrinkage during drying is small, and deformation can be suppressed. In this specification, the content of the dispersion medium in the honeycomb formed body refers to a value measured by a loss on drying method.

[0038] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, silica gel, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, and phenol. One type of pore-forming material may be used alone, or two or more types may be used in combination. From the viewpoint of increasing the porosity of the honeycomb structure after firing, the content of the pore-forming material is preferably 1 part by mass or more, more preferably 6 parts by mass or more, and even more preferably 9 parts by mass or more, relative to 100 parts by mass of the cordierite-forming raw material. From the viewpoint of ensuring the strength of the honeycomb structure after firing, the content of the pore-forming material is preferably 30 parts by mass or less, more preferably 27 parts by mass or less, and even more preferably 24 parts by mass or less, relative to 100 parts by mass of the cordierite-forming raw material.

[0039] Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Furthermore, from the viewpoint of increasing the strength of the honeycomb formed body before firing, the content of the binder is preferably 4 parts by mass or more, more preferably 4.5 parts by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the cordierite-forming raw material. From the viewpoint of suppressing cracks due to abnormal heat generation during the firing process, the content of the binder is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, relative to 100 parts by mass of the cordierite-forming raw material. One type of binder may be used alone, or two or more types may be used in combination.

[0040] The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, or the like. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the cordierite-forming raw material.

[0041] The honeycomb formed body can be dried by a conventionally known drying method, such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, etc. Among these, a drying method that combines hot air drying with microwave drying or dielectric drying is preferred, since it can dry the entire honeycomb formed body quickly and uniformly.

[0042] After drying the honeycomb formed body, plugging portions are formed on both end faces of the honeycomb formed body. Each plugging portion can be formed by filling the openings of the inlet cells and outlet cells where the plugging portions are to be formed with a plugging portion forming slurry, and then drying and firing the filled slurry. The material of the honeycomb formed body can be used for the plugging portion forming slurry. For example, when the honeycomb formed body contains a cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder, the plugging portion forming slurry can contain the cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder, without being limited thereto.

[0043] For example, the slurry for forming plugging portions contains 30 to 60 parts by mass of a dispersion medium, 5 to 20 parts by mass of a pore-forming material, and 0.2 to 2.0 parts by mass of a binder relative to 100 parts by mass of the cordierite-forming raw material. In a preferred embodiment, the slurry for forming plugging portions contains 35 to 50 parts by mass of a dispersion medium, 8 to 16 parts by mass of a pore-forming material, and 0.2 to 1.5 parts by mass of a binder relative to 100 parts by mass of the cordierite-forming raw material.

[0044] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0045] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, silica gel, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, phenol, etc. One type of pore-forming material may be used alone, or two or more types may be used in combination.

[0046] Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. One type of binder may be used alone, or two or more types may be used in combination.

[0047] The slurry for forming plugged portions may contain a dispersant as appropriate. Examples of dispersants include ethylene glycol, dextrin, fatty acid soap, and polyalcohol. The dispersant may be used alone or in combination of two or more.

[0048] The openings of the cells can be filled with the slurry for forming plugging portions, for example, by the following "squeegee method." As shown in Fig. 4, a film 121 is attached to the upper end face (here, the outlet end face 106 in the figure) of the dried honeycomb formed body 400 fixed using a chuck 120, and a laser is irradiated onto the film 121 at positions corresponding to the arrangement conditions of the plugging portions, thereby forming a plurality of holes 126 in the film 121.

[0049] Thereafter, the plugging portion forming slurry 124 is placed on the film 121, and the squeegee 122 is moved along the film 121 in the direction of the arrow in Fig. 4. As a result, a certain amount of the plugging portion forming slurry 124 is filled into the cells 125 that are opened at positions corresponding to the holes 126 of the film 121.

[0050] The depth of the plugging portion can be changed by the number of times the squeegee 122 is moved, the contact angle between the squeegee 122 and the film 121, the pressing pressure of the squeegee 122 against the film 121, and the viscosity of the plugging portion forming slurry 124, etc.

[0051] After the plugging portion forming slurry 124 is filled, the film 121 is peeled off, and the entire honeycomb formed body 400 is dried. As a result, the plugging portion forming slurry 124 filled in the cells 125 is dried, and the plugging portions before firing are formed. The drying can be performed, for example, under conditions of a drying temperature of 100 to 230°C for about 60 to 150 seconds. After drying, the plugging portions protrude from the end face of the honeycomb formed body by the thickness of the film, and can be scraped off as necessary.

