Honeycomb structure

Abstract

Provided is a honeycomb structure capable of suppressing peeling of a plugged portion at the time of film peeling. A honeycomb structure includes an outer peripheral side wall, a plurality of first cells, and a plurality of second cells; the plurality of first cells are arranged on the inner peripheral side of the outer peripheral side wall, extend from a first bottom surface to a second bottom surface, have an opening portion at the first bottom surface, and have a plugged portion at the second bottom surface; the plurality of second cells are arranged on the inner peripheral side of the outer peripheral side wall, extend from the first bottom surface to the second bottom surface, have a plugged portion at the first bottom surface, and have an opening portion at the second bottom surface; the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with a partition wall; and the plugged portion is composed of a ceramic containing MgO: 9.0 to 13.4 mass%, Al2O3: 29.8 to 35.0 mass%, and SiO2: 49.8 to 57.2 mass%, and the arithmetic mean height Sa of the plugged portion of the first bottom surface and the second bottom surface is 18.0 μm or less, respectively.

Description

Technical Field

[0001] This invention relates to honeycomb structures. Background Technology

[0002] Exhaust gases from internal combustion engines such as diesel engines contain a large amount of carbon-based particulate matter, which contributes to environmental pollution. Therefore, diesel engines and similar engines typically have particulate filters (DPFs) installed in their exhaust systems to capture these particles. In recent years, particulate matter from gasoline engines has also been recognized as a problem, leading to the increasing adoption of gas-line particulate filters (GPFs) in gasoline engines as well.

[0003] As a filter, a wall-flow honeycomb structure is known, which is formed by alternately arranging an outer peripheral sidewall, a plurality of first cells and a plurality of second cells with partitions. The plurality of first cells are arranged on the inner peripheral side of the outer peripheral sidewall, extending from a first bottom surface to a second bottom surface. The first bottom surface is open and has a sealing portion on the second bottom surface. The plurality of second cells are arranged on the inner peripheral side of the outer peripheral sidewall, extending from the first bottom surface to the second bottom surface. The first bottom surface has a sealing portion and the second bottom surface is open.

[0004] In wall-flow honeycomb structures, the sealing sections serve to prevent captured particulate matter from leaking out of the filter (erosion). Therefore, the sealing sections are formed at specified locations and depths without peeling off, which is important for ensuring filter performance.

[0005] Patent Document 1 addresses the issue of providing a honeycomb filter in which the sealing portion and the substrate do not crack or the sealing portion does not peel off or fall off from the substrate. It also describes a honeycomb filter characterized in that the sealing material is composed of ceramic pulverized material of the same material as the ceramic substrate.

[0006] Patent Document 2 addresses the issue of obtaining a ceramic honeycomb filter with excellent thermal shock resistance, and describes a honeycomb filter made of a material mainly composed of cordierite crystals, wherein at least a portion of the sealing portion is made of an amorphous oxide matrix, which is formed by ceramic particles and colloidal oxides present between them.

[0007] Patent document 3 addresses the issue of providing a honeycomb structure that can suppress defects such as seal peeling during can filling and effectively prevent erosion, and describes a honeycomb structure in which the average porosity of the seal portion is controlled to be less than 4%.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2002-136817

[0011] Patent Document 2: Japanese Patent Application Publication No. 2005-125318

[0012] Patent Document 3: Japanese Patent Application Publication No. 2021-159868 Summary of the Invention

[0013] The problem that the invention aims to solve

[0014] When forming the sealing sections, a masking film is temporarily adhered to the bottom surface of the honeycomb structure to distinguish the cells where sealing sections are to be formed from other cells. The film will eventually be peeled off, but localized peeling of the sealing sections may occur at this time, requiring a considerable amount of time for correction, and sometimes resulting in defective products. In the existing technology, the problem of sealing section peeling during film removal cannot be considered adequately addressed, and there is room for improvement.

[0015] The present invention was made in view of the above circumstances. In one embodiment, the objective is to provide a honeycomb structure capable of suppressing the peeling of the sealing portion during membrane peeling.

[0016] Methods for solving problems

[0017] The inventors conducted in-depth research to address the aforementioned problems and discovered that controlling the composition and surface roughness of the sealing portion is crucial in resolving these issues. This invention is based on this insight, as illustrated below.

[0018] [Method 1] A honeycomb structure comprising an outer peripheral sidewall, a plurality of first cells, and a plurality of second cells; the plurality of first cells are disposed on the inner peripheral side of the outer peripheral sidewall, extending from a first bottom surface to a second bottom surface, having an opening on the first bottom surface and a sealing portion on the second bottom surface; the plurality of second cells are disposed on the inner peripheral side of the outer peripheral sidewall, extending from the first bottom surface to the second bottom surface, having a sealing portion on the first bottom surface and an opening on the second bottom surface; the plurality of first cells and the plurality of second cells are alternately arranged adjacent to each other with partitions between them; the sealing portion is made of ceramic containing MgO: 9.0–13.4 wt%, Al2O3: 29.0–35.5 wt%, and SiO2: 50.0–58.0 wt%, and the arithmetic mean height Sa of the sealing portion on the first bottom surface and the second bottom surface is 18.0 μm or less.

[0019] [Method 2] According to Method 1, the honeycomb structure wherein the sealing portion is composed of ceramic containing MgO: 9.0-12.0% by mass, Al2O3: 29.8-32.0% by mass, and SiO2: 54.0-57.2% by mass.

[0020] [Method 3] The honeycomb structure according to Method 1 or 2, wherein the arithmetic mean height Sa of the sealing portion of the first bottom surface and the second bottom surface is 5.0 to 17.5 μm respectively.

[0021] [Method 4] The honeycomb structure according to Method 1 or 2, wherein the arithmetic mean height Sa of the sealing portion of the first bottom surface and the second bottom surface is 5.0 to 12.0 μm respectively.

[0022] [Method 5] A honeycomb structure according to any one of Methods 1 to 4, wherein the sealing portion is in an unfired state.

[0023] [Method 6] According to Method 5, the honeycomb structure wherein the ceramic constituting the sealing portion contains cordierite particles and silicone that binds the particles together.

[0024] [Method 7] A honeycomb structure according to any one of Methods 1 to 4, wherein the sealing portion is fired.

[0025] [Method 8] The honeycomb structure according to Method 7, wherein the ceramic constituting the sealing portion is a sintered body of cordierite.

[0026] [Method 9] In any one of Methods 1 to 8, the median particle size of the ceramic constituting the sealing portion of the honeycomb structure is 5 to 25 μm.

[0027] [Method 10] A honeycomb structure according to any one of Methods 1 to 9, wherein the average porosity of the sealing portion of the first bottom surface and the second bottom surface is 30% to 70%, respectively.

[0028] [Method 11] A honeycomb structure according to any one of Methods 1 to 10, wherein the partition is made of ceramic with cordierite as the main component.

[0029] [Method 12] A honeycomb structure according to any one of Methods 1 to 11, wherein the average depth of the sealing portion of the first bottom surface and the second bottom surface is 3 to 7 mm respectively.

