Honeycomb structure

Abstract

To provide a honeycomb structure which can maintain maintenance cost at a low level, and easily detects the timing of maintenance on the basis of a PM accumulation amount by a pressure sensor.SOLUTION: There is provided a column-shaped honeycomb structure in which each of a plurality of introduction cells and a plurality of discharge cells are adjacent to each other across partition walls in at least one of the plurality of introduction cells and the plurality of discharge cells. A cell density based on the total number of the plurality of introduction cells and the plurality of discharge cells is 22 to 70 pieces / cm2. Wach of the thicknesses of the partition walls is within the range of 0.15 mm or more and 0.38 mm or less. An opening ration on the inlet end face is 44% or more. When the total area of the surfaces of all the partition walls partitioning the plurality of introduction cells excluding the introduction cell adjacent to the outer peripheral side wall is represented by S1, and the total area of the surfaces of all the partition walls sandwiched between the adjacent introduction cells among the plurality of introduction cells excluding the introduction cell adjacent to the outer peripheral side wall is represented by S2, 33%≤S2 / S1≤75% is satisfied.SELECTED DRAWING: Figure 5A

Description

[Technical Field]

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

[0002] Diesel engines have better thermal efficiency than gasoline engines, but they produce particulate matter (PM) such as soot and ash due to diffuse combustion. This particulate matter is known to be carcinogenic, so it is essential to prevent its release into the atmosphere. For this reason, Europe and other countries are now imposing strict regulations that restrict the number of PM particles in addition to the traditional weight-based restrictions.

[0003] However, there is a limit to how much PM emissions can be reduced by improving combustion, and the only effective method at present is to install a filter called a Diesel Particulate Filter (DPF) in the exhaust. A wall-flow type filter, designed so that exhaust gas passes through porous partition walls, is effective for this purpose. Specifically, a wall-flow type filter has many inlet cells and many exhaust cells adjacent to each other via porous partition walls, and can be constructed using a honeycomb structure that captures PM as the exhaust gas passes through the partition walls.

[0004] Wall-flow filters made of honeycomb structures have the problem of increasing pressure loss as PM accumulates within the filter over time. To address this issue, these filters reduce pressure loss by injecting extra fuel after each PM buildup to raise the exhaust gas temperature and burn the soot (filter regeneration). Additionally, because ash does not burn even at high temperatures, trucks and off-road vehicles, which travel longer distances (i.e., have longer filter operating times) than passenger cars, require periodic cleaning of the honeycomb structure to remove ash that accumulates within the filter and reduce pressure loss. If pressure loss increases quickly during PM buildup, filter regeneration and cleaning must be performed more frequently, resulting in increased fuel consumption and maintenance costs. Therefore, efforts have been made to reduce pressure loss during PM buildup by adjusting the arrangement and size of the inlet and outlet cells (Patent Document 1, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 104057 [Patent Document 2] International Publication No. 2013 / 187444 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventionally, the timing of filter regeneration or cleaning is determined by measuring the pressure loss between the filter inlet and outlet using a pressure sensor. However, if the pressure loss remains low after a large amount of PM has accumulated on the filter, it becomes difficult to predict the amount of PM accumulation due to the pressure loss when filter regeneration is controlled using a pressure sensor, resulting in excessive PM accumulation and filter damage. Therefore, it is desirable to minimize the pressure loss after PM accumulation as much as possible to reduce the frequency of filter regeneration and cleaning and thereby reduce maintenance costs, while at the same time increasing the change in pressure loss (pressure loss slope) in response to the amount of PM accumulated, making it easier for the pressure sensor to detect the amount of PM accumulation appropriate for filter regeneration or cleaning.

[0007] The present invention has been made in consideration of the above circumstances, and in one embodiment, an object of the present invention is to provide a honeycomb structure that can keep maintenance costs low and that makes it easy to detect when maintenance is required using a pressure sensor based on the amount of PM accumulation. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention, which is exemplified below. [Aspect 1] A columnar honeycomb structure comprising: an outer peripheral side wall; a plurality of inlet cells arranged on an inner peripheral side of the outer peripheral side wall, extending from an inlet end face to an outlet end face, having openings at the inlet end faces and having plugging portions at the outlet end faces; and a plurality of outlet cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet end face to the outlet end face, having plugging portions at the inlet end faces and having openings at the outlet end faces, each of the plurality of inlet cells and the plurality of outlet cells is adjacent to at least one of the plurality of inlet cells and the plurality of outlet cells with a partition wall interposed therebetween; A cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 22 to 70 cells / cm 2 and the thickness of each of the partition walls is in the range of 0.15 mm or more and 0.38 mm or less, The opening ratio at the inlet end surface is 44% or more, and When the total surface area of ​​all partition walls partitioning the plurality of introduction cells excluding the introduction cells adjacent to the peripheral side wall is S1, and the total surface area of ​​all partition walls sandwiched between adjacent introduction cells among the plurality of introduction cells excluding the introduction cells adjacent to the peripheral side wall is S2, 33%≦S2 / S1≦75% is satisfied. Honeycomb structure. [Aspect 2] 2. The honeycomb structure according to embodiment 1, wherein the opening areas of the plurality of introduction cells are all the same except for the one adjacent to the outer peripheral side wall. [Aspect 3] 3. The honeycomb structure according to aspect 1 or 2, wherein the opening areas of the plurality of inlet cells and the plurality of outlet cells are all the same except for those adjacent to the outer peripheral side wall. [Aspect 4] 4. The honeycomb structure according to any one of aspects 1 to 3, wherein the opening shapes of the plurality of introduction cells are all square except for one adjacent to the outer peripheral side wall. [Aspect 5] 5. The honeycomb structure according to any one of aspects 1 to 4, wherein the opening shapes of the plurality of inlet cells and the plurality of outlet cells are all square except for those adjacent to the outer peripheral side wall. [Aspect 6] 6. The honeycomb structure according to any one of aspects 1 to 5, wherein the plurality of introduction cells have the same opening shape and opening area except for the one adjacent to the outer peripheral side wall. [Aspect 7] 5. The honeycomb structure according to embodiment 4, wherein the square has a side length of 0.90 mm or more and 1.90 mm or less. [Aspect 8] 6. The honeycomb structure according to embodiment 5, wherein the square has a side length of 0.90 mm or more and 1.90 mm or less. [Aspect 9] 9. The honeycomb structure according to any one of aspects 1 to 8, wherein the plurality of discharge cells are not adjacent to each other. [Aspect 10] The average linear expansion coefficient of the partition wall from room temperature to 800°C in the direction in which the inlet cells and the outlet cells extend is 1.0 × 10 -6 10. The honeycomb structure according to any one of aspects 1 to 9, wherein the temperature is 100° C. / ° C. or lower. [Aspect 11] 11. The honeycomb structure according to any one of aspects 1 to 10, wherein the partition walls contain cordierite. [Aspect 12] 12. The honeycomb structure according to any one of aspects 1 to 11, wherein the thickness of each of the partition walls is in the range of 0.18 mm or more and 0.30 mm or less. [Aspect 13] The cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 26 to 62 cells / cm 2 13. The honeycomb structure according to any one of aspects 1 to 12, wherein the range is: [Aspect 14] 14. The honeycomb structure according to any one of aspects 1 to 13, wherein at least one of the plurality of inlet cells is not adjacent to any of the plurality of outlet cells. [Aspect 15] 3. The honeycomb structure according to embodiment 1 or 2, wherein at least one discharge cell among the plurality of discharge cells is adjacent to only the inlet cell. [Aspect 16] The ratio of the number of the plurality of inlet cells to the number of the plurality of outlet cells is 1.5 to 2.0, and the cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 47 to 62 cells / cm 2 or the ratio of the number of the plurality of inlet cells to the number of the plurality of outlet cells is 3.0 to 4.0 and the cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 28 to 43 cells / cm 2 3. The honeycomb structure according to claim 1, wherein the thickness is in the range of 1. [Effects of the Invention]

