Particulate filter and slurry for inside coat

Abstract

To provide a particulate filter having high PM collection performance.SOLUTION: A particulate filter is provided with a wall flow type base material and an inside coat layer. In the cumulative pore size distribution of a partition wall based on the mercury press-in method of the partition wall having the inside coat layer formed in the particulate filter, cumulative 50% pore size (D50) exists in a range of 9.0 μm-20.0 μm; a ratio D10 / D50 of cumulative 10% pore size (D10) to cumulative 50% pore size (D50) exists in 0.1-0.45; a ratio D90 / D50 of cumulative 90% pore size (D90) to cumulative 50% pore size (D50) is 2.0-4.0. In the particulate filter, high PM collection performance is realized by sufficiently minimizing the diameter of a large pore 18l and suppressing the clogging of a small pore 18s.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a particulate filter and a slurry for an internal coat.

Background Art

[0002] Exhaust gas discharged from an internal combustion engine such as an automotive engine contains harmful gas components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO x x), and particulate matter (PM) mainly composed of carbon. Regarding this PM, as with harmful gas components, there are concerns about its impact on the human body. For this reason, a particulate filter for collecting PM in the exhaust gas is disposed in the exhaust system of the internal combustion engine.

[0003] Such a particulate filter includes, for example, a wall-flow type substrate. The wall-flow type substrate includes an inlet-side cell having an opening only at the end on the exhaust gas inflow side, an outlet-side cell having an opening only at the end on the exhaust gas outflow side, and a porous partition wall separating both cells. The exhaust gas supplied to such a wall-flow type substrate flows into the inlet-side cell, passes through the partition wall, and is then discharged from the outlet-side cell. At this time, PM is collected in the pores of the partition wall.

[0004] Further, in this type of particulate filter, a coat layer is formed inside (the peripheral wall of the pores of the partition wall) and / or outside (the surface in contact with the inlet-side cell of the partition wall) of the partition wall of the substrate for the purpose of improving the PM collection performance. For example, Patent Document 1 discloses a particulate filter in which by applying a coat layer inside the partition wall, the blow-through of PM to the outlet-side cell is controlled and PM can be stably collected. This internal coat layer is formed by permeating an internal coat slurry inside the partition wall and then performing a drying process and a firing process. Since the large pores in the partition wall are reduced in diameter by this internal coat layer, the PM collection performance is improved.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2020-81912 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] By the way, in recent years, in response to the increasing consideration for the environment, the development of a particulate filter that can exhibit better PM collection performance than conventional ones has been demanded. When the present inventor conducted studies to meet such requirements, attention was paid to the variation in the pore diameter of the partition wall. If there is such a variation in the pore diameter of the partition wall, when the internal coat layer is formed, there is a possibility that the large pores are not sufficiently reduced in diameter and the small pores are blocked. In this case, PM blow-through may occur in which PM flows out to the outlet side cell through the large pores, which may cause a decrease in PM collection performance.

[0007] The technology disclosed herein has been made in view of such a point, and its object is to provide a particulate filter that can appropriately prevent PM blow-through to the outlet side cell and exhibit excellent PM collection performance. [Means for Solving the Problems]

[0008] In order to achieve the above object, a particulate filter having the following configuration is provided by the technology disclosed herein.

[0009] The particulate filter disclosed herein is disposed in the exhaust system of an internal combustion engine and is used to capture particulate matter in exhaust gas discharged from the internal combustion engine. This particulate filter at least comprises inlet cells only open at the end on the exhaust gas inlet side, outlet cells only open at the end on the exhaust gas outlet side, and a wall-flow type substrate having porous partition walls separating the inlet cells and the outlet cells, and an inner coating layer formed on the peripheral walls of pores inside the partition walls. In the particulate filter disclosed herein, the cumulative 50% pore diameter (D 50 ) is in the range of 9.0 μm to 20.0 μm, and the cumulative 50% pore size (D 50 ) to the cumulative 10% pore size (D 10 ) ratio D 10 / D 50 is 0.1 to 0.45, and the cumulative 50% pore diameter (D 50 ) to the cumulative 90% pore size (D 90 ) ratio D 90 / D 50 is 2.0~4.0.

[0010] In the particulate filter having the above-mentioned configuration, an inner coating layer is selectively formed on large pores among a plurality of pores formed in the partition walls of the substrate. In such a particulate filter, it has been confirmed by experiments that the cumulative pore size distribution of the partition walls satisfies the above-mentioned condition. In addition, in such a particulate filter, the large pores that cause PM to pass through are sufficiently small in diameter, and small pores that can contribute to PM capture are maintained, so that the particulate filter can exhibit high PM capture performance.

[0011] In a preferred embodiment of the particulate filter disclosed herein, the cumulative 50% pore diameter (D 50 ) to the cumulative 50% pore diameter (D 50 ) and the cumulative 10% pore size (D 10 ) and the ratio of the difference (D 50 -D 10 ) / D 50is between 0.55 and 0.65. By this, further PM collection performance can be exhibited.

[0012] In a preferred embodiment of the particulate filter disclosed herein, for the cumulative 50% pore diameter (D 50 ), the ratio of the difference between the cumulative 90% pore diameter (D 90 ) and the cumulative 50% pore diameter (D 50 ), (D 90 -D 50 ) / D 50 is between 1.00 and 2.00. By this, further PM collection performance can be exhibited.

[0013] In a preferred embodiment of the particulate filter disclosed herein, for the cumulative 50% pore diameter (D 50 ), the ratio of the difference between the cumulative 90% pore diameter (D 90 ) and the cumulative 10% pore diameter (D 10 ), (D 90 -D 10 ) / D 50 is between 1.50 and 2.50. By this, further PM collection performance can be exhibited.

[0014] Also, as another aspect of the technology disclosed herein, an inner coat slurry used for forming an inner coat layer of the particulate filter is provided. This slurry contains at least a heat-resistant material, a binder, and a viscosity increasing agent upon temperature rise. And, for this inner coat slurry, the ratio of the viscosity V 20 at 20 °C to the viscosity V 60 at 60 °C based on dynamic viscoelasticity measurement, V 60 / V 20 is 10 or more and 100 or less.

[0015] The slurry for the internal coat of the above structure (hereinafter, also simply referred to as "slurry") has the property that its viscosity increases by 10 times or more in a high-temperature environment (around 60 °C). By using such a slurry, an internal coat layer can be selectively formed in large pores. Specifically, when this slurry is filled into the partition walls at room temperature, the slurry adheres to the peripheral walls of the large pores, and the small pores are blocked by the slurry. When high-temperature air blowing is performed in this state, since the viscosity of the slurry greatly improves, the state where the slurry adheres to the peripheral walls of the large pores is maintained. At this time, in the technology disclosed herein, since the air permeability of the large pores decreases, the pressure of the air blowing is likely to be applied to the slurry blocking the small pores. As a result, a particulate filter can be manufactured in which the large pores are reduced in diameter and the small pores are maintained (that is, the variation in the pore diameter is suppressed).

