Honeycomb structure

Abstract

To provide a honeycomb structure capable of maintaining low maintenance cost and satisfying requirement characteristics of easy detection of a maintenance needing period by a pressure sensor on the basis of a PM deposition amount.SOLUTION: This columnar honeycomb structure comprises: an outer peripheral side wall; a plurality of introduction cells; and a plurality of discharge cells. At least some of the introduction cells are adjacent to at least some of the discharge cells with a partition wall therebetween. A cell density based on the total number of the introduction cells and the discharge cells is 35-47 cell / cm2. 0.78≤Din / Dout≤0.94 is satisfied, in which Dout denotes an average value among opening diameters of the discharge cells excluding those adjacent to the outer peripheral side wall among the discharge cells, and Din denotes an average value among opening diameters of the introduction cells excluding those adjacent to the outer peripheral side wall among the introduction cells.SELECTED DRAWING: Figure 1

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 on 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 due to PM accumulation 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 modifying the arrangement and size of the inlet and outlet cells (see Patent Documents 1 and 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 drop between the filter inlet and outlet using a pressure sensor. However, if pressure drop remains low after a large amount of PM accumulates on the filter, predicting the amount of PM accumulation based on the pressure drop becomes difficult when filter regeneration is controlled using a pressure sensor, resulting in excessive PM accumulation and filter damage. Therefore, it is desirable to prevent excessive pressure drop after PM accumulation, thereby reducing the frequency of filter regeneration and cleaning and reducing maintenance costs. At the same time, it is desirable to increase the change in pressure drop (pressure drop slope) in response to the amount of PM accumulated, making it easier for the pressure sensor to detect the appropriate amount of PM accumulation for filter regeneration or cleaning. Furthermore, the filter must have a practical thermal capacity sufficient to prevent excessive temperature rise during filter regeneration.

[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 satisfy the required characteristics of having a practical heat capacity that does not cause excessive temperature rise during filter regeneration, being able to keep maintenance costs low, and being able to easily detect the time when maintenance is necessary 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, at least some of the inlet cells are adjacent to at least some of the outlet cells across a partition wall, A cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 35 to 47 cells / cm 2 and The average opening diameter of the discharge cells excluding those adjacent to the outer peripheral side wall among the plurality of discharge cells is D out The average opening diameter of the plurality of introduction cells excluding those adjacent to the outer peripheral side wall is defined as D in Then, 0.78≦D in / D out ≦0.94, Honeycomb structure. [Aspect 2] The average value D of the opening diameters of the plurality of introduction cells in is 1.07 mm or more and 1.29 mm or less, except for those adjacent to the outer peripheral side wall, The average value D of the opening diameters of the plurality of discharge cells out is 1.27 mm or more and 1.61 mm or less, except for those adjacent to the outer peripheral side wall, 2. The honeycomb structure according to claim 1. [Aspect 3] 3. The honeycomb structure according to embodiment 1 or 2, wherein the partition walls have an average thickness of 0.19 mm or more and 0.26 mm or less. [Aspect 4] 4. The honeycomb structure according to any one of aspects 1 to 3, wherein the partition walls have an average porosity of 52 to 60%. [Aspect 5] A honeycomb structure according to any one of aspects 1 to 4, wherein the ratio of the number of the plurality of discharge cells excluding those adjacent to the outer peripheral side wall to the number of the plurality of inlet cells excluding those adjacent to the outer peripheral side wall is 0.9 to 1.1. [Aspect 6] When the deposition mass of particulate matter including soot per unit volume of the honeycomb structure is 1 g / L, the pressure loss when exhaust gas having a temperature of 250°C and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is defined as P1, When the deposition mass of particulate matter including soot per unit volume of the honeycomb structure is 3 g / L, the pressure loss when exhaust gas having a temperature of 250°C and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is P2, 54%<(P2-P1) / P1 is satisfied, The honeycomb structure according to any one of the first to fifth aspects. [Aspect 7] 7. The honeycomb structure according to any one of aspects 1 to 6, wherein the partition walls contain cordierite. [Aspect 8] 8. The honeycomb structure according to any one of aspects 1 to 7, wherein a catalyst is supported in the inlet cells. [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 accumulation of PM is prevented from becoming excessively large, thereby reducing the frequency of filter regeneration and cleaning processes. At the same time, by increasing the change in pressure loss (pressure loss slope) corresponding to the amount of accumulated PM, it is possible to easily detect the amount of PM accumulation suitable for filter regeneration and cleaning processes using a pressure sensor. Furthermore, since excessive temperature rise does not occur during filter regeneration, the risk of filter damage is also reduced. This allows for maintenance costs to be kept low, and a filter can be obtained in which the time when maintenance is required can be easily detected using a pressure sensor based on the amount of PM accumulation. Therefore, it is possible to reduce the risk of filter damage due to excessive PM accumulation. As such, it can be said that 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. 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) Basic 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, at least some of the inlet cells 108 are adjacent to at least some of the discharge cells 110 of the plurality of discharge cells 110, with partition walls 112 sandwiched between them. When the inlet cells 108 and the discharge cells 110 are adjacent to each other with partition walls 112 sandwiched between them, the surfaces of the partition walls 112 contribute 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 walls 112 located between the adjacent inlet cells 108 and discharge cells 110 and flows into the discharge cells 110. The particulate matter cannot pass through the partition walls 112 and is therefore captured and deposited within the inlet cells 108. After particulate matter has been removed, the clean exhaust gas that entered the exhaust cell 110 travels downstream within the exhaust cell 110 and exits the downstream outlet end face 106 .