[0052] The material of the film is not particularly limited, but polypropylene (PP), polyethylene terephthalate (PET), polyimide, or Teflon (registered trademark) are preferred because they are easy to heat process to form holes in. The film also preferably has an adhesive layer, and the adhesive layer is preferably made of an acrylic resin, a rubber-based material (e.g., a rubber whose main component is natural rubber or synthetic rubber), or a silicone-based resin. The film can preferably be an adhesive film with a thickness of, for example, 20 to 50 μm.

[0053] In addition to the above-mentioned "squeegee method," another method for filling the openings of the cells with the plugging portion forming slurry is the "press-fit method." The "press-fit method" is a method in which an end face of a honeycomb formed body with a film attached and holes drilled therein is immersed in a liquid tank containing the plugging portion forming slurry, and the cells are filled with the plugging portion forming slurry. In this case, the depth of the plugging portions can be changed by changing the depth to which the honeycomb formed body is immersed in the plugging portion forming slurry.

[0054] The honeycomb formed body filled with the plugging portion forming slurry is then subjected to a degreasing process and a firing process, thereby manufacturing a honeycomb structure. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming material is about 300 to 1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb formed body to a temperature range of about 200 to 1000°C. The heating time is not particularly limited, but is usually about 10 to 100 hours. The honeycomb formed body after the degreasing process is called a calcined body. The firing process can be carried out by heating the calcined body to 1300 to 1450°C and holding it for 3 to 24 hours, for example, although it depends on the material composition of the honeycomb structure.

[0055] A catalyst can be supported on the partition walls of the honeycomb structure manufactured in this manner. An example of a method for supporting a catalyst on the partition walls is a method in which a catalyst slurry is introduced into the cells by a conventionally known suction method or the like, and the catalyst is deposited on the surfaces and pores of the partition walls, and then a high-temperature treatment is performed to bake the catalyst contained in the catalyst slurry onto the partition walls and support the catalyst. The types of catalyst are as exemplified above. [Example]

[0056] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0057] (1. Manufacturing of honeycomb structure) [Cordierite Honeycomb Structures: Comparative Examples 1 to 7, Examples 1 to 5] To 100 parts by mass of the cordierite raw material, 2 parts by mass of a pore-forming material, 20 parts by mass of a dispersion medium, and 7 parts by mass of an organic binder were added, and the mixture was mixed and kneaded to prepare a clay. The cordierite raw materials used were alumina, aluminum hydroxide, kaolin, talc, and silica. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. A water-absorbent resin with a median diameter of 20 μm was used as the pore-forming material. In this example, the median diameter of the raw material refers to the particle size (D50) at 50% of the cumulative value in the particle size distribution determined by a laser diffraction / scattering method.

[0058] Next, the clay was extrusion-molded using a die for producing a honeycomb formed body, to obtain a honeycomb formed body having an overall cylindrical shape. The structure of the die was changed depending on the test number.

[0059] Next, the honeycomb formed body was dried in a microwave dryer and further dried in a hot air dryer, and then both end faces of the honeycomb formed body were cut to a predetermined size.

[0060] Next, a slurry for forming plugging portions was prepared using the same material as the honeycomb formed body. Then, using this slurry, plugging portions were formed at the openings of predetermined cells on the inlet end face side of the dried honeycomb formed body and at the openings of the remaining cells on the outlet end face side, so that the inlet cells and the outlet cells were alternately adjacent to each other.

[0061] Next, the honeycomb formed body with each plugged portion formed therein was degreased and fired to produce a honeycomb structure corresponding to each test number. The honeycomb structure thus obtained had a cylindrical shape with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 330 mm. The length of the honeycomb structure in the cell extension direction was 254 mm. The honeycomb structures were prepared in the number required to identify the following properties.

[0062] (2. Structural characteristics of honeycomb structures) Table 1 shows the following structural characteristics of the honeycomb structures manufactured above according to each test number. Partition wall thickness (WT) Cell density (CD) based on the total number of inlet cells and outlet cells The opening area of ​​each of the multiple discharge cells (C out ) of the opening area (C in ) ratio (C in / C out ) The opening area of ​​each of the multiple introduction cells (C in ) Offset (OF) Plugging depth (PD) OF×CD / (WT×PD) Porosity of partition walls Average pore size of partition wall -Opening shape of the introduction cell Discharge cell opening shape

[0063] The thickness (WT) of the partition walls was measured by observation with a scanning electron microscope (SEM) or a microscope. Cell density (CD) refers to the cell density based on the total number of inlet and outlet cells, and was measured according to the method described above. C in / C out and C in was calculated using scanning electron microscope (SEM) observation or a microscope. The offset (OF) was measured by scanning electron microscope (SEM) observation or microscope. The plugging depth (PD) was measured by observation with a scanning electron microscope (SEM) or a microscope. The porosity and average pore diameter of the partition walls were measured by the above-mentioned mercury intrusion method using Autopore 9500 (trade name) manufactured by Micromeritics. The opening shapes of the inlet cell and the outlet cell were identified by observation with a scanning electron microscope (SEM) or a microscope.