[0016] In a preferred embodiment of the slurry for the internal coat disclosed herein, the heat-resistant material includes at least one selected from the group consisting of alumina, ceria, zirconia, silica, magnesia, and calcia. Thereby, an internal coat layer excellent in durability can be formed.

[0017] The binder includes at least one selected from the group consisting of boehmite binders (alumina sols) and zirconia binders. Thereby, since the viscosity of the slurry in a normal-temperature environment can be ensured, it becomes easier to adhere the slurry to the partition walls of the base material.

[0018] In a preferred embodiment of the slurry for the internal coat of the catalyst disclosed herein, the viscosity-increasing agent upon temperature rise includes at least one selected from the group consisting of methyl cellulose, hydroxypropyl methyl cellulose, ammonium sulfate, and starch. Thereby, it becomes easier to selectively adhere an internal coat layer to the large pores of the partition walls.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

MODE FOR CARRYING OUT THE INVENTION

[0020] Hereinafter, preferred embodiments of the technology disclosed herein will be described with reference to the drawings. In addition, matters other than those specifically mentioned in this specification, which are necessary for the implementation of the technology disclosed herein (for example, general matters regarding the arrangement of the particulate filter in the exhaust path, etc.) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common general knowledge in the relevant field. In addition, the notation "A to B" indicating a numerical range in this specification means "A or more and B or less".

[0021] <First Embodiment> 1. Exhaust System of Internal Combustion Engine An example of the use of the particulate filter disclosed here will be described. FIG. 1 is a diagram schematically showing an exhaust system in which the particulate filter is arranged.

[0022] Reference numeral 2 in Fig. 1 is an internal combustion engine. An air-fuel mixture containing oxygen and fuel gas is supplied to this internal combustion engine 2. The internal combustion engine 2 burns this air-fuel mixture to generate kinetic energy. Then, the exhaust gas generated by the combustion of this air-fuel mixture is discharged into an exhaust system composed of an exhaust manifold 3 and an exhaust pipe 4 as shown by the arrow in Fig. 1. In this specification, for convenience of explanation, the side closer to the internal combustion engine 2 in the flow direction of the exhaust gas is referred to as the upstream side, and the side farther from the internal combustion engine 2 is referred to as the downstream side. Further, the internal combustion engine 2 in Fig. 1 is preferably a gasoline engine. That is, the particulate filter disclosed herein can be particularly preferably used as a GPF (Gasoline Particulate Filter) that collects particulate matter PM in the exhaust gas discharged from a gasoline engine.

[0023] Further, a sensor 8 for detecting information on the components and temperature of the exhaust gas is attached to the exhaust pipe 4. This sensor 8 is connected to an engine control unit (ECU) 7. Then, the information detected by the sensor 8 is transmitted to the ECU 7 and used as one of the information for correcting the operation control of the internal combustion engine 2.

[0024] And in the exhaust system (exhaust pipe 4) of the internal combustion engine 2, a particulate filter 1, an exhaust gas purification catalyst 5, and an underfloor catalyst 9 are arranged. The particulate filter 1 collects particulate matter (PM) in the exhaust gas. The specific configuration of such a particulate filter 1 will be described later. Then, the exhaust gas from which PM has been removed by the particulate filter 1 passes through the exhaust gas purification catalyst 5 and the underfloor catalyst 9 and is discharged to the outside of the exhaust system. The exhaust gas purification catalyst 5 and the underfloor catalyst 9 are members including a catalyst body that purifies harmful gas components (NOx, HC, CO) in the exhaust gas. Note that the specific configurations of the exhaust gas purification catalyst 5 and the underfloor catalyst 9 are not characteristic of the technology disclosed herein, so detailed descriptions thereof are omitted. In the exhaust system shown in FIG. 1, the exhaust gas purification catalyst 5 is arranged downstream of the particulate filter 1, but their arrangement positions are not particularly limited. For example, an exhaust gas purification catalyst may be arranged upstream of the particulate filter. Further, the particulate filter disclosed herein may be arranged at the position of the underfloor catalyst.

[0025] 2. Configuration of Particulate Filter Next, an embodiment of the particulate filter disclosed herein will be described. FIG. 2 is a perspective view schematically showing the particulate filter according to this embodiment. FIG. 3 is a view schematically showing a cross section along the cylinder axis direction of the particulate filter shown in FIG. 2. FIG. 4 is an enlarged cross-sectional view of the partition wall of the particulate filter shown in FIG. 3. FIG. 5 is an enlarged cross-sectional view of the partition wall of the base material before forming the inner coat layer.

[0026] As shown in FIGS. 2 to 4, the particulate filter 1 according to this embodiment includes a base material 10 and an inner coat layer 20. Each will be described below.

[0027] ≪Base Material≫ As shown in FIGS. 2 and 3, the base material 10 is a wall-flow type base material in which adjacent inlet cells 12 and outlet cells 14 are partitioned by a porous partition wall 16. In the present embodiment, a cylindrical base material 10 extending along the exhaust gas flow direction A is used. Note that the outer shape of the base material is not limited to a cylindrical shape, and may be an elliptical cylindrical shape, a polygonal cylindrical shape, or the like. Also, the total length and capacity of the base material 10 are not particularly limited, and can be appropriately changed according to the performance of the internal combustion engine 2 (see FIG. 1) and the dimensions of the exhaust pipe 4, etc. Further, for the base material 10, conventionally known materials that can be used for the base material of the particulate filter can be used without particular limitation. As an example of the material of such a base material 10, high heat-resistant materials typified by ceramics such as cordierite, silicon carbide (SiC), and aluminum titanate, and alloys such as stainless steel can be mentioned. For example, cordierite is particularly preferably used as the material of the base material of a gasoline engine particulate filter (GPF) to which high-temperature exhaust gas is likely to be supplied because of its excellent durability against thermal shock.

[0028] As shown in FIG. 3, the inlet cell 12 is a gas flow path in which the end on the exhaust gas inflow side is open and the end on the exhaust gas outflow side is blocked by a sealing portion 12a. As shown in FIG. 2, in the present embodiment, the inlet cell 12 has a substantially square shape in a cross section (typically a cross section along the radial direction) perpendicular to the extending direction X of the partition wall 16. However, the cross-sectional shape of the inlet cell is not particularly limited, and various geometric shapes such as rectangular shapes such as parallelograms, rectangles, trapezoids, triangular shapes, and other polygonal shapes (for example, hexagons, octagons), and circular shapes can be adopted.