[0014] 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 exhibits a filtering function by being adjacent to the inlet cell 108. It is also desirable that none of the plurality of discharge cells 110 are adjacent to each other.

[0015] 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.

[0016] There are no particular restrictions on the height of the honeycomb structure (the length from the inlet end face to the outlet end face) and it may be set appropriately depending on the application and required performance. The height of the honeycomb structure may be, for example, 40 to 450 mm, preferably 60 to 400 mm, and more preferably 100 to 330 mm. There are also no particular restrictions on the relationship between the height of the honeycomb structure and the maximum diameter of each end face (the maximum length of the diameter passing through the center of gravity of each end face of the honeycomb structure). Therefore, the height of the honeycomb structure may be longer or shorter than the maximum diameter of each end face.

[0017] (2) Cell density The cell density is an index that represents the number of cells per unit area when observing the honeycomb structure from the inlet end face or the outlet end face. The cell density based on the total number of multiple inlet cells and multiple outlet cells is 35 to 47 cells / cm. 2 Preferably, the density is 37 to 43 cells / cm. 2 More preferably, it is 40 to 41 cells / cm 2 The cell density is calculated by dividing the total number of the plurality of inlet cells and the plurality of outlet cells (including plugged cells, outlet cells adjacent to the outer peripheral side wall, and inlet cells adjacent to the outer peripheral side wall) by the area of ​​one end face of the honeycomb structure excluding the outer peripheral side wall.

[0018] (3) Aperture diameter ratio (D in / D out ) In conventional honeycomb structures, the opening diameter of the inlet cells is made larger than the opening diameter of the exhaust cells to suppress the increase in pressure drop during PM accumulation. However, it has been found that this type of structure tends to result in a gentle pressure drop gradient. On the other hand, in a honeycomb structure according to one embodiment of the present invention, the opening diameter of the inlet cells is made appropriately smaller than the opening diameter of the exhaust cells to promote the increase in pressure drop during PM accumulation. Furthermore, by making the opening diameter of the inlet cells appropriately smaller than the opening diameter of the exhaust cells, the initial pressure drop can be reduced, which also contributes to improved fuel efficiency.

[0019] Specifically, the average opening diameter of the discharge cells excluding those adjacent to the outer peripheral side wall among the multiple discharge cells is defined as D out The average opening diameter of the multiple inlet cells excluding those adjacent to the outer peripheral side wall is D in Then, 0.78≦D in / D out ≦0.94, and 0.79≦D in / D out ≦0.88 is more preferable, and 0.81≦D in / D out It is even more preferable that ≦0.86 is satisfied. The opening diameter of each of the multiple inlet cells is defined as a circle equivalent diameter calculated based on the opening area of ​​the inlet cell. The average value D in is calculated based on the opening diameters of all the inlet cells excluding those adjacent to the outer peripheral side wall among the plurality of inlet cells. The opening diameter of each of the multiple discharge cells is defined as the equivalent circle diameter calculated based on the opening area of ​​the discharge cell. out is calculated based on the opening diameters of all the discharge cells excluding those adjacent to the outer peripheral side wall among the plurality of discharge cells.