[0009] By using a honeycomb structure according to one embodiment of the present invention as an exhaust gas filter, the pressure loss after PM accumulation can be minimized, thereby reducing the frequency of filter regeneration and cleaning. At the same time, the change in pressure loss (pressure loss gradient) corresponding to the amount of accumulated PM can be increased, making it easier to detect the amount of PM accumulation suitable for filter regeneration and cleaning using a pressure sensor. This allows maintenance costs to be kept low, and a filter can be obtained in which the need for maintenance can be easily detected using a pressure sensor based on the amount of PM accumulation. This reduces the risk of filter damage due to excessive PM accumulation. Furthermore, this effect can be achieved without sacrificing thermal shock resistance. Thus, one embodiment of the present invention can provide a honeycomb structure that is extremely excellent for practical use. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view schematically showing a wall-flow type honeycomb structure. [Figure 2] 1 is a schematic cross-sectional view of a wall-flow type honeycomb structure when observed from a cross section parallel to the cell extension direction. FIG. [Figure 3] FIG. 3 is a schematic partial enlarged view of a partition wall of a honeycomb structure when observed from a cross section perpendicular to the cell extension direction. [Figure 4] FIG. 10 is an explanatory diagram schematically illustrating an example of a method for forming plugging portions by a squeegee method. [Figure 5A] The cell structure and plugging pattern of "irregular 1SQ" are shown schematically. [Figure 5B] The cell structure and plugging pattern of "irregular 2SQ" are shown schematically. [Figure 5C] The cell structure and plugging pattern of "irregular 3SQ" are shown schematically. [Figure 5D] The cell structure and plugging pattern of "irregular 4SQ" are shown schematically. [Figure 5E] The cell structure and plugging pattern of "irregular 5SQ" are shown schematically. [Figure 5F] The cell structure and plugging pattern of "irregular 6SQ" are shown schematically. [Figure 5G] The cell structure and plugging pattern of "irregular 7SQ" are shown schematically. [Figure 5H] The cell structure and plugging pattern of "HEX" are shown schematically. [Figure 5I] The cell structure and plugging pattern of "normal HAC" are shown schematically. [Figure 5J] The cell structure and plugging pattern of "Atypical 1HAC" are shown schematically. DETAILED DESCRIPTION OF THE INVENTION

[0011] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and that appropriate design changes and improvements may be made based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0012] (1. Honeycomb structure) 1 and 2 are a schematic perspective view and a cross-sectional view, respectively, of a cylindrical honeycomb structure 100 applicable to a wall-flow type automotive exhaust gas filter. The honeycomb structure 100 includes an outer peripheral sidewall 102, a plurality of inlet cells 108 arranged on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to each other from an inlet end face 104 to an outlet end face 106, having openings 107 at the inlet end face 104 and plugging portions 109 at the outlet end face 106, and a plurality of discharge cells 110 arranged on the inner peripheral side of the outer peripheral sidewall 102, extending parallel to each other from an inlet end face 104 to an outlet end face 106, having plugging portions 109 at the inlet end face 104 and having openings 107 at the outlet end face 106.

[0013] In this honeycomb structure 100, the plurality of inlet cells 108 and the plurality of discharge cells 110 are adjacent to at least one of the plurality of inlet cells 108 and the plurality of discharge cells 110, respectively, with a partition wall 112 sandwiched between them. When the inlet cells 108 and the discharge cells 110 are adjacent to each other with a partition wall 112 sandwiched between them, the surface of the partition wall 112 (hereinafter, the partition wall 112 separating the inlet cells 108 and the discharge cells 110 is referred to as "partition wall A") contributes to filtration. For example, when exhaust gas containing particulate matter such as soot is supplied to the upstream inlet end face 104 of the honeycomb structure 100, the exhaust gas is introduced into the inlet cells 108 and travels downstream within the inlet cells 108. Because the downstream outlet end face 106 of the inlet cells 108 is plugged, the exhaust gas passes through the partition wall A located between the adjacent inlet cells 108 and discharge cells 110 and flows into the discharge cells 110. Since the particulate matter cannot pass through the partition wall A, it is captured and deposited in the inlet cell 108. After the particulate matter has been removed, the clean exhaust gas that has flowed into the exhaust cell 110 travels downstream within the exhaust cell 110 and flows out from the outlet end face 106 on the downstream side.

[0014] On the other hand, when the inlet cells 108 are adjacent to each other with a partition wall 112 sandwiched between them, the surface of the partition wall 112 (hereinafter, the partition wall 112 separating the inlet cells 108 is referred to as "partition wall B") does not contribute to filtration. When the outlet cells 110 are adjacent to each other with a partition wall 112 sandwiched between them, the surface of the partition wall 112 (hereinafter, the partition wall 112 separating the outlet cells 110 is referred to as "partition wall C") also does not contribute to filtration.

[0015] In addition, when two cells are adjacent across a partition wall, it means that when the partition walls of the honeycomb structure are observed from a cross section perpendicular to the cell extension direction, the two cells are adjacent across opposing wall surfaces of one partition wall, and does not include the case where the two cells are adjacent across the intersection I of the partition walls (see Figure 3).

[0016] The higher the surface area ratio of partition wall A, the lower the pressure loss during PM deposition and the gentler the pressure loss gradient. Meanwhile, the higher the surface area ratio of partition wall B, the higher the pressure loss during PM deposition and the steeper the pressure loss gradient. Therefore, because the balance between partition wall A and partition wall B determines the magnitude of the initial pressure loss and the pressure loss gradient, it is desirable to set it appropriately. Specifically, if the total surface area of ​​all partition walls 112 that separate the multiple inlet cells 108 (excluding the inlet cells 108 adjacent to the outer peripheral side wall 102) is S1, and the total surface area of ​​all partition walls 112 sandwiched between adjacent inlet cells 108 among the multiple inlet cells 108 (excluding the inlet cells 108 adjacent to the outer peripheral side wall 102) is S2, then the ratio is preferably 33%≦S2 / S1≦75%, more preferably 50%≦S2 / S1≦71%, and even more preferably 60%≦S2 / S1≦67%.

