Cylindrical honeycomb structure

Abstract

Provided is a columnar honeycomb structure having a partition wall structure suitable for achieving both light weight and high strength. A columnar honeycomb structure has a peripheral side wall and a plurality of partition walls provided on the inner periphery side of the peripheral side wall and dividing a plurality of cells forming flow paths from a first bottom surface to a second bottom surface, wherein the average pore diameter of the partition walls, as measured by a mercury porosimeter, is 3 to 10 μm, and when the cross sections of the plurality of partition walls are observed by an X-ray microscope, and the porosity (%) is measured from one surface to the other surface in the thickness direction of each partition wall, the average porosity of each partition wall is 40 to 70%, and the difference between the maximum and minimum values of the porosity of each partition wall is 11% or less.

Description

Technical Field

[0001] This invention relates to columnar honeycomb structures. In particular, this invention relates to columnar honeycomb structures for waste gas purification. Background Technology

[0002] The exhaust gases emitted by internal combustion engines, such as automobile engines, contain pollutants including coal, nitrogen oxides (NOx), soluble organic compounds (SOF), hydrocarbons (HC), and carbon monoxide (CO). Therefore, a columnar honeycomb structure is typically installed in the exhaust system of an internal combustion engine, which is loaded with appropriate catalysts (oxidation catalysts, reduction catalysts, three-way catalysts, etc.) according to the pollutants, to purify the exhaust gases.

[0003] The columnar honeycomb structure has an outer peripheral sidewall and multiple partitions. These partitions are disposed on the inner peripheral side of the outer peripheral sidewall and divide the structure into multiple pores that form flow paths from a first bottom surface to a second bottom surface. A catalyst layer containing the aforementioned catalyst can be formed on the surface of the partitions.

[0004] In recent years, the development of columnar honeycomb structures capable of rapidly raising the temperature of the catalyst layer to its activation temperature after engine start-up has been progressing. To achieve this rapid activation, the columnar honeycomb structure needs to be lightweight. This requires thinning the partition walls or increasing their porosity to reduce their heat capacity. This allows the partition walls to heat up quickly after exhaust gas begins to flow, enabling the catalyst layer formed on their surface to reach its activation temperature in a short time. However, there are limitations to thinning the partition walls; therefore, increasing porosity is considered as a method of weight reduction. A concern in this case is the potential reduction in the strength of the columnar honeycomb structure.

[0005] Against this backdrop, the following invention is disclosed in Patent Document 1 (Japanese Patent Application Publication No. 2016-204208), the purpose of which is to provide a honeycomb structure that enables the temperature of the catalyst layer to rise to the activation temperature in a short time, and is difficult to crack even after repeated hot and cold cycles, and the purification performance of the exhaust gas is difficult to reduce.

[0006] A honeycomb structure, characterized by comprising polygonal lattice-shaped pore walls, a plurality of pores surrounded by the lattice walls, and a catalyst layer formed on the surface of the lattice walls.

[0007] Multiple recesses are formed on the aforementioned perforated grid wall.

[0008] When observing the cross-section of the aforementioned perforated wall, the opening ratio of the opening portion of the aforementioned recessed portion (i.e., the deep recessed portion) that is at a depth of 10 μm or more from the aforementioned surface is 10% or more.

[0009] The number of the aforementioned deep recesses (i.e., narrow recesses) with an opening length of 8 μm or less accounts for more than 10% of the total number of the aforementioned deep recesses.

[0010] The number of deep recesses (i.e., wide recesses) with an opening length of 20 μm or more accounts for more than 10% of the total number of deep recesses.

[0011] In addition, existing documents that disclose the porosity of honeycomb structures include Patent Document 2 (Japanese Patent Application Publication No. 2016-190198) and Patent Document 3 (Japanese Patent Publication No. 2019-505365).

[0012] The following invention is disclosed in Patent Document 2.

[0013] A honeycomb structure having polygonal lattice-shaped partitions, wherein the partitions are divided into multiple pores, which form fluid flow paths and extend from one end face to the other.

[0014] The aforementioned partition wall is formed into a porous structure using aggregates and a binder of a different material than the aggregates mentioned above.

[0015] The surface porosity of the surface region of the aforementioned partition wall, extending from the partition wall surface to a depth of 15% of the partition wall thickness, differs from the internal porosity of the internal region, extending from the partition wall surface to a depth of 15% to 50% of the partition wall thickness.

[0016] The aforementioned honeycomb structure shows a difference exceeding 1.5% between the aforementioned internal porosity and the aforementioned surface porosity.

[0017] The following invention is disclosed in Patent Document 3.

[0018] A particulate filter comprising at least one porous ceramic wall having a fine structure having:

[0019] The average bulk porosity, determined by the mercury porosity method, exceeded 55%.

[0020] d50 (pore size) exceeding 16μm

[0021] d90 (fine pore size) less than 37 μm, and,

[0022] The surface porosity measured by X-ray morphology is within 10% of the porosity of the main body located at the midpoint of the aforementioned wall.

