Honeycomb structure and method for manufacturing the same

Abstract

To provide a honeycomb structure capable of achieving both high collection efficiency and low pressure loss performance for particulates in a higher dimension while utilizing excellent thermal shock resistance which is a characteristic of crystalline cordierite.SOLUTION: A honeycomb structure has a plurality of cell channels passing through the inside of the honeycomb structure and partitioned by a porous partition wall. The honeycomb structure contains 80.0 to 94.0 mass% of cordierite as a main crystal phase and ceria included in a sub-crystal phase. A porosity of the porous partition wall measured by a mercury intrusion method is 60% or more. In the porous partition wall, in a volume-based cumulative pore size distribution measured by the mercury intrusion method, a 10% accumulation pore diameter (D10), a 50% accumulation pore diameter (D50) and a 90% accumulation pore diameter (D90) from a small pore side satisfy a relation of (D90-D10) / D50≤1.2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a honeycomb structure and a method for manufacturing the same.

Background Art

[0002] Exhaust gas discharged from internal combustion engines such as diesel engines contains a large amount of particulate matter (particulates) mainly composed of carbon, which causes environmental pollution. Therefore, generally, an exhaust system of a diesel engine or the like is equipped with a filter (Diesel Particulate Filter: DPF) for collecting particulates. In recent years, particulates discharged from gasoline engines have also been regarded as a problem, and gasoline engines are also being equipped with filters (Gasoline Particulate Filter: GPF).

[0003] Such filters often use a honeycomb structure. In addition, as a material constituting the honeycomb structure, cordierite is frequently used because of its high thermal shock resistance. A porous honeycomb structure mainly composed of cordierite is obtained by kneading a raw material composition obtained by appropriately adding a cordierite-forming raw material, a dispersion medium, a pore-forming material, a binder, and various additives to form a clay, and then extruding it through a predetermined die to produce a honeycomb-shaped molded body (honeycomb molded body). This honeycomb molded body can be manufactured by drying and then firing it.

[0004] Conventionally, in a honeycomb structure mainly composed of cordierite, it has been required to have a high cordierite crystal content (phase) in terms of ensuring thermal shock resistance due to low thermal expansion and increasing strength, and various raw material compositions and firing conditions have been studied (Patent Documents 1 to 3).

[0005] In addition, as one of the parameters affecting the performance of the honeycomb structure, the porosity and the pore size distribution are known. And by controlling the porosity and the pore size distribution, techniques have been developed to improve mechanical strength, the coefficient of thermal expansion, etc. and to reduce the pressure loss when exhaust gas flows through (Patent Documents 4 to 8).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Summary of the Invention

Problems to be Solved by the Invention

[0007] On the other hand, in a honeycomb structure having a high cordierite crystal amount (phase), there is still room for improvement from the viewpoint of achieving both high collection efficiency for particulate matter and low pressure loss performance, and further performance improvement is required.

[0008] The present invention has been made in view of the above circumstances, and in one embodiment, an object is to provide a honeycomb structure that can achieve both high collection efficiency for particulate matter and low pressure loss performance in a higher dimension while taking advantage of the excellent thermal shock resistance characteristic of crystalline cordierite. Further, in another embodiment of the present invention, an object is to provide a method for manufacturing such a honeycomb structure. **Means for Solving the Problems**

[0009] The present inventors have found that cordierite crystals synthesized (fired) from a plurality of raw materials of a magnesia source, a silica source, and an alumina source tend to have a broad pore size distribution, which hinders the achievement of both high collection efficiency for particulate matter and low pressure loss performance. The present invention has been completed based on this finding and is exemplified below.

[0010] [Aspect 1] A honeycomb structure, having a plurality of cell channels that pass through the inside of the honeycomb structure and are partitioned by porous partition walls, containing 80.0 to 94.0% by mass of cordierite as the main crystal phase and ceria contained in the secondary crystal phase, wherein the porous partition wall has a porosity of 60% or more as measured by mercury intrusion porosimetry, and in the cumulative pore size distribution based on volume measured by mercury intrusion porosimetry for the porous partition wall, the cumulative 10% pore size (D10), cumulative 50% pore size (D50), and cumulative 90% pore size (D90) from the small pore side satisfy the relationship of (D90 - D10) / D50 ≤ 1.2, a honeycomb structure. [Aspect 2] The honeycomb structure according to Aspect 1, wherein the cumulative 50% pore size (D50) of the porous partition wall is 10 to 20 μm. [Aspect 3] The honeycomb structure according to Aspect 1 or 2, wherein the cumulative 10% pore size (D10) of the porous partition wall is 8 μm or more and the cumulative 90% pore size (D90) is 34 μm or less. [Aspect 4] The honeycomb structure according to any one of Aspects 1 to 3, further containing one or more compounds selected from mullite, spinel, sapphirine, and cristobalite as a secondary crystalline phase. [Aspect 5] The honeycomb structure according to Aspect 4, wherein the total content of ceria and one or more compounds selected from mullite, spinel, sapphirine, and cristobalite is 4.0 to 20.0% by mass. [Aspect 6] The honeycomb structure according to any one of Aspects 1 to 5, wherein the content of ceria is 0.5 to 5.0% by mass. [Aspect 7] The linear expansion coefficient in the direction in which the cell channels extend is 0.6×10 -6 / K to 2.0×10 -6 / K. The honeycomb structure according to any one of Aspects 1 to 6. [Aspect 8] A method for manufacturing a honeycomb structure, After kneading a raw material composition containing a cordierite-forming raw material, ceria, a dispersion medium, a pore-forming material, and a binder to form a green body, the green body is extruded to obtain a honeycomb green body having a plurality of cell channels passing through the inside of the honeycomb green body and partitioned by porous partitions. A step of obtaining a honeycomb green body, A step of firing the honeycomb green body, Including, In the step of firing, when the maximum temperature during firing is X (°C), the holding time at the maximum temperature is Y (hr), and the content of ceria with respect to 100 parts by mass of the cordierite-forming raw material in the honeycomb green body is Z (parts by mass), 160≦(X - 1345)×Y×(Z + 0.5) 2 ≦7680 The manufacturing method is carried out so that the inequality holds.