[0029] On the other hand, the outlet cell 14 is a gas flow path in which the end on the exhaust gas inflow side is blocked by a sealing portion 14a and the end on the exhaust gas outflow side is open. Similar to the above-mentioned inlet cell 12, the outlet cell 14 also has a substantially square shape in a cross section along the radial direction. However, the cross-sectional shape of the outlet cell is not particularly limited, and various geometric shapes such as rectangular shapes such as parallelograms, rectangles, trapezoids, triangular shapes, and other polygonal shapes (for example, hexagons, octagons), and circular shapes can be adopted.

[0030] Further, the partition wall 16 is a porous member that separates the inlet cell 12 and the outlet cell 14. From the perspective of achieving both PM collection performance and pressure loss reduction performance, the thickness of the partition wall 16 is preferably about 50 μm to 1000 μm, and more preferably about 100 μm to 500 μm. A plurality of pores 18 (see FIGS. 4 and 5) that communicate the inlet cell 12 and the outlet cell 14 are formed in the partition wall 16. Here, as shown in FIG. 5, in a normal base material 10, due to manufacturing tolerances, the sizes of the pores 18 in the partition wall 16 vary. Hereinafter, among the plurality of pores 18, pores with a pore diameter of 30 μm or more are referred to as "large pores 18l". Further, pores with a pore diameter of 20 μm or less are referred to as "small pores 18s".

[0031] ≪Inner coating layer≫ As shown in FIG. 3, the particulate filter 1 according to the present embodiment includes an inner coating layer 20. This inner coating layer 20 is formed on the peripheral wall 18b of the pores 18 inside the partition wall 16 (see FIG. 4). As a result, the pores 18 in the partition wall 16 are reduced in diameter, so that the blow-through of PM to the outlet cell 14 can be suppressed. The inner coating layer 20 mainly consists of a granular heat-resistant material. The "heat-resistant material" in this specification is a heat-resistant material defined in JIS R2001. By forming the inner coating layer 20 with such a heat-resistant material, the durability of the inner coating layer 20 can be improved. Examples of the above heat-resistant material include alumina (Al2O3), ceria (CeO2), zirconia (ZrO2), silica (SiO2), magnesia (MgO), calcia (CaO), and the like. Also, although it will be described in detail later, the inner coating layer 20 may contain a noble metal catalyst, an OSC material, etc. as components other than the heat-resistant material.

[0032] Also, as shown in FIG. 3, the internal coat layer 20 in the present embodiment has a first internal coat layer 20a and a second internal coat layer 20b. The first internal coat layer 20a is formed from the inlet surface 16a of the partition wall 16 (the surface in contact with the inlet cell 12) toward the inside of the partition wall 16. Further, the second internal coat layer 20b is formed from the outlet surface 16b of the partition wall 16 (the surface in contact with the outlet cell 14) toward the inside of the partition wall 16. And in the particulate filter 1 according to the present embodiment, in the extending direction X of the partition wall 16, the formation regions of the first internal coat layer 20a and the second internal coat layer 20b partially overlap. Thereby, since it is possible to prevent the exhaust gas from passing through the region where the internal coat layer 20 is not formed, the PM collection performance can be improved.

[0033] Here, as shown in FIG. 4, the internal coat layer 20 in the present embodiment is preferentially formed in the large pores 18l of the partition wall 16. Thereby, since the large pores 18l can be sufficiently reduced in diameter and the small pores 18s can be maintained, high PM collection performance can be exhibited. Hereinafter, the conventional particulate filter 100 and the particulate filter 1 according to the present embodiment will be described in detail while making a comparison.

[0034] FIG. 7 is an enlarged cross-sectional view of the partition wall of a conventional particulate filter. As shown in FIG. 7, also in the conventional particulate filter 100, an internal coat layer 120 is formed on the peripheral wall 118b of the pores 118 in the partition wall 116. This internal coat layer 120 is formed by attaching a slurry to the peripheral wall 118b of the pores 118 and then performing a drying process and a firing process. Here, in the above drying process, high-temperature air blowing that passes through the pores 118 is performed. Since the viscosity of the slurry decreases due to the temperature rise at this time, the slurry adhering to the peripheral wall 118b of the large pores 118l peels off and is discharged in a large amount outside the partition wall 116. As a result, the air permeability of the large pores 118l is further improved, so that less air tries to pass through the small pores 118s. As a result, in the small pores 118s, almost no discharge of the slurry occurs, so that the pores are likely to be blocked. Since almost no exhaust gas passes through the blocked small pores 118s, most of the exhaust gas passes through the large pores 118l. However, as described above, since a large amount of slurry has been discharged from the large pores 118l, the diameter has not been sufficiently reduced. As a result, PM may blow through the large pores 118l, and the PM collection performance may decrease. On the other hand, in addition to the above-described internal coat layer, an external coat layer that covers the entrance 118a of the pores 118 may be provided.

[0035] On the other hand, the internal coat layer 20 of the particulate filter 1 according to the present embodiment is preferentially formed in the large pores 18l (see FIG. 4). That is, in the present embodiment, the large pores 18l are sufficiently reduced in diameter, and the blockage of the small pores 18s is suppressed. As a result, it is possible to suppress the bypass of PM through the large pores 18l. In addition, since the small pores 18s are open, PM can be appropriately collected also in the small pores 18s. As a result, high PM collection performance can be exhibited. Further, in the particulate filter 1 according to the present embodiment, since the small pores 118s are less likely to be blocked due to the deposition of PM, an increase in pressure loss can also be suppressed. Although details will be described later, this selective internal coat layer 20 can be formed by using an internal coat slurry having a viscosity that increases with temperature rise.

[0036] Here, according to the experiments conducted by the present inventors, in the partition wall 16 where the internal coat layer 20 is preferentially formed in the large pores 18l, when measuring the cumulative pore size distribution based on the mercury intrusion method on a number basis, it has been confirmed that the conditions shown in the following formulas (1) to (3) are satisfied. Hereinafter, each formula will be described. 9.0 μm ≤ D 50 ≤ 20.0 μm (1) 0.1 ≤ D 10 / D 50 ≤ 0.45 (2) 2.0 ≤ D 90 / D 50 ≤ 4.0 (3)

[0037] (Regarding formula (1)) As shown in the above formula (1), the partition wall 16 after the formation of the internal coat layer 20 has a cumulative 50% pore size (D 50 ) of 9.0 μm to 20.0 μm. The partition wall 16 whose cumulative 50% pore size (D 50 )(that is, the median diameter) satisfies 20 μm or less is understood to have the large pores 18l sufficiently reduced in diameter, and the pore sizes of the respective pores 18 are distributed relatively on the smaller diameter side. From the viewpoint of further improving the PM collection performance, the cumulative 50% pore size (D 50 ) is preferably 18 μm or less, more preferably 17 μm or less, still more preferably 16 μm or less, and particularly preferably 15 μm or less. On the other hand, for the partition wall 16 whose cumulative 50% pore size (D 50 ) is less than 9.0 μm, an excessive internal coat layer 20 may be formed, and there is a possibility that the small pores 18s are blocked. Therefore, the cumulative 50% pore size (D 50 ) of the partition wall 16 is defined to be 9 μm or more. From the viewpoint of suppressing the pressure loss, the cumulative 50% pore size (D 50 ) is preferably 9.25 μm or more, more preferably 9.5 μm or more, still more preferably 9.75 μm or more, and particularly preferably 10 μm or more.