[0023] Existing technical documents

[0024] Patent documents

[0025] Patent Document 1: Japanese Patent Application Publication No. 2016-204208

[0026] Patent Document 2: Japanese Patent Application Publication No. 2016-190198

[0027] Patent Document 3: Japanese Patent Publication No. 2019-505365 Summary of the Invention

[0028] The problem that the invention aims to solve

[0029] In the invention described in Patent Document 1, the focus is on controlling the depth and width of multiple recesses formed in the pore grid wall (synonymous with "partition wall"). However, even if the depth and width of the recesses near the surface of the partition wall are controlled, stress will concentrate in areas with high porosity when the porosity deviation inside the pore grid wall is large, making it easy for cracks to start from these areas. Furthermore, Patent Document 1 does not provide specific details regarding porosity.

[0030] In the invention described in Patent Document 2, the relationship between the surface porosity of the surface region extending from the partition wall surface to a depth of 15% of the partition wall thickness and the internal porosity of the internal region extending from the partition wall surface to a depth of 15% to 50% of the partition wall thickness is controlled. In the invention described in Patent Document 2, a larger difference between the two is recommended to suppress the increase in pressure loss, but this has a detrimental effect on the strength of the columnar honeycomb structure. Furthermore, if there are locally high porosity areas in each region, stress concentrates at those areas, making it easy for cracks to originate there. Patent Document 2 also describes a surface porosity range of 10% to 50% and an internal porosity range of 20% to 75%, and states that a wide range of porosities can be used. However, the invention described in Patent Document 2 does not aim at lightweighting the columnar honeycomb structure, but rather at increasing heat capacity by suppressing the average porosity; therefore, it does not specifically disclose a columnar honeycomb structure with overall high porosity.

[0031] While the invention described in Patent Document 3 specifies that the porosity of the partition wall surface is within 10% of the porosity at the midpoint of the partition wall, even controlling only the relationship between the surface and the midpoint is insufficient. If there are high porosity portions inside the partition wall outside the midpoint, cracking is likely to originate from these points. Furthermore, since the primary focus is on reducing pressure loss, relatively large pore sizes such as an average bulk porosity exceeding 55% and a d50 exceeding 16 μm are required. However, the coexistence of high porosity and large pore sizes can negatively impact strength.

[0032] As in the inventions described in Patent Documents 1-3, there is still room for improvement in achieving both lightweight and high strength in columnar honeycomb structures. The present invention was made in view of the above circumstances, and its objective is to provide, in one embodiment, a columnar honeycomb structure having a partition structure suitable for achieving both lightweight and high strength.

[0033] Methods for solving problems

[0034] To address the aforementioned issues, the inventors conducted in-depth research and discovered that it is advantageous to control the maximum and minimum porosity values ​​of each partition constituting the columnar honeycomb structure when measuring the porosity from one surface to another in the thickness direction using an X-ray microscope. The following illustrates the invention based on this insight.

[0035] [1] A columnar honeycomb structure having an outer peripheral sidewall and a plurality of partitions, the plurality of partitions being disposed on the inner peripheral side of the outer peripheral sidewall and dividing a plurality of pores forming flow paths from a first bottom surface to a second bottom surface, wherein,

[0036] The average pore size of the septum, as measured by a mercury porosimeter, is less than 10 μm.

[0037] When the cross-sections of the above-mentioned multiple partitions were observed using an X-ray microscope, and the porosity (%) of each partition was measured from one surface to another in the thickness direction, the average porosity of each partition was 40-70%, and the difference between the maximum and minimum porosity of each partition was less than 11%.

[0038] [2] According to the columnar honeycomb structure described in [1], the average pore size of the partition wall, as measured by a mercury porosimeter, is 3 to 10 μm.

[0039] [3] The columnar honeycomb structure according to [1] or [2], wherein the average thickness of the plurality of partitions is 50 to 150 μm.

[0040] [4] The columnar honeycomb structure according to any one of [1] to [3], wherein when the average porosity (%) of each partition is set as x and the difference (%) between the maximum and minimum porosity of each partition is set as y, the following formula (A) holds.

[0041] {5.2176-0.122(x-55)}e -0.283y ≥0.5…(A)

[0042] [5] The columnar honeycomb structure according to any one of [1] to [4], wherein the isostatic breaking strength is 0.5 MPa or more.

[0043] [6] The columnar honeycomb structure according to any one of [1] to [5], wherein the bulk density is 0.15 g / cc to 0.25 g / cc.

[0044] [7] The columnar honeycomb structure according to any one of [1] to [6], wherein the partition is formed of ceramic containing more than 90% by mass of cordierite.

[0045] [8] The columnar honeycomb structure according to any one of [1] to [7], wherein a catalyst layer is provided on the surface of the partition wall.

[0046] Invention Effects

[0047] According to one embodiment of the present invention, a columnar honeycomb structure having a partition structure suitable for balancing lightweight and high strength is provided. Thus, for example, by using this columnar honeycomb structure as a catalyst support, it is possible to achieve the function of rapidly raising the catalyst temperature to the activation temperature while ensuring the required strength. Attached Figure Description

[0048] Figure 1 It is a schematic three-dimensional view of a columnar honeycomb molded body of the wall filter type.