Advantages of the Invention

[0011] According to an embodiment of the present invention, while taking advantage of the excellent thermal shock resistance characteristic of crystalline cordierite, it becomes possible to achieve both a high collection efficiency for particulates and a low pressure loss performance in a higher dimension. Therefore, the honeycomb structure can be suitably used as a filter that requires high performance.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0013] 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 design changes, improvements, etc. can be appropriately added based on the ordinary knowledge of those skilled in the art without departing from the spirit of the present invention.

[0014] (1. Honeycomb Structure) The honeycomb structure according to an embodiment of the present invention has a plurality of cell channels that pass through the inside of the honeycomb structure and are partitioned by porous partitions. In one embodiment, the honeycomb structure is provided as a wall-through type or wall-flow type columnar honeycomb structure. The use of the honeycomb structure is not particularly limited. Exemplarily, it is used in various industrial applications such as heat sinks, filters (e.g., GPF, DPF), catalyst carriers, sliding parts, nozzles, heat exchangers, electrical insulation members, and parts for semiconductor manufacturing devices. Among them, it can be suitably used as a filter for collecting particulate matter contained in exhaust gas from internal combustion engines, boilers, etc., and as a catalyst carrier for exhaust gas purification catalysts. In particular, the honeycomb structure can be suitably used as an automotive exhaust gas filter and / or a catalyst carrier.

[0015] FIG. 1 and FIG. 2 respectively illustrate a schematic perspective view and a cross-sectional view of a wall-through type honeycomb structure 100. This honeycomb structure 100 includes an outer peripheral side wall 102 and a porous partition 112 that is disposed on the inner peripheral side of the outer peripheral side wall 102 and partitions and forms a plurality of cells 108 that form a fluid flow path (cell channel) from a first bottom surface 104 to a second bottom surface 106. In this honeycomb structure 100, both ends of each cell 108 are open, and the exhaust gas that flows into one cell 108 from the first bottom surface 104 is purified while passing through the cell and flows out from the second bottom surface 106. Here, the first bottom surface 104 is regarded as the upstream side of the exhaust gas, and the second bottom surface 106 is regarded as the downstream side of the exhaust gas. However, the distinction between the first bottom surface and the second bottom surface is for convenience, and the second bottom surface 106 may be regarded as the upstream side of the exhaust gas, and the first bottom surface 104 may be regarded as the downstream side of the exhaust gas.

[0016] Figures 3 and 4 respectively illustrate a schematic perspective view and a cross-sectional view of a honeycomb structure 200 of the wall flow type. This honeycomb structure 200 includes an outer peripheral side wall 202 and a porous partition wall 212 disposed on the inner peripheral side of the outer peripheral side wall 202 and partitioning a plurality of cells 208a, 208b that form fluid flow paths (cell channels) from a first bottom surface 204 to a second bottom surface 206. In the honeycomb structure 200, the plurality of cells 208a, 208b are disposed inside the outer peripheral side wall 202, extend from the first bottom surface 204 to the second bottom surface 206, and include a plurality of first cells 208a having an opening at the first bottom surface 204 and having a plugging portion 209 at the second bottom surface 206, and a plurality of second cells 208b disposed inside the outer peripheral side wall 202, extending from the first bottom surface 204 to the second bottom surface 206, having a plugging portion 209 at the first bottom surface 204, and having an opening at the second bottom surface 206. And in this honeycomb structure 200, the first cells 208a and the second cells 208b are alternately adjacent to each other with the porous partition wall 212 interposed therebetween.

[0017] When exhaust gas containing particulate matter such as soot is supplied to the first bottom surface 204 on the upstream side of the honeycomb structure 200, the exhaust gas is introduced into the first cell 208a and proceeds downstream inside the first cell 208a. Since the first cell 208a has a plugging portion 209 at the second bottom surface 206 on the downstream side, the exhaust gas permeates through the porous partition wall 212 partitioning the first cell 208a and the second cell 208b and flows into the second cell 208b. Since the particulate matter cannot pass through the porous partition wall 212, it is collected and deposited inside the first cell 208a. After the particulate matter is removed, the clean exhaust gas that has flowed into the second cell 208b proceeds downstream inside the second cell 208b and flows out from the second bottom surface 206 on the downstream side. Here, the first bottom surface 204 is regarded as the upstream side of the exhaust gas, and the second bottom surface 206 is regarded as the downstream side of the exhaust gas. However, the distinction between the first bottom surface and the second bottom surface is for convenience, and the second bottom surface 206 may be regarded as the upstream side of the exhaust gas, and the first bottom surface 204 may be regarded as the downstream side of the exhaust gas.

[0018] There is no restriction on the bottom surface shape of the honeycomb structure. For example, it can be a round shape such as a circular shape, an elliptical shape, a race track shape, and an oval shape, a polygonal shape such as a triangular shape and a square shape, and other irregular shapes. The illustrated honeycomb structure has a circular bottom surface shape and is cylindrical as a whole.

[0019] The height of the honeycomb structure (the length from the first bottom surface to the second bottom surface) is not particularly restricted and may be appropriately set according to the use and required performance. The height of the honeycomb structure can be, for example, 40 mm to 450 mm. There is also no particular restriction on the relationship between the height of the honeycomb structure and the maximum diameter of each bottom surface (the maximum length among the diameters passing through the center of gravity of each bottom surface of the honeycomb structure). Therefore, the height of the honeycomb structure may be longer than the maximum diameter of each bottom surface, or the height of the honeycomb structure may be shorter than the maximum diameter of each bottom surface.