[0017] For example, the opening shape of each introduction cell is a square with a side length of L, the length of each introduction cell in the cell extension direction (the length from the inlet end face to the outlet end face minus the length of the plugging portion) is H, and the total number of introduction cells excluding the introduction cells adjacent to the outer peripheral side wall is C A Then, S1=L×H×4×C A The total number of partition walls sandwiched between adjacent inlet cells, excluding the inlet cells adjacent to each other on the outer peripheral side walls, is expressed as W A Then, S2=L×H×2×W A It is expressed as:

[0018] In a preferred embodiment, at least one of the plurality of inlet cells 108 is not adjacent to any of the plurality of discharge cells 110. Since such an inlet cell 108 is partitioned only by partition wall B, the area ratio of partition wall B can be effectively increased, and the relative reduction in partition wall A contributes to an increase in the pressure drop gradient. For example, of the plurality of inlet cells 108 excluding the inlet cells 108 adjacent to the outer peripheral side wall 102, it is preferable that 10 to 35% of the inlet cells 108 are not adjacent to any of the plurality of discharge cells 110, and it is more preferable that 20 to 35% of the inlet cells 108 are not adjacent to any of the plurality of discharge cells 110.

[0019] In a preferred embodiment, at least one of the plurality of discharge cells 110 is adjacent only to the inlet cell 108 (i.e., adjacent to neither the discharge cell 110 nor the outer peripheral side wall 102). This is because the discharge cell 110 performs a filtering function by being adjacent to the inlet cell 108. It is desirable that none of the plurality of discharge cells 110 are adjacent to each other.

[0020] In order to reduce the area of ​​the partition walls A while maintaining the frequency of cleaning treatment, it is preferable to set the cell density of the honeycomb structure 100 relatively low. Specifically, the cell density (the number of cells per unit cross-sectional area) based on the total number of the plurality of inlet cells 108 and the plurality of outlet cells 110 is set to 22 to 70 cells / cm in consideration of the balance with suppressing pressure loss during PM accumulation. 2 It is preferable that the density is 26 to 62 particles / cm. 2 Here, the cell density is calculated by dividing the total number of cells (including plugged cells, discharge cells 110 adjacent to the outer peripheral side wall 102, and introduction cells 108 adjacent to the outer peripheral side wall 102) by the area of ​​one end face of the honeycomb structure excluding the outer peripheral side wall.

[0021] From the viewpoint of increasing the pressure drop gradient while suppressing an increase in pressure drop, the preferable range of the cell density also varies depending on the ratio of the number of the plurality of inlet cells 108 to the number of the plurality of outlet cells 110. Specifically, when the ratio (I / O) of the number of the plurality of inlet cells 108 excluding the inlet cells 108 adjacent to the outer peripheral side wall 102 to the number of the plurality of outlet cells 110 excluding the outlet cells 110 adjacent to the outer peripheral side wall 102 is 1.5 to 2.0, the cell density based on the total number of the plurality of inlet cells 108 and the plurality of outlet cells 110 is 47 to 62 cells / cm. 2 When the ratio (I / O) of the number of the plurality of inlet cells 108 excluding the inlet cells 108 adjacent to the outer peripheral side wall 102 to the number of the plurality of outlet cells 110 excluding the outlet cells 110 adjacent to the outer peripheral side wall 102 is 3.0 to 4.0, the cell density based on the total number of the plurality of inlet cells 108 and the plurality of outlet cells 110 is 28 to 43 cells / cm. 2 It is preferable that the range is:

[0022] From the viewpoint of ensuring the strength of the honeycomb structure, the thickness of each partition wall in the honeycomb structure is preferably 0.15 mm or more, more preferably 0.18 mm or more, and even more preferably 0.21 mm or more. Furthermore, from the viewpoint of suppressing pressure loss during PM accumulation, the thickness of each partition wall is preferably 0.38 mm or less, more preferably 0.31 mm or less, more preferably 0.30 mm or less, and even more preferably 0.27 mm or less. Therefore, the thickness of each partition wall is preferably 0.15 to 0.38 mm, more preferably 0.18 to 0.31 mm, more preferably 0.18 to 0.30 mm, and even more preferably 0.21 to 0.27 mm, for example.

[0023] 3 shows a schematic enlarged partial view of the partition walls 112 of the honeycomb structure 100 when observed in a cross section perpendicular to the cell extension direction. The thickness of the partition walls 112 refers to the length D of a line segment N that crosses the partition walls when the line segment N connects the centers of gravity O of adjacent cells in a cross section perpendicular to the cell extension direction (height direction of the honeycomb structure).

[0024] From the viewpoint of suppressing pressure loss during PM accumulation, the opening ratio at the inlet end face 104 is preferably 44% or more, more preferably 50% or more, and even more preferably 54% or more. On the other hand, from the viewpoint of ensuring an outlet-side flow path and suppressing initial pressure loss, the opening ratio at the inlet end face 104 is preferably 60% or less, more preferably 58% or less, and even more preferably 56% or less. Therefore, the opening ratio at the inlet end face 104 is preferably, for example, 44 to 60%, more preferably 50 to 58%, and even more preferably 54 to 56%.

[0025] In this specification, the opening ratio at the inlet end face 104 is a value obtained by dividing the total opening area of ​​the inlet cells 108 at the inlet end face 104 of the honeycomb structure 100 by the area of ​​the inlet end face 104 (the total area of ​​the partition walls 112 excluding the outer peripheral side wall 102, the inlet cells 108, and the discharge cells 110).

[0026] From the viewpoint of suppressing the variation in flow rate between the introduction cells, it is preferable that the opening areas of the introduction cells 108 are all the same except for the introduction cells adjacent to the outer peripheral sidewall 102. Here, "same" is a concept that includes being substantially the same. For example, among the introduction cells 108 except for the introduction cell 108 adjacent to the outer peripheral sidewall 102, the area A of the introduction cell 108 with the smallest opening area is min and the area A of the introduction cell 108 with the largest opening area. max However, 0.90≦A min / A max When the relationship 0.95≦A≦1.00 is satisfied, the opening area is substantially the same. min / A max It is preferable that the relationship be ≦1.00.

[0027] Furthermore, it is more preferable that the opening shapes and opening areas of the multiple introduction cells 108 are all the same except for those adjacent to the outer peripheral sidewall 102. This is because having the same opening shapes as well as opening areas has the advantage of suppressing variations in flow rate between introduction cells. Here, "same" is a concept that includes being substantially the same, such as having the same opening shape in terms of design.

[0028] Furthermore, it is more preferable that the opening areas of the plurality of inlet cells 108 and the plurality of outlet cells 110 are all the same except for those adjacent to the outer peripheral side wall. If the opening areas of the inlet cells 108 and the outlet cells 110 are the same, the flow rate difference between the inlet cells 108 and the outlet cells 110 becomes smaller, which is advantageous in that pressure loss is suppressed. Here, "same" is a concept that includes being substantially the same. For example, the area B of the cell with the smallest opening area among the plurality of inlet cells 108 and the plurality of outlet cells 110 is minand the area B of the cell with the largest opening area among the plurality of inlet cells 108 and the plurality of outlet cells 110. max However, 0.90≦B min / B max When the relationship 0.95≦B≦1.00 is satisfied, they are substantially the same. min / B max It is preferable that the relationship be ≦1.00.