[0049] Figure 2 This is a schematic cross-sectional view of the columnar honeycomb structure of the wall filter type when viewed from a direction orthogonal to the extension direction of the pores.

[0050] Figure 3 It is a schematic three-dimensional view of a columnar honeycomb molded body with a wall flow pattern.

[0051] Figure 4 This is a schematic cross-sectional view of the columnar honeycomb structure of the wall flow pattern when viewed from a direction orthogonal to the extension direction of the pores.

[0052] Figure 5 This is a schematic, enlarged view of a columnar honeycomb structure when viewed from a cross-section orthogonal to the direction of the lattice extension.

[0053] Figure 6 This is an example of a porosity distribution curve when the porosity (%) is measured from one surface to another along the thickness direction D of the partition wall.

[0054] Figure 7 This is a conceptual diagram illustrating a method for determining the location of a surface of a partition on a cross-sectional image.

[0055] Figure 8 The results are plotted in a two-dimensional coordinate system for columnar honeycomb structures numbered 1 to 6, with the horizontal axis representing porosity deviation (Y) and the vertical axis representing isostatic compressive failure strength (S).

[0056] Symbol Explanation

[0057] 100: Columnar honeycomb structure, 102: Outer peripheral sidewall, 104: First bottom surface, 106: Second bottom surface, 108: Cell, 112: Partition, 112a: One surface of the partition, 112b: Another surface of the partition, 200: Columnar honeycomb structure, 202: Outer peripheral sidewall, 204: First bottom surface, 206: Second bottom surface, 208a: First cell, 208b: Second cell, 209: Sealing part, 212: Partition. Detailed Implementation

[0058] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the following embodiments, and should be understood to include appropriate design changes and modifications based on ordinary knowledge of those skilled in the art without departing from the spirit of the invention.

[0059] <1. Columnar honeycomb structure>

[0060] Typically, a columnar honeycomb structure has a columnar honeycomb structure portion, which has an outer peripheral sidewall and a partition wall. The partition wall is disposed on the inner peripheral side of the outer peripheral sidewall and divides a plurality of cells that form a flow path from a first bottom surface to a second bottom surface.

[0061] exist Figure 1 and Figure 2 The diagram illustrates schematic perspective and cross-sectional views of a columnar honeycomb structure 100 applicable as a wall-filter type automotive exhaust gas filter and / or catalyst carrier. The columnar honeycomb structure 100 has a columnar honeycomb structure portion, which includes an outer peripheral sidewall 102 and partition walls 112. The partition walls 112 are disposed on the inner peripheral side of the outer peripheral sidewall 102 and divide a plurality of cells 108 forming a flow path for fluid from a first bottom surface 104 to a second bottom surface 106. In this columnar honeycomb structure 100, each cell 108 is open at both ends. Exhaust gas flowing into a cell 108 from the first bottom surface 104 is purified during its passage through the cell and flows out from the second bottom surface 106.

[0062] exist Figure 3 and Figure 4 The diagram illustrates a schematic perspective view and a cross-sectional view of a columnar honeycomb structure 200 that can be used as a wall-flow type automotive exhaust filter and / or catalyst carrier. The columnar honeycomb structure 200 has a columnar honeycomb structure portion, which includes an outer peripheral sidewall 202 and partition walls 212. The partition walls 212 are disposed on the inner peripheral side of the outer peripheral sidewall 202 and divide the space into multiple cells 208a and 208b forming a flow path for fluid from a first bottom surface 204 to a second bottom surface 206.

[0063] In the columnar honeycomb structure 200, multiple cells 208a and 208b can be classified into multiple first cells 208a and multiple second cells 208b. Multiple first cells 208a are disposed on the inner periphery of the outer peripheral sidewall 202, extending from the first bottom surface 204 to the second bottom surface 206. The first bottom surface 204 is open, and the second bottom surface 206 has a sealing portion 209. Multiple second cells 208b are disposed on the inner periphery of the outer peripheral sidewall 202, extending from the first bottom surface 204 to the second bottom surface 206. The first bottom surface 204 has a sealing portion 209, and the second bottom surface 206 is open. Furthermore, in this columnar honeycomb structure 200, the first cells 208a and second cells 208b are alternately arranged adjacent to each other, sandwiching a partition wall 212.

[0064] If exhaust gas containing particulate matter (PM) such as soot is supplied to the first bottom surface 204 on the upstream side of the columnar honeycomb structure 200, the exhaust gas is introduced into the first cell 208a and proceeds downstream within the first cell 208a. Since the first cell 208a has a sealing portion 209 on the second bottom surface 206 on the downstream side, the exhaust gas flows into the second cell 208b through the partition wall 212 that divides the first cell 208a and the second cell 208b. The particulate matter (PM) cannot pass through the partition wall 212 and is therefore captured and accumulated in the first cell 208a. After the particulate matter (PM) is removed, the clean exhaust gas flowing into the second cell 208b proceeds downstream within the second cell 208b and flows out from the second bottom surface 206 on the downstream side.