[0020] From the viewpoint of pressure loss, the lower limit of the porosity measured by the mercury intrusion method of the porous partition of the honeycomb structure is preferably 60% or more, and more preferably 62% or more. Further, from the viewpoint of the mechanical strength of the honeycomb structure, the upper limit of the porosity measured by the mercury intrusion method of the porous partition is preferably 70% or less, and more preferably 68% or less. Therefore, the porosity of the porous partition is preferably, for example, 60 to 70% as measured by the mercury intrusion method, and more preferably 62 to 68%. In this specification, the "porosity" is measured by the mercury intrusion method defined in JIS R1655:2003. Further, the porosity is the average value when samples (each 0.3 g) of the porous partition are taken without bias from 6 locations of the porous honeycomb structure and the porosity of each is determined as the measured value.

[0021] In addition, it is desirable that the pore size distribution of the porous partition wall be sharp in order to achieve high collection efficiency for particulate matter and low pressure loss performance in a higher dimension. Specifically, in the cumulative pore size distribution based on volume measured by the mercury intrusion method, the cumulative 10% pore size (D10), cumulative 50% pore size (D50), and cumulative 90% pore size (D90) from the small pore side of the porous partition wall preferably satisfy the relationship of (D90 - D10) / D50 ≤ 1.2, more preferably satisfy the relationship of (D90 - D10) / D50 ≤ 1.1, and even more preferably satisfy the relationship of (D90 - D10) / D50 ≤ 1.0. Although the lower limit of (D90 - D10) / D50 is 0, from the viewpoint of ease of manufacture, it is usually the case that 0.5 ≤ (D90 - D10) / D50 is satisfied, and it is typical that 0.8 ≤ (D90 - D10) / D50. Therefore, the porous partition wall can satisfy, for example, 0.5 ≤ (D90 - D10) / D50 ≤ 1.2, and preferably can satisfy 0.8 ≤ (D90 - D10) / D50 ≤ 1.1.

[0022] Conventionally, when the porous partition wall has a high porosity as described above and contains a high proportion of crystalline cordierite, it has been difficult to obtain such a sharp pore size distribution. In addition to the reason that the cordierite crystals are difficult to control the pores formed during firing and thus the pore size distribution tends to be broad, it is also due to the difficulty of controlling the pores derived from the gaps between the particles of the cordierite-forming raw materials. However, by slightly reducing the content of crystalline cordierite, adding ceria, and imparting a device as described later to the manufacturing method, such a sharp pore size distribution can be obtained. As a result, while taking advantage of the excellent thermal shock resistance characteristic of crystalline cordierite, it becomes possible to achieve high collection efficiency for particulate matter and low pressure loss performance in a higher dimension.

[0023] In this specification, D10, D50, and D90 of the porous partition are measured by the mercury intrusion method defined in JIS R1655:2003 using a mercury porosimeter. The mercury intrusion method is a method in which a sample is immersed in mercury in a vacuum state, an equal pressure is applied, mercury is intruded into the sample while gradually increasing the pressure, and the pore size distribution is calculated from the pressure and the volume of mercury intruded into the pores. When the pressure is gradually increased, mercury is intruded into the pores in order from the largest pores, and the cumulative volume of mercury increases. Finally, when all the pores are filled with mercury, the cumulative volume reaches an equilibrium amount. The cumulative volume at this time is the total pore volume (cm 3 / g). And the pore size at the time when mercury with a volume of 10% of the total pore volume is intruded from the small pore side is the cumulative 10% pore size (D10), the pore size at the time when mercury with a volume of 50% of the total pore volume is intruded from the small pore side is the cumulative 50% pore size (D50), and the pore size at the time when mercury with a volume of 90% of the total pore volume is intruded from the small pore side is the cumulative 90% pore size (D90).

[0024] Samples of the porous partition (0.3 g each) are taken without bias from six locations of the honeycomb structure body, the pore size distribution of each is measured, D10, D50, and D90 are obtained, and the average value is taken as the measured value.

[0025] It is desirable to set the cumulative 50% pore size (D50) of the porous partition within an appropriate range according to the application. For example, when using the honeycomb structure body for filter applications, D50 of the porous partition is preferably 20 μm or less, and more preferably 18 μm or less. When D50 of the porous partition is within the above range, the collection efficiency of particulate matter is significantly improved. Also, D50 of the porous partition is preferably 10 μm or more, and more preferably 12 μm or more. When D50 of the porous partition is within the above range, an increase in pressure loss can be suppressed. Therefore, D50 of the porous partition is preferably, for example, 10 to 20 μm, and more preferably 12 to 18 μm.

[0026] Similarly, it is desirable to set the cumulative 10% pore diameter (D10) and the cumulative 90% pore diameter (D90) of the porous partition wall within appropriate ranges according to the application. For example, when using a honeycomb structure for filter applications, it is preferable that D10 is 8 μm or more and D90 is 34 μm or less, more preferably D10 is 9 μm or more and D90 is 32 μm or less, and even more preferably D10 is 10 μm or more and D90 is 30 μm or less. Controlling D10 and D90 within such ranges is advantageous for achieving high collection efficiency for particulate matter and low pressure loss performance in a more advanced level.

[0027] From the perspective of making the pore size distribution sharp, the honeycomb structure preferably has a content of cordierite (2MgO·2Al2O3·5SiO2), which is the main crystal phase, of 80.0 mass% or more, and more preferably 82.0 mass% or more. However, if the content of cordierite, which is the main crystal phase, is too high, it becomes difficult to make the pore size distribution sharp. Therefore, the honeycomb structure preferably has a content of cordierite, which is the main crystal phase, of 94.0 mass% or less, and more preferably 90.0 mass% or less. Accordingly, the honeycomb structure preferably has, for example, a content of cordierite, which is the main crystal phase, of 80.0 to 94.0 mass%, and more preferably 82.0 to 90.0 mass%.