[0029] The opening shape of the inlet cells 108 and the discharge cells 110 is not particularly limited, but may be polygonal (quadrilateral (rectangle, square), pentagon, hexagon, heptagon, octagon, etc.), round (circular, elliptical, oval, egg, oval, etc.), etc. in a cross section perpendicular to the cell extension direction of the honeycomb structure. These shapes may be one type or a combination of two or more types. When the opening shape of the inlet cells 108 and the discharge cells 110 is polygonal, the corners may be rounded. In this specification, rounded corners are treated as polygonal.

[0030] From the viewpoint of suppressing clogging with soot and unburned components, it is preferable that the opening shapes of each of the plurality of inlet cells 108 are all square except for those adjacent to the outer peripheral sidewall 102. Furthermore, it is more preferable that the opening shapes of each of the plurality of inlet cells 108 and the plurality of outlet cells 110 are all square except for those adjacent to the outer peripheral sidewall 102. The length of one side of the square is preferably 0.90 mm or more and 1.90 mm or less, and more preferably 1.00 mm or more and 1.70 mm or less. Note that when the corners of a square are rounded, the length of one side of the square having the rounded chamfered portion R is the length L of one side of the square when it is assumed that the rounded corners are not rounded (see FIG. 3).

[0031] There is no limitation on the end face shape of the honeycomb structure 100, and it may be, for example, a circular shape, an elliptical shape, a round shape such as a racetrack shape or an oval shape, a polygonal shape such as a triangular shape or a quadrangular shape, or any other irregular shape. The illustrated honeycomb structure 100 has a circular end face shape and is cylindrical as a whole.

[0032] There are no particular restrictions on the height of the honeycomb structure (the length from the inlet end face to the outlet end face) and it may be set appropriately depending on the application and required performance. The height of the honeycomb structure may be, for example, 40 mm to 450 mm. There are also no particular restrictions on the relationship between the height of the honeycomb structure and the maximum diameter of each end face (the maximum length of the diameters passing through the center of gravity of each end face of the honeycomb structure). Therefore, the height of the honeycomb structure may be longer than the maximum diameter of each end face, or the height of the honeycomb structure may be shorter than the maximum diameter of each end face.

[0033] From the viewpoint of reducing pressure loss, the lower limit of the average porosity of the partition walls is preferably 41% or more, more preferably 52% or more. Furthermore, from the viewpoint of increasing the mechanical strength of the honeycomb structure, the upper limit of the average porosity of the partition walls is preferably 65% ​​or less, more preferably 60% or less. Therefore, the average porosity of the partition walls is preferably, for example, 41 to 65%, more preferably 52 to 60%. In this specification, the porosity is measured by the mercury intrusion method specified in JIS R1655:2003. Furthermore, the average porosity is determined by taking partition wall samples (0.3 g each) from six positions of the honeycomb structure without bias, and the measured value is the average value when each porosity is determined.

[0034] From the viewpoint of obtaining excellent thermal shock resistance, the average linear expansion coefficient of the partition wall from room temperature to 800° C. in the direction in which the inlet cell 108 and the outlet cell 110 extend is set to 1.0×10 -6 / °C or less, and -6 / °C or less, and more preferably 0.6 × 10 -6 Although there is no lower limit set for the average linear expansion coefficient, taking into consideration ease of manufacture, the average linear expansion coefficient is preferably 0.8×10 -6 / ℃~1.0×10 -6 / °C, and preferably 0.6 x 10 -6 / ℃~0.8×10 -6 / °C, more preferably 0.4 × 10 -6 / ℃~0.6×10 -6 / ° C. The average linear expansion coefficient is measured in accordance with JIS R1618:2002. The average linear expansion coefficient of the partition walls can be controlled by the material and porosity that constitute the partition walls.

[0035] From the viewpoint of obtaining excellent thermal shock resistance, at least the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions contain cordierite (2MgO·2Al2O3·5SiO2) and / or silicon carbide (SiC).

[0036] When the honeycomb structure has cordierite as the main component, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, have a cordierite content of preferably 90% by mass or more, more preferably 91% by mass or more, and even more preferably 92% by mass or more. Although no upper limit is particularly set, from the viewpoint of modifying the properties of the honeycomb structure by adding other ceramics, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, have a cordierite content of preferably 96% by mass or less, more preferably 95% by mass or less, and even more preferably 94% by mass or less. Therefore, when a honeycomb structure has cordierite as its main component, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, preferably have a cordierite content of, for example, 90 to 96 mass%, more preferably 91 to 95 mass%, and even more preferably 92 to 94 mass%.

[0037] The cordierite content can be measured by X-ray diffraction. Specifically, an X-ray diffraction apparatus using Cu Kα rays (e.g., an X'pert PRO apparatus manufactured by PANalytical) is used to perform X-ray analysis measurement in the range of 2θ = 8 to 100° on a sample of the outer peripheral side wall, partition wall, or plugging portion by X-ray diffraction, and the cordierite crystalline phase ratio is measured by analyzing the result using the Rietveld analysis program RIETAN, which is defined as the cordierite content.

[0038] When a honeycomb structure has silicon carbide as a main component, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, have a silicon carbide content of preferably 66% by mass or more, more preferably 67% by mass or more, and even more preferably 68% by mass or more. Although no upper limit is particularly set, from the viewpoint of modifying the properties of the honeycomb structure by adding other ceramics, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, have a silicon carbide content of preferably 76% by mass or less, more preferably 75% by mass or less, and even more preferably 74% by mass or less. Therefore, when a honeycomb structure has silicon carbide as its main component, the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions, preferably have a silicon carbide content of, for example, 66 to 76 mass%, more preferably 67 to 75 mass%, and even more preferably 68 to 74 mass%.

[0039] The silicon carbide content can be measured by X-ray diffraction. Specifically, an X-ray diffraction apparatus using Cu Kα radiation (e.g., an X'pert PRO apparatus manufactured by PANalytical) is used to perform X-ray analysis measurements in the range of 2θ = 8 to 100° on a sample of the outer peripheral side wall, partition wall, or plugged portion by X-ray diffraction. The Rietveld analysis program RIETAN is then used to measure the crystalline phase ratio of metal Si in the sample (= metal Si content (mass%)). Next, the oxygen (O) content (mass%) in the sample is quantified by inert gas fusion. The SiO2 content (mass%) in the sample is calculated by multiplying the oxygen (O) content by 60 / 32. Finally, the silicon carbide content is calculated using the formula: silicon carbide content (mass%) = 100 - metal Si content (mass%) - SiO2 content (mass%).

[0040] The outer peripheral side walls, partition walls, and plugging portions of the honeycomb structure may contain ceramics other than cordierite and SiC. Examples of other ceramics include mullite, zirconium phosphate, aluminum titanate, silicon-silicon carbide composites (e.g., Si-bonded SiC), cordierite-silicon carbide composites, zirconia, spinel, indialite, sapphirine, corundum, titania, silicon nitride, and ceria. These other ceramics may be contained singly or in combination of two or more.

