Columnar honeycomb structure

Abstract

To provide a pillar-shaped honeycomb structure having a partition wall structure suitable for combining light weight, high strength, and suppression of catalyst permeation into the partition walls.SOLUTION: There is provided a pillar-shaped honeycomb structure comprising: an outer peripheral side wall; and a plurality of porous partition walls disposed on an inner peripheral side of the outer peripheral side wall and partitioning a plurality of cells forming flow paths from a first end surface to a second end surface, wherein an average pore diameter of the partition walls measured by a mercury intrusion method specified in JIS R1655: 2003 is 3 to 10 μm, and when a cross-section of the plurality of partition walls is observed with an X-ray microscope and a porosity (%) is measured in a thickness direction from one surface to the other surface of each partition wall, assuming PAVE is an average porosity of each partition wall, P1MIN is a minimum porosity from the one surface to a thickness of 5% of the partition wall, and P2MIN is a minimum porosity from the other surface to a thickness of 5% of the partition wall, 40%≤PAVE≤70%, and {( P1MIN + P2MIN) / 2} / PAVE≤0.9 are satisfied.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to a columnar honeycomb structure. In particular, the present invention relates to a columnar honeycomb structure for exhaust gas purification.

Background Art

[0002] Exhaust gas discharged from internal combustion engines typified by automobile engines contains contaminants such as soot, nitrogen oxides (NOx), soluble organic components (SOF), hydrocarbons (HC), and carbon monoxide (CO). Therefore, in the exhaust gas system of an internal combustion engine, it is generally practiced to install a columnar honeycomb structure carrying an appropriate catalyst (oxidation catalyst, reduction catalyst, three-way catalyst, etc.) according to the contaminants to purify the exhaust gas.

[0003] The columnar honeycomb structure includes an outer peripheral side wall and a plurality of porous partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of cells that form flow paths from a first bottom surface to a second bottom surface. A catalyst layer containing the above-described catalyst can be formed on the surface of the porous partition wall.

[0004] In recent years, after starting the engine, development of a columnar honeycomb structure capable of raising the temperature of the catalyst layer to the activation temperature in a short time has been underway. In order to be able to raise the temperature of the catalyst layer to the activation temperature in a short time, it is necessary to reduce the weight of the columnar honeycomb structure. That is, it is necessary to reduce the heat capacity of the partition wall by thinning the partition wall or increasing the porosity. By doing so, after the exhaust gas starts to flow, the partition wall can be heated up in a short time, and the catalyst layer formed on the surface of the partition wall can be heated up to the activation temperature in a short time. However, since there is a limit to thinning the partition wall, increasing the porosity is considered as a method of reducing the weight. A concern in that case is a decrease in the strength of the columnar honeycomb structure.

[0005] Against this backdrop, Patent Document 1 (Japanese Patent Publication No. 2016-204208) discloses the following invention, which aims to provide a honeycomb structure that can raise the temperature of the catalyst layer to the activation temperature in a short time, is resistant to cracking even after repeated cooling cycles, and does not easily degrade exhaust gas purification performance. The device comprises a polygonal lattice-shaped cell wall, a plurality of cells surrounded by the cell wall, and a catalyst layer formed on the surface of the cell wall. Multiple recesses are formed in the cell wall described above. When observing the cross-section of the cell wall described above, The opening ratio of the opening of the deep recess, which is the recess of the cell wall with a depth of 10 μm or more from the surface, is 10% or more. The number of narrow recesses, which are deep recesses with an opening length of 8 μm or less, accounts for 10% or more of the total number of deep recesses. A honeycomb structure characterized in that the number of deep recesses, which are the deep recesses with an opening length of 20 μm or more, accounts for 10% or more of the total number of deep recesses.

[0006] Furthermore, prior art disclosing the porosity of honeycomb structures can be found in Patent Document 2 (Japanese Patent Publication No. 2016-190198) and Patent Document 3 (Japanese Patent Publication No. 2019-505365).

[0007] Patent Document 2 discloses the following invention. It is equipped with polygonal grid-like partition walls that divide and form multiple cells extending from one end face to the other end face, which form a fluid flow path. The aforementioned partition wall is It is formed porous using aggregate and a binder made of a different material from the aggregate, The surface porosity of the surface region of the partition wall from the partition wall surface to a depth of 15% of the partition wall thickness and the internal porosity of the internal region from the partition wall surface to a depth of 15% to 50% of the partition wall thickness are different. A honeycomb structure exhibiting a relationship where the difference obtained by subtracting the surface porosity from the internal porosity is greater than 1.5%.