[0030] Invention Effects

[0031] According to one embodiment of the present invention, a honeycomb structure capable of suppressing the peeling of the sealing portion during membrane delamination is provided. By suppressing the peeling of the sealing portion, the desired performance required to prevent the sealing portion from being eroded by trapped particulate matter can be stably maintained. Therefore, this honeycomb structure is suitable for use as a honeycomb filter or similar device with excellent quality stability. Attached Figure Description

[0032] Figure 1It is a schematic three-dimensional diagram representing a wall-flow honeycomb structure.

[0033] Figure 2 This is a schematic cross-sectional view of a honeycomb structure with a wall flow pattern when viewed from a section parallel to the direction of the lattice extension.

[0034] Figure 3 This is a schematic enlarged view of the partition wall of a honeycomb structure when viewed from a cross section orthogonal to the direction of the lattice extension.

[0035] Figure 4 This is a schematic partial cross-sectional view used to illustrate the method for measuring the depth of the sealing section.

[0036] Figure 5 This is an illustrative diagram schematically illustrating an example of a sealing section formation method based on a scraper.

[0037] Explanation of reference numerals in the attached figures

[0038] 100: Honeycomb structure, 102: Outer peripheral sidewall, 104: First bottom surface, 106: Second bottom surface, 108: First cell, 109: Sealing section, 110: Second cell, 112: Partition wall, 120: Chuck, 121: Membrane, 122: Scraper, 124: Slurry for forming the sealing section, 125: Cell, 126: Hole, 500: Honeycomb molding body. Detailed Implementation

[0039] Next, while referring to the appendix Figure 1 The embodiments of the present invention will be described in detail below. It should be understood that the present invention is not limited to the following embodiments, and design changes and improvements can be appropriately made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0040] (1. Honeycomb structure)

[0041] exist Figure 1 and Figure 2The diagram illustrates schematic perspective and cross-sectional views of a honeycomb structure 100 applicable as a wall-flow type automotive exhaust filter and / or catalyst carrier. The honeycomb structure 100 includes an outer peripheral sidewall 102, a plurality of first cells 108, and a plurality of second cells 110. The plurality of first cells 108 are disposed on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to a first bottom surface 104 to a second bottom surface 106, having an opening on the first bottom surface 104 and a sealing portion 109 on the second bottom surface 106. The plurality of second cells 110 are disposed on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to a first bottom surface 104 to a second bottom surface 106, having a sealing portion 109 on the first bottom surface 104 and an opening on the second bottom surface 106. In this honeycomb structure 100, the first cells 108 and second cells 110 are alternately arranged adjacent to each other, separated by a partition wall 112.

[0042] For example, if exhaust gas containing particulate matter such as soot is supplied to the first bottom surface 104 on the upstream side of the honeycomb structure 100, the exhaust gas is introduced into the first cell 108 and flows downward within the first cell 108. Since the second bottom surface 106 on the downstream side of the first cell 108 is sealed, the exhaust gas flows into the second cell 110 through the porous partition 112 that divides the first cell 108 and the second cell 110. The particulate matter cannot pass through the partition 112, so it is captured and accumulates in the first cell 108. After the particulate matter is removed, the clean exhaust gas flowing into the second cell 110 flows downward within the second cell 110 and exits from the second bottom surface 106 on the downstream side.

[0043] The bottom shape of the honeycomb structure 100 is not limited; for example, it can be a circle, an ellipse, a racetrack shape, an oblong shape, a polygon, a triangle, a quadrilateral, or other irregular shapes. The honeycomb structure 100 can have a cylindrical shape. The honeycomb structure 100 shown in the figure has a circular bottom shape and is cylindrical overall.

[0044] There are no particular restrictions on the height of the honeycomb structure (the length from the first bottom surface to the second bottom surface); it can be set appropriately according to the application and performance requirements. For example, the height of the honeycomb structure can be set from 40mm to 450mm. There are also no particular restrictions on the relationship between the height of the honeycomb structure and the maximum diameter of each bottom surface (the longest diameter passing through the centroid of each bottom surface). Therefore, the height of the honeycomb structure can be longer than the maximum diameter of each bottom surface, or it can be shorter than the maximum diameter of each bottom surface.

[0045] The shape of the openings in the pores in the cross-section perpendicular to the direction of pore extension is not limited, but quadrilaterals, hexagons, octagons, or combinations thereof are preferred. Squares and hexagons are particularly favored. By forming the pore shape in this way, the pressure loss of fluid flowing through the honeycomb structure is reduced, resulting in excellent purification performance.

[0046] There are no particular restrictions on the pore density (the number of pores per unit cross-sectional area), for example, it can be set to 6 to 2000 pores per square inch (0.9 to 311 pores per cm²). 2 Further preferred settings include 50–1000 holes per square inch (7.8–155 holes per cm). 2 The preferred setting is 100–600 holes per square inch (15.5–92.0 holes per cm). 2 Here, the cell density can be calculated by dividing the total number of cells (including sealed cells) by the bottom area of ​​the honeycomb structure excluding the peripheral sidewalls.

[0047] From the viewpoint of improving the strength of the honeycomb structure and the collection efficiency in filter applications, the average thickness of the partition wall is preferably 150 μm or more, more preferably 170 μm or more, and even more preferably 190 μm or more. Furthermore, from the viewpoint of suppressing pressure loss, the average thickness of the partition wall is preferably 260 μm or less, more preferably 240 μm or less, and even more preferably 220 μm or less. Therefore, the average thickness of the partition wall is preferably, for example, 150–260 μm, more preferably 170–240 μm, and even more preferably 190–220 μm.

[0048] Figure 3 The diagram shows a schematic enlarged view of the partition 112 of the honeycomb structure 100 as observed in a cross-section orthogonal to the direction of the cell extension. The partition thickness refers to the length of line segment N that traverses the partition when connecting the centroids O of adjacent cells to each other in a cross-section orthogonal to the direction of the cell extension (the height direction of the honeycomb structure). The partition thickness direction D refers to the direction parallel to line segment N. The average partition thickness is the average of the thicknesses of all partitions.

[0049] The partition walls can be made of porous material. The average porosity of the partition walls can be adjusted appropriately according to the application, but from the viewpoint of minimizing fluid pressure loss, it is preferably 40% or more, more preferably 50% or more, and even more preferably 60% or more. Furthermore, from the viewpoint of ensuring the strength of the honeycomb structure, the average porosity of the partition walls is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. Therefore, the average porosity of the partition walls is preferably, for example, 40-80%, more preferably 50-75%, and even more preferably 60-70%. The porosity of the partition walls can be determined according to JIS R1655:2003 by mercury infiltration method. Twenty test pieces of partition walls, including the central and peripheral portions of the honeycomb structure, are uniformly collected, and the porosity of each is measured. The average value of these samples is taken as the average porosity.