[0038] (Regarding formula (2)) As shown in the above formula (2), the partition wall 16 of the particulate filter 1 according to the present embodiment has a ratio D of the cumulative 10% pore size (D 10 ) to the cumulative 50% pore size (D 50 )10 / D 50 becomes 0.1 to 0.45. The cumulative 10% pore diameter D 10 means that pores having a diameter less than this value account for 10% of the population. Therefore, the cumulative 10% pore diameter D 10 can be an index indicating the state of the small pores 18s. Also, in this specification, for the standardization of the pore diameter, the cumulative 10% pore diameter D 10 is divided by the cumulative 50% pore diameter D 50 . This ratio D 10 / D 50 is too small (less than 0.1), the small pores 18s are excessively reduced in diameter by the inner coat layer 20, so the PM collection performance tends to be low. Note that the lower limit of the above ratio D 10 / D 50 is preferably 0.15 or more, more preferably 0.2 or more, still more preferably 0.25 or more, and particularly preferably 0.3 or more. On the other hand, when the small pores 18s are completely blocked by the inner coat layer 20, the pores 18 on the medium diameter side are included in the cumulative 10% pore diameter D 10 . In this case, the above ratio D 10 / D 50 increases extremely (exceeds 0.45), and the PM collection performance greatly decreases. Note that the upper limit of the above ratio D 10 / D 50 is preferably 0.44 or less, more preferably 0.43 or less, still more preferably 0.42 or less, and particularly preferably 0.40 or less.

[0039] (Regarding formula (3)) As shown in the above formula (3), the partition wall 16 of the particulate filter 1 according to this embodiment has a ratio D 90 of the cumulative 90% pore diameter (D 50 ) to the cumulative 50% pore diameter (D 90 / D 50 becomes 2.0 to 4.0. The cumulative 90% pore diameter D 90 means that pores having a diameter less than this value account for 90% of the population. Therefore, the cumulative 90% pore diameter D 90 can be an index indicating the state of the large pores 18l. Also, the cumulative 90% pore diameter D 90 is divided by the cumulative 50% pore diameter D 50This ratio D 90 / D 50 If the ratio D is too large (over 4.0), the inner coating layer 20 does not sufficiently reduce the diameter of the large pores 18l, and PM tends to pass through. 90 / D 50 The upper limit of D is preferably 3.8 or less, more preferably 3.6 or less, further preferably 3.4 or less, and particularly preferably 3.0 or less. On the other hand, as described above, when the diameters of the pores 18 are appropriately reduced by the inner coating layer 20, the above D 90 / D 50 The denominator of the cumulative 50% pore size (D 50 ) shifts to the smaller diameter side. As a result, the above ratio D 90 / D 50 increases rapidly (becomes 2.0 or more). In such a case, better PM collection performance can be achieved. 90 / D 50 The lower limit value is preferably 2.2 or more, more preferably 2.4 or more, even more preferably 2.6 or more, and particularly preferably 2.8 or more.

[0040] As described above, in the particulate filter 1 according to this embodiment, the inner coat layer 20 is formed inside the partition wall 16 so as to satisfy the above formulas (1) to (3). It can be said that such a particulate filter 1 realizes a state in which the large pores 18l are sufficiently small in diameter and the small pores 18s are not blocked. This makes it possible to realize high PM trapping performance.

[0041] Although the technology disclosed herein is not limited thereto, the cumulative 10% pore size (D 10 ) and cumulative 90% pore size (D 90 It is preferable that the measured values ​​of each of the above satisfy the following conditions:

[0042] First, the cumulative 10% pore size (D 10) is preferably 1.0 μm or more, more preferably 2.0 μm or more, still more preferably 3.0 μm or more, and particularly preferably 4.0 μm or more. In the particulate filter 1 satisfying such conditions, clogging of the small pores 18s is more preferably suppressed. On the other hand, the cumulative 10% pore diameter (D 10 ) is preferably 8.2 μm or less, more preferably 8.1 μm or less, still more preferably 8.0 μm or less, and particularly preferably 7.8 μm or less. In the particulate filter 1 satisfying such conditions, it is prevented that larger pores 18 are counted in the cumulative 10% pore diameter (D 10 ) due to complete clogging of the small pores 18s.

[0043] Also, the cumulative 90% pore diameter (D 90 ) is preferably 47.8 μm or less, more preferably 47.6 μm or less, still more preferably 47.4 μm or less, and particularly preferably 47.2 μm or less. In the particulate filter 1 satisfying such conditions, the large pores 18l are sufficiently reduced in diameter by the inner coat layer 20. On the other hand, the cumulative 90% pore diameter (D 90 ) is preferably 20 μm or more, more preferably 24 μm or more, still more preferably 26 μm or more, and particularly preferably 28 μm or more. Thereby, an increase in pressure loss due to the formation of an excessive inner coat layer 20 can be suppressed.

[0044] Also, it is more preferable that the cumulative pore diameter distribution of the partition wall 16 after the formation of the inner coat layer 20 satisfies at least one of the following formulas (4) to (6) in addition to the above formulas (1) to (3). Hereinafter, a specific description will be given. 0.55 ≦ (D 50 - D 10 ) / D 50 ≦ 0.65 (4) 1.00 ≦ (D 90 - D 50 ) / D 50 ≦ 2.00 (5) 1.50 ≦ (D 90 - D 10 ) / D 50 ≦ 2.50 (6)

[0045] As shown in the above formula (4), the partition wall 16 after the formation of the inner coat layer 20 has a cumulative 50% pore diameter (D 50 ) and a cumulative 10% pore diameter (D 10 ), and the ratio obtained by dividing the difference between them by the cumulative 50% pore diameter (D 50 ), i.e., (D 50 - D 10 ) / D 50 is preferably 0.55 to 0.65. A partition wall 16 with a small difference (D 50 - D 10 ) means that the variation in pore diameter on the small-diameter side is small. In particular, when the small pores 18s are blocked by the inner coat layer 20, this difference (D 50 - D 10 ) may decrease rapidly. And the above ratio (D 50 - D 10 ) / D 50 is a value obtained by normalizing the difference (D 50 - D 10 ) with the cumulative 50% pore diameter D 50 . When this ratio (D 50 - D 10 ) / D 50 is 0.55 or more, it is understood that the blockage of the small pores 18s by the inner coat layer 20 is suppressed. Therefore, the above ratio (D 50 - D 10 ) / D 50 is preferably 0.55 or more, more preferably 0.56 or more, still more preferably 0.57 or more, and particularly preferably 0.58 or more. On the other hand, when the above ratio (D 50 - D 10 ) / D 50 is too large (more than 0.65), there is a possibility that the inner coat layer 20 is too small and the reduction of the pore diameter of the pores 18 is not sufficient. Therefore, the above ratio (D 50 - D 10 ) / D 50 is preferably 0.65 or less, more preferably 0.63 or less, still more preferably 0.61 or less, and particularly preferably 0.6 or less.