[0065] The bottom shape of the columnar honeycomb structures 100 and 200 is not limited. For example, it can be a circular shape, an ellipse, a racetrack shape, an oblong shape, or other round shapes, as well as a polygonal shape such as a triangle or a quadrilateral shape, and other irregular shapes. The bottom shape of the illustrated columnar honeycomb structures 100 and 200 is circular, and the whole structure is cylindrical.

[0066] There are no particular restrictions on the height of the columnar honeycomb structure (the length from the first bottom surface to the second bottom surface); it can be appropriately set according to the application and performance requirements. There are also no particular restrictions on the relationship between the height of the columnar 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 columnar honeycomb structure can be longer or shorter than the maximum diameter of each bottom surface.

[0067] The materials used for the partitions and outer sidewalls of the columnar honeycomb structure are not limited, and ceramics can be cited as examples. Examples of ceramics include cordierite, mullite, zirconium phosphate, aluminum titanate, silicon carbide (SiC), silicon-silicon carbide composites (e.g., Si-bonded SiC), cordierite-silicon carbide composites, zirconium oxide, spinel, Indian quartz, pseudosapphire, corundum, titanium dioxide, and silicon nitride. Furthermore, these ceramics may contain only one type or two or more types simultaneously.

[0068] In a preferred embodiment, the partition wall is formed of ceramic containing 90% by mass or more cordierite. This means that the mass percentage of cordierite (2MgO·2Al2O3·5SiO2) in 100% by mass of the material constituting the partition wall is 90% by mass or more. More preferably, the mass percentage of cordierite in 100% by mass of the material constituting the partition wall is 95% by mass or more, and even more preferably 99% by mass or more. Except for unavoidable impurities, 100% by mass of the material constituting the partition wall can be cordierite.

[0069] From the viewpoint of ensuring strength, the average thickness of the partitions in the columnar honeycomb structure is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more. Furthermore, from the viewpoint of suppressing pressure loss, the average thickness of the partitions is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 100 μm or less. Figure 5 The diagram shows a schematic, partially enlarged view of the partition 112 (212) of the columnar honeycomb structure 100 (200) as viewed in a cross-section orthogonal to the extending direction of the cells 108 (208a, 208b). In this specification, the thickness of the partition refers to the length of the partition along a line segment L that connects the centroids C of adjacent cells in a cross-section orthogonal to the extending direction of the cells (the height direction of the columnar honeycomb structure). The thickness direction D of the partition refers to the direction parallel to the line segment L. The average thickness of the partition refers to the average thickness of all partitions.

[0070] In a columnar honeycomb structure, the partitions can be made of porous material. When observing the cross-sections of multiple partitions 112 (212) of the columnar honeycomb structure using an X-ray microscope, and measuring the porosity (%) of each partition 112 (212) from one surface 112a (212a) to another surface 112b (212b) in the thickness direction D, from the viewpoint of achieving a lightweight columnar honeycomb structure, the lower limit of the average porosity of each partition is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more. From the viewpoint of ensuring the strength of the columnar honeycomb structure, the upper limit of the average porosity of each partition is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less. Therefore, the average porosity of each partition is preferably, for example, 40-70%, more preferably 45-65%, and even more preferably 50-60%.

[0071] Furthermore, when observing the cross-sections of the multiple partitions 112 (212) of the columnar honeycomb structure using an X-ray microscope, and measuring the porosity (%) of each partition 112 (212) from one surface 112a (212a) to another surface 112b (212b) in the thickness direction D, the difference between the maximum and minimum porosity of each partition is preferably 11% or less, more preferably 9% or less, even more preferably 7% or less, and most preferably 5% or less. There is no particular lower limit to the difference between the maximum and minimum porosity of each partition, but for ease of manufacture, it is generally 1% or more, typically 3% or more. Therefore, the difference between the maximum and minimum porosity of each partition is preferably, for example, 1 to 11%, more preferably 1 to 9%, even more preferably 1 to 7%, and even more preferably 1 to 5%.

[0072] The methods for observing each septum using an X-ray microscope, determining the average porosity of each septum, and determining the difference between the maximum and minimum porosity of each septum are performed according to the following steps.

[0073] First, for the columnar honeycomb structure, samples of the septum were taken from near the first bottom surface, near the center in the height direction, and near the second bottom surface, respectively, at the vicinity of the central axis, near the radial center (near the center between the central axis and the outer peripheral sidewall), and near the outer peripheral sidewall (but excluding the outer peripheral sidewall), with cross-sections orthogonal to the extension direction of the pores (cross-sectional dimensions (20mm x 2mm) x 0.3mm depth). Next, the cross-sections of each sample were observed using an X-ray microscope and CT scanned. The resulting 3D cross-sectional images were then binarized based on brightness, dividing them into multiple voxels representing the spatial portion and the substrate portion (the size of one voxel equals the length of the septum in the wall direction (Y direction): 0.8μm, the length of the septum in the thickness direction (X direction): 0.8μm, and the length of the septum in the depth direction (Z direction): 0.8μm, forming a cube).

[0074] The measurement conditions for X-ray microscopy are 4x magnification.

[0075] Binarization was performed according to Otsu's binarization method.