[0020] (4) Opening diameter From the viewpoint of suppressing the initial pressure loss and preventing the pressure loss after PM accumulation from becoming excessively large, the average opening diameter D of the multiple introduction cells is set. in is preferably 1.07 mm or more and 1.29 mm or less, more preferably 1.13 to 1.21 mm, and even more preferably 1.15 to 1.19 mm, excluding those adjacent to the outer peripheral side wall. out is preferably 1.27 mm or more and 1.61 mm or less, more preferably 1.31 to 1.53 mm, and even more preferably 1.45 to 1.53 mm, excluding those adjacent to the outer peripheral side wall.

[0021] (5) Average thickness of partition walls From the viewpoint of ensuring practical heat capacity and strength of the honeycomb structure while satisfying the above-mentioned predetermined cell density, the average thickness of the partition walls 112 is preferably 0.19 mm or more and 0.26 mm or less, more preferably 0.20 mm or more and 0.24 mm or less, and even more preferably 0.21 mm or more and 0.23 mm or less. FIG. 3 shows a schematic partial enlarged view of the partition walls 112 of a honeycomb structure 100 in which the opening shape of the inlet cells 108 is rectangular and the opening shape of the outlet cells 110 is octagonal, 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 connecting the centers of gravity O of adjacent cells across the partition walls in a cross section perpendicular to the cell extension direction (height direction of the honeycomb structure). The average thickness of the partition walls 112 is calculated based on the thicknesses of all the partition walls 112. In addition, when two cells are adjacent across a partition wall, it means that when the partition wall of the honeycomb structure is observed from a cross section perpendicular to the cell extension direction, the two cells are adjacent across opposing wall surfaces of one partition wall (the sides of the polygon that defines the cell), and does not include cases where the two cells are adjacent across the vertices of the polygon that defines the two cells.

[0022] (6) Average porosity of partition walls From the viewpoint of reducing pressure loss, the lower limit of the average porosity of the partition walls 112 is preferably 52% or more, and more preferably 53% or more. Furthermore, from the viewpoint of increasing the heat capacity and mechanical strength of the honeycomb structure, the upper limit of the average porosity of the partition walls is preferably 60% or less, and more preferably 58% or less. Therefore, the average porosity of the partition walls is preferably, for example, 52 to 60%, and more preferably 53 to 58%. In this specification, the porosity of the partition walls is measured by mercury porosimetry 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 calculating the porosity of each sample, and the measured value is the average value.

[0023] (7) Ratio of the number of inlet cells to the number of outlet cells From the viewpoint of increasing the pressure drop gradient while suppressing an increase in pressure drop, the ratio of the number of the plurality of inlet cells to the number of the plurality of outlet cells is preferably 0.9 to 1.1, more preferably 0.95 to 1.05, even more preferably 0.99 to 1.01, and most preferably 1. When calculating the ratio of the number of outlet cells to the number of outlet cells, the outlet cells adjacent to the outer peripheral side wall and the inlet cells adjacent to the outer peripheral side wall are not counted.

[0024] (8) Cell opening shape The opening shape of the inlet cells is not particularly limited. For example, the cross section perpendicular to the cell extension direction of the honeycomb structure may be polygonal (quadrilateral (rectangle, square), pentagon, hexagon, heptagon, octagon, etc.), round (circular, elliptical, oval, egg, oval, etc.), etc. These shapes may be a single shape or a combination of two or more shapes. Among these, for the reason of reducing pressure loss, it is preferable that the opening shape of each of the multiple inlet cells, except for those adjacent to the outer peripheral side wall, is all quadrangular, and among these, square is more preferable. When the opening shape of the inlet cells and discharge cells is polygonal, the corners may be rounded. Note that in this specification, even rounded corners are treated as polygonal.