[0046] As shown in the above formula (5), the partition wall 16 of the particulate filter 1 according to the present embodiment has a cumulative 90% pore diameter (D 90 ) and a cumulative 50% pore diameter (D 50) difference and cumulative 50% pore diameter (D 50 ) and the ratio (D 90 -D 50 ) / D 50 is preferably 1.00 to 2.00. The above difference (D 90 -D 50 ) of the partition wall 16 with a small difference means that the variation in pore diameter on the large-diameter side is small. In particular, when the pores 18 with a large diameter to a medium diameter are not sufficiently reduced in diameter by the inner coat layer 20, this difference (D 90 -D 50 ) may rapidly decrease. And the above ratio (D 90 -D 50 ) / D 50 is a value obtained by normalizing the above difference (D 90 -D 50 ) with the cumulative 50% pore diameter D 50 . This ratio (D 90 -D 50 ) / D 50 is understood that when it is 1.00 or more, the inner coat layer 20 sufficiently reduces the diameter of the pores 18 with a large diameter to a medium diameter. Therefore, the above ratio (D 90 -D 50 ) / D 50 is preferably 1.00 or more, more preferably 1.20 or more, still more preferably 1.40 or more, and particularly preferably 1.50 or more. On the other hand, when the above ratio (D 50 -D 50 ) / D 50 is too large (when it exceeds 2.00), there is a possibility that the inner coat layer 20 is too small and the reduction in diameter of the large pores 18l is not sufficient. Therefore, the above ratio (D 90 -D 50 ) / D 50 is preferably 2.00 or less, more preferably 1.90 or less, still more preferably 1.80 or less, and particularly preferably 1.70 or less.

[0047] (Regarding formula (6)) As shown in the above formula (6), the partition wall 16 of the particulate filter 1 according to the present embodiment has a difference (D 90 ) between the cumulative 90% pore diameter (D 10 ) and the cumulative 10% pore diameter (D 90 -D 10) and the ratio of the cumulative 50% pore diameter (D 50 ) to (D 90 -D 10 ) / D 50 is preferably from 1.50 to 2.50. The above difference (D 90 -D 10 ) of the partition wall 16 with a small difference means that the overall variation in the pore diameter distribution is small. In particular, when the small pores 18s are blocked by the inner coat layer 20, this difference (D 90 -D 10 ) may decrease rapidly. And the above ratio (D 90 -D 10 ) / D 50 is a value obtained by normalizing the above difference (D 90 -D 10 ) with the cumulative 50% pore diameter D 50 . When this ratio (D 90 -D 10 ) / D 50 is 1.5 or more, it is understood that the blockage of the small pores 18s by the inner coat layer 20 is suppressed. Therefore, the above ratio (D 90 -D 10 ) / D 50 is preferably 1.50 or more, more preferably 1.70 or more, still more preferably 1.90 or more, and particularly preferably 2.00 or more. On the other hand, when the above ratio (D 90 -D 10 ) / D 50 is too large (when it exceeds 0.65), there may be a possibility that the inner coat layer 20 is too small and the variation in the pores 18 of the partition wall 16 is not sufficiently eliminated. Therefore, the above ratio (D 90 -D 10 ) / D 50 is preferably 2.50 or less, more preferably 2.45 or less, still more preferably 2.40 or less, and particularly preferably 2.35 or less.

[0048] 3. Method for manufacturing a particulate filter Next, a method for manufacturing the particulate filter according to the present embodiment will be described. As described above, in the particulate filter 1 according to the present embodiment, the internal coat layer 20 is formed so that the large pores 18l can be sufficiently reduced in diameter without closing the small pores 18s. Such an internal coat layer 20 can be formed by using the following internal coat slurry and performing a high-temperature air blow treatment (drying treatment). Specific description will be given below.

[0049] (1) Internal coat slurry The internal coat slurry is used for forming the internal coat layer 20 of the particulate filter 1. This slurry contains at least a heat-resistant material, a binder, and a temperature-increasing thickener.

[0050] (a) Heat-resistant material As described above, the heat-resistant material is a granular material that becomes the main component of the internal coat layer 20 after firing. Since the details of the heat-resistant material have already been described, redundant descriptions are omitted. Note that the content of the heat-resistant material per liter of slurry is preferably 1 g / L to 60 g / L (more preferably 5 g / L to 50 g / L, still more preferably 10 g / L to 40 g / L, and particularly preferably 10 g / L to 30 g / L).

[0051] (b) Binder The binder is a component that increases the viscosity of the slurry in a normal temperature environment. Thereby, in the penetration of the slurry described later, it becomes easier to adhere the slurry to the peripheral wall 18b of the pores 18. The type of such a binder is not particularly limited, and conventionally known materials can be used without particular limitation. Specific examples of the binder include boehmite binder (alumina sol), zirconia binder, and the like. Note that the content of the binder per liter of slurry is preferably 0.1 g / L to 6 g / L (more preferably 0.5 g / L to 5 g / L, still more preferably 1 g / L to 4 g / L, and particularly preferably 1 g / L to 3 g / L).

[0052] (c) Temperature-increasing thickener The temperature-rising thickening agent is a component that increases the viscosity of the slurry even when the solid content is constant as the temperature rises. Although it will be described in detail later, by imparting temperature-rising thickening properties to the slurry for internal coating, it becomes easier to selectively adhere the internal coating layer 20 to the large pores 18l of the partition wall 16. The content of the temperature-rising thickening agent per liter of slurry is preferably 0.01 g / L to 1.5 g / L (more preferably 0.05 g / L to 0.8 g / L, even more preferably 0.07 g / L to 0.7 g / L, and particularly preferably 0.1 g / L to 0.5 g / L). Also, the type of the temperature-rising thickening agent is not particularly limited, and conventionally known materials can be used without particular limitation. Specific examples of the temperature-rising thickening agent include cellulose derivatives such as methyl cellulose and hydroxypropyl methyl cellulose, starches, and water-soluble sulfates such as ammonium sulfate.