[0028] The honeycomb structure (especially the outer peripheral side wall and the partition wall) preferably contains ceria in the secondary crystal phase from the viewpoint of making the pore size distribution sharp. Further, from the viewpoint of making the pore size distribution sharp, the secondary crystal phase preferably contains one or more compounds selected from mullite, spinel, sapphirine, and cristobalite. The lower limit of the total content rate of ceria and one or more compounds selected from mullite, spinel, sapphirine, and cristobalite in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is preferably 4.0% by mass or more, more preferably 6.0% by mass or more, and still more preferably 8.0% by mass or more from the viewpoint of making the pore size distribution sharp. The upper limit of the total content rate of ceria and one or more compounds selected from mullite, spinel, sapphirine, and cristobalite in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is preferably 20.0% by mass or less, more preferably 18.5% by mass or less, and still more preferably 17.5% by mass or less from the viewpoint of the collection performance. Therefore, in one embodiment, the total content rate of ceria and one or more compounds selected from mullite, spinel, sapphirine, and cristobalite in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is preferably 4.0 to 20.0% by mass, more preferably 6.0 to 18.5% by mass, and still more preferably 8.0 to 17.5% by mass.

[0029] The lower limit of the content rate of ceria in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is more preferably 0.5% by mass or more, and still more preferably 1.0% by mass or more from the viewpoint of making the pore size distribution sharp. The upper limit of the content rate of ceria in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is preferably 5.0% by mass or less, and more preferably 4.0% by mass or less from the viewpoint of the collection performance. Therefore, in one embodiment, the content rate of ceria in the honeycomb structure (especially the outer peripheral side wall and the partition wall) is preferably 0.5 to 5.0% by mass, and more preferably 1.0 to 4.0% by mass.

[0030] The content ratios of cordierite, which is the main crystal phase in the honeycomb structure, and compounds such as ceria contained in the secondary crystal phase are measured by the following method. One sample (3.0 g) is collected from each of two locations, namely, the radial center and the vicinity of the outer periphery at the center in the height direction of the honeycomb structure, of the porous partition wall sample, and each is pulverized to prepare a measurement sample. For each measurement sample, X-ray analysis measurement in the range of 2θ = 8 to 100° is performed by X-ray diffraction using Cu Kα rays, and the analysis is performed using the Rietveld analysis program RIETAN to obtain the mass content ratios of cordierite, ceria, mullite, spinel, sapphirine, and cristobalite. Then, the average value of the mass content ratios of each compound in the two measurement samples is taken as the mass content ratio of each compound, and the total of the average values of the content ratios of each compound is taken as the total content ratio.

[0031] The linear expansion coefficient of the honeycomb structure in the extending direction of the cell channels at 40°C to 800°C is preferably low. For example, the honeycomb structure according to an embodiment of the present invention has a linear expansion coefficient in the range of 0.6×10 -6 / K to 2.0×10 -6 / K, typically 0.6×10 -6 / K to 1.8×10 -6 / K because a sufficient amount of cordierite crystals is ensured. The linear expansion coefficient is measured in accordance with JIS R1618:2002.

[0032] A sample for measuring the linear expansion coefficient of the honeycomb structure is collected by the following procedure. A prismatic sample having a size of 3 mm × 3 mm × 20 mm (length in the extending direction of the cell) is cut out from the center in the radial direction and the height direction of the honeycomb structure portion. The linear expansion coefficient of the sample is measured under the above-described temperature change conditions, and the measured value is used.

[0033] The average thickness of the partition walls in the honeycomb structure is preferably 152 μm or more, more preferably 178 μm or more, and still more preferably 203 μm or more from the viewpoint of ensuring strength. Also, the average thickness of the partition walls is preferably 305 μm or less, more preferably 279 μm or less, and still more preferably 254 μm or less from the viewpoint of suppressing pressure loss. Therefore, the average thickness of the partition walls is preferably, for example, 152 to 305 μm, more preferably 178 to 279 μm, and still more preferably 203 to 254 μm. The thickness of the partition wall refers to the length of the line segment connecting the centers of gravity of adjacent cells when the centers of gravity of adjacent cells are connected by a line segment in a cross section perpendicular to the direction in which the cells extend (the height direction of the honeycomb structure), and the average thickness of the partition wall refers to the average value of the thicknesses of all the partition walls.

[0034] In one embodiment, the plugging portions of the first bottom surface and the second bottom surface both have an average depth of the plugging portion of 2 to 8 mm. By having an average depth of the plugging portion of 2 mm or more, the strength of the plugging portion can be ensured. The average depth of the plugging portion is preferably 3 mm or more. Also, by having an average depth of the plugging portion of 8 mm or less, it is possible to prevent a decrease in the area of the partition walls that collect particulate matter in the cells. The average depth of the plugging portion is preferably 7 mm or less. The depth of the plugging portion in the direction in which the cells extend is measured at 20 arbitrary locations for each bottom surface, and the average value thereof is taken as the average depth of the plugging portion on each bottom surface.

[0035] There is no particular limitation on the cell density (the number of cells per unit cross-sectional area) of the honeycomb structure. For example, it can be 6 to 2000 cells per square inch (0.9 to 311 cells / cm 2 ), preferably 50 to 1000 cells per square inch (7.8 to 155 cells / cm 2 ), and more preferably 100 to 600 cells per square inch (15.5 to 92.0 cells / cm 2 ). Here, the cell density is calculated by dividing the total number of cells (including the plugged cells) by one bottom area excluding the outer peripheral side wall of the honeycomb structure.

[0036] When using the honeycomb structure as a catalyst carrier, a catalyst according to the purpose can be coated on the surface of the partition wall. Examples of the catalyst include, but are not limited to, an oxidation catalyst (DOC) for oxidatively combusting hydrocarbons (HC) and carbon monoxide (CO) to increase the exhaust gas temperature, a PM combustion catalyst for assisting the combustion of PM such as soot, an SCR catalyst and an NSR catalyst for removing nitrogen oxides (NOx), and a three-way catalyst capable of simultaneously removing hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). The catalyst can appropriately contain, for example, noble metals (Pt, Pd, Rh, etc.), alkali metals (Li, Na, K, Cs, etc.), alkaline earth metals (Mg, Ca, Ba, Sr, etc.), rare earths (Ce, Sm, Gd, Nd, Y, La, Pr, etc.), transition metals (Mn, Fe, Co, Ni, Cu, Zn, Sc, Ti, Zr, V, Cr, etc.), and the like.