[0008] Patent Document 3 discloses the following invention. In a particulate filter having at least one porous ceramic wall, the wall is, The average bulk porosity was measured by mercury porosimetry and exceeded 55%. d50 (pore size) exceeding 16 μm, d90 (pore size) less than 37 μm, and Surface porosity measured by X-ray topography, which is within 10% of the bulk porosity at the midpoint of the wall, A particulate filter having a microstructure. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2016-204208 [Patent Document 2] Japanese Patent Publication No. 2016-190198 [Patent Document 3] Special Publication No. 2019-505365 [Overview of the project] [Problems that the invention aims to solve]

[0010] The invention described in Patent Document 1 focuses on a plurality of recesses formed in the cell wall (synonymous with "partition wall") and aims to prevent the catalyst layer from peeling off from the cell wall by controlling the depth and width of the recesses, and is not a technique for controlling the porosity distribution of the partition wall.

[0011] The invention described in Patent Document 2 controls the relationship between the surface porosity of the surface region from the partition surface to a depth of 15% of the partition thickness and the internal porosity of the internal region from the partition surface to a depth of 15% to 50% of the partition thickness. Furthermore, Patent Document 2 states that the surface porosity is in the range of 10% to 50% and the internal porosity is in the range of 20% to 75%, indicating that a wide range of porosity can be adopted. However, the invention described in Patent Document 2 does not aim to reduce the weight of the columnar honeycomb structure, but rather aims to increase the heat capacity by keeping the average porosity low, and therefore does not specifically disclose a columnar honeycomb structure with high porosity overall.

[0012] The invention described in Patent Document 3 focuses on reducing pressure loss and therefore requires an average bulk porosity exceeding 55% and a relatively large pore diameter of d50 exceeding 16 μm. The coexistence of high porosity and large pore diameter tends to negatively affect strength. In addition, increasing porosity to reduce weight makes it easier for the catalyst to permeate into the interior of the partition wall. If the catalyst permeates into the interior of the partition wall, the frequency of contact between the exhaust gas flowing on the partition wall surface and the catalyst decreases, which may prevent the desired purification performance from being achieved.

[0013] Thus, the inventions described in Patent Documents 1 to 3 still have room for improvement in addressing the challenge of achieving a good balance between three functions in a columnar honeycomb structure: weight reduction, high strength, and suppression of catalyst penetration into the partition walls. The present invention has been made in view of the above circumstances, and in one embodiment, aims to provide a columnar honeycomb structure having a partition wall structure suitable for achieving a good balance between three functions: weight reduction, high strength, and suppression of catalyst penetration into the partition walls. [Means for solving the problem]

[0014] The inventor has intensively studied to solve the above problems. As a result, regarding the partition walls constituting the columnar honeycomb structure, in order to reduce the weight while increasing the average porosity, high strength is ensured, and in order to suppress the penetration of the catalyst into the partition walls, it is found that it is advantageous to locally reduce the porosity of the partition wall surface where stress is likely to occur and further reduce the average pore diameter. The present invention completed based on this finding is exemplified below.

[0015] [1] A columnar honeycomb structure comprising an outer peripheral side wall and a plurality of partition walls disposed on the inner peripheral side of the outer peripheral side wall and partitioning a plurality of cells that form flow paths from a first bottom surface to a second bottom surface, The average pore diameter of the partition walls measured by the mercury intrusion method defined in JIS R1655:2003 is 3 to 10 μm, The cross sections of the plurality of partition walls are observed with an X-ray microscope, and the porosity (%) in the thickness direction from one surface to the other surface is measured for each partition wall, and the average porosity in each partition wall is P AVE , , , , , AVE , , , the minimum value of the porosity from one surface of the partition wall to a thickness of 5% is P 1MIN , the minimum value of the porosity from the other surface of the partition wall to a thickness of 5% is P 2MIN Then, 40% ≦ P AVE ≦ 70%, { (P 1MIN + P <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​A columnar honeycomb structure as described in any one of the following [1] to [4], wherein the ratio is ≤60%. [6] A columnar honeycomb structure as described in any one of the following [1] to [5], having a bulk density of 0.15 g / cc to 0.25 g / cc. [7] A columnar honeycomb structure according to any one of the following [1] to [6], wherein the partitions are formed of ceramics containing 90% by mass or more of cordierite. [8] A columnar honeycomb structure according to any one of [1] to [7], wherein the surface of the partition wall is provided with a catalyst layer. [Effects of the Invention]

[0016] According to one embodiment of the present invention, a columnar honeycomb structure is provided having a partition wall structure suitable for combining three functions: lightweight, high strength, and suppression of catalyst penetration into the partition wall. As a result, for example, by using the columnar honeycomb structure as a catalyst support, it becomes possible to raise the catalyst temperature to the activation temperature in a short time while ensuring the desired strength. In addition, since the catalyst supported on the partition wall is less likely to penetrate into the partition wall, the catalyst can be utilized efficiently. [Brief explanation of the drawing]