[0041] In one embodiment, the plugging portions at both the inlet end face and the outlet end face have an average depth of 2 to 8 mm. When the average depth of the plugging portions is 2 mm or more, the strength of the plugging portions can be ensured. The average depth of the plugging portions is preferably 3 mm or more. Furthermore, when the average depth of the plugging portions is 8 mm or less, the area of ​​the partition walls that capture particulate matter in the cells can be prevented from becoming smaller. The average depth of the plugging portions is preferably 7 mm or less. The depth of the plugging portions in the cell extension direction is measured at any 20 points on each end face, and the average value is taken as the average depth of the plugging portions at each end face. The depth of each plugging portion means the length in the cell extension direction from the position of the inlet end face or outlet end face where the plugging portion is formed to the deepest position where the plugging portion exists.

[0042] The honeycomb structure can also be used as a catalyst carrier. A catalyst can be supported on the surface of the partition walls according to the purpose. Examples of catalysts include, but are not limited to, oxidation catalysts (DOCs) for oxidatively burning hydrocarbons (HC) and carbon monoxide (CO) to increase the exhaust gas temperature, PM combustion catalysts for assisting the combustion of PM such as soot, SCR catalysts and NSR catalysts for removing nitrogen oxides (NOx), and three-way catalysts capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst can appropriately contain, for example, noble metals (e.g., Pt, Pd, Rh), alkali metals (e.g., Li, Na, K, Cs), alkaline earth metals (e.g., Mg, Ca, Ba, Sr), rare earth elements (e.g., Ce, Sm, Gd, Nd, Y, La, Pr), transition metals (e.g., Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr), etc.

[0043] The honeycomb structure may be a honeycomb bonded body having a plurality of honeycomb segments and a bonding layer bonding the outer peripheral surfaces of the plurality of honeycomb segments together. The use of a honeycomb bonded body makes it possible to increase the total cross-sectional area of ​​the cells, which is important for ensuring air flow while suppressing the occurrence of cracks. The bonding layer can be formed using a bonding material. The bonding material is not particularly limited, but a paste-like material obtained by adding a solvent such as water to a ceramic material can be used. The bonding material may contain the same material as the partition walls. In addition to bonding the honeycomb segments together, the bonding material can also be used as an outer peripheral coating material after the honeycomb segments are bonded.

[0044] (2. Manufacturing method) A method for manufacturing a cylindrical honeycomb structure according to one embodiment of the present invention will be described below by way of example. First, a raw material composition containing a cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder is kneaded to form a puddle, and the puddle is then extrusion-molded to obtain a cylindrical honeycomb molded body having an outer peripheral sidewall and a cylindrical honeycomb molded body disposed on the inner peripheral side of the outer peripheral sidewall, extending from an inlet end face to an outlet end face, and having openings at both the inlet end face and the outlet end face. Additives such as a dispersant or other ceramic raw materials may be blended into the raw material composition as needed. During extrusion molding, a die having the desired overall shape, cell shape, cell arrangement, partition wall thickness, cell density, etc. can be used.

[0045] The cordierite-forming raw material is a raw material that becomes cordierite when fired, and can be provided, for example, in the form of powder. The cordierite-forming raw material preferably has a chemical composition of 30 to 45 mass% alumina (Al2O3) (including aluminum hydroxide converted to alumina), 11 to 17 mass% magnesia (MgO), and 42 to 57 mass% silica (SiO2).

[0046] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0047] The content of the dispersion medium in the honeycomb formed body before the drying step is preferably 20 to 110 parts by mass, more preferably 25 to 100 parts by mass, and even more preferably 30 to 90 parts by mass, relative to 100 parts by mass of the cordierite-forming raw material. When the content of the dispersion medium in the honeycomb formed body is 20 parts by mass or more relative to 100 parts by mass of the cordierite-forming raw material, the advantage of easily stabilizing the quality of the honeycomb structure is easily obtained. When the content of the dispersion medium in the honeycomb formed body is 90 parts by mass or less relative to 100 parts by mass of the cordierite-forming raw material, the amount of shrinkage during drying is small, and deformation can be suppressed. In this specification, the content of the dispersion medium in the honeycomb formed body refers to a value measured by a loss on drying method.

[0048] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, silica gel, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, and phenol. One type of pore-forming material may be used alone, or two or more types may be used in combination. From the viewpoint of increasing the porosity of the honeycomb structure after firing, the content of the pore-forming material is preferably 3 parts by mass or more, more preferably 6 parts by mass or more, and even more preferably 9 parts by mass or more, relative to 100 parts by mass of the cordierite-forming raw material. From the viewpoint of ensuring the strength of the honeycomb structure after firing, the content of the pore-forming material is preferably 30 parts by mass or less, more preferably 27 parts by mass or less, and even more preferably 24 parts by mass or less, relative to 100 parts by mass of the cordierite-forming raw material.

[0049] Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Furthermore, from the viewpoint of increasing the strength of the honeycomb formed body before firing, the content of the binder is preferably 4 parts by mass or more, more preferably 4.5 parts by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the cordierite-forming raw material. From the viewpoint of suppressing cracks due to abnormal heat generation during the firing process, the content of the binder is preferably 9 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less, relative to 100 parts by mass of the cordierite-forming raw material. One type of binder may be used alone, or two or more types may be used in combination.

[0050] The dispersant may be ethylene glycol, dextrin, fatty acid soap, polyether polyol, or the like. One type of dispersant may be used alone, or two or more types may be used in combination. The content of the dispersant is preferably 0 to 2 parts by mass per 100 parts by mass of the cordierite-forming raw material.

[0051] The honeycomb formed body can be dried by a conventionally known drying method, such as hot air drying, microwave drying, dielectric drying, reduced pressure drying, vacuum drying, freeze drying, etc. Among these, a drying method that combines hot air drying with microwave drying or dielectric drying is preferred, since it can dry the entire honeycomb formed body quickly and uniformly.

[0052] After drying the honeycomb formed body, plugging portions are formed on both end faces of the honeycomb formed body. Each plugging portion can be formed by filling the openings of the inlet cells and outlet cells where the plugging portions are to be formed with a plugging portion forming slurry, and then drying and firing the filled slurry. The material of the honeycomb formed body can be used for the plugging portion forming slurry. For example, when the honeycomb formed body contains a cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder, the plugging portion forming slurry can contain the cordierite-forming raw material, a pore-forming material, a dispersion medium, and a binder, without being limited thereto.

[0053] For example, the slurry for forming plugging portions contains 30 to 60 parts by mass of a dispersion medium, 5 to 20 parts by mass of a pore-forming material, and 0.2 to 2.0 parts by mass of a binder relative to 100 parts by mass of the cordierite-forming raw material. In a preferred embodiment, the slurry for forming plugging portions contains 35 to 50 parts by mass of a dispersion medium, 8 to 16 parts by mass of a pore-forming material, and 0.2 to 1.5 parts by mass of a binder relative to 100 parts by mass of the cordierite-forming raw material.

[0054] Examples of the dispersion medium include water and a mixed solvent of water and an organic solvent such as alcohol, with water being particularly preferred.

[0055] The pore-forming material is not particularly limited as long as it forms pores after firing, and examples thereof include wheat flour, starch, foamed resin, water-absorbent resin, silica gel, carbon (e.g., graphite), ceramic balloons, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, phenol, etc. One type of pore-forming material may be used alone, or two or more types may be used in combination.