[0050] There are no particular limitations on the materials constituting the partition and the outer peripheral sidewalls, but ceramics are preferred from the viewpoint of strength and heat resistance. As ceramics, for example, ceramics containing at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon-silicon carbide composites, silicon nitride, zirconium oxide, spinel, Indian quartz, pseudosapphire, corundum, and titanium dioxide are preferred. Furthermore, these ceramics may contain only one type or two or more types simultaneously. The partition and the outer peripheral sidewalls are preferably formed of a material containing a total of 50% by mass or more of these ceramics, and more preferably of a material containing 80% by mass or more of these ceramics.

[0051] In a preferred embodiment, the outer peripheral sidewalls, partitions, and sealing portions of the honeycomb structure each contain cordierite as a main component. This means that the total mass percentage of cordierite (2MgO·2Al2O3·5SiO2) in 100% by mass of the materials constituting the outer peripheral sidewalls, partitions, and sealing portions is 50% by mass or more. The mass percentage of cordierite in 100% by mass of the materials constituting the outer peripheral sidewalls, partitions, and sealing portions is preferably 70% by mass or more, and more preferably 80% by mass or more.

[0052] The cordierite content can be determined by X-ray diffraction. Specifically, using an X-ray diffraction apparatus that utilizes the Kα rays of Cu (e.g., the X'pert PRO apparatus manufactured by PANalytical), X-ray analysis is performed on samples from the outer peripheral sidewalls, septa, or sealing parts in the range of 2θ = 8–100°. The analysis is performed using the Rietveld analysis program RIETAN, thereby determining the cordierite crystallization ratio, which is taken as the cordierite content.

[0053] Fine-tuning the chemical composition of the sealing portion is advantageous in suppressing its peeling during film delamination. Specifically, the sealing portion is preferably composed of ceramic containing 9.0–13.4 wt% MgO, 29.0–35.5 wt% Al2O3, and 50.0–58.0 wt% SiO2; more preferably, it is composed of ceramic containing 9.0–12.0 wt% MgO, 29.8–32.0 wt% Al2O3, and 54.0–57.2 wt% SiO2; and even more preferably, it is composed of ceramic containing 10.2–11.5 wt% MgO, 30.5–32.0 wt% Al2O3, and 54.5–56.2 wt% SiO2. Compared to ordinary cordierite, this composition contains less MgO and more SiO2, thereby achieving a smoother outer surface of the sealing portion. Furthermore, it also improves the mechanical strength of the sealing portion itself.

[0054] Regarding the chemical composition of the sealing portion, it is preferable to cut the sealing portion from the honeycomb structure to prepare the test sample and perform the test on the test sample. However, in cases where it is difficult to collect 10.0g of test sample from the honeycomb structure, the test sample is prepared by the following method.

[0055] The same sealing slurry used in the fabrication of the sealing section was prepared and poured into a stainless steel mold with a diameter of 60 mm and a length of 15 mm. It was then dried under the same conditions as the actual sealing section and removed from the stainless steel mold. Afterward, it was fired under the same conditions as when firing the actual sealing section. The resulting block was pulverized to prepare a test specimen. If it was possible to cut the sealing section from the honeycomb structure to prepare a test specimen, the cut sealing section was pulverized to prepare the test specimen. Pulverization was carried out under the following conditions: mortar speed: 100 / 120 rpm, mortar speed: 6 / 7 rpm, pulverization time: 5 minutes.

[0056] 10.0 g of the test sample was placed in an alloy crucible, and 6.0 g of lithium tetraborate was added and mixed with a platinum rod. The alloy crucible was placed in a vitrification apparatus (e.g., HERZOG HA-HF16 automated microbead sampler) and vitrified at 1200 °C for 15 minutes (glass microbead method). Qualitative analysis of the glass microbeads in each sample was performed using fluorescence X-ray analysis of Kα rays from Si, Al, and Mg, to determine the mass percentages of SiO2, Al2O3, and MgO.

[0057] The smoothness of the outer surface of the sealing portion can be expressed by the arithmetic mean height Sa. The arithmetic mean height Sa is a parameter of surface roughness specified in ISO 25178, representing the average of the absolute values ​​of the height differences between points relative to the average surface area. Specifically, the arithmetic mean height Sa of the sealing portions on the first and second bottom surfaces is preferably 18.0 μm or less, more preferably 17.5 μm or less, and even more preferably 12.0 μm or less. While no lower limit is specifically set for the arithmetic mean height Sa of the sealing portion, considering manufacturing costs, the arithmetic mean height Sa of the sealing portions on the first and second bottom surfaces is preferably 5.0 μm or more, more preferably 8.0 μm or more, and even more preferably 10.5 μm or more. Therefore, the arithmetic mean height Sa of the sealing portion of the first bottom surface and the second bottom surface is preferably, for example, 5.0 to 18.0 μm, more preferably 5.0 to 17.5 μm, even more preferably 8.0 to 17.5 μm, and even more preferably 5.0 to 12.0 μm.

[0058] In this specification, the arithmetic mean height Sa of the sealing portion of the first bottom surface and the second bottom surface is the average value of the arithmetic mean height Sa of the sealing portion at 5 locations measured without deviation using a laser microscope.

[0059] For a sealing section, the measurement can be performed under the following conditions.

[0060] Measurement instrument: Shape resolution laser microscope (KEYENCE VK-X250 / 260) or a microscope with equivalent performance.

[0061] Parsing software: A multi-file parsing application (VK-1HXM) or software with equivalent performance.

[0062] Objective lens magnification: 10x

[0063] Sample dimensions: 20mm × 20mm × 10mm (depth direction of the sealing section)

[0064] Measurement mode: Surface shape

[0065] Measurement size for each field of view: standard (1024 pixels × 768 pixels)

[0066] Measurement quality: High precision

[0067] Measurement time: 1 minute

[0068] Planar processing: Specify a 750μm × 750μm square area and perform processing to determine the plane (reference plane) used as the measurement reference. Rotate the height data as a whole so that the set reference plane is horizontal, and offset it in the height direction so that the reference plane height is 0.

[0069] Reference plane position: -3μm (offset with a depth of 3μm as the height of 0).

[0070] Ignoring tiny areas: Ignore (number of pixels in tiny areas: ≥6 pixels (surface bumps less than 6 pixels are not recognized as holes)).

[0071] In one embodiment, the sealing portion can be fired. The ceramic constituting the fired sealing portion can be provided, for example, as a sintered body of cordierite. The sintered body of cordierite can be obtained by firing a slurry containing cordierite-based raw materials for forming the sealing portion.

[0072] In another embodiment, the sealing portion may also be in an unfired state. In this case, the ceramic constituting the sealing portion preferably contains cordierite particles and an inorganic binder that binds the particles together. Silica gel is preferred as the inorganic binder.

[0073] Regardless of whether the sealing portion is fired, the median particle size of the ceramic constituting the sealing portion is preferably fine. This allows for a smoother outer surface of the sealing portion. Specifically, the upper limit of the median particle size of the ceramic constituting the sealing portion is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. Furthermore, from the viewpoint of suppressing indentations in the sealing portion, the lower limit of the ceramic constituting the sealing portion is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 12 μm or more. Therefore, the median particle size of the ceramic constituting the sealing portion is preferably, for example, 5 to 25 μm, more preferably 10 to 20 μm, and even more preferably 12 to 15 μm.