[0025] The opening shape of the discharge cell is not particularly limited, and may be set to match the opening shape of the inlet cell. For example, if the opening shape of the inlet cell is rectangular, it is preferable to make the discharge cell octagonal.

[0026] (9) Pressure drop slope If the change in pressure loss (pressure loss gradient) corresponding to the amount of PM accumulated in the honeycomb structure is large, it becomes easier for the pressure sensor to detect the amount of PM accumulation suitable for filter regeneration or cleaning treatment. Specifically, when the deposition mass of particulate matter including soot per unit volume of the honeycomb structure is 1 g / L, the pressure loss when exhaust gas with a temperature of 250°C and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is defined as P1, When the deposition mass of particulate matter including soot per unit volume of the honeycomb structure is 3 g / L, the pressure loss when exhaust gas with a temperature of 250°C and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is P2, It is preferable to satisfy 54%<(P2-P1) / P1, more preferable to satisfy 57%≦(P2-P1) / P1, and even more preferable to satisfy 61%≦(P2-P1) / P1. Furthermore, from the viewpoint of suppressing an excessive increase in pressure drop and ensuring practicality as a filter, it is preferable to satisfy (P2-P1) / P1≦76%, more preferably to satisfy (P2-P1) / P1≦72%, and even more preferably to satisfy (P2-P1) / P1≦69%. Therefore, it is preferable that the pressure loss gradient of the honeycomb structure satisfies, for example, 54%<(P2-P1) / P1≦76%, more preferably 57%≦(P2-P1) / P1≦72%, and even more preferably 61%≦(P2-P1) / P1≦69%.

[0027] From the viewpoint of suppressing an excessive increase in pressure drop and ensuring practicality as a filter, the upper limit of P2 is preferably 5.00 kPa or less, more preferably 4.94 kPa or less, and even more preferably 4.93 kPa or less. From the viewpoint of increasing the pressure drop gradient, the lower limit of P2 is preferably 4.14 kPa or more, more preferably 4.38 kPa or more, and even more preferably 4.91 kPa or more.

[0028] (10)Material From the viewpoint of obtaining excellent thermal shock resistance, at least the partition walls of the honeycomb structure, preferably the outer peripheral side walls and partition walls, more preferably the outer peripheral side walls, partition walls and plugging portions contain one or more materials selected from cordierite, silicon carbide, silicon-silicon carbide composite material, silicon nitride, mullite, alumina and aluminum titanate.

[0029] The outer peripheral side walls, partition walls, and plugging portions of the honeycomb structure may contain ceramics other than those mentioned above. Examples of the other ceramics include zirconium phosphate, cordierite-silicon carbide composite, zirconia, spinel, indialite, sapphirine, corundum, titania, and ceria. These other ceramics may be contained singly or in combination of two or more.

[0030] 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%.

[0031] 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 Malvern 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.

[0032] 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.

[0033] 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.

[0034] The honeycomb structure can also be used as a catalyst carrier. A catalyst suitable for the purpose can be supported on the surface of the partition wall. The catalyst is preferably supported within the inlet cells. 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 may contain, as appropriate, 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.

[0035] (11) Density From the viewpoint of ensuring practical heat capacity, it is preferable that the honeycomb structure has a large mass per volume, i.e., a large density. The density here is a value calculated based on the volume measured from the external dimensions of the honeycomb structure, and does not take into account the internal cell structure or pores. Specifically, the lower limit of the density of the honeycomb structure is 0.36 g / cm. 3 It is preferable that the concentration is 0.37 g / cm or more. 3 More preferably, it is 0.38 g / cm or more. 3 Although there is no particular upper limit to the density of the honeycomb structure, from the viewpoint of ease of manufacture in consideration of the above-mentioned cell structure and materials, it is preferable that the upper limit be 0.41 g / cm. 3 Preferably, it is 0.40 g / cm or less. 3 More preferably, it is 0.39 g / cm or less. 3 Therefore, the density of the honeycomb structure is, for example, 0.36 to 0.41 g / cm 3 or less. 3 It is preferable that the density is 0.37 to 0.40 g / cm 3 More preferably, it is 0.38 to 0.39 g / cm 3 It is even more preferable that:

[0036] (2. Manufacturing method of honeycomb structure) 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.