[0053] Here, the slurry according to the present embodiment has a viscosity V at 20°C based on dynamic viscoelasticity measurement 20 and a viscosity V at 60°C 60 and the ratio V 60 / V 20 such that a temperature-rising thickening agent is added so that it is 10 or more and 100 or less. By making the above ratio V 60 / V 20 10 or more, the internal coating layer 20 can be selectively formed in the large pores 18l. In order to more preferably reduce the diameter of the large pores 18l, the above ratio V 60 / V 20 is preferably 15 or more, more preferably 20 or more, even more preferably 25 or more, and particularly preferably 30 or more. On the other hand, by making the above ratio V 60 / V 20 100 or less, it becomes easier to remove the slurry that has penetrated into the small pores 18s by high-temperature air blowing. The above ratio V 60 / V 20 is preferably 85 or less, more preferably 75 or less, even more preferably 65 or less, and particularly preferably 55 or less.

[0054] (d) Other Additive Materials The slurry may contain various additive materials in addition to the above-described essential components. Other additive materials will be described below.

[0055] As an example of the above-mentioned other material, a thickener can be mentioned. By this, the viscosity of the slurry in a normal temperature environment can be more appropriately ensured, so that it becomes easier to adhere the slurry to the partition wall 16 of the base material 10. The type of such thickener is not particularly limited, and conventionally known materials can be used without particular limitation. Specific examples of the thickener include cellulose polymers such as methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), and hydroxyethyl methyl cellulose (HEMC).

[0056] Also, as another example of the additive material, a noble metal catalyst can be mentioned. By this, a particulate filter 1 provided with a purification function for harmful gas components (HC, CO, NO x ) in the exhaust gas can be obtained. The type of such noble metal catalyst is not particularly limited, and conventionally known materials can be used without particular limitation. Specific examples of the noble metal catalyst include gold (Au), silver (Ag), palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), etc. These noble metal catalysts oxidize CO and HC in the exhaust gas and, at the same time, x function as a three-way catalyst for reducing NO, so that harmful gas components can be purified more efficiently. Also, since these noble metal catalysts promote the combustion of PM collected on the partition wall 16, an increase in the PM deposition pressure loss can also be suppressed.

[0057] Also, when adding a noble metal catalyst to the inner coat layer 20, it is preferable to add an additive for enhancing the catalytic activity of the noble metal catalyst together. As an example of such an additive, an OSC material can be mentioned. This OSC material refers to a material having an oxygen storage capacity (OSC: Oxygen Storage capacity) and capable of occluding and releasing oxygen. By adding this OSC material, it becomes easier to maintain the atmosphere of the exhaust gas in contact with the inner coat layer 20 near the stoichiometric (theoretical air-fuel ratio), so that the catalytic action of the noble metal catalyst can be stabilized. As an example of such an OSC material, ceria-zirconia composite oxide and the like can be mentioned. Further, as additives other than the OSC material, a NOx adsorbent having an NOx occlusion ability, a stabilizer, and the like may be added. Furthermore, the inner coat layer 20 may contain trace components derived from raw materials and manufacturing processes. For example, the inner coat layer 20 may contain one or more compounds (oxides, sulfates, carbonates, nitrates, chlorides) of alkaline earth metals (such as Be, Mg, Ca, Ba), rare earth metals (such as Y, La, Ce), alkali metals (such as Li, Na, K), transition metals (such as Mn, Fe, Co, Ni), etc.

[0058] (2) Penetration of the slurry In the present embodiment, the above-described slurry is penetrated into the inside of the partition wall 16 of the base material 10. For the penetration of the slurry, a conventionally known penetration method (such as a suction method or a pressure method) can be adopted without particular limitation. Note that for the penetration of the slurry, not only the supply amount, viscosity, and components (such as solid content) of the slurry, but also many conditions such as the porosity of the partition wall, the pressure during penetration, and the penetration time are affected. Therefore, it is preferable to conduct preliminary tests with these conditions appropriately changed and control various conditions based on the findings obtained in the tests. In the present embodiment, the penetration of the slurry is carried out at room temperature (around 20°C). As a result, the slurry liquid in a low-viscosity state can be uniformly penetrated into the partition wall 16. As a result, in the large pores 18l of the partition wall 16, the slurry adheres to the peripheral wall 18b of the pores 18. At this time, in the large pores 18l, an opening for communicating the inlet side cell 12 and the outlet side cell 14 remains. On the other hand, in the small pores 18s, the entire pores 18 are blocked by the slurry.

[0059] (3) Drying treatment And in the drying treatment, high-temperature air blowing is performed on the base material 10 after the slurry has penetrated. Due to this high-temperature air blowing, the viscosity of the slurry that has penetrated into the partition wall 16 increases significantly. Specifically, in this embodiment, the slurry has the above ratio V 60 / V 20 is 10 or more, so the viscosity during air blowing increases by 10 times or more. As a result, in the large pores 18l, the slurry adhering to the peripheral wall 18b of the pores 18 is suppressed from peeling off during air blowing. Thereby, the diameter of the large pores 18l can be sufficiently reduced. In addition, due to the reduction in the diameter of the large pores 18l, the air permeability of the large pores 18l decreases. As a result, the slurry filled in the small pores 18s is removed by the pressure of the air blowing. Thereby, clogging of the small pores 18s can be prevented.

[0060] Note that since the appropriate conditions for air blowing can also vary depending on various factors, it is better to set the conditions appropriately based on the results of preliminary tests. For example, the temperature of the air blowing is preferably 50°C to 120°C (more preferably 60°C to 100°C). Also, the air volume of the air blowing is 1.0 m 3 / min to 7.0 m 3 / min (more preferably 1.3 m 3 / min to 6.5 m 3 / min, even more preferably 2.6 m 3 / min to 5.2 m 3 / min, particularly preferably 2.6 m 3 / min to 3.9 m 3 / min) is preferred.

[0061] (4) Firing treatment Next, the base material after high-temperature air blowing is fired. Thereby, the particulate filter 1 (see FIG. 4) according to the present embodiment can be manufactured. As described above, in this particulate filter 1, the large pores 18l are sufficiently reduced in diameter by the internal coat layer 20, and the blockage of the small pores 18s is prevented. Therefore, high PM collection performance can be exhibited. Note that various conditions (firing temperature, firing time, heating rate, etc.) in the firing process can be adopted without particular limitation from conventionally known conditions, and since the technology disclosed herein is not limited thereto, detailed description thereof is omitted.