[0074] Regarding the median particle size of the ceramic constituting the sealing portion, it is preferable to cut the sealing portion from the honeycomb structure to prepare a test sample and measure the sample. However, if it is difficult to prepare a 2.0g test sample from the honeycomb structure, the following method is used to prepare the test sample.

[0075] The same sealing slurry used in the preparation of the sealing section was prepared and poured into a stainless steel mold with a diameter of 60 mm and a length of 15 mm. It was then dried under the same conditions as the actual sealing section and removed from the stainless steel mold. Afterwards, it was fired under the same conditions as the actual sealing section. The resulting block was pulverized using an automatic mortar to prepare a test specimen. If it was possible to cut the sealing section from the honeycomb structure to prepare the test specimen, the cut sealing section was pulverized to prepare the test specimen. Pulverization was carried out under the following conditions: mortar speed: 100 / 120 rpm, mortar speed: 6 / 7 rpm, pulverization time: 5 minutes. 2.0 g of the test specimen was placed in a laser diffraction / scattering particle size distribution measuring device (HORIBA Partica LA-960 was used in this example), and the median particle size (D50) in the cumulative particle size distribution of the volume reference was determined by laser diffraction / scattering.

[0076] In one embodiment, the average depth of the sealing portions on both the first and second bottom surfaces is 3 to 7 mm, preferably 4.2 to 6 mm. A lower limit of 3 mm or more for the average depth of the sealing portions ensures the strength of the sealing portions. An average depth of 4.2 mm or more is preferred. Furthermore, an upper limit of 7 mm or less for the average depth of the sealing portions prevents the area of ​​the partition walls trapping particulate matter within the pores from becoming too small. An upper limit of 6 mm or less is preferred. The depth of the sealing portions at 20 locations on each bottom surface is measured without deviation, and the average value is taken as the average depth of the sealing portions on each bottom surface.

[0077] In this specification, the depth of each sealing portion is determined according to the following steps. First, the sealing portion for which the depth is to be measured is cut in half with a cutting plane parallel to the height direction (direction of cell extension) of the honeycomb structure, thus obtaining a cross-section of the sealing portion. A cross-sectional image of one location of the obtained sealing portion is photographed using a laser microscope (e.g., a KEYENCE VKX250 / 260 shape analysis laser microscope). A cross-sectional image of the sealing portion is generated. The length in the cell extension direction from the end of the outer surface side of the cell on the central axis M (a straight line equidistant from the opposite pair of partitions 112) observed in the cross-sectional image to the deepest point where the sealing portion 109 exists is measured and taken as the depth E of the sealing portion (refer to...). Figure 4 ).

[0078] In one embodiment, the average porosity of the sealing portions on the first and second bottom surfaces is 30% to 70%, preferably 35% to 60%, and more preferably 40% to 50%. Setting the lower limit of the average porosity of the sealing portions to 30% or more is beneficial for mitigating thermal stress and improving thermal shock resistance. The lower limit of the average porosity of the sealing portions is preferably 35% or more, and more preferably 40% or more. Furthermore, setting the upper limit of the average porosity of the sealing portions to 70% or less is advantageous in terms of preventing corrosion. The upper limit of the average porosity of the sealing portions is preferably 60% or less, and more preferably 50% or less.

[0079] The porosity of the sealing section is difficult to measure directly by collecting only samples from the sealing section. Therefore, it can be measured by the mercury injection method specified in JIS 1655:2003 according to the following steps.

[0080] • Collect test pieces of the partition wall section where no sealing section has been formed, and measure the porosity P1 (porosity of the partition wall section) of the test piece.

[0081] • Collect test pieces containing the sealing section and the partition wall section, and measure the porosity P (porosity of the partition wall section + porosity of the sealing section) of the test piece.

[0082] • In a test piece containing a septum wall section with a sealing section, the volume V1 of the septum wall section containing pores is measured.

[0083] • In a test piece containing a partition wall portion with a sealing section, the volume V2 of the sealing section containing pores is measured.

[0084] If the porosity of the sealing section is set as P2, then P, P1, P2, V1 and V2 satisfy the relationship of equation (1).

[0085] P=P1×V1 / (V1+V2)+P2×V2 / (V1+V2)···(1)

[0086] Therefore, P2 can be obtained through equation (2).

[0087] P2=P×(V1+V2) / V2-P1×V1 / V2···(2)

[0088] The porosity P2 of the sealing portion at any 20 points on each bottom surface is measured, and the average value is taken as the average porosity of the sealing portion on each bottom surface.

[0089] It should be noted that in the test piece containing the sealing part and the partition wall part, when the volume ratio of the volume V1 containing the air pores in the partition wall part is set as v1 and the volume ratio of the volume V2 containing the air pores in the sealing part is set as v2, P2 can be calculated by equation (3).

[0090] P2=P×(v1+v2) / v2-P1×v1 / v2···(3)

[0091] When using a honeycomb structure as a catalyst support, a catalyst appropriate to the purpose can be coated on the surface of the partition walls. Examples of catalysts are not limited to these, but include oxidation catalysts (DOC) used to increase exhaust gas temperature by oxidizing and burning hydrocarbons (HC) and carbon monoxide (CO); PM combustion catalysts to assist in the combustion of PM such as soot; SCR 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 may appropriately contain, for example, noble metals (Pt, Pd, Rh, etc.), alkali metals (Li, Na, K, Cs, etc.), alkaline earth metals (Mg, Ca, Ba, Sr, etc.), rare earth elements (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), and transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.).

[0092] (2. Manufacturing method)

[0093] Honeycomb structures with sealed pores can be manufactured using known methods other than the method for forming the sealed pores, which will be illustrated below. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming material, and a binder is mixed to form a blank. The blank is then extruded to form the desired honeycomb structure. Additives such as dispersants can be added to the raw material composition as needed. During extrusion molding, a metal mold with the desired overall shape, pore shape, partition wall thickness, pore density, etc., can be used.

[0094] Ceramic raw materials are the residues remaining after the firing of metal oxides and metals, forming part of the skeleton of the sintered honeycomb body in ceramic form. Ceramic raw materials can be provided, for example, in powder form. Examples of ceramic raw materials include cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon-silicon carbide composites, silicon nitride, zirconium oxide, spinel, Indian quartz, pseudosapphire, corundum, and titanium dioxide. Specifically, there are no limitations; examples include silicon dioxide, talc, alumina, kaolin, serpentine, pyrophyllite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. A single ceramic raw material can be used, or two or more can be used in combination.