[0056] Examples of binders include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. One type of binder may be used alone, or two or more types may be used in combination.

[0057] The slurry for forming plugged portions may contain a dispersant as appropriate. Examples of dispersants include ethylene glycol, dextrin, fatty acid soap, and polyalcohol. The dispersant may be used alone or in combination of two or more.

[0058] The openings of the cells can be filled with the slurry for forming plugging portions, for example, by the following "squeegee method." As shown in Fig. 4, a film 121 is attached to the upper end face (here, the outlet end face 106 in the figure) of the dried honeycomb formed body 400 fixed using a chuck 120, and a laser is irradiated onto the film 121 at positions corresponding to the arrangement conditions of the plugging portions, thereby forming a plurality of holes 126 in the film 121.

[0059] Thereafter, the plugging portion forming slurry 124 is placed on the film 121, and the squeegee 122 is moved along the film 121 in the direction of the arrow in Fig. 4. As a result, a certain amount of the plugging portion forming slurry 124 is filled into the cells 125 that are opened at positions corresponding to the holes 126 of the film 121.

[0060] The depth of the plugging portion can be changed by the number of times the squeegee 122 is moved, the contact angle between the squeegee 122 and the film 121, the pressing pressure of the squeegee 122 against the film 121, and the viscosity of the plugging portion forming slurry 124, etc.

[0061] After the plugging portion forming slurry 124 is filled, the film 121 is peeled off, and the entire honeycomb formed body 400 is dried. As a result, the plugging portion forming slurry 124 filled in the cells 125 is dried, and the plugging portions before firing are formed. The drying can be performed, for example, under conditions of a drying temperature of 100 to 230°C for about 60 to 150 seconds. After drying, the plugging portions protrude from the end face of the honeycomb formed body by the thickness of the film, and can be scraped off as necessary.

[0062] The material of the film is not particularly limited, but polypropylene (PP), polyethylene terephthalate (PET), polyimide, or Teflon (registered trademark) are preferred because they are easy to heat process to form holes in. The film also preferably has an adhesive layer, and the adhesive layer is preferably made of an acrylic resin, a rubber-based material (e.g., a rubber whose main component is natural rubber or synthetic rubber), or a silicone-based resin. The film can preferably be an adhesive film with a thickness of, for example, 20 to 50 μm.

[0063] In addition to the above-mentioned "squeegee method," another method for filling the openings of the cells with the plugging portion forming slurry is the "press-fit method." The "press-fit method" is a method in which an end face of a honeycomb formed body with a film attached and holes drilled therein is immersed in a liquid tank containing the plugging portion forming slurry, and the cells are filled with the plugging portion forming slurry. In this case, the depth of the plugging portions can be changed by changing the depth to which the honeycomb formed body is immersed in the plugging portion forming slurry.

[0064] The honeycomb formed body filled with the plugging portion forming slurry is then subjected to a degreasing process and a firing process, thereby manufacturing a honeycomb structure. The combustion temperature of the binder is about 200°C, and the combustion temperature of the pore-forming material is about 300 to 1000°C. Therefore, the degreasing process can be carried out by heating the honeycomb formed body to a temperature range of about 200 to 1000°C. The heating time is not particularly limited, but is usually about 10 to 100 hours. The honeycomb formed body after the degreasing process is called a calcined body. The firing process can be carried out by heating the calcined body to 1300 to 1450°C and holding it for 3 to 24 hours, for example, although it depends on the material composition of the honeycomb structure.

[0065] A catalyst can be supported on the partition walls of the honeycomb structure manufactured in this manner. An example of a method for supporting a catalyst on the partition walls is a method in which a catalyst slurry is introduced into the cells by a conventionally known suction method or the like, and the catalyst is deposited on the surfaces and pores of the partition walls, and then a high-temperature treatment is performed to bake the catalyst contained in the catalyst slurry onto the partition walls and support the catalyst. The types of catalyst are as exemplified above. [Example]

[0066] The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

[0067] (1. Manufacturing of honeycomb structure) [Cordierite Honeycomb Structures: Examples 1 to 21, Comparative Examples 1 to 9] 5 parts by mass of a pore-forming material, 60 parts by mass of a dispersion medium, and 4 parts by mass of an organic binder were added to 100 parts by mass of the cordierite-forming raw material, and the mixture was mixed and kneaded to prepare a clay. Alumina, aluminum hydroxide, kaolin, talc, and silica were used as the cordierite-forming raw material. Water was used as the dispersion medium. Methylcellulose was used as the organic binder. A water-absorbent resin with a median diameter of 20 μm was used as the pore-forming material. In this example, the median diameter of the raw material refers to the particle size (D50) at 50% of the integrated value in the particle size distribution determined by a laser diffraction / scattering method.

[0068] Next, the clay was extruded using a die for producing honeycomb formed bodies to obtain a honeycomb formed body having an overall cylindrical shape. The cell structure of the honeycomb formed body was in accordance with the "Cell Structure and Plugging Pattern" listed in Table 1 according to the test number. The specific cell structures listed in "Cell Structure and Plugging Pattern" are illustrated in Figures 5A to 5J. Figures 5A to 5J schematically show the opening shapes of the multiple inlet cells and multiple outlet cells observed at the inlet end face, the plugging pattern, and the repeating units that make up the plugging pattern. White cells represent inlet cells, and black cells represent outlet cells. At this stage, plugging portions have not been formed, but plugging portions will be formed at the inlet end face of the outlet cells. In the figures, I / O represents the ratio of the number of multiple inlet cells to the number of multiple outlet cells.

[0069] Next, the honeycomb formed body was dried in a microwave dryer and further dried in a hot air dryer, and then both end faces of the honeycomb formed body were cut to a predetermined size.

[0070] Next, a slurry for forming plugging portions was prepared using the same material as the honeycomb formed body. After that, using this slurry, plugging portions were formed in the openings of predetermined cells on the inlet end face side of the dried honeycomb formed body and in the openings of the remaining cells on the outlet end face side. The plugging portions were formed so as to obtain the "cell structure and plugging pattern" in Table 1 according to the test number.

[0071] Next, the honeycomb formed body with each plugged portion formed therein was degreased at approximately 200 to 1000°C in an air atmosphere, and further fired at approximately 1410 to 1440°C in an air atmosphere to produce a honeycomb structure corresponding to each test number. The honeycomb structure thus obtained had a cylindrical shape with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 330 mm. The length of the honeycomb structure in the cell extension direction was 178 mm. The honeycomb structures were prepared in the number required to specify the following specifications and properties.

[0072] [Silicon carbide honeycomb structure: Example 22, Comparative Example 10] SiC powder and Si powder were mixed in a mass ratio of SiC powder:Si powder = 80:20, and 3 mass parts of a pore-forming material and 7 mass parts of an organic binder were added to 100 mass parts of this mixture, and a dispersion medium was further added, followed by mixing and kneading to prepare a clay. Water was used as the dispersion medium, methyl cellulose was used as the organic binder, and a water-absorbent polymer with a median diameter of 20 μm was used as the pore-forming material.