[0037] (2. Manufacturing method) A manufacturing method of the honeycomb structure according to an embodiment of the present invention will be exemplarily described below. First, after kneading a raw material composition containing a cordierite-forming raw material, a dispersion medium, a pore-forming material, and a binder to form a clay, the clay is extrusion-molded to obtain a honeycomb molded body having a plurality of cell channels that pass through the inside of the honeycomb molded body and are partitioned by porous partition walls. The honeycomb molded body has an outer peripheral side wall and is disposed on the inner peripheral side of the outer peripheral side wall, extending from a first bottom surface to a second bottom surface, and both the first bottom surface and the second bottom surface have openings Comprising a plurality of cell channels This can be achieved. Additives such as a dispersant and other ceramic raw materials may be blended in the raw material composition as needed. When performing extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used.

[0038] The cordierite-forming raw material is a raw material that becomes cordierite by firing and can be provided, for example, in powder form. For example, talc, alumina, aluminum hydroxide, silica, etc. can be used by blending them in appropriate ratios. The cordierite-forming raw material preferably has a chemical composition of alumina (Al2O3) (including the amount of aluminum hydroxide converted to alumina): 30 to 45% by mass, magnesia (MgO): 11 to 17% by mass, and silica (SiO2): 42 to 57% by mass.

[0039] Also, from the viewpoint of making the pore size distribution sharp and promoting the formation of cordierite crystals at a relatively low temperature, it is preferable to add ceria as a sintering aid to the raw material composition. Therefore, the lower limit of the ceria content in the raw material composition or the honeycomb molded body is preferably 0.5 part by mass or more, more preferably 1.0 part by mass or more, based on 100 parts by mass of the cordierite-forming raw material. The upper limit of the ceria content in the raw material composition or the honeycomb molded body is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, from the viewpoint of collection performance, based on 100 parts by mass of the cordierite-forming raw material. Therefore, in one embodiment, the ceria content in the raw material composition or the honeycomb molded body is preferably 0.5 to 5.0 parts by mass, more preferably 1.0 to 4.0 parts by mass, based on 100 parts by mass of the cordierite-forming raw material. Note that the ceria content in the honeycomb molded body relative to 100 parts by mass of the cordierite-forming raw material is equal to Z (parts by mass) described later.

[0040] The ceria added to the raw material composition preferably has an upper limit of the median diameter (D50) in the volume-based cumulative particle size distribution determined by the laser diffraction / scattering method of 10 μm or less, more preferably 8 μm or less, and even more preferably 6 μm or less, from the viewpoint of enhancing the effect of sharpening the pore size distribution in the partition walls and outer peripheral side walls of the honeycomb structure. Further, the ceria added to the raw material composition preferably has a lower limit of the median diameter (D50) in the volume-based cumulative particle size distribution determined by the laser diffraction / scattering method of 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more, from the viewpoint of preventing internal defects due to aggregation. Therefore, for example, the median diameter (D50) of the ceria added to the raw material composition is preferably from 0.1 to 10 μm, more preferably from 0.3 to 8 μm, and even more preferably from 0.5 to 6 μm.

[0041] Examples of the dispersion medium include water, or a mixed solvent of water and an organic solvent such as alcohol. In particular, water can be preferably used.

[0042] The content of the dispersion medium in the honeycomb green 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 with respect to 100 parts by mass of the cordierite-forming raw material. When the content of the dispersion medium in the honeycomb green body is 20 parts by mass or more with respect to 100 parts by mass of the cordierite-forming raw material, the advantage that the quality of the honeycomb structure is likely to be stable can be easily obtained. When the content of the dispersion medium in the honeycomb green body is 110 parts by mass or less with respect to 100 parts by mass of the cordierite-forming raw material, the shrinkage amount during drying is reduced, and deformation can be suppressed. In this specification, the content of the dispersion medium in the honeycomb green body refers to the value measured by the dry weight loss method.

[0043] The pore-forming material is not particularly limited as long as it becomes pores after firing. For example, wheat flour, starch, foamed resin, water-absorbing resin, silica gel, carbon (e.g., graphite), ceramic balloon, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic polymer, phenol, etc. can be mentioned. The pore-forming material may be used alone or in combination of two or more. 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 with respect 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 with respect to 100 parts by mass of the cordierite-forming raw material. When adding ceria, the porosity tends to decrease easily, so the pore-forming material required to achieve the same porosity tends to be more than when no ceria is added.

[0044] Examples of the binder include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Also, from the viewpoint of increasing the strength of the honeycomb green body before firing, the content of the binder is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and even more preferably 6 parts by mass or more with respect to 100 parts by mass of the cordierite-forming raw material. From the viewpoint of suppressing the occurrence of flash 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 with respect to 100 parts by mass of the cordierite-forming raw material. The binder may be used alone or in combination of two or more.

[0045] As the dispersant, ethylene glycol, dextrin, fatty acid soap, polyether polyol, etc. can be used. The dispersant may be used alone or in combination of two or more kinds. The content of the dispersant is preferably 0 to 5 parts by mass with respect to 100 parts by mass of the cordierite-forming raw material.

[0046] For drying the honeycomb molded body, for example, conventionally known drying methods such as hot air drying, microwave drying, dielectric drying, vacuum drying, freeze drying, etc. can be used. Among these, a drying method combining hot air drying with microwave drying or dielectric drying is preferable in that the entire honeycomb molded body can be dried quickly and uniformly.

[0047] When manufacturing a honeycomb structure provided with a plugging portion, the openings of predetermined cells of the honeycomb molded body or the dried body obtained by drying the molded body may be plugged with a plugging material. Each plugging portion can be formed by filling the openings where the plugging portions of the first cell and the second cell are to be formed with a slurry for forming the plugging portion, and then drying and firing the filled slurry. The slurry for forming the plugging portion may be prepared according to a known composition, and for example, may contain a cordierite-forming raw material, a dispersion medium, a pore-forming material, and a binder. The slurry for forming the plugging portion may contain ceria.