[0017] [Figure 1] This is a schematic perspective view showing a wall-through type columnar honeycomb molded body. [Figure 2] This is a schematic cross-sectional view of a wall-through type columnar honeycomb molded body, observed from a direction perpendicular to the direction in which the cells extend. [Figure 3] This is a schematic perspective view showing a wall-flow type columnar honeycomb molded body. [Figure 4] This is a schematic cross-sectional view of a wall-flow type columnar honeycomb molded body, observed from a direction perpendicular to the direction in which the cells extend. [Figure 5] This is a schematic, partially enlarged view of a columnar honeycomb structure observed in a cross-section perpendicular to the direction in which the cells extend. [Figure 6]This is an example of a porosity profile when the porosity (%) is measured along the thickness direction D of the partition wall from one surface to the other. [Figure 7] This is a conceptual diagram illustrating a method for identifying the position of one surface of a partition wall on a cross-sectional image. [Modes for carrying out the invention]

[0018] Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that appropriate design changes, improvements, etc., can be made based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention.

[0019] <1. Columnar honeycomb structure> Generally, a columnar honeycomb structure has a columnar honeycomb structure portion comprising an outer peripheral wall and partition walls disposed on the inner peripheral side of the outer peripheral wall, which divide a plurality of cells that form a flow path from the first bottom surface to the second bottom surface.

[0020] Figures 1 and 2 illustrate schematic perspective and cross-sectional views, respectively, of a columnar honeycomb structure 100 applicable as a wall-through type automotive exhaust gas filter and / or catalyst carrier. This columnar honeycomb structure 100 has a columnar honeycomb structure comprising an outer peripheral wall 102 and partition walls 112 disposed on the inner circumferential side of the outer peripheral wall 102, which divide a plurality of cells 108 that form fluid flow paths from a first bottom surface 104 to a second bottom surface 106. In this columnar honeycomb structure 100, both ends of each cell 108 are open, and exhaust gas flowing from the first bottom surface 104 into one cell 108 is purified as it passes through the cell and flows out from the second bottom surface 106.

[0021] Figures 3 and 4 illustrate schematic perspective and cross-sectional views, respectively, of a columnar honeycomb structure 200 applicable as a wall-flow type automotive exhaust gas filter and / or catalyst carrier. This columnar honeycomb structure 200 has a columnar honeycomb structure comprising an outer peripheral side wall 202 and partition walls 212 disposed on the inner circumferential side of the outer peripheral side wall 202, which divide a plurality of cells 208a, 208b that form fluid flow paths from a first bottom surface 204 to a second bottom surface 206.

[0022] In the columnar honeycomb structure 200, the multiple cells 208a and 208b can be classified into multiple first cells 208a, which are arranged on the inner circumference side of the outer peripheral wall 202, extend from the first bottom surface 204 to the second bottom surface 206, with the first bottom surface 204 being open and the second bottom surface 206 having a sealing portion 209, and multiple second cells 208b, which are arranged on the inner circumference side of the outer peripheral wall 202, extend from the first bottom surface 204 to the second bottom surface 206, with the first bottom surface 204 having a sealing portion 209 and the second bottom surface 206 being open. In this columnar honeycomb structure 200, the first cells 208a and the second cells 208b are arranged alternately adjacent to each other with a partition wall 212 in between.

[0023] When 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 permeates through the porous partition wall 212 that separates the first cell 208a and the second cell 208b and flows into the second cell 208b. Since the particulate matter (PM) cannot pass through the partition wall 212, it is collected and deposited within the first cell 208a. After the particulate matter (PM) is removed, the clean exhaust gas that has flowed 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.

[0024] There are no restrictions on the shape of the base of the columnar honeycomb structures 100 and 200, but they can be, for example, round shapes such as circular, elliptical, racetrack, and oval shapes, polygonal shapes such as triangular and quadrilateral shapes, and other irregular shapes. The columnar honeycomb structures 100 and 200 shown in the figure have a circular base and are cylindrical overall.

[0025] There are no particular restrictions on the height of the columnar honeycomb structure (length from the first base to the second base), and it can be set appropriately according to the application and required performance. There are also no particular restrictions on the relationship between the height of the columnar honeycomb structure and the maximum diameter of each base (referring to the maximum length of the diameter passing through the centroid of each base of the columnar honeycomb structure). Therefore, the height of the columnar honeycomb structure may be longer than the maximum diameter of each base, or the height of the columnar honeycomb structure may be shorter than the maximum diameter of each base.