[0095] In applications such as DPF and GPF filters, cordierite is preferred as the ceramic material. In this case, cordierite-modified raw materials can be used as the ceramic raw material. Cordierite-modified raw materials refer to raw materials that become cordierite through firing. The cordierite-modified raw material preferably consists of the following chemical composition: alumina (Al₂O₃) (including a portion of aluminum hydroxide that can be converted into alumina): 30–45% by mass, magnesium oxide (MgO): 11–17% by mass, and silicon dioxide (SiO₂): 42–57% by mass.

[0096] As a pore-forming material, there are no particular limitations as long as it becomes porous after firing. Examples include wheat flour, starch, foaming resin, water-absorbing resin, silica gel, carbon (e.g., graphite), ceramic cenospheres, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, phenol, etc. One type of pore-forming material can be used alone, or two or more can be used in combination. From the viewpoint of improving the porosity of the fired honeycomb structure, the content of the pore-forming material relative to 100 parts by mass of the ceramic raw material is preferably 0.5 parts by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more. From the viewpoint of ensuring the strength of the fired honeycomb structure, the content of the pore-forming material relative to 100 parts by mass of the ceramic raw 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.

[0097] Examples of adhesives include organic adhesives such as methylcellulose, hydroxypropoxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Furthermore, from the viewpoint of improving the strength of the honeycomb molded body, the adhesive content is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more, relative to 100 parts by mass of the ceramic raw material. From the viewpoint of suppressing cracking caused by abnormal heating during the firing process, the adhesive content 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 ceramic raw material. One type of adhesive can be used alone, or two or more types can be used in combination.

[0098] Dispersants can include ethylene glycol, dextrin, fatty acid soaps, polyether polyols, etc. A single dispersant can be used, or two or more can be used in combination. The preferred content of the dispersant relative to 100 parts by weight of the ceramic raw material is 0 to 2 parts by weight.

[0099] Examples of suitable dispersion media include water or mixtures of water and organic solvents such as alcohols, with water being particularly preferred.

[0100] Before the drying process, the water content of the honeycomb molded body relative to 100 parts by mass of the ceramic raw material is preferably 20 to 90 parts by mass, more preferably 60 to 85 parts by mass, and even more preferably 70 to 80 parts by mass. By ensuring that the water content of the honeycomb molded body is 20 parts by mass or more relative to 100 parts by mass of the ceramic raw material, it is easy to obtain the advantage of stable honeycomb structure quality. By ensuring that the water content of the honeycomb molded body is 90 parts by mass or less relative to 100 parts by mass of the ceramic raw material, the shrinkage during drying is reduced, and deformation can be suppressed. In this specification, the water content of the honeycomb molded body refers to the value measured by the drying loss method.

[0101] The drying of honeycomb molded bodies can be carried out using conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying. Among these methods, a combination of hot air drying and microwave drying or dielectric drying is preferred, considering the ability to dry the honeycomb molded body quickly and uniformly.

[0102] The subsequent processes differ depending on whether the honeycomb structure of the product has a fired sealed portion or an unfired sealed portion, so they will be explained separately for each case.

[0103] (1) The honeycomb structure has a sintered sealed portion.

[0104] The case of a honeycomb structure having fired sealed portions will be described. After drying the honeycomb molded body, unfired sealed portions are formed on both bottom surfaces of the honeycomb molded body. The unfired sealed portions are formed by filling the openings of the first and second cells to which the sealed portions should be formed with a sealing paste, and then drying. Next, the unfired sealed portions are fired together with the honeycomb molded body. Thus, fired sealed portions are formed.

[0105] In one embodiment, the slurry for forming the sealing portion contains cordierite raw material, a dispersion medium, a pore-forming material, and a binder. Exemplarily, the slurry for forming the sealing portion contains, relative to 100 parts by weight of the cordierite raw material, 30-60 parts by weight of the dispersion medium, 5-20 parts by weight of the pore-forming material, and 0.2-2.0 parts by weight of the binder. In a preferred embodiment, the slurry for forming the sealing portion contains, relative to 100 parts by weight of the cordierite raw material, 35-50 parts by weight of the dispersion medium, 8-16 parts by weight of the pore-forming material, and 0.2-1.5 parts by weight of the binder.

[0106] Examples of cordierite raw materials used in the slurry for forming the sealing section include silica, talc, alumina, kaolin, serpentine, pyrophyllite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. The proportions of these raw materials are selected such that the sealed section obtained after firing has the aforementioned chemical composition.

[0107] From the viewpoint of improving the smoothness of the outer surface of the sealing section, cordierite raw materials are preferably as fine as possible. For example, the median particle size (D50) in the cumulative particle size distribution based on volume diffraction / scattering method is preferably talc: 9-31 μm, alumina (and aluminum hydroxide): 3-8 μm, kaolin: 2-9 μm, and silica: 2-8 μm.

[0108] Examples of suitable dispersion media include water or mixtures of water and organic solvents such as alcohols, with water being particularly preferred.

[0109] As a pore-forming material, there are no particular limitations as long as it becomes porous after firing. Examples include wheat flour, starch, foaming resin, water-absorbing resin, silica gel, carbon (e.g., graphite), ceramic cenospheres, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, phenol, etc. A single pore-forming material can be used, or two or more can be used in combination. The median particle size (D50) of the cumulative particle size distribution based on volume, determined by laser diffraction / scattering, is preferably 35–55 μm.

[0110] Examples of adhesives include organic adhesives such as methylcellulose, hydroxypropoxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. One type of adhesive can be used alone, or two or more can be used in combination.

[0111] The slurry for forming the sealing portion may contain a thickener. For example, the thickener may contain 0.1 to 0.5 parts by weight, preferably 0.2 to 0.4 parts by weight, relative to 100 parts by weight of the cordierite raw material. Examples of thickeners used in the slurry for forming the sealing portion include pectin, guar gum, xanthan gum, propylene glycol, and polyethylene oxide. Polyethylene oxide is preferred, as it exhibits high viscosity and flowability modification even at low concentrations. One type of thickener may be used alone, or two or more may be used in combination.

[0112] The slurry for forming the sealing section may contain a dispersant. For example, the dispersant may contain 0.1 to 3 parts by weight, preferably 0.2 to 2 parts by weight, relative to 100 parts by weight of the cordierite raw material. Examples of dispersants include ethylene glycol, dextrin, fatty acid soaps, and polyols. One type of dispersant may be used alone, or two or more may be used in combination.

[0113] The filling of the openings in the pores with slurry to form the sealing section can be achieved, for example, by using a scraper method. Figure 5 As shown, a film 121 is pasted onto the bottom surface (the second bottom surface 106 in the figure) of the upper side of the dried honeycomb molded body 500, which is fixed by a chuck 120. A laser is irradiated onto the position of the film 121 corresponding to the arrangement conditions of the sealing part (e.g., "checkerboard pattern"). Multiple holes 126 are formed through the film 121.

[0114] Then, a slurry 124 for forming the sealing portion is placed on the membrane 121, and the scraper 122 is moved along the membrane 121 towards... Figure 5 The operation moves in the direction of the arrow in the image. As a result, a certain amount of sealing slurry 124 is filled into the pore grid 125 that opens at the position corresponding to the pore 126 of the membrane 121.