[0076] Next, for any predetermined region of a partition in the 3D cross-sectional image (length of the partition in the wall direction (Y direction): 340 μm; length of the partition in the thickness direction (X direction): including the entire thickness and having a spatial portion of more than 50 μm on each side of the partition; length of the partition in the depth direction (Z direction): 300 μm), based on the binarized voxel data, the porosity (%) distribution curve is obtained at intervals of 0.8 μm along the thickness direction (X direction) of the partition from one surface to another (refer to...). Figure 6 The porosity of a 0.8 μm thickness region is calculated using the formula: porosity = (number of voxels in the spatial portion) / (total number of voxels in the region) × 100 (%) for a region with a thickness of 0.8 μm (length of the partition wall in the Y direction: 340 μm, length of the partition wall in the X direction: 0.8 μm, and length of the partition wall in the Z direction: 300 μm). By performing this calculation on the entire predetermined region at intervals of 0.8 μm from the left edge of the image, a porosity (%) distribution curve can be obtained from one surface to another along the thickness direction (X direction) of the partition wall at intervals of 0.8 μm.

[0077] At this time, as Figure 7 As shown, the position of one surface of the partition is set as the position of the most frequent value when measuring the distance M in the thickness direction D (X direction) from a line segment parallel to the wall direction of the partition to one surface of the partition that is being measured. This distance M is measured at 0.8 μm intervals within a length of 340 μm in the wall direction (Y direction perpendicular to the thickness direction (X direction)) of the partition on the binarized image. The position of the other surface of the partition is determined in the same way.

[0078] In this way, the porosity distribution curve of any partition is obtained from each sample, and the average porosity of the partition and the difference between the maximum and minimum porosity values ​​are calculated from the distribution curve. Furthermore, the average value of a total of 9 samples is used as the measurement object, namely, the "average porosity of each partition" and the "difference between the maximum and minimum porosity values ​​of each partition" in the columnar honeycomb structure.

[0079] One standard for the mechanical strength of columnar honeycomb structures is the isostatic breaking strength. The isostatic breaking strength of columnar honeycomb structures is determined by the following test: the columnar honeycomb structure is submerged in water within a pressure vessel, and the water pressure is slowly increased, thereby applying isotropic pressure to the structure. The slow increase in water pressure within the pressure vessel eventually leads to failure at the partition walls and outer peripheral walls of the columnar honeycomb structure. The pressure value at which failure occurs (breaking strength) is the isostatic breaking strength. The isostatic breaking strength is determined based on the automotive standard (JASO M505-87) issued by the Japan Association of Automobile Manufacturers (JASO).

[0080] When using columnar honeycomb structures as automotive exhaust filters and / or catalyst supports, the lower limit of the isostatic breaking strength is preferably 0.5 MPa or more, more preferably 1.0 MPa or more, and even more preferably 1.5 MPa or more. The upper limit of the isostatic breaking strength is not specifically set, but is typically 3.0 MPa or less, and typically 2.5 MPa or less.

[0081] If the average porosity of each partition is constant, the smaller the difference between the maximum and minimum porosity of each partition, the higher the isostatic compressive strength of the columnar honeycomb structure. For example, setting the average porosity of each partition to 55%, the isostatic compressive strength of the columnar honeycomb structure is measured under various variations in the difference between the maximum and minimum porosity of each partition (hereinafter also referred to as "porosity deviation"). When plotted on a two-dimensional coordinate system with the horizontal axis representing porosity deviation (%) (Y) and the vertical axis representing isostatic compressive strength (MPa) (S), S = 5.2176e -0.283Y The approximate formula is largely valid. The partitions are formed of ceramic containing more than 90% cordierite by mass, with an average thickness of 2.3–2.9 mil (58–74 μm) and a pore density of 730–770 pores / square inch (113–119 pores / cm²). 2 When ), this approximation has particularly high accuracy.

[0082] If the influence of the average porosity of each partition is included in the above approximation, then based on experience, the following formula is roughly valid between the average porosity (%) (x) of each partition, the difference between the maximum and minimum porosity of each partition (porosity deviation (%)) (y), and the isostatic breaking strength (MPa) (S).

[0083] S = {5.2176 - 0.122(x - 55)}e -0.283y

[0084] Therefore, preferred formula (A) holds, more preferred formula (B) holds, and even more preferred formula (C) holds.

[0085] {5.2176-0.122(x-55)}e -0.283y ≥0.5···(A)

[0086] {5.2176-0.122(x-55)}e -0.283y ≥1.0···(B)

[0087] {5.2176-0.122(x-55)}e -0.283y ≥1.5···(C)

[0088] From the viewpoint of supporting a catalyst, the lower limit of the average pore size of the partition wall is preferably 3 μm or more. Furthermore, from the viewpoint of preventing catalyst from impregnating the substrate, the upper limit of the average pore size of the partition wall is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. Therefore, the average pore size of the partition wall is preferably, for example, 3 to 10 μm, more preferably 3 to 8 μm, and even more preferably 3 to 6 μm.