[0062] <Other Embodiments> As described above, one embodiment of the particulate filter disclosed herein has been described. However, the particulate filter disclosed herein is not limited to the above-described embodiment. That is, the technology disclosed herein includes those obtained by variously modifying the particulate filter according to the first embodiment in accordance with conventionally known techniques.

[0063] For example, the internal coat layer 20 in the above-described embodiment has a first internal coat layer 20a and a second internal coat layer 20b. However, the internal coat layer only needs to be formed so as to satisfy the above formulas (1) to (3), and is not limited to the above-described embodiment. For example, the internal coat layer may be formed only in the region of the first internal coat layer 20a in FIG. 3, or may be formed only in the region of the second internal coat layer 20b. Further, the internal coat layer may be formed in all regions within the partition walls.

[0064] In addition, the particulate filter may have an outer coat layer. This outer coat layer is a coat layer formed outside the partition wall so as to cover the entrance of the pores 18 (18a in FIG. 3). By providing the outer coat layer, PM can be collected to some extent outside the partition wall (inlet side cell), so that more suitable PM collection performance can be realized. The outer coat layer is formed by supplying slurry to the inlet side cell after forming an inner coat layer in the partition wall. If the large pores are not sufficiently reduced in diameter after the formation of this inner coat layer, a part of the slurry for forming the outer coat layer may penetrate into the pores, so that an outer coat layer with a desired thickness may not be formed. On the other hand, according to the technology disclosed herein, since the large pores can be sufficiently reduced in diameter by the inner coat layer, a highly accurate outer coat layer can be formed.

[0065] Note that the outer coat layer may be formed on the surface of the region of the inlet side surface of the partition wall where the inner coat layer is not formed. For example, as described above, when the inner coat layer is formed only in the region of the second inner coat layer 20b in FIG. 3, it is preferable to form the outer coat layer on the inlet side surface on the upstream side of the partition wall. Thereby, even when the inner coat layer is formed only in a part of the region in the partition wall, sufficient PM collection performance can be ensured.

[0066] [Test Example] Hereinafter, test examples related to the technology disclosed herein will be described. However, the following description is not intended to limit the technology disclosed herein to that shown in the test examples. In this test, a plurality of particulate filters were prepared and the performance of each was evaluated.

[0067] [First Test] 1. Preparation of Test Samples (1) Example 1 First, as the substrate, a cordierite wall flow type substrate with a diameter of 117 mm, a length of 122 mm, an apparent volume of 1.31 L, 300 cells / cm2, and a wall thickness of 210 μm was used. And in this test, an inner coat layer and an outer coat layer were formed on the partition wall of the substrate according to the following procedure.

[0068] Here, first, the slurry for the inner coat layer was prepared. Specifically, in pure water, rhodium hydroxide equivalent to 0.5 g / L in terms of the mass of metallic Rh as the PGM source and Ce·Zr composite oxide equivalent to 90 g / L (CeO2:ZrO2 = 2:7 (mass ratio), CZ) were added, and the mixture was stirred at room temperature for 30 minutes or more. After drying and firing this slurry, it was thoroughly stirred with alumina equivalent to 20 g / L and boehmite binder equivalent to 2.0 g / L in pure water, and then hydroxyethyl cellulose was added as a thickener to adjust the viscosity, and ammonium sulfate was added at 0.2 g / L (0.2 wt%) as a temperature-rising thickener. Thus, the slurry for the inner coat was prepared. Next, the above-mentioned slurry for the inner coat was infiltrated into the partition wall of the substrate to form the inner coat layer. Specifically, the slurry was infiltrated into the region of 70% of the substrate length from the downstream side of the substrate. Then, ventilation drying (high-temperature air blow) was performed at 90 °C. Thereafter, it was fired at 500 °C for 1 hour. Thus, the inner coat layer was formed.

[0069] Next, the slurry for the outer coat was prepared. Specifically, in pure water, platinum nitrate equivalent to 0.8 g / L in terms of the mass of metallic Pt as the PGM source, 40 g / L equivalent of alumina as inorganic oxide particles, and 5.0 g / L equivalent of boehmite binder as a binder were introduced. Then, by performing stirring, the slurry for the outer coat was prepared. Next, the slurry for the outer coat was coated on the region of 40% of the substrate length from the downstream side of the substrate on which the inner coat layer was formed. Then, by firing at 500 °C for 1 hour, the outer coat layer was formed. By the above procedure, a particulate filter having an inner coat layer and an outer coat layer was produced.

[0070] (2) Example 2 In Example 2, a particulate filter was produced under the same conditions as in Example 1 except that the content of the temperature-rising thickener in the slurry for the inner coat was changed to 0.3 g / L (0.3 wt%).

[0071] (3) Example 3 In Example 3, a particulate filter was fabricated under the same conditions as in Example 1, except that the content of the temperature-rising thickener in the inner coat slurry was changed to 0.4 g / L (0.4 wt%).

[0072] (4) Comparative Example In the comparative example, a particulate filter was fabricated under the same conditions as in Example 1, except that the temperature-rising thickener was not added to the inner coat slurry.

[0073] 2. Evaluation Test (1) Evaluation of PM Collection Performance The particulate filter of each sample was installed in a soot generation device (manufactured by CAMBUSTION, DPG Automated Exhaust Filter Testing System), and exhaust gas containing soot was supplied to the particulate filter by burning gasoline. Then, when the soot deposition amount reached 0.02 g / L, the number of PM particles (pieces) in each of the pipes directly below the soot generation device and the pipe directly below the particulate filter was measured. And the ratio of the number of PM particles directly below the particulate filter to the number of PM particles directly below the soot generation device was calculated as the PM collection rate (%). Also, in this test, when the soot deposition amount reached 0.05 g / L, the PM collection rate (%) was measured in the same procedure. The measurement results for each are shown in Table 1.

[0074] (2) Evaluation of Pressure Drop Suppression Performance Also, in this test, the PM deposition pressure drop was also measured. Specifically, in the above evaluation of PM collection performance, when the soot deposition amount reached 1.0 g / L, the pressures before and after the particulate filter were measured. And the difference between the pressures before and after the particulate filter was measured as the pressure drop (Δmbr). The measurement results are shown in Table 1.

[0075]

Table 1

[0076] As shown in Table 1, in Examples 1 to 3, the PM capture rate was significantly higher than that of the comparative example at both 0.02 g / L and 0.05 g / L deposition. This shows that the PM capture performance of the manufactured particulate filter is greatly improved when an inner coating slurry containing a temperature-rising thickener is used. This suggests that an increase in the viscosity of the slurry during the drying process (high-temperature air blow) causes some kind of change in the pores of the partition walls.