[0048] Exemplarily, the slurry for forming the plugging portion contains 30 to 60 parts by mass of the dispersion medium, 5 to 20 parts by mass of the pore-forming material, and 0.2 to 2.0 parts by mass of the binder with respect to 100 parts by mass of the cordierite-forming raw material. In a preferred embodiment, the slurry for forming the plugging portion contains 35 to 50 parts by mass of the dispersion medium, 8 to 16 parts by mass of the pore-forming material, and 0.2 to 1.5 parts by mass of the binder with respect to 100 parts by mass of the cordierite-forming raw material.

[0049] Examples of the dispersion medium include water, or a mixed solvent of water and an organic solvent such as alcohol, etc., and water can be particularly preferably used.

[0050] The pore-forming material is not particularly limited as long as it becomes pores after firing. For example, wheat flour, starch, foamed resin, water-absorbing resin, silica gel, carbon (e.g., graphite), ceramic balloon, polyethylene, polystyrene, polypropylene, nylon, polyester, acrylic resin, phenol, etc. can be mentioned. The pore-forming material may be used alone or in combination of two or more.

[0051] Examples of the binder include organic binders such as methyl cellulose, hydroxypropoxyl methyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. The binder may be used alone or in combination of two or more.

[0052] The slurry for forming the eye-sealing portion may appropriately contain a dispersant. The dispersant can be contained in an amount of 0 to 2.0 parts by mass based on 100 parts by mass of the cordierite-forming raw material, for example. Examples of the dispersant include ethylene glycol, dextrin, fatty acid soap, and polyalcohol. The dispersant may be used alone or in combination of two or more.

[0053] The filling of the slurry for forming the eye-sealing portion into the openings of the cells can be carried out, for example, by the following "squeegee method". As shown in FIG. 5, a film 121 is adhered to the upper bottom surface (here, the second bottom surface 106 in the figure) of the dried honeycomb molded body 500 fixed using a chuck 120, and a laser is irradiated onto the film 121 at a position corresponding to the arrangement conditions (e.g., "checkerboard pattern", etc.) of the eye-sealing portion to form a plurality of holes 126 in the film 121.

[0054] Thereafter, a slurry 124 for forming a sealing portion is placed on the film 121, and an operation of moving the squeegee 122 along the film 121 in the direction of the arrow in FIG. 5 is performed. As a result, a certain amount of the slurry 124 for forming a sealing portion is filled into the cell 125 that opens at a position corresponding to the hole 126 of the film 121.

[0055] The depth of the sealing portion can be changed by the number of times of the moving operation of the squeegee 122, the contact angle between the squeegee 122 and the film 121, the pressing pressure of the squeegee 122 against the film 121, the viscosity of the slurry 124 for forming a sealing portion, and the like.

[0056] After the slurry 124 for forming a sealing portion is filled, the film 121 is peeled off, and the entire honeycomb molded body 500 is dried. As a result, the slurry 124 for forming a sealing portion filled in the cell 125 is dried, and a sealing portion before firing is formed. The drying can be carried out, for example, under the conditions of a drying temperature of 100 to 230°C for about 60 to 100 seconds. After drying, the sealing portion protrudes from the bottom surface of the honeycomb molded body by the thickness of the film, and can be scraped off as necessary.

[0057] The material of the film is not particularly limited, but since it is easy to perform hot processing for forming holes, it is preferably polypropylene (PP), polyethylene terephthalate (PET), polyimide, or Teflon (registered trademark). Further, the film preferably has an adhesive layer, and the material of the adhesive layer is preferably an acrylic resin, a rubber-based (for example, a rubber mainly composed of natural rubber or synthetic rubber), or a silicone-based resin. As the film, for example, an adhesive film having a thickness of 20 to 50 μm can be preferably used.

[0058] In addition to the above " squeegee method", the "press-fitting method" can be mentioned as a method of filling the opening of the cell with the slurry for forming the eye-sealing portion. The "press-fitting method" is a method of attaching a film, immersing the bottom surface portion of the honeycomb formed body with holes in a liquid tank filled with the slurry for forming the eye-sealing portion, and filling the cell with the slurry for forming the eye-sealing portion. In this case, the depth of the eye-sealing portion can be changed by the depth at which the honeycomb formed body is immersed in the slurry for forming the eye-sealing portion.

[0059] If necessary, the honeycomb formed body filled with the slurry for forming the eye-sealing portion is then subjected to a degreasing process and a firing process, whereby a honeycomb structure is manufactured. 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 may be carried out by heating the honeycomb formed body in the 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 green body.

[0060] In the firing process, when the maximum temperature during firing is X (° C), the holding time at the maximum temperature is Y (hr), and the content of ceria with respect to 100 parts by mass of the cordierite-forming raw material in the honeycomb formed body is Z (parts by mass), in order to ensure the required amount of cordierite crystals and make the pore size distribution sharp, it is preferably carried out so that (Equation 1) holds, more preferably carried out so that (Equation 2) holds, and even more preferably carried out so that (Equation 3) holds. 160 ≦ (X - 1345) × Y × (Z + 0.5) 2 ≦ 7680 ··· (Equation 1) 160 ≦ (X - 1345) × Y × (Z + 0.5) 2 ≦ 4840 ··· (Equation 2) 160 ≦ (X - 1345) × Y × (Z + 0.5) 2 ≦ 3720 ··· (Equation 3) The firing process is preferably carried out on the green body. Mullite, spinel, sapphirine and cristobalite do not need to be added to the raw material composition, and an appropriate amount is by-produced when firing under the above conditions and constitutes a secondary crystal phase.

[0061] From the viewpoint of sharpening the pore size distribution, X (°C) is preferably 1430 or less, more preferably 1400 or less, and even more preferably 1380 or less. From the viewpoint of promoting the formation of cordierite crystals, X (°C) is preferably 1345 or more, more preferably 1350 or more, and even more preferably 1355 or more. Therefore, X (°C) is preferably, for example, from 1345 to 1430, more preferably from 1350 to 1400, and even more preferably from 1355 to 1380.