[0026] While not limited to specific materials, ceramics can be used as the materials constituting the partition walls and outer periphery side walls of a columnar honeycomb structure. 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, zirconia, spinel, indialite, sapphirin, corundum, titania, and silicon nitride. These ceramics may be present individually or in combination of two or more.

[0027] In a preferred embodiment, the partition wall is formed of ceramics containing 90% by mass or more of cordierite. This means that the total 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. It is also possible to remove unavoidable impurities and make 100% by mass of the material constituting the partition wall cordierite.

[0028] In a columnar honeycomb structure, the average thickness of the partition walls is preferably 50 μm or more, more preferably 60 μm or more, and even more preferably 70 μm or more, from the viewpoint of ensuring strength. Furthermore, from the viewpoint of suppressing pressure loss, the average thickness of the partition walls is preferably 150 μm or less, more preferably 130 μm or less, and even more preferably 100 μm or less. Figure 5 shows a schematic partial enlargement view of the partition wall 112 (212) of a columnar honeycomb structure 100 (200) observed in a cross section perpendicular to the direction in which cells 108 (208a, 208b) extend. In this specification, the thickness of the partition wall refers to the length of the line segment L that crosses the partition wall when the centroids C of adjacent cells are connected by a line segment L in a cross section perpendicular to the direction in which the cells extend (the height direction of the columnar honeycomb structure). The thickness direction D of the partition wall refers to the direction parallel to the line segment L. The average thickness of a septum refers to the average thickness of all septums.

[0029] In a columnar honeycomb structure, the partitions can be porous. From the viewpoint of catalyst support, the lower limit of the average pore diameter of the partitions in the columnar honeycomb structure is preferably 3 μm or more. Furthermore, from the viewpoint of preventing catalyst penetration into the interior of the partitions, the upper limit of the average pore diameter of the partitions is preferably 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less. Therefore, the average pore diameter of the partitions is preferably, for example, 3 to 10 μm, more preferably 3 to 8 μm, and even more preferably 3 to 6 μm.

[0030] In this specification, the average pore diameter of a partition wall refers to the median diameter (D50) of the pore diameter measured using a mercury porosimeter by the mercury intrusion method specified in JIS R1655:2003. The mercury intrusion method is a method in which a sample is immersed in mercury under vacuum, uniform pressure is applied, and mercury is injected into the sample while the pressure is gradually increased, and the pore diameter distribution is calculated from the pressure and the volume of mercury injected into the pores. As the pressure is gradually increased, mercury is injected into the pores with larger diameters first, increasing the cumulative volume of mercury, and finally, when all pores are filled with mercury, the cumulative volume is flatThe measurement is completed. The cumulative volume at this point is the total pore volume (cm³). 3 The average pore diameter (D50) is defined as the pore diameter at which mercury equivalent to 50% of the total pore volume has been injected.

[0031] To determine the average pore diameter of the septa, samples of the septa (cross-sectional size (10mm vertical x 10mm horizontal) x 10mm deep) with a cross-section perpendicular to the direction of cell extension are taken from near the central axis, near the radial center (near the center between the central axis and the outer peripheral wall), and near the outer peripheral wall (excluding the outer peripheral wall) for each of the following locations in the columnar honeycomb structure: near the first base, near the center in the height direction, and near the second base. The average pore diameter of each sample is then measured. The average of these nine samples is then taken as the "average pore diameter of the septa" of the columnar honeycomb structure being measured.

[0032] Furthermore, the cross-sections of multiple septa 112(212) of the columnar honeycomb structure were observed using an X-ray microscope, and the porosity (%) was measured in the thickness direction D from one surface 112a(212a) to the other surface 112b(212b) for each septa 112(212), and the average porosity of each septa 112(212) was calculated as P AVE P is the minimum value of the porosity from one surface 112a (212a) of the partition wall up to a thickness of 5%. 1MIN P is the minimum value of the porosity from the other surface 112b (212b) of the partition wall up to a thickness of 5%. 2MIN Therefore, from the viewpoint of ensuring strength and suppressing the penetration of the catalyst into the partition wall, {(P 1MIN +P 2MIN ) / 2}÷P AVE It is preferable that ≤0.9 holds. {(P 1MIN +P 2MIN ) / 2}÷P AVE No lower limit is specifically set for the value of {P}, but from the perspective of ease of manufacture, 0.6 ≤ {(P} 1MIN +P 2MIN ) / 2}÷P AVE Generally, ≤0.9 holds true, and 0.7 ≤ {(P 1MIN +P 2MIN ) / 2}÷P AVE Typically, ≤0.9 holds, and 0.8 ≤ {(P 1MIN +P 2MIN) / 2}÷P AVE It is more typical for ≤0.9 to hold.