[0089] In this specification, the average pore size of the partition refers to the median particle size (D50) of the pores measured using a mercury porosimeter via the mercury indentation method specified in JIS R1655:2003. The mercury indentation method involves applying uniform pressure while the sample is immersed in mercury under vacuum, slowly increasing the pressure as mercury is forced into the sample, and calculating the pore size distribution based on the pressure and the volume of mercury injected into the pores. If the pressure is increased slowly, mercury is injected sequentially from the largest diameter pores, increasing the cumulative volume of mercury. When all pores are eventually filled with mercury, the cumulative volume reaches equilibrium. This cumulative volume is called the total pore volume (cm³). 3 / g), the pore diameter (D50) at the moment when 50% of the total pore volume of mercury is pressed in is taken as the average pore diameter.

[0090] To determine the average pore size of the partition wall, samples of the partition wall (section dimensions (10mm long × 10mm wide) × 10mm deep) were taken from near the first bottom surface, near the center in the height direction, and near the second bottom surface of the columnar honeycomb structure. These samples were taken from near the central axis, near the radial center (near the center between the central axis and the outer peripheral sidewall), and near the outer peripheral sidewall (excluding the outer peripheral sidewall), respectively. The average pore size of each sample was then measured. The average value of all nine samples was then used as the measurement object, i.e., the "average pore size of the partition wall" of the columnar honeycomb structure.

[0091] The shape of the openings of the pores in the cross-section orthogonal to the extension direction of the pores is not limited, but quadrilaterals, hexagons, octagons, or combinations thereof are preferred. Squares and hexagons are particularly preferred. By configuring the opening shape of the pores in this way, the pressure loss when exhaust gas flows through the honeycomb structure is reduced, resulting in excellent purification performance when used as a filter. Similarly, by configuring the opening shape of the pores in this way, the pressure loss when fluid flows through the columnar honeycomb structure is reduced, resulting in excellent purification performance of the catalyst.

[0092] There are no particular restrictions on the pore density (number of pores per unit cross-sectional area) in columnar honeycomb structures; for example, it can be 6–2000 pores / square inch (0.9–311 pores / cm²). 2 More preferably, it is 50–1000 holes / square inch (7.8–155 holes / cm²). 2 ), particularly preferred is 100–600 holes / square inch (15.5–92.0 holes / cm²). 2 Here, the pore density is calculated by dividing the number of pores in the columnar honeycomb structure by the area of ​​the bottom side of the columnar honeycomb structure excluding the outer peripheral sidewalls.

[0093] The lower the bulk density of the columnar honeycomb structure, the better, as long as the required strength is ensured. The bulk density of the columnar honeycomb structure is preferably 0.15 g / cc to 0.25 g / cc, more preferably 0.15 g / cc to 0.23 g / cc, and even more preferably 0.15 g / cc to 0.20 g / cc. In this specification, the bulk density of the columnar honeycomb structure is determined by the formula: bulk density (g / cc) = mass of the columnar honeycomb structure (g) ÷ volume (cc) based on the external dimensions of the columnar honeycomb structure.

[0094] When using a columnar honeycomb structure as a catalyst support, a catalyst layer corresponding to the desired effect can be formed on the surface of the partition wall. The catalyst is not limited to any particular type, but examples 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 ternary 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.).

[0095] <2. Method for fabricating columnar honeycomb structures>

[0096] The following is an illustrative description of a method for manufacturing a columnar honeycomb structure. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming agent, and a binder is mixed to form a blank. The blank is then extruded and dried, thereby producing a columnar honeycomb molded body. Additives such as dispersants can be added to the raw material composition as needed. During extrusion molding, a die with the desired overall shape, pore shape, partition wall thickness, pore density, etc., can be used.

[0097] In the drying process, conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, and freeze drying can be used. Among these, a combination of hot air drying and microwave drying or dielectric drying is preferred from the perspective of rapidly and uniformly drying the entire molded body. The sealing portions can be formed by forming sealing portions at predetermined positions on both bottom surfaces of the dried honeycomb molded body and then drying the sealing portions.

[0098] Ceramic raw materials are those that remain after the firing of metal oxides and metals, serving as the framework of the columnar honeycomb structure (columnar honeycomb structure) formed after ceramic firing. Ceramic raw materials can be provided, for example, in powder form. Examples of ceramic raw materials include those used to obtain ceramics such as cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconium oxide, spinel, Indian stone, pseudosapphire, corundum, and titanium dioxide. Specifically, there are no limitations; examples include silica, talc, alumina, kaolin, serpentine, pyrophyllite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. One type of ceramic raw material can be used alone, or two or more can be used in combination. From the viewpoint of reducing the deviation in porosity while simultaneously refining the pore size, it is preferable to use fine silica particles with a median particle size (D50) close to the average pore size of the target septum, for example, 2–7 μm. In addition, fine particles are also preferred for other ceramic raw materials.

[0099] In applications such as DPF and GPF filters, cordierite can be suitable as a ceramic material. In this case, cordierite-modified raw materials can be used as ceramic raw materials. Cordierite-modified raw materials refer to raw materials that become cordierite through firing. Preferably, the cordierite-modified raw material consists of a chemical composition of 30–45% by mass of alumina (Al₂O₃) (including the portion of aluminum hydroxide converted to alumina), 11–17% by mass of magnesium oxide (MgO), and 42–57% by mass of silicon dioxide (SiO₂).