[0062] From the viewpoint of ease of production, Y (hr) is preferably 24 or less, more preferably 16 or less. From the viewpoint of promoting the formation of cordierite crystals, Y (hr) is preferably 7 or more, more preferably 12 or more. Therefore, Y (hr) is preferably, for example, from 7 to 24, more preferably from 12 to 16.

[0063] The preferred conditions for Z (parts by mass) are as described above.

Examples

[0064] Examples for better understanding of the present invention and its advantages are illustrated below, but the present invention is not limited to the examples.

[0065] <Manufacture of honeycomb structure (Comparative Examples 1 to 5, Examples 1 to 9)> (1) Preparation of columnar honeycomb formed body The raw material composition obtained by adding cordierite-forming raw materials, a dispersion medium, a pore-forming material, a binder, a dispersant, and a sintering aid in the mass ratios shown in Table 1 was kneaded to prepare a green body. As the cordierite-forming raw materials, talc, alumina, aluminum hydroxide, and silica were used. Water was used as the dispersion medium. An acrylic polymer was used as the pore-forming material. Methyl cellulose was used as the binder, and ethylene glycol was used as the dispersant. Cerium oxide (median diameter = 1.0 μm in the volume-based cumulative particle size distribution determined by the laser diffraction / scattering method) was used as the sintering aid.

[0066] This green body was put into an extrusion molding machine and extruded through a die of a predetermined shape to obtain a columnar honeycomb molded body. The obtained columnar honeycomb molded body was subjected to dielectric drying and hot air drying, and after further hot air drying, both bottom surfaces were cut to have predetermined dimensions.

[0067] (2) Formation of the plugging portion To 100 parts by mass of the cordierite-forming raw materials, 40 parts by mass of the dispersion medium, 10 parts by mass of the pore-forming material, 2 parts by mass of the binder, and 1 part by mass of the dispersant were added respectively, and kneaded to prepare a slurry for forming the plugging portion. As the cordierite-forming raw materials, talc, alumina, aluminum hydroxide, and silica were used. Water was used as the dispersion medium, a foamed resin was used as the pore-forming material, methyl cellulose was used as the binder, and ethylene glycol was used as the dispersant. Using the "squeegee method" described above, this slurry for forming the plugging portion was filled into both bottom surfaces so that the first cells and the second cells were alternately adjacent to each other. Thereafter, drying was performed under the conditions of 180 °C × 200 seconds in an air atmosphere.

[0068] (3) Firing Next, under an air atmosphere, heat degreasing was carried out under the condition of about 200 °C, and further under an air atmosphere, firing was carried out under the conditions of the maximum temperature shown in Table 1 and the holding time at the maximum temperature, thereby obtaining a columnar honeycomb structure having a plugging portion. When the maximum temperature during firing is X (°C), the holding time at the maximum temperature is Y (hr), and the content of ceria with respect to 100 parts by mass of the cordierite-forming raw material in the honeycomb green body is Z (parts by mass), (X - 1345) × Y × (Z + 0.5) 2 The values are shown in Table 1. The required number of columnar honeycomb structures for the following tests was manufactured.

[0069] (4) Specifications of the honeycomb structure The specifications of the obtained honeycomb structure are as follows. Overall shape: cylindrical with a diameter of 132 mm and a height of 152 mm Cell shape in a cross-section perpendicular to the flow path direction of the cells: square Cell density (number of cells per unit cross-sectional area): 300 cells / square inch (47 cells / cm 2 ) Average thickness of the partition wall: 8.5 mil (216 μm) (nominal value based on the specifications of the base) Average depth of the plugging portion: 5 mm

[0070] <Characteristic evaluation> Various characteristic evaluations were performed on each of the honeycomb structures obtained above.

[0071] (1. Porosity) The porosity (%) of the honeycomb structure was determined according to the mercury intrusion method described above. The results are shown in Table 1.

[0072] (2. Pore size distribution of the porous partition wall) Regarding the porous partition wall of the honeycomb structure, the volume-based cumulative pore size distribution was measured by the mercury intrusion method described above, and the cumulative 10% pore size (D10), cumulative 50% pore size (D50), cumulative 90% pore size (D90), and (D90 - D10) / D50 from the small pore side were determined. The results are shown in Table 1.

[0073] (3. Coefficient of linear expansion: CTE) Samples were collected from the central parts in the radial and height directions of the honeycomb structure by the method described above, and the linear expansion coefficient from 40 °C to 800 °C in the direction in which the cell channels of the honeycomb structure extend was measured according to JIS R1618:2002. The results are shown in Table 1.

[0074] (4. Composition analysis) For the honeycomb structure, using the X’pert PRO device manufactured by PANalytical, composition analysis was performed by the X-ray diffraction method described above, and the mass content ratios of cordierite, mullite, spinel, sapphirine, cristobalite, and ceria were measured respectively. The results are shown in Table 1.

[0075] (5. Evaluation of filter performance) (5-1) Collection performance The honeycomb structure was connected to the outlet side of the engine exhaust manifold of a 1.2L direct injection gasoline engine vehicle, and the number of soot particles contained in the gas discharged from the outlet of the exhaust gas purification device was measured by the PN measurement method. Regarding the driving mode, a driving mode (RTS95) that simulated the worst case of RDE driving was implemented. The cumulative number of soot particles discharged after the mode driving was taken as the number of soot particles of the honeycomb structure to be judged, and the collection efficiency (%) was calculated from the number of soot particles. In the column of "Collection performance" in Table 1, taking the collection efficiency value of the honeycomb structure of Comparative Example 1 as 100%, the honeycomb filters of each example and comparative example were evaluated based on the following evaluation criteria. The results are shown in Table 1. Evaluation "◎": When the value of the collection efficiency ratio (%) exceeds 110% Evaluation "〇": When the value of the collection efficiency ratio (%) exceeds 105% and is 110% or less Evaluation "△": When the value of the collection efficiency ratio (%) exceeds 100% and is 105% or less Evaluation "×": When the value of the collection efficiency ratio (%) is 100% or less