[0064] [Table 1]

[0065] (3. Filter performance) The honeycomb structures prepared above according to the respective test numbers were used as filters, and the following filter performance was evaluated.

[0066] [Collection performance] First, an exhaust gas purification device was fabricated by canning the honeycomb filters of each Example and Comparative Example in a metal case as an exhaust gas purification filter. Next, the fabricated exhaust gas purification device was connected to the outlet side of the exhaust manifold of a 6.7L diesel engine, and the number of soot particles contained in the gas discharged from the outlet of the exhaust gas purification device was measured using the PN measurement method. In determining the number of soot particles, the cumulative number of soot particles discharged after driving in the WHTC (World Harmonized Transient Cycle) mode was used as the number of soot particles in the exhaust gas purification device being evaluated. The soot number ratio (%) of each honeycomb filter was calculated, assuming that the number of soot particles in the exhaust gas purification device using 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. The results are shown in Table 2. Evaluation "Excellent": When the soot count ratio (%) is 80% or less Evaluation "Good": When the soot count ratio (%) is over 80% and 90% or less Evaluation: "Fair": When the soot count ratio (%) is over 90% and less than 100% Evaluation: "Fail": When the soot count ratio (%) exceeds 100%

[0067] [Pressure loss] Exhaust gas emitted from a 6.7 L diesel engine was made to flow into the filters of each Example and Comparative Example, and soot in the exhaust gas was collected in the filter. The soot collection was continued until the amount of soot deposited per unit volume (1 L) of the 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 the filter for 12 m 3 The pressure at the inlet end face and outlet end face of the filter was measured by introducing air at a flow rate of 1 / min. The pressure difference between the inlet end face and the outlet end face was calculated to determine the pressure loss (kPa) of the filter. The pressure loss value of the filter of Comparative Example 1 was set to 100%, and the ratio (%) of the pressure loss of the filters of each Example and Comparative Example was calculated, and the pressure loss of the filters was evaluated based on the following evaluation criteria. The results are shown in Table 2. Evaluation "Excellent": When the pressure loss ratio (%) is 70% or less Evaluation "Good": When the pressure loss ratio (%) is over 70% and 75% or less Evaluation: "Fair": When the pressure loss ratio (%) is over 75% and less than 100% Evaluation: "Fail": When the pressure loss ratio (%) exceeds 100%

[0068] [Catalyst coating] First, an oxidation catalyst was loaded onto the partition walls of a honeycomb filter. The catalyst loading was 10 g / L. Next, 3 g / L of soot was deposited inside the honeycomb filter loaded with the catalyst. In this state, another honeycomb structure (catalyst carrier) loaded with an oxidation catalyst was placed upstream of the honeycomb filter. High-temperature exhaust gas was then passed through the upstream honeycomb structure, and the exhaust gas that had passed through the upstream honeycomb structure was vented through the inlet end of the honeycomb filter to perform continuous regeneration of the filter. The exhaust gas was emitted from a 6.7-liter diesel engine. The regeneration conditions were a gas temperature at the inlet end of 350°C and a gas venting time of 60 minutes. The honeycomb filter was then removed from the continuous regeneration device, and the amount of soot remaining in the honeycomb filter was measured. The percentage (%) of the ratio obtained by dividing the mass of soot reduced by continuous regeneration by the mass of soot initially deposited was determined as the regeneration efficiency (%) during continuous regeneration. The regeneration efficiency value of the filter of Comparative Example 1 was set to 100%, and the regeneration efficiency ratio (%) of the filters of each Example and Comparative Example was calculated, and the catalytic performance of the filter was evaluated based on the following evaluation criteria. It is believed that the higher the catalyst coating property, the more uniformly the catalyst can be coated within the filter, resulting in improved regeneration efficiency. The results are shown in Table 2. "Excellent" rating: Regeneration efficiency rate (%) exceeds 115% Evaluation "Good": When the regeneration efficiency ratio (%) is over 110% and 115% or less Evaluation: "Fair": The regeneration efficiency ratio (%) is greater than 100% and less than 110% Rating "Fail": When the regeneration efficiency rate (%) is less than 100%

[0069] [Ash clogging] First, exhaust gas was introduced into the inlet end face of the honeycomb filter using a 6.7L diesel engine, and a predetermined amount of ash was deposited inside the honeycomb filter. The amount of ash deposited was 30g / L. The honeycomb filter after ash deposition was photographed using computed tomography (CT) to confirm the ash distribution inside the honeycomb filter. A filter was deemed to have passed if no inlet cells were blocked midway with ash and if ash had accumulated on the outlet end face of the inlet cells. A filter was deemed to have failed if even one inlet cell was blocked midway with ash.