[0033] The average porosity (P) of each partition 112 (212) AVE The lower limit of the average porosity (P) of each partition wall 112 (212) is preferably 40% or more, more preferably 45% or more, and even more preferably 50% or more, from the viewpoint of reducing the weight of the columnar honeycomb structure. AVE The upper limit of ) is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less, from the viewpoint of ensuring the strength of the columnar honeycomb structure. Therefore, the average porosity (P) of each partition wall 112 (212) AVE For example, the percentage is preferably 40-70%, more preferably 45-65%, and even more preferably 50-60%.

[0034] Method for observing each septum using an X-ray microscope, and P of each septum AVE and {(P 1MIN +P 2MIN ) / 2}÷P AVE The measurement is performed according to the following procedure. First, samples of the partition wall (cross section size (20 mm long × 2 mm wide) × 0.3 mm deep) with a cross section perpendicular to the direction in which the cells extend are exposed are taken from near the central axis, near the radial center (near the center between the central axis and the outer peripheral wall), and near the outer peripheral wall (but not the outer peripheral wall) of the columnar honeycomb structure. Next, the relevant cross section of each sample is observed with an X-ray microscope and CT scanned. The resulting 3D cross-sectional image is then binarized based on brightness to separate it into a large number of voxels in the spatial and substrate portions (a cube with a voxel size = length in the wall direction (Y direction): 0.8 μm, length in the thickness direction (X direction): 0.8 μm, and length in the depth direction (Z direction): 0.8 μm). The measurement conditions for the X-ray microscope are a magnification of 4x. The binarization process will be performed using Otsu's binarization method.

[0035] Next, for a predetermined region of any one partition wall on the 3D cross-sectional image (length in the wall direction (Y direction): 340 μm, length in the thickness direction (X direction): encompassing the entire thickness and having at least 50 μm of space on each side of the partition wall, length in the depth direction (Z direction): 300 μm), a porosity (%) profile is obtained at 0.8 μm intervals along the thickness direction (X direction) of the partition wall from one surface to the other, based on binarized voxel data (see Figure 6). The porosity of a 0.8 μm thickness is calculated for a 0.8 μm thickness region (length in the wall direction (Y direction): 340 μm, length in the thickness direction (X direction): 0.8 μm, length in the depth direction (Z direction): 300 μm) according to the formula: porosity = (number of voxels in the space) / (total number of voxels in the region) × 100 (%). By performing this calculation at 0.8 μm intervals from the left edge of the screen across the entire predetermined region, a profile of porosity (%) is obtained at 0.8 μm intervals along the thickness direction (X direction) of the partition wall from one surface to the other.

[0036] In this case, the position of one surface of the partition wall is determined as the position of the mode of the distance M measured in the thickness direction D (X direction) from a line segment parallel to the wall surface direction of the partition wall to the surface of the partition wall being measured, as shown in Figure 7. This distance M is measured at 0.8 μm intervals over a length of 340 μm in the wall surface direction of the partition wall (Y direction perpendicular to the thickness direction (X direction)) on the binarized image. The position of the other surface of the partition wall is determined in the same manner.

[0037] In this way, a porosity profile of any one partition is obtained from each sample, and the P of that partition is obtained from that profile. AVE and (P 1MIN +P 2MIN Find {(P 1MIN +P 2MIN ) / 2}÷P AVE Calculate the P of a total of 9 samples. AVE The average value of P in the columnar honeycomb structure that is the subject of measurement is used. AVE Let's assume that the total of 9 samples {(P 1MIN +P 2MIN ) / 2}÷PAVE The average value of {(P 1MIN +P 2MIN ) / 2}÷P AVE Let's assume that.

[0038] Furthermore, a porosity profile of any one partition can be obtained from each sample, and the (P) of that partition can be determined from that profile. 1MIN +P 2MIN ) / 2 is calculated, and the total of 9 samples (P 1MIN +P 2MIN ) / 2 E The average value of the columnar honeycomb structure being measured is (P 1MIN +P 2MIN Let ) / 2. In this case, (P 1MIN +P 2MIN The upper limit of ) / 2 is preferably 70% or less, and more preferably 60% or less, from the viewpoint of ensuring strength and suppressing the penetration of catalyst into the partition wall. (P 1MIN +P 2MIN There is no specific lower limit set for ) / 2, but from the standpoint of ease of manufacture, it is generally 20% or more, and typically 25% or more.