[0076] (5-2) Pressure loss The exhaust gas discharged from a 1.2L direct injection gasoline engine was at 700 °C, 600m 3The honeycomb structure was made to flow in at a flow rate of / h, and the pressures on the inlet end face side and the outlet end face side of the honeycomb structure were measured. Then, by calculating the pressure difference between the inlet end face side and the outlet end face side, the pressure loss (kPa) of the honeycomb structure was determined. In the column of "pressure loss" in Table 1, the pressure loss values of the honeycomb structures of each example and comparative example are shown when the pressure loss value of the honeycomb structure of Comparative Example 1 is taken as 100%. In the pressure loss evaluation, the honeycomb filters of each example were evaluated based on the following evaluation criteria. The results are shown in Table 1. Evaluation "◎": When the value of the pressure loss ratio (%) is 90% or less Evaluation "〇": When the value of the pressure loss ratio (%) exceeds 90% and is 95% or less Evaluation "△": When the value of the pressure loss ratio (%) exceeds 95% and is 100% or less Evaluation "×": When the value of the pressure loss ratio (%) exceeds 100%

[0077] (5-3) Thermal shock resistance The honeycomb structure was placed in an electric furnace preheated to room temperature + 550 °C, heated for a sufficient time (30 minutes) until the entire honeycomb structure reached the same temperature as the heating temperature of the electric furnace, and then air-cooled to room temperature at a cooling rate of 50 °C / min. Due to the thermal shock during this cooling, it was inspected whether cracks occurred on the side surface, end face, or inside of the honeycomb structure. When no cracks occurred when cooled to room temperature, it was regarded as having cleared the heating temperature. The presence or absence of cracks was inspected by visual inspection, tapping sound, etc. For the honeycomb structure that cleared, the heating temperature of the electric furnace was increased in 50 °C steps, and the above test was repeated until cracks occurred. In the evaluation of thermal shock resistance, the honeycomb filters of each example were evaluated based on the following evaluation criteria. The results are shown in Table 1. Evaluation "×": When cracks occurred at room temperature + 550 °C Evaluation "△": When cleared up to room temperature + 550 °C Evaluation "〇": When cleared up to room temperature + 600 °C Evaluation "◎": When cleared up to room temperature + 650 °C

[0078]

Table 1

[0079] (6. Examination) From the results in Table 1, it can be seen that the honeycomb structure according to the examples of the present invention can achieve high levels of thermal shock resistance, high collection efficiency for particulate matter, and low pressure loss performance. In Comparative Examples 1 to 4, since at least one of the cordierite content, porosity, presence or absence of ceria, and (D90 - D10) / D50 was inappropriate, an × was seen in the evaluation of the collection performance or pressure loss.

Explanation of Signs

[0080] 100: Honeycomb structure 102: Outer peripheral side wall 104: First bottom surface 106: Second bottom surface 108: Cell 112: Porous partition wall 120: Chuck 121: Film 122: Squeegee 124: Slurry for forming airtight portion 125: Cell 126: Hole 200: Honeycomb structure 202: Outer peripheral side wall 204: First bottom surface 206: Second bottom surface 208a: First cell 208b: Second cell 209: Airtight portion 212: Porous partition wall 500: Honeycomb formed body

Claims

1. A honeycomb structure, having a plurality of cell channels passing through the inside of the honeycomb structure and partitioned by porous partitions, containing 80.0 to 94.0% by mass of cordierite as the main crystal phase and ceria contained in the secondary crystal phase, wherein the porous partition has a porosity of 60% or more as measured by the mercury intrusion method, the porous partition satisfies the relationship of (D90 - D10) / D50 ≤ 1.2 for the cumulative pore diameter of 10% (D10), cumulative pore diameter of 50% (D50), and cumulative pore diameter of 90% (D90) from the small pore side in the cumulative pore diameter distribution based on volume measured by the mercury intrusion method, a honeycomb structure.

2. The honeycomb structure according to claim 1, wherein the cumulative 50% pore diameter (D50) of the porous partition is 10 to 20 μm.

3. The honeycomb structure according to claim 1, wherein the cumulative 10% pore diameter (D10) of the porous partition is 8 μm or more and the cumulative 90% pore diameter (D90) is 34 μm or less.

4. The honeycomb structure according to claim 1 or 2, wherein the secondary crystal phase further contains one or more compounds selected from mullite, spinel, sapphirine, and cristobalite.

5. The honeycomb structure according to claim 4, wherein the total content of ceria and one or more compounds selected from mullite, spinel, sapphirine, and cristobalite is 4.0 to 20.0% by mass.

6. The honeycomb structure according to claim 1 or 2, wherein the content of ceria is 0.5 to 5.0% by mass.

7. The honeycomb structure according to claim 5, wherein the content of ceria is 0.5 to 5.0% by mass.

8. The linear expansion coefficient in the direction of the cell channel from 40°C to 800°C is 0.6 x 10 -6 / K ~ 2.0 x 10 -6 3. The honeycomb structure according to claim 1, wherein the ratio of the thickness of the honeycomb structure to the thickness of the honeycomb structure is 1 / K.

9. A method for manufacturing a honeycomb structure, comprising kneading a raw material composition containing a cordierite-forming raw material, ceria, a dispersion medium, a pore-forming material, and a binder to form a green body, and then extruding the green body to obtain a honeycomb green body having a plurality of cell channels passing through the inside of the honeycomb green body and partitioned by porous partitions, and firing the honeycomb green body, wherein in the firing step, when the maximum temperature during firing is X (°C), the holding time at the maximum temperature is Y (hr), and the content of ceria relative to 100 parts by mass of the cordierite-forming raw material in the honeycomb green body is Z (parts by mass), 160 ≤ (X - 1345) × Y × (Z + 0.5) 2 ≤ 7680 a manufacturing method implemented so that holds.

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