[0073] Next, the clay was extruded using a die for producing a honeycomb formed body to obtain a honeycomb formed body having an overall rectangular parallelepiped shape. The cell structure of the honeycomb formed body was in accordance with the "cell structure and plugging pattern" shown in Table 1 according to the test number.

[0074] Next, the honeycomb formed body was dried in a microwave dryer and further dried in a hot air dryer, and then both end faces of the honeycomb formed body were cut to a predetermined size.

[0075] Next, a slurry for forming plugging portions was prepared using the same material as the honeycomb formed body. After that, using this slurry, plugging portions were formed in the openings of predetermined cells on the inlet end face side of the dried honeycomb formed body and in the openings of the remaining cells on the outlet end face side. The plugging portions were formed so as to obtain the "cell structure and plugging pattern" in Table 1 according to the test number.

[0076] Next, the honeycomb formed body with each plugged portion formed was degreased at approximately 400°C in an air atmosphere and further fired at approximately 1450°C in an Ar inert atmosphere to produce a honeycomb segment. The honeycomb segment thus obtained had a rectangular parallelepiped shape with square inlet and outlet end faces. The size of one side of the inlet and outlet end faces was 42 mm. The length of the honeycomb segment in the cell extension direction was 178 mm. A plurality of identical honeycomb segments were prepared, and a bonding material was sandwiched between their outer peripheral surfaces. A segment stack consisting of a total of 60 honeycomb segments was produced by combining them in an 8×8 matrix (however, the 4 corners were not required). The entire honeycomb structure was then bonded by applying external pressure as appropriate, and then dried at 120°C for 2 hours to obtain a bonded segment. The outer periphery of this bonded segment assembly was ground to form a cylindrical outer shape, and then a coating material with the same composition as the bonding material was applied to the ground surface to re-form the outer side wall. The honeycomb structure was then dried and hardened in air at 700°C for 2 hours to obtain the honeycomb structure for each test example. The honeycomb structure thus obtained had a cylindrical shape with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 330 mm. The length of the honeycomb structure in the cell extension direction was 178 mm. The honeycomb structures were prepared in the number required to specify the following specifications and characteristics.

[0077] (2. Honeycomb structure specifications) For the honeycomb structures for each test number manufactured above, the partition wall thickness (constant value), cell density, length of one side of the cell opening, offset when there are two types of cell openings, large and small, S2 / S1, proportion of inlet cells that are not adjacent to outlet cells, proportion of outlet cells adjacent only to inlet cells, opening ratio of the inlet end face, average linear expansion coefficient, average porosity of the partition walls, and I / O are shown in Table 1.

[0078] The thickness of the partition walls was measured by observation using a scanning electron microscope (SEM). The cell density means the cell density based on the total number of inlet cells and outlet cells, and was measured according to the method described above. The side length of the cell opening was measured by observation with a scanning electron microscope (SEM). When the cell opening was a single type of square or regular hexagon, the side length of the square or regular hexagon was shown. When there were two types of cell openings, a large octagon and a small square, the side length of the shorter side (the distance between the pair of opposing sides of the octagon of the large cell opening) and the side length of the square of the small cell opening were shown. The offset is the distance between the midpoint of a line segment connecting the centers of gravity of adjacent inlet and outlet cells across a partition wall in a cross section perpendicular to the extension direction of the multiple inlet and outlet cells, and the center of the partition wall that the line segment crosses. The offset was measured by observation with a scanning electron microscope (SEM). S1 represents the total surface area of ​​all partition walls separating the multiple inlet cells, excluding the inlet cells adjacent to the peripheral side wall. S1 was calculated using scanning electron microscope (SEM) observation. S2 represents the total surface area of ​​all partition walls sandwiched between adjacent inlet cells, excluding the inlet cells adjacent to the peripheral side wall. It was calculated using scanning electron microscope (SEM) observation. The average linear expansion coefficient represents the average linear expansion coefficient of the partition wall in the direction in which the inlet and outlet cells extend from room temperature to 800° C., and was measured by taking a sample of the partition wall and following the method described above. The average porosity of the partition walls was measured using Autopore 9500 (trade name) manufactured by Micromeritics according to the above-mentioned mercury intrusion method.

[0079] (3. Characteristics of honeycomb structure) The honeycomb structures prepared above according to the respective test numbers were used as exhaust gas filters, and the following properties were evaluated.

[0080] [Ash pile] A 330 mm diameter x 178 mm long filter was weighed and then installed in the exhaust system of a 13-liter diesel engine. Ash was deposited by repeating the WHTC cycle (World Harmonized Transient Cycle: see global technical regulation No. 4: TRANS / WP (unece.org)). Pressure drop was measured at the filter inlet every 10 hours at a flow rate of 1800 kg / hr and a temperature of 380°C. When the pressure drop reached 25 kPa, the filter was heat-treated in an electric furnace at 600°C for at least 3 hours to burn off the soot. The filter's weight and pressure drop at the same flow rate and temperature were then measured again. The WHTC cycle, heat treatment, weight measurement, and pressure drop measurements at the same flow rate and temperature were repeated every 5 hours until the pressure drop after soot burnoff reached 25 kPa. The weight difference from before the test was calculated, and the calculated value was divided by the volume of the filter to determine the weight (g) of ash accumulation per volume (L) based on the external dimensions of the filter (hereinafter referred to as "ash accumulation") when the pressure loss after burning off the soot reached 25 kPa.

[0081] In Comparative Example 1, which is an existing technology, the ash deposition was 40 g / L. Therefore, the evaluation of ash deposition was based on the following criteria. When the pressure loss reached 25 kPa, if the ash deposition was less than 40 g / L, a score of 0 was given. When the ash deposition was 40 g / L or more, the increase rate relative to 40 g / L multiplied by 1.0 was given a score. The results are shown in Table 1.

[0082] [Pressure drop gradient during PM accumulation] A 330mm diameter x 178mm long filter was installed in the exhaust system of a 13-liter diesel engine, and soot was allowed to accumulate on the filter. The fuel injection pressure was reduced to facilitate soot deposition, and the exhaust gas temperature at the filter inlet was kept below 280°C to prevent soot combustion. The engine was operated under low conditions, with the soot deposition rate in the filter ranging from approximately 1g / L to 6g / L, with pressure loss measured in approximately 1g / L increments. To measure the pressure loss, the engine power was increased, and the pressure and filter weight were measured at the inlet and outlet sides at a flow rate of 1800kg / hr and a temperature of 380°C. The pressure loss for each soot load was calculated. A graph was then created with the soot weight per volume (g / L) based on the filter's external dimensions on the x-axis and pressure loss (kPa) on the y-axis, and a straight line was fitted using the least squares method. Finally, the slope of the pressure drop (the increase in pressure drop kPa per 1 g / L of soot deposition) was calculated when the PM deposition rate increased from 1 g / L to 6 g / L.