[0039] For applications as an automotive exhaust gas filter and / or catalyst carrier, the bending strength of the columnar honeycomb structure is preferably 6.0 MPa or higher, more preferably 7.0 MPa or higher, and 8. 0M It is even more preferable that the bending strength is Pa or higher. There is no specific upper limit set for this bending strength, but it is usually 15.0 MPa or less, and typically 12.0 MPa or less. Here, the bending strength of the columnar honeycomb structure refers to the four-point bending strength measured in accordance with JIS R1664:2004. However, the sample size shall be width w20 mm × thickness t10 mm × total length h approximately 100 mm, with the distance between internal supports (internal span) being 20 mm and the distance between external supports (external span) being 60 mm. Also, the direction of the total length of the sample shall be the direction in which the cells extend. The sampling location shall be near the central axis of the columnar honeycomb structure and near the center in the height direction.

[0040] There are no restrictions on the shape of the cell opening in a cross-section perpendicular to the direction in which the cell extends, but it is preferable that it be a square, hexagon, octagon, or a combination thereof. Among these, squares and hexagons are preferred. By shaping the cell opening in this way, the pressure loss when exhaust gas flows through the honeycomb structure is reduced, resulting in superior purification performance when used as a filter. Furthermore, by shaping the cell opening in this way, the pressure loss when fluid flows through the columnar honeycomb structure is reduced, resulting in superior catalytic purification performance.

[0041] There are no particular restrictions on the cell density (number of cells per unit cross-sectional area) in a columnar honeycomb structure; for example, 6 to 2000 cells / square inch (0.9 to 311 cells / cm²) is possible. 2 ), more preferably 50 to 1000 cells / square inch (7.8 to 155 cells / cm²). 2 ), particularly preferably 100-600 cells / square inch (15.5-92.0 cells / cm²) 2 ) can be expressed as follows. Here, the cell density is calculated by dividing the number of cells in the columnar honeycomb structure by the bottom area of ​​one side of the columnar honeycomb structure, excluding the outer perimeter side wall.

[0042] The bulk density of the columnar honeycomb structure is preferably as low as possible while ensuring the desired strength. 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 measured 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.

[0043] When a columnar honeycomb structure is used as a catalyst support, a catalyst layer can be formed on the surface of the partition wall according to the purpose. Examples of catalysts, though not limited to them, include oxidation catalysts (DOC) for increasing exhaust gas temperature by oxidative combustion of hydrocarbons (HC) and carbon monoxide (CO), PM combustion catalysts for assisting the combustion of PM such as soot, SCR catalysts 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 metals (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.).

[0044] <2. Manufacturing method for columnar honeycomb structures> A method for manufacturing a columnar honeycomb structure is described below as an example. First, a raw material composition containing ceramic raw materials, a dispersion medium, a pore-forming agent, and a binder is kneaded to prepare a clay body. Then, the clay body is extruded and dried to produce a columnar honeycomb molded body. Additives such as dispersants can be added to the raw material composition as needed. When extruding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc., can be used.

[0045] In the drying process, conventional 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 drying method combining hot air drying with microwave drying or dielectric drying is preferred because it can dry the entire molded body quickly and uniformly. The pore seal portion can be formed by forming the pore seal portion at predetermined positions on both bottom surfaces of the dried honeycomb molded body and then drying the pore seal portion.

[0046] Ceramic raw materials are the materials that remain after firing metal oxides and metals, etc., and constitute the framework of the columnar honeycomb molded body (columnar honeycomb structure) after firing as ceramics. Ceramic raw materials can be provided, for example, in the form of powder. Examples of ceramic raw materials include materials for obtaining ceramics such as cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirin, corundum, and titania. Specifically, although not limited to these, examples include silica, talc, alumina, kaolin, serpentine, pyroferrite, brucite, boehmite, mullite, magnesite, and aluminum hydroxide. Ceramic raw materials may be used individually or in combination of two or more types. From the viewpoint of reducing the porosity of the partition surface while refining the pore size, it is preferable to make the median diameter (D50) of the silica particles relatively large, for example, 15 to 30 μm. On the other hand, for other ceramic raw materials, it is preferable to use fine particles having a median diameter (D50) close to the average pore diameter of the target partition, for example, 2 to 10 μm.

[0047] Corgielite can be suitably used as a ceramic material for filter applications such as DPFs and GPFs. In this case, a cordierite-forming raw material can be used as the ceramic raw material. A cordierite-forming raw material is a raw material that becomes cordierite upon firing. The cordierite-forming raw material preferably has a chemical composition of alumina (Al2O3) (including the portion of aluminum hydroxide that is converted to alumina): 30-45% by mass, magnesia (MgO): 11-17% by mass, and silica (SiO2): 42-57% by mass.

[0048] Examples of dispersion media include water, or a mixed solvent of water and an organic solvent such as alcohol, but water is particularly suitable.