[0115] The depth of the sealing section can vary depending on the number of times the scraper 122 moves, the contact angle between the scraper 122 and the membrane 121, the pressing pressure of the scraper 122 on the membrane 121, and the viscosity of the slurry 124 used to form the sealing section.

[0116] After filling the sealing portion with the slurry 124, the excess slurry 124 remaining on the surface of the membrane 121 is wiped away with a scraper 122. Then, the membrane 121 is peeled off, and the honeycomb molded body 500 is dried as a whole. Thus, the sealing portion forming slurry 124 filling the cells 125 is dried, forming the sealing portion before firing. Drying can be carried out, for example, at a drying temperature of 100 to 230°C for about 60 to 150 seconds.

[0117] The membrane material is not particularly limited, but for ease of thermal processing to form pores, polypropylene (PP), polyethylene terephthalate (PET), polyimide, or Teflon (registered trademark) are preferred. Furthermore, the membrane preferably includes an adhesive layer, preferably made of acrylic resin, rubber-based resin (e.g., rubber primarily composed of natural or synthetic rubber), or silicone resin. For example, an adhesive membrane with a thickness of 20–50 μm can be suitably used.

[0118] Besides the aforementioned "scraper method," another method for filling the openings of the pores with the sealing slurry is the "press-in method." The "press-in method" involves immersing the bottom surface of a perforated honeycomb molded body with a film attached into a tank containing the sealing slurry, and then filling the pores with the slurry. In this case, the depth of the sealing portion can vary depending on the depth to which the honeycomb molded body is immersed in the sealing slurry.

[0119] After drying, the sealing portion protrudes from the bottom surface of the honeycomb molded body by an amount equivalent to the film thickness. Therefore, it is preferable to scrape it off and smooth it out (hereinafter also referred to as "smoothing process"). At this time, if the sealing portion has a suitable composition, the outer surface of the sealing portion can be easily smoothed. The method of smoothing process is not limited, but it is preferable to press one bottom surface of the fired ceramic honeycomb structure (hereinafter also referred to as "smoothing fixture") against the outer surface of the sealing portion to be smoothed and rub it. For example, it is preferable to use a material that is the same as the fired material of the honeycomb molded body to be smoothed, such as cordierite. The smoothing fixture may or may not have a sealing portion.

[0120] The bottom surface of the smoothing fixture is preferably smooth. Specifically, the arithmetic mean height Sa of the surface of the partition wall constituting the bottom surface of the smoothing fixture is preferably, for example, 1.0 to 5.0 μm, more preferably 2.0 to 4.0 μm, and even more preferably 2.5 to 3.5 μm. The arithmetic mean height Sa of the surface of the partition wall constituting the bottom surface of the smoothing fixture can be measured by the same method as the method for measuring the arithmetic mean height Sa of the sealing portion described above.

[0121] Furthermore, during the smoothing process, it is preferable to move the two parts relative to each other in a manner where the direction of the side (partition) of the opening shape of the honeycomb molded body to be smoothed is not parallel to the direction of the side (partition) of the opening shape of the opening shape of the smoothing fixture, for example, with an angle of 30° to 60° between the two sides. This is because if the direction of the side (partition) of the opening shape of the honeycomb molded body to be smoothed is parallel to the direction of the side (partition) of the opening shape of the opening shape of the smoothing fixture, gaps are easily generated.

[0122] For a honeycomb molded body filled with a slurry for forming sealing portions, a degreasing process and a firing process are then performed. This produces a honeycomb structure with fired sealing portions. The burn temperature of the adhesive is approximately 200°C, and the burn temperature of the pore-forming material is approximately 300–1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb molded body to approximately 200–1000°C. The heating time is not particularly limited, but is usually around 10–100 hours. The honeycomb molded body after the degreasing process is called a pre-fired body. The firing process also depends on the material composition of the honeycomb structure; for example, it can be carried out by heating the pre-fired body to 1300–1450°C and holding it for 3–24 hours.

[0123] (2) Case where the honeycomb structure has unfired sealed sections.

[0124] Next, the case where the honeycomb structure has unfired sealing portions will be described. In this case, after drying the honeycomb molded body, a degreasing and firing process is performed without forming sealing portions. The conditions for the degreasing and firing processes are as described above. This produces a honeycomb structure without sealing portions. Next, unfired sealing portions are formed on both bottom surfaces of the honeycomb structure. The unfired sealing portions can be formed by filling the openings of the first and second cells where sealing portions should be formed with a sealing portion forming slurry, and then drying.

[0125] In one embodiment, the slurry for forming the sealing portion contains cordierite particles, a dispersion medium, and an inorganic binder. Exemplarily, the slurry for forming the sealing portion contains 10-35 parts by mass of dispersion medium and 10-25 parts by mass of inorganic binder per 100 parts by mass of cordierite particles. In a preferred embodiment, the slurry for forming the sealing portion contains 15-30 parts by mass of dispersion medium and 11-20 parts by mass of inorganic binder per 100 parts by mass of cordierite particles. The proportions of these raw materials are selected such that the sealed portion obtained after drying has the aforementioned chemical composition.

[0126] Cordierite particles contain cordierite as the main component. This means that the total mass percentage of cordierite (2MgO·2Al2O3·5SiO2) in 100% by mass of cordierite particles is 50% by mass or more. Preferably, the mass percentage of cordierite in 100% by mass of cordierite particles is 70% by mass or more, more preferably 80% by mass or more. The method for determining the cordierite content is as described above.

[0127] From the viewpoint of improving the smoothness of the outer surface of the sealing portion, cordierite particles are preferably fine. However, if the cordierite particles are too fine, the porosity decreases. Therefore, in order to obtain the desired porosity, the cordierite particles are preferably not too fine. For cordierite particles, the median particle size (D50) in the cumulative particle size distribution based on volume diffraction / scattering, for example, is preferably 40 μm or less, more preferably 30 μm or less. There is no particular lower limit for the median particle size (D50) of cordierite particles. From the viewpoint of ease of acquisition, the median particle size (D50) of cordierite particles is usually 10 μm or more, typically 20 μm or more. Therefore, the median particle size (D50) of cordierite particles is preferably, for example, 10 to 40 μm, more preferably 20 to 30 μm.

[0128] Examples of suitable dispersion media include water or mixtures of water and organic solvents such as alcohols, with water being particularly preferred.

[0129] Silicone is preferred as an inorganic adhesive.

[0130] In addition to inorganic binders, the slurry for forming the sealing portion may also contain organic binders. For example, relative to 100 parts by weight of cordierite particles, it may contain 0.2 to 2.0 parts by weight, preferably 0.2 to 1.5 parts by weight. Examples of organic binders include methylcellulose, hydroxypropoxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose, polyvinyl alcohol, diutan gum, wellan gum, xanthan gum, guar gum, etc. One type of organic binder may be used alone, or two or more may be used in combination.