[0083] In Comparative Example 1, which is an existing technology, the slope of pressure loss when PM accumulation was from 1 g / L to 6 g / L (hereinafter referred to as "pressure loss slope") was 1.0 kPa. Therefore, the evaluation of the pressure loss slope was based on the following criteria. A pressure loss slope of less than 0.9 kPa was assigned a score of 0. A pressure loss slope of 0.9 kPa to 1.1 kPa was considered to be at the same level as existing technology and assigned a score of 1, and a pressure loss slope of more than 1.1 kPa was assigned a score of the increase rate relative to 1.0 kPa x 1.0. The results are shown in Table 1.

[0084] [Crack Limit] A 330mm diameter x 178mm long filter was installed in the exhaust system of a 13-liter diesel engine, and soot was allowed to accumulate on the filter. The fuel injection pressure was reduced to facilitate soot deposition, and the exhaust gas temperature at the filter inlet was kept below 280°C to prevent soot combustion. The engine was then operated at a low temperature of less than 280°C at the filter inlet, with a flow rate of 600kg / hr. The exhaust gas temperature was then increased at a rate of 4°C / s to 650°C. The engine was then switched to idling, with the gas flow rate at the filter inlet rapidly reduced to 150kg / hr, while fuel injection was initiated to regenerate the filter. After filter regeneration, the filter was visually inspected for cracks. If no cracks were found, the weight of the soot deposits in the filter was increased, and the filter regeneration test was repeated. The weight of the soot deposits in the filter was gradually increased with each test. The maximum soot deposit weight at which cracks could be achieved without causing cracks was then determined. The maximum soot deposition weight (g / L) per volume based on the external dimensions of the filter at this time is defined as the "crack limit."

[0085] The cracking limit that does not cause problems in practical use is 5g / L. Therefore, the cracking limit was evaluated based on the following criteria: A cracking limit of less than 5g / L was given a score of 0; a cracking limit of 5g / L or more was given a score of 1.0. The results are shown in Table 1.

[0086] [comprehensive evaluation] The scores obtained from the above three items were multiplied together to give an overall evaluation. The results are shown in Table 1.

[0087] Comparative Example 1, which is an existing technology, received a score of 1.0 for each evaluation item, and also received an overall rating of 1.0. In contrast, Comparative Examples 2 to 10, which received an overall rating of 0, had significantly lower values ​​compared to existing technologies in at least one of ash deposition, pressure drop gradient during PM deposition, and crack limit. Lower ash deposition increases the frequency of filter regeneration and cleaning processes. Lower pressure drop gradient during PM deposition may reduce the accuracy of soot detection by the pressure sensor, and lower crack limit may result in damage to the filter during actual use, causing malfunctions. Therefore, Comparative Examples 2 to 10 are unsuitable.

[0088] Examples 1 to 22 exceeded the existing technology in at least one of the pressure drop gradients during ash deposition and PM deposition, and also passed the evaluation of the crack limit, so that they also exceeded the existing technology in the overall evaluation.

[0089] In Examples 2, 4, 6 to 8, 10 to 11, 14 to 18, and 20 to 22, the ash deposition was greater than that of the existing technology, and the pressure drop gradient during PM deposition was also greater than that of the existing technology. This resulted in a significant effect of improving the soot detection accuracy of the pressure sensor while reducing the frequency of filter regeneration and cleaning treatments.

[0090] [Table 1] [Explanation of symbols]

[0091] 100: Honeycomb structure 102: Outer wall 104: Inlet end face 106: Outlet end face 107: Opening 108: Introduction cell 109: Plugging part 110: Discharge cell 112: Bulkhead 120: Zipper 121: Film 122: Squeegee 124: Plugging slurry 125: Cell 126: Hole 400: Honeycomb molded body

Claims

1. A columnar honeycomb structure comprising: an outer peripheral side wall; a plurality of inlet cells arranged on an inner peripheral side of the outer peripheral side wall, extending from an inlet end face to an outlet end face, having openings at the inlet end faces and having plugging portions at the outlet end faces; and a plurality of outlet cells arranged on the inner peripheral side of the outer peripheral side wall, extending from the inlet end face to the outlet end face, having plugging portions at the inlet end faces and having openings at the outlet end faces, each of the plurality of inlet cells and the plurality of outlet cells is adjacent to at least one of the plurality of inlet cells and the plurality of outlet cells with a partition wall interposed therebetween; The cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 22 to 70 cells / cm 2 and the thickness of each of the partition walls is in the range of 0.15 mm or more and 0.38 mm or less, The opening ratio at the inlet end surface is 44% or more, and The total surface area of ​​all partition walls that separate the plurality of inlet cells, excluding the inlet cells adjacent to the outer peripheral side wall, is S 1 The total surface area of ​​all partition walls sandwiched between adjacent inlet cells among the plurality of inlet cells excluding the inlet cells adjacent to the outer peripheral side wall is S 2 Then, 33%≦S 2 / S 1 Satisfy ≦75% Honeycomb structure.

2. 2. The honeycomb structure according to claim 1, wherein the opening areas of the plurality of inlet cells are all the same except for the cells adjacent to the outer peripheral side wall.

3. 2. The honeycomb structure according to claim 1, wherein the opening areas of the plurality of inlet cells and the plurality of outlet cells are all the same except for those adjacent to the outer peripheral side wall.

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

5. 3. The honeycomb structure according to claim 1, wherein the opening shapes of the plurality of inlet cells and the plurality of outlet cells are all square except for those adjacent to the outer peripheral side wall.

6. 3. The honeycomb structure according to claim 1, wherein the opening shapes and opening areas of the plurality of inlet cells are all the same except for the one adjacent to the outer peripheral side wall.

7. 5. The honeycomb structure according to claim 4, wherein the length of one side of the square is 0.90 mm or more and 1.90 mm or less.

8. 6. The honeycomb structure according to claim 5, wherein the length of one side of the square is 0.90 mm or more and 1.90 mm or less.

9. 3. The honeycomb structure according to claim 1, wherein none of the plurality of discharge cells are adjacent to each other.

10. The average linear expansion coefficient of the partition wall from room temperature to 800°C in the direction in which the inlet cells and the outlet cells extend is 1.0 × 10 -6 3. The honeycomb structure according to claim 1, wherein the temperature is 100° C. or less.

11. 3. The honeycomb structure according to claim 1, wherein the partition walls contain cordierite.

12. 3. The honeycomb structure according to claim 1, wherein the thickness of each of the partition walls is in the range of 0.18 mm or more and 0.30 mm or less.

13. The cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 26 to 62 cells / cm 2 3. The honeycomb structure according to claim 1, wherein the thickness of the honeycomb structure is in the range of 1000 nm to 1000 nm.

14. 3. The honeycomb structure according to claim 1, wherein at least one of the plurality of inlet cells is not adjacent to any of the plurality of outlet cells.

15. 3. The honeycomb structure according to claim 1, wherein at least one of the plurality of discharge cells is adjacent to only the inlet cell.

16. The ratio of the number of the plurality of inlet cells to the number of the plurality of outlet cells is 1.5 to 2.0, and the cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 47 to 62 cells / cm 2 or the ratio of the number of the plurality of inlet cells to the number of the plurality of outlet cells is in the range of 3.0 to 4.0 and the cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is in the range of 28 to 43 cells / cm 2 3. The honeycomb structure according to claim 1, wherein the thickness of the honeycomb structure is in the range of 1000 nm to 1000 nm.

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