[0049] The porosity-forming agent is not particularly limited as long as it forms pores after firing. Examples include wheat flour, starch, foamed resin, superabsorbent resin, silica gel, carbon (e.g., graphite, coke), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic, phenol, etc. The porosity-forming agent may be used alone or in combination of two or more types. From the viewpoint of increasing the porosity of the honeycomb structure, the content of the porosity-forming agent 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, per 100 parts by mass of ceramic raw material. From the viewpoint of ensuring the strength of the honeycomb structure, the content of the porosity-forming agent 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, per 100 parts by mass of ceramic raw material. From the viewpoint of reducing the pore size while lowering the porosity of the septum surface, it is preferable to make the median diameter (D50) of the pore-forming agent relatively large, for example, 20 to 30 μm.

[0050] Examples of binders include organic binders such as methylcellulose, hydroxypropyl methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. In particular, the combined use of methylcellulose and hydroxypropyl methylcellulose is preferred. Furthermore, from the viewpoint of increasing the strength of the honeycomb molded body before firing, the binder 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, per 100 parts by mass of ceramic raw material. From the viewpoint of suppressing cracking due to abnormal heat generation during the firing process, the binder 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, per 100 parts by mass of ceramic raw material. The binder may be used alone or in combination of two or more types.

[0051] Dispersants such as ethylene glycol, dextrin, fatty acid soap, and polyether polyol can be used. The dispersant may be used individually or in combination of two or more types. The dispersant content is preferably 0 to 2 parts by mass per 100 parts by mass of ceramic raw material.

[0052] The columnar honeycomb molded body may have openings at both ends of all cells, as shown in Figures 1 and 2. Alternatively, the columnar honeycomb molded body may have a cell structure in which one end of each cell is alternately sealed, as shown in Figures 3 and 4. The method for sealing the bottom surface of the columnar honeycomb molded body is not particularly limited, and known methods can be employed.

[0053] There are no particular restrictions on the material of the eye sealing portion, but it is preferable to use ceramics from the viewpoint of strength and heat resistance. Preferably, the ceramic is one that contains at least one selected from the group consisting of cordierite, mullite, zircon, aluminum titanate, silicon carbide, silicon nitride, zirconia, spinel, indialite, sapphirin, corundum, and titania. Preferably, the eye sealing portion is 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. It is even more preferable that the eye sealing portion has the same material composition as the main body portion of the honeycomb molded body, as this allows for the same expansion rate during firing and leads to improved durability.

[0054] A method for forming a sealed cell portion will be explained exemplified below. The sealed cell slurry is stored in a storage container. Next, a mask having an opening in the area corresponding to the cell to be sealed is attached to one of the bottom surfaces. The bottom surface with the mask attached is immersed in the storage container, and the sealed cell slurry is filled into the opening to form the sealed cell portion. The sealed cell portion can be formed on the other bottom surface in the same manner.

[0055] A columnar honeycomb structure can be manufactured by performing a degreasing process and a firing process on the dried columnar honeycomb molded body. The conditions for the degreasing and firing processes can be those known according to the material composition of the honeycomb molded body and do not require special explanation, but specific examples of conditions are given below.

[0056] The degreasing process will now be explained. The combustion temperature of the binder is approximately 200°C, and the combustion temperature of the pore-forming agent is approximately 300-1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb molded body to a temperature range of approximately 200-1000°C. The heating time is not particularly limited, but it is usually around 10-100 hours. The honeycomb molded body after the degreasing process is called a calcined body.

[0057] The firing process depends on the material composition of the honeycomb molded body, but for example, it can be carried out by heating the calcined body to 1350-1600°C in an atmospheric environment and holding it for 3-10 hours. [Examples]

[0058] (1. Manufacturing of honeycomb structures) <Examples 1-2, Comparative Examples 1-2> Depending on the test number, the cordierite-forming raw materials, pore-forming agent A, pore-forming agent B, binder, dispersant, and dispersion medium were added in the proportions shown in Table 1, mixed, and kneaded to prepare the clay. Talc, kaolin, alumina, aluminum hydroxide, and silica A and silica B were used as the cordierite-forming raw materials. Silica A and silica B have different median diameters (D50). Pore-forming agents A and B also have different median diameters (D50). Water was used as the dispersion medium, a polyacrylic acid-based polymer as the pore-forming agent, hydroxypropyl methylcellulose as the binder, and fatty acid soap as the dispersant. Furthermore, the median diameters (D50) of each material listed in Table 1 are volume-based values ​​measured using a laser diffraction particle size distribution analyzer (HORIBA model LA960).

[0059] [Table 1]

[0060] This clay was 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 of the obtained honeycomb molded body, both bottom surfaces were cut to the predetermined dimensions to obtain a cylindrical honeycomb molded body.