[0131] The slurry for forming the sealing portion may contain a dispersant. For example, the dispersant may contain 0.1 to 3 parts by mass relative to 100 parts by mass of cordierite particles, preferably 0.2 to 2 parts by mass. Examples of dispersants include ethylene glycol, dextrin, fatty acid soaps, and polyols. One type of dispersant may be used alone, or two or more may be used in combination.

[0132] The filling of the pore openings with the slurry for sealing the pores can be achieved using known filling methods such as the "scraper method" and the "press-in method" described above. Subsequent membrane peeling and drying conditions are also as described above.

[0133] After drying, the smoothing process described above is preferably performed. At this time, if the sealing portion has a suitable composition, the outer surface of the sealing portion can be easily smoothed. The conditions for the smoothing process are as described above.

[0134] Example

[0135] <Comparative Examples 1-2, Example 1>

[0136] (1) Fabrication of honeycomb molded body

[0137] To 100 parts by weight of cordierite petrochemical raw material, 25 parts by weight of pore-forming material, 80 parts by weight of dispersion medium, 5 parts by weight of binder, and 1 part by weight of dispersant are added respectively. The resulting raw material composition is then mixed to prepare clay. Talc, alumina, aluminum hydroxide, kaolin, and silica are used as the cordierite petrochemical raw material. Water is used as the dispersion medium, water-absorbing resin and silica gel are used as the pore-forming material, methylcellulose is used as the binder, and ethylene glycol is used as the dispersant.

[0138] The clay is fed into an extrusion molding machine and extruded through a metal die of a specified shape to obtain a cylindrical honeycomb molded body. After dielectric drying and hot air drying, the two bottom surfaces are cut to a specified size, and then further hot air dried at 70°C for 2 hours.

[0139] (2) Formation of the sealing section

[0140] To a total of 100 parts by mass of cordierite petrochemical raw materials containing the various raw materials as specified in Table 1, pore-forming materials, dispersion media, organic binders, and dispersants are added according to the mass proportions specified in Table 1, and the mixture is kneaded to prepare a slurry for forming the pore section. The cordierite petrochemical raw materials used are talc, alumina, aluminum hydroxide, kaolin, and silica. The median particle size (D50) of these raw materials is as specified in Table 1. Foaming resin is used as the pore-forming material, water as the dispersion media, methylcellulose as the organic binder, and ethylene glycol as the dispersant. Using the aforementioned "scraper method," the slurry for forming the pore section is filled onto both bottom surfaces in an alternating arrangement of first and second pore sections. Then, after wiping away excess slurry adhering to the membrane with a scraper, the membrane is peeled off and dried at 180°C for 200 seconds under atmospheric conditions.

[0141] For each honeycomb molded body, while observing the condition of the outer surface of the sealing portion immediately after the film was peeled off using an optical microscope (100x magnification), the peeling depth of 5 peeling sites was randomly measured using a ruler, and the peeling of the sealing portion was evaluated according to the following criteria. The results are shown in Table 1.

[0142] ○: ≤1.0mm

[0143] △: 1.1~1.5mm

[0144] ×: ≥1.6mm

[0145] (3) Smoothing process

[0146] A honeycomb structure made of fired cordierite is prepared as a smoothing fixture. The specifications of the honeycomb structure are as follows.

[0147] Overall shape: Cylindrical, 118mm in diameter × 20mm in height

[0148] Hole shape in a cross-section perpendicular to the flow path direction: square

[0149] Pore ​​density (number of pores per unit cross-sectional area): 750 pores / square inch (118 pores / cm²) 2 Average thickness of the partition wall: 2.5 mil (64 μm) (nominal value based on metal mold specifications)

[0150] The arithmetic mean height Sa of the partition walls constituting the bottom surface of the smoothing fixture is 3.3 μm.

[0151] Next, each dried honeycomb molded body undergoes a manual smoothing process for the sealed areas. During the smoothing process, the edges (partitions) defining the opening shape of the honeycomb molded body to be smoothed are moved relative to each other at an angle of 45° to the edges (partitions) defining the opening shape of the smoothing fixture.

[0152] (4) Firing

[0153] Next, the material was degreased by heating at approximately 200°C in an atmospheric atmosphere, and then fired at 1400°C for 10 hours in an atmospheric atmosphere, thereby obtaining a cylindrical honeycomb structure with fired sealed pores. A number of honeycomb structures were prepared to investigate the following properties.

[0154] (5) Specifications of honeycomb structures

[0155] The specifications of the obtained honeycomb structure are as follows.

[0156] Overall shape: Cylindrical, 132mm in diameter × 152mm in height

[0157] Hole shape in a cross-section perpendicular to the flow path direction: square

[0158] Pore ​​density (number of pores per unit cross-sectional area): 300 pores / square inch (47 pores / cm²) 2 Average thickness of the partition wall: 8.5 mil (216 μm) (nominal value based on metal mold specifications)

[0159] Average porosity of the partition wall: 63%

[0160] Average depth of the sealing section: 5mm

[0161] For the outer peripheral sidewalls, partitions, and sealing sections of the cylindrical honeycomb structure, X-ray diffraction was performed in the range of 2θ = 8 to 100° using an X'pert PRO apparatus manufactured by PANalytical that utilizes Cu Kα rays. The ratio of cordierite crystals obtained by analysis using the Rietveld analytical program RIETAN was analyzed, and the results were 75 to 94% by mass.

[0162] (6) Chemical composition of the sealing part

[0163] Since it is difficult to collect test samples from the honeycomb structure, the same sealing slurry used in the fabrication of the sealing section was prepared, and test samples were prepared according to the aforementioned steps. The chemical composition was then determined using the aforementioned method. The results are shown in Table 1.

[0164] (7) Median particle size of the sealing section

[0165] Since it was difficult to collect test samples from the honeycomb structure, the same sealing slurry used in the fabrication of the sealing section was prepared, and test samples were prepared according to the aforementioned steps. The median particle size of the ceramics constituting the sealing section was then determined using the aforementioned method. The results are shown in Table 1.

[0166] (8) Arithmetic mean height Sa of the sealing section

[0167] Using the method described above, the arithmetic mean height Sa of the sealing portion on one bottom surface of the obtained honeycomb structure was measured using a KEYENCE VK X250 / 260 shape-analyzing laser microscope. The results are shown in Table 1. It should be noted that although the arithmetic mean height Sa of the sealing portion on the other bottom surface is not recorded in Table 1, it is at the same level as that on the first bottom surface.

[0168] (9) Average porosity of the sealing section

[0169] The average porosity of the sealing portion on one bottom surface of the obtained honeycomb structure was measured using the method described above. The results are shown in Table 1. It should be noted that although the average porosity of the sealing portion on the other bottom surface is not recorded in Table 1, it is at the same level as that on the first bottom surface.