[0100] Examples of dispersion media include water, or mixtures of water and organic solvents such as alcohols, with water being particularly preferred.

[0101] As a pore-forming agent, there is no particular limitation as long as it forms pores after firing. Examples include wheat flour, starch, foaming resin, water-absorbing resin, silica gel, carbon (e.g., graphite, coke), ceramic microspheres, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, phenol, etc. A single pore-forming agent can be used, or two or more can be used in combination. From the viewpoint of improving the porosity of the honeycomb structure, the content of the pore-forming agent 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 honeycomb structure, the content of the pore-forming agent relative to 100 parts by mass of the ceramic raw material is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 4 parts by mass or less. From the viewpoint of reducing the deviation of porosity while refining the pore size, it is preferable to use a fine pore-forming agent having a median particle size (D50) close to the average pore size of the target partition wall, for example, 5 to 25 μm.

[0102] Examples of adhesives include organic adhesives such as methylcellulose, hydroxypropyl methylcellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. The combined use of methylcellulose and hydroxypropyl methylcellulose is particularly suitable. Furthermore, from the viewpoint of improving the strength of the honeycomb molded body before firing, the adhesive content relative to 100 parts by mass of the ceramic raw material 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. From the viewpoint of suppressing cracking caused by abnormal heating during the firing process, the adhesive content relative to 100 parts by mass of the ceramic raw material 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. One type of adhesive can be used alone, or two or more types can be used in combination.

[0103] 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.

[0104] like Figure 1 and Figure 2 As shown, columnar honeycomb moldings can also have open ends for all cells. Additionally, as... Figure 3 and Figure 4 As shown, the columnar honeycomb structure can also have a lattice structure in which one end of the lattice is alternately sealed. There is no particular limitation on the method for sealing the bottom surface of the columnar honeycomb structure; known methods can be used.

[0105] There are no particular limitations on the material of the sealing portion, but ceramic is preferred from the viewpoint of strength and heat resistance. As the ceramic, it is preferred to contain at least one of the following: cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconium oxide, spinel, Indian stone, pseudosapphire, corundum, and titanium dioxide. The sealing portion is preferably formed of a material containing at least 50% by mass of these ceramics, and more preferably of a material containing at least 80% by mass of these ceramics. Since the expansion rate during firing can be the same, resulting in improved durability, it is even more preferable to have the sealing portion made of the same material composition as the main body of the honeycomb molded body.

[0106] An illustrative explanation of the method for forming a sealing portion is provided. Sealing slurry is pre-stored in a storage container. Next, a mask with openings corresponding to the holes to be sealed is adhered to a bottom surface. The bottom surface with the adhered mask is immersed in the storage container, and the openings are filled with sealing slurry to form the sealing portion. The same method can be used to form a sealing portion on the other bottom surface.

[0107] Columnar honeycomb structures can be manufactured by performing degreasing and firing processes on the dried columnar honeycomb molded body. The conditions for the degreasing and firing processes can be well-known and depend on the material composition of the honeycomb molded body, without special explanation, but examples of specific conditions are given below.

[0108] The degreasing process is explained below. The adhesive burns at approximately 200°C, while the pore-forming agent burns at approximately 300–1000°C. Therefore, the degreasing process simply involves heating the honeycomb molded body to approximately 200–1000°C. The heating time is not specifically limited, but is typically around 10–100 hours. The honeycomb molded body after the degreasing process is called a pre-fired body.

[0109] The firing process also depends on the material composition of the honeycomb molded body. For example, it can be carried out by heating the pre-fired body to 1350-1600°C in an atmospheric atmosphere and holding it for 3-10 hours.

[0110] Example

[0111] <Experiment Nos. 1-8>

[0112] (1. Manufacturing of honeycomb structures)

[0113] According to the test number, cordierite raw materials, pore-forming agent A, pore-forming agent B, binder, dispersant, and dispersion medium were added to the formulations listed in Table 1, and then mixed and kneaded to prepare clay blanks. Talc, kaolin, alumina, aluminum hydroxide, and silica A and silica B were used as cordierite raw materials. The median particle size (D50) of silica A and silica B are different. The median particle size (D50) of pore-forming agent A and pore-forming agent B are also different. Water was used as the dispersion medium, a polyacrylic acid polymer was used as the pore-forming agent, hydroxypropyl methylcellulose was used as the binder, and fatty acid soap was used as the dispersant. Furthermore, the median particle size (D50) of each material listed in Table 1 is a volume-based value measured using a laser diffraction particle size distribution measuring device (HORIBA LA960).

[0114] Table 1

[0115]

[0116] The clay is fed into an extrusion molding machine and extruded horizontally through a predetermined die to obtain a cylindrical honeycomb molded body. After dielectric drying and hot air drying, the two bottom surfaces are cut off to a predetermined size to obtain a cylindrical honeycomb molded body.

[0117] The obtained cylindrical honeycomb molded bodies were degreased at 200°C for 8 hours in an atmospheric atmosphere, and then fired at 1430°C for 4 hours in an atmospheric atmosphere to obtain columnar honeycomb structures. Only the required quantity of each test number's columnar honeycomb structure was manufactured for the following measurements. The specifications of the obtained columnar honeycomb structures are as follows.