[0061] The obtained cylindrical honeycomb molded bodies were degreased by heating at 200°C for 8 hours in an air atmosphere, and then fired at 1430°C for 4 hours in an air atmosphere to obtain columnar honeycomb structures. The number of columnar honeycomb structures required for each test example were manufactured. The specifications of the obtained columnar honeycomb structures are as follows. Overall shape: Cylindrical shape with a diameter of 118mm and a height of 91mm. Cell shape in a cross-section perpendicular to the flow direction of the cell: square Cell density (number of cells per unit cross-sectional area): 750 cells / square inch Average partition thickness: 2.6 mil (66 μm) (Nominal value based on nozzle specifications)

[0062] (2. Measurement of the average pore diameter of the septum) For each columnar honeycomb structure obtained by the above manufacturing method, the average pore diameter of the septa was determined using a Micrometrics Autopore 9505 according to the method described above. The results are shown in Table 2.

[0063] (3. Measurement of the porosity profile of the septum) For each columnar honeycomb structure obtained by the above manufacturing method, the porosity profile of the septum was measured using an X-ray microscope (Zeiss Xradia520Versa) according to the method described above, and P AVE , (P 1MIN +P 2MIN ) / 2, and {(P 1MIN +P 2MIN ) / 2}÷P AVE (P AVE : Average porosity in each septum, P 1MIN: The minimum porosity value up to 5% thickness from one surface of the partition wall, P 2MIN The minimum porosity (up to 5% thickness from the other surface of the partition wall) was determined. The results are shown in Table 2.

[0064] (4. Bulk density) The bulk density of each columnar honeycomb structure obtained by the above manufacturing method was determined according to the method described earlier. The results are shown in Table 2.

[0065] (5. Measurement of bending strength) The bending strength of each columnar honeycomb structure obtained by the above manufacturing method was measured using an INSTRON 3366 dual-column benchtop testing machine according to the method described above. The results are shown in Table 2.

[0066] [Table 2]

[0067] (6. Discussion) Mean porosity (P) in each partition AVE ) Compared to Example 1 and Comparative Example 1, which are similar, {(P 1MIN +P 2MIN ) / 2}÷P AVE Example 1, in which the appropriateness was observed, showed higher bending strength. Similarly, the average porosity (P) in each partition wall AVE ) Compared to Example 2 and Comparative Example 2, which are similar, {(P 1MIN +P 2MIN ) / 2}÷P AVE Example 2, which was more appropriate, showed higher bending strength. [Explanation of Symbols]

[0068] 100: Columnar honeycomb structure 102: Outer perimeter side wall 104: First bottom surface 106:Second bottom 108: Cell 112: Bulkhead 112a: One surface of the partition wall 112b: The other surface of the partition wall 200: Columnar honeycomb structure 202: Outer wall 204: First bottom surface 206:Second bottom 208a: Cell 1 208b: Cell 2 209: Eye sealing part 212: Bulkhead

Claims

1. A columnar honeycomb structure comprising an outer peripheral wall and a plurality of partition walls disposed on the inner peripheral side of the outer peripheral wall, which divide a plurality of cells that form a flow path from a first bottom surface to a second bottom surface, The partition wall is formed of silica-containing ceramics, The average pore size of the septum, as measured by the mercury intrusion method specified in JIS R1655:2003, is 3 to 10 μm. The cross-sections of the aforementioned multiple partitions were observed with an X-ray microscope, and the porosity (%) was measured in the thickness direction from one surface to the other for each partition, and the average porosity of each partition was calculated as P AVE P is the minimum value of the porosity from one surface of the partition wall up to 5% thickness. 1MIN P is the minimum value of the porosity up to 5% thickness from the other surface of the partition wall. 2MIN Therefore, 40% ≤ P AVE ≤70%, {(P 1MIN +P 2MIN ) / 2}÷P AVE The condition ≤ 0.9 holds true. Columnar honeycomb structure.

2. 0.6 ≤ { ( P 1MIN + P 2MIN ) / 2} ÷ P AVE ≤ 0.9 holds for the columnar honeycomb structure according to claim 1.

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

4. A columnar honeycomb structure according to any one of claims 1 to 3, wherein the bending strength measured in accordance with JIS R1664:2004 is 6.0 MPa or more.

5. 50% ≤ P AVE A columnar honeycomb structure according to any one of claims 1 to 4, wherein the ratio is ≤60%.

6. A columnar honeycomb structure according to any one of claims 1 to 5, wherein the bulk density is 0.15 g / cc to 0.25 g / cc.

7. The columnar honeycomb structure according to any one of claims 1 to 6, wherein the partition wall is formed of ceramics containing 90% by mass or more of cordierite.

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

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