[0170] (10) Strength of sealing section

[0171] Nine sealing sections (the center of gravity of the bottom surface, and two equally spaced sections along the ±X and ±Y directions from the center of gravity as the origin O of the XY coordinate system) on one bottom surface of the obtained honeycomb structure, excluding the area within 5 mm of the outer perimeter, were pressed down with a stainless steel pressing rod (cylindrical in diameter 1.1 mm × length 40 mm) inserted from the other bottom surface side, and the applied force was gradually increased. As the applied force increased, the pressing rod soon penetrated the sealing section. The maximum load (sealing section strength) until penetration was measured using a load sensor. The same measurement was performed on the sealing sections of the other bottom surface. Thus, the average value of the strength of a total of 18 sealing sections was determined for a honeycomb structure. Furthermore, the relative values ​​when the average value of Comparative Example 1 was set to 1.0 are shown in Table 1.

[0172] <Examples 2-4>

[0173] (1) Fabrication of a cylindrical honeycomb structure without sealing holes

[0174] A cylindrical honeycomb structure was fabricated under the same conditions as in Example 1. The resulting honeycomb structure was then subjected to dielectric drying and hot air drying, followed by cutting off the two bottom surfaces to a specified size, and further hot air drying at 70°C for 2 hours. Next, it was degreased by heating at approximately 200°C in an atmospheric atmosphere, and then fired at 1400°C for 10 hours in an atmospheric atmosphere, thereby obtaining a cylindrical honeycomb structure without sealed pores.

[0175] (2) Formation of the sealing section

[0176] A slurry for forming the sealing section was prepared by mixing 100 parts by mass of cordierite particles A (cordierite content = 90 wt%) and cordierite particles B (cordierite content = 90 wt%) according to the mass proportions listed in Table 1. Dispersion medium, organic binder, silica gel (inorganic binder), and dispersant were added according to the mass proportions listed in Table 1. The chemical composition of cordierite particles A and B was determined using a quantitative analysis method based on fluorescence X-ray analysis. The results showed that for cordierite particles A, SiO2 was 53.0 wt%, Al2O3 was 32.1 wt%, and MgO was 11.1 wt%. For cordierite particles B, SiO2 was 54.5 wt%, Al2O3 was 30.9 wt%, and MgO was 12.4 wt%. Their median particle size (D50) is shown in Table 1. Water was used as the dispersion medium, sorbent polymer as the organic binder, and ethylene glycol as the dispersant. Using the aforementioned "scraper method," the slurry for forming the sealing portion was filled onto both bottom surfaces with the first and second cells alternately arranged adjacently. Then, after wiping away any excess sealing portion slurry adhering to the membrane with a scraper, the membrane was peeled off and dried at 180°C for 200 seconds in atmospheric conditions.

[0177] For each honeycomb structure, the peeling of the sealing portion was evaluated using the same method as in Example 1. The results are shown in Table 1.

[0178] (3) Smoothing process

[0179] A honeycomb structure made of fired cordierite was prepared as a smoothing fixture. The specifications of the honeycomb structure were the same as those of the smoothing fixture used in Example 1.

[0180] Next, for each honeycomb structure after the sealing portion has dried, the sealing portion is smoothed manually. During smoothing, the edges (partitions) defining the opening shape of the honeycomb molded body to be smoothed are moved relative to each other at an angle of 45° to the edges (partitions) defining the opening shape of the opening shape of the smoothing fixture. This produces a honeycomb structure with an unfired sealing portion. A number of honeycomb structures were prepared to investigate the following characteristics.

[0181] (4) Specifications of honeycomb structures

[0182] The specifications of the obtained honeycomb structure are as follows.

[0183] Overall shape: Cylindrical, 132mm in diameter × 152mm in height

[0184] Hole shape in a cross-section perpendicular to the flow path direction: square

[0185] Pore ​​density (number of pores per unit cross-sectional area): 300 pores / square inch (49 pores / cm²) 2 Average thickness of the partition wall: 8.5 mil (216 μm) (nominal value based on metal mold specifications)

[0186] Average depth of the sealing section: 5mm

[0187] Average porosity of the partition wall: 63%

[0188] For the outer peripheral sidewalls, partitions, and sealing sections of the cylindrical honeycomb structure, X-ray diffraction was performed in the range of 2θ = 8 to 100° using an X'pert PRO apparatus manufactured by PANalytical that utilizes Cu Kα rays. The ratio of cordierite crystals obtained by analysis using the Rietveld analytical program RIETAN was analyzed, and the results were 75 to 94% by mass.

[0189] (5) Characteristics of the sealing section

[0190] The chemical composition, median particle size, arithmetic mean height Sa, average porosity, and sealing strength of the sealing portion were determined using the same method as in Example 1. The results are shown in Table 1.

[0191] [Table 1]

[0192]

Claims

1. A honeycomb structure comprising an outer peripheral wall, a plurality of first cells, and a plurality of second cells; the plurality of first cells are arranged on an inner peripheral side of the outer peripheral wall, extend from a first bottom surface to a second bottom surface, have an opening portion at the first bottom surface, and have a closed portion at the second bottom surface; the plurality of second cells are arranged on the inner peripheral side of the outer peripheral wall, extend from the first bottom surface to the second bottom surface, have the closed portion at the first bottom surface, and have the opening portion at the second bottom surface; the plurality of first cells and the plurality of second cells are alternately arranged with a partition wall therebetween; the closed portion is composed of a ceramic containing MgO: 9.0 to 13.4 mass%, Al203: 29.0 to 35.5 mass%, and Si02: 50.0 to 58.0 mass%, the arithmetic average height Sa of the closed portion of the first bottom surface and the second bottom surface is 18.0 μm or less, respectively.

2. The honeycomb structure of claim 1, wherein, the closed portion is composed of a ceramic containing MgO: 9.0 to 12.0 mass%, Al203: 29.8 to 32.0 mass%, and Si02: 54.0 to 57.2 mass%.

3. The honeycomb structure of claim 1, wherein, the arithmetic average height Sa of the closed portion of the first bottom surface and the second bottom surface is 5.0 to 17.5 μm, respectively.

4. The honeycomb structure of claim 1, wherein, the arithmetic average height Sa of the closed portion of the first bottom surface and the second bottom surface is 5.0 to 12.0 μm, respectively.

5. The honeycomb structure of claim 1, wherein, the closed portion is in an un-fired state.

6. The honeycomb structure of claim 5, wherein, the ceramic constituting the closed portion contains cordierite particles and silica gel that bonds the particles to each other.

7. The honeycomb structure of claim 1, wherein, the closed portion is fired.

8. The honeycomb structure of claim 7, wherein, the ceramic constituting the closed portion is a sintered body of cordierite.

9. The honeycomb structure of claim 1, wherein, the median particle diameter of the ceramic constituting the closed portion is 5 to 25 μm.

10. The honeycomb structure of claim 1, wherein, the average porosity of the closed portion of the first bottom surface and the second bottom surface is 30 to 70%, respectively.

11. The honeycomb structure of claim 1, wherein, the partition wall is composed of a ceramic in which cordierite is a main component.

12. The honeycomb structure of claim 1, wherein, the average depth of the closed portion of the first bottom surface and the second bottom surface is 3 to 7 mm, respectively.

Images