[0118] Overall shape: Cylindrical, 118mm in diameter × 91mm in height

[0119] Hole shape in a cross-section perpendicular to the flow path direction: square

[0120] Pore ​​density (number of pores per unit cross-sectional area): 750 pores / square inch

[0121] Average partition wall thickness: 2.6 mil (66 μm) (nominal value based on die specifications)

[0122] (2. Determination of the porosity distribution curve of the partition wall)

[0123] For each columnar honeycomb structure obtained by the above manufacturing method, the porosity distribution curve of the partition was measured using an X-ray microscope (Zeiss Xradia 520 Versa) according to the aforementioned method. The average porosity of each partition and the difference between the maximum and minimum porosity of each partition (porosity deviation) were determined. The results are shown in Table 2.

[0124] (3. Determination of the average pore size of the partition wall)

[0125] For each columnar honeycomb structure obtained by the above manufacturing method, the average pore size of the septum was determined using a Micrometrics Autopore 9505 oscilloscope, following the aforementioned method. The results are shown in Table 2.

[0126] (4. Bulk density)

[0127] For each columnar honeycomb structure obtained by the above manufacturing method, the bulk density was calculated according to the above method. The results are shown in Table 2.

[0128] (5. Determination of isostatic compressive strength)

[0129] For each columnar honeycomb structure obtained by the above manufacturing method, the isostatic breaking strength was determined based on the automotive standard (JASO M505-87) issued by the China Association of Automobile Manufacturers. The results are shown in Table 2.

[0130] Table 2

[0131] Test No. 1 2 3 4 5 6 7 8 Average porosity of each partition wall (%) 55 55 55 55 55 55 40 70 Deviation of porosity of each partition wall (%) 12.1 9.1 7.0 7.0 4.9 4.3 7.0 7.0 Average pore diameter of partition wall (μm) 4.9 5.7 5.4 5.0 4.5 4.4 4.0 8.0 Bulk density (g / cc) 0.19 0.19 0.19 0.19 0.19 0.19 0.25 0.15 Iso-static pressure failure strength (MPa) 0.18 0.26 0.86 1.17 0.98 1.54 0.97 0.54

[0132] (6. Site Visit)

[0133] Among the columnar honeycomb structures obtained by the above manufacturing method, in tests 1-6 where the "average porosity of each partition" is 55%, the "difference between the maximum and minimum porosity of each partition" (porosity deviation) differs. For tests 1-6, a two-dimensional coordinate system was plotted with the horizontal axis representing porosity deviation (Y) and the vertical axis representing isostatic compressive breaking strength (S). An approximate curve was obtained using the exponential approximation method, yielding S = 5.2176e. -0.283Y ( Figure 8 ).

[0134] Furthermore, if the isostatic compressive breaking strength (S) of the columnar honeycomb structures (test number 7 with an average porosity of 40%) and (test number 8 with an average porosity of 70%) is predicted according to the following formula, the values ​​are 0.97 MPa and 0.47 MPa, respectively. Therefore, it can be seen that the isostatic breaking strength (S) predicted by the following formula for test number 7 with an average porosity of 40% and test number 8 with an average porosity of 70% has a good approximation.

[0135] S={5.2176-0.122(x-55)}e -0.283y 。

Claims

1. A columnar honeycomb structure comprising: an outer peripheral sidewall and a plurality of partitions, the plurality of partitions being disposed on the inner peripheral side of the outer peripheral sidewall and dividing a plurality of pores forming flow paths from a first bottom surface to a second bottom surface; The average pore size of the septum, as measured by a mercury porosimeter, is less than 10 μm. When cross-sections of the plurality of partitions were observed using an X-ray microscope, and the porosity of each partition was measured as a percentage from one surface to another in the thickness direction, the average porosity of each partition was 40-70%, and the difference between the maximum and minimum porosity of each partition was less than 11%. The average thickness of the plurality of partitions is 50–130 μm.

2. The columnar honeycomb structure according to claim 1, wherein, The average pore size of the partition wall, as measured by a mercury porosimeter, is 3–10 μm.

3. The columnar honeycomb structure according to claim 1 or 2, wherein, The average thickness of the plurality of partitions is 60–100 μm.

4. The columnar honeycomb structure according to claim 1 or 2, wherein, When the average porosity of each partition, expressed as a percentage, is set as x, and the difference between the maximum and minimum porosity of each partition, expressed as a percentage, is set as y, the following equation (A) holds. {5.2176-0.122(x-55)}e -0.283y ≥0.5…(A)。 5. The columnar honeycomb structure according to claim 1 or 2, wherein, The isostatic breaking strength is above 0.5 MPa.

6. The columnar honeycomb structure according to claim 1 or 2, wherein, The bulk density is 0.15 g / cc to 0.25 g / cc.

7. The columnar honeycomb structure according to claim 1 or 2, wherein, The partition is made of ceramic containing more than 90% cordierite by mass.

8. The columnar honeycomb structure according to claim 1 or 2, wherein, The surface of the partition wall has a catalyst layer.

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