[0037] 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).

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[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 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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]

[0058] 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.

[0059] (1. Manufacturing of honeycomb structure) [Cordierite Honeycomb Structures: Examples 1 to 10, Comparative Examples 1 to 4] Five 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. Here, the median diameter of the raw material refers to the particle size at 50% of the cumulative value (D50) in the particle size distribution determined by laser diffraction and scattering.

[0060] Next, the clay was extrusion-molded using a die for producing a honeycomb formed body, to obtain a honeycomb formed body having an overall cylindrical shape. The structure of the die was changed depending on the test number.

[0061] 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.

[0062] Next, a slurry for forming plugging portions was prepared using the same material as the honeycomb formed body. Then, using this slurry, plugging portions were formed at the openings of predetermined cells on the inlet end face side of the dried honeycomb formed body and at the openings of the remaining cells on the outlet end face side, so that the inlet cells and the outlet cells were alternately adjacent to each other.

[0063] Next, the honeycomb formed body with each plugging portion formed thereon was degreased and fired to produce a honeycomb structure corresponding to each test number. The honeycomb structure thus obtained had a cylindrical shape with circular inlet and outlet end faces. The diameters of the inlet and outlet end faces were 228.6 mm. The length of the honeycomb structure in the cell extension direction was 184.2 mm. In Comparative Example 1, the opening shape of the inlet cells was octagonal except for those adjacent to the outer peripheral side wall, and the opening shape of the outlet cells was square except for those adjacent to the outer peripheral side wall. In Examples 1 to 10 and Comparative Examples 3 and 4, the opening shape of the inlet cells was square except for those adjacent to the outer peripheral side wall, and the opening shape of the outlet cells was octagonal except for those adjacent to the outer peripheral side wall. In Comparative Example 2, the opening shapes of both the inlet and outlet cells were square. The average depth of the plugging portions at the inlet and outlet end faces was approximately 7 mm. The honeycomb structures were prepared in the number necessary to specify the following properties.

[0064] (2. Structural characteristics of honeycomb structures) Table 1 shows the following structural characteristics of the honeycomb structures manufactured above according to each test number. Cell density Average thickness of partition walls Average opening diameter D of multiple inlet cells excluding those adjacent to the outer side wall in Average opening diameter D of multiple discharge cells excluding those adjacent to the outer side wall out ·Aperture diameter ratio (D in / D out ) Average porosity of partition walls Ratio of the number of inlet cells to the number of outlet cells Density (mass of honeycomb structure ÷ external dimensions)

[0065] 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 average thickness of the partition walls was measured by observation with a scanning electron microscope (SEM) or by a microscope. The opening diameters of the inlet cell and outlet cell were calculated by observation with a scanning electron microscope (SEM) or by using a microscope. The average value D is calculated based on the opening diameter of all discharge cells except those adjacent to the outer peripheral wall. out was calculated. The average value D is calculated based on the opening diameter of all the inlet cells except for those adjacent to the outer wall. in was calculated. The porosity of the partition walls was measured using Autopore 9500 (trade name) manufactured by Micromeritics according to the above-mentioned mercury intrusion method. The ratio of the number of inlet cells to the number of outlet cells was calculated by visually counting the number of outlet cells and the number of outlet cells, excluding those adjacent to the peripheral sidewall.

[0066] (3. Functional properties of honeycomb structures) The honeycomb structures prepared above according to the respective test numbers were used as exhaust gas filters, and the following properties were evaluated.