[0070] [Strength] Strength measurements were performed based on the isostatic fracture strength test specified in M505-87 of the automotive standard (JASO standard) 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 then isostatically compressing it in water. The isostatic strength measured by the isostatic fracture strength test is indicated by the applied pressure value (MPa) at which the honeycomb filter breaks. An isostatic strength of 1.0 MPa or more was considered a pass, and one below 1.0 MPa was considered a fail.

[0071] [Table 2]

[0072] (4. Discussion) From the results of the filter performance tests conducted on the honeycomb structures according to the examples and comparative examples, C in / C out It can be seen that in the examples in which the partition wall thickness (WT), cell density (CD), plugging depth (PD), offset (OF), and OF×CD / (WT×PD) were all appropriate, excellent PM collection performance, low pressure loss, excellent catalyst coating properties when catalyst is loaded, low ash clogging, and excellent mechanical strength were all satisfied. Furthermore, it can be seen that Examples 2 and 3 in which OF×CD / (WT×PD) was optimal were able to satisfy the required properties at a high level. On the other hand, in the comparative examples, C in / Cout It can be seen that because one or more of the following were inappropriate: partition wall thickness (WT), cell density (CD), plugging depth (PD), offset (OF), and OF×CD / (WT×PD), it was not possible to satisfy all of the following: excellent PM collection performance, low pressure loss, excellent catalyst application when catalyst is loaded, low ash clogging, and excellent mechanical strength. [Explanation of symbols]

[0073] 100: Honeycomb structure 102: Outer wall 104: Inlet end face 106: Outlet end face 107: Opening 108: Introduction cell 109: Plugging part 110: Discharge cell 112: Bulkhead 120: Zipper 121: Film 122: Squeegee 124: Plugging slurry 125: Cell 126: Hole 400: Honeycomb molded body

Claims

1. A columnar honeycomb structure comprising: an outer peripheral side wall; a plurality of inlet cells arranged on an inner peripheral side of the outer peripheral side wall, extending from an inlet end face to an outlet end face, having openings at the inlet end faces and having plugging portions at the outlet end face; and a plurality of discharge cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet end face to the outlet end face, having plugging portions at the inlet end face and having openings at the outlet end face, and adjacent to at least one of the plurality of inlet cells with a partition wall interposed therebetween, The opening area (C out ) relative to the opening area (C in ) is 1<C in / C out ≦2.5 is satisfied, The thickness (WT) of the partition wall is 0.18 to 0.25 mm, A cell density (CD) based on the total number of the plurality of inlet cells and the plurality of outlet cells is 49 to 70 cells / cm 2 and The depth (PD) of the plugging portion is 4 to 7 mm, in a cross section of the honeycomb structure perpendicular to an extension direction of the plurality of inlet cells and the plurality of outlet cells, a distance (OF) between a midpoint of a line segment connecting centers of gravity of the inlet cell and the outlet cell adjacent to each other with the partition wall interposed therebetween and a center of the partition wall intersected by the line segment is 0.075 to 0.110 mm, 2≦OF×CD / (WT×PD)≦7 is satisfied, Honeycomb structure.

2. 2. The honeycomb structure according to claim 1, wherein the partition walls have a porosity of 52 to 61%.

3. 3. The honeycomb structure according to claim 1, wherein the partition walls have an average pore diameter of 6 to 10 μm.

4. 3. The honeycomb structure according to claim 1, wherein the opening shapes of the plurality of introduction cells are all hexagonal or octagonal except for the one adjacent to the outer peripheral side wall.

5. 3. The honeycomb structure according to claim 1, wherein the partition walls contain one or more materials selected from the group consisting of cordierite, silicon carbide, silicon-silicon carbide composite material, silicon nitride, mullite, alumina, and aluminum titanate.

6. 3. The honeycomb structure according to claim 1, wherein a catalyst is supported on the partition walls.

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