[0077] [Second test] In the second test, Example 3 and Comparative Example 1 were selected from the samples prepared in the first test. Then, for each example, the viscosity of the inner coating slurry was evaluated, and the pores of the partition walls after the inner coating were analyzed.

[0078] (1) Slurry viscosity evaluation In this test, the viscosity V of each internal coating slurry at 20°C was 20 and viscosity at 60°C V 60 Based on the measurement results, the viscosity V 20 and viscosity V 60 Ratio to V 60 / V 20 was calculated. In this viscosity measurement, a rheometer (model: MARS III) manufactured by Thermo Fisher Scientific Co., Ltd. was used to obtain viscosity change data while raising the temperature from 20°C to 60°C in 150 seconds. The shear rate during the measurement was set to 3.8 (1 / s). The results are shown in Table 2.

[0079] (2) Pore analysis of partition wall Here, first, the particulate filters of each example were disassembled. Then, test pieces (1 cm × 1 cm × 1 cm) were cut out from the partition walls in the region where the outer coat layer was not formed and the inner coat layer was formed (the region from 40% to 70% from the downstream side). Then, the test pieces were placed in a vacuum-evacuated container, and the container was filled with mercury. Then, by applying a continuous and variable pressure to the mercury, the pores of the test pieces were filled with mercury, and the pore size distribution was measured from the change in the height of the mercury liquid level. Also, in this test, a base material without a coat layer was used as a reference example, and pore analysis of the reference example was also performed. The analysis results are shown in FIG. 7 and Table 2.

[0080]

Table 2

[0081] As shown in Table 2, the viscosity of the slurry in the comparative example decreased to 0.3 times during heating. When such a general slurry is used, the following phenomena are expected to occur. First, when the base material after slurry penetration is dried, air preferentially passes through the large pores of the partition wall. At this time, since the viscosity of the slurry has decreased significantly, the slurry adhering to the peripheral wall of the large pores peels off and is discharged outside the partition wall. As a result, the air permeability of the large pores is further improved, so that less air passes through the small pores. As a result, since almost no slurry filled in the small pores is discharged, the small pores are blocked after the firing treatment.

[0082] On the other hand, the viscosity of the slurry in Example 3 increased by about 49 times during heating. When this high-temperature thickening slurry is used, it is expected that even if the air during the drying process passes through the large pores, the slurry adhering to the peripheral wall of the large pores is difficult to peel off. As a result, since the air permeability of the large pores is maintained at a low level, the air tries to pass through the small pores. As a result, the slurry in the small pores is easily discharged, so that the blockage of the small pores by the inner coat layer is suppressed.

[0083] Next, as a result of comparing the pore size distributions of each example, D between the reference example (base material) and the comparative example 50No significant change occurred. In contrast, in Example 3, D 50 was significantly reduced compared to the reference example. From this, it is understood that in Example 3, the pores with medium to large diameters are appropriately reduced in diameter by the inner coat layer. Next, in the comparative example, D 10 / D 50 was increased compared to the reference example and Example 3. This is understood to be because as a result of a large number of small pores being blocked, the pores on the medium diameter side were included in D 10 . On the other hand, in Example 3, since D 10 / D 50 is about the same as that of the reference example, it is understood that the blockage of small pores is suppressed. Next, in Example 3, D 90 / D 50 was significantly increased compared to the reference example and the comparative example. This is because D 90 / D 50 the denominator D 50 was significantly reduced. From this, it is understood that in Example 3, the diameter reduction of pores by the inner coat layer occurs appropriately.

Explanation of symbols

[0084] 1 particulate filter 2 internal combustion engine 3 exhaust manifold 4 exhaust pipe 5 exhaust gas purification catalyst 7 ECU 8 sensor 9 underfloor catalyst 10 substrate 12 inlet side cell 14 outlet side cell 16 partition wall 18 pore 18b peripheral wall 18l large pore 18s small pore 20 inner coat layer 20a first inner coat layer 20b second inner coat layer

Claims

1. A particulate filter disposed in an exhaust system of an internal combustion engine for collecting particulate matter in exhaust gas discharged from the internal combustion engine, comprising: An inlet-side cell having only an end portion on the exhaust gas inflow side opened, an outlet-side cell having only an end portion on the exhaust gas outflow side opened, and a wall-flow type substrate having a porous partition wall partitioning the inlet-side cell and the outlet-side cell; An internal coat layer formed on a peripheral wall of pores inside the partition wall; At least comprising; In the cumulative pore size distribution of the partition wall based on the mercury intrusion method of the partition wall on which the inner coat layer is formed, the cumulative 50% pore size (D ５０ ) is present in the range of 9.0 μm to 20.0 μm, The ratio of the cumulative 10% pore diameter (D ５０ ), to the cumulative 50% pore diameter (D １０ ), D １０ / D ５０ is from 0.1 to 0.45, The cumulative 50% pore diameter (D ５０ ), with respect to the cumulative 90% pore diameter (D ９０ ), the ratio D ９０ / D ５０ is 2.0 to 4.0, A particulate filter.

2. The ratio of the difference between the cumulative 50% pore diameter (D ５０ ), the cumulative 50% pore diameter (D ５０ ), and the cumulative 10% pore diameter (D １０ ), i.e., (D ５０ - D １０ ) / D ５０ is 0.55 to 0.

65. The particulate filter according to claim 1.

3. The ratio of the difference between the cumulative 90% pore diameter (D ５０ ), and the cumulative 50% pore diameter (D ９０ ), to the cumulative 50% pore diameter (D ５０ ), i.e., (D ９０ - D ５０ ) / D ５０ is 1.00 to 2.

00. The particulate filter according to claim 1.

4. The ratio of the difference between the cumulative 90% pore diameter (D ５０ ), and the cumulative 10% pore diameter (D ９０ ), to the cumulative 50% pore diameter (D １０ ), i.e., (D ９０ - D １０ ) / D ５０ is 1.50 to 2.

50. The particulate filter according to claim 1.

5. An internal coat slurry used for forming an internal coat layer of a particulate filter, comprising: At least including a heat-resistant material, a binder, and a temperature-rising thickener; Viscosity V at 20°C based on dynamic viscoelasticity measurement ２０ and viscosity V at 60°C ６０ and the ratio V ６０ / V ２０ is 10 or more and 100 or less, An internal coat slurry.

6. The internal coat slurry according to claim 5, wherein the heat-resistant material includes at least one selected from the group consisting of alumina, ceria, zirconia, silica, magnesia, and calcia.

7. The internal coat slurry according to claim 5, wherein the binder includes at least one selected from the group consisting of boehmite binder (alumina sol) and zirconia binder.

8. The internal coat slurry according to claim 5, wherein the temperature-rising thickener includes at least one selected from the group consisting of methyl cellulose, hydroxypropyl methyl cellulose, ammonium sulfate, and starch.

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