[0067] [Pressure loss characteristics] An exhaust gas filter was installed in the exhaust system of a 13-liter diesel engine, and a soot deposition test was conducted on the filter. The fuel injection pressure was reduced to facilitate soot deposition, and the engine was operated under low exhaust gas temperatures below 280°C at the filter inlet to prevent soot combustion. The pressure loss (initial pressure loss) at the start of the test (before soot deposition), the pressure loss (P1) when the soot deposition amount (g) per liter of filter volume was 1 g / L, and the pressure loss (P2) when the soot deposition amount (g) per liter of filter volume was 3 g / L were measured. The engine power was increased to measure the pressure loss as exhaust gas at a temperature of 250°C and a flow rate of 480 kg / hr passed from the inlet end to the outlet end of the filter. The results are shown in Table 1.

[0068] With Comparative Example 2, which is a representative example of a honeycomb structure according to the prior art, as a standard, the pass criteria for pressure loss characteristics are to satisfy all of the following: The pass criteria for pressure loss characteristics were determined in consideration of the impact on fuel economy. Initial pressure loss is less than 1.01 kPa The pressure loss (P1) when the soot deposition amount is 1g / L is 3.07kPa or less The pressure loss (P2) when the soot deposition amount is 3g / L is 5.00kPa or less. The pressure drop gradient index (P2-P1) / P1 is over 54%

[0069] [Table 1]

[0070] [Consideration] In Comparative Example 1, the opening diameter of the inlet cell was larger than the opening diameter of the outlet cell, and therefore the pressure drop gradient was small. In Comparative Example 2, the opening diameter of the discharge cell and the opening diameter of the inlet cell were the same, and although there was an improvement over Comparative Example 1, the pressure drop gradient was still small. In Comparative Example 3, the opening diameter of the inlet cell was smaller than the opening diameter of the outlet cell, so the pressure drop gradient was large, but the opening diameter of the inlet cell was too small, which resulted in an increase in the initial pressure drop. In Comparative Example 4, the cell density was too small, and the pressure loss during soot deposition increased excessively. In contrast, in Examples 1 to 10, the cell density, opening diameter ratio, etc. were appropriate, so that the initial pressure drop was lower than in Comparative Example 2, while the pressure drop during soot deposition increased appropriately, resulting in a large pressure drop gradient. Also, in view of the density, the examples had a practical heat capacity. [Explanation of symbols]

[0071] 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, at least some of the inlet cells are adjacent to at least some of the outlet cells across a partition wall, A cell density based on the total number of the plurality of inlet cells and the plurality of outlet cells is 35 to 47 cells / cm 2 and The average value of the opening diameter of the discharge cells excluding those adjacent to the outer peripheral side wall among the plurality of discharge cells is D out The average opening diameter of the plurality of introduction cells excluding those adjacent to the outer peripheral side wall is defined as D in Then, 0.78≦D in / D out ≦0.94, Honeycomb structure.

2. The average value D of the opening diameters of the plurality of introduction cells in is 1.07 mm or more and 1.29 mm or less, except for those adjacent to the outer peripheral side wall, The average value D of the opening diameters of the plurality of discharge cells out is 1.27 mm or more and 1.61 mm or less, except adjacent to the outer peripheral side wall; The honeycomb structure according to claim 1 .

3. 2. The honeycomb structure according to claim 1, wherein the partition walls have an average thickness of 0.19 mm or more and 0.26 mm or less.

4. 3. The honeycomb structure according to claim 1, wherein the partition walls have an average porosity of 52 to 60%.

5. The honeycomb structure according to claim 1 or 2, wherein the ratio of the number of discharge cells excluding those adjacent to the outer peripheral side wall among the plurality of discharge cells to the number of inlet cells excluding those adjacent to the outer peripheral side wall among the plurality of inlet cells is 0.9 to 1.

1.

6. When the deposition mass of particulate matter containing soot per unit volume of the honeycomb structure is 1 g / L, the pressure loss when exhaust gas having a temperature of 250° C. and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is defined as P 1 year, When the deposition mass of particulate matter containing soot per unit volume of the honeycomb structure is 3 g / L, the pressure loss when exhaust gas at a temperature of 250° C. and a flow rate of 480 kg / hr passes from the inlet end face to the outlet end face is defined as P 2 Then, 54% < (P 2 -P 1 ) / P 1 fulfill, The honeycomb structure according to claim 1 or 2.

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

8. 3. The honeycomb structure according to claim 1, wherein a catalyst is supported in the inlet cells.

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